Control system configured for simulating virtual synchronous machine of network-building voltage source converter and method thereof

Abstract

A method for networking control using a voltage source converter (VSC) connected to an electrical grid at a common coupling point (PCC) is provided. The method comprises: calculating a converter voltage reference (Vc, ref) of the VSC based at least on a reference current (Ig, ref); calculating a phase angle ([theta] EMF) of an electromotive force EMF voltage vector of the VSC based at least on the active power reference (Pg, ref); calculating a voltage magnitude (VEMF) of the EMF voltage vector based at least on a grid voltage (Vg) at the PCC and a grid voltage reference (Vg, ref); calculating a reference current by feeding the EMF voltage vector via a virtual admittance (5); and limiting the active power reference (Pg, ref) and the voltage magnitude (VEMF) based at least on a maximum allowable current threshold (Ilim) associated with operation of the VSC such that the reference current does not exceed the maximum allowable current threshold.

Description

Technical Field

[0001] The present disclosure relates to power systems, and more particularly to the control of power systems. Background Art

[0002] Conventional synchronous generators provide important ancillary services to the power system, such as synchronizing and damping torque, high short-circuit current and inertia, which are essential to provide the ability to handle large disturbances in the power system, such as, for example, short-circuit faults. The important ancillary services play an important role in why conventional synchronous generators are able to provide so-called grid-forming capabilities.

[0003] Power systems and power generation are undergoing a transformation due to the increasing penetration of renewable energy sources such as photovoltaic panels and wind turbines. In parallel with the increase in renewable energy sources, the integration of power electronic systems such as flexible alternating current transmission systems (FACTS) and high voltage direct current (HVDC) systems has increased. However, the power electronic systems are not yet able to provide important ancillary services.

[0004] Therefore, there is great interest in being able to use converters (eg, converters of FACTS and / or HVDC systems) in power systems to more reliably provide important ancillary services. Summary of the invention

[0005] Therefore, an object of the present invention is to provide a control system and method thereof which allow the use of converters to provide ancillary services. Another object is to provide the ability to use converters for grid control.

[0006] According to a first aspect of the present invention, a control system is provided. The control system is configured for grid control using a voltage source converter (VSC) connected to a grid at a common coupling point (PCC). The control system includes: an alternating current (AC) controller configured to calculate a converter voltage reference of the VSC based at least on a reference current; an active power controller configured to calculate a phase angle of an electromotive force (EMF) voltage vector of the VSC based at least on an active power reference; and a voltage controller configured to calculate a voltage amplitude of an EMF voltage vector based at least on a grid voltage at the PCC and a grid voltage reference. The EMF voltage vector including the phase angle and the voltage amplitude is subtracted from the grid voltage vector and multiplied by a virtual admittance to calculate a reference current. The control system further includes: a current limiter configured to prevent the VSC from operating above a maximum allowable current threshold; an active power reference limiter configured to limit an active power reference input to the active power controller based at least on a maximum allowable current threshold; and a voltage limiter configured to limit a voltage amplitude output from the voltage controller based at least on a maximum allowable current threshold. Limiting the active power reference and limiting the voltage amplitude prevent the reference current from exceeding the maximum allowed current threshold.

[0007] According to a second aspect of the present disclosure, there is provided a method for grid control using a VSC connected to a grid at a PCC. The method comprises: calculating a converter voltage reference of the VSC based at least on a reference current; calculating a phase angle of an EMF voltage vector of the VSC based at least on an active power reference; and calculating a voltage magnitude of the EMF voltage vector based at least on a grid voltage at the PCC and a grid voltage reference. The method further comprises: calculating a reference current by feeding the phase angle and voltage of the EMF voltage vector via a virtual admittance; and limiting the active power reference and the voltage magnitude based at least on a maximum allowed current threshold associated with the operation of the VSC so that the reference current does not exceed the maximum allowed current threshold.

