Photovoltaic power generation system

Abstract

A photovoltaic power generation system, comprising: an inverter circuit, an alternating current starter circuit, and a control unit. The alternating current starter circuit comprises an alternating current start switch, an isolation module, and a charging module which are sequentially connected from a power grid side. The control unit is used for controlling the alternating current start switch to be closed when an alternating current starting instruction is received and a direct current voltage at an input end of the inverter circuit is lower than a peak value of a power grid line voltage plus a threshold, and transmitting electrical energy of the power grid by means of the isolation module. The charging module performs current limiting and rectification processing on alternating current electrical energy outputted by the isolation module, and alternately charges a direct current bus capacitor by means of positive and negative half waves of alternating current. The control unit is further used to: when the direct current bus capacitor is charged to a target voltage required for grid connection, control the alternating current start switch to be turned off and start the inverter circuit.

Description

Photovoltaic power generation system

[0001] Cross-reference to related applications

[0002] The present application is based on Chinese Patent Application No. 202510458672.5, filed on April 11, 2025, and Chinese Patent Application No. 202411349138.2, filed on September 25, 2024, and claims priority to the aforementioned Chinese Patent Applications, the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of power generation, in particular to a photovoltaic power generation system. BACKGROUND

[0004] The combined use of light and storage has become the mainstream trend in the field of new energy. Photovoltaic systems generate electricity during the day, and energy storage systems store excess power. Devices such as energy storage inverters and photovoltaic grid-connected inverters not only work during the day, but also need to charge and discharge batteries or compensate power at night to maintain the smoothness of power supply.

[0005] Because there is no sunlight at night, the solar panels commonly used for direct current power supply cannot power devices such as energy storage inverters and photovoltaic grid-connected inverters. Powering these devices through energy storage batteries may cause over-discharge of the batteries, and even damage them.

[0006] How to start devices such as energy storage inverters and photovoltaic grid-connected inverters at night when there is no sunlight is one of the technical problems that need to be solved in the field. SUMMARY

[0007] The present disclosure aims to at least solve one of the technical problems existing in the prior art. To this end, the present disclosure provides a photovoltaic power generation system that can be safely and reliably started at night when there is no sunlight.

[0008] The present disclosure provides a photovoltaic power generation system, comprising:

[0009] An inverter circuit, an output end of the inverter circuit being connected to a power grid, and a direct current bus capacitor being arranged at an input end of the inverter circuit;

[0010] An alternating current starting circuit, the alternating current starting circuit comprising an alternating current starting switch, an isolation module and a charging module connected in sequence from the power grid side, the alternating current starting switch further being connected to the power grid, and the charging module further being connected to the direct current bus capacitor;

[0011] A control unit is connected with the inverter circuit and the AC starting switch, and is configured to control the AC starting switch to be closed, transmit the power of the power grid through the isolation module, control the charging module to limit and rectify the AC power output by the isolation module, and charge the DC bus capacitor through the positive and negative half waves of the AC power alternately, when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the line voltage of the power grid plus a threshold value and an AC starting instruction is received.

[0012] The control unit is further configured to control the AC starting switch to be opened and start the inverter circuit to make the photovoltaic power generation system operate in grid-connected mode when the DC bus capacitor is charged to a target voltage required for grid connection.

[0013] According to the photovoltaic power generation system, the AC starting circuit is formed by sequentially connecting the AC starting switch, the isolation module and the charging module from the power grid side, the control unit controls the AC starting switch to be closed when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the line voltage of the power grid plus a threshold value and an AC starting instruction is received, the AC starting circuit is turned on to charge the DC bus capacitor, the photovoltaic power generation system can be started safely and reliably at night without sunlight, and the subsequent system grid connection, reactive power compensation, fault restart and other actions can be performed.

[0014] According to one embodiment of the present disclosure, the photovoltaic power generation system further comprises:

[0015] A grid-connected switch device is arranged between the output end of the inverter circuit and the power grid.

[0016] According to one embodiment of the present disclosure, the grid-connected switch device comprises a first grid-connected switch and a second grid-connected switch connected in sequence, the first grid-connected switch is close to the power grid, and the second grid-connected switch is close to the inverter circuit.

[0017] According to one embodiment of the present disclosure, the AC starting switch is connected to a connection point between the first grid-connected switch and the second grid-connected switch, the control unit is further connected with the grid-connected switch device, and the control unit is further configured to control the AC starting switch and the first grid-connected switch to be closed, transmit the power of the power grid through the isolation module, control the charging module to limit and rectify the AC power output by the isolation module, and charge the DC bus capacitor through the positive and negative half waves of the AC power alternately, when the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the line voltage of the power grid plus a threshold value and the AC starting instruction is received.

[0018] Alternatively, the AC starting switch is connected to a connection point between the power grid and the first grid-connected switch, and the control unit is further connected with the grid-connected switch device, and the control unit is further configured to, in a case that the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the power grid line voltage plus a threshold value and the AC starting instruction is received, control the AC starting switch to be closed, transmit the power of the power grid through the isolation module, and perform current limiting and rectification processing on the AC power output by the isolation module by the charging module, and alternately charge the DC bus capacitor through positive and negative half waves of the AC power, and the isolation module isolates the power grid from the DC bus capacitor.

[0019] According to one embodiment of the present disclosure, the closed first grid-connected switch is located on a phase line connected with the AC starting circuit.

[0020] According to one embodiment of the present disclosure, the control unit is configured to, in a case that the residual current detection of the inverter circuit and the insulation impedance detection pass, and the voltage of the DC bus capacitor reaches the target voltage required for grid connection, disconnect the AC starting switch and the first grid-connected switch, and control the inverter circuit to start.

[0021] According to one embodiment of the present disclosure, the control unit is further configured to, in a case that the inverter circuit has started, and the output end voltage of the inverter circuit and the grid-side voltage of the power grid meet the grid connection condition, control the second grid-connected switch and the first grid-connected switch to be attracted, so that the photovoltaic power generation system is operated in a grid-connected mode.

[0022] According to one embodiment of the present disclosure, the control unit is configured to, in a case that the self-checking of the grid-connected switch device passes, control the second grid-connected switch and the first grid-connected switch to be attracted.

[0023] According to one embodiment of the present disclosure, the control unit is further configured to, in a case that the residual current detection of the inverter circuit, the insulation impedance detection of the inverter circuit, or the self-checking of the grid-connected switch device fails, output a starting failure alarm information.

[0024] According to one embodiment of the present disclosure, further comprising:

[0025] An AC auxiliary power supply, the control unit is connected with the power grid through the AC auxiliary power supply, and the AC auxiliary power supply is configured to convert the AC power of the power grid into DC power to supply power to the control unit.

[0026] According to one embodiment of the present disclosure, the DC bus capacitor comprises a positive bus capacitor and a negative bus capacitor, and one end of the positive bus capacitor and one end of the negative bus capacitor are connected to a bus midpoint.

[0027] According to one embodiment of the present disclosure, further comprising:

[0028] The voltage equalization switch device comprises a first voltage equalization switch and a second voltage equalization switch, the first end of the charging module is connected to the bus midpoint, the second end of the charging module is connected to the other end of the positive bus capacitor, the third end of the charging module is connected to the other end of the negative bus capacitor, the first voltage equalization switch is arranged between the second end of the charging module and the other end of the positive bus capacitor, and the second voltage equalization switch is arranged between the third end of the charging module and the other end of the negative bus capacitor.

[0029] The control unit is connected to the voltage equalization switch device, and the control unit is configured to, in the case that the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than a preset voltage threshold, control one of the first voltage equalization switch and the second voltage equalization switch to be open and the other to be closed based on the voltage of the positive bus capacitor and the voltage of the negative bus capacitor.

[0030] In the case that the first voltage equalization switch is closed and the second voltage equalization switch is open, the charging module charges the positive bus capacitor; in the case that the first voltage equalization switch is open and the second voltage equalization switch is closed, the charging module charges the negative bus capacitor.

[0031] According to one embodiment of the present disclosure, the charging module comprises a current-limiting resistor and a rectifier circuit connected in series, the current-limiting resistor is configured to limit the charging current of the DC bus capacitor, and the rectifier circuit is configured to charge the DC bus capacitor.

[0032] According to one embodiment of the present disclosure, the control unit is further configured to, in the case that the input DC voltage of the inverter circuit is lower than the peak value of the grid line voltage plus a threshold value and an AC start instruction is received, output an auxiliary source closing instruction to control the AC start switch to be closed to charge the DC bus capacitor.

[0033] The present disclosure also provides a photovoltaic power generation system comprising a DC bus capacitor, an inverter circuit, a control unit, a pre-charge circuit and a current-limiting resistor.

[0034] The external DC input is connected to the input end of the inverter circuit through a DC bus, the DC bus capacitor is arranged between the DC input and the inverter circuit, the DC bus capacitor is connected in parallel between the DC bus, and the output end of the inverter circuit is connected to the grid.

[0035] The input end of the pre-charge circuit is connected with the current-limiting resistor and then connected with the power grid, the output end of the pre-charge circuit is connected with the DC bus capacitor, and the pre-charge circuit is used to charge the DC bus capacitor from the power grid; the DC bus capacitor is used to start the inverter circuit after the charging is completed.

[0036] The control unit is used to control the operation of the pre-charge circuit and control the inverter circuit to output alternating current for grid connection after the charging of the DC bus capacitor is completed.

[0037] According to one embodiment of the present disclosure, the output end of the inverter circuit is connected with the power grid through a grid connection switch device, the grid connection switch device comprises at least one group of grid connection relays, each group of grid connection relays comprises at least two relays connected in series, the pre-charge circuit is used to charge the DC bus capacitor from the grid connection relays, and the power supply position is spaced from the inverter circuit by at least one relay.

[0038] According to one embodiment of the present disclosure, the DC bus capacitor is divided into a positive bus capacitor and a negative bus capacitor, and a bus midpoint is between the positive bus capacitor and the negative bus capacitor, each of the positive bus capacitor and the negative bus capacitor has one capacitor or at least two capacitors, the at least two capacitors are connected in series or in parallel, and the positive bus capacitor and the negative bus capacitor are connected in series and then connected in parallel between the positive and negative DC bus of the inverter.

[0039] According to one embodiment of the present disclosure, the output end of the pre-charge circuit is divided into three connection points, which are connected with the positive pole, the negative pole and the bus midpoint of the DC bus capacitor respectively, and the pre-charge circuit is used to charge the positive bus capacitor and the negative bus capacitor respectively in the positive and negative half cycles of the power grid.

[0040] According to one embodiment of the present disclosure, the inverter is a single-phase inverter, a split-phase inverter or a three-phase inverter, the grid connection switch device comprises at least two groups of grid connection relays, each group of grid connection relays is arranged on each phase of the AC bus of the inverter, and the input end of the pre-charge circuit is connected with any two output ends of the inverter through a current-limiting resistor.

[0041] According to one embodiment of the present disclosure, the pre-charge circuit comprises a first slow-start switch, a second slow-start switch, a first diode and a second diode, the first slow-start switch and the second slow-start switch are connected in series with a current-limiting resistor to form a first branch and a second branch, one end of the first branch is connected with one phase of the power grid, the other end is connected with the positive pole of the first diode, the negative pole of the first diode is connected with the positive pole of the DC bus capacitor, the positive pole of the second diode is connected with the negative pole of the DC bus capacitor, one end of the second branch is connected with another phase of the power grid, and the other end is connected with the bus midpoint.

[0042] The first diode and the second diode are used to charge the positive bus capacitor and the negative bus capacitor of the DC bus capacitor respectively in the positive half cycle and the negative half cycle of the power grid.

