A Multi-Time-Scale Auxiliary Frequency Regulation Method for Photovoltaic and Energy Storage Power Stations in Regional Power Grids

Abstract

This invention discloses a multi-timescale auxiliary frequency regulation method for photovoltaic (PV) and energy storage (ESS) power stations in a regional power grid. It comprises four parts: power allocation based on the frequency response of multiple PV units within the PV power station; power allocation based on the frequency response of multiple energy storage units within the PV power station; inertial support and primary frequency response at the PV power station level; and collaborative participation of multiple PV power stations in secondary frequency regulation of the regional power grid. For PV power stations containing multiple PV units and energy storage units, a method for overall inertial support and primary frequency regulation control based on virtual synchronous generator control is designed. For regional power grids containing multiple PV power stations, a secondary frequency regulation method based on robust control is established, enabling collaborative participation of multiple PV power stations in secondary frequency regulation of the regional power grid. This invention achieves auxiliary inertia and power support through primary and secondary frequency regulation control establishment and power allocation, enabling it to cope with various frequency fluctuation events occurring in the power grid.

Description

Technical Field

[0001] This invention relates to the field of power grid control technology, and in particular to an auxiliary frequency regulation method for photovoltaic and energy storage power stations in regional power grids that takes into account multiple time scales. Background Technology

[0002] In recent years, with the escalating global energy crisis and environmental pollution, the development and utilization of renewable energy have received considerable attention. Among them, photovoltaic power generation, as a highly efficient and high-quality form of renewable energy, has gained increasing favor and is being applied more and more widely.

[0003] However, as more and more traditional synchronous generators are replaced by renewable energy sources connected via power electronic devices, the overall inertia of the power system decreases, seriously jeopardizing the system's frequency stability and consequently impacting the security and reliability of power supply. To address these issues, some regions have introduced policies requiring renewable energy power plants to possess flexible adjustment capabilities such as inertia support and frequency response. Therefore, for photovoltaic-storage power plants connected to the grid, an auxiliary frequency regulation strategy needs to be designed to solve these problems.

[0004] Currently, most technical solutions for renewable energy participation in frequency response focus on single-type renewable energy and single-time-scale frequency regulation. For example, some researchers have proposed various control schemes for renewable energy units such as photovoltaic, wind power, and energy storage to participate in inertial support, primary frequency regulation, and secondary frequency regulation in coordination with traditional units. However, the control targets of these technical solutions are relatively singular, making them difficult to apply in systems with multiple types of renewable energy. Furthermore, most schemes only focus on frequency regulation at a single time scale, neglecting the coordination and synergy of frequency responses at various time scales. Based on the above-mentioned technical foundations and existing problems, this invention aims to provide an auxiliary frequency regulation strategy for photovoltaic-energy storage power plants with multiple types of renewable energy and multiple time scales, thereby achieving multi-source, multi-time-scale frequency support and effectively alleviating the problem of increased frequency fluctuations and exceeding limits in regional power grids under high renewable energy penetration. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an auxiliary frequency regulation method for photovoltaic and energy storage power stations in regional power grids that takes into account multiple time scales. By coordinating the photovoltaic units and energy storage units within the photovoltaic and energy storage power station, as well as the collaborative control between traditional thermal power units and the photovoltaic and energy storage power station, the method achieves system inertial support and frequency regulation, thereby suppressing frequency fluctuations in the regional system.

[0006] The present invention adopts the following technical solution. A method for auxiliary frequency regulation of a regional power grid photovoltaic-storage power station considering multiple time scales includes four parts: power allocation of frequency response of multiple photovoltaic units within the photovoltaic-storage power station, power allocation of multiple energy storage units within the photovoltaic-storage power station, inertial support and primary frequency response at the photovoltaic-storage power station level, and collaborative participation of multiple photovoltaic-storage power stations in secondary frequency regulation of the regional power grid. During the frequency regulation control process, instructions are issued sequentially from the upper layer to the lower layer. First, the collaborative participation of multiple photovoltaic-storage power stations in secondary frequency regulation of the regional power grid is carried out, then the inertial support and primary frequency response at the photovoltaic-storage power station level are carried out, and finally the power allocation of frequency response of multiple photovoltaic units within the photovoltaic-storage power station and the power allocation of multiple energy storage units within the photovoltaic-storage power station are carried out.

[0007] The inertial support and primary frequency response at the photovoltaic-energy storage power station level are as follows: For a photovoltaic-energy storage power station containing multiple photovoltaic units and energy storage units, all photovoltaic units and energy storage units within the power station are considered as a whole. A method for overall inertial support and primary frequency regulation control of the photovoltaic power station based on virtual synchronous generator control is designed. The frequency control model of the i-th photovoltaic-energy storage power station is expressed as:

[0008]

[0009] In the formula: k p,i J represents the overall active power droop coefficient of the i-th photovoltaic energy storage station; i Let ω be the virtual inertia of the i-th photovoltaic energy storage station; i ω represents the angular velocity at the grid connection point of the i-th photovoltaic energy storage station; n,i D is the reference value for the angular velocity of the i-th photovoltaic energy storage site; i Let ΔP be the damping coefficient of the i-th photovoltaic energy storage station; i t represents the overall active power adjustment of the photovoltaic-storage power station.

