A method for suppressing interaction between multiple VSGs in parallel based on an improved phase-locked loop

Abstract

This application discloses a method for suppressing the interaction of multiple VSGs in parallel based on an improved phase-locked loop (PLL), belonging to the field of power system technology. The method comprises: constructing an equivalent Pω admittance model of multiple VSGs in parallel based on a power-frequency small-signal model of a single VSG that takes into account the influence of the common connection point frequency; analyzing the oscillation characteristics in the current parallel multi-VSG system based on the equivalent Pω admittance model; using an improved PLL to obtain the frequency of the common connection point in the power-frequency small-signal model of the single VSG based on the oscillation characteristics; and adding a feedforward compensation at the frequency generation point of the active power control loop of the single VSG based on the change in the frequency of the common connection point from the rated value to cancel the PCC frequency disturbance. This suppression method suppresses power oscillations between units and improves the dynamic stability of the system by improving the PLL to measure the PCC frequency and introducing feedforward compensation at the frequency generation point.

Description

Technical Field

[0001] The present application relates to the technical field of power systems, and in particular to a method for suppressing interaction of multiple VSGs in parallel based on an improved phase-locked loop. Background Art

[0002] In recent years, renewable energy generation technologies, represented by wind power and photovoltaics, have developed rapidly. A large number of distributed power sources have been connected to the grid through grid-connected inverters, increasing the penetration of renewable energy. Because grid-connected inverters lack the inherent inertia and damping characteristics of synchronous generators, their large-scale integration has led to a decrease in the frequency stability of the power system, limiting the further absorption of renewable energy. Virtual Synchronous Generator (VSG) technology improves system frequency stability by simulating synchronous generators and introducing virtual inertia and virtual damping. However, the introduction of VSGs also brings about power oscillation issues. Especially when multiple machines are operated in parallel, the interaction between VSGs can cause power oscillations to propagate, affecting system stability and power quality.

[0003] As the synchronization reference generator for grid-connected inverters, the dynamic performance of the phase-locked loop (PLL) directly determines the synchronization accuracy of the VSG output power. In weak grids or high harmonic distortion scenarios, traditional PLLs suffer from frequency tracking lag and insufficient interference rejection, leading to reference phase mismatch in multi-VSG parallel systems and further exacerbating power oscillations. Numerous PLL improvement solutions have been investigated, including phase margin optimization, low-pass filtering for noise reduction, dual PLL architectures, TOGI harmonic suppression, and auto-interference rejection control. While these methods suppress power oscillations to a certain extent, they sacrifice dynamic response speed and rely on complex control structures, making it difficult to achieve the core requirements of high-precision phase locking, strong robustness, and low complexity. Summary of the Invention

[0004] In response to the above-mentioned deficiencies in the prior art, the present application provides a method for suppressing the interaction of multiple VSGs in parallel based on an improved phase-locked loop, which solves the problems of poor dynamics and insufficient accuracy of the phase-locked loop and the easy interaction and power oscillation caused by the existing VSGs in parallel.

[0005] In order to achieve the above-mentioned invention objectives, the technical solutions adopted in this application are:

[0006] This application provides a method for suppressing interaction of multiple VSGs in parallel based on an improved phase-locked loop, including:

[0007] S1: Based on the power-frequency small signal model of a single VSG considering the influence of the common connection point frequency, an equivalent Pω admittance model of multiple VSGs in parallel is constructed;

[0008] S2: Analyze the oscillation characteristics of the current system of multiple VSGs in parallel based on the equivalent Pω admittance model of the multiple VSGs in parallel;

[0009] S3: Based on the oscillation characteristics of the current parallel multi-VSG system, an improved phase-locked loop is used to obtain the frequency of the common connection point;

[0010] S4: According to the variation of the frequency of the common connection point from the rated value, a feedforward compensation is added to the frequency generation in the active power control loop of a single VSG to cancel the PCC frequency disturbance.

[0011] Furthermore, the S1 specifically includes:

[0012] S101: Establish a power-frequency small signal model of a single VSG considering the influence of the common connection point frequency;

[0013] S102: Constructing a Pω admittance model of a single VSG based on the power-frequency small signal model of the single VSG;

[0014] S103: Based on the Pω admittance model of the single VSG, an equivalent P / ω admittance model of multiple VSGs in parallel is constructed.

