Fractional order virtual synchronous generator adaptive inertia control method
By introducing a three-state finite state machine and adaptive rotational inertia control with hysteresis threshold, the frequency surge and chattering problems in FOVSG control are solved, and smooth adjustment of virtual inertia is achieved, improving the stability and response speed of the system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUANGXI UNIV
- Filing Date
- 2026-04-29
- Publication Date
- 2026-07-14
Smart Images
Figure CN122393961A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of power system operation and control technology, and in particular to an adaptive moment of inertia control method for a fractional-order virtual synchronous generator. Background Technology
[0002] With the increasing penetration of distributed renewable energy sources such as wind power and photovoltaics into power systems, a large number of power electronic interface devices are being connected to the grid, leading to a significant decrease in the equivalent inertia and damping levels of traditional power systems. This results in risks such as increased frequency fluctuations and power frequency oscillation instability. Virtual synchronous generator (VSG) technology, by simulating the electromechanical characteristics of a synchronous generator in inverter control and introducing virtual inertia and damping, can effectively compensate for the insufficient inertia of power electronic devices, improve the operational stability of renewable energy grid-connected systems, and become one of the core control technologies in microgrid and weak grid scenarios.
[0003] Traditional VSG control uses mostly fixed parameters for virtual rotational inertia and damping coefficients, making it difficult to achieve a trade-off between dynamic and steady-state performance during parameter tuning. Increasing the virtual rotational inertia can suppress frequency transient shocks, but it prolongs the system settling time and exacerbates active power overshoot and oscillations. Increasing the damping coefficient can suppress power oscillations, but it increases power steady-state error and affects primary frequency regulation accuracy. To address this issue, fractional-order virtual synchronous generator (FOVSG) control was proposed. By introducing fractional-order operators into the rotor motion equations, an adjustable fractional-order rotor order is added, expanding the control degrees of freedom and effectively reducing active power overshoot and accelerating system response. However, while suppressing power overshoot, FOVSG control degrades the system's transient frequency response, leading to increased amplitude of instantaneous frequency shocks under grid-connected conditions and affecting grid frequency stability.
[0004] In existing technologies, adaptive moment of inertia control can optimize the transient performance of VSG, that is, it adjusts the virtual moment of inertia online according to the system operating conditions, balancing inertia support and response speed. However, existing adaptive moment of inertia control mostly adopts single threshold switching logic. When the system operating point is close to the threshold boundary, the discrimination quantity will repeatedly cross the boundary, resulting in frequent switching of control modes. The virtual moment of inertia exhibits chattering and spike phenomena, which not only fails to achieve the expected control effect, but also introduces additional harmonics and disturbances, and may even trigger inverter protection actions, threatening the safe and stable operation of the system.
[0005] Therefore, this paper proposes an adaptive moment of inertia control method for a fractional-order virtual synchronous generator. Summary of the Invention
[0006] This invention addresses the shortcomings of existing technologies, specifically the large transient frequency impacts in FOVSG control, frequent switching of single threshold values in traditional adaptive moment of inertia control, and chattering spikes. It proposes a fractional-order virtual synchronous generator adaptive moment of inertia control method, which introduces a more robust switching mechanism to threshold boundaries. This allows the adaptive adjustment to persist for a certain period after being triggered and then stably exit under appropriate conditions. This maintains the continuous and effective action of adaptive adjustment under low threshold and high-sensitivity tuning conditions, reducing spikes caused by ineffective switching and thus improving control performance. The specific technical solution is as follows:
[0007] An adaptive moment of inertia control method for a fractional-order virtual synchronous generator includes a main circuit module and a control module. The main circuit module includes a three-phase inverter bridge arm, a fractional-order LC filter, a PCC point, and a connection to the grid / load. The DC side is connected to a distributed power source or energy storage unit, and the AC side is connected to the PCC point via the fractional-order LC filter. The PCC point can switch between grid-connected and islanded operation modes. The control module includes: a sampling unit for acquiring inverter output voltage, current, grid voltage, and frequency signals; a power calculation unit for calculating real-time output active and reactive power; a FOVSG power outer loop control unit for executing active-frequency and reactive-voltage control and outputting voltage reference commands; an adaptive inertia adjustment unit with built-in three-state finite state machine logic for outputting adaptively adjusted virtual moment of inertia; a voltage and current dual closed-loop control unit for tracking and adjusting the voltage reference commands and outputting modulated waves; and an SPWM modulation unit for generating drive signals for the inverter switching transistors.
