Photovoltaic direct current collection system, control method and storage medium

Abstract

The invention discloses a photovoltaic direct current collection system, a control method and a storage medium. The system comprises photovoltaic group strings PV +, the photovoltaic group strings PV + are connected in parallel in pairs, are connected in parallel after passing through a hybrid solid-state switch, and are used as positive pole input of a DC / DC converter after passing through a switch contact of a direct current isolation switch; the photovoltaic group strings PV-and PV-are connected in parallel in pairs, pass through the switch, then are connected in parallel, and pass through the switch contact of the direct-current isolating switch to serve as the cathode input of the DC / DC converter; the DC-DC converter outputs a DC bus DC-BUS, and the insulation detection circuit is connected to the DC bus DC-BUS in parallel. And one path of PV + and PV-passes through the switch unit Kc and the diode full-bridge rectification unit and then is connected with the DC-BUS in parallel. The invention has the advantages of simple and compact structure, low cost, wide application range, good control effect and the like.

Description

Technical Field

[0001] The present invention mainly relates to the field of photovoltaic technology, and in particular to a photovoltaic direct current collection system, a control method and a storage medium. Background Art

[0002] With the rapid development of the photovoltaic industry, high-power photovoltaic modules (182 / 210) and DC 1500V systems have become the mainstream of the market. The power and current of the DC side of the photovoltaic system are increasing, and the DC system voltage is increasing (it will develop to 2000V in the future). However, the continuous increase of module current and DC side voltage has reduced the system's electricity cost while also bringing higher safety risks to DC side faults.

[0003] In photovoltaic systems, due to the large number of DC-side terminals, a 100-megawatt photovoltaic power station contains tens of thousands of contact points, and the possibility of insulation grounding and arc hazards is extremely high. If the fault cannot be accurately detected and quickly shut down, the continuously burning arc will cause an electrical fire, causing a large amount of property loss and even threatening personal safety. Therefore, the adaptability of photovoltaic modules, insulation detection and fault protection strategies of photovoltaic inverter DC collection systems have become key issues in the field of photovoltaic inverters. Summary of the invention

[0004] The technical problem to be solved by the present invention is: in view of the technical problems existing in the prior art, the present invention provides a photovoltaic DC collection system, a control method and a storage medium with simple and compact structure, low cost, wide application range and good control effect.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: A photovoltaic DC collection system, comprising: Photovoltaic strings PV+, photovoltaic strings PV+ are connected in parallel in pairs, and after passing through the hybrid solid-state switch, they are connected in parallel again, and through the switch contacts of the DC isolation switch, they serve as the positive input of the DC / DC converter; Photovoltaic strings PV-, photovoltaic strings PV- are connected in parallel in pairs, and after passing through switches, they are connected in parallel again, and through the switch contacts of the DC isolation switch, they serve as the negative input of the DC / DC converter; The DC-DC converter outputs a DC bus DC-BUS, and the insulation detection circuit is connected in parallel to the DC bus DC-BUS; Take one of the PV+ and PV-, pass through the switch unit Kc and the diode full-bridge rectifier unit, and then connect them in parallel with the DC-BUS.

[0006] As a further improvement of the present invention: the number of photovoltaic strings PV+ and photovoltaic strings PV- connected in parallel is 2N, where N=1, 2, 3...

[0007] As a further improvement of the present invention: the auxiliary power supply is powered from the DC-BUS, and when the switch unit Kc is closed, the auxiliary power supply is powered to supply power to the hybrid solid-state switch and other loads of the system.

[0008] As a further improvement of the present invention: the structure of the hybrid solid-state switch includes a semiconductor IGBT device S, a mechanical switch unit K and a voltage detection unit V, which are connected in parallel.

[0009] As a further improvement of the present invention: the working process of the hybrid solid-state switch Q includes: Closing: 1) When the system meets the closing conditions, close K; 2) Confirm that K is in the on state through K feedback signal; Opening: 1) When the system receives the opening command, S is turned on; 2) After confirming that S is turned on through voltage detection V, K is opened at the same time; 3) After confirming that K is opened by judging the K feedback signal, S is turned off.

[0010] As a further improvement of the present invention: the system control power source is powered from the DC bus DC-BUS and converted into the control power source through DC / DC conversion; the control power source is used to power the hybrid solid-state switch and the mechanical switch.

