Hybrid VAR compensator with improved efficiency

Abstract

In modern electrical networks thyristor-switched capacitors (TSC) are most used devices
for VAR compensation. These devices don’t contain rotating parts and mechanical contacts,
provide a stepwise control of reactive power and no generation of harmonics to the
network. However, with the help of TSC it’s not possible to ensure smooth control of reactive
power and capacitor banks (CB) are exposed to the negative impact of higher harmonic
components of the network voltage. Hybrid VAR compensator don’t have such
drawbacks. It consists of active filter (AF) and capacitor bank with discrete regulation. The
main drawback of such systems is the necessity of accessing all six terminals of CB, while
most of them are manufactured with three terminals, internally delta-connected. In the article,
the topology and control system of hybrid VAR compensator free from beforementioned
drawback, is proposed. The control system provides operating modes of overcompensation
or undercompensation reactive power. VAR distribution regulator performs redistribution
of reactive power between active filter and capacitor banks with the condition to minimize
active filter’s power. Scheme of the hybrid VAR compensator, which includes a three-phase
three-terminal delta-connected capacitor banks, is shown. Proposed approach allows to
provide smooth control of reactive power, isolate the capacitor bank from harmonic currents
and use a more effective low-voltage power components.

Full text

ВІСНИК ПРИАЗОВСЬКОГО ДЕРЖАВНОГО ТЕХНІЧНОГО УНІВЕРСИТЕТУ
2014р. Серія: Технічні науки Вип. 29
ISSN 2225-6733
174
3. Бурлака В.В. Джерело живлення для дугового GTAW зварювання змінним струмом /
В.В. Бурлака, С.В. Гулаков, С.К. Поднебенна, О.Л. Мостинець // Всеукраїнська науково-
практична конференція молодих учених, спеціалістів, аспірантів «Енергетика, енергозбере-
ження на початку ХХІ століття», 20 березня 2014. – Маріуполь: ДВНЗ «ПДТУ», 2014. – С. 13.
Bibliography:
1. Zaks M.M. Transformers for arc welding / M.M. Zaks, B.A. Kaganskiy, A.A. Pechenin. – L.: En-
ergoatomizdat. Leningrad department, 1988. – 136 pp. (Rus.)
2. Solodskiy S.A. Power sources for arc welding: a tutorial / S.A. Solodskiy, O.G. Brunov,
D.P. Iljashenko // Jurginskiy technology institute – Tomsk: Publishing office of Tomsk Polytech-
nic University, 2012. – 165 pp. (Rus.)
3. Burlaka V.V. Power supply for GTAW arc welding / V.V. Burlaka, S.V. Gulakov,
S.K. Podnebenna, O.L. Mostinets // National Scientific Conference of Young Scientists, Special-
ists, Graduate Students « Energy, energy saving at the beginning of the 21st century», March, 20th,
2014. – Mariupol: PSTU, 2014. – Р. 13. (Ukr.)
Рецензент: В.В. Чигарев
д-р техн. наук, проф., ГВУЗ «ПГТУ»
Статья поступила 10.11.2014
УДК 621.316.727
© Burlaka V.V.1, Gulakov S.V.2, Podnebennaya S.K.3, Savenko O.S.4
HYBRID VAR COMPENSATOR WITH IMPROVED EFFICIENCY
In modern electrical networks thyristor-switched capacitors (TSC) are most used devices
for VAR compensation. These devices don’t contain rotating parts and mechanical con-
tacts, provide a stepwise control of reactive power and no generation of harmonics to the
network. However, with the help of TSC it’s not possible to ensure smooth control of reac-
tive power and capacitor banks (CB) are exposed to the negative impact of higher har-
monic components of the network voltage. Hybrid VAR compensator don’t have such
drawbacks. It consists of active filter (AF) and capacitor bank with discrete regulation. The
main drawback of such systems is the necessity of accessing all six terminals of CB, while
most of them are manufactured with three terminals, internally delta-connected. In the arti-
cle, the topology and control system of hybrid VAR compensator free from beforementioned
drawback, is proposed. The control system provides operating modes of overcompensation
or undercompensation reactive power. VAR distribution regulator performs redistribution
of reactive power between active filter and capacitor banks with the condition to minimize
active filter’s power. Scheme of the hybrid VAR compensator, which includes a three-phase
three-terminal delta-connected capacitor banks, is shown. Proposed approach allows to
provide smooth control of reactive power, isolate the capacitor bank from harmonic cur-
rents and use a more effective low-voltage power components.
Keywords: VAR compensator, capacitor, active filter, thyristor switching capacitors,
voltage source inverter (VSI).
1 канд. техн. наук, доцент, ГВУЗ «Приазовский государственный технический университет»,
г. Мариуполь, vburlaka@rambler.ru
2 д-р техн. наук, профессор, ГВУЗ «Приазовский государственный технический университет»,
г. Мариуполь, gulakov_s_v@pstu.edu
3 канд. техн. наук, доцент, ГВУЗ «Приазовский государственный технический университет»,
г. Мариуполь, podsvet@gmail.com
4 специалист, ГВУЗ «Приазовский государственный технический университет», г. Мариуполь,
savenko-olja@yandex.ru

