CN111064359A - Wide-range bidirectional conversion circuit and control method - Google Patents

Wide-range bidirectional conversion circuit and control method Download PDF

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Publication number
CN111064359A
CN111064359A CN201911340580.8A CN201911340580A CN111064359A CN 111064359 A CN111064359 A CN 111064359A CN 201911340580 A CN201911340580 A CN 201911340580A CN 111064359 A CN111064359 A CN 111064359A
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converter
voltage
current
bridge
input
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Inventor
任小永
朱昕昳
张之梁
陆懿晨
李加明
杨勇
陈乾宏
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Nanjing University of Aeronautics and Astronautics
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Nanjing University of Aeronautics and Astronautics
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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
    • H02M3/005—Conversion of dc power input into dc power output using Cuk 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • 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
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or 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
    • 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
    • H02M3/33576—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 having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33584—Bidirectional 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/79—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/797—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only

Abstract

The invention discloses a wide-range bidirectional conversion circuit and a control method, comprising a three-level bidirectional converter and a control unit, wherein the three-level bidirectional converter is formed by sequentially connecting a non-isolated DC/DC converter, an isolated DC/DC converter and a DC/AC inverter; when the system works in the forward direction, the direct-current power supply or the energy storage equipment realizes grid-connected energy feedback through the non-isolated DC/DC converter, the isolated DC/DC converter and the DC/AC inverter; when the device works reversely, the alternating current voltage supplies power to a direct current load or charges an energy storage device through the rectifying circuit, the isolation DC/DC converter and the non-isolation DC/DC converter. In order to adapt to different power levels and realize higher input current ripple control, the non-isolated converter adopts a multi-phase staggered parallel structure; in order to further widen the input and output range requirements in practical application, the isolated converter can adopt full-bridge/half-bridge variable structure control. The whole system has the advantages of wide range of input direct-current voltage, wide range of output alternating-current voltage, wide load range, small current ripple, high-frequency isolation, high efficiency, energy conservation, environmental protection and the like.

Description

Wide-range bidirectional conversion circuit and control method
Technical Field
The invention discloses a wide direct-current voltage input and wide alternating-current voltage output bidirectional conversion topology, belongs to the technical field of power electronic converters, and is suitable for the fields of multi-electric aircraft power systems, battery energy storage devices, hybrid wind and light complementary systems, electric vehicles, hybrid electric vehicles and the like.
Background
In order to improve the stability and efficiency of a distributed power system and make full use of renewable energy, micro-grids are widely concerned by domestic and foreign scholars, wherein grid-connected bidirectional DC/AC converters are important components. The bidirectional DC/AC converter is required to realize both the rectifier function and the inverter function according to the input/output states. The bidirectional DC/AC converter is mainly applied to the fields of multi-electric aircraft power systems, battery energy storage devices, hybrid wind and solar hybrid systems, electric automobiles, hybrid electric automobiles and the like.
At present, an isolation bidirectional DC/AC converter is mainly formed by cascading a bidirectional DC/DC converter and a bidirectional inverter, and front and rear stages are controlled independently. The scheme is flexible to control and realize, but how to improve the system efficiency of the two-stage power conversion is a big difficulty, and the scheme is not suitable for the conditions of wide input and output voltage range and wide load range.
Disclosure of Invention
The invention provides a wide direct current voltage input and wide alternating current voltage output bidirectional conversion topology aiming at the defects and shortcomings in the prior art. The topological structure is symmetrical, and the requirements of bidirectional conversion of wide direct-current voltage input and wide alternating-current voltage output are met.
The invention provides a control method of the bidirectional conversion topological structure.
In order to solve the technical problem, the invention adopts the following specific technical scheme:
a wide-range bidirectional conversion circuit comprises a three-level bidirectional converter and a control unit, wherein the three-level bidirectional converter is formed by sequentially connecting a non-isolated DC/DC converter, an isolated DC/DC converter and a DC/AC inverter; when the system works in the forward direction, the direct-current power supply or the energy storage equipment realizes grid-connected energy feedback through the non-isolated DC/DC converter, the isolated DC/DC converter and the DC/AC inverter; when the device works reversely, the alternating current voltage supplies power to a direct current load or charges an energy storage device through the rectifying circuit, the isolation DC/DC converter and the non-isolation DC/DC converter. The whole system realizes wide direct current input voltage range, wide alternating current output voltage range, wide load range, small current ripple, high efficiency, high reliability and strong compatibility.
Preferably, the non-isolated DC/DC converter is a synchronous rectification Cuk converter or a synchronous rectification Boost converter; the bidirectional power amplifier has bidirectional working capacity, and the forward input end of the bidirectional power amplifier is provided with a filter inductor, so that higher input current ripple control can be realized. The isolation DC/DC converter selects a full-bridge LLC resonant converter, a T-type LLC resonant converter or a CLLC resonant converter; the DC/AC bidirectional converter is an H-bridge inverter or a T-type inverter.
Preferably, the non-isolated DC/DC converter adopts a multiphase interleaving parallel structure; the non-isolated DC/DC converter adopts an n-phase staggered parallel structure, wherein n is 1-6; when the number of the interleaved parallel converters is m, m is more than or equal to 1 and less than or equal to n, and the driving control signals of the switching tubes of each phase are staggered by 360 degrees/m.
Preferably, the synchronous rectification Cuk converter comprises a first switching tube Q1A second switch tube Q2Filter inductance L1Filter inductance L2Capacitor C1. The input end of the Cuk converter is connected in parallel with a DC tested device or an energy storage device, and the output end is connected in parallel with a bus capacitor Cbus1. Because the output voltage of the Cuk converter is opposite in polarity to the input voltage, when the Cuk converter is connected with the second-stage LLC resonant converter, the output positive electrode of the Cuk converter is connected with the input negative electrode of the LLC resonant converter, and the output negative electrode of the Cuk converter is connected with the input positive electrode of the LLC resonant converter.
