Integrated Output Filter for Parallel Power Converters
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing output filters for power conversion systems with parallel power converters face challenges in effectively filtering high-power applications due to limitations in inductance volume and cost, particularly when dealing with high power and low switching frequencies, as they require increased inductance that may not be feasible in compact form.
Innovation Solution
The proposed output filter utilizes a magnetic core with filtering windings for each power converter and an additional winding connected to the electrical grid, allowing for adjustable inductance by varying the number of turns, providing a compact and efficient solution for both low and high power applications by integrating the filter in a single reactor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional inductance is included at the output of power converters to provide LCL filtering structure, then normal mode current filtering is improved, but inductance volume increases which is not adequate for high power applications
Solution Approach 1:
The patent combines multiple filtering functions (normal mode filtering and crossed current limiting) into a single integrated output filter unit. The filter includes a first reactor with inductance Linv, a second reactor with inductance Lgrid, and an RC branch all connected in one configuration, eliminating the need for separate filtering components and reducing overall volume while maintaining filtering effectiveness.
Solution Approach 2:
The output filter is designed to perform multiple functions simultaneously: it filters normal mode currents through the LCL structure, limits crossed currents through the RC branch, and provides impedance matching. This multi-functional design reduces the need for additional dedicated components, thereby reducing total inductance volume required.
2Reliability
If two-limb Inter-phase reactors (IPR) are used to limit crossed currents in interleaved parallel converters, then crossed current limitation is improved, but leakage inductance is insufficient for high power applications with low switching frequency
Solution Approach 1:
The patent modifies the reactor configuration by introducing a RC branch in parallel with the second reactor, changing the impedance characteristics of the filter. This parameter change allows the system to effectively limit crossed currents at lower switching frequencies typical of high power applications, where traditional IPR leakage inductance would be insufficient.
Solution Approach 2:
The filter uses a composite structure combining reactive elements (reactors with inductances Linv and Lgrid) and resistive-dissipative elements (RC branch). This composite approach provides both the impedance needed to limit crossed currents and the energy dissipation path, enabling effective crossed current limitation in high power applications without relying solely on leakage inductance.
3Reliability
If interleaving is used to reduce harmonic content at output voltages and currents, then harmonic reduction is improved, but uncontrolled crossed currents circulate between converters
Solution Approach 1:
The RC branch acts as an intermediary element that provides a controlled path for crossed currents. Instead of allowing uncontrolled circulation between parallel converters, the RC branch mediates the current flow, dissipating the energy and preventing harmful crossed current circulation while preserving the harmonic reduction benefits of interleaving.
Solution Approach 2:
The patent converts the potentially harmful crossed currents generated by interleaving into a beneficial effect by providing them with a controlled dissipation path through the RC branch. The energy that would otherwise cause harmful circulating currents is instead dissipated in a controlled manner, and the RC branch also provides additional filtering of switching frequency harmonics.
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 configuration optimizes the volume and cost of the output filter, enabling effective filtering of both normal and crossed currents across a wide range of power applications, with adaptable impedance values to suit different power converter topologies and grid characteristics, while reducing the overall size and weight compared to prior art solutions.
Implementation Method 1
Each filtering winding is wounded on a corresponding segment of the magnetic core... allowing for adjustable inductance by varying the number of turns
Implementation Method 2
The output filter comprises a magnetic core for the power converters... providing a compact and efficient solution
Data Source
AI summary
An output filter for a power conversion system having a plurality of power converters connected in parallel, the output filter including a magnetic core and a plurality of filtering windings each wound around a corresponding one of a plurality of segments of the magnetic core and corresponding to one of the plurality of power converters, each of the plurality of filtering windings including a free-end configured for connection to an output of a corresponding one of the plurality of power converters and a second end, the second ends of all of the filtering windings being electrically connected to each other in a common connection; at least one additional winding wound around the additional segment of the magnetic core, the additional winding having a free-end for being connected to an electrical grid and a second end connected to the common connection.