JPH1066264A - Photovoltaic power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photovoltatic power generation system whose chattering can be reduced by a method wherein, when the power generation amount of a solar cell is small so as to agree with a stop condition after the start of the system, whether the system is to be stopped or not is judged on the basis of the inclination of the operating voltage of the solar cell and the start condition of a sole cell voltage is increased whenever the system is stopped automatically. SOLUTION: Immediately after the start of a system, the voltage of a solar cell is read out so as to find its inclination K (S 100, S 101). When the voltage does not agree with a stop condition, the read-out voltage of the solar cell is held so as to continue its operation (S 102, S 103). When the voltage agrees with the stop condition (S 104), the computed inclination K is discriminated (S 105). When the inclination is positive, it is estimated that a panel temperature is lowered, the system is stopped, and the absolute value of the inclination K is investigated before the system is stopped (S 106). When the absolute value of the inclinaiton K is within a prescribed operating-voltage range, the operation of the system is continued. When the absolute value of the inclination K is outside the range, the operation is stopped.

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 the output of an inverter is connected to a commercial power supply, power is obtained from the commercial power supply, or the power generated by a solar cell flows backward to the commercial power supply. The present invention relates to an automatic start method for smoothly performing automatic start for continuous operation of a system.

[0002]

2. Description of the Related Art FIG. 2 shows an example of a photovoltaic power generation system for explaining a conventional example. In FIG. 2, 21 is a solar cell, 22 is an inverter, 23 is an insulating transformer, 24
Is a control unit of the inverter 22 for performing pulse width modulation control (hereinafter referred to as PWM control) or reverse power flow prevention, 25 is a measuring transformer (hereinafter referred to as PT) for monitoring the AC voltage at the interconnection point, and 26 is interconnection. The load device 27 connected to the point is a power distribution system which is a commercial power supply. System switch 28
Is a switch for preventing reverse power flow for preventing a current from flowing from the inverter 22 to the power distribution system 27 when the power distribution system 27 fails. Reference numeral 29 denotes a measuring current transformer (hereinafter referred to as CT) for detecting the output current of the inverter.

The operation of this system is as follows.
The DC power generated by the solar cell 21 is converted into AC power by the inverter 22 and connected to the power distribution system 27 via the insulating transformer 23 and the system switch 28 (hereinafter referred to as interconnection). At this time, the control unit 24 detects the voltage phase based on the detection signal of the PT 25 at the interconnection point, so that the AC voltage at the interconnection point has the same phase as the distribution system 27. Surplus power of the power supplied from the solar cell to the load performs PWM control on the inverter 22 so that the current is returned to the grid side at a power factor of 1. At this time, the power generation amount of the solar cell 21 is greatly affected by weather, temperature, and the like.
Inverter 2 so that the generated power of 1 is always maximized
2 (hereinafter referred to as maximum power tracking control).

[0004] For example, when the power distribution system 27 is out of service due to construction work or accident, or when an excessive output current flows from the inverter 22, the control unit 24 turns off the system switch 28 based on the detection signals of the PT 25 and CT 29. The inverter 22 and the power distribution system 27 are disconnected (hereinafter referred to as "disconnection").

[0005] Such a photovoltaic power generation system is operated unattended, and since the solar cell 21 does not generate power at night, it is disconnected from the power distribution system 27 and automatically connected to the power distribution system 27 in the early morning.

FIG. 3 (a) shows an example of the transition of the open voltage per day of the solar cell. Conventionally, at the time of startup, the voltage E of the solar cell is set to a threshold level, and when the state of the voltage E or higher continues for a certain period of time (for example, 10 minutes) or when the level of the voltage is equal to or higher than the voltage E ', the system is immediately started. On the other hand, the stop condition is such that the inverter stops when the output current of the inverter is, for example, 8% or less of the rating for a predetermined time (for example, 20 minutes). This method is described in “Survey on Basic Specifications of Small-scale Solar Cell System and Promotion of Practical Use”
Moon New Energy Foundation ”. In this example, as a result of operating the system, under a certain environment, a start condition and a stop condition interfere with each other, and a phenomenon as shown in FIG. 3B occurs. As the open voltage of the solar cell, a voltage equal to or higher than the threshold E has continued for the set ΔT, the system is turned on at point a, and a PWM signal is generated. And
If the power generation amount of the solar cell at that time is small, the stop condition is met, and the state is continued for the set ΔT ', so that the system is turned off at the point b and the PWM signal stops. As a result, the solar cell becomes an open-circuit voltage, and the system is turned on at a point c at which a voltage equal to or higher than the threshold E continues for the set ΔT. After that, turn the system on /
Off occurs repeatedly at points d and e. Such a chattering phenomenon is not limited to the time A at the start-up as shown in FIG. 3A, but also appears in a situation such as the time B at the evening or the time C at which the sun hits the clouds.

