Photovoltaic power generation system

Abstract

The application discloses a photovoltaic power generation system, comprising an inverter configured to control a first switch in a boost circuit to be turned on when start-up operation is required and an input voltage is not greater than a start-up voltage; control the boost circuit to perform maximum power tracking operation and output energy to a power grid when start-up operation is required and an input voltage of the boost circuit is greater than the start-up voltage; a contactor configured to control the second switch to be turned on or off the connection between the input end and the output end according to state parameter information collected by a state parameter acquisition unit; and a power module configured to provide a preset voltage to the DC bus when the second switch is off. The application controls the current or voltage of the photovoltaic module to the input end of the inverter through the inverter, realizes the turn-on or off of the contactor, controls the voltage output of the photovoltaic module, has high reliability, is not dependent on communication support, has a wide application range, and improves the stability of the photovoltaic system.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and more particularly to a photovoltaic power generation system. Background Technology

[0002] Photovoltaic power generation technology, as a renewable energy technology, is a new technology for improving climate and achieving carbon neutrality, and has been widely applied after more than a decade of rapid development. However, with the large-scale application of distributed systems, more and more photovoltaic systems are being installed on the roofs of residential buildings or factory buildings. To improve safety, photovoltaic power generation systems are required to be able to shut down quickly. In the event of a safety-related fault, the energy output of the photovoltaic modules is quickly shut off by a module shutdown device, and the module shutdown device restores the energy output of the photovoltaic modules only when power generation is needed after the fault has been cleared.

[0003] In existing photovoltaic power generation systems with module shutdown capabilities, to achieve secondary switching control of the module shutdown device, the inverter or a dedicated central controller needs to continuously send heartbeat communication signals via wireless or power line carrier (PLC) communication. This additional sending and receiving module not only increases costs but also necessitates additional on-site installations, such as providing power to the central controller. Furthermore, both wireless and PLC communication have relatively small coverage areas, making the construction of MW-level distributed commercial and industrial power plants a complex undertaking. Summary of the Invention

[0004] This application provides a photovoltaic power generation system, including:

[0005] An inverter includes at least one boost circuit, the boost circuit including an inductor and a first switch; the inverter is configured to control the first switch in the boost circuit to turn on when startup is required and the input voltage is not greater than the startup voltage; and to control the boost circuit to perform maximum power point tracking and output energy to the grid when startup is required and the input voltage of the boost circuit is greater than the startup voltage.

[0006] A shutdown device has an input terminal connected to one or more photovoltaic modules and an output terminal connected to an inverter via a DC bus. The shutdown device includes a second switch, a status parameter acquisition unit, and a power supply module. The shutdown device is configured to control the second switch to turn on or off the connection between the input terminal and the output terminal based on status parameter information acquired by the status parameter acquisition unit. The power supply module is configured to provide a preset voltage to the DC bus when the second switch is off.

[0007] In one example, the inverter is configured to control the first switch to open when it is not required to start up.

[0008] In one example, the inverter is configured to, when startup is required and the input voltage is not greater than the startup voltage, after controlling the first switch to turn on, if the current flowing through the first switch is greater than a first preset threshold, then control the first switch to turn off; otherwise, continue to control the first switch to turn on so that the output voltage of the shutdown device is short-circuited and pulled low.

[0009] In one example, the inverter is also configured to, after controlling the boost circuit to operate in maximum power point tracking mode, actively perturb the input voltage of the boost circuit so that the output voltage of the shutdown circuit meets the fluctuation condition if the detected current generated by the boost circuit is not greater than a second preset threshold.

[0010] In one example, if the inverter receives a notification from the upper-level monitoring to stop power generation or if the inverter has a safety fault, the inverter does not need to start operation; otherwise, the inverter needs to start operation.

[0011] In one example, the inverter has a safety fault that includes at least one of the following:

[0012] Arcing current was detected in the connected DC system;

[0013] Received a dry contact signal requiring emergency shutdown for maintenance;

[0014] A serious short circuit or overheating fault was detected in the inverter.