Preferably, the LLC resonant converter includes a primary side full-bridge conversion circuit, a resonant circuit, a high-frequency isolation transformer, and a secondary side full-bridge rectification circuit; the primary side full-bridge conversion circuit comprises a third switching tube Q3Fourth switch tube Q4Fifth switch tube Q5The sixth switching tube Q6. The resonant circuit comprises a resonant inductor LrResonant capacitor CrAnd transformer excitation inductance Lm. Switch tube Q3And Q5The middle point of the resonant inductor is sequentially connected with the resonant capacitor in series and then connected with one end of a primary side excitation inductor of the high-frequency transformer, and a switching tube Q4And Q6The middle point of the transformer is connected with the other end of the primary side excitation inductor of the high-frequency transformer. The secondary side full-bridge rectification circuit comprises a seventh switching tube Q7The eighth switch tube Q8The ninth switching tube Q9The tenth switching tube Q10. Switch tube Q7And Q9The middle point is connected with one end of the secondary side of the transformer, and the switching tube Q8And Q10Is connected with the other end of the secondary side of the transformer. The first end and the second end of the LLC resonant converter output are respectively connected with a bus capacitor Cbus2A positive electrode and a negative electrode; and the positive electrode and the negative electrode of the bus capacitor are respectively connected with the first end and the second end of the H-bridge type inverter.
Preferably, the H-bridge converter comprises a first switching tube S1A second switch tube S2A third switching tube S3Fourth switch tube S4And an LCL filter; the LCL filter comprises a filter inductor L3Filter inductor L4And a filter capacitor Cf. Switch tube S1And S2The middle points of the filter inductors L are connected in series in sequence3And L4And then connected to the power grid; switch tube S3And S4Is connected to the grid ground. Filter inductance L3And a filter inductance L4In series, with the midpoint passing through the filter capacitor CfConnected to the network ground, a filter inductance L4The other end is connected to the power grid.
The control method of the wide-range bidirectional conversion circuit adopts the wide-range bidirectional conversion circuit, a control unit comprises a sampling circuit, a DSP and an optical coupling isolation drive circuit, and the control process is as follows when the control unit works in the forward direction:
first, in the constant current mode
1) The input current Iin of the non-isolated DC/DC converter is input into the DSP through a sampling circuit, a sampling signal Iin is compared with an input current reference Iin _ ref, an error signal is calculated by a proportional-integral-derivative controller PID in the DSP and then is compared with a triangular carrier to obtain a pulse width modulation PWM signal, the pulse width modulation PWM signal is input into an isolation driving circuit, the duty ratio of a switching tube of the non-isolated DC/DC converter is controlled respectively, and the input current i is controlledinIs equal to the input current reference iin_ref；
Sampling bus voltage signal Vbus2Sending the voltage difference to a DSP, filtering by a secondary power frequency limiter, and then making a difference with a bus voltage reference value, wherein an error signal obtains a given A of a current inner ring through a PI controller;
2) sampling grid current igAnd the network voltage vacSending the signals into a DSP, calculating the grid voltage sampling signals through a phase-locked loop in the DSP to obtain grid voltage phase information sin (omega)0t); thereby obtaining a current reference signal A sin (omega)0t), where A is the output of the voltage outer loop; grid current igAnd A sin (omega)0t) comparing, wherein the error signal is calculated by a PI controller in the DSP and then compared with a triangular carrier wave to obtain a PWM signal; the PWM signal is processed by an optical coupling isolation drive circuit to obtain a drive signal to control a DC/AC inverter switch tube (S)1～S4) The unit power factor is connected in parallel by switching on and off;
3) input bus voltage V of DC/AC inverterbus2The isolated DC/DC converter works in the state of a DC transformer DCX and inputs V according to the grid-connected voltagebus1Bus voltage following output voltage Vbus2；
Secondly, under the working modes of constant power and constant resistance, the constant power and the constant resistance are respectively converted into corresponding constant current values through formulas (1) and (2), the control of the constant power and the constant resistance is converted into constant current control, and the corresponding control after the conversion is the same as the constant current control scheme;
Figure BDA0002332151880000031
Figure BDA0002332151880000032
wherein P issetAt a constant power setting, RsetIs a constant resistance set value;
thirdly, in the working state of the constant-pressure mode:
1) non-isolated DC/DC converter input voltage VinInput into DSP via sampling circuit to sample signal vinAnd an input voltage reference vin_refAfter the error signal is calculated by PID in DSP, the error signal is compared with triangular carrier to obtain PWM signal, which is input to the isolated drive circuit to control the switch tube (Q) of the non-isolated DC/DC converter1～Q2) Control the input voltage vinIs equal to the input voltage reference vin_ref；
2) Sampling bus voltage signal Vbus2Sending the voltage difference to a DSP, filtering by a secondary power frequency trap, and then making a difference with a bus voltage reference value, wherein an error signal obtains a given A of a current inner ring through a PI controller; sampling grid current igAnd the network voltage vacSending the signals into a DSP, calculating the grid voltage sampling signals through a phase-locked loop in the DSP to obtain grid voltage phase information sin (omega)0t); thereby obtaining a current reference signal A sin (omega)0t) where A is the output of the voltage outer loop; grid current igAnd A sin (omega)0t) comparing, and comparing the error signals with triangular carriers after calculation by a PI controller in the DSP to obtain PWM signals; the PWM signal is processed by an optical coupling isolation drive circuit to obtain a drive signal to control a switching tube (S) of the H-bridge type inverter1～S4) The unit power factor is connected in parallel by switching on and off; input bus voltage V of H-bridge inverterbus2Determined by the grid-connected voltage;
3) the isolated DC/DC converter works in the DCX state of the DC transformer and inputs Vbus1Bus voltage following output voltage Vbus2。
Or reverse work is adopted, and the control process during the reverse work is as follows:
1) bus voltage Vbus2And its reference voltage Vbus2_refComparing the error signal with the absolute value | v of the grid voltage after the error signal is calculated by a PI controlleracMultiplying | to obtain a grid current reference ig_ref(ii) a Grid current reference ig_refWith the current i of the gridgComparing to obtain error signal, calculating the error signal by PI controller, comparing with triangular carrier to obtain PWM signal, inputting into optical coupling isolation drive circuit, and respectively controlling DC/AC inverter rectifier switching tube (S)1～S4) The duty ratio of the output bus voltage V is controlledbus2Is equal to its reference Vbus2_refMeanwhile, the same phase of the voltage and the current of the power grid is realized;
2) the isolated DC/DC converter works in a DCX state, and the output voltage directly follows Vbus2A bus voltage;
3) output voltage VoInputting the signal into DSP via sampling circuit to sample signal VoAnd an output voltage reference Vo_refAfter the error signal is calculated by a Proportional Integral Derivative (PID) controller in a Digital Signal Processor (DSP), the error signal is compared with a triangular carrier to obtain a Pulse Width Modulation (PWM) signal, the PWM signal is input into an isolation driving circuit, the duty ratio of a switching tube of a non-isolation direct current/direct current (DC/DC) converter is controlled respectively, and the output voltage V is controlledoIs equal to the output voltage reference Vo_ref。
Preferably, when different power grades need to be adapted and the requirement of a wide load range is met, the non-isolated DC/DC converter adopts an n-phase staggered parallel structure, and n is 1-6; when the number of the interleaved parallel converters is m, m is more than or equal to 1 and less than or equal to n, and the driving control signals of the switching tubes of each phase are staggered by 360 degrees/m.
