JP2019175219A - Power conversion apparatus and maximum power point follow-up control method - Google Patents

Abstract

To suppress wasteful consumption of generated power even when a power conversion apparatus is used in an overload status of a photovoltaic power generation panel.SOLUTION: A power conversion apparatus installed between a photovoltaic power generation panel and a load leading in power comprises: a power conversion unit which takes out power from the photovoltaic power generation panel; and a controller which has a function performing a maximum power point follow-up control by controlling the power conversion unit so as to utilize property of the power upper limit capable of inputting into the power conversion unit. The controller finds out, when the maximum power point follow-up control reaches a first power point where restriction of the property is performed while approaching the maximum power point from one side of the range of output curve of the photovoltaic power generation panel, a second power point different from the first power point by approaching the maximum power point from the other side within the range.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a power conversion device and a maximum power point tracking control method.

  For example, a power conditioner as a power conversion device is connected to the photovoltaic power generation panel, and grid connection with a commercial power system can be performed via this power conditioner. The power conditioner performs maximum power point tracking control (MPPT (Maximum Power Point Tracking) control) in order to draw the maximum power at that time from the photovoltaic power generation panel (see, for example, Patent Document 1). .

  The capacity of the power conditioner regarding the power that can be input should basically be selected according to the power generated by the photovoltaic power generation panel. However, the amount of power generated by the solar power generation panel varies depending on the solar radiation conditions, and the generated power generated cannot always be output. In addition, the cost of the photovoltaic power generation panel itself is becoming cheaper than before. Therefore, there is a system configuration in which as many solar power generation panels as possible are installed by making the most of the installation space, and the capacity of the power conditioner is slightly reduced. As a result, an “overloaded” state can occur in which the maximum value of the generated power of the photovoltaic power generation panel is greater than the power that can be input to the power conditioner (see, for example, Patent Documents 2 and 3).

JP 2010-66919 A JP 2016-115283 A JP 2014-166209 A

  However, when the power conditioner performs MPPT control in an overloaded state, power can be drawn only within the capacity range of the power conditioner. Therefore, even when the solar power generation panel can generate the maximum power as rated, the maximum power may not be extracted. In such a case, the generated power is wasted.

  In view of such a problem, an object of the present invention is to suppress waste of generated power even when a power conversion device is used in a state where a photovoltaic power generation panel is overloaded.

  The present disclosure includes the following inventions. However, the present invention is defined by the claims.

  The power conversion device according to an expression of the present invention is a power conversion device provided between a solar power generation panel and a load that draws power, and a power conversion unit that extracts power from the solar power generation panel; A control unit that has a function of controlling the power conversion unit to perform maximum power point tracking control and grasps a characteristic of an upper limit of power that can be input to the power conversion device, and the control unit includes the In the maximum power point tracking control, when reaching the first power point that is restricted by the above characteristics while approaching the maximum power point from either side of the value range in the output curve of the photovoltaic power generation panel, It is a power converter which approaches the maximum power point from the other side of the range within the range and searches for a second power point different from the first power point.

  A method according to an aspect of the present invention is a maximum power point tracking control method in a power conversion device provided between a photovoltaic power generation panel and a load that draws power, and the power from the photovoltaic power generation panel The maximum power point tracking control is performed by controlling the power conversion unit that takes out the power, and in the maximum power point tracking control, the maximum power point is approached from either side of the value range in the output curve of the photovoltaic panel. When the first power point that is restricted by the characteristics of the upper limit of power that can be input to the power converter is reached, the maximum power point is approached from the other side of the range within the range. This is a maximum power point tracking control method for searching for a second power point different from the first power point.

  Even if the power conversion device is used in a state where the photovoltaic power generation panel is overloaded, waste of generated power can be suppressed.