[0010] Further optimization yields the following method for coordinating photovoltaic units and energy storage units within a primary frequency regulation photovoltaic power station:

[0011]

[0012]

[0013] Where: ΔP PV,i Let ΔP be the total active power regulation of the i-th photovoltaic power storage station. BESS,i Let P be the total energy storage regulation within the i-th photovoltaic-energy storage site. prc,i Let ΔP be the active power reserve capacity of the i-th photovoltaic power storage facility at the current moment. i This represents the overall active power adjustment for the i-th photovoltaic-storage power station.

[0014] Further optimization involves establishing a robust control-based secondary frequency regulation method for regional power grids containing multiple photovoltaic and energy storage power plants, enabling coordinated participation of multiple photovoltaic and energy storage power plants in the secondary frequency regulation of the regional power grid.

[0015] The state-space model for secondary frequency control of the regional power grid, which includes thermal power units and photovoltaic-storage power plants, is established as follows:

[0016]

[0017] In the formula, Let z(t) be the change in the state variable, u(t) be the output variable, w(t) be the control variable, and w(t) be the disturbance variable. The matrix of the state variables is x. T =[Δf,ΔACE,ΔP] m ,ΔP g ,ΔP c,g ,ΔP PV_BESS,i ,ΔP c,PV,i The matrix w of the perturbation variables T =[ΔP PV,i ,ΔP L ], the matrix of control variables u T =[ΔP c,g ,ΔP c,PV,i ], where i = 1, 2, ..., n; A is the coefficient matrix of the state variables, B u B is the coefficient matrix of the control variables. w Let C be the coefficient matrix of the disturbance variable, and C be the coefficient matrix of the output variable; Δf is the regional power grid frequency deviation, ΔACE is the regional frequency deviation signal, and ΔP is the coefficient matrix of the output variable. m ΔP represents the change in output power of a thermal power unit. g ΔP represents the change in valve position of the thermal power generator speed controller. c,g ΔP is the secondary frequency control input for the speed controller. PV_BESS,i Let ΔP be the change in active power output of the i-th photovoltaic energy storage station. c,PV,i ΔP is the secondary frequency modulation control input for the i-th photovoltaic energy storage station. PV,i Let ΔP be the total active power regulation of the i-th photovoltaic power storage station. L This refers to the load deviation.

[0018] The design is based on robust H ∞ The controlled system's secondary frequency regulation controller is u(s) = K(s)y(s); by solving the following optimization problem and searching for the optimal solution that satisfies the constraints, the optimal robust H of the regional power grid can be obtained. ∞ The optimal control law of controller feedback control;

[0019] minζ 2

[0020] st

[0021]

[0022] X > 0

[0023] In the formula: ζ represents H ∞ The performance indicators of the controller; I is the identity matrix, K is the optimal control law of feedback control, X and W are symmetric positive definite matrices in the solution process, and T represents the transpose.

[0024] Further optimization involves the following power allocation method for the frequency response of multiple photovoltaic units within the photovoltaic-storage power station: For photovoltaic units participating in auxiliary frequency regulation within the power station, a droop control strategy for the inverter of the photovoltaic unit is designed based on the DC-side control method of the photovoltaic unit. The goal is to fully utilize the active power frequency regulation capability of each photovoltaic unit within the power station while ensuring that the remaining adjustable capacity of each photovoltaic unit tends to be consistent. This design enables the power allocation method for the frequency response of multiple photovoltaic units within the power station to achieve frequency tracking at the single-unit level of the photovoltaic unit.

[0025] A portion of the photovoltaic (PV) units in the solar-storage power station operate in load shedding control mode, causing their operating points to deviate from their maximum power points, thus reserving a certain amount of active power reserve capacity for frequency regulation participation. The inverters of the PV units participating in frequency response can employ PQ control (constant power control) to achieve the goal of participating in primary frequency regulation of the power grid by tracking external commands. An active power allocation weighting coefficient α for PV unit l is established. l as follows:

[0026]

[0027] In the formula: l is the number of the photovoltaic unit connected to the photovoltaic and energy storage site, ΔP PV.i Let α be the total active power regulation of the i-th photovoltaic power station; l ΔP is the active power allocation weighting coefficient for photovoltaic unit l, n is the number of photovoltaic units, and ΔP is the active power allocation weighting coefficient for photovoltaic unit l. up,l ΔP represents the surplus active power that the photovoltaic unit can generate. down,l The remaining active power that can be reduced by the photovoltaic unit l; the reference value P of the output active power of the photovoltaic unit l in the load shedding control mode after distribution. prc,ref,l for:

[0028] P prc,ref,l =P e,l +α l ·ΔP PV.i .

