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.
