Alternating-current micro-grid distributed power control method with quantitative event triggering

Abstract

The invention relates to the technical field of micro-grids, and discloses an AC micro-grid distributed power control method with quantitative event triggering. According to the method, due to droop control in an island DC micro-grid, distribution of reactive power and unbalanced power in a system cannot be guaranteed, and a distributed control method with quantitative event triggering is provided for solving the problem. According to the control scheme provided by the invention, communication is reduced on the basis of realizing reactive power and unbalanced power distribution among distributed power generation units by adding a designed distributed secondary controller with a quantitative event triggering method, and parts which cannot be accurately distributed can be readjusted by a negative feedback system through PI control; in addition, the proposed method does not need global power information, each distributed generator only communicates with a neighbor when meeting a triggering condition, the communication burden of a micro-grid communication network is greatly reduced, the stability of the method is proved through a Russell invariant set principle, and Zeno behaviors are also eliminated through an anti-security method.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrids, and in particular to an AC microgrid distributed power control method with quantized event triggering. Background Art

[0002] AC microgrid is a local power supply network composed of distributed power sources, energy storage devices, variable loads, etc. It is an important part of the smart grid. Its working modes can be divided into two types: grid-connected and islanded.

[0003] In the microgrid island mode, a basic requirement is the proper distribution of reactive power between distributed generation units. Reasonable distribution of reactive power can reduce fluctuations in the power grid, reduce the instability of the power grid during operation, and improve the quality of power supply. Reasonable distribution of reactive power can increase the load capacity of the power grid, enabling the power grid system to better cope with sudden load changes.

[0004] However, even if the mismatch in line impedance is small, there may be multiple nodes or lines in the system, and the small mismatch accumulates at different nodes or lines, eventually causing the reactive power distribution error in the entire system to become significant. The design of the droop control algorithm may be very sensitive to small mismatches in line impedance. At the same time, if the algorithm has a low tolerance for mismatches, even small mismatches can lead to significant errors.

[0005] On the other hand, due to the surge in nonlinear loads, the power quality problem of voltage imbalance is becoming increasingly serious. Unbalanced power will cause voltage imbalance in the power grid, which will in turn affect the stability of the system. At the same time, unbalanced power will increase losses in the power grid. Reasonable regulation of unbalanced power can reduce losses and reduce operating costs. Therefore, distributed generators need to properly distribute unbalanced power.

[0006] Since each distributed unit in the microgrid system needs to communicate, when the amount of communication transmitted at one time is too large, the system performance will be degraded, affecting the normal operation of each part of the system. The system cannot respond to requests in time, resulting in a decrease in service quality. Therefore, it is necessary to optimize the communication problems of the system. Summary of the invention

[0007] 1. Technical issues to be resolved In view of the shortcomings of the prior art, the present invention provides an AC microgrid distributed power control method with quantized event triggering, which solves the problem of reactive and unbalanced power distribution in the AC microgrid system by designing a distributed secondary controller. In order to solve the communication congestion problem that may occur during data transmission, this paper adds an event trigger mechanism and a quantization mechanism on the basis of the designed distributed secondary controller, thereby reducing the system communication from the aspects of the number of system communications and the amount of transmitted data, thereby solving the above-mentioned problems.

[0008] (II) Technical solution To achieve the above object, the present invention provides the following technical solution: an AC microgrid distributed power control method with quantized event triggering, comprising the following steps: S1. Measure the parameters required by the controller, including bus voltage, fundamental positive sequence current, fundamental negative sequence current, fundamental positive sequence voltage, fundamental negative sequence voltage and cut-off frequency; S2, using proportional resonant controller; S3, introduce virtual impedance to achieve target control, and realize the distribution of reactive power and unbalanced power by adjusting the virtual impedance of positive sequence, negative sequence and harmonic frequency; S4. Design a distributed reactive power secondary controller based on droop control and distributed control theory; S5. Design a distributed unbalanced power two-stage controller based on droop control and distributed control theory; S6. Pass The invariant set principle is used to prove the stability of the system. By using the contradiction method, it is shown that there is a lower limit on the time interval between each triggered event, which means that the system does not exist. Behavior.

