Power conversion device

Abstract

The invention discloses power conversion equipment, and belongs to the technical field of photovoltaic control. The controller can control the DC conversion circuit to disconnect the output end of the photovoltaic cell from the common end of the photovoltaic cell, and obtain a first input voltage of the input end of the DC conversion circuit. And the controller can control the direct-current conversion circuit to short-circuit the output end of the photovoltaic cell and the common end of the photovoltaic cell, and obtain the input current of the input end of the direct-current conversion circuit. The controller then estimates a maximum output power of the photovoltaic cell based on the first input voltage and the input current. According to the invention, the maximum output power of the photovoltaic cell in various scenes can be obtained.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic control technology, and in particular to a power conversion device. Background Art

[0002] With the rapid development of new energy technologies, the use of photovoltaic cells to power loads has become a trend. Before using a photovoltaic cell to power a load, it is necessary to first evaluate the cell's load capacity. When the cell's load capacity indicates that it can support the load, the cell is connected to the load and powered by the cell. The cell's load capacity can be reflected by its maximum output power. For example, if the cell's maximum output power exceeds the load's operating power, the cell's load capacity is sufficient to support the load.

[0003] Currently, the mainstream method for estimating the maximum output power is to perform the calculation while the photovoltaic cell is supplying power to the load. For example, a controller scans the output voltage and output current of the photovoltaic cell while the photovoltaic cell is supplying power to the load. During the scan, the controller controls the photovoltaic cell to output a voltage of a specified amplitude and obtains the output current when the photovoltaic cell outputs the specified voltage. After the scan is completed, the maximum output power is determined based on the photovoltaic cell's voltage of the specified amplitude and the corresponding output current.

[0004] Since photovoltaic cells are required to supply power to the load during the current estimation process, the applicability of this estimation scheme is limited. Summary of the Invention

[0005] This application provides a power conversion device. This application can obtain the maximum output power of photovoltaic cells in various scenarios. The technical solutions provided by this application are as follows:

[0006] In a first aspect, the present application provides a power conversion device. The power conversion device includes a controller and a DC conversion circuit. The control end of the DC conversion circuit is used to connect to the controller. The input end of the DC conversion circuit is used to connect to the output end of a photovoltaic cell. The output end of the DC conversion circuit is used to connect to a load. Alternatively, the output end of the DC conversion circuit is used to connect to a load through an inverter circuit. The controller is used to: control the DC conversion circuit to disconnect the output end of the photovoltaic cell from the common end of the photovoltaic cell, and obtain a first input voltage at the input end of the DC conversion circuit; control the DC conversion circuit to short-circuit the output end of the photovoltaic cell with the common end of the photovoltaic cell, and obtain an input current at the input end of the DC conversion circuit; and estimate the maximum output power of the photovoltaic cell based on the first input voltage and input current.

[0007] In this implementation, the first input voltage is obtained when the output terminal of the photovoltaic cell is disconnected from the common terminal of the photovoltaic cell, and the input current is obtained when the output terminal of the photovoltaic cell is short-circuited with the common terminal of the photovoltaic cell. The disconnection and short-circuiting are achieved without relying on the control of the voltage control loop and current control loop of the power conversion device. Therefore, this implementation for obtaining the maximum output power of the photovoltaic cell is applicable to scenarios where the voltage control loop and current control loop of the power conversion device are inoperative, such as scenarios where the power conversion device is in standby mode, not connected to the grid during startup, or not loaded. This overcomes the limitation that the maximum output power of the photovoltaic cell can only be estimated while the photovoltaic cell is supplying power to the load. Furthermore, this implementation is not limited to such scenarios. For example, because the implementation principle of this implementation is relatively simple, fewer operations are required on the power conversion device, and its execution process is very fast, with negligible impact on the load, this implementation can also obtain the maximum output power of the photovoltaic cell while the power conversion device is supplying power to the load.

[0008] The first input voltage used to obtain the maximum output power of the photovoltaic cell is the input voltage at the input of the DC converter circuit when the output of the photovoltaic cell is disconnected from the common terminal of the photovoltaic cell. The input current used to obtain the maximum output power is the input current at the input of the DC converter circuit when the output of the photovoltaic cell is short-circuited to the common terminal of the photovoltaic cell. The first input voltage and the input current reflect the output performance of the photovoltaic cell under ideal operating conditions. For example, the product of the first input voltage and the input current is the ideal output power of the photovoltaic cell under ideal operating conditions. There is a gap between the ideal output power and the maximum output power of the photovoltaic cell. The degree to which the maximum output power approaches the ideal output power can be represented by the fill factor of the photovoltaic cell. In one possible implementation, the controller is configured to: obtain the fill factor of the photovoltaic cell, which indicates the degree to which the maximum output power approaches the ideal output power of the photovoltaic cell; and estimate the maximum output power based on the fill factor, the first input voltage, and the input current. For example, the maximum output power is the product of the fill factor, the first input voltage, and the input current.

[0009] In a possible implementation, the DC conversion circuit includes a switching device, the control end of the switching device is the control end of the DC conversion circuit, and the controller is used to provide a pulse signal to the control end of the switching device so that the output end of the photovoltaic cell is short-circuited with the common end of the photovoltaic cell or

[0010] The first input voltage can be considered the output voltage of the photovoltaic cell. Since the output voltage of a photovoltaic cell is positively correlated with its output power, when the output voltage of the photovoltaic cell is low, its output power is also low. Therefore, only when the first input voltage is greater than a first voltage threshold can the photovoltaic cell's load-carrying capacity be sufficient to support the load. Only then is it necessary to continue to obtain the photovoltaic cell's maximum output power and, based on this maximum output power, determine whether to use a power conversion device to supply power to the load. In one possible implementation, the controller is configured to control the DC conversion circuit to short-circuit the output terminal of the photovoltaic cell with the common terminal of the photovoltaic cell when the first input voltage is greater than the first voltage threshold.

[0011] To minimize the impact on the load during the process of obtaining the maximum output power, the scheme for obtaining the maximum output power needs to meet certain conditions in different scenarios. The following examples illustrate these conditions.

[0012] In one possible implementation, in response to a load being connected to the output terminal of the DC converter circuit via the inverter circuit, the controller is configured to: during the process of obtaining the first input voltage and input current, stop obtaining the output current and output voltage of the output terminal of the DC converter circuit, or stop controlling the operating state of the inverter circuit based on the output current and output voltage of the output terminal of the DC converter circuit. If the controller satisfies this condition during the process of obtaining the first input voltage and input current, the AC power provided by the inverter circuit to the AC load is ensured to be unaffected by the process of obtaining the maximum output power.

[0013] In one possible implementation, while the controller is acquiring the first input voltage and input current, the output end of the DC converter circuit does not supply power to the load. In this case, regardless of the operating mode of the power conversion device, the power conversion device does not output electrical energy to the load, and therefore does not affect the load. In one implementation, the output end of the DC converter circuit does not supply power to the load, which can manifest in the following situations: when the inverter circuit is used to connect to an AC load, the output end of the inverter circuit is disconnected from the AC load; when the DC converter circuit is used to connect to a DC load, the output end of the DC converter circuit is disconnected from the DC load.

[0014] In a second aspect, the present application provides a power conversion device. The power conversion device includes a controller and a DC conversion circuit. The control end of the DC conversion circuit is used to connect to the controller. The input end of the DC conversion circuit is used to connect to the output end of the photovoltaic cell. The output end of the DC conversion circuit is used to connect to a load. Alternatively, the output end of the DC conversion circuit is used to connect to a load through an inverter circuit. The controller is used to: after the power conversion device is powered on, send multiple pulse signals with different duty cycles to the DC conversion circuit to change the output current and output voltage of the DC conversion circuit, and multiple times collect the input current and first input voltage of the input end of the DC conversion circuit; based on the multiple collected first input voltage and input current, obtain the maximum output power of the photovoltaic cell.

[0015] In this implementation, the first input voltage and input current are obtained during the process of changes in the output current and output voltage of the DC conversion circuit. This change is generated by the action of multiple pulse signals sent by the controller, and the generation of these multiple pulse signals does not rely on the control of the voltage control loop and current control loop of the power conversion device. Therefore, this implementation scheme for obtaining the maximum output power of the photovoltaic cell is applicable to scenarios where the voltage control loop and current control loop of the power conversion device are inoperative, such as scenarios where the power conversion device is in standby mode, not connected to the grid during startup, or not loaded. This can overcome the limitation that the maximum output power of the photovoltaic cell can only be estimated during the process of the photovoltaic cell supplying power to the load. In addition, this implementation scheme is not limited to application in such scenarios. For example, because the implementation principle of this implementation scheme is relatively simple, it requires fewer operations to be performed on the power conversion device, its execution process is very fast, and the impact on the load is negligible. Therefore, this implementation scheme can also obtain the maximum output power of the photovoltaic cell during the process of the power conversion device supplying power to the load.

[0016] In one possible implementation, the controller is used to obtain the power corresponding to the i-th time based on the input current and the first input voltage collected for the i-th time in multiple times, and determine the maximum value of the multiple corresponding powers as the maximum output power, where i is a positive integer.

[0017] In a possible implementation, the duty cycles of the multiple pulse signals increase sequentially.

[0018] After the controller provides a pulse signal to the DC conversion circuit, under the control of the pulse signal, the electrical energy output by the photovoltaic cell is transferred from the input end of the DC conversion circuit to the output end of the DC conversion circuit. As the charging process progresses, the first input voltage at the input end of the DC conversion circuit decreases, and the first output voltage at the output end of the DC conversion circuit increases. However, because the photovoltaic cell 01 and the power conversion device 02 rely on this first input voltage to maintain normal operation, the controller needs to control the decrease in the first input voltage when providing the pulse signal to the DC conversion circuit. Similarly, if the first output voltage is too high, it will affect the safety of the components in the power conversion device 02. Therefore, when providing the pulse signal to the DC conversion circuit, the controller also needs to control the increase in the first output voltage. In one possible implementation, the controller is further configured to stop sending the pulse signal to the DC conversion circuit when the first input voltage is less than or equal to a second voltage threshold and / or when the output voltage at the output end of the DC conversion circuit is greater than or equal to a third voltage threshold.

