Phase Current Sensing via Zero-Crossing Gain Calibration
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Solution Overview
Problem
Existing methods for determining phase currents in electric machines of motor vehicles are imprecise and slow due to variations in gain factors of phase current sensors, leading to incorrect current control and inverter deactivation.
Innovation Solution
A method to determine phase currents by identifying zero crossings and using characterization values based on gain factors of phase current sensors, selecting those with the highest gain for current control, and calculating the third phase current from the other two, thereby avoiding incorrect current peaks and expanding the inverter's tolerance range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase current sensors are calibrated using traditional methods (offset calibration and PLL-based gain factor determination), then the calibration can be performed, but the process is slow and imprecise
Solution Approach 1:
The patent applies preliminary action by performing offset calibration beforehand to establish accurate zero-current reference points. This preliminary step enables the subsequent simplified gain factor determination method to work effectively, avoiding the need for time-consuming traditional PLL-based calibration during operation.
Solution Approach 2:
The patent changes the calibration approach from PLL-based frequency/phase adjustment to a time-based method using zero crossing detection. By monitoring the time duration between zero crossings and comparing it with expected values, the system determines gain factors more quickly and precisely without the complexity of traditional PLL algorithms.
2Reliability
If phase current sensors have different gain factors, then measurement variations occur, but this leads to incorrect current control and inverter deactivation
Solution Approach 1:
The patent implements feedback by continuously monitoring zero crossing times and comparing measured phase current characteristics against reference values. This feedback mechanism enables real-time detection of gain factor deviations and allows the system to compensate for sensor variations, maintaining accurate current control despite differences in sensor characteristics.
Solution Approach 2:
The patent replaces the mechanical/electrical PLL-based calibration system with an electronic time-measurement system. By using zero crossing detection and time duration measurement, the system achieves more precise gain factor determination without the speed and complexity limitations of traditional PLL mechanisms.
3Adaptability or versatility
If the inverter operates with tolerance range for peak currents, then operating flexibility is maintained, but sensors with low gain factors cause peak currents to depart from tolerance range
Solution Approach 1:
The patent applies preliminary action by determining accurate gain factors for all phase current sensors before inverter operation begins. This pre-calibration ensures that each sensor's characteristics are known, allowing the control system to compensate for gain variations and maintain reliable peak current control throughout the inverter's extended operating range.
Data Source
AI summary
A method for determining phase currents for current control of an electric machine of a drive system for a motor vehicle is provided. Measured characteristics of the phase currents that are supplied to at least three phases of a set of phases of the electric machine and that are measured by at least three phase current sensors of a set of phase current sensors of the drive system are received. Zero crossings in the at least three measured phase current sensor-specific characteristics are identified, a phase current value of at least one other characteristic is determined, per characteristic, for at least one zero crossing. The phase current values are used for determining a characterization value, describing a gain factor of each phase current sensor, for the respective phase current sensor, and the phase currents for the current control are determined based on the characterization values of the phase current sensors.