Predictive Grid Voltage Feedforward for Unbalanced Inverter Control
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Solution Overview
Problem
Existing grid-connected reactive power compensation inverters struggle to accurately provide negative sequence current during unbalanced grid conditions, often sacrificing voltage feedforward control or using time-delayed, harmonic-incomplete filtered signals, which hampers their ability to restore balance among the three phases effectively.
Innovation Solution
A control scheme that combines feedforward and feedback controls, using a predictive algorithm to directly feed forward measured grid voltage to the positive sequence control, preserving instantaneous voltage information and including positive, negative, and harmonic components, thereby enhancing the accuracy of output current control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If filtered voltage feedforward signal is used, then device complexity is reduced, but measurement precision and response speed deteriorate due to time delay and loss of harmonic information
Solution Approach 1:
The patent applies preliminary action by predicting future voltage values based on historical voltage data before they actually occur. The predictive controller calculates anticipated voltage feedforward signals in advance, eliminating the need for filtering operations while maintaining signal accuracy and harmonic information intact.
2Device complexity
If voltage feedforward control is given up, then device complexity is reduced, but productivity and response speed worsen due to inability to provide timely negative sequence current
Solution Approach 1:
The patent uses preliminary action by predicting future voltage values before they occur, enabling the controller to prepare appropriate negative sequence current responses in advance. This predictive approach maintains fast response capability without requiring complex filtering or sacrificing voltage feedforward control.
3Device complexity
If filtered voltage signal is used, then measurement precision of instantaneous voltage is reduced, but device complexity is reduced by using simple filtering
Solution Approach 1:
The patent applies preliminary action by predicting voltage values based on historical data patterns before filtering is needed. This predictive method preserves all harmonic information and instantaneous voltage details while avoiding the information loss inherent in filtering operations.
Data Source
AI summary
A system and method for controlling a grid-connected inverter to provide negative sequence current during unbalanced grid operating conditions. The system uses a combination of feedforward and feedback controls to compute voltage signals which are used to control the inverter switches. The system includes both positive and negative sequence current controllers with voltage feedforward terms. The measured grid voltage is directly fed forward to the positive sequence control through a predictive algorithm, so that the instantaneous voltage information is kept, reducing the influence of grid voltage harmonics on the quality of the output current. The predictive voltages include positive, negative and harmonic component information of the grid voltage signals.