PMSM can be controlled through dierent type of motor control techniques. The decidingfactor being the application requirement and the cost to implement it. One popular way thatdrives control PMSM motor is using closed loop methods. On OJ Drives, sensor-less FieldOriented Control is used to control motor without any external physical sensor which improvesproduct’s reliableness and decreases cost to make it.
It was important to have background knowledge on its theory and application so the embeddedplatform can be understood. The documents used are provided by NXP available in publicdomain12. OJ has customized the software for their customers therefore the diagrams availablein the public domain by NXP is used as a reference in this project. Any addition to thestate machine for the prototype will be shown on it.
Some diagrams that may help the reader to get some understanding is also shown. An overallview of the platform is given in Fig(4.12)4 . Generally the software starts in open loop andtries to align the motor and then merge into closed loop by using estimated rotor angle fromback EMF observer. There are two main loops. Speed loop is where the required speed fromuser is taken and then actual rotor’s speed is then made the same using PI controller.
The other loop is current controlled loop, the current is loop is much faster than speed loop.Here a PI controller uses the response from speed loop to change the current provided to themotor. Park and Clarke Transformations are used to make data from ADC by taking motorscurrent and voltage values and convert them from three phase to two phase. This simpliescontrolling making by making it like a simple DC motor.
They are then converted back intothree phase values using Inverse Park and Clarke transformations to make SVM so they canbe used to run the motor as intended.Since most of the methods were carried out in d-q axis they are also shown in Fig(4.13)5 whichshows a simple way to represent three phase to two phase conversion. Their respective softwarefunctions take care of the complex mathematics. Fig(4.14)6 and Fig(4.15)7 show an overview ofthree phase and two phase diagrams.
They are useful as both d and q axis current and voltageshave been summed to know the total sum present. Further detail can be read in referencesprovided above.The three phase diagram shows phase a,b and c as motors stator phases where they are 120degrees apart from each other. Alpha and beta shows the when they are converted to phasestationary frame of reference. Then d-q shows rotating reference frame which requires angleinformation from back -EMF tracking observer.
This axis is quadrature to each other. Q-axisis used to provide torque control and d-axis is used for eld weakening.There is a separate document like Fig(XX) that shows what variables are used to run thesoftware. But as that diagram was not available for public domain it has not been added inthe report.
The variables will be used to show the measured data from Freemaster.