CN108242884B - Photovoltaic inverter system for one-way MPPT grid connection and short-circuit protection method thereof - Google Patents

Photovoltaic inverter system for one-way MPPT grid connection and short-circuit protection method thereof Download PDF

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CN108242884B
CN108242884B CN201611216361.5A CN201611216361A CN108242884B CN 108242884 B CN108242884 B CN 108242884B CN 201611216361 A CN201611216361 A CN 201611216361A CN 108242884 B CN108242884 B CN 108242884B
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CN108242884A (en
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李俊峰
刘炳
赵帅央
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Beijing Etechwin Electric Co Ltd
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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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • 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
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H02M1/325—Means for protecting converters other than automatic disconnection with means for allowing continuous operation despite a fault, i.e. fault tolerant converters
    • 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

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Abstract

The invention relates to a photovoltaic inverter system for single-path MPPT grid connection and a short-circuit protection method thereof. The short-circuit protection method of the photovoltaic inverter system for single-path MPPT grid connection comprises the following steps: calculating the total number of the photovoltaic modules based on the design capacity of each photovoltaic inverter, the rated power of each photovoltaic module and the number of the photovoltaic modules connected in series in each path; calculating the maximum rated current flowing through the anti-reverse diode module at the direct current side based on the total number of the photovoltaic modules and the short-circuit current of each photovoltaic module; and setting the anti-reverse diode module based on the maximum reverse voltage between the positive and negative output ends of the direct-current busbar of the inverter system and the maximum rated current, so that the on-state average current of the anti-reverse diode module is larger than the maximum rated current, and the reverse repeated peak voltage of the anti-reverse diode module is larger than the maximum reverse voltage.

Description

Photovoltaic inverter system for one-way MPPT grid connection and short-circuit protection method thereof
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a short-circuit protection method of a photovoltaic inverter and a photovoltaic inverter system.
Background
In a single-path MPPT (Maximum Power Point Tracking) photovoltaic inverter, the direct current sides of all photovoltaic inverter modules are connected together through a mother (copper) bar, so that the system can conveniently manage and track the Maximum Power Point in a centralized manner. However, the direct current side may cause a direct current short circuit due to the reduction of the insulation performance or the abnormality of the power tube driving signal, the part with the broken insulation or the bridge arm which is conducted at the same time becomes a short circuit point, so that the energy of the alternating current side (grid side), the supporting capacitor and the direct current side (photovoltaic panel side) forms a short circuit current loop through the point, while the energy of the alternating current side occupies most of the energy, because each photovoltaic inverter module runs in parallel on the direct current side, the energy of the alternating current side (grid side) of other non-fault modules can also be released through the short circuit point by the follow current diode in each photovoltaic inverter module, thereby causing the damage of the power semiconductor switching device in the non-fault module. That is, the short circuit on the dc side of one inverter module may damage the freewheeling diodes in all the inverter modules, thereby further enlarging the influence of the fault, resulting in the shutdown of the entire inverter system, and causing serious operation accidents and large economic losses.
Fig. 1 is a schematic circuit diagram of a conventional single-circuit MPPT photovoltaic inverter when a dc-side short circuit occurs. The description will be given by taking three photovoltaic inverter modules connected in parallel as an example. The black broken line arrow indicates occurrence of a dc-side short circuit, two different sets of broken lines and chain-dotted lines in the figure respectively show short circuit loops formed by ac currents of the respective sets of photovoltaic inverter modules when the dc-side short circuit occurs in the set of photovoltaic inverter modules, and the arrow indicates a flowing direction of the short circuit current. That is, when a short-circuit fault occurs in one group of photovoltaic inverter modules, the fault easily extends to other non-faulty modules without any short-circuit protection.
Disclosure of Invention
Based on the risks and protection requirements existing in the photovoltaic inverter system, the invention provides the following technical scheme.
