Power Electronics (Electrical)

Power Electronic Devices:

• Diode: unidirectional conduction.
• SCR (Thyristor): four-layer, gate-triggered.
• DIAC: bidirectional, no gate.
• TRIAC: AC control (bidirectional).
• MOSFET: fast switching, high frequency.
• IGBT: high power + fast switching (best of both worlds).
• GTO (Gate Turn-Off): can turn off via gate.

SCR characteristics:

• Forward blocking until gate triggered.
• Latching current: min current to keep on.
• Holding current: min to remain on.

Converters:

1. Rectifiers (AC → DC):

• Half-wave: 1 diode.
• Full-wave: 2 or 4 diodes (bridge).
• Three-phase: uses 6 diodes; smoother DC.

2. Inverters (DC → AC):

• VSI (Voltage Source Inverter).
• CSI (Current Source Inverter).
• Used in UPS, solar power.

3. Choppers (DC → DC):

• Step-down (buck).
• Step-up (boost).
• Buck-boost.

4. AC Voltage Controllers (AC → AC):

• TRIAC-based.
• Used for: light dimmers, motor speed control.

Cycloconverters:

• AC → AC at different frequency.

Applications:

• VFD (Variable Frequency Drive): for motor speed control.
• UPS: uninterrupted power supply.
• Solar inverter.
• HVDC transmission.
• Locomotive traction: modern WAG-9, WAP-7 use IGBT-based converters.

RRB JE focus: SCR vs MOSFET, basic rectifier types, applications in locomotives.