Photovoltaic inverter and control method thereof
By detecting the characteristic amount of the photovoltaic string in the photovoltaic inverter, the controller determines whether the switch is closed, solving the damage caused by the reverse connection of the series after the switch device of the photovoltaic inverter is closed, and effectively protecting the string.
Patent Information
- Application Number
- CN202510458170.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-12
- Publication Date
- 2025-08-26
AI Technical Summary
After the switch device of the photovoltaic inverter is closed, the reverse connection of the series leads to one more phenomenon. The existing technology cannot protect the series in time, resulting in rapid damage to the series.
Before the switch device is closed, the characteristic amount of the photovoltaic string is detected by the string state detection device. The controller determines whether the switch device is allowed to close based on the characteristic amount to avoid the phenomenon of one more filling when the string is reversed.
Effectively protect the photovoltaic string, prevent damage caused by reverse connection of the string, and improve the safety and reliability of the photovoltaic inverter.
Smart Images
Figure CN120545941A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of photovoltaic inverters, and in particular to a photovoltaic inverter and a control method thereof. Background Art
[0002] When a PV inverter is first connected to the grid, there may be a situation where the PV strings are reversed or short-circuited. In particular, in extreme cases such as when only one string is connected with the wrong polarity while the others are connected correctly, or when only one string is connected correctly while the others are connected with the wrong polarity, or when one string is short-circuited, once the switch is closed, the strings connected to the same MPPT (Maximum Power Point Tracking) unit will immediately be connected in parallel. This may cause the short-circuit current of multiple strings to flow into one string. The reverse current far exceeds its tolerance and the string will be quickly damaged, resulting in significant economic losses and safety hazards.
[0003] The existing technology is to detect whether the string connection is normal through the controller inside the photovoltaic inverter after the switch device is closed. If there is a polarity reversal or short circuit, the switch device will be quickly driven to disconnect the string from the photovoltaic inverter to protect the photovoltaic inverter and the string from damage as much as possible. However, the existing technology requires a delay of at least milliseconds from the closing of the switch device to the disconnection of the switch device when the string connection abnormality is detected. When the reverse current is large enough, the string has already been damaged, and the existing protection method does not play a role in protecting the string. For example, for a string with a short-circuit current of 20A, when three injections occur, the injected string will withstand three times the overload current, and the damage time is about microseconds. Figure 1 As shown, taking the example of two strings converging and then connecting to the same MPPT unit through a switch, if string PV14 is reversed in polarity, before the switch is closed, at most a one-to-one situation will exist, meaning the short-circuit current from string PV13 will be fed into string PV14. Generally, strings are capable of withstanding a single short-circuit current, so they will not be damaged. However, once the switch is closed, the one-to-one situation will shift to three-to-one situation, rapidly damaging string PV14. By the time the controller detects a reverse polarity situation and disconnects the switch, it's too late. Therefore, if a string reverse polarity or short-circuit fault exists before the switch is closed, closing the switch is generally not allowed, as doing so will likely quickly burn out the components. Summary of the Invention
[0004] In view of this, the purpose of the present application is to provide a photovoltaic inverter and a control method thereof to solve the problem of multiple injection caused by reverse connection of the strings after the switching device is closed, which causes the photovoltaic inverter to be unable to respond in time for protection, thereby causing the strings to be quickly damaged.
[0005] The technical solutions adopted by this application to solve the above technical problems are as follows:
[0006] On one hand, the present application provides a photovoltaic inverter, which includes a string status detection device, a switch device, a DCDC conversion unit, a bus capacitor, and a controller;
[0007] The DCDC conversion unit is used to realize the conversion between DC power and DC power; the input end of the DCDC conversion unit is connected to at least one photovoltaic string to be tested through the switching device, and the output end of the DCDC conversion unit is connected to the bus capacitor;
[0008] The string status detection device is used to detect the characteristic quantity of the photovoltaic string to be tested;
[0009] The controller is configured to obtain a characteristic value of the photovoltaic string to be tested detected by the string status detection device; and determine whether to allow the switching device to be closed based on the characteristic value of the photovoltaic string to be tested.
