Grid-connected inverter sliding mode control method based on reduced-order generalized proportional-integral observer

Abstract

The invention discloses a grid-connected inverter sliding mode control method based on a reduced-order generalized proportional-integral observer, and the method is applied to closed-loop control of a grid-connected inverter. The specific implementation method comprises the steps that a given power reference value is subjected to PQ control to obtain a current reference value, and the form of a reduced-order generalized proportional-integral observer is designed according to a state-space equation of the grid-connected inverter and used for observing the output current value and the total disturbance of the system. A backstepping method is combined with a super-spiral sliding mode to serve as a controller of a current loop, a control law output by the controller is subjected to an SPWM modulation method to obtain a trigger pulse signal of a switch tube, and closed-loop control of the grid-connected inverter is formed. According to the control method, the change of external disturbance can be more effectively resisted, the coupling influence between the d axis and the q axis is reduced, higher robustness and adaptivity to load disturbance are achieved, and stable operation of the grid-connected inverter is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a sliding mode control method for a grid-connected inverter based on a reduced-order generalized proportional-integral observer. Background Art

[0002] In recent years, with the rapid development of distributed power generation technology, power electronic converters have become an important component of distributed power generation. Since most of the energy of renewable energy is difficult to maintain in a stable state during the initial energy conversion, the grid-connected inverter needs to convert the DC voltage into high-quality AC voltage to feed into the grid, and its operating stability is crucial.

[0003] In order to ensure the quality of photovoltaic power generation, various improved control strategies are applied to grid-connected inverters, so as to more effectively control the inverter unit and the power grid. Therefore, in the control of photovoltaic power inverters, designing a control strategy that can meet its stable operation within a certain range can reduce certain energy losses and has important engineering practice significance.

[0004] The control goal of the grid-connected inverter is to achieve accurate tracking of the voltage set value and quickly respond to changes in various external disturbances. Common control strategies include PI control, repetitive control, neural network control, etc. Among these control methods, the PI control strategy has the advantages of easy design and high reliability, and is suitable for a large number of equipment in industry. However, with the development of photovoltaic power generation technology and microgrid technology, higher requirements are placed on the control quality of grid-connected inverters. The super spiral sliding mode in the high-order sliding mode can well suppress chattering and does not contain the information of the first-order derivative of the sliding mode variable, but in order to adapt to the unknown upper bound of the system, the parameters that need to be selected are usually large. Traditional control methods have certain shortcomings in anti-disturbance performance, high-quality voltage control, and dynamic response indicators. Therefore, it is very necessary to design a control strategy that is more robust and adaptive to disturbances of the grid-connected inverter. Summary of the invention

[0005] The purpose of the present invention is to provide a sliding mode control method for a grid-connected inverter based on a reduced-order generalized proportional-integral observer, which improves the disturbance estimation capability of the observer and the error convergence speed of feedback control.

[0006] The technical solution adopted by the present invention is a sliding mode control method for a grid-connected inverter based on a reduced-order generalized proportional-integral observer, wherein the grid-connected inverter is a three-phase full-bridge LC inverter, and is specifically implemented according to the following steps:

[0007] Step 1: Construct the mathematical model of the grid-connected inverter in the dqo rotating coordinate system;

[0008] Step 2: Construct a system equivalent model of the grid-connected inverter;

[0009] Step 3: Design a reduced-order generalized proportional-integral observer based on the system equivalent model;

[0010] Step 4: Apply the observation value output by the observer to the control of the backstepping super-helical sliding mode, and introduce the Lyapunov stability function and virtual error using the backstepping method;

[0011] Step 5: Then, the introduced superhelical structure is applied to the sliding mode control to obtain the backstepping superhelical sliding mode controller, and a compensation controller and an adaptive parameter controller are added to the backstepping superhelical sliding mode controller;

[0012] Step 6: After the control law output in step 5 is subjected to sinusoidal pulse width modulation, the duty cycle obtained is applied to the control of the switch tube of the three-phase full-bridge LC inverter to realize the control of the grid-connected inverter.

