Startup and Fault Tolerance of the SRM Drive with Three-Phase Bridge Inverter

Abstract

When a three-phase SRM (switched reluctance motor) is driven by a three-phase bridge inverter, the phases of SRM should be connected in the same way that in the case of the induction motor, in other words, in delta or stars. When the phase windings are connected in star, the star's center it should be connected to the mid point of the capacitors of the DC bus. To maintain the voltage of the capacitors balanced during the operation of SRM is necessary to use a strategy of energy transfer of the capacitor with more charge for than has less charge. The voltage balance of the DC bus capacitors is obtained with the change of the phase currents direction during the machine operation. This strategy doesn't prevent that in the startup one of the DC bus capacitors is totally discharge. The short circuit of one of the capacitors for a relay during the startup solves the problem of discharge of the capacitor, it allows to operate SRM in very low speed, but it imposes an equivalent performance of an R-Dump inverter, where the discharge resistance of the energy of the turned off phase is the own coil resistance of the phase. In this paper, a SRM startup technique is presented to work with a three phase bridge inverter and machine windings connected in star, without startup relay. The technique bases on allows two phases to conduct at the same time during startup. A comparison of the system proposed with the split and asymmetric half bridge inverters are also presented, analyzing the fault tolerance in the inverter. Experimental results demonstrate the validity of the proposed technique