Motor Control Apparatus for Electric Power Steering
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Solution Overview
Problem
Existing motor control apparatuses for electric power steering systems fail to effectively limit the variations in actual current supplied to the motor during sudden changes in rotational speed, leading to insufficient reduction of impact on the steering mechanism due to sudden stops.
Innovation Solution
The apparatus includes a power converter with switching elements, a motor current detector, a rotational angle measuring unit, and a controller that calculates a voltage command based on motor current parameters and angular acceleration, allowing for voltage corrections to be applied in sequential motor control cycles to reduce current variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the commanded current is limited to the actual current value measured immediately before steering limit situation, then the impact on steering mechanism is reduced, but the current variations due to sudden motor stop cannot be limited when the measured current has already reached the upper limit value
Solution Approach 1:
The patent applies preliminary action by detecting steering limit situations before they fully occur and proactively limiting the commanded current based on predicted current variations. The controller calculates predicted current values considering motor electrical time constants and applies current limits in advance, preventing the harmful current spikes that would otherwise occur during sudden motor stops at steering limits.
Solution Approach 2:
The patent implements feedback by continuously monitoring actual motor current, comparing it with commanded current and predicted current values, and adjusting the current limit accordingly. The controller uses feedback from current sensors and motor state measurements to dynamically modify the commanded current, ensuring reliable current control while preventing harmful current variations during steering limit situations.
2Object-affected harmful factors
If the commanded current is limited after the occurrence of steering limit situation, then the impact reduction effect is achieved, but the response time is delayed and insufficient for effective impact reduction
Solution Approach 1:
The patent detects steering limit situations and applies current limiting in advance before the actual limit is reached. By calculating predicted current values and applying limits proactively, the system eliminates the time delay associated with waiting for the limit situation to occur first, achieving both timely response and effective impact reduction.
Solution Approach 2:
The patent employs dynamic current limiting where the commanded current is adjusted in real-time based on the predicted current trajectory and motor state. The controller dynamically modifies current limits during the control cycle, allowing adaptive response that is both timely and effective in preventing harmful current variations during steering limit situations.
3Object-affected harmful factors
If the commanded current is limited to a value lower than the upper limit value, then the current variations are reduced, but the assist torque control precision is compromised
Solution Approach 1:
The patent changes the parameter of commanded current dynamically based on predicted current values and motor state. Instead of applying a fixed current limit, the controller adjusts the commanded current parameter in real-time, allowing precise assist torque control while simultaneously limiting harmful current variations. The current limit is modified as a function of predicted current, ensuring both current variation reduction and control precision maintenance.
Data Source
AI summary
In an apparatus, an execution determiner determines, for each of sequential first and second motor control cycles, whether to execute a voltage correction task for a voltage command, and obtains, for each of the first and second motor control cycles, a voltage correction as a function of a fundamental voltage correction and the determination result. A voltage corrector corrects, for each of the first and second motor control cycles, the voltage command based on the voltage correction. A correction voltage feedback unit feeds back a value of the voltage correction calculated at the first motor control cycle to a voltage command calculator. The voltage command calculator calculates a value of the voltage command for the second motor control cycle based on the value of the voltage correction fed back from the correction voltage feedback unit in addition to a value of the motor current parameter and a predetermined current command.