CN113013896B - Coordination control method for jointly participating in primary frequency modulation of power grid by light storage - Google Patents

Abstract

The invention discloses a coordination control method for jointly participating in primary frequency modulation of a power grid by light storage, which comprises the following steps: modeling a photovoltaic power generation system and an energy storage system respectively to obtain a photovoltaic power generation system model and an energy storage system model; the photovoltaic power generation system is used for participating in power grid frequency modulation through a dynamic variable load shedding method following system output and frequency change; on the basis of coordinated droop control and positive and negative virtual inertia control, an energy storage combined frequency modulation is adopted on the basis of an energy storage variable coefficient self-adaptive control strategy; the capacity of the stored energy is set, so that the inertial response matched with the synchronous generator set can be provided, and the coordination control of the primary frequency modulation of the light storage support power grid is realized by adopting photovoltaic variable load shedding and configured energy storage combined frequency modulation. The invention can improve the inertia and frequency response capability of the optical storage system, can also take frequency modulation and energy storage capacity into account, is beneficial to exerting comprehensive benefits, and improves the utilization rate of new energy while improving the stability level of the system.

Description

A coordinated control method for the joint participation of photovoltaic and storage in the primary frequency regulation of the power grid

technical field

The invention belongs to the field of grid-connected frequency stability of new energy sources, relates to a primary frequency regulation control method, and in particular relates to a coordinated control method for the combined participation of photovoltaics and storage in the primary frequency regulation of a power grid.

Background technique

With the large increase in the penetration rate of photovoltaic power generation, the frequency regulation characteristics under the disturbance of power system faults deteriorate significantly. In order to improve the utilization rate of photovoltaics, photovoltaic power generation generally works at the maximum power point, does not provide inertia support and does not consider necessary energy reserves, and has extremely limited support for the voltage and frequency of the grid. Taking into account the active support of the system, it is particularly urgent to involve photovoltaic power generation in the frequency and voltage regulation of the system. In addition, from the perspective of using new support means, to give full play to the fast and flexible response characteristics of energy storage, and to carry out coordinated control of photovoltaics and energy storage, it is beneficial to exert comprehensive benefits, and to improve the utilization rate of new energy while improving the stability of the system.

However, the existing photovoltaic frequency regulation strategies still need to be improved on how to realize the dynamic matching between the photovoltaic power frequency characteristic control coefficient and the load shedding reserve capacity, and the flexibility and adaptability of the frequency regulation parameter setting in the energy storage frequency regulation control strategy. Energy storage can not only smooth the power fluctuations of photovoltaics, but also make up for the lack of photovoltaics alone participating in frequency regulation. At present, there are few studies involving the coordination of photovoltaics and storage in large power grids to participate in primary frequency regulation, and an effective technical solution is urgently needed to solve the existing technical problems.

SUMMARY OF THE INVENTION

Purpose of the invention: Aiming at the problem that photovoltaic power generation does not have frequency response capability when connected to the grid through a power electronic interface, to provide a coordinated control method for the joint participation of photovoltaics and storage in primary frequency regulation of the power grid, which can improve the inertia and frequency response capability of the photovoltaics storage system, and can Taking into account the maintenance effect of frequency regulation and energy storage capacity, it is beneficial to exert comprehensive benefits, and improve the utilization rate of new energy while improving the stability of the system.

Technical solution: In order to achieve the above purpose, the present invention provides a coordinated control method for the combined participation of photovoltaic and storage in the primary frequency regulation of the power grid, including the following steps:

S1: Model the photovoltaic power generation system and the energy storage system respectively, and obtain the photovoltaic power generation system model and the energy storage system model; the photovoltaic power generation system includes a photovoltaic array, a boost converter, a grid-connected inverter, a filter and its a control system; the energy storage system includes an energy storage battery, a Buck-Boost converter, a grid-connected inverter, a filter and a control system thereof;

S2: The photovoltaic participates in the grid frequency regulation through a dynamic variable load shedding method that follows the system output and frequency changes; the dynamic variable load shedding method that the photovoltaic follows the system output and frequency changes is: the photovoltaic uses the maximum power point tracking method to obtain The maximum active power output P _mppt is given as the new active power of photovoltaics after variable load shedding control and amplitude limiting, and is output to the control system of the Boost converter;

S3: On the basis of coordinated droop control and positive and negative virtual inertia control, based on the energy storage variable coefficient adaptive control strategy, the energy storage joint frequency modulation is adopted;

S4: Set the capacity of the energy storage so that it can provide an inertial response that matches the synchronous generator set, and use photovoltaic variable load shedding and combined frequency modulation with energy storage to achieve coordinated control of the primary frequency modulation of the photovoltaic power grid.

Further, the photovoltaic power generation system in the step S1 is specifically: the DC voltage V _pv and the DC current I _pv output by the photovoltaic array are passed through the maximum power point tracking controller to generate the DC voltage reference values V _refmppt , V _refmppt and V _PV . The error signal is integrated to obtain a given PV output active power P _ref , P _ref and the active power P _dc on the high-voltage side of the boost converter are controlled by PI to generate a duty cycle d, which drives the boost converter to work, thereby realizing the photovoltaic array. MPPT control; the grid-connected inverter works in the state of unity power factor i _gq ^* = 0, the photovoltaic array is boosted by the Boost converter to obtain the DC voltage U _dc , after making a difference with the voltage reference value U _ref , the current is generated by PI control The reference value _idref of the inner loop is then deviated from the actual current values id and _iq obtained by sampling _. After the PI controller and the current decoupling control, the given voltage u _sq and u _sd are obtained. After wide modulation, the trigger pulse S _g of the grid-connected inverter is obtained, so as to realize the decoupling control of the active and reactive power of the grid-connected inverter and the grid-connected operation.

Further, the energy storage system in the step S1 is specifically: the energy storage system realizes the charging and discharging switching of the energy storage through the buck-boost chopper circuit; sampling the voltage and current _VL and _IL of the low-voltage side of the Buck-Boost, and multiplying them to obtain battery power P _bat . When the DC/DC converter works in the discharge mode, compare the active reference reference P _ref with the battery power P _bat , and use the PI controller to adjust to obtain the duty cycle signal D_Boost, and the frequency generated by the variable frequency sawtooth wave generator. The signals are interpolated together to trigger pulses to generate a pulse signal G _Boost that drives the boost converter. When the converter works in the charging mode, take the inverse number of P _ref , make the difference with the battery power P _bat and multiply it by -1, and then perform the similar control as in the discharging mode to obtain the trigger signal G Buck that drives the action of _Buck .

Further, the control characteristic curve expression of the dynamic variable load shedding in the step S2 is as follows:

σ%=K ₀ ×(P _mppt /P _N +Δf/Δf _max ) (1)

In the formula: P _N is the rated active power of the photovoltaic system under standard conditions; P _mppt is the maximum active power of the photovoltaic system in the current working condition; Δf _max is the maximum allowable frequency deviation of the system; Δf is the system frequency deviation; K ₀ is Load shedding rate in the initial condition; σ _max % is the upper limit of the load shedding rate.

