Method for analyzing influence mechanism of control parameters on sending-end power grid voltage under high-voltage direct-current fault

Abstract

The invention discloses a method for analyzing an influence mechanism of a control parameter on a sending-end power grid voltage under a high-voltage direct-current fault, which is suitable for the field of high-voltage direct-current power transmission. The method comprises the following steps: according to a direct current system characteristic equation and an action process of a direct current control system after a commutation failure, analyzing a generation mechanism and an evolution process of a sending end power grid voltage after the commutation failure; and analyzing the relationship between the reactive power of the direct current system and the direct current, establishing a direct current model for analysis based on the relationship, analyzing the influence of the control parameters on the direct current and the direct current reactive power characteristics, and further obtaining the influence mechanism of the relevant parameters on the transient low / high voltage of the transmitting-end power grid. According to the method for analyzing the influence mechanism of the control parameters on the sending-end power grid voltage under the high-voltage direct-current fault, the influence mechanism of the direct-current control parameters on the sending-end power grid voltage during the commutation failure period is disclosed, and the method has important theoretical significance on the control strategy of the sending-end power grid voltage during the high-voltage direct-current fault.

Description

Technical Field

[0001] The invention belongs to the field of high-voltage direct current transmission, and in particular relates to a method for analyzing the influence mechanism of control parameters on the voltage of a sending-end power grid under a high-voltage direct current fault. Background Art

[0002] In recent years, line commutated-converterbased high voltage direct current (LCC-HVDC) has been widely used in renewable energy DC transmission systems due to its large capacity, low cost, and suitability for long-distance transmission. Commutation failure is one of the common faults in DC systems. The transient change in the reactive characteristics of the DC system during the fault will break the reactive balance between the converter station and the renewable energy station, and then cause serious transient voltage problems in the sending-end system, which seriously threatens the safe and stable operation of the sending and receiving systems. During the commutation failure period, the DC control parameters are closely related to the DC reactive characteristics. Therefore, analyzing the influence mechanism of the control parameters on the transient voltage at the sending end has important theoretical and practical significance.

[0003] Many experts and scholars have previously studied the impact of high-voltage DC faults on the voltage of the DC sending-end grid, but most of them focused on using quasi-steady-state models and electromagnetic transient simulation models for analysis, lacking a more comprehensive mechanism explanation. Summary of the invention

[0004] The object of the present invention is to provide a method for analyzing the influence mechanism of control parameters on the voltage of a sending-end power grid under a high-voltage direct current fault, so as to solve the problems existing in the existing analysis methods.

[0005] To achieve the above object, the technical solution provided by the present invention is to analyze the influence mechanism of control parameters on the voltage of the sending-end power grid under high-voltage direct current fault, characterized in that the analysis method comprises the following steps:

[0006] S1: Analyze the generation mechanism and evolution process of transient voltage at the sending end after commutation failure;

[0007] S2: Based on the DC current characteristics during commutation failure, a DC current analysis model during fault period is established to analyze the influence of control parameters on DC current;

[0008] S3: Based on the relationship between DC current, reactive power characteristics of DC system and sending-end voltage, analyze the influence mechanism of control parameters on sending-end transient voltage;

[0009] S4: Build a simulation model to verify the feasibility and effectiveness of the analysis method.

[0010] 1. S1 comprises the following steps:

[0011] S101: Analyze the generation mechanism of transient voltage in the sending end system;

[0012] S102: Analyze the DC control action process and the voltage change process of the sending-end grid during the DC commutation failure: The sending-end transient voltage equation is shown in equation (1), and the DC current characteristic equation and DC reactive power equation are shown in equations (2) and (3). It can be seen from equations (2) and (3) that during the commutation failure, due to the DC control effect, the DC reactive power characteristics and DC current show a dynamic characteristic of first increasing and then decreasing. The sending-end system first has a reactive power deficit and then a reactive power surplus. According to equation (1), the sending-end voltage will first be low and then high. The dynamic characteristics, where Q ac is the reactive power of the sending-end AC system, Q f The reactive power generated by the reactive power compensation device, Q d Reactive power consumed by the DC system, S ac is the short circuit ratio, U dr0 and U di0 are the ideal no-load DC voltage of the unipolar transformer in the rectifier station and the inverter station respectively; U dr is the voltage between the rectifier station and the ground; X r and X i are the commutation reactances on the rectifier side and the inverter side respectively; R d is the resistance of the DC transmission line; I d is the DC current, α is the trigger angle on the rectifier side; β is the trigger lead angle on the inverter side; P d The active power delivered to the DC system, is the power factor angle.

