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Load Component Database of Household Appliances and Small Office Equipment Ning Lu, Yulong Xie, and Zhenyu Huang
Francis Puyleart and Steve Yang
Pacific Northwest National Laboratory
Bonneville Power Administration
Abstract — This paper discusses the development of a load component database for household appliances and office equipment. To develop more accurate load models at both the transmission and distribution levels, a better understanding of the behaviors of home appliances and office equipment associated with the variations of the power system voltage becomes more and more critical. The Bonneville Power Administration (BPA) has performed a series of voltage tests against home appliances and office equipment since 2005. Since 2006, researchers at Pacific Northwest National Laboratory have collaborated with BPA personnel and developed a load component database based on the appliance testing results to facilitate load modeling work for the Western Electricity Coordinating Council (WECC). In this paper, the testing procedure and results are first presented. Then, the load model parameters are derived and grouped. Recommendations are given for aggregating the individual appliance models to the feeder level, the models of which are used for distribution and transmission level studies. Index Terms—load models, appliance testing, power system simulation.
I. INTRODUCTION Load modeling is critical for power system stability study, because stable operation of a power system depends on the ability to continuously match the electrical output of generating units to the electrical load on the system [1]. The modeling of load is complicated because: • The number of appliance and equipment level loads is very large. • The load characteristics of individual appliance and equipment are diverse. • The capacity, duty cycle, and response to voltage and frequency changes of each individual load are different. • The exact load composition is difficult to estimate. A better understanding of individual load characteristics will This work is supported by Bonneville Power Administration under Contract DE-AC05-76RL01830. Ning Lu, Yulong Xie, and Zhenyu Huang are with the Energy Science and Technology Division, Pacific Northwest National Laboratory, P.O. Box 999, MSIN: K5-20, Richland, WA - 99352, USA (e-mails:
[email protected],
[email protected],
[email protected]). Steve Yang and Francis Puyleart are with the Transmission Business Line, Bonneville Power Administration, Vancouver, WA. Pacific Northwest National Laboratory is operated for the U.S. Department of Energy by Battelle Memorial Institute.
©2008 IEEE.
lay a solid foundation to classify loads and then, group loads with similar characteristics together. After that, a sensitivity study on the aggregated load model can be performed to determine the uncertainty caused by the variation of the load composition of the individual distribution feeders. Traditionally, the load models are classified into two broad categories: static models and dynamic models [1]. Exponential and polynomial model (ZIP) models are commonly used in static load models, in which cases the response of the loads to voltage and frequency changes is very fast and the steady state of the response is reached very quickly. Dynamic load models account for the dynamics of load components. To make reasonable simplification of the aggregated load at bulk power delivery points, it is essential to understand the individual load characteristics. Prior to this research, there was literature published regarding laboratory measurements and models of modern loads [2][3]. However, these experiments were conducted in the mid 1990s. With the advance of technology, power electronic control devices were widely applied to home appliance and office equipment. The load characteristics under voltage and frequency disturbances have changed significantly since then. Therefore, it is necessary to update the previous database with new load model parameters and add new models for unrepresented home appliances and office equipment. Note that the testing conducted so far has not included industrial load. The paper is organized as follows. Section II introduces the testing setup. Section III describes derivation of the model parameters. Load model aggregation is discussed in Section IV. Section V provides conclusion. II. TESTING SETUPS The appliance tests were performed in a BPA facility in Vancouver, WA. To complete all of the tests required, a test bed was setup as described below and in the literature [4]. 1) Power Converter A power source that regulates voltage between 0 to 132 V and allows a current output of up to 50 A was used to power the dish washer, washer, refrigerator, dryer, oven, and range. The frequency can be varied between 45 and 500 Hz. The voltage source required by the power converter is three-phase wye 480 VAC (line-to-line). Two of the three-phase outputs were used to replicate typical house voltage. An executable code created in LabView® allows the power converter to be controlled by
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signals generated with MATLAB® on a laptop. 2) User Interface For an easy and safe user interface, a mock wall was created with typical house circuit protection. A three-wire cable (+120 VAC, neutral, and -120 VAC) was run from the power converter source to three separate 50A/50mV shunt current transformers (CT). Source voltage measurements were taken from the power converter source side of each shunt CT. These two measurements provide an electrical whole system view of the tests. From the shunt CTs, another three wire cable was run to a 120/240V and 100A household load center. Two service breakers were installed: one 120V/20A and the other 240V/30A. From the load center, one 240V/30A outlet and one 120V/20A outlet were mounted to the mock wall so typical 120V/20A or 240V/30A plugs could be used. 3) Testing Scenarios To study both the steady state and dynamic characteristics of the appliances, the following tests were preformed: voltage oscillation, voltage rampup, voltage rampdown and voltage sag. Sample source voltage are shown in Figure 1. Because the inertia of motors used in most household appliances and office equipment are small, their response to voltage changes are very fast. Voltage rampdown cases are, therefore, used to develop the static load model. The voltage oscillation cases are used to verify the performance of the static model, and the sag cases are used to verify whether the model performance is satisfactory when the system undergoes an abrupt change. In the next section, the testing results are discussed, and the derived model parameters are presented.
