Power generation system, photovoltaic optimizer and control method thereof

Abstract

The invention provides a power generation system, photovoltaic optimizers and a control method thereof.The power generation system comprises an inverter and at least two photovoltaic optimizers, the input ends of the photovoltaic optimizers are used for being connected with photovoltaic modules, and the output ends of the at least two photovoltaic optimizers are connected with the input end of the inverter after being connected in series; the output end of the inverter is used for connecting a power grid or a load. The photovoltaic optimizer comprises a BUCK circuit. The photovoltaic optimizer is used for quitting the MPPT state and controlling the input voltage of the BUCK circuit to be reduced under the condition that the temperature of the photovoltaic optimizer is greater than a temperature threshold value; when the temperature of the BUCK circuit is smaller than the temperature threshold value, the input voltage of the BUCK circuit is controlled to be increased, and when the input voltage of the BUCK circuit is larger than the voltage threshold value, the MPPT state is restarted. By adopting the photovoltaic optimizer over-temperature control method and device, under the condition that the photovoltaic optimizer is over-temperature, not only can the temperature of the photovoltaic optimizer be effectively reduced, but also the power generation loss of the photovoltaic optimizer can be effectively reduced.

Description

Technical Field

[0001] The present 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 Art

[0002] PV optimizers are key equipment for increasing the power generation of PV power generation systems. If the temperature is too high, it will cause problems such as unstable operation and easy damage. In order to protect the PV optimizer, most PV optimizers use a protection method of shutting down directly after detecting that the temperature is too high, so that the temperature of the PV optimizer is reduced. However, this protection method will cause a loss of power generation of the PV optimizer. Summary of the invention

[0003] The present application provides a power generation system, a photovoltaic optimizer and a control method thereof, which can effectively reduce not only the temperature of the photovoltaic optimizer but also the power generation loss of the photovoltaic optimizer when the photovoltaic optimizer is overheated.

[0004] In the first aspect, the present application provides a power generation system, which includes an inverter and at least two photovoltaic optimizers, the input end of the photovoltaic optimizer is used to connect the photovoltaic module, the output ends of at least two photovoltaic optimizers are connected in series and connected to the input end of the inverter, and the output end of the inverter is used to connect the power grid or load. The photovoltaic optimizer includes a BUCK circuit, the input end of the BUCK circuit is connected to the input end of the photovoltaic optimizer, and the output end of the BUCK circuit is connected to the output end of the photovoltaic optimizer. The photovoltaic optimizer is used to exit the maximum power point tracking (MPPT) state (i.e., trigger thermal derating) when its own temperature is greater than a temperature threshold, and control the input voltage of the BUCK circuit (i.e., the input voltage of the photovoltaic optimizer) to decrease so that the temperature of the photovoltaic optimizer decreases; when the temperature of the photovoltaic optimizer is less than the temperature threshold, control the input voltage of the BUCK circuit to increase; and when the input voltage of the BUCK circuit is greater than the voltage threshold, 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.

[0005] The photovoltaic optimizer provided in the present application can be understood as a BUCK converter, and the heat loss of the converter (positively correlated with temperature) is mainly determined by the voltage difference between the input voltage and the output voltage of the converter and the size of the output current. Specifically, the smaller the voltage difference between the input voltage and the output voltage of the converter or the output current, the lower the heat loss of the converter. Conversely, the larger the voltage difference between the input voltage and the output voltage of the converter or the output current, the higher the heat loss of the converter. Since the output ends of the multiple photovoltaic optimizers in the power generation system provided in the present application adopt a series connection relationship, and the output current of the photovoltaic optimizer connected in series at the output end is determined by the power generation system, the change in the working state of a single photovoltaic optimizer basically does not affect the output current of the photovoltaic optimizer. Therefore, the method of adjusting the output current of the photovoltaic optimizer cannot reduce the heat loss of the photovoltaic optimizer. Based on this, the photovoltaic optimizer provided by the present application, in the case of overheating, by exiting the MPPT state and reducing its own input voltage, moves its own working point to the left side of the input power Pi-input voltage Vi curve of the photovoltaic optimizer, thereby reducing its own input power to reduce its own output power. Since the output current of the photovoltaic optimizer is basically unchanged, and the output power of the photovoltaic optimizer is reduced, the output voltage of the photovoltaic optimizer can be reduced, so that the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer can be reduced, thereby reducing the heat loss of the photovoltaic optimizer, and achieving the effect of reducing the temperature of the photovoltaic optimizer. In addition, since the photovoltaic optimizer first adopts the method of reducing the input voltage after overheating occurs, rather than directly shutting down, it can also effectively reduce its own power generation loss. Since the photovoltaic optimizer controls its own input voltage to increase after its own temperature drops below the temperature threshold, it can ensure that the temperature of the photovoltaic optimizer is less than the temperature threshold while increasing its own input power as much as possible, so as to further effectively reduce the power generation loss of the photovoltaic optimizer.