[0007]

In a photovoltaic power generation system, the amount of power generated by a solar cell is greatly affected by weather, temperature, and the like. Therefore, control such as maximum power tracking control is performed to increase the power generation efficiency as much as possible. I have to. In addition, since it is necessary to obtain a large amount of power generation per day even when the system is started or stopped, it is necessary to operate the system up to the limit of the power generation amount of the solar cell to obtain as much power as possible. Further, as described above, by repeatedly turning on and off at the time of starting and stopping, stress is applied to the power element due to abrasion of the contact of the switch and the like, and an overcurrent, thereby leading to a factor of shortening the life of the element.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce chattering by eliminating mutual interference between a start condition and a stop condition, thereby extending the operation time of a system, and eliminating unnecessary switching, thereby reducing the contact and power of a switch due to overcurrent. It is to reduce the stress applied to the element.

[0009]

The above object is achieved by monitoring the slope of a voltage (hereinafter referred to as an operating voltage) when the maximum power of the solar cell is generated immediately after the system is started. FIG. 4 is data showing the relationship between the operating voltage of the solar cell, the solar radiation intensity, and the temperature. The operating voltage of a solar cell has a characteristic that it has a certain width, but decreases as the temperature increases. However, when the solar radiation intensity decreases, the operating voltage of the solar cell deviates from the characteristic straight line and gradually decreases. FIG. 5 is an example showing the relationship between the operating voltage and the solar radiation intensity when the maximum power tracking control is performed for one day. In the early morning or evening, the operating voltage tends to be low because the panel temperature is low and the operating voltage is high during the daytime because the panel temperature is high. Further, in the evening, the solar radiation intensity gradually decreases, so that the operating voltage also decreases. Focusing on this, the operating voltage immediately after the system is started is sampled, and the slope is examined. Hereinafter, the description will be made as negative if the inclination is a right-down characteristic, and as plus if the inclination is a right-up characteristic. If the result of sampling the operating voltage immediately after the start of the system is negative, it is presumed that the panel temperature has risen, so that the stop is not performed even if the stop condition is met. In addition, if the result of sampling the operating voltage immediately after the start of the system is positive, it is presumed that the panel temperature has decreased. Therefore, if the stop condition is met, the stop is performed. Furthermore, since the operating voltage range e of the solar cell in the photovoltaic power generation system is determined, if the voltage becomes outside the range, the system is stopped.

Another method is achieved by making the starting conditions variable. Assuming that the solar cell voltage E is the starting voltage in FIG. 5, the system is turned on at the reference voltage point E. However, if the amount of power generated by the solar cell is small, the operating voltage sharply decreases and the system is immediately turned off. Since the voltage of the solar cell becomes an open-circuit voltage and thus meets the start condition, the start condition is increased by a certain value ΔE to E + ΔE. Again, even when the start condition of E + ΔE is satisfied and the system is started, if the power generation amount of the solar cell is small and the system is immediately turned off, the start condition is further increased by ΔE and the start condition is set to E + 2 · ΔE. To raise it. By doing so, it is possible to reduce the frequency of on / off repetition at system startup.

[0011]

FIG. 1 shows an embodiment of the present invention.
First, the voltage of the solar cell is read immediately after the system is started [100]. The voltage of the solar cell is taken in at a fixed sampling time, and the slope K is obtained every time [1
01]. If the stop condition is not met, the read voltage of the solar cell is maintained [102] and the operation is continued [10]
3], but if the stop condition is met, the following processing is performed [1].
04]. The slope of K calculated in [101] is determined [10
5] If it is positive, it is presumed that the temperature of the panel will drop as described above, so it is necessary to stop the system. Before stopping, the absolute value of the slope K is checked [10].
6]. If the absolute value of the slope K is within a predetermined operating voltage range, the operation is continued, but if the absolute value of the slope K is out of the range, the operation is stopped. This is to prevent the system from stopping due to a sudden change in the voltage of the solar cell when the sun hits a cloud. In other words, the slight voltage fluctuation of the solar cell
If the system stops, the chattering phenomenon becomes severe,
The overcurrent due to ON / OFF increases, so that more stress is applied to the switch and the power element, and the life is shortened. Also, the chattering phenomenon can be reduced by increasing the sampling time. If the slope of K is minus, it is presumed that the temperature of the panel has risen. However, it is possible that the solar radiation intensity has fallen. Also check if it is. if,
If the voltage of the solar cell is out of the operating range, the system is stopped.