Further, the droop control method in the step S3 is:

The energy storage is divided into four intervals: S _max : the maximum working limit of the energy storage battery; S _high : the upper limit of the normal operation of the energy storage battery; S _low : the lower limit of the normal operation of the energy storage battery; S _min : The minimum limit for the operation of the energy storage battery;

The Logistic function is used to adaptively control the droop coefficient, and its curve function expression is:

In the formula: P ₀ is the initial value; K is the final value; r measures the speed of the curve growth;

Taking SOC as the independent variable, _P0 and r as the parameters, and the charge-discharge coefficient as the dependent variable, the following equation is constructed:

1) battery discharge

2) Battery charging

In the formula: K _max is the final value of the droop coefficient during charging and discharging; S _soc is the state of charge of the energy storage; K _bc and K _bd are the corresponding coefficients during discharging and charging, respectively.

Further, the positive virtual inertia control method in the step S3 is:

The formula for the positive virtual inertial response is:

ΔP _bess = -M _bp df/dt (5)

In the formula: M _bp is the positive virtual inertia coefficient; M _bp-c and M _bp-d are the positive virtual inertia coefficients when the energy storage is charged and discharged respectively; M _p is the adjustment coefficient that changes with the frequency deviation; n is the parameter; c ₁ is the initial value of the positive virtual inertia coefficient. D _p is the dead zone of the positive virtual inertia frequency change rate.

Further, the negative virtual inertia control method in the step S3 is:

The negative virtual inertia response formula is:

ΔP _bess = -M _bn df/dt (8)

In the formula: M _bn is the negative virtual inertia coefficient; M _bn-c and M _bn-d are the negative virtual inertia coefficients during charging and discharging respectively; b ₁ is the initial value of the negative virtual inertia coefficient; M _b1 is the adjustment of the frequency deviation change coefficient; f _bess-d is the dead zone of energy storage frequency regulation; f _max is the maximum frequency deviation amplitude allowed by the grid.

Further, the method for configuring the energy storage capacity in the step S4 is:

In order to ensure that the configured energy storage can provide an inertial response that matches the synchronous generator set, the capacity of the energy storage is set as follows:

When the generator speed is ω, the rotational kinetic energy of the synchronous generator is

When the motor speed follows the system frequency from ω ₀ to ω ₁

The rotational speed of a synchronous generator is proportional to the system frequency and generally varies within a small range. The grid operation and maintenance guidelines stipulate that the system frequency may rise to 51Hz or drop to 48Hz in a short period of time under special circumstances. Based on the frequency drop analysis, the rotational speed of the rotor of the synchronous generator ranges from 0.95 to 1pu, and the kinetic energy that can be released is:

The energy storage device is only limited by the SOC, and can usually achieve a wide range of power throughput, so a smaller energy storage capacity can achieve the same frequency modulation effect as a conventional generator set. When a photovoltaic power station equipped with energy storage replaces the conventional generator set and is integrated into the power grid, since the charging and discharging time of the energy storage is generally longer than the inertia response time, when the energy storage power meets the requirements, the capacity also meets the requirements.

Assuming that the energy released by the energy storage system within Δt is the same as the kinetic energy of the same rotor, there are:

ΔE _bess = P _bess Δt = 0.0784HS _N (14)

Let Δt=2H

P _bess = 0.0392S _N (15)

In the formula: ΔE _bess and P _bess are the capacity and power of the energy storage, respectively; S _N is the rated capacity of the generator; H is the inertia constant; J is the inertia time constant of the generator.

Further, the method for combined frequency modulation of optical storage and storage in the step S4 is:

1) The energy storage system provides an inertial response that matches the conventional generator set for the initial frequency change of the power system;

2) Photovoltaic uses variable load shedding and frequency regulation strategy and energy storage adaptive control strategy to jointly participate in primary frequency regulation.

The invention proposes a strategy for photovoltaic and energy storage to participate in the primary frequency regulation of the power grid: the photovoltaic adopts a dynamic variable load shedding and frequency regulation strategy that follows the system output and frequency changes, responds to the system frequency fluctuation in real time, and improves the frequency stability of the photovoltaic power station. The energy storage adopts an adaptive control strategy that follows the changes of the state of charge, frequency change rate and frequency deviation. The droop control dynamically adjusts the control coefficient based on the logistic function; positive virtual inertia control combines the effects of frequency deviation and frequency change rate; negative virtual inertia The output is adjusted comprehensively considering the battery SOC, frequency change rate and frequency deviation; the coordination and complementary advantages of the three are realized. In order to minimize the power loss caused by fixed load shedding and reduce the cost of the energy storage system, the measures of photovoltaic variable load shedding and combined frequency regulation with energy storage are adopted: the energy storage provides inertial response for the initial frequency change phase of the power system, and the photovoltaic utilization The variable load shedding operation and energy storage jointly participate in primary frequency regulation, thus realizing the coordinated operation of energy storage and photovoltaic.

The present invention proposes a coordinated control method of utilizing a photovoltaic-storage joint to participate in the primary frequency regulation of the power grid. Due to the influence of environmental factors such as light intensity and temperature, photovoltaic power generation has the characteristics of randomness, volatility and uncertainty. Photovoltaic arrays generally work at the maximum power point, without rotating equipment that can store kinetic energy and provide inertia, and cannot provide the necessary voltage, frequency support and damping for the grid. As the proportion of photovoltaics becomes higher and higher, the power electronic interface gradually replaces the mechanical switch interface on a large scale, and the overall inertia level of the power system decreases, which threatens the safe and stable operation of the power system. more and more necessary. Energy storage can not only smooth the power fluctuations of photovoltaics, but also make up for the lack of photovoltaics alone participating in frequency regulation. In order to minimize the power loss caused by fixed load shedding and reduce the cost of the energy storage system, the measures of variable load shedding of photovoltaics and combined frequency regulation of energy storage are adopted. Therefore, a coordinated control method for the joint participation of photovoltaic and energy storage in primary frequency regulation of the power grid is given. has very important practical significance.

The present invention first analyzes the frequency regulation characteristics of the photovoltaic system and the energy storage system. Secondly, the strategies for photovoltaic and energy storage to participate in the primary frequency regulation of the power grid are respectively proposed: photovoltaic adopts a dynamic variable load shedding and frequency regulation method that follows the system output and frequency changes; energy storage adopts a method that follows the state of charge, frequency change rate and frequency deviation Variation of adaptive control methods. In order to minimize the power loss caused by fixed load shedding and reduce the cost of the energy storage system, the measures of photovoltaic variable load shedding and combined frequency regulation with energy storage are adopted: the energy storage provides inertial response for the initial frequency change phase of the power system, and the photovoltaic utilization The variable load shedding operation and energy storage jointly participate in primary frequency regulation, thus realizing the coordinated operation of energy storage and photovoltaic. Finally, the proposed strategy is simulated and verified by a typical regional power grid example.

