Electrical Machine Zero-Torque Control for Smooth Mode Transitions
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Solution Overview
Problem
The challenge of torque jumps in electrically driven vehicles due to misinterpretation of phase current signs during transitions from traction to regeneration mode, leading to incorrect switch operation and distorted voltage output.
Innovation Solution
Implementing a computer system to determine a limited d current within an allowable interval, different from the optimum d current, to control electrical machines, ensuring a stronger indication of phase current signs and reducing the risk of torque jumps by using a truncated MTPA map to define the limited d current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dead time is implemented on switches to prevent short-circuit, then switch protection is improved, but torque jumps occur during zero torque transitions due to incorrect current sign detection
Solution Approach 1:
The system performs preliminary action by forcing a non-zero d-axis current before the zero torque transition occurs. This preliminary current ensures that the phase current magnitude is sufficient for reliable sign detection, preventing the torque jumps that would otherwise occur during mode transitions.
Solution Approach 2:
The system changes the d-axis current parameter from its optimal value to a limited non-zero value during zero torque transitions. This parameter change ensures the phase current remains above the noise threshold, enabling accurate current sign detection and proper dead time application without causing torque jumps.
2Measurement precision
If optimum d current is used to obtain zero torque, then torque precision is improved, but phase current sign detection becomes unreliable due to noise
Solution Approach 1:
The system changes the d-axis current parameter from the optimal value (which produces zero torque but also zero phase current) to a limited non-zero value. This parameter modification maintains torque precision while ensuring the phase current magnitude is sufficient for reliable sign detection in the presence of noise.
Solution Approach 2:
The system applies a preliminary non-zero d-axis current to ensure the phase current is sufficiently large for noise-resistant sign detection. This preliminary action occurs during the zero torque transition period, preventing detection errors while maintaining torque control accuracy.
3Reliability
If d current is limited to non-zero value, then current sign detection reliability is improved, but torque control precision deviates from optimal
Solution Approach 1:
The system applies partial action by limiting the d-axis current to a non-zero value only during the critical zero torque transition period. This partial application of the current limitation provides sufficient signal for reliable sign detection without excessively deviating from the optimal torque control, as the limitation is temporary and targeted.
Solution Approach 2:
The system dynamically changes the d-axis current parameter based on operating conditions. During zero torque transitions, the parameter is changed to a limited non-zero value for reliable detection. Outside this critical period, the parameter returns to its optimal value, minimizing the impact on overall torque control precision.
Data Source
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AI summary
A computer system is provided. The computer system comprises processing circuitry configured to: determine that zero torque is requested from an electrical machine (10) of a vehicle drivetrain (11); determine a limited d current (Idlim) within an allowable d current interval (Id_min/max), said limited d current (Idlim) being different from an optimum d current (Idopt) to obtain the zero torque request; and control the electrical machine (10) based on the limited d current (Idlim) to obtain the zero torque request.