A grid-connected converter broadband oscillation monitoring device and monitoring method

Abstract

The application provides a grid-connected converter broadband oscillation monitoring device and a monitoring method, and belongs to the field of oscillation monitoring of power systems. The device comprises a disturbance voltage injection module, a response current measurement module, a converter impedance calculation module, a system stability interval and instability interval generation module, and a converter impedance and line impedance vector calculation module. The disturbance voltage injection module is used for injecting a disturbance voltage into a grid-connected point. The response current measurement module is used for measuring a response current generated by the injected disturbance voltage. The converter impedance calculation module is used for receiving the disturbance voltage and the response current, and calculating an equivalent output impedance. The system stability interval and instability interval generation module is used for judging a system stability interval and an instability interval according to the equivalent output impedance. The converter impedance and line impedance vector calculation module is used for calculating a combined impedance phase according to the equivalent output impedance and a line impedance. The stability discrimination module is used for combining the impedance phase, and calculating an oscillation analysis result. The device only needs to use simple vector addition operation processing to monitor the operation state of the system, has a wider application range, and is more accurate.

Description

Technical Field

[0001] This invention belongs to the field of power system oscillation monitoring, specifically relating to a broadband oscillation monitoring device and method for grid-connected converters. Background Technology

[0002] Renewable energy sources are connected to the grid via converters to achieve efficient power transmission. However, converters are prone to broadband oscillation instability due to grid interaction. Currently, broadband oscillation monitoring for this type of system mainly relies on system impedance data, using the Nyquist criterion or Bode plot to determine system stability and analyze its operating status. However, such methods are relatively complex in stability assessment, and may misjudge when the line impedance in low-voltage distribution networks exhibits a greater resistive component than an inductive component or when there is a resistive-capacitive impedance. Therefore, a simple yet highly accurate broadband oscillation monitoring device is necessary. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application proposes a wideband oscillation monitoring device and method for grid-connected converters, providing a new solution for stability testing of new power systems.

[0004] In a first aspect, the present invention provides a broadband oscillation monitoring device for grid-connected converters, comprising:

[0005] The system includes a disturbance voltage injection module, a response current measurement module, a converter impedance calculation module, a system stability and instability range generation module, a converter impedance and line impedance vector calculation module, a stability discrimination module, and a system oscillation analysis result transmission module.

[0006] The disturbance voltage injection module is connected to the grid connection point of the converter grid-connected system and the converter impedance calculation module, respectively. It is used to inject disturbance voltage into the grid connection point, induce the converter to generate response current, and send the injected disturbance voltage to the converter impedance calculation module.

[0007] The response current measurement module is connected to the grid connection point of the converter grid-connected system and the converter impedance calculation module, respectively. It is used to measure the response current generated by the injected disturbance voltage and send the measured response current to the converter impedance calculation module.

[0008] The converter impedance calculation module is connected to the disturbance voltage injection module, the response current measurement module, the system stable range and unstable range generation module, and the converter impedance and line impedance vector calculation module, respectively. It is used to receive disturbance voltage and response current, calculate the equivalent output impedance of the converter, and send the equivalent output impedance to the system stable range and unstable range generation module and the converter impedance and line impedance vector calculation module.

[0009] The system stability interval and instability interval generation module is connected to the converter impedance calculation module and the stability discrimination module, respectively. It is used to receive the equivalent output impedance, determine the system stability interval and instability interval information based on the equivalent output impedance, and send the system stability interval and instability interval information to the stability discrimination module.

[0010] The converter impedance and line impedance vector calculation module is connected to the converter impedance calculation module and the stability discrimination module, respectively, and is used to receive the equivalent output impedance and calculate the composite impedance phase based on the equivalent output impedance and the line impedance.

