There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

High-frequency-link (HFL) power conversion systems (PCSs) are attracting more and more attentions in academia and industry for high power density, reduced weight, and low noise without compromising efficiency, cost, and reliability. In HFL PCSs, dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit. This paper gives an overview of DAB-IBDC for HFL PCSs. First, the research necessity and development history are introduced. Second, the research subjects about basic characterization, control strategy, soft-switching solution and variant, as well as hardware design and optimization are reviewed and analyzed. On this basis, several typical application schemes of DAB-IBDC for HPL PCSs are presented in a worldwide scope. Finally, design recommendations and future trends are presented. As the core circuit of HFL PCSs, DAB-IBDC has wide prospects. The large-scale practical application of DAB-IBDC for HFL PCSs is expected with the recent advances in solid-state semiconductors, magnetic and capacitive materials, and microelectronic technologies.

Overview of Dual-Active-Bridge Isolated Bidirectional DC–DC Converter for High-Frequency-Link Power-Conversion System

A phase-locked loop (PLL) is a nonlinear negative-feedback control system that synchronizes its output in frequency as well as in phase with its input PLLs are now widely used for the synchronization of power-electronics-based converters and also for monitoring and control purposes in different engineering fields In recent years, there have been many attempts to design more advanced PLLs for three-phase applications The aim of this paper is to provide overviews of these attempts, which can be very useful for engineers and academic researchers

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Three-Phase PLLs: A Review of Recent Advances

The phase-locked loops (PLLs) are probably the most widely used synchronization technique in grid-connected applications. The main challenge that is associated with the PLLs is how to precisely and fast estimate the phase and frequency, when the grid voltage is unbalanced and/or distorted. To overcome this challenge, incorporating moving average filter(s) (MAF) into the PLL structure has been proposed in some recent literature. An MAF is a linear-phase finite-impulse-response filter, which can act as an ideal low-pass filter, if certain conditions hold. The main aim of this paper is to present the control design guidelines for a typical MAF-based PLL. The paper starts with the general description of MAFs. The main challenge associated with using the MAFs is then explained, and its possible solutions are discussed. The paper then proceeds with a brief overview of the different MAF-based PLLs. In each case, the PLL block diagram description is shown, the advantages and limitations are briefly discussed, and the tuning approach (if available) is evaluated. The paper then presents two systematic methods to design the control parameters of a typical MAF-based PLL: one for the case of using a proportional-integral (PI) type loop filter (LF) in the PLL, and the other for the case of using a proportional-integral-derivative (PID) type LF. Finally, the paper compares the performance of a well-tuned MAF-based PLL when using the PI-type LF with the results of using the PID-type LF, which provides useful insights into their capabilities and limitations.

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Moving Average Filter Based Phase-Locked Loops: Performance Analysis and Design Guidelines

This paper gives a comprehensive overview on disturbance/uncertainty estimation and attenuation (DUEA) techniques in permanent-magnet synchronous motor (PMSM) drives. Various disturbances and uncertainties in PMSM and also other alternating current (ac) motor drives are first reviewed which shows they have different behaviors and appear in different control loops of the system. The existing DUEA and other relevant control methods in handling disturbances and uncertainties widely used in PMSM drives, and their latest developments are then discussed and summarized. It also provides in-depth analysis of the relationship between these advanced control methods in the context of PMSM systems. When dealing with uncertainties, it is shown that DUEA has a different but complementary mechanism to widely used robust control and adaptive control. The similarities and differences in disturbance attenuation of DUEA and other promising methods such as internal model control and output regulation theory have been analyzed in detail. The wide applications of these methods in different ac motor drives (in particular in PMSM drives) are categorized and summarized. Finally, the paper ends with the discussion on future directions in this area.

