Electric Motor Speed Control With Low-Chattering Sliding Current
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Solution Overview
Problem
Existing speed controllers for electric motors face challenges such as slow response to load changes, leading to motor speed variations that cause vibration and noise, particularly in applications like air conditioners and refrigeration units. Additionally, sliding mode controllers suffer from chattering due to the use of sgn and sqrt functions.
Innovation Solution
A speed controller that calculates the switching current using proportional and integral control with a sliding surface, avoiding the use of sgn and sqrt functions. This approach minimizes chattering and simplifies implementation, allowing for faster and more stable motor speed control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If sliding mode control uses sgn function for switching current calculation, then control response speed is improved, but chattering occurs causing vibration and noise
Solution Approach 1:
The patent replaces the discontinuous sgn function with a continuous approximation function that changes parameters smoothly. The switching current calculation uses a continuous function instead of abrupt sign changes, maintaining fast response while eliminating chattering vibrations and noise in the motor system.
2Measurement precision
If sliding mode control uses sqrt function for switching current calculation, then control precision is improved, but computational complexity increases
Solution Approach 1:
The patent replaces computationally expensive sqrt function with simpler mathematical operations that achieve comparable control precision. This substitution reduces computational complexity and makes the controller more suitable for implementation on resource-constrained microcontrollers while maintaining adequate control accuracy.
3Ease of operation
If conventional PI control is used for speed control, then implementation simplicity is maintained, but responsiveness to load changes deteriorates
Solution Approach 1:
The patent segments the control current into two distinct components: switching current that provides rapid response to load changes, and dynamic current that handles steady-state control. This segmentation allows the system to combine the responsiveness of sliding mode control with the simplicity of PI control implementation.
Solution Approach 2:
The switching current component acts as a preliminary action that anticipates and responds to load changes before they significantly affect motor speed. By calculating and applying the switching current based on sliding surface error, the system proactively compensates for disturbances, improving responsiveness while maintaining implementation simplicity.
Data Source
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AI summary
In one aspect, a speed controller (43) for controlling operation of an electric motor (41) calculates a reference current Iqr, which is for use in calculating drive currents for the electric motor (41), as the sum of a switching current Iq_sw_PI and a dynamic current Iq_eq. The switching current Iq_sw_PI is calculated using at least proportional control with a sliding surface s that is an error function based on the electrical reference speed ωref of the electric motor (41) and the electrical measured speed ωmeasured of the electric motor (41). In another aspect, a speed controller (43) calculates an estimated load torque T̂L using at least proportional control with a sliding surface sobs of a load observer (60) that is an error function based on the rotor speed ωmeasured_r and the estimated speed ω̂ of the rotor.