Method and control system for voltage control of a renewable energy generator

Abstract

An aspect of the present invention relates to a method (100) for controlling a plurality of renewable energy generators (14). The method (100) includes: determining (102) a preliminary reactive power setpoint for the generators (14) based on a reactive power reference value; determining (104) generator-based reactive power limits and voltage-based reactive power limits for the generators (14); generating (106) a dispatch signal for requesting reactive power from the generators based on the preliminary reactive power setpoint and the limits; and dispatching (108) the dispatch signal to the generators (14). The generator-based reactive power limits correspond to the reactive power capacity of the generators. The voltage-based limits are determined by: determining (112) the terminal voltage of the generators; comparing (114) the determined terminal voltage with the voltage limits; and determining (116) the voltage-based reactive power limits based on the comparison.

Description

Technical Field

[0001] This disclosure relates to a method and control system for voltage control in renewable energy power plants. Background Technology

[0002] Renewable power plants (such as wind farms) need to support the voltage levels of the power grids they are connected to. That is, the power plants are controlled to meet requirements set by the plant controllers and power grid operators regarding how reactive power exchange should be controlled to regulate voltage. The primary objective during this "voltage control" is to maintain the voltage level of the power grid within the voltage deadband, which is approximately between 0.9 pu and 1.1 pu. The specific focus is on guiding the voltage level towards the nominal or natural voltage level, typically 1 pu. Maintaining the voltage level within the deadband and near the nominal voltage prevents deviations from the application of emergency measures such as undervoltage or overvoltage ride-through protocols.

[0003] To support voltage recovery during a drop (i.e., a deviation of less than 1 pu within the dead zone), the renewable energy generators of the renewable power plant are controlled to supply reactive power. When the voltage level rises above the nominal level, reactive power is absorbed to lower the voltage level. The supply and absorption of reactive power can be considered in terms of the manner in which they are implemented, and therefore can be considered separately in terms of capacitive and inductive reactive power.

[0004] When controlling generators to provide capacitive or inductive reactive power support, both the local voltage level and the network voltage level are modified. In some networks with so-called “weak grid interconnections,” small changes in reactive power exchange result in large changes in local voltage. Therefore, capacitive reactive power support can cause the local voltage level to rise beyond the dead zone, potentially prompting emergency measures. Similarly, inductive reactive power support can cause the local voltage level to drop beyond the dead zone, resulting in undervoltage ride-through.

[0005] The object of this invention is to address one or more drawbacks associated with the prior art. Summary of the Invention

[0006] According to one aspect of the invention, a method for controlling a plurality of renewable energy generators in a renewable energy power plant is provided. The method includes: determining an initial reactive power setpoint for the generators based on a constrained reactive power reference value for the power plant, the constrained reactive power reference value being obtained by applying a reactive power limit to the reactive power reference value of the power plant; determining reactive power limits for each generator, including determining generator-based reactive power limits and voltage-based reactive power limits for each generator; generating a dispatch signal for requesting reactive power from each generator, the dispatch signal being generated based on the initial reactive power setpoint and the determined reactive power limits, wherein the dispatch signal includes an overall constrained setpoint, wherein if the initial reactive power setpoint exceeds the determined reactive power limit, then the constrained setpoint is the determined reactive power limit, otherwise it is the initial reactive power setpoint; and dispatching the dispatch signal to the generators. The generator-based reactive power limit for each generator corresponds to the reactive power capacity of the generator. For each generator, determining the voltage-based reactive power limit includes: determining the terminal voltage of the renewable energy generator; comparing the determined terminal voltage with a voltage limit; and determining the voltage-based reactive power limit based on the comparison.

[0007] The reactive power limit of the generator can be derived from the current limit of the generator's converter. This method can be performed by the power plant controller. The power plant controller can be configured to communicate with a single controller of multiple renewable energy generators. The terminal voltage level can be the voltage level measured at the terminals of the line-side converter of the generator.

[0008] As can be seen from the above method, two distinct reactive power limits are determined. The first, generator-based limit, indicates the available reactive power and the physical capacity of the generator, typically the current capability of the generator's converters. The second limit is voltage-based, derived from a comparison of the local voltage level with a voltage limit. The voltage-based limit is derived from this comparison to specifically understand the local voltage conditions. Voltage levels can vary across power plants, depending on the different levels of active and / or reactive power generated by generators, different network impedances, and other electrical properties of the lines connecting the generators to form the power plant. Therefore, obtaining an understanding of the voltage levels and implementing voltage-based reactive power limits specific to individual generators is useful.

[0009] Therefore, in implementing such a method, the generator is controlled according to two specified limits, thus protecting it from exceeding its own capacity and from exceeding voltage limits through its reactive power generation. Because changes in reactive power affect voltage levels, particularly local voltage levels in weaker grid interconnections, it is important to monitor voltage levels and react when they approach their limits. Reactive power is controlled according to these voltage levels to prevent exceeding limits, which could otherwise lead to drastic measures that would disrupt the overall operation of the power plant.

[0010] Determining voltage-based reactive power limits may include: if the terminal voltage for a generator is equal to or exceeds a voltage limit, then the voltage-based reactive power limit for that generator is determined to reduce or prevent the terminal voltage from further exceeding the voltage limit.

