Active power control method and control equipment of grid-forming type photovoltaic system and photovoltaic system

Abstract

The invention provides an active power control method and control equipment of a network-forming type photovoltaic system and the photovoltaic system, and belongs to the photovoltaic field. The photovoltaic system comprises a photovoltaic group string and a photovoltaic inverter which are connected in series, and the photovoltaic inverter comprises a booster circuit and an inverter circuit which are connected in series. The method comprises the following steps: acquiring reference active power and actual active power of an inverter circuit; determining the voltage adjustment amount of the photovoltaic string according to the reference active power and the actual active power; adjusting the target voltage of the photovoltaic string according to the voltage adjustment amount to obtain the adjusted target voltage; acquiring the actual voltage of the photovoltaic string and the actual current of the booster circuit; and controlling the booster circuit according to the adjusted target voltage, the actual voltage of the photovoltaic string and the actual current of the booster circuit. According to the invention, the actual active power control of the grid-forming type photovoltaic inverter can be realized, so that the grid-forming type photovoltaic inverter reaches the reference active power.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photovoltaic technology, and particularly relates to an active power control method, a control device and a photovoltaic system of a grid-connected photovoltaic system. BACKGROUND

[0002] The penetration rate of photovoltaic systems in power systems continues to rise, gradually forming a "double-high" power grid pattern characterized by a high proportion of renewable energy and a high proportion of power electronic devices. Under this background, large-scale centralized access of photovoltaic power generation easily leads to a decrease in grid strength, causing weak grid operating conditions and posing a serious challenge to system stability.

[0003] In related technologies, photovoltaic inverters usually adopt a grid-following control strategy, at which time the photovoltaic inverter can be equivalent to a controlled current source, and the phase and amplitude of the output current of the photovoltaic inverter track the grid voltage. However, this control mode cannot provide inertia response capability similar to that of a synchronous generator, and cannot effectively support the system frequency and voltage when the grid is disturbed, thereby exacerbating the operating risk under the "double-high" grid, especially under weak grid conditions, which is more likely to cause oscillation instability and other problems.

[0004] To enhance the stability of the grid, grid-connected control technology has gradually attracted attention. Under this control mode, the photovoltaic inverter can be equivalent to a voltage source, has the ability to actively adjust the output voltage and frequency, and can provide inertia and voltage support for the grid, which helps to improve the dynamic performance under weak grid conditions. However, for grid-connected photovoltaic systems, how to control the active power of the photovoltaic inverter is still a key technical problem that needs to be solved urgently. SUMMARY

[0005] Embodiments of the present application provide a grid-connected photovoltaic system active power control method, a control device and a photovoltaic system to solve the problem that the prior art cannot control the active power of the grid-connected photovoltaic inverter.

[0006] In a first aspect, embodiments of the present application provide a grid-connected photovoltaic system active power control method, the photovoltaic system comprising a photovoltaic string and a photovoltaic inverter connected in series, and the photovoltaic inverter comprising a boost circuit and an inverter circuit connected in series; the method comprising: obtaining a reference active power and an actual active power of the inverter circuit; determining a voltage adjustment amount of the photovoltaic string according to the reference active power and the actual active power; adjusting a target voltage of the photovoltaic string according to the voltage adjustment amount to obtain an adjusted target voltage; obtaining an actual voltage of the photovoltaic string and an actual current of the boost circuit; controlling the boost circuit according to the adjusted target voltage, the actual voltage of the photovoltaic string and the actual current of the boost circuit.

[0007] In a possible implementation, the voltage adjustment amount of the photovoltaic string is determined according to the reference active power and the actual active power, comprising: determining a first difference value of the reference active power and the actual active power; performing proportional-integral control on the first difference value to obtain the voltage adjustment amount of the photovoltaic string.

[0008] In a possible implementation, the target voltage of the photovoltaic string is adjusted according to the voltage adjustment amount to obtain an adjusted target voltage, comprising: taking a sum of the voltage adjustment amount and the target voltage of the photovoltaic string as the adjusted target voltage.

[0009] In a possible implementation, after the target voltage of the photovoltaic string is adjusted according to the voltage adjustment amount to obtain the adjusted target voltage, further comprising: performing amplitude limiting processing on the adjusted target voltage, so that the amplitude-limited target voltage is located between a maximum power point tracking voltage and an open-circuit voltage of the photovoltaic string; Correspondingly, the boost circuit is controlled according to the adjusted target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit, comprising: controlling the boost circuit according to the amplitude-limited target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit.

[0010] In a possible implementation, the boost circuit is controlled according to the adjusted target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit, comprising: determining a reference current of the boost circuit according to the adjusted target voltage and the actual voltage of the photovoltaic string; controlling the boost circuit according to the reference current of the boost circuit and the actual current of the boost circuit.

[0011] In a possible implementation, the reference current of the boost circuit is determined according to the adjusted target voltage and the actual voltage of the photovoltaic string, comprising: determining a second difference value of the adjusted target voltage and the actual voltage of the photovoltaic string; performing proportional-integral control on the second difference value to obtain the reference current of the boost circuit.

[0012] In a possible implementation, the boost circuit is controlled according to the reference current of the boost circuit and the actual current of the boost circuit, comprising: determining a third difference value of the reference current of the boost circuit and the actual current of the boost circuit; performing proportional-integral control on the third difference value to obtain a control amount of the boost circuit. The voltage boosting circuit is controlled according to the control quantity of the voltage boosting circuit.

[0013] In a possible implementation, the photovoltaic system is a string-type photovoltaic system.

