Power generation system, photovoltaic optimizer and control method therefor
By exiting maximum power point tracking mode and reducing the input voltage when the photovoltaic optimizer temperature is too high, the problems of power generation loss and stability caused by excessive photovoltaic optimizer temperature are solved, and temperature control and power generation optimization are achieved.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- HUAWEI DIGITAL POWER TECH CO LTD
- Filing Date
- 2025-11-26
- Publication Date
- 2026-06-04
AI Technical Summary
Existing protection methods for photovoltaic optimizers result in power generation loss and are prone to damage when the temperature is too high.
When the photovoltaic optimizer temperature is too high, it exits the maximum power point tracking state and reduces the input voltage until the temperature drops to the threshold. Then it resumes the maximum power point tracking state and controls the input voltage to increase in order to keep the temperature below the threshold.
It effectively reduces the temperature of the photovoltaic optimizer, reduces power generation loss, improves system stability, and avoids additional losses caused by direct shutdown.
Smart Images
Figure CN2025137659_04062026_PF_FP_ABST
Abstract
Description
Power generation system, photovoltaic optimizer and its control method
[0001] This application claims priority to Chinese Patent Application No. 202411718630.2, filed on November 27, 2024, with the China National Intellectual Property Administration, entitled “Power Generation System, Photovoltaic Optimizer and Control Method Thereof”, the entire contents of which are incorporated herein by reference. Technical Field
[0002] This application relates to the field of power supply technology, and in particular to a power generation system, a photovoltaic optimizer, and a control method thereof. Background Technology
[0003] As a key component in photovoltaic power generation systems, the photovoltaic optimizer is susceptible to problems such as instability and damage if its temperature is too high. To protect the photovoltaic optimizer, many systems employ a protection mechanism that shuts it down immediately upon detecting excessively high temperatures, thus reducing its temperature. However, this protection method results in a loss of power generation from the photovoltaic optimizer. Summary of the Invention
[0004] This application provides a power generation system, a photovoltaic optimizer, and a control method thereof. In the event of overheating of the photovoltaic optimizer, the system can not only effectively reduce the temperature of the photovoltaic optimizer, but also effectively reduce the power generation loss of the photovoltaic optimizer.
[0005] In a first aspect, this application provides a power generation system comprising an inverter and at least two photovoltaic (PV) optimizers. The input terminals of the PV optimizers are connected to photovoltaic modules, and the output terminals of the at least two PV optimizers are connected in series to the input terminal of the inverter. The output terminal of the inverter is used to connect to the power grid or a load. Each PV optimizer includes a BUCK circuit, the input terminal of which is connected to the input terminal of the PV optimizer, and the output terminal of which is connected to the output terminal of the PV optimizer. The PV optimizer is configured to exit Maximum Power Point Tracking (MPPT) state (i.e., trigger thermal derating) and control the input voltage of the BUCK circuit (i.e., the input voltage of the PV optimizer) to decrease when its temperature exceeds a temperature threshold, thereby lowering the temperature of the PV optimizer; when the temperature of the PV optimizer is below the temperature threshold, control the input voltage of the BUCK circuit to increase; and when the input voltage of the BUCK circuit exceeds a voltage threshold, re-enter the MPPT state, wherein the voltage threshold is positively correlated with the input voltage of the BUCK circuit when the PV optimizer exits the MPPT state.
[0006] The photovoltaic optimizer provided in this application can be understood as a BUCK converter. The heat loss of this converter (positively correlated with temperature) is mainly determined by the voltage difference between the input and output voltages and the magnitude of the output current. Specifically, the smaller the voltage difference or output current, the lower the heat loss; conversely, the larger the voltage difference or output current, the higher the heat loss. Since the output terminals of the multiple photovoltaic optimizers in the power generation system provided in this application are connected in series, and the output current of the series-connected photovoltaic optimizers is determined by the power generation system, changes in the operating state of a single photovoltaic optimizer have little impact on its output current. Therefore, adjusting the output current of a photovoltaic optimizer cannot reduce its heat loss. Based on this, the photovoltaic optimizer provided in this application, when experiencing overheating, exits the MPPT state and reduces its own input voltage, shifting its operating point to the left of the input power Pi-input voltage Vi curve. This reduces its input power, thereby reducing its output power. Since the output current of the photovoltaic optimizer remains essentially unchanged, and the output power decreases, the output voltage also decreases. This reduces the voltage difference between the input and output voltages, thus reducing heat loss and lowering the photovoltaic optimizer's temperature. Furthermore, because the photovoltaic optimizer first reduces its input voltage after overheating, rather than shutting down directly, it effectively reduces its power generation loss. Moreover, since the photovoltaic optimizer increases its input voltage after its temperature drops below the temperature threshold, it can maximize its input power while keeping its temperature below the threshold, further effectively reducing power generation loss.
[0007] In conjunction with the first aspect, in a first possible implementation, the photovoltaic optimizer is further configured to maintain a constant input voltage of the BUCK circuit when its own temperature equals a temperature threshold. The photovoltaic optimizer is also configured to control an increase in the input voltage of the BUCK circuit when its own temperature is below a temperature threshold and the input voltage of the BUCK circuit is less than or equal to a voltage threshold.
[0008] In this embodiment, when overheating occurs, the photovoltaic optimizer can rapidly reduce its temperature by first exiting the MPPT state and decreasing its own input voltage. Once its temperature drops to the temperature threshold, it maintains its own input voltage unchanged. When it detects a further decrease in its own temperature, it controls its own input voltage to increase. Therefore, not only can the temperature of the photovoltaic optimizer after triggering thermal derating not exceed the temperature threshold, thus effectively protecting the photovoltaic optimizer from overheating, but it can also maximize its own input power while ensuring that the temperature of the photovoltaic optimizer is below the temperature threshold, thereby further effectively reducing the power generation loss of the photovoltaic optimizer.
