Ghanim Putrus

Impact of electric vehicles on power distribution networks

The market for battery powered and plug-in hybrid electric vehicles is currently limited, but this is expected to grow rapidly with the increased concern about the environment and advances in technology. Due to their high energy capacity, mass deployment of electrical vehicles will have significant impact on power networks. This impact will dictate the design of the electric vehicle interface devices and the way future power networks will be designed and controlled. This paper presents the results of an analysis of the impact of electric vehicles on existing power distribution networks. Evaluation of supply/demand matching and potential violations of statutory voltage limits, power quality and imbalance are presented.

Development of a prototype solid-state fault-current limiting and interrupting device for low-voltage distribution networks

This paper describes the development of a solid-state fault current limiting and interrupting device (FCLID) suitable for low-voltage distribution networks. The main components of the FCLID are a bidirectional semiconductor switch that can disrupt the short-circuit current, and a voltage clamping element that helps to control the current and absorb the inductive energy stored in the network during current interruption. Using a hysteresis-type control algorithm, the short-circuit current can be constrained according to a predefined profile. Insulated-gate bipolar transistors and diodes are used to construct the semiconductor switch. Varistors are used as the voltage clamping element. An effective method is adopted to improve the current sharing between parallel varistors in order to provide the required capability of energy absorption. An overall protection scheme for the FCLID is described. A prototype FCLID for 230-V single-phase, or 400-V three-phase, applications is developed and tested. Analyses and experiments are carried out to define the stresses that the main components in the FCLID are subject to. The results show that the developed prototype is capable of limiting a 3-kA prospective short-circuit current to 120 A for a period of 0.8 s, without exceeding the thermal limits of the chosen switches and varistors

Harmonic analysis and improvement of a new solid-state fault current limiter

This paper presents a harmonic study on a newly developed solid-state fault current limiter. Using this device, the supply voltage sag is reduced when a short-circuit fault occurs on a cable feeder in the downstream network, hence improving the power quality. The device will eventually isolate the faulted part from the healthy network. Harmonics caused by the fault current limiter are analyzed and a method is proposed to prevent undesirable harmonic interactions. Analytical and experimental results are compared with existing regulations. It is verified that, with precautions, the operation of the solid-state fault current limiter will not cause problems to either the supply network or the loads.

Evaluation of the effects of rotor harmonics in a doubly-fed induction generator with harmonic induced speed ripple

This paper is concerned with the low-frequency harmonics which originate from the rotor inverter of a doubly-fed induction generator (DFIG). By including the mechanical speed response, it expands the transformer approach previously taken to analyze the harmonic transfer in the machine. A numerical method is proposed to calculate the stator current sidebands, which can be used to predict the voltage fluctuation at the system busbar. It is shown that the pulsating torque associated with the rotor harmonics can induce speed ripple depending on the inertia, causing a significant change in the stator current spectrum. Experiment and simulation verify the analysis and the proposed calculation method.

The effect of cycling on the state of health of the electric vehicle battery

This paper provides an analysis of the experimental results available for lithium ion battery degradation which has been used to create a model of the effect of the identified parameters on the ageing of an EV battery. The parameters affecting degradation are generally accepted to be; state of charge, depth of discharge, charging rate and battery temperature. Values for each of these parameters have been found for three versions of a typical daily cycling scenario; uncontrolled charging, delayed charging and V2G. A comparison is made of the expected overall degradation using four different charging rates and different charging patterns based on the model. A link is made between the charging patterns and the effect on the power flow at the transformer of a typical section of LV network using a ADMD profile. The analysis shows that delayed charging and V2G slow down the rate of battery degradation. However, fast charging appears to accelerate battery degradation. Delayed charging also helps avoid excessive evening loading and thus will help delay distribution network asset upgrading. Uncontrolled charging increases evening loading and V2G can reduce it. However, the EV then needs more power for charging and the charging after V2G needs to be managed if it is not to create another spike in demand at a later time.

Power quality improvement using a solid-state fault current limiter

This paper describe the use of a fast solid-state fault current limiting and interrupting device, which Is developed by the authors, to enhance the quality of supply in distribution networks by minimizing the disturbance to loads during the occurrence of a fault Performance analysis of the proposed device shows that It also has the capability to improve the imbalance between phases during a single-phase fault. This has significant effect on the performance of harmonic sensitive loads such as power electronic converters connected to the system. The relevant modeling, digital simulation and test results, referring to a realistic three-phase system are reported and discussed.

Smart grids: energising the future

Electrical power systems are the backbone of industry, society and current civilisation. Power engineers have accumulated the necessary skills and procedures, to enable them to operate the system in the most reliable way possible. The main principles of system operation have not changed much, despite the rapid developments in power electronics, computing, information and communication technologies. This paper surveys existing power networks and their limits in meeting modern developments and environmental concerns. There is an evaluation of the impacts of deployment of new low carbon technologies such as distributed generation and electric vehicles on existing networks, together with the main drivers for change and features of the new concept of the ‘smart grid’. The paper also examines the challenges and benefits that the ‘smart grid’ will bring, and describes the enabling technologies.

Power Quality: Overview and monitoring

ldquoPower qualityrdquo (PQ) is a generic term often used in relation with unwanted disturbances of the electricity supply. In recent years, there has been an increased number of PQ related problems. This is mainly due to the rapid growth in the use of equipment that generate PQ disturbances and also increase of equipment that are sensitive to these disturbances. This increased concern about PQ issues from both suppliers and consumers of electricity has increased the demand for advanced PQ monitoring systems. Each PQ disturbance has a unique wave shape resembling its characteristics. Therefore PQ disturbances could be identified by monitoring the voltage/current signal waveform and analysing its features. PQ monitoring instruments can vary from a simple true r.m.s. meter to advanced techniques that are capable of automatically capturing and classifying PQ events. This paper presents an overview of the characteristics, effects and causes of PQ events and addresses recent trends in PQ monitoring.

The interactive effects of multiple EV chargers within a distribution network

Power Quality (PQ) issues are increasingly important owing to the widespread use of power electronic devices, such as switch mode power supply, Electric Vehicle (EV) charging systems, etc. Non linear devices used in EV chargers draw non sinusoidal current and distort the input current from the grid resulting in the injection of Harmonic currents. This paper considers the PQ effects of a number of types of EV charging systems, and examines the effects of multiple instances of such chargers on a simulated network. Some designs will tend to cancel certain harmonics produced by others, and others may magnify the levels of particular harmonics. In addition, the paper explores the ability of the PWM charging system to produce harmonic currents at a chosen phase angle allowing cancellation of particular harmonics.

Energy Efficiency in Electric and Plug-in Hybrid Electric Vehicles and Its Impact on Total Cost of Ownership

There is an increasing awareness, policies and an incentive landscape, which are encouraging and starting to shape future transport as part of a wider ecosystem of infrastructure, use, behaviour and sustainability. However, one of the main barriers for the wider uptake by both fleet and individual users of electric vehicles is the concern of the uncertainties of Total Cost of Ownership (TCO). This contribution is based on a mix of original modelling, simulation and laboratory experimentation studies as well as a review of the academic and policy literature. It focuses on vehicle design and the battery and energy management in electric and plug-in hybrid electric vehicles (EV/PHEV). EV users express concerns about the longevity of the electric battery and hence the life cycle (especially with frequent fast charging), which amounts to a major part of the costs and value of the vehicle. Using the battery to provide ancillary services will add more value to the EV and reduce the effective TCO.