[0011] The stability discrimination module is connected to the converter impedance and line impedance vector calculation module, the system stable interval and unstable interval generation module, and the system oscillation analysis result transmission module, respectively. It is used to receive system stable interval and unstable interval information, synthesize impedance phase, obtain oscillation analysis results based on synthesized impedance phase, system stable interval and unstable interval information, and send the oscillation analysis results to the system oscillation analysis result transmission module.

[0012] The system oscillation analysis result transmission module is connected to both the stability discrimination module and the stability discrimination module, and is used to transmit the oscillation analysis results to the terminal.

[0013] Secondly, the present invention also provides a method for monitoring wideband oscillations in a grid-connected converter, comprising:

[0014] Step S1: Inject disturbance voltages of multiple frequencies into the grid connection point through the disturbance voltage injection module;

[0015] Step S2: The response current measurement module measures the response current at the corresponding frequency of the grid connection point output, and performs frequency domain decomposition on the response current to obtain the amplitude and phase of the response current.

[0016] Step S3: The converter impedance calculation module calculates the equivalent output impedance at each frequency based on the disturbance voltage, response current, and the amplitude and phase of the response current.

[0017] Step S4: The system stability and instability range generation module performs curve fitting using the least squares method based on the equivalent output impedance at each frequency to obtain the frequency domain curve of the converter output impedance; based on the frequency domain curve of the converter output impedance, it generates the stability range and the instability range.

[0018] Step S5: The converter impedance and line impedance vector calculation module synthesizes the equivalent output impedance and line impedance at each frequency to obtain the synthesized impedance phase.

[0019] Step S6: The stability discrimination module determines the range to which the synthesized impedance phase belongs. If the synthesized impedance phase is always within the stable range, the system remains stable, and step S1 is executed; if the synthesized impedance phase passes through the unstable range, the system will experience oscillation, and step S7 is executed.

[0020] Step S8: The system oscillation analysis result transmission module transmits the instability results to the terminal.

[0021] The converter impedance and line impedance vector calculation module synthesizes the equivalent output impedance and line impedance at each frequency to obtain the synthesized impedance phase, as shown in the following formula:

[0022] θ(f f = theta(Z) 1f (f f )+Z g (f f ));

[0023] Where, θ(f) f ) represents the phase of the combined impedance, f f For the frequency range where the impedance is negative, Z 1f (f f Z represents the equivalent output impedance at each frequency. g (f f ) represents the line impedance, and theta() is the phase calculation function.

[0024] The process of generating stable and unstable regions based on the frequency domain curve of the converter output impedance includes:

[0025] Based on the equivalent output impedance at each frequency and the line impedance, an equivalent model of the grid-connected current of the converter is constructed, and the expression is as follows:

[0026] I s =I1+ΔI1=I1+1 / (Z 1f (f f )+Z g (f f ))ΔV g ;

[0027] Where M = M1 + M2; M = I s M1=I1, M2=1 / (Z) 1f (f f )+Z g (f f ))ΔV g M represents the total current of the equivalent model, M1 represents the first branch current I1 of the equivalent model, M2 represents the second branch current ΔI1 of the equivalent model, I1 represents the power frequency current at the grid connection point, ΔI1 represents the disturbance current at the grid connection point, and Z represents the total current. 1f (ff Z represents the equivalent output impedance at each frequency. g (f f ) represents the line impedance, f f For the frequency range where the impedance is negative, ΔV g For grid connection point voltage disturbance;

[0028] If M increases while M2 decreases, or M decreases while M2 increases, then M and M2 mutually inhibit each other's changes, resulting in a stable region; if M and M2 increase or decrease simultaneously, then they cannot mutually inhibit each other, resulting in an unstable region.

