A micro-grid voltage distributed secondary control method and device

Abstract

The application discloses a kind of micro-grid voltage distribution type secondary control method and device, wherein, method includes: step S1, the voltage and current after filter of distributed power supply DG are collected, and the output voltage and output current obtained by collection are carried out Clark and Park coordinate transformation;Step S2, dynamic consistency algorithm is used to realize distributed secondary control structure, and the global voltage average in micro-grid is obtained;Step S3, improved droop control method is used to obtain system voltage reference value;Step S4, by introducing proportional integral differential PID controller, realizes source network load global voltage control in micro-grid.The application realizes micro-grid source network load distributed voltage control, and global voltage average can be obtained in local controller to adjust itself;The application can ensure voltage quality in droop control and improve the safety and stability of micro-grid operation in the case of load fluctuation and the case that distributed power supply exits operation due to fault.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-grid control, and particularly relates to a micro-grid voltage distributed secondary control method and device. BACKGROUND

[0002] In order to realize the "double carbon" goal, reduce the serious pollution caused by fossil fuels to the environment, alleviate the current situation of energy shortage, and improve the problem of environmental pollution, distributed power generation has developed rapidly. The micro-grid composed of distributed power sources (DG), energy conversion devices and loads, etc. has the advantages of autonomy, independence and strong economy. The most important feature of the micro-grid is that it has two different operation modes: island mode and grid-connected mode. When the micro-grid is in grid-connected operation, the micro-grid is connected with the main grid, and energy is exchanged between them, which helps the micro-grid to maintain power balance and ensure stable operation; when the micro-grid is in island operation, the micro-grid needs to rely on its own adjustment ability to complete the control of power and voltage frequency because there is no power support from the main grid.

[0003] In island mode, in order to make the distributed power source share the load more flexibly under load fluctuation, the droop control strategy is often used to control the DG. Each DG completes power distribution and supports voltage frequency by responding to its own droop characteristic curve. The droop control strategy is a classic control strategy in island mode. By simulating the droop characteristic curve of the generator in the grid, each DG reaches a new operating point according to its droop curve to provide voltage and frequency support for power sharing of the system. Since the DGs in the droop control strategy do not interfere with each other, the droop control strategy is plug-and-play. However, the droop control strategy has certain limitations. In the droop control, the voltage is easy to deviate from the rated voltage value and produce offset. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a micro-grid voltage distributed secondary control method and device to improve the safety and stability of micro-grid operation.

[0005] To solve the above technical problems, the present application provides a micro-grid voltage distributed secondary control method, comprising:

[0006] Step S1, collecting the voltage and current of the distributed power source DG after the filter, and performing Clark and Park coordinate transformation on the collected output voltage and output current;

[0007] Step S2, using a dynamic consistency algorithm to realize a distributed secondary control structure to obtain a global voltage average value in the micro-grid;

[0008] Step S3, using an improved droop control method to obtain a system voltage reference value;

[0009] Step S4, the global voltage control of the source and load in the micro-grid is realized by introducing a proportional-integral-derivative (PID) controller.

[0010] Further, the step S1 specifically comprises: collecting the output voltage u oabc and the output current i oabc of the DG after the LC filter. oabc oabc After the Clark and Park coordinate transformation of the output voltage u od and the output current i oq , the direct-axis voltage component u od , the quadrature-axis voltage component u oq , the direct-axis current component i oabc and the quadrature-axis current component i oabc in the rotating coordinate system are obtained.

[0011] Further, the step S2 specifically comprises:

[0012] Step S21, the output active power and the output reactive power of the DG are calculated according to the direct-axis voltage component u od , the quadrature-axis voltage component u oq , the direct-axis current component i od and the quadrature-axis current component i oq in the rotating coordinate system obtained after the coordinate transformation of the output voltage u oabc and the output current i oabc .

[0013] Step S22, the global voltage average in the micro-grid is calculated by using a dynamic consistency algorithm.

[0014] Further, the step S21 calculates the output active power and the output reactive power of the DG in the following manner:

[0015]

[0016] wherein, P i is the output active power of the DG; Q i is the output reactive power of the DG.