[0011] Determining reactive power limits may include: determining a voltage sub-range within an allowable voltage range, which is limited by a voltage limit. If the terminal voltage used for the generator is within the voltage sub-range, determining the reactive power limit may include: determining a voltage-based reactive power limit for the generator to prevent further changes in the terminal voltage toward the voltage limit.

[0012] By utilizing a sub-range limited by a voltage limit, the threshold can be set above the value to which action is taken. When the voltage is approaching but has not yet reached the voltage limit, the method reacts to counteract the change in voltage toward the limit, thereby reducing the likelihood of deviations above the limit.

[0013] Determining a voltage-based reactive power limit may include: determining a reactive power output value for a generator and setting the voltage-based reactive power limit to be equal to the reactive power output value.

[0014] Alternatively, determining the voltage-based reactive power limit may include: determining a latest reactive power setpoint value for the generator, and setting the voltage-based reactive power limit to be equal to the latest reactive power setpoint value.

[0015] In either case, the voltage-based reactive power limit is set to the previous reactive power value, as this represents the value at which the generator is operated within its voltage limit.

[0016] The method may further include: comparing reactive power limits with corresponding preliminary reactive power setpoints; if the preliminary reactive power setpoint for a generator exceeds one or more of the reactive power limits for that generator, determining a reactive power shortage for the generator based on the difference between the exceeded limit and the preliminary setpoint; determining the total reactive power shortage for the power plant as the sum of the determined shortages for each generator; and determining, based on the allocation of the total shortage, an additional amount of reactive power to be provided by each generator, wherein the preliminary reactive power setpoint for each generator does not exceed the reactive power limit for the generator.

[0017] Allocation can be based on the difference between the generator's terminal voltage and the voltage limit. Allocation may include requesting a higher proportion of the total shortage from generators with a larger difference between their terminal voltage level and the voltage limit, compared to the proportion of the total shortage requested from generators with a smaller difference between their terminal voltage level and the voltage limit.

[0018] Alternatively or alternatively, the method may include: monitoring the reactive power output level of a generator, wherein the allocation is based on the difference between the reactive power output level and one or more reactive power limit levels. Alternatively or alternatively, the method may include: monitoring the reactive power output level of a generator; and determining a generation indicator of the reactive power output level, wherein the allocation is based on the determined generation indicator. Alternatively or alternatively, the method may include: monitoring the active power value of each of a plurality of renewable energy generators, wherein the allocation is based on the active power value.

[0019] Determining the initial reactive power setpoint may include dividing the reactive power reference among multiple generators in a power plant.

[0020] The generator-based reactive power limit for each generator can be determined by referring to the PQ data structure, which specifies the reactive power limit level based on active power measurements.

[0021] According to another aspect of the invention, a power plant controller is provided for a power plant having multiple renewable energy generators. The controller includes a processor and a memory module. The memory includes a set of program code instructions that, when executed by the processor, implement the methods described above.

[0022] In the controller or method, the renewable energy generator may include a wind turbine generator.

[0023] Within the scope of this application, it is intended that the various aspects, embodiments, examples, and alternatives set forth in the foregoing paragraphs, claims, and / or the following description and drawings, as well as their individual features, may be used independently or in any combination. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination unless such features are incompatible. Notwithstanding this statement previously, the applicant reserves the right to amend any previously filed claim or accordingly file any new claim, including the right to modify any previously filed claim to be subordinate to any other claim and / or to incorporate any feature of any other claim. Attached Figure Description

[0024] One or more embodiments of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

[0025] Figure 1 A schematic diagram of a power network is shown;

[0026] Figure 2 A block diagram of a voltage controller for a power plant controller is shown;

[0027] Figure 3 A typical PQ diagram for a wind turbine generator is shown;

[0028] Figure 4 A block diagram of a voltage control unit for a wind turbine generator according to an embodiment of the present invention is shown;

[0029] Figure 5 An embodiment of the invention is shown for use Figure 2 The general operating method of the voltage controller dispatcher in the system; and

[0030] Figure 6 The operation method of a dispatcher for allocating reactive power shortages is shown. Detailed Implementation

[0031] Generally, the invention described herein provides a method and controller for implementing voltage control for renewable energy generators. This method and controller ensure that the operation of generators, and in particular generator converters, for providing reactive power support according to a received setpoint does not lead to problematic voltage deviations and mitigates existing deviations. This is achieved by implementing reactive power limits at the power plant controller that take into account both the generator's physical capabilities and the voltage level, so that the local voltage remains within permissible levels.

[0032] Figure 1A typical architecture is shown in which a wind power plant (WPP) (which may also be referred to as a wind farm or wind park) is connected to the main power grid as part of a wider power network. A skilled reader will understand that a WPP includes at least one wind turbine generator (WTG) and is also referred to as a wind farm or wind park. A WTG is generally referred to as a wind turbine. The example shown is merely representative, and a skilled reader will understand that other specific architectures are possible with respect to wind power plants, power plants for other renewable energy sources (e.g., solar power plants, biomass power plants, or ocean / wave / tidal power plants), and hybrid power plants with combinations of different types of renewable energy power plants. Therefore, the invention generally also relates to renewable energy power plants and renewable energy generators, rather than specifically to the wind power plant and generator shown in the figures. The components of wind power plants and power networks are conventional and, therefore, will be familiar to a skilled reader. In addition to... Figure 1 In addition to the components shown and described, other known components may be incorporated, or other known components may be incorporated as... Figure 1 Alternatives to the components shown and described. Such changes will be within the capabilities of a skilled technician.

