A power line conditioner using cascade multilevel inverters for distribution systems

In this paper, a power line conditioner using a cascade multilevel inverter is presented for voltage regulation, reactive power (VAr) compensation, and harmonic filtering. The cascade M-level inverter consists of (M-1)/2 H bridges, in which each bridge has its own separate DC source. This new inverter can: (1) generate almost sinusoidal waveform voltage with only one time switching per line cycle; (2) eliminate transformers of multipulse inverters used in the conventional static VAr compensators; and (3) make possible direct connection to the 13.8 kV power distribution system in parallel and series without any transformer. In other words, the power line conditioner is much more efficient and more suitable to VAr compensation and harmonic filtering of distribution systems than traditional multipulse and pulsewidth modulation inverters. It has been shown that the new inverter is especially suited for VAr compensation. This paper focuses on feasibility and control schemes of the cascade inverter for voltage regulation and harmonic filtering in distribution systems. Analytical, simulated, and experimental results show the superiority of the new power line conditioner.