An electrolytic capacitor-less photovoltaic system and method of operation thereof

Abstract

The application discloses a non-electrolytic capacitor photovoltaic system, which comprises a photovoltaic power generation system, an energy storage module and a control system; the photovoltaic power generation system is adapted to be connected to a power grid, the energy storage module is adapted to be electrically connected to the photovoltaic power generation system, the control system is electrically connected to the photovoltaic power generation system and the energy storage module respectively, and the control system is adapted to control the energy storage module to compensate the photovoltaic power generation system according to the working state of the photovoltaic power generation system. The application also discloses a working method of the non-electrolytic capacitor photovoltaic system, which is applied to the above-mentioned non-electrolytic capacitor photovoltaic system. Through the compensation of the energy storage module to the photovoltaic power generation system, the normal power generation, high-low voltage ride-through and night SVG function of the photovoltaic power generation system can be realized; thus, the traditional electrolytic capacitor can be removed, only a small-capacity and long-life capacitor is needed to meet the bus capacitor demand of the photovoltaic power generation system, and the service life and reliability of the whole photovoltaic power generation system are improved.

Description

Technical Field

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

[0002] Photovoltaic power generation systems typically have a long lifespan, approximately 30 years. To construct long-life and highly reliable photovoltaic systems, in addition to the photovoltaic panels themselves meeting the system's lifespan requirements, the power electronic devices must also avoid using components with short lifespans and low reliability, such as electrolytic capacitors.

[0003] Photovoltaic systems have low-voltage and high-voltage ride-through requirements. When low or high voltage occurs in the grid, power electronic devices need to generate or absorb reactive power to support the grid voltage. This reactive power enters the DC bus, causing voltage fluctuations and affecting output waveform quality. Furthermore, when there are sudden increases or decreases in input or output power, the dynamic power is generally borne by the DC bus, which also causes voltage fluctuations. At night, the photovoltaic panels cannot generate electricity, and the photovoltaic system is idle. In this situation, the photovoltaic system can be used as a reactive power generator (SVG) to send reactive power to the grid. At this time, a large amount of reactive power enters the DC bus, causing voltage fluctuations.

[0004] To address the aforementioned issues, the traditional solution is to increase the DC bus capacitance to suppress bus voltage fluctuations. However, this requires a large capacitance, typically necessitating the use of electrolytic capacitors, which is undesirable from the perspective of long system lifespan and high reliability. Therefore, a highly reliable photovoltaic system is urgently needed. Summary of the Invention

[0005] One of the objectives of this application is to provide a photovoltaic system that can improve system lifespan and reliability by avoiding the use of electrolytic capacitors.

[0006] Another objective of this application is to provide a method for operating a photovoltaic system that can improve system lifespan and reliability by avoiding the use of electrolytic capacitors.

[0007] To achieve the above objectives, the technical solution adopted in this application is as follows: an electrolytic capacitor-free photovoltaic system, comprising a photovoltaic power generation system, an energy storage module, and a control system; the photovoltaic power generation system is adapted to be connected to the power grid, the energy storage module is adapted to be electrically connected to the photovoltaic power generation system, and the control system is electrically connected to both the photovoltaic power generation system and the energy storage module; the control system is adapted to detect the current or voltage value of the bus in the photovoltaic power generation system, and when the detected current or voltage value meets preset conditions, the control system is adapted to control the energy storage module to perform current or voltage compensation on the bus of the photovoltaic power generation system, which can reduce the bus capacitance value of the photovoltaic power generation system, thereby requiring only small-capacity, high-lifespan capacitors to meet system requirements, and thus improving the service life of the entire photovoltaic power generation system.

[0008] Preferably, the photovoltaic power generation system includes a PV module, a DC / DC conversion module, and a DC / AC conversion module connected in sequence via busbars; the photovoltaic power generation system is adapted to be connected to the power grid through the DC / AC conversion module; adjacent busbars between the DC / DC conversion module and the DC / AC conversion module are connected via busbar capacitors.

[0009] Preferably, the energy storage module includes an energy storage unit connected to a bus in the photovoltaic power generation system; or, the energy storage module includes an energy storage unit and a bidirectional DC / DC unit, wherein the energy storage unit is adapted to be connected to a bus in the photovoltaic power generation system via the bidirectional DC / DC unit.

[0010] Preferably, the energy storage module is connected to the bus between the PV module and the DC / DC conversion module in the photovoltaic power generation system, or the energy storage module is connected to the bus between the DC / DC conversion module and the DC / AC conversion module in the photovoltaic power generation system.

[0011] Preferably, the control system includes a bus voltage control module, a circuit detection module, a path selection module, and a current control module; the bus voltage control module is adapted to extract the voltage value of the bus capacitor in the photovoltaic power generation system; the circuit detection module is adapted to extract the current value or voltage value of the bus between the DC / DC conversion module and the DC / AC conversion module in the photovoltaic power generation system; the current control module is adapted to send a current tracking command to the bidirectional DC / DC unit; the path selection module is adapted to connect the bus voltage control module or the circuit detection module to the current control module according to the operating state of the photovoltaic power generation system, so that the current control module sends a current tracking command to the bidirectional DC / DC unit, and then the bidirectional DC / DC unit controls the energy storage unit to compensate the photovoltaic power generation system according to the current tracking command.