[0033] Figure 1 A power network integrating WPP 12 and power plant controller 22 (hereinafter referred to as PPC 22) is shown. WPP 12 includes multiple WTGs 14. Each of the multiple WTGs 14 converts wind energy into electrical energy, which is transmitted from WPP 12 as active power and / or current to the main transmission network or main grid 16 for distribution. In this specification, individual generators may all be referred to as "units".

[0034] Although not shown in the figure, WPP 12 may also include compensation devices configured to provide reactive power or reactive current support as needed, such as a Static Synchronous Compensator (STATCOM) or another type of synchronous compensator. WPP 12 may also include a battery energy storage system.

[0035] Each WTG in WTG 14 is associated with a corresponding WTG controller 15. In some examples, a group of WTGs may share a single semi-centralized WTG controller, resulting in fewer WTG controllers than WTGs. Those skilled in the art will understand that WTG controller 15 can be considered a computer system capable of operating WTG 14 in the manner specified herein, and may comprise multiple modules controlling individual components of the WTGs or simply a single controller. The computer system of WTG controller 15 may be operated by software downloaded via a communication network or programmed onto the computer system from a computer-readable storage medium.

[0036] During normal operation of WPP 12, WTG controller 15 operates to implement active and reactive current and / or power requests received from PPC 22 to provide frequency and voltage support to the main grid 16. During emergencies, WTG controller 15 operates to meet predetermined network requirements and also serves to protect WTG 14 from any potentially harmful conditions.

[0037] WPP 12 is connected to the main power grid 16 (also known as the main power network) via connection network 18. WPP 12 and main power grid 16 are connected at interconnection point (PoI) 20, which is the interface between WPP 12 and main power grid 16. PoI 20 may also be referred to as the common connection point, which may be simply referred to as "PCC" or "PoCC".

[0038] The WTGs 14 are locally interconnected via the local power grid 19 (also known as the local power network or garden grid). The function of the local power grid is to transmit power from each WTG in the WTGs 14 to the main power grid 16 via the connection network 18.

[0039] The Power Plant Controller (PPC) 22 is connected to the main grid 16 at the Point of Measurement (PoM) 24 and to the WTG controller 15. The PPC 22 acts as the command and control interface between the WPP 12 and the grid 16, and more specifically, between the WPP 12 and the grid operator (e.g., the Transmission System Operator (TSO) or Distribution System Operator (DSO) 26). The PPC 22 is a suitable computer system for executing the controls and commands as described above, and therefore incorporates the processing module 28, connectivity module 30, memory module 32, and sensing module 34. The PPC 22 can also receive information about the grid 16 and / or local bus, substations, and networks from the energy management system (not shown). The WPP 12 is able to modify its power or current output in response to commands received from the PPC 22.

[0040] As part of its operation, PPC 22 generates a dispatch signal and sends it to WTG controller 15. WTG controller 15 controls the WTG according to the setpoint contained in the dispatch signal.

[0041] During normal operation, PPC 22 operates in one of several modes. One such mode is voltage regulation, also known as voltage control mode, in which PPC 22 issues a dispatch signal configured to cause WTG 14 to supply or absorb reactive power to regulate the voltage level of the power network. Specifically, PPC 22 supplies a signal to WTG 14 to maintain the voltage level within a voltage range (particularly the dead zone or "acceptable voltage range") between approximately 0.9 pu and 1.1 pu (measured at PoI 20 or PoM 24). In a specific example, the dead zone is between a lower limit or limit of 0.87 pu and an upper limit or limit of 1.13 pu.

[0042] Technicians will understand that each unit of voltage is an expression relative to a reference value. Using a unit quantity system allows for the normalization of values ​​across transformers and other components, which can change values ​​by orders of magnitude.

[0043] PPC 22 can send various dispatch signals and setpoints to WTG controller 15 for implementation according to the mode in which PPC 22 is operating. In this embodiment, PPC 22 is configured to send a signal to WTG controller 15 indicating the reactive power setpoint that WTG 14 should satisfy.

[0044] To regulate voltage, WTG controller 15 generates a control signal that indicates the reactive current setpoint for controlling the line-side converter of WTG 14. The reactive current setpoint is based on the reactive power setpoint assigned to WTG controller 15 by PPC 22.

[0045] There are several limits on the amount of reactive power that WTG 14 can supply. Conventionally, limits for reactive power support have been generated based on the physical limits of WTG 14. Those skilled in the art will be familiar with the fact that available reactive power is related to the maximum current that the WTG's converter can handle. Therefore, these physical limits for each WTG 14 are related to the current limits of the WTG's converter. However, since reactive power directly affects voltage, as will be expected during voltage control mode, it is also important to ensure that voltage limits are not exceeded, i.e., the boundaries of the voltage dead zone, and / or to mitigate voltage deviations if they do occur. Specifically, it is important to control changes in reactive power support made at PPC 22 or at the WTG controller 15 to ensure that voltage limits are implemented to provide such mitigation or prevention. Therefore, measures for voltage control, as indicated by the inventors, are described below to ensure that reactive power support complies with both the reactive power limits set by the physical capabilities of the WTG and the voltage limits of the power grid.

