CN113676071A - Control method of three-level auxiliary inverter - Google Patents

Control method of three-level auxiliary inverter Download PDF

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CN113676071A
CN113676071A CN202110949652.XA CN202110949652A CN113676071A CN 113676071 A CN113676071 A CN 113676071A CN 202110949652 A CN202110949652 A CN 202110949652A CN 113676071 A CN113676071 A CN 113676071A
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target value
sampling
value
output
control
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CN113676071B (en
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曾凡飞
吴强
邸峰
徐逸煌
刘巍
乔亚飞
王媛媛
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CRRC Qingdao Sifang Rolling Stock Research Institute Co Ltd
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CRRC Qingdao Sifang Rolling Stock Research Institute Co Ltd
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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
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • 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
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters

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  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention provides a three-level auxiliary inverter control system and a control method. Sampling the output of the filter, and calculating active power and reactive power; performing power droop control based on the active power and the reactive power, and calculating an output voltage target value and a fundamental frequency target value; and carrying out coordinate transformation on the sampling value according to the fundamental frequency target value, carrying out decoupling calculation according to a coordinate transformation result and the output voltage target value to obtain a fundamental control component and a harmonic control component, and calculating a compensation modulation wave based on each control component. Based on SVPWM principle, according to the compensation modulation wave, PWM modulation signal of three-level inversion unit is generated. The invention can realize the synchronous symmetry of any output fundamental frequency under any integer pulse, reduce low-order harmonic and optimize the output waveform quality.

Description

Control method of three-level auxiliary inverter
Technical Field
The invention relates to the technical field of electrical control, in particular to a control method of a three-level auxiliary inverter.
Background
The auxiliary power supply provides alternating current power supply for loads such as air conditioners, air pumps, compressors, dynamic maps, televisions and lighting on the rail transit vehicle. The requirements of large marshalling and high transportation capacity of vehicles lead the load capacity to be increased continuously, and the capacity of the auxiliary single machine is also increased continuously; meanwhile, due to the limitation of the axle weight of the vehicle and the space of the vehicle bottom equipment, the indexes of the auxiliary total weight and the total volume are smaller and smaller, and the auxiliary power supply with high power, small volume and light weight and high power density becomes a development trend.
Meanwhile, the loads such as a variable frequency air conditioner and a dynamic map often comprise an uncontrolled rectifying circuit, the loads are nonlinear, non-characteristic subharmonics can be added to output voltage, and higher requirements are provided for the waveform quality output by the auxiliary power supply. If a three-phase LC filter is used for filtering low-order harmonics (mainly low-order harmonics of 5,7 and the like), the magnitude of filter parameters needs to be increased, the weight and the volume are greatly increased, and the method is not economical. In a traditional asynchronous SVPWM (space vector pulse width modulation) mode, output voltage contains characteristic subharmonic, third-order, even-order and other sideband harmonics, and if the output voltage is not processed, the output effect is influenced. In order to inhibit low-order harmonics, a specific harmonic elimination SHEPWM modulation method can be adopted to eliminate specified-order harmonics, but pulse angle calculation relates to an transcendental equation, the calculation is complex, the calculation is usually realized by off-line calculation table lookup, and the control dynamics and flexibility are poor.
In addition, due to the redundancy design thinking of the auxiliary system by the vehicle, two or more auxiliary power supply devices are arranged on the vehicle, and a plurality of devices are required to be operated in parallel without interconnection lines by adopting droop control so as to ensure the power supply reliability of the auxiliary system.
At present, due to the limitation of the loss characteristic of a switching device, the two-level inverter topology commonly used by the subway auxiliary power supply is difficult to qualitatively improve the power density and the harmonic characteristic. The three-level inverter topology is used, the voltage stress of each switching device is reduced, the voltage level number of output lines can be increased, the sine output is more approximate to the sine output in the waveform, and the quality of the output waveform is improved under the condition of limiting the switching frequency.
Disclosure of Invention
The invention aims to provide a control system and a control method for a three-level inverter.