[0009] Preferably, a proportional resonant controller is introduced into S2, and its voltage controller model is as follows: In the formula, represents the proportionality coefficient, represents the resonance coefficient, represents the voltage controller cut-off frequency, Indicates the rated angular frequency.

[0010] Preferably, a proportional resonant controller is introduced into S2, and its current controller model is as follows: In the formula, represents the proportionality coefficient, represents the resonance coefficient, represents the current controller cut-off frequency, Indicates the rated angular frequency.

[0011] Preferably, the distributed reactive power controller designed in S4 is expressed as follows: In the formula, represents the reactive power coefficient of the system, Represents the reactive power measurement value of the system, express At the time of event triggering The quantitative value of is the control gain of the system, is the adjacency matrix of distributed generation units.

[0012] Preferably, the event triggering mechanism in S4 is as follows: In the formula, Express satisfaction , , A continuously differentiable function, is the measurement error of the system, that is, the actual measurement value of the system The measured value at the time of triggering The difference between .

[0013] Preferably, the uniform quantizer designed in S4 is as follows: In the formula, represents the quantization interval, satisfying , Indicates less than or equal to The maximum integer, uniform quantization error satisfies , that is, when hour, .

[0014] Preferably, the logarithmic quantizer designed in S4 is as follows: In the formula, the logarithmic quantization error satisfies , which also satisfies hour, ,when When the quantization error Eventually it approaches 0.

[0015] Preferably, the distributed unbalanced power controller designed in S5 is expressed as follows: In the formula, Indicates the unbalanced power reference value of the system, Represents the reactive power measurement value of the system, express Event trigger time The quantitative value of is the control gain of the system, is the adjacency matrix of distributed generation units.

[0016] Preferably, the event triggering mechanism in S5 is as follows: In the formula, To satisfy , , A continuously differentiable function, is the measurement error of the system, that is, the actual measurement value of the system The measured value at the time of triggering The difference between .

[0017] Preferably, the quantizer used for the unbalanced power in S5 is consistent with the quantizer used in S4.

