CN109254616B - Input power control method and photovoltaic inverter - Google Patents

Input power control method and photovoltaic inverter Download PDF

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CN109254616B
CN109254616B CN201811177484.1A CN201811177484A CN109254616B CN 109254616 B CN109254616 B CN 109254616B CN 201811177484 A CN201811177484 A CN 201811177484A CN 109254616 B CN109254616 B CN 109254616B
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characteristic curve
photovoltaic inverter
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CN109254616A (en
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曹金虎
陈鹏
耿后来
俞雁飞
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Sungrow Power Supply Co Ltd
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
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    • G05F1/67—Regulating electric power to the maximum power available from a generator, e.g. from solar cell
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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Abstract

The invention provides an input power control method and a photovoltaic inverter. Then, based on the characteristic parameters, the type of the input characteristic curve is determined. And when the type of the input characteristic curve is a first type, controlling the photovoltaic inverter to execute a first optimization algorithm to obtain a first target input power. And when the type of the input characteristic curve is a second type, controlling the photovoltaic inverter to work at a first fixed voltage point or a first fixed voltage interval, and acquiring second target input power. Therefore, the scheme firstly determines the type of the input characteristic curve, and selects different control methods based on different types, for example, when the input characteristic curve is the curve shown in fig. 1, an optimization algorithm is adopted, and when the input characteristic curve is the curve shown in fig. 2, a fixed voltage point or a fixed voltage interval is determined, so that the voltage of the photovoltaic inverter is not fluctuated or is less fluctuated, and the stable operation of the photovoltaic inverter is ensured.

Description

Input power control method and photovoltaic inverter
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to an input power control method and a photovoltaic inverter.
Background
The pv inverter may be directly connected to the pv panel, and at this time, as shown in fig. 1, an output power curve P ═ f (u) of the pv panel is in a nonlinear relationship, the output power may change with the change of the output voltage, and there is an optimal operating point, i.e., the maximum power point MPP. Generally, a photovoltaic inverter captures a maximum power point of a photovoltaic cell panel by using a first optimization algorithm, so as to obtain a maximum output power P by adjusting an output voltage u of the photovoltaic cell panel.
Besides, as the application scenes of the photovoltaic inverter become wider and wider, the photovoltaic inverter can also be applied to the scene that the photovoltaic cell panel is connected with the power optimizer and then is connected with the photovoltaic inverter. At this time, the input characteristic curve of the photovoltaic inverter is as shown in fig. 2, and the maximum power point MPP of the photovoltaic inverter becomes the optimal operating line segment MN, that is, when the photovoltaic inverter operates at any voltage between the M point and the N point, the photovoltaic inverter can obtain the maximum output power.
However, the first optimization algorithm is not suitable for the situation of fig. 2, which may cause the input voltage of the photovoltaic inverter to fluctuate between the M point and the N point, and the fluctuation of the voltage may affect the unstable operation of the photovoltaic inverter, thereby reducing the service life of the photovoltaic inverter.
Therefore, how to provide a photovoltaic inverter capable of obtaining the maximum input power point and operating stably is a great technical problem to be solved by those skilled in the art.
Disclosure of Invention
In view of this, embodiments of the present invention provide a photovoltaic inverter, which can obtain the maximum input power point and operate stably.
In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions:
an input power control method is applied to a photovoltaic inverter and comprises the following steps:
acquiring characteristic parameters of an input characteristic curve of the photovoltaic inverter;
determining a type of the input characteristic curve based on the characteristic parameters;
when the type of the input characteristic curve is a first type, controlling the photovoltaic inverter to execute a first optimization algorithm to obtain first target input power;
and when the type of the input characteristic curve is a second type, controlling the photovoltaic inverter to work at a first fixed voltage point or a first fixed voltage interval, and acquiring second target input power.
Optionally, the obtaining the characteristic parameter of the input characteristic curve of the photovoltaic inverter includes:
traversing the current input characteristic curve to obtain an actual voltage interval when the power voltage change rate is smaller than a first threshold;
correspondingly, the determining the type of the input characteristic curve based on the characteristic parameters comprises:
comparing the actual voltage interval with a target voltage interval, and determining the type of the input characteristic curve as the first type when the actual voltage interval is included in the target voltage interval; and when the target voltage interval is included in the actual voltage interval, determining that the type of the input characteristic curve is the second type, and the target voltage interval is a set voltage interval when the power voltage change rate is smaller than a first threshold value.
Optionally, the obtaining the characteristic parameter of the input characteristic curve of the photovoltaic inverter includes:
traversing the current input characteristic curve to obtain a power change rate and a voltage change rate within a preset time period;
correspondingly, the determining the type of the input characteristic curve based on the characteristic parameters comprises:
determining the type of the input characteristic curve as the first type when the power change rate is higher than a second threshold and the voltage change rate is lower than a third threshold;
determining the type of the input characteristic curve as the second type when the power rate of change is below the second threshold and the voltage rate of change is above the third threshold.
