Self-adaptive sliding mode control method and system for master-slave alternating-current micro-grid

Abstract

The invention discloses a self-adaptive sliding mode control method and system for a master-slave AC micro-grid, and the method comprises the steps: building an AC micro-grid system, and obtaining a system dynamic equation; an adaptive law is introduced, and an adaptive voltage reference signal is designed to realize adaptive adjustment of dynamic characteristics of the system; designing an adaptive voltage / frequency sliding mode controller to control the voltage and frequency of the micro-grid main unit; and designing a self-adaptive current sliding mode controller to control a slave unit in the micro-grid. The self-adaptive sliding mode control strategy is adopted, the system operation parameters are dynamically adjusted in combination with the self-adaptive reference signals, and the control precision and the system stability are fundamentally improved.

Description

Technical Field

[0001] The present invention relates to a power system, and in particular to an adaptive sliding mode control method and system for a master-slave AC microgrid. Background Art

[0002] In modern power systems, as an important part of distributed power sources, AC microgrids can operate independently in grid-connected or island modes, and are an important means to build future microgrids. In the grid-connected operation mode, the microgrid needs to maintain voltage and frequency synchronization with the large power grid, and ensure the stability and dynamic response ability of the system operation. How to achieve high-precision voltage, frequency and power control in the grid-connected mode is the current research focus and difficulty.

[0003] Existing microgrid grid-connected control methods usually adopt proportional-integral-differential (PID) controllers or control algorithms based on linearized models. These methods can achieve basic synchronization control to a certain extent, but their performance will be significantly limited when facing complex load changes or large power grid disturbances. For example, in a system with strong dynamic characteristics or a large disturbance environment, it is difficult for a PID controller to maintain stable dynamic response and steady-state performance; control algorithms based on linearized models may affect control accuracy due to linearization errors.

[0004] As a robust nonlinear control method, sliding mode control can effectively cope with system uncertainties and external disturbances by designing a sliding surface and a sliding mode law. However, traditional sliding mode control methods may exhibit chattering phenomena in practical applications, which affect system performance.

[0005] Although some literature has explored sliding mode control methods for microgrids. For example, in the literature "Research on Control Strategies of Islanded DC Microgrids Based on Sliding Mode Control, Journal of North China Electric Power University (Natural Science Edition), 2021, 48(1): 15-23, 41.", a grid-connected control strategy based on fixed sliding mode parameters is proposed, but it mainly focuses on basic voltage or frequency control under a single master control architecture, lacking in-depth consideration of the coordinated operation between multiple control units in a master-slave microgrid structure. At the same time, in the literature "Design of the Inverter Side of a Grid Simulator Based on Improved Sliding Mode Control, Electrical Measurement & Instrumentation, 2021, 58(2): 171-177.", an improved sliding mode law is introduced to enhance the anti-disturbance ability of the system, but most still rely on fixed reference signals, and there are problems such as response lag and large steady-state errors when facing complex load changes or system dynamic adjustment requirements. In addition, the sliding mode gain in traditional sliding mode control is fixed, making it difficult to balance system robustness and control accuracy, and easily causing system chattering or even instability. Summary of the Invention

[0006] In view of the above problems, the present invention provides an adaptive sliding mode control method for a master-slave AC microgrid based on a hierarchical design of a master unit and a slave unit, which adopts an adaptive sliding mode control strategy, combines an adaptive reference signal to dynamically adjust the system operation parameters, and fundamentally improves the control accuracy and system stability.

[0007] The technical solution of the present invention is: an adaptive sliding mode control method for a master-slave AC microgrid, including:

[0008] Establish an AC microgrid system to obtain the system dynamic equation;

[0009] Introduce an adaptive law and design an adaptive voltage reference signal to achieve adaptive adjustment of the system dynamic characteristics;

[0010] Design an adaptive voltage / frequency sliding mode controller to control the voltage and frequency of the main unit of the microgrid;

[0011] Design an adaptive current sliding mode controller to control the slave units in the microgrid.

