Decentralized Power Factor Correction

verdeagendaElectronics - Devices

Nov 21, 2013 (3 years and 8 months ago)

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Decentralized Power Factor Correction

J.
Hazra
1
, Balakrishnan Narayanaswamy
1
, Kaushik Das
1
, Ashok Pon Kumar
1
, Deva P Seetharam
1
,
De Silva
Liyanage
2

and Sathyajith Mathew
2

1
IBM
Research India, Bangalore

2
UBD
|

IBM Centre, University Brunei Darussalam, Brunei Darussalam


Tel: (91) 9739257776
, E
-
mail:
jahazra1@in.ibm.com
.



Abstract
:
Power Factor (PF) is a measure of electrical efficiency and is given by the ratio of KW
(kilo watt) to
KVA (kilo volt ampere), where KW is actual power consumed by the load whereas KVA is total power delivered
to the load. The power consumed is called active power and the remaining (KVA
-
KW) is called re
-
active power.
Even though reactive powe
r doesn’t do any actual work, it still needs to be generated and carried. When power
factor is poor (pf<1), reactive power travels through the wires between the load and the utility grid, passing
back and forth through the residential meter which makes the

system less efficient by increasing the system loses.
This also increases the monthly electricity bill when reactive power is charged. In order to improve the power
factor, we propose a system and method that achieves power factor correction with minimal
extra hardware
through intelligent scheduling of electrical loads.


Keywords
: Power system modeling, power flow study
, power loss minimization
.

1. INTRODUCTION

Improving energy efficiency is one of the key goals of smart grid initiatives across the globe. In practice, a
significant portion (5
-
10%) of generated energy is lost in transmission and distribution (T&D) system. In some
countries like India T&D loss is a
s high as 26%[1]. Hence, there is immense potential to improve the energy
efficiency by minimizing the transmission and distribution loss in the grid. For example, according to Federal
Energy Regulatory Commission (FERC), making the US grid even 5 percent
more efficient would save 42
gigawatts of electricity, an amount equal to 42 coal power plants [2]. There are several factors for having such
high T&D loss. Some these key factors are inadequate investment in T&D section which resulted in often
overloading

in distribution system, unplanned growth in sub
-
transmission and distribution for fulfilling the short
term objectives, too many stages of transformation, improper load management, inadequate reactive power
compensation, poor power factor appliances, etc
[1]. Among these factors low power factor is recognized as a
major concern in improving energy efficiency and power industry engineers are striving actively for a
commercial and engineering method for its correction [3]. Power factor correction not only re
duces system loses
but also releases system capacity and improves voltage regulation which enables the utility to provide cheaper
and easier services of the quality desired in modern industry
[4][5]
. Until recently, reactive power was mostly
compensated by
placing centralized capacitor banks near the load centers. However, there are several issues
associated with capacitor banks. Primarily such solution is costly (typically US$100=KV AR), requires large
space to install, and can only supply reactive power bu
t they cannot absorb it. When faced with rapidly
increasing load and voltage drop, capacitors become increasingly less effective and can actually contribute to the
downward spiral characteristic of voltage collapse. For static VAR compensators, their react
ive power output
varies with the square of the voltage. This characteristic makes them poor at coping with voltage instabilities and
preventing voltage collapses. Sometimes they explode due to sudden short circuit. Proper containment, fusing,
and preventiv
e maintenance can help to minimize these hazards, which can be expensive.



Power factor correction (PFC) schemes [
3
] have been proposed for quite some time in the field of power
electronics. The main aim of this PFC has been to reduce Total Harmonic Dist
ortion (THD) and thereby
improving the power factor. Recently, there is a growing trend for providing incentive for good power factor
and/or penalty for poor power factor. For example; Tokyo Electric Power Co. gives its retail customers in Japan,
a financi
al incentive to improve their power factors through discounts on the base rate [
7
]. European Union
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implemented a directive, EN61000
-
3
-
2, which controls the harmonic content and power factor of many products
that are sold to European countries [
8
]. Similarl
y power factor correction can also be achieved using other
equipment like battery energy storage system (BESS) [
6
]. Hence, to avoid penalty, there is a growing trend to
install power factor correction devices (like capacitors) at home or commercial places.