[0010] On the other hand, the present application provides a control method for a photovoltaic inverter, wherein the photovoltaic inverter includes a string state detection device, a switch device, a bus capacitor, and a DCDC conversion unit;
[0011] The DCDC conversion unit is used to realize the conversion between DC power and DC power; the input end of the DCDC conversion unit is connected to at least one photovoltaic string to be tested through the switching device, and the output end of the DCDC conversion unit is connected to the bus capacitor;
[0012] The string status detection device is used to detect the characteristic quantity of the photovoltaic string to be tested;
[0013] The control method includes:
[0014] Acquiring a characteristic value of the photovoltaic string to be tested detected by the string status detection device;
[0015] Whether to allow the switching device to be closed is determined according to the characteristic quantity of the photovoltaic string to be tested.
[0016] The photovoltaic inverter and control method thereof provided in the embodiments of the present application identify, before the switching device is closed, whether the photovoltaic string is reversely connected in polarity based on the characteristic quantity of the photovoltaic string detected by the string status detection device. When the photovoltaic string is identified to be reversely connected in polarity, the switching device is controlled to be unable to close, thereby avoiding the problem of multiple flooding caused by the reverse connection of the strings after the switching device is closed, which causes the photovoltaic inverter to be unable to respond in time for protection, thereby causing the strings to be quickly damaged, thereby achieving the purpose of effectively protecting the strings. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Figure 1Schematic diagram of an existing photovoltaic inverter and its switch device after closing and opening;
[0018] Figure 2 A schematic diagram of a photovoltaic inverter provided in an embodiment of the present application;
[0019] Figure 3 A schematic diagram of another photovoltaic inverter provided in an embodiment of the present application;
[0020] Figure 4 A schematic diagram of current flow in another photovoltaic inverter provided by an embodiment of the present application when there is no reverse polarity connection;
[0021] Figure 5 A schematic diagram of current flow when polarity is reversed in another photovoltaic inverter provided by an embodiment of the present application;
[0022] Figure 6 A schematic diagram of current flow when polarity is reversed in another photovoltaic inverter provided in an embodiment of the present application;
[0023] Figure 7 A schematic diagram of current flow when polarity is reversed in another photovoltaic inverter provided in an embodiment of the present application;
[0024] Figure 8 A schematic diagram of current flow when polarity is reversed in another photovoltaic inverter provided in an embodiment of the present application;
[0025] Figure 9 A schematic diagram of current flow when polarity is reversed in another photovoltaic inverter provided in an embodiment of the present application;
[0026] Figure 10 Schematic diagram of a photovoltaic inverter control method provided in an embodiment of the present application.
[0027] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION
[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application clearer and more understandable, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.
[0029] like Figure 2 As shown, the photovoltaic inverter provided in the embodiment of the present application includes a string state detection device, a switching device, m DCDC conversion units (m is a natural number greater than or equal to 1), a bus capacitor and a controller;
[0030] The DCDC conversion unit is used to realize the conversion between DC power and DC power. More specifically, the DCDC conversion unit is used to realize the MPPT tracking and boosting functions. The input end of the DCDC conversion unit is connected to at least one photovoltaic string to be tested through the switching device, and the output end of the DCDC conversion unit is connected to the bus capacitor.
[0031] The string status detection device is used to detect the characteristic quantity of the photovoltaic string to be tested;
[0032] The controller is configured to obtain a characteristic value of the photovoltaic string to be tested detected by the string status detection device; and determine whether to allow the switching device to be closed based on the characteristic value of the photovoltaic string to be tested.
[0033] In one example, the controller draws power from the grid / DC side. Specifically, when the PV inverter is grid-connected, the controller can draw power from the grid; when the PV inverter is off-grid, the controller can draw power from PV strings other than the one to be tested.
[0034] In one example, the bus capacitor may be in the form of multiple bus capacitors connected in series and / or in parallel.
[0035] For example, Figure 2 C1 and C2 are both bus capacitors, the bus capacitor C1 and the bus capacitor C2 are connected in series, and the output end of the DCDC conversion unit is connected to the bus capacitor C1 and the bus capacitor C2 connected in series.
