Brushless DC Motor Safe-State Control Using Independent ASIC Braking
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Solution Overview
Problem
Existing motor control systems for brushless DC motors face challenges in safely transitioning to a safe operating state during malfunctions, particularly due to errors in the electronic drive control system, which can reduce the likelihood of achieving high safety requirements levels.
Innovation Solution
A motor control device with an application-specific integrated circuit (ASIC) that independently controls the power converter's electronic switches to set the motor into a safe operating state, utilizing a brake bit register, counting register, and timer to manage braking and commutations, ensuring a controlled transition without relying on the programmable control unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the programmable control unit is used to control the motor into a safe operating state, then the system can be operated flexibly, but the reliability is reduced due to errors like bit flips in the control unit
Solution Approach 1:
The control system is segmented into two independent parts: a programmable control unit for normal operation and a hardwired safety circuit for safe operating state transitions. The safety circuit is electrically isolated from the programmable control unit, preventing error propagation while maintaining control flexibility through the programmable unit during normal operation.
Solution Approach 2:
A hardwired safety circuit acts as an intermediary between the error detection mechanism and the power converter. This intermediary directly controls the power converter switches based on error signals, bypassing the programmable control unit to ensure reliable safe state transitions even when the programmable unit fails.
2Loss of time
If the motor is braked immediately upon error detection, then the safety response time is reduced, but the mechanical stress and potential damage increase
Solution Approach 1:
The system performs preliminary action by detecting errors and initiating safe state transitions before catastrophic failure occurs. The hardwired safety circuit continuously monitors for errors and automatically initiates the safe operating state sequence, including controlled braking, before the system reaches a dangerous state.
Solution Approach 2:
The braking process involves controlled parameter changes where the power converter switches are gradually adjusted to reduce motor speed. The system changes the switching states of the power converter in a controlled sequence, allowing the motor to decelerate smoothly rather than being abruptly stopped, thereby reducing mechanical stress.
3Use of energy by moving object
If the power converter is controlled by pulse width modulation during normal operation, then the motor efficiency is improved, but the complexity of the control system increases
Solution Approach 1:
The control system is divided into a programmable control unit that handles complex PWM control for motor efficiency, and a separate hardwired safety circuit that handles only the simple task of detecting errors and initiating safe state transitions. This segmentation allows PWM control to maintain motor efficiency while the safety circuit adds minimal complexity for its specific function.
Data Source
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AI summary
The invention relates to a motor control device (1) for a three-phase brushless DC motor (2). The motor control device (1) comprises a converter (3), which has an electric half-bridge (3.1, 3.2, 3.3) with two electronic switches (H1, H2, H3, L1, L2, L3) for each phase of the brushless DC motor (2), and an integrated application-specific circuit (4) for actuating the electronic switches (H1, H2, H3, L1, L2, L3) of the converter (3). The integrated application-specific circuit (4) can be controlled by a programmable control unit (9) in a normal mode, has a first interface (AAD) for receiving an error signal (5) which signals a malfunction, and is designed to set the converter (3) to a defined operating state (High_Z) independently of the programmable control unit (9) after receiving the error signal (5).