Dual-MPU Motor Control for Smooth Electric Power Steering Torque
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Solution Overview
Problem
Conventional electric power steering apparatuses face challenges in maintaining smooth output torque due to torque ripples, which can be exacerbated by mutual interference between inverter circuits and inadequate current detection accuracy.
Innovation Solution
The electric driving apparatus employs two microprocessor units (MPUs) to collaborate in controlling the output of the control unit, allowing for independent control of each stator winding even if one MPU experiences an abnormality, thereby ensuring continuous operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two inverter circuits are provided with two MPUs collaborating to control them, then redundancy and continuous operation capability are improved, but mutual interference between inverter circuits occurs causing torque ripple
Solution Approach 1:
The patent divides the control system into two independent inverter circuits (first inverter circuit and second inverter circuit), each controlled by its own MPU. This segmentation allows independent control of each circuit to minimize mutual interference while maintaining redundancy. Each inverter circuit can operate independently if the other fails, and their separate control prevents synchronized switching that would cause torque ripple.
Solution Approach 2:
The patent implements periodic switching of the inverter circuits with different switching periods or phases. By stagging the switching actions of the two inverter circuits, the patent reduces mutual interference and torque ripple while maintaining continuous motor operation. The periodic action is designed so that when one inverter is switching, the other is in a stable state.
2Speed
If current detection is performed during switching operation, then real-time control is improved, but detection accuracy deteriorates due to switching noise
Solution Approach 1:
The patent performs current detection at specifically timed moments just before or after the switching operation of the inverter circuits. By detecting current at these preliminary or post-action moments when switching noise is minimal, the patent maintains high detection accuracy while still enabling real-time control. The control system uses this timing information to adjust switching commands accordingly.
3Manufacturing precision
If high-voltage-side switching devices are switched frequently for precise control, then control precision is improved, but current detection accuracy deteriorates because switching time becomes shorter than detection time
Solution Approach 1:
The patent detects current at moments just before the high-voltage-side switching devices are activated. This preliminary detection captures the current state before switching noise begins, ensuring accurate measurement even when switching occurs frequently. The detected current value is then used to determine the appropriate switching command, maintaining both precision and accuracy.
Solution Approach 2:
The patent rushes through the switching operation quickly after detection, minimizing the overlap between detection and switching periods. By completing the switching action rapidly after current detection, the patent ensures that the detection period is not compromised by extended switching noise, maintaining detection accuracy even with frequent switching cycles.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables the electric power steering apparatus to maintain stable and smooth torque assistance, even in the event of an abnormality, by ensuring independent control of each stator winding and reducing interference between inverter circuits.
Implementation Method 1
The high-voltage-side switching device and the low-voltage-side switching device of the each-phase switching arm are on/off-controlled based on a predetermined pattern and output three-phase electric power
Implementation Method 2
When its stator windings are energized by the three-phase electric power outputted from the three-phase inverter circuit, the motor of the electric power steering apparatus generates a rotating magnetic field so as to rotate the rotor
Data Source
Figure 1
Figure 2A~2B
Figure 3A
AI summary
An electric driving apparatus includes a motor 2 and a control unit 1 for driving the motor 2; the motor 2 has a stator 20 that is separated from a rotor 23 and is provided with two groups of coil windings; the control unit 1 mainly includes an input circuit 12 for inputting various kinds of information pieces, an output circuit for driving the coil windings of the motor 2, an MPU (10a, 10b) for calculating a control amount based on the information from the input circuit 12 and outputting a control signal to the output circuit; the control unit 1 has two pieces each of the input circuit, the output circuit, and the MPU, and can supply respective electric currents to the windings of the motor or can cut off the supply; the MPUs each have a CPU (10c, 10d) incorporated therein, a trigger circuit 17 for a trigger signal having a predetermined period; the two CPUs synchronize at least control commands in accordance with the trigger signal and output the control commands.