[0029] In the formula: P e,l This represents the active power output value of photovoltaic unit l at the current moment.

[0030] Further optimization involves the power allocation of multiple energy storage units within the photovoltaic-energy storage power station: For energy storage units participating in auxiliary frequency regulation within the photovoltaic-energy storage power station, based on the control method of the energy storage inverter participating in frequency regulation, with the goal of maintaining the charge state of the energy storage units at 50% while reducing the number of energy storage unit operations, a power allocation scheme for multiple energy storage units within the photovoltaic-energy storage power station is formulated to enable the energy storage units within the photovoltaic-energy storage power station to assist the photovoltaic units in power tracking.

[0031] Further optimization involves designing a weight allocation strategy for multiple energy storage units within a photovoltaic-energy storage facility based on a fuzzy algorithm when allocating power: when discharging energy, energy storage units with higher charge states have higher discharge priority, i.e., higher discharge weight, and their weight decreases as the charge state decreases; when charging energy storage units, energy storage units with lower charge states have higher charging priority, and their weight decreases as the charge state increases.

[0032] The beneficial effects of this invention are that, compared with existing technologies, it comprehensively considers the synergistic effect of multiple types of frequency regulation resources (photovoltaics and energy storage) participating in frequency regulation within the regional power grid under high penetration of new energy sources, and specifically designs control strategies and power allocation schemes for their participation in frequency regulation. Furthermore, this invention also takes into account different time scales, designing a comprehensive control scheme for photovoltaic-energy storage power plants from three time scales: inertial support, primary frequency regulation, and secondary frequency regulation. This scheme is more complete and closer to practical applications than existing technologies, and has high reference value.

[0033] This invention comprehensively considers the multi-timescale frequency response characteristics of photovoltaic and energy storage power plants participating in inertia support, primary frequency regulation, and secondary frequency regulation. It achieves auxiliary inertia and power support through the establishment of primary and secondary frequency regulation controllers and power allocation, enabling it to cope with various frequency fluctuation events occurring in the power grid. Therefore, the purpose of this invention is to provide a multi-timescale auxiliary frequency regulation method for photovoltaic and energy storage power plants in regional power grids, which is suitable for solving the problems of increased frequency fluctuations and exceeding limits in regional power grids under high penetration of new energy sources. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Wherein:

[0035] Figure 1 This is a schematic diagram of the framework control structure of a multi-time-scale assisted frequency regulation method for regional power grid photovoltaic and energy storage stations proposed in this invention;

[0036] Figure 2 This is a schematic diagram illustrating the SOC (State of Charge) division of energy storage units in a power allocation method for multiple energy storage units within a photovoltaic energy storage site proposed in this invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0038] This invention proposes an auxiliary frequency regulation method for regional power grid photovoltaic-storage power plants that considers multiple time scales. It includes four parts: power allocation based on the frequency response of multiple photovoltaic units within the photovoltaic-storage power plant; power allocation based on the frequency response of multiple energy storage units within the photovoltaic-storage power plant; inertial support and primary frequency response at the photovoltaic-storage power plant level; and collaborative participation of multiple photovoltaic-storage power plants in secondary frequency regulation of the regional power grid. During the frequency regulation control process, such as... Figure 1 As shown, commands are issued sequentially from top to bottom. First, multiple photovoltaic (PV) and energy storage (ESS) power plants coordinate to participate in the secondary frequency regulation of the regional power grid. Then, inertial support and primary frequency response at the PV / ESS power plant level are implemented. Finally, power allocation for the frequency response of multiple PV units and the power allocation for multiple energy storage units within the PV / ESS power plant are performed. In the hierarchical design process of this invention, a power allocation method for the frequency response of multiple PV units within the PV / ESS power plant is designed first. Then, a power allocation scheme for multiple energy storage units within the PV / ESS power plant is formulated. Next, an overall control method for the PV / ESS power plant based on virtual synchronous generator control is designed to achieve inertial support and primary frequency response at the PV / ESS power plant level. Finally, a secondary frequency regulation method based on robust control is established to achieve coordinated participation of multiple PV / ESS power plants in the secondary frequency regulation of the regional power grid.

[0039] This embodiment focuses on photovoltaic units participating in auxiliary frequency regulation within a photovoltaic-storage power station. Based on the DC-side control method of photovoltaic units, a droop control strategy for the inverter of the photovoltaic unit is designed. The goal is to fully utilize the active power frequency regulation capability of each photovoltaic unit in the photovoltaic-storage power station while ensuring that the remaining adjustable capacity of each photovoltaic unit tends to be consistent. A power allocation method for the frequency response of multiple photovoltaic units in the photovoltaic-storage power station is designed, realizing frequency tracking at the single-unit level of the photovoltaic unit.

