Alireza Safaee

A New Phase-Locked Loop System for Three-Phase Applications

This paper presents a new three-phase phase-locked loop (PLL) system that primarily estimates the phase angles, frequency, and magnitudes of the a three-phase input signal and also provides a filtered version of the input. It is then extended to the estimation of sequence components, their magnitudes, and phase angles. As compared with the conventional three-phase PLL, this method does not suffer from errors that are caused by signal unbalance and dc offset. It also provides estimate for several other variables which are not included in the conventional three-phase PLL. As compared with the method of using three independent single-phase enhanced PLLs, the proposed method offers a simpler structure. Moreover, the estimated frequency is more accurate and smoother because it uses the information from all three phases to estimate a single value for frequency. The paper also presents a modification that makes the PLL parameters independent from the input signal amplitude. The same modification is applicable to existing methods such as conventional three-phase PLL. Simulation and experimental results are presented to confirm desirable performance of the proposed method.

Bidirectional DC - DC Converters for Energy Storage Systems

Bidirectional dc-dc converters (BDC) have recently received a lot of attention due to the increasing need to systems with the capability of bidirectional energy transfer between two dc buses. Apart from traditional application in dc motor drives, new applications of BDC include energy storage in renewable energy systems, fuel cell energy systems, hybrid electric vehicles (HEV) and uninterruptible power supplies (UPS). The fluctuation nature of most renewable energy resources, like wind and solar, makes them unsuitable for standalone operation as the sole source of power. A common solution to overcome this problem is to use an energy storage device besides the renewable energy resource to compensate for these fluctuations and maintain a smooth and continuous power flow to the load. As the most common and economical energy storage devices in medium-power range are batteries and super-capacitors, a dc-dc converter is always required to allow energy exchange between storage device and the rest of system. Such a converter must have bidirectional power flow capability with flexible control in all operating modes. In HEV applications, BDCs are required to link different dc voltage buses and transfer energy between them. For example, a BDC is used to exchange energy between main batteries (200-300V) and the drive motor with 500V dc link. High efficiency, lightweight, compact size and high reliability are some important requirements for the BDC used in such an application. BDCs also have applications in line-interactive UPS which do not use double conversion technology and thus can achieve higher efficiency. In a line-interactive UPS, the UPS output terminals are connected to the grid and therefore energy can be fed back to the inverter dc bus and charge the batteries via a BDC during normal mode. In backup mode, the battery feeds the inverter dc bus again via BDC but in reverse power flow direction. BDCs can be classified into non-isolated and isolated types. Non-isolated BDCs (NBDC) are simpler than isolated BDCs (IBDC) and can achieve better efficiency. However, galvanic isolation is required in many applications and mandated by different standards. The

A ZVS Pulsewidth Modulation Full-Bridge Converter With a Low-RMS-Current Resonant Auxiliary Circuit

This paper presents the description and analysis of a phase-shift-modulated full-bridge converter with a novel robust passive low-rms-current resonant auxiliary circuit for zero-voltage switching (ZVS) operation of both the leading and lagging switch legs. Detailed time-domain analysis describes the steady-state behavior of the auxiliary circuit in different operating conditions. An in-depth comparative study between a fully specified baseline converter and the equivalent converter using the proposed resonant auxiliary circuit is presented. For a similar peak auxiliary current to ensure ZVS operation, a minimum of 20% reduction in rms current is obtained, which decreases the conduction losses. Key characteristics and design considerations are also fully discussed. Experimental results from a 750-W prototype confirm the predicted enhancements using the proposed resonant auxiliary circuit.