It is a circuit diagram centering on a power converter device. An output curve (solid line) representing the generated power of the photovoltaic power generation panel as a relationship between voltage and power, and a broken line (dotted line) representing the upper limit of power that can be input to the power conversion device as a relationship between voltage and power are shown. It is a graph. It is a flowchart which selects the electric power upper limit which can be input into a power converter device. It is a graph which shows an example of the relationship between the voltage and current which can be drawn out from a photovoltaic power generation panel. An output curve (solid line) representing the generated power of the photovoltaic power generation panel in terms of the relationship between current and power, and a broken line (dotted line) representing the range of power input to the power converter in terms of the relationship between current and power It is a graph to show. It is a flowchart which shows an example of MPPT control with an inversion function with FIG. 7, FIG. It is a flowchart which shows an example of MPPT control with an inversion function with FIG. 6, FIG. FIG. 8 is a flowchart showing an example of MPPT control with an inversion function together with FIGS.

[Summary of Embodiment]
The gist of the embodiment of the present invention includes at least the following.

(1) This is a power conversion device provided between a photovoltaic power generation panel and a load that draws power, and controls a power conversion unit that extracts power from the solar power generation panel, and the power conversion unit. A control unit that has a function of performing maximum power point tracking control and grasps the characteristics of the upper limit of power that can be input to the power conversion device, and the control unit is configured to perform the maximum power point tracking control, When the first power point that is restricted by the characteristic is reached while approaching the maximum power point from either side of the value range in the output curve of the photovoltaic power generation panel, the value range is within the range of the value range. The second power point is searched for a second power point different from the first power point by approaching the maximum power point from the other side.
The “value range” is a current value range or a voltage value range.

  For example, in a power conversion device used in a so-called overloaded state, the power that can be output from the photovoltaic power generation panel may exceed the power upper limit characteristic that can be input to the power conversion device. In this case, even if the control unit attempts to perform maximum power point tracking control, it cannot reach the maximum power point in the output curve of the photovoltaic power generation panel, and the maximum power point on both sides of the maximum power point. There may be point candidates. Therefore, in such a case, by approaching the maximum power point not only from one side of the range but also from the other side, the power point with the highest power can be determined from a plurality of candidates for the maximum power point. You can search. In the power conversion device that performs such control, even if it is overloaded, the maximum power that can be drawn from the photovoltaic power generation panel at that time can be drawn, and the generated power can be used efficiently.

(2) Moreover, in the power converter of (1), for example, when the power point in the maximum power point tracking control reaches the first power point, the control unit is configured to perform voltage or current within the range. Can be controlled to move to another power point that is discontinuous from the previous power point on the output curve.
With such a method, the control unit can approach the maximum power point from the other side of the range.

(3) Moreover, in the power conversion device of (2), when the power point in the maximum power point tracking control reaches the first power point, the control unit converts the voltage or current to the opposite side of the range. You may make it change to the terminal vicinity.
In this case, it is possible to reliably jump to the other side of the range and search for the second power point.

(4) In the power conversion device according to any one of (1) to (3), for example, the control unit stores the first power point and the power thereof as the power point in the maximum power point tracking control. After that, if the power of the second power point is larger than the first power point, the second power point is controlled and stays at the second power point. When the power at the power point is smaller than the first power point, the power point may be returned to the first power point on the control.
In this way, it is possible to always select the larger one of the two power points.

  (5) On the other hand, this is a maximum power point tracking control method in a power conversion device provided between a photovoltaic power generation panel and a load that draws power, and the power conversion takes out power from the photovoltaic power generation panel. The maximum power point tracking control is performed by controlling the unit, and in the maximum power point tracking control, while approaching the maximum power point from either side of the value range in the output curve of the photovoltaic power generation panel, the power When the first power point that is constrained by the characteristics of the upper limit of power that can be input to the converter is reached, the first power point is approached from the other side of the range within the range by approaching the maximum power point. This is a maximum power point tracking control method for searching for a second power point different from.

