CN113363961B - Current sharing and bus voltage recovery control method for direct-current micro-grid distributed power supply - Google Patents

Abstract

The invention discloses a DC micro-grid distributed power supply current equalization method and its bus voltage recovery control method. The invention adopts distributed sparse communication means to carry out two-to-two communication between distributed power supplies. The system has high reliability and only needs to transmit distributed The output current information of the distributed power supply can be used to measure the line impedance between the output terminals of each distributed power supply and the DC bus. Higher precision. The invention can not only compensate the voltage drop of the busbar caused by the droop coefficient, but also compensate the voltage drop of the busbar caused by the voltage drop of the line impedance, and the compensation precision of the busbar voltage is high. The line impedance measurement method adopted in the present invention is not affected by the size of the line impedance itself, and is also not affected by the load properties of the DC micro-grid system, and the measurement error is relatively small.

Description

A DC Micro-grid Distributed Power Supply Current Sharing and Bus Voltage Restoration Control Method

technical field

The invention belongs to the research field of distributed direct current microgrid coordinated control, and in particular relates to a DC microgrid distributed power supply current equalization method and a bus voltage restoration control method thereof.

Background technique

The operation control objectives of the DC microgrid mainly include equipment-level control and system-level control. The equipment-level control is mainly for the physical layer equipment to complete some of its basic control objectives based on local information, and the system-level control is for centralized management and energy optimization of the system. To improve the overall operating efficiency and reliability. From the perspective of system optimal operation, how to realize the reasonable distribution of output power/energy of each distributed power source in the system is one of the key objectives in the system-level control of DC microgrid.

In order to solve the problem of reasonable distribution of distributed power output power in DC micro-grid, scholars have proposed parallel current sharing control technology, because when distributed power is running in parallel, due to the difference in control parameters, and the output of each system is a voltage Due to the nature of the source, a small deviation will cause a large difference in the output current. Therefore, while stabilizing the output voltage, it is required that each distributed power supply can share the same current and have consistent output power. Among the existing current sharing control methods, the decentralized control method based on droop control has become the focus of scholars' research. Droop control does not require a central controller, and all converters are in a parallel and equal relationship. The droop method is also called the adaptive voltage adjustment method. When the load current increases, the output voltage is reduced by changing the droop coefficient, thereby adjusting the output current. This method has simple control and good redundancy, and is the simplest multi-source coordinated control strategy.

However, there are still some problems in the droop control method: First, this method is proposed under the condition of ignoring the line impedance between the distributed power output terminal and the DC microgrid bus, but for the actual microgrid system, the line impedance value cannot be ignored , the existence of line impedance reduces the accuracy of current sharing between distributed power sources, and when the load is heavier, the accuracy of current sharing is lower. Secondly, the realization of droop control will lead to a certain degree of bus voltage drop, which will have a direct impact on the power quality of the DC microgrid system. Finally, when droop control is used, the accuracy of current sharing and the drop of bus voltage cannot be taken into account—by setting a smaller droop coefficient, a lower drop of bus voltage can be obtained, but the accuracy of current sharing is low, and the setting is relatively low. A large droop coefficient can improve the accuracy of current sharing, but it will cause a large drop in the DC bus voltage. Therefore, it is an urgent problem to be solved in the DC microgrid distributed power supply current sharing control technology to ensure high current sharing accuracy while ensuring the stability of the bus voltage.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies, and provide a DC micro-grid distributed power supply current sharing method and its bus voltage recovery control method. On the basis of droop control, sparse communication means are introduced, and current sharing and monitoring are performed by measuring line impedance. Bus voltage accurate compensation. This method only needs to transmit current information, which can greatly improve the accuracy of current sharing among distributed power sources, and at the same time accurately compensate the bus voltage drop caused by droop coefficient and line impedance, thus solving the inherent problems of traditional droop control methods.

