TRIAC AC-AC Controller | Dr. Mithun Mondal

§ 01

Introduction

This experiment studies the single-phase phase-angle controlled AC-AC voltage converter using a TRIAC. The TRIAC conducts on both polarities of the AC supply, enabling bidirectional power control. Applications include light dimmers, motor speed control, and heating element regulation.

§ 02

Theory

AC-to-AC voltage converters regulate output voltage by allowing portions of the input sinusoid to reach the load while blocking the rest. They are called Phase Angle Controlled (PAC) AC-AC converters or AC choppers. The TRIAC acts on both polarities, making it the natural choice for bidirectional control.

R Load Waveforms

Output voltage follows input sinusoid from α to π, and π+α to 2π. No reactive energy storage.

RL Load Waveforms

Inductive load extends conduction beyond voltage zero-crossing. The minimum firing angle is limited by load power factor angle φ.

RMS Output Voltage — R Load

\[V_{o,rms} = V_s\sqrt{\frac{1}{\pi}\left[(\pi - \alpha) + \frac{\sin 2\alpha}{2}\right]}\]

where \(V_s\) = RMS input voltage, α = firing angle. At α = 0: \(V_{o,rms} = V_s\) (full voltage). At α = 180°: \(V_{o,rms} = 0\).

TRIAC waveforms R load — Fig. 3 — Input/output waveforms with R load at various firing angles.

TRIAC waveforms RL load — Fig. 4 — Input/output waveforms with RL load — note extended conduction.

§ 03

Simulation — R Load

Problem 1

Implement the 1-phase phase-controlled bidirectional AC-AC controller with R = 12.5 Ω. Input: 50 V peak (35.35 V RMS), 50 Hz. Observe output voltage waveforms at α = 0°, 45°, 90°, 120°.

TRIAC R-load Simulink model — Fig. 5 — Simulink model: TRIAC AC-AC controller with R load.

TRIAC R-load simulated waveforms — Fig. 6 — Simulated waveforms: input voltage and chopped output voltage (R load).

§ 04

Simulation — RL Load

Problem 2

Implement with R = 12.5 Ω, L = 6 mH. Observe changes in output waveform — note the extended conduction due to inductive load.

TRIAC RL-load Simulink model — Fig. 7 — Simulink model: TRIAC AC-AC controller with RL load.

TRIAC RL-load simulated waveforms — Fig. 8 — Simulated waveforms: extended conduction with RL load.

§ 05

Hardware — R Load

Hardware TRIAC R-load circuit — Fig. 9 — Hardware wiring: TRIAC AC-AC controller with R = 12.5 Ω.

Connect circuit as in Fig. 9 (R = 12.5 Ω). Switch ON 3φ supply and POWER MODULE MCBs.
Switch ON SCR-Diode Power Module MCB. Increase voltage to 35.35 V RMS.
Switch ON driver power switch. Connect CRO probes across R load.
Vary firing angle and record RMS output voltage at each setting.

§ 06

Hardware — RL Load

Hardware TRIAC RL-load circuit — Fig. 10 — Hardware wiring: TRIAC AC-AC controller with RL load (12.5 Ω, 6 mH).

Connect circuit as in Fig. 10 (R = 12.5 Ω, L = 6 mH). Repeat hardware steps 1–4 from R-load procedure.
Note minimum firing angle limited by load power factor angle φ = arctan(ωL/R).

§ 07

Results

I) R-Load — Simulation

S.No	Firing Angle (time)	Firing Angle (degrees)
1.	0 ms	0°
2.	2.5 ms	45°
3.	5 ms	90°
4.	6.66 ms	120°

I) R-Load — Hardware

S.No	Firing Angle (time)	Firing Angle (degrees)
1.	0 ms	0°
2.	2.5 ms	45°
3.	5 ms	90°
4.	6.66 ms	120°

II) RL-Load — Simulation

S.No	Firing Angle (time)	Firing Angle (degrees)
1.	0 ms	0°
2.	2.5 ms	45°
3.	5 ms	90°
4.	6.66 ms	120°

II) RL-Load — Hardware

S.No	Firing Angle (time)	Firing Angle (degrees)
1.	0 ms	0°
2.	2.5 ms	45°
3.	5 ms	90°
4.	6.66 ms	120°