ADVANCED DC VOLTAGE ADJUSTMENT USING SWITCHED CAPACITORS
A voltage booster system for use, for example, in an electric vehicle places a switched capacitor voltage converter between a high voltage battery and the vehicle's electrical load, typically a traction power inverter for driving the vehicle's electric motor. The battery input to the converter is pulsed to couple a charging voltage to the converter while the converter is disconnected from the load. The converter is then coupled to the load during the period that the pulse input is disconnected.
1 . A voltage booster system comprising:
a battery coupled to a first bus;
a switched capacitor voltage converter having an input coupled to the first bus and an output coupled to an electric load via a second bus, the converter including at least first and second capacitors coupled to a plurality of switches; and
a controller unit operative to provide a pulsating voltage to the converter input, the pulsating voltage varying between a preselected voltage level during a first phase and a substantially zero voltage level during a second phase, the controller further operative to control the plurality of switches so as to couple the at least first and second capacitors in parallel during the first phase and so as to couple the at least first and second capacitors in series during the second phase.
2 . The voltage booster system of claim 1 , wherein the control unit is further operative to control the plurality of switches so as to decouple the at least first and second capacitors from the electric load during the first phase and to couple the at least first and second capacitors to the electric load during the second phase.
3 . The voltage booster system of claim 2 further comprising a smoothing filter coupled across the converter outlet.
4 . The voltage booster system of claim 1 wherein the battery comprises a high voltage battery system of an electric vehicle.
5 . The voltage booster system of claim 4 wherein the electric load comprises a traction power inverter module operative to generate a three-phase voltage signal at an inverter output.
6 . The voltage booster system of claim 5 further comprising an electric motor coupled for receipt of the three-phase voltage signal.
7 . A method for boosting voltage available from a battery system during an electric load, the method comprising:
placing a switched capacitor voltage converter between the battery system and the load;
coupling the battery system to the converter and decoupling the converter from the load during a first phase;
decoupling the battery system from the converter and coupling the converter to the load during a second phase;
placing the at least first and second capacitors of the converter in parallel across a battery system output during the first phase; and
placing the at least first and second capacitors in series across an output of the converter during the second phase.
8 . The method of claim 7 further comprising placing a smoothing filter across the converter output.