Method and device for controlling flexible power recovery of grid-forming inverter, and storage medium

Abstract

The invention discloses a flexible power recovery control method and device for a grid-forming inverter and a storage medium, and belongs to the technical field of photovoltaic new energy grid connection. The method comprises the steps that an active power dispatching instruction and current operation parameters of the inverter are acquired; determining a transient stability power boundary constraint condition of the current operation point based on the parameters; according to the instruction and the boundary condition, calculating the minimum adjustment step length required for meeting transient stability; comparing the minimum step length number with a preset expected step length number, and adaptively selecting one of two control modes of variable-step-length step climbing or inertial link equivalent recovery according to a comparison result; shaping the scheduling instruction according to the selected mode, and generating a smooth active power reference signal; and finally, inputting the signal into a droop control loop to realize stable control of power output of the inverter. According to the invention, the problems of long transient transition time, large output waveform overshoot, transient instability and the like of the grid-forming inverter under high-power scheduling are solved.

Description

A method, device, and storage medium for flexible power recovery control of grid-connected inverters. Technical Field

[0001] This invention relates to a method, device, and storage medium for flexible power recovery control of grid-connected inverters, belonging to the field of photovoltaic new energy grid connection technology. Background Technology

[0002] In recent years, the large-scale integration of renewable energy with power electronic converters has become a global trend. Renewable energy typically uses grid-connected inverters to inject active power into the grid, maximizing the advantages of renewable energy. However, with the accelerated evolution of high-voltage power systems, grid strength is continuously weakening. The negative resistance characteristics introduced by the asymmetric phase-locked loop of the grid-connected inverter can cause harmonic oscillations, degrading the stability of the grid-connected system. To ensure the safe and reliable operation of high-penetration grid-connected systems, grid-connected inverters with voltage inertia support, grid self-synchronization, and weak grid oscillation suppression characteristics, drawing on the physical mechanisms of synchronous generators, have become a hot research topic.

[0003] Inverter grid control technology achieves grid-connected self-synchronization by simulating the rotor motion equations of a synchronous generator. When system disturbances occur, grid-connected inverters face synchronous instability (i.e., transient instability) problems similar to those of synchronous generators. Among these, research on small-disturbance stability based on eigenvalue analysis, sensitivity analysis, and impedance analysis is relatively mature. However, the extreme transient instability and grid disconnection problems caused by large disturbances such as transmission line faults, grid voltage drops, and large load switching are new areas of focus, such as the London blackout triggered by lightning strikes leading to voltage dips and power oscillations.

[0004] However, during peak load periods, new power systems require high-power dispatch to meet electricity demand, and existing research rarely focuses on the transient stability of distributed generation under high-power and extreme power dispatch during peak loads. If grid-connected inverters cannot achieve power balance during high-power dispatch, the system will experience transient instability, which can lead to system collapse in severe cases. Therefore, transient stability control of grid-connected inverters under high-power dispatch is of great significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a power flexible recovery control method, device and storage medium for grid-connected inverters, which solves the problems of long transient transition time, large output waveform overshoot and transient instability of grid-connected inverters under high power dispatch.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0007] In a first aspect, the present invention provides a method for flexible power recovery control of a grid-connected inverter, comprising:

[0008] Obtain external active power dispatch commands and the current operating parameters of the grid-connected inverter system;

[0009] Based on the current operating parameters, determine the power boundary constraints that satisfy the transient stability requirements at the current operating point;

[0010] Based on the active power scheduling command and the power boundary constraints, calculate the minimum power adjustment step size required to satisfy the transient stability requirements;

[0011] The minimum power adjustment step size is compared with the preset desired step size, and the corresponding power flexible recovery control mode is selected based on the comparison result.

[0012] Based on the selected power flexible recovery control mode, the active power dispatch command is shaped to generate a shaped active power reference signal;

[0013] The shaped active power reference signal is input to the droop control loop of the grid inverter to control the power output of the inverter.

