CN110336476B - Closed-loop zero-sequence voltage optimization injection method for cascaded H-bridge converter - Google Patents

Closed-loop zero-sequence voltage optimization injection method for cascaded H-bridge converter Download PDF

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CN110336476B
CN110336476B CN201910700479.2A CN201910700479A CN110336476B CN 110336476 B CN110336476 B CN 110336476B CN 201910700479 A CN201910700479 A CN 201910700479A CN 110336476 B CN110336476 B CN 110336476B
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sequence voltage
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何晋伟
杜李扬
李梦一
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Tianjin University
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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
    • 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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Abstract

The invention discloses a closed-loop zero-sequence voltage optimization injection method for a cascaded H-bridge converter, which is applied to the interphase power control of the cascaded H-bridge converter, can expand the regulation range of the interphase power of the cascaded H-bridge, improves the utilization rate of the direct-current bus voltage of the converter and adopts a closed-loop control modeAnd overmodulation of the three-phase modulation wave after being injected into zero-sequence voltage is prevented. It is characterized in that: obtaining basic frequency component V of three-phase original modulation wave and zero sequence signal of cascade H bridgezero，f(ii) a Then the modulated signals are respectively sent into an overmodulation component extraction function fextObtaining an overmodulation component extraction signal Dover(ii) a Then D isoverThe signal is respectively passed through low-pass filtering transfer function, gain coefficient and base frequency wave trap to obtain zero sequence signal component V for inhibiting overmodulationzero，h(ii) a Finally, V is converted intozero，hFundamental frequency component V of zero sequence signalzero，fAdding to obtain optimized zero sequence voltage Vzero，opAnd injecting the modulated wave into the original modulated wave, and outputting corresponding switching signals.

Description

Closed-loop zero-sequence voltage optimization injection method for cascaded H-bridge converter
Technical Field
The invention relates to the technical field of converters, in particular to a closed-loop zero-sequence voltage optimization injection method, which is particularly applied to the interphase power control of a cascaded H-bridge converter, can expand the zero-sequence voltage injection range, improve the direct-current bus voltage utilization rate of the converter and prevent overmodulation of a three-phase modulation wave injected into the zero-sequence voltage in a closed-loop control mode.
Background
The converter technology is a technology for converting electric energy from direct current to alternating current or from alternating current to direct current, and plays an important role in the industrial application at present. The cascade H-bridge converter is widely applied to high-voltage and high-power energy supply occasions, and adopts the principle that an H-bridge circuit formed by four switching tubes is used as a basic unit, a main circuit is built in a series connection mode, and the switching states of the switching tubes are controlled by matching a corresponding modulation method, so that the input/output current waveform is approximate to sine. The three-phase cascade H-bridge converter is formed by adopting cascade H-bridge module units, and the output power of each module unit needs to be balanced, namely interphase power balance and in-phase power balance. For the inter-phase power equalization, the industry generally injects a specific zero sequence signal into the three-phase modulation signal, so as to flexibly adjust the output power of each phase. After zero sequence voltage is injected, the amplitude of a modulation signal possibly exceeds the amplitude of a carrier wave, and the overmodulation problem occurs, so that the power balance of the cascaded H bridge and the electric energy quality of an output current cannot meet the requirements.
Disclosure of Invention
The invention provides a closed-loop zero-sequence voltage optimized injection method for a cascaded H-bridge converter, aiming at the problem that after zero-sequence voltage injection, the amplitude of a modulation signal may exceed the amplitude of a carrier wave and overmodulation occurs.