[0040] To achieve maximum power output, photovoltaic (PV) generators typically employ Maximum Power Point Tracking (MPPT) control on the DC side. While MPPT ensures maximized utilization of PV energy, it results in poor controllability of the PV generator's active power output, failing to meet system frequency regulation requirements. Therefore, to achieve active power control of PV generators, some PV generators in the PV-storage power station are operated in Reverse Load Control (PRC) mode. This deviates the PV generator's operating point from its maximum power point, reserving a certain amount of active power reserve capacity for frequency regulation. In Reverse Load Control mode, when the grid frequency fluctuates, the PV system can adjust its output power upwards or downwards to suppress grid frequency fluctuations.

[0041] The reference value for the active power output of a photovoltaic unit operating in load shedding control mode can be expressed as:

[0042] P prc,ref,l =P mppt,l ·γ l

[0043] In the formula: l is the number of the photovoltaic unit connected to the photovoltaic and energy storage site; P prc,ref,l P is a reference value for the active power output of the photovoltaic unit in PRC (Programmable Grid Control) mode. mppt,l The estimated value of the maximum active power output of the photovoltaic (PV) unit can be obtained by measuring adjacent PV units operating in MPPT mode; γ l γ is the active power adjustment factor for photovoltaic unit l. l ∈[0,1], and in the steady state we have γ l =0.5γ l,max , where γ l,max This is the active power adjustment factor corresponding to the maximum adjustable active power of photovoltaic unit l.

[0044] Photovoltaic inverters that participate in frequency response can use PQ control to achieve the goal of participating in the primary frequency regulation of the power grid by tracking external commands.

[0045] To fully utilize the active power frequency regulation capabilities of each photovoltaic (PV) unit within a solar-energy storage facility, while ensuring that the remaining adjustable capacity of each PV unit is consistent, all PV units within a single facility using load shedding control will receive frequency regulation commands proportionally. First, the adjustable active power surplus of a single PV unit is calculated:

[0046] ΔP up,l =P mppt,l -P e,l

[0047] ΔP down,l =P e,l -P mppt,l ·γ l,max

[0048] Where: ΔP up,l ΔP represents the surplus active power that the photovoltaic unit can generate. down,l P represents the surplus active power that can be reduced from the photovoltaic unit. e,l Let be the active power output value of photovoltaic unit l at the current moment. Based on this, the active power allocation weighting coefficient α of photovoltaic unit l is defined. l as follows:

[0049]

[0050] Where: ΔP PV.i Let α be the total active power regulation of the i-th photovoltaic power station;l is the active power distribution weight coefficient of the photovoltaic unit l, and n is the number of photovoltaic units.

[0051] In summary, after distribution, the reference value P of the active power output by the photovoltaic unit l in the load shedding control mode is prc,ref,l as follows:

[0052] P prc,ref,l = P e,l + α l ·ΔP PV.i .

[0053] In this embodiment, for the energy storage units participating in auxiliary frequency modulation inside the photovoltaic and energy storage power station, according to the control method of the energy storage inverter for the energy storage units participating in frequency modulation, with the goal of keeping the state of charge (SOC) of the energy storage units at 50% and reducing the action times of the energy storage units, a power distribution scheme for multiple energy storage units inside the photovoltaic and energy storage power station is formulated to enable the energy storage units inside the photovoltaic and energy storage power station to assist the photovoltaic units in power tracking.

[0054] In an actual photovoltaic power station, using a single photovoltaic unit for frequency modulation is often limited by its power regulation range, affecting the frequency modulation effect. Therefore, currently, the method of configuring energy storage units is generally used to improve the active power regulation ability of the photovoltaic and energy storage power station. The energy storage inverters participating in frequency modulation generally adopt droop control to simulate the power-frequency droop characteristics of a generator set equipped with a governor when participating in the primary frequency modulation of the power grid to achieve primary frequency modulation. Since the droop control method of the energy storage inverter has been widely used, it will not be elaborated here. For the active reference power P bess,ref,i of each energy storage unit inside the photovoltaic and energy storage power station, it will be obtained by the following power distribution strategy.

[0055] When designing the energy storage power distribution scheme, to avoid overcharging and over-discharging during the power distribution process of the energy storage units inside the photovoltaic and energy storage power station and reduce the action times of the energy storage, a reasonable action plan needs to be designed according to its state of charge. Define the state of charge of the energy storage unit as SOC, SOC ∈ [0, 1], where SOC = 1 indicates that the energy of the energy storage unit is completely saturated and cannot absorb energy continuously, and SOC = 0 indicates that the energy of the energy storage unit has been exhausted and cannot release energy continuously. Divide SOC into different intervals, and the requirements for charging and discharging are different for each interval:

[0056] 1) Charging overlimit area: SOC max < SOC < 1, the energy storage unit has too much electricity, denoted as "H", with the highest priority for discharging, and the output range is 0 ≤ P ≤ P max ;

[0057] 2) Charging warning area: SOC high < SOC < SOC max , the energy storage unit has high electricity, denoted as "MH", with a relatively high priority for discharging, and the output range is -P H<P<P max ;

[0058] 3) Normal working area: SOC low <SOC<SOC high The energy storage unit has a normal charge level and is in a charge / dischargeable phase, denoted as "M", with an output range of -P. max ≤P≤P max ;

[0059] 4) Discharge warning zone: SOC min <SOC<SOC low When the energy storage unit has a low charge level, it is denoted as "ML". It has a high charging priority and its output range is -P. max ≤P≤P L ;

[0060] 5) Discharge over-limit region: 0 <SOC<SOC min If the energy storage unit's charge is too low, it is denoted as "L". Charging priority is highest, and the output range is -P. max ≤P≤0.

