WO2018148932A1 - Dc to dc converter - Google Patents

Dc to dc converter Download PDF

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Publication number
WO2018148932A1
WO2018148932A1 PCT/CN2017/073925 CN2017073925W WO2018148932A1 WO 2018148932 A1 WO2018148932 A1 WO 2018148932A1 CN 2017073925 W CN2017073925 W CN 2017073925W WO 2018148932 A1 WO2018148932 A1 WO 2018148932A1
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WO
WIPO (PCT)
Prior art keywords
transformer
rectifier circuit
power
circuit
power semiconductor
Prior art date
Application number
PCT/CN2017/073925
Other languages
French (fr)
Inventor
Kuenfaat YUEN
Tinho LI
Lin Ma
Kai TIAN
Original Assignee
Abb Schweiz Ag
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Filing date
Publication date
Application filed by Abb Schweiz Ag filed Critical Abb Schweiz Ag
Priority to PCT/CN2017/073925 priority Critical patent/WO2018148932A1/en
Publication of WO2018148932A1 publication Critical patent/WO2018148932A1/en

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33573—Full-bridge at primary side of an isolation transformer
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/01—Resonant DC/DC converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0032—Control circuits allowing low power mode operation, e.g. in standby mode
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • H02M1/0058—Transistor switching losses by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Definitions

  • the invention relates to conversion of DC power input into DC power output, and more particularly to DC to DC conversion with intermediate conversion in AC power.
  • an isolated DC to DC power converter applied to high power generally adopts a full-bridge phase-shift circuit structure.
  • the full-bridge phase-shift circuit can achieve zero-voltage switching (ZVS) .
  • a phase-shift pulse width modulation (PWM) control method of a fixed switching frequency can also be implemented to the full-bridge phase-shift circuit structure.
  • PWM phase-shift pulse width modulation
  • the full-bridge phase-shift circuit structure may lose a soft-switch effect when operating under a light load (or empty load) state, and a circulating loss generated in a heavy load operation is great, which leads to decrease of efficiency.
  • Patent US 20110283909 A1 discloses a full-bridge phase-shift converter having zero-voltage-switching (ZVS) circuit.
  • An auxiliary inductor is provided to reinforce sufficient inductive energy on the lagging phase leg, thus achieving normally zero-voltage-switching operations of the full-bridge phase-shift converter.
  • the demand for higher power efficiency is increasing unabated.
  • New problems are surfacing as the energy stored in the auxiliary inductor is mainly used for ZVS turn-on of the power semiconductor switching element in the lagging phase leg, but finds no path to supply power to the load. Therefore, circulating power is generated in the electrical loop constituted of the ZVS circuit and the power semiconductor switching element to be ZVS turned on. This brings out undesirable power loose.
  • Another problem is that the power is provided through the full-bridge phase-shift converter to the load. As a result, the rated current for each power semiconductor switching element is relatively high.
  • a DC to DC converter including: a first H-bridge converter circuit, a second H-bridge converter circuit sharing a phase leg with the first H-bridge converter circuit, a first rectifier circuit, a second rectifier circuit, a first transformer having primary winding connected to output terminal of the first H-bridge converter circuit and secondary winding connected to input terminal of the first rectifier circuit, a second transformer having primary winding connected to output terminal of the second H-bridge converter circuit and secondary winding connected to input terminal of the second rectifier circuit; wherein: an output terminal of the first rectifier circuit and an output terminal of the second rectifier circuit are connected in series.
  • the power output terminal of the second rectifier circuit can keep outputting the base voltage to the reference voltage terminal of the first rectifier circuit.
  • the base voltage can serve as a part of a rated output power of the DC-DC converter.
  • the first rectifier circuit can compensate an insufficient part of the rated output power to provide the output power to a load. Since the first transformer and the second transformer commonly provide power to the load during a power transmitting period, transformers with a smaller power level can be used to implement the first transformer and/or the second transformer. By using the transformers with smaller power level, a volume of the DC-DC converter is decreased.
  • the first H-bridge converter circuit is operable in phase-shift mode with a switching frequency, having the shared leg as lagging leg and a leading leg; and the second H-bridge converter circuit is operable in bi-polar mode with the switching frequency.
  • a resonant tank may be arranged between the output terminal of the second H-bridge converter circuit and the primary winding of the second transformer.
  • the rated current for each power semiconductor switching element may be decreased.
  • the output voltage of the DC to DC converter may be regulated by adjusting the phase-shift angle of the phase shift stage.
  • the DC-DC converter may provide regulated wide range output voltage as of superimposition of the first rectifier output voltage on the second rectifier output voltage.
  • the first H-bridge converter circuit is operable with duty cycle of substantially 50%and the second H-bridge converter circuit is operable with duty cycle of substantially 50%.
  • the switching frequency is fixed at resonant frequency substantially determined by resonant components of the resonant tank. Therefore, the LLC stage operates at the optimal operation point, retaining a high power efficiency and outputting a constant DC base voltage.
  • the resonant component of the resonant tank includes an inductive element and a capacitive element.
  • the first rectifier circuit is of full-wave rectification.
  • Figure 1 shows a circuit block schematic diagram of a DC-DC converter according to an embodiment of present invention
  • Figure 2 is a circuit schematic diagram of the DC-DC converter according to an embodiment of present invention.
  • Figure 3 shows a timing diagram of the signals according to an embodiment of present invention.
  • Figures 4A and 4B show the equivalent circuits of the DC-DC converter according to an embodiment of present invention including a LLC stage and a phase-shift stage.
  • FIG. 1 shows a circuit block schematic diagram of a DC-DC converter according to an embodiment of present invention.
  • the DC-DC converter 1 includes a switching circuit 10, a first transformer 11, a first rectifier circuit 12, a second transformer 13 and a second rectifier circuit 14.
  • the switching circuit 10 is coupled to a primary winding of the first transformer 11 and a primary winding of the second transformer 13.
  • the switching circuit 10 provides an input power Vin to the primary winding of first transformer 11 and the primary winding of the second transformer 13.
  • An AC input terminal of the second rectifier circuit 14 is coupled to a secondary winding of the second transformer 13.
  • the second rectifier circuit 14 rectifies an output power of the secondary winding of the second transformer 13 to provide a base voltage Vb.
  • a terminal of the first rectifier circuit 12 is coupled to an output terminal of the second rectifier circuit 14 and receives the base voltage Vb to serve as a reference voltage of the first rectifier circuit 12.
  • the first rectifier circuit 12 and the second rectifier circuit 14 can be regarded as being connected in series.
  • An AC input terminal of the first rectifier circuit 12 is coupled to a secondary winding of the first transformer 11.
  • a power output terminal of the first rectifier circuit 12 serves as a power output terminal of the DC-DC converter 1 to provide an output voltage Vout.
  • the first rectifier circuit 12 rectifies an output power of the secondary winding of the first transformer 11 to provide an adding voltage Va.
  • the base voltage Vb can lift the adding voltage Va to obtain the output voltage Vout complied with a rated specification. Therefore, the base voltage Vb of the second rectifier circuit 14 can lift the output voltage Va at the power output terminal of the first rectifier circuit 12.
  • the power output terminal of the second rectifier circuit 14 can keep outputting the base voltage Vb to the reference voltage terminal of the first rectifier circuit 12.
