Centralized multi-bus DC micro-grid secondary control system and method

Abstract

The invention provides a centralized multi-bus DC micro-grid secondary control system and method, and the method comprises the steps: carrying out the primary control of the voltage of a corresponding DC bus through droop control and voltage and current double-closed-loop control, so as to guarantee that the output voltage of a local converter tracks the reference voltage in real time; and performing secondary control on the DC micro-grid by using a secondary control signal which is a difference value between the virtual voltage drop of the local converter and an integral of an error between the virtual voltage drop of the local converter and the mean value of the virtual voltage drops of all the converters, so that the average bus voltage is adjusted to a voltage rated value. According to the invention, for the multi-bus DC micro-grid comprising a plurality of buses, centralized control is carried out by using the virtual voltage drop of the converter and the mean value of all the virtual voltage drops, and effective average bus voltage regulation and load current sharing are realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC microgrid control, and specifically relates to a centralized multi-bus DC microgrid secondary control system and method. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention, and do not necessarily constitute prior art.

[0003] As a flexible energy system integrating renewable energy, distributed energy storage, and various loads, DC microgrids show great potential in improving energy utilization efficiency and enhancing grid resilience. However, due to the continuous expansion of the access scale of renewable energy and the influence of various control circuits and topologies, the commonly used droop control method cannot simultaneously meet voltage restoration and current sharing, easily causing voltage and current fluctuations, resulting in a decrease in control accuracy, and problems such as overcurrent, bus voltage drop, and inaccurate current distribution.

[0004] Some research scholars have proposed some solutions. However, they are generally only applicable to microgrid systems with a single DC bus. Due to the existence of line impedance between buses in a multi-bus DC microgrid, there is an irreconcilable contradiction between bus voltage restoration and load current sharing, that is, it is impossible to simultaneously adjust the voltages of all buses to the nominal value and achieve current sharing.

[0005] On the other hand, current existing solutions require the current information of the converter and the corresponding bus voltage information. However, in an actual operating environment, it is often challenging to obtain the bus voltage; and the information that the converter needs to obtain often includes the current information of the converter, the bus voltage information, or the average value of the estimated bus voltage, etc. This often requires a higher communication bandwidth in scenarios that require communication, which often exacerbates the communication burden of the communication network. The control objectives in a DC microgrid mainly include bus voltage regulation and load current sharing.

[0006] In addition, for a multi-bus DC microgrid, due to the inevitable contradiction between bus voltage regulation and load current sharing, bus voltage regulation often cannot restore the voltage on each bus to the nominal value, which is difficult to control. Summary of the Invention

[0007] To solve the above problems, the present invention proposes a centralized multi-bus DC microgrid secondary control system and method. For a multi-bus DC microgrid including multiple buses, the present invention uses the virtual voltage drop of the converter and the average value of all virtual voltage drops for centralized control to achieve effective average bus voltage regulation and load current sharing.

[0008] According to some embodiments, the present invention adopts the following technical solutions:

[0009] A secondary control system for a centralized multi-bus DC microgrid, which is applied to a microgrid including multiple DC buses. Adjacent DC buses are connected through circuit impedance. A converter is provided on each DC bus, and each converter is configured with a controller. The controllers communicate with each other. Each controller includes:

[0010] A primary control unit for performing primary control on the voltage of the corresponding DC bus through droop control and voltage-current double closed-loop control to ensure that the output voltage of the local converter tracks the reference voltage in real time;

[0011] A secondary control unit for performing secondary control on the DC microgrid with a secondary control signal to adjust the average bus voltage to the rated voltage value. The secondary control signal is the difference between the virtual voltage drop of the local converter and the integral of the error between the virtual voltage drop of the local converter and the average value of the virtual voltage drops of all converters.

[0012] As an alternative implementation, each converter is connected to a central controller through a communication network. The central controller is used to receive the virtual voltage drop information of all converters, calculate the average value of the virtual voltage drops of all converters, and then send it back to each converter.

[0013] As an alternative implementation, the process of the primary control unit for performing primary control on the voltage of the corresponding DC bus through droop control and voltage-current double closed-loop control includes that the primary control unit adopts droop control to generate a reference voltage;

[0014] Adopt voltage-current double closed-loop PI control so that the output voltage of the converter can track the converter reference voltage without error. Based on the error between the output voltage and the reference voltage, calculate the reference current through voltage PI control. Based on the error between the output current and the reference current, output a PWM control signal through current PI control.

