Motor Current Determination with Filter Delay Compensation
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Solution Overview
Problem
Existing methods for controlling the current of electric motors and generators fail to effectively compensate for time delays caused by filters, particularly in high-speed devices with small synchronous resistance and inductance, leading to degraded performance due to high-frequency noise and increased delay times.
Innovation Solution
A method and device that determine the time delay caused by filters by analyzing the phase characteristics versus the operating frequency, using low-pass, anti-aliasing, and finite impulse response filters, and compensate for this delay to improve current control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter of second or more higher order is installed to remove electrical noise, then noise elimination performance is improved, but time delay increases resulting in degraded control performance
Solution Approach 1:
The patent applies preliminary action by calculating the group delay of the filter in advance based on its transfer function characteristics, and using this pre-calculated delay value to compensate for the phase shift before control operations are performed. This allows the system to proactively correct the time delay issue rather than reacting to it after it degrades control performance.
Solution Approach 2:
The patent changes the parameter of group delay by calculating it from the filter's transfer function and using this calculated value to adjust the phase of the current signal. By modifying the phase parameter based on the known group delay, the system compensates for the time delay introduced by the filter while maintaining noise elimination performance.
2Loss of time
If bandwidth of filter is set higher to minimize group delay, then time delay is reduced, but high-frequency noise and switching noise cannot be effectively eliminated
Solution Approach 1:
The patent introduces an intermediary approach by using a lookup table that stores pre-calculated group delay values for different filter configurations. This lookup table acts as a mediator between the filter design and the control algorithm, allowing the system to select appropriate delay compensation values without having to recalculate complex transfer functions in real-time, thus enabling effective noise filtering while maintaining acceptable time delay.
Solution Approach 2:
The patent performs preliminary calculation of group delay values and stores them in a lookup table before actual control operations. This pre-computation allows the system to quickly retrieve and apply appropriate delay compensation values during real-time control, enabling the use of higher-order filters for noise elimination without suffering from excessive time delay.
3Object-affected harmful factors
If low-pass filter and anti-aliasing filter are installed to remove electrical noise, then noise elimination is improved, but delay time increases due to the filters
Solution Approach 1:
The patent changes the phase parameter of the current signal by an amount equal to the calculated group delay. By adjusting the phase parameter based on the known delay characteristics of the filter combination, the system compensates for the time delay introduced by the low-pass and anti-aliasing filters while maintaining their noise elimination functionality.
Solution Approach 2:
The patent implements a feedback mechanism where the group delay value, calculated from the filter's transfer function, is used to adjust the phase of the current signal in a closed-loop manner. This feedback approach ensures that the phase compensation accurately counteracts the delay introduced by the filter combination, maintaining optimal control performance despite the presence of multiple noise-filtering stages.
Data Source
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AI summary
Provided, according to one embodiment, is a method for determining a current of an electric motor or a generator, the method comprising the steps of: acquiring characteristics of a filter for eliminating noise occurring in a process for determining a current of an electric motor or a generator; determining a time delay caused by the filter, on the basis of a change in a phase indicating the characteristics of the filter, the change resulting from a change in an operating frequency of the electric motor or the generator; and determining the current of the electric motor or the generator by compensating the time delay.