CN111510009A - Photovoltaic inverter without leakage current and control method thereof - Google Patents

Photovoltaic inverter without leakage current and control method thereof Download PDF

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CN111510009A
CN111510009A CN202010432419.XA CN202010432419A CN111510009A CN 111510009 A CN111510009 A CN 111510009A CN 202010432419 A CN202010432419 A CN 202010432419A CN 111510009 A CN111510009 A CN 111510009A
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power grid
switching tube
current
voltage
intermediate capacitor
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CN111510009B (en
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姚志垒
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Shanghai Maritime University
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Shanghai Maritime University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/123—Suppression of common mode voltage or current
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a non-leakage current photovoltaic inverter and a control method thereof, wherein the photovoltaic inverter comprises a photovoltaic component, an intermediate capacitor, a first filter inductor, a coupling inductor, a first switching tube, a second switching tube, a third switching tube, a diode and the like, and the intermediate capacitor voltage is controlled to be equal to the photovoltaic component voltage by adjusting the duty ratio of the first switching tube; the second switching tube and the third switching tube are complementary switches, and unit power factor and non-unit power factor output are realized by controlling the current of the power grid. The advantages are that: the photovoltaic inverter without leakage current can output reactive power, and has the advantages of no common-mode leakage current, high reliability, low voltage ride through technology and the like.

Description

Photovoltaic inverter without leakage current and control method thereof
Technical Field
The invention relates to the technical field of inverters, in particular to a leakage-current-free 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. This common mode leakage current can cause electromagnetic interference, increase system loss, even pose a threat to personal safety. 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 aims to provide a non-leakage current photovoltaic inverter and a control method thereof, wherein the photovoltaic inverter comprises a photovoltaic module, an intermediate capacitor, a first filter inductor, a coupling inductor, a first switching tube, a second switching tube, a third switching tube, a diode and the like, and the voltage of the intermediate capacitor is controlled to be equal to the voltage of the photovoltaic module by adjusting the duty ratio of the first switching tube; the second switching tube and the third switching tube are complementary switches, and unit power factor and non-unit power factor output are realized by controlling the current of the power grid. The photovoltaic inverter without leakage current can output reactive power, and has the advantages of no common-mode leakage current, high reliability, low voltage ride through technology and the like.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a leakage current-free photovoltaic inverter, comprising:
the negative electrode of the photovoltaic module is connected with the negative electrode of the power grid, and the negative electrode of the photovoltaic module and the negative electrode of the power grid are grounded together;
the first end of the intermediate capacitor is connected with the negative electrode of the photovoltaic component;
a first end of the filter inductor is respectively connected with a negative electrode of the photovoltaic module and a first end of the intermediate capacitor, a second end of the filter inductor is connected with a positive electrode of the photovoltaic module through a first switching tube, and a second end of the filter inductor is also connected with a second end of the intermediate capacitor through a diode; the filter inductor, the first switching tube and the photovoltaic module form a first closed circuit; the filter inductor, the diode and the intermediate capacitor form a second closed circuit;
the coupling inductor comprises a primary winding and a secondary winding, wherein the homonymous end of the primary winding of the coupling inductor is connected with the anode of a power grid, the synonym end of the primary winding of the coupling inductor is connected with the anode of the photovoltaic module through a second switching tube, and the primary winding of the coupling inductor, the power grid, the photovoltaic module and the second switching tube form a third closed circuit;
the dotted end of the secondary winding of the coupling inductor is connected with the positive electrode of the power grid, and the different-dotted end of the secondary winding of the coupling inductor is connected with the second end of the intermediate capacitor through a third switching tube, so that the secondary winding of the coupling inductor, the power grid, the intermediate capacitor and the third switching tube form a fourth closed circuit;
and the input end of the control driving unit is respectively connected with the power grid and the intermediate capacitor, and the output end of the control driving unit is respectively connected with the first switching tube, the second switching tube and the third switching tube, and is used for respectively driving and controlling the on-off of each switching tube to communicate with each closed circuit so as to drive and adjust the current information of the power grid and the voltage information of the intermediate capacitor.
