CN109617426B - Power electronic transformer circuit, power electronic transformer and control method - Google Patents
Power electronic transformer circuit, power electronic transformer and control method Download PDFInfo
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- CN109617426B CN109617426B CN201811557395.XA CN201811557395A CN109617426B CN 109617426 B CN109617426 B CN 109617426B CN 201811557395 A CN201811557395 A CN 201811557395A CN 109617426 B CN109617426 B CN 109617426B
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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
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
- H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
- H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
- H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M5/4585—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
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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
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without 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
- H02M7/217—Conversion of ac power input into dc power output without 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
- H02M7/219—Conversion of ac power input into dc power output without 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 in a bridge configuration
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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
- H02M1/00—Details of apparatus for conversion
- H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
- H02M1/007—Plural converter units in cascade
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- Dc-Dc Converters (AREA)
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Abstract
The invention discloses a power electronic transformer circuit, a power electronic transformer and a control method of the power electronic transformer, wherein a multi-winding transformer is arranged among a cascade H bridge, an inversion H bridge and a rectification H bridge which are arranged at the input end of a direct current power grid which are connected with a three-phase alternating current power grid, the input end of the multi-winding transformer is respectively connected with H bridge modules which are connected from the three-phase alternating current power grid, the input power of each H bridge module comprises a direct current component and a secondary pulse component, the secondary pulse power is in a rule of three-phase symmetry and negative sequence, after the multi-winding transformer is input from the three H bridge modules, the output power of the multi-winding transformer is equal to the synthesis of the input power of three ports according to the power balance relation, the secondary pulse power is mutually counteracted, and only the direct current component is transmitted to. The direct current capacitor in the cascade H bridge does not need to store pulsating power, the size of the direct current capacitor can be obviously reduced, the size of the power electronic transformer is further reduced, and the voltage and current stress of a power device is reduced.
Description
Technical Field
The present invention relates to the field of power electronics technologies, and in particular, to a power electronic transformer circuit, a power electronic transformer, and a control method for a power electronic transformer.
Background
Compared with a traditional Line Frequency Transformer (LFT), a Power Electronic Transformer (PET) not only can significantly reduce the volume and weight of a Transformer and a passive filter element in a system, but also can realize functions of reactive compensation, harmonic compensation, power flow control, redundancy backup, power system fault protection and the like, and is one of key technologies in the development of a smart power grid. The power electronic transformer is not only suitable for traditional AC/AC electric energy conversion, but also can be used for AC/DC power grid interconnection. In high-voltage and high-power AC/DC application, compared with a power frequency transformer, the power electronic transformer can obviously reduce the volume, weight and loss of a system, and has obvious economic benefit and considerable application prospect.
In high voltage, high power applications, power electronic transformers typically employ a multilevel topology with a modular structure to improve system reliability. According to the development of the current modular multilevel topology, AC/DC power electronic transformers can be classified into two major topologies, namely, cascaded H-bridge (CHB) based topologies and Modular Multilevel Converter (MMC) based topologies.
Power electronic transformer based on cascade H bridge: a total of three stages of power electronic conversion. The first stage is a cascade H bridge connected with an alternating current power grid, and the H bridge in the cascade H bridge realizes AC/DC conversion; the second stage is DC/AC high-frequency inversion, and the AC side is connected with a high-frequency transformer; the third stage is AC/DC conversion of high frequency transformer connection. The two H-bridge converters of the second and third stages and the intermediate high-frequency transformer are collectively referred to as a Dual Active Bridge (DAB). The direct current sides of all the AC/DC converters of each phase are connected in parallel to form a direct current bus, and the direct current bus can be connected with a direct current power grid.
Power electronic transformer based on modular multilevel converter: the alternating current network side is connected with a three-phase modular multilevel converter, a plurality of capacitors are connected in series on a direct current bus of the modular multilevel converter, each capacitor is connected with a double-active bridge, and the output direct current sides of all the double-active bridges are connected in parallel and can be connected into a direct current network. The other power electronic transformer topology based on the modular multilevel converter is that double active bridges are led out from capacitors of each sub-module of the modular multilevel converter, and finally the direct current sides of the double active bridges are connected in parallel.
The power electronic transformer based on the cascade H bridge introduces secondary pulsating power at the alternating current input side of each phase, and the secondary pulsating power needs larger direct current capacitance or a secondary resonance branch circuit to absorb the secondary pulsating power.
In the above power electronic transformer based on the modular multilevel converter, the capacitors of the sub-modules of the modular multilevel converter need to absorb the fundamental ripple power and have a lower frequency than the secondary ripple power, which means that a large capacitor is still needed to store the ripple power, and the volume of the capacitor occupies a large proportion of the total volume of the modular multilevel converter.
In summary, in the power electronic transformer circuit in the prior art, because the ac input introduces the pulsating power, the pulsating power has to be stored by using the capacitor with a larger volume to prevent the pulsating power from damaging the circuit, so that the volume of the whole power electronic transformer is increased, which is not favorable for the simplification of the system and further is not favorable for the long-term development.
Therefore, how to solve the problem that a power electronic transformer is required to provide a large capacitor to store the pulsating power introduced by the ac input in the power grid is a technical means that needs to be solved by those skilled in the art.
