Frequency modulation control method and device for network tracking / constructing hybrid photovoltaic power station

Abstract

The invention discloses a frequency modulation control method and device for a network tracking / constructing hybrid photovoltaic power station. The method comprises the following steps: respectively establishing a network tracking type photovoltaic equivalent unit and a network constructing type photovoltaic equivalent unit; calculating a frequency modulation power amplitude limiting value of the grid-following type photovoltaic equivalent unit by taking the short-circuit ratio as a reference; when the system is subjected to power disturbance, distributing a corresponding first network following type frequency modulation instruction value and a corresponding first network constructing type frequency modulation instruction value to the overall frequency modulation power requirement of the photovoltaic power station according to the steady-state operation power proportion of the network following type photovoltaic equivalent unit and the network constructing type photovoltaic equivalent unit respectively; if the first tracking network type frequency modulation instruction value is greater than the frequency modulation power amplitude limiting value, the tracking network type photovoltaic equivalent unit participates in system frequency modulation according to the frequency modulation power amplitude limiting value; and adding the difference value between the first grid-following type frequency modulation instruction value and the frequency modulation power amplitude limiting value and the first grid-constructing type frequency modulation instruction value to serve as a final frequency modulation instruction value of the grid-constructing type photovoltaic equivalent unit, so that the mixed type photovoltaic power station stably supports the system frequency under the low short circuit ratio.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to a frequency modulation control method and device for a hybrid photovoltaic power station. Background Art

[0002] As power electronic converters are integrated into power systems on a large scale as grid interfaces for renewable energy sources, the inertia of power systems has significantly decreased. At present, most grid-connected inverters are synchronized using phase-locked loops (PLLs) in practice, which enable them to passively follow the grid frequency, also known as grid-following (GFL) control; however, grid-following control cannot establish voltage in weak grids (low short-circuit ratio). In contrast, grid-forming (GFM) converters act as coupled oscillators in the grid, which can establish voltage and frequency and synchronize spontaneously. Therefore, grid-forming converters can usually adapt to very weak grids. In order to balance economic benefits and weak grid adaptability, photovoltaic power stations are generally equipped with grid-following photovoltaic units and grid-forming photovoltaic units. However, the frequency regulation instructions assigned by traditional field frequency regulation controllers according to the working point may cause the frequency regulation of the grid-following units to be unstable under low short-circuit ratio conditions and cannot achieve coordinated control between the grid-following and grid-forming photovoltaic units. At present, there are many solutions for improving the frequency regulation capability of hybrid grid-following / grid-forming photovoltaic power stations, such as:

[0003] 1. The "optimal configuration of energy storage for the integrated source-grid-load-storage system considering frequency stability constraints under 100% new energy scenarios" disclosed in the prior art studies the frequency support capabilities of grid-following and grid-building new energy stations and demand-side response, and sets a reasonable virtual inertia time constant based on the actual operating status of the system and expected fault scenarios, introduces VSG technology to provide virtual inertia support for the system and establishes an integrated system frequency response model; however, the capacity ratio obtained in this article is based on its limited system structure and is not universal, and only considers the setting of the control capacity of the grid-following / grid-building wind turbines, without considering the problem that the grid-following control frequency regulation capability cannot function normally under low short-circuit ratio.

[0004] 2. The prior art also discloses "An Overview of Grid-following / Grid-building Hybrid Mode Control of High-penetration New Energy Power Generation Grid-connected Converters". This solution points out that station-level hybrid mode control is the application of hybrid mode control at the system level. It can not only be promoted on the basis of single-machine hybrid mode control such as switching hybrid mode control, fusion hybrid mode control, compensation hybrid mode control and synchronous hybrid control, but also can be achieved through hybrid configuration of grid-following / grid-building converters at the physical level. It has high flexibility in capacity configuration of power stations, but the difficulty of optimizing configuration increases with the expansion of system scale, and it also does not take into account the dynamic process of system frequency modulation.

[0005] 3. The prior art also discloses “How Many Grid-Forming Converters Do We Need? A Performance From Small Signal Stability and Power Grid Strength”. This solution starts from the perspective of small signal analysis, explores the voltage source behavior of the grid-forming inverter and can enhance the grid strength. Then, from the perspective of the system admittance matrix, it studies the influence of the capacity ratio between the grid-forming inverter and the grid-forming inverter on the equivalent grid strength, and gives a method on how to configure the grid-forming inverter in the grid and how many grid-forming inverters are needed. However, this method starts from the steady-state operating point of the system, and does not consider the short-circuit ratio change caused by the dynamic behavior of the port power when the new energy station participates in frequency modulation.