[0009] In conjunction with the first aspect or the first possible implementation of the first aspect, in the second possible implementation, when the input voltage of the BUCK circuit decreases, the input current of the BUCK circuit increases.
[0010] In conjunction with the first aspect to the second possible implementation, in the third possible implementation, when the input voltage of the BUCK circuit decreases, the input power of the BUCK circuit decreases.
[0011] In conjunction with the first to third possible embodiments, in a fourth possible embodiment, the photovoltaic optimizer further includes a controller. The temperature of the photovoltaic optimizer includes the temperature of the controller and the temperature of the switching transistors or capacitors in the BUCK circuit.
[0012] In this embodiment, the temperature of the photovoltaic optimizer can be understood as the temperature of any device located inside the photovoltaic optimizer. In other words, the photovoltaic optimizer can perform over-temperature protection when any device inside triggers thermal derating, making it highly applicable.
[0013] Secondly, this application provides a photovoltaic optimizer. The input terminal of the photovoltaic optimizer is used to connect to a photovoltaic module, and the output terminal of the photovoltaic optimizer is used to connect to the input terminal of an inverter after being connected in series with the output terminals of other photovoltaic optimizers. The photovoltaic optimizer includes a BUCK circuit, the input terminal of which is connected to the input terminal of the photovoltaic optimizer, and the output terminal of which is connected to the output terminal of the photovoltaic optimizer. The photovoltaic optimizer is configured to exit the MPPT state and control the input voltage of the BUCK circuit to decrease when its own temperature exceeds a temperature threshold, thereby lowering the temperature of the photovoltaic optimizer; to control the input voltage of the BUCK circuit to increase when the temperature of the photovoltaic optimizer is below the temperature threshold; and to re-enter the MPPT state when the input voltage of the BUCK circuit exceeds a voltage threshold, wherein the voltage threshold is positively correlated with the input voltage of the BUCK circuit when the photovoltaic optimizer exits the MPPT state.
[0014] In conjunction with the second aspect, in the first possible implementation, the photovoltaic optimizer is further configured to maintain a constant input voltage to the BUCK circuit when its own temperature equals a temperature threshold. The photovoltaic optimizer is also configured to control an increase in the input voltage of the BUCK circuit when its own temperature is below a temperature threshold and the input voltage of the BUCK circuit is less than or equal to a voltage threshold.
[0015] In conjunction with the second aspect or the first possible implementation of the second aspect, in the second possible implementation, when the input voltage of the BUCK circuit decreases, the input current of the BUCK circuit increases.
[0016] In conjunction with the second aspect to the second possible implementation, in the third possible implementation, when the input voltage of the BUCK circuit decreases, the input power of the BUCK circuit decreases.
[0017] In conjunction with the second to third possible implementations, in a fourth possible implementation, the photovoltaic optimizer further includes a controller. The temperature of the photovoltaic optimizer includes the temperature of the controller and the temperature of the switching transistors or capacitors in the BUCK circuit.
[0018] Thirdly, this application provides a control method for a photovoltaic (PV) optimizer, applied to a PV optimizer. The input terminal of the PV optimizer is used to connect to a PV module, and the output terminal of the PV optimizer is connected in series with the output terminals of other PV optimizers and then connected to the input terminal of an inverter. The PV optimizer includes a BUCK circuit, the input terminal of which is connected to the input terminal of the PV optimizer, and the output terminal of which is connected to the output terminal of the PV optimizer. The method includes: when the temperature of the PV optimizer is greater than a temperature threshold, controlling the PV optimizer to exit the MPPT state and controlling the input voltage of the BUCK circuit to decrease, thereby lowering the temperature of the PV optimizer; when the temperature of the PV optimizer is less than the temperature threshold, controlling the input voltage of the BUCK circuit to increase; and when the input voltage of the BUCK circuit is greater than a voltage threshold, controlling the PV optimizer to re-enter the MPPT state, wherein the voltage threshold is positively correlated with the input voltage of the BUCK circuit when the PV optimizer exits the MPPT state.
[0019] In conjunction with the third aspect, in the first possible implementation, the photovoltaic optimizer also maintains a constant input voltage to the BUCK circuit when its own temperature equals a temperature threshold. Conversely, when its own temperature is below the temperature threshold and the input voltage to the BUCK circuit is less than or equal to a voltage threshold, the photovoltaic optimizer controls the input voltage of the BUCK circuit to increase.
[0020] In conjunction with the third aspect or the first possible implementation of the third aspect, in the second possible implementation, when the input voltage of the BUCK circuit decreases, the input current of the BUCK circuit increases.
[0021] In conjunction with the third aspect to the second possible implementation, in the third possible implementation, when the input voltage of the BUCK circuit decreases, the input power of the BUCK circuit decreases.
[0022] In conjunction with the third aspect to the third possible implementation, in the fourth possible implementation, the photovoltaic optimizer further includes a controller. The temperature of the photovoltaic optimizer includes the temperature of the controller and the temperature of the switching transistors or capacitors in the BUCK circuit.
