Inverter device and photovoltaic system

Abstract

The embodiment of the utility model provides an inverter device and a photovoltaic system, and the inverter device comprises a photovoltaic optimizer group which comprises a plurality of photovoltaic optimizers and is connected between a photovoltaic group string and a DC bus; the photovoltaic group string comprises a plurality of photovoltaic modules; wherein each photovoltaic optimizer is provided with an MPTT module, and each photovoltaic optimizer is respectively connected between the corresponding photovoltaic module and the direct current bus; the charging protection device is connected in series between the direct current bus and the energy storage battery; the charging protection device comprises a bus disconnecting switch used for disconnecting the direct current bus and the energy storage battery. Therefore, assembly-level MPPT control for the photovoltaic assembly is achieved, and the energy storage battery and the inverter equipment can be protected in the charging process through the charging protection device connected between the direct-current bus and the energy storage battery in series.

Description

Technical Field

[0001] The utility model relates to the technical field of power electronics, and in particular to an inverter device and a photovoltaic system. Background Art

[0002] The inverter device is a device that is directly connected to the photovoltaic module and is used to store the electricity generated by each photovoltaic module into the energy storage battery. The more mature inverter device on the market is the string photovoltaic inverter, which can convert the photovoltaic electricity generated by the photovoltaic string into alternating current, and further convert it into direct current to charge the battery.

[0003] However, string-type photovoltaic inverters can only implement MPPT (Maximum Power Point Tracking) for photovoltaic strings, and cannot implement component-level MPPT control for each photovoltaic module. In addition, various uncontrollable factors may occur during the process of photovoltaic inverter equipment charging the energy storage battery, which may interfere with the reliability and charging efficiency of the energy storage battery, and in severe cases, cause irreversible damage to the inverter equipment, and the current inverter equipment lacks the corresponding protection module.

[0004] In response to the above problems, the industry has not yet proposed a better technical solution. Summary of the invention

[0005] The utility model provides an inverter device and a photovoltaic system, so as to at least solve the problems in the prior art that the string photovoltaic inverter cannot realize component-level MPPT control and lacks a safety module.

[0006] In a first aspect, an embodiment of the utility model provides an inverter device, comprising: a photovoltaic optimizer group, comprising a plurality of photovoltaic optimizers, connected between a photovoltaic string and a DC bus; the photovoltaic string comprises a plurality of photovoltaic modules connected in series; wherein each of the photovoltaic optimizers is configured with an MPTT module, and each of the photovoltaic optimizers is respectively connected between a corresponding photovoltaic module and a DC bus; a charging protection device, connected in series between the DC bus and an energy storage battery; the charging protection device comprises a bus disconnect switch, which is used to disconnect the connection from the DC bus to the energy storage battery.

[0007] In a second aspect, an embodiment of the utility model provides a photovoltaic system, comprising: at least one group of photovoltaic strings; at least one inverter device as described above; wherein the output end of each of the photovoltaic strings is respectively connected to the input end of the corresponding inverter device.

[0008] The beneficial effects of the embodiments of the utility model are:

[0009] A corresponding photovoltaic optimizer is set for each photovoltaic module in the photovoltaic string. The MPTT module set in the photovoltaic optimizer is used to perform component-level MPPT control on each connected photovoltaic module, which can achieve more precise regulation. In addition, by connecting the charging protection device in series between the DC bus and the energy storage battery, when unexpected working conditions occur during the process of the photovoltaic inverter device charging the energy storage battery, the bus disconnect switch in the charging protection device can be used to disconnect the charging connection from the DC bus to the energy storage battery, thereby protecting the energy storage battery and the inverter device during the charging process. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0011] Figure 1 A schematic diagram of a connection structure of an example of a string photovoltaic inverter in the current related technology is shown;

[0012] Figure 2 A schematic diagram of a connection structure of another example of a string photovoltaic inverter in the current related technology is shown;

[0013] Figure 3 A schematic diagram of a connection structure of an example of an inverter device according to an embodiment of the utility model is shown;

[0014] Figure 4 A schematic diagram of a connection structure of an example of a charging protection device according to an embodiment of the utility model is shown;

