Flux Weakening Control for Interior Permanent Magnet Motors
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Solution Overview
Problem
The control of permanent magnet motors generating composite torque becomes unstable due to interference with torque control during flux weakening, leading to uncontrollable motor terminal voltage exceeding the maximum inverter output voltage.
Innovation Solution
A motor control device with a torque computing section, flux weakening angle computing section, and flux weakening amplitude computing section that computes and adjusts the flux weakening current vector to ensure the motor terminal voltage remains within the inverter's maximum output, using a combination of magnet torque and reluctance torque calculations to stabilize the control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flux weakening control is executed by causing negative d-axis current to flow in permanent magnet motors, then the terminal voltage is reduced to within inverter capacity, but the torque control becomes unstable due to interference with the desired torque generation
Solution Approach 1:
The patent segments the current control into two independent components: torque control (q-axis current) and flux weakening control (d-axis current). By separating these functions into orthogonal control dimensions, the patent eliminates the interference between torque generation and flux weakening, allowing each to operate independently without compromising the other's performance.
Solution Approach 2:
The patent utilizes the two-dimensional dq coordinate system to resolve the contradiction by assigning torque control to the q-axis dimension and flux weakening control to the d-axis dimension. This dimensional separation transforms a one-dimensional conflict into a two-dimensional solution space, enabling simultaneous optimization of both torque accuracy and voltage control.
2Reliability
If constant torque curve following control is used in interior permanent magnet motors, then flux weakening control can be performed, but the control complexity increases due to curvilinear torque curve management
Solution Approach 1:
The patent implements dynamic adjustment of the d-axis current based on real-time operating conditions (speed, load, voltage limits) rather than following a fixed curvilinear torque curve. The control system dynamically determines the optimal d-axis current magnitude to achieve flux weakening while maintaining torque accuracy, adapting to changing conditions without requiring complex pre-defined torque curves.
Solution Approach 2:
The patent changes the control parameter from following a complex curvilinear torque curve to directly controlling the d-axis and q-axis currents independently. By transforming the control parameters into the dq coordinate system and managing them separately, the patent simplifies the control logic while maintaining flux weakening effectiveness across varying operating conditions.
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 stabilizes the flux weakening control, preventing torque control disturbances and ensuring the motor terminal voltage is managed within safe limits, enhancing the motor's operational stability and efficiency.
Implementation Method 1
an electric motor which is capable of generating magnet torque and reluctance torque
Implementation Method 2
magnetic flux generated by permanent magnet and magnetic flux generated by the armature current
Data Source
AI summary
A motor control device includes a torque computing section which computes an output torque of an electric motor which is capable of generating magnetic torque by permanent magnets and reluctance torque, a flux weakening angle computing section which determines an angle of a flux weakening current vector that is added to a reference current vector so that a command torque value and the computed torque value correspond with each other, a voltage acquiring section which acquires a terminal voltage of the motor, a flux weakening amplitude computing section which determines an amplitude of the flux weakening current vector so that the terminal voltage of the motor is not more than a maximum voltage applicable to the motor, and a command current computing section which computes a command current vector by adding the flux weakening current vector to the reference current vector.