WO2023066407A1 - Method and apparatus for controlling three-phase four-bridge-arm auxiliary converter - Google Patents

Abstract

Disclosed in the present application are a method and apparatus for controlling a three-phase four-bridge-arm auxiliary converter. The control method comprises: a voltage collection step, involving: collecting a three-phase output voltage; a first compensation result acquisition step, involving: obtaining a positive-sequence component and a negative-sequence component of the three-phase output voltage by means of positive and negative synchronous rotation coordinate transformation and according to the three-phase output voltage, and performing closed-loop controlling on the positive-sequence component and the negative-sequence component, so as to obtain a positive-sequence component compensation result and a negative-sequence component compensation result; a second compensation result acquisition step, involving: obtaining a zero-sequence voltage component of the three-phase output voltage by means of a symmetrical component method and according to the three-phase output voltage, and performing feedback compensation on the zero-sequence voltage component, so as to obtain a zero-sequence component compensation result; and a three-phase output voltage balance step, involving: performing three-dimensional space rotation vector modulation according to the positive-sequence component compensation result, the negative-sequence component compensation result and the zero-sequence component compensation result, so as to obtain a control pulse, and applying the control pulse to a bridge arm of an inverter unit, so as to obtain a balanced three-phase output voltage.

Description

Control method and device for three-phase four-leg auxiliary converter

This application claims the priority of the Chinese patent application submitted to the China Patent Office on May 26, 2022, with the application number 202210579548.0 and the application name "Control method and device for three-phase four-arm auxiliary converter", the entire content of which Incorporated in this application by reference.

technical field

The present application belongs to the technical field of auxiliary converters, and in particular relates to a control method and device for a three-phase four-leg auxiliary converter.

Background technique

The train auxiliary converter converts high-voltage direct current (DC1500V/DC750V) into three-phase alternating current (AC380V) to provide electric energy for train medium-voltage loads. The conventional medium-voltage load is relatively single, and the unbalanced load is less, and the three-phase three-wire output system can meet the requirements. However, with the development of urban rail transit, the medium-voltage loads of urban rail trains are becoming more and more complex. In addition to balancing loads, the introduction of loads such as electric heating, lighting, single-phase sockets, and dynamic maps requires the auxiliary converter to have a certain single-phase The load carrying capacity generally adopts the three-phase four-wire output system.

The train auxiliary converter usually electrically isolates the grid power supply side and the train load side. Conventional isolation technologies include power frequency transformer isolation and high frequency transformer isolation. The former often uses a D/Yn type transformer, and the output N line is drawn from the secondary side of the power frequency transformer; in the high-frequency transformer isolation topology, the output N line is drawn out from the midpoint of the three-phase filter capacitor or the midpoint of the front-end support capacitor. When an auxiliary converter using power frequency isolation technology is connected to a single-phase unbalanced load, its single-phase load current flows into the transformer, which will cause unbalanced magnetic circuits on the secondary side of the transformer, and long-term work will cause uneven heating of the windings , affect the insulation performance, but have little effect on the output voltage. For auxiliary converters using high-frequency isolation technology, when the N line is drawn from the midpoint of the three-phase filter capacitor and connected to a single-phase unbalanced load, the single-phase load current flows into the three-phase filter capacitor, which will not only cause output voltage imbalance (See Figure 1, where Figure 1 shows the U-phase with a load of 1kW, the upper part is the output voltage waveform, and the lower part is the output current waveform), and working in an unbalanced state for a long time will reduce the service life of the three-phase filter capacitor; when the N line is connected by The midpoint of the front-end support capacitor is drawn out. When connected to a single-phase unbalanced load, although the impact on the output voltage is small, the single-phase load current flows into the front-end DC side support capacitor, which will bring additional current stress to the front-end support capacitor and increase losses. At the same time, the series capacitor increases the stray inductance of the loop, which will generate a high voltage spike when the power device is turned off, which will affect the service life of the device. Obviously, the performance of the auxiliary converter using power frequency isolation technology is better than that of the high-frequency isolation auxiliary converter under unbalanced load conditions, but it has no advantages in terms of volume, weight, noise, etc., which is different from the current advocated "green The concept of "travel" is contrary.

At present, auxiliary converters based on high-frequency isolation technology are the main development direction in the field of urban rail transit. In order to improve the single-phase load carrying capacity of high-frequency auxiliary converters, it is urgent to develop an improved high-frequency auxiliary converter that overcomes the above defects A control method and device for a three-phase four-arm auxiliary converter with a single-phase load carrying capacity of the converter.

Contents of the invention

Aiming at at least one of the above technical problems existing in the prior art, the present application provides a control method for a three-phase four-leg auxiliary converter, wherein the inverter unit of the three-phase four-leg auxiliary converter includes a first Four bridge arms, the output point of the fourth bridge arm is connected to the AC output N line through an inductor, and the control method includes:

Voltage collection step: collecting three-phase output voltage;

The first compensation result obtaining step: obtain the positive sequence component and the negative sequence component of the three-phase output voltage through positive and negative synchronous rotating coordinate transformation according to the three-phase output voltage, and carry out the positive sequence component and the negative sequence component Closed-loop control obtains positive sequence component compensation results and negative sequence component compensation results;

The second compensation result obtaining step: obtaining the zero-sequence voltage component of the three-phase output voltage through a symmetrical component method according to the three-phase output voltage, performing feedback compensation on the zero-sequence voltage component to obtain a zero-sequence component compensation result;

Three-phase output voltage balancing step: performing three-dimensional space rotation vector modulation according to the positive sequence component compensation result, the negative sequence component compensation result and the zero sequence component compensation result to obtain a control pulse, and applying the control pulse to the The bridge arm of the inverter unit obtains a balanced three-phase output voltage.

