The Hongkong Electric Co., Ltd. (HK Electric) has partnered with The Hong Kong Polytechnic University (PolyU) to carry out an evaluation of the performance of retired electric vehicle (EV) battery ...and to develop a hybrid battery energy storage system (HBESS) for redeployment of the retired EV battery, together with new gel-type valve regulated lead-acid (VRLA) battery, in a proposed standalone photovoltaic (PV) system on Po Toi Island. Based on the evaluation, the remaining useful capacity inside the retired EV battery is found capable of extending the service life of VRLA battery up to more than 20% through an effective coordination among different types of batteries by the HBESS. This paper presents the design and analysis for the system configuration, major components, and a specialized energy management system aiming at optimizing the performance of the HBESS.
Underground-cable (UC) systems are expected to substitute overhead lines (OVH) in the near future because of governmental policies and environmental concerns. Compared to OVH, due to being more ...capacitive and less resistive, UC systems tend to increase voltage magnitudes and short circuit currents all along the line. In addition, PV systems are also known to cause significant voltage rise problems in distribution grids. Assuming the combined dominance of UC and renewable energy systems in future power grids, new challenges are needed to be identified in advance. Existing and prospective problems should be revealed to better understand the dynamics behind them. Therefore, this study is divided into three parts. First, the case of complete transition from OVH to UC is technically analyzed in terms of voltage profiles and short circuit currents. Second, PV systems, as renewable energy sources, are attached to the problem. Then, the challenges associated with the combination of these two systems are identified. Third, to mitigate the voltage related problems, a two-stage strategy is proposed using shunt reactors and reactive power support capabilities of PV inverters. According to the simulation results, the proposed strategy can be a promising solution in dealing with the voltage variations and voltage unbalance problems.
Hong Kong people has been becoming more and more aware of the necessity of environmental protection. Various emerging green technologies have been introduced to Hong Kong in recent years. To enhance ...the rate of usage of alternative energy and to reduce the use of fossil fuels such as coal for thermal and electricity generation, Hong Kong Government has proposed a program called "Feed-in Tariff for Solar Power Scheme on business and residential buildings in Hong Kong". Using electricity generated by solar panels, citizens can gain benefits for selling electricity to power companies. However, despite the advantages of using solar electricity, its efficiency and low installation cost, acceptance by the local people and electricity companies are still one major concern on the successful implementation of this scheme. This report analyzed the potential concern by collecting questionnaire, studying the financial aspect and some case studies to find out if this scheme could be successfully implemented in future.
At present, in the distribution network consisting of DC power sources such as PV array, energy storage systems (ESS), data centers and charging, it is an ideal way to select a DC distribution ...network or a DC microgrid. This paper first establishes a model of DC microgrid consisting of PV array, direct-drive wind turbine generators, ESS and DC load, where PV array and direct drive wind turbines generators operate in MPPT control mode and ESS use improved droop control method. Ensure that the DC microgrid is rapidly entering a new stable point when the load or renewable energy resources (RES) input is constantly changing, so that the microgrid remains stable within a certain range. On the basis of voltage stability, the relationship between the MPPT curve of RES and the sagging characteristics of ESS is studied. The optimal control method of RES and ESS is adopted to appropriately change the operating characteristics of RES and it is no longer mandatory to operate at MPPT. Instead, run near this point to ensure optimal operation of the grid. The simulation results verify the effectiveness of the improved energy storage droop control mode and combined optimal control mode of RES and ESS.