[0012] The system dynamic equation is:

[0013]

[0014] Wherein, V out is the capacitor voltage, i L is the filter inductor current, V dc is the input voltage or link voltage, u is the input controller signal, i out is the output current, L is the filter inductor, C is the filter capacitor, d is the differential symbol, and dt represents the first derivative with respect to time t.

[0015] The adaptive voltage reference signal is:

[0016] V ref_new = V ref *β

[0017] Wherein, V ref = V m *sin(ωt)

[0018]

[0019] Wherein, V ref_new is the adaptive voltage reference signal, V ref is the initial voltage reference signal, V m is the reference voltage amplitude, ω is the angular frequency, V amp is the output voltage amplitude, and β is the adaptive adjustment factor.

[0020] The design of the voltage / frequency sliding mode controller includes:

[0021] Select the deviation x1 of the actual voltage and the adaptive voltage reference signal, and the derivative x2 of the deviation as the new state variables, and rewrite the system dynamic equation as follows:

[0022]

[0023] where w(t) is a disturbance variable that changes with time,

[0024] where |w(t)| ≤ η1, and η1 is the upper bound of system uncertainty;

[0025] Select the sliding mode surface function as:

[0026] S1 = λx1 + x2

[0027] where S1 is the sliding mode surface function, λ > 0 is the coefficient of the sliding mode surface function, and the voltage control law obtained from the rewritten system dynamic equation and the sliding mode surface function is as follows:

[0028] u = u eq -(K V + ε)sign(S1)

[0029] where u eq is the equivalent control quantity used to cancel the known part of the system dynamics; K V is the voltage switching gain, and ε is a positive small disturbance suppression coefficient.

[0030] Design the following adaptive law for the estimated value of the upper bound of system uncertainty:

[0031]

[0032] where is the estimated value of the upper bound η1 of system voltage uncertainty; c1 > 0 is the adjustable coefficient of adaptive estimation.

[0033] Replace K V in the voltage control law with then the adaptive voltage control law is:

[0034]

[0035] where

[0036]

[0037] Design the current sliding mode controller to include:

[0038] Reference current generation: The main unit calculates in real time the reference current i ref that the slave unit should bear;

[0039] State variable selection: Define the deviation between the actual output current and the reference current as the state variable; specifically:

[0040]

[0041] In the formula, x3 is the current error, x4 is the rate of change of the current error, and i out is the output current;

[0042] Establish the dynamic equation of the slave unit output current as follows:

[0043]

[0044] In the formula, i c is the filter capacitor current, and u I is the current input controller signal;

[0045] Select the adaptive current sliding mode surface function:

[0046] S2 = λ2x3 + x4

[0047] In the formula, S2 is the adaptive current sliding mode surface function, and λ2 > 0 is the coefficient of the adaptive current sliding mode surface function;

[0048] Construct the equivalent control law as:

[0049]

[0050] In the formula, u iq is the current equivalent control quantity;

[0051] The current control law obtained from the dynamic equation of the slave unit output current and the adaptive current sliding mode surface function is as follows:

[0052] u I = u iq -(K I + ε)·sign(S2)

[0053] In the formula, K I is the current switching gain.

[0054] Design the following adaptive law for the estimated value of the upper bound of the system current uncertainty:

[0055]

[0056] In the formula, is the estimated value of the upper bound η2 of the system current uncertainty; c2 > 0 is the adjustable coefficient of the adaptive estimation.

[0057] Replace K I in the current control law with Then the adaptive current control law is:

[0058]

[0059] An adaptive sliding mode control system for a master - slave AC micro - grid, comprising:

[0060] A building module, configured to build an AC micro - grid system and obtain the system dynamic equation;

[0061] A reference signal generation module, configured to introduce an adaptive law and design an adaptive voltage reference signal to achieve adaptive adjustment of the system dynamic characteristics;

[0062] A master unit control module, configured to design an adaptive voltage / frequency sliding mode controller to control the voltage and frequency of the micro - grid master unit;

[0063] A slave unit control module, configured to design an adaptive current sliding mode controller to control the slave units in the micro - grid.

