JP2731117B2 - Maximum power point tracking control method and apparatus for solar cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling maximum power point tracking of a solar cell, for example, in a solar power generation system comprising a solar cell and a power converter such as an inverter, the output of the solar cell. Used to maximize power usage.

[0002]

2. Description of the Related Art In a photovoltaic power generation system provided with a voltage-type current control type inverter and used in connection with a commercial power system, a so-called hill-climbing method is used to maximize the power generation capacity of a solar cell. Conventionally, maximum power point tracking control (MPPT control) has been performed.

FIG. 13 is a diagram for explaining conventional MPPT control. 13 (a) is a diagram of a characteristic curve showing the relationship between the operating voltage Vop of the solar cell and the output power Po, and FIG. 13 (b) is a diagram showing conventional MPPT control until reaching the maximum power point. FIG. 13C is a diagram showing conventional MPPT control near the maximum power point.

As shown in FIG. 13 (a), the output power Po of the solar cell changes according to the operating voltage Vop, and its characteristic curve has a substantially mountain shape. The top of the characteristic curve is the output power P
is the maximum power point (Pmax point) at which o becomes the maximum, and the operating voltage Vop at that time is the optimum operating voltage (optimal operating point) V
ops. In addition, the characteristic curve changes according to the fluctuation of the amount of solar radiation and the temperature of the sun, and therefore, the optimum operating voltage Vop
s also changes accordingly.

In order to make maximum use of the output power Po of the solar cell, it is sufficient to operate the solar cell at the maximum power point. However, since the maximum power point always fluctuates according to the amount of solar radiation and the temperature, MPPT control for tracking the power point is required.
In the MPPT control, the output power Po of the solar cell is periodically measured, and the operating voltage Vop is controlled so that the output power Po increases.

That is, as shown in FIG. 13, the operating voltage Vop is shifted in the increasing direction and the decreasing direction by a change width ΔV around the current operating voltage Vopc, respectively.
The output power Po at that time is measured as indicated by a white circle in the graph of the output power Po. Each step SP1,2,3 ...
Each time, the point where the output power Po is the largest in the step is detected, and the center point of the next steps SP2, SP3, SP4 is moved to that point.

[0007] In the vicinity of the point P1 in FIG.
The operating voltage Vop exceeds the optimal operating voltage Vops,
Since the output power Po increases along the decreasing direction of the operating voltage Vop, the operating voltage Vop is increased as shown in FIG.
Decrease as a whole while repeatedly increasing and decreasing by the change width ΔV around the operating voltage Vopc at each time. At this time, the output power Po increases while increasing or decreasing according to the change in the operating voltage Vop.

In the vicinity of the optimum operating point in FIG. 13A, the operating voltage Vop is equal to or close to the optimum operating voltage Vop. Therefore, even if the operating voltage Vop is increased or decreased. , The output power Po decreases. Therefore, in this case, the operating voltage Vop is
The increase / decrease of the change width ΔV is repeated around the optimum operation voltage Vops. At this time, the output power Po always decreases in accordance with a change from the optimum operating voltage Vops.

The variation width ΔV of the operating voltage Vop for each step SP is constant irrespective of the magnitude of the operating voltage Vop. That is, regardless of whether the operating voltage Vop is near the maximum power point or far from the maximum power point, the change width ΔV in each step SP and the next step S
The movement width when proceeding to P is always constant.

In order to change the operating voltage Vop, in the inverter, the operating voltage Vop of the solar cell is changed.
The control is performed such that the voltage command value, which is the target value of the inverter, is changed at a predetermined cycle, thereby changing the current command value defining the output current of the inverter.

[0011]

However, the conventional MPP
In the T control, the operating voltage Vop always changes periodically, and the output power Po always changes accordingly. In particular, in the vicinity of the maximum power point, the output power Po always decreases due to the change in the operating voltage Vop, and the power loss is correspondingly reduced. Further, since the magnitude of the change width ΔV is always constant regardless of the magnitude of the operating voltage Vop, the change width ΔV is large even near the maximum power point. For this reason, the power loss near the maximum power point becomes remarkable, which is one of the factors that lowers the usage efficiency of the solar cell.

If the change width ΔV of the operating voltage Vop is reduced, it takes a longer time from the start of the inverter to the point when the maximum power point is reached, and the utilization efficiency of the solar cell during that time decreases. Further, the operating voltage Vop is constantly changing, and this causes disturbance of the stability of the control of the inverter. Therefore, in order to maintain the stability, the operating voltage Vop is required.
The changing speed of p, that is, the response speed of the MPPT control cannot be made too high.

