Photovoltaic network construction type support control method and device based on variable step power tracking

Abstract

The invention provides a photovoltaic network construction type support control method and device based on variable step power tracking, and belongs to the technical field of new energy grid-connected control. The method comprises the following steps: acquiring a current voltage tracking step length, photovoltaic output voltages before and after disturbance control and photovoltaic output currents before and after disturbance control; correspondingly calculating photovoltaic output power before and after disturbance control according to the photovoltaic output voltage before and after disturbance control and the photovoltaic output current before and after disturbance control; determining a sign bit according to the photovoltaic output power before and after disturbance control and the photovoltaic output voltage before and after disturbance control; and determining the voltage step length when the maximum power tracking MPPT is awakened next time based on the sign bit and the current voltage tracking step length, thereby realizing the quick response of frequency and inertia by utilizing standby active power. According to the method, the stability of original fixed step length tracking is improved, inertia and damping virtual synchronous control can be provided at the same time, and the system frequency stability is better supported.

Description

Technical Field

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

[0002] At present, the low-carbon transformation of the power system is accelerating, and renewable energy power generation is experiencing sustained and rapid growth, with the proportion of installed capacity rising continuously. The inertia of the power system has been significantly reduced, and the active frequency adjustment capacity is seriously insufficient. In recent years, high-proportion renewable energy power grids in countries such as the United Kingdom and Australia have experienced large-scale power outages caused by frequency instability, causing significant economic and social losses and adverse international impacts. Therefore, the future power system requires renewable energy sites to have certain inertia support and frequency adjustment capabilities.

[0003] Since the output voltage and output current of photovoltaic cells have strong nonlinearity with the changes of sunshine intensity and battery junction temperature, there is a unique maximum power output point (Maximum PowerPoint, MPP) under a specific working environment. In actual application systems, the radiation intensity of natural light and the transmittance of the atmosphere keep changing dynamically. In order to obtain as much electrical energy as possible under the same sunshine intensity and battery junction temperature, there is a problem of maximum power point tracking (Maximum power point tracking, MPPT). In traditional solutions, the maximum power point is quickly located by the constant voltage tracking method, but there is a problem of poor accuracy. At present, patent CN110362146A provides an adaptive MPPT control strategy based on the variable step size perturbation observation method, which introduces an adaptive variable step size factor, and then adaptively changes the size of the perturbation step size, so that the perturbation step size can be adaptively adjusted according to the distance between the working point of the photovoltaic power generation system and the maximum power point.

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

[0005] Continuously applying disturbances to the voltage will produce large power fluctuations near the maximum power point. Summary of the invention

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

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

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

[0009] The photovoltaic output power before and after the disturbance control is calculated according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control;

[0010] Determine the sign bit according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control;

[0011] The voltage step size when waking up the MPPT next time is determined based on the sign bit and the current voltage tracking step size.

[0012] In a possible implementation, determining the sign bit according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control includes:

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

[0014]

[0015] Among them, 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; u(k-1) is the output voltage after disturbance control.

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

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

[0018] When the voltage tracking step is equal to the maximum value of the step limit and the sign bits are both equal to the set value, the minimum value of the step limit is selected as the basic step value; otherwise, the current voltage tracking step is used as the basic step value;

[0019] Determine the output active power command according to the current photovoltaic output voltage and the current photovoltaic output current;

[0020] 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, the voltage step size for waking up the MPPT next time is determined based on the first functional formula; otherwise, the voltage step size for waking up the MPPT next time is determined based on the second functional formula; wherein the first functional formula and the second functional formula are piecewise linear functions obtained based on fitting of the photovoltaic PU characteristic curve.

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

[0022] In a possible implementation, the piecewise linear function obtained based on the photovoltaic PU characteristic curve fitting includes:

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

[0024]

[0025] The first functional formula is:

[0026]

[0027] The second functional formula is:

[0028]

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

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

[0031] The interference voltage is adjusted according to the voltage step size and sign bit when the MPPT is woken up next time.

[0032] In a possible implementation, adjusting the interference voltage according to the voltage step and the sign bit when the MPPT is awakened next time 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 a possible implementation, the method further includes:

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

[0037] In a possible implementation, the photovoltaic output power before and after the disturbance control is calculated according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control, including:

[0038] The photovoltaic output power before disturbance control is calculated according to the photovoltaic output voltage and photovoltaic output current before disturbance control, and the photovoltaic output power after disturbance control is calculated according to the photovoltaic output voltage and photovoltaic output current after disturbance control; wherein, the photovoltaic output power calculation formula is as follows:

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

[0040] Among them, P(k) is the photovoltaic output power; u(k) is the photovoltaic output voltage; i(k) is the photovoltaic output current.

