A DC coordinated rapid frequency modulation control method and control device thereof

Abstract

The present application provides a DC coordinated rapid frequency modulation control method and a control device thereof, which are applied to a multi-converter interconnected power transmission system. The multi-converter interconnected power transmission system includes at least two converters, at least one of which is an AC-DC converter, and the DC side of the converter is connected or directly connected through a transmission line. The control method includes: when a frequency disturbance occurs on the AC side of one of the converters, determining a frequency change; determining additional power based on the frequency change; and the remaining at least one converter provides the additional power to adjust the AC power on the AC side of the disturbed converter.

Description

Technical Field

[0001] The present application relates to the technical field of flexible direct current transmission of power systems, and in particular to a direct current coordinated rapid frequency modulation control method and a control device thereof. Background Art

[0002] With the continuous development of new energy and energy storage technologies, the proportion of power electronic equipment connected to the AC power grid continues to increase. Under traditional control technology (current follower type), power electronic equipment exhibits current source characteristics, that is, power electronic equipment connected to the AC power grid does not provide the inertia required for the stability of the AC power grid frequency. With the introduction of grid-type control and the continuous development of power electronic technology, there is hope that this drawback can be solved.

[0003] There is no shortage of related research in the prior art. For example, patent CN110649643B (A wind farm multi-terminal flexible direct current control method and system that can actively support the grid frequency) proposes to transfer the grid-side frequency to the wind farm through DC voltage synchronous control, thereby achieving the effect of transferring the wind farm's rotational inertia to the grid, so as to achieve the role of supporting the stability of the grid frequency. However, its technical features are limited to using DC voltage as a transmission tool for the main grid frequency. The core purpose is to transfer the inertia of the wind farm to the AC grid. In this technology, the DC network only plays a transmission role and cannot reflect the frequency support characteristics of the DC network for the AC network.

[0004] The fundamental reason for the disturbance of AC grid frequency is the imbalance of AC grid power. When AC power is insufficient, the grid frequency decreases, and when AC power is surplus, the AC grid frequency increases. Therefore, the core point of the DC grid's frequency support for the AC grid is to supplement or absorb the unbalanced AC power in a timely and rapid manner. Similarly, the reason for the DC voltage fluctuation of the DC network is also the imbalance of DC power. The AC grid can also provide voltage support for the DC grid by supplementing and absorbing power. Summary of the invention

[0005] An embodiment of the present application provides a DC coordinated fast frequency modulation control method, which is applied to a multi-converter interconnected transmission system, wherein the multi-converter interconnected transmission system includes at least two converters, at least one of which is an AC-DC converter, and the DC side of the converter is connected or directly connected through a transmission line. The control method includes: when a frequency disturbance occurs on the AC side of one of the converters, determining a frequency change; determining additional power based on the frequency change; and at least one remaining converter provides the additional power to adjust the AC power on the AC side of the disturbed converter.

[0006] According to some embodiments, determining the frequency change includes:

[0007] Δω=(ω c-ω g ),

[0008] ω c =ω g +L((U dc -U dcr )+k(s)(P acref -P acins ))

[0009] Among them, Δω is the frequency change, ω c is the output frequency of the disturbed converter, ω g is the grid frequency or power frequency to which the disturbed converter is connected, k(s) is the transfer function, U dc is the measured DC voltage of the disturbed converter, U dcr is the rated DC voltage, P acref is the power command value of the disturbed converter, P acins is the measured power of the disturbed converter, and L is a constant.

[0010] According to some embodiments, k(s) is a constant or or constant and combination.

[0011] According to some embodiments, determining the additional power based on the frequency change includes: determining the steady-state AC output power of the disturbed converter, the steady-state DC output power of the converter providing additional power, and the steady-state control coefficient of the disturbed converter; determining the transient control coefficient of the disturbed converter based on the frequency change; determining the additional power based on the steady-state AC output power of the disturbed converter, the steady-state DC output power of the converter providing additional power, the steady-state control coefficient of the disturbed converter, and the transient control coefficient of the disturbed converter.