[0014] In a second aspect, an embodiment of the present application provides an active power control device of a grid-connected photovoltaic system, the photovoltaic system comprising a photovoltaic string and a photovoltaic inverter connected in series, the photovoltaic inverter comprising a voltage boosting circuit and an inverter circuit connected in series; the device comprises: a first obtaining module configured to obtain a reference active power and an actual active power of the inverter circuit; a voltage adjustment quantity determining module configured to determine a voltage adjustment quantity of the photovoltaic string according to the reference active power and the actual active power; a target voltage adjusting module configured to adjust a target voltage of the photovoltaic string according to the voltage adjustment quantity, to obtain an adjusted target voltage; a second obtaining module configured to obtain an actual voltage of the photovoltaic string and an actual current of the voltage boosting circuit; a control module configured to control the voltage boosting circuit according to the adjusted target voltage, the actual voltage of the photovoltaic string, and the actual current of the voltage boosting circuit.

[0015] In a third aspect, an embodiment of the present application provides a control device, comprising a processor and a memory, the memory being configured to store a computer program, and the processor being configured to invoke and run the computer program stored in the memory to execute the active power control method of the grid-connected photovoltaic system as described in the first aspect or any possible implementation manner of the first aspect.

[0016] In a fourth aspect, an embodiment of the present application provides a photovoltaic system, comprising a photovoltaic string, a voltage boosting circuit, an inverter circuit, and a control device as described in the third aspect. The voltage boosting circuit is connected to the photovoltaic string and the inverter circuit respectively; and the voltage boosting circuit is controlled by the control device.

[0017] In a fifth aspect, an embodiment of the present application provides a computer readable storage medium, the computer readable storage medium storing a computer program, the computer program being executed by a processor to implement the active power control method of the grid-connected photovoltaic system as described in the first aspect or any possible implementation manner of the first aspect.

[0018] The active power control method of the grid-connected photovoltaic system, the control device and the photovoltaic system provided by the embodiment of the present application, the reference active power and the actual active power of the inverter circuit are used to determine the voltage adjustment amount of the photovoltaic string, and the target voltage of the photovoltaic string is adjusted according to the voltage adjustment amount, so that the adjusted target voltage is obtained. The photovoltaic string is connected with the boost circuit, which is equivalent to adjusting the reference input voltage of the boost circuit. Then, the boost circuit is controlled according to the adjusted target voltage, the actual voltage of the photovoltaic string and the actual current of the boost circuit. The boost circuit is connected with the inverter circuit, and the actual active power control of the grid-connected inverter circuit can be realized by controlling the boost circuit, so that the reference active power is reached. Therefore, the output power of the photovoltaic inverter can be adjusted according to the demand, so as to meet the actual use demand. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0020] Figure 1 is a structural schematic diagram of a photovoltaic system provided by an embodiment of the present application; Figure 2 is a structural schematic diagram of a photovoltaic system provided by another embodiment of the present application; Figure 3 is a flow chart of the implementation of the active power control method of the grid-connected photovoltaic system provided by an embodiment of the present application; Figure 4 is a schematic diagram of the control loop of the boost circuit provided by an embodiment of the present application; Figure 5 is a schematic diagram of the active power control device of the grid-connected photovoltaic system provided by an embodiment of the present application; Figure 6 is a schematic diagram of the control device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0021] In the following description, specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments without these specific details. In other instances, well-known systems, devices, circuits and methods have been described in detail to avoid unnecessary detail.

[0022] In order to make the objects, technical solutions and advantages of the present application clearer, the following will be described by specific embodiments in conjunction with the drawings.

[0023] Referring to Figure 1 , a structural schematic diagram of a photovoltaic system provided by an embodiment of the present application is shown. The photovoltaic system can include a photovoltaic string 11 and a photovoltaic inverter 15 connected in series; the photovoltaic inverter 15 includes a boost circuit 12 and an inverter circuit 13 connected in series; the photovoltaic system can also include a control device (not shown in the figure) for controlling the boost circuit 12. Figure 1 As shown in Figure 1 , the boost circuit 12 is connected to the photovoltaic string 11 and the inverter circuit 13, respectively; the boost circuit 12 is controlled by the control device. The control device is used to perform the active power control method of the grid-connected photovoltaic system in the subsequent embodiments.

[0024] The photovoltaic string 11 can include a plurality of photovoltaic components connected in series; or, the photovoltaic string 11 can include a plurality of photovoltaic components, some of which are connected in series, and the series-connected photovoltaic components are connected in parallel; and the like. The photovoltaic component can convert solar energy into direct current, and the photovoltaic string 11 can aggregate the conversion capabilities of a plurality of photovoltaic components together to output the direct current required by the subsequent boost circuit 12.

[0025] The first output end of the photovoltaic string 11 is connected to the first input end of the boost circuit 12, and the second output end of the photovoltaic string 11 is connected to the second input end of the boost circuit 12. The boost circuit 12 is used to boost the direct current output by the photovoltaic string 11 to output the direct current required by the subsequent inverter circuit 13.

[0026] Exemplarily, referring to Figure 1 , the boost circuit 12 can include an inductor L, a diode D and a switch tube S; the first end of the inductor L serves as the first input end of the boost circuit 12, the second end of the inductor L is connected to the anode of the diode D and the first end of the switch tube S, respectively, the cathode of the diode D serves as the first output end of the boost circuit 12, and the second end of the switch tube S serves as the second input end and the second output end of the boost circuit 12. Among them, the switch tube S can be a power tube, which can be a MOS tube (Metal-Oxide-Semiconductor Field-Effect Transistor) or an IGBT module (Insulated Gate Bipolar Transistor Module), or other types of switch tubes, which are not specifically limited here. It should be noted that Figure 1 the topology of the boost circuit 12 shown is only illustrative, and in actual application, the boost circuit 12 can also include other devices and can be other topologies, which are not specifically limited here.

[0027] The first output end of the boost circuit 12 is connected with the first input end of the inverter circuit 13, the second output end of the boost circuit 12 is connected with the second input end of the inverter circuit 13, and the output end of the inverter circuit 13 can be connected with the power grid 14. The inverter circuit 13 is used for converting direct current into alternating current, providing support for the power grid 14, and improving the stability of the power grid 14.

[0028] The embodiment of the present application does not limit the specific composition of the photovoltaic string 11 and the specific topology of the boost circuit 12 and the inverter circuit 13, and any achievable composition or structure can be used.