One aspect of the present invention relates to a short-circuit protection method for a photovoltaic inverter system for single-path MPPT grid connection, which is used for connecting a plurality of parallel photovoltaic inverters to an inverter system of a photovoltaic module through respective dc busbars, wherein in each of the photovoltaic inverters, an anti-reverse diode module is respectively connected in series between a positive connection end of a switch module of each of the photovoltaic inverters and a positive output end of the dc busbar, and between a negative connection end of the switch module of each of the photovoltaic inverters and a negative output end of the dc busbar, and the short-circuit protection method includes: calculating the total number of the photovoltaic modules based on the design capacity of each photovoltaic inverter, the rated power of each photovoltaic module and the number of the photovoltaic modules connected in series in each path; calculating the maximum rated current flowing through the anti-reverse diode module at the direct current side based on the total number of the photovoltaic modules and the short-circuit current of each photovoltaic module; and setting the anti-reverse diode module based on the maximum reverse voltage between the positive and negative output ends of the direct-current busbar of the inverter system and the maximum rated current, so that the on-state average current of the anti-reverse diode module is larger than the maximum rated current, and the reverse repeated peak voltage of the anti-reverse diode module is larger than the maximum reverse voltage.
According to the short-circuit protection method, the photovoltaic inverter further comprises a radiator for radiating the anti-reverse diode modules, and the total power consumption of the anti-reverse diode modules in each photovoltaic inverter is calculated; and calculating the thermal resistance and the heat dissipation power of the heat sink based on the total power consumption, the thermal resistance parameter from the inside of the inverse diode module to the shell, the thermal resistance parameter from the shell to the heat sink and a preset environmental temperature.
According to the short-circuit protection method, slope resistance and threshold voltage are calculated based on the volt-ampere characteristic curve of the anti-reverse diode module; calculating the average value and the root mean square value of the on-state current flowing through the anti-reverse diode module in one period; and calculating the total power consumption of the anti-reverse diode module based on the slope resistance, the threshold voltage, the average value and the square root value of the on-state current.
According to the short-circuit protection method, the photovoltaic inverter further comprises a heat radiation fan used for the radiator, and the air volume of the heat radiation fan is calculated based on the total power consumption and the environmental parameters.
Another aspect of the present invention provides a photovoltaic inverter system for single-pass MPPT grid connection, the inverter system being disposed between a photovoltaic module and a grid and including a plurality of photovoltaic inverters, each of the photovoltaic inverters including: the switch module comprises a positive connecting end and a negative connecting end; the photovoltaic inverters connected in parallel are connected to the photovoltaic assembly through the respective direct current bus; and the anti-reverse diode modules are respectively connected in series to the switch module between the positive connecting end and the positive output end of the direct-current busbar and between the negative connecting end and the negative output end of the direct-current busbar so as to prevent short-circuit current from flowing into the single-circuit MPPT photovoltaic inverter which does not break down when a direct-current side short circuit occurs.
According to the photovoltaic inverter system, the short-circuit current of the anti-reverse diode module is greater than the maximum rated current of the anti-reverse diode module flowing through the direct current side, and the reverse rated voltage of the anti-reverse diode module is greater than the maximum reverse voltage between the positive and negative electrode output ends of the direct current busbar of the inverter system.
According to the photovoltaic inverter system, the positive connecting end of the switch module is connected with the positive output end of the direct-current busbar in series, the positive terminal of the anti-reverse diode module is connected with the positive output end of the direct-current busbar, the negative terminal of the anti-reverse diode module is connected with the positive connecting end of the switch module, the negative connecting end of the switch module is connected with the negative output end of the direct-current busbar in series, the positive terminal of the anti-reverse diode module is connected with the negative connecting end of the switch module, and the negative terminal of the anti-reverse diode module is connected with the negative output end of the direct-current busbar.
According to the photovoltaic inverter system, more than two reverse prevention diodes are arranged in a single photovoltaic inverter.
