1-7 AC power system as compared with DC power system In the DC power system the controller will chop the battery current in repetition and control the frequency cycles of ON and OFF. The motor performance will change in proportion with the frequency cycles between ON and OFF, thereby the inching at start to the max. performance is controlled. The AC power system in the new models includes a controller that transforms the battery current into a three- phase alternating current. The motor power is controlled by changing the sinusoidal waveform (frequency, amplitude, etc.) of the three-phase alternating current.
Motor drive voltage, motor construction, and controller details differ between DC and AC power systems, as follows: Comparison between DC and AC power systems Motor voltage Motor construction Controller DC power system Mean voltage Commutator Brush Motor Battery Contactor Microcomputer control r ON Controller Battery OFF Mean voltage voltage • A chopper circuit converts the bat- tery current (DC) into a rectangular waveform and controls the mean voltage at a desired level. • Brushes and commutator require servicing. • Complex mechanism • Motor power can be controlled sim- ply via the mean DC voltage. • Contactors for reversing the motor rotation are required.
AC power system Sine wave Stator ferrit core Stator coil Battery Motor Microcomputer control r Controller Battery voltage Motor voltage • Controller converts battery current (DC) into AC. • Brushes and commutator, which re- quire servicing, arer not used. • Compact and lightweight • A control module converts DC into three-phase AC. • Contactor for reversing the motor rotation are not required.