CN116581818A - Off-grid parallel control method for photovoltaic power station, inverter and parallel inversion system - Google Patents
Off-grid parallel control method for photovoltaic power station, inverter and parallel inversion system Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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- 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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
- H02J7/35—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering with light sensitive cells
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- 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
- H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
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- 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 application provides a photovoltaic power station off-grid parallel control method, an inverter and a parallel inversion system, wherein if a photovoltaic subarray connected with any inverter in the parallel inversion system is shielded, once the direct voltage of the inverter is reduced, the direct voltage is detected to be lower than the direct voltage average value, at the moment, a control unit of the control unit does not take an alternating current command value which is still unchanged in the prior art as the reference input quantity of a self current loop to carry out output current regulation, but controls the reference input quantity of the self current loop to be reduced; furthermore, the corresponding direct current voltage can rise due to the reduction of the output current, and finally the direct current voltage reaches the preset range of the average value of the direct current voltage; by the principle, each direct-current voltage can be maintained in a preset range of the average value of the direct-current voltage in real time, so that the triggering of direct-current under-voltage protection and the load power failure caused by out-of-control of off-grid alternating-current voltage are avoided.
Description
Technical Field
The application relates to the technical field of photovoltaic power generation control, in particular to an off-grid parallel control method, an inverter and a parallel inversion system of a photovoltaic power station.
Background
With the increase of application scenes of photovoltaic power stations, the on-load demand of off-grid output of the inverter is more and more concerned. The existing multi-machine off-grid parallel control technology is that on the basis that a plurality of inverters are connected in parallel through an alternating current output side, a control unit in one inverter is used as a control host, an alternating current command value is generated through a voltage regulator of the control host, and the alternating current command value is sent to control units in other parallel inverters through parallel communication; and then, the control unit in each inverter respectively adjusts output current through a current regulator of the control unit according to the same alternating current command value, and finally, off-grid alternating voltage output by multiple inverters in parallel is controlled to a target value, so that stable active and reactive power is provided for an alternating current load.
However, according to the multi-machine off-grid parallel control strategy, stable active power and reactive power can be provided for the load only under the condition that the photovoltaic subarrays connected with each inverter are sufficient in receiving illumination; when the photovoltaic subarrays connected with any inverter are shielded, the alternating current command value output by the control host remains unchanged, and at the moment, the direct current voltage of the corresponding inverter is rapidly reduced due to the fact that the shielded photovoltaic subarrays cannot provide sufficient energy, so that the direct current undervoltage protection of the inverter is triggered; if the load power connected to the AC output side after the parallel connection of multiple machines is larger, the off-grid AC voltage at the moment can be out of control because the photovoltaic power station cannot provide sufficient current, and finally the inverter protection and the load outage are caused.
Disclosure of Invention
In view of the above, the application provides an off-grid parallel control method, an inverter and a parallel inversion system for a photovoltaic power station, which are used for solving the problems that the corresponding inverter triggers direct current under-voltage protection when the photovoltaic subarray is shielded and the load is powered down due to out-of-control off-grid alternating current voltage.
In order to achieve the above purpose, the present application provides the following technical solutions:
the first aspect of the application provides an off-grid parallel control method of a photovoltaic power station, which is applied to control units inside inverters in a parallel inversion system, wherein alternating current sides of the inverters are connected in parallel; the off-grid parallel control method for the photovoltaic power station comprises the following steps:
each control unit respectively determines whether the direct current voltage of the inverter where the control unit is positioned is lower than the direct current voltage average value of all the inverters;
for the inverter with the direct-current voltage lower than the direct-current voltage average value, the control unit controls the reference input quantity of the self current loop to be reduced until the corresponding direct-current voltage reaches the preset range of the direct-current voltage average value.
Optionally, each control unit determines whether the dc voltage of the inverter where the control unit is located is lower than the dc voltage average value of all the inverters, including:
any control unit obtains the direct current voltage of each inverter, calculates the direct current voltage average value and sends the direct current voltage average value to other control units; or, each control unit respectively acquires direct current voltages of other inverters, and calculates and obtains the average value of the direct current voltages;
each control unit respectively calculates the difference value of the corresponding direct current voltage minus the average value of the direct current voltage;
and the control unit with the difference value of a negative value determines that the corresponding direct-current voltage is lower than the average value of the direct-current voltage.
