Secondary cooperative restoration control method for island interconnected microgrid based on back-to-back converter

Abstract

The application discloses a kind of secondary collaborative recovery control methods of island interconnection microgrid based on back-to-back converter, its steps include:1, the topological structure of ring interconnection microgrid group comprising N microgrid units and N back-to-back converter head-to-tail connection is built;2, the primary and distributed secondary controller capable of realizing frequency, voltage recovery and accurate active, reactive power sharing of distributed power in microgrid unit is constructed;3, the primary and secondary controller capable of realizing accurate active power sharing and common coupling point voltage recovery between microgrid units in back-to-back converter is constructed.The application can realize the goal of frequency, voltage recovery of distributed power in microgrid unit, accurate active, reactive power sharing, accurate active power sharing between microgrid units and common coupling point limited voltage recovery, and uses event-triggered control strategy, reduces communication data burden.

Description

Technical Field

[0001] This invention relates to the field of secondary collaborative recovery control for islanded interconnected AC microgrids, specifically to a power sharing and common coupling point voltage recovery control method for islanded interconnected microgrid units based on back-to-back converters. Background Technology

[0002] Interconnecting multiple geographically adjacent microgrids (MGs) to form a microgrid cluster (MGC) is an effective way to absorb distributed generation (DG) and improve the reliability of power supply at the end of distribution networks in remote mountainous areas, island regions, and even cities. Besides traditional impedance lines and circuit breakers (CBs) as basic interconnection schemes, back-to-back converters (BTBCs) using power electronic interconnection devices have become a new solution for solving the problem of multi-microgrid interconnection and integration due to their advantages such as good anti-interference effect, strong regulation capability, and fast fault recovery speed. However, in this case, inherent voltage amplitude or frequency deviations and mismatches between all microgrid units are unavoidable. Energy transmission in back-to-back converter interconnected microgrids is no longer based on impedance-based energy transmission patterns. The grid frequency changes from a global variable to a local variable, and different microgrid units can operate asynchronously at different frequencies. In this asynchronous interconnection mode, load disturbances in each microgrid unit can only be automatically addressed by regional distributed power sources. This ultimately increases the difficulty of the entire interconnected microgrid power management task, such as active and reactive power sharing and voltage and frequency recovery control.

[0003] Furthermore, back-to-back converter interconnected microgrids can operate at completely different frequencies, rather than sharing a global frequency. This means that without proper back-to-back converter control design, inaccurate active power sharing among all microgrids is unavoidable. Finally, some studies have indicated that by employing a generalized or normalized droop control strategy in back-to-back converters, frequency deviation and proportional active power sharing between the loads on both sides can be gradually restored. However, these methods are limited to the primary droop control level; when secondary recovery control is enabled individually at each microgrid unit level, active power sharing among all microgrid units still cannot be achieved. In summary, many problems remain unresolved in the hierarchical control research of back-to-back converter islanded interconnected microgrids, especially the decoupling problem of frequency recovery and active power sharing among microgrid units at the secondary control level. Therefore, how to design primary and secondary control for back-to-back converters to ensure active power sharing and frequency and voltage recovery among microgrid units is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] Aiming at the problems existing in the existing back-to-back converter-based islanded interconnected AC microgrid in terms of power sharing and point of common coupling voltage recovery, the present invention proposes a secondary cooperative recovery control method for islanded interconnected microgrids based on back-to-back converters, which is expected to realize frequency recovery, global accurate active power sharing and point of common coupling voltage compensation for the back-to-back converter interconnected microgrid system without a microgrid central control device, thereby ensuring the operation stability of the islanded interconnected AC microgrid.

