A method for suppressing parallel oscillation of grid-forming and grid-following converters and related devices

Abstract

This invention discloses a method and related device for suppressing oscillations in parallel connection of grid-connected and grid-connected converters, belonging to the field of power grid control technology. The method includes: establishing a system model of a grid, grid-connected converters, and grid-connected converters in parallel connection according to the current grid connection scenario; constructing a sequence impedance model of the grid-connected converter based on the control model of the grid-connected converter; introducing a voltage outer loop bandwidth parameter and constructing a sequence impedance model of the grid-connected converter based on the control model of the grid-connected converter; calculating the equivalent aggregate impedance of the system at the grid connection point based on the sequence impedance models of the grid-connected and grid-connected converters, and establishing a stability criterion based on the real part of the equivalent aggregate impedance; and adjusting the impedance characteristics at the grid connection point by adjusting the voltage outer loop bandwidth parameter of the grid-connected converter according to the stability criterion, so that the positive resistance characteristic of the grid-connected converter cancels the negative damping of the grid-connected converter, thereby achieving oscillation suppression of the parallel connection of grid-connected and grid-connected converters.

Description

Technical Field

[0001] This invention belongs to the field of power grid control technology, and particularly relates to a method and related device for suppressing parallel oscillations of grid-connected and grid-following converters. Background Technology

[0002] With the advancement of the "dual carbon" target, the proportion of new energy sources, represented by wind power and photovoltaics, in the power system is increasing. Traditional grid-following (GFL) converters typically rely on phase-locked loops (PLLs) to control the power grid voltage phase. However, existing research shows that under weak grid conditions, the PLL of the GFL converter introduces negative damping characteristics, making it highly susceptible to coupling with the grid impedance and triggering sub-synchronous oscillations (SSOs), which seriously threaten the safe and stable operation of the system.

[0003] Grid-Forming (GFM) converters, due to their ability to construct voltage and frequency, are considered a key technology for improving the stability of high-proportion renewable energy systems. Existing research also shows that GFM converters exhibit "positive resistance" characteristics in the subsynchronous / supersynchronous frequency band, which can mitigate the negative damping introduced by GFL converters. However, current mechanistic analyses are mostly qualitative, lacking a precise quantitative description of the relationship between the key control parameter of GFM, the outer loop bandwidth of voltage, and the overall impedance characteristics of the system.

[0004] In practical engineering, how to establish an accurate mathematical model to quantify the impedance reshaping effect of GFM on GFL based on specific grid connection scenarios, and how to eliminate oscillations by setting control parameters, is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and related device for suppressing parallel oscillations of grid-connected and grid-following converters. By combining the physical mechanism of GFM oscillation suppression with an accurate sequence impedance mathematical model, the system impedance characteristics at the grid connection point are reshaped by adjusting the voltage outer loop bandwidth of GFM, thereby ensuring the stability of the parallel system.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0007] In a first aspect, the present invention provides a method for suppressing parallel oscillations of grid-type and grid-following converters, comprising:

[0008] A parallel system model is established based on the current grid connection scenario. The parallel system model includes the grid, grid-connected converters and grid-linked converters connected in parallel, as well as the control models of grid-linked converters and grid-connected converters. The control model of the grid-connected converter includes the voltage outer loop.

[0009] Based on the small-signal linearization analysis of the phase-locked loop, a sequence impedance model of the grid converter is constructed according to the control model of the grid converter; wherein, the sequence impedance model of the grid converter characterizes the output impedance of the grid converter in the positive sequence coordinate system.

[0010] Based on the impedance characteristic analysis dominated by the voltage outer loop, the voltage outer loop bandwidth parameter is introduced, and the sequence impedance model of the grid converter is constructed according to the control model of the grid converter; wherein, the sequence impedance model of the grid converter characterizes the output impedance of the grid converter in the positive sequence coordinate system.

[0011] Based on the sequence impedance models of grid-connected converters and grid-connected converters, the equivalent aggregate impedance of the system at the grid connection point is calculated, and a stability criterion based on the real part of the equivalent aggregate impedance is established. The grid connection point is the intersection of the grid, grid-connected converters, and grid-connected converters connected in parallel in the parallel system model.

[0012] Based on the stability criterion, the voltage outer loop bandwidth parameter of the grid converter is adjusted to adjust the impedance characteristics of the grid connection point, so that the positive resistance characteristics of the grid converter compensate for the negative damping effect of the grid converter.

[0013] Optionally, a parallel system model is established based on the current grid connection scenario, including:

[0014] Determine the short-circuit capacity ratio of the power grid and calculate the power grid impedance;

[0015] The outer power loop bandwidth and inner current loop bandwidth of the grid-connected converter are determined based on the grid impedance. The outer power loop PI parameters and inner current loop PI parameters of the grid-connected converter are then tuned using these bandwidths.

[0016] ,

[0017] ,

[0018] ,

[0019] ,

[0020] ,

[0021] ,

[0022] in, and To match the current loop PI parameters of the grid-connected converter, To match the inner loop bandwidth of the current in a grid-type converter. This refers to the angular frequency corresponding to the inner loop bandwidth of the grid converter current. To match the filter inductor of the grid-type converter, To match the equivalent series resistance of the filter inductor coil in the grid converter, and To match the power loop PI parameters of the grid-connected converter, To match the power outer loop bandwidth of the grid converter, The angular frequency corresponding to the outer loop bandwidth of the grid converter's power circuit. The voltage component along the d-axis;

[0023] A dual closed-loop control model for a grid-connected converter, from the power outer loop to the current inner loop, is established; wherein, the reference value of the output current of the power outer loop of the grid-connected converter is... , As the inner loop current input of the grid-connected converter;

[0024] The bandwidth of the grid-connected converter's current inner loop is determined based on the grid impedance, and the PI parameters of the grid-connected converter's current inner loop are then tuned using this bandwidth.

[0025] ,

[0026] ,

[0027] ,

[0028] in, The bandwidth of the inner current loop for a grid-type converter. This refers to the angular frequency corresponding to the inner current loop bandwidth of a grid-type converter. , The PI parameters for the inner current loop of a grid-type converter. For filtering inductors in grid-type converters;

[0029] The initial bandwidth of the outer voltage loop of the grid-type converter is set, and the initial PI parameters of the outer voltage loop are calculated from the initial bandwidth and the quantitative relationship between the outer voltage loop PI parameters and the bandwidth:

[0030] ,

[0031] ,

[0032] ,

[0033] in, This refers to the initial bandwidth of the outer voltage loop of a grid-type converter. The angular frequency corresponding to the initial bandwidth of the outer voltage loop of the grid-type converter. , The initial PI parameters for the outer voltage loop of the grid-type converter. For filtering capacitors in grid-type converters;

[0034] A dual closed-loop control model for a grid-type converter, from the outer voltage loop to the inner current loop, is established; wherein, the reference value of the output current of the outer voltage loop of the grid-type converter is used as the input of the inner current loop of the grid-type converter.

