Photovoltaic inverter

Abstract

The utility model discloses a photovoltaic inverter which comprises a DC / DC conversion unit, a DC / AC conversion unit and a DC bus capacitor. The photovoltaic inverter further comprises a first switch group, a second switch group and a controller. One end of the first switch group is connected with the multi-path photovoltaic group string, and the other end of the first switch group is connected with the input end of the DC / DC conversion unit; the second switch group comprises a first input end, a first output end, a second input end and a second output end, the first input end is connected with the positive electrode end of at least one photovoltaic group string in the multiple photovoltaic group strings, and the second input end is connected with the negative electrode end of at least one photovoltaic group string; at least one of the first output end and the second output end is connected with at least one phase of output end of the three-phase output end of the DC / AC conversion unit; the controller is connected with the positive DC bus and the negative DC bus. According to the photovoltaic inverter provided by the invention, the reverse connection fault can be identified and eliminated when the photovoltaic group string is reversely connected, an anti-reverse diode and / or a current-limiting resistor do not need to be added, and the system cost is reduced.

Description

Technical Field

[0001] This application relates to the field of photovoltaic technology, and in particular to a photovoltaic inverter. Background Technology

[0002] With the development of photovoltaic modules and power devices (such as MOSFETs and diodes), a single MPPT (Maximum Power Tracking Unit) has multiple string branches connected in parallel in various application scenarios. In this scenario, when the DC side is first powered on, the inverter's bus capacitor is not energized. When any DC switch on the DC side is closed, there will be an inrush current on the DC-side diodes. This inrush current may damage the DC-side diodes, thus leading to a series of DC-side soft-start solutions.

[0003] The current industry-standard solution for soft start is to use a test switch with an anti-reverse diode or current-limiting resistor. When the inverter is powered on for the first time, the test switch is closed. After the bus capacitors are fully charged, the other DC input switches are closed. These DC input switches are typically remotely controllable trip switches. The test switch is then opened only after all other DC input switches are closed, completing the entire DC power-on soft start process for the inverter. Alternatively, the test switch can also be a remotely controllable trip switch, which then opens the DC switches after the inverter has completed the entire DC soft start process.

[0004] As can be seen from the above scheme, in addition to a test switch, the entire soft start circuit also adds a reverse protection diode and / or a current limiting resistor, making the wiring more complex and increasing the cost. Utility Model Content

[0005] This application provides a photovoltaic inverter to identify and eliminate reverse connection faults when photovoltaic strings are reverse connected, without the need to add anti-reverse diodes and / or current-limiting resistors, thus reducing system costs.

[0006] This application provides a photovoltaic inverter, including a DC / DC conversion unit, a DC / AC conversion unit connected to the DC / DC conversion unit via a positive DC bus and a negative DC bus, and a DC bus capacitor connected between the positive DC bus and the negative DC bus;

[0007] The photovoltaic inverter also includes a first switch group, a second switch group, and a controller;

[0008] One end of the first switch group is connected to a multi-channel photovoltaic array, and the other end of the first switch group is connected to the input terminal of the DC / DC conversion unit.

[0009] The second switch group includes a first input terminal, a first output terminal, a second input terminal, and a second output terminal. The first input terminal is connected to the positive terminal of at least one of the multiple photovoltaic strings, the second input terminal is connected to the negative terminal of the at least one photovoltaic string, and at least one of the first output terminal and the second output terminal is connected to at least one of the three-phase output terminals of the DC / AC conversion unit.

[0010] The positive terminal of the controller is connected to the positive DC bus, and the negative terminal of the controller is connected to the negative DC bus.

[0011] In one example, the first output terminal and the second output terminal are connected to two of the three-phase output terminals of the DC / AC conversion unit.

[0012] In one example, the first output terminal is connected to one of the three-phase output terminals of the DC / AC converter unit, and the second output terminal is connected to the negative DC bus or the negative input terminal of the DC / DC converter unit.

[0013] In one example, the first output terminal is connected to the positive DC bus or the positive input terminal of the DC / DC converter unit, and the second output terminal is connected to one of the three-phase output terminals of the DC / AC converter unit.

