Energy storage converter control method based on fractional order superspiral terminal sliding mode

Abstract

The invention discloses an energy storage converter control method based on a fractional order superspiral terminal sliding mode, the energy storage converter comprises a front-stage converter and a rear-stage converter, specifically, a given power reference value is subjected to PQ control to obtain a current reference value, a state space averaging method is adopted to establish a disturbed state space averaging model of the rear-stage converter, and the disturbed state space averaging model of the rear-stage converter is calculated. A high-gain observer is designed according to a state-space equation, a disturbance estimation part in the observer is improved, a lag compensation link is introduced, output of the observer serves as feed-forward compensation and is combined with output feedback control, a fractional order super-spiral terminal sliding mode controller is designed, the fractional order super-spiral terminal sliding mode controller serves as current inner loop control, and the current inner loop control is achieved. SPWM modulation is carried out on the control rate output by the controller to obtain a control signal of a switching tube, and control over the output current of the converter is achieved. According to the method, the chattering problem which is difficult to avoid in integer-order nonsingular terminal sliding mode control in the prior art is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to a control method for an energy storage converter based on a fractional order super-spiral terminal sliding mode. BACKGROUND

[0002] With the rapid development of the global economy, energy demand continues to rise, traditional fossil energy reserves are gradually depleted, and environmental pollution problems are becoming increasingly serious. Under this background, the development of renewable energy has become a global consensus. The large-scale application of clean energy such as wind power and photovoltaic power is accelerating, and new power supply modes such as distributed power systems, microgrids and direct current grids have become a research hotspot. At the same time, the vigorous development of low-carbon and environmentally friendly technologies such as new energy vehicles provides unprecedented opportunities for the use of new energy, but also brings multiple challenges to system stability, economy and safety.

[0003] Among many new energy technologies, energy storage technology is particularly important as a key link to achieve efficient energy utilization and stable system operation. Renewable energy sources such as photovoltaic and wind power have significant intermittency and volatility, and energy storage converters (PCS) as the core interface equipment between energy storage systems and power grids bear key functions such as bidirectional energy regulation, voltage stabilization and power smoothing. Such converters have complex characteristics such as multiple inputs and multiple outputs, strong coupling and nonlinearity, and their control performance directly determines the overall operating efficiency and reliability of the system. However, in actual working conditions, energy storage converters need to cope with multiple external disturbances such as electromagnetic interference, harmonic noise, as well as internal uncertainties such as model parameter drift and load sudden change, which puts higher requirements on the dynamic response speed, disturbance rejection ability and robustness of the control strategy.

[0004] Although the traditional PI double closed-loop control architecture performs well in steady-state conditions, it often has slow dynamic response and insufficient disturbance rejection ability when dealing with challenges such as weakening of the power grid and intensification of voltage and frequency fluctuations caused by high proportion of renewable energy access, which seriously affects the fault ride-through capability of the system. Although traditional sliding mode control has strong robustness, its inherent high-frequency chattering problem restricts its application in engineering practice. More importantly, most existing methods use a single control framework, which makes it difficult to simultaneously consider multiple control objectives such as voltage / frequency support, harmonic suppression and oscillation damping, and they perform poorly in multi-disturbance coupling scenarios caused by high proportion of renewable energy access. The lack of control performance not only limits the full play of the energy storage system, but also may affect the overall stable operation of the power grid. Therefore, researching new PCS control methods with strong adaptability, fast dynamic response and multiple function coordination has become a key technical issue for promoting the construction of new power systems, and is also a focus of current academic research and engineering practice. SUMMARY

[0005] The application aims to provide a fractional order hyper-spiral terminal sliding mode based energy storage converter control method, which solves the chattering problem of the integer order non-singular terminal sliding mode control in the prior art.

