Multi-objective control method and system for high-voltage power quality management equipment

Abstract

The present invention discloses a multi-objective control method and system for high-voltage power quality management equipment, comprising: obtaining the three-phase current output by the inverter, the equivalent inductance on the AC side, and the equivalent resistance data; obtaining the g-axis and h-axis coordinate vectors of the reference voltage in the GH coordinate system; dividing each sector in the space vector diagram into type I small sectors and type II small sectors in the GH coordinate system; calculating the switching states of candidate vectors in the large sector where the reference voltage vector is located; reordering the candidate vectors based on the principle of minimum switching loss, determining the duty cycle of each candidate vector based on the distance between each candidate vector and the reference vector, and ultimately generating a five-segment PWM signal for controlling the switching transistors of the three-phase three-level circuit. The present invention eliminates high common-mode voltage vectors, can solve the problem of leakage current generated between the energy storage battery, the power grid, and the parasitic capacitors, and ensures safe operation of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage direct-mounted power quality management equipment, and in particular to a multi-objective control method and system suitable for high-voltage power quality management equipment. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The large-scale access of new energy sources (photovoltaic and wind power) to the power grid can easily lead to voltage fluctuations and frequency deviations in the grid, seriously affecting the power quality of the grid.

[0004] Power quality management equipment is used to compensate for reactive power, eliminate harmonics, and smooth out grid voltage fluctuations. Traditional low-voltage power quality management systems utilize multiple units in parallel, which is prone to resonance and requires bulky step-up transformers. High-voltage cascade topology power management systems, while ideal, require numerous components.

[0005] In addition, current high-voltage hybrid topology power management equipment generally has problems such as large computational complexity, voltage balancing control, and large leakage current. It is unable to quickly and accurately track current and cannot adapt to scenarios with frequent grid failures in high-proportion new energy power systems. Summary of the Invention

[0006] In order to solve the above problems, the present invention proposes a multi-objective control method and system suitable for high-voltage power quality management equipment. For hybrid multi-level cascaded high-voltage power quality management equipment, multi-objective control can be achieved, including fast current tracking speed, reduced current distortion rate, reduced calculation amount, reduced leakage current, and improved voltage balancing accuracy.

[0007] In some embodiments, the following technical solutions are adopted:

[0008] A multi-objective control method applicable to high-voltage power quality management equipment, comprising:

[0009] Obtain the three-phase current output by the inverter, the AC side equivalent inductance and equivalent resistance data;

[0010] Based on the data, a mathematical model is established to represent the voltage value between the three phases A, B, and C and the neutral point N of the load;

[0011] Discretizing the mathematical model, and then performing coordinate transformation to obtain g-axis and h-axis coordinate vectors of the reference voltage in the gh coordinate system;

[0012] In the gh coordinate system, each sector in the space vector diagram is divided into type I small sectors and type II small sectors; the switching states of the candidate vectors in the large sector where the reference voltage vector is located are calculated;

[0013] The candidate vectors are reordered based on the principle of minimum switching loss, and the duty cycle of each candidate vector is determined based on the distance between each candidate vector and the reference vector. Finally, a five-segment PWM signal is formed to control the switch tube of the three-phase three-level circuit.

[0014] In other embodiments, the following technical solutions are adopted:

[0015] A multi-objective control system suitable for high-voltage power quality management equipment, comprising:

[0016] The data acquisition module is used to obtain the three-phase current output by the inverter, the AC side equivalent inductance and equivalent resistance data;

[0017] A model building module is used to establish a mathematical model representing the voltage value between the three phases A, B, and C and the load neutral point N based on the data;

[0018] A coordinate conversion module is used to discretize the mathematical model and then perform coordinate transformation to obtain the g-axis and h-axis coordinate vectors of the voltage value in the gh coordinate system;

[0019] The candidate vector selection module divides each sector in the space vector diagram into type I small sectors and type II small sectors in the gh coordinate system; calculates the switching state of the candidate vectors in the large sector where the reference voltage vector is located;

[0020] The switch control model reorders candidate vectors based on the principle of minimum switching loss, determines the duty cycle of each candidate vector based on the distance between each candidate vector and the reference vector, and ultimately forms a five-segment PWM signal for controlling the switch of the three-phase three-level circuit.