[0008] The active-frequency control equations for FOVSG are as follows:
[0009] (1)
[0010] In equation (1), J is the virtual moment of inertia, and D is the virtual damping coefficient. The rated angular frequency, λ represents the angular frequency deviation, and λ is the adjustable fractional rotor order. This is a reference value for active power. To output electromagnetic power, This is the active power droop coefficient;
[0011] The reactive power-voltage control equation is as follows:
[0012] (2)
[0013] In equation (2), E is the output electromotive force of VSG. This is the output voltage reference value. This is the reactive power droop factor. This is a reference value for reactive power. To output reactive power, U is the integral coefficient of the excitation circuit, and U is the output voltage of the VSG.
[0014] The specific principles for dividing the power frequency oscillation process into intervals and adjusting the virtual moment of inertia are as follows:
[0015] A complete power frequency oscillation cycle is divided into four intervals, interval a: >0、 >0, interval b: >0、 <0, interval c: <0、 <0, interval d: <0、 >0;
[0016] The adjustment principle is as follows: increase the virtual moment of inertia J in intervals a and c to suppress frequency oscillations and transient shocks; decrease the virtual moment of inertia J in intervals b and d to accelerate frequency recovery and system response.
[0017] The specific formula for calculating the virtual moment of inertia of a three-state finite state machine is as follows:
[0018] Reference moment of inertia :
[0019] (3)
[0020] In equation (3), This is the initial value of the moment of inertia.
[0021] Increased moment of inertia :
[0022] (4)
[0023] In equation (4), and This is the adjustment coefficient.
[0024] Decreasing moment of inertia :
[0025] (5)
[0026] In equation (5), This is the adjustment coefficient.
[0027] Hysteresis thresholds include cut-in control thresholds With resection control threshold And satisfy Minimum stay time To determine the minimum dwell time after the activation of the state of increased / decreased rotational inertia, a dwell time is accumulated using a sampling counter. Only when the dwell time meets the minimum requirement... Only when the state is switched back to the baseline state is the state allowed to switch back. The sign decision dead zone is the numerical range near the zero value, which is used to avoid false state switching caused by frequent jumps of the coupled discriminant near the zero value.
[0028] The definition of the coupling discriminant is:
[0029] Define the coupling discriminant:
[0030] (6)
[0031] The sign in equation (6) is used to determine whether the moment of inertia increases or decreases;
[0032] The following thresholds are defined for frequency deviation and rate of change of frequency:
[0033] (7)
[0034] In equation (7), This indicates that the disturbance is significant enough to trigger... Enter the remaining states; This indicates that the disturbance has significantly subsided, and it is permissible to switch back to the previous state. .
[0035] The specific logic for entering, maintaining, and removing each state is as follows:
[0036] (1) Reference moment of inertia
[0037] Maintenance Mechanism: When the system is in the small disturbance region, that is, when the amplitude of the angular frequency deviation or the rate of change of the angular frequency has not reached the threshold level, the reference inertia is maintained. .
[0038] Cut-off mechanism: When the system is disturbed and the amplitude of the angular frequency deviation and the rate of change of the angular frequency reach the threshold level, that is, when both conditions are met... , This region is a highly dynamic area. At this time, according to... The symbol selection cut-in state is used to improve... Robustness is determined near zero by introducing a dead zone. Therefore, excision Enter The conditions are:
[0039] (8)
[0040] resection Enter The conditions are:
[0041] (9)
[0042] (2) State of increasing moment of inertia
[0043] Entry mechanism: When the system is in a highly dynamic region and Cut in at the right time Upon entry, the execution counter is cleared to provide a timing reference for the minimum dwell time constraint.
[0044] Maintenance Mechanism: Even if the criteria fluctuate instantaneously after entry, the state remains unchanged until the exit conditions are met and the dwell time is satisfied. At the same time The interval does not switch to other branches, and the sign criterion is maintained.
[0045] Switching mechanism: When This indicates that the dynamic trend has shifted from the same direction to the opposite direction, allowing for a change in the direction of the trend. Switch to .
[0046] Resection mechanism: Resection occurs when the system dynamics have been significantly mitigated, i.e., when both the release criterion and the residence time are met. From the entry point The conditions are:
[0047] (9)
[0048] The hysteresis threshold ensures that the exit conditions are more lenient than the entry conditions, and the dwell time ensures that the exit will not be triggered by instantaneous fluctuations.
[0049] (3) State of increasing moment of inertia
[0050] Entry mechanism: When the system is in a highly dynamic region and Cut in at the right time Upon entry, the counter is also cleared.
[0051] Maintenance Mechanism: Maintain as long as the exit condition is not met. And continuously output the corresponding inertia adjustment law; at the same time The region remains unchanged from the current branch to avoid branch switching and jitter.