[0005] To achieve the above objective, the present invention adopts the following technical solution: The secondary cooperative recovery control method for islanded interconnected microgrids based on back-to-back converters according to the present invention is characterized by comprising the following steps: S1: Construct an islanded interconnected microgrid, comprising N microgrid units MG1, … , MG k , … , MG N and S back-to-back converters; wherein, MG k represents the k th microgrid unit; k ∈ N ; the k th microgrid unit MG k consists of n k distributed generators DG k,1 , …, DG k,i , … , , wherein DG k,i represents the i th distributed generator; let the first distributed generator DG k,1 be the leader, and the remaining n k −1 distributed generators DG k,2 , … , be followers; any t th back-to-back converter consists of two back-to-back connected inverters; t ∈ S ; and S = N ; S2: Construct primary and distributed secondary controllers capable of realizing frequency, bounded voltage recovery and accurate active / reactive power sharing of distributed generators in microgrid units: S21: Use formula (1) to construct the k th microgrid unit MG k the i th distributed generator DG k.iThe primary controller for droop control is used to achieve automatic differential frequency control and voltage control within the microgrid unit when there is no communication. (1) In equation (1), ω k,i and V k,i The first i Distributed power supply (DG) k,i Output frequency and voltage; ω ref and V ref These are reference values ​​for frequency and voltage; and The first i Distributed power supply (DG) k,i The active power droop coefficient and the reactive power droop coefficient; and They are the first i Distributed power supply (DG) k,i The output active power and reactive power; and These are the deviations from the maximum permissible frequency and the maximum permissible voltage, respectively. and They are the first i Distributed power supply (DG) k,i The rated active power and rated reactive power; From equation (2), we obtain the first... i Distributed power supply (DG) k,i Active power distribution ratio α k,i And reactive power sharing ratio coefficient β k,i : (2) In equation (2), , They represent DG k,i The difference between the frequency reference value and the output frequency, and the difference between the voltage reference value and the output voltage; S22: Using equation (3), the compensation signal generated by the distributed secondary controller is added to the droop control equation of equation (1), thereby obtaining the first... i Distributed power supply (DG) k,i Output frequency Used to achieve the second control under secondary control k MG Micro Network k The rated frequency recovery and active power of all distributed power sources are equally distributed: (3) In equation (3), DG generated by distributed secondary controller k,i The frequency compensation signal is obtained from equation (4): (4) In equation (4), and They represent DG k,i Frequency compensation signal Medium-frequency elements and active elements, and have: (5) In equation (5), and Representing frequency elements and active elements The coefficient; Indicates the first k MG Micro Network k Middle and the first i Distributed power supply (DG) k.i The set of sequence numbers of other distributed power sources that communicate directly; It means DG k.i With the j Distributed power supply (DG) k.j The coefficient indicating whether direct communication is possible; if direct communication is possible, then... Take 1, otherwise Set to 0; DG k.i Can the coefficients of the reference value be received directly? If DG k.i If the reference value can be received, then Take 1, otherwise Set to 0; ω k,j It's DG k,j The frequency; α k,j It's DG k,j The active power distribution ratio coefficient; A distributed voltage observer is constructed using equation (6) to estimate the voltage level of the first voltage. i Distributed power supply (DG) k.i Voltage: (6) In equation (6), yes t Moment DG k,i The voltage estimate; yes t Moment DG k,i The voltage; and They ares Moment DG k,i and DG k,j The voltage estimate; t 0 represents the initial time. Calculate the voltage element in the compensation voltage signal of the distributed secondary control using equation (7). and reactive elements Used to achieve the second control under secondary control k MG Micro Network k Voltage recovery and reactive power are equally distributed among all distributed power sources: (7) In equation (7), and Representing voltage elements respectively coefficients and reactive elements The coefficient; and They are DG k,i and DG k,j Estimated voltage value; It is an estimate of the voltage reference value; It's DG k,j The reactive power distribution ratio coefficient; S3: Constructing the basic control structure of a voltage source inverter in a back-to-back converter: The first t The two inverters in a back-to-back converter are denoted as VSC. t,1 VSC t,2 Among them, VSC t,1 The constant power control strategy is adopted, which controls the active and reactive power flow according to pre-allocated instructions; VSC t,2 A constant DC voltage control strategy is used to stabilize the DC capacitor voltage; The reference current inside VSC1 is calculated using equation (8): (8) In equation (8), and Representing the first t VSC in a back-to-back converter t,1 Internal d-axis and q-axis reference currents; and Representing the first t VSC in a back-to-back converter t,1 The output active power reference value and reactive power reference value; VSC t,1 Internal d-axis voltage; VSC is obtained from equation (9) t,2Reference current and DC voltage control parameters on the side: (9) In equation (9), and Representing the first t VSC in a back-to-back converter t,2 Internal d-axis and q-axis reference currents; and Representing the first t VSC in a back-to-back converter t,2 The output active power reference value and reactive power reference value; VSC t,2 Internal d-axis voltage; and These represent the proportional control coefficient and integral control coefficient for constant DC voltage control, respectively. and Representing the first t Actual and reference values ​​of DC capacitors in a back-to-back converter; S4: Construct primary and secondary controllers in a back-to-back converter capable of achieving precise active power sharing and common point-of-coupling voltage recovery among microgrid units: S41. Construct the first using equation (10). t A primary controller for simulating droop control of a back-to-back converter is used to realize the droop control of the two sides of the back-to-back converter. k Each microgrid unit MG k and the l Each microgrid unit MG l Frequency dynamic balance: (10) In equation (10), and These are the proportional and integral coefficients for the simulated droop control; and Representing the first k Each microgrid unit MG k and the l Each microgrid unit MG l The frequency; Indicates the first t The first of the back-to-back converters s VSC t,s The reactive power reference value; s =1,2; By incorporating the compensation signal generated by the secondary controller into the control formula of formula (10) using formula (11), a droop control formula considering secondary control is obtained, which is used to obtain the first two sides of the back-to-back converter. k Each microgrid unit MGk and the l Each microgrid unit MG l The active power equalization ratio coefficient is used to achieve global active power equalization: (11) In equation (11), It is the first after adding the compensation signal t VSC in a back-to-back converter t,1 The output active power reference value; It is the first after adding the compensation signal t VSC in a back-to-back converter t,s The reference value of the output reactive power; and They represent the first t VSC in a back-to-back converter t,1 The active power compensation value and reactive power compensation value; S42, Construct the first using equation (12) t A sliding mode secondary controller for equal active power distribution between two back-to-back converters is used to achieve equal active power distribution control. (12) In equation (12), Indicates the first t VSC in a back-to-back converter t,1 The differential value of active power compensation; and ≥0 indicates two proportional control coefficients; 0≤γ≤1 is the fractional power constant of the finite-time integrator; and These are the proportional control coefficient and integral control coefficient of the active power secondary controller, respectively. and They are the first k Each microgrid unit MG k and the l Each microgrid unit MG l The active power distribution ratio coefficient; It is an improved symbolic function, and has: (13) In equation (13), x It is the independent variable of the symbolic function; Construct the first using equation (14) t VSC on both sides of the back-to-back converter t,s A secondary controller for reactive power is used to achieve voltage compensation at the point of common coupling. (14) In equation (14), Indicates the first t VSC in a back-to-back converter t,s The reactive power compensation value; This is the ratio of reactive power output to capacity. Indicates the first t The capacity of a back-to-back converter; It is the first t VSC in a back-to-back converter t,s Reactive power output of the secondary controller; and These represent the proportional control coefficient and integral control coefficient of the reactive power secondary controller, respectively. This indicates that it is connected to the VSC in the back-to-back converter. t,s The side k The voltage at the common coupling point of a microgrid.