[0041] In a second aspect, an embodiment of the present invention provides a photovoltaic grid-type support control device based on variable step-size power tracking, comprising:

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

[0043] A power calculation module, used to calculate the photovoltaic output power before and after the disturbance control according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control;

[0044] A sign bit calculation module, used for determining a sign bit according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control;

[0045] The voltage step determination module is used to determine the voltage step when waking up the MPPT next time based on the sign bit and the current voltage tracking step.

[0046] The embodiment of the present invention provides a photovoltaic grid-type support control method and device based on variable step power tracking, by obtaining the current voltage tracking step, the photovoltaic output voltage before and after the disturbance control, and the photovoltaic output current before and after the disturbance control, the photovoltaic output power before and after the disturbance control is calculated according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control, and the accuracy and reliability of the data are ensured based on the actual operation data of the photovoltaic system. Subsequently, the sign bit is determined according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control, and the voltage step size when the MPPT is awakened next time is determined based on the sign bit and the current voltage tracking step size, so as to realize real-time monitoring and dynamic adjustment of the system state, and ensure that the photovoltaic system is always in the optimal operating state. In the embodiment of the present application, the traditional disturbance increment method based on power maximization is transformed into a disturbance amount with a signed coefficient based on the principle of output power tracking frequency modulation power instruction, so as to realize accurate tracking of frequency modulation power and effectively reduce the power fluctuation that may occur near the maximum power point. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

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

[0049] Figure 2 is a graph showing the PU characteristic of a photovoltaic cell provided by an embodiment of the present invention;

[0050] Figure 3 It is the specific control flow chart of the perturbation and observation method;

[0051] Figure 4 It is a flow chart of a photovoltaic grid-type support control method based on variable step-size power tracking provided by an embodiment of the present invention;

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

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

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

[0055] Figure 8 This is a system simulation waveform diagram after the variable step-size power tracking control strategy is added to the present invention;

[0056] Fig. 9 It is a structural schematic diagram of a photovoltaic grid-type support control device based on variable step-size power tracking provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0058] Before introducing the present application scheme, a basic introduction is first given to the photovoltaic grid control principle and the active standby photovoltaic grid support control requirements.

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

[0060] The grid-side converter control is combined with the 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. The step length ustep of the voltage reference value under the MPPT control awakening is then obtained.

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

[0062]

[0063] Where: ω0 is the rated angular frequency, ω ref To generate the angular frequency reference, θ ref To generate the AC side voltage phase reference value, J is the virtual rotor inertia, D p is the damping coefficient, P is the actual active power output by the grid-side inverter, and Pref It is the grid-side active power reference value.

[0064] In order to maintain the balance of system active power, this application introduces the primary frequency regulation link 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 is the primary frequency modulation coefficient, P set is the power tracking value calculated according to the variable-step power tracking method proposed in the present invention.

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

[0068]

[0069] Where, e is the voltage at the three-phase output terminal of SG, i f is the excitation current, M f is the virtual excitation mutual inductance, and θ is the system phase. f Considered as a constant, the inverter output port voltage can be simplified as:

[0070]

[0071] Where, E is the inverter output voltage amplitude, u oabc is the output voltage of the three-phase inverter.

[0072] The traditional SG maintains the stability of the terminal voltage through the automatic voltage regulator in the excitation control system. In the embodiment of the present application, the PI controller is used to continuously adjust the excitation current to reduce the error of the inverter output voltage, thereby simulating the automatic voltage regulation function of the SG:

[0073]

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

[0075] Active standby photovoltaic grid support control requirements are as follows:

[0076] When the photovoltaic grid type without energy storage is not in the frequency modulation state, its output power is less than the current maximum power due to the need to reserve backup power. The k times of the current maximum power is called the backup working point, where k∈[0,1]. When the photovoltaic inverter operates in the active standby state, the randomness of the light makes the acquisition of the maximum power point unpredictable. In the embodiment of the present application, the maximum power point is determined by performing MPPT once at intervals. Specifically, the photovoltaic inverter is selected to determine the time interval for the global search of MPPT.