Optionally, a control unit that obtains the dc voltage of each inverter and calculates the average value of the dc voltage is a control host in each control unit.
Optionally, the reference input amount of the self current loop is controlled to be reduced until the corresponding direct current voltage reaches the preset range of the average value of the direct current voltage, including real-time or periodic execution:
according to the difference value of the average value of the direct current voltage subtracted from the corresponding direct current voltage, calculating to obtain a corresponding instruction compensation quantity;
and superposing the alternating current command value by the command compensation quantity, and replacing the alternating current command value by a superposition result to serve as a reference input quantity of a self current loop.
Optionally, after each control unit determines whether the dc voltage of the inverter where the control unit is located is lower than the dc voltage average value of all the inverters, the method further includes:
for the inverter with the direct-current voltage higher than the direct-current voltage average value, the control unit controls the reference input quantity of the self current loop to rise until the corresponding direct-current voltage reaches the preset range of the direct-current voltage average value.
Optionally, the reference input quantity of the self current loop is controlled to be increased until the corresponding direct current voltage reaches the preset range of the average value of the direct current voltage, including real-time or periodic execution:
according to the difference value of the average value of the direct current voltage subtracted from the corresponding direct current voltage, calculating to obtain a corresponding instruction compensation quantity;
and superposing the alternating current command value by the command compensation quantity, and replacing the alternating current command value by a superposition result to serve as a reference input quantity of a self current loop.
Optionally, the calculating to obtain the corresponding command compensation amount according to the difference value of the average value of the direct current voltage subtracted from the corresponding direct current voltage includes:
and calculating the product of the difference value and the adjustment coefficient as the command compensation amount.
Optionally, the adjustment coefficient is: the product of the preset coefficient and the AC rated current of the inverter where the control unit is located.
Optionally, before the control unit controls the reference input amount of the self current loop to change, the method further includes:
and the control host in each control unit generates an alternating current instruction value and transmits the alternating current instruction value to other control units.
A second aspect of the present application provides an inverter including: the device comprises a main circuit, a control unit and an acquisition unit; wherein,,
the main circuit is controlled by the control unit;
the acquisition unit is used for acquiring direct current voltage, alternating current output voltage and alternating current output current of the main circuit;
and the control unit is used for controlling the reference input quantity of the self current loop to be reduced when the direct current voltage is lower than the direct current average value until the direct current voltage reaches the preset range of the direct current average value.
Optionally, the control unit is further configured to: when the direct current voltage of the main circuit is higher than the direct current voltage average value, the reference input quantity of the self current loop is controlled to rise until the direct current voltage reaches the preset range of the direct current average value.
Optionally, the inverter is connected in parallel with other inverters through an ac side, and the control unit is further configured to: and obtaining the direct current voltage of each inverter, calculating the direct current voltage average value, and sending the direct current voltage average value to control units in other inverters.
Optionally, the inverter is connected in parallel with other inverters through an ac side, and the control unit is further configured to: an alternating current command value is generated and issued to a control unit in the other inverter.
Optionally, the control unit is configured to control the change of the reference input amount of the self current loop, and specifically is configured to perform the following steps in real time or periodically:
calculating a difference value of the direct current voltage minus the average value of the direct current voltage;
according to the difference value, calculating to obtain a corresponding instruction compensation quantity;
and superposing the alternating current command value by the command compensation quantity, and replacing the alternating current command value by a superposition result to serve as a reference input quantity of a self current loop.
Optionally, the instruction compensation amount is: the product of the difference and the adjustment coefficient;
the adjustment coefficient is as follows: the product of a preset coefficient and the total current of the alternating current output side of the parallel inverter system.
A third aspect of the present application provides a parallel inverter system, comprising: at least two inverters;
the direct current sides of the inverters are respectively connected with corresponding photovoltaic subarrays;
the alternating current side of each inverter is connected to the alternating current output side of the parallel inverter system in parallel;
the control units inside the inverters are in communication connection;
each control unit is used for executing the off-grid parallel control method of the photovoltaic power station according to any one of the first aspect.
