Capacitor current loop design for dynamic characteristics enhancement of current source inverters

The CL-type filters adopted in grid-connected current source inverters (CSIs) causes resonance. Capacitor voltage feedback (CVF) based active damping (AD) can suppress this resonance, and has the advantage of simple implementation. However, the amplitude of the filter capacitor voltage is much larger than the amplitude of the direct current, which leads to an inability to obtain the optimal damping ratio when CVF-AD is employed. Thus, the dynamic characteristics and stability of the system are reduced. This can be solved by connecting a high-pass filter in series in the damping branch. However, the bandwidth of the high-pass filter is coupled with the controller parameters, which increases the difficulty of system parameter design. To address this issue, the inverter current is decomposed into the grid current and the capacitor current depending on the circuit. Then the capacitor current loop (CCL) is constructed. On this basis, the CCL and the damping branch are based on the optimal virtual resistor, which can filter out the fundamental component of the feedback filter capacitor voltage to approximately realize the function of a high-pass filter. Additionally, this approach can effectively improve the dynamic performance and stability of the system, as validated by experimental results.