Inverter Voltage Control for Transformer Excitation Inrush
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing methods for controlling excitation inrush current during transformer connection to a power grid, such as introducing additional hardware or soft-start after voltage reduction, either increase system costs or reduce power grid reliability and can cause relay protection failures.
Innovation Solution
An inverter system with a controller that reduces and adjusts the output voltage of a conversion circuit to keep the magnetic flux of the transformer's iron core below saturation levels, preventing excitation inrush current and maintaining power grid reliability by avoiding saturation and potential divergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an additional bypass branch is introduced to prevent direct connection, then excitation inrush current is reduced, but system cost increases
Solution Approach 1:
The patent introduces a controllable switch as an intermediary component between the inverter output and transformer primary winding. This switch enables selective connection/disconnection without requiring additional bypass branches, thereby reducing excitation inrush current while avoiding the cost and complexity of hardware additions.
Solution Approach 2:
The patent changes the connection state parameter of the controllable switch (on/off) to control the flow of excitation inrush current. By adjusting this parameter dynamically, the system can prevent direct connection during switching operations without requiring physical bypass branches, thus resolving the contradiction between current reduction and system cost.
2Object-affected harmful factors
If soft-start after voltage reduction is used, then excitation inrush current is reduced, but power grid reliability decreases
Solution Approach 1:
The patent applies preliminary action by detecting potential excitation inrush current conditions before they occur and preemptively controlling the controllable switch to prevent direct connection. This proactive approach eliminates the need for post-voltage-reduction soft-start methods, thereby reducing inrush current while maintaining power grid reliability through immediate prevention rather than delayed response.
3Object-affected harmful factors
If voltage is reduced to prevent saturation, then excitation inrush current is reduced, but relay protection apparatus may be mistakenly operated
Solution Approach 1:
The patent extracts the problematic direct connection path by using the controllable switch to isolate the transformer primary winding from the inverter output during switching operations. This separation prevents voltage reduction measures that could trigger relay protection misoperation, while still achieving excitation inrush current reduction through controlled disconnection.
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
Effectively reduces excitation inrush current, prevents transformer damage, and maintains power grid reliability by dynamically managing the output voltage to prevent saturation and ensure stable magnetic flux.
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
a method for controlling an excitation inrush current generated during no-load switch-on is mainly to introduce an additional bypass branch to prevent the transformer from being directly connected to the power grid, or to actively reduce a voltage
Data Source
Figure 1~2
Figure 3~5
Figure 6
AI summary
This application provides an inverter, a power grid power supply system, and a method for controlling an excitation inrush current. The inverter includes a conversion circuit and a controller. The controller reduces an output voltage of the conversion circuit when an output current of the conversion circuit is greater than a current threshold, to enable magnetic flux of an iron core in a transformer to be less than saturation magnetic flux. 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. According to this application, an insulation failure of the transformer caused by an excitation inrush current and damage to the transformer may be prevented, a midpoint potential divergence of a multi-level inverter and an overcurrent of the inverter can be avoided, failure of the entire power grid caused by maintaining of a low voltage level can be avoided, and power supply reliability of the power grid power supply system can be improved.