http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

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

This paper presents supercapacitor (SCAP) and battery modeling with an original energy management strategy in a hybrid storage technology. The studied dc power supply is composed of SCAPs and batteries. SCAPs are dimensioned for peak power requirement, and batteries provide the power in steady state. A bidirectional dc/dc converter is used between SCAPs and the dc bus. Batteries are directly connected to the dc bus. The originality of this study is focused on SCAP behavior modeling and energy management strategy. The proposed strategy is based on a polynomial (RST) controller. For reasons of cost and existing components (not optimized) such as batteries and semiconductors, the experimental test benches are designed in reduced scale. The characterized packs of SCAPs include two modules of ten cells in series for each one and present a maximum voltage of 27 V. The proposed strategy is implemented on a PIC18F4431 microcontroller for two dc/dc converter topology controls. Experimental and simulation results obtained from the polynomial control strategy are presented, analyzed, and compared with that of classical proportional-integral control.

DC/DC Converter Design for Supercapacitor and Battery Power Management in Hybrid Vehicle Applications—Polynomial Control Strategy

This paper proposes a combined system of a thyristor-controlled reactor (TCR) and a shunt hybrid power filter (SHPF) for harmonic and reactive power compensation. The SHPF is the combination of a small-rating active power filter (APF) and a fifth-harmonic-tuned LC passive filter. The tuned passive filter and the TCR form a shunt passive filter (SPF) to compensate reactive power. The small-rating APF is used to improve the filtering characteristics of SPF and to suppress the possibility of resonance between the SPF and line inductances. A proportional-integral controller was used, and a triggering alpha was extracted using a lookup table to control the TCR. A nonlinear control of APF was developed for current tracking and voltage regulation. The latter is based on a decoupled control strategy, which considers that the controlled system may be divided into an inner fast loop and an outer slow one. Thus, an exact linearization control was applied to the inner loop, and a nonlinear feedback control law was used for the outer voltage loop. Integral compensators were added in both current and voltage loops in order to eliminate the steady-state errors due to system parameter uncertainty. The simulation and experimental results are found to be quite satisfactory to mitigate harmonic distortions and reactive power compensation.

A Combination of Shunt Hybrid Power Filter and Thyristor-Controlled Reactor for Power Quality

Grid-connected converters exposed to weak grid conditions and severe fault events are at risk of losing synchronism with the external grid and neighboring converters. This predicament has led to a growing interest in analyzing the synchronization mechanism and developing models and tools for predicting the transient stability of grid-connected converters. This paper presents a thorough review of the developed methods that describe the phenomena of synchronization instability of grid-connected converters under severe symmetrical grid faults. These methods are compared where the advantages and disadvantages of each method are carefully mapped. The analytical derivations and a detailed simulation model are verified through experimental tests of three case studies. Steady-state and quasi-static analysis can determine whether a given fault condition results in a stable or unstable operating point. However, without considering the dynamics of the synchronization unit, transient stability cannot be guaranteed. By comparing the synchronization unit to a synchronous machine, the damping of the phase-locked loop is identified. For accurate stability assessment, either nonlinear phase portraits or time-domain simulations must be performed. Until this point, no direct stability assessment method is available which consider the damping effect of the synchronization unit. Therefore, additional work is needed on this field in future research.

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An Overview of Assessment Methods for Synchronization Stability of Grid-Connected Converters Under Severe Symmetrical Grid Faults

In this paper, a dc link active power filter (APF) for three-phase diode rectifier is proposed. The proposed dc link APF, which is composed of two series-connected bidirectional boost converters, intends to eliminate the input current harmonics. It is paralleled at the dc link of the diode rectifier and is coupled to the ac input with three line-frequency switches. Compared with the full power processed power factor correction (PFC) solution, the dc link APF is partially power processed in that it only compensates for the harmonic current component at the dc link. Thus, it features with lower power processing. Moreover, it exhibits better total harmonic distortion of the ac line current when compared with the traditional ac side shunt APF. Voltage and current loop models are developed for average current control, and the selection of the current loop bandwidth is presented. Switching stresses of the ac APF, the dc link APF, and the six-switch PFC are also calculated and analyzed. Experimental and simulation results demonstrate the effectiveness of this dc link APF.

