Photovoltaic optimizer and control method

Abstract

The invention relates to a photovoltaic optimizer and a control method, and the control method comprises the steps: monitoring the size of an input voltage, and switching among a closing mode, a protection mode and a maximum power tracking mode, thereby not carrying out the maximum power point tracking in the protection mode when the output power of a photovoltaic module is insufficient due to the shielding and other factors, and achieving the maximum power point tracking. The input voltage is kept to be greater than the first threshold value by adjusting the duty ratio, so that the normal work of the photovoltaic optimizer is maintained, the phenomenon that the photovoltaic optimizer is restarted repeatedly or the output voltage jitters violently due to sudden power drop or insufficient power is avoided, and the stability and the reliability of the photovoltaic optimizer are improved.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaics, and in particular to a photovoltaic optimizer and a control method. Background Art

[0002] As an important part of renewable energy, the efficiency and stability of photovoltaic systems are increasingly valued by the industry. Photovoltaic optimizers monitor and adjust the current and voltage of photovoltaic modules in real time, so that they can maximize the power generation efficiency of photovoltaic modules under different environmental conditions and improve the power generation of the entire photovoltaic system. In addition, photovoltaic optimizers can also realize component-level fault detection and isolation, greatly enhancing the reliability and stability of the system.

[0003] However, the photovoltaic system faces complex and changeable environmental challenges in actual operation. The power generation of photovoltaic modules is greatly affected by the light intensity and temperature coefficient. In particular, factors such as sunrise and sunset, weather changes and random shading will cause the output power of photovoltaic modules to change greatly. These changes are often sudden and unpredictable, which poses a severe test to the normal operation of photovoltaic optimizers. For example, when the output power of photovoltaic modules drops sharply, the photovoltaic optimizer will quickly adjust the output voltage and current to maintain the maximum power point, but this adjustment will also cause the input voltage and current of the photovoltaic optimizer (that is, the output voltage and output current of the photovoltaic module) to change rapidly, causing the output voltage of the photovoltaic optimizer to fluctuate violently, and may also cause the input voltage of the photovoltaic optimizer to be lower than its starting voltage threshold, causing the photovoltaic optimizer to stop running; the stopping of the photovoltaic optimizer will cause the photovoltaic module to be in an open circuit state, that is, the output current is zero and the output voltage is the open circuit voltage, and the open circuit voltage is generally greater than the starting voltage threshold of the photovoltaic optimizer, which will cause the photovoltaic optimizer to restart again. After starting, it will stop running again because it needs to maintain the maximum power point, thus falling into a vicious cycle of repeated restarts.

[0004] The severe jitter and repeated restart of the photovoltaic optimizer output may affect the power generation efficiency at best, or even cause device damage at worst. In the long run, it will not only easily damage the power devices and reduce the service life of the photovoltaic optimizer, but also seriously affect the normal operation of the photovoltaic system. Therefore, how to improve the stability and reliability of the photovoltaic optimizer is an urgent problem to be solved. Summary of the invention

[0005] In view of this, the embodiments of the present application provide a photovoltaic optimizer and a control method to solve at least one problem existing in the background technology.

[0006] In a first aspect, an embodiment of the present application provides a photovoltaic optimizer control method, which is applied to a photovoltaic system, wherein the photovoltaic system includes: an inverter, a photovoltaic string and a central controller, wherein the photovoltaic string is connected to the central controller and the inverter respectively; the photovoltaic string includes a plurality of photovoltaic units connected in series, each of the photovoltaic units includes the photovoltaic optimizer and at least one photovoltaic component connected to the photovoltaic optimizer, the photovoltaic optimizer includes a controller and a voltage conversion circuit, and the controller is used to output a PWM signal to control the on and off of a switch tube in the voltage conversion circuit; the method includes: Acquire the input voltage of the photovoltaic optimizer; wherein the input voltage of the photovoltaic optimizer is the output voltage of the photovoltaic module; Based on the input voltage, the photovoltaic optimizer is controlled to switch between a shutdown mode, a protection mode and a maximum power tracking mode; wherein, If the input voltage is less than the first threshold, the photovoltaic optimizer operates in a shutdown mode; in the shutdown mode, the PWM signal is in a closed state; If the input voltage is greater than or equal to the first threshold and less than or equal to the second threshold, the photovoltaic optimizer operates in a protection mode; in the protection mode, the duty cycle of the PWM signal is adjusted based on the input voltage to keep the input voltage greater than the first threshold; If the input voltage is greater than the second threshold, the photovoltaic optimizer operates in a maximum power tracking mode; in the maximum power tracking mode, the duty cycle of the PWM signal is adjusted based on the output voltage and output current of the photovoltaic optimizer so that the photovoltaic component connected to the photovoltaic optimizer operates at a maximum power point.

