Power generation system
阅读说明：本技术 发电系统 (Power generation system ) 是由 M.贝希莱 R.韦泽 P.阿尔-霍卡耶姆 E.罗尔 于 2018-04-20 设计创作，主要内容包括：本发明涉及一种发电系统,包括：用于将机械功率转换成输出侧处的电功率的同步发电机(3),所述输出侧被配置用于连接AC电网(1)；第一整流器(12)和第二整流器(13),每个整流器具有连接到发电机(3)的输出侧的AC侧(14)和DC侧(15)；被配置用于激励所述发电机(3)的励磁器(9)；以及具有输入侧(17)和输出侧(19)的选择器装置(18),所述输入侧(17)连接到第一整流器(12)的DC侧(15)和第二整流器(13)的DC侧(15),并且所述输出侧(19)连接到励磁器(9),由此选择器装置(18)被配置用于串联或并联地切换DC侧(15),或者用于对应于任意分流比率将DC功率从第一整流器(12)和第二整流器(13)传输到输出侧(19)。(The invention relates to a power generation system comprising: a synchronous generator (3) for converting mechanical power into electrical power at an output side, the output side being configured for connection to an AC electrical grid (1); a first rectifier (12) and a second rectifier (13), each rectifier having an AC side (14) and a DC side (15) connected to an output side of the generator (3); an exciter (9) configured for exciting the generator (3); and a selector means (18) having an input side (17) and an output side (19), the input side (17) being connected to the DC side (15) of the first rectifier (12) and the DC side (15) of the second rectifier (13), and the output side (19) being connected to the exciter (9), whereby the selector means (18) is configured for switching the DC sides (15) in series or in parallel, or for transferring DC power from the first rectifier (12) and the second rectifier (13) to the output side (19) corresponding to an arbitrary shunt ratio.)
1. A power generation system, comprising:
a synchronous generator (3) for converting mechanical power into electrical power provided at an output side, the output side being configured for connection to an AC electrical grid (1),
at least two rectifiers (12, 13) comprising a first rectifier (12) and a second rectifier (13), each rectifier having an AC side (14) and a DC side (15) connected to the output side of the generator (3),
an exciter (9) configured for exciting the generator (3), and
a selector means (18) having an input side (17) and an output side (19), the input side (17) being connected to the DC side (15) of the at least two rectifiers (12, 13) and the output side (19) being connected to the exciter (9), whereby
The selector means (18) are configured for switching the DC side (15) in series or in parallel, or for transmitting DC power from the at least two rectifiers (12, 13) to the output side (19) corresponding to an arbitrary shunt ratio.
2. The power generation system according to the preceding claim, comprising:
a step-up transformer (2) connected to the output side of the generator (3) and configured for connecting the AC grid (1) such that the step-up transformer (2) is connected in series between the generator (3) and the grid (1), and
a first step-down transformer (16) connected in series between the AC side (14) of the at least two rectifiers (12, 13) and the step-up transformer (2),
a first step-down transformer (16) connected in series between the AC side (14) of at least one of the at least two rectifiers (12, 13) and the step-up transformer (2), and a second step-down transformer (26) connected in series between the AC side (14) of at least one other of the at least two second rectifiers (12, 13) and the step-up transformer (2), or
A first step-down transformer (16) connected in series between the AC side (14) of at least one of the at least two rectifiers (12, 13) and the step-up transformer (2), and a second step-down transformer (26) connected in series between the AC sides (14) of the at least two rectifiers (12, 13).
3. Power generation system according to the preceding claim, whereby a first step-down transformer (16) and/or if the second step-down transformer (26) provided as a single transformer with isolated secondary windings is provided with or without a phase shift scheme and/or comprises delta-Y connections.
4. The power generation system according to any of the preceding claims, whereby at least one of the at least two rectifiers (12, 13) is provided as a thyristor bridge rectifier, comprising a storage device (27) connected in series with at least one of the at least two rectifiers (12, 13), and/or being electrically isolated from each other.
5. The power generation system according to any of the preceding claims, whereby at least one of the at least two first rectifiers (12, 13) comprises a plurality of three-phase thyristor bridge rectifiers (14) connected in series and/or in parallel.