  For example, in a power conversion device used in a so-called overloaded state, the power that can be output from the photovoltaic power generation panel may exceed the power upper limit characteristic that can be input to the power conversion device. In this case, even if the maximum power point tracking control is performed, the maximum power point in the output curve of the photovoltaic power generation panel cannot be reached, and practical maximum power point candidates are placed on both sides of the maximum power point. Exists. Therefore, in such a case, by approaching the maximum power point not only from one side of the range but also from the other side, the power point with the highest power can be selected from a plurality of candidates for the maximum power point. You can search. By performing such control, even a power conversion device used in an overloaded state can extract the maximum power that can be drawn from the photovoltaic power generation panel at that time, and efficiently use the generated power be able to.

[Details of the embodiment]
Hereinafter, a power converter according to an embodiment of the present invention will be described with reference to the drawings. The numerical values appearing in the present embodiment are merely examples, and are not limited to the described values.

<< Circuit configuration example of power conversion device >>
FIG. 1 is a circuit diagram centering on a power converter 1 (power conditioner). In the figure, the power conversion device 1 is provided between the photovoltaic power generation panel 2 and the AC power path 3. The AC electric circuit 3 is connected to the commercial power system 4. The power conversion device 1 is connected to the storage battery 5.

  The power conversion apparatus 1 includes two DC / DC converters 6 and 7, a DC bus 8, and an inverter 9. If it demonstrates sequentially from a main circuit element, the direct current | flow side capacitor | condenser 11 will be provided in parallel with the input in the direct current input terminal side connected with the photovoltaic power generation panel 2. FIG. The input voltage is converted to a desired voltage by the DC / DC converter 6 and output to the DC bus 8. The DC / DC converter 6 includes a DC reactor 12, a switching element Q1, and a diode 13. The switching element Q1 is a MOS-FET (Metal-Oxide-Semiconductor Field Effect Transistor), for example, and has a body diode. In the example of FIG. 1, all the other switching elements Q2 to Q9 are also MOS-FETs, but may be other semiconductor switches such as an IGBT (Insulated Gate Bipolar Transistor).

  A DC / DC converter 7 is provided between the DC-side capacitor 15 connected in parallel with the storage battery 5 and the DC bus 8. The DC / DC converter 7 is bidirectional, and performs a step-up operation when the storage battery 5 is discharged, and performs a step-down operation when the storage battery 5 is charged. The DC / DC converter 7 includes a DC reactor 16, a low-side switching element Q2, and a high-side switching element Q3.

  The voltage of the DC bus 8, that is, the voltage across the intermediate capacitor 14, is applied to an inverter 9 composed of switching elements Q4, Q5, Q6, Q7, Q8, and Q9 that form a full bridge circuit. The inverter 9 converts the DC voltage of the DC bus 8 into a single-phase three-wire AC voltage. The AC reactors 17, 18, 19 and the AC capacitors 20, 21 function as a filter circuit that prevents high-frequency noise generated by the inverter 9 from appearing on the AC circuit 3. For example, between the AC electric circuit U-W lines, +101 V and -101 V are output with the O line set to 0 potential between 202 V, the U-O line, and the W-O line, respectively.

  The storage battery 5 can be charged with the generated power of the photovoltaic power generation panel 2, and can also be charged using the power from the commercial power system 4. When charging the storage battery 5 using power from the commercial power system 4, the inverter 9 functions as a rectifier from AC to DC.

  As a circuit element for measurement / control, a voltage sensor 22 and a current sensor 23 are provided. The voltage sensor 22 detects the power generation voltage of the solar power generation panel 2 and sends the detection output to the control unit 24. The current sensor 23 detects a current drawn from the photovoltaic power generation panel 2 and sends a detection output to the control unit 24. In addition, although the voltage sensor and current sensor for measurement / control are provided in various places, illustration is omitted here. The control unit 24 controls on / off of the switching elements Q1, Q2, Q3, and Q4 to Q9 based on the detection output sent from each sensor.

  The control unit 24 includes, for example, a computer, and realizes necessary control functions by causing the computer to execute software (computer program). The software is stored in a storage device (not shown) of the control unit 24.

