Doing THD calc

fft_meas.py

@@ -5,7 +5,11 @@ import fft
 
 class fft_meas(object):
 	"""docstring for fft_meas"""
+	# 61000-4-7 says 200ms
+	# 10-cycles for 50Hz
+	# 12-cycles for 60Hz
 	def __init__(self, fs=50e3, tn=0.2):
+
 		self.fs = fs
 		self.ts = 1/fs
 		self.tn = tn
@@ -19,25 +23,94 @@ class fft_meas(object):
 		self.b = 0
 		self.c = 0
 		self.Y_C = 0
+
+		# 61000-4-7: 3.2.3
+		# Upto the 40 Harmonic per 3.3.1 Note 2
+		# Harmonic order
+		self.Y_H = np.zeros(40)
+		# 61000-4-7: 3.2.3
+		# Upto the 40 Harmonic per 3.3.2 Note 2
+		# Grouped Harmonic order
+		self.Y_g = np.zeros(40)
+		# 61000-4-7: 3.2.2 
+		self.h = np.zeros(40)
+
+		self.THD = 0
+		self.THDG = 0
+		
+
 		self.phi = 0
-
+		self.base_freq = 0
-	def step(self, data, time, f_H1, unit):
-
-		if time - self.time > self.ts:
-			self.time = time
-			self.idx += 1
-
-			self.data[self.idx] = data
-
-			if self.idx == self.N-1:
-
-						
-				self.freq , self.a, self.b , self.c, self.Y_C, self.phi = fft.fft(x=self.data, fs=self.fs)
-
-				self.idx = -1
 
 
+	def step(self, y, base_freq, unit):
+
+		self.idx += 1
+
+		self.data[self.idx] = y
+
+		if self.idx == self.N-1:
+
+			self.freq , self.a, self.b , self.c, self.Y_C, self.phi = fft.fft(x=self.data, fs=self.fs)
 			
+			self.calc_Y_H(base_freq)
+			self.calc_THD()
+
+			self.calc_Y_g(base_freq)
+			self.calc_THDG()
+
+
+
+			self.idx = -1
+
+
+	def calc_Y_H(self, base_freq):
+		# 61000-4-7: 3.2.3
+			if np.abs(base_freq-50) < np.abs(base_freq-60):
+				self.base_freq = 50
+			else:
+				self.base_freq = 60			
+
+			if self.base_freq == 50:
+				for k in range(len(self.Y_H)):
+					self.Y_H[k] = self.Y_C[int(10*k)]
+					self.h[k] = self.freq[int(10*k)]
+			elif self.base_freq == 60:
+				for k in range(len(self.Y_H)):
+					self.Y_H[k] = self.Y_C[int(12*k)]
+					self.h[k] = self.freq[int(12*k)]
+
+	def calc_THD(self):
+		# 61000-4-7: 3.3.1
+		self.THD = 0
+		for k in range(2, len(self.Y_H)):
+			self.THD += np.power(self.Y_H[k]/self.Y_H[1],2)
+			self.THD =  np.sqrt(self.THD)
+
+	def calc_Y_g(self, base_freq):
+		# 61000-4-7: 3.2.4
+			if np.abs(base_freq-50) < np.abs(base_freq-60):
+				self.base_freq = 50
+			else:
+				self.base_freq = 60			
+
+			if self.base_freq == 50:
+				for k in range(len(self.Y_g)):
+					self.Y_g[k] = self.Y_C[int(10*k)-1] + self.Y_C[int(10*k)] + self.Y_C[int(10*k)+1]
+					self.h[k] = self.freq[int(10*k)]
+			elif self.base_freq == 60:
+				for k in range(len(self.Y_g)):
+					self.Y_g[k] = self.Y_C[int(12*k)-1] + self.Y_C[int(12*k)] + self.Y_C[int(12*k)+1]
+					self.h[k] = self.freq[int(12*k)]
+
+	def calc_THDG(self):
+		# 61000-4-7: 3.3.1
+		self.THDG = 0
+		for k in range(2, len(self.Y_H)):
+			self.THDG += np.power(self.Y_g[k]/self.Y_g[1],2)
+			self.THDG =  np.sqrt(self.THDG)
+		print(self.THDG)
+		
 	def plot(self):
 		#fs, a, b, c, YC, phi = ftt.fft(Ph1, sample_freq)
 
@@ -47,3 +120,11 @@ class fft_meas(object):
 		plt.title("Simple plot")
 		plt.show()
 		
+	def plot_Y_H(self):
+
+		plt.stem(self.h, self.Y_H, use_line_collection=True)
+		plt.xlabel("Harmonic order h")
+		plt.ylabel("RMS value Y_H,h")
+		plt.title("Harmonic spectrum (IEC 61000-4-7: 3.2.3)")
+		plt.grid(True)
+		plt.show()

fundamental_freq_meas.py

@@ -0,0 +1,51 @@
+import numpy as np
+import matplotlib.pyplot as plt
+
+
+class fundamental_freq_meas(object):
+	"""docstring for fft_meas"""
+	def __init__(self, fs=50e3, tn=10):
+		self.fs = fs
+		self.ts = 1/self.fs
+		self.tn = tn
+		self.time = 0
+		self.y_old = 0
+		self.tn_start_time = 0
+		self.tn_end_time = 0
+		self.zerocross_count = 0
+		# Calculated Frequency
+		self.freq = 50
+
+		self.t_zc = 0
+
+	def step(self, y, zerocross_flag):
+
+		# Integrate time
+		self.time += self.ts
+
+		if zerocross_flag:
+			denom = (y - self.y_old)
+			if denom != 0.0:  # avoid divide-by-zero
+				# linear interpolation to find zero-crossing time
+				frac = -self.y_old / denom
+				self.t_zc = (self.time - self.ts) + frac * self.ts
+
+				# store first crossing time
+				if self.zerocross_count == 0:
+					self.tn_start_time = self.t_zc
+
+				self.zerocross_count += 1
+				self.tn_end_time = self.t_zc  # always keep last crossing time in this window
+
+		# window finished (independent of whether a crossing happened exactly here)
+		if self.time >= self.tn:
+			if self.zerocross_count >= 2 and self.tn_end_time > self.tn_start_time:
+				self.freq = (self.zerocross_count - 1) / (self.tn_end_time - self.tn_start_time)
+
+			# reset window state
+			self.zerocross_count = 0
+			self.tn_start_time = 0.0
+			self.tn_end_time = 0.0
+			self.time -= self.tn  # avoids drift vs. self.time = 0
+
+		self.y_old = y

