Control method for resisting actuator fault and saturation of island alternating-current micro-grid

Abstract

The invention provides a control method for resisting actuator faults and saturation of an island alternating-current micro-grid. The control method comprises the following steps: establishing an island alternating-current micro-grid system model; establishing an actuator fault model; establishing an actuator saturation model; establishing an island micro-grid model under actuator fault and saturation; establishing a system model for saturation compensation of the actuator; establishing a preset time disturbance observer of the frequency sum; establishing a distributed preset time voltage observer; establishing a preset time disturbance observer of the voltage sum; and establishing a distributed predefined time fault-tolerant controller based on the disturbance observer. According to the method, the problem of inaccurate frequency / voltage regulation and power distribution under the condition of actuator fault and saturation in the island alternating-current micro-grid is solved, and effective regulation and accurate power distribution of the frequency / voltage of the micro-grid within predefined time are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of fault-tolerant control under actuator failure and saturation effects in an isolated AC microgrid, and in particular, to a control method for an isolated AC microgrid against actuator failure and saturation. In particular, it relates to a control method for an isolated AC microgrid against actuator failure and saturation based on a distributed predetermined time disturbance observer. Background Art

[0002] The development of renewable energy is driven by the high concern for environmental issues. A large amount of renewable energy is integrated into the power system through power electronic devices. Microgrid (MG) is a key operation mode to utilize the output power of renewable energy / distributed generators (DG). However, due to the randomness of renewable energy and the low inertia of microgrid, microgrid in island mode may suffer from stability and power quality degradation. In addition, accurate power distribution of all DGs must be ensured to maintain the safety and reliability of the island microgrid. Therefore, it is crucial to design efficient control methods for island microgrids, which can help promote the penetration of renewable energy.

[0003] In order to improve the dynamic performance of the island microgrid, a hierarchical control strategy including primary and secondary control is proposed. Primary control provides the fastest response to system disturbances, but the steady-state error is large and it is difficult to achieve accurate power distribution. Therefore, secondary control is designed to overcome the shortcomings of primary control. Distributed control can meet the minimum communication requirements, reduce the communication and computing burden, thereby improving the reliability of the controller and simplifying the "plug and play" function of DG. Therefore, distributed control is often used as a secondary controller for performance improvement.

[0004] Different distributed control methods have been proposed to improve the performance of island microgrids. For example, power allocation and voltage adjustment are achieved through distributed consensus, the inertia of the microgrid is compensated by limiting the changes in frequency and voltage, or distributed predictive control is adopted. However, these methods mainly guarantee the asymptotic stability of the island microgrid, while in the face of the intermittent and random nature of renewable energy / loads, the control strategy needs to have stronger robustness and accelerated convergence speed.

[0005] The finite time consensus method has strong robustness and high accuracy, and can stabilize the island microgrid within a finite time. However, the convergence time of the finite time consensus method depends on the initial state of the system, which is difficult to monitor in real time in practical applications. The fixed time consensus method can keep the system stable within a fixed time without considering the initial state of the system, but it is highly conservative and computationally complex. The predefined time consensus method can ensure system convergence within a predefined time with low conservatism, so it is proposed as a secondary controller for island AC microgrids to ensure frequency / voltage recovery and accurate power distribution.

[0006] However, the above control methods do not consider actuator faults, including bias faults and partial efficiency loss faults. Actuator faults are a serious threat in the actual operation of isolated AC microgrids, which can lead to system performance degradation or critical events, thereby deteriorating the operating characteristics of isolated microgrids. Therefore, it is necessary to study fault-tolerant operations considering actuator faults. In addition, due to the actual physical limitations of isolated AC microgrids, the actuator output will experience saturation and the control input amplitude cannot exceed the limit set by the digital controller, which poses a challenge to the control algorithm. Therefore, control methods that consider actuator saturation are particularly important. At present, methods for the stability of predefined convergence time of isolated microgrids under actuator faults and saturation are still relatively limited. Summary of the invention

[0007] In view of the defects in the prior art, an object of the present invention is to provide a control method for an islanded AC microgrid to resist actuator failure and saturation.

[0008] The control method for preventing actuator failure and saturation of an islanded AC microgrid provided by the present invention comprises:

[0009] Step 1: Establish an isolated AC microgrid system model to achieve preliminary frequency and voltage regulation;

[0010] Step 2: Establish an actuator fault model to describe and predict the dynamic behavior of the actuator when a fault occurs;

[0011] Step 3: Build an actuator saturation model to help the controller cope with the physical limitations of the actuator output and ensure that the system remains stable and performs optimally under saturation conditions.

