New Yaskawa AC SERVO MOTOR 200V 0.89A SGM-02VGNK83 Industrial Servo Motor

The ac drives consist of three main parts, namely: three-phase full wave rectifier, dc bus filter, and pulse width modulation (PWM) inverter. The block diagram of the power stage of an ac drive is shown in Fig. 2.11.

The three-phase full wave rectifier converts the three-phase as voltage of the power supply into dc voltage. Although ac drives are usually supplied by a three-phase power supply, there are also ac drives supplied by single phase ac power supplies to control three-phase induction motors. The power electronic devices used in this portion of the ac drive can be either diodes or SCR (silicon controlled rectifier) [39, 45]

Although the output of a rectifier is dc, it is not ideal, i.e. the dc voltage contains ripples. Thus, a dc bus filter at the second stage is used to reduce the ripple content of the dc bus voltage. The third and last stage is a PWM inverter which converts the dc voltage from the dc bus filter into three-phase balanced ac voltage. The operating frequency and magnitude of this three-phase ac voltage applied to the motor terminals can be controlled in order to maintain the developed torque of the motor constant from zero to rated frequency. The power electronic devices that constitute the switches in a PWM inverter for ac drives are in most cases the so-called IGBT (insulated gate bipolar transistor) [39, 46, 47], due to their high current capability, very low control power, high frequency commutation, and low losses. The schematic circuit switching-element diagram of an ac drive is shown in Fig. 2.12.