A three-phase converter switching control method based on a dwell time constraint

Abstract

A three-phase converter switching control method based on residence time constraint, step 1, a four-dimensional switching model is established by comprehensively considering the three-phase input current and output DC voltage regulation of the three-phase voltage type converter; step 2, the input AC voltage cycle of a three-phase voltage type converter is divided into 6 sectors, and a subsystem set meeting the system stable control in each sector is established; step 3, a linear matrix inequality group is solved; step 4, a switching rule is designed to realize the selection of the switching mode of the three-phase voltage type converter in the next control cycle; step 5, the residence time corresponding to the switching mode obtained in step 4 is calculated; and step 6, the switching state is output to realize the control of the three-phase voltage type converter. Compared with the traditional three-phase voltage type converter based on the linear model of the double closed loop proportional integral control method, the method has the advantages that the control process is simple, there is no control parameter, the single loop control of the DC side voltage and the AC side current can be realized, and the control effect is good.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a three-phase converter switching control method based on dwell time constraints. Background Technology

[0002] Three-phase voltage source converters, as key components for transmitting voltage and current between AC and DC, are widely used in high-power industrial power supplies, power system transmission / transformation equipment, motor speed control, new energy power generation systems, and new energy vehicle charging / discharging systems. Achieving accurate system modeling and high-performance control of three-phase voltage source converters is crucial for improving energy utilization efficiency, reducing carbon emissions, and enhancing the performance of these new energy power equipment.

[0003] However, due to the nonlinear operating characteristics of the power switching devices in a three-phase voltage source converter (VBP), the VBP is a typical nonlinear system. Traditional modeling and control methods for VBPs typically rely on establishing linearized models and pulse width modulation (PWM) techniques. The linearization model of a VBP ignores the high-frequency components of the system state caused by the operation of high-frequency power switching devices and controls the linearized system state based on the duty cycle (i.e., the average value of the switching pulse width within the control cycle). Therefore, traditional linearized models cannot accurately describe the operation of a three-phase VBP. Furthermore, traditional control methods based on linearized models require complex rotating coordinate transformations and vector modulation processes, and suffer from drawbacks such as numerous control parameters, difficulty in tuning control parameters, and the fact that pre-set control parameters only exhibit good control performance near a predefined system operating point. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide a three-phase converter switching control method based on dwell time constraints. This method treats the operating states of the three-phase voltage source converter under different switching states as different subsystems, and establishes a three-phase voltage source converter switching model to achieve an accurate description of the operating states of the three-phase voltage source converter. Simultaneously, based on the three-phase voltage source converter switching model, switching rules are designed to achieve synchronous control of the system's AC current and DC voltage.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a three-phase converter switching control method based on dwell time constraints, characterized by comprising the following steps:

[0006] Step 1: Establish a four-dimensional switching model that comprehensively considers the regulation of the three-phase input current and output DC voltage of the three-phase voltage source converter;

[0007] Step 2: Divide the AC input voltage cycle of a three-phase voltage source converter into 6 sectors and establish a set of subsystems that satisfy the system stability control within each sector;

[0008] Step 3: Solve the system of linear matrix inequalities;

[0009] Step 4: Design switching rules to achieve the switching mode selection of the three-phase voltage source converter in the next control cycle;

[0010] Step 5: Calculate the dwell time corresponding to the switching mode obtained in Step 4;

[0011] Step 6: Output switch status to realize three-phase voltage converter control.

[0012] Step 1 specifically includes:

[0013] Based on Kirchhoff's voltage and current laws, a four-dimensional switching affine model of a three-phase voltage source converter is established as follows:

[0014]

[0015] In formula (1), x(t) = [i a (t) i b (t) i c (t) U dc (t)] T Let be the state vector of the three-phase voltage source converter system, where t is time and i a (t),i b (t),i c (t) represents the AC current state of the three-phase voltage source converter, U dc (t) represents the DC voltage state of the three-phase voltage-source converter; This represents the time derivative of the state vector x(t); Indicates the current and voltage state i a (t),i b (t),i c (t) and U dc (t) is the time derivative; U a (t),U b (t),U c (t) represents the AC voltage state of the three-phase voltage source converter; L represents the AC side filter inductance of the three-phase voltage source converter; R represents the inductance and equivalent resistance of the circuit of the three-phase voltage source converter; C represents the DC side filter capacitor of the three-phase voltage source converter; R L S is the DC-side load resistance of the three-phase voltage source converter. i For the i-phase bridge arm switching states of a three-phase voltage source converter, i = a, b, c, S i=1 means that the upper switching device of phase i is turned on and the lower switching device is turned off, and vice versa. i =0 means that the upper switching device of phase i is open and the lower switching device is open; For affine terms; The switching matrix is ​​p = 1, ..., 8, and its value varies with S. i The values ​​of i, b, and c vary, corresponding to changes in the subscript p, depending on the different three-phase bridge arm switch states S. a ,S b ,S c With different values, the three-phase voltage source converter has a total of 8 switching modes, corresponding to 8 subsystems and vector matrix A. p p = 1, ..., 8, specifically described as:

[0016] Switching to mode 1 corresponds to subsystem S u1 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [0,0,0] represents a three-phase voltage source converter where the lower switch of phase a is on and the upper switch is off, the lower switch of phase b is on and the upper switch is off, and the lower switch of phase c is on and the upper switch is off. The vector matrix is ​​as follows:

[0017] Switching to mode 2 corresponds to subsystem S u2 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [0,0,1] represents a three-phase voltage source converter where the lower switch of phase a is on and the upper switch is off, the lower switch of phase b is on and the upper switch is off, and the upper switch of phase c is on and the lower switch is off. The vector matrix is ​​as follows:

[0018] Switching to mode 3 corresponds to subsystem S u3 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [0,1,0] represents a three-phase voltage source converter where the lower switch of phase a is on and the upper switch is off, the upper switch of phase b is on and the lower switch is off, and the lower switch of phase c is on and the upper switch is off. The vector matrix is ​​as follows:

[0019] Switching to mode 4 corresponds to subsystem S u4 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c[0,1,1] represents a three-phase voltage source converter where the lower switch of phase a is on and the upper switch is off, the upper switch of phase b is on and the lower switch is off, and the upper switch of phase c is on and the lower switch is off. The vector matrix is ​​as follows:

[0020] Switching to mode 5 corresponds to subsystem S u5 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [1,0,0] represents a three-phase voltage source converter where the upper switch of phase a is on and the lower switch is off, the lower switch of phase b is on and the upper switch is off, and the lower switch of phase c is on and the upper switch is off. The vector matrix is ​​as follows:

[0021] Switching to mode 6 corresponds to subsystem S u6 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [1,0,1] represents a three-phase voltage source converter where the upper switch of phase a is on and the lower switch is off, the lower switch of phase b is on and the upper switch is off, and the upper switch of phase c is on and the lower switch is off. The vector matrix is ​​as follows:

[0022] Switching to mode 7 corresponds to subsystem S. u7 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [1,1,0] represents a three-phase voltage source converter where the upper switch of phase a is on and the lower switch is off, the upper switch of phase b is on and the lower switch is off, and the lower switch of phase c is on and the upper switch is off. The vector matrix is ​​as follows:

[0023] Switching to mode 8 corresponds to subsystem S u8 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [1,1,1] represents a three-phase voltage source converter where the upper switch of phase a is on and the lower switch is off, the upper switch of phase b is on and the lower switch is off, and the upper switch of phase c is on and the lower switch is off. The vector matrix is ​​as follows:

[0024] To facilitate system control, auxiliary variables are defined. in i ar(t),i br (t),i cr (t) represents the expected value of the AC current in the three-phase voltage source converter, U dcr (t) represents the expected DC voltage of the three-phase voltage source converter. Based on the four-dimensional switching affine model and auxiliary variables, the switching error model of the three-phase voltage source converter can be obtained as follows:

[0025]

[0026] In formula (2) express The derivative with respect to time t.

[0027] Step 2 specifically refers to:

[0028] A three-phase AC voltage cycle is divided into 6 sectors. Within each sector, a subsystem set consisting of 4 subsystems is defined. In actual three-phase voltage source converter control, the subsystem state can only be selected from the subsystem set within the sector where the AC voltage state is located. The specific sector division and subsystem set definitions are as follows:

[0029] 1) Three-phase AC phase voltage U a ≥U b >U c For sector 1, the set of three-phase voltage-source converter subsystems that meet the system stability control requirements is as follows:

[0030] 2) Three-phase AC phase voltage U b >U a ≥U c For sector 2, the set of three-phase voltage-source converter subsystems that meet the system stability control requirements is as follows:

[0031] 3) Three-phase AC phase voltage U b ≥U c >U a For sector 3, the set of three-phase voltage-source converter subsystems that meet the system stability control requirements is as follows:

[0032] 4) Three-phase AC phase voltage U c >U b ≥U a For sector 4, the corresponding three-phase voltage-source converter subsystem combination that meets the system stability control requirements is as follows:

[0033] 5) Three-phase AC phase voltage U c ≥U a >U bFor sector 5, the corresponding three-phase voltage-source converter subsystem combination that meets the system stability control requirements is as follows:

[0034] 6) Three-phase AC phase voltage U a >U c ≥U b For sector 6, the corresponding three-phase voltage-source converter subsystem combination that meets the system stability control requirements is as follows:

[0035] 4. The three-phase converter switching control method based on dwell time constraints according to claim 1, characterized in that step 3 specifically comprises:

[0036] Solve for the set of subsystems within the corresponding 6 sectors The switching matrix A corresponding to the four subsystems p convex combination matrix A λj j = 1, ..., 6, p = 1, ..., 8, specifically represented as:

[0037] For sector 1, the subsystem set is: Therefore, there is

[0038] A λ1 =λ1A3+λ2A5+λ3A6+λ4A7 (3)

[0039] In equation (3), λ1, λ2, λ3, and λ4 are convex combination functions, and their values ​​should satisfy λ1 + λ2 + λ3 + λ4 = 1.

[0040] For sector 2, the subsystem set is: Therefore, there is

[0041] A λ2 =λ1A3+λ2A4+λ3A5+λ4A7 (4)

[0042] For sector 3, the subsystem set is: Therefore, there is

[0043] A λ3 =λ1A2+λ2A3+λ3A4+λ4A7 (5)

[0044] For sector 4, the subsystem set is: Therefore, there is

[0045] A λ4 =λ1A2+λ2A3+λ3A4+λ4A6 (6)

[0046] For sector 5, the subsystem set is: Therefore, there is

[0047] Aλ5 =λ1A2+λ2A4+λ3A5+λ4A6 (7)

[0048] For sector 6, the subsystem set is: Therefore, there is

[0049] A λ6 =λ1A2+λ2A5+λ3A6+λ4A7 (8)

[0050] Based on equations (3)-(8) above, calculate the following linear matrix inequalities to obtain a positive definite symmetric matrix P that satisfies the following requirements:

[0051]

[0052] In equation (9) Representing matrix A λj Transpose operation of (j=1,…,6).

[0053] Step 4 specifically includes:

[0054] Define the switching rule function as follows

[0055]

[0056] Where σ represents the switching mode, which is determined by the sector subsystem subset at the current control moment. In the four subsystems, j = 1, ..., 6, choose the function that makes j = 1, ..., 6. The subsystem n with the smallest calculated value is generated; argmin indicates that the minimum value is taken for calculation. Indicates a subset from the subsystem Select n from A; n Subsystem subset The switching matrix corresponding to the nth subsystem, j = 1, ..., 6;

[0057] Step 5 specifically includes:

[0058] Design the dwell time T for each subsystem. Here, dwell time refers to the time during which the subsystem maintains its effect on the actual three-phase voltage source converter. The dwell time T is specifically defined as follows:

[0059]

[0060] in

[0061]

[0062]

[0063] in, Let i be the error between the sampled value and the expected value of the AC three-phase current of the three-phase voltage source converter in the k-th control cycle; a (k), i b (k), i c (k) represents the sampled values ​​of the three-phase AC current of the three-phase voltage-source converter in the k-th control cycle; u a (k), u b (k), u c (k) represent the sampled values ​​of the three-phase AC voltage of the three-phase voltage-source converter in the k-th control cycle; U dc (k) is the sampled value of the DC side voltage of the three-phase voltage-source converter in the kth control cycle.

[0064] Step 6 specifically includes:

[0065] The switching mode obtained in step 4 and the dwell time in step 5 are applied to the three-phase voltage source converter. The specific control can be obtained by comparing the desired dwell time T with the carrier wave.

[0066] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0067] 1) Compared with the traditional linearized model of three-phase voltage source converter, the present invention proposes a three-phase voltage source converter switching model that establishes an approximation-free and linearized process, which can accurately describe the working process of the converter;

[0068] 2) The designed switching control strategy can directly select the state of the subsystem acting in the next control cycle of the three-phase voltage source converter based on the switching rules. Compared with the traditional dual-closed-loop proportional-integral control method based on a linearized model, it eliminates the need for complex coordinate transformations and vector modulation processes, requires no control parameters, and the controller is simple to implement while achieving better control performance.

[0069] 3) The method employed simultaneously adjusts the action time of the subsystem, i.e., the residence time. Compared to methods that do not adjust the residence time, the method of this invention can improve the system control performance. Attached Figure Description

[0070] Figure 1 This is a circuit diagram of a three-phase voltage source converter.

