Investigation On Stator Flux Control Based IPMSM Driving System

With the merits of high power density,high power factor,simple structure,high reliability,etc.,the permanent magnet synchronous motor(PMSM)has been widely used in the wind energy conversion,new energy vehicle,numerical control machine,aerospace industry,etc.As the actuator,the property of the PMSM driving system directly determine the whole performance of the set of equipment.Therefore,this dissertation mainly focuses on improving the performance of the PMSM driving system.For the PMSM,compared with the surface mounted PMSM(SPMSM),the interior PMSM(IPMSM)owns higher torque-current ratio,wider speed range and stronger flux-weakening control ability.Additionally,the research on the control strategies of the SPMSM has been thoroughly done,while the development of the control strategies on the IPMSM is hysteretic and difficult for the asymmetry of the Ld and Lg,As a result,this dissertation mainly focuses on the control of the IPMSM,and tries to use the proposed stator flux control scheme to enhance the dynamic and steady-state performance.Due to the utilization of the space vector pulse widith modulation(SVPWM)in the proposed control scheme,the common-mode voltage(CMV)with high amplitude is produced in the IPMSM driving system.Thus,the modified PWM algorithms are adopted in this dissertation to reduce the CMV outputs and avoid the damage of the bearings.Considering that power switches in the IPMSM driving system are fragile,the three-phase four-switch inverter(TPFSI)is provided to remedy the single phase fault of the inverter.The relevant control strategies of TPFSI are investigated,and the stator flux control scheme is introduced to the TPFSI based IPMSM driving system.Firstly,the derivative of the stator flux for the IPMSM with respect to the time is developed,based on which the state-space model for the IPMSM for both the rotary coordinate and static coordinate are established.Then,the stator flux control scheme is proposed and implemented under both the rotary and static coordinates.For the proposed scheme,the position relationship between the stator and rotor flux vectors is analyzed firstly.With the desired torque angle which is the output of the speed outer loop,the desired stator flux vector is calculated.To achieve a closed-loop estimation of the stator flux vector,a deadbeat full-order state observer is constructed.To realize the c]osed-loop control of the stator flux vector,the state feedback gain matrix is devised,and a variable is obligated to regulate the control performance of stator flux control loop.Finally,the stator flux error vector and the devised state feedback gain matrix are used to calculate the desired stator voltage vector,and a space vector modulation(SVM)module is employed to generate the gate pulses for the inverter.Compared with the traditional PI+SVM DTC control scheme,no torque control loop exists in the proposed scheme,and the torque output of the IPMSM is adjusted by the by the stator flux control loop,thus,a faster dynamic response of the torque output is obtained.The experiment results have validated the proposed control scheme.Since the high common-mode voltage(CMV)output of the inverter with the space vector PWM(SVPWM)will damage the bearing of the IPMSM,this dissertation employs the AZSPWM1 and NSPWM to reduce the CMV amplitude output of the inverter.As the dead-time is necessary for the normal operation of the inverter,the influence imposed by the dead-time on the CMV output for AZSPWM1 and NSPWM are analyzed respectively,and the conditions when the CMV spikes appear are revealed.Subsequently,to inhibit the CMV spikes,the time durations for the relevant voltage vectors are limited,and the effects following on the applicable linear modulation range for both the AZSPWM1 and NSPWM are investigated.Finally,by combining the modified AZSPWM1 and NSPWM,the hybrid modulation is created and the CMV spikes are eliminated in full power factor range and wide modulation range.And then,the hybrid modulation is employed in the stator flux control system.Experiments are implemented to verify the feasibility of the proposed hybrid modulation.To remedy the single phase fault of the inverter,the control strategies of the TPFSI are researched.Firstly,the basic principle of the TPFSI for different phase-faults is presented,and a SVPWM algorithm with no sector identifications and trigonometric function calculations is developed.Secondly,the relationship between the fundamental component of the neutral point voltage and the ?-axis component of the stator current is revealed,based on which a simple algorithm is developed to replace the second-order low pass filter to extract the DC component of the neutral point voltage.And then,a proportional-integral(PI)controller is utilized to regulate the DC component error of the neutral point voltage and eliminate the DC offset in the neutral point voltage.After that,the relationship between the maximum linear modulation index and theload power factor is revealed,and to enlarge the linear modulation range of the TPFSI in low-frequency,a control scheme with no change of the DC-link conditions is proposed.Corresponding experiments are implemented to verify the effectiveness of the proposed scheme.Finally,the stator flux control scheme is employed in the TPFSI based IPMSM driving system,and experiments for validation are implemented.