According to the photovoltaic inverter system, the photovoltaic inverter system further comprises a radiator, and the radiator is used for radiating the inverse diode preventing module.
According to the photovoltaic inverter system, the heat radiator further comprises a heat radiation fan, and the heat radiator radiates heat through the air quantity generated by the heat radiation fan.
According to the invention, the photovoltaic inverter module can be effectively protected by the anti-reverse diode module. In addition, the expansion of the dc short-circuit failure in the photovoltaic inverter system can be effectively prevented.
Drawings
Fig. 1 is a schematic circuit diagram of a conventional photovoltaic inverter system for single MPPT grid connection when a dc side short circuit occurs;
fig. 2 is a schematic circuit diagram of a single-path MPPT photovoltaic grid-connected inverter system according to the present invention when a dc-side short circuit occurs;
FIG. 3 is a flow chart of the inverter module setting for the photovoltaic inverter to which the present invention relates;
FIG. 4 is a model schematic diagram of Matlab/Simulink simulation of a photovoltaic inverter system for single-path MPPT photovoltaic grid connection according to the present invention;
FIG. 5 is a schematic diagram of the DC short circuit current of the failed photovoltaic inverter module # 1;
fig. 6 is a schematic of the dc short circuit current of non-faulty pv inverter module # 2;
fig. 7 is a schematic of the dc short circuit current of non-faulty photovoltaic inverter module # 3.
Detailed Description
The present invention may be better understood by consideration of the following description of specific embodiments thereof in conjunction with the accompanying drawings, in which like or similar reference numerals indicate like or similar features.
Features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is in no way limited to any specific configuration and algorithm set forth below, but rather covers any modification, replacement or improvement of elements, components or algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.
Fig. 2 is a schematic circuit diagram of the inverter system for single-path MPPT photovoltaic grid connection according to the present invention when a dc-side short circuit occurs. The inverter system is arranged between the photovoltaic module and the grid. The inverter system includes a plurality of groups of photovoltaic inverter modules. Each photovoltaic inverter module includes: a switch module 10, the switch module 10 including a positive connection end and a negative connection end; a plurality of photovoltaic inverters connected in parallel are connected to a photovoltaic module through the direct current bus bar (not shown in the figure); and the reverse-preventing diode module 20, the reverse-preventing diode module 20 is respectively connected in series between the positive connecting end of the switch module 10 and the positive output end of the direct-current busbar, and between the negative connecting end of the switch module 10 and the negative output end of the direct-current busbar, so as to prevent short-circuit current from flowing into the photovoltaic inverter module which is not in fault when the direct-current side short circuit occurs.
In the following description, three groups of inverter modules are connected in parallel and connected to the photovoltaic module through respective dc busbars. The switch module of each photovoltaic inverter module comprises a first bridge arm, a second bridge arm and a third bridge arm, the first bridge arm, the second bridge arm and the third bridge arm respectively comprise an upper bridge arm and a lower bridge arm which are connected in series, the upper bridge arm and the lower bridge arm respectively comprise a power semiconductor switch module formed by connecting a power semiconductor switch device and a freewheeling diode in parallel, the upper ends of the upper bridge arms are connected with each other to form a positive electrode connecting end, and the lower ends of the lower bridge arms are connected with each other to form a negative electrode connecting end. The inverter module further includes a support capacitor connecting the positive electrode connection end and the negative electrode connection end, and a filter reactor (not shown) connecting a connection point of the upper arm and the lower arm to a power grid. The power semiconductor switching devices may be an SCR (silicon controlled rectifier), a GTO (Gate self-turn-off thyristor), a GTR (giant transistor), a VMOSFET (vertical MOS field effect transistor), an IGBT (Insulated Gate Bipolar transistor), and the like, and hereinafter, the parallel structure of the IGBT and the freewheeling diode is referred to as an IGBT module by taking an example in which the power semiconductor switching device is an Insulated Gate Bipolar Transistor (IGBT).
