Patent Description:
A multi-channel MPPT (Maximum Power Point Tracking) inverter includes a DC-AC converter and at least one DC-DC converter. An input terminal of each of the DC-DC converters serves as one of input terminals of the multi-channel MPPT inverter and is connected to a corresponding photovoltaic battery string. Output terminals of all the DC-DC converters are connected together, to connect to a direct current side of the DC-AC converter. An alternating current side of the DC-AC converter serves as an output terminal of the multi-channel MPPT inverter and is connected to an input terminal of an AC power grid.

During an operation of the multi-channel MPPT inverter, each of the DC-DC converters performs DC-DC conversion on an output voltage of the photovoltaic battery string in real time, and then the DC-AC converter performs DC-AC conversion on an output of each of the DC-DC converters to obtain an AC power. The obtained AC power is inputted into the AC power grid, thereby realizing grid connection of a photovoltaic power generation system.

However, the inverter in such two-stage conversion usually has low conversion efficiency. <CIT> discloses a method for providing maximum power point tracking for an energy generating device using a local buck-boost converter coupled to the device. The method includes operating in a tracking mode, which includes initializing a conversion ratio for the buck-boost converter based on a previous optimum conversion ratio. A device power associated with the initialized conversion ratio is calculated. The conversion ratio is repeatedly modified and a device power associated with each of the modified conversion ratios is calculated. A current optimum conversion ratio for the buck-boost converter is identified based on the calculated device powers. The current optimum conversion ratio corresponds to one of a buck mode, a boost mode and a buck-boost mode for the buck-boost converter. <CIT> discloses a first controller. The first controller controls the DC-DC converter to perform a step-up operation when a voltage on the DC bus is lower than a first reference voltage and controls the DC-DC converter to suspend the step-up operation when the voltage is equal to or higher than the first reference voltage. A second controller controls the inverter to maintain the voltage on the DC bus constant when the voltage on the DC bus is lower than a second reference voltage and controls the inverter to maximize an output power of the inverter when the voltage is equal to or higher than the second reference voltage.

In view of the above, a multi-channel MPPT inverter and a method for controlling the multi-channel MPPT inverter are provided in an embodiment of the present disclosure, to solve the problem of low conversion efficiency of the multi-channel MPPT inverter in the conventional technology.

Technical solutions provided by the embodiments of the present disclosure are as follows.

According to one aspect of the present disclosure, a method for controlling a multi-channel MPPT inverter is provided. The method includes:.

The detection parameters include: a voltage of a power grid, a DC bus voltage of the multi-channel MPPT inverter, and an input voltage, an MPPT algorithm command voltage, and an operation state of each of the DC-DC converters in the multi-channel MPPT inverter.

In an embodiment, after determining whether the overall input level of the multi-channel MPPT inverter meets the preset condition for operating under the high input voltage mode based on the detection parameters, the method further includes:
keeping each of the DC-DC converters in performing the MPPT algorithm, if the overall input level of the multi-channel MPPT inverter does not meet the preset condition for operating under the high input voltage mode.

In an embodiment, the preset condition for operating under the high input voltage mode includes at least one of the following:.

In an embodiment, the determining whether the overall input level of the multi-channel MPPT inverter meets the preset condition for operating under the high input voltage mode based on the detection parameters includes:.

In an embodiment, after determining whether each of the DC-DC converters in the multi-channel MPPT inverter is in the operating state, the method further includes:.

In an embodiment, the preset difference condition includes at least one of the following conditions:.

In an embodiment, the determining whether the input level difference among all the DC-DC converters meets the preset difference condition based on the detection parameters includes:.

According to another aspect of the present disclosure, a multi-channel MPPT inverter is provided, which includes a DC-AC converter, a controller, and at least one DC-DC converter. An input terminal of each of the DC-DC converters serves as one of input terminals of the multi-channel MPPT inverter and is connected to a corresponding photovoltaic battery string. Output terminals of all the DC-DC converters are connected together to a DC side of the DC-AC converter. An AC side of the DC-AC converter serves as an output terminal of the multi-channel MPPT inverter, and is connected to an input terminal of an AC power grid. An output terminal of the controller is connected to a control terminal of each of the DC-DC converters and a control terminal of the DC-AC converter. The controller is configured to perform any one of the above methods for controlling the multi-channel MPPT inverter.

