PM Machine Control via Dynamic Axis Switching
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Solution Overview
Problem
Current field-weakening techniques for permanent magnet (PM) machines, particularly d-axis current control, are inadequate for weak flux PM machines at high velocities and large demagnetizing currents, leading to instability and limited control over stator voltage, especially during transient operations and parameter mismatches.
Innovation Solution
A system and method for controlling PM machines that generate modified d-axis and q-axis voltage commands based on current commands, using a field-weakening voltage loop to correct errors and regulate stator voltage, transitioning between d-axis and q-axis current control depending on torque levels to maintain stability and efficiency across varying load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If d-axis current control is used to field-weaken the back EMF in strong magnet flux PM machines, then the back EMF is reduced, but the control becomes inadequate for weak flux PM machines at high velocity with large demagnetizing current
Solution Approach 1:
The patent implements dynamic switching between d-axis current control and q-axis current control based on operating conditions. The controller selectively activates d-axis control for strong flux machines at moderate speeds, while transitioning to q-axis control for weak flux machines at high speeds with large demagnetizing currents, ensuring optimal and stable control across all operating ranges
Solution Approach 2:
The patent changes the control parameter from d-axis current to q-axis current based on machine characteristics and operating conditions. By monitoring machine flux strength, velocity, and demagnetizing current levels, the system adapts the control strategy to use the appropriate axis current control mode, resolving the inadequacy of fixed d-axis control
2Stability of the object's composition
If look-up tables are used for feed-forward control, then steady state control is stable, but transient operations and parameter mismatches cause voltage deviations
Solution Approach 1:
The patent introduces feedback control mechanisms that continuously monitor actual machine parameters and compare them with look-up table predictions. When deviations are detected during transient operations or parameter mismatches, the feedback loop generates corrective voltage commands to maintain accurate control, combining the steady-state accuracy of look-up tables with the adaptive response of feedback control
Solution Approach 2:
The patent uses look-up tables to pre-calculate optimal control parameters for steady state operation, providing stable baseline control. Additionally, the system prepares for transient conditions by implementing real-time parameter adaptation and feedback correction mechanisms that activate when deviations occur, ensuring both steady-state stability and transient responsiveness
3Power
If negative d-axis current is increased to reduce total flux, then the d-axis flux is reduced, but the total voltage magnitude increases causing instability
Solution Approach 1:
The patent inverts the conventional approach by using q-axis current control instead of increasing negative d-axis current to reduce total flux at high speeds. This alternative control strategy achieves flux reduction and voltage control without the destabilizing effect of increased total voltage magnitude, resolving the contradiction between flux control capability and voltage stability
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 provides stable and efficient control of PM machines under light, no-load, and high-load conditions, ensuring dynamic response and maintaining current regulation within voltage limits, even under non-ideal operating parameters.
Implementation Method 1
the presence of the magnet generates a magnetic flux, even when lacking a stator current. This flux typically results in a back electromotive force (EMF) that is proportional to the motor speed
Data Source
AI summary
Methods and systems are provided for controlling permanent magnet machines under varying loads. The method comprises generating a d-axis voltage command and a q-axis voltage command, producing a modified d-axis current command based on the q-axis voltage command and a d-axis current command, converting the modified d-axis current command to a modified d-axis voltage command, and transmitting the modified d-axis voltage command and the q-axis voltage command to the PM machine. The d-axis voltage command is based on a d-axis current command.