[0064] In the operation of the present invention, the master unit realizes stable control of the micro - grid voltage and frequency, and the slave units flexibly adjust the output power according to the master unit reference signal to achieve dynamic load sharing and system power balance. The controller parameters are adaptively adjusted according to the system operation state, which can not only suppress chattering but also improve the robustness to non - linear disturbances. This method exhibits good dynamic response ability and low steady - state error under complex load conditions, and has higher engineering practicability and promotion value compared with the existing control methods. Brief Description of the Drawings

[0065] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. In the drawings, the parts are not necessarily drawn to actual scale.

[0066] Figure 1 is a schematic structural diagram of the present invention,

[0067] Figure 2 is a schematic diagram of an independent DG unit with a single - phase inverter and an LC filter,

[0068] Figure 3 is a schematic principle control block diagram of the master unit,

[0069] Figure 4 is a master - slave unit control block diagram,

[0070] Figure 5 is a schematic diagram of the load current,

[0071] Figure 6 is a schematic diagram of the voltage and current of each state of the circuit,

[0072] Figure 7 Schematic diagram of comparison between basic reference signal and adaptive reference signal

[0073] Figure 8 Schematic diagram of current in current loop during step change of load current Specific implementation manners

[0074] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

[0075] As shown in the present invention Figure 1-8 An adaptive sliding mode control method for a master - slave AC micro - grid includes:[[]]

[0076] S1. Establish an AC micro - grid system and obtain the system dynamic equation;

[0077] Different from the existing methods that only model based on simplified topologies or ignore the high - frequency dynamic characteristics of the controlled object, the present invention adopts a complete modeling method based on Kirchhoff's voltage and current laws, considering filter, inductor and capacitor parameters and load characteristics. By constructing an equivalent circuit model including an inverter, inductor, capacitor and load, a dynamic equation with state variables of filter capacitor voltage V out and inductor current i L is established, which helps to accurately design a sliding mode controller subsequently, improving the description accuracy of the model and the effectiveness of the controller. This step provides an accurate system basis for subsequent design and is a prerequisite for the implementation of the control strategy.

[0078] S2. Introduce an adaptive law and design an adaptive voltage reference signal to achieve adaptive adjustment of the system dynamic characteristics;

[0079] In traditional fixed - reference - value control, the system is easily affected by load disturbances and external parameter changes, resulting in large tracking errors and poor dynamic performance. To solve the above problems, the present invention introduces an adaptive law based on the error signal to adjust the reference voltage signal in real time, making it dynamically follow the actual grid state changes, thereby improving the robustness of the control system. This step provides a variable target for the controller and is the key to improving the system dynamic performance.

[0080] S3. Design an adaptive voltage / frequency sliding mode controller to control the voltage and frequency of the main unit of the micro - grid;

[0081] Based on the reference voltage signal, an adaptive controller with a sliding mode surface and a switching control structure is designed to enable the main unit to have the ability of voltage / frequency steady-state regulation. Different from the traditional PI control, this method has stronger robustness in suppressing interference and resisting nonlinear changes, and is especially suitable for microgrid systems containing inverters. This controller ensures the power quality of the main node of the system and is the core of the master-slave cooperative control.

[0082] S4. Design an adaptive current sliding mode controller to control the slave units in the microgrid;

[0083] According to the voltage / frequency regulation result of the main unit, the slave units adjust the output current through the tracking error and the adaptive law to achieve load sharing and power balance. Compared with the traditional passive response mode of the slave units, this method can achieve dynamic coordination among multiple slave nodes, enhancing the scalability and self-adaptability of the entire system. This step is the basis for the master-slave architecture to achieve cooperative control.

[0084] In the operation of the present invention, an adaptive reference value is designed and used to replace the constant reference signal, thereby improving the steady-state performance of the system and enhancing the control effect.

[0085] Compared with the control method using a constant reference value, by introducing a real-time adjustable reference value, the present invention can maintain a small steady-state error under different loads and system states. The adaptive reference value strategy can significantly improve the system response speed and error convergence performance, and is the key link to improving the overall control quality.

