Hierarchical Control Method for Distributed Event-Driven in AC / DC Hybrid Microgrid

Abstract

The present invention relates to a hierarchical control method for a hybrid AC-DC microgrid with distributed event-driven, comprising the following steps: 1) Designing the primary control strategies of AC and DC power sources and the primary control strategy of the interconnected converter in the AC and DC microgrid subsystems; 2) Designing a distributed event-driven economic dispatch algorithm, an average bus voltage discovery algorithm, an output power proportional distribution algorithm for the interconnected converter, and a distributed discovery algorithm for the incremental cost error of power generation between the AC and DC microgrid subsystems; 3) Designing a secondary control strategy based on the above algorithms, and each power generation unit and the interconnected converter realize distributed secondary control and optimization of the hybrid AC-DC microgrid by adjusting their secondary compensation terms. In addition, event trigger mechanisms are proposed for the distributed control algorithms designed in the present invention, thus greatly reducing the communication cost.

Description

Technical Field

[0001] The present invention relates to a hierarchical control method for a hybrid AC-DC microgrid based on distributed event-driven, belonging to the technical field of power systems. Background Art

[0002] A hybrid AC-DC microgrid can integrate distributed power sources and distributed loads on the AC or DC side of the microgrid according to the equipment type, thus reducing the demand for power conversion devices and having the characteristics of flexibility and high efficiency. However, due to its complex structure, the reliable and economic operation of a hybrid AC-DC microgrid poses certain challenges. Most of the control strategies for traditional hybrid AC-DC microgrids adopt a centralized control method, which has disadvantages such as poor flexibility and susceptibility to single-point failures. In addition, most traditional controls only consider the optimal secondary control within the AC and DC microgrid subsystems, and it is difficult to meet the optimal operation requirements of the entire hybrid microgrid system. Summary of the Invention

[0003] In view of the above deficiencies of the prior art, the present invention provides a hierarchical control method for a hybrid AC-DC microgrid based on distributed event-driven.

[0004] The technical solution adopted by the present invention to solve its technical problems is as follows: For a hierarchical control method for a hybrid AC-DC microgrid based on distributed event-driven, an agent is configured for each power generation unit in the AC microgrid subsystem and the DC microgrid subsystem, and an agent is assigned to the interconnection converter of the AC-DC microgrid subsystem to form a communication topology among the agents, so that the network formed by the remaining agents is still connected when any one agent fails, and the distributed hierarchical control of the hybrid AC-DC microgrid is realized according to the distributed algorithm.

[0005] The hierarchical control method for a hybrid AC-DC microgrid based on distributed event-driven includes the following steps:

[0006] Construct a primary control strategy for the AC power source through the agent of the AC power source in the AC microgrid subsystem, and control the AC power source according to the primary control strategy of the AC power source;

[0007] Construct a primary control strategy for the DC power source through the agent of the DC power source in the DC microgrid subsystem, and control the DC power source according to the primary control strategy of the DC power source;

[0008] Construct a primary control strategy for the interconnection converter through the agent of the interconnection converter of the hybrid AC-DC microgrid, and control the interconnection converter according to the primary control strategy of the interconnection converter.

[0009] The hierarchical control method for a hybrid AC-DC microgrid based on distributed event-driven includes the following steps:

[0010] 3-1) The primary control strategy for the AC power source is as follows:

[0011]

[0012] Among them, f i (t) and f nom respectively represent the frequency of the i-th power supply and the nominal frequency of the AC microgrid subsystem. The superscript AC represents the AC microgrid subsystem, represents the frequency-active power droop factor, represents the output power of the i-th AC power supply, and respectively represent the first and second secondary compensation terms;

[0013] The primary control strategy of the DC power supply described in 3-2) is as follows:

[0014]

[0015] Among them, and respectively represent the output voltage of the i-th power supply and the system nominal voltage. The superscript DC represents the DC microgrid subsystem, represents the voltage-active power droop factor, represents the output power of the i-th AC power supply, and respectively represent the first and second secondary compensation terms;

[0016] The primary control strategy of the interconnected converter described in 3-3) is as follows:

[0017]

[0018] Among them, represents the output power of the i-th interconnected converter, represents the droop factor of the interconnected converter, and respectively represent the first and second secondary compensation terms, f pu (t) and respectively represent the per-unit value of the frequency of the AC microgrid subsystem and the per-unit value of the voltage of the DC microgrid subsystem, and can be calculated through the following formulas respectively

[0019]

[0020] Among them, f max and f min respectively represent the maximum and minimum system frequencies allowed by the AC microgrid subsystem, v max and v min respectively represent the maximum and minimum voltages of the DC microgrid subsystem, represents the average bus voltage of the nodes where the power generation units of the DC microgrid subsystem are located.

