CN115117930A - A Microgrid Current Distribution Method Based on Distributed and Distributed Hybrid Control - Google Patents

Abstract

The invention discloses a microgrid current distribution method based on distributed and distributed hybrid control, comprising: S1. Divide all distributed energy sources of the microgrid into K clusters, and the kth cluster contains n _k distributed energy sources. Energy, the microgrid is in an island operation state; S2, designate the first distributed energy source of each cluster as the leading distributed energy source, which is used to receive the DC bus voltage signal; S3, construct the secondary controller of each distributed energy source; S4. . Construct a DC microgrid model based on the droop control and the secondary controller; S5 , obtain the current distribution ratio between the distributed energy resources within the cluster and the total current distribution ratio of the distributed energy resources between the clusters according to the DC microgrid model. The method can effectively realize voltage recovery and current distribution, and has good system stability, high flexibility and safety.

Description

A Microgrid Current Distribution Method Based on Distributed and Distributed Hybrid Control

technical field

The invention belongs to the field of microgrid operation control, and in particular relates to a microgrid current distribution method based on distributed and distributed hybrid control.

Background technique

The microgrid consists of distributed generators (DG), energy storage systems and local loads. The voltage stabilization and current distribution of DC microgrids in the islanding operation mode is one of the common research problems. By introducing a droop control strategy in the primary control, the researchers realize the distributed current distribution among the distributed power sources. However, this strategy can cause bus voltage deviations.

To solve the problem of busbar deviation, a secondary control strategy is usually designed to compensate for the voltage deviation caused by droop control. At present, the common secondary control mainly includes centralized control, distributed control 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 of failure. Distributed control restores the bus voltage to its nominal value by constructing a secondary controller that introduces a neighbor communication strategy. The difference between distributed and distributed control is that distributed control requires bus voltage information without neighbor information communication. In addition, some advanced control strategies considering imperfect communication environment, such as event-triggered communication, time delay, etc., are also studied. The results show that the greater the amount of communication, the better the control performance. However, the more communication there is, the more likely it is to suffer a cyber attack, and the more expensive the communication is. The secondary control strategy of the existing method only adopts distributed or distributed alone, and it is difficult to improve the security and flexibility of the DC microgrid.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the above problems, and propose a microgrid current distribution method based on distributed and distributed hybrid control, so as to effectively realize voltage recovery and current distribution, with good system stability, high flexibility and safety.

To achieve the above object, the technical scheme adopted by the present invention is:

A microgrid current distribution method based on distributed and distributed hybrid control proposed by the present invention includes the following steps:

S1. Divide all distributed energy sources of 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, the microgrid is in an island operation state;

S2. Designate the first distributed energy source of each cluster as the leading distributed energy source 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,

为第k个簇中第i个分布式能源的电压调节控制项，

为第k个簇中第i个分布式能源的电流分配控制项，τ为指数系数，且0＜τ＜1，λ_k,i和α_k,i依次为第k个簇中第i个分布式能源的电压调节控制项的比例和积分系数，β_k,i为第k个簇中第i个分布式能源的电流分配控制的积分系数，取β_k,i＝γ_k(R_k,i+d_k,i)，调节参数γ_k＞0，R_k,i为第k个簇中第i个分布式能源的传输线电阻，d_k,i为第k个簇中第i个分布式能源的下垂系数，i＝1,...,n_k，e^V为母线电压偏差，

为第k个簇中第i个分布式能源的输入共识误差；where 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 term of the i-th distributed energy resource in the k-th cluster,

is the current distribution control term for the i-th distributed energy source in the k-th cluster, τ is the exponential coefficient, and 0<τ<1, λ _k,i and α _k,i are the i-th distribution in the k-th cluster in turn is the proportional and integral coefficient of the voltage regulation control term of the energy source, β _k,i is the integral coefficient of the current distribution control of the i-th distributed energy source in the k-th cluster, take β _k,i =γ _k (R _k,i +d _k,i ), the adjustment parameter γ _k > 0, R _k,i is the transmission line resistance of the i-th distributed energy source in the k-th cluster, and d _k,i is the i-th distributed energy source in the k-th cluster The droop coefficient of , i=1,...,n _k , e ^V is the bus voltage deviation,

is the input consensus error of the i-th distributed energy resource in the k-th cluster;

S4. Build 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 source in the k-th cluster, and V ^* is the nominal voltage value of the DC bus;

S5. According to the DC microgrid model, the current distribution ratio between the distributed energy resources within the cluster and the total current distribution ratio of the distributed energy resources between the clusters are obtained, wherein:

The current distribution ratio among distributed energy sources within a cluster satisfies the following conditions:

The total current distribution ratio of distributed energy resources among clusters satisfies 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 source in the kth cluster, and I _l,j is the lth cluster. The current output value of the jth distributed energy source, 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 source in the lth cluster, and l =1,...,K,j=1,...,n _k , α _k is the voltage control integral coefficient of the first distributed energy source in the kth cluster, α _l is the first distribution in the lth cluster The voltage control integral coefficient of the energy source.