[0013] The present invention is also characterized in that:

[0014] Step 1 is as follows:

[0015] The DC side voltage of the grid-connected inverter is provided by a DC power supply. Under the condition of balanced three-phase voltage of the power grid, according to Kirchhoff's law, the variable relationship of the grid-connected inverter in the abc coordinate system is:

[0016]

[0017] In formula (1), L is the filter inductor, C is the filter capacitor, i La 、i Lb 、i Lc are the three-phase currents flowing through the inductor, u a 、u b 、u c is the three-phase voltage on the inverter side of the energy storage converter, u ga 、u gb 、u gc is the three-phase voltage of the AC power grid, i a 、i b 、i c is the grid-side three-phase current of the energy storage converter;

[0018] The mathematical model of the AC side of the converter in the dqo coordinate system is obtained by transforming equation (1) into:

[0019]

[0020] In formula (2), ω is the grid voltage angular frequency, u d 、u q Respectively represent the components of the AC voltage on the d and q axes, i Ld 、i LqRespectively represent the components of the inductor current on the d and q axes, i d 、i q They represent the components of the grid-side current on the d and q axes, respectively, and u dr =s d u dc ,u qr =s q u dc ,s d 、s q are the d and q axis switching functions, s j (j=a,b,c) is the switching function, which is specifically defined as:

[0021]

[0022] Step 2 is as follows:

[0023] On the basis of the three-phase balance of the grid voltage, the d-axis direction of the grid voltage is taken as the direction of the voltage vector. According to the instantaneous power theory, the power equation is obtained as follows:

[0024]

[0025] In formula (4), P ref , Q ref are the reference values ​​of active power and reactive power respectively, i dref ,i qref They are the current reference values ​​of the set active power and reactive power respectively;

[0026] The current reference values ​​of active power and reactive power are obtained from formula (4):

[0027]

[0028] The internal and external disturbances and parameter perturbations of the system are uniformly expressed as lumped disturbances, and the second-order differential of equation (2) is obtained:

[0029]

[0030] In formula (6), b d 、b q are the d-axis and q-axis control gain, respectively, and f d 、f q are the equivalent d-axis and q-axis lumped disturbances respectively. The lumped disturbance includes the unmodeled part of the system, the coupled part, and the internal and external disturbances of the system. The lumped disturbance expression is:

[0031]

[0032] Let the state variable x d1 =i d , x q1 =i q , Then equation (6) can be expressed as the spatial state equation:

[0033]

[0034] In order to further improve the observation accuracy, the lumped disturbance is expanded, and the spatial state model of equation (8) is reconstructed as:

[0035]

[0036] Step 3 is as follows:

[0037] Define z d1 、z d2 、z d3 、z q1 、z q2 、z q3 x d2 、x d3 , x q2 、x q3 , The observed value of , according to formula (9), the form of the reduced-order generalized proportional integral observer is:

[0038]

[0039] In formula (10), β1, β2, β3 and h1, h2, h3 are the observer gains of the d-axis and q-axis respectively.

[0040] Step 4 is as follows:

[0041] Let the grid-side current i of the d and q axes be d 、i q The deviation between the grid-side current reference value and d 、e q for:

[0042]

[0043] In formula (11), i dref for i d The reference value of i qref for i q Reference value of

[0044] According to the recursive design idea of ​​the backstepping method, the virtual control variable p is defined d , p q for:

[0045]

[0046] In formula (12), a1 and a2 are constants, and y1 and y2 are defined as the grid-side output currents of the system d-axis and q-axis respectively;

[0047] In order to meet the system stability requirements, the Lyapunov function V is selected d , V q for:

[0048]

[0049] Deriving equation (13) and substituting equation (11) and equation (12) into it, we can obtain:

[0050]

[0051] make k1, k2 are constants, and combined with equation (11) and equation (12), we get:

[0052]

[0053] So formula (14) is transformed into:

[0054]

[0055] From formula (16), we know that when p d , p q When it converges to 0, the system reaches stability, so the design of the state error feedback law is simplified to the virtual control quantity p d , p q The sliding surface s is designed here d ,s q for:

[0056]

[0057] In formula (17), γ1 and γ2 are the gains of the sliding surface.