[0021] In other embodiments, the following technical solutions are adopted:

[0022] A terminal device includes a processor and a memory, wherein the processor is used to implement various instructions; the memory is used to store multiple instructions, and the instructions are suitable for the processor to load and execute the above-mentioned multi-objective control method applicable to high-voltage power quality management equipment.

[0023] In other embodiments, the following technical solutions are adopted:

[0024] A computer-readable storage medium stores a plurality of instructions, wherein the instructions are suitable for being loaded and executed by a processor of a terminal device, the multi-objective control method applicable to high-voltage power quality management equipment.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention abandons the high common-mode voltage vector and can solve the problem of leakage current between the energy storage battery, the grid, and the parasitic capacitor when the energy storage battery is connected to the DC side in order to suppress the grid frequency deviation, thereby ensuring the safe operation of the system.

[0027] (2) The present invention selects three low common-mode vectors closest to the reference voltage, sorts these three vectors, selects the optimal sequence to achieve minimum switching loss, and calculates the duty cycle of the three vectors according to the integer coordinates of the nearest three vectors in the gh coordinate system.

[0028] (3) The control method of the present invention can achieve current tracking speed and accuracy; for the three candidate vectors, the optimal switching sequence is adopted to reduce the system switching loss and improve the system efficiency; by selecting redundant vectors, the balanced control of the midpoint voltage and flying capacitance can be achieved; the low common mode vector is selected in combination with the withstand voltage value of the switch tube, the number of levels, the number of modules, and the position of the voltage vector, and any high level output can be achieved by simply changing the modulation index.

[0029] (4) The present invention can select the number of H-bridges according to the actual voltage level requirements. Therefore, the topology and control method of the present invention can be widely used in different occasions such as photovoltaics, energy storage, SVG, etc., and has strong scalability and practicality.

[0030] Other features and advantages of additional aspects of the present invention will be given in part in the following description and in part will become obvious from the following description or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the topology of a hybrid multi-level cascade power quality management device in an embodiment of the present invention;

[0032] Figure 2 Schematic diagram of multi-objective control applicable to high-voltage power quality management equipment in an embodiment of the present invention;

[0033] Figure 3 Type I and type II sectors of the simplified space vector diagram in an embodiment of the present invention, and the coordinate values corresponding to the vectors;

[0034] 4(a)-(b) are schematic diagrams showing calculation of vector switch states in large sectors No. 1 and No. 2, respectively, according to an embodiment of the present invention;

[0035] Figures 5(a)-(d) are simulation diagrams using seven levels as an example; Figure 5(a) is a schematic diagram of a 4A to 7A current jump; Figure 5(b) is a schematic diagram of the current FFT at 4A; Figure 5(c) is a schematic diagram of the current FFT at 7A; and Figure 5(d) is a simulation diagram of a line voltage jump.

[0036] Figure 6(a) is a schematic diagram of the three-phase suspended capacitor voltage; Figure 6(b) is a schematic diagram of the midpoint voltage;

[0037] Figure 7 This is a schematic diagram of seven-level common-mode voltage simulation. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0039] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0040] Example 1

[0041] In one or more embodiments, a high voltage power quality management device is disclosed, combined with Figure 1 Specifically, it includes: a three-phase cascade H-bridge inverter composed of H-bridge units, a three-phase three-level circuit with a capacitor connected at the star connection point of the three-phase cascade H-bridge; the function of the three-phase three-level circuit is to generate reactive power and smooth out grid voltage fluctuations.

[0042] This embodiment proposes two types of sectors: Type I and Type II. These sectors are calculated based on the 120° gh coordinate system. Unlike the traditional 90° αβ coordinate system, the coordinate system used in this embodiment can divide all sectors in the space vector diagram into the above-mentioned Type I and Type II sectors. This eliminates the calculation step of determining small sectors by determining the amplitude and phase angle of the reference voltage, greatly reducing the amount of calculation.

