Reactive power compensation in distributed system using centralized control

lectric devices perform 
the highest efficiency, prolong, and decrease losses. Notwithstanding, it is complex to 
solve voltage quality problem because it contains several minor problems as voltage 
deviation, voltage fluctuation, flicker, harmonic, asymmetric voltage [1]. There are also a 
bunch of ways to deal with voltage regulation. For the case which needs to adjust quickly, 
Static Var Compensator (SVC) or STATCOM will be used. However, both of them are 
centralized devices while the loads are distributed in plural types and locate at different 
positions. The loads are often accessed from a common connection point via transmission 
line (TL). On these TLs, the voltage attenuation and heat loss will occur. The centralized 
voltage control devices such as SVC or STATCOM could not reduce the TLs losses and it 
is difficult to calculate required voltage in each load [2]. 
Therefore, the aim of this paper is to propose a system of voltage control distributed 
devices using centralized control in order to increase the efficiency of the voltage quality’s 
adjustment and improvement on specific load in factories [3, 4]. By this solution, active 
power’s loss is decreased; the electric device’s performance is higher and prolongs their 
longevity [4]. 
2. VOLTAGE REGULATION DISTRIBUTED SYSTEM USING CENTRALIZED 
CONTROL 
Figure. 1 illustrates a voltage regulation distributed system using centralized control. 
2.1. The main elements of system 
- The controller: including power measurement systems through current and voltage 
signals in each branch. The voltage regulation process will be calculated by changing 
both central and peripheral equipments power. 
- Central control reactor 1.6: is the Thyristor Control Reactor (TCR) device basically. 
To combine switch on/off peripherals and vary TCR opening phase angle, the 
device’s power is adjusted smoothly. 
- Central reactive power compensation device 0.6: to add needed-power for voltage 
regulation system or replacing a device which has a failure. 
- The peripherals 2.6, 3.6, m.6 are the hamonics filters, capacitors or mixed harmonic 
filter and capacitor that switch on/off based on harmonic order at distributed load 
system 2.5, 3.5, m.5 (non linear, linear and mixed none linear, linear loads 
respectively). 1.5 is unbalanced load which is close in distance with transformer. 
Nghiên cứu khoa học công nghệ 
Tạp chí Nghiên cứu KH&CN quân sự, Số 68, 8 - 2020 55 
Figure 1. Schematic of voltage regulation distributed system using centralized control. 
2.2. The system’s working principles 
The central controller determines optimal harmonics filter order, voltage and reactive 
power compensation of each load branch. Then, adjusting the peripheral’s power and the 
central reactor’s opening angle in combination. When a branch of the distributed device is 
switched off, the opening angle α turns to αmin (at this position, the reactor power is 
maximum and equals to closed branch’s reactive power, thus, device’s total power is 
zero). Continuously, adjusting TCR angle in order to reach expected optimized power 
(executed by the controller). If the angle α reaches the maximum value αmax, and the 
reactive power is still not enough, the process of switch off the next branches similarly. 
The peripherals’s power could be regulated by reference power factor, voltage, or reactive 
power. 
2.3. The system’s advantages and disadvantages 
 Advantages: 
- The system improves the voltage quality at each load. 
- Reducing the power losses which affect. 
- Reducing cost because of using only a controller. 
Disadvantages: 
- The system requires complex adjustment. 
2.4. Control algorithm of the system 
The Decentralizing voltage regulation system with centralized control (DCS) algorithm 
is based on the calculation of minimizing the active power loss across the entire factory, 
based on the formula for calculating the active power loss at each electrical load in the 
factory as after [5]: 
Kỹ thuật điều khiển & Điện tử 
N. T. Dung, D. N. Quang, P. T. Dung, “Reactive power  using centralized control.” 56 
 (1) 
where: Rtđ is the equivalent resistance of the electrical system, Ohm 
 Ptt is the total active power of the whole factory, kW 
 Qtt is the total reactive power of the entire factory, kvar 
 Qbu is the reactive power compensation of the, kvar; 
 Upt is the voltage at the load, kV 
 pB: Loss of active power of compensator, kW / kvar; 
 is the change of motor efficiency according to reactive power. 
The relationship curve between the voltage variation and the variation in motor 
efficiency can be expressed as follows: 
 (2) 
For K and C, the constants are determined based on the experimental curve proposed 
by Nema [6]. From this, it is possible to determine the value of the remaining optimal 
reactive power running into the electrical system (Qtt - Qbu) according to the parameters 
of the electrical system and the effective power Ptt of the load. 
For calculating the optimal reactive power compensation based on minimization active 
power loss criterion, using the formula as following: 
 (3) 
From (1) and (2), obtain: 
).(2
)(
21 KPK
p
QQ
tt
bu
butt
 (4) 
with 
21
.
pt
td
U
X
KK and 
2
3
2
10
.
pt
td
U
RK
Solving the above equations with each load will give optimal results of the DCS control 
process at each load. Basically, for faster respond of DCS, loads will be arranged by 
priority by THD and harmonics order, the individual power, distance from transformer, 
power changing speed The process of calculation and control of each block of load will 
take into account this order of priority from more complicated to the lesser ones. From this 
calculation, each unit of DCS will have one optimal value Qopt i of reactive power 
compensation from formula (4). The controller will regulate reactive power of each unit to 
Qopt i . The DCS control algorithm is presented in figure 2. 