[0006] The present invention provides an electronic device, including a memory and a processor, wherein the memory is used to store a program that supports the processor in executing the secondary collaborative recovery control method, and the processor is configured to execute the program stored in the memory.

[0007] The present invention discloses a computer-readable storage medium on which a computer program is stored, wherein the computer program, when executed by a processor, performs the steps of the secondary collaborative recovery control method.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention addresses the problems of power sharing and voltage recovery at the common coupling point in existing back-to-back converter islanded AC microgrids. Based on the back-to-back converter, a novel controller is designed. By designing a primary controller and a secondary controller in the back-to-back converter, power sharing between microgrid units and voltage recovery at the common coupling point are achieved step by step, thereby effectively ensuring the stability of the islanded AC microgrid operation.

[0009] 2) Compared with other methods, the back-to-back converter secondary collaborative recovery control method proposed in this invention firstly achieves active power equalization and common coupling point voltage recovery, without changing the underlying control methods of distributed power sources and back-to-back converters in the microgrid. Furthermore, the method proposed in this invention requires less data acquisition and is simple to operate, effectively ensuring the real-time performance of the control algorithm and making it easy to promote in engineering practice. Attached Figure Description

[0010] Figure 1 This is a microgrid topology diagram of the present invention, which uses back-to-back converters for physical interconnection. Figure 2This is a structural topology diagram of the back-to-back converter interconnection microgrid simulated in this invention. Figure 3 This is a communication topology diagram of the back-to-back converter interconnection microgrid system simulated in this invention. Detailed Implementation

