Photovoltaic additional control method, device, terminal and medium for suppressing ultra-low frequency oscillation

Abstract

The present invention discloses a photovoltaic additional control method, device, terminal and medium for suppressing ultra-low frequency oscillation, including obtaining a photovoltaic characteristic curve, determining the limit parameters and steady-state DC voltage of a photovoltaic additional controller; calculating the slope at the steady-state operating point according to the photovoltaic characteristic curve, and calculating the gain parameters of the photovoltaic additional controller; using the change amount of the system frequency as the input of the photovoltaic additional controller, and the output of the photovoltaic additional controller as the reference value of the photovoltaic DC voltage controller; obtaining the dq-axis reference values of the voltage through the photovoltaic DC voltage controller and the photovoltaic DC current controller, and obtaining a control signal for controlling the photovoltaic output power; the present invention obtains the control parameters of the photovoltaic additional controller through photovoltaic array parameters, the negative damping torque of the hydropower unit, the change amount of the system frequency, etc., and adjusts the DC voltage of the photovoltaic array through the photovoltaic additional controller, thereby changing the output power of the photovoltaic, and further realizing the suppression control of ultra-low frequency oscillation.

Description

Technical Field

[0001] The present invention relates to the technical field of multi - energy complementary control, and particularly relates to a photovoltaic additional control method, device, terminal and medium for suppressing ultra - low - frequency oscillation. Background Technique

[0002] The multi - energy complementary system can utilize the combined advantages of different resources to improve the stability of power output. The water - light complementary system is a common form in the multi - energy complementary system. On the one hand, it solves the problem of long - distance access of photovoltaic power stations to the system. On the other hand, through the fast regulation ability of hydropower stations, the output of photovoltaic power stations can be smoothed, which can effectively reduce the impact of the output of photovoltaic power stations changing with weather conditions on the system.

[0003] In recent years, some ultra - low - frequency oscillation events with oscillation frequencies lower than 0.1 Hz have occurred in China's power grid. The main reasons are the "water hammer effect" of hydropower units and unreasonable parameter settings of governors. Under special off - grid or asynchronous grid - connected conditions, systems dominated by hydropower units are extremely prone to ultra - low - frequency oscillation accidents, which endanger the safe and stable operation of the power grid.

[0004] Since ultra - low - frequency oscillation is strongly correlated with the primary frequency regulation process of hydropower units, the existing ultra - low - frequency oscillation suppression control methods mainly optimize the governor parameters, sacrificing the primary frequency regulation ability to enhance the damping in the ultra - low - frequency band. While focusing on improving damping to suppress ultra - low - frequency oscillation, the primary frequency regulation ability of the units is often ignored, putting the system into new stability risks. Photovoltaics in the water - light complementary system also have active regulation ability. Using photovoltaics to suppress oscillation can avoid severely weakening the frequency regulation ability of the system. However, there is a lack of means to use photovoltaics to suppress oscillation in the existing ultra - low - frequency oscillation suppression research.

[0005] Therefore, there is an urgent need for a control method that utilizes the regulation ability of photovoltaics to achieve ultra - low - frequency oscillation suppression. Summary of the Invention

[0006] The technical problem to be solved by the present invention is the existence of ultra - low - frequency oscillation in the water - light complementary system. The purpose is to provide a photovoltaic additional control method, device, terminal and medium for suppressing ultra - low - frequency oscillation, which solves the problem of suppressing ultra - low - frequency oscillation through photovoltaics.

[0007] The present invention is realized through the following technical solutions:

[0008] A photovoltaic additional control method for suppressing ultra - low - frequency oscillation includes:

[0009] Obtain the photovoltaic characteristic curve, and determine the limit parameter and steady - state DC voltage of the photovoltaic additional controller;

[0010] Calculate the slope at the steady - state operating point according to the photovoltaic characteristic curve, and calculate the gain parameter of the photovoltaic additional controller;

[0011] The change amount of the system frequency is used as the input of the photovoltaic additional controller, and the output of the photovoltaic additional controller is the reference value of the photovoltaic DC voltage controller;

[0012] The reference value output by the photovoltaic additional controller passes through the photovoltaic DC voltage controller and the current controller to obtain the dq-axis reference values of the voltage, and a control signal for controlling the photovoltaic output power is obtained.

