Evaluation of microcontroller architectures for PMSM control
Examensarbete för masterexamen
Electric power engineering (MPEPO), MSc
Due to hybridization of vehicles, electrical motors like permanent magnet synchronous motors (PMSM) are playing a major role in the automotive industry. In order to upgrade the microcontroller used for the prototype of the PMSM control in Volvo Group Truck Technology, a study on available micro-controllers presently on the market and to evaluate a few of the suitable micro-controllers is necessary. In this thesis a evaluation of Texas instrument micro-controllers TMS320F28377D and TMS570LS1227 are performed. In the first part of the thesis, a digital control algorithm has been implemented in the Matlab simulink and effect of various digital control parameters like ADC resolution, PWM resolution, ratio of switching frequency to electrical frequency of stator current etc. has been discussed. Based on the simulation minimum requirements of PWM and ADC resolution has been found to be 10 bit. Also the simulation results showed that for the drive system under consideration the ratio fsw=felec should be 40 or more to have a better torque control. In the second part of the thesis the best available micro-controllers suitable for PMSM control has been listed and the two of the most suitable micro-controllers TMS320F28377D and TMS570LS1227 has been selected for further evaluation. In the third part of the thesis, the digital control algorithm has been implemented in both the selected micro-controllers and the motor control performance has been evaluated using the hardware in the loop simulation with the real time motor model implemented on a dSpace system. The CPU utilization for the ISR in TMS570LS1227 for a switching frequency of 20 kHz and a CPU clock frequency of 80 MHz is measured to 30:2%. But for TMS320F28377D, the CLA executes the ISR. So its CPU utilization is almost 0% and its CLA utililization is 23:8% with the same switching frequency of 20 kHz and the CLA clock frequency of 80 MHz. The fault response time for the micro-controllers to block the gate pulses has been found to be sufficient to protect both the PMSM and the VSC. The fault response time has been measured to be 20 ns for TMS570LS1227 and 60 ns for TMS320F28377D. Also the effect of PWM and ADC resolution on the motor control has been compared with the simulated results and found to have the same effect on the real system. The real system torque response do not look like the designed first order response due to the presence of the additional impedance in the hardware connecting the micro-controller evaluation board and dSpace. Though both the evaluated controllers is suitable for PMSM control, TMS570LS1227 has been developed by Texas Instrument with safety features that helps to achieve ASIL-D. But it doesn`t have any special units to perform mathematical operation fast and to take care of some of the critical tasks independent of the CPU. TMS320F28377D has, a fast processing mathematical unit and a CLA to take care of critical tasks independent of the CPU. Though it has some safety features to achieve ASIL-D, it is not assured that it will be possible to achieve, unless application developers work on it. Based on the evaluation of the micro-controllers a suitable architecture that provides the powerful control performance and safety features that helps in achieving ASIL-D has been suggested.
Elkraftteknik , Electric power engineering