Neutral-Point Voltage Balancing in Three-Level Inverters Using an Optimized Virtual Space Vector PWM with Reduced Commutations

Abstract

Neutral-point voltage unbalance seriously distorts the output waveform and may result in the shoot-through of switching devices in neutral-point-clamped three-level inverters. Compared with the nearest three vector pulsewidth modulation (PWM), the nearest three virtual space vector PWM (NTV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PWM) can balance neutral-point voltage without the limitation of modulation index and power factor angle. However, the switching period of NTV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PWM is increased by one-third at the same switching loss, causing one-fourth lower switching frequency and degrading the acoustic noise performance in some motor drives. To overcome this drawback of NTV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PWM, an optimized NTV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PWM is proposed and verified in experiments. The optimized NTV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PWM reduces the number of switches in a switching period from 4 to 3, and it shortens the switching period by about one-fourth, transferring the switching noise to about one-third higher frequency. The proposed technique is suitable for motor drives where switching noise is expected to be low and the feedback of current as well as neutral-point potential are available.