Principle of inverter iGBT drive circuit
The principle of an VFD IGBT (Insulated Gate Bipolar Transistor) drive circuit revolves around the controlled switching of IGBTs to convert DC (direct current) into AC (alternating current). This process enables the operation of variable frequency drives (VFDs), motor drives, power supplies, and renewable energy applications.
Working Principle of an IGBT Drive Circuit in an Inverter
Gate Drive Control
The IGBT is a voltage-controlled semiconductor device with a gate-emitter voltage (V_GE) that determines its switching state.
A gate driver circuit provides the necessary voltage (typically 15V for ON and -5V to 0V for OFF) and current to switch the IGBT efficiently.
Pulse Width Modulation (PWM) Switching
The inverter generates an AC waveform by switching the IGBTs in a specific sequence using PWM signals.
A microcontroller or DSP (Digital Signal Processor) generates PWM signals, which the gate driver amplifies to control the IGBT.
High and Low Side Switching
The inverter typically consists of a three-phase or single-phase H-bridge circuit, where IGBTs are arranged in complementary pairs (upper and lower switches).
The gate driver ensures proper timing to prevent shoot-through (both switches conducting simultaneously).
Isolation and Protection
Isolation: To prevent high voltage damage, optocouplers or transformers are used to isolate the control circuit from the power stage.
Protection: Includes short-circuit protection, over-temperature protection, and desaturation detection to prevent IGBT failure.
Dead Time Insertion
A small delay (dead time) is introduced between switching transitions to prevent both IGBTs in a leg from turning on simultaneously.
Bootstrapping for High-Side Drive
Since the upper IGBT requires a gate voltage higher than the collector voltage, a bootstrap circuit (diode and capacitor) provides the necessary high-side drive voltage.