Active support cooperative control method for network construction type VSG power grid fault

Abstract

The invention discloses a network construction type VSG power grid fault active support cooperative control method, and belongs to the technical field of new energy grid-connected control. According to the method, the power grid voltage is monitored in real time, and a cooperative strategy is dynamically triggered: when the voltage drops below a set value, a cooperative control mechanism is started, including (1) self-adaptive active power adjustment based on a power angle stability margin and dynamic correction of a power instruction value to suppress kinetic energy accumulation of a rotor; (2) voltage tracking type reactive compensation is superposed in a reactive control loop, reactive current is increased in real time according to the drop depth, continuous reactive support is provided, and steady-state overcurrent is restrained; and (3) inputting a virtual resistance inductor, and limiting a transient over-current peak value by suppressing a dq-axis coupling current component. When the voltage is normal, the conventional VSG control mode is maintained. According to the invention, power-reactive power-impedance three-dimensional cooperation is realized, power angle stability, current limitation and voltage support are considered, and the stability and active support capability of the network-forming VSG under the power grid drop fault are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of virtual synchronous generator control technology, and in particular to a method for active fault support in a grid-type VSG power grid. Background Technology

[0002] Compared with traditional fossil fuels, new energy sources, mainly wind power and photovoltaics, are more efficient and environmentally friendly. Moreover, wind and solar energy are inexhaustible and can effectively address energy crises and environmental pollution problems. Therefore, new energy power generation technologies have received high attention and widespread application from countries around the world.

[0003] With the large-scale centralized or decentralized grid connection of high-proportion renewable energy sources (such as wind power and photovoltaics), the traditional power system structure, operation mode, and stability mechanism dominated by synchronous generators have undergone profound changes. The synchronous stability of the power grid has gradually shifted from "physical synchronization," dominated by the electromechanical transient characteristics of synchronous machines, to "control synchronization," dominated by the multi-timescale control of renewable energy converters. Against this backdrop, grid-forming converters (GFMs) have become a research hotspot due to their ability to actively support the power grid. Among them, virtual synchronous generator (VSG) technology, by simulating the physical characteristics of synchronous generators (such as inertia, damping, frequency regulation, and voltage regulation), can provide necessary inertia and voltage support for the power grid, thereby improving the transient stability of power grids with high proportions of renewable energy.

[0004] However, when grid faults occur (such as short circuits or voltage drops), the grid-connected operation of VSGs faces severe challenges: voltage drops can cause VSG output power imbalance, leading to loss of power synchronization, power angle sync failure, or even system collapse; during faults, VSG output current may far exceed the equipment's tolerance limits, threatening converter safety. When designing VSG transient control methods, both stability and current limiting requirements must be considered simultaneously. Therefore, how to design VSG control methods under fault transients, enabling effective transient synchronization and current limiting during fault processes, and achieving active support control of VSGs under transient conditions, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a collaborative control method for active support of grid-type VSG in the event of grid faults, so as to solve the technical problems of stability and current limiting of grid-type VSG under grid voltage drop faults.

[0006] This invention discloses a grid-type VSG (Variable Residual Gas Grid) active fault support and collaborative control method. The grid-type VSG includes an inverter, a DC power supply connected to the DC side of the inverter, an LC filter circuit connected to the AC side of the inverter, an SVPWM modulation module controlling the inverter, and a control module controlling the input signal of the SVPWM modulation module. The output terminal of the LC filter circuit is connected to the power grid. The control module includes an active power control loop, a reactive power control loop, a virtual impedance control module, and a voltage-current dual control loop. It monitors the grid voltage in real time, and when a fault occurs where the grid voltage drops beyond the maximum allowable fluctuation value, the following adjustments are made:

[0007] 1) Modify the power command value of the active power control loop, changing the constant active power command value before the fault to an adaptive value that follows changes in grid voltage; the expression for the power command value of the active power loop is as follows:

[0008]

[0009] Among them, P ref P is the power command value. ref0 The power command value before the fault; P ref0 ×M is the power command value during a fault, M is the active power command adjustment coefficient, and the value of M is (U F V gF ) /

[0010] (U N V gN ), where V gF U F These represent the mains voltage and VSG output voltage amplitudes during the fault, respectively, in V. gN U N Let V be the mains voltage and the VSG output voltage amplitude under normal conditions, respectively. g ε represents the detected grid voltage value, and ε is the maximum allowable fluctuation value of the grid voltage.

