Power supply transmission device, power supply conversion device and photovoltaic system

Abstract

The invention provides a power supply transmission device, a power supply conversion device and a photovoltaic system. The power supply conveying device comprises a direct current bus, a power conversion circuit and a bus capacitor; the DC bus transmits the output voltage of the photovoltaic module to a power grid; the power conversion circuit converts alternating voltage on one side of a power grid into direct voltage and comprises a first output end and a second output end, the first output end is connected to a positive direct current bus in the direct current buses, and the second output end is connected to a negative direct current bus in the direct current buses; the bus capacitor is connected between a positive DC bus and a negative DC bus in the DC buses. According to the scheme, the power conversion circuit can charge the bus capacitor, when charging is needed, the alternating voltage of the power grid is converted into the direct voltage to be transmitted to the two sides of the bus capacitor to charge the bus capacitor, a bypass circuit does not need to be arranged in the system, and the power conversion circuit can be achieved through existing devices in a traditional photovoltaic system; the size and the cost of the photovoltaic system are reduced, and the reliability is improved.

Description

Technical Field

[0001] The disclosed embodiments of the present application relate to the field of power electronics technology, and more specifically, to a power transmission device, a power conversion device, and a photovoltaic system. Background Art

[0002] In a photovoltaic system, a bus is used to connect the photovoltaic power generation components to the grid. The bus near the photovoltaic power generation components is a DC bus. The DC bus is connected to the AC / DC converter and then to the grid through a three-phase AC bus. Bus capacitors are connected between the positive and negative DC busbars, and bus switches are provided on each phase of the AC busbar. When the photovoltaic power generation components supply power to the grid, the bus capacitors need to be pre-charged first.

[0003] In traditional photovoltaic systems, a bypass circuit is usually set on the AC bus. The bypass circuit includes a bypass resistor and a bypass switch. When the bus capacitor needs to be pre-charged, the bypass switch and the bus switch on the one-phase AC bus can be opened. The bus capacitor can be pre-charged through the bypass circuit. After the bus capacitor is pre-charged, the bypass circuit is cut off. However, the bypass circuit is large in size, high in cost, and has poor reliability, resulting in a large volume, high cost, and poor reliability of the entire photovoltaic system.

[0004] Therefore, how to reduce the size and cost of photovoltaic systems and improve their reliability has become an urgent problem to be solved. Summary of the invention

[0005] According to the embodiments of the present application, the present application proposes a power transmission device, a power conversion device and a photovoltaic system to reduce the volume and cost of the photovoltaic system and improve its reliability.

[0006] According to one aspect of the present application, a power transmission device is disclosed for use in a photovoltaic system, the device comprising a DC bus, a power conversion circuit and a bus capacitor; the DC bus is used to transmit the output voltage of the photovoltaic module to the power grid; the power conversion circuit is used to convert the AC voltage on one side of the power grid into a DC voltage, wherein the power conversion circuit comprises a first output terminal and a second output terminal, the first output terminal is used to be connected to a positive DC bus in the DC bus, and the second output terminal is connected to a negative DC bus of the DC bus; the bus capacitor is connected between the positive DC bus and the negative DC bus in the DC bus; wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on one side of the power grid, the power conversion circuit charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on one side of the power grid, the power conversion circuit stops charging the bus capacitor.

[0007] The above scheme uses a power conversion circuit, which can be used to charge the bus capacitor: when charging is required, the AC voltage of the power grid can be converted into a DC voltage and transmitted to both sides of the bus capacitor to charge the bus capacitor. Therefore, there is no need to set up a bypass circuit in the system, and the power conversion circuit can be implemented using existing devices in traditional photovoltaic systems, thereby reducing the size and cost of the photovoltaic system and improving its reliability.

[0008] In a second aspect of the present application, a power conversion device is provided, comprising a first output terminal, a second output terminal and a ground terminal, and a DC conversion module, which is connected to a DC bus through the first output terminal and the second output terminal and is grounded through the ground terminal; wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on one side of the power grid, the DC conversion module charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on one side of the power grid, the DC conversion module stops charging the bus capacitor, and / or, when the difference between the ground voltage of the positive DC bus and the ground voltage of the negative DC bus in the DC bus exceeds a preset difference value, the DC conversion module generates a compensation voltage between the second output terminal and the ground terminal so that the difference between the ground voltage of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

[0009] The above scheme can be used for charging the bus capacitor: when charging is needed, the AC voltage of the power grid can be converted into a DC voltage and transmitted to both sides of the bus capacitor to charge the bus capacitor. Therefore, there is no need to set up a bypass circuit in the system, which reduces the size and cost of the photovoltaic system and improves its reliability.

