WO2016166787A1

WO2016166787A1 - Solar power generation system

Info

Publication number: WO2016166787A1
Application number: PCT/JP2015/061314
Authority: WO
Inventors: 嶋田　隆一
Original assignee: 国立大学法人東京工業大学; クリーンエナジーファクトリー株式会社
Priority date: 2015-04-13
Filing date: 2015-04-13
Publication date: 2016-10-20
Also published as: JP6037585B1; JPWO2016166787A1

Abstract

The purpose of the present invention is to perform MPPT control by a simple method for individual strings in a solar power generation system that has strings 2 formed by serially connecting a plurality of solar cell panels 1, the DC power generated by the solar cell panels being converted by a power converter 3 connected to the strings 2, and supplied to a load or a power system. Therefore, in this solar power generation system, current measurement devices 4 for measuring the current in the strings 2 are serially connected to the strings 2, and reverse-flow-prevention diodes 5 are serially connected to the strings 2 in order to prevent the current in the strings 2 from flowing in reverse. In addition, a DC power source 7 for boosting the voltage in the strings 2 by a predetermined value is connected in parallel to the reverse-flow-prevention diodes 5 via switches 6, and a control device 8 is provided for performing control so that the switches 6 are closed and a voltage of predetermined value is supplied from the DC power source 7 to the strings 2 when the current measured by the current measurement devices 4 is equal to or less than a predetermined value.

Description

Solar power system

The present invention relates to a photovoltaic power generation system, and more particularly to a photovoltaic power generation system including a control device for extracting more electric power for each solar cell string in which a large number of solar cell panels are connected in series.

Large-scale solar power generation facilities are installed in a wide space with thousands to tens of thousands of solar panels (hereinafter referred to as “panels”) connected in series and in parallel.
Generally, when a solar cell array is configured by connecting a plurality of solar cell strings (hereinafter referred to as “strings”) in which a number of panels are connected in series, a string having a standard such as a generated voltage is selected and used. Things have been done.

By connecting a large number of strings in parallel, the current is increased, and the generated power of the strings is output to the power system by a connected inverter device called a power conditioner that collectively converts the string into AC.
The power conditioner can change the voltage of the string by maximum power point tracking (hereinafter referred to as “MPPT”) control so that the DC power of the string can be converted with an optimum voltage. The power conditioner includes a DC / DC converter for controlling the voltage step-up / step-down, and supplies a voltage to a voltage source capacitor of an inverter that converts the voltage into an AC voltage for connection to an external power system.

However, since the input voltage to the power conditioner is determined as a single common string as a whole of the strings connected in parallel, the maximum power point is not necessarily the individual string.
The voltage at the maximum power point of each string is not the same in a wide mega solar site and is particularly sensitive to temperature changes. When panels are installed on slopes, it is considered that there is a difference of several tens of degrees (° C) in the surface temperature between panels due to differences in height, wind flow, etc.

For example, there is an observation result that the temperature difference becomes 60 degrees (° C.) when the temperature of the panel decreases due to the sun, and the temperature of the panel increases again when the sun shines. Since the voltage at the maximum power point changes by about 0.5% with a temperature difference of 1 degree, the voltage change of about 30% may occur even in the same panel even in the worst case. Therefore, the panel arrangement at the mega solar site should be arranged so that there is no temperature difference.

Another problem arises when the output of the panel in the string is deteriorated due to breakage or deterioration over time, or due to dirt or partial shade on the panel surface. In that case, since the current of the string becomes equal to the current of the panel having the smallest current, the output of the entire string is lowered.
Since the voltage of the inverter that collects the power of each string operates so as to match the voltage of the other normal strings, the MPPT control of the string whose output is lowered is not performed. Therefore, MPPT control for each string is required.

In view of this situation, the string is replenished with current to restore the current so that the operating point voltage of the string whose output has decreased due to performance degradation or environmental changes of some panels approaches the maximum power point voltage. Therefore, it is necessary to perform control so that the recovered current of the string is supplied to the power conditioner.
In such a case, each panel constituting the string includes a voltage detection means and a power detection means for detecting the amount of power output from the panel, and is further necessary based on the detected panel voltage and power amount. There has been proposed a solar power generation system provided with a power replenishing means for replenishing an appropriate power (see Patent Document 1).

