A method and device for adaptive damping control of parallel grid-connected converters

Abstract

The present invention discloses an adaptive damping control method and device for a parallel grid-connected converter. This method analyzes the transient stability of a parallel GFM converter system under non-uniform damping conditions and proposes an adaptive damping control strategy based on dynamic frequency adjustment. Specifically, it includes: establishing a transient model of a non-uniformly damped parallel GFM converter, analyzing the influence mechanism of damping on transient stability under different fault levels, and designing a control method for dynamically adjusting the damping coefficient. Theoretical derivation and simulation verification show that this method can significantly suppress power angle oscillation and improve the transient stability of the system under different fault levels. The present invention solves the defect that the traditional fixed damping strategy cannot adapt to multi-fault scenarios by adjusting the damping parameters in real time, and provides an effective solution for the stable operation of a high-proportion new energy power system.

Description

Technical Field

[0001] The present invention belongs to the field of electrical engineering, and more specifically, relates to an adaptive damping control method and device for a parallel grid-connected converter, which is suitable for transient stability control of the converter. Background Art

[0002] Grid-connected converters, with characteristics similar to synchronous generators, are becoming an important research area for improving power system stability. GFM converters can mimic the operating characteristics of synchronous generators, providing inertial support and frequency regulation, thereby improving the dynamic performance of power systems. They can play a key role in microgrids and even in power systems powered entirely by converters, effectively supporting stable system operation.

[0003] However, current research on GFM converters still has many limitations. Most studies focus on single-machine systems, and research on the transient stability of dual-machine parallel systems is relatively scarce. In actual power system applications, dual-machine parallel operation is very common, and its transient stability is crucial for the reliable operation of the system. Existing studies analyzing dual-machine parallel systems often assume that the damping settings of the two GFM converters are uniform. However, the reality is that the damping setting range of GFM converters is wider and more flexible than that of synchronous generators. The damping coefficient of synchronous generators is typically set at around 1-3 p.u., while the damping setting range of GFM converters can reach 8-50 p.u. In the highly diversified power systems of the future, the damping settings of different GFM converters will inevitably vary significantly, making it difficult to simply consider them uniform.

[0004] Furthermore, previous studies of the impact of damping on transient stability have often failed to fully consider the effects of varying fault severity. Differences in fault severity can lead to significant changes in the system's operating state, which in turn affects the effectiveness of damping on transient stability. Considering only a single fault severity or failing to fully analyze the damping effects under varying fault severity limits research conclusions and prevents them from providing comprehensive and accurate guidance for the operation and control of actual power systems. For example, some studies have focused only on specific minor or severe faults, ignoring the impact of continuous changes in fault severity on the system. This results in the proposed control strategies being insufficiently adaptable to different fault scenarios.

[0005] Therefore, studying the impact of nonuniform damping on the transient stability of parallel GFM converters and proposing effective control strategies is of great practical significance and urgency for ensuring the stable operation of power systems and promoting the efficient use of renewable energy. This will not only help fill the current research gaps but also provide a solid theoretical foundation and technical support for the planning, design and operation of future power systems. Summary of the Invention

[0006] In response to the shortcomings of the existing technology and the need for improvement, the present invention aims to solve the transient stability problem of a parallel GFM converter system with non-uniform damping under different fault severity levels. By establishing an accurate system model, deeply analyzing the damping influence mechanism, and proposing an adaptive damping control method, the transient stability of the system under various fault conditions can be improved to ensure the reliable operation of the power system.

[0007] To achieve the above object, according to a first aspect of the present invention, there is provided an adaptive damping control method for a parallel grid-connected converter, comprising the following steps:

[0008] 1) A transient model of a parallel GFM converter with non-uniform damping is established. In this transient model, the GFM converter is connected to the common coupling point PCC via an LC filter consisting of an inductor Lf and a capacitor Cf. The GFM converter control loop includes a reactive power-voltage loop and an active power-frequency loop. The reactive power-voltage loop uses constant terminal voltage control to maintain output voltage stability. The active power-frequency loop uses a virtual synchronous machine (VSG) control to simulate the inertia and damping characteristics of the synchronous machine. The reactive power-voltage loop and the active power-frequency loop control the amplitude and phase of the GFM output voltage, respectively.

