A control method for a converter and a converter

Abstract

The present application discloses a control method and a converter for a converter, including: constructing a two-cycle voltage space vector diagram, where the midline of any sector coincides with the single-cycle large vector; calculating the reference voltage vectors of adjacent first control cycle and second control cycle to obtain a first reference voltage vector and a second reference voltage vector; combining the first reference voltage vector and the second reference voltage vector to obtain a third reference voltage vector; calculating the length of the projection of the third reference voltage vector onto the midline of the sector where it is located, and in response to the projection length being less than half of the single-cycle large vector length, selecting a zero vector as the optimal voltage vector, and in response to the projection length being greater than or equal to half of the single-cycle large vector length and less than the single-cycle large vector length, selecting a single-cycle small vector as the optimal voltage vector. The present application can reduce the calculation burden of the control system and the switching frequency of the converter, and achieve efficient current tracking and midpoint voltage balance of the converter.

Description

Technical Field

[0001] The present application relates to the technical field of commutation equipment, and in particular to a control method and a converter for a converter. Background Art

[0002] Traditional finite control set model predictive control methods bring a high computational burden and a large switching frequency while achieving fast dynamic response, which has a certain impact on the efficiency, stability of the system and the durability of the hardware.

[0003] Existing finite control set model predictive control methods design controllers by directly optimizing a finite number of switching states. However, this method causes frequent switching of the converter switching states and makes the controller bear high computational complexity, which in turn leads to a slow response speed of the control system to the converter and cannot meet the requirements of clean energy systems for the high reliability of power electronic equipment. Summary of the Invention

[0004] In order to solve the deficiencies of the prior art, the present application adopts the following technical solutions:

[0005] In a first aspect, a control method for a converter provided by the present application, the converter is applied in a power system, and the control method includes the following steps:

[0006] Construct a two-cycle voltage space vector diagram, the two-cycle voltage space vector diagram includes six equal sectors, and the median line of any sector coincides with the single-cycle large vector;

[0007] Calculate the reference voltage vectors of adjacent first control cycles and second control cycles to obtain a first reference voltage vector and a second reference voltage vector;

[0008] Combine the first reference voltage vector and the second reference voltage vector to obtain a third reference voltage vector;

[0009] Calculate the angle of the third reference voltage vector, and calculate the length of the projection of the third reference voltage vector onto the median line of the sector where it is located. In response to the projection length being less than 1 / 2 of the single-cycle large vector length, select the zero vector as the optimal voltage vector for the first control cycle and the second control cycle. In response to the projection length being greater than or equal to 1 / 2 of the single-cycle large vector length and less than the single-cycle large vector length, select the single-cycle small vector as the optimal voltage vector for the first control cycle and the second control cycle, and the single-cycle small vector is the single-cycle small vector on the median line of the sector where the third reference voltage vector is located.

[0010] In summary, a control method for a converter provided by the present application constructs a two-cycle voltage space vector diagram, converts the voltage requirements of two consecutive control cycles into an equivalent composite vector, and the control system can complete the optimization of two control cycles within one decision cycle, reducing the frequent switching of switch states through cross-cycle optimization; and quickly eliminates unnecessary candidate voltage vectors through geometric projection, simplifies complex calculations into geometric judgments based on the sector midline, significantly reduces the calculation amount while ensuring control accuracy, realizes the rapid selection of the optimal voltage vector, and improves the response speed of the control system.

[0011] Further, the control method further includes:

[0012] Perform secondary partitioning on the two-cycle voltage space vector diagram. After secondary partitioning, six large sectors are obtained. The midline of any large sector coincides with the medium vector in a single cycle, and any large sector is divided into four equal small sectors. Define the inner area and the outer area of the two-cycle voltage space vector diagram. Among them, the inner area is composed of six small sectors connected to the center of the two-cycle voltage space vector diagram, and the outer area is composed of the remaining 18 small sectors;

[0013] In response to the projection length being greater than or equal to the length of the single-cycle large vector, locate the target large sector and the target small sector where the third reference voltage vector is located, and substitute the voltage vectors of the three vertices forming the target small sector into the predicted current calculation, and calculate the optimal voltage vector with the goal of minimizing the first cost function.

