CN107147319B - Non-isolated photovoltaic grid-connected inverter, photovoltaic grid-connected power generation system and control method - Google Patents

Non-isolated photovoltaic grid-connected inverter, photovoltaic grid-connected power generation system and control method Download PDF

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CN107147319B
CN107147319B CN201710587318.8A CN201710587318A CN107147319B CN 107147319 B CN107147319 B CN 107147319B CN 201710587318 A CN201710587318 A CN 201710587318A CN 107147319 B CN107147319 B CN 107147319B
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power switch
unidirectional power
grid
current
inductor
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CN107147319A (en
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周小杰
李敬兆
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Anhui University of Science and Technology
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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
    • H02M7/53—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 using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—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 using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • 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
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H02J3/383—
    • H02J3/385—
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30—Electrical components
    • 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
    • Y02E40/40—Arrangements for reducing harmonics

Abstract

The invention discloses a non-isolated photovoltaic grid-connected inverter, a photovoltaic grid-connected power generation system and a control methodPVCapacitor CPVAre respectively passed through a unidirectional power switch VT1Unidirectional power switch VT2And inductor LcAre connected with one-way power switch VT3Unidirectional power switch VT4Connected in parallel with the inductor L after being connected in seriescAt both ends of the same. The photovoltaic grid-connected power generation system comprises the non-isolated photovoltaic grid-connected inverter. The utility model also discloses a control method to photovoltaic grid-connected power generation system. By adopting the current source type inverter, the invention reduces the use of components, reduces the volume and the use cost of the inverter and avoids the defect of the earth leakage current.

Description

Non-isolated photovoltaic grid-connected inverter, photovoltaic grid-connected power generation system and control method
Technical Field
The invention relates to the technical field of solar photovoltaic power generation, in particular to a single-phase single-stage non-isolated current source type inverter, a photovoltaic grid-connected power generation system and a control method.
Background
With the increasing concern on the environment and energy problems, the photovoltaic grid-connected power generation has gained wide attention as a renewable energy utilization technology. However, the early investment of the photovoltaic grid-connected power generation system is large, the power generation cost is high, and the like, so that the popularization of the photovoltaic grid-connected power generation system is seriously hindered.
The grid-connected photovoltaic power generation system generally comprises a photovoltaic cell panel and a grid-connected inverter, converts solar radiation energy received by the photovoltaic cell panel into high-voltage direct current through high-frequency direct current, and then outputs sinusoidal alternating current with the same frequency and phase as the voltage of a power grid to the power grid after inversion of the inverter. The grid-connected inverter comprises a voltage-type inverter and a current-type inverter, and the current-type inverter can improve direct-current input voltage and has short-circuit protection capability. And because the current mode inverter does not have direct current bus capacitance, the life of current mode inverter has been improved.
However, the use of the inverter is limited by the cost and the volume of the inverter, and the current solution is to use a non-isolated inverter, and since a heavy isolation transformer is omitted in the photovoltaic grid-connected system, the system has the advantages of simple structure, light weight, low cost and the like. However, in the photovoltaic grid-connected system without the isolation transformer, the photovoltaic cell panel is not isolated from the public power grid, which causes the voltage connection between the photovoltaic cell panel and the power grid, so that the ground capacitance exists between the photovoltaic cell panel and the ground, thereby generating the leakage current of the photovoltaic cell panel to the ground, reducing the working efficiency of the inverter, increasing the distortion of the grid-connected current, and reducing the safety of the photovoltaic grid-connected.
Disclosure of Invention
The invention aims to provide a non-isolated photovoltaic grid-connected inverter, a photovoltaic grid-connected power generation system and a control method, and aims to solve the problem of floor drain current of a photovoltaic cell panel.