[0009] 2) Based on the transient model, the impact mechanism of damping on transient stability is analyzed. An active power model is established with the ground resistance at the time of the fault as a variable. By studying the variation of the admittance parameter in the active power expression under different fault severity, the active power surface under different fault severity is obtained.

[0010] 3) Based on the active power curves under different fault severity, the damping impact evaluation indicators E1 and E2 are introduced. The actual power angle swing trajectory and the changes in the evaluation indicators are observed, and the impact mechanism of damping on transient stability under different fault severity is analyzed;

[0011] 4) Based on the mechanism of the impact of damping on transient stability under different fault severity obtained in step 3), the controller of the parallel GFM converter is used to sample the frequency changes of the active power-frequency loop output of the leading and lagging units in real time during system operation. The frequency change is introduced as a variable into the transient damping control strategy, and the damping coefficient of the converter is adjusted in real time. Overregulation is prevented through a negative feedback loop to optimize the transient stability of the system.

[0012] Furthermore, the algorithm formula for controlling the virtual synchronous machine VSG is:

[0013]

[0014] Among them, δ GFM is the power angle generated by the active power circuit, and Represent the actual frequency of GFM and the rated frequency of the system, P GFM and P ref are the actual electromagnetic power and reference power, J and D respectively p They are the virtual inertia coefficient and virtual damping coefficient of the VSG algorithm respectively; when establishing the model, the connection mode of each converter in the parallel GFM converter is determined. The two converters are connected to the common coupling point PCC through line impedances Z1 and Z2. The equivalent load impedance is Z L , the grounding resistance during fault is Z F , thereby determining the equivalent circuit and each admittance value of the system.

[0015] Furthermore, the expressions of the admittance values ​​are as follows:

[0016]

[0017] Among them, Y 11 and Y 22 is the self-admittance of the two converter nodes, Y 12 is the mutual admittance of the two nodes. Under normal circumstances, Z3 = Z L ; In case of fault, Z3 = Z L / / Z F .

[0018] Furthermore, in step 2), the active power expression under different fault degrees is as follows:

[0019]

[0020] Among them, P GFM1 and P GFM2 are the actual active power of the leading and lagging units respectively, U1 and U2 are the output terminal voltages of the two units respectively, δ 12 = δ GFM1 - δ GFM2 , G 11 , G 12 and G 22 Y 11 、Y 12 and Y 22 The real part of Y 12 The admittance angle.

[0021] Furthermore, the damping impact evaluation indicators E1 and E2 are expressed as:

[0022]

[0023] Among them, D p1 and D p2 are the damping coefficients of the leading and lagging units respectively, and are the differences between the output frequencies of the two units and the rated frequencies, reflecting the frequency changes of the units; δ io and δ ic is the converter power angle when the fault occurs and clears, t o and t c Corresponding to the fault occurrence and clearing moments; during the analysis process, based on the changes in active power model parameters with the fault severity, the impact of damping on transient stability under different fault severity is determined.

[0024] Furthermore, the transient damping control strategy is specifically as follows:

[0025] when > 0, D * p1 = D p1 + k Dp1 k 12 ;

[0026] when < 0, D * p1 = D p1 -k Dp1 k 12 ;

[0027] when > 0, D * p2 = D p2 + k Dp2 k 12 ;

[0028] when < 0, D * p2 = D p2 -k Dp2 k 12 ;

[0029] Among them, D * p1 and D * p2 is the converter damping coefficient after real-time adjustment, k Dp1 and k Dp2 is the control coefficient, and k is introduced 12 Used for judgment = - The sign of , forming a negative feedback loop, when = 0 to stop damping adjustment; when implemented, the frequency of the converter is monitored in real time. and , adjust the damping coefficient according to the control strategy formula to optimize the transient stability of the system.