6. The power generation system of any one of the preceding claims, whereby
The at least two rectifiers (12, 13) are each provided as a three-phase thyristor bridge rectifier (20),
each DC side (15) comprising a first line (21) at a first potential and a second line (22) at a second potential, whereby the second potential is lower than the first potential,
the selector means (18) comprising a switch (25) arranged between the second line (22) of the first rectifier (12) and the first line (21) of the second rectifier (13), and
the second line (22) of the first rectifier (12) and the second line (22) of the second rectifier (13) are connected to the exciter (9), and the first line (21) of the second rectifier (13) and the first line (21) of the first rectifier (12) are connected to the exciter (9).
7. The power generation system according to the preceding claim, whereby the selector means (18) comprises a first diode (23) and a second diode (24), and the second line (22) of the first rectifier (12) is connected to the exciter (9) via the first diode (23) arranged in blocking direction and the second line (22) of the second rectifier (13), and the first line (21) of the second rectifier (13) is connected to the exciter (9) via the second diode (24) arranged in forward direction and the first line (21) of the first rectifier (12).
8. The power generation system according to claim 6, whereby the selector means (18) comprises a first circuit breaker (23) and a second circuit breaker (24), and the second line (22) of the first rectifier (12) is connected to the exciter (9) via the first circuit breaker (23) and the second line (22) of the second rectifier (13), and the first line (21) of the second rectifier (13) is connected to the exciter (9) via the second circuit breaker (24) and the first line (21) of the first rectifier (12).
9. The power generation system according to any of the three preceding claims, whereby the switch (25) is provided as an electrical switch, a mechanical breaker and/or a semiconductor switch.
10. The power generation system according to any of the preceding claims, whereby the generator (3) comprises a main machine (10) and the exciter (9) comprises a field winding or a brushless rotor (11) for exciting the main machine (10).
11. The power generation system according to any of the preceding claims, whereby the generator (3) comprises a field winding (8) and the exciter (9), the exciter (9) being configured for exciting the generator (3) by feeding DC power to the field winding.
12. The power generation system according to any of the preceding claims, whereby the generator (3) comprises a rotor (4), a stator (5) and a prime mover (6) rotating the rotor (4), the step-down transformer is connected to the stator (5), and the power generation system comprises a regulator (7) connected to the generator (3) and configured for controlling the mechanical power of the prime mover (6).
13. The power generation system according to any of the preceding claims, whereby the selector means (18) is configured for exchanging power from the first rectifier (12) and the second rectifier (13) to the output side (19) corresponding to the split ratio, and the split ratio is 1:3, 1:4, 1:5 or 1: 6.
14. A method of extending the duration of operation of a power generation system, comprising:
a synchronous generator (3) for converting mechanical power into electrical power provided at an output side, the output side being configured for connection to an AC electrical grid (1),
at least two rectifiers (12, 13) comprising a first rectifier (12) and a second rectifier (13), each rectifier having an AC side (14) and a DC side (15) connected to the output side of the generator (3),
an exciter (9) configured for exciting the generator (3), and
a selector means (18) having an input side (17) and an output side (19), the input side (17) being connected to the DC side (15) of the at least two rectifiers (12, 13) and the output side (19) being connected to the exciter (9), whereby the method comprises the steps of:
-switching the DC side (15) in series or in parallel by the selector means (18), or for transferring DC power from the at least two rectifiers (12, 13) to the output side (19) corresponding to an arbitrary shunt ratio.
15. The method of claim 14, comprising:
a step-up transformer (2) connected to the output side of the generator (3) and configured for connection to the electrical grid (1) such that the step-up transformer (2) is connected in series between the generator (3) and the electrical grid (1), and
a first step-down transformer (16) connected in series between the AC side (14) of the at least two rectifiers (12, 13) and the step-up transformer (2),
a first step-down transformer (16) connected in series between the AC side (14) of the first rectifier (12) and the step-up transformer (2), and a second step-down transformer (26) connected in series between the AC side (14) of the second rectifier (13) and the step-up transformer (2), or
A first step-down transformer (16) connected in series between the AC side (14) of at least one of the at least two rectifiers (12, 13) and the step-up transformer (2), and a second step-down transformer (26) connected in series between the AC sides (14) of the at least two rectifiers (12, 13).
Technical Field
The invention relates to a power generation system comprising: synchronous generator for converting mechanical power into electrical power and comprising: field winding (field winding); a step-up transformer connected to the generator and configured for connection to an AC grid such that the step-up transformer is connected in series between the generator and the grid; and an exciter configured to excite the generator by feeding DC power to the field winding.
