CN111668817A - Photovoltaic grid-connected control method and system for blocking fault current - Google Patents

Photovoltaic grid-connected control method and system for blocking fault current Download PDF

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Publication number
CN111668817A
CN111668817A CN202010517472.XA CN202010517472A CN111668817A CN 111668817 A CN111668817 A CN 111668817A CN 202010517472 A CN202010517472 A CN 202010517472A CN 111668817 A CN111668817 A CN 111668817A
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China
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voltage
current
grid
short
converter
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赵力
黄学劲
梁耀林
陈喆
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Dongguan Power Supply Bureau of Guangdong Power Grid Co Ltd
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Dongguan Power Supply Bureau of Guangdong Power Grid Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
    • H02H3/087—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current for dc applications
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/38—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to both voltage and current; responsive to phase angle between voltage and current
    • 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
    • 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 embodiment of the invention discloses a photovoltaic grid-connected control method and system for blocking fault currentduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc(ii) a According to the obtained anode voltage to ground UduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two signals determines whether the direct current micro-grid has short circuit fault; and setting the conduction duty ratio of the converter according to the short-circuit fault condition of the direct-current microgrid so as to switch the working state of the converter. According to the technical scheme provided by the embodiment of the invention, the working state of the converter is switched according to the short-circuit fault condition of the direct-current micro-grid, so that the direct-current micro-grid is shortWhen the circuit is in fault, the photovoltaic power generation system can be blocked to provide short-circuit current for the direct-current micro-grid, and the short-circuit fault current level of the direct-current micro-grid is further reduced.

Description

Photovoltaic grid-connected control method and system for blocking fault current
Technical Field
The embodiment of the invention relates to the technical field of photovoltaic grid connection, in particular to a photovoltaic grid connection control method and system for blocking fault current.
Background
With the increasingly prominent problem of fossil energy shortage, photovoltaic power generation technology is rapidly developed as a renewable direct current power supply technology.
It is expected that the distributed photovoltaic system will be more connected to the direct current micro-grid in a direct current mode in the future. However, the direct-current microgrid has the characteristics of small coverage area, small line impedance, short power supply radius and the like, and once a short-circuit fault occurs, the fault current rises quickly and has large amplitude, so that serious impact can be caused on the system.
Disclosure of Invention
The embodiment of the invention provides a photovoltaic grid-connected control method and system for blocking fault current, so that the fault current can be blocked when a short-circuit fault occurs in a direct-current micro-grid, and the fault current level of the direct-current micro-grid can be reduced.
In a first aspect, an embodiment of the present invention provides a photovoltaic grid-connected control method for blocking a fault current, where the control method is applied to a photovoltaic power generation system, the photovoltaic power generation system includes a photovoltaic array and a converter, which are connected in sequence, and the photovoltaic array is connected to a dc microgrid through the converter;
the photovoltaic grid-connected control method for blocking the fault current comprises the following steps:
obtaining the voltage U of the converter to earth of the anode of the DC micro-grid sideduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc；
According to the obtained voltage U of the anode to earthduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two signals determines whether the direct current micro-grid has short-circuit fault;
and setting the conduction duty ratio of the converter according to the short-circuit fault condition of the direct-current microgrid so as to switch the working state of the converter.
Optionally, the setting of the conduction duty ratio of the converter according to the short-circuit fault condition of the dc microgrid to switch the operating state of the converter includes:
and if the direct-current micro-grid does not have the short-circuit fault, setting the conduction duty ratio of the converter to be a first preset value, and switching the converter to a maximum power tracking control state.
Optionally, the first preset value is a duty ratio obtained by using a maximum power tracking control method.
Optionally, the setting of the conduction duty ratio of the converter according to the short-circuit fault condition of the dc microgrid to switch the operating state of the converter includes:
and if the direct-current microgrid has a short-circuit fault, setting the conduction duty ratio of the converter to be a second preset value, and switching the converter to a fault current blocking state.
Optionally, the second preset value is a duty ratio for keeping the inverter in a conducting state all the time.
