Recent Advances in Electrical & Electronic Engineering - Volume 7, Issue 1, 2014

This paper provides a stochastic technique for the economic assessment of battery storage system which gives assistance to intermittent wind power. The Discrete Time Markov chain battery storage model is firstly introduced to represent the fluctuating battery SOC in the charging and discharging process. Utilizing the limiting theorem for Markov chains, the life time of battery can be predicted by the stationary distribution probability of the residual battery energy. Then corresponding annualized cost is used as the economic evaluation of battery storage system. The result provides a quick economic estimation of battery in a wind power system.

As a basic parameter for the tower load-endurance analysis, it is very important to get insight of dynamic characteristics of the conductor tension during galloping. Taking the advantage of the comprehensive test centre built on real overhead transmission line by SGCC (‘State Grid Company of China’ for short), conductor galloping with artificial airfoils had been observed on 500kV 6-bundled transmission line, during which the conductor tension was measured and recorded. Through the frequency spectrum analysis and the correlation analysis with wind, characteristics of the conductor dynamic tension during galloping were obtained, which could be used as one critical parameter for galloping, not only for the reliable analysis of tower-line system but also for the monitoring and identification of transmission line galloping. In summary, the characteristics of conductor dynamic tension during galloping could be used for galloping pre-warning and the performance evaluation of anti-galloping measures.

As a kind of novel machine, the brushless doubly fed machine (BDFM) without the electric brush and slip ring has gained more and more attention in its AC speed regulation and variable-speed constant-frequency generation system applications due to its good operation performance. For the speed regulation of the BDFM as the external disturbance existing, a proportional integral minus delay (PIMD) controller combining with the H∞ robust control method is proposed. The PIMD controller utilizes the minus delay method and adjusts the delay time to eliminate the known external sinusoidal disturbance input signal. The controller combining with the H∞ robust control strategy can effectively restrain the unknown uncertainties of the system, and further enhance the system robustness. The simulation results show that the proposed PIMD controller can enable the system to have better robustness against external disturbances, and greatly improves the interference rejection performance of the system.

Traditional video coding methods are able to achieve wonderful performance improvements in data compression. However, these methods have high computational complexity and hardware resource consumption, which are not suitable for some applications, such as wireless multi-media sensor network (WMSN) where low complexity video coding (LCVC) methods are modern technologies. In this survey, some typical LCVC methods are explored, including the cropping and improving of the traditional video encoder, Distributed Video Coding (DVC), Compressive Sensing (CS) video encoder, Underdetermined Blind Signal Separation (UBSS) and Two-Dimensional Singular Value Decomposition (2-D SVD) based video encoder. These technologies could obtain better trade-off between high compression ratio and well reconstructed video quality with lower encoding complexity. Moreover, some known architectures of the mentioned LCVC methods are analyzed, as well as the brief performance analysis and comparison. Finally, some applications of low complexity video coding are described, such as wireless video surveillance system and mobile video equipment.

Power balance is important for power systems, specifically for the microgrid with renewable energy. Integrating pumped-storage system (PSS) to microgrid can keep balance of the power and increase the utilization of wind energy. This paper focuses on the development of a control strategy for PSS of the microgrid with wind power. Firstly the simulation model of microgrid composed of wind power system, PSS and variable load is developed. Then the energy storage components of the system are analyzed, including the wind power system with the battery energy storage system (BESS) and the PSS. Simulation experiments have been conducted to test the effectiveness of the PSS model. Finally, a fuzzy control strategy is proposed to solve the storage control problem. Simulations in different operation modes, such as gridconnected mode, islanded mode and conversion of the two modes, have been designed to verify whether the control strategy can ensure the power balance when the load and wind power change. The results indicate that the output power of the PSS can follow the setting power quite well, and the features of the proposed fuzzy approach are highlighted by comparing fuzzy control and PI-based PQ control.

This paper presents a novel optimization technique for the design of multi-stage switched capacitor (SC) biquad-based circuits, using multi-objective constraint programming. Optimization methods, namely single objective and multi-objective in the design areas of SC circuits that are adopted in optimal capacitance assignment are briefly introduced. A sample design (4th order SC biquad-based circuit) with multiple objectives is given for demonstrating the efficiency of the proposed optimization method, which can meet multiple targets (for example, more than two optimal goals– gain of op-amp and size of total capacitance area), showing 6% reduction of total capacitance area, while maintaining the same frequency responses. Also, this paper demonstrates an overview of optimization techniques for the design of different SC biquad-based circuits, using constraint programming. In particular, the progresses achieved on adopting optimization approaches in Operational Amplifiers (OA) are briefly reviewed and then compared.

In this study, a coordinated droop control strategy of dual-source energy storage system with virtual coordinate transformation is proposed by researching on the operation characteristics of low voltage (LV) wind/photovoltaic hybrid microgrid, which is prepared with battery energy storage system (BESS) and super capacitor energy storage system (SCESS). Using virtual coordinate transformation-based droop control not only solves the coupling problem between active and reactive power of LV microgrid, but also enables a coordinated control on BESS and SCESS to achieve smooth handoff from grid-connected mode to isolated mode of LV microgrid for wind, photovoltaic and energy storage. Using PSCAD/EMTDC simulation software, the models of wind turbine system, photovoltaic generation system and dual-source energy storage system are established to form LV microgrid. The effectiveness and feasibility of the proposed control strategy are proved, and the choosing of droop factor of BESS and SCESS is analyzed by simulation.

This paper presents a new harmonic suppression rectifier transformer with filters and a transformer filtering technology to improve power quality of industrial rectifier system. According to the special circuit topology of the new rectifier transformer, the current relationship is deduced between the grid side and valve side windings, along with the valve side and filtering windings, and the implementation conditions of the transformer filtering technology are described. Then, the harmonic transfer mathematic model is established to analyze the effects of filters on harmonic transfer characteristics, and the relationship between the grid side voltage and current is deduced to analyze the reactive power compensation characteristics. Theoretical analysis shows that the transformer filtering technology can prevent the harmonic currents from flowing into the primary winding of the new rectifier transformer and the reactive power can be partly compensated in the secondary winding, which means that the effects of the harmonic and reactive currents on the transformer can be greatly reduced. Finally, the experimental results verify the correctness of the theoretical analysis and calculation.

In this paper, a compact (17.7 mm x 12 mm) triple band-notched UWB antenna is presented. For inserting desirable notches, three concentric ring resonators have been placed on the back side of antenna in a manner that the first resonance frequency of each resonator coincides with one of the desired notches. Considering that the second resonance frequency of outer ring resonator places in UWB frequency band, an EBG using sinusoidal variation of the characteristic impedance of outer resonator is used to reject the spurious notch. CST simulation results verify good performance of the antenna and show acceptable frequency and time domain characteristics such as wide frequency band width (3 GHz - 10.3 GHz) with good return loss( greater than 17 dB in most parts of band), fairly deep notches, approximately omnidirectional patterns and low group delay variations.