In present and future electrical networks more and more cyber physical renewable energy infeed are to be integrated. To ensure nevertheless the safe grid operation with an increasing number of these infeeds, reliable certification is required. Due to the lack of the retroactive effects from the conventional test method, the dynamic behaviors during the test are different from the real situation. In order to realize the retroactive effects, this paper presents a power Hardware-in-the-Loop (PHIL) test system. This paper focused on an optimized PHIL interface algorithm, to avoid the instability from the ideal transfer method. Finally, the PHIL test system has been built in the laboratory. The function of the PHIL test system is verified by a set of PHIL tests for photovoltaic inverter.
During the recent decades, one of the most demanded control devices are frequency converters for induction motor. As we know from literature frequency converters have several control methods. The objective of this publication is to compare torque pulsation of induction motor applying two most popular control methods FOC (Field Oriented Control) and DTC (Direct Torque Control). Squirrel cage induction motor with 1.5kW power was tested experimentally.
This paper addresses the modeling of lightning performance of medium voltage air cable using Alternative Transient Program - Electromagnetic Transient Program (ATP-EMTP). By means of simulation using digital models and Transient Analysis Control System (TACS) features developed within the ATP-EMTP, the lightning overvoltage performance of air cable is analyzed. The analyses are made under the influence of direct stroke to wooden poles, to messenger wires and to nearby trees. The simulation includes models of air cable, messenger wire and distribution poles while considering other factors which are the frequency dependence of the cable parameters, models of wooden-porcelain insulation and shield wire. Adequate flashover model is useful for predicting the crest value of the overvoltages on the distribution line and also for assessing the accurate effect of providing different protection options for the air cables. Based on the simulation results, practical recommendations are proposed for improvement in the lightning performance of air distribution cables.
With a wide range of power electronics-related applications in power systems, harmonic currents are increasing at an alarming rate which has greatly deteriorated the power quality in electrical power networks. Moreover, some of electronic controlled equipments used in power systems, such as cycloconverters, produce sub-harmonics, a type of waveform distortion, which can severely degrade the power system performance. Therefore, they must be closely monitored. Moreover, Fast Fourier Transform cannot accurately analyze waveforms containing sub-harmonics because the synchronization of the sampling procedure to sub-harmonics is practically infeasible. The detection of sub-harmonics requires a different approach from that used for harmonics analysis. In most analysis methods the voltage waveform is expected to be a pure sinusoid with a given frequency and amplitude. Standard tools of harmonic analysis based on the Fourier transform assume that only harmonics are present in the investigated signal and the periodicity intervals are fixed, while periodicity intervals in the presence of interharmonics and sub-harmonics can be variable and very long. Two novel approaches to analyze non-stationary signals are shown in this paper. The first is the "Root-Music" harmonic retrieval method that is an example of high-resolution eigenstructure-based method, the second is a numerical method based on moving average.
The investment in wind farms is increasing rapidly and in many aspects the industry is maturing. Instead of connecting single wind turbine or small wind farms to the distribution network, the energy companies and manufactures are connecting large wind farms to the transmission network. These farms can contain 200 plus turbines and have a rated capacity of greater than 500 MW up to several GW.Providing proper protection for these farms is a major challenge. In the UK, any wind farm rated above 100 MW is required to obey the grid code which means the protection consideration will be directed for grid connection and will be different from wind farms which are connected to the distribution network. In addition to the considerations of a grid connected generator, the particular characteristics of the types of turbine involved add further complications.This paper reviews the existing technologies used for protecting large wind farms and how they will affect the protection of the local transmission feeders and busbars. It is a challenge for the wind farm's protection to achieve 120 ms fault clearance for the transmission network and 800 ms fir a back up protection.Since wind turbines have different characteristics to those of conventional power plant, the paper discusses the special features and settings for the protection schemes used for large wind farms.
Following a system disturbance when there is a loss of grid, under current UK practice, all distributed generators have to be disconnected automatically from the network in less than 500 msecs and remain disconnected until the normal grid supply is restored. They can then be resynchronised and reconnected to the grid supply. However, these distributed generators offer the potential to maintain supplies to consumers during loss of grid, an opportunity which is currently being lost.This paper explores new techniques to enable distributed generators in distributed networks to provide continuity of supply during power system disturbances which result in loss of grid, and thereby enhances the quality of supply to consumers.
Renewable energy sources, which emit no or little greenhouse gasses, can help in reducing the dependency on finite reserves of fossil fuels and lower overall green house gas emissions. Following on successes in addressing the threats to the atmosphere and in order to achieve stabilized emissions against a background of growth in energy use, governments generally have set out policies and goals for the development of renewable energy.Cyprus is a European country whose energy generation is fully reliant on imported oil. The challenge has arisen to determine the best solution to tackle supply needs together with the environmental need to reduce green house gas emissions and become less reliant of fossil fuels.This paper reports recent research to identify and quantify the most economically feasible and technically favourable renewable energy resource for Cyprus. The paper provides an insight into available resources because of Cyprus's geographical location and their capital costs if they are to be exploited. Therefore, it sets a common base to enable economical comparison of renewable resources.
The growth in the use of distributed generation is driven by a selection of drivers including the demand for greater exploitation of sources of renewable energy, the economics of small and medium scale units and the opportunities for independent power supplies. Currently, these generators are operated simply to deliver preset levels of power to the network with the unit's control scheme operating as a slave.This paper highlights the opportunities to develop the control schemes so that they can enhance their impact and contribution on the network. The first opportunity is to maximise the active power delivered to the network by introducing local voltage control by reactive power control. The second opportunity is to enable the generator to support the local supply in event of a loss of grid connection. By maintaining the supply to adjacent consumers, the generator is not only continuing to generate, but is also improving the quality of supply to that part of the network.
The distributed generation as the latest electricity production paradigm has also consistently broadened the possibility of adopting cogeneration systems for small-scale applications. Furthermore, the adoption of intrinsically efficient electro-energetic technologies, such as heat pumps, gives the energy system designer new opportunities to exploit in order to obtain higher energy saving and therefore economic benefits. In this work, the main aspects related to the modelling, characterization, planning and evaluation of cogeneration systems combined with electric heat pumps are shown. The profitability of adopting different configurations is explored from an energy saving standpoint, considering internal combustion engines and microturbines as prime movers. The focus is, in particular, on analyses aimed at accounting for different regulation strategies as well as load levels, considering numerical applications with equipment available in the market.
Trigeneration is spreading as an important energy production technique, above all considering that several distributed generation technologies give the possibility of adopting cogeneration and then trigeneration also on a small-scale basis. In this work a generalized approach to trigeneration characterization, planning and evaluation, introduced by the authors in previous works, is followed. In particular, the energy saving potentiality of direct-fired and water fed absorption chillers, as well as engine-driven chillers, is explored, considering microturbines and internal combustion engines as prime movers. All the numerical applications refer to equipment commercially available.
