STATCOM impedance characteristic reconstruction method based on real-time digital simulator

Abstract

The invention relates to a STATCOM impedance characteristic reconstruction method based on a real-time digital simulator, and belongs to the technical field of new energy electromagnetic transient simulation modeling. The method comprises the following steps: firstly, establishing a STATCOM single machine infinite bus system based on a real-time digital simulator; secondly, introducing voltage feed-forward control in a control link of the STATCOM to carry out impedance reconstruction, injecting a three-phase voltage disturbance signal into a body of the STATCOM when the STATCOM operates normally, and collecting three-phase voltage and current signals of a machine end of the STATCOM at the same time; and finally, the impedance characteristic of the STATCOM is calculated according to the collected voltage and current signals. According to the method, the impedance characteristic of the STATCOM is transformed, so that the negative damping characteristic of the STATCOM can be remarkably improved, and the oscillation risk of a power system is effectively reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic transient simulation modeling of new energy, and in particular relates to a STATCOM impedance characteristic reconstruction method based on a real-time digital simulator. Background Art

[0002] Against the backdrop of the continuous depletion of fossil energy, with the advancement of power electronics technology and the implementation of my country's "dual carbon" energy strategy, the penetration rate of new energy represented by wind power and photovoltaics has increased significantly. At present, wind farms or photovoltaic power stations are equipped with reactive compensation equipment represented by STATCOM for reactive compensation to improve the transmission efficiency of the system. However, STATCOM composed of power electronic devices tends to show negative damping impedance characteristics, which will increase the risk of sub- and super-synchronous oscillations in the power grid and affect the safe operation of the power system. Therefore, how to reduce the negative damping characteristics of STATCOM and at the same time make it provide positive damping as much as possible to improve the operational stability of the power system is a problem that needs to be solved urgently. Summary of the invention

[0003] The purpose of the present invention is to reduce the negative damping characteristics of STATCOM and improve the operating stability of the power system. A STATCOM impedance characteristic reconstruction method based on a real-time digital simulator is provided. The method can significantly improve its negative damping characteristics by introducing voltage feedforward control in the STATCOM control link to perform impedance reconstruction.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A STATCOM impedance characteristic reconstruction method based on a real-time digital simulator comprises the following steps:

[0006] Step (1), building a STATCOM single machine infinite system based on a real-time digital simulator;

[0007] Step (2), introducing voltage feedforward control in the conventional control topology of STATCOM to perform impedance reconstruction;

[0008] Step (3), according to the control topology after the impedance reconstruction by introducing the voltage feedforward control in step (2), modify the control program of the STATCOM to replace the original control program without introducing the voltage feedforward control link;

[0009] Step (4), using the STATCOM controller of the control program of step (3) as the STATCOM controller of the STATCOM single-machine infinite system based on the real-time digital simulator, carrying out impedance characteristic calculation of the STATCOM, and obtaining the positive sequence impedance Z1;

[0010] Step (5), since Z1 obtained in step (4) is a complex number with a certain value, the amplitude and phase of Z1 can be obtained by running the complex number, which is the reconstructed impedance characteristic;

[0011] The specific method of step (2) is as follows:

[0012] The final output modulation signal U of the STATCOM conventional control topology ds , U qs The expression is:

[0013]

[0014] Among them, i d 、i q are the currents of STATCOM in dq axis in dq coordinate system respectively; i dref 、i qref are the given current values ​​of the dq axis current loop in the dq coordinate system respectively; K d is the feedforward decoupling coefficient; s is the complex variable in Laplace transform; U ds It represents the d-axis voltage output by the conventional control topology; U qs It represents the q-axis voltage finally output by the conventional control topology;

[0015] H i The expression of (s) is:

[0016]

[0017] Where: K p_i , K i_i They are the proportional and integral coefficients of the current loop PI control respectively;

[0018] In the control link of the conventional control topology of STATCOM, voltage feedforward control is introduced to reconstruct the impedance, that is, to increase -v d H Y (s) and -v q H Y (s) link, after adding impedance reconstruction control, the final output modulation signal U of STATCOM ds1 , U qs1 The expression of is shown in formula (5);

[0019]

[0020] Among them, U ds1 It represents the d-axis voltage output by the control topology after the voltage feedforward control is introduced to reconstruct the impedance; U qs1 It represents the q-axis voltage finally output by the control topology after the voltage feedforward control is introduced to reconstruct the impedance;

[0021] In formula (5), H Y The expression of (s) is:

[0022]

[0023] Where: k dm is the proportional coefficient of impedance reconstruction; ω H ,ω L They are the upper cutoff frequency and lower cutoff frequency of the bandpass filter in the reconstruction control link respectively.