[0013]

[0014]

[0015]

[0016] 2. S2 comprises the following steps:

[0017] S201: According to the DC current characteristics during the fault, a DC current transfer function model with DC control during the fault is established in stages to obtain DC current analysis models at different stages. According to the DC current and reactive power characteristic curves of the sending-end commutation bus during the commutation failure, based on the transient voltage generation mechanism obtained in S102, the commutation failure can be modeled and analyzed in stages;

[0018] S202: Analyze the influence of the control parameters on the DC current according to the DC current analysis model obtained in S201.

[0019] 3. S3 comprises the following steps:

[0020] S301: According to the generation mechanism of transient voltage at the sending end under commutation failure described in S1, the generation mechanism of transient voltage at the sending end caused by DC control parameters is obtained.

[0021] 4. S4 comprises the following steps:

[0022] S401: Build a high-voltage direct current transmission model to obtain transient change curves of direct current and sending-end voltage under different parameters after a fault occurs;

[0023] S402: Verify the consistency of the simulation results with the analysis method proposed in the present invention.

[0024] Compared with the prior art, the method provided by this application has the following beneficial effects:

[0025] The present invention constructs a method for analyzing the influence mechanism of control parameters on the voltage of the sending-end power grid under high-voltage direct current fault. The method starts from the mechanism of transient voltage generation due to commutation failure, points out that the DC reactive power consumption level increases first and then decreases during the fault period, which is an important reason for the voltage of the sending end to decrease first and then increase. Then, the DC current is modeled in stages according to the DC current characteristics during the fault period, and the influence of control parameters on the DC current and DC reactive power characteristics is analyzed, thereby obtaining the influence on the transient voltage of the sending end. The problem that the present invention can solve is: to obtain an analysis method for analyzing the influence mechanism of DC control parameters on the voltage of the sending end; to analyze in detail the influence mechanism of DC control parameters on the transient voltage of the sending end during commutation failure, and to analyze the influence degree of each parameter on the transient voltage of the sending end. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the steady-state equivalent circuit diagram of the DC system.

[0027] Figure 2 This is the block diagram of the DC system control structure.

[0028] Figure 3 This is the DC current variation curve during commutation failure.

[0029] Figure 4 It is the reactive power variation curve of commutation bus during commutation failure.

[0030] Figure 5 This is the logic block diagram of the DC current reference value in the DC rising stage.

[0031] Figure 6 This is the block diagram of the constant current control structure on the rectifier side during the DC step-down phase.

[0032] Figure 7 This is the simulation waveform after changing the fixed turn-off angle control proportional coefficient. Figure 7 (a) is the DC current waveform. Figure 7 (b) is the voltage waveform at the sending end.

[0033] Figure 8 This is the simulation waveform after changing the integral coefficient of fixed turn-off angle control. Figure 8 (a) is the DC current waveform. Figure 8 (b) is the voltage waveform at the sending end.

[0034] Fig. 9 This is the simulation waveform after changing the constant current control proportional coefficient. Fig. 9 (a) is the DC current waveform. Fig. 9 (b) is the voltage waveform at the sending end.

[0035] Fig.10 This is the simulation waveform after changing the constant current control integral coefficient. Fig.10 (a) is the DC current waveform. Fig.10 (b) is the voltage waveform at the sending end.

[0036] Fig.11 To change VDCOL control I low Post-simulation waveform. Fig.11 (a) is the VDCOL characteristic curve, Fig.11 (b) is the voltage waveform at the sending end.