[0035] Optionally, the small-signal linearization analysis based on the phase-locked loop (PLL) involves constructing a sequence impedance model for the grid-connected converter based on the control model of the grid-connected converter, including:

[0036] Substituting the power outer-loop PI parameters and current inner-loop PI parameters of the grid-connected converter into the dual-closed-loop control model of the grid-connected converter, we obtain the closed-loop transfer function of the current inner loop and the open-loop transfer function of the power outer loop:

[0037] ,

[0038] ,

[0039] in, To provide the closed-loop transfer function of the inner current loop of the grid-type converter. To obtain the open-loop transfer function of the outer power loop of the grid converter, For frequency variables;

[0040] A small-signal model of the phase-locked loop (PLL) is established, and the open-loop transfer function of the PLL and the relationship between phase perturbation and q-axis voltage perturbation are obtained:

[0041] ,

[0042] in, To obtain the open-loop transfer function of the phase-locked loop of the grid converter. For phase perturbation, This refers to the q-axis voltage perturbation. This represents the steady-state amplitude of the grid voltage.

[0043] Based on the closed-loop transfer function of the current inner loop, the open-loop transfer function of the power outer loop, and the open-loop transfer function of the phase-locked loop, the admittance matrix of the grid-type converter in the dq rotating coordinate system is derived.

[0044] Based on the frequency mapping principle, the admittance matrix in the dq rotating coordinate system is mapped to the positive sequence coordinate system to establish the sequence impedance model of the grid converter:

[0045] ,

[0046] in, To compare the output impedance of the grid converter in the positive sequence coordinate system, To determine the admittance of the grid converter in the positive sequence coordinate system, DC side voltage For reference current value, The imaginary unit, It is the power frequency angular frequency.

[0047] Optionally, the impedance characteristic analysis based on the voltage outer loop introduces the voltage outer loop bandwidth parameter and constructs a sequence impedance model for the grid-type converter based on the control model of the grid-type converter, including:

[0048] Substituting the initial PI parameters of the outer voltage loop and the inner current loop into the dual closed-loop control model of the grid converter, we obtain the closed-loop transfer function of the inner current loop and the open-loop transfer function of the outer voltage loop:

[0049] ,

[0050] ,

[0051] in, This is the closed-loop transfer function for the inner current loop of a grid-type converter. The open-loop transfer function of the outer voltage loop of the grid-type converter. For frequency variables;

[0052] Establish the motion equations of the virtual synchronous machine rotor and obtain the virtual admittance:

[0053] ,

[0054] in, For virtual admittance, For virtual inertia, For virtual damping;

[0055] Based on the open-loop transfer function of the outer voltage loop, the closed-loop transfer function of the inner current loop, and the virtual admittance, the equivalent impedance of the grid converter in the dq rotating coordinate system is derived:

[0056] ,

[0057] in, The output impedance of the grid-type converter in the dq rotating coordinate system;

[0058] Based on the frequency mapping principle, the equivalent impedance in the dq rotating coordinate system is mapped to the positive sequence coordinate system to obtain the positive sequence output impedance of the grid converter:

[0059] ,

[0060] in, The output impedance of the grid-type converter in the positive sequence coordinate system. The imaginary unit, It is the power frequency angular frequency.

[0061] Optionally, the calculation of the system equivalent aggregate impedance at the grid connection point based on the sequence impedance model of the grid-connected converter and the sequence impedance model of the grid-connected converter includes:

[0062] By equating the output impedance of the grid-connected converter in the positive sequence coordinate system to the Norton model, the equivalent current source and equivalent parallel impedance of the grid-connected converter are obtained.

[0063] The output impedance of the grid converter in the positive sequence coordinate system is equivalent to the Thevenin model, and the equivalent voltage source and equivalent series impedance of the grid converter are obtained.

[0064] By equating the power grid to the Thevenin model, we obtain the equivalent voltage source and the equivalent series impedance of the power grid.

[0065] Based on the equivalent series impedance of the parallel grid-connected converters and the equivalent series impedance of the power grid, the equivalent impedance on the system side is obtained:

[0066] ,

[0067] in, The equivalent impedance on the system side. This is the equivalent series impedance of the power grid;

[0068] The equivalent aggregate impedance of the system at the grid connection point is obtained by comparing the equivalent impedance of the system side with the equivalent parallel impedance of the grid-connected converter.

[0069] Optionally, establishing a stability criterion based on the real part of the system's equivalent aggregate impedance includes: using whether the sum of the real part of the system-side equivalent impedance and the real part of the equivalent parallel impedance of the grid-connected converter is greater than zero as the stability criterion for the parallel system under the current bandwidth parameters.

[0070] ,

[0071] in, This represents the real part of the system-side equivalent impedance. This is the real part of the equivalent parallel impedance of the grid converter.

[0072] Optionally, adjusting the grid connection point impedance characteristics by setting the outer loop bandwidth parameter of the grid-connected converter according to the stability criterion includes:

[0073] If the parallel system does not meet the stability criterion under the current grid-type converter voltage outer loop bandwidth parameters, iteratively execute the following steps until the stability criterion is met:

[0074] The target bandwidth is set according to the voltage outer loop bandwidth parameters of the current grid-type converter; the target bandwidth is greater than twice the angular frequency corresponding to the subsynchronous oscillation frequency of the current parallel system, and is far away from the switching frequency;

[0075] Based on the quantitative relationship between the voltage outer loop PI parameters and the voltage outer loop bandwidth parameters of the grid-type converter, the voltage outer loop PI parameters after tuning are calculated according to the target bandwidth.

[0076] Update the output impedance of the grid converter in the positive sequence coordinate system based on the adjusted outer loop PI parameters of the voltage.

[0077] Update the system equivalent aggregate impedance based on the updated output impedance;

[0078] Based on the updated system equivalent aggregate impedance, verify whether the parallel system under the current grid-type converter voltage outer loop bandwidth parameters meets the stability criterion.

[0079] Secondly, the present invention provides a parallel oscillation suppression device for grid-type and grid-connected converters, comprising:

[0080] Parallel System Model Construction Module: Used to build a parallel system model based on the current grid connection scenario; the parallel system model includes the grid connected in parallel, grid-connected converters and grid-linked converters, as well as the control models of grid-connected converters and grid-connected converters; the control model of grid-connected converters includes the voltage outer loop;

[0081] The grid-connected converter sequence impedance model construction module is used for small-signal linearization analysis based on phase-locked loops. It constructs the grid-connected converter sequence impedance model based on the control model of the grid-connected converter. The grid-connected converter sequence impedance model characterizes the output impedance of the grid-connected converter in the positive sequence coordinate system.