[0077] The process of realizing active standby in photovoltaic grid configuration is divided into the startup phase, frequency modulation phase, and awakening phase. Frequency modulation cannot be performed during the MPPT process, which affects the frequency modulation effect. In order to reduce the number of awakening times, the photovoltaic curve is judged to be changed by detecting whether the power and voltage of the standby working point have changed, thereby determining whether the MPPT needs to be awakened.

[0078] Then, the variable step-size power tracking method based on the perturbation observation method 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. In order to ensure the photoelectric conversion efficiency of the photovoltaic power generation system, it is necessary to implement MPPT control 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 cell by changing the duty cycle of the front-stage DC-DC conversion circuit to achieve the purpose of maximum power tracking control. Figure 2 The PV characteristic curve of the photovoltaic cell shown in the figure shows that when the working point is located on the left side of the maximum power point, the higher the voltage, the greater the output power of the photovoltaic cell. When the working point is located on the right side 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, and the working area of ​​the photovoltaic cell is judged based on this. Different control instructions are used to achieve maximum power tracking control for different working areas.

[0080] Figure 3 This is a specific control flow chart of the disturbance observation method. The disturbance observation method is a typical self-optimizing control method with a simple structure and fewer measurement parameters required by the algorithm. Figure 3As shown, after each parameter acquisition is completed, the output voltage needs to be disturbed according to a given step size, and the power sampling values ​​before and after the disturbance are compared, and the voltage disturbance direction at the next moment is selected according to the comparison result. This is repeated until the maximum power point of the photovoltaic cell is found. If the power increases after the disturbance, it means that the actual working point is approaching the maximum power point of the photovoltaic cell, the disturbance direction is correct, and the disturbance direction remains unchanged next time; if the power decreases after the disturbance, it means that the actual working point is deviating from the maximum power point of the photovoltaic cell, the disturbance direction is wrong, and the disturbance direction needs to be changed at the next moment. However, since the algorithm needs to continuously apply disturbances to the voltage, power fluctuations will occur near the maximum power point. The embodiment of the present application aims to improve the traditional disturbance observation method to avoid power fluctuations near the maximum power point.

[0081] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0082] Figure 4 FIG. 1 is a schematic diagram of a photovoltaic grid-type support control method based on variable step-size power tracking provided by an embodiment of the present invention. Figure 4 As shown, the following steps are included:

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

[0084] S402, calculating the photovoltaic output power before and after the disturbance control according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control.

[0085] S403, determining a sign bit according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control.

[0086] S404, determining the voltage step size for waking up the MPPT next time based on the sign bit and the current voltage tracking step size.

[0087] In this embodiment, by obtaining the current voltage tracking step, the photovoltaic output voltage before and after the disturbance control, and the photovoltaic output current before and after the disturbance control, the photovoltaic output power before and after the disturbance control is calculated according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control, and based on the actual operation data of the photovoltaic system, the accuracy and reliability of the data are ensured. Subsequently, the sign bit is determined according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control, and the voltage step size when the MPPT is awakened next time is determined based on the sign bit and the current voltage tracking step size, so as to realize real-time monitoring and dynamic adjustment of the system state, and ensure that the photovoltaic system is always in the optimal operating state. In this embodiment of the application, the traditional disturbance increment method based on power maximization is transformed into a disturbance amount with a signed coefficient based on the principle of output power tracking frequency modulation power instruction, so as to realize accurate tracking of frequency modulation power and effectively reduce the power fluctuation that may occur near the maximum power point. This improvement not only improves 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 tracking, and can provide inertial and damping virtual synchronous control at the same time, so as to better support the system frequency stability.

[0088] In a possible implementation, determining the sign bit according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control includes:

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

[0090]

[0091] Among them, 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; u(k-1) is the output voltage after disturbance control.

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

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

[0094] When the voltage tracking step is equal to the maximum value of the step limit and the sign bits are both equal to the set value, the minimum value of the step limit is selected as the basic step value; otherwise, the current voltage tracking step is used as the basic step value;

[0095] Determine the output active power command according to the current photovoltaic output voltage and the current photovoltaic output current;

[0096] 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, the voltage step size for waking up the MPPT next time is determined based on the first functional formula; otherwise, the voltage step size for waking up the MPPT next time is determined based on the second functional formula; wherein the first functional formula and the second functional formula are piecewise linear functions obtained based on fitting of the photovoltaic PU characteristic curve.

