| | Category | EN | P11 | High Efficiency High Power Factor Electric Vehicle Battery Charger |
| | Abstract | Electric vehicles are the future of our transportation system. Electrical |
| | vehicles are much more efficient than gasoline powered vehicles, have |
| | zero carbon emissions, and reduce our dependency on fossil fuels. One |
| | of the biggest obstacles to widespread electric vehicle usage is our |
| | inability to build high efficiency multi-kilowatt battery charging systems. |
| | Because high power battery chargers necessitate high power factor, |
| | current charging systems incorporate active power factor correction |
| | circuits. These lower the overall efficiency of the charger. In this project, I |
| | present a new charger design that can maintain both high power factor |
| | and high efficiency. |
| | The main challenge to a unity power factor charger is that the voltage |
| | of the battery itself nullifies charging voltage less than the current battery |
| | voltage. This only allows the battery to be charged in a very narrow band |
| | around the peak of the input voltage, and this distorts the current |
| | waveform and reduces power factor. Previous methods of achieving unity |
| | power factor have utilized boost converters in series with the main H- |
| | bridge DC/DC converter. While this does give excellent power factor, it |
| | adds the loss of the boost converter onto the loss of the system. This is |
| | the result of the boost converter operating continuously independent of |
| | input voltage, even if the input voltage is sufficient to charge the battery. |
| | This particular implementation of the boost converter reduces the overall |
| | efficiency of the system and increases production cost, for the high |
| | power boost converter is large and expensive. My project presents a new |
| | design in which the boost converter can be intelligently turned on and off |
| | based on the instant input voltage, and is only activated when the charging |
| | voltage multiplied by the transformer turns ratio slips below the battery |
| | voltage. This new design has the following advantages: |
| | |
| | 1. The boost converter only activates a small portion of the time, and only |
| | delivers about 18% of the charger’s total power, reducing both cost and |
| | size. |
| | 2. Because 82% of the power passes solely through the H-bridge |
| | converter, the efficiency of the system is raised. |
| | 3. The boost converter only requires simple software algorithm to control. |
| | |
| | |
| | A thorough mathematical analysis of the relationship between the |
| | conduction angle of the battery charging current (the percentage of time in |
| | which the battery is actually receiving power) and the resulting power |
| | factor was conducted. Fourier analysis of the charging current was |
| | performed to calculate the power factor. |
| | A computer simulation of this system using the electronic simulation tool |
| | Powersim was conducted. Both simulation and theoretical examination of |
| | this design have yielded up to 98% power factor and 94% charging |
| | efficiency. |
| | Bibliography |