[0023] It should be understood that the implementations and beneficial effects of the above-mentioned aspects of this application can be referenced from each other. Attached Figure Description
[0024] Figure 1 is a schematic diagram of the application scenario of the power generation system provided in this application;
[0025] Figure 2 is a structural schematic diagram of the power generation system provided in this application;
[0026] Figure 3 is another structural schematic diagram of the power generation system provided in this application;
[0027] Figure 4 is a waveform diagram of the voltage and current of the photovoltaic optimizer provided in this application;
[0028] Figure 5 is a schematic diagram of the power P-voltage V curve of the photovoltaic optimizer provided in this application;
[0029] Figure 6 is another waveform diagram of the voltage and current of the photovoltaic optimizer provided in this application;
[0030] Figure 7 is another waveform diagram of the voltage and current of the photovoltaic optimizer provided in this application;
[0031] Figure 8 is a flowchart illustrating the control method of the photovoltaic optimizer provided in this application. Detailed Implementation
[0032] The power generation system provided in this application is applicable to various fields, including photovoltaic power generation, photovoltaic-storage hybrid power generation, new energy smart microgrids, and power transmission and distribution. The power generation system provided in this application is suitable for different application scenarios, such as photovoltaic power supply scenarios, photovoltaic-storage hybrid power supply scenarios, and UPS power supply scenarios. The following explanation uses a photovoltaic power supply scenario as an example.
[0033] Referring to Figure 1, which is a schematic diagram of the application scenario of the power generation system provided in this application, the power generation system provided in this application is the photovoltaic power generation system shown in Figure 1. This photovoltaic power generation system includes photovoltaic optimizers 11, ..., 1n and inverter 2, where n is an integer greater than 1. The input terminal of photovoltaic optimizer 11 is connected to photovoltaic module 31, ..., the input terminal of photovoltaic optimizer 1n is connected to photovoltaic module 3n, and the output terminals of photovoltaic optimizers 11, ..., 1n are connected in series to the input terminal of inverter 2. The output terminal of inverter 2 is connected to the AC power grid or household appliances. Each of the n photovoltaic optimizers includes a BUCK circuit. The input terminal of the BUCK circuit in each photovoltaic optimizer is connected to the input terminal of its respective photovoltaic optimizer, and the output terminal of the BUCK circuit in each photovoltaic optimizer is connected to the output terminal of its respective photovoltaic optimizer.
[0034] After the photovoltaic power generation system starts operating, the n photovoltaic optimizers are in MPPT (Multi-Level Testing) mode. Specifically, the n photovoltaic optimizers adjust their respective input voltages to perform MPPT on the output power of photovoltaic modules 31 to 3n, maximizing the output power of the photovoltaic modules connected to each optimizer. Simultaneously, the n photovoltaic optimizers also perform DC-DC conversion on the DC power output from their respective connected photovoltaic modules, and output the converted DC power to the input terminal of inverter 2. Inverter 2 sequentially boosts and inverts the DC power at its input terminal to obtain AC power that meets the requirements of the AC power grid, thereby enabling the supply of power to various types of electrical equipment, including those connected to the AC power grid.
[0035] During the process of n photovoltaic optimizers outputting power to inverter 2, if any photovoltaic optimizer detects that its own temperature exceeds the temperature threshold T1, it indicates that the photovoltaic optimizer has overheated. This photovoltaic optimizer then exits the MPPT state and reduces the input voltage of its internal BUCK circuit to lower its temperature. Subsequently, if the overheated photovoltaic optimizer's own temperature falls below the temperature threshold T1, it increases the input voltage of its internal BUCK circuit. When the input voltage of the internal BUCK circuit exceeds a voltage threshold, it re-enters the MPPT state. The voltage threshold is positively correlated with the input voltage of the internal BUCK circuit when any photovoltaic optimizer exits the MPPT state.
[0036] Understandably, when a photovoltaic (PV) optimizer experiences overheating, it exits the MPPT (Multi-Pulse Test) state and reduces its input voltage, shifting its operating point to the left of the input power Pi-input voltage Vi curve. This reduces its input power, thereby lowering its output power. Since the output current of the PV optimizer connected in series at the output terminal remains essentially unchanged, and the output power decreases, the output voltage decreases. This reduces the voltage difference between the input and output voltages, thus reducing heat loss and lowering the PV optimizer's temperature. Furthermore, because the PV optimizer first reduces its input voltage after overheating, rather than shutting down directly, it effectively reduces its power generation loss. Moreover, once the PV optimizer's temperature drops below the temperature threshold T1, it increases its input voltage. Therefore, it can maximize its input power while keeping its temperature below the temperature threshold T1, further effectively reducing power generation loss.
[0037] The above are merely examples of application scenarios for the power generation system provided in this application, and are not exhaustive. This application does not limit the application scenarios.
[0038] The working principle of the power generation system and photovoltaic optimizer provided in this application is illustrated below with reference to Figures 2 to 7.
[0039] Referring to Figure 2, which is a schematic diagram of the power generation system provided in this application, the power generation system includes a photovoltaic optimizer 11, a photovoltaic optimizer 12, ..., a photovoltaic optimizer 1n, and an inverter 2, where n is an integer greater than 1. The input terminals i111 and i112 of the photovoltaic optimizer 11 are used to connect to photovoltaic modules 31, the input terminals i121 and i122 of the photovoltaic optimizer 12 are used to connect to photovoltaic modules 32, ..., and the input terminals i1n1 and i1n2 of the photovoltaic optimizer 1n are used to connect to photovoltaic modules 3n. The output terminals of the photovoltaic optimizers 11, 12, ..., and 1n are connected in series to the input terminal of the inverter 2. Specifically, the output terminal o111 of the photovoltaic optimizer 11 is connected to the input terminal i21 of the inverter 2, the output terminal o112 of the photovoltaic optimizer 11 is connected to the output terminal o121 of the photovoltaic optimizer 12, ..., and the output terminal o1n2 of the photovoltaic optimizer 1n is connected to the input terminal i22 of the inverter 2. The output terminals o21 and o22 of inverter 2 are used to connect to the power grid.