Disclosure of Invention
The invention aims to provide a power electronic transformer circuit, a power electronic transformer and a control method of the power electronic transformer, which are used for reducing the volume of a required capacitor on the premise of avoiding pulse power from damaging a power grid circuit.
In order to solve the technical problem, the invention provides a power electronic transformer circuit, which comprises an H-bridge module, a multi-winding transformer and a second rectification H-bridge, wherein the input end of the H-bridge module is connected with a three-phase alternating current power grid;
each H-bridge module comprises a first rectification H-bridge and an inversion H-bridge connected with the first rectification H-bridge, and each first rectification H-bridge forms a cascade H-bridge;
the H-bridge module comprises a first H-bridge module, a second H-bridge module and a third H-bridge module, wherein the input ends of the first H-bridge module, the second H-bridge module and the third H-bridge module are respectively connected with three phase lines of the three-phase alternating current power grid;
the first input end of the multi-winding transformer is connected with the output end of the first H-bridge module, the second input end of the multi-winding transformer is connected with the output end of the second H-bridge module, the third input end of the multi-winding transformer is connected with the output end of the third H-bridge module, and one multi-winding transformer uniquely corresponds to one first H-bridge module, one second H-bridge module and one third H-bridge module.
In order to solve the above technical problem, the present invention further provides a power electronic transformer, including the above power electronic transformer circuit, further including:
the detection circuit is used for acquiring circuit parameters;
and the controller is respectively connected with each H-bridge module, each second rectification H-bridge and the detection circuit and is used for carrying out closed-loop control according to the circuit parameters and generating a control instruction for each H-bridge module and/or the second rectification H-bridge so as to balance the input power of each H-bridge module.
In order to solve the above technical problem, the present invention further provides a method for controlling a power electronic transformer, based on the above power electronic transformer, including:
the detection circuit acquires circuit parameters;
and the controller performs closed-loop control according to the circuit parameters to generate control instructions for each H-bridge module and/or the second rectifying H-bridge so as to balance the input power of each H-bridge module.
Optionally, the circuit parameters specifically include an ac current value of the three-phase ac power grid and a voltage value of a dc capacitor in each H-bridge module;
correspondingly, the controller performs closed-loop control according to the circuit parameter to generate a control instruction for each H-bridge module and/or the second rectifying H-bridge, so as to balance the input power of each H-bridge module, specifically including:
the controller calculates the voltage average value of the voltage value of each direct current capacitor;
the controller generates an active component of the alternating current input current instruction according to a difference value between a preset voltage value and the voltage average value;
the controller performs closed-loop control on the active component, a preset reactive component of an alternating input current instruction and the alternating current to generate a modulation wave instruction;
and the controller distributes the modulation wave instruction to each first rectification H bridge through an SPWM (sinusoidal pulse width modulation) strategy.
Optionally, the controller distributes the modulated wave instruction to each first rectification H bridge through an SPWM modulation strategy, which specifically includes:
the controller performs independent closed-loop control on the voltage value of each direct current capacitor, and generates the regulating quantity of the H-bridge module where the direct current capacitor is located by combining the polarity of alternating current side current corresponding to the direct current capacitor;
and the controller generates a control instruction for a switching device of a first rectification H-bridge in the H-bridge module according to the adjustment quantity of the H-bridge module and the modulation wave instruction.
Optionally, the circuit parameters specifically include a dc voltage value of the dc power grid, an ac current value of the three-phase ac power grid, and an ac voltage value of the three-phase ac power grid;
correspondingly, the controller performs closed-loop control according to the circuit parameter to generate a control instruction for each H-bridge module and/or the second rectifying H-bridge, so as to balance the input power of each H-bridge module, specifically including:
the controller performs closed-loop control on the direct-current voltage value to generate a direct-current power instruction;
the controller extracts and calculates the pulsating power of the alternating current voltage value and the alternating current value to obtain a feedforward instruction;
and the controller generates control instructions for the inverter H bridge and the second rectifier H bridge according to the direct-current power instruction and the feedforward instruction.
Optionally, the circuit parameters specifically include a dc voltage value of the dc power grid, an ac current value of the three-phase ac power grid, an ac voltage value of the three-phase ac power grid, and a voltage value of a dc capacitor of each H-bridge module;
correspondingly, the controller performs closed-loop control according to the circuit parameter to generate a control instruction for each H-bridge module and/or second rectifying H-bridge, so as to balance the input power of each H-bridge module, so as to balance each input power, specifically including:
the controller performs closed-loop control on the direct-current voltage value to generate a direct-current power instruction;
the controller extracts and calculates the pulsating power of the alternating current voltage value and the alternating current value to obtain a feedforward instruction;
the controller performs secondary pulsating voltage control on the voltage value of each direct current capacitor to obtain a feedback instruction;
and the controller generates control instructions for the inverter H bridge and the second rectifier H bridge according to the direct-current power instruction, the feedforward instruction and the feedback instruction.