The purpose of the invention is realized by the following technical scheme:
the closed-loop zero-sequence voltage optimization injection method for the cascaded H-bridge converter comprises the following steps of:
(1) obtaining three-phase original modulation wave d of cascade H bridge by current controllera、db、dc；
(2) Obtaining zero sequence voltage amplitude E to be injected through interphase power controllerzeroAnd phase angle thetazeroGenerating fundamental frequency component V of zero sequence signal by using amplitude and phase angle of zero sequence voltagezero，fThe calculation formula is as follows:
Vzero，f＝Ezero sin(ωf·t+θzero) (1-1)
wherein ω isfIs the cut-off frequency, t is the sampling time;
(3) will signal da、db、dcAre fed separately into overmodulation component extraction functions fextObtaining a waveform of an overmodulation component
Figure BDA0002150637410000011
Figure BDA0002150637410000021
Will be provided with
Figure BDA0002150637410000022
And
Figure BDA0002150637410000023
adding them to obtain a signal DoverOvermodulation component extraction function DoverThe expression is as follows:
Figure BDA0002150637410000024
Figure BDA0002150637410000025
wherein d isi(i is a, b and c) is a three-phase original modulation wave, and threshold is a modulation wave overmodulation threshold which is 0.95;
(4) d obtained in the step (3)overRespectively low-pass filtered transfer function Gf(s), gain factor K and fundamental trap Gtrap(s) obtaining a zero sequence signal component V for suppressing overmodulationzero，h(ii) a Wherein G isf(s) is a low pass filter transfer function expressed as:
Figure BDA0002150637410000026
wherein ω iscutThe cutoff angular frequency of the first-order low-pass filter, s is a variable of the complex frequency domain;
(5) v obtained in the step (4)zero，hAnd (3) obtaining a zero sequence signal fundamental frequency component V in the step (2)zero，fAdding to obtain optimized zero sequence voltage Vzero，opAnd will optimize the zero sequence voltage Vzero，opInjected into the original modulated wave da、db、dcIn the step (2), a switching signal S is obtaineda、Sb、Sc。
Further, the steps (2) to (5) jointly form a three-phase output power control structure, and the transfer function formula corresponding to the control structure is as follows:
Vzero，h＝[fext(da)+fext(db)+fext(dc)]·Gf(s)·K·Gtrap(s) (1-5)
Figure BDA0002150637410000027
ωcfor the trap to cut off the angular frequency, omega0The angular frequency is corresponding to the power frequency;
Figure BDA0002150637410000028
ωcutcut off the angular frequency for the first order low pass filter;
Vzero，op＝Vzro，f+Vzero，h (1-8)
Sa＝da+Vzero，op (1-9)
Sb＝db+Vzero，op (1-10)
Sc＝dc+Vzero，op (1-11)
compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the method is applied to the interphase power control of the cascaded H-bridge converter, omits the complex trigonometric function calculation, directly realizes the optimized fast generation of irregular zero sequence voltage by the proportional-integral control of the power error with lower operation amount; through an overmodulation extraction function, the amplitude of a modulation signal after zero sequence voltage injection is reduced, and the occurrence of an overmodulation condition is reduced, so that the interphase power regulation range of the cascaded H bridge is expanded; meanwhile, the accuracy and precision of inter-phase power control can be improved through closed-loop control, and the method has certain engineering practice significance.
Drawings
Fig. 1 is a schematic diagram of a topology structure of a three-phase cascaded H-bridge grid-connected converter in the implementation of the invention.
Fig. 2a is a schematic diagram of a control structure of a three-phase cascade H-bridge grid-connected converter in the implementation of the present invention.
Fig. 2b is a structure diagram of the zero sequence voltage optimization controller in the implementation of the present invention.
Fig. 3 is a voltage waveform diagram of the net side of the present invention.
Fig. 4a is a net side current waveform for a three phase power balanced and equal case.
Fig. 4b is a net side current waveform for achieving three-phase power redistribution and balancing by using a closed-loop zero-sequence voltage injection method.
Fig. 4c is a network side current waveform for realizing three-phase power redistribution and balance by adopting the closed-loop zero-sequence voltage optimization injection method provided by the invention.
Fig. 5a is a diagram of the effect of three-phase power control when three-phase power is balanced and equal.
Fig. 5b is a diagram of the effect of three-phase power control for realizing three-phase power redistribution and balance by using a closed-loop zero-sequence voltage injection method.
Fig. 5c is a diagram of the effect of three-phase power control for realizing three-phase power redistribution and balance by using the closed-loop zero-sequence voltage optimization injection method provided by the present invention.
Fig. 6a is the output modulation signal waveform of the cascaded H-bridge converter under the condition of three-phase power balance and equality.
Fig. 6b is a waveform of an output modulation signal of the cascaded H-bridge converter under the condition that the closed-loop zero-sequence voltage injection method is adopted to realize three-phase power redistribution and balance.
Fig. 6c shows the output modulation signal waveform of the cascaded H-bridge converter under the condition that the closed-loop zero-sequence voltage optimized injection method provided by the invention is adopted to realize the redistribution and balance of the three-phase power.
FIG. 7a is a zero sequence voltage V before the present invention is appliedzero，fAnd (4) injecting a waveform diagram.
FIG. 7b is the zero sequence voltage V after the closed loop zero sequence voltage optimization injection method proposed by the present inventionzero，opAnd (4) injecting a waveform diagram.
Detailed Description
The following describes a specific embodiment of the present invention for power equalization of a cascaded H-bridge converter in conjunction with a diagram so that those skilled in the art can better understand the present invention. Taking a cascade H-bridge converter operated in a grid-connected mode as an example, fig. 1 is a topological structure schematic diagram of a specific embodiment of the invention under the working condition, and fig. 2a and 2b are control structure schematic diagrams. As shown in fig. 1, the cascaded converter is formed by connecting H-bridge converter module units with the same structure in series, and the direct current side of each module unit can be connected to source load equipment such as a battery, a photovoltaic and a direct current load, so that a low-voltage source load device is connected to a medium-high voltage power grid. Because the power emitted by each module is different, and the three-phase grid-connected current needs to be balanced, zero-sequence signals must be injected into the three-phase modulation signals to ensure that the three-phase output power meets the requirement and the three-phase current is balanced, when the power emitted by each phase has larger difference, the amplitude of the injected zero-sequence signals is larger, the condition of overmodulation of a certain phase can occur, and at the moment, the overmodulation of the three-phase modulation signals needs to be inhibited by applying the invention, and the quality of the current and the electric energy is ensured not to.