While the photovoltaic power generation panel 2 is generating power, the power conversion device 1 performs grid-connected operation with the AC power path 3. Thereby, the electric power feeding to the load (not shown) of the consumer connected to AC electric circuit 3 and the reverse tide (power sale) to commercial power system 4 can be performed. Furthermore, the storage battery 5 can also be charged using the generated power of the photovoltaic power generation panel 2 as necessary.
For example, at night, the storage battery 5 can be discharged to supply power to a customer's load connected to the AC circuit 3.

<MPPT control>
Here, the DC / DC converter 6 that constitutes a power conversion unit together with the inverter 9 performs maximum power point tracking control (MPPT (Maximum Power Point Tracking) control) under the control of the control unit 24. By performing the MPPT control, the maximum power at that time can be extracted from the photovoltaic power generation panel 2 whose power generation amount varies depending on the solar radiation from the sun.

  In addition, the power conversion device 1 is used in a state where the power that can be output from the photovoltaic power generation panel 2 may exceed the power upper limit characteristic with respect to the input power upper limit characteristic. That is, the power converter 1 is used in an overloaded state.

  FIG. 2 shows an output curve (solid line) representing the generated power of the photovoltaic power generation panel 2 in terms of the relationship between voltage and power, and a broken line representing the upper limit of power that can be input to the power converter 1 in terms of the relationship between voltage and power. It is a graph which shows (dotted line). The electric power that can be drawn from the photovoltaic power generation panel 2 is a value on the output curve, and cannot take a value that is not on the output curve. In addition, the power conversion device 1 has an upper limit of power that can be input due to restrictions on the performance of electronic components used inside. Generally, the power converter 1 (the control unit 24) itself sets an upper limit of power that can be input by software.

<Setting the upper limit of power that can be input>
FIG. 3 is a flowchart for selecting an upper limit of power that can be input to the power conversion apparatus 1. This process is executed by the control unit 24 at a cycle longer than the execution cycle of the MPPT control. In FIG. 3, the power generation voltage of the solar power generation panel 2 detected by the voltage sensor 22 (FIG. 1) is expressed as “PV voltage”.

  First, in step Sp1, the control unit 24 determines whether or not the PV voltage is less than 50V. In the case of “Yes”, the power upper limit is 0 W (step Sp2). In the case of “No”, the control unit 24 determines whether or not the PV voltage is 50 V or more and less than 200 V (Step Sp3).

In the case of “Yes” in Step Sp3, the power upper limit is PV voltage × I ₁ (that is, proportional increase) (Step Sp4). In the case of “No”, the control unit 24 determines whether or not the PV voltage is 200 V or more and less than 330 V (step Sp5). In the case of “Yes”, the power upper limit is 2150 W (that is, fixed) (step Sp6). In the case of “No”, the control unit 24 determines whether or not the PV voltage is 330 V or more and less than 450 V (Step Sp7).

In the case of “Yes” in Step Sp7, the power upper limit is −I ₂ × PV voltage + P ₁ (that is, proportional decrease) (Step Sp8). In the case of “No”, the control unit 24 sets the power upper limit to 0 W (step Sp9). Subsequently, the control unit 24 determines whether the power upper limit obtained by the determination so far is greater than 0 W and less than 2150 W (step Sp10). If “Yes” here, the MPPT inversion flag is 1 (step Sp11), and if “No”, the MPPT inversion flag is 0 (step Sp12). The MPPT inversion flag indicates whether an inversion operation described later is necessary (= 1) or not (= 0). That is, if the power upper limit is 0 W or the constant maximum value 2150 W, it is not necessary to execute the reversing operation described later. In addition, the MPPT inversion flag may be set to 2. In the case of “2”, the maximum power point is aimed from the short-circuit side (maximum current).
The upper limit (dotted line) of the input power shown in FIG. 2 is set by the processing of the flowchart of FIG.

《Overloading and MPPT control》
Returning to FIG. 2, when the generated power curve is compared with “mountain”, MPPT control is also called a hill-climbing method. For example, the voltage is gradually lowered from the vicinity of the highest end of the curve of the generated power (about 430 V in this example) toward the maximum power point, and the mountain is climbed. Before and after lowering the voltage for one step, the power is compared with each other, and the direction in which the voltage is changed is reversed (increased) when the power changes from increasing to decreasing. By repeatedly performing such a search, it is possible to perform control to follow the maximum power point.

