Sliding Mode Control Method of Energy Storage Inverter Based on Reduced-Order Generalized Proportional-Integral Observer

Abstract

The present invention discloses a control method based on a reduced-order generalized proportional-integral observer for terminal complementary sliding mode, and applies it to the closed-loop control of an energy storage converter. First, the mathematical model of the controlled object in the d-q rotating coordinate system and the given formula of the current reference value are elaborated for the design of the controller. Second, aiming at the problem of low accuracy in observing the total disturbance, a reduced-order generalized proportional-integral observer is adopted on the basis of the traditional observer. To effectively reduce the current tracking error of the system and improve the convergence speed of the system simultaneously, the nonlinear terms of the terminal sliding mode are introduced on two complementary sliding surfaces respectively. Finally, through experimental verification, compared with the prior art, the control strategy designed by the present invention can resist more external disturbance changes, effectively shorten the convergence time after the system is subjected to external disturbances, reduce the tracking error of the current value, thereby improving the tracking performance and robustness of the system, and contributing to the stable operation of the energy storage converter.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and particularly relates to a control method for an energy storage converter based on a reduced-order generalized proportional-integral observer and terminal complementary sliding mode. Background Art

[0002] In recent years, due to the large-scale use of non-renewable energy sources such as coal by people, increasingly serious environmental problems have been caused. Therefore, in order to respond to the trend of global warming, China has been continuously developing various new energy technologies. The grid connection of a power conversion system (PCS) is one of the main development directions of new energy power generation at present. The energy storage converter has functions such as AC-DC conversion, voltage and frequency control, etc., so it plays a crucial role in new energy fields such as new energy grid connection and microgrid construction. Therefore, improving the control strategy of the energy storage converter is the key to ensuring the stable operation of the energy storage system.

[0003] The energy storage converter system can realize independent control of active power and reactive power, and the centralized output has strong controllability, and can be applied to island power grids and passive networks connected to photovoltaic and pure new energy output. The energy storage converter has the functions of converting the alternating current of the power grid into direct current for energy storage in the battery pack, and converting the direct current of the battery pack into alternating current and outputting it to the power grid, which can maintain a high conversion efficiency, reduce energy loss, and improve the utilization rate of energy. Therefore, designing a control strategy that can meet the stable operation of the energy storage converter has very important engineering practical significance.

[0004] In terms of control strategies, existing traditional control methods such as PID control, fuzzy control, and adaptive control have certain limitations when dealing with nonlinear systems. Although the model predictive control method can be widely applied to nonlinear systems, it has deficiencies such as a large number of data training times and a relatively slow control response speed. Some literature has proposed using a terminal sliding mode control method to achieve the purpose of controlling a permanent magnet synchronous motor, which improves the convergence speed of the system. Some literature has designed a complementary sliding mode to reduce the influence of uncertain factors on the motor servo system. Some literature has applied a generalized proportional-integral observer to a Buck circuit, making the system have good anti-interference performance. Summary of the Invention

[0005] The purpose of the invention is to provide a control method for an energy storage converter based on a reduced-order generalized proportional-integral observer and terminal complementary sliding mode. The designed controller can effectively solve the problems existing in the existing traditional active disturbance rejection control, such as insufficient estimation accuracy of the total external disturbance of the energy storage converter, long transient time after large load disturbances on the bus, and the coupling effect between the internal d-axis and q-axis of the system.

[0006] The technical solution adopted by the present invention is a control method for an energy storage converter based on a reduced-order generalized proportional-integral observer and a terminal complementary sliding mode, which is specifically implemented according to the following steps:

[0007] Step 1: Establish a mathematical model of the energy storage converter in the d-q rotating coordinate system according to the impedance elements inside the energy storage converter;

[0008] Step 2: Convert the mathematical model established in Step 1 into the form of a system of state variable equations;

[0009] Step 3: Design a reduced-order generalized proportional-integral observer according to the system of state variable equations in Step 2;

[0010] Step 4: Apply the observed values obtained from the observer in Step 3 to the control of the terminal complementary sliding mode;

[0011] Step 5: Introduce a composite variable-speed reaching law into the terminal complementary sliding mode controller in Step 4;

[0012] Step 6: Obtain the control law according to the above steps, and through SPWM modulation, obtain the modulation signal of the switching tubes of the energy storage converter, and apply the modulation signal to the control of the switching tubes, so as to realize the closed-loop control of the energy storage converter.