In the single-circuit MPPT pv grid-connected pv inverter system of fig. 1, broken line arrows indicate short-circuiting on the dc side, broken lines indicate the flow paths of short-circuiting currents, arrows in a broken line frame indicate the flow directions of short-circuiting currents, since the pv inverter modules share the same dc voltage, if the dc side is short-circuited, the dc side of each pv inverter module is short-circuited, and since there is a short-circuiting loop from the ac side-free wheel diode-dc short-circuiting point, if no protection device is added, the pv inverter modules will have short-circuiting currents from the grid side to the dc side short-circuiting point through the IGBT modules, the short-circuiting type is similar to an ac three-phase short-circuiting, and depending on the magnitude of the instantaneous line voltage, the short-circuiting currents pass through the upper arm from the ac phase, pass through the dc short-circuiting point, then flow into the lower arm, and return to the other phase of the line voltage, the three line voltages are all output from the upper bridge arm and return from the lower bridge arm, and the total current flowing through the direct current short-circuit point is the set of short-circuit currents under the driving of the three line voltages, so that the direct current side short-circuit currents are all from the positive pole to the negative pole of the direct current side, the short-circuit currents have consistent directivity, and the direction is just opposite to the direction of the direct current when the grid-connected inverter system normally operates. The power diode is a semiconductor device with unidirectional conductivity, and the short-circuit current has the unidirectional property and is opposite to the direction of the direct current in normal operation, so that the diffusion of the short-circuit current can be well prevented by additionally arranging the anti-reverse diode on the direct current side, and the current circulation requirement in normal operation can be met.
Based on the above analysis, the single-pass MPPT photovoltaic inverter shown in fig. 2 further includes a reverse diode prevention module 20 for short-circuit protection. In fig. 2, broken line arrows indicate occurrence of a dc-side short circuit, broken lines indicate a flow path of a short-circuit current, and arrows indicate a flow direction of the short-circuit current. The anti-reverse diode module 20 is respectively connected in series between the positive connection end of the switch module 10 and the positive output end of the dc bus bar, and between the negative connection end of the switch module 10 and the negative output end of the dc bus bar. The positive terminal of the anti-reverse diode module 20 connected in series between the positive connection end of the switch module 10 and the positive output end of the dc bus bar is connected to the positive output end of the dc bus bar, and the negative terminal of the anti-reverse diode module is connected to the positive connection end of the switch module 10; the positive terminal of the anti-reverse diode module 20, which is connected in series between the negative connection end of the switch module 10 and the negative output end of the direct-current busbar, is connected with the negative connection end of the switch module, and the negative terminal of the anti-reverse diode module 20 is connected with the negative output end of the direct-current busbar. In this circuit, a plurality of the reverse blocking diode modules 20 may be connected in series to perform protection as necessary.
The on-state average current of the anti-reverse diode module 20 is greater than the maximum rated current flowing through the anti-reverse diode module through the dc bus, and the reverse repetitive peak voltage of the anti-reverse diode module is greater than the maximum reverse voltage between the positive and negative output terminals of the dc bus of the inverter system.
The inverter module further comprises a radiator, and the radiator is used for radiating the reverse-proof diode module so as to effectively protect the reverse-proof diode.
The inverter module further comprises a heat dissipation fan, and the heat dissipation fan enables the radiator to dissipate heat timely and reliably.
The single-path MPPT photovoltaic inverter system provided with the anti-reverse diode module is explained above. The short-circuit protection method of the reverse diode protection module described above will be described below.
Fig. 3 is a setting flowchart of the reverse prevention diode module of the photovoltaic inverter according to the present invention. The embodiment of the invention provides a short-circuit protection method of an anti-reverse diode module, which specifically comprises the following steps: s1, calculating the total number of the photovoltaic modules based on the design capacity of each photovoltaic inverter, the rated power of each photovoltaic module and the number of the photovoltaic modules connected in series in each path; s2, calculating the maximum rated current flowing through the anti-reverse diode module on the direct current side based on the total number of the photovoltaic modules and the short-circuit current of each photovoltaic module; and S3, setting the anti-reverse diode module based on the maximum reverse voltage between the positive and negative electrode output ends of the direct-current busbar of the inverter system and the maximum rated current, so that the on-state average current of the anti-reverse diode module under direct current is larger than the maximum rated current, and the reverse repeat peak voltage of the anti-reverse diode module is larger than the maximum reverse voltage.