To achieve the above object, a first aspect of the present invention provides a non-isolated photovoltaic grid-connected inverter, including: capacitor C connected with photovoltaic cell panel in parallelPVCapacitor CPVAre respectively passed through a unidirectional power switch VT1Unidirectional power switch VT2And inductor LcAre connected with one-way power switch VT3Unidirectional power switch VT4Connected in parallel with the inductor L after being connected in seriescAt both ends of the same.
Wherein, the capacitor CPVIs a decoupling capacitor.
Wherein, the capacitor CPVPositive pole and unidirectional power switch VT1Collector connection of, unidirectional power switch VT1And the inductor LcOne end of the first electrode is connected with the base electrode and the base electrode is grounded;
capacitor CPVNegative pole and unidirectional power switch VT2Emitter-connected, unidirectional power switch VT2Collector of and the inductor LcThe other end of the first resistor is connected with the base electrode and the base electrode is grounded;
unidirectional power switch VT3Emitter and unidirectional power switch VT4Collector connection of, unidirectional power switch VT4And the inductor LcOne end of the unidirectional power switch VT is connected with the base electrode of the unidirectional power switch VT3Collector of and the inductor LcThe other end of the first resistor is connected with the base electrode and the base electrode is grounded.
In a second aspect, a grid-connected photovoltaic power generation system is provided, which includes:
photovoltaic cell panel, filter, non-isolated photovoltaic grid-connected inverter, photovoltaic cell panel and capacitor CPVAnd one port of the filter is connected with the non-isolated photovoltaic grid-connected inverter, and the other end of the filter is connected with a power grid.
Wherein the filter comprises a capacitor CfAnd an inductor LfCapacitor CfAnd inductor LfIs connected with a unidirectional power switch VT3Emitter and unidirectional power switch VT4Collector connecting wire connection, capacitor CfThe other end of the capacitor is connected with the negative electrode of the photovoltaic cell panel, and a capacitor CfAnother end of (8), inductance LfThe other ends of the two ends of the power grid are respectively connected with the two ends of the power grid.
In a third aspect, a control method for the above-mentioned photovoltaic grid-connected power generation system is provided, which includes:
controlling the unidirectional power switch VT1And unidirectional power switch VT2Conducting unidirectional power switch VT3And unidirectional power switch VT4Open, the photovoltaic panel couples the inductor LcCharging, the system works in the inductor LcA charging mode;
controlling the unidirectional power switch VT1And unidirectional power switch VT3Conducting unidirectional power switch VT2And unidirectional power switch VT4Open, the photovoltaic panel and the inductor LcDischarging, wherein the non-isolated photovoltaic grid-connected inverter outputs forward current and is connected with an inductor LcWhen the current values are the same, the system works in a mode that the inverter outputs forward current;
controlling the unidirectional power switch VT2And unidirectional power switch VT4Conducting unidirectional power switch VT1And unidirectional power switch VT3Shut down, the non-isolated pv grid inverter outputting a reverse current and interacting with inductor LcWhen the current values are the same, the system works in a mode that the inverter outputs reverse current;
controlling the unidirectional power switch VT3And unidirectional power switch VT4Conducting unidirectional power switch VT1And unidirectional power switch VT2Open, inductor LcThe current value is kept unchanged, the output current value of the non-isolated photovoltaic grid-connected inverter is zero, and the system works in an inductor LcFreewheel mode.
The current hysteresis control is carried out on the non-isolated photovoltaic grid-connected inverter, and the current hysteresis control comprises control over a positive half period of grid-connected current and control over a negative half period of the grid-connected current.
The grid-connected current positive half cycle control specifically comprises the following steps:
acquisition of t1Current i at timegAt ig＜iminTime, control the unidirectional power switch VT1And unidirectional power switch VT3Conducting, the system works in a mode that the inverter outputs forward current to control igIncreasing to track grid-connected current given value iref；
At imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＜iLC-refControlling said unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcA charging mode;
at imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＞iLC-refControlling said unidirectional power switch VT3And unidirectional power switch VT4When the system is conducted, the system works in the inductor LcA freewheel mode;
at ig＞imaxIf it is determined that i isLC＞iLC-refControlling said unidirectional power switch VT2And unidirectional power switch VT4On, the system works in the mode that the inverter outputs reverse current to control igDecrease;
at ig＞imaxIf it is determined that i isLC＜iLC-refSaid unidirectional power switch VT1Unidirectional power switch VT2Conducting and the system works in the electricityFeeling LcCharging mode to control igIs reduced in which iLC-refIs an inductive current iLCTo the reference value of (c).