[0029] Beneficial effects:

[0030] This application proposes a broadband oscillation monitoring device and method for grid-connected converters. Compared with existing impedance-based monitoring equipment that requires complex data processing, this device only needs to use simple vector addition operations to monitor the system's operating status. Compared with existing impedance-based monitoring equipment that may misjudge in some scenarios, this device is applicable not only to low-resistance and high-inductance line impedances, but also to high-resistance and low-inductance line impedances, as well as resistive-capacitive line impedances, thus having a wider range of applications and higher accuracy. Attached Figure Description

[0031] Figure 1 A schematic diagram of a grid-connected converter broadband oscillation monitoring device according to an embodiment of the present invention;

[0032] Figure 2 A flowchart of a broadband oscillation monitoring method for grid-connected converters according to an embodiment of the present invention;

[0033] Figure 3 A flowchart illustrating a method for monitoring wideband oscillations in a grid-connected converter according to an embodiment of the present invention. Detailed Implementation

[0034] The specific implementation methods of this application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0035] Example 1:

[0036] This embodiment provides a wideband oscillation monitoring device for grid-connected converters, such as... Figure 1 As shown, it includes:

[0037] The system includes a disturbance voltage injection module (module A), a response current measurement module (module B), a converter impedance calculation module (module C), a system stability and instability range generation module (module D), a converter impedance and line impedance vector calculation module (module E), a stability discrimination module (module F), and a system oscillation analysis result transmission module (module G).

[0038] The disturbance voltage injection module is connected to the grid connection point of the converter grid-connected system and the converter impedance calculation module, respectively. It is used to inject disturbance voltage into the grid connection point, induce the converter to generate response current, and send the injected disturbance voltage to the converter impedance calculation module.

[0039] The response current measurement module is connected to the grid connection point of the converter grid-connected system and the converter impedance calculation module, respectively. It is used to measure the response current generated by the injected disturbance voltage and send the measured response current to the converter impedance calculation module.

[0040] The converter impedance calculation module is connected to the disturbance voltage injection module, the response current measurement module, the system stable range and unstable range generation module, and the converter impedance and line impedance vector calculation module, respectively. It is used to receive disturbance voltage and response current, calculate the equivalent output impedance of the converter, and send the equivalent output impedance to the system stable range and unstable range generation module and the converter impedance and line impedance vector calculation module.

[0041] The system stability interval and instability interval generation module is connected to the converter impedance calculation module and the stability discrimination module, respectively. It is used to receive the equivalent output impedance, determine the system stability interval and instability interval information based on the equivalent output impedance, and send the system stability interval and instability interval information to the stability discrimination module.

[0042] The converter impedance and line impedance vector calculation module is connected to the converter impedance calculation module and the stability discrimination module, respectively, and is used to receive the equivalent output impedance and calculate the composite impedance phase based on the equivalent output impedance and the line impedance.

[0043] The stability discrimination module is connected to the converter impedance and line impedance vector calculation module, the system stable interval and unstable interval generation module, and the system oscillation analysis result transmission module, respectively. It is used to receive system stable interval and unstable interval information, synthesize impedance phase, obtain oscillation analysis results based on synthesized impedance phase, system stable interval and unstable interval information, and send the oscillation analysis results to the system oscillation analysis result transmission module.

[0044] The system oscillation analysis result transmission module is connected to both the stability discrimination module and the stability discrimination module, and is used to transmit the oscillation analysis results to the terminal.

[0045] In this embodiment, the A module has an A1 port and an A2 port. The A1 port is connected to the grid connection point of the converter grid connection system and is used to inject a disturbance voltage ΔV into the grid connection point to excite the converter to generate a response current ΔI. The A2 port is used to output the injected voltage disturbance information.

[0046] The B module has a B1 port and a B2 port. The B1 port is connected to the grid connection point of the converter grid connection system and is used to measure the response current ΔI generated by the injected disturbance voltage ΔV. The B2 port is used to output the measured current response information.

[0047] The C module has ports C1, C2, C3 and C4. Ports C1 and C2 are used to receive voltage disturbance information and current response information, respectively. This module is used to calculate the equivalent output impedance Z1 of the converter. Ports C3 and C4 are used to output the equivalent output impedance Z1 of the converter.