[0043] According to one embodiment of the present disclosure, the pre-charge circuit comprises a second slow-start switch, a first diode, a second diode, a protection resistor and a pre-charge switch, the second slow-start switch is connected in series with a current-limiting resistor to form a first branch, one end of the second branch is connected to one phase of the power grid, and the other end is connected to the positive electrode of the first diode, the negative electrode of the first diode is connected to the positive electrode of the DC bus capacitor, the positive electrode of the second diode is connected to the negative electrode of the DC bus capacitor, the protection resistor and the pre-charge switch are connected in series to form a second branch, and the second branch is connected in parallel to both ends of the other phase grid-connected relay.

[0044] According to one embodiment of the present disclosure, the pre-charge circuit comprises a second slow-start switch, one end of the circuit connected in series with the second slow-start switch and a current-limiting resistor is connected to one phase of the power grid, and the other end is connected to the bus midpoint to form a second loop, and a bridge arm in an inverter circuit connected to the other phase of the power grid is taken as a first loop, the bridge arm comprises two series-connected switch tubes, and the bridge arm is connected in parallel to the DC bus capacitor, and is used to charge the positive bus capacitor and the negative bus capacitor of the DC bus capacitor respectively in the positive half cycle and the negative half cycle of the power grid.

[0045] According to one embodiment of the present disclosure, the first loop further comprises a protection resistor and a pre-charge switch, and the circuit formed after the protection resistor and the pre-charge switch are connected in series is connected in parallel to both ends of the other phase grid-connected relay.

[0046] According to one embodiment of the present disclosure, the pre-charge circuit comprises a first protection resistor, a first pre-charge switch, a second protection resistor and a second pre-charge switch, any phase of the inverter circuit comprises a first bridge arm and a second bridge arm, the first bridge arm comprises two series-connected switch tubes connected in parallel to the DC bus capacitor, the second bridge arm comprises two reverse-connected switch tubes, one end of the second bridge arm is connected to the bus midpoint, and the other end is connected to the midpoint of the first bridge arm, one end of the first loop formed after the first protection resistor and the first pre-charge switch are connected in series is connected to the grid-connected relay of one phase, and the other end is connected to the midpoint of the first bridge arm, one end of the second loop formed after the second protection resistor and the second pre-charge switch are connected in series is connected to the grid-connected relay of the other phase, and the other end is connected to the second bridge arm.

[0047] According to one embodiment of the present disclosure, an AC auxiliary power supply is further included, the input end of the AC auxiliary power supply is connected to the power grid, and the output end is connected to the control unit, and the AC auxiliary power supply is used to supply power to the control unit.

[0048] The disclosure also provides an AC side starting method based on the photovoltaic power generation system as described above, which comprises the following working steps:

[0049] The starting state of the inverter is judged, if it is AC starting, the slow start switch in the pre-charge circuit is closed, the DC bus capacitor is charged through the power grid, otherwise the grid connection is directly started;

[0050] The voltage of the DC bus capacitor is detected, if the DC bus capacitor reaches the required voltage for grid connection, the slow start switch in the pre-charge circuit is disconnected, the grid connection is started after the disconnection is completed, otherwise the charging of the DC bus capacitor is maintained;

[0051] In the process of starting and stopping the pre-charge circuit, the current limiting resistor or the protection resistor is used for current limiting protection and limiting common mode current impact of the DC bus capacitor charging.

[0052] Compared with the prior art, the photovoltaic power generation system and the AC side starting method of the photovoltaic power generation system of the present disclosure have the following advantages and beneficial effects:

[0053] The photovoltaic inverter of the present disclosure optimizes the circuit structure, charges the DC bus capacitor through the pre-charge circuit after taking AC power from the power grid side, starts the inverter circuit when the DC bus capacitor voltage reaches the required voltage for grid connection, thereby completing the starting and grid connection of the photovoltaic power generation system at night or in the absence of sunlight, saving cost investment, and at the same time ensuring higher equipment working stability and reliability.

[0054] The present disclosure uses the original grid-connected relay near the power grid side in the photovoltaic power generation system and the relay control strategy to add a protection to the DC bus capacitor charging circuit, avoids taking AC power directly from the AC power grid, thereby preventing the problem of overvoltage of the DC bus capacitor caused by the AC power grid continuously charging the DC bus capacitor when the newly added slow start switch (which can use a relay or a power switch device) in the pre-charge circuit is stuck and cannot be disconnected, that is, the starting relay is stuck and cannot be disconnected, and if the DC bus capacitor voltage is high, the grid-connected relay can be disconnected to cut off the connection between the pre-charge circuit and the AC power grid, thereby completing the protection.

[0055] The slow start circuit structure designed by the present disclosure can charge the half direct bus capacitor respectively by using the half-wave rectification principle, for example, charging the positive bus capacitor in the positive half cycle of the grid voltage and charging the negative bus capacitor in the negative half cycle of the grid voltage, so as to achieve the effect of voltage doubling, which can raise the bus voltage to 2 times the peak value of the line voltage, and at the same time avoids complex rectifier circuit and isolation DC / DC circuit, so that the control mode is simpler. Moreover, since the pre-charge circuit can charge the bus voltage to 2 times the peak value of the line voltage, the control unit can control the inverter circuit to output alternating current with the same amplitude and phase as the grid voltage, so that when the attraction and grid connection switch device is attracted, the inverter circuit output has no voltage difference with the grid voltage, so there is no impact current, realizing the soft start of the inverter, and improving the working safety and reliability of the inverter.

[0056] The present disclosure is compatible with the strategy mechanism of overvoltage protection of the direct current bus capacitor when charging the direct current bus capacitor. When the voltage of the direct current bus capacitor is too high, the control unit can send a control signal to urgently cut off the grid relay or cut off the switch or relay in the pre-charge circuit.

[0057] In addition, the photovoltaic power generation system of the present disclosure has good compatibility and can be applied to three-phase three-wire system, three-phase four-wire system, split-phase system and single-phase system, and has strong adaptability.

[0058] Additional aspects and advantages of the present disclosure will be in part apparent and in part pointed out hereinafter in the description of embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0059] The above and / or additional aspects and advantages of the present disclosure will become apparent and be readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings, in which:

[0060] Fig. 1 is a schematic structural diagram of a photovoltaic power generation system according to an embodiment of the present disclosure;

[0061] Fig. 2 is a schematic structural diagram of a photovoltaic power generation system according to another embodiment of the present disclosure;

[0062] Fig. 3 is an equivalent topology diagram of Fig. 2;

[0063] Fig. 4 is a schematic structural diagram of a photovoltaic power generation system according to another embodiment of the present disclosure;

[0064] Fig. 5 is a schematic structural diagram of a photovoltaic power generation system according to another embodiment of the present disclosure;

[0065] Fig. 6 is an equivalent topology diagram of Fig. 5;

[0066] Fig. 7 is a schematic structural diagram of a photovoltaic power generation system according to another embodiment of the present disclosure;

[0067] Fig. 8 is a schematic diagram of a structure of a photovoltaic power generation system according to an embodiment of the present disclosure;

[0068] Fig. 9 is a schematic diagram of a structure of a photovoltaic power generation system according to an embodiment of the present disclosure;

[0069] Fig. 10 is a schematic diagram of a flow of an AC starting machine of a photovoltaic power generation system according to an embodiment of the present disclosure;

[0070] Fig. 11 is a schematic diagram of a framework structure of a photovoltaic power generation system according to an embodiment 1 of the present disclosure after being connected with a DC input and an AC power grid;

[0071] Fig. 12 is a schematic diagram of a connection structure between a pre-charge circuit of a photovoltaic power generation system according to an embodiment 1 of the present disclosure and a power grid;

[0072] Fig. 13 is a schematic diagram of a circuit structure of a three-phase photovoltaic power generation system according to an embodiment 2 of the present disclosure after being connected with an AC power grid, wherein power is taken from a grid-connected switch of a pre-charge circuit;

[0073] Fig. 14 is a schematic diagram of a framework structure of a single-phase photovoltaic power generation system according to an embodiment 3 of the present disclosure after being connected with an AC power grid;

[0074] Fig. 15 is a schematic diagram of a circuit structure of a three-phase photovoltaic power generation system according to an embodiment 4 of the present disclosure after being connected with an AC power grid;

[0075] Fig. 16 is a schematic diagram of a circuit structure of a three-phase photovoltaic power generation system according to an embodiment 5 of the present disclosure after being connected with an AC power grid;

[0076] Fig. 17 is a schematic diagram of a circuit structure of a three-phase photovoltaic power generation system according to an embodiment 6 of the present disclosure after being connected with an AC power grid;

[0077] Fig. 18 is a schematic diagram of a working flow of an AC side starting method of a photovoltaic power generation system according to an embodiment 7 of the present disclosure;

[0078] Fig. 19 is a schematic diagram of a working flow of an AC side starting method of a photovoltaic power generation system according to an embodiment 8 of the present disclosure.

[0079] Reference signs: inverter circuit 100, DC input port 101, battery pack unit 102, pre-charge circuit 108, DC bus capacitor 200, AC starting switch 310, isolation module 320, current-limiting resistor 331, rectifier circuit 332, voltage-sharing switch device 340, first grid-connected switch 410, second grid-connected switch 420, control unit 510, AC auxiliary power supply 520, power grid 600. DETAILED DESCRIPTION

[0080] With reference to the drawings and embodiments of the present disclosure, the technical solutions in the embodiments of the present disclosure will be clearly described. Obviously, the described embodiments are only some of the embodiments of the present disclosure, but not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art are within the scope of protection of the present disclosure.

[0081] The terms "first", "second", and the like in the specification and claims of the present disclosure are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present disclosure can be implemented in an order other than that illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of a kind and do not limit the number of objects, for example, the first object can be one or more. In addition, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / ", generally indicates that the objects before and after are in an "or" relationship.

[0082] The photovoltaic power generation system provided by the embodiments of the present disclosure will be described in detail below in combination with the drawings, through specific embodiments and application scenarios.

[0083] As shown in FIG. 1, the photovoltaic power generation system includes an inverter circuit 100, an alternating current starting circuit, and a control unit 510.

[0084] The inverter circuit 100 can convert direct current into alternating current, the output end of the inverter circuit 100 is connected with a power grid 600, and the input end of the inverter circuit 100 is provided with a direct current bus capacitor 200.

[0085] In this embodiment, the direct current input port 101 of the inverter circuit 100 can be connected with a solar panel or the like, and when there is sunlight during the day, the direct current input port 101 can be used to charge the direct current bus capacitor 200 to start the photovoltaic power generation system.

[0086] It can be understood that for the photovoltaic power generation system connected with an energy storage device, the battery pack unit 102 of the energy storage device can be arranged at the input end of the inverter circuit 100.

[0087] The alternating current starting circuit can use the alternating current of the power grid 600 to charge the direct current bus capacitor 200 when there is no direct current input at the direct current input port 101, so as to realize the alternating current starting of the photovoltaic power generation system.

[0088] In this embodiment, the alternating current starting circuit includes an alternating current starting switch 310, an isolation module 320, and a charging module connected in sequence from the power grid 600 side, the alternating current starting switch 310 is further connected with the power grid 600, and the charging module is further connected with the direct current bus capacitor 200.

[0089] The AC starting switch 310 can control the on-off of the power transmission between the power grid 600 and the DC bus capacitor 200.

[0090] It should be noted that the isolation module 320 can also achieve electrical isolation between the power grid 600 and the DC bus capacitor 200 when transmitting power from the power grid 600 to the DC bus capacitor 200, preventing leakage when the power grid 600 charges the DC bus capacitor 200.

[0091] In actual execution, the isolation module 320 can be a device that transmits power while achieving electrical isolation, such as an isolation transformer.

[0092] The charging module converts the AC power of the power grid 600 into DC power through rectification, current limiting, etc., charges the DC bus capacitor 200, and raises the voltage of the DC bus capacitor 200.