Background
Synchronous generators are a major source of commercial electrical energy and are commonly used to convert the mechanical power output of steam turbines, gas turbines, reciprocating engines or water turbines into electrical power that is fed to a power grid. Synchronous generators typically include a rotor that is disposed in the center of the generator containing magnets, whereby the stator is electrically connected to a load such as an electrical grid. The magnets generate a magnetic field that induces the rotor to rotate and therefore the magnetic field to rotate at the same speed, inducing (induce) currents into the fixed armature. Typically, the synchronous generator is connected to the grid via a step-up transformer, and the field winding of the generator is fed via an exciter. The regulator (governor) controls the mechanical power of a prime mover (primary mover) that rotates the rotor of the generator, which in turn is supplied with a DC field current. The exciter typically draws AC power received from the grid through a step-down transformer and provides DC power to the field windings of the synchronous generator.
Under normal operating conditions, the voltage at the armature/stator is one per unit. However, the grid may experience various single or multiple line-to-line or line-to-ground faults, which result in a substantial drop in the voltage at the terminals. When this drop occurs at the terminals of the generator, it affects the voltage at the input of the step-down transformer and causes a drop in power at the output terminals of the exciter feeding the field winding of the synchronous generator. If such a fault persists for a relatively long period of time, the generator may lose synchronicity and the power plant including the generator is shut down, resulting in large-scale ripple and large economic losses on the power grid.
Document WO2014/032668a1 describes a connection system for connecting a generator to a DC electrical power system. The first rectifier is connected in parallel with the second rectifier. The first rectifier or the second rectifier will only rectify when the voltage exceeds the AC equivalent of the DC link voltage.
Document CN102185550A shows a wind turbine connected to a power grid. The exciter has a field winding that is excited by a field controller having a dedicated energy source.
Disclosure of Invention
It is therefore an object of the present invention to provide a power generation system and corresponding method for extending the duration of operation of a power plant grid fault.
The object of the invention is solved by the features of the independent claims. Preferred embodiments are described in the dependent claims.
Accordingly, the object is solved by a power generation system comprising: a synchronous generator for converting mechanical power into electrical power provided at an output side, the output side being configured for connection to an AC electrical grid; at least two rectifiers including a first rectifier and a second rectifier, each rectifier having an AC side connected to the step-up transformer and a DC side; an exciter configured to excite the generator; and a selector arrangement having an input side and an output side, the input side being connected to the DC sides of the at least two rectifiers, and the output side being connected to the exciter, whereby the selector arrangement is configured for switching the DC sides in series or in parallel, or for transferring power from the at least two rectifiers to the output side corresponding to an arbitrary split ratio (split ratio).
The key point of the invention is therefore that the power generation system is able to increase the voltage available to the exciter by, for example, switching the DC side in series, thereby doubling the voltage, without requiring a second source of electrical power such as a battery or capacitor. In other words, the power generation system allows for dynamically reconfiguring the topology of the excitation system comprising the first rectifier, the second rectifier, the exciter and the selector means online during a voltage drop at the terminals of the generator, i.e. during a so-called low voltage ride through LVRT. Thus, the power generation system may increase the excitation system voltage capability during severe voltage dips (voltage dip) in the grid due to various types of faults, thereby ensuring that the excitation system meets grid code requirements.
During normal operating conditions, the DC sides, which are the outputs of the first and second rectifiers, may be connected in parallel. During LVRT conditions, the selector means may connect the outputs of the first and second rectifiers in series, thereby increasing the total output voltage available to the field winding via the exciter. Having at least two rectifiers, a first rectifier and a second rectifier, allows for redundant operation and results in a significant reduction of the required cost and space when compared to prior art solutions requiring a second source of electrical power. The proposed solution has the further advantage that existing installations can be easily upgraded, since the additional hardware required for the second rectifier and the exciter only requires a small volume.
In summary, the power generation system is characterized by great flexibility in designing the step-up transformer and rectifier for continuous operation (e.g., in case of redundant operation) or for short-time operation (e.g., in case only voltage increase during LVRT is desired). The proposed excitation system can be applied to direct excitation systems as well as indirect excitation systems with or without external sources. For example, an additional cabinet (cabin) may be attached to the existing excitation system that provides additional voltage boost by switching the DC sides of the rectifiers in parallel during a fault while on standby during normal operating conditions. Furthermore, the proposed solution is very attractive for retrofit situations, while it also allows reducing situations where the existing excitation system is oversized in order to handle ride-through conditions for longer periods of time.