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

In the formula, λ _k is the voltage control proportional coefficient of the first distributed energy source in the kth cluster.

满足如下公式：Preferably, the bus voltage deviation e ^V and the input consensus error

Satisfy the following formula:

e ^V =V ^* -V _b

为第k簇第i个分布式能源的邻居二次控制器集合，u_k,j为第k簇第j个分布式能源的二次控制信号。In the formula,

is the neighbor secondary controller set of the i-th distributed energy source in the k-th cluster, and u _k,j is the secondary control signal of the j-th distributed energy source in the k-th cluster.

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

This application designs a hybrid secondary controller for the islanded 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 in the same cluster. The distributed control strategy is adopted between different clusters to ensure that the communication between the 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 more To further realize the distribution of current among distributed energy sources in a cluster according to the droop ratio, the total current distribution ratio of distributed energy resources among clusters only obeys the distribution of leading distributed energy resources, effectively realizes voltage recovery and current distribution, and has good system stability, flexibility and stability. High security.

Description of drawings

Fig. 1 is the flow chart of the microgrid current distribution method of the present invention;

Fig. 2 is the control block diagram of the i-th distributed energy source in the k-th cluster of the present invention;

3 is a comparison diagram of the bus voltage and output current before and after starting the secondary controller according to the present invention;

Fig. 4 is a comparison diagram of busbar voltage and output current before and after the present invention accesses and disconnects standby DG;

5 is a comparison diagram of the bus voltage and output current before and after the present invention connects and disconnects the resistive load;

FIG. 6 is a comparison diagram of the busbar voltage and output current before and after the present invention connects and disconnects the constant power load.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of the present application. The terms used herein in the specification of the present application are for the purpose of describing specific embodiments only, and are not intended to limit the present application.

The present application provides a distributed and distributed hybrid control microgrid current distribution method in order to overcome the problem that the prior art is difficult to meet the flexibility and safety requirements of the microgrid.

As shown in Figure 1-6, a microgrid current distribution method based on distributed and distributed hybrid control includes the following steps:

Follow the steps below:

S1. Divide all distributed energy sources of 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 operating in an island state. In order to realize hybrid control, all distributed energy DGs are first decomposed into K clusters, and the kth cluster contains n _k DGs. In practical applications, the distributed energy DGs that are close to each other can be divided into the same cluster.

S2. Designate the first distributed energy resource of each cluster as the leading distributed energy resource for receiving the DC bus voltage signal V _b . Without loss of generality, the first distributed energy resource of each cluster is designated as the leading distributed energy resource, which is used to receive the DC bus voltage feedback signal V _b , and the total current distribution ratio of the DGs among the clusters only obeys the leadership of the leading DG. distribution to achieve current distribution and voltage recovery in microgrids.

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,

为第k个簇中第i个分布式能源的电压调节控制项，

为第k个簇中第i个分布式能源的电流分配控制项，τ为指数系数，且0＜τ＜1，λ_k,i和α_k,i依次为第k个簇中第i个分布式能源的电压调节控制项的比例和积分系数，β_k,i为第k个簇中第i个分布式能源的电流分配控制的积分系数，取β_k,i＝γ_k(R_k,i+d_k,i)，调节参数γ_k＞0，R_k,i为第k个簇中第i个分布式能源的传输线电阻，d_k,i为第k个簇中第i个分布式能源的下垂系数，i＝1,...,n_k，e^V为母线电压偏差，

为第k个簇中第i个分布式能源的输入共识误差。where u _ki is the secondary control signal of the i-th distributed energy source in the k-th cluster,

is the voltage regulation control term of the i-th distributed energy resource in the k-th cluster,

is the current distribution control term for the i-th distributed energy source in the k-th cluster, τ is the exponential coefficient, and 0<τ<1, λ _k,i and α _k,i are the i-th distribution in the k-th cluster in turn β k,i is the proportional and integral coefficient of the voltage regulation control term of the type energy source, β _k,i is the integral coefficient of the current distribution control of the ith distributed energy source in the k th cluster, take β _k,i =γ _k (R _k,i +d _k,i ), the adjustment parameter γ _k > 0, R _k,i is the transmission line resistance of the i-th distributed energy source in the k-th cluster, and d _k,i is the i-th distributed energy source in the k-th cluster The droop coefficient of , i=1,...,n _k , e ^V is the bus voltage deviation,

is the input consensus error of the i-th distributed energy resource in the k-th cluster.