In order to achieve the purpose, the invention adopts the technical scheme that:
a three-level auxiliary inverter control system comprises a three-level inverter, a transformer, a filter and a load which are connected in sequence; the control system includes:
a sampling unit: the sampling circuit is arranged at the output end of the filter and is used for collecting an output voltage sampling value and an output current sampling value;
a droop control unit: for calculating an active power P and a reactive power Q based on the output voltage sample value and the output current sample value, and calculating an output voltage target value U based on the active power and the reactive powerrAnd fundamental frequency target value f0；
A coordinate transformation unit: fundamental frequency target value f calculated based on droop control unit0Determining coordinate conversion angle to calculate output voltage sampling value and output current sampling value to perform rotation coordinate conversion to obtain fundamental voltage output value UdVoltage decoupling output value U with 6k +/-1 subharmonic component(6k±1)d、U(6k±1)q；
A harmonic decoupling calculation unit: by the output voltage target value UrFor inputting the target value, the fundamental voltage is used to output a value UdPerforming PI control calculation to obtain fundamental wave control component Ud0(ii) a By U(6k±1)dFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)d0To U with(6k±1)qFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)q0；
A harmonic compensation calculation unit: controlling the component U according to the fundamental waved06k + -1 subharmonic component control component U(6k±1)d0、U(6k±1)q0And the harmonic compensation calculation is calculated,obtaining a compensated modulated wave Uα、Uβ；
Synchronous symmetrical modulation unit: based on Uα、UβJudging the sector of the reference vector, and converting Uα、UβAs modulated given wave, at carrier frequency fsGenerating a three-level inverter modulation signal; wherein f iss＝6N*f0Following the fundamental frequency target value f0The carrier frequency is dynamically adjusted, where N is the number of samples per sector.
In some embodiments of the present invention, the harmonic compensation unit is configured to calculate the compensation modulation wave as follows:
Uα＝Udo*cosθ-(U(6k±1)do*cos(6k±1)θ-(-1)(6k±1)％3+1*U(6k±1)qo*sin(6k±1)θ)；
Uβ＝Udo*sinθ-((-1)(6k±1)％3+1*U(6k±1)do*sin(6k±1)θ+U(6k±1)qo*cos(6k±1)θ)。
in some embodiments of the invention, the sampling unit is configured to sample data by carrier frequency.
In some embodiments of the invention, the droop control unit is configured to calculate the output voltage target value U as followsrAnd fundamental frequency target value f0：
Ur＝311-Kq*Q；
f0＝50-Kp*P；
Wherein, Kq、KpThe sag factor.
Some embodiments of the invention include the steps of:
s1: a sampling step: starting a three-level auxiliary inverter system, starting output current sampling and output voltage sampling, wherein the sampling frequency is the carrier frequency fsCalculating active power P and reactive power Q after sampling;
s2: and (3) droop control: calculating an output voltage target value U based on a droop control strategyrAnd fundamental frequency target value f0；
S3: and (3) coordinate transformation: based on the fundamental frequency target value f0Determining fundamental wave angle theta, calculating output voltage sampling value and output current sampling value, and performing rotation coordinate transformation to obtain fundamental wave voltage output value UdVoltage decoupling output value U with 6k +/-1 subharmonic component(6k±1)d、U(6k±1)qWherein k is an integer;
s4: decoupling calculation: by the output voltage target value UrFor inputting the target value, the fundamental voltage is used to output a value UdPerforming PI control calculation to obtain fundamental wave control component Ud0(ii) a By U(6k±1)dFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)d0To U with(6k±1)qFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)q0；
S5: and harmonic compensation calculation: controlling the component U according to the fundamental waved06k + -1 subharmonic component control component U(6k±1)d0、U(6k±1)q0Calculating harmonic compensation calculation to obtain compensated modulation wave Uα、Uβ；
S6: a sector judgment step: based on SVPWM principle, compensating modulation wave Uα、UβJudging a large sector number B and a small sector number S of the reference vector;
s7: a pulse modulation step: calculating vector comparison time according to a volt-second balance principle; determining a switching sequence according to M, N, B and S, and distributing PWM pulse duty ratios of switching devices; given frequency f according to fundamental wave0Determining a carrier frequency fsDetermining a triangular carrier waveform; based on the comparison time and the triangular carrier, 12 paths of synchronous symmetrical modulation PWM pulses are output.