[0015] In one example, the shutdown device is configured to control the second switch to disconnect the connection between the input terminal and the output terminal when a safety fault is determined to exist in the shutdown device based on the status parameter information collected by the status parameter acquisition unit.

[0016] In one example, the safety fault of the shut-off device includes at least one of the following:

[0017] Input voltage is too low; temperature is too high; arc current information is sampled in the output current; reverse current exists in the output current; the phenomenon of low output voltage and high output current persists for more than the preset time.

[0018] In one example, the circuit breaker is configured to, when it is determined that there is no safety fault in the circuit breaker, control the second switch to turn on if the output current of the circuit breaker is greater than a third preset threshold, or if the output voltage of the circuit breaker meets a set condition when the output current of the circuit breaker is not greater than the third preset threshold; otherwise, control the second switch to turn off.

[0019] In one example, the output voltage of the shut-off device satisfies at least one of the following conditions:

[0020] The output voltage of the switch meets the fluctuation condition.

[0021] The output voltage of the shutdown device is pulled low by a short circuit.

[0022] The photovoltaic power generation system provided in this application controls the current or voltage from the photovoltaic modules to the inverter input terminal through an inverter, thereby turning on or off the circuit breaker and controlling the voltage output of the photovoltaic modules. It has high reliability, does not rely on communication support, has a wide range of applications, and improves the stability of the photovoltaic system. Attached Figure Description

[0023] Figure 1 A schematic diagram of a photovoltaic power generation system provided for an embodiment of this application;

[0024] Figure 2 A schematic diagram of another photovoltaic power generation system provided for an embodiment of this application;

[0025] Figure 3 A schematic diagram of another photovoltaic power generation system provided for the embodiments of this application;

[0026] Figure 4 This is a schematic diagram of the shut-off device provided in the embodiments of this application;

[0027] Figure 5 This is a schematic diagram of the inverter start-up control process provided in the embodiments of this application;

[0028] Figure 6 This is a schematic diagram of the control flow for whether the inverter needs to be started and operated according to the embodiments of this application;

[0029] Figure 7 This is a schematic diagram of the shutdown control flow provided in the embodiments of this application;

[0030] Figure 8 This is a schematic diagram illustrating the detection of whether a shutdown device has a safety fault, as provided in the embodiments of this application.

[0031] Figure 9 This is a schematic diagram of the control flow for whether the output voltage of the shut-off device provided in the embodiments of this application meets the set conditions.

[0032] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0033] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer and more understandable, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application.

[0034] In the description of this application, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," and "right," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] Figure 1 This is a schematic diagram of a photovoltaic power generation system provided in the embodiments of this application.

[0036] like Figure 1 As shown, the photovoltaic power generation system includes n photovoltaic modules, n power off switches, and an inverter.

[0037] The input terminals of n circuit breakers are connected one-to-one with the output terminals of n photovoltaic modules. The output terminals of the n circuit breakers are cascaded. The positive output terminal of the cascaded circuit breaker is connected to the positive input terminal of the inverter through the positive DC bus, and the negative output terminal of the cascaded circuit breaker is connected to the negative input terminal of the inverter through the negative DC bus.

[0038] The inverter includes a first boost circuit (shown by the dashed box in the figure), which includes, for example, an inductor L1, a switch Q1, and a diode D1; the boost circuit is not limited to the form shown in the figure. By controlling the switch Q1 in the first boost circuit, maximum power point tracking (MPPT) can be performed on the voltage between the positive and negative DC buses, and finally, the voltage is inverted by the inverter circuit in the inverter and connected to the AC grid. The switch Q1 includes, but is not limited to, IGBTs, IGCTs, MOSFETs, etc.; in other examples, diode D1 can be replaced by other devices, such as IGBTs, MOSFETs, etc.

[0039] Figure 2 This is a schematic diagram of another photovoltaic power generation system provided in the embodiments of this application.

[0040] and Figure 1 The example differs in that the photovoltaic power generation system includes 2n photovoltaic modules, and the input of each switch is connected to multiple photovoltaic modules, such as two photovoltaic modules.

