阅读说明：本技术 一种光伏逆变器及其控制方法 (Photovoltaic inverter and control method thereof ) 是由 姚志垒 于 2020-05-20 设计创作，主要内容包括：本发明公开了一种光伏逆变器,包括：光伏组件、中间电容、第一滤波电感、第二滤波电感、第三滤波电感、第一二极管、第二二极管、第一开关管、第二开关管、第三开关管、第四开关管以及驱动控制电路；第一滤波电感、第二滤波电感、第三滤波电感只在半个工频周期工作,第一开关管和第二开关管分别为电网电压的负半周和正半周高频开关,第三开关管和第四开关管工频开关。本发明通过控制第一滤波电感和第二滤波电感的电流值,从而保证了电网电流与电网电压同频同相,实现了单位功率因数输出,同时电网的每半个工频周期只有1个开关管高频开关,从而降低了开关损耗,提高了系统变换效率。本发明的光伏逆变器无共模漏电流,且具有高可靠性。(The invention discloses a photovoltaic inverter, comprising: the photovoltaic module comprises a photovoltaic module, an intermediate capacitor, a first filter inductor, a second filter inductor, a third filter inductor, a first diode, a second diode, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a drive control circuit; the first filter inductor, the second filter inductor and the third filter inductor work in a half power frequency period only, and the first switch tube and the second switch tube are respectively a negative half-cycle high-frequency switch and a positive half-cycle high-frequency switch of the power grid voltage, and the third switch tube and the fourth switch tube are respectively a power frequency switch. The invention ensures that the current of the power grid and the voltage of the power grid are in the same frequency and phase by controlling the current values of the first filter inductor and the second filter inductor, realizes the output of unit power factor, and simultaneously, only 1 switch tube high-frequency switch is arranged in each half power frequency period of the power grid, thereby reducing the switching loss and improving the conversion efficiency of the system. The photovoltaic inverter disclosed by the invention has no common-mode leakage current and high reliability.)

1. A photovoltaic inverter, comprising:

the negative electrode of the photovoltaic module is connected with the negative electrode of the power grid and is grounded together with the power grid, and the photovoltaic module is used for providing electric energy for the photovoltaic inverter;

the anode of the intermediate capacitor is connected with the cathode of the photovoltaic module, and the intermediate capacitor is used for providing current for the negative half cycle work of the power frequency cycle of the grid voltage;

the first end of the first filter inductor is connected with the anode of the photovoltaic component through a first switch tube, the second end of the first filter inductor is respectively connected with the cathode of the photovoltaic component and the anode of the intermediate capacitor, and the first filter inductor, the photovoltaic component and the first switch tube are connected in series to form a first loop;

the first end of the second filter inductor is connected with the anode of the photovoltaic module through a second switch tube, the second end of the second filter inductor is connected with the cathode of the photovoltaic module through a power grid, and the second filter inductor is connected with the power grid, the photovoltaic module and the second switch tube in series to form a second loop;

a first end of the third filter inductor is connected with the anode of the intermediate capacitor through a power grid, a second end of the third filter inductor is connected with the cathode of the intermediate capacitor through a third switching tube, and the third filter inductor is connected with the third switching tube, the intermediate capacitor and the power grid in series to form a third loop;

the first end of the first filter inductor is also connected with the first end of a first diode, the second end of the first diode is connected with the negative electrode of the intermediate capacitor, and the first filter inductor, the intermediate capacitor and the first diode are connected in series to form a first follow current loop;

the first end of the second filtering inductor is also connected with the first end of a second diode, the second end of the second diode is connected with the negative electrode of the power grid through a fourth switching tube, and the second filtering inductor is connected with the power grid, the fourth switching tube and the second diode in series to form a second follow current loop;

and the input end of the control driving unit is respectively connected with the power grid, the photovoltaic module, the first filter inductor and the second filter inductor, and the output end of the control driving unit is respectively connected with the first switch tube, the second switch tube, the third switch tube and the fourth switch tube and is used for driving and controlling the switch of each switch tube so as to drive and adjust the current information of the power grid.

2. The pv inverter of claim 1 further comprising a filter connected in parallel with the pv module for filtering voltage information of the pv module, wherein the filter employs a filter capacitor.

3. The photovoltaic inverter of claim 1, wherein the first loop is a negative half cycle operating loop of a power frequency cycle of the grid voltage; the second loop is a positive half cycle working loop of a power frequency cycle of the power grid voltage; the third loop is a negative half cycle working loop of a power frequency cycle of the power grid voltage; the first follow current loop is a negative half cycle working loop of a power frequency cycle of the power grid voltage; the second follow current loop is a positive half cycle working loop of a power frequency cycle of the power grid voltage; the first switch tube is a high-frequency switch of the negative half cycle of the power grid voltage power frequency cycle, the second switch tube is a high-frequency switch of the positive half cycle of the power grid voltage power frequency cycle, the third switch tube is a power frequency switch of the negative half cycle of the power grid voltage power frequency cycle, and the fourth switch tube is a power frequency switch of the positive half cycle of the power grid voltage power frequency cycle.

