Overview
The reference design demonstrates sensorless control of the 3-Phase Switched Reluctance (SR) motor using 56F80x or 56F83XX Digital Signal Controllers. It can also be adapted to 56F81XX Digital Signal Controllers. The concept of this application is that of a sensorless speed closed loop SR drive using flux linkage position estimation. An inner current loop with PI controller is included. The change in phase resistance during motor operation due to its temperature dependency creates errors in the position estimation and significantly affects the performance of the drive. Therefore, a novel algorithm for on-the-fly estimation of the phase resistance is included.
The Digital Signal Controller runs the main control algorithm. Rotor position is evaluated using the sensorless flux linkage estimation algorithm. The actual flux linkage is calculated at the rate of the PWM frequency and is compared with the reference flux linkage for a given commutation angle. When the actual flux linkage exceeds the reference, the commutation of the phases is done; the actual phase is turned off and the following phase is turned on. Flux linkage error is used for estimation of the phase resistance at low speeds (US Patent No.: 6,366,865). The actual speed of the motor is determined using the commutation instances. Based on the speed error, the speed controller generates the desired phase current. When the phase is commutated, it is turned on with a duty cycle of 100%. Then, during each PWM cycle, the actual phase current is compared with the desired current. As soon as the actual current exceeds the desired current, the current controller is turned on. The current controller controls the output duty cycle until the phase is turned off (following commutation). Finally, the 3-Phase PWM control signals are generated. The procedure is repeated for each commutation cycle of the motor.
Features
- Sensorless control of an SR motor using a flux linkage estimation technique
- Targeted for 56F80X, 56F83XX, and 56F81XX Digital Signal Controllers
- Running on a 3-Phase SR HV Motor Control Development Platform
- The control technique: current control with a speed closed loop
- Position estimation based on flux linkage estimation
- Phase resistance measurement during start-up
- Phase resistance estimation at low speeds
- Motor starts from any position with rotor alignment
- Encoder position reference for evaluation of sensorless position estimation
- Manual interface
- FreeMASTER software control interface and monitor
- Fault protection
