Implementation and Analysis of Direct Torque Control for Permanent Magnet Synchronous Motor Using Gallium Nitride based Inverter

Permanent magnet synchronous machines (PMSMs) attract considerable attention in various industrial applications, such as electric and hybrid electric vehicles, due to their high efficiency and high-power density. In this thesis, the mathematical model of PMSM and two popular control strategies, field-oriented control (FOC) and direct torque control (DTC), are analyzed and compared. The results demonstrated that the DTC has better dynamic response in comparison to FOC. Moreover, DTC can eliminate the use of position sensor, which will save the cost of the PMSM drive system. Therefore, this thesis focuses on the design and implementation of high-performance DTC for PMSMs with a Gallium Nitride (GaN) based high switching frequency motor drive. First, the characteristics and operation principles of a PMSM are introduced. Then, the mathematical models of a PMSM under different coordinate systems are investigated. Consequently, a PMSM model is developed based on the dq rotating reference frame and implemented in the MATLAB/Simulink for validation. Two advanced PMSM control strategies, FOC and DTC, are investigated and compared in terms of control performance through comprehensive simulation studies and the results demonstrate that DTC has better dynamic performance. Conventional DTC contributes to higher torque ripple in the PMSM due to the limited switching frequency in a conventional semiconductor-based motor drive, which inevitably deteriorates the drive performance. Therefore, this thesis aims to reduce the torque ripple in the DTC based PMSM drive by using the new generation wide bandgap switching devices. More specifically, DTC is improved by using the optimized space vector pulse width modulation strategy and a higher switching frequency contributed by the GaN based motor drive. Finally, the proposed DTC-SVM based PMSM control strategy is implemented on the digital signal processor (DSP) and evaluated on the laboratory GaN based PMSM drive. Both the simulation and experimental results show that the proposed improvement in the DTC can further improve the PMSM drive performance

Empirical analysis of AdaBoost algorithms on license plate detection

AdaBoost algorithm is an effective license plate detection method in the field of license plate recognition technology. A through analysis of three boosting algorithms (namely Discrete, Real and Gentle AdaBoost) is presented for license plate detection, including the algorithm details and experiment comparisons. The experimental results show the Gentle AdaBoost algorithm obtains an overall better results in terms of high detection rate and low false positive rate than the discrete AdaBoost algorithm or real AdaBoost algorithm. ©2009 IEEE

Bayesian document segmentation based on complex wavelet domain hidden Markov tree models

A texture-based Bayesian document segmentation method is investigated in this paper. This Bayesian method is used to fuse texture likelihood and prior contextual knowledge to achieve document segmentation. The texture likelihood is based on a complex wavelet domain hidden Markov tree (HMT) model and the prior contextual is based on a hybrid tree model. A redundant wavelet domain Gaussian mixture model is employed to capture pixel-level features in the HMT model. Several document images are segmented to verify the proposed method. Comparisons with other corresponding models are made. © 2008 IEEE

An interactive image inpainting algorithm based on Markov Random Field

A novel approach to image inpainting is introduced in this paper. The novelty lies in the combination of pixel-diffusing technique and a user interaction mechanism. This combination takes both local geometrical information via the pixel-diffusing technique and global structure information via the user interaction to improve the image inpainting quality. The user interaction mechanism manually specifies important missing structure information by drawing some curves from the known to the unknown regions and synthesizes image structure along these user-specified curves in the unknown region using structure information selected around the curves in the known region. The pixel-diffusing technique builds on the Markov Random Field (MRF) model to exploit the image contextual knowledge. The interactive inpainting algorithm fills in the remaining unknown regions based on the MRF model. The experiment results show this interactive algorithm is reasonable and efficient. ©2009 IEEE

Spatial Properties of Soil Physical Quality Index S in Black Soil Croplands under Permanent Gully Erosion

Soil physical quality (SPQ) is a limiting factor affecting crop production. However, the impact of gully erosion on the SPQ index S, defined by Dexter as the inflection point of the soil water retention curve (SWRC), remains unclear, especially when considering different latitudinal regions. This study aimed to apply Dexter’s S-theory to evaluate the distribution of index S in black soils adjacent to various gully positions and investigate its relationship with bulk density (Bd), soil organic matter (SOM), and particle percentage. Soil properties (SWRC, Bd, SOM, and particle percentage) from nine gullies in croplands in three latitudinal regions (Harbin, Hailun, and Nenjiang in Heilongjiang province) were determined at the gully edge (GE0) and 50 m beyond the edge into the croplands (GE50) at the following gully units: head, mid-upper, middle, mid-lower, tail, and conjunctions between main gully and gully branch. The S-index was calculated using parameters such as n, θs, and θr, with SWRC data fitted into the van Genuchten model. The results showed spatial variations in the S-index across latitudinal regions, with slightly higher S-values in Harbin than in Hailun and Nenjiang. The S-index also showed noticeable differences at GE0 and GE50 and at the junctions between the main gully and its branches. Approximately 51% of the samples at GE0 and 28.2% of the samples at GE50 had S-values below 0.035, which Dexter proposed as the boundary between good and poor SPQ, indicating a degradation of SPQ at the gully-surrounding areas. A decreased S-index in the gully vicinity was significantly (p −3 for GE0 and GE50) and decreased SOM (36.80 vs. 39.36 g kg−1 for GE0 and GE50). In summary, this study indicates that gully erosion affects the farmland S-index at the gully-surrounding areas through SOM and Bd. Accordingly, measures suited to the increase in the S-index of the gully-surrounding areas may be implemented to maximize the crop yield of farmlands

Engineered periosteum-diaphysis substitutes with biomimetic structure and composition promote the repair of large segmental bone defects

The repair of large segmental bone defects remains a big challenge due to limited self-healing capacity of bone. Digging into the structure and composition of natural long bone let us realize that the periosteum cambium on the surface of diaphysis plays a crucial role in bone repair. In this study, we explored the feasibility of using a tissue-engineered periosteum-diaphysis substitute to repair the large segmental bone defects. To create an artificial periosteum cambium, bone marrow mesenchymal stem cells (BMSCs) and endothelial progenitor cells (EPCs) were co-cultured on electrospun silk fibroin (SF) fibrous membranes for mimicking the cellular composition and microstructure of cambium layer of the native periosteum. These SF membranes supported the adhesion and proliferation of both BMSCs and EPCs. In addition, we found that a 1:1 ratio of BMSCs and EPCs supported osteogenesis and angiogenesis optimally. This biomimetic periosteum layer was integrated with artificial diaphysis made of tubular SF scaffolds to construct a biomimetic periosteum-diaphysis substitute. Animal studies confirmed that the biomimetic periosteum-diaphysis substitutes promoted the repair of critical-size bone defects of rabbit radius. Furthermore, the transplanted biomimetic periosteum-diaphysis substitute could prevent the growth of fibrous tissues in the bone defect, and thus reduce the occurrence of nonunion. This study described a promising tissue engineering strategy for the repair of large segmental bone defects