Adaptive power oscillation damping controller for grid-forming converters

Abstract

The present disclosure provides a method and control unit for controlling a power unit (14) connected at a node (20) to a power grid (16). The method includes obtaining a power oscillation damping (POD) signal (POD) from a POD controller based on power oscillations in the power grid. The method further includes calculating a first voltage measurement (U1) measured at the node (20) and a first voltage reference (U2). ref1 ) or an estimated short circuit ratio (SCR) of the power grid. The method further includes adding the POD signal to an input signal (In2) of the power unit regulator (108) to generate an intermediate reference signal (ref i ), the input signal is based on a reference value of the power grid and a corresponding measurement of the power grid. The method further includes obtaining a composite reference signal (ref c ) and operating the power units using the determined composite reference signal to damp oscillations in the grid.

Description

[Technical Field]

[0001] Technical Field The present disclosure relates generally to the field of power systems, and more particularly to the control of power units. [Background technology]

[0002] background Low frequency electromechanical inter-area (power) oscillations are common in power systems and grids. These power oscillations are a cause for concern regarding the reliable operation of the system.

[0003] Different types of power units, such as grid-coupled synchronous machines, power converters, or wind farms / power plants, can be used to damp such inter-area oscillations. Specifically, the voltage at the connection point between the power grid and the power unit can be modulated using reactive power injection. This function is often achieved by an auxiliary control function in the power unit, commonly known as a power oscillation damping (POD) controller. Traditionally, a POD control signal is added to the voltage reference of the power unit's AC voltage regulator. Thus, the POD signal is used to manipulate the power unit's composite voltage reference to achieve damping.

[0004] In recent years, there has been an increasing demand for power converters that exhibit voltage source behavior, also known as grid-forming behavior. However, the requirements imposed on grid-forming power converters, such as grid support for stability and a wide range of short-circuit ratios (SCRs), may not be compatible with traditional POD controllers.

[0005] For example, to achieve stable performance for a wide range of SCRs, the outer voltage control loop of a grid-forming converter is very slow, while POD control may require a faster response time to counteract power oscillations on the grid.

[0006] Furthermore, in some applications, the goal of POD control is to modulate the PCC voltage in the same phase as the observed inter-area oscillation. However, conventional POD controllers often include filters to generate the POD output. These filters often introduce a phase difference between the POD controller's input and output. The power unit control loop may introduce additional phase differences between the POD controller's contribution and the actual output voltage modulation measured at the connection point. These phase delays can complicate the goal of zero phase difference between the actual inter-area oscillation and the output voltage modulation. If the phase difference is too large, the POD control may not be successful in damping the inter-area oscillation and may potentially lead to undesirable high-frequency oscillations. Summary of the Invention [Problem to be solved by the invention]

[0007] overview SUMMARY OF THE INVENTION It is therefore an object of the present invention to overcome at least some of the above-mentioned drawbacks and to provide an improved method and controller for controlling a power unit.

[0008] This and other objects are achieved by the methods and devices defined in the accompanying independent claims. Further embodiments are defined by the dependent claims. [Means for solving the problem]

[0009] According to a first aspect of the present disclosure, a method for controlling a power unit connected to a power grid at a node is provided. The method includes obtaining a power oscillation attenuation (POD) signal from a POD controller based on power oscillations in the power grid. The method further includes determining a gain value based on a difference between a first voltage measurement measured at the node and a first voltage reference or an estimated short circuit ratio (SCR) of the power grid. The method further includes summing the POD signal to an input signal of the power unit regulator to obtain an intermediate reference signal from the power unit regulator. The input signal is based on a reference value of the power grid and a corresponding measurement value of the power grid. The method further includes determining a composite reference signal based on summing the POD signal multiplied by the gain value to the intermediate reference signal, and operating the power unit using the determined composite reference signal to attenuate power oscillations in the grid.

[0010] According to a second aspect of the present disclosure, a control unit for a power unit connected to a power grid at a connection point is provided. The control unit includes a power unit regulator. The control unit is configured to obtain a POD signal from a POD controller based on power oscillations in the power grid. The control unit is further configured to determine a gain value based on a difference between a first voltage measurement measured at the connection point and a first voltage reference or an estimated SCR of the power grid. The control unit is further configured to add the POD signal to an input signal of the power unit regulator to obtain an intermediate reference signal from the power unit regulator. The input signal is based on a reference value of the power grid and a corresponding measurement value of the power grid. The control unit is further configured to determine a composite reference signal based on adding the POD signal multiplied by the gain value to the intermediate reference signal, and operate the power unit using the determined composite reference signal to damp power oscillations in the grid.

