Island microgrid secondary control method and system based on voltage reactive hybrid error

Abstract

The invention discloses a secondary control method and system of an island micro-grid based on voltage reactive hybrid errors, and belongs to the field of secondary control of an alternating current micro-grid, and the method comprises the steps: for each bus and each inverter connected with the bus, obtaining a state quantized value uploaded by each inverter in real time from a communication network, and obtaining a bus voltage; and for the ith inverter, respectively calculating a voltage reactive hybrid error # imgabs0 # and a frequency active hybrid error # imgabs1 #, calculating a voltage control signal # imgabs3 # and a frequency control signal # imgabs4 # according to # imgabs2 #, calculating a reference voltage # imgabs6 # and a reference frequency # imgabs7 # according to # imgabs5 #, and then carrying out double-closed-loop PI control to obtain a PWM (Pulse Width Modulation) signal, and acting the PWM signal on the ith inverter to realize secondary control. According to the invention, the offset of the bus voltage and the frequency can be compensated while the power among the distributed power supplies is proportionally distributed, so that the normal operation of the load is ensured.

Description

Technical Field

[0001] The present invention belongs to the field of secondary control of AC microgrids, and more specifically, to a secondary control method and system for an island microgrid based on voltage-reactive mixed error. Background Art

[0002] As the proportion of renewable energy such as wind and solar energy in the power grid continues to increase, traditional centralized power grids are difficult to fully adapt to its changes. The microgrid system is a new type of networking that comprehensively utilizes various distributed energy sources. It organically combines distributed power sources, loads, energy storage units, and control devices to form an independent and controllable system that complements the large power grid. The distributed power sources interact with the bus in voltage and power through inverters.

[0003] Microgrids appear as a single controlled source to large power grids, which overcomes the random fluctuations of energy in traditional distributed generation and meets the user's requirements for power quality. It has important research significance. According to the nature of the microgrid bus voltage, it can be divided into DC microgrids, AC microgrids, and AC / DC hybrid microgrids. Since AC microgrids and large power grids belong to the same AC power category, and have great similarities with conventional distribution networks in operation and control, the current focus of microgrid research is still AC microgrids. In isolated microgrids, it is a very important issue to achieve bus voltage and frequency regulation, as well as the proportional distribution of reactive and active power output by each distributed power source.

[0004] Traditional droop control can achieve power distribution among distributed power sources, but it will cause bus voltage and frequency deviations and cannot guarantee the normal operation of the load. Summary of the invention

[0005] In view of the defects of the prior art and the need for improvement, the present invention provides a secondary control method and system for an island microgrid based on voltage-reactive mixed error, the purpose of which is to compensate for the deviation of bus voltage and frequency while achieving proportional power distribution among distributed power sources to ensure the normal operation of the load.

[0006] To achieve the above object, according to one aspect of the present invention, a secondary control method for an isolated island microgrid based on voltage-reactive mixed error is provided, comprising: dividing each bus in the isolated island microgrid and the inverter connected to the bus into a control object, and performing distributed secondary regulation on each control object respectively; the distributed secondary regulation comprises:

[0007] Obtain the real-time status data quantization value uploaded by each inverter in the current control object from the communication network of the isolated microgrid, and obtain the bus voltage V bus ; The quantized value of the state data includes the quantized active power, reactive power and frequency of the inverter;

[0008] For the i-th inverter, calculate its voltage-reactive mixed error Sum frequency active mixed error And follow Calculating the voltage control signal and frequency control signal i=1, 2...N, N represents the total number of inverters in the current control object;

[0009] according to Calculate the reference voltage of the i-th inverter and reference frequency Then double closed-loop PI control is performed to obtain the PWM signal for controlling the i-th inverter, and the PWM signal acts on the i-th inverter to achieve secondary control;

[0010] in, Including bus voltage V bus With bus voltage rating V * The error between the reactive power of the ith inverter and its neighboring nodes; Including the frequency w of the i-th inverter i With frequency rating w * The error between and the error between active power; P i represents the active power of the i-th inverter, m i represents the active droop coefficient of the i-th inverter; represents the frequency coupling gain, represents the frequency difference between the ith inverter and its neighbor nodes; the neighbor node of the ith inverter represents the inverter node that can directly communicate with the ith inverter through the communication network.