[0006] The technical scheme adopted by the application is a fractional order hyper-spiral terminal sliding mode based energy storage converter control method, the energy storage converter comprises a front-stage converter and a rear-stage converter, specifically, a current reference value is obtained from a given power reference value through PQ control, a disturbed state space average model of the rear-stage converter is established by using a state space average method, a high gain observer is designed according to a state space equation, the disturbance estimation part in the observer is improved, a lag compensation link is introduced, the output of the observer is combined as a feedforward compensation and an output feedback control, a fractional order hyper-spiral terminal sliding mode controller is designed, the current inner loop control is realized by taking the fractional order hyper-spiral terminal sliding mode controller as the current inner loop control, the control rate output by the controller is subjected to SPWM modulation to obtain the control signal of the switching tube, and the control of the converter output current is realized.

[0007] The application also has the following characteristics: The method is implemented according to the following steps: Step 1: constructing a mathematical model of the rear-stage converter in a d-q coordinate system according to the impedance elements of the rear-stage converter; Step 2: converting the mathematical model into a space state model, expanding the total disturbance into the space state model, and constructing an equivalent model of the rear-stage converter; Step 3: designing a high gain observer according to the equivalent model of the rear-stage converter; Step 4: improving the high gain observer and introducing a lag compensation link; Step 5: designing a fractional order hyper-spiral terminal sliding mode controller and applying the observation value obtained from the high gain observer to the controller; Step 6: introducing a fractional order hyper-spiral reaching law according to the fractional order hyper-spiral terminal sliding mode controller to obtain a comprehensive control law of the rear-stage converter; Step 7: obtaining the control law through the control method constructed according to the above steps, and obtaining the duty ratio of the switching tube of the energy storage converter through SPWM modulation, so as to realize the closed loop control of the energy storage converter.

[0008] Step 1 specifically includes, obtaining the variable relationship of the rear-stage converter in a abc coordinate system according to the topological structure of the rear-stage converter through Kirchhoff's law: (1) In formula (1), i a , i b ,i c for the grid-side a, b, c three-phase current, i La 、 i Lb 、 i Lc for the a, b, c three-phase current flowing through the inductance, L 、 C for the filter inductance, filter capacitance, u a 、 u b 、 u c for the inverter-side a, b, c three-phase voltage, u ga 、 u gb 、 u gc for the a, b, c three-phase AC grid voltage; The mathematical model of the inverter AC side in d-q coordinates obtained by coordinate transformation of equation (1) is the equivalent model of the rear converter: (2) In equation (2), R for the circuit equivalent resistance parameter, ω for the grid voltage angular frequency, u d 、u q respectively represent the components of the AC voltage of the inverter on the d, q axes, i d 、 i q respectively represent the components of the inductance current on the d, q axes, i wd 、 i wq respectively represent the components of the grid-side current on the d, q axes, u dr = s d u dc , u qr = s q u dc , s d 、 s q respectively for the d, q axis switching function, the switching function is defined as: (3).

[0009] Step 2 is specifically, On the basis of three-phase balance of the power grid voltage, taking the direction of the d-axis of the power 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 , Q ref are the reference values of the set active power and reactive power respectively, i dref , i qref are the current reference values of the set active power and reactive power respectively; The active power and reactive power in the circuit are calculated by formula (4): (5) The active power and reactive power control includes the power outer loop and the current inner loop, and the power outer loop is calculated by the current inner loop reference value of formula (5) i dref , i qref , and then the current inner loop control rate is designed by the differential equation of formula (2) to control the output; The mathematical transformation of formula (2) is: (6) In formula (6), b d , b q are the control amount gains respectively, f d , f q are the equivalent d-axis and q-axis lumped disturbances respectively, and the lumped disturbance f d , f q includes the system unmodeled part, the coupling part and the system internal and external disturbances, and its expression is: (7) For the above-mentioned second-order nonlinear system, the deviation between the d-axis and q-axis inductance side current i Ld , i Lq and the current reference value is e d , e q (8)​ In formula (8), i Ldref is a reference value, i Ld is a reference value, i Lqref is a reference value; i Lq is a reference value; The second order derivative of formula (8) is: (9) In formula (9), b d is a d-axis control quantity gain, b q is a q-axis control quantity gain.

