Adaption of the Current Load Model to Consider

Residential Customers Having Turned to LED

Lighting

Daniel-Leon Schultis

Albana Ilo

Institute of Energy Systems and Electrical Drives

TU Wien

Vienna, Austria

daniel-leon.schultis@tuwien.ac.at

Abstract—Recent measurements show that the substitution of

General Incandescent Lamps by the high efficiency LEDs

changes the behavior of the modern residential customers.

They consume less active power and behave capacitive in the

evening. Actually, also the extended load models, which

consider the load composition and power factors of individual

load subcategories, describe an inductive behavior of the load

during the whole day. This paper presents an adapted load

model that considers residential customers having turned to

LED lighting. The current load models are adapted to reflect

the estimated load composition and the recent measurements.

The corresponding ZIP-coefficients are calculated and

provided for download in a public data repository. They change

during the day and reach high values when the reactive power

consumption of the residential customer changes the sign. In

this case, the capacitive and inductive power contributions of

the single load devices within the residential customer plant

compensate each other.

Index Terms—Distribution grids, load modelling, power flow

analysis, residential customers, ZIP model.

I. INTRODUCTION

The goal of this paper is to review the current state-of-the-art of the modelling of the reactive power part of residential loads for power flow analysis; and to derive an adapted load model that considers residential customers having turned to LED lighting. The distribution system engineer’s decisions concerning the integration of Distributed Energy Resources rely on the results of power flow studies. For performing distribution grid analysis, models are developed for all pertinent system components including Distributed Generation, distribution feeders, loads, etc. Much attention has been paid to model the active power part of the load devices connected to distribution grids by categorizing customers in residential, commercial, etc., and by developing ZIP models for different load categories and subcategories [1,2]. The reactive power part is derived from the active one using constant power factor and ZIP models [1,3]. During the day, the residential load have always shown a slightly inductive behavior [4].

Recent measurements on residential customer plants have shown that their reactive power behavior varies during the

day [5]. The development of high efficiency LEDs [6] and their increasing use is changing the reactive power behavior of the customers in the evening.

This paper presents an adapted load model that considers residential customers having turned to LED lighting. Section II describes the used methodology. The current state-of-art of load modelling of residential customers is discussed in Section III. Section IV describes the adapted load model, while its comparison with the current model is given in Section V. Conclusions are presented in Section VI.

II. METHODOLOGY

Fig. 1 shows the methodology used to derive the adapted load model of residential customers.

Figure 1. Methodology used to derive the adapted load model.

The estimated load composition and recent active (P) and reactive power (Q) measurements of modern residential customers are used to adapt the current load model.

For both load models, i.e. the current and the adapted one, the reactive power is calculated in two different ways: a) simplified with a fixed power factor of 0.95 inductive; and b) extended by considering the load composition and power factors of individual load subcategories.

III. CURRENT LOAD MODELS

A. Load Classification

All types of load devices within residential customer plants are divided into four general load categories [1,2]: Switch-Mode Power Supply (SMPS) loads, motors, resistive loads, and lighting, Table I. SMPS loads may possess active

(aPFC), passive (pPFC) or no Power Factor Correction (noPFC). Motors are split in directly connected Single-Phase Induction Motors (SPIM) and Single-phase Adjustable Speed Drives (SASD). SPIMs are sub-categorized in Inductor-Run (IR) motors with Constant or Quadratic Torque (CT or QT) and Capacitor-Run (CR) motors with CT. SASDs are split in low and high Power (lowP and highP) drives each with CT or QT. Lighting devices are sub-categorized in General Incandescent Lamps (GIL), Compact Fluorescent Lamps (CFL) and Light-Emitting Diodes (LED).

B. Load Profile

Fig. 2 shows the load profiles of the current load model for various load categories and sub-categories [2].

Figure 2. Load profiles of the current load model for various load

categories and sub-categories.

The lumped active power consumption ,

lpd

nom tP of the

customers for nominal grid voltage and time-point t is determined by

, ·lpd lpd peak

nom t tP f P (1)

where lpd

tf is the customers’ lumped load profile factor for

time-point t as shown in Fig. 2; and peak

P is their peak winter active power demand.

In many cases, the lumped reactive power consumption of residential customers is determined by using a fixed power factor of 0.95 inductive [3], as in

,

, , tan(arccos(0.95))·lpd fixPF lpd

nom t nom tQ P , (2)

where ,

,

lpd fixPF

nom tQ is the lumped reactive power consumption

with fixed power factor for nominal grid voltage and time-point t.