[0017] The calculated output active power P i and the output reactive power Q i are filtered through an LC low-pass filter to filter out the harmonic components and obtain an instantaneous power signal:

[0018]

[0019] wherein, G LPF (s) is the transfer function of the LC low-pass filter; ω c is the cut-off frequency.

[0020] Further, the step S22 specifically comprises:

[0021] The global average voltage value U is calculated by using a dynamic consistency algorithm avgi (t), U avgj (t) is as follows:

[0022]

[0023]

[0024] Wherein, τ represents a time constant, U avgi (τ), U avgj (τ) are the voltage average values obtained by nodes i, j within a time constant, U i (t) is a dynamic time-varying input signal introduced in the dynamic consistency algorithm, N i represents the set of nodes adjacent to node i, the adjacency matrix A ij =[a ij ]∈R n×n represents the connection relationship between nodes i, j, U avgi (t), U avgj (t) are the global voltage average values obtained by nodes i, j, respectively.

[0025] The elements of the adjacency matrix A ij =[a ij ]∈R n×n can be determined by the following formula:

[0026]

[0027] Wherein, m represents the weight between edges, and G=(V, E) represents a graph, wherein V={1, 2,..., n} is the node set of the graph G, is an ordered pair set of nodes, used to represent the edges between nodes, each edge is represented by a pair of nodes (i, j), (i, j)∈E represents that nodes i, j are connected.

[0028] Further, the step S3 replaces the fixed coefficient in the traditional droop control with a first function of power, and the equation of the improved droop control is:

[0029] f i =f N -(M i -m i P i )(P i -P Ni )

[0030] U i =UN -(N i -n i Q i (Q) i -Q Ni )

[0031] Among them, f i f is the system frequency reference value; N The system's rated frequency; M i The active droop coefficient constant term; m i P is the active power droop coefficient. i For DG to output active power; P Ni The rated active power of DG; U N The system's rated voltage; U i This is the system voltage reference value; N i n is the constant term for reactive power droop coefficient; i Q is the reactive power droop factor; Ni The rated reactive power of DG; Q i It outputs reactive power to DG.

[0032] Further, step S4 specifically includes:

[0033] The rated voltage value U of the microgrid system N With global voltage average value U avgi The input signal to the PID controller is obtained by taking the difference. After passing through the PID controller, its output is used as the compensation amount δU of the system voltage. i The compensation amount δU of the system voltage i for:

[0034] δU i =(k P +k I / s+k D s)(U N -U avgi )

[0035] Where, k P k is the proportional gain of the PID controller. I k is the integral proportional coefficient of the PID controller. D U represents the derivative coefficient of the PID controller. avg i represents the global average voltage obtained at node i;

[0036] The compensation amount δU of the system voltage i With system voltage reference value U i By superimposing these values, the system voltage reference value in the distributed two-level control law is obtained. The system voltage reference value in the secondary control law for:

[0037]

[0038] wherein, U i is the system voltage reference value; δU i is the compensation of the system voltage; U N is the system rated voltage; n i is the reactive droop coefficient; Q Ni is the DG rated reactive power; Q i is the DG output reactive power.

[0039] The analysis of the dynamic consistency algorithm can obtain the steady state:

[0040]

[0041] The application also provides a micro-grid voltage distributed secondary control device, comprising:

[0042] The acquisition module is used for acquiring the voltage and current of the distributed power supply DG after the filter, and performing Clark and Park coordinate transformation on the acquired output voltage and output current;

[0043] The first calculation module is used for realizing the distributed secondary control structure by using the dynamic consistency algorithm, and obtaining the global voltage average value in the micro-grid;

[0044] The second calculation module is used for obtaining the system voltage reference value by using the improved droop control method;

[0045] The control module is used for realizing the global voltage control of the source network load in the micro-grid by introducing the PID controller.

