A conveyor system includes an electric motor to move a conveyor. A voltage determining device is coupled to an alternating-electricity source that supplies alternating electricity to the conveyor system. A power supply appliance supplies power between the electric motor and the alternating-electricity source. The power supply appliance includes an inverter and an inverter control. The inverter includes a rectifying bridge and a motor bridge. The rectifying bridge input is coupled to the alternating-electricity source and the rectifying bridge output is coupled to the motor bridge input. The motor bridge output is coupled to the electric motor. The inverter control is coupled between the voltage determining device and the motor bridge. The inverter control is responsive to frequency and phase of the determined voltage of the alternating-electricity source to adjust the frequency and phase of the motor bridge output voltage such that the motor bridge output voltage is made to be essentially constant.