According to the off-grid parallel control method for the photovoltaic power station, for each inverter which is connected in parallel through an alternating current side in a parallel inversion system, firstly, whether the direct current voltage of the inverter where the control unit is located is lower than the direct current average value of all the inverters is respectively determined by the control unit in each inverter; if the photovoltaic subarrays connected with any inverter are shielded, once the corresponding direct current voltage is reduced, the fact that the direct current voltage is lower than the direct current average value can be detected, at the moment, the corresponding control unit does not take the alternating current command value which is still unchanged in the prior art as the reference input quantity of the self current loop to carry out output current adjustment, and controls the reduction of the reference input quantity of the self current loop; furthermore, the corresponding direct current voltage is raised due to the reduction of the output current, and finally reaches the preset range of the average value of the direct current voltage, and then the reduction control of the reference input quantity is stopped; by the principle, each direct-current voltage can be maintained in a preset range of the average value of the direct-current voltage in real time, so that the triggering of direct-current under-voltage protection and the load power failure caused by out-of-control of off-grid alternating-current voltage are avoided.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following description will briefly explain the embodiments or the drawings to be used in the description of the prior art, and it is obvious that the drawings in the following description are only embodiments of the present application, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a parallel inverter system according to an embodiment of the present application;
fig. 2 is a block diagram of a multi-machine off-network parallel control strategy provided in the prior art;
fig. 3 is a schematic diagram of a relationship between dc side current and voltage of an inverter in a parallel inverter system according to an embodiment of the present application;
fig. 4 is a flowchart of a photovoltaic power station off-grid parallel control method provided by an embodiment of the present application;
fig. 5 is a partial flowchart of a photovoltaic power station off-grid parallel control method provided by an embodiment of the present application;
fig. 6 is another flowchart of a photovoltaic power station off-grid parallel control method according to an embodiment of the present application;
fig. 7 is a block diagram of a multi-machine off-network parallel control strategy according to an embodiment of the present application.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In the present disclosure, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises an element.
Referring to fig. 1, each inverter in the parallel inverter system is connected in parallel through an ac side, and the dc sides of each inverter are respectively connected with corresponding photovoltaic subarrays; inside the inverter, its main circuit 101 is controlled by its control unit 102; the control units 102 of the respective inverters are communicatively connected.
The control strategy in the prior art is shown in fig. 2, and it is assumed that the number of inverters in the parallel inverter system is n, where a control unit in one inverter is used as a control host to control an ac voltage command value U required by an off-grid load ref As the reference input quantity of the self voltage ring and using the actual AC side output voltage U of the parallel inverter system out As a feedback input quantity of the self-voltage ring, the deviation between the two is used for generating an alternating current command value I through a voltage regulator (a unit voltage regulator shown in the figure) ref And the control unit is transmitted to the control units in other parallel inverters through parallel communication; the control unit in each inverter then uses the same AC current command value I ref As the reference input quantity of the self current loop and corresponding to the alternating current output current I of the inverter outi (i=1, 2, …, n) is taken as a feedback input quantity of a self current loop, the deviation between the two is used for providing an input signal for a PWM (Pulse Width Modulation ) module through a self current regulator (corresponding one of a unit 1 current regulator and a unit n current regulator shown in the figure), and further a switch driving signal is generated through the corresponding PWM module to control the action of a main circuit in a corresponding inverter, so that the regulation of the output current of the corresponding inverter is realized, finally, the off-grid alternating voltage output by multiple machines in parallel is controlled to a target value, and stable active and reactive power is provided for an alternating load.
Referring to the current-voltage curve shown in fig. 3, if the initial operating point of any inverter is "P1", when the illumination suddenly drops from 1000W/square meter to 800W/square meter, the dc voltage of the inverter whose photovoltaic subarray is blocked will be suddenly lowered because the ac current command value Iref outputted by the voltage regulator of the control host is unchanged, and the operating point moves to "P2", thereby triggering the dc under-voltage protection of the inverter.