[0046] Further, the second calculation module replaces the fixed coefficient in the traditional droop control with the first function of power, and the improved droop control equation is:

[0047] f i =f N -(M i -m i P i )(P i -P Ni )

[0048] U i =U N -(N i -n i Q i )(Q i -Q Ni )

[0049] wherein, f iis the system frequency reference value; f N is the system rated frequency; M i is the active droop coefficient constant term; m i is the active droop coefficient; P i is the DG output active power; P Ni is the DG rated active power; U N is the system rated voltage; U i is the system voltage reference value; N i is the reactive droop coefficient constant term; n i is the reactive droop coefficient; Q Ni is the DG rated reactive power; Q i is the DG output reactive power.

[0050] Further, the control module is specifically used for:

[0051] The micro-grid system rated voltage value U N is subtracted from the global voltage average value U avgi to obtain an input signal of a PID controller, and the output of the PID controller is used as a system voltage compensation amount δU i , wherein the system voltage compensation amount δU i is:

[0052] δU i = (k P +k I / s+k D s) (U N -U avgi )

[0053] wherein k P is a proportional amplification coefficient of the PID controller, k I is an integral proportional coefficient of the PID controller; k D is a differential coefficient of the PID controller; U avgi is the global voltage average value obtained by the node i;

[0054] The system voltage compensation amount δU i is superimposed with the system voltage reference value U i to obtain a system voltage reference value in a distributed secondary control law The system voltage reference value in the secondary control law is:

[0055]

[0056] wherein U i is the system voltage reference value; δU i is the system voltage compensation amount; U N ​is the system rated voltage; n i is the reactive droop coefficient; Q Ni is the DG rated reactive power; Q i is the DG output reactive power.

[0057] The analysis of the dynamic consistency algorithm can obtain the steady state:

[0058]

[0059] The implementation of the present application has the following beneficial effects: the present application introduces distributed secondary control on the basis of improving droop control, and each distributed power source can obtain the global average voltage locally through the dynamic consistency algorithm, so that the voltage regulation object of the micro-grid is converted from the output voltage of a specific DG to the global average voltage, and the global average voltage is adjusted to the rated voltage through the introduction of a PID controller in the reactive-voltage droop equation, so that the output voltage of the DG is clustered around the rated voltage value, and adaptive regulation of the voltage is realized; the present application also realizes distributed control through the dynamic consistency algorithm, and realizes decentralization, so that the global voltage average value can be obtained in the local controller to perform self-regulation; the present application can realize that the output voltage can be distributed around the rated voltage in the case of load fluctuation and the case that the DG exits operation due to failure, so as to ensure the voltage quality in the droop control and improve the safety and stability of the micro-grid operation. BRIEF DESCRIPTION OF DRAWINGS

[0060] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0061] Figure 1 is a flowchart of a micro-grid voltage distributed secondary control method according to an embodiment of the present application.

[0062] Figure 2 is a control principle schematic diagram of the embodiment of the present application.

[0063] Figure 3 is a system simulation structure diagram in the embodiment of the present application.

[0064] Figure 4 is a system communication topology diagram in the embodiment of the present application.

[0065] Figure 5 is a simulation result diagram under load fluctuation in the embodiment of the present application.

[0066] Figure 6is a simulation result diagram in the case that the DG is out of operation due to a fault. DETAILED DESCRIPTION

[0067] The following description of the embodiments is made with reference to the drawings, which are intended to illustrate specific embodiments in which the application can be implemented.

[0068] Referring to Figure 1 , the embodiment one of the application provides a micro-grid voltage distributed secondary control method, which comprises the following steps.

[0069] In step S1, the voltage and current of the distributed power source DG after the filter are collected, and the output voltage and output current obtained are subjected to Clark and Park coordinate transformation.

[0070] In step S2, a dynamic consistency algorithm is used to realize the distributed secondary control structure, and the global voltage average value in the micro-grid is obtained.

[0071] In step S3, an improved droop control method is used to obtain the system voltage reference value.

[0072] In step S4, a proportional-integral-derivative (PID) controller is introduced to realize the global voltage control of the source and network load in the micro-grid.

