CN110855150B - Virtual impedance-based direct current solid-state transformer control method - Google Patents

Virtual impedance-based direct current solid-state transformer control method Download PDF

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CN110855150B
CN110855150B CN201911157313.7A CN201911157313A CN110855150B CN 110855150 B CN110855150 B CN 110855150B CN 201911157313 A CN201911157313 A CN 201911157313A CN 110855150 B CN110855150 B CN 110855150B
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current
output
virtual impedance
double
active full
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CN110855150A (en
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任春光
孟祥齐
贾燕冰
韩肖清
秦文萍
张佰富
郭东鑫
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Taiyuan University of Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/3353—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 at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter

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  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention relates to a direct current solid-state transformer, in particular to a direct current solid-state transformer control method based on virtual impedance. The invention solves the problem that the input voltage sharing of each module of the traditional direct current solid-state transformer can not ensure the output current sharing due to different parameters. According to the method, circulation control of virtual impedance is added in the control on the basis of traditional control, wherein circulation of each module is the difference between output average current and respective output current. And finally, the output current of each module is adjusted through the virtual impedance, so that the output currents of the modules are the same, and current sharing control is realized. Therefore, output current sharing is realized, and meanwhile, the output voltage is kept stable. The invention is suitable for the direct current solid-state transformer and has good practicability.