Therefore, the application provides an off-grid parallel control method for a photovoltaic power station, which aims to solve the problems that a corresponding inverter triggers direct-current under-voltage protection when a photovoltaic subarray is shielded and a load is powered down due to out-of-control off-grid alternating-current voltage.
Referring to fig. 4, the off-grid parallel control method for the photovoltaic power station comprises the following steps:
s101, each control unit respectively determines whether the direct current voltage of the inverter where the control unit is located is lower than the direct current voltage average value of all the inverters.
In practical applications, the S101 may specifically include the one shown in fig. 5:
s201, any control unit obtains direct current voltage of each inverter, calculates to obtain a direct current voltage average value and sends the direct current voltage average value to other control units; or, each control unit respectively obtains the direct current voltage of other inverters, and calculates to obtain the average value of the direct current voltage.
In practical application, the AC command value I can be generated and sent by any control unit, such as a control host, i.e. with a voltage outer loop ref The control unit of the power supply unit reads the direct current voltage UDC collected by the control unit in the power supply unit and other parallel inverters i The DC voltage average UDC is calculated by avg ：
Wherein n is the number of inverters in the parallel inverter system.
Alternatively, each control unit may read the DC voltage UDC collected by itself and other control units in the parallel inverter i And calculate the average value UDC of the DC voltage by the above method avg : depending on the specific application environment, the method is not limited herein, and is within the scope of the present application.
S202, each control unit calculates the difference value of the corresponding direct current voltage minus the average value of the direct current voltage.
The corresponding difference value calculated by each control unit is UDC i -UDC avg ，i＝1，2，…，n。
S203, for the control unit with the difference value of negative values, determining that the corresponding direct current voltage is lower than the direct current voltage average value.
In particular, for UDC i -UDC avg <0, indicating that the corresponding direct current voltage is lower than the direct current average value; the other control units determine that the corresponding direct current voltage is not lower than the direct current voltage average value, and specifically comprise the following two cases: for UDC i -UDC avg A control unit of =0, which indicates that its corresponding dc voltage is equal to the dc voltage average; for UDC i -UDC avg >0, indicating that its corresponding dc voltage is higher than the dc voltage average value.
S102 is performed for an inverter having a dc voltage lower than the dc voltage average value.
S102, the control unit controls the reference input quantity of the self current loop to be reduced until the corresponding direct current voltage reaches the preset range of the average value of the direct current voltage.
I.e. UDC i -UDC avg <0, no longer with the ac current command value I shown in fig. 2 ref Directly used as the reference input quantity of the self current loop, but controls the reduction of the reference input quantity, and further, the reference input quantity and the corresponding alternating current output current I outi After the deviation between the current regulators and the PWM modules, the output current of the corresponding inverter is controlled to be reduced; under the condition that the off-grid alternating current voltage of the parallel inverter system is stable, the output current of any inverter is reduced, so that the direct current voltage of the inverter is raised; through the continuous operation of the current loop, the reduction control of the reference input quantity can be stopped when the corresponding direct current voltage reaches the preset range of the average value of the direct current voltage. In practical application, the preset range is not particularly limited, and the difference between the preset range and the average value of the direct current voltage can be represented to be smaller.
According to the off-grid parallel control method for the photovoltaic power station, if the photovoltaic subarrays connected with any inverter are shielded, once the corresponding direct-current voltage is reduced, the fact that the direct-current voltage is lower than the direct-current voltage average value can be detected through S101, at the moment, the corresponding control unit does not take an alternating-current command value which is still unchanged in the prior art as the reference input quantity of the self-current loop to regulate the output current, and the reference input quantity of the self-current loop is controlled to be reduced through S102; furthermore, the corresponding direct current voltage is raised due to the reduction of the output current, and finally reaches the preset range of the average value of the direct current voltage, and then the reduction control of the reference input quantity is stopped; by the principle, each direct-current voltage can be maintained in a preset range of the average value of the direct-current voltage in real time, so that the triggering of direct-current under-voltage protection and the load power failure caused by out-of-control of off-grid alternating-current voltage are avoided.
