Energy storage auxiliary photovoltaic unit frequency modulation control method and device under multiple working conditions

Abstract

The application is suitable for the technical field of data processing, and provides a frequency modulation control method, device and terminal equipment of energy storage auxiliary photovoltaic unit under multiple working conditions. The frequency modulation control method comprises the following steps: acquiring photovoltaic grid-connected point data; confirming that the photovoltaic unit is in a low-voltage ride-through process based on the photovoltaic grid-connected point data and low-voltage ride-through requirements of the photovoltaic unit; the low-voltage ride-through process comprises a normal operation stage, a fault stage and a fault recovery stage; if the photovoltaic unit is in the fault stage, a first frequency modulation control strategy is started; if the photovoltaic unit is in the fault recovery stage, different first, second and third frequency modulation control strategies are started according to whether the frequency offset of the photovoltaic unit system exceeds the frequency modulation dead zone and whether the energy storage system assists inertia support. The frequency modulation control method is suitable for both the scene of frequency change caused by power fluctuation and the scene of frequency change caused by fault disturbance, and effectively improves the system frequency stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy, and particularly relates to a method and device for frequency regulation control of a photovoltaic unit assisted by energy storage under multiple working conditions. BACKGROUND

[0002] In view of the phenomenon that photovoltaic units are prone to off-grid under fault disturbance, the Chinese national standard GB / T 19964-2012 stipulates that, when suffering from low-voltage fault, the photovoltaic unit should be able to ensure off-grid operation within a certain voltage drop range and time range.

[0003] Existing data has researched photovoltaic low-voltage ride-through control strategies, thereby reducing the risk of photovoltaic unit off-grid under power grid fault; however, there are few researches on how to improve the frequency stability of the system after suffering from fault.

[0004] Existing data has researched the control strategies of active and reactive currents during low-voltage ride-through for photovoltaic high-penetration systems with prominent frequency stability problems; and researched the photovoltaic power generation characteristics during fault and recovery process, thereby improving the control strategies of photovoltaic units. However, the existing fault ride-through control methods focus on the reactive power support during fault ride-through and the active power recovery rate during fault recovery, and do not focus on the frequency regulation under fault.

[0005] In a large-scale photovoltaic grid-connected system, although the photovoltaic unit has realized fault ride-through and can provide voltage support to the system, the problem of transient frequency drop of the system is serious. If the photovoltaic system does not participate in frequency regulation during fault, with the increase of photovoltaic penetration, the frequency stability of the system becomes poor, and the frequency drop may be so serious that the system low-frequency load shedding protection is triggered, causing power failure.

[0006] At present, the methods for enabling photovoltaic power stations to have frequency regulation capability mainly include reserving active reserve or configuring energy storage devices, and using corresponding active control systems to realize primary frequency regulation and inertia support. It should be noted that, limited by the step length of the power tracking algorithm and the second-level response speed, the inertia support effect of the active reserve scheme is weak, and it is difficult to implement in actual engineering. There is an urgent need for a method that enables photovoltaic units to have frequency regulation capability under fault disturbance working conditions. SUMMARY

[0007] To overcome the problems in the related art, the embodiments of the present application provide a method and device for frequency regulation control of a photovoltaic unit assisted by energy storage under multiple working conditions, which can be used not only in the frequency change scene caused by power fluctuation, but also in the frequency change scene caused by fault disturbance, thereby improving the frequency stability of the system.

[0008] The application is implemented by the following technical solutions:

[0009] In a first aspect, embodiments of the present application provide a method for frequency regulation control of a photovoltaic (PV) unit assisted by an energy storage system under multiple operating conditions, comprising:

[0010] acquiring data of a grid-connected point of the PV unit;

[0011] confirming that the PV unit is in a low voltage ride through (LVRT) process based on the data of the grid-connected point of the PV unit and a LVRT requirement of the PV unit; the LVRT process comprises a normal operation stage, a fault stage and a fault recovery stage;

[0012] in the LVRT process, if the PV unit is in the fault stage, starting a first frequency regulation control strategy;

[0013] if the PV unit is in the fault recovery stage, starting different first, second and third frequency regulation control strategies according to whether a frequency deviation of the PV unit system exceeds a frequency regulation dead zone and whether the energy storage system assists inertia support.

[0014] In a possible implementation manner of the first aspect, the acquiring of the data of the grid-connected point of the PV unit comprises:

[0015] acquiring a voltage of the grid-connected point of the PV unit and a system frequency;

[0016] measuring a current system frequency deviation and a change rate of the current system frequency based on the current system frequency;

[0017] calculating a difference between the voltage of the grid-connected point of the PV unit and a voltage reference of the grid-connected point of the PV unit.

[0018] In a possible implementation manner of the first aspect, the fault stage is from a voltage drop time point of the grid-connected point of the PV unit to a voltage recovery time point at which the voltage of the grid-connected point of the PV unit recovers to a preset voltage, and the fault recovery stage is from the voltage recovery time point at which the voltage of the grid-connected point of the PV unit recovers to the preset voltage to a time point at which the system recovers to a normal operation voltage; the normal operation voltage is a voltage in the normal operation stage.

[0019] The preset voltage is obtained based on a voltage reference of the grid-connected point of the PV unit.

