Guoyi Xu

Improvement of the Hilbert Method via ESPRIT for Detecting Rotor Fault in Induction Motors at Low Slip

The traditional Hilbert method to detect broken rotor bar fault in induction motors is reviewed and its major drawbacks are clearly revealed, namely, deteriorating or even completely failing when a motor operating at low slip due to the fixed constraints of fast Fourier transform (FFT) is used in this method. To overcome this, the estimation of signal parameters via rotational invariance technique (ESPRIT) is then introduced to replace FFT, and an improved Hilbert method is thus presented by conjugating the Hilbert transform and ESPRIT together. Experimental results of a small motor in a laboratory and a large motor operating on an industrial site are reported to demonstrate the effectiveness of the improved Hilbert method.

An ESPRIT-SAA-Based Detection Method for Broken Rotor Bar Fault in Induction Motors

This paper presents a novel detection method for broken rotor bar fault (BRB) in induction motors based on the estimation of signal parameters via rotational invariance technique (ESPRIT) and simulated annealing algorithm (SAA). The performance of ESPRIT is tested with the simulated stator current signal of an induction motor with BRB. It shows that even with short-time measurement data, the technique is capable of correctly identifying the frequencies of the BRB characteristic components but with a low accuracy on the amplitudes and initial phases of those components. The SAA is then used to determine their amplitudes and initial phases and shows satisfactory results. Finally, experiments on a 3-kW, 380-V, 50-Hz induction motor are conducted to demonstrate the effectiveness of the ESPRIT-SAA-based method in detecting BRB with short-time measurement data. It proves that the proposed method is a promising choice for BRB detection in induction motors operating with small slip and fluctuant load.

Coordinated DC Voltage Control of Wind Turbine With Embedded Energy Storage System

This paper investigates dc voltage control strategies for output power smoothing of a fully rated converter-based wind turbine with energy storage device connected to the common dc link via a bidirectional dc/dc converter. Since the dc link voltage ripple reflects power oscillation, coordinated dc voltage control schemes are used for the ac network side converter and energy storage system to ensure that generated high-frequency power fluctuation is absorbed by the energy storage system, whereas the low-frequency components are transmitted to the connected ac network. Two methods have been proposed: one is based on proportional-integral (PI) voltage controller and low-pass filter with large time constant, and the other is based on PI with low natural frequency and droop controller with large droop gain. The detailed controller designs are described and system stability is assessed and shown to be stable. Both the MATLAB/Simulink simulations and experimental results are presented to demonstrate the effectiveness of the proposed methods for power smoothing.

Wind turbines with energy storage for power smoothing and FRT enhancement

The continued development of high power wind turbines raises the standards of operation requirement. This paper evaluates the ability of an energy storage device with a bidirectional dc-dc converter connected to the dc link of a direct driven wind turbine for output power smoothing and fault ride through enhancement. Method based on simple dc voltage measurement and coordinated dc voltage loops of the grid side dc-ac and the energy storage dc-dc converters are proposed to provide a versatile power smoothing control. Further studies on wind turbine fault ride through capability in the presence of energy storage and dc damping resistor are outlined. Simulation results based on a 3 MW wind turbine are presented to validate the effectiveness of the proposed power smoothing strategy. It also shows that with energy storage, the size of the dc damping resistor can be reduced.