Sharif Digital Repository

Modular multilevel converter (MMC) is among the promising topologies used in high-voltage/power purposes, especially for high-voltage direct-current (HVDC) transmission systems. In this paper, a modified model predictive control (MPC) strategy for an MMC-HVDC system is presented. In the proposed MPC strategy, output current, circulating current and capacitors voltage are controlled separately. In order to reduce the computational burden of the controller, the output current is controlled directly without any optimization. For suppression of the circulating current, capacitors voltage variations are employed to settle the converter arms voltages to their reference values. In addition, the... 

A novel high-voltage direct current (HVdc) power supply which has no transformer or voltage multiplier circuit is presented and analyzed in this paper. This is made possible upon the diodes storage delay phenomenon. This proposed power supply is compact, lightweight, and low cost. Its basic structure includes a diode with a proper reverse recovery specification that plays the role of a step-up transformer in the conventional HVdc supplies and a high-voltage capacitor which stabilizes the output voltage. This structure has remarkable advantages over the conventional transformer-based HVdc supplies, such as compactness, a low ripple output, and a low-cost power supply. Performance of the... 

Optimal probabilistic neural network-based method has been porposed in this paper to identify different types of fault in high voltage direct current (HVDC) system. Probabilistic neural network is a type of artificial neural networks capable of approximating the optimal classifier. The particle swarm optimization is porposed to achive an optimal value of smoothing factor for PNN which is an important parameter. The main purpose of this paper is fast and accurate fault classification, for this purpose simple HVDC system has been evaluated under various fault type condition to examine the efficacy of the proposed method. The performance of the proposed method is investigated using... 

Wind power generation is increasing fast as a clean renewable energy resource. Offshore wind farms are popular due to advantages such as higher and smoother wind speeds, less farm site limitations, etc. High capacitive currents and need to expensive compensations, make use of high-voltage-direct-current (HVDC) power transmission indispensable for longdistance wind farm power generations. Steady-state and transient performance improvements of HVDC systems have always been an interesting industrial and academic research area. In this paper, a novel control method is proposed to improve the steady-state operation of HVDC system. Moreover, a new fault detection scheme is proposed to improve the... 

The effect of electrostatic field on the aggregation rate and aggregate size of asphaltene particles precipitated from three different crude oil samples suspended in a mixture of toluene and n-heptane (a model oil) was investigated. An electrode-embedded glass micro-model utilizing a high-voltage direct current power supply was utilized in this study. The asphaltene particle size and the rate of aggregation under the electric field were monitored using a high-resolution optical microscope and the average aggregate size for asphaltene particles was estimated using image processing software. To investigate the effects of structural parameters on asphaltene aggregation rate, aggregate size and...