The grid-connected current negative half-cycle control specifically comprises the following steps:
acquisition of t1Current i at timegAt ig＞imaxTime, control the unidirectional power switch VT2And unidirectional power switch VT4On, the system works in the mode that the inverter outputs reverse current to control igDecrease;
at imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＜iLC-refControlling said unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcA charging mode;
at imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＞iLC-refControlling said unidirectional power switch VT3And unidirectional power switch VT4When the system is conducted, the system works in the inductor LcA freewheel mode;
at ig＜iminIf it is determined that i isLC＞iLC-refControlling said unidirectional power switch VT1And unidirectional power switch VT3Conducting, the system works in a mode that the inverter outputs forward current to control igIncreasing to track grid-connected current given value iref；
At ig＞imaxIf it is determined that i isLC＜iLC-refSaid unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcCharging mode to control igAnd decreases.
Wherein control igIncreasing to track grid-connected current given value irefThe method specifically comprises the following steps:
collecting the output voltage of the photovoltaic cell panel by using a voltage sensor, collecting a voltage alternating current signal of the power grid, and collecting the output current of the photovoltaic cell panel by using a current sensor;
calculating the maximum power of the photovoltaic cell panel according to a maximum power tracking algorithm;
calculating a given amplitude of grid-connected current according to the maximum power of the photovoltaic cell panel;
filtering the voltage alternating current signal of the power grid through a low-pass filter, and then entering a single-phase-locked loop to obtain a phase angle signal;
calculating a given value i of the grid-connected current according to the phase angle signal and the given amplitude of the grid-connected currentrefTo realize control igIncreasing tracking grid-connected current given value iref。
Compared with the prior art, the invention has the following technical effects: the non-isolated photovoltaic grid-connected inverter provided by the invention adopts four unidirectional power switches to control the unidirectional flow of current, and an anti-parallel diode is not required to be added in the inverter. Meanwhile, in a photovoltaic grid-connected power generation system, the capacitance of the photovoltaic cell panel to the ground is bypassed, a 220V/380V low-voltage power distribution system in China widely adopts a running mode that a neutral point is directly grounded, and the one-way power grid grounding resistance is approximate to zero, so that the voltage at two ends of the capacitance of the photovoltaic cell panel to the ground is constant, the current flowing through the capacitance of the photovoltaic cell panel to the ground is approximate to zero, and the phenomenon of electricity leakage to the ground of a photovoltaic grid-connected inverter is eliminated.
Drawings
The following detailed description of embodiments of the invention refers to the accompanying drawings in which:
FIG. 1 is a schematic circuit diagram of a non-isolated photovoltaic grid-connected inverter according to the present invention;
FIG. 2 is a schematic structural diagram of a grid-connected photovoltaic power generation system according to the present invention;
FIG. 3 is a schematic diagram of a path of a non-isolated photovoltaic grid-connected inverter to a ground leakage current according to the present invention;
FIG. 4 is a schematic diagram of an equivalent circuit of a photovoltaic grid-connected power generation system in an inductive charging mode according to the present invention;
FIG. 5 is a schematic diagram of an equivalent circuit of a photovoltaic grid-connected power generation system in the mode that an inverter outputs forward current;
FIG. 6 is a schematic diagram of an equivalent circuit of the photovoltaic grid-connected power generation system in the inverter output reverse current mode;
FIG. 7 is a schematic circuit diagram of a photovoltaic grid-connected power generation system operating in an inductive freewheeling mode according to the present invention;
FIG. 8 is an equivalent schematic diagram of the present invention employing a current hysteresis loop to control a non-isolated photovoltaic grid-connected inverter;
FIG. 9 is a schematic flow chart of the present invention for controlling the positive half cycle of the grid-connected current;
FIG. 10 is a schematic flow chart of the present invention for controlling the negative half cycle of the grid-connected current;
FIG. 11 is a diagram of the real-time calculation of the grid-connected current given value i in the present inventionrefIs a schematic flow diagram.
