Stacked Controlled-cell Power Conversion Architecture for Grid-connected Photovoltaic Systems

Applications

The price of the power electronics required to extract the maximum power of photovoltaic (PV) modules and to interface the PV system to the grid is becoming a larger part of the overall system cost. This technology is a design to minimize this cost and increase the power yield of PV systems.

Problem Addressed

The power extracted from maximum power point operation of a series- or parallel- connected set of PV cells may be substantially lower than the power that could be extracted if each cell were operated at its own individual maximum power point (MPP). In this architecture, an integrated circuit switched-mode MPP controller is connected to each cell, forming a “controlled cell”.

Technology

The MPP controllers are fabricated in a low-voltage complementary metal-oxide-semiconductor (CMOS) process, with power switches and control logic all integrated on a monolithic die. The controlled cells can be stacked in series to achieve a high output voltage, which enables the use of a high-power, highly efficient centralized inverter in grid-tied applications. In the new architecture, individual cells can each be operated at any current level below the current in the series controlled-cells string connections. By adjusting the duty ratio, the local MPP tracker can autonomously achieve MPP operation so long as the cell current at its MPP is equal to or less than that in the string. In this manner, the system level controller, implemented by the grid-interface inverter, can adjust the string current such that there is just sufficient string current available for the cell with the highest MPP current.

Advantages

  • Increases power yield
  • Reduces cost of manufacturing and installation
  • Improves reliability and lifetime