Integrated control and protection architecture for islanded PV-battery DC microgrids:Design, analysis and experimental verification

Direct current (dc) microgrids have gained significant interest in research due to dc generation/storage technologies—such as photovoltaics (PV) and batteries—increasing performance and reducing in cost. However, proper protection and control systems are critical in order to make dc microgrids feasible. This paper aims to propose a novel integrated control and protection scheme by using the state-dependent Riccati equation (SDRE) method for PV-battery based islanded dc microgrids. The dc microgrid under study consists of photovoltaic (PV) generation, a battery energy storage system (BESS), a capacitor bank and a dc load. The aims of this study are fast fault detection and voltage control of the dc load bus. To do so, the SDRE observer-controller—a nonlinear mathematical model—is employed to model the operation of the dc microgrid. Simulation results show that the proposed SDRE method is effective for fault detection and robust against external disturbances, resulting in it being capable of controlling the dc load bus voltage during disturbances. Finally, the dc microgrid and its proposed protection scheme are implemented in an experimental testbed prototype to verify the fault detection algorithm feasibility. The experimental results indicate that the SDRE scheme can effectively detect faults in a few milliseconds

Housing equilibrium price framework for Malaysian middle Class group in affordable housing market

Failure in getting housing equilibrium price for affordable housing market has become a hot topic that is often discussed in the press due to the imbalance between housing demanded and supplied. The basic purpose of the research was to investigate the relationship between macroeconomic housing demand and supply detenninant factors and affordable housing needs in Malaysia, and to dete1111ine the equilibrium house price for middle-class income in the affordable housing market. The research involved the development of theoretical framework by synthesising the models and framework developed by past researchers on the housing equilibrium price framework. It also uses time series analysis together with regression analysis to collect and analyse data. As initial, 371 respondents from household's side and 32 respondents from developer's side in Melaka Tengah were selected as samples as case study in Melaka. During data analysed, around 200 questionnaires from households and 32 questionnaires from developers can be used. The data was analysed using SPSS software to investigate the relationship between macroeconomic housing demand and supply determinant factors towards the needs f and supply of afordable housing market. From the investigation, current house price, monetary status and population changes are the most critical factors that lead to the needs of affordable housing supplies. Meanwhile, developers put the interest rate, government interventions and population changes as the catalyst to develop the affordable housing projects. On the other hand, the empirical data of housing prices are collected from NAPIC from 2006 to 2015. The equilibrium price calculated from the sales perfonnance within four quarter reported by NAPIC is examined using linear regression method. Based on these themes, the research contended that the housing equilibrium price can be achieved using empirical data from demand and supply with supported from current house price, monetary status and population changes the interest rate, government interventions and population changes. Hence, government is the key player and be a pulling effect in controlling the housing price by using the housing demand and supply determinant factor to create a win-win situation between middle-class income and housing developers

Automated Detection of Faults in Overhead Transmission Lines

Capstone Project submitted to the Department of Engineering, Ashesi University in partial fulfillment of the requirements for the award of Bachelor of Science degree in Electrical and Electronic Engineering, May 2021Electricity is a significant aspect of our daily lives. social activities and industries heavily depend on electricity to function. Transmission line protection is an essential issue in power system engineering because 85-87% of power system faults occur in transmission lines. Proper detection of various faults which do occur on transmission lines is very important. This project presents an impedance technique to detect and classify the different shunt faults on transmission lines for quick and reliable protection schemes. Discrimination among different types of faults on the transmission lines is achieved by applying evolutionary programming tools. MATLAB software is used to simulate operating and fault conditions on high voltage transmission line, namely single phase to ground fault, line to line fault, double line to ground and three-phase short circuit fault. These faults are isolated from the system using a designed impedance relay and the distance of the fault is calculated and provided. This research project successfully designed a functional and cost effective fault detection prototype and its simulation was also successful.Ashesi Universit

Fault Protection In DC Distribution Systems Via Coordinated Control of Power Supply Converters and Bus Tie Switches