[0019] In one possible implementation, the controller is also used to obtain a second input voltage at the input end of the DC conversion circuit when the DC conversion circuit disconnects the output end of the photovoltaic cell from the common end of the photovoltaic cell; the controller is used to send multiple pulse signals with different duty cycles to the power conversion device when the second input voltage is greater than a fourth voltage threshold, so as to change the output current and output voltage of the DC conversion circuit.

[0020] In one possible implementation, in response to the output end of the DC conversion circuit being connected to a load through the inverter circuit, the controller is used to: stop obtaining the output current and output voltage of the output end of the DC conversion circuit during the process of the controller obtaining the first input voltage and input current, or stop controlling the working state of the inverter circuit based on the output current and output voltage of the output end of the DC conversion circuit.

[0021] In a possible implementation, when the controller obtains the first input voltage and the input current, the output end of the DC conversion circuit does not supply power to the load.

[0022] In a third aspect, the present application provides a photovoltaic system, comprising a photovoltaic cell and a power conversion device provided in the first aspect, the second aspect, and any possible implementation thereof of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of a photovoltaic power station providing power to an AC load, as provided in an embodiment of the present application;

[0024] Figure 2 This is a schematic structural diagram of an implementation scenario involving a power conversion device provided in an embodiment of the present application;

[0025] Figure 3 This is a structural diagram of an implementation scenario involving another power conversion device provided in an embodiment of the present application;

[0026] Figure 4 This is a structural diagram of another implementation scenario involving a power conversion device provided in an embodiment of the present application;

[0027] Figure 5 This is a flow chart of a first implementation scheme for obtaining the maximum output power of a photovoltaic cell by a power conversion device provided in an embodiment of the present application;

[0028] Figure 6 This is a schematic diagram of a Boost circuit, a DC conversion circuit provided in an embodiment of the present application;

[0029] Figure 7 This is a flow chart of a first implementation scheme for obtaining the maximum output power of a photovoltaic cell using another power conversion device provided in an embodiment of the present application;

[0030] Figure 8 This is a flow chart for estimating the maximum output power of a photovoltaic cell provided in an embodiment of the present application;

[0031] Figure 9 This is a volt-ampere characteristic curve of a photovoltaic cell provided in an embodiment of the present application;

[0032] Figure 10 This is a schematic diagram of providing a pulse signal to a DC / DC Boost conversion circuit in a two-stage photovoltaic inverter according to an embodiment of the present application;

[0033] Figure 11 is a schematic diagram of a simulation waveform provided in an embodiment of the present application;

[0034] Figure 12 is a schematic diagram of a power-voltage characteristic provided in an embodiment of the present application;

[0035] Figure 13 This is a flow chart of a second implementation scheme for obtaining the maximum output power of a photovoltaic cell by a power conversion device provided in an embodiment of the present application;

[0036] Figure 14 This is a schematic diagram of providing multiple pulse signals to a Boost circuit according to an embodiment of the present application;

[0037] Figure 15 is a schematic diagram showing the change in duty cycle of a pulse sequence over time provided by an embodiment of the present application;

[0038] Figure 16This is a flow chart of a second implementation scheme for obtaining the maximum output power of a photovoltaic cell using another power conversion device provided in an embodiment of the present application;

[0039] Figure 17 This is a flow chart of obtaining the maximum output power of a photovoltaic cell provided by an embodiment of the present application;

[0040] Figure 18 This is a schematic diagram of an actual volt-ampere characteristic curve provided in an embodiment of the present application;

[0041] Figure 19 is a schematic diagram of another simulation waveform provided in an embodiment of the present application;

[0042] Figure 20 This is a schematic diagram of a photovoltaic volt-ampere characteristic curve reproduced using sampled data provided in an embodiment of the present application;

[0043] Figure 21 This is a schematic diagram of providing a pulse sequence to a DC / DC Boost conversion circuit in a two-stage photovoltaic inverter provided by an embodiment of the present application. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0045] To facilitate understanding, the technology and background involved in the embodiments of this application are explained below.

[0046] With the rapid development of new energy technologies, using renewable energy power stations to supply loads has become a trend. These power stations can serve as a primary source of power for loads or as a supplement to the power supply. For example, when both a renewable energy power station and the AC grid supply power to loads, the renewable energy power station can supplement the AC grid. In another example, after a power outage, a renewable energy power station can serve as a black start power source, or as a supplement to the black start power source, driving other power sources in the system to start up, thereby improving the reliability, power supply guarantee, and emergency response capabilities of the power supply system. Black starts are an effective measure to ensure power restoration. A black start occurs when, after a power outage, self-starting generators in the system are started without relying on external power sources. This activates generators without self-starting capabilities, gradually expanding the scope of the power supply system's recovery and ultimately restoring the entire system. When conventional black start power sources, such as hydropower and gas-fired units, are unavailable, using renewable energy power stations to achieve black starts can effectively alleviate the pressure on the power grid during sudden large-scale power outages, enhance the resilience of regional power grids, broaden the application prospects of renewable energy power generation, and pave the way for the development of grid-friendly renewable energy generators.

[0047] A new energy power station is, for example, a photovoltaic power station. Figure 1 This is a schematic diagram of a photovoltaic power station providing power to an AC load according to an embodiment of the present application. Figure 1 As shown, the photovoltaic inverter device includes a controller, a DC conversion circuit, and an inverter circuit. The input of the DC conversion circuit is connected to the output of the photovoltaic cell, and the output of the DC conversion circuit is connected to the input of the inverter circuit. The output of the inverter circuit is connected to the load via an AC circuit breaker. The control terminals of the DC conversion circuit and the inverter circuit are both connected to the controller. When the photovoltaic power station includes multiple photovoltaic cells connected in parallel, the photovoltaic inverter device includes multiple DC conversion circuits, with the multiple photovoltaic cells corresponding to the multiple DC conversion circuits. When the photovoltaic inverter device supplies power to the load, the operating states of the DC conversion circuit and the inverter circuit are controlled by the controller. The controller controls the operating state of the DC conversion circuit by providing a pulse-width modulation (PWM) signal to the control terminal of the DC conversion circuit. The duty cycle of the PWM signal is determined based on the output voltage and output current of the photovoltaic cell. This control process involves the controller controlling the operating state of the DC conversion circuit through a voltage control loop and a current control loop. The controller controls the operating state of the inverter circuit by providing a corresponding PWM signal to the control terminal of the inverter circuit. The duty cycle of the PWM signal is determined according to the output current and output voltage of the DC converter circuit. The control process is the process in which the controller controls the working state of the inverter circuit through the voltage control loop and the current control loop.

[0048] When the load capacity of the PV power station connected to the PV inverter meets the startup conditions, the AC circuit breaker closes, and the PV inverter transitions from standby mode to operational mode, enabling loaded operation. The standby state refers to a state where the PV inverter is powered on and the switches in the power conversion equipment are operational, but the voltage and current control loops of the PV inverter are not yet functional. The load capacity of a PV power station can be reflected by the maximum output power of the PV cells. For example, in a scenario where a PV power station drives an AC grid black start, when the maximum output power of the PV cells in the PV station exceeds the set startup threshold, it indicates that the load capacity of the PV cells is sufficient to start the relevant power supply equipment in the AC grid. At this point, the PV inverter can transition to operational mode, supplying PV cell power to the AC grid and AC loads, thereby restoring the AC grid and supplying power to the AC loads. Therefore, accurately estimating the maximum output power is crucial. When the maximum output power is estimated inaccurately, even if the photovoltaic inverter device is switched to operating mode, the photovoltaic power station may be unable to bear the load and the photovoltaic inverter device may need to be switched back to non-operating mode, resulting in the need to repeatedly start and stop the photovoltaic inverter device. Starting and stopping the photovoltaic inverter device is achieved by opening and closing the AC circuit breaker. Repeated starting and stopping of the photovoltaic inverter device requires frequent opening and closing of the AC circuit breaker, which will affect the life of the AC circuit breaker. Although it is possible to avoid repeated starting and stopping of the photovoltaic inverter device by reducing the start-stop frequency of the photovoltaic inverter device, this may reduce the power generation of the photovoltaic cell and affect the energy utilization rate. This problem is particularly prominent in microgrid systems and independent photovoltaic power generation systems with high solar-to-energy ratios.