International Publication No. 2013/018826

However, the invention described in Patent Document 1 is excellent in that the optimum MPPT control is performed by detecting the voltage and the electric energy for each panel, but each panel is individually operated as long as each panel operates normally as designed. Although there is no need to perform MPPT control, there is a waste that power conversion loss is added, and voltage detection means and power detection are present in all hundreds to thousands of panels. There is a problem that it is too expensive to install the means.
It is also necessary to avoid contention between MPPT control performed on individual strings and MPPT control performed on the entire string by the power conditioner.
The present invention has been made in view of the above-described problems. The present invention does not perform MPPT conversion for every string, not for every panel, and keeps normal strings as they are. It is not an accurate MPPT control only for a degraded string, but “PTF (Effective Power Point Tracking)” control, that is, EPPT (Effective Power Point Tracking) control, is performed for each string in a simple manner. An object of the present invention is to provide a photovoltaic power generation system capable of performing both control and MPPT control of a power conditioner that converts current of all strings.

In order to achieve the above object, a photovoltaic power generation system according to the present invention connects a string formed by connecting a plurality of solar cell panels in series, and DC power generated by each of the solar cell panels to the string. A photovoltaic power generation system that converts the power of the string and supplies it to a load or a power system, the current measuring means connected in series to the string to measure the current of the string, and the current of the string In order to prevent backflow of the string, a backflow prevention diode connected in series with the string, a DC power source connected in parallel with the backflow prevention diode, and for increasing the voltage of the string by a predetermined value, and the current When the current measured by the measuring means is less than a predetermined value, a voltage having a predetermined value is supplied from the DC power source to the string. Characterized by comprising a Gosuru control means.

According to the above configuration, by monitoring the current for each string and replenishing the necessary voltage to the string whose output current is abnormally reduced, the current of the string can be recovered and supplied to the power conditioner. Therefore, the generated power of the string can be used effectively.

1 is a diagram showing a first embodiment of a photovoltaic power generation system according to the present invention. It is a figure for demonstrating the reason which can recover | restore an electric current by replenishing a predetermined voltage with respect to the string in which performance deteriorated. It is a figure which shows 2nd Embodiment of the solar energy power generation system which concerns on this invention. It is a figure which shows the modification of 2nd Embodiment of the solar energy power generation system which concerns on this invention. It is a figure for demonstrating operation | movement of a magnetic energy regeneration switch. It is a figure which shows 3rd Embodiment of the solar energy power generation system which concerns on this invention. It is a figure which shows the modification of 3rd Embodiment of the solar energy power generation system which concerns on this invention. It is a figure which shows 4th Embodiment of the solar energy power generation system which concerns on this invention.

Hereinafter, modes for carrying out the present invention will be specifically described.

[First Embodiment: FIG. 1]
FIG. 1 is a diagram showing a first embodiment of a photovoltaic power generation system according to the present invention.
The photovoltaic power generation system shown in FIG. 1 converts a plurality of strings 2 configured by connecting a plurality of panels 1 in series, and DC power generated by each panel 1 by a power converter 3 connected to the strings 2. To supply the load. The power converter 3 charges the voltage source capacitor through a DC / DC converter that controls the DC current to obtain the maximum power by collecting currents of a plurality of strings, and voltage-type pulse width modulation (Pulse Width Modulation). Modulation (hereinafter referred to as “PWM”). The inverter is linked to a three-phase alternating current by an inverter and is called a power conditioner.

This solar power generation system includes a current measuring device 4 connected in series to the string 2 to measure the current of the string 2 and a reverse flow connected in series to the string 2 to prevent a reverse flow of the current of the string 2. A prevention diode 5 and a DC power supply 7 connected in parallel with the backflow prevention diode 5 via the voltage supply switch 6 and for raising the voltage of the string 2 by a predetermined value are provided.
In addition, when the current measured by the current measuring device 4 is less than or equal to a predetermined value, the control device 8 that controls to turn on the voltage supply switch 6 and replenish the string 2 with a predetermined voltage from the DC power source 7 is also provided. I have. The control device 8 may be a dedicated device, or a general-purpose computer may be used.

