JPH08221143A - Maximum electric power follow-up control method for solar light power generation system - Google Patents

Abstract

PURPOSE: To speedily transfer to proper maximum electric power follow-up control when the sunshine increases thereafter even if the output voltage of a solar battery drops at low-sunshine time. CONSTITUTION: A command value voltage Vset which increases in steps of width Vstep is added to the control signal of an inverter, the current output electric power Pnow of the solar battery is compared with the value obtained by increasing or decreasing last output electric power Ppast by set electric power Phist where a dead zone is set, and the command value voltages Vpast and Vnow are increased or decreased in steps of width Vstep according to the comparison result to set a next-time command value voltage; when the output electric power is in the dead zone, the command value voltage Vnot is forcibly decreased with the step width Vstep to set a next-time command value voltage and the inverter is driven under maximum electric power follow-up control. If the output electric power of the solar battery drops below a set value Pmin at low-sunshine time, a voltage at which the inverter can be driven is regarded as a lower limit of operation irrelevantly to the last output electric power Ppast and the output voltage Vcell of the solar battery is lowered to drive the inverter continuously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a maximum power tracking control method for a solar power generation system, and more specifically, in controlling the maximum power tracking of a solar power generation system, when the output of a solar cell is reduced during low solar radiation. Control method.

[0002]

2. Description of the Related Art In recent years, as a petroleum alternative energy, a solar power generation system, which is pollution-free, inexhaustible, and highly safe, has been put into practical use, and a distributed power source including a solar cell and an inverter and an electric power system are connected to each other. Photovoltaic power generation systems are attracting attention.

FIG. 6 is a circuit diagram showing the configuration of the solar power generation system 1, in which the DC power generated by the solar cell 2 is converted into AC power by the inverter 3 and then the power is supplied to the load and excess power is supplied. AC power is transmitted to the system power supply 4. In the figure, 5 is a control circuit of the inverter 3, which takes in the output current Iinv, the system voltage Vs, and the system current Is of the inverter 3 and follows the command signal of the control circuit 5,
The inverter 3 is driven by I control or PWM control.

By the way, the output of the solar cell 2 is shown in FIG.
When the output voltage Vcell of the solar cell 2 is increased, the output power P increases for a while and the maximum output voltage Vpmax reaches the maximum output Pmax, and then a certain voltage Vx. When the above is reached, the output power P drops sharply, and further, the output voltage Vcell is raised and the output power P becomes zero at the open circuit voltage Voc.

Therefore, the solar power generation system 1 usually employs a maximum power follow-up control method of controlling the output of the inverter 3 so that the output power P of the solar cell 2 is always maximized.

This maximum power tracking control method of the solar power generation system 1 sets a command value voltage for obtaining a control signal of the control circuit 5, and sequentially changes the command value voltage by a predetermined step width to make a solar cell. The current output power of 2 is compared with the previous output power, and the operating area on the PV characteristic curve of the solar cell 2 at that time is determined by the increase or decrease of the power, and according to the determined operating area. By setting the next command value voltage to drive the inverter 3 by
The output power of the solar cell 2 is controlled to be always the maximum.

For example, when the output power of the solar cell 2 obtained when the previously set command value voltage is raised by a predetermined step width is larger than the previous output power, the operating point of the solar cell 2 is It is determined that it is on the left side of the convex shape of the PV characteristic curve, and the next command value voltage is set to a voltage obtained by further increasing the current command value voltage by a predetermined step width.
When the output power of the solar cell 2 is smaller than the output power of the previous time, it is determined that the operating point of the solar cell 2 is on the right side of the convex shape of the PV characteristic curve, and the next command value voltage is The command voltage is set to a voltage lower by a predetermined step width.

In such a maximum power tracking control method for the solar power generation system 1, the PV characteristic curve of the solar cell 2 has a convex shape, and the operating point of the solar cell 2 is on both sides of the apex of the PV characteristic curve. When it is located at, the inverter 3 is controlled so as to move to its apex side, and the inverter 3 is always drive-controlled so that the output of the solar cell 2 is maximized.