  • the base voltage Vb can serve as a part of a rated output power of the DC-DC converter 1.
  • the first rectifier circuit 12 can compensate an insufficient part of the rated output power to provide the output power Vout (rated output power) to a load. Since the first transformer 11 and the second transformer 13 commonly provide power to the load during a power transmitting period, transformers with a smaller power level (transformers with a smaller volume) can be used to implement the first transformer 11 and/or the second transformer 13. By using the transformers with smaller power level, a volume of the DC-DC converter 1 is decreased.
  • FIG. 2 is a circuit schematic diagram of the DC-DC converter according to an embodiment of present invention.
  • the DC-DC converter 1 includes the switching circuit 10, the first transformer 11, the first rectifier circuit 12, the second transformer 13 and the second rectifier circuit 14.
  • the switching circuit 10 the first transformer 11, the first rectifier circuit 12, the second transformer 13 and the second rectifier circuit 14.
  • the first transformer 11 includes a first terminal and a second terminal of a primary winding of the first transformer 11 coupled to the switching circuit 10.
  • a first terminal and a second terminal of a secondary winding of the first transformer 11 are coupled to the first rectifier circuit 12.
  • the second transformer 13 includes a first terminal and a second terminal coupled to the switching circuit 10.
  • An AC input terminal of the first rectifier circuit 12 is coupled to the secondary winding of the first transformer 11.
  • the first rectifier circuit 12 can rectify an AC current of the secondary winding of the first transformer 11 into a DC current.
  • An output terminal of the first rectifier circuit 12 is coupled to an output terminal of the second rectifier circuit 14 to receive the base voltage Vb output by the second rectifier circuit 14. Based on the voltage (the base voltage Vb) at the reference voltage terminal of the first rectifier circuit 12, the first rectifier circuit 12 can provide the output voltage Va to the power output terminal of the DC-DC converter 1.
  • An AC input terminal of the second rectifier circuit 14 is coupled to the secondary winding of the second transformer 13.
  • An output terminal of the second rectifier circuit 14 is coupled to the output terminal of the first rectifier circuit 12 for providing the base voltage Vb.
  • the second rectifier circuit 14 can rectify an AC current of the secondary winding of the second transformer 13 into a DC current, and increase a voltage of the secondary winding of the second transformer 13 by a predetermined multiple.
  • a capacitor 20 is coupled across the DC output terminals of the second rectifier circuit 14.
  • the capacitor 20 can filter an AC component of a voltage Vb at the DC output terminal of the second rectifier circuit 14.
  • An AC filter 21, for example using LC circuit may be coupled across the output terminals of the series-connected first rectifier circuit 12 and second rectifier circuit 14, filtering an AC component of the output voltage Vout of the DC-DC converter 1.
  • the switching circuit 10 comprises an inverter side bus (collectively) formed by voltage rails 22a, 22b.
  • the switching circuit 10 also comprises a first phase leg 10a formed by an upper power semiconductor switch S1 and lower power semiconductor switch S2, a second phase leg 10b formed by an upper power semiconductor switch S3 and lower power semiconductor switch S4, and a third phase leg 10c formed by an upper power semiconductor switch S5 and lower power semiconductor switch S6, each of the phase legs 10a-10c electrically coupled between the voltage rails 22a, 22b.
  • the power semiconductor switches S1-S6 may, for example, take the form of metal oxide semiconductor field effect transistors (MOSFETs) , insulated gate bipolar transistors (IGBTs) and/or other switches suitable for high power operation.
  • MOSFETs metal oxide semiconductor field effect transistors
  • IGBTs insulated gate bipolar transistors
  • the switching circuit 10 further comprises power semiconductor diodes Ds1-Ds6, electrically coupled in anti-parallel across respective ones of the power semiconductor switches S1-S6.
  • power semiconductor device includes semiconductor devices designed to handle large currents, large voltages and/or large amounts of power with respect to standard semiconductor devices, including power semiconductor switches devices, power semiconductor diodes, and other such devices used in power distribution, for example, grid or transportation related applications.
  • the power semiconductor diodes Ds1-Ds6 may be formed as part of the power semiconductor switches S1-S6, for example as body diodes, while in other embodiments the power semiconductor diodes Ds1-Ds6 may take the form of discrete semiconductor devices.
  • each phase leg 10a, 10b, 10c is a phase node A, B, C, upon which the respective phase of a three phase output of the switching circuit 10 appears during operation. While illustrated as a single switch and diode, each of the power semiconductor switches S1-S6 and/or diodes Ds1-Ds6 may take the form of one or more power semiconductor switches and/or diodes electrically coupled in parallel.
  • a controller 23 controls the power semiconductor switches S1-S6 via control signals 24.
  • the switching circuit 10 may further comprise an input capacitor (not shown) , electrically coupled across the voltage rails 22a, 22b of the inverter side bus 22.
  • phase nodes A and B of the phase legs 10a, 10b are electrically coupled to the primary winding of the second transformer 13, and the phase nodes B and C of the phase legs 10b, 10c are electrically coupled to the primary winding of the first transformer 11.
  • the first phase leg 10a and the second phase leg 10b constitute a second H-bridge converter circuit 26
  • the second phase leg 10b and the third phase leg 10c constitute a first H-bridge converter circuit 25.
  • the first H-bridge converter circuit 25 and the second H-bridge converter circuit 26 share the second phase leg 10b.
  • a second resonant tank 28 may be arranged between the output terminal of the second H-bridge converter circuit 26 and the primary winding of the second transformer 13.
  • the resonant components of the resonant tank 28 include an inductive element 28a and a capacitive element 28b.
  • a first resonant tank 27 may be arranged between the output terminal of the first H-bridge converter circuit 25 and the primary winding of the first transformer 11.
  • the resonant components of the resonant tank 27 include an inductive element 27a and a capacitive element 27b.
  • the first rectifier circuit may perform full-wave rectification, for example in topology of H-bridge made up of power diodes D1 to D4.
  • the second rectifier circuit may perform full-wave rectification, for example in topology of H-bridge made up of power diodes D5 to D8.
  • the controller 23 provides control signals 24 to control the power semiconductor switches S1-S6 of the switching circuit 10.
  • the controller 23 may take the form of a microcontroller such as a microprocessor, digital signal processor (DSP) and/or application specific integrated circuit (ASIC) .
  • Controller 23 may receive input signals such as voltage and current measurements from a voltage sensor and/or current sensor that sense voltage or current with respect to the input from the power source VI.
  • the controller 23 may additionally or alternatively receive voltage and/or current signals from a voltage sensor and/or current sensor that measure output voltage and/or current.
  • FIG 3 shows a timing diagram of the signals according to an embodiment of present invention.
  • S1 to S6 respectively represent the switching signals applied to the semiconductor switches S 1-S6 of the switching circuit 10; a horizontal axis represents time t, Is1 to Is6 respectively represent currents conducting or freewheeling via the semiconductor switches S1-S6; the voltage Vout generated at the output terminals of DC-DC converter 1; the base voltage Vb generated at the output terminals of the second rectifier circuit 14; the voltage Vpri1 applied to the primary winding of the first transformer 11 and its current Ipri1; the voltage Vpri2 applied to the primary winding of the second transformer 13 and its current Ipri2.