In order to achieve the above purpose, the following steps are included:

S1, the DC micro-grid distributed power supply locally adopts the droop control strategy to sample the local output current information;

S2, each distributed power supply in the DC micro-grid distributed power supply communicates with the adjacent distributed power supply, and sends local output current information to the adjacent distributed power supply;

S3, after each distributed power source obtains the output current information of the adjacent distributed power source, calculate the ratio of the local output current to the output current of the adjacent distributed power source;

S4. Adjust the droop control coefficient of the DC microgrid distributed power supply according to the ratio of the local output current to the output current of the adjacent distributed power supply. The output current ratio of the adjacent distributed power supply;

S5, the local controller of each distributed power supply uses the ratio of the local output current before and after the change of the droop control coefficient to the output current of the adjacent distributed power supply to calculate the line impedance between the local output terminal and the DC bus;

S6, setting the corresponding droop coefficients of each distributed power supply, so that the total equivalent output impedance of each distributed power supply is equal;

S7, obtaining the average value of the output current of all distributed power supplies in the DC microgrid;

S8, the local controller of each distributed power supply uses the product of the average value of the output current and the total equivalent output impedance as the compensation amount of the voltage reference value, and sends it to the voltage control loop of the droop control.

In S3, the ratio of the local output current to the output current of the adjacent distributed power is calculated by the local controller.

In S5, the measurement method of the line impedance between the local output terminal and the DC bus is as follows:

Among them, R _li is the line impedance value between the distributed power supply i and the DC bus, k is the increase of the droop coefficient in S4, R _d is the initial droop coefficient of each distributed power supply in S1, x ₁ and x ₂ are respectively The droop coefficient is the ratio of the output current of distributed power source i to the output current of adjacent distributed power sources before and after the change.

In S6, the droop coefficient set for each distributed power supply should be:

R _di +R _li ＝R _dj +R _lj ＝...＝R _dn +R _ln ＝R

Among them, R _di R _dj ,…,R _dn are the set droop coefficients of the DC microgrid distributed power supply i,j,…,n respectively, R _li ,R _lj ,…,R _ln are the DC microgrid distributed power supply The line impedance between the i,j,...,n output terminal and the DC bus, R is the total equivalent output impedance of each distributed power supply.

In S7, the dynamic expression of the current observer based on the consensus algorithm is used to obtain the average value of the output current of all distributed power sources in the DC microgrid.

In S7, the calculation method of the dynamic expression of the current observer based on the consensus algorithm is as follows:

Among them, i _oi is the output current value of the i-th distributed power supply, i _avgi and i _avgj are the average value of the distributed power output current of the whole system obtained by the i-th and j-th distributed power supply using the local current observer, a _ij is the communication weight factor in the communication network topology, when there is a communication association between distributed power source i and distributed power source j, a _ij =1, otherwise, a _ij =0.

Obtaining the average output current of all distributed power sources in the DC microgrid is calculated by the local controller.

In S8, the calculation method of the voltage reference value of the voltage loop in droop control is as follows:

U _refi ＝(U ^* -R _di i _oi )+Ri _avgi

Among them, U ^* , U _refi are the voltage reference value of distributed power supply i before and after voltage compensation respectively, and Ri _avgi is the voltage compensation amount of distributed power supply i.

Compared with the prior art, the present invention uses distributed sparse communication means to communicate between distributed power sources. The system reliability is high, and only the output current information of distributed power sources needs to be transmitted to measure the output current of each distributed power source. The line impedance between the output terminal and the DC bus is equal to the total output impedance of each distributed power supply by compensating the corresponding droop coefficient, so as to achieve the purpose of current sharing, and the accuracy of current sharing is high. The invention can not only compensate the voltage drop of the busbar caused by the droop coefficient, but also compensate the voltage drop of the busbar caused by the voltage drop of the line impedance, and the compensation precision of the busbar voltage is high. The line impedance measurement method adopted in the present invention is not affected by the size of the line impedance itself, nor is it affected by the load properties of the DC micro-grid system, and the measurement error is small, which solves the problem that the current sharing accuracy in the traditional droop control method is affected by the line. Impedance effects and bus voltage drop problems.

Description of drawings

Figure 1 shows the droop control method adopted for the power sharing of DC microgrid distributed power supply;

Figure 2 is an equivalent circuit diagram of two distributed power supply droop control;

Figure 3 is a communication topology diagram of a DC microgrid distributed power supply;

Figure 4 is a schematic diagram of the parallel operation control of two distributed power supplies;

Figure 5 is a block diagram of DC micro-grid distributed power supply current sharing and bus voltage recovery control;

Fig. 6 is a simulation waveform diagram of the DC bus voltage when the strategy control of the invention is adopted;

Fig. 7 is a simulation waveform diagram of the DC bus voltage (before load change) when the strategy control of the invention is adopted;

