Background
Photovoltaic power generation is a new energy power generation technology which utilizes the photovoltaic effect of a semiconductor interface to directly convert light energy into electric energy. The solar cells are connected in series and then are packaged and protected to form a large-area solar cell module, and then the photovoltaic power generation device is formed by matching with components such as a power controller and the like. The photovoltaic power generation device transmits electric energy to a power grid through the inverter to form a grid-connected photovoltaic power generation system. With the continuous increase of the scale of the photovoltaic grid-connected power generation system connected to the power grid, the problems of power flow, stability and peak shaving of a power system and coordination among a plurality of photovoltaic power stations are brought to power grid dispatching, and the capacity of the power grid for accepting photovoltaic power generation is influenced.
At present, the droop control method is generally adopted to adjust the active output and the grid frequency of the photovoltaic grid-connected power generation system, but the traditional droop control method has small active-frequency supporting force on the grid, cannot meet the requirement of grid frequency stability during large-scale photovoltaic grid connection, and is also not beneficial to the consumption of the grid on photovoltaic power generation.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a photovoltaic power station frequency adjusting method and system.
In a first aspect, a technical solution of a method for adjusting a frequency of a photovoltaic power plant according to the present invention is:
calculating an active power output regulating quantity of the photovoltaic power station according to the grid-connected point frequency of the photovoltaic power station, and correcting an active power reference value of the photovoltaic power station according to the active power output regulating quantity;
carrying out active power regulation on the photovoltaic power station according to the grid-connected point frequency and the active power reference value;
and acquiring the grid-connected point frequency after the active power is adjusted, and adjusting the frequency hysteresis of the power grid according to the grid-connected point frequency.
Further, the invention provides a preferable technical scheme as follows:
the method for calculating the active power output regulating quantity of the photovoltaic power station according to the grid-connected point frequency of the photovoltaic power station comprises the following steps:
comparing the grid-connected point frequency and a threshold value thereof:
if f > fupThen, the active power output of the photovoltaic power station is reduced by the following formula (1):
Pfup=Kp_fup×(f-fup) (1)
if f is less than fdownThen, the active output increase of the photovoltaic power station is shown as the following formula (2):
Pfdn=Kp_fdn×(fdown-f) (2)
wherein f is the frequency of the grid connection point, fupAnd fdownUpper and lower limits, K, of the grid-connected point frequency, respectivelyp_fupAnd Kp_fdnAll are proportionality coefficients;
the correcting the active power reference value of the photovoltaic power station comprises the following steps:
if f > fupThen, the corrected active power reference value is shown as the following formula (3):
Ppoi_ref=Ppoi_ref0-Pfup (3)
if f is less than fdownThen, the corrected active power reference value is shown as the following formula (4):
Ppoi_ref=Ppoi_ref0+Pfdn (4)
wherein, Ppoi_ref0Is the initial value of the active power reference value.
Further, the invention provides a preferable technical scheme as follows: the active power regulation comprises an active power reduction regulation and an active power increase regulation;
the adjusting active power to the photovoltaic power station comprises:
comparing the grid-connected point frequency and a threshold value thereof: if f > fupPerforming active power reduction adjustment on the photovoltaic power station; if f is less than fdownPerforming active power increase regulation on the photovoltaic power station;
wherein f is the frequency of the grid connection point, fupAnd fdownRespectively an upper limit value and a lower limit value of the grid-connected point frequency.
Further, the invention provides a preferable technical scheme as follows:
the active power reduction adjustment of the photovoltaic power station comprises:
comparing the corrected active power reference value and the lower limit value thereof: if the active power reference value is larger than the lower limit value, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the active power reference value; and otherwise, sending an active control instruction to each photovoltaic inverter in the photovoltaic power station according to the lower limit value of the active power reference value.
Further, the invention provides a preferable technical scheme as follows:
the adjusting the active power increase of the photovoltaic power station comprises:
comparing the corrected active power reference value and the upper limit value thereof: if the active power reference value is smaller than the upper limit value, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the active power reference value; otherwise, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the upper limit value of the active power reference value.
