CN109193777B - Power optimizer and photovoltaic power generation system - Google Patents
Power optimizer and photovoltaic power generation system Download PDFInfo
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Abstract
The invention provides a power optimizer and a photovoltaic power generation system, wherein the input end of a converter in the power optimizer is connected with at least one photovoltaic module as the input end of the power optimizer. The output end of the converter is used as the output end of the power optimizer, and the output ends of the plurality of power optimizers are connected in series. The controller is electrically connected with the converter, acquires a first electric parameter of the converter, and controls the converter to be in a power conversion mode when the first electric parameter is smaller than a first threshold value, so that the converter performs power conversion on the direct current electric energy of the photovoltaic assembly. When the first electric parameter is larger than the first threshold value, the converter is controlled to be in a direct-through mode, so that the output end of the converter is directly communicated with the input end, and at the moment, only one stage of power conversion of the inverter exists between the photovoltaic module at the input end of the converter and the power grid or the load, and the loss of the DC/DC conversion efficiency of the converter is eliminated. The greater the number of converters in the pass-through mode in a photovoltaic power generation system, the higher its system efficiency.
Description
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a power optimizer and a photovoltaic power generation system.
Background
With the rapid development of photovoltaic power generation, the requirements on the power generation efficiency of photovoltaic modules are gradually improved. Generally, as shown in fig. 1, in order to improve the power generation efficiency of the photovoltaic module, a power optimizer may be connected in parallel to the photovoltaic module, and the power optimizer connected in series may be connected in parallel to an inverter, so that the inverter converts direct current into alternating current to implement grid connection.
Specifically, the Power optimizer is a DC/DC converter, such as a buck, boost, 4-switch symmetric buck boost converter, for implementing MPPT (Maximum Power Point Tracking) on the photovoltaic module, so as to obtain the Maximum output Power of the photovoltaic module, and eliminate series mismatch and parallel mismatch of the photovoltaic module.
However, the inventor finds that the power optimizer adds a one-stage DC/DC power converter to the photovoltaic power generation system, that is, the DC power of the photovoltaic module needs to be converted by the power optimizer and then transmitted to the subsequent power grid or load by the inverter through DC/AC, and the two-stage power conversion results in low system efficiency of the photovoltaic power generation system.
Therefore, how to provide a power optimizer and a photovoltaic power generation system, which can improve the conversion efficiency of the photovoltaic power generation system, is a great technical problem to be solved urgently by those skilled in the art.
Disclosure of Invention
In view of this, the embodiment of the invention provides a power optimizer and a photovoltaic power generation system, which can improve the conversion efficiency of the photovoltaic power generation system.
In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions:
a power optimizer comprising: a converter and a controller;
the input end of the converter is connected with at least one photovoltaic module and is used as the input end of the power optimizer;
the output end of the converter is used as the output end of the power optimizer, and the output ends of the plurality of power optimizers are connected in series;
the controller is electrically connected with the converter, a first electric parameter of the converter is obtained, and when the first electric parameter is smaller than a first threshold value, the converter is controlled to be in a power conversion mode, so that the converter performs power conversion on the direct current electric energy of the photovoltaic module; and when the first electric quantity is larger than the first threshold value, controlling the converter to be in a through mode so that the output end and the input end of the converter are directly communicated, wherein the first electric quantity comprises any one or more of output power, output voltage and input current of the converter.
Optionally, the converter performs power conversion on the dc electric energy of the photovoltaic module, and includes:
and the converter performs maximum power point tracking on the photovoltaic assembly and outputs the maximum power of the photovoltaic assembly to the output end of the converter.
Optionally, the apparatus further comprises a memory, wherein the memory stores the first threshold.
Optionally, the first threshold is less than or equal to 1.1 times of the rated power of the power optimizer.
Optionally, the first threshold value is determined based on a first electrical quantity of at least two of the converters;
the time interval between the acquisition of the first electrical parameter by at least two controllers is less than a first preset time.
Optionally, the first threshold is determined based on a first electrical quantity of at least two of the converters, including:
determining a maximum value of a first electrical quantity of a plurality of said converters as said first threshold value;
determining an average value of a first electrical quantity of a plurality of said converters as said first threshold value;
determining an average value of the first parameters with the minimum value removed from the first electrical parameters of the plurality of converters as the first threshold value;
determining an average value of a part of the first quantities of the plurality of the converters as the first threshold value;
determining a weighted average of different coefficients of a first electrical quantity of a plurality of said converters as said first threshold value.
