JP3339895B2 - Reverse charging operation prevention method and device - Google Patents

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 operated in connection with a low-voltage distribution line. More specifically,
TECHNICAL FIELD The present invention relates to a reverse charging operation prevention method and a reverse charging operation protection method for stopping a photovoltaic power generation system when power supplied from a commercial power supply of a commercial power system to a distribution line is stopped.

[0002]

2. Description of the Related Art In the near future, in the near future, solar cells will be installed on roofs and roofs mainly for general low-voltage consumers such as private houses, and the output from the solar cells will be connected to the commercial power system via an inverter. Grid-connected photovoltaic power generation systems are expected to be widely spread.

[0003] When a large number of photovoltaic power generation systems, mainly low voltage consumers, are connected to the commercial power system,
It is difficult to centrally control all of these solar power systems from a power company.

Therefore, when an accident occurs inside the photovoltaic power generation system or when an accident occurs in a distribution line,
Or, when performing maintenance work on distribution lines,
We consider that it is most appropriate to improve the operation reliability of each solar power generation system by adopting an autonomous protection system using an accident detection function and incorporating it into each individual solar power generation system. Have been.

[0005] Even if the operation reliability of the system is improved by the autonomous protection method, the distribution line is not supplied from the system power supply due to the occurrence of a distribution line accident or maintenance work of the distribution line. When the supply of power from the system power supply to the distribution line is stopped due to disconnection, it is necessary to reliably prevent reverse charging from the solar power generation system to the distribution line in order to ensure safety on the distribution line side. For this reason, it is considered that the autonomous protection system needs to have a system over / under voltage detection function and a system frequency abnormality detection function. By incorporating such two abnormality detection functions into each photovoltaic power generation system, it was thought that it was possible to correctly cope with most of the internal accidents and wiring accidents that could normally occur.

[0006]

However, recently,
Under special conditions where the power generated by the photovoltaic power generation system and the power consumption of the low-voltage load are balanced, even if the power supply from the system power supply to the distribution line stops, both the system over / under voltage and the system frequency abnormality will occur. It could not be detected, and as a result, it was found that the photovoltaic power generation system fell into a so-called reverse charging operation state in which the operation continued while charging the distribution line. If such a reverse charging operation occurs, the distribution line operator may be exposed to the danger of electric shock.Furthermore, since an overcurrent occurs due to a mismatch between the system power supply phase and the distribution line voltage phase, the distribution equipment and load equipment may not be operated. It has been pointed out that there is a risk of causing destruction, and this is a problem.

According to the present invention, when the power supply from the system power supply to the distribution line is stopped, the interconnection between the photovoltaic power generation system and the distribution line is reliably shut off, and the interconnection is protected by a simple device. It is an object of the present invention to provide a method and apparatus for preventing reverse charging operation.

[0008]

In order to achieve the above object, a method for preventing reverse charging operation according to the present invention comprises converting a DC power generated by a solar cell into an AC power using an inverter, and converting the AC power into a commercial power system via a transformer. In a photovoltaic power generation system that supplies a commercial power distribution line to which power is supplied, a harmonic voltage flowing out of the distribution line due to magnetic hysteresis of a transformer is detected by comparison with a preset value , The outflow of current from the photovoltaic power generation system is stopped to prevent reverse charging of distribution lines. Here, in the present invention, it is preferable to use a current control type as the inverter, but the present invention is not particularly limited to this.

Further, the reverse charging operation preventing device according to the present invention is configured such that a power supply of a commercial power system is connected to a distribution line of commercial power supplied through a transformer, and DC power generated by the solar cell is converted to AC power by an inverter. In a photovoltaic power generation system that is supplied after being converted into a power supply, a means for detecting a harmonic voltage flowing out to a distribution line, a means for comparing the harmonic voltage with a predetermined value, and an operation of the inverter based on the comparison result And means for stopping.

Further, the reverse charging operation preventing device according to the present invention is configured such that a power supply of a commercial power system is connected to a distribution line of commercial power supplied through a transformer, and DC power generated by the solar cell is converted to AC power by an inverter. In a photovoltaic power generation system that is supplied after being converted into a power supply, a means for detecting a harmonic voltage flowing out to a distribution line, a means for comparing the harmonic voltage with a predetermined value, and an inverter and a distribution line based on the comparison result And a shutoff means for opening and closing the connection.