  However, when the voltage reaches point A in FIG. 2, the upper limit of the input power to the power conversion apparatus 1 with respect to the voltage at point A becomes the upper limit, so that MPPT control is stagnated at point A. As the upper limit of power that can be input, the power at point B is larger in this example, but cannot be reached at point B in the conventional MPPT control.

FIG. 4 is a graph showing an example of the relationship between the voltage and current that can be drawn from the photovoltaic power generation panel 2. The point where voltage × current is the largest is the maximum power point P _max . As shown in the figure, there is a one-to-one relationship between voltage and current. In addition, this curve changes so that it may swell or squeeze in the direction of a vertical axis | shaft and a horizontal axis with solar radiation conditions.

FIG. 5 shows an output curve (solid line) representing the generated power of the photovoltaic power generation panel 2 in terms of the relationship between current and power, and the range of power input to the power converter 1 in terms of the relationship between current and power. It is a graph which shows a broken line (dotted line).
As in FIG. 2, the power that can be drawn from the photovoltaic power generation panel 2 is a value on this output curve, and cannot take a value that is not on the output curve.

  In MPPT control, by performing either one of the voltage step control along the output curve shown in FIG. 2 and the current step control along the output curve shown in FIG. 5, the other is also controlled as a result. The

<< Example of MPPT control with inversion function >>
Next, MPPT control with an inversion function will be described by taking control by current step as an example.
6 to 8 are flowcharts showing an example of MPPT control with an inversion function, and one flowchart is shown by three drawings for convenience of illustration. “X” in FIG. 6 is connected to “X” in FIG. “Y” and “Z” in FIG. 7 are connected to “Y” and “Z” in FIG. 8, respectively.

  First, FIG. 6 is a flowchart showing the first half of normal control of MPPT control. The MPPT control is repeatedly executed by the control unit 24. In the figure, the control unit 24 uses PV power (photovoltaic power), voltage, and voltage from the photovoltaic power generation panel 2 based on detection outputs of the voltage sensor 22 (FIG. 1) and the current sensor 23 (FIG. 1). Each information of current is acquired (step S1). Next, the control unit 24 determines whether or not the current PV power acquired in Step S1 is larger than the previous PV power stored (Step S2).

  If the determination in step S2 is “Yes”, the control unit 24 determines whether or not the MPPT control, that is, the current position of mountain climbing has passed the maximum power point (step S3). If the determination in step S3 is “Yes”, the control unit 24 sets the MPPT direction in the “downhill” direction (step S4) and sets the current step in the downhill direction (step S5). On the other hand, if determination of step S3 is "No", the control part 24 will set an electric current step to a mountain climbing direction (step S6).

  If the determination in step S2 is “No”, the control unit 24 determines whether or not the current position by the MPPT control is before the maximum power point (step S7). If the determination in step S7 is “Yes”, the control unit 24 sets the MPPT direction in the hill-climbing direction (step S8) and sets the current step in the hill-climbing direction (step S9). On the other hand, if determination of step S7 is "No", the control part 24 will set an electric current step in the hill-down direction (step S10).

  FIG. 6 shows an example of the current step. In the case of the voltage step, “current step...” In steps S5, S6, S9, and S10 is simply replaced with “voltage step. The others are the same.

  7 and 8 are flowcharts showing the latter half of the MPPT control including the inversion function. Hereinafter, the flow will be described according to the situation.

<When the power upper limit is 2150 W or 0 W>
In this case, since the MPPT inversion flag is 0 (step Sp12 in FIG. 3) in step S11, the determination is “No”, and the process proceeds to step S31 in FIG. If it is determined in step S31 that the MPPT inversion flag is not 2, the process jumps to step S17 in FIG. 7 to determine the current command value and update the switching duty ratio (step S18).

