METHOD OF SYNCHRONIZING A GENERATOR WITH A POWER SUPPLY NETWORK

Abstract

A method of synchronizing a generator (3) with a power supply grid (4) having a grid frequency including the following steps: f) mechanically driving the generator (3) by means of an internal combustion engine (2), in particular a gas engine, creating a generator rotary speed corresponding to a generator frequency generated by the generator (3) at the prevailing generator rotary speed, g) closed-loop or open-loop control of the internal combustion engine (2) such that the generator frequency is in a tolerance range, wherein the grid frequency is within the tolerance range, h) detecting a phase angle difference between a current generated by the generator (3) and/or a voltage generated by the generator (3) on the one hand and a grid current and/or a grid voltage on the other hand, i) synchronizing the voltage generated by the generator (3) and/or the current generated by the generator (3) on the one hand with the grid voltage and/or the grid current on the other hand by the phase angle difference (Δφ) being reduced, in particular minimized, and j) electrically connecting the generator (3) to the power supply grid (4), wherein at least one temporary change in an ignition timing of at least one cylinder unit (9) of the internal combustion engine (2) is performed to reduce the phase angle difference (Δφ).

Claims

1. A method of synchronizing a generator (3) with a power supply grid (4) having a grid frequency including the following steps: a) mechanically driving the generator (3) by means of an internal combustion engine (2), in particular a gas engine, creating a generator rotary speed corresponding to a generator frequency generated by the generator (3) at the prevailing generator rotary speed, b) closed-loop or open-loop control of the internal combustion engine (2) such that the generator frequency is in a tolerance range, wherein the grid frequency is within the tolerance range, c) detecting a phase angle difference between a current generated by the generator (3) and/or a voltage generated by the generator (3) on the one hand and a grid current and/or a grid voltage on the other hand, d) synchronizing the voltage generated by the generator (3) and/or the current generated by the generator (3) on the one hand with the grid voltage and/or the grid current on the other hand by the phase angle difference (Δφ) being reduced, in particular minimized, and e) electrically connecting the generator (3) to the power supply grid (4), characterised in that at least one temporary change in an ignition timing of at least one cylinder unit (9) of the internal combustion engine (2) is performed to reduce the phase angle difference (Δφ).

2. A method as set forth in claim 1 characterised in that the at least one temporary change in the ignition timing is effected in accordance with a switching rule (S), wherein the switching rule (S) is a function:
S=f(Δn.sub.gsetpoint,Δφ) of a deviation relative to the setpoint generator rotary speed (Δn.sub.g.sub.setpointl) and the phase angle difference (Δφ).

3. A method as set forth in claim 2 characterised in that the temporary change in the ignition timing is effected at the condition S>ε wherein S=ε if Δn.sub.g.sub.setpointl=Δφ=0.

4. A method as set forth in at least one of the preceding claims characterised in that the temporary change in the ignition timing occurs relative to a predeterminable nominal ignition timing (t.sub.nom).

5. A method as set forth in at least one of the preceding claims characterised in that an ignition timing (t.sub.temp) which is changed in accordance with the temporary change in the ignition timing is temporarily changed relative to the predeterminable nominal ignition timing (t.sub.nom).

6. A method as set forth in at least one of the preceding claims characterised in that in step d)—preferably intermittently—switching is effected from the nominal ignition timing (t.sub.nom) to the changed ignition timing (t.sub.temp) and vice-versa.

7. A method as set forth in at least one of the preceding claims characterised in that the nominal ignition timing (t.sub.nom) corresponds to the ignition timing in step b) and/or c).

8. A method as set forth in at least one of the preceding claims characterised in that the temporary change in the ignition timing is effected substantially in discrete steps.

9. A method as set forth in at least one of the preceding claims characterised in that a throttle valve of the internal combustion engine (2), in particular a gas engine, is subjected to open-loop and/or closed-loop control in such a way that the generator rotary speed increases during the step d) if the ignition timing were to remain substantially at the predeterminable nominal ignition timing (t.sub.nom).

10. A method as set forth in at least one of the preceding claims characterised in that the temporary change in the ignition timing is terminated with the connection of the generator (3) to the power supply grid (4).

11. An internal combustion engine, in particular a gas engine, including at least one cylinder unit and an open-loop and/or closed-loop control unit (6), wherein the open-loop and/or closed-loop control unit (6) is adapted to provide for open-loop or closed-loop control of the internal combustion engine (2) according to the method as set forth in at least one of the preceding claims.