[0061] Where P is the charging and discharging power of the energy storage unit, and SOC is the state of charge. max The State of Charge (SOC) is the maximum value of the energy storage unit. max =0.9; SOC high The state of charge (SOC) of the energy storage unit is the high-order threshold. high =0.6, SOC low The state of charge (SOC) threshold of the energy storage unit. low =0.4, SOC min The state of charge (SOC) of the energy storage unit is the minimum value. min =0.1; P max P represents the maximum charge / discharge power of the energy storage unit. L The energy storage unit is in a state of charge of [SOC]. min SOC low The smoothing power limit set within the specified range; P H The energy storage unit is in a state of charge of [SOC]. high SOC max The smoothing power limit set within the specified range is expressed as follows:

[0062]

[0063]

[0064] In the formula, a is a coefficient that determines the charge state of the energy storage unit.

[0065] Next, a fuzzy algorithm is used for weight allocation. This fuzzy controller uses the total regulating power P of the energy storage units within the site, calculated in step S3. bess,ref The system takes the real-time SOC of each energy storage unit as input, outputs the charge and discharge weight of each energy storage unit, and determines the charge and discharge sequence according to the weight from large to small. The goal is to stabilize the SOC of each energy storage unit at around 0.5 and keep the energy storage unit in a chargeable and dischargeable state.

[0066] The SOC fuzzy subset of the energy storage unit is defined as five parts: [H, MH, M, ML, L], representing [charging limit exceedance zone, charging warning zone, normal operation zone, discharging warning zone, and discharging limit exceedance zone]. The weight D(t) is defined as ranging from [0,1], and its fuzzy subset is also divided into five parts: [D, MD, M, MX, X], representing [large, relatively large, medium, relatively small, and small]. The corresponding rules are as follows: when the energy storage unit discharges, the higher the SOC, the higher the discharge priority, i.e., the larger the weight D(t), and D(t) decreases as the SOC decreases; when the energy storage unit charges, the lower the SOC, the higher the charging priority, and D(t) decreases as the SOC increases. The resulting charging and discharging fuzzy rules for the energy storage unit are shown in Tables 1 and 2.

[0067] Table 1. Charging Fuzzy Rule Table

[0068]

[0069] Table 2. Discharge Ambiguity Rule Table

[0070]

[0071] The above fuzzy rules can be used to obtain the output priority of different energy storage units under each condition, thereby realizing the rational allocation of power of energy storage units in different states within the photovoltaic-energy storage site.

[0072] This embodiment designs a PV-storage power station containing multiple photovoltaic (PV) units and energy storage units, and implements a holistic control method based on virtual synchronous generator control. This method achieves inertial support and primary frequency response at the PV-storage power station level, suppressing dynamic frequency fluctuations. All PV units and energy storage units within the PV-storage power station are treated as a single unit in the power station control design. Externally, the PV-storage power station can be viewed as an equivalent virtual synchronous generator. Dynamic inertial support and primary frequency adjustment are achieved by real-time acquisition of the power deviation and power change rate at the grid connection point. Internally, an active power allocation strategy for the PV units and energy storage units is designed to achieve rapid power compensation.

[0073] The virtual synchronous generator control structure equates the inertia and damping characteristics of a synchronous generator, and expresses the relationship between frequency and active power as follows:

[0074]

[0075] In the formula: ω is the system angular velocity; J is the virtual inertia; D is the damping coefficient; ω n This is the reference value for angular velocity; P m P represents mechanical power, θ represents the output power angle; e For active power output; P ref K is the active power reference value. ω t is the angular velocity droop gain coefficient; t is time.

[0076] Analogous to the virtual synchronous generator equations, and temporarily disregarding reactive power and voltage control, the frequency control model for the i-th photovoltaic-storage power station can be expressed as:

[0077]

[0078] In the formula: k p,i J represents the overall active power droop coefficient of the i-th photovoltaic energy storage station; i Let ω be the virtual inertia of the i-th photovoltaic energy storage station; i ω represents the angular velocity at the grid connection point of the i-th photovoltaic energy storage station; n,i D is the reference value for the angular velocity of the i-th photovoltaic energy storage site; i Let ΔP be the damping coefficient of the i-th photovoltaic energy storage station; i This refers to the overall active power adjustment of the photovoltaic and energy storage power station.

