Semiconductor Relay Circuit for Battery Inrush Current Control

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Solution Overview

Problem

Existing relay units in motor-driven vehicles, such as hybrid and electric cars, face issues with size, weight, reliability, and noise due to the use of mechanical contact type relays and current limiting resistors, which fail to effectively manage inrush currents and suffer from low reliability and noise generation.

Innovation Solution

A semiconductor device configuration using an insulated gate bipolar transistor (IGBT) and a reverse blocking IGBT, eliminating the need for mechanical contact type relays and current limiting resistors, allows for efficient current control between the battery and inverter circuit, reducing size and weight while enhancing reliability and minimizing noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If mechanical contact type relays and current limiting resistors are used to manage inrush currents, then the relay unit can control current flow between battery and inverter circuit, but the size and weight of the relay unit increase

Engineering Contradiction:

Improverelay reliabilityVSAvoidrelay unit weight

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The patent replaces mechanical contact type relays with semiconductor switching elements (MOSFETs or IGBTs) that have no moving parts. This substitution eliminates the need for mechanical contacts that can weld or generate arcs, while significantly reducing the size and weight of the relay unit. The semiconductor-based main switch unit and precharge switch unit provide reliable current control without the drawbacks of mechanical components.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent extracts and eliminates the current limiting resistor from the circuit by using semiconductor switching elements with inherent current control capabilities. The MOSFETs or IGBTs can limit inrush current through their switching characteristics without requiring external resistors, thereby reducing the overall size and weight of the relay unit while maintaining reliability.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If mechanical contact type relays are used for main relay and pre-charging relay circuit, then the relay unit can control current flow, but noise is produced when opening and closing

Engineering Contradiction:

Improverelay reliabilityVSAvoidnoise generation

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent replaces mechanical contact type relays with semiconductor switching elements (MOSFETs or IGBTs) that switch electronically without mechanical movement. This substitution completely eliminates the noise generated by mechanical contacts opening and closing, while maintaining reliable current control through the semiconductor devices' switching capabilities.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If current limiting resistor is used to limit inrush current, then inrush current from battery is controlled, but the resistor needs to be increased in size due to power consumption

Engineering Contradiction:

Improvecurrent control reliabilityVSAvoidresistor size

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the passive current limiting resistor with active semiconductor switching elements that provide superior current control without the power dissipation and size requirements of resistors. The semiconductor switches control current flow through their on/off states and can be precisely controlled to limit inrush current without converting excessive power to heat.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Ease of operation

If mechanical contact type main relay is used for high-voltage high-current control, then current flow can be controlled, but contact welding occurs and reliability decreases

Engineering Contradiction:

Improvecurrent control capabilityVSAvoidrelay durability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent replaces mechanical contact type relays with semiconductor switching elements (MOSFETs or IGBTs) that have no moving parts or contacts. This substitution eliminates the fundamental problem of contact welding that occurs in mechanical relays under high-voltage high-current conditions, while maintaining full current control capability through electronic switching. The semiconductor devices can handle high currents without the reliability issues inherent in mechanical contact systems.

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 semiconductor device configuration reduces the size and weight of the relay unit, improves reliability by avoiding contact welding and electric arcs, and minimizes noise, while effectively managing inrush currents.

Implementation Method 1

a transistor 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

Methodology Applied

Scientific EffectInsulated gate bipolar transistor operation:

Implementation Method 2

connected in antiparallel to the IGBT

Methodology Applied

Scientific EffectReverse blocking:

Data Source

PatentUS11784639B2Semiconductor device, semiconductor module, relay unit, battery unit, and vehicle

Publication Date: 2023.10.10 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.