Plug-in Gate-loop Compensators for Series-connected IGBT Drivers in a Solid-state Fault Current Limiter

A solid-state fault current limiter (SSFCL) is the key protective equipment in a direct current distribution network. In order to meet the high voltage requirements and reduce costs, implementing a SSFCL based on series-connected insulated gate bipolar transistors (IGBTs) is a promising approach. However, voltage unbalancing of IGBTs would be introduced if the gate-loops of the IGBTs are non-identical. In this paper, a plug-in gate-loop compensator with discrete gate voltage feedback and pulsewidth current compensation is proposed. The main merits are: 1) with the plug-in structure, the extra current sources only provide small power to fine-tune the gate-loop without affecting the functions provided by the commercial IGBT gate driver; 2) the gate-emitter voltages of IGBTs are compared with the preset thresholds to obtain control criterion, and the pulsewidths of the current sources are controlled for gate-loop compensation, thus both analog-digital and digital-analog converters are avoided; 3) the control law is easy to implement in FPGA, and is robust to voltage variation of power-loops. With the proposed compensator, the voltage unbalancing is alleviated immediately at the present switching cycle, and further eliminated cycle-by-cycle during the current limitation process. Experimental results verify the feasibility of the proposed compensator.