JPH0744251A - Power control device and power supply device using the same - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a power supply device having a control for obtaining the maximum output from a solar cell or the like which is a power source, the fluctuation of voltage and current of the solar cell is small, and the followability is good. To do. A solar power generation device comprising: a power conversion unit connected to a solar cell that is a power source; and a maximum output control circuit that controls the operation of the power conversion unit so that the output power of the solar cell is maximized. A power supply device characterized in that the voltage width or current width to be scanned when searching for the optimum operating point is 1% or more of the previously stored optimum operating point voltage or optimum operating point current. [Effect] The maximum output can be obtained with little fluctuation in voltage and current from the power supply and good followability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power control device and a power supply device using the power control device. More specifically, the present invention relates to a power control device capable of obtaining a maximum output from a power supply such as a solar cell and a power supply using the power control device. It relates to the device.

[0002]

2. Description of the Related Art In recent years, interest in the environment and energy has rapidly increased, such as depletion of fossil fuels such as oil and coal, global warming, and radioactive contamination due to nuclear accident. Under such circumstances, solar cells, wind power generation, thermoelectric power generation, etc. are expected from the world as renewable and inexhaustible clean energy sources.

In a device using such a power source,
A system in which a power source supplies power to an independent load such as a power source system or a secondary battery through a power conversion unit such as an inverter or a chopper is adopted. The solar cell, which is one of the power supplies, has voltage-current characteristics and voltage-power characteristics as shown in FIG. 2 as the output characteristics of the solar cell with the incident solar radiation amount as a parameter. Alternatively, the output greatly changes depending on the voltage, and the output becomes maximum at a certain operating point. (Here, the voltage value and the current value at the optimum operating point where the output from the power source is the maximum will be referred to as the optimum operating point voltage Vop and the optimum operating point current Iop.) The output from the solar cell is the amount of solar radiation. The solar cell output tends to increase as the amount of solar radiation increases. Focusing on the optimum operating point in each amount of solar radiation, the optimum operating point current Iop increases with an increase in the amount of solar radiation, while the optimum operating point voltage Vop does not change much with changes in the amount of solar radiation and is almost constant. .

In order to maximize the electric power supplied from the power source having such characteristics, it is necessary to set the operating point to the optimum operating point by controlling the operation of the power conversion means.

As one of the control methods for maximizing the output of the power source, there is a method of controlling the output voltage of the solar cell, which is the power source, with a constant voltage. This is the optimum operating point voltage Vo of the solar cell.
The fact that p becomes almost constant voltage with respect to changes in the amount of solar radiation is used. However, in the case of controlling with a certain constant voltage, for example, when the temperature changes, the optimum operating point voltage Vop changes, and the electric power taken out sharply drops from the maximum electric power, and another electric power can be effectively taken out from the solar cell. There is a problem that it does not exist. In addition, the output characteristics differ depending on the power source used, and setting the voltage poses a problem.For many years when the power source is used, the output characteristics of the solar cell, etc. can vary depending on the output characteristics of the power source itself, variations in the amount of solar radiation, and the degree of contamination. Since it is affected by various factors, it is very difficult to predict the set voltage.

As a method for overcoming such problems,
There is a control method that always follows the optimum operating point. In order to search for the optimum operating point of the solar cell, the voltage or current at the operating point is changed, and the optimum operating point is controlled based on the information such as the voltage or current obtained there. is there. As an example of this control method, there is a method in which the operating point of the solar cell is changed, the current and voltage are sampled at a plurality of operating points, and the voltage is controlled to the voltage at the maximum power level. No. 62-42213. Further, Japanese Patent Publication No. 63-57807 discloses a method in which the operating point is controlled to be changed so that the electric current differential value of the electric power obtained by changing the operating point of the solar cell becomes zero. Further, Japanese Patent Application Laid-Open No. 62-85312 discloses a method in which the operating point of a solar cell is changed from one operating point to another and the output powers of these two points are compared to determine the direction of change in the operating point voltage. Etc. are disclosed.

[0007]

However, conventionally, when the optimum operating point is always followed, the operating point voltage or the operating point voltage when changing the operating point of the power supply in order to obtain the information necessary to follow the optimum operating point. No study has been conducted on the magnitude of change in the operating point current.

