Method for regulating bus voltage and controlling power distribution accuracy of direct current microgrid

Abstract

The application provides a bus voltage regulation and power distribution precision controllable method of a direct current micro-grid, which comprises the following steps: step 1, all the distributed power sources participating in the coordinated control in the micro-grid are provided with corresponding distributed coordinated controllers, and each distributed coordinated controller is connected with the converter controller of the corresponding distributed power source; step 2, the distributed coordinated controllers are connected through a communication network; and step 3, a compound consistency algorithm containing a power consistency term and a voltage consistency term and a droop control method with a correction amount are adopted to control the distributed power sources in the micro-grid system. The application has the beneficial effects that the application adopts a distributed scheme, has stronger expansibility, compared with the existing centralized control scheme, allows the random exit and access of the load in the micro-grid, and when the node in the system fails or the load of the node is transformed, does not affect the normal work of the remaining nodes, and the stability of the system is stronger.

Description

Technical Field

[0001] This invention relates to the field of DC microgrid control, and more particularly to a method for controlling the accuracy of bus voltage regulation and power distribution in a DC microgrid. Background Technology

[0002] Replacing traditional fossil fuels with distributed renewable energy is an effective way to address environmental pollution. Distributed renewable energy generation systems typically have DC characteristics. Integrating distributed energy resources using DC microgrids can improve efficiency, reduce the use of inverters, and lower construction and operating costs. Therefore, DC microgrids are becoming an increasingly popular power supply system.

[0003] The basic control objectives of a DC microgrid are twofold: bus voltage regulation and power output distribution. Bus voltage regulation refers to using the control system to ensure that the bus voltage of the DC microgrid reaches or stabilizes near the rated voltage. However, due to the use of traditional droop control methods and the existence of transmission line impedance between different buses, there is a voltage drop between the actual bus voltage and the rated value, and the voltages of different buses are not consistent.

[0004] In DC microgrids, power distribution is equivalent to the proportional distribution of distributed generation (DG) output power, meaning that the output power of all DG sources is proportional to their respective rated output power. A key function of traditional droop control methods is to achieve this proportional power distribution. However, when the transmission line impedance between buses is not negligible, the effectiveness of power distribution using traditional droop control methods deteriorates. To improve the problems caused by droop control methods and transmission line impedance, a more effective approach is to use a consensus algorithm-based distributed control method to compensate for the errors caused by traditional droop control. While consensus algorithms can achieve proportional power distribution, they cannot control the consistency of bus voltage. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a method for controlling the accuracy of bus voltage regulation and power distribution in a DC microgrid.

[0006] This invention provides a method for controlling the accuracy of bus voltage regulation and power distribution in a DC microgrid, comprising the following steps:

[0007] Step 1: All distributed power sources participating in the coordinated control in the DC microgrid are equipped with their corresponding distributed coordinated controllers, and each distributed coordinated controller is connected to the converter controller of its corresponding distributed power source.

[0008] Step 2: Distributed coordination controllers are connected via a communication network.

[0009] Step 3: Use a composite consensus algorithm that includes both power consensus terms and voltage consensus terms, and a droop control method with corrections to control the distributed power sources in the microgrid system.

[0010] As a further improvement of the present invention, in step 2, the nodes in the communication network are divided into leader nodes and follower nodes. The leader node is a virtual node in the distributed coordination controller, used to provide a static rated voltage reference value. Follower nodes are distributed power sources.

[0011] As a further improvement of the present invention, in step 2, the connection between follower nodes adopts one-way or two-way communication, and the communication connection between follower nodes is represented by matrix A:

[0012]

[0013] In the formula: any element a in A ij Let be a non-negative real number, representing the communication weighting coefficient from node j to node i. When a communication connection exists between node j and node i, a ij The value of a is greater than 0, otherwise a ij =0, where N is the number of distributed power sources participating in coordinated control in the microgrid.