[0049] Currently, methods for estimating the maximum output power of a photovoltaic power station mainly include perturbation, scanning, and model methods. The perturbation method requires periodically enabling the maximum output power tracking algorithm of the photovoltaic inverter device, causing the photovoltaic cell to periodically operate at its maximum output power point while simultaneously monitoring the output power of the photovoltaic cell to determine the maximum output power of the photovoltaic cell. This method relies on the photovoltaic inverter's current and voltage control loops to control the operating states of the DC converter and inverter circuits during the process of enabling the maximum output power tracking algorithm. The scanning method requires controlling the photovoltaic cell voltage to vary over a wide range while the photovoltaic cell supplies power to the load. The photovoltaic inverter's current and voltage control loops are then used to control the operating states of the DC converter and inverter circuits based on the varying voltage. The photovoltaic cell voltage and current are sampled during this variation, and the volt-ampere characteristic curve of the photovoltaic cell within the voltage range is reproduced based on the sampling results. The maximum output power is then calculated based on this volt-ampere characteristic curve. This approach also requires the PV inverter to have a certain output power. If the PV inverter's output power is zero, such as when the PV inverter is in standby mode, not connected to the grid, or unloaded, this method is not feasible. The model method perturbs the PV cell's operating point (the perturbation amplitude is generally smaller than that of the perturbation and scanning methods) or utilizes historical data on PV cell operating point fluctuations, combined with a mathematical model of the PV cell, to infer the current maximum output power. This method relies on the PV inverter's current and voltage control loops to control the operating states of the DC converter and inverter circuits during the perturbation process. Furthermore, because this approach relies on mathematical modeling, estimation errors can be significant when PV cell characteristics change. For example, when a PV cell ages or is partially shaded, its power-voltage (PV) curve may shift from a single peak to multiple peaks, resulting in significant estimation errors. In addition, this solution also requires that the photovoltaic inverter device has a certain output power. If the output power of the photovoltaic inverter device is zero, such as the photovoltaic inverter device is in standby, startup and not connected to the grid or no load state, this method will not be able to estimate the maximum output power of the photovoltaic cell.

[0050] As can be seen, current methods for estimating the maximum output power of photovoltaic cells all rely on the voltage and current control loops of the photovoltaic inverter to regulate the output voltage and current of the photovoltaic cell. If the voltage and current control loops of the photovoltaic inverter are inoperative, such as when the photovoltaic inverter is in standby mode, the maximum output power cannot be estimated. Furthermore, current perturbation and scanning methods both cause significant power fluctuations during normal operation of the photovoltaic inverter. If these methods are directly applied when the photovoltaic inverter is started but not connected to the grid or underloaded, the resulting power fluctuations will have nowhere to be absorbed, which can easily cause the DC bus capacitor to over- or under-voltage protection, causing the photovoltaic inverter to exit the startup state. Model-based methods, on the other hand, rely on offline mathematical models. If the characteristics of the photovoltaic cell change, the estimation error of these methods will be further increased. Therefore, there is an urgent need to develop power conversion devices suitable for photovoltaic inverters in standby, startup, not connected to the grid, or underloaded states.

[0051] Based on this, an embodiment of the present application provides a power conversion device. The power conversion device includes a controller and a DC conversion circuit. The control end of the DC conversion circuit is used to connect to the controller. The input end of the DC conversion circuit is used to connect to the output end of the photovoltaic cell. The output end of the DC conversion circuit is used to connect to a load. Alternatively, the output end of the DC conversion circuit is used to connect to the load through an inverter circuit. The controller can control the DC conversion circuit and obtain an input current and a first input voltage at the input end of the DC conversion circuit, and then obtain the maximum output power of the photovoltaic cell based on the input current and the first input voltage.

[0052] In one implementation, the controller can control the DC conversion circuit to disconnect the output terminal of the photovoltaic cell from the common terminal of the photovoltaic cell and obtain a first input voltage at the input terminal of the DC conversion circuit. Furthermore, the controller can control the DC conversion circuit to short-circuit the output terminal of the photovoltaic cell with the common terminal of the photovoltaic cell and obtain an input current at the input terminal of the DC conversion circuit. The controller then estimates the maximum output power of the photovoltaic cell based on the first input voltage and input current.

[0053] In this implementation, the first input voltage is obtained when the output terminal of the photovoltaic cell is disconnected from the common terminal of the photovoltaic cell, and the input current is obtained when the output terminal of the photovoltaic cell is short-circuited with the common terminal of the photovoltaic cell. The disconnection and short-circuiting are achieved without relying on the control of the voltage control loop and current control loop of the power conversion device. Therefore, this implementation for obtaining the maximum output power of the photovoltaic cell is applicable to scenarios where the voltage control loop and current control loop of the power conversion device are inoperative, such as scenarios where the power conversion device is in standby mode, not connected to the grid during startup, or not loaded. This overcomes the limitation that the maximum output power of the photovoltaic cell can only be estimated while the photovoltaic cell is supplying power to the load. Furthermore, this implementation is not limited to such scenarios. For example, because the implementation principle of this implementation is relatively simple, fewer operations are required on the power conversion device, and its execution process is very fast, with negligible impact on the load, this implementation can also obtain the maximum output power of the photovoltaic cell while the power conversion device is supplying power to the load.

[0054] In another implementation scheme, after the power conversion device is powered on, the controller can send multiple pulse signals with different duty cycles to the DC conversion circuit to change the output current and output voltage of the DC conversion circuit, and collect the input current and the first input voltage of the input end of the DC conversion circuit multiple times, and then obtain the maximum output power of the photovoltaic cell based on the multiple collected first input voltage and input current.

[0055] In this implementation, the first input voltage and input current are obtained during the process of changes in the output current and output voltage of the DC conversion circuit. This change is generated by the action of multiple pulse signals sent by the controller, and the generation of these multiple pulse signals does not rely on the control of the voltage control loop and current control loop of the power conversion device. Therefore, this implementation scheme for obtaining the maximum output power of the photovoltaic cell is applicable to scenarios where the voltage control loop and current control loop of the power conversion device are inoperative, such as scenarios where the power conversion device is in standby mode, not connected to the grid during startup, or not loaded. This can overcome the limitation that the maximum output power of the photovoltaic cell can only be estimated during the process of the photovoltaic cell supplying power to the load. In addition, this implementation scheme is not limited to application in such scenarios. For example, because the implementation principle of this implementation scheme is relatively simple, it requires fewer operations to be performed on the power conversion device, its execution process is very fast, and the impact on the load is negligible. Therefore, this implementation scheme can also obtain the maximum output power of the photovoltaic cell during the process of the power conversion device supplying power to the load.

[0056] This article provides a detailed introduction to the technical solution of this application from multiple perspectives, including implementation scenarios, method flow, hardware devices, and software devices.

[0057] The following first illustrates an implementation scenario of the embodiment of the present application with examples.

[0058] Figure 2 This is a schematic diagram of a power conversion device according to an embodiment of the present application. Figure 2 As shown, the implementation scenario includes: photovoltaic cell 01, power conversion device 02 and load 03. Power conversion device 02 includes controller 021 and DC conversion circuit 022. DC conversion circuit 022 has a control end, an input end and an output end. The control end of DC conversion circuit 022 is used to connect to controller 021. The input end of DC conversion circuit 022 is used to connect to the output end of photovoltaic cell 01. The output end of DC conversion circuit 022 is used to connect to load 03. At this time, load 03 can be regarded as a DC load. Or, as Figure 3 As shown, the power conversion device 02 further includes an inverter circuit 023. At this time, the output end of the DC conversion circuit 022 is used to connect to the load 03 through the inverter circuit 023. The load 03 can be regarded as an AC load. Optionally, the power conversion device 02 can also include a circuit breaker ( Figure 2 and Figure 3 (not shown), or a circuit breaker is connected between the power conversion device 02 and the load 03.

[0059] The implementation scenario may optionally include one or more photovoltaic cells 01, and the power conversion device 02 may include one or more DC conversion circuits 022. When the implementation scenario includes multiple photovoltaic cells 01, Figure 2 and Figure 3 As shown, multiple photovoltaic cells 01 are connected in parallel, and multiple DC conversion circuits 022 of the power conversion device 02 are connected in parallel. The input end of each DC conversion circuit 022 is used to connect to a photovoltaic cell 01. The output ends of the multiple parallel DC conversion circuits 022 are connected in parallel and then connected to the input end of the inverter circuit 023.

[0060] The power conversion device 02 may optionally include one or more stages of DC conversion circuits 022, which are not specifically limited in the embodiments of the present application. When the power conversion device 02 includes multiple stages of DC conversion circuits 022, the multiple stages of DC conversion circuits 022 are connected in series. When the load 03 is an AC load, the power conversion device 02 may be a circuit with two or more stages, one of which is an inverter circuit 023, and the remaining stages are all DC conversion circuits 022, and the DC conversion circuits 022 of different stages are connected in series. For example, Figure 3 As shown, the power conversion device 02 is a two-stage circuit, with multiple parallel DC conversion circuits 022 as one stage and an inverter circuit 023 as the other stage. When the load 03 is a DC load, the power conversion device 02 may include at least one stage, wherein each stage is a DC conversion circuit 022, and the sub-circuits of different stages are in series. For example, Figure 2As shown, the power conversion device 02 is a one-stage circuit. The number of stages of the power conversion device 02 can be set according to application requirements. For example, the power conversion device 02 can also include more stages of DC conversion circuits 022, which are not specifically limited in the present embodiment.

[0061] The DC conversion circuit 022 is used to receive DC power from the photovoltaic cell 01, perform voltage conversion on the DC power, and output the converted DC power. Optionally, the DC conversion circuit 022 is a direct current to direct current (DC / DC) conversion circuit. For example, the DC conversion circuit 022 is a boost converter circuit (Boost circuit), a step-down converter circuit (Buck circuit), or other types of circuits capable of performing DC voltage conversion, which are not specifically limited in the embodiments of the present application.

[0062] The inverter circuit 023 is used to convert direct current into alternating current and provide the alternating current to an AC load. The inverter circuit 023 is also called a direct current to alternating current (DC / AC) conversion circuit. The inverter circuit 023 can be connected to an AC busbar via an AC circuit breaker, and the AC busbar can be connected to an AC grid with the same voltage and frequency. Alternatively, the inverter circuit 023 can be connected to another AC busbar via a transformer. Several AC loads can be connected to the AC busbar. In this case, the power conversion device 02 is equivalent to a photovoltaic inverter.