In some embodiments of the invention, the method further comprises the steps of:
s8: repeating the modulation step: and setting i as the number of samples, wherein each fundamental wave period has 6N samples, if i is not more than 6N, performing vector operation of a sampling position, adding 1 for each sampling and calculation, and setting i to zero until the sampling finishes 6N calculations in one period, and performing sampling and operation of the next fundamental wave period again.
In some embodiments of the present invention, the harmonic compensation unit in step S5 is configured to calculate the compensation modulation wave as follows:
Uα＝Udo*cosθ-(U(6k±1)do*cos(6k±1)θ-(-1)(6k±1)％3+1*U(6k±1)qo*sin(6k±1)θ)；
Uβ＝Udo*sinθ-((-1)(6k±1)％3+1*U(6k±1)do*sin(6k±1)θ+U(6k±1)qo*cos(6k±1)θ)。
in some embodiments of the present invention, in step S2, the target value U of the output voltagerAnd fundamental frequency target value f0The calculation method comprises the following steps:
Ur＝311-Kq*Q；
f0＝50-Kp*P；
wherein, Kq、KpThe sag factor.
The invention improves the traditional three-level asynchronous modulation SVPWM modulation strategy on the basis of using a three-level inverter topology, designs an optimized synchronous symmetrical SVPWM control strategy based on harmonic compensation and capable of droop control, and has the advantages that:
(1) synchronous symmetrical SVPWM modulation realizes the synchronous symmetry of output line voltage waveform under any integer pulse, and the setting of pulse number frequency value is better and flexible. The calculation method is still a space vector calculation mode, and does not relate to transcendental equations, so that the real-time calculation dynamic property and flexibility are better.
(2) By dynamically adjusting the switching frequency, the output fundamental frequency and the carrier frequency maintain a fixed ratio, and the fundamental frequency is adjusted according to power droop under the condition of not influencing synchronous symmetrical modulation; by adjusting the output voltage, droop control can be achieved and parallel operation can be achieved.
(3) By matching with a harmonic compensation control strategy, output low-order harmonics (such as 5-order harmonics, 7-order … 6k +/-1-order harmonics and the like) which cannot be filtered by the filter are extracted, harmonic compensation is carried out according to the same phase as a synchronous symmetrical SVPWM (space vector pulse width modulation) modulation wave, the content of low-order characteristic harmonics such as 5-order harmonics, 7-order … 6k +/-1-order harmonics and the like is further reduced, three-level output waveform optimization is realized, the total harmonic distortion rate is reduced, the output waveform quality is optimized, the switching frequency is favorably reduced, the efficiency is improved, the selection of filter selection parameters and a radiator is reduced, and the light weight of the whole machine is realized.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions 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 to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a schematic diagram of a three-level inverter control system.
Fig. 2 is a flowchart of a three-level inverter control method.
Fig. 3 is a sector definition diagram.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The first embodiment of the present invention first provides a three-level inverter control system.
First, describing the structure of the three-level boost inverter, referring to fig. 1, the three-level boost inverter includes:
supporting the capacitor: the three-level inverter is connected to the power input of the power grid, provides direct-current power input for the three-level inverter, and plays a role in supporting and filtering the power input of the power grid.
A three-level inverter: the direct current is inverted into alternating current, and an I-shaped topological structure or a T-shaped topological structure in the prior art can be adopted.
Power frequency transformer: the function of power supply isolation and voltage value change in different voltage grades is achieved by converting input high-voltage alternating current into medium-voltage alternating current.
Three-phase LC filter: high-frequency components of a high-voltage pulse waveform containing higher harmonics are filtered, a quasi-sinusoidal waveform is output, the lower the cut-off frequency of the filter is, the better the filtering effect is, and the larger the weight and the size are.
And (3) alternating current load: because the three-level auxiliary inverter system is applied to the railway vehicle, the load corresponds to the electric equipment on the vehicle, such as an air conditioner, an air pump, a compressor, a dynamic map, a television, lighting and the like, and part of the load has a nonlinear load characteristic.
With continued reference to fig. 1, the three-level inverter control system architecture includes the following sections.
