Inverter Neutral Capacitor for AC Charging Ripple Reduction
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Solution Overview
Problem
Electric vehicles experience current ripples during AC grid charging, which require additional circuitry and a large DC-link capacitor to filter, increasing cost, volume, and weight, and are not effectively addressed by existing technologies.
Innovation Solution
A powertrain system with a wye wound electric machine and an inverter, where a capacitor is coupled between the neutral terminal and the negative terminal of the inverter, and the inverter switches are modulated to absorb reactive power from the AC grid, reducing current ripples by operating as a low-frequency current compensator during charging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If additional circuitry and large DC-link capacitors are used to filter current ripples during AC grid charging, then current ripple filtering is improved, but cost, volume, and weight increase
Solution Approach 1:
The inverter is designed to perform multiple functions: it serves as both the charging converter and a low-frequency current compensator. By utilizing the inverter's existing switches and circuitry to generate compensating currents that cancel ripples, the system eliminates the need for separate filtering components, thereby reducing weight while maintaining ripple filtering capability
Solution Approach 2:
The inverter acts as an intermediary between the AC grid and the battery charger. It introduces compensating currents that counteract the ripple currents, effectively filtering the harmful effects without requiring physical filtering components. This mediator approach allows ripple cancellation through electromagnetic interaction rather than passive component filtering
2Object-affected harmful factors
If additional circuitry and large DC-link capacitors are used to filter current ripples during AC grid charging, then current ripple filtering is improved, but cost increases
Solution Approach 1:
The inverter performs dual functions as both charging converter and ripple compensator, eliminating the need for additional filtering circuitry and capacitors. This consolidation of functions reduces component count and manufacturing cost while maintaining effective ripple filtering
Solution Approach 2:
The inverter serves as an intermediary that introduces compensating currents to cancel ripples, replacing the need for expensive passive filtering components with active electromagnetic compensation, thereby reducing overall system cost
3Object-affected harmful factors
If additional circuitry and large DC-link capacitors are used to filter current ripples during AC grid charging, then current ripple filtering is improved, but volume increases
Solution Approach 1:
The inverter is designed to simultaneously perform charging conversion and ripple compensation functions. By using the inverter's switches to generate compensating currents, the system eliminates the need for bulky DC-link capacitors and additional filtering circuitry, significantly reducing charger volume
Solution Approach 2:
The inverter acts as an intermediary that provides ripple compensation through active current injection, replacing the need for large physical filtering components. This approach reduces volume by using electromagnetic fields rather than physical capacitor banks for ripple filtering
4Object-affected harmful factors
If the inverter operates as a low-frequency current compensator to absorb reactive power, then current ripple is reduced, but device complexity increases
Solution Approach 1:
The inverter's existing switches are utilized for dual purposes: standard charging conversion and ripple compensation. The control system generates compensating currents by modulating the inverter switches, achieving ripple reduction without adding physical complexity, though control algorithm complexity increases
Solution Approach 2:
The control system monitors the ripple currents and dynamically adjusts the inverter switch modulation to generate compensating currents. This feedback mechanism automatically counteracts ripples in real-time, managing the complexity through intelligent control rather than additional hardware
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
This solution effectively reduces current ripples during AC grid charging, minimizing the need for additional circuitry and large capacitors, thereby reducing the weight and cost of the charger while improving charging efficiency.
Implementation Method 1
modulating switches of an inverter according to reactive power from the AC grid to induce a field in a wye wound electric machine
Implementation Method 2
couple a capacitor between a neutral terminal of the electric machine and a negative terminal of the inverter to absorb reactive power from the AC grid
Data Source
AI summary
A powertrain for a vehicle includes a wye wound electric machine and a controller. The electric machine is coupled with an inverter. The controller is configured to, in response to an electrical connection between the vehicle and an AC grid, couple a capacitor between a neutral terminal of the electric machine and a negative terminal of the inverter to absorb reactive power from the AC grid.