[0082] The sequence impedance model construction module for grid-type converters is used for impedance characteristic analysis based on the voltage outer loop. It introduces the voltage outer loop bandwidth parameter and constructs the sequence impedance model of the grid-type converter according to the control model of the grid-type converter. The sequence impedance model of the grid-type converter characterizes the output impedance of the grid-type converter in the positive sequence coordinate system.

[0083] Stability criterion construction module: used to calculate the system equivalent aggregate impedance at the grid connection point based on the sequence impedance model of the grid-connected converter and the sequence impedance model of the grid-connected converter, and to establish a stability criterion based on the real part of the system equivalent aggregate impedance; where the grid connection point is the intersection point of the grid, the grid-connected converter and the grid-connected converter in the parallel system model.

[0084] Parallel oscillation suppression module: Used to adjust the grid connection point impedance characteristics by setting the voltage outer loop bandwidth parameter of the grid converter according to stability criteria, so that the positive resistance characteristics of the grid converter compensate for the negative damping effect of the grid converter.

[0085] Thirdly, the present invention provides a computer storage medium storing a computer program thereon, which, when executed by a processor, implements the parallel oscillation suppression method for grid-type and grid-following converters as described in any one of the first aspects.

[0086] Fourthly, the present invention provides an electronic terminal, including a processor and a memory connected to the processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the steps of the parallel oscillation suppression method for grid-type and grid-connected converters as described in any one of the first aspects are performed.

[0087] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: Based on small-signal linearization analysis, the sequence impedance expressions of the GFL converter and the GFM converter in the parallel system are derived, the negative resistance characteristic data of the GFL is quantified, the equivalent aggregate impedance of the system at the grid connection point is calculated, and the system stability is evaluated using the stability criterion based on the real part of the impedance. Finally, the voltage outer loop bandwidth parameter of the GFM converter is adjusted through the quantitative relationship of the bandwidth parameter, so that it exhibits a lower output impedance and stronger voltage rigidity at the subsynchronous oscillation frequency, providing sufficient positive resistance to offset the negative damping introduced by the GFL converter, effectively weakening the negative damping coupling effect introduced by the GFL converter phase-locked loop under weak grid conditions, significantly shortening the active power oscillation decay time, enabling rapid return to steady state, accurately suppressing the resonant components of the parallel system in a specific frequency band, reducing the risk of subsynchronous / supersynchronous instability, and ensuring the safe and stable operation of the parallel system. Attached Figure Description

[0088] Figure 1 The diagram shown is a flowchart of a method for suppressing oscillations in parallel connection of grid-type and grid-following-type converters according to an embodiment of the present invention.

[0089] Figure 2 The diagram shown is a parallel system model architecture diagram in one embodiment of the present invention;

[0090] Figure 3 The diagram shown is a schematic diagram of the PCC point current spectrum when the bandwidth is low in one embodiment of the present invention.

[0091] Figure 4 The figure shown is a schematic diagram of the PCC point current spectrum when the bandwidth is increased in one embodiment of the present invention.

[0092] Figure 5The diagram shown is a power waveform diagram when the bandwidth is low in one embodiment of the present invention. Detailed Implementation

[0093] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0094] Example 1

[0095] This embodiment proposes a method for suppressing parallel oscillations of grid-type and grid-following converters. For a parallel system containing a grid-type GFM converter and a grid-following GFL converter, it explains how to quantitatively suppress subsynchronous / supersynchronous oscillations through sequence impedance modeling, aggregated impedance analysis, and voltage loop bandwidth tuning. Figure 1 As shown, the method includes the following steps:

[0096] S1. Construct a hybrid power grid system architecture and control model: Collect basic data such as grid impedance, converter rated capacity, and filter parameters, establish a parallel system model including an infinite grid, GFM converter, and GFL converter, and clarify the control strategy and reference parameters of each converter.

[0097] S2, Constructing the sequence impedance model of the grid converter: Based on the small-signal linearization analysis of the phase-locked loop, derive the output impedance of the GFL converter in the positive sequence coordinate system and quantify its negative resistance characteristics in a specific frequency band.

[0098] S3. Constructing the sequence impedance model of the grid-type converter: Based on the impedance characteristic analysis dominated by the voltage outer loop, the voltage loop bandwidth parameter is introduced to derive the accurate impedance expression of the GFM converter in the positive sequence coordinate system.

[0099] S4. Constructing the system aggregate impedance model and stability criterion: Based on Thevenin and Norton's equivalent theorem, calculate the system equivalent aggregate impedance at the point of common coupling (PCC) and establish a stability criterion based on the real part of the impedance.

[0100] S5, Voltage Loop Bandwidth Setting and Oscillation Suppression: Based on the stability criterion, the GFM control model is updated by setting the outer loop bandwidth parameter of the GFM voltage, and the impedance characteristics of the PCC point are reshaped to offset the negative damping of the GFL with the positive resistance characteristics of the GFM.

[0101] S1 specifically includes:

[0102] S11, Establishment of the control model for the grid converter: In the abc three-phase stationary coordinate system, the active power on the system side... and reactive power The instantaneous power equation is:

[0103] ,

[0104] ,

[0105] in, , , , , , These represent the three-phase voltages and currents, a, b, and c, respectively.

[0106] Transforming the coordinate system into a dq rotating coordinate system via the inverse Park transform, to ensure that the d-axis component of the grid-side voltage is aligned with the direction of the grid-side voltage vector, let the q-axis component of the grid-side voltage be... ,get:

[0107] ,

[0108] ,

[0109] in, Let be the active power on the grid side in the dq coordinate system. Let be the reactive power on the grid side in the dq coordinate system. The inverter-side d-axis voltage component. This represents the d-axis current component on the inverter side. This represents the q-axis current component on the inverter side.

[0110] Because the grid side is connected to an infinitely large power grid, its voltage is constant, that is... It remains unchanged, so we only need to... Adjusting the inverter allows you to regulate its output active power; similarly, you only need to adjust the... By making adjustments, the reactive power output of the inverter can be regulated.

[0111] If you want to control the d-axis voltage component on the grid side and grid-side q-axis voltage component If the control of the d-axis and q-axis is coupled, it will be difficult to design the controller. However, the decoupled dq-axis equation is only related to the d-axis or q-axis alone. Therefore, the feedforward decoupling method is used to reduce the difficulty of controller design.

[0112] In this embodiment, the voltage outer loop in the VSC basic control method is replaced with a P control loop, and a Q control loop is added to the q-axis current control. A grid-connected converter dual closed-loop control model is established from the power outer loop to the current inner loop, and the current inner loop adopts feedforward decoupling control.

[0113] Ignoring the sampling delay of the inner current loop signal and the small inertia of PWM control, the current loop structure is shown in the figure above.

