Control Philosophy

In order to obtain optimal performance of the permanent magnet synchronous motor it was required to implement a field oriented control system (FOC). This philosophy provides the ability to control the speed of the permanent magnet synchronous motor much like a brushed DC motor. Brushed DC motors can achieve speed control by independently altering the torque and flux by varying the field winding currents. Permanent magnet synchronous motors are unable to provide this behavior as the rotor flux provided across the air gap is constant due to the permanent magnets. FOC provides a solution to this problem by varying the stator currents to achieve a given speed. This is done through the use of 2 current sensors, a rotor position sensor and 2 mathematical transforms. The transforms are known as the clarke and park transform and they allow for the 3 phase stator currents to be represented within the rotor reference frame. The rotor reference frame currents are known as direct and quadrature axis currents and they represent the flux and torque respectively [1][2].

A Simulink model was prepared to simulate a field oriented control system for a PMSM. Its represented in 4 components, the specified IGBT bridge, SPWM generated gate pulses, the PMSM and the field oriented control loop composed of 3 PI controllers. Each of these components can be observed directly below [3][4][5][6].

The Simulink model of the field oriented controller was tested by injecting 3 different speeds of 2700, 450 and 1200 RPM to demonstrate the controllers ability to react to set point changes. These 3 requests were provided over a 1 second interval. The responses associated with the speed of the motor, the stator currents, the motor torque and the controlled direct and quadrature axis currents are shown below.

The field oriented controllers response to the 3 different speed requests resulted in excellent transient and steady state behavior. The motors speed doesn’t experience overshoot when reacting to the steps indicating strong transient performance. The motor is able to achieve and maintain speed at steady state within a respectable amount of time.

  

Citations

[1] A. Kronbreg, “Design and Simulation of Field Oriented Control and Direct Torque Control for a Permanent Magnet Synchronous Motor with Positive Saliency,” Uppsala Universitet, 2012. [Online]. Available: http://www.diva-portal.org/smash/get/diva2:534947/FULLTEXT01.pdf. [Accessed:  7-Jun-2019].

 

[2] P. R. R.Prathyusha, “Field Oriented Control of Permanent Magnet Synchronous Motor,” International Journal of Computer Science and Mobile Computing, 2014. [Online]. Available: https://ijcsmc.com/docs/papers/March2014/V3I3201485.pdf. [Accessed: 06-Jun-2019].

 

[3] S. B. O. O. C. Kivanc, “MATLAB Function Based Approach to FOC of PMSM Drive,” IEEE European Modelling Symposium, 2015. [Online]. Available: http://uksim.info/ems2015/data/0206a096.pdf. [Accessed: 12-Jul-2019].

 

[4] “Park Transform,” MathWorks Documentation, 2019. [Online]. Available: https://www.mathworks.com/help/physmod/sps/ref/parktransform.html. [Accessed: 12-Jul-2019].

 

[5] P. H. Tran, “MATLAB/SIMULINK IMPLEMENTATION AND ANALYSIS OF THREE PULSE-WIDTH-MODULATION (PWM) TECHNIQUES,” Boise State University, 2012. [Online]. Available: https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1268&context=td. [Accessed: 12-Jul-2019].

 

[6] D. V. Munoz, “Design, Simulation and Implementation of a PMSM Drive System,” Chalmers University of Technology, 2011. [Online]. Available: https://publications.lib.chalmers.se/records/fulltext/152505.pdf. [Accessed: 16-Jul-2019].

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