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

Power electronics

Active power decoupling methods are developed to deal with the inherent ripple power at twice the grid frequency in single-phase systems generally by adding active switches and energy storage units. They have obtained a wide range of applications, such as photovoltaic (PV) systems, light-emitting diodes (LEDs) drivers, fuel cell (FC) power systems, and electric vehicle (EV) battery chargers, etc. This paper provides a comprehensive review of active power decoupling circuit topologies. They are categorized into two groups in terms of the structure characteristics: independent and dependent decoupling circuit topologies. The former operates independently with the original converter, and the latter, however, shares the power semiconductor devices with the original converter partially and even completely. The development laws for the active power decoupling topologies are revealed from the view of “duality principle,” “switches sharing,” and “differential connection.” In addition, the exceptions and special cases are also briefly introduced. This paper is targeted to help researchers, engineers, and designers to construct some new decoupling circuit topologies and properly select existing ones according to the specific application.

Review of Active Power Decoupling Topologies in Single-Phase Systems

This paper presents a literature overview of all techniques proposed until the submission of this paper in terms of mitigating power oscillation in single-phase applications. This pulsating energy is the major factor for increasing the size of passive components and power losses in the converter and can be responsible for losses or malfunctioning of the dc sources. Reduction of power ripple at twice the fundamental frequency is one of the key elements to increase power converter density without lack of dc stiffness. Pulsation reduction is achieved by incorporating control techniques or auxiliary circuitries with energy storage capability in reactive elements to avoid this oscillating power to propagate through the converter, creating what is called as single-phase power decoupling. The topologies are divided as: rectifiers, inverters, and bidirectional. Among them, it is possible to classify as isolated and nonisolated converters. The energy storage method may be classify as: capacitive and inductive. For the power decoupling technique, it is convenient to divide as control and topology. The power decoupling technique may be implemented as series or parallel with respect to the ac, dc or link side. This paper represents the best reference on this topic.

Low-Frequency Power Decoupling in Single-Phase Applications: A Comprehensive Overview

Existing methods of incorporating an active filter into an AC/DC converter for eliminating electrolytic capacitors usually require extra power switches. This inevitably leads to an increased system cost and degraded energy efficiency. In this paper, a concept of active-filter integration for single-phase AC/DC converters is reported. The resultant converters can provide simultaneous functions of power factor correction, DC voltage regulation, and active power decoupling for mitigating the low-frequency DC voltage ripple, without an electrolytic capacitor and extra power switch. To complement the operation, two closed-loop voltage-ripple-based reference generation methods are developed for controlling the energy storage components to achieve active power decoupling. Both simulation and experiment have confirmed the eligibility of the proposed concept and control methods in a 210-W rectification system comprising an H-bridge converter with a half-bridge active filter. Interestingly, the end converters (Type I and Type II) can be readily available using a conventional H-bridge converter with minor hardware modification. A stable DC output with merely 1.1% ripple is realized with two 50-μF film capacitors. For the same ripple performance, a 900-μF capacitor is required in conventional converters without an active filter. Moreover, it is found out that the active-filter integration concept might even improve the efficiency performance of the end converters as compared with the original AC/DC converter without integration.

Integration of an Active Filter and a Single-Phase AC/DC Converter With Reduced Capacitance Requirement and Component Count

A grid-tie solar inverter with a series voltage compensator for reducing the high-voltage dc-link capacitance is presented. The compensator obtains energy from the dc link to sustain the voltage on its dc side and generates an ac voltage to counteract the voltage ripple on the dc link. As the compensator processes small ripple voltage on the dc link and reactive power, it can be implemented with low-voltage devices, and thus, its volt-amp rating is small. As the required energy storage of the dc link, formed by a reduced value of the dc-link capacitor and the compensator, is reduced, the architecture allows replacing popularly used electrolytic capacitors with alternatives of longer lifetime, such as power film capacitors, or extending the system lifetime even if there is a significant reduction in the capacitance of electrolytic capacitors due to aging. Detailed mathematical analysis on the static and dynamic behaviors of the overall system, and the control method will be presented. A simplified design procedure for the compensator will be given. A 2-kW, 220-V, 50-Hz prototype has been built and evaluated. The theoretical predictions are compared favorably with experimental results. Finally, the implementation cost with electrolytic-capacitor and compensator for the dc link will be compared.

