Wind power generation system integrated with energy storage and control method

Abstract

This invention discloses an integrated energy storage wind power generation system and control method. A power-speed curve provides a reference speed for the permanent magnet synchronous generator (PMSG). A multi-port converter on the motor side controls the active power generated by the PMSG and the power distribution between the DC bus port and the energy storage battery port. A multi-port converter on the grid side controls the DC bus voltage and the grid-connected active power. In this structure, the DC bus capacitor and the energy storage battery are directly connected to a back-to-back multi-port converter, improving the system's power density and energy conversion efficiency. Control on the motor side and the grid side enables power flow regulation among the PMSG, the grid, the energy storage battery, and the DC bus capacitor.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and more specifically, relates to an integrated energy storage wind power generation system and control method. Background Technology

[0002] Wind-storage integrated systems have attracted widespread attention due to their advantages in mitigating wind power generation fluctuations and enhancing grid support capabilities. Among these, the power electronic interface, as a core component of the wind-storage power generation system, is a decisive factor in its electrical performance, conversion efficiency, and grid-connected power quality. Currently, the power electronic interfaces of wind-storage integrated systems can be mainly divided into two categories: The first type directly connects the high-voltage battery to the DC bus of a back-to-back inverter. While ensuring conversion efficiency, this sacrifices the ability to regulate the DC bus voltage. The second type connects the energy storage to the DC bus via a DC-DC converter. Although this retains the adjustable DC bus voltage, the increased number of power conversion stages reduces conversion efficiency. Therefore, wind power systems urgently need a new integrated energy storage structure that can improve conversion efficiency while preserving the ability to regulate the DC bus voltage. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide an integrated energy storage wind power generation system and control method. Based on a multi-port converter, the DC bus capacitor and the energy storage battery are directly connected to the DC bus of the back-to-back multi-port converter as DC source ports. This not only retains the regulation capability of the DC bus voltage, but also eliminates the need for an additional DC-DC converter, thereby improving the power density and conversion efficiency of the entire system.

[0004] To achieve the above-mentioned objectives, this invention proposes an integrated energy storage wind power generation system, including a wind turbine, a permanent magnet synchronous generator, a motor-side multi-port converter, a DC bus capacitor, an energy storage battery, a grid-connected multi-port converter, a filter, and a power grid.

[0005] A control method for an integrated energy storage wind power generation system, characterized by comprising the following steps:

[0006] (1) Obtain the AC side voltage reference u of the motor-side multi-port converter in the stationary αβ coordinate system. mαβ Reference power of the energy storage battery required on the motor side and the power generation reference of permanent magnet synchronous generators

[0007] (2) Obtain the AC side reference voltage u of the grid-connected multi-port converter in the stationary αβ coordinate system. gαβ Reference power of energy storage battery required on the grid-connected side

[0008] (3) Based on the virtual two-level model, the three-phase duty cycle d on the motor side is generated by space vector synthesis of the reference voltage. mx The duty cycle d of the three phases on the grid-connected side gx x = a, b, c correspond to the three phases on the motor side or grid-connected side;

[0009] (4) Calculate the zero-sequence component d that needs to be injected into the modulation wave on the motor side. m0 And the zero-sequence component d that needs to be injected into the modulated wave on the grid-connected side. g0 ;

[0010] (5) The zero-sequence component d on the motor side m0 Injected three-phase duty cycle d mx This is then converted into the three-phase duty cycle d of the first and second switching transistors of each bridge arm in a practical three-level frame. mx1 With d mx2 ; The zero-sequence component d on the grid-connected side g0 Injected three-phase duty cycle d gx This is then converted into the three-phase duty cycle d of the first and second switching transistors of each bridge arm in a practical three-level frame. gx1 With d gx2 ;

[0011] (6) Set the three-phase duty cycle d on the motor side mx1 d mx2 Three-phase duty cycle d on the grid-connected side gx1 d gx2 The signal is compared with the carrier wave to generate the corresponding drive signal on the switch, which controls the active device to perform switching operation and output voltage and power.

[0012] The objective of this invention is achieved as follows:

[0013] This invention discloses an integrated energy storage wind power generation system and control method. A power-speed curve provides a reference speed for the permanent magnet synchronous generator (PMSG). A multi-port converter on the motor side controls the active power generated by the PMSG and the power distribution between the DC bus port and the energy storage battery port. A multi-port converter on the grid side controls the DC bus voltage and the grid-connected active power. In this structure, the DC bus capacitor and the energy storage battery are directly connected to back-to-back multi-port converters, improving the system's power density and energy conversion efficiency. Control on the motor side and the grid-connected side enables power flow regulation among the PMSG, the grid, the energy storage battery, and the DC bus capacitor.

[0014] Meanwhile, the wind power generation system and control method with integrated energy storage of the present invention also have the following beneficial effects:

[0015] (1) Based on the multi-port converter, the DC bus capacitor and energy storage battery are directly connected to the DC bus of the back-to-back inverter as DC source ports. This can maintain an adjustable DC bus voltage, eliminate the need for an additional DC-DC converter, reduce the weight, volume and cost of the entire system, and improve conversion efficiency.

[0016] (2) The control method proposed in this invention realizes the speed control and grid-connected current control of permanent magnet synchronous generator by adopting a virtual two-level model under the space vector framework. It simplifies the reference voltage vector synthesis under the condition of DC port voltage imbalance, and obtains the three-phase duty cycle based on the zero-sequence component injected by the reference power, thereby adjusting the power flow between the motor, the grid, the energy storage battery and the DC bus capacitor. Attached Figure Description

[0017] Figure 1 This is a simplified circuit diagram of a wind power generation system with integrated energy storage according to the present invention;

[0018] Figure 2 This is a schematic diagram of the overall control principle of a wind power generation system with integrated energy storage according to the present invention.