[0008] There has always been interest in being able to implement a grid-type converter rather than a grid-following converter. A grid-type converter should be able to behave as a controllable voltage source. However, how to deal with the limitation of the current of a grid-type converter has always been a huge challenge, especially if the grid-forming nature of the converter should be maintained during abnormal conditions in the grid to which it is connected. Several types of limiting methods, schemes or strategies have been proposed, ranging from hard limits on the reference current sent to the current controller to the manipulation of the virtual impedance and / or voltage of the emulator. However, all limiting strategies focus primarily on the operation of the converter in the event of a voltage sag in the grid, and typically require the activation of a phase-locked loop (PLL) to ensure synchronization. A PLL may be necessary when inertia is to be provided by the converter (i.e., as an auxiliary service) and the system is exposed to a high rate of change of frequency (RoCoF).

[0009] The present disclosure is based on the idea of ​​using the limitation of the active power reference and / or the voltage amplitude to prevent the reference current from exceeding the maximum allowed current threshold (i.e., reducing the reference current by limiting the active power reference and / or the voltage amplitude so that it does not exceed the maximum allowed current threshold), thereby maintaining the grid-forming capability of the converter. This further allows the current exchanged between the converter and the grid to be maintained within the limits of the converter without the current limiter having to prevent the operation of the converter.

[0010] The active power controller and the voltage controller can each be understood as part of a respective outer control loop, while the AC controller can be understood as part of an inner control loop. Thus, the limitation of the active power reference and the limitation of the voltage amplitude are performed at the outer loop, while the calculation of the converter voltage reference of the VSC is performed in the inner loop.

[0011] The outer loop including the active power controller can provide the inverter with networking properties similar to those of a synchronous machine, and can form a certain relationship between the power balance and the internal frequency of the inverter. Further, the outer loop including the active power controller can be regarded as a synchronization loop and can be kept relatively fast in order to provide dynamic performance and / or disturbance (such as, for example, phase angle jump) suppression. In other words, the outer loop including the active power controller can provide synchronization, which in turn can eliminate the need for a backup phase-locked loop PLL configured to provide synchronization.

[0012] Further, the present disclosure is based on the idea that the above mentioned limitations are dynamic, since the limitations made by the active power reference limiter and / or the voltage limiter are based on non-static parameters. This allows the control system and method to adapt to a grid with changing conditions, and also allows the control system and method to be adjusted and tuned.

[0013] The active power reference may be the sum of the active power setpoint and the inertia active power reference. The control system may further include an inertia phase locked loop IPLL unit, which is configured to calculate the inertia active power reference based on the grid voltage at the PCC and the converter voltage reference. Thus, the converter voltage reference is obtained from the AC controller feedback. The active power setpoint may be received by the system operator (i.e., the transmission system operator TSO) or may be predetermined. The implementation of both IPLL and the active power controller may provide decoupling of inertia supply and power synchronization. Therefore, for power synchronization, PLL may not be required.

[0014] The IPLL may be configured to calculate the inertia active power reference based on the calculated grid frequency derivative and / or the desired inertia time constant. The grid frequency derivative may be calculated by monitoring the grid frequency at the PCC and calculating the derivative of the monitored grid frequency. The desired inertia time constant may be predetermined or received by the system operator. Thus, the resulting amount of active power and / or energy to be supplied to the grid by the converter may be predetermined or received by the system operator.

[0015] The IPLL may further include an anti-windup function, so that excessive overshoot of the output of the IPLL may be avoided or reduced.

[0016] The AC controller may be configured to calculate a converter voltage reference for the VSC based on the reference current, the grid voltage at the PCC and the grid current at the PCC. In other words, the AC controller may have as input at least the reference current, the grid voltage at the PCC and the grid current at the PCC.

[0017] The active power reference limiter may be configured to limit the active power reference input to the active power controller based on a maximum allowed current threshold, a grid voltage at the PCC, and / or a reactive power at the PCC. In other words, the active power reference limiter may have as input a maximum allowed current threshold, a grid voltage at the PCC, and / or a reactive power at the PCC.

[0018] The active power reference limiter may be configured to limit the active power reference input to the active power controller to be below an active power threshold value, which is calculated according to the following equation:

[0019]

[0020] Therefore, the active power threshold may be equal to the square root of the square of the reactive power at the PCC minus the square of the absolute value of the grid voltage at the PCC multiplied by the square of the maximum allowed current threshold.