Optionally, a communication circuit is also included,
the communication circuit is used for receiving the first threshold value sent by an external device and transmitting the first threshold value to the controller,
or the like, or, alternatively,
the communication circuit is used for receiving the first electric parameters sent by other converters and transmitting the first electric parameters to the controller, so that the controller determines the first threshold value based on the first electric parameters of at least two converters.
Optionally, the controller further obtains a second threshold, and controls the converter to be in the through mode or the standby mode when the first electrical parameter is smaller than the second threshold, where the second threshold is smaller than the first threshold.
A photovoltaic power generation system, comprising: a bus converter and at least two of the above-described power optimizers;
the output ends of the plurality of power optimizers are connected in series, and the photovoltaic group strings after being connected in series are electrically connected with the direct current bus;
the bus converter performs maximum power point tracking on the direct current electric energy of the direct current bus and converts the direct current electric energy into preset direct current or preset alternating current.
Optionally, characterized in that said first threshold value is determined on the basis of a first electrical quantity of at least two of said converters;
the time interval between the acquisition of the first electrical parameter by at least two controllers is less than a first preset time.
Optionally, the first threshold is determined based on a first electrical quantity of at least two of the converters, including:
determining a maximum value of a first electrical quantity of a plurality of said converters as said first threshold value;
determining an average value of a first electrical quantity of a plurality of said converters as said first threshold value;
determining an average value of the first parameters with the minimum value removed from the first electrical parameters of the plurality of converters as the first threshold value;
determining an average value of a part of the first quantities of the plurality of the converters as the first threshold value;
determining a weighted average of different coefficients of a first electrical quantity of a plurality of said converters as said first threshold value.
Optionally, a communication host is also included,
the communication host is configured to transmit the first threshold to a plurality of the controllers,
or the like, or, alternatively,
the communication host is configured to communicate the first electrical parameter of the converter to a plurality of the controllers to cause the controllers to determine the first threshold based on the first electrical parameters of at least two of the converters.
Optionally, the controller further obtains a second threshold, and when the first electrical parameter is smaller than the second threshold, controls the converter to be in a pass-through mode or a standby mode, where the second threshold is smaller than the first threshold.
Based on the technical scheme, the invention provides a power optimizer which comprises a converter and a controller. Wherein, the input of converter links to each other with at least one photovoltaic module, as the input of power optimizer. The output end of the converter is used as the output end of the power optimizer, and the output ends of the plurality of power optimizers are connected in series. The controller is electrically connected with the converter, acquires a first electric parameter of the converter, and controls the converter to be in a power conversion mode when the first electric parameter is smaller than a first threshold value, so that the converter performs power conversion on the direct current electric energy of the photovoltaic assembly. When the first electrical parameter is larger than the first threshold value, the converter is controlled to be in a direct connection mode, so that the output end of the converter is directly communicated with the input end, and at the moment, the photovoltaic power generation system only has one-stage power conversion, so that the system efficiency of the photovoltaic power generation system is improved.
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 optimizer system according to the prior art;
FIG. 2 is a schematic diagram of a further prior art optimizer system;
fig. 3 is a schematic structural diagram of a power optimizer system according to an embodiment of the present invention;
fig. 4 is a waveform diagram of a power optimizer system according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of another waveform of a power optimizer system according to an embodiment of the present invention;
fig. 6 is a schematic diagram of another waveform of a power optimizer system according to an embodiment of the present invention.
Detailed Description
In combination with the background art, although the power optimizer maximizes the output power of each photovoltaic module and eliminates the series-parallel mismatch of the photovoltaic modules, a primary DC/DC power converter is added to the photovoltaic power generation system, the DC power of the photovoltaic modules needs to be converted by the power optimizer through DC/DC conversion and then transmitted to a secondary power grid or a load through the DC/AC of the inverter, and the system efficiency of the photovoltaic power generation system is low due to the two-stage power conversion. Especially, when the series-parallel mismatch between the photovoltaic modules is small, or when the series-parallel mismatch exists only in a part of time periods (shielded by moving shadows) in a day, the power generation capacity improvement caused by the MPPT performed by the power optimizer may not make up for the power generation capacity loss caused by the efficiency loss of the DC/DC conversion, so that the power generation capacity of the system is reduced.
Accordingly, as shown in fig. 3, an embodiment of the present invention provides a power optimizer, including: an inverter and a controller.
And the input end of the converter is connected with at least one photovoltaic module and used as the input end of the power optimizer. The output end of the converter is used as the output end of the power optimizer, and the output ends of the power optimizers are connected in series.
