This paper proposes a novel space vector pulse width modulation (SVPWM) technique to address the capacitor voltage balancing issue in MMCs. The MMC topology consists of cascade connected identical and individual controllable submodules (SMs) to generate higher level output voltages. The characteristic of DC floating capacitor of SM complicates the modulation technique for MMC. This work presents a study of different carrier based modulation techniques for MMC. In this paper, a novel SVPWM technique and analogue sorting algorithm are implemented to control the SM capacitor voltages. The proposed SVPWM technique and existing carrier based modulation techniques for a five level MMC are implemented in MATLAB/Simulink environment. The simulation results of the proposed modulation technique is presented and compared with the existing carrier based modulation techniques.
A new neutral-point-clamped pulsewidth modulation (PWM) inverter composed of main switching devices which operate as switches for PWM and auxiliary switching devices to clamp the output terminal potential to the neutral point potential has been developed. This inverter output contains less harmonic content as compared with that of a conventional type. Two inverters are compared analytically and experimentally. In addition, a new PWM technique suitable for an ac drive system is applied to this inverter. The neutral-point-clamped PWM inverter adopting the new PWM technique shows an excellent drive system efficiency, including motor efficiency, and is appropriate for a wide-range variable-speed drive system.
In this paper, a new simplified space-vector pulse width modulation (SVPWM) method for a three-level inverter is proposed. This method is based on the simplification of the space-vector diagram of a three-level inverter into that of a two-level inverter. If simplified by the proposed method, all the remaining procedures necessary for the three-level SVPWM are done like conventional two-level inverter and the execution time is greatly reduced. The DC-link neutral-point potential control algorithms are implemented more easily. The proposed method can be applied to the multi-level inverters above three-level. The validity of the new SVPWM method is verified by experiment with a 1000 kVA three-level insulated gate bipolar transistor (IGBT) inverter.