[0010] A third aspect of the present application provides a photovoltaic system; the photovoltaic system includes photovoltaic components, a power grid, and any of the above-mentioned power transmission devices.

[0011] The above scheme uses a power conversion circuit, which can be used to charge the bus capacitor: when charging is required, the AC voltage of the power grid can be converted into a DC voltage and transmitted to both sides of the bus capacitor to charge the bus capacitor. Therefore, there is no need to set up a bypass circuit in the system, and the power conversion circuit can be implemented using existing devices in traditional photovoltaic systems, thereby reducing the size and cost of the photovoltaic system and improving its reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present application will be further described below in conjunction with the accompanying drawings and implementation methods, in which:

[0013] Figure 1 It is a schematic diagram of the circuit structure of an embodiment of the photovoltaic system of the present application;

[0014] Figure 2It is a circuit structure diagram of an embodiment of a power conversion device of the present application. DETAILED DESCRIPTION

[0015] In order to enable those skilled in the art to better understand the technical solution of the present application, the technical solution of the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0016] In a photovoltaic system, bus capacitors are usually connected across the positive and negative busbars of the DC bus. Before the photovoltaic modules supply power to the grid, the bus capacitors need to be pre-charged to reduce the damage to the power equipment caused by the large current generated when the circuit is powered on. In addition, after the photovoltaic system is used for a long time, the voltage between the positive and negative busbars on the DC bus and the ground may be unequal, resulting in a large leakage current, which in turn reduces the life of the photovoltaic modules.

[0017] In view of this, in order to pre-charge the bus capacitor before power supply and alleviate the problem of unequal voltages between the positive and negative bus bars to the ground, the existing photovoltaic system will connect a bypass circuit to the three-phase AC bus connected to the power grid after the DC bus. The bypass circuit includes a bypass resistor and a bypass switch. When the bus capacitor needs to be pre-charged, the bypass switch is closed to form a pre-charging loop for the bus capacitor through the bypass circuit and one of the three-phase AC bus bars. After the bus capacitor is pre-charged, the bypass circuit is disconnected and the three-phase AC bus is turned on, thereby completing the pre-charging of the bus capacitor before the photovoltaic module supplies power; and, an additional set of switching power supplies is provided, which are respectively connected to the positive DC bus and the negative DC bus, so as to output a compensation voltage to make the positive and negative DC bus voltages to the ground equal when the positive and negative DC bus voltages to the ground are unequal, thereby preventing leakage current. However, since the bypass resistor and bypass switch used in the bypass circuit need to withstand large current and voltage and interrupt large current, their size and cost are extremely large and their reliability is not high. In addition, the additional switching power supply further increases the size and cost of the entire photovoltaic system.

[0018] Therefore, the present application proposes a power transmission device and a photovoltaic system to at least reduce the volume and cost of the photovoltaic system and improve its reliability.

[0019] It should be noted that, in this article, the “unequal” or “equal” mentioned in “the positive and negative bus voltages to the ground on the DC bus are not equal” or “the positive and negative DC bus voltages to the ground are equal”, etc., should be understood by those skilled in the art that it does not mean that the values ​​need to be strictly unequal or equal, but can float within a certain acceptable range. For example, when the absolute value of the difference between the absolute values ​​of the positive and negative DC bus voltages to the ground is within 5% of the normal DC bus voltage value, the positive and negative DC bus voltages to the ground are considered to be equal, otherwise the positive and negative DC bus voltages to the ground are considered to be unequal.

[0020] In addition, it should be understood that the “photovoltaic module” mentioned in this article may include a photovoltaic panel.

[0021] Please refer to Figure 1 , Figure 1 It is a schematic diagram of the circuit structure of an embodiment of a photovoltaic system of the present application; the photovoltaic system may include photovoltaic components, a power grid, and a power transmission device 100.