[0012] Preferably, the control system further includes a capacitor voltage control module, the output terminal of which is adapted to be electrically connected to the current control module, the input terminal of which is adapted to be electrically connected to the energy storage unit, and the capacitor voltage control module is adapted to send an adjustment signal to the current control module according to the operating state of the energy storage unit, thereby the current control module controls the bidirectional DC / DC unit to adjust the operating state of the energy storage unit according to the adjustment signal.

[0013] Preferably, the circuit detection module is a high- and low-frequency current extraction module, which is adapted to extract the current difference between the bus and the output side of the DC / DC conversion module and the input side of the DC / AC conversion module in the photovoltaic power generation system; the bidirectional DC / DC unit is adapted to use the component of a set frequency range in the current difference as an output command to control the energy storage unit to compensate the bus.

[0014] Preferably, the circuit detection module is a bus voltage over-limit control module, which is adapted to extract the voltage value of the bus in the photovoltaic power generation system; when the extracted voltage value is within the set upper and lower limits, the bidirectional DC / DC unit does not compensate the bus; when the extracted voltage value exceeds the set upper and lower limits, the bidirectional DC / DC unit is adapted to use the difference between the extracted voltage value and the set upper and lower limits as an output command to control the energy storage unit to compensate the bus.

[0015] Preferably, the control system further includes a drive blocking module, the input terminal of which is connected to the current control module, and the output terminal of which is connected to the bidirectional DC / DC unit. When the extracted bus voltage value or the voltage value of the energy storage unit exceeds a set upper or lower limit, the drive blocking module is adapted to connect the current control module to the bidirectional DC / DC unit, so that the bidirectional DC / DC unit controls the energy storage unit to compensate the bus; otherwise, the drive blocking module is adapted to block the bidirectional DC / DC unit.

[0016] A method for operating an electrolytic capacitor-free photovoltaic system includes the following steps:

[0017] S100: When the PV module is in power generation mode, the path selection module connects the circuit detection module and the current control module;

[0018] S200: The circuit detection module can extract the current or voltage value of the bus in the photovoltaic power generation system, and control the current control module to send output commands to the bidirectional DC / DC unit based on the extracted current or voltage value.

[0019] S300: The bidirectional DC / DC unit controls the energy storage unit to compensate the bus in the photovoltaic power generation system according to the output command;

[0020] S400: When the PV module is in non-power generation mode, the photovoltaic power generation system is used as a reactive power generator; at this time, the path selection module connects the bus voltage control module and the current control module.

[0021] S500: The bus voltage control module can extract the voltage value of the bus capacitor in the photovoltaic power generation system, and control the current control module to send output commands to the bidirectional DC / DC unit according to the extracted voltage value.

[0022] S600: The bidirectional DC / DC unit controls the energy storage unit to provide reactive power compensation to the grid according to the output command, so that the DC bus section on the PV module side does not need to bear the reactive power component.

[0023] Preferably, step S200 further includes the following steps:

[0024] S210: When the circuit detection module extracts the current value of the bus in the photovoltaic power generation system, the circuit detection module can use the component of the extracted current value in the set frequency range as the output command; and when the circuit detection module extracts the voltage value of the bus in the photovoltaic power generation system, the following steps are performed;

[0025] S220: When the extracted voltage value is within the set upper and lower limits, the drive blocking module is in a blocked state, so that the bidirectional DC / DC unit does not compensate the bus.

[0026] S230: When the extracted voltage value exceeds the set upper and lower limits, the drive blocking module connects the current control module to the bidirectional DC / DC unit; thus, the bidirectional DC / DC unit can use the difference between the extracted voltage value and the set upper and lower limits as an output command.

[0027] Compared with the prior art, the beneficial effects of this application are as follows:

[0028] (1) By compensating the photovoltaic power generation system through the energy storage module, the photovoltaic power generation system can realize normal power generation, high and low voltage ride-through, and nighttime SVG functions. As a result, the traditional electrolytic capacitors can be removed, and only small-capacity, long-life capacitors are needed to meet the bus capacitor requirements of the photovoltaic power generation system, thereby improving the service life and reliability of the entire photovoltaic power generation system.

[0029] (2) The energy storage unit in the energy storage module has a large voltage variation range, absorbs and releases a large amount of energy, and has strong reactive power support capability. It can meet the various functional requirements of the photovoltaic power generation system. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall process of the present invention.

[0031] Figure 2 This is a circuit diagram of the photovoltaic power generation system in this invention.

[0032] Figure 3 This is a circuit diagram of one embodiment of the energy storage module in this invention.

[0033] Figure 4 This is a schematic diagram of one embodiment of the connection between the energy storage module and the photovoltaic power generation system in this invention.

[0034] Figure 5 This is a schematic diagram of another embodiment of the connection between the energy storage module and the photovoltaic power generation system in this invention.

[0035] Figure 6 This is a schematic diagram of another embodiment of the connection between the energy storage module and the photovoltaic power generation system in this invention.