Optionally, the controller generates a control instruction for the inverter H bridge and the second rectifier H bridge according to the direct-current power instruction, the feedforward instruction, and the feedback instruction, and specifically includes:
the controller sums the value of the direct current power instruction, the value of the feedforward instruction and the value of the feedback instruction to obtain a power instruction sum;
the controller calculates the voltage average value of the voltage value of each direct current capacitor;
the controller acquires the sum of leakage inductance between the input end and the output end of a phase T-shaped equivalent circuit of the power electronic transformer circuit;
the controller calculates a phase shift angle according to the power instruction sum, the voltage average value and the leakage inductance sum;
and the controller performs phase shift control according to the phase shift angle to generate control instructions for the switching element of the inverter H bridge and the switching element of the second rectification H bridge.
Optionally, the phase shift angle is calculated according to the power command sum, the voltage average value, and the leakage inductance sum, specifically by the following formula:
wherein φ is the phase shift angle, pinIs the sum of the power commands, the ωsFor the angular frequency of the three-phase AC network, LtIs the sum of the leakage inductance and the UdcFor the value of the DC voltage, the UcIs the average value of the voltage.
The invention provides a power electronic transformer circuit, which comprises an H-bridge module, a multi-winding transformer, a second rectification H-bridge, a first rectification H-bridge and a second rectification H-bridge, wherein the input end of the H-bridge module is connected with a three-phase alternating current power grid; each H-bridge module comprises a first rectification H-bridge and an inversion H-bridge connected with the first rectification H-bridge, and each first rectification H-bridge forms a cascade H-bridge; the H-bridge module comprises a first H-bridge module, a second H-bridge module and a third H-bridge module, wherein the input ends of the first H-bridge module, the second H-bridge module and the third H-bridge module are respectively connected with three phase lines of a three-phase alternating current power grid; the first input end of the multi-winding transformer is connected with the output end of the first H-bridge module, the second input end of the multi-winding transformer is connected with the output end of the second H-bridge module, the third input end of the multi-winding transformer is connected with the output end of the third H-bridge module, and one multi-winding transformer uniquely corresponds to one first H-bridge module, one second H-bridge module and one third H-bridge module. The first H-bridge module, the second H-bridge module and the third H-bridge module are respectively connected with three phase lines of a three-phase alternating current power supply, the input power of each H-bridge module comprises a direct current (active) component and a secondary pulse component, the secondary pulse power is in a three-phase symmetry and negative sequence rule, after the power input by the first H-bridge module, the second H-bridge module and the third H-bridge module is input into the multi-winding transformer, the output power of the multi-winding transformer is equal to the synthesis of the input power of three ports according to the power balance relation, the secondary pulse power is mutually offset, and only the direct current component is transmitted to a direct current output end. Therefore, on the premise of avoiding the problem that the pulsating power damages a power grid circuit, the direct current capacitor in the power electronic transformer circuit provided by the invention does not need to store the pulsating power, and the volume of the direct current capacitor can be obviously reduced, so that the volume of the power electronic transformer is reduced, the voltage and current stress of a power device is reduced, and the power density of a system is improved. The invention also provides a power electronic transformer and a control method of the power electronic transformer, which have the beneficial effects and are not repeated herein.
Drawings
In order to more clearly illustrate the embodiments or technical solutions of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
Fig. 1 is a circuit diagram of a power electronic transformer circuit according to an embodiment of the present invention;
fig. 2 is an equivalent circuit diagram of a first rectifying H-bridge according to an embodiment of the present invention;
fig. 3 is an equivalent circuit diagram of a power electronic transformer circuit according to an embodiment of the present invention;
fig. 4 is a flowchart of a control method of a power electronic transformer according to an embodiment of the present invention;
fig. 5 is a flowchart illustrating a first specific implementation manner of step S40 in fig. 4 according to an embodiment of the present invention;
fig. 6 is a control block diagram of a first rectifying H-bridge according to an embodiment of the present invention;
fig. 7 is a flowchart illustrating a second specific implementation manner of step S40 in fig. 4 according to an embodiment of the present invention;
FIG. 8 is a flowchart illustrating a third specific implementation manner of step S40 in FIG. 4 according to an embodiment of the present invention;
fig. 9 is a control block diagram of an inverter H-bridge and a second rectifier H-bridge according to an embodiment of the present invention;
fig. 10(a) is a steady-state simulation waveform diagram of input-output voltage and current at the ac input side according to an embodiment of the present invention;
fig. 10(b) is a simulated waveform diagram of a dc output side voltage according to an embodiment of the present invention;
fig. 11(a) is a simulated waveform diagram of input power of a multi-winding transformer according to an embodiment of the present invention;
fig. 11(b) is a simulated waveform diagram of output power of a multi-winding transformer according to an embodiment of the present invention;
FIG. 12 is a waveform diagram illustrating dynamic adjustment of DC capacitor voltage in a single H-bridge module according to an embodiment of the present invention.
Detailed Description
The core of the invention is to provide a power electronic transformer circuit, a power electronic transformer and a control method of the power electronic transformer, which are used for reducing the volume of a required capacitor on the premise of avoiding the pulse power from damaging a power grid circuit.
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a circuit diagram of a power electronic transformer circuit according to an embodiment of the present invention; fig. 2 is an equivalent circuit diagram of a first rectifying H-bridge according to an embodiment of the present invention; fig. 3 is an equivalent circuit diagram of a power electronic transformer circuit according to an embodiment of the present invention.