[0011]

Therefore, when the supply of electric power from the commercial power system is stopped, the AC power output from the photovoltaic power generation system to the commercial power distribution line is increased due to the magnetic hysteresis characteristic of the transformer of the commercial power system. Wave voltage is generated. In the reverse charging operation prevention method, the outflow of current from the photovoltaic power generation system is stopped by detecting this harmonic voltage. Also,
If a current control type having a high impedance is used for an inverter used for DC / AC conversion, a harmonic voltage generated in a distribution line is increased, and it becomes easier to extract the harmonic voltage.

[0012] In the reverse charging operation prevention device, the leakage to the distribution line
The detected harmonic voltage is compared with a predetermined value, and when the power supply from the commercial power supply to the distribution line is stopped, the harmonic voltage increases. If it is larger, the operation of the inverter is stopped.

According to another aspect of the present invention, a harmonic voltage flowing into a distribution line is detected, and the detected harmonic voltage value is compared with a predetermined value. Block the connection between

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the present invention will be described below in detail with reference to the embodiments shown in the drawings.

1 to 5 show an embodiment of a method and apparatus for preventing reverse charging operation according to the present invention. In the present invention, the configuration of the photovoltaic power generation system is not particularly important except for the inverter, and a detailed description thereof will be omitted.

Referring to FIG. 1, first, the configuration of a commercial power system interconnected with a photovoltaic power generation system will be described. The photovoltaic power generation system 1 is connected to a commercial distribution line 3 and a low-voltage load 4 at an interconnection point 2, and is configured to supply the output AC power to the low-voltage load 4. The commercial distribution line 3 mainly connects a pole transformer 31 that converts high-voltage AC into low-voltage AC and supplies power to low-voltage consumers, and a secondary winding of the pole transformer 31 to the interconnection point 2. Low voltage side commercial distribution line 3L
And a high-voltage commercial distribution line 3H connecting the primary winding of the pole transformer 31 to the circuit breaker 51 of the substation 5. The substation 5 mainly includes a circuit breaker 51 and a main transformer 5 for distribution.
The AC power from the system power supply 6 of the commercial power system is supplied to the primary winding of the pole transformer 31 via the main distribution transformer 52 and the circuit breaker 51. Further, a high voltage load 7 is connected to the high voltage side commercial distribution line 3H.

Next, a description will be given of the reverse charging operation prevention device for the solar power generation system 1 shown in FIG. The output of the solar cell 11 is connected to the input terminal of the current control type inverter 12. The current control type inverter 12 is configured to convert the input DC power into AC power and output it from an output terminal. The current control type inverter 12 can be controlled so that the AC output current becomes a sine wave of the fundamental frequency, and the impedance can be regarded as substantially infinite when viewed from the AC side, that is, from the harmonic generation source. An output terminal of the current control type inverter 12 is connected to the interconnection point 2 via an interconnection contactor 13 as a breaking means. The operation of the current control type inverter 12 can be stopped by an inverter stop signal Ss which is a stop control signal from the operation control device 15. The interconnecting contactor 13 is opened by an interconnecting contactor disconnection signal So that is a stop control signal from the operation control device 15. The operation control device 15 takes in the voltage at the interconnection point 2 and increases the harmonic voltage flowing out to the low-voltage side commercial distribution line 3L due to the magnetic hysteresis of the pole transformer 31 when the power supply from the commercial power supply is stopped. When the detected increase in the harmonic voltage is equal to or greater than a predetermined value, the stop control signal (the inverter stop signal Ss and the interconnection contactor disconnection signal S
o) is formed and output.

The operation control device 15 includes a third harmonic filter 16 and an absolute value comparator 17. The third harmonic filter 16 has a function of resonating with the third harmonic voltage of the commercial distribution line 3 and outputs a harmonic signal proportional to the absolute value of the third harmonic voltage to the absolute value comparator 17. The absolute value comparator 17 compares the absolute value of the harmonic from the third harmonic filter 16 with a preset set voltage value. If the output value of the harmonic is larger than the set voltage value, the inverter stops. The signal Ss can be output to the current control type inverter 12, and the interconnection contactor disconnection signal So can be output to the interconnection contactor 13.

Next, with reference to FIGS. 2 to 5, it will be described below that the embodiment of the present invention is constructed as described above so that interconnection protection can be achieved.

FIG. 2 shows an example of harmonic spectrum characteristics of the exciting current of the pole transformer 31 in the configuration of FIG. In the figure, the horizontal axis indicates the order, and the vertical axis indicates the amount of harmonics. As is apparent from FIG.
Of the excitation current includes a relatively large harmonic component due to the magnetic hysteresis characteristic of the pole transformer 31, and the third harmonic is the largest.

