Grid Impedance Identification and Structured-h2 Optimization Based Controller Design of Active Front-end in Embedded AC Networks

The increasing use of power electronics systems and distributed generation in modern power networks has raised important issues regarding the effects that inter-connected converters systems can have on the performance and stability of the whole grid. Interactions between locally optimized converters, designed not taking into account the external influence of the system in which they are operating, may lead to performance degradation or even system instability and failure. This paper will deal with the problem of active-front end control design taking into account of system interactions with other power converters in the grid. A globally optimized local converter control tuning method, which is based on a state space model identification of the unknown grid system seen from the converter at its point of common coupling (PCC), is here proposed. The plant for the control design will then be not only represented by the local converter dynamics, but will also include the identified system at the PCC. In order to describe and validate the concept, a simplified notional system, comprising of two interconnected converter systems coupled on the same AC bus is analyzed. The effectiveness and advantages of the proposed method is validated by experiments with a traditionally designed PI controller for comparison.