[0014] As a further improvement of the present invention, in step 3, the reference voltage of the distributed power source is solved by a composite consensus algorithm including a power consensus term and a voltage consensus term, as follows:

[0015]

[0016] In the formula: θ is the adjustment parameter for bus voltage regulation accuracy and power distribution accuracy, P i Let P be the real-time output power of the i-th distributed power source. i * Let P be the rated output power of the i-th distributed power source. i b P represents the reference output power of the i-th distributed power source. j To represent the real-time output power of the j-th distributed power source during system operation. V represents the reference output power of the j-th distributed power source. ref R represents the rated voltage of the system. Li This represents the i-th load. a is a process variable of the controller. ij I is a non-negative real number. iV represents the real-time output current of the i-th distributed power source during operation. i Let K be the bus voltage of the i-th distributed power source. i K represents the weight coefficient of a key node. If the i-th node is a key node, then K... i =1, the controller of this node can know the rated voltage of the system; otherwise, K i =0, the controller of this node cannot know the rated voltage of the system.

[0017] As a further improvement of the present invention, the sag control method with correction amount in step 3 is as follows:

[0018] Based on the reference value V of the rated output voltage of the distributed power source i * The formula for calculating the output operating point voltage of a distributed power source is as follows:

[0019] V i =V i * -r i I i (3)

[0020] In the formula: V i * Let r be the reference voltage for the i-th distributed power source. i V is the droop coefficient of the i-th distributed source; i Let V be the output operating point voltage of the i-th power supply. i As the input voltage reference value for the distributed power converter controller.

[0021] As a further improvement of the present invention, in step 3... V is transmitted from node j to node i via the inter-node communication network. ref It originates from the virtual leader node and does not require transmission through the communication network.

[0022] As a further improvement of the present invention, in step 3, the accuracy of power distribution and bus voltage regulation of each distributed power source can be set by the adjustment parameter θ according to the set criteria, which are shown in the table below.

[0023] Consistency setting table

[0024]

[0025] The beneficial effects of this invention are as follows: 1. Compared with existing centralized control schemes, the distributed scheme of this invention has stronger scalability, allowing distributed power sources in the microgrid to randomly exit and connect; at the same time, when a node in the DC microgrid system experiences a fault or its load changes, it does not affect the normal operation of other nodes, resulting in stronger stability of the DC microgrid system; in addition, the accuracy of power allocation and bus voltage regulation in the control method of this invention can be manually set; 2. Through a distributed coordination controller, this invention can achieve adjustable accuracy in bus voltage regulation and proportional power control, allowing the load in the DC microgrid system to operate more safely and stably; it also provides a certain degree of protection for the power source, preventing irreversible damage caused by prolonged full-power operation; 3. By employing a composite consensus algorithm including power consistency terms and voltage consistency terms in the secondary control, this invention can achieve adjustable accuracy in power allocation and bus voltage regulation in the DC microgrid. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a DC microgrid in an embodiment of the present invention;

[0027] Figure 2 This is a block diagram of the distributed controller principle for voltage consistency and proportional current distribution in an embodiment of the present invention;

[0028] Figure 3 This is a flowchart of the distributed coordinated control method for voltage and power distribution in a DC microgrid according to the present invention. Detailed Implementation

[0029] Figure 1 It contains four distributed generation (DG) sources, each connected to a bus, and each bus is connected to a load (L). The buses are connected to each other via transmission lines, which are connected by resistors (r). ij Modeling. Additionally... Figure 1 The dashed line indicates a communication network connection, and the arrow indicates the direction of communication. Figure 2 In this context, Gi(s) represents a proportional-integral (PI) controller. It should be specifically noted that the control method disclosed in this invention is applicable to, but not limited to, other methods. Figure 1 The network topology and its configuration are shown in the figure.

[0030] This invention discloses a method for controllable bus voltage regulation and power distribution accuracy in a DC microgrid. This method employs a distributed coordination controller for each distributed power source and introduces a sparse communication network between these controllers. Precision control parameters allow for the manual setting of the accuracy of bus voltage regulation and proportional power distribution. A virtual leader node method is used to compensate for voltage drops and power distribution deviations relative to rated values ​​caused by droop control. Compared to existing methods, this invention achieves more efficient control of the DC microgrid.