Compared with the conventional technology, in the method for controlling a multi-channel MPPT inverter according to the present disclosure, after determining that each of DC-DC converters is in an operating state based on the received detection parameters of the multi-channel MPPT inverter, if it is further determined that the overall input level of the multi-channel MPPT inverter meets the preset condition for operating under an high input voltage mode, each of the DC-DC converters is turned off and the DC-AC converter in the multi-channel MPPT inverter is controlled to perform the MPPT algorithm. Therefore, in a case that the photovoltaic battery string outputs a higher voltage due to operating under the high input voltage mode, reactive power by the DC-DC converters at a previous stage is avoided, reducing power loss of the previous stage, and thereby improving the conversion efficiency of the multi-channel MPPT inverter.

In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or in conventional technology, the drawings used in the description of the embodiments or the conventional technology are briefly described below. Apparently, the drawings in the following description show only some embodiments of the present disclosure, and those skilled in the art can obtain other drawings according to the provided drawings without any creative work.

The technical solutions in the embodiments of the present disclosure are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present disclosure.

In the present disclosure, terms "include", "comprise" or any other variants are intended to be non-exclusive. Therefore, a process, method, article, or device including multiple elements includes not only the elements but also other elements that are not enumerated, or also includes elements inherent for the process, method, article or device. Without more limitations, elements defined by the statement "comprising (including)a/an. " does not exclude other similar elements which may exist in the process, method, article or device including such elements.

In order to solve the problem of low conversion efficiency of the multi-channel MPPT inverter during operation in the conventional technology, a method for controlling a multi-channel MPPT inverter is provided in an embodiment of the present disclosure. Specifically, as shown in <FIG>, the method includes the following steps S110 to S210.

In step S110, detection parameters of the multi-channel MPPT inverter are received.

The detection parameters of the multi-channel MPPT inverter include: a voltage of a power grid, a DC bus voltage of the multi-channel MPPT inverter, and an input voltage, an MPPT algorithm command voltage, and an operation state of each of DC-DC converters in the multi-channel MPPT inverter.

In step S120, it is determined whether each of the DC-DC converters in the multi-channel MPPT inverter is in an operating state based on the detection parameters of the multi-channel MPPT inverter.

It should be noted that after the multi-channel MPPT inverter is turned on, each of the DC-DC converters should be in an operating state, that is, under control of an MPPT algorithm. If each of the DC-DC converters is in the operating state, proceed to step S130.

In step S130, it is determined whether an overall input level of the multi-channel MPPT inverter meets a preset condition for operating under a high input voltage mode based on the detection parameters.

The overall input level of the multi-channel MPPT inverter is a parameter characterizing a state of all input voltages of the multi-channel MPPT inverter, such as a difference between an input voltage of each of the DC-DC converters and a peak voltage of a power grid if the input voltage of each of the DC-DC converters is distributed within a certain range, or a DC bus voltage of the multi-channel MPPT inverter under influence of the input voltage of each of the DC-DC converters. The parameter may be selected according to specific application environment, which falls within the scope of the present disclosure.

It should be noted that, normally, an input level of each of the DC-DC converters in the multi-channel MPPT inverter, that is, a power generation level of a photovoltaic battery string connected to each of the DC-DC converter, does not largely differ from each other. If an input level of a DC-DC converter is significantly lower than input levels of other DC-DC converters, it indicates that the photovoltaic battery string connected to the DC-DC converter is seriously shaded. If the input levels of most of the DC-DC converters are significantly increased, it indicates that lighting conditions are better at this time, for example, at noon, the power generation levels of the photovoltaic battery strings are high, satisfying the preset condition for operating under the high input voltage mode.

The preset condition for operating under the high input voltage mode may include at least one of the following two conditions.

The second preset voltage is preset according to an actual situation and represents a degree to which the input voltage of each of the DC-DC converters is greater than the peak voltage of the power grid. A larger second preset voltage indicates a greater degree to which the input voltage of each of the DC-DC converters is greater than the peak voltage of the power grid in controlling each of the DC-DC converters to switch the operation state. The third preset voltage is preset according to the actual situation and represents a range within which the input voltage of each of the DC-DC converters is distributed. A smaller third preset voltage indicates a narrower range within which the input voltage of each of the DC-DC converters can be distributed in controlling each of the DC-DC converters to switch the operation state.