Optionally, the obtaining the characteristic parameter of the input characteristic curve of the photovoltaic inverter includes:
acquiring first power when the voltage of the photovoltaic inverter is a first preset voltage and second power when the voltage of the inverter is a second preset voltage;
correspondingly, the determining the type of the input characteristic curve based on the characteristic parameters comprises:
and judging whether the absolute value of the difference value between the first power and the second power is smaller than a first preset power difference value, if so, determining that the type of the input characteristic curve is the second type, and if not, determining that the type of the input characteristic curve is the first type.
Optionally, the controlling the photovoltaic inverter to operate at the first fixed voltage point includes:
acquiring a lower limit voltage value and an upper limit voltage value of the input characteristic curve target power line segment;
acquiring the output grid voltage of the photovoltaic inverter;
calculating to obtain the minimum input voltage of the photovoltaic inverter based on the output grid voltage of the photovoltaic inverter;
comparing the minimum input voltage, the lower limit voltage value and the upper limit voltage value, and when the minimum input voltage is greater than the lower limit voltage value and less than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point; when the minimum input voltage is smaller than the lower limit voltage value, determining the lower limit voltage value as the first fixed voltage point; when the minimum input voltage is greater than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point.
Optionally, the comparing the minimum input voltage, the lower limit voltage value, and the upper limit voltage value includes:
when the minimum input voltage is larger than the lower limit voltage value and smaller than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point, and controlling the DC/DC direct current converter to be in a stop working state; when the minimum input voltage is smaller than the lower limit voltage value, determining that the lower limit voltage value is the first fixed voltage point, and controlling the DC/DC converter to be in a stop working state; and when the minimum input voltage is greater than the upper limit voltage value, determining that the upper limit voltage value is the first fixed voltage point, and controlling the DC/DC direct current converter to be in a boosting working state.
Optionally, the controlling the photovoltaic inverter to operate at the first fixed voltage point includes:
and traversing the input characteristic curve, and determining the voltage working point when the output power is maximum as the first fixed voltage point.
Optionally, the controlling the photovoltaic inverter to operate in a first fixed voltage interval includes:
traversing the input characteristic curve to determine a voltage working point U when the output power is maximumMN；
Determining a voltage interval [ UMN-(U2-U1)/2,UMN+(U2-U1)/2]Is the first fixed voltage interval, where U2 is the power voltage rate of changeU1 is the maximum value of the set voltage interval when the power voltage change rate is smaller than the first threshold value, and U1 is the minimum value of the set voltage interval when the power voltage change rate is smaller than the first threshold value.
A photovoltaic inverter comprising:
the acquisition module is used for acquiring characteristic parameters of an input characteristic curve of the photovoltaic inverter;
a first determining module, configured to determine a type of the input characteristic curve based on the characteristic parameter;
the control module is used for controlling the photovoltaic inverter to execute a first optimization algorithm to obtain first target input power when the type of the input characteristic curve is a first type; and when the type of the input characteristic curve is a second type, controlling the photovoltaic inverter to work at a first fixed voltage point or a first fixed voltage interval, and acquiring second target input power.
Optionally, the obtaining module includes:
the first traversal unit is used for traversing the current input characteristic curve and acquiring an actual voltage interval when the power voltage change rate is smaller than a first threshold;
accordingly, the first determining module comprises:
the first comparison unit is used for comparing the actual voltage interval with a target voltage interval, and when the actual voltage interval is included in the target voltage interval, determining that the type of the input characteristic curve is the first type; and when the target voltage interval is included in the actual voltage interval, determining that the type of the input characteristic curve is the second type, and the target voltage interval is a set voltage interval when the power voltage change rate is smaller than a first threshold value.
Optionally, the obtaining module includes:
the second traversal unit is used for traversing the current input characteristic curve to obtain a power change rate and a voltage change rate within a preset time period;
accordingly, the first determining module comprises:
the second comparison unit is used for determining the type of the input characteristic curve to be the first type when the power change rate is higher than a second threshold value and the voltage change rate is lower than a third threshold value; determining the type of the input characteristic curve as the second type when the power rate of change is below the second threshold and the voltage rate of change is above the third threshold.
Optionally, the obtaining module includes:
the photovoltaic inverter comprises a first obtaining unit, a second obtaining unit and a control unit, wherein the first obtaining unit is used for obtaining first power when the voltage of the photovoltaic inverter is a first preset voltage and second power when the voltage of the inverter is a second preset voltage;
accordingly, the first determining module comprises:
and the judging module is used for judging whether the absolute value of the difference value between the first power and the second power is smaller than a first preset power difference value, if so, determining that the type of the input characteristic curve is the second type, and if not, determining that the type of the input characteristic curve is the first type.
Optionally, the control module includes:
the second acquisition unit is used for acquiring a lower limit voltage value and an upper limit voltage value of the input characteristic curve target power line segment;
the third acquisition unit is used for acquiring the output grid voltage of the photovoltaic inverter;
the calculation unit is used for calculating and obtaining the minimum input voltage of the photovoltaic inverter based on the output grid voltage of the photovoltaic inverter;
a comparing unit, configured to compare the minimum input voltage, the lower limit voltage value, and the upper limit voltage value, and determine that the minimum input voltage is the first fixed voltage point when the minimum input voltage is greater than the lower limit voltage value and smaller than the upper limit voltage value; when the minimum input voltage is smaller than the lower limit voltage value, determining the lower limit voltage value as the first fixed voltage point; when the minimum input voltage is greater than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point.
