Fault-Tolerant PM Motor DC Bus Overvoltage Control
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Solution Overview
Problem
In multi-channel permanent magnet motor systems, particularly in aerospace applications, faults in one channel can lead to induced back emf causing DC bus overvoltage, potentially damaging power components due to unregulated regenerative power flow, especially in systems designed for size/weight reduction where back emf exceeds component voltage ratings.
Innovation Solution
Implementing a control method that monitors operating conditions and faults, applying field weakening, regenerative, or short circuit configurations to maintain DC bus voltage below the overvoltage threshold, using fault identifying circuitry to manage specific fault types and adjust control techniques based on motor speed and back emf.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the system is designed for size and weight reduction with higher back emf, then torque/power density is improved, but DC bus overvoltage risk increases during faults
Solution Approach 1:
The control circuit proactively detects faults and applies protective control actions (field weakening, regenerative braking, or short circuiting) before DC bus overvoltage can occur. This preliminary anti-action prevents the harmful effect by counteracting the back emf that would otherwise cause overvoltage during fault conditions.
Solution Approach 2:
The system dynamically changes operating parameters by applying field weakening control to reduce the back emf constant, or by switching to regenerative braking mode to convert excess energy back to the DC bus, or by short circuiting motor terminals to dissipate energy. These parameter changes allow the system to maintain high power density while preventing DC bus overvoltage during faults.
2Reliability
If multi-channel redundancy is implemented for fault tolerance, then system reliability is improved, but device complexity increases
Solution Approach 1:
The control circuits of multiple channels are merged into a coordinated fault management system. When a fault is detected in one channel, the control circuit integrates information from both channels and applies unified protective control strategies, allowing the healthy channel to compensate while maintaining simplified overall control logic.
Solution Approach 2:
The control circuit is designed with universal fault detection and protective control capabilities that can handle various fault types (open circuit, short circuit, overcurrent) across multiple channels. This multi-functional design allows a single control architecture to manage redundancy without requiring separate complex control paths for each fault scenario.
3Productivity
If fault tolerant operation continues after detecting a fault, then system availability is improved, but risk of permanent damage from unregulated back emf increases
Solution Approach 1:
The control circuit continuously monitors operating conditions including current, voltage, and fault status in real-time. Based on this feedback, it dynamically adjusts control strategies to maintain safe operation during fault conditions, applying field weakening or regenerative braking as needed to prevent back emf from exceeding safe levels while allowing continued productive operation.
Solution Approach 2:
The system transitions dynamically between different operational modes during fault conditions. It can switch from normal operation to field weakening mode, then to regenerative braking mode, or to short circuit protection mode depending on the severity and type of fault. This dynamic adaptability allows continued operation when safe while preventing damage when conditions deteriorate.
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
Prevents DC bus overvoltage and reduces risk of permanent damage to motor components by effectively managing induced back emf during faults, ensuring continued operation and reducing drag torque and torque ripples.
Implementation Method 1
applying field weakening, regenerative, or short circuit configurations to maintain DC bus voltage below the overvoltage threshold
Implementation Method 2
faults in one channel can lead to induced back emf causing DC bus overvoltage, potentially damaging power components due to unregulated regenerative power flow
Data Source
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AI summary
The technology disclosed herein relates to methods and apparatus for controlling channels of a multi-channel fault tolerant electric motor system experiencing a particular fault, the control maintaining the voltage in the respective DC bus of the channel with the fault below the DC bus overvoltage threshold for that channel, the particular fault being one that as a result of the continued rotation of the rotor of the motor could potentially cause the voltage in the respective DC bus for the channel with the fault to increase above a DC bus overvoltage threshold for that channel.