[0019] Figure 3 This is a schematic diagram of a virtual two-level model of a multi-port converter on the motor side;

[0020] Figure 4 This is a schematic diagram of a grid-connected multi-port converter viewed as a virtual two-level model;

[0021] Figure 5 Based on zero-order component d m0 A schematic diagram of the injected power distribution control scheme;

[0022] Figure 6 Based on zero-order component d g0 A schematic diagram of the injected power distribution control scheme;

[0023] Figure 7 This is a simulation operation diagram of the wind power generation system with integrated energy storage according to the present invention; 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] In this embodiment, as Figure 1As shown, the present invention provides an integrated energy storage wind power generation system, characterized in that it includes: a wind turbine 1, a permanent magnet synchronous generator 2, a motor-side multi-port converter 3, a DC bus capacitor 4, an energy storage battery 5, a grid-connected side multi-port converter 6, a filter 7, and a power grid 8.

[0027] The motor-side multi-port converter 3 includes a first bridge arm, a second bridge arm, and a third bridge arm; wherein the low-voltage DC ports of the first bridge arm, the second bridge arm, and the third bridge arm are connected to the energy storage battery 5, and their high-voltage DC ports are connected to the DC bus capacitor 4; the output terminals of the first bridge arm, the second bridge arm, and the third bridge arm are respectively connected to the permanent magnet synchronous generator 2.

[0028] The first bridge arm of the motor-side multiport converter 3 includes the first switching transistor S. ma1 Second switch S ma2 Third switching transistor Fourth switching transistor Its second bridge arm includes the fifth switching transistor S. mb1 The sixth switch S mb2 Seventh switch tube Eighth switching transistor Its third bridge arm includes the ninth switch S mc1 10th switch S mc2 Eleventh switch tube Twelfth switching transistor

[0029] Where S ma1 S mb1 S mc1 The collectors of all are connected to the positive terminal of DC bus capacitor 4; The emitter of the capacitor is connected to the negative terminal of the energy storage battery; the negative terminal of the DC bus capacitor 4 is connected to the positive terminal of the energy storage battery 5.

[0030] The output end of the wind turbine 1 is connected to the permanent magnet synchronous generator 2;

[0031] The grid-connected multi-port converter 6 includes a first bridge arm, a second bridge arm, and a third bridge arm; wherein the low-voltage DC ports of the first bridge arm, the second bridge arm, and the third bridge arm are connected to the energy storage battery 5, and their high-voltage DC ports are connected to the DC bus capacitor 4; the output terminals of the first bridge arm, the second bridge arm, and the third bridge arm are respectively connected to the filter 7.

[0032] The first arm of the grid-connected multiport converter 6 includes a first switching transistor S. ga1 Second switch S ga2 Third switching transistor Fourth switching transistor Its second bridge arm includes the fifth switching transistor S. gb1 The sixth switch Sgb2 Seventh switch tube Eighth switching transistor Its third bridge arm includes the ninth switch S gc1 10th switch S gc2 Eleventh switch tube Twelfth switching transistor

[0033] Where S ga1 S gb1 S gc1 The collectors of all are connected to the positive terminal of DC bus capacitor 4; The emitter is connected to the negative terminal of the energy storage battery 5;

[0034] The input terminals of the filter 7 are respectively connected to S ga2 S gb2 S gc2 The emitter is connected, and its output terminal is connected to the power grid 8.

[0035] In this embodiment, the present invention also provides a control method for a wind power generation system with integrated energy storage, the control principle of which is as follows: Figure 2 As shown, the specific steps include:

[0036] (1) Obtain the AC side voltage reference u of the motor-side multi-port converter in the stationary αβ coordinate system. mαβ Reference power of the energy storage battery required on the motor side and the power generation reference of permanent magnet synchronous generators

[0037] (1.1) Based on the power demand P of the power grid gref Maximum power generation of wind turbines And the state of charge (SOC) of the energy storage, and obtain the power reference of the permanent magnet synchronous generator through energy management strategies. Power reference with motor-side energy storage battery port

[0038] (1.2) Based on the obtained power reference of the permanent magnet synchronous generator By combining the power-speed curve provided by the manufacturer, the reference speed value of the permanent magnet synchronous generator can be obtained.

[0039] (1.3) The rotational speed ω of the permanent magnet synchronous generator is obtained through a position encoder. e ,Will With the speed ω of the permanent magnet synchronous generator e The difference is used as input, and the motor-side q-axis reference current is obtained through the output of the speed PI control module.

[0040] (1.4) The position angle θ of the three-phase AC motor is obtained by the position encoder. m This will further reduce the three-phase current i on the motor side. mabc The q-axis current i is obtained through the T1 coordinate transformation unit. mq With d-axis current i md In this embodiment, the formula for the T1 coordinate transformation unit is:

[0041]

[0042] (1.5) With the q-axis current i on the motor side mq The difference is used as input, and the q-axis component u of the motor-side reference voltage is obtained through the output of the q-axis PI control module. mq ;

[0043] (1.6) Set the q-axis reference current on the motor side. With the motor side d-axis current i md The difference is used as input, and the d-axis component u of the motor-side reference voltage is obtained through the output of the d-axis PI control module. md Additionally, the d-axis reference current Set to 0;

[0044] (1.7), will u mq u md As the input to the T2 coordinate transformation unit, the output is converted into the motor-side reference voltage u in the αβ axis coordinate system. mαβ ;

[0045] In this embodiment, the formula for the T2 coordinate transformation unit is:

[0046]

[0047] (2) Obtain the AC side reference voltage u of the grid-connected multi-port converter in the stationary αβ coordinate system. gαβ Reference power of energy storage battery required on the grid-connected side

[0048] (2.1) The phase angle θ of the fundamental component of the grid voltage is obtained through the phase-locked loop output. g The three-phase grid voltage e abc With θ g The d-axis grid voltage component e is obtained through the output of the T1 coordinate transformation unit. d With q-axis grid voltage component e q ;

[0049] (2.2) P gref The reactive power demand Q of the power grid gref ed With e q As input to the grid-connected side reference current calculation module, the d-axis reference current of the grid-connected side is obtained from the output. With q-axis reference current

[0050] (2.3) Set the d-axis reference current With the d-axis current i on the grid-connected side gd The difference is used as the input to the d-axis PI control module, and the output is the d-axis component u of the motor-side reference voltage. gd ;

[0051] (2.4) Set the q-axis reference current With grid-connected side q-axis current i gq The difference is used as the input to the q-axis PI control module, and the output is the q-axis component u of the motor-side reference voltage. gq ;

[0052] In this embodiment, i gd with i gq The three-phase current i on the grid-connected side gabc With θ g The output is obtained through the T2 coordinate transformation unit;

[0053] (2.5), will u gd with u gq As the input to the T1 coordinate transformation unit, the output is converted into the grid-connected side reference voltage u in the αβ axis coordinate system. gαβ ;

[0054] (2.6) Set the total reference voltage of the DC port to... Total voltage u at DC port d The difference is used as the input of the voltage PI module, and its output is compared with P. gref Subtract to obtain the reference power of the energy storage battery required on the grid-connected side.

