String type inverter control method and device and string type inverter system

Abstract

The invention relates to the technical field of new energy, and mainly provides a string type inverter control method and device and a string type inverter system, the system comprises N photovoltaic input sources, N-1 boost circuits and additional circuits, the N-1 boost circuits and the additional circuits are correspondingly connected with the N photovoltaic input sources, and the N-1 boost circuits and the additional circuits are also connected with an inverter circuit. The method comprises the following steps: acquiring a feedback value of bus voltage of an inverter circuit; calculating a given value of the bus voltage according to the feedback value and the input current of the additional circuit, and obtaining a deviation between the feedback value and the given value; adjusting the feedback value of the bus voltage based on the deviation between the feedback value and a given value, and calculating a given current component of the inverter circuit according to the adjusted feedback value; and calculating a voltage component of the inverter circuit according to the given current component to determine a target output voltage of the inverter circuit. On the basis, the Nth boost circuit is replaced by the additional circuit, so that the condition of voltage redundancy is avoided, and the system cost is further reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy, and in particular to a control method and device for a string inverter and a string inverter system. Background Art

[0002] In distributed photovoltaic power station scenarios such as household and industrial and commercial, it is a common phenomenon that the orientations of various photovoltaic strings are inconsistent. Therefore, string photovoltaic inverters are widely used in distributed photovoltaic power stations. Among them, string photovoltaic inverters have multiple independent MPPT tracking circuits to maintain the maximum power tracking of the energy of each string photovoltaic panel when the orientations of the photovoltaic strings are different, thereby maximizing the power generation efficiency of the photovoltaic power station.

[0003] However, in distributed usage scenarios, the MPPT voltage configuration of photovoltaic strings is usually higher, much higher than the bus voltage of the inverter. When the string input voltage is higher than the bus voltage, the boost circuit will work in diode pass mode and the boost circuit will not work. Therefore, in most scenarios, the boost circuit of the string inverter is wasted, which increases the system cost. In addition, the controllable voltage of the traditional string inverter includes N input voltages and bus voltages, that is, N+1 controllable voltages, while only N controllable voltages are required to achieve N-way MPPT tracking, that is, there is redundant voltage in the circuit, resulting in a waste of resources. Summary of the invention

[0004] The embodiments of the present invention provide a control method and device for a string inverter and a string inverter system, aiming to solve the technical problem of high cost of the string inverter system in the prior art.

[0005] In order to solve the above technical problems, a technical solution adopted in an embodiment of the present invention is: to provide a control method of a string inverter, which is applied to a string inverter system, wherein the string inverter system includes N photovoltaic input sources, N-1 boost circuits and additional circuits, wherein the N-1 boost circuits and the additional circuits are connected to the N photovoltaic input sources respectively, and the N-1 boost circuits and the additional circuits are also connected to the inverter circuit, and the method includes:

[0006] Obtaining a feedback value of the bus voltage of the inverter circuit and an input current of the additional circuit;

[0007] Calculating a given value of the bus voltage according to the feedback value and an input current of the additional circuit, and obtaining a deviation between the feedback value and the given value;

[0008] adjusting the feedback value of the bus voltage based on the deviation between the feedback value and the given value, and calculating the given current component of the inverter circuit according to the adjusted feedback value;

[0009] A voltage component of the inverter circuit is calculated according to the given current component to determine a target output voltage of the inverter circuit.

[0010] Optionally, obtaining a feedback value of a bus voltage of the inverter circuit includes:

[0011] Respectively acquiring input voltages of the N photovoltaic input sources to obtain N photovoltaic input voltages;

[0012] Determine a maximum photovoltaic input voltage according to the N photovoltaic input voltages, and record the photovoltaic input source corresponding to the maximum photovoltaic input voltage as the Nth photovoltaic input source;

[0013] The input voltage of the Nth photovoltaic input source is input into the additional circuit to obtain a feedback value of the bus voltage of the inverter circuit.

[0014] Optionally, the additional circuit includes a first diode, an anode of the first diode is connected to the positive electrode of the Nth photovoltaic input source, and a cathode of the first diode is connected to the inverter circuit, wherein the positive electrode of the Nth photovoltaic input source and the first diode, the inverter circuit and the negative electrode of the Nth photovoltaic input source form a first target loop;

[0015] The step of inputting the input voltage of the Nth photovoltaic input source into the additional circuit to obtain a feedback value of the bus voltage of the inverter circuit includes:

[0016] The maximum photovoltaic input voltage of the Nth photovoltaic input source is input to the first diode according to the first target loop to obtain a feedback value of the bus voltage of the inverter circuit.

