Three-phase three-level four-bridge-arm inverter control method and system

Abstract

The present application provides a three-phase three-level four-bridge-arm inverter control method and system, which relates to the field of inverter control technology. The method includes: obtaining the values ​​of load voltage, load current and reference load voltage in a vector coordinate system, and calculating the voltage error; calculating the vector values ​​of the voltage error and the load current by a deadbeat control algorithm, and obtaining the first d-axis and q-axis components of the reference output current in the dq coordinate system; obtaining the second d-axis and q-axis components of the output current; calculating the difference between the first and second d-axis components and the first and second q-axis components, and obtaining the d-axis and q-axis current errors; calculating the d-axis and q-axis current errors, the second d-axis and q-axis components, and the third d-axis and q-axis components of the load voltage by a sliding mode control algorithm, and inputting the results into an SPWM modulation module to control the inverter. The voltage outer loop is controlled by the deadbeat control algorithm, and the current inner loop is controlled by the sliding mode control algorithm, which can reduce the complexity of the control process.

Description

Technical Field

[0001] The present application relates to the field of inverter control technology, and in particular to a three-phase three-level four-bridge-arm inverter control method and system. Background Art

[0002] In renewable energy power generation systems, such as solar photovoltaic power stations and wind farms, direct current needs to be converted into alternating current to connect to the grid or power local loads. As a key link in energy conversion, the control algorithm of the three-phase inverter directly affects the power quality and power generation efficiency. The DC voltage output by solar photovoltaic cells needs to be converted into three-phase alternating current that meets the grid standards by a three-phase inverter, and the electric energy generated by wind turbines also relies on three-phase inverters for effective power conversion and control before being connected to the grid. In these application scenarios, different environmental conditions and load characteristics require the inverter to accurately and stably output three-phase alternating current.

[0003] When controlling the inverter, the proportional-integral control algorithm (PI) or the sliding mode control algorithm (SMC) can be used. However, the three-phase inverter is a complex nonlinear system, which is affected by many factors, such as load changes, grid voltage fluctuations, and nonlinear characteristics of switching devices. PI has limitations when dealing with complex situations, such as high harmonic content of the output voltage, slow dynamic response speed, and sensitivity to parameter changes. In addition, the process of adjusting the controller parameters is relatively complicated. Although SMC has the advantages of strong robustness and a wide range of applications, its control accuracy cannot meet the requirements and there is a jitter phenomenon. Summary of the invention

[0004] The present application provides a three-phase three-level four-bridge-arm inverter control method and system to solve the problem of complex inverter control process.

[0005] In a first aspect, the present application provides a three-phase three-level four-bridge-arm inverter control method, which is applied to a three-phase three-level four-bridge-arm inverter, wherein the inverter includes four parallel bridge arms, each bridge arm includes four transistors, and a filter is provided between the bridge arm and the load, wherein the filter includes an inductor and a capacitor; the method includes:

[0006] Obtaining a load voltage, a load current and a reference load voltage, so as to obtain a transformed load voltage, a transformed load current and a transformed reference load voltage according to the load voltage, the load current and the reference load voltage; the transformed load voltage and the transformed reference load voltage are voltages in a vector coordinate system, and the transformed load current is a current in a vector coordinate system;

[0007] performing a difference operation on the converted load voltage and the converted reference load voltage to obtain a voltage error of the load;

[0008] The voltage error and the transformed load current are calculated by a deadbeat control algorithm to obtain a first d-axis component and a first q-axis component, wherein the first d-axis component and the first q-axis component are currents of the reference output current in a dq coordinate system;

[0009] Obtaining an output current to obtain a second d-axis component and a second q-axis component according to the output current, wherein the output current is an actual current output by the inverter, and the second d-axis component and the second q-axis component are currents of the output current in a dq coordinate system;

[0010] performing a difference operation on the first d-axis component and the second d-axis component to obtain a d-axis current error, and performing a difference operation on the first q-axis component and the second q-axis component to obtain a q-axis current error;

[0011] Acquire a third d-axis component and a third q-axis component according to the load voltage, wherein the third d-axis component and the third q-axis component are voltages of the load voltage in a dq coordinate system;

[0012] The d-axis current error, the q-axis current error, the second d-axis component, the second q-axis component, the third d-axis component and the third q-axis component are calculated by a sliding mode control algorithm to obtain a fourth d-axis component and a fourth q-axis component, wherein the fourth d-axis component and the fourth q-axis component are voltages of the reference output voltage in a dq coordinate system;

[0013] The fourth d-axis component and the fourth q-axis component are input to an SPWM modulation module to control the inverter.

[0014] Optionally, the bridge arm includes a three-phase bridge arm and a neutral bridge arm, and the acquiring of the load voltage, the load current and the reference load voltage to obtain the transformed load voltage, the transformed load current and the transformed reference load voltage according to the load voltage, the load current and the reference load voltage includes:

[0015] Respectively obtaining a load voltage and a load current obtained by the load through the three-phase bridge arm, and a reference load voltage of the load;

[0016] Vector coordinate transformation is performed on the load voltage, the load current and the reference load voltage respectively, so as to transform the load voltage, the load current and the reference load voltage from a three-phase stationary coordinate system to a vector coordinate system, thereby obtaining a transformed load voltage, a transformed load current and a transformed reference load voltage.

