JP2002140123A - Electric power converter and control method therefor, and generating set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which a grounding location cannot be specified sometimes without allowing accurate coping with a grounding fault, because the grounding fault is dissolved sometimes naturally when a time passes after it was generated and because grounding is dissollved sometimes before a person in charge for maintenance service reaches to the site even when the person goes to the site by a contact about generation of the grounding with a user. SOLUTION: When a grounding is detected (S1), linkage is released (S2), the grounding position in a solar cell array is detected (S3), and information for showing the detected grounding position is recorded in a memory (S4).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter, a control method thereof, and a power generator, for example, a power converter linked to a commercial power system, a control method thereof, and a power generator.

[0002]

2. Description of the Related Art The practical use of residential photovoltaic power generation systems has progressed rapidly, and a large number of photovoltaic power generation systems have been operated in the market. As the number of operations increases, the absolute number of failures in the market also tends to increase, and the response to services becomes more important.

A ground fault is one of the most frequently occurring failures in electrical equipment. As a method of detecting a ground fault in a photovoltaic power generation system, a system disclosed in JP-A-9-285015, which detects a ground fault by measuring a leakage current,
The wiring from the solar cell array disclosed in JP-A-10-285965 has a three-wire structure of a positive electrode / 0 V / negative electrode, detects an array that is grounded by a ground fault overvoltage relay, and removes the grounded array from the system. There are ways to do that.

[0004] In addition, a power converter (hereinafter referred to as an "inverter")
In recent photovoltaic power generation systems, transformerless inverters (hereinafter referred to as “systems”) that make the solar cell array and the commercial power system (hereinafter referred to as “system”) non-insulated in order to reduce the cost of the entire system. The use of a "transformerless inverter") is the mainstream. The transformerless inverter generally has a ground fault detection function based on the above-described leakage current measurement in order to detect a ground fault during operation.

[0005]

After a ground fault has occurred,
It often resolves naturally over time. There are also such cases in solar power generation systems,
Even when the maintenance service personnel arrives at the site even when the maintenance service employee arrives at the site due to the notification of the occurrence of the ground fault from the user, the ground fault may be resolved by the time the maintenance service employee arrives at the site. In such a case,
Since the position of the ground fault cannot be specified, the ground fault cannot be dealt with accurately.

In order to detect a ground fault position, a method of measuring a ground voltage is effective. However, in a photovoltaic power generation system using a transformerless inverter which is currently mainstream, a type B solar cell array is operated during operation. Since it is directly connected to the grounded low-voltage power system, the ground voltage is fixed, and the ground fault position cannot be detected.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to enable a search for a ground fault position in a power generator using a transformerless inverter without being affected by the grounding of the system. I do.

Another object of the present invention is to make it possible to indicate the position of the ground fault even after the ground fault is resolved.

[0009]

The present invention has the following arrangement as one means for achieving the above object.

A power converter according to the present invention is a power converter that receives DC power from a DC power supply composed of a number of power generation cells, converts the DC power into AC power, and supplies the AC power to a commercial power system. Ground fault detecting means for detecting a ground fault of the DC power supply, opening and closing means for opening and closing the connection between the DC power side and the AC power side, and ground fault position detection for detecting a ground fault position in the DC power supply. Means for detecting a ground fault position after the ground fault is detected and the opening / closing means is opened.

[0011] Further, there is provided a power converter for inputting DC power of a DC power supply comprising a large number of power generation cells, converting the DC power into AC power, and supplying the AC power to a commercial power system, for detecting a ground fault on the DC power side. Ground fault detecting means, and a ground fault position detecting means for detecting a ground fault position in the DC power supply,
The ground fault position detecting means detects a ground fault position when a ground fault is detected, and records information indicating the detected ground fault position in a memory.

A control method according to the present invention is a control method for a power converter that inputs DC power of a DC power supply composed of a number of power generation cells, converts the DC power into AC power, and supplies the AC power to a commercial power system. When a ground fault on the power side is detected, the switching means for opening and closing the connection between the DC power side and the AC power side is opened, and after the switching means is opened, the ground in the DC power supply is opened. It is characterized by detecting a tangling position.

[0013] A method of controlling a power converter that inputs DC power of a DC power supply comprising a number of power generation cells, converts the DC power into AC power, and supplies the AC power to a commercial power system, wherein a ground fault on the DC power side is avoided. Upon detection, a ground fault position in the DC power supply is detected, and information indicating the detected ground fault position is recorded in a memory.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A photovoltaic power generator according to an embodiment of the present invention will be described below in detail with reference to the drawings. The inverters described below are all transformerless inverters.