[0006] In summary, the current strategies for improving the frequency regulation capability of hybrid photovoltaic power stations with grid connection / grid construction are mostly considered from the perspective of capacity ratio, and lack consideration of the dynamic change of port short-circuit ratio during frequency regulation. Hybrid photovoltaic power stations have the greatest adaptability to grid strength under the set capacity ratio, but with the further increase of new energy penetration, the electrical distance between the power station and the main grid will further increase, which will further reduce its short-circuit ratio, and there is a problem that the frequency regulation capability may not be able to be exerted; when considering the frequency regulation control at the photovoltaic power station site level, the method of allocating frequency regulation instructions according to the respective working points of different units in the power station is more convenient, but this strategy does not take into account the problem that the grid-connected photovoltaic unit may touch the lower limit of its short-circuit ratio adaptation and cause frequency regulation instability when the power is increased in a short time, and lacks practical engineering considerations. Therefore, the current frequency regulation strategy of hybrid photovoltaic power stations with grid connection / grid construction needs to be further optimized. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the present invention provides a frequency modulation control method and device for a hybrid grid-following / grid-building photovoltaic power station, which fully utilizes the complementary characteristics of grid-following and grid-building wind turbines in control performance, solves the problem that grid-following photovoltaic units are prone to output frequency modulation instability under low short-circuit ratio conditions, effectively improves the frequency active support capability of the hybrid grid-following / grid-building photovoltaic power station, and ensures the frequency safety and stability of the power system.

[0008] The present invention adopts the following technical solution.

[0009] In a first aspect, the present invention provides a frequency modulation control method for a grid-connected / grid-connected hybrid photovoltaic power station, the method comprising the following steps:

[0010] S1. Establishing grid-following photovoltaic equivalent units and grid-building photovoltaic equivalent units in photovoltaic power stations respectively;

[0011] S2. Calculate the frequency modulation power limit value of the grid-connected photovoltaic equivalent unit based on the short-circuit ratio;

[0012] S3. When a power disturbance occurs in the system, the frequency modulation power demand of the photovoltaic power station as a whole is allocated with the corresponding first grid-following type frequency modulation command value and the first grid-forming type frequency modulation command value according to the steady-state operating power proportions of the grid-following type and grid-forming type photovoltaic equivalent units respectively;

[0013] S4, determining whether the first network type frequency modulation instruction value is greater than the frequency modulation power limit value;

[0014] If not, the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit participate in the system frequency modulation according to the first grid-following frequency modulation instruction value and the first grid-building frequency modulation instruction value respectively;

[0015] If so, the grid-following photovoltaic equivalent unit participates in the system frequency regulation according to the frequency regulation power limit value, and the difference between the first grid-following frequency regulation instruction value and the frequency regulation power limit value is added to the first grid-forming frequency regulation instruction value as the final frequency regulation instruction value of the grid-forming photovoltaic equivalent unit, so as to realize the hybrid photovoltaic power station to stably support the system frequency under a low short-circuit ratio.

[0016] Optionally, in step S1, the operating parameters of the established grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit are as follows:

[0017]

[0018] Where P ieq , Q ieq , P GFL_eq and S GFL_eq They are the steady-state active power, steady-state reactive power, rated active power and rated capacity of the grid-following photovoltaic equivalent unit respectively; P i , Q i , P i GFL and S i GFL are the active power, reactive power, rated active power and rated capacity of the i-th grid-connected photovoltaic unit in the photovoltaic power station; n is the total number of grid-connected photovoltaic units in the photovoltaic power station; P jeq , Q jeq , P GFM_eq and S GFM_eq are the steady-state active power, steady-state reactive power, rated active power and rated capacity of the grid-connected photovoltaic equivalent unit; P j , Q j , P j GFM and S j GFMare the active power, reactive power, rated active power and rated capacity of the jth grid-connected photovoltaic unit in the photovoltaic power station; m is the total number of grid-connected photovoltaic units in the photovoltaic power station.

[0019] Optionally, in step S1, the established equivalent collection line parameters of the grid-connected photovoltaic equivalent unit include:

[0020]

[0021] In the formula, Z ieq is the equivalent collector line impedance of the grid-following photovoltaic equivalent unit; U ieq and I ieq are the voltage and current of the grid-following equivalent photovoltaic unit; U pcc R1 is the voltage value of the low voltage side of the main transformer of the photovoltaic power station; GFL_eq and X1 GFL_eq They are respectively the positive-sequence resistance and positive-sequence inductance of the equivalent collector line impedance of the grid-following equivalent photovoltaic unit. Re represents the real part of the complex number, and Im represents the imaginary part of the complex number.

[0022] Optionally, in step S2, the step of calculating the frequency modulation power limit value of the grid-connected photovoltaic equivalent unit based on the short-circuit ratio includes:

[0023] Based on the equivalent collection line parameters and power of the grid-connected photovoltaic equivalent unit, a short-circuit ratio calculation model of the grid-connected photovoltaic equivalent unit is constructed, and its expression is as follows:

[0024]

[0025] Where gSCR is the short-circuit ratio of the grid-connected photovoltaic equivalent unit; P eq and Q eq They are respectively the active power and reactive power of the grid-following equivalent photovoltaic unit; R1 GFL_eq and X1 GFL_eq They are respectively the positive sequence resistance and positive sequence inductance of the equivalent collector line impedance of the grid-following equivalent photovoltaic unit;

[0026] The lower limit of the steady-state short-circuit ratio gSCR of the grid-connected photovoltaic equivalent unit min Substitute it into the short-circuit ratio calculation model to find the maximum output power P that can be accepted without frequency modulation instability. GFL_max , thereby obtaining the frequency modulation power limit value ΔP of the grid-following photovoltaic equivalent unit limit =ΔP limit =P GFL_max -P ieq .

