A grid-connected inverter device with transient stability enhancement structure

Abstract

The utility model relates to power electronic conversion and network construction control technical field, propose a kind of network construction inverter device with transient stability enhancement structure, including main circuit module, control signal generation module and hardware transient promotion module;Main circuit module includes DC power supply, three-phase full-bridge inverter, LC filter and power grid simulator;Control signal generation module includes reactive power compensation unit, virtual oscillator unit and with current limiter's inner loop control unit;The input end of reactive power compensation unit output end is connected with the virtual oscillator unit, and the input end of with current limiter's inner loop control unit is connected with the output end of virtual oscillator unit;Hardware transient promotion module includes power angle feedback support channel and voltage feedback reset channel;The output end of power angle feedback support channel is connected with virtual oscillator unit, and the output end of voltage feedback reset channel is connected with reactive power compensation unit.The utility model solves the problem that existing strategy may still appear transient instability in operation, recovery difficult.

Description

Technical Field

[0001] This utility model relates to the field of power electronic conversion and grid control technology, and in particular to a grid inverter device with a transient stability enhancement structure. Background Technology

[0002] With the large-scale integration of renewable energy, traditional synchronous generators in power systems are gradually being replaced by new energy devices with power electronic converters as interfaces. Compared with rotating electrical machines, power electronic interface devices lack natural inertia and damping characteristics, making the system more sensitive to voltage and frequency disturbances and significantly reducing transient stability. To address this, grid-forming (GFM) inverters have emerged, capable of independently establishing and regulating voltage and frequency, and are considered one of the key technologies for maintaining the stable operation of new power systems. Virtual Oscillator Control (VOC) is a typical grid-forming control strategy, based on the theory of nonlinear coupled oscillators. It can achieve rapid self-synchronization and power sharing of multiple inverters through local signals without communication coordination, thus gaining widespread attention in distributed power systems. The subsequently proposed Dispatchable Virtual Oscillator Control (dVOC) further introduces active and reactive power setting mechanisms, enabling inverters to achieve precise power adjustment while maintaining synchronous operation.

[0003] However, traditional VOC and dVOC controls generally suffer from reactive power steady-state error, resulting in a large steady-state error in the inverter's output reactive power. This necessitates an additional reactive power compensation loop to achieve accurate reactive power tracking. Furthermore, when transient faults such as voltage dips or short circuits occur in the grid, the output current of the grid-connected inverter rises rapidly, easily exceeding the device's rated value and causing overheating or even damage. Therefore, current-limiting mechanisms are typically introduced to ensure hardware safety.

[0004] However, in actual operation, when the current limiting circuit activates, the dynamic coupling relationship between the inverter's internal power angle and voltage is disrupted, significantly reducing the system's transient stability. Furthermore, during grid voltage recovery, control latch-up may occur, preventing the system from returning to its pre-fault stable state and severely impacting the continuous operation of grid-connected inverters and the grid's support capabilities. Although academia and engineering have proposed various transient stability enhancement strategies, existing solutions generally neglect the coupling effect between the current limiting circuit and the reactive power compensation circuit, potentially leading to transient instability and recovery difficulties in actual operation. Utility Model Content

[0005] To address the shortcomings of existing technologies, the purpose of this utility model is to provide a grid-connected inverter device with a transient stability enhancement structure. By introducing a power angle feedback support channel and a voltage feedback reset channel into the hardware transient enhancement module, the system can maintain transient stability under grid dips or overcurrent conditions and achieve smooth system reset after fault recovery.

[0006] The solution adopted in this utility model is as follows: A grid-connected inverter device with a transient stability enhancement structure includes a main circuit module, a control signal generation module, and a hardware-based transient enhancement module. The main circuit module includes a DC power supply, a three-phase full-bridge inverter, an LC filter, and a grid simulator. The control signal generation module includes a DSP controller, which processes the sampled signals from the main circuit module and outputs a current limiting ratio. The DSP controller includes a power angle signal δ and a voltage amplitude signal V; the DSP controller comprises a reactive power compensation unit, a virtual oscillator unit, and an inner loop control unit with a current limiter; the output of the reactive power compensation unit is connected to the input of the virtual oscillator unit, and the output of the virtual oscillator unit is connected to the input of the inner loop control unit with a current limiter; the hardware transient boosting module includes a power angle feedback support channel and a voltage feedback reset channel; the output of the power angle feedback support channel is connected to the virtual oscillator unit, and the output of the voltage feedback reset channel is connected to the reactive power compensation unit.

