Hybrid cascaded H-bridge multilevel inverter motor drive DTC control for Electric Vehicles

This paper presents a hybrid cascaded H-bridge multilevel motor drive DTC control scheme for electric (EV) or hybrid electric vehicles (HEV). The control method is based on direct torque control operating principles. The stator voltage vector reference is computed from the stator flux and torque errors imposed by the flux and torque controllers. This voltage reference is then generated using a hybrid cascaded H-bridge multilevel inverter, where each phase of the inverter can be implemented using a DC source, which would be available from fuel cells, batteries, or ultracapacitors. This inverter provides nearly sinusoidal voltages with very low distortion, using less switching devices. Due to the small dv/dt's, torque ripple is greatly reduced. In addition, the multilevel inverter can generate a high and fixed switching frequency output voltage with less switching losses, since only the small power cells of the inverter operate at high switching rate. Therefore a high performance and also efficient torque and flux controller is obtained, enabling a DTC solution for multilevel inverter powered motor drives.