[0020] In a possible implementation manner of the first aspect, if the PV unit is in the fault stage, the starting of the first frequency regulation control strategy comprises:

[0021] adjusting a voltage of the PV power station, and the energy storage system does not assist frequency regulation of the PV unit; the energy storage system performs constant power charging to keep energy storage power at a preset maximum energy storage power;

[0022] in the charging process, if the energy storage power is greater than the preset maximum energy storage power, stopping the charging;

[0023] The first frequency modulation control strategy is a frequency modulation control strategy for the energy storage auxiliary photovoltaic unit under fault.

[0024] In a possible implementation manner of the first aspect, if the photovoltaic unit is in the fault recovery stage, determining whether the system frequency deviation exceeds a frequency modulation dead zone comprises:

[0025] When the system frequency deviation is greater than the preset frequency range, the system frequency deviation exceeds the frequency modulation dead zone;

[0026] When the system frequency deviation is less than or equal to the preset frequency range, the system frequency deviation does not exceed the frequency modulation dead zone.

[0027] In a possible implementation manner of the first aspect, if the system frequency deviation does not exceed the frequency modulation dead zone, the first frequency modulation control strategy is started.

[0028] In a possible implementation manner of the first aspect, if the system frequency deviation exceeds the frequency modulation dead zone, it is determined whether the energy storage system assists inertia support, and the second frequency modulation control strategy and the third frequency modulation control strategy are started.

[0029] The determination of whether the energy storage system assists inertia support and the starting of the second frequency modulation control strategy and the third frequency modulation control strategy comprise:

[0030] If the energy storage system does not assist inertia support, the second frequency modulation control strategy is started.

[0031] The second frequency modulation control strategy comprises:

[0032] The energy storage system assists the photovoltaic unit to perform primary frequency modulation, and the energy storage system discharges according to a primary frequency modulation power; the primary frequency modulation power is determined based on a product of a primary frequency modulation coefficient and the frequency deviation.

[0033] If the energy storage system assists inertia support, the third frequency modulation control strategy is started.

[0034] The third frequency modulation control strategy comprises:

[0035] The energy storage system assists the photovoltaic unit to perform primary frequency modulation and inertia support, and the energy storage system discharges according to a sum of a primary frequency modulation power reference value and an inertia support power reference value; the primary frequency modulation power is determined based on a product of a primary frequency modulation coefficient and the frequency deviation; and the inertia support power is determined based on a product of a virtual inertia coefficient and the frequency differential.

[0036] If the energy storage power is less than or equal to a preset minimum energy storage power during the discharging process, the discharging is stopped.

[0037] The frequency offset exceeds the frequency modulation dead zone, and is caused by load fluctuation.

[0038] The second frequency modulation control strategy and the third frequency modulation control strategy are frequency modulation control strategies for the energy storage system assisting the photovoltaic unit under load fluctuation.

[0039] In a second aspect, the embodiments of the present application provide a device for frequency modulation control of a photovoltaic unit assisted by energy storage under multiple working conditions, comprising: an acquisition module configured to acquire photovoltaic grid point data;

[0040] A confirmation module is configured to confirm, based on the photovoltaic grid point data and a low voltage ride through requirement of a photovoltaic unit, that the photovoltaic unit is in a low voltage ride through process; the low voltage ride through process comprises a normal operation stage, a fault stage and a fault recovery stage.

[0041] A first control module is configured to, in the low voltage ride through process, if the photovoltaic unit is in the fault stage, start a first frequency modulation control strategy.

[0042] A second control module is configured to, if the photovoltaic unit is in the fault recovery stage, start different first frequency modulation control strategies, second frequency modulation control strategies and third frequency modulation control strategies according to whether a frequency offset of the photovoltaic unit system exceeds a frequency modulation dead zone and whether an energy storage system assists inertia support.

[0043] In a third aspect, the embodiments of the present application provide a terminal device, comprising a memory and a processor, the memory stores a computer program capable of running on the processor, and the processor implements the method for frequency modulation control of a photovoltaic unit assisted by energy storage under multiple working conditions according to any one of the first aspect when executing the computer program.

[0044] In a fourth aspect, the embodiments of the present application provide a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the method for frequency modulation control of a photovoltaic unit assisted by energy storage under multiple working conditions according to any one of the first aspect.

[0045] In a fifth aspect, the embodiments of the present application provide a computer program product, which, when running on a terminal device, enables the terminal device to execute the method according to any one of the first aspect.

[0046] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0047] The embodiment of the present application proposes a frequency modulation strategy of energy storage assisting photovoltaic unit, which can improve the frequency stability of the system, and further improve the frequency stability of the system, by judging whether the frequency offset of the system exceeds the frequency modulation dead zone and whether the energy storage system assists inertia support in different stages of the low voltage ride through process of the photovoltaic unit.

[0048] It can be understood that the beneficial effects of the above-mentioned second aspect to the fifth aspect can be referred to the related description in the first aspect, which will not be repeated here.

