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ANALYSIS OF HARMONIC DISTORTION DUE TO VARIABLE
FREQUENCY DRIVES Jagdeep Kaur Brar1
Research Scholar
Dr. Sarbjeet Kaur Bath2
Professor of Electrical Engineering
(1) & (2) Department of Electrical Engineering,
Giani Zail Singh Campus College of Engineering & Technology,
Maharaja Ranjit Singh Punjab Technical University Bathinda, Punjab, India
[email protected] ,[email protected]
Abstract: The electric power systems operate on frequencies of 50 Hz or 60Hz. Different types of loads produce
current and voltage waveforms with frequencies that are integer multiples of the fundamental frequency (50 or 60
Hz) which produce electrical pollution known as power system harmonics. Today the use of power electronic devices
has increased manifold. Mostly power electronic devices are non linear in nature. The main sources of harmonics
are power semiconductor devices, electric furnaces, fluorescent lamps, rotating machines, saturated devices like
transformers, variable frequency drives (VFDs), and adjustable speed drives (ASDs) in modern industry. The
processes of cement industry and textile industry with the excessive use of non-linear loads have an impact on the
power quality of the connected electric network. Harmonic distortion is a very significant phenomenon that affects
the plant distribution network as well as grid performance [7].In this paper, harmonic distortion produced by
variable frequency drives has been analyzed by simulating these drives on two standard test systems of IEEE 6 bus
system and IEEE 9 bus system with the help of ETAP software.
Keywords – Harmonic analysis, Total harmonic distortion, IEEE 6 Bus system, IEEE 9 Bus system, Variable
frequency drive.
1. INTRODUCTION
In the modern power system, the use of power electronic devices is increasing day by day which
are non-linear loads that create power quality issues. These power electronic devices are
commonly used for printers, variable frequency drives, air conditioners, computers, power
electronic converters, inverters, adjustable speed drives, welding machines, uninterruptible
power supplies (UPS), arcing devices, electric oven, furnaces, switched mode power supplies,
saturation devices such as transformers, rotating devices, etc. All power electronic devices are
the main cause of non-linear loads, which cause many power quality problems in electrical
power systems. Non-liner loads produce non -sinusoidal waveform that results in a distorted
current waveform and distorted voltage waveform and also draws a large amount of reactive
power (VARs). Due to the wide use of non-linear loads in the industrial, residential, and
commercial areas, power quality issues have become more important. Total harmonic distortion
(THD) can be defined as the ratio of the sum of the powers of all harmonic components to the
power of the fundamental frequency component and is a measurement of the harmonic
distortion present in a fundamental signal.
2. VARIABLE FREQUENCY DRIVES
The adjustable speed drive system is necessary for controlling the speed and torque of AC
motor by changing frequency and input voltage for both electrical and mechanical systems. This
system is called as variable frequency drives. Variable frequency drives are connected with
motor loads for controlling speed of the motor. The motor load consumes about25% of the
world's energy. Variable frequency drives use power electronic devices that are main cause of
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harmonic distortion [1]. In the modern industry, these devices are utilized with important loads
for their working [15]. VFDs have large number of advantages like speed control of motors,
energy saving and starting current limitation of motor etc. These devices are considered as the
harmonic sources as well as inter harmonic sources. VFDs consist of three stages such as
rectifier stage, inverter stage and control stage. The block diagram of VFD is shown in Figure1
[16].
Figure 1: Block diagram of variable frequency drive
To get a variable frequency voltage, the AC voltage available at a fixed frequency is first
converted to DC voltage with the help of a rectifier. Then an inverter is used to convert this DC
voltage to AC voltage at the desired frequency and voltage level. The amount of harmonic
distortion depends on the design of filters and inverters. In Figure 1, a variable frequency drive
system has been connected with three phase motor load. The control system is used to control
the output voltage at desired levels. Basically the control system is an electronic circuit that
takes the feedback information from load (three phase motor load) and controls the output
voltage and frequency to a desired level [8].