Optionally, the determining whether the direct-current microgrid has a short-circuit fault according to the acquired magnitude relationship among the positive-electrode voltage to ground, the negative-electrode voltage to ground, the positive-electrode voltage to ground and the setting voltage includes:
if 2| Udd|>UsetOr 2| Udu|>UsetDetermining that the direct-current micro-grid has no ground short circuit fault;
if 2| Udd|≤UsetOr 2| Udu|≤UsetAnd determining that the direct current microgrid has a ground short circuit fault.
Optionally, the | Udu| is the minimum value of the voltage of the anode to the ground, and | UddAnd | is the minimum value of the voltage of the negative electrode to the ground.
Optionally, the determining whether the direct-current microgrid has a short-circuit fault according to the acquired magnitude relationship among the positive-electrode voltage to ground, the negative-electrode voltage to ground, the positive-electrode voltage to ground and the setting voltage includes:
if Udc|>UsetDetermining that the DC microgrid has not occurredAn interelectrode short-circuit fault;
if Udc|≤UsetAnd determining that the inter-electrode short-circuit fault of the direct-current micro-grid occurs.
Optionally, the | UdcAnd | is the minimum value of the voltage between the positive electrode and the negative electrode.
In a second aspect, an embodiment of the present invention further provides a photovoltaic grid-connected control system for blocking a fault current, where the control system includes:
the photovoltaic grid-connected control system for blocking the fault current is electrically connected with a photovoltaic power generation system, the photovoltaic power generation system comprises a photovoltaic array and a current converter which are sequentially connected, and the photovoltaic array is connected with a direct-current micro-grid through the current converter;
the photovoltaic grid-connected control system for blocking the fault current comprises:
a parameter obtaining module, configured to obtain a voltage-to-ground voltage U of the positive electrode of the converter on the dc microgrid sideduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc；
A short-circuit fault determination module for determining the voltage U of the positive electrode to ground according to the obtained voltage UduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two signals determines whether the direct current micro-grid has short-circuit fault;
and the state switching module is used for setting the conduction duty ratio of the converter according to the short-circuit fault condition of the direct-current microgrid so as to switch the working state of the converter.
According to the embodiment of the invention, the voltage U of the anode of the converter on the side of the direct-current microgrid to ground is obtainedduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd according to the obtained anode voltage to ground UduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe size relationship between the direct current micro-grid and the inverter determines whether the direct current micro-grid has short-circuit fault, and the conduction duty ratio of the inverter is set according to the short-circuit fault condition of the direct current micro-grid so as to switch the working state of the inverter. Relative toIn the prior art, according to the technical scheme provided by the embodiment of the invention, the working state of the converter is switched according to the short-circuit fault condition of the direct-current microgrid, so that the direct-current microgrid can block the photovoltaic power generation system from supplying short-circuit current to the direct-current microgrid when the short-circuit fault occurs, and the short-circuit fault current level of the direct-current microgrid is further reduced.
