Passive Filter with Coupled Inductor for Battery Ripple Attenuation
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Solution Overview
Problem
In energy storage systems like electric vehicles and hybrid vehicles, the energy source is exposed to variable frequency current ripple due to converter operations, leading to power losses and battery degradation, which existing solutions like lumped inductors fail to adequately address effectively.
Innovation Solution
A passive filter system comprising a coupled-inductor with magnetically coupled windings and bypass capacitors is introduced between the energy storage device and the inverter, forming series resonant circuits to attenuate alternating currents at specific frequencies, reducing ripple currents and maintaining a constant voltage at the energy storage device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC-DC converter is used to decouple the energy source from ripple current, then the energy source is protected from ripple current, but the system cost and power loss increase significantly
Solution Approach 1:
A passive filter circuit is introduced as an intermediary component between the energy storage device and the inverter. This filter, comprising coupled inductors and capacitors, actively attenuates ripple current at its source while allowing the energy storage device to remain directly connected to the DC bus, thus protecting against ripple without the significant power losses associated with active DC-DC converters.
2Ease of manufacture
If the energy source is directly connected to the DC bus to avoid converter cost, then system cost is reduced, but the energy source is exposed to variable frequency ripple current causing power losses and heating
Solution Approach 1:
The passive filter serves as a cost-effective intermediary that can be directly integrated into the system without requiring complex active conversion stages. It provides the necessary ripple attenuation functionality while maintaining the simple direct-connection architecture, thus achieving both cost reduction and energy loss mitigation.
Solution Approach 2:
The passive filter utilizes resonant circuits formed by coupled inductors and capacitors to create frequency-selective attenuation. By tuning the resonant frequencies of these circuits to match the ripple frequencies generated by the inverter, the filter effectively 'vibrates' at the same frequency as the ripple current, creating destructive interference that cancels out the harmful ripple components.
3Loss of energy
If lumped inductors are used to limit ripple components, then ripple current is reduced, but the solution is inadequate for variable frequency ripple and adds unwanted characteristics
Solution Approach 1:
The passive filter employs coupled inductors with magnetically coupled windings that provide dynamic response to varying ripple frequencies. The coupling between windings creates frequency-dependent impedance characteristics that automatically adapt to the variable frequency ripple generated by the inverter, unlike fixed lumped inductors that are only effective at specific frequencies.
Solution Approach 2:
The filter combines multiple passive components (coupled inductors, capacitors) into a composite circuit structure that leverages the complementary strengths of each component. The coupled inductors provide frequency-selective impedance while the capacitors provide resonant attenuation, creating a composite filtering solution that is more effective than any single component alone.
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 passive filter effectively reduces or eliminates alternating currents at the energy storage device, providing greater attenuation than traditional filters, with potential size, weight, and cost reductions, while maintaining a stable voltage and extending battery life.
Implementation Method 1
Each of the at least one first bypass capacitor is coupled in series with a corresponding winding of the at least two magnetically coupled windings to define a series resonant circuit having a determined notch frequency
Implementation Method 2
The first coupled-inductor includes at least two magnetically coupled windings
Implementation Method 3
The passive filter may reduce or eliminate alternating current at the energy storage device
Data Source
AI summary
A system may be provided that includes an energy storage device, and an inverter electrically coupled to the energy storage device. The system also includes a passive filter electrically coupled between the energy storage device and the inverter. The passive filter includes a first coupled-inductor and at least one first bypass capacitor. The first coupled-inductor includes at least two magnetically coupled windings. The passive filter is configured to reduce or eliminate alternating current at the energy storage device.