[0058] Based on the equivalent control method, according to the sliding surface given by equation (17), the equivalent control law u is designed dreq ,u qreq for:

[0059]

[0060] Step 5 is as follows:

[0061] The improved super-helical sliding mode reaching law is used as the switching control law of the sliding mode surface, and the d-axis switching control law is as follows:

[0062]

[0063] In formula (19), for The estimated value of is the adaptive parameter of the controller, is a compensation controller;

[0064] The design of the adaptive parameter controller is as follows:

[0065]

[0066] In formula (20), a, b, c, k1, k2, k3, w1, w2, w3 are all normal numbers, and ε is a sufficiently small normal number;

[0067] Similarly, the q-axis switching control law is designed as:

[0068]

[0069] In formula (21), for The estimated value of is the adaptive parameter of the controller, is a compensation controller;

[0070] Step 6 is as follows:

[0071] Therefore, the comprehensive control law of the three-phase inverter is:

[0072]

[0073] The output obtained by the backstepping super-spiral sliding mode control based on the reduced-order generalized proportional-integral observer constructed in the above steps is used to obtain the switching duty cycle through sinusoidal pulse width modulation, and the switching duty cycle is applied to the control of the switching tube of the three-phase full-bridge LC inverter to realize the control of the grid-connected inverter.

[0074] The beneficial effects of the present invention are:

[0075] The present invention is based on a grid-connected inverter sliding mode control method of a reduced-order generalized proportional integral observer. Aiming at the problem of low observation accuracy of traditional observers, the high-order derivatives of external disturbances are estimated; in view of the fact that the traditional backstepping method cannot guarantee the robustness of the system, the backstepping method is combined with the sliding mode control to overcome the interference of external disturbances on the model; secondly, since the internal discontinuity of the sliding mode control will cause a certain amount of jitter in the output of the system when it reaches the sliding mode surface, a super-helical structure is used to smooth the jitter; in the control of the super-helical sliding mode, a compensation controller is added to achieve stable control of the system within a limited time; an adaptive parameter controller is designed to facilitate the selection of internal parameters of the controller; according to the improvement of the above structure, the controller is finally realized to control faster and more accurately. This control strategy can improve the disturbance estimation ability of the observer and the error convergence speed of the feedback control, thereby improving the transient response ability of the entire control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 It is a general control block diagram of the sliding mode control method of the grid-connected inverter based on the reduced-order generalized proportional-integral observer of the present invention;

[0077] Figure 2 It is the main circuit topology diagram of the energy storage converter;

[0078] Figure 3 It is a d-axis control block diagram of the grid-connected inverter in the present invention;

[0079] Figure 4 It is the transient simulation waveform of the three-phase current on the grid side controlled by PI;

[0080] Figure 5 It is a transient simulation waveform diagram of the three-phase current on the grid side controlled by the present invention;

[0081] Figure 6 It is the transient waveform of three-phase current on the grid side under PI control in the first working condition;

[0082] Figure 7 It is a transient waveform diagram of three-phase current on the grid side controlled by the present invention under working condition 1;

[0083] Figure 8 This is the transient waveform of the three-phase current on the grid side under PI control in the second working condition;

[0084] Fig. 9 It is a transient waveform diagram of three-phase current on the grid side controlled by the present invention under working condition 2;

[0085] Fig.10 This is the harmonic analysis diagram of the grid current under PI control;

[0086] Fig.11 It is a harmonic analysis diagram of the grid current controlled by the present invention. DETAILED DESCRIPTION

[0087] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0088] Example 1

[0089] This embodiment provides a sliding mode control method for a grid-connected inverter based on a reduced-order generalized proportional-integral observer. The grid-connected inverter is a three-phase full-bridge LC inverter, such as Figure 1 As shown, the specific implementation steps are as follows:

[0090] Step 1: Construct the mathematical model of the grid-connected inverter in the dqo rotating coordinate system;

[0091] like Figure 2 As shown, the DC side voltage of the grid-connected inverter is provided by a DC power supply. Under the condition of balanced three-phase voltage of the power grid, according to Kirchhoff's law, the variable relationship of the grid-connected inverter in the abc coordinate system is:

[0092]

[0093] In formula (1), L is the filter inductor, C is the filter capacitor, i La 、i Lb 、i Lc are the three-phase currents flowing through the inductor, u a 、u b 、u c is the three-phase voltage on the inverter side of the energy storage converter, u ga 、u gb 、u gc is the three-phase voltage of the AC power grid, i a 、i b 、i c is the grid-side three-phase current of the energy storage converter;

[0094] The mathematical model of the AC side of the converter in the dqo coordinate system is obtained by transforming equation (1) into:

[0095]

[0096] In formula (2), ω is the grid voltage angular frequency, u d 、u q Respectively represent the components of the AC voltage on the d and q axes, i Ld 、i Lq Respectively represent the components of the inductor current on the d and q axes, i d 、i q They represent the components of the grid-side current on the d and q axes, respectively, and u dr =s d u dc ,uqr =s q u dc ,s d 、s q are the d and q axis switching functions, s j (j=a,b,c) is the switching function, which is specifically defined as:

[0097]

[0098] Step 2: Construct a system equivalent model of the grid-connected inverter;

[0099] On the basis of the three-phase balance of the grid voltage, the d-axis direction of the grid voltage is taken as the direction of the voltage vector. According to the instantaneous power theory, the power equation is obtained as follows:

[0100]

[0101] In formula (4), P ref , Q ref are the reference values ​​of active power and reactive power respectively, i dref ,i qref They are the current reference values ​​of the set active power and reactive power respectively;

[0102] The current reference values ​​of active power and reactive power are obtained from formula (4):

[0103]

[0104] The internal and external disturbances and parameter perturbations of the system are uniformly expressed as lumped disturbances, and the second-order differential of equation (2) is obtained:

[0105]

[0106] In formula (6), b d 、b q are the d-axis and q-axis control gain, respectively, and f d 、f q are the equivalent d-axis and q-axis lumped disturbances respectively. The lumped disturbance includes the unmodeled part of the system, the coupled part, and the internal and external disturbances of the system. The lumped disturbance expression is:

[0107]

[0108] Let the state variable x d1 =i d , x q1 =i q , Then equation (6) can be expressed as the spatial state equation:

[0109]

[0110] In order to further improve the observation accuracy, the lumped disturbance is expanded, and the spatial state model of equation (8) is reconstructed as:

[0111]

[0112] Step 3: Design a reduced-order generalized proportional-integral observer based on the system equivalent model;

[0113] Step 4: Apply the observed value of the observer to the control of the backstepping superhelical sliding mode, introduce the Lyapunov stability function and virtual error using the backstepping method, and then apply the introduced superhelical structure to the sliding mode control to obtain the backstepping superhelical sliding mode controller;

[0114] Step 5: Add compensation controller and adaptive parameter controller to the backstepping super-helical sliding mode controller;

[0115] Step 6: The output of the backstepping super-spiral sliding mode control based on the reduced-order generalized proportional-integral observer constructed in the above steps is used to obtain the switching duty cycle through sinusoidal pulse width modulation, and the switching duty cycle is applied to the control of the switching tube of the three-phase full-bridge LC inverter to realize the control of the grid-connected inverter.

[0116] Example 2

[0117] This embodiment provides a sliding mode control method for a grid-connected inverter based on a reduced-order generalized proportional-integral observer. Based on Embodiment 1, step 3 is specifically as follows:

[0118] Define z d1 、z d2 、z d3 、z q1 、z q2 、z q3 x d2 、x d3 , x q2 、x q3 , The observed value of , according to formula (9), the form of the reduced-order generalized proportional integral observer is:

[0119]

[0120] In formula (10), β1, β2, β3 and h1, h2, h3 are the observer gains of the d-axis and q-axis respectively.