Description

Virtual impedance-based direct current solid-state transformer control method
Technical Field
The invention relates to the field of direct-current solid-state transformers, in particular to a direct-current solid-state transformer control method based on virtual impedance.
Background
With the exhaustion of fossil energy and the increasingly prominent environmental problems, the application of various distributed power supplies is widely regarded, and meanwhile, researchers at home and abroad develop the research of direct-current micro-grids. In a direct-current micro-grid, large-capacity DC/DC converters are required to be interconnected between each distributed power supply and a direct-current bus, and between a direct-current bus with a high voltage level and a direct-current bus with a low voltage level.
The existing literature proposes a control strategy under the condition that the transmission efficiency among modules in a direct current transformer (DCSST) is the same. In practical application, the transmission efficiency of each submodule is uneven due to different main circuit parameters, so that the DCSST adopting the control strategy cannot simultaneously guarantee input voltage equalization and output current equalization. In order to ensure output current sharing when the DCSST adopts input voltage sharing control, current sharing control needs to be added on the basis of the existing double-loop control strategy. The traditional DC/DC converter parallel side current sharing mainly comprises a maximum current method, an average current method and a droop control method. However, these current sharing control methods mainly rely on PI parameter adjustment to perform current sharing, and the current sharing effect is not ideal, and it is not obvious to improve the output non-current sharing caused by different main circuit parameters of the DCSST, and at the same time, it needs to perform complex operation. In view of the disadvantages of the conventional control, some researchers propose that the output characteristics of the parallel system can be changed without additional power consumption by adopting the virtual impedance control, so as to realize the adjustment of the output current. The document proposes to add a virtual impedance to adjust output current sharing on the basis of voltage and current double loop control of the inverter, but the virtual impedance increases the output impedance of the whole system and affects the output characteristics of the whole system. Therefore, there is a need for a method for effectively reducing the output current imbalance caused by different module parameters.
Disclosure of Invention
The invention aims to solve the problem that input voltage sharing cannot ensure output current sharing due to inconsistent transmission efficiency of each module in a direct-current solid-state transformer. Aiming at the defects of the existing control strategy, a direct current solid-state transformer control method based on virtual impedance is designed.
On the basis of the existing modularized control method, the output current sharing strategy based on the virtual impedance is introduced. A virtual impedance module is added in the control module, and the output circulation current is adjusted through the virtual impedance module, so that the output current of each module is balanced.
The invention is realized by adopting the following technical scheme:
a control method of a direct current solid-state transformer based on virtual impedance is realized by connecting m double-active full-bridge converters (DAB) through an Input Series Output Parallel (ISOP) structure; a virtual impedance link is introduced on the basis of the control of an input voltage equalizing ring and an output voltage ring of the existing double-active full-bridge converter, so that the output current is equalized; the method comprises the following specific steps: input voltage-sharing reference value U of DC solid-state transformer in input voltage-sharing ringinM and input voltage value of each double-active full-bridge converterU iniAfter difference making, the difference is input into a grading ring PI controller GscOutputting phase shift ratio correction signals of each double-active full-bridge converter; u shapeinInputting a bus voltage for the direct current transformer;
reference value of output voltage of DC solid-state transformer in output voltage loopU orefWith the actual value of the voltage at the output of each dual-active full-bridge converterU outiAfter difference making, the difference is processed by an output voltage ring PI controller GdcOutputting a basic phase-shift ratio signal, and subtracting the basic phase-shift ratio signal from the phase-shift ratio correction signal of each double-active full-bridge converter; then the circulation current of each double-active full-bridge converter passes through a virtual impedance link to further adjust the phase-shift ratio, and a final phase-shift ratio signal of each double-active full-bridge converter is obtainedD iFinally, a pulse PWM driving signal is output through a phase shifting module, and the circulating current passes through a virtual impedance ZvAnd regulating and controlling the circulating current so that the output current of each double-active full-bridge converter is the same.
Compared with the prior art, the virtual impedance-based direct current solid-state transformer control method has the advantages that: (1) the existing control method can not ensure output current sharing by using input voltage sharing control under the condition that parameters of each module are different, and the method can ensure output current sharing. (2) By using the virtual impedance-based current sharing control, the defects that the traditional current sharing control method mainly depends on PI parameter adjustment to share current and the current sharing effect is not ideal can be overcome, and the reliability of DCSST is improved.
Drawings
Fig. 1 is a block diagram of a dc solid-state transformer according to the present invention;
FIG. 2 is a block diagram of a dual active full bridge converter according to the present invention;
FIG. 3 is a control block diagram of a DC solid-state transformer based on virtual impedance according to the present invention;
in fig. 1: the direct current solid-state transformers are connected by m double active full bridge converters (DABs) through an Input Series Output Parallel (ISOP) structure.U inAndU outrespectively representing the input and output bus voltages of the direct current transformer;i inandi outthe input current and the output current of the direct current transformer are respectively;i iniandi outirespectively outputting the current of each DAB input side;U iniandU outifor each DAB input output side voltage. Wherein: i =1,2, …, m.
In fig. 2: c1 and C2 are the input and output capacitances of each module. T is a high-frequency transformer, the primary side and the secondary side of the high-frequency transformer are respectively connected with a full-bridge circuit H1 and H2, the high-frequency transformer provides the functions of electrical isolation and voltage conversion, an auxiliary inductor provides the function of transient energy storage, and each field effect transistor (MOSFET) on a bridge arm is connected with a diode in an anti-parallel mode to provide a path for bidirectional flow of energy. U1 and U2 are respectively input and output voltage values of each module (DAB);i Lis primary side current of high frequency transformer, ULAs auxiliary inductor voltage, Up and Us are the primary and secondary side voltages of the high frequency transformer, respectively.
In fig. 3: zvAs a result of the virtual impedance,U orefthe voltage reference is output for DCSST.G sc、G dcAnd the PI regulators are respectively an input equalizing ring and an output voltage ring. DiThe phase shift is the phase shift.U inAndU outrespectively representing the input and output bus voltages of the direct current transformer;i out outputting current for the direct current transformer; i outi for each DAB output side current;i avand outputting the average current for the DCSST. U ini AndU outifor each DAB input output side voltage. Wherein: i =1,2, …, m. The phase shift module can generate a drive waveform after phase shift of the MOSFET. In the input voltage-sharing ring, the voltage-sharing reference value and the input voltage value of each moduleU iniAfter making the difference, the difference is passed through a PI controller GscAnd outputting a phase shift correction signal. Output voltage reference value in output voltage loopU orefAnd the actual value of the output voltageU outiAfter making the difference, the difference is passed through a PI controller GdcOutputting the basic phase shift ratio signal, and making difference with each phase shift ratio correction signal. Then the circulation current of each module passes through a virtual impedance link, and then the phase shift ratio is adjusted to obtain the final phase shift ratio signal of each moduleD iAnd finally, outputting a pulse PWM driving signal through a phase-shifting controller.G sc、G dcAnd the phase shift module and the virtual impedance are realized by the DSP.
Detailed Description
1. And the derivation control model is a method for introducing virtual impedance to realize current sharing in DAB double closed loop and single loop control through mathematical derivation on the basis of establishing a DCSST small signal model.
2. Control method based on virtual impedance. In the dashed box as shown in fig. 3 is the loop control with the addition of a virtual impedance, where the loop of each module is the difference between the output average current and the respective output current. And finally, the output current of each module is adjusted through the virtual impedance, so that the output currents of the modules are the same, and current sharing control is realized. Meanwhile, the input voltage-sharing ring can guarantee input voltage-sharing, and the output voltage ring can guarantee output voltage stability.
The specific implementation is as follows: on the basis of the existing modularized control method, the output current sharing strategy based on the virtual impedance is introduced. A virtual impedance module is added in the control module, and the output circulation current is adjusted through the virtual impedance module, so that the output current of each module is balanced. As shown in FIG. 3, in which Z isvAs a result of the virtual impedance,U orefthe voltage reference is output for DCSST.G sc、G dcAnd the PI regulators are respectively an input equalizing ring and an output voltage ring. DiThe phase shift is the phase shift.U inAndU outrespectively representing the input and output bus voltages of the direct current transformer; i out outputting current for the direct current transformer; i outi for each DAB output side current;i avand outputting the average current for the DCSST. U ini AndU outifor each DAB input output side voltage. Wherein: i =1,2, …, m. The phase shift module can generate a drive waveform after phase shift of the MOSFET.
And (3) outputting a voltage ring: reference value of output voltageU orefAnd the actual value of the output voltageU outiAfter making the difference, the difference is passed through a PI controller GdcOutputting a basic phase shift ratio signal. And the stability of the output voltage is ensured.
Inputting a grading ring: voltage-sharing reference value and input voltage value of each moduleU iniAfter making the difference, the difference is passed through a PI controller GscAnd outputting a phase shift correction signal. The input voltage balance of all DAB modules is ensured.
Virtual impedance control: circulating current of each DAB module to output current of each DAB modulei outiAnd average currenti avThe difference of (2), circulating current passing through the virtual impedance ZvAnd adjusting, and controlling the circulation current to enable the output currents of the modules to be the same.
Circulating current of each double-active full-bridge converter module to output current of each double-active full-bridge converter modulei outiAnd average currenti avThe difference of (a).
G sc、G dcAnd the phase shift module and the virtual impedance are realized by a DSP microprocessor.