[0046] Regarding the context, about Figure 2 and Figure 4 The initial description is of the reactive power setpoints generated by the PPC 22 and the implementation of these setpoints by the WTG controller 15.

[0047] Figure 2 A schematic diagram of the PPC voltage control unit 40, contained within the processing module 28 of the PPC 22, is shown. The control unit 40 is configured to determine a reactive power reference value and generate multiple reactive power setpoints that together achieve the reference value. These setpoints are then assigned to the WTG controller 15.

[0048] like Figure 2 As shown, the PPC voltage control unit 40 includes a reactive power controller 42. The reactive power controller 42 receives a voltage reference "U". 参考 ", and the measured voltage "U" at PoI 20 PoI The reactive power controller 42 determines the deviation between the measured voltage and the voltage reference, and generates and outputs the reactive power reference value "Q". 参考 Reactive power reference value Q 参考 It is the reactive power output at PoI 20 that will be satisfied by WPP 12.

[0049] When discussing measured values ​​in these examples, this is envisioned to encompass direct measurements and determinations made through other means. Measurements may be determined indirectly based on surrogate values, or described as the values ​​being measured.

[0050] The reactive power reference value is transmitted through the reactive power reference limiter 44. Limiter 44 applies a reactive power limit to the reference value and outputs a restricted reference value "Q". 参考限值 To calculate the reference limit imposed by limiter 44, PPC22 receives reactive power capacity values ​​from each WTG 14. These capacity values ​​include the capacitive reactive power capacity "Q". 可用容性 "and inductive reactive power capability" Q 可用感性These capability values ​​correspond to the maximum available reactive power that each WTG 14 can supply and absorb, respectively. The capability values ​​indicate physical limits for the WTG 14; that is, they are reactive power values ​​that the WTG 14 cannot exceed without causing damage to the system. Specifically, these physical limits are related to, or derived from, the current limits of the WTG's converter. In some cases, the WTG 14 can be controlled to absorb or supply a larger amount of reactive power, but only for a very short period. In embodiments, available reactive power or reactive power capability includes the absolute maximum reactive power that the WTG can provide, i.e., without considering the current generation of the WTG. In other embodiments, available reactive power or reactive power capability can be available reactive power other than current generation, i.e., the difference between the maximum value and the measured value. In each case, the PPC and WTG controllers are adapted to take this readout into account, and the assigned setpoints can differ accordingly. Generally, in this application, embodiments are presented under the assumption that reactive power capability is an absolute value.

[0051] The limits for the reactive power reference limiter 44 are generated by summing the capacitive reactive power capabilities of all WTG 14s in WPP 12 and the inductive reactive power capabilities of all WTG 14s in WPP 12, thus providing an upper and lower limit for the reference value. Therefore, the limits can be expressed by the formula:

[0052] Q 参考限值 = [

[0053] The capacitive and inductive reactive power capabilities received from WTG 14 are typically generated based on PQ charts. (An example of a PQ chart is provided in...) Figure 3 (As shown in the figure) The reactive power capability of WTG 14 is defined based on the active power output level and voltage level of WTG 14. Figure 3 The PQ chart in the image plots active power in megawatts (on the x-axis) relative to reactive power in megavolt-amperes (on the y-axis). In this example, the solid line forming a trapezoidal shape represents the power generation capability of the WTG 14 when the power converter is operating at the nominal voltage (1 pu). Lines formed by short dashes are also shown, representing the terminal voltage at its lower voltage limit (0.87 pu); and lines formed by longer dashes represent the terminal voltage at the upper voltage limit (1.13 pu). Skilled readers will understand that this shape is typical for any PQ chart used with a generator for a WTG. Therefore, the lines shown on the PQ chart define the long-term power generation capability of the WTG 14. As will be understood, PQ charts can be generated for multiple voltage levels within the voltage dead zone.

[0054] Back Figure 2 The restricted reference value Q 参考限值 The reactive power is transmitted to the reactive power distributor 46. The reactive power distributor 46 generates a single reactive power setpoint "Q". 设定点n "To be assigned to each WTG 14. The reactive power dispatcher 46 generates a reactive power setpoint by allocating restricted reference values ​​among the WTGs 14 and further restricting them based on the respective WTG's capacity value and the WTG's terminal voltage. As will be described below, the dispatcher 46 can reallocate additional reactive power if further restrictions are imposed. After the reactive power setpoint has been generated, the dispatcher 46 sends the setpoint to its corresponding WTG controller 15."

[0055] Figure 4 An example of a WTG voltage control unit 60 for WTG 14 is shown, which is housed within a WTG controller 15.

