Multi-string inverter EMC filter with shared current-compensated choke
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Solution Overview
Problem
Multi-string inverters with current-compensated chokes face challenges in optimizing mass and effectiveness across various operating modes, particularly when dealing with hard-coupled DC inputs, leading to saturation and inadequate attenuation of higher-frequency common-mode interference.
Innovation Solution
Implementing a single current-compensated choke with n+1 choke windings on a common core for multiple inputs, which redistributes reverse currents without magnetizing the core, and using series-damped filter capacitors to suppress resonances and maintain electromagnetic compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate current-compensated chokes are used for each input, then each input is protected against core saturation, but the overall filter mass increases and filter effectiveness is not optimal across all operating modes
Solution Approach 1:
The patent combines multiple separate current-compensated chokes into a single shared choke structure with multiple windings. Instead of having individual chokes for each DC input, the invention uses one common magnetic core with multiple windings that serve all inputs, thereby reducing total filter mass while maintaining protection against core saturation through the current compensation mechanism.
Solution Approach 2:
The shared current-compensated choke structure serves multiple functions simultaneously: it provides interference suppression for all DC inputs, handles hard-coupled input configurations, prevents core saturation through current compensation, and reduces overall filter mass. This multi-functional design optimizes the EMC filter for various operating modes of the multi-string inverter.
2Adaptability or versatility
If DC inputs are hard-coupled to operate as a single photovoltaic generator, then uniform MPP tracking is achieved, but asymmetric DC current distribution causes core saturation and reduces interference suppression effectiveness
Solution Approach 1:
The invention changes the magnetic circuit parameters by using a shared current-compensated choke structure with multiple windings. This configuration allows the choke to handle asymmetric DC current distributions resulting from hard-coupled inputs, as the current compensation mechanism prevents core saturation even when current distribution is uneven across inputs.
Solution Approach 2:
The patent implements a scaled version of the current-compensated choke concept, where a single choke structure with multiple windings replicates the protection function that would otherwise require separate chokes for each input. This copied structure maintains the interference suppression effectiveness while adapting to hard-coupled input configurations.
3Weight of stationary object
If a single shared current-compensated choke is used for multiple inputs, then filter mass is reduced, but the choke must handle higher total currents and potential asymmetric current distribution
Solution Approach 1:
The patent merges multiple choke functions into a single shared choke structure. By combining the magnetic circuits and using a common core with multiple windings, the filter mass is reduced while the structure is designed to handle the cumulative current stress from all connected DC inputs through proper winding configuration and core selection.
Solution Approach 2:
The invention employs composite magnetic core structures and winding configurations that can handle higher total currents and asymmetric current distributions. The use of appropriate magnetic materials and winding arrangements allows the single shared choke to manage the increased stress from multiple inputs while maintaining interference suppression effectiveness.
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 reduces the overall mass of the EMC filter while ensuring effective interference suppression across all operating modes, including hard-coupled DC inputs, and maintains electromagnetic compatibility by preventing core saturation and unwanted magnetization.
Implementation Method 1
chokes in all current-carrying lines from the at least two inputs being formed by choke windings on a common core of a current-compensated choke
Implementation Method 2
the direct current flowing from the at least two inputs through the common current-carrying line not magnetizing the core of the current-compensated choke
Implementation Method 3
filter capacitors, which are connected in series with one another and lead from the common current-carrying line to earth
Implementation Method 4
series-damped filter capacitors to suppress resonances and maintain electromagnetic compatibility
Data Source
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AI summary
The invention relates to an inverter (1) having a DC/AC converter (11), an intermediate DC voltage circuit (10) on the DC input side of the DC/AC converter (11), a plurality of DC/DC converters (7), which are connected in parallel to each other to the output side of the intermediate DC circuit (10), a plurality of inputs (2) leading to in each case one of the DC/DC converters (7) and an EMC filter (9) connected between the inputs (2) and the DC/DC converter (7). The EMC filter (9) comprises chokes (25, 26) in all current-carrying lines (5, 6) between the inputs (2) and the DC/DC converters (7) and filter capacitors (19, 20) leading from all current-carrying lines (5, 6) between the inputs (2) and the DC/DC converters (7) to earth (PE). A common current-carrying line (6) leads from at least two inputs (2) - in addition to a dedicated current-carrying line (5) in each case - to the two associated DC/DC converters (7); and the chokes (25, 26) in all the current-carrying lines (5, 6) from the at least two inputs are formed by choke coils on a common core (18) of a current-compensated choke (17).