[0012] Step 4: Establish an island microgrid model under actuator faults and saturation to accurately describe the dynamic behavior of the system and enable the controller to achieve fault tolerance and saturation compensation;

[0013] Step 5: Establish a system model for actuator saturation compensation so that the controller can handle the output limitation of the actuator and mitigate the impact of saturation effect on system performance;

[0014] Step 6: Establish a scheduled time disturbance observer of frequency and , accurately estimate the deviation caused by external disturbance or actuator failure, and achieve error convergence within a predetermined time to enhance the response speed and accuracy of the controller;

[0015] Step 7: Establish a distributed scheduled time voltage observer to accurately estimate the voltage deviation of each distributed generator and achieve error convergence within the scheduled time;

[0016] Step 8: Establish a scheduled time disturbance observer for the voltage and , accurately estimate the deviation caused by external disturbance or actuator fault, and achieve error convergence within a predetermined time to enhance the response speed and accuracy of the controller;

[0017] Step 9: Establish a distributed predefined time fault tolerant controller based on disturbance observer to achieve frequency and voltage regulation and accurate sharing of active power and reactive power within a predetermined time.

[0018] Preferably, the step 1 comprises:

[0019] The islanded AC microgrid system model contains multiple inverter-based distributed generators DG, each DG consists of an LCL filter, a DC voltage source, and a voltage source inverter. The control framework of the microgrid includes power, current, and voltage control loops;

[0020] The droop control based on the ω-P and UQ relationship is described as:

[0021] ω i =ω ni -m i P i (1)

[0022] U i =U ni -n i Q i (2)

[0023] Among them, U i and ω i Respectively represent the output voltage amplitude and angular frequency of the i-th DG; U ni and ω ni is the rated value of droop control; n i and m i is the droop coefficient; P i and Q i represent the active power and reactive power of the i-th DG respectively.

[0024] Preferably, the step 2 comprises:

[0025] Actuator failures include bias failures and partial efficiency loss failures. The actuator failure model of the i-th device is expressed as:

[0026] u 0i =(1-ρ i ) i +φ i (3)

[0027] Among them, u 0i and u i Respectively represent the output and input control signals of the i-th device; ρ i is a continuous time-varying function that reflects the severity of partial efficiency loss failures, ranging from 0 ≤ ρ i <1;φ i It is a bias fault.

[0028] Preferably, the step 3 comprises:

[0029] The saturation controller is described as:

[0030]

[0031] Among them, γ i is the actual output of the controller; u max and -u max are the maximum and minimum values ​​of the controller output respectively.

[0032] Preferably, step 4 comprises:

[0033] First, based on formula (1), the frequency ω i The dynamic characteristics are expressed as:

[0034]

[0035] Among them, u fi Indicates frequency ω i Dynamic characteristics of They are ω i ,ω ni , P i The first derivative of i is the coefficient, which is a constant;

[0036] Secondly, for m i P i Take the derivative and get the auxiliary controller u for active power distribution pi for:

[0037]

[0038] Considering the actuator failure and saturation, substituting equations (3) and (4) into equations (5) and (6), the dynamic characteristics of the frequency are obtained as follows:

[0039]

[0040] Among them, γ fi Indicates the actual output of the frequency controller; u f0i represents the output control signal of the frequency under the consideration of actuator failure; φ fi Indicates the bias fault of the frequency actuator; γ pi Indicates the actual output of the active power controller; u p0i Represents the output control signal of active power considering actuator failure; φ pi Indicates the bias fault of the active power actuator; Δu fi =γ fi -u f0i ,Δu pi =γ pi -u p0i ;

[0041] Then, the control input ω for frequency recovery and accurate active power distribution is obtained ni :

[0042] ω ni =∫(γ fi +γ pi )dt (9)

[0043] Similarly, based on formula (2), the dynamic characteristic of voltage u is vi It is expressed as:

[0044]

[0045] in, U i , U ni , Q i The first derivative of ;

[0046] Reactive power auxiliary controller qi for:

[0047]

[0048] Taking into account actuator failure and saturation, the dynamic characteristics of the voltage are obtained as follows:

[0049]

[0050] Among them, γ vi represents the actual output of the voltage controller; u v0i Represents the output control signal of the voltage under actuator failure consideration; φ vi Indicates the bias fault of the voltage actuator; γ qi Represents the actual output of the reactive power controller; u q0iRepresents the output control signal of reactive power considering actuator failure; φ qi Indicates the bias fault of the reactive power actuator; Δu vi =γ vi -u v0i ,Δu qi =γ qi -u q0i ;

[0051] Then, the control input U for voltage restoration and accurate reactive power distribution is obtained ni :

[0052] U ni =∫(γ vi +γ qi )dt (14).