[0021] The first - order secondary compensation term of the AC micro - grid subsystem and the first - order secondary compensation term of the DC micro - grid subsystem are as follows:

[0022]

[0023] Among them, the superscript \(H\in\{AC, DC\}\) represents the type of the micro - grid subsystem, \(AC\) represents the AC micro - grid, and \(DC\) represents the DC micro - grid; is the PI controller coefficient, represents the set of neighbor agents of the \(i\) - th agent in the micro - grid subsystem of type \(H\), and the Laplacian matrix element and the virtual incremental cost are defined as follows respectively

[0024]

[0025] where \(\xi\) is a real number, \(n\) H,i and \(n\) H,j represent the number of neighbor nodes of the \(i\) - th and \(j\) - th agents in the micro - grid subsystem of type \(H\) respectively;

[0026]

[0027] Among them, the superscript \(H\) represents the type of the micro - grid subsystem, the subscripts \(i\) and \(j\) represent the power source index numbers, represents the incremental cost, and are the generation cost coefficients, is the output power, and represent the lower and upper limits of the incremental cost respectively, and represent the lower and upper limits of the output power constraint respectively; \(a\) i 、\(b\) i represent the coefficients of the generation cost function;

[0028] The event - triggering condition is as follows:

[0029]

[0030] Among them, is the threshold parameter, \(T\) s is the secondary - control sampling and control step - size, and \(t\) represents the current time; represents the event - triggering decision variable. Only when does agent \(i\) communicate with its neighbor agents and transmit data to its neighbor agents for generating the first - order secondary compensation term of the AC micro - grid subsystem and the first - order secondary compensation term of the DC micro - grid subsystem.

[0031] In the primary control strategy of the interconnected inverter, the first secondary compensation term is as follows to achieve proportional distribution of the output power of the interconnected inverter:

[0032]

[0033] Where and represent the proportional and integral term coefficients respectively, represents the nominal value of the output power of the jth interconnected inverter, and its definition is as follows:

[0034]

[0035] Where and represent the output power and the nominal active output capacity of the jth interconnected inverter respectively, represents the Laplacian matrix element corresponding to the interconnected inverter; represents the number of neighbor nodes corresponding to the ith interconnected inverter agent;

[0036] The event trigger condition is as follows:

[0037]

[0038] Where is the threshold parameter, T s is the sampling and control step of the secondary control; represents the event trigger decision variable. Only when does the agent i communicate with its neighbor agents and transmit data to its neighbor agents for calculating the first secondary compensation term in the primary control strategy of the interconnected inverter.

[0039] The second secondary compensation term of the primary control strategy of the AC power supply is as follows to achieve frequency restoration control of the AC microgrid subsystem:

[0040]

[0041] Where and represent the proportional and integral term coefficients respectively.

[0042] The second secondary compensation term of the primary control strategy of the DC power supply is designed as follows to achieve voltage restoration control of the DC microgrid subsystem:

[0043]

[0044] Where and They respectively represent the proportional and integral term coefficients.

[0045] The average bus voltages of the AC microgrid subsystem and the DC microgrid subsystem are distributively identified by the following formula:

[0046]

[0047] Among them, the superscript H represents the type of microgrid subsystem, and the subscripts i and j represent the power source index numbers. represents the power source output voltage. represents the discovered average bus voltage, and η represents the learning rate factor.

[0048] The event triggering conditions are as follows:

[0049]

[0050] Among them is the threshold parameter, T s is the sampling and control step length for secondary control. represents the event triggering decision variable. Only when is true, will agent i communicate with its neighboring agents and transmit data to its neighboring agents for discovering the average bus voltages of the AC microgrid subsystem and the DC microgrid subsystem.

