Research On Permanent Magnet Traction System For Urban Rail Transit Based On DSP

With the wide application of the permanent-magnet traction system in urban rail trains, the reliability has been paid more attention. Several permanent-magnet synchronous machines are used together to obtain more traction effort, and one inverter only can feed one permanent-magnet synchronous machine (PMSM). When one inverter fails, the corresponding PMSM will be isolated from the traction system. As a result, the performances of the whole traction system will be influenced. Therefore, it is necessary to investigate a more reliable permanent-magnet traction system for urban rail transit.A fault-tolerant permanent magnet traction module (FTPMTM) is studied in this thesis, and the pulse width modulation(PWM) strategies of the control system for FTPMTM under normal and fault-tolerant mode are emphasized.The main research contents of this thesis are as follows.1 The background and the significance of this thesis are described. The development status of modern tram, permanent-magnet traction system and PWM strategy of motor vector control system are introduced.2 The FTPMTM is introduced in detial. The topologies under normal mode, isolation mode, and fault-tolerant mode are given. The DSP-based FTPMTM is proposed, which can simulate the fixed failed bridge arm with the fixed inverter.The mathematical model of PMSM and the principle of vector control are analyzed.3 The principle and implementation procedure of space vector pulse width modulation (SVPWM) algorithm are introduced, and the Fast Minimum Duty-cycle Point Tracking Method(FMDPT) algorithm is proposed. The simulations and experiments of both SVPWM and FMDPT are carried out and their results are compared. By comparing with SVPWM, the effectiveness of FMDPT is validated.4 A DSP-based method is proposed to measure the code execution time of PWM strategies for PMSM vector control system. Under the same conditions, the code execution time of SVPWM and FMDPT are measured by the proposed method. It is verified the code execution time of FMDPT is shorter. The five phase Minimum Duty-cycle Point Tracking (MDPT) method is firstly realized by DSP28335 in the five-inverter-two-PMSM system.By using DSP28335, the switches of the permanent-magnet traction system among normal mode, isolation mode and fault-tolerant mode are realized.5 Based on DSP28335, an experimental platform for the permanent-magnet traction system is developed. The main circuit and control circuit are designed. A method is proposed to calculate the value of PMSM’s rotor position.