Comparative evaluation of control schemes for a high bandwidth three-phase AC source

This paper presents a comparative evaluation of a conventional cascaded PI-based control scheme (2 control loops with feedforward) with two different Model Predictive Control (MPC) schemes for a high performance AC source with 5 kHz – 3 dB small-signal bandwidth. The prediction horizon of the MPC is 2. One of the MPC schemes considers direct selection of the switching states and the other one considers, in addition, the use of a modulation stage in order to obtain a constant switching frequency and to improve the steady-state output voltage behavior. The AC source considered in this work is based on a three-level T-Type converter with a two-stage LC output filter. The frequency characteristics of the system for the three control schemes are obtained, including reference tracking transfer function, output impedance and attenuation of DC-link voltage harmonics.