[0093] In some embodiments, the charging module includes a current limiting resistor 331 and a rectifier circuit 332 connected in series, the current limiting resistor 331 is used to limit the charging current of the DC bus capacitor 200, and the rectifier circuit 332 is used to charge the DC bus capacitor 200.

[0094] The rectifier circuit 332 can convert the AC power provided by the power grid 600 into DC power to charge the DC bus capacitor 200 and raise the voltage of the DC bus capacitor 200.

[0095] In actual execution, the rectifier circuit 332 can be a half-wave rectifier, a full-wave rectifier, a bridge rectifier, etc.

[0096] It can be understood that the current limiting resistor 331 is used to limit the charging current, and the current limiting resistor 331 is arranged on both positive and negative branches of the AC starting circuit, which can suppress the magnetizing inrush current at the moment of power-on of the isolation module 320, prevent the excessive current from causing the switches such as the AC starting switch 310 to stick, and also prevent the excessive magnetizing inrush current from tripping the circuit breaker on the AC side.

[0097] The control unit 510 is connected with the inverter circuit 100 and the AC starting switch 310, and the control unit 510 is used to control the AC starting switch 310 to be closed under the condition that the input DC voltage of the inverter circuit 100 is lower than the peak value of the power grid line voltage plus a threshold value and an AC starting instruction is received, transmit the power of the power grid 600 through the isolation module 320, limit and rectify the AC power output by the isolation module 320 through the charging module, charge the DC bus capacitor 200 through the positive and negative half waves of the AC power alternately, and isolate the power grid 600 and the DC bus capacitor 200 through the isolation module 320, so that the power grid 600 does not leak during the charging process.

[0098] In this embodiment, the voltage at the input end of the inverter circuit 100 is detected, and when the input end DC voltage of the inverter circuit 100 is lower than the peak-peak value of the grid line voltage plus a threshold value, it indicates that the DC input of the photovoltaic power generation system cannot power the inverter circuit 100, that is, the photovoltaic power generation system may be in the case of no sunlight at night.

[0099] The peak-peak value of the grid line voltage refers to the difference between the maximum value of the positive half cycle and the minimum value of the negative half cycle of the grid 600 line voltage in a complete cycle, and when the input end DC voltage of the inverter circuit 100 is lower than the peak-peak value of the grid line voltage plus a predetermined threshold value (which can be positive), it indicates that the inverter circuit 100 has no DC input, and the photovoltaic power generation system may be in the case of no sunlight at night.

[0100] When the input end DC voltage of the inverter circuit 100 is lower than the peak-peak value of the grid line voltage plus a threshold value, and the control unit 510 receives an AC start instruction, the control unit 510 controls the AC start switch 310 to be closed, the AC start circuit is turned on, the isolation module 320 outputs AC power, and the AC power is converted into a certain size of DC power through the current limiting resistor 331 and the rectifier circuit 332 of the charging module, and then output to the DC bus capacitor 200. The DC bus capacitor 200 is charged by the positive and negative half waves of the AC power alternately.

[0101] It can be understood that during the charging process of the DC bus capacitor 200, the voltage of the DC bus capacitor 200 gradually rises, and the voltage of the DC bus capacitor 200 is detected in real time to determine whether the start condition of the inverter circuit 100 is met.

[0102] In this embodiment, the control unit 510 is also configured to control the AC start switch 310 to be opened when the DC bus capacitor 200 is charged to a target voltage required for grid connection, and start the inverter circuit 100 to enable the photovoltaic power generation system to operate in grid-connected mode.

[0103] The target voltage required for grid connection is the voltage required for the photovoltaic power generation system to operate in grid-connected mode, which can be set according to the voltage of the grid 600.

[0104] In the related art, due to no sunlight at night, the solar cell panel commonly used for DC power supply cannot power the energy storage inverter and the photovoltaic grid-connected inverter and other devices; starting these devices by using the energy storage battery for power supply may cause over-discharge of the battery, and even damage the battery.

[0105] In the embodiment of the present disclosure, the photovoltaic power generation system is provided with an alternating current starting circuit, the alternating current starting circuit comprises an alternating current starting switch 310, an isolation module 320 and a charging module connected in sequence from the power grid 600 side, and the control unit 510 controls the alternating current starting switch 310 to be closed under the condition that the direct current voltage at the input end of the inverter circuit 100 is lower than the peak-peak value of the power grid line voltage plus a threshold value and the alternating current starting instruction is received, and the alternating current starting circuit is turned on to charge the direct current bus capacitor 200. The photovoltaic power generation system can be normally started at night without sunlight, and the inverter circuit 100 can complete the actions of grid connection, reactive power compensation, fault restart and the like.

[0106] It should be noted that when the alternating current starting circuit is turned on, a charging loop from the power grid 600 to the direct current bus capacitor 200 is formed, and the isolation module 320 in the alternating current starting circuit can realize electrical isolation, which can effectively prevent the occurrence of electric leakage when the power grid 600 charges the direct current bus capacitor 200. Compared with the related art in which a charging loop from the grid side to the bus capacitor and then back to the grid side is formed, the embodiment of the present disclosure can form a complete charging loop without returning to the grid side again, which can effectively reduce the probability of electric leakage in the process of charging the direct current bus capacitor 200 by the power grid 600, and can safely and reliably start the photovoltaic power generation system at night without sunlight.

[0107] According to the photovoltaic power generation system provided in the embodiment of the present disclosure, the alternating current starting circuit is formed by sequentially connecting the alternating current starting switch 310, the isolation module 320 and the charging module from the power grid 600 side, the control unit 510 controls the alternating current starting switch 310 to be closed under the condition that the direct current voltage at the input end of the inverter circuit 100 is lower than the peak-peak value of the power grid line voltage plus a threshold value and the alternating current starting instruction is received, and the alternating current starting circuit is turned on to charge the direct current bus capacitor 200. The photovoltaic power generation system can be safely and reliably started at night without sunlight, which is helpful for the execution of subsequent system grid connection, reactive power compensation, fault restart and the like.

[0108] In some embodiments, the photovoltaic power generation system can further comprise an alternating current auxiliary power supply 520.

[0109] As shown in FIG. 1, the control unit 510 is connected with the power grid 600 through the alternating current auxiliary power supply 520, and the alternating current auxiliary power supply 520 is used to convert the alternating current energy of the power grid 600 into direct current energy to supply power to the control unit 510.

[0110] In this embodiment, the alternating current auxiliary power supply 520 converts the alternating current energy of the power grid 600 into direct current energy, and outputs the direct current energy to the control unit 510 to supply power to the control unit 510, thereby ensuring the stable operation of the control unit 510 in the scenario of night without sunlight.

[0111] In some embodiments, the photovoltaic power generation system can further comprise a grid-connected switch device, which is arranged between the output of the inverter circuit 100 and the power grid 600.

[0112] It can be understood that the grid-connected switch device is a key component for connecting the inverter circuit 100 and the power grid 600, and can control the power transmission between the inverter circuit 100 and the power grid 600, safely and stably connect the power output by the inverter circuit 100 to the power grid 600 at a proper time, and realize the grid-connected operation of the photovoltaic power generation system, and can disconnect the connection with the power grid 600 when the power grid 600 has an abnormality or a fault, and protect the equipment of the photovoltaic power generation system.

[0113] As shown in FIG. 5, the AC starting circuit comprises an AC starting switch 310, an isolation module 320 and a charging module connected in sequence from the power grid 600 side, and the control unit 510 controls the AC starting switch 310 to be closed, and the power is transmitted from the power grid 600 to the DC bus capacitor 200 through the AC starting switch 310, the isolation module 320 and the charging module.

[0114] In this embodiment, when the AC starting circuit is turned on, a charging circuit from the power grid 600 to the DC bus capacitor 200 is formed, and the charging circuit for the DC bus capacitor 200 can not pass through the grid-connected switch device, which can improve the safety and reliability of the starting of the photovoltaic power generation system.

[0115] In some embodiments, the grid-connected switch device comprises a first grid-connected switch 410 and a second grid-connected switch 420 connected in sequence, the first grid-connected switch 410 is close to the power grid 600, and the second grid-connected switch 420 is close to the inverter circuit 100.

[0116] In this embodiment, the first grid-connected switch 410 close to the power grid 600 and the second grid-connected switch 420 close to the inverter circuit 100 of the grid-connected switch device are connected in series, the control unit 510 controls the first grid-connected switch 410 and the second grid-connected switch 420 to be closed when the inverter circuit 100 is started and the grid-connected condition is met, and the grid-connected operation of the photovoltaic power generation system is realized.

[0117] In some embodiments, the AC starting switch 310 is connected to a connection point between the power grid 600 and the first grid-connected switch 410, and the control unit 510 is also connected to the grid-connected switch device, and the control unit 510 is further configured to, in a case that the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the line voltage of the power grid 600 plus a threshold value, and an AC starting instruction is received, control the AC starting switch 310 to be closed, transmit the power of the power grid 600 through the isolation module 320, and perform current limiting and rectification processing on the AC power output by the isolation module 320 by the charging module, and charge the DC bus capacitor 200 through the positive and negative half waves of the AC power alternately, so that the isolation module 320 isolates the power grid 600 from the DC bus capacitor 200, and the power grid 600 does not have a leakage current during the charging process.

[0118] In this embodiment, the AC starting switch 310 is connected to the power grid 600, and there is no grid-connected switch between the AC starting switch 310 and the power grid 600, and the control unit 510 is configured to, in a case that the DC voltage at the input end of the inverter circuit 100 is lower than the peak-to-peak value of the line voltage of the power grid 600 plus a threshold value, and an AC starting instruction is received, control the AC starting switch 310 to be closed, transmit the power of the power grid 600 through the isolation module 320, and perform current limiting and rectification processing on the AC power output by the isolation module 320 by the charging module, and charge the DC bus capacitor 200 through the positive and negative half waves of the AC power alternately, so that the isolation module 320 isolates the power grid 600 from the DC bus capacitor 200, and the power grid 600 does not have a leakage current during the charging process.

[0119] For example, as shown in FIG. 4, for a three-phase system of A, B, and C, the second grid-connected switch 420 close to the inverter circuit 100 includes K A1 , K B1 , and K C1 , the first grid-connected switch 410 close to the power grid 600 includes K A2 , K B2 , and K C2 , the phase line connected to the AC starting circuit is B and C, and there is no grid-connected switch between the AC starting switch 310 and the power grid 600.

[0120] In this embodiment, after receiving the AC starting instruction, the control unit 510 controls the S1, S2, S3, and S4 of the AC starting switch 310 to be closed, and turns on the AC starting circuit to charge the DC bus capacitor 200.

[0121] In some embodiments, the AC starting switch 310 is connected to a connection point between the first grid-connected switch 410 and the second grid-connected switch 420, and the control unit 510 is further connected to the grid-connected switch device, and the control unit 510 is further configured to, in a case that the input DC voltage of the inverter circuit 100 is lower than the peak value of the grid line voltage plus a threshold value, and an AC starting instruction is received, control the AC starting switch 310 and the first grid-connected switch 410 to be closed, transmit the power of the grid 600 through the isolation module 320, and perform current limiting and rectification processing on the AC power output by the isolation module 320 by the charging module, and charge the DC bus capacitor 200 through the positive and negative half waves of the AC power.

[0122] As shown in FIG. 2, the AC starting switch 310 is connected to a connection point between the first grid-connected switch 410 and the second grid-connected switch 420, the first grid-connected switch 410 close to the grid 600 is controlled to be closed, and the AC starting switch 310 is controlled to be closed, the AC starting circuit is turned on, and the DC bus capacitor 200 is charged through the isolation module 320 and the charging module.

[0123] As shown in FIG. 3, in order to charge the DC bus capacitor 200, the AC power output by the grid 600 sequentially passes through the first grid-connected switch 410, the AC starting switch 310, the isolation module 320, the current limiting resistor 331 and the rectification circuit 332, and is supplied to the DC bus capacitor 200.