Detailed Description
To further illustrate the features of the present invention, refer to the following detailed description of the invention and the accompanying drawings. The drawings are for reference and illustration purposes only and are not intended to limit the scope of the present disclosure.
Example one
As shown in fig. 1, the present embodiment discloses a non-isolated photovoltaic grid-connected inverter, including: capacitor CPVInductor LcAnd four unidirectional power switches, capacitors CPVAre respectively passed through a unidirectional power switch VT1Unidirectional power switch VT2And inductor LcAre connected with one-way power switch VT3Unidirectional power switch VT4Connected in parallel with the inductor L after being connected in seriescAt both ends of the same.
Further, the capacitor CPVIs a decoupling capacitor. The decoupling capacitors are arranged at two ends of the power supply and can provide a relatively stable power supply, so that the input direct-current power supply cannot be short-circuited due to the fault of the switching device. Meanwhile, the inverter in the embodiment is a current source type inverterThe transformer can increase the input voltage, so that a single photovoltaic cell panel can be directly connected with a single-phase power grid.
Further, a capacitor CPVPositive pole and unidirectional power switch VT1Collector connection of, unidirectional power switch VT1And the inductor LcOne end of the first electrode is connected with the base electrode and the base electrode is grounded;
capacitor CPVNegative pole and unidirectional power switch VT2Emitter-connected, unidirectional power switch VT2Collector of and the inductor LcThe other end of the first resistor is connected with the base electrode and the base electrode is grounded;
unidirectional power switch VT3Emitter and unidirectional power switch VT4Collector connection of, unidirectional power switch VT4And the inductor LcOne end of the unidirectional power switch VT is connected with the base electrode of the unidirectional power switch VT3Collector of and the inductor LcThe other end of the first resistor is connected with the base electrode and the base electrode is grounded.
In the embodiment, the grid-connected inverter adopts a current source type inverter and a capacitor CPVCurrent i ofPVThe photovoltaic inverter has the advantages that unidirectional outflow is carried out from the positive electrode of the photovoltaic cell panel, the requirements can be met only by the unidirectional power switch, and the anti-parallel diode is not required to be added, so that the number of components in the inverter is reduced, the cost of the inverter is reduced, and the size of the inverter is reduced.
Example two
As shown in fig. 2, the present embodiment discloses a grid-connected photovoltaic power generation system, including: photovoltaic cell panel 10, filter 20, non-isolated photovoltaic grid-connected inverter 30, photovoltaic cell panel 10 and capacitor CPVAnd one port of the filter 20 is connected with the non-isolated photovoltaic grid-connected inverter 30, and the other end is connected with the power grid 40.
Further, the filter 20 comprises a capacitor CfAnd an inductor LfCapacitor CfAnd inductor LfIs connected with a unidirectional power switch VT3Emitter and unidirectional power switch VT4Collector connecting wire connection, capacitor CfThe other end of the anode is connected with the cathode of the photovoltaic cell panel,capacitor CfAnother end of (8), inductance LfThe other ends of the two ends of the power grid are respectively connected with the two ends of the power grid.