[0036] In one example, the DCDC conversion unit includes at least one of a boost circuit, a buck circuit, and a buck-boost circuit.
[0037] In a specific implementation, the power device used in the DCDC conversion unit may be a silicon device or a silicon carbide device.
[0038] In one example, different numbers of photovoltaic strings to be tested have different connection methods, and the number of photovoltaic strings to be tested is a natural number greater than or equal to 1.
[0039] like Figure 2As shown, 2n PV strings to be tested are paired in parallel and then connected to the same DCDC converter unit via a switch. Before the switch is closed, there are at most two PV strings to be tested in parallel. After the switch is closed, all 2n strings are connected in parallel. Specifically, PV11 is paired with PV12, PV13 is paired with PV14, ... PV1(2n-1) is paired with PV1(2n), PV21 is paired with PV22, PV23 is paired with PV24, ... PV2(2n-1) is paired with PV2(2n), PVm1 is paired with PVm2, PVm3 is paired with PVm4, ... PVm(2n-1) is paired with PVm(2n). That is, the positive pole of PV11 is connected to the positive pole of PV12 and then connected to the positive pole of DCDC converter unit 1 via switch S11. The negative pole of PV11 is connected to the negative pole of PV12 and then connected to the negative pole of DCDC converter unit 1 via switch K11. The others are similar.
[0040] It is understandable that the connection mode of the photovoltaic strings to be tested is not limited to the case of being connected in pairs in parallel.
[0041] refer to Figure 8 It can be understood that three photovoltaic strings to be tested are paired and connected in parallel, that is, the positive pole of PV11 is connected to the positive pole of PV12 and the positive pole of PV13, and then connected to the positive pole of MPPT1 through switch S11, the positive pole of PV14 is connected to the positive pole of PV15 and the positive pole of PV16, and then connected to the positive pole of MPPT1 through switch S12, the negative pole of PV11 is connected to the negative pole of PV12 and the negative pole of PV13, and then connected to the negative pole of MPPT1 through switch K11, and the negative pole of PV14 is connected to the negative pole of PV15 and the negative pole of PV16, and then connected to the negative pole of MPPT1 through switch K12.
[0042] refer to Figure 9 To understand, the positive pole of PV11 is connected to the positive pole of PV12, the positive pole of PV13 and the positive pole of PV14, and then connected to the positive pole of MPPT1 through switch S11. The negative pole of PV11 is connected to the negative pole of PV12 and then connected to the negative pole of MPPT1 through switch K11. The negative pole of PV13 is connected to the negative pole of PV14 and then connected to the negative pole of MPPT1 through switch K12.
[0043] In other examples, it is also feasible to directly connect a single photovoltaic string to be tested to the switch device.
[0044] In one example, the switch device may be composed of a plurality of switches or may be an independent switch.
[0045] In one example, the string state detection device includes a current sampling device, and the current sampling device includes at least one of the following: a current transformer, a magnetoresistive sensor, a Hall element, and a current sampling resistor.
[0046] Furthermore, the string status detection device further includes a voltage sampling device, and the voltage sampling device includes a voltage dividing resistor and / or a voltage sensor.
[0047] In one example, the current sampling device is connected between the photovoltaic string to be tested and the switching device.
[0048] by Figure 3 For example, one end of the current sampling device A1 is connected to the negative pole of the photovoltaic string PV11 to be tested, and the other end of the current sampling device A1 is connected to the switch K11 in the switch device; one end of the current sampling device A2 is connected to the negative pole of the photovoltaic string PV12 to be tested, and the other end of the current sampling device A2 is connected to the switch K11 in the switch device; one end of the current sampling device A3 is connected to the negative pole of the photovoltaic string PV13 to be tested, and the other end of the current sampling device A3 is connected to the switch K12 in the switch device; one end of the current sampling device A4 is connected to the negative pole of the photovoltaic string PV14 to be tested, and the other end of the current sampling device A4 is connected to the switch K12 in the switch device.
