Applied Mechanics and Materials Vols. 556-562

Abstract: Due to the intermittence and fluctuation of intermittent sources, microgrid needs energy storage system to make it functioning safely and stably, and the primary problem to be researched is how to determine the capacity of energy storage system. Microgrids of different conditions need energy storage systems of different capacities. This paper proposed an optimal sizing method for hybrid wind-solar-battery microgrids in island mode based on the modified particle swarm optimization. The method solves the optimal design problem on the premise that microgrids function safely, it also takes various restrictions of batteries into account, and finally the best sets of batteries are selected to achieve the optimal economic. A case study was presented to verify the effectiveness of the optimal sizing method.

Abstract: In order to improve the bandwidth efficiency for the communication system effectively, a designing method for orthogonal pulse based sinusoidal and cosinusoidal functions is put forward. The orthogonal pulse is designed by parameter setting, sub-band division, parameter solution and pulse solution from the point signal character. The orthogonal pulse’s spectrum is mixed or overlapped in frequency domain. It can not only be formed little relative bandwidth signal, but also large relative bandwidth signal. The system bandwidth efficiency can reach 2Baud/Hz when the orthogonal pulse is used in information transmission.

Abstract: In order to study the response of the log-periodic antenna (LPDA) to a square wave pulse, it has been irradiated in a square wave pulse using GTEM cell and high-frequency noise generator. And the waveform and frequency spectrum signals are measured. Before the test, the pulse field in GTEM cell has been calibrated. The results showed that field intensity in it changes with the voltage varies linearly strictly at the same point, but with the height of core plate increases, the field intensity decays exponentially but not strictly linear attenuation relationships. Experiment results show that it is feasible to acquire antenna’ square wave pulse response using GTEM cell, and the results is instructive for the analysis of the impulse response and protection for a log-periodic antenna.

Abstract: This paper presents an investigation of argon capacitively coupled plasma at low pressure. A two-dimensional, time-dependent fluid model is used to describe the production, transport, and destruction of electrons and positive ions. The model is solved for a GEC(gaseous electronics conference) Cell reactor type (with 4cm diameter and 2.5cm interelectrode distance) operating at frequency 13.56MHz, pressure 1Torr and applied voltage 1000V, in pure argon. Two-dimensional distributions are presented in the stationary state, including electron temperature and species density i.e. electron, ion and metastable atom. The electric field and electric potential at different phases in one RF cycle is also studied.

Abstract: A novel method for electrical equipments condition assessment is proposed based on Markov prediction. Firstly, the condition representation parameters are induced according to the general volt-ampere characteristics, which can be identified by least square method. Secondly, the number of samples falling into different intervals is counted and the state transition probability matrix is calculated. Last, the distribution of parameters in future detection periods is predicted and the equipments condition is assessed by the ratio of the length of current operation time and the estimated life. Take a single phase two-winding transformer as an example, Monte Carlo simulation is used to generate the leakage inductance data and the electrical data is derived by PSCAD. The equipment condition assessment results verify the effectiveness and feasibility of this proposed method.

Abstract: A design of program controlled function signal generator is introduced. LPC2138 is used as a controller to make the adjustment of frequency, waveform and amplitude programmable. We control the frequency by switching the capacitance and setting the input current of MAX038. We used DS1267 to control the amplitude of output signal with high-speed FET-Input operational amplifier OPA132. Our system is equipped with a keyboard and a LCD screen. We used EEPROM memory chip FM25CL16 to save and load waveform parameters. The circuit works well and the output waveform is stable and reliable.

Abstract: In order to modulate the spectral phase properties of the ultra-short optical pulse in two dimensions by the liquid crystal spatial light modulator (LC-SLM), a setup named quasi-zero-dispersion nested folded 4f system is proposed, in which a grating disperses the ultra-short optical pulse frequency components in the vertical direction and a prism disperses the ultra-short optical pulse frequency components in the horizontal direction. Because the frequencies are dispersed in two directions, the LC-SLM is utilized more effectively and the optical frequency resolution for arbitrary temporal waveform generation is higher than the conventional zero dispersion 4f system. In theory, the quasi-zero-dispersion nested folded 4f system can generate arbitrary desired temporal waveform ultra-short optical pulse. Based on the system, Femtosecond pulse beam with Gaussian temporal waveform is used for experimentation, and an optical pulse train and several other temporal profiles were obtained. All the experimental results indicated that the quasi-zero-dispersion nested folded 4f system is reliable for arbitrary ultra-short optical pulse waveform generation, which fit well with the theoretical analysis. In the future, if a proper high dispersive optical element substitutes the prism in the quasi-zero-dispersion nested folded 4f system, the setup we proposed here will be widely used in the optical pulse shaping areas.

Abstract: Lightning is one of the most important reason of outage of distribution line. And nearly 90% of the accidents of lightning failure is result of lightning induced overvoltage. In order to protect the distribution line from lightning, it is required to have a comprehensive understanding of characteristic of lightning induced overvoltage. Due to the advantage of reduced scale experiment, which are controllable and practical, the characteristic of lightning induced overvoltage is got from it. Comparing the results of experiment with the results of calculation, it is found that changes of overvoltage with height and distance match well with the calculated results, which show that the reduced scale experiment is effective and proper.

Abstract: With the rapid development of flexible HVDC technology in China, the demand for the DC grid of new energy generation projects growth. This paper studies the topology of the DC grid photovoltaic converter, a topological scheme is proposed and detailed analysis of the topology of the work mode is presented. For the device extension problem of equipment used in high-voltage direct current power level, a connecting scheme based on modular IPOS program and a control strategy of uniform duty cycle are given. In this paper, the equivalent controlled source method for small-signal dynamic modeling is established, and the stability of the control scheme is analyzed using Bode diagram. Finally, a 10kW prototype platform topology programs is built and control strategies experimentally is verified. This paper has important reference value for the HVDC grid-connected research of new energy power generation and the research of small power scale AC-DC hybrid microgrid network.

Abstract: According to the output characteristics of photovoltaic (PV) array and battery charging characteristics, this article used DSP to design a PV charging system with maximum power point tracking (MPPT) ,and the three-state charging method was implemented on it. The incremental conductance (INC) algorithm was applied in fast-charge stage to track maximum power point. PI regulator algorithm was exploited to realize constant voltage charge in the stage of over-charge and float-charge, and the charge voltage was compensated by the sampling temperature. Experimental and simulation results indicated that this method can be used to improve the energy efficiency of PV cell, and extend the lifetime of battery.