CURRENT ISSUE
Contests
FEATURE ARTICLE
|
|
Issue #217 August 2008
Subcategory Winner - Microchip 2007 Design Contest
INTELLIGENT ENERGY SOLUTIONS
Electric Vehicle Inverter Design
Build A System For Powering AC Induction Motors
by Dan Hall, Tristan Kasmer, Doug Krahn, Adam McIntyre, and Dena Ponech
Start | Power Inverter | Gate Drivers | Control Board | Space Vector Modulation | PID Tuning | Altering Motor Control Parameters | HMI | Protocol | Firmware/Software | Sources & PDF
GATE DRIVERS
Gate driver circuits are required to control the IGBTs. These circuits provide appropriate firing and off-time voltages to the gate-emitter connection. They also provide optical isolation of control signals from the high voltages that are being controlled. We chose the off-the-shelf gate driver assembly BG2B-5015 kit from Powerex.[3]
To produce the firing voltages, the circuit employs an isolated DC/DC converter module represented by the DC/DC converter module block diagram (see Figure 2).[4] The DC/DC converter enables the driver board to be run off of a single DC supply that takes 15 V and converts it to an isolated 24 VDC. This voltage is then placed across a resistor and Zener diode network that provides isolated 15.8 V at VCC, pin 3, and –8.2 V at VEE, pin 1, with respect to the zero reference point VE1, pin 2. The transformer in the DC/DC converter also provides 2,500-VRMS protection to the gate driver assembly module.
 |
| Figure 2 —These are gate driver board circuit connections to one IGBT. Bottom transistor connections are removed for simplicity. |
The DC/DC converter provides an isolated power output to pins 4 and 6 on a hybrid IC IGBT gate driver represented by the gate driver assembly module block diagram (see Figure 2).[5] The gate driver assembly uses the control input at pin 13 and 14 to bias the gate-emitter connection in the gate driver module appropriately to turn the IGBT on or off. The 15.8-V signal at VO, pin 5, ensures that the IGBT will be saturated in the on state. The –8.2-V signal ensures that the IGBT will not be switched on by noise or Miller capacitance between the collector and the gate. The output stage of this assembly provides high current to the gate so proper control of load currents can be obtained. As the current passing through the IGBT increases, the amount of gate current must also increase to keep the IGBT saturated. The gate driver assemblies we used for our inverter project are capable of driving an IGBT that can switch up to 400 A. The gate current required to control this amount of current is approximately 5 A DC. The gate driver assembly also provides optical isolation of control signals via high-speed open-collector optocouplers that protect up to 2,500 VRMS. This ensures that the control signals, pins 13 and 14, and high-voltage signals are well insulated from one another, thus protecting the microcontroller that is producing the inverter drive logic.
Previous | Next *| Subscription Deals |*
|