The invention proposes a photovoltaic variable load shedding and frequency regulation method: the photovoltaic adopts the maximum power point tracking method to obtain the maximum active power output P _mppt , which is given as a new photovoltaic active power after variable load shedding control and amplitude limiting, and is output to the Boost conversion controller control system. On the one hand, the variable load shedding control coefficient can dynamically change the output following the system frequency deviation and the maximum active power output. On the other hand, the load shedding rate of the system is adjusted inversely, so that the system has the ability of primary frequency regulation, avoiding the use of load shedding and drooping. When the control strategy is used, the selection of the slope of the droop characteristic has flexible adaptability.

The invention proposes an adaptive control method for battery energy storage: the droop control is based on the characteristics of the Logistic function, uses symmetry to set only one function in the charging and discharging interval, and adopts the SOC partition to adaptively adjust the droop coefficient, avoiding segmentation The complexity of the function setting; the positive and negative virtual inertia coefficients use the frequency deviation change function as an adjustment factor, and are set in combination with the frequency change rate and SOC change characteristics; the coordination of the three not only ensures the state of charge of the energy storage, but also plays a role in the energy storage. One FM advantage.

The present invention proposes a coordinated control method for the combined participation of photovoltaic and storage in the primary frequency regulation of the power grid. The energy storage system provides an inertial response similar to that of the conventional generator set in the initial stage of the frequency change of the power system; the photovoltaic uses the variable load shedding frequency regulation strategy and the energy storage adaptive control strategy to jointly participate in the primary frequency regulation. It not only effectively utilizes the load shedding reserve capacity of photovoltaics, but also reduces the proportion of energy storage capacity allocation.

The innovation of the invention lies in that the photovoltaic adopts the variable load shedding and frequency regulation method, on the one hand, it can dynamically change the output power following the system frequency deviation and the maximum active power output; It avoids the problem of selecting the slope of the droop characteristic when using the virtual droop control strategy, and has flexibility. Its innovation is also that the droop control is based on the Logistic function, and uses the SOC partition to adaptively adjust the droop coefficient; the positive and negative virtual inertia coefficients use the frequency deviation change function as the adjustment factor, and are set in combination with the frequency change rate and SOC change characteristics; Coordination and complementary advantages, with better adaptability. It not only ensures the state of charge of the energy storage, but also takes advantage of the primary frequency modulation of the energy storage. Finally, the energy storage provides inertial response for the initial frequency change stage of the power system, and the photovoltaic uses variable load shedding operation and energy storage to jointly participate in primary frequency regulation, thereby realizing the coordinated operation of energy storage and photovoltaic.

Beneficial effect: Compared with the prior art, the present invention adopts the dual-loop control strategy of the power outer loop and the current inner loop for both photovoltaic and energy storage. One FM capability. The positive and negative inertia control and droop control of variable coefficients in the energy storage control strategy can dynamically adjust the output of the energy storage, which not only ensures the state of charge of the energy storage, but also takes advantage of the primary frequency modulation of the energy storage. Photovoltaic adopts the variable load shedding and frequency modulation control method. The control method of this strategy is simple, and can follow the frequency deviation and output changes to dynamically change the photovoltaic load shedding coefficient, avoiding the inflexibility of control parameter selection in conventional control strategies. The energy storage is used to provide inertial support for the power grid during the initial frequency drop stage, and a frequency regulation is performed in conjunction with photovoltaics, which greatly improves the frequency stability of the system. At 19.05% and 28.57% of the photovoltaic ratio, the energy storage capacity is saved by 3% and 2.5% respectively, which not only effectively utilizes the load shedding reserve capacity of photovoltaics, but also reduces the proportion of energy storage capacity allocation.

Description of drawings

Fig. 1 is a flow chart of the primary frequency regulation coordination control process of the combined photovoltaic and storage power grid of the present invention;

FIG. 2 is a schematic diagram of the photovoltaic power generation system of the present invention;

3 is a schematic diagram of a photovoltaic variable load shedding strategy of the present invention;

4 is a schematic diagram of an energy storage system of the present invention;

FIG. 5 is a schematic diagram of setting up an energy storage working area according to the present invention;

Fig. 6 is the change curve diagram of energy storage droop control coefficient K _b with P ₀ and r of the present invention;

FIG. 7 is a graph showing the variation curve of the regulation factor M _p and the energy storage frequency modulation output in the positive virtual inertia control of the energy storage according to the present invention;

Fig. 8 is the change curve diagram of the adjustment factor M _b1 and the negative virtual inertia coefficient M _bn in the energy storage negative virtual inertia control of the present invention;

FIG. 9 is a schematic diagram of a frequency regulation simulation model of a typical regional power grid with three machines and nine nodes by simulation analysis and simulation according to an embodiment of the present invention;

Fig. 10 is a characteristic curve diagram of frequency and photovoltaic output under photovoltaic load shedding and standby simulated by the present invention;

Fig. 11 is a frequency and SOC comparison diagram of the fixed K method and the variable K method when the initial SOC of the energy storage is 0.6 by the simulation analysis of the present invention;

Fig. 12 is a frequency and SOC comparison diagram of the fixed K method and the variable K method when the initial SOC of the energy storage is 0.3 by the simulation analysis of the present invention;

Fig. 13 is the frequency change curve and result diagram of the energy storage under different frequency modulation modes of the simulation analysis and simulation of the present invention;

FIG. 14 is the frequency, photovoltaic output and energy storage output characteristic curves under 19.05% photovoltaic ratio under the combined frequency modulation of photovoltaic and storage under the simulation analysis and simulation of the present invention;

FIG. 15 is the frequency, photovoltaic output and energy storage output characteristic curves under 28.57% photovoltaic ratio under the combined frequency modulation of photovoltaic and storage under the simulation analysis and simulation of the present invention.

Detailed ways

Below in conjunction with the accompanying drawings and specific embodiments, the present invention will be further clarified. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. Modifications of equivalent forms all fall within the scope defined by the appended claims of this application.

The present invention provides a coordinated control method for the combined participation of photovoltaics and storage in primary frequency regulation of a power grid. The overall design principle, method flow and simulation analysis of the scheme are described below.