In the single-circuit MPPT photovoltaic inverter system, when photovoltaic power generation is carried out, unidirectional flexible direct current from a photovoltaic module such as a crystalline silicon solar panel flows through the direct current side of the photovoltaic inverter, and the design capacity W, the bearable overload coefficient k and the rated power W of the photovoltaic module of each photovoltaic inverter unit are known1And the number of the photovoltaic modules connected in series at each input is S, then the combiner box outputsThe total number of lanes N is shown in formula 1.
Figure BDA0001190145550000071
The short-circuit current of each photovoltaic module is known as I1The current is a calibration parameter and represents the maximum safe current capable of passing through. The rated current In flowing out from the dc side through the anti-reverse diode module is shown In equation 2.
In＝I1X N formula 2
Considering current fluctuation and other abnormal conditions at ordinary times, a 1.1-time reliability coefficient is set, so that the maximum rated current I flowing through the reverse-proof diode finallyNAs shown in the following formula 3.
IN＝1.1×In Formula 3
In addition, the maximum reverse voltage U between the positive and negative poles of the dc bus bar of the inverter module is known in consideration of the operating overvoltageDMThe U isDMThe setting is made according to engineering experience.
Based on maximum rated current INAnd maximum reverse voltage UDMThe reverse protection diode for short circuit protection is selected so that the on-state average current of the reverse protection diode under direct current is larger than the maximum rated current and the reverse repetition peak voltage of the reverse protection diode is larger than the maximum reverse voltage.
The following description will be given with specific examples.
For example, the design capacity W of each photovoltaic inverter unit is 210kW, and the sustainable overload factor is 1.1. Taking the currently marketed British 260W (i.e. rated power 260W) photovoltaic module as an example, the number S of the photovoltaic modules connected in series in each circuit is 22. Based on the above, the total number of output paths N of the combiner box is as follows:
n210000 x 1.1/260/22 x 40 channels
The total input path number of the photovoltaic inverter is 40. According to the specific parameters of the photovoltaic modules, the short-circuit current of each photovoltaic module connected in series is 8.98A.
The rated current In of the dc side flowing through the anti-reflux diode is 8.98 × 40 502.88A
Taking the fluctuation of current and other abnormal conditions into consideration, the reliability coefficient of 1.1 is taken, so that the maximum rated current I finally flows through the direct current side diodeN＝1.1×502.88A＝553.168A。
According to engineering experience, the maximum reverse voltage U between the positive and negative output ends of the direct current busbar of the inverter system is considered under the condition of considering the operation overvoltageDM＝1500V。
Selecting MDK800 diode module (common cathode, two parallel diodes) of xX model, and repeating peak voltage U in reverse directionRRM2600V, and the average current in the on state is IFThe reverse repetitive peak voltage is the highest peak voltage that the diode module can repeatedly apply, and the on-state average current is a parameter for which the rated current is nominal, and two anti-reverse diode modules are set to be connected in series on the dc side. I isF＞INAnd the current meets the requirements. In addition, the inverse peak voltage U of the diode moduleRRMGreater than the maximum reverse voltage UDMAnd therefore the voltage also meets the requirements.
Optionally, the peak voltage U is repeated in reverse when the diode is selectedRRMPreferably the maximum reverse voltage U that can be sustained in the circuit in which the diode operatesDM2 to 3 times higher than that of U, for exampleDMIn the case of 1500V, if the reverse repetition peak voltage is 3 times the maximum reverse voltage, the reverse repetition peak voltage needs to reach 4500V, and the tolerable reverse repetition peak voltage of two diodes connected in series is 2600V × 2 5200V, which is greater than 4500V, so the reverse repetition peak voltage U of the diode is now equal to the maximum reverse voltageRRMBut also meets the requirements.