[0037] Fig.12 To change VDCOL control U high Post-simulation waveform. Fig.12 (a) is the VDCOL characteristic curve, Fig.12 (b) is the voltage waveform at the sending end.

[0038] Fig.13 To change VDCOL control U low Post-simulation waveform. Fig.13 (a) is the VDCOL characteristic curve, Fig.13 (b) is the voltage waveform at the sending end. DETAILED DESCRIPTION

[0039] In order to clearly understand the technical solution of the present invention, its detailed structure will be presented in the following description. The present invention is further described below in conjunction with the accompanying drawings and implementation examples, but is not intended to limit the scope of the present invention.

[0040] The present invention provides a method for analyzing the influence mechanism of control parameters on the voltage of a sending-end power grid under a high-voltage direct current fault, comprising the following steps:

[0041] S1: Analyze the generation mechanism and evolution process of transient voltage at the sending end after commutation failure;

[0042] S2: Based on the DC current characteristics during commutation failure, a DC current analysis model during fault period is established to analyze the influence of control parameters on DC current;

[0043] S3: Based on the relationship between DC current, reactive power characteristics of DC system and sending-end voltage, analyze the influence mechanism of control parameters on sending-end transient voltage;

[0044] S4: Build a simulation model to verify the feasibility and effectiveness of the analysis method.

[0045] The S1 comprises the following steps:

[0046] S101: Analyze the generation mechanism of transient voltage in the sending-end system.

[0047] Analysis of the transient voltage generation mechanism of the sending-end power grid: When the system is in steady-state operation, the reactive power consumption of the DC system is about 40% to 60% of the active power transmission level. Almost all of this reactive power is provided by the reactive power compensation device at the converter bus, and the reactive power exchange between the DC system and the AC system is close to 0. When the DC system fails, the DC reactive power consumption level will change significantly, causing the reactive power balance of the sending-end system to be destroyed, resulting in transient voltage problems in the sending-end power grid. The transient voltage change equation can be approximated as equation (1), where ΔU L is the transient voltage change of the commutation bus, and ΔQ is the reactive power change at the sending end.

[0048]

[0049] S102: Analyze the DC control action process and the sending-end grid voltage change process during the DC commutation failure.

[0050] The DC current of the DC system is positively correlated with the DC reactive power characteristics. The reactive power equation of the DC system is shown in equation (2), and the relationship between reactive power and DC current is shown in equation (3), where Q d is the DC reactive power consumption level, P d is the DC active power transmission level, U dr is the voltage between the rectifier station and the ground, U dr0 is the ideal no-load DC voltage of the rectifier station, X r is the commutation reactance on the rectifier side, α is the trigger angle on the rectifier side, is the power factor angle.

[0051]

[0052]

[0053] Figure 1 The figure shows the steady-state equivalent circuit diagram of the DC system. Figure 2The control structure block diagram of the DC system is shown in Figure 4. The main control links on the rectifier side are constant current control and low voltage current limiting control, and the main control links on the inverter side are constant current control, low voltage current limiting control, fixed shutdown angle control and current deviation control. When a fault occurs at the DC receiving end, the DC voltage on the inverter side drops, and the shutdown angle on the inverter side also drops. The DC current characteristic equation is shown in formula (4), where U di0 is the ideal no-load DC voltage of the inverter station, R d is the DC transmission line resistance, X i is the inverter side commutation reactance, and β is the inverter side trigger lead angle. At this time, the DC current rises rapidly, and the DC reactive power consumption level also rises rapidly. At this time, the reactive power balance at the sending end is broken, resulting in reactive power shortage, and a transient low voltage appears at the sending end; the rectifier side constant current control function increases the trigger angle to suppress the rise of DC current. According to formula (4), at this time, the DC current drops rapidly, and the DC reactive power consumption level also drops immediately. At this time, the reactive power compensation at the sending end is not exited in time, resulting in reactive power surplus at the sending end, resulting in overvoltage. Therefore, the sending end voltage presents a transient characteristic of first low and then high during the commutation failure.