[0030] An adaptive damping control device for a non-uniformly damped parallel GFM converter, comprising:

[0031] A transient model establishment module is used to establish a transient model of a parallel GFM converter with non-uniform damping. In the transient model, the GFM converter is connected to a common coupling point PCC via an LC filter including an inductor Lf and a capacitor Cf. The GFM converter control loop includes a reactive power-voltage loop and an active power-frequency loop. The reactive power-voltage loop uses constant terminal voltage control to maintain output terminal voltage stability. The active power-frequency loop uses a virtual synchronous machine (VSG) control to simulate the inertia and damping characteristics of the synchronous machine. The reactive power-voltage loop and the active power-frequency loop control the amplitude and phase of the GFM output voltage, respectively.

[0032] The active power surface acquisition module is used to analyze the impact of damping on transient stability based on the transient model. The active power model is established using the ground resistance at the time of the fault as a variable. By studying the variation of the admittance parameter in the active power expression under different fault severity, the active power surface under different fault severity is obtained.

[0033] The damping influence mechanism acquisition module is used to introduce the damping influence evaluation indicators E1 and E2 based on the active power surface under different fault severity, observe the actual power angle swing trajectory and the changes in the evaluation indicators, and analyze the influence mechanism of damping on transient stability under different fault severity;

[0034] The damping coefficient adjustment module is used to obtain the influence mechanism of damping on transient stability under different fault degrees based on the damping influence mechanism. During system operation, the controller of the parallel GFM converter is used to sample the frequency changes of the active power-frequency loop output of the leading and lagging units in real time, and the frequency change is introduced as a variable into the transient damping control strategy to adjust the damping coefficient of the converter in real time. The negative feedback loop is used to prevent overregulation and optimize the transient stability of the system.

[0035] Furthermore, the algorithm formula for controlling the virtual synchronous machine VSG is:

[0036]

[0037] Among them, δ GFM is the power angle generated by the active power circuit, and Represent the actual frequency of GFM and the rated frequency of the system, P GFM and Pref are the actual electromagnetic power and reference power, J and D respectively p They are the virtual inertia coefficient and virtual damping coefficient of the VSG algorithm respectively; when establishing the model, the connection mode of each converter in the parallel GFM converter is determined. The two converters are connected to the common coupling point PCC through line impedances Z1 and Z2. The equivalent load impedance is Z L , the grounding resistance during fault is Z F , thereby determining the equivalent circuit and each admittance value of the system.

[0038] Furthermore, the active power expressions under different fault levels are as follows:

[0039]

[0040] Among them, P GFM1 and P GFM2 are the actual active power of the leading and lagging units respectively, U1 and U2 are the output terminal voltages of the two units respectively, δ 12 = δ GFM1 - δ GFM2 , G 11 , G 12 and G 22 Y 11 、Y 12 and Y 22 The real part of Y 12 The admittance angle.

[0041] Furthermore, the damping impact evaluation indices E1 and E2 are expressed as follows:

[0042]

[0043] Among them, D p1 and D p2 are the damping coefficients of the leading and lagging units respectively, and are the differences between the output frequencies of the two units and the rated frequencies, reflecting the frequency changes of the units; δ io and δ ic is the converter power angle when the fault occurs and clears, t o and t c Corresponding to the fault occurrence and clearing moments; during the analysis process, based on the changes in active power model parameters with fault severity, the impact of damping on transient stability under different fault severity levels is determined;

[0044] The transient damping control strategy is as follows:

[0045] when > 0, D * p1 = Dp1 + k Dp1 k 12 ;

[0046] when < 0, D * p1 = D p1 -k Dp1 k 12 ;

[0047] when > 0, D * p2 = D p2 + k Dp2 k 12 ;

[0048] when < 0, D * p2 = D p2 -k Dp2 k 12 ;

[0049] Among them, D * p1 and D * p2 is the converter damping coefficient after real-time adjustment, k Dp1 and k Dp2 is the control coefficient, and k is introduced 12 Used for judgment = - The sign of , forming a negative feedback loop, when = 0 to stop damping adjustment; when implemented, the frequency of the converter is monitored in real time. and , adjust the damping coefficient according to the control strategy formula to optimize the transient stability of the system.

[0050] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0051] 1. We conducted an in-depth analysis of the operating characteristics of the GFM converter under varying fault conditions. By exploring the damping influencing mechanism, we were able to precisely adjust the damping coefficient based on the fault condition, effectively preventing transient instability. This not only improved the converter's stability during faults but also provided a strong guarantee for the reliable operation of the power system in complex fault environments.

