Compensation of reactive current, harmonic current and unbalanced current are important to improve the quality of electric energy, the key point of which relies on a fast and accurate harmonic detection algorithm. An improved harmonic detection algorithm based on multi-synchronous rotating frame transformation in three-phase four-wire system in distribution network is designed in this paper. Compared to traditional approaches, the improved algorithm keeps high accuracy and dynamic response for selective harmonic detection by using PI controllers with feedback. And the steady-state and dynamic performance of harmonic detection algorithm are analyzed by the frequency domain methods. Finally, the effectiveness of the algorithm is verified by simulation.

A vector control strategy applied to a multi-DC-port bidirectional DC/AC converter is presented in this paper, which can distribute the power of each DC source in a wide range. Port vectors corresponding to each DC port are defined, and the relationship between port vector and port power is analyzed, which maps the distribution of DC port power to the composition of port vectors. By controlling the magnitude and phase of the port vectors, the magnitude and direction of power flow are controlled for each corresponding port, even with a very low voltage of an auxiliary DC port. Compared with traditional n-level SVPWM, the number of vectors is reduced from 3nto n, which leads to an easier control strategy in multi-port converters. Several typical scenarios are shown in this paper. And the proposed vector control strategy is verified in MATLAB/Simulink.