Preferably, when the range of the output voltage needs to be expanded, a full-bridge/half-bridge variable structure control mode is adopted for the LLC resonant converter, and when the LLC resonant converter needs to be in a full-bridge structure, an upper tube of one bridge arm is kept normally open, a lower tube is kept normally closed, and the LLC resonant converter can be switched to be in a half-bridge structure; for the T-type LLC resonant converter, a full-bridge/half-bridge variable structure control mode is adopted, a switch tube for connecting a voltage-dividing bus capacitor and one bridge arm is closed, and the bridge arm is kept normally open, so that the T-type LLC resonant converter can be switched to a half-bridge structure; the voltage of the half-bridge resonant cavity after switching is half of the input voltage, and the voltage transformation ratio of the LLC resonant converter is half of that before switching; the mode switching is determined by the required ac output voltage, thereby extending the range of output voltages.
The wide direct current voltage input and wide alternating current voltage output bidirectional conversion circuit and the control method adopt a variable structure mode to expand the load and voltage range according to different application requirements. The multi-phase parallel structure can process large input current and has a ripple cancellation effect on the current. In practical application, a control method for shielding different phases is adopted for the staggered parallel CUK circuit according to the size of the load and an efficiency optimization algorithm; when the number of the interleaved parallel converters is m, the driving control signals of the switching tubes of each phase are staggered by 360 degrees/m. The scheme can adapt to different power grades and meet the requirement of efficiency improvement in a wide voltage and wide load range.
The wide direct-current voltage input and wide alternating-current voltage output bidirectional conversion circuit provided by the invention is a three-level cascade topology of a non-isolated DC/DC converter, an isolated DC/DC converter and a DC/AC bidirectional converter, the first-level interleaved parallel CUK converter can process larger current and has the advantage of input current ripple cancellation, and because the input end is provided with an inductor, high input current ripple control can be realized; a control method of dynamically shielding a plurality of paths is adopted for the interleaved parallel CUK converters according to different input currents, so that the load range is widened, and the requirement of improving the efficiency in a wide load range is met; the LLC resonant converter always works at a constant frequency at a resonance point, ZVS of a switching tube and ZCS of a secondary side synchronous rectifier tube can be realized in a full-load range, the high efficiency of the converter is realized, and meanwhile, the high-frequency isolation function is realized; in addition, the LLC resonant converter can be controlled by adopting a full-bridge/half-bridge variable structure according to the requirements of input and output voltage ranges, and the ranges of the input and output voltages are widened. The H-bridge bidirectional converter can realize the functions of forward inversion grid connection and reverse rectification filtering, and has high conversion efficiency.
The invention has the following beneficial effects:
1. the bidirectional conversion topological structure has wide direct current input and alternating current output voltage range, is suitable for the fields of multi-electric aircraft power systems, battery energy storage devices, hybrid wind and light complementary systems, electric automobiles, hybrid electric automobiles and the like, and has the advantages of wide input and output voltage range, wide load range, high efficiency, high reliability, strong compatibility and the like.
2. The forward input end of the CUK converter is provided with the filter inductor, so that very high input current ripple control can be realized, and the CUK converter is suitable for occasions with high requirements on input current ripples, such as electronic loads, batteries and the like.
3. The CUK converter adopts a staggered parallel technology, adapts to different power levels, reduces capacitance volume and ripple current, can realize the function of voltage boosting and reducing, and meets the requirement of bidirectional work of the whole topology. According to the difference of input current, a plurality of Cuk circuits can be dynamically shielded, the load range is widened, the requirement of efficiency improvement in a wide load range is met, and the high-voltage Cuk circuit has the advantages when the forward input is low-voltage large current.
4. In the control method, the LLC resonant converter works in a DCX state, the gain is always 1, the control is simple, the efficiency is high, high-frequency isolation is realized, and the safety of client equipment is effectively protected; and the zero-voltage switching-on of the primary side switching tube and the zero-current switching-off of the secondary side rectifying tube can be realized in a full-load and wide input voltage range, so that the switching loss is greatly reduced, the efficiency is improved, and the electromagnetic interference is reduced.
5. According to the requirements of direct current input and alternating current output voltages, the LLC resonant converter adopts full-bridge/half-bridge variable structure control, the voltage of a switched half-bridge resonant cavity is half of the input voltage, and therefore the voltage transformation ratio of the LLC resonant converter is half of that before switching. The full-bridge/half-bridge variable structure control method widens the range of input and output voltages.
In order to adapt to different power levels and realize higher input current ripple control, the non-isolated converter can adopt a multiphase staggered parallel structure; in order to further widen the input and output range requirements in practical application, the isolated converter can adopt full-bridge/half-bridge variable structure control. The whole system has the advantages of wide range of input direct-current voltage, wide range of output alternating-current voltage, wide load range, small current ripple, high-frequency isolation, high efficiency, energy conservation, environmental protection and the like.
