Common positive electrode DC / DC converter and photovoltaic inverter system formed by components of the common positive electrode family

Abstract

The present invention discloses a common positive DC / DC converter and a photovoltaic inverter system composed of a common positive group, including a photovoltaic connection unit, a switch control unit, an energy storage unit, a polarity output control unit, and an inverter connection unit; one end of the switch control unit and the positive bus terminal of the inverter connection unit are both connected to the positive photovoltaic terminal of the photovoltaic connection unit, the negative photovoltaic terminal of the photovoltaic connection unit is connected to one end of the energy storage unit, the other end of the energy storage unit and the negative terminal of the polarity output control unit are both connected to the other end of the switch control unit, the positive terminal of the polarity output control unit is connected to the negative bus terminal of the inverter connection unit, and the midpoint of the positive bus terminal and the negative bus terminal of the inverter connection unit is grounded. The photovoltaic inverter system composed of the common positive group includes a plurality of photovoltaic strings, an inverter unit, and at least one common positive DC / DC converter, and is applied to a photovoltaic inverter system with a voltage level of 1000V - 3000V and higher, effectively suppressing the PID effect of the photovoltaic panel.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic circuits, and particularly to a common positive DC / DC converter and a photovoltaic inverter system composed of a common positive group. Background Art

[0002] With the continuous development of the photovoltaic industry, the power rating of inverters has been increasing continuously. Reducing system costs and minimizing system losses have become important research directions for the healthy and sustainable development of inverters. Up to now, most of the existing centralized, decentralized, and string inverters in the market adopt the method of increasing the system voltage to reduce the system current, minimize losses, and reduce costs. At the same time, with the increase in the voltage level of the photovoltaic inverter system, the scheme for suppressing the PID effect (Potential Induced Degradation) of photovoltaic panels has become the focus of attention.

[0003] In order to reduce the cost of existing power cables and system hardware costs in traditional photovoltaic inverter systems, the midpoint of the bus (BUS_M) is grounded to reduce the safety specification level of the DC side to the ground. If the traditional DC / DC converter method is adopted, a negative high voltage is formed between its negative pole and the ground, and the voltage value is half of the bus voltage. The problem is that the positive and negative poles (BUS+BUS-) of this system are not allowed to be grounded. Once a grounding fault occurs, the voltage of the DC side to the ground is the full bus voltage, which will exceed the traditional safety specification design. Therefore, the traditional method of grounding the negative pole cannot be used to suppress the PID effect of photovoltaic panels. Summary of the Invention

[0004] Aiming at the defects existing in the above-mentioned prior art, the purpose of the present invention is to provide a common positive DC / DC converter and a photovoltaic inverter system composed of a common positive group, which can effectively suppress the PID effect of photovoltaic panels, further reduce system costs and have reliability, and can be applied to photovoltaic inverter systems such as decentralized and string types.

[0005] To achieve the above object, the present invention provides a common positive DC / DC converter for a photovoltaic inverter system, including a photovoltaic connection unit, a switch control unit, an energy storage unit, a polarity output control unit, and an inverter connection unit; one end of the switch control unit and the positive extreme of the bus of the inverter connection unit are both electrically connected to the positive extreme of the photovoltaic of the photovoltaic connection unit, the negative extreme of the photovoltaic of the photovoltaic connection unit is electrically connected to one end of the energy storage unit, the other end of the energy storage unit and the negative extreme of the polarity output control unit are both electrically connected to the other end of the switch control unit, the positive extreme of the polarity output control unit is electrically connected to the negative extreme of the bus of the inverter connection unit, and the midpoint of the positive extreme and the negative extreme of the bus of the inverter connection unit is grounded.