[0006] In combination with the first aspect, in a first possible implementation manner, the photovoltaic optimizer is further configured to maintain the input voltage of the BUCK circuit unchanged when its own temperature is equal to the temperature threshold. The photovoltaic optimizer is configured to control the input voltage of the BUCK circuit to increase when its own temperature is less than the temperature threshold and the input voltage of the BUCK circuit is less than or equal to the voltage threshold.

[0007] In this embodiment, when overheating occurs, the photovoltaic optimizer can quickly reduce its own temperature by first exiting the MPPT state and reducing its own input voltage, keep its own input voltage unchanged when its own temperature drops to the temperature threshold, and control its own input voltage to increase when it detects that its own temperature has further dropped. Therefore, not only can the temperature of the photovoltaic optimizer after triggering thermal derating not exceed the temperature threshold, so as to effectively realize over-temperature protection of the photovoltaic optimizer, but also the input power of the photovoltaic optimizer can be increased as much as possible while ensuring that the temperature of the photovoltaic optimizer is less than the temperature threshold, so as to further effectively reduce the power generation loss of the photovoltaic optimizer.

[0008] In combination with the first aspect or the first possible implementation manner of the first aspect, in a second possible implementation manner, when the input voltage of the BUCK circuit decreases, the input current of the BUCK circuit increases.

[0009] In combination with the first aspect to the second possible implementation manner of the first aspect, in a third possible implementation manner, when the input voltage of the BUCK circuit decreases, the input power of the BUCK circuit decreases.

[0010] In combination with the first aspect to the third possible implementation manner of the first aspect, in a fourth possible implementation manner, the photovoltaic optimizer further includes a controller. The temperature of the photovoltaic optimizer includes the temperature of the controller, the temperature of the switch tube or the capacitor in the BUCK circuit.

[0011] 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 internal device triggers thermal derating, and has strong applicability.

[0012] In the second aspect, the present application provides a photovoltaic optimizer, the input end of the photovoltaic optimizer is used to connect the photovoltaic module, and the output end of the photovoltaic optimizer is used to connect to the input end of the inverter after being connected in series with the output end of other photovoltaic optimizers. The photovoltaic optimizer includes a BUCK circuit, the input end of the BUCK circuit is connected to the input end of the photovoltaic optimizer, and the output end of the BUCK circuit is connected to the output end of the photovoltaic optimizer. The photovoltaic optimizer is used to exit the MPPT state when its own temperature is greater than a temperature threshold, and control the input voltage of the BUCK circuit to decrease so that the temperature of the photovoltaic optimizer decreases; when the temperature of the photovoltaic optimizer is less than the temperature threshold, control the input voltage of the BUCK circuit to increase; and re-enter the MPPT state when the input voltage of the BUCK circuit is greater than the 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.

[0013] In combination with the second aspect, in a first possible implementation, the photovoltaic optimizer is further configured to maintain the input voltage of the BUCK circuit unchanged when its own temperature is equal to the temperature threshold. The photovoltaic optimizer is configured to control the input voltage of the BUCK circuit to increase when its own temperature is less than the temperature threshold and the input voltage of the BUCK circuit is less than or equal to the voltage threshold.

[0014] In combination with the second aspect or the first possible implementation manner of the second aspect, in a second possible implementation manner, when the input voltage of the BUCK circuit decreases, the input current of the BUCK circuit increases.

[0015] In combination with the second aspect to the second possible implementation manner of the second aspect, in a third possible implementation manner, when the input voltage of the BUCK circuit decreases, the input power of the BUCK circuit decreases.

[0016] In combination with the second aspect to the third possible implementation manner of the second aspect, in a fourth possible implementation manner, the photovoltaic optimizer further includes a controller. The temperature of the photovoltaic optimizer includes the temperature of the controller, the temperature of the switch tube or the capacitor in the BUCK circuit.

[0017] In the third aspect, the present application provides a control method for a photovoltaic optimizer, which is applied to a photovoltaic optimizer. The input end of the photovoltaic optimizer is used to connect a photovoltaic module, and the output end of the photovoltaic optimizer is used to connect to the input end of the inverter after being connected in series with the output end of other photovoltaic optimizers. The photovoltaic optimizer includes a BUCK circuit, the input end of the BUCK circuit is connected to the input end of the photovoltaic optimizer, and the output end of the BUCK circuit is connected to the output end of the photovoltaic optimizer. The method includes: when the temperature of the photovoltaic optimizer is greater than a temperature threshold, controlling the photovoltaic optimizer to exit the MPPT state, and controlling the input voltage of the BUCK circuit to decrease so that the temperature of the photovoltaic optimizer decreases; when the temperature of the photovoltaic 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 the voltage threshold, controlling the photovoltaic optimizer 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.

[0018] In combination with the third aspect, in a first possible implementation, the photovoltaic optimizer also maintains the input voltage of the BUCK circuit unchanged when its own temperature is equal to the temperature threshold. The photovoltaic optimizer also controls the input voltage of the BUCK circuit to increase when its own temperature is less than the temperature threshold and the input voltage of the BUCK circuit is less than or equal to the voltage threshold.

[0019] In combination with the third aspect or the first possible implementation manner of the third aspect, in a second possible implementation manner, when the input voltage of the BUCK circuit decreases, the input current of the BUCK circuit increases.