A sampling unit: the sampling circuit is arranged at the output end of the three-phase LC filter and used for collecting an output voltage sampling value and an output current sampling value. Preferably, the sampling unit is configured to sample data by carrier frequency.
A droop control unit: for calculating an active power P and a reactive power Q based on the output voltage sample value and the output current sample value, and calculating an output voltage target value U based on the active power and the reactive powerrAnd fundamental frequency target value f0。
The calculation method of the droop control unit for the target value is as follows:
Ur＝311-Kq*Q；
f0＝50-Kp*P；
wherein, Kq、KpThe sag factor.
Through droop control, parallel operation of a plurality of auxiliary converters can be realized.
A coordinate transformation unit: fundamental frequency target value f calculated based on droop control unit0Determining coordinate conversion angle to calculate output voltage sampling value and output current sampling value to perform rotation coordinate conversion to obtain fundamental voltage output value UdVoltage decoupling output value U with 6k +/-1 subharmonic component(6k±1)d、U(6k±1)qWherein k is an integer; for example, 5 timesTaking harmonic as an example, the angle used by the fundamental component in the rotation transformation is theta, and the angle used by the 5 th harmonic is 5 x theta; obtaining a voltage decoupling output value U of the 5 th harmonic component after coordinate transformation5d、U5q. The coordinate transformation process of other harmonics is the same as that of the 5 th harmonic, and is not repeated.
A harmonic decoupling calculation unit: by the output voltage target value UrFor inputting the target value, the fundamental voltage is used to output a value UdPerforming PI control calculation to obtain fundamental wave control component Ud0(ii) a By U(6k±1)dFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)d0To U with(6k±1)qFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)q0. Three sets of PI control logics referring to FIG. 1, U obtained by three sets of PI calculationsd0、U(6k±1)d0、U(6k±1)q0And the harmonic compensation calculation unit is used for calculating the harmonic compensation component of the harmonic compensation calculation unit.
A harmonic compensation calculation unit: controlling the component U according to the fundamental waved06k + -1 subharmonic component control component U(6k±1)d0、U(6k±1)q0Calculating harmonic compensation calculation to obtain compensated modulation wave Uα、Uβ；
The harmonic compensation unit is configured to calculate a compensation modulation wave as follows:
Uα＝Udo*cosθ-(U(6k±1)do*cos(6k±1)θ-(-1)(6k±1)％3+1*U(6k±1)qo*sin(6k±1)θ)；
Uβ＝Udo*sinθ-((-1)(6k±1)％3+1*U(6k±1)do*sin(6k±1)θ+U(6k±1)qo*cos(6k±1)θ)。
according to the above calculation method, the calculation of 6k +/-1 th harmonic is sequentially completed, wherein the value of k depends on the specific control calculation requirement.
Still taking the 5 th harmonic as an example, the method for calculating the compensation modulation wave is as follows:
Uα＝Udo*cosθ-(U5do*cos5θ+U5qo*sin5θ)；
Uβ＝Udo*sinθ-(-U5do*sin5θ+U5qo*cos5θ)。
and performing harmonic compensation operation on the fundamental wave control component and the harmonic wave control component in the same phase of synchronous symmetric modulation to obtain a given signal of harmonic compensation modulation.
Synchronous symmetrical modulation unit: based on Uα、UβJudging the sector of the reference vector, and converting Uα、UβAs modulated given wave, at carrier frequency fsGenerating a three-level inverter modulation signal; wherein f iss＝6N*f0Where N is the number of samples per sector, and the carrier frequency is based on the fundamental frequency target value f0The carrier frequency and the fundamental wave frequency can meet a fixed proportion by the change of (2), the carrier frequency can be dynamically adjusted, and the output fundamental wave frequency can be adjusted according to a droop control strategy under the condition of not changing the relative symmetrical position of the space vector.
A second embodiment of the present invention provides a three-level inverter control method, which specifically includes the following steps with reference to fig. 2.
A given pulse number M is preset in a control system, and the sampling number N of each sector is 6N.
S1: a sampling step: and starting the three-level auxiliary inverter system, and starting output current sampling and output voltage sampling by the three-phase voltage and current sampling unit. The sampling frequency being the carrier frequency fs. And calculating active power P and reactive power Q after sampling.
