﻿ 微电网孤岛运行故障分析 Fault Analysis of Isolated Island Operation of Micro-Grid

Journal of Electrical Engineering
Vol.04 No.01(2016), Article ID:17089,11 pages
10.12677/JEE.2016.41007

Fault Analysis of Isolated Island Operation of Micro-Grid

Junjie Jiang, Rong Ju

School of Electrical and Automation Engineering, Nanjing Normal University, Nanjing Jiangsu

Received: Feb. 16th, 2016; accepted: Mar. 1st, 2016; published: Mar. 8th, 2016

ABSTRACT

Micro-grid system is a new development direction of distributed generation system. In this paper, the operation characteristics of PQ and VF control inverter are analyzed, the mathematical model is established based on the control strategy of inverter, and the critical condition of the fault is derived. According to the working characteristics of the micro-grid in grid connected operation and islanded operation, by using the node voltages and currents in fault condition, micro-grid voltage and current equations in the run time are derived, and the fault analysis method is established. At last, by using the PSCAD, a simulation system of isolated island operation of low voltage of 380 V is built, testing the validity of the proposed method.

Keywords:Micro-Grid, PQ Control Strategy, VF Control Strategy, Equivalent Model, Mathematical Analysis

1. 引言

2. DG的控制特性与等值模型

2.1. PQ控制器特性

(1)

(2)

(3)

UDG为DG并网点的电压，EDG为DG出口侧电压，Z为等效滤波阻抗，IDG为逆变器输出电流，R为故障发生时的等效阻抗。参见图2，故障点所处的位置不同将导致故障发生时的等效电阻R发生改变。

Figure 1. PQ control principle

Figure 2. PQ control structure diagram

(4)

(5)

2.2. 恒压恒频控制(VF控制)模式输出特性分析

Figure 3. EDG voltage (equivalent fault resistance = 21, resistance = 25 Ω)

Figure 4. Inverter output current IDG (equivalent fault R = 21, R = 25 Ω)

Figure 5. Inverter output power (equivalent fault R = 21, R = 25 Ω)

Figure 6. EDG voltage (equivalent fault R = 1, R = 3 Ω)

Figure 7. Inverter output current IDG (equivalent fault R = 1, R = 3 Ω)

Figure 8. Inverter output power (equivalent fault R = 1, R = 3 Ω)

Figure 9. VF control principle

1) 电压恒定工作状态

(6)

2) 最大电流饱和状态

(7)

Figure 10. VF control structure diagram

Figure 11. EDG voltage of VF control (equivalent fault R = 10, R = 8 Ω, R = 2 Ω)

Figure 12. Inverter output current IDG of VF control (equivalent fault R = 10, R = 8 Ω, R = 2 Ω)

3. DG的三相短路故障分析与验证

Figure 13. Isolated island operation microgrid

(8)

1) VF控制DG能够稳定电压，PQ控制DG能稳定输出额定功率，此时可根据公式(2)，公式(3)，公式(6)与公式(8)求解故障电路。

2) VF控制DG不能够稳定电压，处于电流饱和状态，PQ控制DG能稳定输出额定功率，此时可根据公式(5)，公式(7)与公式(8)求解故障电路。

3) VF控制DG 与PQ控制DG都处于电流饱和状态，此时可根据公式(5)，公式(7)以及公式(8)求解故障电路。

4. 算例验证

Table 1. Fault analysis results in microgrid (three-phase short circuit resistance Zf = 3 Ω)

Table 2. Fault analysis results in microgrid (three-phase short circuit resistance Zf = 5 Ω)

5. 结论

1) 对于采用PQ控制的DG，在输出状态随着故障等效电阻R的不同，以DG最大输出电压EDGMAX与最大输出电流IMAX，以及参考功率Pref和Qref作为划分故障状态的边界条件。当处于最大输出电压或者最大输出电流状态时，则输出功率无法保证。

2) 对于采用VF控制的DG，由于有参考电压的钳制，因此与PQ控制不同，只存有电压恒定于参考值状态，或者电流饱和状态，因此以Uref和IMAX，作为划分故障的边界条件。当处于电流饱和状态时，则系统的电压和频率将无法稳定。

4) 微电网系统由于电流存在双向流动，而且是多个控制系统的互相耦合，因此分析较为复杂。本文所推导的关于PQ控制与VF控制逆变器的故障特性分析，在理清各个控制策略对于微电网系统影响的同时，将会有助于微电网系统继电保护研究与分析。

Fault Analysis of Isolated Island Operation of Micro-Grid[J]. 电气工程, 2016, 04(01): 44-54. http://dx.doi.org/10.12677/JEE.2016.41007

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