1. A coordinated control method for the joint participation of photovoltaic and storage in the primary frequency regulation of the power grid

The present invention will firstly propose a strategy for photovoltaic and energy storage to participate in primary frequency regulation of the power grid: photovoltaic adopts a dynamic variable load shedding and frequency regulation strategy that follows system output and frequency changes. The energy storage adopts an adaptive control strategy that follows the changes of the state of charge, frequency change rate and frequency deviation. The droop control dynamically adjusts the control coefficient based on the logistic function; positive virtual inertia control combines the effects of frequency deviation and frequency change rate; negative virtual inertia The output is adjusted comprehensively considering the battery SOC, frequency change rate and frequency deviation; the coordination and complementary advantages of the three are realized. Further, in order to minimize the power loss caused by fixed load shedding and reduce the cost of the energy storage system, the measures of photovoltaic variable load shedding and combined frequency regulation with energy storage are adopted: the energy storage provides inertial response for the initial frequency change phase of the power system. , PV utilizes variable load shedding operation and energy storage to jointly participate in primary frequency regulation, thus realizing the coordinated operation of energy storage and PV. Finally, the proposed strategy is simulated and verified by a typical regional power grid example.

1.1. Models of photovoltaic power generation systems and energy storage systems

Model the photovoltaic power generation system and the energy storage system separately. As shown in Figure 2, the photovoltaic power generation system is mainly composed of photovoltaic arrays, Boost converters, grid-connected inverters, filters and their control systems. As shown in Figure 4, the energy storage system is mainly composed of an energy storage battery, a Buck-Boost converter, a grid-connected inverter and a filter and its control system.

1.2. PV variable load shedding backup frequency modulation method

It can be seen from Figure 3 that the photovoltaic adopts the maximum power point tracking method to obtain the maximum active power output P _mppt , which is given as the new active power of the photovoltaic after variable load shedding control and amplitude limiting, and is output to the boost converter control system. Among them, the variable load shedding control characteristic curve is expressed as follows.

σ%=K ₀ ×(P _mppt /P _N +Δf/Δf _max ) (1)

When the system frequency decreases, Δf is negative, the load shedding coefficient dynamically follows the frequency deviation and becomes smaller, and the active power output is increased. When the system frequency increases, Δf is positive, and the load shedding coefficient dynamically increases with the frequency deviation, reducing the active power output. Thereby, it participates in the primary frequency regulation in response to the frequency change of the power system. In the variable load shedding and frequency modulation control strategy proposed in this paper, on the one hand, the control coefficient σ% can dynamically change the output power following the system frequency deviation and the maximum active power output. On the other hand, the load shedding rate of the system is reversely adjusted, so that the system has the ability of primary frequency modulation. It avoids the problem of selecting the slope of the droop characteristic when using the control strategy of load shedding and droop, and has flexible adaptability.

1.3 Energy storage adaptive frequency regulation strategy

The droop control dynamically adjusts the control coefficient based on the logistic function, see Figure 6, and selects P ₀ and r through the change curve; the logistic curve has natural concavo-convex. The adaptive strategy of energy storage can take into account the effects of frequency regulation and SOC retention. When the energy storage is discharged and the energy storage capacity is sufficient, the curve is convex, which can ensure that the unit regulation power of the energy storage is at a relatively larger value. If the energy storage capacity is not sufficient, the curve is downward convex. As the SOC decreases, the discharge speed becomes slower. At this time, the unit regulated power is at a small value to maintain the SOC effect. Positive virtual inertial control combines the effects of frequency deviation and frequency change rate; it can take into account the characteristics that the initial frequency change rate is large, and then gradually decreases until the change rate becomes 0 at the maximum frequency deviation point. The control coefficient in the initial stage is slightly smaller, and the control coefficient is larger in the vicinity of the maximum frequency deviation point. The energy storage can output evenly, and simultaneously improve the initial frequency change rate and the maximum frequency deviation. Negative virtual inertia comprehensively considers battery SOC, frequency change rate and frequency deviation to adjust the output; considering the frequency recovery stage, the maximum frequency deviation is large, but the frequency change rate is low. At this time, a larger coefficient can be multiplied to make the system frequency recover quickly . With the extension of time, the frequency deviation decreases, and the SOC value of the energy storage decreases. At this time, multiply the smaller coefficient to ensure the SOC maintenance effect of the energy storage. The coordination and complementary advantages of the three have been realized.

1.4 Coordinated control method of solar-storage joint participation in primary frequency regulation of power grid

The energy storage system provides an inertial response similar to that of a conventional generator set in the initial stage of the frequency change of the power system. Photovoltaic uses variable load shedding and frequency regulation strategy and energy storage adaptive control strategy to jointly participate in primary frequency regulation. It not only effectively utilizes the load shedding reserve capacity of photovoltaics, but also reduces the proportion of energy storage capacity allocation.

2. Method flow

As shown in FIG. 1 , the present invention provides a method for controlling the primary frequency regulation of a power grid by a combined photovoltaic-storage system.

Referring to Figure 1, the specific steps are as follows:

S1: Models of photovoltaic power generation systems and energy storage systems are given. The photovoltaic power generation system is mainly composed of photovoltaic array, boost converter, grid-connected inverter, filter and its control system. The energy storage system is mainly composed of energy storage battery, Buck-Boost converter, grid-connected inverter, filter and its control system.

S2: The existing photovoltaic frequency regulation strategy mainly starts from the use of virtual synchronous generator technology, or the control of photovoltaic output voltage not to operate at the maximum power point to reserve load shedding and frequency regulation for backup. However, it lacks flexibility in matching the power frequency characteristic control coefficient with the load shedding reserve capacity. Therefore, a dynamic variable load shedding method that follows the system output and frequency changes is adopted to participate in the grid frequency regulation, respond to the system frequency fluctuations in real time, and improve the photovoltaic power station. frequency stability.

S3: In order to enhance the economy of photovoltaic frequency regulation, the combined frequency regulation of energy storage is adopted. The flexibility and adaptability of frequency regulation parameter settings in the existing energy storage frequency regulation control strategies still need to be improved. Under the characteristics of coordinated droop control and positive and negative virtual inertial control, this paper proposes an energy storage variable coefficient adaptive control strategy that follows the changes of state of charge, frequency deviation and frequency change rate. Good maintains the state of charge of the stored energy.

S4: In order to minimize the power loss caused by fixed load shedding when the photovoltaic frequency is adjusted separately, and to reduce the cost of the energy storage system. The capacity of the stored energy is set so that it provides an inertial response similar to that of a synchronous generator set. Finally, photovoltaic variable load shedding and combined frequency modulation with energy storage are used to realize the coordinated control of primary frequency modulation of the photovoltaic-storage-supported power grid.

