Analysis system and analysis method for judging oscillation transmission between SEF and DCV in VSC-HVDC system under control of double-end VSG

Abstract

The invention discloses an analysis system and analysis method for judging oscillation transmission between an SEF and a DCV in a VSC-HVDC system under control of a double-end VSG, and belongs to the technical field of virtual synchronous generator control and flexible direct current transmission. The analysis system comprises a rectification side loop, an inversion side loop and a transmission coupling loop; and composition links / coupling terms of three loops are specifically provided. The analysis method comprises the following steps: firstly, calculating Gf1 (s), Gf1v1 (s) and Gv1f1 (s); then determining the key oscillation frequency of the system according to a peak point in the amplitude-frequency characteristic of the Gf1 (s); calculating the amplitudes of the amplitude-frequency characteristic curves of the Gf1v1 (s) and the Gv1f1 (s) at the key oscillation frequency point, and respectively recording the amplitudes as' Mv 'and' Mf '; and finally, judging whether oscillation transmission occurs between the SEF and the DCV or not according to the positive and negative values of the Mv and the Mf. According to the method, a new physical perspective is provided for the oscillation transfer effect of the VSC-HVDC under the control of the double-end VSG, and the oscillation transfer state of the VSC-HVDC system is judged from the physical perspective; and the oscillation transmission generation condition of the VSC-HVDC system under the control of the double-end VSG can be judged more intuitively and clearly.

Description

Technical Field

[0001] The present invention relates to the technical fields of virtual synchronous generator control technology and flexible DC transmission technology, and particularly relates to an oscillation transfer analysis system and an analysis method for determining the oscillation transfer between the SEF and the DCV in a VSC-HVDC system under dual-terminal VSG control. Background Art

[0002] With the large-scale penetration of new energy distributed generation into the power system, the traditional power grid is no longer the previous rigid power system and has become flexibly controllable. As a result, the inertia and damping of the system have been greatly reduced, which easily leads to an increase in the amplitude of system frequency and voltage fluctuations. Moreover, the volatility and randomness of renewable energy further exacerbate this oscillation form. In order to improve the inertia and damping of the system, the virtual synchronous generator (VSG) control technology is introduced into the power electronic converters of distributed generation units to improve the inertia and damping of the grid-connected system. The control structure of the VSC-HVDC (voltage source converter high voltage direct current transmission) system under dual-terminal VSG control can support the operation of both the sending end and the receiving end of the system simultaneously, providing sufficient inertia and damping performance for the system. However, due to its novelty, the oscillation transfer mechanism of the VSC-HVDC system under dual-terminal VSG control has rarely been effectively explained at present.

[0003] Traditional stability analysis methods include: eigenvalue analysis method and impedance criterion analysis method. The eigenvalue analysis method writes differential equations for each state variable to obtain the state matrix of the state variables, and then calculates the eigenvalues of the state matrix to obtain the closed-loop dominant poles of the system, that is, the closed-loop eigenvalues (characteristic roots), to determine the damping ratio and stability of the system; it can better identify the dominant oscillation modes of the system and the damping ratio of the system, and the time-domain transient response of the system under step disturbance can be better analyzed from the oscillation modes and the damping ratio; however, it cannot identify the physical essence of system instability and is not applicable to large-scale high-order power systems because the high-order power system will cause the order of the eigenvalue matrix to increase, greatly increasing the calculation amount and the calculation burden.

[0004] Compared with the eigenvalue analysis method, the impedance analysis method is another relatively intuitive analysis method for identifying the stability analysis method of power electronic power systems. The impedance analysis method obtains the equivalent impedance of the object under study (usually a power electronic converter or a grid-connected converter) through small-signal modeling means, then uses the frequency-domain scanning method to scan each frequency band of the entire converter impedance, and finally determines the damping and stability of the power electronic converter by comparing the scanned frequency-domain analysis results with the theoretical calculation results. The impedance analysis method can reveal the passive characteristics and stability mechanism of the system from the perspective of the impedance characteristics of the network port. However, the network port characteristics ignore the internal connections between the various state variables of the system and the dynamic interactions between the various state variables. Moreover, the impedance analysis method cannot well intuitively reveal the physical essence of the system. Summary of the Invention

[0005] Aiming at the defects existing in the above-mentioned prior art, the technical problem to be solved by the present invention is to propose an oscillation transfer analysis system and analysis method for determining the oscillation transfer between the SEF and the DCV in the VSC-HVDC system under double-end VSG control, providing a new physical perspective for the oscillation transfer analysis of the VSC-HVDC system under double-end VSG control, and determining the oscillation transfer state from a physical perspective.