[0073] Specifically, referring to Figure 2 , since the three-phase inverter is modulated by sinusoidal pulse width modulation, a large amount of harmonics will be mixed in the output voltage, and the high-order harmonics need to be removed by the LC filter before the electric energy is sent to the public load end or directly connected to the large power grid. First, the output voltage u oab c and the output current i oabc of the DG after the LC filter are collected, and the output voltage u oabc and the output current i oabc are subjected to Clark and Park coordinate transformation, so as to obtain the rotating coordinate system voltage component u od , the rotating coordinate system voltage component u oq , the rotating coordinate system current component i od and the rotating coordinate system current component i oq .

[0074] The formula of the Clark coordinate transformation is as follows:

[0075]

[0076] wherein, u α , u β , i α , i β are the voltage values and current values in the stationary coordinate system obtained by the Clark coordinate transformation; u a , u b , uc a b c The i-th DG output voltage and current three-phase component collected by the power control outer loop module; C abc / αβ The Clark coordinate transformation matrix, specifically:

[0077]

[0078] The formula of the Park coordinate transformation is:

[0079]

[0080] Wherein, u od , u oq , i od , i oq are the direct-axis voltage component, the quadrature-axis voltage component, the direct-axis current component and the quadrature-axis current component in the rotating coordinate system after Park coordinate transformation; P αβ / dq The Park coordinate transformation matrix, specifically:

[0081]

[0082] Step S2 specifically includes the following two steps:

[0083] Step S21, according to the output voltage u oabc and the output current i oabc , the direct-axis voltage component u od , the quadrature-axis voltage component u oq , the direct-axis current component i od and the quadrature-axis current component i oq obtained after coordinate transformation in the rotating coordinate system, the output active power and the output reactive power of the DG are calculated:

[0084]

[0085] Wherein, P i is the DG output active power; Q i is the DG output reactive power;

[0086] The output active power P i and the output reactive power Q i obtained from the above formula contain a large number of high-order harmonic components, which will interfere with the system and affect the control accuracy if used as the input signal of the next control module, and may cause the droop control to be unstable, so an LC low-pass filter is needed to filter out the harmonic components to obtain a relatively stable instantaneous power signal:

[0087] ​​​

[0088] where G LPF (s) is the transfer function of the LC low-pass filter; ω c is the cut-off frequency.

[0089] Step S22, the dynamic consistency algorithm is used to calculate the global voltage average value in the micro-grid.

[0090] The global average voltage U avg is defined as:

[0091]

[0092] where U i is the system voltage reference value.

[0093] The dynamic consistency algorithm is used to calculate the global average voltage value U avgi (t), U avgj (t) is as follows:

[0094]

[0095]

[0096] where τ represents a time constant, U avgi (τ), U avgj (τ) are the voltage average values obtained by nodes i, j within a time constant, U i (t) is a dynamic time-varying input signal introduced in the dynamic consistency algorithm, N i represents the set of nodes adjacent to node i, the adjacency matrix A ij =[a ij ]∈R n×n represents the connection relationship between nodes i, j, U avgi (t), U avgj (t) are the global voltage average values obtained by nodes i, j.

[0097] The elements of the adjacency matrix A ij =[a ij ]∈R n×n can be determined by the following formula:

[0098]

[0099] where m represents the weight between edges, and G=(V, E) is usually used to represent a graph, where V={1, 2,...n} is the node set of the graph G, is the ordered pair set of nodes, which is used to represent the edges between nodes, and each edge is represented by a pair of nodes (i, j), (i, j)∈E represents that nodes i, j are connected.

[0100] Droop control is a control mode adopted in microgrid peer-to-peer control mode. DGs can realize automatic distribution of load power by responding to each droop characteristic curve. Since each DG's droop characteristic curve does not interfere with each other, only through their own local information to make decisions on their own output, DGs are equal in status, there is no master control unit and slave control unit, so step S3 can realize the peer-to-peer control mode of microgrid by adopting droop control on DGs.