As shown in fig. 1, the power electronic transformer circuit includes an H-bridge module having an input terminal connected to a three-phase ac power grid, a multi-winding transformer having an input terminal connected to an output terminal of the H-bridge module, and a second rectifying H-bridge having an input terminal connected to an output terminal of the multi-winding transformer and an output terminal connected to a dc power grid;
each H-bridge module comprises a first rectification H-bridge and an inversion H-bridge connected with the first rectification H-bridge, and each first rectification H-bridge forms a cascade H-bridge;
the H-bridge module comprises a first H-bridge module, a second H-bridge module and a third H-bridge module, wherein the input ends of the first H-bridge module, the second H-bridge module and the third H-bridge module are respectively connected with three phase lines of a three-phase alternating current power grid;
the first input end of the multi-winding transformer is connected with the output end of the first H-bridge module, the second input end of the multi-winding transformer is connected with the output end of the second H-bridge module, the third input end of the multi-winding transformer is connected with the output end of the third H-bridge module, and one multi-winding transformer uniquely corresponds to one first H-bridge module, one second H-bridge module and one third H-bridge module.
In a specific implementation, the input side to the output side comprises three stages of power electronic conversion in total: the first stage is high-frequency rectification corresponding to a first rectification H bridge AC/DC; the second stage is high-frequency inversion corresponding to H bridge DC/AC inversion; the third stage is high-frequency rectification corresponding to the second rectification H bridge AC/DC. The first rectifying H bridge AC/DC cascade forms a cascaded H bridge.
The definition H-bridge module comprises first H-bridge modules a _ 1-a _ N, second H-bridge modules b _ 1-b _ N and third H-bridge modules C _ 1-C _ N, wherein the input ends of the first H-bridge modules a _ 1-a _ N, the second H-bridge modules b _ 1-b _ N and the third H-bridge modules C _ 1-C _ N are respectively connected with three phase lines (a phase, b phase and C phase) of a three-phase alternating current power grid, each H-bridge module comprises a first rectification H-bridge AC/DC and an inversion H-bridge DC/AC, and a direct current capacitor C for stabilizing direct current voltage is connected between the.
The second stage and the third stage are electrically isolated by adopting a three-input-single-output multi-winding transformer, and the specific connection mode is that the ith first H bridge module a _ i, the ith second H bridge module b _ i and the ith third H bridge module c _ i are respectively connected with three input ends of the ith multi-winding transformer (i is less than or equal to N). The output end of each multi-winding transformer is connected with a second rectification H bridge AC/DC (high-frequency rectifier), and the output ends of N second rectification H bridges are connected in parallel to form a direct-current feeder line.
Referring to fig. 2, the first rectified H-bridge AC/DC, the inverted H-bridge DC/AC and the second rectified H-bridge AC/DC are H-bridge converters, each branch is formed by a switching element, for example, the first rectified H-bridge AC/DC includes switching elements S1, S2, S3 and S4.
Referring to fig. 3, taking the first H-bridge module as an example, the first rectifying H-bridge AC/DC includes switching elements S1, S2, S3 and S4, the inverting H-bridge DC/AC includes switching elements S5, S6, S7 and S8, and the second rectifying H-bridge AC/DC includes switching elements S9, S10, S11 and S12. The cascaded H-bridge can be considered to comprise 3N first H-bridge modules as shown in fig. 3, so that the power electronic transformer circuit of the present invention still has a modular structure.
Let a phase input voltage usaCurrent isaComprises the following steps:
usa＝Us sin(w1t)
wherein U issIs the phase voltage amplitude, IsIs the amplitude of the phase current, w1Is the fundamental angular frequency and is the power factor angle. Considering that the input power is equally distributed among the H-bridge modules, taking the first H-bridge module a _1 as an example, the input power ps_a1Comprises the following steps:
obtaining the input power p of a second H-bridge module b _1 and a third H-bridge module c _1 under the condition of three-phase symmetrys_b1、ps_c1：
The input power of each H-bridge module of the power electronic transformer circuit comprises a direct current (active) component and a secondary pulsating component, the secondary pulsating power is in a three-phase symmetry and negative sequence rule, and the amplitude P of the secondary pulsating power is2And the active power PdcAre equal.
In the power electronic transformer circuit in the prior art, the secondary pulsating power can only be absorbed by a direct current capacitor in a power electronic transformer module, so that a larger direct current capacitor is needed.
In the embodiment of the present invention, the output sides of the first H-bridge module a _1, the second H-bridge module b _1, and the third H-bridge module c _1 of the power electronic transformer circuit are respectively connected to the input terminals of the 1 st multi-winding transformer, and similarly, the ith first H-bridge module a _ i, the ith second H-bridge module b _ i, and the ith third H-bridge module c _ i are respectively connected to the three input terminals of the ith multi-winding transformer. According to the power balance relation, the output power of the multi-winding transformer is equal to the synthesis of the input power of the three ports, the secondary pulsating power is mutually counteracted, and only the direct current component is transmitted to the direct current output. If the pulsating power input from the ac network side is also all transferred to the power channel consisting of the multi-winding transformer:
the last output power po1Comprises the following steps:
wherein p isin_a1、pin_b1、pin_c1The input power of a phase, b phase and c phase in the three-phase alternating current circuit are respectively.