  • the power semiconductor switches S1-S6 of each phase leg 10a-10c of the switching circuit 10 each generate a nearly 50%duty cycle square waveform.
  • the first H-bridge converter circuit 25 is phase shift controlled to generate square waveform across phase nodes B and C.
  • the first H-bridge converter circuit 25 combined with the inductive element 28a, the capacitive element 28b, the leakage inductance of the first transformer 11 and the power diodes D1 to D4 may form ZVS turn-on phase-shift stage
  • ZVS turn-on of the power semiconductor switches S3-S6 of the first H-bridge converter circuit 25 may be achieved.
  • the second H-bridge converter circuit 26 is b-polar controlled to generate square waveform across phase nodes A and B.
  • Figures 4A and 4B show the equivalent circuits of the DC-DC converter according to an embodiment of present invention including a LLC stage and a phase-shift stage.
  • the second H-bridge converter circuit 26 combined with the inductive element 27a, the capacitive element 27b, the leakage inductance of the second transformer 13 and the power diodes D5 to D8 form a LLC stage.
  • ZVS turn-on of the power semiconductor switches S1-S4 is achieved largely by the energy stored in the magnetizing inductance of the second transformer 13.
  • Lagging leg of the phase-shift stage (the second phase-leg 10b) is shared by the two stages of phase-shift stage and LLC stage.
  • the LLC stage offers ZV turn-on ability to the lagging leg of phase-shift stage even at light load condition. It is because the current via S3 and S4 is the sum of the LLC stage and phase-shift stage. The LLC stage current will dominate in the lagging leg at light load, therefore ZV turn-on across the lagging leg switches can be realized.
  • the control signals for the first H-bridge converter circuit 25 and the second H-bridge converter circuit 26 are frequency locked to each other, they may operate substantially at the same switching frequency.
  • the output voltages of the LLC stage and phase-shift stage are connected in series at the output side.
  • the LLC converter provides a constant output voltage Vb while the phase-shift converter provides a regulated wide range output voltage, namely Va.
  • the first power semiconductor switch S1, the fourth power semiconductor switch S4 and the fifth power semiconductor switch S5 are turned on, and the second power semiconductor switch S2, the third power semiconductor switch S3 and the sixth power semiconductor switch S6 are turned off.
  • the voltage of the input power Vin is exerted to the primary winding of the first transformer 11 via the first resonant tank 27.
  • An inducted AC current of the secondary winding of the first transformer 11 is rectified to a DC current by the first rectifier circuit 12.
  • the DC power output by the first rectifier circuit 12 can be provided to the output voltage Vout to the load. Meanwhile, the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28.
  • An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14.
  • the DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Vb to the load.
  • the DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection.
  • the base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the power transmitting period T1, the first transformer 11 and the second transformer 13 can commonly provide electric power to the load.
  • the first power semiconductor switch S1 and the fourth power semiconductor switch S4 are turned on, and the second power semiconductor switch S2, the third power semiconductor switch S3, the fifth power semiconductor switch S5 and the sixth power semiconductor switch S6 are turned off.
  • the resonant elements 27a, 27b of the first resonant tank 27 and the parasitic capacitances of the fifth power semiconductor switch S5 and the sixth power semiconductor switch S6 are respectively discharged and charged by the energy of the magnetizing inductor of the primary winding of the first transformer 11.
  • the body diode Ds6 of the sixth power semiconductor switch S6 is forward biased, such that the sixth power semiconductor switch S6 may be turned on under a zero voltage.
  • the first resonant tank 27, the first transformer 11, the fourth power semiconductor switch S4, and the antiparallel diode Ds6 constitute freewheeling electrical loop, and thus the first transformer 11 essentially provides no power to the load.
  • the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28.
  • An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14.
  • the DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Vb to the load.
  • the DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection.
  • the base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the second period T2, the second transformer 13 mainly provides electric power to the load.
  • the first power semiconductor switch S1, the fourth power semiconductor switch S4 and the sixth power semiconductor switch S6 are turned on, and the second power semiconductor switch S2, the third power semiconductor switch S3 and the fifth power semiconductor switch S5 are turned off.
  • the ZVS turn on is achieved for the power semiconductor switch S6 of the leading phase leg of the first H-bridge converter circuit 25 operating in phase shift mode.
  • the first resonant tank 27, the first transformer 11, the fourth power semiconductor switch S4, and the sixth power semiconductor S6 constitute freewheeling electrical loop, and thus the first transformer 11 essentially provides no power to the load. Meanwhile, the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28.
  • An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14.
  • the DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Vb to the load.
  • the DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection.
  • the base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the third period T3, the second transformer 13 mainly provides electric power to the load.
  • the sixth power semiconductor switch S6 is turned on, and the first power semiconductor switch S1, the second power semiconductor switch S2, the third power semiconductor switch S3, the fourth power semiconductor switch S4 and the fifth power semiconductor switch S5 are turned off.
  • the energy stored in the magnetizing inductor of the primary winding of the first transformer 11 might not be sufficient enough for forward-biasing the body diode Ds3 of the third power semiconductor switch S3 of the lagging phase leg of the first H-bridge converter circuit 25.
  • the resonant elements 28a, 28b of the second resonant tank 28 and the parasitic capacitances of the third power semiconductor switch S3 and the fourth power semiconductor switch S4 are respectively discharged and charged by the energy of the magnetizing inductor of the primary winding of the second transformer 13.
  • the body diodes Ds2, Ds3 of the second power semiconductor switch S2 and the third power semiconductor switch S3 are forward biased, such that the second power semiconductor switch S2 and the third power semiconductor switch S3 may be turned on under a zero voltage.
  • the ZVS turn on condition is achieved for the power semiconductor switch S3 of the lagging phase leg of the first H-bridge converter circuit 25 operating in phase shift mode, as well.
  • part of the energy stored in the second resonant tank 28 is transferred to the load through the second transformer 13 based on the principle of LLC converter operation.
  • the first, second, third and fourth periods T1, T2, T3, T4 constitute of the first half cycle of the modulation scheme of the DC to DC converter. Consequently, during a fifth period T5, the second power semiconductor switch S2, the third power semiconductor switch S3 and the sixth power semiconductor switch S6 are turned on, and the first power semiconductor switch S1, the fourth power semiconductor switch S4 and the fifth power semiconductor switch S5 are turned off.
  • the voltage of the input power Vin is exerted to the primary winding of the first transformer 11 via the first resonant tank 27.
  • An inducted AC current of the secondary winding of the first transformer 11 is rectified to a DC current by the first rectifier circuit 12.
  • the DC power output by the first rectifier circuit 12 can be provided to the output voltage Vout to the load.
  • the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28.
  • An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14.
  • the DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Va to the load.
  • the DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection.
  • the base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the power transmitting period T1, the first transformer 11 and the second transformer 13 can commonly provide electric power to the load.
  • the second power semiconductor switch S2 and the third power semiconductor switch S3 are turned on, and the first power semiconductor switch S1, the fourth power semiconductor switch S4, the sixth power semiconductor switch S6 and the fifth power semiconductor switch S5 are turned off.
