Transcript Power Meter

Power Meter
ECE 4512 Senior Design I
Department of Electrical & Computer Engineering
Mississippi State University
Team
Advisor:
Professor Raymond S. Winton
Team Leader:
Wei-Keat Quek
Contribution: A/D Converter, LCD Display, & Documentation
Team Members:
Matthew Hemphill
Contribution: Voltage-sensing circuit & Documentation
Scott Fredrick
Contribution: Current-sensing circuit & Documentation
James Nixon
Contribution: Microcontroller & Documentation
Motivation
To provide average American householders with a
portable & accurate digital power meter
• Importance
– Can educate consumers, save them money, & aid in purchase
decisions
– Can aid in troubleshooting problem circuits & in making
decisions to conserve energy
• Relevance
– Allows for concrete, practical design experience based on
curriculum
– Allows for group collaboration and division of tasks based
on each member’s specialty
Problem Statement
• To accurately sense the voltage and current
used over a range of typical household
devices.
• To achieve reliable power measurements by
taking phase differences between the
voltage and current, i.e. the power factor,
into account.
Design Requirements
•
•
•
•
Voltage-sensing circuit (0 to 120 Vrms)
Current-sensing circuit (0 to 30 A)
Power Factor Calculation (DS87Cx20 Microcontroller)
Power (9 V Battery)
Design Requirements
• Display (4-digit LCD)
•
•
•
•
Power Measurement Range (0 to 3600 W)
Energy Measurement Range (0 to 86.4 kWhrs)
Tolerance (+/- 3%)
Size & Packaging (Plastic enclosure –
4” x 8” x 1.5” (W x L x D))
Digital Power
Measurement
Voltage-Sensing Circuit
vo = (1 + 2*R4/R3)(v2 – v1)
where  = R2/R1
Simulation
Simulation Results
Voltage Input (Vp-p)
180
170
160
150
140
130
120
110
100
90
Vo (Vp-p)
5.0110
4.7227
4.4322
4.1637
3.9022
3.6260
3.3447
3.0547
2.7774
2.5067
Vo Scaled by 36 Percent error (%)
180.396
0.2200
170.017
0.0101
159.559
0.2755
149.893
0.0712
140.479
0.3423
130.536
0.4123
120.409
0.3410
109.409
0.0280
99.9864
0.0136
90.2412
0.2680
Monte Carlo Simulation
Current-Sensing Circuit
Simulation
Simulation Results
Voltage Input (Vp-p) Vo (mVp-p)
180
68.743
170
64.775
160
61.459
150
57.585
140
52.740
130
48.959
120
46.029
110
42.131
100
37.895
90
34.303
I (mA)
68.743
64.775
61.459
57.585
52.740
48.959
46.029
42.131
37.895
34.303
I (Rsense) (mA) Percent error (%)
68.714
0.0422
64.803
0.0432
61.433
0.0423
57.587
0.0035
52.717
0.0436
48.935
0.0491
46.001
0.0608
42.092
0.0927
37.872
0.0607
34.280
0.0671
Monte Carlo Simulation
A/D Conversion
Power Factor Calculation
Sampling & Displacement
• Sampling rate >= 1/(8*fo) where fo = 60 Hz
• Displacement = -/ where  = 2f
Example
•  =  * displacement = 2(60 Hz)*1.5 ms = 0.565 rad/s
Power
• P = Vrms*Irms*cos() = (127.6 V)/(68.714 mA)(0.8446) = 7.4 W
Maclaurin Series
• cos() = 1 - ^2/2! + ^4/4! - ^6/6! + … + (-1)^k ^2k/2k! + …
C Code
•After the first three harmonics, cos () = cos(0.565) = 0.8446.
C Program Flow
Select
functio
n
Start
Pinstantaneous
Calculate real
power
Pavg
Input
time
Time out
or
disconnect
?
Receive digital
voltage value
(Reference)
Receive digital
current value
Yes
Display output
End
No
Has first
zerocrossing
been
reached?
