Integrated Local Control of Active Power and Voltage Support for Three-Phase Three-Wire Converters

Abstract

The derivation of a robust control algorithm is presented to provide decoupled active power regulation and local grid voltage support in three-phase three-wire grid-connected converters (GCCs). Unlike conventional control schemes, the proposed strategy is designed to be harmonic sequence asymmetric for the purpose of local voltage unbalance correction. A frequency-domain Norton equivalent model is derived to illustrate the working principle of the strategy. Accordingly, by following a frequency-domain decoupled method, the fundamental positive-sequence, the harmonic symmetrical sequences and the fundamental negative-sequence components are regulated independently. Consistent to the model analysis, simulation results validate reduction of local voltage unbalance and total harmonic distortion. Since no external sensors are required for the implementation of the strategy, it is a local approach, applicable to already-existing GCC systems. Moreover, in view of the higher switching frequencies as attainable by devices from the next SiC generation, the accuracy and dynamic behavior of the control algorithms can be much enhanced, improving therefore the quality of the processed energy.