Current switching control method and system for Z-source inverter of photovoltaic power generation system

Abstract

The invention relates to a current switching control method and system for a Z-source inverter of a photovoltaic power generation system, and the method comprises the steps: building a current switching affine model based on the Z-source inverter in the photovoltaic power generation system; establishing a current error switching affine model according to the current switching affine model; based on the current switching affine model and the current error switching affine model, establishing a plurality of subsystems of the Z-source inverter; establishing a switching table according to the plurality of subsystems of the Z-source inverter; and determining the states of an upper switching tube and a lower switching tube in the Z-source inverter in the next control period according to the switching table through a preset switching rule. The method has the advantages that the working state of the Z-source inverter in the photovoltaic power generation system can be accurately described, the switching states of the Z-source inverter in different control periods can be directly selected based on the switching rule, complex coordinate transformation and pulse width modulation processes are not needed, no control parameters exist, and high robustness is achieved under the condition that circuit parameters are uncertain.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic power generation technology in new energy technologies, and specifically relates to a current switching control method and system for a Z-source inverter in a photovoltaic power generation system. Background Technology

[0002] Z-source inverters in photovoltaic power generation systems, due to their unique impedance network structure, can achieve buck-boost conversion and allow bridge arm shoot-through, making them important in fields such as new energy grid connection. However, traditional Z-source inverter control methods, especially pulse width modulation strategies based on voltage modulation, have significant shortcomings in terms of dynamic performance, model accuracy, and control robustness. Summary of the Invention

[0003] The purpose of this invention is to provide a switching control method for Z-source inverters based on a current-switching affine model, so as to overcome the shortcomings of the prior art, such as inaccurate model description, limited control performance, and reliance on complex pulse width modulation algorithms.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a current switching control method for a Z-source inverter in a photovoltaic power generation system, comprising:

[0005] Based on the Z-source inverter in the photovoltaic power generation system, a current switching affine model is established; based on the current switching affine model, a current error switching affine model is established.

[0006] Based on the current switching affine model and the current error switching affine model, multiple subsystems of the Z-source inverter are established.

[0007] Based on the multiple subsystems of the Z-source inverter, a switching table is established;

[0008] Based on the preset switching rules and the switching table, the state of the upper and lower switching transistors inside the Z-source inverter in the next control cycle is determined.

[0009] Preferably, the step of establishing a current-switching affine model based on the Z-source inverter in the photovoltaic power generation system; and establishing a current error-switching affine model based on the current-switching affine model, includes:

[0010] A control method based on a switching model is adopted, taking the three-phase AC current of the Z-source inverter in the photovoltaic power generation system as the state of the controlled system, and establishing a current switching affine model based on the working principle of the Z-source inverter in direct-drive mode and non-direct-drive mode.

[0011] Based on the current switching affine model, the current error switching affine model of the Z-source inverter is obtained by subtracting the actual value from the expected value in the current switching affine model.

[0012] Preferably, the current-switching affine model satisfies the following formula:

[0013]

[0014] In the above formula: Let R represent the derivative of the state vector of the controlled system with respect to time t, R represent the AC side resistance of the Z-source inverter, and L represent the AC side inductance of the Z-source inverter. i represents the state vector of the controlled system. a (t), i b (t), i c (t) represents the three-phase AC current of the Z-source inverter at time t; e a (t), e b (t), e c (t) represents the AC three-phase voltage measured by the Z-source inverter at time t; V c V represents the capacitor voltage value of the Z-source inverter; pv P represents the output voltage on the photovoltaic side of the Z-source inverter; k For discrete switching functions, k = a, b, c, where a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively; in the discrete switching function, S k =1 indicates that in the Z-source inverter, the upper switch of the k-phase bridge arm is on while the lower switch is off. k =0 indicates that the upper switch of the k-phase bridge arm in the Z-source inverter is off and the lower switch is on; Z=1 indicates that the Z-source inverter is in shoot-through mode; Z=0 indicates that it is in non-shoot-through mode. Let I represent the state matrix of the controlled system, and let I represent the identity matrix. This indicates the switching affine term of the controlled system.

[0015] Preferably, the switching affine term of the controlled system satisfies the following formula:

[0016]

[0017] In the above formula: e represents the switching affine term of the controlled system. a (t), e b (t), e c (t) represents the AC three-phase voltage measured at time t of the Z-source inverter, V. c This represents the capacitor voltage value of the Z-source inverter, V. pv The output voltage on the photovoltaic side of the Z-source inverter is represented by P, where T represents the transpose of the matrix, L represents the inductance value on the AC side of the Z-source inverter, and P represents the output voltage on the photovoltaic side of the Z-source inverter. kLet k represent the discrete switching function, where k = a, b, c, and a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively.

[0018] Preferably, the current error switching affine model satisfies the following formula:

[0019]

[0020] In the above formula, This represents the derivative of the state error vector with respect to time t. Represents the state error vector, where: , , ; This represents the difference between the actual and expected values ​​of the AC phase a current of the Z-source inverter at time t. This represents the difference between the actual and expected values ​​of the b-phase current on the AC side of the Z-source inverter at time t. This represents the difference between the actual and expected values ​​of the c-phase current on the AC side of the Z-source inverter at time t; a (t), i b (t), i c (t) represents the actual value of the three-phase AC current of the Z-source inverter at time t; i ar (t), i br (t), i cr (t) represents the expected value of the three-phase AC current on the Z-source inverter at time t; e a (t), e b (t), e c (t) represents the AC three-phase voltage of the Z-source inverter at time t; To switch affine terms, P k Let S represent the discrete switching function, k = a, b, c, where a, b, and c represent phases a, b, and c on the AC side of the Z-source inverter, respectively. k =1 indicates that in the Z-source inverter, the upper switch of the k-phase bridge arm is on while the lower switch is off. k =0 indicates that the upper switch of the k-phase bridge arm in the Z-source inverter is off and the lower switch is on; Z=1 indicates that the Z-source inverter is in shoot-through mode; Z=0 indicates that it is in non-shoot-through mode. Let I represent the state matrix of the controlled system, and let I represent the identity matrix.

