A microgrid current distribution method based on decentralized and distributed hybrid control

Abstract

The present invention discloses a microgrid current distribution method based on decentralized and distributed hybrid control, comprising: S1, dividing all distributed energy sources of the microgrid into K clusters, wherein the kth cluster contains n k The distributed energy in each cluster is in an island operation state; S2, the first distributed energy in each cluster is designated as the leading distributed energy to receive the DC bus voltage signal; S3, the secondary controller of each distributed energy is constructed; S4, the DC microgrid model is constructed based on the droop control and the secondary controller; S5, the current distribution ratio between the distributed energy in the cluster and the total current distribution ratio of the distributed energy between clusters are obtained according to the DC microgrid model. This method can effectively realize voltage recovery and current distribution, with good system stability, high flexibility and safety.

Description

Technical Field

[0001] The present invention belongs to the field of microgrid operation control, and in particular relates to a microgrid current distribution method based on decentralized and distributed hybrid control. Background Art

[0002] Microgrids are composed of distributed energy sources (DG), energy storage systems, and local loads. In the island operation mode, voltage stability and current distribution of DC microgrids are one of the common research issues. Researchers have achieved decentralized current distribution among distributed power sources by introducing a droop control strategy in primary control. However, this strategy will cause bus voltage deviation.

[0003] To solve the bus deviation problem, a secondary control strategy is usually designed to compensate for the voltage deviation caused by droop control. At present, common secondary controls mainly include centralized, distributed and decentralized control. Centralized control requires a powerful central controller to process information, and has disadvantages such as high implementation cost and easy single point failure. Distributed control restores the bus voltage to the nominal value by constructing a secondary controller that introduces a neighbor communication strategy. The difference between decentralized and distributed control is that decentralized control requires bus voltage information but does not have neighbor information communication. In addition, some advanced control strategies that take into account imperfect communication environments, such as event-triggered communication and time delay, have been studied. The results show that the greater the communication volume, the better the control performance. However, the more exchanges, the greater the possibility of cyber attacks and the higher the cost of communication. The secondary control strategies of existing methods only use decentralized or distributed methods alone, which is difficult to improve the security and flexibility of DC microgrids. Summary of the invention

[0004] The purpose of the present invention is to address the above problems and propose a microgrid current distribution method based on decentralized and distributed hybrid control to effectively achieve voltage recovery and current distribution, with good system stability, high flexibility and safety.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The present invention proposes a microgrid current distribution method based on decentralized and distributed hybrid control, comprising the following steps:

[0007] S1. Divide all distributed energy resources in the microgrid into K clusters. The kth cluster contains n k Distributed energy resources, n k ≥1, k=1,...,K, K≤N, N is the number of distributed energy resources, and the microgrid is in an island operation state;

[0008] S2. Designate the first distributed energy in each cluster as the leading distributed energy for receiving the DC bus voltage signal V b ;

[0009] S3. Construct the secondary controller of each distributed energy source. The formula of the i-th secondary controller of the k-th cluster is as follows:

[0010]

[0011] in,

[0012]

[0013]

[0014] In the formula, u k,i is the secondary control signal of the i-th distributed energy source in the k-th cluster, is the voltage regulation control item of the i-th distributed energy in the k-th cluster, is the current distribution control item of the i-th distributed energy in the k-th cluster, τ is the exponential coefficient, and 0<τ<1, λ k,i and α k,i are the proportional and integral coefficients of the voltage regulation control term of the i-th distributed energy in the k-th cluster, β k,i is the integral coefficient of the current distribution control of the i-th distributed energy in the k-th cluster, and β k,i =γ k (R k,i +d k,i ), adjusting parameter γ k >0, R k,i is the transmission line resistance of the ith distributed energy source in the kth cluster, d k,i is the droop coefficient of the i-th distributed energy in the k-th cluster, i=1,...,n k , e V is the bus voltage deviation, is the input consensus error of the i-th distributed energy source in the k-th cluster;

