Study of auxiliary railway power supply facing catenary transient overvoltage

In this contribution, we investigate the possibility of eliminating the crowbar circuit which is normally used to protect the auxiliary railway supply system in case of a catenary transient overvoltage. The idea is to act at the control level by suspending the operation of the auxiliary inverter when the input voltage reaches some given threshold. Experimental results are firstly presented for an inertial-type load in order to get an insight into the ensuing phenomena. Then, a theoretical analysis is carried on to explain the experimental observations, with emphasis on the freewheeling sequence of the inverter output currents. The subsequent voltage oscillations across the inverter switches are also justified. Considering a numerical example with realistic parameters values, it is shown that the freewheeling stage is not dangerous for the power devices of the auxiliary inverter. The switch voltages oscillations could however be destructive, depending on the value of the inverter dc input voltage at the time these oscillations start (rather than their peak value itself).