[0029] In some possible implementation manners, the photovoltaic inverter 15 can further include a direct-current bus (not shown in the figure) connected between the boost circuit 12 and the inverter circuit 13. Figure 1

[0030] In some possible implementation manners, the above-mentioned one set of series-connected photovoltaic strings 11, the boost circuit 12 and the inverter circuit 13 can be used as one photovoltaic unit 10. The photovoltaic system can include one photovoltaic unit 10, as shown in FIG. 1; the photovoltaic system can also include at least two photovoltaic units 10, as shown in FIG. 2. Figure 1 Figure 2 The output ends of the photovoltaic units 10 are connected in parallel, and the parallel connection is connected with the power grid 14.

[0031] When the photovoltaic system includes at least two photovoltaic units 10, the boost circuits 12 of the photovoltaic units 10 can be controlled by the same control device, or can be controlled by respective control devices corresponding to the photovoltaic units 10 respectively. That is, the photovoltaic system can include one control device used for controlling the boost circuits 12; the photovoltaic system can also include control devices corresponding to the photovoltaic units 10 one by one, and each control device controls the boost circuit 12 in the corresponding photovoltaic unit 10 based on the reference active power and the actual active power of the inverter circuit 13 in the corresponding photovoltaic unit 10, the actual voltage of the photovoltaic string 11 and the actual current of the boost circuit 12, and the like.

[0032] The active power control method of the grid-connected photovoltaic system provided by the embodiment of the present application will be described below based on Figure 1 and Figure 2 , in combination with Figure 3

[0033] Referring to Figure 3 ​​​Fig. 1 shows a flowchart of a method for controlling active power of a grid-connected photovoltaic system according to an embodiment of the present application, which shows a flowchart of a method for controlling active power of a grid-connected photovoltaic system provided by an embodiment of the present application. The main body for executing the method for controlling active power of a grid-connected photovoltaic system is a control device. The control device can be a controller, such as a DSP (Digital Signal Processor), etc.

[0034] As described above, the photovoltaic system includes a photovoltaic string and a photovoltaic inverter connected in series. The photovoltaic inverter includes a boost circuit and an inverter circuit connected in series.

[0035] Referring to Figure 3 The method for controlling active power of a grid-connected photovoltaic system is described in detail as follows. In S301, a reference active power and an actual active power of the inverter circuit are obtained.

[0036] The actual active power of the inverter circuit is the actual output active power of the inverter circuit, which can be obtained by measurement or calculated according to the actual output voltage and the actual output current of the inverter circuit, etc. without specific limitation here.

[0037] The reference active power of the inverter circuit is the target value of the output active power of the inverter circuit, i.e. the power value that the actual active power of the inverter circuit needs to reach, which can also be referred to as the given active power or the target active power of the inverter circuit, etc. The reference active power of the inverter circuit can be issued by a host computer or a dispatch center to the control device according to the actual demand, i.e. the value of the active power that needs to be output by the inverter circuit.

[0038] The method for obtaining the reference active power and the actual active power of the inverter circuit is not limited in the embodiments of the present application, and any achievable method can be used.

[0039] In the embodiments of the present application, the reference active power and the actual active power of the inverter circuit can also be understood as the reference active power and the actual active power of the photovoltaic inverter to which the inverter circuit belongs.

[0040] In S302, a voltage adjustment amount of the photovoltaic string is determined according to the reference active power and the actual active power.

[0041] Based on the reference active power of the inverter circuit and the actual active power of the inverter circuit, the voltage adjustment amount of the photovoltaic string can be determined in the embodiments of the present application. The voltage adjustment amount of the photovoltaic string is used to adjust the target voltage of the photovoltaic string.

[0042] The method for determining the voltage adjustment amount of the photovoltaic string according to the reference active power and the actual active power is not limited in the embodiments of the present application, and any achievable method can be used.

[0043] In S303, the target voltage of the photovoltaic string is adjusted according to the voltage adjustment amount, and an adjusted target voltage is obtained.

[0044] The target voltage of the photovoltaic string is a target output voltage of the photovoltaic string, that is, the actual output voltage of the photovoltaic string needs to be controlled to reach the target voltage. The specific value of the target voltage of the photovoltaic string can be set according to actual needs, which is not limited here.

[0045] Since the photovoltaic string is connected with the boost circuit, the target voltage of the photovoltaic string is equivalent to the target input voltage of the boost circuit.

[0046] The embodiment of the present application adjusts the target voltage of the photovoltaic string according to the voltage adjustment amount, and obtains the adjusted target voltage of the photovoltaic string, which is equivalent to adjusting the target input voltage of the boost circuit according to the voltage adjustment amount, and obtaining the adjusted target input voltage of the boost circuit.

[0047] In S304, the actual voltage of the photovoltaic string and the actual current of the boost circuit are obtained.

[0048] The actual voltage of the photovoltaic string is the actual output voltage of the photovoltaic string. The actual current of the boost circuit is the actual current flowing through the inductor of the boost circuit.

[0049] The actual voltage of the photovoltaic string and the actual current of the boost circuit can be obtained by a corresponding acquisition device, or can be obtained by other means, which is not limited here.

[0050] In S305, the boost circuit is controlled according to the adjusted target voltage, the actual voltage of the photovoltaic string and the actual current of the boost circuit.

[0051] The embodiment of the present application can control the boost circuit according to the adjusted target voltage, the actual voltage of the photovoltaic string and the actual current of the boost circuit, and the ultimate goal is to make the actual active power of the inverter circuit reach its reference active power, and meet the use demand.

[0052] The embodiment of the present application does not limit the specific implementation means of controlling the boost circuit according to the adjusted target voltage, the actual voltage of the photovoltaic string and the actual current of the boost circuit, and any implementable means can be used.

[0053] It should be noted that the photovoltaic string, the boost circuit and the inverter circuit in the embodiment of the present application are structures in the same photovoltaic unit.