[0015] Furthermore, the Pω admittance model of the single VSG includes the active command disturbance source , a single-ended network of a first mechanical admittance and a second mechanical admittance, the mechanical admittance of the model satisfies the following relationship:

[0016]

[0017]

[0018]

[0019] in, is the synchronization coefficient, and are the first mechanical admittance and the second mechanical admittance, respectively. 、 are the steady-state values ​​of the VSG filter port voltage and the common connection point voltage, is the reactance of the line, is the filter port voltage and PCC voltage The steady-state phase angle difference between is the Laplace operator, and is the virtual inertia and damping coefficient of the active loop, is the reference value of angular frequency.

[0020] Furthermore, the oscillation characteristic is that the oscillation in the parallel multi-VSG system is propagated through the PCC frequency disturbance.

[0021] Furthermore, the S3 specifically includes:

[0022] S301: Based on the oscillation characteristics of the current parallel multi-VSG system, using an improved phase-locked loop to calculate the true phase angle of the common connection point;

[0023] S302: Performing differentiation processing on the true phase angle to obtain the frequency of the common connection point.

[0024] Furthermore, the improved phase-locked loop specifically comprises: a phase detector, a PI controller, an integrator and a feedforward summing link connected in sequence;

[0025] A1: Use the phase detector to receive the three-phase AC voltage signal of the common connection point in the parallel multi-VSG system, and transform the three-phase AC voltage signal into a two-phase rotating coordinate system to obtain the voltage of the common connection point. Axis and Shaft voltage components:

[0026]

[0027] in, is the dq transformation matrix, is the amplitude of the voltage signal at the common connection point, Public connection point Shaft voltage component, for Shaft voltage component, To improve the intermediate estimated phase angle obtained by the phase-locked loop measurement, is the true phase angle of the voltage, 、 、 is the ABC three-phase voltage at the common connection point;

[0028] A2: Shaft voltage component Perform linearization and obtain The amount of change:

[0029]

[0030] in, For public connection points The change in the shaft voltage component, is the true phase angle value of the common connection point, The intermediate estimated phase angle value obtained by measuring the improved phase-locked loop;

[0031] A3: Generate frequency estimates using a PI controller :

[0032]

[0033] in, and To improve the parameters of the phase-locked loop PI controller;

[0034] A4: Use the integrator to estimate the frequency conduct Integral processing to obtain the intermediate estimated phase angle value of the improved phase-locked loop ;

[0035] A5: Using the feedforward summation link The change in the intermediate estimated phase angle value of the improved phase-locked loop Add them together to eliminate the dynamic error of the phase-locked loop and obtain the true phase angle of the common connection point:

[0036] .

[0037] Furthermore, the transfer function of the improved phase-locked loop is:

[0038]

[0039] in, The transfer function of the improved phase-locked loop.

[0040] The beneficial effects of this application are:

[0041] The present application discloses a method for interactive suppression of multiple VSGs in parallel based on an improved phase-locked loop. The improved phase-locked loop measures the PCC frequency and compensates for the feedforward amount, thereby quickly suppressing oscillations and improving the dynamic stability of the system. Compared with the traditional phase-locked loop, the improved phase-locked loop adds a feedforward summation link, and the measured frequency and phase angle have no overshoot or fluctuation problems, thus achieving error-free tracking, ensuring accurate PCC frequency measurement, and enhancing the suppression effect. At the same time, based on the PCC frequency measured by the improved phase-locked loop, a feedforward compensation amount is added to effectively weaken the interactive oscillations between units and improve the dynamic stability of the system. In addition, the present application only requires local measurement signals to achieve interactive suppression, has a simple control structure, and has low implementation cost. It is suitable for multi-VSG systems and has high practical value and promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0043] Figure 1 This is a structural diagram of multiple VSGs provided by this application connected in parallel to a common connection point PCC.

[0044] Figure 2 A schematic diagram of a method for parallel multi-VSG interaction suppression based on an improved phase-locked loop provided in this application.