[0014] Furthermore, determining the power boundary constraints that satisfy the transient stability requirements at the current operating point includes:

[0015] Based on the current operating parameters, establish the power angle-active power characteristic curve of the grid inverter;

[0016] Based on the equal area rule, the acceleration area and deceleration area are calculated on the power angle-active power characteristic curve when a power step dispatch is performed from the current operating point; wherein, the expressions for the acceleration area S+ and the deceleration area S- are:

[0017] ;

[0018] Among them, V g δ is the voltage amplitude of the power grid, where V is the voltage amplitude. g The angle by which I lags behind the inverter output voltage amplitude q For reactive current, X l Assuming the line reactance is given, the grid-connected inverter initially operates at the reference active power point P0, δ s1 Let δ be the stable equilibrium angle at the initial operating point. When the reference active power value P0 suddenly increases to the reference active power value P1, δ s2 δ is the power angle at the stable equilibrium point of the operating point after the power is increased. u2 The work angle at an unstable equilibrium point;

[0019] Using the acceleration area equal to the deceleration area as the critical transient stability criterion, the limit scheduling power step size starting from the current operating point is determined as the power boundary constraint condition.

[0020] Furthermore, the calculation of the minimum power adjustment step size required to satisfy the transient stability requirement includes:

[0021] The total power scheduling amount is determined based on the difference between the active power scheduling command and the current operating point power.

[0022] Using the limit power scheduling step size as a constraint, calculate the minimum number of step sizes required to decompose the total power scheduling amount into multiple consecutive power steps.

[0023] Furthermore, the step of selecting the corresponding power flexible recovery control mode based on the comparison results includes:

[0024] When the minimum power adjustment step size is less than or equal to the desired step size, the variable step power step ramp control mode is selected.

[0025] When the minimum power adjustment step size is greater than the desired step size, the equivalent recovery control mode based on the inertial element is selected.

[0026] Furthermore, when the variable step power step ramp control mode is selected, the shaping process of the active power scheduling command includes:

[0027] The total power scheduling amount is decomposed into multiple consecutive power step steps;

[0028] In this process, the power step size at each step is no greater than the current limit power step size calculated from the starting power point of that step based on the power boundary constraints.

[0029] Furthermore, when the equivalent recovery control mode based on the inertial element is selected, the shaping of the active power scheduling command is achieved through an equivalent inertial element;

[0030] The transfer function of the equivalent inertial element is: ,in This is the steady-state gain coefficient. The inertial time coefficient; For the Laplace operator;

[0031] The inertial time coefficient The value of is determined based on the time scale of transient stability analysis and the desired power ramp-up response curve, so that the change rate of the shaped power reference signal is accelerated in the initial stage and slowed down when approaching the target value.

[0032] Furthermore, when the equivalent inertial element is used, the control equation for the active power loop of the grid inverter is:

[0033] ;

[0034] Where, m p n is the active power droop factor. q This is the reactive power droop factor. The rated frequency is the mains frequency, E0 is the rated voltage amplitude, and E... * P is the given value for voltage amplitude. f Q is the active power output after inverter filtering. f P0 is the reactive power output after inverter filtering, Q0 is the reference active power, and Q0 is the reference reactive power value. The reference angular frequency for the power grid is used. Furthermore, the droop control loop simulates the rotor motion equation of a synchronous generator, and adjusts the inverter's output frequency and phase angle based on the deviation between the shaped active power reference signal and the actual output active power of the inverter.

[0035] Secondly, the present invention provides a grid-connected inverter power flexible recovery control device for implementing the grid-connected inverter power flexible recovery control method described in any one of the preceding claims, comprising:

[0036] The parameter acquisition module is used to acquire external active power dispatch commands and the current operating parameters of the grid inverter system;

[0037] The constraint determination module is used to determine the power boundary constraint conditions that meet the transient stability requirements at the current operating point based on the current operating parameters.