[0101] The traditional droop control model of microgrid includes active power droop equation and reactive power droop equation:

[0102] The active and reactive power droop equations are:

[0103] f i = f N -m i (P i -P Ni )

[0104] U i = U N -n i (Q i -Q Ni )

[0105] Wherein, f i is the system frequency reference value; f N is the rated system frequency; m i is the active power droop coefficient; P i is the DG output active power; P Ni is the DG rated active power; U N is the system rated voltage; U i is the system voltage reference value; n i is the reactive power droop coefficient; Q Ni is the DG rated reactive power; Q i is the DG output reactive power.

[0106] The traditional droop control sacrifices the accurate control of frequency and voltage according to the movement of DG operating point on the droop characteristic curve, so the droop control is essentially a differential control. When the load fluctuation is large, the traditional control will appear a linear decreasing trend, the output voltage fluctuation range is large, and it is difficult to realize the reasonable distribution of power among parallel inverters, so the traditional droop control needs to be improved. In this embodiment, the fixed coefficient in the traditional droop control is replaced by the first function of power, and the improved droop control equation is:

[0107] f i = f N -(M i -mi P i )(P i -P Ni )

[0108] U i =U N -(N i -n i Q i )(Q i -Q Ni )

[0109] wherein f i is a system frequency reference value; f N is a system rated frequency; M i is an active droop coefficient constant term; m i is an active droop coefficient; P i is a DG output active power; P Ni is a DG rated active power; U N is a system rated voltage; U i is a system voltage reference value; N i is a reactive droop coefficient constant term; n i is a reactive droop coefficient; Q Ni is a DG rated reactive power; Q i is a DG output reactive power.

[0110] The droop coefficient of the improved droop control is no longer constant, but is dynamically adjusted with the actual output active power and reactive power. When the load changes, the droop of the voltage amplitude and frequency of each parallel inverter is dynamically adjusted, which reduces the excessive droop of the micro-grid voltage amplitude and frequency caused by the inverter current sharing control when the load changes, thereby avoiding large fluctuations in the AC bus voltage amplitude and frequency in the micro-grid, thus increasing the stability and reliability of the micro-grid inverter parallel system.

[0111] Since the droop control relies on sacrificing voltage to obtain reactive power, there will be a deviation in the voltage in the distributed secondary control of reactive power, and the voltage needs to be controlled in the secondary control. In order to ensure that the voltage output by each DG is adjusted to the rated value, the step S4 is adopted to realize the accurate control of the global voltage of the source network load. Specifically:

[0112] The micro-grid system rated voltage value U N is subtracted from the global voltage average value U avgi to obtain the input signal of the PID controller, and the output of the PID controller is used as the compensation amount δU i of the system voltage, wherein the compensation amount δU i of the system voltage is:

[0113] δUi = (k P +k I / s+k D s)(U N -U avgi )

[0114] wherein k P is a proportional amplification coefficient of the PID controller, k I is an integral proportional coefficient of the PID controller; k D is a differential coefficient of the PID controller; U avgi is a global voltage average value obtained by the node i.

[0115] The compensation amount δU i of the system voltage is superposed with the system voltage reference value U i , so that the system voltage reference value in the distributed secondary control law is obtained The system voltage reference value in the secondary control law is:

[0116]

[0117] wherein U i is the system voltage reference value; δU i is the compensation amount of the system voltage; U N is the system rated voltage; n i is a reactive droop coefficient; Q Ni is a DG rated reactive power; Q i is a DG output reactive power.

[0118] The analysis of the dynamic consistency algorithm can obtain that at steady state:

[0119]

[0120] The above formula shows that at steady state, the estimation value U avgi of the global average voltage in the local distributed controller of each DG can accurately track the global voltage U avg , and the estimation values of all DGs are consistent.