Preferably, it further comprises:
the input end of the first voltage sensor is connected with a power grid, the output end of the first voltage sensor is connected with the input end of the control driving unit, and the first voltage sensor monitors and acquires voltage information of the power grid in real time, generates a power grid voltage feedback signal and transmits the power grid voltage feedback signal to the control driving unit;
the input end of the second voltage sensor is connected with the intermediate capacitor, the output end of the second voltage sensor is connected with the input end of the control driving unit, the second voltage sensor monitors and collects the voltage information of the intermediate capacitor in real time, an intermediate capacitor voltage feedback signal is generated, and the intermediate capacitor voltage feedback signal is transmitted to the control driving unit;
the input end of the current sensor is connected with a power grid, the output end of the current sensor is connected with the input end of the control driving unit, the current sensor monitors and collects current information of the power grid in real time, a power grid current feedback signal is generated, and the power grid current feedback signal is transmitted to the control driving unit.
Preferably, the control driving unit includes:
the input end of the digital signal processor is respectively connected with the first voltage sensor, the second voltage sensor and the current sensor, voltage signal processing and current signal processing are respectively carried out according to the power grid voltage feedback signal, the intermediate capacitor voltage feedback signal and the power grid current feedback signal, and a first switch tube logic signal, a second switch tube logic signal and a third switch tube logic signal are respectively generated;
and the input end of the driving circuit is connected with the output end of the digital signal processor, the output end of the driving circuit is respectively connected with the first switching tube, the second switching tube and the third switching tube, and the driving circuit generates the first driving signal, the second driving signal and the third driving signal according to a first switching tube logic signal, a second switching tube logic signal and a third switching tube logic signal respectively and correspondingly drives the switching of each switching tube.
Preferably, it further comprises:
the filter is connected in parallel with two ends of the photovoltaic assembly and used for filtering the voltage information of the photovoltaic assembly;
the filter is a filter capacitor.
Preferably, the primary winding and the secondary winding of the coupling inductor have the same number of turns;
and/or the first switching tube and/or the second switching tube and/or the third switching tube are MOS tubes or IGBT tubes;
and/or the intermediate capacitor is a polar capacitor or a non-polar capacitor;
and/or the second switching tube and the third switching tube are complementary switches.
Preferably, a control method based on the no-leakage-current photovoltaic inverter includes:
s1, the second voltage sensor monitors and collects voltage information of the intermediate capacitor in real time to generate an intermediate capacitor voltage feedback signal;
s2, the control driving unit performs driving control according to the intermediate capacitor voltage feedback signal, performs driving adjustment on the first switching tube for the first time, and completes adjustment of voltage information of the intermediate capacitor;
s3, respectively monitoring and acquiring voltage information and current information of a power grid in real time by the first voltage sensor and the first current sensor, and respectively generating a power grid voltage feedback signal and a power grid current feedback signal;
and S4, the control driving unit performs driving control according to the power grid voltage feedback signal and the power grid current feedback signal, performs secondary driving adjustment on the second switching tube and the third switching tube, and completes adjustment of current information of the power grid.
Preferably, the step S2 specifically includes:
s21, adjusting the opening of the first switch tube by the control driving unit according to the voltage information of the middle capacitor monitored by the second voltage sensor in real time, and communicating the first closed circuit;
s22, the photovoltaic module provides electric energy for the filter inductor;
s23, after the energy storage of the filter inductor is finished, the first switch tube is closed, the second closed circuit is communicated, and the second switch tube is used as a first follow current circuit of the first closed circuit;
and S24, the filter inductor after energy storage transmits the stored electric energy to the intermediate capacitor through the diode, the charging of the intermediate capacitor is completed, and the voltage information of the intermediate capacitor is improved.
Preferably, the step S4 is specifically:
the third closed circuit and the fourth closed circuit are complementary circuits, the fourth closed circuit is a second follow current circuit of the third closed circuit, the first voltage sensor and the current sensor respectively monitor voltage information of a power grid and current information of the power grid in real time, and the control driving unit adjusts the opening and closing of the second switching tube and the third switching tube to enable a power grid current feedback signal to approach a power grid current reference signal so as to complete adjustment of the current information of the power grid.
Preferably, the step S4 specifically includes:
when the second switching tube is adjusted to be opened and the third switching tube is closed, the third closed circuit is communicated, and the photovoltaic module provides forward electric energy for the coupling inductor, so that the current information of the power grid is improved;
and adjusting the third switching tube to be opened and the second switching tube to be closed, so that the fourth closed circuit is communicated, and the intermediate capacitor provides negative electric energy for the coupling inductor, thereby reducing the current information of the power grid.