[0014] Further, the control method further includes setting

[0015] The first cost function is expressed by the following formula:

[0016] ;

[0017] In the formula, i * αβ represents the reference current, represents the predicted current in the stationary coordinate system of the (k + j)-th control cycle.

[0018] Further, the control method further includes:

[0019] Construct an extended super-local model, and the extended super-local model includes a linear part and a nonlinear part of the power system disturbance parameters;

[0020] Design an extended sliding mode observer, and the extended sliding mode observer is configured to estimate the nonlinear part and the linear part of the extended super-local model;

[0021] According to the deadbeat control principle, the reference voltage vectors of the first control period and the second control period are obtained based on the estimation results.

[0022] Further, the extended super-local model is represented by the following formula:

[0023] ;

[0024] In the formula, is the system state variable gain, is the unknown term of the system non-linearity; represents the unknown term of the linear part, represents the voltage.

[0025] Further, the extended sliding mode observer is represented by the following formula:

[0026] ;

[0027] In the formula, represents the gain, represents the control function.

[0028] Further, the first reference voltage vector is represented by the following formula:

[0029] ;

[0030] The second reference voltage vector is represented by the following formula:

[0031] ;

[0032] In the formula, the estimated currents at time and time are estimated using the voltage at time k.

[0033] Further, the third reference voltage vector is obtained by adding the first reference voltage vector and the second reference voltage vector.

[0034] Further, the control method further includes:

[0035] Setting a second cost function and a third cost function, in response to the optimal voltage vector being a single-period small vector, aiming to minimize the second cost function, obtaining the optimal switching state of the single-period small vector; in response to the optimal voltage vector being a zero vector, aiming to minimize the third cost function, obtaining the optimal switching state of the zero vector;

[0036] Wherein, the second cost function is represented by the following formula:

[0037] ;

[0038] The third cost function is expressed by the following formula:

[0039] ;

[0040] In the formula, represents the switching state of the three-phase inverter .

[0041] In a second aspect, the present application also provides a converter, which includes a three-level neutral-point clamped inverter circuit and a controller. The controller controls the three-level neutral-point clamped inverter circuit by using the above control method. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a flowchart of the steps of a control method for a converter provided by an embodiment of the present application;

[0043] Figure 2 is a schematic diagram of the topology structure of an inverter provided by an embodiment of the present application;

[0044] Figure 3 is a schematic diagram of the basic voltage vectors of an inverter provided by an embodiment of the present application;

[0045] Figure 4 is a two-cycle voltage space vector schematic diagram of the control method for a converter provided by an embodiment of the present application;

[0046] Figure 5 is a flowchart of the steps of obtaining a first reference voltage vector and a second reference voltage vector in the control method for a converter provided by an embodiment of the present application;

[0047] Figure 6 is a two-cycle voltage space vector schematic diagram for secondary partitioning in the control method for a converter provided by an embodiment of the present application;

[0048] Figure 7 is a schematic diagram of the process of simplifying and locating the optimal voltage vector in the control method for a converter provided by an embodiment of the present application;

[0049] Figure 8 is a schematic diagram of the process of maintaining the neutral-point voltage balance in the control method for a converter provided by an embodiment of the present application;

[0050] Figure 9a is a schematic diagram of the experimental results under the parameter matching condition of the converter provided by an embodiment of the present application;

[0051] Figure 9b is a schematic diagram of the experimental results under the parameter mismatch condition of the converter provided by an embodiment of the present application. Detailed Implementation Modes

[0052] The following will describe the present application in detail with reference to the specific implementation modes shown in the accompanying drawings. However, these implementation modes do not limit the present application, and any structural, method, or functional transformation made by those of ordinary skill in the art based on these implementation modes is included within the protection scope of the present application.