The controller is electrically connected with the converter, a first electric parameter of the converter is obtained, and when the first electric parameter is smaller than a first threshold value, the converter is controlled to be in a power conversion mode, so that the converter performs power conversion on the direct current electric energy of the photovoltaic module; and when the first electric quantity is larger than the first threshold value, controlling the converter to be in a through mode so that the output end and the input end of the converter are directly communicated. At the moment, only one stage of power conversion of the inverter DC/AC exists between the photovoltaic module at the input end of the converter and the power grid or the load, and the loss of the DC/DC conversion efficiency of the converter is eliminated. The greater the number of converters in the pass-through mode in the photovoltaic system, the higher the system efficiency of the photovoltaic power generation system.
It should be noted that, in this embodiment, the converter is a DC/DC converter, and can operate in a power conversion mode, and is configured to perform power conversion on the DC electric energy of the photovoltaic module at the input end, and then output the converted DC electric energy to the output end; alternatively, it may operate in a pass-through mode, with the input and output terminals in direct communication. The DC/DC converter may be one of buck, boost, 4-switch symmetric buck boost, and other DC/DC converters that can perform power conversion.
And the power conversion mode of the converter is mainly used for carrying out MPPT on the electric energy of the photovoltaic module at the input end, and besides, the converter can also be slowly started, operated in a limited power mode and the like. In which a soft start (also called soft start) is used for the start phase of the converter, and the converter is smoothly operated from the standby phase to the power conversion operation mode, for example, from the standby state to the maximum power point current at a speed of 0.2A/s of the input current change rate. The power-limited operation is used for reducing the output power when the operation state of the converter per se is close to a critical value (for example, the output voltage reaches the critical value, the ambient temperature reaches the critical value), so as to protect the converter per se, or reducing the output power after receiving an externally issued power-limited operation instruction.
In the photovoltaic string, the output currents of the power optimizers connected in series are equal, so that the power optimizers with larger output voltages have larger output power. In addition, the output power of the power optimizer is totally from the photovoltaic module at the input end, and the power magnitude is positively correlated with the input current of the power optimizer (the output current of the photovoltaic module). The first electrical quantity may thus be any of the input power or output power, the output voltage, the input current of the power optimizer.
In addition, in this embodiment, the first electrical parameter is acquired by the sampling circuit, or acquired by the sampling circuit and then calculated by the controller. Referring to fig. 3, if the first electrical parameter is the output voltage Vo, the output voltage Vo is collected by the voltage sampling circuit and transmitted to the controller, the controller compares the output voltage Vo with a first threshold (e.g., 30V), if the output voltage Vo is lower than the first threshold, the converter is controlled to perform power conversion operation, and if the output voltage Vo is higher than the first threshold, the converter is controlled to operate in the through mode. If the first electrical parameter is the input power or the output power of the dc electrical energy converted by the converter, the input power is calculated according to the collected input voltage and input current, or the output power is calculated according to the collected output voltage and output current. The input power is substantially equal to the output power, differing by only one converter efficiency, and therefore the output power may also be replaced by the input power.
Specifically, in this embodiment, the first threshold may be a fixed value, for example, the first threshold is less than or equal to 1.1 times of the rated power of the power optimizer. Of course, the first threshold value can also be a variable value, for example, the first threshold value is determined on the basis of at least two first electrical variables of the converter, the time interval between the at least two first electrical variables of the converter being less than a first predetermined time period.
Wherein the first threshold is determined based on a first electrical quantity of at least two of the converters, including:
determining a maximum value of a first electrical quantity of a plurality of said converters as said first threshold value;
determining an average value of a first electrical quantity of a plurality of said converters as said first threshold value;
determining an average value of the first parameters with the minimum value removed from the first electrical parameters of the plurality of converters as the first threshold value;
determining an average value of a part of the first quantities of the plurality of the converters as the first threshold value;
determining a weighted average of different coefficients of a first electrical quantity of a plurality of said converters as said first threshold value.
Illustratively, the first threshold may be a fixed value, such as 80% rated power, 110% rated power, etc., and the power optimizer further includes a memory for storing the first threshold, wherein the first threshold is not lost when the memory is powered down, and the memory may be one of EEPROM, FLASH, ROM, and other memories that are not volatile data when the memory is powered down.
When the converter operates in power conversion, the internal switching tube can work in high-frequency chopping mode, large switching loss and heat are generated, and extra heat dissipation measures need to be added during product design. For a combination of performance and cost considerations, heat dissipation is typically designed to allow the converter to operate with a light overload, such as a 110% rated power for a long period of time, and at higher input power, the converter may be powered down or over-temperature protected to prevent product damage caused by heat generation exceeding the rate of heat dissipation.