[0040] In this system, the photovoltaic optimizer can be a converter with a step-down function, such as a Buck converter or a Buck-Boost converter. For ease of description, the following explanation uses a Buck converter as an example of the photovoltaic optimizer, combined with the power generation system shown in Figure 3.
[0041] Referring to Figure 3, which is another structural schematic diagram of the power generation system provided in this application, the photovoltaic optimizer 11 includes a Buck circuit 111, a controller 112, and a diode D1. The two input terminals of the Buck circuit 111 are connected to the input terminals i111 and i112 of the photovoltaic optimizer 11, respectively, and the two output terminals of the Buck circuit 111 are connected to the output terminals o111 and o112 of the photovoltaic optimizer 11, respectively. The cathode of the diode D1 is connected to the output terminal o111 of the photovoltaic optimizer 11, and the anode of the diode D1 is connected to the output terminal o112 of the photovoltaic optimizer 11. The circuit structures of photovoltaic optimizers 12 to 1n are the same as those of photovoltaic optimizer 11, and will not be described again here. Inverter 2 includes a Boost circuit 21 and a DC / AC circuit 22. The two input terminals of the Boost circuit 21 are connected to the input terminals i21 and i22 of the inverter 2, respectively. The two output terminals of the Boost circuit 21 are connected to the two input terminals of the DC / AC circuit 22, respectively. The two output terminals of the DC / AC circuit 22 are connected to the output terminals o21 and o22 of the inverter 2, respectively.
[0042] To facilitate understanding, the working principle of the over-temperature protection of the photovoltaic optimizer in this application is first introduced as follows: The photovoltaic optimizer in the power generation system can be understood as a BUCK converter. The heat loss of this converter is mainly determined by the voltage difference between the input voltage and the output voltage and the magnitude of the output current. Specifically, the smaller the voltage difference or output current between the input voltage and the output voltage, the lower the heat loss of the converter; conversely, the larger the voltage difference or output current, the higher the heat loss. Since the output terminals of the multiple photovoltaic optimizers in the power generation system provided in this application are connected in series, and the output current of the photovoltaic optimizers connected in series is determined by the power generation system, changes in the operating state of a single photovoltaic optimizer have little effect on its output current. Therefore, adjusting the output current of the photovoltaic optimizer cannot reduce its heat loss. When a photovoltaic (PV) optimizer in a power generation system overheats, if it reduces its power output by increasing its input voltage, the output current of the PV optimizer connected in series at the output terminal remains essentially unchanged. Therefore, the reduced output power leads to a decrease in the PV optimizer's output voltage, increasing the voltage difference between the input and output voltages. This results in increased heat loss and a further rise in the PV optimizer's temperature. Conversely, if the PV optimizer reduces its power output by decreasing its input voltage, the output current of the PV optimizer connected in series at the output terminal remains essentially unchanged. Therefore, the reduced output power leads to a decrease in the PV optimizer's output voltage, decreasing the voltage difference between the input and output voltages. This reduces heat loss and lowers the PV optimizer's temperature, thus achieving overheat protection.
[0043] Since each photovoltaic optimizer in the power generation system operates on the same principle, for ease of description, the following detailed description will take photovoltaic optimizer 11 as an example.
[0044] In one embodiment, after the photovoltaic optimizer 11 operates, the controller 112 performs MPPT on the output power of the photovoltaic module 31 by adjusting the input voltage of the Buck circuit 111 (i.e., the input voltage of the photovoltaic optimizer 11), thereby maximizing the output power of the photovoltaic module 31, i.e., putting the photovoltaic optimizer 11 in MPPT state. Simultaneously, the controller 112 detects the temperature of the photovoltaic optimizer 11 using at least one temperature sensor. If the temperature of the photovoltaic optimizer 11 exceeds a temperature threshold T1, the controller controls the photovoltaic optimizer 11 to exit the MPPT state and reduces its input voltage to lower its temperature. Subsequently, if the temperature of the photovoltaic optimizer 11 is below the temperature threshold T1, the controller 112 increases the input voltage of the photovoltaic optimizer 11. If the input voltage of the photovoltaic optimizer 11 exceeds a voltage threshold, the controller controls the photovoltaic optimizer 11 to re-enter the MPPT state. The voltage threshold is positively correlated with the input voltage when the photovoltaic optimizer 11 exits the MPPT state. Temperature sensors include negative temperature coefficient thermistors (NTC) or positive temperature coefficient thermistors (PTC).
[0045] In this application, the temperature of the photovoltaic optimizer 11 refers to the internal temperature of the photovoltaic optimizer 11, including but not limited to the temperature of the controller 112, the temperature of key components such as the switching transistors (e.g., Q1 or Q2) or capacitors (e.g., C1 or C2) in the Buck circuit 111, and the cavity temperature of the photovoltaic optimizer 11. Furthermore, the temperature threshold T1 in this application is determined by the rated temperature of the device being measured within the photovoltaic optimizer 11, and is typically close to but lower than the rated temperature of the device being measured. For example, when the temperature of the photovoltaic optimizer 11 is the temperature of the switching transistor in the Buck circuit 111, the temperature threshold T1 can be 130°C; when the temperature of the photovoltaic optimizer 11 is the temperature of the controller 112 or the temperature of the capacitors in the Buck circuit 111, the temperature threshold T1 can be 100°C.