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Disturbance/Uncertainty Estimation and Attenuation Techniques in PMSM Drives—A Survey

Efficient and precise sensorless speed control of a permanent-magnet synchronous motor (PMSM) requires accurate knowledge of rotor flux, position, and speed. In the literature, many sensorless schemes have been presented, in which the accurate estimation of rotor flux magnitude, position, and speed is guaranteed by detecting the back electromotive force (EMF). However, these schemes show great sensitivity to stator resistance mismatch and system noise, particularly, during low-speed operation. In this paper, an indirect-rotor-field-oriented-control scheme for sensorless speed control of a PMSM is proposed. The rotor-flux position is estimated by direct integration of the estimated rotor speed to reduce the effect of the system noise. The stator resistance and the rotor-flux speed and magnitude are estimated adaptively using stable model reference adaptive system estimators. Simple stability analysis and design of the estimators are performed using linear-control theory applied to an error model of the PMSM in a synchronous rotating reference frame. The convergence of rotor position- and speed-estimation errors to zero is guaranteed. Experimental results show excellent performance

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Sensorless Indirect-Rotor-Field-Orientation Speed Control of a Permanent-Magnet Synchronous Motor With Stator-Resistance Estimation

It is well-documented that back-EMF MRAS-based speed sensorless induction motor drives can suffer from instability problems especially at low-speed operation, and that MRAS schemes using flux estimation suffer from drift problems associated with direct integration. Sensorless IM drives are also sensitive to stator resistance mismatch, particularly at low speeds. Novel stable MRAS speed and stator resistance estimators based on back-EMF quantities, and which are capable of being operated simultaneously, are proposed. Full details of the theoretical foundation and of the design procedure are given. The stability of the estimators is assured by appropriate location of the closed-loop poles of the estimators. Extensive simulation and experimental investigations have been performed to verify the stability of the proposed estimators in the motoring, generating and braking modes of operation.

A stable back-EMF MRAS-based sensorless low-speed induction motor drive insensitive to stator resistance variation

In this paper, a control scheme is proposed for a three-phase isolated photovoltaic (PV)-diesel microgrid without energy-storage element. The scheme aims to: track maximum power from the PVA, regulate the load voltage, compensate the load unbalance viewed by the diesel generator, and to control the diesel-engine speed. The first three tasks are achieved by controlling the pulse width modulation inverter interfacing the PV array to the system. The fourth is realized by a modified fuzzy logic controller of the diesel engine. The obstacles encountered on operating the system under certain probable loading conditions are addressed. Two different operation strategies are proposed to provide high-quality power under all loading scenarios, and to achieve the targets of the control scheme. The system operation is investigated under a variety of conditions to prove the aptness of the proposed techniques.

Flexible Operation Strategy for an Isolated PV-Diesel Microgrid Without Energy Storage

This paper investigates the use of adaptive repetitive and resonant control approaches for the control of a single-phase hybrid cascaded multilevel converter designed to interface with power grids of highly distorted voltage waveform. The proposed repetitive/resonant control (RPC/RSC) is used for the extraction of clean phase angle, frequency, and magnitude information of the fundamental grid voltage together with the control of the converter current and mitigation of current harmonics under distorted grid voltage and variable frequency. The RPC time period and the RSC resonant frequency are updated adaptively using the estimated grid frequency while interpolation is used to preserve the RPC rejection capability under noninteger number of time steps per period. Detailed modeling and experimental investigation of the proposed control scheme are carried out.

Repetitive and Resonant Control for a Single-Phase Grid-Connected Hybrid Cascaded Multilevel Converter

More-electric aircraft (MEA) has become a dominant trend for modern aircraft. On-board MEA, many functions, which are conventionally driven by pneumatic and hydraulic power, are replaced with electrical subsystems. Starting aircraft engines with an electric motor instead of using pneumatic power from the auxiliary power unit is one of the major characteristics of future aircraft. This paper presents the development of a novel electric starter–generator system for aircraft applications. This paper describes the main achievements of the AEGART (EU CleanSky Project) project in the key areas, including electric machines, power electronic converters, thermal management, and overall system control design. The developed prototype has been tested successfully, and the test results are presented in this paper.

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Mohamed Rashed

Papers

Sensorless Indirect-Rotor-Field-Orientation Speed Control of a Permanent-Magnet Synchronous Motor With Stator-Resistance Estimation

A stable back-EMF MRAS-based sensorless low-speed induction motor drive insensitive to stator resistance variation

Flexible Operation Strategy for an Isolated PV-Diesel Microgrid Without Energy Storage

Repetitive and Resonant Control for a Single-Phase Grid-Connected Hybrid Cascaded Multilevel Converter

Development of Aircraft Electric Starter–Generator System Based on Active Rectification Technology