[0086] Specifically,

[0087] Establish an AC microgrid system as Figure 2 shown to obtain the system dynamic equation;

[0088] The AC microgrid system includes a single-phase inverter with an LC filter, and its model is as Figure 2 shown.

[0089] Through Kirchhoff's voltage law and current law, the following basic circuit equations are obtained:

[0090]

[0091] where V inv is the inverter output voltage (V inv = uV dc ), u is the input controller signal, V out is the capacitor voltage, i L is the filter inductor current, i out is the output current, and i c is the filter capacitor current.

[0092] Combining equations (1) and (2) gives the dynamic equation (3) of the system, which is the basis for the subsequent design of the sliding mode controller and the construction of the adaptive law, as follows:

[0093]

[0094] Where the capacitor voltage V out and the inductor current i L are regarded as state variables. V dc is the input voltage or link voltage, i out and i c are the output current and the filter capacitor current respectively. L is the filter inductor used to suppress high-frequency fluctuations in the current; C is the filter capacitor used to filter out voltage ripples and stabilize the output voltage; d is the differential symbol used to describe the rate of change of system variables (such as current, voltage) with time; dt represents the first derivative with respect to time t, reflecting the instantaneous change rate of the variable.

[0095] This system dynamic equation is used for the subsequent design of the sliding mode surface and the establishment of the controller adjustment strategy, ensuring that the controller has higher accuracy and robustness in response to the system's dynamic behavior.

[0096] Introduce an adaptive law to design an adaptive voltage reference signal.

[0097] The present invention proposes an adaptive reference voltage signal scheme whose amplitude varies according to system conditions. The change in the amplitude of the reference signal of this scheme depends on system conditions such as load changes and steady-state errors, and improves steady-state parameters including THD (i.e., total harmonic distortion) and steady-state errors by adaptively adjusting the amplitude of the controller reference signal to improve the performance of the controller.

[0098] The expression of this scheme is as follows:

[0099] V ref = V m *sin(ωt) (4)

[0100] V ref_new = V ref *β (5)

[0101]

[0102] Where V ref is the initial voltage reference signal, the reference voltage amplitude is V m , the angular frequency is ω, and the controller should make the system output a voltage with a constant amplitude and angular frequency. V amp is the amplitude of the inverter output voltage. β is the adaptive adjustment factor used to adjust the amplitude of the output reference voltage.

[0103] The adaptive voltage reference signal is denoted as Vref_new indicates that it has a new amplitude, which is variable and is obtained by the ratio of the main (old) reference voltage amplitude V m (which we expect the output to have this reference quantity) to the output voltage amplitude V amp .

[0104] If this ratio is less than it means that the output voltage amplitude is greater than the desired reference signal amplitude. Therefore, the value of the adaptive reference signal amplitude should be less than the main (old) reference voltage amplitude V m so that the output signal amplitude can tend to the amplitude of V ref_new as soon as possible, so that the output voltage signal has a low steady-state error and tends to zero, and the amplitude is close to the main amplitude reference signal;

[0105] If this ratio is greater than it means that the output voltage amplitude is less than the desired reference signal amplitude. Therefore, the value of the adaptive reference signal amplitude should be greater than the main (old) reference voltage amplitude V m so that the output signal amplitude can tend to the amplitude of V ref_new as soon as possible, so that the output voltage signal has a low steady-state error and tends to zero, and the amplitude is close to the main amplitude reference signal.

[0106] The adaptive voltage reference signal V ref_new is used to compare with the grid output voltage to generate an error signal, which is used as the input quantity of the subsequent controller.

[0107] To achieve the global coordinated control of the system voltage and frequency, an adaptive voltage / frequency sliding mode controller is designed to control the "main unit" in the microgrid.

[0108] The main unit refers to the core control node in the microgrid that has the functions of generating the adaptive voltage reference signal and global scheduling, and is mainly responsible for the stability of the output voltage and frequency; while the "slave unit" refers to the modular sub-node that receives the control signal of the main unit and performs local power regulation according to the adaptive reference current, and its main task is current control and load tracking.