[0024] Furthermore, preferably, in the STATCOM stand-alone infinite system based on the real-time digital simulator, the STATCOM body is connected to the 35kV bus, then boosted to 220kV through the main transformer, and then connected to the infinite power grid. The STATCOM controller transmits PWM control signals to the RT-LAB simulator via optical fiber, and the STATCOM controller is connected to the analog output board of the simulator via a DB37 connection line to collect the three-phase voltage and current signals of the power grid.

[0025] Further, preferably, the specific method of step (4) is:

[0026] (4.1) The amplitude of the disturbance voltage injected into the STATCOM body is A%*U n , three-phase positive sequence voltage disturbance signal with frequency f:

[0027]

[0028] Where: U a+ , U b+ , U c+ are the three-phase positive sequence voltage disturbance signals, t is the time, A and f are positive integers greater than or equal to 1, U n is the nominal voltage of the STATCOM grid connection point;

[0029] (4.2) Collect the instantaneous value data of three-phase voltage and current at the STATCOM machine end.

[0030] (4.3) The three-phase voltage and current instantaneous value data collected in (4.2) are Fourier transformed using the fast Fourier transform function to extract the three-phase voltage amplitude and phase at frequency f;

[0031] (4.4) Then the positive sequence voltage ΔU at frequency f p (f), positive sequence current ΔI p (f) for;

[0032]

[0033] Among them, Ua+ (f) U b+ (f) U c+ (f) three-phase voltage amplitude at frequency f;

[0034] U θa+ (f) U θb+ (f) U θc+ (f) three-phase voltage phase at frequency f;

[0035] I a+ (f) I b+ (f) I c+ (f) three-phase current amplitude at frequency f;

[0036] I θa+ (f) I θb+ (f) I θc+ (f) The three-current voltage phase at frequency f;

[0037] (4.5) Calculate the positive sequence impedance Z1 at frequency f:

[0038] Z1=ΔU p (f) / ΔI p (f) (4).

[0039] Furthermore, preferably, in (4.3), the FFT function in Matlab is used to perform Fourier transform on the three-phase voltage and current instantaneous value data collected in (4.2).

[0040] Furthermore, it is preferred that ω H ,ω L 3000Hz and 1Hz respectively.

[0041] In step (1) of the present invention, a STATCOM stand-alone infinite system based on a real-time digital simulator (such as RT-LAB) is built; in the STATCOM stand-alone infinite system based on the real-time digital simulator, the STATCOM body is connected to the 35kV bus, then boosted to 220kV by a main transformer, and then connected to the infinite power grid, the STATCOM controller transmits PWM control signals to the RT-LAB simulator via optical fiber, the STATCOM controller is connected to the analog output board of the simulator via a DB37 connection line, and the three-phase voltage and current signals of the power grid are collected, such as Figure 1 shown.

[0042] At present, the commonly used control topologies of STATCOM are as follows: Figure 2 As shown, the final output modulation signal U ds , U qs The expression is:

[0043]

[0044] Figure 2 Middle: v a 、v b 、v c 、i a 、i b 、i c are the output voltage and current of STATCOM respectively; Q ref is the reactive power given value; Q is the reactive power output value of STATCOM; θ PLL is the phase difference of the phase-locked loop output; SPWM means sinusoidal pulse width modulation; v d 、v q and i d 、i q are the voltage and current of STATCOM in dq coordinate system respectively; i dref 、i qref are the given current values ​​of the dq axis current loop in the dq coordinate system respectively; K d is the feedforward decoupling coefficient; s is the complex variable in Laplace transform.