[0051] The second secondary compensation term in the primary control strategy of the interconnected converter is as follows to achieve the optimal power distribution between the AC and DC microgrid subsystems:

[0052]

[0053] Among them and are respectively the coefficients of the proportional term and the integral term.

[0054] The incremental power generation cost error between the AC and DC microgrid subsystems is as follows:

[0055]

[0056] Among them represents the incremental power generation cost error between the AC and DC microgrid subsystems discovered by the i-th interconnected converter, η is the learning rate factor. represents the Laplacian matrix element corresponding to the interconnected converter, e λ,i (t) is defined as follows

[0057]

[0058] Event triggering conditions:

[0059]

[0060] Among them is the threshold parameter, T s is the sampling and control step size for secondary control represents the event-triggered decision variable. Only when does the agent i communicate with its neighboring agents and transmit data to its neighboring agents for exploring the incremental cost error of power generation between the AC-DC microgrid subsystems.

[0061] The present invention has the following beneficial effects and advantages:

[0062] 1. The present invention adopts a distributed method to implement the distributed hierarchical control of the AC-DC hybrid microgrid system, which is not affected by single-point failures, and the event-triggered communication mechanism can reduce communication costs;

[0063] 2. The present invention does not require global information, and each agent only needs to communicate with its neighbors, which has high information security;

[0064] 3. The present invention integrates the traditional economic dispatch layer (the third layer) into the secondary control layer, which improves the efficiency of the AC-DC hybrid microgrid;

[0065] 4. By appropriately controlling the power transmitted by the interlinking converter between the AC and DC microgrid subsystems, the economic dispatch of the entire AC-DC hybrid microgrid system can be achieved, thereby reducing the operating cost of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 is the schematic diagram of the distributed hierarchical control method for the AC-DC hybrid microgrid. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0067] The following further elaborates the present invention in detail with reference to embodiments.

[0068] The present invention is used for the distributed hierarchical control of the AC-DC hybrid microgrid. First, an agent is configured for each distributed generator (DG) in the AC microgrid subsystem and the DC microgrid subsystem respectively, and an agent is assigned to the interlinking converter (IC) of the AC-DC microgrid subsystem. According to the N-1 rule, the communication topology between the agents is designed so that the network formed by the remaining agents is still fully connected when any one agent fails, and the distributed hierarchical control of the AC-DC hybrid microgrid is realized based on a series of designed distributed algorithms.

[0069] The present invention includes the following steps:

[0070] 1) Design the distributed control architecture of the AC-DC hybrid microgrid system, as Figure 1 shown, and assign an agent to each power generation unit and interconnected converter in the system for data communication and implementing distributed control algorithms;

[0071] 2) Design the primary control strategy for AC power sources in the AC microgrid subsystem, design the primary control strategy for DC power sources in the DC microgrid subsystem, and design the primary control strategy for the interconnected converters in the AC-DC hybrid microgrid.

[0072] 3) Design a distributed event-driven economic dispatch algorithm and use it to calculate the first secondary compensation term for AC and DC power sources;

[0073] 4) Design an event-driven average bus voltage discovery algorithm;

[0074] 5) Design an event-driven output power proportional distribution algorithm for interconnected converters and use it to calculate the first secondary compensation term for interconnected converters;

[0075] 6) Design a secondary control strategy for frequency restoration in the AC microgrid subsystem and use it to calculate the second secondary compensation term for AC power sources;

[0076] 7) Based on the average bus voltage discovery algorithm in step 4), design a secondary control strategy for voltage restoration in the DC microgrid subsystem and use it to calculate the second secondary compensation term for DC power sources;

[0077] 8) Design a distributed discovery algorithm for the incremental cost error of power generation and an event trigger mechanism between the AC-DC microgrid subsystems, and calculate the second secondary compensation term for interconnected converters to achieve optimal power distribution between the AC-DC microgrid subsystems.

[0078] 1. Design the distributed control architecture and assign agents to each power source in the AC-DC hybrid microgrid. First, configure an agent for each power source in the AC microgrid subsystem and the DC microgrid subsystem respectively, and assign an agent to the interconnected converter of the AC-DC microgrid subsystem. Build a communication network between the agents. Each agent should have the following functions: obtain local information (the current output power p i ) of this power generation unit; communicate with neighboring agents and implement relevant distributed algorithms. In this implementation, a microprocessor with A / D and communication interfaces is used.