Further, the invention provides a preferable technical scheme as follows: the frequency hysteresis regulation comprises an over-frequency hysteresis regulation and an under-frequency hysteresis regulation;
the frequency hysteresis adjustment of the power grid according to the grid-connected point frequency comprises the following steps of comparing the grid-connected point frequency and a threshold value thereof: if f > fupPerforming over-frequency hysteresis regulation on the power grid; if f is less than fdownThe power grid performs under-frequency hysteretic regulation;
wherein f is the frequency of the grid connection point, fupAnd fdownRespectively an upper limit value and a lower limit value of the grid-connected point frequency.
Further, the invention provides a preferable technical scheme as follows: the method for adjusting the over-frequency hysteresis of the power grid according to the frequency of the grid-connected point comprises the following steps:
judging whether the grid-connected point frequency after the active power reduction adjustment of the photovoltaic power station is continuously increased or not: if the power is increased, the active power reduction and adjustment are continuously carried out on the photovoltaic power station; otherwise, acquiring the maximum value of the grid-connected point frequency and calculating the active output reduction of the photovoltaic power station corresponding to the maximum value according to the following formula;
Pfup_max=Kp_fup×(f-fup_max) (5)
wherein f isup_maxThe maximum value of the grid-connected point frequency is obtained;
comparing the grid-connected point frequency with an over-frequency hysteresis threshold value: if the grid-connected point frequency is greater than the over-frequency hysteresis threshold value, the active output decrement P is determinedfup_maxModified photovoltaicAn active power reference value of the power station, and an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the corrected active power reference value;
the corrected active power reference value is shown as the following formula (6):
Ppoi_ref=Ppoi_ref0-Pfup_max (6)。
further, the invention provides a preferable technical scheme as follows: the method for adjusting the under-frequency hysteresis of the power grid according to the frequency of the grid-connected point comprises the following steps:
judging whether the grid-connected point frequency after the active power increase adjustment of the photovoltaic power station continuously drops or not: if the power is reduced, the active power of the photovoltaic power station is continuously increased and adjusted; otherwise, acquiring the minimum value of the grid-connected point frequency and calculating the active output reduction of the photovoltaic power station corresponding to the minimum value according to the following formula;
Pfdn_min=Kp_fdn×(f-fdn_min) (7)
wherein f isdn_minThe minimum value of the grid-connected point frequency is obtained;
comparing the grid-connected point frequency with an under-frequency hysteresis threshold value: if the grid-connected point frequency is smaller than the lower-frequency hysteresis threshold value, the active output decrement P is determinedfdn_maxCorrecting an active power reference value of the photovoltaic power station, and sending an active control instruction to each photovoltaic inverter in the photovoltaic power station according to the corrected active power reference value;
the modified active power reference value is shown as the following formula (8):
Ppoi_ref=Ppoi_ref0+Pfdn_max (8)。
in a second aspect, the technical solution of the frequency adjustment system for a photovoltaic power station in the present invention is:
the system comprises:
the active power regulating module is used for calculating an active output regulating quantity of the photovoltaic power station according to the grid-connected point frequency of the photovoltaic power station and correcting an active power reference value of the photovoltaic power station according to the active output regulating quantity; and performing active power regulation on the photovoltaic power station;
and the frequency hysteresis adjusting module is used for acquiring the grid-connected point frequency of the photovoltaic power station after the active power adjusting module adjusts the active power, and adjusting the frequency hysteresis of the power grid according to the grid-connected point frequency.
Further, the invention provides a preferable technical scheme as follows: the active power regulating module comprises an active output regulating quantity calculating unit and an active power reference value correcting unit; the active output adjustment quantity calculation unit comprises an active output decrement calculation model and an active output increment calculation model;
the active output reduction calculation model is represented by the following formula (9):
Pfup=Kp_fup×(f-fup) (9)
wherein f > fup,fupIs the upper limit value, K, of the grid-connected point frequencyp_fupIs a proportionality coefficient;
the active output increment calculation model is shown as the following formula (10):
Pfdn=Kp_fdn×(fdown-f) (10)
wherein f is less than fdown,fdownTo a lower limit value of the grid-connection point frequency, Kp_fdnIs a proportionality coefficient;
the calculation model of the active power reference value correction unit is shown as the following formula (11):
wherein, Ppoi_ref0Is the initial value of the active power reference value.