[0015] S4. A DC microgrid model is constructed based on droop control and secondary controller. The DC microgrid model is as follows:

[0016] V b =V * -(R k,i +d k,i )I k,i +u k,i

[0017] In the formula, I k,i is the current output value of the i-th distributed energy in the k-th cluster, V *is the nominal voltage value of the DC bus;

[0018] S5. According to the DC microgrid model, the current distribution ratio between distributed energy sources within the cluster and the total current distribution ratio of distributed energy sources between clusters are obtained, where:

[0019] The current distribution ratio between distributed energy sources within the cluster meets the following conditions:

[0020]

[0021] The total current distribution ratio of distributed energy between clusters meets the following conditions:

[0022]

[0023] In the formula, R k,1 is the transmission line resistance of the first distributed energy source in the kth cluster, d k,1 is the droop coefficient of the first distributed energy in the kth cluster, I l,j is the current output value of the jth distributed energy in the lth cluster, R l,1 is the transmission line resistance of the first distributed energy source in the lth cluster, d l,1 is the droop coefficient of the first distributed energy in the lth cluster, l=1,...,K,j=1,...,n k , α k is the voltage control integral coefficient of the first distributed energy in the kth cluster, α l is the voltage control integral coefficient of the first distributed energy in the lth cluster.

[0024] Preferably, the i-th secondary controller of the k-th cluster also satisfies the following conditions:

[0025]

[0026]

[0027] In the formula, λ k is the voltage control proportional coefficient of the first distributed energy in the kth cluster.

[0028] Preferably, the bus voltage deviation e V and input consensus error Satisfies the following formula:

[0029] e V =V * -V b

[0030]

[0031] In the formula, is the set of neighbor secondary controllers of the i-th distributed energy resource in the k-th cluster, u k,j is the secondary control signal of the jth distributed energy source in the kth cluster.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This application designs a hybrid secondary controller for an isolated DC microgrid system, which has the advantages of both distributed and decentralized control methods, that is, all distributed energy sources are divided into multiple clusters, and a distributed control strategy is adopted within the same cluster, while a decentralized control strategy is adopted between different clusters to ensure that the communication between distributed energy sources in the same cluster is reliable and safe, and the proposed secondary controller can quickly restore the voltage to the nominal value, and further realize the current distribution between distributed energy sources in the cluster according to the droop ratio. The total current distribution of distributed energy between clusters is better than that of only following the distribution of the leading distributed energy source, effectively realizing voltage recovery and current distribution, and having good system stability, high flexibility and safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of the microgrid current distribution method of the present invention;

[0035] Figure 2 is a control block diagram of the i-th distributed energy source in the k-th cluster of the present invention;

[0036] Figure 3 It is a comparison diagram of bus voltage and output current before and after starting the secondary controller of the present invention;

[0037] Figure 4 This is a comparison diagram of bus voltage and output current before and after the standby DG is connected and disconnected in the present invention;

[0038] Figure 5 This is a comparison diagram of bus voltage and output current before and after the resistive load is connected and disconnected in the present invention;

[0039] Figure 6 It is a comparison diagram of bus voltage and output current before and after the constant power load is connected and disconnected in the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0041] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0042] In order to overcome the problem that the prior art is difficult to meet the flexibility and safety requirements of microgrids, the present application provides a microgrid current distribution method with decentralized and distributed hybrid control.

[0043] like Figure 1-6 As shown, a microgrid current distribution method based on decentralized and distributed hybrid control includes the following steps:

[0044] Follow these steps:

[0045] S1. Divide all distributed energy resources in the microgrid into K clusters. The kth cluster contains n k Distributed energy resources, n k ≥1, k=1,...,K, K≤N, N is the number of distributed energy sources, and the microgrid is in an island operation state. In order to achieve hybrid control, all distributed energy sources DG are first decomposed into K clusters, and the kth cluster contains n k In practical applications, distributed energy DGs that are close to each other can be divided into the same cluster.