<Climbing from the vicinity of the open point-A point reached-Preparation for reversal>
When climbing from the vicinity of the open point (the left end of the output curve in FIG. 5) by MPPT control, if the MPPT inversion flag is 1 in step S11, the control unit 24 sets the current power to the power upper limit (ie, point A). It is determined whether or not (step S12). Here, it is “Yes”, and it is determined whether or not the current power is smaller than the power B before inversion (step S13). Again, “Yes”, and the control unit 24 stores the power at the point A before inversion (step S14), temporarily sets the voltage command value to 50 V (minimum value) (step S15), The command value is set to 10.75A (maximum value) (step S16).

  Thereafter, the current command value is determined (step S17) and the switching duty ratio is updated (step S18).

<In the middle of climbing from the vicinity of the open point, or in the middle of reversing and moving to the vicinity of the short-circuit point>
In this case, “Yes” is determined in Step S11, “No” in Step S12, and in Step S22, it is determined whether or not the current PV voltage is less than 100V and becomes “No”. Thereafter, the determination of the current command value (step S17) and the update of the switching duty ratio are performed (step S18). The short-circuit point is the right end of the output curve in FIG.

<When moving near the short-circuit point by reversal>
In this case, “Yes” in Step S11, “No” in Step S12, “Yes” in Step S22, and the control unit 24 sets the MPPT inversion flag to 2 (Step S23). Thereafter, the determination of the current command value (step S17) and the update of the switching duty ratio are performed (step S18).

<When point A power is greater than point B power>
In this case, both “Yes” in steps S11 and S12, and “No” in step S13. The control unit 24 increments (+1) the automatic inversion counter (step S19), and if the automatic inversion counter does not exceed 100 (“No” in step S20), hereinafter, determination of the current command value (step S17), and The switching duty ratio is updated (step S18).

<Regular reversal>
In this case, both “Yes” in steps S11 and S12, and “No” in step S13. The control unit 24 increments (+1) the automatic inversion counter (step S19). When the automatic inversion counter exceeds 100 (“Yes” in step S20), the automatic inversion counter is reset (step S21). Stores the power at point A before inversion (step S14), provisionally sets the voltage command value to 50V (minimum value) (step S15), and sets the current command value to 10.75A (maximum value). Set (step S16). Thereafter, the determination of the current command value (step S17) and the update of the switching duty ratio are performed (step S18).

<Climbing from the vicinity of the short-circuit point -B point arrival -reversal preparation>
When climbing from the vicinity of the short-circuit point (the right end of the output curve in FIG. 5) by MPPT control, if the MPPT inversion flag is 0 in step S11, the control unit 24 sets the current power to the power upper limit (ie, point B). It is determined whether or not (step S32). Here, it is “Yes”, and it is determined whether or not the current power is smaller than the power A before inversion (step S33). Again, “Yes”, and the control unit 24 stores the power at point B before inversion (step S34), and temporarily sets the voltage command value to 450 V (maximum value) (step S35). The command value is set to 0A (minimum value) (step S36).

  Thereafter, the current command value is determined (step S17) and the switching duty ratio is updated (step S18).

<In the middle of climbing from the vicinity of the short-circuiting point, or while reversing and moving to the vicinity of the open point>
In this case, “No” in Step S11, “Yes” in Step S31, “No” in Step S32, and in Step S42, it is determined whether or not the current PV voltage is larger than 400V, and becomes “No”. Thereafter, the determination of the current command value (step S17) and the update of the switching duty ratio are performed (step S18).

<When moving near the short-circuit point by reversal>
In this case, “No” in step S11, “Yes” in step S31, “No” in step S32, “Yes” in step S42, and the control unit 24 sets the MPPT inversion flag to 1 (step S43). Thereafter, the determination of the current command value (step S17) and the update of the switching duty ratio are performed (step S18).

<When point B power is greater than point A power>
In this case, “Yes” is set in steps S11, S31, and S32, and “No” is set in step S33. The controller 24 increments (+1) the automatic inversion counter (step S39), and if the automatic inversion counter does not exceed 100 (“No” in step S40), hereinafter, determination of the current command value (step S17), and The switching duty ratio is updated (step S18).