Modeling and Design of Series Voltage Compensator for Reduction of DC-Link Capacitance in Grid-Tie Solar Inverter

A series voltage compensator is proposed for power factor corrector (PFC) in power conversion systems. The introduced concept can reduce the dc-link capacitors used for balancing input and output power, limiting voltage ripple and maintaining certain period of hold-up time if required. Therefore, it allows replacing aluminum electrolytic capacitors by alternative ones with long lifetime while achieving high power density and cost effectiveness. The voltage compensator processes the ripple voltage of the dc-link and supplies reactive power only. It can be implemented by low voltage switching devices and passive components. Simulated and experimental results of a boost PFC converter verify the theoretical predications.

A novel concept to reduce the DC-link capacitor in PFC front-end power conversion systems

A unified derivation of second-order switching surface for boundary control is proposed. It is applicable for a range of basic dc/dc converters and their derivatives. The switching surface dictates the switching instants of the main switch in the converter. The distinct feature of this control method is that the entire converter can ideally reach the steady state in two switching actions after it is subject to a large-signal disturbance. The control method addresses a complete operation of the converter and does not differentiate startup, transient, and steady-state periods. Moreover, the same control law is applicable for converters operating in continuous or discontinuous conduction modes, and with minimum or nonminimum phase characteristics. The proposed derivation method is general-oriented and can identify the circuit variables needed in the switching function. The design procedures and performance of the proposed control method have been evaluated on a 200W 48/48V buck-boost converter prototype.

A unified derivation of second-order switching surface for boundary control of DC-DC converters

A novel concept for reduction of dc-link capacitors is proposed in this paper. It is based on introducing a voltage compensator connected in series with the dc bus line. The compensator processes the ripple voltage and reactive power only and thus can be implemented with switches and capacitors of low voltage ratings. The overall required energy storage is reduced, allowing the replacement of electrolytic capacitors by alternatives with longer lifetime and comparable or reduced volume and cost. A general theory that illustrates the proposed concept is presented. The theoretical predictions are favorably verified by simulations and experiments.

Study of a new technique to reduce the dc-link capacitor in a power electronic system by using a series voltage compensator

A dc-link module composed of dc-link capacitors and a series voltage compensator has been proposed. It has been verified that the module can reduce the dc-link capacitance to 10–20% while achieving a very low voltage ripple across its output terminals. This paper investigates the required dc-link capacitance when a certain period of hold-up time is considered. Trade-off design conditions are presented and the hold-up time is compared with the solution without the series voltage compensator. The analysis is crucial to power converters connected to critical loads when hold-up time is required. The theoretical predictions have been verified by experimental results.

/pdf/hold-up-time-analysis-of-a-dc-link-module-with-a-series-4yjo9uj425.pdf

Hold-up time analysis of a dc-link module with a series voltage compensator

A reliable and adequate communication network is crucial for smart grid applications. It is important to evaluate the performance of network infrastructure with respect to the diverse requirements imposed by various smart grid applications to ensure system reliability. Due to the complex dynamics involving communication and electrical systems, analytical study on smart grid faces challenges. As a result, comprehensive simulation platforms are needed for the study of interdependency between the heterogeneous systems. In this paper, we discuss the design of our smart grid co-simulation platform which combines power system simulator PSCAD/EMTDC with network simulator OPNET. In addition, we report a case study on Vehicle-to-Grid (V2G) voltage support application with respect to WiMAX / WiFi vehicle-to-infrastructure scenarios.

Henry Chung

Papers

A novel concept to reduce the DC-link capacitor in PFC front-end power conversion systems

A unified derivation of second-order switching surface for boundary control of DC-DC converters

Study of a new technique to reduce the dc-link capacitor in a power electronic system by using a series voltage compensator

Hold-up time analysis of a dc-link module with a series voltage compensator

The development of a smart grid co-simulation platform and case study on Vehicle-to-Grid voltage support application