[0018] Compared with the prior art, the present invention provides an AC microgrid distributed power control method with quantized event triggering, which has the following beneficial effects: A new type of distributed two-level controller is designed, which adds event trigger mechanism and quantization mechanism, reduces the number of communications and the amount of communication data of the microgrid system, and provides control performance almost the same as the traditional periodic control scheme. The LaSalle invariant set principle is used to analyze the stability of the designed controller system to illustrate the realization of reactive power and unbalanced power distribution problems. The designed controller can avoid Zeno behavior by contradiction. The effectiveness of the proposed distributed auxiliary controller is verified by simulation experiments. The controller can cope with changes in load demand well and has strong robustness. Under the premise of ensuring stability, it meets the plug-and-play requirements of the microgrid system. In summary, compared with the traditional droop control strategy, the present invention significantly reduces the calculation and communication burden of the controller while achieving the power distribution goal. The effectiveness of the controller and the feasibility of the method are verified by proof and experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the steps of the method of the present invention; Figure 2 It is a block diagram of the overall control scheme of the microgrid of the present invention; Figure 3 is the equivalent circuit of the microgrid under positive sequence frequency; Figure 4 is the microgrid equivalent circuit under negative sequence frequency; Figure 5 The AC microgrid model used in the embodiments; Figure 6 A topological diagram of the AC microgrid distributed power sources used in the embodiment; Figure 7 Bus voltage output diagram used in the embodiment; Figure 8 The output diagram of the product of the droop coefficient and the reactive power after adding the reactive power controller with uniform quantization designed by the present invention to Example 1; Fig. 9 The output diagram of the product of the droop coefficient and the reactive power after adding the reactive power controller with logarithmic quantization designed by the present invention to Example 1; Fig.10 An output diagram of the ratio of unbalanced power to unbalanced power reference value after adding the unbalanced power controller with uniform quantization designed by the present invention to Example 2; Fig.11 An output diagram of the ratio of unbalanced power to unbalanced power reference value after adding the unbalanced power controller with logarithmic quantization designed by the present invention to Example 2; Fig.12 The distributed event-triggered control reactive power controller event triggering time series diagram with quantized information designed by the present invention is added to Example 1; Fig.13 The event triggering time series diagram of the unbalanced power controller designed by the present invention and having quantized information is added to Example 2; Fig.14 The quantizer output diagram after adding the distributed event-triggered control reactive power controller with quantization information designed by the present invention to Example 1; Fig.15 It is an output diagram of the ratio of unbalanced power to unbalanced power reference value after adding the unbalanced power controller designed by the present invention and adding the unbalanced power controller with a smaller quantization level in Example 2; Fig.16 This is an output diagram of the ratio of unbalanced power to unbalanced power reference value after adding the unbalanced power controller designed by the present invention and adding an unbalanced power controller with a larger quantization level in Example 2; Fig.17 It is an output diagram of the ratio of unbalanced power to unbalanced power reference value after adding the unbalanced power controller with uniform quantization designed by the present invention under variable load in Example 2; Fig.18 The output diagram of the ratio of unbalanced power to unbalanced power reference value after adding the unbalanced power controller with logarithmic quantization designed by the present invention in Example 2 under variable load conditions; Fig.19 A comparison chart of the number of communications between the distributed event-triggered reactive power controller with quantized information designed by the present invention and the traditional periodic communication in Example 1; Fig. 20This is a comparison chart of the number of communications between the distributed event-triggered unbalanced power controller with quantized information designed by the present invention and the traditional periodic communication after implementation in Example 2. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] See also Figure 1 , a distributed power control method of an AC microgrid with quantized event triggering, comprising the following steps: First, establish the communication network of the system and introduce the knowledge of graph theory: The communication structure of AC microgrid is generally represented by a graph. The communication topology of the network layer does not need to be the same as the topology of the physical layer. It is usually represented by an undirected graph. To indicate that Is indivual A finite set of vertices, the adjacency matrix , edge set Included in ,picture It is considered that for all edges , are all undirected, agents The set of agents that can receive information is Indicates that if ,but ,besides ,main body The degree of Definition, the degree matrix is ​​given by Definition, symmetric semi-positive Laplace matrix Defined as , if the figure is connected, then the matrix The row and column sums of are both zero; S1. Measure the parameters required by the controller, including bus voltage, fundamental positive sequence current, fundamental negative sequence current, fundamental positive sequence voltage, fundamental negative sequence voltage and cut-off frequency; Measuring system cutoff frequency , low pass filter Reference voltage ,exist In the coordinate system Voltage measurement value and , basic positive (negative) sequence current in microgrid and ( and ), and thus obtain the values ​​of active power and unbalanced power, the calculation formula is as follows: in, Represents the reactive power value in the system, Represents the unbalanced power value in the system; The control objectives of the designed distributed reactive power controller are as follows: in is the reactive power coefficient of the system, Represent the reactive