[0010] Step 3 is specifically: The d-axis system state variable is set as: (10) In formula (10), x d1 , x d2 , x d3 is a d-axis state variable; The q-axis system state variable is set as: (11) In formula (11), x q1 , x q2 , x q3 is a q-axis state variable; A high-gain observer is designed for observing the d-q axis current as follows: (12) In formula (12), z d1 , z d2 , z d3 , z q1 , z q2 , z q3 are respectively e d , e q , , , f d , fq the observation value of the high gain coefficient, a 1、 a 2、 a 3 is a high gain coefficient, and .

[0011] Step 4 is specifically, To suppress the high-frequency noise on the high gain observer to introduce a lag compensation link, the design is as follows: (13) In formula (13), z d4 、 z q4 To improve the f d 、 f q the observation value of the high gain coefficient, a d4 、 a q4 is a constant greater than 1, τ is a lag time constant, s represents the complex frequency domain.

[0012] Step 5 is specifically, The fractional order non-singular fast terminal sliding mode surface is designed as follows: (14) In formula (14), 、 、 、 is the sliding mode surface gain, and is a positive real number, 0 a< 1, the gain of the fractional order sliding mode surface exponential term = = = = 0.5, the sign function 、 , represents the fractional order differential operator, which is defined as follows: (15) In formula (15), t and t 0 are the upper and lower limits of the operator, respectively, t > t 0, a is the fractional order, 0 a <1, R( a ) is the real part of a ; The first derivative of the fractional order non-singular fast terminal sliding mode surface is obtained from formula (14) as follows: (16) By combining formula (6), formula (8) and formula (14), the d, q axis equivalent control law is obtained u dreq , u qreq is: (17).

[0013] Step 6 is specifically, The following d, q axis fractional order hyper-spiral approaching law is introduced u drsw , u qrsw : (18) In formula (18), k d1 , k d2 , k d3 , k q1 , k q2 , k q3 is the approaching law gain, is the approaching law exponential gain; Therefore, the d, q axis comprehensive control law of the rear converter is obtained u dr , u qr is: (19).

[0014] The beneficial effects of the present application are: The energy storage converter control method based on the fractional order hyper-spiral terminal sliding mode of the present application reduces the influence of high-frequency noise on the observation value by introducing a lag compensation link in the designed observer, realizes high-precision dynamic compensation for internal parameter disturbance and external environmental change of the energy storage converter system, innovatively adopts a fractional order terminal sliding mode control architecture in the control strategy, effectively solves the common chattering problem in traditional linear sliding mode control, and compared with the conventional terminal sliding mode method, by introducing the fractional order hyper-spiral approaching law, the convergence precision of the system at the equilibrium point is significantly improved while the singularity is eliminated, so that the system exhibits better robustness and adaptability when dealing with complex working conditions. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is the control block diagram of the energy storage converter control method based on the fractional order hyper-spiral terminal sliding mode of the present application; Figure 2This is the topology diagram of the downstream converter; Figure 3 This is a block diagram of the dq axis control of the downstream converter of the present invention; Figure 4 This is a transient waveform diagram of the three-phase current on the grid side under PI control; Figure 5 This is a transient waveform diagram of the three-phase current on the power grid side controlled by the present invention; Figure 6 This is a transient waveform diagram of the grid-side current under PI control when the active power suddenly increases from 35kW to 80kW. Figure 7 This is a transient diagram of the grid-side current controlled by the present invention when the active power suddenly increases from 35kW to 80kW; Figure 8 This is a transient waveform diagram of the grid-side current under PI control when the active power jumps from 80kW to 35kW. Figure 9 This is a transient diagram of the grid-side current controlled by the present invention when the active power jumps from 80kW to 35kW. Figure 10 This is a diagram showing the harmonic analysis of the power grid current under PI control. Figure 11 This is a diagram showing the harmonic analysis of the power grid current controlled by this invention. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0017] Example 1 This embodiment provides a control method for an energy storage converter based on fractional-order superspiral terminal sliding mode, such as... Figure 1 As shown, the energy storage converter includes a front-end converter and a back-end converter. Specifically, a reference value for the current is obtained from a given power reference value through PQ control. A disturbed state-space average model of the back-end converter is established using the state-space averaging method. A high-gain observer is designed based on the state-space equations, and the disturbance estimation part in the observer is improved by introducing a hysteresis compensation stage. The output of the observer is combined with feedforward compensation and output feedback control to design a fractional-order superspiral terminal sliding mode controller. The fractional-order superspiral terminal sliding mode controller is used as the inner loop current control. The control law output by the controller is modulated by SPWM to obtain the control signal of the switching transistor, thereby realizing the control of the converter output current.

