Design and power quality analysis of hybrid renewable energy system for Tho Chu island, Viet Nam

due 
to factors such as solar radiation, temperature, pressure, aging of solar panels and 
dirt sticks to the glass surface of panels. Therefore, the AC/DC conversion ratio is 
usually in the range: 0.8 ≤
𝑃𝑖𝑛𝑣𝑒𝑟𝑡𝑒𝑟
𝑃𝑎𝑟𝑟𝑎𝑦
≤ 1 
The decision to install the PV system will need to comply the power range and 
specifications of the selected inverter. There are usually the following limits [10]: 
- Parray 100 kW requires 
using 3-phase inverter. 
- 10 kW < Parray < 100 kW, it is possible to use a 3-phase inverter or multiple 
single-phase inverters split evenly across phases. 
The input and output parameters of selected inverter are suitable for the 
parameters of the solar panels and the grid connected. From the above analysis, the 
author uses the 3-phase inverter 400kW. 
2.2.3. Selecting diesel generator and an energy storage system 
Because of the PV system capacity is fluctuated and not very large, choosing 
the hybrid ratio between PV system and diesel generators is so extremely 
important, which directly affects the power quality of the system. Besides, there is 
only one diesel generator with the task of balancing the power, so the paper 
proposes the rated power of diesel generator should be 400kW. In the case of 
losing the solar source, the diesel generator will burden the entire system. 
The energy storage system is only charged from PV source. The most important 
task of the energy storage system is to ensure the operation of the system during 
diesel generator’s failure. The energy storage system on the island is designed to 
provide an average load of 24 hours and the system can work well during 12 hours 
of maintenance of the diesel generator twice a year. 
After calculating all the system parameters, we have a HRES design including: 
PV system with the configuration of installing panels consisting of 10 panels 
connected in series to raise the Vmpp(20/60
0C) = 550/463V and 127 series in 
parallel will have Impp(STC) = 748 A; Seil_Soleil 400 inverter is connected directly 
to a 400kW diesel generator and battery storage system with a capacity of 
14400Ah. 
2.3. Analysis of the power supply capacity and evaluation of economic 
efficiency of the HRES 
2.3.1. Analysis of the power supply capacity 
From configuration parameters of the systems, the operability of HRES is 
simulated via PVsyst. Meteonorm data is used for meteorological data. 
With the configurations established for HRES, the simulation results as 
generating power, power generating times, annual electricity consumption will be 
evaluated. The simulation systems parameters are illustrated in figure 2. The 
obtained results are presented in table 2 and figure 3. 
Electronics & Automation 
Le Duc Tung, “Design and power quality analysis  for Tho Chu island, Vietnam.” 70 
Table 2. The simulation results. 
Parameters Values 
PV system power 400 kWp 
Inverter power 360 kWac 
Electrical energy 562 MWh/year 
Conversion factor 0.724 
Average annual power 
output 
1404 
kWh/kWp/year 
Average daily power output 3.68kWh/kWp/day 
PV system loss 0.92kWh/kWp/day 
Figure 2. The simulation systems parameters. 
Thus, the PV system has produced 562 MWh/year to meet 66% of electricity 
consumption on the island. The main operating time of the diesel generator is from 
18h to 21h, at this time the energy stored in the battery storage is exhausted, the 
generator operates only under load or no load in other times of the day. 
Figure 3. The total electrical power generated by PV system 
and the required power of the load. 
Research 
Journal of Military Science and Technology, Special Issue, No.66A, 5 - 2020 71 
The economic values will be calculated specifically about the benefits that the 
HRES brings to evaluate its effectiveness in next section. 
2.3.2. Evaluation of economic efficiency 
The financial evaluation for the islanded-hybrid system is analyzed based on the 
annual power output simulation and the following assumptions: 
- 400kWp PV system has an annual electricity output of 562MWh / year. The 
life cycle of PV system is 20 years. The aging of the panels reduces the output 
power of the panels 1% / year. 
- Total money needed for the whole project: 100% bank loan for 20 years with 
an annual interest rate of 7% / year. 
- Installation costs are calculated as 41% of the total project cost. 
- The system's operating time is 20 years with the inflation index being 
7%/year. Operation and maintenance cost for the entire system is $19 / year. 
