Induction Motor Vector Control with Transient Slip Frequency Compensation
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Solution Overview
Problem
Existing induction motor control systems face instability and vibrations in speed control when attempting to enhance speed response due to changes in magnetic flux and primary resistance values, particularly when using m-t coordinates.
Innovation Solution
A power conversion device and motor control system that utilizes stationary coordinates for voltage command generation, incorporating a slip frequency command calculation that includes both steady-state and transient values, allowing for stable speed control by vector control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the speed response of the induction motor is enhanced by increasing the proportional gain and integral gain in speed control, then the speed control accuracy is improved, but the system becomes unstable and vibrations occur due to changes in magnetic flux in m-t coordinates
Solution Approach 1:
The patent changes the coordinate system from m-t coordinates to d-q coordinates for magnetic flux representation. This parameter change in the control approach allows high-gain speed control to be implemented without the instability and vibrations that occur in m-t coordinates, as the d-q coordinate system provides a more stable framework for representing magnetic flux during transient states.
Solution Approach 2:
The patent introduces an intermediary approach by using d-q coordinates as a mediator between the speed control system and the magnetic flux representation. This intermediary coordinate system enables the decoupling of speed and flux control, allowing independent optimization of speed response without adversely affecting magnetic flux stability.
2Adaptability or versatility
If the primary resistance value R1 changes depending on winding temperature, then the motor operates under varying conditions, but torque loss occurs and control accuracy deteriorates in m-t coordinate systems
Solution Approach 1:
The patent changes the coordinate system parameter from m-t to d-q coordinates, which fundamentally alters how the control system handles primary resistance variations. In d-q coordinates, the control equations are less sensitive to R1 changes, thereby reducing torque loss and maintaining control accuracy even when winding temperature and primary resistance vary during operation.
3Device complexity
If a simple steady-state slip frequency calculation is used, then the control structure is simple, but the speed response is slow and cannot achieve high-response speed control
Solution Approach 1:
The patent applies dynamics by transitioning from a static steady-state slip frequency calculation to a dynamic calculation that accounts for transient states. The d-q coordinate system enables the development of dynamic control equations that respond to changing operating conditions, thereby achieving high-speed response without requiring overly complex control structures.
Solution Approach 2:
The patent implements preliminary action by pre-defining the d-q coordinate transformation relationships and slip frequency calculation formulas that work effectively across both steady-state and transient conditions. This preliminary mathematical framework enables fast response without requiring complex real-time adjustments during operation.
Data Source
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AI summary
To provide a power conversion device and a motor control system capable of implementing stable speed control even if a speed response is enhanced. Therefore, there are provided a power converter 2 that converts DC power into AC power and outputs the AC power to an induction motor based on AC voltage command values vu*, vv*, and vw* in stationary coordinates, and a controller CT that calculates the voltage command values in the stationary coordinates by vector control. The controller CT adds, to a steady-state value of a slip frequency determined by a d-axis current (id) , a q-axis current (iq), and a secondary time constant (T2), a transient value determined by differential calculation using the d-axis current (id) and the q-axis current (iq) to calculate a slip frequency command value ωs**.