On the basis of the above embodiment, the off-grid parallel control method for a photovoltaic power station provided in this embodiment provides specific examples of some implementation forms for S102, for example, in S102, the control unit performs: the step of controlling the reference input quantity of the self current loop to be reduced until the corresponding direct current voltage reaches the preset range of the average value of the direct current voltage can specifically comprise the following steps of real-time or periodic execution:
(1) And according to the difference value of the corresponding direct current voltage minus the average value of the direct current voltage, calculating to obtain the corresponding command compensation quantity.
The instruction compensation amount can be calculated by calculating the difference UDC i -UDC avg And the adjustment coefficient KxI N As the product of the instruction compensation quantity I COMPi The method comprises the steps of carrying out a first treatment on the surface of the That is, the following calculation formula is adopted for calculation:
I COMPi ＝K×I N ×(UDC i -UDC avg )；
wherein, K is a preset coefficient, the specific value of which can be determined according to the practical application environment and is not limited herein; i N Is the ac rated current of the inverter in which the control unit is located.
(2) And superposing the alternating current command value by using the command compensation quantity, and using the superposition result to replace the alternating current command value as the reference input quantity of the self current loop.
Directly using the AC current command value I in the prior art ref The reference input quantity of the current loop is different from that of the embodiment COMPi +I ref As reference input of the current loop and with the AC output current I of the corresponding inverter outi The deviation is input to a current regulator, and the output current of the corresponding inverter is regulated through the corresponding PWM module.
The photovoltaic subarrays connected with any inverter are shielded, and direct current of the photovoltaic subarrays is direct currentPressing UDC i When the drop occurs, the corresponding difference UDC i -UDC avg I.e. negative, the command compensation quantity I obtained COMPi Also negative, the reference input of the current loop is derived from the ac current command value I ref Become smaller I COMPi +I ref I.e. the reference input is reduced; furthermore, the corresponding dc voltage will rise due to the decrease of the output current, and finally reach the preset range of the average value of the dc voltage.
In addition, in practical application, the off-grid parallel control method of the photovoltaic power station may further include, as shown in fig. 6 (shown by way of example on the basis of fig. 4), after S101, performing, for an inverter with a dc voltage higher than a dc voltage average:
s103, the control unit controls the reference input quantity of the self current loop to rise until the corresponding direct current voltage reaches the preset range of the average value of the direct current voltage.
Moreover, the specific procedure of S103 may take the same implementation form as S102, that is, in S103, the control unit performs: controlling the reference input quantity of the self current loop to rise until the corresponding direct current voltage reaches the preset range of the average value of the direct current voltage, and also comprising the steps (1) and (2) which are executed in real time or periodically; the specific process is just described above, and no further description is given.
Fig. 7 is a block diagram of a control strategy corresponding to the off-grid parallel control method of the photovoltaic power station according to the present embodiment, which is different from the prior art shown in fig. 2 in that the reference input amount of the current loop in each control unit no longer directly adopts the ac current command value I ref But is in I COMPi +I ref As the reference input quantity. The specific control strategy is as follows:
firstly, a control unit of any inverter reads direct current voltage UDC collected by other control units in parallel inverters i (i=1, 2, …, n), the dc voltage average value UDC is calculated by the following formula avg ：
Then, the control unit of each inverter calculates the DC voltage UDC of each inverter i And the direct current flattening average value UDC avg Difference UDC between i -UDC avg And multiplying by the adjustment factor KxI N Finally according to I COMPi ＝K×I N ×(UDC i -UDC avg ) Calculating the instruction compensation quantity I of each control unit COMPi 。
Then, the control unit of each inverter calculates the command compensation amount I COMPi An alternating current command value I generated by a control host ref Summing, the obtained result is used as new reference input quantity of current loop in the corresponding control unit and is matched with AC output current I of corresponding inverter outi And after the deviation is calculated, inputting the calculated deviation into a current regulator, and finally generating a switch driving signal through a PMW module.
In practical applications, each regulator shown in fig. 7 may be a PI regulator, but is not limited thereto, and may be any regulator depending on the specific application environment.