[0056] The WTG voltage control unit 60 includes a reactive power controller 62. The reactive power controller 62 receives a setpoint Q. 设定点n This is part of the dispatch signal from the PPC voltage control unit 40. Additionally, the controller 62 receives the locally measured reactive power level Q. 测量 This means the level was measured locally at the WTG 14 terminal. Figure 4 The input to the boxes described in the text can be filtered to remove anomalous data before it is used in the boxes.

[0057] Based on the setpoint Q received from the PPC voltage control unit 40 设定点n and the measured reactive power level Q 测量 The reactive power controller 62 generates control signals for controlling the WTG 14 to meet the reactive power setpoint. When the voltage control unit 60 is housed within the line-side converter, the control signals include a reactive current setpoint for controlling the line-side converter.

[0058] Importantly, to ensure that the WTG capacity limit is not exceeded, the reactive power controller 62 generates control signals relative to inputs from the reactive power upper limit unit 64 and the reactive power lower limit unit 66. These units 64, 66 are based on the wind turbine's capacity value Q. 可用容性 and Q 可用感性 A reactive power limit is applied, and a signal is provided to the reactive power controller 62 to limit the permissible range of reactive power that can be requested by the control signal.

[0059] Therefore, WTG 14 is controlled to provide reactive power support based on its physical capabilities as defined by the PQ chart in both the PPC and WTG voltage control units.

[0060] As described above, voltage control is implemented between PPC 22 and WTG controller 15 to ensure that WTG 14 complies with local voltage limits. To enforce these limits, PPC 22 monitors the voltage level at the terminals of WTG 14 and applies voltage-based reactive power limits to its reactive power setpoint, which is allocated based on the monitored voltage level. Additionally, the reactive power allocation performed by reactive power distributor 46 is adjusted to take the voltage limits into account, such that reactive power setpoints are allocated to help maintain the turbines within their voltage limits.

[0061] PPC 22 utilizes the determined local voltage level to ensure control of WTG 14 based on its individual characteristics. That is, the local voltage level depends on the characteristics of the power grid to which the WTG is connected. The voltage level is variable, depending on several parameters, and therefore, the local voltage level can differ at different generators. For example, the active and reactive power generation of the WTG can differ, and both affect the local voltage level. Furthermore, different impedances may exist between the WTG and the local connection network, and other parameters affecting the voltage may also vary between WTGs. Therefore, determining the local voltage for the WTG and its use in comparison with the voltage level ensures that each WTG is adequately satisfied and does not exceed the limits set for it on its own.

[0062] According to Figure 5 and Figure 6 Methods 100 and 200 shown describe how dispatcher 46 responds to a reception-limited reference value Q. 参考限值 The operation. Figure 5 A method 100 for general operation of dispatcher 46 is shown, wherein if the monitored voltage of WTG 14 is close to a voltage limit, a voltage limit is applied to the WTG setpoint. Figure 6 Method 200 is shown for how to allocate reactive power shortages (which may occur if limits are implemented) among some WTGs to ensure that WPP 12 complies with the requested reactive power reference values.

[0063] Although methods 100 and 200 are discussed as being executed by dispatcher 46, it will be understood that methods 100 and 200 may be executed elsewhere in PPC 22 as needed. For example, dispatcher 46 may perform the task of assigning setpoints to WTG14, while other intermediate modules may execute methods 100 and 200 to apply limits and allocate shortages.

[0064] First turn Figure 5In method 100, at step 102, a preliminary reactive power setpoint for WTG 14 in WPP 12 is determined. The preliminary reactive power setpoint is based on a reactive power reference value for WPP 12, which in the above embodiment is a restricted reactive power reference value Q. 参考限值 As will be described below, the initial reactive power setpoint can be determined by equally dividing the reference value among WTG 14, such that the initial reactive power setpoint for each WTG is equal. This can be written as dividing the constrained reference value Q... 参考限值 Divide by the number N of WTG 14 to give the initial reactive power setpoint Q. 参考限值WTG , making Q 参考限值WTG =Q 参考限值 / N. The initial setpoint can be determined in other ways.

[0065] At the next step 104 of method 100, at least one reactive power limit for each WTG is determined. This step 104 includes steps 110, 112, 114, and 116, shown on the right side of method 100. These steps include: determining, 110, a generator-based reactive power limit corresponding to the generator's reactive power capability. Determining the reactive power limit in 104 further includes: determining, 112, a measured terminal voltage; comparing, 114, the measured terminal voltage with a voltage limit; and, depending on or based on the comparison, determining, 116, a second voltage-based reactive power limit. Each of these steps is discussed in more detail below.

[0066] After the limit has been determined in step 104, a dispatch signal is generated in step 106. The dispatch signal is used to dispatch reactive power to WTG 14 to request reactive power from WTG 14 according to a setpoint. The dispatch signal is generated based on the preliminary setpoint determined in step 102 and the limit determined in step 104. The dispatch signal may include a general restricted setpoint, wherein the preliminary setpoint has been compared with the determined limit, and if the preliminary setpoint exceeds the limit, the restricted setpoint is the limit, and otherwise it is the preliminary setpoint. Alternatively, the dispatch signal may include both a preliminary setpoint and a limit for the WTG controller 15 to apply the limit to the setpoint. In a further alternative, the setpoint included in the dispatch signal may be a preliminary setpoint already limited by one of the limits (i.e., the reactive power capability limit), and the dispatch signal may also pass a voltage-based reactive power limit to the WTG controller 15 for subsequent application.