[0031] This invention discloses a method for controlling the bus voltage regulation and power distribution accuracy of a DC microgrid, comprising the following steps:

[0032] Step 1: All distributed power sources participating in the coordinated control in the DC microgrid are equipped with their corresponding distributed coordinated controllers, and each distributed coordinated controller is connected to the converter controller of its corresponding distributed power source.

[0033] Step 2: Distributed coordination controllers are connected via a communication network.

[0034] In step 2, the nodes in the communication network are divided into leader nodes and follower nodes. The leader node is a virtual node in the distributed coordination controller, used to provide a static rated voltage reference value. Follower nodes are distributed power sources.

[0035] Connections between follower nodes can be one-way or two-way communication. The basic requirement of a communication network is that there must be a direct or indirect communication path from the leader node to all follower nodes.

[0036] The communication connections between follower nodes are represented by matrix A:

[0037]

[0038] In the formula: any element a in A ij ,i,j∈[1,N] are non-negative real numbers, and are the communication weighting coefficients from node j to node i. When there is a communication connection between node j and node i, a ij The value of a is greater than 0, otherwise a ij =0, where N is the number of distributed power sources participating in coordinated control in the microgrid.

[0039] Step 3: The distributed coordinating controller is controlled by a composite consensus algorithm that includes both power consensus terms and voltage consensus terms, and by a droop control method with correction.

[0040] This invention implements the control of the distributed coordination controller in two layers: the primary control layer adopts a droop control method with correction; the secondary control layer adopts a composite consensus algorithm that includes both power consensus terms and voltage consensus terms.

[0041] Secondary control layer: The reference voltage of the distributed generation is obtained through a composite consensus algorithm that includes power consensus terms and voltage consensus terms.

[0042]

[0043] In the formula: θ is the adjustment parameter for bus voltage regulation accuracy and power distribution accuracy, P i Let P be the real-time output power of the i-th distributed power source. i * Let P be the rated output power of the i-th distributed power source. i b P represents the reference output power of the i-th distributed power source. j To represent the real-time output power of the j-th distributed power source during system operation. V represents the reference output power of the j-th distributed power source. ref R represents the rated voltage of the system. Li This represents the i-th load. a is a process variable of the controller. ij I is a non-negative real number. i V represents the real-time output current of the i-th distributed power source during operation. i Let K be the bus voltage of the i-th distributed power source. i K represents the weight coefficient of a key node. If the i-th node is a key node, then K... i =1, the controller at this critical node knows the system's rated voltage; otherwise, K i =0,K i Nodes with a value of 0 are ordinary nodes. Ordinary nodes cannot know the rated voltage of the system, therefore K... i The controller of a node with voltage = 0 cannot know the system's rated voltage. V i * In a consistency control method with correction parameters, the control signal from the primary control of a distributed controller is output to the secondary control. The correction parameter refers to the error in power distribution and bus voltage regulation caused by the primary control, V. i * It is the output of the secondary control and also the input signal of the primary control.

[0044] Primary control layer: Employs a droop control method with correction parameters, as detailed below:

[0045] Based on the reference voltage V of the distributed power sourcei * Calculate the output operating point voltage of the distributed power source:

[0046] V i =V i * -r i I i (3)

[0047] In the formula: V i * Let r be the reference voltage for the i-th distributed power source. i V is the droop coefficient of the i-th distributed source; i Let V be the output operating point voltage of the i-th power supply. i As the input voltage reference value for the distributed power converter controller.

[0048] V is transmitted from node j to node i via the inter-node communication network. ref It originates from the virtual leader node and does not require transmission through the communication network.

[0049] The accuracy of power distribution and bus voltage regulation of each distributed power source can be manually set by the adjustment parameter θ according to actual needs. The setting criteria are shown in the table below.