The load profile is decomposed into different load sub-categories, allowing to calculate a more accurate value for the

reactive power [2]. The active ,

i

nom tP and reactive power

,

i

nom tQ

consumption of load sub-category i for nominal grid voltage and time-point t are given by

, ·i i peak

nom t tP f P (3a)

and,

for ind. cos

for cap. cos

· ·tan ,

· ·tan ,

i

i

i peak i

i t

nom t i peak i

t

f PQ

f P

(3b)

where i

tf is the load profile factor of load sub-category i and

for time-point t. Normalizing (3) on peak winter demand yields

,

, ,/

NORM i i peak

nom t nom tP P P (4a)

and,

, ,/

NORM i i peak

nom t nom tQ Q P (4b)

Adding up the power consumption of each load category yields the lumped power consumption, as in

, ,

lpd i

nom t nom tiP P

(5a)

and, ,

lpd i

nom t nom tiQ Q

(5b)

TABLE I. MODEL DATA OF LOAD SUBCATEGORIES.

Category

Subcategory Active power ZIP

coefficients

Reactive power ZIP

coefficients

Power

factor Ref.

Share of category

Estimated

in [7]

Adapted

load

model

i name ,Z i

PC

,I i

PC ,P i

PC ,Z i

QC ,I i

QC ,P i

QC cosi

is [%]

,A is [%]

SMPS

1 aPFC 0.00 0.00 1.00 - - - 1 [3,7] 27.00 27.00

2 pPFC 0.00 0.00 1.00 0.45 -1.44 1.99 0.970 ind. [3,7] 27.00 27.00

3 noPFC 0.00 0.00 1.00 3.63 -9.88 7.25 0.994 cap. [3,7] 46.00 46.00

Moto

rs

Directly

connected

SPIM

4 IR_QT 0.10 0.10 0.80 1.40 -0.90 0.50 0.620 ind. [2,3,7] 35.00

29.48

5 IR_CT 0.63 -1.20 1.57 1.40 -0.90 0.50 0.620 ind. [1,7] 5.52

6 CR_CT 0.50 -0.62 1.12 1.54 -1.43 0.89 0.900 ind. [2,3,7] 25.00 25.00

SA

SD

lowP 7 QT -0.27 0.76 0.51 3.67 -10.31 7.64 0.990 cap. [1,7]

20.00 9.70

8 CT 0.40 -0.89 1.49 3.32 -10.50 8.18 0.990 cap. [1,7] 10.30

highP 9 QT -0.27 0.76 0.51 0.54 -1.65 2.11 0.896 ind. [1,7]

20.00 9.70

10 CT 0.40 -0.89 1.49 1.54 -3.95 3.41 0.896 ind. [1,7] 10.30

Resistive 11 - 1.00 0.00 0.00 - - - 1 [2,3] 100.00 100.00

Lighting

12 GIL 0.43 0.69 -0.12 - - - 1 [2,3] 0.00 0.00

13 CFL -0.01 0.96 0.05 -0.10 0.73 0.37 0.910 cap. [3,7] 100.00 0.00

14 LED 0.69 0.92 -0.61 1.84 -0.91 0.07 0.480 cap. [6,8] - 100.00

Fig. 3 shows the lumped P-consumption of the current load model for nominal grid voltage according to (1); and furthermore, its lumped Q-consumption with fixed power factor calculated according to (2), and with variable power factor calculated according to (5b).

Figure 3. Lumped P- and Q-consumption of the current simplified and

extended-load-model for nominal grid voltage.

In both cases, the current load model shows an inductive behavior for the entire time horizon of 24 hours. Both curves are generally similar. Therefore, for simplicity, the reactive power of the load is calculated using constant power factor.

C. ZIP Model

For ,

0i

nom tP and

,0

i

nom tQ , active and reactive power

voltage dependency of each load subcategory i is considered

by using a ZIP model [2] according to

2

, , ,

,· ·

i i Z i NORM I i NORM P i

t nom t P t P t PP P C U C U C (6a)

2

, , ,

,· ·

i i Z i NORM I i NORM P i

t nom t Q t Q t QQ Q C U C U C (6b)

with /NORM

t t nomU U U (6c)

where ,Z i

PC ,

,I i

PC ,

,P i

PC and

,Z i

QC ,

,I i

QC ,

,P i

QC are P- and Q-

ZIP coefficients of load subcategory i; i

tP and

i

tQ are the

actual P- and Q-consumption of load subcategory i for time-

point t; t

U is the actual- and nom

U the nominal grid voltage.

