Grid-Side Current Control for Converter Passivity at Resonance
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Solution Overview
Problem
Power electronics converters exhibit active behavior in specific frequency ranges, leading to the stimulation of oscillations and resonances in power grids, as they behave as energy sources rather than consumers, which is undesirable for grid stability.
Innovation Solution
Implementing a control system with a grid-side current controller that employs multiple feedback control algorithms with different control cycle times and proportional gains, where faster feedback paths counteract slower control outputs within Safe Operating Area limits to enhance converter passivity and prevent active power injection into the grid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a time discrete current controller is used in power electronics converters, then the converter can be controlled to deliver power to the grid, but the delay introduced by the time discrete control causes active behavior in the frequency range between 300 to 1000 Hz
Solution Approach 1:
The controller is divided into multiple independent feedback control algorithms operating at different cycle times. The first feedback control algorithm operates at a first control cycle time for overall power control, while the second feedback control algorithm operates at a second control cycle time (faster) specifically to counteract active behavior. This segmentation allows each algorithm to specialize in different frequency ranges and control objectives.
Solution Approach 2:
The second feedback control algorithm is designed to counteract the active behavior before it can significantly impact the grid. By detecting the active behavior through the faster feedback loop and applying counteracting control actions, the system prevents the harmful effects of resonance stimulation rather than merely responding after the problem occurs.
2Object-generated harmful factors
If the control cycle time is reduced to improve passivity and reduce active behavior, then the converter can better dampen grid oscillations, but the control system complexity increases
Solution Approach 1:
Instead of reducing the control cycle time for all control functions, the system segments the control into two algorithms with different cycle times. The faster second algorithm specifically targets active behavior correction, while the first algorithm maintains the original control cycle time for overall power management. This selective approach improves passivity without unnecessarily increasing complexity across the entire control system.
Solution Approach 2:
The faster control cycle is applied locally only to the feedback loop that needs to counteract active behavior, rather than globally to all control functions. The second feedback control algorithm operates with a shorter cycle time specifically for active behavior correction, while other control functions maintain their original cycle times, optimizing performance where needed without uniformly increasing complexity.
Data Source
AI summary
A method performed by a control system of a power electronics converter. A first part of a grid-side current controller runs a first feedback control algorithm having a first control cycle time and includes at least proportional control using a proportional gain. A third part of the controller runs a third feedback control algorithm having the first control cycle time and acting on an output from the first control algorithm after SOA limits have been applied and includes counteracting the proportional control of the first feedback control algorithm. A second part of the controller runs a second feedback control algorithm having a second control cycle time, less than the first control cycle time, and acting on an output from the third control algorithm with the same polarity as the first control algorithm and includes proportional control using the proportional gain.