[0013] The features of the present invention also lie in:

[0014] Specifically, Step 1 is as follows:

[0015] Under the condition of balanced three-phase grid voltage, according to Kirchhoff's law, the variable relationship of the energy storage converter in the abc coordinate system is obtained as:

[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 respectively, u a , u b , u c are the three-phase voltages on the inverter side of the energy storage converter, u ga , u gb , u gc are the three-phase voltages of the AC grid, i a , i b , i c are the three-phase grid-side currents of the energy storage converter;

[0018] After coordinate transformation of formula (1), the mathematical model of the AC side of the energy storage converter in the d-q coordinate system is obtained as:

[0019]

[0020] In Equation (2), R is the parasitic parameter of the filter inductor, ω is the angular frequency of the grid voltage, and u d , u q represent the components of the AC voltage on the d-axis and q-axis respectively, and i Ld , i Lq represent the components of the inductor current on the d-axis and q-axis respectively, and i d , i q represent the components of the grid-side current on the d-axis and q-axis respectively, u dr = s d u dc , u qr = s q u dc , u dc is the output voltage value of the DC voltage source, and s d , s q are the switching functions on the d-axis and q-axis respectively, and s j (j = a, b, c) is the switching function, and its specific definition is as follows:

[0021]

[0022] Step 2 is specifically as follows:

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

[0024]

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

[0026] The current reference values of the active power and reactive power are obtained from Equation (4) as follows:

[0027]

[0028] Unify the internal and external disturbances and parameter perturbations of the system and represent them with lumped disturbances, and take the second-order differential of Equation (2) to obtain:

[0029]

[0030] In Equation (6), b d , b q are the control quantity gains on the d-axis and q-axis respectively, and f d , f qThey are the lumped disturbances on the d- and q-axes after equivalence. The lumped disturbances include the unmodeled part of the system, the coupling part, and the internal and external disturbances of the system. The expression of the lumped disturbances is as follows:

[0031]

[0032] In Equation (7), ω is the angular frequency of the grid voltage;

[0033] Let the state variable x d1 = i d , x q1 = i q , Then Equation (6) can be expressed by the state-space equation as follows:

[0034]

[0035] To further improve the observation accuracy, the lumped disturbances are expanded, and the state-space model of Equation (8) is reconstructed as follows:

[0036]

[0037] Step 3 is specifically as follows:

[0038] Define z d1 , z d2 , z d3 , z q1 , z q2 , z q3 to be the observed values of x d2 , x d3 , x q2 , x q3 , respectively. According to Equation (9), the form of the reduced-order generalized proportional-integral observer is designed as follows:

[0039]

[0040] In Equation (10), β1, β2, β3 and h1, h2, h3 are the observer gains on the d-axis and q-axis respectively.

[0041] Step 4 is specifically as follows:

[0042] Let the deviations e d , e q between the grid-side currents i d , i q on the d-axis and q-axis and the reference values of the grid-side currents be as follows:

[0043]

[0044] In Equation (11), idref For i d 's reference value, i qref is the reference value of i q ;

[0045] The terminal sliding mode surfaces of the d and q axes of the design are s dg and s qg respectively. The complementary sliding mode surfaces orthogonal to the terminal sliding mode surfaces are s dc and s qc respectively. Then s dg and s dc and s qg and s qc The specific functional forms are as follows:

[0046]