[0036] Figure 7 This is a circuit diagram of one embodiment of the control system in this invention.

[0037] Figure 8 This is a circuit diagram of another embodiment of the control system in this invention.

[0038] Figure 9 This is a circuit diagram of another embodiment of the control system in this invention.

[0039] Figure 10 This is a schematic diagram of the overall circuit connection of one embodiment of the present invention.

[0040] Figure 11 This is a schematic diagram of the overall circuit connection of another embodiment of the present invention.

[0041] Figure 12 This is a schematic diagram of the overall circuit connection of another embodiment of the present invention.

[0042] In the diagram: 1. Photovoltaic power generation system; 100. Grid; 2. Energy storage module; 21. Bidirectional DC / DC unit; 22. Energy storage unit; 3. Control system; 31. Bus voltage control module; 32. Circuit detection module; 33. Path selection module; 34. Capacitor voltage control module; 35. Current control module; 36. Drive blocking module. Detailed Implementation

[0043] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0044] In the description of this application, it should be noted that the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., which indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are 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 should not be construed as limiting the specific protection scope of this application.

[0045] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0046] One aspect of this application provides a capacitor-free photovoltaic system, such as... Figures 1 to 12 As shown, one preferred embodiment includes a photovoltaic power generation system 1, an energy storage module 2, and a control system 3. The photovoltaic power generation system 1 can be connected to the power grid 100; the energy storage module 2 can be electrically connected to the photovoltaic power generation system 1; the control system 3 is electrically connected to both the photovoltaic power generation system 1 and the energy storage module 2, and the control system 3 can control the energy storage module 2 to compensate the photovoltaic power generation system 1 according to the operating status of the photovoltaic power generation system 1.

[0047] Understandably, during the day, photovoltaic power generation system 1 can generate photovoltaic power and transmit the generated electricity to the power grid 100. During this process, affected by factors such as weather, photovoltaic power generation system 1 includes normal power generation states and abnormal power generation states (high and low voltage ride-through) due to overvoltage or undervoltage. At night, photovoltaic power generation system 1 cannot generate power and is in an idle state; at this time, photovoltaic power generation system 1 is used as a reactive power generator (SVG) to send reactive power to the power grid 100.

[0048] In this embodiment, as Figures 2 to 6 As shown. The circuit connection structure of the photovoltaic power generation system 1 is well known in the art, specifically including a PV module, a DC / DC conversion module, and a DC / AC conversion module connected sequentially via busbars. The photovoltaic power generation system 1 can be connected to the power grid 100 through the DC / AC conversion module. Adjacent busbars between the DC / DC conversion module and the DC / AC conversion module are connected via busbar capacitors C. dc1 and C dc2 Establish a connection.

[0049] Understandably, during the day, PV modules can convert light energy into electrical energy through sunlight; the converted electrical energy can then be transmitted to the power grid via the bus through the DC / DC conversion module and the DC / AC conversion module.

[0050] To suppress voltage fluctuations on the busbar caused by high- and low-voltage ride-throughs or reactive power transmission, traditional photovoltaic systems use large-capacity electrolytic capacitors as busbar capacitors. However, electrolytic capacitors have a short lifespan and low reliability, failing to meet the long-life requirements of photovoltaic systems.

[0051] Therefore, this application addresses the aforementioned bus voltage fluctuation problem by adding an energy storage module 2. During the day, when the photovoltaic power generation system 1 is in the aforementioned high-low voltage ride-through state, the control system 3 can control the energy storage module 2 to compensate the current or voltage of the photovoltaic power generation system 1, ensuring that the photovoltaic power generation system 1 can always be in a normal power generation state. At this time, the bus capacitor C in the photovoltaic power generation system 1... dc1 and C dc2 It only needs to handle the switching frequency component generated during the operation of the DC / DC converter module; thus, the bus capacitor C dc1 and C dc2 The required capacitance value will be greatly reduced, i.e., the bus capacitance C in the photovoltaic power generation system 1 of this application. dc1 and C dc2 Capacitors with small capacitance and long lifespan, such as film capacitors, are characterized by their small size, large capacitance, and high stability.

[0052] Meanwhile, at night, when the photovoltaic power generation system 1 acts as a reactive power generator (SVG) to send reactive power to the grid 100, the grid 100 transmits the reactive power command to the DC / AC conversion module. At this time, the control system 3 can control the energy storage module 2 to provide the required reactive power to the grid 100. Thus, during the above process, the bus voltage will be supported by the energy storage module 2; therefore, the bus of the photovoltaic power generation system 1 does not need to bear the reactive power component required by the grid 100, but only the switching frequency component.

[0053] One embodiment of this application, such as Figures 1 to 12 As shown, the energy storage module 2 has various structures, including but not limited to the following two structures:

[0054] Structure 1: such as Figure 6 As shown, the energy storage module 2 includes an energy storage unit 22, which is directly connected to the bus in the photovoltaic power generation system 1.

[0055] Structure 2: such as Figures 1 to 5 and Figures 7 to 12As shown, the energy storage module 2 includes an energy storage unit 22 and a bidirectional DC / DC unit 21. The energy storage unit 22 can be connected to the bus in the photovoltaic power generation system 1 through the bidirectional DC / DC unit 21.