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

[0098] In a possible implementation, the piecewise linear function obtained based on the photovoltaic PU characteristic curve fitting includes:

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

[0100]

[0101] The first functional formula is:

[0102]

[0103] The second functional formula is:

[0104]

[0105] in, is the output active power instruction; P o is the instantaneous active power; U o is the photovoltaic output voltage; U oc for ...; U for ...; U mpp for ...; P mpp for ...; P o for……; for…….

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

[0107] The interference voltage is adjusted according to the voltage step size and sign bit when the MPPT is woken up next time.

[0108] In a possible implementation, adjusting the interference voltage according to the voltage step and the sign bit when the MPPT is awakened next time 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 a possible implementation, the method further includes:

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

[0113] In a possible implementation, the photovoltaic output power before and after the disturbance control is calculated according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control, including:

[0114] The photovoltaic output power before disturbance control is calculated according to the photovoltaic output voltage and photovoltaic output current before disturbance control, and the photovoltaic output power after disturbance control is calculated according to the photovoltaic output voltage and photovoltaic output current after disturbance control; wherein, the photovoltaic output power calculation formula is as follows:

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

[0116] Among them, P(k) is the photovoltaic output power; u(k) is the photovoltaic output voltage; i(k) is the photovoltaic output current.

[0117] according to Figure 5 As shown in the figure, after calculating the step size of voltage tracking and the sign bit of dP / dU, in order to prevent power oscillation caused by excessive disturbance voltage step size, the voltage step size must be limited. The maximum value of the limit is considered to be the maximum voltage step size of the traditional disturbance observation method. Sign coefficient of variable step size power tracking and output active power instruction Instantaneous active power P o The size of dI / dU is related to the sign bit. When P o When it is on the right side of the photovoltaic curve, the DC side voltage is disturbed in the direction of voltage reduction; if P o When it is on the left side of the photovoltaic curve, the DC side voltage is disturbed in the direction of increasing voltage; when When P o Never reach At this time, when operating in MPPT mode, the disturbance voltage step will be disturbed at the maximum disturbance limit value. This situation causes power vibration near the maximum power point. Therefore, when the maximum power point is reached, the disturbance step is limited to the minimum value. See Figure 5 The part of judging the perturbation step size. When , since the process of instantaneous active power reduction cannot be disturbed in the direction of the left half plane, the DC side voltage is always disturbed in the direction of increase.

[0118] Since there is a contradiction between the dynamic and steady-state performance of tracking when using fixed step power tracking, variable step power tracking is considered. The size of the disturbance voltage step 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 step of the disturbance voltage can be calculated based on the power difference. The relationship between the photovoltaic array output power, output current and output voltage is:

[0119]

[0120] In the formula, I s is the short-circuit current; I ph is the photocurrent of the cell 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; and Y is the Boltzmann constant.

[0121] Since this formula is a transcendental function and its parameters are unknown, it is not feasible to calculate the disturbance voltage step size through it. Therefore, the present invention uses the photovoltaic output voltage and output current at the current moment to fit the PU curve into a piecewise linear function curve, which is specifically shown as follows: Figure 6 As shown. The piecewise linear function can be expressed as:

[0122]

[0123] Therefore, the step length of waking up the MPPT is:

[0124]

[0125] According to the active standby control requirements of PV-PSG, the power and voltage of the maximum power point can be obtained once every 10 minutes, and then the open circuit voltage corresponding to the maximum power point can be obtained by the table lookup method. This can be achieved through the relationship between the output power, output current and output voltage of the photovoltaic array. Before the next MPPT wake-up, the coefficient of U in the formula is a fixed value, which is equivalent to a proportional regulator. Its value is related to the current maximum power point and open circuit voltage, and the power difference can be adjusted differentially.

[0126] In a power grid that includes photovoltaic power sources, a VSG control unit can exist alone or in combination with multiple VSG control units. This application mainly discusses the power system composed of photovoltaics, synchronous machines and active loads. The analysis and research conducted on this basis is limited to the microgrid model of a single VSG unit, but the research is not limited to the power system with photovoltaic systems as new energy power generation units. For other similar systems that use new energy as power sources, this research still has certain reference value. Figure 7 The system topology diagram used in the simulation of the present invention is shown. As shown in the figure, the system is composed of: a constant power unit G1, a frequency modulation unit G2, a photovoltaic power generation unit and a load.

