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This paper introduces a new method that no previous study has been done in this photovoltaic power generation similar to this paper to harness maximum potential power from photovoltaic power generation. The completely mathematical model added the relation between diode factor of the generation and p-n junction temperature is proposed to use in this method. The maximum power point tracker combines the iterative and bisectional technique, the completely mathematical model of PVgPVG and the system of equations that converts value of parameters from standard test condition to any working condition, measuring sensors to measure power of solar irradiance and p-n junction temperature to determine parameters at maximum power point at any working condition. The voltage controller is designed to drive this generation to expect working state to harness maximum power. An experimental model corresponding to this method was designed and operated in real conditions in Viet Nam. Experimental results show the high accuracy of analyzing in theory and high capability to bring this method out real applications to harness all available energy of this generation.

Background:The power and voltage losses have been greatly concerned in the distribution system planning and operation because low normal voltage, high impedance and load density of the system lead to increases in losses and decreases in bus voltages.Method:Therefore, an optimization model for the distribution system reinforcement improving efficiency of distribution systems by integrating capacitors is proposed. The optimal allocation and sizing of capacitors are determined concurrently with optimal upgrading sizing and timeframe of feeders and substations. The objective function of model is to minimize life cycle cost over reinforcement scheme including investment and operation costs of equipment in distribution systems (including feeders, substations and capacitors) and costs for purchasing energy from the electric market.Conclusion:The typical load curves for each day and season with uncertainties modeled by a Probability Distribution Function (PDF) and Time of Use (TOU) price applied to enhance accuracy of calculation results and suitability for real operation conditions. General Algebraic Modeling System (GAMS) is applied to undertake calculations in a test system.

This paper presents a novel approach to complete the mathematical model for photovoltaic power generation. In this approach, the relation between the diode factor and temperature at p-n junction is added into the its mathematical model corresponding to each structure of this generation made from semiconductors. Using calculation results from the iterative and bisectional technique to determine maximum power point, the system of equations converting some parameters from standard test condition to any operational condition, datasheet published by manufacturers, the mathematical model is tested to ensure that the diode factor only depend on temperature at p-n junction. Moreover, the least square method is used to create the function representing this relation from only some pair-values. Calculated results of the proposed modeling that applied in a MF165EB3 panel show the high accuracy about value of maximum power and good meaning in control when using results of iterative and bisectional technique at any operational condition.

Nitrous oxide (N2O) emisison from paddy soil via the soil nitrification and denitrification processes makes an important contribution to atmospheric greenhouse gas concentrations. The soil N2O emission processes are controlled not only by biological, physical and chemical factors but also by farming practices. In recent years, modeling approach has become popular to predict and estimate greenhouse gas fluxes from field studies. In this study, the DeNitrification–DeComposition (DNDC) model were calibrated and tested by incorporating experimental data with the local climate, soil properties and farming management, for its simulation applicability for the irrigated rice system in Duy Xuyen district, a delta lowland area of Vu Gia-Thu Bon River Basin regions. The revised DNDC was then used to quantitatively estimate N2O emissions from rice fields under a range of three management farming practices (water management, crop residue incorporation and nitrogen fertilizer application rate). Results from the simulations indicated that (1) N2O emissions were significantly affected by water management practices; (2) increases in temperature, total fertilizer N input substantially increased N2O emissions. Finally, five 50-year scenarios were simulated with DNDC to predict their long-term impacts on crop yield and N2O emissions. The modelled results suggested that implementation of manure amendment or crop residue incorporation instead of increased nitrogen fertilizer application rates would more efficiently mitigate N2O emissions from the tested rice-based system. Phát thải nitơ ôxít (N2O) từ canh tác lúa nước (thông qua quá trình nitrat hóa và phản nitrat hóa) đóng góp đáng kể vào tổng lượng khí nhà kính có nguồn gốc từ sản xuất nông nghiệp. Quá trình phát thải N2O là không chỉ phụ thuộc vào các yếu tố sinh-lý-hóa học mà còn phụ thuộc các phương pháp canh tác. Trong những năm gần đây, việc ứng dụng mô hình hóa nhằm tính toán và ước lượng sự phát thải khí nhà kính ngày càng trở lên phổ biến. Trong nghiên cứu này, số liệu quan trắc từ thí nghiệm đồng ruộng và dữ liệu về đất đai, khí hậu, biện pháp canh tác được sử dụng để kiểm nghiệm và phân tích độ nhạy của mô hình DNDC (mô hình sinh địa hóa). Sau đó, mô hình được sử dụng để tính toán lượng N2O phát thải trong canh tác lúa nước dưới các phương thức canh tác khác nhau (về chế độ tưới, mức độ vùi phụ phẩm, bón phân hữu cơ, phân đạm) tại huyện Duy Xuyên, thuộc vùng đồng bằng thấp của lưu vực sông Vu Gia-Thu Bồn. Kết quả kiểm định chỉ ra rằng (1) sự phát thải N2O bị ảnh hưởng đáng kể do sự thay đổi chế độ tưới; (2) nhiệt độ tăng và lượng phân bón N tăng sẽ làm tăng phát thải N2O. Kết quả mô phỏng về tác động lâu dài (trong 50 năm) của các yếu tố đến năng suất cây trồng và phát thải N2O cho thấy: Việc sử dụng phân hữu cơ và phụ phẩm nông nghiệp thay thế cho việc bón phân đạm sẽ giúp giảm phát thải N2O đáng kể., Journal of Vietnamese Environment, Vol 8 No 4 (2016)