[0020] In combination with the third aspect to the second possible implementation manner of the third aspect, in a third possible implementation manner, when the input voltage of the BUCK circuit decreases, the input power of the BUCK circuit decreases.

[0021] In combination with the third aspect to the third possible implementation manner of the third aspect, in a fourth possible implementation manner, the photovoltaic optimizer further includes a controller. The temperature of the photovoltaic optimizer includes the temperature of the controller, the temperature of the switch tube or the capacitor in the BUCK circuit.

[0022] It should be understood that the implementation and beneficial effects of the above-mentioned aspects of the present application can be referenced to each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of an application scenario of the power generation system provided by this application;

[0024] Figure 2 It is a structural schematic diagram of a power generation system provided by the present application;

[0025] Figure 3 is another structural schematic diagram of the power generation system provided by the present application;

[0026] Figure 4 is a waveform diagram of voltage and current of a photovoltaic optimizer provided by the present application;

[0027] Figure 5 is a schematic diagram of a power P-voltage V curve of a photovoltaic optimizer provided in the present application;

[0028] Figure 6 is another waveform diagram of the voltage and current of the photovoltaic optimizer provided by the present application;

[0029] Figure 7 is another waveform diagram of the voltage and current of the photovoltaic optimizer provided by the present application;

[0030] Figure 8 It is a flow chart of the control method of the photovoltaic optimizer provided in this application. DETAILED DESCRIPTION

[0031] The power generation system provided in this application can be applied to various application fields such as photovoltaic power generation, photovoltaic storage hybrid power generation, new energy smart microgrid, power transmission and distribution, etc. The power generation system provided in this application is applicable to different application scenarios, such as photovoltaic power supply scenario, photovoltaic storage hybrid power supply scenario, UPS power supply scenario, etc. The photovoltaic power supply scenario is used as an example for explanation.

[0032] See also Figure 1 , Figure 1 This is a schematic diagram of the application scenario of the power generation system provided by this application. In the photovoltaic power supply scenario, the power generation system provided by this application is Figure 1 The photovoltaic power generation system shown in the figure includes photovoltaic optimizers 11, ..., photovoltaic optimizers 1n and inverter 2, where n is an integer greater than 1. The input end of the photovoltaic optimizer 11 is connected to the photovoltaic assembly 31, ..., the input end of the photovoltaic optimizer 1n is connected to the photovoltaic assembly 3n, the output end of the photovoltaic optimizer 11, ..., the output end of the photovoltaic optimizer 1n is connected in series to the input end of the inverter 2, and the output end of the inverter 2 is connected to the AC power grid or household equipment. The n photovoltaic optimizers all include a BUCK circuit, the input end of the BUCK circuit in each photovoltaic optimizer is connected to the input end of the photovoltaic optimizer in which it is located, and the output end of the BUCK circuit in each photovoltaic optimizer is connected to the output end of the photovoltaic optimizer in which it is located.

[0033] After the photovoltaic power generation system starts to operate, the n photovoltaic optimizers are in the MPPT state. Specifically, the n photovoltaic optimizers adjust their respective input voltages to perform MPPT on the output power of photovoltaic components 31 to 3n, so that the output power of the photovoltaic components connected to each photovoltaic optimizer is maximized. At the same time, the n photovoltaic optimizers also perform DC conversion on the DC power output by the photovoltaic components connected to them, and output the DC power after DC conversion to the input end of the inverter 2. The inverter 2 sequentially boosts and inverts the DC power at its input end to obtain AC power that meets the requirements of the AC power grid, thereby realizing the power supply to various types of electrical equipment such as the AC power grid.

[0034] In the process of n photovoltaic optimizers outputting electric energy to inverter 2, if any photovoltaic optimizer detects that its own temperature is greater than the temperature threshold T1, it means that any photovoltaic optimizer is overheated, and the photovoltaic optimizer exits the MPPT state and controls the input voltage of the internal BUCK circuit to decrease, so as to reduce the temperature of any photovoltaic optimizer that is overheated. Afterwards, if any photovoltaic optimizer that is overheated controls the input voltage of the internal BUCK circuit to increase when its own temperature is less than the temperature threshold T1, and re-enters the MPPT state when the input voltage of the internal BUCK circuit is greater than the voltage threshold. Among them, the voltage threshold is positively correlated with the input voltage of the internal BUCK circuit when any of the above photovoltaic optimizers exits the MPPT state.

[0035] It can be understood that when the photovoltaic optimizer is overheated, it exits the MPPT state and reduces its own input voltage, so that its own operating point moves to the left side of the input power Pi-input voltage Vi curve of the photovoltaic optimizer, thereby reducing its own input power to reduce its own output power. Since the output current of the photovoltaic optimizer connected in series at the output end is basically unchanged, and the output power of the photovoltaic optimizer is reduced, the output voltage of the photovoltaic optimizer can be reduced, so that the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer can be reduced, thereby reducing the heat loss of the photovoltaic optimizer, and achieving the effect of reducing the temperature of the photovoltaic optimizer. In addition, since the photovoltaic optimizer first adopts the method of reducing the input voltage after overheating occurs, rather than directly shutting down, it can also effectively reduce its own power generation loss. Since the photovoltaic optimizer controls its own input voltage to increase after its own temperature drops below the temperature threshold T1, it can ensure that the temperature of the photovoltaic optimizer is less than the temperature threshold T1 while increasing its own input power as much as possible, so as to further effectively reduce the power generation loss of the photovoltaic optimizer.