[0015] Figure 5 An operation flow chart of an example of a control method of a charging protection device according to an embodiment of the utility model is shown;

[0016] Figure 6 A schematic diagram showing a connection structure of another example of an inverter device according to an embodiment of the utility model is shown;

[0017] Figure 7 A structural block diagram of an example of an inverter device according to an embodiment of the utility model is shown;

[0018] Figure 8 A control signal timing diagram for charging an energy storage battery through an inverter device according to an embodiment of the utility model is shown;

[0019] Fig. 9A structural block diagram of an example of a photovoltaic system according to an embodiment of the utility model is shown. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the embodiment of the utility model clearer, the technical solution in the embodiment of the utility model will be clearly and completely described below in conjunction with the drawings in the embodiment of the utility model. Obviously, the described embodiment is a part of the embodiment of the utility model, not all of the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0021] It should be noted that the inverter equipment in the current related technology generally adopts string photovoltaic inverters. Figure 1 , which shows that a relatively mature photovoltaic inverter and energy storage converter are coupled on the AC side of the power grid to realize photovoltaic charging of batteries. The advantages of this solution are mature market products, stable and reliable systems, and a complete supply chain. At the same time, it meets the new energy storage needs of the existing photovoltaic market. However, its disadvantages are also obvious. During the operation of the inverter equipment, photovoltaic power needs to be converted into AC power, and then AC power is converted into DC power, resulting in high cost and low energy conversion efficiency for charging energy storage batteries. In addition, this type of string photovoltaic inverter can only achieve maximum power tracking for photovoltaic strings, and cannot achieve component-level maximum power tracking for each photovoltaic module.

[0022] In such Figure 2 In the hybrid photovoltaic energy storage system shown, the battery charging and discharging DC coupling is realized, and the photovoltaic power conversion efficiency is high. However, its disadvantages are that the system is complex, the cost is high, and the system is large in size and weight, inconvenient to install and difficult to maintain. Figure 1 Similar to the example described, it can only achieve maximum power tracking for PV strings, but cannot achieve component-level maximum power tracking for each PV module.

[0023] In view of this, Figure 3 A schematic diagram of a connection structure of an example of an inverter device according to an embodiment of the utility model is shown.

[0024] like Figure 3As shown, the inverter device includes a photovoltaic optimizer group and a charging protection device 320. Specifically, the photovoltaic optimizer group includes N photovoltaic optimizers connected in series (i.e., photovoltaic optimizers 311, 313...31n), which are connected between the photovoltaic string and the DC bus, and N is a natural number greater than 1. The photovoltaic string includes the same number of photovoltaic modules as the photovoltaic optimizers, i.e., N photovoltaic modules, and each photovoltaic optimizer is respectively connected between the corresponding photovoltaic module and the DC bus. In addition, a high-voltage DC output is formed by connecting a plurality of photovoltaic optimizers in series, and a corresponding MPTT module is respectively configured for each photovoltaic optimizer, thereby enabling component-level MPPT control of the connected photovoltaic modules to achieve more precise MPTT regulation.

[0025] In some embodiments, the number of photovoltaic components in a photovoltaic string may be diverse, for example, it may be designed and laid out by a photovoltaic power plant operator, and may be inconsistent with the number of photovoltaic optimizers in a photovoltaic optimizer group. In this case, a photovoltaic optimizer group may be used to simultaneously manage multiple photovoltaic strings (for example, another photovoltaic optimizer group including photovoltaic optimizers 321, 323...32n), or multiple photovoltaic optimizer groups may be integrated to support the management of a group of photovoltaic strings, which is not limited here.

[0026] The charging protection device 330 is connected in series between the DC bus and the energy storage battery to achieve charging protection for the energy storage battery. In some embodiments, the charging protection device 330 includes a bus disconnect switch, which can disconnect the connection from the DC bus to the energy storage battery by controlling the bus disconnect switch.

[0027] It should be understood that the bus disconnect switch can be controlled to conduct or shut down in a variety of ways to meet the needs of various business application scenarios. For example, when an abnormal operating condition of the energy storage battery is detected during charging, or when an abnormal voltage of the DC bus is detected, the abnormality detection is realized by, for example, using the existing detection components configured in the device for various types of charging abnormalities, and then controlling the disconnection of the bus disconnect switch to ensure the safety and reliability of the inverter device and the energy storage battery during the charging process of the energy storage battery using the inverter device.