[0027] Optionally, in step S3, the expressions of the first mesh-type frequency modulation instruction value and the first mesh-type frequency modulation instruction value are as follows:

[0028]

[0029] In the formula, ΔP GFL_ideal Indicates the first grid-type frequency regulation command value assigned to the grid-type photovoltaic equivalent unit, ΔP GFM_ideal represents the first grid-type frequency modulation instruction value assigned to the grid-type photovoltaic equivalent unit, P ieq and P jeq are the steady-state active power of the grid-following and grid-building photovoltaic equivalent units respectively; ΔP total It is the overall frequency modulation power demand of the photovoltaic power station.

[0030] Optionally, in step S4, if the first grid-type frequency modulation instruction value is greater than the frequency modulation power limit value, the frequency modulation instruction value ΔP of the grid-type photovoltaic equivalent unit is GFL_ref The frequency modulation command value ΔP of the grid-type photovoltaic equivalent GFM_ref The expressions are:

[0031]

[0032] In the formula, ΔP GFL_ideal is the first grid-type frequency modulation command value, ΔP GFM_ideal is the first network-type frequency modulation instruction value, ΔP limit is the frequency modulation power limit value, ΔP total It is the overall frequency modulation power demand of the photovoltaic power station.

[0033] Optionally, in step S4, after obtaining the final frequency modulation command value of the grid-type photovoltaic equivalent unit, the method further includes: calculating the inertia coefficient J of the grid-type photovoltaic unit participating in the system frequency modulation under the final frequency modulation command value. ref and droop coefficient D ref , and the calculation formulas are as follows:

[0034]

[0035] In the formula, ΔP GFM_ideal is the first network-type frequency modulation instruction value, ΔP GFM_ref The final frequency modulation command value of the grid-type photovoltaic equivalent unit; J and D are respectively the frequency modulation command value ΔP of the first grid-type GFM_ideal The inertia coefficient and droop coefficient under.

[0036] In a second aspect, the present invention provides a frequency modulation control device for a hybrid photovoltaic power station with a grid connection, and executes the steps of any method described in the first aspect of the present invention, the device comprising:

[0037] The equivalent module is used to respectively establish the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit in the photovoltaic power station;

[0038] A calculation module, used to calculate the frequency modulation power limit value of the grid-connected photovoltaic equivalent unit based on the short-circuit ratio;

[0039] An allocation module is used to allocate the corresponding first grid-following type frequency modulation instruction value and the first grid-forming type frequency modulation instruction value to the overall frequency modulation power demand of the photovoltaic power station according to the steady-state operating power proportion of the grid-following type and grid-forming type photovoltaic equivalent units when a power disturbance occurs in the system;

[0040] A frequency modulation module, used to determine whether the first network-type frequency modulation instruction value is greater than the frequency modulation power limit value;

[0041] If not, the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit participate in the system frequency modulation according to the first grid-following frequency modulation instruction value and the first grid-building frequency modulation instruction value respectively;

[0042] If so, the grid-following photovoltaic equivalent unit participates in the system frequency regulation according to the frequency regulation power limit value, and the difference between the first grid-following frequency regulation instruction value and the frequency regulation power limit value is added to the first grid-forming frequency regulation instruction value as the final frequency regulation instruction value of the grid-forming photovoltaic equivalent unit, so as to realize the hybrid photovoltaic power station to stably support the system frequency under a low short-circuit ratio.

[0043] In a third aspect, the present invention provides a terminal, including a processor and a storage medium;

[0044] The storage medium is used to store instructions;

[0045] The processor is used to operate according to the instructions to execute the steps of any one of the methods described in the first aspect of the present invention.

[0046] In a fourth aspect, 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 one of the methods described in the first aspect of the present invention.

[0047] The beneficial effect of the present invention is that, compared with the prior art,

[0048] 1. The present invention combines the site-level control and the unit-level control, and from the perspective of the possibility of instability in the frequency modulation of the grid-following photovoltaic unit under the condition of low short-circuit ratio, proposes a coordinated frequency modulation strategy for the grid-following / grid-building photovoltaic units taking into account the short-circuit ratio; when a power disturbance occurs in the photovoltaic power station, the photovoltaic power station site frequency modulation controller transmits the frequency modulation power instruction limit to each grid-following photovoltaic unit; in order to ensure the frequency modulation capability of the site, a grid-building photovoltaic frequency modulation parameter that compensates for the grid-following photovoltaic frequency modulation limit is proposed, and the frequency modulation power shortage of the grid-following photovoltaic unit is compensated by adjusting the frequency modulation parameters of the grid-building photovoltaic unit; the problem of frequency modulation instruction allocation of the hybrid photovoltaic power station with the grid and the grid under the condition of low short-circuit ratio is effectively solved; the present invention can improve the low short-circuit ratio adaptability of the hybrid photovoltaic power station with the grid without losing the frequency modulation power of the photovoltaic power station, thereby ensuring the frequency safety and stability of the power system.

[0049] 2. The present invention uses equivalent line parameters to construct a short-circuit ratio calculation model that takes into account both accuracy and calculation speed, thereby reducing the computational burden of the station controller and improving the efficiency of the frequency modulation response.