[0124] In this embodiment, the charging loop of the DC bus capacitor 200 does not pass through the second grid-connected switch 420 to return to the grid 600, which can reduce the probability of leakage and switch sticking during charging.

[0125] It can be understood that the AC starting switch 310 is connected to a connection point between the first grid-connected switch 410 and the second grid-connected switch 420, the first grid-connected switch 410 and the AC starting switch 310 are controlled to act, and the AC starting circuit is turned on, which can reduce the probability of mis-turning on the AC starting circuit when the first grid-connected switch 410 or the AC starting switch 310 sticks.

[0126] In some embodiments, the closed first grid-connected switch 410 is located on the phase line connected to the AC starting circuit.

[0127] In actual implementation, the number of the first grid-connected switch 410 can be one or more, and the number of the second grid-connected switch 420 can also be one or more.

[0128] When the AC starting circuit is controlled to be turned on, the closed first grid-connected switch 410 is located on the phase line connected to the AC starting circuit, that is, the first grid-connected switch 410 on the phase line which is not connected to the AC starting circuit can not be closed.

[0129] For example, as shown in FIG. 2, for a three-phase system of A, B, C, the second grid-connected switch 420 close to the inverter circuit 100 includes K A1 , K B1 , K C1 , the first grid-connected switch 410 close to the grid 600 includes K A2 , K B2 , K C2 , and the phase line connected to the AC starting circuit is B and C.

[0130] In this embodiment, after receiving the AC starting instruction, the control unit 510 controls K B2 , K C2 of the first grid-connected switch 410 to be closed, and controls S1, S2, S3, and S4 of the AC starting switch 310 to be closed, so as to turn on the AC starting circuit and charge the DC bus capacitor 200.

[0131] In some embodiments, the control unit 510 is configured to disconnect the AC starting switch 310 and the first grid-connected switch 410 when the remaining current detection and the insulation impedance detection of the inverter circuit 100 pass, and the voltage of the DC bus capacitor 200 reaches the target voltage required for grid connection, so as to control the inverter circuit 100 to start.

[0132] In this embodiment, the AC starting circuit is turned on to charge the DC bus capacitor 200, and during the voltage rise of the DC bus capacitor 200, the photovoltaic power generation system performs the remaining current detection and the insulation impedance detection, and judges whether the voltage of the DC bus capacitor 200 reaches the threshold voltage required for grid connection. When the remaining current detection and the insulation impedance detection pass, and the bus voltage reaches the threshold voltage required for grid connection, the control unit 510 controls the AC starting switch 310 and the first grid-connected switch 410 to be disconnected, so as to disconnect the starting circuit, and controls the inverter circuit 100 to start.

[0133] Wherein, the residual current detection (RCD) judges whether there is a leakage situation by detecting the difference between the current flowing into and flowing out of the circuit, and the insulation impedance detection (ISO) is used to evaluate the insulation performance between the photovoltaic power generation system and the ground, and judges whether there is a risk of insulation drop or leakage by measuring the insulation resistance between the internal circuit of the system and the ground.

[0134] It can be understood that, before controlling the inverter circuit 100 to start, performing the remaining current detection and the insulation impedance detection can improve the safety and reliability of the operation of the photovoltaic power generation system.

[0135] In some embodiments, the control unit 510 is further configured to control the second grid-connected switch 420 and the first grid-connected switch 410 to be closed when the inverter circuit 100 has started and the output voltage of the inverter circuit 100 and the grid-side voltage of the power grid 600 meet the grid-connected condition, so that the photovoltaic power generation system is operated in grid-connected mode.

[0136] It can be understood that after the inverter circuit 100 is started, the control unit 510 controls the output of the inverter circuit 100, so that the output voltage of the inverter circuit 100 follows the grid-side voltage of the power grid 600 to meet the grid-connected condition, and the second grid-connected switch 420 and the first grid-connected switch 410 are closed to realize the connection between the inverter circuit 100 and the power grid 600.

[0137] In actual implementation, the grid-connected condition can include that the output voltage of the inverter circuit 100 and the grid-side voltage of the power grid 600 are synchronized in amplitude, frequency and phase, the frequency of the output of the inverter circuit 100 is consistent with the frequency of the power grid 600, and the voltage waveform of the output of the inverter circuit 100 is close to the sine wave waveform of the power grid 600, etc.

[0138] In some embodiments, the control unit 510 is configured to control the second grid-connected switch 420 and the first grid-connected switch 410 to be closed when the grid-connected switch device self-checking is passed.

[0139] In this embodiment, before the second grid-connected switch 420 and the first grid-connected switch 410 are closed, the second grid-connected switch 420 and the first grid-connected switch 410 of the grid-connected switch device are self-checked, and when the self-checking of the second grid-connected switch 420 and the first grid-connected switch 410 is passed, the second grid-connected switch 420 and the first grid-connected switch 410 are controlled to be closed.

[0140] In actual implementation, the self-checking of the grid-connected switch device can include detection of switch position, switch sticking, switch electrical performance, etc., and when the self-checking of the grid-connected switch device is passed, the second grid-connected switch 420 and the first grid-connected switch 410 are controlled to be closed to realize grid connection, which can improve the safety and reliability of the photovoltaic power generation system in grid-connected operation.

[0141] It should be noted that during the process of starting the photovoltaic power generation system in AC mode, the residual current detection of the inverter circuit 100, the insulation impedance detection of the inverter circuit 100 or the self-checking of the grid-connected switch device can be performed, and when the residual current detection of the inverter circuit 100, the insulation impedance detection of the inverter circuit 100 or the self-checking of the grid-connected switch device are all passed, the AC starting of the photovoltaic power generation system can be completed, and the system is operated in grid-connected mode.

[0142] In some embodiments, the control unit 510 is further configured to output a start-up failure alarm information in a case where the residual current detection of the inverter circuit 100, the insulation impedance detection of the inverter circuit 100, or the self-check of the grid-connected switch fails.

[0143] In the AC start-up process, if at least one of the residual current detection of the inverter circuit 100, the insulation impedance detection of the inverter circuit 100, or the self-check of the grid-connected switch fails, the AC start-up fails, the start-up failure alarm information is outputted to prompt the staff that the current AC start-up fails, and information prompting the staff to maintain the related circuit can also be outputted.

[0144] In some embodiments, the DC bus capacitor 200 includes a positive bus capacitor and a negative bus capacitor, one end of the positive bus capacitor and one end of the negative bus capacitor are connected to the bus midpoint.

[0145] In this embodiment, the DC bus is divided into a positive bus and a negative bus, the DC bus capacitor 200 includes a positive bus capacitor connected to the positive bus and a negative bus capacitor connected to the negative bus, and the connection point of the positive bus capacitor and the negative bus capacitor is the bus midpoint.

[0146] For example, as shown in FIG. 2, the DC bus capacitor 200 includes a positive bus capacitor C1 and a negative bus capacitor C2, and C1 and C2 are connected to the bus midpoint.

[0147] In some embodiments, the photovoltaic power generation system can further include a voltage equalization switch device 340.

[0148] In this embodiment, the voltage equalization switch device 340 includes a first voltage equalization switch and a second voltage equalization switch, the first end of the charging module is connected to the bus midpoint, the second end of the charging module is connected to the other end of the positive bus capacitor, the third end of the charging module is connected to the other end of the negative bus capacitor, the first voltage equalization switch is arranged between the second end of the charging module and the other end of the positive bus capacitor, and the second voltage equalization switch is arranged between the third end of the charging module and the other end of the negative bus capacitor.

[0149] The charging module branches into two branches, the branch in which the second end is located is connected to the positive bus capacitor, and the branch in which the third end is located is connected to the negative bus capacitor, the first end of the charging module is connected to the bus midpoint, forming a circuit that can charge the positive bus capacitor and the negative bus capacitor separately.

[0150] In the first voltage equalization switch is closed and the second voltage equalization switch is open, the charging module charges the positive bus capacitor; in the first voltage equalization switch is open and the second voltage equalization switch is closed, the charging module charges the negative bus capacitor.

[0151] The control unit 510 is connected with the voltage equalization switch device 340, and the control unit 510 is configured to, in a case where a voltage difference between the positive bus capacitor and the negative bus capacitor is greater than a preset voltage threshold, control one of the first voltage equalization switch and the second voltage equalization switch to be open and the other to be closed based on a voltage of the positive bus capacitor and a voltage of the negative bus capacitor.

[0152] In this embodiment, during the process of charging the DC bus capacitor 200, the voltages of the positive bus capacitor and the negative bus capacitor are monitored in real time, and when the voltage difference (i.e., the voltage difference) between the positive bus capacitor and the negative bus capacitor is greater than the preset voltage threshold, it indicates that the positive and negative bus voltages are not equal, and the control unit 510 controls the conduction and shutdown of the first voltage equalization switch and the second voltage equalization switch in the voltage equalization switch device 340, to charge the positive bus capacitor or the negative bus capacitor alone, to reduce the voltage difference between the positive bus capacitor and the negative bus capacitor, so that the positive and negative bus voltages are equalized.

[0153] It should be noted that the preset voltage threshold is a preset voltage difference threshold, and the preset voltage threshold can be a positive value greater than 0, and the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than the preset voltage threshold, that is, the absolute value of the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than the preset voltage threshold.

[0154] In actual execution, when it is determined that the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than the preset voltage threshold, the capacitor with the smaller voltage is determined according to the voltages of the positive bus capacitor and the negative bus capacitor, and the control unit 510 controls the conduction and shutdown of the first voltage equalization switch and the second voltage equalization switch to charge the capacitor with the smaller voltage alone, to reduce the voltage difference between the two capacitors, so that the positive and negative bus voltages are equalized.

[0155] For example, as shown in FIG. 2, the DC bus capacitor 200 includes a positive bus capacitor C1 and a negative bus capacitor C2, the C1 and the C2 are connected to the bus midpoint, the charging module includes a current limiting resistor 331 and a rectifier module, the current limiting resistor 331 includes R1 and R2, the rectifier module includes D1 and D2, one end of R2 is connected to the bus midpoint (i.e., the first end of the charging module is connected to the bus midpoint), and one end of R1 is connected to C2 through D1 and to C1 through D2.

[0156] In this embodiment, the voltage equalization switch device 340 includes S7 and S8, S8 arranged between D2 and C1 is used as the first voltage equalization switch, and S7 arranged between D1 and C2 is used as the second voltage equalization switch, when S8 is closed and S7 is open, the charging module charges C1, and when S8 is open and S7 is closed, the charging module charges C2.

[0157] When the voltage difference between C1 and C2 is greater than the preset voltage threshold, and the voltage of C1 is greater than the voltage of C2, the control unit 510 controls S8 to be open and S7 to be closed, and the charging module charges C2 to reduce the voltage difference between C1 and C2.

[0158] When the voltage difference between C1 and C2 is greater than the preset voltage threshold, and the voltage of C1 is less than the voltage of C2, the control unit 510 controls S8 to close S7 to open, and the charging module charges C1 to reduce the voltage difference between C1 and C2.

[0159] In this embodiment, by monitoring the voltages of the positive bus capacitor and the negative bus capacitor, the on-off of the first voltage-sharing switch and the second voltage-sharing switch is controlled to charge the positive bus capacitor or the negative bus capacitor separately, so that the positive bus and the negative bus maintain voltage balance during the charging of the DC bus capacitor 200, and the safety of the charging process is improved.

[0160] In some embodiments, the control unit 510 is further configured to output an auxiliary source closing instruction to control the AC starting switch 310 to close to charge the DC bus capacitor 200 when the input DC voltage of the inverter circuit 100 is lower than the peak value of the grid line voltage plus a threshold value, and an AC starting instruction is received.

