Research On The Key Technology Of High-Speed Permanent Magnet Brushless Motor Drive System

High-Speed Permanent Magnet Motor(HSPMM)is featured with high power density,low weight,small size,and high operating efficiency.Therefore,HSPMM has gained much attention in the application such as blowers,centrifugal compressor,micro-gas turbine,electric-spindle and so on.The performance of the high-speed motor drive system is one of the important issues for HSPMM.Due to the high operation frequency,when the HSPMM is driven by the general inverter,three issues remain to be solved: 1)The significant control delay causes the instability of the drive system at high operating frequency,which also significantly degrades the reliability of HSPMM drive system;2)At the high operating frequency,the rotor position estimated error cannot be ignored,which may cause the deterioration of the control performance.If the rotor position estimated error is too serious,it may also cause the instability;3)The low carrier-frequency-ratio and the small phase inductance will cause large current ripple and electromagnetic force ripple exist in the drive system at high operating frequency.The ripple will cause large iron loss and the vibration,which will degrade the reliability of the drive system.In this paper,the key technologies of the HSPMM drive system is investigated in detail.Firstly,the system stability issue with the consideration of the control delay at high operating frequency is investigated.The dynamic model of the current control loop with the consideration of the control delay is established and it is pointed out that the control delay will cause an extra-cross-coupling unit and two time-delay units.Based on the analysis results,two improved control strategies are proposed in this paper.Firstly,the stability issue caused by the extra-cross-coupling unit and two time-delay units is analyzed in detail: 1)The extra-cross-coupling unit causes the degradation of the equivalent resistance in the dynamic model of the current control loop,and then the damping-ratio is degraded by the extra-cross-coupling,and meanwhile the system stability is degraded.If the damping-ratio becomes negative value,the control system will lose the stability;2)The two time-delay units in forward path of the current control loop in the dq-axis will cause the degradation of the stability margin,which may cause large current overshoot.Secondly,in order to eliminate the extra-cross-coupling,this paper firstly proposes a ‘damping-integral’current regulator.In the proposed ‘damping-integral’ regulator,the damping-ratio is compensated through injecting the active-damping,and then the impact of the extra-cross-coupling is effectively eliminated.Finally,to compensate the stability margin,a ‘double-sampling-current-predictor’,which can predict the stator current of the next step without any sensitive parameters,is proposed in this paper,and the stability margin can be effectively compensated by the proposed ‘double-sampling-current-predictor’.With the cooperation of the ‘damping-integral’ current regulator and the ‘double-sampling-currentpredictor’,the system stability is effectively improved at high operating frequency.Obvious estimation error exists in the rotor position estimator at high operating frequency.In this paper,the estimation error caused by different kinds of non-ideal factors,including the control delay,filters,procedure of discretization,and parameter error,are analyzed in detail.It is pointed out that the estimated error cannot be directly corrected through quantification since the causes of the estimated error are abundant.In order to effectively correct the position estimated error,a ‘double-phase-lockloop(DPLL)’ correction strategy is firstly proposed.The DPLL can effectively correct the estimated error caused by the filters and the procedure of discretization.The DPLL is featured with good steady and dynamic performance.However,the DPLL cannot achieve the full correction.To achieve the full correction,an ‘minimum-current-tracking(MCT)’ correction strategy is proposed.The MCT strategy can effectively correction the estimated error caused by all non-idea factors.However,the correcting speed of the MCT strategy is a bit slow.In order the combine the advantages of the two correction strategies,a hybrid correction strategy is proposed.The principle of the hybrid correction strategy is that the tracking target of the MCT strategy is set as the reference of the DPLL strategy,and then the hybrid correction strategy can achieve rapid and full correction in the full speed range.Low carrier-frequency-ratio and small inductance lead to large ripple at high operating frequency.In order to solve this problem,in this paper,the improve power topology and the improved modulation strategy are investigated from the perspective of the hybrid of silicon-carbide-MOSFET(SiC-MOSFET)and silicon-IGBT(Si-IGBT).A BUCK-type SiC/Si hybrid two-stage inverter is firstly designed in this paper.The topology of the designed hybrid inverter consists of a SiC-MOSFET based half bridge and a Si-IGBT based three-phase full bridge voltage-source-inverter(VSI).The SiC-MOSFET can insert the‘zero-voltage’ to the VSI and create ZVS condition for the Si-IGBT.In order to mitigate the current ripple,three improved SVPWM strategies is proposed in this paper.The switching loss of the inverter is substantially reduced in the proposed two improved SVPWM strategies,and then the current ripple is effectively suppressed.In this paper,a 200 VA drive system is designed for a 550000rpm/110 W ultra-high-speed permanent magnet motor,and a 10 k VA drive system drive system is designed for a 18000rpm/10 k W high-speed permanent magnet synchronous motor.At last,the effectiveness and the superiority of the proposed schemes are verified through sufficient simulations and experiments on the two high-speed prototypes.