Sectional type collaborative frequency modulation control method for network tracking / constructing type hybrid photovoltaic power station

Abstract

The invention belongs to the technical field of frequency modulation control of a power system, and particularly relates to a sectional type collaborative frequency modulation control method for a network tracking / constructing type hybrid photovoltaic power station, which comprises the following steps of: dividing a frequency modulation process into three time periods according to a frequency disturbance response curve, and enabling each time period to correspond to an interval; and for each interval, by taking the core frequency modulation target of the interval as a guide, designing a frequency modulation control instruction of the grid-type photovoltaic unit, so that the frequency modulation control instruction is coordinated with the frequency modulation response of the grid-type photovoltaic unit. The frequency disturbance response process is divided into different stages, and the frequency modulation purpose of each stage is taken as an optimization target, and parameters and instructions of network type control are dynamically optimized, so that the parameters and instructions and network type control form cooperative complementation, and the optimal frequency support effect is realized in the whole frequency modulation process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power system frequency modulation control, and particularly relates to a segmented collaborative frequency modulation control method for a follow / grid hybrid photovoltaic power station. BACKGROUND

[0002] With the increasing penetration of new energy such as photovoltaic in the power system, the proportion of traditional thermal power frequency modulation capacity is decreasing, and the system inertia and frequency modulation capacity are facing challenges. Currently, photovoltaic units mainly adopt two control modes, follow-grid type and grid-forming type, which have significant differences in frequency modulation response characteristics. I. Grid-forming photovoltaic control has no frequency modulation dead zone, can quickly respond to frequency changes, and has better suppression effect on frequency change rate (RoCoF) and minimum frequency, but in the frequency recovery stage, the instruction will change in the opposite direction with RoCoF, hindering the frequency rise.

[0003] II. Follow-grid photovoltaic control relies on dead zone setting to avoid frequent action, although the response can be optimized through parameter adjustment, but separate design may lead to incoordination with grid-forming response, and blindly increasing frequency modulation power will impact power electronic devices and shorten the service life.

[0004] Currently, most researches focus on the optimization of a single control strategy, or simply run two controls in parallel, and fail to fully utilize the complementary characteristics of the two controls in different frequency modulation stages. If the follow-grid and grid-forming controls can be organically coordinated, and the parameters can be designed and the instructions can be allocated for different stages in the whole frequency disturbance process, the overall frequency support effect can be better than that of a single control. Therefore, there is an urgent need for a collaborative control method that can coordinate the advantages of the two controls and make up for their respective disadvantages. SUMMARY

[0005] Embodiments of the application provide a segmented collaborative frequency modulation control method for a follow / grid hybrid photovoltaic power station. The method divides the frequency disturbance response process into different stages, and takes the frequency modulation purpose of each stage as the optimization target, dynamically optimizes the parameters and instructions of the follow-grid control, so that the follow-grid control and the grid-forming control form a synergistic complement, thereby achieving optimal frequency support effect in the whole frequency modulation process.

[0006] The application is implemented in the following way, A segmented collaborative frequency modulation control method for a follow / grid hybrid photovoltaic power station, comprising the following steps: According to the frequency disturbance response curve, the frequency modulation process is divided into three time periods, and each time period corresponds to an interval; For each interval, the frequency modulation control instruction of the follow-grid photovoltaic unit is designed in the direction of the core frequency modulation target of the interval, so that the frequency modulation control instruction is coordinated with the frequency modulation response of the grid-forming photovoltaic unit.

[0007] Further, the three time periods include: T1 interval: from the start of frequency disturbance to the frequency deviation not exceeding the frequency modulation dead zone; T2 interval: from the frequency deviation exceeding the frequency modulation dead zone to the system frequency reaching the lowest point; T3 interval: from the frequency lowest point to the frequency recovering to the steady state.

[0008] Further, for each interval, the frequency modulation control instruction of the grid-following type photovoltaic unit is designed in the light of the core frequency modulation target of the interval, including: In the T1 interval, the frequency modulation target is that the station does not respond to small frequency fluctuations in the system, and the steady-state active instruction value of the grid-following type photovoltaic unit is adjusted for compensation.