[0079] Next, we design the power distribution method within the photovoltaic-storage power station. Considering that active power reduction by photovoltaic units increases curtailment costs and that curtailment restrictions limit photovoltaic active power regulation capabilities, while the cost and maintenance of energy storage units are relatively high, and frequent starts-up of energy storage units will reduce their lifespan, we design the following photovoltaic-storage coordination method for primary frequency regulation:

[0080]

[0081]

[0082] Where: ΔP PV,i Let ΔP be the total active power regulation of the i-th photovoltaic power storage station. BESS,i Let P be the total energy storage regulation within the i-th photovoltaic-energy storage site. prc,i Let ΔP be the active power reserve capacity of the i-th photovoltaic power storage facility at the current moment. i This represents the overall active power adjustment for the i-th photovoltaic-storage power station.

[0083] As shown in the above formula, when the grid connection frequency of the photovoltaic-storage power station exceeds the dead zone, the droop control of the photovoltaic-storage power station calculates the overall active power adjustment in real time. This overall active power adjustment is then compared with the current photovoltaic active power reserve capacity within the power station, such as ΔP.i ≤P prc,i Then only the frequency support of photovoltaic participation within the photovoltaic and energy storage facility is required, i.e., ΔP PV,i =ΔP i ΔP BESS,i =0; for example Then the surplus optical power in the photovoltaic energy storage station is supplemented by the energy storage unit, i.e., ΔP PV,i =P prc,i ΔP BESS,i =ΔP i -P prc,i .

[0084] This embodiment addresses a regional power grid containing multiple photovoltaic and energy storage (PV) power plants. It establishes a robust control-based secondary frequency regulation method to enable coordinated participation of multiple PV and energy storage plants in the secondary frequency regulation of the regional power grid, thereby reducing the steady-state deviation of the regional frequency. First, a dynamic model of the regional power grid's frequency regulation is established. Taking a regional power grid including thermal power units and virtual synchronized PV and energy storage plants as an example, and considering the impact of fluctuations in photovoltaic output and load, a state-space model for the secondary frequency control of the regional power grid is established.

[0085] The frequency response model of the regional power grid is as follows:

[0086]

[0087] In the formula: Δf is the frequency deviation of the regional power grid, H is the inertia coefficient of the regional power grid, D is the load damping coefficient of the regional power grid, and ΔP m ΔP represents the change in output power of a thermal power unit. PV_BESS,i Let ΔP be the change in active power output of the i-th photovoltaic energy storage station. L Let be the load deviation, and s be the complex frequency.

[0088] The governor model for thermal power units is as follows:

[0089]

[0090] Where: ΔP g T represents the change in valve size of the thermal power generator speed controller. g Let ΔP be the time constant of the speed controller. c,g R is the secondary frequency control input for the speed controller. g This is the droop coefficient for primary frequency modulation.

[0091] The turbine model of a thermal power unit is as follows:

[0092]

[0093] In the formula: T ch This is the turbine time constant.

[0094] The dynamic model of the virtual synchronized photovoltaic energy storage site is as follows:

[0095]

[0096] Where: ΔP c,PV,i T is the secondary frequency modulation control input for the i-th photovoltaic energy storage site. PV,i Let be the time constant of the i-th photovoltaic energy storage station.

[0097] Regional frequency deviation signal model:

[0098] ΔACE=β·Δf

[0099] ΔACE is the regional frequency deviation signal, and β is the regional frequency deviation coefficient;

[0100] Therefore, the state-space model for the secondary frequency control of the regional power grid, which includes thermal power units and solar power and energy storage stations, is obtained as follows:

[0101]

[0102] In the formula, Let z(t) be the change in the state variable, u(t) be the output variable, w(t) be the control variable, and w(t) be the disturbance variable. The matrix of the state variables is x. T =[Δf,ΔACE,ΔP] m ,ΔP g ,ΔP c,g ,ΔP PV_BESS,i ,ΔP c,PV,i The matrix w of the perturbation variables T =[ΔP PV,i ,ΔP L ], the matrix of control variables u T =[ΔP c,g ,ΔP c,PV,i ], where i = 1, 2, ..., n; A is the coefficient matrix of the state variables, B u B is the coefficient matrix of the control variables. w Let C be the coefficient matrix of the disturbance variable, and let C be the coefficient matrix of the output variable.

[0103] Based on the frequency regulation dynamic model of the regional power grid, a secondary frequency control strategy for the regional power grid is designed. Due to uncertain power disturbances such as photovoltaic output and load in the regional power grid, the control model has bounded errors. Therefore, a robust H-based strategy is considered. ∞ The control design incorporates a secondary frequency modulation controller to reduce the impact of various uncertainties on the control and improve the system's robustness.