The non-isolated DC/DC converter adopts a CUK converter, and has bidirectional working capacity, a forward input end is provided with a filter inductor, the bidirectional conversion circuit works in the forward direction and is used as an electronic load or used as a battery in the reverse direction, the requirement on current ripple is higher, and the forward input end is provided with the filter inductor at the moment, so that higher input current ripple control can be realized; the isolation DC/DC converter adopts LLC resonance topology to play a role in high-frequency isolation, and energy is transferred efficiently.
Drawings
FIG. 1 is a schematic circuit diagram of the present invention (also referred to as abstract diagram);
FIG. 2 is a four-phase interleaved parallel Cuk expansion diagram of the present invention;
FIG. 3 is a control diagram of the forward operation constant current mode of the present invention;
FIG. 4 is a control diagram of the constant voltage mode of forward operation of the present invention;
FIG. 5 is a reverse operation control diagram of the present invention;
FIG. 6 is a switching diagram of the bridge LLC resonant converter structure of the invention;
FIG. 7 is a switching diagram of the T-type LLC resonant converter structure of the invention;
FIG. 8 is a graph of LLC full/half bridge variable structure bus voltage of the present invention;
FIG. 9 is a development of N-interleaved parallel Cuk of the present invention;
FIG. 10 is an expanded view of the DC/AC bi-directional converter of the present invention;
fig. 11 is an expanded view of the CLLC resonant converter of the present invention;
fig. 12 is an expanded view of the synchronous rectification Boost converter of the present invention;
FIG. 13 is a system control flow diagram of the present invention;
in the figure: 1-Cuk converter; 2-LLC-DCX converter; 3-H bridge type inverter
Symbolic illustration of components in the drawings
VinInput voltage Vbus2Bus voltage
L1～L2Cuk inductor LrResonance inductor
C1～C2Cuk capacitor CrResonance capacitor
Q1～Q10MOSFET S1～S4IGBT
Cbus1Bus capacitor L3～L4Filter inductor
Cbus2Bus capacitor CfFilter capacitor
Vbus1Grid voltage of bus voltage Grid
The specific implementation mode is as follows:
the invention is described in further detail below with reference to the accompanying drawings. The specific embodiments described herein are only used for explaining the present invention, and are not limiting to the present invention, for example, the non-isolated DC/DC converter in the embodiments may be a single-phase or multi-phase synchronous rectification Cuk converter, and may also be a synchronous rectification Boost converter; the isolation DC/DC converter can be an LLC resonant converter or a CLLC resonant converter; the DC/AC bidirectional converter may be H-type, T-type, etc., and several combinations of designs shown in fig. 1, 9, 10, 11, and 12 are within the scope of this patent.
The first embodiment is as follows: wide direct-current voltage input and wide alternating-current voltage output bidirectional conversion topological structure
As shown in fig. 2, the wide-range bidirectional conversion circuit of the present invention adopts a three-stage bidirectional converter design, including a non-isolated/isolated bidirectional direct current/direct current converter (DC/DC), a direct current/alternating current (DC/AC) bidirectional converter and a system control unit.
When the converter works in the forward direction, the direct-current power supply or the energy storage equipment realizes grid-connected energy feedback through the non-isolated DC/DC converter, the isolated DC/DC converter and the DC/AC inverter; when the device works reversely, the alternating current voltage supplies power to a direct current load or charges an energy storage device through the rectifying circuit, the isolation DC/DC converter and the non-isolation DC/DC converter. The non-isolated DC/DC converter is a staggered parallel connection CUK converter, and has bidirectional working capacity, a forward input end is provided with a filter inductor, the bidirectional conversion circuit works in the forward direction and is used as an electronic load or used by a reverse working battery, the requirement on current ripple is higher, and the forward input end is provided with the filter inductor, so that higher input current ripple control can be realized; the isolation DC/DC converter adopts LLC resonance topology to play a role of high-frequency isolation, and energy is transferred efficiently; the DC/AC converter adopts an H-bridge inverter, and the control unit comprises a sampling circuit and Digital Signal Processing (DSP) digital control.
The main technical indexes of the wide-range bidirectional conversion topology design example of the invention are shown in table 1.
TABLE 1 technical indices
Figure BDA0002332151880000071
The first-stage non-isolated DC/DC converter is formed by a plurality of Cuk converters connected in parallel in an interlaced mode, and each Cuk converter comprises a first switching tube Q1A second switch tube Q2A third switching tube Q3Fourth switch tube Q4Fifth switch tube Q5The sixth switching tube Q6Seventh switching tube Q7The eighth switch tube Q8. Switch tube Q1、Q2Inductance L1、L2And a capacitor C1Switching tube Q3、Q4Inductance L3、L4And a capacitor C2Switching tube Q5、Q6Inductance L5、L6And a capacitor C3And a switching tube Q7、Q8Inductance L7、L8And a capacitor C4And forming a four-phase interleaved parallel Cuk converter. The input end of the Cuk converter is connected in parallel with a DC tested device or an energy storage device, and the output end is connected in parallel with a bus capacitor Cbus1. Because the output voltage of the Cuk converter is opposite in polarity to the input voltage, when the Cuk converter is connected with the second-stage LLC resonant converter, the output positive electrode of the Cuk converter is connected with the input negative electrode of the LLC resonant converter, and the output negative electrode of the Cuk converter is connected with the input positive electrode of the LLC resonant converter. Wherein the switch tubeQ1～Q8Are all MOS tubes.
The second-stage isolation DC/DC converter adopts an LLC resonant converter and comprises a primary side full-bridge conversion circuit, a resonant circuit, a high-frequency isolation transformer and a secondary side full-bridge rectification circuit; the primary side full-bridge conversion circuit comprises a ninth switching tube Q9The tenth switching tube Q10The eleventh switch tube Q11The twelfth switching tube Q12. The resonant circuit comprises a resonant inductor LrResonant capacitor CrAnd transformer excitation inductance Lm. Switch tube Q9And Q11The middle point of the resonant inductor is sequentially connected with the resonant capacitor in series and then connected with one end of a primary side excitation inductor of the high-frequency transformer, and a switching tube Q10And Q12The middle point of the transformer is connected with the other end of the primary side excitation inductor of the high-frequency transformer. The secondary side full-bridge rectification circuit comprises a thirteenth switching tube Q13The fourteenth switching tube Q14The fifteenth switch tube Q15Sixteenth switching tube Q16. Switch tube Q13And Q15The middle point is connected with one end of the secondary side of the transformer, and the switching tube Q14And Q16Is connected with the other end of the secondary side of the transformer. The first end and the second end of the output of the two-stage non-isolated/isolated DC/DC converter are respectively connected with a bus capacitor Cbus2A positive electrode and a negative electrode; and the anode and the cathode of the bus capacitor are respectively connected with the first end and the second end of the DC/AC bidirectional converter. Wherein the switching tube Q9～Q16Are all MOS tubes.