[0013] Optionally, the method for obtaining the photovoltaic characteristic curve includes:

[0014] Determine the parameters of the photovoltaic array, and determine the calculation formula of the photovoltaic characteristic curve as: Where, P PV is the output power of the photovoltaic array, U DC is the DC voltage of the photovoltaic array, m is the number of parallel-connected photovoltaic cells, n is the number of series-connected photovoltaic arrays, C1 and C2 are both the factory parameters of the photovoltaic cells, and U oc is the open-circuit voltage of the photovoltaic cell.

[0015] Optionally, the method for obtaining the limiting parameter and the steady-state DC voltage includes:

[0016] Taking the highest point of the photovoltaic characteristic curve as the maximum power point of the photovoltaic array, the DC voltage corresponding to the maximum power point is the lower limit value of the output of the photovoltaic additional controller, and the zero-crossing point on the right side of the curve is the upper limit value of the output of the photovoltaic additional controller;

[0017] Reserve 1-x of the photovoltaic output, and set the DC voltage corresponding to the x power point as the steady-state DC voltage of the photovoltaic array, where 0 < x < 1.

[0018] As an embodiment, x = 90%.

[0019] Optionally, the calculation formula for the slope at the steady-state operating point is: Where, K PU is the slope at the steady-state operating point of the photovoltaic array, and I SC is the short-circuit current of the photovoltaic cell;

[0020] The calculation formula for the gain parameter of the photovoltaic additional controller according to the slope at the steady-state operating point and the negative damping torque of the hydro-generator set is: Where K c is the gain parameter of the photovoltaic additional controller, and D m is the damping torque generated by the mechanical power of the hydro-generator set.

[0021] Optionally, the calculation formula for the reference value of the photovoltaic DC voltage controller is:

[0022] Among them, U * DC is the output of the PV additional controller, and U * DC0 is the steady-state DC voltage of the PV array, Δω is the change in system frequency, and U * DCmin is the lower limit value of the output of the PV additional controller, and U * DCmax is the upper limit value of the output of the PV additional controller.

[0023] Optionally, the method for obtaining the control signal is as follows: The output U of the PV additional controller * DC obtains the dq-axis reference values after passing through the PV DC voltage controller and the current controller. Among them, the mathematical expressions of the DC voltage controller and the current controller are: Among them, i * d is the d-axis current reference value output by the DC voltage controller, and K pv and K iv are respectively the proportional coefficient and the integral coefficient of the DC voltage controller, and U dc is the measured value of the PV DC voltage, v d and v q are respectively the voltage d-axis and q-axis reference values output by the current controller, and K pi and K ii are respectively the proportional coefficient and the integral coefficient of the current controller, i d and i q are respectively the d-axis and q-axis components of the inverter output current, e d and e q are respectively the d-axis and q-axis components of the inverter output voltage, ω is the rated value of the system angular frequency, and L is the value of the filter inductor;

[0024] The control signal is obtained by performing Park transformation and PWM modulation on the voltage dq-axis reference values, and the output power of the PV is controlled through the control signal. A PV additional control device for suppressing ultra-low frequency oscillations includes:

[0025] The first calculation module is used to obtain the PV characteristic curve according to the PV array parameters;

[0026] The second calculation module is used to determine the limiting parameters and the steady-state DC voltage of the PV additional controller;

[0027] The third calculation module is used to calculate the slope at the steady-state operating point according to the PV characteristic curve;

[0028] The fourth calculation module is used to calculate the gain parameters of the PV additional controller;

