A simulation research on passive harmonic filters for variable frequencies

TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
Số 16 67 
A SIMULATION RESEARCH ON PASSIVE HARMONIC FILTERS 
FOR VARIABLE FREQUENCIES 
MÔ PHỎNG BỘ LỌC SÓNG HÀI THỤ ĐỘNG VỚI TẦN SỐ BIẾN ĐỔI 
Anh Tuan Bui 
Electric Power University 
Ngày nhận bài: 17/6/2018, Ngày chấp nhận đăng: 2/7/2017, Phản biện: TS. Nguyễn Ngoc Khoát 
Abstract: 
This article presents the principle of passive harmonic filters with variable frequency based on a 
nonlinear harmonic reducer depending on working characteristics. A schematic diagram of a 
harmonic filter with variable frequencies will be proposed. By simulating the operation principle of 
the device, this paper demonstrates the effectiveness of this device compared with conventional 
passive harmonic filters including low price, compact size, but the harmonic filtering quality is still the 
same. 
Keywords: 
Harmonics, harmonic filters, power quality, power losses. 
Tóm tắt: 
Bài báo trình bày nguyên lý làm việc của bộ lọc sóng hài thụ động với tần số biến đổi dựa trên một 
thiết bị phi tuyến phát thải sóng hài theo đặc tính làm việc. Sơ đồ nguyên lý hoạt động của thiết bị 
lọc sóng hài thụ động với tần số biến đổi sẽ được đề xuất. Thông qua việc mô phỏng nguyên lý hoạt 
động của thiết bị sẽ chứng minh được tính hiệu quả của thiết bị này so với các thiết bị lọc sóng hài 
thụ động thông thường như: giá thành rẻ, kích thước gọn nhẹ nhưng tính năng lọc sóng hài không 
thay đổi. 
Từ khóa: 
Sóng hài bậc cao, bộ lọc sóng hài, chất lượng điện năng, tổn thất điện năng. 
1. INTRODUCTION 
At present, harmonics filtering in 
electrical systems is one of the most 
important issues to improve power 
quality, to increase efficiency and lifespan 
of electrical appliances, to reduce power 
losses in electrical systems. In fact, high-
power nonlinear devices are being used 
extensively in power grid such as: single 
phase or three-phase rectifiers and 
inverters, SVC, In many countries, the 
percentage of nonlinear loads can be as 
high as 80-90% [2]. 
These nonlinear devices often cause 
harmonic spectrum which varies both in 
amplitude and in frequency [1], [2]. 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
68 Số 16 
Therefore, in order to put harmonics 
within the limits [3] we need to use 
harmonic filters. If using classical 
harmonic filters (single frequency filters), 
it will need to use a lot of filters to reduce 
the impact of different harmonic 
frequencies. This leads to an increase of 
the equipment cost. Therefore, a variable 
frequency harmonic filter can reduce the 
cost of production and improve the 
efficiency of harmonic filter. 
In this article, the simulation results of the 
passive harmonic filter with variable 
frequencies will be present. It is used for a 
harmonics reduction system depending on 
working characteristics of a compensating 
device using smooth - adjust thyristor 
system - by MATLAB - Simulink 
program. The simulation results introduce 
the harmonic filtering efficiency of this 
device which is more effective than the 
common passive harmonic filters. 
2. CIRCUIT DIAGRAM USING 
HARMONIC FILTER WITH VARIABLE 
FREQUENCIES 
2.1. Circuit principle 
A schematic diagram of a harmonic filter 
with variable frequencies is used to filter 
harmonics for a single-phase turbo 
scroller (TCR) as shown in Fig.1. The 
inductor X0 has a capacity of 100 kVAr, 
thyristor T0 pairs anti-parallels. 
The working principle of this device can 
be described as follows: By determining 
and changing the firing angle α, from 90o 
to 180
o
, it is possible to smoothly adjust 
the reactive power of the inductor X0 
from 100 kVAr to 0 kVAr. 
The change in the reactive power of the 
inductor X0 is determined by the formula 
[4]: 
 2
2
2
2
2
1 2sin222sin22 
 