[0022] Please continue to refer to Figure 1 A power transmission device 100 proposed in the present application may include a DC bus, a power conversion circuit 110 and a bus capacitor C1; the DC bus is used to transmit the output voltage of the photovoltaic module to the power grid; the power conversion circuit 110 is used to convert the AC voltage on one side of the power grid into a DC voltage, wherein the power conversion circuit 110 includes a first output terminal O1 and a second output terminal O2, the first output terminal O1 is used to connect to the positive DC bus Vbus+ in the DC bus, and the second output terminal O2 is connected to the negative DC bus Vbus- of the DC bus; the bus capacitor C1 is connected between the positive DC bus Vbus+ and the negative DC bus Vbus- in the DC bus; wherein, when the voltage of the bus capacitor C1 is lower than the peak value of the AC voltage on one side of the power grid, the power conversion circuit 110 charges the bus capacitor C1; when the voltage of the bus capacitor C1 is higher than the peak value of the AC voltage on one side of the power grid, the power conversion circuit 110 stops charging the bus capacitor C1.

[0023] The above scheme uses the power conversion circuit 110, which can be used to charge the bus capacitor C1: when charging is required, the AC voltage of the power grid can be converted into a DC voltage and transmitted to both sides of the bus capacitor C1 to charge the bus capacitor C1. Therefore, there is no need to set up a bypass circuit in the system, and the power conversion circuit 110 can be implemented using existing devices in traditional photovoltaic systems, thereby reducing the size and cost of the photovoltaic system and improving its reliability.

[0024] Furthermore, in some embodiments, the power conversion circuit 110 also includes a ground terminal (not marked in the figure); when the difference between the ground voltage of the positive DC bus Vbus+ and the ground voltage of the negative DC bus Vbus- in the DC bus exceeds a preset difference value, the power conversion circuit 110 generates a compensation voltage between the second output terminal O2 and the ground terminal so that the difference between the ground voltage of the positive DC bus Vbus+ and the negative DC bus Vbus- in the DC bus is less than the preset difference value.

[0025] Specifically, in some implementation scenarios, the above-mentioned preset difference value can be 5% of the normal voltage value of the bus, or other values, which are not limited in the present application; in addition, those skilled in the art can understand that judging whether the voltages of the positive and negative buses to the ground are "equal" can be judging whether the absolute values ​​of the voltages to the ground of the two are "equal".

[0026] In some embodiments, the power conversion circuit 110 also includes a DC conversion module 111, which is connected to the DC bus through a first output terminal O1 and a second output terminal O2; when the relevant pins of the control module 112 detect that the voltage of the bus capacitor C1 is lower than the peak value of the AC voltage on the grid side, the corresponding control signal output pin of the control module 112 generates a level for driving the first switch S4 and the second switch S5, thereby driving the first switch S4 to turn on and the second switch S5 to turn off, and the DC conversion module 111 charges the bus capacitor C1; when the relevant pins of the control module 112 detect that the voltage of the bus capacitor C1 is higher than the peak value of the AC voltage on the grid side, the control module 112 generates a corresponding level signal to drive the first switch S4 to turn off and the second switch S5 to turn on, and stop charging the bus capacitor C1.

[0027] In some embodiments, the DC conversion module 111 is also grounded through the ground terminal; when the difference between the ground voltage of the positive DC bus Vbus+ and the ground voltage of the negative DC bus Vbus- in the DC bus exceeds a preset difference value, the power conversion circuit 110 generates a compensation voltage between the second output terminal O2 and the ground terminal to make the difference between the ground voltage of the positive DC bus Vbus+ and the negative DC bus Vbus- in the DC bus less than the preset difference value.

[0028] In some implementation scenarios, the DC conversion module 111 may include a DC converter, which may be implemented based on any circuit topology structure of a three-level topology, a forward topology, a buck-boost topology, a flyback topology, a half-bridge topology, a full-bridge topology, etc., which is not limited in this application. It is understood that the DC converter may be used to convert a DC power with a higher voltage and / or unstable into a DC power with a lower voltage and / or stable for subsequent use.

[0029] In some embodiments, the power conversion circuit 110 further includes a switch module; the switch module includes a first switch S4 and a second switch S5, wherein the first output terminal O1 of the power conversion circuit 110 is connected to the positive DC bus Vbus+ through the first switch S4, and the ground terminal of the power conversion circuit 110 is grounded through the second switch S5; when the voltage of the bus capacitor C1 is lower than the peak value of the AC voltage on the grid side, the first switch S4 is turned on, the second switch S5 is turned off, and the power conversion circuit 110 charges the bus capacitor C1; when the voltage of the bus capacitor C1 is higher than the peak value of the AC voltage on the grid side, the power conversion circuit 110 stops charging the bus capacitor C1; and / or, when the difference between the ground voltage of the positive DC bus Vbus+ and the ground voltage of the negative DC bus Vbus- in the DC bus exceeds a preset difference value, the power conversion circuit 110 generates a compensation voltage between the second output terminal O2 and the ground terminal so that the difference between the ground voltage of the positive DC bus Vbus+ and the negative DC bus Vbus- in the DC bus is less than the preset difference value.