[0011] The connection point may be, for example, a point of common coupling (PCC) or a point of coupling (POC), and thus the first voltage measurement measured at the connection point may be equivalent to the PCC voltage.

[0012] The POD signal may be, for example, a voltage or reactive power signal. The POD signal may be obtained from a POD controller. Such a POD controller may be external to the control unit of the power unit. Alternatively, the control unit of the power unit may comprise the POD controller.

[0013] The POD signal is added to the input of a power unit controller. The power unit controller may be configured to provide an output, i.e., an intermediate reference signal, determined to minimize the error represented by the input signal. The error may be, for example, the difference between a desired (reference) value and a measured value from the grid or the power unit. Adding the POD signal to the input of the power unit controller may provide that the intermediate reference signal is adapted to minimize the power oscillations represented by the POD signal.

[0014] However, according to the present control method and the present control unit, the reference signal used to operate the power unit, i.e., the composite reference signal, is further determined based on the POD signal multiplied by a gain. For example, the POD signal may be fed forward to the composite reference signal.

[0015] Specifically, the composite reference signal is determined by adding the POD signal multiplied by the gain value to the intermediate reference signal. Therefore, the POD signal scaled by the adaptive gain can directly affect the composite reference signal, which can reduce the phase difference between the composite reference signal and the POD signal.

[0016] The gain may be based on the difference between a first voltage measurement at the node and a first voltage reference. By adding this summation to the determination of the composite reference signal, the phase shift between the POD signal and the composite reference signal may be minimized.

[0017] The first reference voltage may be a desired voltage at the connection point. The difference between the first voltage measurement value and the first voltage reference value may be referred to hereinafter as a first voltage error, since it represents the difference between the desired value and the actual (measured) value of the first voltage. Therefore, the gain may be adaptively changed based on the first voltage error.

[0018] Alternatively, the gain may be based on an estimated short circuit ratio (SCR) of the grid. The estimated SCR may be received from a dedicated SCR estimator. Such an SCR estimator may be external to the control unit of the power unit. Alternatively, the control unit of the power unit may comprise an SCR estimator.

[0019] Adapting the gain based on the SCR can ensure that adequate attenuation is provided over a wide range of short circuit ratios (SCRs). For example, for grids with higher SCRs, the gain can be higher.

[0020] The disclosed control method can provide for adequate damping of low-frequency electromechanical power oscillations in the grid. In embodiments where the power unit is a grid-forming power converter, power oscillations (or "oscillations") can be damped while maintaining the converter's voltage source behavior for a wide range of SCRs. The control method can be compatible with grid-forming control without (or at least with less) undesirable interaction with voltage regulation. Furthermore, the proposed adaptive POD can damp oscillations with a smaller phase difference between the actual oscillations and the voltage modulation, even when the short-circuit ratio varies widely.

[0021] According to some embodiments, determining the gain value may include providing the difference between the first voltage measurement and the first voltage reference or the estimated SCR to a first controller. The method may further include determining the gain value based on an output from the first controller.

[0022] According to some embodiments, the control unit may include a first controller. The control unit may be further configured to provide the difference between the first voltage measurement and a first voltage reference or the estimated SCR to the first controller and to determine a gain value based on an output from the first controller.

[0023] Further controllability and adjustability of the gain adaptation may be provided by feeding a signal (i.e., the first voltage error or estimated SCR) to a controller and basing the gain on the output of the controller. The controller may be, for example, a PI controller.

[0024] According to some embodiments, the method may further include obtaining a gain value from a lookup table based on an output from the first controller.

[0025] According to some embodiments, the control unit may comprise a look-up table, and the control unit may be further configured to obtain the gain value from the look-up table based on the output from the first controller.

[0026] Alternatively, the lookup table may be implemented without the first controller. In such an embodiment, the gain value may be obtained from the lookup table based on the first voltage error or the estimated SCR.

[0027] According to some embodiments, the power unit regulator may comprise a voltage regulator. The method may further include obtaining a first reference voltage and a first voltage measurement, and determining an input of the power unit regulator based on the first voltage reference and the first voltage measurement.

[0028] The control unit may be further configured to obtain a first reference voltage and a first voltage measurement, and determine an input of the power unit regulator based on the first voltage reference and the first voltage measurement.

[0029] The voltage regulator may be an automatic voltage controller and may be configured to provide a reference signal adapted to control the power unit to minimize the first voltage error, i.e., so that the first voltage measurement approaches the first voltage reference.

[0030] According to some embodiments, the power unit regulator may comprise a reactive power regulator. The method may further include obtaining a first reactive power measurement measured at the connection point and a first reactive power reference. The method may further include determining an input of a power unit regulator based on the first reactive power reference and the first reactive power measurement.