- All costs of research and system analysis such as technical assistance, 
environmental research, economic analysis, operating licenses, land rental fees, 
land taxes, site clearance fees and others related cost are considered as free. 
Insurance expenses do not belong to the project cost. Incentives such as reductions 
in greenhouse gas emissions, subsides encourage clean energy development and 
another fund are unavailable. 
 From the evaluated results for the HRES project on Tho Chu Island, the cost 
per unit of electricity produced by the solar and battery system is $0.18/kWh. 
Much lower than the cost of electricity powered by diesel generator, but still high, 
this is caused using battery storage systems. In addition, the HRES also reduces 
CO2 emissions. With the conversion rate in Vietnam is 407g CO2/kWh, the HRES 
will reduce 4162 tons of CO2 in 20 years. 
3. ANALYSIS AND EVALUTION OF THE POWER QUALITY 
OF THE DISIGN SYSTEM 
After calculating the design of the HREA for a remote area, in order to ensuring 
the power supply for the load, it is necessary to examine the frequency, voltage 
quality and the total harmonic distortion voltage (THDv) of the power supply 
system. So firstly, it’s needed to model, simulate equipment in the HRES and 
detailed evaluation based on the specified standards. The parameters are evaluated 
according to IEC standards, national standards TCVN 7447-7-712: 2015 
(IEC60364-7-712: 2002), Circular No. 39/2015/TT-BCT [6, 9, 10]. 
3.1. Modeling HRES 
The system model is built with Matlab/Simulink consisting of a 3-phase 380V 
power grid, 50Hz frequency, a 400kWp Photovoltaic system connected to a 
400kW Diesel generator via an inverter, a battery storage systems (240V, 
14400Ah), which provide for variable loads with peak power of 275kW. The 
whole HRES model is presented as in the figure 4. 
Photovoltaic array: 400kWp photovoltaic system consists of 1270 Sunpower 
Electronics & Automation 
Le Duc Tung, “Design and power quality analysis  for Tho Chu island, Vietnam.” 72 
315Wp panels divided equally into 4 parallel arrays, each array is controlled by a 
DC/DC converter. Each array consists of a row of 5 panels in series and 64 rows 
in parallel. 
DC/DC converter using Boost booster including P&O algorithm to track MPP points. 
Inverter 3-phase SVC voltage source: PV inverter operated with P/Q control 
scheme, the active and reactive power outputs of PV are fixed to set-point values 
Pref and Qref [11]. 
Harmonic filters consisting of L and C, which filter out higher order harmonic 
components. 
Diesel generator using synchronous generator model with its parameters 
referred from 400V-670VA-50Hz-1500RPM generator parameter in library of 
MATLAB’s synchronized generator. 
Battery storage system using the Buck-Boost Converter (Bidirectional DC/DC 
Converter bloc). The supply voltage for the Buck-Boost Converter has a range of 
560V to 655V and the battery voltage ranges from 180V to 261.3V. 
Figure 4. HRES simulated by Matlab/Simulink. 
3.2. Preliminary analysis and evaluation of the power quality of HRES on Tho 
Chu island 
We consider two scenarios to preliminary power quality assessment of the 
hybrid power system: the solar radiation changed and the load changed. 
3.2.1. Scenario 1: the solar radiation changed. 
Before time t=2s, the system operates stably, solar radiation Irr = 600 W/m2; 
panel surface temperature T=45oC. Power of 3-phase symmetrical load P=275kW. 
At t=2s, the solar radiation is reduced from 600 W/m2 to 200 W/m2 on a battery 
platform. At t=6s, this solar radiation increases from 200 W/m2 to 600 W/m2. 
When the solar radiation changes, figure 5 shows that the frequency during the 
fluctuation exceeds the range of +0.5 Hz, but still within the frequency range of the 
inverter. The voltage at the power plant connection point ranges from 216V to 
225V and is within the allowable length (0.95-1.1pu). The total harmonic 
distortion at the connection point is 4.25% and is within the permissible range (less 
than 6.5%). 
Research 
Journal of Military Science and Technology, Special Issue, No.66A, 5 - 2020 73 
Figure 5. Frequency, voltage and THDv at PV connection point (scenarios 1). 