The photovoltaic power generation system is mainly composed of photovoltaic arrays, boost converters, grid-connected inverters, filters and their control systems. In this embodiment, the DC voltage V _pv and the DC current I _pv output by the photovoltaic array are passed through the maximum power point tracking controller to generate the DC voltage reference value V _refmppt , and the error signals of V _refmppt and V _PV are integrated to obtain the photovoltaic output active power Given P _ref , P _ref and the active power P _dc on the high-voltage side of the boost converter are controlled by PI to generate a duty cycle d, which drives the boost converter to work, thereby realizing the MPPT control of the photovoltaic array. The control of the inverter is essentially a double closed-loop control system, which is mainly composed of an inner loop (current control loop) and an outer loop (power control loop). Normally, the inverter works in the state of unity power factor, and the current reference value of reactive power is i _qref =0. After the photovoltaic array is boosted by the Boost converter, the DC voltage U _dc is obtained, and after making a difference with the voltage reference value U _ref , the current inner loop reference value _idref is generated through PI control. Then, the deviation from the actual current values _id and i _q obtained by sampling is controlled by the PI controller and the current decoupling to obtain the voltage given u _sq , u _sd . Finally, after coordinate transformation, the trigger pulse S _g of the inverter is obtained through pulse width modulation. In this way, the decoupling control of the active and reactive power of the inverter and the grid-connected operation are realized.

The energy storage system is mainly composed of energy storage battery, Buck-Boost converter, grid-connected inverter, filter and its control system. The buck-boost chopper circuit realizes the charging and discharging switching of the energy storage. The voltage and current _VL and _IL of the low-voltage side of the Buck-Boost are sampled, and multiplied to obtain the battery power P _bat . When the DC/DC converter works in the discharge mode, compare the active reference reference P _ref with the battery power P _bat , and use the PI controller to adjust to obtain the duty cycle signal D_Boost, and the frequency generated by the variable frequency sawtooth wave generator. The signals are interpolated together to trigger pulses to generate a pulse signal G _Boost that drives the boost converter. When the converter works in the charging mode, take the inverse number of P _ref , make the difference with the battery power P _bat and multiply it by -1, and then perform the similar control as in the discharging mode to obtain the trigger signal G Buck that drives the action of _Buck . The main control principle of the grid-connected inverter is similar to that of the photovoltaic power generation system, and will not be repeated here.

In step S2 of this embodiment, the dynamic variable load shedding method for the output and frequency changes of the photovoltaic follower system is as follows:

The photovoltaic adopts the maximum power point tracking method to obtain the maximum active power output P _mppt , which is given as the new active power of the photovoltaic after variable load shedding control and amplitude limiting, and is output to the control system of the Boost converter.

The variable load shedding control characteristic curve is expressed as follows:

σ%=K ₀ ×(P _mppt /P _N +Δf/Δf _max ) (1)

In the formula: P _N is the rated active power of the photovoltaic system under the standard condition, MW; P _mppt is the maximum active power of the photovoltaic system under the current working condition, MW; Δf _max is the maximum allowable frequency deviation of the system, taken as 0.5Hz; Δf is the system frequency deviation, Hz; K ₀ is the load shedding rate in the initial situation, so that the photovoltaic has the ability to participate in frequency regulation at any time; σ _max % is the upper limit of the load shedding rate; K ₀ and σ _max % can be determined according to the output of the photovoltaic power station Situation ok.

It can be seen from formula (1) that when the system frequency decreases, Δf is negative, the load shedding coefficient dynamically follows the frequency deviation, and the active power output is increased. When the system frequency increases, Δf is positive, and the load shedding coefficient dynamically increases with the frequency deviation, reducing the active power output. Thereby, it participates in the primary frequency regulation in response to the frequency change of the power system. In the variable load shedding and frequency modulation control strategy proposed in this paper, on the one hand, the control coefficient σ% can dynamically change the output power following the system frequency deviation and the maximum active power output. On the other hand, the load shedding rate of the system is reversely adjusted, so that the system has the ability of primary frequency modulation. It avoids the problem of selecting the slope of the droop characteristic when using the control strategy of load shedding and droop, and has flexible adaptability.

The droop control method in step S3 of this embodiment is:

Referring to FIG. 5 , in this embodiment, the battery energy storage is divided into five intervals: S _max : the maximum limit value of the battery operation, which is 0.9 here; S _high : the upper limit value of the normal operation of the battery, which is 0.55 here; S _low : the lower limit of the normal operation of the battery, which is 0.45 here; S _min : the minimum limit of the battery's operation, which is 0.1 here.

Logistic functions are inherently exponential, bumpy, and saturated. This embodiment adopts it to adaptively control the droop coefficient. The adaptive strategy of energy storage can take into account the effects of frequency regulation and SOC retention. Its curve function expression:

In the formula: P ₀ is the initial value, the larger the P ₀ value, the shorter the time to reach saturation; K is the final value; r measures the growth speed of the curve, the larger the r, the faster the growth.

When the energy storage is discharged and the energy storage capacity is sufficient, the curve is upwardly convex, which can ensure that the unit regulating power of the energy storage is at a relatively larger value. When the energy storage capacity is insufficient, the curve is downward convex, and as the SOC decreases, the discharge speed becomes slower. At this time, the unit regulating power is at a small value to maintain the SOC effect. When the energy storage is charged, the process is similar to the above. Take SOC as the independent variable, P ₀ and r as the parameters, and the charge-discharge coefficient as the dependent variable. Construct the following equation.

1) battery discharge

2) Battery charging

In the formula: K _max is the final value of the droop coefficient during charging and discharging; S _soc is the state of charge of the energy storage; K _bc and K _bd are the corresponding coefficients during discharging and charging, respectively.

The K _b curves when r and P ₀ are changed respectively are shown in Fig. 6 . It can be seen that when r and P ₀ are too large, K _b only has a large change following the SOC in a small range, and the adaptive ability is relatively weak. When r and P ₀ become smaller, K _b is more sensitive to changes in SOC.

In order to make the energy storage battery fully utilized within the upper and lower limits (0.45, 0.55) of normal work. Select r and P ₀ appropriately. Ensure that there is a larger control coefficient within the maximum limit of energy storage work and the upper limit of normal operation of energy storage. Taking the energy storage discharge as an example, when the SOC is greater than the upper limit of the normal operation of the energy storage, the coefficient changes with the SOC and is still at a relatively large value. When the SOC is less than the lower limit of the normal operation of the energy storage, more consideration is given to the SOC maintenance effect and the control coefficient is reduced. In this paper, r is taken as 8, and P ₀ is taken as 0.02.

The droop control proposed in this embodiment is based on the characteristics of the Logistic function. By using symmetry, only one function is set in each charge and discharge interval, and the SOC partition is used to adjust the droop coefficient adaptively, which not only makes full use of the frequency regulation capability of battery energy storage, but also takes into account It can maintain the effect of SOC and avoid the complexity of setting the piecewise function.

In this embodiment, the variable coefficient positive virtual inertia control method in step S3 is:

The virtual inertial control strategy simulates the inertial response process of the synchronous generator. Since the rotor speed of the generator cannot be changed suddenly, the mechanical power remains unchanged for a short time, while the increase of electromagnetic power causes the rotor speed to drop, releasing kinetic energy. The inertia response formula is as follows:

ΔP _bess = -M _b df/dt (5)

Where: M _b is the inertia coefficient.