[0063] When load 03 is a DC load, power conversion device 02 functions as a voltage converter placed between photovoltaic cell 01 and the DC load. This voltage converter is used to change the voltage amplitude of the DC power output by photovoltaic cell 01. Alternatively, when photovoltaic cell 01 comprises multiple panels, the panels are connected via power conversion device 02, thereby achieving connectivity among the multiple panels in photovoltaic cell 01. In this case, power conversion device 02 functions as a photovoltaic optimizer, which optimizes and manages the panels to ensure consistency across the photovoltaic cell 01.

[0064] Figure 4 This is a structural diagram of another implementation scenario involving a power conversion device provided in an embodiment of the present application. Figure 4As shown, the implementation scenario may also include: an upper-level controller 04. The upper-level controller 04 is used to control the operating state of the power conversion device 02. For example, the power conversion device 02 can receive the command signal sent by the upper-level controller 04 and operate according to the instructions of the command signal. The power conversion device 02 can also send its own operating information to the upper-level controller 04, so that the upper-level controller 04 can send a command signal to the power conversion device 02 based on the operating information. For example, in a black start scenario, after the power conversion device 02 obtains the maximum output power of the photovoltaic cell 01 to which it is connected, it sends the maximum output power to the upper-level controller 04. If the upper-level controller 04 determines that the maximum output power meets the startup conditions, it sends a startup instruction to the power conversion device 02. The power conversion device 02 is started according to the startup instruction to achieve grid-connected / loaded operation. Alternatively, the upper-level controller 04 provides a startup condition to the power conversion device 02. After the power conversion device 02 obtains the maximum output power of the photovoltaic cell 01 to which it is connected, if the maximum output power meets the startup condition, the power conversion device 02 automatically starts and achieves grid-connected / loaded operation. Optionally, the upper-level controller 04 can be a microgrid-level / grid-level controller.

[0065] It should be understood that the above content is an illustrative description of the implementation scenario of the power conversion device provided in the embodiment of the present application, and does not constitute a limitation on the implementation scenario of the power conversion device. Ordinary technicians in this field know that as business needs change, its implementation scenario can be adjusted according to application requirements, and the embodiments of the present application do not list them one by one.

[0066] In the present application, the operation of obtaining the maximum output power of the photovoltaic cell 01 is performed by the controller 021 of the power conversion device 02 .

[0067] In one implementation, the controller is used to: control the DC conversion circuit to disconnect the output terminal of the photovoltaic cell from the common terminal of the photovoltaic cell to obtain a first input voltage at the input terminal of the DC conversion circuit; control the DC conversion circuit to short-circuit the output terminal of the photovoltaic cell with the common terminal of the photovoltaic cell to obtain an input current at the input terminal of the DC conversion circuit; and estimate the maximum output power of the photovoltaic cell based on the first input voltage and the input current.

[0068] Optionally, the controller estimates the maximum output power of the photovoltaic cell based on the first input voltage and the input current, including: obtaining a fill factor of the photovoltaic cell, where the fill factor indicates how close the maximum output power is to an ideal output power of the photovoltaic cell; and estimating the maximum output power based on the fill factor, the first input voltage, and the input current. For example, the maximum output power is the product of the fill factor, the first input voltage, and the input current.

[0069] In one possible implementation, the DC conversion circuit includes a switching device, the control end of the switching device is the control end of the DC conversion circuit, and the controller is used to provide a pulse signal to the control end of the switching device so that the output end of the photovoltaic cell is short-circuited or disconnected from the common end of the photovoltaic cell.

[0070] Optionally, the controller is configured to control the DC conversion circuit to short-circuit the output terminal of the photovoltaic cell and the common terminal of the photovoltaic cell when the first input voltage is greater than a first voltage threshold.

[0071] In the present application, in response to the output end of the DC conversion circuit being connected to a load through the inverter circuit, the controller is used to: stop obtaining the output current and output voltage of the output end of the DC conversion circuit during the process of the controller obtaining the first input voltage and input current, or stop controlling the working state of the inverter circuit based on the output current and output voltage of the output end of the DC conversion circuit.

[0072] Alternatively, during the process of the controller acquiring the first input voltage and input current, the output end of the DC conversion circuit does not supply power to the load.

[0073] In another implementation, the controller is configured to: after the power conversion device is powered on, send multiple pulse signals with different duty cycles to the DC conversion circuit to change the output current and output voltage of the DC conversion circuit, and repeatedly collect input current and first input voltage at the input terminal of the DC conversion circuit; and obtain the maximum output power of the photovoltaic cell based on the multiple collected first input voltage and input current. Optionally, the duty cycles of the multiple pulse signals increase sequentially. Furthermore, the controller is configured to stop sending pulse signals to the DC conversion circuit when the first input voltage is less than or equal to a second voltage threshold, and / or when the output voltage at the output terminal of the DC conversion circuit is greater than or equal to a third voltage threshold.

[0074] The controller obtains the maximum output power of the photovoltaic cell based on the first input voltage and input current collected multiple times, including: obtaining the power corresponding to the i-th time based on the input current and first input voltage collected multiple times, and determining the maximum value of the multiple corresponding powers as the maximum output power, where i is a positive integer.

[0075] Optionally, the controller is also used to obtain a second input voltage at the input end of the DC conversion circuit when the DC conversion circuit disconnects the output end of the photovoltaic cell from the common end of the photovoltaic cell, and when the second input voltage is greater than a fourth voltage threshold, send multiple pulse signals with different duty cycles to the power conversion device to change the output current and output voltage of the DC conversion circuit.

[0076] In the present application, in response to the output end of the DC conversion circuit being connected to a load through the inverter circuit, the controller is used to: stop obtaining the output current and output voltage of the output end of the DC conversion circuit during the process of the controller obtaining the first input voltage and input current, or stop controlling the working state of the inverter circuit based on the output current and output voltage of the output end of the DC conversion circuit.

[0077] Alternatively, during the process of the controller acquiring the first input voltage and input current, the output end of the DC conversion circuit does not supply power to the load.

[0078] The following describes the principle of how the power conversion device obtains the maximum output power of the photovoltaic cell.

[0079] According to the previous description, the power conversion device can be optionally connected to one or more photovoltaic cells. The principle will be explained below by taking the maximum output power of one photovoltaic cell as an example. Therefore, unless otherwise specified, the photovoltaic cells mentioned below refer to the photovoltaic cell whose maximum output power is to be obtained. When the power conversion device is connected to multiple photovoltaic cells, the controller can obtain the maximum output power of each photovoltaic cell separately according to the implementation method, and then determine the maximum output power of the multiple photovoltaic cells based on the maximum output power of the multiple photovoltaic cells. For example, the sum of the maximum output power of the multiple photovoltaic cells is determined as the maximum output power of the multiple photovoltaic cells. The following describes two implementation methods for obtaining the maximum output power of the photovoltaic cells.

[0080] The first implementation scheme for obtaining the maximum output power of photovoltaic cells for power conversion equipment is as follows: Figure 5 As shown, the implementation scheme includes the following steps:

[0081] Step 501: A controller controls a DC conversion circuit to disconnect the output terminal of a photovoltaic cell from the common terminal of the photovoltaic cell, and obtains a first input voltage of an input terminal of the DC conversion circuit.

[0082] After the power conversion device is powered on, the controller can control the DC conversion circuit to disconnect the output terminal of the photovoltaic cell from the common terminal of the photovoltaic cell, and obtain a first input voltage at the input terminal of the DC conversion circuit when the output terminal of the photovoltaic cell is disconnected from the common terminal of the photovoltaic cell. The first input voltage can be obtained by measuring the input voltage at the input terminal of the DC conversion circuit, or by measuring the output voltage at the output terminal of the photovoltaic cell.

[0083] In one implementation, the controller may optionally obtain a first input voltage at the input terminal of the DC converter circuit when the power conversion device is powered on and the controller does not send a PWM signal to the DC converter circuit to instruct the DC converter circuit to perform voltage conversion. When the controller does not send a PWM signal to the DC converter circuit to instruct the DC converter circuit to perform voltage conversion, it can be considered that the controller has not yet controlled the DC converter circuit to operate in accordance with the PWM signal. This is a control process in which the controller controls the DC converter circuit to be in a non-operating state in order to obtain the first input voltage.

[0084] In another possible implementation, the controller may send a control signal to the DC conversion circuit, so that the DC conversion circuit, under the action of the control signal, disconnects the output terminal of the photovoltaic cell from the common terminal of the photovoltaic cell. For example, the DC conversion circuit may optionally include a switching device, and the control terminal of the switching device is the control terminal of the DC conversion circuit. The controller may optionally provide a control signal to the control terminal of the switching device, so that the output terminal of the photovoltaic cell is disconnected from the common terminal of the photovoltaic cell. For example, Figure 6 A schematic diagram of a DC conversion circuit 022 provided in an embodiment of the present application is a Boost circuit. Figure 6 As shown, the DC conversion circuit 022 includes an inductor, an insulated gate bipolar transistor (IGBT), and a diode. The first end of the inductor serves as the input of the DC conversion circuit 022 and is connected to the output of the photovoltaic cell. The second end of the inductor is connected to the first electrode of the IGBT and the first end of the diode, respectively. The second electrode of the IGBT is connected to the common terminal of the photovoltaic cell. The third electrode of the IGBT serves as the control terminal of the DC conversion circuit 022 and is used to receive a control signal provided by the controller 021. The second end of the diode serves as the output of the DC conversion circuit 022. After the controller 021 powers on the power conversion device, it provides an inactive level (e.g., a low level) to the third electrode of the IGBT in the DC conversion circuit 022, thereby keeping the IGBT off under the effect of the inactive level. The IGBT in the off state is equivalent to disconnecting the output of the photovoltaic cell from the common terminal of the photovoltaic cell. The controller controls the DC conversion circuit to disconnect the output end of the photovoltaic cell from the common end of the photovoltaic cell through a control signal. Under the action of the control signal, the DC conversion circuit can stably maintain the output end of the photovoltaic cell and the common end of the photovoltaic cell in a disconnected state, which helps to ensure that the obtained first output voltage can more truly reflect the working state of the photovoltaic cell.