[0036] The above is only an example of the application scenarios of the power generation system provided by the present application, and is not an exhaustive list. The present application does not limit the application scenarios.

[0037] Combine the following Figures 2 to 7 The working principles of the power generation system and photovoltaic optimizer provided in this application are illustrated.

[0038] See also Figure 2 , Figure 2 Schematic diagram of the power generation system provided by this application. Figure 2 As shown, 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. Among them, the input terminals i111 and i112 of the photovoltaic optimizer 11 are used to connect the photovoltaic module 31, the input terminals i121 and i122 of the photovoltaic optimizer 12 are used to connect the photovoltaic module 32, ..., and the input terminals i1n1 and i1n2 of the photovoltaic optimizer 1n are used to connect the photovoltaic module 3n. The output terminal of the photovoltaic optimizer 11, the output terminal of the photovoltaic optimizer 12, ..., and the output terminal of the photovoltaic optimizer 1n are connected in series and then connected 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. Output terminals o21 and o22 of the inverter 2 are used to connect to a power grid.

[0039] The photovoltaic optimizer in the power generation system can be a converter with a step-down function, such as a Buck converter or a Buck-Boost converter. For ease of description, the photovoltaic optimizer is taken as an example as follows. Figure 3 The power generation system shown is introduced.

[0040] See also Figure 3 , Figure 3 is another structural schematic diagram of the power generation system provided by the present application. Figure 3 As shown, the photovoltaic optimizer 11 includes a Buck circuit 111, a controller 112 and a diode D1, wherein the two input ends of the Buck circuit 111 are respectively connected to the input ends i111 and i112 of the photovoltaic optimizer 11, and the two output ends of the Buck circuit 111 are respectively connected to the output ends o111 and o112 of the photovoltaic optimizer 11; the cathode of the diode D1 is connected to the output end o111 of the photovoltaic optimizer 11, and the anode of the diode D1 is connected to the output end o112 of the photovoltaic optimizer 11. The circuit structures of the photovoltaic optimizers 12 to 1n are the same as the circuit structures of the photovoltaic optimizer 11, and are not repeated here. The inverter 2 includes a Boost circuit 21 and a DC / AC circuit 22, wherein the two input ends of the Boost circuit 21 are respectively connected to the input ends i21 and i22 of the inverter 2, the two output ends of the Boost circuit 21 are respectively connected to the two input ends of the DC / AC circuit 22, and the two output ends of the DC / AC circuit 22 are respectively connected to the output ends o21 and o22 of the inverter 2.

[0041] For ease of understanding, the working principle of over-temperature protection of the photovoltaic optimizer in this application is first introduced here, as follows: the photovoltaic optimizer in the power generation system can be understood as a BUCK converter, and the heat loss of the converter is mainly determined by the voltage difference between the input voltage and the output voltage of the converter and the size of the output current. Specifically, the smaller the voltage difference between the input voltage and the output voltage of the converter or the output current, the lower the heat loss of the converter. Conversely, the larger the voltage difference between the input voltage and the output voltage of the converter or the output current, the higher the heat loss of the converter. Since the output ends of the multiple photovoltaic optimizers in the power generation system provided by this application adopt a series connection relationship, and the output current of the photovoltaic optimizer connected in series at the output end is determined by the power generation system, the change in the working state of a single photovoltaic optimizer basically does not affect the output current of the photovoltaic optimizer. Therefore, the method of adjusting the output current of the photovoltaic optimizer cannot reduce the heat loss of the photovoltaic optimizer. When a photovoltaic optimizer in the power generation system overheats, if the photovoltaic optimizer reduces power by increasing its own input voltage, since the output current of the photovoltaic optimizer connected in series at the output end remains basically unchanged, the output power reduction of the photovoltaic optimizer will reduce the output voltage of the photovoltaic optimizer, thereby increasing the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer, which will increase the heat loss of the photovoltaic optimizer and further increase the temperature of the photovoltaic optimizer. On the contrary, if the photovoltaic optimizer reduces power by reducing its own input voltage, since the output current of the photovoltaic optimizer connected in series at the output end remains basically unchanged, the output power reduction of the photovoltaic optimizer will reduce the output voltage of the photovoltaic optimizer, thereby reducing the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer, which will reduce the heat loss of the photovoltaic optimizer and reduce the temperature of the photovoltaic optimizer to achieve over-temperature protection of the photovoltaic optimizer.

[0042] Since the working principle of each photovoltaic optimizer in the power generation system is the same, for the convenience of description, the photovoltaic optimizer 11 is taken as an example for detailed introduction below.