[0047] In Equation (12), λ1, λ2 ≥ 0, λ1 and λ2 are the gains of the sliding mode surface, 0 < m1 = a1 / b1 < 1, 0 < m2 = a2 / b2 < 1, and a1, b1, a2, and b2 are all positive odd numbers;

[0048] From Equation (12), the relationship between the two sliding mode surfaces is:

[0049]

[0050] In Equation (13), s d and s q are respectively the sums of the sliding mode surfaces of the d and q axes, that is, s d = s dc + s dg , s q = s qc + s qg ;

[0051] Step 5 is specifically as follows:

[0052] Select the Lyapunov function V d for judging the stability of the system. V q is:

[0053]

[0054] Take the first-order differential of Equation (14) to get:

[0055]

[0056] According to Equation (15), in order for the terminal complementary sliding mode function to meet the Lyapunov stability requirements, it is necessary to satisfy:

[0057]

[0058] According to Equation (16), the equivalent control laws for the d-axis and q-axis are as follows:

[0059]

[0060] Taking the composite variable-speed reaching law as the switching control law of the sliding mode, the switching control laws for the d-axis and q-axis are as follows:

[0061]

[0062] In Equation (18), k1, k2, and k3 are the gains of the d-axis reaching law greater than 0, and k4, k5, and k6 are the gains of the q-axis reaching law greater than 0; δ1 and δ2 are the exponential parameters of the d-axis and q-axis respectively, and their specific representation forms are as follows:

[0063] δ = γ + (ε - γ)e -μs (19)

[0064] In Equation (19), γ > 1, 0 < ε < 1, μ > 0, and s represents the sliding mode surface.

[0065] Step 6 is specifically as follows

[0066] Combining the equivalent control law of Equation (17) and the switching control law of Equation (18), the comprehensive control laws of the energy storage converter for the d-axis and q-axis are obtained as follows:

[0067]

[0068] The beneficial effects of the present invention are:

[0069] The energy storage converter control method based on the reduced-order generalized proportional-integral observer and terminal complementary sliding mode of the present invention uses the generalized proportional-integral observer to replace the traditional extended state observer to estimate the matched and unmatched disturbances; and the reduced-order structure can reduce the parameters of the observer and is easier to implement in engineering; replacing the traditional sliding mode control with the terminal complementary sliding mode can ensure the stability of the system when it reaches the sliding mode surface and achieve convergence more quickly. To further weaken the chattering when reaching the sliding mode surface, the composite variable-speed reaching law is used as the switching control law of the sliding mode surface, ultimately enhancing the robustness and applicability of the system. Description of the Drawings

[0070] Figure 1 is the overall control block diagram of the energy storage converter control method based on the reduced-order generalized proportional-integral observer and terminal complementary sliding mode of the present invention;

[0071] Figure 2 is the simplified control block diagram of the energy storage converter control method based on the reduced-order generalized proportional-integral observer and terminal complementary sliding mode of the present invention;

[0072] Figure 3 is the main circuit topology diagram of the energy storage converter;

[0073] Figure 4 It is the transient simulation waveform diagram of d-q axis current under PI control;

[0074] Figure 5 It is the transient simulation waveform diagram of d-q axis current controlled by the control method of the present invention;

[0075] Figure 6 It is the transient waveform diagram of d-q axis current under PI control under Condition 1;

[0076] Figure 7 It is the transient waveform diagram of d-q axis current controlled by the control method of the present invention under Condition 1;

[0077] Figure 8 It is the transient waveform diagram of d-q axis current under PI control under Condition 2;

[0078] Figure 9 It is the transient waveform diagram of d-q axis current controlled by the control method of the present invention under Condition 2;

[0079] Figure 10 It is the harmonic analysis diagram of grid current under PI control;

[0080] Figure 11 It is the harmonic analysis diagram of grid current of the control method of the present invention;

[0081] Figure 12 It is the grid current waveform diagram of the energy storage converter of the control method of the present invention. Detailed implementation manners

[0082] The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0083] Embodiment 1