[0017] Optionally, the additional circuit includes a second diode, a cathode of the second diode is connected to the negative electrode of the N-th photovoltaic input source, and an anode of the second diode is connected to the inverter circuit, wherein the positive electrode of the N-th photovoltaic input source and the inverter circuit, the second diode and the negative electrode of the N-th photovoltaic input source form a second target loop;

[0018] The step of inputting the input voltage of the Nth photovoltaic input source into the additional circuit to obtain a feedback value of the bus voltage of the inverter circuit includes:

[0019] The maximum photovoltaic input voltage of the Nth photovoltaic input source is input to the second diode according to the second target loop to obtain a feedback value of the bus voltage of the inverter circuit.

[0020] Optionally, the additional circuit includes an IGBT tube / field effect tube, a first end of the IGBT tube / field effect tube is connected to the positive electrode of the N-th photovoltaic input source, and a second end of the IGBT tube / field effect tube is connected to the inverter circuit, wherein the IGBT tube / field effect tube also includes a parasitic diode tube, an anode of the parasitic diode is connected to the positive electrode of the N-th photovoltaic input source, a cathode of the parasitic diode is connected to the inverter circuit, and the positive electrode of the N-th photovoltaic input source, the parasitic diode, the inverter circuit and the negative electrode of the N-th photovoltaic input source form a third target loop;

[0021] The step of inputting the input voltage of the Nth photovoltaic input source into the additional circuit to obtain a feedback value of the bus voltage of the inverter circuit includes:

[0022] The maximum photovoltaic input voltage of the Nth photovoltaic input source is input to the parasitic diode according to the third target loop to obtain a feedback value of the bus voltage of the inverter circuit.

[0023] Optionally, calculating the given value of the bus voltage according to the feedback value and the input current of the additional circuit, and obtaining a deviation between the feedback value and the given value, includes:

[0024] Obtaining a feedback value of the bus voltage;

[0025] Calculating the input power of the additional circuit according to the feedback value of the bus voltage and the input current of the additional circuit;

[0026] Using an MPPT algorithm to perform maximum power tracking on the input power of the additional circuit to obtain a given value of the bus voltage;

[0027] The difference between the feedback value of the bus voltage and the given value is calculated to obtain a deviation between the feedback value and the given value.

[0028] Optionally, adjusting the feedback value of the bus voltage based on the deviation between the feedback value and the given value, and calculating the current component of the inverter circuit according to the adjusted feedback value, includes:

[0029] adjusting the feedback value according to the difference so that the difference between the feedback value and the given value is within a preset voltage range;

[0030] The load limit requirement of the inverter circuit is obtained, and an adjusted feedback value is calculated according to the load limit requirement to obtain a given current component of the inverter circuit.

[0031] Optionally, calculating the voltage component of the inverter circuit according to the given current component to determine the target output voltage of the inverter circuit includes:

[0032] Obtaining an output current component of the inverter circuit;

[0033] adjusting the output current component according to the given current component to obtain a target current component;

[0034] The target output current component is converted to obtain a voltage component of an inverter circuit, and a target output voltage of the inverter circuit is determined according to the voltage component.

[0035] Optionally, the method further includes:

[0036] Acquiring an input voltage and an input current of the photovoltaic input source, and calculating a photovoltaic input power according to the input voltage and the input current;

[0037] Using the MPPT algorithm, maximum power tracking is performed based on the photovoltaic input power to obtain a corresponding photovoltaic output voltage;

[0038] determining a target duty cycle according to the photovoltaic output voltage and the input voltage of the photovoltaic input source;

[0039] The input voltage of the photovoltaic input source is boosted according to the target duty cycle so that the N-1 boost circuits output a maximum voltage.

[0040] In order to solve the above technical problems, another technical solution adopted by the embodiment of the present invention is: to provide a control device of a string inverter, which is applied to a string inverter system, wherein the string inverter system comprises N photovoltaic input sources, N-1 boost circuits and additional circuits, wherein the N-1 boost circuits and the additional circuits are connected to the N photovoltaic input sources respectively, and the N-1 boost circuits and the additional circuits are also connected to the inverter circuit, and the device comprises:

[0041] A first acquisition module, used to acquire a feedback value of the bus voltage of the inverter circuit and an input current of the additional circuit;

[0042] A second acquisition module, used for calculating a given value of the bus voltage according to the feedback value and an input current of the additional circuit, and acquiring a deviation between the feedback value and the given value;

[0043] A regulating module, configured to regulate the feedback value of the bus voltage based on a deviation between the feedback value and the given value, and calculate the current component of the inverter circuit according to the regulated feedback value;

[0044] A calculation module is used to calculate the voltage component of the inverter circuit according to the current component, so as to determine the maximum output voltage of the inverter circuit based on the voltage component.