[0053] To address the deficiencies of the prior art, in a first aspect, the present application provides a control method for a converter and a converter. The converter is applied in a power system, such as Figure 1 As shown, the control method includes the following steps:

[0054] Step S11: Construct a two-cycle voltage space vector diagram. The two-cycle voltage space vector diagram includes six equal sectors, and the midline of any sector coincides with the single-cycle large vector.

[0055] Step S12: Calculate the reference voltage vectors of adjacent first and second control cycles to obtain a first reference voltage vector and a second reference voltage vector.

[0056] Step S13: Combine the first reference voltage vector and the second reference voltage vector to obtain a third reference voltage vector.

[0057] Step S14: Calculate the angle of the third reference voltage vector, and calculate the length of the projection of the third reference voltage vector onto the midline of the sector where it is located. In response to the projection length being less than half of the single-cycle large vector length, select the zero vector as the optimal voltage vector for the first and second control cycles. In response to the projection length being greater than or equal to half of the single-cycle large vector length and less than the single-cycle large vector length, select the single-cycle small vector as the optimal voltage vector for the first and second control cycles. The single-cycle small vector is the single-cycle small vector on the midline of the sector where the third reference voltage vector is located.

[0058] Specifically, taking an NPC (Neutral Point Clamped) inverter as an example, the topological structure of the NPC-type inverter is as Figure 2 As shown, establish the mathematical model of the NPC-type inverter in the stationary coordinate system, as Figure 3 As shown, nineteen basic voltage vectors are obtained according to the 27 different switching states of the inverter. Classified according to their magnitudes, these voltage vectors can be divided into the following four categories: zero vectors, small vectors, medium vectors, and large vectors.

[0059] Among them, the zero vector V1 corresponds to three switching states: V1 (OOO, PPP, NNN); the inner circle consists of six small vectors, and each small vector corresponds to two switching states: V2 (POO, ONN), V3 (PPO, OON), V4 (OPO, NON), V5 (OPP, NOO), V6 (OOP, NNO), V7 (ONO, POP); the outer circle consists of 12 medium vectors / large vectors, and each medium vector / large vector corresponds to one switching state. The medium vectors include: V9 (PON), V11 (OPN), V13 (NPO), V15 (NOP), V17 (ONP), V19 (PNO); the large vectors include: V8 (PNN), V10 (PPN), V12 (NPN), V14 (NPP), V16 (NNP), V18 (PNP).

[0060] Based on Figure 3 , considering that the optimal voltage vectors in two adjacent control cycles are the same, a two-cycle voltage space vector diagram is generated, as Figure 4 shown. The two-cycle voltage space vector diagram includes six sectors A - F. The midline of each sector coincides with the single-cycle large vector, and the length of the midline of each sector is twice the length of the corresponding large vector. For example, the midline of sector A coincides with the single-cycle large vector V8, and the length of the midline of sector A, V8 + V8, is twice the length of the single-cycle large vector V8.

[0061] For ease of explanation, the current control cycle is denoted as k, then the control cycle k + 1 is denoted as the first control cycle, and the control cycle k + 2 is denoted as the second control cycle. Based on the voltage condition of the current control cycle k, current prediction is performed for two adjacent control cycles, the first control cycle and the second control cycle, so as to dynamically calculate the reference voltage vectors for two adjacent control cycles. When the reference voltage vectors of two adjacent control cycles are the same, the switching state of the inverter does not need to be switched, thereby reducing the switching frequency. For ease of explanation, the reference voltage vector of the first control cycle is denoted as the first reference voltage vector, and the reference voltage vector of the second control cycle is denoted as the second reference voltage vector.