[0056] It is understood that the bidirectional DC / DC unit 21 may employ, but is not limited to, a bidirectional BUCK / BOOST circuit; the energy storage unit 22 may employ, but is not limited to, supercapacitors and thin-film capacitors. Supercapacitors are preferred because they have the characteristics of long service life, high charge / discharge cycles, small size, and high power density.

[0057] Meanwhile, when a high- or low-voltage crossover occurs on the busbar of the photovoltaic power generation system 1, the energy storage unit 22 performs current or voltage compensation on the busbar under the control of the control system 3. When the photovoltaic power generation system 1 is used as a reactive power generator (SVG) to send reactive power to the grid 100, the energy storage unit 22 performs reactive power compensation to the grid 100 under the control of the control system 3.

[0058] In this embodiment, there are multiple ways to connect the energy storage module 2 to the photovoltaic power generation system 1; including but not limited to the following three methods:

[0059] Method 1: For example Figure 4 As shown, the energy storage unit 22 is connected to the busbar on the DC / AC conversion module side of the photovoltaic power generation system 1 through the bidirectional DC / DC unit 21.

[0060] Method 2: For example Figure 5 As shown, the energy storage unit 22 is connected to the busbar on the PV module side of the photovoltaic power generation system 1 through the bidirectional DC / DC unit 21.

[0061] Method 3: For example Figure 6 As shown, the energy storage unit 22 is directly connected to the busbar on the PV module side of the photovoltaic power generation system 1.

[0062] It is understandable that when the energy storage module 2 is connected to the photovoltaic power generation system 1 using the second method described above, the bus voltage on the PV module side of the photovoltaic power generation system 1 is determined by the output voltage of the PV module, which to some extent limits the energy throughput capacity of the energy storage unit 22.

[0063] When the energy storage module 2 is connected to the photovoltaic power generation system 1 using the above-mentioned method 3, and when the energy storage unit 22 provides reactive power to the grid 100 at night, it needs to go through the bidirectional DC / DC unit 21 and the DC / DC conversion module, which will cause the efficiency of the energy storage unit 22 to decrease.

[0064] Therefore, the preferred connection method between the energy storage module 2 and the photovoltaic power generation system 1 in this application is the method described above.

[0065] One embodiment of this application, such as Figure 1 , Figures 7 to 12 As shown, the control system 3 includes a bus voltage control module 31, a circuit detection module 32, a path selection module 33, and a current control module 35. The bus voltage control module 31 is connected to the bus capacitor in the photovoltaic power generation system 1 to detect the voltage value of the bus capacitor in the photovoltaic power generation system 1. The circuit detection module 32 is connected to the bus of the photovoltaic power generation system 1 to extract the current or voltage value of the photovoltaic power generation system 1. The current control module 35 can be connected to the bidirectional DC / DC unit 21, thereby enabling it to send current tracking commands to the bidirectional DC / DC unit 21. The path selection module 33 can connect the bus voltage control module 31 and the current control module 35, or connect the circuit detection module 32 and the current control module 35, depending on the operating state of the photovoltaic power generation system 1. This allows the current control module 35 to send a current tracking command to the bidirectional DC / DC unit 21 based on the compensation signal issued by the bus voltage control module 31 or the circuit detection module 32. In turn, the bidirectional DC / DC unit 21 controls the energy storage unit 22 to compensate the photovoltaic power generation system 1 based on the current tracking command.

[0066] In this embodiment, as Figures 7 to 12 As shown, the path selection module 33 is a Str switch circuit; the Str value corresponding to the output terminal of the bus voltage control module 31 is marked as 2, and the Str value corresponding to the output terminal of the circuit detection module 32 is marked as 1. When the photovoltaic power generation system 1 generates electricity to the grid 100 during the day, Str=1 in the path selection module 33, and the path selection module 33 connects the output terminal of the circuit detection module 32 with the current control module 35. When the photovoltaic power generation system 1 is used as a reactive power generator (SVG) to send reactive power to the grid 100 at night, Str=2 in the path selection module 33, and the path selection module 33 connects the output terminal of the bus voltage control module 31 with the current control module 35.

[0067] In this embodiment, the control system 3 can be divided into a current-type control system and a voltage-type control system according to the different control methods.

[0068] When control system 3 is a current-type control system, such as Figure 7 and Figure 10As shown, the circuit detection module 32 is a high- and low-frequency current extraction module. This module can detect the current values ​​of the busbar in the photovoltaic power generation system 1 at the PV module side and the DC / AC conversion module side. When a low-voltage or high-voltage event occurs in the power grid 100 (high-low voltage ride-through), the high- and low-frequency current extraction module can extract the current difference between the busbar in the photovoltaic power generation system 1 at the output side of the DC / DC conversion module and the input side of the DC / AC conversion module. The module then uses the component of the extracted current difference within a set frequency range as the output command of the bidirectional DC / DC unit 21, sending it along the path selection module 33 to the current control module 35. This allows the current control module 35 to send a current tracking command to the bidirectional DC / DC unit 21 based on the received output command. Thus, the bidirectional DC / DC unit 21 can control the energy storage unit 22 to compensate for the current in the busbar based on the received current tracking command.