[0049] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present specification. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0051] Figure 1 is a flowchart of the frequency modulation control method provided by an embodiment of the present application;

[0052] Figure 2 is a control block diagram of the light storage system provided by an embodiment of the present application;

[0053] Figure 3 is a control model diagram of the energy storage device provided by an embodiment of the present application;

[0054] Figure 4 is a control flowchart of the energy storage assisting photovoltaic unit frequency modulation provided by an embodiment of the present application;

[0055] Figure 5 is a total model diagram of the light storage system provided by an embodiment of the present application;

[0056] Figure 6 is a frequency response curve diagram when the system adopts different control strategies under load fluctuation provided by an embodiment of the present application;

[0057] Figure 7 is a frequency response curve diagram when the system adopts different control strategies under fault disturbance provided by an embodiment of the present application;

[0058] Figure 8 is a structural schematic diagram of the energy storage assisting photovoltaic unit frequency modulation control device provided by an embodiment of the present application;

[0059] Figure 9 is a structural schematic diagram of the terminal device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0060] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known methods, devices, circuits, and

[0061] It will be understood that the terms "comprises" and / or "comprising," when used in this specification, include the presence of one or more features, integers, steps, operations, elements, and / or components described in the specification, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0062] It will be understood that the term "and / or," when used in the specification and in the following claims, is intended to mean one or more of the associated listed items can be present, and includes the possibilities of one or more of the associated listed items being present, and all possible combinations of the associated listed items.

[0063] As used in the specification and in the claims, the term "if can be interpreted as meaning "when," or "once," or "in response to a determination," or "in response to a detection" depending on the context. Similarly, the phrase "if it is determined" or "if [a described condition or event] is detected" can be interpreted as meaning "once it is determined" or "in response to the determination," or "once [the described condition or event] is detected" or "in response to the detection [of the described condition or event]," depending on the context.

[0064] In addition, the terms "first," "second," "third," etc. as used in the description and the claims of this specification are used as identifiers to distinguish between different features, steps, etc. and are not intended to signify relative importance or order of.

[0065] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present application. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" or "in some embodiments" or "in other embodiments" or "in still other embodiments," etc. in various places throughout this specification are not necessarily all referring to the same embodiment, unless otherwise specifically so stated. Furthermore, the term "comprising" or "containing" or "including" or "having" or "comprises" or "contains" or "includes" or "has" as used in this specification, is specifically intended to mean "including, but not limited to," unless otherwise specifically indicated otherwise.

[0066] In large-scale photovoltaic grid-connected systems, although photovoltaic unit fault ride-through has been achieved and can provide voltage support to the system, the problem of system transient frequency drop is serious. If the photovoltaic system does not participate in frequency modulation during the fault, with the increase of photovoltaic penetration, the system frequency stability becomes poor, and the frequency drop may be so serious that the system low-frequency load shedding protection is triggered, causing power failure.

[0067] Currently, the methods for photovoltaic power station to have frequency modulation capability mainly include reserving active reserve or configuring energy storage devices, and using corresponding active control system to realize primary frequency modulation and inertia support. It should be pointed out that, limited by the step length and second-level response speed of the power tracking algorithm, the inertia support effect that can be achieved by the active reserve scheme is weak, and it is difficult to implement in actual engineering. There is an urgent need for a method that can enable photovoltaic units to have frequency modulation capability under fault disturbance conditions.

[0068] Based on the above problems, a multi-condition energy storage assisted photovoltaic unit frequency modulation control method is provided in the embodiments of the present application, which comprises: acquiring photovoltaic grid-connected point data; confirming that the photovoltaic unit is in a low voltage ride-through process based on the photovoltaic grid-connected point data and the low voltage ride-through requirement of the photovoltaic unit; the low voltage ride-through process includes a normal operation stage, a fault stage and a fault recovery stage; if the photovoltaic unit is in the fault stage, a first frequency modulation control strategy is started; if the photovoltaic unit is in the fault recovery stage, different first, second and third frequency modulation control strategies are started according to whether the frequency offset of the photovoltaic unit system exceeds the frequency modulation dead zone and whether the energy storage system assists the inertia support. The method improves the system frequency stability by the energy storage assisted photovoltaic unit frequency modulation strategy, thereby improving the system frequency stability.

[0069] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0070] Figure 1 is a schematic flow chart of the energy storage assisted photovoltaic unit frequency modulation control method provided by an embodiment of the present application, referring to Figure 1 The detailed description of the energy storage assisted photovoltaic unit frequency modulation control method is as follows:

[0071] In step 101, photovoltaic grid-connected point data is acquired.

[0072] Specifically, the photovoltaic grid-connected point data is acquired, including: acquiring photovoltaic grid-connected point voltage U and system frequency f; based on the current system frequency f, calculating the current system frequency offset Δf and the change rate df / dt of the current system frequency; calculating the difference U between the photovoltaic grid-connected point voltage and the photovoltaic grid-connected point voltage standard value N .

[0073] The system frequency offset Δf is the difference between the current system frequency f and the rated frequency f N .

[0074] In step 102, based on the photovoltaic grid-connected point data and the low voltage ride-through requirement of the photovoltaic unit, it is determined that the photovoltaic unit is in a low voltage ride-through process; the low voltage ride-through process includes a normal operation phase, a fault phase and a fault recovery phase.

[0075] Specifically, from the moment of photovoltaic grid-connected point voltage drop to the moment of voltage recovery to the preset voltage, it is the fault phase; from the moment of voltage recovery to the preset voltage to the moment of system recovery to the normal operation voltage, it is the fault recovery phase; the normal operation voltage is the voltage of the normal operation phase; the preset voltage is obtained based on the photovoltaic grid-connected point voltage standard value.

