Active support pre-synchronization control method based on synchronous machine three-order model

Abstract

The invention discloses an active support pre-synchronization control method based on a synchronous machine third-order model. The method comprises the following steps: introducing a frequency integral feedback link to construct an active support model; correcting the active support model according to the small signal analysis result; introducing the amplitude pre-synchronization controller into an excitation voltage loop of the active support model, introducing the phase pre-synchronization controller into an active frequency loop of the active support model, and constructing a pre-synchronization control model based on active support; starting a phase pre-synchronization controller and an amplitude pre-synchronization controller based on the pre-synchronization signal, and regulating and controlling the voltage and current of the unit; and closing the phase pre-synchronization controller and the amplitude pre-synchronization controller based on the grid-connected signal, starting a frequency integral feedback link, and regulating and controlling the voltage and current of the unit. The method has the beneficial effects that the pre-synchronization control complexity and the voltage disturbance after grid connection are reduced, and the stability of a grid-connected system is improved.

Description

Technical Field

[0001] The present application relates to the technical field of new energy grid connection, and in particular to an active support pre-synchronization control method based on a third-order model of a synchronous machine. Background Art

[0002] With the rapid economic development, large-scale development and utilization of new energy, the access of a large number of new energy stations and cross-regional DC transmission has resulted in a lack of grid inertia, leading to a decrease in the stability of the voltage at the grid connection point. For power systems with a high proportion of new energy grid connection, due to insufficient voltage and frequency support, the power system's anti-interference ability and post-fault recovery ability have been seriously deteriorated. Therefore, how to improve the support and recovery capabilities of power grids with a high proportion of new energy has become an important issue that needs attention.

[0003] The Chinese patent "A Microgrid Island Detection, Pre-synchronization Control Method and Device", publication number: CN115864516A, publication date: March 28, 2023, specifically discloses an island detection method that is used intermittently under different conditions through the AFD detection method and the AFDPF detection method. When the frequency difference is large, a smaller disturbance current is applied. When the frequency difference is small, a larger disturbance current is added to increase the detection speed to avoid the impact of long-term injection of interference current on power quality; the pre-synchronization control method increases the compensation amount for the voltage frequency or amplitude of the microgrid through the pre-synchronization method when the microgrid is in an island state and before the grid is connected, so that the voltage frequency and amplitude of the microgrid can be consistent with the large grid. However, this scheme uses a phase-locked loop to construct a voltage phase angle pre-synchronization control structure, which is complex to control, and does not disclose how to solve the grid-connected frequency disturbance problem after the pre-synchronization is completed.

[0004] The Chinese patent "Grid-connected pre-synchronization control method for photovoltaic storage microgrid based on virtual synchronous generator", publication number: CN110112787A, publication date: August 9, 2019, specifically discloses the use of a phase-locked loop to obtain the voltage amplitude, frequency and phase information on the microgrid bus side and the large grid side, and realizes the grid-connected pre-synchronization of the photovoltaic storage microgrid by adding and controlling the pre-synchronization unit in the inverter. It can eliminate the current shock at the moment of microgrid grid connection and realize the smooth switching of the microgrid from island mode to grid-connected mode. Similarly, this solution also uses a phase-locked loop to construct pre-synchronization control, which is complex to control, and does not disclose how to solve the grid-connected frequency disturbance problem after the pre-synchronization is completed. Summary of the invention

[0005] The present application aims to solve the problems in the prior art of complex synchronization control during grid connection and low voltage tracking accuracy of pre-synchronization control after grid connection, and provides an active support pre-synchronization control method based on the third-order model of synchronous machine. In the pre-synchronization stage, an amplitude pre-synchronization controller based on amplitude difference and a phase pre-synchronization controller based on voltage component difference are used to achieve voltage synchronization between the unit and the grid, reduce the impact current generated at the moment of grid connection, and make the grid connection process smooth. After grid connection, the frequency integral feedback link is switched to follow the voltage, further optimizing the frequency control of the unit, enhancing the system's resistance to frequency disturbances, and improving system stability. In the pre-synchronization stage, a more flexible pre-synchronization controller is used to make real-time adjustments according to different grid conditions and unit states, and after grid connection, the pre-synchronization controller is turned off to start the frequency integral feedback link, which not only avoids control conflicts, but also uses a more accurate frequency integral feedback link to maintain synchronization, thereby improving the accuracy of the system.