Because the DC/DC converter in the power optimizer can support through operation, for example, with the 4-switch symmetrical buck boost converter in fig. 2, when S1 and S3 are turned on and S2 and S4 are turned off, that is, the DC/DC converter is in through operation, at this time, the electric energy at the input end is directly transmitted to the output end, and the converter has no high-frequency chopping loss of the switching tube, so that the heat generation amount is greatly reduced, and a larger direct current electric energy can be input.
Therefore, in this embodiment, the first threshold of the power optimizer may be set to 110% of rated power, when the input power is lower than 110% of rated power, the power optimizer performs power conversion operation to perform MPPT on the input photovoltaic module, and when the input power is higher than 110% of rated power, the power optimizer enters through operation to transmit all the power at the input end to the output end, and at this time, the power optimizer does not perform MPPT any more.
As shown in fig. 4, the nominal power of the photovoltaic module is measured in an STC environment with illumination of 1000W/m2 and an ambient temperature of 25 ℃, when the illumination exceeds 1000W/m2 or the ambient temperature is lower than 25 ℃, the output power exceeds the nominal power, and the shaded portion shown in fig. 4 is the extra output power of the photovoltaic module when the illumination exceeds 1000W/m2, therefore, when a power optimizer with the same power is selected according to the nominal power in the photovoltaic system, the nominal power of the photovoltaic module is used as the rated power by using the power optimizer of the present embodiment, and the first threshold is selected as the rated power, which does not cause the extra output power of the photovoltaic module to be limited by the power optimizer. When the output power of the photovoltaic assembly does not exceed the nominal power, the power optimizer carries out MPPT work, and when the output power of the photovoltaic assembly exceeds the nominal power, the power optimizer enters direct operation to ensure that all the output power of the photovoltaic assembly can be output to the photovoltaic group string.
Besides, for the photovoltaic module with double-sided power generation, the back surface power generation power is about 5% -30% of the front surface nominal power according to different ground surface reflection conditions, the power optimizer of the embodiment can be completely selected according to the front surface nominal power, the first threshold is selected as the nominal power, when the total output power of the power optimizer does not exceed the front surface nominal power, the power optimizer carries out MPPT operation, when the total output power exceeds the front surface nominal power, the power optimizer enters direct operation, and all the output power of the double-sided photovoltaic module can be ensured to be output to the photovoltaic module string.
In addition, because the output power of the photovoltaic module is related to illumination and ambient temperature, the illumination and the ambient temperature do not reach the STC environment in most of time, and the output power of the photovoltaic module is lower than the nominal power in most of time. For example, in the morning, evening, cloudy, and rainy weather, the output power of the photovoltaic module cannot reach the nominal power. Fig. 5 shows the output power variation of a 300W device during one week, which reaches 300W only during noon on day 2 during 1 week. If the photovoltaic module is provided with the power optimizer of 300W, the power optimizer is in a light load state within 90% of the time, and the rated power of the power optimizer cannot be reached. According to the embodiment, a power optimizer with the rated power of 250W can be adopted, when the output power of the photovoltaic module does not exceed 250W, the power optimizer carries out MPPT (maximum power point tracking) operation, when the output power of the photovoltaic module exceeds 250W, the power optimizer enters direct operation, and all the output power of the photovoltaic module can be ensured to be output to the photovoltaic group string. Compared with a power optimizer of 300W, the power optimizer of 250W is adopted in the embodiment, so that the equipment cost of the power optimizer can be greatly reduced.
It can be seen that according to this embodiment, when the input power exceeds the first threshold, it may be considered that the photovoltaic module at the input end is not shaded by a shadow or the like, which affects the power generation amount, the power optimizer enters a direct operation, the MPPT on the photovoltaic module at the input end is abandoned, and the photovoltaic module maintains the maximum power output by the photovoltaic inverter at the subsequent stage executing the MPPT. Therefore, the problem that when the photovoltaic module is not shaded and subjected to series-parallel mismatch, the power optimizer and the photovoltaic inverter two-stage converter simultaneously carry out power conversion operation, so that the system power generation efficiency is low is solved.
That is, the first threshold may also be a varying value, specifically: when the operating environments of the photovoltaic system and the photovoltaic assembly are different, different first threshold values are selected so that the photovoltaic system and the photovoltaic assembly are kept in the optimal operating state.