Preferably, in the step S4,
inputting the grid voltage feedback signal into a first analog-to-digital conversion module in a digital signal processor, performing analog-to-digital conversion to generate a first digital signal, and dividing the first digital signal into two paths;
the first path of first digital signal, a power grid voltage rated value, a power grid current rated value and an active power reference signal are transmitted to a low voltage ride through algorithm together, low voltage ride through calculation is carried out, and a reference current peak value and a power factor angle of a power grid are generated, wherein the value of the active power reference signal is set by a maximum power tracking algorithm or the inside of a digital signal processor, and the values of the power grid voltage rated value, the power grid current rated value and an intermediate capacitor reference voltage are set by the inside of the digital signal processor;
transmitting the second path of first digital signal to a phase-locked loop, and outputting the phase of the power grid voltage;
and subtracting the phase of the voltage of the power grid from the power factor angle of the power grid, performing sinusoidal operation, and multiplying the obtained result by the reference current peak value of the power grid to generate a power grid current reference signal.
Compared with the prior art, the invention has the following advantages:
(1) the invention relates to a non-leakage current photovoltaic inverter which mainly comprises a photovoltaic module, an intermediate capacitor, a first filter inductor, a coupling inductor, a first switching tube, a second switching tube, a third switching tube, a diode and the like, wherein the voltage of the intermediate capacitor is controlled to be equal to the voltage of the photovoltaic module by adjusting the duty ratio of the first switching tube; in addition, the second switching tube and the third switching tube are complementary switches, and the output of unit power factor and non-unit power factor is realized by controlling the current of the power grid;
(2) the photovoltaic inverter without leakage current can output reactive power, and has the advantages of no common-mode leakage current, high reliability, low voltage ride through technology and the like.
Drawings
FIG. 1 is a circuit diagram of a no-leakage current photovoltaic inverter of the present invention;
fig. 2 is a control schematic diagram of a leakage current-free photovoltaic inverter according to the present invention.
Detailed Description
The present invention will now be further described by way of the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings. It should be noted that all the switching tubes and diodes in the present invention are considered to be ideal devices, and the factors such as switching time and conduction voltage drop are not considered, and all the inductors and capacitors in the present invention are also considered to be ideal elements.
As shown in fig. 1, a non-isolated photovoltaic inverter according to the present invention includes a photovoltaic module 1, an intermediate capacitor 2, a filter inductor 3, a coupling inductor 4, a control driving unit, a diode 5, and a first switching tube S1A second switch tube S2And a third switching tube S3。
The cathode of the photovoltaic module 1 is connected with the cathode of the power grid U, and the cathode of the photovoltaic module 1 and the cathode of the power grid U are grounded together; the first end of the intermediate capacitor 2 is connected to the negative pole of the photovoltaic module 1.
In the present embodiment, the photovoltaic module 1 is a photovoltaic cell PV; the intermediate capacitor 2 is a polar capacitor or a non-polar capacitor.
The first end of the filter inductor 3 is respectively connected with the negative electrode of the photovoltaic module 1 and the first end of the intermediate capacitor 2, and the second end of the filter inductor is connected with the first end of the intermediate capacitor 2 through a first switch tube S1Connected to the anode of the photovoltaic module 1, and the second terminal thereof is also connected to the second terminal of the intermediate capacitor 2 via a diode 5. The filter inductor 3 and the first switch tube S1And the photovoltaic module 1 form a first closed circuit; the filter inductor 3, the diode 5 and the intermediate capacitor 2 form a second closed circuit.
The coupling inductor 4 comprises a primary winding NpAnd secondary winding Ns. Wherein, the primary winding N of the coupling inductor 4pThe homonymous terminal of the power grid U is connected with the positive electrode of the power grid U, and the heteronymous terminal of the power grid U is connected with the positive electrode of the power grid U through a second switch tube S2Is connected with the positive electrode of the photovoltaic module 1, and then is coupled with the primary winding N of the inductor 4pWith electric wire netting U, photovoltaic module 1 and second switch tube S2A third closed circuit is formed. Wherein, the second switch tube S2In the third closed circuit is a positive half cycle high frequency switch of the power grid U.
Secondary winding N of coupling inductor 4sThe homonymous end of the first switch tube is connected with the positive electrode of the power grid U, and the heteronymous end of the first switch tube is connected with the positive electrode of the power grid U through a third switch tube S3A secondary winding N of the coupling inductor 4 is connected with the second end of the intermediate capacitor 2sAnd the power grid, the intermediate capacitor 2 and the third switch tube S3A fourth closed circuit is formed. Wherein the third switch S3In the fourth closed circuit is a negative half cycle high frequency switch of the power grid U.