[0012] According to some embodiments, determining the additional power based on the steady-state AC output power of the disturbed converter, the steady-state DC output power of the converter providing the additional power, the steady-state control coefficient of the disturbed converter, and the transient control coefficient of the disturbed converter includes:

[0013] ΔP' dc =2(H'-H0)s(ω c -ω g )+k c (P ac -P dc )

[0014] Among them, ΔP' dc is the additional power, P ac is the steady-state AC output power of the disturbed converter, P dcTo provide the steady - state DC output power of the additional power converter, H0 is the steady - state control coefficient of the perturbed converter, ω c is the output frequency of the perturbed converter, ω g is the grid frequency or power frequency of the perturbed converter, k c is an arbitrary constant between 0 and 10000, s is the differential symbol, and H' is the transient control coefficient of the perturbed converter.

[0015] According to some embodiments, determining the transient control coefficient of the perturbed converter based on the frequency change amount includes:

[0016] When |Δω|>Th1 or , if Δω and have the same sign (both positive or both negative), increase H', if Δω and have opposite signs, decrease H';

[0017] When |Δω|<Th1 and , H' = H0;

[0018] where, Th1 is a constant, and its value range is 0 - 10Hz, Th2 is a constant, and its value range is 0 - 50Hz / s.

[0019] According to some embodiments, the perturbed converter adopts AC - side power synchronization control or / and DC - voltage synchronization control.

[0020] According to some embodiments, the other side of the converter is connected to an AC network or an energy storage system or a power generation device, and at least one of the converters operates in a rectification mode or an inversion mode.

[0021] According to some embodiments, the additional power provided by the i - th additional - power - providing converter is:

[0022] ΔP′ dci =λ i ΔP dc '

[0023] λ i is determined according to the power output capacity of the i - th converter itself, and satisfies ∑λ i =1.

[0024] According to some embodiments, the perturbed converter calculates the value of ΔP' dci and transmits it to the i - th additional - power - providing converter, and the i - th additional - power - providing converter controls the output of the additional power ΔP' dci .

[0025] According to some embodiments, when the communication between converter stations is interrupted, the additional power provided by the i - th additional - power - providing converter is:

[0026] ΔP′ dci =K vi U dcr s(U dci -U dcr )

[0027] Among them, U dcr is the rated DC voltage, U dci To provide the additional power converter i's DC measured voltage, K vi It is a control adjustment parameter that provides additional power, and s is the differential sign.

[0028] An embodiment of the present application also provides a DC coordinated fast frequency regulation control device, which is applied to a multi-converter interconnected transmission system, wherein the multi-converter interconnected transmission system includes at least two converters, at least one of which is an AC-DC converter, and the DC side of the converter is connected or directly connected through a transmission line. The control device includes a frequency change determination unit, an additional power determination unit and a power adjustment unit. The frequency change determination unit is used to determine the frequency change when a frequency disturbance occurs on the AC side of one of the converters; the additional power determination unit determines the additional power based on the frequency change; and the power adjustment unit is used to control at least one remaining converter to provide the additional power to adjust the AC power on the AC side of the disturbed converter.

[0029] The technical solution provided in the embodiment of the present application proposes a DC coordinated rapid frequency modulation control method and a control device thereof, introduces the concept of DC extra power, establishes the relationship between DC extra power and the frequency disturbance of the AC power grid, and when the frequency disturbance occurs in the AC power grid, the DC power grid can quickly output the disturbance power to the AC power grid or absorb the disturbance power from the AC power grid, thereby realizing the rapid frequency support of the DC power grid to the AC power grid from the power perspective, and at the same time, the AC power grid can also support the DC voltage. In this way, bidirectional power support of AC and DC can be realized, and the power transmission capacity of the DC system and the AC system is fully utilized, which is beneficial to maintaining the voltage stability of the DC system and also beneficial to the frequency support of the AC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of a multi-converter interconnected power transmission system according to an embodiment of the present application.

[0031] Figure 2 It is a flow chart of a DC coordinated rapid frequency modulation control method according to an embodiment of the present application.

