A back-to-back multi-port converter predictive control method based on vector decomposition

Abstract

This invention discloses a predictive control method for back-to-back multiport converters based on vector decomposition. First, it obtains the stator current reference on the machine side, the capacitor voltage reference on the grid side, and the battery port power references on both the machine side and the grid side. Then, it equates the back-to-back multiport converter to a back-to-back two-level converter, obtaining simplified basic voltage vectors for machine-side and grid-side control. Next, it establishes predictive models for the machine-side stator current and the grid-side inductor current, and further establishes loss functions for machine-side and grid-side control. By optimizing the loss functions, it obtains the optimal basic voltage vectors and their durations on the machine side and grid side, respectively, and then synthesizes the desired voltage vectors on the machine side and grid side. Finally, it equates the back-to-back multiport converter to four virtual two-level converters associated with the DC port, and decomposes the output voltage vectors of the four virtual two-level converters according to the calculated scaling factor, thus obtaining the switching sequence of the back-to-back multiport converter.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and more specifically, relates to a predictive control method for back-to-back multiport converters based on vector decomposition. Background Technology

[0002] Wind-storage nanogrids have become an important form of achieving stable and reliable power supply in remote areas due to their advantages in smoothing wind power generation fluctuations and providing inertia support. As a key enabling device for wind-storage nanogrids, existing power electronic converters mostly adopt a bus structure, connecting the energy storage battery to the DC bus through an additional DC / DC converter to achieve wind-storage integration. Although this achieves relative decoupling in control, the introduction of an additional DC / DC converter significantly increases the system's size, weight, and cost. Furthermore, multi-stage energy conversion leads to additional power losses, thereby reducing the overall system conversion efficiency. In contrast, back-to-back multi-port converters can directly integrate energy storage batteries through additional DC ports, thus avoiding the use of an additional DC / DC converter. This not only reduces system cost but also improves system power density and conversion efficiency.

[0003] However, due to the direct integration of energy storage batteries, back-to-back multiport converters exhibit time-varying energy storage port voltages. This means that control of the AC generator and grid side needs to be implemented under unbalanced port voltages. Furthermore, with DC port power regulation simultaneously affected by both the generator-side and grid-side converters, this topology requires simultaneous DC bus voltage regulation and energy storage port power control. Therefore, a back-to-back multiport converter control method that can adapt to unbalanced port voltage conditions and simultaneously achieve multiple system control objectives is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a predictive control method for back-to-back multi-port converters based on vector decomposition. This method can not only achieve stator current control of AC generators and voltage and current control on the grid side under unbalanced port voltages, but also achieve flexible DC bus voltage control and energy storage port power control, enabling the system to operate stably in multiple working modes and achieve good adaptability to various operating conditions.

[0005] To achieve the above-mentioned objectives, the present invention provides a predictive control method for back-to-back multiport converters based on vector decomposition, characterized by comprising the following steps:

[0006] S1. Obtain reference value: Obtain the stator current reference value on the turbine side through the wind power maximum power point tracking module. The grid-side capacitor voltage reference is obtained through the active power control and reactive power control modules of the AC measurement system. The grid-side battery port power reference is obtained based on the DC bus voltage and grid frequency. The power reference at the engine-side battery port is obtained based on the battery's state of charge. Among them, the generator side is referred to as the generator side, and the grid side is referred to as the grid side;

[0007] S2. Perform equivalent two-level modeling on the back-to-back multi-port converter to obtain the basic voltage vector for machine-side and grid-side control.

[0008] S3. Establish prediction models for the stator current on the machine side and the inductor current on the grid side, and then establish the loss function for machine-side control. Loss function of network-side control Then, the optimal basic voltage vector is obtained by minimizing the loss function, and the duration of the optimal basic voltage vector is calculated. The desired voltage vector on the generator side is then synthesized from this result. and the desired voltage vector on the grid side ;

[0009] S4. Decouple the back-to-back multi-port converters into four two-level sub-converters; calculate the scaling factor of the desired voltage vector decomposition based on the total power and the power reference of the battery ports on both sides. , The output voltage vectors of the four virtual two-level converters are calculated respectively. , , , Then, the duty cycle of each phase of each virtual two-level converter is calculated based on the output voltage vector.