[0076] The determination of whether the photovoltaic unit is in the low voltage ride-through process is made in combination with the low voltage ride-through requirement of the photovoltaic unit proposed in the Chinese national standard "Technical Regulation of Photovoltaic Power Station Access to Power System" GB / T19964-2012.

[0077] For example, from the moment of grid-connected point voltage drop to the moment of voltage recovery to 0.9pu, it is the fault period; from the moment of voltage recovery to 0.9pu to the moment of system recovery to the pre-fault operation level, it is the fault recovery phase; wherein pu is the photovoltaic grid-connected point voltage standard value.

[0078] In step 103, during the low voltage ride-through process, if the photovoltaic unit is in the fault phase, the first frequency modulation control strategy is started.

[0079] Specifically, if the photovoltaic unit is in the fault phase, the first frequency modulation control strategy is started, including: adjusting the photovoltaic power station voltage, the energy storage system does not assist the photovoltaic unit frequency modulation; the energy storage system performs constant power charging to keep the energy storage capacity at a preset maximum energy storage capacity; during the charging process, if the energy storage capacity is greater than the preset maximum energy storage capacity, the charging is stopped.

[0080] The above first frequency modulation control strategy is the energy storage assisted photovoltaic unit frequency modulation control strategy under fault.

[0081] For example, during the fault period, the grid voltage drops severely, and the active power output by the photovoltaic power station cannot be sent to the grid; and the national standard stipulates that the power station needs to provide dynamic reactive power support for the grid during the fault period to assist in the recovery of the fault voltage, the priority of voltage adjustment of the photovoltaic power station is higher than that of frequency adjustment, and the energy storage device does not need to assist the photovoltaic unit in frequency modulation. At this time, the energy storage system is charged at a constant power, that is, the energy storage power reference value P scref of the energy storage device is equal to the initial set power P sc0 of the supercapacitor energy storage device, so that the energy storage power SOC max remains at the maximum energy storage power SOC

[0082] In step 104, if the photovoltaic unit is in the fault recovery stage, different first frequency modulation control strategies, second frequency modulation control strategies and third frequency modulation control strategies are started according to whether the frequency deviation of the photovoltaic unit system exceeds the frequency modulation dead zone and whether the energy storage system assists the inertia support.

[0083] Specifically, if the photovoltaic unit is in the fault recovery stage, it is judged whether the frequency deviation Δf of the photovoltaic unit system exceeds the frequency modulation dead zone, including: when the system frequency deviation Δf is greater than the preset frequency range, the system frequency deviation Δf exceeds the frequency modulation dead zone; when the system frequency deviation Δf is less than or equal to the preset frequency range, the system frequency deviation does not exceed the frequency modulation dead zone.

[0084] Specifically, if the frequency deviation Δf of the photovoltaic unit system does not exceed the frequency modulation dead zone, the first frequency modulation control strategy is started.

[0085] Specifically, if the system frequency deviation Δf exceeds the frequency modulation dead zone, it is judged whether the energy storage system assists the inertia support, and the second frequency modulation control strategy and the third frequency modulation control strategy are started; whether the energy storage system assists the inertia support is judged, and the second frequency modulation control strategy and the third frequency modulation control strategy are started.

[0086] If the energy storage system does not assist the inertia support, the second frequency modulation control strategy is started. The second frequency modulation control strategy includes: the energy storage system assists the photovoltaic unit to perform primary frequency modulation, and the energy storage system discharges according to the primary frequency modulation power; the primary frequency modulation power is determined based on the product of the primary frequency modulation coefficient and the frequency deviation.

[0087] If the energy storage system assists the inertia support, the third frequency modulation control strategy is started. The third frequency modulation control strategy includes: the energy storage system assists the photovoltaic unit to perform primary frequency modulation and inertia support, and the energy storage system discharges according to the sum of the primary frequency modulation power reference value and the inertia support power reference value; the primary frequency modulation power is determined based on the product of the primary frequency modulation coefficient and the frequency deviation; and the inertia support power is determined based on the product of the virtual inertia coefficient and the frequency differential.

[0088] If the stored energy is less than or equal to the preset minimum stored energy during discharge, the discharge will stop. A frequency offset exceeding the frequency regulation dead zone is caused by load fluctuations; the third frequency regulation control strategy is an auxiliary frequency regulation control strategy for the energy storage system under load fluctuations.

[0089] For example, the system frequency offset exceeds the frequency regulation dead zone ±0.033Hz; during the fault recovery phase, the frequency cannot recover instantly like voltage but requires a period of time to rise. Furthermore, considering that inertia support will prevent the frequency from rising and inhibit rapid frequency recovery, only primary frequency regulation by the energy storage-assisted photovoltaic unit is needed to activate the second frequency regulation control strategy. The supercapacitor energy storage system adjusts the frequency regulation based on the primary frequency regulation power ΔP. sc1 Discharge occurs, i.e., P scref =ΔP sc1 ; where the primary frequency modulation power ΔP sc1 From the first frequency modulation coefficient k f The frequency deviation is determined by the product of the frequency offset Δf; when the frequency deviation exceeds the limit value Δf max When (d%PN / kf): ΔP sc1 =d%P N , Among them, d%P N This is for backup power for energy storage.