12. A computer program product for synchronizing a generator (3) with a power supply grid (4) having a grid frequency with commands which cause an executing computer: f) to actuate an internal combustion engine (2), in particular a gas engine, for mechanically driving the generator (3) with the creation of a generator rotary speed, wherein the generator rotary speed corresponds to a generator frequency generated by the generator (3) at the present generator rotary speed, g) to provide for closed-loop or open-loop control of the internal combustion engine (2) such that the generator frequency is in a tolerance range, wherein the grid frequency is within the tolerance range, h) to receive or calculate at least one detection signal, which detection signal corresponds to a phase angle difference between a current generated by the generator (3) and/or a voltage generated by the generator (3) on the one hand and a grid current and/or a grid voltage on the other hand, i) to actuate the internal combustion engine for synchronizing the voltage generated by the generator (3) and/or the current generated by the generator (3) on the one hand with the grid voltage and/or the grid current on the other hand by the phase angle difference (Δφ) being reduced, in particular minimized, and j) to output a trigger signal for electrically connecting the generator (3) to the power supply grid (4), characterised in that the commands cause the computer to reduce the phase angle difference by at least one temporary change in an ignition timing of at least one cylinder unit of the internal combustion engine (2).

13. A computer-readable storage medium having a computer program product as set forth in claim 12.

Description

[0058] Further particularities, advantages and details of the present invention are described by way of example by means of the specific description hereinafter with reference to the Figures in which:

[0059] FIG. 1 shows a first embodiment of a genset, and

[0060] FIGS. 2a-2e show measurements and actuating signals for carrying out an embodiment of a method according to the invention.

[0061] FIG. 1 shows a first embodiment of a genset 1.

[0062] The genset 1 includes an internal combustion engine 2 which is connected to a generator 3 for power generation by way of a mechanical shaft 5 (for example this can also be implemented in the form of a prolongation of the crankshaft of the internal combustion engine 2).

[0063] In addition in principle a transmission could also be provided between the crankshaft of the internal combustion engine.

[0064] In this embodiment the internal combustion engine 2 has a plurality of cylinder units 9, wherein the cylinder units 9 can be subjected to open-loop or closed-loop control by way of a central open-loop or closed-loop control unit 6 during operation of the internal combustion engine 2, by for example the ignition, the fuel feed, the air feed and/or other parameters of combustion being subjected to open-loop or closed-loop control by suitable valves, open-loop or closed-loop control members, by means of the open-loop or closed-loop control unit 6.

[0065] The generator 3 can be connected to a power supply grid 4 by way of an electrical connection 10, wherein the electrical connection 10 can be in the form of a switch connecting the electric lines of the generator 3 to the power supply grid 4.

[0066] In addition there is provided a first sensor 7 to be able to ascertain a characteristic parameter for the generated voltage or the generated current of the generator 3. A frequency of the voltage and/or the current of the generator 3 can be ascertained by means of that characteristic parameter of the generated voltage or the current of the generator 3 by way of the open-loop or closed-loop control unit 6.

[0067] In this embodiment that first sensor 7 is in the form of a rotary speed sensor at the shaft 5, the measured rotary speed in this embodiment corresponding to the generator rotary speed of the generator 3. If there were a transmission, then the generator rotary speed could be ascertained on the basis of a known transmission ratio. A frequency of the current generated by the generator 3 and the voltage of the generator 3 is known by the known generator rotary speed.

[0068] In addition this embodiment shows a second sensor 8, by means of which a frequency of the current and/or the voltage of the power supply grid 4 can be ascertained and can be fed to the open-loop or closed-loop control unit 6.

[0069] It can further be provided that the open-loop or closed-loop control unit 6 is connected to the electrical connection 10, wherein the electrical connection 10 between the generator 3 and the power supply grid 4 can be created and/or interrupted by the open-loop or closed-loop control unit 6.

[0070] Thus, by way of the open-loop or closed-loop control unit 6, it can be provided that as required the internal combustion engine 2 is started to drive the generator 3.

[0071] The rotary speed of the internal combustion engine 2 and therewith the generator frequency can be subjected to open-loop or closed-loop control by way of the open-loop or closed-loop control unit 6 in such a way that the generator frequency approaches the grid frequency until the generator frequency is in the tolerance range 12 around the grid frequency.

[0072] There is then a phase angle difference between the grid voltage and/or the grid current on the one hand and the generator voltage and/or the generator current on the other hand. In order to be able to couple the generator to the power supply grid 4 to deliver electrical energy, the phase angle difference generally now has to be reduced, in particular minimized (this is also referred to as synchronization of the generator 3 with the power supply grid 4).

[0073] According to the invention that is effected by changing the ignition timing of at least one cylinder unit 9 of the internal combustion engine 2.