[0121] In order to further illustrate the beneficial effects of the present application, the following examples are given for introduction:

[0122] In order to verify the effectiveness of the method proposed in the present application, a four-DG parallel operation model is built in MATLAB as shown in Figure 3 , the communication topology structure is as shown in Figure 4 , and the simulation parameters are as shown in Table 1:

[0123] Table 1 System simulation parameters

[0124] ​

[0125] Simulation analysis when load fluctuates: the public load Load2 is put into use at t=2s in the simulation, and the simulation result of the control method is as shown in Figure 5

[0126] Simulation analysis when DG exits operation due to fault: Load2 is set to be put into use at t=1.5s, and DG3 is simulated to be cut off and directly exit operation due to fault at t=3s, and the simulation result graph of the control method is as shown in Figure 6

[0127] The simulation experiment analysis shows that the application can precisely distribute the reactive power output of the DG according to the DG capacity ratio in the case of load fluctuation and the case that the DG exits operation due to fault, can solve the voltage deviation problem, and has good dynamic performance.

[0128] Corresponding to the micro-grid voltage distributed secondary control method in the foregoing embodiment one, the application provides a micro-grid voltage distributed secondary control device, which comprises:

[0129] A collection module is configured to collect the voltage and current of the distributed power supply DG after the filter, and perform Clark and Park coordinate transformation on the collected output voltage and output current.

[0130] A first calculation module is configured to realize the distributed secondary control structure by using a dynamic consistency algorithm, and obtain the global voltage average value in the micro-grid.

[0131] A second calculation module is configured to obtain the system voltage reference value by using an improved droop control method.

[0132] A control module is configured to realize the global voltage control of the source network load in the micro-grid by introducing a PID controller.

[0133] Further, the second calculation module replaces the fixed coefficient in the traditional droop control with a first function of power, and the improved droop control equation is:

[0134] f i =f N -(M i -m i P i )(P i -P Ni )

[0135] U i =U N -(N i -n i Q i )(Q​​i -Q Ni )

[0136] wherein, f i is the system frequency reference value; f N is the system rated frequency; M i is the active droop coefficient constant term; m i is the active droop coefficient; P i is the DG output active power; P Ni is the DG rated active power; U N is the system rated voltage; U i is the system voltage reference value; N i is the reactive droop coefficient constant term; n i is the reactive droop coefficient; Q Ni is the DG rated reactive power; Q i is the DG output reactive power.

[0137] Further, the control module is specifically configured to:

[0138] obtaining the difference between the micro-grid system rated voltage value U N and the global voltage average value U avgi to obtain the input signal of the PID controller, and through the PID controller, the output thereof is taken as the compensation amount δU i of the system voltage, wherein the compensation amount δU i of the system voltage is:

[0139] δU i = (k P + k I / s + k D s) (U N - U avgi )

[0140] wherein, k P is the proportional amplification coefficient of the PID controller, k I is the integral proportional coefficient of the PID controller; k D is the differential coefficient of the PID controller; U avgi is the global voltage average value obtained by the node i;

[0141] superimposing the compensation amount δU i of the system voltage and the system voltage reference value U i to obtain the system voltage reference value U in the distributed secondary control law, wherein the system voltage reference value U in the secondary control law is:

[0142]

[0143] Wherein, U i is a system voltage reference value; δU i is a compensation amount of the system voltage; U N is a system rated voltage; n i is a reactive droop coefficient; Q Ni is a DG rated reactive power; Q i is a DG output reactive power.

[0144] The analysis of the dynamic consistency algorithm can obtain the steady state:

[0145]

[0146] The working principle and working process of the embodiment are the same as the foregoing description of the first embodiment of the application, and will not be repeated here.

[0147] From the foregoing description, it can be seen that, compared with the prior art, the beneficial effects of the application are that: the application introduces distributed secondary control on the basis of improving droop control, and through a dynamic consistency algorithm, each distributed power source can obtain a global average voltage at the local, the voltage regulation object of the micro-grid is converted from the output voltage of a specific DG to the global average voltage, the global average voltage is adjusted to the rated voltage through the introduction of a PID controller in the reactive-voltage droop equation, so that the output voltage of the DG is clustered around the rated voltage value, and the adaptive regulation of the voltage is realized; the application also realizes distributed control through the dynamic consistency algorithm, realizes decentralization, and the global voltage average value can be obtained in the local controller to perform self-regulation; the application can realize that the output voltage can be distributed around the rated voltage in the case of load fluctuation and the case of DG failure, ensures the voltage quality in the droop control, and improves the safety and stability of the micro-grid operation.

