EV Charging Circuit for Transformerless Insulation Measurement

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Solution Overview

Problem

Existing charging devices for battery electric vehicles lack cost-effective and safe methods for insulation measurement without using transformers, which are essential for ensuring proper insulation of the vehicle's electrical system relative to ground potential.

Innovation Solution

An electrical circuit arrangement that includes a power converter with AC and DC terminals, DC switches, and a discharge resistor, allowing for transformerless insulation measurement by setting DC voltages and using the discharge resistor as a voltage divider to determine insulation resistances, while incorporating a pre-charging circuit to limit currents during hard ground faults.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If transformerless charging device is used, then costs and weight are reduced, but insulation measurement capability and safety are compromised

Engineering Contradiction:

ImprovecostsVSAvoidinsulation measurement capability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The charging device components (power converter, DC switches, discharge resistor) are designed to perform both their primary charging function and insulation measurement function. The power converter can operate in charging mode or measurement mode, and the DC switches serve both connection purposes and measurement circuit configuration. This multi-functionality eliminates the need for separate transformer-based insulation measurement equipment, reducing costs while maintaining measurement capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The system changes operational parameters (voltage levels, switch configurations, measurement modes) to enable insulation measurement without a transformer. By adjusting the DC voltage through the power converter and configuring DC switches in specific patterns, the system can measure insulation resistance using the existing discharge resistor as a reference element, transforming the charging device into a measurement instrument through parameter manipulation.

Inventive Principle:

Principle #35Parameter changes

2Weight of stationary object

If transformerless charging device is used, then weight is reduced, but insulation measurement capability is compromised

Engineering Contradiction:

ImproveweightVSAvoidinsulation measurement capability

Core Design Contradiction:

Weight of stationary objectVSReliability

Solution Approach 1:

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If DC switches are used for connection, then transformerless operation is enabled, but current control during ground faults becomes critical

Engineering Contradiction:

Improvedevice complexityVSAvoidcurrent control during ground faults

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The discharge resistor is pre-configured in the circuit and the DC switches are designed to control current flow before ground faults occur. The control unit is programmed with predetermined switch configurations that limit current during normal operation and automatically activate protective configurations when ground faults are detected, enabling preliminary current control without requiring additional protective equipment.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control unit continuously monitors the electrical parameters and uses feedback to adjust DC switch configurations. When ground faults are detected through voltage or current measurements, the control unit automatically changes switch states to limit fault current, creating a closed-loop control system that maintains safety without transformers through real-time feedback and adaptive switch control.

Inventive Principle:

Principle #23Feedback

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

Enables safe and cost-effective insulation measurement in battery electric vehicles by utilizing existing charging device components, minimizing costs and maintaining high safety standards without the need for transformers.

Implementation Method 1

using the discharge resistor as a voltage divider to determine insulation resistances

Methodology Applied

Scientific EffectVoltage divider principle: Ohm's Law

Implementation Method 2

set a DC voltage at the DC terminals by clocking the power converter

Methodology Applied

Scientific EffectAC to DC conversion: Electromagnetic Induction

Implementation Method 3

A first DC terminal of the DC terminals is connectable to a first EV terminal of the EV terminals via a first DC switch

Methodology Applied

Scientific EffectElectrical switching: Relay

Data Source

PatentUS20250283933A1Electrical circuit arrangement and method for insulation measurement on a battery electric vehicle

Publication Date: 2025.09.11 SMA SOLAR TECH AG

AI summary

The application discloses an arrangement/method for insulation measurement on an electric vehicle (EV). The arrangement is configured to be connected to a battery of the EV via EV terminals. The arrangement has a power converter with AC terminals for connecting to an AC grid and DC terminals. A first DC terminal is connectable to a first EV terminal via a first DC switch and a second DC terminal is connectable to a second EV terminal via a second DC switch or via a parallel circuit composed of the second DC switch and a third DC switch. The arrangement is configured to, when the power converter and the AC grid are connected: connect one of the DC terminals to the corresponding EV terminal by closing one of the DC switches, set a DC voltage at the DC terminals by clocking the power converter, and perform the insulation measurement.