[0043] In one embodiment, after the photovoltaic optimizer 11 works, the controller 112 performs MPPT on the output power of the photovoltaic assembly 31 by adjusting the input voltage of the Buck circuit 111 (i.e., the input voltage of the photovoltaic optimizer 11), so that the output power of the photovoltaic assembly 31 is maximized, that is, the photovoltaic optimizer 11 is in the MPPT state. At the same time, the controller 112 detects the temperature of the photovoltaic optimizer 11 through at least one temperature sensor in the photovoltaic optimizer 11, and controls the photovoltaic optimizer 11 to exit the MPPT state when the temperature of the photovoltaic optimizer 11 is greater than the temperature threshold T1, and controls the input voltage of the photovoltaic optimizer 11 to decrease, so that the temperature of the photovoltaic optimizer 11 decreases. Afterwards, when the temperature of the photovoltaic optimizer 11 is less than the temperature threshold T1, the controller 112 controls the input voltage of the photovoltaic optimizer 11 to increase, and when the input voltage of the photovoltaic optimizer 11 is greater than the voltage threshold, controls the photovoltaic optimizer 11 to re-enter the MPPT state. Among them, the voltage threshold is positively correlated with the input voltage when the photovoltaic optimizer 11 exits the MPPT state. The temperature sensor includes a negative temperature coefficient thermistor (NTC) or a positive temperature coefficient thermistor (PTC).

[0044] The temperature of the photovoltaic optimizer 11 in the present application 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 switch tube (such as Q1 or Q2) or capacitor (such as C1 or C2) in the Buck circuit 111, the cavity temperature of the photovoltaic optimizer 11, etc. In addition, the temperature threshold T1 in the present application is determined by the rated temperature of the temperature device being measured in the photovoltaic optimizer 11, which is usually close to the rated temperature of the temperature device being measured and lower than the rated temperature of the temperature device being measured. Exemplarily, when the temperature of the photovoltaic optimizer 11 is the temperature of the switch tube 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 capacitor in the Buck circuit 111, the temperature threshold T1 can be 100°C.

[0045] Specifically, when the temperature of the photovoltaic optimizer 11 is greater than the temperature threshold T1, it means that the photovoltaic optimizer 11 is overheated, and 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, so that the temperature of the photovoltaic optimizer 11 is reduced. When the temperature of the photovoltaic optimizer 11 is equal to the temperature threshold T1, the controller 11 keeps the input voltage of the photovoltaic optimizer 11 unchanged. And when the temperature of the photovoltaic optimizer 11 is less than the temperature threshold T1 and the input voltage of the photovoltaic optimizer 11 is less than or equal to the voltage threshold, that is, when it is detected that the temperature of the photovoltaic optimizer 11 has further decreased, the controller 112 controls the input voltage of the photovoltaic optimizer 11 to increase. Afterwards, when the input voltage of the photovoltaic optimizer 11 is greater than the voltage threshold, the controller 112 adjusts the input voltage of the photovoltaic optimizer 11 so that the photovoltaic optimizer 11 re-enters the MPPT state.

[0046] For ease of understanding, the following is an example. Figure 4 A waveform diagram of the voltage and current of the photovoltaic optimizer 11 shown, and Figure 5 The schematic diagram of the power P-voltage V curve of the photovoltaic optimizer 11 is shown to introduce this embodiment.

[0047] like Figure 4 As shown, the three black solid lines from top to bottom respectively represent the input voltage Vi, the output voltage Vo and the input current Ii of the photovoltaic optimizer 11. In the time period from t0 to t1, the photovoltaic optimizer 11 is in the MPPT state.

[0048] At time t1, the ambient temperature rises, and the photovoltaic optimizer 11 detects that its own temperature is greater than the temperature threshold T1. At this time, the input operating point of the photovoltaic optimizer 11 is Figure 5 Since the output terminals of n photovoltaic optimizers in the power generation system are connected in series, the output currents of the n photovoltaic optimizers are the same and fixed. Therefore, the output operating point of the photovoltaic optimizer 11 is always at Figure 5 When the output current I o is constant at I c, the output power Po-output voltage Vo of the photovoltaic optimizer is on the straight line. 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 can be obtained as follows: Figure 5 The photovoltaic optimizer 11 exits the MPPT state from time t1 and enters the power limiting state, and controls the input voltage Vi from v1 (corresponding to Figure 5 The input voltage value corresponding to the input working point b1 (40V) starts to decrease, and correspondingly, the input current I i of the photovoltaic optimizer 11 starts to increase, and the output voltage Vo of the photovoltaic optimizer 11 starts to increase from v2 (corresponding to Figure 5The output voltage value (26V) corresponding to the output working point c1 decreases. Here, in the power limiting state, the output power of the photovoltaic optimizer 11 is less than the maximum output power of the photovoltaic optimizer 11.