In this embodiment, the photovoltaic system includes 1 photovoltaic string, or a plurality of photovoltaic strings connected in parallel, each photovoltaic string is formed by connecting at least 2 power optimizer outputs in series, and each power optimizer input is connected to at least 1 photovoltaic module. All photovoltaic groups are coupled on a direct current bus in series, a bus converter is coupled between the direct current bus and a load of a photovoltaic system, and MPPT is carried out on electric energy on the direct current bus and the electric energy is converted into an electric energy form required by the load. The bus converter is most commonly an inverter for MPPT the dc power on the dc bus and converting the dc power into ac power for use by ac loads or for transmission to an ac power grid. In other embodiments, the bus converter may also be a DC/DC converter, such as a storage converter, coupled between the DC bus and the storage battery, performing power conversion to MPPT the electrical energy on the DC bus, and storing the electrical energy in the storage battery.
The photovoltaic system further comprises a communication host which is used for communicating with at least 2 power optimizers in the photovoltaic power generation system and obtaining a first electrical parameter of the power optimizers through communication. The communication host can be a stand-alone device, and can also be integrated in other devices of the photovoltaic system, such as a photovoltaic inverter, a combiner box, a grid-connected box or 1 power optimizer therein. The communication host communicates with the power optimizer through wireless communication (such as WiFi, Lora, Zigbee and the like) or PLC communication.
After the communication host computer obtains the first electrical parameter of the power optimizer, first mathematical operation is carried out to obtain a first threshold value, and the first threshold value is sent to at least 1 power optimizer through communication. In order to ensure that the change of the operating state of the photovoltaic system can be responded in time, the communication host acquires the first electrical parameter, calculates the first threshold value, and issues the first electrical parameter to the power optimizer, wherein the operation is performed at regular time, for example, every 1 minute, and the operation is recommended to be performed for no more than 60 minutes.
In addition, the communication between the communication host and the power optimizer adopts a master-slave mode. If the number of the power optimizers in the photovoltaic system is large, the communication host needs long time for one time of communication polling, and if the communication host waits for one time of communication polling, the time span of the acquired first electrical parameters of different power optimizers is large, and large errors can be generated when the first electrical parameters are calculated. Therefore, after the first electrical parameter of the few power optimizers is acquired, the communication host can start to calculate and send the first threshold value so as to improve the response speed of the system. For example, the photovoltaic system is provided with 100 power optimizers with the numbers of 1-100, the communication host can calculate and issue the first threshold value after the communication polling of 10 power optimizers with the numbers of 1-10 is finished, the first threshold value is calculated and issued again after the communication polling of 10 power optimizers with the numbers of 11-20 is finished, and according to the mode of jumping over time, the speed of calculating and issuing the first threshold value is 10 times higher than the speed of recalculating and issuing by 100 power optimizers after the polling is finished. The communication host can also calculate and issue a first threshold value after polling 10 power optimizers with the numbers of 1-10, recalculate and issue the first threshold value by 10 power optimizers with the numbers of 2-11 after polling the power optimizer No. 11, recalculate and issue the first threshold value by 10 power optimizers with the numbers of 3-12 after polling the power optimizer No. 12, and roll and move the calculation and issue of the first threshold value … …, so that the speed can be increased by 100 times.
Further, the communication host may also issue the first threshold value through a broadcast instruction, or may carry the newly calculated first threshold value in a unicast instruction for querying the first electrical parameter issued to the single power optimizer. Whether broadcast or unicast instructions, all power optimizers in the photovoltaic system may receive and resolve the first threshold.
In summary, in this embodiment, the power optimizer further includes a communication circuit, configured to perform interactive communication with the communication host, where the communication circuit receives a command issued by the communication host to obtain the first electrical parameter and the other electrical parameters, replies communication data including the first electrical parameter, and receives a first threshold issued by the communication host, and the communication circuit may also monitor communication between the communication host and the other power optimizers.
The calculation of the first threshold value may also be performed directly in the power optimizer. When the communication host communicates with the power optimizers to obtain the operating data, each power optimizer can monitor the reply signals of other power optimizers, intercept the first electrical parameter in the reply signals, and then obtain the first threshold value according to the first operation. In order to increase the response speed when the number of power optimizers in the photovoltaic system is large, the power optimizers may also calculate the first threshold value by using the first electrical parameters of the partial power optimizers in a manner similar to the above-mentioned communication host in a time sequence backward rolling transition or jumping transition, for example, by selecting the first electrical parameters of the other power optimizers monitored in the last 5 minutes. Of course, the power optimizer may also include its own electrical parameter when calculating the first threshold value by using the first electrical parameters of other power optimizers.
In particular, the first operation is used to calculate a suitable first threshold.