P
V Q
(a)
P
Q
(b) Figure 2: (a) The time series plot of a voltage rampdown case, (b) The PV and QV curves generated from the voltage rampdown case. The static load model is represented by ZIP models [2]: _
_
P = P0 ( p1 V 2 + p2 V + p3 ) _ 2
_
Q = Q0 ( q1 V + q2 V + q3 ) _
V V0 where P0 and Q0 are the initial real and reactive power values, V =
_
Figure 1: Sample testing signals III. ZIP MODEL PARAMETERS DERIVATION A static load model expresses the characteristics of the load at any instant of time as algebraic functions of the bus voltage magnitude and frequency at that instant [4]. This paper focuses on developing the static load model using the testing results obtained by 60 second voltage rampdown tests, as shown in Figure 2.
when V is 1, and (p1, p2, p3) and (q1, q2, q3) are the coefficients defining the proportion of each component. Curve fitting is used to derive the model parameters from the real power versus voltage (PV) curves and the reactive power versus voltage (QV) curves. If motor stalling phenomena were observed for motor type loads such as refrigerators, the loads were represented by the single-phase motor model, the parameter derivation of which is not discussed in this report. Please refer to reference [4] for details. The following home appliances have been tested: a washer, a dryer, an oven, a range, a refrigerator, a dish washer, a
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Real Power
A Complete Table of ZIP Parameters Vmin (pu)
Pf
1 0.8 0.6
Dishwasher (HD) Dishwasher (NW) Dishwasher (PP) Dryer Oven Range
P
0.4 Q 0.2
Reactive Power
0 Z
I
P
Z
I
P
DishWasher_HD
120
500
0.99
0
0.95
0.00
0.00
0.00
0.00
0.00
DishWasher_NW
120
600
1.00
0
0.99
0.00
0.00
0.00
0.00
0.00
DishWasher_PP
120
685
1.00
0
1.00
0.00
0.00
0.00
0.00
0.00
DRYER
240 4900
1.00
56
1.02
0.00
0.00
0.10
0.00
0.00
OVEN
240 3050
1.00
0
0.99
0.00
0.00
0.00
0.00
0.00
RANGE
240 4100
1.00
0
0.97
0.00
0.00
0.00
0.00
0.00
FAN - speed 1
120
145
0.97
0
0.87
0.14
-0.01
0.11
0.16
-0.01
FAN - speed 2
120
145
0.96
0
0.74
0.27
-0.02
0.03
0.28
-0.02
FAN - speed 3
120
187
0.94
0
0.39
0.66
-0.05
-0.10
0.46
-0.03
FAN - speed 3B
120
187
0.95
0
0.45
0.57
-0.04
-0.03
0.34
-0.02
Halogen_100W
120
100
1.00
0
0.66
0.39
0.00
0.00
0.00
0.00
LightBulb_100W
120
100
1.00
0
0.64
0.40
0.00
0.00
0.00
0.00
CompFluore_19W
120
19
0.91
14
-0.42
1.50
-0.06
0.66
-1.16
0.06
CompFluore_23W
120
23
0.90
23
-0.28
1.35
-0.05
0.58
-1.11
0.05
CompFluore_20W
120
18
0.91
17
-0.30
1.36
-0.05
0.60
-1.08
0.04
Fluore_T8_32W
120
56
0.86
12
0.35
0.72
-0.04
0.28
-0.90
0.03
Fluore_T12_40W
120
50
0.88
10
0.34
0.71
-0.03
0.20
-0.76
0.02
Fluore_T8_32W
120
61
0.93
10
-0.03
1.10
-0.05
0.32
-0.75
0.03
Fluore_T12_40W
120
52
0.94
10
0.06
0.97
-0.03
0.24
-0.60
0.02
CRT
120
225
1.00
60
0.00
0.00
1.00
0.00
0.00
0.15
LCD
120
150
1.00
60
0.00
0.00
1.00
0.00
0.00
0.15
ClothesWasher
120
Refrigerator
120
compressor type load (constant torque load)
Table 1: ZIP model parameters of the appliances tested
0
0.2
0.4 0.6 0.8 Voltage (p.u.)
