A frequency regulation standby balance control method based on three-terminal flexible DC transmission system

Abstract

The present invention discloses a frequency regulation standby balance control method based on a three-terminal flexible direct current transmission system, comprising the following steps: S1, real-time monitoring and collection of bus frequency and active power data of each new energy station and traditional synchronous power plant grid connection point of the flexible direct current transmission system through a measuring device, and determining the control mode of each converter station of the three-terminal flexible direct current transmission system, the topological connection between each converter station, and the AC system connected to each converter station; S2, based on the measured bus frequency data of the synchronous power plant after disturbance, the bus frequency deviation control amount of the new energy station is calculated; S3, based on the change of the AC bus frequency and through the primary frequency regulation and virtual inertia algorithm, the active power supported by the receiving end frequency of the new energy station participating in the flexible direct current transmission system is calculated in real time. The present invention can improve the utilization rate of the primary frequency regulation standby of new energy, reduce "wind abandonment and solar abandonment", improve the frequency support level of the new energy station to the power grid, and improve the system operation stability.

Description

Technical Field

[0001] The present invention relates to the field of frequency stability control of power systems, and in particular to a frequency regulation standby balance control method based on a three-terminal flexible direct current power transmission system. Background Art

[0002] In the existing technology, with the continuous increase in the proportion of new energy access, large-scale centralized development of new energy and long-distance transmission to peak power consumption areas through ultra-high voltage flexible direct current transmission technology has become the mainstream. The frequency anti-interference ability of the power system has decreased, and the characteristics of insufficient frequency regulation capability have become increasingly apparent. Therefore, it is of great significance for the new energy base at the sending end to use a three-terminal flexible direct current transmission system with a grid-type converter station to provide frequency support for the receiving-end power grid.

[0003] Considering that the flexible DC transmission system itself does not have frequency regulation related control functions, the use of a fixed active power control method for the receiving-end converter station will affect the change of the DC voltage when the power transmitted from the receiving-end converter station to the receiving-end power grid changes.

[0004] At the same time, since photovoltaic and other new energy bases do not have the ability to establish an AC power grid or have very weak capabilities, the converter station on the sending end of the new energy infrastructure usually adopts a grid-type control with frequency establishment capabilities such as voltage / frequency droop control (V / F control), which enables the sending end converter station to have the ability to control the frequency of the sending end new energy base. Therefore, it is feasible to dynamically change the deviation of the frequency of the sending end converter station through the deviation of the DC voltage.

[0005] The sending-end new energy base evaluates the frequency deviation online through the measurement data of the synchronous phasor measurement unit (PMU), and calculates the power participating in the primary frequency regulation and virtual inertia support of the receiving end in real time, providing frequency support for the receiving-end power grid. Therefore, the method of using a three-terminal flexible DC transmission system with a grid-type converter station in the sending-end new energy base to provide frequency support for the receiving-end power grid is of great significance, and it can improve the frequency stability of the receiving-end power grid. Summary of the invention

[0006] The purpose of the present invention is to provide a frequency regulation standby balance control method based on a three-terminal flexible direct current transmission system, which can improve the utilization rate of the primary frequency regulation standby of new energy, reduce "wind abandonment and solar abandonment", improve the frequency support level of new energy stations to the power grid, and improve the system operation stability.

[0007] To achieve the above object, the present invention provides a frequency regulation standby balance control method based on a three-terminal flexible direct current transmission system, comprising the following steps:

[0008] S1. Use the measuring device to monitor and collect the bus frequency and active power data of each new energy station and the traditional synchronous power plant at the sending end of the flexible DC transmission system in real time, and determine the control mode of each converter station of the three-terminal flexible DC transmission system, the topological connection between each converter station, and the AC system connected to each converter station;

[0009] S2. Calculate the control amount of the bus frequency deviation of the new energy station based on the measured bus frequency data of the sending-end synchronous machine power plant after the disturbance;

[0010] S3. Based on the change of AC bus frequency and through primary frequency modulation and virtual inertia algorithm, the active power supported by the receiving frequency of the new energy station participating in the flexible DC transmission system is calculated in real time.