[0038] The calculation module is used to calculate the minimum power adjustment step size required to meet the transient stability requirements based on the active power scheduling command and the power boundary constraints.

[0039] The comparison and selection module is used to compare the minimum power adjustment step size with the preset expected step size, and select the corresponding power flexible recovery control mode based on the comparison result.

[0040] The shaping module is used to shape the active power dispatching command according to the selected power flexible recovery control mode, and generate a shaped active power reference signal.

[0041] The control module is used to input the shaped active power reference signal to the droop control loop of the grid inverter to control the power output of the inverter.

[0042] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the methods described above.

[0043] Fourthly, the present invention provides an electronic device, comprising:

[0044] Memory, used to store computer programs / instructions;

[0045] A processor for executing the computer program / instructions to implement the steps of any of the methods described above.

[0046] Fifthly, the present invention provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of any of the methods described above.

[0047] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0048] 1. This invention provides a power flexible recovery control method, device and storage medium for grid-connected inverters. By analyzing the transient stability boundary through the equal area rule, a power ramping scheduling strategy is proposed, which effectively prevents the inverter from becoming unstable during power surges and significantly improves the transient stability of the system under high power scheduling.

[0049] 2. When the recovery step length is large, the present invention uses an inertial element to simulate the variable step length climbing process, eliminating the need for online calculation of the climbing step length for each step, reducing the computational burden on the controller, and making it easier to implement in engineering. Attached Figure Description

[0050] Figure 1 is an electrical schematic diagram of a grid-connected inverter power flexible recovery control method provided in an embodiment of the present invention;

[0051] Figure 2 is a curve showing the sinusoidal relationship between the inverter output active power P and the power angle δ when the reference active power increases, according to an embodiment of the present invention.

[0052] Figure 3 is a block diagram of power flexible recovery control selection for grid-connected inverters provided in an embodiment of the present invention. Detailed Implementation

[0053] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0054] Example 1: This example introduces a power flexible recovery control method for grid-connected inverters, including:

[0055] Obtain external active power dispatch commands and the current operating parameters of the grid-connected inverter system;

[0056] Based on the current operating parameters, determine the power boundary constraints that satisfy the transient stability requirements at the current operating point;

[0057] Based on the active power scheduling command and the power boundary constraints, calculate the minimum power adjustment step size required to satisfy the transient stability requirements;

[0058] The minimum power adjustment step size is compared with the preset desired step size, and the corresponding power flexible recovery control mode is selected based on the comparison result.

[0059] Based on the selected power flexible recovery control mode, the active power dispatch command is shaped to generate a shaped active power reference signal;

[0060] The shaped active power reference signal is input to the droop control loop of the grid inverter to control the power output of the inverter.

[0061] Figure 1 shows the topology of the grid-connected inverter system implemented in this embodiment. The system includes a three-phase six-switch grid-connected inverter main circuit, a pf / qv droop control unit, a power flexible recovery control unit, and a single-unit infinite grid. The grid-connected inverter main circuit consists of a DC voltage source, a three-phase six-switch bridge arm, a filter inductor Lf, a filter capacitor Cf, and a line reactance L1. After filtering by an LCL filter, the inverter is connected to the infinite grid via the line reactance L1. The droop control unit is implemented by simulating the rotor motion equation of a synchronous generator, and its control equation is:

[0062] ;

[0063] Where, m p n is the active power droop factor. q This refers to the reactive power droop factor. The rated frequency is the mains frequency; E0 is the rated voltage amplitude; P f Q is the active power output after inverter filtering. f P0 is the reactive power output after inverter filtering; P0 is the reference active power value; Q0 is the reference reactive power value.