[0045] In formula (1), H i The expression of (s) is:

[0046]

[0047] Where: K p_i , K i_i They are the proportional and integral coefficients of the current loop PI control respectively;

[0048] Figure 2 Medium H Q The expression of (s) is:

[0049]

[0050] Where: K p_Q , K i_Q They are the proportional and integral coefficients of the reactive outer loop PI control respectively;

[0051] Figure 2 ZhongzhongH PLL The expression of (s) is:

[0052]

[0053] Where: K p_PLL , K i_PLL They are the proportional and integral coefficients of the phase-locked loop PI control respectively;

[0054] Introducing voltage feedforward control in the STATCOM control link to reconstruct impedance, that is, increasing -v d H Y (s) and -v q H Y (s) link, after adding impedance reconstruction control, the final output modulation signal U of STATCOM ds1 , U q s1 The expression of is shown in formula (5), and the final control topology is as follows Figure 3 shown.

[0055]

[0056] In formula (5), H Y The expression of (s) is:

[0057]

[0058] Where: k dm is the proportional coefficient of impedance reconstruction; ω H ,ω L They are respectively the upper cutoff frequency and the lower cutoff frequency of the bandpass filter in the reconstruction control link, and their values ​​can be determined according to actual needs.

[0059] The present invention uses the fast Fourier transform function to perform Fourier transform on the three-phase voltage and current instantaneous value data collected in (4.2), and can extract the three-phase voltage amplitude and phase at frequency f: U a+ (f) U b+ (f) U c+ (f); U θa+ (f) U θb+ (f) U θc+ (f); the amplitude and phase of the three-phase current are I a+ (f) I b+ (f) I c+ (f); I θa+ (f) I θb+ (f) I θc+ (f).

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] In view of the problem that "STATCOM composed of power electronic devices tends to show negative damping impedance characteristics, which will increase the risk of sub- and super-synchronous oscillations in the power grid and affect the operational safety of the power system", the present invention provides a STATCOM impedance characteristic reconstruction method based on a real-time digital simulator. The method can significantly improve its negative damping characteristics by introducing voltage feedforward control in the STATCOM control link to perform impedance reconstruction.

[0062] like Figure 4 As shown, using Figure 2 Conventional control methods and adoption Figure 3 Compared with the impedance reconstruction method with voltage feedforward control, the reconstructed phase-frequency characteristic curve exceeds ±90°( Figure 4 The part within the two dashed lines in the figure is much less than that before reconstruction (the phase is between ±90°, indicating that STATCOM provides positive damping, otherwise it provides negative damping). BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 The schematic diagram of the impedance characteristic evaluation of the single-infinity system STATCOM based on the real-time simulator;

[0064] Figure 2 This is the conventional control topology diagram of STATCOM at the current stage;

[0065] Figure 3 This is the STATCOM control topology diagram after adding impedance reconstruction;

[0066] Figure 4 This is a comparison diagram of the positive sequence phase-frequency characteristics before and after reconstruction of STATCOM under the inductive 20% QN condition. DETAILED DESCRIPTION

[0067] The present invention is further described in detail below in conjunction with embodiments.

[0068] Those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the art or the product specifications are used. If the manufacturer of the materials or equipment used is not specified, they are all conventional products that can be purchased.

[0069] Example 1

[0070] A STATCOM impedance characteristic reconstruction method based on a real-time digital simulator comprises the following steps:

[0071] Step (1), building a STATCOM single machine infinite system based on a real-time digital simulator;

[0072] Step (2), introducing voltage feedforward control in the conventional control topology of STATCOM to perform impedance reconstruction;

[0073] Step (3), according to the control topology after the impedance reconstruction by introducing the voltage feedforward control in step (2), modify the control program of the STATCOM to replace the original control program without introducing the voltage feedforward control link;

[0074] Step (4), using the STATCOM controller of the control program of step (3) as the STATCOM controller of the STATCOM single-machine infinite system based on the real-time digital simulator, carrying out impedance characteristic calculation of the STATCOM, and obtaining the positive sequence impedance Z1;

[0075] Step (5), since Z1 obtained in step (4) is a complex number with a certain value, the amplitude and phase of Z1 can be obtained by running the complex number, which is the reconstructed impedance characteristic;

[0076] The specific method of step (2) is as follows:

[0077] The final output modulation signal U of the STATCOM conventional control topology ds , U qs The expression is:

[0078]

[0079] Among them, i d 、i q are the currents of STATCOM in dq axis in dq coordinate system respectively; i dref 、i qref are the given current values ​​of the dq axis current loop in the dq coordinate system respectively; K d is the feedforward decoupling coefficient; s is the complex variable in Laplace transform; U ds It represents the d-axis voltage output by the conventional control topology; U qs It represents the q-axis voltage finally output by the conventional control topology;

