Electrical circuit, in particular used for generating electrical power

An electrical circuit, in particular a circuit used for generating electric power, wherein this circuit comprises a generator with n phases, a converter and a transformer to which a p-phase load can be connected. The converter comprises m partial converters, each of the partial converters is composed of p units and each of these units is provided with n/m switching circuits. The switching circuits of the individual units are connected symmetrical to the generator.

The invention relates to an electrical circuit for generating electrical power in accordance with the preamble to claim1.

An electrical circuit for generating electric power is known from the U.S. Pat. No. 5,694,026, for which a turbine is directly coupled mechanically to a multiphase generator. This generator, in turn, is connected via a converter and a transformer to an electric power grid. No mechanical transmission is provided between the turbine and the generator. In the generator operation, the turbine is supplied with fuel, so that the generator is driven by the turbine and generates electrical power which is then fed via the converter and the transformer into the power supply grid.

A matrix converter is known, for example, from the reference DE 100 51 222 A1 which can be used in particular for generating electric power. When using such a matrix converter, the generator does not necessarily have to be operated with the frequency of the connected power grid, but can also be operated at a higher frequency. One disadvantage of this matrix converter is that the thyristors in this converter are current-carrying only for short intervals which leads to current peaks and thus also to high loads.

It is the object of the present invention to create an electrical circuit which makes it possible to achieve lower loads for the thyristors.

This object is solved with a circuit as disclosed in claim1.

According to the invention, a generator with n phases, a converter and a transformer are provided to which a p-phase load can be connected. The converter is composed of m number of partial converters, each of the partial converters comprises p number of units, and each unit, in turn, has n/m number of switching circuits. The switching circuits for the individual units are connected symmetrical to the generator.

As a result of the symmetrical connection of the individual units with the generator, current peaks and thus also high loads are avoided for the switching circuits. The current flowing through the individual switching circuits is thus reduced, in particular by a factor which corresponds to the number m of the partial converters. The current-carrying interval of the individual thyristors for the switching circuits is furthermore extended, again by a factor of m.

According to a particularly advantageous embodiment of the invention, the switching circuits of each unit are connected to each p-phase of the generator, wherein the switching circuits of successively following units are preferably connected to generator phases which are offset by one phase. The symmetry achieved in this way makes it possible to effect an especially far-reaching reduction in the load for the switching circuits.

The generator windings of a first and especially advantageous embodiment of the invention are connected in series, relative to each other, and a transformer comprising a primary winding and a secondary winding is provided. The switching circuits of each unit are preferably interconnected on the output side, wherein the units belonging to the individual partial converters are connected to the same secondary winding, thereby achieving in a simple manner a galvanic separation of the partial converters relative to each other.

With a second and especially advantageous embodiment of the invention, the generator windings form m series connections which are switched parallel to each other, and the transformer comprises a primary winding and a single secondary winding. The switching circuits of each unit are advantageously interconnected on the output side, wherein all units of the partial converters are connected to the secondary winding. A simple galvanic separation of the partial converters is achieved in this way as well.

The system10shown inFIG. 1for generating power comprises a turbine11which is mechanically directly connected to an electric generator12. A series-connected transmission or the like does not exist. The generator12is connected to an electrical converter13to which an electrical transformer14is connected. The transformer14is furthermore connected to a non-depicted electrical load, for example to an electric power grid. The present exemplary embodiment therefore relates to a three-phase load or a three-phase electric power grid.

During the operation, the turbine11is put into rotation, for example, with the aid of fuels. By way of the direct mechanical connection, the generator12is also put into rotation and thus generates in a generator operation an output voltage with a rotational speed-dependent frequency. With the aid of the converter13, this changeable frequency of the output voltage is converted to an essentially fixed frequency which corresponds, for example, to the frequency of the electric power grid. Following this, the output voltage is increased with the aid of the transformer14to a predetermined voltage, for example the voltage of the electric power grid. In this way, electric power is on the whole generated by the aforementioned system10and is then fed, for example, into the electric power grid.

FIG. 2shows in further detail the generator12, the converter13and the transformer14of a first exemplary embodiment, as well as the electrical interconnection.

The generator12is a synchronous generator, comprising a total number of n windings. In the following, the generator12is also referred to as n-phase generator and, in particular, can be a 27-phase synchronous generator with a polygonal shape for the windings.

An equivalent circuit diagram for the generator12is shown inFIG. 2. It follows fromFIG. 2that each of the n windings has a line resistance Rg and a winding inductance Lg. In the generator operation for the generator12, a voltage Ug is induced in each of the n windings, thereby resulting in a current ig to the converter13.

A differentiation can be made between the line resistances Rg, the winding inductances Lg, the voltages Ug and the currents ig with the aid of the numbers “1” to “n” which is indicated inFIG. 2in that the variables belonging together are respectively assigned the corresponding digit.