However, the change amount of the operating point voltage or the operating point current affects the output power taken out from the power source, and since the slope of the output power is steep, the changing amount of the operating point voltage or the operating point current is large. It can be seen that the output power decreases. Moreover, the voltage and current of the solar cell and the like change greatly and are not stable.

This is an example of a conventional control method for obtaining the maximum power, in which the current and the voltage are sampled at a plurality of operating points and the voltage is controlled so that the voltage becomes the maximum power. , It was thought that the temperature change of the solar cell was very slow, so the sampling interval was sufficient for several tens of minutes or more, but the change of the weather was fast, and the temperature of the solar cell was strongly affected by the sunlight. However, if the voltage is kept constant for a certain period of time or longer, it is possible to obtain only a significantly reduced output power from the maximum output, deviating from the optimum operating point. Therefore, it is desirable to always follow the optimum operating point so that the maximum output is obtained. At this time, regarding the magnitude of the change in the operating point, the smaller the magnitude, the better the efficiency but the slower the response. On the other hand, the control circuit for controlling the power conversion means requires high-precision components if the magnitude of the change in the operating point is reduced, and an increase in cost cannot be avoided. From this, it was found that setting the magnitude of change in the operating point is an important issue.

Further, the operating point is controlled so that the current differential value of the electric power obtained by changing the operating point of the solar cell becomes zero, or the operating point of the solar cell is changed from one operating point to another. The same applies to the case of changing and comparing the electric powers of the two points to determine the change direction of the operating point voltage, and again, the setting of the magnitude of the change of the operating point is important.

The present invention has been made in order to solve the above-mentioned problems, and a power control device having a control for extracting the maximum output from the power supply and obtaining the maximum output with good tracking performance, and a power supply using the same. The purpose is to provide.

[0012]

The above-mentioned object is to provide an output control means for detecting an operating point of input power, an optimum operating point stored in the output control means or an operating point close to the optimum operating point and the operating point. And a voltage difference or a current difference at the compared operating points are stored, and the power control device controls the power converting means to 1% or more of the optimal operating point voltage or the optimal operating point current.

Further, the input power is achieved by a power supply device which is a solar cell, a wind power generator, or a thermoelectric generator.

[0014]

It is generally said that the smaller the change in the operating point, the more power is taken out from the solar cell.

With respect to this point, according to the research conducted by the inventors of the present application, a sampling period of 1/30 s, which is often used, is usually used.
Under the condition of ec, if the magnitude of change in the operating point is 1% of the value that the optimum operating voltage or the optimum operating current can take,
It has been clarified that the smaller the size, the more power can be taken out from the power supply, but if it is less than 1%, the power taken out from the power supply will decrease. As a result of detailed examination, it was found that the power reduction at 1% or less was due to a delay in response or an abnormal operation in searching for an optimum operating point. In other words, if the magnitude of the change in the operating point becomes smaller, the response will not only be delayed, but the output power of the power supply will decrease due to the case where the optimum operating point cannot be normally tracked due to the influence of solar radiation during the search. Occurs.

In the power control device of the present invention and the power supply device using the power control device, when the output control means sets the optimum operating point or a point closer to the optimum operating point, the optimum operating point or the optimum operating point is previously set. From the operating points that are determined to be close to each other, while setting the optimal operating point or the operating point that is determined to be closer to the optimal operating point, the operation that was determined to be the previous optimal operating point or the point closest to the optimal operating point. The optimum operating point voltage or current determines the voltage difference or current difference between the operating point with the most voltage or current difference from that point and the previous optimal operating point or the operating point determined to be close to the optimal operating point. By setting the value to be 1% or more of the obtained value, it is possible to suppress a response delay and an abnormal operation of the optimum operating point search, and to take out more electric power from the power supply.