[0114] Therefore, the open-loop function of the inner current loop is:

[0115] ,

[0116] in, To determine the open-loop transfer function of the inner current loop of the grid converter. and To match the current loop PI parameters of the grid-connected converter, For frequency variables, To match the filter inductor of the grid-type converter, This is the equivalent series resistance of the filter inductor coil in a grid-type converter;

[0117] The closed-loop transfer function of the inner current loop is:

[0118] ,

[0119] in, This is the closed-loop transfer function of the inner current loop of the grid-type converter.

[0120] Determine the short-circuit capacity ratio of the power grid and calculate the power grid impedance. Determine the inner current loop bandwidth based on the grid impedance. The proportional-integral (PI) parameter of the current inner loop is tuned by the current inner loop bandwidth. If the current inner loop bandwidth is set... The PI controller parameters for the current loop are tuned as follows:

[0121] ,

[0122] ,

[0123] ,

[0124] in, To match the inner loop bandwidth of the current in a grid-type converter. This refers to the angular frequency corresponding to the inner loop bandwidth of the grid converter current. The value here is 0.001. The value here is 0.375.

[0125] Substituting the above parameters into the characteristic equation, we obtain: Therefore, the two characteristic roots are s1=-628.5 and s2=-3755, so the system is stable.

[0126] Simplifying the transfer function of the inner current loop into a first-order inertial element, the controlled function of the outer power loop is:

[0127] ,

[0128] in, is the controlled function of the power outer loop;

[0129] The open-loop transfer function of the power outer loop is:

[0130] ,

[0131] in, This is the open-loop transfer function for the outer power loop of the grid-type converter.

[0132] Determine the power outer loop bandwidth based on grid impedance. The power outer loop PI parameters are tuned by the power outer loop bandwidth. The PI controller parameters for the power outer loop are tuned as follows:

[0133] ,

[0134] ,

[0135] ,

[0136] in, and To match the power loop PI parameters of the grid-connected converter, To match the power outer loop bandwidth of the grid converter, This refers to the angular frequency corresponding to the outer power loop bandwidth of the grid-connected converter. It also refers to the reference value of the outer power loop output current of the grid-connected converter. , As the input for the inner current loop.

[0137] S12, Establish a dual-closed-loop control model for the grid-type converter, from the outer voltage loop to the inner current loop, with the outer voltage loop output current reference value as follows: , As the inner current loop input, establish the voltage equation for the inductor branch and the current equation for the capacitor branch:

[0138] ,

[0139] ,

[0140] in, For the filter inductor of the grid converter, For filtering capacitors in grid-type converters, The three-phase current on the inverter side. For the three-phase current on the grid side, This refers to the three-phase AC output voltage on the grid side. This refers to the three-phase AC output voltage on the inverter side.

[0141] The dynamic equations of voltage and current in the dq coordinate system are obtained through coordinate transformation:

[0142] ,

[0143] ,

[0144] in, This refers to the q-axis voltage component on the inverter side. The angular frequency corresponding to the target frequency of the droop control output. The d-axis current component on the grid side. This represents the q-axis current component on the grid side.

[0145] Virtual Synchronous Generator (VSG) control mainly simulates the mechanical characteristics of a synchronous generator, i.e., the rotor motion equation, and then derives the angular frequency of the system. The amplitude of the output voltage is then obtained through reactive power-voltage droop control. The two are combined to obtain the reference three-phase AC output voltage.

[0146] First, the rotor motion equations are given:

[0147] ,

[0148] in, For virtual rotational inertia, The angular frequency corresponding to the rated frequency. For virtual damping, and These are virtual mechanical torque and virtual electromagnetic torque, respectively.

[0149] ,

[0150] in, For virtual mechanical power, Electromagnetic power;

[0151] Virtual mechanical power Determined by the active-frequency droop characteristic:

[0152] ,

[0153] in, Set the active power output value for the VSG. This is the droop factor, which is approximated here as the droop factor in the active-frequency droop. The reciprocal of, that is Virtual moment of inertia Take 3 kg·m², damping coefficient Take 100 N·m·s / rad.

[0154] because Combining the above VSG control-related formulas, we obtain:

[0155] ,

[0156] in, This refers to the rated active power.

[0157] The specific formula for droop control is given below:

[0158] Active power-frequency (pf) droop formula:

[0159] ,

[0160] in, PF droop coefficient This represents the actual active power output by the inverter.

[0161] Reactive power-voltage (QV) droop formula:

[0162] ,

[0163] in, The magnitude of the target voltage output for droop control. This is the rated voltage amplitude. This is the QV droop coefficient. This represents the actual reactive power output of the inverter. This is the rated reactive power.

[0164] From the above, we can obtain the expression for the droop coefficient:

[0165] .

[0166] The reference three-phase AC output voltage is obtained through the above analysis, and then the reference inverter-side output voltage is obtained through voltage and current dual closed-loop control. , will get The reference three-phase modulation voltage is obtained after dq-abc inverse transformation. The inverter switching signal is generated by SPWM to control the IGBT operation and output AC voltage.

[0167] Based on the dynamic equation of the capacitor voltage, the reference value of the outer loop output current is obtained through PI control and compensation of the rotating coupling term:

[0168] ,

[0169] in, and For the voltage loop PI parameters of the grid-type converter, Provides the d-axis output reference voltage for the grid side. This provides the q-axis output reference voltage for the grid side. Because... Therefore, the result is .

[0170] The principle of deriving the current reference value from the voltage reference value is as follows: when the output voltage is lower than the reference value, the inductor current needs to be increased so that more energy is injected into the capacitor through the inductor, thereby increasing the capacitor voltage, i.e., the output voltage; when the output voltage is higher than the reference value, the inductor current needs to be reduced, or even the current can be reversed to extract energy from the capacitor and reduce the output voltage.

[0171] Therefore, the core function of the voltage loop is to calculate, based on the voltage error, "how much inductor current is needed to pull the voltage back to the reference value, i.e., the output current reference value." .

[0172] The goal of the current loop is to make the dq-axis inductor current... Fast tracking of the reference value of the outer loop voltage output This suppresses load disturbances and switching harmonics. Specifically, it involves collecting the three-phase inductor current. The result is obtained through the abc-dq coordinate transformation. The input current error is controlled via a PI controller. Thus, the modulation voltage reference value is obtained, and the compensation rotational coupling term is obtained as follows:

[0173] ,

[0174] ,

[0175] in, Provide the d-axis input reference voltage for the inverter side. Provide the q-axis input reference voltage for the inverter side. and This is the reference value for the modulation voltage. and These are the PI parameters for the inner current loop of the grid-type converter. Coupling term compensation is used to eliminate crosstalk between the d and q axes.

[0176] The maximum allowable frequency deviation is ,so The rated power is 100kW, and the maximum active power fluctuation is ,so , .

[0177] The maximum voltage deviation is ±5% of the rated value. Since the rated voltage is 220V, The rated reactive power is 50 kvar, and the maximum reactive power fluctuation is... ,so , .