[0029] A fifth calculation module, which is used to take the change amount of the system frequency as the input of the photovoltaic additional controller, and the output of the photovoltaic additional controller is the reference value of the photovoltaic DC voltage controller;

[0030] A sixth calculation module, which is used to obtain the dq-axis reference values of the voltage after the reference value output by the photovoltaic additional controller passes through the photovoltaic DC voltage controller and the current controller, and obtain the control signal for controlling the photovoltaic output power. A photovoltaic additional control terminal for suppressing ultra-low frequency oscillation includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of a photovoltaic additional control method for suppressing ultra-low frequency oscillation as described above are implemented.

[0031] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of a photovoltaic additional control method for suppressing ultra-low frequency oscillation as described above are implemented.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0033] By adding a photovoltaic additional controller in the photovoltaic system, and obtaining the control parameters of the photovoltaic additional controller through photovoltaic array parameters, the negative damping torque of the hydropower unit, the change amount of the system frequency, etc., the photovoltaic additional controller adjusts the DC voltage of the photovoltaic array, thereby changing the output power of the photovoltaic, and further realizing the suppression control of ultra-low frequency oscillation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings illustrate exemplary embodiments of the present invention and are used in conjunction with the description to explain the principles of the present invention. These drawings are included to provide a further understanding of the present invention, and the drawings are included in this specification and form a part of this specification, and do not constitute a limitation to the embodiments of the present invention.

[0035] Figure 1 is a flowchart of the photovoltaic additional control method for suppressing ultra-low frequency oscillation according to the present invention.

[0036] Figure 2 is a control block diagram of the photovoltaic additional control method for suppressing ultra-low frequency oscillation according to the present invention.

[0037] Figure 3 is a topology diagram of a water-light complementary system provided in the second embodiment according to the present invention;

[0038] Figure 4 is a characteristic curve diagram of a photovoltaic array provided in the second embodiment according to the present invention;

[0039] Figure 5It is the system frequency variation diagram provided by Embodiment 2 of the present invention.

[0040] Figure 6 It is the active power variation diagram of the photovoltaic output provided by Embodiment 2 of the present invention. Detailed implementation manners

[0041] The following details the implementation manners of the present invention. The examples of the implementation manners are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. The implementation manners described below by referring to the drawings are exemplary and are only used to explain the present invention, and cannot be construed as a limitation to the present invention.

[0042] Those skilled in the art of the present technology can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of those of ordinary skill in the art in the field to which the present invention belongs. It should also be understood that terms such as those defined in a general dictionary should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless defined as here.

[0043] For the convenience of understanding the embodiments of the present invention, the following will further explain and illustrate with several specific embodiments in conjunction with the drawings, and each embodiment does not constitute a limitation to the embodiments of the present invention.

[0044] Embodiment 1

[0045] A photovoltaic additional control method for suppressing ultra-low frequency oscillations in the present invention aims to add a photovoltaic additional controller in the photovoltaic and calculate control parameters. The controller adjusts the DC voltage of the photovoltaic array according to the change amount of the frequency, thereby changing the output power of the photovoltaic, and further realizing the suppression control of ultra-low frequency oscillations. As Figure 1 and Figure 2 shown, the photovoltaic additional control method in this embodiment specifically includes:

[0046] S1. Determine the parameters of the photovoltaic array, obtain the photovoltaic characteristic curve, and determine the limit parameters and steady-state DC voltage of the photovoltaic additional controller;

[0047] The calculation formula for determining the photovoltaic characteristic curve is: wherein, the parameters of the photovoltaic array include but are not limited to: P PV is the output power of the photovoltaic array, U DC is the DC voltage of the photovoltaic array, m is the number of parallel-connected photovoltaic cells, n is the number of series-connected photovoltaic arrays, C1 and C2 are both the factory parameters of the photovoltaic cells, and U oc is the open-circuit voltage of the photovoltaic cell.