[0090] During the fault recovery phase, if the system frequency exceeds the frequency regulation dead zone due to load fluctuations, a third frequency regulation control strategy is activated to reduce quasi-steady-state frequency deviation and suppress rapid frequency drops. The energy storage system assists the photovoltaic unit in primary frequency regulation and inertia support. The energy storage system adjusts the primary frequency regulation power ΔP. sc1 and inertia support power ΔP sc2 The sum of these two quantities is used for discharge, i.e., P scref =ΔP sc1 +ΔP sc2 Primary frequency modulation power ΔP sc1 Based on the first frequency modulation coefficient k f The power is determined by the product of the frequency offset Δf and the inertia support power, which is based on the virtual inertia coefficient k. H The frequency offset is determined by the product of the system frequency derivative; the frequency offset Δf exceeds the frequency regulation dead zone, caused by load fluctuations; the third frequency regulation control strategy is the frequency regulation control strategy for energy storage-assisted photovoltaic units under load fluctuations. During discharge, if SOC ≤ SOC min Then the discharge will stop.

[0091] For example, the energy storage control strategy is a frequency modulation control strategy in which the energy storage device participates. The power obtained under the energy storage control strategy is used to control the DC-DC conversion between the photovoltaic system and the energy storage device, i.e., the supercapacitor energy storage device is connected to both ends of the DC capacitor of the photovoltaic unit through the DC / DC converter; the inverter of the photovoltaic unit also controls the DC-AC conversion, and finally the active power P LV of the photovoltaic storage system is output to the power grid. Figure 2 As shown in the control block diagram of the photovoltaic storage system.

[0092] For example, the energy storage device can be a supercapacitor energy storage device. In addition to participating in primary frequency modulation, the energy storage device can also provide fast inertia support power, as shown in Figure 3 , i.e., frequency deviation feedback is used for primary frequency modulation, and the primary frequency modulation power reference value ΔPsc1 is:

[0093]

[0094] where k f is the primary frequency modulation coefficient.

[0095] Inertia frequency modulation is performed using frequency differentiation, and the inertia support power reference value ΔP sc2 is:

[0096] ΔP sc2 = -k H df / dt

[0097] where k H is the virtual inertia coefficient, P N is the rated power of the photovoltaic inverter, and d%P N is the energy storage standby power.

[0098] For example, the output active reference value P scref of the energy storage device and the DC side voltage U SC of the energy storage device are used to calculate the target control current I L *, proportional-integral control, amplitude limiting, and modulation are performed based on the target control current I L * and the actual current I L , and the finally obtained power signal is used to control the DC / DC converter.

[0099] Since the inertia support plays a role in preventing frequency changes in the system, when the system frequency is lower than the normal value, the inertia support can prevent the frequency from continuing to drop but can inhibit the recovery of the frequency; when the system frequency is higher than the normal value, the inertia support can prevent the frequency from continuing to rise but can inhibit the frequency from falling back to the normal value. Therefore, under different working conditions, the role of the inertia support in improving the frequency stability of the system is different, and the energy storage device should also use different frequency modulation control strategies for different working conditions.

[0100] For example, the control process of energy storage assisting in frequency regulation of photovoltaic units, such as Figure 4 As shown. The system collects the photovoltaic grid-connected voltage U and system frequency f(k), calculates the current system frequency offset Δf and the rate of change of the current system frequency df / dt; and determines whether the photovoltaic unit is in a low-voltage ride-through process: the judgment condition is: 0≤U(k)≤0.9, and t(k)-t0≤t limit Where t0 is the instant the voltage drop occurs, t limit This represents the longest allowable voltage drop period. If the criteria are met, the photovoltaic unit is in a low-voltage ride-through process, and the energy storage system performs constant-power charging, i.e., the system's energy storage power reference value P. scref The initial set power P of the supercapacitor energy storage device sc0 Equal to maintain the SOC of the energy storage capacity at the maximum SOC of the energy storage capacity. max If SOC(k) exceeds the upper limit, then the system's energy storage power reference value P scref =0.

[0101] If the judgment condition is not met, then the system frequency offset Δf exceeds the frequency modulation dead zone of 0.033Hz; if the system frequency offset Δf does not exceed the frequency modulation dead zone of 0.033Hz, then the system's energy storage power reference value P... scref The initial set power P of the supercapacitor energy storage device sc0 Equal; if the system frequency offset Δf exceeds the frequency modulation dead zone of 0.033Hz, then use equation (2) to determine ΔP. sc1 =-k f Δf(0.033Hz≤|Δf|≤d%P N / k f Equations (3) and (4) ΔP sc1 =d%P N (|Δf|≥d%P N / k f Determine which interval the system frequency offset Δf falls within, and select the primary frequency modulation power reference value ΔPsc1 based on the interval range.

[0102] If the product of the frequency offset and the rate of frequency change is greater than zero, the energy storage system adjusts the frequency based on the primary frequency regulation power ΔP. sc1 Discharge occurs, i.e., P scref =ΔP sc1 Otherwise, the energy storage system will adjust the primary frequency regulation power ΔP. sc1 and inertia support power ΔP sc2 The sum of these two quantities is used for discharge, i.e., P scref =ΔP sc1 +ΔP sc2If SOC(k) exceeds the lower limit during discharge, i.e., SOC(k) ≤ SOC min Then discharge will stop. During the charging process, if SOC(k) > SOC max Then charging will stop.

