Harmonic analysis of single-phase grid-connected converter with L filter for distributed generator

Characteristics of harmonic current generated by single-phase converter with L filter for distributed generator are studied. The variation of transient current in a carrier cycle is derived by the differential equation of the system in time domain. Then compared transient current and fundamental current generated by convertor with no grid, harmonic current under condition of different modulation ratio is analyzed. When and why harmonic current is the largest and smallest in a fundamental cycle is presented through the study of variation tracking capacity of transient current. The maximum and minimum TDD/ with a fixed carrier ratio is proposed. The current generated by the joint action of converter and grid voltage source is also analyzed to explain the relationship of variation tracking and harmonic currents. Simulation results in different operation mode verified the correctness of the proposed theoretical results.