[0079] 2. Design the primary control strategies for AC power sources, DC power sources, and interconnected converters

[0080] 1) Design the primary control strategy for AC power sources

[0081]

[0082] Among them, f i (t) and f nom represent the frequency of the i-th power supply and the system nominal frequency respectively. The superscript AC represents the AC microgrid subsystem, represents the frequency-active power droop factor, represents the output power of the i-th AC power supply, and represent the first and second secondary compensation terms respectively.

[0083] 2) Design the primary control strategy of the DC power supply

[0084]

[0085] Among them, and represent the output voltage of the i-th power supply and the system nominal voltage respectively. The superscript DC represents the DC microgrid subsystem, represents the voltage-active power droop factor, represents the output power of the i-th AC power supply, and represent the first and second secondary compensation terms respectively.

[0086] 3) Design the primary control strategy of the interconnection converter

[0087]

[0088] Among them, represents the output power of the i-th interconnection converter, represents the droop factor of the interconnection converter, and represent the first and second secondary compensation terms respectively. f pu (t) and represent the per-unit value of the frequency of the AC microgrid subsystem and the per-unit value of the voltage of the DC microgrid subsystem respectively, and can be calculated through the following formulas respectively

[0089]

[0090] Among them, f max and f min represent the maximum and minimum system frequencies allowed in the AC microgrid subsystem respectively, v max and v min represent the maximum and minimum voltages of the DC microgrid subsystem respectively, v DC (t) represents the average voltage of each node in the DC microgrid subsystem.

[0091] 3. Design an event-driven distributed economic dispatch algorithm

[0092] The first secondary compensation term of the AC microgrid subsystem and the DC microgrid subsystem is designed as follows:

[0093]

[0094] Where the superscript H ∈ {AC, DC} represents the type of the microgrid subsystem (AC represents the AC microgrid, and DC represents the DC microgrid). is the controller coefficient, represents the set of neighbor agents of the i-th agent in the H-type microgrid subsystem, and are defined as follows respectively

[0095]

[0096] Where ξ is a real number, n H,i and n H,j represent the number of neighbor nodes of the i-th and j-th agents in the microgrid subsystem of type H respectively.

[0097]

[0098] Where the superscript H represents the type of the microgrid subsystem, and the subscripts i and j represent the power source index numbers, represents the incremental cost, and are the generation cost coefficients, is the output power, and represent the lower and upper limits of the incremental cost respectively, and represent the lower and upper limit constraints of the output power respectively.

[0099] To reduce the communication cost, the following event trigger condition is designed:

[0100]

[0101] Where is the threshold parameter, T s is the sampling and control step of the secondary control.

[0102] Only when agent i communicates with its neighbor agents and transmits data to its neighbor agents.

[0103] 4. Design an event-driven average bus voltage discovery algorithm:

[0104] The average bus voltages of the AC microgrid subsystem and the DC microgrid subsystem can be distributively identified by the following formula

[0105]

[0106] Among them, the superscript H represents the type of microgrid subsystem, and the subscripts i and j represent the power source index numbers. represents the power source output voltage. represents the average bus voltage detected, and η represents the learning rate factor.

[0107] To reduce the communication cost, the following event trigger condition is designed:

[0108]

[0109] Among them is the threshold parameter, and T s is the sampling and control step for secondary control.

[0110] Only when Agent i will communicate with its neighboring agents and transmit data to its neighboring agents.

[0111] 5. Design an event-driven output power proportional distribution algorithm for interconnected converters:

[0112] To achieve the proportional distribution of the output power of interconnected converters, the first quadratic compensation term is designed as follows:

[0113]

[0114] Among them and represent the proportional and integral term coefficients respectively. represents the nominal value of the output power of the jth interconnected converter, and its definition is as follows:

[0115]

[0116] Among them and represent the output power of the jth interconnected converter and the nominal active output capacity respectively.

[0117] To reduce the communication cost, the following event trigger condition is designed:

[0118]

[0119] Among them is the threshold parameter, and T s is the sampling and control step for secondary control.

[0120] Only when Agent i will communicate with its neighboring agents and transmit data To its neighboring agents.