[0048] The limiting parameters of the photovoltaic additional controller are as follows: taking the highest point of the photovoltaic characteristic curve as the maximum power point of the photovoltaic array, the DC voltage corresponding to the maximum power point is the lower limit value of the output of the photovoltaic additional controller, and the zero crossing point on the right side of the curve is the upper limit value of the output of the photovoltaic additional controller;

[0049] The method for obtaining the steady-state DC voltage is that, in order to suppress ultra-low frequency oscillations, it is necessary to reserve 1 - x of the photovoltaic output (i.e., photovoltaic output). Therefore, the power point corresponding to x (0 < x < 1, x = 90% in this embodiment) at the highest power point is taken as the steady-state point, and the DC voltage corresponding to the x power point is set as the steady-state DC voltage of the photovoltaic array.

[0050] That is, reserve 10% of the photovoltaic output, and the DC voltage corresponding to 90% of the maximum power point is the steady-state DC voltage of the photovoltaic array.

[0051] S2. Calculate the slope at the steady-state operating point according to the photovoltaic characteristic curve, and calculate the gain parameter of the photovoltaic additional controller;

[0052] The calculation formula for the slope at the steady-state operating point is: where K PU is the slope at the steady-state operating point of the photovoltaic array, and I SC is the short-circuit current of the photovoltaic cell;

[0053] Calculate the gain parameter of the photovoltaic additional controller according to the slope at the steady-state operating point and the negative damping torque of the hydro-generator set. The calculation formula is: where K c is the gain parameter of the photovoltaic additional controller, and D m is the damping torque generated by the mechanical power of the hydro-generator set, and this parameter is generally negative.

[0054] S3. Use the change in system frequency as the input of the photovoltaic additional controller, and the output of the photovoltaic additional controller is the reference value of the photovoltaic DC voltage controller; the calculation formula for the reference value of the photovoltaic DC voltage controller is: where U * DC is the output of the photovoltaic additional controller, U * DC0 is the steady-state DC voltage of the photovoltaic array, Δω is the change in system frequency, U * DCmin is the lower limit value of the output of the photovoltaic additional controller, and U * DCmax is the upper limit value of the output of the photovoltaic additional controller. The specific parameters are obtained through step S1.

[0055] S4. The reference value output by the PV additional controller passes through the PV DC voltage controller and the PV DC current controller to obtain the dq-axis reference values of the voltage. After determining the dq-axis reference values, the control signal for controlling the PV output power is obtained through Park transformation and PWM modulation. The PV additional controller controls the PV output power through the control signal.

[0056] The method for obtaining the control signal is as follows: The output U of the PV additional controller * DC passes through the PV DC voltage controller and the current controller to obtain the dq-axis reference values. Among them, the mathematical expressions of the DC voltage controller and the current controller are: where i * d is the d-axis current reference value output by the DC voltage controller, K pv and K iv are the proportional coefficient and the integral coefficient of the DC voltage controller respectively, U dc is the measured value of the PV DC voltage, v d and v q are the voltage d-axis and q-axis reference values output by the current controller respectively, K pi and K ii are the proportional coefficient and the integral coefficient of the current controller respectively, i d and i q are the d-axis and q-axis components of the inverter output current respectively, e d and e q are the d-axis and q-axis components of the inverter output voltage respectively, ω is the rated value of the system angular frequency, and L is the value of the filter inductor;

[0057] The control signal is obtained by performing Park transformation and PWM modulation on the voltage dq-axis reference values, and the PV output power is controlled through the control signal.

[0058] Embodiment 2

[0059] This embodiment provides a specific water-light complementary system containing a hydropower unit and a PV as an example to verify the effectiveness of a PV additional control method for suppressing ultra-low frequency oscillations proposed by the present invention. The topological structure of the water-light complementary system provided in this embodiment is as Figure 3 shown. The result of verifying the effectiveness of the present invention comes from a commercial simulation software (PowerSystems Computer Aided Design, PSCAD).

