Motor Drive Device Segmentation for Fail-Safe Steering
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Solution Overview
Problem
Conventional electric power steering devices face issues with excessive current flow through inverters and coil groups due to failed control systems, leading to abnormal steering operations and the need for high-rating components, which hinders size and cost reduction.
Innovation Solution
A motor drive device with multiple control systems that individually supply currents to coil groups, featuring a current command value setting unit, controller, and failure detector, where a main computing device executes functions for all systems, and an auxiliary device takes over in case of failure, allowing for fail-safe operation and preventing excessive current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple control systems share a common computing device, then device complexity is reduced, but excessive current flow occurs when the computing device fails, requiring high-rating components
Solution Approach 1:
The patent divides the control system into multiple independent control units (first control unit, second control unit, etc.), each capable of independently controlling its associated inverter and coil group. This segmentation allows the system to isolate failures to specific units while maintaining operation of other units, preventing excessive current flow from affecting the entire system.
Solution Approach 2:
Each control unit is equipped with dedicated failure detection functionality and current command value setting capabilities specific to its controlled components. This local quality ensures that failure detection and current control are tailored to the specific needs of each control unit, enabling precise fault isolation and preventing abnormal current flow from propagating across the entire system.
2Reliability
If high-rating components are used to prevent excessive current, then reliability improves, but device size and cost increase
Solution Approach 1:
By segmenting the control system into independent control units with individual failure detection and current control capabilities, the patent enables each inverter and coil group to be controlled by appropriately-rated components. This eliminates the need for oversized high-rating components that would be required if a single failed control unit could affect the entire system, thereby reducing device weight while maintaining reliability.
3Reliability
If high-rating components are used to prevent excessive current, then reliability improves, but manufacturing cost increases
Solution Approach 1:
The segmented control architecture allows each control unit to use components rated for normal operating conditions rather than requiring expensive high-rating components designed to withstand abnormal current surges. This significantly reduces manufacturing costs while maintaining system reliability through isolated failure containment.
4Device complexity
If feedback control is performed with total current value, then control simplicity is maintained, but abnormal current flow occurs during system failure
Solution Approach 1:
The patent implements separate feedback control loops for each control unit, where each unit independently controls its own current based on its own command value and feedback. This segmentation of control logic prevents abnormal current flow during failures by isolating each control loop, while maintaining control simplicity within each individual unit.
Solution Approach 2:
Each control unit performs feedback control using locally-generated current command values and locally-measured feedback signals. This local quality of control ensures that each unit can independently detect and respond to abnormal conditions without being affected by failures in other units, thereby maintaining control safety while preserving the simplicity of feedback control logic within each unit.
Data Source
AI summary
A motor drive device includes a plurality of control systems that individually supply drive currents to a plurality of coil groups included in a motor. The motor drive device independently sets the current command values for the respective control systems. Based on the set current command values, drive instructions are supplied to drive circuits of inverters with respect to the respective control systems, thereby supplying drive currents from the inverters to the coil groups. The motor drive device detects a failure in any of the inverters and the coil groups with respect to each control system, and stops only the failed control system or causes only the failed control system to fall back. The motor drive device further includes a main computing device, and an auxiliary computing device. Consequently, if the auxiliary computing device is normal even in case the main computing device fails, driving of the motor can be continued using one or some of the control systems.