Vienna rectifier as generator-side converter of wind energy conversion system (WECS) using a permanent-magnet synchronous generator (PMSG) has several advantages compared to conventional back-to-back inverter, such as higher efficiency and improved total harmonic distortion. On the other hand, direct torque control (DTC) of the generator in WECS is of interest, particularly for low-power applications due to several merits, including fast torque response, insensitivity to PMSG model and associated parameters, elimination of rotor position sensor, and reduced computations. In this paper, the effects of Vienna rectifier voltage vectors on instantaneous PMSG torque and stator flux are derived, and DTC of PMSG by the Vienna rectifier is implemented, considering the constraints imposed by the Vienna rectifier. Experimental tests for a 1-kW prototype are presented, which confirm the simulations and theoretical results.

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. 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.

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.

A new non-isolated, high step-up DC-DC converter is proposed based on the current-fed Cockcroft-Walton Voltage Multiplier (CW-VM) that can be used as the boosting power stage of converter for low-voltage low power renewable energy sources such as photovoltaic and fuel cells. The proposed converter employs two low-voltage common-emitter switches. Utilizing the current-fed CW-VM eliminates some problems associated with the conventional voltage-fed type such as voltage ripple and load-dependent voltage droop. Other advantages of the proposed converter are continuous input current, high voltage gain, and high efficiency. Steady state operation principles, specifications, and design considerations of the proposed converter are illustrated. Furthermore, efficiency analysis of the converter is performed and discussed. Experimental tests for a 200 W prototype are carried out which confirm the theoretical analysis.

A new approach for minimization of total harmonic distortion (THD) of a multilevel flying capacitor inverter (MFCI) based on the selective harmonic elimination named stochastic THD (STHD) strategy is proposed. In the STHD strategy, the step voltage levels of multilevel inverter are considered to be varying due to unbalanced capacitor voltages. Moreover, this paper improves modeling of harmonic elimination by considering the effects of dissipative snubbers, blanking time, gate-drive circuits, and computation time in microcontrollers on the THD calculation. Switching instants are deviated from the desired moments by regarding the mentioned effects. In the proposed strategy, the switching angle variations and unbalancing of flying capacitor voltages are evaluated by 2 m + 1 point estimate strategy. Then, the formulation is combined with new modified cuckoo search algorithm and a self-adaptive mutation tactic for the establishment of new robust algorithm for minimization of the THD. The proposed STHD strategy is capable of determining the best switching angles pattern in low switching frequency without measuring current and capacitor voltages, as well as not using any controller. The proposed strategy is applied on three MFCIs and the results show that the proposed method effectively minimizes specific harmonics with low THD.

Employing conventional three-phase inverter in variable speed single-phase drive suffers from limited maximum output voltage applied to motor or voltage utility factor (VUF). In this study, a z-source inverter (ZSI) has been used to drive a single-phase induction motor (SPIM). By the proposed topology, VUF and consequently torque speed characteristic of the single-phase motor is improved. The equations for employing ZSI in SPIM drive and modulation method are described. Results of two simulations using conventional inverter and ZSI are presented. The results show that using ZSI leads to an increase in motor electromagnetic torque compared to conventional three-phase inverter due to improved VUF. The experimental results confirm the theory and simulation.