  • the resonant elements 27a, 27b of the first resonant tank 27 and the parasitic capacitances of the sixth power semiconductor switch S6 and the fifth power semiconductor switch S5 are respectively discharged and charged by the energy of the magnetizing inductor of the primary winding of the first transformer 11.
  • the body diode Ds5 of the fifth power semiconductor switch S5 is forward biased, such that the fifth power semiconductor switch S5 may be turned on under a zero voltage.
  • the first resonant tank 27, the first transformer 11, the third power semiconductor switch S3, and the antiparallel diode Ds5 constitute freewheeling electrical loop, and thus the first transformer 11 essentially provides no power to the load.
  • the resonant voltage generated by the first resonant tank 27 is exerted to the primary winding of the first transformer 11 via the first resonant tank 27, instead of the input power Vin.
  • the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28.
  • An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14.
  • the DC power output by the second rectifier circuit 14 can be stored in the capacitor 20.
  • the capacitor 20 can provide the output voltage Vb to the load.
  • the DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection.
  • the base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the second period T2, the second transformer 13 mainly provides electric power to the load.
  • the second power semiconductor switch S2, the third power semiconductor switch S3 and the fifth power semiconductor switch S5 are turned on, and the first power semiconductor switch S1, the fourth power semiconductor switch S4 and the sixth power semiconductor switch S6 are turned off.
  • the ZVS turn on is achieved for the fifth power semiconductor switch S5 of the leading phase leg of the first H-bridge converter circuit 25 operating in phase shift mode.
  • the first resonant tank 27, the first transformer 11, the third power semiconductor switch S3, and the antiparallel diode Ds5 constitute freewheeling electrical loop, and thus the first transformer 11 essentially provides no power to the load. Meanwhile, the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28.
  • An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14.
  • the DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Vb to the load.
  • the DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection.
  • the base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the third period T3, the second transformer 13 mainly provides electric power to the load.
  • the fifth power semiconductor switch S5 is turned on, and the second power semiconductor switch S2, the first power semiconductor switch S1, the fourth power semiconductor switch S4, the third power semiconductor switch S3 and the sixth power semiconductor switch S6 are turned off.
  • the energy stored in the magnetizing inductor of the primary winding of the first transformer 11 might not be sufficient enough for forward-biasing the body diode Ds4 of the fourth power semiconductor switch S4 of the lagging phase leg of the first H-bridge converter circuit 25.
  • the resonant elements 28a, 28b of the second resonant tank 28 and the parasitic capacitances of the fourth power semiconductor switch S4 and the third power semiconductor switch S3 are respectively discharged and charged by the energy of the magnetizing inductor of the primary winding of the second transformer 13.
  • the body diodes Ds1, Ds4 of the first power semiconductor switch S1 and the fourth power semiconductor switch S4 are forward biased, such that the first power semiconductor switch S1 and the fourth power semiconductor switch S4 may be turned on under a zero voltage.
  • the ZVS turn on condition is achieved for the power semiconductor switch S4 of the lagging phase leg of the first H-bridge converter circuit 25 operating in phase shift mode, as well.
  • part of the energy stored in the second resonant tank 28 is transferred to the load through the second transformer 13 based on the principle of LLC converter operation.
  • the DC-DC converter 1 can provide the output voltage Vout to the load.
  • the electric power shown by a slash shading part of figure 3 is provided by the second transformer 13.
  • the second transformer 13 can keep outputting the base voltage Vb to provide a part of the rated output power through the second rectifier circuit 14 during the periods T1 to T8.
  • the first transformer 11 can provide the adding voltage Va during these periods T1 to T8 to compensate the insufficient part of the rated output power. Therefore, transformers with a smaller power level (transformers with a smaller volume) can be used to implement the first transformer 11 and/or the second transformer 13. By using the transformers with smaller power level, a volume of the DC-DC converter 1 is decreased.
  • the energy stored in the auxiliary inductor is not only used for ZVS turn-on of the power semiconductor switching element in the lagging phase leg, but also transfers power to the load through the second transformer 13. Therefore, the power loose resulted in the circulating power is decreased.
  • the power since the power has more than one transmission paths, namely via the first transformer and the second transformer, the rated current for each power semiconductor switching element may be decreased.
  • the switching frequency may be fixed at resonant frequency substantially determined by resonant components 28a, 28b of the second resonant tank 28. Therefore, the LLC stage operates at the optimal operation point, retaining a high power efficiency and outputting a constant DC voltage Vb.
  • the output voltage Vout may be regulated by adjusting the phase-shift angle of the phase shift stage.

Abstract

Disclosed is a DC to DC converter (1). The DC to DC converter includes a first H-bridge converter circuit, a second H-bridge converter circuit sharing a phase leg with the first H-bridge converter circuit, a first rectifier circuit (12), a second rectifier circuit (14), a first transformer (11) and a second transformer (13). The primary winding of the first transformer is connected to the output terminals of the first H-bridge converter circuit, and the secondary winding of the first transformer is connected to the input terminals of the first rectifier circuit. The primary winding of the second transformer is connected to the output terminals of the second H-bridge converter circuit, and the secondary winding of the second transformer is connected to the input terminals of the second rectifier circuit. One of the output terminals of the first rectifier circuit and one of the output terminals of the second rectifier circuit are connected in series. The first rectifier circuit can compensate an insufficient part of the rated output power to provide the output power to a load. Since the first transformer and the second transformer commonly provide power to the load during a power transmitting period, transformers with smaller power level can be used to implement the first transformer and/or the second transformer, thereby the volume of the DC-DC converter being decreased.

Description

DC TO DC CONVERTER Technical Field
The invention relates to conversion of DC power input into DC power output, and more particularly to DC to DC conversion with intermediate conversion in AC power.
Background Art
Presently, an isolated DC to DC power converter applied to high power generally adopts a full-bridge phase-shift circuit structure. The full-bridge phase-shift circuit can achieve zero-voltage switching (ZVS) . A phase-shift pulse width modulation (PWM) control method of a fixed switching frequency can also be implemented to the full-bridge phase-shift circuit structure. However, the full-bridge phase-shift circuit structure may lose a soft-switch effect when operating under a light load (or empty load) state, and a circulating loss generated in a heavy load operation is great, which leads to decrease of efficiency.
In addressing this problem, Patent US 20110283909 A1 discloses a full-bridge phase-shift converter having zero-voltage-switching (ZVS) circuit. An auxiliary inductor is provided to reinforce sufficient inductive energy on the lagging phase leg, thus achieving normally zero-voltage-switching operations of the full-bridge phase-shift converter. The demand for higher power efficiency, however, is increasing unabated. New problems are surfacing as the energy stored in the auxiliary inductor is mainly used for ZVS turn-on of the power semiconductor switching element in the lagging phase leg, but finds no path to supply power to the load. Therefore, circulating power is generated in the electrical loop constituted of the ZVS circuit and the power semiconductor switching element to be ZVS turned on. This brings out undesirable power loose. Another problem is that the power is provided through the full-bridge phase-shift converter to the load. As a result, the rated current for each power semiconductor switching element is relatively high.
