Enhanced bipolar Stacked Switched Capacitor energy buffers

2012 Twenty-Seventh Annual IEEE Applied Power Electronics Conference and Exposition (APEC)

Perreault

2012

Abstract-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.

Section: B N-m Bipolar Ssc Energy Buffermentioning

confidence: 99%

Stacked switched capacitor energy buffer architecture

Chen

2012 Twenty-Seventh Annual IEEE Applied Power Electronics Conference and Exposition (APEC)

Perreault

2012

“…Figure 7 illustrates the difference in switching frequency operating range across a halfline cycle for the micro-inverter without and with the MEB (computed using (13), (14), respectively). When the resonant frequency of the inverter is chosen to be 300 kHz, the MEB compresses the switching frequency range from 300-950 kHz to 300-410 kHz.…”

Section: B Design Of the Dc-ac Converter Stagementioning

confidence: 99%

“…It also creates the opportunity to exploit non-electrolytic capacitors that have a lower energy density but a longer life. The size of C BUF can potentially be further reduced by using a Stacked Switched Capacitor (SSC) energy buffer instead of a single capacitor [12], [13].…”

Section: A Design Of the Mebmentioning

confidence: 99%

“…The new technique shares some of the benefits of both variable-topology cascade converter structures [16] and switched-capacitor energy buffers [12], [13], while enabling very high efficiency to be maintained. The new power converter architecture incorporates a Multilevel Energy Buffer and Voltage Modulator (MEB) to achieve compression of the high-frequency inverter operating range, thereby improving the efficiency of the high-frequency-link dc-ac converter stage.…”

Section: Introductionmentioning

confidence: 99%

“…Many approaches have been employed to handle twice-line-frequency energy concerns, including energy buffers interfaced within the high-frequency portion of the inverter system [6]- [8], "dc" interface energy buffers that have wider operating range than simple capacitors placed across the panel or elsewhere [9]- [13], and active power filters placed on the ac side of the system [14], among other approaches. To reduce the required operating ranges of the high-frequency parts of the system, cascaded power stages (such as variable switched-capacitor stages) have sometimes been employed (e.g., [15], [16]).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A Multilevel Energy Buffer and Voltage Modulator for Grid-Interfaced Microinverters

Chen

IEEE Trans. Power Electron.

Perreault

2015

Self Cite

Abstract-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 microinverter by increasing its efficiency and reducing the total size of the twice-line-frequency energy buffering capacitance.

Improved capacitance ratio optimization methodology for stacked switched capacitor energy buffers

Pervaiz

2015 IEEE Applied Power Electronics Conference and Exposition (APEC)

2015

Self Cite

The recently proposed stacked switched capacitor (SSC) energy buffers with film or ceramic capacitors can increase the lifetime of single-phase ac/dc converters by eliminating the relatively short lifetime electrolytic capacitors used for twice-linefrequency energy buffering. This paper presents an improved methodology to minimize the passive volume of SSC energy buffers by optimally selecting their capacitance ratios while taking into account the variation in capacitor energy density with voltage rating. The proposed methodology is compared with the state-ofthe-art approach for both unipolar and bipolar SSC energy buffers. It is shown that for designs with 10% voltage ripple, it reduces the passive volume by up to 43% depending on the capacitor technology and type of SSC energy buffer. The effectiveness of the proposed optimization methodology is validated using a prototype SSC energy buffer designed for an 8-W offline LED driver.Keywords-ac/dc power conversion, dc/ac power conversion, energy buffer, switched capacitor, twice line frequency.