Patent ID: 12261436

DESCRIPTION OF EMBODIMENTS

FIG.1shows a power plant100which comprises a plurality of power generating units101such as wind turbines. The power plant100may be a renewable power plant comprising only renewable power generating units. In general, the power generating units101may consist of different types of power generating units, e.g. different types of renewable power generating units such as solar power units103(e.g. photovoltaic solar panels) and wind turbines. According to an embodiment, at least one of the power producing units101of the power plant100is a wind turbine. The power plant100may comprise at least three power generating units101of the same or different types, i.e. a mix, of different types of power generating units. For example, the power plant100may consist only of wind turbines102and in this case at least three wind turbines102, In another example, the power plant100comprises at least two wind turbines102and at least one or two other power generating units101.

The power plant is connectable with an electrical power grid (not shown) for supplying power from the power generating units101to the electrical power grid.

The power plant100is controlled by a central controller110, The central controller110is arranged to control power generation from the power generating units101according to a power plant reference Pref which defines the desired power to be supplied to the grid from the power plant100. Furthermore, the central controller is arranged to dispatch power set-points Pset to the power generating units, i.e. individual power set-points to each power generating unit101which sets the desired power productions. The power set-points Pset may be determined by the central controller110dependent on the power plant reference Pref so that the sum of power set-points Pset corresponds to the power plant reference Pref.

The central controller110may in addition be configured to control the power plant's reactive power production, grid frequency control and/or other functions190such as determining maximal allowed power production values Pmax.

Throughout this description, power reference is used for the demanded power for the wind power plant, whereas power set-point is used for the demanded power for the individual power generating units.

Thus, an objective of the central controller110comprised by the central controller is to ensure that the demanded power (e.g. from the Transmission System Operator (TSO)) is delivered as fast as possible, this applies both to increases and decreases in the power plant reference, Pref.

The wind turbine101may comprise a tower and a rotor with at least one rotor blade, such as three blades. The rotor is connected to a nacelle which is mounted on top of the tower and being adapted to drive a generator situated inside the nacelle. The rotor is rotatable by action of the wind. The wind induced rotational energy of the rotor blades is transferred via a shaft to the generator. Thus, the wind turbine is capable of converting kinetic energy of the wind into mechanical energy by means of the rotor blades and, subsequently, into electric power by means of the generator. The generator may include a power converter for converting the generator AC power into a DC power and a power inverter for converting the DC power into an AC power to be injected into the electrical power grid.

The generator of the wind turbine102, or other power generating unit101, is controllable to produce power corresponding to the power set-point Pset provided by the central controller110. For wind turbines, the output power may be adjusted according to the power set-point by adjusting the pitch of the rotor blades or by controlling the power converter to adjust the power production. Similar adjustment possibilities exist for other power generating units101.

Herein any reference to power such as power plant reference Pref, power set points Pset_i, available power Paval_i and other power values can define active, reactive or apparent power levels.

The available power Paval_i of a wind turbine102can be determined based on the current wind speed and other parameters limiting the power production. For example, the available power Paval_i may be defined as the maximum possible power output of a wind turbine under the given wind conditions. Thus, the available power will be close to the power output according to the power optimised power curve of a specific turbine. The power curve used herein is understood as the power Coefficient (Cp) optimised power curve for the specific turbine. In other words, the power curve represents the maximum power output of a turbine under normal operation as a function of the wind speed.

As shown inFIG.1, according to an embodiment, the power generating units101may be arranged as selections of one or more power generating units101of different priorities. For example, the power generating units101may be arranged or grouped into of selection of one or more power generating units101of first priority pl1, one or more power generating units101of second priority pl2, and optionally one or more selections of power generating units101of priorities from three pl3to optionally four pl4or higher priority levels pln. In principle, each selection may comprise only one power generating unit101so that the number of priorities equals the number of power generating units101.

FIG.2exemplifies the central controller110and an arrangement of the power generating units101into selections of priorities pl1, pl2, pl3, although the power generating units could be grouped into more priorities levels.