[0010] S5. Generate modulation waveforms for the duty cycles of each phase of each sub-converter, and then compare the amplitude of the modulation waveform with that of the triangular carrier wave within one switching cycle to generate a pulse sequence for the back-to-back multi-port converter, thereby controlling the switching action of each bridge arm.

[0011] The objective of this invention is achieved as follows:

[0012] This invention presents a predictive control method for back-to-back multiport converters based on vector decomposition. First, it obtains reference values ​​for the stator current on the machine side, the capacitor voltage on the grid side, and the battery port power on both the machine and grid sides. Then, it equates the back-to-back multiport converter to a back-to-back two-level converter, obtaining simplified basic voltage vectors for machine and grid side control. Next, it establishes predictive models for the stator current on the machine side and the inductor current on the grid side, and subsequently establishes loss functions for machine and grid side control. By optimizing the loss functions, it obtains the optimal basic voltage vectors and their durations on the machine and grid sides, respectively, and then synthesizes the desired voltage vectors on both sides. Finally, it equates the back-to-back multiport converter to four virtual two-level converters associated with the DC port, and decomposes the output voltage vectors of the four virtual two-level converters based on the calculated scaling factor, thus obtaining the switching sequence of the back-to-back multiport converter.

[0013] Meanwhile, the back-to-back multiport converter predictive control method based on vector decomposition of the present invention also has the following beneficial effects:

[0014] (1) Connecting the energy storage battery directly to the additional DC port provided by the back-to-back multi-port converter eliminates the need for an additional DC-DC converter, thereby reducing the weight, volume and cost of the entire system and improving conversion efficiency.

[0015] (2) In view of the inherent multi-control objectives and their coupling characteristics of back-to-back multi-port converters, this invention proposes a predictive control method for back-to-back multi-port converters based on vector decomposition. While ensuring the control of the machine side and grid side under unbalanced port voltage, it also realizes DC bus voltage regulation and energy storage port power control through flexible system power flow control.

[0016] (3) The back-to-back multi-port converter predictive control method based on vector decomposition of the present invention avoids the complex structure and time-consuming parameter tuning process brought about by traditional multiple linear controllers, and improves the dynamic response speed of the system. Attached Figure Description

[0017] Figure 1 This is a simplified circuit diagram of a back-to-back multi-port converter connecting a wind-storage nanogrid;

[0018] Figure 2 This is a schematic diagram of the power flow path of the back-to-back multi-port converters connecting the wind-storage nanogrid;

[0019] Figure 3 This is a schematic diagram of the predictive control principle of a back-to-back multiport converter based on vector decomposition according to the present invention.

[0020] Figure 4 This is a schematic diagram of the equivalent two-level model of a back-to-back multi-port converter;

[0021] Figure 5 This is a schematic diagram of a multi-port converter decomposed into a two-level sub-converter;

[0022] Figure 6 This is a steady-state experimental diagram of a wind-storage nanogrid;

[0023] Figure 7 This is a dynamic experimental diagram of a wind-storage nanogrid connected to a grid under sudden power fluctuations. Detailed Implementation

[0024] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0025] Example

[0026] Figure 1 This is a simplified circuit diagram of a back-to-back multi-port converter connecting a wind-storage nanogrid.

[0027] In this embodiment, as Figure 1 As shown, the wind-storage nanogrid based on back-to-back multi-port converters is characterized by comprising: a wind turbine 1, a permanent magnet synchronous generator 2, a turbine-side multi-port converter 3, a DC bus capacitor 4, an energy storage battery 5, a grid-side multi-port converter 6, a filter 7, and a load 8.

