1MHz Scalable Cascaded Z-Source Inverter Using Gallium Nitride (GaN) Device

Currently, implementation of photo-voltaic (PV) systems into power grids is limited.  The reason for the limited use of PV systems in power grids is that the interface between the grid and the PV source very inefficient.  These inefficiencies are caused by module mismatch, orientation mismatch, partial shading, and maximum power point (MPPT) inefficiencies.  This technology provides a scalable cascaded Z-source inverter which can integrate distributed renewable energy sources and/or storages having a wide voltage range. The inverter uses a low voltage Gallium Nitride (GaN) device, which can be used to facilitate modular structure.  The GaN transistor is able to facilitate this structure due to ultra-high frequency, a small AC filter, and a DC electrolyte capacitor.  A comprehensive Z-source network design has been developed based on an innovative equivalent AC circuit model for the single phase photovoltaic system.  The invention is also suitable for hybrid renewable energy sources/storages application in wide system operation range.  A flexible and reliable control system is developed to improve the photovoltaic energy harvesting capability.

Advantages

• Single energy conversion and boost function can be achieved simultaneously
• Independent maximum power point tracking for each Z-source inverter module can implement an efficient photovoltaic energy conversion
• This inverter is immune to shoot-through faults especially operating at high switching frequency and enhance the system reliability
• The scalable cascaded Z-source inverter is able to interface flexibly with different distributed renewable energy sources or storages in a wide voltage range, including:
  • wind power
  • solar power
  • battery
  • fuel cell
  • ultra-capacitor

Applications

• Photo-voltaic systems
• Plug-in electric hybrid vehicle
• Motor drives
• Uninterruptible power supply