This research presents a maximum power point tracking system (MPPT) for the variable DC voltage bus inverter which has inconstant of DC bus voltage and compensated field orient controlled with controlling program without using compensated circuit and DC-DC converter to gain a highest power, constant torque, low lost energy, suitable for small system and low cost.This system uses solar cell for source energy to drive three phase centrifugal pump motor.From an experiment by comparing V/F ratio which uses to feed the three phase centrifugal pump motor,the result shows that field orient compensation which is controlled with controlling program has a constant in V/F ratio and meets theoretical for speed control of three phase induction motor within constant torque.