[0054] The voltage adjustment amount of the photovoltaic module string is determined by the reference active power and the actual active power of the inverter circuit, and the target voltage of the photovoltaic module string is adjusted according to the voltage adjustment amount, to obtain an adjusted target voltage. The photovoltaic module string is connected with the boost circuit, which is equivalent to adjusting the reference input voltage of the boost circuit. Then, the boost circuit is controlled according to the adjusted target voltage, the actual voltage of the photovoltaic module string and the actual current of the boost circuit. The boost circuit is connected with the inverter circuit, and the actual active power control of the grid-connected inverter circuit can be realized by controlling the boost circuit, so that the reference active power is reached. Therefore, the output power of the photovoltaic inverter can be adjusted according to the demand, so as to meet the actual use demand.

[0055] The traditional inverter circuit adopts the grid-connected mode, and needs to rely on the power grid to provide stable voltage and frequency to operate. According to the reference active power of the inverter circuit, the target voltage of the photovoltaic module is directly adjusted in the embodiment of the application, and then the active power injected into the power grid is controlled, so as to realize the grid-connected control of the photovoltaic system. The photovoltaic system can provide inertia support and primary frequency modulation for the power grid like the traditional synchronous generator. When the frequency of the power grid changes, the photovoltaic system can help the power grid restore the stable frequency by quickly adjusting the active power output, instead of being passively disconnected or shut down.

[0056] In addition, the power control loop is moved to the boost circuit in the embodiment of the application, and the working point of the photovoltaic module string is changed by directly adjusting the target voltage, so that the output power is quickly changed. This source control is faster in response speed and better in dynamic performance than the control on the inverter circuit side. The output active power of the inverter circuit is tracked to the reference active power by the closed-loop control of the reference active power and the actual active power of the inverter circuit in the embodiment of the application, so as to reduce the power fluctuation and error.

[0057] The boost circuit in the front stage is finely controlled in the embodiment of the application, so as to reduce the fluctuation of the direct-current bus voltage of the inverter circuit in the rear stage. A more stable direct-current bus voltage creates better conditions for the control of the inverter circuit, and helps to output higher quality electric energy (for example, reducing harmonics).

[0058] In some possible implementation manners, the target voltage of the photovoltaic module string can be a preset output voltage of the photovoltaic module string in the CVT (Constant Voltage Tracking) mode.

[0059] In a preferred implementation, the target voltage of the photovoltaic string can be a maximum power point tracking (MPPT) voltage of the photovoltaic string, i.e., an output voltage corresponding to a maximum power point of the photovoltaic string.

[0060] Specifically, before S301, the method can further include: controlling the photovoltaic system to operate in a grid-following mode, and obtaining an MPPT voltage of the photovoltaic string in the grid-following mode; controlling the photovoltaic system to operate in a grid-forming mode, and continuing to perform S301 to S305.

[0061] In the grid-following mode, the MPPT voltage of the photovoltaic string can be obtained according to an MPPT algorithm in the related art. Alternatively, I-V curve scanning can be performed in a full voltage range of the photovoltaic string, and the MPPT voltage corresponding to the maximum power point can be determined based on the I-V curve obtained by scanning.

[0062] In the embodiments of the present application, the target voltage of the photovoltaic string is set to the MPPT voltage of the photovoltaic string, which can significantly improve the active power control accuracy and dynamic performance of the inverter circuit. Specifically, the MPPT voltage of the photovoltaic string is the voltage corresponding to the maximum power that the photovoltaic string can output at present. When the active power closed-loop control is not performed, the photovoltaic string tracks the MPPT voltage and outputs the maximum power, so that the inverter circuit can output the maximum active power. When the grid needs to operate at a reduced capacity, i.e., the inverter circuit needs to reduce the active power, the reference active power is reduced, and the target voltage of the photovoltaic string needs to be adjusted accordingly, which is no longer the MPPT voltage, so that the actual active power of the inverter circuit is the adjusted reference active power.

[0063] That is, the embodiments of the present application adjust the output voltage of the photovoltaic string based on the MPPT voltage. If there is no MPPT voltage as a reference, the control device blindly searches for the target power point on an unknown curve, which can cause the adjustment process to oscillate, be slow or inaccurate. In the embodiments of the present application, the control device has an accurate reference coordinate based on the MPPT voltage, which can accurately know that the target voltage needs to be moved by a voltage adjustment amount to both sides from the MPPT voltage to reduce the power. The new working point of the photovoltaic string obtained in this way is very accurate, and thus the active power control of the inverter circuit is also very accurate, which improves the active power control accuracy of the inverter circuit. Since the target voltage of the photovoltaic string is the accurate MPPT voltage, the control device does not need to search for the target working point in the entire voltage range, so the response speed is also accelerated.

[0064] In some embodiments, in S302, the voltage adjustment amount of the photovoltaic string is determined according to the reference active power and the actual active power, including: determining a first difference value of the reference active power and the actual active power; performing proportional-integral (PI) control on the first difference value to obtain the voltage adjustment amount of the photovoltaic string.

[0065] Referring to Figure 4 , the reference active power is P ref , the actual active power is P fdb , and the voltage adjustment amount of the photovoltaic string is U1. The reference active power P ref is subtracted by the actual active power P fdb to obtain the first difference value, and the first difference value is subjected to PI control to obtain the voltage adjustment amount U1 of the photovoltaic string.

[0066] In some possible implementations, the above-mentioned PI control on the first difference value to obtain the voltage adjustment amount of the photovoltaic string can include: inputting the first difference value into a first preset PI controller to obtain the voltage adjustment amount U1 of the photovoltaic string output by the first preset PI controller.

[0067] wherein the parameters of the first preset PI controller have been pre-set so that the first preset PI controller can output the voltage adjustment amount U1 of the photovoltaic string according to the first difference value of the reference active power P ref and the actual active power P fdb .