In the present study, the analysis of the harmonic distortion produced by the use of variable
frequency drives has been done by applying these VFD systems for standard test systems of
IEEE 6 bus and IEEE 9 bus as presented in the following sections.
3. IEEE 6 BUS SYSTEM
Bus input data, for the 6 buses, which consists of bus voltage (KV), apparent power (MVA),
reactive power (MVAr) is shown in Table 1[12].IEEE 6 Bus system consists of five
transformers T1-T5 for which transformer power rating and voltage ratings of primary and
secondary windings are given in Table 2.
Table 1: Bus input data for IEEE 6 bus system
Bus ID Bus
Voltage
KV
Bus
MVA
rating
Bus
MVAr
Rating
VTHD VIHD
Bus 1. 4.160 0.00 0.00 2.50 1.50
Bus 2. 4.160 13.00 0.00 2.50 1.50
Bus 3. 4.160 13.00 5.00 2.50 1.50
Bus 4. 4.160 0.357 0.152 2.50 1.50
Bus 5. 4.160 0.357 0.152 2.50 1.50
Bus 6. 4.160 0.357 0.152 2.50 1.50
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Table 2: Transformer input data for IEEE 6 bus system
Transformer ID Power
Rating
MVA
Primary
Voltage Rating
KV
Secondary
Voltage Rating
KV
T1 2.0 4.160 4.160
T2 2.0 4.160 4.160
T3 2.0 4.160 4.160
T4 2.0 4.160 4.160
T5 2.0 4.160 4.160
Synchronous machine data, in terms of power rating, voltage rating and speed of motor is sho
wn in Table 3
.Table 3: Machine input data for IEEE 6 bus system
Machine ID Bus
ID
MVA KV RPM
U1 Bus 1 100 4.160 0.00
Motor 1 Bus 3 0.388 4.160 1000
Motor 2 Bus 4 0.388 4.160 1500
Motor 3 Bus 5 0.388 4.160 1500
Motor 4 Bus 6 0.388 4.160 1500
4. HARMONIC ANALYSIS WITHOUT VFDs FORIEEE 6 BUS SYSTEM
IEEE 6-bus system with the above given input data has been simulated without VFDs using
ETAP software, the simulation diagram for it, is shown in Figure 2. It consists of 6-buses, 5-
transformers and 4-synchronous machines. After the program is run, the obtained voltage
waveforms are shown in Figure 3 and the voltage harmonic spectrum captured at all the buses is
shown in Figure 4.
Figure 2: Simulation diagram without VFDs for IEEE 6 bus system
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Figure 3: Voltage waveforms at all buses without VFDs for IEEE 6 bus system
Figure 4: Voltage harmonic spectrum without VFDs for IEEE 6 bus system
5. HARMONIC ANALYSIS WITH VFDs FOR IEEE 6 BUSSYSTEM
Single line diagram of Figure 5 shows the IEEE 6-bus system using variable frequency drives
with each synchronous machine, connected to bus 3,4,5,6.
Figure 5: Simulation diagram with VFDs for IEEE 6 bus system
Total harmonic distortion produced in the under consideration power system with voltage
waveform and its harmonic spectrum captured at all the buses, are shown in figure 6 & 7
respectively.
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Figure 6: Voltage waveforms with VFDs for IEEE 6 bus system
Figure 7: Voltage spectrumwith VFDs for IEEE 6 bus system
6. COMPARISON OF HARMONIC DISTORTION WITH AND WITHOUT VFDs FOR
IEEE 6 BUS SYSTEM
Total harmonic distortion and harmonic order produced due to the use of variable frequency
drives and without their use are compared as shown in Table 4.