A new fault protection method responds to the current needs of emerging dc power distribution systems by coordinating electronic power converters and mechanical contactors to rapidly isolate short circuit faults while maintaining continuity of power to loads. This work is important because the increasing performance, higher efficiency, and decreasing cost of electronic power converters have spurred a rediscovery and proliferation of dc power distribution systems. Although dc distribution offers advantages such as higher transmission efficiency, higher power density, higher reliability, and ease of interfacing asynchronous sources, enthusiasm for adopting dc technologies suffers from widespread concern over the means to protect dc distribution systems against short-circuit faults. The developed fault protection method rapidly limits the fault current, de-energizes the main distribution bus, reconfigures the bus via mechanical contactors, and re-energizes the system. The entire process can be accomplished fast enough to comply with the requirements of CBEMA and IEEE standards on power quality. A fast and reliable fault detection method has been developed in order to coordinates power converters and contactors. With this method the source power converters independently enter into current-limiting mode as soon as they recognize a fault condition. The bus segmentizing contactors autonomously decide whether to open or not based on their local interpretation of time-to-trip curves as functions of apparent equivalent circuit resistance. This method allows converter and contactors to coordinate to provide fault protection for dc distribution systems independently on communication failures. Simulation and experimental results show that fault current can be limited within few milliseconds, faults can be isolated within 20 ms and that the system can be re-energized within 100 ms. Moreover, this work provides system design considerations and limitations on components and system parameters

Failure analysis informing intelligent asset management

With increasing demands on the UK’s power grid it has become increasingly important to reform the methods of asset management used to maintain it. The science of Prognostics and Health Management (PHM) presents interesting possibilities by allowing the online diagnosis of faults in a component and the dynamic trending of its remaining useful life (RUL). Before a PHM system can be developed an extensive failure analysis must be conducted on the asset in question to determine the mechanisms of failure and their associated data precursors that precede them. In order to gain experience in the development of prognostic systems we have conducted a study of commercial power relays, using a data capture regime that revealed precursors to relay failure. We were able to determine important failure precursors for both stuck open failures caused by contact erosion and stuck closed failures caused by material transfer and are in a position to develop a more detailed prognostic system from this base. This research when expanded and applied to a system such as the power grid, presents an opportunity for more efficient asset management when compared to maintenance based upon time to replacement or purely on condition

Modeling and detection of high impedance arcing fault in medium voltage networks

In this dissertation, a universal arc representation using the Electromagnetic Transient Program (EMTP) is first developed. It is accomplished based on the bilateral interaction between EMTP network and Transient Analysis Control System (TACS) field. This arc modeling procedure is used as a useful guide to present a new model for high impedance arcing faults due to leaning trees. At the Power Systems and High Voltage Laboratory, Helsinki University of Technology (TKK), Finland, experiments have been performed to measure the fault characteristics due to leaning trees and therefore to verify the proposed model. Towards investigating detection facilities of this fault type, the fault model is incorporated at different locations in 20 kV Medium Voltage (MV) networks using the ATPdraw program, which is a graphical interface utilized to simplify the ATP/EMTP processing. Then, phase quantities and residual components are taken at different measuring nodes in the simulated networks. It is revealed that the main feature of this fault type that can enhance its detection is the periodicity of electromagnetic transients created by repetitions of the arc-reignition after each current zero-crossing. This feature is obtained considering different earthing concepts. Different detection techniques are proposed based on Discrete Wavelet Transform (DWT). The absolute sum of the wavelet coefficients in the respective frequency band is investigated for the detection purposes while several selectivity functions are proposed for the first time. The selectivity functions are presented using Logic Functions, fundamental current components and transient power directionalities. Test cases provide evidence of the efficacy of the proposed techniques. This dissertation is written in a form of the article dissertation. Its core depends on both of a summary and six original publications.reviewe

Bidirectional DC-DC Converter with Digital Droop Parameterization

The key for decentralized battery systems is a robust and communication-less control strategy for autonomous power sharing of parallel-connected DC-DC converters. Battery systems improve the reliability and quality of power supply in renewable energy systems and enable power supply for off-grid, mobile applications, including islanded grids, home storage, and electric vehicles. In many cases, components with different elec trical properties require different voltage levels. An adaptation is consequently essential and is normally implemented in DC grids for the batteries via bidirectional DC-DC converters. The power flow in both directions can thus be ensured. To achieve a power distribution in parallel connected DC-DC converters, a droop control in the form of a virtual internal resistor can be used. This paper presents a novel approach of a DC DC converter with a digitally parameterizable droop resistor, whose voltage regulation is based on an analog operational amplifier circuit to ensure low delays and robustness. The droop resistor is adjusted with a microcontroller, which offers the possibility to apply a higher-level control for load sharing via an interface. Mathematical correlations are used to clearly define the parameters of the control. Furthermore, the circuit was completely simulated and tested in the hardware setup. The shown results verify the functionality and indicate only minor deviations. Therefore, this circuit is important for future use in distributed battery systems

