Hybrid control based method and system for enhancing transient stability performance of grid-connected inverters

Abstract

This invention discloses a method and system for enhancing the transient stability of grid-connected inverters based on hybrid control, relating to the field of power electronic grid-connected control technology. The method includes the following steps: constructing a hybrid grid control architecture; generating a grid voltage modulation signal in the grid-connected control branch using a virtual synchronous generator control strategy; generating a grid-following voltage modulation signal in the grid-following control branch using a dq-axis current limiting control loop; linearly weighting and fusing the grid voltage modulation signal and the grid-following voltage modulation signal, and setting dynamic fusion weights based on an adaptive adjustment mechanism according to changes in the grid connection point voltage; driving the grid-connected inverter according to the final modulation signal, and introducing dynamic adjustment based on droop characteristics for the active power reference in the grid-connected control branch. This invention can simultaneously achieve enhanced hybrid control with synchronous stability, current limiting, and fault ride-through capability under complex operating conditions such as weak grids and deep voltage dips.

Description

Technical Field

[0001] This invention relates to the field of power electronic grid-connected control technology, and in particular to a method and system for enhancing the transient stability performance of grid-connected inverters based on hybrid control. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the large-scale grid connection of renewable energy sources such as wind power and photovoltaics based on power electronic interfaces, the power system exhibits characteristics of low inertia, weak damping, and a weak grid, significantly weakening the traditional stabilization mechanism that relies on the inertia and damping of synchronous generators. Against this backdrop, how grid-connected inverters can achieve synchronous stability, controllable current, and voltage support under both normal and fault conditions of the grid has become a key technical issue for ensuring the safe operation of the system.

[0004] Existing grid-connected inverter control strategies mainly include grid-following (GFL) control and grid-forming (GFM) control. GFL control relies on a phase-locked loop (PLL) to obtain the grid phase and has advantages such as high current regulation accuracy and fast dynamic response, making it suitable for strong grid operation scenarios. However, in weak grids or when there is a severe voltage drop, the PLL is prone to loss of lock or oscillation, leading to current runaway or even grid connection failure, and its stability is significantly limited.

[0005] GFM control establishes voltage and frequency independently through a virtual synchronous generator, providing voltage support and power regulation under weak grid conditions, which is beneficial for system stability recovery. However, due to the lack of physical inertia, its virtual inertia relies entirely on the control algorithm, making it prone to overcurrent risks and power angle divergence during large disturbances or deep voltage drops, resulting in limited transient stability margin.

[0006] To overcome the aforementioned shortcomings, various hybrid control strategies combining GFL and GFM have been proposed in recent years. Among them, the mode-switching method switches the control mode under different operating conditions, but it is prone to introducing dynamic discontinuities and stability risks. The signal fusion or parallel structure-based method avoids the mode-switching problem by integrating the control outputs of GFL and GFM, and has gradually become a research hotspot.

[0007] However, existing hybrid control strategies mostly focus on steady-state or small-disturbance analysis, with insufficient research on transient behavior under large disturbance conditions such as deep voltage drops. During a voltage sag, the inverter's transferable power decreases significantly. If the reference power is not adjusted in time, it may lead to a continuous acceleration of the power angle and trigger synchronization instability. Simultaneously, there is a coupling relationship between the voltage support of the GFM branch and the current regulation of the GFL branch, which can easily cause short-term over-limit fault current. Furthermore, in the absence of an effective power angle convergence and power coordination mechanism, even if the current does not reach the hardware limit, the system may still lose synchronization during a fault. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for enhancing the transient stability of grid-connected inverters based on hybrid control. This enhanced hybrid control can simultaneously achieve synchronous stability, current limiting, and fault ride-through capability under complex operating conditions such as weak grids and deep voltage dips, thereby improving the operational reliability of grid-connected inverters in high-proportion power electronic systems.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution: The first aspect of this invention provides a method for enhancing the transient stability performance of a grid-connected inverter based on hybrid control, comprising the following steps: Construct a hybrid network control architecture, including network-based control branches and follow-network control branches; A virtual synchronous generator control strategy is used to generate grid voltage modulation signals in the grid-type control branch; A dq-axis current limiting control loop is used to generate a grid-modulated voltage signal in the grid-type control branch. The grid voltage modulation signal and the grid connection voltage modulation signal are linearly weighted and fused, and the dynamic fusion weight is set according to the voltage change at the grid connection point based on an adaptive adjustment mechanism to obtain the final modulation signal. The grid-connected inverter is driven by the final modulation signal, and when the grid voltage drops or the grid current enters the transient control region, the active power reference in the grid-type control branch is dynamically adjusted based on the droop characteristic.

[0010] Furthermore, the phase-locked loop is eliminated in the grid-type control branch, and the voltage phase angle output by the grid-type control branch is used as a unified coordinate for angle transformation.

[0011] Furthermore, the specific steps for generating grid voltage modulation signals in the grid-type control branch using the virtual synchronous generator control strategy are as follows: A virtual synchronous generator control algorithm model is constructed by simulating the frequency and power angle dynamics of a synchronous generator using a virtual synchronous machine mechanism, including virtual moment of inertia, virtual damping coefficient, and reactive power droop coefficient. The output of the virtual synchronous generator control algorithm model includes the grid voltage modulation signal, which includes amplitude and phase.

