METHOD FOR CONTROLLING A POWER SOURCE

Abstract

Method for controlling at least one power source (1), the at least one power source (1) supplying electrical power to at least one power consumer (3) via an electrical power supply grid (2), wherein the following steps are carried out: measuring and/or determining electrical quantities, preferably a frequency and a power disturbance, of the power supply grid (2) during a time period where the electric power supply grid (2) is excited and/or perturbed, such that there is a frequency deviation from a nominal frequency of the power supply grid, deriving at least one parameter (H,D,K.sub.P,K.sub.I,K.sub.D) of a dynamic grid response model from measured values and/or determined values of the measurement and/or determination of the electrical quantities of the power supply grid (2), and adapting a control algorithm defining a control response of the at least one power source (1) depending on the at least one parameter (H,D,K.sub.P,K.sub.I,K.sub.D) of the dynamic grid response model.

Claims

1. A method for controlling at least one power source, the at least one power source supplying electrical power to at least one power consumer via an electrical power supply grid, the method comprising: measuring and/or determining electrical quantities, comprising a frequency and a power disturbance, of the power supply grid during a time period where the electric power supply grid is excited and/or perturbed, such that there is a frequency deviation from a nominal frequency of the power supply grid; deriving at least one parameter (H, D, K.sub.P, K.sub.I, K.sub.D) of a dynamic grid response model from measured values and/or determined values of the measurement and/or determination of the electrical quantities of the power supply grid; and adapting a control algorithm defining a control response of the at least one power source depending on the at least one parameter (H, D, K.sub.P, K.sub.I, K.sub.D) of the dynamic grid response model.

2. The method according to claim 1, comprising deriving as the at least one parameter (K.sub.P, K.sub.I, K.sub.D, H, K.sub.D, K.sub.P, D) or in addition to the at least one parameter (K.sub.P, K.sub.I, K.sub.D, H, K.sub.D, K.sub.P, D) a grid inertia parameter (H, K.sub.D) and/or a grid damping parameter (K.sub.P, D) from the measured values and/or the determined values, wherein the grid inertia parameter (H, K.sub.D) is indicative of the collective inertia of the at least one power source and the at least one power consumer and/or wherein the grid damping parameter (K.sub.P,D) is indicative of a load damping of the power supply grid.

3. The method according to claim 2, wherein the at least one parameter (K.sub.P, K.sub.I, K.sub.D, H, K.sub.D, K.sub.P, D) comprises a collective proportional grid control parameter (K.sub.P) and/or a collective integral grid control parameter (K.sub.I) and/or a collective derivative grid control parameter (K.sub.D).

4. The method according to claim 1, comprising actively exciting and/or perturbing the power supply grid before and/or during the time period by modifying the power output of the at least one power source and/or modifying the power consumption of the at least one power consumer.

5. The method according to claim 4, comprising using an estimated power modification of the at least one power source and/or the at least one power consumer for deriving the at least one parameter (H, D, K.sub.P, K.sub.I, K.sub.D) of the dynamic grid response model.

6. The method according to claim 4, comprising exciting and/or perturbing the power supply grid by modifying the power output of a genset, using skip firing of at least one cylinder of the genset and/or changing or forcing a position of a compressor bypass valve and/or exciting a generator voltage.

7. The method according to claim 1, comprising measuring at least two of the following as the electrical quantities of the power supply grid: grid frequency and/or grid voltage and/or grid current and/or grid power and/or generator power and/or changes or change rates thereof.

8. The method according to claim 1, comprising measuring the electrical quantities at the site and/or terminals of the at least one power source.

9. The method according to claim 2, comprising adapting the control of the at least one power source using the grid inertia parameter (H, K.sub.D) and/or the grid damping parameter (K.sub.P, D).

10. The method according to claim 2, wherein adapting the control algorithm of the at least one power source includes scheduling gains of the control and/or inputting the at least one parameter (K.sub.P, K.sub.I, K.sub.D, H, K.sub.D, K.sub.P, D) in a model of a model based controller or a state space controller.