[0054]

[0055] The S2 comprises the following steps:

[0056] S201: According to the DC current characteristics during the fault period, a DC current transfer function model including DC control during the fault period is established in stages to obtain DC current analysis models at different stages.

[0057] Figure 3 is the DC current characteristic curve during commutation failure, Figure 4 is the reactive characteristic curve of the commutation busbar during commutation failure. Figure 3 It can be seen that after commutation failure, the DC current change characteristic is first rising and then falling; Figure 4 It can be seen that after the commutation failure, the commutation bus at the sending end first has reactive power shortage and then reactive power surplus. Therefore, segmented modeling is carried out according to the DC current change characteristics during the commutation failure.

[0058] Figure 5 The block diagram of the DC current reference value transfer function in the DC rising stage. In the early stage of commutation failure, the DC voltage on the inverter side drops rapidly, causing the inverter side turn-off angle to drop. The fixed turn-off angle control function increases the trigger lead angle to suppress the turn-off angle drop. Figure 5 We can get equations (5) and (6), where K p and K i is the PI parameter for fixed cut-off angle control, s is the Laplace operator, γ ref is the cut-off angle reference value, γ meas is the measured value of the turn-off angle, β 0is the initial value of the inverter trigger lead angle, β ref U is the trigger advance angle reference value output by the turn-off angle difference after passing through the PI regulator, low and U high are the lower and upper limits of the DC voltage, respectively, I low and I high are the lower and upper limits of DC current respectively, U di It is the voltage between the pole and the ground of the inverter station.

[0059]

[0060]

[0061] Figure 6 The DC current transfer function block diagram in the DC drop stage. The DC voltage drop on the inverter side causes the DC current reference value to drop. In this stage, the constant current control and VDCOL control on the rectifier side work together to increase the trigger angle α to suppress the rise of DC current. The DC current drops rapidly, and the system is not in a steady state before this stage. Therefore, considering the impact of the initial fault current, combined with Figure 6 We can get equations (7), (8) and (9), I dref (s) is the DC current reference value, I df (s) is the initial fault current, K p and K i is the constant current control PI parameter, K cα is the proportional gain coefficient of the converter link, T cα is the delay coefficient, K m is the gain factor of the measurement link, T m To measure the link delay coefficient.

[0062] I d (s) = G dref (s)I dref (s)+G df (s)I df (s) (7)

[0063]

[0064]

[0065] S202: Analyze the influence of the control parameters on the DC current according to the DC current analysis model obtained in S201.

[0066] By performing the inverse transformation of equations (6) and (7), the corresponding time domain equations can be obtained to analyze the influence of each control parameter on the DC current. It can be seen that increasing the fixed turn-off angle PI parameter will reduce the DC rising phase current and improve the transient low voltage; and it can be known that K PImpact change initial, K i Affects the rate of change, and this stage is very short, so K i The impact is small; increasing the constant current control ratio parameter will reduce the DC current peak value, improve the DC current low value, improve the transient low voltage and suppress the transient overvoltage; increasing the integral coefficient will improve the transient low voltage and worsen the transient overvoltage; when increasing I low After that, the low voltage level will be deteriorated and the overvoltage will be suppressed; when U high and increase U low After that, the low voltage level will be improved and overvoltage will be suppressed.

[0067] The S3 comprises the following steps:

[0068] S301: Based on the influence of the control parameters obtained in S202 on the DC current and DC reactive power characteristics, combined with the generation mechanism of the transient voltage at the sending end in S101, the influence mechanism of the DC control parameters on the transient voltage at the sending end can be finally obtained.

[0069] The S4 comprises the following steps:

[0070] S401: Based on the high voltage direct current (HVDC) transmission model, transient change curves of DC current and sending-end voltage under different parameters after a fault occurs are obtained.