[0028] In this embodiment, as Figure 1 As shown, the topology of the back-to-back multi-port converter is an improvement on the back-to-back cascaded topology of two diode-clamped (NPC) three-level converters. On the DC side, the positive and negative terminals of the back-to-back cascaded multi-port converters are connected to a DC capacitor, while an energy storage battery is connected between the neutral and ground lines. On the AC side, due to the back-to-back cascaded structure, the AC side has two independent three-phase AC ports, which are connected to the generator and the load, respectively.

[0029] from Figure 2 As can be seen, the power flow path from the energy storage battery to the generator and load reduces the intermediate DC / DC converter compared to traditional back-to-back converters. This not only reduces the system cost but also improves the system's power density and conversion efficiency.

[0030] The following is combined Figure 3 This invention provides a detailed description of a predictive control method for back-to-back multiport converters based on vector decomposition, specifically including the following steps:

[0031] S1. Obtain reference value: Obtain the stator current reference value on the turbine side through the wind power maximum power point tracking module. The grid-side capacitor voltage reference is obtained through the active power control and reactive power control modules of the AC measurement system. The grid-side battery port power reference is obtained based on the DC bus voltage and grid frequency. The power reference at the engine-side battery port is obtained based on the battery's state of charge. Among them, the generator side is referred to as the generator side, and the grid side is referred to as the grid side;

[0032] S1.1 Acquire the DC bus voltage of the back-to-back multi-port converter Energy storage battery voltage Three-phase current on the machine side Three-phase inductor current on the grid side Three-phase capacitor voltage on the grid side and the three-phase current of the grid-side load , Indicates three phases;

[0033] S1.2, The generator speed is acquired through an encoder. and angle ,Will The stator current reference is obtained by sending it to the maximum power point tracking module. ;Will Send in The coordinate transformation unit obtains the stator current measurement value in the rotating coordinate system. ;Will Send in The coordinate transformation unit obtains the stator current measurement value in the stationary coordinate system. ;

[0034] In this embodiment, Coordinate transformation unit and The coordinate transformation units are as follows:

[0035] , ;

[0036] S1.3, will , , Send in separately The coordinate transformation unit obtains the inductor current in the stationary coordinate system. Grid-side capacitor voltage Grid-side load current Then , The active power on the grid side is obtained by sending it into the grid-side power calculation module. reactive power ;Will , Compared with the given grid-side active power reference Reactive power reference Together, they are fed into the active and reactive power control module to obtain the grid-side capacitor voltage reference. Reference angle and frequency deviation ;

[0037] S1.4, will With a given DC bus voltage reference The difference is fed into the PI control module to obtain the DC bus output power. ; frequency deviation Power is obtained by sending it to the PD control module. ; grid-side power reference and , Subtract the values ​​and feed them into the limiting module to obtain the grid-side energy storage battery port power reference. The SoC of the energy storage battery is sent to the battery energy management module to obtain the power reference of the battery port on the aircraft side. .

[0038] S2. Perform equivalent two-level modeling on the back-to-back multi-port converter to obtain the basic voltage vector for machine-side and grid-side control.

[0039] S2.1. Treat back-to-back multiport converters as having ideal DC voltage. For a two-level back-to-back converter, establish an equivalent two-level vector model, such as... Figure 4 As shown, this can reduce the number of voltage vector traversals and reduce the amount of computation.

[0040] S2.2 In the established equivalent two-level vector model, the simplified machine-side voltage vector is expressed as: The simplified grid-side voltage vector is expressed as .