[0043] Based on the above-mentioned high-voltage power quality management equipment, this embodiment proposes a multi-objective control method suitable for high-voltage power quality management equipment, combined with Figure 2 , specifically including the following process:

[0044] (1) Obtain the three-phase current output by the inverter, the AC side equivalent inductance and equivalent resistance data;

[0045] (2) establishing a mathematical model representing the voltage values between the three phases A, B, and C and the load center point N based on the data;

[0046] In this embodiment, the established mathematical model is specifically:

[0047]

[0048] Among them, u xN (x=a,b,c) represents the voltage value between x and N points, i a ,i b and i c is the inverter output three-phase current, L is the equivalent inductance on the AC side, R L is the equivalent resistance.

[0049] (3) discretizing the mathematical model and then performing coordinate transformation to obtain the g-axis and h-axis coordinate vectors of the voltage value in the gh coordinate system;

[0050] In this embodiment, the mathematical model of formula (1) is discretized to obtain:

[0051]

[0052] Among them, u * xN (k)(x=a,b,c) is the predicted voltage between point x and point N at time k, i x (k) is the output current value of the three-phase AC side at time k, i x * (k+1) is the predicted value of the AC side current at time k+1. s is the sampling period.

[0053] Convert equation (2) into a vector in gh coordinates:

[0054]

[0055] Among them, V g With V h are the g-axis and h-axis coordinates of the above voltage value in the gh coordinate system, that is, the coordinates of the reference vector in the gh coordinate system.

[0056] [abc / αβ] is the Clarke transform formula. f(n) is a function of variable n and can be expressed as:

[0057]

[0058] Where n is the number of multi-level levels, U dc is the DC bus voltage.

[0059] Rounding down the coordinates obtained by formula (3) yields

[0060]

[0061] Among them, floor is the rounding function, V g0With V h0 It is V g (k) and V h (k) The coordinates after rounding down. They are denoted as g0 and h0 respectively; thus, the integer coordinates of the reference vector in the gh coordinate system are obtained, which are Figure 3 The position of V0 shown in ; from the coordinates of V0, the coordinates of the other three vectors (V1, V2, V3) closest to it can be calculated. At this time, Figure 3 The coordinates of the four vectors shown in the gh coordinate system have been obtained. The reference vector (including decimal coordinates) calculated by formula (3) is located in the parallelogram enclosed by V0, V1, V2, and V3.

[0062] (4) In the gh coordinate system, each sector in the space vector diagram is divided into type I small sectors and type II small sectors; the switching state of the candidate vectors of the large sector where the reference voltage vector is located is calculated;

[0063] The process of calculating the switching state of the candidate vectors of the large sector where the reference voltage vector is located specifically includes:

[0064] Based on the coordinates of the reference vector and the number of redundant switches in the three vectors closest to the reference voltage vector,

[0065] Calculating all switching states of three vectors closest to the reference voltage vector when the reference voltage vector is located in the type I small sector and the type II small sector of the odd large sector; and selecting the vector with the smallest common mode voltage from the switching states as a candidate vector;

[0066] Calculating all switching states of three vectors closest to the reference voltage vector when the reference voltage vector is located in the type I small sector and the type II small sector of the even large sector; and selecting the vector with the smallest common mode voltage from the switching states as a candidate vector;

[0067] Based on the large sector where the reference voltage vector is located, the switching state of its candidate vector is determined.

[0068] Specifically, to reduce the amount of calculation, the reference voltage is rotated counterclockwise to the first large sector. In the gh coordinate system, it is determined whether the reference voltage is located in a type I small sector or a type II small sector, and the coordinates of the three vectors closest to the reference voltage are calculated respectively.

[0069] In this embodiment, the method for determining the sector in which the reference voltage is located is:

[0070]

[0071] Among them, ss=1 indicates that it is located in type I sector, and ss=2 indicates that it is located in type II sector.