[0006] To achieve the above technical objectives, the present application provides a technical solution, which is an active support pre-synchronization control method based on a third-order model of a synchronous machine, comprising the following steps: S1: Introducing a frequency integral feedback link based on the third-order model of the synchronous machine to construct an active support model; S2: Performing small signal analysis based on the active support model, and correcting the active support model according to the small signal analysis results; S3: Constructing a phase pre-synchronization controller and an amplitude pre-synchronization controller, introducing the amplitude pre-synchronization controller into the excitation voltage loop of the active support model, and introducing the phase pre-synchronization controller into the active frequency loop of the active support model to construct a pre-synchronization control model based on active support; S4: Starting the phase pre-synchronization controller and the amplitude pre-synchronization controller based on the pre-synchronization signal, and regulating the unit voltage and current according to the pre-synchronization control model based on active support; S5: Turning off the phase pre-synchronization controller and the amplitude pre-synchronization controller based on the grid-connected signal, starting the frequency integral feedback link, and regulating the unit voltage and current according to the pre-synchronization control model based on active support.

[0007] Furthermore, the construction of an active support model by introducing a frequency integral feedback link based on the third-order model of the synchronous machine includes: constructing an active support initial model including an active frequency loop, an excitation voltage regulation loop, an excitation circuit control loop and a virtual impedance control according to the third-order model of the synchronous machine; introducing a frequency integral feedback link in the active frequency loop to construct an active support model.

[0008] Furthermore, the performing of small signal analysis based on the active support model and correcting the active support model according to the small signal analysis results include: determining the dynamic equation of the grid-connected system based on the active support model; performing linearization processing on the dynamic equation to obtain the small signal model of the grid-connected system; performing small signal analysis using the small signal model of the grid-connected system, and correcting the active support model according to the small signal analysis results.

[0009] Furthermore, the dynamic equations of the grid-connected system at least include an electromagnetic power equation and a voltage equation.

[0010] Furthermore, the linearization of the dynamic equations to obtain the small signal model of the grid-connected system includes: linearizing the electromagnetic power equation and the voltage equation to obtain the influence relationship of electromagnetic power change, the influence relationship of q-axis electromotive force change and the influence relationship of inverter-end voltage change; constructing the small signal model of the grid-connected system based on the influence relationship of electromagnetic power change, the influence relationship of q-axis electromotive force change and the influence relationship of inverter-end voltage change.

[0011] Furthermore, the modifying of the active support model according to the small signal analysis results includes: obtaining a small signal analysis result set based on the grid-connected structure parameter adjustment; and selecting the grid-connected structure parameter with the highest stability according to the small signal analysis result set to modify the active support model.

[0012] Furthermore, the construction of a phase pre-synchronization controller and an amplitude pre-synchronization controller includes: constructing a phase pre-synchronization controller based on the voltage components of the grid voltage in a two-phase stationary coordinate system and the voltage components of the grid connection point voltage in a two-phase stationary coordinate system; constructing an amplitude pre-synchronization controller based on the grid voltage amplitude and the grid connection point voltage amplitude.

[0013] Furthermore, the construction of a phase pre-synchronization controller based on the voltage components of the grid voltage in the two-phase stationary coordinate system and the voltage components of the grid connection point voltage in the two-phase stationary coordinate system includes: constructing a phase pre-synchronization controller based on the sum of the squares of the differences between the voltage components of the grid voltage in the two-phase stationary coordinate system and the voltage components of the grid connection point voltage in the two-phase stationary coordinate system.

[0014] Furthermore, starting the phase pre-synchronization controller and the amplitude pre-synchronization controller based on the pre-synchronization signal also includes: after receiving the pre-synchronization signal, determining whether the first closing condition is met, if so, starting the phase pre-synchronization controller and the amplitude pre-synchronization controller, if not, issuing an alarm prompt.

[0015] Furthermore, the method of closing the phase pre-synchronization controller and the amplitude pre-synchronization controller based on the grid-connected signal and starting the frequency integral feedback link also includes: after receiving the grid-connected signal, determining whether the second closing condition is met, if so, starting the frequency integral feedback link, if not, issuing an alarm prompt.

[0016] The beneficial effects of the present application are as follows: by using an amplitude pre-synchronization controller and a phase pre-synchronization controller in the pre-synchronization stage to synchronize the unit with the grid voltage, the impact current generated at the moment of grid connection is reduced, and the grid connection process is smoothed. After grid connection, the frequency integral feedback link is switched to follow the voltage, further optimizing the frequency control of the unit, enhancing the system's resistance to frequency disturbances, and improving system stability. In the pre-synchronization stage, a more flexible pre-synchronization controller is used to make real-time adjustments according to different grid conditions and unit states, and after grid connection, the pre-synchronization controller is turned off to start the frequency integral feedback link, which not only avoids control conflicts, but also uses a more accurate frequency integral feedback link to maintain synchronization, thereby improving the accuracy of the system.