[0021] Preferably, the switching affine term satisfies the following formula:

[0022]

[0023] In the above formula, To switch affine terms, e a(t), e b (t), e c (t) represents the AC three-phase voltage measured at time t of the Z-source inverter, V. c This represents the capacitor voltage value of the Z-source inverter, V. pv The output voltage on the photovoltaic side of the Z-source inverter is represented by , T represents the transpose of the matrix, and L represents the inductance value on the AC side of the Z-source inverter. This represents the product of the AC side phase a resistance value and its expected current value of the Z-source inverter. This represents the product of the AC side b-phase resistance value and its expected current value of the Z-source inverter. P represents the product of the AC side c-phase resistance value and its expected current value of the Z-source inverter. k Let k represent the discrete switching function, where k = a, b, c, and a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively.

[0024] Preferably, the establishment of multiple subsystems of the Z-source inverter based on the current switching affine model and the current error switching affine model includes:

[0025] Based on the current switching affine model and the current error switching affine model, a correspondence between the switching states of different switching transistors inside the Z-source inverter and the dynamics of the Z-source inverter is established.

[0026] Based on the switching states of different switching transistors inside the Z-source inverter, the AC side output voltage of the Z-source inverter undergoes periodic changes.

[0027] Based on the AC side output voltage cycle of the Z-source inverter, the dynamic model of the Z-source inverter corresponding to the switching states of different switching transistors is divided into multiple subsystems.

[0028] Preferably, the step of establishing a switching table based on multiple subsystems of the Z-source inverter includes:

[0029] The acquired complete three-phase AC voltage cycle is divided into 6 sectors with a phase angle interval of 60°.

[0030] Within each sector, based on the magnitude relationship of the three-phase voltages and the current error switching affine model, multiple subsystems that satisfy the convex combination condition and the existence condition of the common Lyapunov function are selected to form the switching subsystem subset corresponding to that sector; a complete switching table is formed by all sectors and their corresponding switching subsystem subsets.

[0031] Preferably, determining the state of the upper and lower switching transistors inside the Z-source inverter in the next control cycle according to the preset switching rules and the switching table includes:

[0032] Obtain the current error state vector, three-phase voltage, capacitor voltage, photovoltaic output voltage, and inductance value at the current moment;

[0033] The current sector is determined based on the current three-phase voltage magnitude relationship, and the corresponding switching subsystem subset is obtained according to the switching table.

[0034] For each subsystem in the set of switching subsystems, calculate its corresponding switching function value based on the current error switching affine model;

[0035] Compare the switching function values ​​of all subsystems in the switching subsystem subset, and select the subsystem that minimizes the switching function value;

[0036] The switching vector corresponding to the selected subsystem is used as the switching state output for the next control cycle to control the on and off of the upper and lower switching transistors of each phase bridge arm of the Z-source inverter.

[0037] The switching rule satisfies the following formula:

[0038]

[0039] In the above formula, This represents the selected subsystem, and argmin represents the minimization function. This represents the various subsystems in the currently selected switching subset; P represents the product of the state error vector and the switching function value. k Let k represent the discrete switching function, where k = a, b, c, and a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively.

[0040] Secondly, the present invention provides a current switching control system for a Z-source inverter in a photovoltaic power generation system, characterized in that it includes:

[0041] The current error switching affine model construction module is used to establish a current switching affine model based on the Z-source inverter in the photovoltaic power generation system; and to establish a current error switching affine model based on the current switching affine model.

[0042] The subsystem construction module is used to establish multiple subsystems of the Z-source inverter based on the current switching affine model and the current error switching affine model.

[0043] The switching table construction module is used to establish a switching table based on the multiple subsystems of the Z-source inverter;

[0044] The determination module is used to determine the state of the upper and lower switching transistors inside the Z-source inverter in the next control cycle according to the preset switching rules and the switching table.

[0045] The beneficial effects of this invention are:

[0046] This invention, based on a current-switching affine model and a current-error-switching affine model, effectively overcomes the shortcomings of traditional control methods in terms of dynamic performance, model accuracy, and control robustness by establishing a subsystem and a switching table and directly selecting the switching state according to the switching rules. This method can accurately describe the nonlinear switching dynamics of a Z-source inverter in shoot-through and non-shoot-through modes, thereby improving current tracking accuracy and dynamic response speed. It eliminates the need for complex coordinate transformations and pulse width modulation processes, directly determining the switching state through the switching table, simplifying the control structure and enhancing system real-time performance. Furthermore, the control process does not rely on manually tuned parameters, exhibiting strong adaptability to circuit parameter uncertainties and significantly improving the system's robustness and reliability under actual operating conditions. Attached Figure Description

[0047] Figure 1 This is a circuit topology diagram of the Z-source inverter in the photovoltaic power generation system of the present invention;

[0048] Figure 2 This is a control block diagram of the present invention;

[0049] Figure 3 This is a schematic diagram of sector division in this invention;

[0050] Figure 4 This is a waveform diagram of the three-phase voltage and current and the three-phase bridge arm switch states of the present invention;

[0051] Figure 5 S of the present invention a Switching frequency diagram of the switching transistor;

[0052] Figure 6 This is a diagram showing the results of selecting the subsystem in different sectors according to the present invention;

[0053] Figure 7 This is a waveform diagram of phase a voltage and current under the condition of parameter uncertainty in this invention;

[0054] Figure 8 The diagram shows the dynamic response waveforms of the capacitor voltage and phase a voltage and current of the present invention. Detailed Implementation

[0055] The technical solutions of the present invention will be explained in detail and comprehensively with reference to the accompanying drawings of the embodiments of the present invention. It should be understood that the provided embodiments represent only some examples of the present invention and not all possible implementations. Other implementations that can be deduced by those skilled in the art based on these embodiments without creative work also fall within the protection scope of the present invention.