[0109] Design an adaptive voltage / frequency sliding mode controller to control the voltage and frequency of the main unit of the microgrid.

[0110] Design the voltage / frequency control mode as the main unit to control the frequency and voltage of the microgrid. Select the deviation between the actual voltage and the adaptive voltage reference signal, and the derivative of the deviation as the new state variables. The formula is as follows:

[0111] x1 = V out - V ref_new (7)

[0112]

[0113] In the present invention, Vm, as the amplitude of the initial reference voltage signal, is not regarded as a constant value. Its value will be dynamically and adaptively adjusted according to the system operating state, reflecting the system's adaptability to load changes and steady-state errors.

[0114] According to formulas (7) and (8), the system dynamic equation (3) can be rewritten as follows:

[0115]

[0116] Wherein, w(t) is a disturbance variable that changes with time, representing the total disturbance term in the system caused by external factors such as model uncertainty, parameter fluctuations (such as changes in inductance and capacitance), and DC bus voltage fluctuations. This term is regarded as a time-varying function, rather than a constant value. Since the system uncertainty is bounded, assuming the upper bound is η, where η is a constant greater than 0, thus |w(t)| ≤ η.

[0117] Select the sliding mode surface function as:

[0118] S1 = λx1 + x2 (10)

[0119] Wherein, S1 is the sliding mode surface function, representing the deviation degree of the current system state relative to the ideal sliding mode surface; λ > 0 is the coefficient of the sliding mode surface function, and from formulas (9) and (10), it can be obtained that:

[0120]

[0121] When w(t) = 0,

[0122]

[0123] Finally, the obtained voltage control law is as follows:

[0124] u = u eq -(K V + ε)sign(S1)(13)

[0125] Wherein, u eq is the equivalent control quantity, used to cancel the known part of the system dynamics; K V is the voltage switching gain, and ε is a positive small disturbance suppression coefficient.

[0126] Take the Lyapunov function:

[0127]

[0128] Then there is:

[0129]

[0130] According to the Lyapunov stability theory, when The system is asymptotically stable. That is, if the controller of Equation (13) is adopted, considering the most serious disturbance of the system, K V should be greater than the upper bound of system uncertainty, that is, K V > η. However, in practice, it is difficult to determine the upper bound of uncertainty in real time. Therefore, only when K V is taken large enough can the system be ensured to be stable. However, due to the variable structure of sliding mode control mainly reflected in the chattering caused by the switching of the switching term, too large switching gain will lead to serious chattering of the system, causing the motion state of the system to deviate from the sliding mode surface to a large extent and reducing the robustness of the controller.

[0131] Design the following adaptive law for the estimated value of the upper bound of system uncertainty:

[0132]

[0133] where is the estimated value of the upper bound η1 of system voltage uncertainty; c1 > 0 is the adjustable coefficient of adaptive estimation, and the change rate of the estimated value can be changed by adjusting the size of c1. Therefore, under unknown external disturbances, replace K V in Equation (13) with , then the adaptive voltage control law can be written as:

[0134]

[0135] Next, prove the stability of the proposed control strategy. Redefine the Lyapunov function as:

[0136]

[0137] where is the estimation error of the upper bound of system voltage uncertainty, is the estimated value of η1, and η1 is the estimated value of the upper bound η of system voltage uncertainty;

[0138]

[0139] According to the sliding mode theory, the adaptive sliding mode controller designed by the present invention can ensure the asymptotic stability of the system.

[0140] The "adaptive sliding mode controller" proposed by the present invention is a unified framework for the entire control strategy, and the corresponding functions are implemented in the master unit and the slave unit respectively: in the master unit, an adaptive voltage / frequency sliding mode controller is constructed based on the voltage / frequency state variables to regulate the amplitude and frequency of the system output voltage; in the slave unit, an adaptive current sliding mode controller is constructed based on the output current state to track the reference current command sent by the master unit. Both rely on the sliding mode control and adaptive law design methods to achieve robust control of system uncertainties and disturbances.