Table 4: THD & harmonic order with and without variable frequency drives
Bus
ID
Harmonic Analysis
Percentage &
Harmonic
Order
With VFDs Without
VFDs
Bus 1. THD% 22.76% 22.58%
Harmonic
Order
2,3,4,5,7,9 2,3,4,5,7,9
Bus 2. THD% 20.74% 15.83%
Harmonic
Order
2,3,4,5,7,9,11,13,17,19,23, 25,29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus 3. THD% 23.89% 17.53%
Harmonic
Order
2,3,4,5,7,9,11,13,17,19,23,
25,29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus 4. THD% 23.89% 17.53%
Harmonic
Order
2,3,4,5,7,9,11,13,17,19,23,
25,29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus 5. THD% 23.89% 17.53%
Harmonic
Order
2,3,4,5,7,9,11,13,17,19,23, 25,29,31,35,37,41,43,47,49
2,3,4,5,7,9
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Bus 6. THD% 23.89% 17.53%
Harmonic
Order
2,3,4,5,7,9,11,13,17,19,23, 25,29,31,35,37,41,43,47,49
2,3,4,5,7,9
From the Table 4,it is observed that the total harmonic distortion produced with VFDs is about
5-7% more as compared to without VFDs. Also higher order harmonics, such as; 11th, 17th,19th,
23rd,25th,29th,31st,35th,37th, 41st,43rd,47th,49th are introduced due to the use of variable frequency
drives.
7. IEEE 9 BUS SYSTEM
IEEE 9 bus system consists of eight transformers T1-T8 for which transformer power rating and
voltage rating of primary and secondary winding are given in Table 5.
Table 5: Transformer input data for IEEE 9 bus system
Transformer ID Power
Rating
MVA
Primary
Voltage
Rating
KV
Secondary
Voltage
Rating KV
T1 50.00 115.00 15.80
T2 12.500 15.80 4.160
T3 12.500 15.80 4.160
T4 12.500 15.80 4.160
T5 12.500 15.80 4.160
T6 12.500 15.80 4.160
T7 12.500 15.80 4.160
T8 12.500 15.80 4.160
Bus input data, for the 9 buses, which consists of bus voltage (KV), apparent power (MVA),
reactive power (MVAr) is shown in Table 6 [12]
Table 6: Bus input data for IEEE 9 bus system
Bus ID Bus Voltage
KV
Active
Power MW
Reactive
Power Mvar
VTHD VIHD
Bus 1 115.00 0.00 0.00 2.50 1.50
Bus 2 15.80 0.00 0.00 2.50 1.50
Bus 3 4.160 11.592 4.404 2.50 1.50
Bus 4 4.160 11.592 4.404 2.50 1.50
Bus 5 4.160 11.592 4.404 2.50 1.50
Bus 6 4.160 11.592 4.404 2.50 1.50
Bus 7 4.160 11.592 4.404 2.50 1.50
Bus 8 4.160 11.592 4.404 2.50 1.50
Bus 9 4.160 11.592 4.404 2.50 1.50
Synchronous machine data, in terms of power rating, voltage rating and speed of motors is
shown in Table 7.
Table 7: Machine input data for IEEE 9 bus system
Machine ID Bus ID MVA KV RPM
U1 Bus 1 2000 115.00 0.00
Motor 1 Bus 3 12.400 4.00 1500
Motor 2 Bus 4 12.400 4.00 1500
Motor 3 Bus 5 12.400 4.00 1500
Motor 4 Bus 6 12.400 4.00 1500
Motor 5 Bus 7 12.400 4.00 1500
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Motor 6 Bus 8 12.400 4.00 1500
Motor 7 Bus 9 12.400 4.00 1500
8. HARMONIC DISTORTION WITHOUT VFDs FORIEEE 9 BUSSYSTEM
IEEE-9 bus system with the above given input data has been simulated without VFDs using
ETAP software, the single line circuit diagram for simulation is shown in Figure 8. It consists of
9-buses, 8-transformers and 7-synchronous machines. After the program is run, the obtained
voltage waveforms are shown in Figure 9 and the voltage harmonic spectrum at all the buses is
shown in Figure 10.
Figure 8: Simulation diagram without VFDs for IEEE 9 bus system
Figure 9: Voltage waveforms without VFDs for IEEE 9 bus system
Figure 10: Voltage spectrum without VFDs for IEEE 9 bus system
9. HARMONIC DISTORTION WITH VFDs FOR IEEE 9 BUS SYSTEM
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Single line diagram of Figure 11 shows the IEEE 9-bus system using variable frequency drives
with each synchronous machine, connected to bus 3,4,5,6,7,8,9.