4. The photovoltaic inverter according to claim 1, wherein the first switching tube, the second switching tube, the third switching tube and the fourth switching tube are MOS tubes and/or IGBTs.

5. A photovoltaic inverter as claimed in claim 1, wherein the control drive unit comprises:

the sensor system is respectively connected with the power grid, the photovoltaic module, the first filter inductor and the second filter inductor and is used for outputting a voltage feedback signal of the power grid, a voltage feedback signal of the photovoltaic module, a current feedback signal of the first filter inductor and a current feedback signal of the second filter inductor;

the digital signal processor is connected with the sensor system and used for generating a current reference signal of the first filter inductor and a current reference signal of the second filter inductor according to a voltage feedback signal of a power grid, a voltage feedback signal of the photovoltaic module and a current feedback signal of the photovoltaic module;

the control circuit is respectively connected with the sensor system and the digital signal processor and is used for respectively generating switching logic signals of the first switching tube, the second switching tube, the third switching tube and the fourth switching tube according to a voltage feedback signal of a power grid, a current feedback signal of the first filter inductor and a current feedback signal of the second filter inductor which are output by the sensor system, and a current reference signal of the first filter inductor and a current reference signal of the second filter inductor which are output by the digital signal processor;

and the driving circuit is connected with the control circuit and used for respectively generating a driving signal of the first switching tube, a driving signal of the second switching tube, a driving signal of the third switching tube and a driving signal of the fourth switching tube according to the switching logic signals of the first switching tube, the second switching tube, the third switching tube and the fourth switching tube and driving and controlling the switching of each switching tube.

6. A photovoltaic inverter according to claim 5, wherein the sensor system comprises:

the input end of the first current sensor is connected with the first filter inductor, and the output end of the first current sensor is connected with the driving control unit, and the first current sensor is used for acquiring current information of the first filter inductor and outputting a current feedback signal of the first filter inductor;

the input end of the second current sensor is connected with the second filter inductor, and the output end of the second current sensor is connected with the driving control unit and used for acquiring current information of the second filter inductor and outputting a current feedback signal of the second filter inductor;

the input end of the third current sensor is connected with the photovoltaic module, and the output end of the third current sensor is connected with the driving control unit and used for collecting current information of the photovoltaic module and outputting a current feedback signal of the photovoltaic module;

the input end of the first voltage sensor is connected with the power grid, and the output end of the first voltage sensor is connected with the driving control unit and used for acquiring voltage information of the power grid and outputting a voltage feedback signal of the power grid;

and the input end of the second voltage sensor is connected with the photovoltaic module, and the output end of the second voltage sensor is connected with the driving control unit, and is used for acquiring the voltage information of the photovoltaic module and outputting a voltage feedback signal of the photovoltaic module.

7. A control method for controlling the photovoltaic inverter of any one of claims 1 to 6, characterized by comprising the steps of:

the photovoltaic module charges the capacitance of the intermediate capacitor through the first filter inductor, and adjusts the voltage of the intermediate capacitor to provide voltage for the negative half-cycle work of the power grid;

the power frequency period of the power grid voltage is determined by judging the sign of the power grid voltage feedback signal, and the on/off of a switching tube in the corresponding working period of the power grid voltage is driven and controlled, so that the current of the second filter inductor during the positive half-cycle working of the power grid voltage or the current of the third filter inductor during the negative half-cycle working of the power grid voltage is adjusted, and the power grid current is stably output.

8. The method according to claim 7, wherein the step of adjusting the voltage of the intermediate capacitor comprises the steps of:

the control driving unit controls the first switch tube to be conducted, and the first loop is conducted, so that the first filter inductor stores energy;

collecting a current feedback signal of the first filter inductor in real time, and comparing the current feedback signal with a current reference signal of the first filter inductor;

if the current feedback signal of the first filter inductor is greater than the current reference signal of the first filter inductor, the control driving unit controls the first switch tube to be turned off, and the first follow current loop is conducted, so that the intermediate capacitor is charged, and voltage is provided for negative half-cycle work of a power grid.

9. The method according to claim 7, wherein the step of adjusting the current of the second filter inductor during the positive half-cycle operation of the grid voltage or the current of the third filter inductor during the negative half-cycle operation of the grid voltage comprises the following steps:

monitoring the voltage of the power grid in real time, and judging the sign of a voltage feedback signal of the power grid;

if the voltage feedback signal of the power grid is a positive value, controlling the switch of the second switch tube and/or the fourth switch tube through the control driving unit so as to adjust the current of the second filter inductor, and enabling the current of the second filter inductor to track the reference current of the second filter inductor;

if the voltage feedback signal of the power grid is a negative value, the driving unit is controlled to control the third switching tube and/or the first switching tube to be switched on and switched off, so that the current of the third filter inductor is adjusted, and the current of the first filter inductor tracks the reference current of the first filter inductor.

