Sharif Digital Repository

The flux and torque hysteresis bands are the only gains to be adjusted in direct torque control (DTC). The torque ripple and harmonic loss of motor and switching loss of inverter greatly Influence them. Hence, these variables must be observed in the control process to maximize performance of the system. In this paper, the effects of flux and torque hysteresis bands on inverter switching loss, harmonic loss, and torque ripple of induction motor are investigated. In order to find their optimum values, a cost function consisting motor harmonic losses, torque ripples, and inverter switching losses is defined. Minimizing this cost function leads to the optimum value of the hysteresis bands of... 

The torque ripple and harmonic loss of motor and switching loss of inverter are greatly influenced by sampling time in the direct torque control method. Hence these variables must be observed in the control process to maximize performance of the system. In this paper the effects of sampling time on inverter switching loss, harmonic loss and torque ripple of induction motor are investigated. To find their optimum values a cost function consisting of motor harmonic losses, torque ripples and inverter switching losses are defined. Minimizing this cost function leads to the optimum value of the sampling time. © 2003 IEEE  

Switched Reluctance Motors (SRMs) are widely used in high-speed and low voltage applications because of their attractive features such as robustness and simplicity. No winding on the rotor of this type of motors allows reaching high speed which is desired for many applications. Drive circuits of SRMs also play an important role in their performance and operation. In this paper, a new bifilar drive circuit for this type of motors has been proposed. This novel configuration has been tested and investigated by PSIM software. Results show that the new bifilar drive circuit highly reduces the voltage stresses on semiconductor switches, and also considerably reduces the switching losses which are... 

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 new zero-voltage-switching, high power-factor, bridgeless rectifier is introduced. In this topology, an auxiliary circuit provides soft switching for all of the power semiconductor devices. Thus the switching losses are reduced and the highest efficiency can be achieved. The proposed converter has been analyzed and a design procedure has been introduced. The control circuit for the converter has also been developed. Based on the given approach, a 250 W, 400 Vdc prototype converters has been designed at 100 kHz for universal input voltage (90-264 Vrms) applications. A maximum efficiency of 94.6% and a power factor correction over 0.99 has been achieved. The simulation and... 

A dc-dc resonant converter has the advantage of overcoming switching losses and electromagnetic interference which are the main limitations of high frequency power converters. Nevertheless, the modeling and stability analysis of dc-dc resonant converters are considerably more complex than pulsewidth modulation counterparts. The conventional averaged linearized model of the resonant converter has limitations due to averaging and linearization. First of all, the linearized model has large modeling error in presence of large variations of reference voltage and input voltage. Furthermore, Converging area for stabilizing controllers is smaller in the averaged model. In order to overcome these... 

In this paper, a new zero-voltage-switching high power-factor (PF) rectifier with Line-Modulated Fixed-Off-Time current control is introduced, that off time is a function of the instantaneous line voltage. The auxiliary circuit provides soft switching for all semiconductor devices, without any extra current and voltage stress on the main switches. The proposed converter is bridgeless, and all semiconductor devices are soft switched. In addition, there is no extra stress on the switches. Thus, the conduction and switching losses are reduced and maximum efficiency is achieved. A 250W, with an input ac voltage of 90265 Vrms and an output voltage 400 Vdc, 100 kHz is designed and simulated to... 

In this paper a novel soft switching isolated buck rectifier is proposed. Various switching state sequences of a three-phase three-switch buck-type unity power factor rectifier are reviewed and the value of switching power loss in each state transition is investigated. The switching power loss of the converter is decreased by using zero current switching (ZCS) method. The operation modes of the converter are explained and analyzed. By using an auxiliary circuit with a simple method of energy recovery, the current is diverted away from the main power switches before they are turned off; so, switching losses in the converter are reduced. In this topology, the power transformer has only the... 

In this paper a novel soft switching three-phase pulse width modulation (PWM) rectifier is proposed. Various switching state sequences of a three-phase three-switch buck-type unity power factor rectifier are reviewed and the operation modes of the converter are explained and analyzed. The converter operates under zero current switching (ZCS) condition. By using an auxiliary circuit with a simple method of energy recovery, the current is diverted away from the main power switches before they are to be turned off; so, switching losses in the converter are reduced. The auxiliary circuit consists of two auxiliary switches and a resonant inductance-capacitance circuit connected to the auxiliary... 

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... 

DC-DC quasi-resonant converters (QRC) have the advantage of reducing switching losses and electromagnetic interference (EMI) which are the main disadvantages of high frequency power converters. The control and stabilization of these converters have always been a challenge. Traditionally, the dynamical model of the QRC is obtained using state space averaging followed by linearization about an operating point. The major flaw of this method is that state variables have large variations; thus, the linearized averaged model is not valid. Therefore, it is necessary to obtain a more precise model for the aim of stability analysis and controller design. Due to semiconductors switching, QRCs are... 

Boost converter operating in critical conduction mode is widely used in low-power power factor corrector because of its simplicity and low switching losses. The switching loss due to parasitic capacitor discharge at the on-time instant can also be reduced by a valley switching technique. In this paper, we introduce a new driver topology for the high-side switch in a synchronous boost converter operating in the critical conduction mode to obtain full zero-voltage switching. Using the proposed high-side driver topology, the conventional control circuit is sufficient to control the low-side switch, and no additional control circuit is required to adjust the timing of the switches. Finally, the... 

LLC resonant converter has been used widely as dc-dc converter for achieving constant dc voltage. In this paper, an LLC resonant converter, by adding an inductance to its conventional topology and considering the rectifying stage stray inductances, is proposed for an adjustable wide range regulated current source (20-200 A dc) for using as ion implanter's filament power supply. The additional inductor increases output current adjustment range and efficiency, especially at light loads. Transformer's leakage inductances and rectifying stage stray inductances have been considered. Because of these inductances, the rectifier stage always works in continuous conduction mode, and its conduction... 

LLC-LC resonant converter is a suitable circuit topology to design switched-mode power supplies for wide-output-voltage and wide-output-load applications. In this paper, a design procedure is introduced to optimize this converter. Unlike soft switching techniques for pulse width modulated converters, which usually apply an active auxiliary circuit to reduce switching losses and EMI, in the proposed converter, not only such circuits are not used, but also all of the parasitic elements are merged to the converters main components. Zero-voltage switching (ZVS) operation is realized for all power devices under all operating conditions. Thus, this converter is a suitable choice for...