A bypass diode 9 and a capacitor 10 are connected to the panel 1 in parallel.
The bypass diode 9 functions to maintain the power generation of the string 2 by bypassing the current in the solar cell module that is shaded or failed. Further, the capacitor 10 serves to reduce the influence of changes in the generated voltage due to sunlight and temperature changes and stabilize the generated voltage of the panel.
Also, what is denoted by reference numeral 11 is a connection / disconnection switch for switching connection / disconnection of the string 2 to the power converter 3, and for switching operation / maintenance.

When the generated current of a specific panel decreases due to some factor such as partial shadow of the panel, performance deterioration, temperature change, etc., the current of the string including the defective panel becomes abnormally smaller than the current of other strings. That is, since the current of the string becomes equal to the current of the defective panel, the current of the entire string is lowered.
In the photovoltaic power generation system shown in FIG. 1, the reason why the current of the string 2 whose current has decreased can be recovered by supplementing a predetermined voltage from the DC power supply 7 will be described with reference to FIG. 2.

FIG. 2 is a diagram for explaining the reason why a current can be recovered by replenishing a predetermined voltage to a string with degraded performance.
FIG. 2A shows that the MPPT voltage at the maximum power point differs depending on the panel temperature in a mega solar in which an array is configured by connecting a large number of strings in parallel.
As can be seen, the MPPT voltage at 25 ° C. is about 260V, while the MPPT voltage at 50 ° C. is about 210V.

If a string that is now 25 ° C suddenly rises to 50 ° C, the MPPT voltage of that string will drop to about 210V, but the inverter will be 260V just like any other normal string connected in parallel. In order to continue the control at, the power of the string whose output is reduced is reduced to about 400 W.
Therefore, if a voltage of about 20% (about 50V) is replenished in series from the DC power source 7, the voltage of the string whose output is reduced can be made about 210V (= 260V-50V). That is, since the string whose output is reduced can be driven by the MPPT voltage, the power is recovered to about 1600 W.

As can be seen from FIG. 2A, since the curve on the left side of the MPPT voltage is gentle, the replenishing voltage may be somewhat large. Of course, it is natural to control in a range where the electric power obtained is larger than the electric power to be supplemented.
FIG. 2B shows that the MPPT voltage at the maximum power point of the string is lowered when a part of the panel in the string 2 is in the shade. In this case, if a voltage of about 50 V (about 20%) is replenished, the power recovers from about 600 W to about 1600 W.

Returning to FIG. 1, when the current measuring device 4 measures the current of each string 2 and sends it to the control device 8, the control device 8 checks whether or not the current value of each string 2 is equal to or less than a predetermined value. Then, a string having a current value equal to or smaller than a predetermined value is found, the switch 6 of the string is turned on, and a predetermined voltage is injected from the DC power source 7 to the string. For example, the predetermined value may be set to 20% of a normal average current value, and a string that falls below the predetermined average current value may be determined to be abnormal.
It is considered that the replenishing voltage is highly effective when it is a voltage corresponding to a generated voltage of about 20% of the maximum output point voltage of a normal string. As shown in FIG. 2, the replenishment voltage depends on the voltage of the maximum power point to move, and the magnitude of the maximum power point movement in the non-standard state differs depending on the mega solar depending on the installation conditions of the mega solar, weather conditions, and the like. Because it seems, decide while driving.

In this case, when a voltage is injected, a defective panel whose capacity has been reduced is supplemented with a voltage sufficient to turn on the bypass diode 9, so that other normal panel currents pass through the bypass diode 9 of the defective panel. Flow, string 2 restores current.
Therefore, it is observed whether or not the current of the string 2 increases by replenishing the voltage. If it increases, the replenishment of the voltage is continued as it is. When the current of the string 2 does not increase, the voltage supply is stopped. This is because the normal string does not increase the current and does not interfere with the MPPT control by the power conditioner.

Although there is an optimum value of the voltage to be replenished, it is also a feature of the present invention that the optimum value is not obtained but it is sufficient if it is equal to or higher than that voltage. The voltage is about one or two panels. Even if an extra voltage is injected, the string current is limited to the current of each panel, so it does not become so large, and the surplus power does not become a loss, and the power only flows to the power conditioner 3. So there are few problems.
Further, the DC power source 7 may be one in which AC power output from the power conditioner 3 is generated by a transformer diode rectifier.