[0178] because Approximately equal to ,so Approximately 15915 W / rad, and Here we adopt some empirical values, let 3 , 100 .

[0179] The inner loop PI parameters consider the filter inductor. The voltage dynamics, neglecting grid-side voltage disturbances, yield the transfer function:

[0180] ,

[0181] in, For the current loop transfer function of the grid-type converter;

[0182] PI control process:

[0183] ,

[0184] in, The control equations for the current loop PI controller of the grid-type converter;

[0185] Open-loop transfer function of the inner current loop:

[0186] ,

[0187] in, The open-loop transfer function of the inner current loop of a grid-type converter;

[0188] Current inner loop closed-loop transfer function:

[0189] ,

[0190] in, This is the closed-loop transfer function of the inner current loop of a grid-type converter.

[0191] The inductance L = 1mH and the current loop bandwidth is The phase margin is approximately 45°. The amplitude-frequency response of the open-loop transfer function satisfies the following condition at the bandwidth. ,Will Substituting, we get:

[0192] ,

[0193] In the high frequency band Approximately:

[0194] ,

[0195] in, The angular frequency corresponding to the inner loop bandwidth of the grid-type converter current;

[0196] By substituting the relevant parameters into the definition of phase margin, we can derive the following:

[0197] ,

[0198] Design the current loop bandwidth of the grid converter , The value is set to 0.001. Based on the bandwidth of the inner current loop, the PI parameters of the inner current loop are adjusted as follows:

[0199] ,

[0200] ,

[0201] ,

[0202] Voltage loop PI parameters of grid converter considering capacitance When the voltage dynamics are negligible and the load current disturbance is ignored, the transfer function is:

[0203] ,

[0204] in, The voltage outer loop transfer function of the grid-type converter;

[0205] The PI controller component is as follows:

[0206] ,

[0207] in, The control equations for the outer loop PI controller of the grid-type converter voltage;

[0208] Therefore, the open-loop transfer function of the voltage outer loop is:

[0209] ,

[0210] in, This is the open-loop transfer function of the outer voltage loop of the grid-type converter.

[0211] Filter capacitor Initial bandwidth of voltage loop The phase margin is 45°. Based on the same logic as the current loop, the corresponding parameters are calculated as follows:

[0212] ,

[0213] ,

[0214] ,

[0215] in, for The corresponding angular frequency, , These are the initial PI parameters for the outer voltage loop of the grid-type converter.

[0216] The instability of the GFL converter mainly stems from the dynamic response of the PLL under weak power grid conditions. Specifically, S2 includes:

[0217] A small-signal model of the phase-locked loop (PLL) is established, and the open-loop transfer function of the PLL and the relationship between phase perturbation and q-axis voltage perturbation are obtained:

[0218] ,

[0219] in, To obtain the open-loop transfer function of the phase-locked loop of the grid converter. For phase perturbation, This refers to the q-axis voltage perturbation. This represents the steady-state amplitude of the grid voltage.

[0220] The GFL current control reference value is typically set to... , Phase perturbation This causes a change in the current projection in the dq coordinate system:

[0221] ,

[0222] in, This represents the current projection change along the q-axis. This is the initial current value.

[0223] We obtain the q-axis input admittance by combining the following equations:

[0224] ,

[0225] in, The q-axis input admittance.

[0226] According to the frequency mapping principle, when the control transfer function in the dq coordinate system is mapped to the positive-sequence impedance in the stationary coordinate system, the frequency variable... It needs to be translated as Therefore, the positive sequence impedance of the GFL is:

[0227] ,

[0228] in, To compare the output impedance of the grid converter in the positive sequence coordinate system, To determine the admittance of the grid converter in the positive sequence coordinate system, DC side voltage For reference current value, The imaginary unit, It is the power frequency angular frequency.

[0229] This impedance expression shows that in the frequency band near the PLL bandwidth, the GFL converter exhibits a significant negative resistance characteristic, which is the root cause of oscillations resulting from the inductive impedance coupling between the system and the weak grid. Quantifying this negative resistance characteristic data... This is used to establish stability criteria.

[0230] The output impedance characteristics of the GFM converter are affected by the voltage closed-loop control, and S3 specifically includes:

[0231] The equivalent impedance of the GFM converter in the dq coordinate system Simplified to the reciprocal of the voltage loop open-loop gain:

[0232] ,

[0233] GFM uses VSG control, and the virtual mechanical impedance must also be considered. Virtual admittance From virtual inertia and virtual damping constitute:

[0234] ,

[0235] Based on the LC filter parameters and coordinate transformation, the total positive sequence impedance of the GFM converter is:

[0236] ,

[0237] in, The output impedance of the grid-type converter in the positive sequence coordinate system;

[0238] Ignoring higher-order minor terms, the core influencing terms are simplified to:

[0239] .

[0240] According to the above formula, the positive sequence impedance characteristic of GFM is directly affected by the outer loop bandwidth of the voltage. Adjustment. In the sub-synchronous frequency band, the real part of this impedance is always positive, that is, it behaves as a positive resistance, which has the ability to suppress oscillation.

[0241] When the system experiences asymmetric oscillations, a negative-sequence component appears. According to the frequency coupling mechanism, the negative-sequence component in the dq coordinate system is as follows: The frequency harmonics require the coordinate transformation operator to be transformed into... The negative sequence impedance of GFM is:

[0242] .

[0243] Bandwidth parameter in the open-loop transfer function of the voltage outer loop As a tuning object, it is used to adjust the output impedance in the sequence impedance model of the grid-type converter.

[0244] S4 specifically includes:

[0245] The output impedance of the GFL converter in the positive sequence coordinate system is equivalent to the Norton model, thus obtaining the equivalent current source of the GFL converter. and equivalent parallel impedance The output impedance of the GFM converter in the positive sequence coordinate system is equivalent to the Thevenin model, thus obtaining the equivalent voltage source of the GFM converter. and equivalent series impedance By equating the power grid to the Thevenin model, the equivalent voltage source of the power grid is obtained. Equivalent series impedance with the power grid .

[0246] According to Thevenin's theorem, the equivalent parallel impedance of the system as seen from the PCC point of the GFL converter. It is formed by connecting the mains impedance and the GFM impedance in parallel:

[0247] ,

[0248] in, The equivalent series impedance of the power grid. This represents the output impedance of the grid-type converter in the positive sequence coordinate system.

[0249] The necessary and sufficient condition for system stability is that the total loop impedance does not have negative damping characteristics throughout the entire frequency domain. According to the impedance-based stability criterion, the sum of the real parts of the total system impedance must be greater than zero.

[0250] ,

[0251] in, This represents the real part of the equivalent parallel impedance of the GFL converter, which is negative in a specific frequency band. To provide the real part of the equivalent impedance on the system side, a sufficient positive real part must be provided to offset the negative value of the real part of the equivalent parallel impedance of the GFL converter.