[0052] 2. The adaptive damping control strategy proposed in this paper fully considers the differences in system responses under different fault types. By dynamically adjusting the damping coefficient, it ensures that the system maintains good transient stability under various fault severity levels. This strategy is independent of specific fault scenario assumptions and is highly versatile, operating effectively in power systems of varying sizes and structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is the system topology diagram of parallel grid-connected converters;

[0054] Figure 2 It is the control block diagram of a single-machine grid converter;

[0055] Figure 3 It is the active power surface diagram under different fault degrees;

[0056] Figure 4 It is the control block diagram of the adaptive damping method;

[0057] Figure 5 It's Z F = 0.15pu using the constant damping method simulation results;

[0058] Figure 6 It's Z F = 0.15pu when the adaptive damping method is used for the simulation results;

[0059] Figure 7 It's Z F = 0 when the constant damping method is used for the simulation results;

[0060] Figure 8 It's Z F = 0 when the adaptive damping method is used for the simulation results.

[0061] Figure 9 The present invention is a flowchart of an adaptive damping control method for a parallel grid-connected converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0062] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0063] like Figure 9 As shown, an embodiment of the present invention provides an adaptive damping control method for a parallel grid-connected converter, comprising the following steps:

[0064] 1) Establish a transient model of parallel GFM converters with non-uniform damping, which includes two GFM converters, two transmission lines, and an AC microgrid with loads (such as Figure 1 As shown in the figure). Figure 2 As shown, the GFM converter is connected to an inductor L f and capacitor C f The LC filter is connected to the point of common coupling (PCC). The converter control loop consists of reactive-voltage and active-frequency loops. To maintain output voltage stability, the reactive-voltage loop uses constant terminal voltage control. To simulate the inertia and damping characteristics of a synchronous machine, the active-frequency loop uses VSG control, simulating the rotor equation of a synchronous generator to achieve power synchronization and provide inertia and damping for the system.

[0065] The algorithm formula for the virtual synchronous machine VSG control is:

[0066]

[0067] Among them, δ GFM is the power angle generated by the active power circuit, and Represent the actual frequency of GFM and the rated frequency of the system, P GFM and P ref are the actual electromagnetic power and reference power, J and D respectively p are the virtual inertia coefficient and virtual damping coefficient of the VSG algorithm respectively.

[0068] When building the model, it is necessary to clarify the connection mode of each converter in the parallel GFM converter. Each converter is connected through line impedance Z1 and Z2, and the equivalent load impedance is Z L , the grounding resistance during fault is Z F , based on which the equivalent circuit and admittance values ​​of the system are determined. The admittance expressions are as follows:

[0069]

[0070] Among them, Y 11 and Y 22 is the self-admittance of the two converter nodes, Y 12 is the mutual admittance of the two nodes. Under normal circumstances, Z3 = Z L ; In case of fault, Z3 = Z L / / Z F .

[0071] 2) The influence mechanism of damping on transient stability is analyzed based on the transient model. An active power model is established with the grounding resistance at the time of fault as the variable. By studying the variation of the admittance parameter in the active power expression under different fault severity, the active power surfaces under different fault severity are obtained.

[0072] Specifically, considering that the external characteristics of the GFM converter can be equivalent to a voltage source, according to the circuit structure, the active power expression under different fault degrees is obtained as follows:

[0073]

[0074] Among them, P GFM1 and P GFM2 are the actual active power of the leading and lagging units respectively, U1 and U2 are the output terminal voltages of the two units respectively, δ 12 = δ GFM1 - δ GFM2 , G 11 , G 12 and G 22 Y 11 、Y 12 and Y 22 The real part of Y 12 The admittance angle.

[0075] According to the two power expressions, the active power surface diagram under different fault degrees is drawn, such as Figure 3 As shown, when the system failure degree is different and causes Z F When the power changes, the active power of the two units also varies, showing results higher or lower than the reference power in different areas.

