Development Of Three Level Regenerative Braking Energy Feedback Converter For Metro

The distance between urban subway stations is short,trains start and stop frequently,so the energy generated by train regenerative braking is considerable.The use of regenerative braking energy has been widely concerned in recent years.The regenerative braking energy feedback method compensates for the disadvantage of the existing traction power supply system,establishes the energy path between the AC and DC systems,and compensates the reactive power at the same time.It has been widely used in the subway.The two-level topology can feed the converter with a power switching device of 3300 V voltage level,and the switching device has high price and low switching frequency,which causes problems such as large volume and large noise of the filter on the grid side.In this paper,the development of three-level energy feedback converters is carried out for the problems of two-level energy feedback converters.The main work is as follows:Main circuit topology selection.Analyze the working principle and characteristics of the cascaded H-bridge,flying capacitor,T-type neutral point clamp and diode neutral point clamp topology commonly used in multi-level fields.According to the subway application environment,the cost of diode clamp topology is low,and the voltage stress of the switching device is small.The neutral point clamp topology was selected for its stability and economic benefits.Then according to the design requirements,calculate the DC side voltage divider capacitor,filter circuit parameters calculation and device selection.Control strategy and simulation.Firstly,the control method of the converter is studied.For the subway operation environment,the direct current control scheme based on the grid voltage orientation is selected,and the energy feedback start voltage is calculated for the outer voltage loop.At the same time,the current command generation algorithm is designed.Secondly,the three-level SPWM modulation and SVPWM modulation are analyzed.In this way,the equivalent relationship between them is established.Aiming at the problem of neutral point potential offset,the influence of switching state on neutral point potential is studied.Based on this,The SVPWM-based adjusted positive and negative small vector scheme and the SPWM-based zero-sequence injection scheme are studied.The hardware and software design of the energy feedback system.A matching signal conditioning board for the ARM+FPGA control core board is designed to complete functions such as analog sampling,digital I/O,temperature detection,PWM output,and pre-drive processing.The communication function is realized by ARM,the control and modulation functions of the system is realized by FPGA.At the same time,the design of the monitoring interface of the host computer is completed.System verification.A 1kW experimental platform was built to verify the current control algorithm and modulation algorithm.The experimental results show that: The ARM+FPGA core architecture selected by the system can realize the control of the converter and the Ethernet communication reliably.The paper designs the hardware design and software part of the feedback converter by using the regenerative braking energy feedback converter project commissioned by the enterprise.The experimental platform was built to verify the core algorithm of grid-connected control and modulation of the three-level energy feedback converter.And the system scheme and control algorithm have yet to be further verified on the engineering prototype.