[0015] As an alternative implementation, the secondary control signal is specifically:

[0016]

[0017] where k i represents the droop coefficient in the droop control function of the converter on the i-th bus, R i and I i respectively represent the line resistance and output current between the converter on the i-th bus and the i-th DC bus, is the virtual voltage drop of the converter on the i-th bus, represents the average of the virtual voltage drops of all converters obtained by the central controller, n is the number of converters, and u i is the secondary control signal of the converter on the i-th bus.

[0018] As an alternative implementation, when the secondary control unit performs secondary control on the DC microgrid with the secondary control signal to adjust the average bus voltage to the rated voltage value, the bus voltage after compensating the secondary control signal is:

[0019]

[0020] where represents the bus voltage after compensating the secondary control signal, Vref is the rated voltage value, u i is the secondary control signal of the converter on the i-th bus, and k i represents the droop coefficient in the droop control function of the converter on the i-th bus, R i and I i respectively represent the line resistance and output current between the converter on the i-th bus and the i-th DC bus.

[0021] A centralized multi-bus DC microgrid secondary control method is applied to a microgrid including multiple DC buses. Adjacent DC buses are connected through circuit impedance. A converter is provided on each DC bus, and the method includes the following steps:

[0022] Perform primary control on the voltage of the corresponding DC bus through droop control and voltage-current double closed-loop control to ensure that the output voltage of the local converter tracks the reference voltage in real time;

[0023] Perform secondary control on the DC microgrid with the secondary control signal to adjust the average bus voltage to the rated voltage value. The secondary control signal is the difference between the virtual voltage drop of the local converter and the integral of the error between it and the average of the virtual voltage drops of all converters.

[0024] A computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by a processor, the steps in the above method are completed.

[0025] An electronic device includes a memory, a processor, and computer instructions stored on the memory and running on the processor. When the computer instructions are run by the processor, the steps in the above method are completed.

[0026] A computer program product includes a computer program, characterized in that when the computer program is executed by a processor, the steps in the above method are implemented.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] Compared with the traditional droop control, the converter communicates with the central controller and realizes the average bus voltage regulation and load current sharing of the multi-bus DC microgrid including multiple buses through a secondary controller designed based on the local virtual voltage drop and the average value of the virtual voltage drop.

[0029] Existing control methods for multi-bus DC microgrids often require measuring the bus voltage, which is often difficult to directly obtain in actual operation. Based on the concept of virtual voltage drop, the present invention proposes a secondary controller. Compared with existing research, it does not require direct measurement of the bus voltage, and since only one variable needs to be exchanged with the central controller, it further reduces the need for communication bandwidth and alleviates the communication burden; the control goal can be achieved without the feedback of the bus voltage.

[0030] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given and described in detail in conjunction with the accompanying drawings. Brief Description of the Drawings

[0031] The schematic diagrams of the specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0032] Figure 1 It is a schematic diagram of the topology structure of a multi-bus DC microgrid in an embodiment;

[0033] Figure 2 It is a schematic diagram of the secondary control of a multi-bus DC microgrid in an embodiment;

[0034] Figure 3(a) is a diagram of the bus voltage result in the case of a step-change resistive load in an embodiment;

[0035] Figure 3(b) is a diagram of the converter output current result in the case of a step-change resistive load in an embodiment;

[0036] Figure 3(c) is a diagram of the average bus voltage result in the case of a step-change resistive load in an embodiment;

[0037] Figure 4(a) is a diagram of the bus voltage result in the case of a constant power load in an embodiment;

[0038] Figure 4(b) is a diagram of the converter output current result in the case of a constant power load in an embodiment;

[0039] Figure 4(c) is a diagram of the average bus voltage result in the case of a constant power load in an embodiment;

[0040] Figure 5(a) is a diagram of the bus voltage result in the case of bus plugging and unplugging in an embodiment;

[0041] Figure 5(b) is a graph showing the converter output current results in the case of bus plugging and unplugging for an embodiment;

[0042] Figure 5(c) is a graph showing the average bus voltage results in the case of bus plugging and unplugging for an embodiment. Detailed implementation manners

