Smoothing power ripple in single phase chargers at minimized dc-link capacitance

To be able to use film capacitances in the dc-link of single phase chargers, the needed capacity has to be reduced. This can be achieved by directly controlling the dc-link voltage with the high bandwidth of the dc-dc converter, but in this case the complete fluctuation of the grid power is seen by the battery. In order to reduce the stress on batteries through micro cycles and to increase the efficiency of the system, the power flow should be smoothed towards the battery. The control strategy presented in this paper smooths the power ripple by controlling the dc link voltage by a dynamic reference value. A method is shown to determine the reference value from the control values of the inverter in the fixed reference frame system. The strategy is analytically described and the effect is shown in simulation and by measurements on a prototype system.