The present invention has been made in view of the above-described problems, and minimizes power loss near a maximum power point while maintaining control stability, thereby improving solar cell utilization efficiency. The purpose is to let them.

[0014]

According to a first aspect of the present invention, there is provided a method for periodically measuring the output power of a solar cell and controlling the operating voltage of the solar cell stepwise so as to increase the output power. In the maximum power point tracking control method for a battery, the operating voltage is increased or decreased in any direction,
When the operating voltage changes by a set number of times, control is performed so that the change width of the operating voltage is relatively large, and when the operating voltage changes so as to repeat the increasing direction and the decreasing direction, This is a method of controlling the change width to be relatively small.

According to a second aspect of the present invention, there is provided an apparatus for measuring the output power of a solar cell periodically and controlling the operating voltage of the solar cell in a stepwise manner so that the output power increases. In the point tracking control device, a first output power that is used as a reference for comparison is set based on the measured output power.
Control means, a second control means for comparing the old output power with the output power measured this time, and when the output power measured this time is larger than the old output power, the operating voltage is the same as the previous time. A third control unit that controls the operating voltage to change in the direction opposite to the previous output power when the output power measured this time is smaller than the old output power. 4th control means, 5th control means for controlling the change width of the operating voltage to be relatively large when the operating voltage changes by a set number of times in the same direction, and And a sixth control unit configured to control the change width of the operating voltage to be relatively small when the number of changes has been set to repeat the direction and the decreasing direction.

In the apparatus according to the third aspect of the present invention, the fifth aspect
The control means has a first counter for counting addition or subtraction in accordance with the direction of the change when the third control means performs control to change the operating voltage; When the counter reaches a set count value, the change range of the operating voltage is controlled to be relatively large, and the sixth control unit controls the fourth control unit,
When controlling to change the operating voltage,
It has a second counter for counting, and when the second counter reaches a set count value, the change in the operating voltage is controlled to be relatively small.

In the apparatus according to the fourth aspect of the present invention, the third
The control means and the fourth control means, when comparing the old output power and the output power measured this time, a third counter or a fourth counter which performs addition or subtraction counting according to the comparison result. And controlling to change the operating voltage when the third counter or the fourth counter reaches a set count value.

[0018]

According to the present invention, based on the previously measured output power, the old output power serving as a reference for comparison is set. The old output power and the output power measured this time are compared, and various controls on the operating voltage are performed according to the comparison result.

For example, when the output power measured this time is larger than the old output power, control is performed so that the operating voltage changes in the same direction as the previous time. When the output power measured this time is smaller than the old output power, control is performed so that the operating voltage changes in a direction opposite to the previous time. When the old output power and the output power measured this time are the same, control is performed so that the operating voltage does not change.

When the operating voltage changes in the same direction by a set number of times, control is performed such that the change width of the operating voltage becomes relatively large. Conversely, if the operating voltage changes by the set number of times in the opposite direction to the previous time, that is, if it changes by the number of times set to repeat the increasing direction and the decreasing direction, the operating voltage changes. Control is performed so that the width is relatively small.

Note that the periodical measurement of the output power of the solar cell need not be a constant period. The measurement of the output power includes obtaining a value related to the output power.

[0022]

FIG. 1 is a block diagram showing the overall configuration of a photovoltaic power generation system 1 according to the present invention.

The solar power generation system 1 includes a solar cell 10,
And a voltage-source current control type inverter 20, and a commercial power system 5 via a protection relay (not shown) or the like.
Has been linked with. A load Z such as various home appliances is connected to the distribution line 6.

The inverter 20 includes an inverter main circuit 21 including a plurality of switching elements, a microcomputer 24 of one chip, and a digital signal processor (DS).
P) 25, a transformer PT1 for detecting the output voltage Vo, and an AD converter 2 for converting the output voltage Vo into a digital signal Sb
6. Current transformer CT2 for detecting output current Io, output current I
It comprises an AD converter 27 for converting o into a digital signal Sc, a gate circuit 28, a driver circuit 29 and the like.

The microcomputer 24 includes the solar cell 1
Current amplitude command value Iam indicating control target value of output current of 0
In addition to generating p and sending it to the DSP 25, it controls the entire inverter 20.

