Enhanced Interleaved PWM Scheme with Flux Compensation for Three-Parallel Connected Inverters

A pulse width modulation (PWM) scheme is described for a 3-phase voltage source converter (VSC). The VSC uses three inverter legs in each phase, which are connected in parallel using coupled inductors with crossed coupled windings to lower the series output inductance. The parallel connected inverters are controlled with three 120° phase-shifted carriers. Instead of changing carriers on the $\pm 1/3$ crossover of the 3-phase reference signals to improve the quality of the PWM line voltages, the reference signals are modified. This modulation scheme generates high-quality 4 -level phase and 7 level PWM line voltages without generating flux jumps in the coupled inductors. In addition, the PWM voltage step is ${\mathrm {V_{dc}}}/3$ and the frequency of the PWM line voltage is six times greater than the switching frequency, which can easily be filtered with a small filter inductor. The modulation scheme significantly reduces the cross-sectional area, weight, and material cost of the magnetic cores of the VSC, which is suitable for mobile applications such as aerospace and electric vehicles where weight-light magnetics is required. The enhancement of the PWM scheme is appreciated with lower current THD
f
and load voltage harmonic volt-seconds. The feasibility of the modulation scheme is confirmed with PLECS simulation and experimental results of a 10 kW(300 Vdc, 208 V/28 A) laboratory prototype.