[0045] Figure 3 A method for considering the common connection point frequency ω provided in this application pcc Schematic diagram of the power-frequency small signal model of a single VSG affected by the load.

[0046] Figure 4 Schematic diagram of the Pω admittance model of a single VSG provided in this application.

[0047] Figure 5 This is a schematic diagram of an equivalent Pω admittance model of multiple VSGs connected in parallel provided by this application.

[0048] Figure 6 A schematic diagram of a traditional phase-locked loop control structure provided in this application.

[0049] Figure 7 A schematic diagram of a traditional phase-locked loop linearization model provided in this application.

[0050] Figure 8 A schematic diagram of an improved phase-locked loop structure provided in this application.

[0051] Figure 9 This is a schematic diagram of an improved phase-locked loop linearization model provided in this application.

[0052] Figure 10 Schematic diagram of a parallel multi-VSG interaction suppression method provided in this application.

[0053] Figure 11 This application provides an improved closed-loop small-signal model of the active power control loop of the VSG.

[0054] Figure 12 This is a schematic diagram of a VSG parallel four-machine system provided in this application.

[0055] Figure 13 A comparison chart of the measurement results of a traditional phase-locked loop and an improved phase-locked loop provided in this application.

[0056] Figure 14 This is a verification diagram of the parallel multi-VSG interaction suppression method provided in this application. DETAILED DESCRIPTION

[0057] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field based on this application are within the scope of protection of this application.

[0058] As the scale of parallel connections of multiple VSGs increases, dynamic system interaction issues are becoming increasingly prominent. Due to differences in parameters such as virtual inertia and damping coefficients between VSGs, as well as mismatched line impedances, parallel systems are prone to low-frequency power oscillations and circulating current surges. These issues not only degrade power quality but can also trigger cascading instabilities, hindering the large-scale application of VSG technology. Existing research mainly adopts the following methods for the mutual suppression of multiple VSGs: (1) Based on small signal modeling and eigenvalue analysis: By establishing a small signal model of the VSG multi-machine grid-connected system, the influence of different parameters on the low-frequency characteristic roots of the system is analyzed. This method can reveal the oscillation mechanism, but fails to provide an effective control strategy to actively suppress the power oscillation between multiple machines; (2) Based on distributed mutual damping control: A communication network is used to introduce mutual damping control between VSGs to reduce power oscillations. This method can effectively suppress oscillations, but the introduction of communication increases the complexity of the system and may cause communication delay problems; (3) Based on virtual impedance regulation: By introducing virtual impedance to optimize the power distribution characteristics of VSG, power oscillations are weakened. However, when the virtual impedance parameters are not properly selected, this method may cause coupling of active and reactive loops, affecting the regulation performance of the system; (4) Based on bandpass damped power feedback: By constructing a bandpass filtered damped power feedback, the system stability is improved. However, this method increases the order of the control system.

[0059] It's worth noting that none of the aforementioned methods fully consider the impact of the dynamic characteristics of the phase-locked loop (PLL) on the stability of multi-VSG interactions. As the synchronization reference generator for grid-connected inverters, the dynamic performance of the PLL directly determines the synchronization accuracy of the VSG output power. In weak grid conditions or high harmonic distortion scenarios, traditional PLLs suffer from frequency tracking lag and insufficient interference immunity, leading to reference phase mismatch in the multi-VSG parallel system and further exacerbating power oscillations. Existing PLL improvement schemes include: (1) using phase margin constraints to optimize PLL parameters to improve its adaptability to weak power grids, but it is still difficult to ensure stability when the grid impedance changes greatly; (2) introducing a low-pass filter in the front stage of the PLL to weaken harmonic and noise interference, but this method will introduce phase lag, affecting the transient response of the system; (3) an improvement scheme based on dual PLL to widen the phase-locked range and improve dynamic characteristics, but it increases the complexity of the system and is sensitive to parameter setting; (4) a PLL scheme based on a third-order generalized integrator (TOGI) to suppress the influence of grid harmonics, however, this method may introduce additional phase offset in the low-frequency range, affecting the frequency tracking accuracy; (5) using an anti-disturbance control strategy to enhance the PLL's ability to suppress disturbances, but it is still necessary to balance the dynamic response speed with the steady-state accuracy, and it is difficult to take into account both fast locking and zero-error tracking.