[0021] The active power reference limiter may be further configured to limit the active power reference input to the active power controller based on a grid code from a system operator. In addition, the active power reference limiter may be further configured to limit the active power reference based on active power and / or reactive power at the PCC, thereby avoiding potential system collapse, which may occur, for example, when the grid is operating very weakly. The active power and reactive power at the PCC may be understood to be measured at the PCC.

[0022] A grid voltage reference and / or an active power setpoint may be received from a system operator.

[0023] The grid voltage reference may be reduced by the output of a droop function having as input the reactive power at the PCC before input to the voltage controller. The reactive power at the PCC may be measured and / or received. Thus, droop may be provided, thereby increasing the stability of the converter and therefore the stability within the grid.

[0024] The voltage controller may be further configured to calculate the voltage magnitude of the EMF voltage vector by subtracting the grid voltage from the grid voltage reference, integrating the subtracted grid voltage reference, and adding the rated system voltage to the integrated and subtracted grid voltage reference. The rated system voltage may be predetermined and constant.

[0025] The difference between the voltage amplitude of the voltage controller and the voltage amplitude output from the voltage limiter may be multiplied by a feedback gain and subtracted from the grid voltage reference input to the voltage controller.

[0026] The voltage limit value calculated by the voltage limiter to limit the voltage amplitude output from the voltage controller may be calculated by summing the grid voltage at the PCC and the voltage drop across the virtual impedance. The virtual impedance may be equal to the inverse of the virtual admittance. The voltage drop across the virtual impedance may be calculated by subtracting the grid voltage vector multiplied by the virtual admittance from the EMF voltage vector including the phase angle and the voltage amplitude. Therefore, the voltage drop across the virtual impedance may be calculated by subtracting the grid voltage vector divided by the virtual impedance from the EMF voltage vector including the phase angle and the voltage amplitude.

[0027] The voltage limit value calculated by the voltage limiter to limit the voltage amplitude output from the voltage controller can be calculated according to the following equation:

[0028]

[0029] Q max can be the maximum amount of reactive power available, and (R V +jX V ) may be a virtual impedance equal to the inverse of the virtual admittance. Thus, the voltage limit may be equal to the sum of: the grid voltage at the PCC; and the active power reference minus the maximum amount of available reactive power divided by the conjugate of the grid voltage at the PCC, multiplied by the virtual impedance.

[0030] The maximum amount of available reactive power may be determined based on the allowed apparent power and the active power reference.

[0031] The relationship between the permitted apparent power and the maximum amount of available active power and available reactive power may be as follows:

[0032]

[0033] Furthermore, the allowed apparent power can be calculated by the following equation:

[0034] S=V g *I lim .

[0035] Based on the above, the maximum amount of available reactive power can be calculated according to the following formula:

[0036]

[0037] The current limiter may be configured to perform current limiting according to a geometric shape so as to at least partially maintain the angle of the reference current. For example, the current limiter may be configured to perform circular current limiting so that if the current limiter is operated to limit the reference, the angle of the reference current is maintained. However, the geometric shape is not limited to a circle, and may be, for example, an ellipse, a square, or a hexagon, or any geometric shape.

[0038] The maximum allowed current threshold may be based on at least one of: an ambient temperature at the VSC, a safe operating area SOA of the VSC, and a temperature of semiconductors of the VSC.

[0039] The method according to the second aspect of the present disclosure may further comprise preventing the VSC from operating above the maximum allowed current threshold if the reference current is above the maximum allowed current threshold.

[0040] Note that other embodiments are conceivable using all possible combinations of the features recited in the above embodiments, alternatives or examples. Therefore, the present disclosure also relates to all possible combinations of the features mentioned herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Example embodiments will now be described in more detail with reference to the following drawings.

[0042] Figure 1 A control system according to an exemplary embodiment of the present disclosure is illustrated.

[0043] Figure 2 A portion of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0044] Figure 3 An active power controller of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0045] Figure 4 An inertia PLL of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0046] Figure 5 A portion of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0047] Figure 6 and Figure 7 A voltage controller of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0048] Figure 8 A voltage source converter connected to a grid according to an exemplary embodiment of the present disclosure is illustrated.

[0049] Fig. 9 A flow chart according to an exemplary embodiment of the present disclosure is illustrated.