[0046] S2. Designate the first distributed energy in each cluster as the leading distributed energy for receiving the DC bus voltage signal V b Without loss of generality, the first distributed energy in each cluster is designated as the leading distributed energy, which is used to receive the DC bus voltage feedback signal V b , the total current distribution of DGs among clusters is more than just following the distribution of the leading DG to achieve the current distribution and voltage recovery of the microgrid.

[0047] S3. Construct the secondary controller of each distributed energy source. The formula of the i-th secondary controller of the k-th cluster is as follows:

[0048]

[0049] in,

[0050]

[0051]

[0052] In the formula, u ki is the secondary control signal of the i-th distributed energy source in the k-th cluster, is the voltage regulation control item of the i-th distributed energy in the k-th cluster, is the current distribution control item of the i-th distributed energy in the k-th cluster, τ is the exponential coefficient, and 0<τ<1, λ k,i and α k,i are the proportional and integral coefficients of the voltage regulation control term of the i-th distributed energy in the k-th cluster, β k,i is the integral coefficient of the current distribution control of the i-th distributed energy in the k-th cluster, and β k,i =γ k (R k,i +d k,i ), adjusting parameter γ k >0, R k,i is the transmission line resistance of the ith distributed energy source in the kth cluster, d k,i is the droop coefficient of the i-th distributed energy in the k-th cluster, i=1,...,n k , e V is the bus voltage deviation, is the input consensus error of the i-th distributed energy source in the k-th cluster.

[0053] S4. A DC microgrid model is constructed based on droop control and secondary controller. The DC microgrid model is as follows:

[0054] V b =V * -(R k,i +d k,i )I k,i +u k,i

[0055] In the formula, I k,i is the current output value of the i-th distributed energy in the k-th cluster, V * is the nominal voltage of the DC bus.

[0056] like Figure 2As shown, the DC microgrid model includes two parts: primary control and secondary control. That is, a secondary controller is introduced as a compensation item on the basis of primary control to quickly restore the DC bus voltage signal to the nominal voltage value. The primary control is mainly based on the droop control strategy, and also includes a voltage loop, a current loop and a pulse modulator (PWM) to control the power input of each distributed energy source into the microgrid and realize the precise distribution of the output power of each distributed energy source. For example, reference: Guo F, Xu Q, Wen C, et al. Distributed secondary control for power allocation and voltage restoration in islanded DC microgrids [J]. IEEE Transactions on Sustainable Energy, 2018, 9 (4): 1857-1869., which is a prior art well known to those skilled in the art and will not be repeated here. It is easy to understand that each distributed energy source is connected to the common node of the microgrid, such as through the corresponding connected step-down DC / DC converter and LC filter to the common node of the microgrid, and the microgrid is in an island operation state. It can achieve the purpose of precise distribution by adaptively adjusting the current distribution of each distributed energy source under load fluctuation.

[0057] S5. According to the DC microgrid model, the current distribution ratio between distributed energy sources within the cluster and the total current distribution ratio of distributed energy sources between clusters are obtained, where:

[0058] The DC bus voltage signal V b Restore to the nominal voltage value, meet V * =V b ,u k,i =u k,j , when the selected droop coefficient is much larger than the corresponding transmission line resistance, the output current distribution ratio between the DGs can be obtained, then

[0059] The current distribution ratio between distributed energy sources within the cluster meets the following conditions:

[0060]

[0061] The total current distribution ratio of distributed energy between clusters meets the following conditions:

[0062]

[0063] In the formula, R k,1 is the transmission line resistance of the first distributed energy source in the kth cluster, d k,1 is the droop coefficient of the first distributed energy in the kth cluster, I l,jis the current output value of the jth distributed energy in the lth cluster, R l,1 is the transmission line resistance of the first distributed energy source in the lth cluster, d l,1 is the droop coefficient of the first distributed energy in the lth cluster, l=1,...,K,j=1,...,n k , α k is the voltage control integral coefficient of the first distributed energy in the kth cluster, α l is the voltage control integral coefficient of the first distributed energy in the lth cluster.

