Inverter AC side starting circuit, inverter and photovoltaic system

Abstract

The utility model relates to an inverter AC side starting circuit, an inverter and a photovoltaic system, the inverter AC side starting circuit can realize AC-DC conversion only by adding a rectification unit through changing the structure of a hardware circuit, and then a switch tube and an anti-parallel diode of a corresponding bridge arm of the inverter are utilized to form a BOOST boost circuit. Therefore, on the premise that the cost and the bus charging speed are balanced, power can be taken from the alternating current side for grid-connected starting of the inverter and the photovoltaic system. In addition, the switching adjustment of the circuit architecture can be realized only by adding a diode, the input cost is low, and the implementation and popularization are easy.

Description

Technical Field

[0001] The utility model relates to the field of on-grid and off-grid control, and in particular to an inverter AC side starting circuit, an inverter, and a photovoltaic system. Background Art

[0002] Photovoltaic inverter power generation systems convert the direct current (DC) generated by solar panels into AC power through DC-DC and DC-AC conversion, achieving grid-connected power generation. However, in certain situations, such as at night when the solar panels are out of power, the PV inverter power generation system may also require grid connection. For example, the PV inverter power generation system may need to generate reactive power for power compensation at night. Since there is no sunlight at night, the solar panels are out of power and cannot provide energy for the PV inverter power generation system to achieve grid connection. Therefore, when the solar panels are out of power, the inverter is required to draw power from the AC side and supply it to the DC bus capacitor to start the inverter unit and achieve grid connection.

[0003] Existing inverter AC power startup circuits require AC-DC conversion followed by DC-DC conversion. Both the AC-DC and DC-DC conversion modules require additional components for circuit construction and design, significantly increasing the cost of the inverter AC power supply. Without the addition of a DC-DC conversion module for DC boosting, charging the bus capacitors using only AC-DC conversion from the AC side of the inverter will be slow.

[0004] Therefore, in summary, how to reasonably adjust the circuit structure to achieve efficient charging of the bus capacitor while reducing costs is the technical problem that this application aims to solve. Utility Model Content

[0005] A main purpose of the present invention is to overcome at least one of the above-mentioned defects, and to provide an inverter AC side starting circuit, an inverter, and a photovoltaic system, which can realize grid-connected starting of the inverter or photovoltaic system by taking power from the AC side under the premise of balancing cost and bus charging speed.

[0006] In order to achieve the above purpose, the technical solution adopted by the utility model is:

[0007] The utility model provides an inverter AC side starting circuit, which is used to charge the bus capacitor on the DC side of the inverter to complete grid-connected startup. The inverter includes at least one phase DC / AC inverter circuit, and each phase DC / AC inverter circuit includes an inverter inductor, an inverter capacitor, a first bridge arm, and a second bridge arm. The first bridge arm is two switching tubes connected in series in sequence, and the first bridge arm is connected in parallel with the bus capacitor. The second bridge arm is two switching tubes connected in reverse series, and one end of the second bridge arm is connected to the midpoint of the bus capacitor, and the other end is connected to the midpoint of the first bridge arm. The inverter AC side starting circuit includes a rectifier unit, the input side of the rectifier unit draws power from the AC side of the inverter, and the output side of the rectifier unit is connected to the inverter capacitor of a certain phase.

[0008] In the DC / AC inverter circuit of a certain phase in the inverter, the inverter inductor, the body diode of a switch tube in the first bridge arm, and the other switch tube constitute a BOOST boost circuit. The input voltage of the BOOST boost circuit is the capacitor voltage of the inverter capacitor, and the output voltage of the BOOST boost circuit is used to charge the bus capacitor.

[0009] According to one embodiment of the present invention, the rectifier unit includes at least one rectifier diode and at least one control switch, each rectifier diode is connected in series with a control switch to form a first loop, one end of the first loop is connected to a phase live wire of the AC power grid, and the other end is connected to the inverter capacitor.

[0010] According to one embodiment of the present invention, one end of the inverter capacitor is connected to the first loop and the inverter inductor, and the other end of the inverter capacitor is connected to the bus capacitor.