Figure 11: Simulation diagram with VFDs for IEEE 9 bus system
Total harmonic distortion produced in the under consideration power system with voltage
waveform and its harmonic spectrum obtained at all the buses are shown in Figures 12 & 13
respectively.
Figure 12: Voltage waveforms with VFDs for IEEE 9 bus system
Figure 13: Voltage spectrumswith VFDs for IEEE 9 bus system
10. COMPARISON OF HARMONIC DISTORTION WITH AND WITHOUT VFDs FOR
IEEE 9 BUS SYSTEM
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Total harmonic distortion and harmonic order produced due to the use of variable frequency
drives and without their use are compared as shown in Table 8.
Table 8: THD & harmonic order with or without variable frequency drives
Bus
No.
Harmonic analysis
Percentage
&
Harmonic
order
With VFDs Without
VFDs
Bus
1
THD% 23.55% 22.87%
Harmonic
order
2,3,4,5,6,7,9,11,13,17,19,23,25 2,3,4,5,6,7,9
Bus
2
THD% 28.23% 14.91%
Harmonic
order
2,3,5,7,9,11,13,17,19,23,25,29,
31,35,37,41,43,47,49
2,3,4,5,7,9
Bus
3
THD% 27.66% 17.06%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25, 29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus
4
THD% 27.53% 17.06%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25,
29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus
5
THD% 27.53% 17.06%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25,
29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus
6
THD% 43.31% 17.06%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25,
29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus
7
THD% 43.31% 17.06%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25, 29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus
8
THD% 43.75% 17.06%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25,
29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus
9
THD% 43.33% 17.06%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25,
29,31,35,37,41,43,47,49
2,3,4,5,7,9
From the Table 8, it is observed that the total harmonic distortion produced with VFDs is about 5-7
% more as compared to without VFDs. Also higher order harmonics, such as; 11th, 17th,19th,
23rd,25th,29th,31st,35th,37th, 41st,43rd,47th,49th, are introduced due to the use of variable frequency
drives.
11. HARMONIC DISTORTION AFTER USING 11th
ORDER SINGLE TUNED
FILTER
11th order harmonic filter has been used to reduce the higher order harmonic for IEEE 6 bus and
IEEE 9 bus system.
11.1 Harmonic Distortion With 11th
Order Harmonic Filter For IEEE 6 Bus System
Simulation diagram of Figure 14 shows the IEEE 6-bus system using 11th order harmonic single
order filter, that is used to reduced higher order harmonic such as; 11th, 17th,19th,
23rd,25th,29th,31st,35th,37th, 41st,43rd,47th, and 49thorder harmonic.
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Figure 14: Simulation diagram with single tuned filter for IEEE 6 bus system
Distortion produced in the voltage waveforms and the harmonic spectrum at all the buses, is
shown in Figure 15 & 16 respectively.
Figure 15: Voltage waveforms with single tuned filter for IEEE 6 bus system
Figure 16: Voltage spectrum with single tuned filter for IEEE 6 bus system
11.2 Comparison of Harmonic Distortion With and Without Using Single Tuned Filter For
IEEE 6 bus system
Total harmonic distortion and harmonic order due to the use of single tuned filter and without
their use are compared as shown in Table 9.
Table 9: Harmonic distortion with and without single tuned filter for VFD system for IEEE 6
bus system
Bus
No.