[0006] Preferably, the photovoltaic connection unit includes a photovoltaic capacitor, the switch control unit includes a switching transistor, the energy storage unit includes an inductive coil, the polarity output control unit includes a diode, and the inverter connection unit includes at least one inverter capacitor; one end of the photovoltaic capacitor is electrically connected to the positive photovoltaic terminal, one end of the inverter capacitor is electrically connected to the positive bus terminal, and both the positive photovoltaic terminal and the positive bus terminal are electrically connected to the collector terminal of the switching transistor; the other end of the photovoltaic capacitor is electrically connected to the negative photovoltaic terminal, and one end of the inductive coil is electrically connected to the negative photovoltaic terminal; the other end of the inductive coil and the emitter terminal of the switching transistor are both electrically connected to the negative terminal of the diode; the other end of the inverter capacitor is electrically connected to the negative bus terminal, and the positive terminal of the diode is electrically connected to the negative bus terminal; the midpoint of the inverter capacitor is grounded.

[0007] Preferably, the inverter capacitor includes at least two first capacitors and a second capacitor, and the midpoint of the series connection of the first capacitor and the second capacitor is grounded.

[0008] To achieve the above object, the present invention further provides a photovoltaic inverter system composed of a common positive DC / DC converter, including a photovoltaic string, an inverter unit, and at least one common positive DC / DC converter. The two ends of the photovoltaic string are respectively electrically connected to the positive photovoltaic terminal and the negative photovoltaic terminal of the common positive DC / DC converter, and the two ends of the inverter unit are respectively electrically connected to the positive bus terminal and the negative bus terminal of the common positive DC / DC converter. The midpoint of the two ends of the inverter unit is grounded.

[0009] Preferably, a first controllable circuit unit and a leakage current detection unit are further provided at the midpoint of the two ends of the inverter unit. One end of the first controllable circuit unit is electrically connected to the midpoint of the bus, and the leakage current detection unit is provided between the other end of the first controllable circuit unit and the ground.

[0010] Preferably, the first controllable circuit unit includes a first DC grounding switch and a first DC resistor. One end of the first DC grounding switch is electrically connected to the midpoint of the bus, the other end of the first DC grounding switch is electrically connected to one end of the first DC resistor, and the leakage current detection unit is further electrically connected between the other end of the first DC resistor and the ground.

[0011] Preferably, a grid-connected transformer is further provided on the inverter unit side. After the neutral point of the transformer is electrically connected to the midpoint of the bus of the inverter unit, a second controllable circuit unit is further provided. One end of the first controllable circuit unit is electrically connected to the neutral point of the transformer and the midpoint of the bus of the inverter unit, and the other end of the second controllable circuit unit is grounded.

[0012] Preferably, the second controllable circuit unit includes a second AC grounding switch and a second DC resistor, one end of the second AC grounding switch is electrically connected to the neutral point of the transformer, the other end of the second AC grounding switch is electrically connected to one end of the second DC resistor, and the other end of the second DC resistor is grounded.

[0013] Preferably, the leakage current detection unit is further electrically connected between the other end of the second DC resistor and the ground.

[0014] Preferably, the leakage current detection unit comprises a Hall sensor to quickly detect a system leakage current fault.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. A common positive DC / DC converter has the ability to protect 1000V system, 1200V system, 1500V system, 2000V system, 3000V system and higher-level photovoltaic inverter systems, and can also effectively suppress the PID effect of photovoltaic panels.

[0017] 2. The first controllable circuit unit cooperates with the bus midpoint grounding to reduce the safety level of the DC side and reduce the risk of damage to the photovoltaic inverter system caused by grounding faults through the leakage current detection unit.

[0018] 3. The photovoltaic inverter system with a common positive DC / DC converter and a first DC resistor controllable grounding can not only suppress the PID effect of the photovoltaic panel, but also prevent the DC side from generating a long-term continuous high voltage to the ground and damaging the system when a grounding fault occurs in the system through the first DC resistor grounding. In addition, the photovoltaic inverter system quickly detects the grounding fault through the Hall sensor and handles the fault.

[0019] 4. The photovoltaic inverter system composed of the common positive DC / DC converter is also suitable for photovoltaic inverter systems of 1000V-3000V and higher voltage levels. It has protection capabilities for 1000V systems, 1200V systems, 1500V systems, 2000V systems, 3000V systems and higher-level photovoltaic inverter systems, and can also effectively suppress the PID effect of photovoltaic panels.

