Z-source converter based grid-interface for variable-speed permanent magnet wind turbine generators

A Z-source inverter based grid-interface for a variable-speed wind turbine connected to a permanent magnet synchronous generator is proposed. A control system is designed to harvest maximum wind energy under varied wind conditions with the use of the permanent magnet synchronous generator, diode-rectifier and Z-source inverter. Control systems for speed regulation of the generator and for DC- and AC- sides of the Z-source inverter are investigated using computer simulations and laboratory experiments. Simulation and experimental results verify the efficacy of the proposed approach

Development of a Comprehensive Model and a Multiloop Controller for Z-Source Inverter DG Systems

This paper presents the modeling and design of a closed-loop controller for a Z-source inverter. The Z-source inverter is a recently proposed single-stage power converter, and it is capable of operating in both buck and boost modes. Hence, this inverter gives an economical solution for power conversion in distributed generation (DG) applications, particularly by eliminating the need for a two-stage conversion. Moreover, applications such as DG demand quality output waveforms, and additionally, when the system is subjected to input- and load-side disturbances, their effects need to be minimized. This can be achieved with closed-loop controlling. Toward this end, the system is modeled first with large- and small-signal modeling techniques, and relevant transfer functions are derived. The dc-side of the Z-source inverter shows a non-minimum-phase characteristic, and the output voltage of a Z-source impedance network shows a significant overshoot and undershoot, following a step change in the input due to energy resettling. These effects could be transferred to the ac-side, giving rise to the undershoot and overshoot in the ac output as well. Hence, the proposed controllers should be able to minimize such effects. The ac- and dc-sides are considered separately when designing the controllers. An indirect controller is employed in the dc-side, whereas the ac-side controller is designed in the synchronous reference frame. The modulation index, shoot-through time, and saturation levels are appropriately selected so that the dc-side effects are prevented from propagating into the ac-side. The simulation results are obtained using a state-space-averaged inverter model, and an experimental prototype is built in a laboratory to prove the efficacy of the proposed algorithm. Simulation and experimental results show good reference-tracking and disturbance-rejection properties, validating the desired functionality of the proposed controller

Controller design for variable-speed permanent magnet wind turbine generators interfaced with Z-source inverter

Increased awareness of environmental concerns has caused greater interest in developing power sources based on renewable technologies, such as wind. Due to the intermittent nature of the wind speed, output voltage and frequency of the direct driven permanent magnet synchronous generators (PMSG) are normally unsteady. Recently proposed Z-source inverter has been considered as a potential solution for grid interfacing wind power generators, thanks to buck-boost function that the single stage Z-source inverter can offer. Two control methodologies, namely unified controller for isolated operation and a multi-loop controller for grid interfaced operation are investigated in this paper. Theoretical analysis of these two control schemes is presented and experimental results to verify the effectiveness of the control method are also included