Research On Key Technologies Of PMSM Control In Rail Transit

Permanent magnet synchronous motors(PMSMs) have been gradually applied to rail transit systems in recent years.The traction drive unit of the rail transit system features high voltage,high current and wide operating speed range,and has the speciality of operating at low switching frequency or at even square-wave condition.When the PMSM is applied to the rail transit traction drive system,motors in six-step operation are under flux-weakening control,and the torque performance is of great importance to the high speed steady operation of rail transit system.The research on key technologies is approached,including flux-weakening control strategy,current locus control strategy,motor parameter identification and compensation strategy,and operation strategy for high-speed neutral zone.The main contents are followed as:Based on the mathematical model of PMSM,a study approach that operation limit curves are simplest in current plane and current locus should be controlled is proposed by analysing operation limit curves in current plane,voltage plane and flux plane.Current loci of different common basic control methods are focused and analysed on current plane.For the non-flux-weakening region,the pre-controlled strategy should be introduced;for the flux-weakening region,the right controllable current loci should be designed.To implement the motor control in six-step operation with unique adjustment,this paper proposes the Single q-axis Current Regulator-Variable Voltage Angle(SQCR-VVA) flux-weakening control strategy.In order to verify the controllability relationship between voltage angle and torque rigorously,monotonic relationship between voltage angle and torque for the whole operation is proved and the effective voltage angle range is set.Using the single current regulator,the flux-weakening control algorithm is the same for traction and braking operation.The good dynamic control is also achieved at the same time.With small signal model method,the current-closed controllability of the method are expounded,and the design of current controller parameters is given.For the different torque characteristic curves in rail transit system,the current locus control strategy is proposed by the polynomial fitting control in non-flux-weakening region,the improved two-step-regulated control in flux-weakening region and improved transition control between non-flux-weakening and flux-weakening strategies.Current loci of percentage-damped and percentage-limited torque characteristic curves are achieved based on the basic current loci of constant-speed-variable-torque and constant-torque-variable-speed operation the through the current locus control strategy.An off-line parameter identification method and an on-line parameter compensation strategy are proposed to improve the accuracy of torque.For the off-line method,simple operation conditions are designed to implement the identification of six parameters based on the low-switching-frequency feature.For the on-line strategy,the compensation of q-axis inductance and d-axis flux is achieved to get more accurate torque by the impact of inaccurate motor parameters on d-axis current.In order to apply the proposed control strategies in flux-weakening region to the actual high power PMSM drive system,a unified project that realises the same algorithm in simulation and experimental accurately is implemented.For the coasting operation in high speed range,SQCR-VVA flux-weakening control method is checked on low-braking-torque condition.For the pulse-shut-down condition of inverter,the abnormal uncontrolled rectification operation and rechanging current are analysed and the safety speed should be set.For the non-over-current response restart process in neutral section,a zero-q-axis-current control strategy is proposed based on the restart logic.Finally,the mentioned control strategies have been tested on 180kW PMSM platform with ground experiment and 1.2MW PMSM platform with field experiment.The experimental results verified the features of SQCR-VVA flux-weakening control strategy,current locus control strategy,parameter identification and compensation strategy,and restart process control strategy in six-step operation in the real rail transit system.