Model Predictive Direct Current Control for a grid-connected converter: LCL-filter versus L-filter

This paper presents a modified Model Predictive Direct Current Control (MPDCC) strategy for use with a Neutral Point Clamped (NPC) converter connected to the grid via an LCL-filter. The modified MPDCC strategy incorporates an Active Damping (AD) scheme based on the Virtual Resistor (VR) concept, which suppresses spectral content around the resonant frequency of the LCL-filter, enabling low levels of grid current distortion to be achieved with low switching frequencies. Through simulation the proposed scheme is compared against conventional MPDCC with a direct connection to the grid (L-filter). By comparing the trade-off curves of grid current distortion against device switching losses, it is shown that the performance of the proposed strategy is superior to that of conventional MPDCC with a direct grid-connection across a range of operating points.