S4. Build 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 resource in the k-th cluster, and V ^* is the nominal voltage value of the DC bus.

As shown in Figure 2, the DC microgrid model consists of two parts: primary control and secondary control, that is, on the basis of primary control, a secondary controller is introduced as a compensation item 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), which are used to control the power input to the microgrid by each distributed energy source and realize the precise distribution of the output power of each distributed energy source. Literature: 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., this field The prior art well-known to persons will not be repeated here. It is easy to understand that each distributed energy source is connected to the public node of the microgrid, for example, connected to the public node of the microgrid through the corresponding step-down DC/DC converter and LC filter, and the microgrid is in an island operation state. It can achieve the purpose of accurate distribution by adaptively adjusting the current distribution of each distributed energy source under the condition of load fluctuation.

S5. According to the DC microgrid model, the current distribution ratio between the distributed energy resources within the cluster and the total current distribution ratio of the distributed energy resources between the clusters are obtained, wherein:

The DC bus voltage signal V _b is restored to the nominal voltage value through the secondary controller, satisfying V ^* =V _b , uk _,i =u _k,j , when the selected droop coefficient is much larger than the corresponding transmission line resistance, it can be Obtain the output current distribution ratio among the DGs, then

The current distribution ratio among distributed energy sources within a cluster satisfies the following conditions:

The total current distribution ratio of distributed energy resources among clusters satisfies 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 source in the kth cluster, and I _l,j is the lth cluster. The current output value of the jth distributed energy source, 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 source in the lth cluster, and l =1,...,K,j=1,...,n _k , α _k is the voltage control integral coefficient of the first distributed energy source in the kth cluster, α _l is the first distribution in the lth cluster The voltage control integral coefficient of the energy source.

In one embodiment, the i-th secondary controller of the k-th cluster also satisfies the following conditions:

In the formula, λ _k is the voltage control proportional coefficient of the first distributed energy source in the kth cluster.

满足如下公式：In one embodiment, the bus voltage deviation e ^V and the input consensus error

Satisfy the following formula:

e ^V =V ^* -V _b

为第k簇第i个分布式能源的邻居二次控制器集合，u_k,j为第k簇第j个分布式能源的二次控制信号。In the formula,

is the neighbor secondary controller set of the i-th distributed energy source in the k-th cluster, and u _k,j is the secondary control signal of the j-th distributed energy source in the k-th cluster.

Traditional droop control has a trade-off between voltage deviation and current distribution accuracy. Therefore, the present invention compensates the bus voltage deviation by introducing a secondary controller, that is, adding a secondary control signal to the primary control (droop control), which can quickly restore the voltage to the nominal value and realize a reasonable distribution of current.

The effectiveness of the application method is further described below by specific examples:

1) Parameter setting: In this experiment, an island DC microgrid with 6 distributed energy sources (DGs) was constructed based on the real-time simulator OPAL-RT. The proposed secondary controller is implemented and executed on a digital signal processor control board. Among them, the main electrical parameters and controller parameters are shown in Table 1.

Table 1 Main electrical parameters and controller parameters

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 , and the third cluster includes DG _{3, 1.} DG _3,2 , DG _3,3 , among which DG _3,3 is the backup DG, the backup DG is disconnected in the initial state, and the nominal DC bus voltage V ^* is 48V.

2) Experimental results

It can be seen from the simulation results in Fig. ₃ that after the secondary controller is started, the voltage is restored to the _nominal voltage of _48V . _,1 :I _3,2 ≈ 3:1 sag ratio distribution, 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 allocation.

From the simulation results in Figure 4, it can be seen that under the secondary controller, the voltage can be restored to the nominal voltage of 48V when the standby DG is connected and disconnected. And when the standby DG is connected, only the current distribution ratio in the third cluster changes from I _3,1 :I _3,2 ≈3:1 to I _3,1 :I _3,2 :I _3,3 ≈3 :1:2, the other cluster current distributions did not change.

From the simulation results in Figure 5, it can be seen that under the secondary controller, on the basis of connecting a 2Ω load, and then connecting and disconnecting a resistive load (4Ω) in parallel, the voltage can be restored to the nominal voltage of 48V, and the current distribution ratio is not Change.

From the simulation results in Figure 6, it can be seen that under the secondary controller, on the basis of connecting the 2Ω load, and then connecting and disconnecting the constant power load (P=100W) in parallel, the voltage can be restored to the nominal voltage of 48V, and the current distribution than unchanged.

The present application designs a hybrid secondary controller for the islanded DC microgrid system, which has the advantages of both distributed and decentralized control methods. Specifically, all DGs are divided into multiple clusters, and the DGs in the same cluster adopt a distributed control strategy, while different clusters adopt a distributed control strategy. The proposed secondary controller can restore the voltage to the nominal value within a limited time, and further realizes the current distribution among the DGs within the cluster according to the droop ratio, and the total current distribution ratio of the DGs among the clusters only obeys the distribution of the leader DG.