10. The method according to claim 9, wherein when the voltage feedback signal of the grid is a positive value, the method specifically includes the following steps:

the control driving unit controls the fourth switching tube to be conducted, and other switching tubes are turned off;

then, the second current sensor collects a current feedback signal of the second filter inductor in real time and compares the current feedback signal with a current reference signal of the second filter inductor;

if the current feedback signal of the second filter inductor is smaller than the current reference signal of the second filter inductor, the control driving unit controls the conduction of the second switching tube, and the conduction of the second loop regulates the current increase of the second filter inductor;

if the current feedback signal of the second filter inductor is greater than the current reference signal of the second filter inductor, the control driving unit controls the second switching tube to be switched off, and the second follow current loop is switched on so as to adjust the current of the second filter inductor to be reduced;

when the voltage feedback signal of the power grid is a negative value, the method specifically comprises the following steps:

the control driving unit controls the third switching tube to be conducted, other switching tubes are turned off, and the third loop is conducted;

then, the first current sensor collects a current feedback signal of the first filter inductor in real time and compares the current feedback signal with a current reference signal of the first filter inductor;

if the current feedback signal of the first filter inductor is smaller than the current reference signal of the first filter inductor, the control driving unit controls the first switch tube to be conducted, the first loop is conducted, so that the first filter inductor stores energy, and the third loop regulates the current increase of the third filter inductor;

if the current feedback signal of the first filter inductor is greater than the current reference signal of the first filter inductor, the control driving unit controls the first switch tube to be turned off, the first follow current loop is conducted, so that the first filter inductor charges the intermediate capacitor, and the third loop adjusts the current of the third filter inductor to be reduced.

Technical Field

The invention relates to the technical field of photovoltaics, in particular to a photovoltaic inverter and a control method thereof.

Background

Since the non-isolated photovoltaic inverter has no isolation between the photovoltaic module and the grid, common mode leakage current may be generated through the parasitic capacitance to ground of the photovoltaic module. The common mode leakage current can cause electromagnetic interference, increase system loss and even threaten the personal safety series connection. The german VDE012611 standard specifies that the effective value of the common-mode leakage current of the non-isolated photovoltaic inverter should be less than 300 mA. If the system detects that it exceeds this value, the non-isolated photovoltaic inverter will shut down.

Experts and scholars at home and abroad develop a series of effective researches on how to inhibit the common-mode leakage current of the non-isolated photovoltaic inverter. The common methods are as follows: improved modulation techniques, increased switching devices, increased filters, and improved control methods, among others. However, the effect of suppressing the common mode leakage current by the above method is easily affected by the variation of the parasitic capacitance of the photovoltaic module to the ground and the circuit parameters, so it is necessary to research an inverter topology and a control method thereof capable of fundamentally eliminating the common mode leakage current.

Disclosure of Invention

The invention provides a photovoltaic inverter capable of effectively eliminating common-mode leakage current of a non-isolated photovoltaic inverter and a control method thereof.

In order to achieve the above object, the present invention provides a photovoltaic inverter including: the photovoltaic module comprises a photovoltaic module, an intermediate capacitor, a first filter inductor, a second filter inductor, a third filter inductor, a first diode, a second diode, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a drive control circuit;

the photovoltaic module is used for providing electric energy for a topological circuit of the photovoltaic inverter, the negative electrode of the photovoltaic module is connected with the negative electrode of a power grid, and the photovoltaic module and the power grid are grounded together, so that common-mode leakage current of the photovoltaic inverter can be eliminated;

the intermediate capacitor is used for providing current for the negative half cycle work of the power frequency cycle of the power grid voltage, and the anode of the intermediate capacitor is connected with the cathode of the photovoltaic module;

the first end of the first filter inductor is connected with the anode of the photovoltaic module through a first switch tube, the second end of the first filter inductor is respectively connected with the cathode of the photovoltaic module and the anode of the intermediate capacitor, the first filter inductor is connected with the photovoltaic module and the first switch tube in series to form a first loop, and the first loop is a negative half-cycle working loop of a power frequency cycle of a power grid voltage;

the first end of the second filter inductor is connected with the anode of the photovoltaic module through a second switch tube, the second end of the second filter inductor is connected with the cathode of the photovoltaic module through a power grid, the second filter inductor is connected with the power grid, the photovoltaic module and the second switch tube in series to form a second loop, and the second loop is a positive half-cycle working loop of a power grid voltage power frequency cycle;

the first end of the third filter inductor is connected with the anode of the intermediate capacitor through a power grid, the second end of the third filter inductor is connected with the cathode of the intermediate capacitor through a third switching tube, the third filter inductor is connected with the third switching tube, the intermediate capacitor and the power grid in series to form a third loop, and the third loop is a negative half-cycle working loop of a power grid voltage power frequency cycle;

the first end of the first filter inductor is also connected with the first end of a first diode, the second end of the first diode is connected with the negative electrode of the intermediate capacitor, the first filter inductor, the intermediate capacitor and the first diode are connected in series to form a first follow current loop, and the first follow current loop is a negative half-cycle working loop of a power frequency cycle of the power grid voltage;

the first end of the second filter inductor is further connected with the first end of a second diode, the second end of the second diode is connected with the negative electrode of the power grid through a fourth switching tube, the second filter inductor is connected with the power grid, the fourth switching tube and the second diode in series to form a second follow current loop, and the second follow current loop is a positive half-cycle working loop of the power grid voltage power frequency cycle;

and the input end of the control driving unit is respectively connected with the power grid, the photovoltaic module, the first filter inductor and the second filter inductor, and the output end of the control driving unit is respectively connected with the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, and is used for driving and controlling the switch of each switch tube so as to drive and adjust the current information of the power grid.

