EVSE Contactor State Detection via Differential Amplifier Isolation

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Solution Overview

Problem

Existing contactor state detection circuits in electric vehicle supply equipment (EVSE) lack physical isolation, which can lead to power flow between line and load sides even when contacts are open, posing safety risks and requiring improved methods to determine contact states accurately.

Innovation Solution

The EVSE incorporates a differential amplifier circuit connected only to the load side of the contactor, amplifying voltage differences between connections and using control electronics to compare these differences to a threshold voltage to determine whether the contacts are closed, thereby ensuring physical isolation and accurate state determination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a contactor state detection circuit is connected to both line side and load side outputs of contactor sets, then the circuit can detect contact state, but physical isolation is lost and power may flow between line and load sides even when contacts are open

Engineering Contradiction:

Improvecontact state detection accuracyVSAvoidphysical isolation safety

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The detection circuit is segmented into two separate circuits: a first detection circuit connected only to line side outputs and a second detection circuit connected only to load side outputs. This segmentation maintains physical isolation between line and load sides while enabling contact state detection through coordinated operation of both circuits.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A signal intermediary mechanism is introduced where the first detection circuit detects voltage at line side outputs and generates a first signal, while the second detection circuit detects voltage at load side outputs and generates a second signal. The contactor state is determined by comparing these intermediary signals rather than directly connecting line and load sides.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a detection circuit is connected only to load side outputs of contactor sets, then physical isolation is maintained, but contact state detection accuracy is reduced

Engineering Contradiction:

Improvephysical isolation safetyVSAvoidcontact state detection accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The results from two separate detection circuits (first circuit detecting line side voltage and second circuit detecting load side voltage) are merged through logical comparison in the control circuit. This combination maintains physical isolation while achieving accurate contact state detection by considering both voltage sources.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The detection system is designed with multi-functionality: the first detection circuit serves both as a line side voltage detector and as part of the contact state determination system, while the second detection circuit serves both as a load side voltage detector and as part of the contact state determination system. This universal approach enables accurate detection while maintaining isolation.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

This solution provides reliable and safe contact state detection by ensuring physical isolation between line and load sides, reducing the risk of power flow when contacts are open and improving the accuracy of contactor state determination, while also simplifying the circuitry and reducing costs.

Implementation Method 1

an amplifier circuit electrically connected to the load side output of the first set of contacts via a first connection and to the load side output of the second set of contacts via a second connection, the amplifier circuit being structured to amplify a voltage difference between a first voltage at the first connection and a second voltage at the second connection

Methodology Applied

Scientific EffectVoltage amplification:

Data Source

PatentUS10150374B2Electric vehicle supply equipment and a method of determining a state of a contactor in electric vehicle supply equipment

Publication Date: 2018.12.11 EATON INTELLIGENT POWER LTD

AI summary

Electric vehicle supply equipment includes a contactor having a first set of contacts and a second set of contacts, an amplifier circuit electrically connected to the load side output of the first set of contacts via a first connection and to the load side output of the second set of contacts via a second connection, the amplifier circuit being structured to amplify a voltage difference between a first voltage at the first connection and a second voltage at the second connection, and control electronics structured to compare the amplified voltage difference to a threshold voltage and to determine whether the first and second sets of contacts are closed based on the comparison between the amplified voltage difference and the threshold voltage.