Stacked Switched Capacitor Energy Buffer Architecture

Electrolytic capacitors are often used for energy buffering applications, including buffering between single-phase ac and dc. While these capacitors have high energy density compared to film and ceramic capacitors, their life is limited. This paper presents a stacked switched capacitor (SSC) energy buffer architecture and some of its topological embodiments, which when used with longer life film capacitors overcome this limitation while achieving effective energy densities comparable to electrolytic capacitors. The architectural approach is introduced along with design and control techniques. A prototype SSC energy buffer using film capacitors, designed for a 320 V dc bus and able to support a 135 W load, has been built and tested with a power factor correction circuit. It is shown that the SSC energy buffer can successfully replace limited-life electrolytic capacitors with much longer life film capacitors, while maintaining volume and efficiency at a comparable level

A multilevel energy buffer and voltage modulator for grid-interfaced micro-inverters

Micro-inverters operating into the single-phase grid from solar photovoltaic (PV) panels or other low-voltage sources must buffer the twice-line-frequency variations between the energy sourced by the PV panel and that required for the grid. Moreover, in addition to operating over wide average power ranges, they inherently operate over a wide range of voltage conversion ratios as the line voltage traverses a cycle. These factors make the design of micro-inverters challenging. This paper presents a multilevel energy buffer and voltage modulator (MEB) that significantly reduces the range of voltage conversion ratios that the dc-ac converter portion of the micro-inverter must operate over by stepping its effective input voltage in pace with the line voltage. The MEB also functions as an active energy buffer to reduce the twice-line-frequency voltage ripple at the output of the solar panel. The small additional loss of the MEB can be compensated by the improved efficiency of the dc-ac converter stage, leading to a higher overall system efficiency. A prototype micro-inverter incorporating a MEB, designed for 27 V to 38 V dc input voltage, 230 V rms ac output voltage, and rated for line cycle average power of 70 W, has been built and tested in grid-connected mode. It is shown that the MEB can successfully enhance the performance of a single-phase grid-interfaced micro-inverter by increasing its efficiency and reducing the total size of the twice-line-frequency energy buffering capacitance

High Efficiency Resonant DC/DC Converter Utilizing a Resistance Compression Network

This paper presents a new topology for a high-efficiency dc/dc resonant power converter that utilizes a resistance compression network (RCN) to provide simultaneous zero-voltage switching and near-zero-current switching across a wide range of input voltage, output voltage, and power levels. The RCN maintains desired current waveforms over a wide range of voltage operating conditions. The use of ON/OFF control in conjunction with narrowband frequency control enables high efficiency to be maintained across a wide range of power levels. The converter implementation provides galvanic isolation and enables large (greater than 1:10) voltage conversion ratios, making the system suitable for large step-up conversion in applications such as distributed photovoltaic converters. Experimental results from a 200-W prototype operating at 500 kHz show that over 95% efficiency is maintained across an input voltage range of 25-40 V with an output voltage of 400 V. It is also shown that the converter operates very efficiently over a wide output voltage range of 250-400 V, and a wide output power range of 20-200 W. These experimental results demonstrate the effectiveness of the proposed design

Impedance control network resonant dc-dc converter for wide-range high-efficiency operation

This paper introduces a new resonant converter architecture that utilizes multiple inverters and a lossless impedance control network (ICN) to maintain zero voltage switching (ZVS) and near zero current switching (ZCS) across wide operating ranges. Hence, the ICN converter is able to operate at fixed frequency and maintain high efficiency across wide ranges in input and output voltages and output power. The ICN converter architecture enables increase in switching frequency (hence reducing size and mass) while achieving very high efficiency. A prototype 200 W, 500 kHz ICN resonant converter designed to operate over an input voltage range of 25 V to 40 V and output voltage range of 250 V to 400 V is built and tested. The prototype ICN converter achieves a peak efficiency of 97.2%, maintains greater than 96.2% full power efficiency at 250 V output voltage across the nearly 2:1 input voltage range, and maintains full power efficiency above 94.6% across its full input and output voltage range. It also maintains efficiency above 93.4% over a 10:1 output power range across its full input and output voltage range owing to the use of burst-mode control.National Science Foundation (U.S.) (Award 1307699

Design of resistive-input class E resonant rectifiers for variable-power operation