And carrying out simulation verification on the parameter setting. Fig. 4 is a model schematic diagram of Matlab/Simulink simulation of a single-pass MPPT photovoltaic inverter system according to the present invention. The method comprises the steps of establishing a simulation model according to the working condition that an anti-reverse diode m is additionally arranged on the direct current side of the photovoltaic inverter modules connected in parallel, wherein the simulation model comprises a fault module #1, non-fault modules #2 and #3 and the anti-reverse diode module m connected in series when a direct current short circuit occurs, and a short circuit equivalent switch with internal resistance is used at a direct current short circuit point. The condition that a direct current side of one photovoltaic inverter module is short-circuited can be simulated by controlling the short-circuit equivalent switch. The main simulation parameters are as follows: the line voltage Up-p of the power supply/transformer is 315V, the frequency F is 50Hz, the internal resistance R is 8.5 mOmega, and L is 18.6 uH; r1 and L1 of the reactor are respectively 1.12 mOmega and 0.03 mH; short-circuit resistance R2 ═ 1m Ω; DC support capacitance: c ═ 3.32 mF; the internal resistance R3 of the reverse prevention diode is 1 momega; the short equivalent switch will be turned on 0.3s after the simulation starts, i.e. the dc short occurs at 0.3 s.
Simulation results are shown in fig. 5, 6 and 7, and fig. 5 is a schematic diagram of the dc short-circuit current of the failed pv inverter module # 1; fig. 6 is a schematic of the dc short circuit current of non-faulty pv inverter module # 2; fig. 7 is a schematic of the dc short circuit current of non-faulty photovoltaic inverter module 3 #. The #1 module is a fault module (short circuit occurs), and the #2 and #3 modules are non-fault modules. It can be seen that, by adding the anti-reverse diode module to the dc side, when a fault occurs, the dc current of the #1 module is about 14kA, and no short-circuit current flows through the dc sides of the #2 and #3 modules. The short-circuit current of the 1# module is switched out of a main loop under the protection action of the alternating-current circuit breaker, and the #2 and #3 modules normally and stably operate.
After the anti-reverse diode module is selected, protection of the anti-reverse diode module is considered next. The photovoltaic inverter system further comprises a heat sink for dissipating heat from the anti-reverse diode module, thereby effectively protecting the anti-reverse diode module.
Optionally, calculating a total power consumption of the anti-reverse diode modules in one inverter module; and calculating the thermal resistance and the heat dissipation power of the heat sink based on the total power consumption, the thermal resistance parameter from the inside of the inverter chip to the shell, the thermal resistance parameter from the shell to the heat sink and the highest ambient temperature.
Optionally, in the calculation of the total power consumption of the power diode module, a slope resistance and a threshold voltage are obtained based on a volt-ampere characteristic curve of the anti-reverse diode module; calculating the average value and the root mean square value of the on-state current in one period; and calculating the total power consumption of the anti-reverse diode module based on the slope resistance, the threshold voltage, the average value and the square root value of the on-state current.
For the current flowing through the dc bus of the photovoltaic inverter module, the on-state loss is the main cause of heat generation. The slope resistance of the diode voltage-current characteristic curve is set as rdWill UTOSetting the average value of the on-state current in one period as IAVSetting the root mean square value of the on-state current in one period as IRMSAnd meanwhile, the on-state loss engineering calculation formula of the anti-reverse diode module is shown as a formula 4.