[0064] The power angle-active power characteristic of a grid-connected inverter can be described by the following equation:

[0065] ;

[0066] Where P is the active power output of the inverter, Q is the reactive power output of the inverter, and I... d For active current, I q For reactive current, V i V represents the output voltage amplitude of the inverter.g δ is the voltage amplitude of the power grid, where V is the voltage amplitude. g Lagging behind V i Angle, X l This refers to the line reactance.

[0067] As shown in Figure 2, the critical transient stability criterion is that the acceleration area S+ = the deceleration area S-. Based on this criterion, the maximum allowable power step ΔPmax that can guarantee the transient stability of the system starting from the current operating point P0 can be determined, which is the limit scheduling power boundary.

[0068] In specific calculations, the current operating conditions need to be considered, including the initial power angle δ0, system parameters (E, V, X), etc. The above integral equation is solved numerically to obtain ΔPmax at different operating points.

[0069] As shown in Figure 3, let the step size of the external active power dispatch command be ΔP = |Pref0 - P0|, and the limit dispatch power step size be ΔPmax. Then, the minimum number of step sizes required for flexible recovery control is Nmin. Let the desired number of step sizes be Nset (determined according to the system response speed requirements), then:

[0070] Case 1: When Nmin≤Nset, use variable step power step ramp control;

[0071] Case 2: When Nmin > Nset, flexible recovery control is used, which is simulated by an inertial element.

[0072] The specific execution process is as follows:

[0073] (1) Case 1: Variable step power step ramp control (Nmin≤Nset);

[0074] When the number of steps required for flexible recovery control is less than or equal to the desired number of steps, variable step power step ramp control is adopted. The specific steps are as follows: Calculate the actual number of steps N = max(Nmin, Nset), ensuring that the power change in each step does not exceed the current point's limit power step size; decompose the total power scheduling amount ΔP into N consecutive power step steps; ensure that the step amount in each step |Pref_i - Pref_{i-1}| ≤ ΔPmax_i, where ΔPmax_i is the limit power step size calculated from the power point of step i-1; if the calculated step amount in a certain step exceeds the current limit power step size, adjust the step amount of that step to ΔPmax_i and increase the total number of steps accordingly; execute each power step step in sequence, waiting for the system to stabilize before executing the next step.

[0075] (2) Case 2: Flexible recovery control of inertial element simulation (Nmin>Nset);

[0076] When the number of step sizes required for flexible recovery control is greater than the desired number of step sizes, an inertial element is used to simulate the variable step power step climbing process.

[0077] The improved control equation for the active power loop is:

[0078] ;

[0079] Where, m p n is the active power droop factor. q This is the reactive power droop factor. The rated frequency is the mains frequency, E0 is the rated voltage amplitude, and E... * P is the given value for voltage amplitude. f Q is the active power output after inverter filtering. f P0 represents the reactive power output after inverter filtering, and Q0 represents the reference active power value and the reference reactive power value. The reference angular frequency of the power grid. This is the steady-state gain coefficient. The inertial time coefficient; For the Laplace operator.

[0080] Inertial parameter design principles: Typically, it is set to 1 to ensure that Pref = Pref0 in steady state. The value of needs to be determined based on the time scale of the transient stability analysis and the desired power ramp-up response curve. Generally, this is achieved through the following steps: determining the maximum power ramp-up rate based on the system's maximum allowable rate of change of power angle; designing the power ramp-up curve to have a rapid rise rate in the initial stage, while slowing down as it approaches the target power; and determining the optimal rate through simulation verification and optimization. This value achieves a balance between fast response and transient stability. A typical example... The value ranges from 0.1 to 1.0, and the specific value needs to be determined based on the actual system parameters.

[0081] Through the above specific embodiments, the present invention has achieved the following technical advancements:

[0082] Improving system stability: By analyzing the transient stability boundary using the equal area rule, a power ramping scheduling strategy is proposed, which effectively prevents the inverter from becoming unstable during power surges and significantly improves the transient stability of the system under high power scheduling.