[0011] In this embodiment, a secondary collaborative recovery control method for an islanded interconnected microgrid based on a back-to-back converter is proposed. This method involves designing primary and secondary controllers in the back-to-back converter to achieve power sharing among microgrid units and voltage recovery at the common coupling point. The method includes the following steps: S1: Constructing an interconnected micronetwork of isolated islands, including... N Microgrid units MG1, …, MG k , … , MG N and S A back-to-back converter; among which, MG k Indicates the first k Each microgrid unit; k ∈ N ;No. k Each microgrid unit MG k Depend on n k Distributed power supply (DG) k,1 , …, DG k,i , … , DG k, n k Composition, of which DG k,i Indicates the first i One distributed power source; let the first distributed power source DG k,1 As the leader, the rest n k -1 distributed generation (DG) k,2 , … , DG k, n k For followers; any number t A back-to-back converter consists of two inverters connected back-to-back. t ∈ S For ease of discussion, this embodiment only analyzes the ring-type back-to-back converter interconnected microgrid system. S = N The main control structure of this back-to-back converter interconnected microgrid system includes microgrid units and back-to-back converters, such as... Figure 1 As shown. The communication topology of the back-to-back converter interconnected microgrid system discussed is as follows. Figure 2 As shown.

[0012] S2: Construct primary and distributed secondary controllers capable of restoring distributed power frequency, bounded voltage, and accurately sharing active and reactive power in microgrid units: S21: To achieve communication-free automatic frequency and voltage control within an AC microgrid unit, distributed power sources typically employ primary control with droop characteristics. The first stage is constructed using equation (1). k Each microgrid unit MG k The Middle i Distributed power supply (DG) k.i The primary controller for droop control: (1) In equation (1), ω k,i and V k,i The first i Distributed power supply (DG) k,i Output frequency and voltage; ω ref and V ref These are reference values ​​for frequency and voltage; and The first i Distributed power supply (DG) k,i The active power droop coefficient and the reactive power droop coefficient; and They are the first i Distributed power supply (DG) k,i The output active power and reactive power; and These are the deviations from the maximum permissible frequency and the maximum permissible voltage, respectively. and They are the first i Distributed power supply (DG) k,i The rated active power and rated reactive power; it can be seen from equation (15) that the frequency and voltage deviations are related to the active and reactive power output of the distributed power source. Therefore, the first equation can be obtained from equation (16). i Distributed power supply (DG) k,i Active power distribution ratio α k,i And reactive power sharing ratio coefficient β k,i : (2) In equation (2), and They represent DG k,i The difference between the frequency reference value and the output frequency, and the difference between the voltage reference value and the output voltage; S22: All distributed power sources within a microgrid unit share a unified frequency; therefore, active power sharing control can be automatically completed simply by implementing droop control. Considering the inherent frequency deviation, a distributed secondary control method is further adopted to generate a compensation signal. By adding the droop control law, the compensation signal generated by the distributed secondary controller can be added to the droop control formula of formula (1) using formula (3), thus obtaining the first result after adding the compensation signal. i Distributed power supply (DG) k,i Output frequency Used to achieve the second control under secondary control k MG Micro Network k The rated frequency recovery and active power of all distributed power sources are equally distributed: (3) In equation (3), DG generated by distributed secondary control k,i The frequency compensation signal is obtained from equation (18): (4) In equation (4), and They represent DG k,i Frequency compensation signal Medium-frequency elements and active elements, and have: (5) In equation (5), and Representing frequency elements and active elements The coefficient; Indicates the first k MG Micro Network k Middle and the first i Distributed power supply (DG) k.i The set of sequence numbers of other distributed power sources that communicate directly; It means DG k.i With the j Distributed power supply (DG) k.j The coefficient indicating whether direct communication is possible; if direct communication is possible, then... Take 1, otherwise Set to 0; DG k.i Can the coefficients of the reference value be received directly? If DG k.i If a reference value can be received, then Take 1, otherwise Set to 0; ω k,j It's DG k,j The frequency; αk,j It's DG k,j The active power distribution ratio coefficient; However, due to line impedance mismatch, the output voltages of each distributed generation (DG) within a microgrid unit differ, creating an inherent contradiction between voltage recovery and accurate reactive power equilibration. Therefore, this method aims to achieve accurate reactive power equilibration and voltage recovery across all DGs within each microgrid unit. To achieve this, a distributed voltage observer is designed to estimate the voltage of each DG. k.i The voltage is calculated so that the estimated value converges to the weighted average voltage of all distributed sources. A distributed voltage observer is constructed using equation (6) to estimate the voltage of the first source. i Distributed power supply (DG) k.i Voltage: (6) In equation (6), yes t Moment DG k,i The voltage estimate; yes t Moment DG k,i The voltage; and They are s Moment DG k,i and DG k,j The voltage estimate; t 0 represents the initial time. Therefore, similar to equation (5), equation (7) is used to calculate the voltage element in the compensation voltage signal of the distributed secondary control. and reactive elements Used to achieve the second control under secondary control k MG Micro Network k Voltage recovery and reactive power are equally distributed among all distributed power sources: (7) In equation (7), and Representing voltage elements respectively coefficients and reactive elements The coefficient; and They are DG k,i and DG k,j The voltage estimate; It is an estimate of the voltage reference value; It's DG k,j The reactive power equalization ratio coefficient; through the fine design of the secondary controller with Equation (19) and Equation (21), frequency and voltage recovery control, as well as accurate active and reactive power equalization, can be realized simultaneously.