[0031] The control unit may be further configured to obtain a first reactive power measurement value measured at the connection point and a first reactive power reference, and determine an input of the power unit regulator based on the first reactive power reference and the first reactive power measurement value.

[0032] For example, the reactive power regulator may be configured to minimize a first reactive power error based on a first reactive power reference and a first reactive power measurement.

[0033] According to some embodiments, the oscillation may be a power oscillation in the range of 0.2 to 2 Hz. It should be noted that other embodiments may be envisioned that use all possible combinations of the features listed in the above embodiments, and therefore the present disclosure also relates to all possible combinations of the features referred to herein.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments will be described in more detail below with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a schematic diagram of a grid-forming power electronic converter connected to a power grid according to some embodiments. [Figure 2] FIG. 2 is a block diagram illustrating a control unit for operating a power unit according to some embodiments. [Figure 3] FIG. 2 is a block diagram illustrating a control unit for operating a power unit according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0036] As shown in the figures, the sizes of elements and regions may be exaggerated for illustrative purposes and, therefore, are provided to illustrate the general structure of the embodiments. Like reference numerals refer to like elements throughout.

[0037] Detailed Description Exemplary embodiments are described more fully below with reference to the accompanying drawings, in which presently preferred embodiments are shown. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided for thoroughness and completeness, so as to fully convey the scope of the invention to those skilled in the art.

[0038] FIG. 1 shows a schematic diagram of a power unit 14 coupled to a power grid 16 at a node 20 .

[0039] The power unit 14 may be a converter configured to convert power (DC or AC) from a power source into power (AC or DC) suitable for the power grid 16. The converter may be a grid-forming power converter controlled to emulate a voltage source connected to a node through an impedance.

[0040] Alternatively, the power unit 14 may be a synchronous machine, a wind farm or a wind power station.

[0041] 2 shows a schematic diagram of a control unit 100 for controlling the power units 14 to provide power oscillation damping (POD) to the grid 16. The control unit 100 may be configured to perform the method described in the second aspect of the present disclosure.

[0042] The control unit 100 receives an input signal In2 and an (intermediate) reference signal ref i The POD signal POD is obtained, for example from a POD controller, based on power oscillations observed on the grid 16. The POD signal POD may be based on measurements made at the connection points 20, such as voltage measurements or reactive power measurements. The POD signal POD is determined by the power oscillations that the POD signal POD represents based on a (intermediate) reference signal ref i is added to the input signal In2 so as to be taken into account by the power unit regulator 108 when calculating / determining

[0043] In the voltage control mode, the power unit regulator 108 may be a voltage regulator, such as an AC voltage regulator. The input signal In2 may be a voltage signal. For example, the input signal In2 may be a first voltage error signal.

[0044] In the reactive power control mode, the power unit regulator 108 may be a reactive power regulator. The input signal In2 may be a reactive power signal. For example, the input signal In2 may be a first reactive power error signal.

[0045] According to the method and control unit 100 provided by the present disclosure, a synthetic reference signal ref is used to operate the power unit 14. c Specifically, a gain value G is determined (in box 102) based on the input In1. The input In1 is coupled to a first voltage reference signal U ref1 and the first voltage measurement signal U1 measured at node 20. Alternatively, input I1 may be an estimated short circuit ratio (SCR) of grid 16.

[0046] The POD signal POD is multiplied by a gain G to provide a modified POD signal G,POD. c is the intermediate reference signal ref i and is determined (in box 104) based on the modified POD signal G,POD.

[0047] 3 schematically illustrates an exemplary embodiment of control unit 200 in voltage control mode. The embodiment illustrated in FIG. 3 includes several optional features, according to some embodiments. While the features described below are shown in the same figure, it will be understood that different embodiments may include some, one, or none of the features illustrated in FIG. 3.

[0048] First, the gain G is determined in box 102 as described above. The control unit 200 then calculates the first voltage measurement U1 and the first voltage reference U2 as shown in FIG. ref,1 The first controller 210 may provide an output based on the difference between the SCR and the first voltage error, i.e., a first voltage error. Alternatively, or additionally, the first controller 210 may determine the output based on the estimated SCR. For example, the first controller 210 may be a PI controller. A gain G may be determined based on the output of the first controller 210.

[0049] Additionally, the control unit 200 may further comprise a lookup table 212. The lookup table may associate different input values ​​with appropriate gain values ​​G. In FIG. 3, the lookup table 212 is implemented with the first controller 210. In such an embodiment, the lookup table 212 may associate different output values ​​from the first controller 210 with appropriate gain values ​​G. Alternatively, the lookup table may directly associate the first voltage error or estimated SCR with appropriate gain values ​​G.

