CN214707568U

CN214707568U - Six-switch boosting common-ground five-level inverter device

Info

Publication number: CN214707568U
Application number: CN202120752863.XU
Authority: CN
Inventors: 李文娟; 吴玉博; 周宇琦
Original assignee: Harbin University of Science and Technology
Current assignee: Harbin University of Science and Technology
Priority date: 2021-04-14
Filing date: 2021-04-14
Publication date: 2021-11-12
Anticipated expiration: 2031-04-14

Abstract

The utility model discloses a six switches step up five level inverter devices altogether, including DC power supply, two electric capacity, eight diodes, six Insulated Gate Bipolar Transistors (IGBT), a filter inductance and electric wire netting. The proposed inverter topology, which can generate at least five output voltage levels with only six unidirectional power switches, improves the power quality and reduces the size of the output filter. By means of the common ground, the negative terminal of the photovoltaic panel is directly connected to the zero point of the grid, the common mode voltage of the inverter can be made constant and the leakage current problem eliminated. The series-parallel switch conversion of the super capacitor unit can realize double boosting characteristics in single machine operation, and the peak value of the power grid voltage can be met by using a lower input voltage value.

Description

Six-switch boosting common-ground five-level inverter device

Technical Field

The utility model relates to a photovoltaic grid-connected inverter field, concretely relates to six switches boost five level inverter devices altogether.

Background

For at least the past decade, transformerless photovoltaic grid-connected inverters have been considered the most efficient and most popular solar inverters. These inverters are powered by a set of series connected photovoltaic panels (strings), which can be connected directly to the grid, providing high efficiency, low cost and high power density. Various converters and control techniques have been widely pursued in both academic and industrial areas in order to meet different grid codes and safety standards. An effective structure of the transformerless photovoltaic grid-connected inverter should solve the problem of leakage current caused by variable common-mode voltage, the problem of voltage ratio, such as the compromise between the number of photovoltaic main strings and the amplitude of grid voltage, and the problem of power quality.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide a six switches boost five level inverter devices altogether, utilize its inherent characteristic and the unipolar pulse width modulation scheme that steps up to improve the performance of the system of being incorporated into the power networks.

In order to achieve the above purpose, the utility model adopts the following technical scheme:

the circuit provided by the utility model comprises a DC power supply and an electric capacity C₁Capacitor C₂Eight diodes, a first switch tube S₁A second switch tube S₂A third switch tube S₃And a fourth switching tube S₄The fifth switch tube S₅The sixth switching tube S₆A first filter inductor L₁And a power grid.

DC power supply output side anode and diode D₂Anode and fifth switch tube S₅Is connected with the collector of the first switching tube S, the output cathode of the direct current power supply is connected with the sixth switching tube S₆Emitter and grid zero and second switch tube S₂Emitter and diode D₁The cathodes are connected.

Further, a fifth switch tube S₅Emitter and capacitor C₁Negative electrode of (2) and sixth switching tube S₆Is connected to the collector of the collector.

First switch tube S₁Emitter and second switch tube S₂Collector and capacitor C₂Positive electrode and third switching tube S₃Is connected to the collector of the collector.

Further, the first switch tube S₁Collector and diode D₂Cathode and capacitor C₁The positive electrodes of (a) and (b) are connected.

Third switch tube S₃Emitter and fourth switching tube S₄Collector and first filter inductor L₁Are connected at one end.

Fourth switch tube S₄Emitter and diode D₁Anode and capacitor C₂Are connected with each other.

Further, a first filter inductor L₁And the other end of the second switch is connected with the power grid.

Further, a diode D₁Is connected to the grid.

Furthermore, the switch tubes are all Insulated Gate Bipolar Transistors (IGBT).

Compared with the prior art, the utility model discloses the advantage that the circuit has does: the proposed inverter topology, which can generate at least five output voltage levels with only six unidirectional power switches, improves the power quality and reduces the size of the output filter. By means of the common ground, the negative terminal of the photovoltaic panel is directly connected to the zero point of the grid, the common mode voltage of the inverter can be made constant and the leakage current problem eliminated. The series-parallel switch conversion of the super capacitor unit can realize double boosting characteristics in single machine operation, and the peak value of the power grid voltage can be met by using a lower input voltage value.

Drawings

FIG. 1 is an attached drawing of the utility model

Fig. 2-7 are mode diagrams of operation within positive and negative half periods of the grid voltage.

Detailed Description

The present invention will be further described with reference to the accompanying drawings. Other details not relevant to the present invention have been omitted for the sake of clarity and conciseness. It should also be noted that the processes or symbols described below, if not specifically described in detail, are understood or implemented by those skilled in the art with reference to the prior art.

The circuit structure of the present invention is shown in fig. 1, and for the convenience of analyzing the circuit, the devices in the circuit structure are all regarded as ideal devices.

Fig. 2 to 7 are schematic diagrams of the operation of the photovoltaic inverter circuit in a time period, in which circuit components and connecting lines, which are not shown with respect to fig. 1, are in an off state in order to make the circuit representation more clear. Current path of zero level of output voltage during positive half cycle:

for fig. 2, to have the proposed inverter output voltage zero level in the positive half-cycle, three power switches S must be used₆，S₂And S₃And (5) closing. Thus, for parallel conducting state switch S in a supercapacitor cell₆Capacitor C₁Diode D of a supercapacitor cell by forward biasing₂Charging to an input direct voltage value (V) in each direction of the network current_dc)。C₂And disconnecting the power grid.