[0069] It is understood that the AC frequency used in my country's power grid 100 is 50Hz or 60Hz; therefore, a frequency range with a frequency greater than 50Hz or 60Hz can be used as the set frequency range. Simultaneously, to improve system efficiency, the upper limit of the frequency range can be set to 1000Hz; that is, the frequency range set in this application is 50Hz or 60Hz to 1000Hz. The current difference extracted within the aforementioned set frequency range will cause bus fluctuations; therefore, the bidirectional DC / DC unit 21 can compensate for the current difference in the bus within the aforementioned set frequency range through the energy storage unit 22; thus, the current component in this frequency range will not flow into the bus, and the bus only needs to bear the switching frequency component.

[0070] In this embodiment, as Figure 10 As shown, the high- and low-frequency current extraction module includes at least two first extraction modules. One first extraction module is used to connect to any phase line in the bus, and the other first extraction module is used to connect to the neutral line in the bus. Each first extraction module includes a bandpass filter unit (BPF) and a data acquisition unit connected in series. The input terminal of the data acquisition unit is connected to the bus to detect the current i at the PV module side of the bus. pv_p and i pv_n and the current i located on the DC / AC conversion module side invp and i invn Among them, i pv_p and i invp i represents the current flowing through the phase line. pv_n and i invn This represents the current flowing through the neutral line. A bandpass filter (BPF) is used to filter the current i... pv_p and i invp The difference and current i pv_n and i invnThe current component in the frequency range of the difference passes through the set frequency range and is used as the output command of the bidirectional DC / DC unit 21.

[0071] When control system 3 is a voltage-type control system, such as Figure 8 and Figure 9 as well as Figure 11 and Figure 12 As shown, the circuit detection module 32 is a bus voltage over-limit control module. This module detects the voltage value of the bus between the DC / DC conversion module and the DC / AC conversion module in the photovoltaic power generation system 1, and compares the detected voltage value with a set range. When the detected voltage value is within the upper or lower limit of the set voltage value, the bidirectional DC / DC unit 21 does not compensate the bus. When the detected voltage value exceeds the upper or lower limit of the set voltage value, the bus voltage over-limit control module extracts the difference between the detected voltage value and the upper or lower limit of the set voltage value as an output command for the bidirectional DC / DC unit 21, and sends it to the current control module 35 along the path selection module 33. This allows the current control module 35 to send a current tracking command to the bidirectional DC / DC unit 21 according to the output command. Thus, the bidirectional DC / DC unit 21 can control the energy storage unit 22 to compensate the bus voltage according to the received current tracking command, ensuring that the bus voltage is always maintained within the set upper and lower limits.

[0072] Understandably, the connection position between the bus voltage over-limit control module and the bus can be set according to actual needs. For example... Figure 8 and Figure 9 as well as Figure 11 and Figure 12 As shown, in order to improve detection accuracy and more conveniently protect the bus capacitor, the bus voltage over-limit control module directly detects the voltage value flowing through the bus capacitor.

[0073] In this embodiment, as Figure 8 and Figure 9 as well as Figure 11 and Figure 12 As shown, the bus voltage over-limit control module includes at least two second extraction modules, one of which is used to connect to the bus capacitor C. dc1 Another second extraction module is used to connect the bus capacitor C. dc2The second extraction module includes a selection switch unit and a pair of detection modules. The selection switch unit has two input terminals, labeled "1" and "2" respectively. The input terminals of both detection modules are connected to the corresponding bus capacitors to detect their voltage values. The output terminals of both detection modules are connected to the input terminal labeled "1" of the selection switch unit. The other input terminal of the selection switch unit, labeled "2", is connected to a low level "0". The output terminal of the selection switch unit is connected to the path selection module 33. Therefore, the second extraction module can control the bidirectional DC / DC unit 21 and the energy storage unit 22 for compensation based on the voltage value of the bus capacitors.

[0074] Understandably, within the same second extraction module, there are two detection modules: one module compares the voltage value of the bus capacitor with the upper limit of the set voltage value, and the other module compares the voltage value of the bus capacitor with the lower limit of the set voltage value.

[0075] Specifically, such as Figure 8 and Figure 9 as well as Figure 11 and Figure 12 As shown, the detection module includes an interconnected acquisition unit and a PI control unit; the input terminal of the acquisition unit is connected to the bus capacitor and detects the voltage value of the bus capacitor. At the same time, the acquisition unit can also compare the detected voltage value with the set voltage value and send the comparison result to the selection switch unit through the PI control unit for controlling the energy storage module 2.

[0076] The specific working process of the bus voltage over-limit control module is as follows:

[0077] (1) Two acquisition units of the same second extraction module detect the same bus capacitor to obtain the corresponding voltage value v. dc1 or v dc2 ; where v dc1 and v dc2 Corresponding to the bus capacitor C dc1 and C dc2 The voltage value.

