CN212033777U

CN212033777U - Improved non-isolated photovoltaic inverter device

Info

Publication number: CN212033777U
Application number: CN202020973451.4U
Authority: CN
Inventors: 李文娟; 李佳航
Original assignee: Harbin University of Science and Technology
Current assignee: Harbin University of Science and Technology
Priority date: 2020-06-01
Filing date: 2020-06-01
Publication date: 2020-11-27
Anticipated expiration: 2030-06-01

Abstract

The utility model discloses a modified non-isolated form photovoltaic inverter device, including photovoltaic array, seven Insulated Gate Bipolar Transistors (IGBT), seven diodes, an electric capacity, two buffer circuit, two filter inductance and electric wire netting because have single direct current side electricity in the circuitThe problem of voltage unbalance caused by two or more capacitors in the traditional circuit can be solved, and a seventh switching tube S is added in the circuit₇And the two buffer circuits can keep the common-mode voltage constant in a working period, and can effectively inhibit common-mode leakage current in a system. The utility model discloses the circuit has ensured that dc-to-ac converter and photovoltaic grid-connected system can normally operate steadily, makes photovoltaic grid-connected system have higher reliability and security.

Description

Improved non-isolated photovoltaic inverter device

Technical Field

The utility model relates to a photovoltaic grid-connected inverter field, concretely relates to non-isolated form photovoltaic inverter device of modified.

Background

At present, fossil energy is a main energy source of all countries in the world, the total storage amount of the fossil energy is limited, the problem of environmental pollution is easily caused in the development and utilization process, all countries in the world is promoted to accelerate the pace of upgrading and transformation of energy industry, and solar energy has the characteristics of no pollution, large total amount and wide distribution, and is an ideal choice for large-scale utilization. The photovoltaic inverter is a key link of photovoltaic grid connection, and the traditional photovoltaic inverter has the defects of large volume, low efficiency and high cost due to the isolation transformer. Therefore, the non-isolated photovoltaic inverter is greatly developed by virtue of unique advantages, when the non-isolated photovoltaic inverter works normally, a leakage current loop is formed between an inverter system, a power grid and the ground, if the non-isolated photovoltaic inverter does not inhibit, the leakage current in the system can cause grid-connected current distortion, the system loss is increased, and even the personal safety is threatened. The suppression or elimination of the common mode leakage current is a key problem which must be solved by a non-isolated photovoltaic inverter.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to overcome prior art's is not enough, provides a modified non-isolated form photovoltaic inverter device, has realized the suppression to the leakage current.

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

the utility model provides a circuit includes photovoltaic array, electric capacity C_dcSeven 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 S₆Seventh switching tube S₇A first filter inductor L₁A second filter inductor L₂Two buffer circuits, electric wire netting.

Photovoltaic array output side anode and capacitor C_dcPositive and fifth switch tube S₅Is connected with the collector, the negative electrode at the output side of the photovoltaic array is connected with a capacitor C_dcNegative electrode and sixth switching tube S₆Are connected.

First switch tube S₁A second switch tube S₂A third switch tube S₃And a fourth switching tube S₄Form a conventional H-type inverterBridge connection mode.

Seventh switching tube S₇Is connected with the fifth switch tube S₅Emitter and first switching tube S₁Collector electrode of (1), seventh switching tube S₇Is connected with a sixth switching tube S₆Collector and third switching tube S₃I.e. in parallel with the H inverter bridge at the back end of the circuit.

Further, the buffer circuit includes a resistor R_sAnd a capacitor C_sThe constant common-mode voltage of the circuit can be ensured during the freewheeling period without fluctuation, and the fifth switch tube S can be reduced₅And a sixth switching tube S₆Switching losses of (2).

Further, a first filter inductor L₁One end of (1) and a first switch tube S₁Is connected with the other end of the second filter inductor L, and the other end of the second filter inductor L is connected with a power grid₂One end of the first switch tube and the fourth switch tube S₄The other end is connected with the power grid.

Further, a first filter inductor L₁Value of and second filter inductance L₂Are equal in value.

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 inverter topology has a single direct current side capacitor, and solves the problem of voltage unbalance caused by two or more capacitors in the traditional circuit. By adding a seventh switch tube S in the circuit₇And the two buffer circuits can keep the common-mode voltage constant in a working period, can effectively inhibit common-mode leakage current, and simultaneously improve the efficiency of the photovoltaic grid-connected power generation system.

Drawings

Fig. 1 is an abstract attached drawing of the utility model.

Fig. 2a-2d 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 be noted that the processes and symbols described below, if not otherwise specified, 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. 2a to 2b are diagrams of the operating modes 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. The network voltage is divided into positive and negative half periods, and the first switch tube S is arranged in the positive half period₁Is always in a conducting state, and the third switch tube S₃Is always in the off state. When the modulated wave is larger than the carrier wave, the fourth switch tube S₄The fifth switch tube S₅And a sixth switching tube S₆Conducting the second switch tube S₂And a seventh switching tube S₇Turn off, when the modulated wave is less than the carrier wave, the second switch tube S₂And a seventh switching tube S₇Conducting the fourth switching tube S₄The fifth switch tube S₅And a sixth switching tube S₆And (6) turning off. Namely the fourth switch tube S₄The fifth switch tube S₅The sixth switching tube S₆And a second switch tube S₂Seventh switching tube S₇The switching timings are complementary.