In this embodiment, the primary winding N of the coupling inductor 4pNumber of turns of and secondary winding NsAre equal and the coupling inductance 4 is able to output reactive power. In addition, the second switch tube S2And a third switching tube S3Are complementary switches.
The input end of the control drive unit is respectively connected with the power grid and the intermediate capacitor 2, and the output end of the control drive unit is respectively connected with the first switch tube S1A second switch tube S2And a third switching tube S3And the connection is used for respectively driving and controlling the on-off of each switching tube to communicate with each closed circuit, so as to drive and regulate the current information of the power grid and the voltage information of the intermediate capacitor 3.
The leakage current free photovoltaic inverter of the present invention further comprises a first voltage sensor 6, a second voltage sensor 7 and a current sensor 8.
The input end of the first voltage sensor 6 is connected with the power grid U, the output end of the first voltage sensor is connected with the input end of the control driving unit, and the first voltage sensor 6 monitors and collects voltage information U of the power grid U in real timegGenerating a grid voltage feedback signalNumber ugfAnd transmitting the data to the control driving unit.
The input end of the second voltage sensor 7 is connected with the intermediate capacitor 2, the output end of the second voltage sensor is connected with the input end of the control driving unit, and the second voltage sensor 7 monitors and collects the voltage information u of the intermediate capacitor 2 in real timecGenerating an intermediate capacitor voltage feedback signal ucfAnd transmitting the data to the control driving unit.
The input end of the current sensor 8 is connected with the power grid U, the output end of the current sensor is connected with the input end of the control driving unit, and the current sensor 8 monitors and acquires current information i of the power grid U in real timegGenerating a grid current feedback signal igfAnd transmitting the data to the control driving unit.
As shown in fig. 2, the control driving unit of the present invention includes a digital signal processor DSP and a driving circuit.
The input end of the digital signal processor is respectively connected with the first voltage sensor 6, the second voltage sensor 7 and the current sensor 8, and the digital signal processor feeds back a signal u according to the voltage of the power gridgfIntermediate capacitor voltage feedback signal ucfAnd a grid current feedback signal igfRespectively processing the voltage signal and the current signal, and respectively generating a logic signal O of the first switching tube1A second switch tube logic signal O2And a third switching tube logic signal O3。
The input end of the driving circuit is connected with the output end of the digital signal processor, and the output end of the driving circuit is respectively connected with the first switch tube S1A second switch tube S2And a third switching tube S3Connected according to the first switch tube logic signal O1A second switch tube logic signal O2And a third switching tube logic signal O3Generating the first, second and third driving signals, and driving the respective switching tubes accordingly (S)1～S3) Opening and closing of (3).
In addition, the inverter of the invention further comprises a filter which is connected in parallel with two ends of the photovoltaic component 1 and is used for supplying electricity to the photovoltaic component 1The voltage information is filtered, and the filter voltage u at both ends of the filterinNamely the voltage information of the photovoltaic module 1, and the regulation and control of the voltage information u ensure the voltage information u of the intermediate capacitor 2cEqual to the voltage information u of the photovoltaic module 1in。
In this embodiment, the filter is a filter capacitor Cin. The filter capacitor CinEither polar or non-polar. The first switch tube S1A second switch tube S2And a third switching tube S3Is a Metal Oxide Semiconductor (MOS) Transistor or an Insulated Gate Bipolar Transistor (IGBT).
The invention also provides a control method of the leakage-current-free photovoltaic inverter, which comprises the following steps:
s1, the second voltage sensor 7 monitors and collects the voltage information u of the middle capacitor 2 in real timecGenerating an intermediate capacitor voltage feedback signal ucf。
S2, the control drive unit feeds back a signal u according to the intermediate capacitor voltagecfPerforming drive control, performing first drive adjustment on the first switch tube S1Completing the voltage information u of the intermediate capacitor 2cAnd (4) adjusting.
Wherein the step S2 specifically includes:
s21, the second voltage sensor 7 monitors the voltage information u of the intermediate capacitor 2 in real timecVoltage information u of the intermediate capacitor 2cIs 0 and is much smaller than the voltage information u of the photovoltaic module 1inThen, the control drive unit adjusts the first switch tube S1And when the first closed circuit is opened, the first closed circuit is communicated. The current passes through the first switch tube S from the positive electrode of the photovoltaic module 11And the filter inductor 3 returns to the negative electrode of the photovoltaic module 1.