[0060] The design parameters of the water-light complementary system are as follows:

[0061] The capacity of the hydropower unit is 45 MW, and the damping at ultra-low frequency is 17.4. The capacity of the photovoltaic system is 5 MW. The number of series-connected units in the photovoltaic array is 29, and the number of parallel-connected units is 750. The open-circuit voltage of the photovoltaic cell is 37 V, and the short-circuit current is 8.4 A. The parameters C1 and C2 are 2.217×10 -6 and 0.0768 respectively. The line is an impedance-type line, with a resistance value of 0.0007 Ω and an inductance value of 0.0021 H. Load 1 is 20 MW + 10 MVar, and load 2 is 5 MW.

[0062] Figure 4 It is the characteristic curve diagram of the photovoltaic array provided in the second embodiment. Refer to Figure 4 , the upper limit value and the lower limit value of the output of the photovoltaic additional controller are 0.871 kV and 1.073 kV respectively, the steady-state DC voltage is 0.96 kV, the slope at the steady-state operating point is 13.9526, and the gain parameter of the photovoltaic additional controller is 1.247.

[0063] The total system simulation time is 50 seconds, and load 2 is input as a disturbance at 0 second. For comparison, Figure 5 It is the system frequency variation diagram provided in the second embodiment; Figure 6 It is the diagram of the change in the active power output of the photovoltaic provided in the second embodiment.

[0064] Refer to Figure 5 , it can be seen that after load 2 is input at 0 second, the system undergoes ultra-low frequency oscillation. Without photovoltaic additional control, the system enters a long-term oscillation state and cannot recover stability; while with photovoltaic additional control, the system frequency can quickly tend to be stable, and the ultra-low frequency oscillation is effectively suppressed.

[0065] Refer to Figure 6 , it can be seen that without photovoltaic additional control, the active power output of the photovoltaic is constant and does not participate in the frequency regulation of the system; while with photovoltaic additional control, the photovoltaic output can respond to the frequency change of the system and participate in oscillation suppression.

[0066] In summary, in this embodiment, by adding an additional controller to the photovoltaic and calculating the control parameters, the controller adjusts the DC voltage of the photovoltaic array according to the change in frequency, thereby changing the output power of the photovoltaic and suppressing ultra-low frequency oscillation. This method solves the problem that the traditional method does not utilize the active regulation ability of the photovoltaic when suppressing ultra-low frequency oscillation.

[0067] Embodiment 3

[0068] This embodiment provides a photovoltaic additional control device for suppressing ultra-low frequency oscillation, including a first calculation module, a second calculation module, a third calculation module, a fourth calculation module, a fifth calculation module, and a sixth calculation module.

[0069] Multiple processing modules can be independent processing chips that communicate with each other, or they can be multiple software modules in a single processing chip to achieve control within the same processing chip.

[0070] The first calculation module is used to obtain the photovoltaic characteristic curve based on the photovoltaic array parameters. The operation method within the first calculation module includes: determining the parameters of the photovoltaic array, obtaining the photovoltaic characteristic curve, and determining the limiting parameters and steady-state DC voltage of the photovoltaic additional controller.

[0071] The calculation formula for determining the photovoltaic characteristic curve is: Among them, the parameters of the photovoltaic array include but are not limited to: P PV is the output power of the photovoltaic array, U DC is the DC voltage of the photovoltaic array, m is the number of parallel-connected photovoltaic cells, n is the number of series-connected photovoltaic arrays, C1 and C2 are both factory parameters of the photovoltaic cells, and U oc is the open-circuit voltage of the photovoltaic cell.

