Inverter Overvoltage Protection Behind EMC Filter
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Solution Overview
Problem
Inverters used in photovoltaic systems face the challenge of transient overvoltages being coupled into the wiring, which can pose a threat to electronic and electrical components, as existing surge arresters upstream of the DC voltage input stage do not completely divert these overvoltages, leading to increased voltage levels after the EMC filter that can cause dangerous oscillations.
Innovation Solution
The overvoltage protection device connects surge arresters behind the EMC filter between the current-carrying lines and earth, eliminating the need for arresters between lines, and uses a series connection of varistors and fuses with a monitoring device to detect and extinguish arcs, allowing for non-self-extinguishing fuses and centralized monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surge arresters are connected upstream of the DC voltage input stage to divert transient overvoltages, then the inverter is protected to the maximum extent, but the transient overvoltages still excite oscillations in the EMC filter that can reach dangerous levels after the filter
Solution Approach 1:
The protection system is segmented into two stages: primary protection with surge arresters upstream of the EMC filter to handle initial overvoltages, and secondary protection with additional surge arresters downstream of the filter to handle oscillations. This segmentation allows each stage to address specific aspects of overvoltage protection, preventing oscillations from reaching dangerous levels while maintaining overall protection effectiveness.
Solution Approach 2:
The EMC filter acts as an intermediary element between the primary surge arresters and the inverter input stage. The patent recognizes that while the filter attenuates overvoltages, it also generates oscillations. The secondary surge arresters are positioned to address these filter-induced oscillations, making the filter's behavior manageable while preserving its electromagnetic compatibility function.
2Device complexity
If surge arresters are connected between current-carrying lines and earth behind the EMC filter, then the number and cost of surge arresters is reduced, but protection against line-to-line overvoltages may be compromised
Solution Approach 1:
The patent applies local quality by connecting surge arresters from each current-carrying line to earth individually behind the EMC filter, rather than using a comprehensive line-to-line protection scheme. This localized approach to earth referencing reduces the number of required arresters while providing sufficient protection for the specific application context, where earth-referenced overvoltages are the primary concern after the filter.
3Ease of manufacture
If non-self-extinguishing fuses are used in the surge arrester, then cost is reduced, but arc extinction becomes more difficult
Solution Approach 1:
A monitoring device is introduced as an intermediary between the non-self-extinguishing fuse and the harmful arc effect. This monitoring device detects arc conditions and triggers active arc extinction measures, such as opening contactors to interrupt the circuit. This allows the use of cheaper non-self-extinguishing fuses while maintaining safety by actively managing the arc extinction process through external control.
Solution Approach 2:
The monitoring device provides feedback on the operational state of the surge arrester and fuse, detecting conditions such as persistent arcs. Based on this feedback, the system activates appropriate responses including opening contactors to extinguish arcs. This feedback mechanism enables the use of cost-effective non-self-extinguishing fuses while ensuring arc safety through active monitoring and response.
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 effectively protects the inverter from transient overvoltages, reduces the number and cost of surge arresters required, and ensures continuous operation even after irreversible changes, with the monitoring device ensuring safe arc extinction and alerting for fuse replacement.
Implementation Method 1
a varistor (26) and a fuse (27) connected in series
Implementation Method 2
a fuse (27) connected in series, with a monitoring device (29) for arc extinction
Implementation Method 3
the safety fuse (27) is thermally coupled to the varistor (26)
Implementation Method 4
a monitoring device (29) for arc extinction, which detects the voltage drop across the fuse (27)
Implementation Method 5
an EMC filter (7) which comprises interference suppression inductors (12) and interference suppression capacitors (13, 14)
Data Source
Figure 1
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AI summary
The apparatus has a direct current voltage input stage (6) including two current-carrying lines (22, 24) and an electromagnetic compatibility filter (7) comprising suppression capacitors (13, 14) and suppression inductors (12), where the current-carrying lines are provided for dissipating overvolatges with respect to earth. Overvoltage arresters (16, 17) of a direct current source (15) are arranged in a housing of an alternating current converter (5) behind the compatibility filter on the current-carrying lines.