Magnetic integrated LCL filter design for a 2.5 kW three-phase grid-connected inverter with double closed-loop control

Output filter is an essential part of a grid-connected inverter used for improving the quality of a grid-injected current. The use of LCL filters in power converters in microgrid applications is more preferred compared with L or LC filters because of their better harmonic attenuation capability. However, LCL filter still occupies a main part of the weight and volume of the whole system. Thus, more progress can be further developed with this consideration. In this paper, based on a 2.5 kW three-phase voltage source inverter, a magnetic-integrated LCL filter is designed by sharing an EIE-type core to reduce weight and size significantly. With the magnetic coupling influence taken into consideration, more effective design principles of the filter are discussed according to theoretical analysis and mathematical modeling. Meanwhile, a double closed-loop control strategy is utilized to eliminate the resonance introduced by the LCL filter and stabilize the system. Simulation and practical experiments are conducted with a detailed comparison between the discrete and integrated LCL filters, which can verify the feasibility and validity of the proposed method.