Brief Summary of the Invention
According to an aspect of present invention, it provides a DC to DC converter, including: a first H-bridge converter circuit, a second H-bridge converter circuit sharing a phase leg with the first H-bridge converter circuit, a first rectifier circuit, a second rectifier circuit, a first transformer having primary winding connected to output terminal of the first H-bridge converter circuit and secondary winding connected to input terminal of the first rectifier circuit, a second transformer having primary winding connected to output terminal of the second H-bridge converter circuit and secondary winding connected to input terminal of the second rectifier circuit； wherein: an output terminal of the first rectifier circuit and an output terminal of the second rectifier circuit are connected in series.
The power output terminal of the second rectifier circuit can keep outputting the base voltage to the reference voltage terminal of the first rectifier circuit. The base voltage can serve as a part of a rated output power of the DC-DC converter. The first rectifier circuit can compensate an insufficient part of the rated output power to provide the output power to a load. Since the first transformer and the second transformer commonly provide power to the load during a power transmitting period, transformers with a smaller power level can be used to implement the first transformer and/or the second transformer. By using the transformers with smaller power level, a volume of the DC-DC converter is decreased.
Preferably, the first H-bridge converter circuit is operable in phase-shift mode with a switching frequency, having the shared leg as lagging leg and a leading leg； and the second H-bridge converter circuit is operable in bi-polar mode with the switching frequency. A resonant tank may be arranged between the output terminal of the second H-bridge converter circuit and the primary winding of the second transformer. During the second and fourth freewheeling periods T4 and T8, the energy stored in the auxiliary inductor is not only used for ZVS turn-on of the power semiconductor switching element in the lagging phase leg, but also drives power to the load through the second transformer. Therefore, the power loose resulted in the circulating power is decreased. In addition, since the power has more than one transmission paths, namely via the first transformer and the second transformer, the rated current for each power semiconductor switching element may be decreased. Finally, the output voltage of the DC to DC converter may be regulated by adjusting the phase-shift angle of the phase shift stage. Thus, the DC-DC converter may provide regulated wide range output voltage as of superimposition of the first rectifier output voltage on the second rectifier output voltage.
Preferably, the first H-bridge converter circuit is operable with duty cycle of substantially 50％and the second H-bridge converter circuit is operable with duty cycle of substantially 50％.
Preferably, the switching frequency is fixed at resonant frequency substantially determined by resonant components of the resonant tank. Therefore, the LLC stage operates at the optimal operation point, retaining a high power efficiency and outputting a constant DC base voltage.
Preferably, the resonant component of the resonant tank includes an inductive element and a capacitive element.
Preferably, the first rectifier circuit is of full-wave rectification.
Brief Description of the Drawings
The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the drawings, in which:
Figure 1 shows a circuit block schematic diagram of a DC-DC converter according to an embodiment of present invention；
Figure 2 is a circuit schematic diagram of the DC-DC converter according to an embodiment of present invention；
Figure 3 shows a timing diagram of the signals according to an embodiment of present invention； and
Figures 4A and 4B show the equivalent circuits of the DC-DC converter according to an embodiment of present invention including a LLC stage and a phase-shift stage.
The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.
Preferred Embodiments of the Invention
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be  described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. Note, the headings are for organizational purposes only and are not meant to be used to limit or interpret the description or claims. Furthermore, note that the word "may" is used throughout this application in a permissive sense (i.e., having the potential to, being able to) , not a mandatory sense (i.e., must) . "The term "include" , and derivations thereof, mean "including, but not limited to" . The term "connected" means "directly or indirectly connected" , and the term "coupled" means "directly or indirectly connected" .
Figure 1 shows a circuit block schematic diagram of a DC-DC converter according to an embodiment of present invention. The DC-DC converter 1 includes a switching circuit 10, a first transformer 11, a first rectifier circuit 12, a second transformer 13 and a second rectifier circuit 14. The switching circuit 10 is coupled to a primary winding of the first transformer 11 and a primary winding of the second transformer 13. The switching circuit 10 provides an input power Vin to the primary winding of first transformer 11 and the primary winding of the second transformer 13.
An AC input terminal of the second rectifier circuit 14 is coupled to a secondary winding of the second transformer 13. The second rectifier circuit 14 rectifies an output power of the secondary winding of the second transformer 13 to provide a base voltage Vb. A terminal of the first rectifier circuit 12 is coupled to an output terminal of the second rectifier circuit 14 and receives the base voltage Vb to serve as a reference voltage of the first rectifier circuit 12.Therefore, the first rectifier circuit 12 and the second rectifier circuit 14 can be regarded as being connected in series.
An AC input terminal of the first rectifier circuit 12 is coupled to a secondary winding of the first transformer 11. A power output terminal of the first rectifier circuit 12 serves as a power output terminal of the DC-DC converter 1 to provide an output voltage Vout. The first rectifier circuit 12 rectifies an output power of the secondary winding of the first transformer 11 to provide an adding voltage Va. Based on the serial connection structure, the base voltage Vb can lift the adding voltage Va to obtain the output voltage Vout complied with a rated specification. Therefore, the base voltage Vb of the second rectifier circuit 14 can lift the output voltage Va at the power output terminal of the first rectifier circuit 12.
The power output terminal of the second rectifier circuit 14 can keep outputting the base voltage Vb to the reference voltage terminal of the first rectifier circuit 12. The base voltage Vb can serve as a part of a rated output power of the DC-DC converter 1. The first rectifier circuit 12 can compensate an insufficient part of the rated output power to provide the output power Vout (rated output power) to a load. Since the first transformer 11 and the second transformer 13 commonly provide power to the load during a power transmitting period, transformers with a smaller power level (transformers with a smaller volume) can be used to implement the first transformer 11 and/or the second transformer 13. By using the transformers with smaller power level, a volume of the DC-DC converter 1 is decreased.
Figure 2 is a circuit schematic diagram of the DC-DC converter according to an embodiment of present invention. The DC-DC converter 1 includes the switching circuit 10, the first transformer 11, the first rectifier circuit 12, the second transformer 13 and the second rectifier circuit 14. The switching circuit 10, the first transformer 11, the first rectifier circuit 12, the second transformer 13 and the second rectifier circuit 14.
As shown in figure 2, the first transformer 11 includes a first terminal and a second terminal of a primary winding of the first transformer 11 coupled to the switching circuit 10. A first terminal and a second terminal of a secondary winding of the first transformer 11 are coupled  to the first rectifier circuit 12. The second transformer 13 includes a first terminal and a second terminal coupled to the switching circuit 10.
An AC input terminal of the first rectifier circuit 12 is coupled to the secondary winding of the first transformer 11. The first rectifier circuit 12 can rectify an AC current of the secondary winding of the first transformer 11 into a DC current. An output terminal of the first rectifier circuit 12 is coupled to an output terminal of the second rectifier circuit 14 to receive the base voltage Vb output by the second rectifier circuit 14. Based on the voltage (the base voltage Vb) at the reference voltage terminal of the first rectifier circuit 12, the first rectifier circuit 12 can provide the output voltage Va to the power output terminal of the DC-DC converter 1.