[0009] Further, adjusting the steady-state active instruction value of the grid-following type photovoltaic unit for compensation includes: Reducing the steady-state output of the grid-following type photovoltaic unit so that the total output at the station level remains unchanged within the frequency dead zone range; The frequency modulation power of the grid-connected type photovoltaic unit is represented as: , is the inertia constant, representing the resistance of the system to frequency changes, represents the angular frequency of the system, is the damping coefficient, representing the suppression ability of the system to frequency deviation, represents the rated frequency, represents time; Within the frequency modulation dead zone range, adjusting the steady-state output of the grid-following type photovoltaic unit compensates for the grid-connected type frequency modulation response, so that the station does not respond to the system frequency within the dead zone range, and the steady-state active instruction value of the grid-following type photovoltaic unit is: , , represents the steady-state active instruction value of the grid-following type photovoltaic unit, represents the initial steady-state active power of the grid-following type photovoltaic unit, represents the lower limit value of the frequency modulation dead zone, represents the upper limit value of the frequency modulation dead zone.

[0010] Further, for each interval, the frequency modulation control instruction of the grid-following type photovoltaic unit is designed in the light of the core frequency modulation target of the interval, including: In the T2 interval, the frequency modulation target is to maximize the frequency change rate and raise the frequency lowest point, and the inertia coefficient of the grid-following type photovoltaic unit control is optimized with the frequency modulation response instruction value of the grid-connected type photovoltaic unit as the reference, so that the frequency modulation output curve of the grid-following type photovoltaic unit approximates the effect of the grid-connected type control.

[0011] Further, the inertia coefficient of the grid-following type photovoltaic unit is represented as: , represents the inertia coefficient of the grid-connected photovoltaic unit, represents the system angular frequency, is the damping coefficient, representing the suppression ability of the system to frequency deviation, represents the rated frequency, represents time, is the grid frequency.

[0012] Further, in the T3 interval, the frequency recovery to the steady state is the target, and the inertia response instruction of the grid-connected photovoltaic unit is designed to be the opposite number of the inertia response of the grid-forming photovoltaic unit.

[0013] Further, the inertia control instruction value of the grid-connected photovoltaic unit is: , wherein, represents the inertia control instruction value of the grid-connected photovoltaic unit, represents the initial inertia power deviation of the grid-connected photovoltaic unit, the frequency change rate of the grid-forming photovoltaic unit, the frequency output by the grid-forming photovoltaic unit, represents the inertia coefficient of the photovoltaic unit.

[0014] Compared with the prior art, the application has the beneficial effects that: for the first time, the frequency response process is segmented, and the specific target of each stage is controlled in coordination to achieve fine and optimized control from the initial disturbance to the recovery period.

[0015] The grid-forming control has the advantages of fast initial response and flexible configuration of the grid-connected control parameters, while avoiding the disadvantages of the grid-forming control being not conducive to frequency recovery and the grid-connected control possibly impacting the equipment.

