Patent Application
20100013315
The present invention relates to power supply devices in general and more particularly a high voltage power supply device which is more efficient and environmental friendly than prior art devices. The present invention also relates to a method of supplying power.
The reliability of today's power distribution systems is generally high. This means that periods of power failure are rare and they are often short, i.e., less than one second, when they appear. This is acceptable for most applications and is built into the design of the power distribution systems. This means that achieving completely failure free distribution of electrical power with current power distribution systems is almost impossible.
However, there are highly critical loads, such as semi-conductor or pharmaceutical factories, oil refineries and gas compressing plants, wherein each power failure or disruption is very costly and therefore unacceptable. The electrical power supply to highly critical loads is therefore often arranged through a highly reliable power supply, which essentially eliminates the risk of power failures. These highly reliable power supplies, which conventionally are provided close to the load, can comprise one or preferably two or more electrical power generators, such as gas turbines operating as generators of electrical energy. Such a prior art system is schematically shown in
One drawback with this kind of highly reliable power supplies is however that they are not very efficient and environmental friendly. The nature of these generators, i.e., that they cannot supply momentary power unless they are already running, is such that they must be operated more or less continuously. Also, the fuel used for gas turbine emits large amounts of hydrocarbons. Furthermore, when two or more turbines are run in parallel, such as in the example of
It is known to provide a voltage source converter (VSC) supplying reactive power to a power distribution system to provide for voltage control and stability, i.e., to keep the voltage of the power distribution lines within set limits. A prior art power supply device or unit, generally referenced 101, is schematically shown in
An object of the present invention is to provide a power supply device acting a power backup in case of failure of an electrical power distribution network or as a stand-alone power supply for highly critical loads.
The invention is based on the realization that a reactive power supply device, such as a voltage source converter, in combination with an energy store, such as a battery, and a generator can be combined into a unit that provides power backup for both active and reactive power to highly critical loads.
According to a first aspect of the invention an electri-cal power supply device for high voltage is provided comprising a voltage converter having an AC side and a DC side; an electrical energy store connected to the DC side of the voltage converter, the power supply device being characterized by a second voltage converter having an AC side and a DC side, wherein the DC sides of the first and second voltage converters are interconnected and wherein the electrical energy store is connected to lines interconnecting the voltage converters, and an electrical power generator, which is connected to the AC side of the second voltage converter, wherein the high voltage power supply device is adapted to connect a load to the AC side of the first voltage converter. The power supply device can thereby supply electrical energy during prolonged periods of time or even act as a stand-alone power supply device.
In the case the power supply device is used stand-alone, it is preferred to connect in parallel two sets of power supply devices to further improve the reliability.
In a preferred embodiment, the electrical power generator is a gas turbine.
According to a second aspect of the invention a method of supplying high voltage power is provided, comprising the following steps: providing a first voltage converter having an AC side and a DC side, connecting an electri-cal energy store to the DC side of the first voltage converter, and operating the first voltage converter to supply electrical power on the AC side thereof, the method being characterized by providing a second voltage converter having an AC side and a DC side, wherein, interconnecting the DC sides of the first and second voltage converters, connecting the electrical energy store to lines interconnecting the voltage converters, connecting an electrical power generator to the AC side of the second voltage converter, connecting a load to the AC side of the first voltage converter, upon detecting power failure, powering up the electrical power generator, supplying electrical power from the electrical energy store to the AC side of the first voltage converter during the power up time of the electrical power generator, and supplying electrical power from the electrical power generator after the power up time thereof.
Further preferred embodiments are defined by the dependent claims.
Other features and advantages of the present invention will become more apparent to a person skilled in the art from the following detailed description in conjunction with the appended drawings in which:
In the following a detailed description of preferred embodiments of the present invention will be given. In this description, the term “high voltage” will be used for voltages of 1 kV and higher.
The voltage converter 20 is preferably of the general kind that is used with a voltage source converter (VSC), such as the VSC manufactured by ABB Corporation and marketed under the name STATCOM. It comprises transistors, preferably insulated-gate bipolar transistor (IGBT) power semi-conductors for switching (with frequencies up to 1.5 kHz), which enables quick response, filtering etc.
The electrical energy store 10 is preferably dimensioned so that it can provide a high voltage of at least 1 kV, and more preferably at least 10 kV, and deliver electrical power of at least 1 MW, more preferably at least 10 MW, and even more preferably at least 100 MW during at least 5 minutes, and more preferably during at least 20 minutes, and even more preferably during at least 30 minutes. The battery preferably comprises a plurality—up to several thousands of serially connected battery cells to achieve the high voltages required for this application. The cells are preferably designed so that if one cell malfunctions, then it is short circuited, resulting in continued operation of the battery, albeit at a slightly lower voltage level. An example of a battery which can be used is the one manufactured by the company MES-Dea under the trade mark ZEBRA™.
The power supply device 201 additionally comprises a generator of electrical power, generally designated 40, which can be a gas turbine, for example. The output of this electrical power generator is connected to the AC side of the second voltage converter.
A transformer 50 is shown connected between the power supply device 201 and a distribution line 60, to which a highly critical load is connected. This transformer is only necessary if the line voltage is so high, such as 36 kV, that the power supply device is unable to reach this voltage level without step-up transforming.
An overall control system (not shown) controls the power supply device during operation thereof.
An example of a circuit configuration between the high voltage battery 10 and the voltage converter 20 is shown in
This configuration can advantageously be used as follows. The combination of the battery 10 and the first voltage converter 20 is used like in the above described prior art device of
When the generator is operational after its power up time, it begins to deliver electrical power to the highly critical load. This is effected by supplying the AC side of the second voltage converter 30 with AC power, which is rectified by the second voltage converter 30 and transmitted to the first voltage converter 20, which in turn converts the power to three-phase AC power, which is supplied to the highly critical load.
The magnetization of the power generator 40 determines the amount of generated reactive power in the generator. However, it is preferred to have the generator deliver as much active power as possible since the converter arrangement can supply the required reactive power.
By using the back-to-back configuration of the two voltage converters 20, 30, the speed of the generator 40 is essentially independent of the frequency of the power distribution network since the voltage from the generator is first converted to DC voltage and then again converted to AC voltage. This in turn means that the generator can run at optimum speed when considering efficiency, resulting in a more efficient overall system.
Since the battery 10 takes care of the delivery of momentary electrical power during failure of the power distribution network, the generator 10 can be in cold standby most of the times.
In
The dual configuration shown in
It is realized that the second embodiment 301 can be connected to an electrical distribution network as well and not just operate as a stand-alone power supply device.
Preferred embodiments of a power supply device have been described. It will be realized that these can be varied within the scope of the appended claims. Thus, the gene-rator 40 can be something different than a gas turbine, such as a diesel generator.
The electrical energy store has been described as a battery. It will be appreciated that this store also could comprise a large capacitor, which is charged in some suitable way to supply power in case of power failure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07445014.9 | Mar 2007 | EP | regional |
The present application is a continuation of pending International patent application PCT/SE2008/000224 filed on Mar., 27, 2008, which designates the United States and claims priority from European patent application number 07445014.9 filed on Mar. 30, 2007, the content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/SE2008/000224 | Mar 2008 | US |
| Child | 12570352 | US |