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Бурлака В.В., Гулаков С.В., Поднебенная С.К., Савенко О.С. Гибридный компен-
сатор реактивной мощности с повышенной эффективностью. Предложены
схемные решения гибридного компенсатора реактивной мощности, состоящего из
последовательного активного фильтра и батареи конденсаторов с тиристорным
переключением ступеней. Рассмотрена работа системы управления гибридным
компенсатором. Предложенное решение позволяет «изолировать» БК от токов
высших гармоник и обеспечить плавное регулирование реактивной мощности.
Ключевые слова: компенсатор реактивной мощности, конденсатор, активный
фильтр, конденсатор с тиристорным переключением, автономный инвертор на-
пряжения.
Бурлака В.В., Гулаков С.В., Поднебенна С.К., Савенко О.С. Гібридний компенса-
тор реактивної потужності з підвищеною ефективністю. Запропоновані схемні
рішення гібридного компенсатора реактивної потужності, що складається з по-
слідовного активного фільтру і батареї конденсаторів з тиристорним перемикан-
ням ступенів. Розглянуто роботу системи управління гібридним компенсатором.
Запропоновані рішення дозволяють «ізолювати» батерею конденсаторів від стру-
мів вищих гармонік і забезпечити плавне регулювання реактивної потужності.
Ключові слова: компенсатор реактивної потужності, конденсатор, активний
фільтр, конденсатор з тиристорним перемиканням, автономний інвертор напруги.
Description of the problem. Reactive power (RP) flowing in the network reduce the lifetime of
the equipment, increase power losses and decrease the network capacity. The conventional methods of
reactive power compensation have several disadvantages: synchronous condensers require installation
of a large number of additional equipment, fixed capacitor banks are not regulated, and mechanically
switched capacitors don’t provide continuity of control and have relatively large response time. There-
fore, in modern electrical networks with the 0.4 kV voltage level advanced VAR compensators, which
don’t contain rotating parts and mechanical relays, are widely used.
Analysis of the last researches and publications. Application of thyristor-controlled compen-
sators, static compensators and active filters is the actual solution of the problem of reactive power
compensation. Among these devices, thyristor-switched capacitors are most commonly used in mod-
ern power networks.
TSC (Fig. 1) consists of the capacitor banks with thyristor-switched stages and inductors, which
serve to limit the rate of change of thyristor current and / or to change the reactance of the network to
prevent resonances. To ensure a "soft" thyristor switching its firing is performed at the moment, when
the capacitor voltage and the network voltage have the same value.
L
4C
SW3
T1
C
SW1
2C
SW2
8C
SW4
LLL
Fig. 1 – The circuit configuration based on the TSC device
Compensators of the TSC type allow to regulate the reactive power stepwisely, have high re-
sponse time and no generation of harmonics to the network.

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In such devices effective solution is to install a capacity of CB stages proportionally to the
power of two (Fig. 1) [1]. It makes possible to get 2n regulation steps for n CB stages. For example, for
the circuit that includes 4 capacitors with the reactive power – 1, 2, 4 and 8 kVAr, you can get 16 steps
of regulation – from 0 to 15 kVAr with the 1 kVAr steps.
A significant disadvantage of the TSC is also the fact that the capacitor banks are exposed to the
negative impact of higher harmonic components which present in the network voltage. Working under
the conditions of non-sinusoidal CB current waveform could lead to resonance overvoltage, over-
current, and as a result, overheating of the banks and their failure.
Stepless control of reactive power can be achieved by connection of the CB and controlled im-
pedance in series (Fig. 2). Moreover, by performing this resistance with high impedance at the fre-
quencies of the higher harmonics, it’s possible to achieve a significant reduction of the harmonic’s
level in the CB current. Herewith, the frequency response of the network in the point of the hybrid
compensator’s connection isn’t changed, thus risk of resonance on the frequencies of higher harmonics
doesn’t appear.
Zn
ZH
VAR compensator
Network
uc(t)
u(t)
en(t) С
X(? )
Fig. 2 – The equivalent circuit of the hybrid VAR compensator
It’s possible to implement such reactance by applying the serial active filter [2, 3]. Generally AF
is implemented as voltage source inverter with high-capacity storage capacitor in the DC link and LC
low pass filter in the AC link. The resulting scheme of hybrid VAR compensator is shown in Fig. 3.
network
RL
en(t) ZL
C1C2Cm
SW1S W2SWm
AF
UDC Ump
ic(t)
iL(t)
in(t)
LFСF
VT1VD1
VT2
VD2
CDC
Fig. 3 – The single-phase circuit of the hybrid VAR compensator
The disadvantage of this hybrid VAR compensator is the need to use six terminals of the three-
phase capacitor bank, while in practice the majority of three-phase CB are produced with internal con-
nection "delta". In this case, the capacitor bank has only three terminals.

