A New $LCL$ -Filter With In-Series Parallel Resonant Circuit for Single-Phase Grid-Tied Inverter

When designing a higher order output power filter for a transformerless grid-tied converter using pulsewidth modulation (PWM), the requirements on the leakage current, the electromagnetic interference (EMI) noise, and the harmonics of the grid-injected current should be addressed. For an LCL-filter-based single-phase grid-tied full-bridge inverter system, it is possible to decrease the total inductance as well as the size and the cost, if the harmonic currents around the switching frequency can be fully suppressed. In this paper, the grid-injected current harmonics and the conducted EMI noise are investigated for the conventional LCL-filter-based system. Based on this, a modified LCL-filter topology using an extra parallel LrCr resonant circuit is proposed to reduce the total inductance value, without increasing the capacitive reactive power. The validity is verified through the experiments on a 500-W 110-V/50-Hz prototype.