[0017] The phase synchronization controller adjusts the voltage component difference between the PCC and the grid on the αβ axis to approach 0, and uses the PI regulator to compensate the unit output frequency, thereby achieving phase synchronization between the PCC voltage and the grid voltage, omitting the phase-locked link to simplify the control strategy and improving the stability and reliability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a block diagram of the active support pre-synchronization control method of the present application based on the third-order model of the synchronous machine.

[0019] Figure 2 This is a block diagram of active power control with frequency modulation characteristics of an active supported pre-synchronization control method based on a third-order model of a synchronous machine in this application.

[0020] Figure 3 This is a frequency response diagram of different values ​​of the frequency modulation integral parameter of the active support pre-synchronization control method based on the third-order model of the synchronous machine in this application.

[0021] Figure 4 This is the characteristic root trajectory diagram of the active support pre-synchronization control method based on the third-order model of the synchronous machine in this application when D remains unchanged and H changes.

[0022] Figure 5 This is the characteristic root trajectory diagram of the active support pre-synchronization control method based on the third-order model of the synchronous machine in this application when D changes and H remains unchanged.

[0023] Figure 6 This is a schematic diagram of the pre-synchronization control principle of the active support pre-synchronization control method based on the third-order model of the synchronous machine in this application.

[0024] Figure 7 This is a block diagram of a phase synchronization controller of an active supported pre-synchronization control method based on a third-order model of a synchronous machine in this application.

[0025] Figure 8This is a block diagram of the amplitude synchronization controller of the active support pre-synchronization control method based on the third-order model of the synchronous machine in this application.

[0026] Fig. 9 Schematic diagram of the voltage and current synchronization process of island-to-grid connection without pre-synchronization control.

[0027] Fig.10 This is a schematic diagram of the phase synchronization process of island-to-grid connection based on the active support pre-synchronization control method of the third-order model of the synchronous machine in this application.

[0028] Fig.11 This is a schematic diagram of the voltage and current synchronization process of an island-to-grid connection using an active support pre-synchronization control method based on a third-order model of a synchronous machine in this application.

[0029] Fig.12 This is a schematic diagram of the A-phase voltage comparison of the active support pre-synchronization control method based on the third-order model of the synchronous machine in this application. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below in conjunction with the drawings and examples. It should be understood that the specific implementation method described here is only an optimal embodiment of the present application, which is only used to explain the present application and does not limit the scope of protection of the present application. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0031] like Figure 1 As shown, as the first embodiment of the present application, the active support pre-synchronization control method based on the third-order model of the synchronous machine includes the following steps: S1: Based on the third-order model of synchronous machine, the frequency integral feedback link is introduced to construct an active support model; S2: Perform small signal analysis based on the active support model, and modify the active support model according to the small signal analysis results; S3: construct a phase presynchronization controller and an amplitude presynchronization controller, introduce the amplitude presynchronization controller into the excitation voltage loop of the active support model, introduce the phase presynchronization controller into the active frequency loop of the active support model, and construct a presynchronization control model based on active support; S4: starting the phase presynchronization controller and the amplitude presynchronization controller based on the presynchronization signal, and regulating the voltage and current of the unit according to the presynchronization control model based on active support; S5: Based on the grid-connected signal, the phase pre-synchronization controller and the amplitude pre-synchronization controller are turned off, the frequency integral feedback link is started, and the unit voltage and current are regulated according to the pre-synchronization control model based on active support.

[0032] In the process of island-to-grid transition, the frequency of the systems on both sides may be different, which will cause a large impact current to be generated at the moment of grid connection. By introducing frequency integral feedback, the system can respond to frequency deviation faster and adjust the output power, thereby reducing the frequency difference and the impact current. At the same time, the influence of frequency integral feedback on the dynamic characteristics of the system is evaluated by small signal analysis, and the active support model is corrected based on the analysis results to ensure that the active support model can still accurately reflect the actual behavior of the system under complex working conditions such as island-to-grid transition, thereby improving the flexibility and adaptability of the active support model. Then, the phase pre-synchronization controller and the amplitude pre-synchronization controller are constructed to introduce the excitation voltage loop and the active frequency loop of the active support model respectively, and the pre-synchronization control model based on active support is constructed. The phase pre-synchronization controller and the amplitude pre-synchronization controller are started in the pre-synchronization stage before grid connection, so as to realize the precise control of frequency, phase and voltage amplitude before grid connection, so as to reduce the impact during grid connection and improve the stability of the system.