[0048] The D module has a D1 port and a D2 port, where the D1 port is used to receive the calculated impedance information and the D2 port is used to output the system stability range and instability range information obtained by the module.

[0049] The E module has an E1 port and an E2 port, where the E1 port is used to receive the calculated impedance information, and the E2 port is used to output the phase θ of the vector sum of the converter impedance Z1 and the line impedance Zg obtained by the module.

[0050] The F module has F1 port, F2 port and F3 port, wherein F1 port is used to receive information on the stable and unstable regions of the system, F2 port is used to receive information on the phase θ of the vector sum of the converter impedance Z1 and the line impedance Zg, and F3 port is used to output the oscillation analysis results.

[0051] The G module has a G1 port and a G2 port. The G1 port is used to receive the oscillation analysis results, and the G2 port is used to transmit the analysis results to the background to provide a basis for the next operation of the power staff.

[0052] The modules are connected as follows: Port A1 of module A is connected to the grid connection point of the converter grid-connected system, and port A2 is connected to port C1 of module C; Port B1 of module B is connected to the grid connection point of the converter grid-connected system, and port B2 is connected to port C2 of module C; Ports C3 and C4 of module C are connected to port D1 of module D and port E1 of module E, respectively; Port D2 of module D is connected to port F1 of module F; Port E2 of module E is connected to port F2 of module F; Port F3 of module F is connected to port G1 of module G, and port G2 is connected to the data backend.

[0053] Example 2:

[0054] This embodiment also provides a method for monitoring wideband oscillations in grid-connected converters, such as... Figure 2 , Figure 3 The following are included:

[0055] Step S1: Inject disturbance voltages of multiple frequencies into the grid connection point through the disturbance voltage injection module;

[0056] In this embodiment, multiple small disturbance voltage signals ΔV at frequencies (f1, f2, f3, ...) are injected into the grid connection point through a disturbance injection module. The amplitude of these voltage signals should not exceed the grid connection point voltage V. g 5% of the amplitude is used to generate the current response signal ΔI corresponding to the frequency (f1, f2, f3, ...). It should be noted that the disturbance voltage includes positive and negative sequence, and the current response also includes positive and negative sequence.

[0057] Step S2: The response current measurement module measures the response current at the corresponding frequency of the grid connection point output, and performs frequency domain decomposition on the response current to obtain the amplitude and phase of the response current.

[0058] In this embodiment, the response current measurement module outputs a current signal I to the grid connection point. g Measurements are performed, and the current signal output by the system is decomposed in the frequency domain using the FFT algorithm to obtain the amplitude |ΔI| and phase θ(ΔI) information of the current response signal ΔI at the frequency (f1,f2,f3,…) corresponding to the injected voltage disturbance signal ΔV, which is then used for impedance calculation.

[0059] Step S3: The converter impedance calculation module calculates the equivalent output impedance at each frequency based on the disturbance voltage, response current, and the amplitude and phase of the response current.

[0060] In this embodiment, the converter impedance calculation model C is combined with the voltage disturbance signal ΔV=|ΔV|e in step S1. j θ(ΔV) And the current response signal ΔI=|ΔI|e in step S2 jθ(ΔI) Calculate the impedance information at each frequency (f1, f2, f3, ...). The specific calculation formula is: Z1 = -ΔV / ΔI = -|ΔV|e jθ(ΔV) / |ΔI|e jθ(ΔI) The impedance also includes positive and negative sequence, where Z1 is the equivalent output impedance at each frequency.

[0061] Step S4: The system stability and instability range generation module performs curve fitting using the least squares method based on the equivalent output impedance at each frequency to obtain the frequency domain curve of the converter output impedance; based on the frequency domain curve of the converter output impedance, it generates the stability range and the instability range.

[0062] In this embodiment, the impedance points (f1, f2, f3, ...) at each frequency point are curve-fitted using the least squares method to obtain the frequency domain curve Z1(f) of the converter output impedance, while retaining the frequency range Z where the impedance is negative. 1f (ff ), where f f This refers to the frequency range where the impedance is negative.