In some embodiments of the present application, the step of obtaining the first compensation result includes:

The step of obtaining the two-phase conversion voltage: performing 3/2 conversion and PARK conversion on the three-phase output voltage to obtain the two-phase conversion voltage;

Double DQ transformation step: performing the positive and negative synchronous rotation coordinate transformation on the two-phase transformation voltage and removing the double frequency component to obtain four variables;

Filtering step: performing low-pass filtering on the four variables to obtain DC components U _dpFltr , U _qpFltr , U _dnFltr , U _qnFltr ;

PID control step: take the output voltage target value as a given value, use the DC component U _dpFltr as a feedback value, obtain the output result U _dpout through PID control, use 0 as a given value, and use the DC components U _qpFltr , U _dnFltr and U _qnFltr are used as feedback values, and the output results U _qpout , U _dnout , and U _qnout are respectively obtained through PID control, wherein the output result U _dpout and the output result U _qpout are the positive sequence component compensation results, the output result U _dnout and the output result U _qnout is the negative sequence component compensation result.

In some embodiments of the present application, the method of performing 3/2 transformation and PARK transformation on the three-phase output voltage in the step of obtaining the two-phase transformation voltage is as follows:

Among them, U _α and U _β are two-phase conversion voltages; UN, VN, WN are three-phase output voltages.

In some embodiments of the present application, the method of performing the positive and negative synchronous rotation coordinate transformation on the two-phase conversion voltage in the double DQ transformation step is as follows:

Forward transformation:

Negative sequence transformation:

Among them, U _α and U _β are the two-phase conversion voltage;

is the synchronous rotation angle, which is obtained by integrating the output result of closed-loop PID control on the Q-axis component.

In some embodiments of the present application, the method for removing double frequency components in the double DQ transformation step is as follows:

In some embodiments of the present application, in the filtering step, after the decoupled variable is passed through a low-pass filter, DC components U _dpFltr , U _qpFltr , U _dnFltr and U _qnFltr can be obtained; wherein, the low-pass filter The cut-off frequency of the device LPF should be set below 100Hz.

In some embodiments of the present application, the step of obtaining the second compensation result includes:

The zero-sequence voltage component acquisition step: according to the three-phase output voltage, the zero-sequence voltage component is obtained by a symmetrical component method;

PR control step: using the zero-sequence voltage component as a feedback value and 0 as a target value to obtain an output result _Unout through proportional-resonance control, _which is the compensation result of the zero-sequence component.

In some embodiments of the present application, the three-phase output voltage balancing step includes:

Transformation step: performing 3/2 inverse transformation and PARK inverse transformation on the positive sequence component compensation result and the negative sequence component compensation result respectively to obtain a three-phase conversion voltage, and according to the three-phase conversion voltage and the zero-sequence component compensation As a result, a first voltage, a second voltage and a third voltage are obtained;

The step of obtaining the three-dimensional modulated wave voltage: according to the first voltage, the second voltage and the third voltage, the three-dimensional modulated wave is obtained through sector judgment, vector action time calculation and seven-segment switching voltage vector action sequence;

The control pulse obtaining step: comparing the three-dimensional modulation wave with the triangular carrier wave to obtain the control pulse corresponding to the switching device of each bridge arm of the inverter unit;

Control and adjustment step: correspondingly control the action of each of the switching devices according to each of the control pulses.

In some embodiments of the present application, the step of obtaining the control pulse includes:

When the triangular carrier wave is larger than the three-dimensional modulation wave, a high-level pulse is output, and when the triangular carrier wave is smaller than the three-dimensional modulation wave, a low-level pulse is output.

In some embodiments of the present application, the controlling and adjusting step includes: the switching device of the upper bridge arm of each bridge arm acts oppositely to the switching device of the lower bridge arm.

Another aspect of the embodiment of the present application provides a control device for a three-phase four-leg auxiliary converter, which is used in the control method described in any one of the above items, the inverter of the three-phase four-leg auxiliary converter The variable unit includes a fourth bridge arm, the output point of the fourth bridge arm is connected to the AC output N line through an inductance, and the control device includes:

The voltage acquisition unit collects the three-phase output voltage;

The first compensation result acquisition unit obtains the positive sequence component and the negative sequence component of the three-phase output voltage through positive and negative synchronous rotating coordinate transformation according to the three-phase output voltage, and performs the positive sequence component and the negative sequence component on the positive sequence component and the negative sequence component. Closed-loop control obtains positive sequence component compensation results and negative sequence component compensation results;

The second compensation result acquisition unit obtains the zero-sequence voltage component of the three-phase output voltage through a symmetrical component method according to the three-phase output voltage, and performs feedback compensation on the zero-sequence voltage component to obtain a zero-sequence component compensation result;

The three-phase output voltage balance unit performs three-dimensional space rotation vector modulation according to the positive sequence component compensation result, the negative sequence component compensation result and the zero sequence component compensation result to obtain a control pulse, and applies the control pulse to the The bridge arm of the inverter unit obtains a balanced three-phase output voltage.

In some embodiments of the present application, the first compensation result acquisition unit includes:

A two-phase conversion voltage obtaining module, which performs 3/2 conversion and PARK conversion on the three-phase output voltage to obtain a two-phase conversion voltage;

A double DQ transformation module, which performs the positive and negative synchronous rotation coordinate transformation on the two-phase conversion voltage and obtains four variables after removing the double frequency component;

A low-pass filtering module, performing low-pass filtering on the four variables to obtain DC components U _dpFltr , U _qpFltr , U _dnFltr , U _qnFltr ;

The PID control module takes the output voltage target value as a given value, uses the DC component U _dpFltr as a feedback value, obtains an output result U _dpout through PID control, takes 0 as a given value, and uses the DC components U _qpFltr , U _dnFltr and U _qnFltr are used as feedback values, and the output results U _qpout , U _dnout , and U _qnout are respectively obtained through PID control, wherein the output result U _dpout and the output result U _qpout are the positive sequence component compensation results, the output result U _dnout and the output result U _qnout is the compensation result of the negative sequence component.

