Inverter transient stability method and system based on adaptive phase compensation

Abstract

The invention discloses an inverter transient stability method and system based on adaptive phase compensation, belongs to the technical field of grid-connected inverter control, and aims to solve the contradiction between fault current limiting and transient stability in the prior art. According to the invention, a phase compensation coefficient for self-adaptively adjusting according to the real-time power grid voltage and the change rate thereof is introduced into the synchronous loop of the virtual synchronous generator, and the coefficient can dynamically optimize the equivalent active power reference, the equivalent inertia and the damping of the system and cooperate with the voltage feedback of the reactive loop, so that the real-time performance of the system is improved. Therefore, the stability margin of the system is effectively expanded during the power grid fault period. On the premise of not sacrificing the fault current limiting capability, the transient stability and the fault ride-through capability of the inverter are remarkably enhanced, power and frequency oscillation is effectively inhibited, collaborative optimization of multiple performance indexes is realized, and the method has the advantages of simple structure and high robustness.

Description

Technical Field

[0001] This invention relates to the fields of power electronics and power system control technology, and particularly to a transient stability method and system for inverters based on adaptive phase compensation. It is a control method and system for enhancing the transient stability of grid-connected inverters, especially those using virtual synchronous generator control, under grid fault conditions. Background Technology

[0002] As renewable energy continues to account for an increasing proportion of the global energy mix, distributed power sources using inverters as interfaces are being connected to the grid in large numbers. Traditional grid-connected inverters mostly use phase-locked loops (PLLs) for grid synchronization and grid-following control. This control method is prone to stability issues in weak grid environments and lacks inertia and damping support capabilities, posing a challenge to grid stability.

[0003] Therefore, grid-based control technologies that can simulate the dynamic characteristics of synchronous generators, especially virtual synchronous generator (VSG) technology, have attracted widespread attention. VSG technology significantly enhances grid stability by endowing inverters with capabilities such as autonomous synchronization, inertia support, and primary frequency regulation. In VSG control, virtual impedance is typically introduced to limit inrush currents during faults and to decouple active and reactive power.

[0004] However, existing technologies have an inherent contradiction: while the introduction of virtual impedance effectively limits fault current, it also weakens the electrical connection between the inverter and the grid, leading to a decrease in the maximum transmission power of the power-angle characteristic curve. During severe grid voltage dips, a fixed active power reference value causes the system's acceleration area to be much larger than its deceleration area, easily triggering power angle instability, resulting in system oscillations or even grid disconnection.

[0005] While some improvement strategies exist, such as segmented adaptive virtual impedance and hybrid synchronous control, they often focus on optimizing a single performance characteristic or introduce complex mode-switching logic. These strategies struggle to achieve comprehensive and coordinated optimization across multiple key performance indicators, including transient stability, dynamic response speed, and fault current limiting capability. Furthermore, their adaptability and robustness in dealing with rapid and significant grid disturbances still require improvement. Therefore, a novel control strategy is urgently needed that can proactively and adaptively enhance the transient stability of the VSG without sacrificing fault current limiting capability. Summary of the Invention

[0006] This invention aims to resolve the contradiction between using virtual impedance for fault current limiting and maintaining system transient stability in existing VSG control technology. Specifically, this invention provides an inverter transient stabilization method and system based on adaptive phase compensation, which can adaptively adjust the control strategy according to grid operating conditions. This allows for effective fault current suppression, significant improvement in transient stability margin, and excellent dynamic response performance under severe grid voltage disturbances.

[0007] To address the aforementioned technical problems, this invention discloses a transient stabilization method for inverters based on adaptive phase compensation, comprising the following steps:

[0008] Step 1: Real-time acquisition of grid voltage and output active power of the grid-connected inverter at the common coupling point.

[0009] Step 2: Based on the grid voltage and its time change rate, dynamically calculate an adaptive phase compensation coefficient.

[0010] Step 3: In the synchronous loop of the inverter, the adaptive phase compensation coefficient is used to weight and combine the deviation signal between the active power reference value and the actual output active power, as well as a feedback signal based on the common coupling point voltage, to generate the input control signal of the synchronous loop.

[0011] Step 4: Based on the input control signal generated in Step 3, adjust the output angular frequency and phase angle of the inverter to generate a pulse width modulation signal to drive the inverter switching transistor.

