Semiconductor Relay Unit Using IGBTs for EV Battery Precharge

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Solution Overview

Problem

Existing motor-driven vehicles, such as hybrid and electric cars, face issues with large and heavy mechanical contact type relays that cause reliability problems, noise, and limited lifespan due to welded contacts and electric arcs, particularly when handling high-voltage high-current flows.

Innovation Solution

Replace mechanical contact type relays with insulated gate bipolar transistors (IGBTs) and reverse blocking IGBTs to function as main and pre-charging relays, eliminating the need for current limiting resistors and mechanical relays, thereby reducing size, weight, and noise while maintaining reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If mechanical contact type relays are used for main relay and pre-charging relay, then the relay unit can be constructed with simple structure, but the size and weight of the relay unit become large

Engineering Contradiction:

Improverelay structureVSAvoidrelay unit weight

Core Design Contradiction:

Device complexityVSWeight of stationary object

Solution Approach 1:

The patent replaces mechanical contact type relays with semiconductor switches (IGBTs and MOSFETs) in the relay unit. This substitution eliminates the mechanical moving parts, contacts, and arcs associated with traditional relays, thereby significantly reducing the size and weight of the relay unit while maintaining the same functional capabilities of controlling high-voltage current flow between the battery and inverter circuit.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Device complexity

If mechanical contact type relays are used for main relay and pre-charging relay, then the relay unit can be constructed with simple structure, but the reliability of the relay decreases due to welded contacts and electric arcs

Engineering Contradiction:

Improverelay structureVSAvoidrelay reliability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If mechanical contact type relays are used for main relay and pre-charging relay, then the relay unit can be constructed with simple structure, but noise is produced when opening and closing

Engineering Contradiction:

Improverelay structureVSAvoidnoise

Core Design Contradiction:

Device complexityVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If current limiting resistor is used in pre-charging relay circuit, then inrush current can be limited, but the resistor consumes power and increases in size

Engineering Contradiction:

Improveinrush current controlVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent replaces the current limiting resistor with a semiconductor switch (MOSFET or IGBT) controlled by a control circuit. The control circuit regulates the switching timing and duty cycle to limit inrush current during pre-charging, eliminating the continuous power consumption and heat generation associated with resistive current limiting while maintaining effective inrush current control.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS12395169B2Semiconductor device, semiconductor module, relay unit, battery unit, and vehicle

Publication Date: 2025.08.19 ROHM CO LTD

AI summary

A semiconductor device includes a first terminal for a battery, a second terminal for an inverter circuit, and a transistor. The semiconductor device is configured to control a voltage applied to a control terminal of the transistor to allow supply of a current from the first terminal to the second terminal and allow supply of a current from the second terminal to the first terminal. A withstand voltage between the first terminal and the second terminal is greater than or equal to a voltage between the battery and the inverter circuit.