JPS58175925A - Defect detecting system for solar light generating system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a failure detection method for a power generation system that extracts power from a plurality of solar cells connected in series and parallel to a common DC bus.

Since a single solar cell is approximately IW at most, a large number of solar cells are connected in series and parallel to form a power generation system.

A conventional power generation system of this type is shown in FIG. (1a) to (1n) are a solar cell unit consisting of a plurality of solar cell panels connected in series, or a plurality of solar cell panels connected in series; (2a); Reverse current blocking diodes to prevent reverse battery, (3a) and (3b) are DC common busbars,
(4a) + (41)) is a DC breaker, and (5) is a load for this power generation system.In addition to the normal impedance load, it may be another DC power source or an AC power system via an inverter.

Next, the operation will be explained. The voltage-current characteristics of the solar cell exhibit nonlinear characteristics as shown in FIG. 2 (A) or (B). Here, the sun in Figure 1 is ike units) (la) ~ l (
The characteristics up to 1) in total are shown in Figure 2 (A). (In)
(with the same characteristics). Now, if there were no backflow blocking diodes (2a) to (2n), when the breaker (4) is opened, the solar cell's current would be zero and it would try to show an open circuit voltage, but since it is connected in parallel, the VO balance.

At this time, a forward current A flows through the units (1a) to (>l), and a reverse current Itl flows through the units (1n). At this time, the relationship rb=-(n-1)Ia naturally holds true, and when there are many parallels, even if the difference in characteristics is small, a large reverse current flows, which may damage the solar cell. In the event of a grounding or short-circuit accident, the balance will be disrupted and a large reverse current will be supplied from other solar cell units, resulting in damage. For this reason, in Figure 1, a backflow blocking diode (2
a) to (2n) to each solar cell unit (la) to (In
) to solve the above problem.

However, in the unlikely event that the above-mentioned backflow blocking diode is damaged,
If the reverse blocking ability were lost, there was a possibility that it would lead to solar cell damage as mentioned above. (As mentioned above, the solar cell will only be damaged when the diode fails and other conditions are satisfied.) However, in this type of system, energy is transferred between many unit solar cells, so Unless a circuit breaker is provided for each unit, damage to the solar cells cannot be prevented once abnormal current flows. However, trying to improve the reliability by connecting diodes in series led to an increase in loss, and it was also extremely time-consuming to check each diode one by one.

This invention was made to solve the problem. By applying a test voltage all at once from the DC bus, it is possible to discover failures in reverse blocking diodes and prevent damage to the solar cells. That is.

An embodiment of the present invention will be described below with reference to the drawings. Third
In the figure, (1) to (5) are the same as in FIG. 1 above. (6) is solar cell unino) (la) ~ (1n)
(7) is a resistor connected in series with the DC power supply (6),
(8) is means for measuring the current supplied by the DC power supply (6), and (9) is a switch for connecting these (6) to (8) to the DC common bus (3). αQ is a breaker provided as necessary to short-circuit between the DC buses (3a) and (3b).

Next, the operation will be explained. Now, the DC breaker (4a)
+ (41)) is opened and the switch (9) is closed when the system is under no load. Now, if all the reverse blocking diodes (2a) to (2n) have a healthy reverse blocking ability, the current supplied from the applied DC power supply (6) will be Only the leakage current of the system will flow. On the other hand, if even one of the diodes does not have reverse blocking ability, the DC power supply (6
) A reverse current flows due to the difference between the voltage of 2 nits and the open circuit voltage of the solar cell, and since this value is limited by the series resistance (7), the solar cell will not be damaged.

In this case, the leakage current of the diode is several orders of magnitude lower than the rated current, and the allowable reverse current of the solar cell is more than 10 times the rated value for a short time, so if the number of parallel connections n is large, In the practical range, there is a difference between the two values and it is possible to distinguish them sufficiently.As a result, by detecting this reverse current with the current measuring means (8), damage to the reverse current blocking diode can be detected at once. can be discovered.

According to this method, as mentioned above, secondary damage to the solar cell can be detected only by damage to the diode before the conditions for secondary damage to the solar cell are satisfied, such as variations in open circuit voltage, grounding, short circuit conditions, etc. Effective in prevention.

Furthermore, even when there is no solar radiation, if a voltage is applied to the solar cell, the solar cell exhibits diode characteristics, so this detection method can be applied as is, so failures can be detected when the system is not operating, such as at night. This can be done without affecting system operation.

Furthermore, even if a diode fails during the day when there is high solar radiation and this is discovered, the probability of immediate secondary damage to the solar cell is relatively small, but it is impossible to completely prevent this. , short-circuit the DC common bus (3a) and (3b) using a circuit breaker αQ, etc., or if a power converter etc. is installed between the load (5), C,
If continuous control is performed so that the DC bus voltage is lowered, even if a grounding or short-circuit accident occurs repeatedly during this period, no reverse current will flow to the solar cells and no secondary damage will occur.

In the embodiment shown in FIG. 3, a fixed voltage higher than the open circuit voltage of the solar cell unit is used as the DC power source, but a variable voltage source may be used to increase the voltage for removal. Further, the current measuring means (8) is not limited to the configuration shown in the figure, but may be any method as long as it can measure and detect the voltage drop of the resistor (7) and the current of the DC power source (6).

Furthermore, the switch (9) is not necessarily necessary;
If even some loss is allowed, it can be connected all the time and failure detection can be done by
It is also possible to use the logic of circuit breaker (4a) + (4b).

As described above, according to the present invention, when there is no load, a voltage higher than the open circuit voltage is applied to the DC bus through the resistor, and the supplied current at this time prevents damage to the reverse current blocking diode at once. Since this is detected, secondary damage to the solar cell due to damage to the backflow blocking diode can be easily prevented.

Figure 1 is a diagram showing the configuration of a conventional solar battery generation system, Figure 2 is a diagram showing the characteristics of a solar cell for explaining Figure 1, and Figure 3 is a diagram showing the solar cell characteristics according to embodiments of the present invention. In Figure 0, which is a complete diagram of a failure detection method for a battery power generation system, (la) to (In) - solar cell units,
(2a)-(2n)-backflow blocking diodes, (3a)+
(3b) - DC common bus, (4a), (4b) -
DC breaker, (5) - load, (6) - DC power supply, (
7) - resistance, (8) - current measuring means, (9) - switch, 0* - short circuit breaker.

In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Agent Shin Kuzuno Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) In a solar cell power generation system in which a plurality of series bodies consisting of a plurality of series-connected solar cells and diodes connected in series to the solar cells in a direction that blocks reverse current are connected in parallel to a common bus bar. A solar power generation system characterized in that when the power generation system is under no load, a DC voltage higher than the open circuit voltage of the system is applied between the common bus bars through a resistor, and a failure is detected using the current at this time. fault detection method. (2) A failure detection method for a solar power generation system according to claim 1, characterized in that a short-circuit breaker is provided between the DC bus bars, and the breaker is short-circuited when a failure is detected. (3) A failure detection method for a solar power generation system according to claim 1, characterized in that when a failure is detected, the DC bus voltage is maintained at a low value.