[0014] In one example, the number of switches in the first switch group is greater than or equal to the number of the multiple photovoltaic strings, and each of the multiple photovoltaic strings is connected to the input terminal of the DC / DC converter unit through at least one switch in the first switch group.

[0015] In one example, the second switch group includes a first switch connected between the first input terminal and the first output terminal, and a second switch connected between the second input terminal and the second output terminal.

[0016] In one example, the DC / DC converter unit includes an inductor, a diode, and a switching transistor;

[0017] One end of the inductor is connected to the positive input terminal of the DC / DC converter unit, the other end of the inductor is connected to the anode terminal of the diode and the first terminal of the switching transistor, the cathode terminal of the diode is connected to the positive output terminal of the DC / DC converter unit, and the second terminal of the switching transistor is connected to the negative input terminal and the negative output terminal of the DC / DC converter unit.

[0018] In one example, the DC / AC conversion unit includes three-phase bridge arms, each phase bridge arm having a connection point connected to one phase output terminal of the DC / AC conversion unit, and each connection point having a switching transistor between the positive DC bus and the negative DC bus, the switching transistor having diodes connected in anti-parallel.

[0019] In one example, the DC bus capacitor includes a first capacitor and a second capacitor connected in series.

[0020] In one example, the three-phase output of the DC / AC conversion unit is also connected to a filter unit, which includes a star-connected filter capacitor, and the center point of the star-connected filter capacitor is connected to the connection point between the first capacitor and the second capacitor.

[0021] The photovoltaic inverter provided in this application can identify and eliminate reverse connection faults when the photovoltaic string is reverse connected, without the need to add anti-reverse diodes and / or current-limiting resistors, thus reducing system costs. Attached Figure Description

[0022] Figure 1 A specific circuit diagram of a photovoltaic inverter provided in the embodiments of this application;

[0023] Figure 2 This is another specific circuit diagram of a photovoltaic inverter provided in an embodiment of this application;

[0024] Figure 3 Another specific circuit diagram of a photovoltaic inverter provided in an embodiment of this application;

[0025] Figure 4 This is a schematic diagram of a DC / DC converter unit provided in an embodiment of this application;

[0026] Figure 5 This is a schematic diagram of a DC / AC conversion unit provided in an embodiment of this application.

[0027] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0028] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer and more understandable, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application.

[0029] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0030] This application provides a photovoltaic inverter, including a DC / DC conversion unit, a DC / AC conversion unit connected to the DC / DC conversion unit via a positive DC bus BUS+ and a negative DC bus BUS-, and a DC bus capacitor connected between the positive DC bus BUS+ and the negative DC bus BUS-.

[0031] The photovoltaic inverter also includes a first switch group K2, a second switch group K1, and a controller;

[0032] One end of the first switch group K2 is connected to the multi-channel photovoltaic array, and the other end of the first switch group K2 is connected to the input terminal of the DC / DC conversion unit.

[0033] The second switch group K1 includes a first input terminal, a first output terminal, a second input terminal, and a second output terminal. The first input terminal is connected to the positive terminal of at least one of the multiple photovoltaic strings, the second input terminal is connected to the negative terminal of the at least one photovoltaic string, and at least one of the first output terminal and the second output terminal is connected to at least one of the three-phase output terminals of the DC / AC conversion unit.

[0034] The positive terminal of the controller is connected to the positive DC bus BUS+, and the negative terminal of the controller is connected to the negative DC bus BUS-.

[0035] In one example, a photovoltaic string may include one or more photovoltaic panels, each of which consists of multiple photovoltaic cells.

[0036] For example, Figure 1 As shown, one end of the first switch group K2 is connected to n photovoltaic strings, PV1 to PVn in the figure. PV1+ is the positive terminal of the first photovoltaic string PV1, PV1- is the negative terminal of the first photovoltaic string PV1, and so on.

[0037] In one example, the first output terminal and the second output terminal are connected to two of the three-phase output terminals of the DC / AC conversion unit.

[0038] For example, Figure 1 As shown, the first input terminal of the second switch group K1 is connected to the positive terminal of the first photovoltaic string PV1, the second input terminal of the second switch group K1 is connected to the negative terminal of the first photovoltaic string PV1, the first output terminal of the second switch group K1 is connected to the A-phase output terminal of the DC / AC conversion unit, and the second output terminal of the second switch group K1 is connected to the B-phase output terminal of the DC / AC conversion unit.

