RST Controller with Estimator for Periodic Disturbance Rejection
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Solution Overview
Problem
Existing methods for rejecting periodic disturbances in axis-position control loops, particularly in motor systems, face challenges such as varying disturbance frequencies and increased computational complexity when transitioning from speed control to position control, leading to suboptimal robustness and potential instability.
Innovation Solution
A method is introduced that incorporates an RST-type controller with an additional estimator block for load disturbance estimation and a modifier block with frequency-dependent parameters, allowing for dynamic adjustment of sensitivity functions to reject sinusoidal disturbances while maintaining robustness by ensuring predefined margin levels, and enabling optional sinusoidal disturbance rejection based on real-time computations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If adaptive control methods are used to estimate and compensate for ripple amplitude and phase, then periodic disturbances are attenuated, but the compensation is only partial when ripple amplitudes are not constant over 360 degrees
Solution Approach 1:
The controller uses dynamic gain sequencing based on angular position to adaptively reject periodic disturbances. The gains are varied as a function of the angular position of the axis, allowing the controller to effectively compensate for non-sinusoidal ripple patterns that change throughout the rotation cycle, thereby resolving the limitation of static adaptive control methods
Solution Approach 2:
The invention changes the parameters (gains) of the controller based on the angular position of the axis. By sequencing the gains according to the angular position, the controller can adapt to the varying characteristics of periodic disturbances throughout the rotation cycle, improving compensation effectiveness for non-constant ripple amplitudes
2Object-affected harmful factors
If sinusoidal disturbance rejection is implemented at variable frequency proportional to angular speed, then periodic disturbances are rejected, but the controller requires gains sequenced according to angular function increasing device complexity
Solution Approach 1:
The RST controller is designed to perform multiple functions: it provides robust stability for the position control loop while simultaneously implementing variable-frequency sinusoidal disturbance rejection. By integrating both functions into a single controller structure with gain sequencing, the invention avoids the need for separate control systems, thereby managing complexity while achieving comprehensive disturbance rejection
3Reliability
If RST-type controller is used for position control with variable frequency disturbance rejection, then robustness is improved, but computational complexity increases when transitioning from speed control to position control
Solution Approach 1:
The controller parameters, including the gain sequencing functions and disturbance rejection parameters, are pre-computed and stored as lookup tables based on angular position. During real-time operation, the controller simply retrieves and applies the appropriate pre-computed parameters rather than calculating them on-the-fly, significantly reducing computational complexity while maintaining robust performance
Data Source
AI summary
A method and a device for robust rejection of the periodic disturbances in a motor-position control structure of the RST type, wherein the assembly including the motor, the position sensor, the element for computing the functions 1/So(z−1) and Ro(z−1), in a loop, is called central controller. Within the framework of the invention, to the central controller are added two additional computing elements, the first one being an estimator block E(z−1) and the second one a modifier block Q(z−1), as well as an additional loop, the estimator block E(z−1) allowing a load disturbance estimation signal {circumflex over (v)}(t) to be computed, the modifier block Q(z−1) receiving the load disturbance estimation signal {circumflex over (v)}(t) as an input, to produce a modified signal, which is applied to a negative input of an additional adder arranged upstream from the element for computing the function 1/So(z−1) and then forming the additional loop, the modifier block having a variable transfer function.