Investigation On Key Technique For Open Winding Permanent Magnetic Synchronous Generator System

Due to the advantage of simple structure,high power density,high efficiency and flexible topology,permanent magnet synchronous generator(PMSG)has been widely applied in various generation field,e.g.,wind power,gas turbine power generation,aerospace,vehicle integration and industrial and flywheel energy storage.With the increasement of generation system capacity,the power level of PMSG increases rapidly.Meanwhile,the capacity of corresponding full-scale power converter will also increase.With the limitation of existed switching device,high power converter usually takes a high cost.The high voltage large current also pose a threat to converter's operation performance and reliability.In order to break through the limitation of existed motor structure and improve the operation performance,open winding permanent magnet synchronous machine(OW-PMSG)has been widely concerned as a novel topology.In this paper,OW-PMSG has been selected as the main research object.Aiming at isolated and commom dc bus structure,both-side controllable and single-side controllable topology,the corresponding control method,modulation technique,fault-tolerant operation capability,and scope of application have been investigated.The target of this paper is to explore OW-PMSG's advantage in high performance,high reliability,low cost and other aspects.The research results obtained in this paper is listed as following:1.Aiming at the zero sequence current phenomenon existed in the common dc-bus supplied OW-PMSG system,this paper investigates its formative mechanism,and proposes the optimized control strategy and modulation technique.Since the zero sequence circuit exists in this system,the mathematical model for OW-PMSG system in three-dimensional space coordinates is rebuilt.The relationship between zero sequence current and third harmonic back electromotive force,zero sequence voltage generated by the converters has been studied.This paper expands the control strategy and modulation technique from two-demensional space to three-denmensional coordinates,and proposes a zero sequence current suppression strategy based on the zero vector redistribution modulation strategy.The available modulation range is also analyzed.Both the control method and improved PWM technique are implemented in the experiment setup.2.In order to achieve the sustainable operation for OW-PMSG both-side controllable system under fault state,this paper investigates the fault-tolerant operation strategy for in commom dc bus structure.Under fault tolerant operation,the three phase four switch(TPFS)converter is reconfigured as the bridge arm device breaks down in three phase six switch(TPSS)converter.By discussing the space vector diagram under different fault condition,corresponding control strategy and modulation strategy are proposed.Moreover,the linear modulation mechanism for TPFS converter considering neutral point voltage fluctuation is studied.The relationship between pwer factor angle(PFA),capacitor fluctuation and maximum linear modulation ratio has been derived.Furthermore,a genelized maximum voltage utilization method for multilevel converter under fault condition is proposed.3.In order to simplify the whole system,the OW-PMSG system with the integration of full controlled and uncontrolled converter is investigated in this paper,in which half the amount of controllable power switches are needed compared with the conventional open winding system fed by two voltage source converters.The voltage space vector of open winding PMSG is modulated by controlled converter,which will be integrated with the voltage vector by uncontrolled converter to implement the operation of open winding PMSG.In order to analyze and compare the operation capability on the different dc voltage ratio,the available modulation range of the open winding PMSG is analyzed in detail.Moreover,unity power factor control is proposed as the optimized control method to achieve the maximum modulation index.4.The OW-PMSG fed by semi-controlled converter is a promising configuration due to lower expense,simplified driving circuit,reliable operation capability.When supplied by a common dc bus,the open winding PMSG system can be more simplified.Due to the voltage output by the diode converter is decided by the three-phase current polarity,the available voltage vector modulation range of voltage source converter(VSC)is limited.As a result,the current zero crossing duration behavior is determined by the power factor angle(PFA),which will lead to zero crossing voltage pulse disturbance,serious electromagnetic interference(EMI)and unexpected diode switching loss.This paper aims to reduce the current zero crossing duration by injecting the third harmonic current into the zero sequence current.A proportional resonant regulator is proposed to control the zero sequence current.