Resonant rectifiers have important application in very-high-frequency power conversion systems, including dc-dc converters, wireless power transfer systems, and energy recovery circuits for radio-frequency systems. In many of these applications, it is desirable for the rectifier to appear as a resistor at its ac input port. However, for a given dc output voltage, the input impedance of a resonant rectifier varies in magnitude and phase as output power changes. A design method is introduced for realizing single-diode “shunt-loaded” resonant rectifiers, or class E rectifiers, that provide near-resistive input impedance over a wide range of output power levels. The proposed methodology is demonstrated in simulation for a 10:1 power range.MIT Skoltech InitiativeMassachusetts Institute of Technology. Center for Integrated Circuits and SystemsMassachusetts Institute of Technology. Microsystems Technology Laboratorie

Impedance Control Network Resonant dc-dc Converter for Wide-Range High-Efficiency Operation

This paper introduces a new resonant converter architecture that utilizes multiple inverters and a lossless impedance control network (ICN) to maintain zero voltage switching (ZVS) and near zero current switching (ZCS) across wide operating ranges. Hence, the ICN converter is able to operate at fixed frequency and maintain high efficiency across wide ranges in input and output voltages and output power. The ICN converter architecture enables increase in switching frequency (hence reducing size and mass) while achieving very high efficiency. Three prototype 200 W, 500 kHz ICN resonant converters, one with low-Q, one with medium-Q and one with high-Q resonant tanks, designed to operate over an input voltage range of 25 V to 40 V and an output voltage range of 250 V to 400 V are built and tested. The low-Q prototype ICN converter achieves a peak efficiency of 97.1%, maintains greater than 96.4% full power efficiency at 250 V output voltage across the nearly 2:1 input voltage range, and maintains full power efficiency above 95% across its full input and output voltage range. It also maintains efficiency above 94.6% over a 10:1 output power range across its full input and output voltage range owing to the use of burst-mode control.National Science Foundation (U.S.) (Award 1307699

Methodology for the optimal design of PEV charging systems with multiple chargers and distributed resources

Increased penetration of plug-in electric vehicles (PEVs) will necessitate deployment of numerous PEV chargers. Pairing these chargers with renewable distributed generation (DG) and storage can potentially alleviate negative impacts on the distribution grid and help meet renewable portfolio goals. The optimal design of such integrated charging systems depends on many factors, including geographic location and charging profiles. This paper presents an optimization methodology for designing integrated PEV charging systems with multiple chargers and distributed resources. This methodology is used to investigate optimal designs for charging systems at a retail business and on a university campus. When PEV charging can introduce a demand charge, it is shown that the optimal design depends on the time of charging and the level of existing load. When non-negligible distribution system losses exist between charger locations, it is shown that the optimal size and location of DG and storage depends on the charging profile of the different chargers and the distribution efficiency.Siemens Corporatio

Architecture and System Analysis of Microgrids with Peer-to-Peer Electricity Sharing to Create a Marketplace which Enables Energy Access

More than 1.3 billion people in the world lack access to electricity and this energy poverty is a major barrier to human development. This paper describes a new concept of peer-to-peer electricity sharing which creates a marketplace for electricity. In this marketplace, the people who can afford power generating sources such as solar panels can sell electricity to people who are unable to afford generating sources or who might have access to electricity but require more electricity at certain times. These ad-hoc microgrids created by sharing of resources provide affordable electricity and are enabled by a Power Management Unit (PMU) described in this paper.MIT Tata Center for Technology and Desig

Design and evaluation of a reconfigurable stacked active bridge dc/dc converter for efficient wide load-range operation

This paper presents the design and implementation of a large-step-down soft-switched dc-dc converter based on the active bridge technique which overcomes some of the limitations of the conventional Dual Active Bridge (DAB) converter. The topology comprises a double stacked-bridge inverter coupled to a reconfigurable rectifier through a special three-winding leakage transformer. This particular combination of stages enable the converter to run in an additional low-power mode that greatly increases light-load efficiency by reducing core loss and extending the zero-voltage switching (ZVS) range. The converter is implemented with a single compact magnetic component, providing power combining, voltage transformation, isolation, and energy transfer inductance. A 175 kHz, 300 W, 380 V to 12 V GaN-based prototype converter achieves 95.9% efficiency at full load, a peak efficiency of 97.0%, an efficiency above 92.7% down to 10% load and an efficiency above 79.8% down to 3.3% load.National Science Foundation (U.S.) (Award Number 1307699)MIT Skoltech Initiativ