[0045] In order to solve the above technical problems, another technical solution adopted in the embodiment of the present invention is: to provide a string inverter system, the string inverter system comprising:

[0046] N photovoltaic input sources; N-1 boost circuits; additional circuits; inverter circuits; and

[0047] A controller, wherein the controller includes at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor so that the at least one processor can perform the method as described above.

[0048] Different from the related art, the present invention provides a control method, device and string inverter system of a string inverter, wherein the string inverter system includes N photovoltaic input sources, N-1 boost circuits and additional circuits, wherein the N-1 boost circuits and the additional circuits are connected to the N photovoltaic input sources, and the N-1 boost circuits and the additional circuits are also connected to the inverter circuit. The method includes mainly obtaining the feedback value of the bus voltage of the inverter circuit; calculating the given value of the bus voltage according to the feedback value and the input current of the additional circuit, and obtaining the deviation between the feedback value and the given value; adjusting the feedback value of the bus voltage based on the deviation between the feedback value and the given value, and calculating the given current component of the inverter circuit according to the adjusted feedback value; calculating the voltage component of the inverter circuit according to the given current component to determine the target output voltage of the inverter circuit. Based on this, by replacing the Nth boost circuit with an additional circuit, voltage redundancy is avoided, thereby reducing system costs, and the given value of the bus voltage is calculated through the additional circuit and feedback value, thereby achieving precise control of the bus voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and the figures in the drawings do not constitute proportional limitations unless otherwise stated.

[0050] Figure 1 is a structural block diagram of a string inverter system provided by an embodiment of the present invention;

[0051] Figure 2 is a circuit diagram of a boost circuit provided by an embodiment of the present invention;

[0052] Figure 3a-3c is a circuit diagram of a string inverter system provided by an embodiment of the present invention;

[0053] Figure 4 is a schematic diagram of the structure of a controller provided by an embodiment of the present invention;

[0054] Figure 5 is a method flow chart of a control method of a string inverter provided by an embodiment of the present invention;

[0055] Figure 6 It is a structural block diagram of a control device for a string inverter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0057] It should be noted that, if there is no conflict, the various features in the embodiments of the present invention can be combined with each other, and all are within the protection scope of the present invention. In addition, although the functional modules are divided in the device schematic diagram and the logical order is shown in the flow chart, in some cases, the steps shown or described can be performed in a different order from the module division in the device schematic diagram or the order in the flow chart.

[0058] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in this specification includes any and all combinations of one or more of the related listed items.

[0059] See also Figure 1 , Figure 1 is a structural block diagram of a string inverter system provided by an embodiment of the present invention, such as Figure 1 As shown, the string inverter system 100 includes N photovoltaic input sources 10, N-1 boost circuits 20, additional circuits 30 and inverter circuits 40, wherein the N photovoltaic input sources 10 are connected to the N-1 boost circuits 20 and additional circuits 30, respectively, and the N-1 boost circuits 20 and additional circuits 30 are also connected to the inverter circuit 40. The N photovoltaic input sources 10 are used to receive solar energy and convert the solar energy into direct current and output it to the corresponding boost circuits 20 and additional circuits 30, wherein the N photovoltaic input sources 10 have different orientations, and the direct current outputted in different orientations is also different.

[0060] In some embodiments, Figure 1As shown, the string inverter system 100 further includes a controller 50, and the controller 50 is connected to the N-1 boost circuits 20 respectively. Figure 2 As shown, the N-1 boost circuits 20 each include an inductor L, a diode D1 and a transistor Q1, and the control end of the switch tube Q1 is connected to the controller 50; when the photovoltaic input source 10 outputs direct current, the inductor L will receive the direct current, and at this time, the controller 50 will control the on and off of the switch tube Q1 to control the charging and discharging of the inductor L, thereby boosting the direct current, and outputting the boosted direct current to the inverter circuit 40 through the diode D1, wherein the voltage input to the inverter circuit 40 is the bus voltage. However, when the illumination condition of the photovoltaic input source 10 is good, the direct current output by the photovoltaic input source 10 may be greater than the bus voltage of the inverter circuit 40 without boosting, so that the direct current directly flows into the inverter circuit 40 through the diode D1, that is, the switch tube Q1 cannot normally boost the direct current, so that the boost circuit 20 cannot work normally.