[0078] (2) The detected voltage value v can be obtained through two acquisition units of the same second extraction module. dc1 With respect to the upper limit of the set voltage value v dc1_up and the lower limit v dc1_down Compare; or, use the detected voltage value v dc2 With respect to the upper limit of the set voltage value v dc2_up and the lower limit v dc2_down Compare them.

[0079] (3) If v dc1 ∈[vdc1_up v dc1_down ] or v dc2 ∈[v dc2_up v dc2_down If the corresponding selection switch unit connects the low level "0" to the path selection module 33, then the bidirectional DC / DC unit 21 and the energy storage unit 22 will not work.

[0080] (4) If v dc1 [v dc1_up v dc1_down ] or v dc2 [v dc2_up v dc2_down If the acquisition unit determines v, then dc1 or v dc2 The system detects whether the voltage exceeds the upper limit or falls below the lower limit of the set voltage value, and extracts the difference between the set voltage value and the detected voltage value. At this time, the corresponding selection switch unit connects the output of the detection module to the path selection module 33; thus, the extracted voltage difference can be used as an output command of the bidirectional DC / DC unit 21, sent along the path selection module 33 to the current control module 35, so that the current control module 35 sends a current tracking command to the bidirectional DC / DC unit 21 according to the output command. Therefore, the bidirectional DC / DC unit 21 can control the energy storage unit 22 to compensate the bus voltage according to the received current tracking command, ensuring that the bus voltage is always maintained within the set upper and lower limits.

[0081] Understandably, compared to the direct control of the bus current by a current-type control system, a voltage-type control system provides indirect control, thus its dynamic response speed is slower than that of a current-type control system. However, a voltage-type control system can save at least four current sensors compared to a current-type control system, resulting in lower costs. Therefore, those skilled in the art can choose between a current-type control system and a voltage-type control system based on actual needs.

[0082] Meanwhile, the control system 3 can not only compensate for the voltage or current of the bus, but also compensate for the input or output power of the bus.

[0083] In this embodiment, as Figures 7 to 12 As shown, the bus voltage control module 31 includes a pair of detection modules, one of which has its input terminal connected to the bus capacitor C. dc1 To connect, another detection module is connected to the bus capacitor C. dc2 Connect the components. Each detection module includes a data acquisition unit and a PI control unit.

[0084] At night, when the photovoltaic power generation system 1 acts as a reactive power generator (SVG) to send reactive power to the grid 100, the bidirectional DC / DC unit 21 controls the energy storage unit 22 to supply reactive power to the grid 100. During this process, the acquisition units of the two detection modules respectively transmit the detected bus capacitance C dc1 and C dc2 voltage value v dc1 and v dc2 With the set instruction value v dc1_ref and v dc2_ref Compare them. If v dc1 >v dc1_ref and / or v dc2 >v dc2_ref At this time, the PI control unit can send an output command to the current control module 35 through the path selection module 33, so that the bidirectional DC / DC unit 21 can adjust the reactive power output of the energy storage unit 22 to ensure that the adjusted V dc1 ≤v dc1_ref and v dc2 ≤v dc2_ref .

[0085] In this embodiment, as Figures 7 to 12 As shown, the current control module 35 includes a pair of detection modules; one detection module's input terminal can be connected to the bus voltage control module 31 via the path selection module 33; the other detection module's input terminal can be connected to the circuit detection module 32 via the path selection module 33. Each detection module includes a connected acquisition unit and a PI control unit. The corresponding acquisition unit can receive the output commands from the bus voltage control module 31 and the circuit detection module 32, and send corresponding duty cycle signals d1 and d2 to the bidirectional DC / DC unit 21 through the corresponding PI control unit; thus, the bidirectional DC / DC unit 21 can control the energy storage unit 22 to perform voltage, current, or power compensation according to the received duty cycle signals.

[0086] In this embodiment, as Figures 7 to 12 As shown, the control system 3 also includes a capacitor voltage control module 34. The output terminal of the capacitor voltage control module 34 can be electrically connected to the current control module 35, and the input terminal of the capacitor voltage control module 34 can be electrically connected to the energy storage unit 22. The capacitor voltage control module 34 can send an adjustment signal to the current control module 35 according to the working state of the energy storage unit 22, and then the current control module 35 controls the bidirectional DC / DC unit 21 to adjust the working state of the energy storage unit 22 according to the adjustment signal.

[0087] Specifically, such as Figures 3 to 12 As shown, the energy storage unit 22 includes at least two sets of supercapacitors, which can be labeled C. sc1 and Csc2 Among them, supercapacitor group C sc1 Used for voltage, current, or power compensation of the busbar of photovoltaic power generation system 1 when it is generating electricity during the day; Supercapacitor group C sc2 When the photovoltaic power generation system 1 is used as a reactive power generator (SVG) to send reactive power to the grid 100 at night, it replaces the bus to send reactive power to the grid 100.

[0088] Meanwhile, the capacitor voltage control module 34 includes a pair of detection modules; the input terminal of one of the detection modules is connected to the supercapacitor bank C. sc1 The output terminal is connected to the acquisition unit of the current control module 35 used for circuit detection module 32; the input terminal of the other detection module is connected to the supercapacitor group C. sc2 The connection is established, and the output terminal is connected to the acquisition unit in the current control module 35 used to connect the bus voltage control module 31.

