The patent's assignee for patent number 8767422 is
News editors obtained the following quote from the background information supplied by the inventors: "Interface arrangements are known to be connected between an Alternating Current (AC) system, often denoted AC grid and a Direct Current (DC) system, like a High Voltage Direct Current (HVDC) system. Such an arrangement typically includes a converter, such as a voltage source converter, for conversion between AC and DC and having a DC side connected to the DC system and an AC side for coupling to the AC system.
"For safety reasons an interface arrangement is often connected between two such systems via circuit breakers. This type of connection is for instance shown in US 2008/0084643.
"If faults occur in such a DC system or in the interface arrangement, it is of interest to open the DC system from the AC system. This is normally done through opening the circuit breakers. This opening can normally not be performed immediately when the fault occurs, because the current has to be alternating with zero-crossings.
"These faults also put a lot of stress on the electronic components used in the converter, like overvoltage and fault current stress. It is therefore of interest to limit this stress applied on the components of the converter caused by a fault."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "The present invention addresses this situation. The invention is thus directed towards limiting the stress applied on a converter at the occurrence of a fault.
"This objective is according to one aspect of the invention achieved through an interface arrangement for connection between an AC system and a DC system and comprising a converter for conversion between AC and DC, the converter having a DC side for connection to the DC system and an AC side for being coupled to the AC system, a set of circuit breakers coupled between the AC side of the converter and the AC system, and a breaker assisting unit comprising a set of branches connected between the AC side of the converter and ground, where each branch includes a switch in series with an impedance element.
"The objective is also achieved by a method of disconnecting a DC system from an AC system, where the DC system is coupled to the AC system via a converter for conversion between AC and DC and a set of circuit breakers and to ground via a breaker assisting unit comprising a set of branches, where each branch includes a switch in series with an impedance element, wherein the circuit breakers are closed and the switches are open in normal operation, the method comprising the steps of: obtaining an indication of a fault, closing the switches of the branches based on the indication for ensuring zero-crossings in currents flowing through the circuit breakers, and opening the circuit breakers at such zero-crossings.
"The expression 'coupled' used is intended to cover the possibility of an indirect electrical connection between two elements. There may thus be one or more elements placed between two elements defined as being coupled to each other. The expression 'connected' is on the other hand intended to mean a direct electrical connection of two entities to each other without any entity between them.
"The invention has a number of advantages. The switches of the breaker assisting unit are quickly closed when a fault takes place and thereby the converter is protected against stresses such as overvoltage stresses and fault current stresses. The closing also ensures the existence of zero crossings of the fault currents for ensuring a safer opening of the circuit breakers."
For additional information on this patent, see: Jiang-Hafner, Ying; Sheng, Baoliang. Interface Arrangement between AC and DC Systems Using Grounding Switch. U.S. Patent Number 8767422, filed
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