[0083] Simplified control structure and enhanced practicality: When the recovery step size is large, an inertial element is used to simulate the variable step size climbing process, eliminating the need for online calculation of each climbing step size, reducing the computational burden on the controller, and making it easier to implement in engineering. Compared with traditional control methods, this invention requires significantly fewer computational resources, making it more suitable for practical engineering applications.

[0084] Example 2: This example provides a grid-connected inverter power flexible recovery control device, including:

[0085] The parameter acquisition module is used to acquire external active power dispatch commands and the current operating parameters of the grid inverter system;

[0086] The constraint determination module is used to determine the power boundary constraint conditions that meet the transient stability requirements at the current operating point based on the current operating parameters.

[0087] The calculation module is used to calculate the minimum power adjustment step size required to meet the transient stability requirements based on the active power scheduling command and the power boundary constraints.

[0088] The comparison and selection module is used to compare the minimum power adjustment step size with the preset expected step size, and select the corresponding power flexible recovery control mode based on the comparison result.

[0089] The shaping module is used to shape the active power dispatching command according to the selected power flexible recovery control mode, and generate a shaped active power reference signal.

[0090] The control module is used to input the shaped active power reference signal to the droop control loop of the grid inverter to control the power output of the inverter.

[0091] The specific functions of each module described above are explained in the relevant content of the method in Embodiment 1, and will not be repeated here.

[0092] Example 3: This example provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any of the methods described in Example 1.

[0093] Example 4: This example provides an electronic device, including:

[0094] Memory, used to store computer programs / instructions;

[0095] A processor for executing the computer program / instructions to implement the steps of any of the methods described in Embodiment 1.

[0096] Example 5: This example provides a computer program product, including a computer program / instructions, which, when executed by a processor, implement the steps of the method described in any one of Examples 1.

[0097] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0098] Those skilled in the art will understand that embodiments of this disclosure can be provided as methods, systems, or computer program products. Therefore, this disclosure can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this disclosure can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0099] This disclosure is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations 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, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in one or more flowchart illustrations and / or one or more block diagrams.

[0100] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means that implement the functions specified in one or more flowcharts and / or one or more block diagrams.

[0101] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and / or one or more block diagrams.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure and not to limit its protection scope. Although this disclosure has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading this disclosure, they can still make various changes, modifications or equivalent substitutions to the specific implementation of the invention, but these changes, modifications or equivalent substitutions are all within the protection scope of the pending claims.

Claims

1. A method for flexible power recovery control of a grid-connected inverter, characterized in that, include: Obtain external active power dispatch commands and the current operating parameters of the grid-connected inverter system; Based on the current operating parameters, determine the power boundary constraints that satisfy the transient stability requirements at the current operating point; Based on the active power scheduling command and the power boundary constraints, calculate the minimum power adjustment step size required to meet the transient stability requirements; compare the minimum power adjustment step size with the preset expected step size, and select the corresponding power flexible recovery control mode based on the comparison result; Based on the selected power flexible recovery control mode, the active power dispatch command is shaped to generate a shaped active power reference signal; the shaped active power reference signal is input to the droop control loop of the grid inverter to control the power output of the inverter.

2. The grid-connected inverter power flexible recovery control method according to claim 1, characterized in that, The determination of the power boundary constraints that satisfy the transient stability requirements at the current operating point includes: establishing the power angle-active power characteristic curve of the grid-connected inverter based on the current operating parameters; and calculating the acceleration area and deceleration area when performing a power step dispatch from the current operating point on the power angle-active power characteristic curve based on the equal area rule; wherein, the expressions for the acceleration area S+ and the deceleration area S- are: Among them, V g δ is the voltage amplitude of the power grid, where V is the voltage amplitude. g The angle by which I lags behind the inverter output voltage amplitude q For reactive current, X l Assuming the line reactance is given, the grid-connected inverter initially operates at the reference active power point P0, δ s1 Let δ be the stable equilibrium angle at the initial operating point. When the reference active power value P0 suddenly increases to the reference active power value P1, δ s2 δ is the power angle at the stable equilibrium point of the operating point after the power is increased. u2 The power angle at the unstable equilibrium point is used as the critical transient stability criterion, and the limit scheduling power step size starting from the current operating point is determined as the power boundary constraint condition, with the acceleration area equal to the deceleration area as the critical transient stability criterion.