[0076] 3) Based on the active power surfaces under different fault severity, the damping impact evaluation indicators E1 and E2 are introduced. The actual power angle swing trajectory and the changes in the evaluation indicators are observed, and the impact mechanism of damping on transient stability under different fault severity is analyzed.

[0077] Specifically, referring to the definition of damping energy, E1 and E2 are set as the damping impact evaluation indicators of GFM1 and GFM2, which can be used to describe the damping effect of damping on transient stability from fault occurrence to fault clearance. E1 and E2 can be written as:

[0078]

[0079] Among them, D p1 and D p2 are the damping coefficients of the leading and lagging units respectively, and are the differences between the output frequencies of the two units and the rated frequencies, reflecting the frequency changes of the units; δio and δ ic is the converter power angle when the fault occurs and clears, t o and t c Corresponding to the time when the fault occurs and is cleared.

[0080] Setting the grounding resistance Z F The pu is gradually reduced from 0.15 to 0, and the degree of the simulated fault is gradually deepened. The E1 and E2 of the two units under each working condition are obtained, as shown in Table 1. F The damping effect evaluation indexes E1 and E2 of GFM1 and GFM2 gradually increase and change from negative to positive. p1 The impact on transient stability changes from harmful to beneficial, D p2 On the contrary, the impact on transient stability changes from beneficial to harmful.

[0081] Table 1 E1 and E2 at different fault levels

[0082]

[0083] 4) Based on the mechanism of the impact of damping on transient stability under different fault severity obtained in step 3), the controller of the parallel GFM converter is used to sample the frequency changes of the active power-frequency loop output of the leading and lagging units in real time during system operation. The frequency change is introduced as a variable into the transient damping control strategy, and the damping coefficient of the converter is adjusted in real time. Overregulation is prevented through a negative feedback loop to optimize the transient stability of the system.

[0084] Specifically, considering that the impact of damping varies under different fault conditions and it is difficult to predict the severity of the fault in advance, it is quite challenging to meet the transient stability requirements of different working conditions under a constant damping setting. Therefore, an adaptive damping control strategy is introduced, such as Figure 4 The basic idea of ​​designing adaptive damping control is that each converter adjusts the damping coefficient in real time according to the frequency change of the active power-frequency loop output to improve the transient stability of the system. > 0, D p1 It is beneficial to transient stability, so D should be increased. p1 On the contrary, when < 0, D should be reduced p1 . D p2 The situation is similar. >0, D p2 It is harmful to transient stability, so D should be reduced p2 .when < 0, D should be increased p2 Therefore, the following transient damping control strategy is designed:

[0085] when > 0, D * p1 = D p1 + k Dp1 k 12 ;

[0086] when < 0, D * p1 = D p1 -k Dp1 k 12 ;

[0087] when > 0, D * p2 = D p2 + k Dp2 k 12 ;

[0088] when < 0, D * p2 = D p2 -k Dp2 k 12 ;

[0089] Among them, D * p1 and D * p2 is the converter damping coefficient after real-time adjustment, k Dp1 and k Dp2 is the control coefficient. When implementing the adaptive damping control strategy, the fundamental purpose of damping adjustment is to limit The size of δ 12 When the fault causes or When the fluctuation is large, the damping needs to be adjusted significantly to achieve However, adjusting the damping coefficient too much may cause decreases to less than 0, which may even further lead to δ 12 is less than 0, thus changing the lead-lag relationship between the two converters, which will seriously deviate from the steady-state equilibrium point and is not conducive to the recovery of the system after the fault is cleared. Therefore, k is introduced 12 The frequency difference between the two converters Make real-time judgments and form a negative feedback loop to prevent over-regulation.

[0090] An embodiment of the present invention further provides an adaptive damping control device for a non-uniformly damped parallel GFM converter, comprising:

[0091] A transient model establishment module is used to establish a transient model of a parallel GFM converter with non-uniform damping. In the transient model, the GFM converter is connected to a common coupling point PCC via an LC filter including an inductor Lf and a capacitor Cf. The GFM converter control loop includes a reactive power-voltage loop and an active power-frequency loop. The reactive power-voltage loop uses constant terminal voltage control to maintain output terminal voltage stability. The active power-frequency loop uses a virtual synchronous machine (VSG) control to simulate the inertia and damping characteristics of the synchronous machine. The reactive power-voltage loop and the active power-frequency loop control the amplitude and phase of the GFM output voltage, respectively.

