JPH10207560A - Solar light power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform control so that a maximum electric power follow-up point does not deviate greatly from an optimum operation point even in the case of abrupt variation in the intensity of the sunshine and to effectively utilize the output power of a solar battery by controlling an operation point so that an AC output current command value or electric energy on the input or output side of a power transformer increases. SOLUTION: The DC output voltage of the solar battery 1 is denoted as Vdc, the DC current as Idc, the AC output voltage of an inverter 2 as Vac, and the AC current as Iac. The AC output current Iac corresponding to an AC output current command Iq* flows so that the DC output voltage Vda has a specified DC output voltage command value Vdcref*. When sunshine conditions change to change the output DC voltage Vdc of the solar battery 1, the output voltage command value Vdcref* is also altered to generate a new AC output current command value Iq*. This operation is repeated to enable control following up the best sunshine conditions at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic power generation system in which DC power generated by a solar cell is converted into AC power by a power converter composed of an inverter or the like and supplied to a load as an independent power source, or generated power. The present invention relates to a photovoltaic power generation system in which not only a load but also a surplus power flows backward to a power system, and more particularly to a photovoltaic power generation system that controls the generated power of a solar cell to be maximized in weather conditions at that time.

[0002]

2. Description of the Related Art A photovoltaic power generation system mainly comprises a solar cell and a power converter such as an inverter.
It converts solar light energy into electrical energy and supplies it to the load. This system can be roughly divided into two types. One is a system that includes a storage battery for charging the output power of the solar cell in the daytime and can be used at night.

The other is a system without a storage battery. When the amount of power generated by the solar cell is smaller than the load, the system supplies the insufficient power from the power system. Reverse power flow to the side and cut off from the power system during the absence of sunlight. This method can sell surplus power to a power company, which is a great advantage for users.

[0004] Since any method uses a solar cell,
It is the same that the amount of power obtained varies depending on the amount of solar radiation and temperature. Therefore, conventionally, a photovoltaic power generation system has been proposed in which the output power of a solar cell is measured and the power conversion device is controlled to perform maximum power tracking control that maximizes the use of solar energy.

The maximum power follow-up control is disclosed in Japanese Patent Publication No. 5-6872.
No. 2, Japanese Patent Application Laid-Open No. 60-234468, and many others have been filed, and their outline is as shown in FIG. DC power generated by the solar cell 1 is converted into AC power by a power converter 2 such as an inverter, and supplies power to a load and is connected to a power system 4.

A sensor 6 for measuring the DC output voltage of the solar cell 1, a current sensor 10 for measuring the output current, and a current sensor 7 for measuring the output current on the AC side are provided between the solar cell 1 and the power system 4. And voltage sensors 8 and 9 for measuring the output voltage.

[0007] In the case of Japanese Patent Publication No. Hei 5-68722, in order to extract the output power of the solar cell 1 to the maximum, the output values of the voltage / current sensors 6 and 10 on the DC side are multiplied and converted into an electric energy, and the value is converted to an electric energy. Control is performed to maximize this. Specifically, the output voltage of the solar cell 1 is slightly increased and the amount of power at that time is obtained. If the amount of change is in the increasing direction, the reference value is maintained in the increasing direction. Invert in the decreasing direction.

In the case of Japanese Patent Application Laid-Open No. 60-234468, the output value of the voltage / current sensors 7 and 8 on the AC side is multiplied and converted into electric energy, and the operating point of the solar cell is increased in the direction of increasing the electric power. It is shifted to maximize the amount of AC power. Although these methods can follow the same or small changes in the solar radiation conditions, the tracking operation may become unstable with rapid changes in the solar radiation intensity, and the processing method at that time is mentioned. Not.

[0009]

In the above conventional example, the maximum power follow-up control for a sudden change in the solar radiation condition is not sufficient. In particular, when the solar radiation intensity increases sharply, the maximum power point is shifted from the optimum operating point. There is a problem that the output power of the solar cell is so far away that the output power of the solar cell cannot be used effectively.

An object of the present invention is to control the maximum power follow-up point so that it does not greatly deviate from the optimum operating point even when the solar radiation intensity changes abruptly, and to effectively use the output power of the solar cell. .

