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

This paper investigates diagnostic techniques for electrical machines with special reference to induction machines and to papers published in the last ten years. A comprehensive list of references is reported and examined, and research activities classified into four main topics: 1) electrical faults; 2) mechanical faults; 3) signal processing for analysis and monitoring; and 4) artificial intelligence and decision-making techniques.

Advances in Diagnostic Techniques for Induction Machines

DC microgrids (MGs) have been gaining a continually increasing interest over the past couple of years both in academia and industry. The advantages of dc distribution when compared to its ac counterpart are well known. The most important ones include higher reliability and efficiency, simpler control and natural interface with renewable energy sources, and electronic loads and energy storage systems. With rapid emergence of these components in modern power systems, the importance of dc in today's society is gradually being brought to a whole new level. A broad class of traditional dc distribution applications, such as traction, telecom, vehicular, and distributed power systems can be classified under dc MG framework and ongoing development, and expansion of the field is largely influenced by concepts used over there. This paper aims first to shed light on the practical design aspects of dc MG technology concerning typical power hardware topologies and their suitability for different emerging smart grid applications. Then, an overview of the state of the art in dc MG protection and grounding is provided. Owing to the fact that there is no zero-current crossing, an arc that appears upon breaking dc current cannot be extinguished naturally, making the protection of dc MGs a challenging problem. In relation with this, a comprehensive overview of protection schemes, which discusses both design of practical protective devices and their integration into overall protection systems, is provided. Closely coupled with protection, conflicting grounding objectives, e.g., minimization of stray current and common-mode voltage, are explained and several practical solutions are presented. Also, standardization efforts for dc systems are addressed. Finally, concluding remarks and important future research directions are pointed out.

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DC Microgrids—Part II: A Review of Power Architectures, Applications, and Standardization Issues

DC microgrids and distribution systems: An overview

This paper describes a new analytical model for the influence of rolling-element bearing faults on induction motor stator current. Bearing problems are one major cause for drive failures. Their detection is possible by vibration monitoring of characteristic bearing frequencies. As it is possible to detect other machine faults by monitoring the stator current, a great interest exists in applying the same method for bearing fault detection. After a presentation of the existing fault model, a new detailed approach is proposed. It is based on the following two effects of a bearing fault: 1. the introduction of a particular radial rotor movement and 2. load torque variations caused by the bearing fault. The theoretical study results in new expressions for the stator current frequency content. Experimental tests with artificial and realistic bearing damage were conducted by measuring vibration, torque, and stator current. The obtained results by spectral analysis of the measured quantities validate the proposed theoretical approach.

/pdf/models-for-bearing-damage-detection-in-induction-motors-zq7k8exor2.pdf

Models for Bearing Damage Detection in Induction Motors Using Stator Current Monitoring

A single-phase bidirectional AC-DC boost rectifier is proposed for a 380V DC power distribution system to control bidirectional power flows and to improve its power conversion efficiency. To reduce the switches' losses of the proposed full-bridge AC-DC rectifier using an unipolar switching method, switching devices employ IGBTs, MOSFETs, and SiC diodes. Using the analysis of the rectifier's operating modes, each switching device can be selected by considering switch stresses. In addition, a simple and intuitive frequency detection method for a single-phase SRF-PLL is proposed using fast period detector and FIR filter to improve the tracking dynamics of PLL under fundamental frequency variations. Experimental results will verify the performance of the proposed methods using a 5 kW prototype rectifier.

Single-phase bidirectional AC-DC boost rectifier for DC distribution system

Cell balancing performance is an important factor in determining the operational efficiency of the active cell balancing circuit. Thus, this study approached this need by developing an enhanced switching pattern. The circuit is designed to transfer energy between arbitrary source and target cells. It has been operated in flyback and buck-boost modes according to the position of the source and target cells. In this circuit, the coupling coefficient of the transformer considerably affects the balancing performance of the flyback operation. The energy transferred to the non-target cell is increased by the low-coupling coefficient due to the leakage inductance. Therefore, the high energy transfer ratio cannot be achieved using conventional switching patterns. In this paper, a new flyback switching pattern is proposed, which can minimize the effect of the coupling coefficient in the cell balancing operation. The proposed switching pattern uses the cells which do not participate in the balancing process to control the voltage applied to each winding, which results in a high energy transfer ratio irrespective of the coupling coefficient. In addition, an enhanced operating method has been proposed to improve the cell balancing speed by reducing the energy transfer path in specific cell conditions. The performance of the proposed switching pattern was verified in a 15 W cell balancing circuit.

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Enhanced Switching Pattern to Improve Cell Balancing Performance in Active Cell Balancing Circuit Using Multi-Winding Transformer

http://koreascience.or.kr:80/article/JAKO201625059045837.pdf

Design Methodology of 500 W Wireless Power Transfer Converter for High Power Transfer Efficiency

A wireless power transfer (WPT) converter for ‘Energy Hub’ system is proposed in home applications. For high power factor capability, the proposed system adopts an additional secondary power factor correction (PFC) circuit. It can operate both of resistive AC load and capacitive DC load, which is multi-functional in the energy hub system. The proposed WPT converter can obtain high power factor without bulky passive or active PFC filter in the primary side by using the secondary PFC circuit. In addition, the proposed WPT converter can reduce the number of power stages to improve cost-effectiveness. In this paper, the operational principles of the proposed WPT converter will be analyzed to obtain proper design methodology. Its performance will be verified by experimental results using a 500 W prototype converter.

Wireless power transfer converter for Energy Hub applications with high power factor capability

In order to improve the reliability and the stability of DC microgrids (MG) and performance of DC bus voltage regulator, at the same time, a new concept of DC bus control signal (DBCS) algorithm based on pulse frequency variation is proposed. In conventional power management algorithms such as centralized control, power line signaling (PLS), and DC bus signaling (DBS), the reliability of DC MGs could be degraded. In this paper, the switching ripple carried on the dc-bus voltage is presented as the operating information for communication between interfaced converters in DC MG. By varying the switching frequency of a grid-connected DC-DC converter according to the load conditions, all DC MG components connected to the DC bus can be aware of the operating status. Experimental results verify the practical feasibility and the effectiveness of the proposed strategy through the 3.3 kW prototype dual active bridge converter.

Jee-Hoon Jung

Papers

Single-phase bidirectional AC-DC boost rectifier for DC distribution system

Enhanced Switching Pattern to Improve Cell Balancing Performance in Active Cell Balancing Circuit Using Multi-Winding Transformer

Design Methodology of 500 W Wireless Power Transfer Converter for High Power Transfer Efficiency

Wireless power transfer converter for Energy Hub applications with high power factor capability

A novel DC bus control signal using pulse frequency modulation for DC microgrids