[0007] Furthermore, the DC side of the three-phase full-bridge inverter is connected to a DC power supply and a bus capacitor, while the AC side is connected in parallel to the grid simulator port via an LC filter.

[0008] Furthermore, the output of the control signal generation module is pulse width modulated to generate a PWM signal, which is then input to the three-phase full-bridge inverter of the main circuit module.

[0009] Furthermore, the hardware-based transient boosting module detects whether the current limiter in the inner-loop control unit with the current limiter is in a current-limiting state; if the current limiter is in a current-limiting state, the hardware-based transient boosting module operates; if the current limiter is not in a current-limiting state, the hardware-based transient boosting module does not operate; specifically: The hardware-based transient boosting module includes a current limiting detection unit, which comprises a comparator and an analog switch array; the current limiting ratio... Input comparator input, current limiting ratio Compare with 1 and output the signal LIMIT_FLAG, which is then input to the analog switch array; =1, LIMIT_FLAG=0, the analog switch array is in the off state, and the hardware transient boosting module is not working; <1, LIMIT_FLAG =1, the analog switch array is in the on state, and the hardware transient boosting module is working.

[0010] Furthermore, when the analog switch array is in the open state, the output OUT1 of the power angle feedback support channel is input to the virtual oscillator unit, and the output OUT2 of the voltage feedback reset channel is input to the reactive power compensation unit.

[0011] Furthermore, the power angle feedback support channel includes a differential operational amplifier, a first multiplication simulator, and a first gain amplifier; the input terminal of the differential operational amplifier receives the current limiting ratio. The first multiplication simulator inputs the power angle signal δ and the signal after differential operation, respectively, and outputs them to the virtual oscillator unit after passing through the first gain amplifier.

[0012] Furthermore, the voltage feedback reset channel includes a differential operational amplifier, a second multiplier simulator, and a second gain amplifier; the input terminal of the differential operational amplifier receives the current limiting ratio. The second multiplier simulator inputs the voltage amplitude signal V and the signal after differential operation, respectively, and outputs them to the reactive power compensation unit after passing through the second gain amplifier.

[0013] Furthermore, the virtual oscillator unit adopts a simulated Hopf oscillator structure, consisting of a virtual inductor and a virtual capacitor; In the virtual oscillator unit circuit, the difference between the sampled grid-connected point current and the current reference obtained from the upper-level command is input to the virtual oscillator unit. After coordinate system transformation, a two-phase quadrature current signal is obtained. The two-phase quadrature current signal is multiplied by the current gain. One phase is used as the control signal of the controlled current source to output the controlled current. The other phase is multiplied by the resistivity factor and used as the control signal of the controlled voltage source. Together with the virtual inductor, virtual capacitor, Hopf nonlinear controlled voltage source, and Hopf nonlinear current source, it forms a Hopf oscillation circuit. The current on the virtual inductor is multiplied by the resistivity factor and combined with the voltage on the virtual capacitor to obtain a two-phase quadrature voltage signal. After voltage gain and coordinate system transformation, a three-phase grid voltage is obtained and the grid voltage signal is output.

[0014] Furthermore, in the reactive power compensation unit circuit, the sampled grid-connected point current and voltage are used to obtain the grid-connected point power based on instantaneous power theory. The difference between the grid-connected point power and the reactive power reference command input subtractor is obtained and input to the reactive power compensation unit. The difference is then input to the integrator after passing through a proportional gain circuit to obtain the voltage deviation. The deviation and the voltage reference value are then superimposed by an adder to obtain the final voltage reference amplitude. The final voltage reference amplitude is then input to the virtual oscillator unit after voltage gain, serving as the correction input for the Hopf nonlinear controlled voltage source and the Hopf nonlinear current source.

[0015] Furthermore, the current limiter of the inner loop control unit with the current limiter is a circular current limiter; In the inner-loop control unit circuit with a current limiter, the input three-phase grid voltage is transformed to obtain the d-axis reference voltage V and the q-axis reference voltage O. These are then subtracted from the real-time voltage components of the grid connection point voltage on the d-axis and q-axis to obtain two deviations. These two deviations are then passed through a proportionalizer and an integrator to obtain the filter current reference. The current limiter monitors the filter current reference in real time. When the current exceeds the limit, it triggers a limiting action and outputs a limited filter current reference to achieve overcurrent protection. The limited filter current reference and the acquired filter current are subtracted to obtain a deviation, which is then passed through a proportionalizer and an integrator to obtain the inverter terminal voltage reference. The inverter terminal voltage reference is then pulse-width modulated to obtain a PWM signal, which is input to the main circuit module to control the orderly switching of the switching transistors of the three-phase full-bridge inverter.

