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Total harmonic distortion (THD) is a power-quality metric that quantifies the harmonic content present in an electrical voltage or current waveform relative to its fundamental component ^[1]. For a periodic waveform, THD is defined as the ratio of the root-sum-square of the amplitudes of all harmonic components—excluding the fundamental—to the amplitude of the fundamental component, usually expressed as a percentage ^[2]. The harmonics considered are integer multiples of the fundamental power frequency and arise from nonlinear loads and power-electronic converters ^[3]. THD may be evaluated for voltage (THD_V) or current (THD_I); a higher THD indicates a waveform that deviates more strongly from a pure sinusoid ^[2]. THD is distinct from total demand distortion (TDD), which normalizes harmonic current to the maximum demand current rather than to the fundamental ^[1]. Limits on harmonic distortion at the point of common coupling are established in power-quality standards, and THD serves as the primary figure of merit for waveform quality in such assessments ^[3].