Research On Indirect Current Control And Second-Order Ripple Power Compensation For Railway Traction Converter

Multi-megawatt traction converter has a high power level and is switching at lowfrequency. Some control methods which need high bandwidth and high dynamic responsesare difficult for practical application of the high power converter. So the indirect currentcontrol is easy to realize in the single-phase full-bridge PWM rectifier for railway traction.Suffering from the low-speed dynamic response, and the cross-coupling between activepower and reactive power, conventional indirect current control is not an ideal solution forpower conversion. To realize the independent control of active and reactive power, a dqreference frame decoupled method is introduced. In order further improving the dynamicperformance of conventional indirect current control, a novel transitions eliminationmethod is proposed. The controller is designed for a3kilowatt prototype. Simulation andexperiment results proved this method to be effective.Because of instantaneous power of single-phase converter, there is some second-orderripple power at the dc side. As a result, there are a lot of even-order harmonic componentsin the dc bus voltage. Adding passive components are mainstream conventional hardwaremethods. An LC filter is often needed at the dc link to absorb the ripple power. However,this greatly reduces the power density. Some new products use a pure-capacitor dc linkfilter. However, the capacitance has to be enlarged significantly to withstand the pulsatingpower alone. As a result, only electrolytic capacitors can be the choice, which are inferior tofilm capacitors in reliability, therefore causing an increased burden on maintenance. Toomuch energy stored in the dc link capacitor bank also complicates short-circuit protection.The active compensation methods, which are classified into inductance energy storage andcapacitance energy storage, cost much and complicate the controller. A repetitive dc linkvoltage predictor which costs less is proposed in this paper for eliminating beat current.Simulations and experiments show that compared with conventional methods, the proposedone can reduce the steady-state beat current more effectively. The dynamic beat currentduring load on is a little higher.