[0016] Through the coordinated control, the whole station can more effectively suppress the frequency change rate, raise the lowest frequency point, and accelerate the frequency recovery under frequency disturbance, thereby significantly improving the frequency stability of the high-proportion new energy power grid. The method is based on the existing grid-connected / grid-forming control architecture, and is easy to engineer and promote. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A new energy and thermal power bundling model provided by the embodiment of the application; Figure 2 A method flowchart provided by the embodiment of the application; Figure 3 Grid-connected / grid-forming photovoltaic unit frequency modulation response curves (a) and frequency curves (b) under different steady-state outputs provided by the embodiment of the application; Figure 4A segmented diagram of the frequency modulation response curve of a grid-connected photovoltaic system with a steady-state output of 0.9 pu, provided for embodiments of this application; Figure 5 A comparison diagram of the inertia frequency modulation response of the follower / grid-type photovoltaic unit in the collaborative control provided in the embodiments of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0019] See Figure 1 The method in this application is used in a system structure that is a bundled model of new energy and thermal power, including a photovoltaic power station and a synchronous machine. T1 represents the inertia constant of the synchronous machine, indicating its resistance to grid frequency changes. Z1 represents the equivalent impedance of the synchronous machine connection to the grid, and represents the resistance and reactance of the transmission line. T2 represents the inertia constant of the photovoltaic power station, indicating its resistance to grid frequency changes. Z2 represents the equivalent impedance of the photovoltaic power station connection to the grid. L1 and L2 represent the inductances of the two transmission lines, respectively. Referring to the system parameter table in Table 1... Table 1 System Parameter Table: Parameter Value Synchronous machine capacity 100 MVA Rated frequency 50 Hz Synchronous machine inertia time constant 3s Synchronous machine frequency regulation dead band ± 0.033 Hz T1 voltage class 220 kV / 63 kV T1 capacity 100 MVA T2 voltage class 220 kV / 66 kV T2 capacity 120 MVA Photovoltaic plant capacity 120 MVA Photovoltaic frequency regulation dead band ± 0.05 Hz Load capacity 100 MW Load disturbance 10 MW See Figure 2 The flowchart of the segmented coordinated frequency regulation control method for a grid-connected hybrid photovoltaic power plant shown includes: dividing the frequency regulation process into three time periods based on the frequency disturbance response curve, with each time period corresponding to an interval; For each interval, guided by the core frequency regulation target of that interval, the frequency regulation control command of the grid-connected photovoltaic unit is designed so that the frequency regulation control command is coordinated with the frequency regulation response of the grid-connected photovoltaic unit.

[0020] In one embodiment, the three time periods include: T1 range: from the start of the frequency disturbance until the frequency deviation does not exceed the frequency modulation dead zone; T2 range: from the point where the frequency deviation exceeds the frequency modulation dead zone until the system frequency reaches its lowest point; T3 range: from the lowest frequency point to the frequency recovering to a steady state.

[0021] Frequency monitoring and range determination, following the frequency modulation response of grid-connected photovoltaic units under different steady-state outputs, such as... Figure 3 As shown.

[0022] Depend on Figure 3It can be seen that the difference in frequency modulation response between the follow / grid-connected photovoltaic has similarity under the same steady-state output, and the frequency modulation response curve of the follow / grid-connected photovoltaic under the condition of taking the steady-state output as 0.9 p.u. is as follows and is segmented as follows: T1—not exceeding the frequency modulation dead zone; T2—exceeding the frequency modulation dead zone to the frequency reaching the lowest point; T3—frequency recovery stage.

[0023] In an embodiment, for each interval, the frequency modulation control instruction of the follow-grid photovoltaic unit is designed in the direction of the core frequency modulation target of the interval, including: In the T1 interval, the frequency modulation target is that the station does not respond to small frequency fluctuations in the system, and the steady-state active instruction value of the follow-grid photovoltaic unit is adjusted for compensation.

[0024] In the T2 interval, the frequency modulation target is to maximize the frequency change rate and raise the frequency lowest point, and the inertia coefficient of the follow-grid photovoltaic unit control is optimized with reference to the frequency modulation response instruction value of the grid-connected photovoltaic unit, so that the frequency modulation output curve of the follow-grid photovoltaic unit approximates the effect of the grid-connected control.

[0025] In the T3 interval, the frequency modulation target is to make the frequency recover to the steady state as soon as possible, and the inertia response instruction of the follow-grid photovoltaic unit is designed to be the opposite number of the inertia response of the grid-connected photovoltaic unit.

[0026] For details, see Figure 4 The station control system monitors the grid frequency in real time, and the control system detects the frequency deviation. According to the preset frequency modulation dead zone threshold (such as ±0.03 Hz), it is judged whether the current is in the T1 interval, the T2 interval or the T3 interval.