[0043] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0044] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0045] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0046] In the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0047] Embodiment 1

[0048] A centralized multi-bus DC microgrid secondary control method is applied to a multi-bus DC microgrid including multiple DC buses, where each DC bus is connected through a circuit impedance, and each DC bus includes a converter and a load unit. Through the controllers provided on each converter, hierarchical control of the primary controller and the secondary control of the multi-bus DC microgrid is performed, specifically as follows:

[0049] Adopt preset PI control parameters, and through droop control and voltage-current double-loop PI control, perform primary control on the voltage of each bus to ensure that the output voltage of the converter tracks the reference voltage in real time;

[0050] Based on the virtual voltage drop of the converter and the average value of the virtual voltage drops of all converters, calculate the secondary control signal for compensating the bus voltage deviation and ensuring the equal sharing of the load current, and perform secondary control on the DC microgrid to adjust the average bus voltage to the rated voltage value.

[0051] The converter in this embodiment can be a DC-DC converter or an AC-DC converter.

[0052] A secondary control method for a centralized multi-bus DC microgrid in this embodiment is based on the virtual voltage drop and the average value of the virtual voltage drop to effectively regulate the average bus voltage and equalize the load currents in a multi-bus DC microgrid with multiple DC buses. The specific implementation process is as follows:

[0053] The control object of this embodiment is a multi-bus DC microgrid, which is composed of multiple DC buses connected through line impedances, and each DC bus includes a converter and a load unit.

[0054] The hierarchical control is to set a secondary control unit (or called secondary controller) on the primary control unit of each converter, connect each converter to the communication network, so that it can realize the information interaction between the local virtual voltage drop and the average value of the virtual voltage drop with the central controller, and thus obtain the secondary control signal: and update the DC bus voltage and the output voltage of the converter to track the reference voltage according to the secondary control signal; among them, the definition process of the secondary control signal is to define the secondary control signal as the difference between the average value of the virtual voltage drop and the integral of the error between the local virtual voltage drop and the virtual voltage drop by introducing the virtual voltage drop.

[0055] Based on the topology of the multi-bus DC microgrid, the droop gain of the converters on the bus, the DC bus voltage, and the open-loop DC rated voltage (i.e., the voltage rated value of the bus), the overall control objective is constructed.

[0056] Next, the topology of the multi-bus DC microgrid and the droop control and control objectives in the primary control are introduced first.

[0057] The topology of the DC microgrid is as Figure 1 shown, which includes n DC buses, and each bus includes a converter and a load unit, and the converter provides current to all load units. The primary control in the hierarchical control adopted in this embodiment mainly includes droop control and voltage-current double-loop PI control.

[0058] This invention assumes that each converter has selected appropriate voltage-current double-loop PI control parameters, so that the output voltage V i of each converter can track the reference voltage signal Among them, the droop control function of each converter can be expressed as:

[0059] V i ref =V ref -k i I i

[0060] where k iis the droop gain of the converter on the i-th bus, I i is the output current of the converter on the i-th bus.

[0061] The bus voltage on the i-th bus can be expressed as:

[0062] V b i = V i - R i I i

[0063] where Vi represents the output voltage of the converter on the i-th bus, and R i represents the line resistance from the converter on the i-th bus to the i-th DC bus.

[0064] Figure 1 shows the electrical network structure of the multi-bus DC microgrid studied in this paper. This structure is usually modeled as an undirected and strongly connected graph G e =(V e , E e ), where V e ={1, 2,..., n} represents the set of all buses in the microgrid, represents the distribution lines in the microgrid. Each element G ij ∈ E e corresponds to the line admittance between bus i and bus j. If bus i and j are connected, then G ij = G ji > 0; otherwise, G ij = G ji = 0.

[0065] Let I Li represent the load current on bus i, represent the set of other buses electrically connected to bus i. According to Kirchhoff's current law (KCL), the relationship between the voltage and current on bus i can be expressed as:

[0066]

[0067] The above expression can be written in vector form:

[0068] I - I L = L e V b

[0069] where I = [I1,..., I n T , In addition, L e represents the graph G e ​The Laplacian matrix is defined as follows: when i = j, when i ≠ j, L e (i,j) = -G ij .