The synchronous generator may be provided as any synchronous generator known from the prior art, for example as a permanent magnet generator, whereby the magnetic field of the rotor is generated by permanent magnets. Other suitable types of generators may use electromagnets to generate a magnetic field in the rotor windings, whereby the dc current in the rotor field windings is provided by a brushless exciter on the same shaft. The step-up transformer is preferably provided as a transformer known from the prior art, preferably as a so-called medium voltage MV power transformer. The AC grid has a voltage of, for example, 110 kV.
Transferring power from the first rectifier and the second rectifier to the output side corresponding to any of the split ratios may involve adjusting an operating set point of the first rectifier relative to an operating set point of the second rectifier according to the split ratio. In the exemplary case of a thyristor-based rectifier, such as a thyristor bridge rectifier, the respective operating set point can be adjusted by adjusting the firing angle (firing angle) of the corresponding rectifier. The firing angle is commonly referred to as the cycle of voltage or current on the AC side of the rectifier. For example, the firing angles of the first rectifier may be set to provide two portions of the total power to be supplied, and the firing angles of the second rectifier may be set to provide three portions of the total power to be supplied, resulting in a split ratio of 2: 3. Other split ratios can be obtained in the same manner. Adjusting the operating set points, such as firing angles in the case of thyristor-based rectifiers, can be extended to configurations with more than two rectifiers, i.e. transmitting power from a plurality of rectifiers to the output side corresponding to any shunt ratio may involve adjusting the operating set points of the respective rectifiers relative to each other according to the shunt ratio. As a further example and as an alternative, for configurations that include rectifiers, each rectifier has a thyristor-based configuration (such as a thyristor bridge rectifier), one rectifier may be configured as a voltage source, and one or more additional rectifiers may be configured as thyristor bridge rectifiers. After a predetermined or adjustable amount of time has elapsed, the voltage source may be depleted (e.g., switched off), resulting in an arbitrary shunt ratio corresponding to that amount of time.
Transmitting power from the first rectifier and the second rectifier to the output side corresponding to the split ratio means: for example, with a split ratio of 2:3, two parts of the DC power are supplied by the first rectifier and three parts of the DC power are supplied by the second rectifier to the exciter. In a further embodiment more than two rectifiers are provided, each rectifier having an AC side and a DC side connected to the step-up transformer, whereby the input side of the selector means is connected to the DC side of the rectifier, and the selector means is configured for switching connecting the DC sides of all rectifiers, respectively, in series or in parallel, or for transferring power from the rectifiers to the output side corresponding to the split ratio. Thus, for example, with three rectifiers, the split ratio may be 3:1: 1. In general, the split ratio may be [ r1: r2: r3], where r1, r2, and r3 may each be real numbers so that splitting in power injection (and even extraction) is possible in any way. The splitting of the power according to the splitting ratio is preferably performed by separately controlling the rectifiers, which is preferably performed when two rectifiers are connected in series.
According to a preferred embodiment, the power generation system comprises: a step-up transformer connected to an output side of the generator and configured for connection to an AC grid such that the step-up transformer is connected in series between the generator and the grid; a first step-down transformer connected in series between the AC sides of the at least two rectifiers and the step-up transformer; a first step-down transformer connected in series between the AC side of at least one of the at least two rectifiers and the step-up transformer, and a second step-down transformer connected in series between the AC side of at least another of the at least two rectifiers and the step-up transformer; or a first step-down transformer connected in series between the AC side of at least one of the at least two rectifiers and the step-up transformer, and a second step-down transformer connected in series between the AC sides of the at least two rectifiers. The second step-down transformer may have the same input-output voltage and thus be used for electrical isolation.
In the case of the second alternative as described before, having the two step-down transformers each arranged in series with a respective rectifier and arranged in parallel between the selector means and the step-up transformer means that a separate step-down transformer is provided for each rectifier converter, with its primary side preferably connected to the stator/armature of the generator. A third alternative utilizes a first step-down transformer as a main transformer, which supplies voltage from the stator/armature of the generator to the two rectifiers, supplemented by an additional transformer (i.e. a second step-down transformer arranged between the two rectifiers), whereby said second step-down transformer provides electrical isolation between the two rectifier converters. Preferably, the second step-down transformer in the third alternative comprises a voltage ratio of 1:1, but alternative ratios are also possible.
