Lijuan Chen

Integration of Energy Harvester for Self-Powered Wireless Sensor Network Nodes

This paper reports an energy harvester suitable for self-powered wireless sensor network (WSN) nodes consisting of a piezoelectric cantilever, an energy harvesting circuit, and a storage capacitor. Having the same size as a credit card, the proposed WSN nodes can be easily integrated into various applications, such as motor and air conditioning equipment. The WSN node is powered by an integrated bimorph piezoelectric generator that harvests energy from ambient vibration. The paper has developed a method to optimize the harvester parameters to attune it to the dominant vibration frequency. Tests carried out on the proposed harvester show that the proposed design can meet the energy requirements of a WSN node and achieve an efficiency of 79%.

A Step-up Vibration Energy Harvester Based on Piezoelectric Bimorph Cantilever

Enabling technologies for wireless sensor networks have gained considerable attention in research communities over the past few years. With the advantage of high power density, piezoelectric vibration energy harvester is promising in self-powered wireless sensor networks. In this work, modeling of piezoelectric generator based on a bimorph cantilever is discussed and functional characteristics of the bimorph piezoelectric cantilever are given. Corresponding step-up energy harvesting circuit according to the practical application requirements is developed. Then an integrated environmental vibration energy harvester with a size of approximately 83mm × 55mm × 12mm was fabricated. The results shows that the energy harvester is able to provide a stable 3.3V supply voltage under 37Hz working frequency.

Correlation modeling among multi-wind farms based on Copula-ARMA wind speed model

In recent researches, wind speed model of single wind farm has been used to study the traditional wind farms modeling, ignoring the correlation between series of multiple wind speeds. Based on Copula function and ARMA model, a dependent model for multivariate wind speed series is proposed. Firstly, Copula multivariate distribution model is used to capture spatial dependencies, and then ARMA model is utilized to describe the temporal correlation. Finally, pick the spatial dependence of copula and the temporal characteristic of ARMA model to build Copula-ARMA wind speed model. The model is verified by the actual wind speed, results show that the proposed model can maintain the auto correlation, cross correlation and statistic characteristics of wind speed series. Research results can be applied to site selection, reliability assessment and capacity credit evaluation of large-scale clustered wind farms, providing basis for planning of large-scale wind power base.

Capacity credit assessment of wind power considering energy storage

As the scale of wind power basis continuously increases, wind power is becoming an important new energy to replace part of the traditional energy. However, it cannot be accurately predicted due to its fluctuation and intermittence. So we usually think the wind power only has the value of electrical quantity, and ignore the value of its power capacity. In this paper, energy storage is used to solve the problems and to maximize the value of power capacity. Firstly, a method of calculating the capacity credit of wind power considering the added energy storage is proposed. Then, the strategy of energy storage for improving the capacity credit is also given, which is very meaningful in the application of wind power. Finally, the study employs data from IEEE-RTS 89 to verify the feasibility of the proposed method. The results reveal that the higher capacity credit of wind power is ensured by suitable energy storage strategy.

Study of a Distribution Line Overload Control Strategy Considering the Demand Response

Abstract—Relieving distribution-line overload is an important measure for boosting the reliability of electric power systems. Increasing capacity and load shifting are the current commonly used methods for relieving distribution-line overload. The present study proposes the use of a new method for relieving distribution-line overload considering the demand response. First, based on the demand elasticity matrix, a control strategy for the electricity price-load-overload degree is formed. This strategy revises the load-level curve and effectively reduces the power-system overload risk. Under electricity price responses, situations of overload are still present, but by using a response strategy based on stimulus demand, this strategy regards the minimum economic loss from overload as the target function for interruptible load cutoff. The influence of different load-interrupt schemes on the degree of relief is discussed. Finally, the study employs data from a specific domestic demonstration area to verify the feasibility of the proposed method. The results reveal that by maximally reducing the line overload risk via demand-response means, the safe operation of distribution lines is ensured.

Frequency regulation strategy for decentralized V2G control

Vehicle-to-grid (V2G) has the potential to provide the frequency regulation service. In this paper, a frequency regulation strategy for decentralized V2G was proposed, which not only guaranteeing the primary and secondary frequency regulation, but also considering the charging demands from EV customers. According to the state of charge (SOC) of each EV, two kinds of participation patterns were presented. One is available anytime pattern. The customers can use their EVs at any time. In this pattern, EVs only participate in the primary frequency regulation. Another is fixed time pattern. EVs can only be used at a fixed time. EVs can easily switch between the primary and secondary frequency regulation according to the current SOC. Simulations on a two-area interconnected power system with wind power have indicated the effectiveness of the proposed methods.

Current status and development trend on capacity credit of intermittent renewable energy

As the renewable energy scale increases rapidly, evaluation of intermittent energy capacity credit (IECC) is becoming one of the hottest issues in power system planning. Ignoring IECC will lead to serious waste; however, high expectations of IECC will bring risk to the reliability of power system. In order to evaluate IECC accurately, firstly, uncertainly factors on IECC are analyzed from multiple angles, and the main assessment process of IECC is presented. Based on the various IECC calculation methods of single intermittent energy, the adaptive methods of wide-scale multiple intermittent energy are put forward. Finally, improvement measures of capacity credit are advanced from aspects of multiple energy output correlation, power grid side, demand side, and energy storage. The research hotspots and developing directions are discussed.

Novel Low-Frequency Rectangular-Loop Piezoelectric Energy Harvester

The ambient energy harvesting based on piezoelectric has become an important subject in recent research publications. A new rectangular-loop piezoelectric energy harvester(RLPEH) is proposed. The characteristic is analyzed by the finite element analysis (FEA) which includes the static analysis, modal analysis and harmonic response analysis. The analysis results show that the RLPEH could reduce the resonant frequency and improve the output voltage. The three order resonant frequency is 18.6Hz, 40.8Hz and 85.4Hz. The output voltage is 42V under 3m/s2 of acceleration and the effective bandwidth is 18.7Hz with output voltage above 10V.

Piezoelectric Performance Analysis of the Single-Sided Trapezoidal Loop Shaped Piezoelectric Cantilever Beam

In order to improve the energy harvesting efficiency of piezoelectric cantilever beam (PCB) in the environment. This paper presents a new type of piezoelectric cantilever beam which is the single-sided trapezoidal loop shaped PCB. By theory analysis, the equivalent circuit model was established, resonant angular frequency is inversely proportional to the length of cantilever beam. Based on finite element analysis method, the piezoelectric performance of single-sided trapezoidal loop shaped PCB and that of single-sided rectangular loop shaped PCB are compared with the same areas. The analysis results show that the coupling voltage of the former is larger, the output power of single-sided trapezoidal loop shaped PCB is improved, and the theoretical derivation of the inverse relationship between the frequency and length is verified.

Research on Interactive Coordinated Control System for V2G Application

The objective of study on the interactive coordinated control system (ICCS) is to meet the demand of V2G (Vehicle-to-grid) application. The interactive manners and contents of V2G are analyzed. And the requirements of the ICCS are proposed from several aspects, including functionality, interactive information and interactive terminal. The research may provide guidance for the two-way power and information interaction of future large-scale V2G applications.