[0062] Combining the first reference voltage vector and the second reference voltage vector, a third reference voltage vector is obtained. Based on the adoption of the same voltage vector in two adjacent cycles, the synthesized third reference voltage vector essentially represents the comprehensive control requirements within two cycles. Transforming the voltage requirements of two consecutive control cycles into an equivalent composite vector can reduce the switching frequency while maintaining control performance. Based on the third reference voltage vector, the control system can complete the optimization of two control cycles within one decision cycle, reducing the frequent switching of switching states through cross-cycle optimization, thereby reducing the computational burden and improving real-time performance.

[0063] Calculate the angle of the third reference voltage vector to determine the six - equal - division sector where the third reference voltage vector is located. The angle of the third reference voltage vector can be expressed by the following formula:

[0064] (1);

[0065] In the formula, represents the vector length of the third reference voltage vector on the β - axis in the coordinate system, represents the vector length of the third reference voltage vector on the α - axis in the coordinate system.

[0066] Project the third reference voltage vector onto the mid - line of the sector where it is located, and calculate the projection length of the third reference voltage vector. For the convenience of description, denote the projection length of the third reference voltage vector as l n , and denote the length of the single - cycle large vector as 2 l 1. According to the principle of equal - amplitude transformation, the length 2 l 1 of the single - cycle large vector is 2 / 3 of the DC bus voltage.

[0067] Compare the projection length of the third reference voltage vector with the length of the single - cycle large vector. If the projection length of the third reference voltage vector is less than 1 / 2 of the length of the single - cycle large vector, select the zero vector as the optimal voltage vector for the first control period and the second control period. The switching state of the inverter corresponding to the zero vector does not change, reducing the switching loss.

[0068] If the projection length of the third reference voltage vector is greater than or equal to 1 / 2 of the length of the single - cycle large vector and less than the length of the single - cycle large vector, select the single - cycle small vector on the mid - line of the sector where the third reference voltage vector is located as the optimal voltage vector for the first control period and the second control period. While ensuring the output voltage accuracy, further reduce the switching frequency.

[0069] According to the above description, a control method for a converter provided by this application constructs a two - cycle voltage space vector diagram, converts the voltage requirements of two consecutive control periods into an equivalent composite vector. The control system can complete the optimization of two control periods within one decision period, reduce the frequent switching of the switching state through cross - cycle optimization; and quickly exclude unnecessary candidate voltage vectors through geometric projection, simplify complex calculations into geometric judgments based on the sector mid - line, significantly reduce the calculation amount while ensuring the control accuracy, realize the rapid selection of the optimal voltage vector, and improve the response speed of the control system.

[0070] Further, if the projection length of the third reference voltage vector is greater than or equal to the single-cycle large vector length, the two-cycle voltage space vector diagram is partitioned twice to locate the sector position where the third reference voltage vector is located, and the optimal voltage vector is obtained based on the predicted current. The specific implementation method will be elaborated in detail below.

[0071] As an implementation method, as Figure 5 shown, in step S12, calculating the reference voltage vectors of adjacent first and second control periods further includes the following steps:

[0072] Step S121, constructing an extended superlocal model, where the extended superlocal model includes a linear part and a nonlinear part of the power system disturbance parameters.

[0073] Step S122, designing an extended sliding mode observer, where the extended sliding mode observer is configured to estimate the nonlinear part and the linear part of the extended superlocal model.

[0074] Step S123, based on the deadbeat control principle, obtaining the reference voltage vectors of the first and second control periods based on the estimation results.

[0075] Specifically, constructing an extended superlocal model to replace the mathematical model of a traditional NPC (Neutral Point Clamped) inverter. The extended superlocal model is used to describe the dynamic behavior of the power system, decomposing the power system disturbance parameters into a linear part and a nonlinear part, and selecting appropriate gain parameters so that the control strategy can adapt to load parameter changes or nonlinear disturbances, reducing the dependence on an accurate mathematical model. The extended superlocal model can enable the controller to achieve effective control by real-time estimating disturbances without relying on accurate parameters, improving the robustness of the control system. As an implementation method, the extended superlocal model is represented by the following formula:

[0076] (2);