According to the above configuration, the current for each string 2 is monitored by the current measuring device 4, the string whose output current is abnormally reduced is selected, and the necessary voltage (voltage for about one panel) is replenished. Since the current of the string can be supplied to the power conditioner, the generated power of the string can be used effectively.
Table 1 below shows the effect of the present invention by simulation using PSIM. For each case where the performance of some of the 10-panel strings deteriorates, the power required for replenishment is compared with the power increased by that (excluding the power required for replenishment). It is shown. Thereby, the effect of the present invention was verified.

[Second Embodiment: FIG. 3]
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing a second embodiment of the photovoltaic power generation system according to the present invention. In the second embodiment, the power generation current is recovered by boosting the power generation voltage of the string 2 in which the power generation current has decreased by a boost chopper. In the first embodiment of FIG. 1, a necessary voltage is supplemented using the external DC power supply 7, but in the second embodiment, a boost chopper circuit is used to boost the generated voltage itself of the string 2.

In FIG. 3, the step-up chopper circuit includes an inductor 12, a semiconductor switch 13 that performs a switching operation of the current of the string 2, a backflow prevention diode 5, and a DC capacitor 14. A control device 8 that controls the gate voltage of the semiconductor switch 13 to perform on / off control is provided. The semiconductor switch is preferably a MOSFET or an IGBT, for example. One control device 8 may be provided for the entire system or may be provided for each string. When provided for each string, it is sufficient to perform control to maximize the current detected by the current measuring device 4. This is because the voltage is determined by the output high voltage DC bus. The MPPT of this string is also characterized in that simple control with only current measurement is sufficient.
Since a general boost chopper circuit is used here, description of the operation principle is omitted.

In FIG. 3, the control device 8 constantly monitors the current value of each string 2 measured by the current measuring device 4, and the control device 8 determines whether or not the current value of the string 2 is abnormal. Since the criteria for determination are the same as in the first embodiment, description thereof is omitted.
If the control device 8 determines that the current value of the string 2 is abnormal, the control device 8 gives an on / off signal to the gate of the semiconductor switch 13 to perform PWM control. As a result, the voltage of the string 2 connected to the power conditioner 3 increases, and the string 2 recovers the current.

Since the increase in the voltage of the string 2 is about 20% (the voltage for about one or two panels), the PWM duty ratio (Duty) of the semiconductor switch 13 is about 20%.
Since the control device 8 constantly monitors the current value of the string 2, the control unit 8 gradually increases the duty ratio, and controls to stop increasing the duty ratio when the increase in the current of the string 2 stops. Also good. This is because even if the voltage is further increased, if the voltage returns to normal, the current does not increase in the string, and this does not disturb the MPPT control by the power conditioner.

Note that the negative terminal of the DC capacitor 14 of the boost chopper circuit in the second embodiment is connected to the positive side of the string 2 instead of the ground. Accordingly, the voltage applied to the DC capacitor 14 is only about one or two panels (about 30 to 100 V), and a small capacitor with a small rated voltage can be used.

Further, if the semiconductor switch 13 of the boost chopper circuit in the second embodiment is kept on, it can be used as a switch for short-circuiting the string 2.
A panel with a constant current characteristic does not flow over the maximum current even if it is short-circuited. By short-circuiting, the voltage becomes a voltage that is not dangerous to the human body, and the output current becomes zero by the reverse current prevention diode 5, so that the direct current Even so, the connection / cutoff switch 11 can be disconnected from the output high voltage DC bus without generating an arc.

[Modifications of Second Embodiment: FIGS. 4 and 5]
Next, a modification of the second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a diagram showing a modification of the second embodiment of the photovoltaic power generation system according to the present invention.
The modification of the second embodiment shown in FIG. 4 is obtained by replacing the semiconductor switch 13 in the second embodiment shown in FIG. 3 with a magnetic energy recovery switch (hereinafter referred to as “MERS”) 13. Other than that, the second embodiment is the same as the second embodiment.