It should be noted that a schematic diagram of a path of the non-isolated photovoltaic grid-connected inverter to the ground leakage current is shown in fig. 3, where CGroundRepresenting the capacitance, R, of the photovoltaic panel 10 to groundGroundRepresenting the earth resistance, i, of the unidirectional network 40C groundDenotes the flow through CGroundCurrent of (2), i.e., leakage current:
Figure GDA0002418654630000061
due to CGroundIs bypassed, is a low-voltage distribution system of 220V/380V in China, and widely adopts an operation mode of directly grounding a neutral point, so that R is a high-voltage distribution systemGround≈0，CGroundThe voltage across is constant. Thus, it is possible to provide
Figure GDA0002418654630000071
Therefore, the non-isolated photovoltaic grid-connected inverter 30 disclosed in the embodiment eliminates the phenomenon of the earth leakage current, and improves the efficiency of the inverter.
EXAMPLE III
As shown in fig. 4 to 7, the present embodiment discloses a control method for the above-mentioned photovoltaic grid-connected power generation system, wherein in fig. 4 to 7, a broken line indicates that the circuit is in an off state, and a solid line indicates that the circuit is in an on state. The control process includes four modes:
inductor LcAnd (3) charging mode: as shown in fig. 4, controlling a unidirectional power switch VT1And unidirectional power switch VT2Conducting unidirectional power switch VT3And unidirectional power switch VT4Off, photovoltaic panel 10 to inductor LcCharging, single-phase grid 40 and inductor LfCapacitor CfForming a closed loop, non-isolated output current i of the photovoltaic grid-connected inverter 30invIs zero.
Inverter output forward current mode: as shown in fig. 5, controlling the unidirectional power switch VT1And unidirectional power switch VT3Conducting unidirectional power switch VT2And unidirectional power switch VT4Disconnected, photovoltaic panel 10 and inductor LcDischarging to release energy, and outputting forward current i by the non-isolated photovoltaic grid-connected inverter 30invAnd is connected to the inductor LcThe same current value iLC＝iinv。
Inverter output reverse current mode: as shown in fig. 6, controlling the unidirectional power switch VT2And unidirectional power switch VT4Conducting unidirectional power switch VT1And unidirectional power switch VT3When the grid-connected photovoltaic inverter 30 is closed, the non-isolated grid-connected photovoltaic inverter 30 outputs reverse current iinvAnd is connected to the inductor LcCurrent value iLCThe same is true.
Inductor LcA freewheeling mode: as shown in fig. 7, controlling the unidirectional power switch VT3And unidirectional power switch VT4Conducting unidirectional power switch VT1And unidirectional power switch VT2Open, inductor LcCurrent value iLCKeeping unchanged, and outputting current value i of non-isolated photovoltaic grid-connected inverter 30invIs zero.
Further, the current hysteresis control is adopted for the non-isolated photovoltaic grid-connected inverter 3 in the embodiment, and the control includes control over a positive half cycle of grid-connected current and control over a negative half cycle of the grid-connected current.
In practical application, for convenience of operation, the practical grid-connected current uses igIndicating, for grid-connected current set-point irefRepresentative, inductance LcGiven reference value of current iLC-refIt is shown that since the inverter in the present embodiment is a current source type inverter, the reference current value iLC-refIs a direct current quantity.
iref＝Irefsin(ωt+θ)，
Wherein, IrefThe amplitude is given to the grid-connected current, omega is the angular frequency of the power grid, and theta is an initial phase angle.
Because the non-isolated photovoltaic grid-connected inverter 30 outputs current iinvIs a PWM current having a value equal to the inductor LcCurrent iLCFor energy output by the photovoltaic panel 10 to the single-phase grid 40, iinvShould be greater than IrefI.e. inductance LcGiven reference value i of currentLC-refShould be greater than IrefIn this embodiment, i is setLC-ref＝3Iref. In order to ensure the unit power factor grid connection, the grid connection current should be in phase with the grid voltage, so the voltage expression of the grid 40 is: u. ofg＝Umsin (ω t + θ), where ugFor instantaneous value of network voltage, UmIs the grid voltage amplitude.