[0050] 3 shows the control unit 200 in voltage control mode. In such an embodiment, the power unit regulator 108 may comprise a voltage regulator, such as an AC voltage regulator. The input of the voltage regulator is connected to a first voltage reference U ref,1to subtract the first voltage measurement U1 from the POD signal U POD which in the illustrated embodiment is based on voltage measurements at the grid.

[0051] Alternatively, the control unit may be in a reactive power control mode. In such an embodiment, the first regulator 108 may comprise a reactive power regulator. The reactive power regulator may be configured to calculate a first reactive power measurement (Q1, not shown), a first reactive power reference (Q ref1 , not shown), and the POD signal (Q POD , not shown) based on the intermediate reference signal ref i The POD signal may be based on reactive power measurements taken on the grid.

[0052] As mentioned above, the synthesized reference signal ref c is the intermediate reference signal ref i and the modified POD signal G,POD. In FIG. 3, the synthesized reference signal U ref,c The determination of the corrected POD signal U G,POD the intermediate reference signal U ref,i This includes adding to

[0053] In Figure 3, the intermediate reference signal U ref,i and the composite reference signal U ref,c However, if power unit 14 is configured to receive a current reference, then the composite voltage reference signal U ref,c is multiplied by the virtual admittance Y to obtain the composite current reference signal I ref,c The composite current reference signal may be used, for example, in a grid-forming power converter controlled to emulate a voltage source connected to a node through an impedance.

[0054] Those skilled in the art will appreciate that the present invention is by no means limited to the preferred embodiments described above, but on the contrary, many modifications and variations are possible within the scope of the appended claims.

[0055] Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements, or in various combinations with or without the other features and elements.

[0056] Furthermore, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.

[0057] Itemized List of Embodiments 1. A method for controlling a power unit (14) connected to a power grid (16) at a node (20), the method comprising: Obtaining a power oscillation damping (POD) signal (POD) based on oscillations in the power grid; The gain value (G) is The first voltage measurement (U1) measured at the connection point and the first voltage reference (U ref1 ) or Estimated short circuit ratio (SCR) of the power grid and The POD signal is added to the input signal (In2) of the power unit controller (108) to generate an intermediate reference signal (ref i ) and A composite reference signal (ref c ) and operating the power units using the determined composite reference signal to damp oscillations in the grid; A method comprising:

[0058] 2. The gain value is determined by providing a difference between the first voltage measurement and a first voltage reference or an estimated SCR to a first controller; determining a gain value based on an output from the first controller; The method according to item 1, comprising:

[0059] 3. The method of item 2, further comprising obtaining a gain value from a lookup table based on an output from the first controller.

[0060] 4. The method of any of the preceding items, wherein determining the composite reference signal includes adding the POD signal multiplied by the gain value to the intermediate reference signal.

[0061] 5. The power unit regulator comprises a voltage regulator, and the method comprises: obtaining a first reference voltage and a first voltage measurement; determining an input of a power unit regulator based on the first voltage reference and the first voltage measurement; 3. The method of any of the preceding items, further comprising:

[0062] 6. The power unit regulator comprises a reactive power regulator, and the method comprises: Obtaining a first reactive power measurement measured at the point of interconnection and a first reactive power reference; determining an input of a power unit regulator based on the first reactive power reference and the first reactive power measurement; 5. The method according to any one of items 1 to 4, further comprising:

[0063] 7. The method of any of the preceding items, wherein the vibration is a power vibration in the range of 0.2 to 2 Hz.

[0064] 8. A control unit for a power unit (14) connected to a power grid (16) at a connection point (20), the control unit comprising a power unit regulator (108), the control unit comprising: Obtaining a power oscillation damping (POD) signal (POD) based on oscillations in the power grid; The gain value (G) is The first voltage measurement (U1) measured at the connection point and the first voltage reference (U ref1 ) or Estimated short circuit ratio (SCR) of the power grid Determined based on The POD signal is added to the input signal (In2) of the power unit controller (108) to generate an intermediate reference signal (ref i ) and A composite reference signal (ref c ) is determined, Operating a power unit using the determined composite reference signal to damp oscillations in the grid The control unit is configured to:

[0065] 9. Further comprising a first controller, wherein the control unit: providing a difference between the first voltage measurement and a first voltage reference or an estimated SCR to a first controller; Determine the gain value based on the output from the first controller Item 9. The control unit according to item 8, further configured to:

[0066] 10. The control unit of item 9, further comprising a look-up table, wherein the control unit is further configured to obtain a gain value from the look-up table based on an output from the first controller.