[0068] In the embodiments of the present application, when subjected to external interference, such as temporary changes in light caused by cloud cover, slight fluctuations in power grid frequency, etc., the reference active power can be automatically and smoothly restored. Specifically, any interference that causes the actual active power to deviate from the reference active power will immediately generate a power error, i.e., the above-mentioned first difference value. The PI control will take the first difference value as input and automatically output a voltage adjustment amount in the correction direction to drive the actual active power to return to the reference active power. This process is closed-loop and automatic, without the need for external intervention, and has good robustness.

[0069] In addition, due to the existence of the integral element in the PI control, as long as the first difference value exists (i.e., the first difference value is not 0), the integral element will continue to accumulate regardless of how small the first difference value is, and the voltage adjustment amount will be continuously adjusted until the first difference value is completely eliminated, so that the actual active power of the photovoltaic system can be accurately stabilized at the reference active power, achieving zero steady-state error.

[0070] The proportional part in the PI control provides a quick response, and once the first difference (i.e., the first difference is not 0) appears, an adjustment effect is immediately generated, and the integral part is responsible for fine correction, and the two parts cooperate with each other, so that the power change can be quickly responded to, and oscillation and excessive overshoot will not be generated due to too fast response, and the balance between speed and stability can be achieved.

[0071] In some embodiments, in S303, the target voltage of the photovoltaic string is adjusted according to the voltage adjustment amount, to obtain an adjusted target voltage, including: The sum of the voltage adjustment amount and the target voltage of the photovoltaic string is taken as the adjusted target voltage.

[0072] Referring to Figure 4 , the voltage adjustment amount is U1, and the target voltage of the photovoltaic string is U CVT The sum of the two is taken to obtain the adjusted target voltage.

[0073] In the embodiments of the present application, when the reference active power change or the actual active power change is generated, a voltage adjustment amount that is not 0 is generated, the voltage adjustment amount is summed with the target voltage of the photovoltaic string to obtain an adjusted target voltage, that is, the actual output voltage of the photovoltaic string needs to be adjusted from the target voltage to the adjusted target voltage, so as to adjust the actual active power of the inverter circuit, so that the actual active power of the inverter circuit is the reference active power, and the control of the active power of the grid-connected photovoltaic inverter is realized.

[0074] In some embodiments, after S303, the above method further includes: The adjusted target voltage is subjected to amplitude limiting processing, so that the amplitude-limited target voltage is located between the maximum power point tracking voltage and the open circuit voltage of the photovoltaic string; Correspondingly, in the above S305, the boost circuit is controlled according to the adjusted target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit, including: The boost circuit is controlled according to the amplitude-limited target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit.

[0075] The interval of the above maximum power point tracking voltage and open circuit voltage contains the maximum power point tracking voltage and does not contain the open circuit voltage.

[0076] The P (power) -V (voltage) curve of the photovoltaic string is that the power first increases with the increase of the voltage, then reaches the maximum power point tracking voltage of the photovoltaic string, the power reaches the maximum value, and then the power decreases with the increase of the voltage until the open circuit voltage of the photovoltaic string, the power becomes 0. The maximum power point tracking voltage of the photovoltaic string has a certain proportional relationship with the open circuit voltage of the photovoltaic string. In the embodiment of the present application, the maximum power point tracking voltage of the photovoltaic string is obtained by multiplying the open circuit voltage of the photovoltaic string by a preset proportional coefficient. The preset proportional coefficient can be located in the range of 0.75-0.85, for example, it can be 0.78, 0.8 or 0.82, etc. The open circuit voltage of the photovoltaic string can be determined by querying the product parameters, or can be determined by actual measurement, which is not specifically limited here. In the embodiment of the present application, the maximum power point tracking voltage of the photovoltaic string can also be determined by the method in the foregoing embodiment, which is not specifically limited here.

[0077] The embodiment of the present application limits the amplitude of the adjusted target voltage to obtain the amplitude-limited target voltage. The amplitude-limited target voltage is located between the maximum power point tracking voltage and the open circuit voltage of the photovoltaic string. Specifically, if the adjusted target voltage is located in the above interval, the amplitude-limited target voltage is the adjusted target voltage, and if the adjusted target voltage is not located in the above interval, the amplitude-limited target voltage is the critical value closest to the adjusted target voltage in the above interval.

[0078] The embodiment of the present application increases the amplitude limiting processing, limits the amplitude-limited target voltage between the maximum power point tracking voltage and the open circuit voltage of the photovoltaic string, so that the photovoltaic string can always work in its feasible region, and ensures the effectiveness of the control.

[0079] In addition, the embodiment of the present application limits the amplitude-limited target voltage of the photovoltaic string between the maximum power point tracking voltage and the open circuit voltage of the photovoltaic array, which is equivalent to adjusting the actual voltage of the photovoltaic string to between the maximum power point tracking voltage and the open circuit voltage of the photovoltaic string, i.e. limiting in the region where the power decreases with the increase of the voltage, i.e. if the actual voltage of the photovoltaic string rises, its actual power will decrease; if the actual voltage of the photovoltaic string decreases, its actual power will increase. Assuming that there is a disturbance that makes the actual voltage of the photovoltaic string rise, its actual power will naturally decrease, and the power reduction will not be able to support a higher voltage, so that its actual voltage will be pulled back to the origin, and vice versa. It is equivalent to forming a negative feedback mechanism, so that the working point is more stable.

[0080] When the grid needs more power, the inverter circuit increases the output power, causing the actual voltage of the bus to decrease, and then causing the actual voltage of the photovoltaic string to decrease, so that the actual power of the photovoltaic string increases, thereby supplementing the energy consumed by the inverter circuit and helping the photovoltaic system to restore balance. When the grid needs less power, the inverter circuit reduces the output power, causing the actual voltage of the bus to increase, and then causing the actual voltage of the photovoltaic string to increase, so that the actual power of the photovoltaic string decreases, thereby reducing the energy supplied to the inverter circuit and helping the photovoltaic system to restore balance.