As shown in fig. 8, in the hysteresis control process, the on/off states of four unidirectional power switches are controlled according to the current tracking deviation, wherein the hysteresis loop width is represented by H, and the actual grid-connected current igShould satisfy the control result of imin＜ig＜imaxWherein:
imax＝iref+H＝Irefsin(ωt+θ)+H,
imin＝iref-H＝Irefsin(ωt+θ)-H。
further, as shown in fig. 9, the control process for the positive half cycle of the grid-connected current specifically includes:
acquisition of t1Current i at timegAt ig＜iminTime, control the unidirectional power switch VT1And unidirectional power switch VT3Conducting, the system works in a mode that the inverter outputs forward current to control igIncreasing to track grid-connected current given value iref；
At imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＜iLC-refControlling said unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcA charging mode;
at imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＞iLC-refControlling said unidirectional power switch VT3And unidirectional power switch VT4When the system is conducted, the system works in the inductor LcA freewheel mode;
at ig＞imaxIf it is determined that i isLC＞iLC-refControlling said one-way workRate switch VT2And unidirectional power switch VT4On, the system works in the mode that the inverter outputs reverse current to control igDecrease;
at ig＞imaxIf it is determined that i isLC＜iLC-refSaid unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcCharging mode to control igIs reduced in which iLC-refIs an inductive current iLCTo the reference value of (c).
Further, as shown in fig. 10, the control process for the negative half cycle of the grid-connected current includes:
acquisition of t1Current i at timegAt ig＞imaxTime, control the unidirectional power switch VT2And unidirectional power switch VT4On, the system works in the mode that the inverter outputs reverse current to control igDecrease;
at imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＜iLC-refControlling said unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcA charging mode;
at imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＞iLC-refControlling said unidirectional power switch VT3And unidirectional power switch VT4When the system is conducted, the system works in the inductor LcA freewheel mode;
at ig＜iminIf it is determined that i isLC＞iLC-refControlling said unidirectional power switch VT1And unidirectional power switch VT3Conducting, the system works in a mode that the inverter outputs forward current to control igIncreasing to track grid-connected current given value iref；
At ig＞imaxIf it is determined that i isLC＜iLC-refSaid unidirectional power switch VT1Unidirectional power switchOff VT2When the system is conducted, the system works in the inductor LcCharging mode to control igAnd decreases. The following were used:
it should be noted that, the DC-side voltage of the inverter in the voltage-type photovoltaic grid-connected inverter must be greater than the peak value of the single-phase ac grid voltage, and generally is above 350V, to achieve grid-connected operation, and the output voltage of a single photovoltaic module cannot be reached.
According to the maximum power P of the photovoltaic panel 10mppTo calculate and obtain a given value i of grid-connected currentrefAnd tracking the maximum power of the photovoltaic cell panel by tracking the current given value. Therefore, the tracking of the maximum power of the photovoltaic cell panel can be realized by the inverter.
Pgrid＝ηPmpp，
Figure GDA0002418654630000091
Figure GDA0002418654630000092
Wherein, PgridRepresenting the power output by the non-isolated pv grid inverter 30 to the single-phase grid 40, η is the efficiency of the non-isolated pv grid inverter 30.
As shown in fig. 11, control igIncreasing to track grid-connected current given value irefThe method specifically comprises the following steps:
acquiring the output voltage U of the photovoltaic cell panel 10 by using a voltage sensorPVCollecting the instantaneous value u of the voltage of the network 40gAnd collecting the output current I of the photovoltaic cell panel 10 by means of a current sensorPV；
Calculating the maximum power of the photovoltaic cell panel 10 according to a maximum power tracking algorithm;
it should be noted that the maximum power tracking algorithm herein includes, but is not limited to, a disturbance observation method, a conductance modulation method, and the like.