[0011]

In order to achieve the above object, the present invention provides an AC output current command value for determining an AC output current of a power converter, or an input or output side of a power converter. Electric energy and operating point of solar cell (operating voltage)
The operating point is controlled so that the AC output current command value or the electric energy on either the input side or the output side of the power converter is increased using the DC output voltage command value that determines

Further, when the operating point has increased or decreased a predetermined number of times in the same direction, the moving direction is forcibly reversed, and thereafter, the AC output current command value or the electric power on either the input side or the output side of the power converter. The control for increasing the amount is repeatedly performed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a control block diagram, FIG. 2 is a schematic flow chart of the maximum power follow-up control, FIG. 3 is a voltage / power characteristic example of a solar cell for explaining a control operation according to the present invention, and FIG. FIG. 5 shows an example of voltage / power characteristics of a solar cell for explaining the maximum power follow-up control.

[0015] As shown in FIG.
The DC output power of the solar cell 1 is converted into AC power by the inverter 2 and power is supplied to a load (not shown) via the switch 41. The inverter 2 includes a capacitor 21 connected between input terminals and a bridge-connected 4
A control pulse is supplied to the switching elements 22, 23, 24, 25, the diodes 26, 27, 28, 29 connected in anti-parallel to the switching elements 22 to 25, and the switching elements 22 to 25, and A pulse width control device 30 for performing pulse width control is provided.

Recently, when the condition of the power characteristic is satisfied, surplus power after use in a load can be reversely flowed to the power system 4 side. The condition of the power characteristic is determined by measuring the values of the voltage sensors 8 and 9 and the current sensor 7 by the automatic voltage control device 5 through the interface board (I / F) 31, and according to the state, the power generation is performed. It opens and closes the protection device 3 inserted between the system and the power system 4. Therefore, the microcomputer (CPU) 5
1. The automatic voltage controller 5 including the analog-digital converter 52 and the power supply 53 determines whether the output of the inverter 2 is coordinated with the power system side 4 in addition to the protection relation, and Is also started and stopped.

The solar cell 1 has, for example, output characteristics as shown in FIG. The horizontal axis represents the DC output voltage Vdc of the solar cell 1, and the vertical axis represents the power Pdc. There is such a characteristic that the power Pdc also increases until the voltage Vdc reaches a certain value, and the power Pdc decreases from a certain value. In other words, when the DC power Vdc is in the area A with the point Pmax at which the DC power Pdc reaches the maximum value, the DC power Vdc increases as the DC voltage Vdc increases.
Is in the region B, it decreases as the DC voltage Vdc increases.

The AC voltage Vac is controlled to a constant voltage, for example, 100 (V) in order to link with the power system 4. Therefore, even if the power Pdc on the DC side changes, only the output current Iac changes on the AC side, and the DC output voltage Vdc is controlled so that the maximum power Pmax is obtained under the temperature and solar radiation intensity conditions at that time. .

Therefore, although the magnitude of the maximum power Pmax and the DC voltage Vdc at that time vary depending on the solar radiation intensity and the temperature, the DC output voltage Vdc can be controlled so as to always follow the maximum power point Pmax depending on weather conditions. If this is the case, efficient system operation can be achieved.

FIG. 1 is a control block diagram for explaining the present invention. Based on the DC output voltage command value Vdcref * for setting the DC output voltage Vdc and the value of the DC output voltage Vdc of the solar cell 1, the digital voltage current command value Iq for setting the AC side output current by the automatic voltage controller (AVR). * Is calculated. In consideration of the current control device (ACR) using the AC output current command value Iq * and the voltage phase θ on the power system side 4 and the like, the inverter 2 is controlled by the pulse width modulation device (PWM) to obtain a desired AC. Outputs output voltage and current.

Now, the DC output voltage of the solar cell 1 is Vdc,
DC current is Idc and AC output voltage of inverter 2 is Va
c, Assuming that the AC current is Iac, the DC output power Pdc and the AC output power Pac are expressed as follows.

Pdc = Vdc × Idc Pac = Vac × Iac Pac = Pdc × η (η: inverter efficiency) Therefore, the DC output voltage Vdc is equal to the output voltage command value Vdcr.
ef * and the AC current Iac are determined by the AC output current command value Iq *, respectively. The AC output current command value I is set so that the DC output voltage Vdc becomes the specified DC output voltage command value Vdcref *.
The size of q * is determined. That is, the AC output current Iac corresponding to the AC output current command value Iq * flows. When the solar radiation condition changes and the output DC voltage of the solar cell changes, the output voltage command value Vdcref * is also changed, and a new AC output current command value Iq * is generated. By repeating this operation, it is possible to perform control that always follows the best solar radiation condition. The direction in which the DC output voltage Vdc is changed differs between the region A and the region B as shown in FIG.