Optionally, the photovoltaic inverter includes a DC/DC converter, and the comparing unit includes:
the comparison subunit is configured to determine that the minimum input voltage is the first fixed voltage point and control the DC/DC converter to be in a stop state when the minimum input voltage is greater than the lower limit voltage value and smaller than the upper limit voltage value; when the minimum input voltage is smaller than the lower limit voltage value, determining that the lower limit voltage value is the first fixed voltage point, and controlling the DC/DC converter to be in a stop working state; and when the minimum input voltage is greater than the upper limit voltage value, determining that the upper limit voltage value is the first fixed voltage point, and controlling the DC/DC direct current converter to be in a boosting working state.
Optionally, the control module includes:
and the first traversal module is used for traversing the input characteristic curve and determining the voltage working point when the output power is maximum as the first fixed voltage point.
Optionally, the control module further includes:
a second traversal module for traversing the input characteristic curve to determine a voltage working point U at which the output power is maximumMN；
A second determining module for determining a voltage interval [ UMN-(U2-U1)/2,UMN+(U2-U1)/2]The first fixed voltage interval is defined as U2, where U2 is the maximum value of the set voltage interval when the power voltage change rate is smaller than the first threshold, and U1 is the minimum value of the set voltage interval when the power voltage change rate is smaller than the first threshold.
Based on the technical scheme, the invention provides an input power control method which is applied to a photovoltaic inverter and firstly obtains characteristic parameters of an input characteristic curve of the photovoltaic inverter. Then, based on the characteristic parameters, the type of the input characteristic curve is determined. And when the type of the input characteristic curve is a first type, controlling the photovoltaic inverter to execute a first optimization algorithm to obtain a first target input power. And when the type of the input characteristic curve is a second type, controlling the photovoltaic inverter to work at a first fixed voltage point or a first fixed voltage interval, and acquiring second target input power. Therefore, the scheme firstly determines the type of the input characteristic curve, and selects different control methods based on different types, for example, when the input characteristic curve is the curve shown in fig. 1, an optimization algorithm is adopted, and when the input characteristic curve is the curve shown in fig. 2, a fixed voltage point or a fixed voltage interval is determined, so that the voltage of the photovoltaic inverter is not fluctuated or is less fluctuated, and the stable operation of the photovoltaic inverter is ensured.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic diagram of an input characteristic of a photovoltaic inverter;
FIG. 2 is a schematic diagram of yet another input characteristic of a photovoltaic inverter;
FIG. 3 is a schematic diagram of voltage fluctuations for a photovoltaic inverter;
fig. 4 is a flowchart illustrating an input power control method according to an embodiment of the present invention;
fig. 5 is a schematic flowchart of a method for controlling input power according to an embodiment of the present invention;
fig. 6 is a schematic diagram of an input power control method applied to an input characteristic curve according to an embodiment of the present invention;
fig. 7 is a schematic flowchart of an input power control method according to an embodiment of the present invention;
fig. 8 is a schematic flowchart of an input power control method according to an embodiment of the present invention;
fig. 9 is a schematic flowchart of a method for controlling input power according to an embodiment of the present invention;
fig. 10 is a flowchart illustrating a method for controlling input power according to another embodiment of the present invention.
Detailed Description
It can be known by combining the background art that the application of the first optimization algorithm to the situation of fig. 2 can cause the input voltage of the photovoltaic inverter to fluctuate between the M point and the N point, and the fluctuation of the voltage can affect the unstable operation of the photovoltaic inverter, thereby reducing the service life of the photovoltaic inverter.
Specifically, for a low-voltage operation area, a photovoltaic inverter with a DC/DC direct-current converter (e.g., a photovoltaic inverter with a Boost system) has a Boost converter working in a voltage fluctuation range for a long time, which may increase the loss of the photovoltaic inverter and reduce the efficiency. Meanwhile, a critical point of the Boost converter working may be included between the voltage boundary points M and N corresponding to the maximum output power, and when the voltage fluctuates up and down, the Boost converter is frequently switched between an operating state and a stop state, so that the stability and reliability of the photovoltaic inverter are reduced.
Besides, for a high-voltage operation area, the photovoltaic inverter operates at high voltage, the voltage stress is high, the voltage stress of the power switching tube device is large, the loss of the alternating current filter is large, the stable operation of the photovoltaic inverter is not facilitated, and the service life is influenced.
Fig. 3 shows the actual operation effect of the photovoltaic inverter, wherein curve 1 is the inverter input voltage curve after the photovoltaic cell panel is connected with the power optimizer, and the voltage fluctuation is large. And the curve 2 is a photovoltaic cell panel direct-connected inverter input voltage curve, and the voltage is stable.
