A photovoltaic grid-type support control method and device based on variable step-size power tracking

Abstract

This invention provides a photovoltaic grid-connected control method and device based on variable step-size power point tracking (MPPT), belonging to the field of new energy grid-connected control technology. The method includes: acquiring the current voltage tracking step size, the photovoltaic output voltage before and after disturbance control, and the photovoltaic output current before and after disturbance control; calculating the photovoltaic output power before and after disturbance control based on the photovoltaic output voltage and current before and after disturbance control; determining the sign bit based on the photovoltaic output power and voltage before and after disturbance control; and determining the voltage step size for the next wake-up of maximum power point tracking (MPPT) based on the sign bit and the current voltage tracking step size, thereby utilizing reserve active power to achieve rapid frequency and inertia response. This invention improves the stability of the original fixed step-size tracking and provides inertial and damped virtual synchronization control, better supporting system frequency stability.

Description

Technical Field

[0001] This invention relates to the field of new energy grid-connected control technology, and in particular to a photovoltaic grid-type support control method and device based on variable step size power tracking. Background Technology

[0002] Currently, the low-carbon transformation of the power system is accelerating, and new energy power generation is experiencing sustained and rapid growth, with its installed capacity continuously increasing. The power system's inertia has significantly decreased, and its active power frequency regulation capability is severely insufficient. In recent years, high-proportion renewable energy power grids in countries such as the UK and Australia have experienced large-scale blackouts caused by frequency instability, resulting in significant economic and social losses and adverse international repercussions. Therefore, future power systems require renewable energy power plants to possess a certain level of inertia support and frequency regulation capability.

[0003] Because the output voltage and current of photovoltaic cells exhibit strong nonlinearity with changes in solar irradiance and junction temperature, a unique maximum power output point (MPP) exists under specific operating conditions. In practical applications, both the intensity of natural light radiation and atmospheric transmittance are dynamically changing. To obtain as much electrical energy as possible under the same solar irradiance and junction temperature, the problem of maximum power point tracking (MPPT) arises. Traditional solutions use a constant voltage tracking method to quickly locate the vicinity of the maximum power point, but this suffers from poor accuracy. Currently, patent CN110362146A provides an adaptive MPPT control strategy based on a variable step-size perturbation observation method. This strategy introduces an adaptive variable step-size factor, which adaptively changes the size of the perturbation step, allowing the perturbation step to be adjusted adaptively according to the distance between the operating point of the photovoltaic power generation system and the maximum power point.

[0004] In the process of implementing the embodiments of this application, it was found that the related technology has at least the following technical problems:

[0005] Applying a continuous disturbance to the voltage will result in significant power fluctuations near the maximum power point. Summary of the Invention

[0006] This invention provides a photovoltaic grid-type support control method and device based on variable step size power tracking to solve the problem of large power fluctuations occurring near the maximum power point.

[0007] In a first aspect, embodiments of the present invention provide a photovoltaic grid-type support control method based on variable step-size power tracking, comprising:

[0008] Obtain the current voltage tracking step size, the photovoltaic output voltage before and after disturbance control, and the photovoltaic output current before and after disturbance control;

[0009] Based on the photovoltaic output voltage and photovoltaic output current before and after disturbance control, the photovoltaic output power before and after disturbance control is calculated accordingly.

[0010] The sign bit is determined based on the photovoltaic output power and photovoltaic output voltage before and after disturbance control.

[0011] The voltage step size for the next MPPT wake-up is determined based on the sign bit and the current voltage tracking step size.

[0012] In one possible implementation, determining the sign bit based on the photovoltaic output power and photovoltaic output voltage before and after disturbance control includes:

[0013] The photovoltaic output power and output voltage before and after disturbance control are input into the sign bit calculation formula to calculate the sign bit; whereby the sign bit calculation formula is:

[0014]

[0015] Where P(k) is the photovoltaic output power before disturbance control; P(k-1) is the photovoltaic output power after disturbance control; u(k) is the output voltage before disturbance control; and u(k-1) is the output voltage after disturbance control.

[0016] In one possible implementation, determining the voltage step size for the next MPPT wake-up based on the sign bit and the current voltage tracking step size includes:

[0017] Obtain the previous voltage tracking step size corresponding to the current voltage tracking step size, and obtain the sign bit corresponding to the previous voltage tracking step size;

[0018] When the voltage tracking step size is equal to the maximum step size limit and the sign bit is equal to the set value in both cases, the minimum step size limit is selected as the base step size; otherwise, the current voltage tracking step size is used as the base step size.

