Abstract:This paper presents an enhanced control strategy for Wind Energy Conversion System (WECS) using Doubly-Fed Induction Generator (DFIG). A robust Super-Twisting (STW) sliding mode control for variable speed wind turbine is developed to produce the optimal aerodynamic torque and improve the dynamic performance of the WECS. The electromagnetic torque of the DFIG is directly tracked using the proposed control to achieve maximum power extraction. The performance and the effectiveness of the STW control strategy are compared to conventional Sliding Mode (SM) and Proportional-Integral (PI) controllers. The proposed STW algorithm shows interesting features in terms of chattering reduction, finite convergence time and robustness against parameters variations and system disturbances.

Abstract:Introduction: Event reports recorded by intelligent electronic devices (IEDs) such as digital relays and fault recorders during disturbances depict the status and system parameters of the power system. Incorrect relay settings and unknown system parameters can lead to relay misoperation but information regarding these are available by performing a comprehensive analysis of fault records. Hence, it is necessary to regularly make a comprehensive assessment of the functioning of the relay to ensure reliable operation. Case description: The objective of this paper is to demonstrate various aspects of evaluating relay performance and verifying circuit parameters which are used in relay settings using field data in two case studies. Discussion and Evaluation: While scrutinizing the relay’s operation, this paper also presents key insights on verifying circuit parameters using the same relay event records. Conclusions: The lessons learned from the case studies presented in this paper will equip a protection engineer to inspect the operation of a relay during a transmission line fault, help gain a better understanding of the fault event and take possible actions to prevent future occurrence of similar events.

Abstract:This paper presents a coordination strategy of Load Frequency Control (LFC) and digital frequency protection for an islanded microgrid (MG) considering high penetration of Renewable Energy Sources (RESs). In such MGs, the reduction in system inertia due to integration of large amount of RESs causes undesirable influence on MG frequency stability, leading to weakening of the MG. Furthermore, sudden load events, and short circuits caused large frequency fluctuations, which threaten the system security and could lead to complete blackouts as well as damages to the system equipment. Therefore, maintaining the dynamic security in MGs is one of the important challenges, which considered in this paper using a specific design and various data conversion stages of a digital over/under frequency relay (OUFR). The proposed relay will cover both under and over frequency conditions in coordination with LFC operation to protect the MG against high frequency variations. To prove the response of the proposed coordination strategy, a small MG was investigated for the simulation. The proposed coordination method has been tested considering load change, high integration of RESs. Moreover, the sensitivity analysis of the presented technique was examined by varying the penetration level of RESs and reducing the system inertia. The results reveal the effectiveness of the proposed coordination to maintain the power system frequency stability and security. In addition, the superiority of the OUFR has been approved in terms of accuracy and speed response during high disturbances.

Abstract:This paper proposes a residue theorem based soft sliding mode control strategy for a permanent magnet synchronous generator (PMSG) based wind power generation system (WPGS), to achieve the maximum energy conversion and improved in the system dynamic performance. The main idea is to set a soft dynamic boundary for the controlled variables around a reference point. Thus the controlled variables would lie on a point inside the boundary. The convergence of the operating point is ensured by following the Forward Euler method. The proposed control has been verified via simulation and experiments, compared with conventional sliding mode control (SMC) and proportional integral (PI) control.

Abstract:Solar cells convert sun light into electricity, but have the major drawbacks of high initial cost, low photo-conversion efficiency and intermittency. The current-voltage characteristics of the solar cells depend on solar insolation level and temperature, which lead to the variation of the maximum power point (MPP). Herein, to improve photovoltaic (PV) system efficiency, and increase the lifetime of the battery, a microcontroller-based battery charge controller with maximum power point tracker (MPPT) is designed for harvesting the maximum power available from the PV system under given insolation and temperature conditions. Among different MPPT techniques, perturb and observe (P&O) technique gives excellent results and thus is used. This work involves the design of MPPT charge controller using DC/DC buck converter and microcontroller. A prototype MPPT charge controller is tested with a 200 W PV panel and lead acid battery. The results show that the designed MPPT controller improves the efficiency of the PV panel when compared to conventional charge controllers.