[0011] According to one embodiment of the present invention, the inverter AC side startup circuit includes a first control switch S1, which is arranged between the inverter capacitor and the first bridge arm and is used to control the on-off of the connection loop between the inverter capacitor and the first bridge arm.

[0012] According to one embodiment of the present invention, the inverter AC side startup circuit includes a fourth control switch S4, the other end of the first loop is connected to one end of the inverter capacitor, and the other end of the inverter capacitor is connected to the neutral line of the AC grid after being connected in series with the fourth control switch S4.

[0013] According to one embodiment of the present invention, an inverter relay is provided on the connection line between the inverter inductor and the AC power grid, one end of the inverter capacitor is connected between the inverter inductor and the inverter relay, and the other end is connected to the midpoint of the bus capacitor via a second control switch S2.

[0014] According to one embodiment of the present invention, the output side of the rectifier unit is connected between the inverter inductor and the inverter relay.

[0015] According to one embodiment of the present invention, a sixth control switch S6 is further provided between the second bridge arm and the midpoint of the bus capacitor, which is used to disconnect the connection between the midpoint of the bus capacitor and the second bridge arm when power is taken from the AC side to charge the bus capacitor.

[0016] In particular, the present application also provides an inverter, which includes the inverter AC side starting circuit as described above.

[0017] In particular, the present application also provides a photovoltaic system, which includes the inverter as described above.

[0018] Compared with the prior art, the advantages and beneficial effects of the inverter AC side starting circuit, inverter, and photovoltaic system of the utility model patent application are:

[0019] The inverter AC side starting circuit of the present application can achieve AC-DC conversion by simply adding a rectifier unit by changing the structure of the hardware circuit, and then use the switch tube and anti-parallel diode of the corresponding bridge arm of the inverter to form a BOOST boost circuit to achieve DC-DC boost conversion. In this way, it is possible to take power from the AC side to start the inverter and photovoltaic system in grid connection while balancing cost and bus charging speed.

[0020] In addition, the present application only requires adding diodes to achieve switching adjustments of the circuit architecture, which has low investment costs and is easy to implement and promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Hereinafter, some specific embodiments of the present invention will be described in detail in an exemplary and non-limiting manner with reference to the accompanying drawings. The same reference numerals in the accompanying drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the accompanying drawings:

[0022] Figure 1 It is a structural diagram of the inverter AC side starting circuit according to Example 1 of the present utility model. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0024] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] Example 1:

[0026] This embodiment describes an inverter AC side startup circuit, which is used to charge the bus capacitor on the DC side of the inverter to complete grid-connected startup. The inverter of this embodiment has three-phase outputs: phase A, phase B, and phase C. Each phase output is correspondingly provided with a DC / AC inverter circuit. Each phase DC / AC inverter circuit includes an inverter inductor, an inverter capacitor, a first bridge arm, and a second bridge arm. The first bridge arm is two switching tubes connected in series in sequence, and the first bridge arm is connected in parallel with the bus capacitor. The second bridge arm is two switching tubes connected in reverse series, and one end of the second bridge arm is connected to the midpoint of the bus capacitor, and the other end is connected to the midpoint of the first bridge arm.

[0027] This embodiment takes a C-phase DC / AC inverter circuit as an example to construct a BOOST boost circuit.

[0028] The inverter AC side startup circuit of this embodiment includes a rectifier unit, the input side of which draws power from the AC side of the inverter or the AC power grid, and the output side of which is connected to the inverter capacitor C1 of phase C. In the DC / AC inverter circuit of phase C in the inverter, the inverter inductor L1, the body diode D1 of a switch tube in the first bridge arm, and another switch tube Q1 form a BOOST boost circuit, the body diode D1 is connected in series with the signal electrode of the switch tube Q1, and the inverter inductor L1 is connected to the connection point of the series-connected body diode D1 and the switch tube Q1. The input voltage of the BOOST boost circuit is the capacitor voltage of the inverter capacitor, and the output voltage of the BOOST boost circuit is the charging of the bus capacitor.