Preferably, the photovoltaic inverter further includes a filter, and the filter is connected in parallel with the photovoltaic module and is configured to filter voltage information of the photovoltaic module.

Preferably, the filter adopts a filter capacitor.

Preferably, the first switching tube, the second switching tube, the third switching tube and the fourth switching tube adopt MOS tubes and/or IGBTs.

Preferably, the first switch tube is a high-frequency switch of a negative half cycle of a power grid voltage power frequency cycle, the second switch tube is a high-frequency switch of a positive half cycle of the power grid voltage power frequency cycle, the third switch tube is a power frequency switch of the negative half cycle of the power grid voltage power frequency cycle, and the fourth switch tube is a power frequency switch of the positive half cycle of the power grid voltage power frequency cycle.

Preferably, the intermediate capacitor and the filter capacitor are polar capacitors or non-polar capacitors.

Preferably, the control driving unit includes:

the sensor system is respectively connected with the power grid, the photovoltaic module, the first filter inductor and the second filter inductor and is used for outputting a voltage feedback signal of the power grid, a voltage feedback signal of the photovoltaic module, a current feedback signal of the first filter inductor and a current feedback signal of the second filter inductor;

the digital signal processor is connected with the sensor system and used for generating a current reference signal of the first filter inductor and a current reference signal of the second filter inductor according to a voltage feedback signal of a power grid, a voltage feedback signal of the photovoltaic module and a current feedback signal of the photovoltaic module;

the control circuit is respectively connected with the sensor system and the digital signal processor and is used for respectively generating switching logic signals of the first switching tube, the second switching tube, the third switching tube and the fourth switching tube according to a voltage feedback signal of a power grid, a current feedback signal of the first filter inductor and a current feedback signal of the second filter inductor which are output by the sensor system, and a current reference signal of the first filter inductor and a current reference signal of the second filter inductor which are output by the digital signal processor;

and the driving circuit is connected with the control circuit and used for respectively generating a driving signal of the first switching tube, a driving signal of the second switching tube, a driving signal of the third switching tube and a driving signal of the fourth switching tube according to the switching logic signals of the first switching tube, the second switching tube, the third switching tube and the fourth switching tube and driving and controlling the switching of each switching tube.

Preferably, the sensor system comprises:

the input end of the first current sensor is connected with the first filter inductor, and the output end of the first current sensor is connected with the driving control unit, and the first current sensor is used for acquiring current information of the first filter inductor and outputting a current feedback signal of the first filter inductor;

the input end of the second current sensor is connected with the second filter inductor, and the output end of the second current sensor is connected with the driving control unit and used for acquiring current information of the second filter inductor and outputting a current feedback signal of the second filter inductor;

the input end of the third current sensor is connected with the photovoltaic module, and the output end of the third current sensor is connected with the driving control unit and used for collecting current information of the photovoltaic module and outputting a current feedback signal of the photovoltaic module;

the input end of the first voltage sensor is connected with the power grid, and the output end of the first voltage sensor is connected with the driving control unit and used for acquiring voltage information of the power grid and outputting a voltage feedback signal of the power grid;

and the input end of the second voltage sensor is connected with the photovoltaic module, and the output end of the second voltage sensor is connected with the driving control unit, and is used for acquiring the voltage information of the photovoltaic module and outputting a voltage feedback signal of the photovoltaic module.

The invention also provides a control method of the photovoltaic inverter, which comprises the following steps:

the photovoltaic module charges the capacitance of the intermediate capacitor through the first filter inductor, and adjusts the voltage of the intermediate capacitor to provide voltage for the negative half-cycle work of the power grid;

the power frequency period of the power grid voltage is determined by judging the sign of the power grid voltage feedback signal, the on-off of a switching tube in the corresponding working period of the power grid voltage is driven and controlled, and the current of a second filter inductor during the positive half-cycle working of the power grid voltage or the current of a third filter inductor during the negative half-cycle working of the power grid voltage is adjusted, so that the power grid current is stably output.

Preferably, the adjusting the voltage of the intermediate capacitor specifically includes the following steps:

the control driving unit controls the first switch tube to be conducted, and the first loop is conducted, so that the first filter inductor stores energy;

collecting a current feedback signal of the first filter inductor in real time, and comparing the current feedback signal with a current reference signal of the first filter inductor;

if the current feedback signal of the first filter inductor is greater than the current reference signal of the first filter inductor, the control driving unit controls the first switch tube to be turned off, and the first follow current loop is conducted, so that the intermediate capacitor is charged, and voltage is provided for negative half-cycle work of a power grid.

