Permanent Magnet Motor Speed Command Correction Under Power Limits
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Solution Overview
Problem
Existing power conversion devices fail to effectively limit both power and current in a field weakening region, leading to potential overcurrent issues when large load torque is applied, which can disrupt stable operation.
Innovation Solution
A power conversion device with a speed command correction computation unit that adjusts the speed command value based on speed information, torque command, and primary current to limit current and power within predetermined limits, preventing overcurrent and ensuring stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If speed control input is restricted to limit power output, then power is controlled within limit values, but primary current becomes excessive when large load torque is applied
Solution Approach 1:
The invention changes the control parameters from only power-based speed command correction to a dual-parameter approach that simultaneously considers both power and current magnitude. By computing correction values based on both power limit values and current magnitude limit values, the system adapts the speed command to satisfy both constraints, resolving the contradiction between power control and current protection.
2Adaptability or versatility
If d-axis current command value is not limited, then magnetic flux control is flexible, but current becomes excessive causing operation disruption
Solution Approach 1:
The invention introduces current magnitude limit values as a new control parameter that constrains the d-axis current command value. This parameter change maintains the flexibility of magnetic flux control through d-axis current adjustment while preventing excessive current conditions that would disrupt operation, by computing speed command corrections based on both power and current magnitude constraints.
Data Source
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AI summary
Provided is a power converter in which both power and a current are restricted to realize highly stable control characteristics. A power conversion device 100 includes a permanent magnet motor 1, a power converter 2 that supplies power to the permanent magnet motor 1, and a speed command correction computation unit 11, 11a, 11b, 11c, or 11d that corrects a speed command value ωr* in accordance with speed information ωrc, a torque command value τ*, and a primary current ic. The speed command correction computation unit 11, 11a, 11b, 11c, or 11d computes a limit value of the power to limit a current value of the permanent magnet motor 1 to a predetermined limit value imax* or less if load torque that is larger than a torque value of the permanent magnet motor 1 which varies depending on a direct current voltage of the power converter 2 is applied, and corrects the speed command value ωr* in such a way that the power does not increase to the limit value of the power.