Energy storage converter control method based on fractional order hyper-spiral recurrent terminal sliding mode

Abstract

The application discloses a control method of energy storage converter based on fractional order hyper-spiral recursive terminal sliding mode, and the energy storage converter comprises a front-stage converter and a rear-stage converter. A given power reference value is subjected to PQ control to obtain a current reference value. A disturbed state space average model of the rear-stage converter is established by using a state space average method. A hyper-spiral sliding mode observer is designed, and a disturbance estimation part in the observer is improved. A lag compensation link is introduced. The output of the observer is combined with output feedback control as feedforward compensation. A fractional order hyper-spiral recursive terminal sliding mode controller is designed. The fractional order recursive terminal sliding mode controller is used as a current inner loop control. The control rate output by the controller is subjected to SPWM modulation to obtain a control signal of a switching tube, so that the control of the converter output current is realized. The application solves the chattering problem which is difficult to avoid in the traditional integer order sliding mode controller.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, specifically relating to a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode. Background Technology

[0002] As the global pursuit of sustainable energy intensifies, renewable energy sources such as wind and solar power are increasingly accounting for a larger share of the power sector. However, renewable energy is intermittent and volatile. For example, wind power generation is affected by unstable wind speeds, and solar power generation depends on sunlight conditions, making it difficult to maintain a stable power output. This poses a serious challenge to the stable operation of the power grid, potentially causing power quality problems such as voltage fluctuations and frequency deviations, and even threatening grid security. To address these issues, energy storage systems have emerged. These systems can store excess energy and release it when energy supply is insufficient, thereby effectively smoothing out power fluctuations in renewable energy generation and enhancing grid stability.

[0003] The Power Conversion System (PCS), as the core component of an energy storage system, plays a crucial role in conversion and control, undertaking the important task of bidirectional energy conversion between the battery and the grid. During charging, it converts AC power generated by the grid or renewable energy generation into DC power for storage in the battery; during discharging, it inverts the DC power back into AC power for use by the load or for feedback to the grid. The quality of its control performance directly determines the overall efficiency of the energy storage system, including charging and discharging efficiency, power quality, and system reliability. It must not only precisely control the energy conversion but also monitor the battery status and grid operating parameters in real time, responding quickly based on this information and adjusting its own operating state to ensure coordinated operation between the energy storage system and the grid.

[0004] Currently, there are numerous control methods for energy storage converters. Traditional PI control, with its simple principle and ease of implementation, was widely used in the early stages. However, when faced with complex scenarios involving nonlinearity, multiple constraints, and rapid dynamic power changes, PI control exhibits problems such as response lag and poor stability. When grid voltage or frequency changes abruptly, the PI controller struggles to quickly adjust the energy storage converter output, leading to significant power fluctuations and impacting grid stability. In the control field, many problems remain to be solved. On the one hand, with the continuous growth of renewable energy generation capacity and the expanding scale of energy storage systems, PCS (Power Conversion System) needs higher control accuracy and faster dynamic response speed to better adapt to the complex and ever-changing grid environment and large-scale energy storage demands. On the other hand, PCS control strategies need to further improve energy conversion efficiency, reduce costs, and enhance economic benefits while ensuring system stability and reliability. Simultaneously, how to achieve complementary advantages among different control methods and develop more intelligent, efficient, and reliable control technologies is also an important research topic. Summary of the Invention

[0005] The purpose of this invention is to provide a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode, which solves the chattering problem that is difficult to avoid in traditional integer-order sliding mode controllers.

[0006] The technical solution adopted in this invention is a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode. The energy storage converter includes a front-end converter and a back-end converter. A current reference value 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 superspiral sliding mode observer is designed, and the disturbance estimation part in the observer is improved by introducing a hysteresis compensation link. The output of the observer is combined with feedforward compensation and output feedback control to design a fractional-order superspiral recursive terminal sliding mode controller. The fractional-order recursive terminal sliding mode controller is used as the current inner loop 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.