[0016] The beneficial effects of this utility model are as follows: This invention improves the inverter's ability to resist transient instability during grid dips and current limiting processes by using a hardware-based power angle feedback support channel and voltage feedback reset channel structure.

[0017] The hardware-based transient boosting module of this invention collects the status of the internal current limiter and performs corresponding actions without needing to obtain any information from the power grid side, while ensuring the active / reactive power tracking capability under normal operating conditions.

[0018] The device of this invention has a reset capability during the power grid restoration phase, effectively avoiding the latch-up phenomenon present in traditional virtual oscillators.

[0019] This invention adopts a modular hardware structure. The DSP controller only serves as a signal coordination unit, eliminating the need to rewrite the control algorithm and facilitating engineering implementation.

[0020] Advantages of the present invention in additional aspects will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] The accompanying drawings, which form part of this specification, are used to provide a further understanding of this utility model. The illustrative embodiments of this utility model and their descriptions are used to explain this utility model and do not constitute an improper limitation of this utility model.

[0022] Figure 1 This is a block diagram of a grid-connected inverter device with a transient stability enhancement structure according to this utility model; Figure 2 This is a schematic diagram of the virtual oscillator unit circuit structure of this utility model; Figure 3 This is a schematic diagram of the reactive power compensation unit circuit structure of this utility model; Figure 4 This is a schematic diagram of the inner loop control unit circuit structure with current limiter of this utility model; Figure 5 This is a schematic diagram of the hardware-based transient boosting module structure of this utility model. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this utility model.

[0025] like Figure 1 As shown, this embodiment proposes a grid-connected inverter device with a transient stability enhancement structure, including a main circuit module, a control signal generation module, and a hardware-based transient enhancement module.

[0026] Main circuit module: The main circuit module includes a DC power supply, a three-phase full-bridge inverter, an LC filter, and a grid simulator. The DC side of the three-phase full-bridge inverter is connected to the DC power supply and the bus capacitor, while the AC side is connected in parallel to the grid simulator port via the LC filter. The grid and its line impedance are simulated by the grid simulator. The LC filter consists of an inverter-side filter inductor L. f Filter capacitor C f Composition, simulating grid voltage v g The simulated grid-side impedance is inductance L. g ; Capacitor voltage v c For the system grid connection point (PCC) voltage, i g This refers to the grid-side current, i.e., the current at the grid connection point.

[0027] In this embodiment, the three-phase full-bridge inverter adopts a three-phase full-bridge topology, consisting of six IGBT power devices. The six switching transistors are switched on and off using PWM modulation to achieve the inversion effect. The control signal generation module obtains the corresponding control signal within the DSP controller based on the sampled voltage and current at the grid connection point. After PWM modulation, the resulting PWM signal is applied to the switching transistors of the main circuit.

[0028] Control signal generation module: The control signal generation module includes a DSP controller, which processes the sampled signals from the main circuit module and outputs the current limiting ratio. The power angle signal δ and voltage amplitude signal V are used. The DSP controller includes a reactive power compensation unit, a virtual oscillator unit, and an inner loop control unit with a current limiter. The output of the reactive power compensation unit is connected to the input of the virtual oscillator unit, and the output of the virtual oscillator unit is connected to the input of the inner loop control unit with a current limiter.

[0029] Specifically, the virtual oscillator unit adopts a simulated Hopf oscillator structure, consisting of a virtual inductor C and a virtual capacitor L. This part simulates the limiting cycle characteristics of the Hopf oscillator.

[0030] like Figure 2 As shown, in the virtual oscillator unit circuit, the sampled grid-connected point current i g The current reference i obtained from the superior command gref The difference is input to the virtual oscillator unit, and after transformation to the abc-αβ coordinate system, two-phase quadrature current signals are obtained; the two-phase quadrature current signals are multiplied by the current gain k. i Then, the control signal of one phase, acting as the controlled current source, outputs the controlled current i. oso The other phase current signal, multiplied by a resistive factor ε, serves as the control signal for the controlled voltage source, which, along with the virtual inductance, virtual capacitance, and Hopf nonlinear controlled voltage source v, contributes to this control. m Hopf nonlinear current source i m This forms a Hopf oscillator circuit; the current through the virtual inductor, multiplied by the resistance factor ε, and the voltage across the virtual capacitor are combined to obtain two orthogonal voltage signals; these signals are then passed through a current gain k. v The three-phase grid voltage V∠θ is obtained by transforming the coordinate system into αβ-abc, and the grid voltage signal is output.