[0084] This embodiment provides an energy storage converter control method based on a reduced-order generalized proportional-integral observer and terminal complementary sliding mode, as Figure 1-2 shown, and is specifically implemented according to the following steps:

[0085] Step 1: According to the impedance elements inside the energy storage converter, establish its mathematical model in the d-q rotating coordinate system;

[0086] As Figure 3 shown, under the condition of balanced three-phase grid voltage, according to Kirchhoff's law, the variable relationship of the energy storage converter in the abc coordinate system is obtained as:

[0087]

[0088] In formula (1), L is the filter inductor, C is the filter capacitor, i La 、iLb and i Lc are the three-phase currents flowing through the inductor, and u a , u b , u c are the three-phase voltages on the inverter side of the energy storage converter, and u ga , u gb , u gc are the three-phase voltages of the AC power grid, and i a , i b , i c are the three-phase currents on the grid side of the energy storage converter;

[0089] The mathematical model of the AC side of the energy storage converter in the d-q coordinate system is obtained by coordinate transformation of Equation (1) as follows:

[0090]

[0091] In Equation (2), R is the parasitic parameter of the filter inductor, ω is the angular frequency of the grid voltage, u d , u q represent the components of the AC voltage on the d and q axes respectively, and i Ld , i Lq represent the components of the inductor current on the d and q axes respectively, and i d , i q 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 , u dc is the output voltage value of the DC voltage source, and s d , s q are the switching functions on the d and q axes respectively, and s j (j = a, b, c) is the switching function, and its specific definition is as follows:

[0092]

[0093] Step 2: Convert the mathematical model established in Step 1 into the form of a state variable equation system;

[0094] Based on the three-phase balance of the grid voltage, taking the d-axis direction of the grid voltage as the direction of the voltage vector, according to the instantaneous power theory, the power equation is obtained as follows:

[0095]

[0096] In Equation (4), P ref , Q ref are the reference values of the set active power and reactive power respectively, and i dref, i qref They are the current reference values of the set active power and reactive power respectively.

[0097] The current reference values of the active power and reactive power obtained from Equation (4) are respectively:

[0098]

[0099] Unify the internal and external disturbances and parameter perturbations of the system and represent them with lumped disturbances, and take the second-order differential of Equation (2) to obtain:

[0100]

[0101] In Equation (6), b d , b q are the gains of the d-axis and q-axis control variables respectively, f d , f q are the equivalent d-axis and q-axis lumped disturbances respectively. The lumped disturbances include the unmodeled part, the coupling part, and the internal and external disturbances of the system. The expression of the lumped disturbances is:

[0102]

[0103] In Equation (7), ω is the angular frequency of the grid voltage;

[0104] Let the state variable x d1 = i d , x q1 = i q , Then Equation (6) is expressed by the state space equation as:

[0105]

[0106] To further improve the observation accuracy, expand the lumped disturbances, and then the state space model of Equation (8) is reconstructed as:

[0107]

[0108] Step 3: Design a reduced-order generalized proportional-integral observer according to the state variable equation system in Step 2;

[0109] Step 4: Apply the observed values obtained from the observer in Step 3 to the control of the terminal complementary sliding mode;

[0110] Step 5: Introduce a composite variable-speed reaching law into the terminal complementary sliding mode controller in Step 4;

[0111] Step 6: Obtain the control law according to the above steps, and through SPWM modulation, obtain the modulation signals of the switching tubes of the energy storage converter. Apply the modulation signals to the control of the switching tubes, thereby realizing the closed-loop control of the energy storage converter.

[0112] Embodiment 2

[0113] This embodiment provides a control method for an energy storage converter based on a reduced-order generalized proportional-integral observer and terminal complementary sliding mode. On the basis of Embodiment 1, Step 3 is specifically as follows:

[0114] Define z d1 、z d2 、z d3 、z q1 、z q2 、z q3 as the observed values of x d2 、x d3 、 x q2 、x q3 、 respectively. According to Equation (9), design the form of the reduced-order generalized proportional-integral observer as:

[0115]

[0116] In Equation (10), β1, β2, β3 and h1, h2, h3 are the observer gains of the d-axis and q-axis respectively.