[0063] In this embodiment, the system stable range and unstable range generation module D is based on the obtained converter output impedance frequency domain curve Z. 1f (f f The system executes a method to generate stable and unstable operating intervals, generating positive-sequence stable intervals, positive-sequence unstable intervals, negative-sequence stable intervals, and negative-sequence unstable intervals.

[0064] Step S5: The converter impedance and line impedance vector calculation module synthesizes the equivalent output impedance and line impedance at each frequency to obtain the synthesized impedance phase.

[0065] In this embodiment, the vector calculation model E for converter impedance and line impedance is based on the converter output impedance Z obtained in step 4. 1f (f f The system synthesizes the impedance with the known line impedance, calculates the phase of the synthesized impedance, including the positive sequence phase and the negative sequence phase, and thus obtains the phase information of the synthesized impedance.

[0066] The converter impedance and line impedance vector calculation module synthesizes the equivalent output impedance and line impedance at each frequency to obtain the synthesized impedance phase, as shown in the following formula:

[0067] θ(f f = theta(Z) 1f (f f )+Z g (f f ));

[0068] Where, θ(f) f ) represents the phase of the combined impedance, f f For the frequency range where the impedance is negative, Z 1f (f f Z represents the equivalent output impedance at each frequency. g (f f ) represents the line impedance, and theta() is the phase calculation function.

[0069] Step S6: The stability discrimination module determines the range to which the synthesized impedance phase belongs. If the synthesized impedance phase is always within the stable range, the system remains stable, and step S1 is executed; if the synthesized impedance phase passes through the unstable range, the system will experience oscillation, and step S7 is executed.

[0070] In this embodiment, the stability discrimination module determines the location of the calculated system synthesized phase at θ(f) fWithin the range of f, stability is determined and oscillation frequency band information is obtained, and the stability determination result is output; if the system synthesizes phase θ(f) f If the system remains within the stable interval, then the system remains stable, and step S1 is executed; if the synthesized phase θ(f) of the system remains within the stable interval, then the system remains stable. f If the system passes through the instability region, it will oscillate. This determination process needs to be applied to both the positive-sequence impedance phase and the negative-sequence impedance phase. Then, step S7 is executed.

[0071] Step S8: The system oscillation analysis result transmission module transmits the instability results to the terminal.

[0072] In this embodiment, the instability results, including information such as the oscillation frequency band, are transmitted to the backend (i.e., the terminal) through the system oscillation analysis result transmission module, providing power workers with a basis for the next step of operation.

[0073] The process of generating stable and unstable regions based on the frequency domain curve of the converter output impedance includes:

[0074] Based on the equivalent output impedance at each frequency and the line impedance, an equivalent model of the grid-connected current of the converter is constructed, and the expression is as follows:

[0075] I s =I1+ΔI1=I1+1 / (Z 1f (f f )+Z g (f f ))ΔV g ;

[0076] Where M = M1 + M2; M = I s M1=I1, M2=1 / (Z) 1f (f f )+Z g (f f ))ΔV g M represents the total current of the equivalent model, M1 represents the first branch current I1 of the equivalent model, M2 represents the second branch current ΔI1 of the equivalent model, I1 represents the power frequency current at the grid connection point, ΔI1 represents the disturbance current at the grid connection point, and Z represents the total current. 1f (f f Z represents the equivalent output impedance at each frequency. g (f f ) represents the line impedance, f f For the frequency range where the impedance is negative, ΔV g For grid connection point voltage disturbance;

[0077] If M increases while M2 decreases, or M decreases while M2 increases, then M and M2 mutually inhibit each other's changes, resulting in a stable region; if M and M2 increase or decrease simultaneously, then they cannot mutually inhibit each other, resulting in an unstable region.