In FIG. 4, the MERS 13 connects a series circuit of a MOSFET (S1) and a diode (d1) and a series circuit of a diode (d2) and a MOSFET (S2) in parallel, and connects between the anode of the diode d1 and the cathode of the diode d2. A second DC capacitor C1 for regenerating magnetic energy is connected.
The control device 8 controls the MOSFET (S1) and the MOSFET (S2) to be turned on / off simultaneously. Although PWM control is performed in the same manner as in the second embodiment, it is characterized by soft switching with little switching loss and noise. Further, since the MERS is in parallel conduction, switching is possible even when one MOSFET has a malfunction such as inoperative or open, and reliability is improved.
In order to eliminate the switching loss, it is necessary to turn on or off at zero voltage or zero current, but the MERS 13 can realize it. This will be described with reference to FIG.

FIG. 5 is a diagram for explaining the operation of MERS. FIG. 5A shows a state when the MOSFET (S1) and the MOSFET (S2) are turned off from on. When S1 and S2 are turned off at the same time, the magnetic energy stored in the inductor 12 in FIG. 4 is charged in the capacitor C1 through the path indicated by the arrow in FIG. When all the magnetic energy is stored in the capacitor C1, no more current flows and the current becomes zero.

If S1 and S2 are turned on in this state, the state transitions to the state shown in FIG. 5B, and the current rises slowly from zero due to the inductance of the line, so that soft switching is realized. At this time, current flows in the direction of the arrow. When the electric charge is discharged from the capacitor C1 and the voltage of the capacitor C1 becomes substantially zero, the diodes d1 and d2 are connected in a parallel conduction state in the forward direction, and the state shown in FIG. 5C is obtained. If S1 and S2 are turned off after the voltage of capacitor C1 is completely zero in the state of FIG. 5C, the voltage of the capacitor is zero at the moment of turning off. Soft switching is realized without generating a surge at the time of interruption, and the state shown in FIG. By repeating the cycles of FIGS. 5A to 5C, soft switching without switching loss becomes possible.

By using MERS as a switch for DC / DC conversion, the primary advantage is that magnetic energy is regenerated without being consumed by the resistor, but soft switching is a problem in DC / DC conversion of solar power generation. It is also a great advantage that the switching noise is reduced. Application of MERS that reduces switching noise has an effect of preventing mega-solars that occupy a large area from being exposed to noise and causing interference with nearby wireless communication and electromagnetic interference: EMI (Electro-Magnetic Interference).

[Third Embodiment: FIG. 6]
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a diagram showing a third embodiment of the photovoltaic power generation system according to the present invention. In the first embodiment of FIG. 1, a necessary voltage is supplemented by using an external DC power supply 7, but in the third embodiment, a voltage generated by stepping down the voltage of the string 2 with a step-down chopper (panels of about 1 to 2). The voltage for the sheet) is injected as a supplementary voltage to the ground side of the string 2.

In FIG. 6, the step-down chopper circuit includes an inductor 12, a semiconductor switch 13, a backflow prevention diode 5, and a DC capacitor 14. Moreover, the control apparatus 8 which controls the gate voltage of the semiconductor switch 13 and performs on-off control is provided. The semiconductor switch is preferably a MOSFET or an IGBT, for example. One control device 8 may be provided for the entire system or may be provided for each string.
Since a general step-down chopper circuit is used here, the explanation of the operation principle is omitted.

Further, the voltage value to be replenished and the control operation of the control device 8 are basically the same as those in the second embodiment, and thus the description thereof is omitted.
Further, the voltage applied to the DC capacitor 14 is only about one or two panels (about 30 to 100 V), and a small capacitor with a small rated voltage can be used as in the second embodiment.

Further, if the semiconductor switch 13 of the step-down chopper circuit in the third embodiment is kept on, it can be used as a switch for short-circuiting the string 2.
A panel with constant current characteristics does not flow beyond the maximum current even if short-circuited, and the voltage becomes a voltage that is not dangerous to the human body, and the output current becomes zero by the backflow prevention diode 5, so even if it is a direct current, The connection / disconnection switch 11 can be disconnected from the output high voltage DC bus.