S2: and (3) droop control: calculating an output voltage target value U based on a droop control strategyrAnd fundamental frequency target value f0。
Ur＝311-Kq*Q；
f0＝50-Kp*P；
Wherein, Kq、KpThe sag factor.
S3: and (3) coordinate transformation: based on the fundamental frequency target value f0Determining fundamental wave angle theta, calculating output voltage sampling value and output current sampling value, and performing rotation coordinate transformation to obtain fundamental wave voltage output value UdVoltage decoupling output value U with 6k +/-1 subharmonic component(6k±1)d、U(6k±1)qWherein k is an integer.
S4: decoupling calculation: by the output voltage target value UrFor inputting the target value, the fundamental voltage is used to output a value UdPerforming PI control calculation to obtain fundamental wave control component Ud0(ii) a By U(6k±1)dFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)d0To U with(6k±1)qFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)q0。
S5: and harmonic compensation calculation: controlling the component U according to the fundamental waved06k + -1 subharmonic component control component U(6k±1)d0、U(6k±1)q0Calculating harmonic compensation calculation to obtain compensated modulation wave Uα、Uβ；
The harmonic compensation unit is configured to calculate a compensation modulation wave as follows:
Uα＝Udo*cosθ-(U(6k±1)do*cos(6k±1)θ-(-1)(6k±1)％3+1*U(6k±1)qo*sin(6k±1)θ)；
Uβ＝Udo*sinθ-((-1)(6k±1)％3+1*U(6k±1)do*sin(6k±1)θ+U(6k±1)qo*cos(6k±1)θ)。
s6: a sector judgment step: based on SVPWM principle, compensating modulation wave Uα、UβAnd judging the large sector number B and the small sector number S of the reference vector.
S7: a pulse modulation step: calculating vector comparison time according to a volt-second balance principle; determining a switching sequence according to M, N, B and S, and distributing PWM pulse duty ratios of switching devices; according to the baseWave given frequency f0Determining a carrier frequency fsDetermining a triangular carrier waveform; outputting 12 paths of synchronous symmetrical modulation PWM pulses based on the comparison time and the triangular carrier;
s8: repeating the modulation step: and setting i as the number of samples, wherein each fundamental wave period has 6N samples, if i is not more than 6N, performing vector operation of a sampling position, adding 1 for each sampling and calculation, and setting i to zero until the sampling finishes 6N calculations in one period, and performing sampling and operation of the next fundamental wave period again.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (8)

1. The control system of the three-level auxiliary inverter is characterized in that the three-level auxiliary inverter comprises a three-level inverter, a transformer, a filter and a load which are connected in sequence; the control system includes:
a sampling unit: the sampling circuit is arranged at the output end of the filter and is used for collecting an output voltage sampling value and an output current sampling value;
a droop control unit: for calculating an active power P and a reactive power Q based on the output voltage sample value and the output current sample value, and calculating an output voltage target value U based on the active power and the reactive powerrAnd fundamental frequency target value f0；
A coordinate transformation unit: fundamental frequency target value f calculated based on droop control unit0Determining coordinate conversion angle to calculate output voltage sampling value and output current sampling value to perform rotation coordinate conversion to obtain fundamental voltage output value UdVoltage decoupling output value U with 6k +/-1 subharmonic component(6k±1)d、U(6k±1)q；
A harmonic decoupling calculation unit: by the output voltage target value UrFor inputting the target value, the fundamental voltage is used to output a value UdPerforming PI control calculation to obtain fundamental wave control component Ud0(ii) a By U(6k±1)dFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)d0To U with(6k±1)qFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)q0；
A harmonic compensation calculation unit: controlling the component U according to the fundamental waved06k + -1 subharmonic component control component U(6k±1)d0、U(6k±1)q0Calculating harmonic compensation calculation to obtain compensated modulation wave Uα、Uβ；
Synchronous symmetrical modulation unit: based on Uα、UβJudging the sector of the reference vector, and converting Uα、UβAs modulated given wave, at carrier frequency fsGenerating a three-level inverter modulation signal; wherein f iss＝6N*f0Following the fundamental frequency target value f0The carrier frequency is dynamically adjusted, where N is the number of samples per sector.
