EV-06 — Inverter / Power Electronics

ASSUMPTION — This lesson introduces inverter architecture at an engineering level. A specific model’s semiconductor type is not presented as fact without official disclosure.

1. What Is an Inverter?

The inverter is the power-electronics unit that converts the battery’s DC into the variable-frequency AC the electric machine needs. Motor speed and torque are continuously controlled through it.

FACT — By varying the inverter’s output frequency and magnitude, motor speed and torque are set; this replaces the gear-shifting logic of a conventional transmission.

2. DC Link and Switching

• DC link — the DC bus between the battery and the switching bridge; a capacitor damps voltage ripple.
• 3-phase bridge — six semiconductor switches (three half-bridges) produce the U/V/W phases (see diagram).

3. Semiconductor Types

Switch	Trait
MOSFET	Low loss, high switching speed; good at low/medium voltage
IGBT	High voltage/current; low conduction loss, slower switching
SiC MOSFET	High voltage + high frequency; low switching loss

FACT — SiC (silicon carbide) switches fast at high voltage, giving an efficiency advantage in 800V-class systems, but at higher cost.

4. Gate Driver and PWM

• Gate driver — turns the control signal into the switch’s gate-drive voltage.
• PWM (Pulse Width Modulation) — varies the on/off duty of the switches to control average output voltage and frequency.

5. Losses

• Conduction loss — from current through the switch (I²R / Vce·I).
• Switching loss — from the voltage×current overlap at each turn-on/off; grows with frequency.

6. 650V vs 800V

FACT — At the same power, higher voltage means lower current, reducing conduction (I²R) loss and cable cross-section. But insulation, creepage/clearance, component cost, safety, and EMI increase.

7. FAQ

Why is SiC advantageous at 800V?

FACT — SiC can switch fast with low loss at high voltage, giving an efficiency gain in 800V systems.

What does the DC-link capacitor do?

FACT — It damps switching-induced voltage ripple and provides an energy store for the switches.

8. Summary

• The inverter converts DC to variable-frequency AC.
• A 3-phase bridge produces U/V/W with six switches.
• SiC offers an efficiency advantage at 800V; IGBT is common at high current.
• Losses are conduction + switching.

9. Sources and Verification Note

Semiconductor/topology knowledge is established textbook/IEEE material; no model-specific claim is made.

• IEEE, DOE AFDC — power electronics and EV inverters.

Next Lesson

• EV-07 — Electric Drive Control (FOC): Id/Iq, Clarke/Park transforms, and SVPWM.