An AC input terminal of the second rectifier circuit 14 is coupled to the secondary winding of the second transformer 13. An output terminal of the second rectifier circuit 14 is coupled to the output terminal of the first rectifier circuit 12 for providing the base voltage Vb. The second rectifier circuit 14 can rectify an AC current of the secondary winding of the second transformer 13 into a DC current, and increase a voltage of the secondary winding of the second transformer 13 by a predetermined multiple. A capacitor 20 is coupled across the DC output terminals of the second rectifier circuit 14. The capacitor 20 can filter an AC component of a voltage Vb at the DC output terminal of the second rectifier circuit 14. An AC filter 21, for example using LC circuit, may be coupled across the output terminals of the series-connected first rectifier circuit 12 and second rectifier circuit 14, filtering an AC component of the output voltage Vout of the DC-DC converter 1.
The switching circuit 10 comprises an inverter side bus (collectively) formed by  voltage rails  22a, 22b. The switching circuit 10 also comprises a first phase leg 10a formed by an upper power semiconductor switch S1 and lower power semiconductor switch S2, a second phase leg 10b formed by an upper power semiconductor switch S3 and lower power semiconductor switch S4, and a third phase leg 10c formed by an upper power semiconductor switch S5 and lower power semiconductor switch S6, each of the phase legs 10a-10c electrically coupled between the  voltage rails  22a, 22b. The power semiconductor switches S1-S6 may, for example, take the form of metal oxide semiconductor field effect transistors (MOSFETs) , insulated gate bipolar transistors (IGBTs) and/or other switches suitable for high power operation.
The switching circuit 10 further comprises power semiconductor diodes Ds1-Ds6, electrically coupled in anti-parallel across respective ones of the power semiconductor switches S1-S6. The term "power semiconductor device" includes semiconductor devices designed to handle large currents, large voltages and/or large amounts of power with respect to standard semiconductor devices, including power semiconductor switches devices, power semiconductor diodes, and other such devices used in power distribution, for example, grid or transportation related applications. In some embodiments, the power semiconductor diodes Ds1-Ds6 may be formed as part of the power semiconductor switches S1-S6, for example as body diodes, while in other embodiments the power semiconductor diodes Ds1-Ds6 may take the form of discrete semiconductor devices.
Between the pair of power semiconductor switches S 1, S2, S3, S4, S5, S6 forming each  phase leg  10a, 10b, 10c respectively, is a phase node A, B, C, upon which the respective phase of a three phase output of the switching circuit 10 appears during operation. While illustrated as a single switch and diode, each of the power semiconductor switches S1-S6 and/or diodes Ds1-Ds6 may take the form of one or more power semiconductor switches and/or diodes electrically coupled in parallel. A controller 23 controls the power semiconductor switches S1-S6 via control signals 24. The switching circuit 10 may further comprise an input capacitor (not shown) , electrically coupled across the  voltage rails  22a,  22b of the inverter side bus 22.
The phase nodes A and B of the  phase legs  10a, 10b are electrically coupled to the primary winding of the second transformer 13, and the phase nodes B and C of the  phase legs  10b, 10c are electrically coupled to the primary winding of the first transformer 11. As shown in figure 2, the first phase leg 10a and the second phase leg 10b constitute a second H-bridge converter circuit 26, and the second phase leg 10b and the third phase leg 10c constitute a first H-bridge converter circuit 25. The first H-bridge converter circuit 25 and the second H-bridge converter circuit 26 share the second phase leg 10b.
A second resonant tank 28 may be arranged between the output terminal of the second H-bridge converter circuit 26 and the primary winding of the second transformer 13. For example, the resonant components of the resonant tank 28 include an inductive element 28a and a capacitive element 28b. A first resonant tank 27 may be arranged between the output terminal of the first H-bridge converter circuit 25 and the primary winding of the first transformer 11. For example, the resonant components of the resonant tank 27 include an inductive element 27a and a capacitive element 27b.
The first rectifier circuit may perform full-wave rectification, for example in topology of H-bridge made up of power diodes D1 to D4. Similarly, the second rectifier circuit may perform full-wave rectification, for example in topology of H-bridge made up of power diodes D5 to D8.
The controller 23 provides control signals 24 to control the power semiconductor switches S1-S6 of the switching circuit 10. The controller 23 may take the form of a microcontroller such as a microprocessor, digital signal processor (DSP) and/or application specific integrated circuit (ASIC) . Controller 23 may receive input signals such as voltage and current measurements from a voltage sensor and/or current sensor that sense voltage or current with respect to the input from the power source VI. The controller 23 may additionally or alternatively receive voltage and/or current signals from a voltage sensor and/or current sensor that measure output voltage and/or current.
Figure 3 shows a timing diagram of the signals according to an embodiment of present invention. In figure 3, S1 to S6 respectively represent the switching signals applied to the semiconductor switches S 1-S6 of the switching circuit 10； a horizontal axis represents time t, Is1 to Is6 respectively represent currents conducting or freewheeling via the semiconductor switches S1-S6； the voltage Vout generated at the output terminals of DC-DC converter 1； the base voltage Vb generated at the output terminals of the second rectifier circuit 14； the voltage Vpri1 applied to the primary winding of the first transformer 11 and its current Ipri1； the voltage Vpri2 applied to the primary winding of the second transformer 13 and its current Ipri2.
The power semiconductor switches S1-S6 of each phase leg 10a-10c of the switching circuit 10 each generate a nearly 50％duty cycle square waveform. The first H-bridge converter circuit 25 is phase shift controlled to generate square waveform across phase nodes B and C. The first H-bridge converter circuit 25 combined with the inductive element 28a, the capacitive element 28b, the leakage inductance of the first transformer 11 and the power diodes D1 to D4 may form ZVS turn-on phase-shift stage The skilled person should understand that with the help of the resonant tank 27, ZVS turn-on of the power semiconductor switches S3-S6 of the first H-bridge converter circuit 25 may be achieved. However, the power semiconductor switches S3-S4 of the lagging phase 10b may lose soft-switching at lighter load, in spite that the power semiconductor switches S5, S6 of the leading leg 10c may still keep ZVS turn-on. The second H-bridge converter circuit 26 is b-polar controlled to generate square waveform across phase nodes A and B. Figures 4A and 4B show the equivalent circuits of the DC-DC converter according to an embodiment of present  invention including a LLC stage and a phase-shift stage. The second H-bridge converter circuit 26 combined with the inductive element 27a, the capacitive element 27b, the leakage inductance of the second transformer 13 and the power diodes D5 to D8 form a LLC stage. Where the switching frequency is fixed at resonant frequency substantially determined by the  resonant components  28a, 28b of the resonant tank 28, ZVS turn-on of the power semiconductor switches S1-S4 is achieved largely by the energy stored in the magnetizing inductance of the second transformer 13. Lagging leg of the phase-shift stage (the second phase-leg 10b) is shared by the two stages of phase-shift stage and LLC stage. The LLC stage offers ZV turn-on ability to the lagging leg of phase-shift stage even at light load condition. It is because the current via S3 and S4 is the sum of the LLC stage and phase-shift stage. The LLC stage current will dominate in the lagging leg at light load, therefore ZV turn-on across the lagging leg switches can be realized. Because the control signals for the first H-bridge converter circuit 25 and the second H-bridge converter circuit 26 are frequency locked to each other, they may operate substantially at the same switching frequency. As shown in figures 4A and 4B, the output voltages of the LLC stage and phase-shift stage are connected in series at the output side. The LLC converter provides a constant output voltage Vb while the phase-shift converter provides a regulated wide range output voltage, namely Va. The final output voltage of the converter is Vout ＝ Va + Vb.