11. A system configured to perform the method of claim 1, comprising at least one power source, comprising a genset, for producing electrical power, wherein the at least one power source is configured for being connected to the electric power supply grid and wherein the at least one power source includes a control unit capable of controlling the operation of the at least one power source, a measuring device configured for measuring and/or determining the electrical quantities of the power supply grid during the time period where the power supply grid is excited and/or perturbed, such that there is the frequency deviation from the nominal frequency of the power supply grid, and a computing device configured for receiving measured values and/or determined values from the measuring device and for outputting data to the at least one power source, wherein the computing device is configured to derive at least one parameter (H, D, K.sub.P, K.sub.I, K.sub.D) of the dynamic grid response model from the measured values and/or the determined values of the measurement and/or the determination of the electrical quantities of the power supply grid and/or from electrical quantities of the power supply grid determined otherwise, and output the at least one parameter (K.sub.P, K.sub.I, K.sub.D, H, K.sub.D, K.sub.P, D) and/or instructions for an adapted control of the at least one power source based on the at least one parameter (K.sub.P, K.sub.I, K.sub.D, H, K.sub.D, K.sub.P, D) of the dynamic grid response model to the control unit of the at least one power source.

12. The system according to claim 11, wherein the computing device is integrated into the control unit of the at least one power source.

13. The system according to claim 11, wherein the genset comprises an engine for driving a generator by combusting a fuel and a control unit for the engine and/or the generator, wherein the control unit is adapted to receive as input: at least one parameter (H, D, K.sub.P, K.sub.I, K.sub.D) of the dynamic grid response model and/or instructions for an adapted control of the at least one power source based on the at least one parameter (K.sub.P, K.sub.I, K.sub.D, H, K.sub.D, K.sub.P, D) of the dynamic grid response model, wherein the control unit is further configured to adapt the control of the engine and/or the generator based on the at least one parameter (K.sub.P, K.sub.I, K.sub.D, H, K.sub.D, K.sub.P, D) of the dynamic grid response model and/or the instructions.

14. A non-transitory computer readable medium storing instructions executable by one or more processors, wherein the instructions are for controlling the at least one power source according to the method of claim 1, wherein the instructions cause the one or more processors to perform the following functions: from a measuring device receiving measured values and/or determined values of the electrical quantities of the power supply grid during the time period where the power supply grid is excited and/or perturbed, such that there is the frequency deviation from the nominal frequency of the power supply grid, and deriving the at least one parameter (H, D, K.sub.P, K.sub.I, K.sub.D) of dynamic grid response model from measured values and/or determined values of the measurement or determination of the electrical quantities of the power supply grid, and adapting the control algorithm defining the control response of the at least one power source depending on the at least one parameter (H, D, K.sub.P, K.sub.I, K.sub.D) of the dynamic grid response model.

15. A controller having the instructions of claim 15 stored on memory and executable by one or more processors.

16. A method, comprising: monitoring one or more electrical parameters of a power grid during a time period having an excitation and/or a perturbance of the power grid, wherein the power grid exhibits a frequency deviation from a nominal frequency during the time period; deriving at least one parameter of a dynamic grid response model from the one or more electrical parameters of the power grid; adapting a control algorithm defining a control response of at least one power source depending on the at least one parameter of the dynamic grid response model; and controlling the at least one power source based on the control algorithm.

17. The method of claim 16, wherein the one or more electrical parameters comprise a frequency and a power disturbance.

18. The method of claim 16, comprising actively exciting and/or perturbing the power grid before and/or during the time period.

19. A system, comprising: a controller configured to control at least one power source coupled to a power grid, wherein the controller is configured to: monitor one or more electrical parameters of the power grid during a time period having an excitation and/or a perturbance of the power grid, wherein the power grid exhibits a frequency deviation from a nominal frequency during the time period; derive at least one parameter of a dynamic grid response model from the one or more electrical parameters of the power grid; adapt a control algorithm defining a control response of the at least one power source depending on the at least one parameter of the dynamic grid response model; and control the at least one power source based on the control algorithm.

20. The system of claim 19, comprising the at least one power source comprising a combustion engine coupled to an electrical generator, wherein the one or more electrical parameters comprise a frequency and a power disturbance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0118] Further details and advantages of the invention are apparent from the figures and the accompanying description of the figures. The figures show:

[0119] FIG. 1 illustrates a schematic of an embodiment of the system according to embodiments of the invention,

[0120] FIG. 2 illustrates a schematic of an embodiment of the power source according to embodiments of the invention,

[0121] FIG. 3 illustrates an exemplary schematic for the control of an embodiment of a genset according to embodiments of the invention,

[0122] FIG. 4 illustrates frequency and power diagrams showing a grid perturbation, and

[0123] FIG. 5 illustrates a diagram showing a grid perturbation.

DETAILED DESCRIPTION

[0124] FIG. 1 shows a schematic of an embodiment of the system 10 according to aspects of the invention.

[0125] There is a plurality of power sources 1, in this case connected to the power supply grid 2.

[0126] The power sources 1 include respective control units 5 capable of controlling the operation of the at least one power source (see FIG. 2).