[0013] S3: Constructing the basic control structure of a voltage source inverter in a back-to-back converter: The first t The two inverters in a back-to-back converter are denoted as VSC. t,1 VSC t,2 Among them, VSC t,1 The constant power control strategy is adopted, which controls the active and reactive power flow according to pre-allocated instructions; VSC t,2 A constant DC voltage control strategy is used to stabilize the DC capacitor voltage; The internal reference current of VSC1 is calculated using equation (8): (8) In equation (8), and Representing the first t VSC in a back-to-back converter t,1 Internal d-axis and q-axis reference currents; and Representing the first t VSC in a back-to-back converter t,1 The output active power reference value and reactive power reference value; VSC t,1 Internal d-axis voltage; It's worth noting that although the structure of a back-to-back converter is relatively complex, it is essentially a passive component. Regarding reactive power flow control, due to the isolation effect of the DC capacitors, VSC... t,1 Output reactive power With VSC t,2 Output reactive power Irrelevant. VSC is obtained from equation (9). t,2 Reference current and DC voltage control parameters on the side: (9) In equation (9), and Representing the first t VSC in a back-to-back converter t,2 Internal d-axis and q-axis reference currents; and Representing the first t VSC in a back-to-back converter t,2 The output active power reference value and reactive power reference value; VSC t,2 Internal d-axis voltage; and These represent the proportional control coefficient and integral control coefficient for constant DC voltage control, respectively. and Representing the first t Actual and reference values ​​of DC capacitors in a back-to-back converter; Here, the traditional hierarchical control method can still be used to achieve frequency / voltage recovery, as shown in equation (24). However, the compensation signal of the back-to-back converter cannot intelligently and automatically calculate the transferred power in real time to achieve active power sharing. The traditional hierarchical control method is designed based on equation (10): (10) In equation (10), and Representing the first k Each microgrid unit MG k and j microgrid units MG l The frequency; and They are the first k Each microgrid unit MG k and the l Each microgrid unit MG l The active power distribution ratio coefficient.