[Configuration] FIG. 1 is a block diagram showing a configuration example of a solar power generation device according to an embodiment.

The DC power generated by the solar cell array 1 is supplied to the inverter 2 via the backflow prevention diode 6. The inverter 2 converts supplied DC power into AC power, and supplies AC power to the system 3 in which one of its lines is grounded.

The solar cell array 1 has a nominal output of 75 W, an operating voltage of 14 V, an operating current of 5.36 A, and is connected in series with 30 solar cell modules having an area of 2.2 m ² and has a 2.25 kW output. The system 3 is a 200 V 60 Hz single-phase three-wire power system.

Inverter The main configuration of the inverter 2 includes a primary-side capacitor 21 such as an electrolytic capacitor, a switching circuit 22, a connecting reactor 23, a disconnecting switch 8, a ground fault current detector 9, and a control. Part 7 Such a configuration is very common, and a detailed description is omitted. In addition, various changes can be made to the above-described components and the arrangement thereof without departing from the spirit of the present invention.

The control unit 7 controls the power flowing from the solar cell array 1, controls the switching circuit 22 for supplying the output power of the inverter 2 to the system 3, and controls the switching of the switch 8. .

The ground fault position detector 4 and the memory 5 included in the inverter 2 are characteristic components of the inverter 2. The ground fault position detector 4 includes a detector 41 for detecting a voltage between the DC power supply electrodes, a detector 42 for detecting a ground voltage of the DC power supply electrode, and a calculation unit 43 for calculating a ground fault position. Is stored in the memory 5.

Of course, the ground fault position detector 4 and the memory 5
It can be configured integrally with the control unit 7, and in practice, it is desirable to adopt such a configuration. This is because the control unit 7 is, in most cases, a digital control device using a microprocessor and generally includes an arithmetic operation unit (ALU) and a memory.
It is very convenient for realizing. The input impedance of the detectors 41 and 42 is assumed to be sufficiently high.

[Operation] When a ground fault occurs, the control unit 7 releases the connection between the inverter 2 and the system 3 by the switch 8, and then causes the ground fault position detector 4 to detect the ground fault position. The detection result is recorded in the memory 5. Hereinafter, the operation of detecting the ground fault position will be described in detail.

In a normal operation in which no ground fault occurs,
DC power from the solar cell array 1 is converted into AC power by the inverter 2 and supplied to the system 3 (reverse power flow).
Of course, in this state, the switch 8 is closed.

When a ground fault occurs in the solar cell array 1, a ground fault current flows through the type 3 grounding of the system 3, and this is detected by the ground fault current detector 9. The control unit 7 notified of this information blocks the switching circuit 22 and sets the switch 8 to the open state.

The arrangement of the ground fault current detector 9 is not limited to the AC output side of the inverter 2 but may be the DC input side of the inverter 2. It is important that a ground fault can be detected during operation of the photovoltaic power generator. Because,
Since the system 3 is grounded, if the transformerless inverter 2 is used, the ground voltage of the DC circuit will be fixed. During the inverter operation (when the switch 8 is closed), even if the ground voltage is measured, the ground fault itself will not occur. Is not detectable. Therefore, the inverter is operating (switch 8 is closed)
In the above, the ground fault current detector 9 is essential as a means capable of detecting a ground fault.

In the embodiment, a general zero-phase current detector is used as the ground fault current detector 9, and the threshold value of the current for determining a ground fault is set to 100 mA. Also, as shown in FIG.
When conducting an experiment for detecting a ground fault position, an electric wire is connected between the second and third solar cell modules 102 and 103 from the positive electrode side, and the other end of the electric wire is connected to the ground potential.

FIG. 2 is a flowchart showing an example of a procedure for detecting a ground fault position and recording a detection result according to the embodiment.
Performed by 7.

When the occurrence of a ground fault is detected, the control unit 7 (S
1), the switch 8 is opened (S2). After the inverter 2 and the system 3 are separated, the control unit 7 causes the ground fault position detector 4 to detect the ground fault position (S3), and stores the detected position information in the memory 5 (S4).