[0077] In the formula, represents the system state variable gain, represents the unknown term of the system nonlinearity; represents the unknown term of the system linear part, represents the voltage, represents the system output current in the

[0078] An extended sliding mode observer is designed. The extended sliding mode observer introduces a discontinuous control term to estimate the linear part and the nonlinear part in the extended super-local model in real time. By using the extended sliding mode observer to estimate the power system disturbance in real time, a more accurate understanding of the power system disturbance parameters can be obtained, providing a reliable basis for subsequent control decisions. Moreover, the extended sliding mode observer is configured to separately estimate the nonlinear part and the linear part in the extended super-local model, enabling the extended sliding mode observer to accurately estimate the disturbance, realizing that the controller can compensate for parameter mismatch and nonlinear effects in real time, and ensuring the stable operation of the power system. As an implementation method, the extended sliding mode observer is expressed by the following formula:

[0079] (3);

[0080] In the formula, represents the gain, represents the control function.

[0081] Based on the estimation result of the extended sliding mode observer in the current control period k, the current state of the first control period k + 1 is predicted according to the voltage in the current control period k, and the first reference voltage vector of the first control period k + 1 is calculated through the deadbeat control principle; further, the current state of the second control period k + 2 is predicted according to the voltage in the current control period k, and the above calculation process is repeated to obtain the second reference voltage vector of the second control period k + 2.

[0082] By predicting two control periods, the controller can comprehensively optimize the selection of the voltage vector within adjacent periods. If the directions of the reference voltage vectors of the two control periods are the same, the same voltage vector can be selected, thus avoiding frequent switching of the switching state, achieving a balance between high-precision current tracking and low switching losses, and improving the control performance of the converter.

[0083] As an implementation method, the first reference voltage vector is expressed by the following formula:

[0084] (4);

[0085] In the formula, represents the first reference voltage vector, represents the predicted current in the stationary coordinate system of the (k + 1)-th control period, represents the predicted value of the system nonlinear unknown term in the (k + 1)-th control period, Ts represents the control period, represents the reference current of the (k + 2)-th control period in the coordinate system.

[0086] The second reference voltage vector is expressed by the following formula:

[0087] (5);

[0088] Wherein, represents the second reference voltage vector, represents the predicted current in the stationary coordinate system at the (k + 2)-th control period, represents the predicted value of the system non-linear unknown term at the (k + 2)-th control period, Ts represents the control period, represents the reference current at the (k + 3)-th control period in the coordinate system.

[0089] As an implementation manner, the third reference voltage vector is obtained by adding the first reference voltage vector and the second reference voltage vector. The third reference voltage vector is represented by the following formula:

[0090] (6);

[0091] Wherein, represents the third reference voltage vector.

[0092] By calculating the angle of the third reference voltage vector and calculating the length of the projection of the third reference voltage vector onto the midline of the sector where it is located, different voltage vector positioning strategies are adopted to obtain the optimal voltage vector. Based on the magnitude relationship between the projection length of the third reference voltage vector and the single-cycle large vector, wherein, the implementation manners of obtaining the optimal voltage vector in the two cases where the projection length of the third reference voltage vector is less than 1 / 2 of the single-cycle large vector length and the projection length of the third reference voltage vector is greater than or equal to 1 / 2 of the single-cycle large vector length have been described above and will not be elaborated here.

[0093] As an optional implementation manner, when the projection length of the third reference voltage vector is greater than or equal to the single-cycle large vector length, the implementation manner of obtaining the optimal voltage vector includes: performing secondary partitioning on the two-cycle voltage space vector diagram. After the secondary partitioning, six large sectors are obtained. The midline of any large sector coincides with the single-cycle medium vector, and any large sector is divided into four equal small sectors. The inner region and the outer region of the two-cycle voltage space vector diagram are defined. Among them, the inner region consists of six small sectors connected to the center of the two-cycle voltage space vector diagram, and the outer region consists of the remaining 18 small sectors.