<Regular reversal>
In this case, “Yes” is set in steps S11, S31, and S32, and “No” is set in step S33. The control unit 24 increments (+1) the automatic inversion counter (step S39). When the automatic inversion counter exceeds 100 (“Yes” in step S40), the control unit 24 resets the automatic inversion counter (step S41). Stores the power at point B before inversion (step S34), provisionally sets the voltage command value to 450V (maximum value) (step S35), and sets the current command value to 0A (minimum value). (Step S36). Thereafter, the determination of the current command value (step S17) and the update of the switching duty ratio are performed (step S18).

<Summary>
The inversion function of MPPT control in the flowcharts illustrated in FIGS. 7 and 8 can also be described as follows. That is, in the MPPT control of the current step, on the output curve of the generated power in FIG. 5, for example, climbing from the low value side of the current and approaching the maximum power point, the power upper limit characteristic that can be input to the power converter 1 May stop at point A. In that case, the control unit 24 sets the current command value as the maximum value (however, only current on the solid line actually flows), approaches the maximum power point from the opposite side of the current value range, that is, the opposite side of the peak. Reach the point.

  If the power at point B is greater than the power at point A, then point B is the actual maximum power point obtained in this state. If the power at point A is greater than the power at point B, the process returns to point A. Since the output curve of the photovoltaic power generation panel 2 changes from moment to moment depending on the solar radiation conditions, the points A and B are not always the same, and the magnitude relationship also changes, so they are not fixed power points.

  Similarly, in the MPPT control of the voltage step, on the output curve of the generated power in FIG. 2, for example, climbing from the high voltage side to approach the maximum power point, the power upper limit characteristic that can be input to the power converter 1 May stop at point A. In this case, the control unit 24 reaches the point B by approaching the maximum power point from the opposite side of the voltage range, that is, the opposite side of the peak, with the voltage command value as the lowest value.

  If the power at point B is greater than the power at point A, then point B is the actual maximum power point obtained in this state. If the power at point A is greater than the power at point B, the process returns to point A. Since the output curve of the photovoltaic power generation panel 2 changes from moment to moment depending on the solar radiation conditions, the points A and B are not always the same, and the magnitude relationship also changes, so they are not fixed power points.

Further, the main part can be explained universally as follows, for example.
When the control unit 24 executes the MPPT control having the inversion function as shown in FIGS. 7 and 8, the maximum power point is set from either one of the voltage or current value range in the output curve of the photovoltaic power generation panel 2. When approaching the first power point (point A or point B) that is restricted by the characteristics of the upper limit of power that can be input to the power conversion device 1 while approaching, the other is within the range of the voltage or current value range. A second power point (point B or point A) different from the first power point can be searched by approaching the maximum power point from the side.

  In the power conversion device 1 used in an overloaded state, the power that can be output from the photovoltaic power generation panel 2 may exceed the input power upper limit characteristic. In this case, even if the control unit 24 tries to perform the maximum power point tracking control, it cannot reach the maximum power point in the output curve of the photovoltaic power generation panel 2, and is effectively located on both sides of the maximum power point. There are maximum power point candidates (points A and B). Therefore, in such a case, by approaching the maximum power point not only from one side of the range but also from the other side, the power point with the highest power can be selected from a plurality of candidates for the maximum power point. You can search. In the power conversion device 1 that performs such control, the maximum power that can be drawn from the photovoltaic power generation panel 2 at that time can be extracted even when the power is overloaded, and the generated power can be used efficiently.

  In the above embodiment, when the first power point is reached, the control unit 24 changes the voltage or current to the vicinity of the terminal on the opposite side of the value range (near the upper limit or lower limit of the output curve). In this case, it is possible to reliably jump to the other side of the range and search for the second power point.