[0012] Furthermore, the specific steps for generating the grid-connected voltage modulation signal in the grid-connected control branch using the dq-axis current limiting control loop are as follows: Construct a current dual-loop PI control structure in the dq coordinate system; The current dual-loop PI control structure uses the voltage phase angle of the grid-type control branch output as the transformation angle of the dq coordinate system to generate the grid voltage modulation signal.

[0013] Furthermore, the dynamic fusion weights are defined as a function that changes over time. The value is determined by the voltage amplitude at the grid connection point, and the piecewise functional relationship is as follows: , in, , The voltage criterion threshold is, and ; , , These correspond to the fusion weighting coefficients for normal operation, fault operation, and deep voltage drop states, respectively. This represents the voltage amplitude at the grid connection point.

[0014] Furthermore, a minimum current safety threshold is set by deriving the relationship between the current threshold and the power angle threshold; the minimum current safety threshold is used to determine whether to enter the transient control region.

[0015] A second aspect of the present invention provides a system for enhancing the transient stability performance of a grid-connected inverter based on hybrid control, comprising: The hybrid control architecture module is configured to build a hybrid mesh control architecture, including mesh control branches and follow-me control branches; The grid-type control branch module is configured to generate grid voltage modulation signals in the grid-type control branch using a virtual synchronous generator control strategy; The grid-type control branch module is configured to generate a grid-type voltage modulation signal in the grid-type control branch using a dq-axis current limiting control loop; The linear fusion module is configured to perform linear weighted fusion of the grid voltage modulation signal and the grid connection voltage modulation signal, and to set dynamic fusion weights based on an adaptive adjustment mechanism according to the change of grid connection point voltage to obtain the final modulation signal. The modulation drive module is configured to drive the grid-connected inverter according to the final modulation signal, and to introduce dynamic adjustment based on droop characteristics to the active power reference in the grid-type control branch when the grid voltage drops or the grid current exceeds a set threshold.

[0016] A third aspect of the present invention provides a computer-readable storage medium storing a computer program adapted for loading by a processor and executing the steps of the method for enhancing the transient stability performance of a grid-connected inverter based on hybrid control as described in the first aspect of the present invention.

[0017] A fourth aspect of the present invention provides a computer device comprising: A processor, adapted to execute computer programs; A computer-readable storage medium storing a computer program, which, when executed by the processor, implements the method for enhancing the transient stability performance of a grid-connected inverter based on hybrid control as described in the first aspect of the present invention.

[0018] A fifth aspect of the present invention provides a computer program product or computer program comprising computer instructions stored in a computer-readable storage medium. A processor of a computer device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the computer device to perform the steps in the method for enhancing the transient stability performance of a grid-connected inverter based on hybrid control as described in the first aspect of the present invention.

[0019] The above one or more technical solutions have the following beneficial effects: This invention discloses a method and system for enhancing the transient stability of grid-connected inverters based on hybrid control. It constructs a parallel control structure of a grid-connecting control branch and a grid-following control branch, and linearly fuses the voltage modulation signals generated by the two branches to form a unified modulation reference for the inverter. The grid-connecting control branch is used to establish and maintain the grid connection point voltage and frequency, achieving synchronization support; the grid-following control branch is used to implement current closed-loop regulation and amplitude limiting control, suppressing overcurrent during faults. Subsequently, this invention introduces an adaptive modulation weight adjustment mechanism based on the grid connection point voltage amplitude, dynamically adjusting the relative contribution ratio of the grid-connecting and grid-following control branches in modulation fusion under different grid operating conditions. This ensures that the inverter maintains grid-connecting dominance characteristics when the voltage is normal, and weakens the equivalent voltage source strength during voltage dips and faults, thereby reducing acceleration power and suppressing current rise. Simultaneously, an active power regulation mechanism based on droop characteristics is introduced into the grid-connecting control branch, dynamically reducing active power commands during grid voltage dips to suppress power angle acceleration and enhance synchronization stability. The above control methods can achieve synchronous and stable operation and current safety control of grid-connected inverters under weak grid conditions and grid fault conditions, thereby improving the reliability of system operation.

[0020] The method of this invention can significantly improve transient synchronization stability. Traditional GFM control is prone to losing synchronization under deep voltage dips due to reduced transmittable power. This invention, through an active power reference reduction mechanism using current as an indicator, effectively compresses the acceleration region and expands the deceleration region, preventing the power angle from exceeding the unstable equilibrium point. Therefore, it can ensure that the inverter maintains synchronization stability even under severe faults such as 30%–60% voltage dips.

[0021] This invention enables fast and accurate current limiting, protecting hardware safety. Because the GFL branch provides a strict current closed loop and the reference instruction includes a limiter, this invention can control the current rise rate during faults, limiting the maximum current to a set threshold and preventing damage to the driver or switching devices due to overcurrent.

[0022] This invention provides a method that can maintain stable phase synchronization without the need for a PLL. The control architecture of this invention completely eliminates the PLL in the GFL branch, instead using the GFM output angle as the common angle. This eliminates the problems of PLL jitter and phase-locked loop loss, achieves phase angle continuity during faults, and is suitable for weak and ultra-weak grid environments.