[0017]

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

(Embodiment 1) FIG. 1 shows a block diagram of an example of a power device using a power control device according to the present invention. In this power supply device, the output terminal of the solar cell 1 which is the power supply is connected to the inverter 3 of the power conversion means 2, and the AC output of the inverter 3 is connected to the AC power system 10 via the transformer 9. As a switching element used in the inverter 3, an IGBT (Insulate) is used.
d Gate Bipolar Transisto
r), GTO (Gate Turn Off), MOS
There are FETs. The output voltage and output current of the power supply 1 are
It is detected and obtained by the voltage detecting means 6 for detecting the voltage of the output control means 5 and the current detecting means 7 for detecting the current. The detected voltage value Vs output from the voltage detection means 6 and the detected voltage value Is output from the current detection means are MPP.
It is input to the T control circuit 8. The MPPT control circuit 8 includes an A / D conversion circuit 11 that captures a voltage value Vs and a current value Is of a power source into a digital amount, and a storage circuit that stores the voltage value Vs and the current value Is captured by the A / D conversion circuit 11. 12, a voltage command circuit 13 that reads data from the memory circuit 12, calculates a reference voltage Vref, and outputs a command voltage, and a command voltage output from the voltage command circuit 13 to a command voltage V ^* of the subsequent analog amount ^. Output as
It is composed of the A / A conversion circuit 14, and more specifically, can be easily realized by a one-chip microcomputer or DSP and outputs the command voltage V ^* . The command voltage V ^* and the detected voltage value V output by the MPPT control circuit 8 of the maximum output control means
The difference of s is input to the gate control circuit 4 of the power conversion means 2. The gate control circuit 4 controls the inverter 3 so that the detected voltage value Vs becomes the command voltage V ^* . Specifically, the gate pulse applied to the switching element in the inverter 3 is controlled by changing the on / off duty ratio of the gate pulse by means of instantaneous current value control or sinusoidal triangular wave comparison.

In the power device having the above structure, as a method of controlling the maximum output, a method of changing the operating points of the solar cell 1 at a plurality of points and controlling the output power so that the output voltage becomes the maximum operating point voltage Take The maximum output control algorithm of this power device will be described in more detail with reference to FIGS. 3 and 4. The processing described below is repeated to follow the maximum output point. Here, in the MPPT control circuit 8, it is determined that the optimum operating point or a point closer to the optimum operating point, and the operating point set there is referred to as a reference point. Further, when setting the reference point in the output control means 5, an operating point having the longest distance from the previous reference point during the period from the setting of the previous reference point to the setting of the new reference point, The distance of the previous reference point will be referred to as the maximum reference point separation width. Also, at this time,
The voltage width is called the maximum reference point isolation voltage width ΔVs, and the current width is called the maximum reference point isolation current width ΔIs.

This control algorithm is as shown in FIG. First, as an initial setting process, the maximum reference point isolation voltage width ΔVs is set in advance to a value of 2% of the value considered as the optimum operating point voltage Vop. Further, the current voltage is read, and this is set as the reference voltage Vref, and the current operating point is set as the reference point. After performing this processing, the subsequent processing is repeated.

First, the command voltage V ^{* is set} to the reference voltage Vref.
Centered on the maximum operating point voltage Vop, the maximum reference point separation variation width ΔVs, which is 2%, is changed to positive or negative, and the voltage Vs and the current Is at the plurality of operating points are sequentially changed to (Vs ₁ , Is).
₁ ), (Vs ₂ , Is ₂ ) ... In this example, the change of the command voltage V ^* is initially smaller than the reference voltage Vref by 2% of the optimum operating point voltage Vop from the reference voltage Vref, that is, by the maximum reference point isolation voltage width ΔVs. The voltage Vs _{3 is} reduced to the voltage Vs ₂ , and then the voltage Vs ₃ is larger than the reference voltage Vref by 2% of the optimum operating point voltage Vop, that is, the maximum reference point isolation voltage width ΔVs.
Up to. During this change, the voltage Vs and the current Is are read and stored at a plurality of operating points. In this embodiment, the voltage Vs and the current Is at the three operating points are set.
Read and memorize.

Next, the read voltage Vsi and current Is
From i, the power Psi at each point is calculated by the following formula.

Psi = Vsi × Isi From the calculated power Psi, the point at which the power becomes maximum is searched for, and the voltage at the operating point at which the power becomes maximum is taken as the next reference voltage Vref. In this case, the voltage with the maximum power is Vs ₃ , and this voltage value is set to the next reference voltage Vref.
And The reference voltage Vref determined in this way is
A new reference point is set with the command voltage V ^* .