[0121] Step 4 is as follows:

[0122] Let the grid-side current i of the d and q axes be d 、iq The deviation between the grid-side current reference value and d 、e q for:

[0123]

[0124] In formula (11), i dref for i d The reference value of i qref for i q Reference value of

[0125] According to the recursive design idea of ​​the backstepping method, the virtual control variable p is defined d , p q for:

[0126]

[0127] In formula (12), a1 and a2 are constants, and y1 and y2 are defined as the grid-side output currents of the system d-axis and q-axis respectively;

[0128] In order to meet the system stability requirements, the Lyapunov function V is selected d , V q for:

[0129]

[0130] Deriving equation (13) and substituting equation (11) and equation (12) into it, we can obtain:

[0131]

[0132] make k1, k2 are constants, and combined with equation (11) and equation (12), we get:

[0133]

[0134] So formula (14) is transformed into:

[0135]

[0136] From formula (16), we know that when p d , p q When it converges to 0, the system reaches stability, so the design of the state error feedback law is simplified to the virtual control quantity p d , p q The sliding surface s is designed here d ,s q for:

[0137]

[0138] In formula (17), γ1 and γ2 are the gains of the sliding surface.

[0139] Based on the equivalent control method, according to the sliding surface given by equation (17), the equivalent control law u is designed dreq ,u qreq for:

[0140]

[0141] Example 3

[0142] This embodiment provides a sliding mode control method for a grid-connected inverter based on a reduced-order generalized proportional-integral observer. Based on Embodiment 1-2, step 5 is specifically as follows:

[0143] The improved super-helical sliding mode reaching law is used as the switching control law of the sliding mode surface, and the d-axis switching control law is as follows:

[0144]

[0145] In formula (19), for The estimated value of is the adaptive parameter of the controller, is the compensation controller;

[0146] The design of the adaptive parameter controller is as follows:

[0147]

[0148] In formula (20), a, b, c, k1, k2, k3, w1, w2, w3 are all positive constants, and ε is a sufficiently small positive constant. is the compensation controller;

[0149] Grid-connected inverter d-axis control Figure 3 As shown;

[0150] Similarly, the q-axis switching control law is designed as:

[0151]

[0152] In formula (21), for The estimated value of is the adaptive parameter of the controller, is the compensation controller;

[0153] Therefore, the comprehensive control law of the three-phase inverter is:

[0154]

[0155] From the above content, it can be seen that the grid-connected inverter sliding mode control method based on reduced-order generalized proportional-integral observer of the present invention has the following advantages:

[0156] 1) The reduced-order generalized proportional-integral observer used in the present invention does not need to establish an accurate mathematical model of the grid-connected inverter, especially for inverters with large internal circuit parameter changes and high frequencies. The observer utilizes the integral chain characteristics of interference to achieve a higher-precision estimation of interference and improve the estimation accuracy of time-varying disturbances such as the external environment. At the same time, the use of a reduced-order observer can reduce controller parameters and simplify the controller structure.

[0157] 2) The backstepping sliding mode controller adopted in the present invention obtains the current in the two-phase rotating coordinate system by transforming the three-phase output current through the dqo coordinate system, thereby obtaining the current error as input, and then introduces the Lyapunov stability function and virtual error to make the system continuously corrected in the stable direction, thereby ensuring the global stability of the system when subjected to internal and external disturbances.

[0158] 3) The super-helical sliding mode adopted by the present invention does not need to add the derivative information of each order of the sliding mode, and as a high-order sliding mode, it can better suppress chattering. The sliding mode is mainly composed of two parts. First, since the sliding mode contains a function of a continuous sliding variable, the control signal also appears to be a continuous state; second, there is an integral of a discontinuous time derivative in the sliding mode, thereby avoiding the occurrence of excessive chattering.

[0159] 4) The present invention introduces a compensation controller and an adaptive parameter controller into the super spiral algorithm. Since the upper limit of the system is often difficult to determine in practical applications, a compensation term is added to achieve the stability of the system in a limited time. In order to quickly obtain a lower switching gain, an adaptive parameter controller is used to ensure that the grid-connected inverter has good dynamic performance and ensure the robustness of the control system.