[0117] Step 4 is specifically as follows:

[0118] Let the deviations e d 、e q between the grid-side currents i d 、i q of the d-axis and q-axis and the grid-side current reference values be:

[0119]

[0120] In Equation (11), i dref is the reference value of i d , and i qref is the reference value of i q ;

[0121] Design the terminal sliding mode surfaces of the d-axis and q-axis as s dg 、s qg respectively, and the complementary sliding mode surfaces orthogonal to the terminal sliding mode surfaces as s dc 、s qc . Then s dg 、s dc 、s qg 、s qc The specific functional forms are as follows:

[0122]

[0123] In Equation (12), λ1, λ2 ≥ 0, where λ1 and λ2 are the gains of the sliding mode surface, 0 < m1 = a1 / b1 < 1, 0 < m2 = a2 / b2 < 1, and a1, b1, a2, and b2 are all positive odd numbers;

[0124] From Equation (12), the relationship between the two sliding mode surfaces is:

[0125]

[0126] In Equation (13), s d , s q are respectively the sums of the sliding mode surfaces on the d-axis and q-axis, that is, s d = s dc + s dg , s q = s qc + s qg .

[0127] Select the Lyapunov function V d , V q as:

[0128]

[0129] Take the first-order differential of Equation (14) to get:

[0130]

[0131] According to Equation (15), to make the terminal complementary sliding mode function satisfy the Lyapunov stability requirement, it is necessary to satisfy:

[0132]

[0133] According to Equation (16), the equivalent control laws for the d-axis and q-axis are obtained as:

[0134]

[0135] Example 3

[0136] This example provides a control method for an energy storage converter with terminal complementary sliding mode based on a reduced-order generalized proportional-integral observer. On the basis of Examples 1-2, step 5 is specifically as follows:

[0137] Taking the composite variable speed reaching law as the switching control law of the sliding mode, the switching control laws for the d-axis and q-axis are as follows:

[0138]

[0139] In Equation (18), k1, k2, and k3 are the gains of the d-axis reaching law greater than 0, and k4, k5, and k6 are the gains of the q-axis reaching law greater than 0; δ1 and δ2 are the variable exponential parameters of the d- and q-axes, and their specific representation forms are as follows:

[0140] δ = γ + (ε - γ)e -μs (19)

[0141] In Equation (19), γ > 1, 0 < ε < 1, μ > 0, and s represents the sliding mode surface.

[0142] Step 6 is specifically as follows:

[0143] Combining the equivalent control law of Equation (17) and the switching control law of Equation (18), the comprehensive control laws of the energy storage converter on the d- and q-axes are obtained as follows:

[0144]

[0145] From the above content, it can be seen that the energy storage converter control method based on the terminal complementary sliding mode of the reduced-order generalized proportional integral observer of the present invention has the following advantages:

[0146] 1) The reduced-order generalized proportional integral observer adopted by the present invention is a high-order processing of the extended state observer, which does not require an accurate mathematical model of the energy storage converter and can estimate the time-varying disturbances during the operation of the energy storage converter more accurately. The reduced-order form can simplify the structure of the observer.

[0147] 2) The terminal complementary sliding mode controller adopted by the present invention uses the complementary sliding mode surface to reduce the sliding mode variable error, so that while the current error converges to zero along the intersection of the terminal sliding mode surface and its complementary sliding mode surface, the system has a higher convergence speed and control accuracy. The composite variable speed reaching law is composed of the exponential reaching law and the variable power reaching law. The control parameters in the reaching law can be adaptively changed according to the sliding mode function. When the controlled object is far from the equilibrium point, the parameter value increases to increase the sliding mode approaching speed; when the controlled object is close to the equilibrium point, the parameter value gradually decreases to weaken the chattering generated during the approaching motion.