[0011] The active power control loop calculates the VSG electrical angle based on the power command value, and then calculates the d-axis current and q-axis current based on the VSG output current and the VSG electrical angle.

[0012] 2) The reactive power control loop superimposes reactive power compensation on the excitation control to reduce the vector difference between the VSG output voltage and the grid voltage; the control equations of the reactive power control loop are as follows:

[0013] ΔQ=K q (U ref -U N )

[0014]

[0015] Where: ΔQ is the reactive power compensation amount, k q U is the reactive power compensation coefficient. ref U is the amplitude of the reference voltage. N The normal output voltage amplitude of the VSG; Q ref Q is the commanded value for active power. e is the actual active power output of VSG, kp is the proportional coefficient of the PI controller, ki is the integral coefficient of the PI controller, and s is the Laplace operator;

[0016] Then E is decomposed into d-axis reference voltage and q-axis reference voltage;

[0017] 3) The virtual impedance control module controls the d-axis current i obtained in step 1). d and q-axis current i q The d-axis reference voltage E of the power grid is calculated from the d-axis reference voltage and q-axis reference voltage obtained in step 2). dref and q-axis reference voltage E qref .

[0018] 4) The voltage and current dual control loop adjusts the input signal of the SVPWM modulation module according to the output current and voltage of VSG and the grid d-axis reference voltage and q-axis reference voltage calculated in step 3).

[0019] Furthermore, in step 3), the virtual impedance control module calculates the virtual resistance R using the following formula. v and virtual inductance L v Value:

[0020]

[0021] in, K x K is the long-term current withstand factor of the inverter. y V is the peak current withstand factor of the inverter. gF U represents the voltage amplitude of the power grid during a fault. F δ represents the amplitude of the VSG output voltage during a fault. F For the angle deviation, I F The fault current is ω, and R and L are the equivalent resistance and inductance of the VSG, respectively; ω is the angular frequency.

[0022] Furthermore, the resistance-to-inductance ratio must meet the following constraints:

[0023]

[0024] Among them, K x and K y These are the inverter's peak current rating and the inverter's long-term current rating, respectively.

[0025] Furthermore, the value of ε is set to V. gN ×10%.

[0026] The beneficial effects of this invention are:

[0027] This invention relates to a grid-type VSG active support and collaborative control method for grid faults. By monitoring the grid voltage in real time, a collaborative strategy is dynamically triggered: when the voltage drops below a set value, a collaborative control mechanism is activated, including (1) adaptive active power adjustment based on the power angle stability margin, dynamically correcting the power command value to suppress rotor kinetic energy accumulation; (2) superimposing voltage tracking reactive power compensation in the reactive power control loop, increasing the reactive current in real time according to the drop depth, providing continuous reactive power support, and suppressing steady-state overcurrent; (3) inputting virtual resistance inductance, limiting the peak value of transient overcurrent by suppressing the dq-axis coupled current component. When the voltage is normal, the traditional VSG control mode is maintained. This invention can effectively reduce the deviation between the VSG output power and the command value during a fault, avoid power angle loss of synchronization, significantly improve the synchronization stability of the VSG under voltage drop conditions, reduce the vector difference between the VSG output voltage and the grid voltage, thereby reducing the steady-state fault current, and accurately suppress transient overcurrent and current spikes, ensuring that the peak value of the output current does not exceed the short-time tolerance limit of the inverter, and avoiding equipment damage. Attached Figure Description

[0028] Figure 1 This is the topology model of a network-type VSG system, where U dc U is the voltage of the DC voltage source. g L is the grid voltage. f and C f To separate the filter inductor and filter capacitor of the LC filter, R g L g For the line resistance and inductance on the power grid side, i abc and u abc These are the output current and voltage of the VSG, U ref and δ ref These represent the amplitude and phase angle of the reference voltage, ω and ω', respectively. n Here, θ represents the angular frequency and the rated angular frequency, respectively; θ is the VSG electrical angle output by the active power loop; and E is the voltage reference value output by the reactive power loop. dref E qref These are the d-axis and q-axis components of the reference voltage output by the reactive power loop, respectively, and Q. e P e These represent the actual active power and reactive power output by the VSG, respectively, Q. ref P ref These are the command values ​​for active power and reactive power, respectively, J and D. p k qThese are the virtual moment of inertia, the active power-frequency droop coefficient, and the reactive power compensation coefficient, respectively. The entire control loop consists of active power control, reactive power control, virtual impedance control, and voltage-current dual-loop control.