[0032] Figure 3a-Figure 3b It is a block diagram of the frequency control of the AC voltage output of a disturbed converter according to an embodiment of the present application.

[0033] Figure 4 It is a schematic diagram of a DC coordinated fast frequency modulation control device according to an embodiment of the present application. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0035] It should be understood that the terms "include" and "comprising" used in the specification and claims of the present application indicate the presence of described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0036] Figure 1 It is a schematic diagram of a multi-converter interconnected power transmission system according to an embodiment of the present application.

[0037] The multi-converter interconnected power transmission system includes at least two converters, including at least one AC-DC converter 101 for AC-DC conversion, and the remaining converters may be DC-DC converters 102 for DC-DC conversion and / or AC-DC converters 103 for AC-DC conversion.

[0038] The DC side of the converter is connected through a transmission line or directly, and the other side of the converter is connected to an AC network or an energy storage system or a power generation device. At least one converter in the system operates in a rectifier mode or an inverter mode.

[0039] In this embodiment, the converter 101 operates in an inverter mode, the converter 102 is a DC-DC chopper circuit, and the converter 103 operates in a rectifier mode.

[0040] Figure 2 It is a flow chart of a DC coordinated rapid frequency modulation control method according to an embodiment of the present application, which is applied to the multi-converter interconnected power transmission system as described above.

[0041] In S10, when a frequency disturbance occurs on the AC side of one of the converters, a frequency variation is determined.

[0042] Δω=(ω c -ω g ).

[0043] ω c =ω g +L((U dc -U dcr )+k(s)(P acref-P ac ))

[0044] Wherein, Δω is the frequency change, ω c is the output frequency of the disturbed converter, ω g is the grid frequency value or power frequency connected to the disturbed converter, k(s) is the transfer function, U dc is the measured DC voltage of the disturbed converter, U dcr is the rated DC voltage, P acref is the power command value of the disturbed converter, P acj is the measured power of the disturbed converter, and L is a constant.

[0045] According to some embodiments, k(s) is a constant or or a combination of a constant and .

[0046] In S20, the additional power is determined based on the frequency change, which specifically includes the following steps S21 - S23.

[0047] S21, determine the steady-state AC output power P ac of the disturbed converter, the steady-state DC output power P dc of the additional power converter, and the steady-state control coefficient H0 of the disturbed converter.

[0048] S22, determine the transient control coefficient of the disturbed converter based on the frequency change.

[0049] H' is the transient control coefficient of the disturbed converter, which satisfies the following variation law.

[0050] Δω = (ω c - ω g ).

[0051] When |Δω| > Th1 or , if the signs of Δω and are the same (both positive or both negative), increase H', if the signs of Δω and are opposite, decrease H'.

[0052] When |Δω| < Th1 and , H' = H0.

[0053] Wherein, Th1 is a constant, and its value range is 0 - 10Hz. Th2 is a constant, and its value range is 0 - 50Hz / s.

[0054] In this embodiment, H' is taken according to the following formula.

[0055]

[0056] Among them, H1 and H2 are constants with a value range of 0-H0, and functions f1 and f2 are as follows.

[0057]

[0058]

[0059] a, b, c, d are constants, where a≥0, c≥0.

[0060] S23, determining the additional power based on the steady-state AC output power of the disturbed converter, the steady-state DC output power of the converter providing the additional power, the steady-state control coefficient of the disturbed converter, and the transient control coefficient of the disturbed converter.

[0061] The additional power is ΔP dc '.

[0062] Satisfy ΔP' dc =2(H'-H0)s(ω c -ω g )+k c (P ac -P dc )

[0063] Among them, P ac is the steady-state AC output power of the disturbed converter, with the positive direction from the disturbed converter to the AC grid, P dc To provide additional power converter steady-state DC output power, the positive direction is flowing into the disturbed converter, H0 is the steady-state control coefficient of the disturbed converter, ω c is the output frequency of the disturbed converter, ω g is the grid frequency or power frequency of the disturbed converter, k c is an arbitrary constant between 0 and 10000, and s is the differential sign.