If the overall input level of the multi-channel MPPT inverter meets the preset condition for operating under the high input voltage mode, proceed to step S140. If the overall input level of the multi-channel MPPT inverter does not meet the preset condition for operating under the high input voltage mode, proceed to step S210.

In step S140, each of the DC-DC converters is turned off, and a DC-AC converter in the multi-channel MPPT inverter is controlled to perform an MPPT algorithm.

Each of the DC-DC converters is turned off by controlling a switch in each of the DC-DC converters. After turning off each of the DC-DC converters, the DC-DC converter cannot perform the MPPT algorithm on the photovoltaic battery string connected to the DC-DC converter itself, while the DC-AC converter performs the MPPT algorithm on the photovoltaic battery string.

In step S210, each of the DC-DC converters is kept in performing the MPPT algorithm.

It should be noted that step S110 and step S120 in the embodiment may be performed separately according to their own cycles, and the cycles may be the same or different. If the cycles are the same, as a whole, the multi-channel MPPT inverter is controlled once every cycle during the operation of the multi-channel MPPT inverter. If the cycle is set to be minimal, the multi-channel MPPT inverter may be controlled in real time.

Alternatively, step S110, step S120, step S130, step S140, and step S210 may be performed circularly according to the above logic, that is, after performing steps S140 or S210 in the above process, the method returns to perform step S110, forming a loop.

Compared with the conventional technology, in the method for controlling a multi-channel MPPT inverter according to the present disclosure, after determining that each of the DC-DC converters is in an operating state, if it is further determined that the overall input level of the multi-channel MPPT inverter meets the preset condition for operating under the high input voltage mode, each of the DC-DC converters is turned off and the DC-AC converter in the multi-channel MPPT inverter is controlled to perform the MPPT algorithm. Therefore, in a case that the photovoltaic battery string outputs a higher voltage during operating under the high input voltage mode, reactive power by the DC-DC converters at a previous stage is avoided, reducing power loss of the previous stage, and thereby improving the conversion efficiency of the multi-channel MPPT inverter.

It should be noted that, according to another technical solution in the conventional technology, if a maximum input voltage among the input voltages of all the DC-DC converters is greater than the peak voltage of the power grid, then at least one of the DC-DC converters switches its operation state, such that the MPPT algorithm will be performed by the DC-AC converter. However, since such switching condition is less strict, the DC-DC converter in the multi-channel MPPT inverter will frequently switch its operation state during the operation of the multi-channel MPPT inverter. Moreover, it is not limited that each of the DC-DC converters switches the operation state, thus the DC-AC converter cannot perform multi-channel MPPT algorithms simultaneously, resulting in lower conversion efficiency of maximum static power of the multi-channel MPPT inverter.

Compared with the above technical solution in the conventional technology, in the method for controlling a multi-channel MPPT inverter according to the present disclosure, the switching condition is strict, the switching frequency is low, and thus the operating voltage range of multi-channel maximum power point tracking can be increased. Moreover, each of the DC-DC converters is controlled to switch the operation state, achieving higher conversion efficiency of maximum static power.

According to another embodiment, a method for controlling a multi-channel MPPT inverter is provided. Based on the above embodiments, after each of the DC-DC converters is controlled to be turned off in step S140, the method in the embodiment circularly proceeds to step S120, and at this time all the DC-DC converters are not in the operating state. Then as shown in <FIG>, the method further includes the following steps S150 to S220.

In step S150, it is determined whether an input level difference among all the DC-DC converters meets a preset difference condition based on the detection parameters.

The input level difference among all the DC-DC converters refers to a difference between the input voltage of each of the DC-DC converters and the peak voltage of the power grid, a difference between the input voltages of all the DC-DC converters, or a difference between MPPT algorithm command voltages received by all the DC-DC converters, which may be selected according to specific application environment and is within the scope of the present disclosure.

In practice, the preset difference condition may include at least one of the following three conditions.

The sixth preset voltage is preset according to the actual situation. A larger sixth preset voltage indicates a larger difference between the MPPT algorithm command voltages received by two of the DC-DC converters, and indicates a larger difference between forecasted radiant intensities received by two photovoltaic battery strings connected to the two DC-DC converters.