[0080] H i The expression of (s) is:

[0081]

[0082] Where: K p_i , K i_i They are the proportional and integral coefficients of the current loop PI control respectively;

[0083] In the control link of the conventional control topology of STATCOM, voltage feedforward control is introduced to reconstruct the impedance, that is, to increase -v d H Y (s) and -v q H Y (s) link, after adding impedance reconstruction control, the final output modulation signal U of STATCOM ds1 , U qs1 The expression of is shown in formula (5);

[0084]

[0085] Among them, U ds1 It represents the d-axis voltage output by the control topology after the voltage feedforward control is introduced to reconstruct the impedance; U qs1 It represents the q-axis voltage finally output by the control topology after the voltage feedforward control is introduced to reconstruct the impedance;

[0086] In formula (5), H Y The expression of (s) is:

[0087]

[0088] Where: k dm is the proportional coefficient of impedance reconstruction; ω H ,ω L They are the upper cutoff frequency and lower cutoff frequency of the bandpass filter in the reconstruction control link respectively.

[0089] Example 2

[0090] A STATCOM impedance characteristic reconstruction method based on a real-time digital simulator comprises the following steps:

[0091] Step (1), building a STATCOM single machine infinite system based on a real-time digital simulator;

[0092] Step (2), introducing voltage feedforward control in the conventional control topology of STATCOM to perform impedance reconstruction;

[0093] Step (3), according to the control topology after the impedance reconstruction by introducing the voltage feedforward control in step (2), modify the control program of the STATCOM to replace the original control program without introducing the voltage feedforward control link;

[0094] Step (4), using the STATCOM controller of the control program of step (3) as the STATCOM controller of the STATCOM single-machine infinite system based on the real-time digital simulator, carrying out impedance characteristic calculation of the STATCOM, and obtaining the positive sequence impedance Z1;

[0095] Step (5), since Z1 obtained in step (4) is a complex number with a certain value, the amplitude and phase of Z1 can be obtained by running the complex number, which is the reconstructed impedance characteristic;

[0096] The specific method of step (2) is as follows:

[0097] The final output modulation signal U of the STATCOM conventional control topology ds , U qs The expression is:

[0098]

[0099] Among them, i d 、i q are the currents of STATCOM in dq axis in dq coordinate system respectively; i dref 、i qref are the given current values ​​of the dq axis current loop in the dq coordinate system respectively; K d is the feedforward decoupling coefficient; s is the complex variable in Laplace transform; U ds It represents the d-axis voltage output by the conventional control topology; U qs It represents the q-axis voltage finally output by the conventional control topology;

[0100] H i The expression of (s) is:

[0101]

[0102] Where: K p_i , K i_i They are the proportional and integral coefficients of the current loop PI control respectively;

[0103] In the control link of the conventional control topology of STATCOM, voltage feedforward control is introduced to reconstruct the impedance, that is, to increase -v d H Y (s) and -v q H Y (s) link, after adding impedance reconstruction control, the final output modulation signal U of STATCOM ds1 , U qs1 The expression of is shown in formula (5);

[0104]

[0105] Among them, U ds1 It represents the d-axis voltage output by the control topology after the voltage feedforward control is introduced to reconstruct the impedance; U qs1 It represents the q-axis voltage finally output by the control topology after the voltage feedforward control is introduced to reconstruct the impedance;

[0106] In formula (5), H Y The expression of (s) is:

[0107]

[0108] Where: k dm is the proportional coefficient of impedance reconstruction; ω H ,ω L They are respectively the upper cutoff frequency and the lower cutoff frequency of the bandpass filter in the reconstruction control link, and their values ​​can be determined according to actual needs.

[0109] In the STATCOM stand-alone infinite system based on real-time digital simulator, the STATCOM body is connected to the 35kV bus, then boosted to 220kV through the main transformer, and then connected to the infinite power grid. The STATCOM controller transmits PWM control signals to the RT-LAB simulator through optical fiber. The STATCOM controller is connected to the analog output board of the simulator through a DB37 connection line to collect the three-phase voltage and current signals of the power grid.