[0148] The above only discloses the preferred embodiments of the application, and of course cannot limit the scope of the right of the application, so the equivalent changes made according to the claims of the application still belong to the scope covered by the application.

Claims

1. A microgrid voltage distributed secondary control method, characterized in that, The method comprises the steps of: Step S1, collect output voltage u of LC filter after distributed power supply DG oabc and output current i oabc , and perform Clark and Park coordinate transformation on the collected output voltage u oabc and output current i oabc to obtain rotating coordinate system direct axis voltage component u od , quadrature axis voltage component u oq , direct axis current component i od and quadrature axis current component i oq ; Step S2, a dynamic consistency algorithm is used to realize a distributed two-level control structure, and a global voltage average value in the micro-grid is obtained; the dynamic consistency algorithm passes through an adjacency matrix A ij =[a ij ]∈R n×n , which represents a connection relationship between nodes i and j, and elements of the adjacency matrix A ij =[a ij ]∈R n×n satisfy: where m represents the weight between edges, and G=(V, E) represents a graph, where V={1, 2,... n} is the node set of the graph G, is an ordered pair set of nodes, used to represent edges between nodes, each edge is represented by a pair of nodes (i, j), (i, j) E represents that nodes i and j are connected; The dynamic consistency algorithm is used to calculate the global average voltage value U avgi (t), U avgj The formula of (t) is as follows: where τ represents a time constant, U avgi (t), U avgj (t) are the voltage average values within a time constant τ obtained by nodes i, j, respectively, U i (t), U j (t) are the dynamic time-varying input signals of nodes i, j introduced in the dynamic consensus algorithm, N i denotes the set of nodes adjacent to node i, N j denotes the set of nodes adjacent to node j, U avgi (t), U avgj (t) are the global voltage average values obtained by nodes i, j, respectively; In step S3, a system voltage reference value is obtained by using an improved droop control method; wherein a first function of power is used to replace fixed coefficients in traditional droop control, and an improved droop control equation is: f i = f N - (M i - m i P i ) (P i - P Ni ) U i = U N - (N i n i Q i ) (Q i - Q Ni ) wherein, f i is the system frequency reference value; f N is the system rated frequency; M i is the active droop coefficient constant term; m i is the active droop coefficient; P i is the DG output active power; P Ni is the DG rated active power; U N is the system rated voltage; U i is the system voltage reference value; N i is the reactive droop coefficient constant term; n i is the reactive droop coefficient; Q Ni is the DG rated reactive power; Q i is the DG output reactive power; In step S4, a global voltage control of a source and a load in the micro-grid is realized by introducing a proportional-integral-derivative (PID) controller; specifically, the step S4 comprises: The micro-grid system rated voltage value U N is compared with the global voltage average value U avgi The difference is the input signal of the PID controller, and the output of the PID controller is the compensation amount δU i of the system voltage i is: δU i = (k P + k I / s + k D s) (U N - U avgi ) wherein k P is the proportional gain of the PID controller, k I is the integral proportional gain of the PID controller; k D is the derivative gain of the PID controller; U avgi is the global voltage average obtained by the node i; The compensation amount δU of the system voltage is calculated according to the following formula: i The system voltage reference value U is calculated according to the following formula: i The system voltage reference value U in the distributed secondary control law is calculated according to the following formula: The system voltage reference value U in the distributed secondary control law is calculated according to the following formula: U = U + δU Wherein, U i is the system voltage reference value; δU i is the compensation of the system voltage; U N is the system rated voltage; n i is the reactive droop coefficient; Q Ni is the DG rated reactive power; Q i is the DG output reactive power; According to analysis of the dynamic consistency algorithm, it can be obtained that, at a steady state:

2. The method of claim 1, wherein, The step S2 specifically comprises: Step S21, according to the output voltage u oabc and the output current i oabc The rotating coordinate system direct axis voltage component u od , the quadrature axis voltage component u oq , the direct axis current component i od and the quadrature axis current component i oq , the output active power and the output reactive power of the DG are calculated; In step S22, a dynamic consistency algorithm is used to calculate a global voltage average value in the micro-grid.

