Improved Stability and Damping Characteristics of LCL-Filter Based Distributed Generation System

Abstract

The voltage source inverter is a key component in the distributed power generation systems where the LCL-filter is a popular choice for interfacing with the grid. However, the well-known resonance issue associated with the LCL-filter deteriorates the control performance and risk the inverter system stability. The inverter control design plays a significant role to ensure the quality of the injected grid current and stable operation according to the requirements of grid interconnection standards. This paper deals with an alternative control design method that modifies the internal damping loop design to improve the stability and damping characteristics. The proposed design employs a compensator across the filter and feedbacks the output of the augmented plant at the reference voltage point, and named as parallel feedforward compensation method. The filter capacitor current measured for damping loop implementation, and a high-pass filter compensator adopted in the proposed configuration. The proportional capacitor current feedback compensation method is considered for comparative studies. The current loop stability and control performance characteristics are investigated in detail under the resonance frequency and filter parameters variation condition. The significant outcomes of the proposed scheme are faster dynamic response, higher delay compensation capability, relatively improved resonance suppression, and potential for better tracking performance. An experimental prototype is developed to validate the efficacy of the proposed method.