Power Converter Pre-Charging via Grid Side Converter
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Solution Overview
Problem
Current methods for pre-charging main converters in regenerative energy power plants require additional hardware and are costly, leading to increased complexity and potential inrush currents when connecting to the power grid.
Innovation Solution
A method that utilizes a pre-charge unit connected to the power grid and at least one converter path to pre-charge multiple converter paths, reducing the need for additional hardware by using energy from the power plant to pre-charge the main converter and its components before connecting to the grid, thereby minimizing inrush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a pre-charge unit is used to pre-charge the main converter before connecting to the power grid, then inrush currents are minimized and the power grid is protected, but additional hardware is required which increases device complexity and cost
Solution Approach 1:
The invention enables the main converter to pre-charge itself using its own generator and converter paths before connecting to the power grid. The generator produces energy that is used to charge the DC link and magnetize the transformer, eliminating the need for an external pre-charge unit. This self-service approach reduces hardware complexity while still minimizing inrush currents.
Solution Approach 2:
The invention performs preliminary charging of the DC link and magnetization of the transformer before the main converter connects to the power grid. By using the generator to produce energy in advance and store it in the DC link capacitor and transformer magnetic field, the system prepares itself for connection, thereby reducing inrush currents when the grid breaker closes.
2Object-affected harmful factors
If the main transformer is kept always magnetized (not disconnected from grid when converter is disconnected), then inrush currents are reduced, but the grid breaker cannot fully disconnect the transformer from the grid
Solution Approach 1:
The invention separates the disconnection function into two stages: the generator breaker disconnects the generator from the main converter, and the grid breaker disconnects the main converter (including transformer) from the power grid. This segmentation allows the transformer to be fully disconnected when needed, while still enabling pre-charging before connection to minimize inrush currents.
Solution Approach 2:
The invention performs preliminary magnetization of the transformer and charging of the DC link before connecting to the power grid. This preliminary action ensures the transformer is already magnetized when connection occurs, minimizing inrush currents, while still allowing full disconnection capability when the grid breaker opens.
3Power
If a pre-charge unit is dimensioned to deliver only the energy needed for magnetization, then the power class of the pre-charge unit is much lower than the power plant, but additional hardware is required
Solution Approach 1:
The invention eliminates the need for a separate pre-charge unit by using the power plant's own generator to provide the pre-charging energy. The generator produces energy that is used to charge the DC link and magnetize the transformer, making the system self-sufficient and avoiding additional hardware regardless of power class requirements.
Solution Approach 2:
The generator serves multiple functions: it generates power for the power plant operation and simultaneously provides energy for pre-charging the DC link and magnetizing the transformer. This multi-functionality eliminates the need for dedicated pre-charge hardware and utilizes existing components for multiple purposes.
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 approach simplifies the pre-charging process, reduces hardware requirements, and effectively minimizes inrush currents by using the power plant's energy to pre-charge the main converter and its components before connecting to the power grid, enhancing operational efficiency and reducing the risk of damage.
Implementation Method 1
pre-charging the at least one converter path using the energy provided from the pre-charge unit
Implementation Method 2
as long as the grid side converter magnetizes the main transformer
Data Source
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AI summary
The present invention provides a method for connecting a main converter (200) e.g. for use in a power plant (204) for regenerative energy having a generator (206), to a power grid (212), the main converter (200) comprising a grid breaker (214) provided at a power grid side (210) of the main converter (200), and at least two converter paths (216) comprising each a central DC link (218), a grid side converter (220) and a generator side converter (222), both connected to the DC link (218), and a pre-charge unit (232) connected to the power grid (212) and to at least one of the at least two converter paths (216), comprising the steps of providing energy from the pre-charge unit (232) to at least one of the at least two converter paths (216), pre-charging the at least one converter path (216) using the energy provided from the pre-charge unit (232), pre-charging at least one further converter path (216) of the at least two converter paths (216) using the energy provided from the pre-charge unit (232) via the at least one converter path (216) through the grid side converter (220) of the at least one converter path (216) and the grid side converter (220) of the at least one further converter path (218), and connecting the main converter (200) to the power grid (212) by closing the grid breaker (214). The present invention also provides a respective main converter (200) adapted to perform the above method and a software package for upgrading a main converter (200) to perform the above method.