Single-Phase Fully Controlled Converter

§ 01

Introduction

This experiment studies the single-phase fully controlled converter using four thyristors (SCRs) in a bridge configuration. The firing angle α controls the mean DC output voltage continuously from maximum (α = 0°) to zero (α = 180°), enabling precise power regulation.

§ 02

Theory

A fully controlled converter uses thyristors only. With R load: single-quadrant operation (V_o ≥ 0, I_o ≥ 0). With RL load: two-quadrant operation (V_o can be negative, I_o ≥ 0 always).

Single-phase fully controlled bridge circuit — Fig. 1 — Single-phase fully controlled bridge converter circuit diagram.

Voltage and current waveforms — Fig. 2 — Output voltage and current waveforms for different firing angles.

Average Output Voltage

\[V_{out} = \frac{2V_s}{\pi}\cos\alpha,\quad I_{avg} = \frac{V_{avg}}{R}\]

where \(V_s\) is the RMS input voltage. At \(\alpha = 0\): \(V_{out} = 2V_s/\pi\) (maximum). At \(\alpha = 90\deg\): \(V_{out} = 0\). For \(V_s = 35.35\text{ V}\): \(V_{out,max} = 31.83\text{ V}\).

Firing Sequence: Positive half-cycle: SCRs T1 & T2 triggered at ωt = α. Negative half-cycle: SCRs T3 & T4 triggered at ωt = π + α. Current flows in the same direction through the load in both half-cycles.

§ 03

Simulation — R Load (Problem 1)

Problem Statement

Implement the 1-phase fully controlled full-wave rectifier with R = 12.5 Ω. Input: 50 V peak (35.35 V RMS), 50 Hz. Observe output waveforms at firing angles 0°, 45°, 90°, 135°.

Simulink R-load controlled converter — Fig. 3 — Simulink model: fully controlled bridge with R load and pulse generator.

Waveforms at alpha=45 degrees — Fig. 4 — Simulated waveforms at α = 45° (R load).

§ 04

Simulation — RL Load (Problem 2)

Problem Statement

Add L = 6 mH in series with R = 12.5 Ω. Observe the effect of inductance on output waveforms at the same firing angles.

Simulink RL-load controlled converter — Fig. 5 — Simulink model: fully controlled bridge with RL load.

§ 05

Hardware — R Load

Hardware circuit R-load controlled converter — Fig. 6 — Hardware wiring: single-phase fully controlled converter with R load (12.5 Ω).

Connect circuit as in Fig. 6 (R = 12.5 Ω). Switch ON 3φ supply MCB.
Switch ON POWER MODULE and SCR–Diode module MCBs. Set voltage to 35.35 V RMS.
Switch ON driver power switch. Connect CRO probes across R load.
Vary firing angle and record results per the observation table below.

§ 06

Hardware — RL Load

Hardware circuit RL-load controlled converter — Fig. 7 — Hardware wiring: single-phase fully controlled converter with RL load (12.5 Ω, 6 mH).

Connect circuit as in Fig. 7 (R = 12.5 Ω, L = 6 mH). Repeat steps 1–4 from R Load procedure.
Connect CRO probes across both R and L. Note the effect of inductance on firing angle range.

§ 07

Results

Required waveforms to attach: Input Voltage, Input Current, Output Voltage, Output Current, Thyristor Voltage, Thyristor Current (Simulink at α = 45°; DSO at α = 45°).

I) R-Load — Simulation Observation Table

S.No	Firing Angle (time)	Firing Angle (degrees)
1.	0 ms	0°
2.	2.5 ms	45°
3.	5 ms	90°
4.	7.5 ms	135°

I) R-Load — Hardware Observation Table

S.No	Firing Angle (time)	Firing Angle (degrees)
1.	0 ms	0°
2.	2.5 ms	45°
3.	5 ms	90°
4.	7.5 ms	135°

II) RL-Load — Simulation Observation Table

S.No	Firing Angle (time)	Firing Angle (degrees)
1.	0 ms	0°
2.	2.5 ms	45°
3.	5 ms	90°
4.	7.5 ms	135°

II) RL-Load — Hardware Observation Table

S.No	Firing Angle (time)	Firing Angle (degrees)
1.	0 ms	0°
2.	2.5 ms	45°
3.	5 ms	90°
4.	7.5 ms	135°