Research On Circulating Current Based On Parallel Energy Feedback Unit

Parallel energy feedback system can be used to transfer the energy back to the power system, which can achieve the "energy regeneration" of the traditional variable speed control system to improve the energy efficiency. However, there will be the circulating current in the parallel energy feedback system, the circulating current will deteriorate the grid connected current harmonics, increase the switching loss, and bring adverse effects to the control performance.In this thesis, the characteristics of the circulating current in parallel energy feedback system are studied in detail. The basic working principle of the energy feedback system and the simplified model of the current research on the circulating current of the parallel energy feedback system are introduced at first, also the system control principle of the energy feedback unit is analyzed. Based on the single switch period in a particular sector, the circulating current commutations in different vector states are analyzed, and the circulating current equations are obtained. At the same time, the position distributions of the current in each sector are explained by tabular forms, and the circulating current characteristics are summarized. Meanwhile the estimation method of the circulating current peak value is derived from the point of view of the switching vector conduction time. The key factors that affect the current are discussed, and the method to improve the hardware topology to suppress the circulating current are obtained in this paper. Finally, the relationships between the switch state vector and the circulating current are analyzed. To eliminate the effects of zero vector, the principle of the AZSPWM modulation strategy which will suppress circulating current is discussed. Implementation method of this modulation strategy is expressed based on the SVPWM modulation strategy.A simulation model of parallel energy feedback system based on Saber platform is designed to validate the correctness of the theoretical analysis about the circulating current. Through simulation results demonstrate the validity of the proposed circulating current suppression method.