The central controller110may be configured to dispatch power setpoints Pset_i to individual power generating units101, where the power setpoints are used by the power controller of each power generating unit, such as a wind turbine102, for controlling the generation of power according to the supplied power setpoint. The power setpoints Pset_i may be determined based on the power reference Pref and possibly other input signals such as the available power of the individual power generating units Paval_i.

For a wind turbine102, the available power Paval_i is the power available from a wind turbine102at the given time, calculated based on the current wind speed and other parameters limiting the power production. For other power generating units such as photovoltaic solar panels, the available power Paval_i may be determined based on the incident solar power and performance characteristics of the solar panels.

The central controller110is configured to determine the available power production capability Paval_pl1, Paval_pl2, . . . Paval_pln, of selections of one or more power generating units101of different priorities ranging from the first priority pl1, to one or more higher priorities pl2, . . . , pln. The available power production capability Paval_plx of a given selection of power generating unit101is determined based on the available power Paval_i of individual power generating units, e.g. by summing the available power Paval_i of units101of a given priority group pl1, . . . pln.

The central controller110is further configured to determine maximal allowed power production values Pmax for each power generating unit101in one or more selections of generating units101of second or higher priorities pl2, . . . , pln. The maximal allowed power production values Pmax may be provided as individual power levels for each power generating unit, or may be a common power level for two or more power generating units. For example, maximal allowed power production values Pmax_pl2_imay be determined for individual power generating units of the selection of units101of priority pl2. The maximal allowed power production values Pmax are determined dependent on power production gaps Pgap1, . . . , Pgapn and the available power production capabilities Paval_pl2, . . . , Paval_pln of selections of power generating units101of the second or higher priorities pl2, . . . , pln, as described in detail elsewhere.

The power generating units101have associated nominal power specifications Pnom which specify a maximal power level that the power generating unit101is capable of producing, a maximal power production limit, a recommended power production limit or other specification of nominal power setpoints Pnom. The nominal power setpoints Pnom may be provided as individual power levels for each power generating unit, or may be a common power level for two or more power generating units

The power production of each power generating unit101may be constrained according to minimum power setpoints Pmin. The minimum power setpoints Pmin may be provided as individual power levels for each power generating unit, or may be a common power level for two or more power generating units. For a wind turbine102, the minimum power setpoint Pmin may be given from the power production specification, i.e. the minimum power setpoint is defined by the minimum power production capability, or other defined minimum power limits such as user defined power limits. For a solar panels, the minimum power setpoint may be defined according to the specifications of the solar panel. Thus, the minimum power setpoint Pmin represents the smallest possible power production set-point of a power generating unit101.

Accordingly, the maximal allowed power production specification Pmax of a power generating unit101can at least be set to the nominal power setpoint Pnom and the minimum power setpoint Pmin.

The selections of the power generating units101of the first, second and/or higher priorities pl1, pl2, . . . , pln may be predetermined selections, or may be selected according to rules. For example, the priority settings of the power generating units may be performed according to load histories, estimated or scheduled remaining life time, remaining time to next service, power tariff prices per produced power quantity, including combinations thereof. For example, if a number of power generating units have a high accumulated load, but a relative long time to the next service, they may be given a low priority in order to limit additional loads. A power generating unit having a low scheduled remaining life time, but otherwise performs satisfactorily, may be given a high priority. Power generating units having a high tariff price may be given a high priority in order to maximize operation revenue.

As long as changes of the conditions (such as remaining life time or any other conditions mentioned above) for determining the selections would not result in a change of the selections of power generating units, i.e. the grouping into different priorities, the selections may be maintained. Alternatively, if the selections are predetermined, e.g. determined by the operator, the selections may be maintained as long as desired. Accordingly, the selections may be maintained irrespective of the power plant reference or the power produced by the power generating units.