[0081] It should be noted that after the clipping processing provided in the embodiments of the present application is added, the adjusted target voltage in the subsequent embodiments can be replaced by the clipped target voltage. For example, the boost circuit is controlled according to the clipped target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit, including: determining the reference current of the boost circuit according to the clipped target voltage and the actual voltage of the photovoltaic string; and controlling the boost circuit according to the reference current of the boost circuit and the actual current of the boost circuit. The reference current of the boost circuit is determined according to the clipped target voltage and the actual voltage of the photovoltaic string, including: determining the second difference value of the clipped target voltage and the actual voltage of the photovoltaic string; and performing proportional integral control on the second difference value to obtain the reference current of the boost circuit.

[0082] In some embodiments, in S305, the boost circuit is controlled according to the adjusted target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit, including: determining the reference current of the boost circuit according to the adjusted target voltage and the actual voltage of the photovoltaic string; controlling the boost circuit according to the reference current of the boost circuit and the actual current of the boost circuit.

[0083] Referring to Figure 4 , the actual voltage of the photovoltaic string is U pv , and the actual current of the boost circuit is I boost .

[0084] Since the photovoltaic string is connected to the boost circuit, the adjusted target voltage of the photovoltaic string is also the voltage that the input voltage of the boost circuit needs to reach, and the actual voltage of the photovoltaic string is also the actual input voltage of the boost circuit. Therefore, based on the two, the reference current of the boost circuit, i.e. the current that the boost circuit needs to reach, can be obtained. Based on this, the control amount of the boost circuit, specifically the control amount of the switch tube in the boost circuit, can be obtained according to the actual current of the boost circuit, and the switch tube of the boost circuit is controlled according to the control amount.

[0085] According to the adjusted target voltage and the actual voltage of the photovoltaic string, the reference current of the boost circuit is determined, which is equivalent to generating the current instruction according to the voltage outer loop; the boost circuit is controlled according to the reference current of the boost circuit and the actual current of the boost circuit, which is equivalent to performing fast tracking according to the current inner loop. The voltage outer loop is responsible for macro comparison, which compares the adjusted target voltage and the actual voltage of the photovoltaic string, calculates the reference current of the boost circuit required to reach the adjusted target voltage, and the response of the voltage outer loop is relatively stable to ensure stability. The current inner loop is responsible for micro execution, and the current is the fastest changing physical quantity in the power device. After receiving the current instruction from the voltage outer loop, the current inner loop can force the actual current to quickly and accurately track the reference current through the high-frequency PWM (Pulse Width Modulation) method. Because the response speed of the current inner loop is extremely fast, it can quickly offset the disturbance from the photovoltaic side or the DC bus side, and provide a stable bottom support for the voltage outer loop. Based on the above voltage outer loop and current inner loop, the system can maintain stable operation and is not easy to oscillate when facing input voltage fluctuations, load changes and the like.

[0086] In some embodiments, the above determining the reference current of the boost circuit according to the adjusted target voltage and the actual voltage of the photovoltaic string comprises: determining a second difference value of the adjusted target voltage and the actual voltage of the photovoltaic string; performing proportional integral control on the second difference value to obtain the reference current of the boost circuit.

[0087] Referring to Figure 4 , the adjusted target voltage is subtracted from the actual voltage U pv The difference value obtained is called the second difference value. PI control is performed on the second difference value to obtain the reference current of the boost circuit.

[0088] In a possible implementation, performing proportional integral control on the second difference value to obtain the reference current of the boost circuit can comprise: inputting the second difference value into a second preset PI controller to obtain the reference current of the boost circuit output by the second preset PI controller.

[0089] The parameters of the second preset PI controller have been pre-set, so that the second preset PI controller can output the reference current of the boost circuit according to the second difference value of the adjusted target voltage and the actual voltage of the photovoltaic string.

[0090] In the embodiments of the present application, when external interference occurs, such as cloud passing by causing temporary change of light, the actual voltage of the photovoltaic string can automatically and smoothly recover to the adjusted target voltage. Specifically, any interference that causes the actual voltage of the photovoltaic string to deviate from the adjusted target voltage will immediately generate a voltage error, i.e., the second difference, and the PI control will take the second difference as input and automatically output a reference current of the boost circuit in a correction direction to drive the actual voltage of the photovoltaic string to recover to the adjusted target voltage. This process is closed-loop and automatic, and does not require external intervention, and has good robustness.

[0091] In addition, due to the existence of the integral element in the PI control, as long as the second difference exists (i.e., the second difference is not 0), the integral element will continuously accumulate regardless of how small the second difference is, and will continuously adjust the reference current of the boost circuit until the second difference is completely eliminated, so that the actual voltage of the photovoltaic system can be accurately stabilized at the adjusted target voltage, achieving zero steady-state error.

[0092] The proportional element in the PI control provides fast response, and will immediately produce an adjustment effect as soon as the second difference (i.e., the second difference is not 0) occurs. The integral element is responsible for fine correction, and the two work together to enable fast response to power changes and prevent oscillation and excessive overshoot due to too fast response, achieving a balance between speed and stability.

[0093] In some embodiments, the above control of the boost circuit according to the reference current of the boost circuit and the actual current of the boost circuit includes: determining a third difference between the reference current of the boost circuit and the actual current of the boost circuit; performing proportional-integral control on the third difference to obtain a control amount of the boost circuit; controlling the boost circuit according to the control amount of the boost circuit.

[0094] Referring to Figure 4 , the present application subtracts the actual current I boost of the boost circuit from the reference current of the boost circuit to obtain a third difference. PI control on the third difference can obtain a control amount of the boost circuit, and the boost circuit is controlled according to the control amount of the boost circuit, so as to finally realize that the actual active power of the inverter circuit is the reference active power. The control amount of the boost circuit can include the duty cycle of the switch tube of the boost circuit or the drive signal (PWM signal) of the switch tube of the boost circuit. If the control amount of the boost circuit can include the duty cycle of the switch tube of the boost circuit, the drive signal of the switch tube can be generated based on the duty cycle. The switch tube is controlled according to the drive signal of the switch tube.

