Variable Speed Motor Control for Near-Zero Rotation
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Solution Overview
Problem
Variable speed electric motor systems using induction motors face challenges in controlling the number of rotations near 0 rpm, limiting the degree of freedom of the output shaft, especially when using a combination of constant and variable speed electric motors with a planetary gear transmission device.
Innovation Solution
A control method that adjusts the ratio of forward and reverse direction minimum rotation instructions to control the variable speed electric motor, allowing it to operate within an uncontrollable range by alternating between forward and backward rotations to approximate the desired number of rotations, thereby increasing the degree of freedom of the output shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an induction motor is used as a variable speed electric motor to widen the variable speed range, then the rotation direction can be changed and maximum rotations in both forward and reverse directions are achieved, but it is not possible to hold the number of rotations in the vicinity of 0 rpm
Solution Approach 1:
The patent applies periodic action by alternately operating the variable speed electric motor in forward and reverse directions at minimum rotation speeds. The control device switches between forward direction minimum rotation number instruction and reverse direction minimum rotation number instruction, creating a periodic motion pattern that averages to approximately 0 rpm over time. This allows the output shaft to achieve rotation numbers in the vicinity of 0 rpm that would otherwise be uncontrollable with a standard induction motor.
2Adaptability or versatility
If the variable speed electric motor operates at minimum rotation speeds in forward and reverse directions to achieve uncontrollable rotation ranges, then the degree of freedom of the output shaft is increased, but the motor cannot maintain steady rotation near 0 rpm
Solution Approach 1:
The patent applies dynamics by transitioning from static minimum rotation operation to dynamic alternating operation. Instead of maintaining a fixed minimum rotation in one direction, the control device dynamically switches between forward and reverse directions, adjusting the operation pattern based on the desired output rotation number. This dynamic approach enables the system to achieve and maintain average rotation speeds near 0 rpm while preserving the ability to access uncontrollable rotation ranges.
3Ease of operation
If the control device uses alternating forward and reverse direction minimum rotation instructions to approximate desired rotation numbers, then controllability in the uncontrollable range is improved, but the system complexity increases
Solution Approach 1:
The patent applies universality by designing the control device to perform multiple functions: it controls the variable speed electric motor's rotation direction, adjusts minimum rotation speeds, and calculates appropriate operation patterns for both controllable and uncontrollable rotation ranges. The same control device handles both forward and reverse direction operations, unified the control logic for approximating desired rotation numbers through alternating operations, reducing the need for separate control mechanisms for different operating modes.
Data Source
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AI summary
A control method of a variable speed electric motor system, which includes an electric device (50) and a planetary gear transmission device (10), the control method includes: a step of accepting an instruction for a number of rotations of an output shaft; a step of calculating a number of rotations of a variable speed electric motor based on the number of rotations of the output shaft; a step of determining whether the calculated number of rotations of the variable speed electric motor is in an uncontrollable range; and a step of performing uncontrollable speed range operation for repeatedly and alternately performing a forward direction minimum rotation number instruction for driving the variable speed electric motor at a minimum number of rotations in a forward direction, and a reverse direction minimum rotation number instruction for driving the variable speed electric motor at a minimum number of rotations in a reverse direction, when the calculated number of rotations of the variable speed electric motor is in the uncontrollable range, wherein the electric device comprises: a constant speed electric motor which has a constant speed rotor (52) connected to the constant speed input shaft of the transmission device; and the variable speed electric motor which has a variable speed rotor (72) connected to the variable speed input shaft of the transmission device and controlling number of rotations in the forward direction and the reverse direction, and has the uncontrollable range in which control in a range between the minimum number of rotations in the forward direction and the minimum number of rotations in the reverse direction is not possible.