[0023] This invention enables true synergy between GFM and GFL, rather than a switching parallel connection. A linear fusion modulation mechanism achieves mode-free switching without abrupt changes. Dynamic allocation between GFM and GFL functions is natural and smooth. An adaptive modulation weighting mechanism based on grid connection point voltage amplitude dynamically adjusts the relative contribution ratio of grid-connected control branches and grid-following control branches under different grid operating conditions, thereby enhancing transient stability and current safety during faults.

[0024] This invention deeply integrates the synchronization capability of GFM, the current regulation capability of GFL, and a current-based transient power angle control strategy within a unified modulation framework, providing an efficient and feasible solution for improving transient stability, current safety, and fault ride-through capability in high-proportion power electronic systems. The invention features a simple structure, low parameter requirements, and minimal dependence on grid information, making it valuable for engineering applications and promising for widespread adoption. The method significantly improves fault ride-through capability (FRT). Simulation results show that under deep voltage dips, the current is limited to a safe range, the PCC voltage does not oscillate violently, active power recovers smoothly, and the power angle falls back quickly without significant oscillations. Overall, the FRT capability is superior to traditional GFM solutions.

[0025] Advantages of additional aspects of the invention 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

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a diagram illustrating the overall structure of the grid-connected inverter with enhanced transient stability based on hybrid control in Embodiment 1 of the present invention. Figure 2 The diagram shows a simulation comparison of the PCC voltage characteristics of the method in Embodiment 1 of the present invention and the traditional GFM control; wherein, (a) is a schematic diagram of the PCC voltage characteristics of the network control, and (b) is a schematic diagram of the PCC voltage characteristics of the hybrid control. Figure 3 The following are schematic diagrams comparing the current response simulation of the method of Embodiment 1 of the present invention with that of traditional GFM control; (a) is a schematic diagram of the current response of the network control, and (b) is a schematic diagram of the current response of the hybrid control. Figure 4 This is a schematic diagram showing a simulation comparison of the active power response of the method in Embodiment 1 of the present invention and the traditional GFM control. Detailed Implementation

[0028] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the 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.

[0029] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0030] With the large-scale integration of renewable energy, the power system is gradually exhibiting a high proportion of inverter-dominated characteristics. Under weak grid or fault conditions, traditional grid-connected control strategies face the following key technical bottlenecks: Synchronization instability is a prominent issue. GFL control relies on PLL to obtain phase, and during a fault, the PLL is prone to losing lock, leading to phase drift, sudden current changes, or even loss of synchronization. Although GFM has voltage source properties, under deep voltage dips, it may still experience a sudden drop in transmittable power, causing power angle acceleration and exceeding the unstable equilibrium point, resulting in instability.

[0031] Uncontrollable current leads to hardware risks. A sudden drop in grid voltage causes a sharp increase in the voltage vector difference between the inverter output and the grid. If the controller lacks an active current limiting mechanism, the grid-connected current will surge, potentially triggering protection actions or damaging IGBTs. The advantages of GFM and GFL are difficult to leverage simultaneously. GFM's synchronization and voltage support capabilities are naturally complementary to GFL's fast current control capabilities, but existing switching or simple weighted hybrid control methods suffer from mode abrupt changes, jitter, or insufficient dynamic coordination. Transient power angle dynamics cannot be actively adjusted. Existing methods mostly optimize hybrid control from a steady-state or small-signal perspective. However, during severe voltage drops, the power angle of the grid-connected inverter increases rapidly as the transmittable power decreases, lacking a control strategy that can directly constrain transient energy accumulation.

[0032] Therefore, this invention, through the method of Embodiment 1, achieves a hybrid control system that combines synchronous steady-state and current constraint, actively reduces acceleration energy during faults, eliminates the need for PLLs and mode switching, and provides dynamic continuous control, thereby solving the aforementioned problems. The specific details are as follows: Example 1: Embodiment 1 of this invention provides a method for enhancing the transient stability performance of grid-connected inverters based on hybrid control, which is based on linear modulation fusion and... Hybrid control of grid-connected inverters with droop regulation enhances the inverter's synchronization stability and current safety during transient voltage dips, enabling coordinated operation of voltage support, power regulation, and current limiting functions. By constructing a fusion modulation framework of grid-following control (GFL) and grid-connected control (GFM), combined with a current threshold-driven active power reference droop regulation mechanism, the angle stability and transient current behavior under severe voltage dip conditions are significantly improved without relying on a phase-locked loop (PLL), thereby enhancing the fault ride-through capability and operational reliability of the grid-connected inverter.

[0033] Specifically, the following steps are included: Step 1: Construct a hybrid network control architecture, including network control branches and follow-network control branches.

[0034] In one specific implementation, such as Figure 1 As shown, a parallel control architecture is established, which includes a grid-type control branch (GFM branch) and a follow-grid type control branch (GFL branch). The phase-locked loop is removed from the GFL branch, and the voltage phase angle output by the GFM branch is used as the unified coordinate transformation angle.

[0035] This embodiment, without employing a phase-locked loop (PLL), linearly fuses the voltage modulation signal generated by the grid-connected control path and the voltage modulation signal generated by the grid-following control path according to preset weights. Simultaneously, it introduces an adaptive modulation weight adjustment mechanism based on the grid connection point voltage amplitude, thereby forming a unified modulation reference quantity for the inverter. Based on this fusion structure, the inverter can simultaneously obtain the synchronous support capability of grid-connected control and the rapid current regulation capability of grid-following control, achieving coordinated control of voltage support, power angle synchronization, and overcurrent suppression to enhance the inverter's transient stability during faults.