[0006] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] An oscillation transfer analysis system for determining the oscillation transfer between the SEF and the DCV in the VSC-HVDC system under double-end VSG control includes a rectifier-side loop, an inverter-side loop, and a transfer coupling loop;

[0008] The rectifier-side loop includes a voltage outer loop, a virtual inertia damping loop, a physical transfer link of the rectifier station phase angle - rectifier station active power coupled with the rectifier station voltage - reactive power inner loop, and a rectifier station active power - DC side voltage coupling link;

[0009] The inverter-side loop includes a virtual inertia damping loop and an inverter station phase angle - inverter station active power transfer link coupled with the inverter station voltage - reactive power;

[0010] The transfer coupling loop includes three coupling terms: rectifier station phase angle - inverter station active power, rectifier station phase angle - inverter station reactive power, and inverter station active power - DC side voltage.

[0011] Further, in the rectifier side loop, the outer voltage loop is formed by comparing the DC side voltage reference value with the actual DC side voltage and then passing through a proportional-integral controller. The output value is used as the rectifier station active power reference value. After comparing it with the actual rectifier station active power, the phase angle information of the rectifier station is generated through a virtual inertia damping loop. Then, through the physical transfer link between the rectifier station phase angle and the rectifier station active power coupled with the rectifier station voltage-reactive power inner loop, the small-signal value of the rectifier station active power is obtained. Finally, through the rectifier station active power-DC side voltage coupling link, it is added to the transfer coupling term between the received-end converter output active power and the sending-end converter DC side voltage to obtain the small-signal value of the DC side voltage.

[0012] Further, in the inverter side loop, after comparing the inverter station active power reference value with the actual inverter station active power, the phase angle information of the inverter station is generated through a virtual inertia damping link. Then, through the transfer link between the inverter station phase angle and the inverter station active power coupled with the inverter station voltage-reactive power, the small-signal value of the inverter side active power is obtained.

[0013] The present invention also provides an oscillation transfer analysis method for determining between SEF and DCV in a VSC-HVDC system under double-end VSG control. Based on the above-mentioned oscillation transfer analysis system for determining between SEF and DCV in a VSC-HVDC system under double-end VSG control, the analysis method includes the following steps:

[0014] (1) Calculate the rectifier side frequency iteration function G f1 (s), the transfer function G f1v1 (s) from SEF to DCV, and the transfer function G v1f1 (s) from DCV to SEF;

[0015] (2) Determine the key oscillation frequency of the system according to the peak point in the amplitude-frequency characteristic of G f1 (s);

[0016] (3) Calculate the amplitudes of the amplitude-frequency characteristic curves of G f1v1 (s) and G v1f1 (s) at the key oscillation frequency point, and denote them as 'M v ' and 'M f ' respectively;

[0017] (4) Judge whether oscillation transfer occurs between SEF and DCV according to the positive and negative of M v and M f .

[0018] Further, in step (1),

[0019]

[0020] Represents the transfer coupling term from the active power input at the AC side of the sending - end converter to the DC - side voltage of the sending - end converter, Represents the transfer coupling term from the phase angle of the electrical node at the AC - side outlet of the sending - end converter to the active power input at the AC side of the sending - end converter, Represents the transfer coupling term from the DC - side voltage of the receiving - end converter to the active power input at the AC side of the sending - end converter, Represents the transfer coupling term from the phase angle of the electrical node at the AC - side outlet of the sending - end converter to the active power output at the AC side of the receiving - end converter, Represents the transfer coupling term from the phase angle of the electrical node at the AC - side outlet of the receiving - end converter to the active power output at the AC side of the receiving - end converter.

[0021] Furthermore, in step (1),

[0022] G f1 (s)=G f1v1 (s)G v1f1 (s).

[0023] Furthermore, step (4) is specifically: when M f is greater than 0, there is a positive amplification effect from DCV to SEF, and there is a risk of resonance in SEF; when M f is less than 0 and M v is greater than 0, there is a positive amplification effect from SEF to DCV, and there is a risk of resonance in DCV; when M f and M v are both less than 0, a negative transfer effect is formed between DCV and SEF, and the system is stable.