[0019] The active power output command is determined based on the current photovoltaic output voltage and current photovoltaic output current.

[0020] When the output active power command is greater than or equal to the instantaneous active power, or when the output active power command is less than the instantaneous active power and the sign bit is less than zero, the voltage step size for the next MPPT wake-up is determined based on the first function; otherwise, the voltage step size for the next MPPT wake-up is determined based on the second function; wherein, the first function and the second function are piecewise linear functions obtained by fitting the characteristic curve of the photovoltaic PU.

[0021] In one possible implementation, having both sign bits equal to the set value includes: the product of the two sign bits being negative one.

[0022] In one possible implementation, the piecewise linear function obtained by fitting the photovoltaic PU characteristic curve includes:

[0023] By utilizing the photovoltaic output voltage and photovoltaic output current, the PU curve is fitted into a piecewise linear function curve:

[0024]

[0025] The first function is:

[0026]

[0027] The second function is:

[0028]

[0029] in, To output active power command; P o U represents instantaneous active power. o U is the output voltage of the photovoltaic system. oc U is the withstand voltage of the photovoltaic array; U is the instantaneous voltage of the photovoltaic array; U mpp P represents the voltage value corresponding to the maximum power point of the photovoltaic array. mpp P represents the maximum power of the photovoltaic array. o This represents the instantaneous active power of the photovoltaic array.

[0030] In one possible implementation, after determining the voltage step size for the next MPPT wake-up based on the sign bit and the current voltage tracking step size, the method further includes:

[0031] The interference voltage is adjusted based on the voltage step size and sign bit during the next MPPT wake-up.

[0032] In one possible implementation, adjusting the interference voltage based on the voltage step size and sign bit at the next MPPT wake-up includes:

[0033] When the sign bit is less than zero, the interference voltage is u(k) = u(k) - u step (k)flag(k);

[0034] Otherwise, the interference voltage is u(k) = u(k) + u step (k)flag(k).

[0035] In one possible implementation, the method further includes:

[0036] Record the current voltage tracking step size and the corresponding sign bit calculation result.

[0037] In one possible implementation, the step of calculating the photovoltaic output power before and after disturbance control based on the photovoltaic output voltage and photovoltaic output current before and after disturbance control includes:

[0038] Calculate the photovoltaic output power before disturbance control based on the photovoltaic output voltage and current before disturbance control, and calculate the photovoltaic output power after disturbance control based on the photovoltaic output voltage and current after disturbance control; the formula for calculating photovoltaic output power is as follows:

[0039] P(k)=u(k)*i(k)

[0040] Where P(k) is the photovoltaic output power; u(k) is the photovoltaic output voltage; and i(k) is the photovoltaic output current.

[0041] Secondly, embodiments of the present invention provide a photovoltaic grid-type support control device based on variable step-size power tracking, comprising:

[0042] The acquisition module is used to acquire the current voltage tracking step size, the photovoltaic output voltage before and after disturbance control, and the photovoltaic output current before and after disturbance control;

[0043] The power calculation module is used to calculate the photovoltaic output power before and after disturbance control based on the photovoltaic output voltage and photovoltaic output current before and after disturbance control.

[0044] The sign bit calculation module is used to determine the sign bit based on the photovoltaic output power and photovoltaic output voltage before and after disturbance control.

[0045] The voltage step size determination module is used to determine the voltage step size for the next MPPT wake-up based on the sign bit and the current voltage tracking step size.

[0046] This invention provides a photovoltaic (PV) grid-type support control method and apparatus based on variable step-size power point tracking (MPPT). By acquiring the current voltage tracking step size, the PV output voltage before and after disturbance control, and the PV output current before and after disturbance control, the PV output power before and after disturbance control is calculated based on the PV output voltage and current before and after disturbance control. This ensures the accuracy and reliability of the data based on the actual operating data of the PV system. Subsequently, the sign bit is determined based on the PV output power and PV output voltage before and after disturbance control, and the voltage step size for the next MPPT wake-up is determined based on the sign bit and the current voltage tracking step size. This enables real-time monitoring and dynamic adjustment of the system state, ensuring that the PV system is always in optimal operating condition. This embodiment transforms the traditional disturbance increment method based on power maximization into a disturbance quantity with a signed coefficient based on the principle of output power tracking frequency modulation power commands. This achieves accurate tracking of frequency modulation power and effectively reduces power fluctuations that may occur near the maximum power point. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is an overall block diagram of photovoltaic grid-type support control based on variable step size power tracking provided in the embodiments of the present invention;