[0053] Preferably, step 5 comprises:

[0054] Design saturation compensators for frequency and mP, voltage and nQ respectively, and the expressions are:

[0055]

[0056] Among them, h i express a ij The weighted adjacency matrix A represents the communication topology of the isolated AC microgrid. ij ), if the i-th distributed generator can receive information from the j-th distributed generator, then a ij =1, otherwise a ij =0; j represents the remaining nodes in the summation symbol except the i node itself; N i represents the node set of all distributed generators; k1, k2, k3 and k4 are positive numbers; and is the state variable of the compensation system; N represents the number of distributed generators; b i represents the gain coefficient. If the i-th distributed generator can obtain the reference value information, then b i =1, otherwise b i =0.

[0057] Preferably, step 6 comprises:

[0058] First, define the consistency error:

[0059]

[0060] Among them, e 1i and e 2idenote the consistency error based on the frequency and active power information of adjacent nodes respectively; ω0 is the nominal value of the virtual leader; b i represents the communication coefficient between the follower and the leader, where b i =1 or b i =0;

[0061] Then, we get e 1i and e 2i The derivative of :

[0062]

[0063] in,

[0064] Substituting equations (7), (8), (15) and (16) into equation (20), we get:

[0065]

[0066] Among them, Δ 1i =h i (φ fi -ρ i u fi ),

[0067] Design a scheduled time observer to evaluate Δ 1i , whose expression is:

[0068]

[0069] Among them, ε 1i represents the deviation between the frequency state quantity and the frequency consistency error; θ1 represents the gain coefficient of the preset time observer; V1 represents V1 = ε 1i 2 ; τ1 is a positive parameter; χ1 represents a gain coefficient greater than Υ, Υ is a positive constant greater than zero; 0<θ1<1, χ1>Υ; Yes 1i The observed value, T s represents a positive constant;

[0070] The predefined time observer in formula (23) can be The disturbance Δ is observed within 1i , where κ>1;

[0071] Similarly, design a scheduled time observer to evaluate Δ 2i , whose expression is:

[0072]

[0073] Among them, ε 2i represents the deviation between the active power state quantity and the active power consistency error; θ2 represents the gain coefficient of the preset time observer; V2 represents V2 = ε 2i 2 ; χ2 represents a gain coefficient greater than Υ, Υ is a positive constant greater than zero; τ2 is a positive parameter; 0<θ2<1, χ2>γ; Yes 2i The observed value, T s represents a positive constant;

[0074] The predefined time observer in formula (24) can be The disturbance Δ is observed within 2i .

[0075] Preferably, the step 7 comprises:

[0076] Design a distributed scheduled time voltage observer to obtain the average voltage bus voltage, and its expression is:

[0077]

[0078] Among them, β1 and β2 are positive odd numbers and β1<β2; w1 and w2 are positive numbers.

[0079] Preferably, step 8 comprises:

[0080] First, define the consistency error as follows:

[0081]

[0082] Among them, e 3i represents the consistency error based on the average voltage information of adjacent nodes; e 4i Represents the consistency error based on the reactive power information of adjacent nodes;

[0083] Derivative of formula (26) yields:

[0084]

[0085] Substituting equations (10)-(11) and (17)-(18) into equation (27), we obtain:

[0086]

[0087] Among them, Δ 3i =h i (φ fi -ρ i u vi ),

[0088] Then, a predetermined time observer is designed to observe Δ 3i and Δ 4i The value of is expressed as:

[0089]

[0090] Similarly, the predefined time observer in equations (30) and (31) is s3 and T s4 The disturbance Δ is observed within 3i and Δ 4i .

[0091] Preferably, step 9 comprises:

[0092] Based on the scheduled time observer (23)-(24) and (30)-(31), the distributed scheduled time fault tolerant controller based on disturbance observer is designed as:

[0093]

[0094]

[0095] Among them, b f represents the gain coefficient of the distributed scheduled time frequency fault tolerant controller under saturation state; b p represents the gain coefficient of the distributed scheduled time active power fault tolerant controller under saturation state; b v represents the gain coefficient of the distributed predetermined time voltage fault tolerant controller under saturation state; b q represents the gain coefficient of the distributed scheduled time active power fault tolerance controller under saturation state; μ1, μ2, μ3, μ4 represent the gain coefficients of the frequency, active power, voltage and reactive power controllers respectively, 0<μ1, μ2, μ3, μ4<1; T di is the upper bound of the convergence of the consistency error;

[0096] The distributed scheduled time fault tolerant controller based on disturbance observer can si +T di Frequency and voltage regulation as well as accurate sharing of active and reactive power are achieved within the system.

