Smoothing Time Constant Research Articles

Coordinated Control of a Hybrid Energy Storage System for Improving the Capability of Frequency Regulation and State-of-Charge Management

The paper proposes a coordinated operation method of two independent storages for managing state-of-charge (SOC) and for providing ancillary service concerning frequency regulation (FR); furthermore, this article also introduces the power allocation scheme between two storages in consideration of the coverage of the frequency band for each storage along with the SOC management scheme of the supercapacitor and battery. We also provide a guideline for the storage sizing on the basis of the smoothing time constant. Additionally, we verify the advantage of the HESS in extending the lifetime of the battery, which is estimated by a real-time state-of-health (SOH) calculation method. The Bode plot of the proposed method is analyzed to observe the power spectrum coverage in the frequency domain through the case studies using PSCAD/EMTDC and MATLAB.

Virtual Capacity of Hybrid Energy Storage Systems Using Adaptive State of Charge Range Control for Smoothing Renewable Intermittency

This paper presents a method for improving capability of a Hybrid Energy Storage System (HESS) comprised of a battery and supercapacitor (SC), for smoothing power fluctuations of renewable energy sources by adaptively controlling the state of charge (SOC) allocation range using automatic SOC management. The proposed method secures the preset SOC range of both battery and SC for power smoothing applications of renewables and also has the ability to significantly smooth power fluctuations using the virtual capacity concept of an energy storage system (ESS) by extending the SOC usage range. The bode plots of the proposed method are analyzed to observe the coverage of the power spectrum in the frequency domain in each storage based on the case studies. A criterion of HESS sizing, both battery and SC, is also developed based on the SOC range, smoothing time constant, and the power rating of renewables. The proposed method for the integration of HESS on renewable energy sources is verified with simulation results and characteristic analysis using PSCAD/EMTDC and MATLAB software.

Power Management Approach to Minimize Battery Capacity in Wind Energy Conversion Systems

In a wind-battery hybrid power system, minimal battery capacity is a crucial requirement to achieve economic operation. In this paper, an optimal power control strategy based on a first-order low-pass filter is proposed to minimize the battery capacity by adjusting the filter smoothing time constant. We demonstrate the mathematical relationship between the filter smoothing time constant and the fluctuation mitigation requirement during one sampling time, so the optimal filter smoothing time constant can be easily computed to minimize the battery capacity. Moreover, an online short-term power control is also considered to maintain the battery state of charge within a safe range and to regulate the battery power below its rating. The proposed power management approach is simple and easy to implement. In order to verify the effective features of the proposed power management approach, a case study is carried out along with some experimental verification.

C/A code cross-correlation at a high doppler offset

C/A code cross-correlation affects signal acquisition and tracking in global positioning system (GPS) receivers. This paper investigates the cross-correlation-induced tracking errors, which can be substantial when the two Doppler frequencies are apart by an integer number of kilohertz. Carrier smoothing is an effective mitigation against the pseudorange errors, although the residual could still be significant if a short smoothing time constant is used.

Determination of characteristic parameters of battery energy storage system for wind farm

Integrating a battery energy storage system (BESS) with a wind farm can smooth power fluctuations from the wind farm. Battery storage capacity (C), maximum charge/discharge power of battery (P) and smoothing time constant (T) for the control system are three most important parameters that influence the level of smoothing (LOS) of output power transmitted to the grid. The economic cost (EC) of a BESS should also be taken into consideration when determining the characteristic parameters of BESS (C, P). In this study, an artificial neural network-based long-term model of evaluated BESS technical performance and EC is established to reflect the relationship between the three parameters (C, P, T) and LOS of output power transmitted to the grid, the EC of BESS. After that, genetic algorithm is used to find optimal parameter combination of C, P and T by optimising the objective function derived from the mathematical model constructed. The simulation results of the example indicate that the parameter combination of C, P and T obtained by the proposed method can better not only meet the technical demand but also achieve maximum economic profit.

Disturbance Margin for Quantifying Limits on Power Smoothing by Wind Turbines

Wind turbines can, in principle, be operated to smooth wind power fluctuations by allowing wider variations in turbine speed and generator torque to store and release energy. This ability must be constrained by turbine speed and generator torque limits. To present, work in the literature is conceptual and does not indicate what extent of smoothing is possible before component limits are reached, nor does it quantify sensitivity to variations in the input wind speed. This paper introduces a method for quantifying how much wind variation a wind turbine can absorb in variable speed mode while still being guaranteed to operate within its component limits. One can apply this method to obtain the dependence of maximum tolerable wind disturbance on the smoothing time constant, and thus make design decisions. This paper shows that the analysis of torque speed intersections, as standardly applied in electric machine theory, is of limited use for studying power smoothing. The new conclusions and design choices made available by the proposed method are illustrated with a series of computation examples. The method is shown to agree asymptotically with two limiting cases that can be calculated based on torque-intersection analysis. The method is based on new theory for computing invariance kernels for nonlinear planar systems, and can be adapted to assess the robustness of other control laws.

Weiner filters for gravitational-wave antennas: Characteristics and applications

We report on the application of Wiener filters to the data of Weber-type gravitational-wave antennas, with particular reference to data processed by means of lock-in amplifiers driven at the frequencies of the modes of the detector. After a review of some basic results concerning the filtering of the data, we briefly examine the relationship between Wiener filters and matched filters. The discussion that follows is centred on various aspects related to the practical application of Wiener filters as well as on their limitations, also addressing the dependence of their performance on the values of their parameters. Finally, we consider some applications of non-optimal Wiener filters: by reducing the filter smoothing time constant, the time resolution can be increased; by increasing it, the filter becomes an estimator of the Brownian motion.

Eleven-centimeter broadband correlation radiometer

A broadband hybrid-junction radiometer operating at 2700 MHz is described. It employs twin receiving channels, each with two-stage synchronously pumped degenerate paramps, and has an overall effective bandwidth of 200 MHz. Installed on the 210-ft radio telescope at Parkes, New South Wales, it gives a system noise temperature of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80\deg</tex> K and an rms recorder fluctuation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.006\deg</tex> K for a 2-second smoothing time constant.