Lei Dong

Wind power prediction using wavelet transform and chaotic characteristics

In the electricity system, supply and demand must be equal at all times. Wind power generation is fluctuating due to the variation of wind. As more and more wind power generation is integrated into the power system, it is very important to predict the wind power production to contribute the system reserve reduction and the operational costs of the power plants. This paper brings wavelet transform into the time series of wind power and verifies that the decomposed series all have chaotic characteristic, so a new method of wind power prediction in short-term with Artificial Neural Network (ANN) model based on wavelet transform is presented. To test the approach, the wind power data from the Fujin wind farm and Saihanba wind farm of China are used for this study. The prediction results are presented and compared to the no wavelet transform method and ARMA method. The results show that the new method based on wavelet transform neural networks will be a useful tool in wind power prediction.

A Smooth LVRT Control Strategy for Single-Phase Two-Stage Grid-Connected PV Inverters

Based on the inherent relationship between dc-bus voltage and grid feeding active power, two dc-bus voltage regulators with different references are adopted for a grid-connected PV inverter operating in both normal grid voltage mode and low grid voltage mode. In the proposed scheme, an additional dc-bus voltage regulator paralleled with maximum power point tracking controller is used to guarantee the reliability of the low voltage ride-through (LVRT) of the inverter. Unlike conventional LVRT strategies, the proposed strategy does not require detecting grid voltage sag fault in terms of realizing LVRT. Moreover, the developed method does not have switching operations. The proposed technique can also enhance the stability of a power system in case of varying environmental conditions during a low grid voltage period. The operation principle of the presented LVRT control strategy is presented in detail, together with the design guidelines for the key parameters. Finally, a 3 kW prototype is built to validate the feasibility of the proposed LVRT strategy.

Studies on wind farms ultra-short term NWP wind speed correction methods

Ultra-short term wind speed forecast for wind farm is of great significance to the real-time scheduling of wind power system. In this paper, NWP (Numerical Weather Prediction) wind speed time series and measured wind speed time series were decomposed into different bands by wavelet multi-resolution analysis. Pearson product-moment correlation coefficient was used to verify the correction premise. Then the linear correction method was used to correct the low frequency stationary NWP wind speed. To test the approach, the data from Yilan wind farm of Heilongjiang province were used. The results show that when a strong correlation exists in the system deviation of training periods and testing periods, the prediction accuracy of ultra-short term wind speed will be significantly improved.

A New Orthogonal Signal Generator with DC Offset Rejection for Single-Phase Phase Locked Loops

This paper presents a new orthogonal signals generator (OSG) with DC Offset rejection for implementing a phase locked loop (PLL) in single-phase grid-connected power systems. An adaptive filter (AF) based on the least mean square (LMS) algorithm is used to constitute the OSG in this study. The DC offset in the measured grid voltage signal can be significantly rejected in the developed OSG technique. This generates two pure orthogonal signals that are free from the DC offset. As a result, the DC offset rejection performance of the presented single-phase phase locked loop (SPLL) can be enhanced. A mathematical model of the developed OSG and the principle of the adaptive filter based SPLL (AF-SPLL) are presented in detail. Finally, simulation and experimental results demonstrate the feasibility of the proposed AF-SPLL.

The design and application of an unmanned surface vehicle powered by solar and wind energy

The development of unmanned surface vehicles (USVs) for reconnaissance or other littoral missions is attracting increasing attention. In order to increase the sustainability of USVs, a new hybrid driving system powered by solar energy and wind energy is designed for the proposed USV. The developed USV is based on a catamarans prototype boat, and is equipped with a wing sail. In addition, the superficial of the USV is covered with PV panels for providing sustainable energy generation. The batteries based storage system is used for storing extra electricity as well as providing electricity for the control system and electrical system. To achieve tasks independently and intelligently, the USV is integrated with an automatic control system. The USV is discussed in detail, and some testing results are presented to validate its feasibility.

Long-Term Wind Power Prediction Based on Rough Set

In long-term wind power prediction, dealing with the relevant factors correctly is the key point to improve the prediction accuracy. This paper presents a prediction method with rough set analysis. The key factors that affect the wind power prediction are identified by rough set theory. The chaotic characteristics of wind speed time series are analyzed. The rough set neural network prediction model is built by adding the key factors as the additional inputs to the chaotic neural network model. Data of Fujin wind farm are used for this paper to verify the new method of long-term wind power prediction. The results show that rough set method is a useful tool in long-term prediction of wind power.

Non-grid-connected wind power generating system with permanent magnet synchronous generator and buck/boost converter

In this paper, a distributed generation wind energy conversion system based on non-grid-connected and using a direct-drive permanent magnet synchronous generator (DD-PMSG) is proposed with a dual-loop PI controller. This energy system is suitable for applications in remote areas not connected to the grid such as Radio Base Stations (RBS) for mobile phone communications. Analysis, simulation, and prototyping test results are presented.