Improved performance and control of hybrid cascaded H-bridge inverter for utility interactive renewable energy applications

This paper presents capacitor voltage balance control methods for hybrid cascaded H-bridge inverter with single DC source to remove higher order of harmonics, the power quality is therefore improved with low THD of output power for utility interactive inverters. In addition, a new control strategy based on voltage frequency regulation is proposed in this paper to achieve faster and smoother transition from grid-connected mode to stand-alone mode. For sensitive and mission critical local loads, a seamless transition between two operation modes is very valuable, especially for the transition from grid-tied mode to stand-alone mode in the case of utility fault. The proposed method not only implement fast transition, the load voltage waveform also becomes continuous during transients. The proposed control methods can be easily applied for multi-bus micro-grid control system with least modification. The simulation and experimental results of single-phase utility interactive inverter confirmed the validity of proposed control algorithms.