[0071] Figure 2 This is a sector division diagram for a three-phase voltage source converter.

[0072] Figure 3 The simulated waveform of the DC-side voltage of a three-phase voltage-source converter using the method of this invention is shown.

[0073] Figure 4 The simulation waveforms of the three-phase voltage and current of the three-phase voltage-source converter using the method of the present invention are shown.

[0074] Figure 5 The DC-side voltage simulation comparison waveforms of a three-phase voltage-source converter using traditional dual-closed-loop proportional gain control, traditional model predictive control, and the method of this invention are presented.

[0075] Figure 6 The simulation waveforms of phase a voltage and current of a three-phase voltage-type converter using traditional dual-closed-loop proportional gain control, traditional model predictive control, and the method of this invention are presented. Detailed Implementation

[0076] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0077] Example

[0078] The circuit diagram of the three-phase voltage source converter of the present invention is as follows: Figure 1 As shown, where U a U b U c For the AC voltage of the three-phase voltage source converter, i a i b i c For the AC current of the three-phase voltage source converter, U dc For the DC voltage of the three-phase voltage source converter; L a =L b =L c =L is the AC side filter inductance of the three-phase voltage source converter; R is the inductance and equivalent resistance of the circuit of the three-phase voltage source converter; C is the DC side filter capacitor of the three-phase voltage source converter; R L S is the DC-side load resistance of the three-phase voltage source converter. j (j=1,…,6) represents the switching state of the j-th switching device in the three-phase voltage source converter, S j =1 represents the j-th switching device being turned on, otherwise S j =0 means that the j-th switching device is off.

[0079] Based on Kirchhoff's voltage and current laws, a four-dimensional switching affine model of a three-phase voltage source converter is established as follows:

[0080]

[0081] In formula (1), x(t) = [i a (t) i b (t) ic (t) U dc (t)] T Let be the state vector of the three-phase voltage source converter system, where t is time; This represents the time derivative of the state vector x(t); Indicates the current and voltage state i a (t),i b (t),i c (t) and U dc (t) is the time derivative; S i (i = a, b, c) represents the switching state of the i-phase bridge arm of the three-phase voltage source converter, S i =1 means that the upper switching device of phase i is turned on and the lower switching device is turned off, and vice versa. i =0 means that the upper switching device of phase i is open and the lower switching device is open; For affine terms; Let S be the switching matrix (p = 1, ..., 8), whose value changes with S. i The values ​​of (i = a, b, c) vary, corresponding to changes in the subscript p, depending on the different three-phase bridge arm switch states S. a ,S b ,S c With different values, the three-phase voltage source converter has a total of 8 switching modes, corresponding to 8 subsystems and vector matrix A. p (p = 1, ..., 8), specifically described as follows:

[0082] Switching to mode 1 corresponds to subsystem S u1 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [0,0,0] represents a three-phase voltage source converter where the lower switch of phase a is on and the upper switch is off, the lower switch of phase b is on and the upper switch is off, and the lower switch of phase c is on and the upper switch is off. The vector matrix is ​​as follows:

[0083] Switching to mode 2 corresponds to subsystem S u2 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [0,0,1] represents a three-phase voltage source converter where the lower switch of phase a is on and the upper switch is off, the lower switch of phase b is on and the upper switch is off, and the upper switch of phase c is on and the lower switch is off. The vector matrix is ​​as follows:

[0084] Switching to mode 3 corresponds to subsystem S u3At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [0,1,0] represents a three-phase voltage source converter where the lower switch of phase a is on and the upper switch is off, the upper switch of phase b is on and the lower switch is off, and the lower switch of phase c is on and the upper switch is off. The vector matrix is ​​as follows:

[0085] Switching to mode 4 corresponds to subsystem S u4 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [0,1,1] represents a three-phase voltage source converter where the lower switch of phase a is on and the upper switch is off, the upper switch of phase b is on and the lower switch is off, and the upper switch of phase c is on and the lower switch is off. The vector matrix is ​​as follows:

[0086] Switching to mode 5 corresponds to subsystem S u5 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [1,0,0] represents a three-phase voltage source converter where the upper switch of phase a is on and the lower switch is off, the lower switch of phase b is on and the upper switch is off, and the lower switch of phase c is on and the upper switch is off. The vector matrix is ​​as follows:

[0087] Switching to mode 6 corresponds to subsystem S u6 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [1,0,1] represents a three-phase voltage source converter where the upper switch of phase a is on and the lower switch is off, the lower switch of phase b is on and the upper switch is off, and the upper switch of phase c is on and the lower switch is off. The vector matrix is ​​as follows:

[0088] Switching to mode 7 corresponds to subsystem S. u7 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [1,1,0] represents a three-phase voltage source converter where the upper switch of phase a is on and the lower switch is off, the upper switch of phase b is on and the lower switch is off, and the lower switch of phase c is on and the upper switch is off. The vector matrix is ​​as follows:

[0089] Switching to mode 8 corresponds to subsystem S u8 At this time, the three-phase bridge arm switch state combination [S] a ,S b ,S c [1,1,1] represents a three-phase voltage source converter where the upper switch of phase a is on and the lower switch is off, the upper switch of phase b is on and the lower switch is off, and the upper switch of phase c is on and the lower switch is off. The vector matrix is ​​as follows:

[0090] To facilitate system control, auxiliary variables are defined. in i ar (t),i br (t),i cr (t) represents the expected value of the AC current in the three-phase voltage source converter, U dcr (t) represents the expected DC voltage of the three-phase voltage source converter. Based on the four-dimensional switching affine model and auxiliary variables, the switching error model of the three-phase voltage source converter can be obtained as follows:

[0091]

[0092] In formula (2) express The derivative with respect to time t.

[0093] Step 2 above specifically refers to:

[0094] Divide a three-phase AC voltage cycle into 6 sectors, such as Figure 2 As shown. Within each sector, a subsystem set consisting of four subsystems is defined. In actual three-phase voltage source converter control, the subsystem (switching mode) state can only be selected from the subsystem set within the sector where the AC side voltage state is located. The specific sector division and subsystem set definitions are as follows:

[0095] 1) Three-phase AC phase voltage U a ≥U b >U c For sector 1, the set of three-phase voltage-source converter subsystems that meet the system stability control requirements is as follows:

[0096] 2) Three-phase AC phase voltage U b >U a ≥U c For sector 2, the set of three-phase voltage-source converter subsystems that meet the system stability control requirements is as follows:

[0097] 3) Three-phase AC phase voltage U b ≥Uc >U a For sector 3, the set of three-phase voltage-source converter subsystems that meet the system stability control requirements is as follows:

[0098] 4) Three-phase AC phase voltage U c >U b ≥U a For sector 4, the corresponding three-phase voltage-source converter subsystem combination that meets the system stability control requirements is as follows:

[0099] 5) Three-phase AC phase voltage U c ≥U a >U b For sector 5, the corresponding three-phase voltage-source converter subsystem combination that meets the system stability control requirements is as follows:

[0100] 6) Three-phase AC phase voltage U a >U c ≥U b For sector 6, the corresponding three-phase voltage-source converter subsystem combination that meets the system stability control requirements is as follows:

[0101] The above sector division and subsystem combination can be summarized as the following switching table:

[0102] Table 1 Switching Table

[0103]

[0104] Step 3 above specifically refers to:

[0105] Solve for the set of subsystems within the corresponding 6 sectors The switching matrix A corresponding to the four subsystems p A convex combination matrix A of (p = 1, ..., 8) λj (j = 1, ..., 6), specifically represented as:

[0106] For sector 1, the subsystem set is: Therefore, there is

[0107]

[0108] In equation (3), λ1, λ2, λ3, and λ4 are convex combination functions, and their values ​​should satisfy λ1 + λ2 + λ3 + λ4 = 1. For sector 2, the subsystem set is... Therefore, there is

[0109]

[0110] For sector 3, the subsystem set is: Therefore, there is

[0111]

[0112] For sector 4, the subsystem set is: Therefore, there is

[0113]

[0114] For sector 5, the subsystem set is: Therefore, there is

[0115]

[0116] For sector 6, the subsystem set is: Therefore, there is

[0117]

[0118] Based on equations (3)-(8) above, calculate the following linear matrix inequalities to obtain a positive definite symmetric matrix P that satisfies the following requirements.

[0119]

[0120] In equation (9) Representing matrix A λj Transpose operation of (j=1,…,6).

[0121] Step 4 above specifically refers to:

[0122] Define the switching rule function as follows

[0123]

[0124] Where σ represents the switching mode, which is determined by the sector subsystem subset at the current control moment. In the four subsystems, choose to make the function The subsystem n with the smallest calculated value is generated; argmin indicates that the minimum value is taken for calculation. Indicates a subset from the subsystem Select n from A; n Subsystem subset The switching matrix corresponding to the nth subsystem.

