| As a low-carbon and clean renewable energy generation method,wind power generation has broad development prospects.At present,wind power generators are developing towards permanent magnet direct drive and larger capacity per unit.This dissertation studies the novel modular fractional-slot winding with low space harmonic content for large permanent magnet direct-drive wind generators(PMDDWGs),which can promote the improvement of modular design technology of large wind generators.Therefore,it has important theoretical significance and engineering application value.The magnetomotive force(MMF)composition of the conventional multi-phase symmetrical AC winding is firstly investigated in detail,and then the MMF harmonic analysis method for multi-phase symmetrical AC winding is established.On this basis,a novel modular fractional-slot winding with low space harmonic content is proposed,which can reduce the space harmonic content of winding MMF on the premise of modularization,thereby improving the comprehensive electromagnetic performance of large modular PMDDWG.The main research work of this dissertation is as follows:(1)The development status and trend of wind power market and technology are introduced,clarifying the background and significance of this research.The research status of modular winding is comprehensively reviewed,including fundamental theory,performance analysis and novel winding design.(2)The MMF harmonic analysis of the conventional multi-phase symmetrical AC winding is conducted.The phase-splitting star of slots is proposed,whose distribution pattern is described by introducing the concept of the number of essential cell machines.On this basis,the harmonic analysis of the MMF generated by phase-winding belonging to multi-phase symmetrical AC winding with any number of phases,slot/pole combinations and winding layers(double layer or single layer)is conducted,and the general formula for calculating distribution factors is derived.By observing the spatial phase relations among phase-winding MMFs,the harmonic distribution of the resultant MMF is obtained,and a set of MMF harmonic analysis method for multi-phase symmetrical AC winding is finally established,which provides a theoretical foundation for the research and development of novel modular winding.(3)A novel modular fractional-slot winding with low space harmonic content for large PMDDWG is proposed.Firstly,a dual m-phase superimposing winding is constructed by shifting and superimposing two sets of conventional single-layer fractional-slot concentrated windings,which can reduce the non-working slot-harmonic content in the resultant winding MMF.The optimal number of phases and pole/slot combination of dual m-phase superimposing winding is selected,namely dual three-phase,24 slots and 10 poles.A mathematical model is established to describe the deflection effect of the MMF space vector generated by a type of special coil with different turns per coil side.Moreover,the composite coil with different turns per coil side is proposed,which extends the range of the coil-side turn ratio that can be physically realized to the whole set of positive real numbers.By applying the composite coil with different turns per coil side to 24-slot/10-pole dual three-phase superimposing winding,a novel modular fractional-slot winding with low space harmonic content can be finally formed,which almost eliminates the first harmonic component in its resultant MMF.(4)A modular prototype equipped with the proposed novel modular winding is manufactured.Some experiments are conducted on this prototype to verify the correctness of the MMF harmonic analysis of the proposed winding.(5)The electromagnetic characteristics of a 10 MW PMDDWG equipped with the proposed winding are analyzed and compared with those of other three PMDDWGs using three types of common windings,respectively.The no-load and load characteristics of the four generators are analyzed with finite element method,including no-load magnetic field,no-load back electromotive force,cogging torque,armature reaction field,synchronous reactance,power factor,radial magnetic force,load torque,loss and efficiency,etc.In addition,the analysis of short circuit fault is also conducted,in terms of short circuit current,braking torque,irreversible demagnetization,faulty radial magnetic force and voltage jump in non-fault phases.The comparison results show that the modular PMDDWG with the proposed novel winding has lower harmonic content in the armature reaction field,exhibiting an excellent and balanced comprehensive electromagnetic performance,good short circuit current suppression ability and resistance to irreversible demagnetization.This dissertation has made some innovative contributions to the winding MMF harmonic theory and the design and analysis of novel modular winding with low space harmonic content,which is beneficial to promoting the development of winding theory and the technical progress of large PMDDWG. |