In some embodiments of the present application, the second compensation result acquisition unit includes:

A zero-sequence voltage component acquisition module, which obtains the zero-sequence voltage component through a symmetrical component method according to the three-phase output voltage;

The PR control module uses the zero-sequence component as a feedback value and 0 as a target value to obtain an output result _Unout through proportional-resonant control, and the output result _Unout is a compensation result of the zero-sequence component.

In some embodiments of the present application, the three-phase output voltage balancing unit includes:

A transformation module, performing 3/2 inverse transformation and PARK inverse transformation on the positive sequence component compensation result and the negative sequence component compensation result respectively to obtain a three-phase conversion voltage, according to the three-phase conversion voltage and the zero sequence component compensation As a result, a first voltage, a second voltage and a third voltage are obtained;

The SVPWM modulation module, according to the first voltage, the second voltage and the third voltage, obtains a three-dimensional modulation wave through sector judgment, vector action time calculation and seven-segment switch voltage vector action sequence;

The control pulse obtaining module compares the three-dimensional modulation wave with the triangular carrier wave to obtain the control pulse corresponding to the switching device of each bridge arm of the inverter unit;

The control and adjustment module controls the action of each switching device according to each of the control pulses.

Compared with the prior art, the effect of this application is that the control method and device of the three-phase four-arm auxiliary converter of the application are decomposed by the symmetrical component method, and then the positive sequence, negative sequence and zero sequence components are respectively compensated, to overcome imbalances.

Additional features and advantages of the application will be set forth in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the application. The objectives and other advantages of the application will be realized and attained by the structure pointed out in the written description as well as the appended drawings.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present application. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

FIG. 1 is a waveform diagram of voltage unbalance phenomenon in the prior art;

FIG. 2 is a schematic circuit diagram of a three-phase four-leg auxiliary converter according to an embodiment of the present application;

Fig. 3 is the flowchart of the control method of the embodiment of the present application;

Fig. 4 is the flowchart of step S2 in Fig. 3;

Fig. 5 is the flowchart of step S3 in Fig. 3;

Fig. 6 is the flowchart of step S4 in Fig. 3;

FIG. 7 is a schematic structural diagram of a control device according to an embodiment of the present application;

FIG. 8 is a waveform diagram of a balanced three-phase output voltage according to an embodiment of the present application;

FIG. 9 is a flow chart of obtaining a DC component in an embodiment of the present application;

Fig. 10 is the flowchart of PID control in the embodiment of the present application;

Fig. 11 is a flow chart of PR control in the embodiment of the present application;

FIG. 12 is a schematic diagram of SVPWM modulation in the embodiment of the present application;

Fig. 13 is a schematic structural diagram of a control device provided by another embodiment of the present application.

In the picture:

1. Processor; 10. Memory; 11. Voltage acquisition unit; 12. First compensation result acquisition unit; 121. Two-phase conversion voltage acquisition module; 122. Double DQ conversion module; 123. Low-pass filter module; 124. PID Control module; 13. Second compensation result acquisition unit; 131. Zero-sequence voltage component acquisition module; 132. PR control module; 14. Three-phase output voltage balance unit; 141. Conversion module; 142. SVPWM modulation module; 143. Control Pulse acquisition module; 144. Control and adjustment module.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments It is a part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of this application.

The exemplary embodiments and descriptions of the present application are used to explain the present application, but not to limit the present application. In addition, elements/members with the same or similar numbers used in the drawings and embodiments are used to represent the same or similar parts.

Regarding the "first", "second", "S1", "S2", ... etc. used herein, it does not refer to the meaning of sequence or order, nor is it used to limit the application, it is only for the purpose of distinguishing the following Elements or operations described by the same technical terms.

Regarding the directional terms used herein, such as: up, down, left, right, front or rear, etc., only refer to the directions of the drawings. Accordingly, the directional terms used are for illustration and not for limitation of the present invention.

As used herein, "comprising", "comprising", "having", "comprising" and so on are all open terms, meaning including but not limited to.

As used herein, "and/or" includes any or all combinations of the stated things.

The terms "approximately" and "about" used herein are used to modify any quantity or error that may vary slightly, but these slight changes or errors will not change its essence. Generally speaking, the range of slight changes or errors modified by such terms may be 20% in some embodiments, 10% in some embodiments, 5% in some embodiments or other numerical values. Those skilled in the art should understand that the aforementioned values can be adjusted according to actual needs, and are not limited thereto.

Certain terms used to describe the present application are discussed below or elsewhere in this specification to provide those skilled in the art with additional guidance in describing the present application.

Please refer to FIG. 2-FIG. 3. FIG. 2 is a schematic circuit diagram of a three-phase four-leg auxiliary converter according to an embodiment of the present application; FIG. 3 is a flowchart of a control method according to an embodiment of the present application. As shown in Figures 2-3, the three-phase four-leg auxiliary converter of the embodiment of the present application adds a fourth bridge arm on the basis of the traditional three-phase three-leg converter composed of bridge arms S3, S4 and S5 Sn, and at the same time, the output point of the fourth bridge arm Sn is connected to the AC output N line through the inductor Ln. In the embodiment of the present application, through the switching action of the fourth bridge arm Sn, the unbalanced load current can flow into the bridge arm, so as to ensure the balance of the output voltage and the balance of the three-phase filter capacitor current, and improve the quality of the output voltage waveform. The control method of the embodiment of the present application includes:

Voltage collection step S1: collecting three-phase output voltages;

The first compensation result acquisition step S2: Obtain the positive sequence component and negative sequence component of the three-phase output voltage through positive and negative synchronous rotating coordinate transformation and double DQ transformation according to the three-phase output voltage, for the positive sequence component and the obtained The positive sequence component compensation result and the negative sequence component compensation result are obtained by performing closed-loop control on the above negative sequence component;

The second compensation result acquisition step S3: Obtain the zero-sequence voltage component of the three-phase output voltage through a symmetrical component method according to the three-phase output voltage, and perform feedback compensation on the zero-sequence voltage component to obtain a zero-sequence component compensation result;

Three-phase output voltage balancing step S4: according to the positive sequence component compensation result, the negative sequence component compensation result and the zero sequence component compensation result, perform three-dimensional space rotation vector modulation to obtain a control pulse, and apply the control pulse to the The bridge arm of the inverter unit obtains a balanced three-phase output voltage.