Yes
Calculate displacement
between current and voltage
No
UMPS Simulation
Vcc
LCD
4
P1.6
P1.7
P3.0-P3.7
EA
31
40
DS87Cx20
Vcc
P2.1
P2.2
7-14 5/1
10 K
22
30 pF
19
SW2
4 MHz
20
3
10-17
0.1 F
GND
2
7
8
23
XTAL1
6
Vcc
XTAL2
18
30 pF
SW1
UMPS Simulation
c:\temp\lcd.asm
org 0
ajmp Main
org 020h
Main:
mov CKCON,#%00001000
mov TMOD,#%00000001
mov TCON,#%00010000
mov IE,#%10000010
; LCD Display
mov P1,#03Fh
CPU Registers
; Program Main
;
;
;
;
;
Use Internal /4 Clock for Timer0
Timer0 - Uses Internal Clock
- Run in Mode 1
Start Timer0 running
Enable the Timer 0 Interrupt
P1
0000003F
P3
00000007
; Make sure all LCD lines are Low
acall Dlay5
acall Dlay5
acall Dlay5
; Wait 15 ms for the Display to Power Up
mov P3,#$7
clr
P1.6
setb P1.7
clr
P1.7
; Output a 7 on the Display Line
; Clear the RS Line
; Toggle the LCD "E" Clock
acall Dlay5
; Wait 5 ms for the instruction to execute
:
SP
07
Resources
7
SW1
SW2
Conclusions/Future Work
Conclusions
• Ensure our tolerance levels are met
• Meet challenge of accuracy
Future Improvements
• Expand functions for both AC & DC
measurements
• Expand measuring range
• Improve tolerance levels
• Allow PC connectivity
• Improve internal power consumption
References
[1]
“ADC 0801/ADC 0802 ADC 0803 ADC 0804 ADC 0805 8 bit µP Compatible A/D Converters”,
National Semiconductor Corporation, U.S.A., 2000.
[2] “EDC190 4-Digit 7-Segment Liquid Crystal Display”, Microelectronic Company, U.S.A., June 1987.
[3] Fisher, G. J., “An Enhanced Power Meter for SPICE2 Circuit Simulation,” IEEE Transactions On
Computer-Aided Design, Harris Semiconductor, Melbourne, FL, May, 1998.
[4] Garverick, S. L., McGrath, D. T., Baetsch, R. D., and Fujino, K., “A Programmable Mixed-Signal ASIC
for Power Metering,” IEEE International Solid-State Circuits Conference, GE Corporate Research
and Development, Schenectady, NY, January, 1991.
[5] Graf, Rudolf F., Encyclopedia of Electronic Circuits, Vol. 3, TAB Books Inc., 1991.
[6] Hanselman, Duane, and Littlefield, Bruce, Mastering MATLAB: A Comprehensive Tutorial and
Reference, The MATLAB Curriculum Series, Upper Saddle River, NJ: Prentice Hall, 1996.
[7] Hayes, Thomas C., and Horowitz, Paul, Student Manual for the Art of Electronics, Cambridge
University Press, 1989.
[8] Helps, Richard, “Op-amps Note,” http://www.et.byu.edu/~rhelps/EET444/html/op-amps_note.htm
(11/9/00).
[9] "High-Speed Microcontroller User Guide", Dallas Semiconductor, http://www.dalsemi.com/
References (cont.)
[10] Horowitz, Paul, and Hill, Winfield, The Art of Electronics, 2nd ed. Cambridge University Press, 1989.
[11] Lamego, M. M., Sousa, G. C. D., and Vierira, J. L. F., “A Single Phase Microcontroller Based Energy
Meter,” IEEE Instrum. And Meas. Tech. Conf.Proc., Electrical Engineering Dept., Universidade
Federal do Espirito Santo, May, 1998.
[12] Landee, Robert W., and Davis, Donavan C., Electronics Designer’s Handbook, 2nd ed. New York:
McGraw-Hill, 1977.
[13] Lapuh, R., Visocnik, I., and Arnsek, A., “Single DVM Sampling Power Meter For Low Frequencies,”
IEEE Instrum. And Meas. Tech. Conf. Proc., Slovenian Institute of Quality and Metrology, Ljubljana,
Slovenia, May 2000.
[14] Lenk, John D., Circuit Encyclopedia & Troubleshooting Guide, Vols. 1 & 2, New York: McGraw-Hill,
1974.
[15] Liu, L. X., Chen, T. P., and Chua, S. W., “Influence of Frequency Difference between Current and
Voltage on AC Power Measurement Result,” National Measurement Centre of Singapore Productivity
and Standards Board, Singapore, 2000.
[16] May, R., “A PIC Based AC Power Meter,” www.edtn.com/embapps/emba027.htm, July, 1998.
[17]
Neamen, Donald A., Electronic Circuit Analysis and Design, Boston, MA: WCB McGraw-Hill,
1996.
References (cont.)
[19] Svensson, S., “Preferred Methods for Power-Related Measurements,” 8th International Conference on
Harmonics and Quality of Power ICHQP ’98, Swedish National Testing and Research Institute, Boras,
Sweden, October 1998.
[20] Tuinenga, Paul W., Spice: A Guide to Circuit Simulation & Analysis Using PSpice, 3rd ed. Englewood
Cliffs, NJ: Prentice Hall, 1995.
[21] Voland, Gerald, Engineering by Design, Reading, MA: Addison-Wesley, 1999.
[22] Woodward, W. S., “Optical isolator computes watts,” Electronic Design, 102-103, October 14, 1994.
[23] Ziemer, R., Tranter, W., and Fannin, D., Signals and Systems: Continuous and Discrete, 4th ed.
Upper Saddle River, NJ: Prentice Hall, 1998.