Reduction of voltage harmonics in an open-end winding induction motor driven by a dual-inverter with a floating capacitor in a partial-load condition

Abstract

In this paper, a control strategy for reducing voltage harmonics of an induction motor in a low-torque condition is proposed. The motor drive system consists of an open-end winding induction motor and two voltage source inverters (VSIs); the dual-inverter has a DC voltage source and a floating capacitor. The motor losses, especially those caused by pulse width modulation in a VSI, increase when the inverter operates at a low modulation index (MI). In proposed method, the use of the output voltage difference between the inverters constituting the dual-inverter lowers the harmonics by keeping the MI high owing to the phase angle difference variation between the two inverters. The performance of harmonics reduction is theoretically analyzed and experimentally verified. The experimental results show that the voltage THD is reduced by 15 percentage points (pp) and 51 pp, compared with those of single-inverter and conventional dual-inverter operations, respectively, at a torque of 0.5 Nm (0.1 p.u.). By improving the motor efficiency using the proposed method, the total efficiency can be improved even if the inverter efficiency is slightly reduced.