[0007] The invention is further characterized by:

[0008] The specific steps are as follows:

[0009] Step 1: Based on the impedance elements of the subsequent converter, construct a mathematical model of the subsequent converter in the dq coordinate system;

[0010] 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;

[0011] Step 3: Design a super-helical sliding mode observer based on the equivalent model of the subsequent converter;

[0012] Step 4: Design a fractional-order superspiral recursive terminal sliding mode controller and apply the observations obtained in Step 3 to the controller;

[0013] Step 5: Based on the fractional-order superspiral recursive terminal sliding mode controller, add the fractional-order superspiral reaching law;

[0014] Step 6: Based on the control method constructed in the above steps, the control law is obtained. The duty cycle of the energy storage converter switching transistor is obtained through SPWM modulation, thereby realizing the closed-loop control of the energy storage converter.

[0015] Step 1 specifically involves:

[0016] 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:

[0017] (1)

[0018] 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.

[0019] 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:

[0020] (2)

[0021] 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 qu dc , s d , s q These are the d-axis and q-axis switching functions, respectively. The switching functions are defined as follows:

[0022] (3).

[0023] Step 2 specifically involves:

[0024] Assuming the three-phase voltage of the power grid is balanced, and taking the d-axis direction of the power grid voltage as the direction of the voltage vector, the power equation is obtained according to the instantaneous power theory:

[0025] (4)

[0026] In equation (4), P ref , Q ref These are the set reference values ​​for active power and reactive power, respectively. i dref , i qref These are the set current reference values ​​for active power and reactive power, respectively.

[0027] The active power and reactive power in the circuit can be calculated using equation (4):

[0028] (5)

[0029] Active and reactive power control includes an outer power loop and an inner current loop. The outer power loop uses the reference value of the inner current loop calculated by equation (5). i dref , i qref Then, the current inner loop control law is designed using the differential equation (2) to control the output;

[0030] Mathematical transformation of equation (2) yields:

[0031] (6)

[0032] In equation (6), b d , b q These are the control quantity gains. f d , f q These are the equivalent lumped disturbances along the d and q axes, respectively. f d , fq Including the unmodeled parts of the system, the coupled parts, and internal and external disturbances, its expression is:

[0033] (7)

[0034] For the aforementioned second-order nonlinear system, consider the inductor-side currents on the d and q axes. i Ld , i Lq Deviation from the reference value of the inductive current e d , e q for:

[0035] (8)

[0036] In equation (8), i Ldref for i Ld Reference value, i Lqref for i Lq Reference value;

[0037] Taking the second derivative of equation (8), we get:

[0038] (9)

[0039] In equation (9) b d This refers to the gain of the d-axis control quantity. b q This is the gain of the q-axis control quantity.

[0040] Step 3 specifically involves:

[0041] A super-helical sliding mode observer was designed for observing the dq-axis current as follows:

[0042] (10)

[0043] In equation (10), z d1 , z d2 , z d3 , z q1 , z q2 , z q3 They are respectively e d , e q , , , f d , f q The observed values, , , , , , It is a positive number;

[0044] To suppress high-frequency noise, a hysteresis compensation element is introduced, designed as follows:

[0045] (11)

[0046] In equation (11), z d4 , z q4 For the improved f d , f q The observed values, a d4 , a q4 It is a constant greater than 1. τ The time lag constant is s This represents the complex frequency domain.

[0047] Step 4 specifically involves:

[0048] To construct a recursive terminal sliding mode controller, design non-singular terminal sliding functions for the d and q axes. , as follows:

[0049] (12)

[0050] In equation (12), λ 1. λ 2. λ 3. λ 4 is a positive real number. , ;

[0051] Design the sliding function based on equation (12). , as follows:

[0052] (13)

[0053] In equation (13), , It is a positive real number. , All are greater than 1;

[0054] The following recursive terminal sliding surfaces for the d and q axes are designed using equations (12) and (13). s d , s q :

[0055] (14)

[0056] In equation (14), λ 5. λ 6 is a positive real number.