[0056] Example 1:

[0057] The present invention provides a current switching control method for a Z-source inverter in a photovoltaic power generation system, comprising the following steps:

[0058] Step 1: Based on the Z-source inverter in the photovoltaic power generation system (e.g., Figure 1 Establish a current switching affine model; based on the current switching affine model, establish a current error switching affine model;

[0059] Step 2: Based on the current switching affine model and the current error switching affine model, establish multiple subsystems of the Z-source inverter;

[0060] Step 3: Establish a switching table based on the multiple subsystems of the Z-source inverter;

[0061] Step 4: Based on the preset switching rules and the switching table, determine the state of the upper and lower switching transistors inside the Z-source inverter for the next control cycle.

[0062] In step 1 above, based on the Z-source inverter in the photovoltaic power generation system, a current switching affine model is established; based on the current switching affine model, a current error switching affine model is established, including the following steps:

[0063] Step 1.1: Using a control method based on a switching model, the three-phase AC current of the Z-source inverter in the photovoltaic power generation system is taken as the state of the controlled system. Based on the working principle of the Z-source inverter in direct-drive mode and non-direct-drive mode, a current switching affine model is established.

[0064] Step 1.2: Based on the current switching affine model, the current error switching affine model of the Z-source inverter is obtained by subtracting the actual value from the expected value in the current switching affine model.

[0065] Furthermore, the current-switching affine model described in step 1 satisfies the following formula:

[0066] (1)

[0067] In the above formula: Let R represent the derivative of the state vector of the controlled system with respect to time t, R represent the AC side resistance of the Z-source inverter, and L represent the AC side inductance of the Z-source inverter. i represents the state vector of the controlled system. a (t), i b (t), i c (t) represents the three-phase AC current of the Z-source inverter at time t; e a (t), e b (t), e c(t) represents the AC three-phase voltage measured by the Z-source inverter at time t; V c V represents the capacitor voltage value of the Z-source inverter; pv P represents the output voltage on the photovoltaic side of the Z-source inverter; k For discrete switching functions, k = a, b, c, where a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively; in the discrete switching function, S k =1 indicates that in the Z-source inverter, the upper switch of the k-phase bridge arm is on while the lower switch is off. k =0 indicates that the upper switch of the k-phase bridge arm in the Z-source inverter is off while the lower switch is on; Z=1 indicates that the Z-source inverter is in shoot-through mode (i.e., both upper and lower switches of the same bridge arm are on at the same time); Z=0 indicates that it is in non-shoot-through mode. Let I represent the state matrix of the controlled system, and let I represent the identity matrix. This indicates the switching affine term of the controlled system.

[0068] Furthermore, the switching affine terms of the controlled system satisfy the following formula:

[0069]

[0070] In the above formula: e represents the switching affine term of the controlled system. a (t), e b (t), e c (t) represents the AC three-phase voltage measured at time t of the Z-source inverter, V. c This represents the capacitor voltage value of the Z-source inverter, V. pv The output voltage on the photovoltaic side of the Z-source inverter is represented by P, where T represents the transpose of the matrix, L represents the inductance value on the AC side of the Z-source inverter, and P represents the output voltage on the photovoltaic side of the Z-source inverter. k Let k represent the discrete switching function, where k = a, b, c, and a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively.

[0071] Furthermore, the current error switching affine model described in step 1 satisfies the following formula:

[0072] (2)

[0073] In the above formula, This represents the derivative of the state error vector with respect to time t. Represents the state error vector, where: , , ; This represents the difference between the actual value and the expected value of the a-phase current on the AC side of the Z-source inverter at time t (i.e., the error value of the a-phase current). To switch affine items, This represents the difference between the actual value and the expected value of the b-phase current on the AC side of the Z-source inverter at time t (i.e., the error value of the b-phase current). This represents the difference between the actual and expected values ​​of the c-phase current on the AC side of the Z-source inverter at time t (i.e., the error value of the c-phase current); a (t), i b (t), i c (t) represents the actual value of the three-phase AC current of the Z-source inverter at time t; i ar (t), i br (t), i cr (t) represents the expected value of the three-phase AC current on the Z-source inverter at time t; e a (t), e b (t), e c (t) represents the AC three-phase voltage measured by the Z-source inverter at time t; P k Let S represent the discrete switching function, k = a, b, c, where a, b, and c represent phases a, b, and c on the AC side of the Z-source inverter, respectively. k =1 indicates that in the Z-source inverter, the upper switch of the k-phase bridge arm is on while the lower switch is off. k =0 indicates that the upper switch of the k-phase bridge arm in the Z-source inverter is off and the lower switch is on; Z=1 indicates that the Z-source inverter is in shoot-through mode; Z=0 indicates that it is in non-shoot-through mode. Let I represent the state matrix of the controlled system, and let I represent the identity matrix.

[0074] Furthermore, the switching affine term satisfies the following formula:

[0075]

[0076] In the above formula, To switch affine terms, e a (t), e b (t), e c (t) represents the AC three-phase voltage measured at time t of the Z-source inverter, V. c This represents the capacitor voltage value of the Z-source inverter, V. pv The output voltage on the photovoltaic side of the Z-source inverter is represented by , T represents the transpose of the matrix, and L represents the inductance value on the AC side of the Z-source inverter. This represents the product of the AC side phase a resistance value and the expected current value of the Z-source inverter. This represents the product of the AC side b-phase resistance value and the expected current value of the Z-source inverter. This represents the product of the AC side c-phase resistance value and the expected current value of the Z-source inverter.

