Space Vector PWM in Matlab/Simulink & 5V-15V Interface circuit

Discussion in 'Homework Help' started by wongkenji, Mar 7, 2007.

  1. wongkenji

    Thread Starter Member

    Mar 7, 2007
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    Hi Everyone,

    I'm new here and I hope someone can help me with my project. I need to design a Space Vector PWM circuit block connected to my DS1102 PWM hardware block in Simulink. Anybody have any ideas?

    My second question is about designing an interface circuit between the 5V output of the DS1102 PWM block and a 15V inverter input. I've asked the dSPACE people for help but I'm still quite unclear about the circuit as there are no values to the resistors. My tutor also told me to use a line driver instead of using just single resistors which will take up too much space and it'll be bulky. I have no idea how to use a line driver as I've never encountered one before.

    Hope someone will be able to help and I wish I found this place earlier.

    Cheers,
    Ken-ji
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    I can't help you with the Space Vector PWM since I have no idea what that is. Could you possibly construct a brief explanation.

    As to level shifting there are a number of viable solutions. Probably the most straight forward is to use an NPN transitor as a common emiter switch. The base resistor value is computed so that with 5V on one side and the transistor base at 0.7V there is sufficient base current to turn the transistor on so that it can sink the required collector current. The collector resistor is computed by looking at the current available from the higher voltage supply when the transitor is on. When the transitor turns off this resistor will have to pull the output back up to the supply rail. That's all there is to it.

    Check out the following link:
    http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/transwitch.html#c4

    A typical line driver would be a 26LS31, and the companion part is the 26LS32 line receiver.
     
  3. wongkenji

    Thread Starter Member

    Mar 7, 2007
    21
    0
    Thanks for your reply, it's the same as the circuit diagram I've attached right? Except that it is missing the switch. Would you know what values to use for the components? Here's what the dSPACE support people wrote:

    Here is some advice from hardware development. As far as we see you need an open collector output to pull the cathode (pin 2 of the H11L1 opto coupler) to GND when the DS1102 PWM output is high, and to leave the pin open when PWM is low. Attached is a basic schematic of a circuit to use for this purpose. We cannot dimension the components for your, you will probably need some help of a circuit designer to complete this if you cannot determine the component values yourself.

    Note that the PWM outputs of the DS1102 are directly provided by the TMS320P14 slave DSP. The DSP's digital I/O lines are very limited to only IOH high-level output current : -300 µA and IOL low-level output current : 2 mA.


    http://img.photobucket.com/albums/v208/kenji_britney/PWM_FET_Circuit.jpg

    For some information about Space Vector Pulse Width Modulation, try looking at this: http://eee.ucc.ie/research/control/publications/cmex_paper.pdf
    There's some guidelines on how to design a CMEX SVPWM in Matlab but I have no idea how to do it. Anyone good with Matlab?
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    I see a MOSFET switch with a resistor divider network on the input and a load resistor on the output. The divider on the input limits the gate current and also the switching speed, but guarantees that if the input is floating the MOSFET will be off. The output load resistor will determine how fast the output will rise to the 15V supply rail when the MOSFET turns off. What you want is a logic level device that will be switched on by the logic level specification.

    I don't have time to search for a candidate part at the moment. Perhaps you could offer some financial inducement, or one of the other members might do it from the goodness of their heart.
     
  5. wongkenji

    Thread Starter Member

    Mar 7, 2007
    21
    0
    Oh ok, about the line driver, it's suppose to replace the resistors right? But how do I go about doing that? The line drivers are AND/OR gates with 2 inputs and 1 output. Correct me if I'm wrong but are the 2 inputs replacing resistors R2 and R3?
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    The MOSFET level shifter, and the line driver are alternative solutions to the problem of shifting a logic signal in the range [0..5] volts to one in the range [0..15] volts. In adition to the problem of voltage levels you need to be concerned about the sense of the signal.

    In other words. Is it important that 0V on the logic side corresponds to 0V on the oputput, and 5V on the logic side corresponds to 15V on the output.

    We have a specification for the signal source (300 uA source, 2 mA sink), but there is no specification for the input except 0-15V. What kind of an input is it, what is the threshold, and similar questions.

    What you need to do is obtain the datasheet for a line driver, like the 26LS31, or the datasheet for a logic level MOSFET and study them carefully. I know you are having trouble, but trust me, this process will lead to a better solution. At this time, with your frustration level mounting, I believe you will find the line driver an easier solution to get your arms around.
     
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