[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

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

Energy storage systems (ESSs) are enabling technologies for well-established and new applications such as power peak shaving, electric vehicles, integration of renewable energies, etc. This paper presents a review of ESSs for transport and grid applications, covering several aspects as the storage technology, the main applications, and the power converters used to operate some of the energy storage technologies. Special attention is given to the different applications, providing a deep description of the system and addressing the most suitable storage technology. The main objective of this paper is to introduce the subject and to give an updated reference to nonspecialist, academic, and engineers in the field of power electronics.

Energy Storage Systems for Transport and Grid Applications

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

Unipolar sinusoidal pulsewidth modulation (SPWM) full-bridge inverter brings high-frequency common-mode voltage, which restricts its application in transformerless photovoltaic grid-connected inverters. In order to solve this problem, an optimized full-bridge structure with two additional switches and a capacitor divider is proposed in this paper, which guarantees that a freewheeling path is clamped to half input voltage in the freewheeling period. Sequentially, the high-frequency common-mode voltage has been avoided in the unipolar SPWM full-bridge inverter, and the output current flows through only three switches in the power processing period. In addition, a clamping branch makes the voltage stress of the added switches be equal to half input voltage. The operation and clamping modes are analyzed, and the total losses of power device of several existing topologies and proposed topology are fairly calculated. Finally, the common-mode performance of these topologies is compared by a universal prototype inverter rated at 1 kW.

An Optimized Transformerless Photovoltaic Grid-Connected Inverter

This paper proposes an improved Z-source inverter topology. Compared to the traditional Z-source inverter, it can reduce the Z-source capacitor voltage stress significantly to perform the same voltage boost, and has inherent limitation to inrush current at startup. The control strategy of the proposed Z-source inverter is exactly the same as the traditional one, so all the existing control strategy can be used directly. A soft-start strategy is also proposed to suppress the inrush surge and the resonance of Z-source capacitors and inductors. The operation principle of the proposed topology and comparison with the traditional topology are analyzed in detail. Simulation and experimental results are given to demonstrate the new features of the improved topology.

Improved Z-Source Inverter With Reduced Z-Source Capacitor Voltage Stress and Soft-Start Capability

An LCL-type filter is widely used in the grid-connected inverter. However, with only injected grid current control, the current harmonics and low bandwidth caused by the resonance peak cannot be tolerated. The active damping (AD) method with an extra feedback provides a high rejection of the resonance so that the dynamic is improved; however, the high-precision sensing circuit for the extra feedback increases the cost. In this paper, with the signal flow graph and response-fitting methods, an AD method based on the feedback of the injected grid current has been proposed. Then, the novel closed-loop current control requires accurately sensing the injected grid current only, while no observation is needed. Compared with the extra feedback methods, the cost and the complexity are reduced while the reliability is improved. Based on the study of the relation between the controller and the system dynamic, a straightforward design has been proposed. The robustness, harmonic rejection, and digital implementation have been studied. Compared with the conventional control methods, the proposed one promises the satisfactory performance with both analog and digital implementations. Simulations and experiments have verified the proposed control and design strategies.

Active Damping-Based Control for Grid-Connected $LCL$ -Filtered Inverter With Injected Grid Current Feedback Only

The current-voltage-fed bidirectional dc-dc converter, which refers to a current-fed inverter at low voltage side and a voltage-fed inverter at high voltage side, can realize zero voltage switching (ZVS) for the switches with the use of phase-shift (PS) technology. However, the current-fed switches suffer from high voltage spike and high circulating conduction loss. In order to solve these problems, a novel phase-shift plus pulsewidth modulation (PSP) control ZVS bidirectional dc-dc converter is proposed in this paper. By adopting active clamping branch and PSP technology, the converter can realize ZVS for all switches in a wide range of load variation while input or output voltage varies. In addition, a novel control strategy with one port voltage regulation and another port current regulation is proposed to make energy bidirectional conversion freely. The operation principle is analyzed and verified by a 28 V/270 V conversion prototype rated at 1.5 kW.

A ZVS Bidirectional DC–DC Converter With Phase-Shift Plus PWM Control Scheme

The current-voltage-fed bidirectional DC-DC converter can realize ZVS for the switches with the use of the phase-shift (PS) technology, however the current-fed switches suffer from high voltage spike and high circulating conduction losses. In order to solve these problems, a novel phase-shift plus PWM (PSP) control ZVS bi-directional DC-DC converter is proposed, which adopts active clamping branch and PWM technology. The novel converter can realize ZVS for all power switches from no load to full load. The operation principle is analyzed and verified by a 28V/270V conversion prototype rated at 1.5kW.

Shaojun Xie

Papers

An Optimized Transformerless Photovoltaic Grid-Connected Inverter

Improved Z-Source Inverter With Reduced Z-Source Capacitor Voltage Stress and Soft-Start Capability

Active Damping-Based Control for Grid-Connected $LCL$ -Filtered Inverter With Injected Grid Current Feedback Only

A ZVS Bidirectional DC–DC Converter With Phase-Shift Plus PWM Control Scheme

A New ZVS Bidirectional DC-DC Converter With Phase-Shift Plus PWM Control Scheme