[0064] In S30, at least one remaining converter provides additional power to adjust the AC power on the AC side of the disturbed converter.

[0065] like Figure 1 As shown in the embodiment, when the frequency disturbance occurs in the AC side of the converter 101, the above formula can be used to calculate the control of the remaining one or more converters to provide additional power, so as to achieve the effect of supporting the AC side frequency. The additional power can be positive or negative, and the DC grid can quickly output to the AC grid or absorb the disturbance power from the AC grid.

[0066] The additional power provided by the i-th additional power converter is:

[0067] ΔP′ dci =λ i ΔPdc '

[0068] λ i Determined according to the power output capacity of the i-th converter itself and satisfying ∑λ i =1.

[0069] According to some embodiments, the disturbed converter calculates ΔP' dci The value is transmitted to the additional power converter i, which controls the output of the additional power ΔP′ dci .

[0070] According to some embodiments, when the communication between converter stations is interrupted, the additional power converter i is provided to output additional power ΔP' dci , can also be calculated according to the following formula.

[0071] ΔP′ dci =K vi U dcr s(U dci -U dcr )

[0072] Among them, U dcr is the rated DC voltage, U dci To provide the additional power converter i's DC measured voltage, K vi It is a control adjustment parameter that provides additional power, and s is the differential sign.

[0073] The controller of the converter 101 adopts AC power measurement synchronous control (using active power as an intermediate link to connect the converter and the AC system to achieve synchronous operation) or DC voltage synchronous control (using DC voltage as an intermediate link to connect the converter and the DC system to achieve synchronous operation) or a combination thereof.

[0074] Figure 3a-Figure 3b It is a block diagram of the frequency control of the AC voltage output of a disturbed converter according to an embodiment of the present application.

[0075] Figure 1 In the embodiment, the frequency ω of the AC voltage output by the inverter 101 is c , the control block diagram is as follows Figure 3a-Figure 3b As shown, it satisfies:

[0076] ω c =ω g +L((U dc -U dcr )+k(s)(P acref -P acins )).

[0077] Among them, ω gis the frequency of the grid to which the disturbed converter is connected, which can also be replaced by the power frequency, and k(s) is a constant K d (like Figure 3a shown) or transfer function (like Figure 3b As shown), U dc is the measured DC voltage of the disturbed converter, U dcr is the rated DC voltage, P acref is the power command value of the disturbed converter, P acins is the measured power of the disturbed converter, and L is a constant or system transfer function.

[0078] When the DC voltage fluctuates, such as U dc The AC voltage frequency output by the AC side of the converter 101 decreases, and the electrical angle of the output AC voltage lags behind that before the fluctuation. This lag causes the AC side to provide power support to the DC side, thereby achieving the effect of supporting the DC voltage. And vice versa.

[0079] ΔP dc ' is the total additional power, the total additional power is provided by other converters connected to the DC network, and the additional power provided by converter 102 is as follows.

[0080] ΔP′ dc102 =λ 102 ΔP dc '

[0081] The additional power provided by the inverter 103 is as follows.

[0082] ΔP′ dc103 =λ 103 ΔP dc '

[0083] When multiple converters are provided, the following formula must be satisfied.

[0084] ∑λ i =1

[0085] In this embodiment, if only the converters 102 and 103 provide the additional power, then: 102 +λ 103 =1.

[0086] When the communication between the converter stations is interrupted, the converters 102 and 103 can be controlled as follows to provide additional power. The converter i outputs additional power ΔP' dci ,satisfy:

[0087] ΔP dci =K vi U dcr s(U dci -U dcr )

[0088] Among them, U dcr is the rated DC voltage, U dci To provide the additional power converter i's DC measured voltage, K vi To provide control adjustment parameters for additional power, i is the inverter number, representing inverter 102, inverter 103 or other inverters.

[0089] Figure 4 Schematic diagram of a DC coordinated rapid frequency modulation control device according to an embodiment of the present application. The DC coordinated rapid frequency modulation control device is applied to the multi-converter interconnected power transmission system as described above.