Wherein the control drive unit adjusts the first switching tube S1Turning on the digital signal processor in response to the intermediate capacitor voltage feedback signal ucfProcessing the voltage signal to generate a logic signal O of the first switch tube1(ii) a Logic signal O of the first switch tube1Transmitted to a driving circuit for drivingThe circuit generates a first driving signal to perform a first switch S1The opening and closing of (2) is driven.
In this embodiment, the intermediate capacitor voltage feedback signal ucfAnd the second analog-to-digital conversion AD2 module in the digital signal processor is transmitted to perform analog-to-digital conversion to generate a second digital signal. The second digital signal is compared with the intermediate capacitor reference voltage uC_refAfter calculation (subtraction), the voltage is transmitted to the current regulator, and the voltage regulation signal of the intermediate capacitor 2 is output. Comparing the voltage regulating signal of the intermediate capacitor 2 with the triangular wave to output a first switch logic signal O1。
Wherein the first switch logic signal O1And is output by a waveform (PWM) port of the digital signal processor.
S22, the photovoltaic module 1 provides electric energy for the filter inductor 3, and the current i of the filter inductor 3L1And (4) rising. S23, after the energy storage of the filter inductor 3 is finished, the first switch tube S1And closing, and enabling the second closed circuit to be communicated and used as a freewheeling circuit of the first closed circuit. S24, the filter inductor 3 after storing energy transmits the stored electric energy to the intermediate capacitor 2 through the diode 5, and the current i of the filter inductor 3L1The voltage decreases to complete the charging of the intermediate capacitor 2 and increase the voltage information u of the intermediate capacitor 2c。
S3, monitoring and acquiring voltage information U of power grid U in real time by first voltage sensor 6 and current sensor 8 respectivelygAnd current information igRespectively generating a grid voltage feedback signal ugfAnd a grid current feedback signal igf。
S4, the control drive unit feeds back a signal u according to the power grid voltagegfAnd a grid current feedback signal igfPerforming drive control, performing secondary drive adjustment on the second switch tube S2And a third switching tube S3To make the current of the power grid feed back a signal igfApproaching to the grid current reference signal ig_refSo as to complete the regulation of the current information of the power grid U.
Wherein the digital signal processor feeds back a signal u according to the power grid voltagegfAnd a grid current feedback signal igfProcessing the voltage and current signals to generate a second switch tube logic signal O2And a third switching tube logic signal O3(ii) a Logic signal O of the second switch tube2And a second switch tube logic signal O3The second driving signal and the third driving signal are generated by the driving circuit to carry out a second switching tube S2And a third switching tube S3The opening and closing of (2) is driven. The second switch tube logic signal O2And a third switching tube logic signal O3And is output by a waveform (PWM) port of the digital signal processor.
In the present embodiment, the grid voltage is fed back to the signal ugfThe first digital signal is input into a first analog-to-digital conversion module AD1 in the digital signal processor DSP for analog-to-digital conversion to generate a first digital signal, and the first digital signal is divided into two paths.
The first path of first digital signal and the voltage rated value U of the power grid UgNU current rating I of power gridgNAnd an active power reference signal IdTransmitting the signals to a low voltage ride through algorithm together for low voltage ride through calculation to generate a reference current peak value I of a power grid Ugm_refAnd a power factor angle θ;
the low voltage ride through algorithm is shown in formula (1):
Figure BDA0002501035530000091
in the formula IgmIs the peak value of the current rating of the network, i.e.
Figure BDA0002501035530000092
UgIs the effective value of the grid voltage; wherein θ is shown in formula (2):
Figure BDA0002501035530000093
wherein, the active power reference signal IdThe value of (a) is set internally by a maximum power tracking algorithm or a digital signal processor; u voltage rating of power gridValue UgNU current rating I of power gridgNAnd an intermediate capacitive reference voltage uC_refIs set internally by the digital signal processor.
Transmitting the second path of first digital signal to a phase-locked loop to output a power grid voltage ugPhase of
Figure BDA0002501035530000095
Will the network voltage ugPhase of
Figure BDA0002501035530000096
Carrying out sine operation after subtracting the power factor angle theta of the power grid U, and multiplying the obtained result by the reference current peak value I of the power grid Ugm_refGenerating a grid current reference signal ig_refWherein, in the step (A),
Figure BDA0002501035530000094
reference signal i of power grid currentg_refAnd a grid current feedback signal igfThe logic signal O of the second switching tube is output through the current regulator after the subtraction of the adder-subtractor2Logic signal O of the second switch tube2Outputting a third switch tube logic signal O through an inverter3. The second switch tube logic signal O2And a third switching tube logic signal O3And the signals are respectively transmitted to the driving circuits, and second driving signals and third driving signals are respectively generated through a second driving circuit and a third driving circuit of the driving circuits, so that the corresponding switches are driven to be opened and closed. The current regulator can adopt PI control, hysteresis control or proportional resonance control and the like.
