Motor Drive Weak-Field Current Correction for Voltage-Limited Torque
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional weak field control in motor drive systems leads to surplus current flow and a drop in motor driving efficiency when the current instruction becomes excessively large and the voltage across the motor terminals drops below the maximum output voltage of the inverter.
Innovation Solution
A motor drive device that controls torque based on d-axis and q-axis currents, incorporating a d-axis current instruction generating unit, a current instruction correcting unit to add a positive correction quantity, and a voltage feedback control unit to add a negative correction quantity, ensuring the voltage across the motor terminals does not exceed a given maximum output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage feedback control uses a limiter to correct current instruction only when voltage exceeds maximum output voltage, then the control prevents overvoltage conditions, but the control fails to activate when voltage drops below maximum output voltage causing surplus current flow
Solution Approach 1:
The patent inverts the conventional limiter logic by creating a correction quantity generation mechanism that activates based on voltage being equal to or greater than a reference value, rather than only when voltage exceeds maximum. This inverted approach allows the control to generate appropriate correction quantities in previously unaddressed operating conditions, preventing surplus current flow while maintaining voltage control reliability
Solution Approach 2:
The patent changes the activation parameter of the feedback control from voltage exceeding maximum output voltage to voltage being equal to or greater than a reference value. This parameter change enables the control system to respond appropriately in a broader range of operating conditions, eliminating the surplus current issue while preserving voltage control stability
2Power
If current instruction is increased to meet torque requirements, then torque output is improved, but voltage across motor terminals drops below maximum output voltage causing feedback control to fail
Solution Approach 1:
The patent applies preliminary action by generating correction quantities based on a reference voltage comparison before the voltage drops too low. This allows the control system to proactively adjust the current instruction to prevent the feedback control from failing, ensuring both torque requirements are met and feedback control remains active
Solution Approach 2:
The patent enhances the feedback mechanism by continuously monitoring voltage against a reference value and generating correction quantities accordingly. This improved feedback loop ensures that when current instruction increases for torque requirements, the system responds with appropriate corrections to maintain feedback control activation and prevent operational failures
Data Source
AI summary
A motor drive device controls torque generated by a motor, based on a d-axis current and a q-axis current. The motor drive device includes a d-axis current instruction generating unit that calculates a first d-axis current instruction, a current instruction correcting unit that generates a positive correction quantity that is added to the first d-axis current instruction when a voltage across terminals of the motor is equal to or larger than a given value, and a voltage feedback control unit that generates a negative correction quantity that is added to the first d-axis current instruction to prevent the voltage across the terminals of the motor from exceeding a given maximum output voltage. The motor drive device controls the torque, based on a second d-axis current instruction created by adding the positive correction quantity and the negative correction quantity to the first d-axis current instruction and on a q-axis current instruction.