Further, the invention provides a preferable technical scheme as follows: the active power regulating module comprises a first comparing unit, an active power reducing regulating unit and an active power increasing regulating unit;
the first comparison unit is used for comparing the grid-connected point frequency and the threshold thereof: if the grid-connected point frequency is larger than the upper limit value of the grid-connected point frequency, the active power reduction adjusting unit performs active power reduction adjustment on the photovoltaic power station; if the grid-connected point frequency is smaller than the lower limit value of the grid-connected point frequency, the active power increasing and adjusting unit performs active power increasing and adjusting on the photovoltaic power station;
the active power reduction adjusting unit is configured to compare the corrected active power reference value and a lower limit value thereof: if the active power reference value is larger than the lower limit value, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the active power reference value; otherwise, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the lower limit value of the active power reference value;
the active power increase adjusting unit is used for comparing the corrected active power reference value and the upper limit value thereof: if the active power reference value is smaller than the upper limit value, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the active power reference value; otherwise, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the upper limit value of the active power reference value.
Further, the invention provides a preferable technical scheme as follows: the frequency hysteresis regulating module comprises a second comparing unit, an over-frequency hysteresis regulating unit and an under-frequency hysteresis regulating unit;
the second comparison unit is used for comparing the grid-connected point frequency and the threshold thereof: if the frequency of the grid-connected point is greater than the upper limit value of the grid-connected point, the over-frequency hysteresis regulating unit carries out over-frequency hysteresis regulation on the power grid; and if the frequency of the grid-connected point is smaller than the lower limit value of the grid-connected point, the under-frequency hysteresis regulating unit carries out under-frequency hysteresis regulation on the power grid.
Further, the invention provides a preferable technical scheme as follows:
the over-frequency hysteresis adjusting unit includes: the over-frequency grid connection point trend judgment subunit and the over-frequency active power regulation subunit are connected with the power supply;
the over-frequency grid-connected point trend judgment subunit is used for judging whether the grid-connected point frequency continues to rise or not: if the active power is increased, controlling an active power adjusting module to continuously perform active power reduction adjustment on the photovoltaic power station; otherwise, calculating the active output reduction of the photovoltaic power station corresponding to the maximum value of the grid-connected point frequency;
the over-frequency active power regulating subunit is used for comparing the grid-connected point frequency with an over-frequency hysteresis threshold value: and if the grid-connected point frequency is greater than the over-frequency hysteresis threshold, correcting the active power reference value of the photovoltaic power station according to the active power output reduction calculated by the over-frequency grid-connected point trend judgment subunit, and sending an active control instruction to each photovoltaic inverter in the photovoltaic power station according to the corrected active power reference value.
Further, the invention provides a preferable technical scheme as follows:
the under-frequency grid-connected point trend judgment subunit is used for judging whether the grid-connected point frequency continues to decrease: if the active power of the photovoltaic power station is reduced, controlling an active power adjusting module to continuously increase and adjust the active power of the photovoltaic power station; otherwise, calculating the active output reduction of the photovoltaic power station corresponding to the minimum value of the grid-connected point frequency;
the under-frequency active power regulating subunit is used for comparing the grid-connected point frequency with an under-frequency hysteresis threshold value: and if the grid-connected point frequency is smaller than the under-frequency hysteresis threshold, correcting the active power reference value of the photovoltaic power station according to the active power output reduction calculated by the under-frequency grid-connected point trend judgment subunit, and sending an active control instruction to each photovoltaic inverter in the photovoltaic power station according to the corrected active power reference value.
Compared with the closest prior art, the invention has the beneficial effects that:
1. according to the photovoltaic power station frequency adjusting method, the active output adjusting quantity of the photovoltaic power station is calculated through the grid-connected point frequency, the active output of the photovoltaic power station can be reduced or increased when the grid-connected point frequency exceeds the limit, and the power grid frequency is supported to be restored to the normal operation range; meanwhile, the frequency hysteresis adjustment can be carried out on the power grid according to the frequency of the grid-connected point, and the power grid frequency is controlled in a hysteresis interval, so that the supporting strength of the power grid frequency is increased.