[0055] (3) Based on the virtual two-level model, the three-phase duty cycle d on the motor side is generated by space vector synthesis of the reference voltage. mx The duty cycle d of the three phases on the grid-connected side gx x = a, b, c correspond to the three phases on the motor side or grid-connected side;

[0056] (3.1) Obtain the three-phase duty cycle d on the motor side mx ;

[0057] (3.1.1) In this embodiment, the motor-side multi-port converter is considered to have an ideal DC voltage u. d A two-level converter is used to establish a virtual two-level converter model, such as... Figure 3As shown, this simplifies the reference vector synthesis under unbalanced DC port voltage, reducing the computational load. Then, based on a two-level model, it is divided into six sectors S1 to S6, as follows:

[0058]

[0059] (3.1.2) Based on the position angle θ of the three-phase AC motor m Determine the reference voltage vector u mαβ Within the corresponding sector, two adjacent basic voltage vectors and the zero vector are selected to synthesize the reference voltage vector u. mαβ Then solve for the reference voltage vector u. mαβ The corresponding volt-second balance equation yields the three-phase duty cycle d on the motor side. mx ;

[0060] Wherein, the reference voltage vector u mαβ The volt-second balance equation corresponding to the sector is:

[0061] First sector:

[0062]

[0063] Second sector:

[0064]

[0065] Third sector:

[0066]

[0067] Fourth sector:

[0068]

[0069] Fifth sector:

[0070]

[0071] Sector 6:

[0072]

[0073] Among them, T s T7 is the sampling period, T1 is the duration of the zero vector, and T2 is the duration of V1 and V2 of two adjacent basic voltage vectors, respectively.

[0074] (3.2) Obtain the three-phase duty cycle d on the grid-connected side gx ;

[0075] (3.2.1) In this embodiment, the grid-connected multi-port converter is considered to have an ideal DC voltage u. dA two-level converter is used to establish a virtual two-level converter model, such as... Figure 4 As shown, this simplifies the reference vector synthesis under unbalanced DC port voltage, reducing the computational load. Then, based on a two-level model, it is divided into six sectors S7 to S12, as follows:

[0076]

[0077] (3.2.2) Based on the phase angle θ of the fundamental component of the grid voltage g Determine the reference voltage vector u gαβ Within the corresponding sector, two adjacent basic voltage vectors and the zero vector are selected to synthesize the reference voltage vector u. gαβ Then solve for the reference voltage vector u. gαβ The corresponding volt-second balance equation yields the three-phase duty cycle d on the grid-connected side. gx ;

[0078] Wherein, the reference voltage vector u gαβ The volt-second balance equation corresponding to the sector is:

[0079] Sector 7:

[0080]

[0081] Eighth sector:

[0082]

[0083] Ninth sector:

[0084]

[0085] Tenth sector:

[0086]

[0087] Eleventh sector:

[0088]

[0089] Twelfth sector:

[0090]

[0091] Among them, T s T9 is the sampling period, T3 is the duration of the zero vector, and T4 is the duration of V3 and V4 of two adjacent basic voltage vectors, respectively.

[0092] (4) Calculate the zero-sequence component d that needs to be injected into the modulation wave on the motor side. m0 And the zero-sequence component d that needs to be injected into the modulated wave on the grid-connected side. g0;

[0093] (4.1) Calculate the zero-sequence component d that needs to be injected into the modulation wave on the motor side. m0 ;

[0094] (4.1.1) Under the carrier frame, based on the three-phase duty cycle d on the motor side ma d mb d mc The size relationship is divided into 6 regions R1-R6;

[0095] Where, if d ma >d mb >d mc If so, it is divided into region R1;

[0096] If d mb >d ma >d mc If so, it is divided into region R2;

[0097] If d mb >d mc >d ma Then it is divided into region R3;

[0098] If d mc >d mb >d ma Then it is divided into region R4;

[0099] If d mc >d ma >d mb Then it is divided into region R5;

[0100] If d ma >d mc >d mb Then it is divided into region R6;

[0101] (4.1.2) The zero-sequence component d on the motor side m0 With three-phase duty cycle d ma d mb d mc Add them together to generate the three-phase duty cycle d′ after injecting the zero-sequence component. ma d′ mb d mc ;

[0102]

[0103] (4.1.3) Calculate the DC port voltage ratio:

[0104]

[0105] Among them, ub u is the port voltage of the energy storage battery. d This is the voltage at the bus capacitor port.