1
Figure 4: The PV and QV curves (modeling results) 1.2 1
Measurement Model
P
0.8 Power
Appliance
S0 V(V) (VA)
Figure 3: The testing results: PV and QV curves (For dishwasher there are three operation modes: Heat and Dry, Normal Wash, Pot and Pan)
Reactive Power (p.u.)
computer with a CRT or LCD monitor, and a heavy duty fan used for ventilation in household and small business. The lighting loads tested are listed below: • Light #1: A fluorescent light uses two 48' T-8 32 W or T-12 40 W, instant-on electronic ballast. • Light #2: A fluorescent light uses two 48' T-8 32 Watt or T-12 40 Watt, Instant-on, no flicker Electronic Ballast. • Light #3: A compact fluorescent light, 100 W light output, 120 V, 60 Hz, 23 Watt, 0.33 A. • Light #4: A compact fluorescent light, 75 W light output, 120 V, 60 Hz, 19 Watt, 0.295 A, contains mercury. • Light #5: A compact fluorescent light, 75 Watt light output, 120 V, 60 Hz, 20 W, 0.289 A. • Light #6: A halogen light, 120 V, 100 W. • Light #7: A conventional light bulb, 120 V, 100 W. The ZIP model parameters derived from the testing results are shown in Table 1. The PV and QV curves of the appliance measurements and the modeling are shown in Figure 4 through Figure 9. Note that if the reactive power of a device is less than 0.1 p.u., its ZIP parameters for reactive power calculation are considered to be zero to simplify the ZIP model. As shown in Figure 9, the PV and QV curves of refrigerators and clothes washers are hard to model using a single ZIP models. We therefore put them into the compressor type load category, which will be addressed together with our air conditioner performance modeling studies.
0.6 Q
0.4 0.2 0 -0.2 0
0.2
0.4 0.6 voltage (V)
0.8
1
Figure 5: The PV and QV curves of the fan at different speeds
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P
Q
(a) Figure 6: The PV and QV curves of halogen and light bulbs 1.5
Power
1
P
Measurement Model
P
0.5
Q
0 Q -0.5 -1 0
(b) 0.2
0.4 0.6 voltage (V)
0.8
1
Figure 9: (a) The PV and QV curves for refrigerator, (b) the PV and QV curves for clothes washers.
Figure 7: The PV and QV curves of all fluorescent lights tested IV. ZIP LOAD AGGREGATION
1.2
In power system load modeling, aggregated load models representing the group behavior of the individual load components rather than accurate individual appliance models per se are needed. Therefore, parameters of the aggregate ZIP load model are calculated as the weighted average of the respective ZIP parameters of the n load components in the group, which can be represented as
P 1
Power
0.8 0.6 0.4 Q
0.2
ZIPagg =
j
j
j =1
0 -0.2 0
∑α ZIP n
0.2
0.4 0.6 voltage (V)
0.8
1
Figure 8: The PV and QV curves of CRT and LCD monitors
In the above equation, ZIP is substituted by p1 to p3 and q1 to q3 of the ZIP model. αj is KVAj/KVAagg. The aggregated ZIP model parameters are represented as: 1 k= p1agg + p 2 agg + p3agg _
_
Pagg = P0 ( kp1agg V 2 + kp2 agg V + kp3 agg ) _
_
Qagg = Q0 (kq1agg V 2 + kq2 agg V + kq3 agg ) _
V =
V V0
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where k is an adjustment factor to guarantee that the aggregated power is also 1 p.u. when voltage is 1 p.u..
