UPS Safety Switch Control With Normally Closed Coil Isolation

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Solution Overview

Problem

Conventional uninterruptible power supplies (UPS) with normally open safety switches have high coil costs, high losses, and safety risks due to frequent coil energization, especially in battery mode, prohibiting the use of normally closed switches.

Innovation Solution

A UPS design using a normally closed safety switch with a transistor-controlled coil and a processor to manage switch states based on AC voltage, ensuring the switch is closed during normal operation and open during battery mode, thereby avoiding electric shocks and reducing costs and losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a normally open safety switch is used in the UPS, then the switch can be controlled to open during battery mode, but the coil must be frequently energized causing high costs and high losses

Engineering Contradiction:

Improvesafety switch control reliabilityVSAvoidcoil energy loss

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent inverts the conventional approach by using a normally closed safety switch instead of a normally open switch. This inversion allows the switch to remain closed during normal AC operation (avoiding frequent coil energization) and only opens when needed during battery mode, thereby dramatically reducing coil energy loss while maintaining safety control reliability

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the default state parameter of the safety switch from 'normally open' to 'normally closed'. This parameter change fundamentally alters the operating characteristics, allowing the switch to maintain a stable closed state during normal operation and only transition to open state when controlled by the processor during battery mode, thus reducing energy loss

Inventive Principle:

Principle #35Parameter changes

2Reliability

If a normally open safety switch is used in the UPS, then the switch can isolate the AC input during battery mode, but electric shock risks arise due to potential AC leakage

Engineering Contradiction:

Improvebattery mode operation reliabilityVSAvoidelectric shock risk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent inverts the safety switch configuration to normally closed, which combined with the output switch control strategy, creates a more reliable isolation mechanism. The normally closed switch ensures that the AC input path is inherently connected during normal operation and can be reliably controlled to open during battery mode, preventing AC leakage and electric shock risks

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The processor monitors the operating mode (AC mode or battery mode) and provides feedback control to the safety switch and output switch. This feedback mechanism ensures that the switches are in the correct state for the current operating mode, reliably isolating the AC input during battery mode to prevent electric shock while maintaining proper operation

Inventive Principle:

Principle #23Feedback

3Power

If a normally open safety switch with high voltage coil is used, then the switch can handle AC voltage, but the coil volume and cost increase

Engineering Contradiction:

Improveswitch handling powerVSAvoidcoil volume

Core Design Contradiction:

PowerVSVolume of stationary object

Solution Approach 1:

The patent replaces the high-voltage AC-powered coil with a low-voltage DC-powered coil that is controlled by the processor. This substitution allows the use of a much smaller, lower-power coil while achieving the same switching function through electronic control, thereby reducing coil volume and cost while maintaining the ability to handle AC voltage through the switch

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The design effectively prevents electric shocks, reduces costs, and minimizes losses by using a normally closed safety switch with transistor control, ensuring safe and efficient operation in both normal and battery modes.

Implementation Method 1

a coil (112) wound on the magnetic core 111... When the coil 112 is not energized, the normally open safety switch 114 is open; when the coil 112 is energized, the normally open safety switch 114 is closed

Methodology Applied

Scientific EffectMagnetic field generation: Electromagnet

Data Source

PatentEP4018528B1Uninterruptible power supply

Publication Date: 2026.03.18 EATON INTELLIGENT POWER LTD

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AI summary

The present invention provides an uninterruptible power supply, comprising: an AC input terminal and an AC output terminal; a normally closed safety switch device comprising a normally closed safety switch connected between the AC input terminal and the AC output terminal, a magnetic core, and a coil wound on the magnetic core, wherein a first terminal of the coil is connected to a DC power supply; a first electronically controllable switch connected between a second terminal of the coil and ground; an inverter configured to convert DC to AC and transmit the AC to the AC output terminal; and a control device configured to control the switch state of the first electronically controllable switch on the basis of the AC voltage on the AC input terminal and control the operating state of the inverter on the basis of the voltage on the second terminal of the coil. The uninterruptible power supply of the present invention has the advantages of low cost and low loss, and improves safety.