DC power source for a high voltage power apparatus

#The present invention relates to a dc power source for a high voltage power apparatus connected to a high voltage electrical power system, the dc power source comprising one or more strings including a plurality of dc power source members connected in series, and switches configured to connect and disconnect the strings. By a high voltage electrical power system should be understood an electrical system within the range of 3 kV and upwards, preferably in the range of 10 kV and upwards. By a dc power source should be understood dc power source members connected in series to be within the range of 3 kV and upwards. With a power apparatus is meant an apparatus that is capable of controlling reactive power and/or active power. Examples of power apparatus are a power compensator and an uninterruptible power supply (UPS).

#Within flexible alternating current transmission systems (FACTS) a plurality of control apparatus are known. One such FACTS apparatus is a static compensator (STATCOM). A STATCOM comprises a voltage source converter (VSC) having an AC side connected to a high voltage electrical power system and a DC side connected to a temporary electric power storage means such as capacitors. The STATCOM can supply reactive power to or absorb reactive power from the transmission line.

#As opposed to the STATCOM, which only compensate for reactive power, another concept is to connect a dc power source to a compact STATCOM, and thus being able to perform active power compensation. The construction may be used e.g. as a spinning reserve and for compensating for fluctuating energy levels in the power system.

#The present invention will be more fully described by way of example with reference to the accompanying drawings in which:

#FIG. 1 shows an embodiment of a dc power source in accordance with the present invention;

#FIG. 2A shows a schematic figure of a solid-state switch and parallel-connected thyristors;

#An example of a dc power source according to the invention is illustrated in FIG. 1. FIG. 1 shows a dc power source 3 for a high voltage power apparatus 1 connected to a high voltage electrical power system 19 according to an embodiment of the invention. Examples of high voltage power apparatus are a power compensator and an uninterruptible power supply (UPS). High voltage electrical power systems can be networks for transmission or distribution of electrical energy as well as industries, hospitals and such. The same reference numerals are used throughout the figures for same or corresponding parts. The power apparatus 1 comprises a high voltage dc power source 3 and a voltage source converter 2. To be able to produce and absorb not only reactive power but also active power, the dc power source 3 is connected to the dc side of the voltage source converter 2. The ac side of the converter is connected to the high voltage electrical power system 19.

#The dc power source 3 comprises one or more strings 4a-c connected in parallel, the number of strings depending on the desired amount of active power. In the example illustrated in FIG. 1, three strings 4a-c are shown. Each string 4a-c comprises a plurality of dc power source units 8, 10, 12. The dc power source units 8, 10, 12 in turn comprises a plurality of series-connected dc power source members (not shown in FIG. 1). The total number of dc power source members in each string 4a-c depends on the voltage level of the voltage source converter 2 to which they are connected and the voltage level of the dc power source members used in the string 4a-c. The dc power source members can be of different types, such as battery cells, photovoltaic cells, fuel cells and super capacitors. These different types could also be combined.

#In each string 4a-c a plurality of solid-state switches 7, 9, 11, 13 are distributed among dc power source units 8, 10, 12. Examples of solid-state switches are IGBTs, GTOs, IGCTs and MOSFETs. Each dc power source unit 8, 10, 12 is provided with a solid-state switch 9, 11, 13 configured to connect and disconnect the corresponding dc power source unit 8, 10, 12. The voltage of the dc power source units 8, 10, 12 is adapted to be below the breaking capability of the switches 9, 11, 13. All switches 7, 9, 11, 13 in the string are arranged so that they are turned on and off simultaneously, implying that each switch 7, 9, 11, 13 only has to withstand the voltage over its corresponding dc power source unit 8, 10, 12 when the string 4a-c is disconnected.