In the initial disturbance stage, df/dt is large, while Δf is small, and the droop control alone cannot meet the frequency modulation requirements. After adding positive virtual inertia control, the frequency deviation can be reduced to a certain extent while reducing the initial frequency change rate. The response time of positive virtual inertia is very short, regardless of the state of charge of the stored energy. Its response formula is:

ΔP _bess = -M _bp df/dt (6)

In the formula: M _bp is the positive virtual inertia coefficient; M _bp-c and M _bp-d are the positive virtual inertia coefficients when the energy storage is charged and discharged respectively; M _p is the adjustment coefficient that changes with the frequency deviation; n is the parameter; c ₁ is the initial value of the positive virtual inertia coefficient; D _p is the dead zone of the positive virtual inertia frequency change rate.

In this embodiment, the regulation coefficient M _p and the energy storage frequency modulation output change curve are specifically shown in FIG. 7 . The size and rate of change of M _p are related to the value of n. If the value of n is too small, the value of M _p will be small, and the positive virtual inertia ability cannot be fully exerted; if the value of n is too large, a slight increase of △f will lead to M _p increases sharply, and the frequency curve will jitter. After comprehensive consideration, this paper chooses n=6.

The positive virtual inertia strategy proposed in this embodiment can take into account the characteristics that the initial frequency change rate is large, and then gradually decreases until the change rate becomes 0 at the maximum frequency deviation point. The control coefficient in the initial stage is slightly smaller, and the control coefficient is larger in the vicinity of the maximum frequency deviation point. The energy storage can output evenly, and simultaneously improve the initial frequency change rate and the maximum frequency deviation.

In step S3 of this embodiment, the variable coefficient negative virtual inertia control method is:

When the frequency deviation reaches a maximum and frequency recovery begins, the polarity of the frequency change rate changes. The response output of positive virtual inertia is opposite to the direction of frequency regulation demand. If it is not corrected, it will be a new disturbance to the system, which is not conducive to the recovery of grid frequency. Therefore, to switch to negative virtual inertia control, the action time of negative virtual inertia is longer, and the SOC of energy storage needs to be considered. Its response formula is:

ΔP _bess = -M _bn df/dt (9)

In the formula: M _bn is the negative virtual inertia coefficient; M _bn-c and M _bn-d are the negative virtual inertia coefficients during charging and discharging respectively; b ₁ is the initial value of the negative virtual inertia coefficient; M _b1 is the adjustment of the frequency deviation change coefficient; f _bess-d is the dead zone of energy storage frequency modulation; f _max is the maximum allowable frequency deviation amplitude of the power grid, which is taken as 0.5Hz here.

In this embodiment, the change curve diagrams of the adjustment coefficient M _b1 and the negative virtual inertia coefficient M _bn are specifically shown in FIG. 8 . When n is too large, M _b1 decreases sharply at first and then decreases slowly as the frequency deviation decreases, which is not conducive to the utilization of the negative virtual inertia control capability; when n becomes smaller, the decreasing trend of M _b1 gradually tends to be linear and stable. In this paper, n is taken as 2.

The negative virtual inertia strategy proposed in this embodiment takes into account the frequency recovery stage, the maximum frequency deviation is large, but the frequency change rate is low. At this time, a larger coefficient can be multiplied to make the frequency of the system recover quickly. With the extension of time, the frequency deviation decreases, and the SOC value of the energy storage decreases. At this time, multiply the smaller coefficient to ensure the SOC maintenance effect of the energy storage.

The method for configuring the energy storage capacity in step S4 of this embodiment is:

In order to ensure that the configured energy storage can provide a similar inertial response to that of the synchronous generator set, the capacity of the energy storage is set as follows:

When the generator speed is ω, the rotational kinetic energy of the synchronous generator is

When the motor speed follows the system frequency from ω ₀ to ω ₁

The rotational speed of a synchronous generator is proportional to the system frequency and generally varies within a small range. The grid operation and maintenance guidelines stipulate that the system frequency may rise to 51Hz or drop to 48Hz in a short period of time under special circumstances. Based on the frequency drop analysis, the rotational speed of the rotor of the synchronous generator ranges from 0.95 to 1pu, and the kinetic energy that can be released is:

The energy storage device is only limited by the SOC, and can usually achieve a wide range of power throughput, so a smaller energy storage capacity can achieve the same frequency modulation effect as a conventional generator set. When a photovoltaic power station equipped with energy storage replaces the conventional generator set and is integrated into the power grid, since the charging and discharging time of the energy storage is generally longer than the inertia response time, when the energy storage power meets the requirements, the capacity also meets the requirements.

Assuming that the energy released by the energy storage system within Δt is the same as the kinetic energy of the same rotor, there are:

ΔE _bess = P _bess Δt = 0.0784HS _N (15)

Here, the inertia time constant H of the generator set is about 5s, so that Δt=2H.

P _bess = 0.0392S _N (16)

In the formula: ΔE _bess and P _bess are the capacity and power of the energy storage, respectively; S _N is the rated capacity of the generator; H is the inertia constant; J is the inertia time constant of the generator. It can be seen from equation (16) that when the energy storage of 3.92% of the rated power of the photovoltaic power station is configured, an inertial response similar to that of the synchronous generator set can be achieved. Considering the upper and lower regulation of energy storage, the capacity of energy storage can be relaxed to 5% of the rated power.

In the step S4 of this embodiment, the method for combined frequency modulation of optical storage and storage is as follows:

1) The energy storage system provides an inertial response similar to that of the conventional generator set in the initial stage of the frequency change of the power system.

2) Photovoltaic uses variable load shedding and frequency regulation strategy and energy storage adaptive control strategy to jointly participate in primary frequency regulation.

3. Simulation analysis

Based on the typical system of IEEE3 machine and 9 nodes, the PSCAD simulation system model is built, as shown in Figure 9. Hydropower unit G1, thermal power unit G2, G3 are all composed of governor and prime mover to participate in frequency regulation, their total rated capacity is 567.5MVA, and the total load is 315+j115MVA. Firstly, the bus8 busbar is connected to photovoltaic and energy storage respectively to verify the effectiveness of the strategy proposed in this paper. Finally, the combination of photovoltaic and storage is invested to simulate the superiority of the combined photovoltaic and storage system participating in the coordinated control strategy of primary frequency regulation of the power grid.

