Effect of minimizing input capacitance in VSI-based renewable energy source converters

Most of single or three-phase converters used in interfacing renewable energy sources (RES) to the power grid originate from VSI-based topologies. A common practice is to connect a capacitor between the RES and the VSI switch matrix to filter the pulsating current drawn by the converter. When a converter is supplied by a RES, one is usually interested in controlling the converter input voltage for maximal power transfer. The VSI incorporates a RHP-zero in its control-to-output transfer function when the operating point is moved from the constant voltage to constant current region of the source. The frequency of the zero can be given based on the input capacitance, voltage and current. The RHP-zero will turn into a RHP-pole in the input voltage control loop, which leads to constraints between the capacitor sizing and control system design. This paper gives scientific insight into the capacitor sizing and control design, of which the latter is often ignored in the analyses but is an essential part of interfacing RES into the grid.