[0125] Step 5 above specifically refers to:

[0126] Design the dwell time T for each subsystem. Here, dwell time refers to the time that the subsystem (switching mode) maintains its effect on the actual three-phase voltage source converter. The dwell time T is specifically defined as:

[0127]

[0128] in

[0129]

[0130]

[0131] in, Let i be the error between the sampled value and the expected value of the AC three-phase current of the three-phase voltage source converter in the k-th control cycle; a (k), i b (k), i c (k) represents the sampled values ​​of the three-phase AC current of the three-phase voltage-source converter in the k-th control cycle; u a (k), u b (k), u c (k) represent the sampled values ​​of the three-phase AC voltage of the three-phase voltage-source converter in the k-th control cycle; U dc (k) is the sampled value of the DC side voltage of the three-phase voltage-source converter in the kth control cycle.

[0132] Step 6 above specifically refers to:

[0133] The switching mode obtained in step 4 and the dwell time in step 5 are applied to the three-phase voltage source converter. The specific control can be obtained by comparing the desired dwell time T with the carrier wave.

[0134] Simulation and experimental verification

[0135] A Matlab / Simulink simulation model was built to verify the control method of this invention. The simulation and experimental parameters are as follows: the effective value of the three-phase AC phase voltage is 220V, its frequency f = 50Hz, the input filter inductor L = 0.02H, the inductor and circuit equivalent resistance R = 1Ω, the output filter capacitor C = 1500μF, and the load R... L =300Ω, desired DC side voltage U dcr =600V, the desired AC side current is The convex combination functions are λ1 = 0.25, λ2 = 0.25, λ3 = 0.25, and λ4 = 0.25. The symmetric matrix is ​​definite.

[0136] Depend on Figure 3 The DC-side voltage waveform of the three-phase voltage-source converter using the method of this invention shows that its DC voltage quickly reaches its expected value (600V) and there is no overshoot or steady-state regulation error during the voltage change process.

[0137] Figure 4The simulation waveforms of the three-phase voltage and current of the three-phase voltage source converter using the method of this invention are shown. As can be seen from the simulation waveforms, the AC side current of the three-phase voltage source converter using the method of this invention achieves synchronous tracking control of its corresponding three-phase AC voltage, i.e., unity power factor control. The actual simulation measurement shows that the system power factor is 0.9992.

[0138] Figure 5 The simulation waveforms of the DC-side voltage of a three-phase voltage source converter using traditional dual-loop proportional-integral control, traditional model predictive control, and the method of this invention are compared. The simulation waveforms show that, compared to traditional dual-loop proportional-integral control and traditional model predictive control, the DC-side voltage waveform transformation process of the three-phase voltage source converter using the method of this invention has no overshoot, no stability error, and a faster response speed.

[0139] Figure 6 Simulated waveforms of phase a voltage and current of a three-phase voltage source converter using traditional dual-loop proportional-integral control, traditional model predictive control, and the method of this invention are presented. The simulation waveforms show that the phase a current waveform using the method of this invention exhibits a sinusoidal variation and its phase is consistent with the input voltage, thus achieving unity power factor control. Compared to traditional dual-loop proportional-integral control and traditional model predictive control methods, the phase a current waveform of the three-phase voltage source converter using the method of this invention has the fastest response speed.

[0140] The simulation and experimental results above verify the effectiveness and advancement of the three-phase converter switching control method based on dwell time constraints proposed in this invention.