[0017] Optionally, after the step of acquiring the load voltage, the load current and the reference load voltage to obtain the transformed load voltage, the transformed load current and the transformed reference load voltage according to the load voltage, the load current and the reference load voltage, the step further includes:

[0018] respectively obtaining the output voltage and the output current of the three-phase bridge arm, wherein the output voltage is the actual voltage output by the inverter;

[0019] Performing vector coordinate transformation on the output voltage and the output current respectively, so as to transform the output voltage and the output current from a three-phase stationary coordinate system to a vector coordinate system, thereby obtaining a transformed output voltage and a transformed output current;

[0020] Decoupling the load voltage and the load current through a first transformation matrix so that the transformed load voltage and the transformed load current satisfy a first state equation;

[0021] The output voltage and the output current are decoupled by a first transformation matrix so that the transformed output voltage and the transformed output current satisfy a second state equation.

[0022] Optionally, the vector coordinate system is In the vector coordinate system, the expression of the first state equation is:

[0023] ;

[0024] in, is the differential operator, , , They are Quantity, Quantity and Transformation load voltage of components; , , They are Quantity, Quantity and The transformed output current of the components; , , They are Quantity, Quantity and Component transformation load current; is the capacitance of the filter;

[0025] The expression of the second state equation is:

[0026] ;

[0027] in, is the inductance of the three-phase bridge arm; is the inductance of the neutral bridge arm; , , They are Quantity, Quantity and The transformed output voltage of the component.

[0028] Optionally, the operating the voltage error and the transformed load current by a deadbeat control algorithm to obtain a first d-axis component and a first q-axis component comprises:

[0029] The voltage error and the transformed load current are calculated according to the first state equation and the second state equation to obtain a transformed reference output current, wherein the transformed reference output current is a current in a vector coordinate system;

[0030] The transformed reference output current is subjected to dq coordinate transformation through a second transformation matrix to transform the transformed reference output current from a vector coordinate system to a dq coordinate system, thereby obtaining a first d-axis component and a first q-axis component of the reference output current.

[0031] Optionally, the control equation for transforming the reference output current is:

[0032] ;

[0033] ;

[0034] ;

[0035] in, for time The transformation of the components reference output current, for time The transformation of the components reference output current, for time The transformation of the components reference output current, for time Components of the transformed load current, for time Components of the transformed load current, for time Components of the transformed load current, for time The transformation of the components references the load voltage, for time The transformation of the components references the load voltage, for time The transformation of the components references the load voltage, for time The transformed load voltage of the component, for time The transformed load voltage of the component, for time The transformed load voltage of the component, is the sampling period.

[0036] Optionally, the acquiring the output current to acquire the second d-axis component and the second q-axis component according to the output current includes:

[0037] The output current on each phase bridge arm is subjected to dq coordinate transformation to transform the output current from a three-phase stationary coordinate system to a dq coordinate system, thereby obtaining a second d-axis component and a second q-axis component of the output current.

[0038] Optionally, the method further includes:

[0039] Defining a sliding vector of the sliding mode control algorithm according to the d-axis current error and the q-axis current error;

[0040] The sliding vector is derived to use a reaching law to weaken the chattering generated by the sliding mode control algorithm.

[0041] Optionally, the control equations of the fourth d-axis component and the fourth q-axis component of the reference output voltage are:

[0042] ;

[0043] in, is the fourth d-axis component, i.e., the d-axis component of the reference output voltage, is the fourth q-axis component, i.e., the q-axis component of the reference output voltage; , , , are the parameters of the sliding mode control algorithm, , ; is a symbolic function; is the d-axis current error, is the q-axis current error; is the third d-axis component, is the third q-axis component, is the second d-axis component, is the second q-axis component, is the angular frequency.

[0044] A second aspect of the present application provides a three-phase three-level four-bridge-arm inverter control system, which is applied to the method described in the first aspect, and the system includes:

[0045] Acquisition conversion module: used for acquiring load voltage, load current and reference load voltage, so as to obtain transformed load voltage, transformed load current and transformed reference load voltage according to the load voltage, load current and reference load voltage; the transformed load voltage and the transformed reference load voltage are voltages in a vector coordinate system, and the transformed load current is a current in a vector coordinate system;

[0046] A calculation module: used for performing a difference operation on the converted load voltage and the converted reference load voltage to obtain a voltage error of the load;

[0047] A deadbeat control module: used for calculating the voltage error and the transformed load current by a deadbeat control algorithm to obtain a first d-axis component and a first q-axis component, wherein the first d-axis component and the first q-axis component are currents of the reference output current in a dq coordinate system;

[0048] The acquisition conversion module is further used to acquire the output current, so as to acquire the second d-axis component and the second q-axis component according to the output current, wherein the output current is the actual current output by the inverter, and the second d-axis component and the second q-axis component are the currents of the output current in the dq coordinate system;

[0049] The calculation module is further used for performing a difference operation on the first d-axis component and the second d-axis component to obtain a d-axis current error, and performing a difference operation on the first q-axis component and the second q-axis component to obtain a q-axis current error;

[0050] The acquisition conversion module is further used to obtain a third d-axis component and a third q-axis component according to the load voltage, wherein the third d-axis component and the third q-axis component are voltages of the load voltage in a dq coordinate system;

[0051] A sliding mode control module: used for calculating the d-axis current error, the q-axis current error, the second d-axis component, the second q-axis component, the third d-axis component and the third q-axis component through a sliding mode control algorithm to obtain a fourth d-axis component and a fourth q-axis component, wherein the fourth d-axis component and the fourth q-axis component are voltages of the reference output voltage in a dq coordinate system;

[0052] SPWM modulation module: used for receiving the fourth d-axis component and the fourth q-axis component to control the inverter.