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The objective of the article is to propose a hybrid VAR compensator topology suitable for us-
ing with three-terminal delta-connected capacitor banks while maintaining all advantages of hybrid
approach – smooth VAR control and harmonic current suppression.
Basic material. To control the gates of transistors VT1 and VT2 a control system is to be used
the schematic diagram of which is shown in Fig. 4. Hysteresis control of inverter with current feed-
back was applied (the current loop, Fig. 4). The reference current )(tiREF is determined as the sum of
the in-phase )(tiP and quadrature )(tiq components.
iREF(t)
ic(t)
UREF
UDC
P
sin

t
in(t)
sin(

t-90o)
Low-pass
filter
Iqc
IqREF
Regu lat or
Iq
Iq
ip(t)
iq(t)
PLL
un(t)
2
2
Volt age regula tor
VR
Current
regulator
CR
Ump UDC/2
Regul ato r
Ump
icor(t)
To the powe r
switc hes
To the othe r
pha ses
iout(t)
Сurren t сircuit CC
VAR
distribution
regulator
CB
Fig. 4 – Block diagram of the VAR compensator control system
Formation of the in-phase current component is implemented by the regulator of DC link volt-
age DC
U. This current has a small value since the active power consumed by the AF is spent only for
losses therein. For this reason, in further analysis of the hybrid VAR compensator’s properties this
current will be ignored.
PLL (Phase Locked Loop) block is used for the eduction of the in-phase and quadrature compo-
nents of the fundamental frequency from the network voltage. These signals are used for the formation
of in-phase and quadrature components of the reference current.
Eduction of the quadrature component from the network current is carried out by multiplying
with the reference signal from the PLL and the subsequent low-pass filtering. As a low-pass filter,
first-order sinc-filter with an interval of integration equal to the network period is used. The obtained
signal Iqc with the reference current IqREF is supplied to the adder. Using a non-zero current IqREF allows
to perform overcompensation or under-compensation of reactive power. The difference signal is input
signal for the regulator of the reactive current amplitude Iq, the output signal of this regulator is used
for formation of iq(t).
VAR distribution regulator performs redistribution of power between CB and AF with the con-
dition to minimize the AF power, i.e. it’s chosen such CB capacity, at which output voltage AF will be
minimal for a given reactive power.
Maintaining average voltage at the midpoint of the half-bridge on the level DC
U5,0 relative to
the negative bus of the AF DC-link is performed by the regulator mp
U, the output of which is the cor-
rection current )(ticor . In this case it’s sufficient to use P-regulator with a small gain. Without this
regulator uncontrolled constant voltage component will be present on the CB, the correct control of the
current of VAR compensator will be impossible.

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Fig. 5 shows the equivalent circuit of the hybrid VAR compensator, which includes a three-phase
CB with three terminals. In the equivalent circuit active filters are represented as current sources.
CB
ic
uapf_c
A
B
C
ia
N
uapf_a
Fig. 5 – The equivalent circuit of the hybrid VAR compensator
Figure 6 shows a generalized diagram of a hybrid VAR compensator topology which includes
three-phase CB with the three terminals, and its control system. One phase (on the fig. 6 - phase B) is
connected directly to the network, and the other two - through the secondary windings of transformers.
The primary transformer windings are "open-delta" connected and connected to the VSI.
A
B
C
N
CB
UDC
CDC
Т1
Т2
iaic
a
c
n
VT1 VT3 VT5
VT2 VT4 VT6
Control
system
To the control electrodes
VT1-VT6
UAN, UAN, UAN
ia, ic
UDC, Q, Qref
uapf_a
uapf_с
Fig. 6 – Scheme of the hybrid VAR compensator
Block diagram of the control system is shown in Figure 7.
The control system similar to scheme in Figure 4: low-pass filtering of the network voltage is
performed, the received signal is shifted by 90° with the help of PLL block. To obtain a reference
value of in-phase and quadrature current components multiplication by the scaling coefficients GREF