[0104] Design robust H ∞ The controller method involves solving for a controller u(s) = K(s)y(s) such that the controlled closed-loop system satisfies the following two performance indices:

[0105] Performance Indicator I: The closed-loop system has internal stability, that is, all eigenvalues ​​of the closed-loop system state matrix are within the left half of the open-complex plane;

[0106] Performance Indicator II: Closed-loop transfer function T from disturbance variable to output variable wz H of (s) ∞ The norm is less than 1, that is:

[0107] ||T wz (s)|| ∞ <ζ

[0108] In the formula, ζ represents H ∞ The performance indicators of the controller. By finding the range of values ​​for the variable ζ and determining the minimum value of ζ, the optimal H of the regional power grid can be obtained. ∞ A controller is a controller that minimizes the disturbance suppression of a closed-loop system.

[0109] Based on the aforementioned derivation of the regional power grid state-space equations, performance index II can be further expressed in the following form:

[0110] ||Τ wz (s)|| ∞ =||(C[sI-(Α+B) u K)] -1 B w )|| ∞ <ζ

[0111] In the formula: I is the identity matrix, and K is the optimal control law of feedback control.

[0112] If, for a given constant ζ>0, there exist two performance indices that satisfy the above two conditions, and if and only if there exist constants and symmetric positive definite matrices X and W such that the following matrix inequality holds, then the regional power grid can be asymptotically stable:

[0113] minζ 2

[0114] st

[0115]

[0116] X > 0

[0117] Here, T represents the transpose. By solving the above optimization problem and searching for the optimal solution that satisfies the constraints, the optimal robustness H of the regional power grid can be obtained. ∞ The optimal control law for controller feedback control.

[0118] The above embodiments are merely explanations of the present invention and are not intended to limit the present invention. After reading this specification, those skilled in the art can make modifications to these embodiments without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A method for auxiliary frequency regulation of photovoltaic and energy storage power stations in a regional power grid considering multiple time scales, characterized in that, The system comprises four parts: power allocation based on the frequency response of multiple photovoltaic units within a photovoltaic-storage power station; power allocation based on the frequency response of multiple energy storage units within a photovoltaic-storage power station; inertial support and primary frequency response at the photovoltaic-storage power station level; and collaborative participation of multiple photovoltaic-storage power stations in secondary frequency regulation of the regional power grid. During the frequency regulation control process, commands are issued sequentially from the upper to the lower levels. First, multiple photovoltaic-storage power stations collaboratively participate in secondary frequency regulation of the regional power grid. Then, inertial support and primary frequency response at the photovoltaic-storage power station level are implemented. Finally, power allocation based on the frequency response of multiple photovoltaic units within a photovoltaic-storage power station and power allocation based on the frequency response of multiple energy storage units within a photovoltaic-storage power station are implemented. The inertial support and primary frequency response at the photovoltaic-energy storage power station level are as follows: For a photovoltaic-energy storage power station containing multiple photovoltaic units and energy storage units, all photovoltaic units and energy storage units within the power station are considered as a whole. A method for overall inertial support and primary frequency regulation control of the photovoltaic power station based on virtual synchronous generator control is designed. The frequency control model of the i-th photovoltaic-energy storage power station is expressed as: ； In the formula: Let be the overall active power droop coefficient of the i-th photovoltaic energy storage station; Let be the virtual inertia of the i-th optical energy storage station; Let be the angular velocity at the grid connection point of the i-th photovoltaic energy storage station; This is the reference value for the angular velocity of the i-th photovoltaic energy storage site; Let be the damping coefficient of the i-th photovoltaic energy storage station; t represents the overall active power adjustment of the photovoltaic-storage power station; For a regional power grid containing multiple photovoltaic and energy storage power plants, a robust control-based secondary frequency regulation method is established to enable multiple photovoltaic and energy storage power plants to collaboratively participate in the secondary frequency regulation of the regional power grid. The state-space model for the secondary frequency control of the regional power grid containing thermal power units and photovoltaic and energy storage power plants is established as follows: ； In the formula, The change in the state variable. For output variables, To control variables, The matrix of perturbation variables and state variables The matrix of perturbation variables Matrix of control variables where i = 1, 2, ..., n; The coefficient matrix of the state variables. The coefficient matrix of the control variables, The coefficient matrix of the disturbance variable. This is the coefficient matrix for the output variables; This refers to the frequency deviation of the regional power grid. This is a regional frequency deviation signal. This represents the change in output power of the thermal power unit. This refers to the change in valve position of the thermal power unit speed controller. This is the secondary frequency regulation control input for the speed controller. Let be the change in active power output of the i-th photovoltaic energy storage station. This is the secondary frequency modulation control input for the i-th photovoltaic energy storage station. Let be the total active power regulation of the photovoltaic power generation system at the i-th photovoltaic-storage power station. This refers to the load deviation. Design robust H ∞ The controller method involves solving for the secondary frequency modulation controller u(s) = K(s)y(s) of the system, ensuring that the controlled closed-loop system meets the following two performance indicators: Performance Indicator I: The closed-loop system has internal stability, that is, all eigenvalues ​​of the closed-loop system state matrix are within the left half of the open-complex plane; Performance Indicator II: Closed-Loop Transfer Function from Disturbance Variable to Output Variable H ∞ The norm is less than 1, that is: ； In the formula, ζ represents H ∞ The performance index of the controller is determined by finding the range of values ​​for the variable ζ, and then determining the minimum value of ζ, which is the solution for obtaining the optimal H of the regional power grid. ∞ A controller, that is, a controller that minimizes the disturbance suppression of a closed-loop system; Based on the aforementioned derivation of the regional power grid state-space equations, performance index II is further expressed in the following form: ； In the formula: It is the identity matrix. The optimal control law for feedback control; If, for a given constant ζ > 0, there exist two performance indices that satisfy the above two conditions, and if and only if there exist constants and symmetric positive definite matrices X and W such that the following matrix inequality holds, then the regional power grid can be asymptotically stable: ； Where X and W are symmetric positive definite matrices in the solution process, and T represents the transpose; by solving the optimization problem and searching for the optimal solution that satisfies the constraints, the optimal robust H of the regional power grid is obtained. ∞ The optimal control law for controller feedback control.