[0018] The specific steps are as follows: Step 1: Based on the impedance elements of the subsequent converter, construct a mathematical model of the subsequent converter in the dq coordinate system; Step 2: Transform the mathematical model into a state-space model, extend the total disturbance into the state-space model, and construct the equivalent model of the subsequent converter; Step 3: Design a high-gain observer according to the equivalent model of the rear converter; Step 4: Improve the high-gain observer and introduce a lag compensation link; Step 5: Design a fractional-order hyper-spiral terminal sliding mode controller, and apply the observed values obtained by the high-gain observer to the controller; Step 6: According to the fractional-order hyper-spiral terminal sliding mode controller, introduce a fractional-order hyper-spiral reaching law to obtain the comprehensive control law of the rear converter; Step 7: Obtain the control law according to the control method constructed in the above steps, and obtain the duty ratio of the energy storage converter switch tube through SPWM modulation, so as to realize the closed-loop control of the energy storage converter.

[0019] Embodiment 2 The embodiment provides an energy storage converter control method based on a fractional-order hyper-spiral terminal sliding mode. Based on embodiment 1, the rear converter circuit topology is as shown in Figure 2 The DC side voltage is provided by a DC voltage source with an amplitude of u in The inverter outputs a certain power to supply the AC load. In the figure, C dc is a DC side voltage stabilizing capacitor, u dc is a voltage value across the DC side voltage stabilizing capacitor, i o represents a DC bus current, u a u b u c is a three-phase voltage on the inverter side, i La i Lb i Lc is a three-phase current flowing through the inductor, L C is a filter parameter, R is a circuit equivalent resistance parameter, u ga u gb u gc is an AC grid voltage, i a i b i c is a three-phase current on the grid side.

[0020] Step 1 is specifically,​​​​​​​​​ Based on the topology of the subsequent converter, Kirchhoff's laws are applied to obtain the following information about the subsequent converter: abc Relationships between variables in a coordinate system: (1) In equation (1), i a , i b , i c The three-phase currents (a, b, and c) on the grid side are... i La , i Lb , i Lc The three-phase currents a, b, and c flowing through the inductor are... L , C For filter inductors and filter capacitors, u a , u b , u c The voltages of phases a, b, and c on the inverter side are... u ga , u gb , u gc The voltages of the three-phase AC power grid are a, b, and c. Equation (1) is transformed by coordinates to obtain the mathematical model of the inverter's AC side in the dq coordinates, which is also the equivalent model of the subsequent converter: (2) In equation (2), R These are the equivalent resistance parameters of the circuit. ω The angular frequency of the grid voltage. u d 、u q These represent the components of the inverter's AC voltage on the d and q axes, respectively. i d , i q These represent the components of the inductor current on the d and q axes, respectively. i wd , i wq These represent the components of the grid-side current on the d and q axes, respectively. u dr = s d u dc , u qr= s q u dc , s d 、 s q are d, q-axis switching functions, the switching function is defined as: (3).

