Fig. 1. DTC-SVM. Under the assumed orientation, the electromagnetic torque is calculated by (1) (2) (3) stronger performance of interferences for the inside and outside perturbation without depending on the controlled system mathematics model, making the all system works with better robustness and adaptability. It brings new meaning to the notion of robustness and disturbance rejection [4]. where usd and u sq are the direct component and the quadrature component ofthe applied voltage vector. R s is the stator resistance. i sd and i sq are the direct and quadrature component of the stator current respectively. we is the synchronous angular speed. f//s is the stator flux, np is the pole pairs, and T e is the electromagnetic torque. II. CONTROL METHOD A. DTC-SVM Overview The block diagram of DTC-SVM in stator-flux-oriented (SFO) coordinates is shown in Fig.l. The control strategy relies on a description of the stator voltage components, expressed in stator flux reference frame as [5]:Abstract-The well-known direct torque control (DTC) is a very simple control method for inverter-fed AC drives, which characterized by fast dynamic response, structural simplicity, and low sensitivity to parameter changes. Attempts to combine DTC with SVM have led to new ways. This paper presents a new robust DTC-SVM for high performance induction machine drives. Sim ulation studies have been carried out for the proposed method and results are compared with traditional DTC-SVM. Simulation results show that the new scheme ensures good robustness and adaptability under modeling uncertainty and disturbances.
This paper introduces a novel probability based positron range model accounting for the typical case of inhomogeneous medium in experimental or clinical implementations. A survival probability for given energy, medium type and thickness, is used to describe the propagation of monoenergetic positrons with increasing distance in homogeneous medium. This follows from the fact that annihilation distribution of monoenergetic positrons in homogeneous medium can be approximately expressed as an exponential distribution. Similarly, we consider the transport and annihilation of monoenergetic positrons in each layer of inhomogeneous medium as probability events, which can be easily computed using a set of survival probabilities. The ultimate annihilation distribution is a weighted summation over the energy spectrum. Monte Carlo simulation is used to validate the availability and performance of this model. Simulated and estimated annihilation distributions are presented with close agreement. The new model can be used to improve the image resolution without introducing serious artifacts due to the mismatching between models and fact.
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