The DSP 25 includes a microcomputer 24
Pulse width value Pwm based on current amplitude command value Iamp and feedback signals Sb and Sc sent from
Is calculated and output at high speed.

The gate circuit 28 activates the DSP 2 when an abnormality occurs.
5 is provided to cut off the transmission of the pulse width value Pwm to the driver circuit 29. The driver circuit 29
Based on the pulse width value Pwm, a plurality of PWM pulse signals Pg required as gate control signals for each switching element of the inverter main circuit 21 are generated, and the inverter main circuit 2
Output to 1.

Next, the microcomputer 24 and the DS
The configuration and operation of P25 will be described in more detail.
FIG. 2 is a block diagram functionally showing a part of the contents processed by the microcomputer 24, and FIG. 3 is a block diagram functionally showing a part of the contents processed by the DSP 25.

As shown in FIG. 2, the microcomputer 24 supplies the operating voltage Vop of the solar cell 10, ie, the input voltage Vi to the inverter 20, and the input current Ii of the inverter main circuit 21 detected by the current transformer CT1. ,
AD converters 241 and 24 for converting into digital values
2 are provided. The microcomputer 24 has A
The output power Po of the solar cell 10 is calculated based on the D-converted voltage Vi and the current Ii, an arithmetic process for the MPPT control that maximizes the output power Po is performed, and the current amplitude command value Iamp is output. In the arithmetic processing for the MPPT control, the output power Po (new power Poc) calculated this time and the output power Po which is the reference calculated previously are used.
(Old power Pof), and according to the comparison result,
The voltage command value Vref, which is the target value of the operating voltage Vop (= input voltage Vi), is set to various values, and the current amplitude command value Iamp is calculated by operation so that the operating voltage Vop becomes equal to the voltage command value Vref. Is output to the DSP 25.

As shown in FIG. 3, in the DSP 25, the signal Sb corresponding to the fundamental frequency component is extracted from the commercial AC voltage waveform by the band-pass filter processing unit 251. The signal Sb and the current amplitude command value are output by the multiplication processing unit 252. I
A current command value signal Si, which is a product of the amp and amp, is generated.
The error amplifier unit 253 obtains a current error value E which is a value obtained by multiplying the difference Δi between the current command value signal Si and the output current value Sc by the amplification factor A, and the PWM operation processing unit 254 calculates the current error value E. The pulse width value Pwm is calculated based on this. Further, the peak value of each cycle of the fundamental frequency component is detected by the peak detection unit 255, and the frequency analysis unit 25
6, the fluctuation component Se based on a plurality of peak values.
Is detected.

Next, the contents of the MPPT control executed by the microcomputer 24 will be described. First, a description will be given of the area determination flag FEJ indicating the current position of the operating voltage Vopc in the MPPT control.

FIG. 4 is a diagram for explaining the principle of the MPPT control in the inverter 20. Figure 4
FIG. 4A is a diagram of a characteristic curve showing a relationship between the operating voltage Vop of the solar cell and the output power Po, and FIG. 4B is a diagram showing the operating voltage Vop.
FIG. 4C is a diagram showing MPPT control until the maximum power point is reached when is larger than the optimum operating point, and FIG. 4C is a diagram showing MPPT control near the maximum power point.

In FIG. 4A, when the operating voltage Vop is changed so as to increase the output power Po, the changing direction depends on whether the operating voltage Vopc at that time is higher or lower than the optimum operating voltage Vops. different. That is, in order to increase the output power Po, the operating voltage V
When the opc is higher than the optimum operating voltage Vops, the operating voltage Vopc is reduced, and the operating voltage Vop at that time is reduced.
When c is smaller than the optimum operating voltage Vops, it is necessary to increase the operating voltage Vopc.

Therefore, when the operating voltage Vop is in an area higher than the optimum operating voltage Vops, the area determination flag FEJ is set to "1", and when it is in a smaller area, the area determination flag FEJ is set to "0". To

In the vicinity of the optimum operating voltage Vops, when the operating voltage Vop changes, the optimum operating voltage Vo
Up and down transitions with respect to ps can occur. That is, in this case, the area determination flag FEJ is changed from “1” to “0” or from “0” to “1”.