[0161] In this embodiment, during the AC starting process of the photovoltaic power generation system, the auxiliary source closing instruction is outputted to instruct the auxiliary source in the photovoltaic power generation system and other systems connected thereto to close, so that the power consumption of the photovoltaic power generation system is minimized, the charging rate of the DC bus capacitor 200 is improved, and the efficiency of the AC starting of the photovoltaic power generation system is improved.

[0162] For example, when the input DC voltage of the inverter circuit 100 is lower than the peak value of the grid line voltage plus a threshold value, and an AC starting instruction is received, the control unit 510 outputs an auxiliary source closing instruction to close the DC auxiliary source of the photovoltaic power generation system itself through the auxiliary source closing instruction, and sends the auxiliary source closing instruction to the energy storage unit connected to the photovoltaic power generation system, so that the energy storage unit closes its auxiliary source, greatly improving the charging rate of the DC bus capacitor 200.

[0163] In order for those skilled in the art to have a more comprehensive understanding of the technical solutions of the present disclosure, the present disclosure will be described in detail below in conjunction with specific embodiments, and the implementation process of the present disclosure in actual application scenarios will be fully presented.

[0164] As shown in FIG. 1, the photovoltaic power generation system includes a DC bus capacitor 200, an inverter circuit 100, a first grid-connected switch 410, a second grid-connected switch 420, an AC starting switch 310, an isolation module 320, a charging module, an AC auxiliary power supply 520, and a control unit 510.

[0165] The DC bus capacitor 200 can include a positive bus capacitor and a negative bus capacitor, and the connection point of the positive bus capacitor and the negative bus capacitor is the bus midpoint.

[0166] The control unit 510 is connected with the power grid 600 through the auxiliary AC power supply 520, which is used to convert AC power of the power grid 600 into DC power to supply power to the control unit 510.

[0167] As shown in FIG. 2, for a three-phase system of A, B and C, the second grid-connected switch 420 close to the inverter circuit 100 includes K A1 , K B1 , K C1 The first grid-connected switch 410 close to the power grid 600 includes K A2 , K B2 , K C2 The phase line connected with the AC starting circuit is B and C.

[0168] The AC starting switch 310 includes S1, S2, S3 and S4, the current-limiting resistor 331 includes R1 and R2, the rectifier module includes D1 and D2, and the isolation module 320 is an isolation transformer T1.

[0169] The DC bus capacitor 200 includes a positive bus capacitor C1 and a negative bus capacitor C2, C1 and C2 are connected to the bus midpoint, one end of R2 is connected to the bus midpoint, and one end of R1 is connected to C2 through D1 and connected to C1 through D2.

[0170] In this embodiment, after the control unit 510 receives an AC starting instruction, K B2 , K C2 of the first grid-connected switch 410 are closed, S1, S2, S3 and S4 of the AC starting switch 310 are closed, the AC starting circuit is turned on, and AC power charges C1 and C2 through the isolation transformer T1, the diode D1 and the diode D2.

[0171] The photovoltaic power generation system can also be provided with a voltage equalization switch device 340, S8 between D2 and C1 is used as a first voltage equalization switch, and S7 between D1 and C2 is used as a second voltage equalization switch. When S8 is closed and S7 is opened, the charging module charges C1, and when S8 is opened and S7 is closed, the charging module charges C2.

[0172] During the process of charging the bus, when the positive and negative bus voltages are detected to be uneven, the conduction and turn-off of S7 and S8 are controlled to equalize the positive and negative bus voltages.

[0173] When the voltage difference between C1 and C2 is greater than a preset voltage threshold, and the voltage of C1 is greater than that of C2, the control unit 510 controls S8 to be opened and S7 to be closed, and the charging module charges C2; when the voltage difference between C1 and C2 is greater than the preset voltage threshold, and the voltage of C1 is less than that of C2, the control unit 510 controls S8 to be closed and S7 to be opened, and the charging module charges C1.

[0174] It can be understood that when the pressure difference between C1 and C2 is less than or equal to the preset voltage threshold, it indicates that the positive and negative bus voltage imbalance does not occur, and S7 and S8 are both closed, and C1 and C2 are charged at the same time.

[0175] Fig. 2 shows a specific topology of the inverter circuit 100 in the embodiment of the present disclosure, each phase bridge arm of the inverter circuit 100 is composed of four controllable switching tubes, each phase is connected to the second grid-connected switch 420 through an LC filter circuit, and the inverter circuit 100 of the photovoltaic power generation system includes, but is not limited to, topologies such as T-type, I-type, ANPC-type, HERIC-type, etc.

[0176] It can be understood that the rectifier circuit 332 is used to convert alternating current into direct current, as shown in Fig. 2, the rectifier circuit 332 can include a half-wave rectification topology structure of two diodes D1 and D2, and the rectifier circuit 332 can also be a full-wave rectification topology structure as shown in Fig. 5, as shown in Fig. 6, the alternating current passes through the isolation transformer T1, the current-limiting resistor 331 (R1 and R2) and the full-wave rectification topology structure, and charges the capacitors C1 and C2.

[0177] The photovoltaic power generation system of the embodiment of the present disclosure can also be applied to a single-phase system, including but not limited to single-phase systems such as HERIC.

[0178] As shown in Fig. 7, the second grid-connected switch 420 close to the inverter circuit 100 includes K A1 , K B1 , the first grid-connected switch 410 close to the grid 600 includes K A2 , K B2 , the alternating current starting switch 310 includes S1 and S2, the current-limiting resistor 331 includes R1 and R2, the rectifier module includes D1 and D2, and the isolation module 320 is an isolation transformer T1.

[0179] D1 and D2 can form a half-wave rectification topology structure, S7 is arranged between D1 and C2, and S8 is arranged between D2 and C1, and the control unit 510 controls the on-off of S7 and S8, so that C1 or C2 can be charged separately when the bus voltage is uneven.

[0180] The inverter circuit 100 shown in Fig. 7 is composed of four controllable switching tubes, as shown in Fig. 8, the inverter circuit 100 can also include more than four controllable switching tubes, and the inverter circuit 100 of the photovoltaic power generation system includes, but is not limited to, topologies such as T-type, I-type, ANPC-type, HERIC-type, etc.

[0181] As shown in Fig. 7 and Fig. 8, after the control unit 510 receives the alternating current starting instruction, S1 and S2 of the alternating current starting switch 310 are controlled to be closed, that is, the alternating current starting circuit is turned on, the alternating current charges C1 and C2 through the isolation transformer T1, the diode D1 and the diode D2.

[0182] The rectifier circuit 332 shown in FIG. 7 and FIG. 8 is a half-wave rectification topology formed by D1 and D2, and as shown in FIG. 9, the rectifier circuit 332 can also be a full-wave rectification topology.

[0183] The following describes the AC starting process of the photovoltaic power generation system including the inverter in detail.

[0184] As shown in FIG. 10, in the absence of a direct current voltage (possibly at night without sunlight), i.e., without a direct current input, the upper computer issues an AC starting instruction.

[0185] The control unit 510 detects the bus voltage, and when the bus voltage is less than the reference voltage required for grid connection (i.e., the target voltage required for grid connection), the DC auxiliary source of the inverter itself is turned off, and the auxiliary source of the energy storage unit connected to the inverter is also turned off, so that the power consumption is minimized.

[0186] The control unit 510 controls the attraction of the AC starting switch 310 to turn on the AC starting circuit, and the power of the power grid 600 is transmitted through the isolation module 320. The charging module performs current limiting and rectification processing on the AC power output by the isolation module 320, and the AC power is alternately charged to the DC bus capacitor 200 through the positive and negative half waves.

[0187] During the charging process of the DC bus capacitor 200, the bus voltage rises, and the bus voltage is detected in real time, and the residual current detection (RCD) and insulation impedance detection (ISO) are performed at the same time.

[0188] It should be noted that the ISO detection can be performed by disconnecting the AC starting switch 310, and after the ISO detection is passed, the AC starting switch 310 is attracted to compensate for the voltage drop during the ISO detection process.

[0189] When the bus voltage is greater than or equal to the reference voltage required for grid connection, the inverter circuit 100 is started, the AC starting switch 310 is disconnected, and the self-checking of the first grid connection switch 410 and the second grid connection switch 420 is performed. After passing the grid connection switch self-checking, the first grid connection switch 410 and the second grid connection switch 420 are controlled to be attracted, and the inverter is connected to the grid for operation.

[0190] During the AC starting process, if the RCD detection, the ISO detection, or the grid connection switch self-checking fails, the AC starting will fail, and the corresponding alarm information will be displayed.

[0191] In this embodiment, the AC starting circuit is formed by sequentially connecting the AC starting switch 310, the isolation module 320, and the charging module from the power grid 600 side, and the control unit 510 controls the on-off of each switch in the system to turn on the AC starting circuit to charge the DC bus capacitor 200. The photovoltaic power generation system can be safely and reliably started at night without sunlight.

[0192] Currently, the power grid often needs the photovoltaic power generation system to generate reactive power at night for power compensation. When the photovoltaic power generation system is not started before night, the photovoltaic power generation system cannot be started because the solar cell panel cannot supply power to the photovoltaic inverter grid-connected unit due to no sunlight at night, so the reactive compensation cannot be completed. At the same time, considering that if the photovoltaic power generation system has been connected to the grid and has not been disconnected before night, but when the photovoltaic power generation system occurs a fault alarm at night, the photovoltaic power generation system suspends work, and after the fault is removed, the photovoltaic grid-connected power generation system also cannot be started again, which affects the progress of the dispatching work. Therefore, the photovoltaic power generation system cannot be started when there is no sunlight, so that the photovoltaic grid-connected power generation system may be affected when performing the dispatching work when there is no sunlight.

[0193] In order to solve the above problems, the prior art uses the rectification function of the inverter circuit to realize the charging of the DC bus capacitor, and reduces the impact current by connecting a current limiting circuit in parallel to the grid-connected switch device, but this scheme can only pre-charge the bus voltage to 1.44 times the grid line voltage, and often cannot reach the required DC bus voltage for grid connection. The bus voltage needs to be raised to the required voltage for grid connection by software control of the inverter circuit operating in a controlled rectification mode, which makes the control more complex. In addition, there is also a scheme to increase an additional rectification circuit to convert the grid voltage into DC, and then raise the bus voltage to the target voltage through an isolation DC / DC circuit, but more devices need to be added and the corresponding control strategy needs to be matched.

[0194] The present disclosure provides a photovoltaic power generation system which can realize the AC side start of the inverter, the start process is safer, and the work is stable and reliable.

[0195] Embodiment 1:

[0196] As shown in FIG. 11, the present embodiment describes a photovoltaic power generation system which includes a DC bus capacitor 200, an inverter circuit 100, a control unit 510, a pre-charging circuit 108 and a current limiting resistor 331;

[0197] An external DC input port 101 is connected to the input end of the inverter circuit 100 through a DC bus, and the DC bus capacitor 200 is arranged at the DC input port 101 and the inverter circuit 100. The output end of the inverter circuit 100 is connected to an AC power grid 600;

[0198] The input end of the pre-charging circuit 108 is connected to the current limiting resistor 331 and then connected to the grid, and the output end of the pre-charging circuit 108 is connected to the DC bus capacitor 200. The pre-charging circuit 108 is used to take power from the AC power grid 600 to charge the DC bus capacitor 200;

[0199] The DC bus capacitor 200 is used to start the inverter circuit 100 after the charging is completed;

[0200] The control unit 510 is configured to control the operation of the pre-charge circuit 108, and control the inverter circuit 100 to output AC power for grid connection after the charging of the DC bus capacitor 200 is completed.

[0201] When the photovoltaic power generation system of the present embodiment is put into use, the solar panel can be connected with the DC / DC boost circuit to form a DC input port 101, the DC / DC boost circuit boosts the DC power output by the solar panel, and the DC input port 101 is connected with the DC bus capacitor 200; the AC power grid 600 is connected with the AC side of the photovoltaic power generation system.