[0064] In one embodiment, the i-th secondary controller of the k-th cluster also satisfies the following condition:

[0065]

[0066]

[0067] In the formula, λ k is the voltage control proportional coefficient of the first distributed energy in the kth cluster.

[0068] In one embodiment, the bus voltage deviation e V and input consensus error Satisfies the following formula:

[0069] e V =V * -V b

[0070]

[0071] In the formula, is the set of neighbor secondary controllers of the i-th distributed energy resource in the k-th cluster, u k,j is the secondary control signal of the jth distributed energy source in the kth cluster.

[0072] Traditional droop control has a trade-off between voltage deviation and current distribution accuracy. Therefore, the present invention introduces a secondary controller to compensate for bus voltage deviation, that is, adding a secondary control signal to the primary control (droop control), which can quickly restore the voltage to the nominal value and achieve reasonable current distribution.

[0073] The effectiveness of the present invention is further illustrated by specific examples below:

[0074] 1) Parameter setting: In this experiment, an islanded DC microgrid with 6 distributed energy resources (DG) is constructed based on the real-time simulator OPAL-RT. The proposed secondary controller is implemented and executed on the digital signal processor control board. The main electrical parameters and controller parameters are shown in Table 1.

[0075] Table 1 Main electrical parameters and controller parameters

[0076]

[0077]

[0078] The islanded DC microgrid with 6 DGs is divided into 3 clusters. The first cluster includes DG 1,1 and DG 1,2 , the second cluster includes DG 2,1 , the third cluster includes DG 3,1 , DG 3,2 , DG 3,3 , where DG 3,3 The standby DG is disconnected in the initial state, and the nominal voltage value of the DC bus is V * It is 48V.

[0079] 2) Experimental results

[0080] from Figure 3 The simulation results show that after the secondary controller starts, the voltage is restored to the nominal voltage of 48V, and the DG in the first and third clusters is I 1,1 :I 1,2 ≈1:2 and I 3,1 :I 3,2 The droop ratio is ≈3:1, and the total current ratio between clusters is I 1,1 +I 1,2 :I 2,1 :I 3,1 +I 3,2 ≈3:4:3 distribution.

[0081] from Figure 4 The simulation results show that under the secondary controller, the voltage can be restored to the nominal voltage of 48V when the backup DG is connected or disconnected. When the backup DG is connected, only the current distribution ratio in the third cluster changes from I 3,1 :I 3,2 ≈3:1 changes to I 3,1 :I 3,2 :I 3,3 ≈3:1:2, and the current distribution of other clusters does not change.

[0082] from Figure 5 The simulation results show that under the secondary controller, on the basis of connecting a 2Ω load, the resistive load (4Ω) is connected and disconnected in parallel, and the voltage can be restored to the nominal voltage of 48V, and the current distribution ratio remains unchanged.

[0083] from Figure 6The simulation results show that under the secondary controller, on the basis of connecting a 2Ω load, and then connecting and disconnecting a constant power load (P=100W) in parallel, the voltage can be restored to the nominal voltage of 48V, and the current distribution ratio remains unchanged.

[0084] This application designs a hybrid secondary controller for an island DC microgrid system, which combines the advantages of distributed and decentralized control methods. Specifically, all DGs are divided into multiple clusters, and DGs in the same cluster adopt a distributed control strategy, while decentralized control strategies are adopted between different clusters. The proposed secondary controller can restore the voltage to the nominal value within a limited time, and further realize the current distribution between DGs in the cluster according to the droop ratio, and the total current distribution ratio of DGs between clusters only follows the distribution of the leading DG.

[0085] It is worth pointing out that the existing distributed control methods and decentralized control methods are special cases of the proposed hybrid control strategy. If K = 1, it is distributed control; if n k =1,k=1,…,K, then it is distributed control.