The H-bridge module comprises an input end, a multi-winding transformer and a second rectification H-bridge, wherein the input end of the H-bridge module is connected with a three-phase alternating current power grid; each H-bridge module comprises a first rectification H-bridge and an inversion H-bridge connected with the first rectification H-bridge, and each first rectification H-bridge forms a cascade H-bridge; the H-bridge module comprises a first H-bridge module, a second H-bridge module and a third H-bridge module, wherein the input ends of the first H-bridge module, the second H-bridge module and the third H-bridge module are respectively connected with three phase lines of a three-phase alternating current power grid; the first input end of the multi-winding transformer is connected with the output end of the first H-bridge module, the second input end of the multi-winding transformer is connected with the output end of the second H-bridge module, the third input end of the multi-winding transformer is connected with the output end of the third H-bridge module, and one multi-winding transformer uniquely corresponds to one first H-bridge module, one second H-bridge module and one third H-bridge module. The first H-bridge module, the second H-bridge module and the third H-bridge module are respectively connected with three phase lines of a three-phase alternating current power supply, the input power of each H-bridge module comprises a direct current (active) component and a secondary pulse component, the secondary pulse power is in a three-phase symmetry and negative sequence rule, after the power input by the first H-bridge module, the second H-bridge module and the third H-bridge module is input into the multi-winding transformer, the output power of the multi-winding transformer is equal to the synthesis of the input power of three ports according to the power balance relation, the secondary pulse power is mutually offset, and only the direct current component is transmitted to a direct current output end. Therefore, on the premise of avoiding the problem that the pulsating power damages a power grid circuit, the direct current capacitor in the power electronic transformer circuit provided by the invention does not need to store the pulsating power, and the volume of the direct current capacitor can be obviously reduced, so that the volume of the power electronic transformer is reduced, the voltage and current stress of a power device is reduced, and the power density of a system is improved.
On the basis of the above detailed description of the embodiments corresponding to the power electronic transformer circuit, the present invention also discloses a power electronic transformer corresponding to the above power electronic transformer circuit, and the power electronic transformer includes the power electronic transformer circuit described in the above embodiments, and further includes:
the detection circuit is used for acquiring circuit parameters;
and the controller is respectively connected with each H-bridge module, each second rectification H-bridge and the detection circuit and is used for carrying out closed-loop control according to circuit parameters and generating a control instruction for each H-bridge module and/or each second rectification H-bridge so as to balance the input power of each H-bridge module.
The power electronic transformer circuit provided by the embodiment is based on the rule that secondary pulsating power input in three phases is in three-phase symmetry and negative sequence, and is counteracted by the multi-winding transformer. However, in actual operation, due to element differences, different operating states, and the like, the pulsating power in the input power of the multi-winding transformer cannot be completely cancelled by each H-bridge module, and in order to avoid damage of the pulsating power to the circuit, the dc capacitor needs to be designed in consideration of the function of storing the pulsating power. In order to further reduce residual pulsating power in the H-bridge modules and reduce the volume of the direct current capacitor, the difference of the pulsating power in each H-bridge module is determined by detecting circuit parameters of a power grid circuit, and the controller controls the balance of the pulsating power in each H-bridge module through the circuit parameters so as to eliminate the pulsating power through the multi-winding transformer as far as possible.
In the above embodiments, it is mentioned that the input side to the output side totally includes three stages of power electronic conversion, corresponding to the first rectifying H bridge, the inverting H bridge and the second rectifying H bridge, respectively, and the first rectifying H bridge AC/DC, the inverting H bridge DC/AC and the second rectifying H bridge AC/DC are all H-bridge converters, and each branch may be equivalently composed of one switching element. In particular implementations, therefore, the controller may control the balance of pulsed power in each H-bridge module by controlling the switching of each switching element.
The power electronic transformer provided by the embodiment of the invention comprises the power electronic transformer circuit provided by the embodiment, circuit parameters are acquired through the detection circuit, and the controller generates control commands for each H-bridge module and/or the second rectification H-bridge according to the circuit parameters so as to balance the input power of each H-bridge module, so that the residual of pulsating power can be further reduced on the basis of the power electronic transformer circuit, and the volume of a required direct current capacitor is further reduced.
On the basis of the above detailed embodiments of the power electronic transformer, the present invention also discloses a control method of the power electronic transformer corresponding to the above power electronic transformer.
Fig. 4 is a flowchart of a control method of a power electronic transformer according to an embodiment of the present invention. As shown in fig. 4, based on the power electronic transformer in the above embodiment, the method for controlling the power electronic transformer includes:
s40: the detection circuit collects circuit parameters.
S41: the controller performs closed-loop control according to the circuit parameters to generate a control instruction for the H-bridge module and/or a second rectifying H-bridge connected to the output end of the multi-winding transformer, so that the input powers are balanced.
In specific implementation, based on the control concept of the power electronic transformer circuit and the controller provided by the embodiment of the present invention, a person skilled in the art can perform closed-loop control on circuit parameters such as current and voltage and a set standard value by collecting the circuit parameters, and generate a control instruction for each H-bridge module and/or a second rectification H-bridge connected to the output end of the multi-winding transformer, so as to achieve the purpose of balancing the input power of each H-bridge module.