[0202] It can be found that, in the present embodiment, AC power is taken from any two phases of the inverter, and then the pre-charge circuit 108 is used to charge the DC bus capacitor 200, and when the voltage of the bus capacitor reaches the required voltage for grid connection, the inverter circuit 100 is started, thereby completing the start-up and grid connection of the photovoltaic power generation system at night or in the absence of sunlight.

[0203] The photovoltaic power generation system of the present embodiment can use the half-wave rectification principle to charge the half bus capacitors, for example, the upper half bus capacitor (positive bus capacitor) is charged during the positive half cycle of the grid voltage, and the lower half bus capacitor (negative bus capacitor) is charged during the negative half cycle of the grid voltage, so as to achieve the effect of doubling the voltage, and the bus voltage can be raised to 2 times the peak value of the line voltage, while avoiding complex rectifier circuits and isolation DC / DC circuits, and the control method is simpler.

[0204] In one embodiment, the inverter further comprises an AC auxiliary power supply 520, the input end of the AC auxiliary power supply 520 is connected with the power grid, the output end is connected with the control unit 510, and the control unit 510 is configured to control the operation of the pre-charge circuit, and control the DC / AC inverter circuit to output AC power for grid connection after the charging of the bus capacitor is completed.

[0205] The DC bus capacitor 200 can be composed of two or more capacitors in series, and each capacitor in the DC bus capacitor 200 is connected in series and then connected in parallel between the positive and negative DC buses of the inverter. The DC bus capacitor 200 can be divided into a positive bus capacitor and a negative bus capacitor, as shown in the DC bus capacitor 200 in FIG. 11, the upper DC bus is the positive DC bus, and the lower DC bus is the negative DC bus. The capacitor in the upper half connected to the positive DC bus is defined as the positive bus capacitor, and the capacitor in the lower half connected to the negative DC bus is defined as the negative bus capacitor. The connection point between the positive bus capacitor and the negative bus capacitor is the bus midpoint. Each of the positive bus capacitor and the negative bus capacitor has at least one capacitor, and in general, the capacitance of the positive bus capacitor and the negative bus capacitor is equal. Of course, two or more capacitors can be arranged in the positive bus capacitor or the negative bus capacitor, and two or more capacitors in the positive bus capacitor or the negative bus capacitor can be connected in series and / or parallel and then connected in series to form the DC bus capacitor 200, but in general, the capacitance of the positive bus capacitor and the negative bus capacitor should be equal.

[0206] As shown in FIG. 11, the output end of the pre-charge circuit 108 is divided into three connection points, which are connected to the positive, negative and bus midpoint of the DC bus capacitor 200, respectively. The pre-charge circuit 108 is used to charge the positive bus capacitor and the negative bus capacitor in the positive and negative half cycles of the power grid, respectively.

[0207] As shown in FIGS. 11 and 12, specifically, the pre-charge circuit 108 includes a first slow-start switch K1, a second slow-start switch K2, a first diode D1 and a second diode D2, the current-limiting resistor 331 includes a current-limiting resistor R1 and a current-limiting resistor R2, the first slow-start switch K1 and the second slow-start switch K2 are connected in series with a current-limiting resistor to form a first branch and a second branch, respectively, the first slow-start switch K1 and the current-limiting resistor R1 are connected in series in the first branch, the second slow-start switch K2 and the current-limiting resistor R2 are connected in series in the second branch, one end of the first branch is connected to one phase of the power grid, the other end is connected to the positive electrode of the first diode D1, the negative electrode of the first diode D1 is connected to the positive electrode of the positive bus capacitor (the positive electrode is the end connected to the positive DC bus of the positive bus capacitor), the positive electrode of the second diode D2 is connected to the negative electrode of the DC bus capacitor 200 (the negative electrode is the end connected to the negative DC bus of the negative bus capacitor), one end of the second branch is connected to the other phase of the power grid, and the other end is connected to the bus midpoint (the connection point between the positive bus capacitor and the negative bus capacitor);

[0208] The first diode D1 and the second diode D2 are used to charge the positive bus capacitor and the negative bus capacitor of the DC bus capacitor 200 in the positive and negative half cycles of the power grid, respectively.

[0209] The photovoltaic power generation system of the embodiment charges the upper half bus capacitor (positive bus capacitor) in the positive half cycle of the grid voltage and charges the lower half bus capacitor (negative bus capacitor) in the negative half cycle of the grid voltage to achieve the effect of voltage doubling, which can raise the bus voltage to 2 times the peak value of the line voltage, and meanwhile avoids complex rectifier circuit and isolation DC / DC circuit, so that the control mode is simpler. Moreover, since the pre-charge circuit 108 can charge the bus voltage to 2 times the peak value of the line voltage at most, the control unit 510 can control the inverter circuit to output alternating current with the same amplitude and phase as the grid voltage, so that when the inverter circuit is connected to the grid, there is no voltage difference between the inverter circuit output and the grid voltage, and thus there is no inrush current, which realizes soft start of the inverter and improves the working safety and reliability of the inverter.

[0210] Embodiment 2

[0211] The photovoltaic power generation system of the embodiment is improved on the basis of the embodiment 1, and the pre-charge circuit 108 is connected to the grid switch device 400.

[0212] The power taking point of the pre-charge circuit 108 connected to the alternating current grid 600 is arranged at the grid switch device 400.

[0213] As shown in FIG. 13, the grid switch device 400 includes at least one group of grid relays, each group of grid relays including two series-connected relays; the input end of the pre-charge circuit 108 is connected to the connection point between the two relays in the grid relay, and the output end of the pre-charge circuit 108 is connected to the DC bus capacitor 200, the pre-charge circuit 108 is used to take power from the midpoint of the grid relay to charge the DC bus capacitor 200, and the control unit 510 is used to control the grid switch device 400 to be connected to the grid or disconnected from the grid.

[0214] 104 and the pre-charge circuit 108.

[0215] The photovoltaic power generation system can be a single-phase inverter, split-phase inverter or three-phase inverter, the grid switch device 400 includes at least two groups of grid relays, one group of grid relays is arranged on each phase of the inverter AC bus, and the pre-charge circuit 108 is connected to any two groups of grid relays in the grid switch device 400.

[0216] Specifically, as shown in FIG. 13, a three-phase inverter with a two-level topology inverter circuit 100 is designed.

[0217] Each phase bridge arm in the inverter circuit 100 is composed of 2 switching tubes, each phase is connected to the grid switch device 400 through an LC filter circuit, and the A, B and C phase lines are respectively connected in series with the grid relays KA2, KB2 and KC2 on the connection path connected to each phase of the grid. One end of the first branch is connected to the grid relay KB2 of the B phase, and one end of the second branch is connected to the grid relay KC2 of the C phase.

[0218] In the absence of a direct current input, a start-up instruction is issued, and the control unit 510 detects the bus capacitor voltage. If the bus capacitor voltage is less than the target voltage, the control unit 510 controls the closing of the grid connection relays KB2 and KC2, and then controls the closing of the first slow-release switch K1 and the second slow-release switch K2 of the pre-charging circuit 108. The alternating current grid 600 charges the bus capacitors C1 and C2 through the pre-charging circuit 108. When the voltage of the bus capacitors C1 and C2 reaches the target voltage, the first slow-release switch K1 and the second slow-release switch K2 of the pre-charging circuit 108 are opened. The control unit 510 can also open the grid connection relays KB2 and KC2 and the first slow-release switch K1 and the second slow-release switch K2 when the bus capacitors C1 and C2 are overvoltage.

[0219] When the bus capacitors C1 and C2 reach the target voltage, the control unit 510 can control the inverter to perform insulation impedance detection, so as to avoid the impedance between the direct current input port 101 (PV side) and the ground being too low, and to avoid a large common-mode current passing through the inverter after the inverter is running, thereby causing damage to the devices.

[0220] The control unit 510 can generate control signals for controlling the on-off of the switching tubes in the inverter circuit 100 based on the grid voltage sampling value. The control unit 510 mainly calculates the duty cycle of the switching tube control signal by comparing the grid voltage sampling value with the bus capacitor voltage value at this time, obtains the pulse width modulation signal corresponding to the switching tube of each phase bridge arm, and then makes the DC / AC inverter circuit 103 output a sinusoidal voltage consistent with the amplitude and phase of the alternating current grid 600, so as to finally not generate an impact current when the grid-tie switching device 400 is closed, and to realize the soft start of the alternating current grid-connected inverter.

[0221] In this embodiment, the alternating current is taken from the midpoint of the two relays in any two-phase grid connection relays of the inverter, and then the pre-charging circuit 108 is used to charge the direct current bus capacitors 200. When the bus capacitor voltage reaches the voltage required for grid connection, the inverter circuit 100 is started, thereby completing the start-up and grid connection of the photovoltaic power generation system at night or in the absence of sunlight.

[0222] That is, the present disclosure uses the original grid connection relay near the grid side in the photovoltaic power generation system and a relay control strategy to add a protection to the bus capacitor charging circuit, avoids directly taking alternating current from the alternating current grid 600, and thus prevents the problem of overvoltage of the bus capacitor caused by the alternating current grid 600 continuously charging the bus capacitor when the slow-release switches in the newly added pre-charging circuit 108 are stuck and cannot be opened. That is, if the start-up relay is stuck and cannot be opened, the grid connection relay can be urgently opened to cut off the connection between the pre-charging circuit 108 and the alternating current grid 600, thereby completing the protection.

[0223] Embodiment 3:

[0224] The photovoltaic power generation system of the embodiment has the same subject structure as the photovoltaic power generation system described in Embodiment 2, and the difference is that the embodiment is specifically designed for the inverter circuit 100 of a single-phase inverter.

[0225] As shown in FIG. 14, the bridge arms corresponding to the live wire and the neutral wire in the inverter circuit 100 are respectively composed of two switch tubes, and are respectively connected to the grid-connected switching device 400 through LC filter circuits. The live wire and the neutral wire are respectively connected in series with the grid-connected relay KA2 and the grid-connected relay KB2 on the connection path connected to the power grid. One end of the first branch is connected to the grid-connected relay KA2 of the live wire, and one end of the second branch is connected to the grid-connected relay KB2 of the neutral wire.

[0226] Embodiment 4

[0227] The photovoltaic power generation system of the embodiment is further limited on the basis of Embodiment 2, specifically in that the circuit connection relationship between the pre-charge circuit 108 and the DC bus capacitor 200 is used, and the first loop and the second loop are constructed by using the power devices in the DC / AC inverter circuit. The inverter in the embodiment is a three-phase inverter.

[0228] Specifically, as shown in FIG. 15, the pre-charge circuit 108 includes the second slow-start switch K2 and the current-limiting resistor R2. One end of the circuit in which the second slow-start switch K2 and the current-limiting resistor R2 are connected in series is connected to a grid-connected relay KC2, and the other end is connected to the bus midpoint to form the second loop. The half-wave circuit in the inverter circuit 100 connected to the other grid-connected relay KA2 is used as the first loop, and the first loop is connected in parallel with the DC bus capacitor 200, for charging the positive bus capacitor and the negative bus capacitor of the DC bus capacitor 200 in the positive half cycle and the negative half cycle of the power grid respectively. The first loop further includes the protection resistor R3 and the pre-charge switch K3. One end of the circuit in which the protection resistor R3 and the pre-charge switch K3 are connected in series is connected to the grid-connected relay KA2 close to the power grid, and the other end is connected to the half-wave circuit. The protection resistor has the same function as the current-limiting resistor, and has the functions of current-limiting protection for charging the bus capacitor and limiting common-mode current impact, etc.

[0229] The half-wave circuit includes two switch tubes connected in series. The other end of the circuit in which the protection resistor and the pre-charge switch are connected in series is connected between the two switch tubes.

