Power Relay Assembly with Series-Parallel FETs for EV Weight Reduction

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Solution Overview

Problem

Conventional power relay assemblies for hybrid electric and electric vehicles are either large and heavy due to gas charging relays or face issues with semiconductor switching elements, such as damage during power cutoff and incomplete power blocking due to internal diodes.

Innovation Solution

A power relay assembly utilizing at least two semiconductor switching elements, including a first and second Field Effect Transistor (FET) connected in parallel and series, with a voltage control circuit and a controller that communicates with a battery management system (BMS) to manage voltage and prevent sparking, eliminating the need for pre-charge resistors and ensuring complete power cutoff.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If gas charging relay is used, then power control function is achieved, but weight and size increase

Engineering Contradiction:

Improvepower control functionVSAvoidweight

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The patent replaces the mechanical gas charging relay with a semiconductor-based switching system consisting of MOSFETs and control circuits. This substitution eliminates the need for gas-filled relay mechanisms while achieving the same power control function, thereby reducing weight and size of the power relay assembly.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the operating parameters by using voltage-controlled MOSFET switching instead of gas-based mechanical switching. The control circuit adjusts gate-source voltages to control current flow, replacing the physical gas discharge mechanism with electrical parameter control, resulting in a more compact and lighter design.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If gas charging relay is used, then power control function is achieved, but volume increases

Engineering Contradiction:

Improvepower control functionVSAvoidvolume

Core Design Contradiction:

ReliabilityVSVolume of stationary object

Solution Approach 1:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Weight of stationary object

If semiconductor switching element is used, then weight and size are reduced, but reliability deteriorates due to damage during power cutoff

Engineering Contradiction:

ImproveweightVSAvoiddurability during power cutoff

Core Design Contradiction:

Weight of stationary objectVSReliability

Solution Approach 1:

The patent implements preliminary action by using the second MOSFET (Q2) to pre-discharge the capacitor connected across the first MOSFET (Q1) before the relay switches off. This preliminary discharge action prevents voltage spikes and inrush currents that could damage the semiconductor switching elements, thereby improving reliability during power cutoff operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent provides beforehand cushioning by incorporating a capacitor parallel to the first MOSFET and using the second MOSFET to control its discharge. This cushioning mechanism absorbs and dissipates energy that would otherwise cause damage during relay switching, protecting the semiconductor elements from electrical stress and improving durability.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

4Weight of stationary object

If semiconductor switching element with internal diode is used, then weight is reduced, but power blocking capability deteriorates

Engineering Contradiction:

ImproveweightVSAvoidpower blocking capability

Core Design Contradiction:

Weight of stationary objectVSReliability

Solution Approach 1:

The patent extracts or removes the reliance on internal diodes for power blocking by implementing an external capacitor-based energy dissipation mechanism. The capacitor parallel to the first MOSFET and controlled by the second MOSFET provides an alternative path for energy dissipation, eliminating the dependence on diode-based power blocking and enabling complete power cutoff capability.

Inventive Principle:

Principle #2Taking out (Extraction)

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 solution reduces the weight and size of the power relay assembly, improves durability by preventing sparking, and ensures reliable power control and emergency shutdown without diode limitations.

Implementation Method 1

a second relay connected to a negative end of the battery and connected to the first relay via a direct current (DC) capacitor

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11702060B2Power relay assembly and vehicle comprising the same and control method of power relay assembly

Publication Date: 2023.07.18 HYUNDAI MOTOR CO LTD

AI summary

A power relay assembly is provided and includes a first relay that is connected to a positive end of a battery and a second relay that is connected to a negative end of the battery and connected to the first relay via a DC capacitor. A first Field Effect Transistor (FET) is connected in parallel with the first relay and a second FET is connected in parallel with the first relay and connected in series with the first FET. A voltage control circuit is configured to adjust a voltage of the first FET with a first voltage or adjust a voltage of the first FET with a second voltage lower than the magnitude of the first voltage.