[0097] Compared with the prior art, the present invention has the following beneficial effects:

[0098] The distributed predefined time fault tolerant controller based on disturbance observer of the present invention solves the problems of inaccurate frequency / voltage regulation and power distribution in the case of actuator failure and saturation in isolated AC microgrid, and realizes effective regulation of microgrid frequency / voltage and accurate power distribution within a predefined time. BRIEF DESCRIPTION OF THE DRAWINGS

[0099] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0100] Figure 1 A simplified system model diagram of an island AC microgrid under actuator failure and saturation of the present invention;

[0101] Figure 2 A distributed communication topology diagram of the present invention;

[0102] Figure 3 This is a framework diagram of the distributed predetermined time fault tolerant control based on disturbance observer of the present invention;

[0103] Figure 4 This is a simulation case result diagram of the present invention. DETAILED DESCRIPTION

[0104] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0105] Example

[0106] The present invention provides a control method for an islanded AC microgrid against actuator failure and saturation based on a distributed predetermined time disturbance observer, comprising the following steps:

[0107] 1) Establish an isolated AC microgrid system model, the details are as follows:

[0108] The simplified system model of the island AC microgrid under actuator fault and saturation is shown in Figure 1 As shown in Figure 1, it contains multiple inverter-based distributed generators (DGs). Each DG consists of an LCL filter, a DC voltage source, and a voltage source inverter. The control framework of the microgrid includes power, current, and voltage control loops to ensure power quality, reliability, and safety.

[0109] Primary control is used in an island microgrid to achieve preliminary frequency and voltage regulation to ensure that the system maintains stable operation without external grid support. The primary droop control based on the ω-P and UQ relationship can be described as:

[0110] ω i =ω ni -m i P i (36)

[0111] U i =U ni -n i Q i (37)

[0112] Among them, U i and ω i Respectively represent the output voltage amplitude and angular frequency of the i-th DG; U ni and ω ni is the rated value of droop control; n i and m i is the droop coefficient. In addition, P i and Q i represent the active power and reactive power of the i-th DG respectively.

[0113] 2) Establish the actuator fault model, the details are as follows:

[0114] In order to accurately describe and predict the dynamic behavior of the actuator when a fault occurs, it is necessary to help design a fault-tolerant control algorithm to ensure that the system can remain stable and operate normally when a fault occurs, and reduce the impact of the fault on system performance. Consider actuator faults, including bias faults and partial efficiency loss faults. Therefore, the actuator fault model of the i-th device can be expressed as:

[0115] u 0i =(1-ρ i ) i +φ i (38)

[0116] Among them, u 0i and u i Respectively represent the output and input control signals of the i-th device. i is a continuous time-varying function that reflects the severity of the partial efficiency loss failure, ranging from 0 ≤ ρ i <1.φ i is a bias fault. Therefore, we can classify the actuator faults into different fault types as shown in Table I.

[0117] Table I Fault Classification

[0118] Fault type <![CDATA[ρ i ]]> <![CDATA[φ i ]]> Normal situation <![CDATA[ρ i =0]]> <![CDATA[φ i =0]]> Bias Fault Conditions <![CDATA[ρ i =0]]> <![CDATA[φ i ≠0]]> Partial performance loss <![CDATA[0≤ρ i <1]]> <![CDATA[φ i =0]]> Bias Failure and Partial Efficiency Loss <![CDATA[0≤ρ i <1]]> <![CDATA[φ i ≠0]]>

[0119] 3) Establish the actuator saturation model, the details are as follows:

[0120] To help the controller cope with the physical limitations of the actuator output, ensure that the system remains stable and performs optimally in saturation. Consider that when the system state changes and the input is not properly constrained, the output of the actuator may have a significant impulse response. The saturation controller can be described as:

[0121]

[0122] Among them, γ i is the actual output of the controller, u max and -u max are the maximum and minimum values ​​of the controller output respectively.

[0123] 4) Establish an island microgrid model under actuator failure and saturation. The details are as follows:

[0124] In order to accurately describe the dynamic behavior of the system, enable the controller to achieve fault tolerance and saturation compensation, and ensure system stability and performance optimization, it is necessary to design the controller based on the island microgrid model under actuator faults and saturation.