3. The method of claim 2, wherein, The step S21 calculates the output active power and the output reactive power of the DG in the following manner: where P i is the DG output active power; Q i is the DG output reactive power; The calculated output active power P i and output reactive power Q i The instantaneous power signal is obtained by passing the output power signal through an LC low-pass filter to filter out the harmonic components. where G LPF (s) is the transfer function of the LC low-pass filter; ω c is the cut-off frequency; P' i is the original output active power containing high harmonic components; Q' i is the original output reactive power containing high harmonic components.

4. A microgrid voltage distributed secondary control device, characterized in that, The method comprises the steps of: The collecting module is used for collecting output voltage u of the distributed power supply (DG) after passing through the LC filter oabc and output current i oabc The output voltage u oabc and the output current i oabc are subjected to Clark and Park coordinate transformation to obtain rotating coordinate system direct-axis voltage component u od , quadrature-axis voltage component u oq , direct-axis current component i od and quadrature-axis current component i oq ; The first calculation module is used for realizing a distributed two-level control structure by using a dynamic consistency algorithm to obtain a global voltage average value in the micro-grid; the dynamic consistency algorithm is realized by using an adjacency matrix A ij =[a ij ]∈R n×n , which represents a connection relationship between nodes i and j, and elements of the adjacency matrix A ij =[a ij ]∈R n×n satisfy: where m represents the weight between edges, and G=(V, E) represents a graph, where V={1, 2,... n} is the node set of the graph G, is an ordered pair set of nodes, used to represent edges between nodes, each edge is represented by a pair of nodes (i, j), (i, j) E represents that nodes i and j are connected; The dynamic consistency algorithm is used to calculate the global average voltage value U avgi (t), U avgj The formula of U(t) is as follows: where τ represents a time constant, U avgi (τ), U avgj (τ) are the voltage average values obtained by nodes i, j within a time constant, respectively, U i (t), U j (t) are the dynamic time-varying input signals of nodes i, j introduced in the dynamic consensus algorithm, respectively, N i denotes the set of nodes adjacent to node i, N j denotes the set of nodes adjacent to node j, U avgi (t), U avgj (t) are the global voltage average values obtained by nodes i, j, respectively; A second calculation module is configured to obtain a system voltage reference value by using an improved droop control method; wherein a first function of power is used to replace fixed coefficients in traditional droop control, and an improved droop control equation is: f i = f N - (M i - m i P i ) (P i - P Ni ) U i = U N - (N i - n i Q i ) (Q i - Q Ni ) wherein, f i is the system frequency reference value; f N is the system rated frequency; M i is the active droop coefficient constant term; m i is the active droop coefficient; P i is the DG output active power; P Ni is the DG rated active power; U N is the system rated voltage; U i is the system voltage reference value; N i is the reactive droop coefficient constant term; n i is the reactive droop coefficient; Q Ni is the DG rated reactive power; Q i is the DG output reactive power; A control module is configured to realize a global voltage control of a source and a load in the micro-grid by introducing a PID controller; specifically, the control module is configured to: The rated voltage value U of the microgrid system N With global voltage average value U avgi The input signal to the PID controller is obtained by taking the difference. After passing through the PID controller, its output is used as the compensation amount δU of the system voltage. i The compensation amount δU of the system voltage i for: δU i = (k P + k I + k D + k N + k avgi ) s where k P is the proportional gain of the PID controller, k I is the integral proportional gain of the PID controller; k D is the derivative gain of the PID controller; U avgi is the global voltage average obtained by the node i; The compensation amount δU of the system voltage i With system voltage reference value U i By superimposing these values, the system voltage reference value in the distributed two-level control law is obtained. The system voltage reference value in the secondary control law for: wherein, U i is the system voltage reference value; δU i is the compensation of the system voltage; U N is the system rated voltage; n i is the reactive droop coefficient; Q Ni is the DG rated reactive power; Q i is the DG output reactive power; According to analysis of the dynamic consistency algorithm, it can be obtained that, at a steady state:

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