Firstly, by obtaining the three-phase output voltage UN, VN, WN, then the three-phase voltage undergoes three-phase-two-phase transformation (3/2 transformation) and PARK transformation, which can eliminate the DC component in the AC voltage, and then through the double DQ Transform, separate the positive sequence component and negative sequence component of the three-phase output voltage, and perform closed-loop control on them respectively to obtain the positive sequence component compensation result and the negative sequence component compensation result. Secondly, the zero-sequence voltage component of the three-phase output voltage UN, VN, WN is obtained by using the symmetrical component method. The zero-sequence voltage component is an AC signal, and the proportional resonant controller (PR controller) is used for feedback compensation to obtain the zero-sequence component compensation. result. Finally, the positive sequence component compensation result, the negative sequence component compensation result and the second step zero sequence component compensation result are applied to the three-dimensional space rotation vector (3D-SVPWM) modulator to obtain the modulation waveform, and the modulation waveform is compared with the carrier to obtain The control pulse, as shown in FIG. 8 , applies the obtained control pulse to the power device of each bridge arm correspondingly, and finally obtains a balanced three-phase output voltage. Among them, Fig. 8 shows U-phase load 1kW, the upper part is the output voltage waveform, and the lower part is the output current waveform.

Please refer to Fig. 4, Fig. 9 and Fig. 10, Fig. 4 is the flowchart of step S2 in Fig. 3; Fig. 9 is the flowchart of DC component obtaining; Fig. 10 is the flowchart of proportional, integral, differential control (PID control). As shown in Figure 4, Figure 9 and Figure 10, the step S2 of obtaining the first compensation result includes:

Two-phase conversion voltage obtaining step S21: performing 3/2 conversion and PARK conversion on the three-phase output voltage to obtain a two-phase conversion voltage;

Double DQ transformation step S22: performing the positive and negative synchronous rotation coordinate transformation on the two-phase conversion voltage and removing the double frequency component to obtain four variables;

Filtering step S23: performing low-pass filtering on the four variables to obtain DC components U _dpFltr , U _qpFltr , U _dnFltr , U _qnFltr ;

PID control step S24: take the output voltage target value as a given value, use the DC component U _dpFltr as a feedback value, obtain an output result U _dpout through PID control, use 0 as a given value, and use the DC components U _qpFltr , U _dnFltr and U _qnFltr are used as feedback values, and the output results U _qpout , U _dnout , and U _qnout are respectively obtained through PID control, wherein the output result U _dpout and the output result U _qpout are the positive sequence component compensation results, the output result U _dnout and the output The result U _qnout is the negative sequence component compensation result.

Specifically, the three-phase output voltages UN, VN, and WN obtained by the voltage acquisition device are obtained through 3/2 transformation-double DQ transformation to obtain the positive and negative sequence components of the three-phase voltage after DC transformation. The calculation method is as follows. First, the three-phase The phase output voltages UN, VN, and WN undergo 3/2 conversion and PARK conversion:

Among them, U _α and U _β are two-phase conversion voltages, and then carry out positive and negative synchronous rotation coordinate transformation, and its synchronous rotation angle

It is obtained by integrating the output result of closed-loop PID control on the Q-axis component, as shown in Fig. 9 .

Forward transformation:

Negative sequence transformation:

Remove the double frequency component and perform decoupling as follows:

After the decoupled variables U _dp , U _qp , U _dn and U _qn pass through the low-pass filter LPF, the DC components U _dpFltr , U _qpFltr , U _dnFltr and U _qnFltr can be obtained. Among them, the cutoff frequency of the low-pass filter LPF should be set below 100Hz. The output voltage target value SIV_V is used as the given value, U _dpFltr is used as the feedback value, and the output result U _dpout is obtained through the PID controller. Similarly, 0 is used as the target value, U _qpFltr , U _dnFltr and U _qnFltr are used as the feedback value, and the PID control is performed The device obtains output results U _qpout , U _dnout , U _qnout .

Please refer to FIG. 5 and FIG. 11 , FIG. 5 is a flow chart of step S3 in FIG. 3 ; FIG. 11 is a flow chart of PR control. As shown in Figure 5 and Figure 11, the second compensation result acquisition step S3 includes:

Zero-sequence voltage component acquisition step S31: Obtain the zero-sequence voltage component by using a symmetrical component method according to the three-phase output voltage;

PR control step S32: using the zero-sequence voltage component as a feedback value and 0 as a target value to obtain an output result _Unout through proportional-resonance control, _which is the compensation result of the zero-sequence component.

Specifically, the zero-sequence voltage components U ₀ of UN, VN, and WN are obtained by using the symmetrical component method as follows:

The zero-sequence component U ₀ of the three-phase voltage is used as the feedback value, and 0 is used as the target value, and the output result U _nout is obtained through the PR controller.