[0053] The present application provides a three-phase three-level four-bridge-arm inverter control method and system, the method comprising: obtaining a transformed load voltage, a transformed load current and a transformed reference load voltage according to a load voltage, a load current and a reference load voltage; performing a difference operation on the transformed load voltage and the transformed reference load voltage to obtain a voltage error of the load; performing a difference operation on the voltage error and the transformed load current through a deadbeat control algorithm to obtain a first d-axis component and a first q-axis component of a reference output current in a dq coordinate system; obtaining a second d-axis component and a second q-axis component according to the output current; performing a difference operation on the first d-axis component and the first q-axis component; The first d-axis component and the second q-axis component are differentially calculated to obtain the d-axis current error, and the first q-axis component and the second q-axis component are differentially calculated to obtain the q-axis current error; the third d-axis component and the third q-axis component of the load voltage are obtained; the d-axis current error, the q-axis current error, the second d-axis component, the second q-axis component, the third d-axis component and the third q-axis component are calculated by a sliding mode control algorithm to obtain the fourth d-axis component and the fourth q-axis component of the reference output voltage in the dq coordinate system; the fourth d-axis component and the fourth q-axis component are input to the SPWM modulation module to control the inverter. The method controls the voltage outer loop by a deadbeat control algorithm and controls the current inner loop by a sliding mode control algorithm, which can reduce the complexity of the control process. The control algorithm has stronger robustness and faster dynamic response speed. While ensuring the control performance, it can reduce the calculation burden of the system and solve the problem of complex inverter control process. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the embodiments are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0055] Figure 1 A topological structure diagram of a three-phase three-level four-bridge-arm inverter provided in an embodiment of the present application;

[0056] Figure 2 A process diagram of a three-phase three-level four-bridge-arm inverter control method provided in an embodiment of the present application;

[0057] Figure 3 A schematic diagram of a grid-connected voltage waveform output by a PI control algorithm provided in an embodiment of the present application;

[0058] Figure 4 A schematic diagram of a grid-connected voltage waveform output by a DB-SMC control algorithm provided in an embodiment of the present application;

[0059] Figure 5 A grid-connected voltage harmonic content diagram output by the PI control algorithm provided in an embodiment of the present application;

[0060] Figure 6 A grid-connected voltage harmonic content diagram output by the DB-SMC control algorithm provided in an embodiment of the present application;

[0061] Figure 7 A transient change waveform diagram of the d-axis component of the grid-connected voltage output by the PI control algorithm provided in an embodiment of the present application;

[0062] Figure 8 This is a waveform diagram of the transient change of the d-axis component of the grid-connected voltage output by the DB-SMC control algorithm provided in an embodiment of the present application. DETAILED DESCRIPTION

[0063] The following embodiments are described in detail, and examples thereof are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following embodiments do not represent all implementations consistent with the present application. They are only examples of systems and methods consistent with some aspects of the present application as detailed in the claims.

[0064] When controlling the inverter, since the three-phase inverter is a complex nonlinear system, PI has limitations in dealing with complex situations, such as high output voltage harmonic content, slow dynamic response, and sensitivity to parameter changes. In addition, the process of adjusting controller parameters is relatively complicated. Although SMC has the advantages of strong robustness and wide application range, its control accuracy cannot meet the requirements and there is jitter phenomenon.

[0065] In order to solve the problem of complex inverter control process, some embodiments of the present application provide a three-phase three-level four-bridge-arm inverter control method, which is applied to a three-phase three-level four-bridge-arm inverter. Therefore, before describing the method of the present application, the structure of the three-phase three-level four-bridge-arm inverter is first described.

[0066] See also Figure 1 , Figure 1 The topological structure diagram of the three-phase three-level four-bridge arm inverter is shown in FIG. The inverter includes four parallel bridge arms, and the four parallel bridge arms include three-phase bridge arms and a neutral bridge arm. The three-phase bridge arms are A-phase bridge arm, B-phase bridge arm and C-phase bridge arm, and the neutral bridge arm is the N-phase bridge arm. Each bridge arm includes four transistors, which can be switch tubes, that is, each bridge arm contains four controllable switch tubes. , , and ,in , and Always complementary conduction, and The A-phase bridge arm includes a switch tube. , , , , and Complementary conduction, and Complementary conduction; the B phase bridge arm includes the switch tube , , , , the C phase bridge arm includes the switch tube , , , , the neutral bridge arm includes the switch tube , , , Among them, the four transistors of the A-phase bridge arm are connected in pairs at point A, the four transistors of the B-phase bridge arm are connected in pairs at point B, and the four transistors of the C-phase bridge arm are connected in pairs at point C. For the neutral point.

[0067] The output ends of the four bridge arms of the inverter are connected to the load, and a filter is arranged between the bridge arm and the load. The filter includes an inductor and capacitor , where the capacitor of the A-phase bridge arm is connected to the A-phase bridge arm at point a, the capacitor of the B-phase bridge arm is connected to the B-phase bridge arm at point b, and the capacitor of the C-phase bridge arm is connected to the C-phase bridge arm at point c.