[0072] The second calculation module is used to determine the limiting parameters and steady-state DC voltage of the photovoltaic additional controller. The operation method within the second calculation module includes: taking the highest point of the photovoltaic characteristic curve as the maximum power point of the photovoltaic array, the DC voltage corresponding to the maximum power point as the lower limit value of the output of the photovoltaic additional controller, and the zero-crossing point on the right side of the curve as the upper limit value of the output of the photovoltaic additional controller; reserving 10% of the photovoltaic output, and the DC voltage corresponding to 90% of the maximum power point as the steady-state DC voltage of the photovoltaic array.

[0073] The third calculation module is used to calculate the slope at the steady-state operating point based on the photovoltaic characteristic curve. The operation method within the third calculation module includes: the calculation formula for the slope at the steady-state operating point is: Among them, K PU is the slope at the steady-state operating point of the photovoltaic array, and I SC is the short-circuit current of the photovoltaic cell.

[0074] The fourth calculation module is used to calculate the gain parameter of the photovoltaic additional controller. The operation method within the fourth calculation module includes: calculating the gain parameter of the photovoltaic additional controller based on the slope at the steady-state operating point and the negative damping torque of the hydro-generator set. The calculation formula is: Among them, K c is the gain parameter of the photovoltaic additional controller, and D m is the damping torque generated by the mechanical power of the hydro-generator set.

[0075] The fifth calculation module is used to take the change in system frequency as the input of the PV additional controller, and the output of the PV additional controller is the reference value of the PV DC voltage controller; the method running in the fifth calculation module includes: taking the change in system frequency as the input of the PV additional controller, and the output of the PV additional controller is the reference value of the PV DC voltage controller; the calculation formula for the reference value of the PV DC voltage controller is:

[0076] The sixth calculation module is used to obtain the dq-axis reference values of the voltage after the reference value output by the PV additional controller passes through the PV DC voltage controller and the current controller, and obtain the control signal for controlling the PV output power. Embodiment 4

[0077] A PV additional control terminal for suppressing ultra-low frequency oscillations includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of a PV additional control method for suppressing ultra-low frequency oscillations as described above are implemented.

[0078] The memory can be used to store software programs and modules. The processor runs the software programs and modules stored in the memory to execute various functional applications and data processing of the terminal. The memory mainly includes a program storage area and a data storage area. Among them, the program storage area can store an operating system, execution programs required for at least one function, etc.

[0079] The data storage area can store data created according to the use of the terminal, etc. In addition, the memory can include high-speed random access memory, and can also include non-volatile memory, such as at least one magnetic disk storage device, flash memory device, or other volatile solid-state storage devices.

[0080] A computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the steps of a PV additional control method for suppressing ultra-low frequency oscillations as described above are implemented.

[0081] Without loss of generality, computer-readable media can include computer storage media and communication media. Computer storage media includes volatile and non-volatile, removable and non-removable media implemented by any method or technology for storing information such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes RAM, ROM, EPROM, EEPROM, flash memory or other solid-state storage technologies, CD-ROM, DVD or other optical storage, magnetic tape cartridges, magnetic tapes, disk storage or other magnetic storage devices. Of course, those skilled in the art know that computer storage media is not limited to the above several. The above-mentioned system memory and mass storage devices can be collectively referred to as memory.

[0082] In the description of this specification, the descriptions referring to terms such as "one embodiment / way", "some embodiments / ways", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment / way or example are included in at least one embodiment / way or example of this application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment / way or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments / ways or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments / ways or examples described in this specification and the features of different embodiments / ways or examples.

[0083] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of this application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0084] Those skilled in the art should understand that the above embodiments are merely for clearly explaining the present invention and are not intended to limit the scope of the present invention. For those skilled in the art, other changes or variations can be made based on the above invention, and these changes or variations are still within the scope of the present invention.

