Motor Control Unit Switching Modes Based on Phase Current Frequency
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Solution Overview
Problem
Existing motor control units in electric vehicles face challenges in accurately controlling the drive motor due to processor-level faults, leading to potential safety issues and difficulty in ensuring safe operation, especially when rotational speeds are excessively high or low, as conventional methods based on back electromotive force detection have weak anti-interference capability and complex circuitry.
Innovation Solution
The motor control unit detects the current frequency of phase windings in the drive motor to determine operating states of switching transistors, switching to alternate or continuous conduction/cutoff modes based on frequency thresholds, improving control accuracy and safety by using a current detection circuit and control module to manage active short circuit or safety pulse off states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If back electromotive force detection is used to determine motor operating state, then the control system can identify high or low rotational speeds, but the anti-interference capability is weak and the circuit complexity increases
Solution Approach 1:
The patent extracts the essential information needed for control (rotational speed indication) from the complex back electromotive force detection method and replaces it with a simpler current frequency detection approach. By detecting only the frequency component of the current signal rather than analyzing the full back electromotive force waveform, the system achieves the same functional goal with reduced circuit complexity and improved anti-interference capability.
Solution Approach 2:
The patent substitutes the electrical measurement approach (back electromotive force detection) with an alternative electrical measurement (current frequency detection). This replacement eliminates the need for complex differential measurements and filtering circuits required for back electromotive force detection, while achieving the same purpose of identifying motor operational states through a more robust current-based measurement.
2Reliability
If processor-level fault detection is implemented to ensure safety, then safety state control can be achieved, but the control accuracy decreases due to fault conditions
Solution Approach 1:
The patent implements preliminary fault detection mechanisms that monitor processor-level conditions before they compromise control accuracy. By detecting faults early and switching to a simplified current frequency-based control mode, the system maintains safety while accepting reduced control precision during fault conditions. The frequency threshold comparison provides a robust, albeit simpler, control strategy that ensures safety when full control accuracy is unavailable.
Solution Approach 2:
The patent changes the control parameter from precise back electromotive force-based measurements to frequency-based measurements when faults are detected. This parameter substitution maintains safety control by using a more robust measurement that is less susceptible to fault-induced errors, even though it may reduce overall control accuracy. The frequency threshold approach provides a reliable fallback control mechanism.
3Speed
If switching transistors operate in alternate conduction mode at high frequencies, then motor control responsiveness is improved, but safety risks increase due to potential accidents at high rotational speeds
Solution Approach 1:
The patent implements dynamic switching between different transistor conduction modes based on the detected current frequency. When the frequency exceeds a predetermined threshold (indicating high motor speed), the system automatically transitions from alternate conduction mode to continuous conduction mode for upper switching transistors and continuous cutoff mode for lower switching transistors. This dynamic adaptation maintains control responsiveness at normal speeds while preventing safety risks at high speeds.
Solution Approach 2:
The patent applies preliminary anti-action by detecting high-frequency conditions that precede potential safety hazards and preemptively changing the switching transistor operating modes to prevent harmful effects. By switching to a mode that limits motor acceleration or torque production before an accident can occur, the system counteracts the potential harmful effect of excessive speed or sudden torque changes at high rotational velocities.
Data Source
AI summary
Embodiments of this application disclose a motor control unit, a powertrain, and an electric vehicle. Bridge arm midpoints of the three bridge arms of the inverter are respectively connected to three phase windings of a drive motor. In response to a current frequency of at least one phase winding being greater than or equal to a first frequency threshold, three upper bridge switching transistors or three lower bridge switching transistors switch from an alternate conduction mode to a continuous conduction mode or a continuous cutoff mode. In response to a current frequency of at least one phase winding being less than a second frequency threshold, the three upper bridge switching transistors and the three lower bridge switching transistors switch from an alternate conduction mode to a continuous cutoff mode. In embodiments of this application, control accuracy of the motor control unit can be improved.