2-2 MAIN CONTROLLERS General AC system The AC motor drive system controller has been provided with: Microcomputer-assisted travel inverter control (converts DC to three-phase AC) CAN (Controller Area Network) communication function between main controller and traveling/material han- dling controller. Communication function between multiple display and SAS controller. This is a multi-functional controller with advanced electronics technology. The controller offers the power select function and power keep function that take full advantage of the AC power system. Power select function:
Allows the operator to select from three traveling modes, H (High power) mode, P (Pow- er) mode, and S (Standard) mode. Power keep function: Maintains a high performance level even when the battery level becomes low and in- creases stress-free operation hours.
(Available when P or S mode is selected.) AC motor maximum output AC and DC power system output characteristics with fully charged battery Torque AC power system output characteristics DC power system output characteristics (DC motor maximum output) Torque AC power system output characteristics with discharged battery DC power system output characteristics with discharged battery Revolution Revolution Compared to the DC motor, the AC motor has higher output and a range of output characteris- tics is obtainable from the increased output. When the battery is discharged, the AC motor provides output characteristics closer to those of a fully charged battery than a DC motor does.
Compared with a DC motor of an equivalent size, an AC motor has a higher output. The output characteristics of an AC motor are determined by the amplitude and frequency of the alternating cur- rent output by the controller. The controller has a map stored in its memory of the optimum combinations of the current and frequency. Using these, the optimum output characteristics can be obtained for all conditions. When the power selection switch is operated, the controller switches the map and changes the output characteristics. The power select function thus enables the output characteristics to be changed in accordance with the vehicle usage conditions.
Power keep function With a DC power system, the output characteristics are determined by the controller output voltage. The maxi- mum output, therefore, is the output from the motor when the battery voltage is fully applied (chopper duty 100%). The output will decrease with the battery voltage as the battery is discharged. With an AC power system, however, it is possible to maintain a high performance even when the battery level becomes low because the combination of the amplitude and frequency of the alternating current is changed as the battery level goes low.