The priority levels pl1, . . . , pln prioritizes the power generating units with respect to their active power productions. Thus, the power production of the one or more power generating units101of the first priority pl1is prioritized over lower priorities pl2, . . . , pln. For example, the power generation of the power generating units of the first priority pl1may be maximized subject to the power plant reference Pref, i.e. so that they are controlled to produce as much power as possible, while lower prioritized power generating units are controlled to produce remaining power, which may not be produced by the first priority units101, by curtailing or pausing these lower prioritized units. Thus, the one or more power generating units101of the first priority pl1may be operated to produce a maximal power up to the power plant reference Pref.

Additionally, the priorities associated with selections of power generating units may used for prioritizing the releasing and pausing of power generating units101, such as wind turbines102, during the operation where the maximal allowed power production Pmax are determined according to the priorities pl1, . . . pln. Accordingly, the power generating unit101with highest priority, i.e. a power generating unit of the selection of units101of first priority pl1, may be released first and paused at the latest, if needed. Oppositely, a power generating unit101of a selection of units101of lowest priority, e.g. third priority pl3, may be released latest and paused at the earliest, if needed.

The power plant100is characterized by a nominal plant power Pplantnom, being the nominal power production capability. The power plant100may be operated in a curtailed mode where the power reference Pref is less than a nominal plant power Pplantnom.

FIG.3illustrates various embodiments of the invention:

In step300, it is initially determined if there is a communication fault in the communication between a power plant controller110and any of the power generating units101.

In step301, if there is a communication fault, the operation of the power generating units101so that the power production of power generating units101of the first priority pl1is maximized subject to the power plant reference Pref is stopped.

In step302, if there is no communication fault, the power generating units of the first priority pl1are controlled to produce as much power as possible, up to the power plant reference Pref.

Further in step302, the first available power production capability Paval_pl1of the selection of power generating units of the first priority pl1is determined. Furthermore, the first power production gap Pgap1is determined as the difference between the power reference Pref and the first available power production capability Paval_pl1, i.e. Pref−Paval_pl1.

In step303it is determined if the first power production gap Pgap1is greater or less than zero. For convenience and simplicity of the explanation, the case where Pgap is equal to zero is included either in the “greater than” or “less than” decision.

In step304, if it is determined that the first power production gap Pgap1is less than zero, or less than or equal to zero, meaning that the power generating units of the first priority pl1are fully capable of producing power according to the power plant reference Pref, then the maximal allowed power production Pmax of the one or more power generating units101of the second priority pl2is set to a minimum power setpoint Pmin, i.e. the minimum power setpoint Pmin associated with individual power generating units, where the setpoints Pmin may be different for different power generating units.

Further in step304, if there are selections of power generating units101having priorities lower than the second priority pl2, such as third and fourth priorities pl3, pl4, then the maximal allowed power production Pmax of power generating units of these lower prioritized selections of power generating units101are also set to the minimum power setpoint Pmin.

In step305, it is determined if the first power production gap Pgap1is greater than zero, and the second available power production capability Paval_pl2is less than the first power production gap Pgap1, i.e. Paval_pl2<Pgap1, meaning that the available power of the second priority selection is insufficient for the remaining power requirement.

In step306, if step305is answered with a yes, the maximal allowed power production Pmax of the power generating units101of the second priority pl2are set to the nominal power setpoints Pnom in order to allow the second priority power generating units to produce as much power as possible. Again, different power generating units may have different nominal power setpoints.

In step307, if step305is answered with a no, because the second available power production capability Paval_pl2is greater than the first power production gap Pgap1, meaning that the available power production capability of the second priority selection is sufficient for the remaining power requirement, the maximal allowed power production Pmax of the power generating units101of the second priority pl2is set according to a distribution of the first power production gap Pgap1among the power generating units101of the second priority pl2. For example, Pgap1may be equally divided among the power generating units of the second priority. In another example, the first power gap Pgap1may be distributed dependent on the available power production capabilities Paval_i of individual power generating units, e.g. according to the relationship of the individual available power production capabilities different power generating unit's of the second priority pl2with the first power gap Pgap1, e.g. determined according to ratios Paval_i/Pgap1. Accordingly, power generating units100having the highest available power production capabilities Paval_pl2may be provided with higher power production levels Pmax than power generating units100having the lowest available power production capabilities Paval_pl2. The examples of distributing the first power gap Pgap1applies equivalently to the distribution of other power gaps Pgap2, . . . Pgapn.