Among them, the PR controller is a proportional-resonant controller, and its s-domain transfer function expression is

K _p is the proportional link coefficient, which is used to increase the open-loop gain and control accuracy; K _r is the resonance link coefficient, which is used to reduce the steady-state error of the system; ω _c is the offset angular frequency, which is the frequency of the reference waveform Positive and negative changes, ω ₀ is the resonant angular frequency. It is generally required that ω ₀ =2×π×50=100π, and ω _c =2×π×0.5=π.

K _p is related to the calculation frequency of the CPU. Usually, increasing K _p will increase the system bandwidth and improve the response speed. The value of K _p is generally between 0.8 and 1.0, and the system will obtain a faster response speed; K _r and CPU It is related to the calculated frequency, generally increasing K _r will increase the resonance gain, but too high resonance gain will reduce the system bandwidth. In some embodiments, the determination method of K _r is as follows: on the basis that K _p has been determined, draw the Bode diagram of the proportional resonant controller G, and adjust K _r so that the resonance gain is greater than 0dB, and the cut-off bandwidth of the controller is less than ω _c , the value of K _r that satisfies the conditions is the selected value.

Please refer to FIG. 6 and FIG. 12. FIG. 6 is a flowchart of step S4 in FIG. 3; FIG. 12 is a schematic diagram of SVPWM (Space Vector Pulse Width Modulation) modulation. As shown in Figure 6 and Figure 12, the three-phase output voltage balancing step S4 includes:

Transformation step S41: performing 3/2 inverse transformation and PARK inverse transformation on the positive sequence component compensation result and the negative sequence component compensation result respectively to obtain a three-phase conversion voltage, according to the three-phase conversion voltage and the zero-sequence component Obtaining a first voltage, a second voltage, and a third voltage as a result of the compensation;

Step S42 of obtaining the three-dimensional modulated wave voltage: according to the first voltage, the second voltage and the third voltage, the three-dimensional modulated wave is obtained through sector judgment, vector action time calculation, and seven-segment switch voltage vector action order;

Control pulse obtaining step S43: comparing the three-dimensional modulation wave with the triangular carrier wave to obtain the control pulse corresponding to the switching device of each bridge arm of the inverter unit;

Control and adjustment step S44: correspondingly control the action of each of the switching devices according to each of the control pulses.

Wherein, the transformation step S41 specifically includes:

The positive sequence component compensation results U _dpout , U _qpout and the negative sequence component compensation results U _dnout , U _qnout obtained in step S24 are respectively subjected to 3/2 inverse transformation and PARK inverse transformation to obtain positive sequence three-phase voltages U _pa , U _pb , U _pc and negative-sequence three-phase voltages U _na , U _nb , U _nc are converted as follows:

According to the above positive sequence three-phase voltage and negative sequence three-phase voltage to obtain the first voltage, second voltage and third voltage, the specific method is as follows:

First voltage: U _a =U _pa +U _na +U _nout

Second voltage: U _b =U _pb +U _nb +U _nout

Third voltage: U _c =U _pc +U _nc +U _nout

Wherein, the control pulse obtaining step S43 includes:

When the triangular carrier wave is larger than the three-dimensional modulation wave, a high-level pulse is output, and when the triangular carrier wave is smaller than the three-dimensional modulation wave, a low-level pulse is output.

Wherein, the control and adjustment step S44 includes: the action of the switching device of the upper bridge arm of each bridge arm is opposite to that of the switching device of the lower bridge arm.

Since S _n , S ₃ , S ₄ , and S ₅ can determine three independent outputs, a three-dimensional coordinate system xyz with three independent variables is required to describe the operating state of the inverter, as shown in Fig. 8 . The x, y, and z voltages obtained in the above steps are applied to the xyz coordinate axes, wherein the x, y, and z voltages are respectively the first voltage, the second voltage, and the third voltage. Similar to the traditional SVPWM modulation technology, the three-dimensional modulation wave voltage is obtained through sector judgment, vector action time calculation, and seven-segment switch voltage vector action sequence, and then the control pulse is obtained by comparing with the triangular carrier wave, and applied to the power device. Sectors are judged as follows:

The parameter label of each sector can be calculated as follows:

RP=1+k ₁ +2×k ₂ +4×k ₃ +8×k ₄ +16×k ₅ +32×k ₆ ;

Then, the modulation wave comparison value is obtained through the calculation result of the voltage vector duty cycle in the following table 1 and the seven-segment voltage vector conversion table in the following table 2. Among them, u _dc is the voltage of the inverter front-end support capacitor C ₄ , and the conversion relationship between T _x and the duty cycle d is as follows, where T _x represents the digital quantity corresponding to the duty cycle, and T _s is the period value corresponding to the switching frequency of the inverter .

Table 1: Calculation Results of Voltage Vector Duty Cycle

Sector ID RP	Voltage vector duty cycle d x	Voltage vector duty cycle d y	Voltage vector duty cycle d z
1	-z/u dc	(-y+z)/u dc	(-x+y)/u dc
5	(z)/u dc	(-y)/u dc	(-x+y)/u dc
7	(-y+z)/u dc	(y)/u dc	(-x)/u dc
8	(-y+z)/u dc	(-x+y)/u dc	(x)/u dc
9	(-z)/u dc	(-x+z)/u dc	(xy)/u dc
13	(z)/u dc	(-x)/u dc	(xy)/u dc
14	(-x+y)/u dc	(x)/u dc	(-y)/u dc
16	(-x+y)/u dc	(xy)/u dc	(y)/u dc
17	(-y)/u dc	(yz)/u dc	(-x+z)/u dc
19	(y)/u dc	(-z)/u dc	(-x+z)/u dc
twenty three	(yz)/u dc	(-z)/u dc	(-x)/u dc
twenty four	(yz)/u dc	(-x+z)/u dc	(x)/u dc
41	(-x)/u dc	(xz)/u dc	(-y+z)/u dc

