Advanced Variable Switching Frequency Control for Improving Weighted Efficiency of Distributed Renewable Generation Systems

Abstract

Energy conversion efficiency and output current harmonic distortion are two key performance measures of small-scale grid-connected distributed generation (DG) systems. As the interface between renewable energy generators and the utility grid, dc-ac converters (i.e. inverters) have been increasingly used in recent years. In this paper, a novel control algorithm termed “variable switching frequency control (VSFC)” is proposed to increase the weighted efficiency of the inverter for renewable energy generators through selection of optimal switching frequencies of pulse width modulation (PWM) in real time, based on estimation of output current harmonic distortion. Both simulation and experimental results indicate the proposed VSFC algorithm ensures that the inverter can operate with maximum efficiencies at different output levels while satisfying standard requirements for grid current harmonic distortion. Furthermore, implementation of this method to improve the inverter efficiency has no impact on inverter costs or control complexity.

Keywords

• Renewable energy
• distributed generation
• variable switching frequency
• predictive control
• weighted efficiency
• current harmonics