Sharif Digital Repository

Non-linear loads such as rectifiers are growing in industry. Three phase inverter with non-linear load can lead to highly distorted output voltage. This paper proposes a method for reducing voltage THD in three phase inverters with non-linear load. The proposed method considers the load current as a disturbance and provide a control strategy to reject it using the disturbance observer method. This method doesn't need any additional sensors or hardware and is implemented digitally in controller. Simulation results show that the presented method will reduce the total harmonic distortion of the output voltage. © 2017 IEEE  

Recent developments in improving lighting efficiency and cost reduction of LED's have caused them to be a suitable alternative for the current lighting systems. In this paper a novel off-line structure is proposed to drive LED's. The proposed circuit has a high power factor and high efficiency and a long lifetime. To increase the life time of the converter, the proposed circuit doesn't use any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode (TM) Flyback converter in order to have power factor correction (PFC). A Buck converter is added to the third winding of the Flyback transformer in order to create two paths for the electrical power. DC power... 

One of the most significant parameters that the electronic designers are trying to increase, is the reliability or the effective lifetime of the circuit. For example the designers are always trying to achieve higher efficiency. One of the most important influence of the greater efficiency is the reduction of the thermal stress on the components, that leads to increase of the reliability. In this paper the reliability of two different industry-based structures as an AC/DC converter, have been compared. These circuits are from two different generations of power supplies in a particular industry, which the first introduced structure has greater efficiency due to soft switching. FIDES method has... 

In this paper, a novel zero-voltage-switching topology for power factor correction bridgeless boost rectifier is proposed. By employing an improved switch cell, ZVS for all the main switches is achieved without additional current or voltage stress. The zero-current-switching is also provided for the auxiliary switch. In all modes of operation of this converter, the input current flows through only two semiconductors. Therefore, conduction loss of this converter is as low as the conventional parent converter. With these features, the efficiency of the proposed converter is very high. A 500 W prototype is designed and simulated to verify the system performance  

PFC converters for higher power are commonly designed for continuous conduction mode (CCM). However, at light load, discontinuous conduction mode (DCM) will appear close to the crossover of the line voltage, causing the converter to switch between the two conduction modes. As a result, the converter dynamics change abruptly, producing input current distortion. In this article a piecewise affine approximation has been employed in modeling a boost power factor correction converter operated in the mixed conduction mode. This approach makes the new model very useful in large signal analysis of PFC rectifiers and design of controller. The results obtained from the proposed model are compared with... 

Excitation Controlled Synchronous Generator-based Wind Turbine (ECSG WT) is a recently proposed Wind Turbine (WT) scheme that has not been fully investigated in detail. This paper intends to analyze the performance of the ECSG WT scheme and compare it with those of two mainstream WT schemes based on electrically excited synchronous generator, i.e., VSC-based full converter WT and diode bridge rectifier-based WT equipped with boost converter on its Direct Current (DC) link. The objective of this comparison is to demonstrate great potentials of ECSG WT to be considered in the wind industry. To do so, two successful Wind Turbine (WT) schemes in the market that are structurally close to ECSG WT... 

Small Permanent Magnet Synchronous Generators (PMSG's) are widely used in low power wind turbines. In order to inject the electrical power, generated by PMSG, to the grid, a back-To-back AC/AC power electronic converter is required. In this paper, a novel low cost efficient AC/DC converter is proposed for rectifier stage to obtain the maximum power per ampere of PMSG by using Power Factor Correction method. The new structure is based on DCM SEPIC converter. Reducing the number of semi-conductor switches has decreased converter cost. Additionally, other advantages of this Converter are employing easy control method to obtain the maximum power per ampere and using Synchronous inductance of... 

This paper presents an analytical model for power harvester circuits used in Ultra-low power applications. Assuming that the MOS devices of the circuit fully operate in the Sub-threshold regime in both forward and reverse regions, closed-form equations for important properties of the rectifier circuit such as output voltage, efficiency and input resistance are derived. The model includes the effect of the compensation voltage on the circuit behavior. There is a good agreement between the simulation results and the model. In addition, the contour plots needed to simultaneously optimize the matching network and the rectifier circuit are derived by the resulting equations. A 50-Stage rectifier... 

The cell membrane is responsible for the transportation of heat between inside and outside the cell. Whether the thermal properties of the cell membrane are affected by the cholesterol concentration or the membrane proteins has not been investigated so far. Although the experimental measurement of the membrane thermal conductivity was not available until very recently, computational methods have been widely used for this purpose. In this study, we carry out molecular dynamics simulations to investigate the relation between the concentration of cholesterol and the thermal conductivity of a model membrane. Our results suggest an increase in the membrane thermal conductivity upon increasing the... 