2. According to the photovoltaic power station frequency adjusting system, the active power adjusting module can reduce or increase the active output of a photovoltaic power station when the grid-connected point frequency exceeds the limit, and the power grid frequency is supported to recover to a normal operation range; the frequency hysteresis adjusting module can carry out frequency hysteresis adjustment on the power grid according to the grid-connected point frequency, and controls the power grid frequency in a hysteresis interval to increase the supporting strength of the power grid frequency.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The following describes a method for adjusting the frequency of a photovoltaic power station according to an embodiment of the present invention with reference to the accompanying drawings.
The method for adjusting the power grid frequency in the embodiment of the invention can comprise the following steps:
step S101: and calculating the active power output regulating quantity of the photovoltaic power station according to the grid-connected point frequency of the photovoltaic power station, and correcting the active power reference value of the photovoltaic power station according to the active power output regulating quantity.
Step S102: and carrying out active power regulation on the photovoltaic power station according to the grid-connected point frequency and the active power reference value.
Step S103: and acquiring the grid-connected point frequency after the active power of the photovoltaic power station is regulated, and regulating the frequency hysteresis of the power grid according to the grid-connected point frequency.
In this embodiment, the active power output adjustment amount of the photovoltaic power station is calculated through the grid-connected point frequency, so that the active power output of the photovoltaic power station can be reduced or increased when the grid-connected point frequency is out of limit, and the grid frequency is supported to be restored to a normal operation range. Meanwhile, the frequency hysteresis adjustment can be carried out on the power grid according to the frequency of the grid-connected point, and the power grid frequency is controlled in a hysteresis interval, so that the supporting strength of the power grid frequency is increased.
Fig. 1 is a schematic flow chart of an implementation of a method for adjusting a frequency of a photovoltaic power station according to an embodiment of the present invention, as shown in the figure, in this embodiment:
further, in step S101, calculating the active power output adjustment amount of the photovoltaic power station according to the grid-connected point frequency of the photovoltaic power station may be implemented by the following steps:
comparing the grid-connected point frequency and a threshold value thereof:
if f > fupThen, the active power output of the photovoltaic power station is reduced by the following formula (1):
Pfup=Kp_fup×(f-fup) (1)
if f is less than fdownThen, the active output increase of the photovoltaic power station is shown as the following formula (2):
Pfdn=Kp_fdn×(fdown-f) (2)
wherein f is the frequency of the grid connection point, fupAnd fdownUpper and lower limits, K, of the grid-connected point frequency, respectivelyp_fupAnd Kp_fdnAll are proportionality coefficients.
Further, the step S101 of correcting the active power reference value of the photovoltaic power station may be implemented by the following steps:
comparing the grid-connected point frequency and a threshold value thereof:
if f > fupThen, the corrected active power reference value is shown as the following formula (3):
Ppoi_ref=Ppoi_ref0-Pfup (3)
if f is less than fdownThen, the corrected active power reference value is shown as the following formula (4):
Ppoi_ref=Ppoi_ref0+Pfdn (4)
wherein, Ppoi_ref0Is the initial value of the active power reference value.
Further, step S102 may further include the following steps.
The active power regulation in this embodiment may include an active power reduction regulation and an active power increase regulation. Carrying out active power regulation to the photovoltaic power station includes:
comparing the grid-connected point frequency and a threshold value thereof: if f > fupPerforming active power reduction adjustment on the photovoltaic power station; if f is less than fdownThe photovoltaic plant is subject to active power augmentation regulation. Wherein,
1. active power reduction regulation for photovoltaic power stations
Comparing the active power reference value corrected in step S101 with its lower limit value: if the active power reference value is larger than the lower limit value, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the active power reference value; otherwise, an active power control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the lower limit value of the active power reference value, and each photovoltaic inverter operates according to the received active power control instruction, where the active power control instruction in this embodiment includes an expected value of the output power of each inverter.
