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In this paper, a new variable-speed wind energy conversion system (WECS) with permanent magnet synchronous generator (PMSG), Vienna rectifier and three-level neutral point clamped (NPC) inverter is proposed. Vienna rectifier is used for flux vector control of PMSG, maximum power point tracking (MPPT) of wind turbine, PMSG efficiency optimization, and balancing of two rectified DC voltages. As power conditioner, a three-level NPC inverter is used to deliver energy to the grid. Vector control of the inverter provides the ability to regulate power factor to any desired value. The results of two simulations (for back-toback inverter and the proposed topology) are presented and compared. The results verify improved efficiency of the proposed WECS compared to WECS using back-to-back inverter. Figure 19. Output current of WECS and its harmonic spectrum. (a) Current using two-level inverter. (b) Current using three-level inverter. (c) Current harmonic spectrum using two-level inverter. (d) Current harmonic spectrum using three-level NPC inverter.

The proper operation of single-phase and three-phase grid-connected power converters depends on the synchronization with utility networks. The major challenge of the synchronization is how to quickly and precisely extract the ac signal and fundamental positive sequence in single-and three-phase power systems respectively. This paper proposes a new detection technique based on a modified Kalman filter and the generalized averaging method (KF-GAM). The method has an open loop structure, and uses the orthogonal signals which are obtained directly from the Kalman filter. The resulted detection system is very simple and robust even in the presence of power quality disturbances, such as voltage imbalance, harmonics, and voltage fluctuations. The proposed technique can detect the fundamental and harmonics frequencies within or less than half a cycle in all situations such as small and considerable frequency variations. Meanwhile, the method guarantees the zero steady-state error in complicated harmonic scenarios, including all typical single-phase and three-phase harmonics. Various case studies are assessed and the performance of the proposed detection method is verified by experiments.

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This paper presents a new structure for non-isolated and non-inverting DC-DC converters with high voltage gain harnessing the fundamentals of the voltage lift technique. The proposed topology is a suitable structure for low voltage applications. The operation principles, the steady-state relations, and different switching strategies to further improve the voltage gain performance of the proposed converter are described. A hybrid utilization of complementary switching approach and simultaneous switching of two switches is proposed to achieve the highest voltage gain in different duty cycles. Furthermore, a theoretical analysis of power losses is provided. The suggested DC-DC converter architecture features high voltage gain, high efficiency, and low stress on semiconductor devices. In order to demonstrate these advantages, the structure is compared with some recently-presented high step-up converters in terms of efficiency, voltage gain, and voltage stress. Moreover, A 200W laboratory prototype is developed with experiments carried out to validate the given theories and feasibility of the proposed converter topology.

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