Ultra High Efficiency Grid-tied Power Conversion

Applications

Connecting electronic devices to the AC distribution system is a well understood task, and significant work has been completed in both sourcing power from, and delivering power to the grid. This technology can be used to improve photovoltaic inverters and power supply circuits. 

Problem Addressed

Modern grid connected machines and devices convert the grid voltage from AC to a more appropriate form such as DC or high-frequency modulated AC. Furthermore, there is an increasing need to increase micro inverter efficiency due to the fact that much of the electricity used today is in residential and commercial environments. The low power level of electrical systems in commercial and residential environments increases the difficulty of sustaining high energy conversion efficiencies. This technology reduces power losses associated with photovoltaic inverters used to convert from Alternating Current (AC) to Direct Current (DC). 

Technology

This invention proposes a new circuit topology and control method for an AC-connected power converter. The DC-connected inverter transforms the DC source into high frequency AC with the transformation stage providing both a voltage gain and appropriate impedance shaping.  The cycloinverter modulates the transfer of the high frequency resonant current in response to the changing voltage of the AC port.  The buffer-block acts in a similar manner, but is controlled to absorb or deliver power to the storage port which compensates for the power mismatch between the DC and AC ports. Positioning of the buffer-block on the high-voltage side of the transformer reduces the required transformer size and enables elimination of electrolytic capacitors for energy buffering.The use of unipolar devices allows full bi-directional power flow (4 quadrant) operation, enabling the converter to perform reactive power compensation on the grid.

Advantages

  • Variable-voltage energy storage to decouple energy buffering from the PV panel voltage
  • Full soft-switching, with only unipolar devices, allows conduction losses to scale back linearly with output power
  • Controllable over wide input and output voltages, and output power levels