The distribution of the of first power production gap Pgap1among the power generating units101could in some situation imply that Pmax for one or more of the power generating units is set to value lower than Pmin, which is undesired, To avoid this, the distribution of the first power production gap Pgap1may be performed so that the maximal allowed power production Pmax of any one of the one or more power generating units101of the second priority pl2cannot be less than the minimum power setpoint Pmin.

Thus, in general, steps302-307provides a method wherein a maximal allowed power production Pmax is set to a non-zero value for each power generating unit in a selection of one or more power generating units101of second priority pl2, where the maximal allowed power production Pmax is determined dependent on whether the first power production gap Pgap1is greater or less than zero and dependent on a comparison of the first power production gap Pgap1with a second available power production capability Paval_pl2of the selection of the one or more power generating units101of the second priority pl2.

In case the power plant100comprises a selection of power generating units of third priority pl3, a second power production gap Pgap2is determined as a difference between the first power production gap Pgap1and the second available power production capability Paval_pl2, and it is determined if the second power production gap Pgap2is greater or less than zero.

If it is determined that the second power production gap Pgap2is less than zero, then the maximal allowed power production Pmax of the one or more power generating units101of the third priority pl3are according to their minimum power setpoint Pmin. This follows the example in step304, when there are selections of power generating units with priorities lower than pl2and Pgap1is less than zero. Accordingly, it this case the determination of the second power production gap Pgap2is not required since when Pgap1<0 if follows that also Pgap2<0.

Further in step306, when the power plant100comprises a selection of power generating units of third priority pl3, since the available power Paval_pl2of power generating units of the second priority pl2is insufficient for satisfying the first power production gap Pgap1, the determined second power production gap Pgap2will be greater than zero.

Further in step306, if it is determined if the third available power production capability Paval_pl3is less than the second power production gap Pgap2, meaning that the available power production capability of the third priority selection pl3is insufficient for the remaining power requirement, the maximal allowed power production Pmax of the one or more power generating units101of the third priority pl3are set to the nominal power setpoints Pnom.

Further in step306, if it is determined that the third available power production capability Paval_pl3is greater than the second power production gap Pgap2, meaning that the available power production capability of the third priority selection pl3is sufficient for the remaining power requirement, the maximal allowed power production Pmax of the one or more power generating units101of the third priority pl3are determined according to a distribution of the second power production gap Pgap2among the one or more power generating units101of the third priority pl3.

Further in step307, when the power plant100comprises a selection of power generating units of third priority pl3, since the available power Paval_pl2of power generating units of the second priority pl2is sufficient for satisfying the first power production gap Pgap1, the determined second power production gap Pgap2will be less than zero. Then the maximal allowed power production Pmax of the one or more power generating units101of the third priority pl3are set according to their minimum power setpoint Pmin.

The determination of the maximal allowed power production Pmax, in situations where the wind turbine park comprises selections of power generating units101of priority pl4or lower priorities up to pln, follows the above principles.

Thus, in general, the above described principles for determining the maximal allowed power production Pmax in a situation where the power generating units comprises selections of power generating units of third priority pl3or lower priorities, provides a method wherein a maximal allowed power production Pmax is set to a non-zero value for each power generating unit in a selection of one or more power generating units101of third priority pl3or lower priorities pl4, . . . , pln, where the maximal allowed power production Pmax is determined dependent on whether the relevant power production gap Pgap2, . . . Pgapn is greater or less than zero and dependent on a comparison of the power production gap with an available power production capability Paval_pl3, . . . Paval_pln of the selection of the one or more power generating units.

The central controller may be configured so that the maximal allowed power production values Pmax of one or more of the power generating units may be set according to other user preferences, or may be set according to user determined maximal allowed power production values Pmax, irrespective of priorities pl1, . . . , pln associated with the power generating unit of interest.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is to be interpreted in the light of the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.