[0046] Specifically, if the temperature of the photovoltaic optimizer 11 exceeds the temperature threshold T1, it indicates that the photovoltaic optimizer 11 has overheated. In this case, the controller 112 controls the photovoltaic optimizer 11 to exit the MPPT state and reduces its input voltage to lower its temperature. If the temperature of the photovoltaic optimizer 11 equals the temperature threshold T1, the controller 11 maintains the input voltage of the photovoltaic optimizer 11 unchanged. If the temperature of the photovoltaic optimizer 11 is less than the temperature threshold T1 and its input voltage is less than or equal to a voltage threshold (i.e., if a further decrease in temperature is detected), the controller 112 increases the input voltage of the photovoltaic optimizer 11. Then, if the input voltage of the photovoltaic optimizer 11 exceeds the voltage threshold, the controller 112 adjusts the input voltage of the photovoltaic optimizer 11 to re-enter the MPPT state.
[0047] For example, to facilitate understanding, this embodiment will be described below with reference to a waveform diagram of the voltage and current of the photovoltaic optimizer 11 shown in Figure 4 and a schematic diagram of the power P-voltage V curve of the photovoltaic optimizer 11 shown in Figure 5.
[0048] As shown in Figure 4, the three solid black lines from top to bottom represent the input voltage Vi, output voltage Vo, and input current Ii of the photovoltaic optimizer 11, respectively. During the time period from t0 to t1, the photovoltaic optimizer 11 is in the MPPT state.
[0049] At time t1, the ambient temperature rises, and the photovoltaic optimizer 11 detects that its own temperature exceeds the temperature threshold T1. At this time, the input operating point of the photovoltaic optimizer 11 is b1 in Figure 5. Since the output terminals of n photovoltaic optimizers in the power generation system are connected in series, the output current of the n photovoltaic optimizers is the same and fixed. Therefore, the output operating point of the photovoltaic optimizer 11 is always located on the straight line of output power Po and output voltage Vo of the photovoltaic optimizer when the output current Io is constant at Ic in Figure 5. Since the output power Po of the photovoltaic optimizer 11 is equal to the input power Pi, the output operating point of the photovoltaic optimizer 11 at time t1 is c1 in Figure 5. The photovoltaic optimizer 11 exits the MPPT state from time t1 and enters the power limiting state. It controls the input voltage Vi to decrease from v1 (corresponding to the input voltage value of 40V corresponding to the input operating point b1 in Figure 5). Correspondingly, the input current Ii of the photovoltaic optimizer 11 begins to rise, and the output voltage Vo of the photovoltaic optimizer 11 begins to decrease from v2 (corresponding to the output voltage value of 26V corresponding to the output operating point c1 in Figure 5). Here, under power-limited conditions, the output power of the photovoltaic optimizer 11 is less than the maximum output power of the photovoltaic optimizer 11.
[0050] During the time interval t1 to t2, as the ambient temperature continues to rise, the temperature of the photovoltaic optimizer 11 remains above the temperature threshold T1. Therefore, the photovoltaic optimizer 11 continues to control the input voltage Vi to decrease. Correspondingly, the input current Ii of the photovoltaic optimizer 11 continues to rise, and the output voltage Vo of the photovoltaic optimizer 11 continues to decrease. The photovoltaic optimizer 11 remains in a power-limiting state. Similarly, during the time interval t1 to t2, as the photovoltaic optimizer 11 controls its input voltage Vi, the change in the operating point of the photovoltaic optimizer 11 can be understood as follows: the input operating point of the photovoltaic optimizer 11 moves to the left from the input operating point b1 along the input power Pi-input voltage Vi curve shown in Figure 5; the output operating point of the photovoltaic optimizer 11 moves to the left from the output operating point c1 along the straight line of output power Po-output voltage Vo when the output current Io is constant at Ic, as shown in Figure 5. Obviously, based on Figure 5, as the input voltage of the photovoltaic optimizer 11 decreases continuously, the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer 11 decreases continuously from ΔV1 (i.e., 40V-26V=14V). Therefore, the heat loss of the photovoltaic optimizer 11 is decreasing continuously.
[0051] At time t2, the input voltage Vi of the photovoltaic optimizer 11 is v3 (corresponding to the input voltage value of 21V at input operating point b2 in Figure 5), and the output voltage Vo of the photovoltaic optimizer 11 is v4 (corresponding to the input voltage value of 14.4V at output operating point c2 in Figure 5). The temperature of the photovoltaic optimizer 11 decreases to the temperature threshold T1, and the ambient temperature no longer increases. The input voltage Vi of the photovoltaic optimizer 11 remains unchanged. Obviously, based on Figure 5, the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer 11 at time t2 is ΔV2 (i.e., 21V - 14.4V = 6.6V). Furthermore, based on Figure 5, if the photovoltaic optimizer 11 exits the MPPT state and increases the input voltage Vi when overheating occurs, the input operating point of the photovoltaic optimizer 11 at time t2 will no longer be b2, but will become b3. Thus, the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer 11 at time t2 will become ΔV3. Obviously, ΔV3 is greater than ΔV1. Therefore, it can be seen that using the input voltage Vi for overheat protection will cause the heat loss of the photovoltaic optimizer 11 to increase continuously, and the temperature of the photovoltaic optimizer 11 will not be reduced, but will instead rise further.
[0052] During the time period from t2 to t3, the ambient temperature no longer rises and remains stable. The temperature of the photovoltaic optimizer 11 remains at the temperature threshold T1, and the input voltage Vi of the photovoltaic optimizer 11 remains constant, so that the photovoltaic optimizer 11 can operate stably under the same power-limited state as at time t2.
[0053] At time t3, the ambient temperature begins to decrease, and the temperature of the photovoltaic optimizer 11 decreases as the ambient temperature decreases. That is, when the temperature of the photovoltaic optimizer 11 is less than the temperature threshold T1, the photovoltaic optimizer 11 begins to control the input voltage Vi to increase, so that its input power begins to increase.
