Electronic Speed Controller for Brushless DC Motor

Discussion in 'General Electronics Chat' started by mwalden824, Feb 12, 2013.

  1. mwalden824

    Thread Starter Member

    Mar 6, 2011
    51
    2
    Hello. I am trying to build an electronic speed controller for a Brushless DC motor but I have a few questions.

    I am going to attach a few pictures of circuits. Really, I just want to know if there is anything wrong with my circuit. While testing, I built the circuit without attaching a microcontroller to it yet, and just manually toggled the HIN and LIN pins of the driver chip. Now I thought that when the HIN and LIN of the driver chip (irs2011 recommended circuit attached below) were connected to LOW, 0 V, that both of the transistors would be off and the connection to the load or motor wire lead would be floating. Now the circuit operates normally when 5V is applied to HIN or LIN, the proper transistors cut on and the voltage is 11.1V and 0 V respectively. But when both LIN and HIN are 0V, it is still 11.1V. Am I correct at assuming that it should float? the datasheet doesn't say much at all.

    I also keep burning these driver chips out for some reason. I've done replaced them several times. Can't figure out what I am doing wrong.

    So what I think should happen is the phase A subcircuit's high transistor should turn on by HIN getting 5V, and phase B subcircuit's low transistor turning on by it's driver LIN getting 5V and the third driver, both LIN and HIN should be 0V. This would pull phase A high to 11.1 V, phase B low to 0V, and leave phase C floating so that current will flow from phase A through the motor exit into phase B and return to ground.

    Now later I will create a circuit that will monitor the floating phase for zero crossings to determine when to switch to the next sequence in the drive pattern, but I am just trying to get this working right first and I don't think it is working correctly.

    One more question, in my circuit I saw on someone else's they used snubbers across the low transistors. I didn't in my circuit even though it is on the schematic, but how do you determine the values? or are they even needed? Also I have a 1000uF and two 0.1uF caps across the transistors. I have seen this done in other circuits. I know there should be some capacitance but does it need to be across each set of transistors, or is it ok like I have it in my circuit?

    Also, ignore the Current Sense circuit. I haven't connected or played around with it yet.
     
  2. antonv

    Member

    Nov 27, 2012
    149
    27
    I don't have any experience with brushless motors but I have a couple of comments:
    - unless you connect a load to the transistors, even just a resistor, you will see weird voltages on the output.
    - I don't know how your circuit is layed out physically but if the high side MOSFETs have their drains separated by a few inches of wire or pc board trace so that the capacitors are only close to one of them then I would add a couple of 0.1 uF caps right at each of the other two's drains too.
     
    mwalden824 likes this.
  3. antonv

    Member

    Nov 27, 2012
    149
    27
    Also, some of these drivers require the high side to be driven with a square wave, not just a steady high voltage, because they use the changing input to also drive the internal charge pump that provides the high side gate drive. I don't know if this one is like that, but something to be aware of.
     
    mwalden824 likes this.
  4. mwalden824

    Thread Starter Member

    Mar 6, 2011
    51
    2
    Well see I actually did build a simple load circuit with LEDs and resistors, and I made it so that each of the drive sequences would light up an LED, and the program I wrote for the MCU would cycle through the 6 drive patterns with a 500 ms delay. I also had a 2.5kHz PWM 2% duty cycle feeding the HIN inputs of the drivers while the LIN inputs were just getting a constant high 5V.

    Now here's the thing, the LED's would cycle through, but there was always three LEDs on, but the brightest LED was the one that was suppose to be lit for that drive sequence. I would think, since the third phase should be floating it would not have a potential to light the other two LEDs, but maybe I'm wrong?

    When I simulated this circuit in Proteus it worked perfectly, and the floating phase's voltage when measured with respect to ground would jump around randomly which I assume that meant it was floating. I am going to try and do some more simulating and circuit testing.