[0049] Figure 2 This is a photovoltaic cell PU characteristic curve provided in an embodiment of the present invention;

[0050] Figure 3 This is a detailed control flowchart for the disturbance observation method;

[0051] Figure 4 This is a flowchart illustrating the photovoltaic grid-type support control method based on variable step-size power tracking provided in an embodiment of the present invention.

[0052] Figure 5 This is a flowchart of the photovoltaic grid-type support control algorithm based on variable step size power tracking of the present invention;

[0053] Figure 6 This is a schematic diagram of the PU curve stability analysis and curve fitting of the present invention;

[0054] Figure 7 This is the system topology diagram containing a photovoltaic power source used in the simulation of this invention;

[0055] Figure 8 This is a simulation waveform diagram of the system after incorporating the variable step size power tracking control strategy of this invention;

[0056] Figure 9 This is a schematic diagram of the structure of the photovoltaic grid-type support control device based on variable step size power tracking provided in an embodiment of the present invention. Detailed Implementation

[0057] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0058] Before introducing the proposed scheme, a basic introduction will be given to the control principle of photovoltaic grid-type structures and the support control requirements of active power reserve photovoltaic grid-type structures.

[0059] The overall block diagram of photovoltaic grid-type support control based on variable step-size power tracking is as follows: Figure 1 As shown, the control principle of photovoltaic grid-type structures is as follows:

[0060] By combining grid-side converter control with MPPT control, the output active power command P*ref is obtained by subtracting the system synchronous angular velocity from the rated angular velocity and adjusting it through PI control. From this, the change step size ustep of the voltage reference value under the MPPT control during this wake-up is obtained.

[0061] The second-order model of a traditional synchronous generator (SG) describes the response of various state variables when the system experiences power imbalance through rotor motion equations. The kinetic energy of the generator rotor changes synchronously with the system frequency. When an imbalance between the input mechanical power and the output electromagnetic power causes a change in the system frequency, the synchronous change in rotor kinetic energy is injected into the grid as inertia-supported power. Grid-based control combines droop control with rotor motion equations to simulate the external characteristics of a synchronous generator, enabling it to provide excellent characteristics such as inertia and damping to the system when renewable energy sources such as wind and solar are connected to the grid. When the number of generator pole pairs is 1, the active power-frequency control equation is:

[0062]

[0063] In the formula: ω0 is the rated angular frequency, ω ref To generate an angular frequency reference value, θ ref To generate the AC side voltage phase reference value, J is the virtual rotor moment of inertia, and D... p P is the damping coefficient, and P is the actual active power output of the grid-side inverter.ref This is a reference value for the active power on the grid side.

[0064] To maintain the balance of active power in the system, this application introduces a primary frequency regulation element of the generator, and obtains the effective reference value in the grid-type control as shown in the following formula:

[0065] P ref =P set +k ω (ω0-ω)

[0066] In the formula, k ω P is the primary frequency modulation coefficient. set The power tracking value is calculated using the step-by-step power tracking method proposed in this invention.

[0067] The relationship between the electromagnetic characteristics and induced electromotive force of a synchronous generator is as follows:

[0068]

[0069] In the formula, e is the three-phase output voltage of SG, and i f M is the excitation current. f Let i be the virtual excitation mutual inductance, and θ be the system phase. For ease of analysis, i... f Treating it as a constant, the inverter output port voltage can be simplified as follows:

[0070]

[0071] In the formula, E is the output voltage amplitude of the inverter, and u oabc This is the output voltage of the three-phase inverter.

[0072] Traditional inverters (SGs) maintain stable terminal voltage through an automatic voltage regulator in the excitation control system. In this embodiment, a PI controller continuously adjusts the excitation current to reduce the error in the inverter output voltage, thereby simulating the automatic voltage regulation function of the SG.

[0073]

[0074] In the formula, u dref u is the d-axis reference value for the output voltage. od The output voltage is measured on the d-axis, k p k i These are the proportional and integral adjustment coefficients, respectively.