[0054] During the period from t3 to t4, the ambient temperature continues to decrease, and the temperature of the photovoltaic optimizer 11 decreases along with the ambient temperature. While ensuring that its own temperature is below the temperature threshold T1, the photovoltaic optimizer 11 continues to increase the input voltage Vi, so that its input power continues to increase.
[0055] At time t4, the input voltage Vi of the photovoltaic optimizer 11 is greater than the voltage threshold Vth, and the photovoltaic optimizer 11 exits the power limiting state and re-enters the MPPT state. The voltage threshold Vth is positively correlated with the input voltage v1 when the photovoltaic optimizer 11 exits the MPPT state, specifically Vth = k*v1 + b, where k = 1.
[0056] It is understandable that when overheating occurs, the photovoltaic optimizer 11 can rapidly reduce its own temperature by first exiting the MPPT state and reducing its own input voltage. When its own temperature drops to the temperature threshold T1, it maintains its own input voltage unchanged, and when it detects that its own temperature has further decreased, it controls its own input voltage to increase. Therefore, it can not only ensure that the temperature of the photovoltaic optimizer 11 after triggering thermal derating does not exceed the temperature threshold T1, thus effectively protecting the photovoltaic optimizer 11 from overheating, but also maximize its own input power while ensuring that the temperature of the photovoltaic optimizer 11 is below the temperature threshold T1, thereby further effectively reducing the power generation loss of the photovoltaic optimizer 11 and thus further effectively reducing the power generation loss of the power generation system.
[0057] It should be noted that in the embodiment shown in Figure 4, the value of k can also be greater than 0 and less than 1. For details, please refer to another waveform diagram of the voltage and current of the photovoltaic optimizer 11 shown in Figure 6; in the embodiment shown in Figure 4, the value of k can also be greater than 1. For details, please refer to yet another waveform diagram of the voltage and current of the photovoltaic optimizer 11 shown in Figure 7. Here, the embodiments shown in Figures 6 and 7 are similar to the embodiment shown in Figure 4, except for the value of k. All other parts are similar and will not be described again here.
[0058] Furthermore, the method used in the above embodiments to reduce the temperature of the photovoltaic optimizer 11 by exiting the MPPT state and reducing its own input voltage is not ideal in some extreme cases. In such cases, it is necessary to shut down the device in time to achieve over-temperature protection for the photovoltaic optimizer 11, as follows:
[0059] In one embodiment, when the temperature of the photovoltaic optimizer 11 exceeds the temperature threshold T1, the controller 112 controls the photovoltaic optimizer 11 to exit the MPPT state and reduces the input voltage of the photovoltaic optimizer 11. Subsequently, if the temperature of the photovoltaic optimizer 11 exceeds the temperature threshold T2, it indicates that the ambient temperature is too high, causing the temperature of the photovoltaic optimizer 11 to rise instead of decrease as the input voltage decreases. In this case, the controller 112 controls the Buck circuit 111 to stop operating, i.e., it controls the switching transistors Q1 and Q2 in the Buck circuit 111 to turn off, thereby bypassing the Buck circuit 111 with diode D1. This prevents other photovoltaic optimizers in the power generation system with temperatures less than or equal to the temperature threshold T1 from generating electricity normally. The temperature threshold T2 is greater than the temperature threshold T1.
[0060] Understandably, if the photovoltaic optimizer 11 detects that its own temperature does not decrease as the input voltage decreases, or even continues to rise, it should shut down promptly. This allows the photovoltaic optimizer 11 to reduce its own temperature as quickly as possible when the ambient temperature is too high, thus achieving over-temperature protection for the photovoltaic optimizer 11. Furthermore, when its own temperature is too high, the photovoltaic optimizer 11 first reduces the input power and then shuts down. Compared to directly shutting down, this effectively reduces the power generation loss of the photovoltaic optimizer 11, thereby effectively reducing the power generation loss of the power generation system.
[0061] In another embodiment, when the temperature of the photovoltaic optimizer 11 is greater than the temperature threshold T1, the controller 112 controls the photovoltaic optimizer 11 to exit the MPPT state and controls the input voltage of the photovoltaic optimizer 11 to decrease. As the input voltage of the photovoltaic optimizer 11 decreases, the input current of the photovoltaic optimizer 11 increases accordingly. When the input current of the photovoltaic optimizer 11 increases to be the same as the output current, and the temperature of the photovoltaic optimizer 11 is still greater than the temperature threshold T1 but less than or equal to the temperature threshold T2, since the photovoltaic optimizer 11 is in a shoot-through mode when the input current and output current are the same, the heat loss of the photovoltaic optimizer is the lowest in the shoot-through mode. However, since the temperature of the photovoltaic optimizer 11 is still greater than the temperature threshold T1 when it is in the shoot-through mode, it indicates that the ambient temperature is too high. Therefore, the controller 112 controls the photovoltaic optimizer 11 to remain in the shoot-through mode. Specifically, it controls the switching transistor Q1 in the Buck circuit 111 to remain constantly on. If the temperature of the photovoltaic optimizer 11 is greater than the temperature threshold T2, it means that even in the direct mode, the temperature of the photovoltaic optimizer 11 cannot be reduced. In this case, the controller 112 controls the Buck circuit 111 to stop working, so that the Buck circuit 111 is bypassed by the diode D1, thereby not affecting the normal power generation of other photovoltaic optimizers in the power generation system whose temperature is less than or equal to the temperature threshold T1.