It is worth pointing out that the existing distributed control methods and decentralized control methods are all special cases of the proposed hybrid control strategy, such as K=1, it is distributed control; such as _nk =1, k=1,… , K, it is distributed control.

In this method, a hybrid secondary controller is designed for the islanded DC microgrid system, which combines the advantages of distributed and decentralized control methods, that is, all distributed energy sources are divided into multiple clusters, and distributed control strategies are used in the same cluster. The distributed control strategy is adopted between different clusters to ensure that the communication between the 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 more To further realize the current distribution among the distributed energy resources in the cluster according to the droop ratio, the total current distribution ratio of the distributed energy resources among the clusters only obeys the distribution of the leading distributed energy resources, effectively realizes the voltage recovery and current distribution, and has good system stability, flexibility and stability. High security.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent relatively specific and detailed embodiments described in the present application, but should not be construed as a limitation on the scope of the patent application. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the appended claims.

Claims (3)

1. A microgrid current distribution method based on distributed and distributed hybrid control is characterized in that: the microgrid current distribution method based on distributed and distributed hybrid control comprises the following steps:

s1, dividing all distributed energy sources of the microgrid into K clusters, wherein the kth cluster contains n _k A distributed energy source, n _k The number of the distributed energy sources is more than or equal to 1, K is equal to or less than N, N is the number of the distributed energy sources, and the micro-grid is in an island operation state;

s2, designating the 1 st distributed energy resource of each cluster as a leader distributed energy resource, and receiving a direct current bus voltage signal V _b ；

S3, constructing secondary controllers of each distributed energy source, wherein the formula of the ith secondary controller of the kth cluster is as follows:

wherein,

in the formula u _k,i For the secondary control signal of the ith distributed energy resource in the kth cluster,

for the voltage regulation control term of the ith distributed energy source in the kth cluster,

distributing a control term for the current of the ith distributed energy source in the kth cluster, wherein tau is an exponential coefficient, and is more than 0 and less than 1, and lambda is _k,i And alpha _k,i The proportional coefficient and the integral coefficient of the voltage regulation control term of the ith distributed energy resource in the kth cluster are sequentially _k,i Distributing and controlling an integral coefficient for the current of the ith distributed energy source in the kth cluster, and taking beta _k,i ＝γ _k (R _k,i +d _k,i ) Adjusting the parameter gamma _k ＞0，R _k,i Transmission line resistance for the ith distributed energy source in the kth cluster, d _k,i The droop coefficient i ═ 1.. multidata n of the ith distributed energy resource in the kth cluster _k ，e ^V In order to be able to measure the bus voltage deviation,

input consensus error of the ith distributed energy resource in the kth cluster;

s4, constructing a direct current microgrid model based on the droop control and the secondary controller, wherein the direct current 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, V, of the ith distributed energy source in the kth cluster ^* The value is the nominal voltage value of the direct current bus;

s5, obtaining a current distribution ratio among the distributed energy sources in the clusters and a total current distribution ratio among the distributed energy sources in the clusters according to the direct-current microgrid model, wherein:

the current distribution ratio among the distributed energy sources in the cluster meets the following conditions:

the total current distribution ratio of the inter-cluster distributed energy meets the following conditions:

in the formula, R _k,1 Transmission line resistance for the 1 st distributed energy source in the kth cluster, d _k,1 Is the droop coefficient, I, of the 1 st distributed energy resource in the kth cluster _l,j Is the current output value, R, of the jth distributed energy source in the ith cluster _l,1 Transmission line resistance for the 1 st distributed energy source in the l cluster, d _l,1 The droop coefficient of the 1 st distributed energy source in the first cluster is 1, and K, j is 1 _k ，α _k Controlling an integral coefficient, alpha, for the voltage of the 1 st distributed energy source in the kth cluster _l And controlling an integral coefficient for the voltage of the 1 st distributed energy source in the l cluster.

2. The microgrid current distribution method based on decentralized and distributed hybrid control of claim 1, characterized in that: the ith secondary controller of the kth cluster further satisfies the following conditions:

in the formula, λ _k And controlling the proportionality coefficient for the voltage of the 1 st distributed energy source in the kth cluster.

3. The microgrid current distribution method based on decentralized and distributed hybrid control of claim 1, wherein the microgrid current distribution method is characterized in thatThe method comprises the following steps: the bus voltage deviation e ^V And input consensus errors

The following formula is satisfied:

e ^V ＝V ^* -V _b

in the formula,

set of neighbor secondary controllers for ith distributed energy of kth cluster, u _k,j The secondary control signal of the jth distributed energy source of the kth cluster.

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