[0014] S4: Construct primary and secondary controllers in a back-to-back converter capable of achieving precise active power sharing and common point-of-coupling voltage recovery among microgrid units: S41. As mentioned above, back-to-back converters play a crucial role in the power sharing control of all microgrid units. The primary control employs a generalized droop control strategy with dual-sided frequency deviation control. Here, it is not difficult to set the same scenario for the generalized droop control strategy based on the voltage deviation. However, a large reactive power exchange will squeeze the active power transmission channel, which will further lead to overcurrent problems in the back-to-back converter. Using equation (11) to construct the first... t A primary controller for simulating droop control of a back-to-back converter is used to realize the droop control of the two sides of the back-to-back converter. k Each microgrid unit MG k and the l Each microgrid unit MG l Faster frequency dynamic balancing: (11) In equation (11), and These are the proportional and integral coefficients for the simulated droop control; Indicates the first t The first of the back-to-back converters s VSC t,s The reactive power reference value; s=1,2; The biggest advantage of this main droop control method is that back-to-back converters do not require a communication network. They only need to use the local frequency signals of both sides to achieve faster frequency balance dynamics between the two microgrid units. However, it can also be found that in the case of secondary control implemented by distributed power sources, this method is of little help in achieving active power sharing control. As the frequency of each microgrid unit gradually recovers to the rated value, the frequency deviation generated by the back-to-back converters is insufficient to exchange active power, and the active power sharing rate of both sides is not equal. Therefore, the main task of the secondary control proposed in this invention is to obtain the active power sharing ratio of both sides, and then achieve active power sharing control within a limited time. However, in the case of secondary control implemented in microgrid units, this method is of little help in achieving global active power sharing. Therefore, the main task of the proposed secondary control is to obtain the active power sharing rate of both sides, and further achieve global active power sharing within a limited time. Using equation (12), the compensation signal generated by the secondary controller is added to the control equation of equation (11) to obtain the droop control equation considering secondary control, which is used to obtain the first two sides of the back-to-back converter. k Each microgrid unit MG k and the l Each microgrid unit MG l The active power equalization ratio coefficient is used to achieve global active power equalization: (12) In equation (12), It is the first after adding the compensation signal t VSC in a back-to-back converter t,1 The output active power reference value; It is the first after adding the compensation signal t VSC in a back-to-back converter t,s The reference value of the output reactive power; and They represent the first t VSC in a back-to-back converter t,1 The active power compensation value and reactive power compensation value; S42. Although the traditional quadratic linear PI controller is the simplest method to recover the proportional gain of unbalanced active power, its convergence speed is far from satisfactory. Therefore, this invention proposes an improved nonlinear sliding mode control to achieve active power sharing control while accelerating the convergence dynamics. The first equation is constructed using equation (13). t A sliding mode secondary controller with equal active power distribution for each back-to-back converter is used to achieve equal active power distribution control and accelerate convergence dynamics. (13) In equation (13), Indicates the first tVSC in a back-to-back converter t,1 The differential value of active power compensation; and ≥0 indicates two proportional control coefficients; 0≤γ≤1 is the fractional power constant of the finite-time integrator; and These are the proportional control coefficient and integral control coefficient of the active power secondary controller, respectively. It is an improved symbolic function, and has: (14) In equation (14), x It is the independent variable of the symbolic function; It is worth noting that by setting γ =1, sliding mode control degenerates into traditional PI control. For reactive power control of back-to-back converters, the control objective is to compensate for the common coupling point voltage under capacity constraints. Using equation (15) to construct the first t VSC on both sides of the back-to-back converter t,s A secondary controller for reactive power is used to achieve voltage compensation at the point of common coupling. (15) In equation (15), Indicates the first t VSC in a back-to-back converter t,s The reactive power compensation value; This is the ratio of reactive power output to capacity. Indicates the first t The capacity of a back-to-back converter; It is the first t VSC in a back-to-back converter t,s Reactive power output of the secondary controller; and These represent the proportional control coefficient and integral control coefficient of the reactive power secondary controller, respectively. This indicates that it is connected to the VSC in the back-to-back converter. t,s The side of the first k The voltage at the common coupling point of each microgrid.

[0015] In this embodiment, an electronic device includes a memory and a processor. The memory stores a program that supports the processor in executing the above-described method, and the processor is configured to execute the program stored in the memory.

[0016] In this embodiment, a computer-readable storage medium stores a computer program, which is executed by a processor to perform the steps of the above method.

[0017] To verify the proposed cooperative control strategy for back-to-back converter interconnected microgrid systems, a system was constructed in Matlab / Simulink as follows: Figure 2 The test system shown has four distributed power sources per microgrid, with primary and distributed secondary control functions. The communication topology is as follows: Figure 3 As shown. Simulation results verify the performance of the system, the proposed method under a series of stage changes, and the test results are obtained. The three specific stages include, stage 1: t = 0 ~ 4s, only droop control is performed within each microgrid unit, and the power transfer command of all back-to-back converters is set to 0. In t At 4s, the primary frequency balance control of the back-to-back converter is activated. Stage 2: In t At 8s, the distributed secondary control strategy is applied to each microgrid unit (except for the back-to-back converters), and at 12s, a light load of 5kW + j5kVar is connected. Phase 3: In t At 16s, the secondary active power sharing and common point of coupling voltage compensation of the back-to-back converters are activated. t = During the period of 16 ~ 40s, the load changes occurred respectively t = 24s and t = 32s.

