Understanding Single-Phase PWM Sine-Triangle Inverters

schema February 24, 2013

Learn how single-phase PWM inverters work using sine-triangle modulation. Explore power circuits, control strategies, output waveforms, and harmonic analysis for efficient AC drive systems.

Understanding Single-Phase PWM Sine-Triangle Inverters

How Single-Phase PWM Inverters Work (Sine-Triangle Modulation)

Pulse Width Modulation (PWM) inverters are broadly utilized in motor drives, UPS structures, and renewable strength packages. The sine-triangle modulation technique is a popular technique for generating extraordinary AC output with minimum harmonics.

1. Power Circuit Structure

A basic single-phase PWM inverter consists of:

DC Source (battery or rectified AC)
Four Switching Devices (IGBTs/MOSFETs in an H-bridge)
Output LC Filter (to smooth the PWM waveform)
Load (inductive/resistive, e.g., motor)

2. Control Strategy: Sine-Triangle PWM

The modulation process involves two signals:

Sinusoidal Reference (VREF)
- Sets the desired output frequency & amplitude.
- Example: 50Hz sine wave for grid applications.
High-Frequency Triangular Carrier (VCAR)
- Typically 1-20 kHz (much higher than VREF).
- Determines switching frequency.

The comparator generates PWM pulses by comparing VREF and VCAR:

When VREF > VCAR → Upper switch ON
When VREF < VCAR → Lower switch ON

3. Output Voltage & Current Waveforms

The PWM output is a high-frequency switched voltage.
After filtering, the load voltage is nearly sinusoidal.
For inductive loads (motors), the current lags but remains sinusoidal due to inductance smoothing.

4. Harmonic Spectrum Analysis

Fundamental component matches VREF (adjustable in frequency/amplitude).
Harmonics are clustered around the carrier frequency (e.g., 10kHz).
Since harmonics are high-frequency, they are easily filtered with small LC components.

5. Advantages & Applications

✔ Variable Frequency & Voltage → Ideal for motor speed control (MAS drives).
✔ Low Harmonic Distortion → Clean output with minimal filtering.
✔ High Efficiency → Reduced switching losses compared to square-wave inverters.

Conclusion

Sine-triangle PWM inverters provide precise, efficient AC power conversion with adjustable frequency and amplitude. This method is essential in variable-frequency drives (VFDs) and renewable energy systems.

Want to simulate this? Try SPICE models or microcontroller-based PWM generators!