[0070] According to the expression of the DC bus voltage, it can be seen that due to the existence of the droop gain and the flow of current between the buses, the control objective of restoring all bus voltages to the nominal value conflicts with the control objective of equal sharing of load currents. Moreover, as the droop gain increases, the deviation of the bus voltage will also increase. To ensure that the global bus voltage can be maintained in a good state, the voltage regulation objective is set here to restore the average bus voltage to the nominal value, and the current sharing objective is to proportionally distribute all load currents according to the capacity of the converters. The control objectives of this embodiment can be expressed as:

[0071]

[0072] where e V represents the average bus voltage regulation error.

[0073] Figure 2 Fig. is a schematic diagram of the secondary control of a multi-bus DC microgrid. By compensating the secondary control signal u i on the basis of the traditional droop control to compensate for the voltage deviation caused by the droop control without affecting the set current sharing ratio; each converter communicates with the central controller through a communication network, thereby sending local virtual voltage drop information to the central controller and receiving the average value of the virtual voltage drop calculated by the central controller. Adding the secondary control signal to the primary control layer, we can obtain:

[0074]

[0075] Furthermore, the secondary control signal can be expressed as:

[0076]

[0077] where is the virtual voltage drop of the converter on the i-th bus, represents the average value of the virtual voltage drop obtained by the central controller, and u i is the secondary control signal on the converter on the i-th bus.

[0078] According to the designed secondary control signal, Conclusion 1 can be obtained.

[0079] Conclusion 1: Through the designed controller u i , the control objectives of average bus voltage regulation and current sharing of a multi-bus DC microgrid can be achieved.

[0080] Proof:

[0081] First, substitute the secondary control signal into the bus voltage expression and sum them up, we can get:

[0082]

[0083] Therefore, the average bus voltage regulation target can be achieved. Next, it will be proved that the control target of load current sharing can also be achieved.

[0084] Substitute the secondary control signal into the topology of the multi-bus DC microgrid, we can get:

[0085]

[0086] The vector form of this equation is:

[0087] I - I L = -L e (k + R)I + L e u

[0088] For a given load, we have:

[0089]

[0090] Introduce a new error definition We have:

[0091]

[0092] Define A = Π n (k + R)I, so:

[0093] e = AI = Π n (k + R)I

[0094] Substitute the secondary control signal into the overall expression of the multi-bus microgrid, we get:

[0095]

[0096] Define B = I n + L e (k + R) and D = (k + R) -1 + L e , where D is a positive definite matrix, so B is also an invertible matrix. Therefore, we can get

[0097]

[0098] There exists a positive definite matrix Q such that:

[0099]

[0100] Consider the following Lyapunov candidate function Taking the derivative of it, we can obtain:

[0101]

[0102] Since D is a positive definite matrix, and if and only if:

[0103] L e e = L e (k + R)I = 0, Therefore, we have:

[0104]

[0105] Since k i >> R i , we can get I i / I j = k i / k i . Therefore, current sharing is achieved, and the proof is completed.

[0106] It should be noted that although many studies have investigated the control methods of multi-bus DC microgrids, they often rely on the measurement of the DC bus voltage, which is often difficult to directly obtain in actual operation. And since it is necessary to communicate the bus voltage information or the average value of the bus voltage and current information, this often requires a larger communication bandwidth, which exacerbates the communication burden to a certain extent. In contrast, a proposed centralized secondary control method for multi-bus DC microgrids does not require the bus voltage as a feedback signal, and the only information to be exchanged is the current signal, reducing the variables to be communicated and alleviating the communication burden.

[0107] Finally, three cases are simulated and verified through the Matlab / Simulink simulation platform to illustrate the effectiveness of the proposed centralized secondary control method for multi-bus DC microgrids. Consider a multi-bus DC microgrid with four buses as shown in Figure 1 , and its schematic diagram is as shown in Figure 1 . Set the parameter of the algorithm as K I = 10, and the other circuit parameters are shown in Table 1.

[0108] Table 1 Circuit parameters

[0109]

[0110]

[0111] Case 1: Step change load

[0112] First, this case evaluated the performance of the proposed secondary control method in ensuring the desired current sharing and voltage stability; specifically, the case study considered the impact of step load changes; the system went through the following four stages:

[0113] 1) Stage 1 (0 - 2 s): A 10 Ω resistive load was connected to each bus, and only droop control was implemented;

[0114] 2) Stage 2 (2 - 4 s): Secondary control was implemented;

[0115] 3) Stage 3 (4 - 6 s): The resistive load on bus 1 became 5 Ω;

[0116] 4) Stage 4 (6 - 8 s): The resistive load on bus 1 was restored to 10 Ω.