[0125] First, based on (1), the frequency ω i The dynamic characteristics can be expressed as:

[0126]

[0127] Among them, u fi Indicates frequency ω i Dynamic characteristics of They are ω i ,ω ni , P i The first derivative of i is the coefficient, which is a constant;

[0128] Secondly, for m i P i Take the derivative and get the auxiliary controller u for active power distribution pi for:

[0129]

[0130] Considering the actuator failure and saturation, substituting (3) and (4) into (5) and (6), the dynamic characteristics of the frequency are obtained as follows:

[0131]

[0132] Among them, γ fi Indicates the actual output of the frequency controller; u f0i represents the output control signal of the frequency under the consideration of actuator failure; φ fi Indicates the bias fault of the frequency actuator; γ pi Indicates the actual output of the active power controller; u p0i Represents the output control signal of active power considering actuator failure; φ pi Indicates the bias fault of the active power actuator; Δufi =γ fi -u f0i ,Δu pi =γ pi -u p0i .

[0133] Then, the control input ω for frequency recovery and accurate active power distribution is obtained ni :

[0134] ω ni =∫(γ fi +γ pi )dt (44)

[0135] Similarly, based on (2), the dynamic characteristics of voltage u can be obtained: vi It is expressed as:

[0136]

[0137] U i , U ni , Q i The first derivative of ;

[0138] Reactive power auxiliary controller qi for:

[0139]

[0140] Taking into account actuator failure and saturation, the dynamic characteristics of the voltage are obtained as follows:

[0141]

[0142] Among them, γ vi represents the actual output of the voltage controller; u v0i Represents the output control signal of the voltage under actuator failure consideration; φ vi Indicates the bias fault of the voltage actuator; γ qi Represents the actual output of the reactive power controller; u q0i Represents the output control signal of reactive power considering actuator failure; φ qi Indicates the bias fault of the reactive power actuator; Δu vi =γ vi -u v0i ,Δu qi =γ qi -u q0i .

[0143] Then, the control input U for voltage restoration and accurate reactive power distribution is obtained ni :

[0144] Uni =∫(γ vi +γ qi )dt (49)

[0145] 5) Establish a system model for actuator saturation compensation. The details are as follows:

[0146] In order to enable the controller to effectively handle the output limitation of the actuator and reduce the impact of saturation effect on system performance, saturation compensation is required. Based on the adaptive auxiliary system, saturation compensators are designed for frequency and mP, voltage and nQ respectively, as follows:

[0147]

[0148] Among them, h i express a ij The weighted adjacency matrix A represents the communication topology of the isolated AC microgrid. ij ), if the i-th distributed generator can receive information from the j-th distributed generator, then a ij =1, otherwise a ij =0; j represents the remaining nodes in the summation symbol except the i node itself; N i represents the node set of all distributed generators; k1, k2, k3 and k4 are positive numbers; and is the state variable of the compensation system; N represents the number of distributed generators; b i represents the gain coefficient. If the i-th distributed generator can obtain the reference value information, then b i =1, otherwise b i =0;

[0149] 6) Establish the scheduled time disturbance observer of frequency and mP, the details are as follows:

[0150] In order to accurately estimate the deviation caused by external disturbances or actuator faults and achieve error convergence within a predetermined time to enhance the response speed and accuracy of the controller, it is necessary to design a disturbance observer based on a predetermined time.

[0151] First, define the consistency error:

[0152]

[0153] Among them, e 1i and e 2i denote the consistency error based on the frequency and active power information of adjacent nodes respectively; ω0 is the nominal value of the virtual leader; b i represents the communication coefficient between the follower and the leader, where bi =1 or b i =0.

[0154] Then, we get e 1i and e 2i The derivative of :

[0155]

[0156] in, Substituting (7)-(8) and (15)-(16) into (20), we obtain:

[0157]

[0158] Among them, Δ 1i =h i (φ fi -ρ i u fi ),

[0159] Design a scheduled time observer to evaluate Δ 1i , whose expression is:

[0160]

[0161] Among them, ε 1i represents the deviation between the frequency state quantity and the frequency consistency error; θ1 represents the gain coefficient of the preset time observer; V1 represents V1 = ε 1i 2 ; τ1 represents a positive parameter that can be set; χ1 represents a gain coefficient greater than γ, γ is a positive constant greater than zero; 0<θ1<1, χ1>γ; Yes 1i The observed value, T s Represents a positive constant.

[0162] The predefined time observer in formula (23) can be The perturbation Δ is accurately observed within 1i , where κ>1.

[0163] Similarly, design a scheduled time observer to evaluate Δ 2i , whose expression is:

[0164]

[0165] Among them, ε 2i represents the deviation between the active power state quantity and the active power consistency error; θ2 represents the gain coefficient of the preset time observer; V2 represents V2 = ε 2i 2; χ2 represents a gain coefficient greater than γ, γ is a positive constant greater than zero; τ2 represents a settable positive parameter; 0<θ2<1, χ2>γ; Yes 2i The observed value, T s Represents a positive constant.