[0041] Figure 3This is a schematic diagram of another photovoltaic power generation system provided in the embodiments of this application.

[0042] and Figure 1 The example differs in that the photovoltaic power generation system also includes m photovoltaic modules and m circuit breakers. The input terminals of the m circuit breakers are connected one-to-one with the output terminals of the m photovoltaic modules. The output terminals of the m circuit breakers are cascaded. The positive output terminal of the cascaded circuit breaker is connected to the positive input terminal of the inverter through another positive DC bus. The negative output terminal of the cascaded circuit breaker is connected to the negative input terminal of the inverter through another negative DC bus.

[0043] The inverter also includes a second boost circuit (shown by the dashed box in the figure), which includes, for example, an inductor L2, a switch Q2, and a diode D2. By controlling the switch Q2 in the second boost circuit, maximum power point tracking (MPPT) can be performed on the voltage between the other positive DC bus and the other negative DC bus. Finally, the voltage is inverted by the inverter circuit in the inverter and connected to the AC grid. Similarly, the switch Q2 includes, but is not limited to, IGBTs, IGCTs, MOSFETs, etc.; in other examples, diode D2 can be replaced by other devices, such as IGBTs, MOSFETs, etc.

[0044] Figure 4 This is a schematic diagram of the shut-off device provided in the embodiments of this application.

[0045] like Figure 4 As shown, the shutdown device includes switch K1, drive unit, input voltage sampling unit, output voltage sampling unit, temperature detection unit, output current sampling unit, processor, auxiliary power supply, low voltage power supply module Vdc, switch K2, and bypass diode D3.

[0046] Switches K1 and K2 include, but are not limited to, relays, IGBTs, IGCTs, MOSFETs, etc.

[0047] Vin is the input voltage of the switch, and Vo is the output voltage of the switch. The connection relationship between the positive or negative input / output terminals of the switch and the photovoltaic modules and inverters can be referred to the aforementioned photovoltaic power generation system.

[0048] Switch K1 is set on the positive or negative branch of the circuit breaker.

[0049] The processor's output is connected to the control terminal of switch K1 via a drive unit. The processor outputs a control signal to drive switch K1 to turn on or off via the drive unit, thereby turning the shut-off device on or off.

[0050] The status parameters of the circuit breaker include input voltage, output voltage, temperature, and output current. These parameters reflect the status of the circuit breaker. The output current refers to the output current including the bypass diode D3 channel. Input voltage, output voltage, temperature, and output current are measured through an input voltage sampling unit, an output voltage sampling unit, a temperature detection unit, and an output current sampling unit, respectively. These units constitute the circuit breaker's status parameter acquisition unit.

[0051] The auxiliary power supply draws power from the input of the circuit breaker, i.e., the output voltage of the photovoltaic module. One output of the auxiliary power supply is used for the auxiliary power supply of the circuit breaker (such as the power supply of the processor in the figure), and the other output generates a low-voltage power module Vdc. One end of the low-voltage power module Vdc is connected to the negative output terminal of the circuit breaker, and the other end of the low-voltage power module Vdc is connected to the positive output terminal of the circuit breaker through switch K2.

[0052] The bypass diode D3 is used to enable the bypass output of the shutdown device when it is open.

[0053] It should be noted that, in other examples, it is also feasible to integrate the driver unit into the processor. It is also feasible to implement the bypass diode D3 using other bypass circuits.

[0054] Figure 5 This is a schematic diagram of the inverter start-up control process provided in the embodiments of this application.

[0055] First, determine whether the inverter needs to be started and operated to generate electricity.

[0056] The prerequisites for whether or not to start generating electricity are: on the one hand, no notification has been received from the upper-level monitoring to stop generating electricity, and on the other hand, the inverter itself does not have any safety faults.