[0049] refer to Figure 6 For understanding, one end of the current sampling device A1 is connected to the positive pole of the photovoltaic string PV11 to be tested, and the other end of the current sampling device A1 is connected to the switch S11 in the switching device; one end of the current sampling device A2 is connected to the positive pole of the photovoltaic string PV12 to be tested, and the other end of the current sampling device A2 is connected to the switch S11 in the switching device; one end of the current sampling device A3 is connected to the positive pole of the photovoltaic string PV13 to be tested, and the other end of the current sampling device A3 is connected to the switch S12 in the switching device; one end of the current sampling device A4 is connected to the positive pole of the photovoltaic string PV14 to be tested, and the other end of the current sampling device A4 is connected to the switch S12 in the switching device.
[0050] In one example, the voltage sampling device is connected in parallel between the positive and negative poles of the photovoltaic string to be tested.
[0051] refer to Figure 7It is understood that the voltage sampling device V1 is connected in parallel between the positive and negative poles of the photovoltaic string PV12 to be tested, that is, one end of the voltage sampling device V1 is connected between the positive pole of the photovoltaic string PV12 to be tested and the switch S11, and the other end of the voltage sampling device V1 is connected between the negative pole of the photovoltaic string PV12 to be tested and the switch K11; the voltage sampling device V2 is connected in parallel between the positive and negative poles of the photovoltaic string PV14 to be tested, that is, one end of the voltage sampling device V2 is connected between the negative pole of the photovoltaic string PV14 to be tested and the switch S12, and the other end of the voltage sampling device V2 is connected between the positive pole of the photovoltaic string PV14 to be tested and the switch K12.
[0052] In one example, the characteristic quantity of the photovoltaic string to be tested includes at least one of the following: string current magnitude, string current direction, string voltage magnitude, and string voltage direction.
[0053] Specifically, it can be the current magnitude, current direction, voltage magnitude, and voltage direction of all or part of the photovoltaic strings to be tested; it can also be the negative current, negative current direction, positive current, positive current direction, etc. of the photovoltaic strings to be tested.
[0054] Taking the working condition of being connected to a switching device after being connected in parallel with two photovoltaic strings to be tested as an example, for the two parallel photovoltaic strings to be tested, it can be the positive current of the two photovoltaic strings to be tested, or the negative current of the two photovoltaic strings to be tested, or the positive current and negative current of the two photovoltaic strings to be tested, or the positive current of one photovoltaic string to be tested and the negative current of the other photovoltaic string to be tested, or only the positive current or negative current of one of the photovoltaic strings to be tested.
[0055] Based on the characteristic values of the PV string under test, the controller can determine whether reverse polarity exists before the switch is closed. If reverse polarity is detected at the DC input, the controller continuously sends trip commands or signals to the switch, preventing it from closing. Furthermore, the controller outputs an alarm message, prompting the user to adjust the wiring of the PV string under test until reverse polarity is determined to be correct. Only then is the switch allowed to close.
[0056] Before the switch device is closed, even if the polarity of the photovoltaic string to be tested is reversed, the maximum loop that can be formed is one-to-one (the short-circuit current of one photovoltaic string to be tested is directly fed into the other photovoltaic string to be tested), which will not cause obvious damage to the photovoltaic string to be tested. At this time, the controller will collect the current of all or part of the photovoltaic strings to be tested through the string status detection device, and judge whether there is a reverse connection problem between the strings based on the magnitude and / or direction of the current. If it is judged that there is a problem, the controller will continuously output a trip signal to not allow the switch device to be closed, thereby protecting the strings. Otherwise, once the switch device is closed, (2n-1) string short-circuit currents may be simultaneously fed into one string, and the injected components will withstand a reverse current of about (2n-1) times their own short-circuit current, which will be quickly damaged.
