基于电流有效值的静止变频器本体差动保护新方法

静止变频器(SFC)是大型抽水蓄能机组水泵工况下启动的重要设备。鉴于目前SFC本体差动保护的不足，提出了一种新的保护方法——幅值差动保护。SFC的网桥侧电流为工频电流，机桥侧电流为变频电流，难以直接进行常规差动电流计算。基于静止变频器的基本原理，尽管电流经过SFC后频率发生变化，但其有效值是不变的，故可利用机、网两侧电流幅值构成差动保护方案。首先通过判断过零点的方式确定变频电流的周期，然后确定电流的有效值，最后提出幅值差动保护方法。在Matlab/Simulink中搭建了抽水蓄能机组静止变频启动模型。仿真结果验证了幅值差动保护具有良好的选择性和速动性。

A novel SFC differential protection method based on current effective value

Static Frequency Converter (SFC) is an important equipment of large pumped storage unit starting under pump operating condition. Given the lack of current SFC differential protection, this paper proposes a new protection method, namely amplitude differential protection. As the SFC current at grid side is power-frequency and the current at generator side is variable-frequency, it is difficult to calculate the conventional differential current directly. Based on the basic principle of SFC, the current frequency changes after current flows through SFC, but the effective value is unchanged. Therefore, SFC current RMS (Root Mean Square) at grid side and generator side can be utilized to constitute differential protection scheme. Firstly, the period of variable-frequency current is obtained by using the zero crossing. Then the effective value of variable-frequency current is determined. Finally, an amplitude differential protection method is proposed. In addition, SFC starting model of pumped storage unit is built in Matlab/Simulink and the good quickness and selectivity of amplitude differential protection is verified by the simulation results.