[0061] Based on this, the embodiment of the present application changes the N-th boost circuit 20 into an additional circuit 30, and the DC power output by the photovoltaic input source 10 is directly input into the inverter circuit 40 through the additional circuit 30, so that when the DC power output by the photovoltaic input source 10 is greater than the bus voltage of the inverter circuit 40, the DC power is directly transmitted to the inverter circuit 40, thereby reducing the amount of calculation of the string inverter system 100 and saving the cost of the string inverter system 100. It should be noted that the controller 50 is also connected to the N photovoltaic input sources 10 respectively. When setting the additional circuit 30, the controller 50 will obtain the one with the largest DC output among the N photovoltaic input sources 10, and connect the additional circuit 30 to the photovoltaic input source 10 with the largest DC output, so that when the output voltage of the photovoltaic input source 10 is greater than the bus voltage, the DC power is directly transmitted to the inverter circuit 40 through the additional circuit 30, thereby avoiding unnecessary calculations. Among them, after the inverter circuit 40 receives the DC power output by the additional circuit 30 and the DC power output by the N-1 boost circuit 20, it will invert all the DC power to convert the DC power into AC power, and after the DC power is converted into AC power, it will control and process the AC power to output a three-phase AC power.

[0062] In some embodiments, see Figure 3a , Figure 3a is a circuit diagram of a string inverter system provided by an embodiment of the present invention, such as Figure 3aAs shown, the additional circuit 30 is a first diode D2, the anode of the first diode D2 is connected to the positive electrode of the N-th photovoltaic input source 10, and the cathode of the first diode D2 is connected to the inverter circuit 40, wherein the positive electrode of the N-th photovoltaic input source 10, the first diode D2, the inverter circuit 40 and the negative electrode of the N-th photovoltaic input source 10 form a first target loop. When the N-th photovoltaic input source 10 converts sunlight into direct current for output, the N-1-way boost circuit 20 will boost the corresponding direct current, and at the same time, the first diode D2 will output the direct current outputted by the N-th photovoltaic input source 10 to the inverter circuit 40 based on the first target loop, wherein the direct current outputted by the N-th photovoltaic input source 10 is the photovoltaic input source with the largest voltage among the N-th photovoltaic input sources 10. When the inverter circuit 40 receives the direct current outputted by the N-1-way boost circuit 20 and the first diode D2, it will invert the direct current to output three-phase alternating current.

[0063] In yet another embodiment, Figure 3b As shown, the additional circuit 30 can also be a second diode D3, the anode of the second diode D3 is connected to the cathode of the inverter circuit 40, and the cathode of the second diode D3 is connected to the cathode of the photovoltaic input source 10, wherein the positive electrode of the N-th photovoltaic input source 10 and the inverter circuit 40, the second diode D3 and the cathode of the N-th photovoltaic input source 10 form a second target loop. That is, when the N-th photovoltaic input source 10 outputs direct current, the direct current will be directly input into the second target loop, so that the inverter circuit 40 receives the input voltage of the N-th photovoltaic input source 10. It should be noted that by setting the second diode D3 in the second target loop, the circulation phenomenon between the N-th photovoltaic input source 10 and the inverter circuit 40 can be effectively prevented.

[0064] In another embodiment, if Figure 3c As shown, the additional circuit 30 can also be an IGBT tube or a field effect tube, the first end of the IGBT tube or the field effect tube is connected to the positive electrode of the photovoltaic input source, and the other end is connected to the positive electrode of the inverter circuit 40. It should be noted that the IGBT tube or the field effect tube includes a parasitic diode, the anode of the parasitic diode is connected to the positive electrode of the N-th photovoltaic input source, the cathode of the parasitic diode is connected to the inverter circuit, and the positive electrode of the N-th photovoltaic input source, the parasitic diode, the inverter circuit and the negative electrode of the N-th photovoltaic input source form a third target loop. When the N-th photovoltaic input source 10 outputs direct current, the direct current will be input to the inverter circuit 40 based on the third target loop, so that the inverter circuit 40 receives the input voltage of the N-th photovoltaic input source 10.

