Energy buffering is necessary in a wide range grid-interface power electronic applications including photovoltaic inverters, motor drives, power supplies, off-line LED drivers and plug-in hybrid electric.
Energy storage requirements of buffer in power conversion system significantly limit miniaturization of grid interface systems. Since the requirement of the buffer is proportional to the system average power and the line period, the size of the buffer cannot be reduced simply through increased switching frequency. Conventional power conversion systems typically utilize electrolytic capacitors to provide high-density energy storage for buffering. However, these capacitors also represent a significant source of system lifetime and reliability problems. Development of energy buffering circuits that eliminate electrolytic capacitors while maintaining high energy storage density and high efficiency is one important key for future grid interface systems that have both a small size and a high reliability.
The invented stacked switched capacitor (SSC) energy buffer circuits include switches and a plurality of energy storage capacitors. The switches are disposed to selectively couple the capacitors to enable dynamic reconfiguration of both the interconnection among the capacitors and their connection to a buffer port. The switches are cooperatively operated as a switching network such that the voltage seen at the buffer port varies only over a small range as the capacitors charge and discharge over a wide range to buffer energy. The switching network need only operate at a relatively low switching frequency, and can take advantage of soft charging of the energy storage capacitors to reduce loss. Thus, efficiency of the SSC energy buffer circuit can be extremely high compared to the efficiency of other energy buffer circuits. Since circuits utilizing the SSC energy buffer do not need to utilize electrolytic capacitors, they overcome the associated limitations. Without electrolytic capacitors, a high effective energy density can be achieved with a relatively high efficiency across a desired operating range.
- Extremely high efficiency since switching network operates at relatively low (line-scale) switching frequency
- Reduced loss with soft/adiabatic charging of stacked switched capacitors
- Operates at a wide range of voltages with efficiency on the level of electrolytic capacitors without the associate limitations