[0060] like Figure 1 As shown, Figure 1 This is a schematic diagram of a structure in which multiple VSGs are connected in parallel to a common connection point (PCC) provided by this application. The right side is its control structure. All control variables and subsequent analysis parameters are expressed in per-unit values. In the main circuit, the VSG output is connected to the PCC via an LC filter through a transmission line. The control part mainly consists of a power outer loop and a voltage-current inner loop. and Represent the filter inductor and filter capacitor respectively, is the parasitic resistance of the filter inductor, and Represents the inductance and resistance of the transmission line, which together constitute the line impedance ; is the grid-side line impedance, and The inverter port voltage is recorded as , the filter port voltage is recorded as , and Represent the inverter output current and filter output current respectively, and is the virtual inertia and damping coefficient of the active loop, is the droop coefficient of the reactive loop, is the reference value of angular frequency, represents the Laplace operator, 、 ... From 1st to 2nd n Virtual synchronous generators, is the grid side voltage, is the inverter three-phase modulation signal (generated by SPWM or SVPWM), is the three-phase current of the filter inductor at the inverter output end, and are the three-phase voltage and current, is a three-phase stationary coordinate system ( abc ) to the two-phase rotating coordinate system ( dq ) transformation module, The voltage at the common connection point is the voltage at the interface between multiple VSGs and the grid after they are connected in parallel. To convert the three-phase current The active component obtained by coordinate transformation ( ) and reactive components ( ), and for of d Axis components and q Axis component, and For the rotating coordinate system d Axis (straight axis) and q Axis (quadrature axis) voltage and current components, and are the instantaneous active power and instantaneous reactive power, and are the reference values ​​of active and reactive power (generated by dispatch or droop control), is the rated angular frequency, is the angular frequency of the VSG output, The coordinate transformation angle is usually provided by a phase-locked loop (PLL) or VSG frequency generation module. is the neutral point voltage, and for d Axis and q The voltage reference value of the axis (generated by droop control or superior instructions), and For actual measurement d Axis and q The voltage component of the axis (obtained by coordinate transformation), refer to Control link, and For actual measurement d Axis andq The current component of the axis (obtained by coordinate transformation), To control the active component of the inverter output current (the component in the same direction as the grid voltage), To control the reactive component of the inverter output current (the component in the direction orthogonal to the grid voltage), and for d Axis and q The modulation signal of the axis (the value range is usually ±1).

[0061] This application uses the following variable representation conventions: subscript " "represents the three-phase components of the variable, subscript" "Indicates that the variable is in Components in the coordinate system, subscript " "Indicates the steady-state value of the variable, subscript" "Indicates the reference value in the control link, the prefix" " represents a small perturbation of the variable relative to the initial operating point.

[0062] When a unit in the system is disturbed or fails, power oscillation will occur. Due to the dynamic coupling between VSG units, the oscillation may propagate within the multi-machine system, affecting the system stability.

[0063] Based on this, the embodiment of the present application provides a method for suppressing the interaction of multiple VSGs in parallel based on an improved phase-locked loop. Figure 2 , Figure 2 A schematic diagram of a method for suppressing interaction of multiple VSGs in parallel based on an improved phase-locked loop provided in an embodiment of the present application includes:

[0064] S1: Based on the power-frequency small signal model of a single VSG considering the influence of the common connection point frequency, an equivalent Pω admittance model of multiple VSGs in parallel is constructed.

[0065] Furthermore, the S1 specifically includes:

[0066] S101: Establish a power-frequency small signal model of a single VSG taking into account the influence of the common connection point frequency.

[0067] The power-frequency small signal model can be found in Figure 3 , Figure 3 A method for considering the frequency of the common connection point provided for this application Schematic diagram of the power-frequency small signal model of a single VSG affected by the is the active power reference value, is the synchronization coefficient, is the output power disturbance of the virtual synchronous generator, is the VSG moment of inertia, is the damping coefficient, is the reference value of angular frequency, is the phase angle.

[0068] S102: Constructing a Pω admittance model of a single VSG based on the power-frequency small signal model of the single VSG.