2. The three-level-aided inverter control system of claim 1, wherein the harmonic compensation unit is configured to calculate the compensation modulation wave as follows:
Uα＝Udo*cosθ-(U(6k±1)do*cos(6k±1)θ-(-1)(6k±1)％3+1*U(6k±1)qo*sin(6k±1)θ)；
Uβ＝Udo*sinθ-((-1)(6k±1)％3+1*U(6k±1)do*sin(6k±1)θ+U(6k±1)qo*cos(6k±1)θ)。
3. the three-level auxiliary inverter control system of claim 1, wherein the sampling unit is configured to sample data by carrier frequency.
4. The three-level-aided inverter control system of claim 1, wherein the droop control unit is configured to meter the following stepsCalculating the target value U of the output voltagerAnd fundamental frequency target value f0：
Ur＝311-Kq*Q；
f0＝50-Kp*P；
Wherein, Kq、KpThe sag factor.
5. A control method of a three-level auxiliary inverter is characterized by comprising the following steps:
s1: a sampling step: starting a three-level auxiliary inverter system, starting output current sampling and output voltage sampling, wherein the sampling frequency is the carrier frequency fsCalculating active power P and reactive power Q after sampling;
s2: and (3) droop control: calculating an output voltage target value U based on a droop control strategyrAnd fundamental frequency target value f0；
S3: and (3) coordinate transformation: based on the fundamental frequency target value f0Determining fundamental wave angle theta, calculating output voltage sampling value and output current sampling value, and performing rotation coordinate transformation to obtain fundamental wave voltage output value UdVoltage decoupling output value U with 6k +/-1 subharmonic component(6k±1)d、U(6k±1)qWherein k is an integer;
s4: decoupling calculation: by the output voltage target value UrFor inputting the target value, the fundamental voltage is used to output a value UdPerforming PI control calculation to obtain fundamental wave control component Ud0(ii) a By U(6k±1)dFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)d0To U with(6k±1)qFor inputting the target value, taking 0 as the target value, performing PI control calculation to obtain 6k +/-1 subharmonic component control component U(6k±1)q0；
S5: and harmonic compensation calculation: controlling the component U according to the fundamental waved06k + -1 subharmonic component control component U(6k±1)d0、U(6k±1)q0Calculating harmonic compensation calculation to obtain compensated modulation wave Uα、Uβ；
S6: a sector judgment step: based on SVPWM principle, compensating modulation wave Uα、UβJudging a large sector number B and a small sector number S of the reference vector;
s7: a pulse modulation step: calculating vector comparison time according to a volt-second balance principle; determining a switching sequence according to M, N, B and S, and distributing PWM pulse duty ratios of switching devices; given frequency f according to fundamental wave0Determining a carrier frequency fsDetermining a triangular carrier waveform; based on the comparison time and the triangular carrier, 12 paths of synchronous symmetrical modulation PWM pulses are output.
6. The three-level-aided inverter control method of claim 5, wherein the method further comprises the steps of:
s8: repeating the modulation step: and setting i as the number of samples, wherein each fundamental wave period has 6N samples, if i is not more than 6N, performing vector operation of a sampling position, adding 1 for each sampling and calculation, and setting i to zero until the sampling finishes 6N calculations in one period, and performing sampling and operation of the next fundamental wave period again.
7. The three-level auxiliary inverter control method according to claim 5, wherein the harmonic compensation unit in step S5 is configured to calculate the compensation modulation wave as follows:
Uα＝Udo*cosθ-(U(6k±1)do*cos(6k±1)θ-(-1)(6k±1)％3+1*U(6k±1)qo*sin(6k±1)θ)；
Uβ＝Udo*sinθ-((-1)(6k±1)％3+1*U(6k±1)do*sin(6k±1)θ+U(6k±1)qo*cos(6k±1)θ)。
8. the method of controlling a three-level-assisted inverter according to claim 1, wherein in step S2, the target value U of the output voltage isrAnd fundamental frequency target value f0The calculation method comprises the following steps:
Ur＝311-Kq*Q；
f0＝50-Kp*P；
wherein, Kq、KpThe sag factor.
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