[0027] For each interval, the frequency modulation control instruction of the follow-grid photovoltaic unit is designed in the direction of the core frequency modulation target of the interval, so that it is coordinated with the frequency modulation response of the grid-connected photovoltaic unit, as follows: T1 interval control: when |Δf| is less than the dead zone threshold, it is determined to be in the T1 interval.

[0028] The control system calculates and issues the steady-state active instruction of the follow-grid photovoltaic unit according to the inertia control instruction value of the follow-grid photovoltaic unit to ensure that the total output of the station is unchanged. is the inertia constant, indicating the resistance of the system to frequency change, is the angular frequency of the system, is the damping coefficient, indicating the suppression ability of the system to frequency deviation, is the rated frequency, is the time; is the steady-state active instruction value of the follow-grid photovoltaic unit, represents the initial steady-state active power of the grid-following photovoltaic unit, , represents the lower limit value of the frequency modulation dead zone, represents the upper limit value of the frequency modulation dead zone.

[0029] In the T2 interval, the frequency modulation target is to maximize the frequency change rate and raise the frequency minimum point. The inertia coefficient of the grid-following photovoltaic unit control is optimized with reference to the frequency modulation response instruction value of the grid-constructing photovoltaic unit, so that the frequency modulation output curve of the grid-following photovoltaic unit approximates the effect of the grid-constructing control.

[0030] T2 interval control: when |Δf| exceeds the dead zone threshold and the frequency continues to drop, it is determined to be in the T2 interval. The control system calls the inertia coefficient formula of the grid-following photovoltaic unit in advance: , represents the inertia coefficient of the grid-following photovoltaic unit, represents the system angular frequency, is the damping coefficient, representing the system's suppression ability to frequency deviation, represents the rated frequency, represents time, is the grid frequency.

[0031] The calculated optimal inertia coefficient of the grid-following unit , and the corresponding inertia response power instruction is generated, which provides power support together with the grid-constructing unit.

[0032] In the T3 interval, the frequency modulation target is to restore the frequency to the steady state as soon as possible. The inertia response instruction of the grid-following photovoltaic unit is designed to be the opposite number of the inertia response of the grid-constructing photovoltaic unit, and the T3 interval control: when it is detected that the frequency reaches the lowest point and starts to rise, it is determined to be in the T3 interval.

[0033] The frequency modulation instruction of the grid-constructing control strictly follows the RoCoF change, and in the frequency recovery stage, it will produce an instruction value opposite to the frequency modulation target, which is not conducive to the system frequency recovery.

[0034] For the recovery stage of the field station level frequency modulation, the frequency should be restored to the steady state as soon as possible. When the RoCoF of the grid-constructing photovoltaic unit passes through the zero point, the inertia response of the grid-following photovoltaic unit is added to the opposite number of the inertia response of the grid-constructing photovoltaic unit, then the inertia response curve of the grid-following photovoltaic unit in the collaborative control should be as shown in Figure 5 .

[0035] The control system calculates the inertia control instruction according to the following formula: , and performs frequency modulation control according to the calculated instruction to make the system frequency recover to the steady state as soon as possible. represents the inertia control instruction value of the grid-connected photovoltaic unit, represents the initial inertia power deviation of the grid-connected photovoltaic unit, represents the frequency change rate of the grid-connected photovoltaic unit, represents the frequency of the grid-connected photovoltaic unit output, represents the inertia coefficient of the photovoltaic unit.

[0036] Restoration to steady state: when the frequency is restored to the dead zone range, the system control strategy returns to the T1 interval mode, and is ready to respond to the next frequency disturbance.

[0037] Through the above segmented cooperative control, the embodiment can effectively improve the overall frequency support capability of the new energy station, and guarantee the safe and stable operation of the power grid.

[0038] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A segmented coordinated frequency regulation control method for a grid-connected hybrid photovoltaic power station, characterized in that, Includes the following steps: Based on the frequency disturbance response curve, the frequency modulation process is divided into three time periods, each corresponding to an interval; For each interval, guided by the core frequency regulation target of that interval, the frequency regulation control command of the grid-connected photovoltaic unit is designed so that the frequency regulation control command is coordinated with the frequency regulation response of the grid-connected photovoltaic unit.