[0067] At step 108, the dispatch signal for each WTG in WTG 14 is dispatched to the relevant WTG controller 15.

[0068] Therefore, method 100 implements voltage-based reactive power limits based on a comparison of voltage levels with voltage limits to ensure local compliance of terminals with voltage limits.

[0069] To broaden the determination of the limit, the first generator-based reactive power limit determined in step 110 includes determining the reactive power capacity value Q already received by PPC 22. 可用感性 and Q 可用容性 .

[0070] Next, voltage-based reactive power limits are determined at steps 112, 114, and 116. The overall objective of method 100 is to prevent the reactive power setpoint provided to the WTG from exceeding the voltage limits. Therefore, in method 100, limits are determined and placed at the setpoint to prevent problematic changes to the voltage level, i.e., to reduce or prevent the terminal voltage from further exceeding the voltage limits.

[0071] According to a specific embodiment, the voltage-based reactive power limit is based on a voltage sub-range. The voltage sub-range is a sub-range within the voltage dead zone, also referred to as the permissible voltage range, which typically lies between approximately 0.9 pu and 1.1 pu. Each sub-range is limited by an outer limit of a wider range and has a predefined width. Therefore, for example, in the case where the permissible range is 0.9 pu to 1.1 pu and the sub-range has a width of 0.03 pu, the sub-range extends from 0.9 pu to 0.93 pu and from 1.07 pu to 1.1 pu.

[0072] In this embodiment, when the monitored voltage falls within the allowable range but not within a sub-range (i.e., between 0.93 pu and 1.07 pu), PPC 22 determines that no additional reactive power limit is needed because the difference between the monitored voltage level and the voltage limit is sufficiently large. When the monitored voltage falls within one sub-range of the sub-range, PPC 22 prevents further voltage changes beyond the 0.9 pu and 1.1 pu limits by setting real-time reactive power limits. The limits are implemented based on the existing reactive power level (the measured reactive power level or the latest reactive power setpoint). PPC 22 takes the existing reactive power level and effectively “holds” the reactive power output of WTG 14 to that level—setting the limit (whether it is an upper or lower limit depends on the sub-range within which the voltage falls) to the existing reactive power level to prevent further changes in reactive power output that would cause the voltage to shift toward its limit.

[0073] Limits are applied based on a comparison between the initial setpoint and the current limit to determine if the setpoint exceeds one or more of the limits. If the initial setpoint does exceed a limit, the setpoint is reset to the limit it exceeded. Otherwise, the setpoint remains the initial setpoint. Therefore, if a voltage-based reactive power limit is calculated because the monitored voltage level is close to the voltage limit, the limit is applied only if the PPC 22 attempts to increase the setpoint above the measured reactive power or a previous setpoint. Thus, the PPC 22 limits the variation of individual reactive power setpoints sent to the WTG 14 to prevent exceeding local voltage limits and reactive power capacity limits.

[0074] In instances where the voltage level exceeds the voltage limit, PPC 22 implements a reactive power limit applied within a sub-range to prevent further deviation from the voltage limit. In other words, if the monitored voltage exceeds the voltage limit and is outside the dead zone and sub-range, the voltage-based reactive power limit is determined to be equal to the measured reactive power output or to be the latest setpoint for reactive power.

[0075] In other embodiments, a voltage limit can be applied that is proportional to the difference between the monitored voltage level and the limit. In some of these embodiments, the limit can be maintained or frozen to an existing reactive power level within a sub-range, but outside the sub-range, the limit may be proportional to the difference.

[0076] Once the terminal voltage returns to an acceptable range (outside the sub-range), the limit for the setpoint can be changed.

[0077] To protect WTG 14 from voltage oscillations, a ramp rate limit can be introduced to ensure that reactive power changes smoothly and slowly enough to prevent disturbances to the voltage level. Without a ramp rate limiter, reactive power changes may be too rapid, potentially causing a rapid rise in voltage levels and exceeding the limit. The use of a ramp rate limiter is particularly suitable for applications of this invention in weak grid environments.

[0078] When imposing a limit on the setpoint helps ensure that the voltage level is not exceeded, PPC 22 operates to satisfy the requested reference value. When limiting the setpoint, some reactive power is inherently "lost" and not taken into account. Therefore, while not necessary, it is useful to be able to provide some form of compensation for the lost reactive power.

[0079] See examples of compensation methods. Figure 6 .exist Figure 6 In method 200, the reactive power shortage caused by implementing one or more limits on the setpoint for the WTG is summed and redistributed among the WTGs that can accommodate the increased reactive power.

[0080] At step 202, for each WTG, the dispatcher 46 compares the initial reactive power setpoint with the relevant determined reactive power limit for WTG 14. This comparison determines whether the initial setpoint exceeds the limit or whether the initial setpoint is equal to or less than the limit.