[0028] Combination Figure 3In the example, each photovoltaic module in the photovoltaic string is connected to a photovoltaic optimizer and then connected in series to form a high-voltage DC output, and multiple photovoltaic string outputs are connected in parallel to the inverter input DC bus. In addition, each photovoltaic optimizer interacts with the inverter system control unit through a power carrier PLC communication method. The inverter system control unit includes a DC / AC inverter unit and a charging protection device 330. The energy storage battery is connected to the DC bus through the charging protection device 330. Furthermore, the inverter converts the high-voltage DC output of the photovoltaic optimizer into AC through DC / AC and connects it to the grid.

[0029] It should be noted that the various units, devices or components in the inverter device of the embodiment of the utility model can exchange data through various communication methods, such as CAN, RS485 or RS232, etc., which should not be limited here.

[0030] Compared with the inverter device provided by the embodiment of the utility model, Figure 1 or Figure 2 The inverter circuit structure in the current related technology can at least achieve the following technical effects: On the one hand, the inverter devices in the current related technology all charge the battery through an independent DC voltage conversion power supply, while the embodiment of the utility model charges the battery through a photovoltaic optimizer, which not only meets the maximum power tracking function of the photovoltaic module, but also controls its output voltage by the system control unit to directly charge the battery. On the other hand, the energy storage battery in the embodiment of the utility model is connected to the DC bus through the charging protection device, and does not need to be connected through the DC power conversion unit, which effectively improves the energy conversion rate.

[0031] Figure 4 A schematic diagram of the connection structure of an example of a charging protection device according to an embodiment of the utility model is shown.

[0032] like Figure 4 As shown, the charging protection device 330 includes a voltage detection unit 331 and a bus disconnect switch S1. Specifically, the voltage detection unit 331 is connected to the bus disconnect switch S1, and is used to detect the ripple voltage of the energy storage battery during the charging process. The specific detection method can partially refer to or draw on the existing detection technology for the ripple voltage during battery charging, which is not limited here. In some embodiments, the voltage detection unit 331 can communicate data with the BMS (Battery Management System) of the energy storage battery to monitor the ripple voltage of the energy storage battery during the charging process, and control the disconnection of the bus disconnect switch S1 when the ripple voltage is large, so as to disconnect the charging connection between the energy storage battery and the inverter device and protect the safety performance of the energy storage battery.

[0033] It should be understood that the existence of ripple voltage in the charging circuit is a normal phenomenon, and disconnecting S1 once the ripple voltage exists will cause the charging efficiency of the energy storage battery to drop significantly.

[0034] In view of this, in order to optimize the small ripple voltage in the charging circuit, combined with Figure 4 In the example in FIG. 3 , the charging protection device 330 further includes a bypass switch S2, which is connected in series between the DC bus and the bus disconnection switch S1, and the resistor R1 and the bypass conduction switch S2 are connected in parallel. In addition, the bypass switch S2 is also connected to the voltage detection unit 331.

[0035] In some embodiments, when the voltage detection unit 331 detects that there is a small ripple voltage in the charging circuit, for example, it meets the preset ripple voltage value range, it controls to disconnect S2 to connect the resistor R1 to the charging circuit to filter the small ripple noise. Therefore, by switching S2 on and off, the influence of bus voltage fluctuation on battery reliability is avoided, and the frequent operation of the disconnection switch S1 caused by bus fluctuation is also avoided, thereby ensuring the charging efficiency of the energy storage battery.

[0036] In some examples of the present invention, Figure 4 As shown, the charging protection device also includes an optical coupler 332, which is connected between the voltage detection unit 331 and the DC bus. Therefore, the voltage detection unit 331 can sample and measure the bus voltage of the DC bus through the optical coupler, and monitor the abnormal floating condition of the DC bus voltage.

[0037] Figure 5 The following is an operation flow chart of an example of a control method of a charging protection device according to an embodiment of the utility model. It should be understood that this method embodiment is only used as an example, and the charging protection device can adopt various non-restrictive control methods to realize charging protection of energy storage batteries and inverter devices during charging, which should not be limited here.