[0024] Furthermore, step (4) is specifically: when M f is less than 0 and M v is greater than 0, the direction of oscillation transfer is from SEF to DCV; when M f is greater than 0 and M v is less than 0, the direction of oscillation transfer is from DCV to SEF; when M f and M v are both greater than 0, the oscillation transfer is bidirectional; when M f and M v are both less than 0, a negative transfer effect is formed between DCV and SEF, and the system is stable.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] Compared with the prior art, the oscillation analysis system proposed in the present invention provides a new physical perspective for the analysis of the oscillation transfer effect of the VSC-HVDC system under dual-terminal VSG control, and determines the occurrence conditions of oscillation transfer from a physical perspective; compared with the traditional eigenvalue analysis method and impedance criterion analysis method, the analysis method for determining the oscillation transfer of the VSC-HVDC system under dual-terminal VSG control proposed in the present invention can more intuitively and clearly evaluate the risk of oscillation transfer in this system.

[0027] The present invention will be explained and described in detail below in conjunction with the accompanying drawings and specific embodiments. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the topological structure and control algorithm of the hardware circuit of the VSC-HVDC system under dual-terminal VSG control;

[0029] Figure 2 It is the oscillation transfer analysis framework proposed in the present invention;

[0030] Figure 3 In the present invention Figure 2 Equivalent transformation form;

[0031] Figure 4 It is the flow chart of the oscillation transfer analysis method proposed in the first embodiment;

[0032] Figure 5 shows the simulation results and the analysis results of the oscillation transfer framework in the first working condition of this embodiment; among them, Figure (a) is the simulation frequency waveform diagram of the first working condition; Figure (b) is the DC voltage frequency wave diagram of the first working condition; Figure (c) is the G f1v1 (s), G v1f1 (s) and G f1 (s) amplitude-frequency characteristic curve diagram;

[0033] Figure 6 shows the simulation results and the analysis results of the oscillation transfer framework in the second working condition of this embodiment; among them, Figure (a) is the simulation frequency waveform diagram of the second working condition; Figure (b) is the DC voltage frequency wave diagram of the second working condition; Figure (c) is the G f1v1 (s), G v1f1 (s) and G f1 (s) amplitude-frequency characteristic curve diagram;

[0034] Figure 7 It is the flow chart of the oscillation transfer analysis method proposed in the second embodiment. Detailed Embodiment

[0035] For the convenience of understanding the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the description of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0037] Specifically, taking the VSC-HVDC system with double-ended VSG control as an example, as Figure 1 shown in the schematic diagram of the hardware circuit topology and the control algorithm of the virtual synchronous generator, the following function model is obtained through the topology and the control algorithm:

[0038]

[0039] In Equation (1), I represents the grid-side current, represents the current at the AC side outlet of the three-phase converter; , , , , respectively represent the phase of the voltage at the AC side outlet of the three-phase converter, the phase of the voltage at the point of common coupling (PCC), the phase of the grid voltage, the phase of the current at the AC side outlet of the three-phase converter, and the phase of the grid-side current; E represents the voltage at the AC side outlet of the three-phase converter; represents the filter resistance; represents the filter inductance; s represents the complex frequency domain variable after Laplace transform; j represents the imaginary unit; represents the grid voltage; represents the voltage at the PCC point; represents the equivalent capacitance of the AC transmission line to the ground.

[0040] According to Kirchhoff's law and the law of conservation of energy, the equation of the DC transmission line is

[0041] (2)

[0042] In Equation (2), is the active power input to the rectifier station on the AC side, is the active power output from the inverter station on the DC line, LPF is the low-pass filter, is the DC-side capacitor, is the voltage across the DC-side capacitor; is the current of the DC transmission line, is the equivalent inductance of the DC transmission line.

[0043] According to the instantaneous power theory, the formulas for P and Q are:

[0044] (3)

[0045] represents the active power transmitted by the sending-end converter and the receiving-end converter, where the subscript 1 represents the sending end and the subscript 2 represents the receiving end; represents the reactive power transmitted by the sending-end converter and the receiving-end converter; represents the value of the real-axis component after the Park transformation of the voltage of the electrical node at the AC-side outlet of the sending-end converter and the receiving-end converter; represents the value of the real-axis component after the Park transformation of the current of the AC-side system at the sending end and the receiving end; represents the value of the imaginary-axis component after the Park transformation of the voltage of the electrical node at the AC-side outlet of the sending-end converter and the receiving-end converter; represents the value of the imaginary-axis component after the Park transformation of the current of the AC-side system at the sending end and the receiving end.