Fig. 8 is a simulation waveform diagram of the DC bus voltage (after load changing) when the inventive strategy control is adopted;

Fig. 9 is a simulation waveform diagram of the output current of the distributed power supply when the strategy control of the invention is adopted;

Figure 10 is a simulation waveform diagram of the output current of the distributed power supply (before load change) when the strategy control of the invention is adopted;

Figure 11 is a simulation waveform diagram of the output current of the distributed power supply (after load change) when the strategy control of the invention is adopted;

Figure 12 is a waveform diagram of the DC bus voltage when only droop control is adopted;

Fig. 13 is the output current waveform diagram of the distributed power supply when only the droop control is adopted.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

The traditional droop control method is shown in Figure 1. It can be seen that in the voltage loop control of the distributed power supply, the output voltage command U _ref of the distributed power supply can be adjusted by adjusting the droop coefficient _Rd , and then the output voltage U ref can be adjusted. _o , so as to adjust the output current i _o of the distributed power supply to achieve the purpose of controlling the output power of the distributed power supply.

Figure 2 is the equivalent circuit of two distributed power sources i and j running in parallel and adopting droop control, where U ^* is the given value of the distributed power output voltage, U _bus is the DC bus voltage value, U _oi and U _oj are respectively The actual output voltage values of distributed power sources i and j, i _oi and i _oj are the output current values of distributed power sources i and j respectively. R _d is the virtual resistance of the output terminal of the distributed power supply, that is, the set droop coefficient, R _li and R _lj are the line impedance between the output terminal of the distributed power supply and the DC bus, and R _L is the equivalent load resistance of the DC microgrid system. According to Kirchhoff's equivalent current-voltage law:

U _oi ＝U ^* -R _d i _oi ，U _oj ＝U ^* -R _d i _oj (1)

U _bus ＝U _oi -R _li i _oi ＝U _oj -R _lj i _oj (2)

Formula (1) (2) can be solved simultaneously:

Among them, R _i and R _j are the equivalent total output impedances of distributed power sources i and j respectively. It can be seen from formula (3) that due to the existence of line impedance, the output current of each distributed power source cannot follow the given The droop coefficient is distributed proportionally. At the same time, it can be seen from (1) (2) that the existence of the droop coefficient and the line impedance leads to the drop of the bus voltage.

In order to solve the problem of droop control, the present invention introduces a DC micro-grid distributed power supply current sharing and bus voltage restoration control method. Figure 3 shows the communication topology of the DC micro-grid distributed power supply when this strategy is used. It can be seen that the control adopts the method of two-to-two communication between distributed power sources. Each distributed power source only communicates with adjacent distributed power sources. The local controllers of each distributed And the measurement information of neighboring nodes can calculate the average value of the measurement information of the whole system. The dynamic expression of the current observer based on the consensus algorithm is as follows:

且收敛于i_oi的算术平均值，即：In the formula, i _oi is the output current information of the i-th distributed power supply, and i _avgi and i _avgj are the average value of the system-wide distributed power output current obtained by the i-th and j-th distributed power supply using the local current observer. a _ij is the communication weight factor in the communication network topology. When distributed power source i and distributed power source j have a communication relationship, a _ij >0, set a _ij =1, otherwise, a _ij =0. It can be proved that as long as the communication network topology contains a directed spanning tree, then when t→∞, there is

And converge to the arithmetic mean of i _oi , namely:

It can be seen that when the consensus algorithm is used for control, when any two distributed power sources have communication failures, or a distributed power source exits due to failure, a cluster of directed spanning trees in the communication network can still be guaranteed. Therefore, this control method has high reliability, and there is no problem that the entire system cannot operate normally due to a failure of a certain distributed power supply or a certain communication line. plug-and-play requirements.

