Applied Mechanics and Materials Vols. 291-294

Abstract: This paper presents an improved topology for three-phase to single-phase matrix converter (3-1 MC), and discusses the power decoupling method, closed-loop control strategy, etc. These studies make the single-output MC have good features, such as sinusoidal input current, low total harmonic distortion (THD), compensating the shortcomings of traditional 3-1 MC caused by the output power pulsation. According to the improved scheme, a novel closed-loop control strategy based on virtual dc voltage feedback is proposed. The strategy completes the closed-loop control of 3-1 MC by taking the virtual dc voltage as outer-loop controlled variable and the input current as inner-loop controlled variable. Consequently, the power factor correction (PFC) of 3-1 MC is achieved, and the control stability is improved. Finally, a series of stimulation and experiments for a prototype with 115V/400Hz output are conducted, the results show that the power decoupling method and control strategy are practically correct and feasible.

Abstract: The effects of compensating and restraining the power system harmonics using active power filter are determined by the detection precision and its dynamic response characters. To improve both of them, a harmonic current detection algorithm based on variable forgetting factor Recursive Least-Squares algorithm is presented. The occurrence of the dynamic process is identified firstly by the judgment condition which is given by the algorithm, and then the forgetting factor is assigned dynamically, so that the convergent speed is significantly improved. The algorithm overcomes the impact of low-pass filter of traditional p-q or ip-iq algorithm, and releases the contradiction cased by the conflicting requirements of forgetting factor value between steady process and dynamic process. So it has better dynamic performance. Simulation and experiments prove the validity and feasibility of the approaches.

Abstract: Because of the powerful filtering ability the third-order LCL filters has been widely used in grid-connected inverters, but there are some problems to be solved on systems stability and control accuracy. A separated-PID control strategy has been proposed according to the PID characteristics and the structural features of a single-phase inverter connected to the grid with a LCL filter. This control strategy has some advantages as a strong dynamic tacking stability, and the system output has a small steady state error. A detailed description is presented on this control strategy applied in the single-phase grid inverter with a LCL filter. According to the Routh-Hurwitz stability criterion, the stability of a grid-connected inverter system based on the proposed control strategy has been analyzed. Finally, waveforms of this inverter have been presented through a simulation to show the steady and dynamic performance of the proposed scheme.

Abstract: The combustion process of CFBB is a system with time-varying, nonlinear, large inertia and time delay. Therefore the control effects of traditional PID control system in the CFBB plant are not satisfactory , especially the overshoot of the main steam pressure control system is very big, and the adjustment time is too long. To improve the performance of the main steam pressure control system, ADRC technology was used . The disturbed signal was added in the different operating conditions, the testing results indicated that the ADRC main steam pressure control system had more excellent performance than the convention PID method.

Abstract: The lift-off problem is a very important problem in eddy current testing, which will influence the measurement accuracy. This paper proposes a novel technique for eliminating the probe lift-off in eddy current nondestructive testing. Firstly, the basic principles and characteristics of eddy current testing were introduced. Secondly, this paper analyzed and studied the coil impedance responses caused by the variations of the probe lift-off. Based on simulation results, this paper presents that choosing proper probe excitation frequency can eliminate the disturbance of coil impedance caused by the lift-off, and obtains better results.

Abstract: Automatic recognition of abnormal patterns in control charts has seen increasing demands nowadays in manufacturing processes. In this paper, we have constructed the recognition model for control chart pattern using one-dimensional discrete wavelet transform and BP neural network. Then, using Monte-Carlo method to generate the data, we have compared between the performances of the model using raw data and the model based on wavelet transform. In order to select the optimal wavelet, we have compared the recognition accuracy of different wavelets (DbN, SymN and CoifN) on different levels. The simulation results show that model based on wavelet transform in this paper have higher recognition accuracy and the recognition accuracy using the wavelet of Coif4 on the level 3 is 97.64% and relatively stable for various patterns.

Abstract: In the process of detecting leak hole in pipeline by intelligent pig with eddy current measuring method, the cut off effect of eddy current field in the closed cross section of leak hole in steel plate is weak due to geometric deformation of eddy current on the edge of the hole produced by destroyed drilling. As a result, the measured signal is very unobvious. Meanwhile, owing to the rough surface of steel plate, the periodic interference generated by movement of the detecting probe cannot be eliminated or be inhibited easily by conventional signal processing methods for its large amplitude and approximate frequency band with the leak hole signals, the signal to noise ratio (SNR) of measured signal is very low and the accurate identification of leak hole cannot be guaranteed. The wavelet transform, with characteristics of time-frequency localization and multiple scales, is a useful and effective method for identifying singularity of the signals and adapts to detect the transient signal or extract non-stationary information in the signals with strong periodic interference and noise. The reconstructing signal SNR will be increased greatly in eddy current detecting of leak hole in the pipeline with wavelet packet analysis of the signal by constructing the self-defined cost function based on maximum SNR to obtain optimal wavelet packet basis function. This ensures good detection and location of leak hole in the pipeline.

Abstract: In order to enhance the accuracy of gait recognition, a new gait feature extraction algorithm is proposed. Firstly, the gait images are preprocessed to extract moving objects, including background modeling, moving object extracting and morphological processing. Secondly, an equidistant slicing curve model based on system of polar coordinate is designed to slice the moving object, and the slicing vector is used to describe the spatial feature; Thirdly, the slicing vector is converted into frequency signal by Fourier transform to extract the frequency feature. Finally, the above two features are fused and used for the classification. The experimental results show that proposed algorithm provides higher correct classification rate than the algorithms using single feature, and meets the requirements of the real-time.

Abstract: The U-tube steam generator(SG), as the joint of primary and secondary circuits, is one of the crucial components in a PWR plant. Because of the swell-and-shrink phenomena, it is very difficult to control the water level of the steam generator. Presently the three-element controller in cascade configuration with two PID controller is widely use. But the determination of the six optimal PID parameters of the cascade controller is a major problem. This paper studies the application of the particle swarm optimization(PSO) methods in determining the parameters of cascade controller of SG water lever. The SG is modeled in Simulink and the PSO algorithm is implemented in MATLAB. Comparing with conventional PID parameter, the proposed method is more efficient in improving the step response characteristics while controlling the water level of SG.

Abstract: This paper presents a principle that compensation balance is flexible used in a certain context of the power grid load growth, in order to keep the system voltage stability and system to maximize the economic operation. Some questions are analyzed and demonstrated which.