The ZIP coefficients fulfil

, , , , , ,

1,Z i I i P i Z i I i P i

P P P Q Q QC C C C C C i (7)

For ,

0i

nom tP and

,0

i

nom tQ , it is 0

i

tP and 0

i

tQ ,

respectively. The addition of the actual power consumptions

of each load subcategory gives the actual lumped power

consumption for time-point t, as in

lpd i

t tiP P

(8a)

lpd i

t tiQ Q

(8b)

For ,

0lpd

nom tP and

,0

lpd

nom tQ , a time-varying lumped ZIP

model is calculated by considering the ZIP coefficients of the

individual load subcategories and thei

tf , as in

2

, , , ,· ·

lpd lpd Z NORM I NORM P

t nom t P t t P t t P tP P C U C U C (9a)

2

, , , ,· ·

lpd lpd Z NORM I NORM P

t nom t Q t t Q t t Q tQ Q C U C U C (9b)

where ,

Z

P tC ,

,

I

P tC ,

,

P

P tC and

,

Z

Q tC ,

,

I

Q tC ,

,

P

Q tC are lumped P-

and Q-ZIP coefficients for time-point t that fulfil

, , , , , ,

1,Z I P Z I P

P t P t P t Q t Q t Q tC C C C C C t (10)

The lumped ZIP coefficients are determined by

, , ,

, , ,·

Z NORM i Z i NORM i

P t nom t P nom ti iC P C P

(11a)

, , ,

, , ,·

I NORM i I i NORM i

P t nom t P nom ti iC P C P

(11b)

, , ,

, , ,·

P NORM i P i NORM i

P t nom t P nom ti iC P C P

(11c)

, , ,

, , ,·

Z NORM i Z i NORM i

Q t nom t Q nom ti iC Q C Q

(11d)

, , ,

, , ,·

I NORM i I i NORM i

Q t nom t Q nom ti iC Q C Q

(11e)

and , , ,

, , ,·

P NORM i P i NORM i

Q t nom t Q nom ti iC Q C Q

(11f)

For ,

0lpd

nom tP and

,0

lpd

nom tQ , it is 0

lpd

tP and 0

lpd

tQ ,

respectively. Fig. 4 shows the lumped ZIP coefficients of the

current extended-load-model according to (11).

Figure 4. Lumped ZIP coefficients of the current extended-load-model.

Between 0:00 and 18:00, P-consumption of the current

extended-load-model mainly behaves as a combination of

two almost equal load parts with constant Z and P. During

the remaining time, also the constant I load part becomes

perceptible. The Q-consumption behaves like a ZIP-load

during the whole time horizon. The ZIP coefficient values

lie within the interval (-1.5, 1.5).

IV. ADAPTED EXTENDED-LOAD-MODEL

A. Estimated Load Composition

In this section are used (1) to (11) with the additional superscripts “C” for the current and “A” for the adapted load

model. Reference [7] estimates the share i

s of each load

subcategory of the corresponding category for residential customers in 2020, Table I. The SMPS load with noPFC have an estimated share of 46%, while that with pPFC and aPFC respectively 27%. In the motor load category, the directly connected IR SPIM has an estimated share of 35%; the directly connected CR SPIM 25%, the low and high power SASD respectively 20%. In the lighting sector is estimated a share of 100% CFL. The estimated shares of IR SPIM, low and high power SASD are allocated to the corresponding load subcategories using

,4 ,4 ,4 ,50.35·

A C C C

r r rs P P P (12a)

,5 ,5 ,4 ,50.35·

A C C C

r r rs P P P (12b)

,7 ,9 ,4 ,4 ,5 ,60.2·

A A C C C C

r r r rs s P P P P (12c)

,8 ,10 ,5 ,6 ,4 ,5 ,60.2·

A A C C C C C

r r r r rs s P P P P P (12d)

where ,A i

s is for the adapted load model the share of load

subcategory i of the corresponding category, and ,C i

rP is for

the current load model the installed rating of load subcategory i, estimated as in

, ,

,max

C i C i

r nom tt

P P (13)

For the lighting load category is assumed a share of 100%

LED instead of CFL, since LED has not been considered in

[7], but is a more efficient technology than CFL with lower

operational costs [9], much higher average lifetime [10] and

rapidly increasing market share [11]. Compared to CFL,

LED has the advantage of no environmental pollution since

it is free of toxic substances such as mercury [10], and it

possesses improvements concerning light intensity,

brightness, color control, and reliability [12].