[0103] For example, building a simulation system in Matlab / Simulink software such as Figure 5 The photovoltaic-storage system shown constructs a 66% high-penetration photovoltaic scenario, replacing the generator system with the photovoltaic-storage system for power generation. In this scenario, the system is subjected to faults and load surge disturbances. The fault disturbance is specifically set as L between bus 8 and bus 9. 22 A three-phase short-circuit fault occurred on the line at 17s, lasting for 250ms. The fault was cleared at 17.25s, and the line returned to normal operation. The specific disturbance caused by the sudden load increase was line L between bus 4 and bus 6. 13 The active power suddenly increased by 30MW at 55s.

[0104] For example, attached Figure 6 The graph shows the frequency response curves of the system under different control strategies during load fluctuations. As can be seen from the frequency response curves under the three control strategies, frequency regulation by energy storage-assisted photovoltaic (PV) units can significantly improve the system's frequency stability. When the energy storage-assisted PV system uses frequency regulation, the primary regulation coefficients of the two control strategies are the same, therefore the steady-state frequencies are the same, both higher than the steady-state frequencies of PV systems without energy storage participation. Since inertia can impede frequency descent, the control strategy of primary frequency regulation and inertia support by energy storage-assisted PV units not only provides primary frequency regulation power to improve frequency stability but also provides inertia support power to slow down the frequency drop rate. Therefore, under load disturbances, the control strategy of primary frequency regulation and inertia support by energy storage-assisted PV units is most beneficial for improving the system's transient frequency stability.

[0105] For example, attached Figure 7From the frequency response curves of the system under different control strategies in the fault, it can be seen from the frequency response curves under different control strategies that the three control strategies do not have frequency regulation effect during the fault, and the frequency response is consistent. After the fault is cleared, the frequency minimum point and the frequency stable value under the two control strategies in which the energy storage participates in frequency regulation are higher than the frequency minimum point and the frequency stable value under the control strategy in which the energy storage does not participate in frequency regulation, and the energy storage auxiliary photovoltaic unit frequency regulation is beneficial to improve the system frequency stability. In the fault recovery and frequency recovery stage, the frequency recovery rate under the control strategy in which the energy storage only assists the photovoltaic unit to perform frequency regulation once is higher than the frequency recovery rate under the control strategy in which the energy storage assists the photovoltaic unit to perform frequency regulation and inertia support. This is because the inertia plays a role in preventing frequency change, and when the frequency rises to a certain level, the energy storage device providing inertia support will actually reduce the active power and prevent the rapid recovery of the frequency. Through analysis, it can be seen that the energy storage auxiliary photovoltaic unit frequency regulation can significantly improve the frequency stability of the power grid during the fault, and the control strategy in which the energy storage auxiliary photovoltaic unit performs frequency regulation once is more conducive to the rapid recovery of the system frequency during the fault. Therefore, after the system is subjected to a fault, in order to rapidly recover the frequency and improve the system frequency stability, the control strategy in which the energy storage auxiliary photovoltaic unit performs frequency regulation once should be adopted.

[0106] It can be seen that the energy storage auxiliary photovoltaic unit frequency regulation control method under multiple working conditions proposed in the present application adopts multiple different frequency regulation control strategies for the photovoltaic unit based on the low voltage ride through process, the frequency deviation, and the frequency regulation dead zone, solves the problem that the existing photovoltaic frequency regulation scheme rarely targets the frequency change working condition caused by fault disturbance, and the problem that the existing photovoltaic fault ride through control method rarely pays attention to frequency regulation during fault recovery, improves the ability of the system to cope with different frequency fluctuations, and more comprehensively enhances the frequency stability of the high photovoltaic system.

[0107] It should be understood that the size of the serial number of each step described above does not mean the order of execution, and the execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0108] The energy storage auxiliary photovoltaic unit frequency regulation control method under multiple working conditions corresponding to the above embodiment, Figure 6 The structure block diagram of the energy storage auxiliary photovoltaic unit frequency regulation control device provided by the embodiments of the present application is shown, and only the parts related to the embodiments of the present application are shown for ease of description.

[0109] Referring to Figure 8 The energy storage auxiliary photovoltaic unit frequency regulation control device in the embodiments of the present application can include an acquisition module 201, a first control module 202, and a second control module 203.

[0110] The device comprises an acquisition module 201 configured to acquire photovoltaic grid point data; a confirmation module 202 configured to confirm that a photovoltaic unit is in a low voltage ride through process based on the photovoltaic grid point data and a low voltage ride through requirement of the photovoltaic unit; the low voltage ride through process comprises a normal operation stage, a fault stage and a fault recovery stage; a first control module 203 configured to start a first frequency modulation control strategy if the photovoltaic unit is in the fault stage in the low voltage ride through process; and a second control module 204 configured to start different first frequency modulation control strategies, second frequency modulation control strategies and third frequency modulation control strategies according to whether a frequency offset of the photovoltaic unit system exceeds a frequency modulation dead zone and whether an energy storage system assists inertia support if the photovoltaic unit is in the fault recovery stage.

[0111] It should be noted that the information interaction between the above devices, the execution process and the like, since based on the same concept as the method embodiments of the present application, the specific functions and the brought technical effects can be referred to the method embodiments part, and will not be described here.

