Very little performance data is available for chopper controlled dc series motors as used in battery powered electric vehicles. This report presents performance data obtained through experimental testing of a 22.4-kW (30 hp) traction motor using two types of excitation: ripple-free dc from a motor-generator set for baseline data and pulse-width modulated (chopped) dc as supplied by a battery and chopper controller. For the same average values of input voltage and current, the power output was independent of the type of excitation. However, at the same speeds, the motor efficiency at low power output (corresponding to low duty cycle of the controller) was 5 to 10 percentage points less on chopped dc than on ripple-free dc. This apparent discrepancy illustrates that for chopped dc waveforms, it is incorrect to calculate input power as the product of average voltage and current. The chopped dc locked-rotor torque was approximately 1 to 3% greater than the ripple-free dc locked-rotor torque for the same average values of current. (ERA citation 04:056873)
展开▼