[0049] In the time period from t1 to t2, as the ambient temperature continues to rise, the temperature of the photovoltaic optimizer 11 is still greater than the temperature threshold T1, and the photovoltaic optimizer 11 continues to control the input voltage Vi to decrease. Correspondingly, the input current I i 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 is still in a power-limited state. Similarly, in the time period from t1 to t2, as the photovoltaic optimizer 11 controls its input voltage Vi, the change of the working point of the photovoltaic optimizer 11 can be understood as follows: the input working point of the photovoltaic optimizer 11 changes along Figure 5 The input power Pi-input voltage Vi curve of the photovoltaic optimizer 11 shown in FIG. 1 moves to the left from the input operating point b1, and the output operating point of the photovoltaic optimizer 11 moves along Figure 5 When the output current I o is constant at I c, the output power Po-output voltage Vo straight line of the photovoltaic optimizer moves to the left from the output operating point c1. Obviously, based on Figure 5 It can be seen that as the input voltage of the photovoltaic optimizer 11 continues to decrease, the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer 11 continues to decrease from ΔV1 (ie 40V-26V=14V), so the heat loss of the photovoltaic optimizer 11 continues to decrease.

[0050] At time t2, the input voltage Vi of the photovoltaic optimizer 11 is v3 (corresponding to Figure 5 The input voltage value corresponding to the input working point b2 is 21V), and the output voltage Vo of the photovoltaic optimizer 11 is v4 (corresponding to Figure 5 The input voltage value corresponding to the output working point c2 is 14.4V), the temperature of the photovoltaic optimizer 11 is reduced to the temperature threshold T1, and the ambient temperature no longer increases, and the input voltage Vi of the photovoltaic optimizer 11 remains unchanged. Figure 5 It can be seen that 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). Figure 5 It can be seen that 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 is no longer b2, but becomes b3. Therefore, it can be seen that the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer 11 at time t2 becomes ΔV3. Obviously, ΔV3 is greater than ΔV1. Therefore, it can be seen that the method of using the input voltage Vi for over-temperature protection will cause the heat loss of the photovoltaic optimizer 11 to continue to increase, and the temperature of the photovoltaic optimizer 11 will not be reduced, but will further rise.

[0051] During the time period from t2 to t3, the ambient temperature no longer rises and remains stable, the temperature of the PV optimizer 11 remains at the temperature threshold T1, and the input voltage Vi of the PV optimizer 11 continues to remain unchanged, so that the PV optimizer 11 maintains stable operation in the same power limiting state as at time t2.

[0052] At time t3, the ambient temperature begins to decrease, and the temperature of the PV optimizer 11 decreases as the ambient temperature decreases, that is, the temperature of the PV optimizer 11 is less than the temperature threshold T1, and the PV optimizer 11 begins to control the input voltage Vi to increase, so that its input power begins to increase.

[0053] During the period from t3 to t4, the ambient temperature continues to drop, and the temperature of the PV optimizer 11 decreases as the ambient temperature drops. While ensuring that its own temperature is less than the temperature threshold T1, the PV optimizer 11 continues to increase the input voltage Vi, so that its input power continues to increase.

[0054] 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 limit state and re-enters the MPPT state. The voltage threshold Vth is positively correlated with the input voltage value v1 when the photovoltaic optimizer 11 exits the MPPT state, specifically Vth=k*v1+b, and k=1.

[0055] It can be understood that when overheating occurs, the photovoltaic optimizer 11 can quickly reduce its own temperature by first exiting the MPPT state and reducing its own input voltage, and keep its own input voltage unchanged when its own temperature drops to the temperature threshold T1, and control its own input voltage to increase when it detects that its own temperature has further dropped. Therefore, not only can the temperature of the photovoltaic optimizer 11 after triggering thermal derating not exceed the temperature threshold T1, so as to effectively realize over-temperature protection of the photovoltaic optimizer 11, but also the input power of the photovoltaic optimizer 11 can be increased as much as possible while ensuring that the temperature of the photovoltaic optimizer 11 is less than the temperature threshold T1, so as to further effectively reduce the power generation loss of the photovoltaic optimizer 11, thereby further effectively reducing the power generation loss of the power generation system.

[0056] It should be noted that Figure 4 In the embodiment shown, the value of k can also be greater than 0 and less than 1. For details, see Figure 6 Another waveform diagram of the voltage and current of the photovoltaic optimizer 11 shown; Figure 4 In the embodiment shown, the value of k can also be greater than 1. For details, see Figure 7 Another waveform diagram of the voltage and current of the photovoltaic optimizer 11 is shown. Here, Figure 6 and Figure 7 The embodiment shown is Figure 4Compared with the embodiment shown in the figure, the only difference is that the value of k is different, and other parts are similar and will not be repeated here.

[0057] In addition, in the above embodiment, the photovoltaic optimizer 11 reduces its own temperature by exiting the MPPT state and reducing its own input voltage. However, the effect is not ideal in some extreme cases. In this case, it is necessary to shut down in time to achieve over-temperature protection for the photovoltaic optimizer 11, as follows:

[0058] In one 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. Afterwards, when the temperature of the photovoltaic optimizer 11 is greater than the temperature threshold T2, it means that the ambient temperature is too high, causing the temperature of the photovoltaic optimizer 11 to increase instead of decrease as the input voltage decreases. Then the controller 112 controls the Buck circuit 111 to stop working, that is, controls the switch tubes Q1 and Q2 in the Buck circuit 111 to turn off, so that the Buck circuit 111 is bypassed by the diode D1, and thus does not affect 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. Among them, the temperature threshold T2 is greater than the temperature threshold T1.