Fig. 5 is a flowchart illustrating a first specific implementation manner of step S40 in fig. 4 according to an embodiment of the present invention; fig. 6 is a control block diagram of the first rectifying H-bridge according to the embodiment of the present invention.
On the basis of the above embodiment, in another embodiment, the circuit parameters specifically include an ac current value of the three-phase ac power grid and a voltage value of a dc capacitor of each H-bridge module;
correspondingly, step S40 specifically includes:
s50: the controller calculates the voltage average value of the voltage values of the direct current capacitors;
s51: the controller generates an active component of the alternating current input current instruction according to a difference value of a preset voltage value and a voltage average value;
s52: the controller performs closed-loop control on the active component, the preset reactive component of the alternating input current instruction and the alternating current to generate a modulation wave instruction;
s53: and the controller distributes the modulated wave command to each first rectifying H bridge through an SPWM (sinusoidal pulse width modulation) strategy.
The direct current voltage balance among all H bridge modules can be realized by controlling the first rectification H bridge AC/DC, and further the input power is balanced.
In one embodiment, as shown in FIG. 6, the sampled value u is first obtained from the DC capacitor voltages of all H-bridge modulesCxj(x is a, b, c; j is 1 to n) and the total average value u is obtainedCControl it to the instruction value uCThe controller outputs an active component i of an alternating current input current instructionsd*. Reactive component i of AC input current commandsqMay be set to 0. AC current value i of three-phase AC network to be detectedsa，isb，iscConversion into i by abc/dq rotation coordinate transformationsd，isq。isdAnd isqGeneration of modulated wave instruction u via closed-loop controlrdAnd urqAnd then u is obtained by dq/abc inverse transformationra，urb，urcAnd the multi-level SPWM modulation strategy is distributed to the first rectifying H bridge in each H bridge module in the cascade connection.
Further, step S53 may include:
the controller carries out independent closed-loop control on the voltage value of each direct current capacitor and generates the regulating quantity of the H-bridge module where the direct current capacitor is located by combining the polarity of the alternating current side corresponding to the direct current capacitor;
the controller generates a control instruction for a switching device of a first rectification H-bridge in the H-bridge module according to the adjustment quantity of the H-bridge module and the modulation wave instruction.
As shown in fig. 6, the voltage value of each dc capacitor is independently closed-loop controlled, and the adjustment amount of the modulation wave of the H-bridge module is obtained by multiplying the polarity determination sign (positive and negative) of the current on the cross current side by the modulation wave to generate a control command for each H-bridge module. This control command is finally executed by turning on and off the switching devices (switching devices S1 to S4 shown in fig. 3) that drive the first rectifying H-bridge.
Fig. 7 is a flowchart illustrating a second specific implementation manner of step S40 in fig. 4 according to an embodiment of the present invention.
On the basis of the above embodiment, in another embodiment, the circuit parameters specifically include a direct-current voltage value of the direct-current power grid, an alternating-current value of the three-phase alternating-current power grid, and an alternating-current voltage value of the three-phase alternating-current power grid;
correspondingly, step S40 specifically includes:
s70: the controller performs closed-loop control on the direct-current voltage value to generate a direct-current power instruction;
s71: the controller extracts and calculates the pulsating power of the alternating current voltage value and the alternating current value to obtain a feedforward instruction;
s72: and the controller generates control instructions for the inverter H bridge and the second rectifier H bridge according to the direct-current power instruction and the feedforward instruction.
The 2 nd and 3 rd stages of the power electronic transformer circuit are implementation links of decoupling control, and are implemented by driving an inverter H-bridge and a second rectifier H-bridge (such as switching devices S5-S12 in fig. 3).
For suppressing voltage variation due to load fluctuation, a DC voltage value udcPerforming closed-loop control with the output being the DC part p of the power commanddc*. To prevent the capacitor in the H-bridge module from absorbing the secondary pulse power, the AC input power p is requiredsSecond order component p in (1)s_2All passed to the input side of the multi-winding transformer. Detecting the value u of AC voltage of secondary pulsating power inputted by each phase of three-phase AC network sidesx(x ═ a, b, c) and the value of the alternating current isx(x ═ a, b, c) and then calculating a feed forward command as a power command, that is, a
By direct current power command pdcFeed-forward command
Control commands to the switching devices (e.g., switching devices S5-S12 in fig. 3) in the inverting H-bridge and the second rectifying H-bridge are generated.
FIG. 8 is a flowchart illustrating a third specific implementation manner of step S40 in FIG. 4 according to an embodiment of the present invention; fig. 9 is a control block diagram of the inverter H-bridge and the second rectifier H-bridge according to the embodiment of the present invention.
On the basis of the above embodiment, in another embodiment, the circuit parameters specifically include a dc voltage value of the dc power grid, an ac current value of the three-phase ac power grid, an ac voltage value of the three-phase ac power grid, and a voltage value of the dc capacitor of each H-bridge module;
correspondingly, step S40 specifically includes:
s80: the controller performs closed-loop control on the direct-current voltage value to generate a direct-current power instruction;
s81: the controller extracts and calculates the pulsating power of the alternating current voltage value and the alternating current value to obtain a feedforward instruction;
s82: the controller performs secondary pulsating voltage control on the voltage value of each direct current capacitor to obtain a feedback instruction;
s83: and the controller generates control instructions for the inverter H bridge and the second rectifier H bridge according to the direct-current power instruction, the feedforward instruction and the feedback instruction.