[0077] In Step 2 above, to establish multiple subsystems of the Z-source inverter based on the current-switching affine model and the current-error switching affine model, the following steps are included:

[0078] Step 2.1: Based on the current-switching affine model and the current-error switching affine model, establish the correspondence between the switching states of different switching tubes inside the Z-source inverter and the dynamics of the Z-source inverter;

[0079] Step 2.2: Based on the switching states of different switching tubes inside the Z-source inverter, form the periodic variation of the output voltage on the AC side of the Z-source inverter;

[0080] Step 2.3: Based on the period of the output voltage on the AC side of the Z-source inverter, divide the dynamic model of the Z-source inverter corresponding to the switching states of different switching tubes into multiple subsystems.

[0081] Step 2 defines the subsystems of the Z-source inverter, including: Based on the current-error switching affine model established in Step 1, by changing the value of the switching function in Equation (2), the control of the three-phase current error can be achieved. By regarding the three-phase ZSI operating states under different switching state combinations in Equations (1) and (2) as different subsystems, a complete three-phase ZSI operating cycle, that is, a complete three-phase AC side AC voltage change cycle, is divided into multiple subsystems (for example, 9 subsystems).

[0082] When in the switching vector [S a S b S c Z], S a = 0, S b = 0, S c = 0, Z = 0, that is, when the switching tube S1 on the a-phase bridge arm of the Z-source inverter is off and the lower switching tube S2 is on, the switching tube S3 on the b-phase bridge arm is off and the lower switching tube S4 is on, the switching tube S5 on the c-phase bridge arm is off and the lower switching tube S6 is on, and the overall Z-source inverter is in a non-through state, it is defined that the current Z-source inverter is operating in subsystem V u1 , denoted as V u1 = [S a S b S c Z] = [0 0 0 0];

[0083] When in the switching vector [S a S b S c Z], S a = 0, S b = 0, S cWhen = 1 and Z = 0, that is, when the switch tube S1 on the a-phase bridge arm of the Z-source inverter is turned off, the lower switch tube S2 is turned on, the switch tube S3 on the b-phase bridge arm is turned off, the lower switch tube S4 is turned on, the switch tube S5 on the c-phase bridge arm is turned on, and the lower switch tube S6 is turned off, and the overall Z-source inverter is in a non-p直通 state, it is defined that the current Z-source inverter works in the subsystem V u2 , denoted as V u2 = [S a S b S c Z] = [0 0 1 0];

[0084] When the switching vector [S a S b S c Z] has S a = 0, S b = 1, S c = 0, and Z = 0, that is, when the switch tube S1 on the a-phase bridge arm of the Z-source inverter is turned off, the lower switch tube S2 is turned on, the switch tube S3 on the b-phase bridge arm is turned on, the lower switch tube S4 is turned off, the switch tube S5 on the c-phase bridge arm is turned off, and the lower switch tube S6 is turned on, and the overall Z-source inverter is in a non-p直通 state, it is defined that the current Z-source inverter works in the subsystem V u3 , denoted as V u3 = [S a S b s S c Z] = [0 1 0 0];

[0085] When the switching vector [S a S b S c Z] has S a = 0, S b = 1, S c = 1, and Z = 0, that is, when the switch tube S1 on the a-phase bridge arm of the Z-source inverter is turned off, the lower switch tube S2 is turned on, the switch tube S3 on the b-phase bridge arm is turned on, the lower switch tube S4 is turned off, the switch tube S5 on the c-phase bridge arm is turned on, and the lower switch tube S6 is turned off, and the overall Z-source inverter is in a non-p直通 state, it is defined that the current Z-source inverter works in the subsystem V u4 , denoted as V u4 = [S a S b S c Z] = [0 1 1 0];

[0086] When the switching vector [S a S b S c Z] has S a = 1, S b = 0, S c It should be noted that there may be some inaccuracies in the translation due to the possible ambiguity of the original text's "非直通状态" (it might be a very specific technical term that could be more precisely translated depending on the context). You may need to further adjust it according to the actual situation.When = 0 and Z = 0, that is, when the switch S1 on the a-phase bridge arm of the Z-source inverter is conducting, the lower switch S2 is off, the switch S3 on the b-phase bridge arm is off, the lower switch S4 is conducting, the switch S5 on the c-phase bridge arm is off, and the lower switch S6 is conducting, and the overall Z-source inverter is in the non-direct-conduction state, it is defined that the current Z-source inverter operates in subsystem V u5 , denoted as V u5 = [S a S b S c Z] = [1 0 0 0];

[0087] When the switching vector [S a S b S c Z] has S a = 1, S b = 0, S c = 1, and Z = 0, that is, when the switch S1 on the a-phase bridge arm of the Z-source inverter is conducting, the lower switch S2 is off, the switch S3 on the b-phase bridge arm is off, the lower switch S4 is conducting, the switch S5 on the c-phase bridge arm is conducting, and the lower switch S6 is off, and the overall Z-source inverter is in the non-direct-conduction state, it is defined that the current Z-source inverter operates in subsystem V u6 , denoted as V u6 = [S a S b S c Z] = [1 0 1 0];

[0088] When the switching vector [S a S b S c Z] has S a = 1, S b = 1, S c = 0, and Z = 0, that is, when the switch S1 on the a-phase bridge arm of the Z-source inverter is conducting, the lower switch S2 is off, the switch S3 on the b-phase bridge arm is conducting, the lower switch S4 is off, the switch S5 on the c-phase bridge arm is off, and the lower switch S6 is conducting, and the overall Z-source inverter is in the non-direct-conduction state, it is defined that the current Z-source inverter operates in subsystem V u7 , denoted as V u7 = [S a S b S c Z] = [1 1 0 0];