Drawings
Fig. 1 is a schematic structural diagram of a photovoltaic power generation system according to an embodiment of the present invention;
fig. 2 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to an embodiment of the present invention;
fig. 3 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a second embodiment of the present invention;
fig. 4 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a third embodiment of the present invention;
fig. 5 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a fourth embodiment of the present invention;
fig. 6 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a fifth embodiment of the present invention;
fig. 7 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a sixth embodiment of the present invention;
fig. 8 is a waveform diagram of a fault current of an inter-electrode short-circuit fault according to a sixth embodiment of the present invention;
fig. 9 is a waveform diagram of a fault current of an anode-to-ground short circuit fault according to a sixth embodiment of the present invention;
fig. 10 is a schematic structural diagram of a photovoltaic grid-connected control system for blocking fault current according to a seventh embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
Example one
Fig. 1 is a schematic structural diagram of a photovoltaic power generation system according to a first embodiment of the present invention, and fig. 2 is a flowchart of a photovoltaic grid-connected control method for blocking a fault current according to a first embodiment of the present invention. The photovoltaic power generation system is a power generation system which directly converts solar radiation energy into electric energy by utilizing the photovoltaic effect of a photovoltaic array and is electrically connected with a public power grid. The connection of the photovoltaic power generation system and the public power grid can adopt an alternating current form and can also adopt a direct current form. Because the photovoltaic system adopts a direct current access mode, the photovoltaic system has higher energy efficiency, and with the popularization and application of a direct current power distribution system, the distributed photovoltaic system can be expected to adopt more direct current modes to access a direct current micro-grid in the future. Therefore, the photovoltaic grid-connected control method for blocking the fault current provided by the embodiment of the invention can be suitable for a distributed photovoltaic power generation system adopting a direct-current access microgrid. Referring to fig. 1, the photovoltaic power generation system includes a photovoltaic array 100 and a converter 200, the photovoltaic array 100 is electrically connected to a dc microgrid 300 through the converter 200, wherein the dc microgrid 300 is wired symmetrically (i.e. positive and negative line voltages of the dc microgrid are symmetrical). The converter 200 may include an inductor L, a diode D, a converter device S and a capacitor C, the converter device S may be an insulated gate bipolar transistor IGBT or a field effect transistor MOSTFE, and the converter 200 is connected to the dc micro-grid 300 through a cable. With reference to fig. 1 and fig. 2, the photovoltaic grid-connected control method for blocking fault current provided by the embodiment of the present invention specifically includes the following steps:
s110, acquiring a positive electrode voltage to ground Udu, a negative electrode voltage to ground Udd and a positive electrode voltage Udc of the inverter on the direct current microgrid side.
Specifically, when the photovoltaic power generation system is connected to the dc microgrid system, the photovoltaic array 100 outputs a dc voltage to the dc microgrid 300. The converter 200 may be a boost chopper circuit structure, and is configured to convert a dc voltage output by the photovoltaic array 100 into a dc voltage required by the dc microgrid 300, and to connect the photovoltaic array 100 and the dc microgrid 300 to each other. The output voltage of the inverter 200 on the dc microgrid 300 side is obtained, wherein the output voltage includes the positive electrode-to-ground voltage Udu, the negative electrode-to-ground voltage Udd, and the inter-positive-negative voltage Udc, and the output voltage of the inverter 200 on the dc microgrid 300 side may be obtained by a voltage sensor, for example.
S120, according to the obtained anode voltage to ground UduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two parts determines whether the direct current micro-grid has short circuit fault.
Specifically, the direct-current voltage output by the photovoltaic array 100 is controlled to be transmitted to the direct-current microgrid 300 side by controlling the on and off of the inverter device S. The short-circuit fault of the dc microgrid 300 generally includes a ground fault and an inter-electrode fault, and when the dc microgrid 300 has a ground fault, the voltage to ground of the electrode drops to a lower voltage value instantaneously; when the inter-electrode fault occurs in the dc micro-grid 300, the inter-electrode voltage also drops to a lower voltage value instantaneously. Therefore, no matter the dc microgrid 300 has a ground fault or an inter-pole fault, the voltage of the side of the dc microgrid 300 connected to the inverter 200 changes, and the voltage U of the positive pole of the inverter 200 on the side of the dc microgrid 300 can be detectedduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcTo determine whether a short circuit fault has occurred to dc microgrid 300. Illustratively, the setting voltage U is setsetIs 0.7 times of rated voltage between poles, and when the obtained voltage U of the anode to earth is detectedduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetWhen the size relationship between the two conditions does not meet the preset condition, it is determined that the short-circuit fault occurs in the direct-current microgrid 300.
And S130, setting the conduction duty ratio of the converter according to the short-circuit fault condition of the direct-current microgrid so as to switch the working state of the converter.
Specifically, the on duty of the converter 200 refers to the duty of the commutation device S, and the current and the voltage output by the converter 200 can be adjusted by adjusting the duty of the commutation device S. When the short-circuit fault of the direct-current microgrid 300 is determined, the converter 200 is switched to a fault current blocking state by adjusting the duty ratio of the converter device S, so that the photovoltaic array 100 is blocked from supplying the short-circuit fault current to the direct-current microgrid 300, and the short-circuit current level of the direct-current microgrid 300 is reduced. When it is determined that the short-circuit fault does not occur in the dc microgrid 300, it is determined that the dc microgrid 300 is in a trip operation state at this time, and the converter 200 is switched to the maximum power tracking control state by adjusting the duty ratio of the converter device S, so that the photovoltaic array 100 can have the maximum power generation amount, and the power demand of the dc microgrid 300 is ensured.