[0252] S5 specifically includes:

[0253] If the parallel system does not meet the stability criterion under the current grid-type converter voltage outer loop bandwidth parameters, iteratively execute the following steps until the stability criterion is met:

[0254] Identify the subsynchronous oscillation frequency of the parallel system and its corresponding angular frequency .

[0255] Set target bandwidth This ensures that the target bandwidth is greater than twice the angular frequency corresponding to the subsynchronous oscillation frequency, and is far from the switching frequency. ≥2 .

[0256] Based on the quantitative relationship between the voltage outer loop PI parameters and bandwidth, the tuned voltage outer loop PI parameters are calculated from the target bandwidth:

[0257] ,

[0258] ,

[0259] in, , These are the PI parameters of the outer loop voltage after tuning.

[0260] Substitute the tuned voltage outer loop PI parameters into the voltage outer loop open-loop transfer function to update the output impedance of the grid converter in the positive sequence coordinate system. .

[0261] Substitute the updated output impedance into the Thevenin model and recalculate the equivalent impedance on the system side. Equivalent polymer impedance to the system.

[0262] Verify whether the stability criterion is met. If not, iteratively increase the target bandwidth until the criterion is met, thus completing the closed-loop tuning of the parallel oscillation suppression parameter.

[0263] To verify the effectiveness of the above method, the following examples are provided for analysis in this embodiment.

[0264] First, the basic parameters of the model are set, including the baseline capacity of GFM / GFL. Both are 170kVA, and the rated voltage of the power grid is... 380V, the reference frequency of the power grid. The frequency is 50Hz, and the reference impedance of the power grid is... .

[0265] Based on step S3 above, the output impedance characteristics of the GFM are significantly affected by the outer loop bandwidth of the voltage. The effect of GFM in the positive sequence coordinate system. It can be represented as the series-parallel relationship between the virtual mechanical impedance and the equivalent impedance of the voltage loop. In the dominant frequency band of the outer voltage loop, the simplified impedance model is mainly determined by the voltage loop parameters.

[0266] At this point, the equivalent output impedance presented by the GFM is... Mainly affected in the low frequency band Modulation. Bandwidth. The larger the value, the stronger the rigid control of the voltage by the GFM, and the smaller the impedance magnitude it presents to the outside world, which can approximate an ideal voltage source. Due to the influence of the phase-locked loop bandwidth, the GFL converter exhibits negative resistance characteristics in the sub-synchronous frequency band, that is, it injects energy into the system. The aggregate impedance at the PCC point is calculated according to step S4 above. When the short-circuit ratio (SCR) decreases, the inductive impedance of the grid increases, and the system resonant frequency shifts to a lower frequency.

[0267] Two sets of voltage loop bandwidths were set for comparative analysis:

[0268] Operating Condition A: ,

[0269] Operating Condition B: ,

[0270] Calculations for operating condition A yield the following parameters before tuning: , The oscillation frequency is The corresponding angular frequency is Raw bandwidth (350) and oscillation frequency (272) Too close. According to control theory, the phase lag is large near the cutoff frequency, which causes the GFM to fail to exhibit ideal voltage source characteristics at this frequency and to fail to effectively absorb the negative damping current generated by the GFL, resulting in a long oscillation duration.

[0271] Based on step S3 above, it is necessary to increase the voltage outer loop bandwidth. This allows the GFM to exhibit lower output impedance and stronger voltage stiffness at the subsynchronous oscillation frequency. To suppress oscillations at the subsynchronous oscillation point, the target bandwidth... It should be at least twice the oscillation frequency and far away from the switching frequency. Target bandwidth setting: Selection criteria: 600 rad / s is much greater than 272 rad / s, ensuring that the voltage loop gain is extremely high and the closed-loop output impedance is extremely low at the subsynchronous oscillation point.

[0272] The adjusted proportional coefficient:

[0273] ,

[0274] The integral coefficients after tuning:

[0275] .

[0276] Building such Figure 2 The parallel system simulation model shown was used to measure the GFM impedance at the subsynchronous oscillation point before and after parameter tuning. The measurement results show that the impedance is higher and the phase lag is larger before the bandwidth is increased, while the impedance is extremely low after the bandwidth is increased. The current spectrum at the PCC point was collected before and after parameter tuning, as shown below. Figure 3 and Figure 4 The acquisition results show that the component of the secondary synchronous oscillation point is more obvious before the bandwidth is increased, while the component of the secondary synchronous oscillation point attenuates after the bandwidth is increased. A simulation was built for this case. The initial simulation state was set to high-voltage loop bandwidth. At 0.4s, the grid short-circuit ratio was reduced from 1.2 to 1.1. It can be seen that with high-voltage loop bandwidth, after the grid short-circuit ratio is reduced, the active power fluctuation is smaller and the transient time is shorter. Switching to low-voltage loop bandwidth at 2s further demonstrates… Figure 5 As can be seen from the waveform, after switching to low bandwidth, the active power exhibits a small oscillation. The oscillation after the voltage loop is slowed down is caused by the poles drifting towards the imaginary axis. At 2.3s, the grid short-circuit ratio is also reduced from 1.2 to 1.1. It can be seen from the waveform that the active power changes abruptly, and the amplitude reduction oscillation converges slowly.

[0277] Example 2

[0278] This embodiment provides a parallel oscillation suppression device for grid-type and grid-following converters, including:

[0279] Parallel System Model Construction Module: Used to build a parallel system model based on the current grid connection scenario; the parallel system model includes the grid connected in parallel, grid-connected converters and grid-linked converters, as well as the control models of grid-connected converters and grid-connected converters; the control model of grid-connected converters includes the voltage outer loop;

[0280] The grid-connected converter sequence impedance model construction module is used for small-signal linearization analysis based on phase-locked loops. It constructs the grid-connected converter sequence impedance model based on the control model of the grid-connected converter. The grid-connected converter sequence impedance model characterizes the output impedance of the grid-connected converter in the positive sequence coordinate system.

[0281] The sequence impedance model construction module for grid-type converters is used for impedance characteristic analysis based on the voltage outer loop. It introduces the voltage outer loop bandwidth parameter and constructs the sequence impedance model of the grid-type converter according to the control model of the grid-type converter. The sequence impedance model of the grid-type converter characterizes the output impedance of the grid-type converter in the positive sequence coordinate system.

[0282] Stability criterion construction module: used to calculate the system equivalent aggregate impedance at the grid connection point based on the sequence impedance model of the grid-connected converter and the sequence impedance model of the grid-connected converter, and to establish a stability criterion based on the real part of the system equivalent aggregate impedance; where the grid connection point is the intersection point of the grid, the grid-connected converter and the grid-connected converter in the parallel system model.

[0283] Parallel oscillation suppression module: Used to adjust the grid connection point impedance characteristics by setting the voltage outer loop bandwidth parameter of the grid converter according to stability criteria, so that the positive resistance characteristics of the grid converter compensate for the negative damping effect of the grid converter.

