Positive-sequence grid voltage detector for distributed generation systems with no tuning requirements

This paper proposes a three-phase positive sequence detector that does not require any parameter to be adjusted. It operates in open loop and there is not any PI controller that needs to be tuned. The scheme includes the use of the Park transformation and moving average filters. Performance of the moving average filter is mathematically analyzed and represented in a Bode diagram. The analysis allows proper selection of the optimal filter's window width for its application in d-q transformed variables. The proposed detector scheme allows fast detection of the grid voltage positive sequence. The MAF completely eliminates any oscillation multiple of the frequency for what it is designed. Thus, this algorithm is not affected by the presence of imbalances or harmonics in the electrical grid. The proposed positive-sequence detector is verified through simulation and experiment. It shows very good performance even under extreme grid voltage conditions.