[0033] Specifically, the third-order model of the synchronous machine is constructed based on the synchronous generator rotor motion equation, transient voltage equation, and excitation circuit equation of the generator without damping winding: Where H is the virtual inertia; D is the damping coefficient; ω0 is the synchronous angular velocity; P m is the mechanical power; P e is the electromagnetic power; Δω is the deviation between the rated speed and the actual speed; δ is the generator power angle; T d ′0 is the time constant of the synchronous generator excitation winding, E q is the q-axis electromotive force, E q ′ is the transient electromotive force of q axis, E qe is the forced no-load electromotive force, i d is the d-axis current component, x d is the d-axis synchronous reactance, x′ d is the d-axis transient reactance, and t is the time.

[0034] At this time, the active support model is constructed by introducing the frequency integral feedback link based on the third-order model of the synchronous machine, including: According to the third-order model of synchronous machine, an initial model of active support including active frequency loop, excitation voltage regulation loop, excitation circuit control loop and virtual impedance control is constructed; A frequency integral feedback link is introduced into the active frequency loop to construct an active support model.

[0035] The control equation of the frequency integral feedback link is: Among them, ω N is the actual angular velocity, ΔP is the compensation power value, and s is the complex frequency variable.

[0036] by Substituting into the control equation we get: Among them, k ω is the frequency modulation integral parameter.

[0037] The frequency integral feedback link is introduced into the active frequency loop to compensate for the load active power fluctuation. Figure 3 As shown, the frequency modulation integral parameter k in the island mode ω The frequency response when taking different values. Figure 3 It can be seen that when k ω = 0, that is, without frequency feedback, the frequency response in the island mode will remain at a non-rated value, which will have an adverse effect on the power equipment in the long run; when frequency feedback regulation is introduced, the system frequency returns to the rated value, and with other parameters unchanged, as k ω As the value of k increases, the initial peak value of the system frequency decreases and the frequency fluctuation increases. Therefore, it is necessary to reasonably select k. ω The numerical value of .

[0038] Performing small signal analysis based on the active support model and modifying the active support model according to the small signal analysis results include: Determine the dynamic equations of the grid-connected system based on the active support model; Linearizing the dynamic equations to obtain a small signal model of the grid-connected system; The small signal model of the grid-connected system is used to perform small signal analysis, and the active support model is modified according to the small signal analysis results.

[0039] The dynamic equations of the grid-connected system include at least the electromagnetic power equation and the voltage equation.

[0040] Electromagnetic power P in active support model e for: P e =U d I d +U q I q =E q 'I q -(X d ′-X q )I d I q ; Among them, U d is the d-axis voltage, I d is the d-axis current, U q is the q-axis voltage, I q is the q-axis current, X′ d is the transient reactance of the d-axis, X qis the synchronous reactance of the q-axis.

[0041] Since the excitation voltage E f and forced no-load electromotive force E qe It is in linear proportion, and its proportional coefficient is x ad / r f Use the per unit value of the excitation voltage to replace the actual value or per unit value of the forced no-load electromotive force. If the excitation voltage E is set f and forced no-load electromotive force E qe The reference values ​​of and present the same proportional relationship, then the per unit values ​​of the excitation voltage and the forced no-load electromotive force are equal. Therefore, the electromagnetic power equation is linearized, that is, the electromagnetic power equation and the third-order model of the synchronous machine are linearized at the stable operating point of the system, and the following is obtained: ΔP e =(E q ′0ΔI q +ΔE q 'I q0 )-(X d ′-X q )(I d0 ΔI q +ΔI d I q0 ); Among them, Δδ is the change of generator power angle, ΔP e is the change in electromagnetic power, ΔE q ′ is the transient electromotive force change, X d is the synchronous reactance of the d-axis, ΔI d is the d-axis current change, E q ′0 is the transient electromotive force at the static operating point, ΔI q is the q-axis current change, I q0 is the q-axis current at the static operating point, I d0 is the d-axis current at the static operating point.

[0042] Linearizing the voltage equation involves: The inverter terminal voltage is expressed in the xy coordinate system: U t ∠θ=U x +jU y ; Among them, U t is the inverter terminal voltage, θ is the phase angle, U x is the x-axis voltage component, U y is the y-axis voltage component, and j is the imaginary unit.

[0043] The transformation matrix from the xy stationary coordinate system to the dq axis coordinate system is: By converting the xy stationary coordinate system to the dq coordinate system, we can obtain: Among them, U g is the amplitude of the generator terminal voltage, and X is the synchronous reactance of the generator.