[0036] like Figure 1 As shown, the hybrid grid control architecture in this embodiment specifically includes a grid-forming (GFM) control branch, a grid-following (GFL) control branch, a modulation signal fusion module, and a PWM generation module, as well as a grid-connected filter and grid interface. Furthermore, the grid-following control branch eliminates the phase-locked loop and uses the voltage phase angle output by the grid-forming control branch as a unified coordinate for angle transformation.

[0037] The network fabrication (GFM) control branch includes a virtual synchronous generator (VSG) network fabrication algorithm for generating voltage reference signals; it includes an active power regulation module, a virtual inertial module, and a frequency and phase angle generation module. The network fabrication control branch introduces... The droop adjustment module adaptively lowers the active power reference when there is overcurrent or excessive power angle increase, thereby suppressing power angle divergence and enhancing transient stability. During fault periods, the inverter output current... It will rise rapidly. The GFL (Gateway Filtering Line) control branch uses closed-loop current control, including a PI current regulator in the dq coordinate system. The GFL control branch does not use a PLL; its coordinate transformation angle is directly taken from the phase angle output of the grid branch, responsible for rapid current regulation and current limiting. The modulation signal fusion module is used to modulate the GFM output voltage signal. Modulation signal with GFL output voltage The signals are linearly combined with dynamic weights. The PWM generation module injects the fused modulation reference signal into the PWM to drive the inverter arm switches. The grid-connected filter interface includes an LC filter and is connected to the grid through the line impedance Zg (composed of Rg and Lg). The hybrid grid control architecture constructed by the above modules can simultaneously achieve grid synchronization support and fast current limiting during fault periods.

[0038] The control flow of the hybrid mesh control architecture is as follows: (1) The voltage reference is dynamically generated by the network branch based on power and frequency.

[0039] (2) The voltage adjustment amount is generated based on the current error of the network branch.

[0040] (3) The two voltage modulation signals are fused according to their weights. The fusion weight of the voltage modulation signals is a dynamic weight that changes with the voltage at the grid connection point.

[0041] (4) If the current exceeds the minimum current threshold Actively reduce active power reference in network branches .

[0042] (5) If the current exceeds The current limiting is applied to the following branch, where, This represents the maximum allowable amplitude of the inverter's output current, and is usually set to 1.2 times the rated current to protect hardware safety.

[0043] (6) The PWM module drives the inverter output.

[0044] (7) During the fault, GFM remains synchronized and GFL remains current-limited. The fusion mechanism coordinates the two to achieve stable operation.

[0045] Step 2: Use a virtual synchronous generator control strategy to generate a grid voltage modulation signal in the grid-type control branch.

[0046] In one specific implementation, the GFM branch uses a virtual synchronous generator control strategy to generate voltage modulation signals. Simultaneously, it establishes and maintains the grid connection point voltage and frequency to achieve synchronous support.

[0047] This embodiment constructs a VSG model, which generates phases It is used not only in step 2.2 to generate the voltage command for the GFM, but also as a unified coordinate transformation angle provided to the GFL branch (replacing the PLL) in step 3. That is, the virtual phase output by this model. It serves as both the voltage phase reference for the network-type branch and the unified reference angle for the dq coordinate transformation of the network-type branch, thereby achieving phase-locked loop-free control.

[0048] Step 2.1: Simulate the frequency and power angle dynamics of a synchronous generator using a virtual synchronous machine mechanism, and construct a virtual synchronous generator control algorithm model, including virtual moment of inertia and virtual damping coefficient. and reactive power droop coefficient .

[0049] Specifically, the network branch uses a virtual synchronous generator (VSG) mechanism to simulate the frequency and power angle dynamics of a synchronous generator, and its angular velocity satisfies a form similar to an oscillating equation: = .

[0050] Where J is the virtual inertia coefficient; For active power reference; This refers to the electrical power output by the inverter to the power grid. The rated angular frequency; is the damping coefficient.

[0051] power angle of inverter With frequency The relationship satisfies: = .

[0052] in, This refers to the power grid frequency.

[0053] Based on the above dynamics, this embodiment utilizes the synchronization capability provided by the GFM module as a common phase angle reference for the entire system. The GFL no longer depends on the PLL, fundamentally avoiding the PLL's lockout failure under deep voltage drops.

[0054] It is important to note that during deep voltage dips in the grid, because the GFM has the rigidity to maintain voltage, directly using the GFM phase instead of the PLL for the GFL will result in a significant deviation between its virtual internal potential phase and the actual grid voltage phase after the voltage dip. Furthermore, directly using it for GFL coordinate transformations will cause an angle between the GFL output current vector and the grid voltage. This leads to an effective power attenuation: .

[0055] in, For the injected effective damping power, For current, when When the volume is large, the effort exerted is greatly reduced.