The isolated bidirectional converter is not limited to the LLC resonant converter, but may be a CLLC resonant converter. The LLC resonant converter may be in a full-bridge configuration or a T-type configuration.
The third-stage DC/AC bidirectional converter adopts an H-bridge type converter and comprises a first switching tube S1A second switch tube S2A third switching tube S3Fourth switch tube S4And an LCL filter; the LCL filter comprises a filter inductor L3Filter inductor L4And a filter capacitor Cf. Switch tube S1And S2The middle points of the filter inductors L are connected in series in sequence3And L4Is then connected to electricityA net; switch tube S3And S4Is connected to the grid ground. Filter inductance L3And a filter inductance L4In series, with the midpoint passing through the filter capacitor CfConnected to the network ground, a filter inductance L4The other end is connected to the power grid. Wherein the switch tube S1～S4Are both IGBTs or MOSFETs.
The DC/AC bidirectional converter is not limited to the H-bridge type inverter, but can be other inverters according to the bus Cbus2Other suitable inverters can be selected, for example, a T-type inverter can be selected when the bus voltage is high.
The transformer transformation ratio in the LLC resonant converter is designed to be 1: and 5, the switching frequency is equal to the resonant frequency, and the gain is 5. Excitation inductance LmDesigned according to the energy required for realizing ZVS of LLC primary side full-bridge switching tube as follows
Figure BDA0002332151880000081
Wherein T issIs LLC switching period, tdeadAs dead time, CossIs a primary side switch tube junction capacitor.
Because the LLC resonant converter operates in an open-loop fixed-frequency state and the switching frequency is approximately equal to the resonant frequency in actual operation. To reduce the problem of high LLC output voltage gain under light load, Lm/LrShould be large enough to make the gain curve sufficiently flat near the resonance point so that the LLC does not suffer from the high output voltage swing during constant frequency light load operation. Actual Lm/LrWith a value of 16, the gain curve is sufficiently flat near the resonance point.
The invention discloses an example of a wide input and output range bidirectional conversion topology design, and specific parameters in a circuit are shown in Table 2
TABLE 2 Circuit parameters
Figure BDA0002332151880000091
The LLC fixed frequency open loop works near a resonance point to realize ZVS switching-on of a switching tube on the primary side of the LLC converter and ZCS switching-off of a rectifying tube on the secondary side, and switching-on and switching-off losses of the switching tube are greatly reduced. In addition, the secondary side adopts a rectifier tube to replace a diode, so that the conduction loss of a secondary side device is greatly reduced.
Example two: the invention discloses a wide direct current voltage input and wide alternating current voltage output bidirectional conversion topology control method, which comprises the following steps:
the wide direct current voltage input and wide alternating current voltage output bidirectional conversion topology control method mainly comprises a forward working control scheme:
firstly, the control scheme during forward operation is as follows:
firstly, in a constant-current mode working state:
cuk input current IinInput into DSP via sampling circuit to sample signal iinAnd an input current reference iin_refComparing, after the error signal is calculated by a Proportional Integral Derivative (PID) controller in the DSP, comparing with a triangular carrier to obtain a Pulse Width Modulation (PWM) signal, inputting the PWM signal into an isolation driving circuit, respectively controlling the duty ratio of a switching tube of the Cuk converter and controlling the input current iinIs equal to the input current reference iin_ref。
Sampling bus voltage signal Vbus2And sending the voltage difference to a DSP, filtering by a secondary power frequency trap, and obtaining a given A of the current inner loop by an error signal through a PI controller. Sampling grid current igAnd the network voltage vacSending the signals into a DSP, calculating the grid voltage sampling signals through a phase-locked loop in the DSP to obtain grid voltage phase information sin (omega)0t) to obtain a current inner loop reference current A sin (ω)0t) (a is the output of the voltage outer loop). The current inner ring comprises bus capacitor voltage balance control, a Proportional Resonance (PR) compensator, capacitor current active damping control and power grid voltage feedforward. Sampling voltage v on two voltage-dividing capacitors of busc1And vc2Taking the difference, multiplying the capacitance difference by a coefficient KgAnd when the voltage is added to a current reference, the balanced voltage division of the bus capacitor is ensured. Compensator Gc(s) use of PR compensator to achieve non-statics tracking of sinusoidal signals. Sampling LCL filter capacitance current icMultiplied by a coefficient KcAdded to the PR compensated reference as active damping to suppress the intrinsic resonance spike. Sampling grid voltage vgAnd carrying out power grid voltage feedforward control to inhibit multiple harmonic components in the current entering the power grid. And the final error signal is calculated by a PI controller in the DSP, and then the triangular carrier wave is compared to obtain a PWM signal. The PWM signal is used for obtaining a driving signal through an optical coupling isolation driving circuit to control a DC/AC H bridge type inverter switching tube (S)1～S4) The unit power factor is connected in parallel by switching on and off. Input bus voltage V of DC/AC bidirectional converterbus2The LLC resonant converter works in a direct current transformer (DCX) state and the input V is determined by grid-connected voltagebus1Bus voltage following output voltage Vbus2. The control method in the constant current mode is shown in fig. 3.
Secondly, under the working mode of constant power and constant resistance, the constant power and the constant resistance can be converted into corresponding constant current values through formulas (1) and (2), so that the control block diagrams of the constant power and the constant resistance can be converted into constant current control block diagrams, and the corresponding control is the same as the constant current control scheme.
Figure BDA0002332151880000101
Figure BDA0002332151880000102
Wherein P issetAt a constant power setting, RsetIs a constant resistance set value.