[0094] In response to the projection length being greater than or equal to the single-cycle large vector length, locate the target large sector and the target small sector where the third reference voltage vector is located, and substitute the voltage vectors at the three vertices of the target small sector into the prediction current calculation to calculate the optimal voltage vector with the goal of minimizing the first cost function.

[0095] Such as Figure 6As shown, the two-cycle voltage space vector diagram is divided into two parts to more accurately locate the reference voltage vector. The entire two-cycle voltage space vector diagram is divided into six large sectors, and the center line of any large sector coincides with the single-cycle center vector. For example, Figure 6 In the equation, the voltage vector V1 and the voltage vector V 10 +V 10 The three vertex voltage vectors V8+V8 form a large sector, the center line of the large sector is the voltage vector V9+V9, and the center line coincides with the vector V9 in a single cycle.

[0096] The voltage space vector diagram is divided more finely, and any large sector is further divided into four smaller sectors to more accurately locate the position of the reference voltage vector. The inner and outer regions of the two-cycle voltage space vector diagram are defined. The inner region consists of six small sectors connected to the center of the two-cycle voltage space vector diagram, and the outer region consists of the remaining 18 small sectors. Each small sector is composed of three vertex voltage vectors. Therefore, different control strategies are adopted in different areas according to the sector location of the third reference voltage vector, improving the flexibility and effectiveness of converter control. Through secondary partitioning, the distribution of the voltage space vector can be analyzed in more detail, providing a basis for the subsequent selection of an appropriate control strategy based on the location of the reference voltage vector.

[0097] The projected length of the third reference voltage vector is compared with the length of the single-cycle large vector. When the projected length of the third reference voltage vector is greater than or equal to the length of the single-cycle large vector, the large sector in which the third reference voltage vector is located is determined based on the angle of the third reference voltage vector. Subsequently, the target small sector is further located within the large sector by dividing the small sectors into four equal parts.

[0098] Each small sector is composed of three vertex voltage vectors, and the voltage vectors of these three vertices are brought into the predicted current calculation. The predicted current calculation is based on the electrical characteristics and mathematical model of the power system. Different voltage vectors are brought into the calculation to obtain the predicted current values under different circumstances. In the predicted current calculation, a first cost function is set, and the calculation is performed with the goal of minimizing the first cost function. By calculating the first cost function value under different voltage vectors, the voltage vector that minimizes the first cost function value is selected as the optimal voltage vector, thereby improving the operating efficiency and stability of the power system. By partitioning the calculation of candidate voltage vectors, the computational complexity is greatly reduced. While ensuring control accuracy, it effectively balances the optimization requirements of computational efficiency and switching frequency.

[0099] As an implementation method, the first cost function is expressed by the following formula:

[0100] (7);

[0101] In the formula, represents the reference current represents the predicted current in the stationary coordinate system at the (k + j)-th control period

[0102] In summary, the control method of the converter provided by this application simplifies the process of locating the optimal voltage vector as shown in Figure 7 By establishing a two-period voltage space vector diagram, the voltage demands of two consecutive control periods are transformed into an equivalent third reference voltage vector. The large sector and small sector where the third reference voltage vector is located are determined. Unnecessary candidate voltage vectors are quickly excluded through geometric projection, and the complex calculation is simplified to a geometric judgment based on the sector midline, thereby realizing the rapid selection of the optimal voltage vector and reducing the switching loss of the converter

[0103] Furthermore, the control method provided by this application also includes a neutral point voltage balance strategy. After obtaining the optimal voltage vector, through the neutral point voltage balance strategy, the optimal switching state of the optimal voltage vector is quickly obtained to maintain the neutral point voltage balance of the converter and reduce the switching frequency of the converter