[0148] Simulation Analysis

[0149] To verify the feasibility of the energy storage converter control method based on the reduced-order generalized proportional-integral observer and terminal complementary sliding mode of the present invention, in the energy storage converter model built on the Matlab / Simulink platform, the control method of the present invention is compared with the traditional PI control. Under the two controls, when the active power suddenly changes, it suddenly increases from the stable output of 20 kW to 70 kW at 0.2 s, and the amplitude of the corresponding three-phase current suddenly increases from 43 A to 150 A; it suddenly drops from 70 kW to 20 kW at 0.25 s, and the amplitude of the corresponding three-phase current suddenly drops from 150 A to 43 A, thus causing the dynamic response of the three-phase current output on the AC side of the energy storage converter. As Figure 4 shown, for the traditional PI control, when i d suddenly changes, the cross-coupling effect on i q . It can be seen that at 0.2 s, i d suddenly increases. Due to the coupling effect, i q has an overshoot of 24.5 A and takes 14.5 ms to stabilize; at 0.25 s, i d suddenly decreases, and i q has an overshoot of 21.2 A and takes 21 ms to stabilize. As Figure 5 shown, for the control of the present invention, when i d suddenly changes, the cross-coupling effect on i q . It can be seen from the figure that at 2 s, i d suddenly increases, and i q only has an overshoot of 10.5 A and reaches stability after 2.3 ms; by comparison, it can be seen that the control of the present invention has an obvious decoupling effect on the d-axis and q-axis currents and can control disturbances faster and finally reach stability.

[0150] 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 large estimation errors occur, improve the ability to suppress the cross-coupling effect between the d-axis and q-axis, and the observer has a simple structure, no additional parameters, and is easy to implement in engineering. Replacing the traditional sliding mode control with the terminal complementary sliding mode can ensure faster convergence in the sliding mode stage and the reaching stage, further eliminate the chattering caused by high-frequency switching, and enhance the stability and robustness of the system.

[0151] To verify the effectiveness of the designed control method of the present invention, a simulation circuit is built on a Hardware-In-the-Loop (HIL) experimental platform and compared with the traditional PI control strategy. It is defined that the power is positive when the voltage and current directions are the same, and the simulation parameters are set as shown in Table 1.

[0152] Table 1 Circuit parameters

[0153]

[0154] As can be seen from Figure 6 , when the active power output by the PCS jumps from 20 kW to 70 kW, i d jumps from 43 A to 150 A. Under the PI control strategy, the transition time when jumping from 20 kW to 70 kW is 28 ms. The jump caused by the sudden increase in power generates a certain amount of overshoot. In addition, due to the coupling between powers, the sudden change in active power also causes a transient process of reactive power, as shown in the boxed part in Figure 6 . As can be seen from Figure 7 , under the control method of the present invention, the transition time of the jump caused by the sudden increase in power is 21 ms, and the fluctuation of the current value during steady-state operation is smaller than that of the PI control.

[0155] As can be seen from Figure 8 , when the active power output by the PCS jumps from 70 kW to 20 kW, i d jumps from 150 A to 43 A. Under the PI control strategy, the transition time when jumping from 70 kW to 20 kW is 28 ms. The jump caused by the sudden decrease in power generates a certain amount of overshoot. In addition, due to the coupling between powers, the sudden change in active power also causes a transient process of reactive power, as shown in the boxed part in Figure 8 . Figure 9 It can be seen that under the control method of the present invention, the transition time of the jump caused by the sudden decrease in power is 21 ms, and the fluctuation of the current value during steady-state operation is smaller than that of the PI control.