[0011] Furthermore, the communication network is an undirected graph containing M+1 nodes, wherein the M+1 nodes correspond to the M inverters and a leader node in the isolated microgrid; the fixed gain between the leader node and the i-th inverter is g i , if there is a communication link between the leader node and the i-th inverter, then g i >0, otherwise, g i =0; if the jth inverter can transmit information to the ith inverter, there is an edge between the corresponding node pairs, and the edge weight is a ij > 0, otherwise, there is no edge between the corresponding node pairs, and the edge weight is a ij =0; represents the set of neighbor nodes of the node corresponding to the i-th inverter in the communication network;

[0012] and,

[0013]

[0014] e v =V bus -V *

[0015]

[0016] Among them, α i =c vi g i , represents the voltage coupling gain; Q i and Q j denote the reactive power of the i-th inverter and the j-th inverter respectively, q(Q i ) and q(Q j ) represent Q i and Q j The quantitative value of n i and n j represent the reactive power droop coefficients of the i-th inverter and the j-th inverter respectively.

[0017] Further,

[0018]

[0019] in, represents the frequency coupling gain; P j represents the active power of the jth inverter, q(P i ) and q(P j ) represent P i and P j The quantitative value of m i and m j They represent the active power droop coefficients of the i-th inverter and the j-th inverter respectively.

[0020] Further,

[0021] Among them, w j represents the frequency of the jth inverter, q(w i ) and q(w j ) represent w i and w j Quantified value of .

[0022] Furthermore, the quantization method used for the state data quantization is uniform quantization.

[0023] According to another aspect of the present invention, a secondary controller of an island microgrid based on voltage-reactive hybrid error is provided, comprising: a control module and an N busDistributed secondary control devices; N bus is the number of buses in the island microgrid;

[0024] The control module is used to divide each bus and the inverter connected to the bus in the isolated microgrid into a control object, and a total of N bus Control objects;

[0025] N bus Distributed secondary control devices are used to control N bus Each control object performs distributed secondary regulation;

[0026] The distributed secondary control device includes: a communication module, a distributed control module, a voltage and frequency control module and a double closed-loop PI control module;

[0027] The communication module is used to obtain the real-time uploaded status data quantization value of each inverter in the current control object from the communication network of the isolated microgrid, and obtain the bus voltage V bus ; The quantized value of the state data includes the quantized active power, reactive power and frequency of the inverter;

[0028] The distributed control module is used to calculate the voltage control signal and frequency control signal of each inverter in the current control object; for the i-th inverter, its voltage control signal and frequency control signal They are and They represent the voltage-reactive mixed error and frequency-active mixed error of the i-th inverter respectively; Including bus voltage V bus With bus voltage rating V * The error between the reactive power of the ith inverter and its neighboring nodes; Including the frequency w of the i-th inverter i With frequency rating w * The error between the active powers; represents the frequency coupling gain, represents the frequency difference between the ith inverter and each of its neighboring nodes; the neighboring node of the ith inverter represents the inverter that can transmit information to the ith inverter through the communication network;

[0029] The voltage-frequency control module is used to calculate the reference voltage and reference frequency of each inverter in the current control object; for the i-th inverter, its reference voltage and reference frequency They are P i represents the active power of the i-th inverter, m irepresents the active droop coefficient of the i-th inverter;

[0030] The dual closed-loop PI control module is used to perform dual closed-loop control according to the reference voltage and reference frequency of each inverter, obtain the PWM signal of each inverter, and act on the corresponding inverter to realize secondary control.

[0031] Furthermore, the communication network is an undirected graph containing M+1 nodes, wherein the M+1 nodes correspond to the M inverters and a leader node in the isolated microgrid; the fixed gain between the leader node and the i-th inverter is g i , if there is a communication link between the leader node and the i-th inverter, then g i >0, otherwise, g i =0; if the jth inverter can transmit information to the ith inverter, it means that there is a communication link between the jth inverter and the ith inverter, then there is an edge between the corresponding node pairs, and the edge weight is a ij > 0, otherwise, there is no edge between the corresponding node pairs, and the edge weight is a ij =0; represents the set of neighbor nodes of the node corresponding to the i-th inverter in the communication network;

[0032] Furthermore, for the i-th inverter, in its distributed secondary control device, the distributed control module includes: a voltage controller and a frequency controller;

[0033] The voltage controller includes:

[0034] The voltage error calculation unit has a first input terminal for receiving a bus voltage rating V * , whose second input terminal is used to receive the bus voltage V bus , which is used to convert V * With V bus Subtract and get the voltage error e v ;