Thirdly, under the working condition of the constant voltage mode, the Cuk input voltage VinInput into DSP via sampling circuit to sample signal vinAnd an input voltage reference vin_refAfter the error signal is calculated by a Proportional Integral Derivative (PID) controller in the DSP, the error signal is compared with a triangular carrier to obtain a Pulse Width Modulation (PWM) signal and the PWM signal is input into an isolation driving circuit to respectively control switching tubes (Q) of the Cuk converter1～Q2) Control the input voltage vinIs equal to the input voltage reference vin_ref. Sampling nutLine voltage signal Vbus2And sending the voltage difference to a DSP, filtering by a secondary power frequency trap, and obtaining a given A of the current inner loop by an error signal through a PI controller. Sampling grid current igAnd the network voltage vacSending the signals into a DSP, calculating the grid voltage sampling signals through a phase-locked loop in the DSP to obtain grid voltage phase information sin (omega)0t) to obtain a current inner loop reference current A sin (ω)0t) (a is the output of the voltage outer loop). The current inner ring comprises bus capacitor voltage balance control, a Proportional Resonance (PR) compensator, capacitor current active damping control and power grid voltage feedforward. Sampling voltage v on two voltage-dividing capacitors of busc1And vc2Taking the difference, multiplying the capacitance difference by a coefficient KgAnd when the voltage is added to a current reference, the balanced voltage division of the bus capacitor is ensured. Compensator Gc(s) use PR compensator to realize non-static tracking of sinusoidal signal. Sampling LCL filter capacitance current icMultiplied by a coefficient KcAdded to the PR compensated reference as active damping to suppress the intrinsic resonance spike. Sampling grid voltage vgAnd carrying out power grid voltage feedforward control to inhibit multiple harmonic components in the current entering the power grid. And the final error signal is calculated by a PI controller in the DSP, and then the triangular carrier wave is compared to obtain a PWM signal. The PWM signal is used for obtaining a driving signal through an optical coupling isolation driving circuit to control a DC/AC H bridge type inverter switching tube (S)1～S4) The unit power factor is connected in parallel by switching on and off. Input bus voltage V of DC/AC bidirectional converterbus2The LLC resonant converter works in a direct current transformer (DCX) state and the input V is determined by grid-connected voltagebus1Bus voltage following output voltage Vbus2. The control method in the constant voltage mode is shown in fig. 4.
Example three: the invention discloses a wide direct current voltage input and wide alternating current voltage output bidirectional conversion topology control method, which comprises the following steps:
the invention discloses a wide direct current voltage input and wide alternating current voltage output bidirectional conversion topology control method, which adopts the following control scheme during reverse work:
bus voltage Vbus2And its reference voltage Vbus2_refComparing the error signal with the absolute value | v of the grid voltage after the error signal is calculated by a PI controlleracMultiplying | to obtain a grid current reference ig_ref(ii) a Grid current reference ig_refWith the current i of the gridgComparing to obtain error signal, calculating the error signal by PI controller, comparing with triangular carrier to obtain PWM signal, inputting into optical coupling isolation drive circuit, and respectively controlling AC/DC converter switching tube (S)1～S4) The duty ratio of the output bus voltage V is controlledbus2Is equal to its reference Vbus2_refAnd meanwhile, the same phase of the voltage and the current of the power grid is realized.
LLC resonant converter works in DCX state, and output voltage directly follows Vbus2The bus voltage.
Output voltage VoInputting the signal into DSP via sampling circuit to sample signal VoAnd an output voltage reference Vo_refAfter the error signal is calculated by a Proportional Integral Derivative (PID) controller in the DSP, the error signal is compared with a triangular carrier to obtain a Pulse Width Modulation (PWM) signal and the PWM signal is input into an isolation driving circuit to respectively control the duty ratio of a switching tube of the Cuk converter and control the output voltage VoIs equal to the output voltage reference Vo_ref. The control method in the reverse operation is shown in fig. 5.
Example four: the invention discloses a topology phase-cut control method for wide direct current voltage input and wide alternating current voltage output bidirectional conversion
The invention discloses a control method of a variable structure of a staggered parallel Cuk converter, which comprises the following steps:
the present embodiment adopts a four-stage staggered parallel structure, and the cut-in and cut-out control of each stage is performed before the circuit works according to the requirement. The control adopts four-way interleaved parallel Cuk converters, and Cuk inputs current IinInput into DSP via sampling circuit to sample signal iinComparing with a value set by an efficiency optimization algorithm, and adopting a four-phase Cuk structure when the input current is 75-100A; when the input current is 50-75A, shielding a one-phase Cuk circuit, and adopting a three-phase Cuk structure; shielding the two-phase Cuk circuit when the input current is 25-50A; and when the input current is less than 25A, shielding the three-phase Cuk circuit. According to the staggered parallel Cuk converterThe number of the driving control signals is m, and the driving control signals of each phase of switching tube are staggered by 360 degrees/m.
The scheme can adapt to different power grades and meet the requirement of efficiency improvement in a wide load range. When the input voltage varies between 8V and 80V, the output bus voltage V is controlledbus1The variation range of (A) is 40-100V.
Example five: the invention relates to a wide direct current voltage input and wide alternating current voltage output bidirectional conversion topology variable structure control method, which is a control method of an LLC resonant converter variable structure, and comprises the following steps:
as shown in fig. 13, in this embodiment, an LLC full-bridge resonant converter is used, and full-bridge/half-bridge variable structure control is performed as required before the circuit operates.
When the LLC resonant converter is in a full-bridge structure, an upper tube of one bridge arm is kept normally open, and a lower tube of the bridge arm is kept normally closed, so that the LLC resonant converter can be switched to a half-bridge structure; when the LLC resonant converter is in a T-type structure, the switching tube connecting the divided-voltage bus capacitor and one bridge arm is closed, and the bridge arm is kept normally open, so that it can be switched to a half-bridge structure, as shown in fig. 6.
When the isolated DC/DC converter is an LLC resonant converter, it can be switched to a half-bridge configuration according to the output voltage requirements, as shown in fig. 7. The voltage of the half-bridge resonant cavity after switching is half of the input voltage, so that the voltage transformation ratio of the LLC resonant converter is half of the voltage before switching.