[0069] In one possible embodiment, Figure 3 in and The part is regarded as an admittance element, and the power-frequency relationship is expressed in the form of a circuit, so that the Pω admittance model of a single VSG is obtained, as shown in Figure 4 As shown, Figure 4 This is a schematic diagram of the Pω admittance model of a single VSG provided in this application.

[0070] Furthermore, the Pω admittance model of the single VSG includes the active command disturbance source , a single-ended network of the first mechanical admittance and the second mechanical admittance, the mechanical admittance of the model satisfies the following relationship:

[0071]

[0072]

[0073]

[0074] in, is the synchronization coefficient, and are the first mechanical admittance and the second mechanical admittance, respectively. 、 are the steady-state values ​​of the VSG filter port voltage and the common connection point voltage, is the reactance of the line, is the filter port voltage and PCC voltage The steady-state phase angle difference between is the Laplace operator, and is the virtual inertia and damping coefficient of the active loop, is the reference value of angular frequency.

[0075] S103: Based on the Pω admittance model of the single VSG, an equivalent Pω admittance model of multiple VSGs in parallel is constructed.

[0076] In one possible embodiment, Figure 4The Pω admittance model of a single VSG shown in FIG is connected in parallel to obtain an equivalent Pω admittance model of multiple VSGs connected in parallel. This model can be found in FIG. Figure 5 , Figure 5 This is a schematic diagram of an equivalent Pω admittance model of multiple VSGs connected in parallel provided by this application.

[0077] S2: Based on the equivalent Pω admittance model of the multiple VSGs connected in parallel, analyze the oscillation characteristics of the current system with multiple VSGs connected in parallel.

[0078] In a possible embodiment, taking the disturbance of the power instruction of unit 1 as an example, Figure 5 It can be analyzed that the interaction process between parallel VSG units mainly includes the following three stages: (1) The power instruction of unit 1 ΔP ref1 A disturbance occurs, causing the unit's own power ΔP 1 changes; (2) Unit 1 power changes cause the frequency of the common connection point offset occurs; (3) PCC The impact of frequency fluctuations, such as Figure 4 As shown in the marked key links of multi-machine interaction, the power of other units also oscillates, forming interactive dynamics within the system.

[0079] S3: Based on the oscillation characteristics of the current parallel multi-VSG system, an improved phase-locked loop is used to obtain the frequency of the common connection point.

[0080] Furthermore, the oscillation characteristic is that the oscillation in the parallel multi-VSG system is propagated through the PCC frequency disturbance.

[0081] Furthermore, the S3 specifically includes:

[0082] S301: Based on the oscillation characteristics of the current parallel multi-VSG system, using an improved phase-locked loop to calculate the true phase angle of the common connection point;

[0083] S302: Performing differentiation processing on the true phase angle to obtain the frequency of the common connection point.

[0084] like Figure 6 As shown, Figure 6 This is a schematic diagram of a traditional phase-locked loop control structure provided by this application. The phase-locked loop is used to obtain the phase angle signal of the grid-connected point voltage. The phase-locked loop control structure includes a phase detector, a PI controller, and a voltage-controlled oscillator. The input of the phase-locked loop control structure is a three-phase voltage, and the output is the corresponding frequency and phase angle, where and Represent the frequency and phase angle measured by the phase-locked loop respectively. Transformations include:

[0085]

[0086] in, for Transformation matrix, is the amplitude of the voltage signal at the common connection point, Public connection point Shaft voltage component, for Shaft voltage component, is the phase angle measured by the phase-locked loop, is the true phase angle of the voltage, 、 、 is the ABC three-phase voltage at the common connection point.

[0087] From the above formula, we can see that the traditional phase-locked loop uses PI control to make , thereby achieving phase angle tracking, under steady-state conditions, ,and , linearizing the q-axis in the above formula, we can get:

[0088]

[0089] Then we can get the traditional phase-locked loop linear model, which can be found in Figure 7 , Figure 7 This is a schematic diagram of a linearized model of a traditional phase-locked loop provided in this application, wherein the transfer function of the traditional phase-locked loop can be expressed as:

[0090]

[0091] in, and are the parameters of the phase-locked loop PI controller.