The adder-subtractor judges a grid current feedback signal igfAnd grid current reference signal ig_refRelative size of (d). When the current of the power grid is fed back to the signal igfLess than grid current reference signal ig_refThe second driving signal and the third driving signal generated by the digital signal processor are the second switch tube S respectively2Opening and third switching tube S3Closing; when the current of the power grid is fed back to the signal igfGreater than grid current reference signal ig_refThe second driving signal and the third driving signal generated by the digital signal processor are the second switch tube S respectively2Closing and third switching tube S3Is opened to regulate the current feedback signal i of the power gridgfApproaching to the grid current reference signal ig_ref。
The step S4 specifically includes:
the third closed circuit and the fourth closed circuit are complementary circuits, the fourth closed circuit is a second follow current circuit of the third closed circuit, and the first voltage sensor 6 and the current sensor 8 respectively monitor the voltage information U of the power grid U in real timegCurrent information i of power grid UgThe control drive unit adjusts a grid current feedback signal igfApproaching to the grid current reference signal ig_ref。
The step S4 specifically includes:
the control drive unit adjusts the second switch tube S2Open, the third switching tube S3When the circuit is closed, the third closed circuit is connected, the photovoltaic module 1 provides forward electric energy for the coupling inductor 4, and a primary winding N of the coupling inductor 4PCurrent rise, coupling the secondary winding N of the inductor 4SCurrent 0, current information i of the gridgLifting;
the control drive unit adjusts the third switch tube S3Open, the second switch tube S2When the circuit is closed, the fourth closed circuit is communicated, the middle capacitor 2 provides negative electric energy for the coupling inductor 4, and a secondary winding N of the coupling inductor 4SCurrent drop of, primary winding NPCurrent 0, current information i of the gridgReducing, the grid current feedback signal igfApproaching to the grid current reference signal ig_ref。
In the present invention, the operating principle (i.e. the control method) of the leakage current-free photovoltaic inverter is as follows:
the second voltage sensor 7 detects and collects the voltage information u of the middle capacitor 2 in real timecIs living in natureBecomes the intermediate capacitor voltage feedback signal ucf(ii) a The control drive unit feeds back a signal u according to the intermediate capacitor voltagecfAdjusting the first switching tube S1Opening the first closed circuit; the photovoltaic module 1 provides electric energy for the filter inductor 3; after the energy storage of the filter inductor 3 is completed, the first switch tube S1And closing, and enabling the second closed circuit to be communicated and serve as a first free-wheeling circuit of the first closed circuit. The filter inductor 3 after energy storage transmits the stored electric energy to the intermediate capacitor 2 through the diode 5, the charging of the intermediate capacitor 2 is completed, and the voltage information u of the intermediate capacitor 2 is improvedcThe voltage information u of the intermediate capacitor can be madecVoltage information u with photovoltaic moduleinThe same is true. Namely by adjusting the first switching tube S1The duty ratio of (1), and the voltage information u of the intermediate capacitor 2c。
The first voltage sensor 6 and the current sensor 8 respectively detect and collect voltage information U of the power grid U in real timegAnd current information igRespectively generating a grid voltage feedback signal ugfAnd generating a grid current feedback signal igf(ii) a The control drive unit controls a power grid current feedback signal igfApproaching to the grid current reference signal ig_ref。
The control drive unit adjusts the second switch tube S2Open, the third switching tube S3When the photovoltaic module is closed, the third closed circuit is connected, the photovoltaic module 1 provides forward electric energy for the coupling inductor 4, and the primary winding N of the coupling inductor 4PCurrent rise of (2), secondary winding NSThe current is 0, and the current information i of the power grid UgAnd (4) improving.