[0071] The CIGRE standard DC control system is adopted, with a rated DC voltage of ±500KV and a maximum DC transmission power of 1000MW. A three-phase short circuit fault is set at the DC receiving end, and the fault duration is 0.05s. The inverter side fixed shutdown angle control PI parameters, the rectifier side constant current control PI parameters and the low-voltage current limiting control parameters are changed respectively to test the DC current variation characteristics and the transient characteristics of the sending-end grid voltage under different control parameters in the simulation model. Figure 7 — Fig.10 These are the DC current and sending-end grid voltage characteristic curves after changing the PI parameters of fixed turn-off angle control and constant current control, respectively. Fig.11 — Fig.13 They are the VDCOL characteristic curve and the sending-end grid voltage curve after changing the low-voltage current limiting control parameters.

[0072] S402: Analyze the simulation results and find out whether they are consistent with the analysis method proposed in the present invention. Figure 7 and Figure 8It can be seen that when the fixed turn-off angle PI parameter is increased, the DC current decreases in the DC current rising stage, the DC reactive power consumption level decreases, the transient low voltage at the sending end is improved, and the impact of the proportional coefficient is greater than the integral coefficient; when the constant current control proportional parameter is increased, the initial value of the DC current decreases in the DC current falling stage, and the rate of decrease slows down, and the minimum value of the DC current increases during the fault, resulting in a larger DC reactive power consumption level, which suppresses the transient overvoltage at the sending end; when the constant current control integral coefficient is increased, the initial value and minimum value of the DC current decrease, which improves the low voltage level but worsens the overvoltage level, but the impact is small; when the I is increased low After that, the low voltage level will be deteriorated and the overvoltage will be suppressed; when U high and increase U low After that, the low voltage level will be improved and overvoltage will be suppressed.

[0073] The simulation results are basically consistent with the results obtained by the analysis method proposed in the present invention, which verifies the practicability and effectiveness of the present invention.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field can still modify or replace the specific implementation methods of the present invention with equivalents. Any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of protection of the pending claims.

Claims

1. A method for analyzing the influence mechanism of control parameters on the voltage of the sending-end power grid under high-voltage direct current fault, characterized in that: The analytical method comprises the following steps: S1: Analyze the generation mechanism and evolution process of transient voltage at the sending end after commutation failure; S2: Based on the DC current characteristics during commutation failure, a DC current analysis model during fault period is established to analyze the influence of control parameters on DC current; S3: Based on the relationship between DC current, reactive power characteristics of DC system and sending-end voltage, analyze the influence mechanism of control parameters on sending-end transient voltage; S4: Build a simulation model to verify the feasibility and effectiveness of the analysis method.

2. The method for analyzing the influence mechanism of control parameters on the voltage of the sending-end power grid under high-voltage direct current fault according to claim 1 is characterized in that: The S1 comprises the following steps: S101: Analyze the generation mechanism of transient voltage in the sending-end system; S102: Analyze the DC control action process and the voltage change process of the sending-end power grid during the DC commutation failure: the DC reactive power characteristics and the DC current first increase and then decrease during the commutation failure, causing the sending-end system to first have a reactive power deficit and then a reactive power surplus, which in turn causes the sending-end voltage to have a dynamic characteristic of first being low and then high.

3. The method for analyzing the influence mechanism of control parameters on the voltage of the sending-end power grid under a high-voltage direct current fault according to claim 1 is characterized in that: The S2 comprises the following steps: S201: According to the DC current characteristics during the fault period, a DC current transfer function model including DC control during the fault period is established in stages to obtain DC current analysis models at different stages; S202: Based on the DC current analysis model obtained in S201, analyze the influence of the control parameters on the DC current.

4. The method for analyzing the influence mechanism of control parameters on the voltage of the sending-end power grid under a high-voltage direct current fault according to claim 1 is characterized in that: The S3 comprises the following steps: S301: According to the generation mechanism of transient voltage at the sending end under commutation failure described in S1, the generation mechanism of transient voltage at the sending end by DC control parameters is obtained.

5. The method for analyzing the influence mechanism of control parameters on the voltage of the sending-end power grid under high-voltage direct current fault according to claim 1 is characterized in that: The S4 comprises the following steps: S401: Building a high-voltage direct current transmission model to obtain transient change curves of direct current and sending-end voltage under different parameters after a fault occurs; S402: Verify the consistency of the simulation results with the analysis method proposed in the present invention.

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