In the equivalent circuit diagram shown inFIG. 2, the induced voltages Ug, the line resistance Rg and the line inductance Lg of each of the n windings form a series connection and these series connections of the n windings are furthermore also connected in series. The currents ig branch off from the individual windings and are insofar parallel connected.

The converter13is a matrix converter composed of a number of units given the reference b. As will be explained later on, these b units form m partial converters, resulting in the connection b=m×p, wherein the references b, m and p must have whole number values. The number m of partial converters must furthermore form a whole-number divisor for the total number of n windings of the generator12.

The present exemplary embodiment consists of three partial converters. For the previously explained 27-phase generator12and the three-phase load, we therefore obtain nine units. InFIG. 2, these nine units are numbered consecutively with the reference numbers161,162,163, . . . ,169.

The first partial converter is composed of the units161,164,167and is given the reference number171inFIG. 2. The second partial converter is composed of the units162,165,168and is given the reference number172. The third partial converter is composed of the units163,166,169and is given the reference number173.

The number of units for each partial converter corresponds to the number of phases of the load and/or the electric power grid to which the converter13is connected via the transformer14. As previously mentioned, the present exemplary embodiment relates to a three-phase load. Each of the partial converters171,172,173of this exemplary embodiment is therefore composed of three units, which results in a total number of 9 units.

In theory, p phases could generally also be present which would then have to be taken into consideration for the number b of units, as well as the number m of partial converters and the number n of generator12windings.

Each of the units161, . . . ,169is provided with n/m switching circuits23. For the aforementioned example of the 27-phase generator12, each of the units161, . . . ,169is thus provided with nine switching circuits23. Finally, each of the switching circuits23is configured with two thyristors that are switched parallel in opposite directions, wherein a series connection of two thyristors that are switched parallel in opposite directions can also be planned, especially in view of a higher blocking voltage.

The switching circuits23for the individual units161, . . . ,169of the partial converters171,172,173are connected symmetrical to the generator12. If we assume for the present exemplary embodiment a 27-phase generator12and a three-phase load and/or a three-phase electric power grid, the switching circuits23of the individual units161, . . . ,169are consequently not connected to successive phases of the generator12, but within each unit there is always only one connection to each third phase.

In the general case with p phases for the load or the electric power grid, a connection thus exists from the switching circuit23of a unit to each p-th phase of the generator12.

The connections between the switching circuits23and the individual units furthermore differ in that the switching circuits23of successively following units161, . . . ,169are always connected to a phase of the generator12that is offset by one phase.

InFIG. 2, the switching circuits23of the units161of the partial converter171are thus connected to the phases1,4,7,10, . . . , n−2 of the generator12. Correspondingly, the switching circuits23of the unit162of the partial converter172are connected to the phases2,5,8,11, . . . , n−1 of the generator12and the switching circuits23of the unit163of the partial converter173are connected to the phases3,6,9,12, . . . , n of the generator12. In a corresponding manner, the units164,165,166,167,168,169are connected to the respective phases of the generator12.

The switching circuits23of an individual unit161, . . . ,169are connected parallel to each other. On the input side, the switching circuits23are connected to the phases of the generator12, as explained.

On the output side, the switching circuits23of an individual unit are interconnected. With a total number of nine units for the three partial converters, we thus obtain nine output lines which are given the references L11, L12, L13, L21, L22, L23, L31, L32and L33inFIG. 2. For the present exemplary embodiment shown inFIG. 2, the second digit characterizes the association with a specific partial converter and the first digit characterizes the association with a specific unit within the respective partial converter.

The transformer14comprises a primary winding19and several secondary windings. In general, the number of secondary windings corresponds to the number m of the partial converters. For the present exemplary embodiment with three partial converters, the transformer14therefore has three secondary windings20,21,22. The primary windings19and the secondary windings20,21,22of the present exemplary embodiment have respectively three tapping points. The number of tapping points generally corresponds to the number p of the load phases and/or the electric power grid. The primary winding19and the secondary windings20,21,22are magnetically coupled.

The three units of each partial converter171,172,173are connected to the three tapping points of the same secondary winding. The connection between the units of the partial converters and the secondary windings is insofar symmetrical.

For the present exemplary embodiment shown inFIG. 2, the output lines L11, L21, L31belonging to the first partial converter171are connected to the tapping points of the secondary winding20, the output lines L12, L22, L32belonging to the second partial converter172are connected to the tapping points of the secondary winding21and the output lines L13, L23, L33belonging to the third partial converter173are connected to the tapping points of the secondary winding22.

The secondary windings20,21,22carry the voltages Usec1, Usec2, Usec3. A voltage Uprim, is present at the primary winding19, wherein this voltage is supplied to the load or fed to the three-phase electric power grid assumed for this example. In general, a p-phase load or a p-phase electric power grid can be connected to the primary winding19.