Measurement of Inter-electrode Voltage and Ground Voltage When the control unit 7 issues a ground fault position detection command, the ground fault position detector 4 uses the detectors 41 and 42 to detect the inter-electrode voltage V41 and the ground voltage V42. Measure. However, since the voltage measurement becomes meaningless if the ground fault is eliminated, it is desirable to measure the voltage as soon as possible after the interconnection is released due to the occurrence of the ground fault.

When the interconnection is released and the power conversion operation of the inverter 2 is stopped, the output current of the solar cell array 1 becomes almost zero, so that the open-circuit voltage of the solar cell array 1 is detected as V41. In the example shown in FIG. 3, for example, the electrode voltage V41
Is measured to be 600 V, and the ground voltage V42 is 40 V because the open circuit voltage of the two solar cell modules 101 and 102 is measured.
V.

An important point of the embodiment is to detect a ground fault position in a state where the solar cell array 1 is electrically separated from the system 3. By employing such a sequence, the influence of the system 3 being grounded can be completely removed.
In a grid-connected power generation system using a transformerless inverter, electrical isolation from the grid 3 is indispensable to search for a ground fault in the DC circuit. In addition, during the night when the solar cell is not generating power, for example, it is conceivable to detect a ground fault position by applying a voltage to the solar cell array 1 from an external power supply. It must be electrically isolated.

Calculation of ground fault position information The ground fault position can be indicated from the ratio between the measured inter-electrode voltage V41 and ground voltage V42. That is, by the arithmetic unit 43,
Perform a simple division to get V42 / V41 = 40/600 = 0.066. This is 6.6% of the whole array from the positive electrode of solar cell array 1.
Indicates that there is a ground fault position at the position.

The precision of the operation result does not need to be very high.
This is because the measure against the ground fault is practically a replacement of the grounded solar cell module, and it is sufficient to obtain ground fault position information indicating the grounded solar cell module. In the case of the embodiment only, the number of solar cell modules is 30, so that the accuracy of expressing the ground fault position in 30 levels is sufficient. On the other hand, the expression of the accuracy such as the ground fault position of 6.6% has an advantage of high versatility, and the degree of the accuracy of the ground fault position may be appropriately determined. Of course, a negative electrode can be used as the reference electrode.

The calculation result indicating the ground fault position obtained in this way is stored in the memory 5. However, since the control power supply is often turned off after the occurrence of the ground fault, the memory 5 is preferably nonvolatile.

In addition to the above-mentioned method of detecting the ground fault position, there is a method disclosed in Japanese Patent Application Laid-Open No. Hei 7-177646, and it is premised that the ground voltage is measured in principle.
For use in a transformerless inverter, it must be electrically separated from system 3.

In the above description, the ratio of the calculation result is stored in the memory 5 as ground fault position information.
The purpose can be achieved even if the measurement voltages V41 and V42 are recorded as they are.

The switch 8 uses a magnet contactor having mechanical contacts. However, when the open-circuit voltage is significantly higher than in the normal operation as in the case of the solar cell array 1, if the full bridge circuit as shown in FIG. It is possible to measure the inter-electrode voltage V41 and the ground voltage V42 simply by using the gate block).
This is because the voltage of the capacitor 21 charged by the solar cell array 1 is high, so that the protection diode of the switching element is reverse-biased, and the solar cell array 1 and the system 3 are substantially separated. In the case of a half-bridge circuit using coupling by a capacitor, it is desirable to execute disconnection (disconnection) by a mechanical contact.

In this way, the recorded ground fault position information is later referred to by the maintenance service personnel, so that even if the ground fault is naturally resolved, a ground fault occurs anywhere in the solar cell array 1. Can be grasped. Of course, if an operation unit, a display device or a communication device for referring to the ground fault position information is added, it is obvious that the operation becomes easier.
Such a configuration is also preferable.

If such ground fault location information is not recorded and the ground fault has been resolved naturally, the maintenance service personnel will be required to provide all of the solar cell modules of the large-area solar cell array 1 (30 sheets in the embodiment). Is 66m ² ), which requires a great deal of labor and concentration to find a small failure.

On the other hand, if the ground fault position information is recorded as in the solar power generation device according to the embodiment, the location (for example, one or at most two solar cell modules) is intensively recorded.
Should be inspected. Therefore, the inspection can be performed extremely efficiently and in a short time, and by intensively searching for a failure point,
Failure points can be found with high probability.