[0085] After the controller provides a control signal to the DC converter circuit, it takes a while for the DC converter circuit to reach a steady state after receiving the control signal. The output voltage of the photovoltaic cell in this steady state more accurately reflects the operating state of the photovoltaic cell. Therefore, to ensure the accuracy of the estimated maximum output power, the controller may optionally obtain a first input voltage at the input of the DC converter circuit after the control signal causes the DC converter circuit to connect the output terminal of the photovoltaic cell to the common terminal and the DC converter circuit reaches a steady state. After providing the control signal to the DC converter circuit, the controller may optionally obtain the first input voltage at the input of the DC converter circuit multiple times, and when the first input voltage remains substantially constant, determine the obtained first input voltage as the first input voltage when the converter circuit reaches a steady state. Alternatively, after the controller begins providing the control signal to the DC converter circuit, it may obtain the first input voltage at the input of the DC converter circuit after a specified time period, and determine the obtained first input voltage as the first input voltage when the DC converter circuit reaches a steady state. The specified time period is the estimated time required for the DC converter circuit to reach a steady state, and this time period may be determined empirically or calculated based on circuit parameters. Alternatively, the controller obtains the first input voltage of the input terminal of the DC conversion circuit when the controller is about to stop providing the control signal to the DC conversion circuit.

[0086] Step 502: The controller controls the DC conversion circuit to short-circuit the output terminal of the photovoltaic cell and the common terminal of the photovoltaic cell, thereby obtaining an input current from the input terminal of the DC conversion circuit.

[0087] In addition to the first output voltage at the output terminal of the DC conversion circuit, in order to obtain the maximum output power of the photovoltaic cell, the controller also needs to obtain the input current at the input terminal of the DC conversion circuit when the output terminal of the photovoltaic cell is short-circuited with the common terminal of the photovoltaic cell. The controller then needs to control the DC conversion circuit to short-circuit the output terminal of the photovoltaic cell with the common terminal of the photovoltaic cell and obtain the input current at the input terminal of the DC conversion circuit during this process. This input current can be obtained by measuring the input current at the input terminal of the DC conversion circuit, or by measuring the output current at the output terminal of the photovoltaic cell.

[0088] In one possible implementation, the controller can send a control signal to the DC conversion circuit, so that the DC conversion circuit, under the action of the control signal, short-circuits the output terminal of the photovoltaic cell with the common terminal of the photovoltaic cell. For example, the DC conversion circuit includes a switching device, the control terminal of the switching device is the control terminal of the DC conversion circuit, and the controller is used to provide a pulse signal to the control terminal of the switching device, so that the output terminal of the photovoltaic cell is short-circuited with the common terminal of the photovoltaic cell. For example, for Figure 6In the illustrated DC converter circuit 022, controller 021 can optionally provide a pulse signal to the third electrode of the insulated gate bipolar transistor in DC converter circuit 022, causing the insulated gate bipolar transistor to conduct in response to the effective level (e.g., a high level) in the pulse signal. This forms a loop between photovoltaic cell 01 and the inductor and insulated gate bipolar transistor in DC converter circuit 022. Because the impedance of the inductor and insulated gate bipolar transistor is relatively low when conducting, this effectively short-circuits the output terminal of photovoltaic cell 01 with the common terminal of the photovoltaic cells.

[0089] Optionally, the pulse signal may satisfy the following condition: the duration of short-circuiting the output terminal of photovoltaic cell 01 and the common terminal of the photovoltaic cell is sufficient to ensure that the DC converter circuit and the photovoltaic cell can reach a steady state during the short-circuiting process. This ensures the validity of the circuit parameters obtained by the controller during the short-circuiting process.

[0090] After the controller provides a pulse signal to the DC converter circuit, it takes a while for the DC converter circuit to reach a steady state after receiving the pulse signal. The output current of the photovoltaic cell in this steady state more accurately reflects the operating state of the photovoltaic cell. Therefore, to ensure the accuracy of the estimated maximum output power, the controller may optionally obtain the input current at the input end of the DC converter circuit after the DC converter circuit short-circuits the photovoltaic cell and the DC converter circuit reaches a steady state. After providing the pulse signal to the DC converter circuit, the controller may optionally obtain the input current at the input end of the DC converter circuit multiple times. When the input current remains substantially constant, the obtained input current is determined as the input current at the time the DC converter circuit reaches a steady state. Alternatively, after starting to provide the pulse signal to the DC converter circuit, the controller may obtain the input current at the input end of the DC converter circuit after a specified time period has passed, and determine the obtained input current as the input current at the time the DC converter circuit reaches a steady state. The specified time period is the estimated time required for the DC converter circuit to reach a steady state, and this time period may be determined empirically or calculated based on circuit parameters. Alternatively, the controller obtains the input current of the input end of the DC conversion circuit when the controller is about to stop providing the pulse signal to the DC conversion circuit.

[0091] Optionally, before the controller provides the pulse signal to the DC conversion circuit, it can also make a judgment in advance to determine whether it is necessary to provide the pulse signal to the DC conversion circuit. Figure 7As shown, the implementation process of step 502 may be as follows: Step 5021: When the first input voltage is greater than a first voltage threshold, the controller controls the DC conversion circuit to short-circuit the output terminal of the photovoltaic cell with the common terminal of the photovoltaic cell, thereby obtaining an input current at the input terminal of the DC conversion circuit. The first input voltage can be considered the output voltage of the photovoltaic cell. Since the output voltage of the photovoltaic cell is positively correlated with its output power, when the output voltage of the photovoltaic cell is low, its output power is also low. Therefore, only when the first input voltage is greater than the first voltage threshold is the load capacity of the photovoltaic cell sufficient to support the load. Only then is it necessary to continue to obtain the maximum output power of the photovoltaic cell and, based on this maximum output power, determine whether to use the power conversion device to supply power to the load. When the first input voltage is less than or equal to the first voltage threshold, the load capacity of the photovoltaic cell cannot support the load, and there is no need to continue to obtain the maximum output power of the photovoltaic cell. The value of the first voltage threshold can be determined based on application requirements. For example, the value of the first voltage threshold can be determined based on the startup conditions of the power conversion device.

[0092] Step 503: The controller estimates the maximum output power of the photovoltaic cell based on the first input voltage and the input current.

[0093] In one possible implementation, Figure 8 As shown, the implementation process of step 503 includes:

[0094] Step 5031: The controller obtains the fill factor of the photovoltaic cell. The fill factor is used to indicate the degree to which the maximum output power is close to the ideal output power of the photovoltaic cell.

[0095] According to the previous description, the first input voltage used to obtain the maximum output power of the photovoltaic cell is the input voltage of the input end of the DC conversion circuit when the output end of the photovoltaic cell is disconnected from the common end of the photovoltaic cell. The input current used to obtain the maximum output power is the input current of the input end of the DC conversion circuit when the output end of the photovoltaic cell is short-circuited with the common end of the photovoltaic cell. Then the first input voltage and the input current reflect the output performance of the photovoltaic cell under ideal operating conditions. For example, the product of the first input voltage and the input current is the ideal output power of the photovoltaic cell under ideal operating conditions. There is a gap between the ideal output power and the maximum output power of the photovoltaic cell, and the degree to which the maximum output power is close to the ideal output power can be represented by the fill factor of the photovoltaic cell. It can be seen that the fill factor is used to characterize the performance of the photovoltaic cell. When the fill factor is larger, the performance of the photovoltaic cell is better. For example, Figure 9 This is a volt-ampere characteristic curve of a photovoltaic cell provided in an embodiment of the present application. Figure 9 As shown, the product of the first input voltage and the input current is the ideal output power of the photovoltaic cell. Figure 9The intersection of the two dotted lines is shown in A. This ideal output power is generally not achievable. The maximum output power is Figure 9 The degree to which the maximum output power approaches the ideal output power can be represented by the fill factor. Figure 9 In the example, the filling factor can be considered as Figure 9 The first area is the area of the region enclosed by the volt-ampere characteristic curve and the coordinate axis. The second area is the area enclosed by the coordinate axis and the Figure 9 The area of the region enclosed by the two dotted lines.

[0096] In one implementation, the manufacturer of the photovoltaic cell can provide the fill factor of the photovoltaic cell. Therefore, the controller can obtain the fill factor. Alternatively, the manufacturer of the photovoltaic cell can provide the photovoltaic cell's volt-ampere characteristic curve, open-circuit voltage, and short-circuit current under different illumination conditions. The controller can obtain a first influence coefficient of the voltage on the fill factor under any illumination condition based on the open-circuit voltage of the photovoltaic cell and the voltage at the maximum power point in the volt-ampere characteristic curve under any illumination condition. For example, the ratio of the voltage at the maximum power point to the open-circuit voltage under any illumination condition is equal to the first influence coefficient under that illumination condition. The controller can obtain a second influence coefficient of the current on the fill factor under that illumination condition based on the short-circuit current of the photovoltaic cell and the current at the maximum power point in the volt-ampere characteristic curve under any illumination condition. For example, the ratio of the current at the maximum power point to the short-circuit current under any illumination condition is equal to the second influence coefficient under that illumination condition. After obtaining the first and second influence coefficients under different illumination conditions, the controller can obtain the fill factor of the photovoltaic cell based on them. For example, the controller processes the first influence coefficient under different illumination conditions to obtain the processed first influence coefficient, processes the second influence coefficient under different illumination conditions to obtain the processed second influence coefficient, and then determines the product of the processed first influence coefficient and the processed second influence coefficient as the fill factor of the photovoltaic cell. Among them, the processed influence coefficient can be selected as the mean or weighted value of the influence coefficients under different illumination conditions, or one with a higher confidence level among the influence coefficients under different illumination conditions, and the embodiments of the present application do not specifically limit it. For example, the value of the first influence coefficient k1 is 0.75, and the value of the second influence coefficient k2 is 0.95, then the product of k1 and k2, 0.7125, is the fill factor FF.

