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![Operating Principle
Phase Control Method:
• Thyristor turns ON at specific point (firing angle α) during half-cycle
• Turns OFF when voltage naturally crosses zero
• Varying firing angle α controls output voltage
RMS output voltage: V = V × √[(π - α + ½sin(2α))/π]](https://image.slidesharecdn.com/threephaseaccontroller-251218104201-10558542/85/Three-Phase-AC-Controller-by-using-thyristor-pptx-4-320.jpg)
![RMS Output Voltage Formula
V = V √[(π - α + ½sin(2α)) / (2π)]
Where:
V = Peak supply voltage
• α = Firing angle (delay angle) in radians
• Range: 0 ≤ α ≤ π](https://image.slidesharecdn.com/threephaseaccontroller-251218104201-10558542/85/Three-Phase-AC-Controller-by-using-thyristor-pptx-23-320.jpg)
Three Phase AC Controller by using thyristor .pptx
- 1. Three-Phase AC Controller PowerElectronics & Control Systems Thyristor-based AC Voltage Regulation Power Systems Engineering • 2025
- 2. What is aThree-Phase AC Controller? AC-to-AC converter that regulates RMS voltage and frequency Uses thyristors (SCRs) or TRIACs as power switches • Converts fixed AC supply into variable AC output • Enables voltage control without changing frequency • Critical for industrial motor speed control applications
- 3. Main Components Power Devices Thyristors(SCR) or TRIACs for switching Gate Circuit Controls firing angle of power devices Load Impedance Resistive or inductive load
- 4. Operating Principle Phase ControlMethod: • Thyristor turns ON at specific point (firing angle α) during half-cycle • Turns OFF when voltage naturally crosses zero • Varying firing angle α controls output voltage RMS output voltage: V = V × √[(π - α + ½sin(2α))/π]
- 5. Three-Phase Controller Topologies(Part 1) Star (Y) Connection: • Four-wire system: R, Y, B phases + neutral • Each phase controlled independently • Simple analysis using single-phase principles • Neutral current contains triplet harmonics
- 6. Three-Phase Controller Topologies(Part 2) Delta (Δ) Connection: • Three-wire system (no neutral required) • Each controller placed in line between phases • Back-to-back thyristor pair per phase • More compact design, no triplet harmonics
- 7. Back-to-Back Thyristor Pair Onethyristor conducts positive half-cycle, other conducts negative half-cycle
- 8. Control Methods Symmetrical Both thyristorshave same firing angle α Asymmetrical Different firing angles or diode replacement
- 9. Firing Circuits (Part1) R Firing Circuit: • Simplest method using variable resistance R • AC supply given to gate terminal • Firing angle range: 0° to 90° • Limited control range but low cost
- 10. Firing Circuits (Part2) RC Firing Circuit: • Capacitor charges through variable resistor R • Two types: Half-wave and Full-wave RC • Greater control range (0° to 180°) • More complex but better performance
- 11. Firing Angle &Output Waveforms Output voltage varies with firing angle α
- 12. Load Characteristics (Part1) Resistive Load (R): • Current and voltage waveforms are in phase • Load impedance: Z = R (constant) • Power factor: PF = 1 (unity) • Examples: heating elements, incandescent lights
- 13. Load Characteristics (Part2) Inductive Load (RL): • Current lags voltage by angle φ Load impedance: Z = √(R² + X²) • Power factor: PF = cos(φ) < 1 • Examples: motors, transformers, inductors
- 14. Harmonic Generation Phase ControlIssues: • Non-sinusoidal output generates harmonics • Odd harmonics: 3rd, 5th, 7th, 9th... • Harmonic content increases as firing angle increases • Requires filtering for EMI reduction
- 15. Power Factor Considerations KeyObservations: • PF = 1.0 at full output (100% voltage) • PF decreases as output voltage reduces • At 50% output: PF ≈ 0.5 (phase angle control) • Affects apparent power and current requirements
- 16. Industrial Applications (Part1) AC Motor Speed Control: Three-phase induction motor drives Heating: Industrial furnaces and heater control Soft Starters: Reduced inrush current on motor startup
- 17. Three-Phase Motor SpeedControl Variable AC output enables smooth motor speed control
- 18. Firing Methods Comparison ZeroCrossover (Burst Pulse): Thyristors switch ON/OFF only at zero voltage crossover points Phase Angle Firing: Thyristors switch ON at any point during half-cycle for smooth control
- 19. Advantages & Disadvantages Advantages •High efficiency • Fast response • Simple design • Compact size Disadvantages • Harmonic distortion • Poor power factor • EMI generation • Heat dissipation
- 20. Design Considerations Thyristor Rating:Peak inverse voltage, average current, power dissipation Heat Management: Proper cooling and thermal design Snubber Circuits: Protect from voltage spikes during switching Gate Drive: Adequate gate current and pulse width
- 21. Three-Phase Star ACVoltage Controller Three independent single-phase controllers in Y-configuration
- 22. Three-Phase Delta ACVoltage Controller Back-to-back thyristors in line connections between phases
- 23. RMS Output VoltageFormula V = V √[(π - α + ½sin(2α)) / (2π)] Where: V = Peak supply voltage • α = Firing angle (delay angle) in radians • Range: 0 ≤ α ≤ π
- 24. MATLAB/Simulink Simulation Key SimulationSteps: • Model three-phase AC source (3 × 120° phase shift) • Implement thyristor gate logic with firing angle control • Measure output voltage and current waveforms • Analyze harmonics using FFT • Visualize power factor variation with load
- 25. Practical Implementation Tips Useoptocoupler isolation for gate drive circuit Add snubber RC circuits across thyristors for spike protection Implement feedback control for precise voltage regulation Consider filtering to reduce harmonic distortion Monitor thyristor temperature for reliable operation
- 26. Key Takeaways Three-phase ACcontrollers are essential for industrial power control Thyristor-based phase control enables efficient voltage regulation Understanding firing circuits, topologies, and harmonic effects is crucial for design
- 27. Thank You! Questions? Three-Phase ACController Presentation • Power Electronics