According to the method, the direct current voltage of all inverters can be maintained at the average value level under the normal working condition, even if the photovoltaic subarrays connected with any inverter are shielded to cause insufficient illumination energy, once the direct current voltage of the inverter is reduced, the reference input quantity of a current loop is reduced through the current compensation algorithm, the input quantity of a current regulator in the current loop is reduced, so that the output current of the corresponding inverter is controlled to be reduced, the direct current voltage of the inverter is raised due to the reduction of the output current, and finally the direct current voltage is controlled to be at the average level before illumination shielding, so that the problem of load outage caused by the uncontrolled alternating current voltage is avoided.
It should be noted that, before S102 in fig. 4 and S102 and S103 in fig. 6, the off-grid parallel control method for the photovoltaic power station further includes: the control host in each control unit generates an alternating current instruction value and transmits the alternating current instruction value to other control units; the specific process of the step can be seen from the working principle of a voltage loop of a control host in the prior art; in addition, the working principle of the current loop of each control unit can also be referred to the prior art, and no description is repeated here.
The control unit may be any control unit, for example, may be the control host, and at this time, the control host is responsible for generating the ac current command value and issuing the ac current command value to other control units, and is also responsible for reading the dc voltages collected by other control units and calculating to obtain the dc voltage average value; of course, the direct current voltage collected by other control units is read and calculated to obtain the direct current voltage average value, and the direct current voltage average value can also be realized by any control unit except the control host, so the direct current voltage average value is not limited herein, and the direct current voltage average value is only required to be within the protection scope of the application according to the specific application environment.
Another embodiment of the present application also provides an inverter, as shown in fig. 1, including: a main circuit 101, a control unit 102 and an acquisition unit (not shown in the figure); wherein the main circuit 101 is controlled by the control unit 102; the acquisition unit is used for acquiring direct current voltage and alternating current output current of the main circuit 101; the control unit 102 is configured to control the reference input amount of the self current loop to decrease when the dc voltage is lower than the dc voltage average value until the dc voltage reaches within a preset range of the dc voltage average value.
In practical applications, the control unit 102 may also be configured to: when the dc voltage of the main circuit 101 is higher than the dc voltage average value, the reference input amount of the self current loop is controlled to rise until the dc voltage reaches within a preset range of the dc voltage average value.
Specifically, when the control unit 102 is configured to control the change of the reference input amount of the self-current loop, whether the reference input amount is controlled to be decreased or increased, the following steps may be performed in real time or periodically: calculating a difference value of the direct current voltage minus the average value of the direct current voltage; according to the difference value, calculating to obtain a corresponding instruction compensation quantity; and superposing the alternating current command value by using the command compensation quantity, and using the superposition result to replace the alternating current command value as the reference input quantity of the self current loop. The specific principles may be referred to the above embodiments, and will not be described herein in detail.
Wherein, the instruction compensation amount is: the product of the difference and the adjustment coefficient; the adjustment coefficient may be specifically: the product of the preset coefficient and the total current of the alternating current output side of the parallel inverter system.
In the parallel inverter system in which the inverters are connected in parallel through the ac side, the dc voltage average value may be calculated by the control unit 102 of any one inverter by reading the dc voltages collected by the control units 102 of the other inverters; for example, the control unit 102 in the present inverter may be directly obtained by calculation after being read, and in this case, the control unit 102 is further configured to: the dc voltage of each inverter is obtained, and the average value of the dc voltage is calculated and sent to the control unit 102 in the other inverters. Alternatively, the control unit 102 in other inverters may be calculated after being read, which is not limited herein, depending on the specific application environment.
When the inverter is connected in parallel to another inverter via the ac side, the control unit 102 is to be used as a control master in each control unit 102, and is to be used for: an ac current command value is generated and issued to the control unit 102 in the other inverter. If the control unit 102 is not used as the control host, it is not required to generate and issue the ac command value, but only needs to receive the ac command value issued by the control host.