main.py

@@ -1,7 +1,6 @@
 
 import numpy as np
-import fft_meas
+import measurements
-import zerocross_meas
 
 
 # to do
@@ -12,33 +11,38 @@ import zerocross_meas
 def main():
 	time = 0
 	delta_t = 1e-6
-	t_stop = 1.1
+	t_stop = 1.2
+
+	ADC_sample_frequency = 50e3
+	ADC_sample_period = 1/ADC_sample_frequency
+	ADC_timer = 0
 
 
 
 	amplitude = 1
-	base_freq = 50
+	base_freq = 60
 
+	Meas_ADC = measurements.measurements(fs=ADC_sample_frequency)
 
-	fft_measurements = fft_meas.fft_meas(fs=50e3, tn=0.2)
-	zerocross = zerocross_meas.zerocross_meas(fs=50e3, tn=1)
 
 	for i in range(0, int(t_stop/delta_t)+1):
+
+
 		Ph1 = np.sin(2*np.pi*time*base_freq)
 
 
-		zerocross.step(x=Ph1, time=time)
+		if time - ADC_timer >= ADC_sample_period:
+			ADC_timer += ADC_sample_period
 
-		fft_measurements.step(data=Ph1, time=time, f_H1=zerocross.freq, unit="I")
+			Meas_ADC.Interupt(Ph1)
 		
 
 
 		time += delta_t
 
+	Meas_ADC.print()
+	Meas_ADC.plot()
 
-	zerocross.print()
-	#fft_measurements.plot()
-	
 
 
 

measurements.py

@@ -0,0 +1,58 @@
+import numpy as np
+import matplotlib.pyplot as plt
+
+import IIR_filter
+
+import zerocross_meas
+import fundamental_freq_meas
+import fft_meas
+
+
+class measurements(object):
+	"""docstring for fft_meas"""
+	def __init__(self, fs=50e3):
+		# Sample Frequency
+		self.fs = fs
+		# Sample Period
+		self.ts = 1/self.fs
+
+		# Low Pass Filter
+		# fs = Sample Frequency, fc = LP Cutoff Frequency
+		self.LPfilter = IIR_filter.IIR_1_Order_LP(fs=self.fs, fc=200)
+
+
+
+		# Zero Crossing Algorithem
+		# fs = Sample Frequency, fc = LP Cutoff Frequency
+		self.zerocross = zerocross_meas.zerocross_meas()
+
+		# Fundamental Frequency Algorithem
+		# fs = Sample Frequency, tn = Time Period for calculations
+		self.base_freq = fundamental_freq_meas.fundamental_freq_meas(fs=self.fs, tn=1)
+
+		# FFT Algorithem
+		# fs = Sample Frequency, tn = Time Period for calculations
+		# 61000-4-7 says 200ms
+		# 10-cycles for 50Hz
+		# 12-cycles for 60Hz
+		self.fft = fft_meas.fft_meas(fs=self.fs, tn=0.2)
+
+
+	def Interupt(self, y):
+
+		# Filter Input
+		y_hat = self.LPfilter.step(y)
+		# Zerocross detection (self.zerocross.flag)
+		self.zerocross.detect(y_hat)
+		# Calculate the Fundamental frequency (self.base_freq.freq)
+		self.base_freq.step(y_hat, self.zerocross.flag)
+		# Calculate the FFT of the signal
+		self.fft.step(y, self.base_freq.freq, unit="I")
+
+
+	def print(self):
+		print(self.base_freq.freq)
+
+	def plot(self):
+		self.fft.plot_Y_H()
+	

zerocross_meas.py

@@ -6,35 +6,25 @@ import IIR_filter
 
 class zerocross_meas(object):
 	"""docstring for fft_meas"""
-	def __init__(self, fs=50e3, tn=1):
+	def __init__(self):
-		self.fs = fs
+		
-		self.ts = 1/self.fs
+		# Old value
-		self.tn = tn
-		self.time = 0
-		self.freq = 0
-		self.freq_ts = 0
-		self.y = 0 
 		self.y_old = 0
-		self.idx = 0
-		self.LPfilter = IIR_filter.IIR_1_Order_LP(fs=self.fs, fc=200)
 
-	def step(self, x, time):
+		# Zerocross flag
-
+		self.flag = False
-		if time - self.time > self.ts:
-			self.time = time	
-			self.y = self.LPfilter.step(x)
-
-			if self.y_old < 0 and self.y > 0:
-				self.idx += 1
 
 
-			if time - self.freq_ts > self.tn:
+	def detect(self, y):
-				self.freq = self.idx / self.tn
-				self.freq_ts = time
-				self.idx = 0
 
+		self.flag = 0
+
+		# If positive zerocross is detected
+		if self.y_old < 0 and y > 0:
+			self.flag = True
+
+		self.y_old = y
 
-			self.y_old = self.y
 
 			
 	def print(self):