[0074] Measurement values and actuation signals from a method according to the invention for synchronizing the generator 3 to the power supply grid 4 are shown by FIGS. 2a through 2e, wherein (as shown in FIG. 2a) an internal combustion engine 2 with a coupled generator 3 is accelerated from the stopped condition until a desired generator rotary speed is reached.

[0075] In that respect FIG. 2a shows the behavior of the generator rotary speed along the synchronization time with the power supply grid 4.

[0076] FIG. 2b shows a phase angle difference in respect of the current and/or the voltage between the generated current and/or voltage of the generator 3 and the current and/or voltage of the power supply grid 4.

[0077] FIG. 2c shows a control signal of the open-loop or closed-loop control unit 6 for the ignition timing of at least one cylinder unit 9 of the internal combustion engine 2, that is to say a control signal for determining the ignition timing. That ignition timing is specified in this Figure with respect to an angle of revolution of the crankshaft of the internal combustion engine 2 before a top dead center point (as is customary in the state of the art).

[0078] FIG. 2d shows an open-loop or closed-loop control signal of the open-loop or closed-loop control unit 6 with respect to a throttle valve of the internal combustion engine 2, wherein the graph shows an opening of the throttle valve between “1” (fully opened) and “0” (fully closed).

[0079] FIG. 2e shows an open-loop or closed-loop control signal of the open-loop or closed-loop control unit 6 for the electrical connection 10 of the generator 3 to the power supply grid 4, wherein a distinction is drawn between a closed connection “1” (control signal for closure of the electrical connection 10) and an opened connection “0”. As can be seen the connection 10 of the generator 3 to the power supply grid 4 is made as soon as the phase angle difference is stabilized in a further tolerance range 12 for an acceptable phase angle difference (connection criterion).

[0080] Those measurement values or actuation signals were gathered simultaneously during the implementation of the embodiment of a method according to the invention on an internal combustion engine 2, the time scale in FIGS. 2a through 2e being the same.

[0081] Thus it can be seen that firstly the internal combustion engine 2 is started up until it exceeds a desired generator rotary speed, wherein firstly the throttle valve is fully opened for acceleration of the internal combustion engine 2 as rapidly as possible.

[0082] In order slowly to slow down the acceleration the throttle valve is closed shortly before reaching the desired rotary speed and the acceleration is reduced and vice-versa in order to move into the desired tolerance range 11 of the rotary speed (or equivalent the generator frequency). Before that hunting of the phase angle difference (FIG. 2b) is to be observed, which naturally is to be attributed to the non-coincidence of the generator frequency with the grid frequency.

[0083] It can be seen from FIG. 2c that synchronization begins at about second 10, by the nominal ignition timing t.sub.nom of a cylinder unit being shifted towards “late” becoming a changed ignition timing t.sub.temp, and that is reset after each cycle or after a predeterminable number of cycles in order to bring the rotary speed of the internal combustion engine (as shown in FIG. 2a) and thus also the generator rotary speed into a predetermined rotary speed band in respect of which a phase angle difference between power supply grid 4 and generator 3 is minimized (or more optimally is eliminated).

[0084] It can further be seen from FIG. 2d that the throttle valve is slightly opened at the beginning of synchronization. That opening makes it possible to increase the rotary speed of the internal combustion engine 2 when the ignition timing corresponds to the nominal ignition timing t.sub.nom and to reduce the rotary speed when the ignition timing corresponds to the changed ignition timing t.sub.temp. In that way it is possible to achieve a better response characteristic in respect of closed-loop control during synchronization.

[0085] As soon as the phase angle difference has been minimized to such an extent that it corresponds to a connection criterion, the generator 3 is connected to the power supply grid 4 by way of the electrical connection 10 by the open-loop or closed-loop control unit 6 and can be changed into a normal operating mode for the genset 1 by the open-loop or closed-loop control unit 6.

[0086] The connection criterion includes for example that the generator rotary speed (see FIG. 2a) is in a predeterminable tolerance range 11 and that the phase angle difference (see FIG. 2a) is in a predeterminable further tolerance range 12.

[0087] The throttle valve is then constantly opened after the generator 3 has been connected to the power supply grid 4 in order to increase the power output of the internal combustion engine 2 and thus the power delivered to the power supply grid 4.

List of References

[0088] 1 genset

[0089] 2 internal combustion engine

[0090] 3 3 generator

[0091] 4 power supply grid

[0092] 5 shaft

[0093] 6 open-loop or closed-loop control unit

[0094] 7 first sensor

[0095] 8 second sensor

[0096] 9 cylinder unit

[0097] 10 electrical connection

[0098] 11 tolerance range

[0099] 12 tolerance range

[0100] t.sub.nom nominal ignition timing

[0101] t.sub.temp changed ignition timing