According to the embodiment of the invention, the voltage U to ground of the anode of the converter 200 on the side of the direct-current microgrid 300 is obtainedduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd according to the obtained anode voltage to ground UduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two conditions determines whether the short-circuit fault occurs in the dc microgrid 300, and the conduction duty ratio of the inverter 200 is set according to the short-circuit fault condition of the dc microgrid 300, so as to switch the operating state of the inverter 200. Compared with the prior art, according to the technical scheme provided by the embodiment of the invention, the working state of the converter 200 is switched according to the short-circuit fault condition of the direct-current microgrid 300, so that the direct-current microgrid 300 can block the photovoltaic power generation system from providing short-circuit current for the direct-current microgrid 300 when short-circuit fault occurs, and the short-circuit fault current level of the direct-current microgrid 300 is further reduced. And the fault current can be blocked only by adding a corresponding control device without additionally adding power equipment, so that the grid-connected cost of the photovoltaic power generation system is reduced.
Example two
Fig. 3 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a second embodiment of the present invention. On the basis of the above embodiment, referring to fig. 3, the photovoltaic grid-connected control method for blocking fault current provided by the embodiment of the present invention includes:
s210, obtaining the voltage U of the converter to earth of the positive electrode of the direct-current microgrid sideduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc。
S220, according to the obtained anode voltage to ground voltage UduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two parts determines whether the direct current micro-grid has short circuit fault.
And S230, if the short-circuit fault does not occur in the direct-current micro-grid, setting the conduction duty ratio of the converter to be a first preset value, and switching the converter to a maximum power tracking control state.
Specifically, according to the acquired anode-to-ground voltage UduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetWhen the magnitude relation between the current values determines that the direct-current microgrid 300 has no short-circuit fault, namely the direct-current microgrid 300 is in a normal operation state, the conduction duty ratio of the converter 200 is set to be a first preset value, and the converter 200 is switched to a maximum power tracking control state, so that the photovoltaic power generation system can output maximum power. The maximum power tracking control state refers to that the photovoltaic array 100 always outputs maximum power by adopting a maximum power tracking technology, so that the utilization rate of the photovoltaic array 100 can be improved. Illustratively, the first preset value is a duty ratio obtained by using a maximum power tracking control method, and when it is determined that the dc microgrid 300 is in a normal operation state, the duty ratio of the converter device S is set to the first preset value, so as to switch the converter 200 to a maximum power tracking control state.
EXAMPLE III
Fig. 4 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a third embodiment of the present invention. On the basis of the foregoing embodiments, referring to fig. 4, a photovoltaic grid-connected control method for blocking fault current according to an embodiment of the present invention includes:
s310, obtaining the voltage U of the converter to earth of the positive electrode of the direct current micro-grid sideduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc。
S320, according to the obtained anode voltage to ground voltage UduAnd the negative electrode is groundedPress UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two parts determines whether the direct current micro-grid has short circuit fault.
S330, if the direct-current micro-grid has no short-circuit fault, setting the conduction duty ratio of the converter to be a first preset value, and switching the converter to a maximum power tracking control state.
And S340, if the direct-current microgrid has a short-circuit fault, setting the conduction duty ratio of the current converter to be a second preset value, and switching the current converter to a fault current blocking state.