[0095] In a possible implementation, the proportional-integral control on the third difference value can obtain the control quantity of the boost circuit, which can include: The third difference value is input into the third preset PI controller to obtain the control quantity of the boost circuit output by the third preset PI controller.

[0096] The third preset PI controller has parameters that are preset, so that the third preset PI controller can output the control quantity of the boost circuit according to the third difference value of the reference current of the boost circuit and the actual current of the boost circuit.

[0097] The embodiment of the present application establishes a current inner loop, and the inductor current (the actual current of the boost circuit) can accurately track the reference value (the reference current of the boost circuit) almost without delay, the response speed is in the order of microseconds to milliseconds, and the super-fast dynamic response and accurate current instruction tracking can be achieved.

[0098] In addition, since the control quantity of the boost circuit is directly determined by the actual current and the reference current of the boost circuit, the reference current or the output of the PI control can be easily limited in amplitude, and the maximum current stress can be limited to a safe absolute value from the root, so that the current can be prevented from running out of control and serious faults such as tube explosion can be avoided even in control failure or extreme external conditions.

[0099] In some embodiments, the photovoltaic system is a string-type photovoltaic system.

[0100] The method provided by the embodiment of the present application can be applied to a string-type photovoltaic system, such as the photovoltaic system shown in Figure 1 or Figure 2 The photovoltaic inverter in the string-type photovoltaic system includes a boost circuit.

[0101] It should be understood that the size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiment of the present application.

[0102] Figure 5 The structure schematic diagram of the active power control device of the grid-connected photovoltaic system provided by the embodiment of the present application is shown, only the parts related to the embodiment of the present application are shown for the convenience of description, and the details are as follows: The photovoltaic system includes a photovoltaic string and a photovoltaic inverter connected in series, and the photovoltaic inverter includes a boost circuit and an inverter circuit connected in series. As Figure 5 The active power control device 30 of the grid-connected photovoltaic system includes a first acquisition module 31, a voltage adjustment quantity determination module 32, a target voltage adjustment module 33, a second acquisition module 34, and a control module 35.

[0103] The first obtaining module 31 is configured to obtain reference active power and actual active power of the inverter circuit. The voltage adjustment amount determining module 32 is configured to determine a voltage adjustment amount of the photovoltaic string according to the reference active power and the actual active power. The target voltage adjusting module 33 is configured to adjust a target voltage of the photovoltaic string according to the voltage adjustment amount, to obtain an adjusted target voltage. The second obtaining module 34 is configured to obtain an actual voltage of the photovoltaic string and an actual current of the boost circuit. The control module 35 is configured to control the boost circuit according to the adjusted target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit.

[0104] In a possible implementation, the voltage adjustment amount determining module 32 is specifically configured to: determine a first difference value of the reference active power and the actual active power; perform proportional-integral control on the first difference value, to obtain the voltage adjustment amount of the photovoltaic string.

[0105] In a possible implementation, the target voltage adjusting module 33 is specifically configured to: take a sum of the voltage adjustment amount and the target voltage of the photovoltaic string as the adjusted target voltage.

[0106] In a possible implementation, after the target voltage adjusting module 33 adjusts the target voltage of the photovoltaic string according to the voltage adjustment amount, to obtain the adjusted target voltage, the target voltage adjusting module 33 further includes: perform amplitude limiting processing on the adjusted target voltage, to make the amplitude-limited target voltage be between a maximum power point tracking voltage and an open-circuit voltage of the photovoltaic string; Correspondingly, the control module 35 is specifically configured to control the boost circuit according to the amplitude-limited target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit.

[0107] In a possible implementation, the control module 35 is specifically configured to: determine a reference current of the boost circuit according to the adjusted target voltage and the actual voltage of the photovoltaic string; control the boost circuit according to the reference current of the boost circuit and the actual current of the boost circuit.

[0108] In a possible implementation, in the control module 35, the reference current of the boost circuit is determined according to the adjusted target voltage and the actual voltage of the photovoltaic string, including: determining a second difference value of the adjusted target voltage and the actual voltage of the photovoltaic string; The second difference is subjected to proportional-integral control to obtain the reference current of the boost circuit.

[0109] In one possible implementation, the control module 35 controls the boost circuit based on the reference current and the actual current of the boost circuit, including: Determine the third difference between the reference current of the boost circuit and the actual current of the boost circuit; The third difference is subjected to proportional-integral control to obtain the control quantity of the boost circuit. The boost circuit is controlled according to the control input of the boost circuit.

[0110] In one possible implementation, the photovoltaic system is a string photovoltaic system.

[0111] Figure 6 This is a schematic diagram of the control device provided in an embodiment of the present invention. Figure 6 As shown, the control device 4 in this embodiment includes a processor 40 and a memory 41. The memory 41 stores a computer program 42, and the processor 40 calls and runs the computer program 42 stored in the memory 41 to execute the steps in the above embodiments of the active power control method for grid-connected photovoltaic systems. Alternatively, the processor 40 calls and runs the computer program 42 stored in the memory 41 to implement the functions of each module / unit in the above embodiments of the device.

[0112] For example, the computer program 42 may be divided into one or more modules / units, which are stored in the memory 41 and executed by the processor 40 to complete the present invention. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program 42 in the control device 4.

[0113] The control device 4 may include, but is not limited to, a processor 40 and a memory 41. Those skilled in the art will understand that... Figure 6 This is merely an example of control device 4 and does not constitute a limitation on control device 4. It may include more or fewer components than shown, or combine certain components, or different components. For example, the control device may also include input / output devices, network access devices, buses, etc.

[0114] The processor 40 can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor.

[0115] The memory 41 can be an internal storage unit of the control device 4, such as a hard disk or a memory of the control device 4. The memory 41 can also be an external storage device of the control device 4, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. Further, the memory 41 can also include both the internal storage unit and the external storage device of the control device 4. The memory 41 is used to store the computer program and other programs and data required by the control device. The memory 41 can also be used to temporarily store data that has been output or will be output.