If the pole transformer 31 is a three-phase transformer with a delta connection, the harmonic current circulates in the transformer or flows out to the commercial distribution line 3 because the phases of the respective phases match. Never. However, in general, 1
The pole transformer 31 installed to supply power to low voltage consumers of 00 [V] or 200 [V] is single-phase or V-connected, so the third harmonic generated by the pole transformer 31 The current will flow out to the commercial distribution line 3.

FIG. 3 is a circuit diagram showing an equivalent circuit at a fundamental frequency of 50 [Hz] or 60 [Hz] when a photovoltaic power generation system employing a current control type inverter is connected to a low voltage commercial distribution line 3L. It is. Here, the photovoltaic power generation output current of the photovoltaic power generation system 1 is Ipv, the low voltage load impedance of the low voltage load 4 is Zl, the transformer exciting current of the pole transformer 31 is It, and the transformer leakage impedance of the pole transformer 31 is Zt1. the transformer excitation impedance pole transformer 31 Zt2, Zh high pressure load impedance of the high voltage load 7, the system voltage source is the output of the power distribution main transformer 52 and Vs, and Zt2 »Zl, When Zh» Zt1 ,
The photovoltaic power generation system 1 supplies power to the low-voltage load (Zl) 4 and the high-voltage load (Zh) 7 via the pole transformer 31, respectively. This state is shown by a dotted line. Note that a1-a2 and b1-b2 indicate interconnection points.

Now, assuming that the effective component and the reactive component of the output power of the photovoltaic power generation system 1 and the total power consumption of the load are in equilibrium, the interconnection point b1-b2 between the substation 5 and the commercial distribution line 3 is assumed.
Becomes zero. Therefore, even if the circuit breaker (S) 51 is opened and the commercial distribution line 3 is disconnected from the substation (commercial power supply) 5 due to a distribution line accident or the like in this state, the conventional system does not The output current 1 and the load current flowing through the low-voltage load 4 and the high-voltage load 7 do not change. As a result, an accident cannot be detected by the system voltage excess / deficiency detection function and the system frequency abnormality detection function, resulting in reverse charging operation. Becomes

However, according to the present invention employing the current control type inverter 12, the transformer operates as a current source having a high impedance when viewed from the AC side, that is, the harmonic generation source, and operates when the power supply to the commercial distribution line 3 is stopped. A harmonic voltage is generated due to the magnetic hysteresis characteristic of 31. Therefore,
The present invention constantly monitors the harmonic voltage generated by the above-described configuration, detects that the harmonic has increased by a predetermined value or more, and disconnects the connection to the distribution line.

The fact that this is true will be described with reference to FIGS. 4 and 5. FIG. FIG. 4 shows an equivalent circuit of the circuit of FIG. 3 in a higher harmonic region. FIG. 5 shows an equivalent circuit when the circuit breaker S is opened in the circuit of FIG. In addition,
In these figures, the harmonic impedance of the low-voltage load 4 is zl, the harmonic component of the transformer exciting current of the pole transformer 31 is it, the transformer leakage harmonic impedance of the pole transformer 31 is zt1, and the pole transformer 31 has a harmonic impedance of zt1. The transformer exciting harmonic impedance is zt2, the harmonic impedance of the high voltage load 7 is zh, the harmonic voltage is v, and zt2 >> zl,
zh >> zt1. In addition, a1-a2 and b1-b2 are:
Indicates the interconnection point.

Here, when viewed from the pole transformer 31 which is a harmonic generation source, the impedance becomes infinite because the current control type inverter 12 can be regarded as a current source of the fundamental frequency. On the other hand, since the system voltage source Vs of the system power supply 6 is a voltage source, the impedance becomes zero. Therefore, it can be seen that the equivalent circuit in the harmonic region may be represented as shown in FIGS. Then, as shown by the dotted line in FIG. 4, the harmonic component it of the exciting current generated from the pole transformer 31 flows into the system power source (indicated by reference numeral 6 in FIG. 1) having a small impedance, and as a result, as shown in FIG. Sign 2
The harmonic voltage v does not appear at the interconnection point (a1-a2) indicated by (1) (v = 0). That is, at the time of normal power supply from the system power supply to the distribution line, the interconnection point (a1-a
2) No harmonic voltage appears at 2.