Based on this, the embodiment of the present invention provides an input power control method, as shown in fig. 4, which can obtain the maximum input power point and operate stably. Specifically, the method comprises the following steps:
s11, acquiring characteristic parameters of an input characteristic curve of the photovoltaic inverter;
s12, determining the type of the input characteristic curve based on the characteristic parameters;
s13a, when the type of the input characteristic curve is a first type, controlling the photovoltaic inverter to execute a first optimization algorithm to obtain first target input power;
and S13b, when the type of the input characteristic curve is a second type, controlling the photovoltaic inverter to work at a first fixed voltage point or a first fixed voltage interval, and acquiring second target input power.
Therefore, the scheme firstly determines the type of the input characteristic curve, and selects different control methods based on different types, for example, when the input characteristic curve is the curve shown in fig. 1, an optimization algorithm is adopted, and when the input characteristic curve is the curve shown in fig. 2, a fixed voltage point or a fixed voltage interval is determined, so that the voltage of the photovoltaic inverter is not fluctuated or is less fluctuated, and the stable operation of the photovoltaic inverter is ensured.
It should be noted that, the inventor, with reference to fig. 1 and fig. 2, obtains a characteristic of an input characteristic curve of the photovoltaic inverter, and then determines whether the photovoltaic panel is connected to the power optimizer based on the characteristic, and gives different control methods for different output characteristic curves.
Specifically, this embodiment provides 3 specific implementation steps how to determine the type of the input characteristic curve based on the characteristic parameters, which are as follows:
the first scheme is as follows:
as shown in fig. 5, in the input power control method, the obtaining of the characteristic parameter of the input characteristic curve of the photovoltaic inverter in step S11 includes:
s51, traversing the current input characteristic curve, and acquiring an actual voltage interval when the power voltage change rate is smaller than a first threshold;
accordingly, the determining the type of the input characteristic curve based on the characteristic parameters in step S12 includes:
s52, comparing the actual voltage interval with a target voltage interval, and determining the type of the input characteristic curve as the first type when the actual voltage interval is included in the target voltage interval; and when the target voltage interval is included in the actual voltage interval, determining that the type of the input characteristic curve is the second type, and the target voltage interval is a set voltage interval when the power voltage change rate is smaller than a first threshold value.
Illustratively, the output characteristic curve P-U of the photovoltaic panel has a maximum power point, as shown by the curve a in fig. 6, near the maximum power point MPP [ P1,P2]The power voltage rate of change dP/dU of the interval tends to 0. The photovoltaic cell panel is connected with the output characteristic curve P-U of the power optimizer and has a maximum power line segment, as shown by the curve b in figure 6, the maximum power line segment [ M, N [ ]]The power voltage change rate dP/dU of the interval also tends to 0, and [ M, N]Interval is far greater than [ P1,P2]An interval.
In the scheme, the photovoltaic inverter starts from the open-circuit voltage Uoc, and firstly, the working voltage interval [ U ] of the MPPT is setMPP1,UMPP2]Secondly, according to the characteristic curve a of the photovoltaic panel, a first threshold ξ is set1And the first threshold ξ1Corresponding voltage interval [ U1,U2]Wherein the voltage interval
Figure RE-GDA0001904301650000091
Then, traversing an input characteristic curve in the working voltage range of the photovoltaic inverter, and recording the power voltage change rate dP/dU < ξ1Interval of time-corresponding voltage [ U3,U4]Defining a voltage interval [ U3,U4]Is an actual voltage interval, wherein the actual voltage interval
Figure BDA0001824144140000091
Then, the actual voltage interval is compared with the target voltage interval, and when the actual voltage interval meets the requirement
Figure BDA0001824144140000092
And controlling the photovoltaic inverter to operate according to the characteristic curve a (the first type), and executing MPP optimizing work to obtain the optimal output power. When the actual voltage interval is satisfied
Figure BDA0001824144140000093
And controlling the photovoltaic inverter to operate according to a characteristic curve b (a second type), stopping MPP optimization, and controlling a fixed voltage point or a fixed voltage interval in the region of a maximum power line segment MN.
Scheme II:
as shown in fig. 7, in the input power control method, the obtaining of the characteristic parameter of the input characteristic curve of the photovoltaic inverter in step S11 includes:
s71, traversing the current input characteristic curve to obtain a power change rate and a voltage change rate in a preset time period;
accordingly, the determining the type of the input characteristic curve based on the characteristic parameters in step S12 includes:
s72, when the power change rate is higher than a second threshold value and the voltage change rate is lower than a third threshold value, determining the type of the input characteristic curve is the first type; determining the type of the input characteristic curve as the second type when the power rate of change is below the second threshold and the voltage rate of change is above the third threshold.
Illustratively, the photovoltaic inverter operates in a normal MPPT mode, and the power change rate dP/dt is lower than a second threshold ξ for a set period of time2The rate of change of voltage dU/dt is above a third threshold ξ3And during the process, the photovoltaic inverter operates according to the characteristic curve b, MPP optimization is stopped, and fixed voltage points or fixed voltage intervals are controlled in the region of the maximum power line segment MN. Otherwise, the inverter operates according to the characteristic curve a, and MPP optimizing work is executed to obtain the optimal output power.