[0050] As illustrated in the figures, the sizes of elements and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structure of the embodiments.Throughout, like reference numerals refer to like elements. DETAILED DESCRIPTION

[0051] Exemplary embodiments will now be described more fully hereinafter 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 and to fully convey the scope of the invention to the skilled person.

[0052] Figure 1 A control system 1 according to an exemplary embodiment of the present disclosure is illustrated. The control system 1 is configured to provide a common coupling point (PCC, not shown, see e.g. Figure 8 ) connected to the grid at a voltage source converter (VSC) (not shown, see e.g. Figure 8 ) to conduct network control.

[0053] The control system 1 comprises an AC controller 4, which is configured to at least g,ref To calculate the VSC converter voltage reference V c,ref The control system 1 can be understood as calculating the converter voltage reference V c,ref To provide control for VSC. Reference current I g,ref It is calculated by the following steps: The voltage vector EMF of the VSC is V EMF Subtract the grid voltage V at the PCC g , and multiplying the subtracted result by the virtual admittance 5. The control system 1 further comprises a current limiter 14 configured to prevent the VSC from being driven above a maximum allowable current threshold I lim Therefore, if the reference current I g,ref Higher than the maximum allowable current threshold I lim, the current limiter 14 can limit the reference current I input to the AC controller 4 g,ref However, during normal operation of the control system, the reference current I g,ref Keep below the maximum allowable current threshold I lim , and as a safety precaution or as a last resort in extreme conditions (such as, for example, a fault in the grid or a fault in the converter), the current limiter 14 may limit the reference current I g,ref .

[0054] The control system 1 further comprises an active power controller 2, which is configured to control the active power based on at least an active power reference P g,ref To calculate the phase angle θ of the voltage vector EMF EMF The control system 1 further comprises an active power reference limiter 12, which is configured to limit the active power reference P input to the active power controller 2. g,ref .

[0055] The control system 1 comprises a voltage controller 3 which is configured to control the grid voltage V g And the grid voltage reference V g,ref To calculate the voltage amplitude V of the EMF voltage vector EMF The control system 1 further comprises a voltage limiter 13, which is configured to be based at least on the maximum allowed current threshold I lim To limit the voltage amplitude V output from the voltage controller 3 EMF .

[0056] The control system 1 is configured to use the active power reference limiter 12 to limit the active power reference P input to the active power controller 2. g,ref And / or use the voltage limiter 13 to limit the voltage amplitude V output from the voltage controller 3 EMF In order to keep the reference current below the maximum allowed current threshold I lim The current limiter 14 is not activated or triggered.

[0057] The control system 1 can be understood as comprising: two outer control loops, which respectively include an active power controller 2 and a voltage controller 3 ; and an inner control loop, which includes an AC controller 4 .

[0058] EMF voltage vector V EMF It can be understood as the phase angle θ calculated by the active power controller 2 and the voltage controller 3 respectively. EMF and voltage amplitude V EMF Therefore, the EMF voltage vector VEMF It can be understood as being calculated by the outer control loop and used by the AC controller 4 in the inner control loop.

[0059] Further, the control system 1 is configured to perform limitations in the outer control loops (ie, by using the active power reference limiter 12 and / or the voltage limiter 13) rather than in the inner control loop. Limitations in the outer control loops may cause the reference current I g,ref However, it reduces rather than limits the reference current I g,ref The control system may be allowed to maintain networking capabilities during such reductions.

[0060] Figure 2 A portion of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0061] Figure 2 The part of the control system shown in FIG. 1 comprises an active power controller 2 , an active power reference limiter 12 and an inertia phase locked loop IPLL unit 6 . Figure 2 This part of the control system shown in can be, for example, Figure 1 , wherein the active power controller 2 and the active power reference limiter 12 may be similar or substantially identical.

[0062] The active power controller 2 is configured to at least g,ref To calculate the phase angle θ of the EMF EMF Active power reference P g,ref The active power reference is received by the active power controller via an active power reference limiter 12, which is configured to limit the active power reference P g,ref .