[0112] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the above-mentioned division of each functional unit and module is exemplified, and in actual application, the above-mentioned functions can be completed by different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be realized in the form of hardware or software function unit. In addition, the specific names of each functional unit and module are only for easy distinction, and do not limit the protection scope of the present application. The specific working process of the unit and module in the above system can refer to the corresponding process in the foregoing method embodiments, and will not be described here.

[0113] The present application also provides a terminal device, which refers to Figure 9 The terminal device 300 can include at least one processor 310 and a memory 320, the memory 320 stores a computer program 321 executable on the at least one processor 310, and the processor 310 implements the steps in any of the above method embodiments when executing the computer program, for example Figure 1 The steps 101 to 104 in the embodiment shown. Alternatively, the processor 310 implements the functions of each module / unit in the above device embodiments when executing the computer program, for example Figure 8 The functions of the modules 201 to 204 shown.

[0114] For example, the computer program can be divided into one or more modules / units, one or more modules / units are stored in the memory 320 and executed by the processor 310 to complete the present application. The one or more modules / units can be a series of computer program segments capable of completing a specific function, which are used to describe the execution process of the computer program in the terminal device 300.

[0115] Those skilled in the art can understand that, Figure 9 The terminal device is only an example and does not constitute a limitation on the terminal device, and can include more or fewer components than shown, or combine certain components, or different components, such as input / output devices, network access devices, buses, etc.

[0116] The processor 310 can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor.

[0117] The memory 320 can be an internal storage unit of the terminal device, or an external storage device of the terminal device, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. The memory 320 is used to store the computer program and other programs and data required by the terminal device. The memory 320 can also be used to temporarily store data that has been output or will be output.

[0118] The bus can be an industry standard architecture (ISA) bus, a peripheral component (PCI) bus, or an extended industry standard architecture (EISA) bus, etc. The bus can be divided into an address bus, a data bus, a control bus, etc. For ease of representation, the bus in the drawings of the present application does not limit to only one bus or one type of bus.

[0119] The energy storage assisted photovoltaic unit frequency modulation control method provided by the embodiments of the present application can be applied to terminal devices such as computers, tablet computers, notebook computers, netbooks, personal digital assistants (PDA), and the like. The embodiments of the present application do not limit the specific type of the terminal device.

[0120] The embodiments of the present application further provide a computer readable storage medium, which stores a computer program. The computer program is executed by a processor to implement the steps in the above-described energy storage assisted photovoltaic unit frequency modulation control method.

[0121] The embodiments of the present application provide a computer program product. When the computer program product is run on a mobile terminal, the mobile terminal is caused to implement the steps in the above-described energy storage assisted photovoltaic unit frequency modulation control method.

[0122] The integrated unit, if implemented in the form of a software function unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on this understanding, all or part of the processes in the above-described embodiments can be completed by a computer program instructing related hardware, and the computer program can be stored in a computer readable storage medium. The computer program is executed by a processor to implement the steps of each method embodiment. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or some intermediate forms. The computer readable medium at least includes any entity or device capable of carrying the computer program code to the photographing device / terminal device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunications signal, and a software distribution medium. For example, a U disk, a mobile hard disk, a magnetic disk or an optical disk, etc. In some jurisdictions, according to legislation and patent practice, the computer readable medium cannot be an electrical carrier signal and a telecommunications signal.

[0123] In the above-described embodiments, the description of each embodiment has its own focus. The parts not described in detail or recorded in a certain embodiment can be referred to the relevant description of other embodiments.

[0124] Those skilled in the art can understand that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0125] In the embodiments provided by the present application, it should be understood that the disclosed apparatus / network device and method can be implemented in other ways. For example, the apparatus / network device embodiments described above are merely schematic. The division of the modules or units is merely a logical function division, and there can be another division manner in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections between the units can be indirect couplings or communication connections through some interfaces, devices or units, and can be electrical, mechanical or in other forms.

[0126] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e. can be located in one place, or can be distributed on a plurality of network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiments.

[0127] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for frequency regulation control of a multi-condition energy storage assisted photovoltaic unit, characterized in that, The method comprises: acquiring photovoltaic grid point data; confirming that a photovoltaic unit is in a low voltage ride through process based on the photovoltaic grid point data and photovoltaic unit low voltage ride through requirements; the low voltage ride through process comprises a normal operation stage, a fault stage and a fault recovery stage; if the photovoltaic unit is in the fault stage in the low voltage ride through process, a first frequency modulation control strategy is started; if the photovoltaic unit is in the fault recovery stage, different first, second and third frequency modulation control strategies are started according to whether the photovoltaic unit system frequency offset exceeds a frequency modulation dead zone and whether an energy storage system assists inertia support; the photovoltaic grid point data comprises voltage, system frequency, system frequency offset and system frequency change rate; if the photovoltaic unit is in the fault stage, the first frequency modulation control strategy is started, which comprises: adjusting photovoltaic power station voltage, and the energy storage system does not assist photovoltaic unit frequency modulation; if the system frequency offset exceeds the frequency modulation dead zone, it is judged whether the energy storage system assists inertia support, and the second and third frequency modulation control strategies are started; judging whether the energy storage system assists inertia support, and starting the second and third frequency modulation control strategies, which comprises: if the energy storage system does not assist inertia support, the second frequency modulation control strategy is started; if the energy storage system assists inertia support, the third frequency modulation control strategy is started; the frequency modulation dead zone of the system frequency offset is ±0.033 Hz.

