PWM-Based AC-AC Converters

Implementation Process of PWM-Based AC/AC Converter Using IGBT

Introduction

AC power control is a widely discussed topic in the field of power electronics. The conventional approach to controlling AC power involves adjusting the voltage magnitude using firing pulses. However, the pulse width modulation (PWM) technique offers a more advanced and efficient method. Despite its advantages, implementing PWM in practical applications poses challenges due to the limitations of semiconductor switches.

Semiconductor switches are integral to every power electronics circuit, but not all switches are suitable for all applications. Their suitability depends on their specific characteristics, which must be carefully considered during design and implementation.

Limitation of IGBT

The Insulated Gate Bipolar Transistor (IGBT) is one of the most popular semiconductor switches in power electronics applications. However, for AC applications, IGBTs can sometimes create issues due to the presence of an anti-parallel diode between the collector and emitter.

Modification

To address this limitation and enable the design of an effective AC/AC controller, a forward diode needs to be connected in series with the IGBT. This modification ensures proper functionality by mitigating the effect of the anti-parallel diode. The modified circuit of the AC/AC controller incorporates this additional diode to resolve the issue.

This modification makes the circuit suitable for practical use. Without it, the output would remain the same as the input because the current would flow through the anti-parallel diode, bypassing control. By adding the forward diode, the IGBT operates as intended, allowing for precise control. With this modification, the PWM technique can be effectively implemented in the circuit.

Theoretical Output:

The PWM output of the circuit is expected to produce a chopped AC waveform, as illustrated in the following picture. The duty cycle and frequency of the PWM can be adjusted to control the output voltage. A lower duty cycle results in a lower output voltage, providing precise control over the system.

Steps for Design and Implementation

If you're planning to develop a power electronics converter circuit, the following steps will guide you through the process:

1. Schematic Simulation: Use MATLAB/SIMULINK to simulate the schematic, understand the circuit’s characteristics, and analyze the switching patterns.
2. Component Selection: Choose the appropriate components and create a hardware schematic in Proteus.
3. Microcontroller Programming: Write and test the code for AVR/Arduino to ensure proper functionality.
4. PCB Design: Design the printed circuit board (PCB) based on the schematic and layout requirements.
5. PCB Manufacturing and Assembly: Manufacture the PCB and perform soldering to assemble the components.
6. Practical Testing: Test the circuit in a real-world environment to verify its performance.

Proteus Design:

To develop the circuit, I followed the steps mentioned above. The PCB design was created using the Proteus 8 platform. The 3D view of the AC/AC controller is shown below.

Output Waveforms:

The circuit was thoroughly tested in the laboratory. The chopped AC output waveform, as observed on the oscilloscope, closely matched the theoretical expectations. The waveform is shown in the figure below.

This prototype was tested for 220V AC at RUET Electronics Lab, Bangladesh.

You can see the prototype test in the following YouTube link and access the relevant resources to reproduce the circuit:

Resources:

• Proteus PCB, Simulation file, Arduino Code : Github
• Video: YouTube