[0160] Simulation Analysis

[0161] In the energy storage converter model built in the Matlab / Simulink platform, the control method of the present invention is compared with the traditional PI control. Under the two control methods, when the active power suddenly changes, the output of the stable operation 20kW suddenly increases to 70kW at 0.22s, and the corresponding three-phase current amplitude suddenly increases from 43A to 150A; at 0.28s, it suddenly drops from 70kW to 20kW, and the corresponding three-phase current amplitude suddenly drops from 150A to 43A, causing the dynamic response of the three-phase current output on the AC side of the three-phase inverter. Figure 4 As shown in the figure, under the traditional PI control, the response time of the three-phase current on the grid side is 17.5ms at 0.22s, and the response time of the three-phase current on the grid side is 20.5ms at 0.28s. Figure 5As shown in the figure, under the control of this paper, the response time of the three-phase current on the grid side is 7.5ms at 0.22s, and the response time of the three-phase current on the grid side is 10.5ms at 0.28s. By comparison, it can be seen that the control strategy of the present invention greatly reduces the transient time and improves the stability of the system.

[0162] In order to verify the effectiveness of the control method of the present invention, a simulation circuit is built in a hardware-in-the-loop (HIL) experimental platform, and a comparative analysis is performed with the traditional PI control strategy. It is defined that the power is positive when the voltage and current directions are consistent. The simulation parameter settings are shown in Table 1.

[0163] Table 1 Circuit parameters

[0164] parameter Numeric Grid voltage amplitude e 311V <![CDATA[DC bus voltage U dc > 800V Filter inductor L 5mH Filter capacitor C 50μF Inductor parasitic resistance R 0.01Ω <![CDATA[DC regulated capacitor C dc > 2.2mF Load power 20kW-70kW <![CDATA[Battery terminal voltage v bat > 400V Battery initial state of charge SOC 50％

[0165] The present invention replaces the traditional extended state observer with a reduced-order generalized proportional integral observer, which can achieve more accurate and faster compensation for lumped disturbances when the estimation error is large, improve the ability to suppress the cross-effect of the d and q axes, and compared with the generalized proportional integral observer, the observer adopts a simple reduced-order structure, does not have additional parameters, and is easy to implement in engineering. The backstepping super-helical sliding mode replaces the traditional sliding mode control, hides the switching function in the integral term, further eliminates the chattering caused by high-frequency switching, adopts the backstepping method to ensure the global stability of the system, and enhances the stability and robustness of the system.

[0166] Depend on Figure 6 It can be seen that when the output active power of the three-phase inverter jumps from 20kW to 70kW, i d The three-phase current changes from 43 A to 150 A, and the amplitude of the three-phase current changes from 43 A to 150 A. When the active power changes from 20 kW to 70 kW under the PI control strategy, the transition time of the three-phase current on the AC side is 21 ms. Figure 7 It can be seen that under the control method of the present invention, the jump caused by the sudden increase in power makes the transition time of the three-phase current on the AC side 13ms, and the fluctuation of the current value during steady-state operation is smaller than that of PI control.

[0167] Depend on Figure 8 It can be seen that when the output active power of the three-phase inverter jumps from 70kW to 20kW, i d The three-phase current changes from 150A to 43A, and the amplitude of the three-phase current changes from 150A to 43A. When the active power changes from 70kW to 20kW under the PI control strategy, the transition time of the three-phase current on the AC side is 27ms. Fig. 9 It can be seen that under the control strategy of this paper, the jump caused by the power sudden drop makes the transition time of the three-phase current on the AC side 18.5ms, and the fluctuation of the current value during steady-state operation is smaller than that of PI control.