[0012] The adaptive phase compensation coefficient in step 2 is calculated as follows: a calculated value of an S-shaped function based on the grid voltage is multiplied by an adjustment term based on the rate of change of the grid voltage, and combined with preset hysteresis control logic to obtain the final adaptive phase compensation coefficient.

[0013] The characteristics of the S-shaped function are as follows: when the grid voltage increases, its output value increases and approaches a preset upper limit; when the grid voltage decreases, its output value decreases and approaches a preset lower limit.

[0014] The characteristic of the adjustment term based on the grid voltage change rate is that when the absolute value of the grid voltage change rate increases, the value of the adjustment term decreases, thereby reducing the value of the adaptive phase compensation coefficient.

[0015] By dynamically adjusting the adaptive phase compensation coefficient, the equivalent active power reference, equivalent inertia, and equivalent damping of the inverter are optimized online in a coordinated manner. When the grid voltage decreases, the adaptive phase compensation coefficient decreases, thereby reducing the equivalent active power reference and increasing the equivalent inertia and equivalent damping.

[0016] It also includes a reactive power control loop that, when a grid voltage dip is detected, increases the reactive power reference value to raise the voltage level at the point of common coupling, thereby synergistically enhancing the transient stability of the system.

[0017] An inverter transient stability system based on adaptive phase compensation includes:

[0018] The signal acquisition unit is used to acquire the grid voltage and output active power of the grid-connected inverter at the common coupling point in real time.

[0019] An adaptive compensation coefficient generation unit, connected to the signal acquisition unit, is used to dynamically calculate an adaptive phase compensation coefficient based on the acquired grid voltage and its time rate of change.

[0020] The synchronous loop control unit receives the adaptive phase compensation coefficient, active power reference value, actual output active power, and common coupling point voltage feedback signal. It then uses these signals to weight and combine the active power deviation signal and voltage feedback signal to generate control commands for adjusting the inverter output angular frequency and phase.

[0021] The PWM signal generation unit generates a pulse width modulation signal to drive the inverter switching transistors based on the control command output by the synchronous loop control unit.

[0022] The adaptive compensation coefficient generation unit specifically includes: an S-shaped function calculation module, a voltage change rate adjustment module, and a hysteresis logic control module, used to collaboratively calculate the adaptive phase compensation coefficient.

[0023] The synchronous loop control unit receives and utilizes the adaptive phase compensation coefficient to dynamically adjust the inverter's equivalent active power reference, equivalent inertia, and equivalent damping.

[0024] It also includes a reactive power control unit, which provides reactive power support to stabilize the voltage at the point of common coupling when the grid voltage drops.

[0025] The core of an inverter transient stabilization method based on adaptive phase compensation lies in introducing an adaptive phase compensation coefficient K into the VSG synchronization loop. a This coefficient is dynamically adjusted based on the real-time collected grid voltage at the point of common coupling (PCC) and its rate of change over time.

[0026] Specifically, the method uses the adaptive coefficient K a The active power deviation signal and the PCC voltage feedback signal are weighted and combined to generate the input of the synchronization loop. When the grid voltage drops, K... aThe value decreases adaptively. This produces three synergistic effects: 1) it reduces the system's equivalent active power reference value, thereby reducing the acceleration area during faults; 2) it increases the system's equivalent inertia J. eq This enables the system to resist more severe disturbances; 3) Increase the system's equivalent damping D eq It can quickly suppress power oscillations.

[0027] Simultaneously, this invention also incorporates reactive power loop control, actively providing reactive power support during voltage dips to raise the PCC point voltage. The increased PCC voltage further increases the system's maximum transmittable power, thereby expanding the system's deceleration area. Through adaptive adjustment of the active power loop and coordinated support of the reactive power loop, this invention, from an energy balance perspective, systematically improves transient stability by both "reducing energy injection (reducing acceleration area)" and "enhancing energy dissipation capability (increasing deceleration area)."

[0028] Compared with the prior art, the present invention has the following significant advantages:

[0029] 1) Multi-objective collaborative optimization: This invention achieves collaborative optimization of multiple mutually constraining performance indicators such as transient stability, dynamic response performance and fault current limiting capability through a unified adaptive adjustment mechanism, overcoming the limitation of traditional methods that "choose one thing and lose another".

[0030] 2) Significantly enhanced transient stability: By dynamically adjusting the equivalent active reference, inertia and damping, and combining reactive voltage support, this method greatly expands the stability margin of the system under severe faults and can effectively prevent power angle instability.