[0021] Embodiment 3 The embodiment provides a control method of a storage converter based on a fractional order super-spiral terminal sliding mode, and on the basis of the embodiments 1-2, the step 2 is specifically: Under the condition of three-phase balance of the grid voltage, the d-axis direction of the grid voltage is taken as the direction of the voltage vector, and according to the instantaneous power theory, a power equation is obtained: (4) In the formula (4), P ref 、 Q ref are reference values of the set active power and reactive power, i dref 、 i qref are current reference values of the set active power and reactive power; The active power and the reactive power in the circuit are calculated according to the formula (4): (5) Active power Reactive power (P, Q) P , Q ) control includes a power outer ring and a current inner ring, the power outer ring is controlled by the current inner ring reference value calculated by the formula (5) i dref 、 i qref , and then the current inner ring control rate is designed by the formula (2) differential equation to control the output; The formula (2) is mathematically transformed to obtain: (6) In the formula (6), b d 、 b q are control amount gains, f d 、 f q are equivalent d, q-axis lumped disturbances, the lumped disturbance f d 、 f qThe system unmodeled part, coupling part and system internal and external disturbance are included, and the expression is: (7) For the above-mentioned second-order nonlinear system, the deviation between the d-axis inductance side current i Ld 、 i Lq and the reference value of the inductance side current is: e d 、 e q (8) In formula (8), i Ldref is the reference value of i Ld , i Lqref is the reference value of i Lq ; The second-order derivative of formula (8) is: (9) In formula (9) b d is the d-axis control amount gain, b q is the q-axis control amount gain.

[0022] Embodiment 4 The embodiment provides a kind of energy storage converter control method based on fractional order super spiral terminal sliding mode, on the basis of embodiment 1-3, step 3 is specifically: The d-axis system state variable is set as: (10) In formula (10), x d1 、 x d2 、 x d3 is the d-axis state variable; the q-axis system state variable is set as: (11) In formula (11), x q1 、 x q2 、 x q3 is the q-axis state variable; High gain observer is designed as follows for observing d-q axis current: (12) ​In formula (12), z d1 、 z d2 、 z d3 、 z q1 、 z q2 、 z q3 are respectively e d 、 e q 、 、 、 f d 、 f q observation values of a 1、 a 2、 a 3 is a high gain coefficient, and .

[0023] Embodiment 5 The embodiment provides a control method of an energy storage converter based on a fractional order super-spiral terminal sliding mode, and on the basis of the embodiments 1-4, the step 4 is specifically, In order to suppress the high-frequency noise to introduce a lag compensation link to the high gain observer, the design is as follows: (13) In formula (13), z d4 、 z q4 In order to improve the observation values of f d 、 f q , a d4 、 a q4 is a constant greater than 1, τ is a lag time constant, and is taken as τ =0.01, s represents a complex frequency domain.

[0024] Embodiment 6 The embodiment provides a control method of an energy storage converter based on a fractional order super-spiral terminal sliding mode, and on the basis of the embodiments 1-5, the step 5 is specifically, In view of the problem that the convergence speed and the chattering suppression performance are difficult to be considered in the traditional integer order sliding mode control, the embodiment provides a non-singular fast terminal sliding mode control strategy based on a fractional order, the sliding mode surface is reconstructed by introducing a fractional order operator, and the finite time convergence characteristics of the non-singular fast terminal sliding mode surface are combined, so that the chattering phenomenon caused by the high-frequency switching of the sign function in the sliding stage of the traditional sliding mode surface is solved. In order to obtain fast and accurate control, the fractional non-singular fast terminal sliding mode surface is designed as follows: (14) In formula (14), , , , is a sliding mode surface gain, and is a positive real number, 0 a< 1, the gain of the fractional sliding mode surface exponential term = = = =0.5, the sign function , , represents a fractional calculus operator, and is defined as follows: (15) In formula (15), t and t 0 are the upper limit and the lower limit of the operator respectively, t t 0, a is a fractional order, 0 a <1, R( a ) is the real part of a ; The first derivative of the fractional non-singular fast terminal sliding mode surface obtained from formula (14) is as follows: (16) By combining formula (6), formula (8) and formula (14), the equivalent control law of the d-axis and the q-axis is obtained u dreq , u qreq as follows: (17).