3.2.2. Scenario 2: the load changed 
Figure 6. Frequency and voltage of HRES (scenarios 2). 
Considering the symmetric 3-phase load. Before time t=2s, the system operates 
stably, solar radiation Irr=600W/m
2; panel surface temperature T=450C and 
Electronics & Automation 
Le Duc Tung, “Design and power quality analysis  for Tho Chu island, Vietnam.” 74 
Pload=275kW. At t=2s, load is reduced from 275kW to 250kW. At t=6s load is 
increased from 250kW to 275kW. 
As the load changes, based on the simulation results (as shown in figure 6), is 
can be seen that the frequency during the fluctuation exceeds the range of +0.5 Hz, 
but still within the frequency range of the inverter. The voltage at the power plant 
connection point is within the allowable length (0.95-1.1pu). The total harmonic 
distortion within the permitted range. The total harmonic distortion at the 
connection point is less than 6.5%. 
The simulation results obtained from the two scenarios above have shown that 
the parameters of voltage and harmonics are within the permissible ranges 
according to the standards. The system frequency fluctuates outside the standard 
range but is still within the inverter's frequency range and returns to the 
permissible range (± 0.2Hz) within 1 second after the noise. Therefore, it is 
necessary to develop more measures to reduce system fluctuations. 
4. CONCLUSION 
This paper presented design calculations and modeling of a HRES for Tho Chu 
island including photovoltaic system, diesel generator and energy storage system. 
PV system is connected to the system at the DC bus. Diesel generator connected to 
the system at the AC bus. The connection between the DC bus and the AC bus is 
made through a DC/AC inverter. These models allow the study of the behavior 
simulation and stability analysis and the responses of HRES in symmetrical 3-
phase load mode. After analyzing and assessing the power quality of the HRES, 
the simulation results show that the design system has operated stably. Frequency, 
voltage and harmonic parameters are within the permissible range as Vietnam 
standard. However, there is still a short time (under 1s) of the frequency fluctuation 
outside the permissible range before returning to a stable value. Therefore, it is 
necessary to apply more measures to reduce the oscillation of the system such as 
increasing the inertia constant for the generator by connecting the generator shaft 
to the flywheel system or using super capacitor storage. 
Acknowledgement: The author would like to thank Mr. Ngo Van Binh (Student 
of HUST) who greatly assisted the calculation of research. 
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TÓM TẮT 
THIẾT KẾ VÀ ĐÁNH GIÁ CHẤT LƯỢNG ĐIỆN NĂNG 
HỆ THỐNG NĂNG LƯỢNG TÁI TẠO LAI CUNG CẤP ĐIỆN 
CHO ĐẢO THỔ CHU, VIỆT NAM 
Sử dụng các nguồn năng lượng tái tạo cung cấp điện cho các khu vực địa 
lý cô lập là giải pháp hiệu quả về mặt kinh tế-kỹ thuật và đảm bảo môi 
trường sống. Đảo Thổ Chu, huyện Phú Quốc, tỉnh Kiên giang hiện được cấp 
điện hoàn toàn bằng các máy phát diesel, gây ô nhiễm môi trường và chí phí 
phát điện cao. Bài báo này trình bày tính toán thiết kế hệ thống lai bao gồm 
máy phát diesel, hệ thống điện mặt trời và hệ acquy lưu trữ cho đảo Thổ 
Chu. Bên cạnh việc tính toán lựa chọn các thiết bị, đảm bảo cung cấp điện 
cho phụ tải, bài báo còn đánh giá chất lượng tần số và chất lượng điện áp, 
xem xét độ biến dạng sóng hài của hệ thống cung cấp điện. Các kết quả mô 
phỏng thu được từ phần mềm PYsyst và Matlab/Simulink minh chứng được 
tính hiệu quả của hệ thống. 
Từ khóa: Đảo Thổ Chu; Hệ thống lai; Hệ thống năng lượng mặt trời; Chất lượng điện năng. 
Received, 12th March, 2020 
Revised, 29th April, 2020 
Published 06th May, 2020 
Author affiliations: 
 School of Electrical Engineering, Hanoi University of Science and Technology. 
 *Corresponding author: tung.leduc1@hust.edu.vn.