[0057] like Figure 3 As shown, taking 1 MPPT unit, 4 PV string inputs, and the string status detection device capable of detecting the negative current of each string as an example, the four strings PV11, PV12, PV13, and PV14 have their own positive and negative poles. After PV11+ and PV12+ are connected together, they are connected to MPPT1 through S11 of the switching device. After PV13+ and PV14+ are connected together, they are connected to MPPT1 through S12 of the switching device. PV11- and PV12- first pass through current sampling devices A1 and A2 respectively, and then converge to K11 of the switching device, and finally connect to MPPT1. PV13- and PV14- first pass through current sampling devices A3 and A4 respectively, and then converge to K12 of the switching device, and finally connect to MPPT1. The controller can obtain the current size and / or direction of the corresponding branch through A1, A2, A3, and A4, and can control the switching device to be in a continuously tripped state, that is, it cannot be closed. Then if the polarity of the four strings are connected correctly, that is, as Figure 3 In the connection mode shown, there is no current loop. When the controller is powered on, it recognizes that the current values of A1, A2, A3, and A4 are less than a certain threshold value. The upper limit of the threshold value is determined by the short-circuit current of a single string, and the lower limit is determined by the sampling accuracy of the current sampling device. Then, no trip signal will be output to the switch device, and the switch device can be closed normally. The current flow after the user closes the switch device is as follows Figure 4 shown.
[0058] However, if there is a reverse connection of the string, take a reverse connection of the string as an example, Figure 5As shown, if PV14 is reversely connected, then PV13+ is connected to PV14-, and PV13- is connected to PV14+. The two strings form a closed loop, and the short-circuit current of PV13 is reversed into PV14. Within the acceptable range of PV14, PV14 is generally not damaged. When the controller is powered on, A3 and A4 will sense currents of equal magnitude and opposite directions. The controller determines that the polarity of the string is reversed by determining that the current value is greater than the threshold and / or there is a current flowing into the negative pole of the string. At this time, the controller continuously outputs a trip signal to the switch device, not allowing the switch device to close. If the user chooses to continue closing the switch device, it will not be closed. At the same time, an alarm will be issued to indicate the string with reverse polarity. The user can adjust the wiring of the corresponding string accordingly. Figure 6 and Figure 5 The difference is that the current sampling devices A1, A2, A3, and A4 sample the magnitude and / or direction of the positive current of the string.
[0059] However, there may be a situation where both strings in parallel are connected in reverse, such as Figure 7 As shown, if the strings PV13 and PV14 are all reversed, then PV13+ is still connected to PV14+, and PV13- is still connected to PV14-. At this time, when the controller is powered on, although there is no current in each string branch, the voltage sampling device V2 in the string status detection device will detect that the voltage polarity of PV14 is negative. At this time, the controller continues to output a trip signal to the switch device, not allowing the switch device to close. If the user chooses to continue closing the switch device, it will not close. At the same time, an alarm will be issued to indicate the string with reverse polarity. The user can adjust the wiring of the corresponding string accordingly. Figure 7 In the example, the voltage sampling device V1 is connected between the positive and negative poles of PV12, and the voltage sampling device V2 is connected between the positive and negative poles of PV14. The voltage sampling devices V1 and V2 can be used to assist in determining whether the string polarity is reversed. That is, at this time, the current sampling devices A1 to A4 cannot determine whether the string polarity is reversed.
[0060] In summary, strings with reverse polarity or short circuit faults can be identified before the switch is closed, thereby effectively preventing the occurrence of multiple supply between strings and playing a role in protecting the strings.
[0061] like Figure 10 As shown, another embodiment of the present application provides a control method for a photovoltaic inverter, and the photovoltaic inverter can refer to the above example. The control method includes:
[0062] S11, obtaining a characteristic value of the photovoltaic string to be tested detected by the string status detection device;
[0063] S12: Determine whether to allow the switching device to be closed based on the characteristic quantity of the photovoltaic string to be tested.
[0064] In one example, determining whether to allow the switching device to be closed based on the characteristic value of the photovoltaic string branch to be tested includes:
[0065] Determine whether to allow the switch device to be closed according to the string current of the photovoltaic string to be tested.
[0066] For example, if the string current is greater than a threshold value and / or the current direction is flowing into the negative pole of the string, the switch device is not allowed to be closed; otherwise, the switch device is allowed to be closed.
[0067] In one example, determining whether to allow the switching device to be closed based on the characteristic value of the photovoltaic string branch to be tested includes:
[0068] Whether to allow the switching device to be closed is determined according to the string current and the string voltage of the photovoltaic string to be tested.