[0127] In order to verify the effectiveness of the strategy proposed in this invention, the typical VSG control is compared with the photovoltaic grid support control with variable step power tracking. First, taking the sudden increase of load as an example, before the disturbance, the generator G1 and the photovoltaic storage unit containing VSG in the system are operating in a steady state, and the system frequency is stable at the power frequency of 50Hz. When the system is running for 25s, a load of 1.5kW is suddenly put into operation.

[0128] In this experiment, the total simulation time is set to 50s. To make the simulation results more intuitive, after the system is running stably, the time span of 20s to 50s is intercepted to observe the results more clearly. In the experimental results obtained, the active output of the system and the synchronous machine and the system frequency changes with and without the variable step-size power tracking control strategy are shown in Figure 2. Figure 8 As shown. It can be clearly seen in the figure:

[0129] In terms of frequency, Figure 8 As shown in (a), when the constraint condition is used as the frequency of superposition control, the red dotted line in the figure indicates that the system frequency takes about 5 seconds to recover to stability, and the maximum frequency deviation of the system is about 0.2Hz. When the control strategy is not added, the frequency response curve of the system is represented by the blue solid line in the figure, and the time for the frequency to recover to stability is about 13s, which is much longer than the frequency recovery time when the system adopts the proposed control strategy. In the same comparison, the maximum frequency deviation of the system without the variable step power tracking control strategy reaches 0.36Hz, which is significantly larger than 0.2Hz.

[0130] In terms of frequency modulation units, Figure 8 As shown in (b), the red dotted line represents the output of the frequency-modulating unit after adding the variable step-size power tracking control, while the blue solid line represents the output of the frequency-modulating unit without adding the control strategy. When this strategy is adopted, it can be seen from the comparison of the change slope that the frequency-modulating unit has achieved a faster response than when it is not adopted, and can achieve frequency modulation under the premise of quickly increasing active power, so that the system can recover stability faster. However, the system that does not adopt the variable step-size power tracking control strategy has a slow response speed, a long response time, and a general regulation effect.

[0131] In terms of system active power, Figure 8As shown in (c), the red dotted line represents the change in system active power after adding the variable step power tracking photovoltaic grid support control method, while the blue solid line represents the change in system active power without adding the variable step power tracking control strategy. After the load changes and the system is disturbed, the adjustment speed can be known by comparing the slopes of the two curves. Obviously, the slope of the red curve is larger, which means that the system adjusts faster and recovers to the original output power after 10 seconds. While the blue line has a relatively slow adjustment speed, the recovery speed is also around 15 seconds. Therefore, it can be said that when the variable step power tracking control strategy is adopted, the system adjustment speed is faster and the system frequency deviation value is smaller. In the process of system restoration and stability, the synchronous generator can respond to system power fluctuations faster, which can improve the support capacity for the grid frequency to a certain extent.

[0132] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean 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 embodiment of the present invention.

[0133] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0134] Fig. 9 The schematic diagram of the structure of the photovoltaic grid-type support control device based on variable step-size power tracking provided by an embodiment of the present invention is shown. For the convenience of explanation, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

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

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

[0137] A power calculation module 902, used to calculate the photovoltaic output power before and after the disturbance control according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control;

[0138] A sign bit calculation module 903, used to determine the sign bit according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control;

[0139] The voltage step determination module 904 is used to determine the voltage step when waking up the MPPT next time based on the sign bit and the current voltage tracking step.

[0140] In this embodiment, by obtaining the current voltage tracking step, the photovoltaic output voltage before and after the disturbance control, and the photovoltaic output current before and after the disturbance control, the photovoltaic output power before and after the disturbance control is calculated according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control, and based on the actual operation data of the photovoltaic system, the accuracy and reliability of the data are ensured. Subsequently, the sign bit is determined according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control, and the voltage step size when the MPPT is awakened next time is determined based on the sign bit and the current voltage tracking step, so as to realize real-time monitoring and dynamic adjustment of the system state, and ensure that the photovoltaic system is always in the optimal operating state. In this embodiment of the application, the traditional disturbance increment method based on power maximization is transformed into a disturbance amount with a signed coefficient based on the principle of output power tracking frequency modulation power instruction, so as to realize accurate tracking of frequency modulation power and effectively reduce the power fluctuation that may occur near the maximum power point. This improvement not only improves 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 description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0142] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example 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 performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0143] If the module / unit is implemented in the form of 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, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the above-mentioned embodiments of the photovoltaic grid-type support control method based on variable step power tracking. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium.

