Power Conversion Device Frequency Correction for Regenerative Speed Control
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Solution Overview
Problem
Existing control methods for induction motors during regenerative operations suffer from deteriorated speed control characteristics due to deviations from ideal vector control states, specifically with the q-axis secondary magnetic flux not being zero, leading to torque shortages and instability.
Innovation Solution
A power conversion device with a frequency correction calculation unit that adjusts the output frequency based on d-axis voltage corrections and speed estimation, incorporating proportional and integration control configurations to maintain accurate q-axis secondary magnetic flux, thereby stabilizing speed control during regenerative operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the q-axis secondary magnetic flux is set to a negative value during regenerative operation, then robustness is secured and torque reduction is prevented, but speed control characteristics deteriorate due to deviation from ideal vector control state
Solution Approach 1:
The invention dynamically switches the q-axis secondary magnetic flux control strategy based on operating conditions. During motor operation, the q-axis secondary magnetic flux is controlled to zero for ideal vector control. During regenerative operation, it is switched to negative value control to prevent torque reduction, while maintaining d-axis magnetic flux at zero to preserve speed control characteristics. This dynamic adaptation resolves the contradiction between robustness and speed control accuracy.
Solution Approach 2:
The invention changes the control parameters (d-axis and q-axis magnetic flux values) based on the operational state of the induction motor. By detecting regenerative operation conditions and adjusting the magnetic flux parameters accordingly, the system achieves both robust torque control during regeneration and accurate speed control during motor operation, eliminating the trade-off between these two performance aspects.
2Measurement precision
If the q-axis secondary magnetic flux is set to zero for ideal vector control, then speed control characteristics improve, but torque reduction occurs during regenerative operation
Solution Approach 1:
The control system dynamically adjusts the q-axis secondary magnetic flux parameter based on operational mode. During motor operation, it maintains zero flux for optimal speed control. During regenerative operation, it switches to negative flux values to generate sufficient torque, preventing the torque reduction that would occur with zero-flux control during regeneration.
Solution Approach 2:
The invention implements parameter changes in the magnetic flux control strategy according to the operational state. By detecting regenerative conditions and modifying the q-axis magnetic flux parameter from zero to negative values, the system ensures adequate torque output during regeneration while maintaining ideal vector control parameters during motor operation.
Data Source
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AI summary
A power conversion device is provided in which stable and high-accuracy speed control characteristics can be obtained even during a regenerative operation. An output frequency value of the power conversion device is controlled according to a speed estimation value or a speed detection value of an induction motor, a slip frequency command value, and a frequency correction value calculated so that a secondary magnetic flux estimation value calculated from a corrected voltage value for current control coincides with or approaches a secondary magnetic flux command value.