The above process is repeated to follow the maximum output point so that the output becomes maximum.

Here, the relationship between the output of the solar cell which is the power source and the maximum reference point isolation voltage width ΔVs will be described. FIG. 5 is a graph showing the relationship between the maximum reference point isolation voltage width ΔVs and the solar cell output power amount under a certain sunlight, and the horizontal axis is the ratio of the maximum reference point isolation voltage width ΔVs to the optimum operating point voltage Vop. The vertical axis represents the amount of electric power obtained from the solar cell for a certain period of a certain amount of solar radiation, as a ratio (electric power efficiency) to the maximum amount of electric power that can be taken out during the period.
When the output is alternating current, at least one cycle time (20 ms for 50 Hz, 16.6 ms for 60 Hz) is required for one change of the operating point to measure the power. Therefore, in the search method that requires three changes, 1
The search time per turn requires 60 ms in a system that outputs 50 Hz alternating current, and 50 ms or more in a system that outputs 60 Hz alternating current. If the search time is longer than this, the load may be an AC system. In FIG. 5, the sampling period is 33.3 ms and the search time is 100 ms.

From FIG. 5, when the maximum reference point isolation voltage width ΔVs is 1%, the power amount efficiency is 99.96%, and when the maximum reference point isolation voltage width ΔVs is less than 1%, the power amount efficiency sharply decreases. I understand that If the sunlight to the solar cell is almost constant, the smaller the maximum reference point isolation voltage width ΔVs, the finer the search, so the energy efficiency is better. However, it is the maximum when the sunlight changes like actual sunshine. If the reference point isolation voltage width ΔVs is too small, an abnormal operation may occur in tracking the optimum operating point and deviate from the optimum operating point.
Further, since the response is delayed, the electric energy efficiency is lowered as shown in FIG.

The maximum reference point isolation voltage width ΔVs is 1% to 2
Although the power efficiency is reduced even in the range of%, the degree of reduction is small and a high power efficiency of 99.96% or more is obtained.

Further, the maximum reference point isolation voltage width ΔVs is 2%.
If the above is satisfied, the larger the maximum reference point isolation voltage width ΔVs, the lower the power amount efficiency. For example, the maximum reference point isolation voltage width ΔVs is 6% and the electric energy efficiency is 99.9%. Therefore, in order to extract more power from the solar cell, it is desirable to set the maximum reference point isolation voltage width ΔVs to 6% or less in the search algorithm of this embodiment.

From the above, the maximum reference point isolation voltage width Δ
By setting Vs to 1% or more of the optimum operating point voltage Vop,
10 bits is sufficient as the resolution of the A / D conversion circuit, and the maximum power can be taken out from the solar cell without using expensive high-precision components such as the resolution of 12 bits.

The maximum reference point isolation voltage width ΔVs is, for example, 2% of the optimum operating point voltage Vop, but since the optimum operating point voltage Vop changes under various conditions as described above, the reference voltage is set. The maximum reference point isolation voltage width ΔVs may be set for each degree, but the magnitude of change in the optimum operating point voltage Vop due to solar radiation fluctuations or temperature changes is considerably smaller than the optimum operating point voltage Vop. The operating point voltage Vop may be regarded as a constant value and the maximum reference point isolation voltage width ΔVs may be set as a constant value, which does not depart from the gist of the present invention. Further, when the magnitude of the optimum operating point voltage Vop is known, the maximum reference point isolation voltage width ΔVs may be set in advance. Otherwise, the voltage value when operating at the optimum operating point is set. It is desirable to set it to the original.

(Embodiment 2) First, as the initial setting process, the maximum reference point isolation voltage width ΔVs is set. The maximum reference point isolation voltage width ΔVs is set to 2% of the value considered as the optimum operating point voltage Vop. At this time, as described in the first embodiment, the magnitude of change in the optimum operating point voltage Vop due to variations in solar radiation, temperature changes, etc. is determined by the optimum operating point voltage Vo.
Since it is smaller than p, the optimum operating point voltage Vo
Assuming that p is constant, the maximum reference point isolation voltage width ΔVs is set as a constant value in advance. Further, in order to set the current operating point as the reference point, the voltage is read and used as the reference voltage Vref. After the above initial processing is completed, the subsequent processing is repeated.