[0050] 3. The present invention makes full use of the complementary characteristics of grid-following and grid-building wind turbines in control performance, and the proposed photovoltaic power station grid-following / grid-building coordinated frequency regulation control strategy has strong versatility and can be applied to the frequency regulation control of hybrid grid-following / grid-building photovoltaic power stations under low short-circuit ratio. It enables the site to ensure the steady-state output of the grid-following photovoltaic units during the frequency regulation period on the premise of meeting the system frequency regulation requirements, thereby further improving the frequency regulation capability of the hybrid grid-following / grid-building photovoltaic power stations. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a flow chart of a frequency modulation control method of a hybrid photovoltaic power station with / with a grid in an embodiment of the present invention;

[0052] Figure 2 Schematic diagram of a change curve of a frequency modulation instruction of a grid-connected photovoltaic unit during a disturbance in an embodiment of the present invention;

[0053] Figure 3 It is a schematic diagram of a change curve of the frequency modulation instruction of the grid-type photovoltaic unit during a disturbance in an embodiment of the present invention;

[0054] Figure 4 It is a schematic diagram of the frequency modulation response of a grid-following / grid-building type photovoltaic equivalent unit under a non-grid-following compensation strategy in an embodiment of the present invention;

[0055] Figure 5 It is a schematic diagram of frequency modulation response of a grid-following / grid-building type photovoltaic equivalent unit under a grid-following compensation strategy in an embodiment of the present invention;

[0056] Figure 61 is a structural principle block diagram of a frequency modulation control device for a hybrid photovoltaic power station with / with a grid in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in the present invention are only part of the embodiments of the present invention, not all of the embodiments. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0058] Embodiment 1:

[0059] Reference Figure 1 The embodiment of the present invention provides a frequency modulation control method for a hybrid photovoltaic power station with a grid connection, which specifically includes the following steps:

[0060] Step S1, respectively establishing a grid-following photovoltaic equivalent unit and a grid-building photovoltaic equivalent unit in a photovoltaic power station;

[0061] Specifically, the basic parameters of the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit directly adopt the basic parameters of the corresponding model photovoltaic unit, including: photovoltaic unit / converter model parameters, frequency modulation controller control parameters during frequency disturbance, voltage ride-through control parameters and voltage recovery control parameters. In this embodiment, the operating parameters of the established grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit are as follows:

[0062]

[0063] Where P ieq , Q ieq , P GFL_eq and S GFL_eq They are the steady-state active power, steady-state reactive power, rated active power and rated capacity of the grid-following photovoltaic equivalent unit respectively; P i , Q i , P i GFL and S i GFL are the active power, reactive power, rated active power and rated capacity of the i-th grid-connected photovoltaic unit in the photovoltaic power station; n is the total number of grid-connected photovoltaic units in the photovoltaic power station; P jeq , Q jeq , P GFM_eq and S GFM_eq are the steady-state active power, steady-state reactive power, rated active power and rated capacity of the grid-connected photovoltaic equivalent unit; P j , Q j , Pj GFM and S j GFM are the active power, reactive power, rated active power and rated capacity of the jth grid-connected photovoltaic unit in the photovoltaic power station; m is the total number of grid-connected photovoltaic units in the photovoltaic power station.

[0064] In this embodiment, for the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit, when the corresponding box transformers are equivalent to two equivalent box transformers, their equivalent box transformer parameters are respectively:

[0065]

[0066] Where RT1 GFL RT1 GFM They are respectively the positive sequence resistance of the unit supporting box transformer in the grid-type photovoltaic cluster, RT1 GFL_eq RT1 GFM_eq Corresponding to the positive sequence resistance of the grid-type and grid-type photovoltaic equivalent unit box transformers; XT1 GFL , XT1 GFM They are respectively the positive sequence inductance of the unit supporting box transformer in the grid-connected photovoltaic cluster, XT1 GFL_eq , XT1 GFM_eq They correspond to the positive sequence inductance of the grid-type and grid-connected photovoltaic equivalent unit box transformers; GM GFL GM GFM They are the excitation conductance of the unit supporting box-type transformer in the grid-type photovoltaic cluster, GM GFL_eq GM GFM_eq Corresponding to the excitation conductance of the grid-type photovoltaic equivalent unit box transformer; BM GFL BM GFM They are the excitation susceptance of the unit supporting box-type transformer in the grid-type photovoltaic cluster, BM GFL_eq BM GFM_eq They correspond to the excitation susceptance of the grid-type and grid-connected photovoltaic equivalent unit box transformers respectively.

[0067] In this embodiment, for the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit, when the corresponding collector line networks are respectively equivalent to two sections of equivalent collector lines, the equivalent collector line parameters are respectively:

[0068]

[0069] In the formula, S i , S j are the apparent power of the i-th and j-th photovoltaic units in the grid-connected photovoltaic cluster, S ieq , S jeq Corresponding to the apparent power of the grid-type photovoltaic equivalent unit; I i ,Ij are the current values ​​of the i-th and j-th photovoltaic units in the grid-type and grid-connected photovoltaic clusters, respectively. ieq ,I jeq They correspond to the current of the photovoltaic equivalent unit of the grid type and the grid type; U ieq , U jeq are the voltages of the photovoltaic equivalent units of the follower and grid-type photovoltaics, respectively; U pcc is the voltage value of the low voltage side of the main transformer of the photovoltaic power station; Z ieq , Z jeq are the equivalent collector line impedances of the grid-type and grid-type photovoltaic equivalent units, respectively; (·) * Represents conjugation.

