Motor Control Device Suppressing Speed Fluctuations
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Solution Overview
Problem
PWM-controlled motors experience abrupt rotational speed changes due to supply voltage fluctuations, leading to issues like sudden changes in fan pressure or abnormal drive sounds, especially when the PWM duty reaches 100% and the motor's rotational speed has not reached the commanded value.
Innovation Solution
A motor control device and method that includes a rotational speed command output unit, a motor rotational speed meter, a PWM duty calculator, and a maximum speed estimator. The maximum speed estimator calculates a maximum rotational speed based on the actual rotational speed and a predetermined upper limit of the PWM duty, restricting the command value to prevent exceeding this maximum speed, thereby stabilizing the motor's speed during voltage fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If feedback control is used to determine PWM duty based on the difference between command speed and detected speed, then the motor can achieve the commanded rotational speed, but when PWM duty reaches 100% the rotational speed cannot be further increased and control becomes impossible
Solution Approach 1:
The system performs preliminary estimation of the maximum achievable rotational speed by calculating what speed would be achieved if PWM duty reaches 100%, based on current motor conditions. This allows the control system to proactively adjust the command value before the PWM duty actually reaches 100%, preventing loss of control capability.
Solution Approach 2:
The system uses feedback from the actual motor rotational speed and current PWM duty to continuously update the estimated maximum speed. This feedback loop enables dynamic adjustment of the command value to maintain effective control while maximizing motor performance.
2Stability of the object's composition
If the command value is simply replaced when PWM duty reaches 100%, then the motor speed can be maintained, but the control response is delayed
Solution Approach 1:
The system proactively restricts the command value based on estimated maximum speed before PWM duty actually reaches 100%. This preliminary action prevents the need for reactive command value replacement, thereby maintaining both speed stability and fast control response without the delays associated with corrective actions.
3Stability of the object's composition
If feedback control suppresses rotational speed changes, then speed stability is improved, but abrupt changes in motor output such as fan pressure or drive sound occur
Solution Approach 1:
The estimated maximum speed acts as an intermediary parameter that mediates between the command value and actual motor speed. By restricting the command value based on this intermediary estimation, the system achieves smooth speed transitions that prevent abrupt changes in motor output, eliminating abnormal sounds and pressure fluctuations while maintaining stability.
Data Source
AI summary
A rotational speed command output unit receives and outputs a command value of a motor rotational speed inputted from outside. A PWM duty calculator calculates a PWM duty based on the command value and an actual rotational speed of a motor. A maximum speed estimator estimates, based on the actual rotational speed measured, a parameter representing a controlled state of the motor, a current PWM duty and a predetermined upper limit of the PWM duty, a maximum rotational speed of the motor to be reached under PWM control with the upper limit of the PWM duty. The command value inputted from outside is restricted not to exceed the maximum rotational speed. In this way, when a motor is PWM-controlled, abrupt changes in the rotational speed of the motor due to supply voltage fluctuations can be suppressed.