power measurement values ​​of the distributed generator itself and its neighbors respectively; The control objectives of the designed distributed reactive power controller are as follows: Unbalanced power: in is the rated unbalanced power of the system, and represent the unbalanced power measurements of the DG itself and its neighbors, respectively; S2, using proportional resonant controller; because The controller encounters difficulties in tracking non-DC variables. A proportional resonant controller is usually used to control the current and voltage in a static reference frame. The present invention adopts a proportional resonant controller as follows: Voltage Controller: Current controller: in, , represents the proportionality coefficient, , represents the resonance coefficient, represents the voltage controller cut-off frequency, represents the current controller cut-off frequency, Indicates the rated angular frequency; S3, introduce virtual impedance to achieve target control, and realize the distribution of reactive power and unbalanced power by adjusting the virtual impedance of positive sequence, negative sequence and harmonic frequency; In order to achieve accurate power distribution, it is necessary to uniformly adjust the two The equivalent impedance of the unit, the virtual impedance is controlled at a specific frequency Equivalent impedance provides an effective method, therefore, reactive power distribution can be achieved by adjusting the virtual impedance of positive sequence, negative sequence and harmonic frequencies; The design uses two islanded microgrid distributed generators with the same rated power, where the feeder impedance presents an inductive characteristic and the distributed generator set is composed of two generators with the same rated power. The controlled voltage source operating under the condition of Department The equivalent impedance is represented as: in express The physical feeder impedance at express Virtual impedance at An unbalanced load is represented by a current source, Equivalent basic negative sequence impedance for: in and They represent the physical feeder impedance and virtual impedance at negative sequence frequency respectively; S4. Design a distributed reactive power secondary controller based on droop control and distributed control theory; Design of a preliminary distributed reactive power two-stage controller: Reactive power: in is the control gain of the system, is the adjacency matrix of distributed generation units; Based on the above controller, an event trigger mechanism is introduced. For the distribution of reactive power, the event trigger condition is designed as follows: In the formula, Express satisfaction , , A continuously differentiable function, defined as is the measurement error of the system, that is, the actual measurement value of the system The measured value at the time of triggering The difference between definition , after adding the event trigger mechanism, the designed distributed reactive power controller can be rewritten as: Reactive power controller: ; A quantization mechanism is added on the basis of adding an event trigger mechanism. The present invention provides two quantizers, namely a uniform quantizer and a logarithmic quantizer. make , the following two quantizers will be introduced: Uniform Quantizer: In the formula, represents the quantization interval, satisfying , Indicates less than or equal to The maximum integer, uniform quantization error satisfies , that is, when hour, ; Logarithmic Quantizer: In the formula, the logarithmic quantization error satisfies , which also satisfies hour, ,when When the quantization error Eventually it tends to 0; The distributed reactive power controller after adding event trigger mechanism and quantization mechanism can be expressed as: Reactive power: in, express At the time of event triggering The quantized value at It will be updated only at the moment and in the time period The inside remains unchanged; If the designed controller fails to accurately realize the distribution of reactive power, the distribution error generated by the local controller is used to adaptively adjust the virtual inductance: in is the static virtual impedance at the fundamental positive sequence to eliminate the reactive power distribution error. It is a proportional-integral controller; S5. Design a distributed unbalanced power two-stage controller based on droop control and distributed control theory; Design of a preliminary distributed unbalanced power two-stage controller: in, is the control gain of the system, is the adjacency matrix of distributed generation units; Based on the above controller, an event trigger mechanism is introduced. For the distribution of unbalanced power, the event trigger condition is designed as follows: In the formula, To satisfy , , A continuously differentiable function, defined as is the measurement error of the system, that is, the actual measurement value of the system The measured value at the time of triggering The difference between definition , after adding the event trigger mechanism, the designed distributed unbalanced power controller is rewritten as: On the basis of adding the event trigger mechanism, the quantization mechanism introduced in the above steps is added. The distributed unbalanced power controller after adding the event trigger mechanism and the quantization mechanism can be expressed as: in, express At the time of event triggering The quantized value at It will be updated only at the moment and in the time period The inside remains unchanged; If the designed controller fails to accurately achieve the unbalanced power distribution, the distribution error generated by the local controller is used to adaptively adjust the virtual inductance: It is used to ensure that the fundamental wave equivalent impedance is inductive and is adaptively adjusted by the integral controller to eliminate the unbalanced power distribution error. It is a proportional-integral controller; S6. Pass The invariant set principle is used to prove the stability of the system. By using the contradiction method, it is shown that there is a lower limit on the time interval between each triggered event, which means that the system does not exist. Behavior; According to the reactive power distribution controller shown above, the following formula can be obtained: From the analysis, we can know that: The above formula can be rewritten as: Design a Lyapunov function , then the derivative of the Lyapunov function can be expressed as: The derivative of the Lyapunov function is expanded, and according to the symmetry of the Laplace matrix and Young's inequality , after simplification, we can get: Bring in the designed event