[0067] 11. The control unit of item 9 or 10, wherein determining the composite reference signal includes adding the POD signal multiplied by the gain value to the intermediate reference signal.

[0068] 12. The power unit regulator comprises a voltage regulator, and the control unit comprises: obtaining a first reference voltage and a first voltage measurement; determining an input of a power unit regulator based on the first voltage reference and the first voltage measurement; 12. The control unit according to any one of items 8 to 11, further configured as follows:

[0069] 13. The power unit regulator comprises a reactive power regulator, and the control unit comprises: obtaining a first reactive power measurement value measured at the point of interconnection and a first reactive power reference; determining an input of a power unit regulator based on the first reactive power reference and the first reactive power measurement; 12. The control unit according to any one of items 8 to 11, further configured as follows:

[0070] 14. A control unit according to any one of items 8 to 13, wherein the vibration is a power vibration in the range of 0.2 to 2 Hz.

Claims

1. A method for controlling an electric power unit (14) connected to an electric power grid (16) at a connection point (20), the method comprising: obtaining a power oscillation damping (POD) signal from a power oscillation damping (POD) controller based on power oscillations in the power grid; The gain value (G) is A first voltage measurement (U １ ), and the first voltage reference (U ref１ ) or The estimated short circuit ratio (SCR) of the power grid and The POD signal is added to the input signal (In2) of the power unit controller (108) to generate an intermediate reference signal (ref i ), wherein the input signal is based on a reference value of the power grid and a corresponding measurement value of the power grid; A composite reference signal (ref ) is generated based on adding the POD signal multiplied by the gain value (G, POD) to the intermediate reference signal. c ) and operating the power unit using the determined composite reference signal to damp the power oscillations in the power grid; A method comprising:

2. said determining said gain value providing the difference between the first voltage measurement and the first voltage reference or the estimated SCR to a first controller; determining the gain value based on an output from the first controller; The method of claim 1 , comprising:

3. The method of claim 2 , further comprising obtaining the gain value from a look-up table based on the output from the first controller.

4. the power unit regulator comprises a voltage regulator, and the method comprises: obtaining the first voltage reference and the first voltage measurement; determining an input of the power unit regulator based on the first voltage reference and the first voltage measurement; The method according to any one of claims 1 to 3, further comprising:

5. the power unit regulator comprises a reactive power regulator, and the method comprises: Obtaining a first reactive power measurement measured at a point of interconnection and a first reactive power reference; determining an input of the power unit regulator based on the first reactive power reference and the first reactive power measurement; The method of any one of claims 1 to 3, further comprising:

6. The method of claim 1, wherein the power oscillation is in the range of 0.2 to 2 Hz.

7. A control unit for a power unit (14) connected to a power grid (16) at a connection point (20), said control unit comprising a power unit regulator (108), said control unit comprising: obtaining a power oscillation damping (POD) signal (POD) from a POD controller based on power oscillations in the power grid; The gain value (G) is A first voltage measurement (U １ ), and the first voltage reference (U ref１ ) or The estimated short circuit ratio (SCR) of the power grid Determined based on The POD signal is added to the input signal (In2) of the power unit controller (108) to generate an intermediate reference signal (ref i ), wherein the input signal is based on a reference value of the power grid and a corresponding measurement value of the power grid; A composite reference signal (ref ) is generated based on adding the POD signal multiplied by the gain value (G, POD) to the intermediate reference signal. c ) is determined, Operating the power unit using the determined composite reference signal to damp the power oscillations in the power grid. The control unit is configured to:

8. The control unit further comprises: providing the difference between the first voltage measurement and the first voltage reference or the estimated SCR to the first controller; determining the gain value based on an output from the first controller; The control unit of claim 7 further configured to:

9. The control unit of claim 8 , further comprising a lookup table, the control unit further configured to obtain the gain value from the lookup table based on the output from the first controller.

10. the power unit regulator comprises a voltage regulator, and the control unit obtaining the first voltage reference and the first voltage measurement; determining an input of the power unit regulator based on the first voltage reference and the first voltage measurement; A control unit according to any one of claims 7 to 9, further configured to:

11. the power unit regulator comprises a reactive power regulator, and the control unit obtaining a first reactive power measurement measured at the connection point and a first reactive power reference; determining an input of the power unit regulator based on the first reactive power reference and the first reactive power measurement; A control unit according to any one of claims 7 to 9, further configured to:

12. The control unit of claim 7, wherein the control unit is configured to obtain the POD signal (POD) from the POD controller based on power oscillations in the power grid in a range of 0.2 to 2 Hz.

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