[0011] Preferably, in step S1, the control mode of each converter station of the three-terminal flexible DC power transmission system is determined as follows:

[0012] Receiving end converter station: fixed active power control and fixed reactive power control;

[0013] No. 1 sending-end converter station: constant DC voltage control and constant reactive power control;

[0014] No. 2 sending-end converter station: voltage-frequency droop control, i.e. V / F control.

[0015] Preferably, in step S1, the topological connection mode between the converter stations of the three-terminal flexible DC transmission system is determined as follows: No. 1 sending-end converter station is DC-connected to the receiving-end converter station, and No. 2 sending-end converter station is DC-connected to No. 1 sending-end converter station in parallel.

[0016] Preferably, in step S1, the AC systems connected to the converter stations of the three-terminal flexible DC transmission system are determined as follows: the receiving-end converter station is connected to the receiving-end power grid; the No. 1 sending-end converter station is connected to the AC transmission system; and the No. 2 sending-end converter station is connected to a large-scale new energy base.

[0017] Preferably, step S2 specifically includes the following steps:

[0018] S21. If the transmission power of the receiving converter station changes suddenly in any way, the DC voltage change is calculated by the following formula:

[0019]

[0020] Among them, P ref is the reference value of the receiving end transmission power, P dcg is the receiving end transmission power, i dgref is the d-axis control current reference value of the receiving converter station, i dg is the d-axis control current of the receiving converter station, v dg is the potential in the d-axis of the converter station, L mgis the equivalent inductance of the AC system connected to the receiving end, R sg is the equivalent resistance of the AC system connected to this receiving end, k p3 , k i3 , k p4 , k i4 They are the inner loop PI parameters and outer loop PI parameters of this converter station respectively;

[0021] S22. If the DC voltage changes, the DC voltage change and the transmitted active power change of the No. 1 sending-end converter station are calculated by the following formula:

[0022] U dcw =U dcg +i dc ·R dc

[0023]

[0024] Among them, C eqw is the equivalent capacitance on the DC voltage side of the converter station, U dcw is the DC voltage at the sending end, i dc is the DC capacitance, R dc is the DC line resistance, P w is the power transmitted from the sending end to the flexible DC system, P dcw is the power transmitted from the sending-end converter station to the DC line, U acw is the AC bus voltage of the AC system to which this sending end is connected, v ds is the potential in the d axis, i ds is the d-axis control current of the sending-end converter station, i dsref is the d-axis control current reference value of the sending-end converter station, U dcsref is the DC voltage reference value, L m is the equivalent inductance of the AC system connected to the sending end, R s is the equivalent resistance of the AC system connected to this sending end, k p1 , k i1 , k p2 , k i2 They are the inner loop PI parameters and outer loop PI parameters of this converter station respectively;

[0025] S23. The change of transmission power of converter station 1 causes frequency disturbance in the connected AC transmission system. If the bus frequency deviation of the AC side of converter station 1 is greater than 0.15Hz, and the primary frequency regulation reserve capacity of the connected AC system is less than 0.5%, the bus frequency deviation control amount of converter station 2 is:

[0026]

[0027] Where: P Nren is the capacity of large-scale new energy base, PNs is the capacity of the AC transmission system, k f is the reserve factor, P resren It is the primary frequency regulation reserve capacity of large-scale new energy base, P sres is the primary frequency regulation reserve capacity of the AC transmission system, K ren K is the primary frequency regulation coefficient of large-scale new energy base, s It is the equivalent difference coefficient of primary frequency regulation of AC transmission system;

[0028] The equivalent adjustment coefficient is calculated by the following formula:

[0029]