The shares,A is of all load subcategories are shown in

Table I. The load profile factors of the adapted load model’s

subcategories are calculated as in

ft

A,i = sA,i · ∑ f

t

C,i3i=1 , ∀ i ∈ (1,3), (14a)

ft

A,i = sA,i · ∑ f

t

C,i10i=4 , ∀ i ∈ (4,10), (14b)

,11 ,11 ,11

·A A C

t tf s f (14c)

In the residential lighting sector, GIL and CFL are

currently in the process of being replaced by LED. The

efficiency increase drastically lowers the number of lamps

required to supply a certain light demand. However, due to

rebound effect [13] it is assumed that the modern customer

increases his light demand by 30%, as considered in

,12 ,13

0,A A

t tf f t (15a)

,14 ,12 ,131.3· · ·

A C GIL LED C CFL LED

t t tf f f (15b)

where 2.6%GIL

, 11%CFL

, and 20%LED

are

efficiency of GIL, CFL and LED lighting, respectively [9].

B. Recent measurements

Recent measurements have shown a capacitive behavior

of a residential customer plant with LED and CFL lighting

and an annual energy consumption of 3000 kWh during

periods of low active power consumption, i.e. at nighttime

[5].

C. Load Profile

The load profiles of the adapted load model for various

load categories and sub-categories are shown in Fig. 5. The

corresponding load profile factors are calculated according

to (14) and (15).

Figure 5. Load profiles of the adapted load model for various load

categories and sub-categories.

The resulting lumped P-consumption of the adapted load

model for nominal grid voltage according to (1) is shown in

Fig. 6; and furthermore, there are shown its lumped Q-

consumption with fixed power factor according to (2), and

with variable power factor according to (5b).

Figure 6. Lumped P- and Q-consumption of the adapted simplified and

extended-load-model for nominal grid voltage

The adapted extended-load-model shows a capacitive

behavior between 21h and 24h, and an inductive behavior

for the remaining time horizon.

D. ZIP Model

Fig. 7 shows the lumped ZIP coefficients according to

(11), and the normalized lumped reactive power

consumption for the nominal grid voltage of the adapted

extended-load-model.

Figure 7. Lumped ZIP coefficients and reactive power consumption for

nominal grid voltage of the adapted extended-load-model.

The ZIP coefficients, especially ,

Z

Q tC and

,

I

Q tC , show

high peaks when reactive power consumption turns from

inductive to capacitive, and vica verse. This is because the

denominator in (11d)-(11f) is almost zero, but not the

reactive power consumption of single load devices. The

capacitive and inductive power contributions of the single

load devices within the residential customer plant

compensate each other.

The data of both, the current and the adapted extended-

load-model of residential customer plants (,

lpd

nom tP ,

,

lpd

nom tQ ,

,

Z

P tC

, ,

I

P tC ,

,

P

P tC ,

,

Z

Q tC ,

,

I

Q tC ,

,

P

Q tC ) are provided for download in a

public data repository [14]; the data is sampled into one

minute time-steps.

V. COMPARISON OF LOAD MODELS

Fig. 8 shows the lumped P- and Q-consumption of the

current and adapted extended-load-model for nominal grid

voltage.

Figure 8. Lumped P- and Q-consumption of the current and adapted

extended-load-model.

The substitution of GILs by high efficient LEDs reduces

the consumption of the active power in the evening up to

17.35% of peak

P . Between 0:00 and 18:00, the inductive Q-

consumption is reduced by 7.68% of peak

P , in average. From

18:00, the inductive Q-consumption steadily decreases, and

even changes to a capacitive one at about 20:45. The

maximum capacitive Q-consumption is about 4.17% of peak

P at 22:00.

VI. CONCLUSIONS

The calculation of the reactive power consumption of the

modern residential customers using the simplified-load-

model, i.e. fix power factor of 0.95 inductive, is inaccurate

compared to the extended-load-model, i.e. considering the

composition and power factors of individual load

subcategories. The use of the modern equipment, in

particular LEDs, reduces the active power consumption and

modifies significantly the reactive power behavior of the

residential customers. Also the inductive power

consumption is reduced, and it even changes to a capacitive

one in the evening. The adapted extended-load-model

considers the new behavior of modern residential customers.

The corresponding ZIP-coefficients are calculated; they

change during the day and reach high values when the

reactive power consumption of the residential customer

changes the sign. In this case, the capacitive and inductive

power contributions of the single load devices within the

residential customer plant compensate each other.

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