[0025] Embodiment 7 The embodiment provides an energy storage converter control method based on a fractional order super spiral terminal sliding mode, and on the basis of embodiments 1-6, step 6 is specifically Considering that the fractional order control has greater flexibility, a fractional order super spiral reaching law is introduced, so that the sliding mode surface has faster reaching speed and better chattering suppression, and the following d-axis and q-axis fractional order super spiral reaching laws are introduced​u drsw 、 u qrsw : (18) In formula (18), k d1 、 k d2 、 k d3 、 k q1 、 k q2 、 k q3 is a reaching law gain, is a reaching law exponential gain; Therefore, the d, q-axis comprehensive control law of the rear converter is obtained u dr 、 u qr is: (19) The d-q axis control of the rear converter is shown in Figure 3 .

[0026] Simulation analysis The energy storage converter model is built in the Matlab / Simulink platform, under two kinds of control, when the active power is suddenly changed, at 0.2s, the output is suddenly increased from 35kW to 80kW, and the corresponding three-phase current amplitude is suddenly increased from 62.5A to 148.6A; at 0.3s, it is suddenly reduced from 80kW to 35kW, and the corresponding three-phase current amplitude is suddenly reduced from A to 62.5A; as shown in Figure 4 , it is the transient waveform diagram of the three-phase current of the grid side under the traditional PI control, the response time of the three-phase current of the grid side is 41.0ms at 0.2s, and the response time of the three-phase current of the grid side is 41.3ms at 0.3s. As shown in Figure 5 , it is the transient waveform diagram of the three-phase current of the grid side under the control of the application, the response time of the three-phase current of the grid side is 15.1ms at 0.2s, and the response time of the three-phase current of the grid side is 14.8ms at 0.3s. Comparison shows that the control strategy of the application greatly reduces the transient time and improves the stability of the system.

[0027] In order to verify the effectiveness of the control method designed by the application, a simulation circuit is built in a hardware-in-the-loop (Hardware-In-the-Loop, HIL) experimental platform, and a traditional PI control strategy is compared and analyzed, and the power is defined as positive when the voltage and current directions are consistent, and the simulation parameter settings are shown in Table 1.

[0028] Table 1 Circuit parameters

[0029] As can be seen from Figure 6 , when the active power output by the inverter suddenly increases from 35 kW to 80 kW, i Ld from 62A to 148A. The transition time when the active power suddenly increases from 35 kW to 80 kW under the PI control strategy is 21 ms. The jump caused by the sudden increase in power produces a certain overshoot, and the coupling between the powers causes a transient process of the DC bus voltage jump when the active power suddenly changes, as shown in the boxed part of Figure 6 . As can be seen from Figure 7 , when the active power output by the inverter suddenly increases from 35 kW to 80 kW under the control method of the application, the transition time of the jump caused by the sudden increase in power is 15 ms, and the fluctuation of the DC bus voltage in the steady state is smaller than that of the PI control.

[0030] As can be seen from Figure 8 , when the active power output by the inverter suddenly decreases from 80 kW to 35 kW, i Ld from 148A to 62A. The transition time when the active power suddenly decreases from 80 kW to 35 kW under the PI control strategy is 26 ms. The jump caused by the sudden decrease in power produces a certain overshoot, and the coupling between the powers causes a transient process of the DC bus voltage when the active power suddenly changes, as shown in the boxed part of Figure 8 . Figure 9 As can be seen from , when the active power output by the inverter suddenly decreases from 80 kW to 35 kW under the control method of the application, the transition time of the jump caused by the sudden decrease in power is 17 ms, and the fluctuation of the current value in the steady state is smaller than that of the PI control.