[0044] Construct the per-value mathematical model of the inverter terminal voltage in the dq coordinate system: Combined and sorted, we get: After incrementalization, the incremental equation is obtained as follows: Among them, δ0 is the generator power angle at the static operating point, ΔU d is the change in d-axis voltage, ΔU q is the change in q-axis voltage.

[0045] According to the effective value of the inverter terminal voltage: The corresponding incremental equation is: Among them, ΔU t is the change of the inverter terminal voltage, U t0 is the inverter terminal voltage at the static operating point, U d0 is the d-axis voltage at the static operating point, U q0 is the q-axis voltage at the static operating point, K5 and K6 are influence coefficients.

[0046] Similarly, based on the equal per-unit values ​​of the excitation voltage and the forced no-load electromotive force, the transfer function of the excitation system is obtained as follows: Where, ΔE f is the change in excitation voltage, K e is the proportional gain constant, T e is the time constant.

[0047] Then the incremental equation of the excitation system transfer function is: Based on the incremental equation of the effective value of the inverter terminal voltage and the incremental equation of the excitation system transfer function, we can obtain: After finishing, we get: Among them, K1, K2, K3, K4, K5, and K6 are influence coefficients.

[0048] Specifically, K1 is: K2 is: K3 is: K4 is: K5 and K6 are:

[0049] In this embodiment, linearizing the dynamic equation to obtain a small signal model of the grid-connected system includes: Linearizing the electromagnetic power equation and the voltage equation to obtain the influence relationship of electromagnetic power change, the influence relationship of q-axis electromotive force change and the influence relationship of inverter terminal voltage change; A small signal model of the grid-connected system is constructed based on the influence of electromagnetic power changes, q-axis electromotive force changes and inverter terminal voltage changes.

[0050] Among them, the influence relationship of electromagnetic power change, the influence relationship of q-axis electromotive force change and the influence relationship of inverter terminal voltage change are: The small signal model of the grid-connected system is obtained by combining the linearized model parameters and eliminating the intermediate algebraic variables: It can be seen that the distribution of characteristic roots is mainly affected by the virtual inertia coefficient H and the damping coefficient D. Different virtual inertia coefficients H and damping coefficients D correspond to different characteristic roots. The stability of the system can be analyzed by analyzing the root locus diagram: Figure 4 The figure shows the characteristic root trajectory diagram when D is constant and H changes. When the damping D is 100 and the inertia H changes from 1 to 20, S1, S2 and S3, S4 are the two main pairs of characteristic roots. Figure 4 It is known that when the virtual inertia H changes, S3 and S4 are both negative real roots, and the characteristic roots do not change significantly. The characteristic roots S1 and S2 change with the virtual inertia H, and the characteristic roots change significantly. Figure 4 In the figure, H changes along the direction of the arrow and gradually increases. Due to the gradual increase of inertia H, the characteristic roots S1 and S2 gradually extend toward the imaginary axis, and the stability of the control system gradually decreases.

[0051] Figure 5 The figure shows the characteristic root trajectory diagram when H is constant and D changes. When the inertia H=2 and the damping D changes from 60 to 140, S1, S2 and S3, S4 are the two pairs of dominant characteristic roots of the system. Figure 5 It can be seen that the characteristic roots S3 and S4 are negative real roots, and the characteristic roots do not change significantly with the change of damping D. As the damping D gradually increases in the direction of the arrow, the characteristic roots S1 and S2 gradually extend toward the negative real axis, and the stability of the control system gradually improves.

[0052] In this embodiment, the stability of the system is analyzed by analyzing the root locus diagram, and the various parameters in the active support model are continuously adjusted to make the characteristic root of the system away from the imaginary axis to improve the stability margin of the system and optimize the dynamic response characteristics. If increasing the proportional gain of the controller causes the system to become unstable (the characteristic root moves to the right half plane of the complex plane), the gain value is appropriately reduced; if reducing the integral time constant can improve the dynamic performance of the system (the characteristic root moves to the lower left of the complex plane), the parameter is further reduced to determine the change in the dynamic performance of the system.

[0053] At this time, the active support model is modified according to the small signal analysis results, including: Obtain a set of small signal analysis results based on grid-connected structure parameter adjustment; The active support model is modified by selecting the grid-connected structure parameters with the highest stability according to the small signal analysis result set.

[0054] In this embodiment, constructing a phase presynchronization controller and an amplitude presynchronization controller includes: A phase presynchronization controller is constructed according to the voltage components of the grid voltage in a two-phase stationary coordinate system and the voltage components of the grid connection point voltage in a two-phase stationary coordinate system; An amplitude pre-synchronization controller is constructed according to the voltage amplitude of the power grid and the voltage amplitude of the grid connection point.

