Rotor side Control of High Power Slip Ring Induction Motor using a Single Thyristor

Abstract

The aim is to create a Simple control mechanism for speed variations of a HIGH POWER SRIM - Slip Ring Induction motor as an extension to the available Non slip power recovery mechanisms available for low power SRIMs. The most basic ways to control the speed of a slip ring induction motor is either from the STATOR OR ROTOR SIDE. The mechanism employed here is to control the speed via a Single thyristor acting as an ON/OFF switch at the rotor side of this slip ring induction motor. The core scheme here is to control the high power machine by directly varying the load current or the rotor side current by the single thyristor after conversion of the available load side current into the DC current by a 3 phase RECTIFIER BRIDGE made of 6 diodes respectively. Thus, all the AC power is converted into simple DC current and is controlled by the thyristor ON/OFF time giving the required speed control as the rotor current is directly proportional to speed and torque in an increasing power scenario as in this case. Even the losses due to non-slip power recovery can be considerably neglected because of the machines high power status. Thus, we are able to simply control a high power SRIM by just varying the amount of ON/OFF time of the thyristor at the rotor end efficiently. Thus, this method is best suited for very high inertia loads, which requires a pull-out torque at almost zero speed and accelerate to full speed with minimum current drawn in a very short time period.