[0056] Therefore, this embodiment does not attempt to forcibly eliminate the transient phase difference. In order to preserve the inertial advantage of GFM (without PLL), this phase difference is adapted through weight adjustment and power reduction: When phase deviation causes uncontrollable or excessive current, the weights automatically tilt towards the GFL side, using the GFL's current limiting loop to forcibly constrain the current amplitude and prevent overcurrent. Since effective power decays due to phase difference, forcibly maintaining a high power reference will only lead to current surges and accelerated instability. This embodiment detects the current... Actively reduce This allows for matching the current low-power transmission capacity and maintaining system synchronization stability during faults.

[0057] Step 2.2: Output the grid voltage modulation signal, including amplitude and phase, based on the virtual synchronous generator control algorithm model.

[0058] Specifically, the voltage reference output by the GFM branch includes amplitude. and phase Two parts: The amplitude is adjusted via reactive power droop control: .

[0059] in, This refers to the rated voltage amplitude of the inverter. This is a reference value for reactive power. This is the measured value of the reactive power output of the inverter.

[0060] Phase is derived from the phase integral of the VSG: .

[0061] The final result is: .

[0062] in, This is the grid voltage modulation signal.

[0063] Introduction of network control branches in this invention The droop adjustment module adaptively lowers the active power reference when there is overcurrent or excessive power angle increase, thereby suppressing power angle divergence and enhancing transient stability. During fault periods, the inverter output current... It will rise rapidly. This embodiment found that before rate limiting is activated, With the angle Approximate monotonic relationship; can be obtained through Determine if the inverter is close to the transient instability region; Alternative Making a threshold judgment makes it easier to implement in engineering.

[0064] Based on the derivation: Set the power angle safety threshold Then the corresponding minimum current threshold satisfy: .

[0065] in, This refers to the voltage amplitude at the grid connection point (PCC). This refers to the voltage amplitude of the power grid. This is the equivalent reactance of the line.

[0066] When in reality At that time, active power reduction is initiated: .

[0067] in, This is the droop coefficient; This method serves as a new active power reference for network branches. It can significantly reduce the acceleration trend of the power angle, making... Stay within the stable zone.

[0068] According to the equal-area rule for transient stability of power systems, the acceleration energy of the virtual power angle depends on the mechanical power (input reference). ) and electromagnetic power (output) The difference is as follows. When a power grid fault occurs, A sudden drop led to Power angle acceleration. That is, according to the equal area rule, the acceleration area during the transient period depends on the unbalanced power. By actively reducing the input reference... This reduces acceleration power, thereby effectively suppressing the power angle. And through calculation... The second derivative (acceleration) is used to prevent the work angle from exceeding the unstable equilibrium point.

[0069] Step 3: Use the dq-axis current limiting control loop to generate a grid-based voltage modulation signal in the grid-based control branch.

[0070] In one specific implementation, the GFL branch uses a dq-axis current limiting control loop to generate a voltage modulation signal. Furthermore, its control angle is provided by the GFM branch to eliminate voltage tracking errors caused by phase-locked loop step loss.

[0071] Step 3.1: Construct a dual-loop PI control structure for current in the dq coordinate system.

[0072] Specifically, the GFL branch is responsible for rapid current regulation, employing dual-loop PI control in the dq coordinate system. Since the PLL is eliminated in the mesh-based control branch of this embodiment, its transformation angle in the dq coordinate system is directly taken from the mesh-based branch output.

[0073] Among them, the dq current control structure is as follows: , .

[0074] in: , The given current is used as a reference; the back EMF term ensures control accuracy. , These are the d-axis and q-axis voltage commands output from the network branch, respectively. , The dq-axis components of the grid voltage; , This is the actual sampling current; , These are the proportional and integral coefficients of the current loop PI controller, respectively. These are the coefficients of the decoupling term.

[0075] The grid-following (GFL) control branch employs closed-loop current control, including a PI current regulator in the dq coordinate system. The GFL control branch does not use a PLL; its coordinate transformation angle is directly taken from the phase angle output of the grid-following branch, responsible for rapid current regulation and current limiting.

[0076] Step 3.3: Construct a current closed-loop and amplitude limiting constraint mechanism in the GFL branch.

[0077] Specifically, to prevent current surge during a fault, this embodiment implements strict dq-axis current regulation in the GFL branch and sets a limiter at the reference current command input. Its current limiting logic is as follows: .

[0078] in, This is the reference vector for the input current before limiting; This is the reference vector for the output current after limiting.

[0079] This embodiment employs a proportional scaling limiting logic. This current limiting logic uses a circular truncation method: when the input current reference vector amplitude... Exceeding the limit At the same time, while keeping the direction (phase angle) of the current vector unchanged, the d-axis and q-axis components are scaled down proportionally so that their combined amplitude is limited to a certain value. Inside the circle.

[0080] The current limiting action will cause the GFL output modulation voltage to drop, thereby automatically reducing the fusion voltage. This further suppresses current. This mechanism ensures that the grid-connected current does not exceed the hardware's allowable range; avoids protection tripping due to sudden current changes; and complements the GFM branch, preventing it from experiencing excessive current surges during voltage support.

[0081] Step 3.2: The current dual-loop PI control structure uses the voltage phase angle of the grid-type control branch output as the transformation angle of the dq coordinate system to generate the grid voltage modulation signal.

[0082] Specifically, the modulation signal output by GFL for: .