Harmonic analysis
Percentage
&
VFD Without single
tuned filter
VFD With
single tuned
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Harmonic
order
filter
Bus
1
THD% 22.76% 22.58%
Harmonic
order
2,3,4,5,7,9 2,3,4,5,7,9
Bus
2
THD% 20.74% 15.85%
Harmonic
order
2,3,4,5,7,9,11,13,
17,19,23,25,29,31,
35,37,41,43,47,49
2,3,4,5,7,9
Bus
3
THD% 23.89% 17.56%
Harmonic
order
2,3,4,5,7,9,11,13,
17,19,23,25,29,31,
35,37,41,43,47,49
2,3,4,5,7,9
Bus
4
THD% 23.89% 17.56%
Harmonic
order
2,3,4,5,7,9,11,13,
17,19,23,25,29,31,
35,37,41,43,47,49
2,3,4,5,7,9
Bus
5
THD% 23.89% 17.56%
Harmonic
order
2,3,4,5,7,9,11,13,
17,19,23,25,29,31,
35,37,41,43,47,49
2,3,4,5,7,9
Bus
6
THD% 23.89% 17.56%
Harmonic
order
2,3,4,5,7,9,11,13,
17,19,23,25,29,31,
35,37,41,43,47,49
2,3,4,5,7,9
From the Table 9, it is observed that the total harmonic distortion produced without single tuned
filter is about 5-7 % more as compared to with single tuned filter. Also higher order harmonics,
such as; 11th, 17th,19th, 23rd,25th,29th,31st,35th,37th, 41st,43rd,47th,49th are reduced due to the use of
single tuned filter.
11.3 Harmonic Distortion with 11th
Order Harmonic Filter For IEEE 9 Bus System
Single line diagram of Figure 17 shows the IEEE 9-bus system using 11th order harmonic single
order filter, that is used to reduced higher order harmonic such as; 11th, 17th,19th,
23rd,25th,29th,31st,35th,37th, 41st,43rd,47th, and 49thorder harmonic.
Figure 17: Simulation diagram with single tuned filter for IEEE 9 bus system
The voltage waveform and its harmonic spectrum at all the buses are shown in Figures 18 &19
respectively.
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Figure 18: Voltage waveforms with single tuned filter for IEEE 9 bus system
Figure 19: Voltage spectrum with single tuned filter for IEEE 9 bus system
11.4 Comparison of Harmonic Distortion With And Without Single Tuned Filter For
IEEE 9 Bus System
Total harmonic distortion and harmonic order reduced due to the use of single tuned filter and
without their use are compared as shown in Table 10.
Table 10: Harmonic distortion with or without single tuned filter for IEEE 9 bus system
Bus No. Harmonic analysis
Percentage
&
Harmonic
order
VFDs Without 11th
order single tuned
filter
VFDs With 11th
order
single tuned filter
Bus 1. THD% 23.55% 21.65%
Harmonic
order
2,3,4,5,6,7,9,11,13,17,19,23,25 2,3,4,5,6,7,9
Bus 2. THD% 28.23% 15.32%
Harmonic
order
2,3,5,7,9,11,13,17,19,23,25,29,
31,35,37,41,43,47,49
2,3,4,5,7,9
Bus 3. THD% 27.66% 14.37%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25, 29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus 4. THD% 27.53% 15.94%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25,
29,31,35,37,41,43,47,49
2,3,4,5,7,9
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Bus 5. THD% 27.53% 15.94%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25, 29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus 6. THD% 43.31% 19.41%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25,
29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus 7. THD% 43.31% 19.41%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25,
29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus 8. THD% 43.75% 19.52%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25,
29,31,35,37,41,43,47,49
2,3,4,5,7,9
Bus 9. THD% 43.33% 19.41%
Harmonic
order
2,3,4,5,7,9,11,13,17,19,23,25, 29,31,35,37,41,43,47,49
2,3,4,5,7,9
From the Table 10, it is observed that the total harmonic distortion has been reduced by about 13%
- 23% with the use of single tuned filter as compared to without using it. Also higher order
harmonics, such as; 11th, 17th,19th, 23rd,25th,29th,31st,35th,37th, 41st,43rd,47th,49th are reduced due to
the use of single tuned filter.
12. CONCLUSION
In this paper, analysis of harmonics produced due to variable frequency drives has been done by
simulating these drives on IEEE 6 bus system and IEEE 9 bus system by using ETAP software.
Total harmonic distortion and harmonic order has been analyzed with and without variable
frequency drives. Then an attempt has been made to reduce the harmonics with the help of tuned
filters.
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