The third scheme is as follows:
as shown in fig. 8, in the input power control method, the obtaining of the characteristic parameter of the input characteristic curve of the photovoltaic inverter in step S11 includes:
s81, acquiring first power when the voltage of the photovoltaic inverter is a first preset voltage and second power when the voltage of the inverter is a second preset voltage;
accordingly, the determining the type of the input characteristic curve based on the characteristic parameters in step S12 includes:
s82, judging whether the absolute value of the difference value between the first power and the second power is smaller than a first preset power difference value, if so, determining that the type of the input characteristic curve is the second type, and if not, determining that the type of the input characteristic curve is the first type.
Illustratively, before the photovoltaic inverter is started, the open-circuit voltage Uoc is recorded, the photovoltaic inverter is rapidly operated to a first preset voltage 0.8 Uoc and a second preset voltage 0.6 Uoc (or other voltage parameters) at a constant voltage, and a first power P3 and a second power P4 corresponding to different voltage points are recorded, wherein when an absolute value | P3-P4| of a difference value between the first power and the second power is lower than a first preset power difference Δ P, the photovoltaic inverter is operated according to a characteristic curve b, the MPP optimization is stopped, and a fixed voltage point or a fixed voltage interval is controlled in a maximum power line segment MN region. Otherwise, the photovoltaic inverter operates according to the characteristic curve a, and MPP optimizing work is executed to obtain the optimal output power.
In summary, according to the above three schemes, when the photovoltaic inverter determines that the input characteristic curve is the curve a, the inverter executes the MPP conventional optimization algorithm. When the photovoltaic inverter judges that the input characteristic curve is a curve b, namely a maximum power line segment MN exists, the photovoltaic inverter is controlled according to a fixed voltage point or a fixed voltage interval.
Specifically, this embodiment further provides two specific implementation methods for controlling the fixed voltage point or the fixed voltage interval, which are as follows:
as shown in fig. 9, the controlling the photovoltaic inverter to operate at the first fixed voltage point includes:
s91, acquiring a lower limit voltage value and an upper limit voltage value of the input characteristic curve target power line segment;
s92, acquiring the output grid voltage of the photovoltaic inverter;
s93, calculating to obtain the minimum input voltage of the photovoltaic inverter based on the output grid voltage of the photovoltaic inverter;
s94, comparing the minimum input voltage, the lower limit voltage value and the upper limit voltage value, and determining that the minimum input voltage is the first fixed voltage point when the minimum input voltage is greater than the lower limit voltage value and less than the upper limit voltage value; when the minimum input voltage is smaller than the lower limit voltage value, determining the lower limit voltage value as the first fixed voltage point; when the minimum input voltage is greater than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point.
That is, in this example, the fixed voltage point control may have the minimum grid-connection voltage as the fixed voltage operating point. Firstly, obtaining the lower limit voltage value U of the maximum power line section MNMAnd upper limit voltage value UNAnd then, obtaining the output grid voltage Uac of the inverter, and calculating the minimum input voltage Udc required by the normal work of the inverter according to the output grid voltage Uac.
Then, for a photovoltaic inverter without a DC/DC converter, the minimum input voltage, the lower limit voltage value and the upper limit voltage value are further compared.
When Udc is used>UMAnd Udc<UNWhen the voltage is higher than the set voltage, controlling the photovoltaic inverter to adjust the input voltage to the Udc for operation;
when Udc is used<UMThen, the photovoltaic inverter is controlled to adjust the input voltage to UMRunning;
when Udc is used>UNAnd controlling the photovoltaic inverter to adjust the input voltage to the Udc for operation.
On the basis of the foregoing embodiments, the present embodiment further provides a case where the photovoltaic inverter includes a DC/DC direct-current converter, and in this case, the comparing the minimum input voltage, the lower limit voltage value, and the upper limit voltage value includes:
when the minimum input voltage is larger than the lower limit voltage value and smaller than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point, and controlling the DC/DC direct current converter to be in a stop working state; when the minimum input voltage is smaller than the lower limit voltage value, determining that the lower limit voltage value is the first fixed voltage point, and controlling the DC/DC converter to be in a stop working state; and when the minimum input voltage is greater than the upper limit voltage value, determining that the upper limit voltage value is the first fixed voltage point, and controlling the DC/DC direct current converter to be in a boosting working state.
In particular, for a photovoltaic inverter with a DC/DC converter, such as a photovoltaic inverter of a Boost DC Boost system.
When Udc is used>UMAnd Udc<UNWhen the voltage is higher than the set voltage, controlling the photovoltaic inverter to adjust the input voltage to the Udc for operation, and stopping the Boost system;
when Udc is used<UMThen, the photovoltaic inverter is controlled to adjust the input voltage to UMThe Boost system stops working when running;
when Udc is used>UNThen, the photovoltaic inverter is controlled to adjust the input voltage to UNAnd operating the Boost system to perform boosting operation.
On the basis of the foregoing embodiment, the present implementation further provides a specific implementation step of controlling the photovoltaic inverter to operate at the first fixed voltage point, including:
and traversing the input characteristic curve, and determining the voltage working point when the output power is maximum as the first fixed voltage point.
