Secondary control method and system for islanded microgrid based on voltage and reactive power hybrid error

Abstract

The application discloses a secondary control method and system of an island micro-grid based on voltage reactive power mixed error, belongs to the field of AC micro-grid secondary control, and comprises the following steps: obtaining state quantitative values uploaded by each inverter in real time and bus voltage from a communication network for each bus and each inverter connected to the bus; calculating voltage reactive power mixed error and frequency active power mixed error of the i-th inverter respectively, and performing double closed-loop PI control on the calculated reference voltage and reference frequency according to the calculated voltage control signal and frequency control signal to obtain a PWM signal, and the PWM signal is applied to the i-th inverter to realize secondary control. The application can realize proportional distribution of power among distributed power supplies, compensate for the deviation of bus voltage and frequency, and ensure normal operation of the load.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of AC micro-grid secondary control, and more particularly relates to a secondary control method and system for island micro-grid based on voltage and reactive power hybrid error. BACKGROUND

[0002] With the increasing proportion of renewable energy such as wind energy and solar energy in the power grid, the traditional centralized power grid is difficult to fully adapt to the changes. The micro-grid system is a new networking form of comprehensive utilization of various distributed energy, which organically combines distributed power supply, load, energy storage unit and control device to form an independently controllable system, which is complementary to the large power grid. The distributed power supply interacts with the bus through the inverter for voltage and power.

[0003] The micro-grid appears as a single controlled source to the large power grid, overcomes the random fluctuation of energy of the traditional distributed power generation, meets the requirements of users for power quality, and has important research significance. According to the nature of the micro-grid bus voltage, it can be divided into DC micro-grid, AC micro-grid and AC / DC hybrid micro-grid. Since the AC micro-grid and the large power grid belong to the same AC power category, and have great similarity in operation and control with the conventional distribution network, the current focus of micro-grid research is still the AC micro-grid. In the island micro-grid, it is a very important problem to realize the regulation of bus voltage and frequency, and the proportional distribution of reactive power and active power output of each distributed power supply.

[0004] The traditional droop control can realize the power distribution among the distributed power supplies, but will cause the deviation of bus voltage and frequency, and cannot guarantee the normal operation of the load. SUMMARY

[0005] In view of the defects and improvement needs of the prior art, the present application provides a secondary control method and system for island micro-grid based on voltage and reactive power hybrid error, which aims to realize the proportional distribution of power among the distributed power supplies while compensating for the deviation of bus voltage and frequency to ensure the normal operation of the load.

[0006] To achieve the above-mentioned purpose, according to one aspect of the present application, a secondary control method for island micro-grid based on voltage and reactive power hybrid error is provided, comprising: dividing each bus in the island micro-grid and the inverter connected to the bus into one control object, and respectively executing distributed secondary regulation on each control object; the distributed secondary regulation comprises:

[0007] obtaining the state data quantization value uploaded by each inverter in the current control object in real time from the communication network of the island micro-grid, and obtaining the bus voltage V bus ; the state data quantization value includes the quantized active power, reactive power and frequency of the inverter;

[0008] For the i-th inverter, calculate its voltage and reactive mixed error respectively Sum frequency active mixed error And follow Calculating the voltage control signal and frequency control signal i=1, 2...N, where 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 is applied to the i-th inverter to achieve secondary control.

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

[0011] Furthermore, the communication network is an undirected graph containing M+1 nodes, where the M+1 nodes correspond to the M inverters and a leader node in the island 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 quantized 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] Furthermore,

[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 quantized value, m i and m j represent the active power droop coefficients of the i-th inverter and the j-th inverter respectively.

[0020] Furthermore,

[0021] Among them, w j represents the frequency of the j-th inverter, q(w i ) and q(w j ) represent w i and w j quantized 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 mixed 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 island 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 dual closed-loop PI control module;

[0027] The communication module is used to obtain the real-time status data quantification 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;

[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 them and the error between the reactive power of the i-th 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 i-th inverter and its neighbor nodes; the neighbor nodes of the i-th inverter represent the inverters that can transmit information to the i-th 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 power droop coefficient of the i-th inverter;

[0030] The dual closed-loop PI control module is used to perform dual closed-loop control based on 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.