[0106] (4.1.4) The three-phase duty cycle waveform d′ generated according to step (4.1.2) ma d′ mb d′ mc Determine the location, and then within the corresponding area, follow the three-phase duty cycle waveform d′ ma d′ mb d′ mc Based on the relationship between the DC port voltage ratio ε and the required zero-sequence component d to be injected into the modulation wave on the motor side, the zero-sequence component d is calculated. m0 :

[0107] (4.1.4.1) When the three-phase duty cycle waveform d′ ma d′ mb d′ mc When the magnitude relationship is located in the first region R1, calculate the zero-sequence component d. m0 The process is as follows:

[0108] When d′ ma ≥d′ mb ≥ε≥d′ mc hour,

[0109] When d′ ma ≥ε>d′ mb ≥d′ mc hour,

[0110] When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up;

[0111] (4.1.4.2) When the three-phase duty cycle waveform d′ ma d′ mb d′ mc When the magnitude relationship is located in the first region R2, calculate the zero-sequence component d. m0 The process is as follows:

[0112] When d′ mb ≥d′ ma ≥ε>d′ mc hour,

[0113] When d′ mb ≥ε>d′ ma ≥d′ mc hour,

[0114] When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up;

[0115] (4.1.4.3) When the three-phase duty cycle waveform d′ ma d′ mb d′ mc When the magnitude relationship is located in the first region R3, calculate the zero-sequence component d. m0 The process is as follows:

[0116] When d′ mb ≥d′ mc ≥ε>d′ ma hour,

[0117] When d′ mb ≥ε>d′ mc ≥d′ ma hour,

[0118] When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up;

[0119] (4.1.4.4) When the three-phase duty cycle waveform d′ ma d′ mb d′ mc When the magnitude relationship is located in the first region R1, calculate the zero-sequence component d. m0 The process is as follows:

[0120] When d′ mc ≥d′ mb ≥ε>d′ ma hour,

[0121] When d′ mc ≥ε>d′ mb ≥d′ ma hour,

[0122] When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up;

[0123] (4.1.4.5) When the three-phase duty cycle waveform d′ ma d′ mb d′ mc When the magnitude relationship is located in the first region R5, calculate the zero-sequence component d. m0The process is as follows:

[0124] When d′ mc ≥d′ ma ≥ε>d′ mb hour,

[0125] When d′ mc ≥ε>d′ ma ≥d′ mb hour,

[0126] When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up;

[0127] (4.1.4.6) When the three-phase duty cycle waveform d′ ma d′ mb d′ mc When the magnitude relationship is located in the first region R6, calculate the zero-sequence component d. m0 The process is as follows:

[0128] When d′ ma ≥d′ mc ≥ε>d′ mb hour,

[0129] When d′ ma ≥ε>d′ mc ≥d′ mb hour,

[0130] When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up;

[0131] (4.2) Calculate the zero-sequence component d that needs to be injected into the modulation wave on the motor side. g0 ;

[0132] (4.2.1) Under the carrier frame, based on the three-phase duty cycle d on the grid-connected side ga d gb d gc The size relationship is divided into 6 regions R7-R12;

[0133] Where, if d ga >d gb >d gc Then it is divided into region R7;

[0134] If d gb >d ga >dgc Then it is divided into region R8;

[0135] If d gb >d gc >d ga Then it is divided into region R9;

[0136] If d gc >d gb >d ga Then it is divided into region R10;

[0137] If d gc >d ga >d gb Then it is divided into region R11;

[0138] If d ga >d gc >d gb Then it is divided into region R12;

[0139] (4.2.2) The zero-sequence component d on the grid-connected side g0 With three-phase duty cycle d ga d gb d gc Add them together to generate the three-phase duty cycle d′ after injecting the zero-sequence component. ga d′ gb d′ gc ;

[0140]

[0141] (4.2.3) Calculate the DC port voltage ratio:

[0142]

[0143] Among them, u b u is the port voltage of the energy storage battery. d This is the voltage at the bus capacitor port.

[0144] (4.2.4) The three-phase duty cycle waveform d′ generated according to step (4.2.2) ga d′ gb d′ gc Determine the location, and then within the corresponding area, follow the three-phase duty cycle waveform d′ ga d′ gb d′ gc Based on the relationship between the DC port voltage ratio ε and the required zero-sequence component d to be injected into the modulated wave on the grid-connected side, the zero-sequence component d is calculated. g0 :

[0145] (4.2.4.1) When the three-phase duty cycle waveform d′ga d′ gb d′ gc When the magnitude relationship is located in the first region R7, calculate the zero-sequence component d. g0 The process is as follows:

[0146] When d′ ga ≥d′ gb ≥ε≥d′ gc hour,

[0147] When d′ ga ≥ε>d′ gb ≥d′ gc hour,

[0148] When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up;

[0149] (4.2.4.2) When the three-phase duty cycle waveform d′ ga d′ gb d′ gc When the magnitude relationship is located in the first region R8, calculate the zero-sequence component d. g0 The process is as follows:

[0150] When d′ gb ≥d′ ga ≥ε>d′ gc hour,

[0151] When d′ gb ≥ε>d′ ga ≥d′ gc hour,

[0152] When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up;

[0153] (4.2.4.3) When the three-phase duty cycle waveform d′ ga d′ gb d′ gc When the magnitude relationship is located in the first region R9, calculate the zero-sequence component d. g0 The process is as follows:

[0154] When d′ gb ≥d′ gc ≥ε>d′ ga hour,

[0155] When d′ gb ≥ε>d′ gc ≥d′ ga hour,

[0156] When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up;

[0157] (4.2.4.4) When the three-phase duty cycle waveform d′ ga d′ gb d′ gc When the magnitude relationship is located in the first region R10, calculate the zero-sequence component d. g0 The process is as follows:

[0158] When d′ gc ≥d′ gb ≥ε>d′ ga hour,

[0159] When d′ mc ≥ε>d′ mb ≥d′ ma hour,

[0160] When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up;

[0161] (4.2.4.5) When the three-phase duty cycle waveform d′ ga d′ gb d′ gc When the magnitude relationship is located in the first region R11, calculate the zero-sequence component d. g0 The process is as follows:

[0162] When d′ gc ≥d′ ga ≥ε>d′ gb hour,

[0163] When d′ gc ≥ε>d′ ga ≥d′ gb hour,

[0164] When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up;

[0165] (4.2.4.6) When the three-phase duty cycle waveform d′ ga d′ gb d′ gc When the magnitude relationship is located in the first region R12, calculate the zero-sequence component d. g0 The process is as follows:

[0166] When d′ ga ≥d′ gc ≥ε>d′ gb hour,

[0167] When d′ ga ≥ε>d′ gc ≥d′ gb hour,

[0168] When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up.