2. The method for auxiliary frequency regulation of regional power grid photovoltaic-storage substations considering multiple time scales as described in claim 1, characterized in that, The coordination method between photovoltaic units and energy storage units inside a primary frequency regulation photovoltaic power station is as follows: ； ； In the formula: Let be the total active power regulation of the photovoltaic power generation system at the i-th photovoltaic-storage power station. Let i be the total energy storage regulation within the i-th photovoltaic-energy storage site. Let ΔP be the active power reserve capacity of the i-th photovoltaic power storage facility at the current moment. i This represents the overall active power adjustment for the i-th photovoltaic-storage power station.

3. The method for auxiliary frequency regulation of regional power grid photovoltaic-storage substations considering multiple time scales as described in claim 1, characterized in that, The power allocation method for the frequency response of multiple photovoltaic units within the photovoltaic-storage power station is as follows: For the photovoltaic units participating in auxiliary frequency regulation within the photovoltaic-storage power station, a droop control strategy for the inverter of the photovoltaic unit is designed based on the DC-side control method of the photovoltaic unit. The goal is to fully utilize the active power frequency regulation capability of each photovoltaic unit within the photovoltaic-storage power station while ensuring that the remaining adjustable capacity of each photovoltaic unit tends to be consistent. This method achieves frequency tracking at the single-unit level of the photovoltaic unit.

4. The method for auxiliary frequency regulation of regional power grid photovoltaic-storage substations considering multiple time scales as described in claim 3, characterized in that, A portion of the photovoltaic (PV) units in the solar-energy storage power station operate in load shedding control mode, causing their operating points to deviate from their maximum power points, thus reserving a certain amount of active power reserve capacity for frequency regulation participation. The inverters of the PV units participating in frequency response employ constant power control, achieving the goal of participating in primary frequency regulation of the power grid by tracking external commands. A system of PV units is established... Active power allocation weighting coefficient as follows: ； In the formula: This refers to the number of the photovoltaic units connected to the photovoltaic and energy storage facility. Let be the total active power regulation of the photovoltaic power generation system at the i-th photovoltaic-storage power station; For photovoltaic units The active power allocation weighting coefficient, where n is the number of photovoltaic units. For photovoltaic units The remaining amount of active power that can be generated; For photovoltaic units The amount of active power that can be reduced; Photovoltaic units in load shedding control mode after allocation Reference value for output active power for: ； In the formula: For photovoltaic units The active power output value at the current moment.

5. The method for auxiliary frequency regulation of regional power grid photovoltaic-storage substations considering multiple time scales as described in claim 1, characterized in that, The power allocation scheme for multiple energy storage units within the photovoltaic-energy storage power station: For energy storage units participating in auxiliary frequency regulation within the photovoltaic-energy storage power station, based on the control method of the energy storage inverter participating in frequency regulation, with the goal of maintaining the charge state of the energy storage unit at 50% while reducing the number of energy storage unit operations, a power allocation scheme for multiple energy storage units within the photovoltaic-energy storage power station is formulated to enable the energy storage units within the photovoltaic-energy storage power station to assist the photovoltaic units in power tracking.

6. The method for auxiliary frequency regulation of regional power grid photovoltaic-storage substations considering multiple time scales as described in claim 5, characterized in that, When allocating power among multiple energy storage units in a photovoltaic-energy storage facility, a weight allocation strategy for energy storage units is designed based on a fuzzy algorithm: when energy storage is discharged, energy storage units with higher charge states have higher discharge priority, i.e., higher discharge weight, and their weight decreases as the charge state decreases. When energy storage units are charged, those with lower charge states have higher charging priority, and their weight decreases as the charge state increases.

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