[0031] like Figure 3 As shown, in the reactive power compensation unit circuit, the sampled grid-connected point current and voltage are used to obtain the grid-connected point reactive power based on instantaneous power theory. The grid-connected point reactive power is then compared with the reactive power reference command input from the upper level through a subtractor to obtain a difference, which is then input into the reactive power compensation unit. The difference is then passed through a proportional gain stage K. I The input is then fed into an integrator to obtain the voltage deviation ΔV. ref Deviation and voltage reference quantity V nom The final voltage reference amplitude V is obtained after superposition by the adder. ref Final voltage reference amplitude V ref via 1 / k i The scaled voltage gain of the virtual oscillator is then input to the virtual oscillator unit as a Hopf nonlinear controlled voltage source v. m Hopf nonlinear current source i m Corrected input.

[0032] In this embodiment, a synchronous rotating coordinate system is established under the inverter reference to obtain vcd v cq and i gd i gq According to existing instantaneous power theory, the inverter's grid-connected power is:

[0033] The above formula represents the prior art, where P e For grid-connected active power, Q e The reactive power is collected at the grid connection point voltage.

[0034] like Figure 4 As shown, in the inner-loop control unit circuit with a current limiter, the input three-phase grid voltage V∠θ is transformed into the abc-dq coordinate system to obtain the d-axis reference voltage V and the q-axis reference voltage 0. These are then compared with the real-time voltage components of the grid connection point voltage on the d-axis and q-axis, respectively, by a subtractor to obtain two deviations. These two deviations on the d and q axes are then passed through a proportionalizer and an integrator to obtain the filter current reference i. Lrefdq The current limiter detects the filter current reference i in real time. Lrefdq When the limit I is exceeded max When the limiting action is triggered, the output limited filter current reference i is generated. ’ Lrefdq This achieves overcurrent protection; the filtered current after limiting is referenced by i. ’ Lrefdq The collected filter current i Ldq The subtractor produces an error value, which is then passed through a proportionalizer and an integrator to obtain the inverter terminal voltage reference U. refdq Simultaneously, feedforward decoupling is introduced on the dq axis to achieve fast dynamic response. Inverter terminal voltage reference U refdq After pulse width modulation, a PWM signal is obtained and input to the main circuit module to control the orderly switching of the switching transistors of the three-phase full-bridge inverter.

[0035] In this embodiment, the current limiter of the inner loop control unit with current limiter is a circular current limiter, and the d-axis and q-axis current references are scaled proportionally. Lrefdq To prevent the integrator from saturating, a reverse anti-saturation device is applied to the voltage loop of the preceding stage.

[0036] The working principles of the circular current limiter and the anti-saturation device are respectively shown below:

[0037]

[0038] Where, k b For anti-saturation gain.

[0039] Hardware-based transient boosting module: The hardware-based transient response module includes a power angle feedback support channel and a voltage feedback reset channel. The output of the power angle feedback support channel is connected to a virtual oscillator unit, and the output of the voltage feedback reset channel is connected to a reactive power compensation unit. The hardware-based transient response module achieves transient stability of the inverter during faults and self-reset operation during fault recovery through two independent analog feedback paths.

[0040] The hardware-based transient boosting module detects whether the current limiter in the inner loop control unit with the current limiter is in a current-limiting state; if the current limiter is in a current-limiting state, the hardware-based transient boosting module works; if the current limiter is not in a current-limiting state, the hardware-based transient boosting module does not work.

[0041] like Figure 5 As shown, the hardware-based transient boosting module includes a current limiting detection unit, which comprises a comparator and an analog switch array. The current limiting ratio is... Input comparator input, current limiting ratio Compare with 1 and output the signal LIMIT_FLAG, which is then input to the analog switch array; =1, LIMIT_FLAG=0, the analog switch array is in the off state, and the hardware transient boosting module is not working; <1, LIMIT_FLAG =1, the analog switch array is in the on state, and the hardware transient boosting module is working.

[0042] When the analog switch array is in the open state, the output OUT1 of the power angle feedback support channel is input to the virtual oscillator unit, and the output OUT2 of the voltage feedback reset channel is input to the reactive power compensation unit.