[0169] (5) The zero-sequence component d on the motor side m0 Injected three-phase duty cycle d mx This is then converted into the three-phase duty cycle d of the first and second switching transistors of each bridge arm in a practical three-level frame. mx1 With d mx2 ; The zero-sequence component d on the grid-connected side g0 Injected three-phase duty cycle d gx This is then converted into the three-phase duty cycle d of the first and second switching transistors of each bridge arm in a practical three-level frame. gx1 With d gx2 ;

[0170] (5.1) Obtain the three-phase duty cycle d mx1 With d mx2 ;

[0171] (5.1.1) d m0 Injected three-phase duty cycle d mx Get d′ mx Then, the voltage is divided at the DC port voltage ratio ε to obtain the three-phase duty cycle d′ of the first and second switching transistors on each bridge arm of the virtual two-level frame. mx1 d′ mx2 :

[0172]

[0173] (5.1.2) d′ mx1 d′ mx2 Converted to the three-phase duty cycle d in a practical three-level frame mx1 dmx2 :

[0174]

[0175] (5.2) Obtain the three-phase duty cycle d gx1 With d gx2 ;

[0176] (5.2.1) For the grid-connected side, d g0 Injected three-phase duty cycle d gx Get d′ gx Then, the voltage is divided at the DC port voltage ratio ε to obtain the three-phase duty cycle d′ of the first and second switching transistors on each bridge arm of the virtual two-level frame. gx1 d′ gx2 :

[0177]

[0178] (5.2.2) d′ gx1 d′ gx2 Converted to the three-phase duty cycle d in a practical three-level frame gx1 d gx2 :

[0179]

[0180] In this embodiment, the three-phase duty cycle d′ mx1 d′ mx2 The splitting mechanism, such as Figure 5 As shown, it's easy to see that either the upper switch's duty cycle is clamped at 0, or the lower switch's duty cycle is clamped at 1. This indicates that the duty cycle waveform has discontinuous characteristics. Therefore, each phase switch operates only once per switching cycle. This optimizes the system's switching losses on top of the efficiency improvement brought by the single-stage structure, further improving the conversion efficiency. The three-phase duty cycle d after zero-sequence injection under the carrier framework is then used to further improve the conversion efficiency. mx1 d mx2 It enables intuitive power allocation, avoids complex trigonometric function calculations under the space vector framework, effectively reduces the computational burden, and improves the dynamic response of the system;

[0181] Furthermore, it should be emphasized that, since the power distribution control structures on the motor side and the grid-connected side are similar and the modulation schemes are the same, the three-phase duty cycle d′ on the grid-connected side is... gx1 d′ gx2 The splitting mechanism, such as Figure 6 As shown, the AC reference voltage u on the grid-connected side gαβ d calculated by the zero-sequence component module g0The space vector modulation based on the virtual two-level model is then converted into the three-phase duty cycle d of the grid-connected side under the actual three-level framework. gx1 d gx2 ;

[0182] (6) Set the three-phase duty cycle d on the motor side mx1 d mx2 Three-phase duty cycle d on the grid-connected side gx1 d gx2 It is compared with the carrier wave to generate the corresponding drive signal on the switching transistor, control the active device to perform switching operation, and output voltage and power;

[0183] (6.1) The three-phase duty cycle d on the motor side mx1 d mx2 Comparing with the carrier wave, the switching transistor S of the multi-port inverter on the motor side is generated. mx1 S mx2 , and The drive signal, where x = a, b, c represents the three phases of the motor, S mx1 S mx2 , and These are the four switching transistors on the corresponding motor side bridge arm, arranged sequentially from top to bottom.

[0184] (6.2) The duty cycle d of the three phases on the grid-connected side gx1 d gx2 Comparing with the carrier wave, the switching transistor S of the grid-connected multi-port inverter is generated. mx1 S mx2 , and The driving signal, where x = a, b, c represents the three phases connected to the grid, S mx1 S mx2 , and These are the four switching transistors, arranged sequentially from top to bottom, on the corresponding grid-connected side bridge arm.

[0185] This embodiment will be described with reference to examples, such as... Figure 7 As shown. The expected power output of the wind turbine is... The reference power of the machine-side energy storage port is DC bus voltage reference value is Matching the power demand P of the power grid gref =500W, Figure 7 The steady-state performance of the wind power generation system was demonstrated by observing the machine-side current i. mabc Total power P of wind turbine generators on the machine side in Power P flowing into the capacitor port from the machine side mh Power P flowing into the battery port from the machine sideml , grid-side current i gabc Power P flowing out of the capacitor port on the grid side gh Power P at the grid-side battery port gl Power P flowing out of the battery port from the grid side g As can be seen, under the control method proposed in this embodiment, the back-to-back wind power generation system can operate stably as expected. The sinusoidal current waveforms on the motor side and the grid-connected side prove that the proposed control method can achieve high power quality. Simultaneously, this control method can also achieve direct and flexible power allocation between the DC bus capacitor and the energy storage battery under conditions of DC-side port voltage imbalance. Furthermore, by adopting the back-to-back multi-port converter topology of this invention, the adjustable DC bus voltage is retained through an independent DC bus capacitor, and the energy storage battery is efficiently integrated in a single-stage manner through an additional port, achieving high power conversion efficiency for the integrated wind and energy storage system. The above results verify the feasibility and effectiveness of the proposed back-to-back multi-port converter topology and control method with integrated energy storage.

