| High-speed electric multiple units(EMUs)have the merit of high efficiency,high speed,high safety,punctuality,and large transportation capacity.It not only facilitates people’s life but also drives the development of the national economy.Traction converter,as the key component of EMUs,is supplied by the single-phase power under the traction network.Thus,the input power will contain an AC component,which will lead to the coupling effect of the internal AC-DC system of the traction converter.The traditional solution is to use the LC resonance branch to decouple the AC power.However,the passive hardware decoupling circuit not only reduces the power density of the traction converter;but also deteriorates the decoupling performance due to the parameter variation of the resonance decoupling capacitator.Therefore,focusing on the AC-DC coupling phenomenon of EMUs traction converter,the coupling mechanism is analyzed in-depth,and active decoupling control strategies are proposed systematically in this paper.The achievements are as follows:(1)The harmonic current suppression strategy is proposed to eliminate the grid-side coupling effect.Therefore,the grid-side current quality can be improved.Firstly,the pulsation mechanism of the DC-link voltage and the source of the grid-side harmonic current are revealed.A harmonic current suppression method based on the improved dual-resonance control is proposed,thus,the grid-side harmonic current is eliminated.Secondly,an improved virtual orthogonal signal construction method is proposed to reduce the number of resonance controllers and simplify control parameter design.Thirdly,a design method of the double closed-loop system based on dual-resonance control is proposed to ensure the stability and harmonic suppression ability of the harmonic current suppression control system.Finally,to improve the frequency-response performance after discretization with high resonant-frequency and low control-frequency of the controller,a digital implementation method with high discretization performance for the controller is proposed.(2)The beat phenomenon suppression strategy is proposed to eliminate the beat current and beat torque.Firstly,the source of beat voltage,beat current,and beat torque is revealed,and the variation rules of them under the different fundamental frequencies of the motor are analyzed.Secondly,the beat suppression method with dual-frequency compensation is proposed,which eliminates the beat current and beat torque at the same time.Thirdly,with the characteristics of single-frequency compensation and amplitude compensation,a comprehensive selection scheme of beat suppression compensation strategies in the full speed range is proposed to maximize beat phenomenon suppression.Finally,the model of the beat phenomenon is built.And a single-frequency compensation strategy based on torque closed-loop feedback is proposed to solve the inaccuracy problem in an open-loop manner for the traction motor vector control system,which provides an engineering implementation method(3)An active power decoupling strategy based on utilizing buck type bi-directional DC/DC converter(BBDC)is proposed to suppress the DC-link voltage pulsation.Therefore,the coupling effect of the AC-DC system of the traction converter is eliminated totally.Firstly,based on the operation characteristics of hybrid EMUs and the topology of its traction converter,the BBDC utilizing strategy is proposed to realize the active power decoupling function and the battery charging and discharging function,which is also suitable for general EMUs traction converters.Secondly,the power coupling characteristics of the BBDC circuit are revealed.The active power decoupling method based on low-frequency AC power elimination is proposed,and the compatible parameter for the BBDC decoupling circuit is designed.Finally,to implement the active power decoupling strategy and compromise the stability and dynamic performance,a double closed-loop control system based on direct resonance control is designed,and the equivalent impedance characteristics of the DC-link under different power decoupling strategies are compared.For all of the theories,models,and approaches above,there are corresponding simulated and experimental results in this paper,explaining their applicability and validity.104 figures,12 tables,145 references... |
PDF Full Text Request