Magnetic Bearing Controller AD Sampling Timing for PWM Noise
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Solution Overview
Problem
Magnetic bearing devices face challenges with spike-shaped noise from PWM amplifiers, which leads to vibration due to insufficient noise reduction processing, requiring limitations on PWM control duty ranges and necessitating additional AD converters for simultaneous signal sampling.
Innovation Solution
A magnetic bearing device with a controller that AD-samples current detection signals and modulated signals within specific periods to minimize noise influence, allowing for PWM control based on displacement information without the need for additional AD converters, and incorporating a carrier generator and displacement sensor to optimize sampling timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If filtering processing is applied to reduce spike-shaped noise in current detection signals, then noise reduction effect is improved, but control stability deteriorates due to signal time delay
Solution Approach 1:
The patent applies preliminary action by strategically timing the AD conversion to occur after the spike-shaped noise has naturally attenuated. The controller is configured to perform AD conversion at a timing when the noise amplitude has decreased to an acceptable level, thereby avoiding the need for filtering that would introduce time delay and maintain control stability.
2Object-affected harmful factors
If variable duty range is limited in PWM control to ensure noise attenuation time, then noise reduction is improved, but PWM control flexibility deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-planning the AD conversion timing to occur after noise attenuation. This allows the PWM duty cycle to vary freely within the full range without being constrained by noise considerations, as the noise has already attenuated by the time measurement occurs.
3Device complexity
If multiple signals are simultaneously sampled using a single AD converter, then device complexity is reduced, but sampling accuracy deteriorates due to signal synchronization requirements
Solution Approach 1:
The patent applies periodic action by using a single AD converter to sequentially sample multiple signals in a predetermined periodic sequence. The controller samples current detection signals and sum signals in turn, with each sampling operation timed to occur after noise attenuation. This periodic sequential sampling approach maintains measurement precision while reducing device complexity.
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 reduces vibration caused by noise and eliminates the need for multiple AD converters, ensuring stable control without unnecessary limitations on PWM duty ranges, thereby enhancing the magnetic bearing's performance.
Implementation Method 1
a pair of electromagnets provided for each of multiple control axes and arranged to face each other with respect to a rotor shaft
Implementation Method 2
the amplitude of the sensor carrier is modulated according to an inductance change due to a levitation gap
Implementation Method 3
a switching voltage is applied from a PWM amplifier to the electromagnet coil to supply an excitation current
Data Source
AI summary
When a duration of current noise caused by a PWM control of each excitation amplifier is Td, a cycle of a PWM carrier signal is Tpwm, an on-duty upper limit of the PWM carrier signal under quiet environment without disturbance is Tonu, and an on-duty lower limit of the PWM carrier signal under the quiet environment without the disturbance is Tonl, the AD sampling period includes a first AD sampling period between a point after a lapse of the time Td after a start of the cycle Tpwm and a point after a lapse of a time (Tpwm−Tonu) from the start of the cycle Tpwm, and a second AD sampling period between a point after a lapse of a time (Tpwm−Tonl+Td) from the start of the cycle Tpwm and an end point of the cycle Tpwm.