Specifically, the second preset value is a duty ratio at which the inverter 200 is always in a conductive state. The photovoltaic array 100 may be equivalent to a current source, and when the dc microgrid 300 has a short-circuit fault, the short-circuit fault current provided by the photovoltaic array 100 to the dc microgrid 300 generally does not exceed 1.5 times of the current in the normal operating state of the dc microgrid 300. The rated current of the converter device S is generally 2-2.5 times of the rated current of the converter 200, and after the short-circuit fault occurs in the dc microgrid 300, the relay protection device of the dc microgrid 300 can rapidly remove the fault in a very short time, so that the converter device S is controlled to be always on and not damaged during the short-circuit fault of the dc microgrid 300. Illustratively, according to the acquired voltage U of the anode to earthduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetWhen the magnitude relation between the two signals determines that the direct current microgrid 300 has a short-circuit fault, the duty ratio of the converter device S is set to be the second preset value, so that the converter device S is in a always-on state, for example, the second preset value may be 0.98. When the converter device S is in a always-on state, the diode D will be blocked, and therefore the photovoltaic array 100 does not provide current to the dc microgrid 300 any more, thereby blocking the photovoltaic power generation system from providing short-circuit current to the dc microgrid 300, and further reducing the level of short-circuit current of the dc microgrid 300. After the relay protection device of the dc microgrid 300 removes the fault, the duty ratio of the converter device S recovers the duty ratio before the fault.
Example four
Fig. 5 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a fourth embodiment of the present invention. On the basis of the foregoing embodiments, referring to fig. 5, a photovoltaic grid-connected control method for blocking a fault current according to an embodiment of the present invention includes:
s410, acquiring the voltage U of the converter to earth of the anode of the converter on the side of the direct-current microgridduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc。
S420, if 2| Udd|>UsetOr 2| Udu|>UsetAnd determining that the direct-current micro-grid has no ground short fault.
S430, if 2| Udd|≤UsetOr 2| Udu|≤UsetAnd determining that the direct current microgrid has a ground short fault.
Specifically, according to the acquired positive voltage-to-ground voltage U of the converter 100 on the side of the dc microgrid 300duNegative electrode to ground voltage UddAnd the setting voltage UsetThe magnitude relationship between the two is used to determine whether the short-circuit fault occurs in the dc microgrid 300. Wherein the setting voltage UsetA setting voltage U for judging whether the DC microgrid 300 has a short-circuit faultsetLess than the interelectrode rated voltage of the dc microgrid 300. Due to UduAnd UddThe positive electrode and the negative electrode are respectively the voltage to ground, and the DC micro-grid 300 adopts a symmetrical wiring mode, so that when 2| U |, the voltage to ground is applieddd|>UsetOr 2| Udu|>UsetIt indicates that the voltage to ground of the pole of the dc microgrid 300 does not drop greatly, and thus it can be determined that the dc microgrid 300 has not failed in a ground short circuit. If 2| U is detecteddd|≤UsetOr 2| Udu|≤UsetIf the voltage of the pole of the dc microgrid 300 decreases to a greater extent, it may be determined that the dc microgrid 300 has a ground short fault. Wherein, | UduL is the minimum value of the voltage of the anode to the ground, | UddAnd l is the minimum value of the voltage of the negative electrode to the ground, so that the accuracy of determining the fault state of the direct-current micro-grid 300 is improved. Illustratively, a rated voltage of 750V, then set to unityConstant voltage UsetAt 0.7 times the rated voltage, i.e. Uset525V. When 2| U is detectedddLess than or equal to 525V or 2UduAnd if the voltage is less than or equal to 525V, determining that the current microgrid 300 has a ground short circuit fault. If 2| Udd|>525V or 2| Udu|>And when the voltage is 525V, determining that the current microgrid 300 has no ground short fault.
And S440, setting the conduction duty ratio of the converter according to the short-circuit fault condition of the direct-current microgrid so as to switch the working state of the converter.
EXAMPLE five
Fig. 6 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a fifth embodiment of the present invention. On the basis of the above embodiment, referring to fig. 6, the photovoltaic grid-connected control method for blocking fault current provided by the embodiment of the present invention includes:
s510, obtaining the voltage U of the converter to earth of the positive electrode of the direct current microgrid sideduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc。
S520, if 2| Udd|>UsetOr 2| Udu|>UsetAnd determining that the direct-current micro-grid has no ground short fault.
