Brush Line Impedance Balancing in Multi-Phase Inverter Circuits
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Solution Overview
Problem
In multi-phase electric circuits with asynchronous machines, asymmetrical current flow occurs due to production-related differences between brushes, leading to potential short-circuiting and exceeding of current-carrying capacity, which existing technologies fail to fully mitigate without a short-circuiting device.
Innovation Solution
The implementation of a multi-phase electric circuit design where each brush is connected to the inverter via a separate brush line, with line impedances larger than brush impedances, creating a series connection that reduces the impact of brush impedance asymmetries and includes a short-circuiting device with anti-parallel power semiconductor devices to prevent short-circuiting of brush lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple brushes are used per phase in the rotor, then the current-carrying capacity is increased, but asymmetrical current flow occurs due to production-related differences between brushes
Solution Approach 1:
The patent divides the electrical connection path into separate segments by providing individual brush lines for each brush. This segmentation isolates the impedance characteristics of each brush line, preventing asymmetrical current distribution caused by variations in brush contact resistance while maintaining high current-carrying capacity through multiple parallel paths.
Solution Approach 2:
The patent applies local quality by assigning unique characteristics to each brush line rather than using a common connection. Each brush line is designed with specific impedance characteristics tailored to its associated brush, compensating for production variations and ensuring balanced current distribution across all brushes in a phase.
2Reliability
If a short-circuiting device is added to protect against malfunctions, then the circuit reliability is improved, but the device complexity increases
Solution Approach 1:
The patent introduces an intermediary impedance element in each brush line that serves dual purposes: it prevents direct short-circuiting between rotor and stator windings while also providing current balancing functionality. This intermediary element protects the circuit without requiring complex additional protection devices.
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 design effectively reduces or eliminates asymmetrical current flow and prevents short-circuiting, ensuring balanced current distribution across brushes and maintaining circuit operation even under malfunctions, thereby enhancing the reliability and efficiency of the electric circuit.
Implementation Method 1
the brush impedance has a negative temperature coefficient. This negative temperature coefficient can then be compensated by a positive temperature coefficient of the respective corresponding line impedance.
Data Source
AI summary
A multi-phase electric circuit including an electric machine and an inverter, wherein machine encompasses a rotor connected to the inverter via at least two brushes for each phase, wherein each of the brushes of each phase is connected to the inverter via a separate brush line.