2. Active power increase regulation for photovoltaic power stations
Comparing the active power reference value corrected in step S101 with its upper limit value: if the active power reference value is smaller than the upper limit value, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the active power reference value; otherwise, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the upper limit value of the active power reference value, and each photovoltaic inverter operates according to the received active control instruction.
Further, in this embodiment, the step S103 of adjusting the frequency hysteresis of the power grid according to the frequency of the grid-connected point may be implemented by the following steps:
1. and acquiring the maximum value of the active output adjustment quantity.
The maximum value of the active power output adjustment amount in this embodiment refers to the maximum value of the active power output that needs to be reduced or increased, and may be determined according to the frequency variation trend of the grid-connected point.
2. Comparing the grid-connected point frequency and a hysteresis threshold thereof: and if the grid-connected point frequency does not reach a hysteresis threshold value, correcting the active power reference value according to the maximum value of the active power output regulating quantity, sending an active control instruction to each photovoltaic inverter in the photovoltaic power station according to the corrected active power reference value, and operating each photovoltaic inverter according to the received active control instruction.
In this embodiment, the frequency hysteresis adjustment includes an over-frequency hysteresis adjustment and an under-frequency hysteresis adjustment, and the frequency hysteresis adjustment of the power grid according to the grid-connected point frequency includes comparing the grid-connected point frequency and a threshold thereof: if f > fupPerforming over-frequency hysteresis regulation on the power grid; if f is less than fdownThe grid makes an under-frequency hysteretic adjustment. These two hysteresis adjusting methods are specifically described below.
1. Over-frequency hysteresis regulation
(1) Judging whether the grid-connected point frequency after the active power reduction adjustment of the photovoltaic power station is continuously increased or not: if the power is increased, continuously performing active power reduction adjustment on the photovoltaic power station, namely returning to the step S102; otherwise, acquiring the maximum value of the grid-connected point frequency and calculating the active output reduction of the photovoltaic power station corresponding to the maximum value according to the following formula;
Pfup_max=Kp_fup×(f-fup_max) (5)
wherein f isup_maxThe maximum value of the grid-connected point frequency.
(2) Comparing the grid-connected point frequency with an over-frequency hysteresis threshold value: if the grid-connected point frequency is greater than the over-frequency hysteresis threshold value, the active output reduction P is determinedfup_maxAnd correcting the active power reference value of the photovoltaic power station, sending an active control instruction to each photovoltaic inverter in the photovoltaic power station according to the corrected active power reference value, and operating each photovoltaic inverter according to the received active control instruction.
The corrected active power reference value is shown as the following formula (6):
Ppoi_ref=Ppoi_ref0-Pfup_max (6)。
FIG. 2 is a schematic diagram of an over-frequency hysteresis adjustment curve according to an embodiment of the present invention, as shown in the drawing, f in this embodimentupIs the upper limit value of the grid-connected point frequency, fup_stopFor the over-frequency hysteresis threshold, when the grid-connected point frequency f is more than fupCarrying out active power reduction regulation on the photovoltaic power station according to the active power reference value calculated by the formula (3) so as to enable the frequency f of the grid-connected pointup_stop<f<fupAnd at the moment, the power grid is subjected to over-frequency hysteresis adjustment, so that the maximum strength support of active power is always kept before the frequency of the power grid returns to the over-frequency hysteresis threshold, and therefore the method can be suitable for the power grid with higher photovoltaic power generation permeability.
2. Under-frequency hysteresis regulation
(1) Judging whether the grid-connected point frequency after the active power increase adjustment of the photovoltaic power station continuously drops or not: if the power level decreases, the active power increase and adjustment of the photovoltaic power station are continuously carried out, namely the step S102 is returned; otherwise, acquiring the minimum value of the grid-connected point frequency and calculating the active output reduction of the photovoltaic power station corresponding to the minimum value according to the following formula;
Pfdn_min=Kp_fdn×(f-fdn_min) (7)
wherein f isdn_minIs the minimum value of the grid-connected point frequency.