[0007] In a second aspect, an embodiment of the present application provides a photovoltaic optimizer, which is applied to a photovoltaic system, and the photovoltaic optimizer includes: A controller and a voltage conversion circuit, wherein the controller is used to output a PWM signal to control the on and off of a switch tube in the voltage conversion circuit; Wherein, the controller comprises: An acquisition unit, used for acquiring an input voltage of the photovoltaic optimizer; wherein the input voltage of the photovoltaic optimizer is the output voltage of the photovoltaic module; A mode selection unit, configured to control the photovoltaic optimizer to switch between a shutdown mode, a protection mode, and a maximum power point tracking mode based on the input voltage; in, If the input voltage is less than the first threshold, the photovoltaic optimizer operates in a shutdown mode; in the shutdown mode, the PWM signal is in a closed state; If the input voltage is greater than or equal to the first threshold and less than or equal to the second threshold, the photovoltaic optimizer operates in a protection mode; in the protection mode, the duty cycle of the PWM signal is adjusted based on the input voltage to keep the input voltage greater than the first threshold; If the input voltage is greater than the second threshold, the photovoltaic optimizer operates in a maximum power tracking mode; in the maximum power tracking mode, the duty cycle of the PWM signal is adjusted based on the output voltage and output current of the photovoltaic optimizer so that the photovoltaic component connected to the photovoltaic optimizer operates at a maximum power point.

[0008] In the embodiment of the present application, the photovoltaic optimizer switches between the shutdown mode, the protection mode and the maximum power point tracking mode by monitoring the size of the input voltage. Therefore, when the output power of the photovoltaic component is insufficient due to factors such as shading, the maximum power point tracking may not be performed in the protection mode. Instead, the duty cycle is adjusted to keep the input voltage greater than the first threshold, thereby maintaining the normal operation of the photovoltaic optimizer and avoiding the phenomenon of repeated restarts of the photovoltaic optimizer due to power drops or power shortages, thereby improving the stability and reliability of the photovoltaic optimizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 A schematic diagram of the structure of a photovoltaic system provided in one embodiment of the present application; Figure 2 A schematic diagram of a voltage conversion circuit structure provided in an embodiment of the present application; Figure 3 A schematic flow chart of a photovoltaic optimizer control method provided in one embodiment of the present application; Figure 4 A schematic diagram of a controller of a photovoltaic optimizer provided in one embodiment of the present application. DETAILED DESCRIPTION

[0010] In order to make the technical solutions and beneficial effects of the present invention more clearly understood, the following is a detailed description by listing specific embodiments. Unless otherwise defined, the technical and scientific terms used herein have the same meanings as those in the technical field to which this application belongs.

[0011] Figure 1 This is a schematic diagram of the structure of a photovoltaic system provided in one embodiment of the present application. Figure 1As shown, the photovoltaic system of the embodiment of the present application includes an inverter, a photovoltaic string and a central controller, and the photovoltaic string is connected to the central controller and the inverter respectively; wherein the central controller is used for monitoring and regulating the photovoltaic string; the inverter is used to convert the direct current output by the photovoltaic string into alternating current and output it. The photovoltaic string includes a plurality of photovoltaic units connected in series, as shown in the figure, photovoltaic unit 1, photovoltaic unit 2, photovoltaic unit 3... photovoltaic unit n is connected in series with the inverter. Each photovoltaic unit includes a photovoltaic optimizer and one or more photovoltaic modules connected to the photovoltaic optimizer. Specifically, photovoltaic optimizer 1, photovoltaic optimizer 2, photovoltaic optimizer 3... photovoltaic optimizer n is connected to photovoltaic module PV1, photovoltaic module PV2, photovoltaic module PV3... photovoltaic module PVn at one end, and photovoltaic optimizer 1, photovoltaic optimizer 2, photovoltaic optimizer 3... photovoltaic optimizer n is connected in series with the inverter at the other end. Optionally, the central controller and the photovoltaic optimizer of each photovoltaic unit can communicate bidirectionally through the power line, thereby realizing information exchange operations such as monitoring and controlling the photovoltaic module. The connection in the embodiments of the present application includes implementation methods such as direct connection or indirect connection, which are not specifically limited in the embodiments of the present application. For example, the central controller can communicate with the photovoltaic optimizer through a magnetic ring coupling on the power line, thereby eliminating the need for additional wiring, which is convenient, simple and cost-effective.

[0012] Figure 1 The photovoltaic system shown includes n photovoltaic optimizers, each of which includes a controller and a voltage conversion circuit. The controller is connected to the voltage conversion circuit, that is, photovoltaic optimizer 1, photovoltaic optimizer 2, photovoltaic optimizer 3... photovoltaic optimizer n respectively include voltage conversion circuit 1, voltage conversion circuit 2, voltage conversion circuit 3... voltage conversion circuit n and controller 1, controller 2, controller 3... controller n. Figure 1 In the photovoltaic system shown, each controller is used to output a pulse width modulation (PWM) signal to control the on and off of a switch tube in a voltage conversion circuit.