FIG. 6 shows another embodiment of the present invention. The starting condition is the voltage E of the solar cell, and the system is started (turned on) as soon as the condition is satisfied. The voltage of the solar cell is
It drops by ΔVdc1 when the system is started. At this time, when the amount of power generated by the solar cell is small, the system is stopped (turned off) because the stop condition is continued for ΔT, whereby the voltage of the solar cell becomes an open circuit voltage. And
The next starting condition is not the initial voltage E, but ΔVdc
The voltage is obtained by adding 1 to the voltage E + ΔVdc1. E + ΔVdc1
Is activated under the activation condition of ΔVdc2
Assume that there was a voltage drop of Even at this point, it is assumed that the power generation amount of the solar cell is small and the system stops after ΔT time. The next starting condition is E + ΔVdc1 + ΔVdc
Start the system as 2. Thereafter, the starting condition is E + の ΔVdcn until the chattering phenomenon of the system stops.
It rises sequentially. As described above, the chattering phenomenon at the time of starting can be reduced by sequentially increasing the starting conditions. At this time, the increase width was a difference between the operating voltage of the solar cell at the time of startup and the voltage E of the initial startup condition,
Realization is possible even if the increment is a constant.

[0013]

According to the present invention, when the power generation amount of the solar cell is small after starting the system and the stop condition is met,
The method of determining whether to stop the system based on the slope of the operating voltage of the solar cell or raising the start condition of the solar cell voltage each time the system automatically stops, the start condition and the stop condition interfere with each other, and the system It is possible to reduce a chattering phenomenon that repeats on / off.
Therefore, abrasion of the contact of the switch due to unnecessary overcurrent due to chattering and stress applied to an electric element such as a power element are reduced, so that deterioration of the life of the element can be prevented. In addition, as a result of reducing the chattering phenomenon in which start and stop are repeated, the operation time of the system per day can be lengthened, so that efficient automatic operation of the system can be realized.

[Brief description of the drawings]

FIG. 1 is a flowchart of an embodiment of the present invention.

FIG. 2 is a block diagram of a solar power generation system.

FIG. 3 is an explanatory diagram of a chattering phenomenon at the time of automatic startup.

FIG. 4 is a characteristic diagram showing a relationship between a solar cell voltage, solar radiation intensity, and temperature.

FIG. 5 is an explanatory diagram of an example of a solar cell voltage transition during one day of operation of the solar power generation system.

FIG. 6 is an explanatory diagram of an example of an automatic startup sequence according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 21 ... Solar cell, 22 ... Inverter, 23 ... Insulation transformer, 24 ... Control part, 25 ... Measurement transformer, 26 ... Load device, 27 ... Distribution system [commercial power supply], 28 ... System switch,
29… Current transformer for measurement.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H02M 7/48 H02N 6/00 H02N 6/00 H01L 31/04 K (72) Inventor Masatoshi Mimori Ibaraki 7-1-1, Omika-cho, Hitachi City, Japan Inside Hitachi Research Laboratory, Hitachi, Ltd. 4-6-6 Kanda Surugadai, Chiyoda-ku, Tokyo Inside Hitachi, Ltd.

Claims (4)

[Claims] 1. A photovoltaic power generator having a solar cell and a power converter for converting DC power generated by the solar cell into predetermined AC power, and interconnecting the power converter with a commercial power supply to transfer power. In the system, the start condition is set to a certain voltage point of the solar cell, the system is started under the condition, and the power generation amount of the solar cell is small immediately after the start, and the solar cell The solar power generation system is characterized in that the operating voltage is sampled at regular intervals, the difference between the sampled operating voltage value and the previously sampled operating voltage value is taken, and if the difference is positive, the system is stopped. system. 2. The method according to claim 1, wherein the difference between the operating voltage value sampled by sampling the operating voltage of the solar cell at a fixed cycle and the operating voltage value sampled last time is negative. Is a photovoltaic power generation system that reads the operating voltage of the solar cell, checks whether the operating voltage is within or outside the operating range, and shuts down the system if the voltage is outside the operating range. 3. A photovoltaic power generator having a solar cell and a power converter for converting DC power generated by the solar cell into predetermined AC power, and interconnecting the power converter with a commercial power supply to transfer power. In the system, the starting condition is set to a certain voltage value of the solar cell, for example, E [v], and the system is started according to the condition.
_When the voltage drop of the solar cell of ₁ [v] occurs, the next starting condition is to start as E + ΔE ₁ [v], and by the start, the voltage drop of the solar cell of ΔE ₂ [v] is reduced from the open circuit voltage. If it occurs, the next start condition is E + ΔE ₁ + Δ
A photovoltaic power generation system, wherein the photovoltaic power generation system is started up as E ₂ [v], and then sequentially sets the startup condition to a value E + ΣΔEn obtained by adding the difference between the open voltage and the operating voltage. 4. The method according to claim 3, wherein the starting condition is set to a certain voltage value of the solar cell, for example, E [v], and when the system is started under the condition, the next starting condition is to add a certain constant α. The photovoltaic power generation system starts with the value E + α [v], the next start condition is E + 2 · α [v], and the start conditions are sequentially E + n · α.