[0072] Figure 4(a)-(b) is Figure 3 The switching state of the vector in is calculated. Figure 3 The calculated coordinates can be obtained through simple addition, subtraction, multiplication, and division. The calculation methods for odd and even large sectors are different. Large sector 1 in Figure 4(a) represents the odd sector, and large sector 2 in Figure 4(b) represents the even sector. It should be noted that the remaining four large sectors (large sectors 3 to 6) do not require additional calculations. They can be obtained by simply reordering the switching states of the odd and even sectors. Therefore, the switching states of the candidate vectors for the large sector where the reference voltage vector is located can also be obtained.

[0073] Therefore, according to whether the reference voltage is located in large sector No. 1 or large sector No. 2 and in type I sector or type II sector, a total of four cases can be divided, namely type I sector of large sector No. 1, type II sector of large sector No. 1, type I sector of large sector No. 2 and type II sector of large sector No. 2.

[0074] At this time, the switching status calculations of vectors V0, V1, V2 and V3 are shown in Table 1 below:

[0075] Table 1 Switch status

[0076]

[0077] The calculated value of the number of redundant switches i is:

[0078]

[0079] That is, the calculation of i at V0 is n-g0, and the same is true for the other three vectors.

[0080] In a multi-level space vector diagram, a vector with the same coordinate often has redundant switching states. The number of these redundant vectors is i. Substituting i calculated by equation (7) into Table 1, all redundant switching states of the vector with the same coordinate can be obtained.

[0081] This embodiment takes a seven-level hybrid topology as an example, so n = 7. Assuming g0 = 2 and h0 = 1, according to formula (7), i(V0) = i(V3) = 5, i(V1) = i(V2) = 6, that is, there are 5 redundant switch states at V0 and V3, and 6 redundant switch states at V1 and V2. When it is located in large sector 1, according to Table 1, taking V0 as an example, substituting i from 1 to 5 into [g0+i-1,h0+i-1,i-1], 5 redundant switch states can be obtained, namely: [2 1 0], [32 1], [43 2], [54 3] and [6 5 4]. Other sectors and vectors are also calculated according to the above steps.

[0082] From all the switching states of the three vectors closest to the reference voltage vector, the vector with the smallest common-mode voltage is selected as the candidate vector;

[0083] In this embodiment, the common mode voltage is defined as

[0084]

[0085] In order to achieve common mode reduction, it is required to select the one with the smallest common mode voltage among all redundant vectors as the candidate vector. When located in the first sector, the absolute value of the common mode voltage corresponding to the smallest common mode voltage vector is:

[0086]

[0087] Similarly, when located in the second sector, the absolute value of the common-mode voltage corresponding to the minimum common-mode voltage vector is

[0088]

[0089] By using equations (9) and (10), the minimum common-mode voltage is calculated, and the corresponding switching state of the minimum common-mode voltage can also be obtained at the same time and selected as a candidate vector. Taking the five vectors [2 1 0], [3 2 1], [4 3 2], [5 4 3], and [6 5 4] as examples, according to equation (8), the common-mode voltage CMV = 9. When located in the first sector, the common-mode voltages corresponding to the five vectors are 6, 3, 0, 3, and 6, respectively. Therefore, the minimum common-mode voltage is 0, the corresponding i is 3, and the minimum switching state is [4 3 2]. The analysis of other sectors and vectors is the same as the above process.

[0090] After determining the switching state of the minimum common-mode voltage vectors of large sectors 1 and 2, it is necessary to determine the switching states of the remaining four large sectors. Assume that the switching state of any vector obtained by large sector 1 is (abc), and the switching state of any vector obtained by large sector 2 is (bac). The vectors of the other large sectors can be obtained as shown in Table 2 below:

[0091] Table 2 Switching status of six large sectors

[0092]

[0093] Finally, the switching states of the candidate vectors of the large sector where the reference voltage vector is located are obtained.

[0094] (5) Based on the principle of minimum switching loss, the candidate vectors are reordered, and the duty cycle of each candidate vector is determined based on the distance between each candidate vector and the reference vector. Finally, a five-segment PWM signal is formed to control the switch tube in the three-phase three-level circuit. In this way, in each sampling period, only two of the three phases have a signal change, and the signal of the remaining phase remains unchanged. This achieves a fixed switching frequency in each sampling period, and the number of switching times is minimized, which reduces the switching loss and is beneficial to the design of the filter.