[0070] Furthermore, the equivalent collection line parameters of the grid-type photovoltaic equivalent units are:

[0071]

[0072] Where R1 GFL_eq 、R1 GFM_eq are the positive sequence resistance of the equivalent collector line impedance of the grid-type photovoltaic equivalent unit, X1 GFL_eq 、X1 GFM_eq They are respectively the positive-sequence inductive reactance of the equivalent collector line impedance of the grid-type photovoltaic equivalent unit, Re is the complex real part, and Im is the complex imaginary part.

[0073] Step S2, calculating the frequency modulation power limit value of the grid-connected photovoltaic equivalent unit based on the short-circuit ratio;

[0074] As a preferred but non-limiting embodiment of the present invention, in step S2 of the present invention, a short-circuit ratio calculation model of a grid-type photovoltaic equivalent unit is constructed based on the equivalent collection line parameters and power of the grid-type photovoltaic equivalent unit, and its expression is as follows:

[0075]

[0076] Where gSCR is the short-circuit ratio of the grid-connected photovoltaic equivalent unit; P eq and Q eq They are respectively the active power and reactive power of the grid-following equivalent photovoltaic unit; R1 GFL_eq and X1 GFL_eq They are respectively the positive-sequence resistance and positive-sequence inductance of the equivalent collector line impedance of the grid-following equivalent photovoltaic unit.

[0077] It should be noted that the calculation of the short-circuit ratio has a variety of calculation expressions according to different requirements. Compared with the traditional calculation method, the short-circuit ratio calculation model constructed by using equivalent line parameters in the present invention can not only improve the calculation accuracy, but also increase the calculation speed to reduce the computational burden of the station controller and further improve the frequency modulation response efficiency.

[0078] When constructing a station, it can be calculated that the lower limit of the stable operation short-circuit ratio of its grid-connected photovoltaic equivalent unit is gSCR. min , gSCR min Substitute into equation (5) to find the maximum output power P that the grid-following photovoltaic equivalent unit can accept without frequency instability. GFL_max , thereby obtaining the frequency modulation power limit value ΔP of the grid-following photovoltaic equivalent unit limit for:

[0079] ΔP limit =P GFL_max -P ieq (6)

[0080] Where P ieq It is the steady-state active output of the grid-following photovoltaic equivalent unit.

[0081] Step S3: when a power disturbance occurs in the system, the frequency modulation power demand of the photovoltaic power station as a whole is allocated with the first grid-following type frequency modulation command value and the first grid-forming type frequency modulation command value according to the steady-state operating power proportions of the grid-following type and grid-forming type photovoltaic equivalent units respectively;

[0082] Specifically, when a power disturbance occurs in the system, the station frequency regulation controller adjusts the power supply voltage according to the steady-state operating point P of the grid-connected photovoltaic equivalent unit. ieq and P jeq Allocate frequency modulation command ΔP GFL_ideal and ΔP GFM_ideal The expressions are:

[0083]

[0084] In the formula, ΔP GFL_ideal Indicates the first grid-type frequency regulation command value assigned to the grid-type photovoltaic equivalent unit, ΔP GFM_ideal represents the first grid-type frequency modulation instruction value assigned to the grid-type photovoltaic equivalent unit, P ieq and P jeq are the steady-state active power of the grid-following and grid-building photovoltaic equivalent units respectively; ΔP total It is the overall frequency modulation power demand of the photovoltaic power station.

[0085] Step S4, determining whether the first network type frequency modulation instruction value is greater than the frequency modulation power limit value;

[0086] If not, the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit participate in the system frequency modulation according to the first grid-following frequency modulation instruction value and the first grid-building frequency modulation instruction value respectively;

[0087] If so, the grid-following photovoltaic equivalent unit participates in the system frequency regulation according to the frequency regulation power limit value, and the difference between the first grid-following frequency regulation instruction value and the frequency regulation power limit value is added to the first grid-forming frequency regulation instruction value as the final frequency regulation instruction value of the grid-forming photovoltaic equivalent unit, so as to realize the hybrid photovoltaic power station to stably support the system frequency under a low short-circuit ratio.

[0088] Specifically, when ΔP GFL_ideal ≤ΔP limit When ΔP GFL_ideal >ΔP limit When the frequency regulation command of the grid-following photovoltaic unit issued by the station frequency regulation controller is ΔP limit In order to limit the frequency regulation of the grid-following photovoltaic unit to prevent instability, the missing frequency regulation power is compensated by the grid-building photovoltaic unit; therefore, the frequency regulation command value expression of the grid-building photovoltaic unit is:

[0089]

[0090] Furthermore, in step S4, after obtaining the final frequency modulation command value of the grid-type photovoltaic equivalent unit, it also includes: calculating the inertia coefficient J of the grid-type photovoltaic unit participating in the system frequency modulation under the final frequency modulation command value ref and droop coefficient D ref , and the calculation formulas are as follows:

[0091]

[0092] In the formula, ΔP GFM_ideal is the first network-type frequency modulation instruction value, ΔP GFM_ref The final frequency modulation command value of the grid-type photovoltaic equivalent unit; J and D are respectively the frequency modulation command value ΔP of the first grid-type GFM_ideal The inertia coefficient and droop coefficient under.

