Magnetic Bearing Current Control Using Estimated Coil Current
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Solution Overview
Problem
Conventional magnetic bearing systems generate significant high-frequency noise due to switching noise from electromagnet power amplifiers and inverters, contaminating current signals and causing undesirable vibration and sound, which complicates control and increases circuit size and cost.
Innovation Solution
A control apparatus that computes an output voltage for electromagnets based on pre-set current command values, using estimated current values instead of detected values to control high-frequency components, and employs a low-frequency feedback circuit and current error correction to suppress noise, reducing the need for expensive current detectors and stabilizing pulse width calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If switching noise from electromagnet power amplifiers and inverters is used to control the magnetic bearing, then the magnetic bearing can be operated, but high-frequency noise contaminates current signals causing undesirable vibration and sound
Solution Approach 1:
The control frequency band is segmented into high-frequency components (controlled by estimated current values to avoid noise) and low-frequency components (controlled by detected current values). This segmentation allows different control strategies for different frequency ranges, eliminating noise contamination in the high-frequency band while maintaining operational control.
Solution Approach 2:
An estimated current value calculation circuit is introduced as an intermediary to provide noise-free current control signals for high-frequency components. Instead of directly using switching noise-contaminated detected current values, the system calculates estimated values based on voltage commands and electromagnetic parameters, acting as a mediator that separates the control function from noise contamination.
2Ease of operation
If detected current values are used to control high-frequency components, then current control is achieved, but noise contamination occurs in the current signals
Solution Approach 1:
The harmful high-frequency noise components are extracted and separated from the current control signal. The system uses estimated current values for high-frequency control, effectively taking out the noise contamination from the control path while maintaining necessary current control functionality.
Solution Approach 2:
Instead of using the actual detected current signal which contains noise, the system creates a copy or estimate of the current value through calculation based on voltage commands and electromagnetic parameters. This copied/estimated value serves the control function without carrying the noise contamination.
3Reliability
If conventional magnetic bearing control systems are used, then the magnetic bearing functions, but circuit size and cost increase due to noise control requirements
Solution Approach 1:
The control system uses readily available voltage command signals and known electromagnetic parameters (inductance, resistance) to calculate estimated current values, making the noise-free control signals self-generated without requiring additional expensive sensors or complex noise filtering circuits.
Solution Approach 2:
The control approach changes from using physical current detection parameters to using calculated current estimation parameters derived from voltage commands and electromagnetic model parameters. This parameter transformation eliminates the need for complex noise filtering hardware while maintaining control functionality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces vibration and noise in magnetic bearings, enabling a smaller, cost-effective magnetic bearing circuit with improved control stability and reduced high-frequency oscillations.
Implementation Method 1
a magnetic bearing is constructed by arranging an upper radial direction electromagnet 105a, a lower radial direction electromagnet 107a, and an axial direction electromagnet 109a
Implementation Method 2
each electromagnet attracts the rotating body 103 in a positive direction or a negative direction of the X axis
Data Source
AI summary
A control apparatus includes a constant storage portion that stores constant values of an electromagnet coil including a resistance value Rm, an inductance Lm, a sampling time Ts, etc. A current storage portion stores previous current command values Ir having been regularly sampled by a microcomputer inside a current control circuit. A low-frequency feedback circuit generates a signal for suppressing an error between DC components and low-frequency components of an input current command value Ir and a detected current value IL and outputs the signal. An output voltage computing circuit calculates, based on the input current command value Ir[n+1], a stored value Ir[n] of the current storage portion, a stored value of a constant storage portion, and the signal of the low-frequency feedback circuit, a voltage for suppling the electromagnet coil with a current in accordance with a command, and outputs the calculated voltage.