The basic steps of the invention for controlling the power of the cascaded H-bridge converter are as follows:
step 1: obtaining three-phase original modulation wave d of cascade H bridge by current controllera、db、dc。
Step 2: obtaining zero sequence voltage amplitude E to be injected through interphase power controllerzeroAnd phase angle thetazeroGenerating fundamental frequency component V of zero sequence signal by using amplitude and phase angle of zero sequence voltagezero，fAdding the three-phase original modulated wave d obtained in the step (1)a、db、dcIn, generating a signal Da、Db、DcThe calculation formula is as follows:
Vzero_f＝Ezero sin(ωf·t+θzero) (1-1)
Da＝Vzero，f+da (1-2)
Db＝Vzero，f+db (1-3)
Dc＝Vzero，f+dc (1-4)
wherein ω isfThe cut-off frequency, t is the sampling time.
And step 3: will signal da、db、dcAre fed separately into overmodulation component extraction functions fext(x) Obtaining a waveform of an overmodulation component
Figure BDA0002150637410000041
Adding them to obtain signal Dover. Overmodulation component extraction function fext(x) The expression is as follows:
Figure BDA0002150637410000042
t is any limit of x.
Therefore, overmodulation component extraction function DoverThe expression is as follows:
Figure BDA0002150637410000043
threshold is a modulation wave overmodulation threshold, and is generally 0.95.
And 4, step 4: d obtained in the step 3overRespectively low-pass filtered transfer function Gf(s), gain factor K and fundamental trap Gtrap(s) obtaining a zero sequence signal component V for suppressing overshootzero，h. Wherein G isf(s) is a low pass filter transfer function expressed as:
Figure BDA0002150637410000051
wherein ω iscutThe angular frequency is cut off for a first order low pass filter.
And 5: v obtained in the step 4zero，hAnd the zero sequence signal fundamental frequency component V obtained in the step twozero，fAdding to obtain optimized zero sequence voltage Vzero，opAnd injecting it into the original modulated wave da、db、dcIn (1), obtain a signal Sa、Sb、ScAnd outputting corresponding driving signals.
The steps 2-5 jointly form a three-phase output power control structure, and the corresponding transfer function formula of the control structure is as follows:
Vzero，h＝[fext(da)+fext(db)+fext(dc)]·Gf(s)·K·Gtrap(s) (1-7)
Figure BDA0002150637410000052
ωcfor the trap to cut off the angular frequency, omega0Angular frequency corresponding to power frequency
Vzero，op＝Vzero，f+Vzero，h (1-10)
Sa＝da+Vzero，op (1-11)
Sb＝db+Vzero，op (1-12)
Sc＝dc+Vzero，op (1-13)
Step 6: and (3) building a simulation model shown in figure 1 by Matlab/Simulink, and verifying the zero sequence voltage optimized injection method provided by the invention.
Fig. 3 is a voltage waveform diagram of the grid side of the present invention, and fig. 4a to 4c are current waveform diagrams of the grid side before and after the present invention is applied. Fig. 4a is a network side current waveform under the condition that three-phase power is balanced and equal, fig. 4b is a network side current waveform for realizing three-phase power redistribution and balance by adopting a closed-loop zero-sequence voltage injection method, and fig. 4c is a network side current waveform for realizing three-phase power redistribution and balance by adopting a closed-loop zero-sequence voltage optimized injection method provided by the invention. As can be seen from fig. 4a, the grid-connected current is in phase with the grid voltage, and the basic power balance control is realized. Fig. 4b shows that the simple zero-sequence voltage injection method causes distortion of grid-connected current waveform due to overmodulation of the H-bridge module, which affects performance and reliability of the grid-connected device, while fig. 4c shows that the zero-sequence voltage optimized injection method provided by the present invention can well solve the overmodulation problem.
