Power Electronic
F. Mohammadi; J. Milimonfared; H. Rastegar; M. Farhadi-Kangarlu
Abstract
A new single-phase transformerless grid-connected PV inverter is presented in this paper. Investigations in transformerless grid-connected PV inverters indicate the existence of the leakage current is directly related to the variable common-mode voltage (CMV), which is presented in detail. On the other ...
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A new single-phase transformerless grid-connected PV inverter is presented in this paper. Investigations in transformerless grid-connected PV inverters indicate the existence of the leakage current is directly related to the variable common-mode voltage (CMV), which is presented in detail. On the other hand, in recent years it has become mandatory for the transformerless grid-connected PV inverters to satisfy new grid-codes such as low-voltage ride-through (LVRT) capability via injecting reactive power during grid faults. Therefore, in this paper, the design of the proposed topology is based on retaining the constant CMV to suppress the leakage current and also to provide reactive power injection capability during grid faults. The control strategies for injecting reactive power in the LVRT condition are also examined. To validate the presented theoretical concepts, the performance and dynamic response of the proposed transformerless PV inverter are investigated by MATLAB/Simulink and the simulation results are presented and discussed.
Power System Stability
M. Nasiri; J. Milimonfared; S. H. Fathi
Abstract
This paper presents a new nonlinear backstepping controller for a direct-driven permanent magnet synchronous generator-based wind turbine, which is connected to the power system via back-to-back converters. The proposed controller deals with maximum power point tracking (MPPT) in normal condition and ...
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This paper presents a new nonlinear backstepping controller for a direct-driven permanent magnet synchronous generator-based wind turbine, which is connected to the power system via back-to-back converters. The proposed controller deals with maximum power point tracking (MPPT) in normal condition and enhances the low-voltage ride-through (LVRT) capability in fault conditions. In this method, to improve LVRT capability, machine-side converter controls dc-link voltage and MPPT is performed by grid side converter. Hence, PMSG output power is reduced very fast and dc-link voltage variation is reduced. Due to nonlinear relationship between dc-link voltage and controller input, nonlinear backstepping controller has good performances. By applying the proposed controller, dc-link overvoltage is significantly decreased. The proposed controller has good performance in comparison with Proportional-Integral (PI) controller and Sliding Mode Controller (SMC). In asymmetrical faults, to decrease grid side active power oscillations, the nonlinear backstepping dual-current controller is designed for positive- and negative- sequence components. The simulation results confirm that the proposed controller is efficient in different conditions.