[0020] 5. By controlling the second controllable circuit unit to control the AC neutral point through the resistor grounding, it is indirectly ensured that the DC positive and negative poles have equal potential to the ground. The DC side can be controllably grounded before the inverter unit is started. When the inverter unit is connected to the grid, the DC side is grounded and the AC side controllable grounding is disconnected to ensure that the positive and negative voltages to the ground of the entire photovoltaic system are half of the entire bus voltage during the grid-connected and off-grid processes, which can reduce the safety level of the DC side and reduce the design cost.

[0021] 6. When a ground fault occurs, the Hall sensor can effectively detect the ground fault and ground through the first DC resistor R1, releasing the high voltage on the DC side to the ground. And before the inverter unit starts, the DC side is controllably grounded, and the DC side ground fault is detected through the Hall sensor on the DC side; after the inverter unit is connected to the grid, the DC side ground connection is disconnected, the AC side is controllably grounded, and the ground fault of the entire system is detected through the Hall sensor on the AC side. The method of controllable AC-DC grounding ensures that the photovoltaic system can detect and handle ground faults during both the grid-connected process and the off-grid process.

[0022] 7. The common positive family DC / DC converter in cooperation with the AC-DC grounded photovoltaic inverter system is also applicable to photovoltaic inverter systems with voltage levels of 1000V - 3000V and higher. It has protection capabilities for 1000V systems, 1200V systems, 1500V systems, 2000V systems, 3000V systems, and higher-level photovoltaic inverter systems, and can also effectively suppress the PID effect of photovoltaic panels. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the solutions in the present invention, the following will give a brief introduction to the drawings required for the description of the embodiments of the present invention. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic structural diagram of the first embodiment of the present invention;

[0025] Figure 2 It is a schematic diagram of the application of the photovoltaic inverter system structure formed by a single common positive electrode DC / DC converter in the second embodiment of the present invention;

[0026] Figure 3 It is a schematic structural diagram of the photovoltaic inverter system formed by a common positive family DC / DC converter composed of several common positive electrode DC / DC converters in the second embodiment of the present invention;

[0027] Figure 4 It is based on the second embodiment of the present invention Figure 4 Further schematic structural diagram;

[0028] Figure 5 It is a schematic structural diagram of the AC-DC grid-connected system based on Figure 5 in the third embodiment of the present invention.

[0029] DESCRIPTION OF THE REFERENCE NUMERALS:

[0030] 1. Photovoltaic connection unit; 2. Switch control unit; 3. Energy storage unit; 4. Polarity output control unit; 5. Inverter connection unit; 6. Photovoltaic string; 7. Inverter unit; 8. First controllable circuit unit; 9. Leakage current detection unit; 10. Second controllable circuit unit. Specific embodiments

[0031] The following describes in detail the preferred embodiments of the present invention with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work fall within the scope of protection of the present invention.

[0032] The terms "including" and "having" and any variations thereof in the specification, claims and above-mentioned drawings of the present invention are intended to cover non-exclusive inclusion. The terms "first", "second", etc. in the specification, claims or above-mentioned drawings of the present invention are used to distinguish different objects, not to describe a specific order. The orientation terms such as "upper", "lower", "left", "right", "front", "rear", "side", etc. in the specification, claims or above-mentioned drawings of the present invention are relative position descriptions with respect to the provided drawings, not for describing the specific order of the actual product.

[0033] Please refer to Figure 1, the first embodiment of the present invention provides a common positive DC / DC converter for a photovoltaic inverter system. The DC / DC converter includes a photovoltaic connection unit 1, a switch control unit 2, an energy storage unit 3, a polarity output control unit 4, and an inverter connection unit 5. One end of the switch control unit 2 and the positive bus terminal BUS+ of the inverter connection unit 5 are both electrically connected to the positive photovoltaic terminal PV+ of the photovoltaic connection unit 1. The negative photovoltaic terminal PV- of the photovoltaic connection unit 1 is electrically connected to one end of the energy storage unit 3. The other end of the energy storage unit 3 and the negative terminal of the polarity output control unit 4 are both electrically connected to the other end of the switch control unit 2. The positive terminal of the polarity output control unit 4 is electrically connected to the negative bus terminal BUS- of the inverter connection unit 5. The midpoint BUS_M between the positive bus terminal BUS+ and the negative bus terminal BUS- of the inverter connection unit 5 is grounded. This common positive DC / DC converter is applied to photovoltaic inverter systems with voltage levels of 1000V - 3000V and higher, specifically 1000V, 1200V, 1500V, 2000V, 2500V, and 3000V. It has protection capabilities for 1000V systems, 1200V systems, 1500V systems, 2000V systems, 3000V systems, and higher-level photovoltaic inverter systems, and can also effectively suppress the PID effect of photovoltaic panels.