[0057] In step 4, the sliding function , , , and sliding surface s d , s q Associated with the two sliding surfaces in the recursive structure, when the second sliding surface is reached for the first time... s d , s q All equal to 0, satisfying the sliding function , , , The finite-time convergence condition is then determined, and subsequently, when the first sliding surface is reached, the sliding function... , , , The tracking error converges to zero. e d , e q It will converge to zero within a finite amount of time.

[0058] Step 5 specifically involves:

[0059] Differentiating equation (14) yields:

[0060] (15)

[0061] Combine equations (6), (8), and (15), and let... , When the value equals 0, the equivalent control law for the d and q axes is obtained. u dreq , u qreq for:

[0062] (16)

[0063] Introducing the fractional superscrew reaching law of the d and q axes u drsw , u qrsw ,as follows:

[0064] (17)

[0065] Therefore, the combined d-axis and q-axis control law of the subsequent converter is obtained. u dr , u qr for:

[0066] (18).

[0067] The beneficial effects of this invention are as follows: Firstly, addressing the issue of low accuracy in extended state observers, this invention designs a superspiral sliding mode observer, employing a superspiral algorithm to accurately estimate external changes and internal parameter disturbances and uncertainties in the energy storage converter system. Secondly, by adopting a fractional superspiral recursive terminal sliding mode control method, compared to most current control methods using linear sliding mode to avoid terminal sliding mode singularity problems, this invention's recursive terminal sliding mode control method solves the non-singularity problem while improving convergence accuracy near the equilibrium point. Thirdly, the introduction of a fractional superspiral reaching law gives the system better dynamic response and faster convergence speed. In summary, this invention effectively solves the coupling effects of external disturbances and the existence of the current inner loop on the energy storage converter in its operating mode, improving control accuracy and convergence speed under disturbance. This invention also exhibits good robustness and can effectively improve the power quality of the power grid. Attached Figure Description

[0068] Figure 1 This is a control block diagram of the energy storage converter control method based on fractional-order superspiral recursive terminal sliding mode of the present invention;

[0069] Figure 2 This is the topology diagram of the downstream converter;

[0070] Figure 3 This is a block diagram of the dq axis control of the downstream converter of the present invention;

[0071] Figure 4 This is a transient waveform diagram of the three-phase current on the grid side under PI control;

[0072] Figure 5 This is a transient waveform diagram of the three-phase current on the power grid side controlled by the present invention;

[0073] Figure 6 This is a transient waveform diagram of the grid-side current under PI control when the active power suddenly increases from 25kW to 65kW.

[0074] Figure 7 This is a transient diagram of the grid-side current controlled by the present invention when the active power suddenly increases from 25kW to 65kW.

[0075] Figure 8 This is a transient waveform diagram of the grid-side current under PI control when the active power jumps from 65kW to 25kW.

[0076] Figure 9 This is a transient diagram of the grid-side current controlled by the present invention when the active power jumps from 65kW to 25kW;

[0077] Figure 10 This is a diagram showing the harmonic analysis of the power grid current under PI control.

[0078] Figure 11 This is a diagram showing the harmonic analysis of the power grid current controlled by this invention. Detailed Implementation

[0079] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0080] Example 1

[0081] This embodiment provides a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode, such as... Figure 1 As shown, the energy storage converter includes a front-end converter and a back-end converter. The current reference value is obtained from a given power reference value through PQ control. The state-space averaging method is used to establish the disturbed state-space average model of the back-end converter. A super-spiral sliding mode observer is designed, and the disturbance estimation part in the observer is improved by introducing a hysteresis compensation link to improve the disturbance estimation capability of the observer and enable the system to have a better dynamic response. The output of the observer is combined with the feedforward compensation and output feedback control to design a fractional-order super-spiral recursive terminal sliding mode controller, which effectively suppresses the sliding mode chattering problem. The fractional-order recursive terminal sliding mode controller is used as the current inner loop control. The control law output of the controller is modulated by SPWM to obtain the control signal of the switching transistor, thereby realizing the control of the converter output current.