[0052] Switching mechanism: When This indicates that the dynamic trend has shifted from the same direction to the opposite direction, allowing for a change in the direction of the trend. Switch to .
[0053] Mechanism of resection: related to the state of increased rotational inertia The resection mechanism is consistent with that of other procedures, and when conditions are met, from Cut in .
[0054] The control flow of the IADJ-FOVSG control strategy is as follows:
[0055] Real-time acquisition of active power, reactive power, terminal voltage, and grid frequency from the inverter output; calculation of angular frequency deviation. With angular frequency change
[0056] Based on the threshold criterion and the coupling discriminant, the state switching of the three-state finite state machine is performed, and the adaptively adjusted virtual moment of inertia J is output.
[0057] The adaptive virtual moment of inertia J is substituted into the rotor motion equation of FOVSG to calculate the output angular frequency and power angle. Combined with the reactive power-voltage control loop of FOVSG, a voltage reference command is generated. Through voltage and current dual closed-loop control and SPWM modulation, a drive signal is generated to control the inverter switching devices.
[0058] An adaptive moment of inertia control method for a fractional-order virtual synchronous generator, applied to a control system based on a fractional-order virtual synchronous generator as described above, is characterized by comprising the following steps:
[0059] S1: Establish the basic control model of the fractional virtual synchronous generator FOVSG, introduce fractional operators into the rotor motion equation of the traditional virtual synchronous generator VSG, and construct the active-frequency control equation and reactive-voltage control equation of FOVSG.
[0060] S2: Divide the power frequency oscillation process of FOVSG into intervals, and determine the adaptive adjustment principle of virtual moment of inertia J based on the dynamic characteristics of the oscillation intervals.
[0061] S3: Construct a virtual rotational inertia adaptive adjustment architecture for a three-state finite state machine, set a base rotational inertia state, a rotational inertia enhancement state, and a rotational inertia reduction state, and design the hysteresis threshold, minimum dwell time constraint, and sign decision dead zone for state switching.
[0062] S4: Define the coupling discrimination quantity, combine the threshold criteria of system angular frequency deviation and angular frequency change rate, determine the entry, hold and cut-off logic of each state, and realize the adaptive segmented adjustment of virtual rotational inertia;
[0063] S5: Combine the adaptive moment of inertia adjustment strategy of step S4 with the FOVSG basic control model of step S1 to construct the IADJ-FOVSG control strategy and complete the transient performance optimization of the virtual synchronous generator in grid-connected and islanded modes.
[0064] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0065] 1. This invention combines adaptive rotational inertia control with hysteresis threshold and minimum dwell time with FOVSG, retaining the advantages of FOVSG such as small active power overshoot and fast response speed, while effectively suppressing the transient frequency impact of FOVSG through adaptive inertia adjustment, achieving simultaneous optimization of power response and frequency stability. Simulation results show that the active power overshoot of the proposed IADJ-FOVSG strategy is only 3.07%, and the frequency recovery time is shortened to 0.117s, with overall performance significantly better than traditional VSG, conventional FOVSG, and single-threshold adaptive VSG control.
[0066] 2. The three-state finite state machine switching mechanism designed in this invention fundamentally solves the problems of frequent switching and virtual inertia chattering spikes near the threshold in traditional single-threshold adaptive control through the triple design of hysteresis threshold, minimum dwell time and decision dead zone. It ensures the smoothness and continuity of the inertia adjustment process, reduces the impact of control disturbances on the system, and improves the safety and stability of grid-connected inverter operation.
[0067] 3. The control strategy of this invention has strong adaptability. It is applicable to the transient performance optimization of active power command step disturbance under grid-connected conditions. It can automatically adjust the virtual inertia according to the system operating conditions without manual parameter tuning and has strong engineering application value. Attached Figure Description
[0068] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.
[0069] Figure 1 This is a graph showing the power frequency oscillation characteristics of a synchronous generator.
[0070] Figure 2 This is a block diagram of the overall structure of adaptive moment of inertia control.
[0071] Figure 3 This is a schematic diagram of the switching process of the three-state finite state machine of the present invention;
[0072] Figure 4 Figure 1 shows a comparison of simulation results for different control strategies. Figure 2 shows a comparison of output active power; Figure 3 shows a comparison of output reactive power; Figure 4 shows a comparison of output frequency; Figure 5 shows a comparison of output angular frequency change rate; Figure 6 shows a comparison of phase a output current; and Figure 7 shows a comparison of rotational inertia change. Detailed Implementation
[0073] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0074] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.
[0075] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.
[0076] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.