If the input level difference among all the DC-DC converters meets the preset difference condition, proceed to step S160. If the input level difference among all the DC-DC converters does not meet the preset difference condition, proceed to step S220.

In step S160, each of the DC-DC converters is controlled to perform the MPPT algorithm.

Each of the DC-DC converters is turned on by controlling a switch. After all the DC-DC converters are turned on, each of the DC-DC converters may perform MPPT algorithm on a photovoltaic battery string which is connected to the DC-DC converter itself, to set a maximum power point for the photovoltaic battery string, thus each of the photovoltaic battery strings is operating at the maximum power point.

In step S220, the DC-AC converter in the multi-channel MPPT inverter is kept in performing the MPPT algorithm.

In the embodiment, by lowering the condition for determining to control all the DC-DC converters back to perform MPPT algorithms, the operating voltage range of the multi-channel maximum power point tracking is further increased.

According to another embodiment of the present disclosure, a specific implementation of step S130 is provided. As shown in <FIG>, the implementation includes the following steps S131 to S133.

In step S131, it is determined whether the DC bus voltage is greater than the first preset voltage.

If the DC bus voltage is greater than the first preset voltage, it is determined that the overall input level of the multi-channel MPPT inverter meets the preset condition for operating under the high input voltage mode, and then proceed to step S140. If the DC bus voltage is less than or equal to the first preset voltage, and then proceed to step S132.

In step S132, it is determined whether a difference between the input voltage of each of the DC-DC converters and the peak voltage of the power grid is greater than the second preset voltage.

If the difference between the input voltage of each of the DC-DC converters and the peak voltage of the power grid is greater than the second preset voltage, proceed to step S133. If a difference between an input voltage of at least one of the DC-DC converters and the peak voltage of the power grid is less than or equal to the second preset voltage, it is determined that the overall input level of the multi-channel MPPT inverter does not meet the preset condition for operating under the high input voltage mode, and then proceed to step S210.

In step S133, it is determined whether the difference between a maximum input voltage and a minimum input voltage among the input voltages of all the DC-DC converters is less than the third preset voltage.

If the difference between the maximum input voltage and the minimum input voltage among the input voltages of all the DC-DC converters is less than the third preset voltage, it is determined that the overall input level of the multi-channel MPPT inverter meets the preset condition for operating under the high input voltage mode, and then proceed to step S140. If the difference between the maximum input voltage and the minimum input voltage among the input voltages of all the DC-DC converters is greater than or equal to the third preset voltage, it is determined that the overall input level of the multi-channel MPPT inverter does not meet the preset condition for operating under the high input voltage mode, and then proceed to step S210.

It should be noted that step S131 may be performed after step S132 and step S133, and step S132 may be performed after step S133, which is not specifically limited herein and depends on the specific situation.

In addition, another implementation of step S130 may only include step S131, or only include step S132 and step S133. In a case of only including step S132 and step S133, step S132 may be performed after step S133 or before step S133, which is not specifically limited herein and depends on the specific situation. In addition, the two implementations of step S130 may depend on specific situations and are not specifically limited herein.

According to another embodiment of the present disclosure, a specific implementation of step S150 is provided. As shown in <FIG>, the implementation includes the following steps S151 to S153.

In step S151, it is determined whether the difference between the input voltage of one of the DC-DC converters in the multi-channel MPPT inverter and the peak voltage of the power grid is less than the fourth preset voltage.

If the difference between the input voltage of the one of the DC-DC converters in the multi-channel MPPT inverter and the peak voltage of the power grid is less than the fourth preset voltage, it is determined that the input level difference among all the DC-DC converters meets the preset difference condition, and then proceed to step S160. If the difference between the input voltage of each of the DC-DC converters in the multi-channel MPPT inverter and the peak voltage of the power grid is greater than or equal to the fourth preset voltage, proceed to step S152.

In step S152, it is determined whether the difference between input voltages of two of the DC-DC converters in the multi-channel MPPT inverter is greater than the fifth preset voltage.