3.1 Simulation verification of photovoltaic frequency regulation optimization strategy

At the bus bar of Bus8 in Fig. 9, a photovoltaic equivalent power supply of 90MW is connected. The load of 16MW will be added when the Bus6 busbar is 3s. Three situations are simulated, such as PV does not participate in frequency regulation and PV adopts variable load shedding control strategy (the initial load shedding rate is 5% and 10% respectively). It can be seen from Figure 10 that when the photovoltaic does not participate in the frequency modulation, the lowest point of the frequency drop is 49.4Hz. After considering the variable load shedding and frequency regulation strategy proposed in this paper, photovoltaic power generation can effectively utilize the load shedding reserve capacity, dynamically adjust with the system frequency changes, and improve the frequency recovery response characteristics. When the initial load shedding rate is 5%, the lowest point of frequency drop is 49.5Hz. When the initial load shedding rate is 10%, the lowest point of frequency drop is 49.65Hz. It can be seen that the larger the initial load shedding level is, the greater the frequency regulation capacity that can be issued during the transient process, and the stronger the ability to participate in the system frequency regulation. However, due to the excessive load shedding level, the working efficiency of the photovoltaic array will decrease, resulting in power loss under normal operation. Therefore, the use of photovoltaic independent frequency regulation is limited by the load shedding capacity, and the frequency regulation effect is still unsatisfactory.

3.2 Validation of energy storage participating in primary frequency modulation adaptive control method

Connect the energy storage equivalent power supply with a capacity of 4.5MW to the Bus8 bus in Figure 9. The simulation compares the frequency modulation characteristics of the droop control constant K method and variable K method (the method used in this paper) under the step load disturbance. A load of 12MW is applied when the bus6 busbar is 3s. The simulations are carried out in two cases where the initial SOC is 0.6 and 0.3.

It can be seen from Figure 11 that when the initial value of SOC is high, that is, when the battery energy is sufficient. The effect of the fixed K method is related to the value of K. The larger the K value, the smaller the maximum frequency deviation, and the better the frequency modulation effect, but the faster the battery energy declines. Through the proper selection of K, the frequency modulation effect and state of charge can be achieved equivalent to the variable K method. As shown in the figure, when the K method is set to K=9, the effect is equivalent to that of the variable K method. Select the fixed K method (K=9) and the variable K method for comparison. It can be seen from Fig. 12 that when the initial SOC = 0.3, that is, when the power is small. In order to take into account the effect of maintaining SOC, the output of droop control is reduced, the maximum frequency deviation of the fixed K method is 0.18Hz, and the variable K method is 0.2Hz. The frequency modulation effect of the variable K method is slightly weaker than that of the fixed K method. However, the fixed K method does not consider the influence of energy storage SOC. The SOC change curve drops rapidly, and it is easy to reach the capacity limit of the energy storage and exit the frequency modulation in advance, resulting in a secondary drop in frequency.

For the same example above, the simulated energy storage does not participate in frequency regulation, uses droop control (fixed K method), droop control (variable K method), droop control + virtual inertia, and the method used in this paper. The effectiveness and superiority of the proposed method. Combining with Figure 13, it can be seen that using the energy storage adaptive control strategy adopted in this paper, the minimum initial frequency change rate is -0.03Hz/s, and the maximum frequency deviation is 0.27Hz. The negative virtual inertia provided after the frequency recovery can significantly increase the frequency Recovery speed. This shows the superiority of the proposed method.

3.3 Verification of the combined frequency modulation control strategy of optical storage and storage

In the simulation system in Fig. 9, 4.5MW energy storage and photovoltaic are connected to the Bus8 bus. When the photovoltaic output is 60MW and 90MW, that is, the power system with the photovoltaic ratio of 19.05% and 28.57%, the load disturbance of 16MW is added. The simulated photovoltaic does not participate in frequency regulation, only energy storage participates in frequency regulation, and only photovoltaic participates in frequency regulation, The frequency characteristics of the system under four frequency modulation modes, including the cooperative participation of optical storage and storage in frequency modulation (the strategy of this paper).

From 14a (frequency curve) and 14b (photovoltaic output curve) in Figure 14, it can be seen that when only conventional generators participate in frequency regulation, the lowest frequency is 49.45Hz at 19.05% photovoltaic ratio. At 28.57% photovoltaic ratio, the lowest frequency is 49.41Hz. It can be seen that the larger the proportion of photovoltaics, the more serious the frequency drop. When PV frequency modulation is added to the system, the frequency modulation effect is obviously improved, but due to the limited PV load shedding reserve, the frequency modulation effect is limited by the total reserve capacity; only in the energy storage frequency modulation mode, the energy storage can actively respond to frequency changes: when the PV ratio is 19.05 %, the energy storage peak power accounts for 13% of the photovoltaic power station, and the frequency minimum point is 51% higher than that without control; when the photovoltaic ratio is 28.57%, the energy storage peak power accounts for 9.2% of the photovoltaic power station, and the frequency minimum point is higher than that of the photovoltaic power station. 54% increase when uncontrolled. When the combined frequency modulation of photovoltaic and storage is adopted, the frequency stability of the power system is greatly improved after the comprehensive utilization of the variable load shedding frequency modulation of photovoltaics and the adaptive adjustment strategy of energy storage. Combining with Figures 14 and 15, it can be seen that the entire primary frequency regulation process not only fully utilizes the load shedding reserve capacity of photovoltaics, but also has no obvious peak characteristics in the output of energy storage frequency regulation, which is conducive to maintaining the state of charge of energy storage. It can be seen from Figure 14c (energy storage output characteristic curve) that when the frequency lowest point returns to a stable value of 49.8 Hz, the energy storage capacity that needs to be configured accounts for 10% of the photovoltaic power station. Also according to Figure 15, it can be seen from Figure 15 that the required energy storage capacity is 6.7%. Compared with the independent regulation of energy storage, it saves 3% and 2.5% respectively after adopting the coordinated control of solar energy storage. To sum up, the proposed method not only reduces the energy storage configuration capacity as much as possible, but also makes the combined frequency modulation effect of the whole photovoltaic storage better.

Claims (7)