Back to figure 3, during a first period T1, the first power semiconductor switch S1, the fourth power semiconductor switch S4 and the fifth power semiconductor switch S5 are turned on, and the second power semiconductor switch S2, the third power semiconductor switch S3 and the sixth power semiconductor switch S6 are turned off. The voltage of the input power Vin is exerted to the primary winding of the first transformer 11 via the first resonant tank 27. An inducted AC current of the secondary winding of the first transformer 11 is rectified to a DC current by the first rectifier circuit 12. The DC power output by the first rectifier circuit 12 can be provided to the output voltage Vout to the load. Meanwhile, the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28. An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14. The DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Vb to the load. The DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection. The base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the power transmitting period T1, the first transformer 11 and the second transformer 13 can commonly provide electric power to the load.
During a second period T2, the first power semiconductor switch S1 and the fourth power semiconductor switch S4 are turned on, and the second power semiconductor switch S2, the third power semiconductor switch S3, the fifth power semiconductor switch S5 and the sixth power semiconductor switch S6 are turned off. Now, the  resonant elements  27a, 27b of the first resonant tank 27 and the parasitic capacitances of the fifth power semiconductor switch S5 and the sixth power semiconductor switch S6 are respectively discharged and charged by the energy of the magnetizing inductor of the primary winding of the first transformer 11. The body diode Ds6 of the sixth power semiconductor switch S6 is forward biased, such that the sixth power semiconductor switch S6 may be turned on under a zero voltage. The first resonant tank 27, the first transformer 11, the fourth power semiconductor switch S4, and the antiparallel diode Ds6 constitute freewheeling electrical loop, and thus the first transformer 11 essentially provides no power to the load. Meanwhile, the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28. An inducted AC current of the secondary winding of the second  transformer 13 is rectified to a DC current by the second rectifier circuit 14. The DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Vb to the load. The DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection. The base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the second period T2, the second transformer 13 mainly provides electric power to the load.
During a third period T3, the first power semiconductor switch S1, the fourth power semiconductor switch S4 and the sixth power semiconductor switch S6 are turned on, and the second power semiconductor switch S2, the third power semiconductor switch S3 and the fifth power semiconductor switch S5 are turned off. The ZVS turn on is achieved for the power semiconductor switch S6 of the leading phase leg of the first H-bridge converter circuit 25 operating in phase shift mode. The first resonant tank 27, the first transformer 11, the fourth power semiconductor switch S4, and the sixth power semiconductor S6 constitute freewheeling electrical loop, and thus the first transformer 11 essentially provides no power to the load. Meanwhile, the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28. An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14. The DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Vb to the load. The DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection. The base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the third period T3, the second transformer 13 mainly provides electric power to the load.
During a fourth period T4, the sixth power semiconductor switch S6 is turned on, and the first power semiconductor switch S1, the second power semiconductor switch S2, the third power semiconductor switch S3, the fourth power semiconductor switch S4 and the fifth power semiconductor switch S5 are turned off. In the condition of a light load, the energy stored in the magnetizing inductor of the primary winding of the first transformer 11 might not be sufficient enough for forward-biasing the body diode Ds3 of the third power semiconductor switch S3 of the lagging phase leg of the first H-bridge converter circuit 25. Now, the  resonant elements  28a, 28b of the second resonant tank 28 and the parasitic capacitances of the third power semiconductor switch S3 and the fourth power semiconductor switch S4 are respectively discharged and charged by the energy of the magnetizing inductor of the primary winding of the second transformer 13. By using the energy stored both in the magnetizing inductors of the first transformer 11 and the second transformer 13, the body diodes Ds2, Ds3 of the second power semiconductor switch S2 and the third power semiconductor switch S3 are forward biased, such that the second power semiconductor switch S2 and the third power semiconductor switch S3 may be turned on under a zero voltage. The ZVS turn on condition is achieved for the power semiconductor switch S3 of the lagging phase leg of the first H-bridge converter circuit 25 operating in phase shift mode, as well. In this stage, part of the energy stored in the second resonant tank 28 is transferred to the load through the second transformer 13 based on the principle of LLC converter operation.
As can be seen from figure 3, the first, second, third and fourth periods T1, T2, T3, T4 constitute of the first half cycle of the modulation scheme of the DC to DC converter. Consequently, during a fifth period T5, the second power semiconductor switch S2, the third power semiconductor switch S3 and the sixth power semiconductor switch S6 are turned on, and the first power semiconductor switch S1, the fourth power semiconductor switch S4 and  the fifth power semiconductor switch S5 are turned off. The voltage of the input power Vin is exerted to the primary winding of the first transformer 11 via the first resonant tank 27. An inducted AC current of the secondary winding of the first transformer 11 is rectified to a DC current by the first rectifier circuit 12. The DC power output by the first rectifier circuit 12 can be provided to the output voltage Vout to the load. Meanwhile, the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28. An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14. The DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Va to the load. The DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection. The base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the power transmitting period T1, the first transformer 11 and the second transformer 13 can commonly provide electric power to the load.
During a sixth period T6, the second power semiconductor switch S2 and the third power semiconductor switch S3 are turned on, and the first power semiconductor switch S1, the fourth power semiconductor switch S4, the sixth power semiconductor switch S6 and the fifth power semiconductor switch S5 are turned off. Now, the  resonant elements  27a, 27b of the first resonant tank 27 and the parasitic capacitances of the sixth power semiconductor switch S6 and the fifth power semiconductor switch S5 are respectively discharged and charged by the energy of the magnetizing inductor of the primary winding of the first transformer 11. The body diode Ds5 of the fifth power semiconductor switch S5 is forward biased, such that the fifth power semiconductor switch S5 may be turned on under a zero voltage. The first resonant tank 27, the first transformer 11, the third power semiconductor switch S3, and the antiparallel diode Ds5 constitute freewheeling electrical loop, and thus the first transformer 11 essentially provides no power to the load. The resonant voltage generated by the first resonant tank 27 is exerted to the primary winding of the first transformer 11 via the first resonant tank 27, instead of the input power Vin. Meanwhile, the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28. An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second rectifier circuit 14. The DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Vb to the load. The DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection. The base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the second period T2, the second transformer 13 mainly provides electric power to the load.
During a seventh period T7, the second power semiconductor switch S2, the third power semiconductor switch S3 and the fifth power semiconductor switch S5 are turned on, and the first power semiconductor switch S1, the fourth power semiconductor switch S4 and the sixth power semiconductor switch S6 are turned off. The ZVS turn on is achieved for the fifth power semiconductor switch S5 of the leading phase leg of the first H-bridge converter circuit 25 operating in phase shift mode. The first resonant tank 27, the first transformer 11, the third power semiconductor switch S3, and the antiparallel diode Ds5 constitute freewheeling electrical loop, and thus the first transformer 11 essentially provides no power to the load. Meanwhile, the voltage of the input power Vin is exerted to the primary winding of the second transformer 13 via the second resonant tank 28. An inducted AC current of the secondary winding of the second transformer 13 is rectified to a DC current by the second  rectifier circuit 14. The DC power output by the second rectifier circuit 14 can be stored in the capacitor 20. Therefore, the capacitor 20 can provide the output voltage Vb to the load. The DC power (base voltage Vb) output by the second rectifier circuit 14 is provided to the terminal of the capacitor 20 through serial connection. The base voltage Vb of second rectifier circuit 14 can lift the output voltage Va of the first rectifier circuit 12. Therefore, during the third period T3, the second transformer 13 mainly provides electric power to the load.