[0077] Unless otherwise defined, 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 disclosure belongs. The terminology used herein is for the purpose of describing embodiments of this disclosure only and is not intended to be limiting of this disclosure.
[0078] This invention provides an embodiment of an adaptive moment of inertia control method for a fractional-order virtual synchronous generator. The specific content of this adaptive moment of inertia control method for a fractional-order virtual synchronous generator includes the following:
[0079] S1: Establish the basic control model of the fractional virtual synchronous generator FOVSG, introduce fractional operators into the rotor motion equation of the traditional virtual synchronous generator VSG, and construct the active-frequency control equation and reactive-voltage control equation of FOVSG.
[0080] The active-frequency control equation of FOVSG is shown in equation (1), where J is the virtual moment of inertia and D is the virtual damping coefficient. The rated angular frequency, λ represents the angular frequency deviation, and λ is the adjustable fractional rotor order. This is a reference value for active power. To output electromagnetic power, This is the active power droop coefficient.
[0081] (1)
[0082] Simultaneously, the reactive power-voltage control equations for FOVSG are constructed, and an integral term is introduced in grid-connected mode to eliminate steady-state voltage error:
[0083] (2)
[0084] In equation (2), E is the output electromotive force of VSG. This is the output voltage reference value. This is the reactive power droop factor. This is a reference value for reactive power. To output reactive power, U is the integral coefficient of the excitation circuit, and U is the output voltage of the VSG.
[0085] S2: Divide the power frequency oscillation process of FOVSG into intervals, and determine the adaptive adjustment principle of virtual moment of inertia J based on the dynamic characteristics of the oscillation intervals.
[0086] refer to Figure 1 The power frequency oscillation characteristics of a synchronous generator are divided into four intervals, and the adjustment principle of the virtual moment of inertia is determined based on the dynamic characteristics of each interval, as shown in Table 1:
[0087] Table 1. Selection principles for different intervals of J
[0088]
[0089] Among them, the coupling discriminant Its sign directly reflects the stage of system oscillation and provides a criterion for the direction of inertia adjustment.
[0090] S3: Construct a virtual rotational inertia adaptive adjustment architecture for a three-state finite state machine, set a base rotational inertia state, a rotational inertia enhancement state, and a rotational inertia reduction state, and design the hysteresis threshold, minimum dwell time constraint, and sign decision dead zone for state switching.
[0091] Design reference moment of inertia Increased moment of inertia Decreasing moment of inertia The inertia calculation formulas for the three operating states are as follows:
[0092] Reference moment of inertia :
[0093] (3)
[0094] In equation (3), This is the initial value of the moment of inertia.
[0095] Increased moment of inertia :
[0096] (4)
[0097] In equation (4), and This is the adjustment coefficient.
[0098] Decreasing moment of inertia :
[0099] (4)
[0100] In equation (5), This is the adjustment coefficient.
[0101] Meanwhile, the core constraint parameters for state switching are: hysteresis threshold, including the cut-in control threshold. With resection control threshold And satisfy Minimum stay time To determine the minimum dwell time after the activation of the state of increased / decreased rotational inertia, a dwell time is accumulated using a sampling counter. Only when the dwell time meets the minimum requirement... Only when the state is switched back to the baseline state is the state allowed to switch back. The sign decision dead zone is the numerical range near the zero value, which is used to avoid false state switching caused by frequent jumps of the coupled discriminant near the zero value.
[0102] The process of switching between the three states is as follows: Figure 3 As shown, the baseline state The excision is triggered by a threshold in the strong dynamic region, enhancing the state. With weakened state The removal is triggered by the hysteresis release condition and is constrained by the minimum dwell time. The switching between states is determined by the sign of the coupling discriminant p.
[0103] S4: Define the coupling discrimination quantity, combine the threshold criteria of system angular frequency deviation and angular frequency change rate, determine the entry, hold and cut-off logic of each state, and realize the adaptive segmented adjustment of virtual rotational inertia;
[0104] (1) Reference moment of inertia
[0105] Maintenance Mechanism: When the system is in the small disturbance region, that is, when the amplitude of the angular frequency deviation or the rate of change of the angular frequency has not reached the threshold level, the reference inertia is maintained. .
[0106] Cut-off mechanism: When the system is disturbed and the amplitude of the angular frequency deviation and the rate of change of the angular frequency reach the threshold level, that is, when both conditions are met... , This region is a highly dynamic area. At this time, according to... The symbol selection cut-in state is used to improve... Robustness is determined near zero by introducing a dead zone. Therefore, excision Enter The conditions are:
[0107] (5)
[0108] resection Enter The conditions are:
[0109] (6)
[0110] (2) State of increasing moment of inertia
[0111] Entry mechanism: When the system is in a highly dynamic region and Cut in at the right time Upon entry, the execution counter is cleared to provide a timing reference for the minimum dwell time constraint.