[0011] The present invention further provides a control method based on the above photovoltaic DC collection system, which includes an insulation resistance detection process, and the process is as follows: Step S1: Manually close Kc, the DC bus DC-BUS is powered, and the control power supply starts; Step S2: Manually close the DC disconnect switch QF; Step S3: close the K11 switch of the positive hybrid solid-state switch Q1 and the negative K21 switch of the PV1 and PV2 inputs, start the insulation detection device, and detect the insulation resistance of PV1 and PV2; then, close the K1N switch in the positive switch QN and the negative K2N switch in turn, and detect the insulation resistance of PV(2N-1) and PV2N; Step S4: If the insulation resistance value test is qualified, the system enters the next self-test process and prepares to start the machine; if the insulation resistance value test is unqualified, the PV branch of the photovoltaic string with unqualified insulation resistance is warned and the system shuts down.

[0012] The present invention further provides a control method based on the above photovoltaic DC collection system, which includes a string reverse connection fault detection process, and the process includes: Step S10: before the photovoltaic string branch switches Q and K are closed, the string branches are connected in parallel in pairs, and by detecting the photovoltaic string current, it is determined whether there is a single string reverse connection fault inside the string branch; Step S20: After step S10 identifies the reverse connection fault in the two-by-two parallel photovoltaic strings, if the two-by-two parallel strings are reversely connected at the same time, step S10 cannot identify it; by detecting the voltage of the two-by-two parallel branches, it is determined whether the two-by-two parallel branches are reversely connected.

[0013] The present invention further provides a control method based on the above photovoltaic DC collection system, which includes a fault string automatic isolation process, and the process includes: Step S100: PV string input fault is detected; Step S200: shut down, start insulation detection, and locate the faulty string; Step S300: when starting the machine, the positive and negative switches of the faulty string branch are not closed; Step S400: other string branches start and operate normally.

[0014] The present invention further provides a storage medium, which can be read by a computer or a processor, and stores a computer program for executing any one of the above methods.

[0015] Compared with the prior art, the advantages of the present invention are: The photovoltaic DC collection system, control method and storage medium of the present invention have a simple and compact structure, low cost, wide application range, good control effect, and can accurately detect the insulation of the photovoltaic group string level. When the photovoltaic module side or the DC bus inside the inverter is short-circuited, the DC side of the inverter quickly breaks the protection without arcing. When multiple components are combined into one MPPT (DC / DC converter), the number of DC isolation switch contacts, DC / DC converter inductors and modules is reduced, the inverter cost is reduced, and the adaptability of the photovoltaic module is improved. In the solution where multiple components are combined into one MPPT, if one component fails, how to quickly isolate the failed component while other components remain in operation to improve the system operation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the structural principle of the present invention in a specific embodiment.

[0017] Figure 2 Schematic diagram of a hybrid switch in a specific embodiment of the present invention.

[0018] Figure 3 It is a schematic diagram of controlling power supply in a specific embodiment of the present invention.

[0019] Figure 4 It is a flow chart of the insulation resistance detection process in a specific embodiment of the present invention.

[0020] Figure 5 It is a schematic diagram of the reverse connection of a single string inside a string branch in a specific embodiment of the present invention.

[0021] Figure 6 It is a schematic diagram of simultaneous reverse connection inside two-by-two parallel branches of a string group in a specific embodiment of the present invention.

[0022] Figure 7 It is a schematic diagram of the flow of string reverse connection detection in a specific embodiment of the present invention.

[0023] Figure 8 It is a schematic diagram of the process of automatic isolation operation of a faulty string in a specific embodiment of the present invention.

[0024] Fig. 9 It is a schematic diagram of the isolation and redundant operation of faulty string branches in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] In the description of the present application, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0027] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0028] In this application, unless otherwise clearly specified and limited, the terms "assemble", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0029] like Figure 1 As shown, the present invention provides a photovoltaic DC collection system, comprising: Photovoltaic strings PV+, photovoltaic strings PV+ are connected in parallel in pairs, and then connected in parallel after passing through the hybrid solid-state switch, and then pass through the switch contacts of the DC isolation switch to serve as the positive input of the DC / DC converter; for example, in this example, PV1+ and PV2+, PV3+ and PV4+, PV5+ and PV6+ are connected in parallel in pairs, and then connected in parallel after passing through the hybrid solid-state switches Q11, Q12, and Q13; Photovoltaic strings PV-, photovoltaic strings PV- are connected in parallel in pairs, and then connected in parallel after passing through switches, and then pass through the switch contacts of the DC isolation switch to serve as the negative input of the DC / DC converter; for example, in this example, photovoltaic strings PV1- and PV2-, PV3- and PV4-, PV5- and PV6- are connected in parallel in pairs, and then connected in parallel after passing through switches K21, K22, and K23; The DC-DC converter outputs a DC bus DC-BUS, and the insulation detection circuit is connected in parallel to the DC bus DC-BUS. Take one of the PV+ and PV- (for example, PV1+ and PV1-), pass through the switch unit Kc and the diode full-bridge rectifier unit (D1, D2, D3, D4), and then connect it in parallel with the DC-BUS.