This work proposes a Monte Carlo-based technique to assess the impacts of different PV penetrations on a real LV network for the North West of England, considering 5-min resolution models for ...domestic load and PV generation. The impacts of PV location are analysed through two scenarios based on location: closer to and further from the distribution transformer. Voltage impacts are measured using EN50160 and the thermal capabilities are examined through a utilisation factor. Additionally, the effects of higher LV busbar voltages are also investigated. Results indicate that voltage issues are more constraining than asset utilisation, particularly with clusters closer to the transformer. (4 pages)
With the elimination of the isolation transformer, such inverters are susceptible to high leakage current, so suppression techniques have been a popular research topic. Various topologies and ...modulation techniques for transformerless PV inverters have hence been introduced and published. Since transformerless PV inverters are mainly meant for grid-tied operation, their performance should only be validated via grid-connected tests. Nevertheless, there is much research that is only verified via simple RL-load tests. Moreover, due to laboratory equipment limitations, such validation is done at less stringent operating conditions, such as with reduced DC-link voltage and reduced power rating. While such validation gives an estimation of the converter's performance, it often raises doubts regarding the merits of the test inverter when connected to the actual grid. In this paper, the influence of test conditions on a transformerless PV inverter is investigated. Based on the analysis, a systematic approach for implementing lab-scale grid-connection is also explained, to allow a valid evaluation of the inverter's true characteristics.
Module temperature (MT) plays an important role in the photovoltaic (PV) energy production. Due to that, the accuracy of MT prediction or MT model is significant in any design and performance ...software or prediction tools. Presently, there are a few MT models developed for equatorial (Af) region such as Malaysia. In Malaysia, retrofitted PV mounting configuration is getting much attention because of the ample roof availability, especially houses, factories and warehouses. In this study, a hybrid technique of principal component analysis (PCA) and multiple linear regressions (MLR) is applied to develop an MT model and further quantify the relative contribution of each ambient variable in the model for retrofitted PV in Malaysia. By using principal component regression (PCR) technique, the result indicates that MT model is confirmed to be free from any multicollinearity problem. The relative contribution of SI, AT, RH, and WS in this model is 41.65%, 29.97%, 26.63%, and 1.75% relatively.
In grid-tied photovoltaic (PV) systems transformerless inverters are attractive due to reduced size, weight and cost. However, the absence of galvanic isolation forms a direct path between PV to ...grid. To meet the safety requirement in transformerless systems, it needs to be designed carefully. A lot of research has been done based on the reduction of the common mode current (CMC) with constant common mode voltage (CMV). Neutral point clamped (NPC) topology is an effective way to eliminate the leakage current. Recently, PNNPC topology has been proposed which is able to eliminate CMC with high-efficiency. Based on the analysis, a modified NPC inverter is proposed in this paper. The proposed topology is sharing the similar CMC elimination capability but with simpler design and higher efficiency. The principle operation and the common-mode behaviour of the proposed topology are discussed and investigated. Theoretical finding of the proposed topology is validated through Matlab/Simulink.
The next generation of photovoltaic (PV) system is expected to provide ancillary service function during grid voltage drop such as low-voltage ride-through (LVRT) capability. During such voltage ...drop, the distributed generation (DG) should remain connected to the grid and at the same time injecting a reactive power to provide a voltage support. The LVRT function in wind-based electricity generation is already established due to its maturity. However, the LVRT implementation in PV system is just at the beginning where there are still many rooms to be investigated and improved. Thus, this paper proposed an enhanced LVRT control strategy which is based on simple PI-scanning to improve the LVRT capabilities. Simulation done in MATLAB environment has confirmed the effectiveness of the system in providing continuous voltage support to the grid.
This is paper presents a comprehensive modelling, simulation and its implementation of photovoltaic module in MATLAB/Simulink environment. Three modelling approaches including mathematical, circuitry ...and functional blocks are presented. Graphical and text based implementation are outlined in this paper. The modelling and simulation results for all three approaches are presented, and the accuracy, pros and cons of each approach are discussed. The presented modelling approach contributes to renewable energy curriculum delivery that help students to gain complete view of modelling and simulation implementation of photovoltaic at the perspective of mathematical, numerical method and circuit theory. The presented models also contribute to the development of photovoltaic module design, simulation, analysis and interactive education tool.
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