Active Filter Phase-Lead Control for Harmonic Current Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The current control methods for parallel active filters, which rely on proportional integral controllers, suffer from delays in arithmetic processing that impede the suppression of harmonic components in power current, particularly when the command value varies significantly.
Innovation Solution
The active filter control device adjusts the phase of the compensating current by leading it with a predetermined phase difference to eliminate delay time, using coordinate systems to synchronize with the AC power supply and simplify the configuration, thereby reducing the harmonic component of the load current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If proportional integral controller is used for current control, then control stability is improved, but control delay increases due to arithmetic processing
Solution Approach 1:
The patent applies preliminary action by predicting future command values based on past command values and their rates of change. The predicted command value is calculated in advance to compensate for the control delay inherent in PI controller arithmetic processing, allowing the system to proactively adjust for the expected lag rather than reactively correcting it after it occurs.
2Speed
If command value varies significantly, then responsiveness is improved, but divergence between command value and compensating current increases due to arithmetic processing delay
Solution Approach 1:
The patent calculates the rate of change of the command value and uses it to predict future command values in advance. This preliminary prediction compensates for the control delay that occurs during arithmetic processing, ensuring that the compensating current accurately tracks even rapidly varying command values without significant divergence.
Solution Approach 2:
The patent employs feedback by continuously monitoring the actual compensating current and comparing it with the predicted command value. The deviation between these values is fed back to the PI controller, which adjusts its output to minimize the error, thereby maintaining accurate current tracking even when command values vary significantly.
3Measurement precision
If control arithmetic processing is performed, then control precision is improved, but time delay increases
Solution Approach 1:
The patent performs preliminary calculations of the command value prediction based on past command values and their rates of change. By computing the predicted command value in advance, the system reduces the actual processing time required during the control loop, while maintaining high control precision through the predictive algorithm.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
Provided is technology for improving, in an active filter, impediment to suppression of a harmonic component of power current caused by arithmetic processing performed by a current controller. The current controller (5) performs processing of generating a three-phase voltage command value V* based on output of a difference current generation unit (3A). The current controller (5) achieves the above-mentioned processing, for example, by performing PI (proportional integral) control, so that a delay time ta occurs. If a deviation Ie is obtained from a command value Ic* and compensating current Ic, the time ta causes a difference between the compensating current Ic and the harmonic component, and becomes an impediment to suppression of the harmonic component of the power current Is. However, by the difference current generating unit (3A) obtaining the deviation Ie from the compensating current Ic and a value Ic*^ obtained by leading a phase of the command value Ic* by a phase corresponding to the time ta, the above-mentioned impediment is eliminated or reduced.