Then, the state in which the area determination flag FEJ is "1" (optimal operating voltage Vops <operating voltage Vop) is changed to the mode M1 and the state in which it is "0" (optimal operating voltage Vops).
> Operating voltage Vop) in mode M2, area determination flag FE
J transitions from “1” to “0” (optimum operating voltage V
(ops> current operating voltage Vopc) in mode M3 and area determination flag FEJ changes from “0” to “1” (optimal operating voltage Vops <current operating voltage Vopc)
Is mode M4. In the modes M1 and M4, the voltage command value Vref is decreased, and in the modes M2 and M3, the voltage command value Vref is increased.

As shown in FIG. 4B, in the MPPT control until reaching the maximum power point, when the operating voltage Vop shifts in the same direction by a certain number of times, the operating voltage Vop
Is controlled so that the change width ΔV of the second line becomes large. FIG.
As shown in (c), in the MPPT control near the optimum operating point, when the increase and decrease of the operating voltage Vop are repeated a fixed number of times, control is performed so that the variation width ΔV of the operating voltage Vop becomes small.

Next, the contents of the MPPT control of the inverter 20 will be described with reference to the flowcharts shown in FIGS. FIG. 5 is a flowchart showing a main routine of the MPPT control process. This main routine is executed at sufficiently short intervals together with the main routine for other processes.

In FIG. 5, it is checked whether or not the MPPT control has been started (# 11). This is because MPPT control is not performed in order to stabilize the entire control system within a certain time after the activation of the inverter 20, and instead constant voltage control is performed. If it is not in the start state (No in # 11), the start counter set to a predetermined value is decremented (# 12), and the voltage command value Vref is set to an initial value (# 13).

In the start state (Yes in # 11), it is checked whether it is the judgment timing (# 1).
4). The determination timing is set to be YES every 0.1 to 1 second, for example, and by this check, the processing after step # 15 is executed at a constant cycle of every 0.1 to 1 second, for example. You.

An average value of the input voltage Vi (operating voltage Vop) is obtained (# 15). The input voltage Vi is periodically sampled in another process (not shown), and an average value within a predetermined period is calculated. When the calculated input voltage Vi is an abnormal value, a process of removing the abnormal value is performed (# 16), and a shift process routine is executed (# 1).
7).

The area determination flag FEJ is checked (# 18). When the area determination flag FEJ is “1”, the average value of the input current Ii is obtained (# 19).
The input current Ii is periodically sampled in another process (not shown), and an average value within a predetermined period is calculated.

The new power Poc, which is the output power Po at that time, is calculated as Poc = Vi × Ii (#
20). The new power Poc and the old power Pof are compared (# 21, # 22). Here, the old power Pof is used as a reference for comparison, and the new power Poc calculated one time before the voltage command value Vref is changed so as to be executed in steps # 49 and 59 described later. Is substituted as the value of the old power Pof by changing the voltage command value Vref.

If the new power Poc and the old power Pof are the same (Yes in # 21), the main routine ends without performing the subsequent processing. That is, in this case, the values of the voltage command value Vref and the old power Pof are not changed. In addition, the same here includes a case where they are completely the same and a case where the difference is within a predetermined range.

When the new power Poc is larger than the old power Pof (Yes in # 22), a DCV-DOWN routine for decreasing the voltage command value Vref is executed (# 2).
3), when the new power Poc is smaller than the old power Pof (No in # 22), P which is a process near the maximum power point
The EEK routine is executed (# 24).

In step # 18, an area determination flag FEJ
Is “0”, the average value of the input current Ii is obtained (# 25), and the new power Poc is calculated as Poc = Vi × Ii (# 26). New power Poc and old power Pof
Are compared (# 27, # 28).

If the new power Poc is the same as the old power Pof (Yes in # 27), the main routine ends without performing the subsequent processing. That is, in this case, the voltage command value Vref and the old power Pof are not changed.

When the new power Poc is larger than the old power Pof (Yes in # 28), a DCV-UP routine for increasing the voltage command value Vref is executed (# 2).
9) If the new power Poc is smaller than the old power Pof (No in # 28), the PEEK routine is executed (# 3).
0).

FIG. 6 is a flowchart showing the DCV-DOWN routine, and FIG. 7 is a flowchart showing the DCV-UP routine. In FIG. 6, first, the UD counter is decremented (# 41). The UD counter is decremented by one each time the DCV-DOWN routine is executed, and the DCV-UP counter described in FIG.
It is incremented by one each time the routine is executed. When the count value of the UD counter reaches a preset lower limit value, a process of changing the voltage command value Vref downward is executed, and when the count value of the UD counter reaches a preset upper limit value. , The process of changing the voltage command value Vref upward is executed.

