EPS Motor Phase Isolation Circuit for Rapid Fault Current Cutoff
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing electric power steering systems lack the ability to instantly isolate electrical current from the motor when a fault is detected, posing potential risks and damage to system components.
Innovation Solution
The system incorporates a phase isolation circuit with bidirectional transient voltage suppressor (TVS) diodes and phase isolation transistors that divert induced current away from the motor drive circuit upon fault detection, ensuring rapid isolation and protection from self-induced currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional motor drive circuits are used without phase isolation, then the system structure is simpler, but the system cannot instantly isolate electrical current from the motor when a fault is detected, posing potential risks and damage to system components
Solution Approach 1:
The motor drive circuit is segmented into multiple independent phases, each with its own isolation transistor and TVS diode. This allows individual phase isolation without affecting other phases, enabling targeted fault containment while maintaining overall system functionality.
Solution Approach 2:
Phase isolation transistors and bidirectional TVS diodes are introduced as intermediary components between the motor controller and motor windings. These intermediaries enable rapid current interruption and transient voltage suppression during faults, protecting the system without requiring complete system shutdown.
2Reliability
If phase isolation circuits with transistors are used, then rapid fault isolation is achieved, but induced currents from the motor can damage the isolation transistors
Solution Approach 1:
Bidirectional TVS diodes are connected in parallel with the isolation transistors to capture and dissipate induced currents from motor windings. This converts the potentially harmful induced currents into a controlled dissipation path, protecting the transistors while maintaining rapid isolation capability.
Solution Approach 2:
The bidirectional TVS diodes are pre-positioned across the isolation transistors to provide immediate protection against voltage spikes and induced currents. When faults occur, the TVS diodes activate instantly to clamp transient voltages, cushioning the transistors from damage before the isolation can be fully established.
3Device complexity
If unidirectional TVS diodes are used, then the circuit is simpler, but they cannot handle bidirectional induced currents from the motor
Solution Approach 1:
Bidirectional TVS diodes are employed to provide universal protection against transient voltages in both directions. These diodes can handle induced currents regardless of polarity, making the protection mechanism universally applicable to all motor winding faults without requiring separate diodes for each current direction.
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
The solution effectively isolates the motor drive circuit from the motor, preventing damage and ensuring rapid fault response within safety-critical time frames, while protecting transistors from induced currents.
Implementation Method 1
a bidirectional transient voltage suppressor (TVS) diode coupled to the phase winding of the electric motor, the bidirectional TVS diode allowing a current to flow bidirectionally therethrough when a voltage across the bidirectional TVS diode exceeds a blocking voltage of the bidirectional TVS diode
Implementation Method 2
a phase isolation transistor configured to operate in a conducting state and a non-conducting state, the phase isolation transistor being coupled to the phase winding of the electric motor
Implementation Method 3
an electric motor comprising a phase winding... the electric motor is able to properly facilitate the steering of the motor vehicle
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An electric power steering system is provided. The electric power steering system includes an electric motor (12), a battery (14) configured to provide power, and a motor drive circuit (18) configured to provide power from the battery (14) to the motor (12). The motor drive circuit (18) includes a set of branches (28a, 28b 28c), each including two transistors (30a, 30b; 30c 30d; 30e, 30f) configured to operate in a conducting or non-conducting state. The electric power steering system includes a phase isolation circuit (20) including a set of phase isolation branches (32a, 32b, 32c), the branches (32a, 32b, 32c) being coupled to the phase windings (26a, 26b, 26c) of the electric motor (12). A phase isolation branch (32a, 32b, 32c) includes a bidirectional TVS diode (36a, 36b, 36c) and a phase isolation transistor (34a, 34b, 34c), the phase isolation transistor (34a, 34b, 34c) being configured to operate in a conducting or non-conducting state. The electric power steering system includes a fault detector configured to detect a fault condition and switch the phase isolation transistors (34a, 34b, 34c) to the non-conducting state in response to detecting the fault condition.