Preferably, the first operation may be calculating a maximum value of the first electrical quantities of the plurality of power optimizers, the maximum value being the first threshold. For example, the power of all the power optimizers in the last 5 minutes is obtained, the maximum value of the power optimizers is calculated, and the maximum value is used as the first threshold value. After the power optimizer obtains the first threshold value through self calculation or issued by a communication host, the power optimizer judges the magnitude of the current power of the power optimizer and the first threshold value, if the current power of the power optimizer does not exceed the first threshold value, the power generation capacity of the photovoltaic module at the input end of the power optimizer is lower than that of other photovoltaic modules in the system, MPPT work is carried out to eliminate the influence on series-parallel mismatch of other photovoltaic modules, if the current power generation capacity of the photovoltaic module at the input end of the power optimizer exceeds the first threshold value, the power optimizer indicates that the power generation capacity state of the photovoltaic module at the input end of the power optimizer is good, the power optimizer can enter direct operation, and the loss of self power conversion operation is eliminated.
Preferably, the first operation may be to calculate an average value of the first electrical quantities of the plurality of power optimizers, the average value being the first threshold. For example, the power of all the power optimizers in the last 5 minutes is obtained, the average value of the power optimizers is calculated, and the average value is used as the first threshold value. If the current power of a certain power optimizer does not exceed the average value, the photovoltaic module at the input end of the power optimizer is indicated to have lower power generation capacity than other photovoltaic modules in the system, MPPT work is carried out to eliminate the influence on series-parallel mismatch of other photovoltaic modules, if the current power of the certain power optimizer exceeds the average value, the power generation capacity state of the photovoltaic module at the input end of the power optimizer is indicated to be good, the power optimizer can enter direct-connection operation, and the loss of self power conversion operation is eliminated.
During the above-mentioned first operation performing the average value calculation, it is also possible to remove a part of the values for which the first electrical parameter is minimal, in order to adjust the probability of the power optimizer entering a pass-through operation. For example, the power values of 30 power optimizers are acquired in the last 1 minute, the power values of the 10 power optimizers with the lowest power values are removed, and the average value of the power values of the remaining 20 power optimizers is used as the first threshold.
In the process of performing the average value calculation by the first operation, the obtained first electrical parameter may be weighted-averaged to adjust the probability of the power optimizer entering the through operation. For example, the power values of 30 power optimizers are acquired in the last 1 minute, the corresponding proportionality coefficients are decreased from large to small according to the power, and finally, the weighted average value is calculated to serve as the first threshold value.
In the process of performing the average value calculation by the first operation, part of the maximum values of the first electrical parameter may be directly selected to adjust the probability of the power optimizer entering the through operation. For example, the power values of 30 power optimizers are acquired in the last 1 minute, the power value of the 10 power optimizers with the largest power value is selected, and the average value is calculated to serve as the first threshold.
The method that partial first electrical parameter minimum values are removed, partial maximum values are selected, different coefficients are selected according to the power size, and then the average value is calculated to serve as the first threshold value can improve the size of the calculated first threshold value, and the situation that a power optimizer corresponding to a photovoltaic module with slightly low generated energy enters direct operation due to partial slight shielding is avoided.
The maximum value, the average value and the weighted average value can be obtained through calculation, then the maximum value, the weighted average value and the coefficient are multiplied or a fixed value is increased or decreased, then the maximum value is used as a first threshold value to adjust the probability of the power optimizer entering the through operation, for example, after the maximum value is obtained through calculation, the probability of the power optimizer entering the through operation is improved, and the probability of the power optimizer entering the through operation is reduced by taking the maximum value of 1.1 as the first threshold value.
In addition, the present embodiment provides the power optimizer further comprising a communication circuit, wherein the communication circuit is configured to transmit the first threshold value to the controller, or the communication circuit is configured to transmit the first electrical parameter of the converter to the controller, so that the controller determines the first threshold value based on the first electrical parameters of at least two converters.
On the basis of the foregoing embodiment, in the power optimizer provided in this embodiment, the controller further obtains a second threshold, and when the first electrical parameter is smaller than the second threshold, controls the converter to be in the through mode or the standby mode, where the second threshold is smaller than the first threshold.
Illustratively, when the power of the photovoltaic module is low, such as weak light, the voltage and the current output to the rear-stage power optimizer are both low, and the fluctuation is large, the accuracy of the power optimizer executing the MPPT will be greatly reduced, and in addition, the self-loss (power consumption of the controller and other control circuits, and power conversion damage of the DC/DC converter) of the power optimizer executing the MPPT accounts for the proportion of the generated power of the photovoltaic module to be increased, so that the power optimizer executes the MPPT unreliably. In this case, the power optimizer is also controlled to perform the direct operation to increase the power generation amount of the photovoltaic power generation system as much as possible.
