机械专业外文翻译----直流电动机调速控制(编辑修改稿)

机械专业外文翻译----直流电动机调速控制(编辑修改稿)内容摘要：

, since this is needed only as a protective feature and is described in next section. Thyristor speed control system with current limitation on the AC side Since the circuit is a singlequadrant converter, the speed of the motor shaft (which is the output from the system) can be controlled in one direction of rotation only. Moreover, regenerative braking cannot be applied to the motor。 in this type of system, the motor armature can suddenly be brought to rest by dynamic braking (. when the thyristor gate pulses are phased back to 180o, a resister can be connected across the armature by a relay or some other means). Rectifier BR1 provides a constant voltage across the shunt field winding, giving a constant field flux. The armature current is controlled by a thyristor which is, in turn, controlled by the pulses applied to its gate. The armature speed increases as the pulses are phased forward (which reduces the delay angle of firing), and the armature speed reduces as the gate pulses are phased back. The speed reference signal is derived from a manually operated potentiometer (shown at the righthand side of ), and the feedback signal or output speed signal is derived from the resistor chain R1 R2, which is connected across the armature. (Strictly speaking, the feedback signal in the system in is proportional to the armature voltage, which is proportional to the shaft speed only if the armature resistance drop, IaRa, is small. Methods used to pensate for the IaRa drop are discussed in Reading Material.)Since the armature voltage is obtained from a thyristor, the voltage consists of a series of pulses。 these pulses are smoothed by capacitor C. The speed reference signal is of the opposite polarity to the armature voltage signal to ensure that overall negative feedback is applied. A feature of DC motor drives is that the load presented to the supply is a mixture of resistance, inductance, and back EMF Diode D in ensures that the thyristor current mutates to zero when its anode potential falls below the potential of the upper armature connection, in the manner outlined before. In the drive shown, the potential of the thyristor cathode is equal to the back EMF of the motor while it is in a blocking state. Conduction can only take place during the time interval when the instantaneous supply voltage is greater than the back of shows that when the motor is running, the peak inverse voltage applied。