According to a further preferred embodiment, a step-down transformer and/or a second step-down transformer provided as a single transformer with isolated secondary windings, is provided with or without a phase shifting scheme and/or comprises delta-Y connections. It is further preferred that the first step-down transformer and/or the second step-down transformer are connected by their primary side to the stator and/or the armature of the generator. In this way, the first rectifier and/or the second rectifier may be fed with an AC voltage by means of a first step-down transformer and/or a second step-down transformer connected to the stator and/or the armature of the generator.
According to another preferred embodiment, at least one of the at least two rectifiers is provided as a thyristor bridge rectifier, comprising storage devices connected in series with at least one of the at least two rectifiers, and/or being electrically isolated from each other. Preferably, the storage means is provided as a battery or a capacitor.
According to another preferred embodiment, at least one of the at least two rectifiers comprises a plurality of three-phase thyristor bridge rectifiers connected in series and/or in parallel. Preferably, the first rectifier and/or the second rectifier comprise a thyristor inverter, a directional diode rectifier, or comprise a self-commutated semiconductor device such as an IGBT arranged in parallel with a diode rectifier. Furthermore, the first rectifier and/or the second rectifier may be realized by using any means known from the prior art for rectifying an alternating current into a direct current, for example as a six-pulse diode rectifier.
As mentioned before, the first rectifier and the second rectifier are preferably provided as three-phase thyristor bridge rectifiers. In this case, according to another preferred embodiment, each DC side comprises a first line on a first potential and a second line on a second potential, whereby the second potential is lower than the first potential, the selector means comprises a switch arranged between the second line of the first rectifier and the first line of the second rectifier, and the second line of the first rectifier and the second line of the second rectifier are connected to the exciter, and the first line of the second rectifier and the first line of the first rectifier are connected to the exciter. Preferably, the first potential is provided as a positive potential, whereby preferably the second potential is provided as a negative potential.
In this way, both thyristor bridges are fed with an AC voltage, preferably provided by one or more step-down transformers connected to the stator terminals of the generator. During normal operation, the switches are preferably open and at least one converter (i.e. at least one of the two rectifiers) provides in operation a DC current via the exciter, e.g. to the rotor windings or brushless. During such normal operation, the other converter (i.e. the other rectifier) may be used for sharing current, e.g. for load balancing, or as a standby converter and/or rectifier.
According to a further embodiment in this respect, the selector means comprises a first diode and a second diode, and the second line of the first rectifier is connected to the exciter via the first diode arranged in the blocking direction and the second line of the second rectifier, and the first line of the second rectifier is connected to the exciter via the second diode arranged in the forward direction and the first line of the first rectifier. In this way, when the switch is closed, the first and second diodes will enter a blocking state, so that the total output voltage available for exciting the generator increases, which is particularly advantageous during LVRT conditions.
In an alternative embodiment of this aspect, the selector means comprises a first circuit breaker and a second circuit breaker, and the second line of the first rectifier is connected to the exciter via the first circuit breaker and the second line of the second rectifier, and the first line of the second rectifier is connected to the exciter via the second circuit breaker and the first line of the first rectifier. Preferably, the first circuit breaker and/or the second circuit breaker is arranged in parallel with the first diode and/or the second diode in order to bypass the respective diode. Providing a circuit breaker has the advantage of reducing conduction losses during normal operation.
According to a further preferred embodiment, the switch is provided as an electrical switch, a mechanical breaker and/or a semiconductor switch (e.g. comprising IGBTs), allowing an easy and cost-effective implementation.
As briefly outlined above, the generator may be provided in different ways. According to a particularly preferred embodiment, the generator comprises a main machine and the exciter comprises a field winding or a brushless rotor for exciting the main machine. In another preferred embodiment, the synchronous generator comprises a field winding and the exciter is configured for exciting the generator by feeding DC power to the field winding. In a still further preferred embodiment, the generator comprises a rotor, a stator, and a prime mover to rotate the rotor, the step-down transformer is connected to the stator, and the power generation system comprises a regulator connected to the generator and configured to control mechanical power of the prime mover.