[0117] The results are shown in Fig. 3(a) - (c). It can be seen that when only primary control was used, the average bus voltage failed to meet the requirements of DC bus voltage regulation. In contrast, once the proposed secondary controller was introduced, the average bus voltage quickly rose to 48 V, and at the same time, the expected proportion of current sharing was effectively achieved. It can be concluded that even under load changes, the proposed secondary control strategy can achieve good power distribution and the regulation of the average bus voltage.

[0118] Case 2: Constant - power load

[0119] First, this case evaluated the performance of the proposed control method when connecting constant - power loads. Specifically, this case included the following four stages:

[0120] Stage 1 (0 - 2 s): A 200 - W constant - power load was connected to each bus, and only droop control was adopted;

[0121] Stage 2 (2 - 4 s): The proposed control strategy was implemented;

[0122] Stage 3 (4 - 6 s): An additional 200 - W constant - power load was connected to bus 1 and bus 3 respectively;

[0123] Stage 4 (6 - 8 s): The constant - power loads on bus 1 and bus 3 were restored to 200 W.

[0124] As shown in Fig. 4(a) - (c), the average bus voltage could not be restored when only primary control was used. And the proposed control scheme can effectively maintain the average DC bus voltage at 48 V even when the constant - power load changes, while ensuring the reasonable distribution of the total load current.

[0125] Case 3: Verification of ready - to - use ability

[0126] Stage 1 (0 - 2 s): A 10 Ω resistive load is connected to each bus, and only primary control is operating.

[0127] Stage 2 (2 - 4 s): The secondary controller starts.

[0128] Stage 3 (4 - 6 s): Bus 4 is disconnected from the system.

[0129] Stage 4 (6 - 8 s): Bus 4 is reconnected to the system.

[0130] As shown in Figs. 5(a) - (c), the simulation results of this case are presented. It can be observed that when Bus 4 is disconnected from the microgrid, its load current is rapidly redistributed among the remaining three converters; when Bus 4 is reconnected, the current among the four converters is reasonably distributed again. In addition, regardless of the connection or disconnection of the converters, the system can always maintain the average voltage regulation performance.

[0131] Embodiment 2

[0132] In one embodiment of this embodiment, a centralized multi - bus DC microgrid secondary control system is provided, which is applied to a multi - bus DC microgrid including multiple DC buses. Each DC bus is connected through a circuit impedance, and each DC bus includes a converter and a load unit. Through the controllers set on each converter, hierarchical control of primary control and secondary control is performed on the multi - bus DC microgrid, specifically:

[0133] Adopting preset PI control parameters, through droop control and voltage - current double - closed - loop PI control, primary control is performed on the voltage of each bus to ensure that the output voltage of the converter tracks the reference voltage in real - time.

[0134] Based on the virtual voltage drop of the converter and the average value of the virtual voltage drops of all converters, a secondary control signal for compensating the bus voltage deviation and ensuring equal sharing of the load current is calculated, and secondary control is performed on the DC microgrid to regulate the average bus voltage to the rated voltage value.

[0135] Embodiment 3

[0136] In one embodiment of this embodiment, a computer program product is provided, including a computer program, which when executed by a processor implements the above - mentioned centralized multi - bus DC microgrid secondary control method.

[0137] Embodiment 4

[0138] In one embodiment of this embodiment, a non-transitory computer-readable storage medium is provided. The non-transitory computer-readable storage medium is used to store computer instructions. When the computer instructions are executed by a processor, the above-mentioned centralized multi-bus DC microgrid secondary control method is implemented.

[0139] Embodiment Five

[0140] In one embodiment of this embodiment, an electronic device is provided, including: a processor, a memory, and a computer program; wherein, the processor is connected to the memory, the computer program is stored in the memory, and when the electronic device runs, the processor executes the computer program stored in the memory so that the electronic device executes and implements the above-mentioned centralized multi-bus DC microgrid secondary control method.