[0168] In order to verify the influence of the control method of the present invention on the power quality of the output current of the three-phase inverter, the grid-connected current of the three-phase inverter with an output active power of 20kW was subjected to Fourier analysis of two steady-state cycles in Matlab / Simulink software. Fig.10 As shown, it is the harmonic analysis of the grid-connected current of the energy storage converter under the traditional PI control, and the THD is 2.68%. Fig.11 The figure shows the harmonic analysis of the grid-connected current of the energy storage converter under the control of the present invention, and the THD is 0.84%. By comparison, it can be seen that the control of the present invention has a stronger harmonic suppression capability and improves the quality of grid-connected power.

[0169] In summary, the present invention is based on the sliding mode control method of the grid-connected inverter of the reduced-order generalized proportional integral observer. The current reference value is obtained by PQ control from the given power reference value. The form of the reduced-order generalized proportional integral observer is designed according to the state space equation of the grid-connected inverter to observe the output current value and the total disturbance of the system; the backstepping method combined with the super spiral sliding mode is used as the controller of the current loop, and the control law output by the controller is subjected to the sinusoidal pulse width modulation method to obtain the control signal of the switch tube to form a closed-loop control of the grid-connected inverter; finally, after simulation and experimental verification, it is concluded that compared with the prior art, the control method of the present invention can more effectively resist the change of external disturbance, reduce the coupling effect between the d and q axes, and has stronger robustness and adaptability to load disturbances, which is conducive to the stable operation of the grid-connected inverter. The present invention effectively solves the problem that when the three-phase inverter is subjected to external time-varying disturbances in the grid-connected working mode, the three-phase current on the grid-connected side can be quickly restored to a stable state, the convergence speed and control accuracy of the grid-connected inverter are improved, and the power quality of the power grid is effectively improved.

Claims

1. A sliding mode control method for a grid-connected inverter based on a reduced-order generalized proportional-integral observer, wherein the grid-connected inverter is a three-phase full-bridge LC inverter, characterized in that: Follow the steps below to implement it: Step 1: Construct the mathematical model of the grid-connected inverter in the dqo rotating coordinate system; Step 2: Construct a system equivalent model of the grid-connected inverter; Step 3: Design a reduced-order generalized proportional-integral observer based on the system equivalent model; Step 4: Apply the observed value of the observer to the control of the backstepping superhelical sliding mode, introduce the Lyapunov stability function and virtual error using the backstepping method, and then apply the introduced superhelical structure to the sliding mode control to obtain the backstepping superhelical sliding mode controller; Step 5: Add compensation controller and adaptive parameter controller to the backstepping super-helical sliding mode controller; Step 6: Apply the switch duty cycle to the control of the switch tube of the three-phase full-bridge LC inverter to realize the control of the grid-connected inverter.

2. The sliding mode control method for grid-connected inverter based on reduced-order generalized proportional-integral observer according to claim 1, characterized in that: The step 1 is specifically as follows: The DC side voltage of the grid-connected inverter is provided by a DC power supply. Under the condition of balanced three-phase voltage of the power grid, according to Kirchhoff's law, the variable relationship of the grid-connected inverter in the abc coordinate system is: In formula (1), L is the filter inductor, C is the filter capacitor, i La 、i Lb 、i Lc are the three-phase currents flowing through the inductor, u a 、u b 、u c is the three-phase voltage on the inverter side of the energy storage converter, u ga 、u gb 、u gc is the three-phase voltage of the AC power grid, i a 、i b 、i c is the grid-side three-phase current of the energy storage converter; The mathematical model of the AC side of the converter in the dqo coordinate system is obtained by transforming equation (1) into: In formula (2), ω is the grid voltage angular frequency, u d 、u q Respectively represent the components of the AC voltage on the d and q axes, i Ld 、i Lq Respectively represent the components of the inductor current on the d and q axes, i d 、i q They represent the components of the grid-side current on the d and q axes, respectively, and u dr =s d u dc ,u qr =s q u dc ,s d 、s q are the d and q axis switching functions, s j (j=a,b,c) is the switching function, which is specifically defined as:

3. The sliding mode control method for grid-connected inverter based on reduced-order generalized proportional-integral observer according to claim 2, characterized in that: The step 2 is specifically as follows: On the basis of the three-phase balance of the grid voltage, the d-axis direction of the grid voltage is taken as the direction of the voltage vector. According to the instantaneous power theory, the power equation is obtained as follows: In formula (4), P ref , Q ref are the reference values ​​of active power and reactive power respectively, i dref ,i qref They are the current reference values ​​of the set active power and reactive power respectively; The current reference values ​​of active power and reactive power are obtained from formula (4): The internal and external disturbances and parameter perturbations of the system are uniformly expressed as lumped disturbances, and the second-order differential of equation (2) is obtained: In formula (6), b d , b q are the d-axis and q-axis control gain, respectively, and f d 、f q are the equivalent d-axis and q-axis lumped disturbances respectively. The lumped disturbance includes the unmodeled part of the system, the coupled part, and the internal and external disturbances of the system. The lumped disturbance expression is: Let the state variable x d1 =i d , x q1 =i q , Then equation (6) can be expressed as the spatial state equation: In order to further improve the observation accuracy, the lumped disturbance is expanded, and the spatial state model of equation (8) is reconstructed as:

4. The sliding mode control method for grid-connected inverter based on reduced-order generalized proportional-integral observer according to claim 3, characterized in that: The step 3 is specifically as follows: Define z d1 、z d2 、z d3 、z q1 、z q2 、z q3 x d2 、x d3 , x q2 、x q3 , The observed value of , according to formula (9), the form of the reduced-order generalized proportional integral observer is: In formula (10), β1, β2, β3 and h1, h2, h3 are the observer gains of the d-axis and q-axis respectively.

5. The sliding mode control method for grid-connected inverter based on reduced-order generalized proportional-integral observer according to claim 4, characterized in that: The step 4 is specifically as follows: Let the grid-side current i of the d and q axes be d 、i q The deviation between the grid-side current reference value and d 、e q for: In formula (11), i dref for i d The reference value of i qref for i q Reference value of According to the recursive design idea of ​​the backstepping method, the virtual control variable p is defined d , p q for: In formula (12), a1 and a2 are constants, and y1 and y2 are defined as the grid-side output currents of the system d-axis and q-axis respectively; In order to meet the system stability requirements, the Lyapunov function V is selected d , V q for: Deriving equation (13) and substituting equation (11) and equation (12) into it, we can obtain: make k1, k2 are constants, and combined with equation (11) and equation (12), we get: So formula (14) is transformed into: From formula (16), we know that when p d , p q When it converges to 0, the system reaches stability, so the design of the state error feedback law is simplified to the virtual control quantity p d , p q The sliding surface s is designed here d ,s q for: In formula (17), γ1, γ2 are the gains of the sliding surface; Based on the equivalent control method, according to the sliding surface given by equation (17), the equivalent control law u is designed dreq ,u qreq for:

6. The sliding mode control method for grid-connected inverter based on reduced-order generalized proportional-integral observer according to claim 5, characterized in that: The step 5 is specifically as follows: The improved super-helical sliding mode reaching law is used as the switching control law of the sliding mode surface, and the d-axis switching control law is as follows: In formula (19), for The estimated value of is the adaptive parameter of the controller, is the compensation controller; The design of the adaptive parameter controller is as follows: In formula (20), a, b, c, k1, k2, k3, w1, w2, w3 are all normal numbers, and ε is a sufficiently small normal number; Similarly, the q-axis switching control law is designed as: In formula (21), for The estimated value of is the adaptive parameter of the controller, For compensation controller.

7. The sliding mode control method for grid-connected inverter based on reduced-order generalized proportional-integral observer according to claim 1, characterized in that: The step 6 is specifically as follows: Therefore, the comprehensive control law of the three-phase inverter is: The output of the backstepping super-spiral sliding mode control based on the reduced-order generalized proportional-integral observer constructed in the above steps is used to obtain the switching duty cycle through SPWM modulation, and the switching duty cycle is applied to the control of the switching tube of the three-phase full-bridge LC inverter to realize the control of the grid-connected inverter.

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