[0035] The reactive power error calculation unit has a first input terminal for receiving the reactive power quantization value q(Q i ), whose second input terminal is used to receive the reactive power quantization value q(Q j ), which is used in accordance with Calculating reactive power error

[0036] A voltage-reactive mixed error calculation unit, wherein the first input end is connected to the output end of the voltage error calculation unit, and the second input end is connected to the output end of the reactive error calculation unit, and is used to calculate the voltage-reactive mixed error according to the voltage-reactive mixed error calculation unit. Calculate voltage and reactive mixed error

[0037] and a first integrating unit, whose input terminal is connected to the output terminal of the voltage-reactive mixed error calculating unit, and which is used to calculate the voltage-reactive mixed error according to Calculate the voltage control signal of the i-th inverter

[0038] The frequency controller includes:

[0039] The frequency error calculation unit has a first input terminal for receiving the frequency quantization value q(w i ), whose second input terminal is used to receive the frequency rated value w * , which is used to convert w * and q(w i ) to obtain the frequency error

[0040] The active power error calculation unit has a first input terminal for receiving the active power quantization value q(P i ), whose second input terminal is used to receive the active power quantization value q(P j ), which is used in accordance with Calculating Active Power Error

[0041] The frequency difference calculation unit has a first input terminal for receiving the frequency quantization value q(w i ), whose second input terminal is used to receive the frequency quantization value q(w j ), which is used in accordance with Calculate the frequency difference between the i-th inverter and each of its neighboring nodes;

[0042] A frequency-active mixed error calculation unit, wherein the first input end is connected to the output end of the frequency error calculation unit, and the second input end is connected to the output end of the active error calculation unit, and is used to calculate the active power according to the frequency error calculation unit. Calculate frequency active mixed error;

[0043] and a second integrating unit, whose first input terminal is connected to the output terminal of the frequency active mixed error calculating unit, whose second input terminal is connected to the output terminal of the frequency difference calculating unit, and which is used to calculate the frequency difference according to the frequency active mixed error calculating unit. Calculate the frequency control signal of the i-th inverter

[0044] According to another aspect of the present invention, an island microgrid system is provided, comprising: an island microgrid, and the above-mentioned voltage-reactive hybrid error-based secondary controller of the island microgrid provided by the present invention.

[0045] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0046] (1) Based on the characteristics that bus voltage and reactive power affect each other, and frequency and active power affect each other in a microgrid, the present invention designs a voltage-reactive mixed error and a frequency-active mixed error, and determines the control signal of each inverter based on the designed mixed error. On the one hand, precise voltage regulation and reactive power distribution can be achieved simultaneously, and precise frequency regulation and active power distribution can be achieved simultaneously, thereby effectively saving control resources. On the other hand, based on the designed voltage-reactive mixed error, a non-droop control is adopted for the voltage, which can compensate for the deviation of the bus voltage while realizing the proportional distribution of the power of the distributed power source, thereby ensuring the normal operation of the load.

[0047] (2) In the present invention, the communication network only transmits discrete values ​​after state quantization, which effectively reduces the occupation of communication bandwidth.

[0048] (3) In the present invention, the state quantization method specifically adopts uniform quantization, which can simplify the design of the quantizer while ensuring the control effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic diagram of a secondary control system of an island microgrid based on voltage-reactive hybrid error provided by an embodiment of the present invention;

[0050] Figure 2 Schematic diagram of distributed secondary control performed on a single DC / AC inverter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0052] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0053] Before explaining the technical solution of the present invention in detail, a communication network used for information interaction in an isolated island microgrid is briefly introduced.

[0054] In the isolated microgrid, distributed power sources exchange information through DC / AC bidirectional inverters, and the total number of inverters is recorded as N. To describe an AC microgrid consisting of N DC / AC inverters and a leader node, the leader node is a virtual node set. Define the undirected graph as where V = {v1,…,v N} represents a collection of nodes, represents the set of edges, A=[a ij ] is the weighted adjacency matrix, a ij is the edge weight. If node j can transmit information to node i, then (v j ,v i )∈E,a ij >0; otherwise, a ij = 0. The adjacent node set of node i is represented as Set the indegree matrix to in Define the Laplacian matrix as At the same time, the fixed gain of the leader node for the i-th DC / AC inverter is set to g i , if there is a communication link between the leader node and the inverter, then g i >0; otherwise, g i =0. is a diagonal matrix with fixed gains on the diagonal, is represented as the set of positive real numbers.