[0104] As an implementation method, as shown in Figure 8 The neutral point voltage balance strategy includes: setting a second cost function and a third cost function. In response to the optimal voltage vector being a single-period small vector, aiming to minimize the second cost function, by continuously adjusting the switching state of the single-period small vector, calculating the values of the second cost function under different switching states, and selecting the switching state that makes the value of the second cost function the smallest as the optimal switching state, the neutral point voltage of the converter is maintained balanced and the operating performance of the converter is improved

[0105] In response to the optimal voltage vector being a zero vector, aiming to minimize the third cost function, by calculating the values of the third cost function under different zero vector switching states, finding the switching state that makes the third cost function the smallest, which is the optimal switching state of the zero vector, ensuring that while reducing the switching loss of the system, the neutral point voltage of the converter is maintained balanced

[0106] Among them, the second cost function is expressed by the following formula

[0107] (8);

[0108] In the formula represents the neutral point voltage, and the neutral point voltage satisfies , where represents the voltage drop of the upper voltage-dividing capacitor C dc ; represents the current flowing into the neutral point, and the neutral point current satisfies , where Sa , S b , S c are the switching states of the three-phase inverter respectively. i a 、i b 、i c are the currents flowing through the three-phase inverter respectively.

[0109] The third cost function is expressed by the following formula:

[0110] (9);

[0111] In the formula, represents the switching states of the three phases .

[0112] For further illustration, the control method of a converter provided by the present application is verified by experimental results below. As Figure 9a and Figure 9b shown, the extended sliding mode observer compensates for parameter mismatch and nonlinear pattern disturbance in real time. When the load inductance deviation is 20%, the THD (Total Harmonic Distortion) value increases by 0.8%, and the THD increase value of the existing control method is 2.1%; the control method of a converter provided by the present application adopts the same voltage vector for adjacent control cycles. According to the method provided by the present application, when the parameters are matched, the switching frequency is 976 Hz, and when the parameters are mismatched, the switching frequency is 1237 Hz. Compared with the traditional control method (the switching frequency is 1607 Hz) in both cases, the switching frequency is significantly reduced, the performance of the converter is improved, and the switching loss is reduced; the control method of a converter provided by the present application reduces the number of candidate voltage vector evaluations from 27 times to 3 times through the partition optimization strategy, and the running time of the controller is reduced by 40%, effectively reducing the calculation burden of the controller.

[0113] According to the above description, for the control method of a converter provided by the present application, a two-cycle voltage space vector diagram is constructed, and the voltage requirements of two consecutive control cycles are converted into an equivalent composite vector. The control system can complete the optimization of two control cycles within one decision cycle, reduce the frequent switching of switching states through cross-cycle optimization; and quickly exclude unnecessary candidate voltage vectors through geometric projection, simplify complex calculations into geometric judgments based on the sector center line, significantly reduce the calculation amount while ensuring the control accuracy, realize the rapid selection of the optimal voltage vector, and improve the response speed of the control system.

[0114] Furthermore, a control method for a converter provided by the present application can select the most suitable switching state according to different types of optimal voltage vectors by minimizing a cost function, thereby achieving efficient current tracking and neutral point voltage balance of the converter.

[0115] In a second aspect, the present application also provides a converter, which includes a three-level neutral-point clamped inverter circuit and a controller. The controller controls the three-level neutral-point clamped inverter circuit by using the control method of the converter described above, reducing the calculation burden of the controller and the switching frequency of the converter, and achieving efficient current tracking and neutral point voltage balance of the converter.

[0116] It can be understood that the term "exemplary" used herein means "serving as an example, instance, or illustration". Any embodiment described as "exemplary" is not necessarily preferred or superior to other embodiments and / or does not exclude combining the features of other embodiments. It should be understood that certain features of the present application described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, the various features of the present application described in the context of a single embodiment may also be provided separately or in any suitable combination or as any other described embodiment of the present application.

[0117] The above-disclosed are only the preferred embodiments of the present application, but they are not intended to limit the scope of the rights of the present application. Those of ordinary skill in the art can understand that within the spirit and scope of the present application and the appended claims, changes, modifications, substitutions, combinations, and simplifications should all be equivalent replacement methods and still fall within the scope covered by the invention.