[0031] 3) Excellent dynamic response performance: The introduction of adaptive damping can quickly suppress power and frequency oscillations, shorten the recovery time after a fault, and enable the system to smoothly and quickly return to a stable operating state.

[0032] 4) Simple structure and strong compatibility: The control strategy of this invention is an improvement on the standard VSG control framework. It does not require the addition of complex hardware or mode switching logic. The control structure is simple and easy to deploy and implement in existing inverter systems.

[0033] 5) Strong robustness: The control strategy directly responds to the root cause of the disturbance, the grid voltage, and has a fast response capability and strong adaptability to disturbances of different degrees and types. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the system control topology according to an embodiment of the present invention.

[0035] Figure 2This is a control block diagram of the adaptive phase compensation control method proposed in this invention.

[0036] Figure 3 It is the adaptive coefficient K a A flowchart of the dynamic adjustment logic.

[0037] Figure 4 These are waveform comparisons of the method of this invention with conventional and reference methods in terms of frequency, active power, and power angle response under a 50% voltage drop condition. Specifically, (a) compares the frequency response performance; (b) compares the active power response performance; and (c) compares the power angle response performance.

[0038] Figure 5 These are waveform comparisons of the method of this invention with conventional and reference methods in terms of frequency, active power, and power angle response under a 30% voltage drop condition. Specifically, (a) compares the frequency response performance; (b) compares the active power response performance; and (c) compares the power angle response performance. Detailed Implementation

[0039] The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings of the embodiments. It should be noted that the embodiments described below are only some examples of the present invention and not all implementations. Any other implementations obtained by those skilled in the art based on these embodiments without creative effort are within the protection scope of the present invention.

[0040] The embodiments of the present invention will now be described in further detail with reference to the accompanying drawings, such as... Figure 1 and Figure 2 The diagram illustrates the principle of adaptive synchronous loop phase compensation control proposed in this invention. The method includes:

[0041] Step 1: Construct a synchronous loop control framework based on adaptive phase compensation.

[0042] In step 1, the specific process is as follows:

[0043] Reference Figure 1 The system control topology shown is illustrated in this invention, and the method is applied to a grid-connected power generation unit with an inverter as its core. (Refer to...) Figure 2 The control block diagram shown illustrates that the core of this invention lies in improving the active power loop, i.e., the synchronization loop, of the virtual synchronous generator. Specifically, the deviation signal between the active power reference value and the actual output active power, along with a voltage feedback signal from the common coupling point, are processed by an adaptive phase compensation coefficient K. aDynamic weighted combination is performed. The weighted combination signal serves as the input to the synchronization loop, and after integrator processing, it generates the inverter's output phase angle, thereby achieving active control of the inverter's output characteristics. Simultaneously, the reactive power loop works in conjunction to provide reactive power support when the grid voltage drops, thus stabilizing the voltage at the PCC point.

[0044] like Figure 3 The figure shows the adaptive phase compensation coefficient K. a The dynamic adjustment principle is as follows:

[0045] Step 2: Design an adaptive coefficient generation strategy based on grid voltage and its rate of change.

[0046] In step 2, the specific process is as follows:

[0047] The adaptive phase compensation coefficient K a The generation of K is crucial for achieving the control effect of this invention. This process uses the real-time acquired grid voltage amplitude and its rate of change over time at the PCC point as dual inputs. First, the grid voltage amplitude is processed through an S-shaped function. This function has the following characteristics: when the voltage is normal, the output value approaches the upper limit; when the voltage drops significantly, the output value approaches the lower limit, thus establishing K. a There is a basic positive correlation with voltage level. Secondly, a regulation term based on the rate of change of voltage is introduced, whose characteristic is that when the voltage changes drastically, the value of this regulation term decreases, thereby dynamically lowering K. a The value is adjusted to instantaneously enhance system damping during transient processes. Finally, hysteresis control logic is incorporated to prevent small voltage fluctuations from causing K to degrade. a Frequent adjustments are made to output the final adaptive phase compensation coefficient.

[0048]

[0049] Where: K a For adaptive phase compensation coefficients; K a0 U is the base gain coefficient; k is the slope coefficient of the S-shaped function; U is the real-time amplitude of the grid voltage; U th The voltage threshold is the S-shaped function; α is the voltage change rate sensitivity coefficient; dU / dt is the grid voltage change rate; U prev The grid voltage value at the previous sampling time; ΔU th This is the dead zone threshold for voltage changes.