[0018] Simulation results show that when the active power sharing controllers of all back-to-back converters are activated, global active power sharing is restored even under load variations. Furthermore, it is readily apparent that the common coupling point voltage is well compensated for through reactive power control of the back-to-back converters. In addition, by setting different parameter modes, it can be seen that the convergence speed is significantly improved when using sliding mode control. The effectiveness of the proposed method is well demonstrated.

Claims

1. A secondary collaborative recovery control method for islanded interconnected microgrids based on back-to-back converters, characterized in that, Includes the following steps: S1: Constructing an interconnected micronetwork of isolated islands, including... N Each microgrid unit MG1, … , MG k , … , MG N and S A back-to-back converter; Among them, MG k Indicates the first k Each microgrid unit; k ∈ N ;No. k Each microgrid unit MG k Depend on n k Distributed power supply (DG) k,1 , … ,DG k,i , … , Composition, of which DG k,i Indicates the first i One distributed power source; let the first distributed power source DG k,1 As the leader, the rest n k -1 distributed generation (DG) k,2 , … , For followers; any number t A back-to-back converter consists of two inverters connected back-to-back. t ∈ S ;and S = N ; S2: Construct primary and distributed secondary controllers capable of restoring distributed power frequency, bounded voltage, and accurately sharing active and reactive power in microgrid units: S21: Construct the first using equation (1) k Each microgrid unit MG k The Middle i Distributed power supply (DG) k.i The primary controller for droop control is used to achieve automatic differential frequency control and voltage control within the microgrid unit when there is no communication. (1) In equation (1), ω k,i and V k,i The first i Distributed power supply (DG) k,i Output frequency and voltage; ω ref and V ref These are reference values ​​for frequency and voltage; and The first i Distributed power supply (DG) k,i The active power droop coefficient and the reactive power droop coefficient; and They are the first i Distributed power supply (DG) k,i The output active power and reactive power; and These are the deviations from the maximum permissible frequency and the maximum permissible voltage, respectively. and They are the first i Distributed power supply (DG) k,i The rated active power and rated reactive power; From equation (2), we obtain the first... i Distributed power supply (DG) k,i Active power distribution ratio α k,i And reactive power sharing ratio coefficient β k,i : (2) In equation (2), , They represent DG k,i The difference between the frequency reference value and the output frequency, and the difference between the voltage reference value and the output voltage; S22: Using equation (3), the compensation signal generated by the distributed secondary controller is added to the droop control equation of equation (1), thereby obtaining the first... i Distributed power supply (DG) k,i Output frequency Used to achieve the second control under secondary control k MG Micro Network k The rated frequency recovery and active power of all distributed power sources are equally distributed: (3) In equation (3), DG generated by distributed secondary controller k,i The frequency compensation signal is obtained from equation (4): (4) In equation (4), and They represent DG k,i Frequency compensation signal Medium-frequency elements and active elements, and have: (5) In equation (5), and Representing frequency elements and active elements The coefficient; Indicates the first k MG Micro Network k Middle and the first i Distributed power supply (DG) k.i The set of sequence numbers of other distributed power sources that communicate directly; It means DG k.i With the j Distributed power supply (DG) k.j The coefficient indicating whether direct communication is possible; if direct communication is possible, then... Take 1, otherwise Set to 0; DG k.i Can the coefficients of the reference value be received directly? If DG k.i If the reference value can be received, then Take 1, otherwise Set to 0; ω k,j It's DG k,j The frequency; α k,j It's DG k,j The active power distribution ratio coefficient; A distributed voltage observer is constructed using equation (6) to estimate the voltage level of the first voltage. i Distributed power supply (DG) k.i Voltage: (6) In equation (6), yes t Moment DG k,i The voltage estimate; yes t Moment DG k,i The voltage; and They are s Moment DG k,i and DG k,j The voltage estimate; t 0 represents the initial time. Calculate the voltage element in the compensation voltage signal of the distributed secondary control using equation (7). and reactive elements Used to achieve the second control under secondary control k MG Micro Network k Voltage recovery and reactive power are equally distributed among all distributed power sources: (7) In equation (7), and Representing voltage elements respectively coefficients and reactive elements The coefficient; and They are DG k,i and DG k,j Estimated voltage value; It is an estimate of the voltage reference value; It's DG k,j The reactive power distribution ratio coefficient; S3: Constructing the basic control structure of a voltage source inverter in a back-to-back converter: The