[0043] Specifically, the power angle feedback support channel includes a differential operational amplifier, a first multiplier simulator, and a first gain amplifier; the input of the differential operational amplifier is the current limiting ratio. Output the signal after differential operation (1- The first multiplication simulator inputs the power angle signal δ and the signal after difference operation (1- ), to obtain (1- )δ, after passing through the first gain amplifier k b1 Output to the virtual oscillator unit.

[0044] The voltage feedback reset channel includes a differential operational amplifier, a second multiplier simulator, and a second gain amplifier; the differential operational amplifier input terminal receives the current limiting ratio. Output the signal after differential operation (1- The second multiplication simulator is input with voltage amplitude signal V and the signal after differential operation (1- ), to obtain (1- V, after passing through the second gain amplifier k b2 Output to the reactive power compensation unit.

[0045] The principle can be expressed as:

[0046] The two channels work together to provide a steady-state solution for the inverter under current limiting and reactive power compensation. During fault and recovery phases, they can prevent the continuous divergence of power angle and voltage, thereby achieving transient stability and smooth reset.

[0047] In this grid-connected inverter unit, a virtual oscillator unit generates a grid voltage signal based on the power command from the upper stage, achieving synchronized frequency and voltage output. A reactive power compensation unit generates a voltage amplitude correction signal and couples it with the virtual oscillator unit to achieve precise reactive power regulation. The inner-loop control unit ensures rapid grid voltage establishment, achieving time-scale separation, while the current limiter monitors the filter current reference in real time; when the current exceeds the limit, it triggers current-limiting protection. The transient boosting module introduces independent power angle feedback support channels and voltage feedback reset channels to ensure transient stability during faults and prevent latch-up during fault recovery.

[0048] In this embodiment, the device operates as follows: When the system is running normally in grid connection, the reactive power compensation unit collects the output reactive power in real time, generates a compensation voltage and sends it to the reactive power loop input terminal of the virtual oscillator unit. Then the virtual oscillator unit outputs the grid voltage amplitude and phase signal, which is filtered by LC to form a stable voltage source, and at the same time realizes zero steady-state error tracking of active and reactive power. When there is a grid fault or other large disturbance such as load change, the inverter device enters the transient adjustment phase; When a voltage drop in the mains is detected that causes the internal current loop reference to exceed the limit, the current limiting control unit triggers a current limiting operation. At the same time, the power angle feedback support channel dynamically corrects the output phase, and the voltage feedback reset channel dynamically corrects the output voltage, thereby preventing transient instability. When the power grid is restored, the power angle feedback support channel and the voltage feedback reset channel work together to gradually restore the voltage amplitude, achieving a smooth transition of the system and automatic recovery of normal operating conditions.

[0049] Although the specific embodiments of the present utility model have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present utility model. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solution of the present utility model are still within the scope of protection of the present utility model.

Claims

1. A grid-connected inverter device with a transient stability enhancement structure, characterized in that, The system includes a main circuit module, a control signal generation module, and a hardware-based transient response module. The main circuit module includes a DC power supply, a three-phase full-bridge inverter, an LC filter, and a grid simulator. The control signal generation module includes a DSP controller, which processes the sampled signals from the main circuit module and outputs a current limiting ratio. The DSP controller includes a power angle signal δ and a voltage amplitude signal V; the DSP controller comprises a reactive power compensation unit, a virtual oscillator unit, and an inner loop control unit with a current limiter; the output of the reactive power compensation unit is connected to the input of the virtual oscillator unit, and the output of the virtual oscillator unit is connected to the input of the inner loop control unit with a current limiter; the hardware transient boosting module includes a power angle feedback support channel and a voltage feedback reset channel; the output of the power angle feedback support channel is connected to the virtual oscillator unit, and the output of the voltage feedback reset channel is connected to the reactive power compensation unit.

2. The grid-connected inverter device with a transient stability enhancement structure as described in claim 1, characterized in that, The DC side of the three-phase full-bridge inverter is connected to the DC power supply and the bus capacitor, while the AC side is connected in parallel to the grid simulator port via an LC filter.

3. The grid-connected inverter device with a transient stability enhancement structure as described in claim 1, characterized in that, The output of the control signal generation module is pulse width modulated to generate a PWM signal, which is then input to the three-phase full-bridge inverter of the main circuit module.