[0230] It can be understood that the photovoltaic power generation system of the embodiment charges the DC bus capacitor 200 by rectifying through the patchy circuit composed of the power devices in the inverter circuit 100. The selected half-wave circuit is composed of the two switch tubes corresponding to the A-phase bridge arm of the three-phase inverter of the embodiment.

[0231] In the absence of DC input, the inverter sends a start-up command, the control unit 510 detects the bus capacitor voltage, and if the bus capacitor voltage is less than the target voltage, the control attracts the grid relay Ka1, Kc1, and then attracts the second slow start switch K2 of the pre-charge circuit 108. The AC power grid 600 charges the bus capacitor C1, C2 through the half-wave circuit of the A-phase bridge arm, and when the C1, C2 voltage reaches the target voltage, the second slow start switch K2 of the pre-charge circuit 108 is disconnected. The control unit 510 can also disconnect KA2, KC2 and the second slow start switch K2 when the bus capacitor C1 and C2 are overvoltage. The presence of the protection resistor R3 and the pre-charge switch K3 can further reduce the impact current when the AC power grid 600 is connected to charge the DC bus capacitor 200.

[0232] Embodiment 5

[0233] This embodiment is an improvement on the photovoltaic power generation system described in Embodiment 4.

[0234] As shown in FIG. 16, the pre-charge circuit 108 includes a first slow start switch K1 and a current limiting resistor R1, which are connected in a first loop with a circuit composed of diode D1 and diode D2, and the reverse-parallel diode D1 and diode D2 are connected to the positive and negative terminals of the DC bus capacitor 200, and the bridge arm transverse tube of the inverter circuit 100 connected by another grid relay KA2

[0235] As a second loop, the second loop is connected to the bus midpoint, thereby forming a loop for charging the bus capacitor.

[0236] Embodiment 6

[0237] The photovoltaic power generation system of this embodiment is further limited based on Embodiment 2, specifically, the circuit connection relationship of the pre-charge circuit 108 and the DC bus capacitor 200, and the use of the freewheeling diode of one-phase bridge arm and the bridge arm transverse tube of another phase bridge arm in the DC / AC inverter circuit to construct a circuit for charging the bus capacitor. The pre-charge circuit includes a first protection resistor, a first pre-charge switch, a second protection resistor, and a second pre-charge switch. Any phase of the DC / AC inverter circuit includes a first bridge arm and a second bridge arm. The first bridge arm is two sequentially connected switch tubes connected in parallel to the DC bus capacitor 200. The second bridge arm is two reverse series connected switch tubes. One end of the second bridge arm is connected to the bus midpoint, and the other end is connected to the midpoint of the first bridge arm. One end of the first loop formed by the series connection of the first protection resistor and the first pre-charge switch is connected to the grid relay of one phase, and the other end is connected to the midpoint of the first bridge arm. One end of the second loop formed by the series connection of the second protection resistor and the second pre-charge switch is connected to the grid relay of another phase, and the other end is connected to the second bridge arm. The inverter in this embodiment is a three-phase inverter.

[0238] Specifically, as shown in FIG. 17, the pre-charge circuit 108 includes a first protection resistor R3, a first pre-charge switch K3, a second protection resistor R4 and a second pre-charge switch K4, to form a half-wave rectifier circuit with the freewheeling diodes of the two switch tubes Qa1 and Qa4 of the A-phase bridge arm and the cross tubes Qc2 and Qc3 of the C-phase bridge arm in the inverter circuit 100, the two switch tubes Qa1 and Qa4 of the A-phase bridge arm are connected in series and then in parallel between the positive and negative DC bus lines, one end of the circuit connected in series with the first protection resistor R3 and the first pre-charge switch K3 is connected to the grid relay KA2 of the A-phase, and the other end is connected to the midpoint of the A-phase bridge arm, i.e. the connecting line between the two switch tubes Qa1 and Qa4, one end of the circuit connected in series with the second protection resistor R4 and the second pre-charge switch K4 is connected to the grid relay KC2 of the C-phase, and the other end is connected to the midpoint of the DC bus capacitor 200 after the series connection of the cross tubes Qc2 and Qc3 of the C-phase bridge arm.

[0239] That is, the photovoltaic power generation system of the present embodiment utilizes the freewheeling diodes existing in the switch tubes in the inverter circuit 100 to construct a half-wave rectifier circuit. Specifically, in operation, in the absence of DC input, the inverter sends a start command, the control unit 510 detects the bus capacitor voltage, if the bus capacitor voltage is less than the target voltage, the control unit 510 controls the grid relays KA2 and KC2 to be attracted, and then controls the first pre-charge switch K3 and the second pre-charge switch K4 of the pre-charge circuit 108 to be attracted, the control unit 510 controls the switch tubes Qc2 and Qc3 of the C-phase bridge arm to be turned on, the AC power grid 600 charges the positive and negative bus capacitors through the freewheeling diodes of the switch tubes Qa1 and Qa4 of the A-phase bridge arm and the switch tubes Qc2 and Qc3 of the C-phase bridge arm, when the voltages of C1 and C2 reach the target voltage, the first pre-charge switch K3 and the second pre-charge switch K4 of the pre-charge circuit 108 are turned off. The control unit 510 can also turn off the KA2, KC2, the first pre-charge switch K3 and the second pre-charge switch K4 when the bus capacitors C1 and C2 are overvoltage. The presence of the protection resistor R3 and the protection resistor R4 can further reduce the impact current when the AC power grid 600 is connected to charge the DC bus capacitor 200.

[0240] Embodiment 7:

[0241] The present embodiment describes an AC side starting method based on the photovoltaic power generation system of embodiment 1, the input end of the pre-charge circuit 108 is directly connected to the AC power grid 600, and the working process of the method is shown in FIG. 18, which includes the following working steps:

[0242] The starting state of the inverter is judged, if it is AC starting, the pre-charge circuit 108 is closed, the bus capacitor is charged by connecting to the power grid, otherwise the grid is directly started;

[0243] The voltage of the DC bus capacitor 200 is detected, and as the bus capacitor voltage gradually rises, if it is detected that the DC bus capacitor 200 reaches the required voltage for grid connection, the slow start switch in the pre-charging circuit 108 is turned off, and after the turning off is completed, the grid connection is started, otherwise the charging of the DC bus capacitor 200 is maintained.

[0244] After the slow start switch in the pre-charging circuit 108 is turned off, the insulation impedance of the inverter is also detected to avoid the impedance of the DC input port 101 side (PV side) to ground being too low, and to avoid a large common-mode current passing through the inverter after the inverter is running, causing device damage. If the obtained ground insulation impedance meets the grid connection requirement, the control unit 510 detects again whether the bus capacitor voltage meets the required voltage for grid connection, and if it meets the required voltage for grid connection, the control signal for controlling the on-off of each switch tube in the DC / AC inverter circuit 103 is generated based on the grid voltage sampling value, to perform soft start of the grid-connected inverter; if the obtained ground insulation impedance cannot meet the grid connection requirement, a fault is reported; if the bus capacitor voltage does not meet the required voltage for grid connection, the slow start switch in the pre-charging circuit 108 is closed again, and the charging of the bus capacitor by connecting to the grid is continued.

[0245] In the process of starting and stopping the pre-charging circuit, the current-limiting resistor or protection resistor is used for current-limiting protection and limiting common-mode current impact of the charging of the bus capacitor.

[0246] The control unit 510 mainly calculates the duty cycle of the switch tube control signal by the grid voltage sampling value and the bus capacitor voltage value at this time, obtains the pulse width modulation signal corresponding to the switch tube of each phase bridge arm, and then makes the inverter circuit 100 output a sinusoidal voltage consistent with the amplitude and phase of the alternating current grid 600, so that the alternating current grid 600 is connected to the DC bus capacitor 200 through the grid connection switch device 400, and the DC bus capacitor 200 is charged by the alternating current grid 600.

[0247] When the grid 600 is connected to the grid, no impact current is generated, and the AC soft start of the AC grid-connected inverter is realized.

[0248] Embodiment 8:

[0249] This embodiment describes an AC side starting method based on the photovoltaic power generation system as in embodiment 2, the input end of the pre-charging circuit 108 is connected to the midpoint (between the two grid connection relays) of the grid connection switch device 400, and the working process of the method is shown in FIG. 19, which includes the following working steps:

[0250] The starting state of the inverter is judged, if it is AC start, the grid connection relay connected to the pre-charging circuit 108 in the grid connection switch device 400 is closed, and the slow start switch in the pre-charging circuit 108 is also closed, the bus capacitor is charged by connecting to the grid, otherwise the grid connection is directly started;

[0251] The voltage of the DC bus capacitor 200 is detected, and as the bus capacitor voltage gradually rises, if it is detected that the DC bus capacitor 200 reaches the required voltage for grid connection, the grid relay connected with the pre-charging circuit 108 in the grid connection switch device 400 and the slow start switch in the pre-charging circuit 108 are disconnected, and after the disconnection is completed, the grid connection is started, otherwise the charging of the DC bus capacitor 200 is maintained.

[0252] After disconnecting the grid relay connected with the pre-charging circuit 108 in the grid connection switch device 400 and the slow start switch in the pre-charging circuit 108, the insulation impedance of the inverter is also detected to avoid the impedance of the DC input port 101 (PV side) to ground being too low, and to avoid a large common-mode current passing through the inverter after the inverter is running, causing device damage. If the obtained ground insulation impedance meets the grid connection requirements, the control unit 510 detects again whether the bus capacitor voltage meets the required voltage for grid connection, and if it meets the required voltage for grid connection, the control signals for controlling the on-off of the switch tubes in the inverter circuit 100 are generated based on the grid voltage sampling value to perform soft start of the grid-connected inverter; if the obtained ground insulation impedance cannot meet the grid connection requirements, a fault is reported; if the bus capacitor voltage does not meet the required voltage for grid connection, the grid relay connected with the pre-charging circuit 108 in the grid connection switch device 400 is closed again, and the slow start switch in the pre-charging circuit 108 is closed, and the charging of the bus capacitor through the grid is continued.

[0253] The control unit 510 mainly calculates the duty cycle of the switch tube control signal through the grid voltage sampling value and the bus capacitor voltage value at this time, obtains the pulse width modulation signal corresponding to the switch tube of each phase bridge arm, and then makes the inverter circuit 100 output a sinusoidal voltage consistent with the amplitude and phase of the AC grid 600, so that no impact current is generated when the grid connection switch device 400 is closed, and the AC soft start of the AC grid-connected inverter is realized.

[0254] The embodiments of the disclosure are described above in combination with the drawings, but the disclosure is not limited to the specific embodiments described above, and the specific embodiments described above are only illustrative and not limiting, and those skilled in the art can make many forms under the inspiration of the disclosure without departing from the scope of the disclosure and the scope protected by the claims.

[0255] In the description of the disclosure, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the disclosure. In the description of the disclosure, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0256] Although the embodiments of the disclosure have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the disclosure, and the scope of the disclosure is defined by the claims and their equivalents.

Claims

1. A photovoltaic power system, wherein, The photovoltaic power generation system comprises: an inverter circuit, an output end of the inverter circuit being connected with a power grid, and an input end of the inverter circuit being provided with a DC bus capacitor; an AC starting circuit, the AC starting circuit comprising, from the power grid side, an AC starting switch, an isolation module and a charging module connected in sequence, the AC starting switch also being connected with the power grid, and the charging module also being connected with the DC bus capacitor; a control unit, the control unit being connected with the inverter circuit and the AC starting switch, and the control unit being used for controlling the AC starting switch to be closed, transmitting the power of the power grid through the isolation module, and controlling the charging module to carry out current limiting and rectification processing on the AC power output by the isolation module, so as to charge the DC bus capacitor through alternating positive and negative half waves of AC power, and the isolation module isolates the power grid from the DC bus capacitor, under the condition that the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the line voltage of the power grid plus a threshold value and an AC starting instruction is received; and the control unit is also used for controlling the AC starting switch to be opened and starting the inverter circuit, so as to make the photovoltaic power generation system operate in parallel with the power grid, under the condition that the DC bus capacitor is charged to a target voltage required for parallel operation.