Sector ID RP	Voltage vector duty cycle d x	Voltage vector duty cycle d y	Voltage vector duty cycle d z
42	(x)/u dc	(-z)/u dc	(-y+z)/u dc
46	(xz)/u dc	(z)/u dc	(-y)/u dc
48	(xz)/u dc	(-y+z)/u dc	(y)/u dc
49	(-y)/u dc	(-x+y)/u dc	(xz)/u dc
51	(y)/u dc	(-x+y)/u dc	(xz)/u dc
52	(-x+y)/u dc	(x)/u dc	(-z)/u dc
56	(-x+y)/u dc	(xz)/u dc	(z)/u dc
57	(-x)/u dc	(xy)/u dc	(yz)/u dc
58	(x)/u dc	(-y)/u dc	(yz)/u dc
60	(xy)/u dc	(y)/u dc	(-z)/u dc
64	(xy)/u dc	(yz)/u dc	(z)/u dc

Table 2: Seven-segment voltage vector conversion table

Please refer to FIG. 7 , which is a schematic structural diagram of the control device of the present application. As shown in Figure 7, the control device includes:

The voltage acquisition unit 11 collects the three-phase output voltage;

The first compensation result acquisition unit 12 obtains the positive sequence component and the negative sequence component of the three-phase output voltage through positive and negative synchronous rotation coordinate transformation according to the three-phase output voltage, and the positive sequence component and the negative sequence component Perform closed-loop control to obtain positive sequence component compensation results and negative sequence component compensation results;

The second compensation result obtaining unit 13 obtains the zero-sequence voltage component of the three-phase output voltage through a symmetrical component method according to the three-phase output voltage, and performs feedback compensation on the zero-sequence voltage component to obtain a zero-sequence component compensation result;

The three-phase output voltage balancing unit 14 performs three-dimensional space rotation vector modulation according to the compensation result of the positive sequence component, the compensation result of the negative sequence component and the compensation result of the zero sequence component to obtain a control pulse, and applies the control pulse to the The bridge arm of the inverter unit obtains a balanced three-phase output voltage.

Wherein, the first compensation result acquisition unit 12 includes:

The two-phase converted voltage obtaining module 121 performs 3/2 conversion and PARK conversion on the three-phase output voltage to obtain a two-phase converted voltage;

The double DQ transformation module 122, performs the positive and negative synchronous rotation coordinate transformation on the two-phase conversion voltage and removes the double frequency component to obtain four variables;

The low-pass filtering module 123 performs low-pass filtering on the four variables to obtain DC components U _dpFltr , U _qpFltr , U _dnFltr , U _qnFltr ;

The PID control module 124 takes the output voltage target value as a given value, uses the DC component U _dpFltr as a feedback value, obtains an output result U _dpout through PID control, takes 0 as a given value, and uses the DC components U _qpFltr , U _dnFltr and U _qnFltr are used as feedback values, and the output results U _qpout , U _dnout , and U _qnout are respectively obtained through PID control, wherein the output result U _dpout and the output result U _qpout are the positive sequence component compensation results, the output result U _dnout and the output The result U _qnout is the negative sequence component compensation result.

Wherein, the second compensation result acquisition unit 13 includes:

The zero-sequence voltage component acquisition module 131 is used to obtain the zero-sequence voltage component by a symmetrical component method according to the three-phase output voltage;

The PR control module 132 uses the zero-sequence component as a feedback value and 0 as a target value to obtain an output result _Unout through proportional-resonant control, and the output result _Unout is the compensation result of the zero-sequence component.

Wherein, the three-phase output voltage balancing unit 14 includes:

The transformation module 141 performs 3/2 inverse transformation and PARK inverse transformation on the positive sequence component compensation result and the negative sequence component compensation result respectively to obtain a three-phase conversion voltage, according to the three-phase conversion voltage and the zero-sequence component Obtaining a first voltage, a second voltage, and a third voltage as a result of the compensation;

The SVPWM modulation module 142, according to the first voltage, the second voltage and the third voltage, obtains a three-dimensional modulation wave through sector judgment, vector action time calculation, and seven-segment switch voltage vector action order;

The control pulse obtaining module 143 compares the three-dimensional modulation wave with the triangular carrier wave to obtain the control pulse corresponding to the switching device of each bridge arm of the inverter unit;

The control adjustment module 144 correspondingly controls the action of each switching device according to each of the control pulses.

The present application also provides another embodiment of the control device of the three-phase four-leg auxiliary converter, as shown in FIG. 13 , in this embodiment, the control device of the three-phase four-leg auxiliary converter includes: processing A device 1 and a memory 10 connected to the processor 1, wherein the processor 1 is used to execute the following program modules stored in the memory 10:

The voltage acquisition unit 11 collects the three-phase output voltage;

The first compensation result acquisition unit 12 obtains the positive sequence component and the negative sequence component of the three-phase output voltage through positive and negative synchronous rotation coordinate transformation according to the three-phase output voltage, and the positive sequence component and the negative sequence component Perform closed-loop control to obtain positive sequence component compensation results and negative sequence component compensation results;

The second compensation result obtaining unit 13 obtains the zero-sequence voltage component of the three-phase output voltage through a symmetrical component method according to the three-phase output voltage, and performs feedback compensation on the zero-sequence voltage component to obtain a zero-sequence component compensation result;

The three-phase output voltage balancing unit 14 performs three-dimensional space rotation vector modulation according to the compensation result of the positive sequence component, the compensation result of the negative sequence component and the compensation result of the zero sequence component to obtain a control pulse, and applies the control pulse to the The bridge arm of the inverter unit obtains a balanced three-phase output voltage.