[0030] Specifically, in some implementation scenarios, the first switch S4 and the second switch S5 can be semiconductor controllable switching devices (such as metal oxide semiconductor crystal field effect transistors, triodes, etc.), optical coupling devices, magnetic coupling devices (such as relays), etc., so that the first switch S4 and the second switch S5 can be turned on or off under the drive level received at their control ends.

[0031] Exemplarily, when the bus capacitor C1 needs to be pre-charged, the control end of the first switch S4 will receive a driving level to drive it to turn on, and the control end of the second switch S5 will receive a driving level to drive it to turn off, and then the first output end O1 and the second output end O2 of the power conversion circuit 110 are respectively connected to the positive and negative electrodes of the bus capacitor C1, and the power conversion circuit 110 converts the AC power on the grid side into DC power and outputs it to both ends of the bus capacitor C1 to charge the bus capacitor C1; when the voltage of the bus capacitor C1 is higher than the peak value of the AC voltage on the grid side, the control end of the first switch S4 will receive a driving level to drive it to turn off, and then the power conversion circuit 110 stops charging the bus capacitor C1, and the photovoltaic module starts to output voltage to the grid side normally.

[0032] Exemplarily, when it is found that the difference between the ground voltage of the positive DC bus Vbus+ and the ground voltage of the negative DC bus Vbus- exceeds a preset difference value, the control end of the second switch S5 will receive a driving level to drive it to turn on, and the control end of the first switch S4 will receive a driving level to drive it to turn off, and then the power conversion circuit 110 injects a compensation voltage into the negative DC bus Vbus- so that the ground voltage of the negative DC bus Vbus- and the ground voltage of the positive DC bus Vbus+ are less than the preset difference value.

[0033] In some embodiments, the power conversion circuit 110 also includes a control module 112; the control module 112 is connected to the switch module and is used to control the on and off of the switch module; when the voltage of the bus capacitor C1 is lower than the peak value of the AC voltage on the grid side, the control module 112 controls the first switch S4 to be turned on and the second switch S5 to be turned off, so that the power conversion circuit 110 charges the bus capacitor C1; when the voltage of the bus capacitor C1 is higher than the peak value of the AC voltage on the grid side, the power conversion circuit 110 is controlled to stop charging the bus capacitor C1; and / or, when the difference between the ground voltage of the positive DC bus Vbus+ and the ground voltage of the negative DC bus Vbus- in the DC bus exceeds a preset difference value, the power conversion circuit 110 generates a compensation voltage between the second output terminal O2 and the ground terminal so that the difference between the ground voltage of the positive DC bus Vbus+ and the negative DC bus Vbus- in the DC bus is less than the preset difference value.

[0034] In some implementation scenarios, the control module 112 may include a microcontroller unit MCU for outputting various control level signals; the MCU may be connected to the first switch S4 and the second switch S5 respectively through the first switch driving circuit S4_driver and the second switch driving circuit S5_driver, and the MCU outputs control level signals to the first switch driving circuit S4_driver and the second switch driving circuit S5_driver, so that they output corresponding driving levels to drive the first switch S4 and the second switch S5 to be turned on or off; exemplarily, the first switch driving circuit S4_driver and the second switch driving circuit S5_driver may be driving circuits for driving metal oxide semiconductor field effect transistors.

[0035] In some embodiments, the power conversion circuit 110 further includes a rectifier module 113 ; the rectifier module 113 is connected to the power grid and the power conversion circuit 110 , and is used to convert the AC voltage on one side of the power grid into a DC voltage and output it to the power conversion circuit 110 .

[0036] In some implementation scenarios, the rectifier module 113 may include a device for rectification based on a rectifier bridge, and its rectification method may include any one of full-wave rectification, half-wave rectification, controlled rectification, uncontrolled rectification, single-phase rectification, three-phase rectification, etc., which can be selected according to different usage scenarios and is not limited in this application.

