Power Electronics Application Guide: Rectifiers, Inverters, and Converters
A guide to power electronics applications in industrial projects. Covers rectifiers, inverters, converters, harmonic mitigation, and selection criteria.
Power Electronics Basics
Power electronics converts electrical power from one form to another (AC to DC, DC to AC, DC to DC, AC to AC).
Key devices: Diodes, thyristors (SCR), MOSFETs, IGBTs, GTOs.
Applications: VFD, UPS, solar inverter, EV charger, HVDC transmission, flexible AC transmission (FACTS).
Rectifiers (AC to DC)
Uncontrolled rectifier: Uses diodes. Simple, cheap, but output voltage fixed (depends on AC input).
Controlled rectifier: Uses thyristors. Output voltage adjustable (by firing angle control).
Applications: DC motor drives, battery charging, electroplating, HVDC transmission.
Issue: Generates harmonics. Requires harmonic filter (passive or active).
Inverters (DC to AC)
Types: Voltage source inverter (VSI), current source inverter (CSI). VSI more common.
PWM (Pulse Width Modulation): Controls output voltage and frequency. Reduces harmonics.
Applications: VFD, UPS, solar inverter, emergency power system.
Selection: Rating (kVA), input voltage, output voltage, efficiency, harmonic distortion (THDi < 5%).
Harmonic Mitigation
Problem: Power electronics generates harmonics (non-linear loads). Harmonics cause overheating, equipment malfunction, power quality issues.
Standards: IEEE 519 (limits harmonic distortion at PCC). THDi < 5% for large loads.
Mitigation methods: 1. Add line reactor (3-5% impedance). 2. Use 12-pulse or 18-pulse rectifier. 3. Active harmonic filter (AHF). 4. Detuned capacitor bank.
Selection Criteria
1. Power rating: kVA or kW (consider future expansion).
2. Input/output voltage: Match supply and load.
3. Efficiency: >95% for modern devices.
4. Harmonic distortion: THDi < 5% (IEEE 519 compliant).
5. Protection: Overload, short circuit, overvoltage, overtemperature.
6. Communication: Modbus, Profibus, Ethernet/IP for integration.