commercial and industrial load components, can be updated. REFERENCES
1.2 Ture P agg curve
Real Power (pu)
1 0.8 0.6
[1]
P agg Curve (with k)
[2]
P agg Curve (without k)
P
Ture Q agg curve Qagg Curve (with k) Qagg Curve (without k)
[3]
0.4 0.2
[4]
Q 0 -0.2 0
0.2
0.4 0.6 voltage (pu)
0.8
1
Figure 10: The aggregated P and Q curves Observations on the aggregated ZIP load model include: • In general, using weighted average, one can obtain a satisfactory representation of the aggregated ZIP load model. • Some loads start to drop off when voltage is below 0.5 and the aggregated curve will not be able to reflect this phenomena. • For some load, the drop off is permanent; for example, some computer load will shut off. Therefore, when system voltage recovers, the aggregated ZIP load model will fail to represent the load. V. CONCLUSIONS In this paper, household appliances and office equipment testing results and their derived ZIP model parameters have been presented. From the load characteristics under different testing conditions such as voltage sags, ramps, and oscillations, one can reach the following conclusions: • Small motor loads with no stalling issues or loads with large ratios of resistive to inductive consumption can be grouped as a constant impedance load. Examples include fans, ovens, dish washers, and dryers (Z type loads). • Loads using power electronic conversion devices as power supplies, such as computers and monitors, behave as a constant power load (P type loads). These loads will be taken off line by under voltage protection devices when the voltage drops below a threshold around 0.5 p.u. • Motor loads having stalling issues usually carry mechanical loads with constant torque. These loads require different models for their running state and stalling state because their real and reactive power will change dramatically when motors stall. Therefore, it is not appropriate to represent them as ZIP models. Future work will be focused on frequency testing and testing industry motors and electronic drives so that the entire load component database, which includes the residential,
[5]
P. Kunder, Power System Stability and Control, McGraw-Hill, New York, 1993. IEEE Task Force on load representation for dynamic performance, “Bibliography on load models for power flow and dynamic performance simulation,” IEEE Trans. on Power Systems, vol. 10, pp. 523–538, Feb. 1995. L.M. Hajagos and B. Danai, “Laboratory measurements and models of modern loads and their effect on voltage stability studies,” IEEE Trans. On Power Systems, vol. 13, pp. 584 – 592, May 1998. F. Puyleart, Development and Analysis of Dynamic Modeling of a Residential Air Conditioner Compressor Motor for use in Power Grid Studies, MSEE Thesis, College of Graduate Studies, University of Idaho, 2006. IEEE Task Force on load representation for dynamic performance, “Load Representation for Dynamic Performance Analysis,” IEEE Trans. On Power Systems, vol. 8, pp. 472-482, May 1993.
Ning Lu (M’98-SM’05) received her B.S.E.E. from Harbin Institute of Technology, Harbin, China, in 1993, and her M.S. and Ph.D. degrees in electric power engineering from Rensselaer Polytechnic Institute, Troy, New York, in 1999 and 2002, respectively. Her research interests are in the modeling and analyzing power system load behaviors and modeling the Solid Oxide Fuel Cell performances. Currently, she is a senior research engineer with the Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, WA. She was with Shenyang Electric Power Survey and Design Institute from 1993 to 1998. Yulong Xie received his B.S. degree in chemistry from Xiangtan University, Xiangtan, China, in 1983, and his M.S. and Ph.D. degrees in chemometrics from Hunan University, Changsha, China, in 1988 and 1993, respectively. His research interest is on the application of multivariate statistical analysis, data mining, chemometrics, stochastic simulation, spatial statistics and optimization in a variety of scientific fields. Currently, he is a senior research scientist with the Environmental Sustainability S&T Division, Pacific Northwest National Laboratory, Richland, WA. Zhenyu Huang (M'01-SM’05) received his B. Eng. from Huazhong University of Science and Technology, Wuhan, China, and Ph.D. from Tsinghua University, Beijing, China, in 1994 and 1999 respectively. From 1998 to 2002, he conducted research at the University of Alberta and McGill University as a post-doctoral fellow, and at the University of Hong Kong. He is currently a senior research engineer at the Pacific Northwest National Laboratory, Richland, WA. His research interests include power system stability and control, high-performance computing applications, and power system signal processing. Francis R. Puyleart (S’99 - M’03) received a Bachelors of Science in Electrical Engineering (Cum Laude) from the University of Portland, Portland, OR in 2003 and a Masters of Science in Electrical Engineering from the University of Idaho, Moscow, ID in 2006. He is an electrical engineer for Bonneville Power Administration, working with Technical Operations. Primary research interests include load modeling, high voltage electronics and generator modeling. He is a registered PE in the state of Washington. Steve Yang received his M.S. degree in Electrical Engineering from Portland State University in 2002. Mr. Yang is with Bonneville Power Administration where his responsibilities include test and measurement systems, generator performance monitoring and model validation, equipment testing. Mr. Yang led the end-use equipment testing program at BPA. He is a member of WECC Modeling and Validation Work Group and WECC Load Modeling Task Force.