During a eighth period T8, the fifth power semiconductor switch S5 is turned on, and the second power semiconductor switch S2, the first power semiconductor switch S1, the fourth power semiconductor switch S4, the third power semiconductor switch S3 and the sixth power semiconductor switch S6 are turned off. In the condition of a light load, the energy stored in the magnetizing inductor of the primary winding of the first transformer 11 might not be sufficient enough for forward-biasing the body diode Ds4 of the fourth power semiconductor switch S4 of the lagging phase leg of the first H-bridge converter circuit 25. Now, the  resonant elements  28a, 28b of the second resonant tank 28 and the parasitic capacitances of the fourth power semiconductor switch S4 and the third power semiconductor switch S3 are respectively discharged and charged by the energy of the magnetizing inductor of the primary winding of the second transformer 13. By using the energy stored both in the magnetizing inductors of the first transformer 11 and the second transformer 13, the body diodes Ds1, Ds4 of the first power semiconductor switch S1 and the fourth power semiconductor switch S4 are forward biased, such that the first power semiconductor switch S1 and the fourth power semiconductor switch S4 may be turned on under a zero voltage. The ZVS turn on condition is achieved for the power semiconductor switch S4 of the lagging phase leg of the first H-bridge converter circuit 25 operating in phase shift mode, as well. In this stage, part of the energy stored in the second resonant tank 28 is transferred to the load through the second transformer 13 based on the principle of LLC converter operation.
After the AC filter 21 filters the AC component of the voltages Va and Vb at the DC output terminal of the first rectifier circuit 12 and the second rectifier circuit 14, the DC-DC converter 1 can provide the output voltage Vout to the load. The electric power shown by a slash shading part of figure 3 is provided by the second transformer 13.
According to figure 3, it is known that the second transformer 13 can keep outputting the base voltage Vb to provide a part of the rated output power through the second rectifier circuit 14 during the periods T1 to T8. The first transformer 11 can provide the adding voltage Va during these periods T1 to T8 to compensate the insufficient part of the rated output power. Therefore, transformers with a smaller power level (transformers with a smaller volume) can be used to implement the first transformer 11 and/or the second transformer 13. By using the transformers with smaller power level, a volume of the DC-DC converter 1 is decreased. Besides, during the second and fourth freewheeling periods T4 and T8, the energy stored in the auxiliary inductor is not only used for ZVS turn-on of the power semiconductor switching element in the lagging phase leg, but also transfers power to the load through the second transformer 13. Therefore, the power loose resulted in the circulating power is decreased. Thirdly, since the power has more than one transmission paths, namely via the first transformer and the second transformer, the rated current for each power semiconductor switching element may be decreased.
In order to increase the transmission efficiency, the switching frequency may be fixed at resonant frequency substantially determined by  resonant components  28a, 28b of the second resonant tank 28. Therefore, the LLC stage operates at the optimal operation point, retaining a high power efficiency and outputting a constant DC voltage Vb. The output voltage Vout  may be regulated by adjusting the phase-shift angle of the phase shift stage. Thus, the DC-DC converter 1 may provide a regulated wide range output voltage, Vout ＝ Va + Vb.
Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no way limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.

Claims (7)

  1. A DC to DC converter, including:
    a first H-bridge converter circuit；
    a second H-bridge converter circuit sharing a phase leg with the first H-bridge converter circuit；
    a first rectifier circuit；
    a second rectifier circuit；
    a first transformer, having primary winding connected to output terminal of the first H-bridge converter circuit and secondary winding connected to input terminal of the first rectifier circuit；
    a second transformer, having primary winding connected to output terminal of the second H-bridge converter circuit and secondary winding connected to input terminal of the second rectifier circuit；
    wherein:
    an output terminal of the first rectifier circuit and an output terminal of the second rectifier circuit are connected in series.
  2. The DC to DC converter according to claim 1, wherein:
    the first H-bridge converter circuit is operable in phase-shift mode with a switching frequency, having the shared leg as lagging leg and a leading leg； and
    the second H-bridge converter circuit is operable in bi-polar mode with the switching frequency.
  3. The DC to DC converter according to claim 2, wherein:
    the first H-bridge converter circuit is operable with duty cycle of substantially 50％； and
    the second H-bridge converter circuit is operable with duty cycle of substantially 50％.
  4. The DC to DC converter according to any of the preceding claims, further including:
    a resonant tank, being arranged between the output terminal of the second H-bridge converter circuit and the primary winding of the second transformer.
  5. The DC to DC converter according to claim 4, wherein:
    the switching frequency is fixed at resonant frequency substantially determined by resonant components of the resonant tank.
  6. The DC to DC converter according to claim 5, wherein:
    the resonant component of the resonant tank includes an inductive element and a capacitive element.
  7. The DC to DC converter according to any of the preceding claims, wherein:
    the first rectifier circuit is of full-wave rectification.
PCT/CN2017/073925 2017-02-17 2017-02-17 Dc to dc converter WO2018148932A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2020061906A1 (en) * 2018-09-27 2020-04-02 Abb Schweiz Ag Power supply cell and power supply system using the same
CN115864614A (en) * 2023-03-03 2023-03-28 深圳市凌康技术有限公司 LLC circuit for wide-output-voltage-range high-power charger and control method thereof

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Publication number Priority date Publication date Assignee Title
US5576940A (en) * 1995-01-09 1996-11-19 General Electric Company Front-end power converter for distributed power systems
CN103887981A (en) * 2014-03-20 2014-06-25 浙江大学 Full-bridge DC-DC converter
US20150103561A1 (en) * 2013-10-11 2015-04-16 Futurewei Technologies, Inc. Apparatus and Method for Multiple Primary Bridge Resonant Converters
CN106059376A (en) * 2016-06-03 2016-10-26 山东航天电子技术研究所 Power supply system suitable for high repetition frequency impulse load
CN106208300A (en) * 2016-07-05 2016-12-07 陕西科技大学 A kind of medical laser charge power supply

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5576940A (en) * 1995-01-09 1996-11-19 General Electric Company Front-end power converter for distributed power systems
US20150103561A1 (en) * 2013-10-11 2015-04-16 Futurewei Technologies, Inc. Apparatus and Method for Multiple Primary Bridge Resonant Converters
CN103887981A (en) * 2014-03-20 2014-06-25 浙江大学 Full-bridge DC-DC converter
CN106059376A (en) * 2016-06-03 2016-10-26 山东航天电子技术研究所 Power supply system suitable for high repetition frequency impulse load
CN106208300A (en) * 2016-07-05 2016-12-07 陕西科技大学 A kind of medical laser charge power supply

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2020061906A1 (en) * 2018-09-27 2020-04-02 Abb Schweiz Ag Power supply cell and power supply system using the same
CN115864614A (en) * 2023-03-03 2023-03-28 深圳市凌康技术有限公司 LLC circuit for wide-output-voltage-range high-power charger and control method thereof

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