[0121] 6. Design the secondary control strategy for frequency restoration of the AC microgrid subsystem:

[0122] To achieve the frequency restoration control of the AC microgrid subsystem, the second - order secondary compensation term of the AC power source is designed as follows:

[0123]

[0124] Where and represent the proportional and integral term coefficients respectively

[0125] 7. Design the secondary control strategy for voltage restoration of the DC microgrid subsystem:

[0126] To achieve the voltage restoration control of the DC microgrid subsystem, the second - order secondary compensation term of the DC power source is designed as follows:

[0127]

[0128] Where and represent the proportional and integral term coefficients respectively

[0129] 8. Design the secondary control strategy of the interconnected converter to achieve the optimal power distribution between the AC and DC microgrid subsystems:

[0130] First, design the distributed exploration algorithm for the incremental cost error of power generation between the AC and DC microgrid subsystems:

[0131]

[0132] Where represents the incremental cost error of power generation between the AC and DC microgrid subsystems explored by the i - th interconnected converter, η is the learning rate factor, and e λ,i (t) is defined as follows

[0133]

[0134] To reduce the communication cost of the distributed exploration algorithm for the incremental cost error of power generation, design the following event - trigger condition:

[0135]

[0136] Where is the threshold parameter, T s is the sampling and control step size of the secondary control.

[0137] Only when will agent i communicate with its neighboring agents and transmit data to its neighboring agents.

[0138] Then, in order to achieve the optimal power distribution among the AC-DC microgrid subsystems, the second secondary compensation term of the interconnected converter is designed as follows:

[0139]

[0140] where and are the coefficients of the proportional term and the integral term, respectively.

Claims

1. A hierarchical control method for an AC / DC hybrid microgrid based on distributed event-driven, characterized in that, Configure an agent for each power generation unit in the AC microgrid subsystem and the DC microgrid subsystem, and allocate an agent for the AC-DC microgrid subsystem interconnection converter to form a communication topology among the agents, so that the network formed by the remaining agents is still connected when any one agent fails, and realize the distributed hierarchical control of the AC-DC hybrid microgrid according to the distributed algorithm; The hierarchical control method includes the following steps: Construct a primary control strategy for the AC power source through the agent of the AC power source in the AC microgrid subsystem, and control the AC power source according to the primary control strategy of the AC power source; Construct a primary control strategy for the DC power source through the agent of the DC power source in the DC microgrid subsystem, and control the DC power source according to the primary control strategy of the DC power source; Construct a primary control strategy for the interconnection converter through the agent of the AC-DC hybrid microgrid interconnection converter, and control the interconnection converter according to the primary control strategy of the interconnection converter; Among them, 3-1) The primary control strategy of the AC power source is as follows: where f i (t) and f nom represent the frequency of the i-th power source and the nominal frequency of the AC microgrid subsystem, respectively. The superscript AC represents the AC microgrid subsystem, denotes the frequency-active power droop factor, represents the output power of the i-th AC power source, and represent the first and second secondary compensation terms, respectively; 3-2) The primary control strategy of the DC power source is as follows: Among them, and respectively represent the output voltage of the i-th power supply and the system nominal voltage, where the superscript DC represents the DC microgrid subsystem, represents the voltage-active droop factor, represents the output power of the i-th AC power supply, and respectively represent the first and second secondary compensation terms; 3-3) The primary control strategy of the interconnection converter is as follows: Among them, represents the output power of the i-th interconnection converter, represents the droop factor of the interconnection converter, and represent the first and second secondary compensation terms respectively, f pu (t) and represent the per-unit value of the frequency of the AC microgrid subsystem and the per-unit value of the voltage of the DC microgrid subsystem respectively, and can be calculated through the following formulas respectively Among them, f max and f min respectively represent the maximum and minimum system frequencies allowed by the AC microgrid subsystem, v max and v min respectively represent the maximum and minimum voltages of the DC microgrid subsystem, represents the average bus voltage of the nodes where the power generation units of the DC microgrid subsystem are located.