[0029] Figure 2 The graph shows the simulation results of the grid voltage and VSG output voltage and current before and after the fault under the traditional control method.

[0030] Figure 3 This is a simulation result diagram of the VSG output power angle before and after the fault under the traditional control method.

[0031] Figure 4 The graph shows the simulation results of the active and reactive power output of the VSG before and after the fault under the traditional control method.

[0032] Figure 5 The figures show the simulation results of the grid voltage, VSG output voltage and current before and after the fault using the method proposed in this invention.

[0033] Figure 6 The figure shows the simulation results of the VSG output power angle before and after the fault using the method proposed in this invention.

[0034] Figure 7 The figures show the simulation results of the active and reactive power output of the VSG before and after the fault, using the method proposed in this invention. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0036] like Figure 1 As shown, the grid-type VSG described in this embodiment includes an inverter, a DC power supply connected to the DC side of the inverter, an LC filter circuit connected to the AC side of the inverter, an SVPWM modulation module for controlling the inverter, and a control module for controlling the input signal of the SVPWM modulation module. The output terminal of the LC filter circuit is connected to the power grid.

[0037] In this embodiment of the active support and collaborative control method for grid-type VSG power grid faults, the control module used to control the input signal of the SVPWM modulation module includes an active power control loop, a reactive power control loop, a virtual impedance control module, and a voltage-current dual control loop. This embodiment of the active support and collaborative control method for grid-type VSG power grid faults includes: real-time monitoring of the grid voltage; when a fault occurs where the grid voltage drops beyond the maximum allowable fluctuation value, the following adjustments are made:

[0038] 1) Modify the power command value of the active power control loop, changing the constant active power command value before the fault to an adaptive value that follows changes in grid voltage. The expression for the power command value of the active power loop is as follows:

[0039]

[0040] Among them, P ref P is the power command value. ref0 The power command value before the fault; P ref0 ×M is the power command value during a fault, M is the active power command adjustment coefficient, and V g Here, ε represents the detected grid voltage value, and ε is the maximum allowable fluctuation value of the grid voltage. In this embodiment, the value of ε is set to V. gN ×10%. M in this step is obtained through the following process:

[0041] Before the fault, the power grid and VSG were operating at a stable point, and the active power output by the VSG was expressed as follows:

[0042]

[0043] Where: V gN and U N These represent the grid voltage and VSG output voltage amplitude before the fault, respectively, δ N The VSG power angle before the fault; X g =ωL g Let L be the mains impedance, ω be the angular frequency, and L be the voltage. g This refers to the line inductance on the power grid side.

[0044] During the fault, the active power P output by the VSG eF for:

[0045]

[0046] Among them, V gF and U F These represent the mains voltage and VSG output voltage amplitude during the fault, respectively, δ F The VSG power angle during a fault.

[0047] During a fault, the transient power angle of the VSG is controlled to be near its rated value, and δ is approximately considered to be... F =δ N The ratio of the active power output during the fault period to that before the fault is:

[0048]

[0049] The active power control loop calculates the VSG electrical angle based on the power command value. The calculation process for the VSG electrical angle is as follows:

[0050]

[0051] Where J is the virtual moment of inertia and D is the damping coefficient.

[0052] Then based on the output current i of the VSG abc Calculate the d-axis current and q-axis current using the VSG electrical angle θ.

[0053] 2) The reactive power control loop superimposes reactive power compensation on the excitation control to reduce the vector difference between the VSG output voltage and the grid voltage; the control equations of the reactive power control loop are as follows:

[0054] ΔQ=K q (U ref -U N )

[0055]

[0056] Where: ΔQ is the reactive power compensation amount, k q U is the reactive power compensation coefficient. ref U is the amplitude of the reference voltage. N The normal output voltage amplitude of the VSG; Q ref Q is the commanded value for active power. e denoted as the actual active power output of the VSG, kp as the proportional coefficient of the PI controller, ki as the integral coefficient of the PI controller, and s as the Laplace operator.

[0057] Then E is decomposed into d-axis reference voltage E dref and q-axis reference voltage E qref .