[0030] Where: K' i is the adjustment coefficient of each synchronous machine, P' i is the capacity of each synchronous machine;

[0031] S24. If the bus frequency deviation of the AC side of converter station No. 1 is greater than 0.15Hz, but the primary frequency regulation reserve capacity of the connected AC system is greater than 0.5%, the bus frequency deviation control amount of converter station No. 2 is:

[0032]

[0033] Preferably, step S3 specifically includes the following steps:

[0034] The frequency data of the busbars of each power plant in the AC system of the new energy base connected to the No. 2 sending-end converter station are measured by the measuring device. If the frequency deviation exceeds the primary frequency regulation dead zone, the total primary frequency regulation and virtual inertia active power control instructions of the new energy base are calculated by the following formulas:

[0035]

[0036]

[0037] Among them, ΔP st1 is the virtual inertia active power adjustment value of each new energy station in the new energy base, ΔP st1 is the active power regulation of each new energy station in the new energy base, K i is the frequency regulation control coefficient for each new energy station, f0 is the rated frequency, Δf is the frequency deviation of the new energy base bus, P Ni is the rated capacity of each new energy station in the new energy base, H i is the inertia time constant of each new energy station, is the frequency change rate; f1 is the frequency modulation dead zone. When the frequency deviation is positive, the frequency modulation dead zone is negative, otherwise it is positive.

[0038] Therefore, the present invention adopts the above-mentioned frequency regulation standby balance control method based on the three-terminal flexible DC transmission system, which can fully utilize the power regulation capability of the sending-end new energy base and the entire flexible DC transmission system, detect the AC bus frequency of the No. 1 converter station at the sending end in real time, and provide power support in time when its standby power is insufficient, thereby improving the system operation stability.

[0039] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a flow chart of a frequency regulation standby balance control method based on a three-terminal flexible direct current transmission system of the present invention;

[0041] Figure 2 is a topological diagram of a three-section flexible direct current transmission system adopted in an embodiment of the present invention;

[0042] Figure 3 is a result diagram after the DC voltage disturbance of the present invention;

[0043] Figure 4 This is a comparison diagram of the bus frequency of the new energy base of the present invention when the bus frequency deviation of the AC side of the No. 1 converter station is greater than 0.15 Hz and the primary frequency regulation reserve capacity of the connected AC system is less than 0.5%;

[0044] Figure 5 This is a comparison chart of the active power command value results of the new energy base of the present invention when the bus frequency deviation on the AC side of the No. 1 converter station is greater than 0.15 Hz and the primary frequency regulation reserve capacity of the connected AC system is less than 0.5%;

[0045] Figure 6 This is a comparison diagram of the bus frequency of a conventional synchronous generator power plant of the present invention when the bus frequency deviation of the AC side of the No. 1 converter station is greater than 0.15 Hz and the primary frequency regulation reserve capacity of the connected AC system is less than 0.5%;

[0046] Figure 7 This is a comparison diagram of the active power command value results of the conventional synchronous machine power plant of the present invention when the bus frequency deviation on the AC side of the No. 1 converter station is greater than 0.15 Hz and the primary frequency regulation reserve capacity of the connected AC system is less than 0.5%;

[0047] Figure 8 This is a comparison diagram of the bus frequency of the new energy base of the present invention when the bus frequency deviation of the AC side of the No. 1 converter station is greater than 0.15Hz, but the primary frequency regulation reserve capacity of the connected AC system is greater than 0.5%;

[0048] Fig. 9This is a comparison chart of the active power command value results of the new energy base of the present invention when the bus frequency deviation on the AC side of the No. 1 converter station is greater than 0.15Hz, but the primary frequency regulation reserve capacity of the connected AC system is greater than 0.5%;

[0049] Fig.10 This is a comparison diagram of the bus frequency of a conventional synchronous generator power plant of the present invention when the bus frequency deviation of the AC side of the No. 1 converter station is greater than 0.15 Hz, but the primary frequency regulation reserve capacity of the connected AC system is greater than 0.5%;