First, the command voltage V ^* is set to a voltage value obtained by adding the maximum reference point isolation voltage width ΔVs to the reference voltage Vref (V
^* ← Vref + ΔVs). The voltage Vs ₁ and the current Is ₁ at this time are read and stored. Next, the command voltage V ^*
Is a voltage value obtained by subtracting the maximum reference point isolation voltage width ΔVs from the reference voltage Vref (V ^* ← Vref + ΔVs). The voltage Vs ₂ and the current Is ₂ at this time are read and stored.

Next, using the voltages and currents of the two operating points that have just been read, Vav, which is the average voltage of the two operating points,
The average current Iav between the two operating points, ΔV, which is the difference between the voltages at the two operating points, and ΔI, which is the difference between the currents at the two operating points, are calculated. That is, the calculation represented by the following equation is performed.

Vav = (Vs ₁ + Vs ₂ ) / 2 Iav = (Is ₁ + Is ₂ ) / 2 ΔV = Vs ₁ −Vs ₂ ΔI = I s ₁ −Is ₂ Vav, Iav, ΔV thus obtained From ΔI, the electric current differential value dP / dI is calculated by the following equation.

DP / dI = Vav + Iav × (ΔV / ΔI) Here, the change in the previous operating point is a voltage change, which is 4% of the optimum operating point voltage Vop, which is very small. / DI can be regarded as a current differential value of electric power.

When the operating point reaches the optimum operating point, the current differential value dP / dI of the electric power obtained here becomes zero, and the output voltage of the solar cell becomes maximum. Electric current differential value dP
When / dI is zero, it is at the optimum operating point, so the reference voltage V
ref is not changed. When the current differential value dP / dI of electric power is larger than zero, the current may be increased, that is, the reference voltage Vref may be decreased, and when dP / dI is smaller than zero, the current may be decreased, that is, the reference voltage Vref.
It suffices to increase ref. The amount of change in the reference voltage Vref is the maximum reference point isolation voltage width ΔVs. This can be summarized as follows.

When dP / dI = 0, Vref remains as it is. When dP / dI> 0, Vref ← Vref−ΔVs When dP / dI <0, Vref ← Vref + ΔVs Value V ^*
And set a new reference point. By repeating such processing, the optimum operating point is tracked and the output is maximized.

Here, the relationship between the solar cell output and the maximum reference point isolation voltage width ΔVs will be described. FIG. 7 is a graph showing the relationship between the maximum reference point isolation voltage width ΔVs and the solar cell output in this control method that maximizes the output power,
The horizontal axis represents the maximum isolation voltage width ΔVs as a ratio to the optimum operating point voltage Vop, and the vertical axis represents the maximum amount of electric power output from the solar cell during a certain period under sunlight. Is expressed as a ratio to (power efficiency). Note that this embodiment also has a control system similar to that of the first embodiment.

According to FIG. 7, the maximum reference point isolation voltage width ΔV
When s is 1%, the power efficiency is 99.9%, and when the maximum reference point isolation voltage width ΔVs is smaller than 1%, the power efficiency is significantly reduced. This is because the maximum reference point isolation voltage width ΔVs is small, so the optimum operating point search may cause an abnormal operation due to the influence of solar light fluctuations, and the power efficiency is reduced due to the slow response.

The maximum reference point isolation voltage width ΔVs is 1% to 2
Although the amount of power consumption is decreased in the range of slightly higher than%, the degree thereof is small and the amount of power efficiency is 99.90% or more.

When the maximum reference point isolation voltage width ΔVs is 2% or more, the amount of electric power sharply decreases as the magnitude increases. For example, the maximum reference point isolation voltage width ΔVs is 5% and the electric energy efficiency is 99.90%, and the maximum reference point isolation voltage width ΔVs is required to extract the maximum power from the solar cell.
Is preferably about 5% or less. In this case, the maximum amount of electric power can be extracted when the maximum reference point isolation voltage width ΔVs is 2.5%.

