Mathematical model analysis and LCL filter design of VSC

VSC (Voltage Source Converter) using PWM control technology injects harmonic current into grid. The AC filter is generally installed at the grid-connected side to filter high-frequency harmonics which were produced by VSC. LCL filter can easily be finished by installing shunt capacitor between converter transformer and converter reactor. For high-voltage large-capacity converter, switching frequency is relatively low and the reactive value of converter reactor is also relatively small, thus the parameter designing of LCL filter is more complicated. In this paper, the impedance-frequency characteristics of primary system and the system-voltage's transfer function are researched, also resonance phenomenon of VSC system is studied. The parameter design method of LCL filter and resonance inhibition method using damping resistor are obtained based on above analysis. The simulation model of VSC grid-connected system is established in PSCAD/EMTDC simulation environment. Simulation results prove the analysis of resonance phenomenon and the rationality of above LCL filter design method.