FCS-MPC and observer design for a VSI with output LC filter and sinusoidal output currents

Abstract

Voltage source inverter (VSI) with output LC filter can be used to generate sinusoidal output voltages with reduced low frequency harmonics content. This application is suitable for uninterruptible power supply (UPS) systems. Finite control set model predictive control (FCS-MPC) has proved to be a good candidate for controlling such kind of devices. FCS-MPC relies on accurate system model to achieve high performance. However, output load is not always known for UPS applications. Under this condition, the use of observers to estimate the output load currents is a good solution. In this paper, a FCS-MPC strategy using an unknown input observer (UIO) is assessed. To design the UIO, the nature of the output load has been considered. This paper is focused on output loads with sinusoidal output currents. Two different UIO are evaluated. The first one uses a conventional approach and the second one takes into account the sinusoidal nature of the output load currents. Experimental results in a VSI prototype show that the second approach can provide superior performance independently of the output load connected to the power inverter.