Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

DC-link capacitors are an important part in the majority of power electronic converters which contribute to cost, size and failure rate on a considerable scale. From capacitor users' viewpoint, this paper presents a review on the improvement of reliability of dc link in power electronic converters from two aspects: 1) reliability-oriented dc-link design solutions; 2) conditioning monitoring of dc-link capacitors during operation. Failure mechanisms, failure modes and lifetime models of capacitors suitable for the applications are also discussed as a basis to understand the physics-of-failure. This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.

/pdf/reliability-of-capacitors-for-dc-link-applications-in-power-2b0em1025t.pdf

Reliability of Capacitors for DC-Link Applications in Power Electronic Converters—An Overview

Hybrid and electric vehicle technology has seen rapid development in recent years. The motor and the generator are at the heart of the vehicle drive and energy system and often utilize expensive rare-earth permanent magnet (PM) material. This paper reviews and addresses the research work that has been carried out to reduce the amount of rare-earth material that is used while maintaining the high efficiency and performance that rare-earth PM machines offer. These new machines can use either less rare-earth PM material, weaker ferrite magnets, or no magnets; and they need to meet the high performance that the more usual interior PM synchronous motor with sintered neodymium-iron-boron magnets provides. These machines can take the form of PM-assisted synchronous reluctance machines, induction machines, switched reluctance machines, wound rotor synchronous machines (claw pole or biaxially excited), double-saliency machines with ac or dc stator current control, or brushless dc multiple-phase reluctance machines.

Automotive Electric Propulsion Systems With Reduced or No Permanent Magnets: An Overview

Reliability of Capacitors for DC-Link Applications in Power Electronic Converters

Selective harmonic elimination pulse width modulation (SHE-PWM) offers tight control of the harmonic spectrum of a given voltage and/or current waveform generated by a power electronics converter. Owing to its formulation and focus on elimination of low-order harmonics, it is highly beneficial for high-power converters operating with low switching frequencies. Over the last decade, the application of SHE-PWM has been extended to include multilevel converters. This paper provides a comprehensive review of the SHE-PWM modulation technique, aimed at its application to multilevel converters. This review focuses on various aspects of multilevel SHE-PWM, including different problem formulations, solving algorithms, and implementation in various multilevel converter topologies. An overview of current and future applications of multilevel SHE-PWM is also provided.

A Review of Multilevel Selective Harmonic Elimination PWM: Formulations, Solving Algorithms, Implementation and Applications

This paper presents an analytical approach for evaluating the magnet eddy-current losses of interior permanent-magnet synchronous machines (IPMSMs) during flux weakening. To investigate the magnet eddy-current losses, an analytical method of the time-varying magnetic flux density in the magnet is proposed based on the armature reaction magnetic field analysis. According to the time-varying magnetic flux density, a coefficient is used to evaluate the magnet eddy-current losses during flux weakening. The coefficient can indicate how the major design parameters in an IPMSM affect magnet eddy-current losses during flux-weakening operation. Finite-element analysis was used to validate the proposed model and calculate the magnet eddy-current losses of IPMSM with different design parameters.

An Analytical Approach to Magnet Eddy-Current Losses for Interior Permanent-Magnet Synchronous Machines During Flux Weakening

In electrical vehicle driving systems, the DC bus usually shows large surge voltages because of the presence of loop parasitic inductance and hard-switching operations of voltage source inverters. The unexpected transient overvoltage mostly accounts for switching devices failures. To guarantee system reliability, high-voltage-rating insulated-gate-bipolar-transistors (IGBTs) are commonly used in practical systems to accommodate potential surge voltages. This eventually results in the increase of power loss and system cost. A comprehensive study is presented in this study to minimise the surge voltage across the DC bus. It starts with a surge voltage model indicating that the commutation loop inductances and the switching dynamics are two critical contributors to voltage spikes. An optimal design approach to lower the stray inductance of the connecting busbar is presented. Considering the characteristics of electric vehicle (EV) inverters controlled by space vector modulation, a slew-rate limiter strategy is proposed to minimise the surge voltage. The low inductance busbar design and control strategy are validated by simulation and experimental test.

Analysis and minimisation of DC bus surge voltage for electric vehicle applications

Silicon carbide (SiC) devices have its unique advantages of high operating temperature, high voltage capability with low switching losses when compared to its silicon counterparts. This paper presents a systematic method for long-term reliability analysis for SiC devices. The reliability block diagrams (RBDs) have been established for a SiC power module with standard wire-bonded package. The reliability function and mean time to failure (MTTF) for this module has been estimated by using the lifetime models for single bond wire and SiC chip. The analysis shows that the bond wires are the weakest line of the whole device's reliability. Therefore, it is obvious that utilizing to the full potential of SiC devices is critical for increasing the reliability of package. Design for novel package structure (e.g. without bond wires) may be a possible solution.

Reliability modeling and analysis of SiC MOSFET power modules

Turn-off delay time is temperature sensitive and can be used to estimate the junction temperature of insulated-gate bipolar transistors (IGBTs). In this paper, a high-resolution measurement circuit is designed to detect the turn-off delay time and estimate the corresponding junction temperature. Details of the circuit are demonstrated. Turn-off delay time at different junction temperature, different switching current and different switching voltage is investigated using the measurement circuit. Based on the experimental results, the junction temperature estimation method is tested on IGBT device IKW40N120T2. Compared with the on-state collector-emitter voltage-based method and short current-based method, turn-off delay time-based method shows the feature of high accuracy and feasible online estimation.

A turn-off delay time measurement and junction temperature estimation method for IGBT

In high power AC speed regulation systems, frequency of inverter is wide and frequency of switching is limited. In this paper, the PWM strategy for vector control of induction motor in medium voltage high power is introduced. Asynchronous modulation and multi-step synchronous modulations are concluded in the PWM strategy. In synchronous modulations, selective harmonic elimination PWM (SHEPWM) is employed because of low switching frequency. The factors impacting smooth transition between different PWM modulation modes are analyzed. The corresponding solutions are put forward. And these methods are verified by some experiments in induction motor with 135kW.

The smooth transition research of different PWM modulations for vector control of induction motor in medium voltage high power

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