[0058] 3) The virtual impedance control module controls the d-axis current i obtained in step 1). d and q-axis current i q and the d-axis reference voltage E obtained in step 2). dref and q-axis reference voltage E qref Calculate the d-axis reference voltage U of the power grid. dref and q-axis reference voltage U qref d-axis reference voltage U dref and q-axis reference voltage U qref The calculation process is as follows:

[0059]

[0060] In this step, the virtual impedance control module calculates the virtual resistance R using the following formula. v and virtual inductance L v Value:

[0061]

[0062] in, K xK is the long-term current withstand factor of the inverter. y V is the peak current withstand factor of the inverter. gF U is the grid voltage during the fault. F The VSG output voltage during a fault is δ. F For the angle deviation, I F The fault current is ω, and R and L are the equivalent resistance and inductance of the VSG, respectively; ω is the angular frequency.

[0063] Furthermore, the resistance-to-inductance ratio must meet the following constraints:

[0064]

[0065] Among them, K x and K y These are the inverter's peak current rating and the inverter's long-term current rating, respectively.

[0066] The aforementioned virtual resistance R v and virtual inductance L v The formula is obtained through the following process:

[0067] The design incorporates virtual impedance to suppress transient inrush currents during voltage dips. Upon a voltage dip fault, the inverter outputs a steady-state current I. F Represented as:

[0068]

[0069] In the formula: U F V gF These represent the inverter output voltage amplitude and grid-side voltage amplitude during the fault, respectively; R and X represent the inverter's equivalent resistance and inductance L, respectively; R v X v These are the virtual resistance value and the virtual inductance L, respectively. x Inductive impedance; j is the imaginary unit.

[0070] Since the internal potential and power angle are considered constant before and after the voltage drop, if the grid voltage drops at t=0, the time-domain expression for the inverter output current after the voltage drop is:

[0071]

[0072] In the formula, For the VSG output current phase, I N This is the output current of the VSG under normal conditions.

[0073] The peak output current of the energy storage VSG, which includes transient overcurrent, derived from the above formula is expressed as follows:

[0074]

[0075] The maximum fault current should be less than the maximum short-time withstand peak impulse current of the VSG, therefore:

[0076]

[0077] Where K y It is the inverter's peak current rating.

[0078] Therefore, the range of values ​​for the virtual impedance-inductance ratio can be obtained as follows:

[0079]

[0080] Where K x It is the long-term current withstand factor of the inverter.

[0081] The virtual resistance and virtual inductance amplitudes considering voltage dip transient overcurrent are:

[0082]

[0083] In the formula,

[0084] 4) The voltage and current dual control loop adjusts the input signal of the SVPWM modulation module according to the output current and voltage of VSG and the grid d-axis reference voltage and q-axis reference voltage calculated in step 3).

[0085] To verify the effectiveness of the active support and coordinated control method for grid-type VSG power grid faults described in the above embodiments, a system as described above was built in MATLAB. Figure 1 The simulation model shown assumes that a three-phase short-circuit fault occurs in the power grid at 2 seconds, the grid voltage drops to 0.35 pu, and the fault lasts for 2 seconds. The system's synchronization stability and current limiting are compared and analyzed under the two conditions: without any improved control method and with the method proposed in this invention.

[0086] Operating Condition 1: No improved control methods are adopted;

[0087] Before t=2s, the system is in a steady state, with stable VSG output current, power, common coupling point voltage, and power angle, and the system is operating normally. At t=2s, a three-phase short-circuit fault occurs, and the grid voltage drops to 0.35pu. Due to the lack of virtual impedance current limiting and reactive power compensation, and the power reference value remaining at the pre-fault state, the common coupling point voltage drops significantly, and the VSG essentially loses its voltage support capability; the VSG output current rises, with the instantaneous peak value approaching 2.5 to 3 times the rated value, triggering overcurrent risk; and the VSG power angle exhibits significant oscillations.

[0088] Simulation results of output voltage, output current, power angle changes, and power changes before and after a VSG fault, without employing any fault recovery control methods, are as follows: Figure 2-4 As shown.

[0089] Operating Condition 2: The active support and collaborative control method for faults in the VSG grid structure proposed in this invention is adopted;

[0090] Before t=2s, the system is in a steady state, with stable VSG output current, power, voltage at the common coupling point, and power angle, indicating normal system operation. At t=2s, a three-phase short-circuit fault occurs, and the grid voltage drops to 0.35pu. Due to the adoption of the grid-type VSG active support and collaborative control method for grid faults described in this invention, the power reference value is changed, reactive power compensation is added, and virtual impedance technology is used. The grid connection point voltage is effectively raised, providing grid support. The peak output current of the VSG is significantly reduced from 2.5pu to 1.15pu, improving the device safety margin. Dynamic reactive power support is sufficient, and the power angle oscillation converges rapidly with little difference from the steady-state value.