In this embodiment, a second threshold is set, and the power optimizer compares the first electrical parameter with the second threshold, and controls the DC/DC converter to operate in the standby mode if the first electrical parameter is lower than the second threshold. For example, the second threshold is set to 50W, and when the input current of the power optimizer is lower than 50W, the through operation is entered.
Fig. 6 is a schematic diagram showing a one-day operation state when the power optimizer sets the first threshold to 300W and the second threshold to 50W. Wherein the shaded portion represents through operation and the remaining portion represents MPPT operation. Under the conditions of low power of weak light in the morning and evening and high power of strong light in the noon, the power optimizer runs in a direct mode, the loss of power conversion of the power optimizer is reduced, and the power generation efficiency of a photovoltaic power generation system is improved.
The second threshold may also be a threshold for controlling the power optimizer to start or wait, the power optimizer compares the first electrical parameter of the power optimizer with the second threshold, and if the first electrical parameter is lower than the second threshold, the power optimizer controls the DC/DC converter to operate in the standby mode without MPPT or direct operation, and after a period of delay, the power optimizer tries to restart the power optimizer to detect whether the first electrical parameter reaches the second threshold. In this way, the number of times of hiccup operation of the power optimizer due to low input power or the number of times of hiccup operation of the inverter at the later stage can be reduced in low-light environments such as morning and evening. For example, the second threshold is set to be 0.05A, when the input current of the power optimizer is lower than 0.05A, the power optimizer enters a standby mode, waits for 5 minutes, then performs MPPT operation again, detects whether the input current exceeds 0.05A, and if the input current exceeds 0.05A, enters the MPPT operation, otherwise, continues to wait for 5 minutes.
In addition, the present embodiment also provides a photovoltaic power generation system, including: a bus converter and at least two of the above power optimizers;
the output ends of the plurality of power optimizers are connected in series, and the photovoltaic group strings after being connected in series are electrically connected with the direct current bus;
the bus converter performs maximum power point tracking on the direct current electric energy of the direct current bus and converts the direct current electric energy into preset direct current or preset alternating current.
Optionally, characterized in that said first threshold value is determined on the basis of a first electrical quantity of at least two of said converters;
the time interval between the first electrical quantities of at least two of the converters is less than a first predetermined time period.
Optionally, the first threshold is determined based on a first electrical quantity of at least two of the converters, including:
determining a maximum value of a first electrical quantity of a plurality of said converters as said first threshold value;
determining an average value of a first electrical quantity of a plurality of said converters as said first threshold value;
determining an average value of the first parameters with the minimum value removed from the first electrical parameters of the plurality of converters as the first threshold value;
determining an average value of a part of the first quantities of the plurality of the converters as the first threshold value;
determining a weighted average of different coefficients of a first electrical quantity of a plurality of said converters as said first threshold value.
Optionally, a communication host is also included,
the communication host is configured to transmit the first threshold to a plurality of the controllers,
or the like, or, alternatively,
the communication host is configured to transmit the first electrical quantities of the converters to a plurality of the controllers, so that the controllers determine the first threshold value based on the first electrical quantities of at least two of the converters.
Optionally, the controller further obtains a second threshold, and when the first electrical parameter is smaller than the second threshold, controls the converter to be in a pass-through mode or a standby mode, where the second threshold is smaller than the first threshold.
The working principle of the photovoltaic power generation system is referred to the working principle of the power optimizer, and the description is not repeated here.
In summary, the present invention provides a power optimizer and a photovoltaic power generation system, wherein the power optimizer includes a converter and a controller. Wherein, the input of converter links to each other with at least one photovoltaic module, as the input of power optimizer. The output end of the converter is used as the output end of the power optimizer, and the output ends of the plurality of power optimizers are connected in series. The controller is electrically connected with the converter, acquires a first electric parameter of the converter, and controls the converter to be in a power conversion mode when the first electric parameter is smaller than a first threshold value, so that the converter performs power conversion on the direct current electric energy of the photovoltaic assembly. When the first electrical parameter is larger than the first threshold value, the converter is controlled to be in a direct connection mode, so that the output end of the converter is directly communicated with the input end, and at the moment, the photovoltaic power generation system only has one-stage power conversion, so that the system efficiency of the photovoltaic power generation system is improved.
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 (11)
1. A power optimizer, comprising: a converter and a controller;
the input end of the converter is connected with at least one photovoltaic module and is used as the input end of the power optimizer;
the output end of the converter is used as the output end of the power optimizer, and the output ends of the plurality of power optimizers are connected in series;
the controller is electrically connected with the converter, acquires output power or input current of the converter, and controls the converter to be in a power conversion mode when the output power or the input current is smaller than a corresponding first threshold value, so that the converter performs power conversion on direct current electric energy of the photovoltaic module; when the output power or the input current is larger than the corresponding first threshold value, the converter is controlled to be in a through mode, so that the output end and the input end of the converter are directly communicated.