[0041]

[Modification] FIG. 4 is a block diagram showing a configuration example of a photovoltaic power generator in which a control unit 7 having a ground fault position detection function and a memory 5 and the like and a transformerless inverter 2 are formed separately.

In the configuration shown in FIG. 4, a switch 44 for switching the object to be measured is further provided.
At 45, the configuration is made so that the inter-electrode voltage V41 and the ground voltage V42 can be measured.

The other components are the same as those in the above-described embodiment. When a ground fault current exceeding a set value is detected, the control unit 7 opens the switch 8.

The operation of this embodiment is almost the same as that of the above embodiment, except that the measurement is performed by switching the electrode voltage V41 and the ground voltage V42 by the switch 44. For example, first, the switch 44 is switched to the electrode side (the upper contact in FIG. 4) to measure the electrode voltage V41, and then to the ground side (FIG. 4).
Then, switch to the lower contact) and measure the ground voltage V42.
In addition, the order of measurement may be either one.

A case where the DC power supply has a plurality of series circuits Next, a preferred embodiment in the case where a DC power supply such as a solar cell array has a plurality of series circuits will be described.

In general, the amount of power generated by a solar cell module is at most several hundred watts, and its withstand voltage is 1000 V or less. For this reason, in many cases, a plurality of series circuits are connected in parallel to constitute a solar cell array having a large power capacity. Figure 5
In order to cope with such a system, a switch 11 for switching a series circuit to be measured is added. Specifically, switches 11a and 11b corresponding to the series circuits 1a and 1b of the solar cell array are added, and the opening and closing of the switches are controlled by the control unit 7.

FIG. 6 is a flowchart showing an example of a procedure for detecting a ground fault position and recording a detection result according to the present embodiment.

When the occurrence of a ground fault is detected, the control section 7 (S
1), the switch 8 is opened (S2). After the inverter 2 and the system 3 are separated, the control unit 7 selects a series circuit to be measured.
(S13). That is, the switch 11a or 11b corresponding to the series circuit to be measured is closed, and the switch corresponding to the series circuit not to be measured is opened.

Next, the ground fault position is detected (S14), and it is determined whether or not the detection has been completed for all the series circuits (S14).
15), if there is an incomplete series circuit, switch switch 11 (S1
6) Re-detect the ground fault position. When the detection of the ground fault position is completed for all the series circuits, the position information and the information indicating the series circuit are stored in the memory 5 as a detection result (S17).

As described above, in this example, the series circuit to be measured is switched using the switch 11 to detect the ground fault position, and the ground fault position and the information of the series circuit are recorded in the memory 5.

If there is no switch 11, only the ratio from the reference electrode can be obtained as information indicating the ground fault position. Therefore, when the solar cell array is composed of a plurality of series circuits as shown in FIG. 5, there are at least as many solar cell modules as there may be a ground fault as the number of series circuits. If the series circuit shown in FIG. 5 is two solar cell arrays, two or four solar cell modules are ground fault candidates. On the other hand, if there is a switch 11,
Since the ground fault position can be detected for each series circuit,
Ground fault candidates can be limited. Compared to Fig. 5,
If the number of series circuits is further increased, the effect of the present example will be greater.

It is to be noted that the recording of the information is not performed after the detection of the ground fault positions of all the serial circuits is completed, but the information is recorded in step S1.
The detection may be performed for each series circuit after the detection of 4. However, care must be taken in the handling of normal series circuits. In other words, in a series circuit with a ground fault,
As 2, a stable voltage is detected. However, the ground voltage V42 of the series circuit in which no ground fault occurs depends on the ground capacitance of the photovoltaic power generation device (mainly, the solar cell array), so that a stable voltage is not always measured. For example, the voltage gradually decreases with time due to the influence of the ground capacitance. In other words, the behavior of the normal series circuit differs from that of the series circuit in which a ground fault has occurred. Therefore, the presence or absence of the transient phenomenon is determined, and the recording is performed after determining the presence or absence of the ground fault. And so on.

As described above, according to the embodiment, the following effects can be obtained.

(1) When a ground fault occurs, the solar cell circuit and the system are electrically separated to detect the ground fault position.
It is possible to search for a ground fault position without being affected by the grounding of the system 3.

(2) When a ground fault occurs, the detected ground fault position is recorded, so that the ground fault position can be indicated even after the ground fault is resolved. This facilitates inspection of the solar cell array by maintenance service personnel.