[0166] The predefined time observer in formula (24) can be The perturbation Δ is accurately observed within 2i .

[0167] 7) Establish a distributed scheduled time voltage observer, the details are as follows:

[0168] In order to quickly and accurately estimate the voltage deviation of each distributed generator and achieve error convergence within the predetermined time to ensure the coordination and stability of system voltage regulation, a distributed predetermined time voltage observer is designed to obtain the average voltage bus voltage, and its expression is:

[0169]

[0170] Among them, β1 and β2 are positive odd numbers and β1<β2; w1 and w2 are positive numbers.

[0171] 8) Establish the scheduled time disturbance observer of voltage and nQ, the details are as follows:

[0172] In order to accurately estimate the deviation caused by external disturbances or actuator faults and achieve error convergence within a predetermined time to enhance the response speed and accuracy of the controller, it is necessary to design a disturbance observer based on a predetermined time.

[0173] First, define the consistency error as follows:

[0174]

[0175] Among them, e 3i represents the consistency error based on the average voltage information of adjacent nodes; e 4i Represents the consistency error based on the reactive power information of adjacent nodes;

[0176] By taking the derivative of formula (26), we can get:

[0177]

[0178] Substituting (10)-(11) and (17)-(18) into (27), we obtain:

[0179]

[0180] Among them, Δ 3i =h i (φfi -ρ i u vi ),

[0181] Then, a predetermined time observer is designed to observe Δ 3i and Δ 4i The value of is expressed as:

[0182]

[0183] Similarly, the predefined time observers (30) and (31) can be used at the predefined time T s3 and T s4 Inner estimate Δ 3i and Δ 4i The value of .

[0184] 9) Establish a distributed predefined time fault tolerant controller based on disturbance observer, the details are as follows:

[0185] In summary, based on the scheduled time observers (23)-(24) and (30)-(31), a new type of distributed scheduled time fault-tolerant controller based on disturbance observer is designed as follows:

[0186]

[0187]

[0188] Among them, b f represents the gain coefficient of the distributed scheduled time frequency fault tolerant controller under saturation state; b p represents the gain coefficient of the distributed scheduled time active power fault tolerant controller under saturation state; b v represents the gain coefficient of the distributed predetermined time voltage fault tolerant controller under saturation state; b q represents the gain coefficient of the distributed scheduled time active power fault tolerance controller under saturation state; μ1, μ2, μ3, μ4 represent the gain coefficients of the frequency, active power, voltage and reactive power controllers respectively, 0<μ1, μ2, μ3, μ4<1; T di is the upper bound of the convergence of the consistency error.

[0189] Therefore, the distributed scheduled time fault tolerant controller based on disturbance observer can be used to si +T di Frequency and voltage regulation as well as accurate sharing of active and reactive power are achieved within the system.

[0190] Distributed communication topology Figure 2 The distributed scheduled time fault tolerant control framework based on disturbance observer is shown in Figure 3 .

[0191] 10) Simulation results,

[0192] Table II Island AC microgrid system model parameters

[0193]

[0194] According to the scheduled time theory and the pre-selected parameters, the scheduled time is determined as The relevant parameters are set as θ1=θ2=θ3=θ4=0.9, χ1=χ2=χ3=χ4=0.1, τ1=τ2=τ3=τ4=0.1, k1=k2=k3=k4=11.5, T s =2,μ1=μ2=μ3=μ4=0.9,T di =0.5.

[0195] Simulation example: Actuator failure

[0196] The bias fault is set to φ i =0.1sin(t), the severity of partial efficiency loss failure ρ i Set to i =0.2sin(t). Load 6 is connected to the microgrid at t=2 seconds, while load 5 is disconnected from the microgrid at t=5 seconds. From the simulation results, it can be seen that the control method proposed in the present invention can achieve average voltage and frequency recovery and accurate power sharing when the actuator fails. The simulation results are shown in Figure 4 .

[0197] Those skilled in the art know that, in addition to implementing the system, device and its various modules provided by the present invention in a purely computer-readable program code, it is entirely possible to implement the same program in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method steps. Therefore, the system, device and its various modules provided by the present invention can be considered as a hardware component, and the modules included therein for implementing various programs can also be considered as structures within the hardware component; the modules for implementing various functions can also be considered as both software programs for implementing the method and structures within the hardware component.

