Fuel Cell Vehicle Regenerative Braking Super Capacitor Overcharge Control

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Solution Overview

Problem

Fuel cell vehicles equipped with super capacitors face issues of overcharging during repeated braking, leading to potential overload and reduced braking performance and energy storage efficiency.

Innovation Solution

A regenerative braking system that includes a super capacitor, a traction motor, a motor control unit, a chopper, a braking resistor, and a hybrid control unit to manage charging voltage, preventing overcharge by switching the chopper on and off based on voltage limits, and utilizing a braking resistor to consume excess energy as heat.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the super capacitor is used to store regenerative braking energy, then energy storage efficiency is improved, but overcharge occurs during repeated braking on downhill

Engineering Contradiction:

Improveregenerative braking energy storage efficiencyVSAvoidsuper capacitor overcharge protection

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

A chopper circuit is introduced as an intermediary device between the traction motor and the super capacitor. The chopper controls the charging process by switching on and off, preventing overcharge of the super capacitor during repeated braking operations on downhill, thus resolving the contradiction between energy storage efficiency and system reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The hybrid control unit monitors the charging voltage of the super capacitor and provides feedback control. When the voltage reaches a predetermined threshold, the control unit activates the chopper to prevent overcharge, ensuring the super capacitor operates within safe voltage limits while maintaining high energy storage efficiency.

Inventive Principle:

Principle #23Feedback

2Reliability

If the chopper is activated to prevent overcharge, then super capacitor protection is improved, but braking performance may be affected

Engineering Contradiction:

Improvesuper capacitor overcharge protectionVSAvoidbraking performance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The chopper is designed with dynamic switching control that adjusts its operation based on real-time voltage conditions. The chopper switches on only when the super capacitor voltage reaches the threshold during braking, and switches off when voltage decreases, dynamically balancing protection needs with braking performance requirements.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The chopper operates in periodic switching mode during braking, turning on when voltage threshold is exceeded and turning off when voltage decreases. This periodic action allows the system to maintain both super capacitor protection and acceptable braking performance by intermittently limiting charge current rather than continuously blocking it.

Inventive Principle:

Principle #19Periodic action

3Reliability

If the braking resistor is used to consume excess energy, then overcharge prevention is improved, but energy is lost as heat

Engineering Contradiction:

Improveovercharge preventionVSAvoidregenerative energy dissipation

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The braking resistor converts the harmful excess energy that would otherwise cause overcharge into useful heat energy. By dissipating the excess regenerative braking energy as heat through the resistor, the system prevents super capacitor overcharge while managing the energy in a controlled manner, transforming a potential problem into a manageable thermal output.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

Prevents overcharge of the super capacitor, enhances braking performance, and improves energy storage efficiency by effectively managing regenerative energy and maintaining stable operation of the fuel cell vehicle.

Implementation Method 1

a super capacitor which is charged while a vehicle runs, and the super capacitor serves to supplement power of a fuel cell stack

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

a braking resistor which is connected to the chopper and the capacitor and consumes regenerative energy generated by a traction motor while the fuel cell vehicle is braked as heat using a resistor

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 3

A polymer electrolyte fuel cell is a device generating electricity while generating water and heat through electrochemical reaction between hydrogen and oxygen

Methodology Applied

Scientific EffectElectrochemical reaction: Fuel Cell

Data Source

PatentUS7420339B2Regenerative braking system of fuel cell vehicle using super capacitor

Publication Date: 2008.09.02 HYUNDAI MOTOR CO LTD

AI summary

A regenerative braking system includes a capacitor which is electrically connected to a stack and is charged by the stack, a traction motor, a motor control unit which control electric power input to the traction motor and electric power output from the traction motor, a chopper which is connected to the capacitor so as to be ON and OFF switched thereby limiting charging voltage of the capacitor, a braking resistor which consumes regenerative energy so as to serve as an auxiliary brake, and a hybrid control unit which turns on the chopper in case that a charging voltage limit of capacitor is exceeded so as to control overcharge of the capacitor and turns off the chopper in case that charging voltage of the capacitor descends. The capacitor is preferably a super capacitor.