An Adaptive ZVS Full-Bridge DC–DC Converter With Reduced Conduction Losses and Frequency Variation Range

This paper presents a description and analysis of a full-bridge converter with a novel passive and robust auxiliary circuit for zero-voltage-switching (ZVS) operation. A generalized time-domain state-space analysis is provided to describe the steady-state behavior of the auxiliary circuit. Complete comparison between the well-known single-inductor auxiliary circuit, and the proposed one is presented. For a similar peak current in the auxiliary branch, needed for ZVS, a minimum of 20% reduction in rms current is achieved to decrease the conduction losses in the power switches and in the auxiliary circuit. Also, 65% reduction in switching frequency variation is obtained. This narrower frequency range reduces the need for very high-frequency operation and the associated gate driver losses as well as the difficulty of electromagnetic interference (EMI) filter design. All the theoretical results are experimentally verified.

Basic families of medium-power soft-switched isolated bidirectional dc-dc converters

This paper is concerned with the investigation of common medium-power isolated bidirectional dc-dc converters (IBDC) which are increasingly being used in many applications such as interfacing renewable energy resources to utility grid, hybrid electric vehicles and UPS systems. Although different varieties of IBDCs have been proposed by researchers, they can be conceptually classified into a few families. This paper provides an insight into the basic operation of each family by investigating the working principles of a representative member of each family. This helps in comparing different characteristics of each family and understanding their advantages and disadvantages for a certain application.

A resonant bidirectional dc-dc converter for aerospace applications

A wide-range input-output bidirectional dc-dc power converter suitable for power rating of several kilowatts is introduced in this paper. This converter provides a high frequency operation with zero voltage switching (ZVS) for all the switches, with no auxiliary circuitry or increased component stresses. The transformer leakage inductance is used as the resonant inductor. The proposed control algorithm includes a combination of variable frequency control and pulse width modulation methods. The control provides the minimum current for any active power level, with no compromise in zero voltage switching, through precise selection of the control variables of frequency, phase shift and duty cycle. The experimental results verify the feasibility and performance of the proposed topology.

An efficient adaptive energy storage using saturable inductors for ZVS phase-shift-modulated full-bridge converters

This paper presents a new design of auxiliary circuit branches for a family of zero-voltage switching phase-shift-modulated dc/dc converters initially reported for fuel cell application. The suggested method applies saturable inductors in auxiliary branches and guarantees zero-voltage switching (ZVS) operation with reduced conduction loss for all the input and load conditions. The suggested approach is compared with linear branch method to validate the analysis. It is shown that the proposed approach offers up to 30% reduction in the conduction loss of auxiliary branches. The latter allows lower safety margins for the switches and the auxiliary branch components, which simplifies converter design, and reduces size, weight, and cost.

Adaptive nonlinear maximum power point tracker for a WECS based on permanent magnet synchronous generator fed by a matrix converter

This paper presents a new control method to track the maximum power point for a Wind Energy Conversion System (WECS). This WECS is based on a permanent magnet synchronous generator (PMSG) fed by a matrix converter. Since the mechanical power generated by the wind turbine is a function of its shaft speed at a given wind velocity, the proposed controller provides the desired voltage at the output of the matrix converter so as to control the generator speed. This controller is based on the nonlinear adaptive backstepping approach which is well suited for this system. This method is able to effectively accommodate the effects of system uncertainties. Theoretical analysis and simulation results verify the feasibility and performance of the proposed approach.

A practical approach to inductive power transfer systems for transportation applications using boucherot bridge method

A practical method for analysis and design of inductive power transfer (IPT) systems is presented. A generalized frequency-domain analysis for steady-state operation of the system is provided. The proposed analytical method facilitates understanding of IPT systems through a systematic approach to designing a practical power transfer solution.

Review and comparison of bi-directional AC-DC converters with V2G capability for on-board EV and HEV

In this paper, recent topologies for bi-directional AC-DC converters are reviewed. The reviewed topologies are efficient, isolated and compact and can be used as an on-board battery charger for EV or HEV. It is assumed that each converter is made up of a set of building blocks and choice of these building blocks results in different topologies. The topologies are divided into two families: single-stage and two-stage. To compare the topologies, two converters from the two families are chosen and compared in terms of efficiency, number of the devices and rating of them.