Claims (3)

1. A control method of a direct current solid-state transformer based on virtual impedance is realized by connecting m double-active full-bridge converters through an input series output parallel structure; the method is characterized in that: virtual impedance is introduced in the control of an input voltage equalizing ring and an output voltage ring of the double-active full-bridge converter, so that the output current is equalized; the method comprises the following specific steps: input equalizer ringInput voltage-sharing reference value U of DC solid-state transformerinM and input voltage value of each double-active full-bridge converterU iniAfter difference making, the difference is input into a grading ring PI controller GscOutputting phase shift ratio correction signals of each double-active full-bridge converter; u shapeinInputting a bus voltage for the direct current transformer;
reference value of output voltage of DC solid-state transformer in output voltage loopU orefWith the actual value of the voltage at the output of each dual-active full-bridge converterU outiAfter difference making, the difference is processed by an output voltage ring PI controller GdcOutputting a basic phase-shift ratio signal, and subtracting the basic phase-shift ratio signal from the phase-shift ratio correction signal of each double-active full-bridge converter; then the circulation current of each double-active full-bridge converter passes through a virtual impedance link to obtain a phase shift ratio correction signal so as to adjust the phase shift ratio and obtain a final phase shift ratio signal of each double-active full-bridge converterD iFinally, a pulse PWM driving signal is output through a phase shifting module, and the circulating current passes through a virtual impedance ZvAnd regulating and controlling the circulating current so that the output current of each double-active full-bridge converter is the same.
2. The method for controlling the virtual impedance-based direct current solid-state transformer according to claim 1, wherein: circulating current of each double-active full-bridge converter module to output current of each double-active full-bridge converter modulei outiAnd average currenti avThe difference of (a).
3. The virtual impedance-based direct current solid-state transformer control method according to claim 1 or 2, wherein:G sc、G dcand the phase shift module and the virtual impedance are realized by a DSP microprocessor.
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Publication number Priority date Publication date Assignee Title
US9712040B1 (en) * 2014-12-30 2017-07-18 Google Inc. Virtual impedance shaping
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CN106452149A (en) * 2016-10-26 2017-02-22 东南大学 Non-interconnected voltage control strategy for ISOP inverter system having characteristic of output voltage rise
CN107181275A (en) * 2017-06-13 2017-09-19 湖南大学 A kind of photovoltaic DC microgrid control method of the system containing distributed energy storage
CN107666249A (en) * 2017-11-03 2018-02-06 南京航空航天大学 LLC resonant converter control method for parallel based on virtual impedance

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