[0097] Step 5032: The controller estimates the maximum output power based on the fill factor, the first input voltage, and the input current.

[0098] In one implementation, the maximum output power of the photovoltaic cell is equal to the product of the fill factor, the first input voltage, and the input current. For example, the maximum output power P, the fill factor FF, the first input voltage V1, and the input current I1 satisfy: P = FF × V1 × I1.

[0099] When the controller obtains the first influence coefficient and the second influence coefficient, the controller can estimate the voltage of the photovoltaic cell when it outputs the maximum output power based on the first influence coefficient and the first output voltage, and estimate the current of the photovoltaic cell when it outputs the maximum output power based on the second influence coefficient and the input current. For example, given the first influence coefficient k1 and the first input voltage V1, the voltage V2 of the photovoltaic cell when it outputs the maximum output power satisfies: V2 = k1 × V1. Similarly, given the second influence coefficient k2 and the input current I1, the current I2 of the photovoltaic cell when it outputs the maximum output power satisfies: I2 = k2 × I1. Then, based on the voltage and current of the photovoltaic cell when it outputs the maximum output power, the maximum output power of the photovoltaic cell is estimated. For example, the maximum output power of the photovoltaic cell is equal to the product of the voltage and current of the photovoltaic cell when it outputs the maximum output power, that is, the maximum output power P = (k1 × V1) × (k2 × I1).

[0100] It should be noted that, as described above, the load in this application can be either a DC load or an AC load, and the process for obtaining the maximum output power can be performed even when the voltage and current control loops of the power conversion device are inoperative, and is not limited to such scenarios. To minimize the impact of the load on the process of obtaining the maximum output power, the scheme for obtaining the maximum output power needs to meet certain conditions in different scenarios. These conditions are illustrated below with examples.

[0101] In one scenario, in response to a load being connected to the output terminal of a DC converter circuit via an inverter circuit, this solution is used in scenarios where a power conversion device is connected to an AC load. In this case, the controller must meet the following conditions: while acquiring the first input voltage and input current, the controller stops acquiring the output current and output voltage of the DC converter circuit, or stops controlling the operating state of the inverter circuit based on the output current and output voltage of the DC converter circuit. The duty cycle of the PWM signal used by the controller to control the inverter circuit is determined based on the output current and output voltage of the DC converter circuit. This duty cycle determines the frequency of the AC power provided by the inverter circuit to the AC load. When the controller stops acquiring the output current and output voltage of the DC converter circuit, or stops controlling the operating state of the inverter circuit based on the output current and output voltage of the DC converter circuit, the output current and output voltage of the DC converter circuit will not affect the AC power provided by the inverter circuit to the AC load. If the controller meets this condition while acquiring the first input voltage and input current, the AC power provided by the inverter circuit to the AC load will not be affected by the process of acquiring the maximum output power. For example, if the inverter circuit is originally supplying power to the load before the acquisition process is executed, then in the process of obtaining the first input voltage and input current, the duty cycle of the PWM signal provided by the controller to the inverter circuit may be equal to the duty cycle of the PWM signal provided to the inverter circuit in the process of supplying power to the load, so as to ensure the stability of power supply to the AC load in the process of obtaining the maximum output power.

[0102] In another scenario, during the process of the controller acquiring the first input voltage and input current, the output end of the DC conversion circuit does not supply power to the load. In this case, regardless of the operating mode of the power conversion device, the power conversion device does not output electrical energy to the load, and therefore does not affect the load. In one implementation, the output end of the DC conversion circuit does not supply power to the load, which can manifest as the following: when the inverter circuit is used to connect to an AC load, the output end of the inverter circuit is disconnected from the AC load; when the DC conversion circuit is used to connect to a DC load, the output end of the DC conversion circuit is disconnected from the DC load.

[0103] The following is an exemplary description of the first implementation scheme for obtaining the maximum output power of a photovoltaic cell.

[0104] Figure 10 Schematic diagram of providing a pulse signal to a DC / DC Boost conversion circuit in a two-stage photovoltaic inverter according to an embodiment of the present application. Figure 10As shown, the photovoltaic inverter includes a DC / DC Boost conversion circuit, the input end of which is connected to a single photovoltaic cell. In the embodiment of the present application, it is assumed that the actual maximum power of the photovoltaic cell is 119 kilowatts (kW) and the DC bus load is 20W (less than 2‰ of the maximum photovoltaic power). When the photovoltaic inverter is in standby mode, the power conversion device proposed in the embodiment of the present application is used to determine the maximum output power of the photovoltaic cell. The implementation steps are as follows:

[0105] Step 1: After the photovoltaic inverter is powered on, the controller immediately measures the output voltage of the photovoltaic cell to obtain the first input voltage V at the input end of the DC / DCBoost conversion circuit. OC It is 1016 volts (V).

[0106] Step 2: The controller applies a pulse signal to the control terminal of the DC / DC Boost converter circuit. The high level in the pulse signal lasts for 1 millisecond. Under the action of this high level, the insulated gate bipolar transistor in the DC / DC Boost converter circuit shorts the output terminal of the photovoltaic cell to the common terminal for 1ms. When the 1ms high level is about to end, the controller measures the output current of the photovoltaic cell to be 157 amperes (A), which is the output current I of the input terminal of the DC / DC Boost converter circuit. SC It is 157A.

[0107] Step 3: Controller with V MPP ≈0.75V OC , I MPP ≈0.95I SC An approximate calculation (ie, FF = 0.7125) yields an estimated value of the maximum output power of 114 kW.

[0108] Step 4: The controller sends the estimated maximum output power to the upper controller, which issues a start-up instruction to the PV inverter based on the estimated value. Alternatively, if the estimated maximum output power is greater than the start-up power threshold set by the PV inverter, the PV inverter automatically starts to connect to the grid / operate with load.

[0109] The simulation waveform in this process is as follows Figure 11 As shown. According to the simulation waveform, it can be seen that after the high level ends, the circuit state quickly returns to the initial value within 0.5ms. Considering this dynamic process, it is expected that this method can complete the acquisition of the maximum output power of the photovoltaic inverter in the standby state within 2ms. Compared with related technologies, this method can achieve a rapid estimation of the maximum output power of the photovoltaic inverter in the standby state. And the power fluctuation caused by this method is small. Even if the DC bus is unloaded, the voltage rise caused by a single short circuit on the DC capacitor by this method is also small. The value of the voltage rise (ΔU) can be obtained by solving LI SC2 =C(U+ΔU) 2 -CU 2 The equation is obtained. L is the inductance of the inductor in the insulated gate bipolar transistor, and C is the capacitance of the capacitor on the DC bus. It can be seen that the energy used to charge the inductor in the first implementation scheme of obtaining the maximum output power of the photovoltaic cell in this application is only 1 / 2LI SC 2 The larger the capacitance of the capacitor on the DC bus, the smaller the fluctuation on the bus caused by short-circuiting the output terminal of the photovoltaic cell and the common terminal.

[0110] The first implementation scheme for obtaining the maximum output power of a photovoltaic cell described above can be called a single-pulse detection method for the maximum output power. This single-pulse detection method is more suitable for estimating the maximum power when the output power-voltage (PV) characteristic curve of the photovoltaic cell is a single-peak. The output power-voltage (PV) characteristic curve being a single-peak means that the characteristic curve has a local peak. For example, Figure 9 and Figure 12 They are schematic diagrams of the volt-ampere characteristics and power-voltage characteristics when the PV characteristic curve of the photovoltaic cell is a single peak.

[0111] The second implementation scheme for obtaining the maximum output power of photovoltaic cells for power conversion equipment is as follows: Figure 13 As shown, the implementation scheme includes the following steps:

[0112] Step 1301: After the controller powers on the power conversion device, it sends multiple pulse signals with different duty cycles to the DC conversion circuit to change the output current and output voltage of the DC conversion circuit, and collects the input current and first input voltage of the input end of the DC conversion circuit multiple times.

[0113] After the power conversion device is powered on, the controller can send multiple pulse signals with different duty cycles to the DC conversion circuit to change the output current and output voltage of the DC conversion circuit, and repeatedly collect the input current and first input voltage at the input end of the DC conversion circuit during this process. The controller sends multiple pulse signals to the DC conversion circuit to activate the DC conversion circuit. Here, when the duty cycles of the multiple pulse signals are different, the on-time and off-time of the components in the DC conversion circuit will change with the duty cycle of the pulse signal, and the output current and output voltage of the DC conversion circuit will change accordingly. In the process of the controller sending multiple pulse signals with different duty cycles to the DC conversion circuit, the input current and first input voltage at the input end of the DC conversion circuit that are collected multiple times can capture the dynamic changes in the circuit characteristics of the photovoltaic cell during this process, and reproduce the current-voltage characteristic (IV) curve of the photovoltaic cell based on the changes. Then, based on the IV characteristic, the maximum output power of the photovoltaic cell can be obtained.