[0013] As an optional specific implementation, the voltage conversion circuit of the embodiment of the present application is a buck circuit. Correspondingly, when the buck circuit operates normally, the output voltage of the photovoltaic optimizer is less than or equal to its input voltage. Figure 2 This is a schematic diagram of a voltage conversion circuit structure provided by an embodiment of the present application. Figure 2As shown, the voltage conversion circuit includes a main switch tube Q1, a bypass switch tube Q2, a capacitor C1, a capacitor C2 and an inductor L. The controller can control the on and off of the switch tube Q1 to adjust the output voltage and the input voltage by outputting a PWM signal. It should be noted that the photovoltaic optimizer of the embodiment of the present application also includes a detection circuit (not shown in the figure) for detecting the voltage and current at the input and output ends of the photovoltaic optimizer. Correspondingly, the controller is connected to the detection circuit to obtain the input voltage, input current, output voltage and output current of the photovoltaic optimizer, thereby adjusting the PWM signal duty cycle to track the maximum power point of the photovoltaic module. It should be noted that the adjustment of the PWM signal duty cycle will cause the output voltage to change, and will also cause the input current and input voltage to change; wherein, the PWM signal is a fixed frequency width modulation signal, and its signal is a fixed switching cycle time. The modulation mode of the duty cycle is changed by changing the conduction time within a switching cycle time. In the embodiment of the present application, the output voltage can be adjusted by changing the duty cycle of the PWM signal.

[0014] Figure 3 Schematic diagram of a photovoltaic optimizer control method provided in an embodiment of the present application. The method is applied to the photovoltaic system of the above embodiment, such as Figure 3 As shown, the method includes: S1. Obtain the input voltage of the photovoltaic optimizer.

[0015] Among them, the input voltage of the photovoltaic optimizer is the output voltage of the photovoltaic module connected to the photovoltaic optimizer. It should be noted that the output voltage and output current of the photovoltaic optimizer in the embodiment of the present application refer to the voltage and current output to the inverter, and the output voltage and output current of the photovoltaic module refer to the voltage and current output to the photovoltaic optimizer, that is, the output voltage of the photovoltaic module is the input voltage of the photovoltaic optimizer, and the output current of the photovoltaic module is the input current of the photovoltaic optimizer.

[0016] S2. Based on the input voltage, control the PV optimizer to switch between shutdown mode, protection mode and maximum power tracking mode.

[0017] The embodiment of the present application controls the switching of the photovoltaic optimizer mode based on the size of the input voltage. By switching the working mode, the input voltage of the photovoltaic optimizer changes smoothly, avoiding the drastic change of the input voltage caused by the power change of the photovoltaic module, thereby improving the reliability and stability of the operation of the photovoltaic optimizer. It should be noted that the opening and closing of the photovoltaic optimizer is based on the size of its input voltage, while the present application switches the mode based on the input voltage of the photovoltaic optimizer without considering the size of the output voltage of the photovoltaic optimizer, so that the opening and closing of the photovoltaic optimizer can be controlled more accurately, thereby maintaining the stability and reliability of the operation of the photovoltaic optimizer. It should be noted that different working modes reflect the inconsistency of the PWM signal duty cycle. For example, in the off mode, the PWM signal is in the off state; in the maximum power tracking mode, the maximum power point of the photovoltaic module is tracked by controlling the PWM signal; in the protection mode, the maximum power point is not tracked by controlling the PWM signal, but the stable operation of the photovoltaic optimizer is maintained.

[0018] As an optional specific implementation, if the input voltage is less than the first threshold, the photovoltaic optimizer is controlled to operate in a shutdown mode; in the shutdown mode, the PWM signal is in a closed state. As an optional specific implementation, the first threshold is the minimum voltage within the operating voltage range of the photovoltaic optimizer. Correspondingly, when the input voltage is less than the first threshold, the photovoltaic optimizer cannot maintain normal operation, that is, the photovoltaic optimizer stops working, and enters the shutdown mode, and the corresponding PWM signal is in a closed state. It should be noted that in the shutdown mode, since the photovoltaic optimizer stops working, the photovoltaic module is in an open circuit state, that is, the photovoltaic module is not connected to a load, the output current is zero, and the output voltage is an open circuit voltage.

[0019] As an optional specific implementation, if the input voltage is greater than or equal to the first threshold and less than or equal to the second threshold, the photovoltaic optimizer operates in a protection mode; in the protection mode, the PWM signal duty cycle is adjusted based on the input voltage to keep the input voltage greater than the first threshold. In the embodiment of the present application, in the protection mode, the PWM signal duty cycle is adjusted according to the input voltage to keep the input voltage greater than the first threshold, so that the photovoltaic optimizer can be kept turned on when the photovoltaic module power drops suddenly or the sunlight is insufficient, preventing the photovoltaic optimizer from being turned off due to insufficient input voltage, thereby reducing the situation where the photovoltaic optimizer is repeatedly restarted. For example, since the photovoltaic module is connected by multiple photovoltaic cells in series or in parallel, when the photovoltaic module is blocked, even if the blocking area is small, it will seriously affect the output current or voltage of the photovoltaic module, thereby causing the output power to drop suddenly. At this time, the bus current in the photovoltaic system may remain relatively stable or change little due to the continued power supply of other unblocked components. At this time, if the PV optimizer of the corresponding shaded component continues to track the maximum power point, it will output the maximum power by maintaining or increasing the duty cycle, which will essentially cause the current provided by the component to the optimizer to remain unchanged or increase (an increase in duty cycle means a longer on-time, allowing more current to pass). Then, since the output power of the component is reduced due to the shade, maintaining or increasing the current will cause the input voltage of the PV optimizer to drop sharply, which can easily cause the PV optimizer to shut down due to undervoltage. When the PV optimizer is shut down due to undervoltage, the PV component is not connected to the load and is in an open circuit state. At this time, the output current of the PV component becomes zero again, which will cause the output voltage of the PV component to be greater than the working voltage of the PV optimizer. The PV optimizer will restart again. At this time, if the PV optimizer is still tracking the maximum power point, it will cause it to shut down again. This process may occur repeatedly, causing the PV optimizer to restart repeatedly. Correspondingly, the repeated restart of the PV optimizer also causes the PV optimizer to change between having output voltage and not having output voltage, resulting in severe jitter in the output voltage.

