Design and testing of a sensorless switched reluctance motor drive with a custom integrated circuit controller

Abstract

The switched reluctance motor (SRM) has become an attractive alternative candidate to conventional ae or dc motors for adjustable speed drive applications. The SRM drive system consists of a power converter and a control section. Making the control section circuits of an SRM drive integratable will make a large contribution to the SRM's acceptability by relieving design and application engineers of the burden of designing controls. Ile objective of this research is to develop an integrated control circuit for an SRM, implementing closed-loop speed control and providing start torque. The target application for this IC version of an SRM drive is an automotive fuel pump running off a 12V power supply with a power rating of 50-IOOW. This thesis presents a breadboard level SRM drive that emirates a custom IC controller implementing closedloop speed control and starting torque.The rotor position sensing information is essential for determining the switching instants to have proper control of speed and torque. A new robust rotor position encoding circuit that, based on the AM encoder technique, uses a new concept to encode the rotor position as a dc signal has been developed during this research and is presented in this thesis. In this circuit, a dc supply voltage is in series with an SRM phase coil and a resistor . The rotor position information is extracted from the voltage across the resistor. This new structure enables the encoder circuit to be merged with the power converter. Only one common ground is needed in the whole systerm This makes the control circuit integratable and also acceptable in automobile applications. In this thesis, a new simple method that gives starting torque to the SRM is presented. Since the SRM drive operates relative to the rotor position, by moving the rotor poles at standstill to an aligned position with a known phase, the SRM can be operated normally by switching on and off the phase current in synchronism with the rotor position. This thesis also presents a new simple senseless closed-loop speed control method. The SRM phase energizing time has a unique relationship with the rotor speed. By monitoring this time, the controller is able to calculate the actual motor speed and then compare it with the reference speed. If the speed error exceeds the allowed range, the controller will change the PAM duty cycle to meet the load requirement until the speed is close to the reference. AR the circuits and methods have been tested on a four phase 12OW SRM.