trigger conditions, and you can get The following relationship: Now bring in the event trigger function The definition of and the definition of quantization error can be concluded: and The changes over time tend to zero, so we only need to ensure It can guarantee ; The characteristics of an invariant set are , that is ,According to Lyapunov theory and Russell invariant set principle, the system can be stable and reactive power distribution can be achieved. In the event trigger mechanism, it is not allowed to have infinite events in a limited time. This situation is Zeno behavior; The present invention can prove by contradiction that there is a lower limit of the time interval between the triggering of two events. Taking the distribution of reactive power as an example, it is proved that the designed controller will not exhibit Zeno behavior. According to the definition of measurement error and the properties of the norm, the following formula can be obtained by scaling: From the definition of event triggering, we can know that , as well as , and through the above analysis, we can know that according to the set event trigger function From the definition of , we can know that the derivative of the norm must be less than a positive constant; From the above analysis, we can know ; If established, then there will be , which contradicts the setting, is constant in the analysis; From the above analysis, it can be seen that there is no Zeno behavior in the system. The stability of the designed unbalanced power controller and the Zeno behavior analysis are consistent with the analysis of reactive power. It is just necessary to change the Lyapunov function to; The beneficial effect of the present invention is that due to the droop control in the isolated DC microgrid, the distribution of reactive power and unbalanced power in the system cannot be guaranteed. To address this problem, this paper proposes a distributed control method with quantized event triggering. The proposed control scheme can reduce communication on the basis of realizing reactive and unbalanced power distribution between distributed power generation units by adding a designed distributed secondary controller with a quantized event triggering method. The part that cannot be accurately distributed can be readjusted through a negative feedback system through PI control. In addition, the proposed method does not require global power information. Each distributed generator communicates with its neighbors only when the triggering conditions are met, which greatly reduces the communication burden of the microgrid communication network. The stability of the method is proved by the Russell invariant set principle, and the Zeno behavior is also eliminated by contradiction. Finally, the present invention verifies the effectiveness of the method through experimental analysis, and the experimental data is given in the following examples; Combination Figure 5 The physical topology diagram and Figure 6 Given the communication topology diagram, the microgrid simulation design model of the embodiment can be determined, and the Laplace matrix of the communication network as follows: In Example 1, the output reactive power of distributed power sources 1 to 5 is 55 kVar, 60 kVar, 65 kVar, 70 kVar, and 75 kVar respectively; the reactive gain is 0.001; In Example 1, the output unbalanced powers of distributed power sources 1 to 5 are 22 kVar, 23 kVar, 24 kVar, 25 kVar, and 26 kVar respectively; the unbalanced power reference value is 1 kVar; Figure 2 The overall control block diagram of the microgrid of the present invention is shown, Figure 3 represents the microgrid equivalent circuit under positive sequence frequency, Figure 4 represents the microgrid equivalent circuit under negative sequence frequency, Figure 5 The schematic diagram of event-triggered control shows that the initial bus voltage is 220V. When the continuous signal is discretized, the simulation step size is selected as 0.02s. Figure 6 represents the AC microgrid model used in the embodiment, Figure 6 , Figure 7 Respectively represent the physical and communication topology diagrams of the microgrid model used in the embodiment, Figure 8 , Fig. 9 The output diagram of the product of the droop coefficient and the reactive power after adding the reactive power controller with a uniform quantizer and a logarithmic quantizer designed by the present invention to Example 1, FIG10, Fig.11The output diagram of the ratio of the unbalanced power to the unbalanced power reference value after adding the unbalanced power controller with uniform quantizer and logarithmic quantizer designed by the present invention to Example 2 is as follows: Figure 8 , Fig. 9 , Fig.10 , Fig.11 It can be seen that after adding the controller designed by the present invention, the reactive power and unbalanced power values ​​have achieved output consistency, proving the effectiveness of the present invention. Fig.13 The event triggering time series diagrams of the distributed event-triggered control power controller with quantization information designed by the present invention are added to Embodiments 1 and 2 respectively, which illustrate that the controller designed by the present invention can avoid Zeno behavior. FIG. 14 is a quantizer output diagram after the distributed event-triggered control reactive power controller with quantization information designed by the present invention is added to Embodiment 1, which illustrates the effectiveness of the quantizer used. Fig.15 , Fig.16 The output diagram of the ratio of unbalanced power to unbalanced power reference value after adding the unbalanced power controller designed by the present invention to Example 2 and adding unbalanced power controllers with different quantization levels illustrates that the smaller the quantization level, the smoother the output curve. Fig.17 , Fig.18 They are the output diagrams of the ratio of unbalanced power to unbalanced power reference value after adding the unbalanced power controller with uniform quantizer and logarithmic quantizer designed by the present invention in Example 2 under variable load, indicating that the controller designed by the present invention has certain robustness and can realize plug-and-play function. Fig.19 , Fig. 20 This is a comparison chart of the number of communications between Examples 1 and 2 using the distributed event-triggered reactive power controller with quantized information designed by the present invention and traditional periodic communication. This intuitively shows that the controller designed by the present invention greatly reduces the number of event triggering times and can better adapt to situations where communication bandwidth is limited.

