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regarding DRV8412-C2-KIT

Chinmay Shah
Expert 1085 points
Part Number: DRV8412
Other Parts Discussed in Thread: DRV8302, , CONTROLSUITE

Dear Friend,

  • The project given in this EVM has used PID for Feedback Current. May we get more torque than open loop DC Motor Control?
  • What is the minimum speed of rotation for any PMDC Motor (e.g. 3000 RPM, 40 V DC Motor, Applied Excitation: 40 V DC, 5 A)?
  • How many MOSFETs are excited at a time for single full H-Bridge? Whether TI has used 4 quadrant PWM techniques or not? If Yes, then is it converted into 4-Quadrant in DRV8302 by selecting some particular Mode, by using Mode Selection pin? 
  • 0
    TI__Mastermind 26065 points

    Hi Chinmay

    1. For PMDC motor driving, the EVM can work in two ways. Voltage control and current control ways. In current control way, the current will be sampled and PID controlled, simular to the constant phase current control of stepper motor. No matter what kind of control, the MAX torque of PMDC motor is just proportion to the MAX current.

    2. Not sure you want minimum or maximum, as the PMDC motor, the minimum speed or maximum speed are all determinded by the motor itself and load conditions as well as the driving current. The kit do nothing about the PMDC speed control. So it is an open loop for speed.

    3. DRV8412 has internal MOSFET bridges. And all controlled as PWMs to half bridges. There are some mode definitions by mode pins. you can refer to the DRV8412 datasheet.

    Also, you can install the controlSUITE software first. Then, you can get all the hardware and software and docs at the path in your computer like following.

    C:\ti\controlSUITE\development_kits\DRV8412-C2-KIT_v131

    Thanks.

    Wilson Zuo

    Motor Application Team

     

  • 0 in reply to Wilson Zuo
    Expert 1085 points

    Thanks Wilson Zuo.

    I've already installed the Control-suit in my Laptop. 

    Also I'd to mentioned somethings that I've already done in my PMDC Motor Control Project. 

    I've import the Example code of PMDC from "C:\ti\controlSUITE\development_kits\DRV8412-C2-KIT_v131" location. (FYI: The project Active Build Config: Flash is not working, the code is not stored in volatile memory, only RAM config is working!)

    I've added/un-comment/modified the Encoder (eQEP) MACRO, and added Speed PID loop for Speed PID. So I got adequate (far more than open loop) torque. 

    But in this way, I must need the PMDC Motor along-with an Encoder. 

    But if I need to enhance the Torque without use of Encoder, then how can I achieve it? Should I use the Current f/b PID? As per my knowledge, during normal operation (rotation), the motor will drag some amount of current, if load increases, then motor will offer same amount of torque by dragging the more current from source! Am I right? 

  • 0 in reply to Chinmay Shah
    TI__Mastermind 26065 points

    Hi Chinmay

    Let is think about the scenarios of with Encoder(speed control) and without simplely as below.

    Scenario 1: Without encoder, when load increasing, the speed drops down, the current (proportion to torque) will increase because BEMF drops with speed. So although the torque increased, but the balance is set to a new point with lower speed.

    Scenario 2: When with encoder and speed loop, if there is still room, the driver will continually increase the output power (PWM duty) to the motor at the same point as scenario 1, trying to rise the speed back to the value before load increased. So this also means in scenario 2, the close loop control brings more torque and dynamic responsing than scenario 1.

    A current PID control only gives you a constant torque, it is very rare that use only a current control for a PMDC motor. The system with only current control will cause the speed changing out of order with regard to the load. A MAX current limit is more often to see but still need a speed control for real application.

    If you want a speed control of PMDC without encoder, you can try hall sensor or sensorless with the BEMF detect method. Blog below may be helpful.

    http://e2e.ti.com/blogs_/b/motordrivecontrol/archive/2013/10/25/easy-cruise-control-for-brushed-motors-using-bemf.aspx

    Thanks

    Wilson Zuo

    Motor Applicaiton Team

  • 0 in reply to Wilson Zuo
    Expert 1085 points

    Thank you very very much Wilson Zuo.