Electric Machine Phase Current Timing With Harmonic-Aware Conversion
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Solution Overview
Problem
In electric machines, particularly those in the automotive sector, accurately detecting phase currents is crucial for maintaining safety standards like ISO 26262, but existing methods face inaccuracies due to phase current measurements not being synchronized, leading to incorrect torque settings and potential safety infringements.
Innovation Solution
A method that determines phase currents by considering both the fundamental and harmonic components, allowing for accurate conversion of phase currents to a common time for closed-loop control, thereby avoiding errors caused by assuming harmonics as part of the fundamental.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If phase currents are measured at different times for different phases due to time offset in PWM driving, then the measurement process can be completed for all phases, but the measurement precision deteriorates because the phase currents are not synchronized
Solution Approach 1:
The patent applies preliminary action by measuring all phase currents during the same PWM switching period before proceeding to torque calculation. This ensures that all current measurements are taken under identical operating conditions, eliminating the time-synchronization error that would occur if measurements were taken across different periods. The measurements are prepared in advance within a single period, and then used together for accurate torque determination.
2Ease of manufacture
If torque is calculated using measured phase currents without considering harmonics, then the calculation is simple and fast, but the manufacturing precision deteriorates due to inaccurate torque values
Solution Approach 1:
The patent applies segmentation by separating the phase current into fundamental component and harmonic component. The current measurement is first obtained, then the fundamental component is extracted using Clarke and Park transformations, and the harmonic component is isolated by subtraction. This segmented approach allows accurate torque calculation based only on the fundamental component while maintaining a systematic and implementable calculation process.
Solution Approach 2:
The patent uses Clarke transformation and Park transformation as intermediary steps to convert the measured phase currents into a coordinate system where the fundamental component can be easily separated from harmonics. These transformation matrices act as intermediaries that facilitate the extraction of accurate current values for torque calculation without requiring complex direct measurement methods.
3Measurement precision
If all phase currents are measured at the same ideal time point, then the measurement precision is maximized, but the device complexity increases due to synchronization requirements
Solution Approach 1:
The patent applies self-service by utilizing the naturally occurring common intervals in the PWM switching periods of different phases. Instead of requiring external synchronization hardware or complex coordination mechanisms, the system automatically identifies and uses the time windows where all phases are simultaneously in the same switching state. This self-organizing approach achieves synchronized measurements without adding device complexity.
Data Source
AI summary
The invention relates to a method for operating an electric machine (100) having a power converter (100) and multiple phases, in which method, phase currents flowing through the phases during operation of the electric machine (100) are determined and are used for continued operation of the electric machine (100), the phase currents being determined taking account of a fundamental wave and at least one harmonic of the current profile of each phase current.