Wherein, the first compensation result acquisition unit 12 includes:

The two-phase converted voltage obtaining module 121 performs 3/2 conversion and PARK conversion on the three-phase output voltage to obtain a two-phase converted voltage;

The double DQ transformation module 122, performs the positive and negative synchronous rotation coordinate transformation on the two-phase conversion voltage and removes the double frequency component to obtain four variables;

The low-pass filtering module 123 performs low-pass filtering on the four variables to obtain DC components U _dpFltr , U _qpFltr , U _dnFltr , U _qnFltr ;

The PID control module 124 takes the output voltage target value as a given value, uses the DC component U _dpFltr as a feedback value, obtains an output result U _dpout through PID control, takes 0 as a given value, and uses the DC components U _qpFltr , U _dnFltr and U _qnFltr are used as feedback values, and the output results U _qpout , U _dnout , and U _qnout are respectively obtained through PID control, wherein the output result U _dpout and the output result U _qpout are the positive sequence component compensation results, the output result U _dnout and the output The result U _qnout is the negative sequence component compensation result.

Wherein, the second compensation result acquisition unit 13 includes:

The zero-sequence voltage component acquisition module 131 is used to obtain the zero-sequence voltage component by a symmetrical component method according to the three-phase output voltage;

The PR control module 132 uses the zero-sequence component as a feedback value and 0 as a target value to obtain an output result _Unout through proportional-resonant control, and the output result _Unout is the compensation result of the zero-sequence component.

Wherein, the three-phase output voltage balancing unit 14 includes:

The transformation module 141 performs 3/2 inverse transformation and PARK inverse transformation on the positive sequence component compensation result and the negative sequence component compensation result respectively to obtain a three-phase conversion voltage, according to the three-phase conversion voltage and the zero-sequence component Obtaining a first voltage, a second voltage, and a third voltage as a result of the compensation;

The SVPWM modulation module 142, according to the first voltage, the second voltage and the third voltage, obtains a three-dimensional modulation wave through sector judgment, vector action time calculation, and seven-segment switch voltage vector action order;

The control pulse obtaining module 143 compares the three-dimensional modulation wave with the triangular carrier wave to obtain the control pulse corresponding to the switching device of each bridge arm of the inverter unit;

The control adjustment module 144 correspondingly controls the action of each switching device according to each of the control pulses.

To sum up, this application increases the single-phase load carrying capacity of the auxiliary converter by adding the fourth bridge arm and neutral line inductance, and adopting positive, negative, and zero-sequence voltage control algorithms. Under the same working conditions, using the control method proposed in this application, the simulation waveform is shown in Figure 8, the single-phase load carrying capacity is greatly enhanced, and the problem of voltage imbalance under non-power frequency isolation and unbalanced load conditions is solved. Compared with the split capacitor scheme in the prior art, the weight and volume of the front-end support capacitor and the three-phase filter capacitor are greatly reduced, and the stray inductance of the loop is reduced, which has certain advantages.

Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that: they can still modify the technical solutions described in the aforementioned embodiments, or perform equivalent replacements for some of the technical features; and these The modification or replacement does not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present application.

Claims (14)

1. A control method for a three-phase four-leg auxiliary converter, characterized in that the inverter unit of the three-phase four-leg auxiliary converter includes a fourth bridge arm, and the output point of the fourth bridge arm is passed through The inductance is connected to the AC output N line, and the control method includes:

   Voltage collection step: collecting three-phase output voltage;

   The first compensation result obtaining step: obtain the positive sequence component and the negative sequence component of the three-phase output voltage through positive and negative synchronous rotating coordinate transformation according to the three-phase output voltage, and carry out the positive sequence component and the negative sequence component Closed-loop control obtains positive sequence component compensation results and negative sequence component compensation results;

   The second compensation result obtaining step: obtaining the zero-sequence voltage component of the three-phase output voltage through a symmetrical component method according to the three-phase output voltage, performing feedback compensation on the zero-sequence voltage component to obtain a zero-sequence component compensation result;

   Three-phase output voltage balancing step: performing three-dimensional space rotation vector modulation according to the positive sequence component compensation result, the negative sequence component compensation result and the zero sequence component compensation result to obtain a control pulse, and applying the control pulse to the The bridge arm of the inverter unit obtains a balanced three-phase output voltage.
2. The control method according to claim 1, wherein the step of obtaining the first compensation result comprises:

   The step of obtaining the two-phase conversion voltage: performing 3/2 conversion and PARK conversion on the three-phase output voltage to obtain the two-phase conversion voltage;

   Double DQ transformation step: performing the positive and negative synchronous rotation coordinate transformation on the two-phase transformation voltage and removing the double frequency component to obtain four variables;

   Filtering step: performing low-pass filtering on the four variables to obtain DC components U _dpFltr , U _qpFltr , U _dnFltr , U _qnFltr ;

   PID control step: take the output voltage target value as a given value, use the DC component U _dpFltr as a feedback value, obtain the output result U _dpout through PID control, use 0 as a given value, and use the DC components U _qpFltr , U _dnFltr and U _qnFltr are used as feedback values, and the output results U _qpout , U _dnout , and U _qnout are respectively obtained through PID control, wherein the output result U _dpout and the output result U _qpout are the positive sequence component compensation results, the output result U _dnout and the output result U _qnout is the negative sequence component compensation result.
3. The control method according to claim 2, wherein the method of performing 3/2 transformation and PARK transformation on the three-phase output voltage in the step of obtaining the two-phase conversion voltage is as follows:

   

   Among them, U _α and U _β are two-phase conversion voltages; UN, VN, WN are three-phase output voltages.
4. The control method according to claim 2, wherein the method of performing the positive and negative synchronous rotating coordinate transformation on the two-phase conversion voltage in the double DQ transformation step is as follows:

   Forward transformation:

   

   Negative sequence transformation:

   

   Among them, U _α and U _β are the two-phase conversion voltage;