[0039] In one example, the first output terminal is connected to one of the three-phase output terminals of the DC / AC converter unit, and the second output terminal is connected to the negative DC bus BUS- or the negative input terminal of the DC / DC converter unit.

[0040] like Figure 2 As shown, the first input terminal of the second switch group K1 is connected to the positive terminal of the first photovoltaic string PV1, the second input terminal of the second switch group K1 is connected to the negative terminal of the first photovoltaic string PV1, the first output terminal of the second switch group K1 is connected to the A-phase output terminal of the DC / AC conversion unit, and the second output terminal of the second switch group K1 is connected to the negative DC bus BUS-.

[0041] In one example, the first output terminal is connected to the positive DC bus BUS+ or the positive input terminal of the DC / DC converter unit, and the second output terminal is connected to one of the three-phase output terminals of the DC / AC converter unit.

[0042] For example, Figure 3 As shown, the first input terminal of the second switch group K1 is connected to the positive terminal of the first photovoltaic string PV1, the second input terminal of the second switch group K1 is connected to the negative terminal of the first photovoltaic string PV1, the first output terminal of the second switch group K1 is connected to the positive DC bus BUS+, and the second output terminal of the second switch group K1 is connected to the B-phase output terminal of the DC / AC conversion unit.

[0043] In one example, the number of switches in the first switch group K2 is greater than or equal to the number of the multiple photovoltaic strings, and each of the multiple photovoltaic strings is connected to the input terminal of the DC / DC converter unit through at least one switch in the first switch group K2.

[0044] For example, Figures 1-3 As shown, the positive or negative terminal of each photovoltaic string in the n-channel photovoltaic array is connected to the input terminal of the DC / DC converter unit through a switch in the first switch group K2.

[0045] In one example, the second switch group K1 includes a first switch connected between the first input terminal and the first output terminal, and a second switch connected between the second input terminal and the second output terminal.

[0046] For example, Figure 1 As shown, the second switch group K1 includes a first switch K11 connected between the first input terminal and the first output terminal of the second switch group K1, and a second switch K12 connected between the second input terminal and the second output terminal of the second switch group K1.

[0047] like Figure 4 As shown, in one example, the DC / DC conversion unit includes an inductor L1, a diode D1, and a switching transistor Q1;

[0048] One end of inductor L1 is connected to the positive input terminal of the DC / DC converter unit, and the other end of inductor L1 is connected to the anode of diode D1 and the first electrode of switch Q1. The cathode of diode D1 is connected to the positive output terminal of the DC / DC converter unit, and the second electrode of switch Q1 is connected to the negative input terminal and the negative output terminal of the DC / DC converter unit. The control terminal of switch Q1 is used to receive a control signal to turn on or off under the action of the control signal.

[0049] In one example, the DC / AC conversion unit includes three-phase bridge arms, each phase bridge arm having a connection point connected to one phase output terminal of the DC / AC conversion unit, and each connection point having a switching transistor between the positive DC bus BUS+ or the negative DC bus BUS-, the switching transistor having diodes connected in anti-parallel.

[0050] For example, Figure 5 As shown, the DC / AC conversion unit includes a three-phase grid-connected inverter, a filter unit and a three-phase grid-connected switch disposed on the AC side of the three-phase grid-connected inverter. The filter unit includes three-phase filter inductors (La~Lc shown in the figure) and three-phase filter capacitors (Ca~Cc shown in the figure). The three-phase filter capacitors are connected in a star configuration, and the center point O2 of the star configuration is connected to the bus midpoint O1. The three-phase grid-connected switch includes a first three-phase grid-connected switch S1 and a second three-phase grid-connected switch S2 connected in series, a voltage divider CX connected between the negative DC bus BUS- and ground PE, a current sampling module for collecting the three-phase currents (Ia, Ib, Ic shown in the figure) flowing through the three-phase grid-connected switch, and a voltage sampling module (not shown in the figure) for collecting the voltage across the voltage divider CX.