[0141] Design an adaptive current sliding mode controller to control the slave unit in the proposed microgrid. The present invention applies a sliding mode controller to control the current of the slave unit. The master unit generates a reference current signal and sends it to the slave unit, and the reference signal is updated according to the load change.

[0142] The design of the current sliding mode controller includes:

[0143] Reference current generation: The master unit calculates the reference current i that the slave unit should bear in real time based on the power-frequency and power-voltage droop control logics, ref and broadcasts this signal to the slave unit through the communication module;

[0144] State variable selection: Define the deviation between the actual output current and the reference current as the state variable:

[0145]

[0146] Modeling of the current dynamic equation: Based on the system structure and the voltage and current relationships in Equations (2) and (3), the dynamic equation of the output current of the slave unit can be established as follows:

[0147]

[0148] where: x3 is the current error, x4 is the rate of change of the current error, V out is the capacitor voltage, i L is the current of the filter inductor, i c is the current of the filter capacitor, V dc is the input voltage or link voltage, u I is the current input controller signal, i out is the output current, L is the filter inductor used to suppress the high-frequency fluctuations in the current; d is the differential symbol used to describe the rate of change of system variables (such as current and voltage) with time; dt represents the first-order derivative with respect to time t, reflecting the instantaneous change rate of the variable.

[0149] Select the adaptive current sliding mode surface function:

[0150] S2 = λ2x3 + x4 (22)

[0151] In the formula, S2 is the adaptive current sliding mode surface function, representing the deviation degree of the current system state relative to the ideal sliding mode surface; λ2 > 0 is the coefficient of the adaptive current sliding mode surface function.

[0152] The equivalent control law is constructed as follows:

[0153]

[0154] In the formula, i ref is the reference current; u iq is the current equivalent control quantity, used to cancel the known part of the system dynamics;

[0155] The current control law obtained from the output current dynamic equation of the slave unit and the adaptive current sliding mode surface function is as follows:

[0156] u I = u iq -(K I + ε)·sign(S2) (24)

[0157] In the formula, K I is the current switching gain.

[0158] The following adaptive law is designed for the estimated value of the upper bound of the system current uncertainty:

[0159]

[0160] In the formula, is the estimated value of the upper bound η2 of the system current uncertainty; c2 > 0 is the adjustable coefficient of the adaptive estimation.

[0161] Replace K I in the current control law with , then the adaptive current control law is:

[0162]

[0163] The present invention also provides an adaptive sliding mode control system for a master - slave AC micro - grid, including:

[0164] A building module, used to build an AC micro - grid system and obtain the system dynamic equation;

[0165] A reference signal generation module, used to introduce an adaptive law and design an adaptive voltage reference signal to achieve adaptive adjustment of the system dynamic characteristics;

[0166] A master unit control module, used to design an adaptive voltage / frequency sliding mode controller to control the voltage and frequency of the micro - grid master unit;

[0167] Slave unit control module, used to design an adaptive current sliding mode controller to control the slave units in the microgrid.

[0168] In the operation of the present invention, the master unit is the central control node responsible for providing the system reference voltage and frequency, and the slave units are the execution nodes that respond to the reference signals sent by the master controller and implement local current control. The two achieve the overall stability and power distribution of the system through master-slave coordinated control.

[0169] In the operation of the present invention, the initial constant sinusoidal reference signal V ref = V m sin(ωt) is replaced by the dynamically adaptive reference signal V ref_new = V ref *β; this replacement process is automatically completed according to the system operation state, thereby enhancing the system's response ability to steady-state error and load disturbance.

[0170] In order to intuitively verify the effect of the method proposed by the present invention, it is described below through experimental results.

[0171] The performance of the sliding mode controller with a rotating reference signal when DG1 is in the independent operation mode is studied. In this case, a constant voltage and frequency are applied to the load, and then the main (voltage / frequency) control mode is selected. In the analysis of this part, a non-linear load is added to study the performance of the controller.

