Master-Follower Drive Control Using Estimated Speed Feedback
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Solution Overview
Problem
Existing master/follower drive arrangements for electric motors face instability issues, particularly when operating close to zero speed in open-loop mode, due to motor model instability and the challenge of synchronizing follower motors with slowly accelerating master motors.
Innovation Solution
A method and computer program for operating a drive arrangement that determines an estimated speed of the master motor and transfers it to the follower drive, allowing the follower drive to operate in a pseudo-closed-loop mode without the need for encoders, thus maintaining accurate operation and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If follower drives are operated in torque control mode to evenly share the load, then load distribution is improved, but motor model instability occurs when operating close to zero speed in open-loop mode
Solution Approach 1:
The patent implements feedback by using the estimated speed from the master motor model as a reference for the follower drive's speed controller. This creates a closed-loop control system where the follower drive receives speed feedback from the master drive's estimated speed, allowing stable operation near zero speed without requiring encoders on follower motors. The feedback mechanism resolves the instability issue by providing speed reference information that prevents the motor model from becoming unstable.
Solution Approach 2:
The patent introduces an intermediary approach by using the master motor's estimated speed as a mediator between the master and follower drives. Instead of directly controlling the follower in open-loop torque mode (which causes instability), the estimated speed acts as an intermediary signal that enables stable follower control. This intermediary speed reference allows the follower drive to operate reliably without direct speed sensing.
2Measurement precision
If encoders are installed on follower motors for accurate speed control, then control precision is improved, but device complexity and costs increase
Solution Approach 1:
The patent applies the copying principle by using the master motor's estimated speed as a copy or reference for the follower drive's speed control. Instead of installing encoders on follower motors to directly measure their speed, the system copies the master's estimated speed information and uses it as the follower speed reference. This copying approach achieves accurate speed control without the complexity and cost of additional encoder hardware on follower motors.
Solution Approach 2:
The master drive's motor model serves itself by generating the estimated speed that is then transferred to control the follower drive. The system utilizes the master drive's own estimation capability to provide control information for the follower, eliminating the need for separate speed sensing on follower motors. This self-service approach reduces device complexity while maintaining control precision.
Data Source
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AI summary
A method for operating a drive arrangement (22) is described. The drive arrangement (22) comprises a master drive (24) for driving a master motor (30) and at least one follower drive (26) for driving a follower motor (32), wherein the master motor (30) and the follower motor (32) are drivable independent from each other via the master drive (24) and, respectively, the follower drive (26) and are physically coupled to the same load (34). The method comprises determining an estimated speed (nest) of the master motor (30); transferring the estimated speed (nest) to the follower drive (26); and operating the follower drive (26) by using the estimated speed (nest) of the master drive (24) as a follower speed reference (nref_f) for the follower drive (26).