Problem

• Grid-forming inverters must synthesize a sinusoidal AC voltage using discrete semiconductor switching, unlike synchronous machines which produce a natural sinusoid through rotation

• Simple switching waveforms (e.g., square waves) introduce significant harmonic distortion, which degrades power quality

• The design challenge becomes how to approximate a sine wave while controlling harmonic content and switching losses

Why it matters

• Harmonics cause heating, electromagnetic interference, and additional filtering requirements, especially in inverter-dominated power systems

• Switching strategies determine the trade-off between waveform quality and switching losses, which becomes critical in both small inverters and large BESS converters

• Understanding harmonic generation enables engineers to design waveforms intentionally rather than relying on trial-and-error modulation schemes

Approach

• Start with waveform symmetry (odd and half-wave symmetry) to ensure DC and even harmonics are automatically eliminated, simplifying harmonic control

• Use Fourier decomposition to express inverter output voltage as a sum of sinusoidal components and identify how switching patterns influence harmonic amplitudes

• Examine modulation strategies such as sinusoidal PWM (SPWM) that approximate a sine wave by comparing a sinusoidal reference with a high-frequency carrier.

Key Insight

• SPWM improves waveform quality by pushing harmonics to high frequencies, allowing filters to remove them more easily

• However, this comes at the cost of very high switching frequency and increased switching losses

• An alternative perspective is to treat waveform synthesis as a harmonic optimisation problem rather than a modulation problem

Contribution

My current focus is using a H-bridge inverter as a practical way to stress and probe the limits of different waveform synthesis methods

• Intentionally pushing simple switching strategies (square wave, SPWM, etc.) to observe where harmonic distortion, switching losses, or filtering requirements start to break down

• Exploring Selective Harmonic Elimination (SHE) implemented on a STM32 as a contrasting approach to see whether targeted harmonic cancellation can extend performance before those limits appear

• Using this process as a hands-on way to understand how switching patterns, Fourier harmonics, and inverter constraints interact when a system is pushed close to its practical limits