Open-End Windings Induction Motor Drive with a Floating Capacitor Bridge at Variable DC Link Voltage

The open-end winding configuration allows feeding an electric motor from two sides. If one of them is connected to an inverter closed on a floating capacitor and operates as a power conditioning system, it is possible to obtain several benefits over the traditional configuration, such as an increase in the constant-power speed range. However, the additional converter causes switching losses that reduce the total efficiency of the drive. In this paper, it is shown how to improve the efficiency of an induction motor drive with open-end windings by controlling the DC-link voltage of the floating bridge depending on the operating conditions. The set-point of the secondary DC link is not calculated as an explicit function of the motor speed, which could depend on many machine parameters, but it is generated by a robust closed-control loop that uses the actual motor state. The variable DC link allows improving the overall efficiency of the drive mainly around the base speed at high values of the torque. Experimental results are shown to confirm the effectiveness of the developed configuration.