[0156] In order to verify the influence of the control method of the present invention on the power quality of the PCS output current, Fourier analysis of the grid-connected current when the PCS outputs active power of 70 kW was carried out for 2 steady-state cycles in Matlab / Simulink software. As shown in Figure 10 , it is the harmonic analysis of the grid-connected current of the energy storage converter under the traditional PI control, and the THD is 3.45%. Figure 11 As shown in the harmonic analysis of the grid-connected current of the energy storage converter under the control of the present invention, the THD is 1.37%. By comparison, it can be seen that the control of the present invention has stronger harmonic suppression ability and improves the power quality of grid connection.

[0157] Figure 12 The grid-side current waveform under the control strategy of the present invention when the load power suddenly changes is shown. It can be seen that the three-phase current waveforms are stable without waveform distortion, and the AC current under the desired power can be achieved, verifying the feasibility of the control of the present invention.

[0158] In summary, the energy storage converter control method based on the terminal complementary sliding mode of the reduced-order generalized proportional integral observer of the present invention effectively solves the problems of external time-varying disturbances and the coupling effects existing inside the current loop in the grid-connected working mode of the energy storage converter, improves the convergence speed and control accuracy of the energy storage converter when disturbed, and effectively improves the power quality of the power grid.

Claims

1. A control method for an energy storage converter based on a reduced-order generalized proportional-integral observer and terminal complementary sliding mode, characterized in that The implementation is specifically carried out according to the following steps: Step 1: Establish a mathematical model of the energy storage converter in the d-q rotating coordinate system based on the impedance elements inside the energy storage converter; Step 2: Transform the mathematical model established in Step 1 into the form of a system of state variable equations; Step 3: Design a reduced-order generalized proportional-integral observer according to the system of state variable equations in Step 2; Step 4: Apply the observed values obtained from the observer in Step 3 to the control of the terminal complementary sliding mode; The specific content of Step 4 is as follows: Let the grid-side currents on the d- and q-axes i d , i q be the deviations from the grid-side current reference values respectively e d , e q be: （11） In formula (11), i dref is i d the reference value of, i qref is i q the reference value of; The terminal sliding mode surfaces of the designed d and q axes are respectively s dg , s qg . The complementary sliding mode surfaces orthogonal to the terminal sliding mode surfaces are s dc , s qc . Then s dg , s dc , s qg , s qc The specific functional forms are as follows: （12） In Equation (12), λ 1、 λ 2≥0, λ 1、 λ 2 are the gains of the sliding surface, 0 < m 1 = a 1 / b 1 < 1, 0 < m 2 = a 2 / b 2 < 1, a 1、 b 1 、a 2、 b 2 are both positive odd numbers; From Equation (12), the relationship between the two sliding mode surfaces is obtained as: （13） In Equation (13), s d , s q are the sums of the sliding mode surfaces on the d- and q-axes, respectively, that is s d = s dc + s dg , s q = s qc + s qg ; Select the Lyapunov function for judging the stability of the system V d , V q as follows: （14） Take the first-order differential of Equation (14) to get: （15） According to Equation (15), in order for the terminal complementary sliding mode function to meet the Lyapunov stability requirements, it is necessary to satisfy: （16） According to Equation (16), the equivalent control laws for the d-axis and q-axis are obtained as: （17） In Equation (17), b d and b q are the d-axis and q-axis control quantity gains respectively, z d1 and z d2 are the observed values of the state variables x d2 and x d3 respectively; Step 5: Introduce a composite variable-speed reaching law into the terminal complementary sliding mode controller in Step 4; Step 6: Apply the control law obtained from the above steps through SPWM modulation to obtain the modulation signal of the switching tubes of the energy storage converter, and apply the modulation signal to the control of the inverter switching tubes, thereby realizing the closed-loop control of the energy storage converter.