[0041] S3. Establish prediction models for the stator current on the machine side and the inductor current on the grid side, and then establish the loss function for machine-side control. Loss function of network-side control Then, the optimal basic voltage vector is obtained by minimizing the loss function, and the duration of the optimal basic voltage vector is calculated. The desired voltage vector on the generator side is then synthesized from this result. and the desired voltage vector on the grid side ;

[0042] S3.1 Establish a prediction model for the machine-side stator current:

[0043] ;

[0044] in, Indicates the first Predicted value of machine-side stator current at time [time]. Indicates the current moment. This indicates the output voltage of the multi-port converter on the generator side. Indicates the system sampling time. This represents the parasitic resistance on the generator stator inductance. Let Re() represent the stator inductance of the generator, and Im() represent the real part of the variable. express The speed of the generator at any given time. Indicates stator flux linkage;

[0045] S3.2 Establish a prediction model for grid-side inductor current:

[0046] ;

[0047] ;

[0048] in, This indicates a reference value for the grid-side inductor current. Indicates the first Predicted value of grid-side inductor current at time t. This indicates the output voltage of the grid-side multi-port converter. This represents the parasitic resistance on the grid-side inductor. Indicates the grid-side inductance. Indicates grid-side capacitance. Indicates the grid-side capacitor voltage reference. This indicates the measured value of the grid-side capacitor voltage;

[0049] S3.3 Establish the loss function for machine-side control Loss function of network-side control ;

[0050] ;

[0051] ;

[0052] S3.4, Vector the machine-side voltage Substitute them sequentially into the machine-side stator current prediction equation to replace The first voltage vector under different voltage vectors was obtained. The predicted value of the machine-side stator current at time 1, then substituted into... Iterate through its current loss function values ​​and select those that make The smallest two adjacent voltage vectors on the machine side are denoted as and ;

[0053] grid-side voltage vector Substitute them sequentially into the grid-side inductor current prediction equation to replace The first voltage vector under different voltage vectors was obtained. The predicted value of the grid-side inductor current at time 1 is then substituted into... Iterate through its current loss function values ​​and select those that make The two smallest adjacent grid-side voltage vectors are denoted as and ;

[0054] S3.5, Calculation and and the current derivative under zero vector action :

[0055] ;

[0056] calculate and and the current derivative under zero vector action ;

[0057] ;

[0058] S3.6 Calculate the duration of action of each vector;

[0059] definition Substitute it into For the loss function Find the partial derivative of the vector action time and set it to zero, i.e. The voltage vector is obtained. and Duration of action ;

[0060] definition Substitute it into For the loss function Find the partial derivative of the vector action time and set it to zero, i.e. The voltage vector is obtained. and Duration of action ;

[0061] S3.7, Expected reference vectors on the synthesizer side and the mesh side .

[0062] S4. Decouple the back-to-back multi-port converters into four two-level sub-converters; calculate the scaling factor of the desired voltage vector decomposition based on the total power and the power reference of the battery ports on both sides. , The output voltage vectors of the four virtual two-level converters are calculated respectively. , , , Then, the duty cycle of each phase of each virtual two-level converter is calculated based on the output voltage vector.

[0063] S4.1, such as Figure 5 As shown, the multi-port converters on the machine side and the grid side are decomposed into two two-level sub-converters 1 and 2, respectively;

[0064] The decomposition coefficients of the network-side and machine-side expected reference vectors are defined as follows: Then the reference vector corresponding to generator-side sub-converter 1 is expressed as: The reference vector corresponding to generator-side sub-converter 2 is represented as: The reference vector corresponding to grid-side sub-converter 1 is represented as: The reference vector corresponding to grid-side sub-converter 2 is ;

[0065] S4.2, Total power on the computer side Calculate the total power on the network side. Then, the decomposition factors are obtained. , This allows us to obtain the reference vectors corresponding to each sub-converter;

[0066] in, Indicates the stator current on the machine side The conjugate value, Indicates grid-side load current The conjugate value;

[0067] S4.3 Since the reference vector angles corresponding to the two sub-converters on the machine side are the same, and the reference vector angles corresponding to the two sub-converters on the grid side are the same, the two sub-converters on the machine side can be divided into six sectors S1-S6, and the two sub-converters on the grid side can be divided into six sectors S7-S12.