[Modification of Third Embodiment: FIG. 7]
FIG. 7 is a diagram showing a modification of the third embodiment of the photovoltaic power generation system according to the present invention.
The modification of the third embodiment shown in FIG. 7 is the same as the third embodiment except that the semiconductor switch 13 in the third embodiment shown in FIG. 6 is replaced with MERS13.
Further, the configuration, operation, and features of the MERS 13 are the same as those of the modified example of the second embodiment, and thus description thereof is omitted.

As described above, since the chopper circuit is connected in parallel with the string 2 in the methods of the second embodiment, the third embodiment, and the modifications thereof, it can also be used as a crowbar switch that protects the string voltage from being short-circuited. Contributes to safety during string installation and maintenance.

[Fourth Embodiment: FIG. 8]
Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a diagram showing a fourth embodiment of the photovoltaic power generation system according to the present invention.
The fourth embodiment is a resistor between the drain and gate of the semiconductor switch 13 in order to short-circuit the semiconductor switch 13 by the voltage of the string in the second embodiment and the third embodiment (including modifications thereof). 15 and a mechanical contact switch 16 for disconnecting between the control device 8 and the gate.

FIG. 8A shows the connection between the drain and gate of the semiconductor switch 13 of the second embodiment shown in FIG. 3 and the third embodiment shown in FIG. A case is shown in which they are connected via a mechanical contact switch 16.
Further, FIG. 8B shows a connection between the drain and gate of the MOSFET (S1) of the MERS 13 in the modification of the second embodiment shown in FIG. 4 and the modification of the third embodiment shown in FIG. In addition, the case where the control device 8 and the gate are connected via the mechanical contact switch 16 is shown. Note that the resistor 15 and the mechanical contact switch 16 may be connected to S2.
Further, the resistance value of the resistor 15 may be a resistance value that does not affect the operation of the control device 8 that performs high-speed PWM control. Specifically, the output impedance of the control device 8 is about 100Ω or less. Therefore, it may be 1 kΩ to 10 kΩ which is 10 to 100 times that.

Solar cell panels that are expected to have a lifetime of 10 years or more require maintenance. In that case, it is necessary to turn off the connection / disconnection switch 11 for each string and disconnect the string 2 from the output high voltage DC bus. However, since the DC power of the string is several hundred volts and several A, this The disconnection by the connection / break switch 11 may cause an arc and is difficult unless a DC breaker having a special structure is used.
Therefore, it is necessary to short the string 2 to a voltage that is not dangerous. In this case, there is a method of short-circuiting the semiconductor switch 13 by continuing to turn on the gate of the semiconductor switch 13 by a signal from the control device 8, but the reliability as a safety device is lacking. That is, the reliability of the power supply of the control device 8 becomes a problem.

In the fourth embodiment, the gate is disconnected from the control device 8 by turning off the mechanical contact switch 16 instead of short-circuiting the semiconductor switch 13 by driving the gate by a signal from the control device 8, and the gate voltage is stringed. The semiconductor switch 13 is short-circuited by raising the voltage. As a result, the drain-source voltage becomes a low voltage threshold voltage. Therefore, as long as voltage is generated in the string, the semiconductor switch 13 can be short-circuited by turning off the mechanical contact switch 16, so that the reliability of the power supply of the control device 8 does not matter.

If the switch 16 is a mechanical contact switch, a signal for driving the gate is required if it is a semiconductor switch, but if it is a mechanical contact switch, a manual switch (for example, a push button switch or a toggle switch) This is because the gate drive signal is unnecessary.
Further, although a voltage for gate control is applied to the mechanical contact switch 16, the voltage is very small (15 V or less) and almost no current flows, so a switch for minute current may be used.

As described above, according to the photovoltaic power generation system according to the present invention, replenishment is performed by measuring the current for each string of the solar battery panel in the mega solar and replenishing the string voltage in an abnormally low current value in series. There is an increase in electric power that exceeds the generated electric power, and the generated electric power can be increased.
In addition, it is possible to continue the power generation of the string by inserting a supplementary voltage source until one string panel is damaged and repaired or replaced. Since the voltage source may be a DC power source capable of outputting a voltage of about 1 to 2 panels (about 30 to 100 V), it may be an industrial general-purpose power source and does not require accuracy.
The description of the embodiment is finished as described above, but it is needless to say that the configurations of the embodiments, operations, and modifications described above can be arbitrarily combined as long as they do not contradict each other.