[0089] When the switching vector [S a S b S c Z] has S a = 1, S b = 1, S cWhen = 1 and Z = 0, that is, when the switch S1 on the a-phase bridge arm of the Z-source inverter is turned on, the lower switch S2 is turned off, the switch S3 on the b-phase bridge arm is turned on, the lower switch S4 is turned off, the switch S5 on the c-phase bridge arm is turned on, and the lower switch S6 is turned off, and the overall Z-source inverter is in a non-through state, it is defined that the current Z-source inverter operates in subsystem V u8 , denoted as V u8 =[S a S b S c Z]= [1 1 1 0];

[0090] When the switching vector [S a S b S c Z] has S a = 1, S b = 1, S c = 1, and Z = 1, that is, when the switch S1 on the a-phase bridge arm of the Z-source inverter is turned on, the lower switch S2 is turned on, the switch S3 on the b-phase bridge arm is turned on, the lower switch S4 is turned on, the switch S5 on the c-phase bridge arm is turned on, and the lower switch S6 is turned on, and the overall Z-source inverter is in a through state, it is defined that the current Z-source inverter operates in subsystem V u9 , denoted as V u9 =[S a S b S c Z]= [1 1 1 1];

[0091] In step 3 above, as Figure 3 shown, establishing a switching table based on multiple subsystems of the Z-source inverter includes the following steps:

[0092] Step 3.1: Divide the obtained complete three-phase AC voltage cycle into 6 sectors at intervals of 60° phase angle;

[0093] Step 3.2: In each sector, according to the magnitude relationship of the three-phase voltages and the current error switching affine model, select multiple subsystems that meet the convex combination condition and the condition for the existence of a common Lyapunov function to form the switching subsystem subset corresponding to this sector; Step 3.3: Form a complete switching table from all sectors and their corresponding switching subsystem subsets.

[0094] Step 3 involves establishing a switching table based on the defined subsystems. This includes dividing a complete three-phase AC voltage cycle into six sectors at 60-degree phase angle intervals. Within each sector, based on the current error switching affine model analysis (satisfying the convex combination condition and the existence condition of the common Lyapunov function), a subset of switching subsystems composed of different subsystems is selected as the subsystem combinations available in the corresponding sector. Specifically, this is described as follows:

[0095] When the phase angle of phase a voltage (assuming it is a sinusoidal waveform) on the AC side of the Z-source inverter is in the range of 0 to 60 degrees, i.e., e a >e b >e c At this time, it is defined as sector 1. At this time, the switching subsystem subset Σ1 corresponding to this sector consists of 4 subsystems, namely subsystem V u5 V u6 V u7 and V u9 , represented as Σ1={V u5 V u6 V u7 V u9};

[0096] When the phase angle of phase a voltage (assuming it is a sinusoidal waveform) on the AC side of the Z-source inverter is in the range of 60 to 120 degrees, i.e. b >e a >e c At this time, it is defined as sector 2. At this time, the switching subsystem subset Σ1 corresponding to this sector consists of 4 subsystems, namely subsystem V u3 V u5 V u7 and V u9 , represented as Σ2={V u3 V u5 V u7 V u9};

[0097] When the phase angle of phase a voltage (assuming it is a sinusoidal waveform) on the AC side of the Z-source inverter is in the range of 120 to 180 degrees, i.e., e b >e c >e a At this time, sector 3 is defined. The corresponding switching subsystem subset Σ1 consists of 4 subsystems, namely subsystem V. u3 V u4 V u7 and V u9 , represented as Σ3={V u3 V u4 V u7 V u9};

[0098] When the phase angle of phase a voltage (assuming it is a sinusoidal waveform) on the AC side of the Z-source inverter is in the range of 180~240 degrees, i.e., e c >e b >e a At this time, sector 4 is defined. The corresponding switching subsystem subset Σ1 consists of 4 subsystems, namely subsystem V. u2 V u3 V u4 and V u9 , represented as Σ4={V u2 V u3 V u4 V u9};

[0099] When the phase angle of phase a voltage (assuming it is a sinusoidal waveform) on the AC side of the Z-source inverter is in the range of 240~300 degrees, i.e., e c >e a >e b At this time, sector 5 is defined. The corresponding switching subsystem subset Σ1 consists of 4 subsystems, namely subsystem V. u2 V u4 V u6 and V u9 , represented as Σ5={V u2 V u4 V u6 V u9};

[0100] When the phase angle of phase a voltage (assuming it is a sinusoidal waveform) on the AC side of the Z-source inverter is in the range of 300~360 degrees, i.e., e a >e c >e b At this time, sector 6 is defined. The corresponding switching subsystem subset Σ1 consists of 4 subsystems, namely subsystem V. u2 V u5 V u6 and V u9 , represented as Σ6={V u2 V u5 V u6 V u9};

[0101] Finally: the sector is divided according to the three-phase voltage state to obtain the sector at the current moment, and then the switching subset that should be selected is determined based on the sector, which is used as the switching table.

[0102] Further, step 4, which involves determining the states of the upper and lower switching transistors inside the Z-source inverter for the next control cycle according to the preset switching rules and the switching table, includes:

[0103] Obtain the current error state vector, three-phase voltage, capacitor voltage, photovoltaic output voltage, and inductance value at the current moment;

[0104] The current sector is determined based on the current three-phase voltage magnitude relationship, and the corresponding switching subsystem subset is obtained according to the switching table.

[0105] For each subsystem in the set of switching subsystems, calculate its corresponding switching function value based on the current error switching affine model;

[0106] Compare the switching function values ​​of all subsystems in the switching subsystem subset, and select the subsystem that minimizes the switching function value;

[0107] The switching vector corresponding to the selected subsystem is used as the switching state output for the next control cycle to control the on and off of the upper and lower switching transistors of each phase bridge arm of the Z-source inverter.

[0108] The switching rule satisfies the following formula:

[0109]

[0110] In the above formula, This represents the selected subsystem, and argmin represents the minimization function. This represents the various subsystems in the currently selected switching subset; P represents the product of the state error vector and the switching function value. k Let k represent the discrete switching function, where k = a, b, c, and a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively.