The control drive unit adjusts the third switch tube S3Open, the second switch tube S2When the circuit is closed, the fourth closed circuit is communicated, the middle capacitor 2 provides negative electric energy for the coupling inductor 4, and the secondary winding N of the coupling inductor 4SCurrent drop of, primary winding NPThe current is 0, and the current information i of the power grid UgReducing, the grid current feedback signal igfApproaching to the grid current reference signal ig_ref。
In summary, the invention provides a non-leakage currentThe photovoltaic inverter comprises a photovoltaic component 1, an intermediate capacitor 2, a coupling inductor 4, a control drive unit and a first switch tube S1A second switch tube S2And a third switching tube S3Etc. by adjusting the first switching tube S1To control the voltage information u of the intermediate capacitor 2cAnd voltage information u of the photovoltaic module 1inBy adjusting the second switching tube S2And a third switching tube S3To regulate the current information i of the network UgThe output of unit power factor and non-unit power factor is realized; the inverter is suitable for occasions of non-isolated photovoltaic inverters, can output reactive power, and has the advantages of no common-mode leakage current, high reliability and low voltage ride through.
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.

Claims (10)

1. A leakage-free photovoltaic inverter, comprising:
the negative electrode of the photovoltaic module is connected with the negative electrode of the power grid, and the negative electrode of the photovoltaic module and the negative electrode of the power grid are grounded together;
the first end of the intermediate capacitor is connected with the negative electrode of the photovoltaic component;
a first end of the filter inductor is respectively connected with a negative electrode of the photovoltaic module and a first end of the intermediate capacitor, a second end of the filter inductor is connected with a positive electrode of the photovoltaic module through a first switching tube, and a second end of the filter inductor is also connected with a second end of the intermediate capacitor through a diode; the filter inductor, the first switching tube and the photovoltaic module form a first closed circuit; the filter inductor, the diode and the intermediate capacitor form a second closed circuit;
the coupling inductor comprises a primary winding and a secondary winding, wherein the homonymous end of the primary winding of the coupling inductor is connected with the anode of a power grid, the synonym end of the primary winding of the coupling inductor is connected with the anode of the photovoltaic module through a second switching tube, and the primary winding of the coupling inductor, the power grid, the photovoltaic module and the second switching tube form a third closed circuit;
the dotted end of the secondary winding of the coupling inductor is connected with the positive electrode of the power grid, and the different-dotted end of the secondary winding of the coupling inductor is connected with the second end of the intermediate capacitor through a third switching tube, so that the secondary winding of the coupling inductor, the power grid, the intermediate capacitor and the third switching tube form a fourth closed circuit;
and the input end of the control driving unit is respectively connected with the power grid and the intermediate capacitor, and the output end of the control driving unit is respectively connected with the first switching tube, the second switching tube and the third switching tube, and is used for respectively driving and controlling the on-off of each switching tube to communicate with each closed circuit so as to drive and adjust the current information of the power grid and the voltage information of the intermediate capacitor.
2. The leakage-free photovoltaic inverter of claim 1, further comprising:
the input end of the first voltage sensor is connected with a power grid, the output end of the first voltage sensor is connected with the input end of the control driving unit, and the first voltage sensor monitors and acquires voltage information of the power grid in real time, generates a power grid voltage feedback signal and transmits the power grid voltage feedback signal to the control driving unit;
the input end of the second voltage sensor is connected with the intermediate capacitor, the output end of the second voltage sensor is connected with the input end of the control driving unit, the second voltage sensor monitors and collects the voltage information of the intermediate capacitor in real time, an intermediate capacitor voltage feedback signal is generated, and the intermediate capacitor voltage feedback signal is transmitted to the control driving unit;
the input end of the current sensor is connected with a power grid, the output end of the current sensor is connected with the input end of the control driving unit, the current sensor monitors and collects current information of the power grid in real time, a power grid current feedback signal is generated, and the power grid current feedback signal is transmitted to the control driving unit.
3. The leakage-free photovoltaic inverter of claim 2, wherein the control drive unit comprises:
the input end of the digital signal processor is respectively connected with the first voltage sensor, the second voltage sensor and the current sensor, voltage signal processing and current signal processing are respectively carried out according to the power grid voltage feedback signal, the intermediate capacitor voltage feedback signal and the power grid current feedback signal, and a first switch tube logic signal, a second switch tube logic signal and a third switch tube logic signal are respectively generated;
and the input end of the driving circuit is connected with the output end of the digital signal processor, the output end of the driving circuit is respectively connected with the first switching tube, the second switching tube and the third switching tube, and the driving circuit generates the first driving signal, the second driving signal and the third driving signal according to a first switching tube logic signal, a second switching tube logic signal and a third switching tube logic signal respectively and correspondingly drives the switching of each switching tube.