Illustratively, when the maximum output power is obtained in the process of traversing the input characteristic curve, the corresponding voltage working point U is recordedMNTo point UMNAs a fixed voltage operating point, the inverter adjusts the input voltage to UMNAnd (5) operating.
In addition, as shown in fig. 10, the present embodiment further provides a specific implementation manner of controlling the photovoltaic inverter to operate in the first fixed voltage interval, including:
s101, traversing the input characteristic curve, and determining a voltage working point U when the output power is maximumMN；
S102, determining a voltage interval [ UMN-(U2-U1)/2,UMN+(U2-U1)/2]Is the first fixedAnd a constant voltage interval, wherein U2 is the maximum value of the constant voltage interval when the power voltage change rate is smaller than the first threshold value, and U1 is the minimum value of the constant voltage interval when the power voltage change rate is smaller than the first threshold value.
Illustratively, the pv inverter operates according to a characteristic curve b, as shown in fig. 6, and the second operating voltage interval [ U ] of the MPPT including the maximum power line MN or partially including MN is resetMPP3,UMPP4]Wherein, in the step (A),
Figure BDA0001824144140000121
the MPPT working voltage range is limited, the fluctuation range of the input voltage of the photovoltaic inverter is reduced, and the operation stability of the photovoltaic inverter is facilitated.
Specifically, the MPPT operating voltage range may be further limited by the fixed voltage interval control. In the process of traversing the input characteristic curve, obtaining a voltage working point U corresponding to the maximum power in the maximum power line MN areaMNTo U withMNSetting MPPT working voltage interval [ U ] for midpointMN-(U2-U1)/2,UMN+(U2-U1)/2]. The photovoltaic inverter may perform MPP optimization for operating within a defined MPPT operating voltage interval.
On the basis of the foregoing embodiments, the present embodiment further provides a photovoltaic inverter, which corresponds to the foregoing method, and includes:
the acquisition module is used for acquiring characteristic parameters of an input characteristic curve of the photovoltaic inverter;
a first determining module, configured to determine a type of the input characteristic curve based on the characteristic parameter;
the control module is used for controlling the photovoltaic inverter to execute a first optimization algorithm to obtain first target input power when the type of the input characteristic curve is a first type; and when the type of the input characteristic curve is a second type, controlling the photovoltaic inverter to work at a first fixed voltage point or a first fixed voltage interval, and acquiring second target input power.
Optionally, the obtaining module includes:
the first traversal unit is used for traversing the current input characteristic curve and acquiring an actual voltage interval when the power voltage change rate is smaller than a first threshold;
accordingly, the first determining module comprises:
the first comparison unit is used for comparing the actual voltage interval with a target voltage interval, and when the actual voltage interval is included in the target voltage interval, determining that the type of the input characteristic curve is the first type; and when the target voltage interval is included in the actual voltage interval, determining that the type of the input characteristic curve is the second type, and the target voltage interval is a set voltage interval when the power voltage change rate is smaller than a first threshold value.
Optionally, the obtaining module includes:
the second traversal unit is used for traversing the current input characteristic curve to obtain a power change rate and a voltage change rate within a preset time period;
accordingly, the first determining module comprises:
the second comparison unit is used for determining the type of the input characteristic curve to be the first type when the power change rate is higher than a second threshold value and the voltage change rate is lower than a third threshold value; determining the type of the input characteristic curve as the second type when the power rate of change is below the second threshold and the voltage rate of change is above the third threshold.
Optionally, the obtaining module includes:
the photovoltaic inverter comprises a first obtaining unit, a second obtaining unit and a control unit, wherein the first obtaining unit is used for obtaining first power when the voltage of the photovoltaic inverter is a first preset voltage and second power when the voltage of the inverter is a second preset voltage;
accordingly, the first determining module comprises:
and the judging module is used for judging whether the absolute value of the difference value between the first power and the second power is smaller than a first preset power difference value, if so, determining that the type of the input characteristic curve is the second type, and if not, determining that the type of the input characteristic curve is the first type.
Optionally, the control module includes:
the second acquisition unit is used for acquiring a lower limit voltage value and an upper limit voltage value of the input characteristic curve target power line segment;
the third acquisition unit is used for acquiring the output grid voltage of the photovoltaic inverter;
the calculation unit is used for calculating and obtaining the minimum input voltage of the photovoltaic inverter based on the output grid voltage of the photovoltaic inverter;
a comparing unit, configured to compare the minimum input voltage, the lower limit voltage value, and the upper limit voltage value, and determine that the minimum input voltage is the first fixed voltage point when the minimum input voltage is greater than the lower limit voltage value and smaller than the upper limit voltage value; when the minimum input voltage is smaller than the lower limit voltage value, determining the lower limit voltage value as the first fixed voltage point; when the minimum input voltage is greater than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point.