[0029] By controlling the on and off of the switch Q1 in conjunction with the controller in the inverter, the DC-DC boost conversion of the BOOST boost circuit can be achieved. This is a prior art and will not be described in detail here.

[0030] The rectifier unit can use a half-wave rectifier circuit, that is, it draws power from one phase of the AC power grid through a rectifier diode. Alternatively, a full-wave rectifier circuit can be used, where a rectifier circuit consisting of two or four rectifier diodes draws power from one or two phases of the AC power grid. Each rectifier diode is connected in series with a control switch to form a first loop, one end of which is connected to a live phase of the AC power grid, and the other end is connected to the inverter capacitor.

[0031] This embodiment uses a full-wave rectifier circuit composed of two rectifier diodes as an example. The first rectifier diode D3, connected in series with the third control switch S3, forms a circuit with one end connected to the A-phase live wire of the AC power grid and the other end connected to one end of the inverter capacitor C1. The second rectifier diode D5, connected in series with the fifth control switch S5, forms a circuit with one end connected to the C-phase live wire of the AC power grid and the other end connected to one end of the inverter capacitor C1. The neutral line of the AC power grid is connected to the other end of the inverter capacitor C1 via a fourth control switch S4.

[0032] In one embodiment, the inverter AC-side startup circuit further includes a first control switch S1. One end of the inverter capacitor C1 is connected to the rectifier circuit in the rectifier unit, and the other end is connected to the neutral line of the AC power grid. Furthermore, one end of the inverter capacitor C1 is connected in series with the inverter inductor L1 and then connected to the midpoint of the first bridge arm of phase C. The other end of the inverter capacitor C1 is connected in series with the first control switch S1 and then connected to one end of the switching transistor Q1. The other end of the switching transistor Q1 is connected in series with the body diode D1 in the forward direction. The first control switch S1 is used to control the on / off state of the circuit connecting the inverter capacitor and the first bridge arm.

[0033] In one embodiment, an inverter relay is provided on the connection line between the inverter inductor of each phase of the inverter and the AC power grid. One end of the inverter capacitor C1 is connected between the inverter inductor L1 and the inverter relay, and the other end is connected to the midpoint of the bus capacitor via a second control switch S2. The output side of the rectifier unit is also connected between the inverter inductor and the inverter relay. Before the grid-connected startup is successful, the inverter relay is disconnected. Therefore, the capacitor voltage input between the inverter inductor L1 and the inverter relay can avoid the influence of the AC power grid on the circuit structure during the charging process. In other words, the presence of the inverter relay can achieve circuit protection before the grid-connected startup to a certain extent.

[0034] Specifically, when taking power from the AC side of the inverter, that is, taking power from the AC grid to start the inverter grid, the second control switch S2 is first opened, and then the control switches S1, S3, S4, and S5 are closed. The AC power obtained from the AC grid is converted into DC power by the rectifier unit and then charged to the inverter capacitor C1. Then, the BOOST boost circuit composed of the inverter inductor L1, the switch tube Q1, and the body diode D1 is used to boost the capacitor voltage of the inverter capacitor C1 to complete the charging of the bus capacitor, realizing the pre-charging of the bus capacitor after the AC side power is taken. After charging is completed, the control switches S1, S3, S4, and S5 are opened, and then the second control switch S2 is closed, and the grid-connected relay or grid-connected contactor is attracted to complete the grid-connected startup.

[0035] Of course, the inverter AC-side startup circuit of this embodiment does not affect DC startup when the DC input is powered. For example, when the solar panel is powered, the control switches S1, S3, S4, and S5 are kept open, and the second control switch S2 is closed. The DC input from the solar panel directly charges the bus capacitor, and then the grid-connected startup is completed.

[0036] In addition, in order to prevent the bus capacitor from being affected by electrical components such as the second bridge arm of the subsequent stage during charging, a sixth control switch S6 can be further provided between the second bridge arm and the midpoint of the bus capacitor, which is used to disconnect the connection between the midpoint of the bus capacitor and the second bridge arm when power is taken from the AC side to charge the bus capacitor.