[0092] The active power surface acquisition module is used to analyze the impact of damping on transient stability based on the transient model. The active power model is established using the ground resistance at the time of the fault as a variable. By studying the variation of the admittance parameter in the active power expression under different fault severity, the active power surface under different fault severity is obtained.

[0093] The damping influence mechanism acquisition module is used to introduce the damping influence evaluation indicators E1 and E2 based on the active power surface under different fault severity, observe the actual power angle swing trajectory and the changes in the evaluation indicators, and analyze the influence mechanism of damping on transient stability under different fault severity;

[0094] The damping coefficient adjustment module is used to obtain the influence mechanism of damping on transient stability under different fault degrees based on the damping influence mechanism. During system operation, the controller of the parallel GFM converter is used to sample the frequency changes of the active power-frequency loop output of the leading and lagging units in real time, and the frequency change is introduced as a variable into the transient damping control strategy to adjust the damping coefficient of the converter in real time. The negative feedback loop is used to prevent overregulation and optimize the transient stability of the system.

[0095] Figure 5 shows the constant damping setting and the fault impedance Z F =0.15pu when the simulation results. The critical stability results are as follows Figure 5 As shown in (a) in the figure, the fault is cleared 465 milliseconds after it occurs. The power angle does not exceed the upper limit of the angle stability. After a period of oscillation, the power angle, frequency, and active power return to the constant value of the steady-state operating point. The unstable waveform is shown in Figure 5 As shown in Figure (b), the fault cleared 466 milliseconds after its occurrence, and the power angle rapidly increased, exceeding the angle limit. Although the power angle gradually returned to a stable value after several cycles, this is unacceptable in engineering practice because it would cause significant abnormal disturbances to the system. Therefore, it was still judged as transient instability.

[0096] Figure 6 shows the fault impedance Z F =0.15pu using the adaptive transient damping control strategy. When the proposed control strategy is adopted, the system can also reach the equilibrium point during the fault period. The two converters can stably output active power, and the frequency difference is zero, and the power angle δ 12 It no longer rises. Therefore, under this operating condition, even if the fault is not eliminated, the system will not lose stability. By setting the fault to clear after 1 second, the system can smoothly return to the steady-state equilibrium point after the fault is cleared, verifying the effectiveness of the proposed control strategy.

[0097] Figure 7 shows the fault impedance Z F = 0 with constant damping setting. The critical stability results are as follows Figure 7 As shown in (a), the fault clearing time is set to 7084 milliseconds. Since active power is independent of the power angle during the fault, the power remains constant. Simultaneously, the frequency also stabilizes to a constant value, the frequency difference remains constant, and increases linearly. After the fault is cleared, the power angle does not exceed the power angle limit, and the system remains stable. However, when the fault clearing time is set to 7085 milliseconds, the power angle exceeds the limit, and the system becomes unstable.

[0098] Figure 8 shows the fault impedance Z F = 0. During the fault period, the proposed control strategy uses and Rapidly stabilize and tend to be equal. After a small oscillation, becomes zero. Therefore, δ 12 The increase in the transient state is not significant, and the system operates at a different equilibrium point during the transient process. Even if the fault is not cleared, the system can always maintain transient stability. By setting the fault to clear after 8 seconds, the system can smoothly return to the steady-state equilibrium point after the fault is cleared, verifying the effectiveness of the proposed control strategy.