2. The distributed event-driven economic dispatch algorithm according to claim 1, wherein: The first secondary compensation term of the AC microgrid subsystem and the first secondary compensation term of the DC microgrid subsystem are as follows: where the superscript H ∈ {AC, DC} represents the type of microgrid subsystem, AC represents the AC microgrid, and DC represents the DC microgrid; is the PI controller coefficient, represents the set of neighbor agents of the i-th agent in the H-type microgrid subsystem, and the Laplacian matrix element and the virtual incremental cost are defined as follows, respectively where ξ is a real number, n H,i and n H,j respectively represent the number of neighbor nodes of the i-th and j-th agents in the microgrid subsystem of type H; Among them, the superscript H represents the type of microgrid subsystem, and the subscripts i and j represent the power source index numbers. represents the incremental cost, and are the power generation cost coefficients, is the output power, and represent the lower and upper limits of the incremental cost respectively, and represent the lower and upper limits of the output power constraint respectively; a i , b i represent the coefficients of the power generation cost function. The event trigger conditions are as follows: Among them, is the threshold parameter, T s is the secondary control sampling and control step size, and t represents the current time; represents the event-triggered decision variable. Only when does agent i communicate with its neighboring agents and transmit data to its neighboring agents, which is used to generate the first secondary compensation term of the AC microgrid subsystem and the first secondary compensation term of the DC microgrid subsystem.

3. The distributed event-driven economic dispatch algorithm according to claim 1, characterized in that: In the primary control strategy of the interconnection converter, the first secondary compensation term is as follows to achieve proportional distribution of the output power of the interconnection converter: where and represent the proportional and integral term coefficients respectively, represents the nominal value of the output power of the j-th interconnected converter, and is defined as follows: where and represent the output power of the j-th interconnected converter and the nominal active output capacity, respectively, represents the Laplacian matrix element corresponding to the interconnected converter; represents the number of neighbor nodes corresponding to the i-th interconnected converter agent; The event trigger conditions are as follows: Among them is the threshold parameter, T s is the sampling and control step size for secondary control; represents the event-triggered decision variable. Only when the agent i communicates with its neighboring agents and transmits data to its neighboring agents for calculating the first secondary compensation term in the primary control strategy of the interconnected converters.

4. The distributed event-driven economic dispatch algorithm according to claim 1, characterized in that The second secondary compensation term of the primary control strategy of the AC power source is as follows to achieve frequency restoration control of the AC microgrid subsystem: wherein and represent the proportional and integral term coefficients, respectively.

5. The distributed event-driven economic dispatch algorithm according to claim 1, characterized in that The second secondary compensation term of the primary control strategy of the DC power source is designed as follows to achieve voltage restoration control of the DC microgrid subsystem: wherein and represent the proportional and integral term coefficients respectively.

6. The distributed event-driven economic dispatch algorithm according to claim 5, wherein: The average bus voltages of the AC microgrid subsystem and the DC microgrid subsystem are distributedly identified by the following formula: Wherein, the superscript H represents the type of microgrid subsystem, and the subscripts i and j represent the power source index numbers. represents the power source output voltage. represents the average bus voltage detected, and η represents the learning rate factor. The event trigger conditions are as follows: Among them is the threshold parameter, T s is the sampling and control step size for secondary control represents the event-triggered decision variable. Only when the agent i communicates with its neighboring agents and transmits data to its neighboring agents for exploring the average bus voltages of the AC microgrid subsystem and the DC microgrid subsystem.

7. The distributed event-driven economic dispatch algorithm according to claim 1, wherein: The second secondary compensation term in the primary control strategy of the interconnection converter is as follows to achieve optimal power distribution between the AC-DC microgrid subsystems: wherein and are the coefficients of the proportional term and the integral term, respectively.

8. The distributed event-driven economic dispatch algorithm according to claim 7, characterized in that: The generation incremental cost error between the AC-DC microgrid subsystems is as follows: Among them represents the generation incremental cost error between the AC-DC microgrid subsystems discovered by the i-th interconnected converter, η is the learning rate factor, represents the Laplacian matrix element corresponding to the interconnected converter, e λ,i (t) is defined as follows Event trigger condition: where is the threshold parameter, T s is the sampling and control step size for secondary control represents the event-triggered decision variable. Only when Agent i communicates with its neighboring agents and transmits data to its neighboring agents to explore the incremental cost error of power generation between the AC and DC microgrid subsystems.

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