[0141] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A three-phase converter switching control method based on dwell time constraints, characterized in that, Includes the following steps: Step 1: Establish a four-dimensional switching model that comprehensively considers the regulation of the three-phase input current and output DC voltage of the three-phase voltage source converter; Based on Kirchhoff's voltage and current laws, a four-dimensional switching affine model is established as follows: (1) In formula (1) Here is the state vector of the three-phase voltage source converter system, where t For time, i a ( t ), i b ( t ), i c ( t This refers to the AC current state of a three-phase voltage source converter. U dc ( t This refers to the DC voltage state of a three-phase voltage source converter. Represents the state vector The derivative with respect to time; Indicates the state of current and voltage i a ( t ), i b ( t ), i c ( t ) and U dc ( t The time derivative; U a ( t ), U b ( t ), U c ( t This refers to the AC voltage state of a three-phase voltage source converter. L This is the AC side filter inductor for a three-phase voltage source converter; R For the inductance and equivalent resistance of the circuit of a three-phase voltage source converter; C For the DC-side filter capacitor of a three-phase voltage source converter; R L For the DC-side load resistor of a three-phase voltage source converter; S i Three-phase voltage source converter i Phase bridge arm switch status, i = a , b , c , S i =1 represents i The upper switching device of the phase bridge arm is turned on while the lower switching device is turned off, and vice versa. S i =0 represents i The upper switching device in the phase bridge arm is open while the lower switching device is closed; For affine terms; To switch matrices, p =1,…,8, and its value follows... S i It varies depending on the value taken. i = a , b , c , corresponding to the subscript p The changes are due to different three-phase bridge arm switch states. S a , S b , S c With different values, the three-phase voltage source converter has a total of 8 switching modes, corresponding to 8 subsystems and vector matrices. ( p =1,…,8); To facilitate system control, auxiliary variables are defined. ,in For the state vector of the three-phase voltage source converter system The corresponding desired system state vector, where t is time, and iar(t), ibr(t), and icr(t) are the desired values ​​of the AC current of the three-phase voltage source converter. U dcr ( t () represents the expected DC voltage value of the three-phase voltage source converter; , , , Based on the four-dimensional switching affine model (1) and auxiliary variables, the switching error model of the three-phase voltage source converter can be obtained as follows: （2） In formula (2) express Regarding time t The derivative; Step 2: Divide the AC input voltage cycle of a three-phase voltage source converter into 6 sectors and establish a set of subsystems that satisfy the system stability control within each sector; In each sector, a subsystem set consisting of 4 subsystems is defined. In actual three-phase voltage source converter control, the subsystem state can only be selected from the subsystem set within the sector where the AC side voltage state is located. Step 3: Solve the system of linear matrix inequalities; Calculate the following linear matrix inequalities to obtain a positive definite symmetric matrix that satisfies the following requirement. P : (9) In equation (9) (j=1,…,6) represents a matrix A λj Transpose operation of (j=1,…,6); Step 4: Design switching rules to achieve the switching mode selection of the three-phase voltage source converter in the next control cycle; Step 4 specifically includes: Define the switching rule function as follows (10) in To switch modes, a subset of the sector subsystem at the current control moment is used. In its four subsystems, j =1,…,6, choose to make the function… The subsystem with the smallest calculated value n produce; This indicates that the minimum value is used for calculation; Indicates a subset from the subsystem Select n from the options; Subsystem subset The switching matrix corresponding to the nth subsystem. j =1,…,6; Step 5: Calculate the dwell time corresponding to the switching mode obtained in Step 4; The dwell time refers to the time during which the subsystem maintains its action on the three-phase voltage-source converter. Step 6: Apply the switching mode obtained in Step 4 and the dwell time obtained in Step 5 to the three-phase voltage source converter, and realize the control of the three-phase voltage source converter by outputting the switching state.

2. The three-phase converter switching control method based on dwell time constraints according to claim 1, wherein in step 1, the eight switching modes are specifically described as follows: Switch to mode 1, corresponding subsystem S u1 At this time, the three-phase bridge arm switch state combination [ S a , S b , S c The expression [0, 0, 0] represents a three-phase voltage source converter. a The lower switch of the phase bridge arm is on while the upper switch is off. b The lower switch of the phase bridge arm is on while the upper switch is off. c The lower switch of the phase bridge arm is turned on while the upper switch is turned off. At this time, the vector matrix... ; Switch to mode 2, corresponding subsystem S u2 At this time, the three-phase bridge arm switch state combination [ S a , S b , S c ] = [0, 0, 1], represents a three-phase voltage source converter. a The lower switch of the phase bridge arm is on while the upper switch is off. b The lower switch of the phase bridge arm is on while the upper switch is off. c The upper switch in the phase bridge arm is turned on while the lower switch is turned off. At this time, the vector matrix... ; Switch to mode 3, corresponding subsystem S u3 At this time, the three-phase bridge arm switch state combination [ S a , S b , S c The expression [0, 1, 0] represents a three-phase voltage source converter. a The lower switch of the phase bridge arm is on while the upper switch is off. b The upper switch on the phase bridge arm is on while the lower switch is off. c The lower switch of the phase bridge arm is turned on while the upper switch is turned off. At this time, the vector matrix... ; Switching to mode 4, corresponding subsystem S u4 At this time, the three-phase bridge arm switch state combination [ S a , S b , S c The expression [0, 1, 1] represents a three-phase voltage source converter. a The lower switch of the phase bridge arm is on while the upper switch is off. b The upper switch on the phase bridge arm is on while the lower switch is off. c The upper switch in the phase bridge arm is turned on while the lower switch is turned off. At this time, the vector matrix... ; Switch to mode 5, corresponding subsystem S u5 At this time, the three-phase bridge arm switch state combination [ S a , S b , S c The expression [1, 0, 0] represents a three-phase voltage source converter. a The upper switch on the phase bridge arm is on while the lower switch is off. b The lower switch of the phase bridge arm is on while the upper switch is off. c The lower switch of the phase bridge arm is turned on while the upper switch is turned off. At this time, the vector matrix... ; Switch to mode 6, corresponding subsystem S u6 At this time, the three-phase bridge arm switch state combination [ S a , S b , S c The expression [1, 0, 1] represents a three-phase voltage source converter. a The upper switch on the phase bridge arm is on while the lower switch is off. b The lower switch of the phase bridge arm is on while the upper switch is off. c The upper switch in the phase bridge arm is turned on while the lower switch is turned off. At this time, the vector matrix... ; Switch to mode 7, corresponding subsystem S u7 At this time, the three-phase bridge arm switch state combination [ S a , S b , S c The expression [1, 1, 0] represents a three-phase voltage source converter. a The upper switch on the phase bridge arm is on while the lower switch is off. b The upper switch on the phase bridge arm is on while the lower switch is off. c The lower switch of the phase bridge arm is turned on while the upper switch is turned off. At this time, the vector matrix... ; Switching to mode 8 corresponds to subsystem S u8 At this time, the three-phase bridge arm switch state combination [S] a , S b , S c The expression [1, 1, 1] represents a three-phase voltage source converter where the upper switch of phase a is on and the lower switch is off, the upper switch of phase b is on and the lower switch is off, and the upper switch of phase c is on and the lower switch is off. The vector matrix is ​​as follows: .