[0050] like Figure 4 and Figure 5 The diagram illustrates the performance verification principle of the control method of this invention under power grid fault conditions, specifically as follows:

[0051] Step 3: Verify and analyze the transient response performance of the proposed control method under typical power grid fault conditions.

[0052] In step 3, the specific process is as follows:

[0053] The adaptive phase compensation control method proposed in this invention is compared with the traditional VSG control method and the existing reference compensation method under different grid voltage drop conditions.

[0054] The reference phase compensation method used in this study is an active power correction mechanism based on voltage feedback. This strategy introduces a supplementary control branch into the traditional VSG active power control loop, utilizing the voltage deviation (V... ref -V g During voltage dips, the active power reference value P is dynamically reduced. ref This indirectly adjusts the synchronization angular velocity ω and the power angle θ, affecting the system's phase dynamics. Since this mechanism can regulate the system's synchronization behavior to a certain extent, this paper considers it a typical existing phase compensation technique and refers to it as the "reference method" in the simulation comparison.

[0055] Reference Figure 4 Under a severe voltage drop of 50%: traditional methods exhibit continuous oscillations and system instability; while reference methods can maintain stability, frequency and power recovery are slow, and oscillation amplitudes are large. The method of this invention demonstrates optimal performance, with minimal frequency drop, smooth active power recovery without overshoot, effective suppression of power angle oscillations, and rapid system recovery to a stable state. Details are as follows:

[0056] like Figure 4 As shown in (a), traditional VSG control causes the system frequency to drop to 49.4 Hz, followed by sustained oscillations exceeding 2 Hz, preventing the system from stabilizing. While existing phase compensation methods can maintain frequency stability, they still exhibit a frequency deviation of approximately 0.4 Hz and have a relatively long recovery time. In contrast, the proposed method limits the minimum frequency to 49.95 Hz and achieves rapid and smooth frequency recovery, with a maximum frequency deviation of only 0.05 Hz. The system stabilizes completely within 2.5 seconds with almost no oscillations, fully demonstrating the superiority of this method in terms of frequency stability and dynamic performance.

[0057] Figure 4 (b) shows that under severe voltage dip conditions, the active power response under conventional VSG control becomes completely unstable. Although existing phase compensation methods can restore active power to a steady state, they exhibit significant initial dips and oscillations. In contrast, the proposed method demonstrates the best dynamic behavior, with the smallest active power dip, a smooth recovery process without overshoot, and the fastest recovery speed, ensuring the stability of power output during faults and significantly improving the transient performance of the system.

[0058] Figure 4 (c) shows that when the voltage drops by 50%, the traditional VSG control completely loses synchronization, and the power angle becomes unstable. While the reference phase compensation method can maintain synchronization, the power angle oscillation is relatively large. In comparison, the method proposed in this paper has the most stable power angle response, the smallest oscillation, and the fastest recovery speed, demonstrating its superior transient power angle stability performance.

[0059] In summary, under the severe fault scenario of a 50% voltage drop, the VSG control strategy proposed in this paper significantly outperforms traditional VSG control and existing phase compensation methods in terms of frequency response, active power regulation, and power angle stability. This strategy effectively suppresses system oscillations, reduces frequency and power fluctuations, significantly shortens recovery time, and reliably maintains system transient synchronization stability, fully demonstrating its enormous potential in improving the fault ride-through capability of grid-connected inverters.

[0060] Reference Figure 5 Further simulations under a 30% voltage drop scenario verified the effectiveness of the method of this invention. Figure 5 As shown, compared with traditional VSG control and existing phase compensation methods, the proposed method also exhibits significant advantages in dealing with minor voltage disturbances. It significantly suppresses fluctuations in frequency, active power, and power angle, accelerates system recovery, and demonstrates stronger damping characteristics and robustness. This indicates that the proposed method is not only applicable to severe grid faults but can also effectively improve the dynamic performance and stability of the system under typical small disturbances.

[0061] comprehensive Figure 4 and Figure 5 The verification results show that by adaptively adjusting the phase compensation coefficient, the present invention can intelligently optimize the equivalent active reference, inertia and damping of the system according to the severity of the disturbance, thereby significantly improving the transient stability and dynamic response performance of the system under various power grid faults.