[0050] Fig.11 It is a comparison diagram of the active power command value results of the conventional synchronous machine power plant of the present invention when the bus frequency deviation on the AC side of the No. 1 converter station is greater than 0.15 Hz, but the primary frequency regulation reserve capacity of the connected AC system is greater than 0.5%. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0052] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0053] Embodiment 1

[0054] like Figure 1 As shown, the present invention provides a frequency regulation standby balance control method based on a three-terminal flexible direct current transmission system, comprising the following steps:

[0055] S1. Use measuring devices to monitor and collect bus frequency and active power data of each renewable energy station and traditional synchronous power plant at the sending end of the flexible DC transmission system in real time, and determine the control mode of each converter station in the three-terminal flexible DC transmission system, the topological connection between each converter station, and the AC system connected to each converter station.

[0056] Among them, the control mode of each converter station of the three-terminal flexible DC transmission system is determined as follows:

[0057] Receiving end converter station: fixed active power control and fixed reactive power control;

[0058] No. 1 sending-end converter station: constant DC voltage control and constant reactive power control;

[0059] No. 2 sending-end converter station: voltage-frequency droop control, i.e. V / F control.

[0060] The topological connection mode between the converter stations of the three-terminal flexible DC transmission system is determined as follows: the No. 1 sending-end converter station is DC-connected to the receiving-end converter station, and the No. 2 sending-end converter station is DC-connected in parallel to the No. 1 sending-end converter station.

[0061] The AC systems connected to each converter station of the three-terminal flexible DC transmission system are determined as follows: the receiving-end converter station is connected to the receiving-end power grid; the No. 1 sending-end converter station is connected to the AC transmission system; and the No. 2 sending-end converter station is connected to a large-scale new energy base.

[0062] S2. Calculate the control amount of the bus frequency deviation of the new energy station based on the measured bus frequency data of the sending-end synchronous machine power plant after the disturbance.

[0063] The specific steps include:

[0064] S21. If the transmission power of the receiving converter station changes suddenly in any way, the DC voltage change is calculated by the following formula:

[0065]

[0066] Among them, P ref is the reference value of the receiving end transmission power, P dcg is the receiving end transmission power, i dgref is the d-axis control current reference value of the receiving converter station, i dg is the d-axis control current of the receiving converter station, v dg is the potential in the d-axis of the converter station, L mg is the equivalent inductance of the AC system connected to the receiving end, R sg is the equivalent resistance of the AC system connected to this receiving end, k p3 , k i3 , k p4 , k i4 They are the inner loop PI parameters and outer loop PI parameters of this converter station respectively;

[0067] S22. If the DC voltage changes, the DC voltage change and the transmitted active power change of the No. 1 sending-end converter station are calculated by the following formula:

[0068] U dcw =U dcg +i dc ·R dc

[0069]

[0070]

[0071] Among them, C eqw is the equivalent capacitance on the DC voltage side of the converter station, U dcw is the DC voltage at the sending end, i dc is the DC capacitance, R dc is the DC line resistance, P w is the power transmitted from the sending end to the flexible DC system, P dcwis the power transmitted from the sending-end converter station to the DC line, U acw is the AC bus voltage of the AC system to which this sending end is connected, v ds is the potential in the d axis, i ds is the d-axis control current of the sending-end converter station, i dsref is the d-axis control current reference value of the sending-end converter station, U dcsref is the DC voltage reference value, L m is the equivalent inductance of the AC system connected to the sending end, R s is the equivalent resistance of the AC system connected to this sending end, k p1 , k i1 , k p2 , k i2 They are the inner loop PI parameters and outer loop PI parameters of this converter station respectively;