(2) Comparing the grid-connected point frequency with the under-frequency hysteresis threshold value: if the grid-connected point frequency is less than the lower frequency hysteresis threshold value, the active output reduction P is determinedfdn_maxAnd correcting the active power reference value of the photovoltaic power station, sending an active control instruction to each photovoltaic inverter in the photovoltaic power station according to the corrected active power reference value, and operating each photovoltaic inverter according to the received active control instruction.
The corrected active power reference value is shown as the following formula (8):
Ppoi_ref=Ppoi_ref0+Pfdn_max (8)。
FIG. 3 is a diagram illustrating an under-frequency hysteresis adjustment curve according to an embodiment of the present invention, as shown in the drawing, f in this embodimentdnIs the lower limit value of the grid-connected point frequency, fdn_stopIs owed toFrequency hysteresis threshold, when the frequency f of the grid-connected point is less than fdnCarrying out active power increase adjustment on the photovoltaic power station according to the active power reference value calculated by the formula (4) so as to enable the frequency f of the grid-connected pointdn<f<fdn_stopAnd at the moment, the power grid is subjected to under-frequency hysteresis regulation, so that the maximum strength support of active power is always kept before the frequency of the power grid returns to the over-frequency hysteresis threshold, and therefore, the method can be suitable for the power grid with higher photovoltaic power generation permeability.
Compared with the traditional frequency droop control method, the power grid frequency adjusting method in the embodiment of the invention has larger active-frequency supporting force on the power grid, the hysteresis point is set on the basis of the original single threshold value, and the maximum force supporting of the active power is always kept before the power grid frequency returns to the hysteresis point, so that the method can be suitable for the power grid with higher photovoltaic power generation permeability.
The invention also provides a photovoltaic power station frequency adjusting system and provides a specific embodiment.
The power grid frequency regulation system in the embodiment comprises an active power regulation module and a frequency hysteresis regulation module. Wherein,
the active power regulating module is used for calculating an active output regulating quantity of the photovoltaic power station according to the grid-connected point frequency of the photovoltaic power station and correcting an active power reference value of the photovoltaic power station according to the active output regulating quantity; and carrying out active power regulation on the photovoltaic power station.
And the frequency hysteresis adjusting module is used for acquiring the grid-connected point frequency after the active power adjusting module adjusts the active power of the photovoltaic power station, and adjusting the frequency hysteresis of the power grid according to the grid-connected point frequency.
In the embodiment, the active power adjusting module calculates the active output adjusting quantity of the photovoltaic power station through the grid-connected point frequency, so that the active output of the photovoltaic power station can be reduced or increased when the grid-connected point frequency exceeds the limit, and the grid frequency is supported to be restored to the normal operation range; the frequency hysteresis adjusting module can carry out frequency hysteresis adjustment on the power grid according to the grid-connected point frequency, and controls the power grid frequency in a hysteresis interval to increase the supporting strength of the power grid frequency.
Further, the active power adjusting module in this embodiment may further include the following structure.
The active power adjusting module in the embodiment includes an active power output adjustment amount calculating unit, an active power reference value correcting unit, a first comparing unit, an active power reducing adjusting unit, and an active power increasing adjusting unit. Wherein,
1. active power output regulating quantity calculating unit
In this embodiment, the active power output adjustment amount calculation unit includes an active power output decrease amount calculation model and an active power output increase amount calculation model.
(1) The active output reduction calculation model is shown in the following equation (9):
Pfup=Kp_fup×(f-fup) (9)
(2) the active output increase calculation model is shown in the following equation (10):
Pfdn=Kp_fdn×(fdown-f) (10)
2. active power reference value correction unit
The calculation model of the active power reference value correction unit in this embodiment is shown as the following formula (11):
wherein, Ppoi_ref0Is the initial value of the active power reference value.
3. First comparing unit
In this embodiment, the first comparing unit is configured to compare the grid-connected point frequency and the threshold thereof. If the grid-connected point frequency is larger than the upper limit value of the grid-connected point frequency, the active power reduction adjusting unit performs active power reduction adjustment on the photovoltaic power station; and if the grid-connected point frequency is smaller than the lower limit value, the active power increasing and adjusting unit increases and adjusts the active power of the photovoltaic power station.