[0059] It is understandable that the photovoltaic optimizer 11 should be shut down in time when it detects that its own temperature has not decreased with the decrease of the input voltage, or even continues to rise, so that the photovoltaic optimizer 11 can reduce its own temperature in the fastest cooling method when the ambient temperature is too high, so as to achieve over-temperature protection for the photovoltaic optimizer 11. In addition, when the temperature of the photovoltaic optimizer 11 is too high, the photovoltaic optimizer 11 adopts the method of first reducing the input power and then shutting down. Compared with the method of directly shutting down, it can effectively reduce the power generation loss of the photovoltaic optimizer 11, thereby effectively reducing the power generation loss of the power generation system.

[0060] 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 the same as the output current, and the temperature of the photovoltaic optimizer 11 is still greater than the temperature threshold T1 and less than or equal to the temperature threshold T2, since the input current of the photovoltaic optimizer 11 is the same as the output current, the photovoltaic optimizer 11 is in the direct-through mode, and the heat loss of the photovoltaic optimizer in the direct-through mode is the lowest, and the temperature of the photovoltaic optimizer 11 in the direct-through mode is still greater than the temperature threshold T1, indicating that the ambient temperature is too high, then the controller 112 controls the photovoltaic optimizer 11 to remain in the direct-through mode, specifically, the switch tube Q1 in the Buck circuit 111 is controlled to remain normally on. When the temperature of the photovoltaic optimizer 11 is greater than the temperature threshold T2, it means that the temperature of the photovoltaic optimizer 11 cannot be reduced even in the pass-through mode, and 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.

[0061] It is understandable that when the photovoltaic optimizer 11 detects that its temperature has not decreased when it is in the direct mode, and even continues to rise to above the temperature threshold T2, it indicates that the ambient temperature is too high, and it will shut down in time to reduce its own temperature in the fastest way to achieve over-temperature protection for the photovoltaic optimizer 11. In addition, when the temperature of the photovoltaic optimizer 11 is too high, the photovoltaic optimizer 11 adopts the method of reducing the input power first and then shutting down. Compared with the direct shutdown method, it can effectively reduce the power generation loss of the photovoltaic optimizer 11, thereby effectively reducing the power generation loss of the power generation system.

[0062] In the present application, when the photovoltaic optimizer is overheated, it exits the MPPT state and reduces its own input voltage, so that its own operating point moves to the left side of the input power Pi-input voltage Vi curve of the photovoltaic optimizer, thereby reducing its own input power to reduce its own output power. Since the output current of the photovoltaic optimizer connected in series at the output end is basically unchanged, and the output power of the photovoltaic optimizer is reduced, the output voltage of the photovoltaic optimizer can be reduced, so that the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer can be reduced, thereby reducing the heat loss of the photovoltaic optimizer, and achieving the effect of reducing the temperature of the photovoltaic optimizer. In addition, since the photovoltaic optimizer first adopts the method of reducing the input voltage after overheating occurs, rather than directly shutting down, it can also effectively reduce its own power generation loss. Since the photovoltaic optimizer controls its own input voltage to increase after its own temperature drops below the temperature threshold T1, it can ensure that the temperature of the photovoltaic optimizer is less than the temperature threshold T1 while increasing its own input power as much as possible, so as to further effectively reduce the power generation loss of the photovoltaic optimizer. 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 the MPPT state, thereby improving the stability of the photovoltaic optimizer and further improving the stability of the power generation system.

[0063] See also Figure 8 , Figure 8 The control method of the photovoltaic optimizer provided in the present application is applicable to Figure 2 and Figure 3 The photovoltaic optimizer 11 shown. The control method of the photovoltaic optimizer may include the steps of:

[0064] S101, controlling the photovoltaic optimizer to be in MPPT state.

[0065] Specifically, the photovoltaic optimizer adjusts the input voltage of the internal Buck circuit (ie, the input voltage of the photovoltaic optimizer) to perform MPPT on the output power of the photovoltaic module, so that the output power of the photovoltaic module connected to it is maximized, so that the photovoltaic optimizer is in the MPPT state.

[0066] 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.

[0067] The temperature of the photovoltaic optimizer refers to the internal temperature of the photovoltaic optimizer, including but not limited to the temperature of the controller, the temperature of key components such as the switch tube or capacitor in the Buck circuit, the cavity temperature of the photovoltaic optimizer, etc. In addition, the temperature threshold T1 is determined by the rated temperature of the temperature device being measured in the photovoltaic optimizer, and is usually close to the rated temperature of the temperature device being measured and lower than the rated temperature of the temperature device being measured.

[0068] In addition, 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.

[0069] S103 , when the temperature of the photovoltaic optimizer is less than the temperature threshold T1 , controlling the input voltage of the photovoltaic optimizer to increase.