[0046] In order to couple the rectifier side and the inverter side together, the phase angle of the rectifier station is also used as the synchronous rotating inertia reference coordinate system for the Park transformation. After that, combining equations (1), (2), and (3), the relationship between , , , can be obtained as:

[0047] (4)

[0048] , , , , , , , respectively represent the transfer coupling terms between the four variables , , and calculated by writing the Kirchhoff equation and the instantaneous power equation for the physical system topology; represents the phase angle information of the electrical node at the AC-side outlet of the converter, represents the voltage information of the electrical node at the AC-side outlet of the converter, It represents the transfer coupling term from the electrical node phase angle at the AC side outlet of the sending converter to the active power output at the AC side of the receiving converter. It represents the transfer coupling term from the electrical node phase angle at the AC side outlet of the sending converter to the reactive power output at the AC side of the receiving converter.

[0049] The small-signal equation of the control algorithm for the three-phase converter in the rectifier station is:

[0050] (5)

[0051] It represents the DC side voltage reference value of the sending converter. It represents the virtual inertia parameter in the active power control loop of the virtual synchronous generator control. It represents the virtual damping parameter in the active power control loop of the virtual synchronous generator control. It represents the rated angular velocity of the virtual synchronous generator. It represents the virtual inertia parameter in the reactive power control loop of the virtual synchronous generator control. It represents the virtual damping parameter in the reactive power control loop of the virtual synchronous generator control. It represents the reactive power reference value input at the AC side of the sending converter.

[0052] The small-signal equation of the control algorithm for the inverter station is:

[0053] (6)

[0054] 2 represents the active power reference value output at the AC side of the receiving converter. It represents the reactive power reference value output at the AC side of the receiving converter.

[0055] Combining equations (4)-(6), the small-signal model of the system as shown in Figure 2 can be obtained. By simplifying and performing equivalent transformation on Figure 2 , the system oscillation transfer judgment framework as shown in Figure 3 can be obtained.

[0056] Then, an oscillation transfer analysis system between SEF and DCV in the VSC-HVDC system under double-end VSG control is obtained, including the rectifier side loop, the inverter side loop, and the transfer coupling loop:

[0057] The rectifier-side loop includes a voltage outer loop, a virtual inertia damping loop, a rectifier station phase angle-rectifier station active power physical transfer link coupled with a rectifier station voltage-reactive power inner loop, and a rectifier station active power-DC side voltage coupling link. The voltage outer loop is formed by comparing the DC side voltage reference value with the actual DC side voltage through a proportional-integral controller. The output value is used as the rectifier station active power reference value, which is compared with the actual rectifier station active power, and then the phase angle information of the rectifier station is generated through the virtual inertia damping loop. Then, through the cross-coupling transfer link of active power-reactive power-terminal voltage-phase angle obtained from the rectifier-side physical topology and the instantaneous power theory formula (i.e., the rectifier station phase angle-rectifier station active power physical transfer link coupled with the rectifier station voltage-reactive power inner loop), the small-signal value of the rectifier station active power is obtained. Finally, through the rectifier station active power-DC side voltage coupling link, it is added to the transfer coupling term of the received converter output active power and the sending converter DC side voltage to obtain the small-signal value of the DC side voltage.

[0058] The inverter-side loop includes a virtual inertia damping loop and an inverter station phase angle-inverter station active power transfer link coupled with an inverter station voltage-reactive power. The inverter station active power reference value is compared with the actual inverter station active power, and then the phase angle information of the inverter station is generated through the virtual inertia damping link. Then, through the cross-coupling transfer link of active power-reactive power-terminal voltage-phase angle obtained from the inverter-side physical topology and the instantaneous power theory formula (i.e., the inverter station phase angle-inverter station active power transfer link coupled with the inverter station voltage-reactive power), the small-signal value of the inverter-side active power is obtained.

[0059] The transfer coupling loop consists of three coupling terms: rectifier station phase angle-inverter station active power, rectifier station phase angle-inverter station reactive power, and inverter station active power-DC side voltage.