[0055] In practical applications, the neighbor node information of each inverter changes very quickly, which makes the communication network have a heavy burden on information transmission. In order to alleviate the information transmission burden of the communication network, the existing control method often adopts state quantization combined with event triggering, that is, only the discrete value after state quantization is transmitted in the communication network to reduce bandwidth occupancy, and information is only transmitted at the time of event triggering to reduce the number of communications. However, the present invention has found through research that stability and security are extremely important for microgrid systems. The implementation of the event triggering mechanism requires the consumption of certain control resources and the selection of the triggering threshold is greatly affected by the system parameters, which is difficult to implement in practical applications. At the same time, the control resources in the microgrid system are often very scarce, which means that while the pressure on the communication network bandwidth is alleviated through the event triggering mechanism, the control performance of the system will be lost.

[0056] In response to the above problems, the present invention only adopts a quantization method, so that each inverter uploads the quantized status information in real time. At the same time, the controller obtains the status quantization information of each inverter from the communication network in real time, and controls each inverter based on the distributed secondary control provided by the present invention. Experimental results show that the present invention can effectively improve the stability of control while meeting the communication bandwidth constraints.

[0057] The distributed secondary control provided by the present invention is suitable for controlling a single-bus island microgrid. For a single-bus island microgrid, the distributed secondary control provided by the present invention can be directly used for control. For a multi-bus microgrid, it can be divided into multiple single-bus island microgrids according to the buses therein, and then the distributed secondary control can be executed separately.

[0058] The distributed secondary control provided by the present invention is based on the characteristics that the bus voltage and reactive power in the microgrid influence each other, and the frequency and active power influence each other. A voltage-reactive mixed error and a frequency-active mixed error are designed, and the control signal of each inverter is determined based on the designed mixed error. The relevant design process of the controller is explained below.

[0059] In a single bus island AC microgrid, if the output voltage of the i-th DC / AC inverter is V i ∠φ i , i=1,…,N, N represents the total number of inverters; the AC bus voltage is V bus ∠0, the impedance of the transmission line is Z i ∠θ i =R i +jX i , then the power flow equation from the i-th DC / AC converter to the AC bus can be described as:

[0060]

[0061] Among them, φ i Represents the phase difference, R i Represents resistance, X i represents the reactance, θ i Represents the phase angle.

[0062] In an AC microgrid, the line impedance is approximately pure inductive, θ i ≈90°. The phase angle deviation between the inverter voltage and the AC bus voltage is very small, φ i ≈0. Therefore, the power flow equation can be approximately simplified as:

[0063]

[0064] Obviously, the phase difference φ v There is a proportional relationship between active power, amplitude and reactive power. Therefore, the droop control equation can be expressed as:

[0065]

[0066] Among them, w i is the frequency of the i-th DC / AC converter after droop control; and are the d-axis and q-axis voltages output by droop control; w ni and V ni are the reference values ​​of the output frequency and voltage of the i-th DC / AC converter; m i and n i is the droop coefficient.

[0067] Under ideal control conditions, the bus voltage V bus Equal to the rated value of the bus voltage V * , and each inverter of the microgrid outputs reactive power in proportion, that is, n1Q2=n2Q2=…=n N Q N ,. Among them, n i represents the reactive power droop system of the i-th inverter, Q i represents the reactive power of the i-th inverter, i=1,…,N.

[0068] According to the above control objectives, the present invention defines the voltage error and reactive error as:

[0069] e v =V bus -V *

[0070]

[0071] Among them, a ij represents the edge weight in the communication network graph, V bus Indicates the current bus voltage, V * Indicates the rated value of the bus voltage; Q i and Q j The table shows the reactive power output by the i-th inverter and the j-th inverter, q(Q i ) and q(Q j ) represent Q i and Q j The quantitative value of n i and n j represent the reactive power droop coefficients of the i-th inverter and the j-th inverter respectively.

[0072] Therefore, the voltage-reactive mixed error function is designed as:

[0073]

[0074] Among them, α i ,β i ∈R + .

[0075] Based on the voltage-reactive power mixed error designed by the present invention, the present invention can simultaneously realize accurate voltage regulation and proportional distribution of reactive power, thereby saving control resources.

[0076] Furthermore, under ideal control, the frequency output by each inverter is equal to the rated frequency w * , and each inverter in the microgrid outputs active power in proportion, that is, m1P2=m2P2=…=m N P N ,. Among them, m i represents the active power droop system of the i-th inverter, P i represents the active power of the i-th inverter, i=1,…,N.