[0099] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk drives, CD-ROMs, optical storage devices, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention may be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0100] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0101] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0102] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0103] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0104] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. An adaptive damping control method for a non-uniformly damped parallel GFM converter, characterized in that: The following steps are involved: 1) A transient model of a parallel GFM converter with non-uniform damping is established. In this transient model, the GFM converter is connected to the common coupling point PCC via an LC filter consisting of an inductor Lf and a capacitor Cf. The GFM converter control loop includes a reactive power-voltage loop and an active power-frequency loop. The reactive power-voltage loop uses constant terminal voltage control to maintain output voltage stability. The active power-frequency loop uses a virtual synchronous machine (VSG) control to simulate the inertia and damping characteristics of the synchronous machine. The reactive power-voltage loop and the active power-frequency loop control the amplitude and phase of the GFM output voltage, respectively. 2) Based on the transient model, the impact mechanism of damping on transient stability is analyzed. An active power model is established with the ground resistance at the time of the fault as a variable. By studying the variation of the admittance parameter in the active power expression under different fault severity, the active power surface under different fault severity is obtained. 3) Based on the active power curves under different fault severity, the damping impact evaluation indicators E1 and E2 are introduced. The actual power angle swing trajectory and the changes in the evaluation indicators are observed, and the impact mechanism of damping on transient stability under different fault severity is analyzed; 4) Based on the mechanism of the impact of damping on transient stability under different fault severity obtained in step 3), the controller of the parallel GFM converter is used to sample the frequency changes of the active power-frequency loop output of the leading and lagging units in real time during system operation. The frequency change is introduced as a variable into the transient damping control strategy, and the damping coefficient of the converter is adjusted in real time. Overregulation is prevented through a negative feedback loop to optimize the transient stability of the system.

2. The method according to claim 1, wherein: In step 1), the algorithm formula for controlling the virtual synchronous machine VSG is: ； Among them, δ GFM is the power angle generated by the active power circuit, and Represent the actual frequency of GFM and the rated frequency of the system, P GFM and P ref are the actual electromagnetic power and reference power, J and D respectively p They are the virtual inertia coefficient and virtual damping coefficient of the VSG algorithm respectively; when establishing the model, the connection mode of each converter in the parallel GFM converter is determined. The two converters are connected to the common coupling point PCC through line impedances Z1 and Z2. The equivalent load impedance is Z L , the grounding resistance during fault is Z F , thereby determining the equivalent circuit and each admittance value of the system.

3. The method according to claim 2, wherein: In step 2), the expressions of the admittance values ​​are as follows: ； Among them, Y 11 and Y 22 is the self-admittance of the two converter nodes, Y 12 is the mutual admittance between the two nodes. Under normal circumstances, Z3 = Z L ; In case of fault, Z3 = Z L / / Z F .

4. The method according to claim 1, wherein: In step 2), the active power expression under different fault degrees is as follows: ； Among them, P GFM1 and P GFM2 are the actual active power of the leading and lagging units respectively, U1 and U2 are the output terminal voltages of the two units respectively, δ 12 = δ GFM1 - δ GFM2 , G 11 , G 12 and G 22 Y 11 、Y 12 and Y 22 The real part of Y 12 The admittance angle.

5. The method according to claim 1, wherein: In step 3), the damping impact evaluation indicators E1 and E2 are expressed as: ； Among them, D p1 and D p2 are the damping coefficients of the leading and lagging units respectively, and are the differences between the output frequencies of the two units and the rated frequencies, reflecting the frequency changes of the units; δ io and δ ic is the converter power angle when the fault occurs and clears, t o and t c Corresponding to the fault occurrence and clearing moments; during the analysis process, based on the changes in active power model parameters with the fault severity, the impact of damping on transient stability under different fault severity is determined.

6. The method according to claim 1, wherein: In step 4), the transient damping control strategy is as follows: when > 0, D * p1 = D p1 + k Dp1 k 12 ; when < 0, D * p1 = D p1 -k Dp1 k 12 ; when > 0, D * p2 = D p2 + k Dp2 k 12 ; when < 0, D * p2 = D p2 -k Dp2 k 12 ; Among them, D * p1 and D * p2 is the converter damping coefficient after real-time adjustment, k Dp1 and k Dp2 is the control coefficient, and k is introduced 12 Used for judgment = - The sign of , forming a negative feedback loop, when = 0, the damping adjustment is stopped; when it is implemented, the frequency of the converter is monitored in real time. and , adjust the damping coefficient according to the control strategy formula to optimize the transient stability of the system.