[0172] Figure 2 The AC microgrid system structure mainly includes: the voltage source V_dc provides the DC-side voltage for the system; the inverter bridge (Q1 and Q2): a single-phase inverter structure is formed using two switching tubes (Q1, Q2) to achieve the energy conversion from DC to AC; Q3: an output relay / isolation switch for the grid connection, controlling whether the DG unit is connected to the main grid or the load, and is used to switch between the island mode and the grid-connected mode; the PWM controller: used to generate the pulse width modulation signals for controlling the conduction / shutdown of Q1 and Q2 to regulate the output AC voltage; the LC filter: composed of an inductor L and a capacitor C, used to filter out the high-frequency harmonics in the inverter output and smooth the output voltage; the load port: connects to the microgrid or the load system. This figure shows the basic structure of the independent operating DG unit, providing a physical basis for the subsequent implementation of master-slave control.

[0173] As Figures 3-4 , the performance of the improved sliding mode controller under non-linear loads is studied, and the transient response during the load step change is shown.

[0174] The master unit part: includes a sliding mode controller and a PWM module, generates control signals by measuring the power and voltage changes, and provides the grid synchronization reference;

[0175] Slave unit part: It includes a sliding mode controller and a PWM module; when the reference value is replaced, an adaptive reference input is generated according to the voltage and frequency information broadcast by the master unit and the local actual value.

[0176] Information interaction line: Information interaction between the master and slave is achieved through a communication module; both ends contain an inverter and an LC filter structure to ensure the quality of voltage output.

[0177] In Figures 5-8 the efficiency of the sliding mode controller under non-linear loads was studied, and the transient response during load step changes was shown. At t = 0.1 s, a secondary load (non-linear load) was connected to the AC bus. Figure 5 is the load current, that is, after adding various inductors, capacitors and non-linear loads, the current change caused by the change of the non-linear load; Figure 6 In a and b in the non-linear load, the switching states of two signals; cd and ef are the currents and voltages of two selection switches respectively; g is the final voltage of the entire circuit; h is the voltage only passing through the IGBT; from Figure 5 it can be clearly seen that in the step alternation of the non-linear load current, the output voltage response is fast. This shows that the controller with an adaptive reference signal corrects the microgrid voltage very quickly. The comparison between the basic reference signal and the adaptive reference signal is as Figure 7 shown, where Figure 7 a is the overall diagram, Figure 7 b is the partial enlarged diagram; this mechanism improves the performance of the controller, and the output voltage is better than the state without an adaptive reference signal; Figure 8 shows the current of the current loop during the step change of the load current. Figure 8 a: is the current output response curve under the control of the controller, showing a small overshoot and fast convergence, and the system current can quickly track the desired reference current; Figure 8 b: is the voltage response curve, showing that the voltage adjustment time is less than half of the grid cycle after the load change occurs, and the system quickly returns to the stable state.

[0178] Experiments show that when the controller proposed in the present invention controls the system, the controller responds quickly to load changes, tracks the voltage reference signal, further reduces the steady-state error, and has good performance.

[0179] The present invention focuses on solving the coordinated control problem between the master unit and the slave unit of the microgrid in the grid-connected operation mode. By designing an adaptive voltage / frequency sliding mode controller and an adaptive current sliding mode controller, the master unit can stably control the grid voltage and frequency, and at the same time ensure the power balance and fast response of the slave unit.

[0180] In addition, by introducing an adaptive reference signal instead of a traditional constant reference signal, the steady-state performance of the system is significantly improved. This method exhibits fast response and low steady-state error under nonlinear loads.

[0181] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although specific embodiments are described in detail herein, those skilled in the art can still modify them or replace some technical features in an equivalent manner, and these changes do not depart from the core idea and protection scope embodied in the embodiments of the present invention.

Claims

1. An adaptive sliding mode control method for a master-slave AC microgrid, characterized in that, Including: Establish an AC microgrid system to obtain the system dynamic equations; Introduce an adaptive law and design an adaptive voltage reference signal to achieve adaptive adjustment of the system dynamic characteristics; Design an adaptive voltage / frequency sliding mode controller to control the voltage and frequency of the main unit of the microgrid; Design an adaptive current sliding mode controller to control the slave units in the microgrid.