This study comprises greenhouse gas (GHG) emission measurements on rice fields in the Vu Gia/Thu Bon Basin in Central Vietnam , as part of an interdisciplinary research project. The experiments were conducted in the delta lowland (DL) and hilly midland (HM), over three seasons (summer–autumn in 2011 and 2012; winter–spring season in 2012) with two water management treatments namely continuous flooding (CF) and alternate wetting and drying (AWD) . GHG emissions were dominated by methane (CH4) emissions showing large difference among seasons, whereas nitrous oxide (N2O) emissions were negligible and irrelevant in the overall carbon footprint . However, temporal patterns were not conclusive over the entire observation period. The observed seasonal CH4 emission rates ranging from 83 to 696 kg CH4 per ha were relatively higher compared to other field studies and can, at least in part, be attributed to organic amendments applied in accordance to farmers’ practice. The practice of AWD reduced CH4 emissions significantly (P < 0.0001) in all seasons, corresponding in average to 71 % of the emissions from CF. On the other hand, AWD had no significant effect on N2O emissions. The average seasonal CH4 emission in the DL (420 kg ha−1) was also significantly higher than in the HM (206 kg ha−1). Compared with IPCC default values, this data set from Vietnamese rice fields indicates a higher emission level and Scaling factor for AWD. The average grain yield across all sites and seasons increased by 4 % (P < 0.0002) relative to CF with the practice of AWD.