Some studies have used the dynamic expression of the consensus algorithm to find the average value of the output voltage and current of all distributed power sources in the local controllers of each distributed power source, and compared them with the command voltage and local output current information, and then corrected the distribution. The current output voltage and current values of the conventional power supply improve the accuracy of the current sharing, and at the same time compensate the DC bus voltage drop caused by the droop coefficient. However, the current research does not consider the impact of the voltage drop caused by the line impedance on the bus voltage drop, and in the low-voltage DC microgrid or the DC microgrid system with large line impedance, the bus voltage drop caused by the line impedance voltage drop is cannot be ignored. Therefore, the present invention proposes a line impedance measurement method. After obtaining the line impedance information of each distributed power supply, the corresponding droop coefficients are set respectively, so that the total equivalent output impedance of each distributed power supply is equal, and then the purpose of current sharing is achieved. At the same time, the local controllers of each distributed power source use the current observer based on the consensus algorithm to obtain the average value of the output current of each distributed power source, and the product of this value and the total equivalent output impedance is used as the local voltage compensation amount, thereby compensating The DC bus voltage drop caused by coefficient and line impedance achieves the purpose of accurately compensating the bus voltage. The specific principle of this method is as follows:

Take two distributed power sources i and j as an example, measure the line impedance, and use droop control locally:

U _bus ＝U ^* -R _i i _oi ＝U ^* -R _j i _oj (7)

R _i =R _d +R _li , R _j =R _d +R _lj (8)

Wherein, U ^* is the command voltage reference value of the distributed power supply i, j. U _bus is the DC bus voltage value, U _refi and U _refj are the actual output voltage reference values of distributed power supply i and j respectively, i _oi and i _oj are the output current values of distributed power supply i and j respectively, and R _d is the droop of distributed power supply Coefficients, R _li , R _lj are the line impedance between the output terminal of distributed power supply i, j and the DC bus, respectively, R _i , R _j are the total equivalent output impedance of distributed power supply i, j respectively. From formula (7), it is easy to get:

Each distributed power supply adds k to the original droop coefficient, which is:

Among them, i _oi ′, i _oj ′ are the output current values of distributed power sources i and j after the droop coefficient is increased, respectively. x ₁ and x ₂ are the output current ratios of distributed power i and j before and after the droop coefficient is increased. From formula (9) (10) can get:

R _li =R _i -R _d (12)

That is, the distributed power source i communicates with the distributed power source j to obtain the current value i _oj , i _oj ′ before and after the change of the droop coefficient. According to (11)(12), the local controller calculates the Line impedance R _li .

Error analysis of the measurement method of the line impedance:

From (13) (14), it can be seen that x″ ₁ , x ₂ ″ are the measurement error values of the ratio of output current i _oi , i _oj and the ratio of output current i _oi ′, i _oj ′, respectively.

From formula (13), we can get:

It can be seen from (12) (15) that the measurement error of the line impedance R _li is composed of the denominator term x ₁ ″-x ₂ ″ of R _i and the numerator term kx ₂ ″, where the denominator term x ₁ ″-x ₂ ″ cannot be eliminated, is an uncontrollable factor, and for the molecular item kx ₂ ″, k<1 should be set to avoid magnifying the error.

In order to make the current evenly divided under steady state and dynamic conditions, the droop coefficients set for each distributed power supply should be:

R _di +R _li ＝R _dj +R _lj ＝...＝R _dn +R _ln ＝R (16)

so that

i _oi ＝i _oj ＝...＝i _on (17)

Among them, R _di R _dj ,…,R _dn are the set droop coefficients of the DC microgrid distributed power supply i,j,…,n respectively, and i _oi ,i _oj ,…, _ion are the DC microgrid distributed power supply i,j,...,n output current value, R is the total equivalent output impedance of the distributed power supply, which should satisfy

Among them, ΔU _max is the maximum voltage drop allowed by the bus voltage, and _IN is the rated current of the bus at full load. In consideration of the line impedance measurement error, the droop coefficient R _di R _dj ,...,R _dn should be as large as possible, and R should be as large as possible, so as to ensure the accuracy of current sharing, and on this basis, the bus voltage compensate. The dynamic expression of the current observer based on the consensus algorithm is shown in formula (4), that is, each distributed power supply only communicates with its adjacent distributed power supply, and the local controller calculates the DC micro The average output current of all distributed power sources in the network system, at this time, the voltage compensation amount on each distributed power source is

ΔU = Ri _avgi = Ri _avgj = ... = Ri _avgn (19)

Then the command voltage reference value of distributed power supply i is

U _refi ＝(U ^* -R _di i _oi )+Ri _avgi (20)

It can be seen that this method only needs to transmit adjacent current information, and can measure the line impedance between the output terminals of each distributed power supply and the DC bus, realize current sharing, and also compensate the bus line impedance caused by the droop coefficient and line impedance. Voltage drop is a more accurate bus voltage compensation method.