[0062] Understandably, if the temperature of the photovoltaic optimizer 11 does not decrease even when it is in direct-on mode, and even continues to rise above the temperature threshold T2, it indicates that the ambient temperature is too high. Therefore, it should shut down promptly to reduce its own temperature as quickly as possible, thus achieving over-temperature protection for the photovoltaic optimizer 11. Furthermore, when its own temperature is too high, the photovoltaic optimizer 11 first reduces its input power before shutting down. Compared to a direct shutdown, this effectively reduces the power generation loss of the photovoltaic optimizer 11, thereby effectively reducing the power generation loss of the power generation system.
[0063] In this application, when the photovoltaic optimizer experiences overheating, it exits the MPPT state and reduces its input voltage, shifting its operating point to the left of the input power Pi-input voltage Vi curve. This reduces its input power and consequently its output power. Since the output current of the photovoltaic optimizer connected in series at the output terminal remains essentially unchanged, and the output power decreases, the output voltage of the photovoltaic optimizer decreases. Consequently, the voltage difference between the input and output voltages decreases, reducing the heat loss of the photovoltaic optimizer and thus lowering its temperature. Furthermore, because the photovoltaic optimizer first reduces its input voltage after overheating, rather than shutting down directly, it can effectively reduce its power generation loss. Moreover, since the photovoltaic optimizer increases its input voltage after its temperature drops below the temperature threshold T1, it can maximize its input power while keeping its temperature below the temperature threshold T1, further effectively reducing the photovoltaic optimizer's power generation loss. Furthermore, since the temperature control of the photovoltaic optimizer in this application adopts closed-loop control, and the input power Pi-input voltage Vi curve of the photovoltaic optimizer is continuous, the input voltage and input current of the photovoltaic optimizer do not jump during the process from triggering thermal derating to restoring MPPT state, thereby improving the stability of the photovoltaic optimizer and thus improving the stability of the power generation system.
[0064] Referring to Figure 8, which is a flowchart illustrating the control method for a photovoltaic optimizer provided in this application, the control method for a photovoltaic optimizer provided in this application is applicable to the photovoltaic optimizer 11 shown in Figures 2 and 3. The control method for the photovoltaic optimizer may include the following steps:
[0065] S101 controls the photovoltaic optimizer to be in MPPT state.
[0066] Specifically, the photovoltaic optimizer adjusts the input voltage of the internal Buck circuit (i.e., the input voltage of the photovoltaic optimizer) to perform MPPT on the output power of the photovoltaic modules, so that the output power of the connected photovoltaic modules is maximized, thus putting the photovoltaic optimizer in MPPT state.
[0067] S102, when the temperature of the photovoltaic optimizer is greater than the temperature threshold T1, control the photovoltaic optimizer to exit the MPPT state and control the input voltage of the photovoltaic optimizer to decrease.
[0068] The temperature of the photovoltaic optimizer refers to its internal temperature, including but not limited to the temperature of the controller, the temperature of key components such as switches or capacitors in the Buck circuit, and the cavity temperature of the photovoltaic optimizer. Furthermore, the temperature threshold T1 is determined by the rated temperature of the device being measured within the photovoltaic optimizer, and is typically close to but lower than the rated temperature of the device being measured.
[0069] Furthermore, based on the input power Pi-input voltage Vi curve of the photovoltaic optimizer, it can be seen that as the input voltage of the photovoltaic optimizer decreases, the input current of the photovoltaic optimizer increases, and the input power of the photovoltaic optimizer decreases.
[0070] S103 controls the input voltage of the photovoltaic optimizer to increase when the temperature of the photovoltaic optimizer is lower than the temperature threshold T1.
[0071] Specifically, as the input voltage of the photovoltaic optimizer decreases, its temperature decreases accordingly. When the photovoltaic optimizer's temperature equals a temperature threshold T1, it maintains a constant input voltage. Conversely, when the photovoltaic optimizer's temperature is below the temperature threshold T1 and its input voltage is less than or equal to a voltage threshold, it increases its input voltage to increase its input power.
[0072] S104 controls the photovoltaic optimizer to re-enter the MPPT state when the input voltage of the photovoltaic optimizer is greater than the voltage threshold.
[0073] Among them, the voltage threshold is positively correlated with the input voltage when the photovoltaic optimizer exits the MPPT state.
[0074] In specific implementation, for more operations performed by the photovoltaic optimizer in the control method of the photovoltaic optimizer provided in this application, please refer to the implementation method performed by the photovoltaic optimizer 11 shown in Figures 2 and 3, which will not be repeated here.
[0075] In this application, when the photovoltaic optimizer experiences overheating, it exits the MPPT state and reduces its input voltage, shifting its operating point to the left of the input power Pi-input voltage Vi curve. This reduces its input power and consequently its output power. Since the output current of the photovoltaic optimizer connected in series at the output terminal remains essentially unchanged, and the output power decreases, the output voltage of the photovoltaic optimizer decreases. Consequently, the voltage difference between the input and output voltages decreases, reducing the heat loss of the photovoltaic optimizer and thus lowering its temperature. Furthermore, because the photovoltaic optimizer first reduces its input voltage after overheating, rather than shutting down directly, it can effectively reduce its power generation loss. Moreover, since the photovoltaic optimizer increases its input voltage after its temperature drops below the temperature threshold T1, it can maximize its input power while keeping its temperature below the temperature threshold T1, further effectively reducing the photovoltaic optimizer's power generation loss.