[0284] The device provided in this embodiment can execute the parallel oscillation suppression method for grid-type and grid-following converters provided in any step of Embodiment 1, and has the corresponding functional modules and beneficial effects of the execution method.

[0285] Example 3

[0286] This embodiment provides a computer storage medium storing a computer program. When the computer program is executed by a processor, it implements the parallel oscillation suppression method for grid-type and grid-following converters as provided in any step of Embodiment 1.

[0287] Example 4

[0288] This embodiment provides an electronic terminal, including a processor and a memory connected to the processor. The memory stores a computer program. When the computer program is executed by the processor, it performs the steps of the parallel oscillation suppression method for grid-type and grid-following converters provided in any step of Embodiment 1.

[0289] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0290] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0291] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0292] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0293] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for suppressing oscillations in parallel operation of grid-type and grid-following type converters, characterized in that, include: A parallel system model is established based on the current grid connection scenario. The parallel system model includes the grid, grid-connected converters and grid-linked converters connected in parallel, as well as the control models of grid-linked converters and grid-connected converters. The control model of the grid-connected converter includes the voltage outer loop. Based on the small-signal linearization analysis of the phase-locked loop, a sequence impedance model of the grid converter is constructed according to the control model of the grid converter; wherein, the sequence impedance model of the grid converter characterizes the output impedance of the grid converter in the positive sequence coordinate system. Based on the impedance characteristic analysis dominated by the voltage outer loop, the voltage outer loop bandwidth parameter is introduced, and the sequence impedance model of the grid converter is constructed according to the control model of the grid converter; wherein, the sequence impedance model of the grid converter characterizes the output impedance of the grid converter in the positive sequence coordinate system. Based on the sequence impedance models of grid-connected converters and grid-connected converters, the equivalent aggregate impedance of the system at the grid connection point is calculated, and a stability criterion based on the real part of the equivalent aggregate impedance is established. The grid connection point is the intersection of the grid, grid-connected converters, and grid-connected converters connected in parallel in the parallel system model. Based on the stability criterion, the voltage outer loop bandwidth parameter of the grid converter is adjusted to adjust the impedance characteristics of the grid connection point, so that the positive resistance characteristics of the grid converter can compensate for the negative damping effect of the grid converter. The calculation of the system equivalent aggregate impedance at the grid connection point based on the sequence impedance models of grid-connected and grid-connected converters includes: By equating the output impedance of the grid-connected converter in the positive sequence coordinate system to the Norton model, the equivalent current source and equivalent parallel impedance of the grid-connected converter are obtained. The output impedance of the grid converter in the positive sequence coordinate system is equivalent to the Thevenin model, and the equivalent voltage source and equivalent series impedance of the grid converter are obtained. By equating the power grid to the Thevenin model, we obtain the equivalent voltage source and the equivalent series impedance of the power grid. Based on the equivalent series impedance of the parallel grid-connected converters and the equivalent series impedance of the power grid, the equivalent impedance on the system side is obtained: ， in, The equivalent impedance on the system side. The equivalent series impedance of the power grid. The output impedance of the grid-type converter in the positive sequence coordinate system; The equivalent aggregate impedance of the system at the grid connection point is obtained by comparing the equivalent impedance of the system side with the equivalent parallel impedance of the grid-connected converter. The establishment of a stability criterion based on the real part of the system's equivalent aggregate impedance includes: using whether the sum of the real part of the system-side equivalent impedance and the real part of the equivalent parallel impedance of the grid-connected converter is greater than zero as the stability criterion for the parallel system under the current bandwidth parameters. ， in, This represents the real part of the system-side equivalent impedance. This is the real part of the equivalent parallel impedance of the grid converter.

2. The method for suppressing parallel oscillations of grid-type and grid-following type converters according to claim 1, characterized in that, The establishment of a parallel system model based on the current grid connection scenario includes: Determine the short-circuit capacity ratio of the power grid and calculate the power grid impedance; The outer power loop bandwidth and inner current loop bandwidth of the grid-connected converter are determined based on the grid impedance. The outer power loop PI parameters and inner current loop PI parameters of the grid-connected converter are then tuned using these bandwidths. ， ， ， ， ， ， in, and To match the current loop PI parameters of the grid-connected converter, To match the inner loop bandwidth of the current in a grid-type converter. This refers to the angular frequency corresponding to the inner loop bandwidth of the grid converter current. To match the filter inductor of the grid-type converter, To match the equivalent series resistance of the filter inductor coil in the grid converter, and To match the power loop PI parameters of the grid-connected converter, To match the power outer loop bandwidth of the grid converter, The angular frequency corresponding to the outer loop bandwidth of the grid converter's power circuit. The voltage component along the d-axis; Establish a double - closed - loop control model of the grid - following converter from the power outer loop to the current inner loop; among which, the output current reference value of the power outer loop of the grid - following converter and serve as the input of the current inner loop of the grid - following converter; The bandwidth of the grid-connected converter's current inner loop is determined based on the grid impedance, and the PI parameters of the grid-connected converter's current inner loop are then tuned using this bandwidth. ， ， ， in, The bandwidth of the inner current loop for a grid-type converter. This refers to the angular frequency corresponding to the inner current loop bandwidth of a grid-type converter. , The PI parameters for the inner current loop of a grid-type converter. For filtering inductors in grid-type converters; The initial bandwidth of the outer voltage loop of the grid-type converter is set, and the initial PI parameters of the outer voltage loop are calculated from the initial bandwidth and the quantitative relationship between the outer voltage loop PI parameters and the bandwidth: ， ， ， in, This refers to the initial bandwidth of the outer voltage loop of a grid-type converter. The angular frequency corresponding to the initial bandwidth of the outer voltage loop of the grid-type converter. , The initial PI parameters for the outer voltage loop of the grid-type converter. For filtering capacitors in grid-type converters; A dual closed-loop control model for a grid-type converter, from the outer voltage loop to the inner current loop, is established; wherein, the reference value of the output current of the outer voltage loop of the grid-type converter is used as the input of the inner current loop of the grid-type converter.