 L
Q
L
E
Q (1) 
QL is the rated power of the inductor; α is 
the firing angle of the thyristor (in 
radians). 
Fig.1. The principle of the proposed harmonic 
filter with variable frequencies 
However, during the control process, the 
harmonics generated is very large and the 
amplitude of the harmonics is highly 
dependent on the firing angle α of the 
thyristor (see Table 1). 
From Table 1, in the TCR device, 
harmonics focus mainly on order 3, 5, 7 
and 9. The values of these harmonics 
depend on the angle α. If using classical 
passive filter, 04 sets should be used. 
However, in this case, we will consider to 
install two harmonic filters, one with 
fixed frequency for filtering 3 harmonic 
order. The other has 3 filter frequencies, 
including orders 5, 7, and 9. The change 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
Số 16 69 
in filter frequency will be achieved by 
closing or opening the capacitor system 
using thyristors T1, T2 and T3. 
Table 1. Harmonics amplitude depending 
on firing angle α [4] 
α (o) 90 120 135 150 180 
I3,А 0 19.9 15.3 6.6 0 
I5,А 0 4.0 3.1 4.0 0 
I7,А 0 1.4 2.2 1.4 0 
I9,А 0 2.0 1.0 0.2 0 
I11,А 0 0.7 0.8 0.7 0 
I13,А 0 0.4 0.5 0.4 0 
I15,А 0 0.7 0.4 0.0 0 
I17,А 0 0.3 0.3 0.3 0 
I19,А 0 0.2 0.3 0.2 0 
2.2. Calculation method for selecting the 
capacity of passive harmonic filters with 
variable frequencies 
The filter in Fig.1 consists of three 
capacitors C1, C2, C3, which have 
different capacitances, each capacitor is 
controlled by two parallel thyristors. The 
resonance frequency of the device when 
closing a capacitor as follows [5], [6]: 
1
1
1
L
C
X
X
 
(2) 
When the second capacitor is connected, 
the equivalent capacitance of two parallel 
capacitors as follows: 
21
2 11
1
CC
Ctd
XX
X
The resonance frequency will be: 
1
21
1
2
2
11
1
L
CC
L
Ctd
X
XX
X
X
 
(3) 
Similarly, when the third capacitor is 
connected, the resonance frequency of the 
device will be: 
1
321
1
3
3
111
1
L
CCC
L
Ctd
X
XXX
X
X
 