[0057] Figure 6 This is a schematic diagram illustrating the control flow for determining whether an inverter needs to be started and operated, as provided in the embodiments of this application. Figure 6 As shown, the reason for the power generation shutdown notification from the upper-level monitoring system could be insufficient power demand, or it could be due to maintenance or repair work in the area, requiring the disconnection of component power for the safety of maintenance personnel. Safety faults affecting the inverter include the detection of DC arcing in the DC system connected to the inverter, the receipt of a dry contact signal requiring emergency shutdown for repairs, or the detection of severe internal short circuits or inverter failure.

[0058] When the inverter does not need to be started, control the switches in all boost circuits (e.g.) Figure 3 When Q1, Q2, etc. in the inverter are disconnected, the inverter circuit in the inverter also stops working. Under this condition, all photovoltaic modules output open-circuit voltage, that is, the photovoltaic modules have no current output.

[0059] If the inverter needs to start up, it checks the input voltage of each boost circuit. If the input voltage of at least one boost circuit is greater than the startup voltage, that boost circuit operates in Maximum Power Point Tracking (MPPT), and the inverter circuit in the inverter outputs energy to the grid. At this time, the photovoltaic module corresponding to that boost circuit generates DC current and outputs power. It then checks whether the current generated by that boost circuit is greater than a set threshold. If it is, the inverter does not actively disturb the input voltage of that boost circuit. The corresponding shutdown circuit breaker checks whether the detected output current is greater than a certain threshold. If so, it directly keeps the shutdown switch K1 on. Conversely, if the sunlight is weak or the inverter has just started up and is not yet loaded, the current generated by that boost circuit is not greater than the set threshold. In this case, the inverter needs to actively disturb the input voltage of that boost circuit within a certain range so that the output voltage detected by the corresponding shutdown circuit breaker meets the fluctuation condition to keep the shutdown switch K1 on.

[0060] Compared to existing technologies, the above control method only actively disturbs the input voltage of the boost circuit when the current generated by the boost circuit is not greater than a set threshold. This significantly reduces the overall disturbance time and thus greatly minimizes power generation loss. If the inverter needs to start up, but at least one boost circuit's input voltage is lower than or equal to the startup voltage, then the switch in that boost circuit is turned on. After a certain time T (e.g., 3 seconds), the current flowing through the switch in the boost circuit is detected; this current is generally equal to the inductor current in the boost circuit. If this current exceeds a certain threshold of the boost circuit's rated current (e.g., 10%), the corresponding circuit breaker is considered to be on, and the photovoltaic module can output energy to the inverter's input. Otherwise, the switch in that boost circuit continues to be turned on to short-circuit the output of the corresponding circuit breaker, ensuring that the circuit breaker's output voltage is pulled low due to the short circuit.

[0061] In situations where photovoltaic (PV) modules have no energy output for extended periods at night, or where no PV modules are connected to a certain boost circuit of the inverter, as described above, the switch of that boost circuit may remain on for an extended period. However, since the PV modules have no energy, this prolonged short circuit does not affect the reliability of the inverter. Alternatively, other intelligent detection methods can be added to identify this issue and, after multiple confirmations, deactivate the switch in that boost circuit, effectively disconnecting it.

[0062] Figure 7 This is a schematic diagram of the shutdown control flow provided in the embodiments of this application.

[0063] First, monitor the status parameters of the circuit breaker itself in real time to determine if there is a safety fault.

[0064] Figure 8 This is a schematic diagram illustrating the detection process for whether a shutdown device has a safety fault, as provided in the embodiments of this application. Figure 8 As shown, the circuit breaker's input voltage, output voltage, output current, and temperature are monitored. If the input voltage is too low, it indicates insufficient light intensity and an undervoltage fault. If the circuit breaker temperature is too high, there is a safety hazard. If arc current information is sampled in the output current, there is a safety hazard. If a large negative current is sampled in the output current (e.g., exceeding 50% of the rated current), there is a reverse current safety hazard. If the output voltage and output current exhibit a prolonged period of low voltage and high current (e.g., voltage below 50% of the rated voltage and current above 50% of the rated current), there is an output short circuit fault.

[0065] If the circuit breaker has a safety fault, then disconnect the switch K1 of the circuit breaker to stop the energy output of the corresponding photovoltaic module.