[0060] From Figure 3 it can be obtained that from to the transfer function and from to the transfer functions are respectively:

[0061] (7)

[0062] represents the transfer coupling term from the sending converter AC side input active power to the sending converter DC side voltage, the transfer coupling term from the electrical node phase angle at the sending converter AC side outlet to the sending converter AC side input active power, represents the transfer coupling term from the receiving converter DC side voltage to the sending converter AC side input active power, Represents the transfer coupling term from the electrical node phase angle at the AC side outlet of the sending - end converter to the active power output at the AC side of the receiving - end converter. Represents the transfer coupling term from the electrical node phase angle at the AC side outlet of the receiving - end converter to the active power output at the AC side of the receiving - end converter.

[0063] And define from to The iterative function G f1 (s) is.

[0064] G f1 (s)=G f1v1 (s)G v1f1 (s) (8)

[0065] It should be noted that, from the perspective of physical meaning, the amplitude - frequency characteristic of G f1 (s) represents the response degree of 'f1' to signals of different frequencies. Therefore, if there are obvious spikes in the amplitude - frequency characteristic diagram, it means that 'f1' is very likely to oscillate at these frequencies.

[0066] The oscillation propagation between SEF (sending - end system frequency) and DCV (DC voltage) can be judged from the amplitude - frequency characteristics of G f1v1 (s) and G v1f1 (s). The principle for selecting the critical frequency point is that, under the selected operating conditions, the frequency at which the peak appears in the amplitude - frequency characteristic of G f1 (s) should be close to the oscillation frequency of f1, and this point is denoted as "ω1". If the amplitude of the amplitude - frequency characteristic of G f1v1 (s) in ω1 is greater than zero, it indicates that f1 has a positive effect on the DC voltage, and the oscillation propagation direction is from f1 to V dc1 , V dc1 Due to the positive effect from f1, there is a risk of resonance; the larger the amplitude, the greater the positive effect in V dc1 , and the greater the oscillation degree. Similarly, the oscillation propagating from V dc1 to f1 can be judged by the amplitude - frequency characteristic of G v1f1 (s) in ω1.

[0067] The oscillation transfer judgment process is as Figure 4 shown. First, calculate the rectifier - side frequency iterative function G f1 (s), the transfer function G f1v1 (s) from SEF to DCV, and the transfer function G v1f1 (s) from DCV to SEF. Then, determine the key oscillation frequency of the system according to the peak point in the amplitude - frequency characteristic of G f1 (s). After that, calculate G f1v1 (s), G v1f1(s) amplitude-frequency characteristic curve at the key oscillation frequency point amplitude, and are respectively denoted as 'M v ' and 'M f '. According to the positive and negative of M v and M f to judge whether there is oscillation transfer between SEF and DCV. If M f is greater than 0, there is a positive amplification effect from DCV to SEF, and there is a risk of resonance in SEF; if M f is less than 0 and M v is greater than 0, there is a positive amplification effect from SEF to DCV, and there is a risk of resonance in DCV; if M f and M v are both less than 0, then there is a negative transfer effect between DCV and SEF, and the system is stable.

[0068] The following is a simulation experiment:

[0069] Condition 1: R f1 = 0.03Ω, L f1 = 9mH, R tr1 = 0.015Ω, L tr1 = 0.05mH, C eq1 = 25000mF, R g1 = 0.015Ω, L g1 = 0.05mH, R f2 = 0.03Ω, L f2 = 9mH, R tr2 = 0.015Ω, L tr2 = 0.5mH, C eq2 = 25000mF, R g2 = 0.015Ω, L g2 = 0.5mH, J p1 = 2000, D p1 = 50240000, J q1 = 300, D q1 = 180000, J p2 = 1000, D p2 = 13690400, J q2 = 300, D q2 = 150000, V dc1ref = 320000V, Q 1ref = 100000Var, P 2ref = 300000000W, Q 2ref = 100000Var.

[0070] Condition 2: R f1 = 0.03Ω, L f1 = 9mH, Rtr1 = 0.015 Ω, L tr1 = 0.05 mH, C eq1 = 25000 mF, R g1 = 0.015 Ω, L g1 = 0.05 mH, R f2 = 0.03 Ω, L f2 = 9 mH, R tr2 = 0.05 Ω, L tr2 = 0.5 mH, C eq2 = 25000 mF, R g2 = 0.05 Ω, L g2 = 0.5 mH, J p1 = 4000, D p1 = 50240000, J q1 = 300, D q1 = 180000, J p2 = 1000, D p2 = 13345000, J q2 = 300, D q2 = 150000, V dc1ref = 320000 V, Q 1ref = 100000 Var, P 2ref = 300000000 W, Q 2ref = 100000 Var.