[0063] This part of the control system further shows an active power threshold unit 22. The active power threshold unit 22 is configured to calculate an active power threshold P lim , the active power controller 2 can be configured to set the active power reference P g,ref The input of the active power threshold unit 22 is shown as the maximum allowed current threshold I lim , grid voltage V at PCC g and reactive power at the PCC. However, the control system is not limited to including Figure 2. For example, the active power threshold unit 22 and the active power reference limiter 12 may be integrated into a single entity. For example, the active power threshold unit 22 may be a part of the active power reference limiter 12. Further, it should be understood that the active power threshold unit 22 (or the active power reference limiter 12 including the active power threshold unit 22) is not limited to receiving only the inputs mentioned above.

[0064] The active power reference P input to the active power reference limiter 12 g,ref is the active power setting value P set,ref and inertia active power reference P H The active power set point P set,ref May be determined by and / or received from the system operator. Inertia active power reference P H is output from the IPLL unit 6, which can be configured to be based on the grid voltage V at the PCC g and the converter voltage reference V c,ref To calculate the inertia active power reference P H .

[0065] Figure 3 An active power controller 2 of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0066] The active power controller 2 may be, for example, Figure 2 The active power controller of this part of the control system shown in Figure 1 The active power controller of the control system shown in FIG. Figure 1 and Figure 2 The active power controller shown in Figure 3 The active power controller shown in is similar or substantially the same.

[0067] Figure 3 The exemplary embodiment of the active power controller 2 shown in comprises a P1 regulator.

[0068] From the active power reference limiter (not shown; see e.g. Figure 1 and Figure 2 ) The output active power reference P g,ref The active power P at PCC is subtracted g And input to the PI regulator.

[0069] The output of the P1 regulator is added with the rated grid frequency ω 额定 and the active power P at PCC is subtracted g , the active power at the PCC has been multiplied by the active damping factor R. This result is then integrated to obtain the phase angle θ EMF .

[0070] Rated grid frequencyω 额定 Can be predetermined and constant.

[0071] It will be understood that the present disclosure is not limited to Figure 3 The active power controller 2 shown in and discussed above. For example, the active power controller 2 may have additional, fewer, or different combinations of inputs and / or a different structure.

[0072] Figure 4 An inertia PLL (IPLL) 6 of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0073] IPLL 6 may be, for example, Figure 2 The IPLL shown in the Figure 2 The IPLL shown in Figure 4 The IPLL shown in FIG. 1 is similar or substantially the same as that shown in FIG.

[0074] IPLL 6 includes a Park Transform block (in Figure 4 The Park transform block is configured to convert the received three-phase ("abc") signal V g (i.e., the grid voltage at the PCC) and the grid phase angle θ at the PCC g The output of the Park Transform block is multiplied by the inverter voltage reference V c,ref (exist Figure 4 The inverter voltage reference V c,ref is an AC controller from the control system (not shown; see e.g. Figure 1 ) received. Then, the multiplication result is divided by the filter reactance L. The division result is input to the P1 regulator, and the inverse of the division result is also calculated, wherein the inverse result becomes the inertia active power reference P H .

[0075] The output of the P1 regulator is added with the rated grid frequency ω 额定 , and then integrate to calculate the grid phase angle θ at the PCC g , the grid phase angle is also fed back to the Park transformation block.

[0076] Figure 5 A portion of a control system 1 according to an exemplary embodiment of the present disclosure is illustrated.

[0077] Figure 5 The part of the control system shown in comprises a voltage controller 3 and a voltage limiter 13 . Figure 5 This part of the control system shown in can be, for example, Figure 1, wherein the voltage controller 3 and the voltage limiter 13 may be similar or substantially identical.

[0078] The voltage controller 3 is configured to calculate the voltage magnitude V of the EMF voltage vector EMF One of the inputs of the voltage controller 3 is the grid voltage reference V g,ref , the grid voltage reference V g,ref The reactive power Q at the PCC is subtracted g , where the reactive power Q at the PCC is g has been subjected to a droop function and for clarity this input is referred to here as the droop grid voltage reference V g,下垂,ref However, it will be understood that the present disclosure is not limited to the use of Figure 5 The droop function shown in the figure can be directly referenced to the grid voltage V g,ref Input to voltage controller 3. Another of the inputs to voltage controller 3 is the grid voltage V at the PCC g A further input of the voltage controller 3 is the output of the voltage limiter 13 , which is fed back to the voltage controller 3 .