[0062] The calculation conditions, illustrations, etc. in the embodiments of this invention are only used to further illustrate the invention and are not exhaustive. They do not constitute a limitation on the scope of protection of the claims. Those skilled in the art, based on the inspiration gained from the embodiments of this invention, can conceive of other substantially equivalent alternatives without inventive effort, all of which are within the scope of protection of this invention.

Claims

1. A transient stabilization method for inverters based on adaptive phase compensation, characterized in that, Includes the following steps: Step 1: Real-time acquisition of grid voltage and output active power of the grid-connected inverter at the common coupling point; Step 2: Based on the grid voltage and its time rate of change, dynamically calculate an adaptive phase compensation coefficient; Step 3: In the synchronous loop of the inverter, the adaptive phase compensation coefficient is used to weight and combine the deviation signal between the active power reference value and the actual output active power, as well as a feedback signal based on the common coupling point voltage, to generate the input control signal of the synchronous loop. Step 4: Based on the input control signal generated in Step 3, adjust the output angular frequency and phase angle of the inverter to generate a pulse width modulation signal to drive the inverter switching transistor.

2. The inverter transient stabilization method based on adaptive phase compensation according to claim 1, characterized in that, The adaptive phase compensation coefficient in step 2 is calculated as follows: a calculated value of an S-shaped function based on the grid voltage is multiplied by an adjustment term based on the rate of change of the grid voltage, and combined with preset hysteresis control logic to obtain the final adaptive phase compensation coefficient.

3. The inverter transient stabilization method based on adaptive phase compensation according to claim 2, characterized in that, The characteristics of the S-shaped function are as follows: when the grid voltage increases, its output value increases and approaches a preset upper limit; when the grid voltage decreases, its output value decreases and approaches a preset lower limit.

4. The inverter transient stabilization method based on adaptive phase compensation according to claim 2, characterized in that, The characteristic of the adjustment term based on the grid voltage change rate is that when the absolute value of the grid voltage change rate increases, the value of the adjustment term decreases, thereby reducing the value of the adaptive phase compensation coefficient.

5. The inverter transient stabilization method based on adaptive phase compensation according to claim 1, characterized in that, By dynamically adjusting the adaptive phase compensation coefficient, the equivalent active power reference, equivalent inertia, and equivalent damping of the inverter are optimized online in a coordinated manner. When the grid voltage decreases, the adaptive phase compensation coefficient decreases, thereby reducing the equivalent active power reference and increasing the equivalent inertia and equivalent damping.

6. The inverter transient stabilization method based on adaptive phase compensation according to claim 1, characterized in that, It also includes a reactive power control loop that, when a grid voltage dip is detected, increases the reactive power reference value to raise the voltage level at the point of common coupling, thereby synergistically enhancing the transient stability of the system.

7. A transient stability system for an inverter based on adaptive phase compensation, characterized in that, include: The signal acquisition unit is used to acquire the grid voltage and output active power of the grid-connected inverter at the common coupling point in real time. An adaptive compensation coefficient generation unit, connected to the signal acquisition unit, is used to dynamically calculate an adaptive phase compensation coefficient based on the acquired grid voltage and its time rate of change. The synchronous loop control unit receives the adaptive phase compensation coefficient, active power reference value, actual output active power, and common coupling point voltage feedback signal, and uses it to weight and combine the active power deviation signal and voltage feedback signal to generate control commands for adjusting the inverter output angular frequency and phase. The PWM signal generation unit generates a pulse width modulation signal to drive the inverter switching transistors based on the control command output by the synchronous loop control unit.

8. The inverter transient stability system based on adaptive phase compensation according to claim 7, characterized in that, The adaptive compensation coefficient generation unit specifically includes: an S-shaped function calculation module, a voltage change rate adjustment module, and a hysteresis logic control module, used to collaboratively calculate the adaptive phase compensation coefficient.

9. The inverter transient stability system based on adaptive phase compensation according to claim 7, characterized in that, The synchronous loop control unit receives and utilizes the adaptive phase compensation coefficient to dynamically adjust the inverter's equivalent active power reference, equivalent inertia, and equivalent damping.

10. The inverter transient stability system based on adaptive phase compensation according to claim 7, characterized in that, It also includes a reactive power control unit, which provides reactive power support to stabilize the voltage at the point of common coupling when the grid voltage drops.

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