[0066] If the circuit breaker has no safety fault, then determine whether the output current of the circuit breaker is greater than the set threshold (e.g., 5% of the rated current). If it is greater, it means that it is generating electricity normally, and control the circuit breaker switch K1 to conduct, so that the energy of the corresponding photovoltaic module can be output. Otherwise, determine whether the output voltage of the circuit breaker meets the set conditions. If the set conditions are met, control the circuit breaker switch K1 to conduct, so that the energy of the corresponding photovoltaic module can be output. If the set conditions are not met, control the circuit breaker switch K1 to open, and stop the energy output of the corresponding photovoltaic module.

[0067] Figure 9 This is a schematic diagram of the control flow for whether the output voltage of the shut-off device provided in the embodiments of this application meets the set conditions.

[0068] like Figure 9As shown, when switch K1 of the circuit breaker is on, it is detected whether the output voltage of the circuit breaker meets the fluctuation condition, that is, it changes within a certain time and a certain range (e.g., a change of 5% or more within 1 second). If the output voltage meets the fluctuation condition, it is determined that the set condition is met; otherwise, it is not met. Alternatively, when switch K1 of the circuit breaker is off, it is detected whether the voltage output from the low-voltage power supply module Vdc of the circuit breaker to the DC bus is pulled down by a short circuit. If not, it means that the switch of the boost circuit in the inverter is not on, and the inverter start-up operation condition is not met. In this case, it is determined that the output voltage of the circuit breaker does not meet the set condition. If the voltage output from the low-voltage power supply module Vdc of the circuit breaker to the DC bus is pulled down by a short circuit, it means that the switch of the boost circuit in the inverter is on, and the inverter start-up operation condition is met. In this case, it is determined that the output voltage of the circuit breaker meets the set condition, and the switch K1 of the circuit breaker is turned on, so that the energy of the corresponding photovoltaic module can be output.

[0069] As an example, for Figure 1-3 The photovoltaic power generation system shown, if the open-circuit voltage of each photovoltaic module is 50V, and the voltage corresponding to the current maximum power point tracking (MPPT) is 40V, using 18 photovoltaic modules connected in series to the inverter, the open-circuit voltage after series connection is 900V, and the voltage corresponding to the maximum power point tracking (MPPT) is 720V. Figure 9 Under the conditions shown, if the sunlight is weak and the current corresponding to the Maximum Power Point Tracking (MPPT) is less than 0.5A, the inverter will cause some fluctuation in the input voltage of the boost circuit, allowing it to fluctuate between 720V±50V, or between 670-770V. According to a certain calculation formula, the output voltage of the corresponding shutdown switch will fluctuate between 37.2-42.7V, satisfying the condition that the voltage fluctuation range is greater than the set value. If the sunlight continues to weaken, the current corresponding to the MPPT will be even smaller and insufficient to compensate for the inverter's own losses. In this case, the inverter will stop operating, disconnect the switch in the boost circuit, and the voltage of the corresponding photovoltaic module will return to the open circuit voltage. The output voltage detected by the shutdown switch will no longer fluctuate, thus disconnecting the switch K1 of the second shutdown switch.

[0070] like Figure 4 As shown, when switch K1 of the shutdown circuit breaker is open, switch K2 corresponding to the low-voltage power module Vdc is turned on. Each shutdown circuit breaker outputs a low voltage of approximately 1V to the DC bus. After the 18 shutdown circuit breakers are connected in series, the input voltage of the inverter is 18V. If the inverter needs to start running at this time, it will control the switch in the boost circuit to turn on, which is equivalent to short-circuiting the output of the shutdown circuit breaker. At this time, the 1V output voltage of the shutdown circuit breaker drops to close to 0V, thus meeting the condition for the shutdown circuit breaker output voltage setting and controlling switch K1 of the shutdown circuit breaker to turn on.