[0068] Define the switch state of each bridge arm as ,in , then according to different switch combinations of the three-phase three-level inverter, three switching states can be generated, namely The values ​​of can be "1", "0" and "-1", and the corresponding three switch states are "P", "Q" and "M". Assume that the neutral point O potential has been balanced, that is, ,in, is the DC side voltage, and Capacitors and capacitors The voltage of each bridge arm is defined as ,in , then the output voltage level of each bridge arm It can be expressed as:

[0069] ; (1)

[0070] The corresponding switch combinations are shown in Table 1:

[0071] Table 1 Combinations of different switch tubes and corresponding output voltage levels

[0072]

[0073] It can be understood that the output voltage of each bridge arm of the inverter is determined by the state of the switch tube on the bridge arm. When the switch tube on the bridge arm is in different states, it will be connected to different power supply potentials (such as positive bus voltage, negative bus voltage or neutral voltage), thereby outputting different voltage levels, that is, The output voltage of the inverter is determined by the four bridge arms, that is, the output voltage of the inverter is related to the output voltage level of each bridge arm. The three-phase bridge arm output voltage of the inverter is defined as , and , then the output voltage of the inverter can be expressed as:

[0074] ; (2)

[0075] in, , and are the output voltages of the inverter A-phase bridge arm, B-phase bridge arm and C-phase bridge arm respectively, , , and They are the output voltage levels of the A-phase bridge arm, the B-phase bridge arm, the C-phase bridge arm, and the neutral bridge arm respectively.

[0076] See also Figure 2 The three-phase three-level four-bridge-arm inverter control method provided in the embodiment of the present application includes:

[0077] S100: Acquire a load voltage, a load current and a reference load voltage to obtain a transformed load voltage, a transformed load current and a transformed reference load voltage according to the load voltage, the load current and the reference load voltage.

[0078] The load voltage and the reference load voltage are transformed into voltages in a vector coordinate system, and the load current is transformed into currents in a vector coordinate system. Obtaining the load voltage, the load current, and the reference load voltage to obtain the transformed load voltage, the transformed load current, and the transformed reference load voltage according to the load voltage, the load current, and the reference load voltage specifically includes the following steps:

[0079] S110: respectively obtaining a load voltage and a load current obtained by the load through the three-phase bridge arm, and a reference load voltage of the load.

[0080] It can be understood that the load voltage is the actual voltage obtained through the inverter bridge arm, the load current is the actual current obtained through the inverter bridge arm, and the load voltage and load current can be obtained through sampling. The reference load voltage is the voltage obtained by the expected load, which is a given value set when the inverter system is established.

[0081] S120: Performing vector coordinate transformation on the load voltage, the load current and the reference load voltage respectively, so as to transform the load voltage, the load current and the reference load voltage from the three-phase stationary coordinate system to the vector coordinate system, and obtaining the transformed load voltage, the transformed load current and the transformed reference load voltage.

[0082] The three-phase stationary coordinate system is The three-phase stationary coordinate system and the vector coordinate system are The vector coordinate system is a three-dimensional rectangular coordinate system, including axis, Axis and axis. The load voltage, load current and reference load voltage are converted from The three-phase stationary coordinate system is transformed into The vector coordinate system can be obtained through existing technology and will not be described in detail here. The three-phase stationary coordinate system is transformed into Vector coordinate system can simplify the control algorithm.

[0083] In some embodiments, after the steps of acquiring the load voltage, the load current and the reference load voltage to obtain the transformed load voltage, the transformed load current and the transformed reference load voltage according to the load voltage, the load current and the reference load voltage, the method further comprises:

[0084] S130: Obtain the output voltage and output current of the three-phase bridge arms respectively.

[0085] S140: Performing vector coordinate transformation on the output voltage and the output current respectively, so as to transform the output voltage and the output current from the three-phase static coordinate system to the vector coordinate system, and obtaining the transformed output voltage and the transformed output current.

[0086] S150: Decoupling the load voltage and the load current through a first transformation matrix so that the transformed load voltage and the transformed load current satisfy a first state equation.

[0087] S160: Decouple the output voltage and the output current through the first transformation matrix so that the transformed output voltage and the transformed output current satisfy the second state equation.

[0088] The output voltage is the actual voltage output by the inverter, and the output current is the actual current output by the inverter, both of which can be obtained through sampling. , and are the output voltages of the inverter phase A bridge arm, phase B bridge arm and phase C bridge arm respectively. The load voltage can be defined as , the load current is , the inductor current of the three-phase bridge arm is ,in , the inductor current on the neutral bridge arm is , then the three-phase load voltages obtained by the load are expressed as , the load current is expressed as , , The inductor currents on the inverter phase A bridge arm, phase B bridge arm and phase C bridge arm are , , ,pass Figure 1 It can be seen that the inductor current , , This is the output current of the three-phase bridge arm of the inverter. By analyzing the nodes on the output side of the inverter using Kirchhoff's law, we can get:

[0089] ; (3)

[0090] ; (4)

[0091] ; (5)

[0092] in, is the differential operator, is the capacitance of the filter. Substituting formula (5) into formula (3) and formula (4) yields:

[0093] ; (6)

[0094] ; (7)

[0095] in, is the inductance of the three-phase bridge arm, which is also the inductance of the filter. is the inductance of the neutral bridge arm. From formula (6) and formula (7), it can be seen that the output voltage and output current are coupled to each other, and the load voltage and load current are also coupled to each other. Therefore, it is necessary to decouple the output voltage and output current, the load voltage and load current. In some embodiments, the first transformation matrix The coupling amount is changed from The three-phase stationary coordinate system is transformed into Decoupling is performed in the vector coordinate system. The first transformation matrix It can be expressed as:

[0096] ; (8)

[0097] After decoupling, the transformed load voltage and the transformed load current satisfy the first state equation, and the expression of the first state equation is:

[0098] ; (9)

[0099] After decoupling, the transformed output current and the transformed output voltage satisfy the second state equation, and the expression of the second state equation is:

[0100] ; (10)

[0101] in, The output voltage is from The three-phase stationary coordinate system is transformed into The voltage in the vector coordinate system is Quantity, Quantity and The transformed output voltage of the components; , , The load voltage is from The three-phase stationary coordinate system is transformed into The voltage in the vector coordinate system is Quantity, Quantity and Transformation load voltage of components; , , Output current , , from The three-phase stationary coordinate system is transformed into The current in the vector coordinate system is Quantity, Quantity and The transformed output current of the components; , , is the load current , , from The three-phase stationary coordinate system is transformed into The current in the vector coordinate system is Quantity, Quantity and Component of the transformed load current.

