﻿ 基于逆变电源组网的电力系统短路电流改进算法
 舰船科学技术  2018, Vol. 40 Issue (6): 89-94 PDF

A improved method for short-circuit current calculation in inverter dominated shipboard power systems
WANG Yun-fan, XU Zheng-xi, WU Da-li
Wuhan Second Ship Design and Research Institute, Wuhan 430205, China
Abstract: Short-circuit current calculation is of great importance for setting system protection scheme as well as electrical equipment selection. As inverters become the main power source of shipboard ac grid in place of traditional generators, there is a significant reduction on fault current magnitude due to the current-limiting characteristic of power electronic converters. As a result, the error of traditional short-circuit current calculation methods could no more be neglected. This paper firstly gives a comparison of short-circuit characteristics of traditional generators and inverters, then proposes an improved method for motor feedback current calculation. Simulations are carried out and it is proved that the improved calculation method has advantages over traditional methods.
Key words: inverter     feedback current     improved calculation method     error analysis
0 引　言

1 电源短路特性分析

1.1 发电机短路特性

1.2 逆变电源短路特性

 图 1 三相逆变器的基本电路拓扑 Fig. 1 Topology of three-phase inverter

 图 2 逆变电源工作模式 Fig. 2 Operation modes of inverters
1.3 逆变电源短路电流计算

2 电动机短路特性分析

 图 3 异步电动机等值电路 Fig. 3 Equivalent circuit of asynchronous motor

 $\left\{ \begin{array}{l}{L_s}\displaystyle\frac{{{\rm{d}}{i_s}}}{{{\rm{d}}t}} + {R_s}{i_s} + M\displaystyle\frac{{{\rm{d}}{i_r}}}{{{\rm{d}}t}} = 0,\\[8pt]{L_r}\displaystyle\frac{{{\rm{d}}{i_r}}}{{{\rm{d}}t}} + {R_r}{i_r} + M\displaystyle\frac{{{\rm{d}}{i_s}}}{{{\rm{d}}t}} = 0{\text{。}}\end{array} \right.$ (1)

 $i = {I_{n0}}{e^{ - t/{T_{{\rm{dc}}}}}} + I^{''}\cos t{e^{ - t/T_{ac}^{''}}}\text{，}$ (2)

 图 4 Tdc的等值电路 Fig. 4 Equivalent circuit of Tdc

 图 5 Tac” 的等值电路 Fig. 5 Equivalent circuit of Tac”

 $\dot E^{''} = \dot U - (r + jx^{''})\dot I = \dot U - \dot Iz^{''}\text{，}$ (3)

 ${i_{0 - }} = \frac{{{U_{0 - }} - {E_{0 - }}^{''}}}{{z^{''}}}\text{，}$ (4)

 ${I^{''}} = \frac{{ - {{\dot E}_{0 + }}^{''}}}{{{z^{''}}}}\text{，}$ (5)

 ${i_{0 + }} = {I_{n0}} - \frac{{{{\dot E}_{0 + }}^{''}}}{{{z^{''}}}}\text{。}$ (6)

 $i = \frac{{{U_{0 - }}}}{{{z^{''}}}}{e^{ - t/{T_a}}} - \frac{{{E_{0 - }}^{''}}}{{{z^{''}}}}\cos t{e^{ - t/T_{dc}^{''}}}\text{。}$ (7)

3 电动机反馈电流改进算法 3.1 传统短路电流计算方法误差

1） 短路电流周期分量

 ${I_{acM}} = \frac{{{V_N}}}{{|Z'|}}{e^{ - t/T_{ac}^{''}}}\text{，}$ (8)

2）短路电流非周期分量

 ${I_{dcM}} = \frac{{\sqrt 2 {V_N}}}{{|Z'|}}{e^{ - t/{T_{{dc}}}}}\text{，}$ (9)

3）最大非对称短路电流

 ${I_{PM}} = \sqrt 2 {I_{acM}} + {I_{dcM}}\text{。}$ (10)

3.2 考虑负载电流影响的改进算法

 ${I_{{N}}} = \frac{{{P_{{N}}}}}{{\sqrt 3 {U_{{N}}}\cos \varphi }}\text{，}$ (11)
 ${I_0} = \left( {0.2 \sim 0.4} \right){I_{{N}}}\text{。}$ (12)
3.3 计入电缆阻抗的改进算法