[0112] Maintenance Mechanism: Even if the criteria fluctuate instantaneously after entry, the state remains unchanged until the exit conditions are met and the dwell time is satisfied. At the same time The interval does not switch to other branches, and the sign criterion is maintained.
[0113] Switching mechanism: When This indicates that the dynamic trend has shifted from the same direction to the opposite direction, allowing for a change in the direction of the trend. Switch to .
[0114] Resection mechanism: Resection occurs when the system dynamics have been significantly mitigated, i.e., when both the release criterion and the residence time are met. From the entry point The conditions are:
[0115] (7)
[0116] The hysteresis threshold ensures that the exit conditions are more lenient than the entry conditions, and the dwell time ensures that the exit will not be triggered by instantaneous fluctuations.
[0117] (3) State of increasing moment of inertia
[0118] Entry mechanism: When the system is in a highly dynamic region and Cut in at the right time Upon entry, the counter is also cleared.
[0119] Maintenance Mechanism: Maintain as long as the exit condition is not met. And continuously output the corresponding inertia adjustment law; at the same time The region remains unchanged from the current branch to avoid branch switching and jitter.
[0120] Switching mechanism: When This indicates that the dynamic trend has shifted from the same direction to the opposite direction, allowing for a change in the direction of the trend. Switch to .
[0121] Mechanism of resection: related to the state of increased rotational inertia The resection mechanism is consistent with that of other procedures, and when conditions are met, from Cut in .
[0122] S5: Combine the adaptive moment of inertia adjustment strategy of step S4 with the FOVSG basic control model of step S1, and construct the IADJ-FOVSG control strategy based on the fractional-order three-phase LC inverter and its decoupling strategy to complete the transient performance optimization of the virtual synchronous generator in grid-connected mode.
[0123] By combining the above adaptive moment of inertia adjustment strategy with FOVSG basic control, a system is constructed as follows: Figure 3 The complete control architecture shown is as follows:
[0124] The three-phase voltage and current output from the inverter are sampled in real time, along with the grid voltage. These samples are then transformed into a dq rotating coordinate system using Clark and Park transformations to calculate the real-time active power output. reactive power ;
[0125] Calculate the system angular frequency deviation With the rate of change of angular frequency And calculate the coupling discriminant p;
[0126] Based on the state switching logic in step 4, the three-state finite state machine is executed to determine the virtual rotational inertia J after adaptive adjustment.
[0127] Substituting the adaptive J into the FOVSG active-frequency control equation, the output angular frequency is calculated. With the angle Simultaneously, the reference value E of the output voltage amplitude is determined through the reactive power-voltage control equation.
[0128] The dq-axis voltage reference command is generated from the power angle and voltage amplitude, and sent to the fractional-order voltage and current dual closed-loop control loop to output a modulated wave.
[0129] The modulated wave is generated into six drive signals by the SPWM module, which control the IGBT switching devices of the three-phase inverter bridge arm, ultimately achieving optimized control of the inverter's transient performance.
[0130] To verify the feasibility of the improved adaptive strategy, in grid-connected mode, the following settings were first configured. and Both are 5kW, at 1s, It suddenly increased to 10kW. Figure 2 The adaptive control of rotational inertia shown is used as a control, when This corresponds to the traditional VSG control situation, denoted as ADJ-VSG. To further suppress power overshoot, when When adopted Figure 3 The state-switching adaptive inertia control shown is denoted as IADJ-FOVSG. To compare the differences between FOVSG and VSG in introducing adaptive inertia, the same method is used... Figure 3 The state switching adaptive control of rotational inertia is shown. This is denoted as IADJ-VSG. Subsequently, IADJ-FOVSG, IADJ-VSG, ADJ-VSG, and... FOVSG and The responses of five VSG control strategies were compared and analyzed. The parameters of the adaptive control are shown in Table 2. Simulation results are as follows: Figure 4 As shown, in order to further compare and analyze the advantages and disadvantages of each control performance, their time-domain indicators are calculated and listed in Table 3.