[0077] According to the above control objectives, the present invention defines the frequency error and the active power error as:

[0078]

[0079]

[0080] Among them, P i and P j The table shows the reactive power output by the i-th inverter and the j-th inverter, q(P i ) and q(P j ) represent P i and P j The quantitative value of m i and m j They represent the active power droop coefficients of the i-th inverter and the j-th inverter respectively.

[0081] Therefore, the frequency active mixed error function is designed as:

[0082]

[0083] Among them, α i ′,β i ′∈R + .

[0084] Based on the frequency-active power mixed error designed by the present invention, accurate frequency regulation and proportional distribution of active power can be achieved simultaneously, thereby saving control resources.

[0085] Based on the proposed reactive mixed error and frequency active mixed error, the secondary voltage and frequency control signals based on the quantized state signal can be given by:

[0086]

[0087] Based on the above voltage and frequency control signals, in the present invention, the voltage regulation adopts non-droop control, and the frequency primary regulation adopts Pf droop control. The reference voltage transmitted to the double closed-loop PI controller and reference frequency It provides an interface for regulating the entire AC microgrid. The reference voltage and reference frequency are designed as:

[0088]

[0089] Based on the above controller design method, on the one hand, precise voltage regulation and reactive power distribution can be achieved simultaneously, and precise frequency regulation and active power distribution can be achieved simultaneously, effectively saving control resources; on the other hand, based on the designed voltage-reactive mixed error, the voltage can be controlled without droop, which can reduce the bus voltage and frequency offset while achieving proportional power distribution of distributed power sources, thereby ensuring the normal operation of the load.

[0090] The following are examples.

[0091] Embodiment 1:

[0092] A secondary control method for an isolated island microgrid based on voltage-reactive mixed error comprises: dividing each bus and the inverter connected to the bus in the isolated island microgrid into a control object, and performing distributed secondary regulation on each control object respectively; Figure 2 As shown in the figure, distributed secondary control includes:

[0093] Obtain the real-time status data quantization value uploaded by each inverter in the current control object from the communication network of the isolated microgrid, and obtain the bus voltage V bus ; The quantized value of the state data includes the quantized active power, reactive power and frequency of the inverter;

[0094] For the i-th inverter, calculate its voltage-reactive mixed error Sum frequency active mixed error And follow Calculating the voltage control signal and frequency control signal i=1, 2...N, N represents the total number of inverters in the current control object;

[0095] according to Calculate the reference voltage of the i-th inverter and reference frequency Then double closed-loop PI control is performed to obtain the PWM signal for controlling the i-th inverter, and the PWM signal acts on the i-th inverter to achieve secondary control;

[0096] in, Including bus voltage V busWith bus voltage rating V * The error between the reactive power of the ith inverter and its neighboring nodes; Including the frequency w of the i-th inverter i With frequency rating w * The error between and the error between active power; P i represents the active power of the i-th inverter, m i represents the active droop coefficient of the i-th inverter; represents the frequency coupling gain, represents the frequency difference between the ith inverter and its neighbor nodes; the neighbor node of the ith inverter represents the inverter node that can directly communicate with the ith inverter through the communication network.

[0097] In this embodiment, for the i-th inverter, the voltage-reactive mixed error is The expression is as follows:

[0098]

[0099] e v =V bus -V *

[0100]

[0101] Among them, α i =c vi g i , represents the voltage coupling gain; Q i and Q j denote the reactive power of the i-th inverter and the j-th inverter respectively, q(Q i ) and q(Q j ) represent Q i and Q j The quantitative value of n i and n j represent the reactive power droop coefficients of the i-th inverter and the j-th inverter respectively.

[0102] In this embodiment, for the i-th inverter, the frequency active mixed error The expression is as follows:

[0103]

[0104] in, represents the frequency coupling gain; P j represents the active power of the jth inverter, q(P i) and q(P j ) represent P i and P j The quantitative value of m i and m j They represent the active power droop coefficients of the i-th inverter and the j-th inverter respectively.

[0105] In this embodiment, the frequency difference between the i-th inverter and each of its neighboring nodes is for:

[0106]

[0107] Among them, w j represents the frequency of the jth inverter, q(w i ) and q(w j ) represent w i and w j Quantified value of .

