Observer based power feedforward control for AC/AC converters

In this paper a disturbance observer based power feedforward is proposed as a new alternative control solution of the input AC/DC stage of a quasi direct AC/AC converter. The observer identifies the DC link current drawn by the output inverter section. The observed load current is then used to constitute the DC link power based feedforward signal added to the output of the converter DC link voltage regulator improving its dynamic response. This solution permits achievement of the fast dynamic response to the load power requirements resulting in DC link voltage variation comparable to the one obtainable by the traditional solutions. Furthermore, the proposed solution overcomes typical drawbacks of the traditional approaches based on the power estimated in the inverter stage such as a fast communication link, etc. The control of the input AC/DC converter can be contained in a DSP separated from the output inverter stage, still maintaining high performance characteristics. This solution is also attractive for the stand alone AC/DC converters suitable for common DC bus systems. The simulation and the experimental comparison of several existing control schemes with the proposed one confirms that the observer based feedforward provides equivalent performance characteristics. The experimental results are obtained from a 7.5 kW quasi direct AC/AC converter. The paper also focuses on the observer design methodology.