[0141] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0142] The present invention is described with reference to the flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the flows and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the specified function in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0143] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device, and the instruction device implements the specified function in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0144] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus, so that a series of operation steps are performed on the computer or other programmable apparatus to generate a computer-implemented process, thereby providing instructions for implementing the process Figure 1 a process or processes and / or blocks Figure 1 steps for the functions specified in a block or blocks.

[0145] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art without creative efforts within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A secondary control system for a centralized multi-bus DC microgrid, characterized in that, Applied to a microgrid with multiple DC buses, adjacent DC buses are connected through circuit impedance. A converter is provided on each DC bus, and each converter is configured with a controller. The controllers communicate with each other. Each controller includes: A primary control unit for performing primary control on the voltage of the corresponding DC bus through droop control and voltage-current double closed-loop control to ensure that the output voltage of the local converter tracks the reference voltage in real time; A secondary control unit for performing secondary control on the DC microgrid with a secondary control signal to adjust the average bus voltage to the rated voltage value. The secondary control signal is the difference between the virtual voltage drop of the local converter and the integral of the error between its virtual voltage drop and the average value of the virtual voltage drops of all converters.

2. The secondary control system of a centralized multi-bus DC microgrid according to claim 1, characterized in that, Each converter is connected to a central controller through a communication network. The central controller is used to receive the virtual voltage drop information of all converters, calculate the average value of the virtual voltage drops of all converters, and then send it back to each converter.

3. The secondary control system of a centralized multi-bus DC microgrid according to claim 2, wherein Communication occurs between the central controller and each controller.

4. The secondary control system of a centralized multi-bus DC microgrid according to claim 1, characterized in that, The process of the primary control unit performing primary control on the voltage of the corresponding DC bus through droop control and voltage-current double closed-loop control includes the primary control unit generating a reference voltage using droop control; Adopting voltage-current double closed-loop PI control to enable the output voltage of the converter to track the converter reference voltage without error. Based on the error between the output voltage and the reference voltage, the reference current is calculated through voltage PI control. Based on the error between the output current and the reference current, the PWM control signal is output through current PI control.

5. The secondary control system of a centralized multi-bus DC microgrid according to claim 1, characterized in that, The secondary control signal is specifically: Among them, k i represents the droop coefficient in the droop control function of the converter on the i-th bus, R i and I i respectively represent the line resistance and output current between the converter on the i-th bus and the i-th DC bus. is the virtual voltage drop of the converter on the i-th bus. represents the mean value of the virtual voltage drops of all converters obtained by the central controller. n is the number of converters, and u i is the secondary control signal of the converter on the i-th bus.

6. A secondary control system for a centralized multi-bus DC microgrid as described in claim 1, characterized in that, During the process of the secondary control unit performing secondary control on the DC microgrid with the secondary control signal to adjust the average bus voltage to the rated voltage value, the bus voltage after compensating the secondary control signal is: Among them, represents the bus voltage after compensating the secondary control signal, Vref is the rated voltage, and u i is the secondary control signal of the converter on the i-th bus, and k i represents the droop coefficient in the droop control function of the converter on the i-th bus, R i and I i respectively represent the line resistance and output current between the converter on the i-th bus and the i-th DC bus.

7. A secondary control method for a centralized multi-bus DC microgrid, which is applied to a microgrid including multiple DC buses, and adjacent DC buses are connected through circuit impedance. Each DC bus is provided with a converter, and the method is characterized in that Including the following steps: Performing primary control on the voltage of the corresponding DC bus through droop control and voltage-current double closed-loop control to ensure that the output voltage of the local converter tracks the reference voltage in real time; Performing secondary control on the DC microgrid with the secondary control signal to adjust the average bus voltage to the rated voltage value. The secondary control signal is the difference between the virtual voltage drop of the local converter and the integral of the error between its virtual voltage drop and the average value of the virtual voltage drops of all converters.

8. A computer-readable storage medium, characterized in that, Used to store computer instructions. When the computer instructions are executed by a processor, the steps in the method described in claim 7 are completed.

9. An electronic device, characterized in that, Including a memory, a processor, and computer instructions stored on the memory and running on the processor. When the computer instructions are run by the processor, the steps in the method described in claim 7 are completed.

10. A computer program product, characterized in that, Including a computer program, characterized in that when the computer program is executed by a processor, the steps in the method described in claim 7 are implemented.

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