Claims

1. A photovoltaic additional control method for suppressing ultra-low frequency oscillations, characterized in that, Including: Obtain the photovoltaic characteristic curve, and determine the limiting parameters and steady-state DC voltage of the photovoltaic additional controller; Calculate the slope at the steady-state operating point according to the photovoltaic characteristic curve, and calculate the gain parameters of the photovoltaic additional controller; Use the change in system frequency as the input of the photovoltaic additional controller, and the output of the photovoltaic additional controller is the reference value of the photovoltaic DC voltage controller; The reference value output by the photovoltaic additional controller passes through the photovoltaic DC voltage controller and the current controller to obtain the dq-axis reference values of the voltage, and obtain the control signal for controlling the photovoltaic output power; Among them, the method for obtaining the photovoltaic characteristic curve includes: determining the parameters of the photovoltaic array, and determining the calculation formula of the photovoltaic characteristic curve as: Among them, P PV is the output power of the photovoltaic array, U DC is the DC voltage of the photovoltaic array, m is the number of parallel-connected photovoltaic cells, n is the number of series-connected photovoltaic arrays, both C1 and C2 are the factory parameters of the photovoltaic cells, U oc is the open-circuit voltage of the photovoltaic cell. The methods for obtaining the limiting parameter and the steady-state DC voltage include: Take the highest point of the photovoltaic characteristic curve as the maximum power point of the photovoltaic array, the DC voltage corresponding to the maximum power point is the lower limit value of the output of the photovoltaic additional controller, and the zero crossing point on the right side of the curve is the upper limit value of the output of the photovoltaic additional controller; Reserve 1 - x of the photovoltaic output, and set the DC voltage corresponding to the x power point as the steady-state DC voltage of the photovoltaic array, where 0 < x < 1; Among them, the calculation formula for the slope at the steady-state operating point is: Among them, K PU is the slope at the steady-state operating point of the photovoltaic array, and I SC is the short-circuit current of the photovoltaic cell; The calculation formula for the gain parameter of the PV additional controller according to the slope at the steady-state operating point and the negative damping torque of the hydropower unit is as follows: Where K c is the gain parameter of the PV additional controller, and D m is the damping torque generated by the mechanical power of the hydropower unit.

2. A photovoltaic additional control method for suppressing ultra-low frequency oscillation according to claim 1, characterized in that, x＝90％。 3. A photovoltaic additional control method for suppressing ultra-low frequency oscillation according to claim 1, characterized in that, The calculation formula for the reference value of the photovoltaic DC voltage controller is: U * DC is the output of the PV additional controller, where U * DC0 is the steady-state DC voltage of the PV array, Δω is the change in the system frequency, and U * DCmin is the lower limit of the output of the PV additional controller, and U * DCmax is the upper limit of the output of the PV additional controller.

4. A photovoltaic additional control method for suppressing ultra-low frequency oscillation according to claim 1, characterized in that, The method for obtaining the control signal is as follows: the output U of the photovoltaic additional controller * DC passes through the photovoltaic DC voltage controller and the current controller to obtain the dq-axis reference values. Among them, the mathematical expressions of the DC voltage controller and the current controller are as follows: where is the d-axis current reference value output by the DC voltage controller, K pv and K iv are the proportional coefficient and integral coefficient of the DC voltage controller respectively, U DC is the measured value of the PV DC voltage, v d and v q are the voltage d-axis and q-axis reference values output by the current controller respectively, K pi and K ii are the proportional coefficient and integral coefficient of the current controller respectively, i d and i q are the d-axis and q-axis components of the inverter output current respectively, e d and e q are the d-axis and q-axis components of the inverter output voltage respectively, ω is the rated value of the system angular frequency, and L is the value of the filter inductor; Obtain the control signal through Park transformation and PWM modulation of the voltage dq-axis reference value, and control the photovoltaic output power through the control signal.

5. A photovoltaic additional control terminal for suppressing ultra-low frequency oscillations, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of a photovoltaic additional control method for suppressing ultra-low frequency oscillations as described in any one of claims 1-4.

6. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of a photovoltaic additional control method for suppressing ultra-low frequency oscillations as described in any one of claims 1-4.

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