[0102] S200: performing a difference operation on the transformed load voltage and the transformed reference load voltage to obtain a voltage error of the load.

[0103] The transformed reference load voltages can be defined as , for changing load voltage , , and transform the reference load voltage The voltage error of the load can be obtained by performing a difference operation.

[0104] S300: Calculating the voltage error and the transformed load current by using a deadbeat control algorithm to obtain a first d-axis component and a first q-axis component.

[0105] Among them, the first d-axis component and the first q-axis component are the reference output current The current in the coordinate system, The coordinate system is a two-phase rotating coordinate system, including a d-axis and a q-axis that are perpendicular to each other. It can be understood that the reference output current is a given value set when the inverter system is established. The voltage error and the transformed load current are calculated by the dead-beat control algorithm (DB) to obtain the first d-axis component and the first q-axis component including:

[0106] S310: Calculate the voltage error and the transformed load current according to the first state equation and the second state equation to obtain a transformed reference output current.

[0107] The process of calculating the voltage error and transforming the load current through the deadbeat control algorithm is the process of controlling the voltage outer loop. The deadbeat control algorithm can calculate the reference value of the next sampling period Ts based on the established system mathematical model and the current sampling value. Quantity and Component analysis and The weight is the same, so in the present application embodiment only Combining the expressions of the first state equation and the second state equation, that is, formula (9) and formula (10), for The derivatives of the transformed output current and transformed load voltage can be expressed as:

[0108] ; (11)

[0109] When the sampling frequency is large enough, the sampling variable transforms the output current and the load voltage. The derivative of the component can be expressed as:

[0110] ; (12)

[0111] ; (13)

[0112] in, is the sampling period, for time The transformed output current of the components, for time The transformed output current of the components, for time The transformed load voltage of the component, for time The transformed load voltage of the component. Combining formulas (11)-(13), Change load voltage at time It can be expressed as:

[0113] ; (14)

[0114] in, for time Component of the transformed load current.

[0115] Combining formulas (11)-(13), Change load voltage at time It can be expressed as:

[0116] ; (15)

[0117] Through The linear estimation of the transformed load voltage at the moment can be obtained:

[0118] ; (16)

[0119] ; (17)

[0120] in, for time Assume that the load current is Keep it constant during the sampling period and replace the transformed reference output current with The value at the moment, according to formula (17), formula (15) can be simplified to:

[0121] ; (18)

[0122] in, for time The transformation of the components references the load voltage, for time According to formula (18), the inverter reference output current obtained by the deadbeat control algorithm is In the vector coordinate system, it can be expressed as:

[0123] ; (19)

[0124] ; (20)

[0125] ;(twenty one)

[0126] in, for time The transformation of the components reference output current, for time The transformation of the components reference output current, for time Components of the transformed load current, for time Components of the transformed load current, for time The transformation of the components references the load voltage, for time The transformation of the components references the load voltage, for time The transformed load voltage of the component, for time The above formula (19)-formula (21) is the control equation for transforming the reference output current.

[0127] S320: Transform the reference output current through the second transformation matrix Coordinate transformation to transform the reference output current from the vector coordinate system to Coordinate system, and obtain the first d-axis component and the first q-axis component of the reference output current.

[0128] conduct The coordinate transformation process is to perform Park transformation on the transformed reference output current through the second transformation matrix, transforming the transformed reference output current from the vector coordinate system to In the coordinate system, the second transformation matrix It can be expressed as:

[0129] ;(twenty two)

[0130] in, for The rotation angle of the coordinate system relative to the vector coordinate system or the three-phase stationary coordinate system. After coordinate transformation, the first d-axis component of the reference output current can be defined as , the first q-axis component is .

[0131] S400: Acquire the output current to acquire a second d-axis component and a second q-axis component according to the output current.

[0132] The second d-axis component and the second q-axis component are the output current The output current on each phase bridge arm can be calculated by Coordinate transformation to transform the output current from the three-phase stationary coordinate system to coordinate system, and obtain the second d-axis component and the second q-axis component of the output current. In some embodiments, the output current may be defined as The second d-axis component and the second q-axis component in the coordinate system are and .

[0133] S500: performing a difference operation on the first d-axis component and the second d-axis component to obtain a d-axis current error, and performing a difference operation on the first q-axis component and the second q-axis component to obtain a q-axis current error.

[0134] In some embodiments, the d-axis current error can be defined as , the q-axis current error is , then the d-axis current error can be expressed as:

[0135] ;(twenty three)

[0136] The q-axis current error can be expressed as:

[0137] ;(twenty four)

[0138] S600: Obtain a third d-axis component and a third q-axis component according to the load voltage.

[0139] The third d-axis component and the third q-axis component are the load voltage The load voltage can be Coordinate transformation to transform the load voltage from the three-phase stationary coordinate system to coordinate system, and obtain the third d-axis component and the third q-axis component. In some embodiments, the load voltage may be defined as The third d-axis component and the third q-axis component in the coordinate system are and .

[0140] Can get The voltage-current relationship expression on the coordinate system is:

[0141] ; (25)

[0142] in and Output voltage Transform to Voltage of the coordinate system; and The load voltage is Transform to The voltage of the coordinate system, i.e., the third d-axis component and the third q-axis component; and is the current transformed from the output current to the dq coordinate system, that is, the second d-axis component and the second q-axis component; is the angular frequency.