However, when the circuit breaker (S) 51 is opened as shown in FIG. 5, that is, when the power supply from the system power supply to the distribution line is stopped, the harmonic current i
t cannot flow into the system power supply 6 side,
As shown by the dotted line, the load flows into the low-pressure load (zl) 4 and the high-pressure load (zh) 7. Therefore,
At the interconnection point (a1-a2) 2, the harmonic voltage v (≠ 0) appears remarkably.

Then, the change of the harmonic voltage v at the interconnection point (a1-a2) 2 is detected by the operation control device 15 of the photovoltaic power generation system 1, and the operation of the photovoltaic power generation system 1 is stopped. It is possible to prevent a reverse charging operation.

Next, the operation of the embodiment of the present invention will be described below with reference to FIG.

In the solar power generation system 1, the solar cell 11
From the current control type inverter 12
, And supplies power to the low-voltage load 4 connected to the commercial distribution line 3 at the interconnection point 2.

The third harmonic filter 16 of the operation control device 15 has a function of resonating with the third harmonic voltage of the commercial distribution line 3 and can output a signal proportional to its absolute value. The voltage of the system point 2 is monitored.

Now, the accident of the commercial distribution line 3 and the commercial distribution line 3
When the circuit breaker 51 in the substation 5 is opened due to maintenance work of the substation 5, the harmonic impedance on the substation 5 side as viewed from the pole transformer 31 of the commercial distribution line 3 increases,
Due to the magnetic hysteresis characteristic of the pole transformer 31,
The third harmonic voltage of the commercial distribution line 3 increases instantaneously. Since the voltage at the interconnection point 2 is constantly monitored by the third harmonic filter 16 of the operation control device 15, the third harmonic filter 16 immediately detects the increase and changes the absolute value of the detection signal to the absolute value. It is supplied to the comparator 17. The absolute value comparator 17 compares the absolute value of the detection signal from the third harmonic filter 16 with a predetermined set voltage value, and compares the absolute value of the detection signal from the third harmonic filter 16 with the set voltage. When the values exceed the values, the inverter stop signal Ss is supplied to the current control type inverter 12 and the interconnection contactor disconnection signal So is supplied to the interconnection contactor 13. As a result, the current control type inverter 12 stops operating, and at the same time, the interconnection contactor 13 is opened. Thereby, the reverse charging operation of the commercial distribution line 3 by the photovoltaic power generation system 1 can be prevented.

As described above, in the present embodiment, in the photovoltaic power generation system 1 that is connected to the commercial power distribution line 3, the current control type inverter 12 is adopted in the photovoltaic power generation system 1, and the power supply to the commercial power distribution line 3 is performed. The operation control device 15 of the photovoltaic power generation system 1 detects the harmonic voltage generated from the pole transformer 31 of the commercial distribution line 3 when the supply is stopped, so that the operation of the photovoltaic power generation system 1 is stopped. Irrespective of the balance between the power generated by the system 1 and the total power consumption of the low-voltage load 4 and the high-voltage load 7, dangerous reverse charging operation of the photovoltaic power generation system 1 can be quickly and reliably prevented with a simple device.

The above embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, the current control type inverter 12
And the third harmonic is generated from the pole transformer 31 and the power supply to the commercial distribution line 3 is stopped according to the magnitude of the third harmonic. May be used. Alternatively, all harmonics equal to or higher than the third harmonic may be used.

Although power is supplied from the pole transformer 31 to the commercial distribution line 3 of the low-voltage customer, any commercial distribution line 3 connected to the photovoltaic power generation system 1 may be used regardless of the pole transformer 31. A transformer installed on the ground or a transformer installed underground may be used.

Further, in this embodiment, a current control type inverter is used as the inverter 12 of the photovoltaic power generation system 1, but the present invention is not particularly limited to this, and a voltage control type inverter can be used. In this case, it is necessary to add impedance, such as inserting a coil in series between the inverter and the transformer, or to amplify the harmonic by an amplifier, in order to make the harmonic appear significantly at the interconnection point.

[0037]

As is apparent from the above description, according to the reverse charging operation prevention method of the present invention, the harmonic voltage generated from the transformer when the power supply from the commercial power supply to the distribution line is stopped is reduced.
Since the photovoltaic power generation system is stopped by detecting it by comparison with a preset value, the photovoltaic power generation is stopped when the commercial power supply is stopped regardless of the balance of the power supply from the commercial power supply and the photovoltaic power generation system. Dangerous reverse charging operation from the system can be quickly and reliably prevented. In particular, when a current control type inverter is used as the inverter of the photovoltaic power generation system, the impedance viewed from the harmonic generation source becomes infinite and the harmonic voltage appears high, so that it is easy to catch the occurrence of the abnormality.