3. The grid-connected inverter power flexible recovery control method according to claim 2, characterized in that, The calculation of the minimum power adjustment step size required to meet the transient stability requirement includes: determining the total power scheduling amount based on the difference between the active power scheduling command and the current operating point power; and calculating the minimum number of steps required to decompose the total power scheduling amount into multiple consecutive power steps, using the limit scheduling power step size as a constraint.

4. The grid-connected inverter power flexible recovery control method according to claim 3, characterized in that, The selection of the corresponding power flexible recovery control mode based on the comparison results includes: when the minimum power adjustment step size is less than or equal to the expected step size, selecting the variable step size power step ramp control mode; when the minimum power adjustment step size is greater than the expected step size, selecting the equivalent recovery control mode based on the inertial element.

5. The grid-connected inverter power flexible recovery control method according to claim 4, characterized in that, When the variable step size power step ramp control mode is selected, the shaping process of the active power scheduling command includes: decomposing the total power scheduling amount into multiple consecutive power step steps; wherein the power step amount of each step is not greater than the current limit power step size calculated from the starting power point of the step according to the power boundary constraint conditions.

6. The grid-connected inverter power flexible recovery control method according to claim 4, characterized in that, When the equivalent recovery control mode based on the inertial element is selected, the shaping of the active power scheduling command is achieved through an equivalent inertial element; the transfer function of the equivalent inertial element is... ,in This is the steady-state gain coefficient. The inertial time coefficient; The Laplace operator; the inertial time coefficient The value of is determined based on the time scale of transient stability analysis and the desired power ramp-up response curve, so that the change rate of the shaped power reference signal is accelerated in the initial stage and slowed down when approaching the target value.

7. The grid-connected inverter power flexible recovery control method according to claim 6, characterized in that, When the equivalent inertial element is used, the control equation for the active power loop of the grid inverter is: ; where m p n is the active power droop factor. q This is the reactive power droop factor. The rated frequency is the mains frequency, E0 is the rated voltage amplitude, and E... * P is the given value for voltage amplitude. f Q is the active power output after inverter filtering. f P0 is the reactive power output after inverter filtering, Q0 is the reference active power, and Q0 is the reference reactive power value. This is the reference angular frequency for the power grid.

8. The grid-connected inverter power flexible recovery control method according to claim 1, characterized in that, The droop control loop simulates the rotor motion equation of a synchronous generator and adjusts the output frequency and phase angle of the inverter based on the deviation between the shaped active power reference signal and the actual output active power of the inverter.

9. A grid-connected inverter power flexible recovery control device, used to implement the grid-connected inverter power flexible recovery control method according to any one of claims 1-8, characterized in that, include: The parameter acquisition module is used to acquire external active power dispatch commands and the current operating parameters of the grid inverter system; The constraint determination module is used to determine the power boundary constraint conditions that meet the transient stability requirements at the current operating point based on the current operating parameters. The calculation module is used to calculate the minimum power adjustment step size required to meet the transient stability requirements based on the active power scheduling command and the power boundary constraints; the comparison and selection module is used to compare the minimum power adjustment step size with the preset expected step size and select the corresponding power flexible recovery control mode based on the comparison result. The shaping module is used to shape the active power dispatching command according to the selected power flexible recovery control mode, and generate a shaped active power reference signal; the control module is used to input the shaped active power reference signal to the droop control loop of the grid inverter to control the power output of the inverter.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When executed by a processor, the computer program implements the steps of the method according to any one of claims 1-8.

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