Technology / IGBT Architecture
Inside the IGBT Inverter — How It Works
IGBT technology is what separates an Emergency Rescue Device from a conventional UPS or ARD system. Understanding how Insulated Gate Bipolar Transistors work explains why ERDs can switch in 3ms, produce pure sine wave output, and handle the brutal demands of a three-phase lift motor.
What Is an IGBT?
The Insulated Gate Bipolar Transistor (IGBT) is a three-terminal power semiconductor device. It combines the easy gate-drive characteristics of a MOSFET with the high-current, low-saturation-voltage output of a bipolar junction transistor (BJT). The result is a switch that can handle high voltages and currents while being controlled by a tiny gate signal — with switching times measured in microseconds.
In a lift ERD, an array of IGBTs forms the inverter bridge. This bridge converts the DC voltage from the battery bank into a three-phase AC output that precisely matches the motor’s requirements — same voltage, same frequency (50Hz), same waveform (pure sine).
| Characteristic | Relay/Contactor | MOSFET | IGBT |
|---|---|---|---|
| Switching Time | 10–50ms | 20–200ns | 0.5–5μs |
| High-Voltage Handling | Excellent | Poor (>600V) | Excellent (up to 6.5kV) |
| High-Current Handling | Excellent | Limited | Excellent |
| Gate Drive Power | High (coil) | Negligible | Low |
| Sine Wave Output | No | Yes (low power) | Yes (high power) |
| Conduction Loss | Very low | Low | Low |
| Cost per kW | Low | Low | Medium |
Comparison of switching technologies used in lift power electronics
How the IGBT Bridge Generates 3-Phase Output
A standard three-phase inverter uses six IGBTs arranged in three half-bridge pairs — one pair per output phase (L1, L2, L3). The controller (typically a DSP or microcontroller) fires these IGBTs in a precise sequence using Pulse Width Modulation (PWM).
PWM works by switching the IGBT on and off at a high frequency (typically 8–20kHz) with a varying duty cycle. When averaged over time, this high-frequency switching produces an effective output voltage that follows a sine wave. The higher the PWM frequency, the smoother the sine wave and the smaller the output filter required.
For a lift motor, the output must match the grid exactly: 415V line-to-line, 50.0Hz, with balanced three-phase output. The ERD’s controller continuously monitors the output voltage and frequency and adjusts the PWM duty cycle in real time to maintain this.
The Pre-Positioned Output Architecture
The key to 3ms switching is not just fast IGBTs — it is the system architecture. In a conventional standby UPS, the inverter only starts when the grid fails. Start-up delay alone can be 5–15ms.
An ERD uses an online or double-conversion architecture. The IGBT inverter runs continuously, generating its output at all times. In normal operation, the grid is powering the lift through the ERD’s bypass path while the inverter simultaneously charges the batteries. The inverter output is always live and always phase-synchronised with the grid.
When the grid fails, the controller simply switches the output from the bypass path to the inverter output. This switch is a logic-level command to the IGBT driver — it takes microseconds. The total time from grid failure detection to full inverter output is under 3ms.
IGBT vs MOSFET — Why Not MOSFET for Lifts?
MOSFETs are excellent for low-voltage, high-frequency switching (as in laptop chargers and small UPS systems). Above 200–300V, MOSFET on-resistance rises sharply, causing significant conduction losses. A 10kVA lift ERD operating from a 400V DC bus would require expensive, high-current MOSFETs in parallel — a design that is neither practical nor reliable.
IGBTs have a nearly flat on-state voltage drop regardless of current, making them ideal for high-power, medium-frequency applications. A single IGBT module rated at 600V, 150A can handle the full output current of a 10kVA ERD with significant headroom. Larger ERDs (15kVA, 20kVA) simply use higher-rated IGBT modules.
Su-vastika’s ERD product range uses IGBT technology across all KVA ratings — from the 10kVA unit for small residential lifts to 30kVA+ for commercial applications. See the Su-vastika Lift Inverter/ERD product page for full specifications.
Output Quality: Why ERD Beats Grid Quality
India’s grid supply routinely suffers from voltage fluctuations (±15% is common), frequency deviations (49.5–50.2Hz), harmonic distortion from industrial loads, and transient voltage spikes. All of these stress the lift motor and VFD controller.
An ERD decouples the lift motor from the grid entirely. The IGBT inverter provides a regulated output regardless of what the grid is doing. Motor terminal voltage stays within ±0.5%. Frequency is exactly 50.0Hz. Total harmonic distortion (THD) is typically under 3%, compared to 8–12% THD on a typical urban grid in India.
The practical effect: reduced motor temperature, longer VFD capacitor life, fewer nuisance trips, and significantly lower maintenance costs. Buildings that run ERDs consistently report 70–80% reduction in lift-related maintenance call-outs.
Size Your ERD
The right IGBT inverter size depends on your motor’s KW rating, lift speed, and desired backup duration. Use our calculator to find the correct KVA.