[0083] Step 4: Linearly weightedly fuse the grid voltage modulation signal and the grid connection voltage modulation signal, and set the dynamic fusion weight based on the adaptive adjustment mechanism according to the change of the grid connection point voltage to obtain the final modulation signal.

[0084] In one specific implementation, the voltage modulation signal and Linear weighted fusion is performed, and an adaptive modulation weight adjustment mechanism based on the voltage amplitude at the grid connection point is introduced to dynamically adjust the relative contribution ratio of the grid-type control branch and the grid-following control branch in modulation fusion under different grid operating conditions, so as to form a modulation signal for driving the grid-connected inverter.

[0085] The modulation signal fusion weights are dynamic weights that vary with the grid connection point voltage. When the grid connection point voltage is in different amplitude ranges, the modulation signals of the grid-type control branch and the grid-following control branch are linearly fused according to different weights. The unified modulation signal is then used to drive the grid-connected inverter via a pulse width modulation module.

[0086] Specifically, in this embodiment, the output voltage of the GFM is modulated. Modulation signal with GFL output voltage Linear combination with weights n: .

[0087] in, The final modulation signal is represented by 'n', which indicates the weight. This embodiment uses the internal phase angle generated by the GFM as the global coordinate system, eliminating the need for a PLL. The GFM handles synchronization and voltage support, while the GFL handles current regulation. The weight 'n' ensures the inverter exhibits GFM-dominated characteristics in weak grid conditions and demonstrates rapid current regulation in strong grid conditions, avoiding instantaneous discontinuities and dynamic shocks caused by mode switching. Through this structure, the inverter maintains both voltage source characteristics and rapid current source regulation capabilities, laying the foundation for transient control. The fused... Input PWM to generate inverter drive signals.

[0088] Based on the existing linear modulation fusion structure, this embodiment further proposes a modulation weight adaptive adjustment mechanism based on the voltage amplitude at the grid connection point, which is used to dynamically adjust the relative contribution ratio of the grid-connected control branch and the grid-following control branch under different grid operating conditions, so as to enhance transient stability and current safety during faults.

[0089] Define the dynamic fusion weights as a function that changes over time. The value is determined by the voltage amplitude at the grid connection point, and the piecewise functional relationship is as follows: .

[0090] in, , The voltage criterion threshold is, and ; , , These correspond to the fusion weighting coefficients for normal operation, fault operation, and deep voltage drop states, respectively. This represents the voltage amplitude at the grid connection point.

[0091] Under normal power grid operating conditions Modulation weights Take the larger value This allows the grid-type control branch to dominate, resulting in a stable voltage source characteristic of the inverter to maintain stable grid connection point voltage and frequency. The range of dynamic fusion weights is determined based on the equivalent voltage source characteristics required by the inverter under different operating conditions. When the grid connection point voltage is within the normal range, the fusion weights... A value of 0.8 to 1.0 can be selected to make the grid-type control branch dominate the modulation fusion, thereby ensuring that the inverter has stable voltage source characteristics to maintain the stability of grid connection point voltage and frequency.

[0092] When the grid connection point voltage drops but has not yet entered the deep voltage collapse range, that is, when the grid connection point voltage drops but has not yet entered the deep fault range. The modulation weights are switched to the intermediate value. , A value of 0.3 to 0.5 can be used to allow the control branches of the grid-type and the follow-grid-type to work together, reducing the equivalent voltage source strength while maintaining synchronization capability, so as to suppress the rapid increase trend of acceleration power and power angle during faults.

[0093] When the grid connection point voltage experiences a deep drop At that time, the modulation weight was further reduced to fusion weight A value of 0.1 to 0.2 can be used to make the grid-type current control branch dominate, significantly weaken the grid-type voltage support strength, thereby reducing the vector difference between the inverter output voltage and the grid voltage, limiting the fault current amplitude and suppressing the continuous injection of transient acceleration energy.

[0094] From a physical perspective, during severe voltage drops, by reducing the weight of the grid-type control branch in modulation fusion, the equivalent voltage source strength of the inverter can be actively weakened, thereby reducing acceleration power input, suppressing rapid power angle divergence, and improving the transient synchronization stability of the system.

[0095] Step 5: Drive the grid-connected inverter according to the final modulation signal, and introduce dynamic adjustment based on droop characteristics for the active power reference in the grid-type control branch when the grid voltage drops or the grid current enters the transient control region.

[0096] In one specific implementation, when the grid voltage drops or the grid-connected current exceeds a set threshold, dynamic adjustment based on droop characteristics is introduced to the active power reference in the GFM branch to suppress power angle acceleration during faults and enhance synchronization stability.

[0097] Specifically, when the output current of the grid-connected inverter does not exceed a set threshold, the rated active power reference is maintained. When the output current reaches or exceeds the threshold, the active power reference is droop-down based on the deviation between the output current and the threshold, and the adjusted active power reference is input to the power synchronization regulation module of the GFM branch. Simultaneously, a current limiting control loop is set in the grid-connected control branch to constrain the dq-axis current reference, thereby suppressing overcurrent during faults and protecting the grid-connected inverter. A minimum current safety threshold is set by deriving the relationship between the current threshold and the power angle threshold; the minimum current safety threshold is used to determine whether to enter the transient control region.