The DC voltage command value Vdc depends on whether or not the value of the AC output current command value Iq * has changed from the previous set value.
The AC output current command value Iq * is maximized by applying feedback to ref * and repeating the operation, so that the solar cell 1
The maximum power can be extracted from These controls are executed by a filter function, a peak value judgment function, and the like.

In the case of the area A, the DC output voltage command value Vdc
When ref * is increased and the DC voltage Vdc is increased, the DC output current command value Iq * is increased and the automatic voltage regulator is automatically controlled so as to increase the AC current Iac. Conversely, in the case of the region B, the DC output voltage command value Vdcref * is increased, and if the DC output voltage Vdc increases, the output current command value is increased.
Iq * is reduced and the AC output current Iac is controlled by the automatic voltage controller to decrease.

When the output voltage command value Vdcref * is set to a certain value, the voltage Vdc of the solar cell 1 is changed to the voltage command value Vdcref while the current command value AC output current command value Iq * is changed by the automatic voltage controller (AVR). Operate repeatedly to be the same as *. The AC output current command value Iq * when the DC output voltage command value Vdcref * and the DC output voltage Vdc of the solar cell become the same is the AC current Iac for the DC output voltage command value Vdcref * at that time.

By repeating this operation several times,
It is possible to obtain the AC output current command value Iq * at the temperature and the sunshine intensity at that time, that is, the maximum power Pmax.
If the weather conditions fluctuate, the DC voltage Vdc changes, and the AC output current command value Iq * also changes, thereby changing the DC output voltage command value Vdcref *. By repeating the same control again, The maximum power Pmax is obtained.

As described above, it is possible to extract the maximum power by monitoring and controlling the AC output current command value Iq * without measuring the DC or AC current value. Since the AC output current command value Iq * is a digital value generated by the control device 5 based on the deviation between the DC output voltage command value Vdcref * and the DC voltage Vdc, noise is lower than an analog value performed using a sensor or the like. And control accuracy can be improved. Also, compared to a conventional device that measures the current to extract the maximum power, the number of sensors can be reduced and the cost can be reduced.

FIG. 2 is a control flow showing the above description. In the figure, N indicates the number of times when the moving direction is the same, and M indicates the upper limit of the number of times of moving N. First, the voltage of the solar cell 1 is read, and proportional integral (PI) control is performed by the automatic voltage controller (AVR) of FIG. 1 to obtain an AC output current command value Iq * for determining the AC output current of the inverter 2.

It is determined whether the obtained AC output current command value Iq * is larger or smaller than the previous AC output current command value Iq *, and if it is smaller, the moving direction flag is set to the opposite direction. , A small voltage ΔVdcref * (here, 1 V) is added to the DC output voltage command value Vdcref *, and the DC output voltage Vdc of the solar cell 1 is detected again.

At this time, whether the minute voltage is applied or subtracted is determined from the maximum power point Pmax in the characteristics shown in FIG.
This is determined depending on whether the solar cell voltage Vdc is operating in a large region or a small region. This is performed by the filter and the peak value judging means.

If the current AC output current command value Iq * is larger than the previous time, it is determined that the output power of the solar cell 1 is large, and a flag is set to make the moving direction of the operating point the same. Further, the number of movement directions N is counted, and it is determined whether the number of movements is larger or smaller than the set number of times M. Thereafter, the minute voltage ΔVdcref * is added to the DC output voltage command value Vdcref * that determines the voltage value of the solar cell, and the DC output voltage of the solar cell 1 is detected again.

FIG. 3 shows the operation according to the flow of FIG. FIG. 3 shows an example of voltage-power characteristics for explaining the operation of the present invention when the solar radiation intensity changes abruptly. When the solar radiation intensity is Pn1, Pn2, Pn3, generally, the maximum power point Pmax is shifted slightly.
For example, if the solar irradiance changes to Pn1 during the control of the solar irradiance Pn2 from the point to the point, the value of the point appears in the control and the power decreases, so that the apparent movement direction is reversed. Judgment is made, and then the direction of movement is reversed to move to the point.