[0111] Step 4 above mainly involves selecting the switching subset Σ for the current sector. i The four subsystems available in (i=1,2,3,4,5,6) allow for different subsystems V. ui The states corresponding to (i=1,2,3,4,5,6,7,8,9) Perform calculations and select the subsystem with the smallest result; the selected subsystem is then output.

[0112] When selecting a subsystem: taking sector I as an example, switch subset Σ1={V u5 V u6 V u7 V u9 When selecting subsystem Vu5 At that time, [P] a , P b , P c ] = [2 / 3, -1 / 3, -1 / 3], then let

[0113]

[0114] When selecting subsystem V u6 At that time, [P] a , P b , P c ] = [1 / 3, -2 / 3, 1 / 3], then let

[0115]

[0116] When selecting subsystem V u7 At that time, [P] a , P b , P c ] = [1 / 3, 1 / 3, -2 / 3], then let

[0117]

[0118] When selecting subsystem V u9 At that time, [P] a , P b , P c ]=[0,0,0], at this time let

[0119]

[0120] like The calculation result is The smallest of the subsystems is selected as subsystem V. u5 The corresponding switch states, the three-phase bridge arm switch states [S] a S b S c Z] = [1 0 0 0], that is, the upper switch S1 of phase a bridge arm is turned on and the lower switch S2 is turned off; the upper switch S3 of phase b bridge arm is turned off and the lower switch S4 is turned on; the upper switch S5 of phase c bridge arm is turned off and the lower switch S6 is turned on.

[0121] like The calculation result is The smallest of the subsystems is selected as subsystem V. u6 The corresponding switch states, the three-phase bridge arm switch states [S] a S b S cZ] = [1 0 1 0], that is, the upper switch S1 of phase a bridge arm is turned on and the lower switch S2 is turned off; the upper switch S3 of phase b bridge arm is turned off and the lower switch S4 is turned on; the upper switch S5 of phase c bridge arm is turned on and the lower switch S6 is turned off.

[0122] like The calculation result is The smallest of the subsystems is selected as subsystem V. u7 The corresponding switch states, the three-phase bridge arm switch states [S] a S b S c Z] = [1 1 0 0], that is, the upper switch S1 of phase a bridge arm is turned on and the lower switch S2 is turned off; the upper switch S3 of phase b bridge arm is turned on and the lower switch S4 is turned off; the upper switch S5 of phase c bridge arm is turned off and the lower switch S6 is turned on.

[0123] like The calculation result is The smallest of the subsystems is selected as subsystem V. u9 The corresponding switch states, the three-phase bridge arm switch states [S] a S b S c Z] = [0 0 0 1], which is the direct zero state, that is, the upper switch tubes S1, S3, S5 and the lower switch tubes S2, S4, S6 of the three-phase bridge arm are simultaneously turned on; the obtained three-phase bridge arm is used as the control signal output.

[0124] The control block diagram of this invention is as follows: Figure 2 As shown, a dual closed-loop control method is employed. The inner loop represents the current switching control method for the Z-source inverter in a photovoltaic power generation system proposed in this invention, while the outer loop controller is a PI controller. As shown in the figure, the outer loop represents the capacitor voltage V in the Z-source network of the Z-source inverter. cz The control loop collects the current capacitor voltage value and compares it with the expected value V. czr The difference is used to obtain the error signal, which is then passed through a PI controller to obtain the expected value of the d-axis current i in the two-phase rotating coordinate system. dr q-axis current expected value i qr The initial value is 0. After coordinate transformation from a two-phase rotating coordinate system to a three-phase stationary coordinate system, the desired value of the three-phase current i is obtained. ar i br i cr .

[0125] Simulation verification

[0126] The simulation parameters of the Z-source inverter are as follows: the three-phase voltage e in the three-phase stationary coordinate system. a , e b , ec Peak voltage 311V, power frequency f=50Hz; AC filter inductance L=50mH, AC equivalent resistance R=3 ohms, capacitance C in the Z-source network. Z =2000 microfarads, inductance value L in the Z-source network Z =30 millihenries; control period T S =0.0001 seconds, input voltage V0 = 550 volts. The expected value of the capacitor voltage V in the Z-source network. cr = 600 volts.

[0127] Figure 4 This is a simulation waveform diagram showing the three-phase AC voltage, three-phase AC current, and three-phase bridge arm switching states of a Z-source inverter using the method of this invention. It should be noted that when the three-phase bridge arm switching state is -1, it indicates a shoot-through state. The three-phase current i... a i b i c The waveform is smooth and symmetrical, and corresponds to the three-phase voltage e. a , e b , e c The waveforms maintain precise synchronization, achieving unity power factor control. Furthermore, the three-phase bridge arm switching waveforms are significantly different from those of the SVPWM modulation method, enabling direct selection of the shoot-through state and verifying the effectiveness of the method presented in this invention.

[0128] Figure 5 For the switching transistor S a1 The spectrum analysis results show that the switching frequencies are concentrated within 10kHz, which is consistent with the expected results.

[0129] Figure 6 To ensure the subsystem selection results are consistent across different sectors, the subsystem selection and switching table design must be followed.

[0130] Figure 7 The simulation waveforms of phase a voltage and phase a current under parameter uncertainty are shown. The simulation results show that the current waveform remains smooth and maintains a good sinusoidal state under parameter uncertainty, accurately synchronizing with the voltage without any phase difference, thus verifying the effectiveness of the method of this invention.

[0131] Figure 8 The transient response waveforms of capacitor voltage Vc, phase a voltage, and phase a current in the Z-source network are shown. At t=1s, the expected value of the capacitor voltage increases from 600V to 700V. The capacitor voltage and grid-connected current respond rapidly, and the current waveform remains smooth and maintains a good sinusoidal state, accurately synchronizing with the voltage, thus verifying the effectiveness of the method of this invention.

