POWER SYSTEM

Abstract

A power system includes at least one generator driven by at least one of a number (N) of prime movers, at least one energy storage device, and at least one control device, wherein the generator and the energy storage device provide electrical energy to a power grid having an external load. The power system includes at least one first measuring device for determining at least one first signal for a computer to determine what amount of electrical power (ΣP.sub.G,i) has to be generated by the at least one generator to meet a power requirement (P.sub.load) of the external load. The at least one control device is configured to receive the at least one first signal and to influence the control of the speed (n.sub.i) of the at least one of the number (N) of prime movers or the frequency (f) of the power grid taking into account the at least one signal to change the mechanical power generated by the at least one of the number (N) of prime movers such that the electrical power provided by the at least one generator approaches the power requirement (P.sub.load) of the external load in situations where the power requirement (P.sub.load) of the external load is at least partially provided for by the at least one energy storage device.

Claims

1. A power system, comprising: a number (N) of prime movers having a variable speed (n.sub.i), configured to generate mechanical power by providing a mechanical drive force, wherein the number (N) of prime movers is one or more; at least one generator configured to receive the drive force of at least one of the number (N) of prime movers to generate an electrical power, wherein the at least one generator is configured to couple with a power grid, and the power grid is configured to transmit the electrical power having a frequency (f) and to couple with an external load; at least one controller configured to control the variable speed (n.sub.i) to a speed reference (n.sub.ref,i) of at least one of the number (N) of prime movers and/or the frequency (f) of the power grid; at least one energy storage device configured to, at least temporarily, provide to the external load and/or receive from the external load, the electrical power via the power grid; at least one first measuring device configured to provide at least one first signal to the at least one controller to determine an amount of electrical power (ΣP.sub.G,i) to be generated by the at least one generator to meet a power requirement (P.sub.load) of the external load; wherein the at least one controller is configured to receive the at least one first signal and to influence the control of the variable speed (n.sub.i) of the at least one of the number (N) of prime movers or the frequency (f) of the power grid taking into account the at least one first signal to change the mechanical power generated by the at least one of the number (N) of prime movers such that the electrical power provided by the at least one generator approaches the power requirement (P.sub.load) of the external load in situations where the power requirement (P.sub.load) the external load is at least partially provided by the at least one energy storage device, and wherein the at least one controller is configured to control the variable speed (n.sub.i) of the at least one of the number (N) of prime movers and, at least temporarily, apply an additive or multiplicative feed-forward-control of actuators of the at least one of the number (N) of prime movers proportional to the received at least one first signal to influence the mechanical power produced by the prime mover, wherein the at least one first signal is representative for the electric power provided by the at least one energy storage device to the power grid.

2. The power system of claim 1, comprising one or more components of the power grid.

3. The power system of claim 1, wherein the at least one controller is configured to control the variable speed (n.sub.i) of the at least one of the number (N) of prime movers (3) and, at least temporarily, apply a correction of the speed reference (n.sub.ref,i) proportional to the received at least one first signal to influence the mechanical power produced by the prime mover.

4. The power system of claim 1, comprising a first control logic and a second control logic, wherein the first control logic is configured to control a state of charge of the at least one energy storage device, wherein the second control logic is configured to determine the electrical power or currents exchanged by the at least one energy storage device with the power grid in dependence on the variable speed (n.sub.i) or the frequency (f) and to determine whether the power system shows transient behavior based on a frequency deviation from a reference value (f.sub.ref) for frequency of the power grid.

5. The power system of claim 1 wherein the at least one first signal is representative for: a command of the electrical power provided by the at least one energy storage device to the power grid; and/or the power requirement (P.sub.load) of external the external load.

6. The power system of claim 1, comprising at least one storage controller configured to track and/or control a sum of power commands from the at least one controller and a first control logic by controlling current magnitudes and voltage levels of the at least one energy storage device, wherein the first control logic is configured to control a state of charge of the at least one energy storage device.

7. The power system of claim 1, comprising at least one second measuring device configured to provide at least one second signal to the at least one controller to determine the variable speed (n.sub.i) of at least one of the number (N) of prime movers or the frequency (f) of the power grid.

8. The power system of claim 7, comprising at least one third measuring device configured to provide at least one third signal to the at least one controller to determine the electrical power provided by the at least one generator to the power grid.

9. A system, comprising: at least one controller, wherein in an operating state of a prime mover configured to drive a generator to provide an electrical power to an external load via a power grid coupled to at least one energy storage device, the at least one controller is configured to, at least temporarily, when a power requirement (P.sub.load) of the external load is at least partially provided by the at least one energy storage device. receive at least one first signal to determine an amount of the electrical power (P.sub.G,i) to be generated by the at least one generator to meet the power requirement (P.sub.load) of the external load; and control a variable speed (n.sub.i) of the prime mover in dependence on the at least one first signal to change a mechanical power generated by the prime mover such that the electrical power provided by the at least one generator approaches the power requirement (P.sub.load) of the external load; wherein the at least one controller is configured to control the variable speed (n.sub.i) of the prime mover and, at least temporarily, apply an additive or multiplicative feed-forward-control of an actuator of the prime mover proportional to the received at least one first signal to influence the mechanical power generated by the prime mover, wherein the at least one first signal is representative for the electric power provided by the at least one energy storage device to the power grid.

