| PMSM (Permanent Magnet Synchronous Motor) has many advantages such as high power density, high efficiency, less maintenance with totally-enclosed design, etc. With the enhancement of environmental awareness, PMSM has received widespread attention in industrial applications both at home and abroad, especially in the field of train traction. This dissertation focuses on urban rail train permanent magnet synchronous traction drive control technology; some key issues to improve system performance are researched. Specific research contents include PMSM current closed-loop control in six-step operation, improvement of special synchronous modulation transient performance with PMSM stator flux control, and inverter DC-link oscillation caused by mismatch of system impedance. These contents are verified by simulations and experiments.In high-speed domain, six-step operation is adopted by urban rail train traction inverter. During six-step operation, inverter output voltage reach maximum amplitude, voltage phase is the only one control freedom degree. Conventional PMSM flux-weakening control scheme is difficult to ensure the current closed-loop control.This dissertation proposes a single d-axis current regulator control scheme for the six-step operation of PMSM based on d-q axis currents cross-coupling effect. This method only needs one control freedom degree, and can guarantee the inverter output voltage modulation degre constant. Clear switch rules of entering and quitting six-step operation are given out. System stability is analyzed based on the pole distribution of closed-loop torque control small-signal model. Also based on small-signal model, the current loop controller parameters design principles are determined. The effects of motor speed and totque on the dynamic response of the system are analyzed.Special synchronous modulation is widely used by urban rail train traction inverter in medium speed domain. Switching patterns of special synchronous modulation are determined by Fourier analysis of assumed steady-state voltages. As a result, its transient responses are bad with over-currents and high instantaneous torque pulses. Stator flux control is proposed to solve this problem. In the proposed solution, the switching patterns of the conventional special synchronous modulation are modified according to the dynamic error between the target and actual stator flux. Then, the specific trajectory of the stator flux and current vector can be guaranteed, which leads to better system transients. In addition, stator flux control is introduced to get smooth mode switching between the special synchronous modulation and the other PWMs in this paper. The target flux is obtained by an integral of the target voltage. The actual PMSM flux is estimated by a minimum order flux state observer based on the extended flux model, which leads to less parameters dependency. Improved rules of flux error elimination in the α-β stationary coordinate system are proposed to achieve fast and accurate flux error elimination.Due to mismatch of output impedances of LC and input impedance of inverter-motor system, traction drive system of urban rail train will lose stability with a large output power. That means DC current and voltage oscillation. For a more accurate model to research this instability phenomenon, this dissertation derives the input admittance formulas of interior PMSM under MTPA (maximum torque per ampere) control. The input admittance formula of interior PMSM under flux-weakening control is also given out. Stabilization policy of full speed domain based on active damping compensation is proposed. Under MTPA control, the system is prone to oscillation. Active damping compensation based on q-axis voltage command is used to suppress oscillation. Under single d-axis current regulator flux-weakening control, the system can keep stable.In this dissertation, a 7.5kW platform and a 300kW platform are set up. Closed-loop current control in whole speed domain is realized and the proposed single current regulator control in six-step operation is verified on the 300kW platform. Based on the 7.5kW platform, the above-mentioned three points are verified. The experimental results show the good performance of the proposed schemes. |
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