[0050] Table 1. Consistency Setting Table

[0051]

[0052] Primary control mainly maintains the stable operation of the microgrid. A DC microgrid system primarily consists of multiple distributed DC power sources, requiring coordination of their output. This involves not only ensuring a stable voltage output but also preventing circulating currents between power supply loops. Appropriate power allocation means distributing the output power of each distributed power source in the microgrid system proportionally to its rated capacity.

[0053] Secondary control is often used to compensate for power distribution deviations and bus voltage deviations caused by primary control, such as traditional droop control, and power transmission line impedance, ultimately achieving precise power distribution and bus voltage regulation.

[0054] This invention employs a distributed approach, offering enhanced scalability. Compared to existing centralized control schemes, the control method of this invention allows for the random disconnection and connection of loads within the microgrid. Furthermore, when the load on a node in a DC microgrid system changes, it does not affect the normal operation of other nodes, resulting in stronger system stability. Compared to existing distributed control schemes, existing consensus algorithms cannot simultaneously achieve consistent voltage regulation and proportional power distribution. In contrast, the control method of this invention can control both the degree of voltage consistency and the precision of proportional power distribution.

[0055] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for controlling the accuracy of bus voltage regulation and power distribution in a DC microgrid, characterized in that, Includes the following steps: Step 1: All distributed power sources participating in the coordinated control in the DC microgrid are equipped with their corresponding distributed coordination controllers, and each distributed coordination controller is connected to the converter controller of its corresponding distributed power source. Step 2: Distributed coordination controllers are connected via a communication network; Step 3: Use a composite consensus algorithm that includes both power consensus terms and voltage consensus terms, and a droop control method with correction to control the distributed power sources in the microgrid system. In step 2, the nodes in the communication network are divided into leader nodes and follower nodes. The leader node is a virtual node in the distributed coordination controller, used to provide a static rated voltage reference value. The follower nodes are distributed power sources; In step 2, the connections between follower nodes employ unidirectional or bidirectional communication, and the communication connections between follower nodes are represented by matrix A: （1）, In the formula: any element in A a ij A non-negative real number, representing a node. j To the node i The communication weighting coefficient, when the node j To the node i When a communication connection exists, a ij The value of is greater than 0, otherwise a ij Equal to 0, N The number of distributed power sources participating in coordinated control in a microgrid; In step 3, the reference voltage of the distributed generation is solved using a composite consensus algorithm that includes power consensus terms and voltage consensus terms, as follows: (2), In the formula: These are the adjustment parameters for bus voltage regulation accuracy and power distribution accuracy. The value of is between 0 and 1. P i For the first i Real-time output power of a distributed power source For the first i The rated output power of a distributed power source, Indicates the first i The reference output power of a distributed power source. P j To be the first during system operation j Real-time output power of a distributed power source Indicates the first j The reference output power of a distributed power source. V ref Indicates the system's rated voltage. R Li Indicates the first i One load, I i For the first i The real-time output current of a distributed power source during operation. For the first i Bus voltage of a distributed power source This represents the weight coefficient of the key node, if the... If a node is a critical node, then The controller at this node can know the system's rated voltage; otherwise... The controller at this node cannot know the system's rated voltage.

2. The method for controlling the bus voltage regulation and power distribution accuracy of a DC microgrid according to claim 1, characterized in that, In step 3, the sag control method with correction is as follows: Based on the reference voltage of the distributed power source The formula for calculating the output operating point voltage of a distributed power source is as follows: （3） In the formula: For the first i The reference voltage of a distributed power source r i For the first i The droop factor of a distributed power source; V i For the first i The output operating point voltage of the power supply will V i As the input voltage reference value for the distributed power converter controller.

3. The method for controlling the bus voltage regulation and power distribution accuracy of a DC microgrid according to claim 1, characterized in that, In step 3, Through the communication network between nodes, by nodes j Transmitted to the node i , V ref It originates from the virtual leader node and does not require transmission through the communication network.

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