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and ВREF is performed. Low-pass filters LPF_2 are introduced to exclude the transformer magnetizing
by the direct current - it’s provided a zero mean value of output inverter voltage uapf_a, uap f_c with the
help of negative feedback. P-controller with the gain 1/3 is used for the formation of zero-sequence
voltage, which is then subtracted from the signal of phase voltage.
LPF_1 PLL
UAN
UBN
UAN
1/3
LPF_1 PLL
UDC -
+
+
+
+
+
UREF
Q
QREF
-
LPF_3
LPF_4
LPF_2
+
+
+
+-
-
-
LPF_2
+
-
+
ia_REF
ic_REF
uapf_a
uapf_c
GREF
BREF
Fig. 7 – Block diagram of the hybrid VAR compensator control system
Such approach to the control of the hybrid VAR compensator can be applied not only in the
case of two single-phase transformers in two phases, but in the case of a three-phase transformer. The
utilized wiring diagram of the transformer is shown in Figure 8.
A
B
C
N
Т1
Т2
iaic
a
c
n
uapf_a
uapf_с
Т1
Т2
uapf_a
uapf_с
A
B
C
Т3
ia
ib
ic
uapf_b
a
c
Tr Tr
CB CB
N
b
Fig. 8 – Wiring diagram of the single-phase and three-phase transformers
The authors also proposed an original method of selection the value of CB capacity and AF
rated power [4].
When selecting the maximum output AF voltage, it should be taken into consideration that:
1) the spectrum of the output AF voltage contains all high order harmonics of the network volt-
age – it’s a condition for ensuring of sinusoidal CB current;

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2) the first harmonic of the output AF voltage determines the value of the hybrid compensator’s RP.
According to [5] in 0.4 kV networks normally permissible value of harmonic distortion is 8%,
the maximum allowable value - 12%. Selecting the maximum output AF voltage of the active filter at
10% of network voltage, it is possible to regulate the value of hybrid compensator’s reactive power in
the range (0,9÷1,1)·Qrated.
It’s economically advisable for hybrid VAR compensator to decrease the output AF voltage,
which allows to use a more effective low-voltage power components.
Conclusions
1. Hybrid VAR compensator, which is consisting of series-connected TSC and AF, is proposed.
It allows to "isolate" TSC from harmonic currents and to provide smooth control of the RP.
2. Proposed is an improved hybrid VAR compensator, which allows to use standard capacitor
banks delta-connected. It simplifies the practical implementation of the device, provides smooth con-
trol of the RP and protection of the CB from harmonic currents.
Bibliography:
1. Reactive Power Compensation Technologies, State-of-the-Art Review / J.W. Dixon, L. Moran,
J. Rodríguez, R. Domke // Proceedings of the IEEE. – 2005 – Vol. 93, Dec. – №12. – Рp. 2144-2164.
2. A Full Compensating System for General Loads, Based on a Combination of Thyristor Binary
Compensator, and a PWM-IGBT Active Power Filter / J.W. Dixon, Y. del Valle, M. Orchard,
M. Ortúzar, L. Morán, C. Maffrand // IEEE Transactions on Industrial Electronics. – 2003. – Vol.
50, Oct. – №5. – Pp. 982-989.
3. Pat. 6876179 USA, Int. Cl. G 05 F 1/70, H 02 M 1/12. Hybrid Reactive Power Compensation De-
vice.
4. Pat. 106174 Ukraine, Int. Cl. G 05 F 1/70, H 02 J 3/18. Method of the reactive power compensation /
V. Burlaka, S. Gulakov, S. Podnebenna; State higher educational establishment «Priazovskyi state
technical university». – №a201310826; filed 09.09.13; published 10.09.14, Bull. №17. – 5 р. (Ukr.)
5. IEEE Standard 1459-2010. Definitions for the Measurement of Electric Power Quantities Under
Sinusoidal, Nonsinusoidal, Balanced, or Unbalanced Conditions. – Approved 2010-2-2. – IEEE-
SA Standards Board, 2010. – 72 p.
Reviewer: I.V. Zhezhelenko
dr. tech. of science, professor «Pryazovskyi state technical university»
Received 30.10.2014
УДК 621.316.925
© Дьяченко М.Д.1, Тесля Ю.А.2
ПРЕДПОСЫЛКИ СОЗДАНИЯ АВТОМАТИЗИРОВАННОЙ СИСТЕМЫ
МОНИТОРИНГА И РАННЕГО ДИАГНОСТИРОВАНИЯ СОСТОЯНИЯ
ВЫСОКОВОЛЬТНЫХ ЛИНИЙ ЭЛЕКТРОПЕРЕДАЧ
В статье рассмотрены основные предпосылки необходимости создания автома-
тизированной системы мониторинга и раннего диагностирования состояния вы-
соковольтных контактных соединений, приведены основные аппаратные и алго-
ритмические решения.
Ключевые слова: контактные соединения, системы мониторинга, системы диаг-
ностирования, сенсорные сети, самоорганизующаяся сеть.
1 канд. техн. наук. доцент, ГВУЗ «Приазовский государственный технический университет, г. Мариуполь,
dmd17@rambler.ru
2 инженер, ООО «ВДТ-Автоматизация», г. Мариуполь, teslyaua@gmail.com