[0108] In order to simplify the design of the quantizer while ensuring the control effect, as a preferred implementation, in this embodiment, the quantization method used for the state data quantization is uniform quantization; the calculation formula for uniform quantization is as follows:

[0109]

[0110] Among them, x i represents the signal to be quantized, q(x i ) represents x i quantization value, ε>0 is the quantization interval, and the uniform quantization error is defined as Δ i =|q(x i )-x i |, and Δ i satisfy

[0111] Embodiment 2:

[0112] A secondary controller for an islanded microgrid based on voltage-reactive hybrid error, such as Figure 1 As shown, it includes: control module and N bus Distributed secondary control devices; N bus is the number of buses in the island microgrid;

[0113] The control module is used to divide each bus and the inverter connected to the bus in the isolated microgrid into a control object, and a total of N bus Control objects;

[0114] N bus Distributed secondary control devices are used to control N bus Each control object performs distributed secondary regulation;

[0115] The distributed secondary control device includes: a communication module, a distributed control module, a voltage and frequency control module and a double closed-loop PI control module;

[0116] The communication module is used to obtain the real-time uploaded status data quantization value of each inverter in the current control object from the communication network of the isolated microgrid, and obtain the bus voltage V bus ; The quantized value of the state data includes the quantized active power, reactive power and frequency of the inverter;

[0117] The distributed control module is used to calculate the voltage control signal and frequency control signal of each inverter in the current control object; for the i-th inverter, its voltage control signal and frequency control signal They are and They represent the voltage-reactive mixed error and frequency-active mixed error of the i-th inverter respectively; Including bus voltage V bus With bus voltage rating V * The error between the reactive power of the ith inverter and its neighboring nodes; Including the frequency w of the i-th inverter i With frequency rating w * The error between the active powers; represents the frequency coupling gain, represents the frequency difference between the ith inverter and each of its neighboring nodes; the neighboring node of the ith inverter represents the inverter that can transmit information to the ith inverter through the communication network;

[0118] The voltage-frequency control module is used to calculate the reference voltage and reference frequency of each inverter in the current control object; for the i-th inverter, its reference voltage and reference frequency They are P i represents the active power of the i-th inverter, m i represents the active droop coefficient of the i-th inverter;

[0119] The dual closed-loop PI control module is used to perform dual closed-loop control according to the reference voltage and reference frequency of each inverter, obtain the PWM signal of each inverter, and act on the corresponding inverter to realize secondary control.

[0120] like Figure 2 As shown, in this embodiment, for the i-th inverter, in its distributed secondary control device, the distributed control module includes: a voltage controller and a frequency controller;

[0121] The voltage controller includes:

[0122] The voltage error calculation unit has a first input terminal for receiving a bus voltage rating V * , whose second input terminal is used to receive the bus voltage V bus , which is used to convert V * With V bus Subtract and get the voltage error e v ;

[0123] The reactive power error calculation unit has a first input terminal for receiving the reactive power quantization value q(Q i ), whose second input terminal is used to receive the reactive power quantization value q(Q j ), which is used in accordance with Calculating reactive power error

[0124] A voltage-reactive mixed error calculation unit, wherein the first input end is connected to the output end of the voltage error calculation unit, and the second input end is connected to the output end of the reactive error calculation unit, and is used to calculate the voltage-reactive mixed error according to the voltage-reactive mixed error calculation unit. Calculate voltage and reactive mixed error

[0125] and a first integrating unit, whose input terminal is connected to the output terminal of the voltage-reactive mixed error calculating unit, and which is used to calculate the voltage-reactive mixed error according to Calculate the voltage control signal of the i-th inverter

[0126] The frequency controller includes:

[0127] The frequency error calculation unit has a first input terminal for receiving the frequency quantization value q(w i ), whose second input terminal is used to receive the frequency rated value w * , which is used to convert w * and q(w i ) to obtain the frequency error

[0128] The active power error calculation unit has a first input terminal for receiving the active power quantization value q(P i ), whose second input terminal is used to receive the active power quantization value q(P j ), which is used in accordance with Calculating Active Power Error

[0129] The frequency difference calculation unit has a first input terminal for receiving the frequency quantization value q(wi ), whose second input terminal is used to receive the frequency quantization value q(w j ), which is used in accordance with Calculate the frequency difference between the i-th inverter and each of its neighboring nodes;

[0130] A frequency-active mixed error calculation unit, wherein the first input end is connected to the output end of the frequency error calculation unit, and the second input end is connected to the output end of the active error calculation unit, and is used to calculate the active power according to the frequency error calculation unit. Calculate frequency active mixed error;

[0131] and a second integrating unit, whose first input terminal is connected to the output terminal of the frequency active mixed error calculating unit, whose second input terminal is connected to the output terminal of the frequency difference calculating unit, and which is used to calculate the frequency difference according to the frequency active mixed error calculating unit. Calculate the frequency control signal of the i-th inverter

[0132] In this embodiment, the specific implementation of each module can refer to the description in the above embodiment 1 and will not be repeated here.

