A Method for Supply Voltage Boosting in an Open-Ended Induction Machine Using a Dual Inverter System With a Floating Capacitor Bridge

An operational approach to an induction machine is presented that uses an open winding connected to a dual inverter system. A floating capacitor inverter bridge boosts the fundamental voltage available to the machine and arbitrarily sets the operating power factor of the main inverter bridge connected to the dc battery power source. During operation, the motor current charges the floating bridge dc capacitor voltage to a naturally stable dc voltage level and the ac voltage delivered to the machine is the resultant sum of the two inverter bridge voltages. Machine voltage boosting is then achieved by adjusting the fundamental phase angle difference between the two inverters to control the charge stored in the floating bridge capacitors. With the floating bridge providing reactive voltage support and therefore boosting the available supply voltage to the induction machine, there are two main outcomes: minimization of the supply current required for operation beyond the base speed of the electric machine, and supply voltage regulation of the drive system. Experimental results are used to verify the operation of the floating bridge arrangement by examining the load power factor angle and the phase difference between the two bridges. Results are presented for a passive RL load to illustrate the supply current reduction at high fundamental frequency operation, and a modified 2-hp, 1800-r/min induction to illustrate the dc voltage supply droop compensation.