That is, if the count value of the UD counter has not reached the lower limit (No in # 42), the count value is stored as it is and the process returns to the main routine (# 43). (Yes in # 42), the UD counter is initialized (# 44), the current voltage command value Vref is read (# 45), and it is confirmed whether or not the voltage command value Vref has not reached the lower limit (# 44). # 4
6) The voltage command value Vref is subtracted by a predetermined value and output as a new voltage command value Vref (# 47).
The F counter is decremented (# 48). Thereafter, the value of the old power Pof, which is a reference for comparison, is updated to the value of the new power Poc (# 49).

When the count value of the F-counter reaches a preset upper limit value or lower limit value, a process of increasing the variation width ΔV of the voltage command value Vref is executed. When the count value reaches a preset upper limit value, an S counter described later supplies a voltage command value Vre.
A process for reducing the change width ΔV of f is executed. In addition,
Variation width ΔV of voltage command value Vref corresponds to variation width ΔV of operating voltage Vop.

In FIG. 7, the UD counter is incremented (# 51). If the count value of the UD counter has not reached the upper limit (No in # 52), the count value is stored as it is and the process returns to the main routine (# 53). If the count value has reached the upper limit (# 52). Yes), the UD counter is initialized (# 54), the voltage command value Vref is read (# 55), it is confirmed whether the voltage command value Vref has not reached the upper limit (# 56), and the voltage command value Vref is determined. And a new value is output as a new voltage command value Vref (# 57), and the F counter is incremented (# 58). Thereafter, the value of the old power Pof, which is a reference for comparison, is updated to the value of the new power Poc (# 59).

FIGS. 8 and 9 are flowcharts showing the PEEK routine. In FIG. 8, first, the area determination flag FEJ is checked (# 61). If the area determination flag FEJ is "1", the current count value of the PEEK counter is read (# 62), and the value is incremented (# 63).

Each time the PEEK counter is executed once, the PEEK counter is incremented or decremented according to the state of the area determination flag FEJ. When the count value of the PEEK counter reaches a preset upper limit value or lower limit value, the UD counter is incremented or decremented. When the UD counter reaches the upper limit value or the lower limit value, a process of changing the voltage command value Vref upward or downward is executed as in the DCV-UP routine or the DCV-DOWN routine.

That is, in the PEEK routine, in order to change the voltage command value Vref, it is a condition that both of the two counters, the PEEK counter and the UD counter, reach the upper limit or the lower limit. For example, PEE
The K counter and the UD counter are both 4 bits and "-
8 ”to“ 0 ”to“ 7 ”, and when the area determination flag FEJ is“ 1 ”, this P
When the EEK routine is continuously executed 49 (= 7 × 7) times, the change for increasing the voltage command value Vref is executed once, and when the area determination flag FEJ is “0”, the PEEK routine is continuously executed. When the execution is performed 64 (= 8 × 8) times, the change for decreasing the voltage command value Vref is executed once. Note that each routine does not necessarily need to be executed continuously. For example, when the input voltage Vi or the input current Ii fluctuates due to the influence of noise, other routines may be executed. When the counter reaches the upper limit or the lower limit, the voltage command value Vref
Changes are made.

Returning to FIG. 8, in step # 64,
If the count value of the PEEK counter has not reached the upper limit, the count value is stored as it is, and the process returns to the main routine (# 65). If the count value has reached the upper limit (Yes in # 64), the PEEK counter is returned. Is initialized (# 66), and the UD counter is incremented (# 6)
7).

If the count value of the UD counter has not reached the upper limit (No in # 68), the count value is stored as it is, and the process returns to the main routine (# 69). (Yes in # 68), the area determination flag FEJ is reset to “0” (#
70), the S counter is incremented (# 71), and
The D counter is initialized (# 72), the current voltage command value Vref is read (# 73), and the voltage command value Vref is read.
Is checked to see if it has reached the upper limit (# 74), the voltage command value Vref is added by a predetermined value and stored in a memory (# 75), and it is output as a new voltage command value Vref (# 75). 76). Then, the old power P, which is the reference for comparison,
The value of of is updated to the value of new power Poc (# 77).

In FIG. 9, when the area determination flag FEJ is "0", the current count value of the PEEK counter is read (# 82), and the value is decremented (# 83).