3. APPLYING THE DISTRIBUTED VOLTAGE REGULATION SYSTEM 
USING CENTRALIZED CONTROL 
The DCS is using to improve power quality index and save electrical energy in M1 
factory- a part of Viettel group. M1 factory located in Hanoi City of Vietnam. The single 
line diagram of M1 factory is shown in figure 2. 
Nghiên cứu khoa học công nghệ 
Tạp chí Nghiên cứu KH&CN quân sự, Số 68, 8 - 2020 57 
Figure 2. The flowchart of the DCS control algorithm. 
Start 
Interrupt synchronous grid 
Check P > PL rated 
and U
H 
> U > U
L
False 
True 
End 
Inputs: U
H
 (high limited voltage), U
L
 (Low limited 
voltage), number of load blocks, the power of each 
peripheral and center units, their characters (filter 
orders, power of each capacitors), R
td
, X
td
, Δp
B
, K
i
Arrange the priority of each load 
(from more complicated to lesser ones). 
Read measurement data. Calculate the optimal 
reactive power compensation and harmonics filters 
for each blocks of load by order of priority 
Generate control pulse to change the harmonics filter 
order and reactive power of each block of loads of 
peripheral and center units with synchronizing of 
voltage regulation by the order of individual load 
priority: Q bu i = Q opt i 
Kỹ thuật điều khiển & Điện tử 
N. T. Dung, D. N. Quang, P. T. Dung, “Reactive power  using centralized control.” 58 
The factory is supplied by 1600kVA and 35/0.4kV transformer with 3 blocks of 
electrical load. It had a centralized reactive power compensation (CC) on 0.4 kV side of 
transformer. The DCS is including 3 devices: two peripheral and one central units as 
shows in figure 3. 
From the survey and measured parameters, the power quality of the plant can be 
evaluated with the following notice: 
- The power of the factory fluctuates strongly, it requires a quick reaction device for 
reactive power compensation. 
- Low voltage at the transformer. The voltage should be increased by 5-8V. 
- Improve the power factor (PF) cosφ to avoid losses. 
The measured parameters correspond to three load blocks, which are recorded with and 
without the installation of the DCS device. They are described in detail in figure 4, figure 
5, figure 6, figure 7, figure 8, and figure 9. 
Figure 3. Single line diagram of M1 factory. 
Nghiên cứu khoa học công nghệ 
Tạp chí Nghiên cứu KH&CN quân sự, Số 68, 8 - 2020 59 
Figure 4. Block 1 parameters of M1 factory without DCS device. 
Main features of block 1 
- The voltage is at an average of 390V 
- Current from 190A ÷ 220A 
- Maximum power is 129 kW 
- Reactive power is 51 kVar 
- Power factor is between 0.91 and 0.92. 
Kỹ thuật điều khiển & Điện tử 
N. T. Dung, D. N. Quang, P. T. Dung, “Reactive power  using centralized control.” 60 
Figure 5. Block 2 parameters of M1 factory without DCS device. 
Main features of block 2 
- The voltage is at an average of 385V 
- Current from 240A ÷ 280A 
- Maximum power is 154 kW 
- Reactive power is 76 kVar 
- Power factor is about 0.87. 
Nghiên cứu khoa học công nghệ 
Tạp chí Nghiên cứu KH&CN quân sự, Số 68, 8 - 2020 61 
Figure 6. Block 3 parameters of M1 factory without DCS device. 
Main features of block 3 
- The voltage is at an average of 395V 
- Current from 190A ÷ 220A 
- Maximum power is 132 kW 
- Reactive power is 55 kVar 
- Power factor is about 0.95. 
Kỹ thuật điều khiển & Điện tử 
N. T. Dung, D. N. Quang, P. T. Dung, “Reactive power  using centralized control.” 62 
Figure 7. Block 1 parameters of M1 factory with DCS device. 
Main features of block 1 after installing DCS 
- The voltage is good at 395V 
- Current from 178-182A 
- Maximum power is 120 kW 
- Reactive power is 28 kVar 
- Power factor is about 0.97. 
Nghiên cứu khoa học công nghệ 
Tạp chí Nghiên cứu KH&CN quân sự, Số 68, 8 - 2020 63 
Figure 8. Block 2 parameters of M1 factory with DCS device. 
Main features of block 2 after installing DCS 
- The voltage is good at 394V 
- Current from 196 ÷ 230A 
- Maximum power is 145kW 
- Reactive power is -3.2 kVar 
- Power factor is about 0.99. 
