Research On Multirate Control In Traction Drive System

In the field of rail transit,high power converters usually operate at low switching frequency,which is limited by the switching loss of the power semiconductors and the heat dissipation.When the multirate control is applied,the digital delay of the current loop can be greatly reduced and the closed-loop control bandwidth can be improved.Aiming at the current loop of traction motor vector control system,the application of multirate control in high-power traction drive system is studied in detail.Based on the principle of multirate control,the sampling schemes under single-rate and multirate control are analyzed,and the digital delay of current loop under single-rate and multirate control is compared.Aiming at the digital delay in the current loop,the influence of digital delay under multirate control is analyzed by combining the complex vector method and coordinate transformation relationship.Based on the previous analysis,the equivalent single-rate state space model of the current loop is established by using multirate method.The system with resistance-inductance and motor load are analyzed by the theory respectively,and the advantages of multirate control were analyzed by comparing the pole distribution under different sampling frequencies,and the accuracy of the theoretical model was verified by simulation.Under the multirate control mode,the control module and the modulation module are independent.To maintain the synchronization between the voltage vector phase and command voltage vector phase,the phase angle regulator should be applied and studied.Proportional,proportional-integral and deadbeat phase angel regulator under different carriers are modeled.According to the theoretical model of the phase angle regulators,the stability conditions are further analyzed,and the parameters range of the regulators are derived.The influence of speed measurement/estimation error on the phase angle regulators is analyzed,and the performance of different phase angle regulators are compared.Based on the principle of the traditional deadbeat control,the improved deadbeat phase angle control strategy is proposed,considering the calculation and update delay in the digital system.And the influence of the delay compensation on the improved deadbeat phase angle regulator is also analyzed.Finally,the effectiveness of multirate control and phase angle regulators are verified by MATLAB/Simulink simulation and PMSM experimental results.