[0020] As an optional specific implementation manner, the second threshold is the lowest voltage of the photovoltaic optimizer operating in the maximum power point tracking mode.

[0021] In the embodiment of the present application, by monitoring the input voltage, when the input voltage is less than or equal to the second threshold, the photovoltaic optimizer operates in the protection mode, and does not perform maximum power point tracking in the protection mode, but adjusts the PWM signal duty cycle to keep the input voltage greater than the first threshold, thereby preventing the photovoltaic optimizer from shutting down due to undervoltage, reducing the phenomenon of repeated restarts, and also maintaining the stability of the photovoltaic optimizer output voltage. It should be noted that the second threshold is greater than the first threshold, and the specific value of the second threshold needs to be determined according to the characteristics of the photovoltaic optimizer and the photovoltaic module, and is not limited in this application.

[0022] It should be noted that the output PWM signal includes a PWM signal with a zero output duty cycle and a PWM signal with a non-zero output duty cycle. In shutdown mode, the photovoltaic optimizer cannot output a PWM signal, that is, the PWM signal is in a closed state; but in protection mode, the photovoltaic optimizer can work normally. At this time, the photovoltaic optimizer can output a PWM signal, and can output a zero or non-zero PWM signal according to the input voltage. At this time, the maximum power point tracking is not performed, but the duty cycle is adjusted to maintain the photovoltaic optimizer in the open state to prevent the photovoltaic optimizer from being shut down due to insufficient input voltage.

[0023] As an optional specific implementation, in the protection mode, the duty cycle of the PWM signal of the photovoltaic optimizer is adjusted according to the comparison result between the input voltage and the third threshold value, so that the input voltage approaches the third threshold value. The third threshold value is greater than the first threshold value and less than the second threshold value. Further, the duty cycle of the PWM signal of the photovoltaic optimizer is adjusted according to the comparison result between the input voltage and the third threshold value, including: if the input voltage is greater than the third threshold value, the duty cycle of the photovoltaic optimizer PWM signal is increased to reduce the input voltage at the next moment, so that the input voltage at the next moment is close to the third threshold value; if the input voltage is less than the third threshold value, the duty cycle of the photovoltaic optimizer PWM signal is reduced to reduce the input voltage at the next moment, so that the input voltage at the next moment is close to the third threshold value. In the embodiment of the present application, the third threshold is a value between the first threshold and the second threshold. In the protection mode, the duty cycle of the PWM signal is adjusted by comparing the input voltage with the third threshold so that the input voltage at the next moment is close to the third threshold. On the one hand, the duty cycle adjustment can be smoother, avoiding drastic changes in the duty cycle, thereby reducing the fluctuation of the PWM signal; on the other hand, the input voltage is maintained stable to a certain extent, so that the output voltage of the photovoltaic optimizer remains relatively stable, improving the overall performance and reliability of the photovoltaic system. It should be noted that whether the duty cycle is increased or decreased, its specific value needs to be determined based on the difference between the input voltage and the third threshold and the duty cycle at the current moment. This application is not limited. For example, the specific adjustment value can be determined by the feedback circuit of the current or input voltage between the photovoltaic module and the photovoltaic optimizer. It should be noted that in the protection mode means that it is already in the protection mode, and does not include the moment of switching from other modes to the protection mode.

[0024] As an optional specific implementation, if the input voltage is greater than the second threshold, the photovoltaic optimizer is controlled to operate in the maximum power tracking mode; in the maximum power tracking mode, a PWM signal is output based on the output voltage and output current of the photovoltaic optimizer, so that the photovoltaic module connected to the photovoltaic optimizer operates at the maximum power point. Specifically, this indicates that the output power of the photovoltaic module is sufficient, and even if the PWM signal duty cycle is adjusted, the input voltage will not be lower than the first threshold. At this time, the photovoltaic optimizer tracks the maximum power point, so that the photovoltaic module outputs the maximum power, thereby improving the power generation efficiency of the photovoltaic system.