If the solar radiation intensity subsequently increases to Pn2, Pn3, the control is performed for the same reason as the point,.
And moves away from the maximum power point Pmax.
In the embodiment of the present invention, in order to prevent this, when the moving direction of the control point is continuously the same, for example, by having a function of reversing the moving direction once every several times, the power is inverted at the time of the reversal. Modified in an increasing direction, avoiding a situation where the vehicle is traveling in the opposite direction.

In the configuration of the above embodiment of the present invention, since the current command value Iq * generated by the microcomputer of the control device 5 is used,
The output current measuring means of the solar cell 1 in the conventional configuration can be omitted.

FIG. 6 shows the output characteristics of the solar cell 1 when the solar irradiance changes, and FIG. 7 shows the output characteristics of the solar cell when the temperature of the module changes. Also in this case, according to the above control, control is performed so as to always maintain the maximum power output point indicated by the dotted line.

FIGS. 8 and 9 show, as a judgment amount, a voltage and a current on the input side or the output side of the conventionally used inverter 2 instead of the AC output current command value Iq *. It is a control block diagram and a control flow showing an embodiment using a converted value.

As already described with reference to FIG. 1, the automatic voltage control device (A) is obtained from the DC output voltage command value Vdcref * for setting the DC output voltage Vdc and the DC output voltage Vdc of the solar cell 1.
VR), a digital command value Iq * for setting the output current on the AC side is calculated. In consideration of the current control device (ACR) using the AC output current command value Iq * and the voltage phase θ on the power system side 4 and the like, the inverter 2 is controlled by the pulse width modulation device (PWM) to obtain a desired AC. Outputs output voltage and current.

The power amount calculating means PC calculates the value of the power amount Pac * based on the AC output currents Iac and Vac of the inverter 2.
Feedback is applied to the DC voltage command value Vdcref * depending on whether or not it has changed from the previous set value, and the power amount Pac * is maximized by repeating the operation, and the maximum power is always taken out of the solar cell 1.

When the output voltage command value Vdcref * is set to a certain value, the voltage Vdc of the solar cell 1 is changed to the voltage command value Vdcref while the current command value AC output current command value Iq * is changed by the automatic voltage controller (AVR). Operate repeatedly to be the same as *. The AC output current command value Iq * when the DC output voltage command value Vdcref * and the DC output voltage Vdc of the solar cell become the same is the AC current Iac for the DC output voltage command value Vdcref * at that time.

By repeating this operation several times,
It is possible to obtain the AC output current command value Iq * at the temperature and the sunshine intensity at that time, that is, the maximum power Pmax.
If the weather conditions fluctuate, the DC voltage Vdc changes, and the AC output current command value Iq * also changes, thereby changing the DC output voltage command value Vdcref *. By repeating the same control again, The maximum power Pmax is obtained.
As described above, by controlling while monitoring the electric energy Pac *, it is possible to extract the maximum electric power.

The AC output current command value Iq * is a digital value generated by the control device 5 based on the deviation between the DC output voltage command value Vdcref * and the DC voltage Vdc. Compared with this, noise is less and control accuracy can be improved.

In FIG. 7, N indicates the number of times when the moving direction is the same, and M indicates the upper limit of the number of times of moving N. First, solar cell 1
Voltage is read, and the automatic voltage controller (AVR) shown in FIG.
Performs proportional integral (PI) control to calculate the electric energy Pdc *.

The calculated power amount Pdc * is the same as the previous power amount Pdc *
It is determined whether it is larger or smaller than the above. If smaller, the flag of the moving direction is set to the opposite direction, and a small voltage ΔVdcref * (here, 1 V) is added to the DC output voltage command value Vdcref *. Again, the DC output voltage Vd of the solar cell 1
c is detected.

At this time, whether the minute voltage is applied or subtracted is determined from the maximum power point Pmax in the characteristic shown in FIG.
This is determined depending on whether the solar cell voltage Vdc is operating in a large region or a small region. This is performed by the filter and the peak value judging means.

If the current power amount Pdc * is large, it is determined that the output power of the solar cell 1 is large, and a flag is set to make the moving direction of the operating point the same. Further, the number of movement directions N
Is counted, it is determined whether it is more or less than the set number of times M, and if less than the set number of times, the moving direction is left as it is,
If the number is large, the moving direction is forcibly reversed. Then, the DC output voltage command value Vdcref * that determines the voltage value of the solar cell,
The DC output voltage of the solar cell 1 is detected again by adding the minute voltage ΔVdcref *. Also in this embodiment, the operating point control method is the same as that shown in FIG. 3, but the stability is improved with respect to the determination because the power amount is used directly. In the above embodiment, the power on the output side of the inverter 2 is obtained, but it is also possible to control based on the power on the input side.

