SiC String Inverter Ground Balancing for Longer Device Life
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Solution Overview
Problem
Photovoltaic system inverters exhibit shorter lifetimes and higher operation and maintenance costs due to mechanical cooling fans and power converter capacitors, with operating temperatures significantly impacting mean time to failure (MTTF).
Innovation Solution
Inverter circuits utilizing silicon carbide (SiC) power MOSFET devices with modular converter architectures that achieve lower loss, higher reliability, and improved power density, incorporating ground-balancing converter modules to equalize terminal voltages and reduce stress on MOSFETs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional inverter designs are used with mechanical cooling fans and power converter capacitors, then the inverter can provide power conversion functionality, but the device lifetime is significantly reduced and operation and maintenance costs increase
Solution Approach 1:
The patent removes mechanical cooling fans and power converter capacitors from the inverter design, extracting the problematic components that limited device lifetime and increased maintenance costs. The ground-balancing converter module is introduced to replace the traditional H-bridge configuration, eliminating the need for large capacitors while maintaining power conversion functionality.
Solution Approach 2:
The patent changes the voltage balancing approach from using large capacitors to using an active ground-balancing converter module that dynamically adjusts voltage levels. This parameter change from passive to active balancing enables the elimination of bulky capacitors and mechanical fans while improving reliability through solid-state operation.
2Device complexity
If higher operating temperatures are tolerated to simplify cooling, then device complexity is reduced, but mean time to failure decreases significantly
Solution Approach 1:
The patent replaces mechanical cooling fans with a solid-state ground-balancing converter module that actively manages voltage and temperature distribution. This substitution eliminates moving parts while providing precise thermal management through electronic control, thereby improving mean time to failure without adding mechanical complexity.
3Loss of energy
If SiC MOSFETs are used to reduce loss and improve efficiency, then energy efficiency is improved, but the inverter requires specialized circuit configurations to manage voltage stress
Solution Approach 1:
The patent introduces a ground-balancing converter module as an intermediary between the SiC MOSFETs and the input terminals. This intermediary actively manages voltage distribution and stress allocation, enabling the use of SiC MOSFETs for reduced power loss while protecting them from excessive voltage stress through dynamic voltage balancing.
Data Source
AI summary
In various implementations, string inverter circuit configurations are provided that allow for increased device lifetimes. In one implementation, for example, an inverter includes a pair of inverter input terminals. A ground-balancing converter module is coupled between the pair of inverter input terminals and ground. The ground is disposed between each of the pair of inverter input terminals. A plurality of converter modules is coupled to an output of the ground-balancing converter module, each of the plurality of converter modules providing an output ac phase of the inverter. In another implementation, a method of controlling an inverter is provided. The method includes controlling a voltage level of each terminal of the pair of inverter input terminals to have equal magnitudes and opposite polarities with respect to a ground voltage.