[0031] In order to verify the influence of the control method of the application on the power quality of the inverter output current, the grid-connected current of the inverter when the active power is 25 kW is subjected to Fourier analysis for two steady-state periods in the 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 3.40%. Figure 11 As shown in , it is the harmonic analysis of the grid-connected current of the inverter under the control of the application, and the THD is 1.51%. As can be seen from the comparison, the control of the application has stronger harmonic suppression ability and improves the power quality of grid connection.

[0032] As can be seen from the above, the energy storage converter control method based on the fractional order super-spiral terminal sliding mode has the following advantages: 1) The improved high-gain observer is used to realize the accurate observation of the internal and external changes and disturbances of the grid-connected energy storage system. The observer introduces a lag compensation link, which reduces the high-frequency noise of the estimated disturbance and improves the disturbance estimation ability; 2) The designed fractional order terminal sliding mode controller can obtain fast and accurate control performance, and has better chattering suppression effect than integer order non-singular terminal sliding mode control; 3) The fractional order super-spiral reaching law used can further reduce the system chattering and improve the system reaching speed; 4) Compared with existing control methods, the convergence accuracy near the equilibrium point is improved, and the system has better dynamic performance and robustness.

Claims

1. A control method of an energy storage converter based on fractional order hyper- spiral terminal sliding mode, the energy storage converter comprising a front converter and a back converter, characterized in that, Specifically, the reference value of the current is obtained from the given power reference value through PQ control, the disturbed state space average model of the post-stage converter is established by using the state space average method, the high gain observer is designed according to the state space equation, the disturbance estimation part of the observer is improved, the lag compensation link is introduced, the output of the observer is combined with the output feedback control as the feedforward compensation, the fractional order hyper-spiral terminal sliding mode controller is designed, the current inner loop control is realized by taking the fractional order hyper-spiral terminal sliding mode controller as the controller, the control signal of the switching tube is obtained by SPWM modulation of the output of the controller, and the control of the converter output current is realized.

2. The control method of the energy storage converter based on fractional order super-twisting terminal sliding mode according to claim 1, characterized in that, The following steps are specifically implemented: Step 1: according to the impedance elements of the post-stage converter, the mathematical model of the post-stage converter in the d-q coordinate system is constructed; Step 2: the mathematical model is converted into a space state model, the total disturbance is expanded into the state space model, and the equivalent model of the post-stage converter is constructed; Step 3: a high gain observer is designed according to the equivalent model of the post-stage converter; Step 4: the high gain observer is improved, and a lag compensation link is introduced; Step 5: a fractional order hyper-spiral terminal sliding mode controller is designed, and the observed value obtained from the high gain observer is applied to the controller; Step 6: according to the fractional order hyper-spiral terminal sliding mode controller, a fractional order hyper-spiral reaching law is introduced to obtain the comprehensive control law of the post-stage converter; Step 7: the control law is obtained according to the control method constructed in the above steps, the duty ratio of the energy storage converter switching tube is obtained through SPWM modulation, and thus the closed-loop control of the energy storage converter is realized.