S530, if 2| Udd|≤UsetOr 2| Udu|≤UsetAnd determining that the direct current microgrid has a ground short fault.
S540, if | Udc|>UsetAnd determining that no inter-electrode short circuit fault occurs in the direct-current micro-grid.
S550, if | Udc|≤UsetAnd determining that the inter-electrode short-circuit fault of the direct-current micro-grid occurs.
Specifically, the voltage U between the positive electrode and the negative electrode of the inverter 100 on the dc microgrid 300 side is acquireddcAnd the setting voltage UsetThe magnitude relationship between the two is used to determine whether the short-circuit fault occurs in the dc microgrid 300. Wherein the setting voltage UsetA setting voltage U for judging whether the DC microgrid 300 has a short-circuit faultsetLess than the interelectrode rated voltage of the dc microgrid 300. I UdcL is positive and negativeMinimum value of inter-voltage, | Udc|>UsetTime, i.e. the voltage U between the positive and negative electrodesdcIs greater than the setting voltage UsetIn time, it can be determined that no inter-electrode short circuit fault occurs in the dc microgrid 300. When | Udc|≤UsetTime, indicates the voltage between the positive and negative electrodesUdcDropping to setting voltage UsetAnd determining that the inter-electrode short-circuit fault of the direct-current micro-grid occurs.
And S560, setting the conduction duty ratio of the converter according to the short-circuit fault condition of the direct-current microgrid so as to switch the working state of the converter.
EXAMPLE six
Fig. 7 is a flowchart of a photovoltaic grid-connected control method for blocking fault current according to a sixth embodiment of the present invention. On the basis of the foregoing embodiments, referring to fig. 7, a specific working principle of the photovoltaic grid-connected control method for blocking fault current provided by the embodiment of the present invention is as follows:
the short-circuit fault of the dc microgrid 300 generally includes a ground fault and an inter-electrode fault, and when the dc microgrid 300 has a ground fault, the voltage to ground of the electrode drops to a lower voltage value instantaneously; when the inter-electrode fault occurs in the dc micro-grid 300, the inter-electrode voltage also drops to a lower voltage value instantaneously. Therefore, no matter the dc microgrid 300 has a ground fault or an inter-pole fault, the voltage of the side of the dc microgrid 300 connected to the inverter 200 changes, and the voltage U of the positive pole of the inverter 200 on the side of the dc microgrid 300 can be detectedduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relationship between the two is used to determine whether the short-circuit fault occurs in the dc microgrid 300. Due to UduAnd UddThe positive electrode and the negative electrode are respectively the voltage to ground, and the DC micro-grid 300 adopts a symmetrical wiring mode, so that when 2| U |, the voltage to ground is applieddd|>UsetOr 2| Udu|>UsetWhen the voltage of the pole of the direct current microgrid 300 does not drop greatly, it is determined that the direct current microgrid 300 has no ground short circuit fault; when | U is detecteddc|>UsetTime, indicates the voltage U between the positive and negative electrodesdcIf no large drop occurs, it is determined that no inter-electrode short circuit fault occurs in the dc microgrid 300. Therefore, when it is determined that neither a ground short fault nor an inter-electrode short fault occurs in the dc microgrid 300, that is, the dc microgrid 300 is in a normal operation state, the conduction duty ratio of the converter 200 is set to the first preset value, and the converter 200 is switched to the maximum power tracking control state, so that the photovoltaic power generation system can output the maximum power.
When 2| U is detecteddd|≤UsetOr 2| Udu|≤UsetIf so, it is indicated that the reduction degree of the voltage to ground of the pole of the direct-current microgrid 300 is large, and it can be determined that the direct-current microgrid 300 has a ground short circuit fault; when | U is detecteddc|≤UsetTime, indicates the voltage U between the positive and negative electrodesdcAnd if the voltage drops greatly, determining that the inter-electrode short-circuit fault occurs in the direct-current micro-grid 300. Therefore, when it is determined that the direct current microgrid 300 has a ground short-circuit fault or an inter-electrode short-circuit fault, that is, the direct current microgrid 300 is in a short-circuit fault state, the duty ratio of the converter device S is set to the second preset value, so that the converter device S is in a always-on state, for example, the second preset value may be 0.98. When the converter device S is in a always-on state, the diode D will be blocked, and therefore the photovoltaic array 100 does not provide current to the dc microgrid 300 any more, thereby blocking the photovoltaic power generation system from providing short-circuit current to the dc microgrid 300, and further reducing the level of short-circuit current of the dc microgrid 300.