Optionally, the photovoltaic inverter includes a DC/DC converter, and the comparing unit includes:
the comparison subunit is configured to determine that the minimum input voltage is the first fixed voltage point and control the DC/DC converter to be in a stop state when the minimum input voltage is greater than the lower limit voltage value and smaller than the upper limit voltage value; when the minimum input voltage is smaller than the lower limit voltage value, determining that the lower limit voltage value is the first fixed voltage point, and controlling the DC/DC converter to be in a stop working state; and when the minimum input voltage is greater than the upper limit voltage value, determining that the upper limit voltage value is the first fixed voltage point, and controlling the DC/DC direct current converter to be in a boosting working state.
Optionally, the control module includes:
and the first traversal module is used for traversing the input characteristic curve and determining the voltage working point when the output power is maximum as the first fixed voltage point.
Optionally, the control module further includes:
a second traversal module for traversing the input characteristic curve to determine a voltage working point U at which the output power is maximumMN；
A second determining module for determining a voltage interval [ UMN-(U2-U1)/2,UMN+(U2-U1)/2]The first fixed voltage interval is defined as U2, where U2 is the maximum value of the set voltage interval when the power voltage change rate is smaller than the first threshold, and U1 is the minimum value of the set voltage interval when the power voltage change rate is smaller than the first threshold.
It should be noted that the working principle of the photovoltaic inverter refers to the above method embodiment, and the description is not repeated here.
In summary, the present invention provides an input power control method and a photovoltaic inverter, where the control method first obtains a characteristic parameter of an input characteristic curve of the photovoltaic inverter. Then, based on the characteristic parameters, the type of the input characteristic curve is determined. And when the type of the input characteristic curve is a first type, controlling the photovoltaic inverter to execute a first optimization algorithm to obtain a first target input power. And when the type of the input characteristic curve is a second type, controlling the photovoltaic inverter to work at a first fixed voltage point or a first fixed voltage interval, and acquiring second target input power. Therefore, the scheme firstly determines the type of the input characteristic curve, and selects different control methods based on different types, for example, when the input characteristic curve is the curve shown in fig. 1, an optimization algorithm is adopted, and when the input characteristic curve is the curve shown in fig. 2, a fixed voltage point or a fixed voltage interval is determined, so that the voltage of the photovoltaic inverter is not fluctuated or is less fluctuated, and the stable operation of the photovoltaic inverter is ensured.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
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 components and steps have been described above generally in terms of their functionality in order to clearly illustrate this 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 implementation. 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 invention.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. 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 invention. Thus, the present invention 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 (12)

1. An input power control method applied to a photovoltaic inverter includes:
acquiring characteristic parameters of an input characteristic curve of the photovoltaic inverter;
determining a type of the input characteristic curve based on the characteristic parameters;
when the type of the input characteristic curve is a first type, controlling the photovoltaic inverter to execute a first optimization algorithm to obtain a first target input power, wherein the first type represents that voltage fluctuation in the input characteristic curve exceeds a preset range;
and when the type of the input characteristic curve is a second type, controlling the photovoltaic inverter to work at a first fixed voltage point or a first fixed voltage interval to obtain a second target input power, wherein the second type represents that the voltage fluctuation in the input characteristic curve is in a preset range.
2. The input power control method according to claim 1, wherein the obtaining the characteristic parameter of the input characteristic curve of the photovoltaic inverter comprises:
traversing the current input characteristic curve to obtain an actual voltage interval when the power voltage change rate is smaller than a first threshold;
correspondingly, the determining the type of the input characteristic curve based on the characteristic parameters comprises:
comparing the actual voltage interval with a target voltage interval, and determining the type of the input characteristic curve as the first type when the actual voltage interval is included in the target voltage interval; and when the target voltage interval is included in the actual voltage interval, determining that the type of the input characteristic curve is the second type, and the target voltage interval is a set voltage interval when the power voltage change rate is smaller than a first threshold value.
3. The input power control method according to claim 1, wherein the obtaining the characteristic parameter of the input characteristic curve of the photovoltaic inverter comprises:
traversing the current input characteristic curve to obtain a power change rate and a voltage change rate within a preset time period;
correspondingly, the determining the type of the input characteristic curve based on the characteristic parameters comprises:
determining the type of the input characteristic curve as the first type when the power change rate is higher than a second threshold and the voltage change rate is lower than a third threshold;
determining the type of the input characteristic curve as the second type when the power rate of change is below the second threshold and the voltage rate of change is above the third threshold.
4. The input power control method according to claim 1, wherein the obtaining the characteristic parameter of the input characteristic curve of the photovoltaic inverter comprises:
acquiring first power when the voltage of the photovoltaic inverter is a first preset voltage and second power when the voltage of the inverter is a second preset voltage;
correspondingly, the determining the type of the input characteristic curve based on the characteristic parameters comprises:
and judging whether the absolute value of the difference value between the first power and the second power is smaller than a first preset power difference value, if so, determining that the type of the input characteristic curve is the second type, and if not, determining that the type of the input characteristic curve is the first type.
5. The input power control method of claim 1, wherein the controlling the photovoltaic inverter to operate at a first fixed voltage point comprises:
acquiring a lower limit voltage value and an upper limit voltage value of the input characteristic curve target power line segment;
acquiring the output grid voltage of the photovoltaic inverter;
calculating to obtain the minimum input voltage of the photovoltaic inverter based on the output grid voltage of the photovoltaic inverter;
comparing the minimum input voltage, the lower limit voltage value and the upper limit voltage value, and when the minimum input voltage is greater than the lower limit voltage value and less than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point; when the minimum input voltage is smaller than the lower limit voltage value, determining the lower limit voltage value as the first fixed voltage point; when the minimum input voltage is greater than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point.