[0055] The phase presynchronization controller is constructed according to the voltage components of the grid voltage in the two-phase stationary coordinate system and the voltage components of the grid connection point voltage in the two-phase stationary coordinate system: The angular frequency difference Δω is calculated based on the square sum of the difference between the voltage component of the grid voltage in the two-phase stationary coordinate system and the voltage component of the grid connection point voltage in the two-phase stationary coordinate system. s Build a phase presynchronization controller: Δω s =(U gα -ΔU 0α ) 2 +(U 0β -ΔU 0β ) 2 ; Among them, Ugα is the α-axis component of the grid voltage in the two-phase stationary coordinate system, ΔU 0α is the change of the α-axis component of the grid-connected point voltage in the two-phase stationary coordinate system, U 0β is the β-axis component of the grid-connected point voltage in the two-phase stationary coordinate system, ΔU 0β is the change in the β-axis component of the grid-connected point voltage in the two-phase stationary coordinate system.

[0056] The amplitude pre-synchronization controller is constructed according to the grid voltage amplitude and the grid connection point voltage amplitude: Calculate the difference ΔU based on the grid voltage amplitude and the grid connection point voltage amplitude s Construct an amplitude presynchronization controller: ΔU s =U gs -ΔU 0s ; Among them, U gβ is the β-axis component of the grid voltage in the two-phase stationary coordinate system, U gs is the grid voltage amplitude, U 0s is the voltage amplitude at the grid connection point.

[0057] The active frequency loop of the active support model with the phase presynchronization controller is: Sθ=ω N +Δω+Δω S ; Where θ is the phase angle.

[0058] The excitation voltage loop of the active support model with the amplitude presynchronization controller is: ΔU s After the PI controller, the excitation voltage loop is introduced: Among them, U ref is the reference value of the excitation voltage, U0 is the initial value of the excitation voltage, U s is the feedback impact value, K e is the proportional gain, T e is the time constant, Δu f is the excitation voltage adjustment. It can be understood that here U s That is ΔU s .

[0059] In this embodiment, the amplitude pre-synchronization controller monitors the voltage amplitudes of the power grid and the unit, and inputs the difference as a reference signal into the excitation controller. The excitation controller adjusts the excitation voltage of the unit according to the difference signal, so that the voltage amplitude of the unit gradually matches the power grid, so as to reduce the voltage difference and impact current when connected to the grid.

[0060] like Figure 6 As shown in the figure, after receiving the grid connection command, the grid voltage is used as the reference value of the amplitude pre-synchronization controller and the phase pre-synchronization controller, and the output is continuously adjusted to synchronize the voltage amplitude and phase. After the grid connection conditions are met, the PCC switch S1 is closed, and the amplitude pre-synchronization controller and the phase pre-synchronization controller can quickly switch modes. By adjusting the output of the power frequency modulator and the excitation regulator, the grid voltage can be tracked and the grid connection impact current can be reduced.

[0061] When the unit switches to the pre-synchronization mode, it receives the pre-synchronization signal, starts the phase pre-synchronization controller and the amplitude pre-synchronization controller based on the pre-synchronization signal, and regulates the unit voltage and current according to the pre-synchronization control model based on active support until the unit system is synchronized with the power grid. At this time, it is considered that the synchronization is completed, and the grid connection signal is received. The phase pre-synchronization controller and the amplitude pre-synchronization controller are closed based on the grid connection signal, and the frequency integral feedback link is started. According to the pre-synchronization control model based on active support, the voltage and current of the unit are regulated. By using the amplitude pre-synchronization controller and the phase pre-synchronization controller in the pre-synchronization stage to synchronize the unit with the grid voltage, the impact current generated at the moment of grid connection is reduced, and the grid connection process is smooth. After grid connection, the frequency integral feedback link is switched to follow the voltage, further optimizing the frequency control of the unit, enhancing the system's resistance to frequency disturbances, and improving the system stability. In the pre-synchronization stage, a more flexible pre-synchronization controller is used to make real-time adjustments according to different conditions of the grid and the state of the unit, and after grid connection, the pre-synchronization controller is closed and the frequency integral feedback link is started, which not only avoids control conflicts, but also uses a more accurate frequency integral feedback link to maintain synchronization and improve the accuracy of the system.