[0092] As can be seen from the above formula, the dynamic characteristics of a traditional phase-locked loop conform to a typical second-order system. Dynamic fluctuations and overshoots are inevitable during its measurement process, resulting in inaccurate frequency and phase angle measurements, thereby affecting control accuracy.

[0093] Furthermore, in order to enhance the oscillation suppression effect, a Figure 8 The phase-locked loop shown, Figure 8 A schematic diagram of an improved phase-locked loop structure provided by the present application, comprising: a phase detector, a PI controller, an integrator and a feedforward summing link connected in sequence;

[0094] A1: Use the phase detector to receive the three-phase AC voltage signal of the common connection point in the parallel multi-VSG system, and transform the three-phase AC voltage signal into a two-phase rotating coordinate system to obtain the voltage of the common connection point. Axis and Shaft voltage components:

[0095]

[0096] in, for Transformation matrix, is the amplitude of the voltage signal at the common connection point, Public connection point Shaft voltage component, for Shaft voltage component, To improve the intermediate estimated phase angle obtained by the phase-locked loop measurement, is the true phase angle of the voltage, 、 、 is the ABC three-phase voltage at the common connection point;

[0097] A2: Shaft voltage component Perform linearization and obtain The amount of change:

[0098]

[0099] in, For public connection points The change in the shaft voltage component, is the true phase angle value of the common connection point, The intermediate estimated phase angle value obtained by measuring the improved phase-locked loop;

[0100] A3: Generate frequency estimates using a PI controller :

[0101]

[0102] in, and To improve the parameters of the phase-locked loop PI controller;

[0103] A4: Use the integrator to estimate the frequency conduct Integral processing to obtain the intermediate estimated phase angle value of the improved phase-locked loop ;

[0104] A5: Using the feedforward summation link The change in the intermediate estimated phase angle value of the improved phase-locked loop Add them together to eliminate the dynamic error of the phase-locked loop and obtain the true phase angle of the common connection point:

[0105] .

[0106] Furthermore, the transfer function of the improved phase-locked loop is:

[0107]

[0108] in, The transfer function of the improved phase-locked loop.

[0109] The input of the improved phase-locked loop is three-phase voltage, and the output is the true frequency and phase angle of the voltage, that is, the transfer function .

[0110] It is understandable that Figure 6 and Figure 8 It can be seen that the improved phase-locked loop only has one more feedforward summation link for solving the phase angle, which is and traditional phase-locked loop to measure phase angle After adding The phase angle is directly differentiated to obtain the frequency. The improved phase-locked loop has the following characteristics: small structural changes, simple control, and no increase in the order of the system.

[0111] In a possible embodiment, in order to analyze how the improved phase-locked loop structure can achieve error-free tracking of frequency and phase angle, the improved phase-locked loop is linearized, such as Figure 9 As shown, Figure 9 This is a schematic diagram of an improved phase-locked loop linearization model provided in this application. Figure 9 It can be seen that , the newly added feedforward branch makes and Add together to cancel out , eliminating the dynamic error of the phase-locked loop and achieving error-free tracking.

[0112] The improved PLL transfer function shows that its numerator and denominator are identical, GPLL*=1, meeting the desired characteristics and ensuring measurement accuracy. The improved PLL only adds a feedforward summation step in the phase angle calculation, but this change significantly improves the dynamic response and accuracy of frequency measurement. Essentially, it eliminates the dynamic errors of the traditional PLL through direct feedforward compensation, allowing the measured frequency to accurately track the true grid frequency, providing more accurate input information for subsequent multi-VSG parallel system control.

[0113] S4: According to the variation of the frequency of the common connection point from the rated value, a feedforward compensation is added to the frequency generation in the active control loop of a single VSG to cancel the PCC frequency disturbance.

[0114] In one possible embodiment, according to the oscillation characteristics of the current parallel multi-VSG system and the variation of the frequency deviation of the common connection point from the rated value, it can be known that the PCC frequency impact is caused by adding a frequency at the power frequency small signal generation point. Therefore, a feedforward compensation opposite to the PCC frequency effect is added to the frequency generation of the active control loop, that is, the positive , will disturb Offset, such as Figure 10 As shown in the upper part, Figure 10 Schematic diagram of a parallel multi-VSG interaction suppression method provided in this application.