[0078] In this embodiment, the stable and unstable regions are obtained based on the dynamic evolution relationship between the current disturbance signal and the fundamental frequency current signal. Further, the stable and unstable regions of the system are obtained using the interaction relationship between M and M2. If M and M2 mutually inhibit each other's changes, a stable region is obtained; otherwise, an unstable region is obtained. M1 is a constant value, and M2 contains (1 / (Z...)... 1f (f f )+Z g (f f The value changes with the current. Combined with 1 / (Z) 1f (f f )+Z g (f f By analyzing the variation of current, the interaction between M and M2 is determined, and thus, the relationship between Z and M2 is obtained. 1f (f f ) and Z g (f f Vector synthesis phase θ(f) f The stable and unstable regions are distinguished by differentiating them; the methods for generating the stable and unstable regions for positive-sequence and negative-sequence phases are the same.

[0079] The device in this embodiment is applicable to various types of line impedance (resistive-inductive or resistive-capacitive). When performing vector synthesis calculations of converter output impedance and line impedance, the line impedance is expressed as Z. g (f f )=R g +jX g (f f Its phase is located in the interval [-90°, 90°], and it is related to the line impedance vector Z. 1f (f f (The interval is [-180°, -90°]) Calculate the composite θ(f) f = theta(Z) 1f (f f )+Z g (f f After )), phase θ(f f The range () may be located anywhere in the planar coordinate system, i.e., [-180°, 180°]. The range generated by the stability range generation module is a combination of 1 / (Z) 1f (f f )+Z g (f fThe range obtained is [-180°, 180°]. Therefore, stability can be determined regardless of the position of the phase of the system's synthesized impedance, and there is no possibility of missed or false judgments; both positive and negative sequences need to be distinguished.

[0080] The device can predict the oscillation frequency range of the system, when θ(f) f Within a certain frequency range f fs When the inner part passes through the instability region, f fs For θ(f) f The frequency band that passes through the instability region, f fs θ(f) in the frequency band fs This implies the possibility of oscillation occurring, i.e., in f fs Within this frequency band, A and A2 cannot suppress each other's variations. This frequency band f fs This refers to the interval where the system has the risk of oscillation, including the frequency bands corresponding to the positive sequence and the frequency bands corresponding to the negative sequence.

[0081] The various embodiments in this application are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0082] The scope of protection of this application is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from the scope and spirit of this disclosure. If such modifications and variations fall within the scope of equivalent technology of this disclosure, then the intent of this disclosure also includes such modifications and variations.

Claims

1. A broadband oscillation monitoring device for grid-connected converters, characterized in that, include: The system includes a disturbance voltage injection module, a response current measurement module, a converter impedance calculation module, a system stability and instability range generation module, a converter impedance and line impedance vector calculation module, a stability discrimination module, and a system oscillation analysis result transmission module. The disturbance voltage injection module is connected to the grid connection point of the converter grid-connected system and the converter impedance calculation module, respectively. It is used to inject disturbance voltage into the grid connection point, induce the converter to generate response current, and send the injected disturbance voltage to the converter impedance calculation module. The response current measurement module is connected to the grid connection point of the converter grid-connected system and the converter impedance calculation module, respectively. It is used to measure the response current generated by the injected disturbance voltage and send the measured response current to the converter impedance calculation module. The converter impedance calculation module is connected to the disturbance voltage injection module, the response current measurement module, the system stable range and unstable range generation module, and the converter impedance and line impedance vector calculation module, respectively. It is used to receive disturbance voltage and response current, calculate the equivalent output impedance of the converter, and send the equivalent output impedance to the system stable range and unstable range generation module and the converter impedance and line impedance vector calculation module. The system stability interval and instability interval generation module is connected to the converter impedance calculation module and the stability discrimination module, respectively. It is used to receive the equivalent output impedance, determine the system stability interval and instability interval information based on the equivalent output impedance, and send the system stability interval and instability interval information to the stability discrimination module. The converter impedance and line impedance vector calculation module is connected to the converter impedance calculation module and the stability discrimination module, respectively, and is used to receive the equivalent output impedance and calculate the composite impedance phase based on the equivalent output impedance and the line impedance. The stability discrimination module is connected to the converter impedance and line impedance vector calculation module, the system stable interval and unstable interval generation module, and the system oscillation analysis result transmission module, respectively. It is used to receive system stable interval and unstable interval information, synthesize impedance phase, obtain oscillation analysis results based on synthesized impedance phase, system stable interval and unstable interval information, and send the oscillation analysis results to the system oscillation analysis result transmission module. The system oscillation analysis result transmission module is connected to both the stability discrimination module and the stability discrimination module, and is used to transmit the oscillation analysis results to the terminal.