With continued reference to fig. 1, a simulation model of the photovoltaic-dc microgrid is established, with the following main simulation parameters: the rated voltage output by the photovoltaic power generation system is 750V, the rated current is 0.144kA, the equivalent capacitance at the outlet of the converter 200 is 3000uF, and the photovoltaic power generation system (comprising the photovoltaic array 100 and the converter 200) is connected to the direct current microgrid 300 through a cable with the length of 100 meters. The cable is installed in a buried mode, the depth is 1m, the radius of the cable is 23mm, and the reactance per kilometer is 0.05 ohm. Fig. 8 is a waveform diagram of a fault current of an inter-electrode short-circuit fault according to a sixth embodiment of the present invention, and fig. 9 is a waveform diagram of a fault current of an anode ground short-circuit fault according to a sixth embodiment of the present invention, where a solid-line waveform diagram is a fault current of a photovoltaic grid-connected control method for blocking a fault current according to the sixth embodiment of the present invention, and a dotted-line waveform diagram is a fault current according to the prior art. Referring to fig. 8 and 9, at 0.4s, an inter-electrode short-circuit fault occurs in the dc microgrid 300, and at the short-circuit moment, due to voltage oscillation on the dc microgrid 300 side, the capacitor C at the outlet of the inverter 200 oscillates and discharges, so that the current output by the photovoltaic power generation system greatly oscillates in the initial stage of the short-circuit, and the short-circuit current is substantially stable after 50 ms. As can be seen from fig. 8 and 9, the short-circuit fault current provided by the photovoltaic power generation system is mainly composed of two parts: one part is an oscillating current component generated by the discharge of the capacitor, and the other part is a stable current component provided by the photovoltaic array 100. After the photovoltaic grid-connected control method for blocking the fault current provided by the embodiment of the invention is adopted, the short-circuit fault current provided by the photovoltaic power generation system only contains the oscillation component provided by capacitor discharge, so that compared with the prior art, the technical scheme provided by the embodiment of the invention can effectively block the short-circuit current provided by the photovoltaic array 100, and further the short-circuit fault current provided by the photovoltaic power generation system is obviously reduced.
EXAMPLE seven
Fig. 10 is a schematic structural diagram of a photovoltaic grid-connected control system for blocking fault current according to a seventh embodiment of the present invention. On the basis of the above embodiments, referring to fig. 10, the photovoltaic grid-connected control system for blocking the fault current provided by the embodiment of the present invention is electrically connected to a photovoltaic power generation system, the photovoltaic power generation system includes a photovoltaic array and a converter, which are sequentially connected, and the photovoltaic array is connected to a dc micro-grid through the converter;
the photovoltaic grid-connected control system for blocking fault current comprises:
a parameter obtaining module 71, configured to obtain a positive voltage-to-ground voltage U of the converter on the dc microgrid sideduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc；
A short-circuit fault determination module 72 for determining the voltage U of the positive electrode to ground according to the obtained voltage UduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two signals determines whether the direct current micro-grid has short circuit fault;
and the state switching module 73 is configured to set a conduction duty ratio of the inverter according to a short-circuit fault condition of the dc microgrid, so as to switch an operating state of the inverter.