Applying conventional dc-voltage-based droop approaches for hybrid ac/dc microgrids interconnected by a single interlinking converter (IC) can properly manage the power flow among ac and dc subgrids. However, due to the effect of line resistances, these approaches may create a circulating power as well as overstressing the ICs in the case of employing multiple ICs for interconnecting the ac and dc subgrids. This paper proposes an autonomous power sharing approach for hybrid microgrids interconnected through multiple ICs by introducing a superimposed frequency in the dc subgrid. Hence, a suitable droop approach is presented to manage the power among the dc and ac sources as well as ICs. The... 

Conventional back-to-back converters with input power factor correction are still the best solution for motor drive applications which are usually subjected to considerable load changes during their operation. Since converter components, especially input-side inductances are designed for nominal power rating, the rated input power factor and input current distortion aren't achievable in light loads. In this paper a control method is proposed to improve the input current distortion and input power factor in light loads. This is achieved by increasing the switching frequency according to the reduction in load. Since conduction and switching losses decrease in light loads, the overall losses by... 

In this paper a single stage structure is proposed for realizing a three-phase unity power factor rectifier. This topology utilizes a forward/flyback transformer to allow the high-frequency isolation. The principle of the operation and the applied control concept is discussed. Space vector modulation is used in order to achieve unity power factor and to have the output voltage be regulated. Furthermore, the system transient is analyzed during turn-on and a novel method is applied to the control system in order to limit inrush current during startup. The proper operation of the soft-start method is confirmed by numerical simulation of a 6KW, 380V/48Vdc. The stability of the closed-loop as... 

In new 400 volt energy distribution systems for telecommunication sites and data centers power density is an influential factor which is commonly desired to be provided such that the systems occupy a small space. On top of that in 400 volt energy distribution systems galvanic isolation is investigated to be inevitable. In this paper a new method is presented that makes it possible to interleave the topology of an isolated low-cost low-size rectifier in which the DC link capacitor of power factor correction stage and DC-DC stage inductor are eliminated and as result it is shown that all the benefits of interleaving such as low current ripple and higher power density are combined with the... 

A major problem in a multiple output converter structure is the different power flow via its various outputs. This problem leads to unwanted input DC-link voltage. This paper studies full bridge based DC-DC converters with multiple outputs. The effect of power flow variation is studied and a regenerative converter topology which controls the DC-link voltage by space voltage vector modulation technique is proposed. The proposed converter has a fast response to control the DC-link voltage in an acceptable band. Simulation and experimental results are presented to verify the analytical studies. © 2018 IEEE  

This paper presents a robust dc-link voltage as well as a current control strategy for a bidirectional interlink converter (BIC) in a hybrid ac/dc microgrid. To enhance the dc-bus voltage control, conventional methods strive to measure and feedforward the load or source power in the dc-bus control scheme. However, the conventional feedforward-based approaches require remote measurement with communications. Moreover, conventional methods suffer from stability and performance issues, mainly due to the use of the small-signal-based control design method. To overcome these issues, in this paper, the power from DG units of the dc subgrid imposed on the BIC is considered an unmeasurable... 

Power density is an influential factor in 400 volt telecom energy distribution systems. In addition, systems are desired to reach an acceptable efficiency while they take advantage of a galvanic isolation. This paper presents a new architecture that is based on push pull topology and its power switches perform ZVS in both their turn on and turn off conditions. Besides, the presented topology uses an interleaving technique that has made it desirable for high power applications. Power loss for the presented topology is calculated and compared to conventional topologies. Finally, by considering the efficiency and power density of the presented topology, it is concluded why this topology is... 

Depending on the reference frame, a proportional integral (PI) or proportional resonant (PR) controller is often utilized for current control in the three-phase PWM rectifiers. Due to the fact that the controller bandwidth is either smaller than the frequency of a specific order harmonic or the controller gain at that frequency is too low the harmonics cannot be effectively eliminated. Among all approaches introduced for harmonic elimination, selective harmonic compensation is believed to have a better performance. Selective harmonic compensation can successfully compensate for harmonics. It, however, forces a considerable computation burden on DSP. This paper proposes a new compensation... 

Rectifiers are an integral part of power harvesting systems. In this paper, the literature on RF power rectifiers is surveyed, starting from the well-known voltage doubler. Effects of using low turn-on voltage devices on forward and reverse losses, and therefore, on conversion efficiency, is discussed. Samples of rectifiers with external devices, such as Schottky diodes are presented. Idea of external Vth cancellation through a rechargeable battery, self Vth cancellation, and floating gate transistors with charge injection onto the gates are demonstrated. Then, standard bridge rectifier and its modified versions, including Vth cancellation technique, are explained. Using low voltage devices... 

This paper presents a robust dc-link voltage as well as a current control strategy for a bidirectional interlink converter (BIC) in a hybrid ac/dc microgrid. To enhance the dc-bus voltage control, conventional methods strive to measure and feedforward the load or source power in the dc-bus control scheme. However, the conventional feedforward-based approaches require remote measurement with communications. Moreover, conventional methods suffer from stability and performance issues, mainly due to the use of the small-signal-based control design method. To overcome these issues, in this paper, the power from DG units of the dc subgrid imposed on the BIC is considered an unmeasurable...