When the current command value is used, since the current command value is a digital quantity, there are advantages that the stability is high and that a DC current sensor is not required. However, a difference may occur between the current command value and the value of the AC current actually flowing due to a shift in response speed or the like. In the method of measuring the point power, the accuracy can be expected to be improved only by increasing the value in order to measure the actual power.

[0047]

According to the configuration of the present invention, the maximum power point can be stably followed even if the weather conditions, especially the solar radiation intensity fluctuate rapidly.

[Brief description of the drawings]

FIG. 1 is a control block diagram for explaining an embodiment of the present invention.

FIG. 2 is a schematic diagram of a control flow for explaining the present invention.

FIG. 3 is a voltage-power characteristic diagram for explaining the present invention.

FIG. 4 is a system configuration diagram for explaining the present invention.

FIG. 5 is an example of voltage / power characteristics of a general solar cell.

FIG. 6 is a system configuration diagram showing another embodiment of the present invention.

FIG. 7 is a schematic diagram of a control flow showing another embodiment of the present invention.

FIG. 8 is a control block diagram for explaining another embodiment of the present invention.

FIG. 9 is a schematic diagram of a control flow showing another embodiment of the present invention.

FIG. 10 is a diagram showing a system configuration example for explaining a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solar cell, 2 ... Inverter, 3 ... Protection device, 5 ... Control device, 6 ... DC voltage sensor.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Keijiro Sakai 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] 1. A solar cell, a power converter that converts DC power generated by the solar cell into AC power and supplies the AC power to a load, and outputs an output current of the power converter to weather conditions such as solar radiation intensity and temperature. In the photovoltaic power generation system, wherein the output power of the solar cell is controlled so as to be maximized under the weather conditions at that time, a detection means for detecting the DC output voltage of the solar cell, and the DC output voltage Generating means for generating a DC voltage command value for controlling the DC output voltage command value and a DC output voltage value of the solar cell according to a difference between the DC output voltage value and the DC output voltage value of the solar cell. Generating means for generating an AC output current command value that is a control amount, wherein the AC output current command value increases when the DC output voltage command value is changed in a first direction by a predetermined amount. The photovoltaic power generation system is characterized in that the direction is changed in the same direction if the direction is changing, and the direction is changed in the opposite direction if the direction is decreasing. 2. The method according to claim 1, wherein when the DC output voltage command value is changed in a first direction by a predetermined amount, the DC output voltage command value is changed in the same direction if the AC output current command value increases. In the case of, a photovoltaic power generation system that changes in the opposite direction, and forcibly operates in the opposite direction when the AC output current command value is continuously operated in the same direction a specific number of times, and thereafter controls in the increasing direction. 3. A solar cell, a power converter that converts DC power generated by the solar cell into AC power and supplies the AC power to a load, and outputs an output current of the power converter to weather conditions such as solar radiation intensity and temperature. In the photovoltaic power generation system, wherein the output power of the solar cell is controlled so as to be maximized under the weather conditions at that time, a detection means for detecting the DC output voltage of the solar cell, and the DC output voltage Generating means for generating a DC voltage command value for controlling the DC output voltage command value and control for determining an AC output current of the power converter according to a difference between the DC output voltage command value and the DC output voltage value of the solar cell. Generating means for generating an AC output current command value, and detecting means for detecting an amount of output power on an inlet side or an output side of the power converter, wherein the DC output voltage When the command value is changed in the first direction by a predetermined amount, the power value is changed in the same direction if the power amount is increasing, and is changed in the opposite direction if the power amount is decreasing. . 4. The method according to claim 3, wherein when the DC output voltage command value is changed in a first direction by a predetermined amount, the DC power voltage command value is changed in the same direction if the power amount is increasing, and is changed in a decreasing direction. It is changed in the opposite direction, and when the power amount on the input side or the output side of the power conversion device is continuously operated in the same direction a specific number of times, the power conversion device is forcibly operated in the reverse direction, and thereafter controlled in the increasing direction. Solar power system.