Abstract:When a fault occurs in a DC system, the fault current rises rapidly with no zero-crossing point which makes fault-line selection and fault-type identification difficult. In this paper, an online detection and protection method based on graph theory, namely the “double D method”, is proposed for fault-line selection and fault-type identification in DC systems. In the proposed method, the entire distribution network is visualized as a “map” with vertices representing the line convergence points and edges representing the connection lines. A network topology matrix “D” is formed by detecting the current directions as the current directions are altered following a fault, whereas the current directions at the ends of non-fault lines remain the same. In order to prevent misjudgment problems arising from power flow reversal, the rates of change of the fault currents are used to further determine whether a fault has occurred and the “double D method” is introduced to identify the fault type. Simulations results with different fault types verify the effectiveness and reliability of the proposed method.

Abstract:Grid resource utilization rate plays a key role in power grid operation. Although the proportion of population and the area in China Southern Power Grid (CSG) and National Grid Plc of UK (NG) are nearly, grid resources utilization of CSG is lower than that of NG. In this paper, the utilization of human resources and equipment resources of CSG and NG have been reviewed. It is discovered that there is a large gap between these two companies. The results show that the utilization in CSG is about 20% to 50% of that in NG. And it is estimated that if the equipment resources utilization of CSG increases to the level of NG in 2012, the coal consumption and thus CO2 emissions would be reduced by 17 million tons and 21 million tons, respectively. As China is a developing country and Britain is a mature developed country, it is to some extent reasonable that grid resources utilization of CSG is lower than that of NG. The benefits of improving equipment resources utilization are illustrated in detail, which provided the reference for developing the grid resource utilization in China.

Abstract:High quality electric power supply is the prime goal in the modern power systems around the world. One of the main ways to achieve this is the protection of the system which needs to be fast, reliable and cost effective. The objective of this paper is to provide protection of equipments in low voltage (LV) distribution system and thereafter to avoid their failure due to abnormal operating conditions. The proposed device provides protection for industrial, commercial and residential equipments by monitoring under voltage, over voltage and over current conditions using microcontroller, transistor and other discrete components. The microcontroller is the heart of this protective device which performs the major control of the device. The designed circuit can withstand the loads and the set voltage range so as to supply the connected load for any voltage variation between 220 and 240 Volts. It can be used to protect loads such as refrigerator, TV, VCR/DVD player etc. against undesirable over and under voltage conditions as well as surges caused due to sudden failure of power supply mains. This device can also be used directly as standalone equipment between the supply mains and the load. The over/under voltage and over current cut-off with time delay provides over/under-voltage and over current protection and also protection against any transients.

Abstract:High resistance fault poses an enormous challenge to the existing algorithms of fault detection and fault classification. In this paper, the standard deviation and accumulation method are employed to perform the fault detection and classification. It is primarily built in two stages. Firstly, the standard deviations for the measured current’s signals of the local and remote terminals is computed to extract the fault feature. Secondly, the cumulative approach is used to enlarge the fault feature to perform the high resistance fault. The proposed scheme is known as Standard Deviation Index (SDI), and it is obtained for the three phases and zero sequence. The proposed algorithm has been tested through different fault circumstances such as multiple faults locations, fault resistances, and fault inception time. Moreover, far-end faults with high-resistance, faults happened nearby the terminal, faults considering variable loading angle, sudden load change, different sampling frequency, bad signaling and a fault occurred in the presence of series compensation are also discussed. The results show that the proposed scheme performed remarkably well regarding the fault with resistance up to 1.5kΩ and can be detected within a millisecond after the fault inception. Additionally, the computational simplicity that characterizes the processes makes it more efficient and suitable for domain applications.

Abstract:There is growing interest in power quality issues due to wider developments in power delivery engineering. In order to maintain good power quality, it is necessary to detect and monitor power quality problems. The power quality monitoring requires storing large amount of data for analysis. This rapid increase in the size of databases has demanded new technique such as data mining to assist in the analysis and understanding of the data. This paper presents the classification of power quality problems such as voltage sag, swell, interruption and unbalance using data mining algorithms: J48, Random Tree and Random Forest decision trees. These algorithms are implemented on two sets of voltage data using WEKA software. The numeric attributes in first data set include 3-phase RMS voltages at the point of common coupling. In second data set, three more numeric attributes such as minimum, maximum and average voltages, are added along with 3-phase RMS voltages. The performance of the algorithms is evaluated in both the cases to determine the best classification algorithm, and the effect of addition of the three attributes in the second case is studied, which depicts the advantages in terms of classification accuracy and training time of the decision trees.