[0065] See also Figure 4 , Figure 4 is a schematic diagram of a controller provided in an embodiment of the present invention, wherein the controller 50 comprises: at least one processor 51, Figure 4 In the example, a processor 51 is used; the memory 52 connected to the at least one processor 51 in communication, Figure 4 The example of connecting through bus is taken in the following.

[0066] The memory 52 stores instructions that can be executed by the at least one processor 51, and the instructions are executed by the at least one processor 51 so that the at least one processor 51 can execute the following control method of the string inverter.

[0067] The memory 52 is a non-volatile computer-readable storage medium that can be used to store non-volatile software programs, non-volatile computer executable programs and modules, such as program instructions / modules corresponding to the control method of the string inverter in the embodiment of the present invention. The processor 51 executes various functional applications and data processing of the controller 50 by running the non-volatile software programs, instructions and modules stored in the memory 52, that is, implements the control method of the string inverter in the following method embodiment.

[0068] The memory 52 may include a program storage area and a data storage area, wherein the program storage area may store an operating system and an application required for at least one function. In addition, the memory 52 may include a high-speed random access memory and may also include a non-volatile memory. For example, it may include at least one disk storage device, a flash memory device, or other non-volatile solid-state storage device. In some embodiments, the memory 52 may optionally include a memory remotely arranged relative to the processor 51.

[0069] The one or more modules are stored in the memory 52, and when executed by the one or more processors 51, execute the control method of the string inverter in any of the following method embodiments, for example, execute the following description Figure 5 The method steps in .

[0070] The controller can execute the method provided in the embodiment of the present invention and has a functional module corresponding to the execution method. For technical details not described in detail in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0071] See also Figure 5 , Figure 5 is a method flow chart of a control method of a string inverter provided by an embodiment of the present invention, such as Figure 5 As shown, the method includes:

[0072] S01. Obtaining a feedback value of the bus voltage of the inverter circuit and an input current of the additional circuit.

[0073] Specifically, when obtaining the feedback value of the bus voltage of the inverter circuit, it is first necessary to obtain the input voltages of N photovoltaic input sources respectively, so as to obtain the N photovoltaic input source voltages corresponding to the N photovoltaic input sources, and then determine the maximum photovoltaic input voltage according to the N photovoltaic input voltages, and record the photovoltaic input source corresponding to the maximum photovoltaic input voltage as the Nth photovoltaic input source. After determining the Nth photovoltaic input source, the input voltage and input current of the Nth photovoltaic input source are input into the additional circuit, and the feedback value of the bus voltage of the inverter circuit and the input current of the additional circuit can be obtained according to the additional circuit.

[0074] In some embodiments, after determining that the input voltage of the Nth photovoltaic input source is the maximum photovoltaic input voltage, if the additional circuit is a first diode, the maximum photovoltaic input voltage will be input to the inverter circuit through the first diode. At this time, the voltage input by the first diode is the feedback value of the bus voltage of the inverter circuit.

[0075] In another embodiment, if the additional circuit is a second diode, the second diode and the inverter circuit form a second target loop, so that the maximum output voltage of the Nth photovoltaic input source can be normally input into the inverter circuit, thereby obtaining a feedback value of the bus voltage of the inverter circuit.

[0076] In another embodiment, when the additional circuit is an IGBT tube / field effect tube, its working principle is similar to that of the first diode and is not described in detail here.

[0077] S02. Calculate a given value of the bus voltage according to the feedback value and an input current of the additional circuit, and obtain a deviation between the feedback value and the given value.

[0078] Specifically, after the feedback value of the bus voltage is determined, the input current of the Nth photovoltaic input source (that is, the input current of the additional circuit) is obtained, and the input power of the additional circuit is calculated according to the feedback value of the bus voltage and the input current of the additional circuit. After the photovoltaic input power is determined, a disturbance voltage or a disturbance current is applied to the feedback value of the bus voltage and the input current of the additional circuit through the MPPT algorithm. At this time, if the input power of the additional circuit increases, the disturbance voltage or the disturbance current is continued to be applied to the input current and the feedback value of the bus voltage until the input power of the additional circuit decreases after the disturbance voltage or the disturbance current is applied, and it is determined that the maximum power tracking is successful. After the maximum power tracking is successful, the output voltage corresponding to the Nth photovoltaic input source at the maximum power point can be obtained according to the maximum power, wherein the output voltage corresponding to the Nth photovoltaic input source at the maximum power point is the given value of the bus voltage.