[0081] At step 204, for a WTG whose initial setpoint exceeds one of the limits used for WTG, a WTG shortage value is determined as the difference between the limit and the initial setpoint. This WTG shortage value indicates the amount of reactive power lost when the initial setpoint is limited by the determined limit. For WTGs whose initial setpoint does not exceed the relevant limit, no shortage is determined. This step is not depicted in method 200.

[0082] At step 206, the WTG shortages are summed to reach a total shortage known as the WPP shortage, which is used as a whole for WPP 12.

[0083] At step 208, the setpoint for the WTG, in the comparison of step 202, does not exceed the WTG's limit. The initial setpoint not exceeding the limit indicates that the WTG will have some reserve capacity to receive a higher reactive power demand than the WTG with the shortage. At step 208, the WPP shortage is allocated among the WTGs whose initial setpoint does not exceed the reactive power limit for that WTG, and PPC 22 determines the additional amount or allocation portion of reactive power to be provided by each of these WTGs. The additional amount is determined based on the allocation of the WPP shortage. Therefore, the setpoint for these WTGs is the initial setpoint plus the additional amount. In other words, the WTG 14 that does not exceed its limit supplements the reactive power shortage so that WPP 12 and PPC 22 meet the reactive power reference values ​​they receive.

[0084] Subsequently, the allocation setpoints that form the portion of the allocation setpoints are either limited based on the determined limits and are only preliminary setpoints, or they include the preliminary setpoints and new setpoints that include additional amounts allocated according to the allocation.

[0085] The allocation can be based on one or more specific parameters, or it can be an equal distribution of the shortage among WTGs.

[0086] In some examples, for each WTG 14, the dispatcher 64 utilizes the monitored local voltage level and determines the difference between the local voltage level and the voltage limit. The local voltage level is generally the terminal voltage level of the WTG, although in some embodiments it may be a different local voltage level. Therefore, the dispatcher allocates the shortage among WTGs with excess capacity based on the determined voltage difference.

[0087] This allocation based on voltage levels can be performed in several ways. According to some embodiments, a threshold difference value is used to perform the allocation of the overall shortage. That is, shortages are allocated to WTGs where the difference between their local voltage level and the limit is less than the threshold. In one example, sub-ranges of voltage can also be used to implement the allocation. In these embodiments, shortages are allocated between WTGs whose measured voltage levels are outside the sub-range and therefore greater than predetermined values ​​far from the limit. Using the example above where the limit is 0.9 pu and 1.1 pu, this would mean that the total shortage would be allocated to WTGs whose monitored local voltages are between values ​​of 0.93 pu and 1.07 pu. In some embodiments, the sub-range used to calculate the allocation can be wider than the sub-range used to determine the voltage-based reactive power limit.

[0088] In some embodiments, the allocation of the overall shortage can be based on the order of magnitude of the difference between the measured voltage and the limit voltage. Specifically, the allocation can be directly or indirectly proportional to the difference. In other words, the amount of additional reactive power requested by a WTG with a higher voltage difference to occupy the shortage can be greater than the amount of additional reactive power requested by a WTG with a lower voltage difference. Therefore, a WTG whose voltage level is closer to the nominal level (1 pu) will be allocated a higher proportion of the shortage than a WTG whose voltage level is farther from the nominal level.

[0089] This can be a direct proportional allocation, whereby the magnitude of the difference directly indicates the amount of additional requested power. In other embodiments, the allocation can be indirect proportional, whereby the voltage differences are categorized in an intermediate manner before allocation occurs. Examples of indirect allocation may include, for instance, defining multiple compartments for classifying WTGs based on their difference levels, wherein each compartment is allocated a certain amount of shortage. Alternatively, WTGs can be sorted according to their voltage difference levels, and a certain amount of reactive power can be allocated based on their position in the order.

[0090] In some embodiments, allocation may also be based on different parameters, such as reactive power and / or active power values, and voltage difference levels. Allocation may also be based on parameters including: the difference between a measured reactive power level and one or more capacity limits; the difference between a threshold and one or more capacity limits; a reactive power generation indicator, i.e., whether the reactive power is capacitive or inductive; and the active power output level or setpoint level of the WTG. In addition to voltage difference, one or more of these parameters may be used to determine allocation.

[0091] What will be understood is that the overall shortage is allocated relative to the capacity value of each WTG. The assignor 46 uses the capacity value to compare with the allocation to ensure compliance with limits. In a specific example, a further shortage value is calculated for the WTGs that allocate the first overall shortage among them, and this further shortage is again reallocated to WTGs with remaining capacity. This process of calculating the shortage value can be iteratively repeated until there is no shortage.

[0092] Although Figure 6 One method for compensating reactive power has been demonstrated, but compensation can be performed in other ways. For example, in some embodiments, PPC 22 can increase the setpoint by a correction factor based on the expected loss caused by the applied limit to ensure that the setpoint is met.

[0093] Simply return to Figure 5 In the above description, it is assumed that steps 106 and 108, which generate and assign the dispatch signal, include setpoints that the WTG can adhere to. However, in some embodiments, the dispatch signal may include an initial setpoint and a limit, such that PPC 22 determines these values, but the WTG controller 15 imposes a limit on the initial setpoint within the voltage controller. In other embodiments, the initial setpoint may be partially limited, and another limit may be passed to the WTG controller 15 along with the partially limited setpoint. Additionally, the setpoint assigned to the WTG may be a voltage setpoint and an alternative to a reactive power setpoint, or an alternative to a reactive power setpoint. These options are available when the WTG controller 15 includes a voltage drop or fall controller for implementing voltage setpoint, reactive power setpoint, and reactive power slope control.

