Range extending apparatus for electric vehicle and control method thereof

An electric vehicle range extending apparatus, for use in an electric vehicle with a main battery pack including a plurality of battery cells, the apparatus comprising:

• a step-down voltage provision unit, having:
• an input port to be coupled to the main battery pack or an auxiliary battery pack, and an output port to output a power balancing signal;
• a cell voltage sensing circuit, for being coupled to the plurality of battery cells and sensing individual voltages of the plurality of battery cells;
• a cell switching circuit, including a plurality of switches, coupled to the plurality of battery cells respectively, and coupled to the output port;
• and
• a control circuit, coupled to the cell voltage sensing circuit, the step-down voltage provision unit, and the cell switching circuit, for controlling the cell switching circuit based on the individual voltages of the plurality of battery cells so as to apply the power balancing signal to at least one of the plurality of battery cells selectively;
• wherein the control circuit determines, among the plurality of battery cells, a first battery cell with a highest voltage and a second battery cell with a lowest voltage, based on the individual voltages of the plurality of battery cells;
• wherein the control circuit determines whether a voltage difference between the first battery cell and the second battery cell is greater than a balance setting value;
• wherein the control circuit determines whether a voltage of the second battery cell lies between a balance starting value and a voltage setting value if the voltage difference between the first battery cell and the second battery cell is greater than the balance setting value;
• wherein the control circuit controls the cell switching circuit so as to apply the power balancing signal selectively to the second battery cell if the voltage of the second battery cell lies between the balance starting value and the voltage setting value;
• and wherein control circuit stops to apply the power balancing signal to the second battery cell if the control circuit determines a voltage difference between the second battery cell and a battery cell having a lowest voltage among the plurality of battery cells except the second battery cell is greater than a balance cut-off value.