In another preferred embodiment, the selector means are configured for transferring or switching power from the first rectifier and the second rectifier to the output side corresponding to a shunt ratio, whereby the shunt ratio is 1:3, 1:4, 1:5 or 1: 6. Further, the split ratio may be [ 1: r ], where r is a real number so that the splitting in power injection (or even extraction) can be done in any way. In this way, load sharing functionality may be achieved by shunting the ratio of DC power provided from the first and second rectifiers in accordance with a given ratio. For redundant operation, the magnetic circuit of the first step-down transformer and/or the second step-down transformer is preferably designed for nominal load conditions with a shunt ratio of 1: 1.
The object of the invention is also solved by a method of prolonging operation during a power generation system comprising a synchronous generator for converting mechanical power into electrical power provided at an output side configured for connection to an AC grid; at least two rectifiers including a first rectifier and a second rectifier, each rectifier having an AC side and a DC side connected to a step-up transformer; an exciter configured for exciting the generator and the selector arrangement with DC power, having an input side and an output side, the input side being connected to the DC sides of the at least two rectifiers and the output side being connected to the exciter, whereby the method comprises the steps of: the DC side is switched in series or in parallel by selector means or for transferring DC power from at least two rectifiers to the output side corresponding to an arbitrary shunt ratio.
According to a further preferred embodiment, the method comprises: a step-up transformer connected to the generator and configured for connection to an AC electrical grid such that the step-up transformer is connected in series between the generator and the electrical grid; a first step-down transformer connected in series between the AC side and the step-up transformer; a first step-down transformer connected in series between the AC side of at least one of the at least two rectifiers and the step-up transformer, and a second step-down transformer connected in series between the AC side of at least another one of the rectifiers and the step-up transformer; or a first step-down transformer connected in series between the AC side of at least one of the at least two rectifiers and the step-up transformer, and a second step-down transformer connected in series between the AC sides of the at least two rectifiers.
Further embodiments and advantages of the method will be derived by the person skilled in the art analogously to the power generation system as described above. The method allows for advantageously increasing the voltage available to the exciter without the need for a second source of electrical power, such as a battery or capacitor. The first rectifier and the second rectifier may advantageously be used for redundant operation and voltage increase during low voltage ride through, thereby significantly reducing cost and space requirements compared to prior art approaches.
Drawings
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
In the drawings:
figure 1 shows schematically a power generation system according to a preferred embodiment of the invention,
figure 2 shows schematically a first rectifier and a second rectifier with selector means of a power generation system according to a preferred embodiment of the invention,
figure 3 schematically shows a power generation system according to a further embodiment of the invention,
FIG. 4 schematically illustrates a power generation system according to a further embodiment of the invention, an
Fig. 5 shows schematically a first rectifier in a further preferred embodiment of the invention.
Detailed Description
Fig. 1, 3 and 4 each schematically illustrate a power generation system according to a preferred embodiment of the present invention. The
A
The selector means 18, e.g. provided as a switch, is configured for switching the
Under normal operating conditions, the DC sides of the
Fig. 2 shows an exemplary embodiment of the
The selector means 18 comprises a
In this way, during normal operation, the
The
The firing angle of any or each of the three-phase thyristor bridge rectifiers 20 may be adjustable. For example, a common firing angle for each of the transistors in the three-phase thyristor bridge rectifier (20) on the left-hand side in fig. 2 may be set to a first angle, and another common firing angle for each of the transistors in the three-phase thyristor bridge rectifier (20) on the right-hand side in fig. 2 may be set to a second angle. Corresponding to the ratio of the first angle to the second angle, the first angle may be adjusted independently of the second angle to achieve a shunt ratio of the rectifier 20. Also, in configurations with more than two rectifiers, the respective firing angles may be adjusted independently of each other in a similar manner.
Fig. 3 and 4 show two further embodiments, each comprising an additional second step-down
In the embodiment shown in fig. 4, a first step-down
Fig. 5 shows an embodiment of the
While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims shall not be construed as limiting the scope.
REFERENCE SIGNS LIST
1 electric network
2 step-up transformer
3 synchronous generator
4 rotor
5 stator
6 prime mover
7 regulator
8 field winding
9 exciter
10 main machine
11 brushless rotor
12 first rectifier
13 second rectifier
14 DC side
15 AC side
16 first step-down transformer
17 input side
18 selector device
19 output side
20 three-phase thyristor bridge rectifier
21 first potential
22 second potential
23 first diode, first circuit breaker
24 second diode, second circuit breaker
25 switch
26 second step-down transformer
27 storage device
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