[0186] 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 wind power generation system with integrated energy storage, characterized in that, include: Wind turbine, permanent magnet synchronous generator, motor-side multiport converter, DC bus capacitor, energy storage battery, grid-connected multiport converter, filter, power grid; The motor-side multi-port converter includes a first bridge arm, a second bridge arm, and a third bridge arm; wherein, the low-voltage DC ports of the first bridge arm, the second bridge arm, and the third bridge arm are connected to the energy storage battery, and their high-voltage DC ports are connected to the DC bus capacitor; the output terminals of the first bridge arm, the second bridge arm, and the third bridge arm are respectively connected to the permanent magnet synchronous generator; The first bridge arm of the motor-side multiport converter includes the first switching transistor S. ma1 Second switch S ma2 Third switching transistor Fourth switching transistor The second bridge arm includes the fifth switching transistor S. mb1 The sixth switch S mb2 Seventh switch tube Eighth switching transistor The third bridge arm includes the ninth switching transistor S. mc1 10th switch S mc2 Eleventh switch tube Twelfth switching transistor Among them, S ma1 S mb1 S mc1 The collectors of all capacitors are connected to the positive terminal of the DC bus capacitor. The emitter of the capacitor is connected to the negative terminal of the energy storage battery; the negative terminal of the DC bus capacitor is connected to the negative terminal of the energy storage battery. The output end of the wind turbine is connected to a permanent magnet synchronous generator; The grid-connected multi-port converter includes a first bridge arm, a second bridge arm, and a third bridge arm; wherein, the low-voltage DC ports of the first bridge arm, the second bridge arm, and the third bridge arm are connected to the energy storage battery, and their high-voltage DC ports are connected to the DC bus capacitor; the output terminals of the first bridge arm, the second bridge arm, and the third bridge arm are respectively connected to the filter; The first arm of the grid-connected multiport converter includes a first switching transistor S. ga1 Second switch S ga2 Third switching transistor Fourth switching transistor The second bridge arm includes the fifth switching transistor S. gb1 The sixth switch S gb2 Seventh switch tube Eighth switching transistor The third bridge arm includes the ninth switching transistor S. gc1 10th switch S gc2 Eleventh switch tube Twelfth switching transistor Among them, S ga1 S gb1 S gc1 The collectors of all are connected to the positive terminal of the DC bus capacitor; The emitter is connected to the negative terminal of the energy storage battery; The input terminals of the filter are respectively connected to S ga2 S gb2 S gc2 The emitter is connected, and its output is connected to the power grid.

2. A control method for a wind power generation system with integrated energy storage, characterized in that, Includes the following steps: (1) Obtain the AC side voltage reference u of the motor-side multi-port converter in the stationary αβ coordinate system. mαβ Reference power of the energy storage battery required on the motor side and the power generation reference of permanent magnet synchronous generators (2) Obtain the AC side reference voltage u of the grid-connected multi-port converter in the stationary αβ coordinate system. gαβ Reference power of energy storage battery required on the grid-connected side (3) Based on the virtual two-level model, the three-phase duty cycle d on the motor side is generated by space vector synthesis of the reference voltage. mx The duty cycle d of the three phases on the grid-connected side gx x = a, b, c correspond to the three phases on the motor side or grid-connected side; (4) Calculate the zero-sequence component d that needs to be injected into the modulation wave on the motor side. m0 And the zero-sequence component d that needs to be injected into the modulated wave on the grid-connected side. g0 ; (5) The zero-sequence component d on the motor side m0 Injected three-phase duty cycle d mx This is then converted into the three-phase duty cycle d of the first and second switching transistors of each bridge arm in a practical three-level frame. mx1 With d mx2 ; The zero-sequence component d on the grid-connected side g0 Injected three-phase duty cycle d gx This is then converted into the three-phase duty cycle d of the first and second switching transistors of each bridge arm in a practical three-level frame. gx1 With d gx2 ; (6) Set the three-phase duty cycle d on the motor side mx1 d mx2 Three-phase duty cycle d on the grid-connected side gx1 d gx2 The signal is compared with the carrier wave to generate the corresponding drive signal on the switch, which controls the active device to perform switching operation and output voltage and power.

3. A control method for an integrated energy storage wind power generation system according to claim 2, characterized in that, The power generation reference of the permanent magnet synchronous generator Power reference at the motor-side energy storage battery port AC side voltage reference u mαβ The specific method for obtaining it is as follows: (3.1) Based on the power demand P of the power grid gref Maximum power generation of wind turbines And the state of charge (SOC) of the energy storage, and obtain the power reference of the permanent magnet synchronous generator through energy management strategies. Power reference with motor-side energy storage battery port (3.2) Based on the obtained power reference of the permanent magnet synchronous generator By combining the power-speed curve provided by the manufacturer, the reference speed value of the permanent magnet synchronous generator can be obtained. (3.3) The rotational speed ω of the permanent magnet synchronous generator is obtained through a position encoder. e ,Will With the speed ω of the permanent magnet synchronous generator e The difference is used as input, and the motor-side q-axis reference current is obtained through the output of the speed PI control module. (3.4) The position angle θ of the three-phase AC motor is obtained through the position encoder. m This will further reduce the three-phase current i on the motor side. mabc The q-axis current i is obtained through the T1 coordinate transformation unit. mq With d-axis current i md ; (3.5) Set the q-axis reference current on the motor side. With q-axis current i mq The difference is used as input, and the q-axis component u of the motor-side reference voltage is obtained through the output of the q-axis PI control module. mq ; (3.6) Set the d-axis reference current Set it to 0, and set the motor-side d-axis reference current to 0. With d-axis current i md The difference is used as input, and the d-axis component u of the motor-side reference voltage is obtained through the output of the d-axis PI control module. md ; (3.7), will u mq u md As input to the T2 coordinate transformation unit, the motor-side reference voltage u in the stationary αβ coordinate system is obtained. mαβ .