Here, the steps S80 to S81 may refer to the detailed description in the above embodiments. Performing secondary pulsating voltage control on the voltage value of each DC capacitor, i.e. using 0 as control commandThe voltage value of the capacitor is subjected to closed-loop control, and a feedback instruction of a power instruction is output
As shown in FIG. 9, for udc *And udcPerforming subtraction operation, and performing DC voltage control to obtain DC power command pdcA first step of; for u is pairedsx(x ═ a, b, c) and isx(x ═ a, b, c) performing a ripple power extraction operation to obtain a feedforward command
Performing secondary pulsation component extraction and negation on the voltage value of the direct current capacitor, and performing secondary pulsation power control to obtain a feedback instruction
According to a DC power command pdcFeed-forward command
And feedback instructions
Control commands to the switching devices (e.g., switching devices S5-S12 in fig. 3) in the inverting H-bridge and the second rectifying H-bridge are generated.
Further, step S83 may specifically include:
value p of DC power instruction for controllerdcValue of feed-forward command
And feedback instructions
Summing the values of (a) to obtain a power command sum:
controller meterCalculating the voltage average value U of the voltage values of the DC capacitorsc；
The controller obtains leakage inductance and L between the input end and the output end of a one-phase T-shaped equivalent circuit of the power electronic transformer circuitt；
The controller sums p according to the power commandsinVoltage average value UcSum of leakage inductance and LtCalculating a phase shift angle phi;
the controller performs phase shift control according to the phase shift angle to generate control instructions for the switching element of the inverting H bridge and the switching element of the second rectifying H bridge.
Wherein, leakage inductance and LtIt can be obtained by calculation or can be preset. The AC side voltage of the H-bridge module at the input end of the multi-winding transformer and the AC side voltage of the inverse H-bridge at the output end of the multi-winding transformer are both square waves with the duty ratio D being 0.5, and the phase difference between the two AC square wave voltages
Calculated according to the transmission power command, the phase difference
Including a dc component and an ac pulsating component.
The phase shift angle phi can be specifically calculated by the following formula:
wherein phi is a phase shift angle, pinIs the sum of power commands, ωsFor the angular frequency, L, of a three-phase AC networktFor the sum of leakage inductance, UdcIs a DC voltage value, UcIs the average value of the voltage.
Fig. 10(a) is a steady-state simulation waveform diagram of input-output voltage and current at the ac input side according to an embodiment of the present invention; fig. 10(b) is a simulated waveform diagram of a dc output side voltage according to an embodiment of the present invention; fig. 11(a) is a simulated waveform diagram of input power of a multi-winding transformer according to an embodiment of the present invention; fig. 11(b) is a simulated waveform diagram of output power of a multi-winding transformer according to an embodiment of the present invention; FIG. 12 is a waveform diagram illustrating dynamic adjustment of DC capacitor voltage in a single H-bridge module according to an embodiment of the present invention.
Adopt MATLAB/Simulink to build the model of the power electronic transformer circuit that this application provided, carry out simulation experiment and verify, the simulation parameter is as follows:
in a power electronic transformer circuit, in a steady state, a voltage current waveform at an alternating current input side is as shown in fig. 10(a), alternating current is a unit power factor sine wave, equivalent switching frequency is improved due to a multilevel modulation effect, and the content of harmonic waves of the alternating current is low. As shown in fig. 10(b), the voltage on the dc output side is stabilized at 750V, the waveform is smooth, and the secondary pulsation component is hardly contained.
The power waveforms of the primary and secondary sides of the power channel (high-frequency multi-winding transformer) of the power electronic transformer circuit are shown in fig. 11(a) and 11(a), the input power of 3 primary windings is direct current power superimposed secondary pulsating component, wherein the secondary pulsating power is obtained according to decoupling control. After being coupled by the power channel, the secondary side only transmits direct current power.
The dynamic adjustment process of the capacitor voltage in the single H-bridge module of the power electronic transformer circuit in the power decoupling control starting process is shown in fig. 12. In fig. 12, t is t1At the moment, decoupling control is started, the peak-to-peak value of capacitor voltage pulsation is rapidly reduced to 4% from 23.3%, and the effectiveness of decoupling control is verified.
Simulation results show that the power electronic transformer circuit, the power electronic transformer and the control method thereof can realize interconnection and power transmission of a three-phase alternating current power grid and a direct current power grid, and the direct current capacitor voltage in the internal module does not contain secondary pulsation components, so that the power electronic transformer circuit, the power electronic transformer and the control method thereof have high reliability and power density.
In the embodiments provided in the present application, it should be understood that the disclosed power electronic transformer circuit, power electronic transformer and control method of power electronic transformer may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, a division of modules is merely a division of logical functions, and an actual implementation may have another division, for example, a plurality of modules or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or modules, and may be in an electrical, mechanical or other form. Modules described as separate parts may or may not be physically separate, and parts displayed as modules may or may not be physical modules, may be located in one place, or may be distributed on a plurality of network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment.