4. Active power reduction regulating unit
In this embodiment, the active power reduction adjusting unit is configured to compare the active power reference value corrected by the active power reference value correcting unit and the lower limit value thereof: if the active power reference value is larger than the lower limit value, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the active power reference value; otherwise, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the lower limit value of the active power reference value.
5. Active power increase regulating unit
In this embodiment, the active power increase adjusting unit is configured to compare the active power reference value modified by the active power reference value modifying unit and the upper limit value thereof: if the active power reference value is smaller than the upper limit value, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the active power reference value; otherwise, an active control instruction is sent to each photovoltaic inverter in the photovoltaic power station according to the upper limit value of the active power reference value.
Further, the frequency hysteresis adjusting module in this embodiment may further include the following structure.
In this embodiment, the frequency hysteresis adjusting module includes a second comparing unit, an over-frequency hysteresis adjusting unit, and an under-frequency hysteresis adjusting unit. Wherein,
1. second comparing unit
The second comparing unit in this embodiment is configured to compare the grid-connected point frequency and the threshold thereof: if the frequency of the grid-connected point is greater than the upper limit value of the grid-connected point, the over-frequency hysteresis regulating unit carries out over-frequency hysteresis regulation on the power grid; and if the grid-connected point frequency is smaller than the lower limit value, the under-frequency hysteresis regulating unit performs under-frequency hysteresis regulation on the power grid.
2. Over-frequency hysteresis regulating unit
In this embodiment, the overfrequency hysteretic regulation unit includes an overfrequency grid connection point trend judgment subunit and an overfrequency active power regulation subunit, and specifically includes:
(1) over-frequency grid connection point trend judgment subunit
The over-frequency grid-connected point trend judging subunit is used for judging whether the grid-connected point frequency continues to rise or not: if the active power is increased, controlling an active power reduction and adjustment unit to continuously perform active power reduction and adjustment on the photovoltaic power station; otherwise, calculating the active output reduction of the photovoltaic power station corresponding to the maximum value of the grid-connected point frequency.
(2) Over-frequency active power regulating subunit
The over-frequency active power regulating subunit is used for comparing the grid-connected point frequency with an over-frequency hysteresis threshold value: and if the grid-connected point frequency is greater than the over-frequency hysteresis threshold, correcting the active power reference value of the photovoltaic power station according to the active power output reduction calculated by the over-frequency grid-connected point trend judgment subunit, and sending an active control instruction to each photovoltaic inverter in the photovoltaic power station according to the corrected active power reference value.
3. Under-frequency hysteresis regulating unit
In this embodiment, the under-frequency hysteresis adjusting unit includes an under-frequency grid-connected point trend determining subunit and an under-frequency active power adjusting subunit, and specifically includes:
(1) sub-unit for judging trend of under-frequency grid-connected points
And the under-frequency grid-connected point trend judgment subunit is used for judging whether the grid-connected point frequency continuously decreases: if the active power is reduced, controlling an active power increasing and adjusting unit to continuously increase and adjust the active power of the photovoltaic power station; otherwise, calculating the active output reduction of the photovoltaic power station corresponding to the minimum value of the grid-connected point frequency.
(2) Sub-unit for adjusting active power under frequency
The under-frequency active power regulating subunit is used for comparing the grid-connected point frequency with an under-frequency hysteresis threshold value: and if the grid-connected point frequency is smaller than the under-frequency hysteresis threshold, correcting the active power reference value of the photovoltaic power station according to the active power output reduction calculated by the under-frequency grid-connected point trend judgment subunit, and sending an active control instruction to each photovoltaic inverter in the photovoltaic power station according to the corrected active power reference value.
The power grid frequency adjusting system in the embodiment of the invention has larger active-frequency supporting force on the power grid, the hysteresis point is arranged on the basis of the original single threshold value, and the maximum force supporting of the active power is always kept before the power grid frequency returns to the hysteresis point, so that the power grid frequency adjusting system can be suitable for the power grid with higher photovoltaic power generation permeability.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.