[0009]

However, when the PV characteristic curve of the solar cell 2 has a convex shape and the operating point is located at the apex thereof, the output power thereof does not change even if the command value voltage is changed. Similarly, when the operating point is located in a region larger than the open circuit voltage Voc, the output power does not change even if the command value voltage is changed. As a result, depending on whether the operating point is located at the apex or in the area larger than the open circuit voltage Voc,
Both had the same phenomenon that the output power did not change.

When the operating point is located in a region larger than the open-circuit voltage Voc as described above, it is the same as when the operating point is located at the apex and cannot be determined. When the operating point sharply decreases the slope on the right side of the PV characteristic curve and reaches the open circuit voltage Voc, the output power of the solar cell 2 does not change even if the command value voltage is changed, and the operating point is opened. There was a case where the voltage was fixed on the Voc side and output power could not be obtained.

Further, the output power of the solar cell 2 is constantly changing depending on the weather condition, and in the conventional method in which the output power of the solar cell 2 is simply compared with the previous output power, the operating point is always greatly moved and stable. There was a problem that the output power could not be obtained.

Further, as the output power of the solar cell decreases during low solar radiation, the measured value of the output power becomes small and it becomes difficult to execute the maximum power follow-up control, which may cause malfunction.

Therefore, the present invention has been proposed in view of the above problems, and an object thereof is that the operating point is P-
It is fixed to the open-circuit voltage side of the V characteristic curve and output power cannot be obtained, and the operating point is prevented from fluctuating significantly due to changes in solar radiation conditions, and further, the output power of the solar cell drops during low solar radiation. Even then, it is an object of the present invention to provide a maximum power follow-up control method for a photovoltaic power generation system, which can promptly shift to an appropriate maximum power follow-up control if the amount of solar radiation increases.

[0014]

As a technical means for achieving the above object, the present invention provides a control signal of an inverter connected to a solar cell with a command value voltage which increases or decreases in a predetermined step width, The output power of this time obtained from the solar cell is compared with a value obtained by increasing or decreasing a predetermined set power in which the dead band is set to the output power of the previous time, and the command value voltage is increased or decreased by the step width based on the comparison result. And set the next command value voltage, and when the output power is within the dead band, set the next command value voltage by decreasing the current command value voltage by a step width, and the output of the solar cell is always the maximum. In the maximum power tracking control method of the solar power generation system that drives the inverter so that, when the output power of the solar cell is reduced to a predetermined value or less during low solar radiation,
Regardless of the previous output power, the output voltage of the solar cell is lowered by setting the voltage at which the inverter can be driven as the operation lower limit, and the inverter is continuously driven.

[0015]

In the method of the present invention, the current output power obtained from the solar cell is compared with the value obtained by increasing or decreasing the predetermined output power in which the dead band is set to the previous output power. The operating point does not change greatly even if the conditions slightly change. Also, when the output power is within the dead band, the command value voltage is reduced by a predetermined step width, so that even if the operating point is in a region larger than the open circuit voltage, the operating point is fixed in that region. There is no such thing.

According to the method of the present invention, the output power of the solar cell is reduced during low solar radiation, and even if the measured value of the output power becomes small and the maximum power follow-up control becomes difficult, When the electric power becomes equal to or less than a predetermined set value, the output voltage of the solar cell is lowered to secure the driveable voltage of the inverter as the operation lower limit, so that the inverter is continuously driven and the amount of solar radiation after that. When the amount of solar radiation increases, an appropriate maximum power follow-up control can be executed.

[0017]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a flow chart for generating a command signal for controlling the maximum power of the solar power generation system 1, FIG.
Shows a block diagram showing constituent elements of a command signal generating section for generating the command signal. First, the structure of the command signal generating section 6 will be described below.

The measuring unit 7 in FIG. 2 is connected to the output circuit of the solar cell 2 and has its output voltage Vcell and output current Ice.
ll is measured. The calculation unit 8 calculates the output power P of the solar cell 2, that is, the current output power Pnow from the output voltage Vcell and the output current Icell measured by the measuring unit 7. The calculated value storage unit 9 temporarily stocks the output power Pnow obtained by the calculation unit 8 and uses it as the previous output power Ppast. The operating area determination unit 10 determines which area of the PV characteristic curve the operating point of the solar cell 2 is in based on the output power Pnow.

