Maxim Integrated 78M6631 - Manual (Page 11)

UG_6631_078 78M6631 Firmware Description Document
Rev 2 11
2.2.5 Voltage and Current Harmonics and Fundamental Measurement
The 78M6631 firmware allows measurement of the harmonic and fundamental components. To enable
the harmonics and fundamental measurements bit 5 of the command register must be set to 1.
Harmonic voltage (Vharm) and current (Iharm) are calculated with the quadratic subtraction of the
Fundamental results from the RMS results (the square root of RMS squared minus Fundamental
squared).
Figure 6 shows the harmonic and fundamental components.
SINE(t)
VA1
X
X
COSINE(t)
SINE(t)
IA1
X
X
COSINE(t)
VSINE_A
VCOS_A
ISINE_A
ICOS_A
Vfund C
Ifund C
Vrms A
Vharm C
Irms A
Iharm C
N
N
N
N
∑ N-1
n=0
∑
N-1
n=0
∑
N-1
n=0
∑
N-1
n=0
PHASE C
X 2 + Y 2
X
Y
X 2 + Y 2
X
Y
V harm B
X 2 - YI 2
X
YI
X 2 - YI 2
X
YI
SINE(t)
VA1
X
X
COSINE(t)
SINE(t)
IA1
X
X
COSINE(t)
VSINE_A
VCOS_A
ISINE_A
ICOS_A
Vfund B
Ifund B
Vrms A
Vharm B
Irms A
Iharm B
N
N
N
N
∑
N-1
n=0
∑
N-1
n=0
∑
N-1
n=0
∑ N-1
n=0
PHASE B
X 2 + Y 2
X
Y
X 2 + Y 2
X
Y
X 2 - YI 2
X
YI
X 2 - YI 2
X
YI
SINE(t)
VA1
X
X
COSINE(t)
SINE(t)
IA1
X
X
COSINE(t)
VSINE_A
VCOS_A
ISINE_A
ICOS_A
Vfund A
Ifund A
Vrms A
VharmA
Irms A
Iharm A
N
N
N
N
∑
N-1
n=0
∑
N-1
n=0
∑
N-1
n=0
∑
N-1
n=0
PHASE A
X 2 + Y 2
X
Y
X 2 + Y 2
X
Y
X 2 - YI 2
X
YI
X 2 - YI 2
X
YI
Figure 6. Voltage and Current Harmonics and Fundamental Measurements
2.2.6 Power Harmonics and Fundamental Measurement
Harmonic Power (Pharm) is calculated by subtracting Fundamental Power (Pfund) from total active
power (Watts).
Quadrature Harmonic Power (Qhram) is calculated by subtracting Fundamental Quadrature Power
(Qfund) from Total Reactive Power (VARs).
SINE(t)
VC1
X
X
COSINE(t)
SINE(t)
IC1
X
X
COSINE(t)
VSINE_C
VCOS_C
ISINE_C
ICOS_C
Complex
Multiply
Complex
Conjugate
QfunC
PfunC
PharmC
∑
N-1
n=0
∑
N-1
n=0
∑
N-1
n=0
∑
N-1
n=0
WATT C
PHASE C
SINE(t)
VB1
X
X
COSINE(t)
SINE(t)
IB1
X
X
COSINE(t)
VSINE_B
VCOS_B
ISINE_B
ICOS_B
Complex
Multiply
Complex
Conjugate
QfunB
PfunB
PharmB
∑
N-1
n=0
∑
N-1
n=0
∑
N-1
n=0
PHASE B
WATT B
SINE(t)
VA1
X
X
COSINE(t)
SINE(t)
IA1
X
X
COSINE(t)
VSINE_A
VCOS_A
ISINE_A
ICOS_A
Complex
Multiply
Complex
Conjugate
QfunA
PfunA
PharmA
∑
N-1
n=0
∑
N-1
n=0
∑
N-1
n=0
∑
N-1
n=0 PHASE A
WATT A
Figure 7. Power Harmonic and Fundamental Measurements