Preferably, the adjusting of the current of the second filter inductor when the positive half cycle of the grid voltage works or the current of the third filter inductor when the negative half cycle of the grid voltage works specifically includes the following steps:

monitoring the voltage of the power grid in real time, and judging the sign of a voltage feedback signal of the power grid;

if the voltage feedback signal of the power grid is a positive value, controlling the switching of the second switching tube and the fourth switching tube through the control driving unit so as to adjust the current of the second filter inductor, so that the current of the second filter inductor tracks the reference current of the second filter inductor;

if the voltage feedback signal of the power grid is a negative value, the driving unit is controlled to control the third switching tube and the first switching tube to be switched on and off, so that the current of the third filter inductor is adjusted, and the current of the first filter inductor tracks the reference current of the first filter inductor.

Preferably, when the voltage feedback signal of the power grid is a positive value, the method specifically includes the following steps:

the control driving unit controls the fourth switching tube to be conducted, and other switching tubes are turned off;

then, the second current sensor collects a current feedback signal of the second filter inductor in real time and compares the current feedback signal with a current reference signal of the second filter inductor;

if the current feedback signal of the second filter inductor is smaller than the current reference signal of the second filter inductor, the control driving unit controls the conduction of the second switching tube, and the conduction of the second loop regulates the current increase of the second filter inductor;

if the current feedback signal of the second filter inductor is greater than the current reference signal of the second filter inductor, the control driving unit controls the second switching tube to be turned off, and the second follow current loop is conducted so as to adjust the current reduction of the second filter inductor.

Preferably, when the voltage feedback signal of the power grid is a negative value, the method specifically includes the following steps:

the control driving unit controls the third switching tube to be conducted, other switching tubes are turned off, and the third loop is conducted;

then, the first current sensor collects a current feedback signal of the first filter inductor in real time and compares the current feedback signal with a current reference signal of the first filter inductor;

if the current feedback signal of the first filter inductor is smaller than the current reference signal of the first filter inductor, the control driving unit controls the first switch tube to be conducted, the first loop is conducted, so that the first filter inductor stores energy, and the third loop regulates the current increase of the third filter inductor;

if the current feedback signal of the first filter inductor is greater than the current reference signal of the first filter inductor, the control driving unit controls the first switch tube to be turned off, the first follow current loop is conducted, so that the first filter inductor charges the intermediate capacitor, and the third loop adjusts the current reduction of the third filter inductor.

The invention has the following advantages:

the photovoltaic module and the power grid are grounded together, common mode leakage current of the photovoltaic inverter can be effectively eliminated, the first switch tube and the second switch tube are respectively high-frequency switches of a negative half cycle and a positive half cycle of a power grid voltage power frequency cycle, only one switch tube works in each half power frequency cycle of the power grid, loss of the switch tubes is reduced, meanwhile, the third switch tube and the fourth switch tube are respectively power frequency switches of the negative half cycle and the positive half cycle of the power grid voltage power frequency cycle, and conversion efficiency of the photovoltaic inverter system is improved. Meanwhile, the current values of the first filter inductor and the second filter inductor are controlled, so that the same frequency and phase of the power grid current and the power grid voltage are ensured, and the unit power factor output is realized.

Drawings

Fig. 1 is a circuit diagram of a photovoltaic inverter according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of a control driving unit of a photovoltaic inverter according to an embodiment of the present invention.

Detailed Description

The photovoltaic inverter and the control method thereof according to the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. Advantages and features of the present invention will become apparent from the following description and from the claims. It is to be noted that the drawings are in a very simplified form and are all used in a non-precise ratio for the purpose of facilitating and distinctly aiding in the description of the embodiments of the invention.

As shown in FIG. 1, the invention provides a photovoltaic inverter, which comprises a photovoltaic module PV, an intermediate capacitor C, and a first filter inductor L₁A second filter inductor L₂A third filter inductor L₃A first diode D₁A second diode D₂A first switch tube S₁A second switch tube S₂A third switch tube S₃And a fourth switching tube S₄A driving control circuit (not shown in FIG. 1) and a filter capacitor C_in。

The intermediate capacitor C and the filter capacitor C_inEither a polar capacitor or a non-polar capacitor is used.

The first switch tube S₁A second switch tube S₂A third switch tube S₃And a fourth switching tube S₄Using metal-oxide-semiconductor fieldsA Transistor of the active-Transistor (MOS) and/or an Insulated Gate Bipolar Transistor (IGBT). In this embodiment, the first switch tube S₁A second switch tube S₂A third switch tube S₃And a fourth switching tube S₄An MOS tube is adopted.

The negative electrode of the photovoltaic module PV is connected with the negative electrode of the power grid and is grounded together with the power grid, and the photovoltaic module PV is used for providing electric energy for a topological circuit of the photovoltaic inverter;

the photovoltaic module PV and the power grid are grounded together, and common-mode leakage current of the photovoltaic inverter can be effectively eliminated.