[0037] In some embodiments, the control module 112 may also be connected to the enable terminal EN of the DC conversion module 111 , and the control module 112 may output a control level signal to control the start and stop of the DC conversion module 111 .

[0038] In some embodiments, please refer to Figure 1 The power conversion circuit may further include a first capacitor C2 and a second capacitor C3.

[0039] In some embodiments, the power transmission device also includes an AC-DC conversion circuit, one end of which is connected to the DC bus and the other end is connected to the three-phase AC bus, for converting the output voltage of the photovoltaic module into AC power and transmitting it to the power grid.

[0040] In some embodiments, the power transmission device further includes a contactor module connected to the inverter circuit; wherein the contactor module is closed when the alternating current output by the inverter circuit has the same amplitude and phase as the alternating current on one side of the power grid.

[0041] In some embodiments, a detection device can be provided to respectively detect the amplitude and phase of the AC power output by the inverter circuit and the AC power on the grid side, and generate a control level signal when the amplitude and phase of the two are the same to drive the contactor module to close.

[0042] The contactor module comprises a first contactor S1, a second contactor S2 and a third contactor S3, which are respectively arranged on each phase of the three-phase AC bus.

[0043] The present application also proposes a power conversion device 200, please refer to Figure 2 , Figure 2 1 is a schematic diagram of the circuit structure of an embodiment of a power conversion device 200 of the present application; the power conversion device 200 includes a first output terminal O1, a second output terminal O2 and a ground terminal (not marked in the figure), and a DC conversion module 111; the DC conversion module 111 is connected to the DC bus through the first output terminal O1 and the second output terminal O2 and is grounded through the ground terminal; wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on one side of the power grid, the DC conversion module 111 charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on one side of the power grid, the DC conversion module 111 stops charging the bus capacitor, and / or, when the difference between the ground voltage of the positive DC bus and the ground voltage of the negative DC bus in the DC bus exceeds a preset difference value, the DC conversion module 111 generates a compensation voltage between the second output terminal O2 and the ground terminal so that the difference between the ground voltage of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

[0044] In some implementation scenarios, the DC conversion module 111 may include a DC converter, which may be implemented based on circuit topologies such as a three-level topology, a forward topology, a buck-boost topology, a flyback topology, a half-bridge topology, and a full-bridge topology, which is not limited in the present application.

[0045] In some embodiments, the power conversion device 200 further includes a switch module; the switch module includes a first switch S4 and a second switch S5, wherein the first output terminal O1 of the power conversion device 200 is connected to the positive DC bus through the first switch S4, and the ground terminal of the power conversion device 200 is grounded through the second switch S5; wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on one side of the power grid, the first switch S4 is turned on, the second switch S5 is turned off, and the power conversion device 200 charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on one side of the power grid, the power conversion device 200 stops charging the bus capacitor; and / or, when the difference between the ground voltage of the positive DC bus and the ground voltage of the negative DC bus in the DC bus exceeds a preset difference value, the power conversion device 200 generates a compensation voltage between the second output terminal O2 and the ground terminal so that the difference between the ground voltage of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

[0046] Specifically, in some implementation scenarios, the first switch S4 and the second switch S5 can be semiconductor controllable switching devices (such as metal oxide semiconductor crystal field effect transistors, triodes, etc.), optical coupling devices, magnetic coupling devices (such as relays), etc., so that the first switch S4 and the second switch S5 can be turned on or off under the drive level received at their control ends.

[0047] In some embodiments, the power conversion device 200 also includes a control module 112, which is connected to the switch module and is used to control the on and off of the switch module; wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on one side of the power grid, the control module 112 controls the first switch S4 to be turned on and the second switch S5 to be turned off, and the power conversion device 200 charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on one side of the power grid, the power conversion device 200 stops charging the bus capacitor; and / or, when the difference between the voltage to ground of the positive DC bus and the voltage to ground of the negative DC bus in the DC bus exceeds a preset difference value, the power conversion device 200 generates a compensation voltage between the second output terminal O2 and the ground terminal so that the difference between the voltage to ground of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

[0048] In some implementation scenarios, the control module 112 may include a microcontroller unit MCU for outputting various control level signals; the MCU may be connected to the first switch S4 and the second switch S5 through the first switch S4 driving circuit S4_driver and the second switch S5 driving circuit S5_driver, respectively, and the MCU outputs control level signals to the first switch S4 driving circuit S4_driver and the second switch S5 driving circuit S5_driver, so that they output corresponding driving levels to drive the first switch S4 and the second switch S5 to be turned on or off; exemplarily, the first switch S4 driving circuit S4_driver and the second switch S5 driving circuit S5_driver may be driving circuits for driving metal oxide semiconductor field effect transistors.