[0115] Can be obtained from Figure 10 It can be seen that the core of the feedforward control method is to measure the PCC frequency in real time and subtract the common connection point frequency from the rated value to obtain the change from the rated value. , it is introduced into the frequency generation link of VSG for feedforward cancellation. The closed-loop small signal model of the active control loop after adopting this method can be seen in Figure 11 , Figure 11 This application provides an improved closed-loop small-signal model of the active power control loop of the VSG. When the frequency measurement is accurate enough, the feedforward control can effectively offset the impact of grid-side frequency fluctuations on the VSG, thereby significantly suppressing the interaction between units and improving system stability.

[0116] In one embodiment of the present application, in order to verify the effectiveness of the proposed control method for oscillation suppression of a multi-VSG parallel system and the indifference of the proposed improved phase-locked loop, a system was built on the MATLAB / Simulink platform. Figure 12 The four-machine VSG parallel system shown in the figure is verified by simulation experiments. Among them, VSG1 and VSG2 are ordinary VSGs, while VSG3 and VSG4 are configured with the mutual suppression method. VSG3 uses a traditional phase-locked loop, while VSG4 uses an improved phase-locked loop.

[0117] The simulation parameters of the system are shown in Table 1. To ensure the rationality of the verification, the bandwidth of the phase-locked loop is set to 25 Hz and the damping ratio is 0.707.

[0118] Table 1 Simulation parameters

[0119]

[0120] (1) Improved phase-locked loop indifference verification

[0121] In order to verify the indifference of the improved phase-locked loop proposed in this application, the grid-side line impedance is set to zero and the grid is V gApply a 0.5Hz frequency drop and recover after 6s to obtain the phase-locked loop measurement frequency curves of VSG3 and VSG4, as shown in Figure 13 As shown, Figure 13 A comparison chart of measurement results of a traditional phase-locked loop and an improved phase-locked loop provided in an embodiment of the present application.

[0122] Depend on Figure 13 It can be seen that the frequency measurement of the traditional phase-locked loop has typical second-order dynamic characteristics, which causes overshoot and fluctuation in the measured frequency. The transfer function of the improved phase-locked loop is 1, which enables it to track the true frequency without error, showing excellent dynamic response and steady-state accuracy.

[0123] (2) Verification of the parallel multi-VSG interaction suppression method

[0124] To further verify the effectiveness of the multi-machine interaction suppression method proposed in this application, a 0.1 pu (0.2 MW) step disturbance is applied to the active power instruction of VSG1 at 3 s, and the active power changes of VSG2, VSG3 and VSG4 are observed. Figure 14 As shown, Figure 14 This is a verification diagram of the parallel multi-VSG interaction suppression method provided in this application.

[0125] The simulations above demonstrate that the proposed interaction suppression method can effectively suppress multi-machine interactions in a parallel multi-VSG system, reducing power oscillations and improving system stability. The proposed phase-locked loop measurement indifference is also verified, and further demonstrated that its application to interaction suppression can more effectively reduce the interaction effects between multiple machines, improving the system's dynamic characteristics and stability.

[0126] The present application discloses a method for suppressing the interaction of multiple VSGs in parallel based on an improved phase-locked loop. The improved phase-locked loop measures the PCC frequency and compensates for the feedforward amount, thereby quickly suppressing oscillations and improving the dynamic stability of the system. Compared with the traditional phase-locked loop, the improved phase-locked loop adds a feedforward summation link, and the measured frequency and phase angle have no overshoot or fluctuation problems, achieving error-free tracking, ensuring accurate PCC frequency measurement, and enhancing the suppression effect. At the same time, based on the PCC frequency measured by the improved phase-locked loop, a feedforward compensation amount is added to effectively weaken the interactive oscillations between units and improve the dynamic stability of the system. In addition, the present application only requires local measurement signals to achieve interactive suppression, has a simple control structure, and has low implementation cost. It is suitable for multi-VSG systems and has high practical value and promotion prospects.