The photovoltaic grid-connected control system for blocking the fault current provided by the embodiment of the invention can execute the photovoltaic grid-connected control method for blocking the fault current provided by any embodiment of the invention, and has a module for executing a corresponding method, so that the photovoltaic grid-connected control system for blocking the fault current provided by the embodiment of the invention has the beneficial effects described in any embodiment.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims (10)

1. The control method is applied to a photovoltaic power generation system, wherein the photovoltaic power generation system comprises a photovoltaic array and a converter which are sequentially connected, and the photovoltaic array is connected with a direct-current micro-grid through the converter;
the photovoltaic grid-connected control method for blocking the fault current comprises the following steps:
obtaining the voltage U of the converter to earth of the anode of the DC micro-grid sideduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc；
According to the obtained voltage U of the anode to earthduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two signals determines whether the direct current micro-grid has short-circuit fault;
and setting the conduction duty ratio of the converter according to the short-circuit fault condition of the direct-current microgrid so as to switch the working state of the converter.
2. The method according to claim 1, wherein the setting of the conduction duty ratio of the converter according to the short-circuit fault condition of the dc micro-grid to switch the operating state of the converter comprises:
and if the direct-current micro-grid does not have the short-circuit fault, setting the conduction duty ratio of the converter to be a first preset value, and switching the converter to a maximum power tracking control state.
3. The grid-connected photovoltaic control method for blocking fault current according to claim 2, wherein the first preset value is a duty ratio obtained by a maximum power tracking control method.
4. The method according to claim 1, wherein the setting of the conduction duty ratio of the converter according to the short-circuit fault condition of the dc micro-grid to switch the operating state of the converter comprises:
and if the direct-current microgrid has a short-circuit fault, setting the conduction duty ratio of the converter to be a second preset value, and switching the converter to a fault current blocking state.
5. The grid-connected photovoltaic control method for blocking fault current according to claim 4, wherein the second preset value is a duty ratio for enabling the converter to be always in a conducting state.
6. The method according to claim 1, wherein the determining whether the short-circuit fault occurs in the dc microgrid according to the obtained magnitude relationship between the positive-electrode voltage to ground, the negative-electrode voltage to ground, and the positive-negative voltage and the setting voltage comprises:
if 2| Udd|>UsetOr 2| Udu|>UsetDetermining that the direct-current micro-grid has no ground short circuit fault;
if 2| Udd|≤UsetOr 2| Udu|≤UsetAnd determining that the direct current microgrid has a ground short circuit fault.
7. The grid-connected photovoltaic control method for blocking fault current according to claim 6, wherein | U |, isdu| is the minimum value of the voltage of the anode to the ground, and | UddAnd | is the minimum value of the voltage of the negative electrode to the ground.
8. The method according to claim 1, wherein the determining whether the short-circuit fault occurs in the dc microgrid according to the obtained magnitude relationship between the positive-electrode voltage to ground, the negative-electrode voltage to ground, and the positive-negative voltage and the setting voltage comprises:
if Udc|>UsetDetermining that no inter-electrode short circuit fault occurs in the direct-current micro-grid;
if Udc|≤UsetAnd determining that the inter-electrode short-circuit fault of the direct-current micro-grid occurs.
9. The grid-connected photovoltaic control method for blocking fault current according to claim 8, wherein | U |, isdcAnd | is the minimum value of the voltage between the positive electrode and the negative electrode.
10. The photovoltaic grid-connected control system for blocking the fault current is characterized in that the photovoltaic grid-connected control system for blocking the fault current is electrically connected with a photovoltaic power generation system, the photovoltaic power generation system comprises a photovoltaic array and a current converter which are sequentially connected, and the photovoltaic array is connected with a direct-current micro-grid through the current converter;
the photovoltaic grid-connected control system for blocking the fault current comprises:
a parameter obtaining module, configured to obtain a voltage-to-ground voltage U of the positive electrode of the converter on the dc microgrid sideduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdc；
A short-circuit fault determination module for determining the voltage U of the positive electrode to ground according to the obtained voltage UduNegative electrode to ground voltage UddAnd a voltage U between the positive and negative electrodesdcAnd the setting voltage UsetThe magnitude relation between the two signals determines whether the direct current micro-grid has short-circuit fault;
and the state switching module is used for setting the conduction duty ratio of the converter according to the short-circuit fault condition of the direct-current microgrid so as to switch the working state of the converter.
CN202010517472.XA 2020-06-09 2020-06-09 Photovoltaic grid-connected control method and system for blocking fault current Pending CN111668817A (en)

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