[0098] This embodiment analyzes the inverter's power angle dynamics during a fault using the equal area method (EEAC). This is due to deep voltage dips... Lower; if The inverter will enter the acceleration zone, and the power angle will... Continue to increase; if Exceeding the Unstable Point If this occurs, the inverter will lose synchronization. Therefore, this embodiment introduces an active power reference transient reduction mechanism to reduce the acceleration area Sac and improve transient stability margin.

[0099] To suppress transient power angle acceleration, this embodiment designs an active power reference dynamic reduction method based on measured current. The principle is as follows: During voltage dips, power reduction causes a rapid increase in the power angle. This increase in power angle corresponds to a corresponding increase in current. Therefore, the risk of power angle exceeding limits can be characterized by a current threshold. This invention derives the relationship between the current threshold and the power angle threshold, ultimately constructing a minimum current safety threshold. It is used to determine whether a transient control region has been entered.

[0100] exist At the same time, maintain the rated active power reference .

[0101] exist At this time, droop control is activated: .

[0102] right Apply nonnegativity constraints to prevent instruction abrupt changes under severe faults.

[0103] This embodiment controls the switching of physical quantities. As a locally measurable indicator, it eliminates the need to estimate impedance or grid phase angle; this mechanism directly reduces transient acceleration energy, effectively expanding the transient stability region; adaptive reduction ,make Can be re-connected with Intersecting surfaces provide sufficient deceleration area, thus preventing loss of synchronization.

[0104] It should be noted that the hybrid control in this embodiment exhibits the following synergistic characteristics: GFM provides synchronization, power angle adjustment, virtual inertia, and damping; GFL realizes fast current control and automatic current limiting; Droop control ensures automatic reduction of acceleration energy during deep drops; unified modulation ensures dynamic continuity and mode abrupt changes throughout the system. These mechanisms together constitute a novel hybrid control framework that can simultaneously address both "synchronization stability" and "current safety".

[0105] Figure 2 , Figure 3 , Figure 4 The simulation results show a comparison between this embodiment and traditional GFM control during a fault. Figure 2 (a) shows that under conventional GFM control, the PCC voltage attempts to maintain its rated value during a fault, resulting in an excessive voltage drop; while Figure 2 (b) shows that under the hybrid control of this embodiment, the PCC voltage can adapt to grid dips, reducing the voltage vector difference between the inverter and the grid. Figure 3 In the diagram, (a) indicates that the conventional GFM current overshoots during a fault, reaching up to 5 p.u.; Figure 3 (b) in the figure illustrates that the method of this embodiment strictly limits the fault current to within the safe threshold of 1.2 pu, and the waveform is smooth and without overshoot.

[0106] The grid voltage dropped from 1.0 pu to 0.4 pu, and the fault lasted for 0.4 seconds. Figure 2 , Figure 3 and Figure 4 It can be seen that: (1) Traditional GFM maintains the PCC voltage close to the rated value when the voltage drops, which causes the voltage difference flowing through the line to increase sharply, resulting in a peak current exceeding 3.0 pu.

[0107] (2) In this embodiment, the inverter voltage modulation signal is effectively reduced by fusion control, so that the current is kept near the limit.

[0108] (3) This embodiment The droop is quickly suppressed during the acceleration phase of the power angle. .

[0109] (4) After the fault is cleared, the system recovers faster than the traditional method.

[0110] Therefore, this embodiment can improve the transient stability and overcurrent resistance of the inverter under deep voltage drops.

[0111] The transient stability enhancement method based on the GFM–GFL hybrid control structure provided in this embodiment can achieve significant improvements in inverter voltage support, power angle synchronization control, rapid current limiting, active power reduction during faults, and transient stability without relying on a PLL. The control algorithm in this embodiment has a clear structure and strong engineering feasibility, and can be widely applied to scenarios such as new energy grid-connected inverters, distributed power interfaces, and microgrid power units.

[0112] Example 2: Embodiment 2 of the present invention provides a system for enhancing the transient stability performance of a grid-connected inverter based on hybrid control, comprising: The hybrid control architecture module is configured to build a hybrid mesh control architecture, including mesh control branches and follow-me control branches; The grid-type control branch module is configured to generate grid voltage modulation signals in the grid-type control branch using a virtual synchronous generator control strategy; The grid-type control branch module is configured to generate a grid-type voltage modulation signal in the grid-type control branch using a dq-axis current limiting control loop; The linear fusion module is configured to perform linear weighted fusion of the grid voltage modulation signal and the grid connection voltage modulation signal, and to set dynamic fusion weights based on an adaptive adjustment mechanism according to the change of grid connection point voltage to obtain the final modulation signal. The modulation drive module is configured to drive the grid-connected inverter according to the final modulation signal, and to introduce dynamic adjustment based on droop characteristics to the active power reference in the grid-type control branch when the grid voltage drops or the grid current exceeds a set threshold.

[0113] Example 3: Embodiment 3 of the present invention provides a computer-readable storage medium storing a computer program adapted for loading by a processor and executing the steps in the method for enhancing the transient stability performance of a grid-connected inverter based on hybrid control as described in Embodiment 1 of the present invention.