[0095] In this embodiment, when the sector is determined according to formula (6), formulas (9) and (10) determine the switching state of the minimum common-mode voltage vector of large sectors No. 1 and No. 2, the switching states of the vectors corresponding to large sectors No. 1 and No. 2 of the six large sectors can be obtained according to Table 2, and finally the switching state of the candidate vector of the large sector where the reference voltage vector is located is obtained.

[0096] In the 120° coordinate system, the distance between the reference vector and the candidate vector is:

[0097]

[0098] Among them, j k (k=1,2,3) are the distances between the three minimum common mode voltage vectors and the reference vector. (g k , h k ) are the coordinates of the three candidate vectors.

[0099] Therefore, the duty cycle is calculated as

[0100]

[0101] At the same time, in order to achieve the minimum switching loss, the three selected candidate vectors need to be sorted, and then the duty cycle calculated according to formula (12) is formed into a five-segment sequence. Let the selected candidate vector be S a (a1,a2,a3),S b (b1,b2,b3) and S c (c1,c2,c3), calculate:

[0102]

[0103] As long as the calculated A, B and C are sorted from large to small, the resulting sequence order will be consistent with it. If A>B>C, then the five-segment sequence is [S a -S b -S c -S b -S a ]. This sequence can achieve minimum switching loss in each sampling cycle.

[0104] In addition, the topology proposed in this embodiment requires control of the midpoint and floating capacitor voltages. All switch combinations and their effects of the seven-level topology of this invention are shown below:

[0105] Table 3 Seven-level A-phase switch status and its impact

[0106]

[0107] It is observed that the same output phase voltage can correspond to different redundant switch combinations. Using different redundant switch combinations, the midpoint voltage and the floating capacitor voltage can be balanced.

[0108] However, since the redundant switch combination corresponding to the same phase voltage level will also affect the DC side capacitor voltage, it is necessary to set a threshold value to control the DC side voltage balance and the floating capacitor voltage balance when selecting the switch combination. P , the lower capacitor voltage is u N , define the DC side capacitor voltage deviation ΔU dc =U P -U N In order to ensure the normal operation of the inverter, ΔU should be controlled dc Is 0. Define the voltage deviation of a phase suspension capacitor ΔU fx =U fx -U dc / 4, the allowable error of the floating capacitor voltage is defined as u error Since the three-phase switch combination can balance the DC side capacitor voltage at the same time, and the suspension capacitor voltage can only be controlled by the switch state of this phase, the suspension capacitor voltage should be controlled first. error When the voltage error of the floating capacitor is within u error When the voltage of the floating capacitor is controlled, priority should be given to controlling the floating capacitor voltage.

[0109]

[0110] Taking phase a as an example, when the phase voltage U ao =-3 / 4U dc When U ao =-2 / 4U dc When, if a >=0, select switch combination 2, if su a <0, select switch combination 3; when U ao =-1 / 4U dc When, if a >=0, select switch combination 5, if su a<0, select switch combination 4; when U ao = 0, if su a >=0, select switch combination 6, if su a <0, select switch combination 7; when U ao =1 / 4U dc When, if a >=0, select switch combination 8, if su a <0, select switch combination 9; when U ao =2 / 4U dc When, if a >=0, select switch combination 10, if su a <0, select switch combination 11; when U ao =3 / 4U dc , select switch combination 12.

[0111] The following simulation results demonstrate the control effect of the proposed method. In the simulation, the DC voltage is 100V, the load is 8Ω, the inductance is 3mL, and the amplitude of the given current jumps from 4A to 7A. As shown in Figure 5(a), the current is undistorted and sinusoidal, and the amplitude also jumps with the given current amplitude. As shown in Figures 5(b) and (c), the THD values at 4A and 7A are 2.14% and 1.11%, respectively, which are within the allowable range. As shown in Figure 5(d), the line voltage jumps from nine levels to eleven levels as the modulation index increases, which is between the line voltage levels of a seven-level converter.