The positive electrode of the intermediate capacitor C is connected with the negative electrode of the photovoltaic module PV and is used for providing current for the negative half cycle work of the power frequency cycle of the grid voltage;

the filter capacitor C_inThe photovoltaic module PV is connected in parallel and used for filtering the voltage information of the photovoltaic module PV;

the first filter inductor L₁A first end thereof and a first switch tube S₁Is connected to the source of the first switching tube S₁The drain of which is connected with the anode of the photovoltaic module PV, and the second end of which is respectively connected with the cathode of the photovoltaic module PV and the anode of the intermediate capacitor C, and the first filter inductor L₁With photovoltaic module PV, first switching tube S₁The first loop is a negative half cycle working loop of a power frequency cycle of the power grid voltage;

the second filter inductor L₂A first end thereof and a second switch tube S₂Is connected to the source of the second switching tube S₂Is connected with the anode of the photovoltaic module PV, the second end of the second filter inductor L is connected with the cathode of the photovoltaic module PV through the power grid, and the second filter inductor L₂With the electric network, the photovoltaic module PV, the second switch tube S₂The second loop is a positive half cycle working loop of the power frequency cycle of the power grid voltage;

the third filter inductor L₃A first end of the capacitor is connected with the anode of the intermediate capacitor C through a power grid, and a second end of the capacitor is connected with the anode of the intermediate capacitor C through a power gridTwo terminals and a third switch tube S₃Is connected to the drain of the third switching tube S₃Is connected with the cathode of the middle capacitor C, and the third filter inductor L₃And a third switch tube S₃The intermediate capacitor C and the power grid are connected in series to form a third loop, and the third loop is a negative half-cycle working loop of a power grid voltage power frequency cycle;

the first filter inductor L₁The first terminal of the first diode and the first diode D₁Is connected to the first terminal of the first diode D₁Is connected with the negative pole of the middle capacitor C, and the first filter inductor L₁An intermediate capacitor C and a first diode D₁The first follow current loop is a negative half cycle working loop of a power frequency cycle of the grid voltage;

the second filter inductor L₂And a second diode D₂Is connected to the first terminal of the second diode D₂Second end and fourth switch tube S₄Is connected with the source electrode of the fourth switching tube S₄Is connected with the negative pole of the power grid, and the second filter inductor L₂And the power grid and a fourth switching tube S₄A second diode D₂The second follow current loop is a positive half cycle working loop of the power frequency cycle of the grid voltage;

the input end of the control drive unit is respectively connected with the power grid, the photovoltaic module PV and the first filter inductor L₁And a second filter inductor L₂Connected with output ends of the first switch tube S₁A second switch tube S₂A third switch tube S₃And a fourth switching tube S₄And the connection is used for driving and controlling the switch of each switch tube so as to drive and adjust the current information of the power grid.

The first switch tube is a high-frequency switch of a negative half cycle of a power grid voltage power frequency cycle, the second switch tube is a high-frequency switch of a positive half cycle of the power grid voltage power frequency cycle, only one switch tube works in each half power frequency cycle of the power grid, and loss of the switch tubes is reduced. The third switch tube is a power frequency switch of a negative half cycle of a power frequency cycle of the power grid voltage, the fourth switch tube is a power frequency switch of a positive half cycle of the power frequency cycle of the power grid voltage, the working frequency of the power frequency switch is equal to that of the power grid voltage, and the conversion efficiency of the photovoltaic inverter system can be effectively improved.

The control drive unit comprises:

sensor system 1, which is connected to the power grid, the photovoltaic module PV and the first filter inductor L, respectively₁And a second filter inductor L₂Connected for outputting a voltage feedback signal u of the grid_gfVoltage feedback signal u of photovoltaic module PV_infCurrent feedback signal i of photovoltaic module PV_infA first filter inductor L₁Current feedback signal i_L1fAnd a second filter inductor L₂Current feedback signal i_L2f；

A digital signal processor 2 connected to the sensor system 1 for feeding back a signal u depending on the voltage of the grid_gfVoltage feedback signal u of photovoltaic module PV_infCurrent feedback signal i of photovoltaic module PV_infGenerating a first filter inductance L₁Current reference signal i_{L1_ref}And a second filter inductor L₂Current reference signal i_{L2_ref}；

A control circuit 3 connected to the sensor system 1 and the digital signal processor 2 respectively for feeding back a signal u according to the voltage of the power grid output by the sensor system 1_gfA first filter inductor L₁Current feedback signal i_L1fA second filter inductor L₂Current feedback signal i_L2fAnd a first filter inductor L output by the digital signal processor 2₁Current reference signal i_{L1_ref}A second filter inductor L₂Current reference signal i_{L2_ref}Respectively generate a first switch tube S₁A second switch tube S₂A third switch tube S₃And a fourth switching tube S₄The switching logic signal of (1);

a driving circuit 4 connected with the control circuit 3 for switching the first switch tube S₁A second switch tube S₂And the third openingClosing pipe S₃And a fourth switching tube S₄Respectively generate a first switch tube S₁A second switching tube S₂Drive signal of, third switching tube S₃And the fourth switching tube S₄For drive-controlling the first switching tube S₁A second switch tube S₂A third switch tube S₃And a fourth switching tube S₄The switch of (2).