10. The system of claim 9, comprising the prime mover coupled to the generator.

11. A method to control at least one prime mover having a variable speed (n.sub.i), wherein the at least one prime mover is configured generate a mechanical drive force to drive at least one generator to generate an electrical power that is provided to a power grid, wherein the power grid is coupled to an external load and at least one energy storage device, wherein the at least one energy storage device is configured to at least temporarily provide electrical power to the power grid, wherein in situations when a power requirement (P.sub.load) of the external load is at least partially provided by the at least one energy storage device, the method comprises: receiving at least one first signal at a controller to determine an amount of electrical power (P.sub.G,i) to be generated by the at least one generator to meet a power requirement (P.sub.load) of the external load, wherein the at least one first signal is representative for the electric power provided by the at least one energy storage device to the power grid; controlling the variable speed (n.sub.i) of the at least one prime mover or a frequency (f) of the power grid in dependence on the at least one signal to change a mechanical power generated by the at least one prime mover such that the electrical power provided by the at least one generator approaches the power requirement (P.sub.load) of the external load; and applying, at least temporarily, an additive or multiplicative feed-forward-control of an actuator of the at least one prime mover proportional to the received at least one first signal to influence the mechanical power generated by the at least one prime mover.

12. The method of claim 11, comprising: controlling a state of charge of the at least one energy storage device; determining the electrical power or currents exchanged by the at least one energy storage device with the power grid in dependence on the variable speed (n.sub.i) or the frequency (f); and identifying transient behavior based on a frequency deviation from a reference value (f.sub.ref) for frequency of the power grid.

13. The method of claim 11, comprising tracking and/or controlling a sum of power commands by controlling current magnitudes and voltage levels of the at least one energy storage device.

14. The system of claim 9, wherein the at least one controller is configured to control the variable speed (n.sub.i) of the prime mover and, at least temporarily, apply a correction of the speed reference (n.sub.ref,i) proportional to the received at least one first signal to influence the mechanical power produced by the prime mover.

15. The system of claim 9, comprising a first control logic and a second control logic, wherein the first control logic is configured to control a state of charge of the at least one energy storage device, wherein the second control logic is configured to determine the electrical power or currents exchanged by the at least one energy storage device with the power grid in dependence on the variable speed (n.sub.i) or the frequency (f) and to identify transient behavior based on a frequency deviation from a reference value (f.sub.ref) for frequency of the power grid.

16. The system of claim 9, comprising at least one storage controller configured to track and/or control a sum of power commands from the at least one controller and a first control logic by controlling current magnitudes and voltage levels of the at least one energy storage device, wherein the first control logic is configured to control a state of charge of the at least one energy storage device.

17. The system of claim 9, wherein the at least one controller is configured to receive at least one second signal to determine the variable speed (n.sub.i) of the prime mover or the frequency (f) of the power grid.

18. The system of claim 17, wherein the at least one controller is configured to receive at least one third signal to determine the electrical power provided by the at least one generator to the power grid.

19. The system of claim 9, comprising the prime mover, the generator, or a combination thereof.

20. The system of claim 9, comprising the at least one energy storage device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] An embodiment of the invention is shown in FIGS. 1 and 2.

[0059] FIG. 1 shows an exemplary power system according to an embodiment of the invention with several prime movers at least temporarily controlled by a method according to the embodiment of the invention.

[0060] FIG. 2 shows a comparison between transient behavior of the power system according to FIG. 1 (solid lines) and a power system according to the prior art (broken lines).

DETAILED DESCRIPTION

[0061] In the power system 1 of FIG. 1, a number N of gensets, each consisting of a prime mover 3 mechanically coupled by an output shaft to a generator 4 is shown. Each prime mover 3 provides mechanical drive force (and thus mechanical power) to its generator 4 and has a speed n.sub.i which can be measured by a second measuring device 8 (shown only for the first prime mover 3). As a result of the mechanical coupling, each generator 4 generates an electrical power P.sub.G,I which is transmitted by a power grid. Together, the generators 4 produce a sum of electrical powers ΣP.sub.G,i. There can be a third measuring device 9 to provide a signal representing the amount of electrical power P.sub.G,i generated by the generator 4 to the control device 5 (only shown for the first prime mover 3). Of course, internal measurement values of the prime mover 3 can be provided to the control device 5 as is shown exemplary by the value p2s (load pressure).

[0062] An external load 2 couples to the power grid and has a momentary load requirement P.sub.Load.