In the negative half period, the second switch tube S₂Is always in a conducting state, and the fourth switching tube S₄Is always in the off state. When the modulated wave is larger than the carrier wave, the third switch tube S₃The fifth switch tube S₅And a sixth switching tube S₆Conducting the first switch tube S₁And a seventh switching tube S₇Turn off, when the modulated wave is less than the carrier wave, the first switch tube S₁And a seventh switching tube S₇Conducting, third switch tube S₃The fifth switch tube S₅And a sixth switching tube S₆And (6) turning off. I.e. the first switch tube S₁Seventh switching tube S₇And a third switch tube S₃The fifth switch tube S₅The sixth switching tube S₆The switching timings are complementary.

The suppression of the common mode leakage current is one of the research focuses of the non-isolated photovoltaic inverter, and is mainly caused by the fluctuation of the common mode voltage.

In the system, V is selected by selecting a common point (0), V, on the negative terminal of the DC bus voltage_A0Is the voltage difference between inverter terminal a and common point (0). V_B0Is the voltage difference between inverter terminal B and common point (0), common mode voltage V_cmIs a V_A0And V_B0Half of the sum.

And defining the photovoltaic inverter circuit as a first working mode when the photovoltaic inverter circuit works in the positive half period of the grid voltage. As shown in fig. 2a, this stage: first switch tube S₁And a fourth switching tube S₄The fifth switch tube S₅The sixth switching tube S₆Conducting the second switch tube S₂A third switch tube S₃Seventh switching tube S₇And (6) turning off. Grid-connected current flows through the positive electrode of the direct current side and the fifth switching tube S₅A first switch tube S₁A first filter inductor L₁AC side power grid and second filter inductor L₂And a fourth switching tube S₄The sixth switching tube S₆And the direct current side negative electrode form a closed loop. During this period, the common mode voltage is 0.5V_dc。

And defining the photovoltaic inverter circuit to work in a follow current state as a second working mode. As shown in fig. 2b, at this stage: first switch tube S₁A second switch tube S₂Seventh switching tube S₇Conducting, third switch tube S₃And a fourth switching tube S₄The fifth switch tube S₅The sixth switching tube S₆And (6) turning off. The current in the circuit flows through the positive electrode of the direct current side, the buffer and the seventh switch tube S₇And a DC-side negative electrode. The current in the other closed loop flows through the first filter inductor L₁AC side power grid and second filter inductor L₂A second switch tube S₂And the first switch tube S₁. During this period, the common mode voltage is 0.5V_dc。

The photovoltaic is carried outThe inverter circuit works in the negative half period of the grid voltage and is defined as a working mode three. As shown in fig. 2c, this stage: a second switch tube S₂A third switch tube S₃The fifth switch tube S₅The sixth switching tube S₆Conducting the first switch tube S₁And a fourth switching tube S₄Seventh switching tube S₇And (6) turning off. Grid-connected current flows through the positive electrode of the direct current side and the fifth switching tube S₅A second switch tube S₂A second filter inductor L₂AC side power grid, first filter inductor L₁A third switch tube S₃The sixth switching tube S₆And the direct current side negative electrode form a closed loop. During this period, the common mode voltage is 0.5V_dc。

The photovoltaic inverter circuit is defined as a fourth working mode when working in a follow current state. As shown in fig. 2d, this stage: first switch tube S₁A second switch tube S₂Seventh switching tube S₇Conducting, third switch tube S₃And a fourth switching tube S₄The fifth switch tube S₅The sixth switching tube S₆And (6) turning off. The current in the circuit flows through the positive electrode of the direct current side, the buffer and the seventh switch tube S₇And a DC-side negative electrode. The current in the other closed loop flows through the second filter inductor L₂AC side power grid, first filter inductor L₁A first switch tube S₁And the second switch tube S₂. During this period, the common mode voltage is 0.5V_dc。

From the above analysis, the common mode voltage V_cm＝0.5V_dcThe constant current source voltage is kept constant in the whole working period, so that the common-mode leakage current can be well inhibited, the quality of system output waveforms is improved, and the safety and the stability of the system are improved.

Claims

1. The improved non-isolated photovoltaic inverter device is characterized in that a main circuit structure comprises a photovoltaic array, seven Insulated Gate Bipolar Transistors (IGBTs), seven diodes, a capacitor, two buffer circuits, two filter inductors and a power grid, wherein the positive electrode of the output side of the photovoltaic array and a capacitor C_dcPositive and fifth switch tube S₅Is connected with the collector, the negative electrode at the output side of the photovoltaic array is connected with a capacitor C_dcNegative electrode and sixth switching tube S₅The emitting electrodes are connected; seventh switching tube S₇Is connected with the fifth switch tube S₅Emitter and first switching tube S₁Collector electrode of (1), seventh switching tube S₇Is connected with the sixth switching tube S₆Collector and third switching tube S₃An emitter of (1); first switch tube S₁A second switch tube S₂A third switch tube S₃And a fourth switching tube S₄Forming an H-shaped inverter bridge connection mode; first inductance L₁One end of (1) and a first switch tube S₁Is connected with the other end of the first inductor L, and the other end of the second inductor L is connected with a power grid₂One end of the first switch tube and the fourth switch tube S₄The other end is connected with the power grid.

2. The improved non-isolated pv inverter apparatus of claim 1 wherein the first filter inductor L₁Value of and second filter inductance L₂Are equal in value.

3. The improved non-isolated photovoltaic inverter device according to claim 1, wherein the switching tubes are Insulated Gate Bipolar Transistors (IGBTs).

4. The improved non-isolated photovoltaic inverter device according to claim 1, wherein a seventh switching tube S in the circuit₇And the two buffer circuits can keep the common-mode voltage constant and effectively restrain the common-mode leakage current.