[0093] It should be noted that, based on the frequency modulation mechanism of the grid-type photovoltaic unit, the frequency modulation response expression of the grid-type photovoltaic equivalent unit is:

[0094]

[0095] Where P jeq is the steady-state active output of the grid-type photovoltaic equivalent unit, J and D are the inertia coefficient and droop coefficient of the grid-type photovoltaic unit before compensating the difference in frequency regulation with the grid-type photovoltaic, R1 GFM_eq 、X1 GFM_eq is the equivalent collection line parameter of the grid-type photovoltaic equivalent unit, U pcc is the positive sequence voltage at the grid connection point, It is the electrical angle between the grid-connected photovoltaic equivalent unit and the grid connection point.

[0096] Combine the following Figure 2 and Figure 3 The allocation process of the above instructions in this embodiment is further described:

[0097] When a power disturbance occurs in a photovoltaic power station, the frequency modulation command of the grid-type photovoltaic unit after adjustment by the station frequency modulation controller changes during the disturbance period as shown in the following figure. Figure 2 As shown; Figure 2 In the limit is the frequency modulation command value limit of the grid-following photovoltaic unit, which is determined by the grid structure and the adaptability of the unit short-circuit ratio; since the steady-state output varies in different time periods, when the steady-state output is strong or weak, the command value limit may be in the inertia control response range or the droop control response range. The corresponding typical frequency modulation response curves of the grid-following photovoltaic equivalent unit are as follows: Figure 2 (a) ΔP GFL_ideal_1 and ΔP GFL_ideal_2 After being restricted by the frequency modulation control method of the present invention, the frequency modulation command change curves of the grid-following photovoltaic unit during the disturbance period when the steady-state output is strong and weak are respectively as shown in Figure 2 (b) ΔP GFL_ref_1 and ΔP GFL_ref_2 shown.

[0098] When a power disturbance occurs in a photovoltaic power station, the frequency modulation command of the grid-type photovoltaic unit changes during the disturbance after being adjusted by the station frequency modulation controller. Figure 3 shown. Figure 3 In the limit To limit the frequency modulation command value of the grid-following photovoltaic unit, when the steady-state output of the photovoltaic unit is strong or weak, the typical frequency modulation response curves of the corresponding grid-following photovoltaic equivalent unit are as follows: Figure 3 (a) ΔP GFM_ideal_1 and ΔP GFM_ideal_2 After compensation by the frequency modulation control method provided by the present invention, the frequency modulation instruction ΔP of the grid-following photovoltaic unit GFL_ref_1 , ΔP GFL_ref_2 The corresponding change curves of the frequency regulation command value of the grid-type photovoltaic unit during the disturbance period after compensating the grid-type frequency regulation deficit are as follows: Figure 3 (b) ΔP GFM_ref_1 , ΔP GFM_ref_2 shown.

[0099] In order to verify the effectiveness of the frequency modulation control method of the grid-connected / grid-connected hybrid photovoltaic power station provided by the present invention, a test was carried out in a photovoltaic / thermal power bundle simulation system. Figure 4 The frequency modulation response of the grid-type photovoltaic equivalent unit when the control method of the present invention is not adopted. It can be seen that the grid-type photovoltaic equivalent unit is prone to power oscillation when participating in system frequency modulation under low short-circuit ratio; Figure 5 By adopting the control method described in the present invention, the frequency regulation response of the following and grid-connected photovoltaic equivalent units can be seen that the grid-connected photovoltaic units can stably participate in the frequency regulation after restriction, and the frequency regulation response of the grid-connected photovoltaic units compensates for the frequency regulation shortage so that the station can still meet the system frequency regulation requirements.

[0100] The beneficial effects of the present invention are as follows:

[0101] 1. The present invention combines the site-level control and the unit-level control, and from the perspective of the possibility of instability in the frequency modulation of the grid-following photovoltaic unit under the condition of low short-circuit ratio, proposes a coordinated frequency modulation strategy for the grid-following / grid-building photovoltaic units taking into account the short-circuit ratio; when a power disturbance occurs in the photovoltaic power station, the photovoltaic power station site frequency modulation controller transmits the frequency modulation power instruction limit to each grid-following photovoltaic unit; in order to ensure the frequency modulation capability of the site, a grid-building photovoltaic frequency modulation parameter that compensates for the grid-following photovoltaic frequency modulation limit is proposed, and the frequency modulation power shortage of the grid-following photovoltaic unit is compensated by adjusting the frequency modulation parameters of the grid-building photovoltaic unit; the problem of frequency modulation instruction allocation of the hybrid photovoltaic power station with the grid and the grid under the condition of low short-circuit ratio is effectively solved; the present invention can improve the low short-circuit ratio adaptability of the hybrid photovoltaic power station with the grid without losing the frequency modulation power of the photovoltaic power station, thereby ensuring the frequency safety and stability of the power system.

[0102] 2. The present invention uses equivalent line parameters to construct a short-circuit ratio calculation model that takes into account both accuracy and calculation speed, thereby reducing the computational burden of the station controller and improving the efficiency of the frequency modulation response.

[0103] 3. The present invention makes full use of the complementary characteristics of grid-following and grid-building wind turbines in control performance, and the proposed photovoltaic power station grid-following / grid-building coordinated frequency regulation control strategy has strong versatility and can be applied to the frequency regulation control of hybrid grid-following / grid-building photovoltaic power stations under low short-circuit ratio. It enables the site to ensure the steady-state output of the grid-following photovoltaic units during the frequency regulation period on the premise of meeting the system frequency regulation requirements, thereby further improving the frequency regulation capability of the hybrid grid-following / grid-building photovoltaic power stations.