Development of DC Circuit Breakers for Medium-Voltage Electrified Transportation

Medium-voltage DC (MVDC) distribution is an enabling technology for the electrification of transportation such as aircraft and shipboard. One main obstacle for DC distribution is the lack of adequate circuit fault protection. The challenges are due to the rapidly rising fault currents and absence of zero crossings in DC systems compared to AC counterparts. Existing DC breaker solutions lack comprehensive consideration of energy efficiency, power density, fault interruption speed, reliability, and implementation cost. In this thesis, two circuit topologies of improved DC circuit breakers are developed: the resonant current source based hybrid DC breaker (RCS-HDCB) and the high temperature superconductor fault current limiter based solid state DC breaker (HTS-FCL-SSDCB). The RCS-HDCB utilizes a controllable resonant current source based upon wide bandgap (WBG) switches that enable low loss and fast fault interruption due to the fast switching speed. The voltage applied by the controllable resonant current source is much lower than the rated voltage of the DC breaker, allowing the utilization of significantly lower voltage rated WBG switches. The conduction path\u27s sole component is a fast-actuating ultra-low resistance vacuum interrupter for high efficiency during normal operation. As the second DC breaker concept, the HTS-FCL-SSDCB is subdivided into a fault current limiter (FCL) and solid state DC breaker (SSDCB). The FCL is based upon a high temperature superconductor cable which has natural fault current limiting capabilities while having negligible insertion losses for normal load currents. The SSDCB utilizes WBG switches to decrease conduction losses compared to Silicon-based breakers. The FCL reduces fault current such that the number of semiconductive switches in the SSDCB is minimized. Both breakers feature a metal-oxide varistor device in parallel to clamp overvoltages and dissipate energy after fault interruption. Modeling, simulation, and analysis in electrical and thermal domains are conducted to verify the functionality of the DC circuit breakers. The simulation results confirm the feasibility of these two DC breakers in their proposed applications of 2.4 kV electric aircraft and 20 kV shipboard MVDC distribution systems

An Improved DC Circuit Breaker Topology Capable of Efficient Current Breaking and Regeneration

The DC power system, due to its convenience of conversion, integration, and use, is getting immense attention in the field of power transmission and distribution. It is superior to traditional AC systems in terms of efficiency, reliability, and control simplicity as well. A DC circuit breaker is one of the important elements of any DC power system. It is a sophisticated technology designed to break DC current only. The breaking of a DC current is always challenging compared to the breaking of an AC current, as DC current does not have natural zero crossing points like AC current has. Moreover, DC current breaking becomes more critical when the current is inductive as energy stored in the network inductance opposes instantaneous current breaking. Hence, this energy needs to be absorbed and dissipated as heat during the current breaking operation, which is exactly what is done in the traditional DC circuit breaker topologies. This paper introduces a new topology for DC circuit breakers with a mechanism to reuse this stored energy instead of dissipating it. The mechanism is analogous to regenerative braking in electric drive systems and can enhance the overall system efficiency. The proposed scheme was analyzed through rigorous computer simulation and was experimentally validated

Detection of Anomalies in the Quality of Electricity Supply

From the last two decades, power quality is getting much attention. Proper functioning of the equipment depends upon the quality of power supplied. Every year, demand of electric power goes on increasing and the power system network is expanding and becoming more complex. On account of thrust on clean power supply, use of renewable sources has dramatically increased in grid but it simultaneously causes power quality problems. In this work, power quality disturbance detection in wind farm integrated with grid is presented. For disturbance detection, time-time transform has been employed. The disturbance signal for the detection purpose is generated in MATLAB/Simulink environment by using a Simulink model