[0056]

As described above, according to the present invention,
In a power generator using a transformerless inverter,
It is possible to search for the ground fault position without being affected by the grounding of the system.

Further, it is possible to indicate the position of the ground fault even after the ground fault is resolved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a solar power generation device according to an embodiment;

FIG. 2 is a flowchart illustrating an example of a procedure for detecting a ground fault position and recording a detection result according to the embodiment;

FIG. 3 is a diagram illustrating a relationship between voltages in a ground fault state;

FIG. 4 is a block diagram showing a configuration example of a photovoltaic power generation device according to a modification;

FIG. 5 is a block diagram illustrating a configuration example of a solar power generation device according to a second modification;

FIG. 6 is a flowchart showing an example of a procedure for detecting a ground fault position and recording a detection result in the configuration shown in FIG. 5;

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02M 7/48 H02M 7/48 R (72) Inventor Naoki Manabe 3-30-2 Shimomaruko, Ota-ku, Tokyo F term in Canon Inc. (reference) 5G004 AA04 AB02 BA01 CA01 5G053 AA06 BA03 CA01 DA01 EB09 FA01 5H007 AA17 BB07 CA01 CB05 CC09 DB02 DB12 DC02 DC05 FA03 FA14 GA09 5H410 BB05 CC02 DD03 DD04 EA10 EA25 EB25 FF25 EB25 FF25 EB25 FF25 EB25 FF25 EB25 FF25 EB25 FF25 LL18 5H420 CC03 EA10 EA45 EB26 EB39 FF04 FF25 LL04 LL09

Claims (13)

[Claims] 1. A power converter for inputting DC power of a DC power supply comprising a number of power generation cells, converting the DC power into AC power, and supplying the AC power to a commercial power system, for detecting a ground fault on the DC power side. Ground fault detecting means, opening and closing means for opening and closing the connection between the DC power side and the AC power side, and ground fault position detecting means for detecting a ground fault position in the DC power supply, The power converter, wherein the ground fault position detecting means detects a ground fault position after the ground fault is detected and the opening / closing means is opened. 2. The power converter according to claim 1, wherein said ground fault position detecting means records information indicating the detected ground fault position in a memory. 3. A power converter for inputting DC power of a DC power supply comprising a number of power generation cells, converting the DC power into AC power, and supplying the AC power to a commercial power system, for detecting a ground fault on the DC power side. Ground fault detecting means, and a ground fault position detecting means for detecting a ground fault position in the DC power supply, wherein the ground fault position detecting means detects a ground fault position when a ground fault is detected. A power converter for recording information indicating a detected ground fault position in a memory. 4. The ground fault position detecting unit detects the ground fault position by detecting an output voltage of the DC power supply and a ground voltage of an electrode of the DC power supply. 4. The power converter according to claim 3. 5. When the DC power supply includes a plurality of series circuits, the DC power supply further includes a switch inserted in series with each series circuit, and the ground fault position detecting means includes a ground fault position for each series circuit. 5. The method according to claim 2, wherein
A power converter according to any one of the above. 6. The power conversion device according to claim 5, wherein the ground fault position detecting means records a detection result of a ground fault position for each of the series circuits in the memory. 7. A power generator comprising the power converter according to any one of claims 1 to 6. 8. A method for controlling a power converter that inputs DC power from a DC power supply comprising a number of power generation cells, converts the DC power into AC power, and supplies the AC power to a commercial power system, wherein a ground fault on the DC power side is provided. When detected, open / close means for opening and closing the connection between the DC power side and the AC power side, and after the open / close means is opened, detect a ground fault position in the DC power supply. A control method characterized by the above-mentioned. 9. The control method according to claim 8, further comprising recording information indicating the detected ground fault position in a memory. 10. A method for controlling a power converter that inputs DC power of a DC power supply composed of a number of power generation cells, converts the DC power into AC power, and supplies the AC power to a commercial power system. A control method comprising: detecting a ground fault position in the DC power supply when detected, and recording information indicating the detected ground fault position in a memory. 11. When the DC power supply includes a plurality of series circuits, controlling the opening and closing of a switch inserted in series in each series circuit to detect a ground fault position for each series circuit. 11. The control method according to claim 9 or claim 10, wherein 12. The control method according to claim 11, further comprising recording a detection result of a ground fault position for each of the series circuits in the memory. 13. A recording medium in which a program code of the control method according to claim 8 is recorded.