Research On The Control Strategy Of CHBR Based On Transformerless Traction Drive System

To reduce the volume and weight of traction drive system,a modular topology based on CHBR is presented,it eliminates the intermediate conversion stages,reduces numbers of devices and transformers,helps to improve the conversion efficiency and further reduces in weight and volume of the traction drive unit.This dissertation is based on the research and development of the transformerless traction drive system and aims to solve some key problems of the control strategies and stable operate region for CHBR,the main contents are as follow:The CHBR is simplified as a single-phase PWM rectifier to analyze the overall strategies.The mathematical model of the single-phase PWM rectifier in stationary and rotating frame are established,respectively.The principle of virtual vector control scheme and proportional-resonant method are introduced,a unified equivalent model in stationary frame of virtual vector control scheme is established,the impact of decoupling approaches and OSG methods on the harmonic performance are also analyzed.The equivalent model and performance are deeply compared to the proportional-resonant method through bode gram anlysis and simulation and experimental test.For dc-link voltage imbalance problem of CHBR,the mathematical model of the dc-link capacitor is established and the mechanism and factor of capacitor voltage imbalance is analyzed.Two conventional are introduced to achieve voltage balance.The conventional regulator is improved by inducing the grid current and other system parameter through anlysis on the close-loop transfer functionThe stable operate region of CHBR is induced through phasor diagram,and the maximum and minimum regulation range balancing strategies are analyzed.A general simplified method of multi-cell CHBR is presented in this article,the relation among the dc-link voltage command,load power and the number of H-bridge units is analyzed to provide the design reference.A coordinate strategy based on between rectifiers and inverters is proposed to guarantee the system stability.Finally,an experimental prototype based on a four-cell CHBR for the transformerless traction drive system is established.The validity and effectiveness of the proposed strategy and analysis is verified through several simulation and experimental tests on a four-cell CHB rectifier.