[0051] The topology of the three-phase grid-connected inverter is not limited. The diagram shows a three-level topology. Each phase arm has a connection point connected to one phase output of the DC / AC conversion unit. Each connection point has a switching transistor between itself and either the positive DC bus BUS+ or the negative DC bus BUS-. These switching transistors have diodes connected in anti-parallel. For example, phase A in the diagram has a connection point A connected to one phase output of the DC / AC conversion unit. Connection point A has two switching transistors between itself and either the positive DC bus BUS+ or the negative DC bus BUS-. These switching transistors have diodes connected in anti-parallel; for example, switching transistor Sa1 has diode Sa2 connected in anti-parallel.

[0052] Both the first three-phase grid-connected switch S1 and the second three-phase grid-connected switch S2 include three independent relays for each phase. For example, the first three-phase grid-connected switch S1 includes three independent relays S11, S12, and S13, and the second three-phase grid-connected switch S2 includes three independent relays S21, S22, and S23. Each group of three independent relays is driven by the same relay, and relays of the same phase are connected in series, for example, relays S11 and S21 are connected in series. The current sampling module is located between the filtering unit and the three-phase grid-connected switch.

[0053] It should be noted that the voltage divider CX can be in the form of a capacitor or a resistor, and is not limited thereto. This embodiment only uses a capacitor-type voltage divider as an example. In other examples, it is also feasible to connect the voltage divider CX between the positive DC bus BUS+ and ground PE.

[0054] In one example, the DC bus capacitor includes a first capacitor C1 and a second capacitor C2 connected in series.

[0055] In one example, the three-phase output terminals of the DC / AC conversion unit are also connected to a filter unit (e.g., La, Lb, Lc, Ca, Cb, Cc in the figure). The filter unit includes a star-connected filter capacitor (e.g., Ca, Cb, Cc in the figure), and the center point of the star-connected filter capacitor is connected to the connection point between the first capacitor C1 and the second capacitor C2.

[0056] It should be noted that the aforementioned switching transistors include, but are not limited to, IGBTs, IGCTs, and IGETs.

[0057] It should also be noted that the aforementioned DC / DC conversion unit, positive DC bus BUS+, negative DC bus BUS-, DC / AC conversion unit, DC bus capacitor, first switch group K2, second switch group K1, and controller can be integrated into one cabinet or assembled into independent cabinets; no specific limitation is made.

[0058] The following combination Figures 1-3 Explain the working principle of the circuit:

[0059] like Figure 1As shown, when the photovoltaic inverter is powered on for the first time, switch group K1 is closed. The controller is energized by the DC bus capacitor and controls the indicator light on the photovoltaic inverter to light up. After the indicator light is on, switch group K2 is closed. Switch group K1 is then opened after all switches in switch group K2 are closed. If the first photovoltaic string PV1 connected to switch group K1 is reverse-connected (i.e., the positions of PV1+ and PV1- are interchanged), the controller detects the current in the detection circuit and / or detects the capacitor voltage. Based on the direction of the current and / or the polarity of the capacitor voltage, it determines whether there is a reverse connection. If a reverse connection fault exists, the controller controls switch group K2 to trip, preventing switch group K2 from closing normally and preventing backflow of current from damaging the photovoltaic string.

[0060] like Figure 2 As shown, when the photovoltaic inverter is first powered on, switch group K1 is closed. The controller is energized by the bus capacitor and controls the inverter's indicator light to illuminate. After the indicator light illuminates, switch group K2 is closed. Switch group K1 is then opened after all switches in switch group K2 are closed. If the inverter indicator light fails to illuminate, it can be determined that the first photovoltaic string PV1 connected to switch group K1 is reverse-connected. Even if there is reverse current, it will not damage the DC-side power devices of the photovoltaic inverter.

[0061] like Figure 3 As shown, when the photovoltaic inverter is first powered on, K1 is closed. The controller is energized by the bus capacitor and the controller controls the inverter's indicator light to illuminate. After the indicator light illuminates, K2 is closed. After all switches in switch group K2 are closed, switch group K1 is opened. If the inverter indicator light fails to illuminate, it can be determined that the first photovoltaic string PV1 connected to switch group K1 is reverse-connected. Even if there is reverse current, it will not damage the DC-side power devices of the photovoltaic inverter.

