Sharif Digital Repository

A Cúk converter operating in discontinuous capacitor voltage mode (DCVM) is an inherent power factor correction converter. A reduced-order switch-network model of a Cúk converter in DCVM is developed, which is valid for both dc-dc and ac-dc applications. The model can be used for controller analysis and design. Moreover, a fast dynamic response controller is proposed, which is an integration of a switching-frequency control unit and a proportional-integral (PI) controller. The PI controller is in charge of duty ratio adjustment. In the proposed controller, unlike conventional PI controllers, switching frequency is no longer fixed and varies as load changes. The switching-frequency control... 

Purpose - The purpose of this paper is to investigate the effect of power on pulsed plasma thruster (PPT) discharge current with respect to its peak, duration, and behavior while the power elevates in a low power range. Design/methodology/approach - A rectangular parallel-plate breech-fed PPT has been developed with a self-inductor coupling element connecting the PPT cathode to the ignitor plug cathode. The PPT has been operated in vacuum chamber at 10-6mbar and its discharge current has been recorded using a Rogowski coil while input power has been changed by means of varying the capacitor voltage at given capacitance and frequency. Findings - The analysis leads to elucidate the effects of... 

Cúk Converter operating in discontinuous capacitor voltage mode is an inherent PFC converter in which, unity power factor can be achieved using constant duty cycle and switching frequency. In this paper, a reduced-order switch network modeling technique is applied to Cúk converter operating in DCVM in order to derive small-signal model of the converter assuming a dc voltage source as the input source of the converter. This model is extended to derive the small-signal behavior of the converter while operating as a PFC converter. The validity of the proposed model is confirmed by both simulation and experimental results. Afterwards, a new control strategy is proposed in which switching... 

Developing efficient and appropriate modeling and control techniques for DC-DC converters is of major importance in power electronics area and has attracted much attention from automatic control theory. Since DC-DC converters have a complex hybrid nature, recently several techniques based on hybrid modeling and control have been introduced. These techniques have shown better results as compared with conventional averaging-based schemes with limited modeling and control abilities. But the current works in this field have not considered all possible dynamics of the converters in both continuous and discontinuous current modes (CCM, DCM) of operations. These dynamics are results of controlled... 

The Cúk converter operating in discontinuous capacitor voltage mode (DCVM) inherently benefits from PFC features as unity power factor can be achieved by using a constant duty cycle and switching frequency. In this paper, the switch network modeling technique is applied to the Cúk converter operating in DCVM in order to develop its small-signal model under the assumption that it is fed by a dc voltage source. Afterwards, the model is extended to derive the small-signal behavior of the converter while operating as a PFC converter. The validity of the proposed model is confirmed by both simulation and experimental results  

This study proposes a new fault detection method for modular multilevel converter (MMC) semiconductor power switches. While in common MMCs, the cells capacitor voltages are measured directly for control purposes, in this study voltage measurement point changes to the cell output terminal improving fault diagnosis ability. Based on this measurement reconfiguration, a novel fault detection algorithm is designed for MMCs semiconductor power switches. The open circuit and short circuit faults are detected based on unconformity between modules output voltage and switching signals. Simulation and experimental results confirm accurate and fast operation of the proposed method in faulty cell... 

A space vector modulation (SVM) approach is proposed to control a four-switch rectifier with power factor correction and compensating the effect of capacitors voltage ripple. The theory and performance of this method are presented, and the method effectiveness is demonstrated by extensive simulations. The simulation results show that the capacitor voltage ripple effects in the output voltage and current shaping can be omitted and the rectifier can work agreeably under high power factor condition although capacitors voltage is not balance. The allowable amount of this unbalanced value of filter capacitors is determined  

One of the major limitations of the multilevel converters is the voltage unbalance between different levels. The techniques to balance the voltage between the different levels normally involve voltage clamping or capacitor charge and discharge control. However, traditional Flying Capacitor Converter (FCC) may be quite limited by the voltage unbalance of flying-capacitors that is the most serious problem. This paper describes operating principles of a new softswitching seven-level converter topology based on FCC for self-voltage stabilization and balancing. By adding power electronic devices to the traditional FCC topology, the proposed topology regulates the DC bus voltage and balances the... 

Several attempts have been made to design suitable controllers for DC-DC converters. However, these designs suffer from model inaccuracy or their inability to desirably function in both continuous and discontinuous current modes. This paper presents a novel switching scheme based on hybrid modeling to control a buck converter using mixed logical dynamical (MLD) methodologies. The proposed method is capable of globally controlling the converter in both continuous and discontinuous current modes of operation by considering all constraints in the physical plant such as maximum inductor current and capacitor voltage limits. Different loads and input voltage disturbances are simulated in MATLAB...