A Novel Hybrid Converter For Multi-MW Offshore Wind Power Generator

Modern multi-MW offshore wind power generators are using multi-level converter structures as well as a parallel configuration of three-level neutral point clamped(3L-NPC)converters to reduce the voltage and current stress on the semiconductor devices.Whereas,these configurations of converters require a higher number of power devices,which increase the system installation cost,control complexity,higher switching loss,and lower the power density for offshore wind energy conversion systems.Therefore,a novel cost-effective and simple structure of a bidirectional three-phase hybrid converter is proposed for multi-MW offshore wind power generation systems.In this thesis,firstly the model of a wind turbine and a PMSG are developed and analyzed.Then the comparative study of generator side 3L-active converters is provided with a recommendation of two popular converters for wind energy conversion applications.Among recommended converters,one is the Vienna rectifier because of its cost-effective and simple design,while the second one is a 3L-NPC converter having a bidirectional power flow option.In the view of comparative study,this article proposes a novel bidirectional three-phase hybrid converter based on parallel combination of a 3L-NPC and n number of Vienna rectifiers for the multi-MW offshore wind generator.The proposed strategy uses a less number of power devices compared to the traditional configuration of parallel 3L-NPC converters,which results in cost-effective,compact in size,simple control circuitry,and good performance of the design.Secondly,this paper studies the FOC as well as current average control schemes for 3-phase PMSG based 3L-NPC and Vienna rectifier respectively.Then,the combination of both deliberated control methods with common outerloop control and separate inner loop control for each paralleled converter is investigated with a 3-phase electric source.Here,a total reference current obtained from combined outer loop control shares to the inner current control loops of each parallel-connected converters.Equal distribution of total current and power among parallel converters ensures the lower current stress on the semiconductor devices.Thirdly,in order to verify the performance of the proposed topology,simulation of a parallel-connected 3L-NPC and a Vienna rectifier converter for 2MW wind turbine based PMSG at different wind speed conditions is carried out in the Matlab/Simulink environment.Finally,a hardware prototype of a 2k W system with a 3-phase electric grid and parallel-connected 3L-NPC and Vienna rectifier is designed and implemented with a common DC-link voltage control.Furthermore,a DSP(TMS320F28335)based experiment with the desired performance of equal sharing of total power and current in parallel converters,regulated DC output voltage,low THD of AC input current,unity power factor are observed which verifies the control of the proposed converter.Both simulation and experimental results validate the performance and effectiveness of the proposed hybrid converter.