[0143] S700: Calculate the d-axis current error, the q-axis current error, the second d-axis component, the second q-axis component, the third d-axis component and the third q-axis component through a sliding mode control algorithm SMC to obtain a fourth d-axis component and a fourth q-axis component.

[0144] The fourth d-axis component and the fourth q-axis component are the reference output voltages at The voltage in the coordinate system, the reference output voltage is the given value set when the inverter system is established.

[0145] The biggest disadvantage of using sliding mode variable structure as algorithm control is its inherent chattering phenomenon. The existence of chattering phenomenon will reduce the stability of the inverter system and greatly reduce the control ability, so it is necessary to weaken the chattering. In some embodiments, the method also includes:

[0146] S710: Define a sliding vector of a sliding mode control algorithm according to a d-axis current error and a q-axis current error.

[0147] In order to obtain the sliding mode of the sliding mode control algorithm on the sliding surface, the sliding vector is defined as:

[0148] ; (26)

[0149] in, is the sliding vector, is the d-axis current error, is the q-axis current error.

[0150] S720: Deriving the sliding vector to weaken the chattering generated by the sliding mode control algorithm by using a reaching law.

[0151] Combining formula (22), formula (23) and formula (25), after taking the derivative of the sliding vector, the sliding vector is expressed as:

[0152] ; (27)

[0153] in, is the derivative of the d-axis current error, is the derivative of the q-axis current error. When stable, the output current is also fixed, so the derivative of the d-axis current error and the derivative of the q-axis current error are 0. In some embodiments, the approach law can be used to weaken the jitter, and then formula (26) can be expressed as:

[0154] ; (28)

[0155] in, is the derivative of the sliding vector; , , , are the parameters of the sliding mode control algorithm, , ; is a symbolic function; when hour, ;when hour, ;when hour, .

[0156] By analyzing the topological structure of the inverter, the following expression can be obtained:

[0157] ; (29)

[0158] Combining formula (28) and formula (29), the control equations of the fourth d-axis component and the fourth q-axis component of the reference output voltage are obtained as follows:

[0159] ; (30)

[0160] in, is the fourth d-axis component, that is, the reference output voltage The voltage in the coordinate system, is the fourth q-axis component, that is, the reference output voltage is Voltage in the coordinate system.

[0161] S800: Input the fourth d-axis component and the fourth q-axis component to the SPWM modulation module to control the inverter.

[0162] It should also be noted that due to and The reference output voltage is The voltage in the coordinate system will be and Before inputting into the SPWM modulation module, and Convert to The voltage in the three-phase stationary coordinate system is then input into the SPWM modulation module. The SPWM modulation module is a space vector pulse width modulation module that can convert continuous voltage signals into discrete switching signals to control the output of the inverter.

[0163] It can be seen from the above embodiments that the present application uses the DB control algorithm to control the voltage outer loop and the SMC control algorithm to control the current inner loop, that is, the control method of the present application is the DB-SMC control algorithm. The present application embodiment simulates and verifies the DB-SMC control algorithm using Matlab software to compare the simulation experimental results of the dual closed-loop PI control algorithm and the DB-SMC control algorithm of the present application. Figure 3-Figure 6 , Figure 3 and Figure 4 middle, , , are the grid-connected voltage output by the inverter, Figure 3 and Figure 4 It can be seen that the DB-SMC control algorithm of the present application significantly weakens the chattering. Figure 5 and Figure 6 In the figure, THD is the total harmonic distortion, which is an indicator to measure the degree of signal distortion. It represents the ratio of the total energy of all harmonic components (i.e. components whose frequencies are integer multiples of the fundamental frequency) in the signal to the fundamental frequency energy. The lower the THD, the purer the signal and the smaller the distortion. It can be seen that the harmonic content of the electric energy output by the DB-SMC control algorithm is lower than that of the PI control algorithm, and the control performance is better. See Figure 7-Figure 8 ,pass Figure 7 and Figure 8 From the transient changes in the d-axis component of the output voltage, it can be seen that the DB-SMC control algorithm has a faster dynamic response speed and a shorter time to restore to steady state.

[0164] Based on the above three-phase three-level four-bridge-arm inverter control method, some embodiments of the present application also provide a three-phase three-level four-bridge-arm inverter control system, which is applied to the method provided in the above embodiment, and the system includes:

[0165] Acquisition conversion module: used to obtain the load voltage, load current and reference load voltage, so as to obtain the transformed load voltage, transformed load current and transformed reference load voltage according to the load voltage, load current and reference load voltage.

[0166] The transformed load voltage and the transformed reference load voltage are voltages in a vector coordinate system, and the transformed load current is a current in a vector coordinate system.

[0167] Calculation module: used to perform difference calculation on the transformed load voltage and the transformed reference load voltage to obtain the voltage error of the load.

[0168] Deadbeat control module: used to calculate the voltage error and the transformed load current through the deadbeat control algorithm to obtain the first d-axis component and the first q-axis component, wherein the first d-axis component and the first q-axis component are the currents of the reference output current in the dq coordinate system.

[0169] The acquisition conversion module is also used to acquire the output current, so as to acquire the second d-axis component and the second q-axis component according to the output current. The output current is the actual current output by the inverter, and the second d-axis component and the second q-axis component are the currents of the output current in the dq coordinate system.

[0170] The calculation module is further used to perform a difference operation on the first d-axis component and the second d-axis component to obtain a d-axis current error, and to perform a difference operation on the first q-axis component and the second q-axis component to obtain a q-axis current error.