[0031] Furthermore, the communication network is an undirected graph containing M+1 nodes, where the M+1 nodes correspond to the M inverters and a leader node in the island 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 * , its second input terminal is used to receive the bus voltage V bus , which is used to 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] The voltage-reactive mixed error calculation unit has a first input terminal connected to the output terminal of the voltage error calculation unit, and a second input terminal connected to the output terminal of the reactive 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, which is used to calculate the voltage-reactive mixed error according to the 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 * With 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] The frequency and active power mixed error calculation unit has a first input end connected to the output end of the frequency error calculation unit and a second input end connected to the output end of the active power error calculation unit, and is used to calculate the active power mixed error according to the frequency and active power mixed 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, and whose second input terminal is connected to the output terminal of the frequency difference calculating unit, for calculating the active mixed error according to the frequency difference 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 mixed 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, it can simultaneously realize precise voltage regulation and reactive power distribution, and simultaneously realize precise frequency regulation and active power distribution, 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 offset 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 the 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 Schematic diagram of a secondary control system of an island microgrid based on voltage-reactive mixed 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 objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining 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 may 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 drawings are used to distinguish similar objects and are not necessarily used 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 island microgrid is briefly introduced.

[0054] In an island microgrid, distributed power sources exchange information through DC / AC bidirectional inverters, and the total number of inverters is N. To describe an AC microgrid containing N DC / AC inverters and a leader node, the leader node is a virtual node set. where V = {v1, …, v N} represents the set 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 set of adjacent nodes of node i is denoted as The in-degree matrix is set as where The Laplacian matrix is defined as At the same time, the fixed gain of the leader node to the i-th DC / AC inverter is set as g i , if there is a communication link between the leader node and the inverter, g i > 0; otherwise, g i = 0. is a diagonal matrix with the diagonal being the fixed gain, is denoted as a set of positive real numbers.

[0055] In practical applications, the neighbor node information of each inverter changes rapidly, which makes the communication network bear a heavy burden of transmitting information. In order to alleviate the information transmission burden of the communication network, the existing control method often simultaneously uses state quantization combined with event triggering, that is, only the discrete values after state quantization are transmitted in the communication network to reduce the bandwidth occupation, and information transmission is only performed at the event triggering time to reduce the communication frequency. However, the present application has found through research that for a microgrid system, stability and safety are extremely important, the implementation of the event triggering mechanism needs to consume certain control resources and the selection of the triggering threshold is greatly affected by system parameters, which is difficult to realize in actual use, and at the same time, the control resources in the microgrid system are often very scarce, which makes it difficult to alleviate the bandwidth pressure of the communication network while losing the control performance of the system through the event triggering mechanism.

[0056] In view of the above problems, the present application only uses a quantization method to make each inverter upload the quantized state information in real time, at the same time, the controller obtains the state quantization information of each inverter from the communication network in real time, and controls each inverter based on the distributed quadratic regulation provided by the present application, and the experimental results show that the present application can effectively improve the stability of the control under the condition of meeting the communication bandwidth constraint.

[0057] The distributed secondary regulation provided by the application is suitable for controlling single-bus island micro-grid; for single-bus island micro-grid, the distributed secondary regulation provided by the application can be directly used for control, and for multi-bus micro-grid, the multi-bus micro-grid can be divided into multiple single-bus island micro-grids according to the buses, and then the distributed secondary regulation is respectively executed.

[0058] The distributed secondary regulation provided by the application is based on the characteristics that the bus voltage and the reactive power in the micro-grid affect each other, and the frequency and the active power affect each other, a voltage-reactive power mixed error is designed, a frequency-active power mixed error is designed, and the control signals of each inverter are determined based on the designed mixed error, and the related design process of the controller is explained below.

[0059] In single-bus island AC micro-grid, 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] Wherein, φ i represents the phase difference, R i represents the resistance, X i represents the reactance, and θ i represents the phase angle.

[0062] In the AC micro-grid, the line impedance is approximately purely 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 and the active power, the amplitude and the reactive power have a proportional relationship. Therefore, the droop control equation can be expressed as:

[0065]

[0066] Wherein, 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 quantized 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 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 quantized value, m i and m j 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 hybrid 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 the following equations:

[0086]

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

[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] Example 1:

[0092] A secondary control method for an island microgrid based on voltage-reactive mixed error includes: dividing each bus and the inverter connected to the bus in the 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 quantification 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 and reactive mixed error respectively Sum frequency active mixed error And follow Calculating the voltage control signal and frequency control signal i=1, 2...N, where 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 is applied to the i-th inverter to achieve secondary control.

[0096] in, Including bus voltage V busWith bus voltage rating V * The error between them and the error between the reactive power of the i-th inverter and its neighboring nodes; Including the frequency w of the i-th inverter i With frequency rating w * The error between the active power and the error between the active power; i represents the active power of the i-th inverter, m i represents the active power droop coefficient of the i-th inverter; represents the frequency coupling gain, represents the frequency difference between the i-th inverter and its neighbor nodes; the neighbor nodes of the i-th inverter represent the inverter nodes that can directly communicate with the i-th 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 quantized 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 j-th inverter, q(P i) and q(P j ) represent P i and P j The quantized value, m i and m j 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 its neighboring nodes is for:

[0106]

[0107] Among them, w j represents the frequency of the j-th inverter, q(w i ) and q(w j ) represent w i and w j quantized 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 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] Example 2:

[0112] A secondary controller for islanded microgrid based on voltage-reactive mixed error, such as Figure 1 As shown, including: 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 island 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 dual closed-loop PI control module;

[0116] The communication module is used to obtain the real-time status data quantification 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;

[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 them and the error between the reactive power of the i-th 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 i-th inverter and its neighbor nodes; the neighbor nodes of the i-th inverter represent the inverters that can transmit information to the i-th 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 power droop coefficient of the i-th inverter;

[0119] The dual closed-loop PI control module is used to perform dual closed-loop control based on 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.