[0038] like Figure 5As shown, in the control method of the charging protection device, the voltage and current of the battery charging circuit are sampled by the voltage detection unit. In the low-power system, after the voltage detection unit establishes communication with the battery BMS, it performs safety and insulation detection on the charging back, and matches the battery charging voltage and current. When the voltage and current meet the charging requirements and the ripple voltage meets the first judgment condition of the safety threshold, the switch S1 is attracted. When the system detects that the bus voltage reaches a stable value and the ripple voltage is lower than the second judgment condition threshold, the switch S2 is attracted. At this time, the photovoltaic optimizer charges the battery normally. When the power of the photovoltaic module fluctuates, the ripple current is greater than the third judgment condition threshold but less than the fourth judgment condition threshold, S2 is disconnected. At this time, the battery is connected in series to the DC bus through a resistor, and the resistor limits the battery charging current for a short time. When the ripple voltage recovers to below the second judgment condition threshold within the specified time, the switch S2 is attracted again; if the ripple voltage exceeds the fourth judgment condition threshold within the specified time, S1 is disconnected. The system will automatically perform new safety detection and charging demand voltage and current matching. The battery charging protection device can avoid the influence of bus voltage fluctuation on battery reliability and also avoid frequent operation of the disconnect switch S1 caused by bus fluctuation, thereby effectively improving the charging efficiency of the energy storage battery.

[0039] Figure 6 A schematic diagram of the connection structure of another example of an inverter device according to an embodiment of the utility model is shown.

[0040] like Figure 6 As shown, the inverter device also includes inductors L1, L2 and capacitors C1. L1 and L2 are respectively connected in series between the DC bus and the charging protection device 330, and the capacitor C1 is connected in parallel between the DC bus and the charging protection device 330. Thus, by connecting the inductor in series and the capacitor in parallel, the ripple signal in the battery charging circuit can be further suppressed.

[0041] Figure 7 A structural block diagram of an example of an inverter device according to an embodiment of the utility model is shown.

[0042] like Figure 7 As shown, the inverter device 700 includes a controller 710 and a photovoltaic optimizer group 720, the photovoltaic optimizer group 720 includes a plurality of photovoltaic optimizers (i.e., 721, 722...72n), and each photovoltaic optimizer is also provided with an IV curve testing unit (not shown), and each photovoltaic optimizer is communicatively connected to the controller and can detect the photovoltaic IV curve of the connected photovoltaic assembly in real time.

[0043] Furthermore, the controller 710 can receive corresponding photovoltaic IV curves from each photovoltaic optimizer to obtain the working status of each photovoltaic component in the photovoltaic string. In some embodiments, the controller 710 is also used to send component power generation control instructions to the target photovoltaic optimizer, such as setting voltage or setting current control instructions, so that the target photovoltaic optimizer controls the configured MPTT module according to the component power generation control instructions to update the working status or MPTT configuration. In this way, the power generation status monitoring of each photovoltaic component is realized, and component-level MPPT control can be performed according to the power generation status, which is conducive to optimizing the power generation efficiency of the photovoltaic component through precise control.

[0044] Figure 8 A control signal timing diagram for charging an energy storage battery through an inverter device according to an embodiment of the utility model is shown.

[0045] like Figure 8 As shown, the energy storage battery BMS 810 sends the charging voltage requirement value and the charging current requirement value to the controller 710, and the controller 710 sends the charging IV curve scanning instruction to each photovoltaic optimizer (for example, 721, 722, etc.), and then each photovoltaic optimizer feeds back the IV curve to the controller 710. Specifically, the voltage and current set values ​​of each photovoltaic optimizer are calculated and sent through all the returned IV curves and the battery charging requirement voltage and current values. Further, the controller 710 sends the component power generation control instruction to each photovoltaic optimizer to control and configure the MPTT module to achieve the maximum power tracking of the MPTT of each photovoltaic optimizer. In addition, the energy storage battery BMS 810 can also exchange the charging voltage and current data with the controller 710 to track and configure the battery charging voltage and current values ​​in real time, so that each photovoltaic optimizer can perform real-time maximum power tracking and adjustment on each component in the string according to the required voltage and current.