[0076] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. A power generation system, characterized in that, The power generation system includes an inverter and at least two photovoltaic optimizers. The input terminal of the photovoltaic optimizer is used to connect to photovoltaic modules. The output terminals of the at least two photovoltaic optimizers are connected in series to the input terminal of the inverter. The output terminal of the inverter is used to connect to the power grid or a load. The photovoltaic optimizer includes a BUCK circuit, the input of which is connected to the input of the photovoltaic optimizer, and the output of which is connected to the output of the photovoltaic optimizer. The photovoltaic optimizer is configured to exit the Maximum Power Point Tracking (MPPT) state and control the input voltage of the BUCK circuit to decrease when the temperature of the photovoltaic optimizer is greater than a temperature threshold; control the input voltage of the BUCK circuit to increase when the temperature of the photovoltaic optimizer is less than the temperature threshold; and re-enter the MPPT state when the input voltage of the BUCK circuit is greater than a voltage threshold, wherein the voltage threshold is positively correlated with the input voltage of the BUCK circuit when the photovoltaic optimizer exits the MPPT state.
2. The power generation system according to claim 1, characterized in that, The photovoltaic optimizer is also used to keep the input voltage of the BUCK circuit constant when the temperature of the photovoltaic optimizer is equal to the temperature threshold. The photovoltaic optimizer is used to control the input voltage of the BUCK circuit to increase when the temperature of the photovoltaic optimizer is less than the temperature threshold and the input voltage of the BUCK circuit is less than or equal to the voltage threshold.
3. The power generation system according to claim 1 or 2, characterized in that, When the input voltage of the BUCK circuit decreases, the input current of the BUCK circuit increases.
4. The power generation system according to any one of claims 1-3, characterized in that, When the input voltage of the BUCK circuit decreases, the input power of the BUCK circuit decreases.
5. The power generation system according to any one of claims 1-4, characterized in that, The photovoltaic optimizer also includes a controller; The temperature of the photovoltaic optimizer includes the temperature of the controller and the temperature of the switching transistors or capacitors in the BUCK circuit.
6. A photovoltaic optimizer, characterized in that, The input terminal of the photovoltaic optimizer is used to connect to the photovoltaic module, and the output terminal of the photovoltaic optimizer is used to connect to the input terminal of the inverter after being connected in series with the output terminals of other photovoltaic optimizers. The photovoltaic optimizer includes a BUCK circuit, the input of which is connected to the input of the photovoltaic optimizer, and the output of which is connected to the output of the photovoltaic optimizer. The photovoltaic optimizer is configured to exit the Maximum Power Point Tracking (MPPT) state and control the input voltage of the BUCK circuit to decrease when the temperature of the photovoltaic optimizer is greater than a temperature threshold; control the input voltage of the BUCK circuit to increase when the temperature of the photovoltaic optimizer is less than the temperature threshold; and re-enter the MPPT state when the input voltage of the BUCK circuit is greater than a voltage threshold, wherein the voltage threshold is positively correlated with the input voltage of the BUCK circuit when the photovoltaic optimizer exits the MPPT state.
7. The photovoltaic optimizer according to claim 6, characterized in that, The photovoltaic optimizer is also used to keep the input voltage of the BUCK circuit constant when the temperature of the photovoltaic optimizer is equal to the temperature threshold. The photovoltaic optimizer is used to control the input voltage of the BUCK circuit to increase when the temperature of the photovoltaic optimizer is less than the temperature threshold and the input voltage of the BUCK circuit is less than or equal to the voltage threshold.
8. The photovoltaic optimizer according to claim 6 or 7, characterized in that, When the input voltage of the BUCK circuit decreases, the input current of the BUCK circuit increases.
9. The photovoltaic optimizer according to any one of claims 6-8, characterized in that, When the input voltage of the BUCK circuit decreases, the input power of the BUCK circuit decreases.
10. The photovoltaic optimizer according to any one of claims 6-9, characterized in that, The photovoltaic optimizer also includes a controller; The temperature of the photovoltaic optimizer includes the temperature of the controller and the temperature of the switching transistors or capacitors in the BUCK circuit.
11. A control method for a photovoltaic optimizer, characterized in that, The photovoltaic optimizer is used to connect photovoltaic modules at its input terminal and to the input terminal of an inverter after being connected in series with the output terminals of other photovoltaic optimizers. The photovoltaic optimizer includes a BUCK circuit, the input terminal of which is connected to the input terminal of the photovoltaic optimizer, and the output terminal of which is connected to the output terminal of the photovoltaic optimizer. The method includes: When the temperature of the photovoltaic optimizer exceeds the temperature threshold, the photovoltaic optimizer is controlled to exit the maximum power point tracking (MPPT) state, and the input voltage of the BUCK circuit is controlled to decrease. When the temperature of the photovoltaic optimizer is lower than the temperature threshold, the input voltage of the BUCK circuit is increased. When the input voltage of the BUCK circuit is greater than a voltage threshold, the photovoltaic optimizer is controlled to re-enter the MPPT state, wherein the voltage threshold is positively correlated with the input voltage of the BUCK circuit when the photovoltaic optimizer exits the MPPT state.
12. The method according to claim 11, characterized in that, The method further includes: When the temperature of the photovoltaic optimizer is equal to the temperature threshold, the input voltage of the BUCK circuit remains constant; When the temperature of the photovoltaic optimizer is lower than the temperature threshold, controlling the input voltage of the BUCK circuit to increase includes: When the temperature of the photovoltaic optimizer is less than the temperature threshold and the input voltage of the BUCK circuit is less than or equal to the voltage threshold, the input voltage of the BUCK circuit is controlled to increase.
13. The method according to claim 11 or 12, characterized in that, When the input voltage of the BUCK circuit decreases, the input current of the BUCK circuit increases.
14. The method according to any one of claims 11-13, characterized in that, When the input voltage of the BUCK circuit decreases, the input power of the BUCK circuit decreases.
15. The method according to any one of claims 11-14, characterized in that, The photovoltaic optimizer also includes a controller; The temperature of the photovoltaic optimizer includes the temperature of the controller and the temperature of the switching transistors or capacitors in the BUCK circuit.