[0132] Furthermore, the control methods of traditional Z-source inverters, especially voltage-modulated pulse-width modulation (PWM) strategies, have long been limited by the inherent relationship between model accuracy and control structure. This limitation manifests in two main ways: first, existing modeling methods are mostly based on state-space averaging, which struggles to accurately describe the transient behavior of current during dynamic processes; second, control strategies typically rely on linear approximations or single-mode assumptions, making them prone to dynamic response lag, output voltage oscillations, and DC-link voltage instability during sudden input voltage changes, drastic load variations, or multi-mode switching. These technical bottlenecks severely restrict the reliable operation and control accuracy of Z-source inverters in application scenarios with frequent dynamic conditions, such as high-performance power electronic systems, grid-connected renewable energy generation, and motor drives.

[0133] To address the aforementioned shortcomings, a modeling method based on switching system theory describes the dynamic behavior of the Z-source inverter under different switching states as a series of subsystems, and switches these subsystems according to the switching signal, thus more accurately characterizing its nonlinear and multimodal hybrid characteristics. This invention's method can explicitly handle the transient process between shoot-through and non-shoot-through states, providing a reliable model foundation for the design of high-precision controllers. Therefore, the switching control strategy based on the current-switching affine model offers a new approach with theoretical rigor and engineering applicability to overcome the shortcomings of traditional modeling methods in terms of dynamic description accuracy. This technology has significant potential in improving the dynamic performance of Z-source inverters, enhancing system robustness, and optimizing overall control performance.

[0134] The present invention mainly achieves the following effects:

[0135] (1) The current switching affine model established in this invention overcomes the description error caused by the approximation process in traditional linear modeling, and realizes accurate modeling of the nonlinear switching dynamics of Z-source inverter, thus providing an accurate theoretical basis for the design of high-performance controllers and system stability analysis.

[0136] (2) Direct selection of the pass-through zero state is realized without relying on complex pulse width modulation algorithms or solving value functions. The pass-through zero state can be directly determined by switching rules, avoiding the problem of high computation and implementation complexity in traditional schemes, and improving the system response speed and control real-time performance.

[0137] (3) No control parameters: The method of the present invention does not contain control parameters that need to be manually tuned. It has inherent strong robustness to circuit parameter uncertainties, which significantly improves the adaptability and reliability of the system under actual working conditions.

[0138] Example 2:

[0139] Based on the method in Example 1, the present invention proposes a current switching control system for a Z-source inverter in a photovoltaic power generation system, comprising:

[0140] The current error switching affine model construction module is used to establish a current switching affine model based on the Z-source inverter in the photovoltaic power generation system; and to establish a current error switching affine model based on the current switching affine model.

[0141] The subsystem construction module is used to establish multiple subsystems of the Z-source inverter based on the current switching affine model and the current error switching affine model.

[0142] The switching table construction module is used to establish a switching table based on the multiple subsystems of the Z-source inverter;

[0143] The determination module is used to determine the state of the upper and lower switching transistors inside the Z-source inverter in the next control cycle according to the preset switching rules and the switching table.

[0144] It should be noted that the relational terms mentioned in the text, such as "first" and "second," are used only to distinguish different entities or operations and do not imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," and variations thereof are intended to cover non-exclusive content, thereby allowing a process, method, article, or apparatus that comprises multiple elements to include not only the listed elements but also other elements not expressly listed or inherent elements. An element defined by "comprising one..." does not exclude the presence of other identical elements in the said process, method, article, or apparatus.

[0145] Although embodiments of the invention have been shown and described herein, those skilled in the art will understand that these embodiments can be varied, modified, substituted, and modified without departing from the principles and spirit of the invention. The scope of protection of the invention is defined by the appended claims and their equivalents.

Claims

1. A current switching control method for a Z-source inverter in a photovoltaic power generation system, characterized in that, include: Based on the Z-source inverter in the photovoltaic power generation system, an affine model for current switching is established. Based on the current switching affine model, establish a current error switching affine model; Based on the current switching affine model and the current error switching affine model, multiple subsystems of the Z-source inverter are established. Based on the multiple subsystems of the Z-source inverter, a switching table is established; Based on the preset switching rules and the switching table, the state of the upper and lower switching transistors inside the Z-source inverter in the next control cycle is determined.

2. The method according to claim 1, characterized in that, Based on the Z-source inverter in the photovoltaic power generation system, a current switching affine model is established; based on the current switching affine model, a current error switching affine model is established, including: A control method based on a switching model is adopted, taking the three-phase AC current of the Z-source inverter in the photovoltaic power generation system as the state of the controlled system, and establishing a current switching affine model based on the working principle of the Z-source inverter in direct-drive mode and non-direct-drive mode. Based on the current switching affine model, the current error switching affine model of the Z-source inverter is obtained by subtracting the actual value from the expected value in the current switching affine model.

3. The method according to claim 2, characterized in that, The current-switching affine model satisfies the following formula: ； In the above formula: Let R represent the derivative of the state vector of the controlled system with respect to time t, R represent the AC side resistance of the Z-source inverter, and L represent the AC side inductance of the Z-source inverter. i represents the state vector of the controlled system. a (t), i b (t), i c (t) represents the three-phase AC current of the Z-source inverter at time t; e a (t), e b (t), e c (t) represents the AC three-phase voltage measured by the Z-source inverter at time t; V c V represents the capacitor voltage value of the Z-source inverter; pv P represents the output voltage on the photovoltaic side of the Z-source inverter; k For discrete switching functions, k = a, b, c, where a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively; in the discrete switching function, S k =1 indicates that in the Z-source inverter, the upper switch of the k-phase bridge arm is on while the lower switch is off. k =0 indicates that the upper switch of the k-phase bridge arm in the Z-source inverter is off and the lower switch is on; Z=1 indicates that the Z-source inverter is in shoot-through mode; Z=0 indicates that it is in non-shoot-through mode. Let I represent the state matrix of the controlled system, and let I represent the identity matrix. This indicates the switching affine term of the controlled system.