[0037] In summary, the inverter AC side startup circuit of the present application, by changing the structure of the hardware circuit, can achieve AC-DC conversion by simply adding a rectifier unit, and then use the switch tube and anti-parallel diode of the corresponding bridge arm of the inverter to form a BOOST boost circuit to achieve DC-DC boost conversion. In this way, it is possible to achieve grid-connected startup of the inverter and photovoltaic system by taking power from the AC side while balancing cost and bus charging speed. In addition, the present application only needs to add a diode to achieve switching adjustment of the circuit architecture, which has low investment cost and is easy to implement and promote.

[0038] Example 2:

[0039] The present application describes an inverter, which includes the inverter AC side starting circuit as described in Example 1.

[0040] Example 3:

[0041] This embodiment describes a photovoltaic system, which includes the inverter described in Embodiment 2.

[0042] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. An inverter AC side startup circuit, used to charge the bus capacitor on the DC side of the inverter to complete grid-connected startup, the inverter comprising at least one phase DC / AC inverter circuit, each phase DC / AC inverter circuit comprising an inverter inductor, an inverter capacitor, a first bridge arm, and a second bridge arm, wherein the first bridge arm comprises two switching tubes connected in series in sequence and connected in parallel with the bus capacitor, and the second bridge arm comprises two switching tubes connected in reverse series, one end of the second bridge arm being connected to the midpoint of the bus capacitor and the other end being connected to the midpoint of the first bridge arm, characterized in that: The inverter AC side starting circuit includes a rectifier unit, the input side of which draws power from the inverter AC side, and the output side of which is connected to the inverter capacitor of a certain phase. In the DC / AC inverter circuit of a certain phase in the inverter, the inverter inductor, the body diode of a switch tube in the first bridge arm, and the other switch tube constitute a BOOST boost circuit. The input voltage of the BOOST boost circuit is the capacitor voltage of the inverter capacitor, and the output voltage of the BOOST boost circuit is used to charge the bus capacitor.

2. The inverter AC side starting circuit according to claim 1, characterized in that: The rectifier unit includes at least one rectifier diode and at least one control switch. Each rectifier diode is connected in series with a control switch to form a first loop. One end of the first loop is connected to a phase live wire of the AC power grid, and the other end is connected to the inverter capacitor.

3. The inverter AC side starting circuit according to claim 2, characterized in that: One end of the inverter capacitor is connected to the first loop and the inverter inductor, and the other end of the inverter capacitor is connected to the bus capacitor.

4. The inverter AC side starting circuit according to claim 3, characterized in that: The inverter AC side startup circuit includes a first control switch S1, which is arranged between the inverter capacitor and the first bridge arm and is used to control the on / off of the connection loop between the inverter capacitor and the first bridge arm.

5. The inverter AC side starting circuit according to claim 2, characterized in that: The inverter AC side startup circuit includes a fourth control switch S4, the other end of the first loop is connected to one end of the inverter capacitor, and the other end of the inverter capacitor is connected in series with the fourth control switch S4 and then connected to the neutral line of the AC grid.

6. The inverter AC side starting circuit according to any one of claims 1 to 5, characterized in that: An inverter relay is provided on the connection line between the inverter inductor and the AC power grid. One end of the inverter capacitor is connected between the inverter inductor and the inverter relay, and the other end is connected to the midpoint of the bus capacitor via a second control switch S2.

7. The inverter AC side starting circuit according to claim 6, characterized in that: The output side of the rectifier unit is connected between the inverter inductor and the inverter relay.

8. The inverter AC side starting circuit according to claim 1, characterized in that: A sixth control switch S6 is further provided between the second bridge arm and the midpoint of the bus capacitor, for disconnecting the midpoint of the bus capacitor from the second bridge arm when charging the bus capacitor with power taken from the AC side.

9. An inverter, characterized in that: The invention comprises the inverter AC side starting circuit according to any one of claims 1 to 8.

10. A photovoltaic system, characterized in that: Comprising the inverter as claimed in claim 9.

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