2. The multi-condition energy storage auxiliary photovoltaic unit frequency modulation control method of claim 1, wherein, the acquisition of the photovoltaic grid point data comprises: acquiring photovoltaic grid point voltage and system frequency; based on the current system frequency, measuring the current system frequency offset and the change rate of the current system frequency; calculating the difference between the photovoltaic grid point voltage and the photovoltaic grid point voltage standard value.

3. The multi-condition energy storage auxiliary photovoltaic unit frequency modulation control method of claim 1, wherein, the fault stage is from the moment when the photovoltaic grid point voltage drops to the moment when the voltage recovers to a preset voltage, and the fault recovery stage is from the moment when the photovoltaic grid point voltage is the preset voltage to the moment when the system recovers to a normal operation voltage; the normal operation stage is from the moment when the photovoltaic grid point voltage is a normal operation voltage; the preset voltage is obtained based on the photovoltaic grid point voltage standard value.

4. The multi-condition energy storage auxiliary photovoltaic unit frequency modulation control method of claim 1, wherein, if the photovoltaic unit is in the fault stage, the first frequency modulation control strategy is started, which comprises: the energy storage system performs constant power charging to keep the energy storage capacity at a preset maximum energy storage capacity; if the energy storage capacity is greater than the preset maximum energy storage capacity during the charging process, the charging is stopped; the first frequency modulation control strategy is a fault-based energy storage assisted photovoltaic unit frequency modulation control strategy.

5. The multi-condition energy storage auxiliary photovoltaic unit frequency modulation control method of claim 1, wherein, if the photovoltaic unit is in the fault recovery stage, it is judged whether the photovoltaic unit system frequency offset exceeds the frequency modulation dead zone, which comprises: when the system frequency offset is greater than a preset frequency range, the system frequency offset exceeds the frequency modulation dead zone; when the system frequency offset is less than or equal to the preset frequency range, the system frequency offset does not exceed the frequency modulation dead zone.

6. The multi-condition energy storage auxiliary photovoltaic unit frequency modulation control method of claim 1, wherein, if the photovoltaic unit system frequency offset does not exceed the frequency modulation dead zone, the first frequency modulation control strategy is started.

7. The multi-condition energy storage auxiliary photovoltaic unit frequency modulation control method of claim 1, wherein, the second frequency modulation control strategy comprises: The energy storage system assists the photovoltaic unit in primary frequency modulation, and the energy storage system discharges according to a primary frequency modulation power; the primary frequency modulation power is determined based on a product of a primary frequency modulation coefficient and the frequency deviation; The third frequency modulation control strategy comprises: The energy storage system assists the photovoltaic unit in primary frequency modulation and inertia support, and the energy storage system discharges according to a sum of a primary frequency modulation power reference value and an inertia support power reference value; the primary frequency modulation power reference value is determined based on a product of the primary frequency modulation coefficient and the frequency deviation; the inertia support power reference value is determined based on a product of a virtual inertia coefficient and the frequency differential; If the energy storage power is less than or equal to a preset minimum energy storage power during the discharging process, the discharging is stopped; The frequency deviation exceeds the frequency modulation dead zone, and is caused by load fluctuation; The third frequency modulation control strategy is a frequency modulation control strategy of the energy storage system assisting the photovoltaic unit under load fluctuation.

8. A multi-condition energy storage auxiliary photovoltaic unit frequency control device, characterized in that, Comprise: An acquisition module is configured to acquire photovoltaic grid-connected point data; the photovoltaic grid-connected point data comprises voltage, system frequency, system frequency deviation and system frequency change rate; A confirmation module is configured to confirm, based on the photovoltaic grid-connected point data and photovoltaic unit low-voltage ride-through requirements, that the photovoltaic unit is in a low-voltage ride-through process; the low-voltage ride-through process comprises a normal operation stage, a fault stage and a fault recovery stage; A first control module is configured to, in the low-voltage ride-through process, if the photovoltaic unit is in the fault stage, start a first frequency modulation control strategy; The starting of the first frequency modulation control strategy comprises: Adjusting the voltage of the photovoltaic power station, and the energy storage system does not assist in frequency modulation of the photovoltaic unit; A second control module is configured to, if the photovoltaic unit is in the fault recovery stage, start different first frequency modulation control strategies, second frequency modulation control strategies and third frequency modulation control strategies according to whether the system frequency deviation exceeds a frequency modulation dead zone and whether the energy storage system assists in inertia support; If the system frequency deviation exceeds the frequency modulation dead zone, it is determined whether the energy storage system assists in inertia support, and the second frequency modulation control strategy and the third frequency modulation control strategy are started; The determination of whether the energy storage system assists in inertia support and the starting of the second frequency modulation control strategy and the third frequency modulation control strategy comprise: If the energy storage system does not assist in inertia support, the second frequency modulation control strategy is started; If the energy storage system assists in inertia support, the third frequency modulation control strategy is started; The frequency modulation dead zone of the system frequency deviation is ±0.033 Hz. 9.A terminal device, comprising a memory and a processor, wherein the memory stores a computer program capable of running on the processor, and the computer program comprises the following steps of: The processor executes the computer program to implement the frequency modulation control method of any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, the computer program comprising instructions that, when executed by a computer, cause the computer to perform the method of any one of claims 1 to 9. The computer program is executed by the processor to implement the frequency modulation control method of any one of claims 1 to 7.

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