[0068] , ;

[0069] S4.4 Define the desired voltage vectors of the machine-side sub-converters. The volt-second balance equations for each sector are:

[0070] First sector S1:

[0071] , ;

[0072] Second sector S2:

[0073] , ;

[0074] Third sector S3:

[0075] , ;

[0076] Sector 4:

[0077] , ;

[0078] Sector 5 (S5):

[0079] , ;

[0080] Sector 6:

[0081] , ;

[0082] in, , , , , , , It is the machine-side sub-converter 1 basic vector , , , , , and The length of stay , , , , , The basic voltage vector of the machine-side sub-converter 2 , , , , and The length of stay , and The duty cycle of each phase of the generator-side sub-converter 1 is given. , and The duty cycle of each phase of the generator-side sub-converter 2;

[0083] S4.4 Define the desired voltage vectors of the grid-side sub-converters. The volt-second balance equations for each sector are:

[0084] Sector 7:

[0085] , ;

[0086] Second sector S8:

[0087] , ;

[0088] Third sector S9:

[0089] , ;

[0090] Fourth sector S10:

[0091] , ;

[0092] Fifth sector S11:

[0093] , ;

[0094] Sector 6, S12:

[0095] , ;

[0096] in, , , , , , , It is the basic vector of the grid-side sub-converter 1. , , , , , and The length of stay , , , , , It is the basic voltage vector of the grid-side sub-converter 2. , , , , and The length of stay , and The duty cycle of each phase of grid-side sub-converter 1, , and The duty cycle of each phase of grid-side sub-converter 2;

[0097] S4.5, according to Determine the sectors where the machine-side sub-converter and the grid-side sub-converter are located, and then solve the volt-second balance equations corresponding to the sectors to obtain the phase duty cycles of each virtual two-level converter.

[0098] S5. Generate modulation waveforms for the duty cycles of each phase of each sub-converter, and then compare the amplitude of the modulation waveform with that of the triangular carrier wave within one switching cycle to generate a pulse sequence for the back-to-back multi-port converter, thereby controlling the switching action of each bridge arm.

[0099] This embodiment will be described with reference to examples, such as... Figures 6-7 As shown. Reference voltage of the DC bus. = 240V, the voltage of the bidirectional DC source simulating the energy storage battery is = 100V, grid-side active power reference is =500W, reactive power reference is =0Var, the reference stator current on the machine side is 8A. Figure 6 The steady-state performance of the back-to-back multiport converter under these experimental conditions was demonstrated by observing the machine-side rotational speed. Stator current of phase a on the machine side Phase a capacitor voltage on the grid side Grid-side phase a load current It can be seen that under the predictive control scheme proposed in this embodiment, the back-to-back multi-port converter can achieve regulation of the machine-side current, construction of the grid-side capacitor voltage, and simultaneous realization of DC bus voltage under unbalanced port voltage. and energy storage battery power The adjustment.

[0100] like Figure 7 As shown, when the grid-side power In the event of sudden changes, the system can quickly adjust the power at the energy storage battery port. This ensures the supply of power to the grid side, verifying the dynamic response speed of the proposed predictive control scheme in achieving power regulation. Simultaneously, the stator current on camera side... This process remains unaffected, which verifies that the proposed scheme achieves decoupled control for different control objectives.