[0034] For ease of understanding, please continue to refer to Figure 1 , the first embodiment provides a specific circuit principle. The photovoltaic connection unit 1 includes a photovoltaic capacitor. The switch control unit 2 includes a switch tube. Specifically, the switch tube is a MOS tube. The energy storage unit 3 includes an inductance coil. The polarity output control unit 4 includes a diode. The inverter connection unit 5 includes at least one inverter capacitor.

[0035] One end of the photovoltaic capacitor is electrically connected to the positive photovoltaic terminal PV+. One end of the inverter capacitor is electrically connected to the positive bus terminal BUS+. Both the positive photovoltaic terminal PV+ and the positive bus terminal BUS+ are electrically connected to the collector terminal of the switch tube. The other end of the photovoltaic capacitor is electrically connected to the negative photovoltaic terminal PV-. One end of the inductance coil is electrically connected to the negative photovoltaic terminal PV-. The other end of the inductance coil and the emitter terminal of the switch tube are both electrically connected to the negative terminal of the diode. The other end of the inverter capacitor is electrically connected to the negative bus terminal BUS-. The positive terminal of the diode is electrically connected to the negative bus terminal BUS-. The capacitance value average midpoint of the inverter capacitor is grounded.

[0036] In order to clearly illustrate the above circuit principle, the present invention conducts a mathematical analysis of the DC / DC converter, and it can be obtained that the voltage difference between PV- of the common-anode DC / DC converter and the ground is (Equation 1.1). When the output voltage of the DC / DC converter is greater than twice the input voltage, the voltage of the negative photovoltaic terminal PV- with respect to the ground is positive. Therefore, the photovoltaic inverter system formed by the common-anode DC / DC converter has a natural advantage in suppressing the PID effect of the photovoltaic panel.

[0037]

[0038] Where, V PV- is the voltage of the negative photovoltaic terminal PV-, V PGND is the ground voltage of the converter, V BUS+ is the voltage of the positive bus terminal BUS+, V BUS- is the voltage of the negative bus terminal BUS-, V PV+ is the voltage of the positive photovoltaic terminal PV+.

[0039] Furthermore, the inverter capacitor in the above specific circuit principle includes at least two first capacitors and a second capacitor, and the midpoint of the series connection of the first capacitor and the second capacitor is grounded.

[0040] Please refer to Figures 2 - 3 , according to a common-anode DC / DC converter of the first embodiment, the second embodiment of the present invention provides a photovoltaic inverter system formed by a common-anode family DC / DC converter, which includes a plurality of photovoltaic strings 6, an inverter unit 7, and at least one common-anode DC / DC converter. The two ends of the photovoltaic string 6 are electrically connected to the positive photovoltaic terminal PV+ and the negative photovoltaic terminal PV- of the common-anode family DC / DC converter respectively, and the two ends of the inverter unit 7 are electrically connected to the positive bus terminal BUS+ and the negative bus terminal BUS- of the common-anode family DC / DC converter respectively, and the midpoint BUS_M of the two ends of the inverter unit 7 is grounded.

[0041] Specifically, Figure 2 is a photovoltaic inverter system formed by using a single common-anode DC / DC converter, which is applied to a photovoltaic inverter system with a bus voltage of 1000V - 3000V and higher voltage levels; Figure 3 is a photovoltaic inverter system formed by using a common-anode family DC / DC converter composed of a plurality of common-anode DC / DC converters.