[0116] Corresponding to the above control device, the embodiment of the present application further provides a photovoltaic system, comprising a photovoltaic string, a boost circuit, an inverter circuit and the above control device. The boost circuit is connected to the photovoltaic string and the inverter circuit respectively; and the boost circuit is controlled by the control device.

[0117] The related description of the photovoltaic system can refer to the description in the foregoing embodiment, and will not be repeated here.

[0118] The embodiment of the present application further provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the steps of the active power control method of any one of the photovoltaic systems.

[0119] The embodiment of the present application further provides a computer program product, which comprises a computer program, and the computer program is executed by a processor to implement the active power control method of any one of the photovoltaic systems.

[0120] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the above-mentioned division of each functional unit and module is exemplified, and in actual application, the above-mentioned functions can be completed by different functional units and modules according to needs, that is, the internal structure of the device is divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be realized in the form of hardware or software. In addition, the specific names of each functional unit and module are only for easy distinction, and do not limit the protection scope of the present application. The specific working process of the units and modules in the above system can refer to the corresponding process in the foregoing method embodiments, which will not be repeated here.

[0121] In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described or recorded in detail in a certain embodiment can be referred to the related description of other embodiments.

[0122] Those of ordinary skill in the art can realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. A person skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0123] In the embodiments provided by the present application, it should be understood that the disclosed devices / control apparatus and methods can be implemented in other ways. For example, the above-described device / control apparatus embodiments are merely illustrative. For example, the division of the modules or units is only a logical function division, and there can be another division manner in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units shown or discussed can be indirect coupling or communication connection through some interface, device or unit, and can be electrical, mechanical or other forms.

[0124] The units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, that is, they can be located in one place, or can be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the embodiment.

[0125] In addition, each function unit in each embodiment of the present application can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software function unit.

[0126] The integrated module / unit, if realized in the form of a software function unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on such understanding, all or part of the processes in the above-mentioned embodiment methods can also be completed by a computer program instructing related hardware, and the computer program can be stored in a computer readable storage medium. When the computer program is executed by a processor, the steps of the above-mentioned active power control method embodiments of each networked photovoltaic system can be implemented. The computer program includes computer program code, which can be in the form of source code, object code, executable files or some intermediate forms, etc. The computer readable medium can include any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier wave signal, telecommunication signal and software distribution medium, etc.

[0127] The above-mentioned embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for controlling the active power of a grid-connected photovoltaic system, characterized in that, The photovoltaic system includes a photovoltaic string and a photovoltaic inverter connected in series, the photovoltaic inverter including a boost circuit and an inverter circuit connected in series; the method includes: Obtain the reference active power and actual active power of the inverter circuit; The voltage adjustment amount of the photovoltaic string is determined based on the reference active power and the actual active power. The target voltage of the photovoltaic string is adjusted according to the voltage adjustment amount to obtain the adjusted target voltage; Obtain the actual voltage of the photovoltaic string and the actual current of the boost circuit; The boost circuit is controlled based on the adjusted target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit.

2. The active power control method for a grid-type photovoltaic system according to claim 1, characterized in that, Determining the voltage adjustment amount of the photovoltaic string based on the reference active power and the actual active power includes: Determine a first difference between the reference active power and the actual active power; The voltage adjustment of the photovoltaic string is obtained by performing proportional-integral control on the first difference.

3. The active power control method for a grid-type photovoltaic system according to claim 1, characterized in that, The step of adjusting the target voltage of the photovoltaic string according to the voltage adjustment amount to obtain the adjusted target voltage includes: The sum of the voltage adjustment amount and the target voltage of the photovoltaic string is taken as the adjusted target voltage.

4. The active power control method for a grid-type photovoltaic system according to claim 1, characterized in that, After adjusting the target voltage of the photovoltaic string according to the voltage adjustment amount to obtain the adjusted target voltage, the method further includes: The adjusted target voltage is subjected to a limiting process so that the limited target voltage is located between the maximum power point tracking voltage and the open circuit voltage of the photovoltaic string. Accordingly, controlling the boost circuit based on the adjusted target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit includes: The boost circuit is controlled based on the target voltage after limiting, the actual voltage of the photovoltaic string, and the actual current of the boost circuit.

5. The active power control method for a grid-connected photovoltaic system according to any one of claims 1 to 4, characterized in that, The step of controlling the boost circuit based on the adjusted target voltage, the actual voltage of the photovoltaic string, and the actual current of the boost circuit includes: The reference current of the boost circuit is determined based on the adjusted target voltage and the actual voltage of the photovoltaic string. The boost circuit is controlled based on its reference current and actual current.

6. The active power control method for a grid-type photovoltaic system according to claim 5, characterized in that, Determining the reference current of the boost circuit based on the adjusted target voltage and the actual voltage of the photovoltaic string includes: Determine a second difference between the adjusted target voltage and the actual voltage of the photovoltaic string; The second difference is subjected to proportional-integral control to obtain the reference current of the boost circuit.

7. The active power control method for a grid-type photovoltaic system according to claim 5, characterized in that, The step of controlling the boost circuit based on the reference current and the actual current of the boost circuit includes: Determine the third difference between the reference current of the boost circuit and the actual current of the boost circuit; The third difference is subjected to proportional-integral control to obtain the control quantity of the boost circuit; The boost circuit is controlled according to the control quantity of the boost circuit.

8. The active power control method for a grid-connected photovoltaic system according to any one of claims 1 to 4, characterized in that, The photovoltaic system is a string photovoltaic system.

9. A control device, characterized in that, It includes a memory and a processor, the memory being used to store a computer program, and the processor being used to call and run the computer program stored in the memory to execute the active power control method for a grid-connected photovoltaic system as described in any one of claims 1 to 8.

10. A photovoltaic system, characterized in that, Includes photovoltaic strings, boost circuit, inverter circuit, and control equipment as described in claim 9; The boost circuit is connected to the photovoltaic string and the inverter circuit respectively; the boost circuit is controlled by the control device.

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