    I keep blowing these damn driver chips and they are not cheap. They're ~$4.00 USD a piece. I really don't get why this is happening. I have checked the wiring on my breadboard so many times I could probably assemble it by heart my now.

    Also, your advice on the caps; so I should keep the one 1000uF across all six transistors like it is in my circuit, but add a 0.1 uF cap across each pair of transistors like the wiring of the 1000uF cap, but just directly across the other pairs of transistors? or did you just mean across the low side transistors?

    Also would the snubbers be necessary? I will just continue to test without them for right now.

    I am about to go to sleep, but tomorrow I will post a picture of my breadboard circuit if that would help.

    I really appreciate your help.
     
  5. mwalden824

    Thread Starter Member

    Mar 6, 2011
    51
    2
    Ok, can I just ask someone one real quick question. In the Recommended circuit I attached in the first post, it shows two capacitors where one of the lines in the symbol is curved. I have always thought this to mean a polarized electrolytic capacitor. But someone told me that that isn't always true.

    So my question is should I use polarized electrolytic capacitors for the circuit? One of the capacitors is part of the charge pump or whatnot. I have been using non-polarized capacitors so far except for the bypass caps across the power to ground rails near the chips and other areas of such. But would it be okay to use a polarized electrolytic cap for the charge pump system in the recommended circuit above? I was thinking that the polarity of this cap might change but I am not sure exactly how these charge pump circuits work.

    Thanks.
     
  6. Ishah

    New Member

    Jan 3, 2013
    3
    0
    Hi May I know what is the different of Brushless DC Motor than common Dc motor..?

    Thanks
     
  7. Ishah

    New Member

    Jan 3, 2013
    3
    0
    Hi I also want to try this Electronic Speed Controller for Brushless DC Motor project but using PIC16F877A. Here I attached my schematic. Can someone check for it?

    Why the previous schematic using the PWM to control it? Can I deal with L293D(Hbridge IC) to control Brushless DC Motor ?


    [​IMG]


    http://postimage.org/image/ajxpy2k3p/
     
    Last edited: Feb 14, 2013
  8. mwalden824

    Thread Starter Member

    Mar 6, 2011
    51
    2
    A brushless DC motor contains no brushes. A normal DC does contain brushes which are contact points where the rotor (the thing that spins) literally touches these conductive brushes in a way that as it rotates it switches the polarity of the current running through it change the polarity of the magnetic field causing the rotor to keep rotating and repeating the process. These brushes are problematic and cause problems because they wear out, reducing the life of the motor, but they have the advantage of simplicity. The brush-less dc motor doesn't have these brushes which makes them great for long term use and they have many other advantages. But they are usually more expensive and more complex to control. A regular dc motor you can just attach a voltage to is and it will spin, while a brush-less dc motor requires a controller which is what I am trying to design. A brush-less dc motor actually requires a signal very similarly to a 3-phase power supply but more digital in nature. The Back EMF is trapezoidal usually and not sinusoidal.

    I looked at your circuit but I don't understand what you are trying to accomplish. I am pretty new to electronics also, but I will try my best to help, just give me more information. I am only a senior in college for a EE degree.
     
  9. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512

    "I also keep burning these driver chips out for some reason. I've done replaced them several times. Can't figure out what I am doing wrong. "

    One thing is that you are using 20V on the Vcc pin. That is the maximum according to the data sheet. Any voltage spike puts you over voltage. A Nmos is fully turned on at ~10V no need to go higher. Use your 11V motor supply for the Vcc.

    As far as the voltage when the phase is off, are you sure the mosfet is wired correct? That the drain and source aren't reversed? If they are the internal diode will conduct and give the problem your experiencing, easy to do.:)

    Snubbers on a motor drive are never a bad idea.

    How are you sensing rotor position in the drive? While a BLDC will rotate with out it with no load, when a load is involved you will need rotor positioning of some type, either from sensors or one of the "sensor less" types of circuits.

    Hope this helps.
     
Loading...