[0133] Embodiment 2:

[0134] An isolated island microgrid system includes: an isolated island microgrid, and the secondary controller of the isolated island microgrid based on voltage-reactive mixed error provided in the above-mentioned embodiment 2.

[0135] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A secondary control method for an island microgrid based on voltage-reactive mixed error, characterized in that: include: Divide each bus and the inverter connected to the bus in the isolated microgrid into a control object, and perform distributed secondary regulation on each control object respectively; The distributed secondary control includes: The real-time uploaded status data quantization value of each inverter in the current control object is obtained from the communication network of the isolated microgrid, and the bus voltage V bus ; The state data quantization value includes the quantized active power, reactive power and frequency of the inverter; For the i-th inverter, calculate its voltage-reactive mixed error Sum frequency active mixed error And follow Calculating the voltage control signal and frequency control signal N represents the total number of inverters in the current control object; according to Calculate the reference voltage of the i-th inverter and reference frequency Then double closed-loop PI control is performed to obtain the PWM signal for controlling the i-th inverter, and the PWM signal acts on the i-th inverter to achieve secondary control; in, Including bus voltage V bus With bus voltage rating V * The error between the reactive power of the ith inverter and its neighboring nodes; Including the frequency w of the i-th inverter i With frequency rating w * The error between and the error between active power; P i represents the active power of the i-th inverter, m i represents the active droop coefficient of the i-th inverter; represents the frequency coupling gain, represents the frequency difference between the ith inverter and each of its neighboring nodes; the neighboring node of the ith inverter represents the inverter node that can directly communicate with the ith inverter through the communication network.

2. The secondary control method of an isolated island microgrid based on voltage-reactive mixed error according to claim 1, characterized in that: The communication network is an undirected graph containing M+1 nodes, wherein the M+1 nodes correspond to the M inverters and a leader node in the isolated island microgrid respectively; the fixed gain between the leader node and the i-th inverter is g i , if there is a communication link between the leader node and the i-th inverter, then g i >0, otherwise, g i =0; if the jth inverter can transmit information to the ith inverter, there is an edge between the corresponding node pairs, and the edge weight is a ij > 0, otherwise, there is no edge between the corresponding node pairs, and the edge weight is a ij =0; Represents a set of neighbor nodes of a node corresponding to the i-th inverter in the communication network; and, yes v =V bus -V * Among them, α i =c vi g i , represents the voltage coupling gain; Q i and Q j denote the reactive power of the i-th inverter and the j-th inverter respectively, q(Q i ) and q(Q j ) represent Q i and Q j The quantitative value of n i and n j represent the reactive power droop coefficients of the i-th inverter and the j-th inverter respectively.

3. The secondary control method of an isolated island microgrid based on voltage-reactive mixed error according to claim 2, characterized in that: in, represents the frequency coupling gain; P j represents the active power of the jth inverter, q(P i ) and q(P j ) represent P i and P j The quantitative value of m i and m j They represent the active power droop coefficients of the i-th inverter and the j-th inverter respectively.

4. The secondary control method of an isolated island microgrid based on voltage-reactive mixed error according to claim 3, characterized in that: Among them, w j represents the frequency of the jth inverter, q(w i ) and q(w j ) represent w i and w j Quantified value of .

5. The secondary control method of an isolated island microgrid based on voltage-reactive mixed error according to any one of claims 1 to 3, characterized in that: The quantization method used for state data quantization is uniform quantization.