[0075] The active power reserve photovoltaic grid-type support control requirements are as follows:

[0076] When a photovoltaic grid without energy storage is not in frequency regulation mode, its output power is less than the current maximum power due to the need to reserve power. The k-fold of the current maximum power is called the standby operating point, where k∈[0,1]. When the photovoltaic inverter operates in active power reserve mode, the randomness of sunlight makes the acquisition of the maximum power point unpredictable. In this embodiment, the maximum power point is determined by performing an MPPT at regular intervals. Specifically, the time interval for the photovoltaic inverter to determine the global MPPT search is selected.

[0077] The process of achieving active power reserve in a grid-connected photovoltaic system is divided into three stages: startup, frequency regulation, and wake-up. Frequency regulation cannot be performed during the MPPT (Multi-Level Photovoltaic Power Reserve) process as it would affect the regulation effect. To reduce the number of wake-ups, changes in the standby operating point power and voltage are detected to determine whether the photovoltaic curve has changed and thus whether the MPPT needs to be woken up.

[0078] Then, the variable step size power tracking method based on perturbation observation is introduced.

[0079] The IV and PV characteristic curves of photovoltaic cells are nonlinear functions affected by factors such as photovoltaic cell parameters, light intensity, and ambient temperature. To ensure the photoelectric conversion efficiency of the photovoltaic power generation system, MPPT control needs to be implemented on the photovoltaic array. When external conditions such as light intensity and ambient temperature change, the bipolar photovoltaic power generation system can control the output voltage of the photovoltaic cells by changing the duty cycle of the front-end DC-DC converter circuit to achieve maximum power point tracking control. Figure 2 As shown in the PV characteristic curve of the photovoltaic cell, when the operating point is located to the left of the maximum power point, the higher the voltage, the greater the output power of the photovoltaic cell; conversely, when the operating point is located to the right of the maximum power point, the lower the voltage, the greater the output power of the photovoltaic cell. During MPPT control, the output voltage, output current, and power of the photovoltaic cell are measured in real time. Based on this, the operating region of the photovoltaic cell is determined, and different control commands are used for different operating regions to achieve maximum power point tracking control.

[0080] Figure 3 This is the control flowchart for the disturbance-observation method. The disturbance-observation method is a typical self-optimizing control method; it has a simple structure and requires relatively few measurement parameters. For example... Figure 3As shown, after each parameter acquisition, the output voltage needs to be perturbed according to a given step size. The power sample values ​​before and after the perturbation are compared, and the voltage perturbation direction for the next moment is selected based on the comparison result. This process is repeated until the maximum power point of the photovoltaic cell is found. If the power increases after the perturbation, it indicates that the actual operating point is approaching the maximum power point of the photovoltaic cell, the perturbation direction is correct, and the perturbation direction remains unchanged for the next moment. If the power decreases after the perturbation, it indicates that the actual operating point is deviating from the maximum power point of the photovoltaic cell, the perturbation direction is incorrect, and the perturbation direction needs to be changed for the next moment. However, since the algorithm needs to continuously apply perturbation to the voltage, power fluctuations will occur near the maximum power point. The embodiments of this application aim to improve the traditional perturbation observation method and avoid power fluctuations near the maximum power point.

[0081] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0082] Figure 4 This is a schematic diagram of the path of the photovoltaic grid-type support control method based on variable step size power tracking provided in the embodiments of the present invention, as shown below. Figure 4 As shown, it includes the following steps:

[0083] S401, obtain the current voltage tracking step size, the photovoltaic output voltage before and after disturbance control, and the photovoltaic output current before and after disturbance control.

[0084] S402, calculate the photovoltaic output power before and after disturbance control based on the photovoltaic output voltage and photovoltaic output current before and after disturbance control.

[0085] S403 determines the sign bit based on the photovoltaic output power and photovoltaic output voltage before and after disturbance control.

[0086] S404 determines the voltage step size for the next MPPT wake-up based on the sign bit and the current voltage tracking step size.

