Analysis of Multi-Sampled Current Control for Active Filters

This paper investigates the multi-sampling techniques applied to the current control in active power filter applications. In active power filter applications with digital control, the main bandwidth limitation derives from A/D conversion time, calculation delays and the sample-and-hold effect for the Digital-Pulse-Width Modulation (DPWM). Using Field Programmable Gate Arrays (FPGAs) and fast A/D converters for the control implementation, it is possible to make the former two negligible with respect to the switching period. Thus, the overall phase lag is dominated by the DPWM, which can be strongly reduced by multiple sampling approach, thus breaking bandwidth limitation of single- sampled solutions. Moreover, as the multi-sampling approach triggers nonlinear behaviors that can negatively impact the filter compensating capabilities, a solution is proposed, based on a simple digital filter, that linearizes the system behavior and does not waste the multi-sampling phase boost property. Simulation and experimental results on a 10 kVA prototype confirm the theoretical expectations.