I am having some difficulties when designing the controller and it would be great if anyone could clear up some theoretical principles...
I have a Mars Pmac BLDC and i am trying to design a full bridge Inverter based on the Microcontroller PIC 18FXFXX31 MCU's.
The motor was purchased from electric motor sport.com and i am completing this task with visions of intigrating regenerative breaking next semester..
So... the Motor comes with three Hall effect sensors that will provide me rotor Flux position and hence the commutation sequence with respect to the 6 Mosfets on the bridge.
Where i am having difficulty in understanding is the following...
Given that we have the Sequence... binary code for each position and hence firing cycle how can i intigrate speed control. From my understanding torque is proportional to the current vector magnitude at the stator windings. but wont the Motor just draw the currents it needs ? Can i just use a potentiomiter as the reference and just modify the PWM duty cycles that will in turn correlate with the RMS volts seen at the motor and hence speed ?
Can i just use a look up table.. for example have the pot chopped into 0-256 bits and then have ranges coprrelating to PWM duty cycles ?
I have been told i need to monitor current by my supervisor.. But im of the impression that i would ahev to intigrate some sort of CT or extra analogue electronics to scale the current given its operating level at apprioximatly 70 apms..
What would be the best and easiest way to have closed loop control ? I dont need the highest of resulutions, its not like it a CNC machine. i just want it to ramp up and down.. Its for a go kart application so i figue knowing rotor position i can just make the angle between rotor flux and stator current 90 to get max torque...
.. the motor has 8 pole pairs. so i was thinking, if it takes one electrical cycle to get 1/8 of a mechanical cycle can i just use a timer or counter to determine the speed ? for the speed reference.. ?? ANd do i even need a speed reference. Given that RMP will be correlated to Voltage applied and hence PWM duty cycle ?
Cheers
engstudent
I have a Mars Pmac BLDC and i am trying to design a full bridge Inverter based on the Microcontroller PIC 18FXFXX31 MCU's.
The motor was purchased from electric motor sport.com and i am completing this task with visions of intigrating regenerative breaking next semester..
So... the Motor comes with three Hall effect sensors that will provide me rotor Flux position and hence the commutation sequence with respect to the 6 Mosfets on the bridge.
Where i am having difficulty in understanding is the following...
Given that we have the Sequence... binary code for each position and hence firing cycle how can i intigrate speed control. From my understanding torque is proportional to the current vector magnitude at the stator windings. but wont the Motor just draw the currents it needs ? Can i just use a potentiomiter as the reference and just modify the PWM duty cycles that will in turn correlate with the RMS volts seen at the motor and hence speed ?
Can i just use a look up table.. for example have the pot chopped into 0-256 bits and then have ranges coprrelating to PWM duty cycles ?
I have been told i need to monitor current by my supervisor.. But im of the impression that i would ahev to intigrate some sort of CT or extra analogue electronics to scale the current given its operating level at apprioximatly 70 apms..
What would be the best and easiest way to have closed loop control ? I dont need the highest of resulutions, its not like it a CNC machine. i just want it to ramp up and down.. Its for a go kart application so i figue knowing rotor position i can just make the angle between rotor flux and stator current 90 to get max torque...
.. the motor has 8 pole pairs. so i was thinking, if it takes one electrical cycle to get 1/8 of a mechanical cycle can i just use a timer or counter to determine the speed ? for the speed reference.. ?? ANd do i even need a speed reference. Given that RMP will be correlated to Voltage applied and hence PWM duty cycle ?
Cheers
engstudent