3. In the three-phase converter switching control method based on dwell time constraints according to claim 2, in step 2, the specific sector division and subsystem set are defined as follows: 1) Phase voltage of three-phase AC side U a ≥ U b > U c For sector 1, the set of three-phase voltage-source converter subsystems that meet the system stability control requirements is as follows: ; 2) Phase voltage of three-phase AC side U b > U a ≥ U c For sector 2, the set of three-phase voltage-source converter subsystems that meet the system stability control requirements is as follows: ; 3) Phase voltage on the three-phase AC side U b ≥ U c > U a For sector 3, the set of three-phase voltage-source converter subsystems that meet the system stability control requirements is as follows: ; 4) Phase voltage on the three-phase AC side U c > U b ≥ U a For sector 4, the corresponding three-phase voltage-source converter subsystem combination that meets the system stability control requirements is as follows: ; 5) Phase voltage on the three-phase AC side U c ≥ U a > U b For sector 5, the corresponding three-phase voltage-source converter subsystem combination that meets the system stability control requirements is as follows: ; 6) Three-phase AC phase voltage U a > U c ≥ U b For sector 6, the corresponding three-phase voltage-source converter subsystem combination that meets the system stability control requirements is as follows: .

4. The three-phase converter switching control method based on dwell time constraints according to claim 3, wherein step 3 is specifically performed as follows: Solve for the set of subsystems within the corresponding 6 sectors The switching matrix A corresponding to the four subsystems (j=1,…,6) p convex combination matrix A λj j=1,…,6 p =1,…,8, specifically represented as: For sector 1, the subsystem set is as follows: Therefore, there is (3) In formula (3) For sector 2, the subsystem set is as follows: Therefore, there is (4) For sector 3, the subsystem set is as follows: Therefore, there is (5) For sector 4, the subsystem set is as follows: Therefore, there is (6) For sector 5, the subsystem set is as follows: Therefore, there is (7) For sector 6, the subsystem set is as follows: Therefore, there is (8) λ 1, λ 2, λ 3, λ 4 is a convex combination function, and its value should satisfy... λ 1+ λ 2+ λ 3+ λ 4 = 1.

5. The three-phase converter switching control method based on dwell time constraints according to claim 4, characterized in that, Step 5 specifically includes: Design the dwell time for each subsystem. T Duration of stay T Specifically defined as: (11) in (12) (13) in, , , The first k The error between the sampled value and the expected value of the AC three-phase current of the three-phase voltage source converter in each control cycle; , , The first k The sampled values ​​of the three-phase AC current of the three-phase voltage source converter in each control cycle; , , The first k The sampled values ​​of the three-phase AC voltage of the three-phase voltage source converter in each control cycle; For the first k The sampled value of the DC-side voltage of the three-phase voltage source converter in each control cycle. For the first k DC-side voltage error value of the three-phase voltage source converter in each control cycle.

6. The three-phase converter switching control method based on dwell time constraints according to claim 5, characterized in that, In step 6, the specific control can be obtained by comparing the desired dwell time T with the carrier wave.

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