[0104] Embodiment 2:

[0105] like Figure 6 As shown, the present invention provides a frequency modulation control device for a hybrid photovoltaic power station with a grid connection, and the device is used to implement the steps of the method in the above embodiment 1, and the device specifically includes:

[0106] The equivalent module is used to respectively establish the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit in the photovoltaic power station;

[0107] A calculation module, used to calculate the frequency modulation power limit value of the grid-connected photovoltaic equivalent unit based on the short-circuit ratio;

[0108] An allocation module is used to allocate the corresponding first grid-following type frequency modulation instruction value and the first grid-forming type frequency modulation instruction value to the overall frequency modulation power demand of the photovoltaic power station according to the steady-state operating power proportion of the grid-following type and grid-forming type photovoltaic equivalent units when a power disturbance occurs in the system;

[0109] A frequency modulation module, used to determine whether the first network-type frequency modulation instruction value is greater than the frequency modulation power limit value;

[0110] If not, the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit participate in the system frequency modulation according to the first grid-following frequency modulation instruction value and the first grid-building frequency modulation instruction value respectively;

[0111] If so, the grid-following photovoltaic equivalent unit participates in the system frequency regulation according to the frequency regulation power limit value, and the difference between the first grid-following frequency regulation instruction value and the frequency regulation power limit value is added to the first grid-forming frequency regulation instruction value as the final frequency regulation instruction value of the grid-forming photovoltaic equivalent unit, so as to realize the hybrid photovoltaic power station to stably support the system frequency under a low short-circuit ratio.

[0112] The frequency modulation control device of the hybrid photovoltaic power station with / grid-connected provided in the embodiment of the present invention and the frequency modulation control method of the hybrid photovoltaic power station with / grid-connected provided in Example 1 are based on the same technical concept, and can produce the beneficial effects as described in Example 1. For the contents not described in detail in this embodiment, please refer to Example 1.

[0113] Embodiment three:

[0114] A terminal provided by an embodiment of the present invention includes a processor and a storage medium;

[0115] The storage medium is used to store instructions;

[0116] The processor is used to operate according to the instruction to execute the steps of the method according to any one of the first embodiments.

[0117] Embodiment 4:

[0118] An embodiment of the present invention provides a computer-readable storage medium, on which a computer program is stored. When the program is executed by a processor, the steps of any method described in Embodiment 1 are implemented.

[0119] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0120] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples of computer-readable storage media (a non-exhaustive list) include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the foregoing. As used herein, a computer-readable storage medium is not to be interpreted as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0121] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0122] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be customized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A frequency modulation control method for a grid-connected / grid-connected hybrid photovoltaic power station, characterized in that: The method comprises the following steps: S1. Establishing grid-following photovoltaic equivalent units and grid-building photovoltaic equivalent units in photovoltaic power stations respectively; S2. Calculate the frequency modulation power limit value of the grid-connected photovoltaic equivalent unit based on the short-circuit ratio; S3. When a power disturbance occurs in the system, the frequency modulation power demand of the photovoltaic power station as a whole is allocated with the corresponding first grid-following type frequency modulation command value and the first grid-forming type frequency modulation command value according to the steady-state operating power proportions of the grid-following type and grid-forming type photovoltaic equivalent units respectively; S4, determining whether the first network type frequency modulation instruction value is greater than the frequency modulation power limit value; If not, the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit participate in the system frequency modulation according to the first grid-following frequency modulation instruction value and the first grid-building frequency modulation instruction value respectively; If so, the grid-following photovoltaic equivalent unit participates in the system frequency regulation according to the frequency regulation power limit value, and the difference between the first grid-following frequency regulation instruction value and the frequency regulation power limit value is added to the first grid-forming frequency regulation instruction value as the final frequency regulation instruction value of the grid-forming photovoltaic equivalent unit, so as to realize the hybrid photovoltaic power station to stably support the system frequency under a low short-circuit ratio.

2. The frequency modulation control method of the grid-connected / grid-connected hybrid photovoltaic power station according to claim 1 is characterized in that: In step S1, the operating parameters of the established grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit are as follows: Where P ieq , Q ieq , P GFL_eq and S GFL_eq They are the steady-state active power, steady-state reactive power, rated active power and rated capacity of the grid-following photovoltaic equivalent unit respectively; P i , Q i , P i GFL and S i GFL are the active power, reactive power, rated active power and rated capacity of the i-th grid-connected photovoltaic unit in the photovoltaic power station; n is the total number of grid-connected photovoltaic units in the photovoltaic power station; P jeq , Q jeq , P GFM_eq and S GFM_eq are the steady-state active power, steady-state reactive power, rated active power and rated capacity of the grid-connected photovoltaic equivalent unit; P j , Q j , P j GFM and S j GFM are the active power, reactive power, rated active power and rated capacity of the jth grid-connected photovoltaic unit in the photovoltaic power station; m is the total number of grid-connected photovoltaic units in the photovoltaic power station.