[0127] It should be noted that those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of this application, and it should be understood that the scope of protection of this application is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in this application without departing from the essence of this application, and such variations and combinations are still within the scope of protection of this application.

Claims

1. A method for suppressing interaction of multiple VSGs in parallel based on an improved phase-locked loop, characterized in that: include: S1: Based on the power-frequency small signal model of a single VSG considering the influence of the common connection point frequency, an equivalent Pω admittance model of multiple VSGs in parallel is constructed; S2: Analyze the oscillation characteristics of the current system of multiple VSGs in parallel based on the equivalent Pω admittance model of the multiple VSGs in parallel; S3: Based on the oscillation characteristics of the current parallel-connected multiple VSG system, using an improved phase-locked loop to obtain the frequency of the common connection point; S4: adding a feedforward compensation amount to the frequency generation in the active power control loop of a single VSG according to the variation of the frequency of the common connection point from the rated value to cancel the PCC frequency disturbance; Said S3 specifically includes: S301: Calculating the true phase angle of the common connection point using an improved phase-locked loop based on the oscillation characteristics of the current multiple VSG system connected in parallel; S302: performing differentiation processing on the true phase angle to obtain the frequency of the common connection point; The improved phase-locked loop specifically comprises: a phase detector, a PI controller, an integrator and a feedforward summing link connected in sequence; A1: Use the phase detector to receive the three-phase AC voltage signal of the common connection point in multiple VSG systems in parallel, and transform the three-phase AC voltage signal into a two-phase rotating coordinate system to obtain the voltage of the common connection point. Axis and Shaft voltage components: in, for Transformation matrix, is the amplitude of the voltage signal at the common connection point, Public connection point Shaft voltage component, for Shaft voltage component, To improve the intermediate estimated phase angle obtained by the phase-locked loop measurement, is the true phase angle of the voltage, 、 、 is the ABC three-phase voltage at the common connection point; A2: Shaft voltage component Perform linearization and obtain The amount of change: in, For public connection points The change in the shaft voltage component, is the true phase angle value of the common connection point, The intermediate estimated phase angle value obtained by measuring the improved phase-locked loop; A3: Generate frequency estimates using a PI controller : in, and To improve the parameters of the phase-locked loop PI controller, is the Laplace operator; A4: Use the integrator to estimate the frequency conduct Integral processing to obtain the intermediate estimated phase angle value of the improved phase-locked loop ,in, is the angular frequency reference value; A5: Using the feedforward summation link The change in the intermediate estimated phase angle value of the improved phase-locked loop Add them together to eliminate the dynamic error of the phase-locked loop and obtain the true phase angle of the common connection point: 。 2. The method for suppressing interaction of multiple VSGs in parallel based on an improved phase-locked loop according to claim 1, characterized in that: Said S1 specifically includes: S101: Establish a power-frequency small signal model of a single VSG considering the influence of the common connection point frequency; S102: Constructing a Pω admittance model of a single VSG based on the power-frequency small signal model of the single VSG; S103: Based on the Pω admittance model of the single VSG, an equivalent Pω admittance model of multiple VSGs in parallel is constructed.

3. The method for suppressing interaction of multiple VSGs in parallel based on an improved phase-locked loop according to claim 2, characterized in that: The Pω admittance model of a single VSG includes the active power command disturbance source , a single-ended network of a first mechanical admittance and a second mechanical admittance, the mechanical admittance of the model satisfies the following relationship: in, is the synchronization coefficient, and are the first mechanical admittance and the second mechanical admittance, respectively. 、 are the steady-state values ​​of the VSG filter port voltage and the common connection point voltage, is the reactance of the line, is the filter port voltage and PCC voltage The steady-state phase angle difference between and are the virtual inertia and damping coefficient of the active loop.

4. The method for suppressing interaction of multiple VSGs in parallel based on an improved phase-locked loop according to claim 1, characterized in that: The oscillation characteristic is that the oscillation in the parallel multiple VSG system is propagated through the PCC frequency disturbance.

5. The method for suppressing interaction of multiple VSGs in parallel based on an improved phase-locked loop according to claim 1, characterized in that: The transfer function of the improved phase-locked loop is: in, The transfer function of the improved phase-locked loop.

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