[0082] Example 2

[0083] This embodiment provides a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode. Based on Embodiment 1, it is implemented according to the following steps:

[0084] Step 1: Based on the impedance elements of the subsequent converter, construct a mathematical model of the subsequent converter in the dq coordinate system;

[0085] 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;

[0086] Step 3: Design a super-helical sliding mode observer based on the equivalent model of the subsequent converter;

[0087] Step 4: Design a fractional-order superspiral recursive terminal sliding mode controller and apply the observations obtained in Step 3 to the controller;

[0088] Step 5: Based on the fractional-order superspiral recursive terminal sliding mode controller, add the fractional-order superspiral reaching law;

[0089] Step 6: Based on the control method constructed in the above steps, the control law is obtained. The duty cycle of the energy storage converter switching transistor is obtained through SPWM modulation, thereby realizing the closed-loop control of the energy storage converter.

[0090] Example 3

[0091] This embodiment provides a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode. Building upon embodiments 1-2, the subsequent converter circuit topology is as follows: Figure 2 As shown, the DC side voltage has an amplitude of u in The DC voltage source provides power, and the inverter outputs a certain amount of power to supply the AC load. In this diagram, C dc This is a DC-side voltage regulator capacitor. u dc This is the voltage across the DC-side voltage regulator capacitor. i o Indicates DC bus current. u a , u b , u c The three-phase voltage on the inverter side. i La , i Lb , i Lc The three-phase current flowing through the inductor, L , C These are the filter parameters. R These are the equivalent resistance parameters of the circuit. u ga , u gb , u gc AC grid voltage, i a , i b , i c This refers to the three-phase current on the grid side.

[0092] Step 1 specifically involves:

[0093] 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:

[0094] (1)

[0095] 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.

[0096] 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:

[0097] (2)

[0098] 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 These are the d-axis and q-axis switching functions, respectively. The switching functions are defined as follows:

[0099] (3).

[0100] Example 4

[0101] This embodiment provides a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode. Building upon embodiments 1-3, step 2 specifically involves...

[0102] Assuming the three-phase voltage of the power grid is balanced, and taking the d-axis direction of the power grid voltage as the direction of the voltage vector, the power equation is obtained according to the instantaneous power theory:

[0103] (4)

[0104] In equation (4), P ref , Q ref These are the set reference values ​​for active power and reactive power, respectively. i dref , i qref These are the set current reference values ​​for active power and reactive power, respectively.

[0105] The active power and reactive power in the circuit can be calculated using equation (4):

[0106] (5)

[0107] Active power and reactive power ( P , Q The control includes a power outer loop and a current inner loop. The power outer loop is calculated using the current inner loop reference value obtained from equation (5). i dref , i qref Then, the current inner loop control law is designed using the differential equation (2) to control the output;

[0108] Mathematical transformation of equation (2) yields:

[0109] (6)

[0110] In equation (6), b d , b q These are the control quantity gains. f d , f q These are the equivalent lumped disturbances along the d and q axes, respectively. f d , f q Including the unmodeled parts of the system, the coupled parts, and internal and external disturbances, its expression is:

[0111] (7)

[0112] For the aforementioned second-order nonlinear system, consider the inductor-side currents on the d and q axes. i Ld , i Lq Deviation from the reference value of the inductive current e d , e q for:

[0113] (8)

[0114] In equation (8), i Ldref for i Ld Reference value, i Lqref for i Lq Reference value;

[0115] Taking the second derivative of equation (8), we get:

[0116] (9)

[0117] In equation (9) b d This refers to the gain of the d-axis control quantity. b q This is the gain of the q-axis control quantity.