[0110] The specific method of step (4) is:

[0111] (4.1) The amplitude of the disturbance voltage injected into the STATCOM body is A%*U n , three-phase positive sequence voltage disturbance signal with frequency f:

[0112]

[0113] Where: U a+ , U b+ , U c+ are the three-phase positive sequence voltage disturbance signals, t is the time, A and f are positive integers greater than or equal to 1, U n is the nominal voltage of the STATCOM grid connection point;

[0114] (4.2) Collect the instantaneous value data of three-phase voltage and current at the STATCOM machine end.

[0115] (4.3) The three-phase voltage and current instantaneous value data collected in (4.2) are Fourier transformed using the fast Fourier transform function to extract the three-phase voltage amplitude and phase at frequency f;

[0116] (4.4) Then the positive sequence voltage ΔU at frequency f p (f), positive sequence current ΔI p (f) for;

[0117]

[0118] Among them, U a+ (f) U b+ (f) U c+ (f) three-phase voltage amplitude at frequency f;

[0119] U θa+ (f) U θb+ (f) U θc+ (f) three-phase voltage phase at frequency f;

[0120] I a+ (f) I b+ (f) I c+(f) three-phase current amplitude at frequency f;

[0121] I θa+ (f) I θb+ (f) I θc+ (f) The three-current voltage phase at frequency f;

[0122] (4.5) Calculate the positive sequence impedance Z1 at frequency f:

[0123] Z1=ΔU p (f) / ΔI p (f) (4).

[0124] In (4.3), the FFT function in Matlab is used to perform Fourier transform on the three-phase voltage and current instantaneous value data collected in (4.2).

[0125] ω H ,ω L 3000Hz and 1Hz respectively, ω H and ω L You can also decide the value according to actual needs.

[0126] Example 3

[0127] A STATCOM impedance characteristic reconstruction method based on a real-time digital simulator comprises the following steps:

[0128] Step (1), building a STATCOM stand-alone infinite system based on a real-time digital simulator (such as RT-LAB): In the STATCOM stand-alone infinite system based on a real-time digital simulator, the STATCOM body is connected to the 35kV bus, then boosted to 220kV through the main transformer, and then connected to the infinite power grid. The STATCOM controller transmits PWM control signals to the RT-LAB simulator through optical fiber, and the STATCOM controller is connected to the analog output board of the simulator through a DB37 connection line to collect the three-phase voltage and current signals of the power grid, such as Figure 1 shown.

[0129] Step (2) introduces voltage feedforward control into the conventional STATCOM control topology to perform impedance reconstruction:

[0130] At present, the conventional control topology of STATCOM is as follows: Figure 2 As shown, the final output modulation signal U ds , U qs The expression is:

[0131]

[0132] Figure 2 Middle: va 、v b 、v c 、i a 、i b 、i c are the output voltage and current of STATCOM respectively; Q ref is the reactive power given value; Q is the reactive power output value of STATCOM; θ PLL is the phase difference of the phase-locked loop output; SPWM means sinusoidal pulse width modulation; v d 、v q and i d 、i q are the voltage and current of STATCOM in dq coordinate system respectively; i dref 、i qref are the given current values ​​of the dq axis current loop in the dq coordinate system respectively; K d is the feedforward decoupling coefficient; s is the complex variable in Laplace transform.

[0133] In formula (1), H i The expression of (s) is:

[0134]

[0135] Where: K p_i , K i_i They are the proportional and integral coefficients of the current loop PI control respectively;

[0136] Figure 2 Medium H Q The expression of (s) is:

[0137]

[0138] Where: K p_Q , K i_Q They are the proportional and integral coefficients of the reactive outer loop PI control respectively;

[0139] Figure 2 ZhongzhongH PLL The expression of (s) is:

[0140]

[0141] Where: K p_PLL , K i_PLL They are the proportional and integral coefficients of the phase-locked loop PI control respectively;

[0142] Introducing voltage feedforward control in the STATCOM control link to reconstruct impedance, that is, increasing -v d H Y (s) and -v q H Y(s) link, after adding impedance reconstruction control, the final output modulation signal U of STATCOM ds , U qs The expression of is shown in formula (5), and the final control topology is as follows Figure 3 shown.

[0143]

[0144] In formula (5), H Y The expression of (s) is:

[0145]

[0146] Where: k dm is the proportional coefficient of impedance reconstruction; ω H ,ω L They are the upper cutoff frequency and lower cutoff frequency of the bandpass filter in the reconstruction control link respectively;

[0147] Step (3), based on Figure 3 The control program of STATCOM is modified by equations (5) and (6), and replaces the original control program without introducing the voltage feedforward control link.