[0079] After obtaining the given value of the bus voltage, the difference between the given value and the feedback value of the bus voltage is calculated, that is, how much the given value is greater than the feedback value. Based on the difference, the deviation between the feedback value and the given value can be determined.

[0080] S03. Adjust the feedback value of the bus voltage based on the deviation between the feedback value and the given value, and calculate the given current component of the inverter circuit according to the adjusted feedback value.

[0081] After determining the deviation between the feedback value and the given value, the feedback value of the bus voltage is adjusted based on the PI controller so that the deviation between the feedback value and the given value is within a preset voltage range. After adjusting the feedback value according to the given value, the controller also obtains the load limit requirement of the string inverter system, wherein the load limit requirement includes over-temperature load limit, active load limit, and modulation ratio load limit.

[0082] After determining the load limit requirement, the maximum allowable load power of the string inverter system is determined according to the load limit requirement, and then the given current component is calculated according to the maximum allowable load power, wherein the given current component includes a d-axis given current component (reactive power) and a q-axis given current component (active power).

[0083] S04. Calculate the voltage component of the inverter circuit according to the given current component to determine the target output voltage of the inverter circuit.

[0084] After obtaining the d-axis given current component and the q-axis given current component, the controller will also obtain the output current component of the inverter circuit, that is, the d-axis output current component and the q-axis output current component of the inverter circuit, and then respectively calculate the deviation between the d-axis current components and the deviation of the q-axis current component. After obtaining the deviation between the d-axis current components and the deviation of the q-axis current component, a PI controller is used to adjust the d-axis output current component and the q-axis output current component according to the deviation between the d-axis current components and the deviation of the q-axis current component, so as to obtain the d-axis target current component and the q-axis target current component. Finally, the d-axis target current component and the q-axis target current component are calculated according to the relationship between current and voltage, so as to obtain the d-axis voltage component and the q-axis voltage component of the inverter circuit. After obtaining the d-axis voltage component and the q-axis voltage component of the inverter circuit, the d-axis voltage component and the q-axis voltage component of the inverter circuit are converted to obtain three-phase alternating current, wherein the three-phase alternating current is the target output voltage.

[0085] In some embodiments, when the inverter circuit receives the feedback value of the bus voltage output by the additional circuit, it also receives the output voltage of the N-1 boost circuit, wherein the output voltage of the N-1 boost circuit is obtained according to the corresponding photovoltaic input source. Specifically, after the N photovoltaic input sources convert the solar energy into the DC output, the N-1 boost circuits will receive the corresponding DC respectively, and the controller will obtain the input voltage and input current of the corresponding photovoltaic input source, and calculate the photovoltaic input power of the photovoltaic input source according to the input voltage and input current. After determining the photovoltaic input power, the MPPT algorithm is used to track the maximum power of the photovoltaic input source. After determining the photovoltaic input power, the MPPT algorithm is used to apply a disturbance voltage or a disturbance current to the input current and input voltage to track the maximum power of the photovoltaic input source. After tracking the maximum power of the photovoltaic input source, the photovoltaic output voltage corresponding to the maximum power is obtained, and the deviation between the photovoltaic output voltage and the input voltage of the photovoltaic input source is calculated to determine the target duty cycle of the boost circuit based on the deviation, and finally the on-off of the switch tube Q1 in the boost circuit is controlled according to the target duty cycle, so that the switch tube Q1 performs a boost process on the input voltage of the photovoltaic input source based on the inductor L until the voltage value of the input voltage corresponds to the photovoltaic output voltage, that is, the voltage value corresponding to the input voltage is increased to the photovoltaic output voltage by the on-off of the switch tube Q1. After the input voltage is boosted, the output voltages of the N-1 boost circuits are all input into the inverter circuit.

[0086] The embodiment of the present invention provides a control method for a string inverter, which is applied to a string inverter system, wherein the string inverter system includes N photovoltaic input sources, N-1 boost circuits and additional circuits, wherein the N-1 boost circuits and the additional circuits are connected to the N photovoltaic input sources, and the N-1 boost circuits and the additional circuits are also connected to the inverter circuit. The method includes mainly obtaining a feedback value of the bus voltage of the inverter circuit; calculating a given value of the bus voltage according to the feedback value and the input current of the additional circuit, and obtaining a deviation between the feedback value and the given value; adjusting the feedback value of the bus voltage based on the deviation between the feedback value and the given value, and calculating a given current component of the inverter circuit according to the adjusted feedback value; and calculating a voltage component of the inverter circuit according to the given current component to determine a target output voltage of the inverter circuit. Based on this, by replacing the Nth boost circuit with an additional circuit, voltage redundancy is avoided, thereby reducing system costs, and the given value of the bus voltage is calculated through the additional circuit and feedback value, thereby achieving precise control of the bus voltage.