[0131] Table 2 Adaptive moment of inertia control parameters
[0132]
[0133] Table 3 Comparison of Adaptive Control Performance
[0134]
[0135] from Figure 4(a) It can be seen that all five control strategies can achieve rapid tracking of active power commands, but their dynamic performance varies significantly. Among them, the traditional VSG has the largest active power overshoot, reaching 15.60%, and its transient oscillation is the most obvious; the overshoot of FOVSG is reduced to 7.32%, but its transient frequency impact is relatively large; after introducing adaptive inertia, the overshoot of ADJ-VSG is further reduced to 8.96%, indicating that adaptive inertia can suppress active power oscillation to a certain extent; the overshoot of IADJ-VSG is 6.99%, which is a further improvement compared to ADJ-VSG; the improved IADJ-FOVSG has the best power performance, with a faster active power response, a smoother adjustment process, and an overshoot of only 3.07%. Combining FOVSG with the improved adaptive inertia strategy can more effectively improve the transient quality of active power. Figure 4 (b) shows the reactive power response curves. All five strategies can achieve reactive power regulation under command disturbances. After introducing adaptive regulation, the amplitude of reactive power transient fluctuations decreases and the convergence process accelerates, indicating that adaptive inertia regulation has a certain improving effect on reactive power response.
[0136] Figure 4 (c) shows the frequency response curves. The maximum frequency deviation of the traditional VSG is 0.110 Hz, and the recovery time to 50 ± 0.01 Hz is 0.298 s, with significant frequency oscillations. The FOVSG shows improved frequency recovery speed, with the recovery time shortened to 0.166 s, but its maximum frequency deviation increases to 0.118 Hz. After introducing adaptive moment of inertia, the ADJ-VSG reduces the maximum frequency deviation to 0.084 Hz and the recovery time to 0.226 s; the IADJ-VSG further reduces the maximum frequency deviation to 0.078 Hz, with a recovery time of 0.219 s. In contrast, although the IADJ-FOVSG does not have the smallest maximum frequency deviation, it has the shortest recovery time of only 0.117 s, indicating that this method has a significant advantage in recovery speed after suppressing frequency disturbances, while also taking into account a smaller frequency deviation, demonstrating better speed and overall dynamic performance. Figure 4 (d) shows the output angular frequency change rate response. Compared with traditional VSG and FOVSG, the introduction of adaptive inertia effectively suppresses the transient impact of the angular frequency change rate, indicating that this type of strategy can improve the transient stability of the system and reduce the peak frequency change rate caused by the active power command step.
[0137] Figure 4 (e) shows the output current waveform of phase a under the five strategies. After the active power command step at 1s, the current amplitude of all five strategies increases accordingly, with the current surge of traditional VSG and FOVSG being relatively more obvious. After introducing the adaptive moment of inertia, the current transition process is smoother and the peak value is smaller, indicating that the adaptive strategy can effectively reduce the current surge caused by active power disturbance.
[0138] Figure 4 (f) shows the dynamic changes of the virtual moment of inertia J under the three adaptive inertia strategies. After the active power command step at 1s, all three controls trigger inertia boosting to suppress transient frequency fluctuations, but J rises more rapidly and changes more smoothly in IADJ-FOVSG. This is because, on the one hand, FOVSG builds up power faster, making the transient frequency deviation and angular frequency change rate change more drastic, thus triggering the adaptive loop earlier; on the other hand, the state-switching adaptive control uses a smaller trigger threshold combined with a minimum dwell time constraint, allowing inertia adjustment to intervene in a timely manner, while avoiding repeated switching near the threshold due to measurement noise and transient oscillations. In contrast, IADJ-VSG has a longer adjustment time, with an additional oscillation cycle. Although ADJ-VSG sets a larger threshold, it can be observed from the magnified local diagram that J still exhibits frequent switching in and out chattering, causing the inertia to jump multiple times in a short period of time.
[0139] In summary, the IADJ-FOVSG combines the dynamic adjustment capability of FOVSG with a state-switching adaptive inertia strategy, achieving a balance of speed, stability, and robustness under active power command step disturbances. Compared with traditional VSG, FOVSG, and ADJ-VSG which only uses basic adaptive inertia control, this method can significantly reduce active power overshoot, shorten frequency recovery time, and effectively reduce reactive power transient fluctuations and current surges. Simultaneously, its rotational inertia adjustment process is smoother, suppressing frequent switching and chattering near the threshold, demonstrating better overall performance.