The amplitude of the voltage Um, can be adjusted through the ratio of the primary winding19to the secondary windings20,21,22and the frequency of the voltage Uprimcan be adjusted by correspondingly triggering the individual thyristors of the switching circuits23.

A galvanic separation of the three partial converters171,172,173is achieved with the aid of the three secondary windings20,21,22.

InFIG. 3, the generator12, the converter13and the transformer14as well as their electrical interconnections are shown in further detail in the second exemplary embodiment. The configuration of the converter13inFIG. 3, in particular the configuration with nine units161, . . . ,169in the three partial converters171,172,173and their electrical connection to the switching circuits23corresponds to the one shown inFIG. 2. The same components are therefore given the same references. In view of these coinciding components, we point to the explanations provided inFIG. 2.

The electrical interconnection between the converter13and the generator12as well as between the converter13and the transformer14inFIG. 3differs considerably from the one shown inFIG. 2. The generator12and the transformer14inFIG. 3furthermore also differ from those shown inFIG. 2, wherein these differences are explained in the following.

The generator12inFIG. 3differs from the one inFIG. 2in that not all n phases are connected in series to each other, as shown forFIG. 2, but that inFIG. 3always only n/m phases form a series connection and that the resulting m series connections are switched parallel to each other. The number of series connections thus corresponds to the number of partial converters. For the present exemplary embodiment with a 27-phase generator12and three partial converters, respectively nine phases of the generator12are connected in series and three such series connections are then switched parallel to each other. InFIG. 3, the aforementioned three series connections are given the reference numbers33,34,36.

Each of the series connections33,34,35of the generator12contains windings which do not follow each other directly, but in all cases only for each p winding. For the present exemplary embodiment of a three-phase load and/or a three-phase electric power grid, the individual series connections33,34,35therefore always contain each third winding. According toFIG. 3, the series connection33contains the windings1,4,7, . . . , n−2, the series connection34contains the windings2,5,8, . . . , n−1, and the series connection35contains the windings3,6,9, . . . , n.

The switching circuits23of the individual units161, . . . ,169for the partial converters171,172,173are connected symmetrical to the series connections33,34,35of the generator12. If, as assumed for the present example, a 27-phase generator12and a three-phase load exist, it means that the switching circuits23of the individual units161, . . . ,169are not connected to successive phases of the series connections33,34,35, but that in all cases only one connection to each third winding exists within a unit.

For the general case with p phases for the load and/or the electric power grid, a connection therefore exists from the switching circuits23of a unit to each p phase of the series connections of the generator12.

The connections between the switching circuits23and the individual units furthermore differ in that the switching circuits23of the successively following units161, . . . ,169are always connected to a phase of the generator12that is offset by one phase.

InFIG. 3, the switching circuits23of the unit161of the partial converter171are therefore connected to the phases1,4,7,10, . . . , n−2 of the series connection33of the generator12.

The switching circuits23of the unit162of the partial converter172are correspondingly connected to the phases2,5,8,11, . . . , n−1 of the series connection34of the generator12, and the switching circuits23of the unit163of the partial converter173are connected to the phases3,6,9,12, . . . , n of the series connection35of the generator12. In a corresponding manner, the units164,165,166,167,168,169are also connected to the phases of the respective series connections33,34,35of the generator12.

A galvanic separation of the three partial converters171,172,173is achieved with the aid of the three series connections33,34,35of the generator12.

The transformer14comprises a primary winding29and a single secondary winding31. For the present exemplary embodiment, the primary winding29and the secondary winding31are respectively provided with three tapping points, wherein the number of tapping points in general corresponds to the number of phases for the connected load. A voltage Usecis present at the secondary winding31, while a voltage Uprimcan be tapped at the primary winding29. The primary winding29and the secondary winding31are magnetically coupled.

Respectively three successively following units of the nine units161, . . . ,169are interconnected and are then connected to one of the three tapping points on the secondary winding31. It means that corresponding units of different partial converters are always connected to the same tapping point on the secondary winding31. The connection between the units of the partial converters and the secondary winding is insofar symmetrical.

For the present exemplary embodiment shown inFIG. 3, the output lines L11, L12, L13belonging to the three partial converters171,172,173are connected to the first tapping point of the secondary winding31, the output lines L21, L22, L23belonging to the three partial converters171,172,173are connected to the second tapping point of the secondary winding31and the output lines L31, L32, L33belonging to the three partial converters171,172,173are connected to the third tapping point of the secondary winding31.

As previously mentioned, the voltage Uprimis present at the primary winding29and is supplied to the load or the three-phase electric power grid for this example. In general, the primary winding29can be connected to a p-phase load.

The amplitude of the voltage Uprimcan be adjusted with the aid of the ratio of primary winding29to secondary winding31, and the frequency of the voltage Uprimcan be adjusted through a corresponding triggering of the individual thyristors of the switching circuits23.