[0030] In a specific application example, the number of PV+ and PV- connected in parallel may be 2N (N=1, 2, 3...).

[0031] In a specific application example, the auxiliary power supply is powered from the DC-BUS. When Kc is closed, the auxiliary power supply is powered to supply power to the hybrid solid-state switch Q and other loads of the system.

[0032] In specific application examples, such as Figure 2 As shown, the structure of the hybrid solid-state switch Q includes a semiconductor IGBT device S, a mechanical switch unit K and a voltage detection unit V, which are connected in parallel. The working process of the hybrid solid-state switch Q includes: Closing: 1) When the system meets the closing conditions, close K; 2) Confirm that K is in the on state through the K feedback signal.

[0033] Opening: 1) When the system receives the opening command, S is turned on; 2) After confirming that S is turned on through voltage detection V, K is opened at the same time; 3) After confirming that K is opened by judging the K feedback signal, S is turned off.

[0034] For specific application examples, see Figure 3 The system control power source is taken from the DC bus DC-BUS and converted into control power source through DC / DC conversion. The control power source is used to power the hybrid solid-state switches Q1-QN and the mechanical switches K21- K2N.

[0035] See also Figure 4Based on the above photovoltaic DC collection system, the present invention provides a control method, which includes an insulation resistance detection process, and the process is as follows: Step S1: Manually close Kc, the DC bus DC-BUS is powered, and the control power supply starts; Step S2: Manually close the DC disconnect switch QF; Step S3: Close the K11 switch of the positive hybrid solid-state switch Q1 and the negative K21 switch of PV1 and PV2 input, start the insulation detection device, and detect the insulation resistance of PV1 and PV2. Then, close the K1N switch in the positive switch QN and the negative K2N switch in turn to detect the insulation resistance of PV(2N-1) and PV2N.

[0036] Step S4: If the insulation resistance value is qualified, the system enters the next self-test process and prepares to start. If the insulation resistance value is unqualified, the PV branch with unqualified insulation resistance is warned and the system shuts down.

[0037] Based on the above photovoltaic DC collection system, see Figure 5-Figure 7 As shown, the present invention provides a control method, which includes a string reverse connection fault detection process. During the construction of a string photovoltaic inverter, photovoltaic string PV reverse connection is a common phenomenon. In the photovoltaic inverter system, there are multiple PV branches in parallel input to the BOOST converter. When one of the PV branches is reversely connected, the current of the multiple strings will flow back to the reverse connection branch, causing the reverse connection string to withstand a large current and be damaged. For this reason, see Figure 7 The process of the string reverse connection fault detection process of the present invention includes: Step S10: Before the photovoltaic string branch switches Q and K are closed, the string branches are connected in parallel in pairs, and the equivalent circuit diagram is shown in FIG5 . Figure 5 If PV2 is reversely connected, the reverse current flows inside PV1 and PV2, and the maximum current is the maximum current of the PV module, which will not damage the PV string. By detecting the PV string current, it can be determined whether there is a single string reverse connection fault inside the string branch.

[0038] Step S20: After step S10 identifies the reverse connection fault in the two-by-two parallel photovoltaic strings, if the two-by-two parallel strings are reversely connected at the same time, step S10 cannot identify it. Figure 6 As shown, by detecting the voltage of the two parallel branches, it is determined whether there is a situation in which the two parallel branches are both reversely connected.

[0039] Based on the above photovoltaic DC collection system, see Figure 8-Figure 9 As shown, the present invention provides a control method, which includes a faulty string automatic isolation process. When a serious fault such as grounding is detected in a string branch, the positive hybrid solid-state switch Q and the negative mechanical switch K of the string branch are disconnected, and other branches continue to maintain redundant operation; Figure 8 As shown, the specific process includes: Step S100: PV input fault is detected; Step S200: shut down, start insulation detection, and locate the faulty string; Step S300: when starting the machine, the positive and negative switches of the faulty string branch are not closed; Step S400: other string branches start and operate normally.

[0040] The present invention further provides a storage medium, which can be read by a computer or a processor and stores a computer program for executing the above method.