[0171] The acquisition conversion module is also used to obtain a third d-axis component and a third q-axis component according to the load voltage, wherein the third d-axis component and the third q-axis component are voltages of the load voltage in a dq coordinate system.

[0172] Sliding mode control module: used to calculate the d-axis current error, q-axis current error, the second d-axis component, the second q-axis component, the third d-axis component and the third q-axis component through the sliding mode control algorithm to obtain the fourth d-axis component and the fourth q-axis component. The fourth d-axis component and the fourth q-axis component are the reference output voltage at Voltage in the coordinate system.

[0173] SPWM modulation module: used for receiving the fourth d-axis component and the fourth q-axis component to control the inverter.

[0174] It can be seen from the above technical scheme that the embodiment of the present application provides a three-phase three-level four-bridge-arm inverter control method and system, the method comprising: obtaining a transformed load voltage, a transformed load current and a transformed reference load voltage according to the load voltage, the load current and the reference load voltage; performing a difference operation on the transformed load voltage and the transformed reference load voltage to obtain a voltage error of the load; performing a difference operation on the voltage error and the transformed load current through a deadbeat control algorithm to obtain a first d-axis component and a first q-axis component of the reference output current in a dq coordinate system; obtaining a second d-axis component and a second q-axis component according to the output current; performing a difference operation on the first d-axis component and the second q-axis component of the reference output current; performing a difference operation on the second d-axis component and the second q-axis component of the reference output current; performing a difference operation on the second d-axis component and the second q-axis component of the reference output current; performing a difference operation on the first ... A d-axis component and a second d-axis component are differentially calculated to obtain a d-axis current error, and a first q-axis component and a second q-axis component are differentially calculated to obtain a q-axis current error; a third d-axis component and a third q-axis component of the load voltage are obtained; the d-axis current error, the q-axis current error, the second d-axis component, the second q-axis component, the third d-axis component and the third q-axis component are calculated by a sliding mode control algorithm to obtain a fourth d-axis component and a fourth q-axis component of the reference output voltage in a dq coordinate system; the fourth d-axis component and the fourth q-axis component are input to an SPWM modulation module to control the inverter. The method controls the voltage outer loop by a deadbeat control algorithm and controls the current inner loop by a sliding mode control algorithm, which can reduce the complexity of the control process. The control algorithm has stronger robustness and faster dynamic response speed. While ensuring the control performance, the calculation burden of the system can be reduced, and the problem of complex inverter control process can be solved.

[0175] Similar parts between the embodiments provided in this application can be referenced to each other. The specific implementation methods provided above are only a few examples under the general concept of this application and do not constitute a limitation on the protection scope of this application. For those skilled in the art, any other implementation methods expanded based on the scheme of this application without creative work belong to the protection scope of this application.

Claims

1. A three-phase three-level four-bridge-arm inverter control method, characterized in that: Applied to a three-phase three-level four-bridge-arm inverter, the inverter includes four bridge arms connected in parallel, each bridge arm includes four transistors, a filter is provided between the bridge arm and the load, the filter includes an inductor and a capacitor; the method includes: Obtaining a load voltage, a load current and a reference load voltage, so as to obtain a transformed load voltage, a transformed load current and a transformed reference load voltage according to the load voltage, the load current and the reference load voltage; the transformed load voltage and the transformed reference load voltage are voltages in a vector coordinate system, and the transformed load current is a current in a vector coordinate system; performing a difference operation on the converted load voltage and the converted reference load voltage to obtain a voltage error of the load; The voltage error and the transformed load current are calculated by a deadbeat control algorithm to obtain a first d-axis component and a first q-axis component, wherein the first d-axis component and the first q-axis component are currents of the reference output current in a dq coordinate system; Obtaining an output current to obtain a second d-axis component and a second q-axis component according to the output current, wherein the output current is an actual current output by the inverter, and the second d-axis component and the second q-axis component are currents of the output current in a dq coordinate system; performing a difference operation on the first d-axis component and the second d-axis component to obtain a d-axis current error, and performing a difference operation on the first q-axis component and the second q-axis component to obtain a q-axis current error; Acquire a third d-axis component and a third q-axis component according to the load voltage, wherein the third d-axis component and the third q-axis component are voltages of the load voltage in a dq coordinate system; The d-axis current error, the q-axis current error, the second d-axis component, the second q-axis component, the third d-axis component and the third q-axis component are calculated by a sliding mode control algorithm to obtain a fourth d-axis component and a fourth q-axis component, wherein the fourth d-axis component and the fourth q-axis component are voltages of the reference output voltage in a dq coordinate system; The fourth d-axis component and the fourth q-axis component are input to an SPWM modulation module to control the inverter.

2. The three-phase three-level four-bridge-arm inverter control method according to claim 1, characterized in that: The bridge arm includes a three-phase bridge arm and a neutral bridge arm, and the acquiring of the load voltage, the load current and the reference load voltage to obtain the transformed load voltage, the transformed load current and the transformed reference load voltage according to the load voltage, the load current and the reference load voltage includes: Respectively obtaining a load voltage and a load current obtained by the load through the three-phase bridge arm, and a reference load voltage of the load; Vector coordinate transformation is performed on the load voltage, the load current and the reference load voltage respectively, so as to transform the load voltage, the load current and the reference load voltage from a three-phase stationary coordinate system to a vector coordinate system, thereby obtaining a transformed load voltage, a transformed load current and a transformed reference load voltage.