[0079] Figure 5 The part of the control system depicted in FIG. 1 shows a voltage limiting unit 23. The voltage limiting unit 23 is configured to calculate a voltage limit value V lim The voltage limiter 13 uses the voltage limit value as the threshold value of the output of the voltage controller 3. lim The calculation can be based on the grid voltage V at the PCC g , reactive power Q at PCC g , and the maximum allowable current threshold I lim .

[0080] However, the control system 1 is not limited to including Figure 5 . For example, the voltage limiting unit 23 and the voltage limiter 13 may be integrated into a single entity. For example, the voltage limiting unit 23 may be a part of the voltage limiter 13. Further, it should be understood that the voltage limiting unit 23 (or the voltage limiter 13 including the voltage limiting unit 23) is not limited to receiving the inputs mentioned above.

[0081] Figure 6 A voltage controller 3 of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0082] The voltage controller 3 may be, for example, Figure 1 and Figure 5 The voltage controller shown in Figure 1 and Figure 5 The voltage controller shown in Figure 6 The voltage controllers shown in are similar or substantially the same.

[0083] Figure 6 The input of the voltage controller 3 shown in FIG. 3 includes the droop grid voltage reference V g,下垂,ref , grid voltage V at PCC g , and the rated system voltage V 额定 . Droop grid voltage reference V g,下垂,ref The grid voltage V at the PCC is subtracted g , and multiply the result by the parameter K iV And calculate the integral. Add the result of the integral to the rated system voltage V 额定 , from which the voltage amplitude V of the EMF voltage vector is calculated EMF .

[0084] It will be appreciated that the grid voltage can be directly referenced to V g,ref Instead of drooping grid voltage reference V g,下垂,ref Input to voltage controller 3, as previously described Figure 5 discussed.

[0085] Figure 7 A voltage controller 3 of a control system according to an exemplary embodiment of the present disclosure is illustrated.

[0086] Figure 7 The voltage controller 3 shown in FIG. Figure 6 The voltage controller shown in is similar to that shown in . Therefore, also refer to Figure 6 and its related text to describe Figure 7 Voltage controller 3.

[0087] Figure 7 The voltage controller 3 shown in FIG. Figure 6 The difference between the voltage controllers shown in Figure 7 The voltage controller 3 shown in FIG. 1 uses a feedback loop. The feedback loop involves: calculating the voltage magnitude V of the EMF voltage vector EMF (This voltage amplitude is calculated by the voltage controller 3) and the limited voltage amplitude V of the EMF voltage vector EMF,lim (This limited voltage amplitude is controlled by a voltage limiter (not shown; see e.g. Figure 1 or Figure 5 ) and then adding the difference to the feedback gain k 反馈 multiplied, and then from the droop grid voltage reference V g,下垂,ref Therefore, if the voltage amplitude V output from the voltage controller 3 is EMF Below the voltage limiter voltage limit V lim, then the outputs of the voltage controller 3 and the voltage limiter are the same, and thus the difference is zero. This feedback of the difference prevents saturation of the integral part of the voltage controller 3. As an alternative to feedback, the voltage controller 3 may include a back calculation in order to prevent saturation of the integral part.

[0088] Figure 8 A voltage source converter (VSC) connected to a grid according to an exemplary embodiment of the present disclosure is illustrated.

[0089] VSC is indicated as a dashed box, which is connected via the filter impedance R f , L f Connected to the (electricity) grid. The output of the VSC is the converter voltage V c , which then passes through the filter impedance R f , L f The VSC is then fed to the PCC. Further, the VSC can be modeled as a voltage source that outputs an electromotive force EMF, a voltage vector V EMF and the VSC virtual impedance R connected in series v1 , L v1 Filter impedance R f , L f And VSC virtual impedance R v1 , L v1 Together they form a virtual impedance Z v . Virtual impedance Z v is the virtual admittance (such as Figure 1 It will be noted that the role of the virtual impedance is not to simulate the electrical characteristics of the synchronous generator, but to serve as the V EMF With V g The connections between 1 and 2 are used to enable the calculation of the converter voltage reference.

[0090] Fig. 9 A flow chart of a method 100 according to an exemplary embodiment of the present disclosure is illustrated.