[0112] As shown in Figure 6(a), the three-phase floating capacitor voltage is controlled at approximately one-quarter of the DC link voltage, 25V. As shown in Figure 6(b), the midpoint voltage is controlled at half the DC link voltage, 50V. Furthermore, the capacitor voltages do not fluctuate significantly before and after a given current amplitude jump. This demonstrates the effectiveness of the proposed method for controlling the midpoint voltage and floating capacitor voltage balance based on a redundant sequence.

[0113] like Figure 7 As shown in the figure, the common-mode voltage is successfully suppressed, with an amplitude between ±12.5V. The common-mode voltage jumps around the time the given current increases from 4A to 7A. This demonstrates that the proposed method can effectively suppress the common-mode voltage and exhibits excellent steady-state and dynamic performance.

[0114] Example 2

[0115] In one or more embodiments, a multi-objective control system applicable to high-voltage power quality management equipment is disclosed, including:

[0116] The data acquisition module is used to obtain the three-phase current output by the inverter, the AC side equivalent inductance and equivalent resistance data;

[0117] A model building module is used to establish a mathematical model representing the voltage value between the three phases A, B, and C and the load neutral point N based on the data;

[0118] A coordinate conversion module is used to discretize the mathematical model and then perform coordinate transformation to obtain the g-axis and h-axis coordinate vectors of the voltage value in the gh coordinate system;

[0119] The candidate vector selection module divides each sector in the space vector diagram into type I small sectors and type II small sectors in the gh coordinate system; calculates the switching state of the candidate vectors in the large sector where the reference voltage vector is located;

[0120] The switch control model reorders candidate vectors based on the principle of minimum switching loss, determines the duty cycle of each candidate vector based on the distance between each candidate vector and the reference vector, and ultimately forms a five-segment PWM signal for controlling the switch of the three-phase three-level circuit.

[0121] Example 3

[0122] In one or more embodiments, a terminal device is disclosed, including a server. The server includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the multi-objective control method for high-voltage power quality management equipment described in Example 1 is implemented. For the sake of brevity, this description is omitted here.

[0123] It should be understood that in this embodiment, the processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), off-the-shelf field-programmable gate arrays (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc.

[0124] The memory may include a read-only memory and a random access memory, and provides instructions and data to the processor. A portion of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the device type.

[0125] During implementation, each step of the above method may be completed by an integrated logic circuit of hardware in a processor or by instructions in the form of software.

[0126] In other embodiments, a computer-readable storage medium is disclosed, storing a plurality of instructions suitable for loading and executing the multi-objective control method for high-voltage power quality management equipment described in Example 1 by a processor of a terminal device.

[0127] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without any creative work are still within the scope of protection of the present invention.

Claims

1. A multi-objective control method for high-voltage power quality management equipment, characterized in that: include: Obtain the three-phase current output by the inverter, the AC side equivalent inductance and equivalent resistance data; Based on the data, a mathematical model is established to represent the voltage value between the three phases A, B, and C and the neutral point N of the load; Discretizing the mathematical model, and then performing coordinate transformation to obtain g-axis and h-axis coordinate vectors of the reference voltage in the gh coordinate system; In the gh coordinate system, each large sector in the space vector diagram is divided into type I small sectors and type II small sectors; Calculate the switching state of the candidate vectors in the large sector where the reference voltage vector is located, specifically including: Based on the coordinates of the reference vector and the number of redundant switches in the three vectors closest to the reference voltage vector, Calculating all switching states of three vectors closest to the reference voltage vector when the reference voltage vector is located in the type I small sector and the type II small sector of the odd large sector; and selecting the vector with the smallest common mode voltage from the switching states as a candidate vector; Calculating all switching states of three vectors closest to the reference voltage vector when the reference voltage vector is located in the type I small sector and the type II small sector of the even large sector; and selecting the vector with the smallest common mode voltage from the switching states as a candidate vector; Determine the switching state of the candidate vector based on the large sector where the reference voltage vector is located; The candidate vectors are reordered based on the principle of minimum switching loss, and the duty cycle of each candidate vector is determined based on the distance between each candidate vector and the reference vector. Finally, a five-segment PWM signal is formed to control the switch tube of the three-phase three-level circuit.