In this case, the output power Pnow is compared with a value obtained by increasing or decreasing a predetermined set power Phist for setting the dead band with respect to the previous output power Ppast stored in the calculated value storage unit 9. That is, the operating point of the solar cell 2 is the left side of the convex shape of the PV characteristic curve based on whether the current output power Pnow is larger or smaller than the previous output power Ppast in consideration of the set power Phist, or within the dead band. Alternatively, it is determined whether it is located on the right side, or is located in a region higher than the apex or the open circuit voltage.

For example, in the PV characteristic curve of FIG.
The previously set command value voltage Vpast is set to a predetermined step width V
Output power Pnow of the solar cell 2 when only step is lifted
If [output power P _{2 in the} figure] changes from the previous output power Ppast [output power P ₁ in the figure], the current output power Pnow [P ₂ ] is the previous output power Ppast [P ₁ ] Is compared with Ppast [P ₁ ] + Phist which is obtained by adding the set power Phist.

The output power Pnow [P ₂ ] of this time is Ppa obtained by adding the set power Phist to the output power Ppast [P ₁ ] of the previous time.
When it is larger than st [P ₁ ] + Phist, it is determined that the output power P of the solar cell 2 is increasing, and the operating point is determined to be on the left side from the apex of the PV characteristic curve. In this way, by providing the dead zone in which the set power of ± Phist is increased or decreased in the determination of the operation area of the solar cell 2, the output characteristics of the solar cell 2 are slightly uneven due to variations in solar radiation conditions as shown in the figure. Even if it fluctuates, if the fluctuation is within the range of the set power Phist, stable output power P is obtained without being affected by the discrimination of the operation region and the operating point does not frequently move.

Further, the command value voltage setting section 11 in FIG.
Sets the command value voltage Vset according to the determination result. That is, on the left side of the apex of the PV characteristic curve, the difference between the command value voltage Vnow of this time and the previous command value voltage Vpast (Vnow-Vpast), that is, the step width Vstep is added to the command value voltage Vnow of this time. The command value voltage Vset is set, and conversely, on the right side of the apex of the PV characteristic curve, the difference (Vpast-Vnow) between the command value voltage Vpast and the command value voltage Vnow of this time, that is, the step, is added to the previous command value voltage Vpast. The command value voltage Vset is obtained by adding the width Vstep. Also,
In the peak of the PV characteristic curve or in a region larger than the open circuit voltage, the command value voltage Vnow minus the step width Vstep is set as the command value voltage Vset. The command value voltage Vnow used when the command value voltage Vset is set is replaced in the command value storage unit 12 as the previous command value voltage Vpast and the data is updated.

In the command value voltage setting section 11, as a result of the output area Pnow being judged to be within the dead band by the operation area judging section 10, it is judged that the operating point is located at the peak of the PV characteristic curve or in the area larger than the open voltage. In this case, since the command value voltage Vset is set by subtracting the step width Vstep from the command value voltage Vnow of this time as described above, for example, the operating point of the solar cell 2 is P- due to a sudden change in the solar radiation condition. Even when the command value voltage Vset is lower than the open voltage, that is, to the right side of the apex of the PV characteristic curve, even when the command value voltage Vset is located in a region higher than the open voltage and suddenly drops from the right side of the apex of the V characteristic curve. Therefore, the operating point is not fixed.

In addition, the upper and lower limit area determination unit 13 in FIG.
Then, it is determined whether the command value voltage Vset is smaller than the minimum lower limit value Vmin [Vset <Vmin] or larger than the maximum upper limit value Vmax [Vset> Vmax]. By setting the upper and lower limits to the command value voltage Vset in this way, for example, when the solar cell 2 is operated between the desired operating voltages V ₁ and V ₂ shown in FIG. 3, the command value voltage Vset is changed from an unnecessarily low voltage. The calculation can be prevented, and the maximum power control can be quickly performed.

