Condition monitoring, nondestructive testing and fault diagnosis are currently considered crucial processes for on-condition maintenance (OCM) to increase the reliability and availability of wind turbines and reduce the wind energy generation cost. Carbon fiber reinforced plastics (CFRP) have been increasingly used to fabricate wind turbine blades. Delamination type damage is inevitable during manufacture or in-service of a CFRP blade. This inner (subsurface) flaw, usually difficult to be detected by artificial visual inspection or machine vision based on CCD or CMOS, severely degrades the load bearing capacity of a blade. Induction infrared thermography (IIT) is an emerging infrared machine vision inspection technology, which has the capability of insight to CFRP based on electromagnetic induction and heat conduction. This paper introduces photothermal thermal-wave radar (TWR) non-destructive imaging (NDI) to IIT, based on cross correlation (CC) pulse compression and matched-filtering and applies TWR principles to CFRP imaging inspection and diagnosis. The experimental studies carried out under the transmission mode have shown that TWR B-scan and phasegram can be used to inspect and diagnose subsurface delaminations in CFRP with improved SNR and shape identification. As a new machine vision inspection method, TWRI will play an important role in the OCM of wind turbine blade.

Defects can affect the generation efficiency and service life of photovoltaic cells and modules, even can cause serious damage to grid connected photovoltaic power generation station. This work proposes active electromagnetic induction infrared thermography (EIIT) defect detection methods for photovoltaic cells and modules, which have the advantages of non-contact, rapid, full-field, subtle and quantitative detection. Firstly, the mechanism of infrared radiation after electromagnetic induction of photovoltaic cells is described and a digital EIIT system is established. Then, the thermal image sequences of photovoltaic cells and modules are obtained under pulse and lock-in modes of excitation. Fast Fourier transform (FFT), Independent component analysis (ICA), and Principal component analysis (PCA) are used to deal with the thermal image sequences. Finally, the visual detection of defects, including scratch, hot spot, micro crack, surface impurity pollution and broken grid in photovoltaic cells and modules are realized. The experimental results have shown that the proposed method can distinguish the background noise and the defects very well, thus providing a reliable and rapid inspection means for the research, testing, manufacturing, service and maintenance of photovoltaic cells and modules.

This paper proposes a novel topology of voltage balance circuit for ALL-DC offshore wind farm with series-connected wind turbine. In the proposed topology, adjacent wind turbines are connected by a voltage balance circuit in parallel, and these wind turbines can both achieve the maximum power point tracking (MPPT) and balance the terminal voltages when the wind speeds of wind turbines are unequal. With the current compensation of voltage balance circuit, this topology can ensure the normal operation of wind farm even if some wind turbines are outage. Furthermore, the double loop controller for the voltage balance circuit is designed which does not require the communication among wind turbines, and the stability analysis is implemented and discussed for tuning the control parameters. The simulation model and the RT-Lab experiment are set up to verify the validity of the proposed topology under unequal wind speeds. Simulation and experiment results confirm the superior performance of the proposed topology with low costs, high fault tolerance and high efficiency.

In order to solve the problems of low efficiency and small area of existing eddy current thermography industrial nondestructive testing (NDT), this work realizes in-field-of-view (FOV) dynamic scanning eddy current pulsed thermography (DSECPT) with the help of blind source separation (BSS) algorithms for continuous detection of large-scaled industrial components. The principle of FOV-DSECPT, including finite length inductive heating of mobile coil, the reconstruction of transient temperature response, and feature extraction, is investigated. The original thermal images can not be used for depth analysis thus new data reconstruction method with good adaptivity for manual movement was proposed. The emerging BSS algorithms, including independent component analysis (ICA) and non-negative matrix factorization (NMF), are employed to process the reconstructed data. Through experimental studies, images using various features from classical and BSS algorithms were compared. The proposed FOV-DSECPT could provide a visualized and effective means for quality control and inspection of large-scaled key components in both manufacturing and service processes.

The accurate information of the initial rotor position is very critical for successful starting of the Surface-mounted Permanent Magnet Synchronous Motor (SPMSM). In order to solve the problems of low accuracy and unreliability in the conventional estimation strategy, in this paper, an improved initial rotor position estimation strategy without any position sensor for SPMSM at standstill is proposed based on rectangular pulse voltage injection. In the work, when the second series of pulse voltages were applied. By the ways of strengthening the effect of weakening or strengthening magnetic fields and increasing the difference between each current of the vector. The improved strategy enhanced reliability and raised the initial position estimation accuracy from 7.5° to 1.875°. The improved strategy does not need any additional hardware. Experimental results demonstrate the validity and usefulness of the improved strategy.

The high voltage DC (HVDC) transmission technology of wind power system, with multi-phase permanent magnetic synchronous generator (PMSG) is proposed in this paper. Each set of three-phase winding of the multi-phase PMSG was connected to a diode rectifier. The output of the diode rectifier was connected by several parallel isolated DC–DC converters. Each DC–DC converter was connected to a sub-module (SM). All SMs and two inductors were connected in a series. The proposed wind power system has several advantages including, transformerless operation, low cost, low voltage stress, and high fault tolerance. The maximum power point tracking (MPPT) and energy balance of the DC–DC converters were achieved by controlling the duty cycles of the DC–DC converters. The HVDC transmission was achieved by the nearest level control (NLC) with voltage sorting. The simulation model with 18-phase PMSG was established. Experimental results were also studied based on RT-Lab.