When the input voltage V of LLC resonant converterbus140-100V, and when the LLC resonant converter is in a full-bridge structure, the output voltage Vbus2200-500V, and the AC output voltage is 117-325 Vac; when V isbus143-80V, and when the LLC resonant converter is in a half-bridge structure, the output voltage Vbus2108-200V, and the AC output voltage is 70-117 Vac; by the full-bridge/half-bridge variable structure control method, the output voltage range of the LLC resonant converter is expanded to 108-500V, so that the alternating current output voltage of the whole topology is expanded to 70-325 Vac.
The bus voltages before and after the full/half bridge configuration are shown in fig. 8. The mode switching is determined by the range of the output ac voltage: when the required output alternating voltage is 117-325 Vac, a full-bridge structure is adopted; when the required output alternating voltage is low and is 70-117 Vac, the half-bridge structure is switched.
In summary, the wide-dc-voltage-input and wide-ac-voltage-output bidirectional conversion topology is applicable to the fields of multi-electric aircraft power systems, battery energy storage devices, hybrid wind and solar hybrid systems, electric vehicles, hybrid electric vehicles and the like, has the advantages of wide input dc voltage range, wide output ac voltage range, wide load range, small current ripple, bidirectional operation, high-frequency isolation, high efficiency, energy conservation, environmental protection and the like, and has the advantages that the existing circuit does not have.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention cannot be limited thereby, for example, the four-phase interleaved Cuk converter in the embodiments may also be single phase or multiple phases, the LLC resonant converter may also be T-type structure, or CLLC resonant converter, and the DC/AC bidirectional converter may also be T-type structure, which are all within the protection scope of the present patent, and any modification made on the basis of the technical solution according to the technical idea of the present invention falls within the protection scope of the present invention.

Claims (9)

1. A wide range bidirectional conversion circuit, characterized by: the three-level bidirectional converter is formed by sequentially connecting a non-isolated DC/DC converter, an isolated DC/DC converter and a DC/AC inverter; when the system works in the forward direction, the direct-current power supply or the energy storage equipment realizes grid-connected energy feedback through the non-isolated DC/DC converter, the isolated DC/DC converter and the DC/AC inverter; when the device works reversely, the alternating current voltage supplies power to a direct current load or charges an energy storage device through the rectifying circuit, the isolation DC/DC converter and the non-isolation DC/DC converter.
2. The wide range bidirectional conversion circuit of claim 1, wherein: the non-isolated DC/DC converter is a synchronous rectification Cuk converter or a synchronous rectification Boost converter; the isolation DC/DC converter selects a full-bridge LLC resonant converter, a T-type LLC resonant converter or a CLLC resonant converter; the DC/AC bidirectional converter is an H-bridge inverter or a T-type inverter.
3. The wide range bidirectional conversion circuit of claim 2, wherein: the non-isolated DC/DC converter adopts a multiphase interleaving parallel structure.
4. The wide range bidirectional conversion circuit of any of claims 1-3, wherein: the synchronous rectification Cuk converter comprises a first switching tube Q1A second switch tube Q2Filter inductance L1Filter inductance L2Capacitor C1(ii) a The input end of the Cuk converter is connected in parallel with a DC tested device or an energy storage device, and the output end is connected in parallel with a bus capacitor Cbus1(ii) a Because the output voltage of the Cuk converter is opposite in polarity to the input voltage, when the Cuk converter is connected with the second-stage LLC resonant converter, the output positive electrode of the Cuk converter is connected with the input negative electrode of the LLC resonant converter, and the output negative electrode of the Cuk converter is connected with the input positive electrode of the LLC resonant converter.
5. The wide range bidirectional conversion circuit of claim 4, wherein: the LLC resonant converter comprises a primary side full-bridge conversion circuit, a resonant circuit, a high-frequency isolation transformer and a secondary side full-bridge rectification circuit; the primary side full-bridge conversion circuit comprises a third switching tube Q3Fourth switch tube Q4Fifth switch tube Q5The sixth switching tube Q6(ii) a The resonant circuit comprises a resonant inductor LrResonant capacitor CrAnd transformer excitation inductance Lm(ii) a Switch tube Q3And Q5The middle point of the resonant inductor is sequentially connected with the resonant capacitor in series and then connected with one end of a primary side excitation inductor of the high-frequency transformer, and a switching tube Q4And Q6The middle point of the transformer is connected with the other end of the primary side excitation inductor of the high-frequency transformer; the secondary side full-bridge rectification circuit comprises a seventh switching tube Q7The eighth switch tube Q8The ninth switching tube Q9The tenth switching tube Q10(ii) a Switch tube Q7And Q9The middle point is connected with one end of the secondary side of the transformer, and the switching tube Q8And Q10The middle point of the transformer is connected with the other end of the secondary side of the transformer; the first end and the second end of the LLC resonant converter output are respectively connected with a bus capacitor Cbus2A positive electrode and a negative electrode; and the positive electrode and the negative electrode of the bus capacitor are respectively connected with the first end and the second end of the H-bridge type inverter.
6. The wide range bidirectional conversion circuit of claim 5, wherein: the H-bridge converter comprises a first switching tube S1A second switch tube S2A third switching tube S3Fourth switch tube S4And an LCL filter; the LCL filter comprises a filter inductor L3Filter inductor L4And a filter capacitor Cf(ii) a Switch tube S1And S2The middle points of the filter inductors L are connected in series in sequence3And L4And then connected to the power grid; switch tube S3And S4Is connected to the power grid ground; filter inductance L3And a filter inductance L4In series, with the midpoint passing through the filter capacitor CfConnected to the network ground, a filter inductance L4The other end is connected to the power grid.