[0071] When switch K1 of the circuit breaker is on, the output voltage is 30-50V, while when switch K1 is off, the voltage output to the DC bus is only about 1V. To increase the accuracy of the detection, instead of directly detecting the output voltage of the circuit breaker when switch K1 is off, we can detect the voltage of the low-voltage power supply module Vdc at the front end of switch K2, or detect the output current of the low-voltage power supply module Vdc. When the inverter needs to start up and the switch in the boost circuit is on, the low-voltage power supply module Vdc outputs a certain current; when the inverter is not running and the switch in the boost circuit is off, the output of the low-voltage power supply module Vdc is open, and there is no current output.

[0072] The preferred embodiments of this application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and spirit of this application shall be within the scope of the claims.

Claims

1. A photovoltaic power generation system, characterized in that, include: An inverter includes at least one boost circuit, the boost circuit including an inductor and a first switch; the inverter is configured to control the first switch in the boost circuit to turn on when startup is required and the input voltage of the boost circuit is not greater than the startup voltage; When startup is required and the input voltage of the boost circuit is greater than the startup voltage, the boost circuit is controlled to perform maximum power point tracking and output energy to the grid. A power off device has an input terminal connected to one or more photovoltaic modules and an output terminal connected to an inverter via a DC bus. The power off device includes a second switch, a status parameter acquisition unit, and a power supply module. The power off device is configured to control the second switch to turn on or off the connection between the input terminal and the output terminal based on the status parameter information acquired by the status parameter acquisition unit. The power module is configured to provide a preset voltage to the DC bus when the second switch is open; The circuit breaker is configured to, when it is determined that there is no safety fault in the circuit breaker, control the second switch to be turned on if the output current of the circuit breaker is greater than a third preset threshold, or if the output voltage of the circuit breaker meets the set conditions when the output current of the circuit breaker is not greater than the third preset threshold; otherwise, control the second switch to be turned off. The circuit breaker is configured to detect whether the voltage output from the power module to the DC bus is pulled low by a short circuit when the second switch is open; if the voltage output from the power module to the DC bus is pulled low by a short circuit, the output voltage of the circuit breaker meets the set condition; if the voltage output from the power module to the DC bus is not pulled low by a short circuit, the output voltage of the circuit breaker does not meet the set condition.

2. The photovoltaic power generation system according to claim 1, characterized in that, The inverter is configured to control the first switch to open when it is not required to start up.

3. The photovoltaic power generation system according to claim 1, characterized in that, The inverter is configured such that when it needs to start up and the input voltage is not greater than the start-up voltage, after controlling the first switch to turn on, if the current flowing through the first switch is greater than a first preset threshold, the first switch is controlled to turn off. Otherwise, continue to control the first switch to be turned on so that the output voltage of the shutdown device is short-circuited and pulled down.

4. The photovoltaic power generation system according to claim 1, characterized in that, The inverter is also configured to, after controlling the boost circuit to operate in maximum power point tracking mode, actively perturb the input voltage of the boost circuit if the detected current generated by the boost circuit is not greater than a second preset threshold, so that the output voltage of the shutdown circuit meets the fluctuation condition.

5. The photovoltaic power generation system according to claim 1, characterized in that, If the inverter receives a notification from the upper-level monitoring system to stop power generation or if the inverter has a safety fault, the inverter does not need to start operation; otherwise, the inverter needs to start operation.

6. The photovoltaic power generation system according to claim 5, characterized in that, The inverter has a safety fault including at least one of the following: Arcing current was detected in the connected DC system; Received a dry contact signal requiring emergency shutdown for maintenance; A serious short circuit or overheating fault was detected in the inverter.

7. The photovoltaic power generation system according to claim 1, characterized in that, The shutdown device is configured to control the second switch to disconnect the connection between the input terminal and the output terminal when it is determined that the shutdown device has a safety fault based on the status parameter information collected by the status parameter acquisition unit.

8. The photovoltaic power generation system according to claim 7, characterized in that, The shutdown device has a safety fault including at least one of the following: Input voltage is too low; temperature is too high; arc current information is sampled in the output current; reverse current exists in the output current; the phenomenon of low output voltage and high output current persists for more than the preset time.

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