[0148] Step (4), the STATCOM controller using the control program of step (3) is Figure 1 As shown in the figure, it is connected to the RT-LAB simulator to calculate the impedance characteristics of STATCOM:

[0149] (4.1) Figure 1 As shown, the amplitude of the disturbance voltage injected into the STATCOM body is A%*U n , three-phase positive sequence voltage disturbance signal with frequency f:

[0150]

[0151] Where: U a+ , U b+ , U c+ are the three-phase positive sequence voltage disturbance signals, t is the time, A and f are positive integers greater than or equal to 1, U n is the nominal voltage of the STATCOM grid-connected point.

[0152] (4.2) Collect the instantaneous value data of three-phase voltage and current at the STATCOM machine end.

[0153] (4.3) Using the FFT function (fast Fourier transform function) in Matlab, the three-phase voltage and current instantaneous value data collected in (4.2) are Fourier transformed to extract the three-phase voltage amplitude and phase at frequency f: U a+ (f) Ub+ (f) U c+ (f); U θa+ (f) U θb+ (f) U θc+ (f); the amplitude and phase of the three-phase current are I a+ (f) I b+ (f) I c+ (f); I θa+ (f) I θb+ (f) I θc+ (f).

[0154] (4.4) Then the positive sequence voltage ΔU at frequency f p (f), positive sequence current ΔI p (f) for;

[0155]

[0156] (4.5) Calculate the positive sequence impedance Z1 at frequency f:

[0157] Z1=ΔU p (f) / ΔI p (f) (4)

[0158] Step (5), according to step (4.5), Z1 can be obtained as a complex number with a certain value, and the amplitude and phase of Z1 can be obtained by operating the complex number.

[0159] Application Examples

[0160] A STATCOM impedance characteristic reconstruction method based on a real-time digital simulator comprises the following steps:

[0161] (I) Taking a certain type of STATCOM as an example, the impedance characteristics evaluation and reconstruction based on the real-time digital simulator are carried out. The rated capacity of the device under test is Q N =34MVar, rated voltage U N =35kV, rated current is I N =560.9A; k dm is 6; H ,ω L 3000Hz and 1Hz respectively.

[0162] (ii) Build a STATCOM stand-alone infinite system based on a real-time simulator, transmit the instantaneous values ​​of the three-phase voltage and current of the simulated main circuit to the STATCOM controller through a DB37 connection line, and the STATCOM controller transmits the PWM control signal to the simulator through an optical fiber;

[0163] (III) Set the initial reactive power of STATCOM to be 20%Q N; Set the amplitude of the voltage disturbance signal to 2%*35kV, the frequency range to [1Hz, 3000Hz], the initial frequency to 1Hz, the sweep frequency step from 1 to 300Hz to 1Hz, and the sweep frequency step from 300 to 3000Hz to 10Hz;

[0164] (iv) Before impedance reconstruction, a three-phase positive sequence voltage disturbance signal is injected into the STATCOM body, and the three-phase voltage and current signal data at the STATCOM machine end are collected at the same time;

[0165] (V) Calculating the impedance characteristics of STATCOM based on the collected three-phase voltage and current signal data;

[0166] (vi) Introducing voltage feedforward control in the STATCOM control link to perform impedance reconstruction, and then injecting three-phase positive-sequence and negative-sequence voltage disturbance signals into the STATCOM body respectively, while collecting three-phase voltage and current signal data at the STATCOM machine end;

[0167] (VII) Calculate the impedance characteristics of STATCOM based on the reconstructed three-phase voltage and current signal data.

[0168] (VIII) Compare the impedance characteristics before and after impedance reconstruction, such as Figure 3 and Figure 4 As shown in FIG. 1 , the portion of the reconstructed impedance characteristic curve exceeding the ±90° dashed line is significantly reduced (exceeding the ±90° dashed line is negative damping), which greatly improves the negative damping characteristics of STATCOM.