[0063] An energy storage device 6 in the form of an accumulator provided with power electronics 12 and a storage control device 11 is also coupled to the power grid. The storage control device 11 receives temperature T, current magnitude I and internal voltage V of the energy storage device 6 and sends control commands u to the power electronics 12 to command exchange of power P.sub.Storage (which can be negative or positive; equivalent values like current can be controlled optionally) with the power grid.

[0064] A computer 10 which in this embodiment together with a SOC control logic 13 forms a master control device receives a speed n (selected from all the speeds n.sub.i or computed from them, e.g., as an average value) and/or a frequency f of the power grid and compares them with reference values n.sub.ref and/or f.sub.ref. If there is a difference between momentary values n and/or f and reference values n.sub.ref and/or f.sub.ref, the computer 10 concludes that a transient behavior of the power system 1 is present and sends a command value P.sub.Storage,cmd for power to be provided to or received from (i.e., exchanged with) the power grid to the storage control device 11. The magnitude of P.sub.Storage,cmd can be, for example, proportional to the absolute speed error and its derivative (PD controller). The amount of power P.sub.Storage provided by energy storage device 6 is measured by a first measuring device 7 and provided via storage control device 11 to the control devices 5 of the prime movers 3 (this signal could also be directly provided to the control devices 5). In this example, only the portion of electrical power which is provided by the energy storage device 6 to the power grid that is used for transient regulation is provided to the control devices 5 by subtracting the command for state of charge control (output of SOC control logic 13). In this example, each control device 5 knows that there is a number N of (in this case identical) prime movers 3 present and can therefore divide the amount of power P.sub.Storage provided by the energy storage device 6 by the number N to determine what amount of electrical power P.sub.G,i has to be generated by the generator 4 coupled to its prime mover 3 to meet a power requirement P.sub.load of the external load 2 (it has to add/subtract enough mechanical power to come up for the share P.sub.Storage/N which, at the moment, is provided for or received by the energy storage device 6). In response to this, each control device 5 sends one or several feed forward command(s) u to actuators of its prime mover 3 to achieve this change by changing speed n.sub.i of the prime mover 3.

[0065] The SOC control logic 13 can be PI or PID and receives the difference between the (externally or internally provided) state of charge set value SOC.sub.set and the feedback value of the state of charge SOC (output of storage control device 11) as an input. Optionally, it can be disabled during transients by the output of computer 10.

[0066] The sum of the outputs of SOC control logic 13 and the computer 10 are used to calculate P.sub.Storage,cmd which is the commanded power to the storage control device 11.

[0067] FIG. 2 shows in solid lines A an exemplary transient behavior of the power system 1 of FIG. 1.

[0068] Between time 0.1 and 0.2, load requirement P.sub.Load of external load 2 suddenly increases which is shown by a sudden small drop in speed n from about 1 to about 0.995. In response to this, power P.sub.S provided by the electric storage device 6 to the external load 2 increases from about 0 to a little above 0.2. According to the disclosed embodiment, after a short sub-transient effect, power P.sub.G provided by all the generators 4 together increases from time 0.2 to about 0.4, such that power P.sub.S provided by the electric storage device 6 to the external load 2 decreases to about 0. At the same time, the speed approaches a steady state and therefore the power produced by the generators is equal to the applied external load.

[0069] The broken lines B show that without the disclosed embodiment, this state is still not achieved by time 0.55 but the long power consumption from the storage device 6 leads to an emptying of energy storage device 6 and a pronounced drop in speed n between time 0.55 and 0.8 until power provided by the prime movers 3 to the generators 4 can compensate for the increased load requirement P.sub.Load of external load 2. This represents a worst-case scenario, but even if it the storage does not become suddenly empty, the speed deviation from its reference is present for an undesired long duration.

[0070] List of Reference Numbers:

[0071] 1 power system

[0072] 2 external load

[0073] 3 prime mover

[0074] 4 generator

[0075] 5 control device

[0076] 6 energy storage device

[0077] 7 first measuring device

[0078] 8 second measuring device

[0079] 9 third measuring device

[0080] 10 computer

[0081] 11 storage control device

[0082] 12 power electronics

[0083] 13 SOC control logic

[0084] N number of prime movers

[0085] n speed of prime mover

[0086] n.sub.i speed of i.sup.th prime mover

[0087] n.sub.ref reference value for speed

[0088] n.sub.ref,i reference value for speed of i.sup.th prime mover

[0089] f frequency of power grid

[0090] f.sub.ref reference value for frequency of power grid

[0091] P.sub.Load power requirement of external load

[0092] P.sub.G,i power generated by i.sup.th generator

[0093] P.sub.Storage power provided by energy storage device

[0094] P.sub.Storage,cmd command value for power provided by energy storage device

[0095] u control command

[0096] SOC state of charge of energy storage device

[0097] T temperature of energy storage device

[0098] V internal voltage of energy storage device

[0099] I current magnitude delivered by/to energy storage device