6. A secondary controller for an island microgrid based on voltage-reactive hybrid error, characterized in that: include: Control module and N bus A distributed secondary control device; N bus is the number of buses in the island microgrid; The control module is used to divide each bus and the inverter connected to the bus in the isolated island microgrid into a control object, and a total of N bus Control objects; The N bus A distributed secondary control device is used to control the N bus Each control object performs distributed secondary regulation; The distributed secondary control device includes: a communication module, a distributed control module, a voltage and frequency control module and a double closed-loop PI control module; The communication module is used to obtain the state data quantization value uploaded in real time by each inverter in the current control object from the communication network of the isolated microgrid, and obtain the bus voltage V bus ; The state data quantization value includes the quantized active power, reactive power and frequency of the inverter; The distributed control module is used to calculate the voltage control signal and frequency control signal of each inverter in the current control object; for the i-th inverter, its voltage control signal and frequency control signal They are and They represent the voltage-reactive mixed error and frequency-active mixed error of the i-th inverter respectively; Including bus voltage V bus With bus voltage rating V * The error between the reactive power of the ith inverter and its neighboring nodes; Including the frequency w of the i-th inverter i With frequency rating w * The error between the active powers; represents the frequency coupling gain, represents the frequency difference between the ith inverter and each of its neighboring nodes; the neighboring node of the ith inverter represents an inverter node that can directly communicate with the ith inverter through the communication network; The voltage-frequency control module is used to calculate the reference voltage and reference frequency of each inverter in the current control object; for the i-th inverter, its reference voltage and reference frequency They are P i represents the active power of the i-th inverter, m i represents the active droop coefficient of the i-th inverter; The dual closed-loop PI control module is used to perform dual closed-loop control according to the reference voltage and reference frequency of each inverter, obtain the PWM signal of each inverter, and act on the corresponding inverter to achieve secondary control.

7. The secondary controller of the isolated island microgrid based on voltage-reactive mixed error according to claim 6, characterized in that: The communication network is an undirected graph containing M+1 nodes, wherein the M+1 nodes correspond to the M inverters and a leader node in the isolated island microgrid respectively; the fixed gain between the leader node and the i-th inverter is g i , if there is a communication link between the leader node and the i-th inverter, then g i >0, otherwise, g i =0; if the jth inverter can transmit information to the ith inverter, there is an edge between the corresponding node pairs, and the edge weight is a ij > 0, otherwise, there is no edge between the corresponding node pairs, and the edge weight is a ij =0; Represents a set of neighbor nodes of a node corresponding to the i-th inverter in the communication network; Furthermore, for the i-th inverter, in its distributed secondary control device, the distributed control module includes: a voltage controller and a frequency controller; The voltage controller comprises: The voltage error calculation unit has a first input terminal for receiving a bus voltage rating V * , whose second input terminal is used to receive the bus voltage V bus , which is used to convert V * With V bus Subtract and get the voltage error e v ; The reactive power error calculation unit has a first input terminal for receiving the reactive power quantization value q(Q i ), whose second input terminal is used to receive the reactive power quantization value q(Q j ), which is used in accordance with Calculating reactive power error A voltage-reactive mixed error calculation unit, wherein the first input end is connected to the output end of the voltage error calculation unit, and the second input end is connected to the output end of the reactive error calculation unit, and is used to calculate the voltage-reactive mixed error according to the output end of the voltage error calculation unit. Calculate voltage and reactive mixed error and a first integrating unit, whose input end is connected to the output end of the voltage-reactive mixed error calculating unit, and which is used to calculate the voltage-reactive mixed error according to Calculate the voltage control signal of the i-th inverter The frequency controller comprises: The frequency error calculation unit has a first input terminal for receiving the frequency quantization value q(w i ), whose second input terminal is used to receive the frequency rated value w * , which is used to convert w * and q(w i ) to obtain the frequency error The active power error calculation unit has a first input terminal for receiving the active power quantization value q(P i ), whose second input terminal is used to receive the active power quantization value q(P j ), which is used in accordance with Calculating Active Power Error The frequency difference calculation unit has a first input terminal for receiving the frequency quantization value q(w i ), whose second input terminal is used to receive the frequency quantization value q(w j ), which is used in accordance with Calculate the frequency difference between the i-th inverter and each of its neighboring nodes; A frequency-active mixed error calculation unit, whose first input end is connected to the output end of the frequency error calculation unit, and whose second input end is connected to the output end of the active error calculation unit, is used to calculate the active power according to the frequency error calculation unit. Calculate frequency active mixed error; and a second integrating unit, whose first input end is connected to the output end of the frequency active mixed error calculating unit, whose second input end is connected to the output end of the frequency difference calculating unit, and which is used to calculate the frequency difference according to the frequency active mixed error calculating unit. Calculate the frequency control signal of the i-th inverter 8. An island microgrid system, characterized in that: include: An isolated island microgrid, and a secondary controller of the isolated island microgrid based on voltage-reactive mixed error as described in claim 6 or 7.

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