[0094] It will be understood that various changes and modifications can be made to this invention without departing from the scope of this application.

Claims

1. A method (100) for controlling a plurality of renewable energy generators (14) of a renewable energy power plant (22), the method (100) comprising: (102) A preliminary reactive power setpoint for each of the generators (14) is determined based on a restricted reactive power reference value for the power plant, the restricted reactive power reference value being obtained by applying a reactive power limit to the reactive power reference value of the power plant. Determine (104) the reactive power limit for each of the generators (14), including determining generator-based reactive power limit and voltage-based reactive power limit for each of the generators (14); Generate (106) an allocation signal for requesting reactive power from each of the generators, the allocation signal being generated based on the preliminary reactive power setpoint and a determined reactive power limit, wherein the allocation signal includes an overall restricted setpoint, the restricted setpoint being the determined reactive power limit if the preliminary reactive power setpoint exceeds the determined reactive power limit, and otherwise being the preliminary reactive power setpoint; and The dispatch signal is dispatched (108) to the generator (14). Wherein, the generator-based reactive power limit for each generator corresponds to the reactive power capacity of the generator, and wherein, for each generator (14), determining (104) the voltage-based reactive power limit includes: Determine the terminal voltage of the renewable energy generator described in (112); The determined terminal voltage is compared with the voltage limit (114); and The voltage-based reactive power limit (116) is determined based on the comparison.

2. The method (100) of claim 1, wherein Determining the voltage-based reactive power limit (104) includes: if the terminal voltage for the generator (14) is equal to or exceeds the voltage limit, then the voltage-based reactive power limit for the generator (14) is determined to reduce or prevent the terminal voltage from further exceeding the voltage limit.

3. The method (100) of claim 1 or claim 2, wherein, Determining the voltage-based reactive power limit (104) includes: determining a voltage subrange within an allowable voltage range, the voltage subrange being limited by the voltage limit; and if the terminal voltage for the generator is within the voltage subrange, determining the voltage-based reactive power limit for the generator to prevent further changes in the terminal voltage toward the voltage limit.

4. The method (100) of claim 1 or claim 2, wherein, Determining the voltage-based reactive power limit (104) includes: determining the reactive power output value for the generator, and setting the voltage-based reactive power limit to be equal to the reactive power output value.

5. The method (100) of claim 1 or claim 2, wherein, Determining the voltage-based reactive power limit (104) includes: determining a latest reactive power setpoint value for the generator, and setting the voltage-based reactive power limit to be equal to the latest reactive power setpoint value.

6. The method (100) according to claim 1 or claim 2, comprising: Compare the reactive power limit with the corresponding preliminary reactive power setpoint (202). If the initial reactive power setpoint for the generator exceeds one or more of the reactive power limits for the generator, a shortage of reactive power for the generator is determined (204) based on the difference between the exceeded limit and the initial setpoint. The total shortage of reactive power for the power plant is determined (206) as the sum of the determined shortages for each generator; as well as Based on the allocation of the total shortage, determine (208) the additional amount of reactive power to be provided by each generator, provided that the initial reactive power setpoint for each generator does not exceed the reactive power limit for the generator.

7. The method (100) of claim 6, wherein, The allocation is based on the difference between the terminal voltage of the generator and the voltage limit.

8. The method (100) of claim 6, wherein, The allocation includes requesting a higher proportion of the total shortage from generators (14) with a larger difference between the terminal voltage level and the voltage limit, compared to the proportion of the total shortage requested from generators (14) with a smaller difference between the terminal voltage level and the voltage limit.

9. The method (100) according to claim 6, comprising: The reactive power output level of the generator (14) is monitored, and the allocation is based on the difference between the reactive power output level and one or more reactive power limit levels.

10. The method (100) according to claim 6, comprising: Monitor the reactive power output level of the generator (14); as well as A generation flag is used to determine the reactive power output level, wherein the allocation is based on the determined generation flag.

11. The method (100) according to claim 6, comprising: The active power value of each of the plurality of renewable energy generators (14) is monitored, wherein the allocation is based on the active power value.

12. The method (100) of claim 1 or claim 2, wherein, Determining the preliminary reactive power setpoint (102) includes: dividing the reactive power reference among the plurality of renewable energy generators in the power plant.

13. The method (100) according to claim 1 or claim 2, wherein, The generator-based reactive power limit for each generator is determined by referring to the PQ data structure, which specifies the reactive power limit level based on active power measurement.

14. A power plant controller (22) for a power plant (12) having multiple renewable energy generators (14), wherein, The controller (22) includes a processor (28) and a memory module (32), wherein the memory module (32) includes a set of program code instructions that, when executed by the processor (28), implement the method (100) according to any one of claims 1 to 13.

15. The method (100) of claim 1 or claim 2, or the power plant controller (22) of claim 14, wherein, The renewable energy generator includes a wind turbine generator.

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