[0087] In this embodiment, by acquiring the current voltage tracking step size, the photovoltaic output voltage before and after disturbance control, and the photovoltaic output current before and after disturbance control, the photovoltaic output power before and after disturbance control is calculated based on the photovoltaic output voltage and current before and after disturbance control. This ensures the accuracy and reliability of the data based on the actual operating data of the photovoltaic system. Subsequently, the sign bit is determined based on the photovoltaic output power and photovoltaic output voltage before and after disturbance control, and the voltage step size for the next MPPT wake-up is determined based on the sign bit and the current voltage tracking step size. This enables real-time monitoring and dynamic adjustment of the system state, ensuring that the photovoltaic system is always in optimal operating condition. This embodiment transforms the traditional disturbance increment method based on power maximization into a disturbance quantity with a signed coefficient based on the principle of output power tracking frequency modulation power commands. This achieves accurate tracking of frequency modulation power and effectively reduces power fluctuations that may occur near the maximum power point. This improvement not only enhances the stability and reliability of the system but also significantly enhances the overall performance and efficiency of the photovoltaic system. It improves the stability of the original fixed step size tracking and provides inertial and damped virtual synchronization control, better supporting system frequency stability.

[0088] In one possible implementation, determining the sign bit based on the photovoltaic output power and photovoltaic output voltage before and after disturbance control includes:

[0089] The photovoltaic output power and output voltage before and after disturbance control are input into the sign bit calculation formula to calculate the sign bit; whereby the sign bit calculation formula is:

[0090]

[0091] Where P(k) is the photovoltaic output power before disturbance control; P(k-1) is the photovoltaic output power after disturbance control; u(k) is the output voltage before disturbance control; and u(k-1) is the output voltage after disturbance control.

[0092] In one possible implementation, determining the voltage step size for the next MPPT wake-up based on the sign bit and the current voltage tracking step size includes:

[0093] Obtain the previous voltage tracking step size corresponding to the current voltage tracking step size, and obtain the sign bit corresponding to the previous voltage tracking step size;

[0094] When the voltage tracking step size is equal to the maximum step size limit and the sign bit is equal to the set value in both cases, the minimum step size limit is selected as the base step size; otherwise, the current voltage tracking step size is used as the base step size.

[0095] The active power output command is determined based on the current photovoltaic output voltage and current photovoltaic output current.

[0096] When the output active power command is greater than or equal to the instantaneous active power, or when the output active power command is less than the instantaneous active power and the sign bit is less than zero, the voltage step size for the next MPPT wake-up is determined based on the first function; otherwise, the voltage step size for the next MPPT wake-up is determined based on the second function; wherein, the first function and the second function are piecewise linear functions obtained by fitting the characteristic curve of the photovoltaic PU.

[0097] In one possible implementation, having both sign bits equal to the set value includes: the product of the two sign bits being negative one.

[0098] In one possible implementation, the piecewise linear function obtained by fitting the photovoltaic PU characteristic curve includes:

[0099] By utilizing the photovoltaic output voltage and photovoltaic output current, the PU curve is fitted into a piecewise linear function curve:

[0100]

[0101] The first function is:

[0102]

[0103] The second function is:

[0104]

[0105] in, To output active power command; P o U represents instantaneous active power. o U is the output voltage of the photovoltaic system. oc For...; U is...; U mpp For...; P mpp For...; P o for……; for…….

[0106] In one possible implementation, after determining the voltage step size for the next MPPT wake-up based on the sign bit and the current voltage tracking step size, the method further includes:

[0107] The interference voltage is adjusted based on the voltage step size and sign bit during the next MPPT wake-up.

[0108] In one possible implementation, adjusting the interference voltage based on the voltage step size and sign bit at the next MPPT wake-up includes:

[0109] When the sign bit is less than zero, the interference voltage is u(k) = u(k) - u step (k)flag(k);

[0110] Otherwise, the interference voltage is u(k) = u(k) + u step (k)flag(k).

[0111] In one possible implementation, the method further includes:

[0112] Record the current voltage tracking step size and the corresponding sign bit calculation result.

[0113] In one possible implementation, the step of calculating the photovoltaic output power before and after disturbance control based on the photovoltaic output voltage and photovoltaic output current before and after disturbance control includes:

[0114] Calculate the photovoltaic output power before disturbance control based on the photovoltaic output voltage and current before disturbance control, and calculate the photovoltaic output power after disturbance control based on the photovoltaic output voltage and current after disturbance control; the formula for calculating photovoltaic output power is as follows:

[0115] P(k)=u(k)*i(k)

[0116] Where P(k) is the photovoltaic output power; u(k) is the photovoltaic output voltage; and i(k) is the photovoltaic output current.