Example:

Taking two distributed power sources as an example, the specific implementation method is described:

Figure 4 is a schematic diagram of the parallel operation control of two distributed power supplies, C ₁ and C ₂ are the output capacitors of the two distributed power supplies, and R _l1 and R _l2 are the distance between the output terminals of the two distributed power supplies and the DC bus. The line impedance of , i _o1 and i _o2 are the output currents of the two distributed power supplies respectively, and R _L is the equivalent resistance of the load. Each distributed power supply adopts droop control locally, and the second-layer control adopts the control strategy described in the invention and improves the bus voltage adjustment rate, as shown in Figure 5. According to the circuit diagram shown in Figure 4 and the control method shown in Figure 5, the inventive strategy is verified on the MATLAB/SIMULINK platform, wherein the rated voltage value of the busbar is 80V, and the line resistance R _l1 of the two distributed power supplies = 2Ω, R _l2 = 2.5Ω, load _RL = 80Ω. The specific implementation steps are as follows:

1. Initially set the droop coefficient of each distributed power supply to 2.5Ω. In the steady state, the local controllers of the two distributed power supplies sample their own output currents respectively, and use the average value filtering method to sample the output current values 5 times respectively. At the same time, a low-pass filter is used to filter out high-frequency components in the output current, and then the average value of the local output current after 5 samples is obtained.

2. Each distributed power supply communicates with the adjacent distributed power supply, and sends its own local output current average value to the adjacent distributed power supply. At this time, each distributed power local controller calculates the ratio of the local output current average value to the adjacent distributed power output current average value through formula (9), and the ratio is recorded as x ₁ .

3. Add 0.5Ω to the droop coefficient of each distributed power supply, repeat step 1 to obtain the average output current of each distributed power supply after the droop coefficient is changed, and repeat step 2 to obtain the local output current of each distributed power supply after the droop coefficient is changed. The ratio of the average value of the output current to the average value of the output current of the adjacent distributed power supply, the ratio is recorded as x ₂ .

4. The local controller of each distributed power supply can calculate the line impedance between the output terminal of the distributed power supply and the DC bus according to formulas (11) and (12). The experimental calculation results in R _l1 =2.0098Ω, R _l2 =2.5107Ω, and the measurement errors from the actual resistance values are 0.49% and 0.43%, respectively.

5. The total output impedance R of each distributed power supply is uniformly set to 5Ω, and the droop coefficients R _d1 = 2.9902Ω and R _d2 = 2.4893Ω of distributed power sources 1 and 2 are calculated from formula (12). At this time, the total output impedance of the two distributed power supplies is basically the same, achieving the purpose of current sharing.

6. When the local controller of each distributed power source communicates with adjacent distributed power sources, the second-layer control uses a current observer based on formula (4) to obtain the average value of the output current of all distributed power sources, and compares this value with the total output impedance The product of R is sent to the voltage control loop as the compensation amount of its own voltage reference command, as shown in equations (19) and (20), which achieves the purpose of accurately compensating the bus voltage drop.

Fig. 6 to Fig. 11 show the simulation results when the above inventive steps are used for experiments. Fig. 6 shows the simulation results of the DC bus voltage using the invented control strategy, where the load is increased at t=1s. Figure 7 and Figure 8 respectively show the steady-state value of the DC bus voltage before and after the load is increased. It can be seen that the steady-state value of the DC bus voltage before and after the load change is the rated voltage of 80V, so it can be seen that this method has a more accurate DC bus voltage compensation. Effect.

Figure 9 shows the output current values of two parallel distributed power supplies when the invented strategy is adopted. Figure 10 and Figure 11 are the steady-state values of the output currents of the two distributed power sources before and after the load change respectively. It can be seen that the output currents of the two distributed power sources before and after the load change are almost the same. The distributed power output current sharing accuracy is higher.

Figure 12 and Figure 13 respectively show the DC bus voltage and the output current values of the two distributed power supplies when only the initial droop coefficient is used for droop control. It can be seen that when only droop control is adopted, due to the influence of inconsistent line impedance, the accuracy of current sharing is poor, and the DC bus voltage also drops to a certain extent. At the same time, when the load is heavier, the accuracy of current sharing is worse. And the DC bus voltage drop is also greater.