4. A grid-connected inverter device with a transient stability enhancement structure as described in claim 1, characterized in that, The hardware-based transient boosting module detects whether the current limiter in the inner-loop control unit with the current limiter is in a current-limiting state; if the current limiter is in a current-limiting state, the hardware-based transient boosting module operates; if the current limiter is not in a current-limiting state, the hardware-based transient boosting module does not operate; specifically: The hardware-based transient boosting module includes a current limiting detection unit, which comprises a comparator and an analog switch array; the current limiting ratio... Input comparator input, current limiting ratio Compare with 1 and output the signal LIMIT_FLAG, which is then input to the analog switch array; =1, LIMIT_FLAG=0, the analog switch array is in the off state, and the hardware transient boosting module is not working; <1, LIMIT_FLAG =1, the analog switch array is in the on state, and the hardware transient boosting module is working.

5. A grid-connected inverter device with a transient stability enhancement structure as described in claim 4, characterized in that, When the analog switch array is in the open state, the output OUT1 of the power angle feedback support channel is input to the virtual oscillator unit, and the output OUT2 of the voltage feedback reset channel is input to the reactive power compensation unit.

6. A grid-connected inverter device with a transient stability enhancement structure as described in claim 1, characterized in that, The power angle feedback support channel includes a differential operational amplifier, a first multiplication simulator, and a first gain amplifier; the input terminal of the differential operational amplifier receives the current limiting ratio. The first multiplication simulator inputs the power angle signal δ and the signal after differential operation, respectively, and outputs them to the virtual oscillator unit after passing through the first gain amplifier.

7. A grid-connected inverter device with a transient stability enhancement structure as described in claim 1, characterized in that, The voltage feedback reset channel includes a differential operational amplifier, a second multiplier simulator, and a second gain amplifier; the input terminal of the differential operational amplifier receives the current limiting ratio. The second multiplier simulator inputs the voltage amplitude signal V and the signal after differential operation, respectively, and outputs them to the reactive power compensation unit after passing through the second gain amplifier.

8. A grid-connected inverter device with a transient stability enhancement structure as described in claim 1, characterized in that, The virtual oscillator unit adopts a simulated Hopf oscillator structure and is composed of a virtual inductor and a virtual capacitor. In the virtual oscillator unit circuit, the difference between the sampled grid-connected point current and the current reference obtained from the upper-level command is input into the virtual oscillator unit, and after coordinate system transformation, two-phase quadrature current signals are obtained. Two-phase quadrature current signals are multiplied by current gain; one phase is used as the control signal of the controlled current source to output the controlled current; the other phase is multiplied by the resistivity factor and used as the control signal of the controlled voltage source, which together with the virtual inductor, virtual capacitor, Hopf nonlinear controlled voltage source, and Hopf nonlinear current source form a Hopf oscillation circuit. The current on the virtual inductor is multiplied by the resistive factor and combined with the voltage on the virtual capacitor to obtain a two-phase orthogonal voltage signal; then, after voltage gain and coordinate system transformation, a three-phase grid voltage is obtained, and the grid voltage signal is output.

9. A grid-connected inverter device with a transient stability enhancement structure as described in claim 8, characterized in that, In the reactive power compensation unit circuit, the grid-connected point current and voltage obtained by sampling are used to obtain the grid-connected point power according to the instantaneous power theory. The difference between the grid-connected point power and the reactive power reference command input from the upper level is obtained by the subtractor and then input to the reactive power compensation unit. The difference is input to the integrator after passing through the proportional gain stage to obtain the voltage deviation. The deviation and the voltage reference value are superimposed by the adder to obtain the final voltage reference amplitude. The final voltage reference amplitude is input to the virtual oscillator unit after voltage gain, serving as the correction input for the Hopf nonlinear controlled voltage source and the Hopf nonlinear current source.

10. A grid-connected inverter device with a transient stability enhancement structure as described in claim 8, characterized in that, The current limiter of the inner loop control unit with current limiter is a circular current limiter; In the inner loop control unit circuit with a current limiter, the input three-phase grid voltage is transformed to obtain the d-axis reference voltage V and the q-axis reference voltage 0. These are then compared with the real-time voltage components of the grid connection point voltage on the d-axis and q-axis, respectively, by a subtractor to obtain two deviations. These two deviations are then passed through a proportionalizer and an integrator to obtain the filter current reference. The current limiter monitors the filter current reference in real time. When the current exceeds the limit, it triggers a limiting action and outputs a limited filter current reference to achieve overcurrent protection. The limited filter current reference and the acquired filter current are subtracted to obtain a deviation, which is then passed through a proportional and integrator to obtain the inverter terminal voltage reference. The inverter terminal voltage reference is pulse-width modulated to obtain a PWM signal, which is input to the main circuit module to control the orderly switching of the switching transistors of the three-phase full-bridge inverter.

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