Claims

1. A control method for a converter, the converter being applied in a power system, characterized in that, The control method includes the following steps: Construct a two-period voltage space vector diagram, which includes six equal sectors, and the midline of any sector coincides with the single-period large vector; Calculate the reference voltage vectors of adjacent first and second control periods to obtain a first reference voltage vector and a second reference voltage vector; Combine the first reference voltage vector and the second reference voltage vector to obtain a third reference voltage vector; Calculate the angle of the third reference voltage vector, and calculate the length of the projection of the third reference voltage vector onto the midline of the sector where it is located. In response to the projection length being less than 1 / 2 of the single-period large vector length, select the zero vector as the optimal voltage vector for the first control period and the second control period. In response to the projection length being greater than or equal to 1 / 2 of the single-period large vector length and less than the single-period large vector length, select the single-period small vector as the optimal voltage vector for the first control period and the second control period. The single-period small vector is the single-period small vector on the midline of the sector where the third reference voltage vector is located; The first reference voltage vector is represented by the following formula: ； The second reference voltage vector is represented by the following formula: ； wherein, the time instant and the estimated current at the time instant is estimated using the voltage at the k-th time instant.

2. The control method of the converter according to claim 1, wherein The control method further includes: Perform secondary partitioning on the two-period voltage space vector diagram. After secondary partitioning, six large sectors are obtained. The midline of any large sector coincides with the single-period medium vector. Moreover, any large sector is divided into four equal small sectors. Define the inner area and the outer area of the two-period voltage space vector diagram. Among them, the inner area consists of six small sectors connected to the center of the two-period voltage space vector diagram, and the outer area consists of the remaining 18 small sectors; In response to the projection length being greater than or equal to the single-period large vector length, locate the target large sector and the target small sector where the third reference voltage vector is located, and substitute the voltage vectors of the three vertices that make up the target small sector into the predicted current calculation to calculate the optimal voltage vector with the goal of minimizing the first cost function.

3. The control method of the converter according to claim 2, wherein The control method further includes setting The first cost function is represented by the following formula: ； In the formula, i * αβ represents the reference current, represents the predicted current in the stationary coordinate system at the (k + j)-th control period.

4. The control method of the converter according to claim 1, characterized in that, The control method further includes: Construct an extended superlocal model, which includes a linear part and a nonlinear part of the power system disturbance parameters; Design an extended sliding mode observer, which is configured to estimate the nonlinear part and the linear part of the extended superlocal model; According to the deadbeat control principle, obtain the reference voltage vectors of the first control period and the second control period based on the estimation results.

5. The control method of the converter according to claim 4, wherein The extended superlocal model is represented by the following formula: ； wherein, is the system state variable gain, is the unknown term of the system nonlinearity; represents the unknown term of the linear part, represents the voltage.

6. The control method of the converter according to claim 5, wherein The extended sliding mode observer is represented by the following formula: ； Wherein, represents the gain, represents the control function.

7. The control method of the converter according to claim 1, wherein The third reference voltage vector is obtained by adding the first reference voltage vector and the second reference voltage vector.

8. The control method of the converter according to any one of claims 1 to 7, characterized in that The control method further includes: Set a second cost function and a third cost function. In response to the optimal voltage vector being a single-cycle small vector, with the goal of minimizing the second cost function, obtain the optimal switching state of the single-cycle small vector; in response to the optimal voltage vector being a zero vector, with the goal of minimizing the third cost function, obtain the optimal switching state of the zero vector. Among them, the second cost function is represented by the following formula: ； The third cost function is represented by the following formula: ； In the formula, represents the switching state of the three-phase inverter .

9. A converter, characterized in that, The converter includes a three-level neutral-point clamped inverter circuit and a controller, and the controller controls the three-level neutral-point clamped inverter circuit by using the control method according to any one of claims 1 to 8.

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