[0046] In the embodiment of the utility model, a photovoltaic optimizer is used to directly charge the battery, and through the interactive control of the optimizer, the inverter and the battery BMS, the reliability problem of the photovoltaic optimizer charging the battery is solved, the system energy conversion efficiency is improved, the system cost, volume, weight, and operation and maintenance difficulty are reduced, and the maximum power tracking of each photovoltaic module is achieved.

[0047] Through the embodiment of the utility model, the direct current output of the photovoltaic optimizer is used to directly charge the battery, which solves the instability and safety problems of direct charging of the battery by the photovoltaic optimizer, and reduces the volume of the inverter by about one third, the weight by about one third, and the cost by about one third. In addition, the battery charging and discharging efficiency is improved by about 3%, achieving more flexible system configuration and more efficient operation and maintenance control.

[0048] Fig. 9 A structural block diagram of an example of a photovoltaic system according to an embodiment of the utility model is shown.

[0049] like Fig. 9 As shown, the photovoltaic system 900 includes M photovoltaic strings (i.e., 911, 913 ... 91m), M inverter devices (i.e., 921, 923 ... 92m) and a storage battery 930, where M is a natural number, the output end of each photovoltaic string is respectively connected to the input end of the corresponding inverter device, and the storage battery 930 is connected to the output end of each inverter device.

[0050] It should be noted that there is no need to use a one-to-one correspondence between PV strings and inverter devices, and one PV optimizer group can be used to manage multiple PV strings at the same time, or multiple PV optimizer groups can be used to jointly manage one PV string. This is not limited here. In addition, for details of the inverter device, please refer to the above combined Figure 1-8 The relevant description in enables the photovoltaic system to achieve the same or corresponding technical effects as the integrated inverter, which will not be elaborated here.

[0051] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the utility model.

Claims

1. An inverter device, characterized in that: The inverter device comprises: A photovoltaic optimizer group, comprising a plurality of photovoltaic optimizers connected in series, connected between a photovoltaic string and a DC bus; the photovoltaic string comprises a plurality of photovoltaic modules; wherein each photovoltaic optimizer is configured with an MPTT module, and each photovoltaic optimizer is respectively connected between a corresponding photovoltaic module and the DC bus; A charging protection device is connected in series between the DC bus and the energy storage battery; the charging protection device comprises a bus disconnect switch for disconnecting the connection from the DC bus to the energy storage battery.

2. The inverter device according to claim 1, characterized in that: The charging protection device also includes: A voltage detection unit is connected to the busbar disconnect switch and is used to detect the ripple voltage of the energy storage battery during the charging process.

3. The inverter device according to claim 2, characterized in that: The charging protection device also includes: A bypass switch connected in series between the DC bus and the bus disconnect switch, and the bypass switch is connected to the voltage detection unit; A resistor is connected in parallel with the bypass switch.

4. The inverter device according to claim 2, characterized in that: The charging protection device also includes: An optical coupler is connected between the voltage detection unit and the DC bus, wherein the optical coupler is used for the voltage detection unit to sample the bus voltage of the DC bus.

5. The inverter device according to any one of claims 2 to 4, characterized in that: The inverter device further includes: An inductor is connected in series between the DC bus and the charging protection device.

6. The inverter device according to any one of claims 2 to 4, characterized in that: The inverter device further includes: A capacitor is connected in parallel between the DC bus and the charging protection device.

7. The inverter device according to claim 2, characterized in that: The inverter device further includes: Controller; Wherein, each of the photovoltaic optimizers also includes an IV curve testing unit, which is communicatively connected to the controller and is used to detect the photovoltaic IV curve of the connected photovoltaic assembly.

8. The inverter device according to claim 7, characterized in that: The controller is also used to send a component power generation control instruction to the target photovoltaic optimizer, so that the target photovoltaic optimizer controls the configured MPTT module according to the component power generation control instruction.

9. A photovoltaic system, characterized in that: The photovoltaic system comprises: At least one set of photovoltaic strings; At least one inverter device according to any one of claims 1 to 8; wherein the output end of each photovoltaic string is respectively connected to the input end of the corresponding inverter device; The energy storage battery is connected to the output end of each of the inverter devices.

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