In addition, functional modules in the embodiments of the present application may be integrated into one processing module, or each of the modules may exist alone physically, or two or more modules are integrated into one module.
The power electronic transformer circuit, the power electronic transformer and the control method of the power electronic transformer provided by the invention are described in detail above. The embodiments are described in a progressive manner in the specification, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
It is further noted that, in the present specification, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
Claims (5)
1. A control method of a power electronic transformer is characterized in that based on the power electronic transformer, the method comprises the following steps:
the detection circuit acquires an alternating current value of a three-phase alternating current power grid and a voltage value of a direct current capacitor in each H-bridge module;
the controller calculates the voltage average value of the voltage value of each direct current capacitor;
the controller generates an active component of the alternating current input current instruction according to a difference value between a preset voltage value and the voltage average value;
the controller performs closed-loop control on the active component, the reactive component of a preset alternating current input current instruction and the alternating current to generate a modulation wave instruction;
the controller performs independent closed-loop control on the voltage value of each direct current capacitor, and generates the regulating quantity of the H-bridge module where the direct current capacitor is located by combining the polarity of alternating current side current corresponding to the direct current capacitor;
the controller generates a control instruction for a switching device of a first rectification H bridge in the H-bridge module according to the adjustment quantity of the H-bridge module and the modulation wave instruction;
the power electronic transformer comprises an H-bridge module, a multi-winding transformer, a second rectification H-bridge and a detection circuit, wherein the input end of the H-bridge module is connected with the three-phase alternating current power grid; the controller is respectively connected with each H-bridge module, each second rectification H-bridge and the detection circuit;
each H-bridge module comprises a first rectification H-bridge and an inversion H-bridge connected with the first rectification H-bridge, and each first rectification H-bridge forms a cascade H-bridge;
the H-bridge module comprises a first H-bridge module, a second H-bridge module and a third H-bridge module, wherein the input ends of the first H-bridge module, the second H-bridge module and the third H-bridge module are respectively connected with three phase lines of the three-phase alternating current power grid;
the first input end of the multi-winding transformer is connected with the output end of the first H-bridge module, the second input end of the multi-winding transformer is connected with the output end of the second H-bridge module, the third input end of the multi-winding transformer is connected with the output end of the third H-bridge module, and one multi-winding transformer uniquely corresponds to one first H-bridge module, one second H-bridge module and one third H-bridge module.
2. The control method according to claim 1, characterized by further comprising:
the detection circuit acquires a direct-current voltage value of the direct-current power grid and an alternating-current voltage value of the three-phase alternating-current power grid;
the controller performs closed-loop control on the direct-current voltage value to generate a direct-current power instruction;
the controller extracts and calculates the pulsating power of the alternating current voltage value and the alternating current value to obtain a feedforward instruction;
and the controller generates control instructions for the inverter H bridge and the second rectifier H bridge according to the direct-current power instruction and the feedforward instruction.
3. The control method according to claim 1, characterized by further comprising:
the detection circuit acquires a direct-current voltage value of the direct-current power grid and an alternating-current voltage value of the three-phase alternating-current power grid;
the controller performs closed-loop control on the direct-current voltage value to generate a direct-current power instruction;
the controller extracts and calculates the pulsating power of the alternating current voltage value and the alternating current value to obtain a feedforward instruction;
the controller performs secondary pulsating voltage control on the voltage value of each direct current capacitor to obtain a feedback instruction;
and the controller generates control instructions for the inverter H bridge and the second rectifier H bridge according to the direct-current power instruction, the feedforward instruction and the feedback instruction.
4. The control method according to claim 3, wherein the controller generates control commands for the inverter H-bridge and the second rectifier H-bridge according to the dc power command, the feedforward command, and the feedback command, and specifically includes:
the controller sums the value of the direct current power instruction, the value of the feedforward instruction and the value of the feedback instruction to obtain a power instruction sum;
the controller calculates the voltage average value of the voltage value of each direct current capacitor;
the controller acquires the sum of leakage inductance between the input end and the output end of a phase T-shaped equivalent circuit of the power electronic transformer circuit;
the controller calculates a phase shift angle according to the power instruction sum, the voltage average value and the leakage inductance sum;
and the controller performs phase shift control according to the phase shift angle to generate control instructions for the switching element of the inverter H bridge and the switching element of the second rectification H bridge.
5. The control method of claim 4, wherein said calculating a phase shift angle from said power command sum, said voltage average and said leakage inductance sum is calculated by the following formula:
wherein φ is the phase shift angle, pinIs the sum of the power commands, the ωsFor the angular frequency of the three-phase AC network, LtIs the sum of the leakage inductance and the UdcFor the value of the DC voltage, the UcIs the average value of the voltage.
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| CN111146951B (en) * | 2020-01-20 | 2021-08-17 | 特变电工西安电气科技有限公司 | Power electronic transformer capable of being started in two directions and control method thereof |
| CN113726200B (en) * | 2020-05-26 | 2024-03-15 | 南京南瑞继保电气有限公司 | Control architecture of power electronic transformer and control method thereof |
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