Active Filter for Battery Ripple Current

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Solution Overview

Problem

Batteries in electric vehicles and energy storage systems face significant power losses and degradation due to exposure to switching frequency ripple components on the DC bus, which traditional methods struggle to mitigate effectively without increasing cost and complexity.

Innovation Solution

An active filter system, comprising switch elements and a controller, is implemented between the battery and inverter to regulate the applied voltage and current, using an H-bridge configuration and capacitors to maintain a constant battery voltage and reduce ripple current, thereby minimizing power losses and heat generation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a DC-DC converter is used to decouple the battery from current ripple, then battery performance and life are improved, but system cost and power loss increase

Engineering Contradiction:

Improvebattery performance and lifeVSAvoidsystem cost and power loss

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

An active filter circuit is introduced as an intermediary component between the battery and the DC bus. This active filter, composed of switching elements and energy storage components, selectively filters current ripple while allowing the DC-DC converter to handle only the average power flow, thus reducing the converter's burden and overall system losses

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The power flow is segmented into two separate paths: one path handles the average power flow through the DC-DC converter, while another path handles the ripple current through the active filter. This segmentation allows each component to be optimized for its specific function, reducing overall system complexity and cost

Inventive Principle:

Principle #1Segmentation

2Device complexity

If the battery is connected directly to the system DC bus, then system cost is reduced, but battery is exposed to switching frequency ripple components causing power losses and heating

Engineering Contradiction:

Improvesystem costVSAvoidpower losses and heating

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The active filter dynamically changes the electrical parameters (impedance, switching frequency) of the connection between battery and DC bus, transforming the rigid direct connection into a controllable, adaptive connection that can filter ripple while maintaining low cost

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If a larger inductor is provided to address ripple current, then ripple current is reduced, but resonance can occur and the inductor becomes sizeable, heavy, and expensive

Engineering Contradiction:

Improveripple currentVSAvoidinductor size and weight

Core Design Contradiction:

Object-affected harmful factorsVSWeight of stationary object

Solution Approach 1:

The passive mechanical inductor is replaced with an active electronic filter circuit using switching elements (MOSFETs or IGBTs) and smaller energy storage components. This substitution eliminates the need for large, heavy inductors while achieving the same ripple current reduction through active control

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The static, passive inductor is replaced with a dynamic, active filter system that can adapt its filtering characteristics in real-time based on operating conditions. The switching elements dynamically adjust the filter's impedance and resonance characteristics, avoiding fixed resonance issues while maintaining effective ripple suppression

Inventive Principle:

Principle #15Dynamics

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 active filter significantly reduces ripple current, extending battery life, reducing the size and cost of inductive components, and enhancing system design flexibility by maintaining a stable battery current and voltage.

Implementation Method 1

a first active filter including a first switch element, second switch element, third switch element, and fourth switch element. Each switch element may be coupled to the first battery or inverter. The first, second, third, and fourth switch elements may be configured to increase or decrease an applied voltage or current of the first battery.

Methodology Applied

Scientific EffectElectrical switching:

Implementation Method 2

a capacitor coupled to the battery, and an inverter coupled to the battery and configured to provide a motive force to system a vehicle. The system may also include an active filter that may include a first switch element, second switch element, third switch element, and fourth switch element.

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS11569759B2System with active filter for a battery

Publication Date: 2023.01.31 WESTINGHOUSE AIR BRAKE TECH CORP

AI summary

A system may be provided that may include a first battery, and an inverter coupled to the battery. The system may also include a first active filter including a first switch element, second switch element, third switch element, and fourth switch element. Each switch element may be coupled to the first battery or the inverter. The first, second, third, and fourth switch elements may be configured to increase or decrease an applied voltage or current of the first battery.