(4) 
The value of 
1CX , 2CX , 3CX and 1LX 
will be selected to match the harmonic 
amplitude caused by the change in load 
power. 
3. SIMULATION RESULTS 
Simulation results were recorded with 
different angles α and calculated in 2 
cases, as follows: 
 Case 1: Do not use filters. 
 Case 2: Use a fixed frequency filter for 
harmonic order 3 and a variable 
frequency filter for harmonic orders 5, 
7 and 9. 
The simulation schematic is shown in 
Fig.2. 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
70 Số 16 
3.1. When the angle α = 127o 
 Case 1: Do not use filters. 
Fig.3. Waveform distortion and THD at α = 127
0 
In this case, the waveform of the current 
is shown in Fig.3. The harmonics are very 
high. The third - order and seventh - order 
harmonics are the highest. The THD 
index is 47.05% (see Fig.3). 
 Case 2: Use a fixed frequency filter for 
harmonic order 3 and a variable 
frequency filter for harmonic order 7. 
Fig.4. Waveform distortion and THD 
when using third - order and seven - order 
filters at α = 127
0
When using filters to filter large harmonic 
frequencies, the waveform is corrected 
closer to the sinusoidal form (see Fig.4). 
The distortion rate is very small. The total 
THD level of the harmonics is 2.33%. 
Fig.2. Matlab - Simulink simulation schematic of a passive filter with variable frequencies 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
Số 16 71 
3.2. The angle α = 1100 
 Case 1: Do not use filters. 
The total harmonic level of the harmonics 
is 23.41%, where the harmonic order 3 
and 5 are the largest (see Fig.5).
Fig.5. Waveform distortion and THD 
when not using filter at α = 110
0 
 Case 2: Use a fixed frequency filter for 
harmonic order 3 and a variable 
frequency filter for harmonic order 5. 
Fig.6. Waveform distortion and THD 
when using filters 3 and 5 - order frequencies 
at α = 110
0 
Since the third harmonic is the largest, 
then to the fifth harmonic. Two harmonics 
filters with frequency orders of 3 and 5 
are used. Thus, wave distortion is much 
reduced compared to the case do not use 
filters and the THD index in this case 
drops to 2.41% (see Fig.6). 
Through the simulation results for two 
firing α of the inductance, when the width 
of angle changes, the amplitude of the 
harmonics also changes. And the use of 
passive harmonic filters with variable 
frequencies will be more effective than 
using single frequency filters (in case 1). 
4. CONCLUSION AND DISCUSSION 
The use of nonlinear loads has many 
advantages compared with previous 
electrical and electronic equipment. 
However, beside these advantages, these 
nonlinear devices generate harmonics that 
reduce the power quality. This results in 
increasing power losses, reducing 
lifespan, especially for electronic devices. 
Through this paper, the author introduced 
a solution using harmonic filters with 
variable frequencies. 
The working principle of this device is 
explained based on the analysis and 
calculation of the harmonics emission of a 
typical non-linear load. The efficiency of 
harmonic filters with variable frequencies 
is indicated clearly through simulation. 
Simulation results show that, at some 
time, variable frequencies harmonic filters 
offer greater efficiency than conventional 
single frequency harmonic filters. In 
addition, this solution also reduces the 
TẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ NĂNG LƯỢNG - TRƯỜNG ĐẠI HỌC ĐIỆN LỰC 
(ISSN: 1859 - 4557) 
72 Số 16 
investment cost and the device is lighter 
than the classical filter. 
These harmonics filters are well suited to 
variable nonlinear loads. And we can 
completely research and produce this 
device. 
REFERENCES 
[1] Bùi Anh Tuấn, Lọc sóng hài với tần số biến đổi, Tạp chí Khoa học và Công nghệ, Trường Đại học 
Công nghiệp Hà Nội, số 44, 02/2018. 
[2] Trần Đình Long, Sách tra cứu về chất lượng điện năng, Nhà xuất bản Bách khoa Hà Nội, 2014. 
[3] Thông tư quy định hệ thống lưới điện phân phối, 18/11/2015. 
[4] George J. Wakileh, Power Systems Harmonics-Fundamentals, Analysis And Filters Design, 
Springer, 2001. 
[5] A. Priyadharshini, N. Devarajan, AR. Uma saranya, R. Anitt, Survey of Harmonics in Non Linear 
Loads, International Journal of Recent Technology and Engineering (IJRTE) ISSN: 2277-3878, 
Volume-1, Issue-1, April 2012. 
[6] Bùi Anh Tuấn, Đinh Ngọc Quang, Báo cáo tổng kết đề tài cấp Bộ Công Thương: “Nghiên cứu, chế 
tạo thiết bị bù công suất phản kháng trong lưới điện hạ áp dựa trên nguyên lý lai”, 2014. 
Biography: 
Anh Tuan Bui, received the B.S and M.Sc. degrees in electrical engineering from 
Hanoi University of Science and Technology, Vietnam in 2001 and 2006, 
respectively. He received the Ph.D. degree in electrical materials from Ampere 
University, Lyon, France in 2011. He is the lecturer at the Faculty of Electrical 
Engineering, Electric Power University, Vietnam. 
His research interests include electromagnetic materials, reactive power 
compensation and power quality.