4. The control method for an integrated energy storage wind power generation system according to claim 2, characterized in that, The AC side reference voltage u on the grid-connected side gαβ Reference power of energy storage battery required on the grid-connected side The specific method for obtaining it is as follows: (4.1) The phase angle θ of the fundamental component of the grid voltage is obtained through the phase-locked loop output. g Then the three-phase grid voltage e abc With θ g The d-axis grid voltage component e is obtained through the output of the T1 coordinate transformation unit. d With q-axis grid voltage component e q ; (4.2) The three-phase grid current i gabc With θ g Inputting the T1 coordinate transformation unit yields the q-axis current i. gq With d-axis current i gd ; ( 4.3) The active power demand P of the power grid gref Reactive power demand Q gref d-axis grid voltage component e d With q-axis grid voltage component e q As input to the grid-connected side reference current calculation module, the d-axis reference current of the grid-connected side is obtained from the output. With q-axis reference current (4.3) Set the d-axis reference current With the d-axis current i on the grid-connected side gd The difference is used as the input to the d-axis PI control module, and the output is the d-axis component u of the grid-connected side reference voltage. gd ; (4.4) Set the q-axis reference current With the q-axis current i on the grid-connected side gq The difference is used as the input to the q-axis PI control module, and the output is the q-axis component u of the grid-connected side reference voltage. gq ; (4.5), will u gd with u gq As the input to the T2 coordinate transformation unit, the output is converted into the grid-connected side reference voltage u in the αβ axis coordinate system. gαβ ; (4.6) Set the DC bus capacitor reference voltage With DC bus capacitor voltage u d The difference is used as the input of the voltage PI module, and its output is compared with P. gref Subtraction yields the reference power of the energy storage battery on the grid-connected side.

5. The control method for an integrated energy storage wind power generation system according to claim 2, characterized in that, The three-phase duty cycle d on the motor side mx The duty cycle d of the three phases on the grid-connected side gx The specific method of obtaining it is as follows: (5.1) Obtain the three-phase duty cycle d on the motor side mx ; (5.1.1) The motor-side multi-port converter is considered to have an ideal DC voltage u. d A two-level converter is constructed, and a virtual two-level model is established, which is divided into six sectors S1 to S6, as follows: (5.1.2) Based on the position angle θ of the three-phase AC motor m Determine the reference voltage vector u mαβ Within the corresponding sector, two adjacent basic voltage vectors and the zero vector are selected to synthesize the reference voltage vector u. mαβ Then solve for the reference voltage vector u. mαβ The corresponding volt-second balance equation yields the three-phase duty cycle d on the motor side. mx ; Wherein, the reference voltage vector u mαβ The volt-second balance equation corresponding to the sector is: First sector: Second sector: Third sector: Fourth sector: Fifth sector: Sector 6: Among them, T s T7 is the sampling period, T1 is the duration of the zero vector, and T2 is the duration of V1 and V2 of two adjacent basic voltage vectors, respectively. (5.2) Obtain the three-phase duty cycle d on the grid-connected side. gx ; (5.2.1) The grid-connected multi-port converter is considered to have an ideal DC voltage u. d A two-level converter is constructed, and a virtual two-level model is established, which is divided into six sectors S7 to S12, as follows: (5.2.2) Based on the phase angle θ of the fundamental component of the grid voltage g Determine the reference voltage vector u gαβ Within the corresponding sector, two adjacent basic voltage vectors and the zero vector are selected to synthesize the reference voltage vector u. gαβ Then solve for the reference voltage vector u. gαβ The corresponding volt-second balance equation yields the three-phase duty cycle d on the grid-connected side. gx ; Wherein, the reference voltage vector u gαβ The volt-second balance equation corresponding to the sector is: Sector 7: Eighth sector: Ninth sector: Tenth sector: Eleventh sector: Twelfth sector: Among them, T s T9 is the sampling period, T3 is the duration of the zero vector, and T4 is the duration of V3 and V4 of two adjacent basic voltage vectors, respectively.