Unfortunately, these
capacitor banks are not only expensive but also compromise with power quality by injecting additional
harmonics to the grid through frequent switching. All these methods require additional equipment for PFC.
Further, mostly these meth
ods concentrate on improving power factor of a certain load. However, there can be
some loads which are inductive while some other loads are capacitive. If these inductive and capacitive loads are
scheduled properly, it can improve the power factor consequ
ently improving the grid efficiency. Another
advantage

In this paper we propose a framework for improving the power factor at a residence, group of residences or
commercial location by intelligent load scheduling without

using any extra hardware
. The basi
c idea of the
reactive power compensation here is to prevent the reactive component of the current from flowing along the
transmission elements. i.e. lines, cables and transformers, simply by co
-
scheduling appliances of opposite
reactance polarity. The flo
w of these reactive currents will then be mainly confined within the loads. As a result,
the transmission elements can be chosen to transmit only the active current component. Accordingly, the
required sizes of these elements will be smaller. We propose to

schedule the appliances following the customer
specific preferences and needs. For example, scheduling inductive load (such as washing machines, dryers etc.)
at the same time as capacitive loads (such as LCD tv) will improve the overall power factor. Prop
osed scheme is
simulated and experimentally verified on Indian appliances and effectiveness of the method is illustrated in this
paper.



2. POWER FACTOR


Power Factor (PF) is

the difference between the power needed to perform work and the electrical energy needed
so the work can be performed.
The power factor of an AC electrical power system is defined as the ratio of the
real power flowing to the load to the appar
ent power in

the circuit,
and is a dimensionless number between 0 and
1. Real power is the capacity of the circuit for performing work in a particular time. Apparent power

/ total
power (S)

in kVA
is the
complex sum of real power / active power / true power (R) in kW
and reactive power
(Q) in kVAr
.

It can be observed from the power triangle below that the power factor (p.f.) is given by the cosine
of the angle between total power and the true power.


S = P + jQ


Power Factor = P / S = P / √(P
2

+ Q
2
)




Figure 1: Power

factor triangle


If the load is inductive or capacitive the power consumed by this load is utilized to store energy instead of doing
work. This power is called reactive power. An inductive load consumes reactive power whereas; a capacitive
load generates
reactive power.
Even though reactive power doesn’t do any actual work, it still needs to be
generated and carried.
When power factor is poor
, reactive power travels through the wires between the load and
the utility grid, passing back and forth through the

residential meter which makes the system less efficient by
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increasing the system loses. This also increases the monthly electricity bill when reactive power is charged.


3. PROPOSED METHOD

In this paper, power factor of any residence or commercial place
has been improved through intelligent
scheduling of available appliances. The main idea behind this is to restrict the back and forth movement of
reactive power between grid and residence/commercial place. Here appliances are scheduled in such a way that
r
eactive power travels within appliances which drastically improves power factor, reduces network loss, relives
line capacity and differs T&D investment. Appliances are classified into three groups i.e. resistive, inductive
and capacitive. Inductive and ca
pacitive appliances are tried to schedule together so that reactive power
circulates between inductive and capacitive appliances. This is illustrated using the following picture. When
either inductive or capacitive loads are scheduled, reactive power circu
lates between main grid and appliances as
shown in Figure 2. On the other hand, when both inductive and capacitive loads are scheduled together, reactive
power circulates within appliances. This improves the system efficiency significantly. However, there
are several
issues with rescheduling appliances. For example appliance like television can’t be rescheduled. Therefore, we
introduced a inconvenience factor while scheduling the appliances.


Figure 2: Reactive power movement in a power network.


Mathematically the problem is formulated as follows:



1 1 2 2
1
* *
d
j j
j
Minimize g E I I
 


 
  
 


;
1 1
k d
jt t
t j
E y R

 
 
 
 
 
 

W
here



E is a cost for consuming reactive power



y is the level of reactive power consumption which is a function the power factor



R is the rate for reactive power, d’ is number of appliances,


is weight factor

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I1 and I2 are measures of the user inconvenience when the operating level and operating time
(respectively) of the device are modified to improve
power factor.


4. PROPOSED ARCHITECTURE FOR POWER FACTOR CORRECTION


The proposed architecture consists of three components i.e. smart meter, consumption profiler and scheduler as
shown in Figure 3. Each of these components is described below:

4.1 Smart Me
ter

Smart meters can be installed at device level or mains level or both. These are already being installed at many
homes due to smart grid initiatives. Smart meters measure active and reactive power consumption of appliances.
From the cumulative signatur
e of power consumption, appliance level active and reactive power consumption
will be determined. This information will be used to classify the appliances (as resistive, inductive or capacitive)
and to monitor the customer behaviour and comfort level.

4.2

Consumption profiler

It analyzes the data collected from
smart meter
s. It r
econstruct
s

active and reactive power consumption of each
appliance
.
The system can either utilize plug level meters (where available) or Non
-
intrusive
.

Appliance Load
Metering (NI
ALM) along with a database of device characteristics to

reconstruct appliance consumption
profiles
.