[0101] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A predictive control method for back-to-back multiport converters based on vector decomposition, characterized in that, Includes the following steps: S1. Obtain reference value: Obtain the stator current reference value on the turbine side through the wind power maximum power point tracking module. The grid-side capacitor voltage reference is obtained through the active and reactive power control modules on the AC side. The grid-side battery port power reference is obtained based on the DC bus voltage and grid frequency. The power reference at the engine-side battery port is obtained based on the battery's state of charge. Among them, the generator side is referred to as the generator side, and the grid side is referred to as the grid side; S2. Perform equivalent two-level modeling on the back-to-back multi-port converter to obtain the basic voltage vector for machine-side and grid-side control. S3. Establish prediction models for the stator current on the machine side and the inductor current on the grid side, and then establish the loss function for machine-side control. Loss function of network-side control Then, the optimal basic voltage vector is obtained by minimizing the loss function, and the duration of the optimal basic voltage vector is calculated. The desired voltage vector on the generator side is then synthesized from this result. and the desired voltage vector on the grid side ; S4. Decouple the back-to-back multi-port converters into four two-level sub-converters; calculate the scaling factor of the desired voltage vector decomposition based on the total power and the power reference of the battery ports on both sides. , The output voltage vectors of the four virtual two-level converters are calculated respectively. , , , Then, the duty cycle of each phase of each virtual two-level converter is calculated based on the output voltage vector. S5. Generate modulation waveforms for the duty cycles of each phase of each sub-converter, and then compare the amplitude of the modulation waveform with that of the triangular carrier wave within one switching cycle to generate a pulse sequence for the back-to-back multi-port converter, thereby controlling the switching action of each bridge arm.

2. The predictive control method for back-to-back multiport converters based on vector decomposition according to claim 1, characterized in that, Step S1 specifically includes: S1.1 Acquire the DC bus voltage of the back-to-back multi-port converter Energy storage battery voltage Three-phase current on the machine side Three-phase inductor current on the grid side Three-phase capacitor voltage on the grid side and the three-phase current of the grid-side load , Indicates three phases; S1.2, The generator speed is acquired through an encoder. and angle ,Will The stator current reference is obtained by sending it to the maximum power point tracking module. ;Will Send in The coordinate transformation unit obtains the stator current measurement value in the rotating coordinate system. ;Will Send in The coordinate transformation unit obtains the stator current measurement value in the stationary coordinate system. ; S1.3, will , , Send in separately The coordinate transformation unit obtains the inductor current in the stationary coordinate system. Grid-side capacitor voltage Grid-side load current Then , The active power on the grid side is obtained by sending it into the grid-side power calculation module. reactive power ;Will , Compared with the given grid-side active power reference Reactive power reference Together, they are fed into the active and reactive power control module to obtain the grid-side capacitor voltage reference. Reference angle and frequency deviation ; S1.4, will With a given DC bus voltage reference The difference is fed into the PI control module to obtain the DC bus output power. ; frequency deviation Power is obtained by sending it to the PD control module. ; grid-side power reference and , Subtract the values ​​and feed them into the limiting module to obtain the grid-side energy storage battery port power reference. The SoC of the energy storage battery is sent to the battery energy management module to obtain the power reference of the battery port on the aircraft side. .

3. The predictive control method for back-to-back multiport converters based on vector decomposition according to claim 1, characterized in that, Step S2 specifically includes: S2.

1. Treat back-to-back multiport converters as having ideal DC voltage. For a two-level back-to-back converter, establish an equivalent two-level vector model; S2.2 In the established equivalent two-level vector model, the simplified machine-side voltage vector is expressed as: The simplified grid-side voltage vector representation is as follows: .