[0041] Those skilled in the art should understand that the above-mentioned embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application can take the form of a computer program product implemented on one or more computer-readable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the process Figure 1 A process or multiple processes and / or boxes Figure 1 These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing device to work in a specific way, so that the instructions stored in the computer-readable memory produce a product including an instruction device, which implements the functions specified in the process. Figure 1 A process or multiple processes and / or boxes Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide for implementing the process in the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0042] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A photovoltaic DC collection system, characterized in that: include: Photovoltaic strings PV+, photovoltaic strings PV+ are connected in parallel in pairs, and after passing through the hybrid solid-state switch, they are connected in parallel again, and through the switch contacts of the DC isolation switch, they serve as the positive input of the DC / DC converter; Photovoltaic strings PV-, photovoltaic strings PV- are connected in parallel in pairs, and after passing through switches, they are connected in parallel again, and through the switch contacts of the DC isolation switch, they serve as the negative input of the DC / DC converter; The DC-DC converter outputs a DC bus DC-BUS, and the insulation detection circuit is connected in parallel to the DC bus DC-BUS; Take one of the PV+ and PV-, pass through the switch unit Kc and the diode full-bridge rectifier unit, and then connect them in parallel with the DC-BUS.

2. The photovoltaic DC collection system according to claim 1, characterized in that: The number of photovoltaic strings PV+ and photovoltaic strings PV- connected in parallel is 2N, where N=1, 2, 3...

3. The photovoltaic DC collection system according to claim 1, characterized in that: The auxiliary power supply is powered from the DC-BUS. When the switch unit Kc is closed, the auxiliary power supply is powered to supply power to the hybrid solid-state switch and other loads of the system.

4. The photovoltaic DC collection system according to any one of claims 1 to 3, characterized in that: The structure of the hybrid solid-state switch includes a semiconductor IGBT device S, a mechanical switch unit K and a voltage detection unit V, which are connected in parallel.

5. The photovoltaic DC collection system according to claim 4, characterized in that: The working process of the hybrid solid-state switch Q includes: Closing: 1) When the system meets the closing conditions, close K; 2) Confirm that K is in the on state through K feedback signal; Opening: 1) When the system receives the opening command, S is turned on; 2) After confirming that S is turned on through voltage detection V, K is opened at the same time; 3) After confirming that K is opened by judging the K feedback signal, S is turned off.

6. The photovoltaic DC collection system according to any one of claims 1 to 3, characterized in that: The system control power is taken from the DC bus DC-BUS and converted into control power through DC / DC conversion; the control power is used to power the hybrid solid-state switch and mechanical switch.

7. A control method for a photovoltaic DC collection system according to any one of claims 1 to 6, characterized in that: Including the insulation resistance detection process, the process is as follows: Step S1: Manually close Kc, the DC bus DC-BUS is powered, and the control power supply starts; Step S2: Manually close the DC disconnect switch QF; Step S3: close the K11 switch of the positive hybrid solid-state switch Q1 and the negative K21 switch of the PV1 and PV2 inputs, start the insulation detection device, and detect the insulation resistance of PV1 and PV2; then, close the K1N switch in the positive switch QN and the negative K2N switch in turn, and detect the insulation resistance of PV(2N-1) and PV2N; Step S4: If the insulation resistance value test is qualified, the system enters the next self-test process and prepares to start the machine; if the insulation resistance value test is unqualified, the PV branch of the photovoltaic string with unqualified insulation resistance is warned and the system shuts down.

8. A control method for a photovoltaic DC collection system according to any one of claims 1 to 6, characterized in that: Including the string reverse fault detection process, the process includes: Step S10: before the photovoltaic string branch switches Q and K are closed, the string branches are connected in parallel in pairs, and by detecting the photovoltaic string current, it is determined whether there is a single string reverse connection fault inside the string branch; Step S20: After step S10 identifies the reverse connection fault in the two-by-two parallel photovoltaic strings, if the two-by-two parallel strings are reversely connected at the same time, step S10 cannot identify it; by detecting the voltage of the two-by-two parallel branches, it is determined whether the two-by-two parallel branches are reversely connected.

9. A control method for a photovoltaic DC collection system according to any one of claims 1 to 6, characterized in that: Including the automatic isolation process of the faulty string, the process includes: Step S100: PV string input fault is detected; Step S200: shut down, start insulation detection, and locate the faulty string; Step S300: when starting the machine, the positive and negative switches of the faulty string branch are not closed; Step S400: other string branches start and operate normally.

10. A storage medium, which can be read by a computer or a processor, characterized in that: The storage medium stores a computer program for executing any one of the methods in claims 7 to 9.

Images