[0042] Please refer to Figure 4, at the midpoint BUS_M of the two ends of the inverter unit 7 provided in the second embodiment, a first controllable circuit unit 8 and a leakage current detection unit 9 are further provided. One end of the first controllable circuit unit 8 is electrically connected to the bus midpoint BUS_M, and the leakage current detection unit 9 is provided between the other end of the first controllable circuit unit 8 and the ground. The cooperation of the first controllable circuit unit 8 and the grounding method of the bus midpoint BUS_M not only reduces the safety regulation level of the DC side, but also can reduce the risk of damage to the photovoltaic inverter system caused by grounding faults through the leakage current detection unit 9.

[0043] Specifically, the first controllable circuit unit 8 includes a first DC grounding switch SW1 and a first DC resistor R1. One end of the first DC grounding switch SW1 is electrically connected to the bus midpoint BUS_M, the other end of the first DC grounding switch SW1 is electrically connected to one end of the first DC resistor R1, and the other end of the first DC resistor R1 is grounded. By controlling the first DC grounding switch SW1, the bus midpoint BUS_M is grounded through the first DC resistor R1, ensuring that the positive and negative voltages to the ground of the entire system are half of the entire bus voltage, which can reduce the safety regulation level of the DC side. Further, the leakage current detection unit 9 is electrically connected between the other end of the first DC resistor R1 and the ground, and can quickly detect the leakage current fault through the leakage current detection unit 9 in case of a grounding fault. Specifically, the leakage current detection unit 9 includes a Hall sensor to quickly detect the leakage current fault on the DC side of the system.

[0044] The photovoltaic inverter system with the common positive family DC / DC converter cooperating with the controllable grounding of the first DC resistor R1 can not only suppress the PID effect of the photovoltaic panel, but also prevent the situation that the DC side generates a long-term continuous high voltage to damage the system when the system has a grounding fault through the grounding method of the first DC resistor R1. And this photovoltaic inverter system quickly detects the grounding fault through the Hall sensor and processes the fault.

[0045] As Figure 4 shown, the photovoltaic inverter system formed by the common positive family DC / DC converter provided in the second embodiment is also applicable to photovoltaic inverter systems with voltage levels of 1000V - 3000V and higher, specifically 1000V, 1200V, 1500V, 2000V, 2500V, and 3000V. It has protection capabilities for 1000V systems, 1200V systems, 1500V systems, 2000V systems, 3000V systems, and higher-level photovoltaic inverter systems, and can also effectively suppress the PID effect of the photovoltaic panel.

[0046] Please refer to Figure 5, according to the photovoltaic inverter system formed by the common positive family DC / DC converter provided in the second embodiment, the difference between the third embodiment of the present invention and the second embodiment is that a grid-connected transformer T1 is further provided on the side of the inverter unit 7, using the principle that the AC neutral point is equipotential with the midpoint Bus_M of the DC bus of the inverter unit 7 after the photovoltaic inverter system is normally grid-connected. After the neutral point of the transformer T1 and the bus midpoint BUS_M of the inverter unit 7 are electrically connected, a second controllable circuit unit 10 is further provided. One end of the first controllable circuit unit 8 is electrically connected to the neutral point of the transformer T1 and the bus midpoint BUS_M of the inverter unit 7, and the other end of the second controllable circuit unit 10 is grounded. By controlling the second controllable circuit unit 10 to control the grounding of the AC neutral point, the equal potential of the DC positive and negative poles to the ground is indirectly ensured.

[0047] Before the inverter unit 7 starts, the DC side is controllably grounded. When the inverter unit 7 is grid-connected, the DC side is grounded, and the AC side controllable grounding is disconnected, ensuring that the positive and negative voltages of the entire system to the ground are half of the entire bus voltage during the grid-connected process and off-grid process of the entire photovoltaic system, which can reduce the safety standard level of the DC side and reduce the design cost.

[0048] The second controllable circuit unit 10 includes a second AC grounding switch SW2 and a second DC resistor R2. One end of the second AC grounding switch SW2 is electrically connected to the neutral point of the transformer T1, the other end of the second AC grounding switch SW2 is electrically connected to one end of the second DC resistor R2, and the other end of the second DC resistor R2 is grounded.