2. A method for monitoring broadband oscillations in a grid-connected converter, implemented using the broadband oscillation monitoring device for a grid-connected converter as described in claim 1, characterized in that, include: Step S1: Inject disturbance voltages of multiple frequencies into the grid connection point through the disturbance voltage injection module; Step S2: The response current measurement module measures the response current at the corresponding frequency of the grid connection point output, and performs frequency domain decomposition on the response current to obtain the amplitude and phase of the response current. Step S3: The converter impedance calculation module calculates the equivalent output impedance at each frequency based on the disturbance voltage, response current, and the amplitude and phase of the response current. Step S4: The system stability and instability range generation module performs curve fitting using the least squares method based on the equivalent output impedance at each frequency to obtain the frequency domain curve of the converter output impedance; based on the frequency domain curve of the converter output impedance, it generates the stability range and the instability range. Step S5: The converter impedance and line impedance vector calculation module synthesizes the equivalent output impedance and line impedance at each frequency to obtain the synthesized impedance phase. Step S6: The stability discrimination module determines the range to which the synthesized impedance phase belongs. If the synthesized impedance phase is always within the stable range, the system remains stable, and step S1 is executed; if the synthesized impedance phase passes through the unstable range, the system will experience oscillation, and step S7 is executed. Step S8: The system oscillation analysis result transmission module transmits the instability results to the terminal.

3. The method for monitoring wideband oscillations in a grid-connected converter according to claim 2, characterized in that, The converter impedance and line impedance vector calculation module synthesizes the equivalent output impedance and line impedance at each frequency to obtain the synthesized impedance phase, as shown in the following formula: θ(f f )= theta(Z 1f (f f )+Z g (f f )); Where, θ(f) f ) represents the phase of the combined impedance, f f For the frequency range where the impedance is negative, Z 1f (f f Z represents the equivalent output impedance at each frequency. g (f f ) represents the line impedance, and theta() is the phase calculation function.

4. The method for monitoring wideband oscillations in a grid-connected converter according to claim 2, characterized in that, The process of generating stable and unstable regions based on the frequency domain curve of the converter output impedance includes: Based on the equivalent output impedance at each frequency and the line impedance, an equivalent model of the converter's grid-connected current is constructed, as shown in the following expression: I s =I1+ΔI1=I1+1 / (Z 1f (f f )+Z g (f f ))ΔV g ; Where M = M1 + M2; M = I s M1=I1, M2=1 / (Z) 1f (f f )+Z g (f f ))ΔV g M represents the total current of the equivalent model, M1 represents the first branch current I1 of the equivalent model, M2 represents the second branch current ΔI1 of the equivalent model, I1 represents the power frequency current at the grid connection point, ΔI1 represents the disturbance current at the grid connection point, and Z represents the total current. 1f (f f Z represents the equivalent output impedance at each frequency. g (f f ) represents the line impedance, f f For the frequency range where the impedance is negative, ΔV g For grid connection point voltage disturbance; If M increases while M2 decreases, or M decreases while M2 increases, then M and M2 mutually inhibit each other's changes, resulting in a stable region; if M and M2 increase or decrease simultaneously, then they cannot mutually inhibit each other, resulting in an unstable region.

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