FIG. 5a is a diagram showing the effect of three-phase power control under balanced and equal three-phase power, λa＝λb＝λc＝1/3，Pa＝Pb＝Pc2000W; FIG. 5b is a three-phase power control effect diagram of three-phase power redistribution and balancing using zero-sequence voltage injection, λa＝0.333，λb＝0.234，λc＝0.433，Pa＝2000W，Pb＝1400W，Pc2600W; FIG. 5c shows the use of a closed loop zeroThree-phase power control effect diagram, lambda, for realizing three-phase power redistribution and balance by using sequence voltage optimization injection methoda＝0.333，λb＝0.234，λc＝0.433，Pa＝2000W，Pb＝1400W，Pc＝2600W。
Fig. 6a is a waveform of an output modulation signal of a cascaded H-bridge converter under the condition that three-phase power is balanced and equal, and fig. 6b is a waveform of an output modulation signal of a cascaded H-bridge converter under the condition that three-phase power is redistributed and balanced by adopting a closed-loop zero-sequence voltage injection method; fig. 6c shows the modulation signal wave output by the cascaded H-bridge converter when the closed-loop zero-sequence voltage optimized injection method provided by the present invention is adopted to implement three-phase power redistribution and balance. Known as Vdc130V, output voltage peak V due to H-bridgepUsually below 3VdcOnly when the power imbalance increases to a critical point, Vp＝3Vdc. As can be seen from the figure, the overmodulation problem occurs in FIG. 6b, and the modulation signal can be controlled to be less than or equal to 3V by adopting the closed-loop zero-sequence voltage optimization injection method as shown in FIG. 6cdc。
FIG. 7a is a zero sequence voltage V before the present invention is appliedzero，fInjecting a waveform diagram; FIG. 7b is the zero sequence voltage V after the zero sequence voltage optimization injection method proposed by the present inventionzero，opAnd (4) injecting a waveform diagram.
In conclusion, the invention discloses a closed-loop zero-sequence voltage optimization injection method, which is applied to the interphase power control of a cascaded H-bridge converter, can expand the regulation range of the interphase power of the cascaded H-bridge, improve the utilization rate of the direct-current bus voltage of the converter, and prevent overmodulation of a three-phase modulation wave after injecting zero-sequence voltage in a closed-loop control mode, and is a novel zero-sequence voltage injection method which is worthy of popularization.
The present invention is not limited to the above-described embodiments. The foregoing description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention, and the above specific embodiments are merely illustrative and not restrictive. Those skilled in the art can make many changes and modifications to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (2)

1. The closed-loop zero-sequence voltage optimization injection method for the cascaded H-bridge converter is characterized by comprising the following steps of:
(1) obtaining three-phase original modulation wave d of cascade H bridge by current controllera、db、dc；
(2) Obtaining zero sequence voltage amplitude E to be injected through interphase power controllerzeroAnd phase angle thetazeroGenerating fundamental frequency component V of zero sequence signal by using amplitude and phase angle of zero sequence voltagezero，fThe calculation formula is as follows:
Vzero，f＝Ezerosin(ωf·t+θzero) (1-1)
wherein ω isfIs the cut-off frequency, t is the sampling time;
(3) will signal da、db、dcAre fed separately into overmodulation component extraction functions fextObtaining a waveform of an overmodulation component
Figure FDA0002692705190000011
Figure FDA0002692705190000012
Will be provided with
Figure FDA0002692705190000013
And
Figure FDA0002692705190000014
adding them to obtain a signal DoverOver-modulation component extraction function fextThe expression is as follows:
Figure FDA0002692705190000015
Figure FDA0002692705190000016
wherein d isi(i is a, b and c) is a three-phase original modulation wave, and threshold is a modulation wave overmodulation threshold which is 0.95;
(4) d obtained in the step (3)overRespectively low-pass filtered transfer function Gf(s), gain factor K and fundamental trap Gtrap(s) obtaining a zero sequence signal component V for suppressing overmodulationzero，h(ii) a Wherein G isf(s) is a low pass filter transfer function expressed as:
Figure FDA0002692705190000017
wherein ω iscutThe cutoff angular frequency of the first-order low-pass filter, s is a variable of the complex frequency domain;
(5) v obtained in the step (4)zero，hAnd (3) obtaining a zero sequence signal fundamental frequency component V in the step (2)zero，fAdding to obtain optimized zero sequence voltage Vzero，opAnd will optimize the zero sequence voltage Vzero，opInjected into the original modulated wave da、db、dcIn the step (2), a switching signal S is obtaineda、Sb、Sc。
2. The closed-loop zero-sequence voltage optimized injection method for the cascaded H-bridge converter according to claim 1, wherein the steps (2) to (5) jointly form a three-phase output power control structure, and the control structure corresponds to a transfer function formula as follows:
Vzero，h＝[fext(da)+fext(db)+fext(dc)]·Gf(s)·K·Gtrap(s) (1-5)
Figure FDA0002692705190000018
ωcfor the trap to cut off the angular frequency, omega0The angular frequency is corresponding to the power frequency;
Figure FDA0002692705190000021
ωcutcut off the angular frequency for the first order low pass filter;
Vzero，op＝Vzero，f+Vzero，h (1-8)
Sa＝da+Vzero，op (1-9)
Sb＝db+Vzero，op (1-10)
Sc＝dc+Vzero，op (1-11)。
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