[0025] In the embodiment of the present application, the photovoltaic optimizer switches between the shutdown mode, the protection mode and the maximum power tracking mode by monitoring the magnitude of the input voltage, so that when the output power of the photovoltaic module is insufficient due to factors such as shading, the maximum power point tracking can be avoided in the protection mode, but the input voltage is kept greater than the first threshold by adjusting the duty cycle, thereby maintaining the normal operation of the photovoltaic optimizer, avoiding the phenomenon of repeated restarts of the photovoltaic optimizer due to power sag or insufficient power, thereby improving the stability and reliability of the photovoltaic optimizer. It should be noted that the adjustment range of the duty cycle is limited. For example, the maximum adjustment range of the duty cycle is 5%-100%. In the embodiment of the present application, the duty cycle is adjusted to make the input voltage change smoothly, so that when the output power of the photovoltaic module increases, decreases or changes drastically, the input voltage of the photovoltaic optimizer can be maintained to change smoothly, thereby reducing the phenomenon of repeated restarts of the photovoltaic optimizer and improving the reliability and stability of the operation of the photovoltaic optimizer.

[0026] As an optional specific implementation, S2 includes: If the input voltage at the previous moment is greater than the second threshold, and the input voltage at the current moment is less than or equal to the second threshold, then at the current moment, the duty cycle of the PWM signal of the photovoltaic optimizer is reduced, and the photovoltaic optimizer is controlled to switch from the maximum power tracking mode to the protection mode. In the embodiment of the present application, the previous moment and the current moment are two consecutive input voltage sampling moments. The input voltage at the previous moment is greater than the second threshold, indicating that the previous moment was in the maximum power tracking mode; the input voltage at the current moment is less than or equal to the second threshold, indicating that the input voltage has decreased at the current moment. At this time, by reducing the duty cycle of the PWM signal, the input voltage can be prevented from continuing to decrease, that is, when the output power of the photovoltaic module is reduced, the output current of the photovoltaic module is reduced by reducing the duty cycle of the PWM signal, thereby avoiding further reduction of the output voltage of the photovoltaic module, and avoiding the output voltage of the photovoltaic module being less than the starting voltage of the photovoltaic optimizer, thereby maintaining the normal operation of the photovoltaic optimizer and avoiding the shutdown of the photovoltaic optimizer. Correspondingly, the photovoltaic optimizer is controlled to switch from the maximum power tracking mode to the protection mode to keep the output voltage of the photovoltaic module greater than the first threshold. For example, at the previous moment T of a photovoltaic modulen At the moment the input voltage is greater than the second threshold, it is in the maximum power tracking mode; due to shading or sunset, the reduced light intensity will cause the output power of the photovoltaic module to decrease, resulting in the current moment T n+1 When the input voltage is less than or equal to the second threshold, the decreasing speed of the output voltage of the photovoltaic module can be slowed down by reducing the duty cycle, that is, V n+2 -V n+1 <V n+1 -V n , where V n Indicates T n The output voltage of the photovoltaic module at the moment, V n+1 Indicates T n+1 The output voltage of the photovoltaic module at the moment, V n+2 Indicates T n+2 The output voltage of the photovoltaic module at the moment, T n+2 Time is T n+1 The next moment of the moment. It should be noted that when a photovoltaic component is blocked, since the bus current does not change much, the degree of drop in the output voltage of the photovoltaic component can be reduced by reducing the duty cycle; if at sunset, the output power of all photovoltaic components is generally reduced, the bus current will also decrease accordingly. At this time, the photovoltaic optimizer can reduce the duty cycle to slow down the drop in the output voltage of the photovoltaic component, maintain the output of the photovoltaic optimizer, and maintain the smooth operation of the photovoltaic system, thereby realizing the slow shutdown of the photovoltaic system, avoiding system fluctuations caused by power mutations, and ensuring the smooth transition of the photovoltaic system at sunset. In the embodiment of the present application, when the photovoltaic component is blocked or sunset causes the power to drop, by monitoring the input voltage, the maximum power tracking mode is switched to the protection mode when the input voltage is less than the second threshold, and the duty cycle of the PWM signal is reduced, so as to effectively slow down the speed of the input voltage reduction, effectively avoid the phenomenon that the photovoltaic optimizer input voltage (i.e., the output voltage of the photovoltaic component) drops suddenly due to the reduction in the output power of the photovoltaic component, and maintain the effective output of the photovoltaic optimizer.