Kỹ thuật điều khiển & Điện tử 
N. T. Dung, D. N. Quang, P. T. Dung, “Reactive power  using centralized control.” 64 
Figure 9. Block 3 parameters of M1 factory with DCS device. 
Main features of block 3 after installing DCS 
- The voltage is good at 400V 
- Current from 168 ÷ 202A 
- Maximum power is 127kW 
- Reactive power is -31 kVar 
- Power factor is about 0.96. 
The experimental process devided by two phases: with CC and with DCS. The 
observing parameters included: block voltages and currents, maximum active and reactive 
power, total active power loss on cables and transformer, the power factors. 
Nghiên cứu khoa học công nghệ 
Tạp chí Nghiên cứu KH&CN quân sự, Số 68, 8 - 2020 65 
The main results of using DCS comparing to use CC are obtained as following: 
- The voltage in blocks is higher and better (from 395-400 V) 
- The maximum active power Pmax is lower 29kW (or 5.67%) 
- The total power loss is lower 3.45kW (or 17.8%) 
- The block current is lower (from 8 to 18%) 
The detail comparison of using CC and DCS is shown on table I. 
Table I. The comparison of technical parameters with using CC and DCS. 
 Items Regime U (V) I (A) Pmax (kW) P (kW) Q (kvar) PF 
Block 1 
With CC 390 220 129 3.84 51 0.92 
With DCS 395 182 120 3.26 28 0.97 
Difference 5.0 -38.0 -9.0 -0.58 -23.0 0.05 
Block 2 
With CC 385 280 154 7.77 76 0.87 
With DCS 394 230 145 5.61 -3 1 
Difference 9.0 -50.0 -9.0 -2.16 -79.0 0.13 
Block 3 
With CC 395 220 132 7.73 55 0.95 
With DCS 400 202 127 7.02 -31 0.96 
Difference 5.0 -18.0 -5.0 -0.71 -86.0 0.01 
As can be seen from table I, with the DCS installation, the power quality is markedly 
improved namely: the voltage keeps stable, the current decreases, the power factor 
increases, especially the energy consumption and power significantly decrease. 
4. CONCLUSION 
The distributed voltage regulation system using centralized control is more complex, 
however, it has high efficiency comparing to the common centralized control systems. 
Furthermore, it helps to adjust voltage better by reducing voltage drop at load. Due to this 
advantage, the loads will be more productive, save energy, and prolong the device’s 
longevity. 
Acknowledgement: This research is funded by the Ministry of Industry and Trade (MOIT) 
under grant number 147.2018.ĐT.BO/HĐKHCN. The authors wish to thank Electric Power 
University (EPU) for their help during our measurement and experimentations 
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1107–1115, May 2015, doi: 10.1109/TSG.2014.2358885. 
[4]. D. I. Brandao, T. Caldognetto, F. P. Marafao, M. G. Simoes, J. A. Pomilio, and P. 
Tenti, ‘Centralized Control of Distributed Single-Phase Inverters Arbitrarily 
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Connected to Three-Phase Four-Wire Microgrids’, IEEE Trans. Smart Grid, vol. 8, 
no. 1, pp. 437–446, Jan. 2017, doi: 10.1109/TSG.2016.2586744. 
[5]. Nguyen Tien Dung, Dinh Ngoc Quang, Bui Anh Tuan, “Giải pháp nâng cao chất 
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[6]. Standard, Nema MG 1-12-45. 
TÓM TẮT 
HỆ THỐNG BÙ CÔNG SUẤT PHẢN KHÁNG 
KIỂU PHÂN TÁN ĐIỀU KHIỂN TẬP TRUNG 
Bài báo đề xuất thiết bị bù công suất phản kháng dạng phân tán điều khiển tập 
trung. Thiết bị này bao gồm hệ thống các tụ bù đặt gần các phụ tải tiêu thụ điện 
nhưng chỉ gồm một bộ điều khiển chung duy nhất. Bộ điều khiển, thu thập dữ liệu về 
dòng điện, điện áp cũng như công suất của từng nhánh phụ tải điện để từ đó, tiến 
hành điều chỉnh trơn công suất phản kháng tổng theo một trình tự ưu tiên, Thiết bị 
này sẽ giúp nâng cao chất lượng điện áp tại các phụ tải điện, giảm tổn thất công 
suất tác dụng và nâng cao tuổi thọ của các thiết bị điện. 
Từ khóa: Bù công suất phản kháng; Thiết bị phân tán điều khiển tập trung; Static Var Compensator (SVC); 
Thyristor Control Reactor (TCR). 
Received date, 29
th
 May, 2020 
Revised manuscript, 17
th
 July, 2020 
Published 03
rd 
August, 2020 
Author affiliations: 
1 
Electric Power University, Hanoi, Vietnam; 
2 
Innovative Grid Solutions Company, Hanoi, Vietnam; 
3
 Le Quy Don Technical University, Hanoi, Vietnam. 
*
Corresponding author: dungnt@epu.edu.vn.