1）电缆阻抗对短路电流起始值的影响

 图 6 基于逆变电源组网的系统短路等效电路 Fig. 6 Equivalent circuit of inverter dominated shipboard power system when fault occurs

 ${I_{ac}}_l = \frac{{{E^{''}} - {I_S}\sqrt {{R_l}^2 + {X_l}^2} }}{{\sqrt {{R_l}^2 + {X_l}^2} + \sqrt {{R_s}^2 + {X'}{{'}^2}} }}\text{，}$ (13)

 ${I_{dcl}} = {i_{0 + }} + {I_{acl}} \approx {I_{ac}}_l\text{。}$ (14)

2）电缆阻抗对衰减时间常数的影响

 图 7 计入线缆阻抗的Tdc的等值电路 Fig. 7 Equivalent circuit of Tdc considering cable impedance

 图 8 计入线缆阻抗的Tac″ 的等值电路 Fig. 8 Equivalent circuit of Tac″ considering cable impedance

 ${T_{dcl}} = \frac{{{x^{''}} + x_l'}}{{2\pi f\left( {{R_s}{\rm{ + }}{R_l}} \right)}} = \frac{{{T_{dc}} + \frac{{x_l'}}{{2\pi f{R_s}}}}}{{1 + \frac{{{R_l}}}{{{R_s}}}}}\text{，}$ (15)
 ${T_{{{ac}}}}{_{\rm{l}}^{''}}{\rm{ = }}\frac{{{x^{''}} + {x_{\rm{l}}}}}{{{R_r}}}{\rm{ = }}{T_{{{ac}}}}^{''}\frac{{{x^{''}} + {x_{\rm{l}}}}}{{{x^{''}}}}\text{。}$ (16)

4 仿真分析与算例验证

 图 9 基于逆变电源组网的船舶电力系统 Fig. 9 Inverter dominated shipboard power system

 图 10 逆变电源短路限流输出 Fig. 10 Short-circuit characteristics of inverter

 图 11 电动机群反馈电流 Fig. 11 Feedback current of induction motors

5 结　语

 [1] 王寓, 王主丁, 张宗益. 国内外常用短路电流计算标准和方法的比较研究[J]. 电力系统保护控制, 2010, 38(20): 148-152. http://www.doc88.com/p-946526357441.html [2] 马伟明. 舰船动力发展的方向——综合电力系统[J]. 海军工程大学学报, 2004, 14(6): 1–11. http://mall.cnki.net/magazine/Article/HJGX200206001.htm [3] DENG Q, LIU X, SOMAN R, et al. Primary and backup protection for fault current limited MVDC shipboard power systems[C]// IEEE Ests. 2015: 40–47. [4] MALJKOVIC'Z, CETTOLO M, PAVLICA M. The impact of the induction motor on short-circuit current[J]. IEEE Industry Applications Magazine, 2001, 7(4): 11–17. [5] 刘楠, 张彦涛. 感应电动机负荷对短路电流影响机理研究[J]. 电网技术, 2012, 36(8): 187–192. LIU Nan, ZHANG Yan-tao. Impact of load induction motor on power system short-circuit current calculation[J]. Power System Technology, 2012, 36(8): 187–192. http://www.cqvip.com/QK/91996X/201208/42713549.html [6] XU Hui-yi. Feedback current impact to distribution network of large capacity motor users[C]// International Conference on E-Product E-Service and E-Entertainment, 2010: 1–3. [7] 吴忠林. 船舶交流电力系统的短路电流[M]. 北京: 国防工业出版社, 1983. [8] 柳彬, 谢炜, 余跃听, 等. 逆变电源短路保护及限流策略[J]. 舰船科学技术, 2011, 33(8): 95–98. LIU Bin, XIE Wei, YU Yue-ting, et al. Research on inverter short-ciruit protection and current-limiting strategy [J]. Ship Science and Technology, 2011, 33(8): 95–98. http://www.cnki.com.cn/Article/CJFDTotal-JCKX201108020.htm [9] 潘再平. 电机学[M]. 杭州: 浙江大学出版社, 2008. 8. [10] 张志, 彭晓涛, 李晓宁, 等. 改进的多母线船舶电力系统短路电流计算方法[J]. 电网技术, 2013, 37(8): 2212–2217. ZHANG Zhi, PENG Xiao-tao, LI Xiao-ning, et al. An improved short-circuit current calculation method for multi-bus ship power system[J]. Power System Technology, 2013, 37(8): 2212–2217. http://www.cqvip.com/QK/91996X/201308/46715508.html