7. A control method of a wide-range bidirectional conversion circuit, which adopts the wide-range bidirectional conversion circuit as claimed in any one of claims 1 to 6, wherein a control unit comprises a sampling circuit, a DSP and an optical coupling isolation drive circuit, and during forward operation, the control process is as follows:
first, in the constant current mode
1) Non-isolated DC/DC converter input current IinInput into DSP via sampling circuit to sample signal iinAnd an input current reference iin_refAfter the error signal is calculated by a Proportional Integral Derivative (PID) controller in a Digital Signal Processor (DSP), the error signal is compared with a triangular carrier to obtain a Pulse Width Modulation (PWM) signal and is input into an isolation driving circuit to respectively control the duty ratio of a switching tube of a non-isolation direct current/direct current (DC/DC) converter and control the input current iinIs equal to the input current reference iin_ref；
Sampling bus voltage signal Vbus2Sending into DSP, filtering by secondary power frequency limiter, and comparing with the reference value of bus voltageThe difference signal obtains a given A of the current inner loop through a PI controller;
2) sampling grid current igAnd the network voltage vacSending the signals into a DSP, calculating the grid voltage sampling signals through a phase-locked loop in the DSP to obtain grid voltage phase information sin (omega)0t); thereby obtaining a current reference signal A sin (omega)0t), where A is the output of the voltage outer loop; grid current igAnd A sin (omega)0t) comparing, wherein the error signal is calculated by a PI controller in the DSP and then compared with a triangular carrier wave to obtain a PWM signal; the PWM signal is processed by an optical coupling isolation drive circuit to obtain a drive signal to control a DC/AC inverter switch tube (S)1～S4) The unit power factor is connected in parallel by switching on and off;
3) input bus voltage V of DC/AC inverterbus2The isolated DC/DC converter works in the state of a DC transformer DCX and inputs V according to the grid-connected voltagebus1Bus voltage following output voltage Vbus2；
Secondly, under the working modes of constant power and constant resistance, the constant power and the constant resistance are respectively converted into corresponding constant current values through formulas (1) and (2), the control of the constant power and the constant resistance is converted into constant current control, and the corresponding control after the conversion is the same as the constant current control scheme;
Figure FDA0002332151870000021
Figure FDA0002332151870000022
wherein P issetAt a constant power setting, RsetIs a constant resistance set value;
thirdly, in the working state of the constant-pressure mode:
1) non-isolated DC/DC converter input voltage VinInput into DSP via sampling circuit to sample signal vinAnd an input voltage reference vin_refComparing, after the error signal is calculated by PID in DSP, comparing with triangular carrier to obtain PWM signal and inputting it to isolated drive electricRespectively controlling non-isolated DC/DC converter switching tubes (Q)1～Q2) Control the input voltage vinIs equal to the input voltage reference vin_ref；
2) Sampling bus voltage signal Vbus2Sending the voltage difference to a DSP, filtering by a secondary power frequency trap, and then making a difference with a bus voltage reference value, wherein an error signal obtains a given A of a current inner ring through a PI controller; sampling grid current igAnd the network voltage vacSending the signals into a DSP, calculating the grid voltage sampling signals through a phase-locked loop in the DSP to obtain grid voltage phase information sin (omega)0t); thereby obtaining a current reference signal A sin (omega)0t) where A is the output of the voltage outer loop; grid current igAnd A sin (omega)0t) comparing, and comparing the error signals with triangular carriers after calculation by a PI controller in the DSP to obtain PWM signals; the PWM signal is processed by an optical coupling isolation drive circuit to obtain a drive signal to control a switching tube (S) of the H-bridge type inverter1～S4) The unit power factor is connected in parallel by switching on and off; input bus voltage V of H-bridge inverterbus2Determined by the grid-connected voltage;
3) the isolated DC/DC converter works in the DCX state of the DC transformer and inputs Vbus1Bus voltage following output voltage Vbus2；
Or the reverse work is carried out, and the control process during the reverse work is as follows:
1) bus voltage Vbus2And its reference voltage Vbus2_refComparing the error signal with the absolute value | v of the grid voltage after the error signal is calculated by a PI controlleracMultiplying | to obtain a grid current reference ig_ref(ii) a Grid current reference ig_refWith the current i of the gridgComparing to obtain error signal, calculating the error signal by PI controller, comparing with triangular carrier to obtain PWM signal, inputting into optical coupling isolation drive circuit, and respectively controlling DC/AC inverter rectifier switching tube (S)1～S4) The duty ratio of the output bus voltage V is controlledbus2Is equal to its reference Vbus2_refMeanwhile, the same phase of the voltage and the current of the power grid is realized;
2) isolated DC/DC conversionThe device works in a DCX state, and the output voltage directly follows Vbus2A bus voltage;
3) output voltage VoInputting the signal into DSP via sampling circuit to sample signal VoAnd an output voltage reference Vo_refAfter the error signal is calculated by a Proportional Integral Derivative (PID) controller in a Digital Signal Processor (DSP), the error signal is compared with a triangular carrier to obtain a Pulse Width Modulation (PWM) signal, the PWM signal is input into an isolation driving circuit, the duty ratio of a switching tube of a non-isolation direct current/direct current (DC/DC) converter is controlled respectively, and the output voltage V is controlledoIs equal to the output voltage reference Vo_ref。
8. The control method of the wide-range bidirectional conversion circuit according to claim 7, wherein when the requirements of adapting to different power levels and meeting the wide-load range requirements are met, the non-isolated DC/DC converter adopts an n-phase staggered parallel structure, and n is 1-6; when the number of the interleaved parallel converters is m, m is more than or equal to 1 and less than or equal to n, and the driving control signals of the switching tubes of each phase are staggered by 360 degrees/m.
9. The control method of the wide-range bidirectional conversion circuit according to claim 7 or 8, wherein when the range of the output voltage needs to be expanded, a full-bridge/half-bridge variable structure control mode is adopted for the LLC resonant converter; when the LLC resonant converter is required to be in a full-bridge structure, an upper tube of one bridge arm is kept normally open, and a lower tube is kept normally closed, so that the LLC resonant converter can be switched to be in a half-bridge structure; for the T-type LLC resonant converter, a full-bridge/half-bridge variable structure control mode is adopted, a switch tube for connecting a voltage-dividing bus capacitor and one bridge arm is closed, and the bridge arm is kept normally open, so that the T-type LLC resonant converter can be switched to a half-bridge structure; the voltage of the half-bridge resonant cavity after switching is half of the input voltage, and the voltage transformation ratio of the LLC resonant converter is half of that before switching; the mode switching is determined by the required ac output voltage, thereby extending the range of output voltages.
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Application publication date: 20200424