3. The frequency modulation control method of the grid-connected / grid-connected hybrid photovoltaic power station according to claim 1, characterized in that: In step S1, the established equivalent collection line parameters of the grid-following photovoltaic equivalent unit include: In the formula, Z ieq is the equivalent collector line impedance of the grid-following photovoltaic equivalent unit; U ieq and I ieq are the voltage and current of the grid-following equivalent photovoltaic unit; U pcc R1 is the voltage value of the low voltage side of the main transformer of the photovoltaic power station; GFL_eq and X1 GFL_eq They are respectively the positive-sequence resistance and positive-sequence inductance of the equivalent collector line impedance of the grid-following equivalent photovoltaic unit. Re represents the real part of the complex number, and Im represents the imaginary part of the complex number.

4. The frequency modulation control method of the grid-connected / grid-connected hybrid photovoltaic power station according to claim 1 or 3, characterized in that: In step S2, the step of calculating the frequency modulation power limit value of the grid-connected photovoltaic equivalent unit based on the short-circuit ratio includes: Based on the equivalent collection line parameters and power of the grid-connected photovoltaic equivalent unit, a short-circuit ratio calculation model of the grid-connected photovoltaic equivalent unit is constructed, and its expression is as follows: Where gSCR is the short-circuit ratio of the grid-connected photovoltaic equivalent unit; P eq and Q eq They are respectively the active power and reactive power of the grid-following equivalent photovoltaic unit; R1 GFL_eq and X1 GFL_eq They are respectively the positive sequence resistance and positive sequence inductance of the equivalent collector line impedance of the grid-following equivalent photovoltaic unit; The lower limit of the steady-state short-circuit ratio gSCR of the grid-connected photovoltaic equivalent unit min Substitute it into the short-circuit ratio calculation model to find the maximum output power P that can be accepted without frequency modulation instability. GFLmax , thereby obtaining the frequency modulation power limit value ΔP of the grid-following photovoltaic equivalent unit limit =ΔP limit =P GFL_max -P ieq .

5. The frequency modulation control method of the grid-connected / grid-connected hybrid photovoltaic power station according to claim 1, characterized in that: In step S3, the expressions of the first network-type frequency modulation instruction value and the first network-type frequency modulation instruction value are respectively as follows: In the formula, ΔP GFL_ideal Indicates the first grid-type frequency regulation command value assigned to the grid-type photovoltaic equivalent unit, ΔP GFM_ideal represents the first grid-type frequency modulation instruction value assigned to the grid-type photovoltaic equivalent unit, P ieq and P jeq are the steady-state active power of the grid-following and grid-building photovoltaic equivalent units respectively; ΔP total It is the overall frequency modulation power demand of the photovoltaic power station.

6. The frequency modulation control method of the grid-connected / grid-connected hybrid photovoltaic power station according to claim 5, characterized in that: In step S4, if the first grid-type frequency modulation command value is greater than the frequency modulation power limit value, the frequency modulation command value ΔP of the grid-type photovoltaic equivalent unit is GFL_ref The frequency modulation command value ΔP of the grid-type photovoltaic equivalent GFM_ref The expressions are: In the formula, ΔP GFL_ideal is the first grid-type frequency modulation command value, ΔP GFM_ideal is the first network-type frequency modulation instruction value, ΔP limit is the frequency modulation power limit value, ΔP total It is the overall frequency modulation power demand of the photovoltaic power station.

7. The frequency modulation control method of the grid-connected / grid-connected hybrid photovoltaic power station according to claim 6, characterized in that: In step S4, after obtaining the final frequency modulation command value of the grid-type photovoltaic equivalent unit, it also includes: calculating the inertia coefficient J of the grid-type photovoltaic unit participating in the system frequency modulation under the final frequency modulation command value ref and droop coefficient D ref , and the calculation formulas are as follows: In the formula, ΔP GFM_ideal is the first network-type frequency modulation instruction value, ΔP GFM_ref The final frequency modulation command value of the grid-type photovoltaic equivalent unit; J and D are respectively the frequency modulation command value ΔP of the first grid-type GFM_ideal The moment of inertia and droop coefficient under.

8. A frequency modulation control device for a hybrid photovoltaic power station with or without a grid, which runs the frequency modulation control method for a hybrid photovoltaic power station with or without a grid as claimed in any one of claims 1 to 7, characterized in that: The device includes: The equivalent module is used to respectively establish the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit in the photovoltaic power station; A calculation module, used to calculate the frequency modulation power limit value of the grid-connected photovoltaic equivalent unit based on the short-circuit ratio; An allocation module is used to allocate the corresponding first grid-following type frequency modulation instruction value and the first grid-forming type frequency modulation instruction value to the overall frequency modulation power demand of the photovoltaic power station according to the steady-state operating power proportion of the grid-following type and grid-forming type photovoltaic equivalent units when a power disturbance occurs in the system; A frequency modulation module, used to determine whether the first network-type frequency modulation instruction value is greater than the frequency modulation power limit value; If not, the grid-following photovoltaic equivalent unit and the grid-building photovoltaic equivalent unit participate in the system frequency modulation according to the first grid-following frequency modulation instruction value and the first grid-building frequency modulation instruction value respectively; If so, the grid-following photovoltaic equivalent unit participates in the system frequency regulation according to the frequency regulation power limit value, and the difference between the first grid-following frequency regulation instruction value and the frequency regulation power limit value is added to the first grid-forming frequency regulation instruction value as the final frequency regulation instruction value of the grid-forming photovoltaic equivalent unit, so as to realize the hybrid photovoltaic power station to stably support the system frequency under a low short-circuit ratio.

9. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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