  However, changing the voltage or current to the vicinity of the end on the opposite side of the value range is an example, and it is not always necessary to be close to the end. For example, referring to FIG. 2, after reaching point A, the voltage is reduced by a predetermined amount (for example, 200V) within the range of the output curve of generated power, and from the point A that is the previous power point on the output curve. May be controlled to move to another power point that is discontinuous. Then, the point B may be reached by approaching the maximum power point from another power point. With this method, the control unit 24 can approach the maximum power point from the other side of the range. Also, the time required for searching for point B is shorter than when moving to the vicinity of the end of the range (50 V in FIG. 2).

  As described above, when the control unit 24 stores the first power point and the power, the control unit 24 moves to the second power point, and the power at the second power point is larger than the first power point. However, if the power at the second power point is smaller than the first power point, the control may return to the first power point. In this way, it is possible to always select the larger one of the two power points.

《Other supplements》
In addition, although the power converter device 1 of the said embodiment is a power conditioner which carries out grid connection to a commercial power system, even if it is a power converter device in the stand-alone photovoltaic power generation system which is not grid-connected, said inversion MPPT control with functions can be applied. However, since the current does not flow unless the load is connected, in the case of a stand-alone, a load that allows the power converter to freely draw the current to be drawn from the photovoltaic power generation panel is required. In the case of reverse tide due to grid connection, the commercial power system becomes a kind of load, so the current can be drawn out in any way.
That is, it is necessary for the power converter to be connected to a load that draws power.

  In addition, although the storage battery 5 shown in FIG. 1 is useful for effective utilization of electric power, it is not an essential facility. If it is a stand-alone power converter connected to a DC load, the inverter 9 can be omitted.

《Supplementary Note》
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Power converter device 2 Photovoltaic power generation panel 3 AC electric circuit 4 Commercial power system 5 Storage battery 6,7 DC / DC converter 8 DC bus 9 Inverter 11 DC side capacitor 12 DC reactor 13 Diode 14 Intermediate capacitor 15 DC side capacitor 16 DC reactor 17 , 18, 19 AC reactor 20, 21 AC side capacitor 22 Voltage sensor 23 Current sensor 24 Control unit Q1-Q9 Switching element

Claims (5)

A power conversion device provided between a photovoltaic power generation panel and a load that draws power,
A power converter that extracts power from the photovoltaic power generation panel;
A control unit that has a function of controlling the power conversion unit to perform maximum power point tracking control and grasps the characteristics of the upper limit of power that can be input to the power conversion device, and
In the maximum power point follow-up control, the control unit reaches a first power point that is restricted by the characteristic while approaching the maximum power point from one side of a value range in the output curve of the photovoltaic power generation panel. If it does, the power converter which searches the 2nd power point different from the said 1st power point by approaching the said maximum power point from the other side of the said value range within the said range.   When the power point in the maximum power point tracking control reaches the first power point, the control unit changes the voltage or current by a predetermined amount within the range, and the power immediately before the output curve is changed. The power converter according to claim 1 which performs control which moves to other power points which become discontinuous from a point.   3. The power according to claim 2, wherein when the power point in the maximum power point tracking control reaches the first power point, the control unit changes the voltage or current to the vicinity of the end on the opposite side of the range. Conversion device.   The control unit moves the power point in the maximum power point tracking control to the second power point after storing the first power point and the power, and the power of the second power point is the first power point. When the power point is larger than 1, the power remains at the second power point. Conversely, when the power at the second power point is smaller than the first power point, the first power point is controlled. The power conversion device according to any one of claims 1 to 3, wherein the power conversion device returns to the point. A maximum power point tracking control method in a power converter provided between a photovoltaic power generation panel and a load that draws power,
Control the power conversion unit that extracts power from the solar power generation panel to perform maximum power point tracking control,
In the maximum power point tracking control, while approaching the maximum power point from either side of the value range in the output curve of the photovoltaic panel, there is a restriction due to the characteristics of the upper limit of power that can be input to the power converter. When reaching the first power point to be received, approach the maximum power point from the other side of the range within the range of the range and search for a second power point different from the first power point;
Maximum power point tracking control method.

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