[0069] For example, whether the switch device is allowed to be closed is first determined according to the string current of the photovoltaic string to be tested, and then whether the switch device is allowed to be closed is determined according to the string voltage of the photovoltaic string to be tested; or, whether the switch device is allowed to be closed is first determined according to the string voltage of the photovoltaic string to be tested, and then whether the switch device is allowed to be closed is determined according to the string current of the photovoltaic string to be tested; or, whether the switch device is allowed to be closed is determined based on both the string current and the string voltage of the photovoltaic string to be tested.
[0070] In one example, the method further includes:
[0071] When the switching device is not allowed to be closed, a trip signal is continuously output to the switching device.
[0072] In one example, the method further includes:
[0073] When the switching device is not allowed to be closed, an alarm message is outputted to enable the user to adjust the connection of the corresponding photovoltaic string to be tested.
[0074] The preferred embodiments of the present application are described above with reference to the accompanying drawings, but are not intended to limit the scope of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and essence of the present application shall fall within the scope of the present application.
Claims
1. A photovoltaic inverter, characterized in that: The photovoltaic inverter includes a string status detection device, a switch device, a DCDC conversion unit, a bus capacitor and a controller; The DCDC conversion unit is used to realize the conversion between DC power and DC power; the input end of the DCDC conversion unit is connected to at least one photovoltaic string to be tested through the switching device, and the output end of the DCDC conversion unit is connected to the bus capacitor; The string status detection device is used to detect the characteristic quantity of the photovoltaic string to be tested; The controller is used to obtain the characteristic value of the photovoltaic string to be tested detected by the string status detection device; Whether to allow the switching device to be closed is determined according to the characteristic quantity of the photovoltaic string to be tested.
2. The photovoltaic inverter according to claim 1, characterized in that: The string status detection device includes a current sampling device, which is connected between the photovoltaic string to be tested and the switch device.
3. The photovoltaic inverter according to claim 2, characterized in that: The string status detection device further includes a voltage sampling device, which is connected in parallel between the positive and negative poles of the photovoltaic string to be tested.
4. The photovoltaic inverter according to claim 1, characterized in that: The characteristic quantity of the photovoltaic string to be tested includes at least one of the following: string current magnitude, string current direction, string voltage magnitude, and string voltage direction.
5. The photovoltaic inverter according to claim 1, characterized in that: The DCDC conversion unit includes at least one of a boost circuit, a buck circuit, and a buck-boost circuit.
6. A control method for a photovoltaic inverter, characterized in that: The photovoltaic inverter includes a string status detection device, a switch device, a bus capacitor and a DCDC conversion unit; The DCDC conversion unit is used to realize the conversion between DC power and DC power; the input end of the DCDC conversion unit is connected to at least one photovoltaic string to be tested through the switching device, and the output end of the DCDC conversion unit is connected to the bus capacitor; The string status detection device is used to detect the characteristic quantity of the photovoltaic string to be tested; The control method includes: Acquiring a characteristic value of the photovoltaic string to be tested detected by the string status detection device; Whether to allow the switching device to be closed is determined according to the characteristic quantity of the photovoltaic string to be tested.
7. The photovoltaic inverter control method according to claim 6, characterized in that: The determining, based on the characteristic quantity of the photovoltaic string to be tested, whether to allow the switching device to be closed includes: Determine whether to allow the switch device to be closed according to the string current of the photovoltaic string to be tested.
8. The photovoltaic inverter control method according to claim 7, characterized in that: The determining, based on the characteristic quantity of the photovoltaic string to be tested, whether to allow the switching device to be closed includes: Whether to allow the switching device to be closed is determined according to the string current and the string voltage of the photovoltaic string to be tested.
9. The photovoltaic inverter control method according to claim 6, characterized in that: The method further comprises: When the switching device is not allowed to be closed, a trip signal is continuously output to the switching device.
10. The photovoltaic inverter control method according to claim 6, characterized in that: The method further comprises: When the switching device is not allowed to be closed, an alarm message is outputted to enable the user to adjust the connection of the corresponding photovoltaic string to be tested.