2. The segmented coordinated frequency regulation control method for a grid-connected hybrid photovoltaic power station according to claim 1, characterized in that, The three time periods include: T1 range: from the start of the frequency disturbance until the frequency deviation does not exceed the frequency modulation dead zone; T2 range: from the point where the frequency deviation exceeds the frequency modulation dead zone until the system frequency reaches its lowest point; T3 range: from the lowest frequency point to the frequency recovering to a steady state.

3. The segmented coordinated frequency regulation control method for a grid-connected hybrid photovoltaic power station according to claim 1, characterized in that, For each interval, guided by the core frequency regulation target of that interval, design the frequency regulation control commands for the grid-connected photovoltaic units, including: In the T1 interval, the frequency regulation target is to prevent the power station from responding to small frequency fluctuations within the system, which is compensated by adjusting the steady-state active power command value of the grid-connected photovoltaic units.

4. The segmented coordinated frequency regulation control method for a grid-connected hybrid photovoltaic power station according to claim 3, characterized in that, Compensation is achieved by adjusting the steady-state active power command value of the grid-connected photovoltaic units, including: Reduce the steady-state output of grid-connected photovoltaic units so that the total output of the power station remains unchanged within the frequency dead zone. The frequency modulation power of a grid-type photovoltaic unit is expressed as: , It is the inertial constant, representing the system's resistance to frequency changes. Represents the system's angular frequency. It is the damping coefficient, which represents the system's ability to suppress frequency deviations. Indicates the rated frequency. Indicates time; Within the frequency regulation dead zone, the steady-state output of the grid-connected photovoltaic units is adjusted to compensate for the grid-connected frequency regulation response, so that the power station does not respond to the system frequency within the dead zone. The steady-state active power command value of the grid-connected photovoltaic units is as follows: , , This represents the steady-state active power command value of the grid-connected photovoltaic unit. This represents the initial steady-state active power of the grid-connected photovoltaic unit. Indicates the lower limit of the FM dead zone, This indicates the upper limit of the frequency modulation dead zone.

5. The segmented coordinated frequency regulation control method for a grid-connected hybrid photovoltaic power station according to claim 2, characterized in that, For each interval, guided by the core frequency regulation target of that interval, design the frequency regulation control commands for the grid-connected photovoltaic units, including: In the T2 range, the frequency regulation objective is to suppress the rate of frequency change to the greatest extent and raise the lowest frequency point. Taking the frequency regulation response command value of the grid-type photovoltaic unit as a reference, the inertia coefficient of the grid-following photovoltaic unit control is optimized so that the frequency regulation output curve of the grid-following photovoltaic unit approximates the effect of the grid-type control.

6. The segmented coordinated frequency regulation control method for a grid-connected hybrid photovoltaic power station according to claim 5, characterized in that, The inertia coefficient of a grid-connected photovoltaic unit is expressed as: , This represents the inertia coefficient of the grid-connected photovoltaic unit. Represents the system's angular frequency. It is the damping coefficient, which represents the system's ability to suppress frequency deviations. Indicates the rated frequency. Indicates time, This refers to the power grid frequency.

7. The segmented coordinated frequency regulation control method for a grid-connected hybrid photovoltaic power station according to claim 2, characterized in that, In the T3 range, the frequency modulation objective is to restore the frequency to a steady state as soon as possible. The inertia response command of the grid-connected photovoltaic unit is designed to be superimposed with the inertia response of the grid-connected photovoltaic unit.

8. The segmented coordinated frequency regulation control method for a grid-connected hybrid photovoltaic power station according to claim 7, characterized in that, The inertia control command value for the grid-connected photovoltaic unit is: , in, This represents the inertial control command value for the grid-connected photovoltaic unit. This indicates the initial inertial power deviation from the grid-connected photovoltaic unit. Frequency change rate of grid-type photovoltaic cells The frequency output of a grid-type photovoltaic unit, This represents the inertia coefficient of a photovoltaic unit.

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