[0072] S23. The change of transmission power of converter station 1 causes frequency disturbance in the connected AC transmission system. If the bus frequency deviation of the AC side of converter station 1 is greater than 0.15Hz, and the primary frequency regulation reserve capacity of the connected AC system is less than 0.5%, the bus frequency deviation control amount of converter station 2 is:

[0073]

[0074] Where: P Nren is the capacity of large-scale new energy base, P Ns is the capacity of the AC transmission system, k f is the reserve factor, P resren It is the primary frequency regulation reserve capacity of large-scale new energy base, P sres is the primary frequency regulation reserve capacity of the AC transmission system, K ren K is the primary frequency regulation coefficient of large-scale new energy base, s It is the equivalent difference coefficient of primary frequency regulation of AC transmission system;

[0075] The equal value adjustment coefficient is calculated by the following formula:

[0076]

[0077] Where: K' i is the adjustment coefficient of each synchronous machine, P' i is the capacity of each synchronous machine;

[0078] S24. If the bus frequency deviation of the AC side of converter station No. 1 is greater than 0.15Hz, but the primary frequency regulation reserve capacity of the connected AC system is greater than 0.5%, the bus frequency deviation control amount of converter station No. 2 is:

[0079]

[0080] S3. Based on the change of AC bus frequency and through primary frequency modulation and virtual inertia algorithm, the active power supported by the receiving frequency of the new energy station participating in the flexible DC transmission system is calculated in real time.

[0081] The specific steps include:

[0082] The frequency data of the busbars of each power plant in the AC system of the new energy base connected to the No. 2 sending-end converter station are measured by the measuring device. If the frequency deviation exceeds the primary frequency regulation dead zone, the total primary frequency regulation and virtual inertia active power control instructions of the new energy base are calculated by the following formulas:

[0083]

[0084] Among them, ΔP st1 is the virtual inertia active power adjustment value of each new energy station in the new energy base, ΔP st1 is the active power regulation of each new energy station in the new energy base, K i is the frequency regulation control coefficient for each new energy station, f0 is the rated frequency, Δf is the frequency deviation of the new energy base bus, P Ni is the rated capacity of each new energy station in the new energy base, H i is the inertia time constant of each new energy station, is the frequency change rate; f1 is the frequency modulation dead zone. When the frequency deviation is positive, the frequency modulation dead zone is negative, otherwise it is positive.

[0085] In this embodiment, the three-terminal flexible DC transmission system topology is selected as follows: Figure 2 As shown, based on this system, the frequency regulation standby balance control method of the three-terminal flexible DC transmission system using a grid-type converter station at the sending-end new energy base is verified:

[0086] In such Figure 2 In the three-terminal flexible DC transmission system shown in the figure, a load sudden increase of 600MW is set at the receiving-end grid, and the system frequency exceeds the dead zone of the synchronous machine speed regulator's primary frequency regulation action. The AC bus frequency of the receiving-end converter station is collected to calculate the power support of the three-terminal flexible DC transmission system for the receiving-end frequency.

[0087] Depend on Figure 3 It can be seen that the change of transmission power at the receiving-end converter station affects the DC voltage, and the collected DC voltage value is used to calculate the AC frequency control value of the sending-end new energy base.

[0088] When the reduction of DC voltage causes the transmission power of station 1 to increase, the bus frequency deviation of the AC side of station 1 is greater than 0.15Hz, and the primary frequency regulation reserve capacity of the connected AC system is less than 0.5%, the bus frequency changes of the sending-end new energy base using the method of the present invention and not using the method of the present invention are as follows: Figure 4As shown, the total control instructions of the new energy base are as follows Figure 5 shown.

[0089] The bus frequency changes of the conventional synchronous machine power plant using the method of the present invention and not using the method of the present invention are as follows: Figure 6 As shown, the power changes of traditional synchronous power plants are as follows: Figure 7 Among them, the control group I does not adopt the present invention, and the experimental group I adopts the present invention.