4.2
Scheduler

Scheduler c
an be installed at home, industry or commercial locations
. It s
tores and processed consumption
history and appliance profiles

and c
omputes schedules for appliances to improve power factor while r
especting
external constraints
e.g. u
ser availability, comfort, etc.


The detailed operation modularity of power factor correction scheme is presented in Figure 4.




Figure 3: Power
factor correction architecture



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Figure 4: Operation modularity of Power Factor Correction scheme

Table 1

Measured capacity and power factor of typical appliances























5. RESULTS


Usage

(hrs/day)

KW

PF

Television (Capacitive)

8

0.2

0.70

Washing machine (Inductive)

2

1.5

0.57

Water pump (Inductive)

1

0.5

0.40

Freezer (Inductive)

13

0.4

0.55

LED lights (Capacitive)

5

0.2

0.70

Electric vehicle (Capacitive)

7

2.0

0.75

Laptop charging (Capacitive)

4

0.4

0.80

Dishwasher (Inductive)

5

1.5

0.70

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Power factor correction through intelligent load scheduling was simulated for a typical household. It was
assumed that the household has appliances like television, washing machine,

water pump, freezer, LED lights,
electric vehicle and dishwasher. Typical power consumption profile of each appliance, collected using plug level
meters, is shown in Table 1.




Figure 5: Power factor minimizing power schedule

Given the consumption chara
cteristics in Table 1, we schedule the devices to minimize inconvenience and power
factor as in Equation (1). For this we use IBMs ILOG CPLEX software [9]. The results of this scheduling are
shown in Figure 5.

For the purposes of illustration, consider
the 8:00AM time slot. Without scheduling the water pump and the
freezer, the net reactive power component would be
-
1.64. However, after scheduling them, the net power factor
drops to
-
1.22, a 25% reduction. This substantial reduction results in reduced ge
neration, transmission and capex
costs as discussed earlier. Similar improvements can be seen in other time slots, particularly in the evening time
slots where peak consumption occurs.

6
. CONCLUSION

& FURTHER RESEARCH

This paper proposes a power factor cor
rection scheme through intelligent load scheduling. Proposed approach
improves power factor
while considering

c
ustomer or user related factors

such as u
ser prefe
rences for device
usage time,

duration and delay
, u
ser preference for device usage intensity an
d change in intensity
, u
ser
preference for device co
-
scheduling and re
-
scheduling
. Improving

power factor by intelligent load scheduling

can reduce the reactive power requirement from grid and can improve system efficiency and reduce m
onthly
electricity bi
ll
. As the proposed scheme avoids use of
additional
costly
hardware like capacitor/inductor bank
, it
is highly cost effective and has a significant potential for real world implementation.


8
. REFERENCES

[1] K. K. Kapil, “Reduction in transmission and
distribution loses, an opportunity for earning carbon credits”, Available online:

http://www.slideshare.net/kris_kapil/cdm
-
in
-
reduction
-
in
-
transmission
-
and
-
distribution
-
losses
.


[2]
Brandon Lorenz
, “
Smart Grid Addresses Energy Efficiency, Power Quality and

Reliability Issues
”, Available online:
http://www.facilitiesnet.com/powercommunication/article/Smart
-
Grid
-
Addresses
-
Energy
-
Efficiency
-
Power
-
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-
and
-
Reliability
-
Issues
--
11361
.


[3] L. W. W. Morrow, “Power
-
factor correction,” Transactions of the America
n Institute of Electrical Engineers
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7, Jan
1925.


[4
] Y. Jiang, F.C. Lee, G. Hua and W. Tang, “A novel single
-
phase power factor correction scheme,” Eighth Annual Applied Power
Electronics Conference and Exposition, pp: 287
-
292, 1993


[5
]

S. Basu and M.H.J. Bollen, “A Novel Common Power Factor Correction Scheme for Homes and Offices,” IEEE Transactions on
Power Delivery, Volume: 20, Issue: 3, pp: 2257
-

2263, 2005


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[6
] D.K. Maly and K.S. Kwan, “Optimal battery energy storage system (BESS)
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-

458, 1995


[7]
Papalexopoulos, Alex D., and George A. Angelidis. "Reactive power management and pricing in the California market."
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[8]
Harmonic Current Emissions
,
Guidelines to

the standard EN 61000
-
3
-
2
, Available online at
http://www.epsma.org/pdf/PFC%20Guide_November%202010.pdf


[9]"IBM ILOG CPLEX Optimizer”,
url

:
http://www
-
01.ibm.com/software/integration/optimization/cplex
-
optimizer/,