[0127] Some of the power sources 1 are gensets 4, others are different power sources.

[0128] There is a measuring device 6 for measuring the frequency f of the power supply grid 2.

[0129] The measuring device 6 is in signal communication with a computing device 7 and transmits the measured values of the frequency f to the computing device 7.

[0130] Power consumers 3 are connected to the power supply grid 2.

[0131] The number of power sources 1, in particular gensets 4, and power consumers 3 is purely exemplary in FIG. 1.

[0132] In this embodiment, it is envisioned that one of the gensets 4 actively modifies its power output in order to put the power supply grid 2 into an excited and/or perturbed state, e.g., employing skip firing, such that the change of the power or power imbalance can be estimated.

[0133] The time period in which the perturbation of the grid is performed can for example be in a range between 200 ms and 1000 ms long.

[0134] Because one of the gensets 4 is used to actively perturb the power supply grid 2, the change in power P can be estimated from the known behaviour of the genset 4.

[0135] During the time period where the power supply grid is excited and/or perturbed, it is therefore known how the power changes (determination of the change of power) and from the measured values of the measuring device 6 how the frequency f deviates from a nominal frequency of the power supply grid 2.

[0136] The computing device 7 is also in signal communication with the control unit 5 of the genset 4, which performs the perturbation of the power supply grid 2.

[0137] The computing device 7 has therefore all the information necessary for deriving at least one parameter of a dynamic grid response model, e.g., K.sub.P, K.sub.I, K.sub.D, 2H+K.sub.D, K.sub.P+D, as described before. These are indicative for a collective control response of the participants of the power supply grid 2 in this case.

[0138] The computing device is furthermore configured to output the at least one parameter and/or instructions for an adapted control of the power sources 1 based on the at least one parameter to the control units 5 of the power sources 1.

[0139] The functions of the computing device 7 can be integrated into the control unit 5 of a genset 4. Such an embodiment is schematically depicted in FIG. 2.

[0140] Operation of gensets 4 in synchronous AC grids 2 in many cases requires robust speed and power control strategies. In synchronous AC grids 2, the rotational speed of a synchronous generator 9 is synchronously coupled to the grid frequency f. Therefore, speed control of the engine 8 and generator shaft means frequency control of the grid 2.

[0141] Depending on the grid inertia, the control priority may shift between speed/frequency and power control. In case of a large public electricity grid 2, the grid inertia is usually much bigger than the inertia of the genset 4 (comprising engine 8, crankshaft, coupling, and generator 9). Operation in such a large grid 2 is referred to as grid parallel or mains parallel operation (MPO). In MPO, the control priority of a genset can be completely shifted to power control, because the speed of the plant will be imposed by the large grid 2.

[0142] In contrast to that, there is the mentioned isolated or island operation, where a genset 4 is supplying a single electrical load or a small number thereof on its own (or a small number of gensets). In this case, the power output of the plant is imposed by the load and the control priority completely shifts to speed/frequency control.

[0143] Between the two extreme cases of MPO and island operation, a genset 4 can operate in a weak grid as well, where for example several small powerplants and loads are connected. In such a weak grid or microgrid operation, speed and power control can be required simultaneously. If, for example, grid size or grid inertia changes over time (i.e. plants are disconnected or reconnected to the grid 2), the grid response characteristics change over time too. Speed and power control of the genset 4 must be robust against such time-variant grid response characteristics.

[0144] To improve controller robustness against time-variant grid response characteristics, it is obviously beneficial to identify these characteristics and adjust the control algorithm accordingly. In many cases of weak grid operation, there is no or not enough knowledge about other participants in the grid to identify the actual grid response characteristic parameters (e.g., grid inertia). In such cases, a method to estimate the actual grid response characteristics, by only using the available local measurements of the genset 4 is desirable.

[0145] FIG. 2 shows an embodiment of a power source 1 in the form of a genset 4.

[0146] The genset 4 comprises an internal combustion engine 8, here a gas engine, which drives a generator 9.

[0147] The measurement device 6 is arranged such that the electrical quantities of the power supply grid 2, e.g., the frequency f of the grid 2, can be measured at the site of the power source 1.

[0148] Again, the power source 1 is configured to actively excite and/or perturb the power supply grid 2, so that the control unit 5 has all the information necessary to derive the at least one parameter, e.g., K.sub.P, K.sub.I, K.sub.D, 2H+K.sub.D, K.sub.P+D, as described before.

[0149] The described embodiments of the present invention therefore allow for the estimation of the grid response from the site of the genset 4 alone without the need to communicate or coordinate with any other participants of the power supply grid 2.