As shown in fig. 2, the sensor system 1 includes:

a first current sensor having an input connected to said first filter inductor L₁The output end of the connection is connected with the drive control unit and used for collecting L the first filter inductor₁And outputs the first filter inductor L₁Current feedback signal i_L1f；

A second current sensor having an input connected to said second filter inductor L₂The output end of the connection is connected with the drive control unit and used for collecting L the second filter inductor₂And outputs a second filter inductor L₂Current feedback signal i_L2f；

The input end of the third current sensor is connected with the photovoltaic module PV, the output end of the third current sensor is connected with the driving control unit, and the third current sensor is used for collecting current information of the photovoltaic module PV and outputting a current feedback signal i of the photovoltaic module PV_inf；

The input end of the first voltage sensor is connected with the power grid, the output end of the first voltage sensor is connected with the driving control unit, and the first voltage sensor is used for collecting voltage information of the power grid and outputting a voltage feedback signal u of the power grid_gf；

The input end of the second voltage sensor is connected with the photovoltaic module PV, the output end of the second voltage sensor is connected with the driving control unit, and the second voltage sensor is used for collecting the voltage information of the photovoltaic module PV and outputting a voltage feedback signal u of the photovoltaic module PV_inf；

The working principle of the digital signal processor 2 is as follows:

voltage of electric networkFeedback signal u_gfThe first analog-to-digital conversion module AD1 of the digital signal processor converts the first analog-to-digital conversion module AD1 into a first digital signal, and the first digital signal outputs the power grid voltage u through a phase-locked loop_gPhase of

Current feedback signal i of photovoltaic module PV_infVoltage feedback signal u of photovoltaic module PV_infRespectively converting the first digital signal and the second digital signal into a first digital signal and a second digital signal through a first analog-to-digital conversion module AD2 and a third analog-to-digital conversion module AD3 of a digital signal processor, and outputting a maximum reference current I through a Maximum Power Point Tracking (MPPT) algorithm_refmAnd input average current I_in；

From the mains voltage u_gPhase ofAnd a maximum reference current I_refmCalculating the second filter inductance L₂Current reference signal i_{L2_ref}The digital signal of (2);

second filter inductor L₂Current reference signal i_{L2_ref}The calculation formula of the digital signal is as follows:

from the mains voltage u_gPhase ofMaximum reference current I_refmAnd input average current I_inCalculating the first filter inductance L₁Current reference signal i_{L1_ref}The digital signal of (2);

first filter inductor L₁Current reference signal i_{L1_ref}The calculation formula of the digital signal is as follows:

second filter inductor L₂Current reference signal i_{L2_ref}Digital signal and first filter inductor L₁Current reference signal i_{L1_ref}The digital signal respectively passes through a first digital-to-analog conversion module DA1 and a second digital-to-analog conversion module DA2 of the digital signal processor to output a second filter inductor L₂Current reference signal i_{L2_ref}And a first filter inductor L₁Current reference signal i_{L1_ref}。

Preferably, the MPPT algorithm uses an algorithm such as a conductance increment method or a disturbance observation method.

The working principle of the control circuit 3 is as follows:

the first filter inductor L₁Current reference signal i_{L1_ref}And a first filter inductor L₁Current feedback signal i_L1fThe first switching tube S is output through a first current regulator after subtraction₁The switching logic signal of (1);

the second filter inductor L₂Current reference signal i_{L2_ref}And a second filter inductor L₂Current feedback signal i_L2fThe subtracted signals are output to a second switch tube S through a second current regulator₂The switching logic signal of (1);

the grid voltage feedback signal u_gfAnd the ground passing comparator outputs a fourth switching tube S₄The switching logic signal of (1);

the fourth switch tube S₄The switch logic signal is output to a third switch tube S through an inverter₃Switching logic signals of (1).

Preferably, the first current regulator and the second current regulator may adopt PI control, hysteresis control, proportional resonance control or the like.

Preferably, the output power factor of the photovoltaic inverter is 1.

The invention also provides a control method of the photovoltaic inverter, which comprises the following steps:

the photovoltaic module PV passes through a first filter inductor L₁The intermediate capacitance C is charged with a capacitance,adjusting the voltage of the intermediate capacitor C to provide voltage for the negative half-cycle work of the power grid;

by determining the grid voltage feedback signal u_gfThe sign of the voltage determines the power frequency period of the power grid voltage, drives and controls the on-off of a switching tube in the corresponding working period of the power grid voltage, and adjusts the second filter inductor L when the positive half cycle of the power grid voltage works₂Third filter inductor L during negative half-cycle operation of current or grid voltage₃Such that the grid current i_gAnd (5) stabilizing the output.

Preferably, the adjusting the voltage of the intermediate capacitor C specifically comprises the following steps:

the control drive unit controls the first switch tube S₁On, the first loop is turned on so that the first filter inductor L₁Energy storage;

real-time acquisition of first filter inductance L₁Current feedback signal i_L1fAnd is connected with the first filter inductor L₁Current reference signal i_{L1_ref}Comparing;

if the first filter inductor L₁Current feedback signal i_L1fGreater than the first filter inductance L₁Current reference signal i_{L1_ref}The control driving unit controls the first switch tube S₁And when the first follow current loop is turned off, the first follow current loop is turned on, so that the middle capacitor C is charged, and voltage is provided for the negative half cycle work of the power grid.