[0117] according to Figure 5 As shown, after calculating the step size and sign bits of dP / dU for voltage tracking, to prevent power oscillations caused by excessively large disturbance voltage step sizes, the voltage step size must be limited. The maximum limit value considers the maximum voltage step size of the traditional disturbance observation method. The sign coefficients and output active power command for variable step size power tracking are also discussed. Instantaneous active power P o The magnitude of dI / dU is related to the sign bit. When When, if P o When located to the right of the photovoltaic curve, the DC-side voltage is disturbed in the direction of decreasing voltage; if P o When located to the left of the photovoltaic curve, the DC-side voltage is disturbed in the direction of increasing voltage; when At that time, due to P o Unable to achieve When operating in MPPT mode, the disturbance voltage step size will fluctuate with the maximum disturbance limit value. This leads to power oscillations near the maximum power point. Therefore, when the maximum power point is reached, the disturbance step size is minimized. See [link / reference]. Figure 5 The perturbation step size is determined in the middle. When Since the instantaneous decrease in active power cannot be disturbed in the direction of the left half-plane, the DC side voltage is always disturbed in the direction of increase.

[0118] Because fixed-step power tracking presents a contradiction between dynamic and steady-state performance, variable-step power tracking is considered. The size of the disturbance voltage step size is related to the difference between the reference power and the inverter output power. If the relationship between power and voltage in the photovoltaic curve is known, the disturbance voltage step size can be calculated based on the power difference. The relationship between the photovoltaic array output power, output current, and output voltage is as follows:

[0119]

[0120] In the formula, I s It is the short-circuit current; I ph I0 is the cell photocurrent that is related to light and temperature; I0 is the reverse saturation current; Q is the charge constant; X is the pn junction coefficient in the photovoltaic array; T is the absolute temperature; Y is the Boltzmann constant.

[0121] Since this formula is a transcendental function and its parameters are unknown, calculating the perturbation voltage step size using it is impractical. Therefore, this invention utilizes the photovoltaic output voltage and output current at the current moment to fit the PU curve into a piecewise linear function curve, specifically as follows: Figure 6 As shown. The piecewise linear function can be expressed as:

[0122]

[0123] Therefore, the step size during this MPPT wake-up can be determined as follows:

[0124]

[0125] According to the active power reserve control requirements of PV-PSG, the power and voltage of the maximum power point can be obtained every 10 minutes. The open-circuit voltage corresponding to the maximum power point is then obtained through a lookup table. This can be achieved using the relationship between the photovoltaic array's output power, output current, and output voltage. Before the next MPPT wake-up, the coefficient of U in the formula is a fixed value, equivalent to a proportional regulator. Its value is related to the current maximum power point and open-circuit voltage, allowing for differential power adjustment.

[0126] In a power grid that includes photovoltaic power, the VSG control unit can exist independently or multiple VSG control units can be combined. This application mainly discusses the power system composed of photovoltaic, synchronous machine and active load. The analysis and research are limited to the microgrid model of a single VSG unit. However, the research is not limited to power systems with photovoltaic systems as new energy power generation units. This research still has certain reference value for other similar systems with new energy as power sources. Figure 7 The system topology diagram used in the simulation of this invention is shown. As shown in the figure, the system consists of the following components: constant power unit G1, frequency regulating unit G2, photovoltaic power generation unit, and load.

[0127] To verify the effectiveness of the strategy proposed in this invention, a comparison was made between typical VSG control and photovoltaic grid-type support control with variable step size power tracking. Taking a sudden load increase as an example, before the disturbance, the generator G1 and the photovoltaic-storage unit containing VSG in the system were operating in steady state, and the system frequency was stable at the power frequency of 50Hz. After 25 seconds of system operation, a load of 1.5kW was suddenly added.

[0128] In this experiment, the total simulation time was set to 50 seconds. To make the simulation results more intuitive, a time span of 20 to 50 seconds was extracted after the system stabilized to provide clearer observations. The experimental results show the changes in active power output and system frequency of the system and synchronous machine after and without the variable step size power tracking control strategy, as follows: Figure 8 As shown in the figure. It can be clearly seen that:

[0129] In terms of frequency, such as Figure 8 As shown in Figure (a), the frequency when using constraints as superimposed control, represented by the red dashed line, takes approximately 5 seconds to recover to a stable frequency, with a maximum frequency deviation of approximately 0.2 Hz. In contrast, the frequency response curve of the system without this control strategy, represented by the blue solid line, takes approximately 13 seconds to recover to a stable frequency, significantly exceeding the recovery time when the proposed control strategy is employed. Similarly, without the variable step size power tracking control strategy, the maximum frequency deviation reaches 0.36 Hz, also considerably larger than 0.2 Hz.