first t The two inverters in a back-to-back converter are denoted as VSC. t,1 VSC t,2 Among them, VSC t,1 The constant power control strategy is adopted, which controls the active and reactive power flow according to pre-allocated instructions; VSC t,2 A constant DC voltage control strategy is used to stabilize the DC capacitor voltage; The reference current inside VSC1 is calculated using equation (8): (8) In equation (8), and Representing the first t VSC in a back-to-back converter t,1 Internal d-axis and q-axis reference currents; and Representing the first t VSC in a back-to-back converter t,1 The output active power reference value and reactive power reference value; VSC t,1 Internal d-axis voltage; VSC is obtained from equation (9) t,2 Reference current and DC voltage control parameters on the side: (9) In equation (9), and Representing the first t VSC in a back-to-back converter t,2 Internal d-axis and q-axis reference currents; and Representing the first t VSC in a back-to-back converter t,2 The output active power reference value and reactive power reference value; VSC t,2 Internal d-axis voltage; and These represent the proportional control coefficient and integral control coefficient for constant DC voltage control, respectively. and Representing the first t Actual and reference values ​​of DC capacitors in a back-to-back converter; S4: Construct primary and secondary controllers in a back-to-back converter capable of achieving precise active power sharing and common point-of-coupling voltage recovery among microgrid units: S41. Construct the first using equation (10). t A primary controller for simulating droop control of a back-to-back converter is used to realize the droop control of the two sides of the back-to-back converter. k Each microgrid unit MG k and the l Each microgrid unit MG l Frequency dynamic balance: (10) In equation (10), and These are the proportional and integral coefficients for the simulated droop control; and Representing the first k Each microgrid unit MG k and the l Each microgrid unit MG l The frequency; Indicates the first t The first of the back-to-back converters s VSC t,s The reactive power reference value; s =1,2; By incorporating the compensation signal generated by the secondary controller into the control formula of formula (10) using formula (11), a droop control formula considering secondary control is obtained, which is used to obtain the first two sides of the back-to-back converter. k Each microgrid unit MG k and the l Each microgrid unit MG l The active power equalization ratio coefficient is used to achieve global active power equalization: (11) In equation (11), It is the first after adding the compensation signal t VSC in a back-to-back converter t,1 The output active power reference value; It is the first after adding the compensation signal t VSC in a back-to-back converter t,s The reference value of the output reactive power; and They represent the first t VSC in a back-to-back converter t,1 The active power compensation value and reactive power compensation value; S42, Construct the first using equation (12) t A sliding mode secondary controller for equal active power distribution between two back-to-back converters is used to achieve equal active power distribution control. (12) In equation (12), Indicates the first t VSC in a back-to-back converter t,1 The differential value of active power compensation; and ≥0 indicates two proportional control coefficients; 0≤γ≤1 is the fractional power constant of the finite-time integrator; and These are the proportional control coefficient and integral control coefficient of the active power secondary controller, respectively. and They are the first k Each microgrid unit MG k and the l Each microgrid unit MG l The active power distribution ratio coefficient; It is an improved symbolic function, and has: (13) In equation (13), x It is the independent variable of the symbolic function; Construct the first using equation (14) t VSC on both sides of the back-to-back converter t,s A secondary controller for reactive power is used to achieve voltage compensation at the point of common coupling. (14) In equation (14), Indicates the first t VSC in a back-to-back converter t,s The reactive power compensation value; This is the ratio of reactive power output to capacity. Indicates the first t The capacity of a back-to-back converter; It is the first t VSC in a back-to-back converter t,s Reactive power output of the secondary controller; and These represent the proportional control coefficient and integral control coefficient of the reactive power secondary controller, respectively. This indicates that it is connected to the VSC in the back-to-back converter. t,s The side of the first k The voltage at the common coupling point of each microgrid.

2. An electronic device, comprising a memory and a processor, characterized in that, The memory is used to store a program that supports the processor in executing the secondary collaborative recovery control method of claim 1, and the processor is configured to execute the program stored in the memory.

3. A computer-readable storage medium storing a computer program, characterized in that, The computer program is executed by the processor to perform the steps of the secondary collaborative recovery control method of claim 1.

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