[0086] This method designs a hybrid secondary controller for the isolated DC microgrid system, which has the advantages of both distributed and decentralized control methods, that is, all distributed energy sources are divided into multiple clusters, and a distributed control strategy is adopted within the same cluster, while a decentralized control strategy is adopted between different clusters to ensure that the communication between distributed energy sources in the same cluster is reliable and safe. The proposed secondary controller can quickly restore the voltage to the nominal value, and further realize the current distribution between distributed energy sources in the cluster according to the droop ratio. The total current distribution of distributed energy between clusters is better than that of only following the distribution of the leading distributed energy source, which effectively realizes voltage recovery and current distribution, and has good system stability, high flexibility and safety.

[0087] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0088] The above-described embodiments only express the more specific and detailed embodiments described in this application, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of this application, which all belong to the protection scope of this application. Therefore, the protection scope of the patent application shall be based on the attached claims.

Claims

1. A microgrid current distribution method based on decentralized and distributed hybrid control, characterized in that: The microgrid current distribution method based on decentralized and distributed hybrid control comprises the following steps: S1. Divide all distributed energy resources in the microgrid into K clusters. The kth cluster contains n k Distributed energy resources, n k ≥1, k=1,...,K, K≤N, N is the number of distributed energy resources, and the microgrid is in an island operation state; S2. Designate the first distributed energy in each cluster as the leading distributed energy for receiving the DC bus voltage signal V b ; S3. Construct the secondary controller of each distributed energy source. The formula of the i-th secondary controller of the k-th cluster is as follows: in, In the formula, u k,i is the secondary control signal of the i-th distributed energy source in the k-th cluster, is the voltage regulation control item of the i-th distributed energy in the k-th cluster, is the current distribution control item of the i-th distributed energy in the k-th cluster, τ is the exponential coefficient, and 0<τ<1, λ k,i and α k,i are the proportional and integral coefficients of the voltage regulation control term of the i-th distributed energy in the k-th cluster, β k,i is the integral coefficient of the current distribution control of the i-th distributed energy in the k-th cluster, and β k,i =γ k (R k,i +d k,i ), adjusting parameter γ k >0, R k,i is the transmission line resistance of the ith distributed energy source in the kth cluster, d k,i is the droop coefficient of the i-th distributed energy in the k-th cluster, i=1,...,n k , e V is the bus voltage deviation, is the input consensus error of the i-th distributed energy source in the k-th cluster; The i-th secondary controller of the k-th cluster also satisfies the following condition: In the formula, λ k is the voltage control proportional coefficient of the first distributed energy in the kth cluster; The bus voltage deviation e V and input consensus error Satisfies the following formula: yes V =V * -V b In the formula, is the set of neighbor secondary controllers of the i-th distributed energy resource in the k-th cluster, u k,j is the secondary control signal of the jth distributed energy source in the kth cluster; S4. Construct a DC microgrid model based on droop control and secondary controller. The DC microgrid model is as follows: V b =V * -(R k,i +d k,i )I k,i +u k,i In the formula, I k,i is the current output value of the i-th distributed energy in the k-th cluster, V * is the nominal voltage value of the DC bus; S5. According to the DC microgrid model, the current distribution ratio between distributed energy sources within the cluster and the total current distribution ratio of distributed energy sources between clusters are obtained, where: The current distribution ratio between distributed energy sources within the cluster meets the following conditions: The total current distribution ratio of distributed energy between clusters meets the following conditions: In the formula, R k,1 is the transmission line resistance of the first distributed energy source in the kth cluster, d k,1 is the droop coefficient of the first distributed energy in the kth cluster, I l,j is the current output value of the jth distributed energy in the lth cluster, R l,1 is the transmission line resistance of the first distributed energy source in the lth cluster, d l,1 is the droop coefficient of the first distributed energy in the lth cluster, l=1,...,K,j=1,...,n k , α k is the voltage control integral coefficient of the first distributed energy in the kth cluster, α l is the voltage control integral coefficient of the first distributed energy in the lth cluster.

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