Problem statement: In Vietnam, rice cultivation plays an important ro le in national economic development and food security. However, rice production is facing many problems associated with rapid industrialization and urbaniz ation in the country. Resultant emissions of solid and liquid wastes are often untreated and discharge d directly to agricultural land. These practices ha ve potential impacts on the environment and human health. Approach: The research was carried out within the frame of the collaborative research proj ect "Towards the mitigation of environment and public health risks due to heavy metal contaminatio n in irrigated rice-based systems of Vietnam" in 2006-2010. The study was implemented in the Lam Thao district, Phu Tho province with the aim to assess the effects of wastewater and other contamin ation sources on the environment and public health. Results: Surface water and soil in the field showed signs o f significant contamination by wastewater from the industrial zones. Bio-indicators (DO, COD, BOD5) in the surface water were also strongly affected by waste. Paddy fields around the industri al zones had an elevated risk of heavy metal contamination (Cu, Zn, As, Cd and Pb), with concent rations exceeding Vietnamese Maximum Acceptable Concentrations (MACs) for Cu, Zn, Cd and Pb. Soil contamination with heavy metals was resulting in elevated concentrations in rice grain. Where consumption of locally-produced food was high, exposure of individuals to heavy metals could present a public health risk. The partial Hazard Quotient (HQ; a ratio derived from comparing estima ted exposure to heavy metals, i.e., Cd, (with toxicologically-derived" safe' daily doses) for ric e and vegetables (water spinach) and the integrated Hazard Quotient of rice and vegetables (HQi) was co nsistently greater in areas with soil contamination than in the reference area using Red River water fo r irrigation. The HQi for Cd was particularly high for children below the age of 13 and it was slightl y higher for females than for males. While toxicologically-derived 'safe' daily doses are very conservative to account for inherent uncertain ty in their derivation, this issue should be raised with famers and policy makers. Conclusion/Recommendations: Due to unrestricted discharge of industrial waste, the soil and water environment has been contaminated, which is demonstrated by accumulation of heavy metals in surface soils. This may in some circumstances pose a risk t o public health. Policies should be developed that enable authorities to mitigate negative environment al impacts of industry and empowers communities to nurture a safer environment whilst maintaining the economic benefits of development.

This paper focuses on the effect of transformer parameters and a line reactor on distribution of power flows in a high-voltage substation and transmission lines. Four case studies that have different values of transformer parameters including rated power, short-circuit impedance and reactance/resistance ratio are supposed in this research. Basing on power flows on transformers in case of the parallel operation, load factor of each transformer and operating parameters are considered in above case studies. Moreover, a line reactor is proposed in this paper to regulate power flows in a system having two power sources. Four operating modes of the proposed line reactor are defined by changing on/off states of switches in this device to modify the value of impedance. The effect of the line reactor on power received from sources and power flows on transmission lines is evaluated in its all modes. Research results are carried out by the ETAP 16.0 software and present high accuracy and reliability for the proposed problems. Research contributions help dispatchers understand the essence of power transmission process, solve real problems and give out effective solutions to operate high-voltage systems.

This paper introduces a new method, called IB-SMC method, to control DC/DC boost converters in systems exploiting photovoltaic power generation. This method combines the sliding mode control technique and iterative-bisectional technique in the maximum power point tracker to change operations modes of photovoltaic power generation. The IB-SMC controller uses voltage sliding surface to evaluate the relation of instantaneous voltage at the input converter and instantaneous voltage at the maximum power point. Using information about the power of electromagnetic radiation from a pyranometer and temperature from a temperature sensor, the sliding surface and hyteresis band are changed by practically operational conditions that help improving energy efficiency of the process exploiting PVg. Simulations are carried out by Matlab/Simulink that show the ability to ensure dynamic stability by tracking instaneous maximum power point at any time whenever having any change of the operational condition, static stability by maintaining the operation point at maximum power point whenever not have any change of the operational condition and help to bring out approximately absolute energy efficiency.

