Inverter Capacitor Arrangement for Ripple Current Suppression
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Solution Overview
Problem
Existing electric power steering devices require multiple capacitors to suppress ripple currents, leading to increased size and complexity, as the influence of ripple currents from one set of inverter circuits can affect others, limiting the effectiveness of reduced wiring impedance in minimizing capacitor count.
Innovation Solution
The capacitors for smoothing are arranged between the bridge circuits of respective phases within the inverter circuits, reducing the number of capacitors needed and minimizing their capacitance, thereby suppressing ripple currents and allowing for downsizing of the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitors are arranged in the immediate vicinities of switching device groups of each phase to suppress ripple currents, then the ripple current suppression effect is improved, but the number of capacitors increases and the device size increases
Solution Approach 1:
The patent merges the functions of multiple phase-specific capacitors into a single common capacitor that serves all three phases. By arranging one capacitor in common for the three phases instead of having separate capacitors for each phase, the patent reduces the total number of capacitors from three to one, thereby reducing device size while maintaining ripple current suppression effectiveness across all phases.
2Quantity of substance
If the number of capacitors is reduced from three to two as in Patent Literature 1, then the device size is reduced, but ripple current influence between different inverter sets increases
Solution Approach 1:
The patent extracts the capacitor from being phase-specific or set-specific and makes it a common component for all phases and both inverter sets. By taking out the capacitor from individual phase arrangements and placing it in a common position, the patent reduces the number of capacitors while the common arrangement allows both inverter sets to share the same smoothing component, thereby reducing ripple current influence between sets.
3Quantity of substance
If wiring impedance is reduced to minimize capacitor requirements, then the number of capacitors can be reduced, but ripple current suppression effectiveness is insufficient when multiple inverter sets are present
Solution Approach 1:
The patent makes the capacitor universal by arranging it in common for all three phases and both inverter sets. Instead of having separate capacitors for each phase or each inverter set, a single capacitor performs the smoothing function for all phases and both sets simultaneously. This multi-functional arrangement reduces the number of capacitors while maintaining effective ripple current suppression across the entire system.
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 configuration effectively suppresses ripple current influence across phases, reducing the number and capacitance of smoothing capacitors, resulting in a more compact and efficient electric power steering device.
Implementation Method 1
capacitors for smoothing are required for suppression of a current fluctuation... capacitors for smoothing are arranged between the bridge circuits of the respective phases... effectively suppresses ripple current influence across phases
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
An electric power steering device includes: an electric motor including multi-phase coils, which is configured to cause a steering mechanism of a vehicle to rotate; and a control unit including a plurality of inverter circuits configured to drive the electric motor, wherein the inverter circuits include capacitors for smoothing, which are small in number than phase number of the electric motor, and the capacitors are arranged between bridge circuits of respective phases of the inverter circuits.