6. The input power control method of claim 5, wherein the photovoltaic inverter comprises a DC/DC converter, and the comparing the minimum input voltage, the lower limit voltage value, and the upper limit voltage value comprises:
when the minimum input voltage is larger than the lower limit voltage value and smaller than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point, and controlling the DC/DC direct current converter to be in a stop working state; when the minimum input voltage is smaller than the lower limit voltage value, determining that the lower limit voltage value is the first fixed voltage point, and controlling the DC/DC converter to be in a stop working state; and when the minimum input voltage is greater than the upper limit voltage value, determining that the upper limit voltage value is the first fixed voltage point, and controlling the DC/DC direct current converter to be in a boosting working state.
7. A photovoltaic inverter, comprising:
the acquisition module is used for acquiring characteristic parameters of an input characteristic curve of the photovoltaic inverter;
a first determining module, configured to determine a type of the input characteristic curve based on the characteristic parameter;
the control module is used for controlling the photovoltaic inverter to execute a first optimization algorithm to obtain first target input power when the type of the input characteristic curve is a first type; and when the type of the input characteristic curve is a second type, controlling the photovoltaic inverter to work at a first fixed voltage point or a first fixed voltage interval, and acquiring a second target input power, wherein the first type represents that the voltage fluctuation in the input characteristic curve exceeds a preset range, and the second type represents that the voltage fluctuation in the input characteristic curve is in the preset range.
8. The photovoltaic inverter of claim 7, wherein the acquisition module comprises:
the first traversal unit is used for traversing the current input characteristic curve and acquiring an actual voltage interval when the power voltage change rate is smaller than a first threshold;
accordingly, the first determining module comprises:
the first comparison unit is used for comparing the actual voltage interval with a target voltage interval, and when the actual voltage interval is included in the target voltage interval, determining that the type of the input characteristic curve is the first type; and when the target voltage interval is included in the actual voltage interval, determining that the type of the input characteristic curve is the second type, and the target voltage interval is a set voltage interval when the power voltage change rate is smaller than a first threshold value.
9. The photovoltaic inverter of claim 7, wherein the acquisition module comprises:
the second traversal unit is used for traversing the current input characteristic curve to obtain a power change rate and a voltage change rate within a preset time period;
accordingly, the first determining module comprises:
the second comparison unit is used for determining the type of the input characteristic curve to be the first type when the power change rate is higher than a second threshold value and the voltage change rate is lower than a third threshold value; determining the type of the input characteristic curve as the second type when the power rate of change is below the second threshold and the voltage rate of change is above the third threshold.
10. The photovoltaic inverter of claim 7, wherein the acquisition module comprises:
the photovoltaic inverter comprises a first obtaining unit, a second obtaining unit and a control unit, wherein the first obtaining unit is used for obtaining first power when the voltage of the photovoltaic inverter is a first preset voltage and second power when the voltage of the inverter is a second preset voltage;
accordingly, the first determining module comprises:
and the judging module is used for judging whether the absolute value of the difference value between the first power and the second power is smaller than a first preset power difference value, if so, determining that the type of the input characteristic curve is the second type, and if not, determining that the type of the input characteristic curve is the first type.
11. The photovoltaic inverter of claim 7, wherein the control module comprises:
the second acquisition unit is used for acquiring a lower limit voltage value and an upper limit voltage value of the input characteristic curve target power line segment;
the third acquisition unit is used for acquiring the output grid voltage of the photovoltaic inverter;
the calculation unit is used for calculating and obtaining the minimum input voltage of the photovoltaic inverter based on the output grid voltage of the photovoltaic inverter;
a comparing unit, configured to compare the minimum input voltage, the lower limit voltage value, and the upper limit voltage value, and determine that the minimum input voltage is the first fixed voltage point when the minimum input voltage is greater than the lower limit voltage value and smaller than the upper limit voltage value; when the minimum input voltage is smaller than the lower limit voltage value, determining the lower limit voltage value as the first fixed voltage point; when the minimum input voltage is greater than the upper limit voltage value, determining that the minimum input voltage is the first fixed voltage point.
12. The pv inverter of claim 11, wherein the pv inverter comprises a DC/DC converter, and wherein the comparing unit comprises:
the comparison subunit is configured to determine that the minimum input voltage is the first fixed voltage point and control the DC/DC converter to be in a stop state when the minimum input voltage is greater than the lower limit voltage value and smaller than the upper limit voltage value; when the minimum input voltage is smaller than the lower limit voltage value, determining that the lower limit voltage value is the first fixed voltage point, and controlling the DC/DC converter to be in a stop working state; and when the minimum input voltage is greater than the upper limit voltage value, determining that the upper limit voltage value is the first fixed voltage point, and controlling the DC/DC direct current converter to be in a boosting working state.
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