[0071] The simulation results of Condition 1 are shown in Figures 5(a) and 5(b), and the oscillation transfer framework analysis results of Condition 1 are shown in Figure 5(c); the simulation results of Condition 2 are shown in Figures 6(a) and 6(b), and the oscillation transfer framework analysis results of Condition 2 are shown in Figure 6(c).

[0072] Comparing Figure 5(c) and Figure 6(c), it can be seen that for Condition 1, G f1v1 (ω1) is smaller while G v1f1 (ω1) is larger, corresponding to the smaller V dc1 and larger f1 in the simulation results [Figures 5(a) and 5(b) and Figures 6(a) and 6(b)]; for Condition 2, G f1v1 (ω1) is larger while G v1f1 (ω1) is smaller, corresponding to the larger V dc1 and smaller f1 in the simulation results [Figures 5(a) and 5(b) and Figures 6(a) and 6(b)], indicating that the theoretical analysis is in good agreement with the simulation results. This proves the effectiveness of the present invention.

[0073] The present invention is also applicable to the oscillation transfer determination of VSC-HVDC systems under any other control technology.

[0074] Embodiment 2: The difference between this embodiment and Embodiment 1 lies in that:

[0075] The oscillation transfer judgment process is as Figure 7 shown. First, calculate the rectifier-side frequency iteration function G f1 (s), the transfer function G f1v1 (s) from SEF to DCV, and the transfer function G v1f1 (s) from DCV to SEF. Then, determine the key oscillation frequency of the system according to the peak point in the amplitude-frequency characteristic of G f1 (s). After that, calculate G f1v1 (s), and the amplitudes of the amplitude-frequency characteristic curves of G v1f1 (s) at the key oscillation frequency point, which are denoted as 'M v ' and 'M f ' respectively. Judge whether oscillation transfer occurs between SEF and DCV according to the positive and negative of M v and M f . If M f is less than 0 and M v is greater than 0, the direction of oscillation transfer is from SEF to DCV; if M f is greater than 0 and M v is less than 0, the direction of oscillation transfer is from DCV to SEF; if M f and M v are both greater than 0, the oscillation transfer is bidirectional; if M f and M v are both less than 0, negative transfer effects are formed between DCV and SEF, and the system is stable.

[0076] Other parts are the same as Embodiment 1.

[0077] Compared with the prior art, the oscillation transfer analysis system proposed in the present invention provides a new physical perspective for VSC-HVDC oscillation transfer and determines the occurrence conditions of oscillation transfer from a physical perspective. Compared with the traditional eigenvalue analysis method and impedance criterion analysis method, the oscillation transfer analysis method for determining the oscillation transfer between SEF and DCV in a VSC-HVDC system under double-end VSG control proposed in the present invention can more intuitively and clearly determine the oscillation transfer state of the VSC-HVDC system under double-end VSG control.

[0078] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious replacement without departing from the concept of the technical solution is within the protection scope of the present invention.

[0079] To enable those of ordinary skill in the art to more conveniently understand the improvements of the present invention over the prior art, some of the drawings and descriptions of the present invention have been simplified, and for the sake of clarity, some other elements have also been omitted in this application document. Those of ordinary skill in the art should be aware that these omitted elements may also constitute the content of the present invention.

Claims

1. An oscillation transfer analysis system for determining the oscillation between the SEF and the DCV in a VSC-HVDC system under double-ended VSG control, characterized in that: It includes a rectifier-side loop, an inverter-side loop, and a transfer coupling loop; The rectifier-side loop includes a voltage outer loop, a virtual inertia damping loop, a physical transfer link of rectifier station phase angle - rectifier station active power coupled with a rectifier station voltage - reactive power inner loop, and a rectifier station active power - DC-side voltage coupling link; The inverter-side loop includes a virtual inertia damping loop and an inverter station phase angle - inverter station active power transfer link coupled with an inverter station voltage - reactive power; The transfer coupling loop includes three coupling terms: rectifier station phase angle - inverter station active power, rectifier station phase angle - inverter station reactive power, and inverter station active power - DC-side voltage.