3. The control method of the energy storage converter based on fractional order super-twisting terminal sliding mode according to claim 2, characterized in that, The step 1 is specifically, According to the topology of the rear converter, by Kirchhoff's law, the rear converter in abc The variable relationship in the coordinate system: （1） In formula (1), i a , i b , i c are a, b, c three-phase currents of the grid side, i La , i Lb , i Lc are a, b, c three-phase currents flowing through the inductance, L , C are filter inductance and filter capacitance, u a , u b , u c are a, b, c three-phase voltages of the inverter side, u ga , u gb , u gc are a, b, c three-phase alternating current grid voltages; The mathematical model of the inverter AC side in the d-q coordinate system, i.e., the equivalent model of the post-stage converter, is obtained by coordinate transformation of formula (1): （2） in formula (2), R is the equivalent resistance parameter of the circuit, ω is the angular frequency of the grid voltage, u d 、u q respectively represent the components of the AC voltage of the inverter on the d, q axes, i d , i q respectively represent the components of the inductance current on the d, q axes, i wd , i wq respectively represent the components of the grid-side current on the d, q axes, u dr s d u dc , u qr s q u dc , s d , s q are respectively the d, q axis switching functions, the switching function being defined as:​​ （3）。 4. The control method of the energy storage converter based on fractional order super-twisting terminal sliding mode according to claim 3, characterized in that, The step 2 is specifically, On the basis of three-phase balance of the grid voltage, the d-axis direction of the grid voltage is taken as the direction of the voltage vector, and according to the instantaneous power theory, the power equation is obtained as: （4） in formula (4), P ref , Q ref are respectively the reference values of the set active power, reactive power, i dref , i qref are respectively the current reference values of the set active power, reactive power; The active power and the reactive power in the circuit are calculated from formula (4): （5） The active power and reactive power control includes a power outer loop and a current inner loop, and the power outer loop controls the current inner loop reference value calculated by formula (5) i dref 、 i qref and then the current inner loop control rate is designed by the differential equation of formula (2) to control the output; The mathematical transformation of formula (2) is as follows: （6） In formula (6), b d , b q respectively are control quantity gains, f d , f q respectively are equivalent d, q axis lumped disturbances, lumped disturbances f d , f q include system unmodeled parts, coupling parts and system internal and external disturbances, and the expression is: （7） For the above second order nonlinear system, the deviation between the d, q axis inductance side current i Ld , i Lq and the inductance side current reference value e d , e q is: （8） In formula (8), i Ldref is i Ld a reference value of i Lqref is i Lq a reference value of The second-order derivative of formula (8) is as follows: （9） In formula (9) b d is a d-axis control amount gain, b q is a q-axis control amount gain.

5. The fractional order hyper- terminal sliding mode based energy storage converter control method of claim 4, wherein, The step 3 is specifically, The d-axis system state variable is set as: （10） In formula (10), x d1 , x d2 , x d3 is a d-axis state variable; The q-axis system state variable is set as: （11） In formula (11), x q1 , x q2 , x q3 q-axis state variable; A high gain observer is designed for observing the d-q axis current as follows: （12） In formula (12), z d1 , z d2 , z d3 , z q1 , z q2 , z q3 are respectively e d , e q , , , f d , f q the observation value of a 1, a 2, a 3 is a high gain coefficient, and .

6. The control method of the energy storage converter based on fractional order super-twisting terminal sliding mode according to claim 5, characterized in that, The step 4 is specifically, In order to suppress the high frequency noise, a lag compensation link is introduced into the high gain observer, and the design is as follows: （13） In formula (13), z d4 , z q4 to improve the post f d , f q observations, a d4 , a q4 is a constant greater than 1, τ is a lag time constant, s denotes the complex frequency domain.

7. The control method of the energy storage converter based on fractional order super-twisting terminal sliding mode according to claim 6, characterized in that, The step 5 is specifically, A fractional order non-singular fast terminal sliding surface is designed as follows: （14） In formula (14), , , , is a sliding mode surface gain, and is a positive real number, 0 a< 1, fractional order sliding mode surface exponential term gain = = = 0.5, sign function , , denotes a fractional order calculus operator, defined as follows: （15） In formula (15), t and t 0 are the upper and lower limits of the operator, respectively, t t 0, a is the fractional order, 0 a <1, R a is the real part of a .​ The first-order derivative of the fractional order non-singular fast terminal sliding surface is obtained from formula (14) as follows: （16） Substitute formula (6), formula (8) and formula (14) into formula (15), the equivalent control law of d, q axis is obtained u dreq , u qreq is: （17）。 8. The control method of the energy storage converter based on fractional order super-twisting terminal sliding mode according to claim 6, characterized in that, The step 6 is specifically, The following d, q axis fractional order hyper-spiral approaching law is introduced u drsw 、 u qrsw : （18） In formula (18), k d1 , k d2 , k d3 , k q1 , k q2 , k q3 is a proportional gain, is a proportional gain, Thus, the d, q-axis comprehensive control law of the rear-stage converter is obtained u dr , u qr is: （19）。

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