[0140] This invention combines adaptive rotational inertia control with hysteresis threshold and minimum dwell time with FOVSG, retaining the advantages of FOVSG such as small active power overshoot and fast response speed, while effectively suppressing the transient frequency impact of FOVSG through adaptive inertia adjustment, achieving simultaneous optimization of power response and frequency stability. Simulation results show that the active power overshoot of the proposed IADJ-FOVSG strategy is only 3.07%, and the frequency recovery time is shortened to 0.117s, with comprehensive performance significantly better than traditional VSG, conventional FOVSG, and single-threshold adaptive VSG control. The three-state finite state machine switching mechanism designed in this invention, through the triple design of hysteresis threshold, minimum dwell time, and decision dead zone, fundamentally solves the problems of frequent switching near the threshold and virtual inertia chattering spikes in traditional single-threshold adaptive control, ensuring the smoothness and continuity of the inertia adjustment process, reducing the impact of control disturbances on the system, and improving the safety and stability of grid-connected inverter operation. The control strategy of this invention has strong adaptability and is suitable for transient performance optimization of active power command step disturbances under grid-connected operating conditions. It can automatically adjust the virtual inertia according to the system operating conditions without manual parameter tuning, and has strong engineering application value. Therefore, the technical solution proposed in this invention solves the problems mentioned in the background art.
[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.
Claims
1. A method for adaptive moment of inertia control of a fractional-order virtual synchronous generator, characterized in that, Includes the following steps: S1: Establish the basic control model of the fractional virtual synchronous generator FOVSG, introduce fractional operators into the rotor motion equation of the traditional virtual synchronous generator VSG, and construct the active-frequency control equation and reactive-voltage control equation of FOVSG. S2: Divide the power frequency oscillation process of FOVSG into intervals, and determine the adaptive adjustment principle of virtual moment of inertia J based on the dynamic characteristics of the oscillation intervals. S3: Construct a virtual rotational inertia adaptive adjustment architecture for a three-state finite state machine, set a base rotational inertia state, a rotational inertia enhancement state, and a rotational inertia reduction state, and design the hysteresis threshold, minimum dwell time constraint, and sign decision dead zone for state switching. S4: Define the coupling discrimination quantity, combine the threshold criteria of system angular frequency deviation and angular frequency change rate, determine the entry, hold and cut-off logic of each state, and realize the adaptive segmented adjustment of virtual rotational inertia; S5: Combine the adaptive moment of inertia adjustment strategy of step S4 with the FOVSG basic control model of step S1 to construct an adaptive moment of inertia control strategy and complete the transient performance optimization of the virtual synchronous generator in grid-connected mode.
2. The adaptive moment of inertia control method for a fractional-order virtual synchronous generator according to claim 1, characterized in that, The system includes a main circuit module and a control module. The main circuit module comprises a three-phase inverter bridge arm, a fractional-order LC filter, a PCC point, and connections to the grid / load. The DC side is connected to a distributed power source or energy storage unit, and the AC side is connected to the PCC point via the fractional-order LC filter. The PCC point can switch between grid-connected and islanded operation modes. The control module includes: a sampling unit for acquiring inverter output voltage, current, grid voltage, and frequency signals; a power calculation unit for calculating real-time output active and reactive power; a FOVSG power outer loop control unit for executing active-frequency and reactive-voltage control and outputting voltage reference commands; an adaptive inertia adjustment unit with built-in three-state finite state machine logic for outputting adaptively adjusted virtual rotational inertia; a voltage and current dual closed-loop control unit for tracking and adjusting the voltage reference commands and outputting modulated waves; and an SPWM modulation unit for generating drive signals for the inverter switching transistors. In step S1, the active-frequency control equation of FOVSG is specifically as follows: In the formula, J is the virtual moment of inertia, and D is the virtual damping coefficient. The rated angular frequency, λ represents the angular frequency deviation, and λ is the adjustable fractional rotor order. This is a reference value for active power. To output electromagnetic power, This is the active power droop coefficient; The reactive power-voltage control equation is as follows: In the formula, E is the output electromotive force of VSG. This is the output voltage reference value. This is the reactive power droop factor. This is a reference value for reactive power. To output reactive power, U is the integral coefficient of the excitation circuit, and U is the output voltage of the VSG.
3. The adaptive moment of inertia control method for a fractional-order virtual synchronous generator according to claim 1, characterized in that, In step S2, the specific principles for dividing the power frequency oscillation process into intervals and adjusting the virtual moment of inertia are as follows: A complete power frequency oscillation cycle is divided into four intervals, interval a: >0、 >0, interval b: >0、 <0, interval c: <0、 <0, interval d: <0、 >0; The adjustment principle is as follows: increase the virtual moment of inertia J in intervals a and c to suppress frequency oscillations and transient shocks; decrease the virtual moment of inertia J in intervals b and d to accelerate frequency recovery and system response.
4. The adaptive moment of inertia control method for a fractional-order virtual synchronous generator according to claim 1, characterized in that, In step S3, the specific formula for calculating the virtual moment of inertia of the three-state finite state machine is as follows: Reference moment of inertia : In the formula, This is the initial value of the moment of inertia. Increased moment of inertia : In the formula, and This is the adjustment coefficient. Decreasing moment of inertia : In the formula, This is the adjustment coefficient.