2. The adaptive sliding mode control method for a master-slave AC microgrid according to claim 1, wherein The system dynamic equations are: where, V out is the capacitor voltage, i L is the filter inductor current, V dc is the input voltage or link voltage, u is the input controller signal, i out is the output current, L is the filter inductor, C is the filter capacitor, d is the differential symbol, and dt represents the first derivative with respect to time t.

3. The adaptive sliding mode control method for a master-slave AC microgrid according to claim 2, wherein The adaptive voltage reference signal is: V ref_new = V ref * β Among them, V ref = V m *sin(ωt) where, V ref_new is the adaptive voltage reference signal, V ref is the initial voltage reference signal, V m is the reference voltage amplitude, ω is the angular frequency, V amp is the output voltage amplitude, and β is the adaptive adjustment factor.

4. The adaptive sliding mode control method for a master-slave AC microgrid according to claim 3, wherein Designing the voltage / frequency sliding mode controller includes: Select the deviation x1 between the actual voltage and the adaptive voltage reference signal and the derivative x2 of the deviation as new state variables, and rewrite the system dynamic equations as follows: where w(t) is a disturbance variable that changes with time, where |w(t)| ≤ η1, and η1 is the upper bound of system uncertainty; Select the sliding mode surface function as: S1 = λx1 + x2 where S1 is the sliding mode surface function, λ > 0 is the coefficient of the sliding mode surface function, and the voltage control law obtained from the rewritten system dynamic equations and the sliding mode surface function is as follows: u = u eq -(K V + ε) sign(S1) where u eq is the equivalent control quantity for canceling the known part of the system dynamics; K V is the voltage switching gain, and ε is a positive small disturbance rejection coefficient.

5. The adaptive sliding mode control method for a master-slave AC microgrid according to claim 4, wherein Design the following adaptive law for the estimated value of the upper bound of system uncertainty: where is the estimated value of the upper bound η1 of the system voltage uncertainty; c1 > 0 is the adjustable coefficient of adaptive estimation.

6. The adaptive sliding mode control method for a master-slave AC microgrid according to claim 5, wherein Replace \(K\) in the voltage control law V with , then the adaptive voltage control law is as follows: where 7. The adaptive sliding mode control method for a master-slave AC microgrid according to claim 6, wherein Designing the current sliding mode controller includes: Reference current generation: The master unit calculates in real time the reference current i that the slave unit should bear ref ; State variable selection: Define the deviation between the actual output current and the reference current as the state variable; specifically: where x3 is the current error, x4 is the rate of change of the current error, and i out is the output current; Establish the output current dynamic equation of the slave unit as follows: where i c is the current of the filter capacitor, and u I is the current input controller signal; Select the adaptive current sliding mode surface function: S2 = λ2x3 + x4 where S2 is the adaptive current sliding mode surface function, and λ2 > 0 is the coefficient of the adaptive current sliding mode surface function; Construct the equivalent control law as: where u iq is the current equivalent control quantity; The current control law obtained from the output current dynamic equation of the slave unit and the adaptive current sliding mode surface function is as follows: u I = u iq - (K I + ε)·sign(S2) where K I is the current switching gain.

8. The adaptive sliding mode control method for a master-slave AC microgrid according to claim 7, wherein Design the following adaptive law for the estimated value of the upper bound of system current uncertainty: where is the estimated value of the upper bound η2 of the system current uncertainty; c2 > 0 is the adjustable coefficient of the adaptive estimation.

9. The adaptive sliding mode control method for a master-slave AC microgrid according to claim 8, wherein Replace K in the current control law with I to obtain The adaptive current control law is then:

10. An adaptive sliding mode control system for a master-slave AC microgrid, characterized in that, Including: A building module for establishing an AC microgrid system to obtain the system dynamic equations; A reference signal generation module for introducing an adaptive law and designing an adaptive voltage reference signal to achieve adaptive adjustment of the system dynamic characteristics; A main unit control module for designing an adaptive voltage / frequency sliding mode controller to control the voltage and frequency of the main unit of the microgrid; A slave unit control module for designing an adaptive current sliding mode controller to control the slave units in the microgrid.

Images