4. The predictive control method for back-to-back multiport converters based on vector decomposition according to claim 1, characterized in that, Step S3 specifically includes: S3.1 Establish a prediction model for the machine-side stator current: ； in, Indicates the first Predicted value of machine-side stator current at time [time]. Indicates the current moment. This indicates the output voltage of the multi-port converter on the generator side. Indicates the system sampling time. This represents the parasitic resistance on the generator stator inductance. Let Re() represent the stator inductance of the generator, and Im() represent the real part of the variable. express The speed of the generator at any given time. Indicates stator flux linkage; S3.2 Establish a prediction model for grid-side inductor current: ； ； in, This indicates a reference value for the grid-side inductor current. Indicates the first Predicted value of grid-side inductor current at time t. This indicates the output voltage of the grid-side multi-port converter. This represents the parasitic resistance on the grid-side inductor. Indicates the grid-side inductance. Indicates grid-side capacitance. Indicates the grid-side capacitor voltage reference. This indicates the measured value of the grid-side capacitor voltage; S3.3 Establish the loss function for machine-side control Loss function of network-side control ; ； ； S3.4, Vector the machine-side voltage Substitute them sequentially into the machine-side stator current prediction equation to replace The first voltage vector under different voltage vectors was obtained. The predicted value of the machine-side stator current at time 1, then substituted into... Iterate through its current loss function values ​​and select those that make The smallest two adjacent voltage vectors on the machine side are denoted as and ; grid-side voltage vector Substitute them sequentially into the grid-side inductor current prediction equation and replace them. The first voltage vector under different voltage vectors was obtained. The predicted value of the grid-side inductor current at time 1 is then substituted into... Iterate through its current loss function values ​​and select those that make The two smallest adjacent grid-side voltage vectors are denoted as and ; S3.5, Calculation and and the current derivative under zero vector action : ； calculate and and the current derivative under zero vector action ; ； S3.6 Calculate the duration of action of each vector; definition Substitute it into For the loss function Find the partial derivative of the vector action time and set it to zero, i.e. The voltage vector is obtained. and Duration of action ; definition Substitute it into For the loss function Find the partial derivative of the vector action time and set it to zero, i.e. The voltage vector is obtained. and Duration of action ; S3.7, Expected reference vectors on the synthesizer side and the mesh side .

5. The predictive control method for back-to-back multiport converters based on vector decomposition according to claim 1, characterized in that, Step S4 specifically includes: S4.1 Decompose the multi-port converters on the machine side and the grid side into two two-level sub-converters 1 and 2 respectively; The decomposition coefficients of the network-side and machine-side expected reference vectors are defined as follows: Then the reference vector corresponding to generator-side sub-converter 1 is expressed as: The reference vector corresponding to generator-side sub-converter 2 is represented as: The reference vector corresponding to grid-side sub-converter 1 is represented as: The reference vector corresponding to grid-side sub-converter 2 is ; S4.2, Total power on the computer side Calculate the total power on the network side. Then, the decomposition factors are obtained. , This allows us to obtain the reference vectors corresponding to each sub-converter; S4.3 Since the reference vector angles of the two sub-converters on the machine side are the same, and the reference vector angles of the two sub-converters on the grid side are the same, the two sub-converters on the machine side can be divided into six sectors S1-S6, and the two sub-converters on the grid side can be divided into six sectors S7-S12. ， ； S4.4 Define the desired voltage vectors of the machine-side sub-converters. The volt-second balance equations for each sector are: First sector S1: ， ； Second sector S2: ， ； Third sector S3: ， ； Sector 4: ， ； Sector 5 (S5): ， ； Sector 6: ， ； in, , , , , , , It is the machine-side sub-converter 1 basic vector , , , , , and The length of stay , , , , , The basic voltage vector of the machine-side sub-converter 2 , , , , and The length of stay , and The duty cycle of each phase of the sub-converter 1 on the machine side is... , and The duty cycle of each phase of the sub-converter 2 on the machine side; S4.4 Define the desired voltage vectors of the grid-side sub-converters. The volt-second balance equations for each sector are: Sector 7: ， ； Second sector S8: ， ； Third sector S9: ， ； Fourth sector S10: ， ； Fifth sector S11: ， ； Sector 6, S12: ， ； in, , , , , , , It is the basic vector of the grid-side sub-converter 1. , , , , , and The length of stay , , , , , It is the basic voltage vector of the grid-side sub-converter 2. , , , , and The length of stay , and The duty cycle of each phase of grid-side sub-converter 1, , and The duty cycle of each phase of grid-side sub-converter 2; S4.5, according to Determine the sectors where the machine-side sub-converter and the grid-side sub-converter are located, and then solve the volt-second balance equations corresponding to the sectors to obtain the phase duty cycles of each virtual two-level converter.

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