Inverter Harmonic Detection for Transformer Inrush Current Control
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Solution Overview
Problem
In new energy power generation systems, the switching of transformers during maintenance leads to excessive inrush currents, causing misoperation of relay protection apparatuses and potential electrical damage to devices like power converters, which affects the reliability of the power supply.
Innovation Solution
A power converter with a controller that adjusts the output voltage based on even harmonic currents, specifically reducing the output voltage when even harmonic currents increase, to quickly exit the magnetic saturation state of inductive loads like transformers, thereby reducing inrush currents without adding hardware devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a harmonic compensation device is added to reduce inrush current impact, then the reliability of power supply is improved, but the system cost increases
Solution Approach 1:
The power converter controller automatically detects even harmonic currents and adjusts output voltage without external compensation devices. The system uses its own control capabilities to mitigate inrush current effects, eliminating the need for separate harmonic compensation equipment and reducing system cost while maintaining reliability.
Solution Approach 2:
The controller dynamically changes the output voltage parameter based on detected even harmonic current levels. When even harmonic currents are detected, the controller reduces output voltage to prevent transformer saturation and inrush current, thereby protecting the system without adding hardware.
2Reliability
If the transformer is switched slowly to reduce current impact and voltage fluctuation, then the reliability of power supply is improved, but the productivity of the power generation system decreases
Solution Approach 1:
The controller performs preliminary detection of even harmonic currents before inrush current occurs during transformer switching. By detecting the presence of even harmonic currents that indicate approaching saturation, the controller proactively adjusts output voltage to prevent inrush current, enabling fast switching without compromising reliability.
Solution Approach 2:
The system implements feedback control by continuously monitoring even harmonic currents and adjusting output voltage in real-time. This closed-loop control allows the transformer to be switched quickly while the controller responds to harmonic current feedback to maintain system reliability, avoiding the power loss associated with slow switching.
3Object-affected harmful factors
If the output voltage is reduced when even harmonic current increases, then the inrush current impact is reduced, but the power output of the converter decreases
Solution Approach 1:
The controller implements periodic monitoring of even harmonic currents and applies voltage reduction only during specific periods when even harmonic currents are detected. During normal operation without even harmonic currents, the converter operates at full power output. This periodic, condition-based control minimizes inrush current impact while maintaining maximum power output during normal conditions.
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
This solution effectively reduces the impact of inrush currents on power converters, ensuring stable operation of new energy power generation systems without increasing hardware costs or adding additional devices.
Implementation Method 1
The controller is configured to control, based on an even harmonic current on a connection line between the DC/AC power conversion circuit and the load, an output voltage at which the power converter outputs the alternating current
Implementation Method 2
The transformer is configured to boost a voltage of the alternating current and further feed, to a medium- and high-voltage network, an alternating current obtained through voltage boosting
Implementation Method 3
The DC/AC power conversion circuit is connected in parallel between the positive direct current bus and the negative direct current bus and configured to convert a direct current from the direct current source into an alternating current
Data Source
Figure 1~2(b)
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AI summary
The present invention provides a power converter, a resisting method in inductive load switching, and a power generation system. The power converter includes a direct current input end, an alternating current output end, a bus capacitor, a DC/AC power conversion circuit, and a controller. The direct current input end is configured to connect to a direct current source. The alternating current output end is configured to connect to a load. The bus capacitor includes a positive bus capacitor and a negative bus capacitor that are connected in series. The positive bus capacitor is connected to a positive direct current bus. The negative bus capacitor is connected to a negative direct current bus. The DC/AC power conversion circuit is connected in parallel between the positive direct current bus and the negative direct current bus, and configured to convert a direct current from the direct current source into an alternating current, and transmit the alternating current to the load through the alternating current output end. The controller is configured to control, based on an even harmonic current on a connection line between the DC/AC power conversion circuit and the load, an output voltage at which the power converter outputs the alternating current, to reduce an absolute value of a voltage difference between the positive bus capacitor and the negative bus capacitor.