[0198] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A control method for an islanded AC microgrid to resist actuator failure and saturation, characterized in that: include: Step 1: Establish an isolated AC microgrid system model to achieve preliminary frequency and voltage regulation; Step 2: Establish an actuator fault model to describe and predict the dynamic behavior of the actuator when a fault occurs; Step 3: Build an actuator saturation model to help the controller cope with the physical limitations of the actuator output and ensure that the system remains stable and performs optimally under saturation conditions. Step 4: Establish an island microgrid model under actuator faults and saturation to accurately describe the dynamic behavior of the system and enable the controller to achieve fault tolerance and saturation compensation; Step 5: Establish a system model for actuator saturation compensation so that the controller can handle the output limitation of the actuator and mitigate the impact of saturation effect on system performance; Step 6: Establish a scheduled time disturbance observer of frequency and , accurately estimate the deviation caused by external disturbance or actuator failure, and achieve error convergence within a predetermined time to enhance the response speed and accuracy of the controller; Step 7: Establish a distributed scheduled time voltage observer to accurately estimate the voltage deviation of each distributed generator and achieve error convergence within the scheduled time; Step 8: Establish a scheduled time disturbance observer for the voltage and , accurately estimate the deviation caused by external disturbance or actuator fault, and achieve error convergence within a predetermined time to enhance the response speed and accuracy of the controller; Step 9: Establish a distributed predefined time fault tolerant controller based on disturbance observer to achieve frequency and voltage regulation and accurate sharing of active power and reactive power within a predetermined time.

2. The control method for anti-actuator failure and saturation of an isolated AC microgrid according to claim 1, characterized in that: The step 1 comprises: The islanded AC microgrid system model contains multiple inverter-based distributed generators DG, each DG consists of an LCL filter, a DC voltage source, and a voltage source inverter. The control framework of the microgrid includes power, current, and voltage control loops; The droop control based on the ω-P and UQ relationship is described as: oh i =ω ni -m i P i (71) U i =U ni -n i Q i (72) Among them, U i and ω i Respectively represent the output voltage amplitude and angular frequency of the i-th DG; U ni and ω ni is the rated value of droop control; n i and m i is the droop coefficient; P i and Q i represent the active power and reactive power of the i-th DG respectively.

3. The control method for anti-actuator failure and saturation of an isolated AC microgrid according to claim 2, characterized in that: The step 2 comprises: Actuator failures include bias failures and partial efficiency loss failures. The actuator failure model of the i-th device is expressed as: you 0i =(1-ρ i )u i +φ i (73) Among them, u 0i and u i Respectively represent the output and input control signals of the i-th device; ρ i is a continuous time-varying function that reflects the severity of partial efficiency loss failures, ranging from 0 ≤ ρ i <1;φ i It is a bias fault.

4. The control method for anti-actuator failure and saturation of an isolated AC microgrid according to claim 3 is characterized in that: The step 3 comprises: The saturation controller is described as: Among them, γ i is the actual output of the controller; u max and -u max are the maximum and minimum values ​​of the controller output respectively.

5. The control method for islanded AC microgrid against actuator failure and saturation according to claim 4, characterized in that: The step 4 comprises: First, based on formula (1), the frequency ω i The dynamic characteristics are expressed as: Among them, u fi Indicates frequency ω i Dynamic characteristics of They are ω i ,ω ni , P i The first derivative of i is the coefficient, which is a constant; Secondly, for m i P i Take the derivative and get the auxiliary controller u for active power distribution pi for: Considering the actuator failure and saturation, substituting equations (3) and (4) into equations (5) and (6), the dynamic characteristics of the frequency are obtained as follows: Among them, γ fi Indicates the actual output of the frequency controller; u f0i represents the output control signal of the frequency under the consideration of actuator failure; φ fi Indicates the bias fault of the frequency actuator; γ pi Indicates the actual output of the active power controller; u p0i Represents the output control signal of active power considering actuator failure; φ pi Indicates the bias fault of the active power actuator; Δu fi =γ fi -u f0i ,Δu pi =γ pi -u p0i ; Then, the control input ω for frequency recovery and accurate active power distribution is obtained ni : oh ni =∫(γ fi +g pi )dt (79) Similarly, based on formula (2), the dynamic characteristic of voltage u is vi It is expressed as: in, U i , U ni , Q i The first derivative of ; Reactive power auxiliary controller qi for: Taking into account actuator failure and saturation, the dynamic characteristics of the voltage are obtained as follows: Among them, γ vi represents the actual output of the voltage controller; u v0i Represents the output control signal of the voltage under actuator failure consideration; φ vi Indicates the bias fault of the voltage actuator; γ qi Represents the actual output of the reactive power controller; u q0i Represents the output control signal of reactive power considering actuator failure; φ qi Indicates the bias fault of the reactive power actuator; Δu vi =γ vi -u v0i ,Δu qi =γ qi -u q0i ; Then, the control input U for voltage restoration and accurate reactive power distribution is obtained ni : U ni =∫(γ vi +γ qi )dt (84)。 6. The control method for islanded AC microgrid against actuator failure and saturation according to claim 5, characterized in that: The step 5 comprises: Design saturation compensators for frequency and mP, voltage and nQ respectively, and the expressions are: Among them, h i express a ij The weighted adjacency matrix A represents the communication topology of the isolated AC microgrid. ij ), if the i-th distributed generator can receive information from the j-th distributed generator, then a ij =1, otherwise a ij =0; j represents the remaining nodes in the summation symbol except the i node itself; N i represents the node set of all distributed generators; k1, k2, k3 and k4 are positive numbers; and is the state variable of the compensation system; N represents the number of distributed generators; b i represents the gain coefficient. If the i-th distributed generator can obtain the reference value information, then b i =1, otherwise b i =0.

