Filter Unit for Power Transmission Neutral Point
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Solution Overview
Problem
Existing systems for transmitting electrical power face increased costs due to the need for a higher design of self-commutated converters to account for asymmetries in AC voltage networks, which cause voltage fluctuations, and require costly filtering to maintain electromagnetic compatibility.
Innovation Solution
A filter unit with high impedance for direct current and low impedance for alternating current is connected to the neutral point of the AC voltage network, using passive components like inductance and capacitance to filter out AC voltage components, reducing voltage fluctuations and system costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the self-commutated converter is designed with higher specifications to handle AC voltage network asymmetry, then voltage fluctuations are reduced, but system costs increase
Solution Approach 1:
A filter unit is introduced as an intermediary component between the unidirectional rectifier and the self-commutated converter. This filter unit includes a first filter connected to a first neutral point and a second filter connected to a second neutral point, which provides a low-impedance path for zero-sequence voltage fluctuations caused by AC network asymmetry, thereby protecting the converter without requiring higher design specifications
Solution Approach 2:
The filter unit changes the impedance parameters of the DC voltage connection by providing high impedance for direct current (through capacitive electrical isolation) and low impedance for alternating current with fundamental frequency (through the filter circuits), thereby selectively filtering voltage fluctuations while maintaining power transmission efficiency
2Object-affected harmful factors
If a DC filter is added to insulate the DC circuit against electromagnetic influences, then electromagnetic compatibility is ensured, but device complexity increases
Solution Approach 1:
The filter unit serves multiple functions simultaneously: it provides electromagnetic isolation between the unidirectional rectifier and self-commutated converter, filters zero-sequence voltage fluctuations from AC network asymmetry, and connects the DC voltage connection to neutral points. This multi-functionality reduces the need for separate filtering components, thereby reducing overall device complexity
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 voltage fluctuations caused by AC voltage network asymmetry, lowers system costs by minimizing the number of expensive switching modules in the modular multi-level converter, and maintains effective filtering without active regulation.
Implementation Method 1
The high impedance for direct currents can be implemented, for example, by electrical isolation, expediently by means of capacitive electrical isolation
Implementation Method 2
The filter unit advantageously includes only passive filter components. Passive filter components are particularly cheap to install and operate
Implementation Method 3
The low impedance of the filter unit for mains-frequency AC currents means that AC voltage components of a voltage on the DC voltage side of the converter are short-circuited to the neutral point
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to an installation (1) for transmitting electrical power comprising a unidirectional rectifier (2) which can be connected at the AC voltage end to a first AC voltage supply system (3), a self-controlled converter (6) which can be connected at the AC voltage end to a second AC voltage supply system (9), and also comprising a DC voltage connection (5) which connects the rectifier and the converter to one another at the DC voltage end. The invention is distinguished by a filter unit (14) which is connected at the DC voltage end to the converter and which forms a current path to a neutral point (15, 34) of the second AC voltage supply system, wherein the current path has a high impedance for a direct current and a low impedance for an alternating current at the fundamental frequency of the second AC voltage supply system. The invention further relates to a modular multistage converter (6) comprising the filter unit (14).