1. a coordinated control method for the joint participation of power grid in primary frequency regulation of power grid, is characterized in that: comprise the steps: S1: Model the photovoltaic power generation system and the energy storage system respectively, and obtain the photovoltaic power generation system model and the energy storage system model; the photovoltaic power generation system includes a photovoltaic array, a boost converter, a grid-connected inverter, a filter and its a control system; the energy storage system includes an energy storage battery, a Buck-Boost converter, a grid-connected inverter, a filter and a control system thereof; S2: The photovoltaic participates in the grid frequency regulation through a dynamic variable load shedding method that follows the system output and frequency changes; the dynamic variable load shedding method that the photovoltaic follows the system output and frequency changes is: the photovoltaic uses the maximum power point tracking method to obtain The maximum active power output P _mppt is given as the new active power of photovoltaics after variable load shedding control and amplitude limiting, and is output to the boost converter control system; S3: On the basis of coordinated droop control and positive and negative virtual inertia control, based on the energy storage variable coefficient adaptive control strategy, the energy storage joint frequency modulation is adopted; S4: Set the capacity of the energy storage so that it can provide an inertial response that matches the synchronous generator set, and use photovoltaic variable load shedding and combined frequency modulation with energy storage to realize the coordinated control of primary frequency modulation of the photovoltaic-storage-supported power grid; The photovoltaic power generation system in the step S1 is specifically: The DC voltage V _pv and DC current I _pv output by the photovoltaic array are passed through the maximum power point tracking controller to generate the DC voltage reference value V _refmppt , and the error signals of V _refmppt and V _PV are integrated to obtain the photovoltaic output active power given P _ref , P _ref and the active power P _dc on the high-voltage side of the boost converter are controlled by PI to generate a duty cycle d, which drives the boost converter to work, thereby realizing the MPPT control of the photovoltaic array; the grid-connected inverter works in unity power factor state i _gq ^* = 0, the photovoltaic array is boosted by the boost converter to obtain the DC voltage U _dc , after making a difference with the voltage reference value U _ref , the current inner loop reference value _idref is generated by PI control, and then compared with the actual current value obtained by sampling After the deviation of _id and i _q is controlled by PI controller and current decoupling, the given voltages u _sq and u _sd are obtained. Finally, the trigger pulse S _g of the grid-connected inverter is obtained after coordinate transformation and pulse width modulation. So as to realize the decoupling control and grid-connected operation of the grid-connected inverter active and reactive power; In the step S1, the energy storage system is specifically: The energy storage system realizes the charging and discharging switching of the energy storage through the buck-boost chopper circuit; the voltage and current _VL and _IL of the low-voltage side of the Buck-Boost are sampled and multiplied to obtain the battery power P _bat ; when the DC/DC converter is working in discharging In mode, the active reference reference P _ref is compared with the battery power P _bat , and the duty cycle signal D_Boost is obtained after adjustment by the PI controller. The pulse signal G _Boost of the boost converter; when the converter works in the charging mode, take the opposite number of P _ref , make the difference with the battery power P _bat and multiply by -1, and then control in the discharging mode to obtain the driving Buck The trigger signal G _Buck for converter action. 2. The coordinated control method for the combined participation of photovoltaic and storage in power grid primary frequency regulation according to claim 1, characterized in that: the control characteristic curve expression of dynamic variable load shedding in the step S2 is as follows: σ _max %=K ₀ ×(P _mppt /P _N +Δf/Δf _max ) (1) In the formula: P _N is the rated active power of the photovoltaic system under standard conditions; P _mppt is the maximum active power of the photovoltaic system in the current working condition; Δf _max is the maximum allowable frequency deviation of the system; Δf is the system frequency deviation; K ₀ is Load shedding rate in the initial condition; σ _max % is the upper limit of the load shedding rate. 3. The coordinated control method for the combined participation of photovoltaic and storage in power grid primary frequency regulation according to claim 1, characterized in that: in the step S3, the droop control method is: The energy storage is divided into four intervals: S _max : the maximum working limit of the energy storage battery; S _high : the upper limit of the normal operation of the energy storage battery; S _low : the lower limit of the normal operation of the energy storage battery; S _min : The minimum limit for the operation of the energy storage battery; The Logistic function is used to adaptively control the droop coefficient, and its curve function expression is:

In the formula: P ₀ is the initial value; K is the final value; r measures the speed of the curve growth; Taking SOC as the independent variable, _P0 and r as the parameters, and the charge-discharge coefficient as the dependent variable, the following equation is constructed: 1) battery discharge

2) Battery charging

In the formula: K _max is the final value of the droop coefficient during charging and discharging; S _soc is the state of charge of the energy storage; K _bc and K _bd are the corresponding coefficients during discharging and charging, respectively. 4. A kind of coordinated control method for the joint participation of optical storage and power grid in primary frequency regulation of power grid according to claim 1, it is characterized in that: in described step S3, the positive virtual inertia control method is: The formula for the positive virtual inertial response is: ΔP _bess = -M _bp df/dt (5)

In the formula: M _bp is the positive virtual inertia coefficient; M _bp-c and M _bp-d are the positive virtual inertia coefficients when the energy storage is charged and discharged respectively; M _p is the adjustment coefficient that changes with the frequency deviation; n is the parameter; c ₁ is the initial value of the positive virtual inertia coefficient; D _p is the dead zone of the positive virtual inertia frequency change rate. 5. The coordinated control method for the combined participation of optical storage and storage in the primary frequency regulation of the power grid according to claim 1, wherein the negative virtual inertia control method in the step S3 is: The negative virtual inertia response formula is: ΔP _bess = -M _bn df/dt (8)

In the formula: M _bn is the negative virtual inertia coefficient; M _bn-c and M _bn-d are the negative virtual inertia coefficients during charging and discharging respectively; b ₁ is the initial value of the negative virtual inertia coefficient; M _b1 is the adjustment of the frequency deviation change coefficient; f _bess-d is the dead zone of energy storage frequency regulation; f _max is the maximum frequency deviation amplitude allowed by the grid. 6. The coordinated control method for the combined participation of photovoltaic and storage in power grid primary frequency regulation according to claim 1, characterized in that: the method for configuring the energy storage capacity in the step S4 is: In order to ensure that the configured energy storage can provide an inertial response that matches the synchronous generator set, the capacity of the energy storage is set as follows: When the generator speed is ω, the rotational kinetic energy of the synchronous generator is

When the motor speed follows the system frequency from ω ₀ to ω ₁

The rotational speed of the synchronous generator is proportional to the system frequency, and generally varies within a small range. The grid operation and maintenance guidelines stipulate that the system frequency may rise to 51Hz or drop to 48Hz in a short period of time under special circumstances. Based on the frequency drop analysis, the synchronous generator rotor The rotational speed range of 0.95 ~ 1pu, the kinetic energy that can be released is:

The energy storage device is only limited by the SOC, and can usually achieve a wide range of power throughput. Therefore, a smaller energy storage capacity can achieve the same frequency regulation effect as a conventional generator set. When a photovoltaic power station equipped with energy storage replaces the conventional generator set and When entering the power grid, since the charging and discharging time of the energy storage is generally longer than the inertia response time, when the power of the energy storage meets the requirements, the capacity also meets the requirements; Assuming that the energy released by the energy storage system within Δt is the same as the kinetic energy of the same rotor, there are: ΔE _bess = P _bess Δt = 0.0784HS _N (14) Let Δt=2H P _bess = 0.0392S _N (15) In the formula: ΔE _bess and P _bess are the capacity and power of the energy storage, respectively; S _N is the rated capacity of the generator; H is the inertia constant; J is the inertia time constant of the generator. 7. The coordinated control method for the joint participation of photovoltaic and storage in power grid primary frequency regulation according to claim 1, characterized in that: the method for combined photovoltaic and storage frequency regulation in the step S4 is: 1) The energy storage system provides an inertial response that matches the conventional generator set for the initial frequency change of the power system; 2) Photovoltaic uses variable load shedding and frequency regulation strategy and energy storage adaptive control strategy to jointly participate in primary frequency regulation.

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