5. The method for adaptive moment of inertia control of a fractional-order virtual synchronous generator according to claim 1, characterized in that, In step S3, the hysteresis threshold includes the cut-in control threshold. With resection control threshold And satisfy Minimum stay time To determine the minimum dwell time after the activation of the state of increased / decreased rotational inertia, a dwell time is accumulated using a sampling counter. Only when the dwell time meets the minimum requirement... Only when the state is switched back to the baseline state is the state allowed to switch back. The sign decision dead zone is the numerical range near the zero value, which is used to avoid false state switching caused by frequent jumps of the coupled discriminant near the zero value.
6. The adaptive moment of inertia control method for a fractional-order virtual synchronous generator according to claim 1, characterized in that, In step S4, the definition of the coupling discriminant is: Define the coupling discriminant: The sign in the formula is used to determine whether the moment of inertia increases or decreases; The following thresholds are defined for frequency deviation and rate of change of frequency: In the formula, This indicates that the disturbance is significant enough to trigger... Enter the remaining states; This indicates that the disturbance has significantly subsided, and it is permissible to switch back to the previous state. .
7. The adaptive moment of inertia control method for a fractional-order virtual synchronous generator according to claim 6, characterized in that, In step S4, the specific logic for entering, maintaining, and removing each state is as follows: (1) Reference moment of inertia state Maintenance Mechanism: When the system is in the small disturbance region, that is, when the amplitude of the angular frequency deviation or the rate of change of the angular frequency has not reached the threshold level, the reference inertia is maintained. . Cut-off mechanism: When the system is disturbed and the amplitude of the angular frequency deviation and the rate of change of the angular frequency reach the threshold level, that is, when both conditions are met... , This region is a highly dynamic area. At this time, according to... The symbol selection cut-in state is used to improve... Robustness is determined near zero, and a dead zone is introduced. Therefore, excision Enter The conditions are: resection Enter The conditions are: (2) State of increasing moment of inertia Entry mechanism: When the system is in a highly dynamic region and Cut in at the right time Upon entry, the execution counter is cleared to provide a timing reference for the minimum dwell time constraint. Maintenance Mechanism: Even if the criteria fluctuate instantaneously after entry, the state remains unchanged until the exit conditions are met and the dwell time is satisfied. At the same time The interval does not switch to other branches, and the sign criterion is maintained. Switching mechanism: When This indicates that the dynamic trend has shifted from the same direction to the opposite direction, allowing for a change in the direction of the trend. Switch to . Resection mechanism: Resection occurs when the system dynamics have been significantly mitigated, i.e., when both the release criterion and the residence time are met. From the entry point The conditions are: The hysteresis threshold ensures that the exit conditions are more lenient than the entry conditions, and the dwell time ensures that the exit will not be triggered by instantaneous fluctuations. (3) State of increasing moment of inertia Entry mechanism: When the system is in a highly dynamic region and Cut in at the right time Upon entry, the counter is also cleared. Maintenance Mechanism: Maintain as long as the exit condition is not met. And continuously output the corresponding inertia adjustment law; at the same time The region remains unchanged from the current branch to avoid branch switching and jitter. Switching mechanism: When This indicates that the dynamic trend has shifted from the same direction to the opposite direction, allowing for a change in the direction of the trend. Switch to . Mechanism of resection: related to the state of increased rotational inertia The resection mechanism is consistent with that of other procedures, and when conditions are met, from Cut in .
8. The adaptive moment of inertia control method for a fractional-order virtual synchronous generator according to claim 1, characterized in that, In step S5, the control flow of the IADJ-FOVSG control strategy is as follows: Real-time acquisition of active power, reactive power, terminal voltage, and grid frequency from the inverter output; calculation of angular frequency deviation. With the rate of change of angular frequency ; Based on the threshold criterion and the coupling discriminant, the state switching of the three-state finite state machine is performed, and the adaptively adjusted virtual moment of inertia J is output. The adaptive virtual moment of inertia J is substituted into the rotor motion equation of FOVSG to calculate the output angular frequency and power angle. Combined with the reactive power-voltage control loop of FOVSG, a voltage reference command is generated. Through voltage and current dual closed-loop control and SPWM modulation, a drive signal is generated to control the inverter switching devices.
9. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device containing the computer-readable storage medium to perform the fractional-order virtual synchronous generator adaptive moment of inertia control method according to any one of claims 1 to 8.
10. A processor, characterized in that, The processor is used to run a program, wherein the program executes a fractional-order virtual synchronous generator adaptive moment of inertia control method according to any one of claims 1 to 8.