6. The control method for an integrated energy storage wind power generation system according to claim 2, characterized in that, The zero-sequence component d to be injected into the modulation wave on the motor side m0 The zero-sequence component d to be injected into the modulated wave on the grid-connected side g0 The specific method of obtaining it is as follows: (6.1) Calculate the zero-sequence component d that needs to be injected into the modulation wave on the motor side. m0 ; (6.1.1) Under the carrier frame, based on the three-phase duty cycle d on the motor side ma d mb d mc The size relationship is divided into 6 regions R1-R6; Where, if d ma >d mb >d mc If so, it is divided into region R1; If d mb >d ma >d mc Then it is divided into region R2; If d mb >d mc >d ma Then it is divided into region R3; If d mc >d mb >d ma Then it is divided into region R4; If d mc >d ma >d mb Then it is divided into region R5; If d ma >d mc >d mb Then it is divided into region R6; (6.1.2) The zero-sequence component d on the motor side m0 With the three-phase duty cycle d ma d mb d mc Add them together to generate the three-phase duty cycle d′ after injecting the zero-sequence component. ma ,d′ mb d mc ; (6.1.3) Calculate the DC port voltage ratio: Among them, u b u is the port voltage of the energy storage battery. d This refers to the voltage at the bus capacitor port. (6.1.4) The three-phase duty cycle waveform d′ generated according to step (6.1.2) ma ,d′ mb ,d′ mc Determine the location, and then within the corresponding area, follow the three-phase duty cycle waveform d′ ma ,d′ mb ,d′ mc Based on the relationship between the DC port voltage ratio ε and the required zero-sequence component d to be injected into the modulation wave on the motor side, the zero-sequence component d is calculated. m0 : (6.1.4.1) When the three-phase duty cycle waveform d′ ma ,d′ mb ,d′ mc When the magnitude relationship is located in the first region R1, calculate the zero-sequence component d. m0 The process is as follows: When d′ ma ≥d′ mb ≥ε≥d′ mc hour, When d′ ma ≥ε>d′ mb ≥d′ mc hour, When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up; (6.1.4.2) When the three-phase duty cycle waveform d′ ma ,d′ mb ,d′ mc When the magnitude relationship is located in the first region R2, calculate the zero-sequence component d. m0 The process is as follows: When d′ mb ≥d′ ma ≥ε>d′ mc hour, When d′ mb ≥ε>d′ ma ≥d′ mc hour, When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up; (6.1.4.3) When the three-phase duty cycle waveform d′ ma ,d′ mb ,d′ mc When the magnitude relationship is located in the first region R3, calculate the zero-sequence component d. m0 The process is as follows: When d′ mb ≥d′ mc ≥ε>d′ ma hour, When d′ mb ≥ε>d′ mc ≥d′ ma hour, When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up; (6.1.4.4) When the three-phase duty cycle waveform d′ ma ,d′ mb ,d′ mc When the magnitude relationship is located in the first region R1, calculate the zero-sequence component d. m0 The process is as follows: When d′ mc ≥d′ mb ≥ε>d′ ma hour, When d′ mc ≥ε>d′ mb ≥d′ ma hour, When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up; (6.1.4.5) When the three-phase duty cycle waveform d′ ma ,d′ mb ,d′ mc When the magnitude relationship is located in the first region R5, calculate the zero-sequence component d. m0 The process is as follows: When d′ mc ≥d′ ma ≥ε>d′ mb hour, When d′ mc ≥ε>d′ ma ≥d′ mb hour, When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up; (6.1.4.6) When the three-phase duty cycle waveform d′ ma ,d′ mb ,d′ mc When the magnitude relationship is located in the first region R6, calculate the zero-sequence component d. m0 The process is as follows: When d′ ma ≥d′ mc ≥ε>d′ mb hour, When d′ ma ≥ε>d′ mc ≥d′ mb hour, When the three-phase duty cycle d mx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. m0 ,give up; (6.2) Calculate the zero-sequence component d that needs to be injected into the modulation wave on the motor side. g0 ; (6.2.1) Under the carrier frame, based on the three-phase duty cycle d on the grid-connected side ga d gb d gc The size relationship is divided into 6 regions R7-R12; Where, if d ga >d gb >d gc Then it is divided into region R7; If d gb >d ga >d gc Then it is divided into region R8; If d gb >d gc >d ga Then it is divided into region R9; If d gc >d gb >d ga Then it is divided into region R10; If d gc >d ga >d gb Then it is divided into region R11; If d ga >d gc >d gb Then it is divided into region R12; (6.2.2) The zero-sequence component d on the grid-connected side g0 With the three-phase duty cycle d ga d gb d gc Add them together to generate the three-phase duty cycle d′ after injecting the zero-sequence component. ga ,d′ gb ,d′ gc ; (6.2.3) Calculate the DC port voltage ratio: Among them, u b u is the port voltage of the energy storage battery. d This refers to the voltage at the bus capacitor port. (6.2.4) The three-phase duty cycle waveform d′ generated according to step (6.2.2) ga ,d′ gb ,d′ gc Determine the location, and then within the corresponding area, follow the three-phase duty cycle waveform d′ ga ,d′ gb ,d′ gc Based on the relationship between the DC port voltage ratio ε and the required zero-sequence component d to be injected into the modulated wave on the grid-connected side, the zero-sequence component d is calculated. g0 : (6.2.4.1) When the three-phase duty cycle waveform d′ ga ,d′ gb ,d′ gc When the magnitude relationship is located in the first region R7, calculate the zero-sequence component d. g0 The process is as follows: When d′ ga ≥d′ gb ≥ε≥d′ gc hour, When d′ ga ≥ε>d′ gb ≥d′ gc hour, When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up; (6.2.4.2) When the three-phase duty cycle waveform d′ ga ,d′ gb ,d′ gc When the magnitude relationship is located in the first region R8, calculate the zero-sequence component d. g0 The process is as follows: When d′ gb ≥d′ ga ≥ε>d′ gc hour, When d′ gb ≥ε>d′ ga ≥d′ gc hour, When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up; (6.2.4.3) When the three-phase duty cycle waveform d′ ga ,d′ gb ,d′ gc When the magnitude relationship is located in the first region R9, calculate the zero-sequence component d. g0 The process is as follows: When d′ gb ≥d′ gc ≥ε>d′ ga hour, When d′ gb ≥ε>d′ gc ≥d′ ga hour, When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up; (6.2.4.4) When the three-phase duty cycle waveform d′ ga ,d′ gb ,d′ gc When the magnitude relationship is located in the first region R10, calculate the zero-sequence component d. g0 The process is as follows: When d′ gc ≥d′ gb ≥ε>d′ ga hour, When d′ mc ≥ε>d′ mb ≥d′ ma hour, When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up; (6.2.4.5) When the three-phase duty cycle waveform d′ ga ,d′ gb ,d′ gc When the magnitude relationship is located in the first region R11, calculate the zero-sequence component d. g0 The process is as follows: When d′ gc ≥d′ ga ≥ε>d′ gb hour, When d′ gc ≥ε>d′ ga ≥d′ gb hour, When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up; (6.2.4.6) When the three-phase duty cycle waveform d′ ga ,d′ gb ,d′ gc When the magnitude relationship is located in the first region R12, calculate the zero-sequence component d. g0 The process is as follows: When d′ ga ≥d′ gc ≥ε>d′ gb hour, When d′ ga ≥ε>d′ gc ≥d′ gb hour, When the three-phase duty cycle d gx When there are other magnitude relationships between d and the DC port voltage ratio ε, it is impossible to calculate d. g0 ,give up.

7. The control method for an integrated energy storage wind power generation system according to claim 2, characterized in that, The three-phase duty cycle d mx1 With d mx2 With the three-phase duty cycle d gx1 With d gx2 The specific method of obtaining it is as follows: (7.1) Obtain the three-phase duty cycle d mx1 With d mx2 ; (7.1.1) d m0 Injected three-phase duty cycle d mx Get d′ mx Then, the voltage is divided at the DC port voltage ratio ε to obtain the three-phase duty cycle d′ of the first and second switching transistors on each bridge arm of the virtual two-level frame. mx1 ,d′ mx2 : (7.1.2) d′ mx1 ,d′ mx2 Converted to the three-phase duty cycle d in a practical three-level frame mx1 d mx2 : (7.2) Obtain the three-phase duty cycle d gx1 With d gx2 ; (7.2.1) For the grid-connected side, d g0 Injected three-phase duty cycle d gx Get d′ gx Then, the voltage is divided at the DC port voltage ratio ε to obtain the three-phase duty cycle d′ of the first and second switching transistors on each bridge arm of the virtual two-level frame. gx1 ,d′ gx2 : (7.2.2) d′ gx1 ,d′ gx2 Converted to the three-phase duty cycle d in a practical three-level frame gx1 d gx2 :

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