[0144] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A photovoltaic grid support control method based on variable step power tracking, characterized in that: include: Obtain the current voltage tracking step, 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 the disturbance control is calculated according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control; Determine the sign bit according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control; The voltage step size when waking up the MPPT next time is determined based on the sign bit and the current voltage tracking step size.

2. The photovoltaic grid support control method based on variable step-size power tracking according to claim 1 is characterized in that: The step of determining the sign bit according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control comprises: The photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control are input into the sign bit calculation formula to calculate the sign bit; wherein, the sign bit calculation formula is: Among them, 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; u(k-1) is the output voltage after disturbance control.

3. The photovoltaic grid support control method based on variable step-size power tracking according to claim 2 is characterized in that: The step of determining the voltage step size for waking up the MPPT next time based on the sign bit and the current voltage tracking step size includes: Obtain the previous voltage tracking step length corresponding to the current voltage tracking step length, and obtain the sign bit corresponding to the previous voltage tracking step length; When the voltage tracking step is equal to the maximum value of the step limit and the sign bits are both equal to the set value, the minimum value of the step limit is selected as the basic step value; otherwise, the current voltage tracking step is used as the basic step value; Determine the output active power command 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, the voltage step size for waking up the MPPT next time is determined based on the first functional formula; otherwise, the voltage step size for waking up the MPPT next time is determined based on the second functional formula; wherein the first functional formula and the second functional formula are piecewise linear functions obtained based on fitting of the photovoltaic PU characteristic curve.

4. The photovoltaic grid support control method based on variable step-size power tracking according to claim 3 is characterized in that: The two sign bits being equal to the set value includes: the product of the two sign bits is negative one.

5. The photovoltaic grid support control method based on variable step-size power tracking according to claim 3 is characterized in that: The piecewise linear function obtained based on the photovoltaic PU characteristic curve fitting includes: Using the photovoltaic output voltage and photovoltaic output current, the PU curve is fitted into a piecewise linear function curve: The first functional formula is: The second functional formula is: in, is the output active power instruction; P o is the instantaneous active power; U o is the photovoltaic output voltage; U oc is the withstand voltage of the photovoltaic array; U is the instantaneous voltage of the photovoltaic array; U mpp is the voltage value corresponding to the maximum power point of the photovoltaic array; P mpp is the maximum power of the photovoltaic array; P o is the instantaneous active power of the PV array.

6. The photovoltaic grid support control method based on variable step-size power tracking according to claim 5 is characterized in that: 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: The interference voltage is adjusted according to the voltage step size and sign bit when the MPPT is woken up next time.

7. The photovoltaic grid support control method based on variable step power tracking according to claim 6 is characterized in that: The step of adjusting the interference voltage according to the voltage step size and the sign bit when the MPPT is awakened next time includes: When the sign bit is less than zero, the interference voltage is u(k)=u(k)-u step (k) flag (k); Otherwise, the interference voltage is u(k)=u(k)+u step (k)flag(k).

8. The photovoltaic grid support control method based on variable step-size power tracking according to claim 3 is characterized in that: Also includes: Record the current voltage tracking step and the corresponding sign bit calculation result.

9. The photovoltaic grid support control method based on variable step-size power tracking according to claim 1 is characterized in that: The photovoltaic output power before and after the disturbance control is calculated according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control, including: The photovoltaic output power before disturbance control is calculated according to the photovoltaic output voltage and photovoltaic output current before disturbance control, and the photovoltaic output power after disturbance control is calculated according to the photovoltaic output voltage and photovoltaic output current after disturbance control; wherein, the photovoltaic output power calculation formula is as follows: P(k)=u(k)*i(k) Among them, P(k) is the photovoltaic output power; u(k) is the photovoltaic output voltage; i(k) is the photovoltaic output current.

10. A photovoltaic grid-type support control device based on variable step-size power tracking, characterized in that: include: An acquisition module is used to acquire the current voltage tracking step, the photovoltaic output voltage before and after the disturbance control, and the photovoltaic output current before and after the disturbance control; A power calculation module, used to calculate the photovoltaic output power before and after the disturbance control according to the photovoltaic output voltage before and after the disturbance control and the photovoltaic output current before and after the disturbance control; A sign bit calculation module, used for determining a sign bit according to the photovoltaic output power before and after the disturbance control and the photovoltaic output voltage before and after the disturbance control; The voltage step determination module is used to determine the voltage step when waking up the MPPT next time based on the sign bit and the current voltage tracking step.

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