7. An adaptive damping control device for a non-uniformly damped parallel GFM converter, characterized in that: include: A transient model establishment module is used to establish a transient model of a parallel GFM converter with non-uniform damping. In the transient model, the GFM converter is connected to a common coupling point PCC via an LC filter including an inductor Lf and a capacitor Cf. The GFM converter control loop includes a reactive power-voltage loop and an active power-frequency loop. The reactive power-voltage loop uses constant terminal voltage control to maintain output terminal voltage stability. The active power-frequency loop uses a virtual synchronous machine (VSG) control to simulate the inertia and damping characteristics of the synchronous machine. The reactive power-voltage loop and the active power-frequency loop control the amplitude and phase of the GFM output voltage, respectively. The active power surface acquisition module is used to analyze the impact of damping on transient stability based on the transient model. The active power model is established using the ground resistance at the time of the fault as a variable. By studying the variation of the admittance parameter in the active power expression under different fault severity, the active power surface under different fault severity is obtained. The damping influence mechanism acquisition module is used to introduce the damping influence evaluation indicators E1 and E2 based on the active power surface under different fault severity, observe the actual power angle swing trajectory and the changes in the evaluation indicators, and analyze the influence mechanism of damping on transient stability under different fault severity; The damping coefficient adjustment module is used to obtain the influence mechanism of damping on transient stability under different fault degrees based on the damping influence mechanism. During system operation, the controller of the parallel GFM converter is used to sample the frequency changes of the active power-frequency loop output of the leading and lagging units in real time, and the frequency change is introduced as a variable into the transient damping control strategy to adjust the damping coefficient of the converter in real time. The negative feedback loop is used to prevent overregulation and optimize the transient stability of the system.

8. The adaptive damping control device for a non-uniformly damped parallel GFM converter according to claim 7, characterized in that: The algorithm formula for the virtual synchronous machine VSG control is: ； Among them, δ GFM is the power angle generated by the active power circuit, and Represent the actual frequency of GFM and the rated frequency of the system, P GFM and P ref are the actual electromagnetic power and reference power, J and D respectively p They are the virtual inertia coefficient and virtual damping coefficient of the VSG algorithm respectively; when establishing the model, the connection mode of each converter in the parallel GFM converter is determined. The two converters are connected to the common coupling point PCC through line impedances Z1 and Z2. The equivalent load impedance is Z L , the grounding resistance during fault is Z F , thereby determining the equivalent circuit and each admittance value of the system.

9. The adaptive damping control device for a non-uniformly damped parallel GFM converter according to claim 7, wherein: The active power expressions under different fault degrees are as follows: ； Among them, P GFM1 and P GFM2 are the actual active power of the leading and lagging units respectively, U1 and U2 are the output terminal voltages of the two units respectively, δ 12 = δ GFM1 - δ GFM2 , G 11 , G 12 and G 22 Y 11 、Y 12 and Y 22 The real part of Y 12 The admittance angle.

10. The adaptive damping control device for a non-uniformly damped parallel GFM converter according to claim 7, wherein: The damping impact evaluation indexes E1 and E2 are expressed as follows: ； Among them, D p1 and D p2 are the damping coefficients of the leading and lagging units respectively, and are the differences between the output frequencies of the two units and the rated frequencies, reflecting the frequency changes of the units; δ io and δ ic is the converter power angle when the fault occurs and clears, t o and t c Corresponding to the fault occurrence and clearing moments; during the analysis process, based on the changes in active power model parameters with fault severity, the impact of damping on transient stability under different fault severity levels is determined; The transient damping control strategy is as follows: when > 0, D * p1 = D p1 + k Dp1 k 12 ; when < 0, D * p1 = D p1 -k Dp1 k 12 ; when > 0, D * p2 = D p2 + k Dp2 k 12 ; when < 0, D * p2 = D p2 -k Dp2 k 12 ; Among them, D * p1 and D * p2 is the converter damping coefficient after real-time adjustment, k Dp1 and k Dp2 is the control coefficient, and k is introduced 12 Used for judgment = - The sign of , forming a negative feedback loop, when = 0 to stop damping adjustment; when implemented, the frequency of the converter is monitored in real time. and , adjust the damping coefficient according to the control strategy formula to optimize the transient stability of the system.

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