Nitrous oxide (N2O) emisison from paddy soil via the soil nitrification and denitrification processes makes an important contribution to atmospheric greenhouse gas concentrations. The soil N2O emission processes are controlled not only by biological, physical and chemical factors but also by farming practices. In recent years, modeling approach has become popular to predict and estimate greenhouse gas fluxes from field studies. In this study, the DeNitrification–DeComposition (DNDC) model were calibrated and tested by incorporating experimental data with the local climate, soil properties and farming management, for its simulation applicability for the irrigated rice system in Duy Xuyen district, a delta lowland area of Vu Gia-Thu Bon River Basin regions. The revised DNDC was then used to quantitatively estimate N2O emissions from rice fields under a range of three management farming practices (water management, crop residue incorporation and nitrogen fertilizer application rate). Results from the simulations indicated that (1) N2O emissions were significantly affected by water management practices; (2) increases in temperature, total fertilizer N input substantially increased N2O emissions. Finally, five 50-year scenarios were simulated with DNDC to predict their long-term impacts on crop yield and N2O emissions. The modelled results suggested that implementation of manure amendment or crop residue incorporation instead of increased nitrogen fertilizer application rates would more efficiently mitigate N2O emissions from the tested rice-based system. Phát thải nitơ ôxít (N2O) từ canh tác lúa nước (thông qua quá trình nitrat hóa và phản nitrat hóa) đóng góp đáng kể vào tổng lượng khí nhà kính có nguồn gốc từ sản xuất nông nghiệp. Quá trình phát thải N2O là không chỉ phụ thuộc vào các yếu tố sinh-lý-hóa học mà còn phụ thuộc các phương pháp canh tác. Trong những năm gần đây, việc ứng dụng mô hình hóa nhằm tính toán và ước lượng sự phát thải khí nhà kính ngày càng trở lên phổ biến. Trong nghiên cứu này, số liệu quan trắc từ thí nghiệm đồng ruộng và dữ liệu về đất đai, khí hậu, biện pháp canh tác được sử dụng để kiểm nghiệm và phân tích độ nhạy của mô hình DNDC (mô hình sinh địa hóa). Sau đó, mô hình được sử dụng để tính toán lượng N2O phát thải trong canh tác lúa nước dưới các phương thức canh tác khác nhau (về chế độ tưới, mức độ vùi phụ phẩm, bón phân hữu cơ, phân đạm) tại huyện Duy Xuyên, thuộc vùng đồng bằng thấp của lưu vực sông Vu Gia-Thu Bồn. Kết quả kiểm định chỉ ra rằng (1) sự phát thải N2O bị ảnh hưởng đáng kể do sự thay đổi chế độ tưới; (2) nhiệt độ tăng và lượng phân bón N tăng sẽ làm tăng phát thải N2O. Kết quả mô phỏng về tác động lâu dài (trong 50 năm) của các yếu tố đến năng suất cây trồng và phát thải N2O cho thấy: Việc sử dụng phân hữu cơ và phụ phẩm nông nghiệp thay thế cho việc bón phân đạm sẽ giúp giảm phát thải N2O đáng kể.

In power systems having photovoltaic generations, controlling the optimal energy is executed by maximum power point algorithms. Most of these algorithms require the information of equivalent photovoltaic parameters such as series and parallel resistor, photo-generated current, reserve saturation current, thermal voltage.

This study estimates the dietary exposure to cadmium (Cd), and associated potential health risks, for individuals living and working in a metal recycling community (n=132) in Vietnam in comparison to an agricultural (reference) community (n=130). Individual-level exposure to Cd was estimated through analysis of staple foodstuffs combined with information from a food frequency questionnaire. Individual-level exposure estimates were compared with published 'safe' doses to derive a Hazard Quotient (HQ) for each member of the study population. Looking at the populations as a whole, there were no significant differences in the diets of the two villages. However, significantly more rice was consumed by working age adults (18-60 years) in the recycling village compared to the reference village (p0.001). Rice was the main staple food with individuals consuming 461±162g/d, followed by water spinach (103±51kg/d). Concentrations of Cd in the studied foodstuffs were elevated in the metal recycling village. Values of HQ exceeded unity for 87% of adult participants of the metal recycling community (39% had a HQ3), while 20% of adult participants from the reference village had an HQ1. We found an elevated health risk from dietary exposure to Cd in the metal recycling village compared to the reference community. WHO standard of 0.4mg Cd/kg rice may not be protective where people consume large amounts of rice/have relatively low body weight.

The analysis results on the operation of reactive power compensators in the Thainguyen power substation in Vietnam show their positive effect on the power system. They have a part in maintaining the voltage at the connection points (220/110/23 kV substation) that equals to the setting value U∗ according to the requirements of the Vietnamese power system dispath center. However, there are still some disadvantages of this substation that need to be overcome: the large number of main devices, much harmonics generated, and very high active power loss. Thus, the author has an idea to solve these problems by application of a bidirectional power converter (BDPC) using a decoupling controller in order to compensate the reactive power corresponding to the setting voltage. The benefit of this new solution is to eliminate the three above fundamental disadvantages. The research results have been verified by simulations in Matlab/Simulink software.