Power-Loss Ride-Through in a Cascaded H-Bridge Inverter Fed Vector Controlled Induction Motor Drive

A Cascaded H-Bridge (CHB) inverter fed drives are quite popular in high power industrial applications. But these drives are very sensitive to power supply disturbances like voltage sags or short-duration power interruptions on the input grid side, which causes the drive to trip on undervoltage protection, thus resulting in production losses. Therefore, it is necessary to employ techniques that improve the resilience of the drive by enabling it to smoothly ’ride-through’ such short duration disturbances. The traditional methods for ride-through in CHB-fed drives generally require extra hardware or DC link voltage sensors, which increases the cost of the drive. This paper proposes an economical and simple method of power-loss ride through for CHB multilevel inverter fed vector controlled induction motor drives. In this method, the kinetic energy stored in the rotating mass is recovered, without using the information of DC link voltages. This proposed strategy maintains all the DC link voltages constant during any momentary voltage sags or supply interruptions by controlling the voltage space phasor. The proposed method provides a reliable ride-through capability without using additional hardware or voltage sensors. The proposed scheme is experimentally validated on a 7-level CHB inverter fed vector controlled 30 kW induction motor drive.