Parallel PV Inverter Protection for DC Bus Overvoltage Faults
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Solution Overview
Problem
When multiple inverters are connected in parallel in a photovoltaic system, a short-circuit in one inverter can lead to an increase in direct current bus voltage, potentially damaging components and causing fault expansion due to direct current bus overvoltage.
Innovation Solution
A photovoltaic system with a controller that monitors circulating currents between inverters, implementing wave blocking to stop switching actions in affected inverters when the current exceeds a threshold, and isolating faulty inverters by turning off grid-connected switches to prevent further damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple inverters are connected in parallel to improve power capacity, then the power capacity of the inverter system is improved, but the risk of fault expansion increases when a short-circuit occurs
Solution Approach 1:
The patent segments the inverter system into multiple independent parallel units, each with its own protection mechanism. When a short-circuit is detected in one inverter, the protection system isolates only the faulty unit while maintaining operation of other parallel inverters, thus preserving power capacity while preventing fault expansion.
Solution Approach 2:
The patent introduces a controller as an intermediary that monitors circulating currents between parallel inverters and detects short-circuit conditions. The controller mediates the protection response by identifying faulty inverters and coordinating the isolation process, preventing uncontrolled fault propagation while maintaining system stability.
2Reliability
If wave blocking is implemented to protect inverters during short-circuit, then the reliability of the inverter system is improved, but the productivity during fault condition decreases
Solution Approach 1:
The wave blocking protection is applied selectively to individual faulty inverters rather than the entire parallel system. This segmentation allows non-faulty inverters to continue operating at full productivity while the protected inverter undergoes wave blocking, thus maintaining system availability during fault conditions.
Solution Approach 2:
The patent applies wave blocking only to the extent necessary for protection - specifically to the faulty inverter and only during the short-circuit condition. Once the fault is isolated, normal operation resumes in unaffected units, minimizing the duration and scope of productivity reduction while ensuring adequate protection.
Data Source
AI summary
A photovoltaic system includes a controller and two groups of inverters. The two groups of inverters include a positive inverter group and a negative inverter group. The positive inverter group includes at least two inverters: a first inverter and a third inverter. The negative inverter group includes at least two inverters: a second inverter and a fourth inverter. Alternating current output ends of the first inverter and the third inverter are connected in parallel. Direct current input ends of the first inverter and the second inverter are connected in series. Alternating current output ends of the second inverter and the fourth inverter are connected in parallel. Direct current input ends of the third inverter and the fourth inverter are connected in series.