[0027] Further, reducing the duty cycle of the PWM signal of the photovoltaic optimizer at the current moment includes: If the input voltage at the current moment is less than the third threshold, the duty cycle of the PWM signal of the photovoltaic optimizer is reduced at the current moment according to the input voltage at the previous moment and the input voltage at the current moment; if the input voltage at the current moment is greater than the third threshold, the duty cycle of the PWM signal of the photovoltaic optimizer is reduced at the current moment according to the input voltage at the previous moment and the third threshold. In the embodiment of the present application, the duty cycle is adjusted at the current moment according to the comparison of the input voltage and the third threshold, so that the fluctuation of the input voltage can be further reduced. Specifically: if the input voltage at the current moment is less than the third threshold, the duty cycle of the PWM signal is reduced according to the difference between the input voltage at the previous moment and the input voltage at the current moment. At this time, the difference is large, and the reduction amplitude of the PWM signal is also greater, so as to slow down the decrease of the input voltage as much as possible; if the input voltage at the current moment is greater than the third threshold, the duty cycle of the PWM signal is reduced according to the difference between the input voltage at the previous moment and the third threshold, so that not only the decrease of the input voltage can be slowed down, but also the input voltage can be made as close to the third threshold as possible, so that the stability of the input voltage is maintained through adjustment, and the output voltage is also changed smoothly, avoiding the violent jitter of the output voltage. For example, the first threshold is 12V, the second threshold is 14V, and the third threshold is 13V. If the current input voltage is between 12V and 13V, the difference between the input voltage at the previous moment and the input voltage at the current moment is greater, and the duty cycle is reduced more at this time, so that the decrease in input voltage can be slowed down as much as possible; if the current input voltage is between 13V and 14V, the duty cycle is adjusted according to the difference between the third threshold and the input voltage at the current moment, so that the input voltage can be adjusted toward the third threshold, maintaining the stability of the input voltage. It should be noted that the larger the difference, the greater the amplitude of the duty cycle adjustment; when the output power of the photovoltaic module remains unchanged, increasing the duty cycle will make the conduction time longer and allow more current, that is, the output current of the photovoltaic module will increase, and correspondingly, the output voltage of the photovoltaic module will decrease; reducing the duty cycle will reduce the output current, and correspondingly, the output voltage of the photovoltaic module will increase.

[0028] As an optional specific implementation, S2 further includes: If the input voltage at the previous moment is less than the first threshold, and the input voltage at the current moment is greater than the first threshold and less than the third threshold, the photovoltaic optimizer is controlled to switch from the shutdown mode to the protection mode at the current moment; a PWM signal with a duty cycle of zero is output at the current moment until the input voltage at a certain moment is greater than the third threshold, and the duty cycle of the PWM signal is increased. Specifically, the duty cycle of the PWM signal is determined according to the input voltage at a certain moment and the third threshold. If the input voltage at the previous moment is less than the first threshold, and the input voltage at the current moment is greater than the third threshold, the photovoltaic optimizer is controlled to switch from the shutdown mode to the protection mode, and the duty cycle of the PWM signal is increased at the current moment. Specifically, the duty cycle of the PWM signal is determined according to the input voltage at the current moment and the third threshold. In the embodiment of the present application, when the power of the photovoltaic module is increased, the duty cycle of the PWM signal is flexibly adjusted by monitoring the size of the input voltage and the third threshold to stabilize the input voltage, prevent repeated restarts caused by sudden drops, and ensure the stability of the output voltage of the photovoltaic optimizer. Specifically, when the input voltage is less than the third threshold, a PWM signal with a duty cycle of zero is output. At this time, the input voltage is still small, and the photovoltaic module can form a path with the photovoltaic optimizer but does not output voltage to the inverter. Therefore, when the input voltage is low, the duty cycle can be prevented from suddenly turning on and causing the input voltage to drop sharply, effectively avoiding repeated restarts of the photovoltaic optimizer; when the input voltage is greater than or equal to the third threshold, the photovoltaic module has reached a certain power, and the corresponding input voltage of the photovoltaic optimizer is also relatively large. At this time, the duty cycle is determined according to the difference between the input voltage and the third threshold, that is, a PWM signal with a duty cycle of not zero is output, so that the input voltage can be maintained near the third threshold for a period of time, thereby making the output voltage change of the photovoltaic optimizer more stable. In the embodiment of the present application, in the process of increasing the power of the photovoltaic module, by comparing the input voltage and the third threshold, the duty cycle of the PWM is flexibly modulated, which effectively solves the problem of output voltage fluctuation that may occur during the photovoltaic module promotion process and ensures the stable start-up and operation of the photovoltaic optimizer. It should be noted that voltage or current sensors can be configured in the photovoltaic system to monitor the output voltage and current of the photovoltaic components in real time. The sensors can work independently of the photovoltaic optimizer. The corresponding photovoltaic optimizer can trigger the corresponding control logic when the input voltage changes according to the preset control logic.

[0029] The present application also provides a photovoltaic optimizer, which is applied to the photovoltaic system of the above embodiment. The photovoltaic optimizer includes: A controller and a voltage conversion circuit, wherein the controller is used to output a PWM signal to control the on and off of a switch tube in the voltage conversion circuit.

[0030] Figure 4 The figure shows a schematic diagram of a controller of a photovoltaic optimizer according to an embodiment of the present application. As shown in the figure, the controller includes: An acquisition unit 301 is used to acquire an input voltage of a photovoltaic optimizer; wherein the input voltage of the photovoltaic optimizer is an output voltage of a photovoltaic module; The mode selection unit 302 is used to control the photovoltaic optimizer to switch between the shutdown mode, the protection mode and the maximum power point tracking mode based on the input voltage.

[0031] Among them, if the input voltage is less than the first threshold, the photovoltaic optimizer operates in the shutdown mode; in the shutdown mode, the PWM signal is in the off state; if the input voltage is greater than or equal to the first threshold and less than or equal to the second threshold, the photovoltaic optimizer operates in the protection mode; in the protection mode, the duty cycle of the PWM signal is adjusted based on the input voltage to keep the input voltage greater than the first threshold; if the input voltage is greater than the second threshold, the photovoltaic optimizer operates in the maximum power tracking mode; in the maximum power tracking mode, the duty cycle of the PWM signal is adjusted based on the output voltage and output current of the photovoltaic optimizer so that the photovoltaic components connected to the photovoltaic optimizer operate at the maximum power point.