Figure BDA0001190145550000091
Continuing with the above example of the selected anti-reverse diode module, the power consumption of the single diode module is
Figure BDA0001190145550000092
The total power consumption of the two diode modules is thus 304W × 2 — 608W. Obtaining the thermal resistance R from the inner part of the chip to the shell according to the product manual of the selected diode modulejc0.019 ℃/W, thermal resistance R from housing to heat sinkcs0.04 ℃/W. Designed maximum ambient temperature of Ta, the heat resistance R from the radiator to the airsaSatisfies the following formula 5.
(Rjc+Rcs+Rsa) X 250+ Ta < 125 deg.C formula 5
Assuming that the designed ambient temperature Ta is 55 ℃, R issa< 0.221 ℃/W. Therefore, the selected radiator should satisfy the thermal resistance R at the ambient temperature of 55 DEG CsaIs less than 0.221 ℃/W, and the heat dissipation power Ps is more than 608W.
Alternatively, the heat resistance R is set tosaAnd calculating the air volume of a heat radiation fan of the radiator based on the total power consumption and the environmental parameters under the limitation of the heat radiation power Ps.
The above example is continued as an example.
Setting the environmental parameters, assuming that humid air with the temperature of 20 ℃, the atmospheric pressure of 760mmHg and the humidity of 65% is standard air, the density of the air is 1200g/m3, and additionally, the constant pressure specific heat of the air is known as Cp being 0.24(Kcal/Kg ℃), 1cal being 4.2J, the maximum temperature rise △ Tc allowed by the diode module being 125-55 ℃ being 70 ℃,
CMM and CFM are both air volumes per minute, the former being in cubic meters per minute and the latter being in cubic feet per minute, with 1CMM being 35.3 CFM.
Based on the above, the heat generated by the anti-reverse diode module 1s is equal to the heat dissipated by the heat sink, i.e., the left and right sides of the equation, Q is the air volume of the heat dissipating fan, and P is the heating power of the diode module.
0.24×(Q/60*1200)×△Tc＝P×1/4.2
Q＝(P×60)/(1200×4.2×0.24×△Tc)＝1.76×P/△Tc＝1.76×608/70＝15.3CFM＝0.433CMM
Therefore, the air volume of the selected heat dissipation fan should not be lower than 0.433m3And/min. The cooling fan is selected based on this.
The short-circuit protection method for the anti-reverse diode of the single-circuit MPPT photovoltaic inverter is described above with reference to specific examples. By setting the proper reverse-prevention diode through the setting, the effective protection of the non-fault module is realized when short circuit occurs. Meanwhile, the set radiator and the set heat dissipation fan are set, so that the anti-reverse diode module in work can be effectively protected.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Also, different features that are present in different embodiments may be combined to advantage. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art upon studying the drawings, the specification, and the claims.

Claims (10)

1. A short-circuit protection method of a photovoltaic inverter system for single-path MPPT grid connection is characterized in that,
the photovoltaic inverter system comprises a plurality of photovoltaic inverters which are connected in parallel, the photovoltaic inverters are connected to a photovoltaic assembly through respective direct current busbars, each photovoltaic inverter comprises a switch module, and anti-reverse diode modules are connected between the positive connecting end of each switch module and the positive output end of each direct current busbar and between the negative connecting end of each switch module and the negative output end of each direct current busbar in series, and the short circuit protection method comprises the following steps:
calculating the total number of the photovoltaic modules based on the design capacity of each photovoltaic inverter, the rated power of each photovoltaic module, the number of the photovoltaic modules connected in series in each circuit and the bearable overload coefficient;
calculating the maximum rated current flowing through the anti-reverse diode module at the direct current side based on the total number of the photovoltaic modules and the short-circuit current of each photovoltaic module; and
setting the anti-reverse diode module based on the maximum reverse voltage between the positive and negative output ends of the direct-current busbar and the maximum rated current, so that the on-state average current of the anti-reverse diode module is larger than the maximum rated current, and the reverse repeated peak voltage of the anti-reverse diode module is larger than the maximum reverse voltage.
