EV Charger Relay Switching at AC Zero Crossing to Reduce Contact Wear

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

The existing electronic power switching circuits for electric vehicle charging devices face significant contact wear due to arcing between relay contacts during opening and closing, which reduces the lifetime of electromechanical relays and increases costs.

Innovation Solution

The proposed electronic power switching circuit utilizes a control unit to synchronize the switching of electromechanical relays with the zero crossing times of the AC load current and supply voltage, thereby minimizing arcing and contact wear.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If electromechanical relays are used to switch large AC voltage supply, then charging capability is improved, but contact wear increases due to arcing

Engineering Contradiction:

Improvecharging powerVSAvoidrelay lifetime

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The control unit synchronizes relay closing with the zero crossing of the AC supply voltage, which is a preliminary action taken before the actual switching event. By anticipating the optimal switching moment (zero crossing), the invention prevents inrush currents and arcing during contact closure, thereby reducing contact wear while maintaining high power charging capability

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control unit continuously monitors the AC supply voltage waveform and uses this feedback information to determine the precise zero crossing moment. This feedback mechanism enables the relay switching to be synchronized with the voltage cycle, minimizing arcing during both opening and closing operations while preserving the ability to deliver high charging power

Inventive Principle:

Principle #23Feedback

2Reliability

If special materials with high contact welding resistance are used, then relay reliability is improved, but cost increases and contact resistance increases

Engineering Contradiction:

Improvecontact welding resistanceVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention replaces the mechanical approach of using special contact materials with an electronic control approach. Instead of relying on expensive specialized materials to prevent welding, the control unit electronically synchronizes switching with voltage zero crossings, eliminating the need for costly material solutions while achieving the same reliability goal

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Strength

If precharge circuits or snubber circuits are added, then inrush current is limited, but device complexity and cost increase

Engineering Contradiction:

Improveinrush current controlVSAvoidcircuit complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The invention substitutes additional passive circuit elements (precharge resistors, snubber circuits) with an active electronic control strategy. The control unit manages inrush current by timing the relay closing at voltage zero crossings, achieving the same protective function without adding complex passive components to the circuit

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The control unit performs multiple functions: it monitors the voltage waveform, determines zero crossing points, and triggers relay switching. This multi-functional approach eliminates the need for separate dedicated circuits for inrush current protection, simplifying the overall device while maintaining effective current control

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 effectively reduces contact wear and extends the lifetime of electromechanical relays, while also eliminating the need for expensive special materials and additional circuitry to manage inrush currents.

Implementation Method 1

Here, the coils generate magnetic fields to attract the movable contacts and ensure contact between the contacts and a static relay contact

Methodology Applied

Scientific EffectMagnetic field generation: Electromagnetic Induction

Implementation Method 2

excessive inrush currents can occur during closing of the relay contacts, ultimately resulting in arcing between the respective contacts. Furthermore, arcing is also present during the turn off (opening) of a relay

Methodology Applied

Scientific EffectArcing: Electric Arc

Data Source

PatentUS20250182991A1Relay contact wear reduction for electric vehicle supply equipment

Publication Date: 2025.06.05 AMPURE CHARGING SYSTEMS INC

AI summary

An electronic power switching circuit comprising a primary circuit with two conducting rails having a first end and a second end, wherein the conducting rails at the first end are configured to be connected to the two phases of an external AC power supply and a secondary circuit with two conducting rails having a first end and a second end, wherein the conducting rails at the first end are connected to the conducting rails at the second end of the primary circuit via electromechanical relays and interposed between the conducting rails and the conducting rails, respectively, wherein said relays are electrically actuated via a control unit, where the control unit controls the switching of the relays depending on the zero crossing time of the load current and/or the power supply voltage.