Specifically, when the power grid works in the negative half cycle, the voltage of the intermediate capacitor C is equal to the sum of the power grid voltage and the voltage of the third filter inductor, and the voltage of the third filter inductor is very small and can be ignored when the third filter inductor is switched on, so that the voltage of the intermediate capacitor C can be approximately equal to the negative half cycle working voltage of the power grid voltage power frequency cycle.

Preferably, the adjusting of the current of the second filter inductor when the positive half cycle of the grid voltage works or the current of the third filter inductor when the negative half cycle of the grid voltage works specifically includes the following steps:

monitoring the voltage of the power grid in real time and judging the voltage feedback signal u of the power grid_gfThe symbol of (a);

if voltage feedback signal u of the power grid_gfA positive value thenThe second switching tube and the fourth switching tube S are controlled by controlling the driving unit₄Thereby adjusting the second filter inductor L₂Current i of_L2So that the second filter inductor L₂Current i of_L2Tracking second filter inductance L₂Current reference signal i_{L2_ref}；

If voltage feedback signal u of the power grid_gfIf the voltage is negative, the driving unit is controlled to control the third switch tube and the first switch tube S₁Thereby adjusting the third filter inductor L₃Current i of_L3So that the first filter inductor L₁Current i of_L1Tracking first filter inductance L₁Current reference signal i_{L1_ref}。

Preferably, the voltage feedback signal u of the power grid_gfWhen the value is positive, the method specifically comprises the following steps:

the control drive unit controls the fourth switch tube S₄Conducting, and turning off other switching tubes;

the second current sensor collects the second filter inductance L in real time₂Current feedback signal i_L2fAnd a second filter inductor L₂Current reference signal i_{L2_ref}Comparing;

if the second filter inductor L₂Current feedback signal i_L2fIs smaller than the second filter inductor L₂Current reference signal i_{L2_ref}The control driving unit controls the second switch tube S₂On, the second loop is turned on to adjust the second filter inductor L₂Current i of_L2Adding, and a second filter inductor L₂Current i of the series network_gIncreasing;

in particular, the fourth switching tube S₄Conducting the second switch tube S₂Is conducted through the second filter inductor L₂With the electric network, the photovoltaic module PV, the second switch tube S₂The second loop formed by the series connection is conducted, and the second filter inductor L₂Current i_L2Linearly rising, current i of the grid_gA linear increase;

if the second filter inductor L₂Current feedback signal i_L2fGreater than the second filter inductance L₂Current reference signal i_{L2_ref}The control driving unit controls the second switch tube S₂Is turned off and the second freewheeling circuit is turned on to regulate the second filter inductor L₂Current i of_L2Reduced, and second filter inductance L₂Current i of the series network_gDecrease;

in particular, the fourth switching tube S₄Conducting the second switch tube S₂Is turned off and is fed through the second filter inductor L₂And the power grid and a fourth switching tube S₄A second diode D₂The second free-wheeling loop formed in series is conductive, and the second filter inductor L₂Current i of_L2Dropping, the current i of the grid_gAnd decreases.

Preferably, the voltage feedback signal u of the power grid_gfWhen the value is negative, the method specifically comprises the following steps:

the control drive unit controls the third switch tube S₃The other switching tubes are switched off, and the third loop is switched on;

the first filter inductance is then collected in real time L₁Current feedback signal i_L1fAnd is connected with the first filter inductor L₁Current reference signal i_{L1_ref}Comparing;

if the first filter inductor L₁Current feedback signal i_L1fIs smaller than the first filter inductor L₁Current reference signal i_{L1_ref}The control driving unit controls the first switch tube S₁The first loop is conducted, so that the first filter inductor stores energy, and the third loop adjusts the third filter inductor L₃An increase in current of (2);

in particular, a first switching tube S₁Conducting, third switch tube S₃Is conducted through the first filter inductor L₁With photovoltaic module PV, first switching tube S₁The first loop formed by the series connection is conducted, and the first filter inductor L₁Current i of_L1Linearly rising and being provided with a third filter inductor L₃And a third switch tube S₃The intermediate capacitor C and the power grid are connected in series to form a third loop which is conducted, the current of a third filter inductor is increased, and the current of the third filter inductor is equal to that of the third filter inductorGrid current i_g；

If the first filter inductor L₁Current feedback signal i_L1fGreater than the first filter inductance L₁Current reference signal i_{L1_ref}The control driving unit controls the first switch tube S₁Off and the first freewheeling circuit on so that the first filter inductor L₁The third loop adjusts the third filter inductor L for the capacitance of the intermediate capacitor C₃The current of (2) is reduced.

Specifically, the first switch tube S₁Turn-off, third switching tube S₃Is conducted by the first filter inductor, the middle capacitor C and the first diode D₁The first free-wheeling loop formed in series is conductive, and the first filter inductor L₁Current i of_L1Reduced voltage rise of the intermediate capacitor C, and a third filter inductor L₃And a third switch tube S₃The intermediate capacitor C and the power grid are connected in series to form a third loop for conduction, the third filter inductive current is reduced and is equal to the power grid current i_g。

While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.