Inverter Phase Current Control for Electric Power Steering Motor
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Solution Overview
Problem
In rotary electric machine controlling apparatuses, increasing inverter phase currents to compensate torque during single-system driving can lead to irreversible demagnetization of permanent magnets, reducing magnetic flux and torque output.
Innovation Solution
The solution involves suppressing demagnetizing fields in permanent magnets by increasing inverter phase currents supplied to normal inverters, allowing for higher current supply without causing irreversible demagnetization, thereby enhancing output while maintaining torque properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If inverter phase currents are increased to compensate torque during single-system driving, then torque output is improved, but irreversible demagnetization of permanent magnets occurs
Solution Approach 1:
The armature winding is divided into two independent three-phase groups (first armature winding 30-1 and second armature winding 30-2), each connected to separate inverters (305 and 306). This segmentation allows the system to operate with one inverter disabled during single-system driving, isolating the demagnetization risk to only the rotor portion exposed to the active inverter's magnetic fields.
Solution Approach 2:
The patent applies different current limits to different phases based on their exposure to demagnetizing fields. The control unit 123 sets a first current limit for phases connected to the abnormal inverter and a second, higher current limit for phases connected to the normal inverter, allowing optimized current distribution that maximizes torque while protecting vulnerable permanent magnets.
2Productivity
If inverter phase currents are increased during single-system driving, then output is improved, but demagnetizing fields increase causing torque degradation
Solution Approach 1:
The control unit dynamically adjusts current limits based on system operating conditions. During single-system driving, it sets differentiated current limits (first current limit for abnormal system phases, second current limit for normal system phases) to optimize the balance between output productivity and torque maintenance, preventing demagnetization while maximizing usable power.
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
This approach enables increased output from the rotary electric machine by preventing irreversible demagnetization of permanent magnets, ensuring stable torque generation during single-system driving.
Implementation Method 1
a rotor 20 that has: a rotor core 21; a rotating shaft 22 that is inserted into and fixed to a central position of the rotor core 21; and permanent magnets 23 that are fixed to the rotor core 21
Implementation Method 2
a stator 1 that has: an annular stator core 2; and an armature winding 3 that is mounted to the stator core 2
Implementation Method 3
two inverters 305, 306 that supply three-phase electric power to the armature winding 3
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
The present invention provides an electric driving apparatus and an electric power steering apparatus that enables improvements in output while suppressing the occurrence of irreversible demagnetization of permanent magnets during single-system driving. In the present electric driving apparatus, coils that constitute a first armature winding and coils that constitute a second armature winding are arranged so as to alternate in a circumferential direction, and a control portion is configured so as to perform single-system driving when one of a first system and a second system fails, the single-system driving stopping driving of an inverter of the system that has failed, and controlling driving of the inverter of the system that has not failed to supply inverter phase currents to an armature winding of the system that has not failed such that the inverter phase currents are set to a second upper limit value that is greater than a first upper limit value.