[0130] Regarding frequency regulation units, by Figure 8 As shown in Figure (b), the red dashed line represents the output of the frequency modulation unit after the implementation of variable step size power point tracking (VPT) control, while the blue solid line represents the output of the frequency modulation unit without this control strategy. By comparing the slope of the change when using this strategy, it can be seen that the frequency modulation unit responds more rapidly than when it does not employ this strategy, and can achieve frequency modulation while quickly increasing active power generation, allowing the system to recover stability more quickly. In contrast, the system without VPT control has a slower response speed, a longer response time, and a generally less effective regulation.

[0131] Regarding the system's active power, by Figure 8As shown in (c), the red dashed line represents the active power change of the system after incorporating the variable step size power point tracking (VPT) control method for photovoltaic grid-based systems, while the blue solid line represents the active power change of the system without the VPT control strategy. After a load change and system disturbance, the adjustment speed can be determined by comparing the slopes of the two curves. The red curve has a significantly steeper slope, indicating a faster adjustment speed, recovering to the original output power within 10 seconds. The blue curve, while having a relatively slower adjustment speed, recovers in about 15 seconds. Therefore, it can be said that with the VPT control strategy, the system adjustment speed is faster, and the system frequency deviation is smaller. During the system's recovery to stability, the synchronous generator can respond to system power fluctuations more quickly, thus improving the system's ability to support grid frequency to a certain extent.

[0132] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0133] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0134] Figure 9 A schematic diagram of the photovoltaic grid-type support control device based on variable step-size power tracking provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below:

[0135] like Figure 9 As shown, the photovoltaic grid-type support control device 9 based on variable step size power tracking includes:

[0136] The acquisition module 901 is used to acquire the current voltage tracking step size, the photovoltaic output voltage before and after disturbance control, and the photovoltaic output current before and after disturbance control;

[0137] The power calculation module 902 is used to calculate the photovoltaic output power before and after the disturbance control based on the photovoltaic output voltage and photovoltaic output current before and after the disturbance control.

[0138] The sign bit calculation module 903 is used to determine the sign bit based on the photovoltaic output power and photovoltaic output voltage before and after disturbance control.

[0139] The voltage step size determination module 904 is used to determine the voltage step size for the next MPPT wake-up based on the sign bit and the current voltage tracking step size.

[0140] In this embodiment, by acquiring the current voltage tracking step size, the photovoltaic output voltage before and after disturbance control, and the photovoltaic output current before and after disturbance control, the photovoltaic output power before and after disturbance control is calculated based on the photovoltaic output voltage and current before and after disturbance control. This ensures the accuracy and reliability of the data based on the actual operating data of the photovoltaic system. Subsequently, the sign bit is determined based on the photovoltaic output power and photovoltaic output voltage before and after disturbance control, and the voltage step size for the next MPPT wake-up is determined based on the sign bit and the current voltage tracking step size. This enables real-time monitoring and dynamic adjustment of the system state, ensuring that the photovoltaic system is always in optimal operating condition. This embodiment transforms the traditional disturbance increment method based on power maximization into a disturbance quantity with a signed coefficient based on the principle of output power tracking the frequency modulation power command. This achieves accurate tracking of the frequency modulation power and effectively reduces power fluctuations that may occur near the maximum power point. This improvement not only enhances the stability and reliability of the system but also significantly enhances the overall performance and efficiency of the photovoltaic system.