[0150] FIG. 3 shows an exemplary schematic for the control of an embodiment of a genset 4 according to aspects of the invention, preferably implemented in the control unit 5 of the genset 4.

[0151] The Engine Controller includes an engine speed control loop, which includes a comparison of a measured engine speed n to a speed reference n.sub.ref. The speed reference n.sub.ref is based on the nominal grid frequency, potentially corrected by frequency-droop or load-sharing line based setpoint shifts, i.e., n.sub.ref is chosen such that the generator 9 driven by the gas engine 8 outputs electric power with a frequency which can be fed into the power supply grid 2.

[0152] The Engine Controller includes a power control loop, which includes a comparison of the power P.sub.G measured at the generator 9. Alternatively or additionally, the comparison could also be based on a mechanical power P.sub.M,1 output by the internal combustion engine 8.

[0153] Based on the comparisons of the engine speed control loop and/or the engine power control loop, the Engine Controller controls actuators of the gas engine 8 with command values u.sub.E.

[0154] The engine's 8 drive shaft drives the generator 9 which generates electrical power which is fed into the power supply grid 2.

[0155] An exemplary method according to embodiments of the invention includes the following three steps (circled numbers 1 to 3 in FIG. 3): [0156] 1) Triggering a suitable power excitation signal on the output of the gas engine 8 of the genset 4 (e.g., skip firing cylinders, force valve positions, excite generator voltage etc., see earlier description). [0157] 2) Estimating the resulting power disturbance AP in the grid and measure the frequency response f of the grid. [0158] 3) Apply an identification routine to compute at least one parameter of a dynamic grid response model (e.g., grid inertia parameter, grid damping parameter) using P and f.

[0159] For the determination of P and f, measurements of P.sub.G and f.sub.G, coming from a phase measurement unit (measuring device 6) of the genset can preferably be used.

[0160] Depending on the excitation method, further engine related signals y.sub.m, like an intake manifold pressure, may be necessary or beneficial.

[0161] Based on the grid response calculated in the third step, the Engine Controller of the internal combustion engine 8 can be adapted, e.g., using gain scheduling or an adaption of the model of a model predictive controller which is part of the Engine Controller.

[0162] FIG. 4 shows results of a simulation of a weak grid with seven gensets 4 as power sources 1 and one load as power consumer 3. Concretely, the time diagrams of FIG. 4 show a grid frequency, a power output of a specific genset 4 (ego engine), a power output of the remaining engines, and a total load and engine (motor) power.

[0163] Generally, the diagrams show the plotted frequency with the specific genset 4 (ego engine) controlled according to embodiments of the invention (solid lines) and without the control according to embodiments of the invention (dashed lines).

[0164] The total load diagram shows a load step occurring at the 100 s mark, which leads to a dip in the grid frequency.

[0165] The specific genset 4 (ego engine) was controlled by a model based controller taking into account a dynamic grid response model according to embodiments of the invention. The diagram of the specific genset 4 shows a large power peak right when the load step occurs followed quick transition to an essentially constant power output. Clearly, the mentioned power peak is able to compensate a large portion of the load step. At the same, time the transition to an essentially steady state is faster compared to the conventional control (dashed line in the same diagram) and also compared to the remaining engines in the diagram below.

[0166] As a consequence, the dip and the back swing in the grid frequency shown in the first diagram is significantly smaller in the simulation according to embodiments of the invention (solid line) compared to the conventional approach (dashed line).

[0167] FIG. 5 shows a diagram of the grid frequency f of a power supply grid 2 taken from measurements of an engine test bench operated in an isolated grid (grey, curve 11) and an identified dynamic grid response model (blue, curve 12).

[0168] In order to show the effect of embodiments of the invention, the time span of the active grid excitation was chosen 960 ms long. As can be seen, the first unmodified Swing Equation mentioned in the introductory part (1.sup.st order model) may model the grid response for a certain time. As soon as the controllers of the participants of the grid start to exert an influence on the frequency, the Swing Equation would not adequately model the grid 2 anymore.

[0169] Here the 2.sup.nd Order Model taking into account the collective control response of the participants of the power supply grid 2 is much more accurate.

LIST OF REFERENCE NUMERALS

[0170] 1. power source [0171] 2. power supply grid [0172] 3. power consumer [0173] 4. genset [0174] 5. control unit [0175] 6. measuring device [0176] 7. computing device [0177] 8. engine [0178] 9. generator [0179] 10. system [0180] 11. curve measurement [0181] 12. curve identified model