[0049] In some embodiments, the power conversion device 200 further includes a rectifier module 113 connected between the power grid and the DC conversion module 111 , for converting the AC voltage on the power grid side into a DC voltage and outputting it to the DC conversion module 111 .

[0050] In some implementation scenarios, the rectifier module 113 may include a device for rectification based on a rectifier bridge, and its rectification method may include full-wave rectification, half-wave rectification, controlled rectification, uncontrolled rectification, single-phase rectification, and three-phase rectification. It can be selected according to different usage scenarios and is not limited in this application.

[0051] In some embodiments, the control module 112 may also be connected to the enable terminal EN of the DC conversion module 111 , and the control module 112 may output a control level signal to control the start and stop of the DC conversion module 111 .

[0052] In some embodiments, the control module 112 may also be connected to the enable terminal EN of the DC conversion module 111 , and the control module 112 may output a control level signal to control the start and stop of the DC conversion module 111 .

[0053] In some embodiments, please refer to Figure 2 The power conversion circuit may further include a first capacitor C2 and a second capacitor C3.

[0054] Exemplarily, when the bus capacitor needs to be pre-charged, the control end of the first switch S4 will receive the driving level output by the first switch S4 driving circuit S4_driver to drive it to turn on, and the control end of the second switch S5 will receive the driving level output by the second switch S5 driving circuit S5_driver to drive it to turn off, and then the first output end O1 and the second output end O2 of the power conversion device 200 are respectively connected to the positive and negative electrodes of the bus capacitor, and the power conversion device 200 obtains direct current through the DC conversion module 111 and outputs it to both ends of the bus capacitor to charge the bus capacitor; when the bus capacitor voltage is higher than the peak value of the AC voltage on the grid side, the control end of the first switch S4 will receive the driving level to drive it to turn off, and then the power conversion device 200 stops charging the bus capacitor, and the photovoltaic module starts to output voltage to the grid side normally.

[0055] Exemplarily, when it is found that the difference between the voltage to ground of the positive DC bus and the voltage to ground of the negative DC bus exceeds a preset difference value, the control end of the second switch S5 will receive a driving level output by the second switch S5 driving circuit S5_driver to drive it to turn on, and the control end of the first switch S4 will receive a driving level output by the first switch S4 driving circuit S4_driver to drive it to turn off, and then the power conversion device 200 injects a compensation voltage into the negative DC bus through the DC conversion module 111, so that the voltage to ground of the negative DC bus and the voltage to ground of the positive DC bus are less than the preset difference value.

[0056] It is easy for a person skilled in the art to know that many modifications and changes can be made to the device and method while maintaining the teaching content of the present application. Therefore, the above disclosure should be considered as limited only by the scope of the appended claims.

Claims

1. A power transmission device for a photovoltaic system, characterized in that: include: A DC bus, used to transmit the output voltage of the PV panels to the grid; A power conversion circuit, used for converting the AC voltage on one side of the power grid into a DC voltage, wherein the power conversion circuit comprises a first output terminal and a second output terminal, the first output terminal is used for connecting to a positive DC bus in the DC bus, and the second output terminal is connected to a negative DC bus of the DC bus; A bus capacitor connected between the positive DC bus and the negative DC bus in the DC bus; When the voltage of the bus capacitor is lower than the peak value of the AC voltage on the grid side, the power conversion circuit charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on the grid side, the power conversion circuit stops charging the bus capacitor.

2. The power transmission device according to claim 1, characterized in that: The power conversion circuit also includes a ground terminal; When the difference between the voltage to ground of the positive DC bus and the voltage to ground of the negative DC bus in the DC bus exceeds a preset difference value, the power conversion circuit generates a compensation voltage between the second output terminal and the ground terminal so that the difference between the voltage to ground of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

3. The power transmission device according to claim 2, characterized in that: The power conversion circuit further includes: A DC conversion module, connected to the DC bus through the first output terminal and the second output terminal; When the voltage of the bus capacitor is lower than the peak value of the AC voltage on one side of the power grid, the DC conversion module charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on one side of the power grid, the DC conversion module stops charging the bus capacitor.