In step # 84, if the count value of the PEEK counter has not reached the lower limit, the count value is stored as it is and the process returns to the main routine (# 85). (Yes in # 84), initializes the PEEK counter (# 86), UD
The counter is decremented (# 87).

If the count value of the UD counter has not reached the lower limit (No in # 88), the count value is stored as it is, and the process returns to the main routine (# 89). (Yes in # 88), the area determination flag FEJ is set to "1"(# 9).
0), the S counter is incremented (# 91), and the UD
The counter is initialized (# 92), the current voltage command value Vref is read (# 93), it is checked whether the voltage command value Vref has reached the lower limit (# 94), and the voltage command value Vref is set to a predetermined value. Is subtracted and stored in the memory (# 95), and is output as a new voltage command value Vref (# 96). Then, the old power P, which is the reference for comparison,
The value of of is updated to the value of new power Poc (# 97).

FIG. 10 is a flowchart showing a shift processing routine. Before entering this routine, in the main routine, the variation width ΔV is initialized to “4”, and both the F counter and the S counter are initialized to “0”.

When the F counter reaches the upper limit value of "3" or the lower limit value of "-3"(# 101 or # 10).
2 and the F counter is initialized to "0"(# 10
3) The change width ΔV of the voltage command value Vref is set to “4” which is a relatively large value (# 104).

If the F counter has not reached either the upper limit value or the lower limit value (No in # 101 and 102), it is checked whether or not the S counter has reached the upper limit value of "3" (see FIG. 4). # 105). If the S counter has reached the upper limit value, the S counter is initialized to “0” (# 106), and the change width ΔV of the voltage command value Vref is set to a relatively small value “1” (# 107).

That is, step # 48 of the DCV-DOWN routine or step # 5 of the DCV-UP routine
At step 8, the F counter is decremented or incremented, but if each routine is repeated three times, or if any routine is executed three times more than the other, the change width ΔV becomes larger at step # 104. Is set to In step # 71 or # 92 of the PEEK routine, the S counter is incremented.
When 1 or step # 92 is executed three times, step #
At 107, the variation width ΔV is set to a small value.

The above processing operation will be described with reference to FIG. 4. In the mode M1 shown in FIG.
When a state in which oc is larger than old power Pof continues for a predetermined number of times, voltage command value Vref is reduced by a predetermined value. When this process is repeated three times, the voltage command value Vr
Even if the change width ΔV of ef is a small change width ΔVs, it is changed to a large change width ΔVf. After the change is once changed to the large change width ΔVf, the same setting does not change any number of times. In the example shown in FIG. 4B, the change width ΔVs is small at the beginning, but this is for the purpose of explanation. In practice, a large change width ΔVf is usually set at the beginning. .

Therefore, in the mode M1 or the mode M2, since the variation width ΔV is large, the optimum operating point can be reached at high speed. The mode M shown in FIG.
In 3 or M4, when the state where the new power Poc is smaller than the old power Pof continues for a predetermined number of times, the voltage command value Vref is changed by a predetermined value. When this process is repeated three times, the change width ΔV of the voltage command value Vref is changed to a small change width ΔVs even if the change width ΔVf is large. After the change is once changed to the small change width ΔVs, it does not change no matter how many times the same setting is performed.
Further, no processing is performed as long as the new power Poc and the old power Pof remain the same. By repeating these processes, operation near the maximum power point is maintained.

Therefore, in the mode M3 or the mode M4, since the variation width ΔV is small, the fluctuation of the output power Po near the optimum operating point is reduced, thereby minimizing the power loss and using the solar cell. Efficiency can be improved.

Further, in the inverter 20 of the present embodiment, when the power reaches the vicinity of the maximum power point by the MPPT control and the state becomes the mode M3 or M4, the change width ΔV becomes small and the PEEK counter and the UD counter Until both reach the upper or lower limit.
Since f is not changed, the input voltage Vi (that is, the operating voltage Vop) does not change during that time, and the output power Po does not change unless the characteristic curve changes due to a change in the amount of solar radiation.

If the new power Poc and the old power Pof are the same, no processing for changing the voltage command value Vref, that is, no increment or decrement of the PEEK counter or the UD counter is performed. As long as the state continues, the voltage command value Vref is the same, and the operation at the same operation voltage Vop is continued. Therefore, as long as the characteristic curve does not change due to a change in the amount of solar radiation, the output power Po does not change.

