Research On Modulation Algorithm Of Vector Control Of Rail Transit Traction Motor

With the rapid development of China's economy and society,the problem of road congestion in most cities is becoming more and more serious,and the more frequent exchanges between cities are becoming more and more demanding for high-speed transportation,as an efficient,safe,environmentally friendly and punctual means of transportation,rail transit has gained a broader development market and better development prospects.As a key part of the rail transit drive,the design of the rail transit traction drive system determines the overall performance of the system,but the inverters operating under under high voltage and high current conditions,the maximum switching frequency of power switching device IGBT is usually limited by switching loss,while asynchronous SVPWM in motor vector control will face serious harmonic problem in low carrier ratio.In this paper,the modulation algorithm and control strategy of the asynchronous traction motor vector control system are studied,which is beneficial to improve the control ability of the traction motor under high power conditions.In this paper,the influence of low switching frequency on the output performance of traction inverter is analyzed,the performance of modulation algorithm is evaluated according to the harmonic performance of modulation mode and the distortion degree of flux linkage,and a set of segmentation modulation strategy is designed and applied successfully in traction motor vector control system.After analyzing the problem that the rail transit traction inverter works at low switching frequency,the vector control principle based on rotor field orientation and the limitation of traditional asynchronous SVPWM modulation strategy in low switching frequency conditions are described.By comparing the characteristics of each synchronous SVPWM algorithm and asynchronous modulation,it is decided to adopt the synchronous modulation strategy to solve the problem of asynchronous SVPWM output waveform asymmetry under low switching frequency conditions,which can effectively improve the output voltage symmetry and reduce the harmonic voltage content and reduce the degree of current harmonic distortion.Then,based on the analysis of the existing synchronous modulation strategy,combined with the needs and experimental conditions of the rail transit traction motor control system,a segmented modulation strategy based on synchronous SVPWM modulation is designed,and including the selection of each modulation algorithm and the design of switching strategy based on DC bus clamp between different modulation methods.This paper verifies the feasibility and effectiveness of the segmentation modulation strategy in the asynchronous traction motor vector control system by building a simulation model based on MATLAB,and realizes the vector control of asynchronous traction motor based on the synchronous SVPWM segmentation modulation strategy.Finally,the hardware and software of the asynchronous motor vector control system are designed in detail.A 3kW asynchronous motor is taken as the control object,and the experimental verification is carried out.It is proved that the segmentation modulation algorithm proposed in this paper is in the asynchronous motor vector control system.Feasibility and effectiveness.