4. The power transmission device according to claim 3, characterized in that: The DC conversion module is grounded via the ground terminal; When the difference between the voltage to ground of the positive DC bus and the voltage to ground of the negative DC bus in the DC bus exceeds a preset difference value, the DC conversion module generates a compensation voltage between the second output terminal and the ground terminal so that the difference between the voltage to ground of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

5. The power transmission device according to claim 2, characterized in that: The power conversion circuit further includes: A switch module, comprising a first switch and a second switch, wherein the first output terminal of the power conversion circuit is connected to the positive DC bus through the first switch, and the ground terminal of the power conversion circuit is grounded through the second switch; Wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on the grid side, the first switch is turned on, the second switch is turned off, and the power conversion circuit charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on the grid side, the power conversion circuit stops charging the bus capacitor; and / or, When the difference between the voltage to ground of the positive DC bus and the voltage to ground of the negative DC bus in the DC bus exceeds a preset difference value, the power conversion circuit generates a compensation voltage between the second output terminal and the ground terminal so that the difference between the voltage to ground of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

6. The power transmission device according to claim 5, characterized in that: The power conversion circuit further includes: A control module, connected to the switch module, and used to control the on and off of the switch module; Wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on the grid side, the control module controls the first switch to be turned on and the second switch to be turned off, and the power conversion circuit charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on the grid side, the power conversion circuit stops charging the bus capacitor; and / or, When the difference between the voltage to ground of the positive DC bus and the voltage to ground of the negative DC bus in the DC bus exceeds a preset difference value, the power conversion circuit generates a compensation voltage between the second output terminal and the ground terminal so that the difference between the voltage to ground of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

7. The power transmission device according to claim 3, characterized in that: The power conversion circuit further includes: A rectifier module is connected to the power grid and the DC conversion module, and is used to convert the AC voltage on one side of the power grid into a DC voltage and output it to the DC conversion module.

8. A power conversion device, characterized in that: comprising a first output terminal, a second output terminal and a ground terminal, and, A DC conversion module is connected to a DC bus through the first output terminal and the second output terminal and is grounded through the ground terminal; wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on one side of the power grid, the DC conversion module charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on one side of the power grid, the DC conversion module stops charging the bus capacitor, and / or, when the difference between the ground voltage of the positive DC bus and the ground voltage of the negative DC bus in the DC bus exceeds a preset difference value, the DC conversion module generates a compensation voltage between the second output terminal and the ground terminal so that the difference between the ground voltage of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

9. The device according to claim 8, characterized in that Also includes: A switch module, comprising a first switch and a second switch, wherein the first output end of the power conversion device is connected to the positive DC bus through the first switch, and the ground end of the power conversion device is grounded through the second switch; Wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on one side of the power grid, the first switch is turned on, the second switch is turned off, and the power conversion device charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on one side of the power grid, the power conversion device stops charging the bus capacitor; and / or, When the difference between the voltage to ground of the positive DC bus and the voltage to ground of the negative DC bus in the DC bus exceeds a preset difference value, the power conversion device generates a compensation voltage between the second output terminal and the ground terminal so that the difference between the voltage to ground of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

10. The device according to claim 9, characterized in that Also includes: A control module, connected to the switch module, and used to control the on and off of the switch module; Wherein, when the voltage of the bus capacitor is lower than the peak value of the AC voltage on the grid side, the control module controls the first switch to be turned on and the second switch to be turned off, and the power conversion device charges the bus capacitor; when the voltage of the bus capacitor is higher than the peak value of the AC voltage on the grid side, the power conversion device stops charging the bus capacitor; and / or, When the difference between the voltage to ground of the positive DC bus and the voltage to ground of the negative DC bus in the DC bus exceeds a preset difference value, the power conversion device generates a compensation voltage between the second output terminal and the ground terminal so that the difference between the voltage to ground of the positive DC bus and the negative DC bus in the DC bus is less than the preset difference value.

11. The device according to claim 8, characterized in that Also includes: The rectifier module is connected between the power grid and the DC conversion module, and is used to convert the AC voltage on one side of the power grid into a DC voltage and output it to the DC conversion module.

12. A photovoltaic system, comprising a photovoltaic module and a power grid, characterized in that: It also includes the power transmission device according to any one of claims 1 to 7.

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