Noise shaping modulation and dynamic current control of NPC inverters for low switching frequency applications

Effective modulation schemes for medium and high voltage inverters is a known challenge, particularly in dynamic applications under closed loop current control. Good dynamic response and harmonic performance need to be achieved alongside elimination of unnecessary switching. This paper explores the application of the noise shaping Feedback Quantizer based Modulation (FBQM) to low switching frequency NPC inverters. Unlike symmetrical PWM schemes, FBQM generates random quantization noise and benefits from variations of reference voltage under closed loop current control. FBQM offers an arbitrary shaping of the output noise by means of a feedback filter. The paper explains about the FBQM application to NPC inverters, provides extensive simulation and experimental data and explores how the number of switching events per device depends on closed loop versus open loop inverter operation. In conclusion, the paper shows that FBQM, despite its simplicity, provides very competitive performance and good suitability for low switching frequency applications.