[0032] Optionally, in the protection mode, the duty cycle of the PWM signal of the photovoltaic optimizer is adjusted according to the comparison result between the input voltage and a third threshold; wherein the third threshold is greater than the first threshold and less than the second threshold.

[0033] Optionally, in the protection mode, adjusting the duty cycle of the PWM signal of the photovoltaic optimizer according to the comparison result between the input voltage and the third threshold value includes: If the input voltage is greater than a third threshold, increasing the duty cycle of the photovoltaic optimizer PWM signal; If the input voltage is less than the third threshold, the duty cycle of the photovoltaic optimizer PWM signal is reduced.

[0034] Optionally, based on the input voltage, control the PV optimizer to switch between shutdown mode, protection mode and maximum power point tracking mode, including: If the input voltage at the previous moment is greater than the second threshold and the input voltage at the current moment is less than or equal to the second threshold, the duty cycle of the PWM signal of the photovoltaic optimizer is reduced at the current moment, and the photovoltaic optimizer is controlled to switch from the maximum power tracking mode to the protection mode.

[0035] Optionally, reducing the duty cycle of the PWM signal of the photovoltaic optimizer at the current moment includes: If the input voltage at the current moment is less than the third threshold, then at the current moment, the duty cycle of the PWM signal of the photovoltaic optimizer is reduced according to the input voltage at the previous moment and the input voltage at the current moment; If the input voltage at the current moment is greater than the third threshold, the duty cycle of the PWM signal of the photovoltaic optimizer is reduced at the current moment according to the input voltage at the previous moment and the third threshold.

[0036] Optionally, based on the input voltage, control the PV optimizer to switch between shutdown mode, protection mode and maximum power point tracking mode, including: If the input voltage at the previous moment is less than the first threshold value, and the input voltage at the current moment is greater than the first threshold value and less than the third threshold value, the photovoltaic optimizer is controlled to switch from the shutdown mode to the protection mode at the current moment; a PWM signal with a duty cycle of zero is output at the current moment, until the input voltage at a certain moment is greater than the third threshold value, and the duty cycle of the PWM signal is increased; If the input voltage at the previous moment is less than the first threshold and the input voltage at the current moment is greater than the third threshold, the photovoltaic optimizer is controlled to switch from the shutdown mode to the protection mode and the duty cycle of the PWM signal is increased; wherein the third threshold is greater than the first threshold and less than the second threshold.

[0037] Optionally, the first threshold is the minimum voltage within the operating voltage range of the photovoltaic optimizer; and the second threshold is the minimum voltage when the photovoltaic optimizer operates in the maximum power point tracking mode.

[0038] It should be noted that the photovoltaic optimizer control method embodiment and the photovoltaic optimizer embodiment provided in the embodiments of the present application belong to the same concept; the technical features in the technical solutions recorded in the embodiments can be arbitrarily combined without conflict.

[0039] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations included in the claims. Various modifications and changes may be made on the basis of the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only express several implementations of the present invention and do not limit the scope of protection of the patent of the present invention.

Claims

1. A photovoltaic optimizer control method, characterized in that: The method is applied to a photovoltaic system, which includes: an inverter, a photovoltaic string and a central controller, wherein the photovoltaic string is connected to the central controller and the inverter respectively; the photovoltaic string includes a plurality of photovoltaic units connected in series, each of the photovoltaic units includes the photovoltaic optimizer and at least one photovoltaic component connected to the photovoltaic optimizer, the photovoltaic optimizer includes a controller and a voltage conversion circuit, and the controller is used to output a PWM signal to control the on and off of a switch tube in the voltage conversion circuit; the method includes: Acquire the input voltage of the photovoltaic optimizer; wherein the input voltage of the photovoltaic optimizer is the output voltage of the photovoltaic module; Based on the input voltage, the photovoltaic optimizer is controlled to switch between a shutdown mode, a protection mode and a maximum power tracking mode; wherein, If the input voltage is less than the first threshold, the photovoltaic optimizer operates in a shutdown mode; in the shutdown mode, the PWM signal is in a closed state; If the input voltage is greater than or equal to the first threshold and less than or equal to the second threshold, the photovoltaic optimizer operates in a protection mode; in the protection mode, the duty cycle of the PWM signal is adjusted based on the input voltage to keep the input voltage greater than the first threshold; If the input voltage is greater than the second threshold, the photovoltaic optimizer operates in a maximum power tracking mode; in the maximum power tracking mode, the duty cycle of the PWM signal is adjusted based on the output voltage and output current of the photovoltaic optimizer so that the photovoltaic component connected to the photovoltaic optimizer operates at a maximum power point.

2. The photovoltaic optimizer control method according to claim 1, characterized in that: In the protection mode, the duty cycle of the PWM signal of the photovoltaic optimizer is adjusted according to the comparison result between the input voltage and a third threshold value; wherein the third threshold value is greater than the first threshold value and less than the second threshold value.