4. The leakage-free photovoltaic inverter of claim 1, further comprising:
the filter is connected in parallel with two ends of the photovoltaic assembly and used for filtering the voltage information of the photovoltaic assembly;
the filter is a filter capacitor.
5. The non-leakage current photovoltaic inverter according to claim 1,
the primary winding and the secondary winding of the coupling inductor have the same number of turns;
and/or the first switching tube and/or the second switching tube and/or the third switching tube are MOS tubes or IGBT tubes;
and/or the intermediate capacitor is a polar capacitor or a non-polar capacitor;
and/or the second switching tube and the third switching tube are complementary switches.
6. A control method based on the non-leakage current photovoltaic inverter as claimed in any one of claims 1 to 5, characterized in that the method comprises:
s1, the second voltage sensor monitors and collects voltage information of the intermediate capacitor in real time to generate an intermediate capacitor voltage feedback signal;
s2, the control driving unit performs driving control according to the intermediate capacitor voltage feedback signal, performs driving adjustment on the first switching tube for the first time, and completes adjustment of voltage information of the intermediate capacitor;
s3, respectively monitoring and acquiring voltage information and current information of a power grid in real time by the first voltage sensor and the first current sensor, and respectively generating a power grid voltage feedback signal and a power grid current feedback signal;
and S4, the control driving unit performs driving control according to the power grid voltage feedback signal and the power grid current feedback signal, performs secondary driving adjustment on the second switching tube and the third switching tube, and completes adjustment of current information of the power grid.
7. The method for controlling a non-leakage current photovoltaic inverter as claimed in claim 6, wherein said step S2 specifically includes:
s21, adjusting the opening of the first switch tube by the control driving unit according to the voltage information of the middle capacitor monitored by the second voltage sensor in real time, and communicating the first closed circuit;
s22, the photovoltaic module provides electric energy for the filter inductor;
s23, after the energy storage of the filter inductor is finished, the first switch tube is closed, the second closed circuit is communicated, and the second switch tube is used as a first follow current circuit of the first closed circuit;
and S24, the filter inductor after energy storage transmits the stored electric energy to the intermediate capacitor through the diode, the charging of the intermediate capacitor is completed, and the voltage information of the intermediate capacitor is improved.
8. The control method of the no-leakage-current photovoltaic inverter as claimed in claim 6, wherein the step S4 is specifically:
the third closed circuit and the fourth closed circuit are complementary circuits, the fourth closed circuit is a second follow current circuit of the third closed circuit, the first voltage sensor and the current sensor respectively monitor voltage information of a power grid and current information of the power grid in real time, and the control driving unit adjusts the opening and closing of the second switching tube and the third switching tube, so that a power grid current feedback signal approaches to a power grid current reference signal, and the adjustment of the current information of the power grid is completed.
9. The method for controlling a non-leakage-current photovoltaic inverter as claimed in claim 6 or 8, wherein the step S4 specifically includes:
when the second switching tube is adjusted to be opened and the third switching tube is closed, the third closed circuit is communicated, and the photovoltaic module provides forward electric energy for the coupling inductor, so that the current information of the power grid is improved;
and adjusting the third switching tube to be opened and the second switching tube to be closed, so that the fourth closed circuit is communicated, and the intermediate capacitor provides negative electric energy for the coupling inductor, thereby reducing the current information of the power grid.
10. The control method of the no leakage current photovoltaic inverter according to claim 8, wherein in the step S4,
inputting the grid voltage feedback signal into a first analog-to-digital conversion module in a digital signal processor, performing analog-to-digital conversion to generate a first digital signal, and dividing the first digital signal into two paths;
the first path of first digital signal, a power grid voltage rated value, a power grid current rated value and an active power reference signal are transmitted to a low voltage ride through algorithm together, low voltage ride through calculation is carried out, and a reference current peak value and a power factor angle of a power grid are generated, wherein the value of the active power reference signal is set by a maximum power tracking algorithm or the inside of a digital signal processor, and the values of the power grid voltage rated value, the power grid current rated value and an intermediate capacitor reference voltage are set by the inside of the digital signal processor;
transmitting the second path of first digital signal to a phase-locked loop, and outputting the phase of the power grid voltage;
and subtracting the phase of the voltage of the power grid from the power factor angle of the power grid, performing sinusoidal operation, and multiplying the obtained result by the reference current peak value of the power grid to generate a power grid current reference signal.
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