Calculating the given amplitude I of the grid-connected current according to the maximum power of the photovoltaic cell panel 10ref；
Filtering a voltage alternating current signal of a power grid 40 by a low-pass filter, and entering a single-phase-locked loop to obtain a phase angle signal sin (ω t + θ);
calculating a given value i of the grid-connected current according to the phase angle signal and the given amplitude of the grid-connected currentrefTo realize control igIncreasing tracking grid-connected current given value iref。
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (9)

1. A non-isolated photovoltaic grid-connected inverter, comprising: capacitor CPVInductor LcAnd four unidirectional power switches, capacitors CPVAre respectively passed through a unidirectional power switch VT1Unidirectional power switch VT2And inductor LcAre connected with one-way power switch VT3Unidirectional power switch VT4Connected in parallel with the inductor L after being connected in seriescWherein:
the capacitor CPVPositive pole and unidirectional power switch VT1Collector connection of, unidirectional power switch VT1And the inductor LcOne end of the first electrode is connected with the base electrode and the base electrode is grounded;
capacitor CPVNegative pole and unidirectional power switch VT2Emitter-connected, unidirectional power switch VT2Collector of and the inductor LcThe other end of the first resistor is connected with the base electrode and the base electrode is grounded;
unidirectional power switch VT3Emitter and unidirectional power switch VT4Collector connection of, unidirectional power switch VT4And the inductor LcIs connected to one end ofGrounding of base and unidirectional power switch VT3Collector of and the inductor LcThe other end of the first resistor is connected with the base electrode and the base electrode is grounded;
in the unidirectional power switch VT1And unidirectional power switch VT2Conducting unidirectional power switch VT3And unidirectional power switch VT4When the grid-connected photovoltaic power generation system is disconnected, the grid-connected photovoltaic power generation system works on the inductor LcA charging mode; the unidirectional power switch VT1And unidirectional power switch VT3Conducting unidirectional power switch VT2And unidirectional power switch VT4When the grid-connected photovoltaic power generation system is disconnected, the grid-connected photovoltaic power generation system works in a mode that an inverter outputs forward current; the unidirectional power switch VT2And unidirectional power switch VT4Conducting unidirectional power switch VT1And unidirectional power switch VT3When the grid-connected photovoltaic power generation system is closed, the grid-connected photovoltaic power generation system works in a mode that an inverter outputs reverse current; the unidirectional power switch VT3And unidirectional power switch VT4Conducting unidirectional power switch VT1And unidirectional power switch VT2When the grid-connected photovoltaic power generation system is disconnected, the grid-connected photovoltaic power generation system works on the inductor LcA freewheel mode; the photovoltaic grid-connected power generation system comprises a photovoltaic cell panel, a filter and the non-isolated photovoltaic grid-connected inverter.
2. The non-isolated photovoltaic grid-connected inverter according to claim 1, wherein the capacitor C isPVIs a decoupling capacitor.
3. A grid-connected photovoltaic power generation system, comprising: photovoltaic panel, filter and non-isolated photovoltaic grid-connected inverter according to any of claims 1-2, photovoltaic panel and said capacitor CPVAnd one port of the filter is connected with the non-isolated photovoltaic grid-connected inverter, and the other end of the filter is connected with a power grid.
4. The grid-connected PV power generation system of claim 3, wherein the filter comprises a capacitor CfAnd an inductor LfCapacitor CfAnd inductor LfIs connected with a unidirectional power switch VT3Emitter and unidirectional power switch VT4Collector connecting wire connection, capacitor CfThe other end of the capacitor is connected with the negative electrode of the photovoltaic cell panel, and a capacitor CfAnother end of (8), inductance LfThe other ends of the two ends of the power grid are respectively connected with the two ends of the power grid.