2. The photovoltaic power system of claim 1, wherein, Further comprising: a parallel operation switch device, the parallel operation switch device being arranged between the output end of the inverter circuit and the power grid.

3. The photovoltaic power system of claim 2, wherein, The parallel operation switch device comprises first and second parallel operation switches connected in sequence, the first parallel operation switch being close to the power grid, and the second parallel operation switch being close to the inverter circuit.

4. The photovoltaic power system of claim 3, wherein, The AC starting switch is connected to a connection point between the first and second parallel operation switches, the control unit is also connected with the parallel operation switch device, the control unit is also used for controlling the AC starting switch and the first parallel operation switch to be closed, transmitting the power of the power grid through the isolation module, and controlling the charging module to carry out current limiting and rectification processing on the AC power output by the isolation module, so as to charge the DC bus capacitor through alternating positive and negative half waves of AC power, and the isolation module isolates the power grid from the DC bus capacitor, under the condition that the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the line voltage of the power grid plus a threshold value and the AC starting instruction is received. Alternatively, the AC starting switch is connected to a connection point between the power grid and the first parallel operation switch, the control unit is also connected with the parallel operation switch device, the control unit is also used for controlling the AC starting switch to be closed, transmitting the power of the power grid through the isolation module, and controlling the charging module to carry out current limiting and rectification processing on the AC power output by the isolation module, so as to charge the DC bus capacitor through alternating positive and negative half waves of AC power, and the isolation module isolates the power grid from the DC bus capacitor, under the condition that the DC voltage at the input end of the inverter circuit is lower than the peak-to-peak value of the line voltage of the power grid plus a threshold value and the AC starting instruction is received.

5. The photovoltaic power system of claim 4, wherein, The closed first parallel operation switch is located on a phase line connected with the AC starting circuit.

6. The photovoltaic power system of claim 4, wherein, The control unit is configured to turn off the AC starting switch and the first grid-connected switch when the residual current detection and the insulation impedance detection of the inverter circuit pass, and the voltage of the DC bus capacitor reaches the target voltage required for grid connection, and control the inverter circuit to start.

7. The photovoltaic power system of claim 3, wherein, The control unit is further configured to control the second grid-connected switch and the first grid-connected switch to be closed when the output voltage of the inverter circuit and the grid-side voltage of the power grid meet the grid connection condition, so that the photovoltaic power generation system is operated in grid-connected mode.

8. The photovoltaic power system of claim 7, wherein, The control unit is configured to control the second grid-connected switch and the first grid-connected switch to be closed when the grid-connected switch device self-checking passes.

9. The photovoltaic power system of any of claims 2-8, wherein, The control unit is further configured to output a start failure alarm information when the residual current detection of the inverter circuit, the insulation impedance detection of the inverter circuit, or the grid-connected switch device self-checking fails.

10. The photovoltaic power system of any of claims 1-9, wherein, Further comprising: An AC auxiliary power supply, the control unit is connected with the power grid through the AC auxiliary power supply, and the AC auxiliary power supply is configured to convert AC power of the power grid into DC power to supply power to the control unit.

11. The photovoltaic power system of any of claims 1-10, wherein, The DC bus capacitor includes a positive bus capacitor and a negative bus capacitor, one end of the positive bus capacitor and one end of the negative bus capacitor are connected to a bus midpoint.

12. The photovoltaic power system of claim 11, wherein, Further comprising: A voltage equalization switch device, the voltage equalization switch device includes a first voltage equalization switch and a second voltage equalization switch, a first end of the charging module is connected to the bus midpoint, a second end of the charging module is connected to the other end of the positive bus capacitor, a third end of the charging module is connected to the other end of the negative bus capacitor, the first voltage equalization switch is arranged between the second end of the charging module and the other end of the positive bus capacitor, and the second voltage equalization switch is arranged between the third end of the charging module and the other end of the negative bus capacitor. The control unit is connected with the voltage equalization switch device, and the control unit is configured to control one of the first voltage equalization switch and the second voltage equalization switch to be turned off and the other to be closed based on the voltage of the positive bus capacitor and the voltage of the negative bus capacitor when the voltage difference between the positive bus capacitor and the negative bus capacitor is greater than a preset voltage threshold. In the case that the first voltage equalization switch is closed and the second voltage equalization switch is turned off, the charging module charges the positive bus capacitor; in the case that the first voltage equalization switch is turned off and the second voltage equalization switch is closed, the charging module charges the negative bus capacitor.

13. The photovoltaic power system of any of claims 1-12, wherein, The charging module includes a current-limiting resistor and a rectifier circuit connected in series, the current-limiting resistor is configured to limit the charging current of the DC bus capacitor, and the rectifier circuit is configured to charge the DC bus capacitor.

14. The photovoltaic power system of any of claims 1-13, wherein, The control unit is further configured to output an auxiliary source closing instruction to control the AC starting switch to be closed to charge the DC bus capacitor when the input DC voltage of the inverter circuit is lower than the peak value of the grid line voltage plus a threshold value, and an AC starting instruction is received.

15. A photovoltaic power system, wherein, The photovoltaic power generation system includes a DC bus capacitor, an inverter circuit, a control unit, a pre-charging circuit, and a current-limiting resistor. The external DC input is connected to the input end of the inverter circuit through a DC bus, and a DC bus capacitor is arranged between the DC input and the inverter circuit, the DC bus capacitor being connected in parallel between the DC bus, and the The output end of the inverter circuit is connected to the power grid. The input end of the pre-charge circuit is connected to the power grid through the current-limiting resistor, and the output end of the pre-charge circuit is connected to the DC bus capacitor, the pre-charge circuit being used to charge the DC bus capacitor from the power grid; the DC bus capacitor is used to start the inverter circuit after the charging is completed. The control unit is used to control the operation of the pre-charge circuit and control the inverter circuit to output alternating current for grid connection after the charging of the DC bus capacitor is completed.

16. The photovoltaic power system of claim 15, wherein, The output end of the inverter circuit is connected to the power grid through a grid connection switch device, the grid connection switch device including at least one group of grid connection relays, each group of grid connection relays including at least two relays connected in series, the pre-charge circuit being used to charge the DC bus capacitor from the grid connection relays, and the power supply position being spaced from the inverter circuit by at least one relay.

17. The photovoltaic power system of claim 15 or 16, wherein, The DC bus capacitor is divided into a positive bus capacitor and a negative bus capacitor, and a bus midpoint is between the positive bus capacitor and the negative bus capacitor, each of the positive bus capacitor and the negative bus capacitor having one capacitor or at least two capacitors, the at least two capacitors being connected in series or in parallel, and the positive bus capacitor and the negative bus capacitor being connected in series and then connected in parallel between the positive and negative DC buses of the inverter.

18. The photovoltaic power system of claim 17, wherein, The output end of the pre-charge circuit is divided into three connection points, which are connected to the positive pole, the negative pole and the bus midpoint of the DC bus capacitor respectively, and the pre-charge circuit is used to charge the positive bus capacitor and the negative bus capacitor in the positive and negative half cycles of the power grid respectively.

19. The photovoltaic power system of claim 17 or 18, wherein, The inverter is a single-phase inverter, a split-phase inverter or a three-phase inverter, the grid connection switch device includes at least two groups of grid connection relays, one group of grid connection relays being arranged on each phase of the inverter, and the input end of the pre-charge circuit is connected to any two output ends of the inverter circuit through the current-limiting resistor.

20. The photovoltaic power system of any of claims 15-19, wherein, The pre-charge circuit includes a first slow-start switch, a second slow-start switch, a first diode and a second diode, the first slow-start switch and the second slow-start switch being connected in series with a current-limiting resistor to form a first branch and a second branch, one end of the first branch being connected to one phase of the power grid, the other end being connected to the positive pole of the first diode, the negative pole of the first diode being connected to the positive pole of the DC bus capacitor, the positive pole of the second diode being connected to the negative pole of the DC bus capacitor, one end of the second branch being connected to another phase of the power grid, and the other end being connected to the bus midpoint. The first diode and the second diode are used to charge the positive bus capacitor and the negative bus capacitor of the DC bus capacitor in the positive and negative half cycles of the power grid respectively.

21. The photovoltaic power system of any of claims 15-19, wherein, The pre-charge circuit comprises a first slow-start switch, a first diode, a second diode, a protection resistor and a pre-charge switch, the first slow-start switch is connected in series with the current-limiting resistor to form a first branch, one end of the first branch is connected to one phase of the power grid, and the other end is connected to the anode of the first diode, the cathode of the first diode is connected to the anode of the DC bus capacitor, the anode of the second diode is connected to the cathode of the DC bus capacitor, the protection resistor and the pre-charge switch are connected in series to form a second branch, and the second branch is connected in parallel to the two ends of the other-phase grid-connected relay.

22. The photovoltaic power system of any of claims 15-19, wherein, The pre-charge circuit comprises a second slow-start switch, one end of the circuit obtained by connecting the second slow-start switch and the current-limiting resistor in series is connected to one phase of the power grid, and the other end is connected to the bus midpoint to form a second loop, the bridge arm in the inverter circuit connected to the other phase of the power grid is used as a first loop, the bridge arm comprises two series-connected switch tubes, and the bridge arm is connected in parallel to the DC bus capacitor, and is used for charging the positive bus capacitor and the negative bus capacitor of the DC bus capacitor in the positive half cycle and the negative half cycle of the power grid, respectively.

23. The photovoltaic power system of claim 22, wherein, The first loop further comprises a protection resistor and a pre-charge switch, and the circuit formed by connecting the protection resistor and the pre-charge switch in series is connected in parallel to the two ends of the other-phase grid-connected relay.

24. The photovoltaic power system of claim 19, wherein, The pre-charge circuit comprises a first protection resistor, a first pre-charge switch, a second protection resistor and a second pre-charge switch, any phase of the inverter circuit comprises a first bridge arm and a second bridge arm, the first bridge arm comprises two series-connected switch tubes connected in parallel to the DC bus capacitor, the second bridge arm comprises two reverse-connected switch tubes, one end of the second bridge arm is connected to the bus midpoint, and the other end is connected to the midpoint of the first bridge arm, one end of the first loop formed by connecting the first protection resistor and the first pre-charge switch in series is connected to the grid-connected relay of one phase, and the other end is connected to the midpoint of the first bridge arm, one end of the second loop formed by connecting the second protection resistor and the second pre-charge switch in series is connected to the grid-connected relay of the other phase, and the other end is connected to the second bridge arm.

25. The photovoltaic power system of any of claims 15-24, wherein, The AC auxiliary power supply is further included, the input end of the AC auxiliary power supply is connected to the power grid, and the output end is connected to the control unit, and the AC auxiliary power supply is used for supplying power to the control unit.

26. An AC side starting method based on the photovoltaic power generation system as claimed in any one of claims 15 to 25, wherein, The working steps comprise the following steps: The starting state of the inverter is judged, if the inverter is started in AC mode, the slow-start switch in the pre-charge circuit is closed, the DC bus capacitor is charged by connecting to the power grid, otherwise the inverter is directly started to connect to the power grid; The voltage of the DC bus capacitor is detected, if the voltage of the DC bus capacitor reaches the required voltage for connecting to the power grid, the slow-start switch in the pre-charge circuit is disconnected, the inverter is started to connect to the power grid after the disconnection is completed, otherwise the charging of the DC bus capacitor is maintained; In the process of starting and stopping the pre-charge circuit, the current-limiting resistor or the protection resistor is used for current-limiting protection and limiting common-mode current impact of the charging of the DC bus capacitor.

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