That is, in the vicinity of the maximum power point, the voltage command value Vref, the operating voltage Vop, and the output power Po
, And power loss due to the conventional fluctuation is greatly suppressed, and the utilization efficiency of the solar cell is improved.

Moreover, since the variation width ΔV of the voltage command value Vref until the optimum operating point is reached is large, the time from the start of the inverter 20 to the maximum power point can be shortened, and the Usage efficiency can be improved.

When the new power Poc is the same as the old power Pof, or when the PEEK routine is entered,
When the characteristic curve changes due to a change in the amount of solar radiation, the DCV-UP routine or the DCV-DOW is triggered by this change.
The process proceeds to the N routine, and the processing of the mode M1 or M2 is executed. Therefore, when the amount of solar radiation fluctuates, it can respond quickly to the maximum power point in a short time.

FIG. 11 is a flowchart showing a shift processing routine according to another embodiment. This shift processing routine
While the shift processing routine of FIG. 10 is a two-stage shift with a large change width ΔVf and a small change width ΔVs,
The shift is performed in multiple stages between the upper limit and the lower limit. Before entering this routine, in the main routine, the variation width ΔV is initialized to the upper limit value, and both the F counter and the S counter are initialized to “0”.

If the F counter is "3" which is the upper limit or "-3" which is the lower limit (Yes in # 111 or 112), the F counter is initialized to "0"(#
113), “2” is added to the current change width ΔV of the voltage command value Vref to obtain “ΔV + 2” (# 114). However, when the new set value of the variation width ΔV exceeds the upper limit (Yes in # 115), the variation width ΔV is set as the upper limit value (# 116).

If the F counter has not reached either the upper limit value or the lower limit value (No in # 111 and 112), it is checked whether or not the S counter has reached the upper limit value of "3" (see FIG. 4). # 117). If the S counter has reached the upper limit value, the S counter is initialized to “0” (# 118), and the current variation width Δ of the voltage command value Vref is set.
“1” is subtracted from V to obtain “ΔV−1” (# 11
9). However, when the new set value of the change width ΔV is below the lower limit (Yes in # 120), the change width ΔV is set to the lower limit (# 121).

FIG. 12 is a flowchart showing a shift processing routine according to still another embodiment. This shift processing routine is the same as the shift processing routine shown in FIGS.
While the counts of the F counter and the S counter are executed in the processing in the routine of FIG. 9, those counts are performed in this shift processing routine. Before entering this routine, in the main routine, the change width ΔV is set to “4”, and the F counter and S
The counters are both initialized to “0”, the upper limit of the F counter is initialized to “3”, and the lower limit of the F counter is initialized to “−3”.

If a subtraction command is issued in another routine (YES in # 131), the F counter is decremented (# 132), and if an addition command is issued (# 13).
3; yes), increments F counter (# 1)
34). When the command is changed from the subtraction command to the addition command or when the command is changed from the subtraction command to the addition command (# 135 or 3
Then, the S counter is incremented (# 1).
37).

If the F counter is at the upper limit value or the lower limit value (Yes at # 138 or 139), the F counter is reset to "0"(# 140), and the voltage command value Vref
A relatively large value “4” is set as the change width ΔV (# 141).

If the F counter is neither the upper limit nor the lower limit (No in # 138 and 139) and the S counter is at the upper limit (Yes in # 142), the S counter is initialized to "0". (# 143), voltage command value Vref
Is set to a relatively small value “1” (# 144).

Also in the embodiment shown in FIGS. 11 and 12, in the mode M3 or the mode M4, since the variation width ΔV is small, the fluctuation of the output power Po near the optimum operating point is reduced, thereby reducing the power loss. The use efficiency of the solar cell can be improved by minimizing it.

In the above embodiment, steps # 49,
The processing of 59, 77, 97 corresponds to the first control means of the present invention, the processing of steps # 21, 22, 27, 28 corresponds to the second control means of the present invention, and the processing of steps # 47, 57 or D
The whole of the CV-DOWN routine and the DCV-UP routine correspond to the third control means of the present invention.
The whole of the 6, 95, 96 or PEEK routine corresponds to the fourth control means of the present invention, and steps # 104, 114, 1
The entire process including the process of 41 or the counting operation of the F counter and the checking operation of the count value corresponds to the fifth control means of the present invention.
The whole process including the process of 44 or the counting operation of the S counter and the checking operation of the count value corresponds to the sixth control means of the present invention. Further, the F counter of the present embodiment is the first counter of the present invention, the S counter is the second counter of the present invention, the UD counter is the third counter of the present invention, and the UD counter and the PEEK counter are the fourth counter of the present invention. On the counter,
Each corresponds.