DC Link Active Power Filter for Three-Phase Diode Rectifier

The investigation shows that power semiconductor devices are the most fragile components of power electronic systems.Improving the reliability of power devices is the basis of a reliable power electronic system, and in recent years, many studies have focused on power device reliability.This paper describes the current state of the art in reliability research for power semiconductor devices, mainly includes failure mechanisms,condition monitoring, lifetime evaluation and active thermal control.Among them,condition monitoring technology are classified and summarized by the failure mechanism and the change rules of characteristic quantities; The method of lifetime estimation isillustrated from the practical point of view;Methods of active thermal control are classified and summarized from the two ideas of reducing loss and loss compensation which are refined by the principle of realization. At last, this paper draws the existing problems and challenges of power devices reliability studies.

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Review of power semiconductor device reliability for power converters

Wide bandgap (WBG) devices offer the advantages of high frequency, high efficiency, and high power density to power converters due to their excellent performance. However, their low parasitic capacitance and fast switching speed also make them more susceptible to switching oscillations. The switching oscillations can cause voltage and current overshoots, shoot-through, electromagnetic interference, additional power loss, and even device damage, which can seriously affect the performance of power converters and systems. However, a comprehensive and in-depth overview is lacking on this topic. This article reviews the types, the causes and negative effects, the effects of parasitic parameters and suppression methods of these switching oscillations, which is helpful for practical engineering. First, the switching oscillations are divided into different types, and their causes and negative effects are reviewed. Then, the effects of different parasitic parameters on the switching oscillations are overviewed. It is found that due to the different physical structures of silicon carbide metal-oxide-semiconductor field-effect transistors, enhancement-mode gallium nitride high-electron mobility transistors (eGaN HEMTs), and cascode GaN HEMTs, the effects are also different. Finally, the main methods of suppressing the switching oscillations are summarized, and the advantages and disadvantages of these methods are presented. Furthermore, future research works on this topic and the conclusion of this paper are drawn, which will help readers deepen their understanding of the switching oscillations of WBG devices, and inspire readers to better use WBG devices for high-frequency and high-efficient power conversion.

A Review of Switching Oscillations of Wide Bandgap Semiconductor Devices

Improving the efficiency and dynamics of power converters is a concerned tradeoff in power electronics. The increase of switching frequency can improve the dynamics of power converters, but the efficiency may be degraded. A double-frequency (DF) buck converter is proposed to address this concern. This converter is comprised of two buck cells: one works at high frequency, and another works at low frequency. It operates in a way that current in the high-frequency switch is diverted through the low-frequency switch. Thus, the converter can operate at very high frequency without adding extra control circuits. Moreover, the switching loss of the converter remains small. The proposed converter exhibits improved steady state and transient responses with low switching loss. An ac small-signal model of the DF buck converter is also given to show that the dynamics of output voltage depends only on the high-frequency buck cell parameters, and is independent of the low-frequency buck cell parameters. Simulation and experimental results demonstrate that the proposed converter greatly improves the efficiency and exhibits nearly the same dynamics as the conventional high-frequency buck converter. Furthermore, the proposed topology can be extended to other dc-dc converters by the DF switch-inductor three-terminal network structure.

Double-Frequency Buck Converter

In this paper, a dual half-bridge LLC resonant converter with magnetic control is proposed for the battery charger application. The primary switches are shared by two LLC resonant networks, and their outputs are connected in series. One of the LLC resonant converters is designed to operate at the series resonant frequency, which is also the highest efficiency operating point, and the constant output voltage characteristic is achieved at this operating point. The second LLC resonant converter adopts magnetic control to regulate the total output current and voltage during both constant current charge mode and constant voltage charge mode. Meanwhile, the function decoupling idea is adopted to further improve the system efficiency. The significant amount of the power is handled by the LLC resonant converter operating at the series resonant frequency, whereas the second LLC resonant converter fulfills the responsibility to achieve closed-loop control. By carefully designing the resonant networks, the zero-voltage switching for primary switches and zero-current switching for secondary diodes can be achieved for whole operation range. A 320-W experimental prototype is built to verify the theoretical analysis, and the maximum efficiency is measured about 95.5%.

Xiong Du

Papers

DC Link Active Power Filter for Three-Phase Diode Rectifier

Review of power semiconductor device reliability for power converters

A Review of Switching Oscillations of Wide Bandgap Semiconductor Devices

Double-Frequency Buck Converter

A Dual Half-Bridge LLC Resonant Converter With Magnetic Control for Battery Charger Application