To sum up, by comparing the simulation results using the invented control strategy with the simulation results using only the droop control, it can be seen that the method has higher current sharing accuracy and bus voltage compensation accuracy.

Claims (8)

1. A method for controlling current sharing and bus voltage recovery of a distributed power supply of a direct-current microgrid is characterized by comprising the following steps:

s1, locally adopting a droop control strategy by a direct-current micro-grid distributed power supply to sample local output current information;

s2, each distributed power supply in the direct-current micro-grid distributed power supplies communicates with an adjacent distributed power supply, and local output current information is sent to the adjacent distributed power supplies;

s3, after each distributed power supply obtains the output current information of the adjacent distributed power supplies, calculating the ratio of the local output current to the output current of the adjacent distributed power supplies;

s4, adjusting droop control coefficients of the direct-current micro-grid distributed power supplies according to the ratio of the local output current to the output current of the adjacent distributed power supplies, and repeating the steps S1-S3, wherein each distributed power supply obtains the ratio of the local output current after the droop control coefficients are changed to the output current of the adjacent distributed power supplies;

s5, calculating the line impedance between a local output end and a direct current bus by using the ratio of the local output current before and after the droop control coefficient is changed and the output current of the adjacent distributed power supply by each distributed power supply local controller;

s6, setting corresponding droop coefficients of all distributed power supplies to enable the total equivalent output impedance of all the distributed power supplies to be equal;

s7, obtaining an average value of output currents of all distributed power supplies of the direct-current micro-grid;

and S8, each distributed power supply local controller takes the product of the average output current value and the total equivalent output impedance as the compensation quantity of the voltage reference value, and sends the compensation quantity into a voltage control loop for droop control.

2. The method according to claim 1, wherein in step S3, a ratio of the local output current to the output current of the adjacent distributed power supplies is calculated by the local controller.

3. The method for current sharing and bus voltage recovery control of the DC microgrid distributed power supply according to claim 1, wherein in S5, a method for measuring line impedance between a local output end and a DC bus is as follows:

wherein R is _li Is the line impedance value between the distributed power supply i and the direct current bus, k is the increment of the droop coefficient in S4, R _d Is the initial droop coefficient, x, of each distributed power supply in S1 ₁ ，x ₂ The output current of the distributed power supply i before and after the droop coefficient is changed and the output current of the adjacent distributed power supplyThe ratio of the flows.

4. The method according to claim 1, wherein in S6, the droop coefficients set for the distributed power supplies are such that:

R _di +R _li ＝R _dj +R _lj ＝…R _dn +R _ln ＝R

wherein R is _di R _dj ,…,R _dn The droop coefficients R are respectively the droop coefficients of the direct current micro-grid distributed power supplies i, j, …, n _li ,R _lj ,…,R _ln The impedance of the line between the output end of the n output ends and the direct current bus is respectively direct current micro-grid distributed power sources i, j, …, and R is the total equivalent output impedance of each distributed power source.

5. The method according to claim 4, wherein in S7, a dynamic expression of a current observer based on a consistency algorithm is adopted to obtain the average value of the output currents of all the distributed power supplies of the DC microgrid.

6. The method for current sharing and bus voltage recovery control of the DC microgrid distributed power supply according to claim 5, characterized in that in S7, the method for calculating the dynamic expression of the current observer based on the consistency algorithm is as follows:

wherein i _oi Is the output current value i of the ith distributed power supply _avgi ,i _avgj Obtaining the average value of output currents of the full-system distributed power supplies a for the ith and the jth distributed power supplies respectively by using a local current observer _ij For communication weight factors in a communication network topology, a when a distributed power source i is in communication association with a distributed power source j _ij =1, otherwise, a _ij ＝0。

7. The method of claim 5, wherein the average value of the output currents of all the distributed power supplies of the DC microgrid is obtained and calculated by a local controller.

8. The method according to claim 6, wherein in S8, the voltage loop voltage reference value calculation method in droop control is as follows:

U _refi ＝(U ^* -R _di i _oi )+Ri _avgi

wherein, U ^* ,U _refi Respectively, the voltage reference value Ri of the distributed power source i before and after voltage compensation _avgi Is the voltage compensation quantity, R, of the distributed power supply i _di Set droop coefficient, i, for direct current microgrid distributed power supply i _oi Is the output current value of the distributed power supply i.

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