UPS Neutral Point Grounding via Gang Switch
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Solution Overview
Problem
Transformer-less UPS systems with ungrounded outputs pose compliance issues and safety concerns due to potential overcurrent and overvoltage problems, which deter their adoption in critical applications.
Innovation Solution
A UPS system with a gang switch or contactor that dynamically couples and decouples the inverter neutral point to ground, ensuring grounding when operating on battery power and decoupling when receiving power from an AC source, thereby maintaining a stable output reference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a transformer-less UPS design is used to reduce cost and complexity, then the UPS system becomes more compact and cost-effective, but the output becomes ungrounded causing safety concerns and compliance issues
Solution Approach 1:
The patent implements a dynamic grounding system where the neutral point grounding switch changes the grounding state based on operating mode. When operating on battery power, the neutral point is grounded to ensure safety and compliance. When operating on utility power, the neutral point is decoupled from ground. This dynamic adaptation resolves the contradiction by making the grounding state flexible rather than fixed.
2Reliability
If the neutral point is continuously grounded to ensure safety compliance, then overcurrent protection and overvoltage prevention are improved, but additional neutral conductors are required increasing installation cost and complexity
Solution Approach 1:
Instead of continuous grounding requiring additional neutral conductors, the patent uses a dynamically controlled grounding switch that connects the neutral point to ground only when needed (battery mode). This eliminates the need for permanent additional conductors while maintaining safety compliance during critical operation.
Solution Approach 2:
The patent changes the grounding parameter dynamically based on operating conditions. The grounding resistance is effectively changed from low (grounded) during battery operation to high (decoupled) during utility operation, optimizing both safety and installation simplicity.
3Device complexity
If the neutral point is decoupled from ground during battery operation to reduce installation complexity, then fewer conductors are needed, but the output becomes ungrounded causing phase-to-ground faults and overvoltage issues
Solution Approach 1:
The patent dynamically switches the neutral point grounding state based on power source. During battery operation, the neutral point is grounded to prevent phase-to-ground faults and overvoltage conditions. During utility operation, it is decoupled. This temporal separation of grounding states eliminates harmful effects only when safe.
4Reliability
If a gang switch is added to dynamically control neutral point grounding, then safety and compliance are improved during battery operation, but device complexity increases
Solution Approach 1:
The patent combines the neutral point grounding switch with the existing DC link disconnect switch into a single gang switch assembly. Both functions (DC link disconnection and neutral point grounding) are performed by one integrated switching mechanism, reducing overall device complexity compared to having separate switches for each function.
Data Source
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AI summary
A UPS system includes an inverter circuit having an input coupled to a DC link and an output configured to be coupled to a load and a gang switch (e.g., a contactor) configured to couple and decouple the DC link to and from a DC power source and to couple and decouple a neutral point of the inverter circuit to and from a ground node. The gang switch may be configured to couple the neutral point to the ground node when the DC link is coupled to the DC power source and to decouple the neutral point from the ground node when the DC link is decoupled from the DC power source.