Inverter Phase Control for Transformer Inrush Current Limiting
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Solution Overview
Problem
The existing methods for controlling excitation inrush current in transformers connected to a power grid suffer from increased system costs and reliability issues, as they either require additional hardware or can cause power grid failures due to soft-start after voltage reduction.
Innovation Solution
An inverter with a conversion circuit and controller that dynamically adjusts output voltage based on current thresholds, magnetic flux phases, and impedance to prevent transformer saturation, thereby reducing excitation inrush current and maintaining magnetic flux below saturation levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If an additional bypass branch is introduced to prevent transformer saturation, then excitation inrush current is reduced, but system cost increases
Solution Approach 1:
The patent changes the control parameters of the inverter by adjusting the initial phase angle of the output voltage and controlling the switching timing. This parameter adjustment allows the magnetic flux to start from zero or a small value rather than immediately reaching saturation, thereby reducing excitation inrush current without adding physical bypass branches or soft-start equipment.
2Object-generated harmful factors
If soft-start after voltage reduction is used to reduce excitation inrush current, then inrush current is controlled, but power grid reliability deteriorates
Solution Approach 1:
The patent performs preliminary action by pre-controlling the initial phase angle of the output voltage before the transformer is energized. The controller sets the initial phase angle to a specific value (such as 0 degrees or 180 degrees) based on the residual magnetism state of the transformer, ensuring that the magnetic flux starts from a non-saturated state. This preliminary phase control prevents excitation inrush current without requiring voltage reduction or soft-start processes that could affect power grid reliability.
3Device complexity
If full-voltage hard switching is used for transformer connection, then system simplicity is maintained, but transformer saturation and inrush current occur
Solution Approach 1:
The patent implements feedback control by detecting the residual magnetism state of the transformer before energization and using this information to adjust the initial phase angle of the output voltage. The controller monitors the transformer's magnetic state and dynamically adjusts the switching strategy, creating a closed-loop control system that prevents excitation inrush current while maintaining system simplicity through intelligent control rather than complex hardware.
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
Prevents transformer damage and power grid failures by effectively managing excitation inrush current, ensuring reliable power supply by avoiding transformer saturation and maintaining stable voltage levels.
Implementation Method 1
total magnetic flux of the transformer is far greater than saturation magnetic flux of the iron core, and the iron core in the transformer is saturated instantaneously
Implementation Method 2
magnetic flux generated by an operating voltage when the transformer is connected
Implementation Method 3
remnant magnetism that is of the iron core in the transformer and that is before and after the output voltage is reduced
Data Source
AI summary
This application provides an inverter, a power grid power supply system, and a method for controlling an excitation inrush current. The controller adjusts the output voltage of the conversion circuit based on a first phase that is of the output voltage of the conversion circuit and that is during reduction of the output voltage, the magnetic flux of the iron core in the transformer, an output voltage that is of the conversion circuit and that is after the output voltage is reduced, and the target voltage value, so as to increase the output voltage of the conversion circuit and keep the magnetic flux of the iron core less than the saturation magnetic flux.