[0114] The duty cycles of the multiple pulse signals are different, including the duty cycles of some pulse signals in the multiple pulse signals being different, or the duty cycles of the multiple pulse signals being completely different. Optionally, the duty cycles of the multiple pulse signals increase sequentially. For example, the duty cycles of the multiple pulse signals can increase linearly starting from 0, such as increasing according to a specified step size starting from 0. Alternatively, the duty cycles of the multiple pulse signals can also increase in other variations, such as increasing exponentially, parabolically, or stepwise starting from 0, which is not specifically limited in the embodiments of the present application. For example, Figure 14 FIG. 1 is a schematic diagram of providing multiple pulse signals to a Boost circuit according to an embodiment of the present application. The relationship between the duty cycle of the multiple pulse signals and the Boost switch carrier is as follows: Figure 15 As shown. Figure 15 It can be seen that the duty cycle of the multiple pulse signals increases from 0 according to the specified step size. Figure 15 The triangle wave in is the Boost switch carrier. Figure 15 The stepped curve in the figure is a schematic diagram of the duty cycle changing over time. Multiple pulse signals can be called a pulse train, which can be regarded as a PWM signal with a gradually increasing duty cycle.

[0115] After the controller provides a pulse signal to the DC conversion circuit, under the control of the pulse signal, the electric energy output by the photovoltaic cell will be transferred from the input end of the DC conversion circuit to the output end of the DC conversion circuit. As the charging process proceeds, the first input voltage of the input end of the DC conversion circuit will decrease, and the first output voltage of the output end of the DC conversion circuit will increase. For example, Figure 6As shown, a capacitor is connected in parallel between the first and second terminals of the insulated gate bipolar transistor. Under the control of the pulse signal, the photovoltaic cell 01 charges the capacitor. As the charging process continues, the first input voltage decreases and the first output voltage increases. However, since the photovoltaic cell 01 and the power conversion device 02 rely on this first input voltage to maintain normal operation, the controller needs to control the magnitude of the decrease in the first input voltage when providing the pulse signal to the DC conversion circuit. Similarly, if the first output voltage is too high, it will affect the safety of the components in the power conversion device 02. Therefore, when providing the pulse signal to the DC conversion circuit, the controller also needs to control the magnitude of the increase in the first output voltage. This control effect can be achieved by the duration of the pulse signal provided by the controller to the DC conversion circuit. In one implementation, the controller obtains the first input voltage and the first output voltage while providing the pulse signal to the DC conversion circuit. When the first input voltage is less than or equal to the second voltage threshold and / or the first output voltage is greater than or equal to the third voltage threshold, the controller stops sending the pulse signal to the DC conversion circuit. The values of the second and third voltage thresholds can be determined according to application requirements. For example, the value of the second voltage threshold can be selected to be equal to the starting voltage of the power conversion device. The value of the third voltage threshold can be selected based on the withstand voltage of the insulated gate bipolar transistor in the DC conversion circuit, such as the third voltage threshold is slightly less than the withstand voltage. In addition, the controller can also be optionally provided with a duty cycle threshold. When the duty cycle of the pulse signal increases to the duty cycle threshold, the controller stops sending the pulse signal to the DC conversion circuit. The value of the duty cycle threshold can be determined according to application requirements. For example, when the DC conversion circuit needs to rely on a PWM carrier to operate, the value of the duty cycle threshold can be selected to be less than or equal to the duty cycle of the PWM carrier to ensure that the duty cycle of the pulse signal is less than the duty cycle of the PWM carrier.

[0116] The first input voltage of the input end of the DC conversion circuit can be obtained by measuring the input voltage at the input end of the DC conversion circuit, or by measuring the output voltage at the output end of the photovoltaic cell. The input current at the input end of the DC conversion circuit can be obtained by measuring the input current at the input end of the DC conversion circuit 022, or by measuring the output current at the output end of the photovoltaic cell. For example, the controller can optionally sample the input current and the first input voltage at the input end of the DC conversion circuit multiple times in the process of providing a pulse sequence to the DC conversion circuit. Figure 15As shown, while providing a pulse sequence to the DC conversion circuit, the controller periodically samples the input current and first input voltage at the input end of the DC conversion circuit n times, obtaining n input currents and n first input voltages. n is a positive integer greater than 1. In this way, the controller can reproduce the volt-ampere characteristic curve of the photovoltaic cell based on the sampled input current and first input voltage, thereby obtaining the maximum output power of the photovoltaic cell based on the volt-ampere characteristic curve.

[0117] Optionally, before the controller provides the pulse sequence to the DC conversion circuit, it can also make a pre-judgment to determine whether it is necessary to provide the pulse sequence to the DC conversion circuit to obtain the maximum output power of the photovoltaic cell. Figure 16 As shown, before the controller provides the pulse sequence to the DC conversion circuit, the method further includes: step 1303, in which the controller obtains a second input voltage at the input end of the DC conversion circuit when the DC conversion circuit disconnects the output end of the photovoltaic cell from the common end of the photovoltaic cell. The implementation process of step 1301 then includes: step 13011, in which the controller sends multiple pulse signals with different duty cycles to the power conversion device when the second input voltage is greater than a fourth voltage threshold, so as to change the output current and output voltage of the DC conversion circuit, and repeatedly collects the input current and first input voltage at the input end of the DC conversion circuit. The value of the fourth voltage threshold can be determined based on application requirements. For example, the value of the fourth voltage threshold can be determined based on the startup conditions of the power conversion device. The fourth voltage threshold can be equal to or different from the first voltage threshold, and this is not specifically limited in the present embodiment. For the implementation process of step 1303, please refer to the relevant description of step 501. For the principle of step 13011, please refer to the relevant description of step 5021, and will not be repeated here.

[0118] Step 1302: The controller obtains the maximum output power of the photovoltaic cell based on the first input voltage and input current collected multiple times.

[0119] In one possible implementation, Figure 17 As shown, the implementation of step 1302 includes:

[0120] Step 13021: The controller obtains the power corresponding to the i-th time based on the input current and the first input voltage collected the i-th time among the multiple times, where i is a positive integer.

[0121] The controller can obtain the power corresponding to the i-th sampling operation based on the input current of the DC converter circuit and the first input voltage obtained in the i-th sampling operation. In one implementation, the power corresponding to the i-th sampling operation is equal to the product of the input current obtained in the i-th sampling operation and the first input voltage.

[0122] Step 13022: The controller determines the maximum output power of the photovoltaic cell based on the maximum value of the multiple corresponding powers.

[0123] After obtaining the power corresponding to each sampling operation in multiple sampling operations, the controller can obtain the maximum output power of the photovoltaic cell based on the multiple powers. In one implementation, the maximum output power of the photovoltaic cell is the maximum value of the multiple powers.

[0124] It should be noted that in order to ensure that the process of obtaining the maximum output power does not affect the load as much as possible, the scheme for obtaining the maximum output power needs to meet certain conditions in different scenarios. The following examples illustrate this. In one case, in response to the output end of the DC conversion circuit being connected to a load through the inverter circuit, the controller is used to stop obtaining the output current and output voltage of the output end of the DC conversion circuit during the process of the controller obtaining the first input voltage and input current, or to stop controlling the working state of the inverter circuit based on the output current and output voltage of the output end of the DC conversion circuit. In another case, during the process of the controller obtaining the first input voltage and input current, the output end of the DC conversion circuit does not supply power to the load. For the principles of these two cases, please refer to the relevant description in the first implementation scheme for obtaining the maximum output power of the photovoltaic cell, which will not be repeated here.

[0125] It should also be noted that to ensure the accuracy of the maximum output power estimate, the controller may estimate the maximum output power of the photovoltaic cell multiple times in a continuous manner according to the implementation method provided above, and obtain a final estimate based on the multiple estimated maximum output powers. For example, the controller may determine the final estimate as an average or weighted value of the multiple estimated maximum output powers.

[0126] The following is an example of the second implementation scheme for obtaining the maximum output power of photovoltaic cells. The two-stage photovoltaic inverter involved in this process is as follows: Figure 14 The pulse sequence provided by the controller to the DC conversion circuit is as follows. Figure 15 Assume that the actual maximum power of the photovoltaic cell is 55kW, its actual volt-ampere characteristic curve is as follows Figure 18 When the photovoltaic inverter is in standby mode, the power conversion device proposed in the embodiment of the present application is used to determine the maximum output power of the photovoltaic cell, and the implementation steps are as follows:

[0127] Step 1: After the photovoltaic inverter is powered on, the controller immediately measures the output voltage of the photovoltaic cell and obtains the second input voltage of the input end of the DC / DCBoost conversion circuit as 1000V. The sample value at this point is recorded.

[0128] Step 2: The controller provides a PWM pulse sequence to the control terminal of the insulated gate bipolar transistor in the DC / DC Boost converter circuit, linearly increasing the duty cycle of the pulse signal in the pulse sequence from 0. Simultaneously, the voltage and current values output by the photovoltaic cell during this process are sampled and stored. The voltage value sampled at the kth time is denoted as Vk, and the current value is denoted as Ik. Providing a PWM pulse sequence is equivalent to applying a series of short pulses of gradually increasing width to the control terminal of the insulated gate bipolar transistor in the DC / DC Boost converter circuit, where the maximum width of the short pulse is less than the PWM period.

[0129] Step 3: When the duty cycle of the pulse signal increases to 1, or the output voltage of the photovoltaic cell drops below 100V, or the output voltage of the DC / DC Boost converter circuit (i.e., the DC bus voltage) rises to exceed the overvoltage protection threshold of 1200V, the controller stops outputting the PWM pulse sequence. Figure 19 As shown in FIG, among the above three judgment conditions, the output voltage of the photovoltaic cell first drops below 100V, and the controller then stops outputting the PWM pulse sequence.

[0130] Step 4: The controller calculates the output power value corresponding to each sampling point using Pk=Vk×Ik based on the voltage and current values recorded in step 2. The output power value of the photovoltaic cell during the process of outputting the PWM pulse sequence of the control signal is as follows: Figure 19 As shown in the figure, both the PV characteristics and the volt-ampere characteristics of the photovoltaic cell have two peaks. The maximum value of 58kW is taken as the estimated maximum output power of the photovoltaic cell. This estimate is close to the actual maximum power of 55kW (within 6%).