3. The photovoltaic optimizer control method according to claim 2, characterized in that: In the protection mode, adjusting the duty cycle of the PWM signal of the photovoltaic optimizer according to the comparison result between the input voltage and the third threshold value includes: If the input voltage is greater than a third threshold, increasing the duty cycle of the photovoltaic optimizer PWM signal; If the input voltage is less than the third threshold, the duty cycle of the photovoltaic optimizer PWM signal is reduced.

4. The photovoltaic optimizer control method according to claim 2, characterized in that: Based on the input voltage, controlling the photovoltaic optimizer to switch between a shutdown mode, a protection mode, and a maximum power tracking mode includes: If the input voltage at the previous moment is greater than the second threshold and the input voltage at the current moment is less than or equal to the second threshold, the duty cycle of the PWM signal of the photovoltaic optimizer is reduced at the current moment, and the photovoltaic optimizer is controlled to switch from the maximum power tracking mode to the protection mode.

5. The photovoltaic optimizer control method according to claim 4, characterized in that: Reducing the duty cycle of the PWM signal of the photovoltaic optimizer at the current moment includes: If the input voltage at the current moment is less than a third threshold, reducing the duty cycle of the PWM signal of the photovoltaic optimizer at the current moment according to the input voltage at the previous moment and the input voltage at the current moment; If the input voltage at the current moment is greater than the third threshold, the duty cycle of the PWM signal of the photovoltaic optimizer is reduced at the current moment according to the input voltage at the previous moment and the third threshold.

6. The photovoltaic optimizer control method according to claim 2, characterized in that: Based on the input voltage, controlling the photovoltaic optimizer to switch between a shutdown mode, a protection mode, and a maximum power tracking mode includes: If the input voltage at the previous moment is less than the first threshold value, and the input voltage at the current moment is greater than the first threshold value and less than the third threshold value, then at the current moment, the photovoltaic optimizer is controlled to switch from the shutdown mode to the protection mode; at the current moment, a PWM signal with a duty cycle of zero is output, until the input voltage at a certain moment is greater than the third threshold value, and the duty cycle of the PWM signal is increased; If the input voltage at the previous moment is less than the first threshold and the input voltage at the current moment is greater than the third threshold, the photovoltaic optimizer is controlled to switch from the shutdown mode to the protection mode, and the duty cycle of the PWM signal is increased; wherein the third threshold is greater than the first threshold and less than the second threshold.

7. The photovoltaic optimizer control method according to claim 1, characterized in that: The first threshold is the minimum voltage within the operating voltage range of the photovoltaic optimizer; and the second threshold is the minimum voltage when the photovoltaic optimizer operates in the maximum power point tracking mode.

8. A photovoltaic optimizer, applied to a photovoltaic system, characterized in that: The photovoltaic system comprises: an inverter, a photovoltaic string and a central controller, wherein the photovoltaic string is connected to the central controller and the inverter respectively; the photovoltaic string comprises a plurality of photovoltaic units connected in series, each of the photovoltaic units comprises the photovoltaic optimizer and at least one photovoltaic component connected to the photovoltaic optimizer, and the photovoltaic optimizer comprises: A controller and a voltage conversion circuit, wherein the controller is used to output a PWM signal to control the on and off of a switch tube in the voltage conversion circuit; Wherein, the controller comprises: An acquisition unit, used for acquiring an input voltage of the photovoltaic optimizer; wherein the input voltage of the photovoltaic optimizer is the output voltage of the photovoltaic module; A mode selection unit, configured to control the photovoltaic optimizer to switch between a shutdown mode, a protection mode, and a maximum power point tracking mode based on the input voltage; in, If the input voltage is less than the first threshold, the photovoltaic optimizer operates in a shutdown mode; in the shutdown mode, the PWM signal is in a closed state; If the input voltage is greater than or equal to the first threshold and less than or equal to the second threshold, the photovoltaic optimizer operates in a protection mode; in the protection mode, the duty cycle of the PWM signal is adjusted based on the input voltage to keep the input voltage greater than the first threshold; If the input voltage is greater than the second threshold, the photovoltaic optimizer operates in a maximum power tracking mode; in the maximum power tracking mode, the duty cycle of the PWM signal is adjusted based on the output voltage and output current of the photovoltaic optimizer so that the photovoltaic component connected to the photovoltaic optimizer operates at a maximum power point.

9. The photovoltaic optimizer according to claim 8, characterized in that: In the protection mode, the duty cycle of the PWM signal of the photovoltaic optimizer is adjusted according to the comparison result between the input voltage and a third threshold value; wherein the third threshold value is greater than the first threshold value and less than the second threshold value.

10. The photovoltaic optimizer according to claim 9, characterized in that: In the protection mode, adjusting the duty cycle of the PWM signal of the photovoltaic optimizer according to the comparison result between the input voltage and the third threshold value includes: If the input voltage is greater than a third threshold, increasing the duty cycle of the photovoltaic optimizer PWM signal; If the input voltage is less than the third threshold, the duty cycle of the photovoltaic optimizer PWM signal is reduced.

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