[0022] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A distributed power control method for AC microgrid with quantized event triggering, characterized in that: The following steps are involved: S1. Measure the parameters required by the controller, including bus voltage, fundamental positive sequence current, fundamental negative sequence current, fundamental positive sequence voltage, fundamental negative sequence voltage and cut-off frequency; S2, using proportional resonant controller; S3, introduce virtual impedance to achieve target control, and realize the distribution of reactive power and unbalanced power by adjusting the virtual impedance of positive sequence, negative sequence and harmonic frequency; S4. Design a distributed reactive power secondary controller based on droop control and distributed control theory; S5. Design a distributed unbalanced power two-stage controller based on droop control and distributed control theory; S6. Pass The invariant set principle is used to prove the stability of the system. By using the contradiction method, it is shown that there is a lower limit on the time interval between each triggered event, which means that the system does not exist. Behavior.

2. The AC microgrid distributed power control method with quantized event triggering according to claim 1 is characterized in that: The proportional resonant controller is introduced in S2, and its voltage controller model is as follows: In the formula, represents the proportionality coefficient, represents the resonance coefficient, represents the voltage controller cut-off frequency, Indicates the rated angular frequency.

3. The AC microgrid distributed power control method with quantized event triggering according to claim 2 is characterized in that: The proportional resonant controller is introduced in S2, and its current controller model is as follows: In the formula, represents the proportionality coefficient, represents the resonance coefficient, represents the current controller cut-off frequency, Indicates the rated angular frequency.

4. The AC microgrid distributed power control method with quantized event triggering according to claim 3 is characterized in that: The distributed reactive power controller designed in S4 is expressed as follows: In the formula, represents the reactive power coefficient of the system, Represents the reactive power measurement value of the system, express At the time of event triggering The quantitative value of is the control gain of the system, is the adjacency matrix of distributed generation units.

5. The AC microgrid distributed power control method with quantized event triggering according to claim 4 is characterized in that: The event triggering mechanism in S4 is as follows: In the formula, Express satisfaction , , A continuously differentiable function, is the measurement error of the system, that is, the actual measurement value of the system The measured value at the time of triggering The difference between .

6. The AC microgrid distributed power control method with quantized event triggering according to claim 5 is characterized in that: The uniform quantizer designed in S4 is as follows: In the formula, Represents the quantization interval, satisfying , Indicates less than or equal to The maximum integer, uniform quantization error satisfies , that is, when hour, .

7. The AC microgrid distributed power control method with quantized event triggering according to claim 6 is characterized in that: The logarithmic quantizer designed in S4 is as follows: In the formula, the logarithmic quantization error satisfies , which also satisfies hour, ,when When the quantization error Eventually it approaches 0.

8. The AC microgrid distributed power control method with quantized event triggering according to claim 7 is characterized in that: The distributed unbalanced power controller designed in S5 is expressed as follows: In the formula, Indicates the unbalanced power reference value of the system, Represents the reactive power measurement value of the system, express Event trigger time The quantitative value of is the control gain of the system, is the adjacency matrix of distributed generation units.

9. The AC microgrid distributed power control method with quantized event triggering according to claim 8, characterized in that: The event triggering mechanism in S5 is as follows: In the formula, To satisfy , , A continuously differentiable function, is the measurement error of the system, that is, the actual measurement value of the system The measured value at the time of triggering The difference between .

10. The AC microgrid distributed power control method with quantized event triggering according to claim 9, characterized in that: The quantizer used in the unbalanced power of S5 is the same as the quantizer used in S4.

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