In the command value voltage setting section 14 in the upper and lower limit regions,
As described above, when the command value voltage Vset is smaller than the lower limit value Vmin, the step width Vst is added to the previous command value voltage Vpast.
When ep is added and when it is larger than the maximum upper limit value Vmax, the step width Vstep is subtracted from the previous command value voltage Vpast and the command value voltage Vset is reset. Also, the command value output unit 1
In 5, the command value voltage Vset is set to the command value voltage Vno of this time.
It is given to the control circuit 5 as w to generate a control signal.

The output decrease determination unit 16 determines that the output power of the solar cell 2 is decreased during low solar radiation. That is, when the solar radiation is low, the P-V characteristic curve shown in FIG. 4 is characterized in that the output power P first decreases, and when it decreases to a certain extent, the open circuit voltage Voc decreases. Therefore, the output decrease determination unit 16 sets a predetermined set value Pmin for the decrease in the output power P. On the other hand, the output decrease command value voltage setting unit 17 subtracts the step width Vstep from the current command value voltage Vnow to reset it as the command value voltage Vset, and replaces the command value voltage Vnow with the previous command value voltage Vpast. And update the data.

In the initial value setting section 18, the command value voltage Vset
Initial voltage Vset ₀ , step width Vst of command value voltage Vset
ep, set power Phist for setting dead band, command value voltage V
The lower limit value Vmin and the upper limit value Vmax of the set, the set value Pmin when the output is reduced, etc. are set. Each of these constituent elements is controlled by the computer 19.

The command signal generator 6 having such a configuration is shown in FIG.
It operates according to the flowchart shown in.

In FIG. 1, in step 101, the output power Ppast of the calculated value storage unit 9, the command value voltage Vpast of the command value storage unit 12, and the command value voltage Vnow of the command value output unit 15.
Are initialized respectively. Here, the command value voltage Vnow
The initial voltage Vset ₀ set to is the drive start voltage of the inverter 3, and an appropriate voltage value on the PV characteristic curve of FIG. 3 is selected.

In step 102, the output voltage Vcell and the output current Icell of the solar cell 2 are taken into the measuring section 7, and the output voltage Vcell and the output current Icell are multiplied [Vcell × Icell] in the calculating section 8 and output. The electric power Pnow is calculated.

In step 103, the output reduction determination unit 16
Thus, the output power Pnow is compared with a predetermined set value Pmin that has been set, and it is determined whether or not the output has decreased due to low solar radiation. As a result, when the output power Pnow of the solar cell 2 decreases due to low solar radiation and becomes smaller than the set value Pmin,
The command value voltage setting unit 17 for output reduction subtracts the step width Vstep from the command value voltage Vnow of this time to obtain the command value voltage Vnow.
The data is updated by resetting as the set and replacing the command value voltage Vnow with the previous command value voltage Vpast.

In this way, based on the command value voltage Vset, the output voltage Vcell of the solar cell 2 is lowered to the lower limit value Vmin which is the voltage that can drive the inverter 3 in step 105 described later, and the lower limit value thereof is set. By maintaining Vmin, the drivable voltage of the inverter 3 is secured and the inverter 3 is continuously driven. If the output power Pnow of the solar cell 1 is larger than the set value Pmin, the next step 104 is executed.

In step 104, the operation area discrimination unit 10
Thus, the output power Pnow is compared with a value obtained by adding the set power Phist to the previous output power Ppast, and the operating region on the PV characteristic curve is determined. After determining the operating area,
The command value voltage setting unit 11 sets the command value voltage Vset according to the operating region. After setting the command value voltage Vset, the command value voltage Vnow is replaced in the command value storage unit 12 as the previous output power Vpast, and the data is updated.

In step 105, the upper and lower limit area discrimination unit 1
3, the command value voltage Vset is the upper and lower limit values Vmin, V
For the command value voltage Vset which is compared with max and exceeds the upper and lower limit values Vmin and Vmax, the command value voltage Vset is reset by the command value voltage setting unit 14 in the upper and lower limit regions.

In step 106, the command value voltage Vse
t is sent to the command value output unit 15 to send the command value voltage Vno of this time.
The output power Pnow calculated in step 102 is sent to the calculated value storage unit 9 and replaced with the previous output power Ppast to update the data.