5. A control method of a grid-connected photovoltaic power generation system according to any one of claims 3 to 4, characterized by comprising:
controlling the unidirectional power switch VT1And unidirectional power switch VT2Conducting unidirectional power switch VT3And unidirectional power switch VT4Open, the photovoltaic panel couples the inductor LcCharging, the system works in the inductor LcA charging mode;
controlling the unidirectional power switch VT1And unidirectional power switch VT3Conducting unidirectional power switch VT2And unidirectional power switch VT4Open, the photovoltaic panel and the inductor LcDischarging, wherein the non-isolated photovoltaic grid-connected inverter outputs forward current and is connected with an inductor LcWhen the current values are the same, the system works in a mode that the inverter outputs forward current;
controlling the unidirectional power switch VT2And unidirectional power switch VT4Conducting unidirectional power switch VT1And unidirectional power switch VT3Shut down, the non-isolated pv grid inverter outputting a reverse current and interacting with inductor LcWhen the current values are the same, the system works in a mode that the inverter outputs reverse current;
controlling the unidirectional power switch VT3And unidirectional power switch VT4Conducting unidirectional power switch VT1And unidirectional power switch VT2Open, inductor LcThe current value is kept unchanged, the output current value of the non-isolated photovoltaic grid-connected inverter is zero, and the system works in an inductor LcFreewheel mode.
6. The control method according to claim 5, further comprising:
and carrying out current hysteresis control on the non-isolated photovoltaic grid-connected inverter, wherein the current hysteresis control comprises control on a positive half cycle of grid-connected current and control on a negative half cycle of the grid-connected current.
7. The control method according to claim 6, wherein the grid-connected current positive half cycle control specifically comprises:
acquisition of t1Current i at timegAt ig＜iminTime, control the unidirectional power switch VT1And unidirectional power switch VT3Conducting, the system works in a mode that the inverter outputs forward current to control igIncreasing to track grid-connected current given value iref；
At imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＜iLC-refControlling said unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcA charging mode;
at imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＞iLC-refControlling said unidirectional power switch VT3And unidirectional power switch VT4When the system is conducted, the system works in the inductor LcA freewheel mode;
at ig＞imaxIf it is determined that i isLC＞iLC-refControlling said unidirectional power switch VT2And unidirectional power switch VT4On, the system works in the mode that the inverter outputs reverse current to control igDecrease;
at ig＞imaxIf it is determined that i isLC＜iLC-refSaid unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcCharging mode to control igIs reduced in which iLC-refIs an inductor LcCurrent iLCTo the reference value of (c).
8. The control method according to claim 7, wherein the grid-connected current negative half-cycle control specifically comprises:
acquisition of t1Current i at timegAt ig＞imaxTime, control the unidirectional power switch VT2And unidirectional power switch VT4On, the system works in the mode that the inverter outputs reverse current to control igDecrease;
at imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＜iLC-refControlling said unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcA charging mode;
at imin＜ig＜imaxIf so, judging the inductor LcCurrent value iLC＞iLC-refControlling said unidirectional power switch VT3And unidirectional power switch VT4When the system is conducted, the system works in the inductor LcA freewheel mode;
at ig＜iminIf it is determined that i isLC＞iLC-refControlling said unidirectional power switch VT1And unidirectional power switch VT3Conducting, the system works in a mode that the inverter outputs forward current to control igIncreasing to track grid-connected current given value iref；
At ig＞imaxIf it is determined that i isLC＜iLC-refSaid unidirectional power switch VT1Unidirectional power switch VT2When the system is conducted, the system works in the inductor LcCharging mode to control igAnd decreases.
9. The control method according to claim 7 or 8, characterized in that the control igIncreasing to track grid-connected current given value irefThe method specifically comprises the following steps:
collecting the output voltage of the photovoltaic cell panel by using a voltage sensor, collecting a voltage alternating current signal of the power grid, and collecting the output current of the photovoltaic cell panel by using a current sensor;
calculating the maximum power of the photovoltaic cell panel according to a maximum power tracking algorithm;
calculating a given amplitude of grid-connected current according to the maximum power of the photovoltaic cell panel;
filtering the voltage alternating current signal of the power grid through a low-pass filter, and then entering a single-phase-locked loop to obtain a phase angle signal;
calculating a given value i of the grid-connected current according to the phase angle signal and the given amplitude of the grid-connected currentrefTo realize control igIncreasing tracking grid-connected current given value iref。
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