Three-Phase Full-Wave Controlled Rectifier

🎯 Introduction

This simulation models a three-phase full-wave controlled rectifier using six thyristors (SCRs) in a bridge configuration. It provides excellent controllability through firing angle adjustment, making it ideal for variable speed drives and voltage regulation applications.

🔧 Circuit Operation

The three-phase full-wave controlled bridge rectifier consists of:

• Six Thyristors (SCRs): Two connected to each phase with gate control
• Bridge Configuration: No center-tap transformer required
• Firing Angle Control: Gate pulses delayed by angle α
• Natural Commutation: Each thyristor conducts for 120° per cycle
• Six-Pulse Operation: Six pulses per cycle with controllable output

📐 Key Parameters & Formulas

• Average Output Voltage: V_avg = (3√3/π) × V_m × cos(α)
• Firing Angle Range: 0° ≤ α ≤ 180°
• Conduction Angle: 120° for each thyristor
• Power Factor: PF = cos(φ) × cos(α)
• Form Factor: FF ≈ 1.001 + f(α)
• Ripple Factor: RF ≈ 0.04 + f(α)
• Rectification Efficiency: η ≈ 95% × cos²(α)
• Transformer Utilization Factor: TUF = 0.74 × cos(α)

🔍 Advantages & Disadvantages

Advantages:

• Excellent output voltage control through firing angle
• Bidirectional power flow capability (rectifier/inverter)
• High power capability and efficiency
• No transformer center-tap required
• Suitable for motor drives and industrial applications
• Fast response to control signals
• Regenerative braking capability

Disadvantages:

• Complex firing circuit required
• Higher harmonic content at large firing angles
• Power factor decreases with firing angle
• Requires gate pulse generation circuit
• Commutation overlap at high currents

🎛️ Firing Angle Control

• α = 0°: Maximum output voltage (same as uncontrolled)
• α = 30°: ~86.6% of maximum voltage
• α = 60°: ~50% of maximum voltage
• α = 90°: Zero average output voltage
• α > 90°: Inverter mode operation
• α = 180°: Maximum negative voltage (full inversion)

📊 Analysis Features

• Firing Angle Control: 0° to 180° range with precise control
• Gate Pulse Generation: Synchronized six-pulse firing
• Harmonic Analysis: Characteristic harmonics (5th, 7th, 11th, 13th...)
• Power Quality: THD analysis and power factor calculation
• Thermal Analysis: Six thyristor temperature monitoring
• Load Analysis: Support for R, RL, RC, RLC, and RLE loads

💡 Design Considerations

• Select thyristors with adequate current and voltage ratings
• Design gate drive circuits for reliable triggering
• Use snubber circuits for thyristor protection
• Consider commutation overlap at high currents
• Monitor thermal balance across all six thyristors
• Design for continuous conduction mode
• Implement proper isolation for gate circuits
• Consider EMI/EMC requirements

⚠️ Important Notes

• Each thyristor pair conducts for 120° intervals
• Gate pulses must be synchronized with AC supply
• Commutation is natural (line commutated)
• Power factor decreases with increasing firing angle
• Can operate in both rectifier and inverter modes
• Widely used in DC motor drives and HVDC systems
• Requires careful thermal management