[0090] When the bus frequency deviation of the AC side of the No. 1 converter station is greater than 0.15Hz, and the primary frequency regulation reserve capacity of the connected AC system is greater than 0.5%, the bus frequency changes of the sending-end new energy base using the method of the present invention and not using the method of the present invention are as follows: Figure 8 As shown, the total control instructions of the new energy base are as follows Fig. 9 shown.

[0091] The bus frequency changes of the conventional synchronous machine power plant using the method of the present invention and not using the method of the present invention are as follows: Fig.10 As shown, the power changes of traditional synchronous power plants are as follows: Fig.11 Among them, the control group II does not adopt the present invention, and the experimental group II adopts the present invention.

[0092] Therefore, the present invention adopts the above-mentioned frequency regulation standby balance control method based on the three-terminal flexible direct current transmission system, which can improve the utilization rate of the primary frequency regulation standby of new energy, reduce "wind abandonment and solar abandonment", improve the frequency support level of new energy stations to the power grid, and improve the system operation stability.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A frequency regulation standby balance control method based on a three-terminal flexible direct current transmission system, characterized in that: The following steps are involved: S1. Use the measuring device to monitor and collect the bus frequency and active power data of each new energy station and the traditional synchronous power plant at the sending end of the flexible DC transmission system in real time, and determine the control mode of each converter station of the three-terminal flexible DC transmission system, the topological connection between each converter station, and the AC system connected to each converter station; In step S1, the control mode of each converter station of the three-terminal flexible DC transmission system is determined as follows: Receiving end converter station: fixed active power control and fixed reactive power control; No. 1 sending-end converter station: constant DC voltage control and constant reactive power control; No. 2 sending-end converter station: voltage-frequency droop control, i.e. V / F control; S2. Calculate the control amount of the bus frequency deviation of the new energy station based on the measured bus frequency data of the sending-end synchronous machine power plant after the disturbance; The change of the transmission power of converter station 1 causes frequency disturbance in the AC transmission system connected to it. If the bus frequency deviation of the AC side of converter station 1 is greater than 0.15Hz, and the primary frequency regulation reserve capacity of the connected AC system is less than 0.5%, the bus frequency deviation control amount of converter station 2 is: in: For large-scale new energy base capacity, is the capacity of the AC transmission system, is the backup factor, Provide primary frequency regulation backup capacity for large-scale new energy bases. It is the primary frequency regulation reserve capacity of the AC transmission system. It is the primary frequency regulation coefficient of large-scale new energy base. It is the equivalent difference coefficient of primary frequency regulation of AC transmission system; The equal value adjustment coefficient is calculated by the following formula: in: is the adjustment coefficient of each synchronous machine, is the capacity of each synchronous machine; If the bus frequency deviation of the AC side of converter station 1 is greater than 0.15Hz, but the primary frequency regulation reserve capacity of the connected AC system is greater than 0.5%, the bus frequency deviation control value of converter station 2 is: S3. Based on the change of AC bus frequency and through primary frequency modulation and virtual inertia algorithm, the active power supported by the receiving frequency of the new energy station participating in the flexible DC transmission system is calculated in real time.

2. A frequency modulation standby balance control method based on a three-terminal flexible direct current transmission system according to claim 1, characterized in that: In step S1, the topological connection mode between the converter stations of the three-terminal flexible DC transmission system is determined as follows: the No. 1 sending-end converter station is DC-connected to the receiving-end converter station, and the No. 2 sending-end converter station is DC-connected to the No. 1 sending-end converter station in parallel.

3. A frequency modulation standby balance control method based on a three-terminal flexible direct current transmission system according to claim 1, characterized in that: In step S1, it is determined that the AC systems to which the converter stations of the three-terminal flexible DC transmission system are connected are: the receiving-end converter station is connected to the receiving-end power grid; the No. 1 sending-end converter station is connected to the AC transmission system; and the No. 2 sending-end converter station is connected to a large-scale new energy base.

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