Further, reverse charging driving prevention device of the present invention, distribution
Means for detecting the harmonic voltage flowing out to the electric wire, means for comparing the harmonic voltage with a predetermined value, and means for stopping the operation of the inverter based on the result of this comparison are included. The operation of the inverter of the photovoltaic power generation system can be stopped by using the harmonics caused by the magnetic hysteresis of the transformer that occurs when the power supply of the photovoltaic power supply stops, and the reverse charging from the system can be reliably stopped.

Further, according to the present invention, the connection between the inverter and the distribution line is cut off by the cut-off means operated by the harmonic generated when the power supply from the commercial power supply system is stopped, so that the current to the distribution line can be more reliably transmitted. The outflow can be stopped.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a photovoltaic power generation system provided with an embodiment of a reverse charging operation prevention device according to the present invention, and a commercial power system connected to the photovoltaic power generation system.

FIG. 2 is a characteristic diagram showing a harmonic spectrum characteristic of an exciting current of a transformer of the commercial power system.

FIG. 3 is a circuit diagram showing an equivalent circuit at a fundamental frequency of a power system interconnected by a photovoltaic power generation system.

FIG. 4 is a circuit diagram showing an equivalent circuit in a harmonic component of a power system interconnected by a photovoltaic power generation system.

FIG. 5 is a circuit diagram showing an equivalent circuit of a high-frequency component when power supply to a commercial distribution line of a power system interconnected by a photovoltaic power generation system is stopped.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photovoltaic power generation system 2 Interconnection point 3 Commercial distribution line 4 Low voltage load 5 Substation 6 System power supply 7 High voltage load 11 Solar cell 12 Current control type inverter 13 Interconnection contactor 14 Exciting device 15 Operation control device 16 Third harmonic filter 17 Absolute value comparator 31 Pole-mounted transformer 3L Low-voltage commercial distribution line 3H High-voltage commercial distribution line 51 Circuit breaker 52 Main transformer for power distribution

──────────────────────────────────────────────────続 き Continuing from the front page (72) Eiji Hashimoto, Inventor 2-1-1-1, Iwatokita, Komae-shi, Tokyo Inside the Komae Research Center, Central Research Institute of Electric Power Industry (72) Akio Kitamura 3, Nakanoshima, Kita-ku, Osaka-shi, Osaka 3-22, Kansai Electric Power Co., Inc. (72) Kazuo Nakaji, Inventor 3-3-22 Nakanoshima, Kita-ku, Osaka City, Osaka Prefecture (72) Inventor, Hiroshi Matsuda 3 Nakanoshima, Kita-ku, Osaka City, Osaka No.3-22, Kansai Electric Power Co., Inc. (56) References JP-A-63-124727 (JP, A) JP-A-61-92131 (JP, A) JP-A-62-172294 (JP, U) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) H02J 3/38 H02H 3/52

Claims (4)

(57) [Claims] In a solar power generation system, a DC power generated by a solar cell is converted into AC power by using an inverter, and the power is supplied to a commercial power distribution line to which power of a commercial power system is supplied via a transformer. previously harmonic voltage is discharged to the distribution line due to transformer magnetic hysteresis
A method for preventing reverse charging operation, wherein the reverse charging operation is detected by comparing with a set value and stopping the outflow of current from the photovoltaic power generation system to prevent reverse charging of the distribution line. 2. The method according to claim 1, wherein a current control type is used for the inverter. 3. A photovoltaic power generation system in which a power source of a commercial power system is connected to a distribution line of commercial power supplied via a transformer, and DC power generated by the solar cell is converted into AC power by an inverter and supplied. in the system, flow to the distribution lines
Means for detecting a harmonic voltage issued, means for comparing the harmonic voltage to a predetermined value, the reverse charging driving prevention, characterized in that it comprises a means for stopping the operation of the inverter by a result of the comparison apparatus. 4. A photovoltaic power generation system in which a power supply of a commercial power system is connected to a distribution line of commercial power supplied through a transformer, and DC power generated by a solar cell is converted into AC power by an inverter and supplied. in the system, flow to the distribution lines
Means for detecting a harmonic voltage issued, means for comparing the harmonic voltage to a predetermined value, that the result of the comparison with a cut-off means for opening and closing a connection between the distribution line and the inverter Reverse charging operation prevention device characterized by the following.