Motor Drive Apparatus Regenerative Current Protection
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Solution Overview
Problem
Conventional motor drive apparatuses for electric power steering systems fail to manage regenerative currents effectively when an inverter circuit or coil set fails, leading to excessive induced voltages that can break down circuit elements.
Innovation Solution
A motor drive apparatus with multiple inverter circuits, an electric power supply on/off control circuit, a failure detection part, and an on/off control part that detects failures and switches to a regenerative current conduction state to direct induced voltages back to the power source, using semiconductor relays with parasitic diodes to manage power flow and prevent circuit damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power supply relay is turned off to interrupt power supply to the failing inverter circuit, then the reliability of the power supply system is improved by isolating the failure, but the motor cannot regenerate induced voltage back to the battery causing excessive voltage that may break down circuit elements
Solution Approach 1:
The patent introduces a diode as an intermediary component connected between the motor and the battery. This diode allows regenerative current to flow from the motor to the battery while blocking reverse current, serving as a mediator that enables voltage regeneration without requiring the power supply relay to remain closed. This resolves the contradiction by providing a unidirectional current path that protects the system while enabling energy recovery.
Solution Approach 2:
The patent converts the potentially harmful excessive induced voltage into a beneficial regenerative current that charges the battery. By providing a controlled path through the diode, the system transforms the harmful effect of back-EMF during motor rotation into useful energy recovery, even when the power supply relay is open for failure isolation.
2Reliability
If two MOSFETs are connected in series with opposite parasitic diode directions to protect against reverse polarity connection, then the reliability against connection errors is improved, but the device complexity increases
Solution Approach 1:
The patent utilizes the inherent parasitic diodes of the MOSFETs as protective elements against reverse polarity connection. By connecting two MOSFETs in series with opposite orientations, the system leverages the natural body diodes to block reverse current flow, eliminating the need for additional protective components. This self-service approach improves reliability while minimizing added complexity.
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
Ensures continuous motor operation by isolating the failing power supply system and directing regenerative currents safely back to the battery, protecting circuit elements from excessive induced voltages and preventing system failure.
Implementation Method 1
A motor generally operates as a generator, which generates an induced voltage when its rotary shaft is rotated by an external force.
Implementation Method 2
The MOSFET has a parasitic diode. In view of a possibility that a power source is connected in reverse polarity through error, two MOSFETs are connected in series so that flow directions of free-wheeling currents of respective parasitic diodes are opposite to each other.
Data Source
AI summary
When a failure detection part detects a failure in an inverter circuit in a first power supply system, a drive control part stops the inverter circuit from driving a motor. An on/off control part turns off a first power supply relay of a power supply on/off part. Under a state that the inverter circuit stops a motor driving operation, a first coil set of the motor generates an induced voltage by rotation caused by an external force. The induced voltage is regenerated to a battery from the inverter circuit through a second power supply relay and a parasitic diode of the first power supply relay. Thus, circuit elements in the power supply system, which is failing, are protected from breaking down.