Sharif Digital Repository

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 this paper a novel T type scheme for 1-phase direct ac/ac converters is proposed. In this topology, frequency changing takes place directly (without common DC voltage bus) through three converters that are connected in a T structure. Unity power factor and precise output voltage regulation is achieved through appropriate control of these three converters. H-bridge converters are implemented, as the basic unit, in each branches of T to make the proposed converter. The converter is controlled such that the average active power of each H-bridges remains zero. So capacitors are implemented in DC links of H-bridges. In comparison to conventional back-to-back converters, life time of each... 

Contrary to the widespread understanding, this paper shows by means of mathematics and numerics that a perfect power factor correction cannot be made at the load terminals only. To achieve a perfect power factor correction, the supply commitment is required as well. In the absence of such commitment, the power factor cannot reach unity unless we refine the very definition of power factor. But the refined power factor is then slightly higher than the conventional one. The refined expression for power factor is a function of the load parameters as well as the line characteristics. For an ideal power system (with no line losses), this coincides with the conventional formula. © 2008 IEEE  

A single-stage structure is proposed for realizing a unity power factor three-phase isolated AC-DC converter for telecommunication power supply modules. This structure is composed by integrating a boost converter to the isolated threephase three-switch buck rectifier. Modified space vector modulation method is applied to the three-phase three-switch isolated unity power factor input buck rectifier based on the space vector modulation for non-isolated buck. The output boost switch operates during heavily unbalanced mains conditions. Input currents are sinusoidal and in phase with the input voltages even for heavily unbalanced input voltages, e.g. loss of one phase. The converter is modeled by... 

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  

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... 

In this paper, a dual-frame hybrid vector control (DFHVC) of vector-modulated VIENNA I rectifier is proposed. The purpose of this novel vector control system is not only to reduce second-order harmonic pulsation on the dc-side and consequently, to reduce odd-order harmonics on the ac side of VIENNA I rectifier under unbalanced mains, but also to ensure a near unity power factor operation of the rectifier under such circumstances. To serve this purpose, at first, a mathematical model of the VIENNA I rectifier under unbalanced condition is derived. In this model, besides demonstrating the nonlinear nature of the DC-link voltage dynamic, a new set of equations for current reference generation... 

Passivity-based control (PBC) is based on a procedure including energy/power shaping and series/parallel damping injection to control several nonlinear systems such as power converters. In this paper, PBC is used to design a controller for three phase/level/switch PWM (Vienna I) rectifier. Passivity-based controller is supposed to regulate the output voltage and the input three phase sinusoidal currents to achieve unity power factor. Parallel damping injection is used for a controller design. Simulation results are presented to confirm the whole system performance and verify the analytical conclusions. It is also shown that the controller is robust to the load and (symmetrical) input... 

In this paper, a unified hybrid vector control of vector modulated VIENNA I rectifier is presented. Feedback linearization technique is used for the DC-link voltage control. For this purpose, at first a mathematical model of the VIENNA I rectifier is derived. Using this model, it is shown that the dynamic of the rectifier falls into two categories; linear inner dynamic which consists of inner current control and neutral-point potential control and nonlinear outer dynamic which consists of the DC-link voltage control. Based on these facts, a hybrid vector control scheme meaning linear vector control of inner dynamics and nonlinear vector control of outer dynamic is devised. Simulations... 

An ac neutral wire is connected to the midpoint of the dc bus of the three level/phase NPC rectifiers and then a new dual Lagrangian model of the rectifier is presented in this paper. At first, the load current can be obtained in two forms: 1. the load current involving the current of capacitor C1 2. The load current involving the current of capacitor C2 and then the new model is founded based on the superposition law, the load current and The Euler-Lagrange description of the rectifier. The new model is two nonlinear state space equations and as a result we define two positive definite Lyapunov function candidates based on two equations. Finally two Lyapunov-based controllers are designed... 

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... 

This paper addresses a nonlinear model predictive controller design for a single-phase PFC rectifier exploiting the Sheppard-Taylor converter. After approximation of the tracking error in the receding horizon by its Taylor-series expansion to any specified order, an analytic solution to the MPC is developed and a closed-form nonlinear predictive controller is introduced. The proposed nonlinear model predictive control (NMPC) derived using approximation can stabilize the original nonlinear systems if certain conditions, which can be met by properly choosing predictive times and the order for Taylor expansion, are satisfied. The main advantage of this digital control method is that unity power... 

In this paper CCM/CVM operation and modeling of the Sheppard-Taylor topology is reviewed and a predictive control strategy is applied for a Sheppard-Taylor-based power factor correction (PFC) rectifier. Compared to conventional boost or buck - boost PFC's, this topology allows a better current tracking at the AC side, with a relatively reduced voltage at the DC side. Consequently, the high frequency AC filters required by the buck PECs are avoided, and the voltage stresses on the boost switches are significantly reduced. Furthermore In predictive control strategy the duty cycle required to achieve unity power factor in a half line period can be calculated in advance. The main advantage of... 

Single-phase ac-dc Power Factor Correction (PFC) rectifiers have attracted considerable attention in recent years due to the adoption of increasingly stringent power quality regulations. In this paper a nonlinear model predictive controller design for a single-phase Flyback PFC rectifier is presented. After approximation of the tracking error in the receding horizon by its Taylor-series expansion to a specified order, an analytic solution to the model predictive control (MPC) is developed and a closed-loop nonlinear predictive controller is introduced. The main advantage of this digital control method is that unity power factor can be achieved over wide input voltage, load current range and...