2. The energy storage converter control method based on the terminal complementary sliding mode of the reduced-order generalized proportional-integral observer according to claim 1, wherein, The specific content of Step 1 is as follows: Under the condition of three-phase voltage balance of the power grid, according to Kirchhoff's law, the variable relationship of the energy storage converter in abc coordinate system is as follows: （1） 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 respectively, u a 、 u b 、 u c are the three-phase voltages on the inverter side of the energy storage converter, u ga 、 u gb 、 u gc are the three-phase voltages of the AC power grid, i a 、 i b 、 i c are the three-phase currents on the grid side of the energy storage converter; After coordinate transformation of Equation (1), the mathematical model of the AC side of the energy storage converter in the d-q coordinate system is: （2） In formula (2), R is the parasitic parameter of the filter inductor, ω is the angular frequency of the grid voltage, u d 、 u q respectively represent the components of the AC voltage on the d-axis and q-axis, i Ld 、 i Lq respectively represent the components of the inductor current on the d-axis and q-axis, i d 、 i q respectively represent the components of the grid-side current on the d-axis and q-axis, u dr = s d u dc , u qr = s q u dc , u dc is the output voltage value of the DC voltage source, s d 、 s q are the switching functions on the d-axis and q-axis respectively, s j is the switching function, j = a, b, c and its specific function definition is: （3）。 3. The control method of the energy storage converter based on the terminal complementary sliding mode of the reduced-order generalized proportional integral observer according to claim 2, characterized in that, The specific content of Step 2 is as follows: On the basis of the three-phase balance of the grid voltage, take the d-axis direction of the grid voltage as the direction of the voltage vector. According to the instantaneous power theory, the power equation is obtained as: （4） In formula (4), P ref and Q ref are respectively the reference values of the set active power and reactive power, i dref , i qref are respectively the current reference values of the set active power and reactive power; From Equation (4), the current reference values of the active power and reactive power are respectively: （5） Unify the internal and external disturbances and parameter perturbations of the system and represent them with lumped disturbances, and take the second-order differential of Equation (2) to get: （6） In formula (6), f d and f q are the lumped disturbances on the d-axis and q-axis after equivalence, respectively. The lumped disturbance includes the unmodeled part, the coupling part, and the internal and external disturbances of the system. The expression of the lumped disturbance is as follows: （7） In Equation (7), ω is the angular frequency of the grid voltage; Let the state variables x d1 = i d , x d2 = , x d3 = f d , x q1 = i q , x q2 = , x q3 = f q Then, Equation (6) can be expressed by the state-space equation as follows: （8） To further improve the observation accuracy, expand the lumped disturbances, and then the state space model of Equation (8) is reconstructed as: （9）。 4. The energy storage converter control method based on the terminal complementary sliding mode of the reduced-order generalized proportional integral observer according to claim 3, characterized in that The specific content of Step 3 is as follows: Definition z d3 and z q1 and z q2 and z q3 are respectively and x q2 and x q3 and observation values. According to Equation (9), the form of the reduced-order generalized proportional-integral observer designed is: （10） In Equation (10), β 1, β 2, β 3, and h 1, h 2, h 3 are the observer gains for the d-axis and q-axis, respectively.

5. The energy storage converter control method based on the terminal complementary sliding mode of the reduced-order generalized proportional-integral observer according to claim 1, wherein The specific content of Step 5 is as follows: Take the composite variable-speed reaching law as the switching control law of the sliding mode. The switching control laws for the d-axis and q-axis are as follows: （18） In formula (18), k 1、 k 2、 k 3 is the gain of the d-axis reaching law greater than 0, k 4、 k 5、 k 6 is the gain of the q-axis reaching law greater than 0; δ 1、 δ 1 and 2 are the d-axis and q-axis variable index parameters respectively, and the specific representation forms are as follows: （19） In formula (19), γ > 1, 0 < ε < 1, s represents the sliding mode surface.

6. The control method of the energy storage converter based on the terminal complementary sliding mode of the reduced-order generalized proportional-integral observer according to claim 5, wherein The specific content of Step 6 is, Combining the equivalent control law of Equation (17) and the switching control law of Equation (18), the comprehensive control laws for the d-axis and q-axis of the energy storage converter are obtained as: （20）。

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