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Explain the basic concept of IGBT inverter ?

  1. Jul 13, 2010 #1
    Hi friends is there anything that can explain the basic concept of IGBT inverter for ac motor drives..?

    Help me please...

  2. jcsd
  3. Jul 13, 2010 #2
    The IGBT is similar to the power transistor, except that it is controlled by the voltage applied to its gate rather than the current flowing into its base, as in power transistors. The current flowing in the gate of an IGBT is extremely small because the impedance of the control gate is very high. This device is equivalent to the combination of a metal-oxide semiconductor field effect transistor (MOSFET) and a power transistor.
    Since the current required to control an IGBT is very small, it can be switched much more quickly than a power transistor. The IGBTs are normally used in high-power, high-frequency applications.
    For more information you can refer to English description of http://electrical-riddles.com/topic.php?lang=fa&cat=9&topic=491"
    Last edited by a moderator: Apr 25, 2017
  4. Jul 13, 2010 #3
    An IGBT inverter uses four IGBT switches in an "H-bridge" configuration to convert a DC voltage to a square wave ac voltage for driving motors. See


    Bob S
  5. Jul 13, 2010 #4


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    An inverter for supplying power to an AC motor converts DC power to AC power, usually at a controlled frequency and voltage.

    These work by controlling a switching device like an IGBT, Mostfet or Bipolar transistor with an oscillator so that the control device is switched on and off between conducting and not conducting.

    The drive may be a square wave or a sinewave. Square wave drive is more efficient but sinewave drive is cleaner and radiates less radio interference.

    IGBTs would be used to directly control high voltage DC so that the motor receives AC power at a suitable frequency, or they may drive the primary of a transformer with a motor connected to the secondary

    The inverter may be used because only a DC supply is available or because the variable frequency output allows the motor speed to be controlled.
  6. Jul 13, 2010 #5
    Hello Hery,

    You're in luck! I used to design drives for brushless motors.
    Essentially, you have three vareities of motors with some minor variations:
    1 - 3 phase induction motor
    2 - 3 phase brushless motor trapazoidal BEMF
    3 - 3 phase brushless motor sinusoidal BEMF
    The induction motor's driven by a waveform whose voltage waveform averages out to be a sine wave, though if you look at any phase all you'll see high and low pulses.
    Brushless motors use magnets instead of the shorted rotor you find in an induction motor. This gains some efficeincy, and doesn't add all that much cost. Some brushless motors are magnetized such that they produce sine waves as the turn while others produce trapazoidal waves.
    The sine wave versions typically have inverters that average a three phase sine wave to drive them. Again, this is the average signal and if you look at the actual signals, they look like pulses.
    Most trapazoidal BEMF motors measure and control the current in the windings, so that one pair of windings is on at any given time and that pair has a fairly constant current. The trick then is to know which pair of windings to energize to ensure that the motor is propelled. Some controllers do this by monitoring the shaft position with Hall sensors and other drives monitor the unused winding to determine proper time to switch.
    In all of these schemes, you'll have three phases to the motor and six transistors. Currently, the best transistor for low voltage drives, such as 200 volts and less, has proven to be the MOSFET. For higher voltages, all the into 1200 volts, the IBGT is the best. Older drives used SCR's but that technology has been pushed aside for IGBTs, and now even higher voltage applications are beginning to use IGBTs by stacking them.
    A few key words: voltage mode control, current mode control, BLDC, vector control, V/F control, sensorless BLDC, IGBT, MOSFET.

    Best Luck

  7. Jul 13, 2010 #6


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    I've only personally used them to on output of controllers for things like turning on heaters, etc.

    One question about brushless motors in general. What is the size range for the two types? Just how big can they be. I guess there would be the limiting factor of magnet size?
  8. Jul 13, 2010 #7
    Good question,

    I'm not certain how crazy a motor designer can go with brushless types. Generally, he gets a big density boost by switching to high energy magnets and better lamination material. Eventually, they get to an upper flux density and start piling on lams. I've seen motors on the order of 100-200 hp that are about 8-10 inches on the side and about 2 feet long. These were made to work from AC mains, so the motor drive's voltage would typically be from a 380V DC power source (rectified)

    None of the stuff I worked with was anywhere near this size. Most of it was about 150 to 8000 watt. Again, people mostly want these to run off of AC mains and are after the power efficiency or the variable speed. Efficiency wise, these were hard to beat. Some topped out over 85%, which was far better than most induction motors. That's why you find them in probably every air conditioner air handler made for the USA.

    As far as the low voltage motors, I've only ran up to 250 watts. That guy had a stack of less than an inch and was about 3.5 inches in diameter. I've seen some real demons though. They're designed into 24 volt air conditioner compressors and hobbyists use them for airplanes and boats.

    As for IGBT's, at a convention I saw switches that ran in the 100's of kv and over a thousand amps. They stacked them in oil with a control board for each switch. fiber optic lines conveyed switch commands, and a toroid on each control board received power from a heavily insulated cable that passed current through each in turn. I think these were designed for transmission line rectifiers and inverters.

  9. Jul 13, 2010 #8


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    That amazing power for that size of package.

    Well that explains why they are so good for those applications. Lots of money to be saved here.

    That's so cool. I'm thinking a sticky like, What have some of your neatest projects been?, might be a good thing.

    Thanks for explaining.
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