A Novel Frequency Locked Loop With Current Harmonic Elimination Method for the Three-Phase Grid-Connected Inverter

Abstract

In order to eliminate the harmonics of the grid connected inverters accurate harmonic detection is essential. Though there are many kinds of different harmonic detection methods are available, it can hardly be achieved without the help of grid frequency detection of the fundamental component. In this paper a novel Lock-In Amplifier based Frequency Locked Loop (LIA-FLL) is proposed for the improved harmonic elimination of the grid-connected three phase inverters. Due to the outstanding performance of the LIA-FLL, the harmonics can be detected and compensated accurately under the grid frequency variation. To demonstrate the superiority of the proposed method, it is applied to a 10 kW three phase grid connected inverters. The results obtained by the proposed method are compared with those obtained by the harmonic elimination method with no FLL. The principle of LIA-FLL is discussed and its performance for the harmonic elimination is proved by the simulation and experiments with a 10KW three phase grid connected inverter under the highly polluted grid condition.

Keywords

• Frequency locked loop
• lock-in amplifier
• harmonic elimination
• three-phase grid-connected inverter