2. A multi-objective control method for high-voltage power quality management equipment according to claim 1, characterized in that: After obtaining the g-axis and h-axis coordinate vectors of the reference voltage in the gh coordinate system, the method further includes: rounding down the obtained coordinate vectors.

3. A multi-objective control method for high-voltage power quality management equipment according to claim 1, characterized in that: When the difference between the g-axis and h-axis coordinate values of the reference voltage in the gh coordinate system is less than or equal to the difference between the g-axis and h-axis coordinate values after rounding, the reference voltage is located in the type I small sector; When the difference between the g-axis and h-axis coordinate values of the reference voltage in the gh coordinate system is greater than the difference between the g-axis and h-axis coordinate values after rounding, the reference voltage is located in the type II small sector.

4. The multi-objective control method for high-voltage power quality management equipment according to claim 1, characterized in that: The candidate vectors are reordered based on the minimum switching loss principle, specifically: the candidate vectors are ordered from large to small according to the sum of the elements in the candidate vectors.

5. The multi-objective control method for high-voltage power quality management equipment according to claim 1, characterized in that: In the gh coordinate system, the distance between each candidate vector and the reference vector is: ，k=(1,2,3) in, j k is the distance between the three candidate vectors and the reference vector, k=1,2,3; ( g k , h k ) are the coordinates of the three candidate vectors; V g With V h are the g-axis and h-axis coordinates of the reference voltage in the gh coordinate system respectively.

6. A multi-objective control method for high-voltage power quality management equipment according to claim 5, characterized in that: The duty cycle of each candidate vector is determined based on the distance between each candidate vector and the reference vector, specifically: in, 、 、 are the distances between the three candidate vectors and the reference vector.

7. A multi-objective control system suitable for high-voltage power quality management equipment, characterized in that: include: The data acquisition module is used to obtain the three-phase current output by the inverter, the AC side equivalent inductance and equivalent resistance data; A model building module is used to establish a mathematical model representing the voltage value between the three phases A, B, and C and the load neutral point N based on the data; A coordinate conversion module is used to discretize the mathematical model and then perform coordinate transformation to obtain the g-axis and h-axis coordinate vectors of the voltage value in the gh coordinate system; The candidate vector selection module divides each large sector in the space vector map into type I small sectors and type II small sectors in the gh coordinate system; Calculate the switching state of the candidate vectors in the large sector where the reference voltage vector is located, specifically including: Based on the coordinates of the reference vector and the number of redundant switches in the three vectors closest to the reference voltage vector, Calculating all switching states of three vectors closest to the reference voltage vector when the reference voltage vector is located in the type I small sector and the type II small sector of the odd large sector; and selecting the vector with the smallest common mode voltage from the switching states as a candidate vector; Calculating all switching states of three vectors closest to the reference voltage vector when the reference voltage vector is located in the type I small sector and the type II small sector of the even large sector; and selecting the vector with the smallest common mode voltage from the switching states as a candidate vector; Determine the switching state of the candidate vector based on the large sector where the reference voltage vector is located; The switch control model reorders candidate vectors based on the principle of minimum switching loss, determines the duty cycle of each candidate vector based on the distance between each candidate vector and the reference vector, and ultimately forms a five-segment PWM signal for controlling the switch of the three-phase three-level circuit.

8. A terminal device comprising a processor and a memory, wherein the processor is used to implement various instructions; the memory is used to store multiple instructions, characterized in that: The instructions are suitable for being loaded by a processor and executing the multi-objective control method applicable to high-voltage power quality management equipment as described in any one of claims 1-6.

9. A computer-readable storage medium storing a plurality of instructions, characterized in that: The instructions are suitable for being loaded by a processor of a terminal device and executing the multi-objective control method applicable to high-voltage power quality management equipment as described in any one of claims 1-6.

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