DESCRIPTION OF SYMBOLS 1 Solar cell panel 2 Solar cell string 3 Power converter (power conditioner)
4 Current measuring device 5 Backflow prevention diode 6 Voltage supply switch 7 DC power supply 8 Control device 9 Bypass diode 10 Capacitor 11 Connection / cutoff switch 12 Inductor 13 Semiconductor switch (magnetic energy regeneration switch)
14 DC capacitor 15 Resistor 16 Mechanical contact switch S1, S2 Semiconductor switch (MOSFET)
C1 Second DC capacitor d1, d2 diode

Claims

A string formed by connecting a plurality of solar cell panels in series, and sunlight supplied to a load or a power system by converting DC power generated by each of the solar cell panels by a power converter connected to the string A solar power generation system,
Current measuring means connected in series to the string to measure the current of the string;
A backflow prevention diode connected in series with the string to prevent backflow of current in the string;
A DC power source connected in parallel with the backflow prevention diode and for increasing the voltage of the string by a predetermined value;
Photovoltaic power generation comprising control means for controlling to supply the voltage of the predetermined value from the DC power source to the string when the current measured by the current measuring means is below a predetermined value. system.
A string formed by connecting a plurality of solar cell panels in series, and sunlight supplied to a load or a power system by converting DC power generated by each of the solar cell panels by a power converter connected to the string A solar power generation system,
Current measuring means connected in series to the string to measure the current of the string;
A step-up chopper circuit inserted between the string and the power converter for increasing the voltage of the string by a predetermined rate;
The step-up chopper circuit is
The element for switching the current of the string is a semiconductor switch, and the negative terminal of the DC capacitor constituting the boost chopper circuit is connected to the positive terminal of the string,
The solar system comprising: a control means for controlling the gate of the semiconductor switch so as to increase the voltage of the string by a predetermined ratio when the current measured by the current measuring means is less than or equal to a predetermined value. Photovoltaic system.
A string formed by connecting a plurality of solar cell panels in series, and sunlight supplied to a load or a power system by converting DC power generated by each of the solar cell panels by a power converter connected to the string A solar power generation system,
Current measuring means connected in series to the string to measure the current of the string;
A step-down chopper circuit for lowering the voltage of the string by a predetermined rate;
The step-down chopper circuit is
The element for switching the current of the string is a semiconductor switch, the plus terminal of the DC capacitor constituting the step-down chopper circuit is connected to the minus terminal of the string, and the minus terminal of the DC capacitor is connected to the ground. Connected,
When the current measured by the current measuring means is less than or equal to a predetermined value, the gate of the semiconductor switch is controlled so that a voltage obtained by dropping the voltage of the string by the predetermined ratio is added in series to the string. A photovoltaic power generation system comprising a control means.
The control means monitors the change in the current value of the string measured by the measurement means while gradually changing the rate of step-up or step-down in the step-up chopper circuit or step-down chopper circuit,
4. The photovoltaic power generation system according to claim 2, wherein control is performed so that the ratio of the step-up or step-down is fixed when the increase in the current value stops. 5.
The element that switches the current of the string is a magnetic energy regenerative switch,
The magnetic energy regenerative switch forms a bridge circuit in which two semiconductor switches and two diodes are arranged diagonally in the same direction, and a second DC capacitor connected between the DC terminals of the bridge circuit With
5. The sunlight according to claim 2, wherein the control unit applies a control signal to a gate of each semiconductor switch of the bridge circuit to simultaneously perform on / off control of each semiconductor switch. Power generation system.
The semiconductor switch is a MOSFET, the drain and gate of the MOSFET are connected by a resistor, and a mechanical contact switch is inserted between the control means and the gate;
5. The photovoltaic power generation system according to claim 2, wherein when the mechanical contact switch is turned off, the string is short-circuited by turning on the MOSFET by a voltage of the string. 6.
The semiconductor switch is a MOSFET, the drain-gate of at least one of the MOSFETs is connected by a resistor, and a mechanical contact switch is inserted between the control means and the gate;
6. The photovoltaic power generation system according to claim 5, wherein when the mechanical contact switch is turned off, the string is short-circuited by turning on the MOSFET according to the voltage of the string.