Current path of the first positive level of the inverter output voltage:

only two power switches S need to be turned compared to the zero level of the positive half-cycle output voltage₁And S₂A first positive level (+ V) of the output voltage is obtained_dc). As shown in fig. 3, the power switch S must be turned on again₆Can maintain C₁Charging operation of (2) while + V_dcBy means of a conducting switch S₁And S₃To the output of the inverter. Here, due to C₂The upcoming charging voltage causes the integrated power diode D₁Reverse biased and thus again excluded from the grid current flow path.

Current path of highest positive level of inverter output voltage:

in order to generate the highest positive level (+ 2V) of the output voltage_dc) As shown in fig. 4. In this case, the power switch S is connected in series in the supercapacitor cell₅Must be opened; c if the current polarity of the injected grid is positive (or negative)₁It is discharged (or charged). Thus, by S₁And S₃On state of (2), input voltage value and C₁The sum of the charging voltages across is converted to an output, producing 2V_dcThe voltage level of (c). Due to the power diode D₁Clamping of two endsThe voltage is positive; it operates in a forward biased state. Thus, depending on the current polarity of the injected grid, C may be adjusted₂Output voltage (+ 2V) charged to super capacitor unit_dc)。

Current path with zero output voltage in negative half cycle:

during operation of the proposed inverter in the negative half-cycle. With respect to fig. 5, the zero level of the output voltage can be produced again by a different current path. Here, the power switch S in the supercapacitor cell₅In the on state, the output voltage of the super capacitor unit will be equal to 2V_dc. Therefore, according to the current direction of the power grid, C can be controlled₁Charging or discharging is performed. Considering C₂(2V_dc) In consideration of S₁Power diode D₁Again in a forward biased state. Thus, can pass through D₁And S₄Again generating a zero level of the inverter output voltage, whereas C is the grid current direction₂Can be charged (or discharged) to 2V_dc。

Current path of a first negative level of the inverter output voltage:

consider FIG. 6 because of the early stage C₂Charging voltage value (2V)_dc) Power diode D₁Will be in a reverse biased state. Thus, with S₆To this end, the output voltage of the supercapacitor cell will be equal to V_dc. Thus, by the switch S being turned on₁And S₄，-V_dcWill be converted to an output independent of the network current direction, C₁Will be charged again to V_dc。

Current path of highest negative level of inverter output voltage:

finally, in order to maximize the negative level (-2V) of the proposed inverter output voltage_dc) Fig. 7 must be considered.

It is clear from the depicted current flow paths, although in each instance of grid current polarity, C₁Can pass through the power switch S in the conducting state₆Charging to V_dcBut, however, doIs a power switch S which can be disconnected by a super capacitor unit₁And disconnecting the power grid. In this case, therefore, the power switches S are switched on simultaneously₂And S₄The output power is from C₂Is provided only directly.

From the above analysis, the maximum value of the output voltage of the inverter is 2V_dcThis reflects the dual voltage boost function of the proposed topology. In order to meet the peak voltage of the grid, the required value of the input voltage is much lower (at least 160V for a maximum voltage of the grid based on 311V). At least five output voltage levels can be generated by only six unidirectional power switches, the power quality is improved, the size of an output filter is reduced, and the peak value of the power grid voltage is met by using a lower input voltage value.

Claims

1. A six-switch boosting common-ground five-level inverter device is characterized by comprising a direct-current power supply, two capacitors, eight diodes, six Insulated Gate Bipolar Transistors (IGBT), a filter inductor and a power grid, wherein the positive electrode of the output side of the direct-current power supply and a diode D₂Anode and fifth switch tube S₅Is connected with the collector of the first switching tube S, the output cathode of the direct current power supply is connected with the sixth switching tube S₆Emitter and grid zero and second switch tube S₂Emitter and diode D₁The cathodes are connected; fifth switch tube S₅Emitter and capacitor C₁Negative electrode of (2) and sixth switching tube S₆The collector electrodes are connected; first switch tube S₁Emitter and second switch tube S₂Collector and capacitor C₂Positive electrode and third switching tube S₃The collector electrodes are connected; first switch tube S₁Collector and diode D₂Cathode and capacitor C₁The positive electrodes of the two electrodes are connected; third switch tube S₃Emitter and fourth switching tube S₄Collector and first filter inductor L₁One end of the two ends are connected; fourth switch tube S₄Emitter and diode D₁Anode and capacitor C₂The negative electrodes are connected; first filter inductor L₁The other end of the power grid is connected with a power grid; diode D₁Is connected to the grid.

2. A six-switch boost common-ground five-level inverter apparatus according to claim 1, characterized in that the apparatus connects the negative terminal of the photovoltaic panel directly to the zero point of the grid through common ground.

3. A six-switch boost common-ground five-level inverter apparatus according to claim 1, characterized in that only six unidirectional power switches are used.