[0169] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A STATCOM impedance characteristic reconstruction method based on a real-time digital simulator, characterized in that: The steps include: Step (1), building a STATCOM single machine infinite system based on a real-time digital simulator; Step (2), introducing voltage feedforward control in the conventional control topology of STATCOM to perform impedance reconstruction; Step (3), according to the control topology after the impedance reconstruction by introducing the voltage feedforward control in step (2), modify the control program of the STATCOM to replace the original control program without introducing the voltage feedforward control link; Step (4), using the STATCOM controller of the control program of step (3) as the STATCOM controller of the STATCOM single-machine infinite system based on the real-time digital simulator, carrying out impedance characteristic calculation of the STATCOM, and obtaining the positive sequence impedance Z1; Step (5), since Z1 obtained in step (4) is a complex number with a certain value, the amplitude and phase of Z1 can be obtained by running the complex number, which is the reconstructed impedance characteristic; The specific method of step (2) is as follows: The final output modulation signal U of the STATCOM conventional control topology ds , U qs The expression is: Among them, i d 、i q are the currents of STATCOM in dq axis in dq coordinate system respectively; i dref 、i qref are the given current values ​​of the dq axis current loop in the dq coordinate system respectively; K d is the feedforward decoupling coefficient; s is the complex variable in Laplace transform; U ds It represents the d-axis voltage output by the conventional control topology; U qs It represents the q-axis voltage finally output by the conventional control topology; H i The expression of (s) is: Where: K p_i , K i_i They are the proportional and integral coefficients of the current loop PI control respectively; In the control link of the conventional control topology of STATCOM, voltage feedforward control is introduced to reconstruct the impedance, that is, to increase -v d H Y (s) and -v q H Y (s) link, after adding impedance reconstruction control, the final output modulation signal U of STATCOM ds1 , U qs1 The expression of is shown in formula (5); Among them, U ds1 It represents the d-axis voltage output by the control topology after the voltage feedforward control is introduced to reconstruct the impedance; U qs1 It represents the q-axis voltage finally output by the control topology after the voltage feedforward control is introduced to reconstruct the impedance; In formula (5), H Y The expression of (s) is: Where: k dm is the proportional coefficient of impedance reconstruction; ω H ,ω L They are the upper cutoff frequency and lower cutoff frequency of the bandpass filter in the reconstruction control link respectively.

2. The STATCOM impedance characteristic reconstruction method based on real-time digital simulator according to claim 1 is characterized in that: In the STATCOM stand-alone infinite system based on real-time digital simulator, the STATCOM body is connected to the 35kV bus, then boosted to 220kV through the main transformer, and then connected to the infinite power grid. The STATCOM controller transmits PWM control signals to the RT-LAB simulator through optical fiber. The STATCOM controller is connected to the analog output board of the simulator through a DB37 connection line to collect the three-phase voltage and current signals of the power grid.

3. The STATCOM impedance characteristic reconstruction method based on real-time digital simulator according to claim 1 is characterized in that: The specific method of step (4) is: (4.1) The amplitude of the disturbance voltage injected into the STATCOM body is A%*U n , three-phase positive sequence voltage disturbance signal with frequency f: Where: U a+ , U b+ , U c+ are the three-phase positive sequence voltage disturbance signals, t is the time, A and f are positive integers greater than or equal to 1, U n is the nominal voltage of the STATCOM grid connection point; (4.2) Collect the instantaneous value data of three-phase voltage and current at the STATCOM machine end. (4.3) The three-phase voltage and current instantaneous value data collected in (4.2) are Fourier transformed using the fast Fourier transform function to extract the three-phase voltage amplitude and phase at frequency f; (4.4) Then the positive sequence voltage ΔU at frequency f p (f), positive sequence current ΔI p (f) for; Among them, U a+ (f) U b+ (f) U c+ (f) three-phase voltage amplitude at frequency f; U θa+ (f) U θb+ (f) U θc+ (f) three-phase voltage phase at frequency f; I a+ (f) I b+ (f) I c+ (f) three-phase current amplitude at frequency f; I θa+ (f) I θb+ (f) I θc+ (f) The three-current voltage phase at frequency f; (4.5) Calculate the positive sequence impedance Z1 at frequency f: Z1=ΔU p (f) / ΔI p (f) (4)。 4. The STATCOM impedance characteristic reconstruction method based on real-time digital simulator according to claim 3 is characterized in that: In (4.3), the FFT function in Matlab is used to perform Fourier transform on the three-phase voltage and current instantaneous value data collected in (4.2).

5. The STATCOM impedance characteristic reconstruction method based on real-time digital simulator according to claim 1 is characterized in that: ω H ,ω L 3000Hz and 1Hz respectively.

Images