[0091] Simulation results of the output voltage, current, power angle, and power changes before and after a VSG fault using the active support and collaborative control method for VSG grid faults of this invention are as follows: Figure 5-7 As shown.

[0092] Simulation results show that the proposed grid-connected VSG active support and coordinated control method for grid faults, when activated, significantly improves the stability and active support capability of grid-connected VSGs under grid slip faults by achieving three-dimensional coordination of power, reactive power, and impedance, while considering power angle stability, current limitation, and voltage support. It can effectively achieve synchronization and active support during VSG fault transients, keeping the voltage and power at the common coupling point between steady-state and transient states essentially consistent, thereby effectively improving the transient synchronization stability of the grid-connected VSG system. The effectiveness of the proposed method has been well demonstrated.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A grid-type VSG active fault support and collaborative control method, wherein the grid-type VSG includes an inverter, a DC power supply connected to the DC side of the inverter, an LC filter circuit connected to the AC side of the inverter, an SVPWM modulation module for controlling the inverter, and a control module for controlling the input signal of the SVPWM modulation module, wherein the output terminal of the LC filter circuit is connected to the power grid; characterized in that: The control module includes an active power control loop, a reactive power control loop, a virtual impedance control module, and a voltage and current dual control loop; it monitors the grid voltage in real time, and when a fault occurs where the grid voltage drops beyond the maximum allowable fluctuation value, it performs the following adjustments: 1) Modify the power command value of the active power control loop, changing the constant active power command value before the fault to an adaptive value that follows changes in grid voltage; the expression for the power command value of the active power loop is as follows: wherein P ref is the power command value, P ref0 is the power command value before the fault; P ref0 x M is the power command value at the time of the fault, M is an active power command adjustment coefficient, and the value of M is (U F V gF ) / (U N V gN ), wherein V gF , U F are the amplitude of the grid voltage and the VSG output voltage at the time of the fault, V gN , U N are the amplitude of the grid voltage and the VSG output voltage at normal times, and V g is the grid voltage detection value, and ε is the maximum allowable fluctuation value of the grid voltage; The active power control loop calculates the VSG electrical angle based on the power command value, and then calculates the d-axis current and q-axis current based on the VSG output current and the VSG electrical angle. 2) The reactive power control loop superimposes reactive power compensation on the excitation control to reduce the vector difference between the VSG output voltage and the grid voltage; the control equations of the reactive power control loop are as follows: ΔQ = K q (U ref -U N ) Where: ΔQ is the reactive power compensation amount, k q U is the reactive power compensation coefficient. ref U is the amplitude of the reference voltage. N The normal output voltage amplitude of the VSG; Q ref Q is the commanded value for active power. e is the actual active power output of VSG, kp is the proportional coefficient of the PI controller, ki is the integral coefficient of the PI controller, and s is the Laplace operator; Then E is decomposed into d-axis reference voltage and q-axis reference voltage; 3) The virtual impedance control module calculates the d-axis reference voltage and q-axis reference voltage of the power grid based on the d-axis current and q-axis current obtained in step 1) and the d-axis reference voltage and q-axis reference voltage obtained in step 2). 4) The voltage and current dual control loop adjusts the input signal of the SVPWM modulation module according to the output current and voltage of VSG and the grid d-axis reference voltage and q-axis reference voltage calculated in step 3).

2. The method for active support and coordinated control of faults in a grid-type VSG power grid according to claim 1, characterized in that: In step 3), the virtual impedance control module calculates the virtual resistance R using the following formula. v and virtual inductance L v Value: in, K x K is the long-term current withstand factor of the inverter. y V is the peak current withstand factor of the inverter. gF U represents the voltage amplitude of the power grid during a fault. F δ represents the amplitude of the VSG output voltage during a fault. F For the angle deviation, I F The fault current is ω, and R and L are the equivalent resistance and inductance of the VSG, respectively; ω is the angular frequency. Furthermore, the resistance-to-inductance ratio must meet the following constraints: Among them, K x and K y These are the inverter's peak current rating and the inverter's long-term current rating, respectively.

3. The method for active support and coordinated control of faults in a grid-type VSG power grid according to claim 1, characterized in that: The value of ε is set to V. gN ×10%.

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