If the difference between the input voltages of the two of the DC-DC converters in the multi-channel MPPT inverter is greater than the fifth preset voltage, it is determined that the input level difference among all the DC-DC converters meets the preset difference condition, and then proceed to step S160. If the difference between the input voltages of any two of the DC-DC converters in the multi-channel MPPT inverter is less than or equal to the fifth preset voltage, then proceed to step S153.

In step S153, it is determined whether the difference between MPPT algorithm command voltages received by two of the DC-DC converters in the multi-channel MPPT inverter is greater than the sixth preset voltage.

If the difference between MPPT algorithm command voltages received by the two of the DC-DC converters in the multi-channel MPPT inverter is greater than the sixth preset voltage, it is determined that the input level difference among all the DC-DC converters meets the preset difference condition, and proceed to step S160. If the difference between MPPT algorithm command voltages received by any two of the DC-DC converters in the multi-channel MPPT inverter is less than or equal to the sixth preset voltage, it is determined that the input level difference among all the DC-DC converters does not meet the preset difference condition, and then proceed to step S220.

It should be noted that the order of step S151, step S152, and step S153 is randomly arranged, which is not specifically limited herein and depends on the specific situation, and is within the protection scope of the present disclosure.

In addition, another implementation of step S150 includes only any one or two of step S151, step S152, and step S153. In a case that the another implementation of step S150 includes only any two of step S151, step S152, and step S153, the order of the two steps is randomly arranged and the two steps may be selected according to the specific situation. In addition, the two implementations of step S150 may depend on specific situations and are not specifically limited herein.

According to another embodiment of the present disclosure, a multi-channel MPPT inverter is provided. <FIG> shows a schematic structural diagram of the multi-channel MPPT inverter, which includes a DC-AC converter <NUM>, a controller <NUM>, and at least one DC-DC converter <NUM>.

An input terminal of each of the DC-DC converters <NUM> serves as one of input terminals of the multi-channel MPPT inverter and is connected to a corresponding photovoltaic battery string <NUM>.

An output terminal of each of the DC-DC converters <NUM> is connected to a DC side of the DC-AC converter <NUM>.

An AC side of the DC-AC converter <NUM> serves as an output terminal of the multi-channel MPPT inverter, and is connected to an input terminal of an AC power grid <NUM>.

An output terminal of the controller <NUM> is connected to a control terminal of each of the DC-DC converters <NUM> and a control terminal of the DC-AC converter <NUM>.

The controller <NUM> is configured to perform the method for controlling the multi-channel MPPT inverter according to any one of the above embodiments.

It should be noted that the controller <NUM> may be arranged independently or may be integrated in a control unit within the DC-AC converter, which is not specifically limited herein and depends on the specific situation, and is within the protection scope of the present disclosure.

Embodiments of the present disclosure are described in a progressive manner, each of the embodiments emphasizes differences from other embodiments, and the same or similar parts among the embodiments may be referred to each other. Since device or device embodiments are similar to method embodiments, the description thereof is relatively simple, and reference may be made to the description of the method embodiments for relevant parts. The device or the device embodiment described above is just schematic. A unit described as a separate component may be or may not be separated in physical, and a component displayed as a unit may be or may not be a physical unit, that is, may be placed in a same position or may be distributed in multiple network units.

Claim 1:
A method for controlling a multi-channel maximum power point tracking MPPT inverter, comprising:
receiving (S110) detection parameters of the multi-channel MPPT inverter;
determining (S120) whether each of DC-DC converters in the multi-channel MPPT inverter is in an operating state based on the detection parameters;
determining (S130) whether an overall input level of the multi-channel MPPT inverter meets a preset condition for operating under a high input voltage mode based on the detection parameters in a case that each of the DC-DC converters is in the operating state, wherein the overall input level of the multi-channel MPPT inverter is a parameter characterizing a state of all input voltages of the multi-channel MPPT inverter; and
turning off (S140) each of the DC-DC converters, and controlling a DC-AC converter in the multi-channel MPPT inverter to perform an MPPT algorithm, in a case that the overall input level of the multi-channel MPPT inverter meets the preset condition for operating under the high input voltage mode;
characterized in that, the detection parameters comprise:
a voltage of a power grid, a DC bus voltage of the multi-channel MPPT inverter, and an input voltage of each of the DC-DC converters, an MPPT algorithm command voltage and an operation state of each of the DC-DC converters in the multi-channel MPPT inverter.