[0062] As can be seen from the above, the DC-side soft-start circuit does not require additional anti-reverse diodes and / or current-limiting resistors. It utilizes the anti-parallel diodes of the switching transistors in the DC / AC converter unit as the anti-reverse and soft-start circuit. The input terminal of the switch in switch group K2 is connected to a photovoltaic string. The inrush current of the entire circuit is small, and the anti-parallel diodes of the switching transistors in the DC / AC converter unit have strong surge current tolerance. The entire soft-start wiring is simple and the cost is lower. When the photovoltaic string connected to the switch in switch group K2 is reverse-connected, the controller identifies the reverse-connected string by detecting the current and voltage, or the controller does not identify the reverse-connected string when it is powered off. The reverse current is small and will not damage the power devices of the photovoltaic inverter.

[0063] The preferred embodiments of this application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and spirit of this application shall be within the scope of the claims.

Claims

1. A photovoltaic inverter, characterized in that, The photovoltaic inverter includes a DC / DC conversion unit, a DC / AC conversion unit connected to the DC / DC conversion unit via a positive DC bus and a negative DC bus, and a DC bus capacitor connected between the positive DC bus and the negative DC bus. The photovoltaic inverter also includes a first switch group, a second switch group, and a controller; One end of the first switch group is connected to a multi-channel photovoltaic array, and the other end of the first switch group is connected to the input terminal of the DC / DC conversion unit. The second switch group includes a first input terminal, a first output terminal, a second input terminal, and a second output terminal. The first input terminal is connected to the positive terminal of at least one of the multiple photovoltaic strings, the second input terminal is connected to the negative terminal of the at least one photovoltaic string, and at least one of the first output terminal and the second output terminal is connected to at least one of the three-phase output terminals of the DC / AC conversion unit. The positive terminal of the controller is connected to the positive DC bus, and the negative terminal of the controller is connected to the negative DC bus.

2. The photovoltaic inverter according to claim 1, characterized in that, The first output terminal and the second output terminal are connected to two of the three-phase output terminals of the DC / AC conversion unit.

3. The photovoltaic inverter according to claim 1, characterized in that, The first output terminal is connected to one of the three-phase output terminals of the DC / AC conversion unit, and the second output terminal is connected to the negative DC bus or the negative input terminal of the DC / DC conversion unit.

4. The photovoltaic inverter according to claim 1, characterized in that, The first output terminal is connected to the positive DC bus or the positive input terminal of the DC / DC converter unit, and the second output terminal is connected to one of the three-phase output terminals of the DC / AC converter unit.

5. The photovoltaic inverter according to claim 1, characterized in that, The number of switches in the first switch group is greater than or equal to the number of channels in the multi-channel photovoltaic string, and each of the multi-channel photovoltaic strings is connected to the input terminal of the DC / DC converter unit through at least one switch in the first switch group.

6. The photovoltaic inverter according to claim 1, characterized in that, The second switch group includes a first switch connected between the first input terminal and the first output terminal, and a second switch connected between the second input terminal and the second output terminal.

7. The photovoltaic inverter according to claim 1, characterized in that, The DC / DC conversion unit includes an inductor, a diode, and a switching transistor; One end of the inductor is connected to the positive input terminal of the DC / DC converter unit, the other end of the inductor is connected to the anode terminal of the diode and the first terminal of the switching transistor, the cathode terminal of the diode is connected to the positive output terminal of the DC / DC converter unit, and the second terminal of the switching transistor is connected to the negative input terminal and the negative output terminal of the DC / DC converter unit.

8. The photovoltaic inverter according to claim 1, characterized in that, The DC / AC conversion unit includes three-phase bridge arms. Each phase bridge arm has a connection point connected to one phase output terminal of the DC / AC conversion unit. Each connection point has a switching transistor between itself and either the positive DC bus or the negative DC bus. Each switching transistor has a diode connected in anti-parallel.

9. The photovoltaic inverter according to claim 1, characterized in that, The DC bus capacitor includes a first capacitor and a second capacitor connected in series.

10. The photovoltaic inverter according to claim 9, characterized in that, The three-phase output terminal of the DC / AC conversion unit is also connected to a filter unit. The filter unit includes a star-connected filter capacitor, and the center point of the star-connected filter capacitor is connected to the connection point between the first capacitor and the second capacitor.

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