   

   is the synchronous rotation angle, which is obtained by integrating the output result of closed-loop PID control on the Q-axis component.
5. The control method according to claim 4, wherein the method for removing double frequency components in the double DQ conversion step is as follows:

   
6. The control method according to claim 5, characterized in that, in the filtering step, after the decoupled variable is passed through a low-pass filter, DC components U _dpFltr , U _qpFltr , U _dnFltr and U _qnFltr can be obtained; Among them, the cutoff frequency of the low-pass filter LPF should be set below 100Hz.
7. The control method according to claim 1, wherein said second compensation result obtaining step comprises:

   The zero-sequence voltage component acquisition step: according to the three-phase output voltage, the zero-sequence voltage component is obtained by a symmetrical component method;

   PR control step: using the zero-sequence voltage component as a feedback value and 0 as a target value to obtain an output result _Unout through proportional-resonance control, _which is the compensation result of the zero-sequence component.
8. The control method according to claim 1, wherein the three-phase output voltage balancing step comprises:

   Transformation step: performing 3/2 inverse transformation and PARK inverse transformation on the positive sequence component compensation result and the negative sequence component compensation result respectively to obtain a three-phase conversion voltage, and according to the three-phase conversion voltage and the zero-sequence component compensation As a result, a first voltage, a second voltage and a third voltage are obtained;

   The step of obtaining the three-dimensional modulated wave voltage: according to the first voltage, the second voltage and the third voltage, the three-dimensional modulated wave is obtained through sector judgment, vector action time calculation and seven-segment switching voltage vector action sequence;

   The control pulse obtaining step: comparing the three-dimensional modulation wave with the triangular carrier wave to obtain the control pulse corresponding to the switching device of each bridge arm of the inverter unit;

   Control and adjustment step: correspondingly control the action of each of the switching devices according to each of the control pulses.
9. The control method according to claim 8, wherein the step of obtaining the control pulse comprises:

   When the triangular carrier wave is larger than the three-dimensional modulation wave, a high-level pulse is output, and when the triangular carrier wave is smaller than the three-dimensional modulation wave, a low-level pulse is output.
10. The control method according to claim 8, wherein the control and adjustment step comprises: the switching device of the upper bridge arm of each bridge arm acts oppositely to the switching device of the lower bridge arm.
11. A control device for a three-phase four-leg auxiliary converter, characterized in that it is used in the control method according to any one of claims 1-10, the inverter of the three-phase four-leg auxiliary converter The variable unit includes a fourth bridge arm, the output point of the fourth bridge arm is connected to the AC output N line through an inductance, and the control device includes:

    The voltage acquisition unit collects the three-phase output voltage;

    The first compensation result acquisition unit obtains the positive sequence component and the negative sequence component of the three-phase output voltage through positive and negative synchronous rotating coordinate transformation according to the three-phase output voltage, and performs the positive sequence component and the negative sequence component on the positive sequence component and the negative sequence component. Closed-loop control obtains positive sequence component compensation results and negative sequence component compensation results;

    The second compensation result acquisition unit obtains the zero-sequence voltage component of the three-phase output voltage through a symmetrical component method according to the three-phase output voltage, and performs feedback compensation on the zero-sequence voltage component to obtain a zero-sequence component compensation result;

    The three-phase output voltage balance unit performs three-dimensional space rotation vector modulation according to the positive sequence component compensation result, the negative sequence component compensation result and the zero sequence component compensation result to obtain a control pulse, and applies the control pulse to the The bridge arm of the inverter unit obtains a balanced three-phase output voltage.
12. The control device according to claim 11, wherein the first compensation result acquisition unit comprises:

    A two-phase conversion voltage obtaining module, which performs 3/2 conversion and PARK conversion on the three-phase output voltage to obtain a two-phase conversion voltage;

    A double DQ transformation module, which performs the positive and negative synchronous rotation coordinate transformation on the two-phase conversion voltage and obtains four variables after removing the double frequency component;

    A low-pass filtering module, performing low-pass filtering on the four variables to obtain DC components U _dpFltr , U _qpFltr , U _dnFltr , U _qnFltr ;

    The PID control module takes the output voltage target value as a given value, uses the DC component U _dpFltr as a feedback value, obtains an output result U _dpout through PID control, takes 0 as a given value, and uses the DC components U _qpFltr , U _dnFltr and U _qnFltr are used as feedback values, and the output results U _qpout , U _dnout , and U _qnout are respectively obtained through PID control, wherein the output result U _dpout and the output result U _qpout are the positive sequence component compensation results, the output result U _dnout and the output result U _qnout is the compensation result of the negative sequence component.
13. The control device according to claim 11, wherein the second compensation result acquisition unit comprises:

    A zero-sequence voltage component acquisition module, which obtains the zero-sequence voltage component through a symmetrical component method according to the three-phase output voltage;

    The PR control module uses the zero-sequence component as a feedback value and 0 as a target value to obtain an output result _Unout through proportional-resonant control, and the output result _Unout is a compensation result of the zero-sequence component.
14. The control device according to claim 11, wherein the three-phase output voltage balancing unit comprises:

    A transformation module, performing 3/2 inverse transformation and PARK inverse transformation on the positive sequence component compensation result and the negative sequence component compensation result respectively to obtain a three-phase conversion voltage, according to the three-phase conversion voltage and the zero sequence component compensation As a result, a first voltage, a second voltage and a third voltage are obtained;

    The SVPWM modulation module, according to the first voltage, the second voltage and the third voltage, obtains a three-dimensional modulation wave through sector judgment, vector action time calculation and seven-segment switch voltage vector action sequence;

    The control pulse obtaining module compares the three-dimensional modulation wave with the triangular carrier wave to obtain the control pulse corresponding to the switching device of each bridge arm of the inverter unit;

    The control and adjustment module correspondingly controls the action of each of the switching devices according to each of the control pulses.

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