As described above, the maximum reference point isolation voltage width ΔV
By setting s to be 1% or more of the optimum operating point voltage Vop, a large amount of electric power can be taken out from a solar cell or the like which is a power source by using an inexpensive component having a not so high resolution.

In the above example, the amorphous solar cell is used as the solar cell, but the voltage-power characteristics of the amorphous solar cell are different from those of the crystalline solar cell with respect to the voltage change near the optimum operating point. There is little change in output power, and maximum output can be extracted even more efficiently.

(Embodiment 3) Still another example of the power supply device according to the present invention will be described. This power supply device has a configuration as shown in FIG. 8, in which the output end of the solar cell 1 which is the power supply is connected to the chopper 15 that outputs DC power, and the output end of the chopper 15 is connected to the DC load 16. It is connected. The maximum output control circuit 5 is the same as the first embodiment or the second embodiment.
The configuration is the same as, and control is performed so that the maximum output is obtained from the solar cell 1. Also. In this power supply,
As a method of controlling the maximum output, as in the first embodiment, a method is used in which the operating points of the solar cell 1 are changed at a plurality of points and the output power is controlled so that the voltage at the operating point becomes the maximum.

The relationship between the power efficiency of the solar cell output and the maximum reference point isolation voltage width ΔVs in the power supply device having such a configuration is the same as that described in the first embodiment, and the maximum reference point isolation voltage width ΔVs is 1. If it is less than%, the energy efficiency is lowered. Therefore, by setting the maximum reference point isolation voltage width ΔVs to 1% or more of the optimum operating point voltage Vop, the maximum electric power can be taken out from the solar cell without using expensive high-precision parts.

By the way, in this example, the power converting means 2 outputs a direct current, and the search time can be shortened and the response can be made faster than the output of an alternating current of 50 Hz or 60 Hz, but the control system has a high-speed response. Will be required and the cost will be higher.

[0047]

As described above, the output control means for detecting the operating point of the input power is compared with the optimum operating point stored in the output controlling means or an operating point close to the optimum operating point and the operating point. , 1% of the optimum operating point voltage or the optimum operating point current storing the voltage difference or the current difference of the compared operating points
Controlling the power conversion means as described above Even though the control system is composed of inexpensive parts with a resolution that is not so high by the power control device, it is possible to extract power very efficiently from the solar cell, which is the power supply. I can.

Further, by using a non-single crystal semiconductor for the solar cell, there is little power reduction when the operating point is changed, and the power of the solar cell can be extracted more efficiently.

[Brief description of drawings]

FIG. 1 is a block diagram of a power supply device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a graph of voltage-current characteristics and voltage-power characteristics of a solar cell.

FIG. 3 is a flowchart of maximum output control according to an embodiment of the present invention.

FIG. 4 is a diagram showing a time chart of an example according to the present invention.

FIG. 5 is a diagram of ΔVs / Vop-electric energy efficiency characteristics of an example according to the present invention.

FIG. 6 is a flow chart of maximum output control of another embodiment according to the present invention.

FIG. 7 shows ΔVs / Vop- of another embodiment according to the present invention.
It is a figure of an electric energy efficiency characteristic.

FIG. 8 is a diagram showing another power supply device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solar cell 2 Power conversion means 3 Inverter 4 Gate control circuit 5 Maximum output control means 6 Voltage detection means 7 Current detection means 8 MPPT control circuit 9 Transformer 10 AC power system 11 A / D conversion circuit 12 Memory circuit 13 Voltage command circuit 14 D / A conversion circuit 15 Chopper 16 DC load

Claims (3)

[Claims] 1. An output control means for detecting an operating point of input power, and an operating point stored in the output controlling means or an operating point close to the optimal operating point are compared with the operating point, and the comparison is made. A power control device, characterized in that the power conversion means is controlled to 1% or more of the optimum operating point voltage or the optimum operating point current that stores the voltage difference or the current difference at the operating point. 2. The input power is a solar cell, a wind power generator,
The power supply device according to claim 1, wherein the power supply device is a thermoelectric generator. 3. The power supply device according to claim 2, wherein the solar cell is an amorphous semiconductor.