In the above embodiment, the upper limit or lower limit of the F counter, S counter, PEEK counter, or UD counter can be various values other than those described above. In the PEEK routine, only a UD counter or only a PEEK counter may be used, or a PE having a large upper limit and a lower limit may be used without using a UD counter.
Only the EK counter may be used. The initial value of each counter is not limited to the above-described embodiment, but may be various values.

In the above embodiment, the cycle and timing for acquiring the input voltage Vi or measuring the output power Po can be variously set. Some or all of the functions executed by the microcomputer 24 or the DSP 25 may be realized by hardware circuits. The circuit configuration, control contents, processing contents of the flowchart, processing sequence, and the like of each part or the whole of the inverter 20 or the photovoltaic power generation system 1 can be variously changed according to the gist of the present invention.

[0084]

According to the first to fourth aspects of the present invention,
Power loss near the maximum power point can be suppressed to a minimum while the stability of control is maintained, and the usage efficiency of the solar cell can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a solar power generation system according to the present invention.

FIG. 2 is a block diagram functionally showing a part of contents processed by a microcomputer.

FIG. 3 is a block diagram functionally showing a part of contents processed by a DSP.

FIG. 4 is a diagram for explaining the principle of MPPT control in an inverter.

FIG. 5 is a flowchart illustrating a main routine of MPPT control processing.

FIG. 6 is a flowchart showing a DCV-DOWN routine.

FIG. 7 is a flowchart showing a DCV-UP routine.

FIG. 8 is a flowchart showing a PEEK routine.

FIG. 9 is a flowchart showing a PEEK routine.

FIG. 10 is a flowchart showing a shift processing routine.

FIG. 11 is a flowchart illustrating a shift processing routine according to another embodiment.

FIG. 12 is a flowchart illustrating a shift processing routine according to another embodiment.

FIG. 13 is a diagram for explaining conventional MPPT control.

[Explanation of symbols]

 Reference Signs List 20 inverter (maximum power point tracking control device) 24 microcomputer (first to sixth control means) Po output power Vop operating voltage Pof old power (old output power) Poc new power (output power measured this time)

Claims (4)

(57) [Claims] 1. A maximum power point tracking control method for a solar cell, comprising periodically measuring the output power of a solar cell and stepwise controlling the operating voltage of the solar cell so that the output power increases. In either of the increasing direction or the decreasing direction, when changing by a set number of times, control is performed such that the change width of the operating voltage is relatively large, and the operating voltage is increased and decreased. A maximum power point tracking control method for a solar cell, wherein the change width of the operating voltage is controlled to be relatively small when the change is repeated. 2. A solar cell maximum power point tracking control device for periodically measuring the output power of a solar cell and controlling the operating voltage of the solar cell stepwise so that the output power increases. First control means for setting an old output power as a reference for comparison based on the output power; second control means for comparing the old output power with the output power measured this time; If the output power measured is large, the third control means controls the operating voltage to change in the same direction as the previous time, and if the output power measured this time is smaller than the old output power, Fourth control means for controlling the operating voltage to change in a direction opposite to the previous direction; and when the operating voltage has changed by a set number of times in the same direction, the change width of the operating voltage is relatively small. To be bigger A fifth control unit that controls the operation voltage so that the change width of the operation voltage becomes relatively small when the operation voltage changes by a set number of times to repeat the increasing direction and the decreasing direction. A maximum power point tracking control device for a solar cell, comprising: control means; 3. The first control means, wherein when the third control means controls to change the operating voltage, a count of addition or subtraction is performed in accordance with a direction of the change. When the first counter reaches a set count value, the control section controls the change width of the operating voltage to be relatively large. A second counter that counts when the control is performed to change the operating voltage, and when the second counter reaches a set count value, the change width of the operating voltage is The maximum power point tracking control device for a solar cell according to claim 2, wherein the maximum power point tracking control device is configured to be controlled to be relatively small. 4. The third control means and the fourth control means, when comparing the old output power with the output power measured this time, count up or down according to the comparison result. A third counter or a fourth counter, and configured to perform control for changing the operating voltage when the third counter or the fourth counter reaches a set count value. The maximum power point tracking control device for a solar cell according to claim 2 or 3.