Motor Control Device Using Duty Shift for Single Current Sensor Detection
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Solution Overview
Problem
Conventional electric power steering systems with single current detectors face challenges in accurately detecting motor currents due to noise interference and difficulty in ensuring necessary detection time, particularly when one phase is ON and two phases are ON, leading to issues with torque ripple and operation sound performance.
Innovation Solution
A motor controlling apparatus with a duty shift function that uniformly adjusts phase duty command values and a PWM output position changing function that adjusts PWM signal output positions, allowing for current detection at fixed timing using a single current sensor, thereby reducing size, weight, and cost while maintaining torque and sound performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single current detector is used to reduce size, weight, and cost, then device complexity and cost are reduced, but measurement precision and reliability of current detection deteriorate due to noise interference and difficulty in ensuring detection time
Solution Approach 1:
The patent dynamically adjusts the PWM output timing based on the duty command values. By changing the output timing adaptively, the system ensures that current detection occurs during periods when the current is stable and detectable, thus maintaining detection accuracy while using only a single current detector. This dynamic adjustment allows the system to overcome the limitations of fixed timing and ensures reliable current measurement across different operating conditions.
Solution Approach 2:
The patent changes the timing parameters of PWM signal output based on the duty command values. By adjusting when the PWM signals are outputted relative to the duty cycle, the system creates optimal conditions for current detection using a single sensor. This parameter adjustment ensures that the detection window coincides with periods of stable current flow, maintaining measurement precision while reducing hardware complexity.
2Manufacturing precision
If PWM control is used to adjust motor voltage for accurate assist torque generation, then control precision is improved, but torque ripple and operation sound performance deteriorate due to noise interference in current detection
Solution Approach 1:
The patent performs preliminary adjustment of PWM output timing based on duty command values before actual current detection occurs. By pre-positioning the PWM output timing, the system ensures that current detection happens during optimal periods when noise interference is minimized. This preliminary action prevents torque ripple and operation sound issues by ensuring clean current detection data is used for feedback control.
Solution Approach 2:
The patent converts the potential harm of PWM switching noise into a benefit by strategically timing the PWM output and current detection. By aligning the detection window with periods when PWM switching effects are minimal, the system uses the PWM control mechanism itself to create favorable detection conditions, thereby maintaining accurate torque control while minimizing torque ripple and operation sound.
3Adaptability or versatility
If current detection timing is varied to accommodate different duty command values, then adaptability is improved, but device complexity and difficulty of detection increase
Solution Approach 1:
The patent implements a universal control mechanism that handles both PWM generation and timing adjustment through a single integrated process. The PWM output timing is adjusted based on duty command values, and this same timing information is used to trigger current detection. This multi-functional approach provides adaptability across different operating conditions while avoiding the need for separate complex timing control mechanisms.
Data Source
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AI summary
[Problem] An object of the present invention is to provide a motor controlling apparatus that comprises a single current sensor and obtains a maximal duty range that current becomes detectable with realizing size reduction, weight saving and cost reduction and an electric power steering apparatus using the same. [Means for solving the problem] A motor controlling apparatus that calculates each phase duty command value for controlling a motor current by means of control calculation, forms PWM waveforms corresponding to each phase duty command value and drives the motor based on the PWM waveforms by an inverter, comprising: a duty shift function that uniformly either increases or decreases each phase duty command value with keeping differences in each phase duty command value; and a PWM output position changing function that decides output positions of each phase PWM signal, and wherein a single current detector is connected to power supply input side or power supply output side of the inverter, timing that a PWM signal of only one phase becomes ON state or PWM signals of two phases become ON state simultaneously is generated at fixed positions of PWM periods, and the motor current is detected.