In step 107, the command value voltage Vset sent to the command value output section 15 is changed to the command value voltage Vnow of this time.
Is added to the control signal of the control circuit 5 to drive and control the inverter 3. Hereinafter, step 102 and subsequent steps are repeated.

As described above, the output power Pnow of the solar cell 2
Is not only compared with the previous output power Ppast, but is also compared with a value obtained by increasing or decreasing a predetermined set power Phist in which the dead band is set to the previous output power Ppast, so that the output characteristics of the solar cell 2 are meteorological conditions, etc. As a result, a stable output can be obtained without a large movement of the operating point even if it changes slightly. When the output power is within the dead band, the next command value voltage is changed from the current command value voltage Vnow to a predetermined step width Vstep.
The operating point is not fixed to a region larger than the open circuit voltage Voc of the P-V characteristic curve by setting only by decreasing the value. Further, by setting the upper and lower limits of the command value voltage Vset and giving the command value voltage Vset in a predetermined operation range early, the system starts up quickly and the maximum power control state can be reached early.

In the above embodiment, the PV characteristic curve having a convex shape that monotonously increases and decreases as shown in FIG. 3 has been described. However, it may not always be as shown in FIG. 3 depending on various conditions such as installation conditions of the solar cell 2. It does not always have a convex shape, and for example, as shown in FIG.
It may be a −V characteristic curve. In the case of such a P-V characteristic curve, the operating point was fixed in the flat band and the maximum output Pmax could not be obtained in the conventional method, but the operating point was fixed in the flat band in the method of the present invention. It is possible to reliably control the drive with the maximum output Pmax.

[0040]

According to the method of the present invention, even if the measured value of the output power becomes small and the execution of the maximum power follow-up control becomes difficult as the output power of the solar cell decreases at the time of low solar radiation, If the output power becomes equal to or lower than a predetermined set value without malfunctioning, the output voltage of the solar cell is secured as the drive lower limit of the inverter and the inverter is continuously driven. If the amount increases, proper maximum power tracking control can be executed promptly, and a highly reliable solar power generation system can be provided.

[Brief description of drawings]

FIG. 1 is a flowchart for creating a command signal for maximum power tracking control by the method of the present invention.

FIG. 2 is a block diagram showing the configuration of a command signal generation unit of a photovoltaic power generation system that executes the method of the present invention.

FIG. 3 is a PV of a solar cell for explaining the method of the present invention.
Waveform diagram showing the characteristic curve

FIG. 4 is a waveform diagram showing a PV characteristic curve for explaining a decrease in output of the solar cell under low solar radiation.

FIG. 5 is a waveform diagram showing another example of the PV characteristic curve of the solar cell.

FIG. 6 is a circuit diagram showing a schematic configuration of a solar power generation system.

FIG. 7 is a waveform diagram showing a PV characteristic curve of a solar cell for explaining a conventional method.

[Explanation of symbols]

 1 Solar power generation system 2 Solar cell 3 Inverter 4 System power supply 5 Control circuit P Output power Vcell Output voltage Vpast Previous command value voltage Vnow Current command value voltage Vset Command value voltage Ppast Last output power Pnow Current output power Phist setting Electric power Vstep Step width Pmin Set value

Claims (1)

[Claims] 1. A dead band for the current output power and the previous output power obtained from the solar cell by applying a command value voltage that increases or decreases with a predetermined step width to a control signal of an inverter connected to the solar cell. The predetermined set power that has been set is compared with the increased or decreased value, and based on the comparison result, the command value voltage is increased or decreased by a step width to set the next command value voltage, and the output power is within the dead band. Sometimes this command value voltage is reduced by a step width to set the next command value voltage, and in the maximum power tracking control method of the solar power generation system that drives the inverter so that the output of the solar cell is always maximized, When the output power of the solar cell decreases at the time of solar radiation and becomes less than a predetermined set value, regardless of the previous output power, the voltage that can be driven by the inverter is set as the lower limit of operation of the solar cell. Output voltage reduces the maximum power follow control method of a solar power generation system is characterized in that so as to continuously drive the inverter.