3. The method for suppressing parallel oscillations of grid-type and grid-following type converters according to claim 2, characterized in that, The small-signal linearization analysis based on phase-locked loop (PLL) constructs a sequence impedance model for the grid-type converter based on the control model of the grid-type converter, including: Substituting the power outer-loop PI parameters and current inner-loop PI parameters of the grid-connected converter into the dual-closed-loop control model of the grid-connected converter, we obtain the closed-loop transfer function of the current inner loop and the open-loop transfer function of the power outer loop: ， ， in, To provide the closed-loop transfer function of the inner current loop of the grid-type converter. To obtain the open-loop transfer function of the outer power loop of the grid converter, For frequency variables; A small-signal model of the phase-locked loop (PLL) is established, and the open-loop transfer function of the PLL and the relationship between phase perturbation and q-axis voltage perturbation are obtained: ， in, To obtain the open-loop transfer function of the phase-locked loop of the grid converter. For phase perturbation, This refers to the q-axis voltage perturbation. This represents the steady-state amplitude of the grid voltage. Based on the closed-loop transfer function of the current inner loop, the open-loop transfer function of the power outer loop, and the open-loop transfer function of the phase-locked loop, the admittance matrix of the grid-type converter in the dq rotating coordinate system is derived. Based on the frequency mapping principle, the admittance matrix in the dq rotating coordinate system is mapped to the positive sequence coordinate system to establish the sequence impedance model of the grid converter: ， in, To compare the output impedance of the grid converter in the positive sequence coordinate system, To determine the admittance of the grid converter in the positive sequence coordinate system, DC side voltage For reference current value, The imaginary unit, It is the power frequency angular frequency.

4. The method for suppressing parallel oscillations of grid-type and grid-following type converters according to claim 3, characterized in that, The impedance characteristic analysis based on the voltage outer loop introduces the voltage outer loop bandwidth parameter and constructs a sequence impedance model for the grid-type converter based on the control model of the grid-type converter, including: Substituting the initial PI parameters of the outer voltage loop and the inner current loop into the dual closed-loop control model of the grid converter, we obtain the closed-loop transfer function of the inner current loop and the open-loop transfer function of the outer voltage loop: ， ， in, This is the closed-loop transfer function for the inner current loop of a grid-type converter. The open-loop transfer function of the outer voltage loop of the grid-type converter. For frequency variables; Establish the motion equations of the virtual synchronous machine rotor and obtain the virtual admittance: ， in, For virtual admittance, For virtual inertia, For virtual damping; Based on the open-loop transfer function of the outer voltage loop, the closed-loop transfer function of the inner current loop, and the virtual admittance, the equivalent impedance of the grid converter in the dq rotating coordinate system is derived: ， in, The output impedance of the grid-type converter in the dq rotating coordinate system; Based on the frequency mapping principle, the equivalent impedance in the dq rotating coordinate system is mapped to the positive sequence coordinate system to obtain the positive sequence output impedance of the grid converter: ， in, The imaginary unit, It is the power frequency angular frequency.

5. The method for suppressing parallel oscillations of grid-type and grid-following type converters according to claim 1, characterized in that, The adjustment of the grid connection point impedance characteristics by setting the outer loop bandwidth parameter of the grid-type converter according to the stability criterion includes: If the parallel system does not meet the stability criterion under the current grid-type converter voltage outer loop bandwidth parameters, iteratively execute the following steps until the stability criterion is met: The target bandwidth is set according to the voltage outer loop bandwidth parameters of the current grid-type converter; the target bandwidth is greater than twice the angular frequency corresponding to the subsynchronous oscillation frequency of the current parallel system, and is far away from the switching frequency; Based on the quantitative relationship between the voltage outer loop PI parameters and the voltage outer loop bandwidth parameters of the grid-type converter, the voltage outer loop PI parameters after tuning are calculated according to the target bandwidth. Update the output impedance of the grid converter in the positive sequence coordinate system based on the adjusted outer loop PI parameters of the voltage. Update the system equivalent aggregate impedance based on the updated output impedance; Based on the updated system equivalent aggregate impedance, verify whether the parallel system under the current grid-type converter voltage outer loop bandwidth parameters meets the stability criterion.

6. A parallel oscillation suppression device for grid-type and grid-following type converters, characterized in that, include: Parallel System Model Construction Module: Used to build a parallel system model based on the current grid connection scenario; the parallel system model includes the grid connected in parallel, grid-connected converters and grid-linked converters, as well as the control models of grid-connected converters and grid-connected converters; the control model of grid-connected converters includes the voltage outer loop; The grid-connected converter sequence impedance model construction module is used for small-signal linearization analysis based on phase-locked loops. It constructs the grid-connected converter sequence impedance model based on the control model of the grid-connected converter. The grid-connected converter sequence impedance model characterizes the output impedance of the grid-connected converter in the positive sequence coordinate system. The sequence impedance model construction module for grid-type converters is used for impedance characteristic analysis based on the voltage outer loop. It introduces the voltage outer loop bandwidth parameter and constructs the sequence impedance model of the grid-type converter according to the control model of the grid-type converter. The sequence impedance model of the grid-type converter characterizes the output impedance of the grid-type converter in the positive sequence coordinate system. Stability criterion construction module: used to calculate the system equivalent aggregate impedance at the grid connection point based on the sequence impedance model of the grid-connected converter and the sequence impedance model of the grid-connected converter, and to establish a stability criterion based on the real part of the system equivalent aggregate impedance; where the grid connection point is the intersection point of the grid, the grid-connected converter and the grid-connected converter in the parallel system model. Parallel oscillation suppression module: used to adjust the grid connection point impedance characteristics by setting the voltage outer loop bandwidth parameter of the grid converter according to stability criteria, so that the positive resistance characteristics of the grid converter can compensate for the negative damping effect of the grid converter. The calculation of the system equivalent aggregate impedance at the grid connection point based on the sequence impedance models of grid-connected and grid-connected converters includes: By equating the output impedance of the grid-connected converter in the positive sequence coordinate system to the Norton model, the equivalent current source and equivalent parallel impedance of the grid-connected converter are obtained. The output impedance of the grid converter in the positive sequence coordinate system is equivalent to the Thevenin model, and the equivalent voltage source and equivalent series impedance of the grid converter are obtained. By equating the power grid to the Thevenin model, we obtain the equivalent voltage source and the equivalent series impedance of the power grid. Based on the equivalent series impedance of the parallel grid-connected converters and the equivalent series impedance of the power grid, the equivalent impedance on the system side is obtained: ， in, The equivalent impedance on the system side. The equivalent series impedance of the power grid. The output impedance of the grid-type converter in the positive sequence coordinate system; The equivalent aggregate impedance of the system at the grid connection point is obtained by comparing the equivalent impedance of the system side with the equivalent parallel impedance of the grid-connected converter. The establishment of a stability criterion based on the real part of the system's equivalent aggregate impedance includes: using whether the sum of the real part of the system-side equivalent impedance and the real part of the equivalent parallel impedance of the grid-connected converter is greater than zero as the stability criterion for the parallel system under the current bandwidth parameters. ， in, This represents the real part of the system-side equivalent impedance. This is the real part of the equivalent parallel impedance of the grid converter.

7. A computer storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the parallel oscillation suppression method for grid-type and grid-following type converters as described in any one of claims 1-5.

8. An electronic terminal, characterized in that, The device includes a processor and a memory connected to the processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the steps of the parallel oscillation suppression method for grid-type and grid-following converters as described in any one of claims 1-5 are performed.

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