[0114] Example 4: Embodiment 4 of the present invention provides a computer device, the device comprising: A processor, adapted to execute computer programs; A computer-readable storage medium storing a computer program, which, when executed by the processor, implements the steps in the method for enhancing the transient stability performance of a grid-connected inverter based on hybrid control as described in Embodiment 1 of the present invention.

[0115] Example 5: Embodiment 5 of the present invention provides a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of a computer device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the computer device to perform the steps in the method for enhancing the transient stability performance of a grid-connected inverter based on hybrid control as described in Embodiment 1 of the present invention.

[0116] The steps and methods involved in Examples 2, 3, 4 and 5 above correspond to those in Example 1. For specific implementation methods, please refer to the relevant description section of Example 1.

[0117] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this application can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0118] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in or transmitted through a computer-readable storage medium. The computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired or wireless means. The computer-readable storage medium can be any available medium that a computer can access or a data processing device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium, an optical medium, or a semiconductor medium, etc.

[0119] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for enhancing the transient stability performance of grid-connected inverters based on hybrid control, characterized in that, Includes the following steps: Construct a hybrid network control architecture, including network-based control branches and follow-network control branches; A virtual synchronous generator control strategy is used to generate grid voltage modulation signals in the grid-type control branch; A dq-axis current limiting control loop is used to generate a grid-modulated voltage signal in the grid-type control branch. The grid voltage modulation signal and the grid connection voltage modulation signal are linearly weighted and fused, and the dynamic fusion weight is set according to the voltage change at the grid connection point based on an adaptive adjustment mechanism to obtain the final modulation signal. The grid-connected inverter is driven by the final modulation signal, and when the grid voltage drops or the grid current enters the transient control region, the active power reference in the grid-type control branch is dynamically adjusted based on the droop characteristic.

2. The method for enhancing the transient stability performance of grid-connected inverters based on hybrid control as described in claim 1, characterized in that, The phase-locked loop is removed from the grid-type control branch, and the voltage phase angle output by the grid-type control branch is used as a unified coordinate for angle transformation.

3. The method for enhancing the transient stability performance of grid-connected inverters based on hybrid control as described in claim 1, characterized in that, The specific steps for generating grid voltage modulation signals in grid-type control branches using a virtual synchronous generator control strategy are as follows: A virtual synchronous generator control algorithm model is constructed by simulating the frequency and power angle dynamics of a synchronous generator using a virtual synchronous machine mechanism, including virtual moment of inertia, virtual damping coefficient, and reactive power droop coefficient. The output of the virtual synchronous generator control algorithm model includes the grid voltage modulation signal, which includes amplitude and phase.

4. The method for enhancing the transient stability performance of grid-connected inverters based on hybrid control as described in claim 1, characterized in that, The specific steps for generating a grid-modulated voltage signal in a grid-type control branch using a dq-axis current limiting control loop are as follows: Construct a current dual-loop PI control structure in the dq coordinate system; The current dual-loop PI control structure uses the voltage phase angle of the grid-type control branch output as the transformation angle of the dq coordinate system to generate the grid voltage modulation signal.

5. The method for enhancing the transient stability performance of grid-connected inverters based on hybrid control as described in claim 1, characterized in that, Define the dynamic fusion weights as a function that changes over time. The value is determined by the voltage amplitude at the grid connection point, and the piecewise functional relationship is as follows: ， in, , The voltage criterion threshold is, and ; , , These correspond to the fusion weighting coefficients for normal operation, fault operation, and deep voltage drop states, respectively. This represents the voltage amplitude at the grid connection point.

6. The method for enhancing the transient stability performance of grid-connected inverters based on hybrid control as described in claim 1, characterized in that, The minimum current safety threshold is set by deriving the relationship between the current threshold and the power angle threshold. Determine whether to enter the transient control region based on the minimum current safety threshold.

7. A system for enhancing the transient stability of grid-connected inverters based on hybrid control, characterized in that, include: The hybrid control architecture module is configured to build a hybrid mesh control architecture, including mesh control branches and follow-me control branches; The grid-type control branch module is configured to generate grid voltage modulation signals in the grid-type control branch using a virtual synchronous generator control strategy; The grid-type control branch module is configured to generate a grid-type voltage modulation signal in the grid-type control branch using a dq-axis current limiting control loop; The linear fusion module is configured to perform linear weighted fusion of the grid voltage modulation signal and the grid connection voltage modulation signal, and to set dynamic fusion weights based on an adaptive adjustment mechanism according to the change of grid connection point voltage to obtain the final modulation signal. The modulation drive module is configured to drive the grid-connected inverter according to the final modulation signal, and to introduce dynamic adjustment based on droop characteristics to the active power reference in the grid-type control branch when the grid voltage drops or the grid current exceeds a set threshold.

8. A computer program product, characterized in that, The computer program product includes a computer program that, when executed by a processor, implements the method for enhancing the transient stability performance of grid-connected inverters based on hybrid control as described in any one of claims 1-6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program adapted to be loaded by a processor and executed as described in any one of claims 1-6: a method for enhancing the transient stability performance of a grid-connected inverter based on hybrid control.

10. A computer device, characterized in that, include: A processor, adapted to execute computer programs; A computer-readable storage medium storing a computer program, which, when executed by the processor, implements the method for enhancing the transient stability performance of a grid-connected inverter based on hybrid control as described in any one of claims 1-6.

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