Study Of Key Problems On Z-source Charger

In this paper, a novel z-source charger is proposed. This charger makes full use ofhard devices in one electric vehicle. The z-source integrated charger uses inverter ascontrollable rectifier and uses z-source network instead of DC/DC converter. In thispaper, several key problems will be studied.First key problem is the control method of z-source charger. Traditional controlmethod of z-source converter is ZSVPWM. While this control method has a problem thatthe short-through time is limited. In this paper, in order to resolve this problem, a newcontrol method is proposed. Using this method the short-through time changes with thecurve of zero vector time. So the short-through time can be whole inserted into zerovector time. In this case, z-source has a higher step-up ratio which can make the systemget a wider range of voltage. And it can conclude that voltage across power switch islower. Therefore, the power losses of switches is lower, and the efficiency of system ishigher. What’s more, a wider range of voltage is benefit to the control of system.Second, grid-side harmonic is studied in this paper. It’s necessary to do research onharmonic of z-source charger. This is because that harmonic of charger has a greatinfluence on grid. In this paper, dual fourier transform is used to analyse the grid-sideharmonic of z-source charger. Through the comparison between SVPWM controlmethod and ZSVPWM control method, it concludes that the harmonic fundamentalcontent of ZSVPWM control method is20%higher than that of SVPWM control method.And the other harmonics content of two control method is nearly the same. Therefore, theTHD of ZSVPWM control method is nearly20%lower than that of SVPWM controlmethod. The result is verified by simulation.Thirdly, grid-side filter is designed. The commutation process of z-source charger isdifferent from traditional charger because of its unique control method. This paperanalyses the commutation process in one section and the curve of grid-side current is got.Then the filter is designed from two aspects. One is to suppress the current ripple, theother is to keep the current’s following speed. Simulation is done using the calculatedinductance value. The accuracy of design is verified by simulation resultAt last, the parameter of main circuit is ensured, and the hardware of control systemand sotfware are designed. The test platform of z-source charger system is built. Theexperimental result shows that z-source charger can realize high power factor.