Electric Machine Phase Current Synchronization With Harmonic Compensation
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Solution Overview
Problem
In electrical machines, particularly those in the automotive sector, accurately measuring phase currents is crucial for torque control to meet safety standards like ISO 26262, but phase currents cannot always be measured simultaneously due to time offsets in control, leading to inaccuracies and potential safety violations.
Innovation Solution
The method involves determining phase currents by accounting for both the fundamental wave and specific harmonics, such as the fifth and seventh harmonics, and converting them to a common time for precise control, allowing for accurate torque regulation and diagnosis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If phase currents are measured at different times due to time offsets in PWM control, then all phases can be controlled with time offsets, but measurement precision deteriorates because currents cannot be measured simultaneously
Solution Approach 1:
The patent applies preliminary action by measuring phase currents at optimal moments (middle of on-time or off-time) before the control cycle completes, and then using mathematical conversion to determine what the currents would have been at a common reference time. This allows the system to prepare accurate current values in advance for torque calculation, resolving the contradiction between time-offset control and simultaneous measurement requirements
Solution Approach 2:
The patent introduces an intermediary mathematical model that converts individually measured phase currents (taken at different times) into equivalent simultaneous current values. This intermediary conversion process, based on the relationship between phase currents and torque, acts as a mediator that reconciles the time offsets in measurement with the requirement for simultaneous current values in torque control
2Manufacturing precision
If phase currents are converted to a common time point, then torque control accuracy improves, but device complexity increases due to additional conversion calculations
Solution Approach 1:
The patent applies parameter changes by transforming phase current measurements from the time domain to an equivalent state at a common reference time using mathematical relationships. Instead of adding complex hardware, the system changes the temporal parameter of the current measurements through calculation, achieving accurate torque control while keeping the physical system simple
3Device complexity
If only fundamental wave is considered in phase current conversion, then calculation simplicity is maintained, but measurement precision deteriorates due to harmonic distortions
Solution Approach 1:
The patent applies the taking out principle by separating the fundamental wave component from harmonic components in the phase current measurements. The conversion process specifically extracts and utilizes only the fundamental wave portions of the currents for torque calculation, deliberately excluding harmonic distortions. This extraction approach maintains calculation simplicity while improving accuracy by focusing only on the relevant fundamental components
Data Source
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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.