2. Short-circuit protection method according to claim 1,
the photovoltaic inverter further comprises a heat sink for dissipating heat from the anti-reverse diode module,
calculating the total power consumption of each anti-reverse diode module;
and calculating the thermal resistance and the heat dissipation power of the heat sink based on the total power consumption, the thermal resistance parameter from the inside of the inverse diode module to the shell, the thermal resistance parameter from the shell to the heat sink and the preset environment temperature.
3. Short-circuit protection method according to claim 2,
the calculating the total power consumption of each inverse diode preventing module specifically includes:
solving slope resistance and threshold voltage based on the volt-ampere characteristic curve of the anti-reverse diode module;
calculating the average value and the root mean square value of the on-state current flowing through the anti-reverse diode module in one period;
and calculating the total power consumption of the anti-reverse diode module based on the slope resistance, the threshold voltage, the average value and the square root value of the on-state current.
4. Short-circuit protection method according to claim 2 or 3,
the photovoltaic inverter further comprises a heat dissipation fan for the heat sink,
and calculating the air volume of the heat radiation fan based on the total power consumption and the environmental parameters.
5. A photovoltaic inverter system for single-path MPPT grid connection is characterized in that,
the photovoltaic inverter system is configured between the photovoltaic module and the power grid and comprises a plurality of photovoltaic inverters,
each of the photovoltaic inverters includes:
the switch module comprises a positive connecting end and a negative connecting end;
the photovoltaic inverters connected in parallel are connected to the photovoltaic assembly through the respective direct current bus; and
the anti-reverse diode modules are respectively connected between the positive connecting end of the switch module and the positive output end of the direct-current busbar in series and between the negative connecting end of the switch module and the negative output end of the direct-current busbar in series, so that short-circuit current is prevented from flowing into the single-circuit MPPT photovoltaic inverter which does not have faults when a direct-current side short circuit occurs;
wherein the photovoltaic inverter system is configured to:
calculating the total number of the photovoltaic modules based on the design capacity of each photovoltaic inverter, the rated power of each photovoltaic module, the number of the photovoltaic modules connected in series in each circuit and the bearable overload coefficient; and the number of the first and second groups,
calculating the maximum rated current flowing through the anti-reverse diode module at the direct current side based on the total number of the photovoltaic modules and the short-circuit current of each photovoltaic module; and the number of the first and second groups,
setting the anti-reverse diode module based on the maximum reverse voltage between the positive and negative output ends of the direct-current busbar and the maximum rated current, so that the on-state average current of the anti-reverse diode module is larger than the maximum rated current, and the reverse repeated peak voltage of the anti-reverse diode module is larger than the maximum reverse voltage.
6. The photovoltaic inverter system of claim 5,
the short-circuit current of the anti-reverse diode module is larger than the maximum rated current of the anti-reverse diode module flowing through the direct current side, and the reverse rated voltage of the anti-reverse diode module is larger than the maximum reverse voltage between the positive and negative electrode output ends of the direct current bus of the inverter system.
7. The photovoltaic inverter system of claim 5,
the positive terminal of the anti-reverse diode module is connected with the positive output end of the direct current bus bar, the negative terminal of the anti-reverse diode module is connected with the positive connecting end of the switch module,
the positive terminal of the anti-reverse diode module is connected with the negative connecting end of the switch module, and the negative terminal of the anti-reverse diode module is connected with the negative output end of the direct-current busbar.
8. The photovoltaic inverter system of claim 5,
more than two reverse prevention diodes are arranged in a single photovoltaic inverter.
9. The photovoltaic inverter system of claim 5,
the anti-reverse diode module is characterized by further comprising a radiator, wherein the radiator is used for radiating the anti-reverse diode module.
10. The photovoltaic inverter system of claim 9,
the radiator is used for radiating through the air quantity generated by the cooling fan.
CN201611216361.5A 2016-12-23 2016-12-23 Photovoltaic inverter system for one-way MPPT grid connection and short-circuit protection method thereof Active CN108242884B (en)

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