2. The power optimizer of claim 1, wherein the converter is configured to power convert the dc electrical energy of the photovoltaic module, and comprises:
and the converter performs maximum power point tracking on the photovoltaic assembly and outputs the maximum power of the photovoltaic assembly to the output end of the converter.
3. The power optimizer of claim 1, wherein the first threshold is determined based on output power or input current of at least two of the converters;
the time interval between the at least two controllers for obtaining the output power or the input current is less than a first preset time.
4. The power optimizer of claim 3, wherein the first threshold is determined based on output power or input current of at least two of the converters, comprising:
determining a maximum value of output power or input current of a plurality of the converters as the first threshold value;
or determining an average value of output power or input current of a plurality of the converters as the first threshold value;
or determining the average value of the partial first electrical parameters with the minimum value removed in the output power or the input current of a plurality of converters as the first threshold value; the first electrical parameter is the output power or the input current of the power optimizer;
or determining an average value of a part of the first electrical quantity in the output power or input current of a plurality of the converters as the first threshold value;
or determining a weighted average of different coefficients of the output power or input current of a plurality of said converters as said first threshold.
5. The power optimizer of claim 1, further comprising a communication circuit,
the communication circuit is used for receiving the first threshold value sent by an external device and transmitting the first threshold value to the controller,
or the like, or, alternatively,
the communication circuit is used for receiving the output power or the input current sent by other converters and transmitting the output power or the input current to the controller, so that the controller determines the first threshold value based on the output power or the input current of at least two converters.
6. The power optimizer of claim 1, wherein the controller further obtains a second threshold value, and controls the converter to be in a pass-through mode or a standby mode when the output power or the input current is less than the second threshold value, and the second threshold value is less than the first threshold value.
7. A photovoltaic power generation system, comprising: a bus converter and at least two power optimizers according to any of the claims 1 to 6;
the output ends of the plurality of power optimizers are connected in series, and the photovoltaic group strings after being connected in series are electrically connected with the direct current bus;
the bus converter performs maximum power point tracking on the direct current electric energy of the direct current bus and converts the direct current electric energy into preset direct current or preset alternating current.
8. Photovoltaic power generation system according to claim 7, characterized in that the first threshold value is determined based on the output power or input current of at least two of the converters;
the time interval between the at least two controllers for obtaining the output power or the input current is less than a first preset time.
9. The photovoltaic power generation system of claim 8, wherein the first threshold is determined based on output power or input current of at least two of the converters, comprising:
determining a maximum value of output power or input current of a plurality of the converters as the first threshold value;
or determining an average value of output power or input current of a plurality of the converters as the first threshold value;
or determining the average value of the partial first electrical parameters with the minimum value removed in the output power or the input current of a plurality of converters as the first threshold value; the first electrical parameter is the output power or the input current of the power optimizer;
or determining an average value of a part of the first electrical quantity in the output power or input current of a plurality of the converters as the first threshold value;
or determining a weighted average of different coefficients of the output power or input current of a plurality of said converters as said first threshold.
10. The photovoltaic power generation system of claim 7, further comprising a communications host,
the communication host is configured to transmit the first threshold to a plurality of the controllers,
or the like, or, alternatively,
the communication host is used for transmitting the output power or the input current of the converters to a plurality of controllers, so that the controllers determine the first threshold value based on the output power or the input current of at least two converters.
11. The photovoltaic power generation system of claim 7, wherein the controller further obtains a second threshold value, controls the converter to be in a pass-through mode or a standby mode when the output power or input current is less than the second threshold value, and the second threshold value is less than the first threshold value.
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| CN110957760B (en) * | 2019-11-27 | 2022-08-26 | 华为数字能源技术有限公司 | Photovoltaic system, optimizer and working state adjusting method of optimizer |
| CN111030176A (en) * | 2019-12-19 | 2020-04-17 | 湖南红太阳新能源科技有限公司 | Photovoltaic micro inverter unit, system and control method |
| CN111402078B (en) * | 2020-03-11 | 2023-06-30 | 阳光新能源开发股份有限公司 | Photovoltaic string diagnosis method, device and controller |
| CN113422388B (en) * | 2021-07-29 | 2024-04-12 | 阳光电源股份有限公司 | Photovoltaic system, direct-current power supply and mode switching method of direct-current power supply |
| CN114362257B (en) * | 2022-03-18 | 2022-07-08 | 北京思凌科半导体技术有限公司 | Distributed power supply system |
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