[0062] like Figure 7 , Figure 8 As shown, u ga ,u gb ,u gc is the component of the grid voltage in the three-phase coordinate system, u 0a ,u 0b ,u 0c is the component of the grid connection point voltage in the three-phase coordinate system, u gα ,u gβ is the component of the grid voltage in the two-phase stationary coordinate system, u 0α ,u 0βis the component of the grid connection point voltage in the two-phase static coordinate system. The phase synchronization controller adjusts the voltage component difference between the PCC and the grid on the αβ axis to approach 0, and uses the difference through the PI regulator to compensate the unit output frequency, realizing the phase synchronization of the voltage at the PCC and the grid voltage, while omitting the phase-locked link to simplify the control strategy and improving the stability and reliability of the system. At the same time, the amplitude of the grid connection point and the grid voltage is calculated using the two-phase static coordinate system. Then the difference between the two is calculated and compensated with the expected error. The compensated signal is fed back to the excitation controller through the PI module to achieve rapid tracking of the grid voltage. By adding an amplitude pre-synchronization controller, the voltage amplitude of the grid and the unit is monitored, and the difference is input into the excitation controller as a reference signal. The excitation controller adjusts the excitation voltage of the unit according to the difference signal, so that the voltage amplitude of the unit gradually matches the grid to reduce the voltage difference and impact current when connected to the grid.

[0063] In this embodiment, starting the phase presynchronization controller and the amplitude presynchronization controller based on the presynchronization signal further includes: After receiving the pre-synchronization signal, it is determined whether the first closing condition is met. If so, the phase pre-synchronization controller and the amplitude pre-synchronization controller are started. If not, an alarm prompt is issued.

[0064] Based on the grid-connected signal, the phase pre-synchronization controller and the amplitude pre-synchronization controller are closed, and the frequency integral feedback link is started, which also includes: After receiving the grid-connected signal, it is determined whether the second closing condition is met. If so, the frequency integral feedback link is started. If not, an alarm is issued.

[0065] The first closing condition is: Among them, ω set is the speed difference judgment threshold, θ set is the phase difference judgment threshold, U set is the voltage difference judgment threshold.

[0066] The second closing condition is: θ0=θ g , U0=U g , Ctrl=1.

[0067] In this embodiment, before grid connection, the switch S1 at the PCC is in an open state, and the switch S2 of the phase amplitude pre-synchronization controller is in an open state, that is, the frequency and phase of the output voltage are not adjusted. When the unit switches to the pre-synchronization mode, the pre-synchronization signal sent by the unit is received. When the first closing condition is met, the switch S2 is closed, S1 remains open, and the pre-synchronization controller is started. After the system is synchronized with the grid, the grid connection signal sent by the unit is received. When the second closing condition is met, the switch S1 is closed, S2 is opened, the pre-synchronization controller exits operation, and the system enters the grid connection mode.

[0068] In some other embodiments, the second closing condition further includes: S2 is disconnected, that is, S1 will be closed only when S2 is disconnected, thereby avoiding control conflict.

[0069] As the second embodiment of the present application, a specific embodiment is provided for illustration. The system is built in the MATLAB / Simulink simulation environment, the local active load is 0.25pu, the reactive load is 0.05pu, the system sends a pre-synchronization signal at 0.5s, and the first closing condition, i.e., the threshold judgment condition, is ω set =0.2πrad / s,θ set =5rad, U set =0.012pu, during the simulation, Figure 1 The circuit breakers S1 shown are all in a closed state, and the system is in a grid-connected state. Fig. 9 This is the simulation result without adding pre-synchronization control; Fig.10 , Fig.11 as well as Fig.12 This is the simulation waveform of the island-to-grid transition process after adding pre-synchronization control. Fig.10 , Fig.11 as well as Fig.12 It can be seen that by introducing the phase synchronization controller and the amplitude synchronization controller, fast and smooth grid connection can be achieved.

[0070] The present application adds a phase pre-synchronization controller and an amplitude pre-synchronization controller to the active-frequency loop and the excitation-voltage loop in the third-order model, thereby ensuring that the frequency, phase and voltage amplitude of the unit are consistent with the power grid, thereby achieving rapid and smooth connection of the unit to the power grid.

[0071] The specific implementation described above is a preferred implementation of the active support pre-synchronization control method based on the third-order model of the synchronous machine in this application, and it is not intended to limit the specific implementation scope of this application. The scope of this application includes but is not limited to this specific implementation. All equivalent changes made in accordance with the shape and structure of this application are within the protection scope of this application.

