Parallel Multilevel Converters for Circulating Current Control
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Solution Overview
Problem
Existing power transmission systems, particularly those using converters, are limited by the maximum voltage and current they can handle, restricting the transferable power, which becomes a bottleneck as industrial systems grow larger.
Innovation Solution
The system employs multiple multilevel converters connected in parallel, with a monitoring device to detect and counteract circulating currents, allowing for higher power transfer without the need for costly transformers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple converters are connected in parallel to increase transferable power, then power transmission capability is improved, but circulating currents occur in closed current meshes
Solution Approach 1:
The control devices of the converters monitor the closed current meshes for circulating currents and provide correction signals to counteract them. This feedback mechanism detects circulating currents in real-time and adjusts converter operation to eliminate them, allowing parallel converter connection without harmful current loops.
Solution Approach 2:
The control devices act as intermediaries between the parallel converters, coordinating their operation to prevent circulating currents. By introducing this control layer, the system manages the interaction between converters and eliminates the harmful effect of circulating currents while maintaining parallel operation benefits.
2Object-generated harmful factors
If conventional transformers are used to prevent circulating currents, then circulating currents are eliminated, but system cost and space requirements increase
Solution Approach 1:
The invention replaces the mechanical/physical solution of using transformers with an electronic control solution. Instead of adding bulky transformer equipment to block circulating currents, the system uses electronic control devices to actively manage converter operation and eliminate circulating currents through coordination.
Solution Approach 2:
The control devices provide a more cost-effective and compact solution compared to transformers. By using electronic control rather than heavy magnetic components, the system reduces both equipment cost and installation space while achieving the same goal of eliminating circulating currents.
3Device complexity
If a single converter is used, then system simplicity is maintained, but maximum transferable power is limited by converter component limitations
Solution Approach 1:
The invention divides the power transmission function across multiple parallel converters instead of relying on a single converter. Each converter handles a portion of the total power, allowing the system to scale power capacity by adding more converter units while maintaining individual converter design simplicity.
Solution Approach 2:
Multiple converters are combined in parallel configuration to achieve higher power transmission capability. By merging the capacity of multiple individual converters, the system overcomes the power limitations of single converter designs while using standardized modular units.
Data Source
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AI summary
To transmit electrical energy from an input-side three-phase system (2) with input-side phases (4) to an output-side three-phase system (3) with output-side phases (5), the input-side phases (4) are connected to the output-side phases (5) via converters (6) connected electrically in parallel, so that closed current meshes are formed across several converters (6). The converters (6) are designed as multilevel converters controlled by a respective control device (7). A monitoring device (18) monitors the closed current meshes for circulating currents and provides the control devices (7) of the converters (6) with at least one correction signal (K), which is taken into account by the control devices (7) of the converters (6) when controlling the converters (6). The correction signal (K) is determined in such a way that the circulating currents in the closed current meshes are counteracted.Alternatively, the control devices (7) of the converters (6) themselves monitor the closed current meshes for circulating currents and counteract the circulating currents in the closed current meshes by controlling the converters (6).