[0141] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0142] Those skilled in the art will recognize that the templates, units, and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this application can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0143] If the module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various embodiments of the photovoltaic grid-type support control method based on variable step-size power tracking. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0144] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A photovoltaic grid-forming support control method based on variable step power tracking, characterized by, The method comprises the following steps: acquiring the current voltage tracking step, the photovoltaic output voltage before and after the perturbation control, and the photovoltaic output current before and after the perturbation control; correspondingly calculating the photovoltaic output power before and after the perturbation control according to the photovoltaic output voltage before and after the perturbation control and the photovoltaic output current before and after the perturbation control; determining the sign bit according to the photovoltaic output power before and after the perturbation control and the photovoltaic output voltage before and after the perturbation control; determining the voltage step of the next time of waking up the MPPT based on the sign bit and the current voltage tracking step; wherein the determination of the voltage step of the next time of waking up the MPPT based on the sign bit and the current voltage tracking step comprises: acquiring the previous voltage tracking step corresponding to the current voltage tracking step and acquiring the sign bit corresponding to the previous voltage tracking step; when the voltage tracking step is equal to the maximum value of the step limit and the sign bit is equal to the set value, selecting the minimum value of the step limit as the basic step value; otherwise, taking the current voltage tracking step as the basic step value; determining the output active power instruction according to the current photovoltaic output voltage and the current photovoltaic output current; when the output active power instruction is greater than or equal to the instantaneous active power, or when the output active power instruction is less than the instantaneous active power and the sign bit is less than zero, determining the voltage step of the next time of waking up the MPPT based on the first function; otherwise, determining the voltage step of the next time of waking up the MPPT based on the second function; wherein the first function and the second function are piecewise linear functions fitted based on the photovoltaic P-U characteristic curve; wherein the piecewise linear functions fitted based on the photovoltaic P-U characteristic curve comprise: fitting the P-U curve into a piecewise linear function curve by using the photovoltaic output voltage and the photovoltaic output current: ； the first function is: ； the second function is: ； wherein, is an output active power command; is an instantaneous active power; is a photovoltaic output voltage; is a photovoltaic array withstand voltage; is a photovoltaic array instantaneous voltage; is a photovoltaic array maximum power point corresponding voltage value; is a photovoltaic array maximum power; is a photovoltaic array instantaneous active power.

2. The variable step size power tracking based PV grid support control method according to claim 1, wherein, the determination of the sign bit according to the photovoltaic output power before and after the perturbation control and the photovoltaic output voltage before and after the perturbation control comprises: inputting the photovoltaic output power before and after the perturbation control and the photovoltaic output voltage before and after the perturbation control into a sign bit calculation formula to calculate the sign bit; wherein the sign bit calculation formula is: wherein, is the photovoltaic output power before perturbation control; is the photovoltaic output power after perturbation control; is the output voltage before perturbation control; is the output voltage after perturbation control.

3. The variable step size power tracking based PV grid support control method according to claim 1, wherein, the product of the two sign bits is -1.

4. The variable step size power tracking based PV grid support control method according to claim 1, wherein, after the determination of the voltage step of the next time of waking up the MPPT based on the sign bit and the current voltage tracking step, the method further comprises: adjusting the interference voltage according to the voltage step of the next time of waking up the MPPT and the sign bit.

5. The variable step size power tracking based PV grid support control method according to claim 4, wherein, the adjustment of the interference voltage according to the voltage step of the next time of waking up the MPPT and the sign bit comprises: When the sign bit is less than zero, the interference voltage is ; Otherwise, the interference voltage is .

6. The variable step size power tracking based PV grid support control method according to claim 1, wherein, further comprising: recording the current voltage tracking step and the corresponding sign bit calculation result.

7. The variable step size power tracking based PV grid support control method according to claim 1, wherein, the corresponding calculation of the photovoltaic output power before and after the perturbation control according to the photovoltaic output voltage before and after the perturbation control and the photovoltaic output current comprises: calculating the photovoltaic output power before the perturbation control according to the photovoltaic output voltage before the perturbation control and the photovoltaic output current, and calculating the photovoltaic output power after the perturbation control according to the photovoltaic output voltage after the perturbation control and the photovoltaic output current; wherein the photovoltaic output power calculation formula is as follows: wherein, Ppv is the photovoltaic output power; Vpv is the photovoltaic output voltage; I Pv is the photovoltaic output current.

8. A variable step power tracking based PV grid support control device for performing the variable step power tracking based PV grid support control method of any one of claims 1 to 7, characterized in that, comprising: The acquisition module is configured to acquire a current voltage tracking step, photovoltaic output voltages before and after the perturbation control, and photovoltaic output currents before and after the perturbation control. The power calculation module is configured to correspondingly calculate photovoltaic output powers before and after the perturbation control according to the photovoltaic output voltages before and after the perturbation control and the photovoltaic output currents before and after the perturbation control. The sign bit calculation module is configured to determine a sign bit according to the photovoltaic output powers before and after the perturbation control and the photovoltaic output voltages before and after the perturbation control. The voltage step determination module is configured to determine a voltage step for next time when the MPPT is woken up based on the sign bit and the current voltage tracking step.

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