[0089] Each detection module of the capacitor voltage control module 34 includes a connected acquisition unit and a PI control unit. The acquisition unit can detect the corresponding supercapacitor group C. sc1 and C sc2 voltage value v sc1 and v sc2 The collected voltage value is then compared with the corresponding set command value v. sc1_ref and v sc2_ref A comparison is made; its specific working principle is the same as or similar to that of the bus voltage control module 31. By setting the capacitor voltage control module 34, the operating voltage of each supercapacitor group in the energy storage unit 22 can be maintained during the operation of the energy storage unit 22.

[0090] Compared to traditional photovoltaic systems, this application adds an energy storage module 2; therefore, when the energy storage module 2 is working, the operation of the bidirectional DC / DC unit 21 will have a negative impact on the efficiency of the circuit, so it is necessary to limit the number of times the bidirectional DC / DC unit 21 operates.

[0091] One embodiment of this application, such as Figure 9 and Figure 12 As shown, the control system 3 also includes a drive blocking module 36. The input terminal of the drive blocking module 36 is connected to the current control module 35, and the output terminal of the drive blocking module 36 is connected to the bidirectional DC / DC unit 21. When the extracted bus voltage value or the voltage value of the energy storage unit 22 exceeds the set upper and lower limits, the drive blocking module 36 can connect the current control module 35 to the bidirectional DC / DC unit 21, so that the bidirectional DC / DC unit 21 controls the energy storage unit 22 to compensate the bus; otherwise, the drive blocking module 36 will block the bidirectional DC / DC unit 21.

[0092] In this embodiment, as Figure 9 and Figure 12 As shown, the drive blocking module 36 is a logic switch structure. The drive blocking module 36 has two input terminals: one connected to the output of the current control module 35, and the other always connected to a drive blocking signal. The output of the drive blocking module 36 is connected to the bidirectional DC / DC unit 21. Therefore, when the bus voltage value extracted by the circuit detection module 32 or the voltage value of the energy storage unit 22 extracted by the capacitor voltage control module 34 exceeds the set upper and lower limits, the drive blocking module 36 can connect the current control module 35 to the bidirectional DC / DC unit 21, thereby enabling the bidirectional DC / DC unit 21 to control the energy storage unit 22 to operate according to the drive signal from the current control module 35. Conversely, when the bus voltage value extracted by the circuit detection module 32 or the voltage value of the energy storage unit 22 extracted by the capacitor voltage control module 34 does not exceed the set upper and lower limits, the drive blocking module 36 can connect the drive blocking signal to the bidirectional DC / DC unit 21, thereby blocking the bidirectional DC / DC unit 21 to reduce additional losses caused by its operation.

[0093] Another aspect of this application provides a method for operating a capacitor-free photovoltaic system, comprising the following steps:

[0094] S100: When the PV module is in power generation mode, the path selection module 33 connects the circuit detection module 32 and the current control module 35.

[0095] S200: The circuit detection module 32 can extract the current value or voltage value of the bus in the photovoltaic power generation system 1, and control the current control module 35 to send an output command to the bidirectional DC / DC unit 21 according to the extracted current value or voltage value.

[0096] S300: The bidirectional DC / DC unit 21 controls the energy storage unit 22 to compensate the bus in the photovoltaic power generation system 1 according to the output command.

[0097] S400: When the PV module is in non-power generation mode, the photovoltaic power generation system 1 is used as a reactive power generator; at this time, the path selection module 33 connects the bus voltage control module 31 and the current control module 35.

[0098] S500: The bus voltage control module 31 can extract the voltage value of the bus capacitor in the photovoltaic power generation system 1, and control the current control module 35 to send output commands to the bidirectional DC / DC unit 21 according to the extracted voltage value.

[0099] S600: The bidirectional DC / DC unit 21 controls the energy storage unit 22 to provide reactive power compensation to the grid 100 according to the output command, so that the DC bus section on the PV module side does not need to bear the reactive power component.

[0100] Preferably, step S200 further includes the following steps:

[0101] S210: When the circuit detection module 32 extracts the current value of the bus in the photovoltaic power generation system 1, the circuit detection module 32 can use the component of the set frequency range in the extracted current value as an output command; and when the circuit detection module 32 extracts the voltage value of the bus in the photovoltaic power generation system 1, the following steps are performed.

[0102] S220: When the extracted voltage value is within the set upper and lower limits, the drive blocking module 36 is in a blocked state, so that the bidirectional DC / DC unit 21 does not compensate the bus.

[0103] S230: When the extracted voltage value exceeds the set upper and lower limits, the drive blocking module 36 connects the current control module 35 to the bidirectional DC / DC unit 21; thus, the bidirectional DC / DC unit 21 can use the difference between the extracted voltage value and the set upper and lower limits as an output command.