[0118] Example 5

[0119] This embodiment provides a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode. Building upon embodiments 1-4, step 3 specifically comprises:

[0120] A super-helical sliding mode observer was designed for observing the dq-axis current as follows:

[0121] (10)

[0122] In equation (10), z d1 , z d2 , z d3 , z q1 , z q2 , z q3 They are respectively e d , e q , , , f d , f q The observed values, , , , , , It is a positive number;

[0123] To suppress high-frequency noise, a hysteresis compensation element is introduced, designed as follows:

[0124] (11)

[0125] In equation (11), z d4 , z q4 For the improved f d , f q The observed values, a d4 , a q4 It is a constant greater than 1. τ The time lag constant is s This represents the complex frequency domain.

[0126] Example 6

[0127] This embodiment provides a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode. Building upon embodiments 1-5, step 4 specifically involves...

[0128] Non-singular fast terminal sliding surfaces (TSS) exhibit fast convergence and good dynamic response. However, most current methods employ linear sliding surfaces to avoid singularity issues. This invention proposes a recursive terminal sliding controller with a novel recursive structure. Compared to traditional methods using linear sliding surfaces to avoid singularity, this controller improves the system's convergence speed while addressing non-singularity problems. Therefore, to construct the recursive terminal sliding controller, non-singular terminal sliding functions for the d and q axes are designed. , as follows:

[0129] (12)

[0130] In equation (12), λ 1. λ 2. λ 3. λ 4 is a positive real number. , ;

[0131] Design the sliding function based on equation (12). , as follows:

[0132] (13)

[0133] In equation (13), , It is a positive real number. , All are greater than 1;

[0134] The following recursive terminal sliding surfaces for the d and q axes are designed using equations (12) and (13):

[0135] (14)

[0136] In equation (14), λ 5. λ 6 is a positive real number.

[0137] Sliding function , , , and sliding surface s d , s q Associated with the two sliding surfaces in the recursive structure, when the second sliding surface is reached for the first time... s d , s q All equal to 0, satisfying the sliding function , , , The finite-time convergence condition is then determined, and subsequently, when the first sliding surface is reached, the sliding function... , , , The tracking error converges to zero. e d , e q It will converge to zero in a finite amount of time. In the recursive structure, each sliding surface is reached sequentially as shown above.

[0138] Example 7

[0139] This embodiment provides a control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode. Building upon embodiments 1-6, step 5 specifically involves...

[0140] Differentiating equation (14) yields:

[0141] (15)

[0142] Combine equations (6), (8), and (15), and let... , When the value equals 0, the equivalent control law for the d and q axes is obtained. u dreq , u qreq for:

[0143] (16)

[0144] Considering the greater flexibility of fractional-order control, a novel fractional-order superspiral reaching law is introduced to achieve faster reaching speed and better chattering suppression on the sliding surface. This involves introducing fractional-order superspiral reaching laws for the d and q axes. u drsw , u qrsw as follows:

[0145] (17)

[0146] Therefore, the combined d-axis and q-axis control law of the subsequent converter is obtained. u dr , u qr for:

[0147] (18);

[0148] Post-stage converter dq axis control, such as Figure 3 As shown.

[0149] Simulation Analysis

[0150] A model of an energy storage converter was built in the Matlab / Simulink platform. Under two control conditions, when the active power suddenly changes, at 0.2s the output suddenly increases from a stable 25kW to 65kW, and the corresponding three-phase current amplitude increases from 45.6A to 112.5A; at 0.3s the output suddenly decreases from 65kW to 25kW, and the corresponding three-phase current amplitude decreases from A to 45.6A; at 0.4s the output suddenly decreases from 25kW to -22kW, and the corresponding three-phase current amplitude decreases from A to 41.6A. Figure 4 The figure shows the transient waveforms of the three-phase current on the grid side under traditional PI control. The response time of the three-phase current on the grid side is 32.1 ms at 0.2 s, 28.5 ms at 0.3 s, and 25.4 ms at 0.4 s. Figure 5 The figure shows the transient waveforms of the three-phase current on the grid side under the control of this invention. The response time of the three-phase current on the grid side is 15.1 ms at 0.2 s, 14.7 ms at 0.3 s, and 15.5 ms at 0.4 s. The comparison shows that the control method of this invention significantly reduces the transient time and improves the stability of the system.