[0091] The method 100 is used for grid control using a voltage source converter VSC connected to a grid at a common coupling point PCC. The method 100 comprises: calculating S140 a converter voltage reference of the VSC based at least on a reference current; calculating S120 a phase angle of an electromotive force EMF voltage vector of the VSC based at least on an active power reference; calculating S130 a voltage amplitude of the EMF voltage vector based at least on a grid voltage at the PCC and a grid voltage reference; calculating S150 a reference current by feeding the phase angle and voltage of the EMF voltage vector via a virtual admittance; and limiting S162 an active power reference and / or limiting S163 a voltage amplitude based at least on a maximum allowed current threshold associated with the operation of the VSC, such that the reference current does not exceed the maximum allowed current threshold.

[0092] The method 100 may include the step of preventing the S170 VSC from operating above a maximum allowed current threshold if the reference current is above a maximum allowed current threshold.

[0093] Method 100 provides an improved way to ensure that the reference current remains below the maximum allowed current threshold without having to use a "hard" current limit. In other words, method 100 provides dynamic limiting of the active power reference and / or voltage amplitude to prevent the reference current from reaching the maximum allowed current threshold.

[0094] The invention has been described above mainly with reference to several embodiments. However, as will be readily appreciated by a person skilled in the art, other embodiments than those disclosed above are equally possible within the scope of the invention as defined by the appended patent claims. Further, although features and elements are described above in particular combinations, each feature or element may be used alone without the other features and elements, or in various combinations with or without the other features and elements.

[0095] Additionally, variations to the disclosed embodiments may be understood and effected by the skilled person in practicing the claimed invention, by studying the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does 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.

Claims

1. A control system (1) configured to perform grid control using a voltage source converter VSC connected to a grid at a common coupling point PCC, the control system comprising: The AC controller (4) is configured to at least g,ref ) calculates the converter voltage reference (V c,ref ); An active power controller (2) is configured to at least g,ref ) calculates the electromotive force EMF voltage vector of the VSC ( V EMF ) phase angle (θ EMF );as well as A voltage controller (3) is configured to adjust the voltage of the grid based on at least the grid voltage (V g ) and the grid voltage reference (V g,ref ) calculates the EMF voltage vector ( V EMF ) voltage amplitude (V EMF ); Among them, including the phase angle (θ EMF ) and the voltage amplitude (V EMF ) of the EMF voltage vector ( V EMF ) minus the grid voltage (V g ) is multiplied by the virtual admittance (5) to calculate the reference current (I g,ref ), The control system further comprises: A current limiter (14) is configured to prevent the VSC from being driven above a maximum allowed current threshold (I lim ) An active power reference limiter (12) is configured to determine the active power reference limiter based at least on the maximum allowed current threshold (I lim ) limits the active power reference (P) input to the active power controller (2) g,ref );as well as A voltage limiter (13) is configured to at least based on the maximum allowed current threshold (I lim ) limits the voltage amplitude (V EMF ); Among them, the active power reference (P g,ref ) and the voltage amplitude (V EMF ) is limited to prevent the reference current (I g,ref ) exceeds the maximum allowable current threshold (I lim ).

2. The control system according to claim 1, wherein: The active power reference (P g,ref ) is the active power setting value (P set,ref ) and inertia active power reference (P H ); and Wherein, the control system further comprises: An inertia phase-locked loop IPLL unit (6) is configured to be based on the grid voltage (V g ) and the converter voltage reference (V c,ref ) calculates the inertia active power reference (P H ).

3. The control system according to claim 2, wherein: The IPLL is configured to calculate the inertia active power reference (P H ).

4. The control system according to claim 2 or 3, wherein: The IPLL further includes an anti-saturation function.

5. A control system according to any one of the preceding claims, wherein: The AC controller (4) is configured to g,ref ), the grid voltage at the PCC (V g ) and the grid current at the PCC (I g ) calculates the converter voltage reference (V c,ref ).

6. A control system according to any one of the preceding claims, wherein: The active power reference limiter (12) is configured to be based on the maximum allowed current threshold (I lim ), the grid voltage at the PCC (V g ) and / or the reactive power (Q g ) limits the active power reference (P) input to the active power controller (2) g,ref ).

