Electrical Machine Zero-Torque Control Using Limited d-Axis Current
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Solution Overview
Problem
The challenge in controlling electrical machines in vehicles is the risk of torque jumps due to misinterpretation of phase current signs, particularly during transitions from traction to regeneration modes, leading to incorrect switch operation and distorted voltage output.
Innovation Solution
Implementing a computer system that determines 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
1Loss of energy
If the phase current is close to zero during mode transitions, then the current magnitude is reduced, but the sign detection becomes unreliable due to noise leading to potential wrong assessment
Solution Approach 1:
The system performs preliminary action by forcing a non-zero d-axis current component before mode transition occurs. This ensures that the phase current maintains sufficient magnitude to overcome noise interference, allowing reliable sign detection during the transition from traction to regeneration mode or vice versa.
Solution Approach 2:
The system changes the current parameters by introducing a limited non-zero d-axis current component (Id_lim) during mode transitions. This parameter modification ensures the phase current remains above the noise threshold, enabling accurate sign detection without requiring high current magnitude for normal operation.
2Reliability
If dead time is applied to switches to prevent short-circuit, then switch protection is improved, but voltage output distortion occurs when current sign is misassessed
Solution Approach 1:
The system uses feedback by continuously monitoring the phase current sign with enhanced reliability through the forced non-zero current component. This accurate feedback ensures the dead time is applied to the correct switch, preventing both short-circuit protection failures and voltage output distortion caused by misassessed current signs.
Data Source
AI summary
A computer system is provided. The computer system has processing circuitry to determine that zero torque is requested from an electrical machine of a vehicle drivetrain; determine a limited d current within an allowable d current interval, the limited d current being different from an optimum d current to obtain the zero torque request; and control the electrical machine based on the limited d current to obtain the zero torque request.