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

[0152] Table 1 Circuit Parameters

[0153]

[0154] Depend on Figure 6 It can be seen that when the inverter's output active power suddenly increases from 25kW to 65kW, i d The voltage jumps from 45A to 115A. Under the PI control strategy, the transition time from 25kW to 65kW is 21ms. The sudden increase in power causes a certain overshoot. In addition, due to the coupling between power sources, the sudden change in active power also causes a transient process of DC bus voltage jump, such as... Figure 6 The portion outlined in the middle. (By...) Figure 7 It can be seen that under the control method of the present invention, when the active power output of the inverter suddenly increases from 25kW to 65kW, the transition time of the jump caused by the sudden increase in power is 15ms, and the fluctuation of the DC bus voltage during steady-state operation is smaller than that of PI control.

[0155] Depend on Figure 8 It can be seen that when the inverter's output active power jumps from 65kW to 25kW, i d The voltage jumps from 115A to 45A. Under the PI control strategy, the transition time when jumping from 65W to 25kW is 27ms. The sudden power reduction causes a certain overshoot. In addition, due to the coupling between power sources, the sudden change in active power also causes a transient process in the DC bus voltage, such as... Figure 8 The middle frame outlines the part. Figure 9 It can be seen that under the control method of the present invention, when the inverter output active power suddenly drops from 65kW to 25kW, the transition time of the jump caused by the sudden power reduction is 14ms, and the fluctuation of the current value during steady-state operation is smaller than that of PI control.

[0156] To verify the impact of the control method of this invention on the power quality of the inverter output current, a Fourier analysis of the grid-connected current for two steady-state cycles was performed in Matlab / Simulink software when the inverter output active power was 20kW. Figure 10 The figure shows the harmonic analysis of the grid-connected current of the energy storage converter under traditional PI control, with a THD of 3.40%. Figure 11 The diagram shows the harmonic analysis of the inverter's grid-connected current under the control of this invention, with a THD of 1.51%. The comparison shows that the control method of this invention has stronger harmonic suppression capabilities and improves the power quality of the grid connection.

[0157] As can be seen from the above, the energy storage converter control method based on fractional-order superspiral recursive terminal sliding mode of the present invention has the following advantages:

[0158] 1) An improved super-helical sliding mode observer is adopted to achieve accurate observation of internal and external changes and disturbances in the grid-connected inverter system. This observer introduces a lag compensation element, which reduces the high-frequency noise in the disturbance estimation and improves the disturbance estimation capability.

[0159] 2) The novel recursive terminal sliding mode control method uses the three-phase output current transformed into a dq coordinate system to obtain the current in a two-phase rotating coordinate system. The tracking error of the current is then used as input. A recursive sliding function is designed, and the sliding function and sliding surface are associated with two layers of sliding surfaces in the recursive structure. When the second sliding surface is reached for the first time, the finite-time convergence condition of the sliding function is satisfied. Then, when the first sliding surface is reached, the sliding function converges to zero, at which point the tracking error e will converge to zero within a finite time. This recursive structure solves the problem of terminal sliding mode singularity and improves the convergence accuracy near the equilibrium point.

[0160] 3) The fractional-order superspiral approach law is adopted, which extends integer-order control to fractional-order control. The control system has better flexibility, achieves more precise control, and reduces the impact of chattering on the system.

[0161] 4) Compared with existing control methods, it improves the convergence accuracy near the equilibrium point, giving the system better dynamic performance and robustness.