7. The control system according to claim 6, wherein: The active power reference limiter (12) is configured to limit the active power reference (P g,ref ) is limited to below the active power threshold (P lim ), the active power threshold is calculated according to the following formula:

8. A control system according to any one of the preceding claims, wherein: The active power reference limiter is further configured to set the active power and / or reactive power (Q) at the PCC based on the grid specification received from the system operator and / or the active power and / or reactive power (Q g ) limits the active power reference (P) input to the active power controller (2) g,ref ).

9. A control system according to any one of the preceding claims, wherein: The grid voltage reference (V g,ref ) and / or active power setting value (P set,ref ) is received from the system operator.

10. A control system according to any one of the preceding claims, wherein: Before being input to the voltage controller, the grid voltage reference (V g,ref ) is subtracted from the output of a droop function having as input the reactive power (Q g ).

11. A control system according to any one of the preceding claims, wherein: The voltage controller (3) is further configured to calculate the voltage magnitude (V EMF ): The grid voltage reference (V g,ref ) minus the grid voltage (V g ), the subtracted grid voltage reference (V g,ref ) and the rated system voltage (V 额定 ) is added to the grid voltage reference (V g,ref ).

12. A control system according to any one of the preceding claims, wherein: The voltage amplitude of the voltage controller (V EMF ) and the voltage amplitude (V EMF ) multiplied by the feedback gain (k 反馈 ) and from the grid voltage reference (V g,ref ) is subtracted.

13. A control system according to any one of the preceding claims, wherein: By adjusting the grid voltage (V g ) and the voltage drop across the virtual impedance to calculate the voltage limit (V lim ), which voltage limit is calculated by the voltage limiter to limit the voltage amplitude (V EMF ), wherein the virtual impedance is equal to the inverse of the virtual admittance, and The voltage drop across the virtual impedance is obtained by including the phase angle (θ EMF ) and the voltage amplitude (V EMF ) of the EMF voltage vector (V EMF ) minus the grid voltage vector (V g ) calculated.

14. The control system according to claim 12 or 13, wherein: The voltage limiter is used to limit the voltage amplitude (V EMF ) voltage limit (V lim ) is calculated according to the following formula: Among them, Q max is the maximum amount of reactive power available, and (R V +jX V ) is a virtual impedance equal to the inverse of the virtual admittance.

15. The control system according to claim 14, wherein: The maximum amount of available reactive power (Q max ) is based on the allowed apparent power and the active power reference (P g,ref ) is confirmed.

16. A control system according to claim 14 or 15, wherein: The maximum amount of available reactive power (Q max ) is calculated according to the following formula:

17. A control system according to any one of the preceding claims, wherein: The current limiter is configured to perform current limiting according to a geometric shape so as to at least partially maintain the reference current (I g,ref ) angle.

18. A control system according to any one of the preceding claims, wherein: The maximum allowable current threshold (I lim ) is based on at least one of the following: The ambient temperature at the VSC, the safe operating area SOA of the VSC, and the temperature of the semiconductors of the VSC.

19. A method (100) for grid control using a voltage source converter (VSC) connected to a grid at a point of common coupling (PCC), the method comprising: At least based on the reference current (I g,ref ) calculates (S140) the converter voltage reference (V c,ref ); At least based on the active power reference (P g,ref ) calculates (S120) the phase angle (θ) of the voltage vector of the electromotive force EMF of the VSC EMF ); At least based on the grid voltage (V g ) and the grid voltage reference (V g,ref ) calculates (S130) the voltage amplitude (V EMF ); By feeding the phase angle (θ) of the EMF voltage vector via virtual admittance (5) EMF ) and the voltage (V EMF ) calculates (S150) the reference current (I g,ref ); as well as Based at least on a maximum allowed current threshold (I lim ) limits (S160) the active power reference (P g,ref )(S162) and the voltage amplitude (V EMF )(S163), so that the reference current (I g,ref ) does not exceed the maximum allowable current threshold (I lim ).

20. The method according to claim 19, further comprising: If the reference current (I g,ref ) is higher than the maximum allowed current threshold, then preventing (S170) the VSC from operating above the maximum allowed current threshold.

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