Whether the control unit 102 in the inverter is used as the control host or not, the control unit can adjust the reference input quantity of the current loop according to the difference value between the corresponding direct current voltage and the average value of the direct current voltage, so that the reference input quantity reaches the preset range of the average value of the direct current voltage, and the triggering of direct current under-voltage protection and the power failure of the load caused by out-of-network alternating current voltage control when the connected photovoltaic subarrays are shielded are avoided. In addition, the working principle of the internal current loop, the working principle of the internal voltage loop if it is used as the control host, and the specific topology of the main circuit 101 can be referred to in the prior art, and will not be described herein.
Another embodiment of the present application also provides a parallel inverter system, as shown in fig. 1, including: at least two inverters; the direct current sides of the inverters are respectively connected with corresponding photovoltaic subarrays, the alternating current sides of the inverters are connected to the alternating current output sides of the parallel inversion system in parallel, the control units in the inverters are in communication connection, and each control unit is used for executing the off-grid parallel control method of the photovoltaic power station according to any embodiment.
The specific process and principle of the off-grid parallel control method for the photovoltaic power station can be seen in the above embodiments, and will not be described in detail herein.
In view of the fact that the existing off-grid multi-machine parallel control strategy can only be applied to a scene with strong illumination, when illumination shielding occurs to a photovoltaic subarray connected with any inverter, direct-current voltage of the photovoltaic subarray suddenly drops to trigger protection, off-grid alternating-current voltage is possibly out of control, and load power is lost; according to the parallel inverter system provided by the embodiment, the off-grid parallel control method of the photovoltaic power station is executed through each control unit, so that alternating current instructions of each control unit can be compensated in real time, the direct current voltage is maintained at the average value level in real time, and more stable power is provided for off-grid loads.
The same and similar parts of the embodiments in this specification are all mutually referred to, and each embodiment focuses on the differences from the other embodiments. In particular, for a system or system embodiment, since it is substantially similar to a method embodiment, the description is relatively simple, with reference to the description of the method embodiment being made in part. The systems and system embodiments described above are merely illustrative, wherein the elements illustrated as separate elements may or may not be physically separate, and the elements shown as elements may or may not be physical elements, may be located in one place, or may be distributed over a plurality of network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art will understand and implement the present application without undue burden.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative elements and steps are described above generally in terms of functionality in order to clearly illustrate the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.
The features described in the various embodiments of the present disclosure may be interchanged or combined with one another in the description of the disclosed embodiments to enable those skilled in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (16)
1. The off-grid parallel control method for the photovoltaic power station is characterized by being applied to control units in all inverters in a parallel inversion system, wherein alternating current sides of all inverters are connected in parallel; the off-grid parallel control method for the photovoltaic power station comprises the following steps:
each control unit respectively determines whether the direct current voltage of the inverter where the control unit is positioned is lower than the direct current voltage average value of all the inverters;
for the inverter with the direct-current voltage lower than the direct-current voltage average value, the control unit controls the reference input quantity of the self current loop to be reduced until the corresponding direct-current voltage reaches the preset range of the direct-current voltage average value.
2. The off-grid parallel control method of a photovoltaic power plant according to claim 1, wherein each control unit determines whether the dc voltage of the inverter where the control unit is located is lower than the dc voltage average value of all the inverters, respectively, and includes:
any control unit obtains the direct current voltage of each inverter, calculates the direct current voltage average value and sends the direct current voltage average value to other control units; or, each control unit respectively acquires direct current voltages of other inverters, and calculates and obtains the average value of the direct current voltages;
each control unit respectively calculates the difference value of the corresponding direct current voltage minus the average value of the direct current voltage;
and the control unit with the difference value of a negative value determines that the corresponding direct-current voltage is lower than the average value of the direct-current voltage.
3. The off-grid parallel control method of a photovoltaic power station according to claim 2, wherein a control unit that obtains the dc voltage of each inverter and calculates the average value of the dc voltages is a control host in each control unit.
4. The off-grid parallel control method of a photovoltaic power plant according to claim 1, wherein controlling the decrease of the reference input quantity of the self current loop until the corresponding dc voltage reaches within a preset range of the average value of the dc voltage comprises performing in real time or periodically:
according to the difference value of the average value of the direct current voltage subtracted from the corresponding direct current voltage, calculating to obtain a corresponding instruction compensation quantity;
and superposing the alternating current command value by the command compensation quantity, and replacing the alternating current command value by a superposition result to serve as a reference input quantity of a self current loop.