Claims

1. A control method for energy storage converters based on fractional-order superspiral recursive terminal sliding mode, characterized in that, 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 1 specifically involves: 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 These are the d-axis and q-axis switching functions, respectively. u dc The voltage across the DC-side regulating capacitor is given by the switching function, which is defined as: （3） 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; specifically, under the premise of three-phase grid voltage balance, take the d-axis direction of the grid voltage as the direction of the voltage vector, and according to the instantaneous power theory, obtain the power equation as follows: （4） In equation (4), P ref , Q ref These are the set reference values ​​for active power and reactive power, respectively. i dref , i qref These are the set current reference values ​​for active power and reactive power, respectively. The active power and reactive power in the circuit can be calculated using equation (4): （5） Active and reactive power control includes an outer power loop and an inner current loop. The outer power loop uses the reference value of the inner current loop calculated by equation (5). i dref , i qref Then, the current inner loop control law is designed using the differential equation (2) to control the output; Mathematical transformation of equation (2) yields: （6） In equation (6), b d , b q These are the control quantity gains. f d , f q These are the equivalent lumped disturbances along the d and q axes, respectively. f d , f q Including the unmodeled parts of the system, the coupled parts, and internal and external disturbances, its expression is: （7） For the aforementioned second-order nonlinear system, consider the inductor-side currents on the d and q axes. i Ld , i Lq Deviation from the reference value of the inductive current e d , e q for: （8） In equation (8), i Ldref for i Ld Reference value, i Lqref for i Lq Reference value; Taking the second derivative of equation (8), we get: （9） In equation (9) b d This refers to the gain of the d-axis control quantity. b q This refers to the gain of the q-axis control quantity. Step 3: Design a super-helical sliding mode observer based on the equivalent model of the subsequent converter; specifically, Step 3 involves designing a super-helical sliding mode observer for observing the dq-axis current as follows: （10） In equation (10), z d1 , z d2 , z d3 , z q1 , z q2 , z q3 They are respectively e d , e q , , , f d , f q The observed values, , , , , , It is a positive number; To suppress high-frequency noise, a hysteresis compensation element is introduced, designed as follows: （11） In equation (11), z d4 , z q4 For the improved f d , f q The observed values, a d4 , a q4 It is a constant greater than 1. τ The time lag constant is s Represents the complex frequency domain; Step 4: Design a fractional-order superspiral recursive terminal sliding mode controller and apply the observations obtained in Step 3 to the controller; Step 5: Based on the fractional-order superspiral recursive terminal sliding mode controller, add the fractional-order superspiral reaching law; Step 6: Based on the control method constructed in the above steps, the control law is obtained. The duty cycle of the energy storage converter switching transistor is obtained through SPWM modulation, thereby realizing the closed-loop control of the energy storage converter.

2. The energy storage converter control method based on fractional-order superspiral recursive terminal sliding mode according to claim 1, characterized in that, Step 4 specifically involves: To construct a recursive terminal sliding mode controller, design non-singular terminal sliding functions for the d and q axes. , as follows: （12） In equation (12), λ 1. λ 2. λ 3. λ 4 is a positive real number. , ; Design the sliding function based on equation (12). , as follows: （13） In equation (13), , It is a positive real number. , All are greater than 1; The following recursive terminal sliding surfaces for the d and q axes are designed using equations (12) and (13). s d , s q : （14） In equation (14), λ 5. λ 6 is a positive real number.

3. The energy storage converter control method based on fractional-order superspiral recursive terminal sliding mode according to claim 2, characterized in that, In step 4, the sliding function , , , and sliding surface s d , s q Associated with the two sliding surfaces in the recursive structure, when the second sliding surface is reached for the first time... s d , s q All equal to 0, satisfying the sliding function , , , The finite-time convergence condition is then met, and subsequently, when the first sliding surface is reached, the sliding function... , , , The tracking error converges to zero. e d , e q It will converge to zero within a finite amount of time.

4. The energy storage converter control method based on fractional-order superspiral recursive terminal sliding mode according to claim 3, characterized in that, Step 5 specifically involves: Differentiating equation (14) yields: （15） Combine equations (6), (8), and (15), and let... , When the value equals 0, the equivalent control law for the d and q axes is obtained. u dreq , u qreq for: （16） Introducing the fractional superscrew reaching law of the d and q axes u drsw , u qrsw ,as follows: （17） Therefore, the combined d-axis and q-axis control law of the subsequent converter is obtained. u dr , u qr for: （18）。

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