[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 * , its second input terminal is used to receive the bus voltage V bus , which is used to 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 to Calculating reactive power error

[0124] The voltage-reactive mixed error calculation unit has a first input terminal connected to the output terminal of the voltage error calculation unit, and a second input terminal connected to the output terminal of the reactive 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, which is used to calculate the voltage-reactive mixed error according to the 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 * With 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 to 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 to Calculate the frequency difference between the i-th inverter and each of its neighboring nodes;

[0130] The frequency and active power mixed error calculation unit has a first input end connected to the output end of the frequency error calculation unit and a second input end connected to the output end of the active power error calculation unit, and is used to calculate the active power mixed error according to the frequency and active power mixed 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, and whose second input terminal is connected to the output terminal of the frequency difference calculating unit, for calculating the active mixed error according to the frequency difference 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] Example 2:

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

[0135] It will be easily understood by those skilled in the art that the above description is merely 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 scope of protection of the present invention.

Claims

1. A secondary control method for an island microgrid based on voltage-reactive mixed error, characterized in that: include: Dividing each bus and the inverter connected to the bus in the island microgrid into a control object, and performing distributed secondary regulation on each control object respectively; The distributed secondary control includes: The real-time status data quantization value uploaded by each inverter in the current control object is obtained from the communication network of the isolated microgrid, and the bus voltage V is obtained. bus ; The quantized value of the state data includes the quantized active power, reactive power and frequency of the inverter; For the i-th inverter, calculate its voltage and reactive mixed error respectively 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 is applied to the i-th inverter to achieve secondary control. in, Including bus voltage V bus With bus voltage rating V * The error between them and the error between the reactive power of the i-th inverter and its neighboring nodes; Including the frequency w of the i-th inverter i With frequency rating w * The error between the active power and the error between the active power; i represents the active power of the i-th inverter, m i represents the active power droop coefficient of the i-th inverter; represents the frequency coupling gain, represents the frequency difference between the i-th inverter and each of its neighboring nodes; the neighboring node of the i-th inverter represents the inverter node that can directly communicate with the i-th inverter through the communication network.

2. The secondary control method of an 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 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 the 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 quantized 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 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 quantized value, m i and m j represent the active power droop coefficients of the i-th inverter and the j-th inverter respectively.

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

5. The secondary control method of an 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 mixed 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 island microgrid into a control object, and a total of N bus Control objects; The N bus Distributed secondary control devices are 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 dual closed-loop PI control module; The communication module is used to 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; 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 them and the error between the reactive power of the i-th 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 i-th inverter and each of its neighboring nodes; the neighboring node of the i-th inverter represents the inverter node that can directly communicate with the i-th 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 power 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 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 the node corresponding to the i-th inverter in the communication network; Moreover, 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 * , its second input terminal is used to receive the bus voltage V bus , which is used to 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 to Calculating reactive power error A voltage-reactive mixed error calculation unit, wherein the first input terminal is connected to the output terminal of the voltage error calculation unit, and the second input terminal is connected to the output terminal 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 and a first integrating unit, whose input end is connected to the output end of the voltage-reactive mixed error calculating unit, which is used to calculate the voltage-reactive mixed error according to the output end of the voltage-reactive mixed error calculating unit. 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 * With 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 to Calculate the frequency difference between the i-th inverter and each of its neighboring nodes; A frequency and active power mixed error calculation unit, wherein the first input terminal is connected to the output terminal of the frequency error calculation unit, and the second input terminal is connected to the output terminal of the active power error calculation unit, and is used to calculate the active power mixed error according to the frequency and active power mixed error calculation unit. Calculate frequency active mixed error; and a second integrating unit, the first input of which is connected to the output of the frequency active mixed error calculating unit, the second input of which is connected to the output of the frequency difference calculating unit, and the second integrating unit is used to calculate the frequency active mixed error according to the frequency difference calculating unit. Calculate the frequency control signal of the i-th inverter 8. An island microgrid system, characterized in that: include: An island microgrid, and a secondary controller for an island microgrid based on voltage-reactive mixed error as described in claim 6 or 7.

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