[0070] Specifically, when the input voltage of the photovoltaic optimizer decreases, the temperature of the photovoltaic optimizer decreases as the input voltage decreases. When the temperature of the photovoltaic optimizer is equal to the temperature threshold T1, the photovoltaic optimizer keeps its input voltage unchanged. And when the temperature of the photovoltaic optimizer is less than the temperature threshold T1 and the input voltage of the photovoltaic optimizer is less than or equal to the voltage threshold, the photovoltaic optimizer increases its input voltage to increase its input power.

[0071] S104, when the input voltage of the photovoltaic optimizer is greater than the voltage threshold, controlling the photovoltaic optimizer to re-enter the MPPT state.

[0072] Among them, the voltage threshold is positively correlated with the input voltage when the photovoltaic optimizer exits the MPPT state.

[0073] In a specific implementation, more operations performed by the photovoltaic optimizer in the control method of the photovoltaic optimizer provided in this application can be found in Figure 2 and Figure 3 The implementation method performed by the photovoltaic optimizer 11 shown is not repeated here.

[0074] In the present application, when the photovoltaic optimizer is overheated, it exits the MPPT state and reduces its own input voltage, so that its own operating point moves to the left side of the input power Pi-input voltage Vi curve of the photovoltaic optimizer, thereby reducing its own input power to reduce its own output power. Since the output current of the photovoltaic optimizer connected in series at the output end is basically unchanged, and the output power of the photovoltaic optimizer is reduced, the output voltage of the photovoltaic optimizer can be reduced, so that the voltage difference between the input voltage and the output voltage of the photovoltaic optimizer can be reduced, thereby reducing the heat loss of the photovoltaic optimizer, and achieving the effect of reducing the temperature of the photovoltaic optimizer. In addition, since the photovoltaic optimizer first adopts the method of reducing the input voltage after overheating occurs, rather than directly shutting down, it can also effectively reduce its own power generation loss. Since the photovoltaic optimizer controls its own input voltage to increase after its own temperature drops below the temperature threshold T1, it can ensure that the temperature of the photovoltaic optimizer is less than the temperature threshold T1 while increasing its own input power as much as possible, so as to further effectively reduce the power generation loss of the photovoltaic optimizer.

[0075] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A power generation system, characterized in that: The power generation system comprises an inverter and at least two photovoltaic optimizers, the input end of the photovoltaic optimizer is used to connect to the photovoltaic module, the output ends of the at least two photovoltaic optimizers are connected in series to the input end of the inverter, and the output end of the inverter is used to connect to the power grid or load; The photovoltaic optimizer comprises a BUCK circuit, the input end of the BUCK circuit is connected to the input end of the photovoltaic optimizer, and the output end of the BUCK circuit is connected to the output end of the photovoltaic optimizer; The photovoltaic optimizer is used 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 further used to keep the input voltage of the BUCK circuit unchanged when the temperature of the photovoltaic optimizer is equal to the temperature threshold; The photovoltaic optimizer is used for controlling 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 to 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 to 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 switch tube or capacitor in the BUCK circuit.

6. A photovoltaic optimizer, characterized in that: The input end of the photovoltaic optimizer is used to connect to the photovoltaic module, and the output end of the photovoltaic optimizer is used to be connected in series with the output end of other photovoltaic optimizers and then connected to the input end of the inverter; The photovoltaic optimizer comprises a BUCK circuit, the input end of the BUCK circuit is connected to the input end of the photovoltaic optimizer, and the output end of the BUCK circuit is connected to the output end of the photovoltaic optimizer; The photovoltaic optimizer is used 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 further used to keep the input voltage of the BUCK circuit unchanged when the temperature of the photovoltaic optimizer is equal to the temperature threshold; The photovoltaic optimizer is used for controlling 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 to 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 to 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 switch tube or capacitor in the BUCK circuit.

11. A control method for a photovoltaic optimizer, characterized in that: Applied to the photovoltaic optimizer, the input end of the photovoltaic optimizer is used to connect the photovoltaic module, and the output end of the photovoltaic optimizer is used to be connected in series with the output end of other photovoltaic optimizers and then connected to the input end of the inverter; the photovoltaic optimizer includes a BUCK circuit, the input end of the BUCK circuit is connected to the input end of the photovoltaic optimizer, and the output end of the BUCK circuit is connected to the output end of the photovoltaic optimizer; The method comprises: When the temperature of the photovoltaic optimizer is greater than a temperature threshold, controlling the photovoltaic optimizer to exit a maximum power point tracking (MPPT) state, and controlling the input voltage of the BUCK circuit to decrease; When the temperature of the photovoltaic optimizer is lower than the temperature threshold, controlling the input voltage of the BUCK circuit to increase; 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 comprises: When the temperature of the photovoltaic optimizer is equal to the temperature threshold, maintaining the input voltage of the BUCK circuit unchanged; When the temperature of the photovoltaic optimizer is less than the temperature threshold, controlling the input voltage of the BUCK circuit to increase includes: When the temperature of the photovoltaic optimizer is lower than the temperature threshold and the input voltage of the BUCK circuit is lower 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 to 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 to 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 switch tube or capacitor in the BUCK circuit.

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