Initial

fft.py

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+import numpy as np
+
+
+def fft(x, fs, X_nom=None, epsilon=None):
+
+	# Implementation from IEC 61000-4-7:2002/AMD1:2008
+
+
+	# Data length
+	N = len(x)
+	# Number of positive-frequency bins
+	K = int(np.floor(N/2))
+	# Frequency axis (0 .. fs/2)
+	#freq = np.linspace(start=0, stop=fs/2, num=K+1, endpoint=True)
+	freq = np.arange(K + 1) * fs / N
+
+	# allocate
+	a = np.zeros(K + 1)
+	b = np.zeros(K + 1)
+	c = np.zeros(K + 1)
+	Y_C = np.zeros(K + 1)
+	phi = np.zeros(K + 1)
+
+	n = np.arange(N)
+
+	# DC
+	c[0] = np.mean(x)         # c0 per IEC
+	a[0] = 2 * c[0]           # not really used; just for completeness
+	b[0] = 0.0
+
+	# k = 1..K
+	for k in range(1, K+1):
+		angle = 2 * np.pi * k * n / N
+		a[k] = (2/N) * np.sum(x * np.cos(angle))
+		b[k] = (2/N) * np.sum(x * np.sin(angle))
+
+		# Nyquist (if N even): do NOT apply the 2/N doubling
+		if (N % 2 == 0) and (k == K):
+			a[k] *= 0.5
+			b[k] *= 0.5
+		c[k] = np.sqrt(a[k]*a[k] + b[k]*b[k])
+
+		# RMS value calculated in Eq.2.
+		Y_C[k] = c[k] / np.sqrt(2)
+
+
+		# Phase: apply dead-band if provided, else always compute
+		if (X_nom is not None) and (epsilon is not None):
+			if (np.abs(a[k]) <= epsilon * X_nom) and (np.abs(b[k]) <= epsilon * X_nom):
+				phi[k] = 0.0
+				continue
+
+		# IEC quadrant handling (equivalent to the piecewise definition)
+		phi[k] = np.arctan2(a[k], b[k])
+
+
+
+	return freq, a, b, c, Y_C, phi