Claims

1. An active support pre-synchronization control method based on a third-order model of a synchronous machine is characterized by: The steps include: S1: Based on the third-order model of synchronous machine, the frequency integral feedback link is introduced to construct an active support model; S2: Perform small signal analysis based on the active support model, and modify the active support model according to the small signal analysis results; S3: construct a phase presynchronization controller and an amplitude presynchronization controller, introduce the amplitude presynchronization controller into the excitation voltage loop of the active support model, introduce the phase presynchronization controller into the active frequency loop of the active support model, and construct a presynchronization control model based on active support; S4: starting the phase presynchronization controller and the amplitude presynchronization controller based on the presynchronization signal, and regulating the voltage and current of the unit according to the presynchronization control model based on active support; S5: Based on the grid-connected signal, the phase pre-synchronization controller and the amplitude pre-synchronization controller are turned off, the frequency integral feedback link is started, and the unit voltage and current are regulated according to the pre-synchronization control model based on active support.

2. The active support pre-synchronization control method based on the third-order model of synchronous machine according to claim 1, characterized in that: The construction of the active support model based on the third-order model of the synchronous machine by introducing the frequency integral feedback link includes: According to the third-order model of synchronous machine, an initial model of active support including active frequency loop, excitation voltage regulation loop, excitation circuit control loop and virtual impedance control is constructed; A frequency integral feedback link is introduced into the active frequency loop to construct an active support model.

3. The active support pre-synchronization control method based on the third-order model of synchronous machine according to claim 1, characterized in that: The performing of small signal analysis based on the active support model and correcting the active support model according to the small signal analysis result comprises: Determine the dynamic equations of the grid-connected system based on the active support model; Linearizing the dynamic equations to obtain a small signal model of the grid-connected system; The small signal model of the grid-connected system is used to perform small signal analysis, and the active support model is modified according to the small signal analysis results.

4. The active support pre-synchronization control method based on the third-order model of synchronous machine according to claim 3, characterized in that: The dynamic equations of the grid-connected system at least include an electromagnetic power equation and a voltage equation.

5. The active support pre-synchronization control method based on the third-order model of synchronous machine according to claim 4, characterized in that: The linearization of the dynamic equation to obtain the small signal model of the grid-connected system includes: Linearizing the electromagnetic power equation and the voltage equation to obtain the influence relationship of the electromagnetic power change, the influence relationship of the q-axis electromotive force change, and the influence relationship of the inverter terminal voltage change; A small signal model of the grid-connected system is constructed based on the influence of electromagnetic power changes, q-axis electromotive force changes and inverter terminal voltage changes.

6. The active support pre-synchronization control method based on the third-order model of synchronous machine according to claim 1 or 5, characterized in that: The modifying of the active support model according to the small signal analysis result comprises: Obtain a set of small signal analysis results based on grid-connected structure parameter adjustment; The active support model is modified by selecting the grid-connected structure parameters with the highest stability according to the small signal analysis result set.

7. The active support pre-synchronization control method based on the third-order model of synchronous machine according to claim 1, characterized in that: The construction of the phase pre-synchronization controller and the amplitude pre-synchronization controller comprises: A phase presynchronization controller is constructed according to the voltage components of the grid voltage in a two-phase stationary coordinate system and the voltage components of the grid connection point voltage in a two-phase stationary coordinate system; An amplitude pre-synchronization controller is constructed according to the voltage amplitude of the power grid and the voltage amplitude of the grid connection point.

8. The active support pre-synchronization control method based on the third-order model of synchronous machine according to claim 7, characterized in that: The phase pre-synchronization controller is constructed according to the voltage component of the grid voltage in the two-phase stationary coordinate system and the voltage component of the grid connection point voltage in the two-phase stationary coordinate system, comprising: A phase presynchronization controller is constructed according to the sum of squares of differences between the voltage components of the grid voltage in a two-phase stationary coordinate system and the voltage components of the grid connection point voltage in a two-phase stationary coordinate system.

9. The active support pre-synchronization control method based on the third-order model of synchronous machine according to claim 1, characterized in that: The starting of the phase pre-synchronization controller and the amplitude pre-synchronization controller based on the pre-synchronization signal also includes: After receiving the pre-synchronization signal, it is determined whether the first closing condition is met. If so, the phase pre-synchronization controller and the amplitude pre-synchronization controller are started. If not, an alarm prompt is issued.

10. The active support pre-synchronization control method based on the third-order model of synchronous machine according to claim 9, characterized in that: The closing of the phase pre-synchronization controller and the amplitude pre-synchronization controller based on the grid-connected signal and the starting of the frequency integral feedback link also include: After receiving the grid-connected signal, it is determined whether the second closing condition is met. If so, the frequency integral feedback link is started. If not, an alarm is issued.

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