4. The method according to claim 3, characterized in that, The switching affine term of the controlled system satisfies the following formula: ； In the above formula: e represents the switching affine term of the controlled system. a (t), e b (t), e c (t) represents the AC three-phase voltage measured at time t of the Z-source inverter, V. c This represents the capacitor voltage value of the Z-source inverter, V. pv The output voltage on the photovoltaic side of the Z-source inverter is represented by P, where T represents the transpose of the matrix, L represents the inductance value on the AC side of the Z-source inverter, and P represents the output voltage on the photovoltaic side of the Z-source inverter. k Let k represent the discrete switching function, where k = a, b, c, and a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively.

5. The method according to claim 2, characterized in that, The current error switching affine model satisfies the following formula: ； In the above formula, This represents the derivative of the state error vector with respect to time t. Represents the state error vector, where: , , ; This represents the difference between the actual and expected values ​​of the AC phase a current of the Z-source inverter at time t. This represents the difference between the actual and expected values ​​of the b-phase current on the AC side of the Z-source inverter at time t. This represents the difference between the actual and expected values ​​of the c-phase current on the AC side of the Z-source inverter at time t; a (t), i b (t), i c (t) represents the actual value of the three-phase AC current of the Z-source inverter at time t; i ar (t), i br (t), i cr (t) represents the expected value of the three-phase AC current on the Z-source inverter at time t; e a (t), e b (t), e c (t) represents the AC three-phase voltage of the Z-source inverter at time t; To switch affine terms, P k Let S represent the discrete switching function, k = a, b, c, where a, b, and c represent phases a, b, and c on the AC side of the Z-source inverter, respectively. k =1 indicates that in the Z-source inverter, the upper switch of the k-phase bridge arm is on while the lower switch is off. k =0 indicates that the upper switch of the k-phase bridge arm in the Z-source inverter is off and the lower switch is on; Z=1 indicates that the Z-source inverter is in shoot-through mode; Z=0 indicates that it is in non-shoot-through mode. Let I represent the state matrix of the controlled system, and let I represent the identity matrix.

6. The method according to claim 5, characterized in that, The switching affine term satisfies the following formula: ； In the above formula, To switch affine terms, e a (t), e b (t), e c (t) represents the AC three-phase voltage measured at time t of the Z-source inverter, V. c This represents the capacitor voltage value of the Z-source inverter, V. pv The output voltage on the photovoltaic side of the Z-source inverter is represented by , T represents the transpose of the matrix, and L represents the inductance value on the AC side of the Z-source inverter. This represents the product of the AC side phase a resistance value and its expected current value of the Z-source inverter. This represents the product of the AC side b-phase resistance value and its expected current value of the Z-source inverter. P represents the product of the AC side c-phase resistance value and its expected current value of the Z-source inverter. k Let k represent the discrete switching function, where k = a, b, c, and a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively.

7. The method according to claim 1, characterized in that, Based on the current-switching affine model and the current-error-switching affine model, multiple subsystems of the Z-source inverter are established, including: Based on the current switching affine model and the current error switching affine model, a correspondence between the switching states of different switching transistors inside the Z-source inverter and the dynamics of the Z-source inverter is established. Based on the switching states of different switching transistors inside the Z-source inverter, the AC side output voltage of the Z-source inverter undergoes periodic changes. Based on the AC side output voltage cycle of the Z-source inverter, the dynamic model of the Z-source inverter corresponding to the switching states of different switching transistors is divided into multiple subsystems.

8. The method according to claim 1, characterized in that, The step of establishing a switching table based on the multiple subsystems of the Z-source inverter includes: The acquired complete three-phase AC voltage cycle is divided into 6 sectors with a phase angle interval of 60°. Within each sector, based on the magnitude relationship of the three-phase voltages and the current error switching affine model, multiple subsystems that satisfy the convex combination condition and the existence condition of the common Lyapunov function are selected to form the switching subsystem subset corresponding to that sector; a complete switching table is formed by all sectors and their corresponding switching subsystem subsets.

9. The method according to claim 1, characterized in that, The step of determining the state of the upper and lower switching transistors inside the Z-source inverter in the next control cycle according to the preset switching rules and the switching table includes: Obtain the current error state vector, three-phase voltage, capacitor voltage, photovoltaic output voltage, and inductance value at the current moment; The current sector is determined based on the current three-phase voltage magnitude relationship, and the corresponding switching subsystem subset is obtained according to the switching table. For each subsystem in the set of switching subsystems, calculate its corresponding switching function value based on the current error switching affine model; Compare the switching function values ​​of all subsystems in the switching subsystem subset, and select the subsystem that minimizes the switching function value; The switching vector corresponding to the selected subsystem is used as the switching state output for the next control cycle to control the on and off of the upper and lower switching transistors of each phase bridge arm of the Z-source inverter. The switching rule satisfies the following formula: ； In the above formula, This represents the selected subsystem, and argmin represents the minimization function. This represents the various subsystems in the currently selected switching subset; P represents the product of the state error vector and the switching function value. k Let k represent the discrete switching function, where k = a, b, c, and a, b, c represent phase a, phase b, and phase c on the AC side of the Z-source inverter, respectively.

10. A current switching control system for a Z-source inverter in a photovoltaic power generation system, characterized in that, include: The current error switching affine model construction module is used to establish a current switching affine model based on the Z-source inverter in the photovoltaic power generation system. Based on the current switching affine model, establish a current error switching affine model; The subsystem construction module is used to establish multiple subsystems of the Z-source inverter based on the current switching affine model and the current error switching affine model. The switching table construction module is used to establish a switching table based on the multiple subsystems of the Z-source inverter; The determination module is used to determine the state of the upper and lower switching transistors inside the Z-source inverter in the next control cycle according to the preset switching rules and the switching table.

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