[0104] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A capacitor-free photovoltaic system, characterized in that, include: A photovoltaic power generation system includes a PV module, a DC / DC conversion module, and a DC / AC conversion module connected sequentially via a busbar. The DC / AC conversion module is connected to the power grid. A busbar capacitor is connected between the DC / DC conversion module and the DC / AC conversion module. An energy storage module, comprising an energy storage unit and a bidirectional DC / DC unit, wherein the energy storage unit is adapted to be connected via the bidirectional DC / DC unit to a bus between a DC / DC conversion module and a DC / AC conversion module in the photovoltaic power generation system; and The control system is electrically connected to both the photovoltaic power generation system and the energy storage module. The control system includes a bus voltage control module, a circuit detection module, a current control module, and a path selection module. The bus voltage control module is adapted to extract the voltage value of the bus capacitor in the photovoltaic power generation system; the circuit detection module is adapted to extract the current or voltage value of the bus on the output side of the DC / DC conversion module and the input side of the DC / AC conversion module in the photovoltaic power generation system; the current control module is adapted to send a current tracking command to the bidirectional DC / DC unit; the path selection module is adapted to connect the bus voltage control module or the circuit detection module to the current control module according to the operating state of the photovoltaic power generation system, so that the current control module sends a current tracking command to the bidirectional DC / DC unit, and then the bidirectional DC / DC unit controls the energy storage unit to compensate the photovoltaic power generation system according to the current tracking command.

2. The electrolytic capacitor-free photovoltaic system as described in claim 1, characterized in that: The control system further includes a capacitor voltage control module. The output terminal of the capacitor voltage control module is adapted to be electrically connected to the current control module, and the input terminal of the capacitor voltage control module is adapted to be electrically connected to the energy storage unit. The capacitor voltage control module is adapted to send an adjustment signal to the current control module according to the operating state of the energy storage unit, so that the current control module controls the bidirectional DC / DC unit to adjust the operating state of the energy storage unit according to the adjustment signal.

3. The electrolytic capacitor-free photovoltaic system as described in claim 1, characterized in that: The circuit detection module is a high- and low-frequency current extraction module, which is adapted to extract the current difference between the bus and the output side of the DC / DC conversion module and the input side of the DC / AC conversion module in the photovoltaic power generation system; the bidirectional DC / DC unit is adapted to use the component of a set frequency range in the current difference as an output command to control the energy storage unit to compensate the bus.

4. The electrolytic capacitor-free photovoltaic system as described in claim 1, characterized in that, The circuit detection module is a bus voltage over-limit control module, which is suitable for extracting the voltage value of the bus in the photovoltaic power generation system. When the extracted voltage value is within the set upper and lower limits, the bidirectional DC / DC unit does not compensate the bus. When the extracted voltage value exceeds the set upper and lower limits, the bidirectional DC / DC unit is adapted to use the difference between the extracted voltage value and the set upper and lower limits as an output command to control the energy storage unit to compensate the bus.

5. The electrolytic capacitor-free photovoltaic system as described in claim 4, characterized in that, The control system further includes a drive blocking module. The input terminal of the drive blocking module is connected to the current control module, and the output terminal of the drive blocking module is connected to the bidirectional DC / DC unit. When the extracted bus voltage value or the voltage value of the energy storage unit exceeds a set upper or lower limit, the drive blocking module is adapted to connect the current control module to the bidirectional DC / DC unit so that the bidirectional DC / DC unit controls the energy storage unit to compensate the bus. Otherwise, the drive blocking module is adapted to block the bidirectional DC / DC unit.

6. A method for operating a capacitor-free photovoltaic system as described in any one of claims 1-5, characterized in that, The work includes the following steps: S100: When the PV module is in power generation mode, the path selection module connects the circuit detection module and the current control module; S200: The circuit detection module extracts the current or voltage value of the bus in the photovoltaic power generation system, and controls the current control module to send output commands to the bidirectional DC / DC unit based on the extracted current or voltage value. S300: The bidirectional DC / DC unit controls the energy storage unit to compensate the bus in the photovoltaic power generation system according to the output command; S400: When the PV module is in non-power generation mode, the photovoltaic power generation system is used as a reactive power generator; at this time, the path selection module connects the bus voltage control module and the current control module. S500: The bus voltage control module extracts the voltage value of the bus capacitor in the photovoltaic power generation system and controls the current control module to send output commands to the bidirectional DC / DC unit according to the extracted voltage value. S600: The bidirectional DC / DC unit controls the energy storage unit to provide reactive power compensation to the grid according to the output command, so that the DC bus section on the PV module side does not need to bear the reactive power component.

7. The operating method of the electrolytic capacitor-free photovoltaic system as described in claim 6, characterized in that, Step S200 includes the following specific steps: S210: When the circuit detection module extracts the current value of the bus in the photovoltaic power generation system, the circuit detection module uses the component of the set frequency range in the extracted current value as the output command; and when the circuit detection module extracts the voltage value of the bus in the photovoltaic power generation system, the following steps are performed; S220: When the extracted voltage value is within the set upper and lower limits, the drive blocking module is in a blocked state, so that the bidirectional DC / DC unit does not compensate the bus. S230: When the extracted voltage value exceeds the set upper and lower limits, the drive blocking module connects the current control module to the bidirectional DC / DC unit; thus, the bidirectional DC / DC unit uses the difference between the extracted voltage value and the set upper and lower limits as the output command.

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