[0090] The DC coordinated rapid frequency modulation control device comprises a frequency variation determination unit 1, an additional power determination unit 2 and a power adjustment unit 3.

[0091] The frequency variation determination unit 1 is used to determine the frequency variation when a frequency disturbance occurs on the AC side of one of the converters. The additional power determination unit 2 determines the additional power based on the frequency variation. The power adjustment unit 3 is used to control at least one of the remaining converters to provide additional power to adjust the AC power on the AC side of the disturbed converter.

[0092] The above embodiments are only for illustrating the technical idea of ​​the present application and cannot be used to limit the protection scope of the present application. Any changes made on the basis of the technical solution in accordance with the technical idea proposed in the present application shall fall within the protection scope of the present application.

Claims

1. A DC coordinated rapid frequency modulation control method, applied to a multi-converter interconnected power transmission system, wherein: The multi-converter interconnected power transmission system includes at least two converters, at least one of which is an AC-DC converter, the DC sides of the converters are connected via a transmission line or directly connected, and the control method includes: When a frequency disturbance occurs on the AC side of one of the converters, the frequency change is determined, including: ， in, , is the disturbed converter output frequency, is the grid frequency value or power frequency to which the disturbed converter is connected, is the transfer function, is the measured DC voltage of the disturbed converter, is the rated DC voltage, is the power command value of the disturbed converter, is the measured power of the disturbed converter, L is a constant; Determining the additional power based on the frequency change includes: Determine the steady-state AC output power of the disturbed converter, the steady-state DC output power of the converter providing the additional power, and the steady-state control coefficient of the disturbed converter; Determining a transient control coefficient of the disturbed converter based on the frequency variation includes: when or When and If the signs are both positive or negative, the value increases. ,like and The sign is opposite, decreasing ; when and hour, ; in, is a constant, and its value range is 0-10Hz. is a constant, and its value range is 0-50Hz / s; The additional power is determined based on the steady-state AC output power of the disturbed converter, the steady-state DC output power of the converter providing the additional power, the steady-state control coefficient of the disturbed converter, and the transient control coefficient of the disturbed converter, including: in, is the steady-state AC output power of the disturbed converter, To provide the additional power converter steady-state DC output power, is the steady-state control coefficient of the disturbed converter, is the output frequency of the disturbed converter, is the grid frequency or power frequency of the disturbed converter, is any constant between 0 and 10000, s is the differential symbol, is the transient control coefficient of the disturbed converter; The remaining at least one converter provides the additional power to adjust the AC power on the AC side of the disturbed converter.

2. The control method according to claim 1, wherein: is a constant or or constant and combination.

3. The control method according to claim 1, wherein: The disturbed converter adopts AC power measurement synchronous control and / or DC voltage synchronous control.

4. The control method according to claim 1, wherein: The other side of the converter is connected to an AC network or an energy storage system or a power generation device, and at least one of the converters operates in a rectification mode or an inversion mode.

5. The control method according to claim 1, wherein: No. The additional power provided by the converter is: According to The power output capacity of each converter is determined and meets .

6. The control method according to claim 5, wherein: The disturbed converter calculates value and transmits it to the converter that provides additional power , additional power is provided by the converter Control output additional power .

7. The control method according to claim 1, wherein: When the communication between converter stations is interrupted, The additional power provided by the converter is: in, is the rated DC voltage, To provide additional power converter The measured DC voltage, It is a control adjustment parameter that provides additional power, and s is the differential sign.

8. A DC coordinated rapid frequency modulation control device, applied to a multi-converter interconnected power transmission system, used to execute the control method according to any one of claims 1 to 7, wherein: The multi-converter interconnected power transmission system comprises at least two converters, at least one of which is an AC-DC converter, the DC sides of the converters are connected via a transmission line or directly connected, and the control device comprises: A frequency variation determination unit, used to determine the frequency variation when a frequency disturbance occurs on the AC side of one of the converters; an additional power determination unit, configured to determine the additional power based on the frequency variation; The power regulating unit is used to control at least one remaining converter to provide the additional power to regulate the AC power on the AC side of the disturbed converter.

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