[0049] Before the photovoltaic system is grid-connected, during the start-up process of the DC / DC converter, the first DC grounding switch SW1 is first closed and grounded through the first DC resistor R1 to ensure the equal voltage of the DC positive and negative poles to the ground during the boost process of the DC / DC converter. When the DC / DC converter boosts to meet the grid-connected condition of the bus of the inverter unit 7, after the inverter unit 7 starts and is grid-connected, the second AC grounding switch SW2 is closed and the first DC grounding switch SW1 is disconnected. By the principle that the midpoint BUS_M of the inverter unit 7 bus is equipotential with the AC neutral point, the equal potential of the DC positive and negative poles to the ground is indirectly ensured. This photovoltaic inverter system can reduce the safety standard level of the DC side to the ground and the system cost through AC and DC grounding, and effectively suppress the PID effect of the photovoltaic panel in cooperation with the common positive family DC / DC converter.

[0050] A leakage current detection unit 9 is connected between the other end of the second DC resistor R2 and the ground, and can quickly detect the leakage current fault through the leakage current detection unit 9 in case of a grounding fault. Specifically, the leakage current detection unit 9 includes a Hall sensor to quickly detect the leakage current fault on the AC side of the system.

[0051] When a ground fault occurs, the Hall sensor can effectively detect the ground fault and ground through the first DC resistor R1 to release the high voltage on the DC side to the ground. And before the inverter unit 7 starts, the DC side is controllably grounded, and the ground fault on the DC side is detected through the Hall sensor on the DC side; after the inverter unit 7 is connected to the grid, the DC side grounding is disconnected, the AC side is controllably grounded, and the ground fault of the entire system is detected through the Hall sensor on the AC side. The method of controllable AC-DC grounding ensures that the photovoltaic system can detect and handle ground faults during both the grid-connected process and the off-grid process.

[0052] The combination of the two Hall sensor solutions can effectively monitor the ground fault of the system, and when a ground fault occurs, the DC side voltage can also be released through the solution of grounding through the first DC resistor R1, preventing the DC side from having a long-term continuous high voltage to the ground, and reducing the risk of damaging the inverter unit 7 when a ground fault occurs.

[0053] Such as Figure 5 shown, the common-positive DC / DC converter combined with the AC-DC grounded photovoltaic inverter system is also applicable to photovoltaic inverter systems with voltage levels of 1000V - 3000V and higher, specifically 1000V, 1200V, 1500V, 2000V, 2500V, and 3000V. It has protection capabilities for 1000V systems, 1200V systems, 1500V systems, 2000V systems, 3000V systems, and higher-level photovoltaic inverter systems, and can also effectively suppress the PID effect of the photovoltaic panel.

[0054] The core of the present invention lies in: the photovoltaic inverter system formed by the common-positive DCDC converter. When the photovoltaic inverter system is operating in grid-connected mode, the potential difference between the negative input voltage (PV-) of the photovoltaic panel and Bus_M (PGND) is positive. This feature can directly suppress the PID effect of the photovoltaic panel, and the stronger the boost ability of the DC / DC converter, the more significant the effect of suppressing PID. Such a common-positive DCDC converter combined with Figure 3 and Figure 4 the formed photovoltaic inverter system can not only suppress the PID effect of the photovoltaic panel but also make the DC side voltage to the ground half of the system voltage, reducing the safety specification level of the DC side to the ground and the design cost of the system. At the same time, the system is equipped with a leakage current detection unit, which can quickly respond when a ground fault occurs in the system and release the high voltage on the DC side to the ground through a resistor to ensure the safety of the system.

[0055] The above is only used to illustrate the technical solution of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; any equivalent structural or equivalent process transformation made by using the content of the specification and drawings of the present invention, directly or indirectly applied to other related technical fields, shall be equally included in the scope of patent protection of the present invention.