2. The oscillation transfer analysis system between SEF and DCV in the VSC-HVDC system under dual-terminal VSG control according to claim 1, characterized in that: In the rectifier-side loop, the voltage outer loop is formed by comparing the DC-side voltage reference value with the actual DC-side voltage and passing through a proportional-integral controller. The output value is used as the rectifier station active power reference value. After comparing it with the actual rectifier station active power, the phase angle information of the rectifier station is generated through the virtual inertia damping loop. Then, through the physical transfer link of rectifier station phase angle - rectifier station active power coupled with a rectifier station voltage - reactive power inner loop, the small-signal value of the rectifier station active power is obtained. Finally, through the rectifier station active power - DC-side voltage coupling link, it is added to the transfer coupling term of the receiving-end converter output active power and the sending-end converter DC-side voltage to obtain the small-signal value of the DC-side voltage.

3. The oscillation transfer analysis system between SEF and DCV in the VSC-HVDC system under dual-terminal VSG control according to claim 1, wherein: In the inverter-side loop, after comparing the inverter station active power reference value with the actual inverter station active power, the phase angle information of the inverter station is generated through the virtual inertia damping link. Then, through the inverter station phase angle - inverter station active power transfer link coupled with an inverter station voltage - reactive power, the small-signal value of the inverter-side active power is obtained.

4. A method for analyzing the oscillation transfer between the SEF and the DCV in a VSC-HVDC system under double-ended VSG control, characterized in that: Based on the oscillation transfer analysis system between SEF and DCV in the VSC-HVDC system under the dual-terminal VSG control described in any one of claims 1-3, the analysis method includes the following steps: (1) Calculate the rectifier side frequency iteration function G f1 (s), the transfer function G f1v1 (s) from SEF to DCV, and the transfer function G v1f1 (s); (2) Determine the key oscillation frequency of the system according to the peak point in the f1 (s) amplitude-frequency characteristic; (3) Calculate G f1v1 (s) and G v1f1 (s) at the amplitude of the key oscillation frequency point of the amplitude-frequency characteristic curve, and record them as 'M v ' and 'M f '; (4) According to M v and M f to determine whether there is an oscillatory transfer between SEF and DCV based on the positive and negative of 5. The oscillation transfer analysis method between SEF and DCV in the VSC-HVDC system under dual-terminal VSG control according to claim 4, wherein: In step (1), Represents the transfer coupling term from the active power input at the AC side of the sending converter to the DC side voltage of the sending converter. Represents the transfer coupling term from the electrical node phase angle at the outlet of the AC side of the sending converter to the active power input at the AC side of the sending converter. Represents the transfer coupling term from the DC side voltage of the receiving converter to the active power input at the AC side of the sending converter. Represents the transfer coupling term from the electrical node phase angle at the outlet of the AC side of the sending converter to the active power output at the AC side of the receiving converter. Represents the transfer coupling term from the electrical node phase angle at the outlet of the AC side of the receiving converter to the active power output at the AC side of the receiving converter.

6. The oscillation transfer analysis method between SEF and DCV in the VSC-HVDC system under double-ended VSG control according to claim 5, characterized in that: In step (1), G f1 (s)=G f1v1 (s)G v1f1 (s).

7. The oscillation transfer analysis method between SEF and DCV in the VSC-HVDC system under dual-terminal VSG control according to claim 4, characterized in that: Step (4) specifically is: At M f When it is greater than 0, there is a positive amplification effect from DCV to SEF, and there is a risk of resonance in SEF; At M f When it is less than 0 and M v When it is greater than 0, there is a positive amplification effect from SEF to DCV, and there is a risk of resonance in DCV; At M f and M v When both are less than 0, a negative transfer effect is formed between DCV and SEF, and the system is stable.

8. The oscillation transfer analysis method between SEF and DCV in the VSC-HVDC system under double-ended VSG control according to claim 4, characterized in that: Step (4) specifically is: At M f less than 0 and M v greater than 0, the direction of oscillatory transmission is from SEF to DCV; At M f greater than 0 and M v less than 0, the oscillation transfer direction is from DCV to SEF; at M f and M v both greater than 0, the oscillation transfer is bidirectional; at M f and M v both less than 0, negative transfer effects are formed between DCV and SEF, and the system is stable.

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