[0087] See also Figure 6 , Figure 6 is a structural block diagram of a control device for a string inverter provided by an embodiment of the present invention, such as Figure 6 As shown, the control device 200 of the string inverter includes a first acquisition module 21, a second acquisition module 22, a regulation module 23 and a calculation module 24;

[0088] The first acquisition module 21 is used to acquire the feedback value of the bus voltage of the inverter circuit and the input current of the additional circuit.

[0089] The second acquisition module 22 is used to calculate the given value of the bus voltage according to the feedback value and the input current of the additional circuit, and to obtain the deviation between the feedback value and the given value.

[0090] The regulating module 23 is used to regulate the feedback value of the bus voltage based on the deviation between the feedback value and the given value, and calculate the current component of the inverter circuit according to the regulated feedback value.

[0091] The calculation module 24 is used to calculate the voltage component of the inverter circuit according to the current component, so as to determine the maximum output voltage of the inverter circuit based on the voltage component.

[0092] It should be noted that the control device of the string inverter described above can execute the control method of the string inverter provided in the embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not fully described in the embodiment of the control device of the string inverter, please refer to the control method of the string inverter provided in the embodiment of the present invention.

[0093] 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 shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0094] Through the description of the above implementation methods, ordinary technicians in this field can clearly understand that each implementation method can be implemented by means of software plus a general hardware platform, and of course, it can also be implemented by hardware. Ordinary technicians in this field can understand that all or part of the processes in the above-mentioned embodiment method can be completed by instructing related hardware through a computer program, and the program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, the storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM), etc.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may also be combined, the steps may be implemented in any order, and there are many other changes in different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they may 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 scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for a string inverter, characterized in that: Applied to a string inverter system, the string inverter system includes N photovoltaic input sources, N-1 boost circuits and additional circuits, the N-1 boost circuits and the additional circuits are connected to the N photovoltaic input sources, and the N-1 boost circuits and the additional circuits are also connected to the inverter circuit, the method includes: Obtaining a feedback value of the bus voltage of the inverter circuit and an input current of the additional circuit; Calculating a given value of the bus voltage according to the feedback value and an input current of the additional circuit, and obtaining a deviation between the feedback value and the given value; adjusting the feedback value of the bus voltage based on the deviation between the feedback value and the given value, and calculating the given current component of the inverter circuit according to the adjusted feedback value; A voltage component of the inverter circuit is calculated according to the given current component to determine a target output voltage of the inverter circuit.

2. The control method of the string inverter according to claim 1, characterized in that: The obtaining of the feedback value of the bus voltage of the inverter circuit comprises: Respectively acquiring input voltages of the N photovoltaic input sources to obtain N photovoltaic input voltages; Determine a maximum photovoltaic input voltage according to the N photovoltaic input voltages, and record the photovoltaic input source corresponding to the maximum photovoltaic input voltage as the Nth photovoltaic input source; The input voltage of the Nth photovoltaic input source is input into the additional circuit to obtain a feedback value of the bus voltage of the inverter circuit.

3. The control method of the string inverter according to claim 2, characterized in that: The additional circuit includes a first diode, an anode of the first diode is connected to the positive electrode of the N-th photovoltaic input source, and a cathode of the first diode is connected to the inverter circuit, wherein the positive electrode of the N-th photovoltaic input source and the first diode, the inverter circuit and the negative electrode of the N-th photovoltaic input source form a first target loop; The step of inputting the input voltage of the Nth photovoltaic input source into the additional circuit to obtain a feedback value of the bus voltage of the inverter circuit includes: The maximum photovoltaic input voltage of the Nth photovoltaic input source is input to the first diode according to the first target loop to obtain a feedback value of the bus voltage of the inverter circuit.

4. The control method of the string inverter according to claim 2, characterized in that: The additional circuit includes a second diode, the cathode of the second diode is connected to the negative electrode of the N-th photovoltaic input source, and the anode of the second diode is connected to the inverter circuit, wherein the positive electrode of the N-th photovoltaic input source and the inverter circuit, the second diode and the negative electrode of the N-th photovoltaic input source form a second target loop; The step of inputting the input voltage of the Nth photovoltaic input source into the additional circuit to obtain a feedback value of the bus voltage of the inverter circuit includes: The maximum photovoltaic input voltage of the Nth photovoltaic input source is input to the second diode according to the second target loop to obtain a feedback value of the bus voltage of the inverter circuit.