Claims

1. A photovoltaic inverter system formed by a common positive family DC / DC converter, Characterized in that: It includes a photovoltaic string and an inverter unit, and at least one common positive DC / DC converter. The common positive DC / DC converter includes a photovoltaic connection unit, a switch control unit, an energy storage unit, a polarity output control unit, and an inverter connection unit; one end of the switch control unit and the positive bus terminal of the inverter connection unit are both electrically connected to the positive photovoltaic terminal of the photovoltaic connection unit. The negative photovoltaic terminal of the photovoltaic connection unit is electrically connected to one end of the energy storage unit. The other end of the energy storage unit and the negative terminal of the polarity output control unit are both electrically connected to the other end of the switch control unit. The positive terminal of the polarity output control unit is electrically connected to the negative bus terminal of the inverter connection unit. The midpoint of the positive and negative bus terminals of the inverter connection unit is grounded; the switch control unit includes a switch tube, and the switch tube is a MOS tube; Both ends of the photovoltaic string are electrically connected to the positive and negative photovoltaic terminals of the photovoltaic connection unit respectively. Both ends of the inverter unit are electrically connected to the positive and negative bus terminals of the inverter connection unit respectively. The midpoint of the two ends of the bus of the inverter unit is grounded; A first controllable circuit unit and a leakage current detection unit are further provided at the midpoint of the two ends of the bus of the inverter unit. One end of the first controllable circuit unit is electrically connected to the midpoint of the bus, and the leakage current detection unit is provided between the other end of the first controllable circuit unit and the ground; A grid-connected transformer is further provided on the inverter unit side. After the neutral point of the transformer and the midpoint of the bus of the inverter unit are electrically connected, a second controllable circuit unit is further provided. One end of the first controllable circuit unit is electrically connected to the neutral point of the transformer and the midpoint of the bus of the inverter unit, and the other end of the second controllable circuit unit is grounded.

2. The photovoltaic inverter system formed by the common positive family DC / DC converter according to claim 1, Characterized in that: The photovoltaic connection unit includes a photovoltaic capacitor, the energy storage unit includes an inductance coil, the polarity output control unit includes a diode, and the inverter connection unit includes at least one inverter capacitor; One end of the photovoltaic capacitor is electrically connected to the positive photovoltaic terminal. One end of the inverter capacitor is electrically connected to the positive bus terminal. The positive photovoltaic terminal and the positive bus terminal are both electrically connected to the drain terminal of the switch tube; the other end of the photovoltaic capacitor is electrically connected to the negative photovoltaic terminal. One end of the inductance coil is electrically connected to the negative photovoltaic terminal; the other end of the inductance coil and the source terminal of the switch tube are both electrically connected to the negative terminal of the diode; the other end of the inverter capacitor is electrically connected to the negative bus terminal. The positive terminal of the diode is electrically connected to the negative bus terminal; the midpoint of the inverter capacitor is grounded.

3. The photovoltaic inverter system formed by the common positive family DC / DC converter according to claim 2, Characterized in that: The inverter capacitor includes at least two first capacitors and a second capacitor. The midpoint of the series connection of the first capacitor and the second capacitor is grounded.

4. The photovoltaic inverter system formed by the common positive family DC / DC converter according to claim 1, characterized in that: The first controllable circuit unit includes a first DC grounding switch and a first DC resistor. One end of the first DC grounding switch is electrically connected to the midpoint of the bus, the other end of the first DC grounding switch is electrically connected to one end of the first DC resistor, and the other end of the first DC resistor is grounded. The leakage current detection unit is further electrically connected therebetween.

5. The photovoltaic inverter system formed by the common positive family DC / DC converter according to claim 4, characterized in that: The second controllable circuit unit includes a second AC grounding switch and a second DC resistor. One end of the second AC grounding switch is electrically connected to the neutral point of the transformer, the other end of the second AC grounding switch is electrically connected to one end of the second DC resistor, and the other end of the second DC resistor is grounded.

6. The photovoltaic inverter system formed by the common positive family DC / DC converter according to claim 5, characterized in that: The leakage current detection unit is further electrically connected between the other end of the second DC resistor and the ground.

7. The photovoltaic inverter system formed by the common positive family DC / DC converter according to claim 6, characterized in that: The leakage current detection unit includes a Hall sensor to detect the leakage current fault of the system.

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