3. The three-phase three-level four-bridge-arm inverter control method according to claim 2, characterized in that: The step of obtaining the load voltage, the load current and the reference load voltage to obtain the transformed load voltage, the transformed load current and the transformed reference load voltage according to the load voltage, the load current and the reference load voltage also includes: respectively obtaining the output voltage and the output current of the three-phase bridge arm, wherein the output voltage is the actual voltage output by the inverter; Performing vector coordinate transformation on the output voltage and the output current respectively, so as to transform the output voltage and the output current from a three-phase stationary coordinate system to a vector coordinate system, thereby obtaining a transformed output voltage and a transformed output current; Decoupling the load voltage and the load current through a first transformation matrix so that the transformed load voltage and the transformed load current satisfy a first state equation; The output voltage and the output current are decoupled by a first transformation matrix so that the transformed output voltage and the transformed output current satisfy a second state equation.

4. The three-phase three-level four-bridge-arm inverter control method according to claim 3, characterized in that: The vector coordinate system is In the vector coordinate system, the expression of the first state equation is: ； in, is the differential operator, , , They are Quantity, Quantity and Transformation load voltage of components; , , They are Quantity, Quantity and The transformed output current of the components; , , They are Quantity, Quantity and Component transformation load current; is the capacitance of the filter; The expression of the second state equation is: ； in, is the inductance of the three-phase bridge arm; is the inductance of the neutral bridge arm; , , They are Quantity, Quantity and The transformed output voltage of the component.

5. The three-phase three-level four-bridge-arm inverter control method according to claim 4, characterized in that: The step of calculating the voltage error and the transformed load current by using a deadbeat control algorithm to obtain a first d-axis component and a first q-axis component includes: The voltage error and the transformed load current are calculated according to the first state equation and the second state equation to obtain a transformed reference output current, wherein the transformed reference output current is a current in a vector coordinate system; The transformed reference output current is subjected to dq coordinate transformation through a second transformation matrix to transform the transformed reference output current from a vector coordinate system to a dq coordinate system, thereby obtaining a first d-axis component and a first q-axis component of the reference output current.

6. The three-phase three-level four-bridge-arm inverter control method according to claim 5, characterized in that: The control equation for transforming the reference output current is: ； ； ； in, for time The transformation of the components reference output current, for time The transformation of the components reference output current, for time The transformation of the components reference output current, for time Components of the transformed load current, for time Components of the transformed load current, for time Components of the transformed load current, for time The transformation of the components reference load voltage, for time The transformation of the components reference load voltage, for time The transformation of the components reference load voltage, for time The transformed load voltage of the component, for time The transformed load voltage of the component, for time The transformed load voltage of the component, is the sampling period.

7. The three-phase three-level four-bridge-arm inverter control method according to claim 5, characterized in that: The obtaining of the output current to obtain the second d-axis component and the second q-axis component according to the output current comprises: The output current is subjected to a dq coordinate transformation to transform the output current from a three-phase stationary coordinate system to a dq coordinate system, thereby obtaining a second d-axis component and a second q-axis component of the output current.

8. The three-phase three-level four-bridge-arm inverter control method according to claim 1, characterized in that: The method further comprises: Defining a sliding vector of the sliding mode control algorithm according to the d-axis current error and the q-axis current error; The sliding vector is derived to use a reaching law to weaken the chattering generated by the sliding mode control algorithm.

9. The three-phase three-level four-bridge-arm inverter control method according to claim 4, characterized in that: The control equations of the fourth d-axis component and the fourth q-axis component of the reference output voltage are: ； in, is the fourth d-axis component, i.e., the d-axis component of the reference output voltage, is the fourth q-axis component, i.e., the q-axis component of the reference output voltage; , , , are the parameters of the sliding mode control algorithm, , ; is a symbolic function; is the d-axis current error, is the q-axis current error; is the third d-axis component, is the third q-axis component, is the second d-axis component, is the second q-axis component, is the angular frequency.

10. A three-phase three-level four-bridge-arm inverter control system, characterized in that: The method applied to any one of claims 1 to 9, wherein the system comprises: Acquisition conversion module: used for acquiring load voltage, load current and reference load voltage, so as to obtain transformed load voltage, transformed load current and transformed reference load voltage according to the load voltage, load current and reference load voltage; the transformed load voltage and the transformed reference load voltage are voltages in a vector coordinate system, and the transformed load current is a current in a vector coordinate system; A calculation module: used for performing a difference operation on the converted load voltage and the converted reference load voltage to obtain a voltage error of the load; A deadbeat control module: used for calculating the voltage error and the transformed load current by a deadbeat control algorithm to obtain a first d-axis component and a first q-axis component, wherein the first d-axis component and the first q-axis component are currents of the reference output current in a dq coordinate system; The acquisition conversion module is further used to acquire the output current, so as to acquire the second d-axis component and the second q-axis component according to the output current, wherein the output current is the actual current output by the inverter, and the second d-axis component and the second q-axis component are the currents of the output current in the dq coordinate system; The calculation module is further used for performing a difference operation on the first d-axis component and the second d-axis component to obtain a d-axis current error, and performing a difference operation on the first q-axis component and the second q-axis component to obtain a q-axis current error; The acquisition conversion module is further used to obtain a third d-axis component and a third q-axis component according to the load voltage, wherein the third d-axis component and the third q-axis component are voltages of the load voltage in a dq coordinate system; A sliding mode control module: used for calculating the d-axis current error, the q-axis current error, the second d-axis component, the second q-axis component, the third d-axis component and the third q-axis component through a sliding mode control algorithm to obtain a fourth d-axis component and a fourth q-axis component, wherein the fourth d-axis component and the fourth q-axis component are voltages of the reference output voltage in a dq coordinate system; SPWM modulation module: used for receiving the fourth d-axis component and the fourth q-axis component to control the inverter.

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