Rotor Position Sensor Offset Determination via DC Link Capacitor Discharge
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Solution Overview
Problem
Existing methods for determining the measuring offset of a rotor position sensor in electric machines are either inaccurate or require significant effort, particularly in automotive applications where high integrity is necessary for safety.
Innovation Solution
A method that actively discharges the DC link capacitor of an inverter while controlling the rotor position sensor, allowing the voltage measurement to determine the offset, thereby reducing effort and improving accuracy by correlating discharge characteristics with the sensor's offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC current measurement is used to determine measuring offset, then a certain ASIL can be achieved, but the measurement causes high effort and is inaccurate
Solution Approach 1:
The patent replaces the mechanical/electrical measurement system (DC current measurement using shunts or Hall sensors) with an electromagnetic measurement system (voltage measurement across the DC link capacitor). This substitution eliminates the need for physical current sensors and their associated errors, achieving both high precision and reduced complexity while maintaining ASIL certification.
2Reliability
If electromagnetic-force-based methods are used to determine measuring offset, then a certain ASIL (e.g., ASIL C) can be achieved, but the voltage measurement has to be performed with very effortful safety measures
Solution Approach 1:
The patent utilizes the existing DC link capacitor and voltage measurement infrastructure already present in the inverter system. The system serves itself by using its own operational characteristics (the discharge behavior of its DC link capacitor) to determine the measuring offset, eliminating the need for additional safety measures or external measurement equipment.
3Measurement precision
If conventional DC current measurement method is used, then measuring offset can be determined, but the effort and inaccuracy are significant
Solution Approach 1:
The patent changes the measurement parameter from DC current to DC voltage. By measuring the voltage across the DC link capacitor instead of measuring current through shunts or Hall sensors, the system achieves higher precision with less effort, as voltage measurement is inherently more accurate and does not require additional mechanical components.
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 method provides a more accurate and less effortful determination of the measuring offset, achieving high integrity without the need for redundant measurements or computations, thus meeting automotive safety standards with a single measurement and computation.
Implementation Method 1
an inverter converting a voltage at a DC link capacitor into an AC current
Implementation Method 2
a rotor position sensor assigned to a rotor of an electric machine
Implementation Method 3
a voltage of the DC link capacitor detected while the power unit is controlled to actively discharge the DC link capacitor
Data Source
AI summary
Method for determining a measuring offset of a rotor position sensor (2) assigned to a rotor (3) of an electric machine (5) comprising stator windings that are supplied by an inverter (6) converting a voltage at a DC link capacitor (7) into an AC current, wherein a candidate value for the measuring offset is determined, comprising the following steps: —controlling a power unit (9) of the inverter (6) to provide the current based on rotor position information (19) measured by the rotor position sensor (2) to the stator windings such that the DC link capacitor (7) of the inverter (6) is actively discharged, —evaluating a plausibility of the candidate value for the measuring offset based on a voltage of the DC link capacitor (7) detected while the power unit (9) is controlled to actively discharge the DC link capacitor (7), and —providing the candidate value as determined measuring offset, if a result of the evaluation is positive.