5. The off-grid parallel control method of a photovoltaic power plant according to claim 1, wherein after each control unit determines whether the dc voltage of the inverter where the control unit is located is lower than the dc voltage average value of all the inverters, the method further comprises:
for the inverter with the direct-current voltage higher than the direct-current voltage average value, the control unit controls the reference input quantity of the self current loop to rise until the corresponding direct-current voltage reaches the preset range of the direct-current voltage average value.
6. The off-grid parallel control method of a photovoltaic power plant according to claim 5, wherein controlling the increase of the reference input quantity of the self current loop until the corresponding dc voltage reaches the preset range of the average value of the dc voltage comprises real-time or periodic execution:
according to the difference value of the average value of the direct current voltage subtracted from the corresponding direct current voltage, calculating to obtain a corresponding instruction compensation quantity;
and superposing the alternating current command value by the command compensation quantity, and replacing the alternating current command value by a superposition result to serve as a reference input quantity of a self current loop.
7. The off-grid parallel control method of a photovoltaic power plant according to claim 4 or 6, wherein the calculating the corresponding command compensation amount according to the difference value of the average value of the corresponding direct current voltage subtracted from the average value of the direct current voltage comprises:
and calculating the product of the difference value and the adjustment coefficient as the command compensation amount.
8. The off-grid parallel control method of a photovoltaic power plant according to claim 7, wherein the adjustment coefficient is: the product of the preset coefficient and the AC rated current of the inverter where the control unit is located.
9. The off-grid parallel control method of a photovoltaic power plant according to any one of claims 1 to 6, further comprising, before the control unit controls the reference input amount of the self current loop to change:
and the control host in each control unit generates an alternating current instruction value and transmits the alternating current instruction value to other control units.
10. An inverter, comprising: the device comprises a main circuit, a control unit and an acquisition unit; wherein,,
the main circuit is controlled by the control unit;
the acquisition unit is used for acquiring direct current voltage, alternating current output voltage and alternating current output current of the main circuit;
and the control unit is used for controlling the reference input quantity of the self current loop to be reduced when the direct current voltage is lower than the direct current average value until the direct current voltage reaches the preset range of the direct current average value.
11. The inverter of claim 10, wherein the control unit is further configured to: when the direct current voltage of the main circuit is higher than the direct current voltage average value, the reference input quantity of the self current loop is controlled to rise until the direct current voltage reaches the preset range of the direct current average value.
12. The inverter according to claim 10, wherein the inverter is connected in parallel with other inverters through an ac side, the control unit further being configured to: and obtaining the direct current voltage of each inverter, calculating the direct current voltage average value, and sending the direct current voltage average value to control units in other inverters.
13. The inverter according to claim 10, wherein the inverter is connected in parallel with other inverters through an ac side, the control unit further being configured to: an alternating current command value is generated and issued to a control unit in the other inverter.
14. Inverter according to any one of claims 10 to 13, characterized in that the control unit is adapted to control the variation of the reference input quantity of the self-current loop, in particular to perform the following steps in real time or periodically:
calculating a difference value of the direct current voltage minus the average value of the direct current voltage;
according to the difference value, calculating to obtain a corresponding instruction compensation quantity;
and superposing the alternating current command value by the command compensation quantity, and replacing the alternating current command value by a superposition result to serve as a reference input quantity of a self current loop.
15. The inverter of claim 14, wherein the command compensation amount is: the product of the difference and the adjustment coefficient;
the adjustment coefficient is as follows: the product of a preset coefficient and the total current of the alternating current output side of the parallel inverter system.
16. A parallel inverter system, comprising: at least two inverters;
the direct current sides of the inverters are respectively connected with corresponding photovoltaic subarrays;
the alternating current side of each inverter is connected to the alternating current output side of the parallel inverter system in parallel;
the control units inside the inverters are in communication connection;
each control unit is used for executing the off-grid parallel control method of the photovoltaic power station according to any one of claims 1 to 9.
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