Application of multi-pulse multilevel inverters is considered in this paper for distributed generation. A five-level twelve-pulse neutral point clamped inverter has been combined with a proton exchange membrane fuel cell in order to investigate load following characteristics of the fuel cell. The fuel cell implemented with a three-phase multi-pulse multilevel inverter is adept of delivering single-phase and three-phase loads both in islanded and grid-connected approach. Changes in power demand from no-load to full-load (120 kW) have been applied to study the characteristics of the system from the perspective of how it can follow the load changes in load demand. It has been observed that the fuel cell model is adept of following power request as per requirement; however, there is a response time of few seconds, because the reformer for the fuel cell requires time to generate fuel and the fuel cell requires time for chemical reactions to take place in it. Implementations of six-pulse and twelve-pulse five-level neutral point clamped and flying capacitor inverters show that total harmonic distortions for six-pulse and twelve-pulse five-level neutral point clamped inverters to be 1.066219% and 0.406149% respectively as compared to 2.466889% and 1.5104075% for flying capacitor inverters. It has been observed that with twelve-pulse neutral point clamped inverter, the output voltage waveform is smoother and close to sinewave. The results of the research work is presented with analyses to validate that multi-pulse multilevel neutral point clamped inverter is a better way out for the fuel cell power generation model as this type of inverters produces smoother waveforms to improve power quality with lower harmonics.
Harmonics reduction of three phase five-level Neutral-Point-Clamped Multilevel Inverter