[0131] Step 5: The controller sends the estimated maximum output power to the upper controller, which issues a start-up instruction to the PV inverter based on the estimated value. Alternatively, if the estimated maximum output power is greater than the start-up power threshold set by the PV inverter, the PV inverter automatically starts to connect to the grid / operate with load.

[0132] according to Figure 19 It can be seen from the simulation waveform shown that the maximum power estimation time of the photovoltaic inverter in the standby state is 11.5ms, which shows that the sampling method proposed in the embodiment of the present application can also realize the rapid estimation of the maximum available power of the photovoltaic inverter in the standby state. Compared with the related art, the power fluctuation caused by this method is smaller. When the DC bus only carries a 20W load (less than 4‰ of the maximum photovoltaic power), this method only causes a DC bus voltage fluctuation of 137V (13.7% of the no-load voltage of the photovoltaic cell). Compared with the aforementioned single-pulse detection method, the use of a pulse sequence to estimate the maximum output power can more accurately reproduce the multi-peak PV characteristics of the photovoltaic cell and obtain the maximum output power under the multi-peak characteristics of the photovoltaic cell. Figure 20 The photovoltaic volt-ampere characteristic curve is reproduced using the sampling data. It can be seen that the curve is consistent with Figure 18 The curves are essentially identical. Furthermore, since the voltage and current of the PV inverter change relatively smoothly during this estimation process, when estimating the maximum available output power based on a pulse sequence, it is possible to further optimize the relevant parameters of the pulse sequence. For example, the duty cycle growth rate in the pulse sequence can be further increased, thereby further shortening the maximum available power estimation time and reducing power / voltage fluctuations during the maximum power estimation process.

[0133] The second implementation scheme for obtaining the maximum output power of a photovoltaic cell described above can be called a maximum output power sequence pulse detection method. This sequence pulse detection method is more suitable for estimating the maximum power when the photovoltaic cell's output power-voltage (PV) characteristic curve has a single peak or multiple peaks.

[0134] The following describes the implementation process of the power conversion device by taking the use of a pulse sequence to estimate the maximum output power of multiple photovoltaic cells as an example.

[0135] Figure 21 Schematic diagram of providing a pulse sequence to a DC / DC Boost conversion circuit in a two-stage photovoltaic inverter according to an embodiment of the present application. Figure 21 As shown, the photovoltaic inverter includes multiple DC / DC Boost conversion circuits, each of which has its input connected to a photovoltaic cell. When multiple photovoltaic cells are connected to the photovoltaic inverter via multiple DC / DC Boost conversion circuits, the maximum output power of each photovoltaic cell is estimated using the same method as when using a pulse sequence to estimate the maximum output power of a single photovoltaic cell. After the estimation of one photovoltaic cell is completed and the circuit returns to its initial state, if the DC bus voltage connected to the DC / DC Boost conversion circuit drops to its initial value before obtaining the maximum output power, the maximum output power of the next photovoltaic cell can be obtained. Ultimately, the sum of the maximum output powers of each photovoltaic cell is taken as the maximum output power of the multiple photovoltaic cells, which is the maximum available power of the photovoltaic inverter. Similarly, the implementation scheme of using pulse signals to estimate the maximum output power of multiple photovoltaic cells can also be extended to the case of estimating the maximum output power of photovoltaic cells when the photovoltaic inverter includes multiple boost conversion circuits.

[0136] It should be noted that the order of the steps of the power conversion device provided in the embodiment of the present application can be appropriately adjusted. For example, step 502 can be optionally performed before step 501, or after step 501. The embodiment of the present application does not specifically limit it. In addition, the steps can also be increased or decreased accordingly according to the circumstances. Any person skilled in the art can easily think of a method of variation within the technical scope disclosed in this application, and all of them should be included in the scope of protection of this application, so they will not be described in detail.

[0137] The present application also provides a photovoltaic system, which includes photovoltaic cells and the power conversion device provided above.

[0138] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the various components described above can refer to the corresponding contents in the aforementioned method embodiments and will not be repeated here.

[0139] Those skilled in the art will understand that all or part of the steps to implement the above embodiments may be accomplished by hardware, or by a program to instruct the relevant hardware, and the program may be stored in a computer-readable storage medium, which may be a read-only memory, a disk, or an optical disk, etc.

[0140] It should be noted that the information (including but not limited to user device information, user personal information, etc.), data (including but not limited to data used for analysis, storage, display, etc.), and signals involved in this application are all authorized by the user or fully authorized by all parties, and the collection, use, and processing of relevant data must comply with the relevant laws, regulations, and standards of the relevant countries and regions. For example, the raw data and executable code involved in this application were obtained with full authorization.

[0141] In the embodiments of the present application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance. The term "at least one" refers to one or more, and the term "plurality" refers to two or more, unless otherwise expressly limited.

[0142] In this application, the term "and / or" simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0143] The above description is merely an optional embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the concepts and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A power conversion device, characterized in that: The power conversion device includes a controller and a DC conversion circuit, wherein the control end of the DC conversion circuit is used to connect to the controller, the input end of the DC conversion circuit is used to connect to the output end of the photovoltaic cell, and the output end of the DC conversion circuit is used to connect to a load, or the output end of the DC conversion circuit is used to connect to a load through an inverter circuit, and the controller is used to: controlling the DC conversion circuit to disconnect the output terminal of the photovoltaic cell from the common terminal of the photovoltaic cell, and obtaining a first input voltage at the input terminal of the DC conversion circuit; controlling the DC conversion circuit to short-circuit the output terminal of the photovoltaic cell and the common terminal of the photovoltaic cell to obtain an input current of the input terminal of the DC conversion circuit; The maximum output power of the photovoltaic cell is estimated based on the first input voltage and the input current.

2. The power conversion device according to claim 1, wherein: The controller is used to: Obtaining a fill factor of the photovoltaic cell, where the fill factor indicates how close the maximum output power is to an ideal output power of the photovoltaic cell; The maximum output power is estimated based on the fill factor, the first input voltage, and the input current.

3. The power conversion device according to claim 2, wherein: The maximum output power is a product of the fill factor, the first input voltage, and the input current.

4. The power conversion device according to any one of claims 1 to 3, characterized in that: The DC conversion circuit includes a switching device, the control end of the switching device is the control end of the DC conversion circuit, and the controller is used to provide a pulse signal to the control end of the switching device, so that the output end of the photovoltaic cell is short-circuited or disconnected from the common end of the photovoltaic cell.

5. The power conversion device according to any one of claims 1 to 4, characterized in that: The controller is used to control the DC conversion circuit to short-circuit the output end of the photovoltaic cell and the common end of the photovoltaic cell when the first input voltage is greater than a first voltage threshold.

6. The power conversion device according to any one of claims 1 to 5, characterized in that: In response to the output end of the DC conversion circuit being connected to the load through the inverter circuit, the controller is configured to: During the process of the controller acquiring the first input voltage and the input current, the controller stops acquiring the output current and the output voltage of the output end of the DC conversion circuit, or stops controlling the working state of the inverter circuit based on the output current and the output voltage of the output end of the DC conversion circuit.

7. The power conversion device according to any one of claims 1 to 5, characterized in that: During the process in which the controller obtains the first input voltage and the input current, the output end of the DC conversion circuit does not supply power to the load.

8. A power conversion device, characterized in that: The power conversion device includes a controller and a DC conversion circuit, wherein the control end of the DC conversion circuit is used to connect to the controller, the input end of the DC conversion circuit is used to connect to the output end of the photovoltaic cell, and the output end of the DC conversion circuit is used to connect to a load, or the output end of the DC conversion circuit is used to connect to a load through an inverter circuit, and the controller is used to: After the power conversion device is powered on, a plurality of pulse signals with different duty cycles are sent to the DC conversion circuit to change the output current and output voltage of the DC conversion circuit, and the input current and the first input voltage of the input end of the DC conversion circuit are collected multiple times; The maximum output power of the photovoltaic cell is obtained based on the first input voltage and the input current collected multiple times.

9. The power conversion device according to claim 8, wherein: The controller is configured to obtain the power corresponding to the i-th time based on the input current and the first input voltage collected the i-th time in the multiple times, and determine the maximum value of the powers corresponding to the multiple times as the maximum output power, where i is a positive integer.

10. The power conversion device according to claim 8 or 9, characterized in that: The duty cycles of the multiple pulse signals increase sequentially.

11. The power conversion device according to any one of claims 8 to 10, characterized in that: The controller is further configured to stop sending the pulse signal to the DC conversion circuit when the first input voltage is less than or equal to a second voltage threshold, and / or when the output voltage at the output end of the DC conversion circuit is greater than or equal to a third voltage threshold.

12. The power conversion device according to any one of claims 8 to 11, characterized in that: The controller is further configured to obtain a second input voltage at the input end of the DC conversion circuit when the DC conversion circuit disconnects the output end of the photovoltaic cell from the common end of the photovoltaic cell; The controller is used to send a plurality of pulse signals with different duty cycles to the power conversion device when the second input voltage is greater than a fourth voltage threshold, so as to change the output current and output voltage of the DC conversion circuit.

13. The power conversion device according to any one of claims 8 to 12, characterized in that: In response to the output end of the DC conversion circuit being connected to the load through the inverter circuit, the controller is configured to: During the process of the controller acquiring the first input voltage and the input current, the controller stops acquiring the output current and the output voltage of the output end of the DC conversion circuit, or stops controlling the working state of the inverter circuit based on the output current and the output voltage of the output end of the DC conversion circuit.

14. The power conversion device according to any one of claims 8 to 12, characterized in that: During the process in which the controller obtains the first input voltage and the input current, the output end of the DC conversion circuit does not supply power to the load.

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