7. The control method for islanded AC microgrid against actuator failure and saturation according to claim 6, characterized in that: The step 6 comprises: First, define the consistency error: Among them, e 1i and e 2i denote the consistency error based on the frequency and active power information of adjacent nodes respectively; ω0 is the nominal value of the virtual leader; b i represents the communication coefficient between the follower and the leader, where b i =1 or b i =0; Then, we get e 1i and e 2i The derivative of : in, Substituting equations (7), (8), (15) and (16) into equation (20), we get: Among them, D 1i =h i (f fi -r i you fi ), Design a scheduled time observer to evaluate Δ 1i , whose expression is: Among them, ε 1i represents the deviation between the frequency state quantity and the frequency consistency error; θ1 represents the gain coefficient of the preset time observer; V1 represents V1 = ε 1i 2 ; τ1 is a positive parameter; χ1 represents a gain coefficient greater than Υ, Υ is a positive constant greater than zero; 0<θ1<1, χ1>Υ; Yes 1i The observed value, T s represents a positive constant; The predefined time observer in formula (23) can be The disturbance Δ is observed within 1i , where κ>1; Similarly, design a scheduled time observer to evaluate Δ 2i , whose expression is: Among them, ε 2i represents the deviation between the active power state quantity and the active power consistency error; θ2 represents the gain coefficient of the preset time observer; V2 represents V2 = ε 2i 2 ; χ2 represents a gain coefficient greater than Υ, Υ is a positive constant greater than zero; τ2 is a positive parameter; 0<θ2<1, χ2>γ; Yes 2i The observed value, T s represents a positive constant; The predefined time observer in formula (24) can be The disturbance Δ is observed within 2i .

8. The control method for islanded AC microgrid against actuator failure and saturation according to claim 7, characterized in that: The step 7 comprises: Design a distributed scheduled time voltage observer to obtain the average voltage bus voltage, and its expression is: Among them, β1 and β2 are positive odd numbers and β1<β2; w1 and w2 are positive numbers.

9. The control method for islanded AC microgrid against actuator failure and saturation according to claim 8, characterized in that: The step 8 comprises: First, define the consistency error as follows: Among them, e 3i represents the consistency error based on the average voltage information of adjacent nodes; e 4i Represents the consistency error based on the reactive power information of adjacent nodes; Derivation of formula (26) yields: Substituting equations (10)-(11) and (17)-(18) into equation (27), we obtain: Among them, D 3i =h i (f fi -r i you vi ), Then, a predetermined time observer is designed to observe Δ 3i and Δ 4i The value of is expressed as: Similarly, the predefined time observer in equations (30) and (31) is s3 and T s4 The disturbance Δ is observed within 3i and Δ 4i .

10. The control method for islanded AC microgrid against actuator failure and saturation according to claim 9, characterized in that: The step 9 comprises: Based on the scheduled time observer (23)-(24) and (30)-(31), the distributed scheduled time fault tolerant controller based on disturbance observer is designed as: Among them, b f represents the gain coefficient of the distributed scheduled time frequency fault tolerant controller under saturation state; b p represents the gain coefficient of the distributed scheduled time active power fault tolerant controller under saturation state; b v represents the gain coefficient of the distributed predetermined time voltage fault tolerant controller under saturation state; b q represents the gain coefficient of the distributed scheduled time active power fault tolerance controller under saturation state; μ1, μ2, μ3, μ4 represent the gain coefficients of the frequency, active power, voltage and reactive power controllers respectively, 0<μ1, μ2, μ3, μ4<1; T di is the upper bound of the convergence of the consistency error; The distributed scheduled time fault tolerant controller based on disturbance observer can si +T di Frequency and voltage regulation as well as accurate sharing of active and reactive power are achieved within the system.

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