5. The control method of the string inverter according to claim 2, characterized in that: The additional circuit includes an IGBT tube / field effect tube, a first end of the IGBT tube / field effect tube is connected to the positive electrode of the N-th photovoltaic input source, and a second end of the IGBT tube / field effect tube is connected to the inverter circuit, wherein the IGBT tube / field effect tube also includes a parasitic diode tube, an anode of the parasitic diode is connected to the positive electrode of the N-th photovoltaic input source, a cathode of the parasitic diode is connected to the inverter circuit, and the positive electrode of the N-th photovoltaic input source, the parasitic diode, the inverter circuit and the negative electrode of the N-th photovoltaic input source form a third target loop; The step of inputting the input voltage of the Nth photovoltaic input source into the additional circuit to obtain a feedback value of the bus voltage of the inverter circuit includes: The maximum photovoltaic input voltage of the Nth photovoltaic input source is input to the parasitic diode according to the third target loop to obtain a feedback value of the bus voltage of the inverter circuit.

6. The control method of the string inverter according to claim 1, characterized in that: The step of calculating the given value of the bus voltage according to the feedback value and the input current of the additional circuit, and obtaining the deviation between the feedback value and the given value, comprises: Obtaining a feedback value of the bus voltage; Calculating the input power of the additional circuit according to the feedback value of the bus voltage and the input current of the additional circuit; Using an MPPT algorithm to perform maximum power tracking on the input power of the additional circuit to obtain a given value of the bus voltage; The difference between the feedback value of the bus voltage and the given value is calculated to obtain a deviation between the feedback value and the given value.

7. The control method of the string inverter according to claim 6, characterized in that: The step of adjusting the feedback value of the bus voltage based on the deviation between the feedback value and the given value, and calculating the current component of the inverter circuit according to the adjusted feedback value, comprises: adjusting the feedback value according to the difference so that the difference between the feedback value and the given value is within a preset voltage range; The load limit requirement of the inverter circuit is obtained, and an adjusted feedback value is calculated according to the load limit requirement to obtain a given current component of the inverter circuit.

8. The control method of a string inverter according to any one of claims 1 to 7, characterized in that: The calculating the voltage component of the inverter circuit according to the given current component to determine the target output voltage of the inverter circuit includes: Obtaining an output current component of the inverter circuit; adjusting the output current component according to the given current component to obtain a target current component; The target output current component is converted to obtain a voltage component of an inverter circuit, and a target output voltage of the inverter circuit is determined according to the voltage component.

9. The control method of a string inverter according to any one of claims 3 to 5, characterized in that: The method further comprises: Acquiring an input voltage and an input current of the photovoltaic input source, and calculating a photovoltaic input power according to the input voltage and the input current; Using the MPPT algorithm, maximum power tracking is performed based on the photovoltaic input power to obtain a corresponding photovoltaic output voltage; determining a target duty cycle according to the photovoltaic output voltage and the input voltage of the photovoltaic input source; The input voltage of the photovoltaic input source is boosted according to the target duty cycle so that the N-1 boost circuits output a maximum voltage.

10. A control device for a string inverter, characterized in that: Applied to a string inverter system, the string inverter system includes N photovoltaic input sources, N-1 boost circuits and additional circuits, the N-1 boost circuits and the additional circuits are connected to the N photovoltaic input sources, the N-1 boost circuits and the additional circuits are also connected to the inverter circuit, and the device includes: A first acquisition module, used to acquire a feedback value of the bus voltage of the inverter circuit and an input current of the additional circuit; A second acquisition module, used for calculating a given value of the bus voltage according to the feedback value and an input current of the additional circuit, and acquiring a deviation between the feedback value and the given value; A regulating module, configured to regulate the feedback value of the bus voltage based on a deviation between the feedback value and the given value, and calculate the current component of the inverter circuit according to the regulated feedback value; A calculation module is used to calculate the voltage component of the inverter circuit according to the current component, so as to determine the maximum output voltage of the inverter circuit based on the voltage component.

11. A string inverter system, characterized in that: The string inverter system comprises: N photovoltaic input sources; N-1 boost circuit; Additional circuits; an inverter circuit; and A controller, wherein the controller comprises at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor so that the at least one processor can execute the method described in any one of claims 1-9.

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