JP4178743B2 - DC leakage detection device for grid-connected inverter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
This invention relates to DC leakage detecting device for system interconnection inverter that detects the leakage of the DC power generator such as a solar cell power generation system.
[0002]
[Prior art]
In recent years, devices using direct current have increased in a wide range of fields. For maintenance management to operate these devices smoothly and safely, for example, the necessity of a direct current leakage detection device used for a direct current leakage breaker, etc. The nature has increased.
[0003]
2. Description of the Related Art Conventionally, a device using a zero-phase current transformer is widely known as a leakage detection device used for an AC leakage breaker. However, a leakage detection device using a zero-phase current transformer cannot detect a DC leakage. For this reason, a zero phase current transformer cannot be used for a DC leakage detection device. Therefore, Hall element type, shunt resistance type, magamp type, flux gate type DC leakage detection devices (Japanese Patent Laid-Open Nos. 47-1644, 53-31176, 59-46859, and 6-6-1) (See each publication such as No. 74978).
[0004]
In the Hall element method, a detected conductor is wound in a toroidal shape directly around a core of a magnetic material in which a gap is disposed in a part, and a magnetic flux in the core based on a change in DC current flowing through the detected conductor. This is a method in which a change is directly detected by a Hall element.
[0005]
In addition, the shunt resistance method is a method in which a shunt resistor is connected in series to the detected conductor and a potential difference generated at both ends of the shunt resistor is detected.
The mag-amplifier system uses a magnetic material core formed by winding a detection coil in a toroidal shape. The detected conductor is penetrated inside the core, and the magnetic material core is saturated with a direct current flowing through the detected conductor. By DC biasing within the density, the alternating magnetic flux generated by applying alternating current to the coil wound around the core in advance generates imbalance when the alternating magnetic flux reaches saturation in the positive and negative directions, and the change Is detected by the detection coil. In this system, in order to change the magnetic flux in the core in advance, a configuration is adopted in which an exciting coil is wound around the core and an alternating current of a predetermined value is supplied.
[0006]
In the fluxgate method, a detection coil is wound in a toroidal shape around a core of an annular magnetic material that can periodically form a magnetic gap in part, and a detection conductor is placed inside this core to detect the detection A magnetic flux is generated in the core by a direct current flowing in the conducting wire, and the magnetic flux generated by the direct current is temporally changed (ON-OFF) by opening and closing the magnetic gap, and the change in the magnetic flux generates the detection coil. This is a method of detecting by electromotive force.
[0007]
[Problems to be solved by the invention]
By the way, in each of the above-mentioned DC leakage detection devices, a Hall element is used or the core structure is complicated, and a large number of electronic circuits are required due to the use of magnetic flux change in principle. Therefore, there was a problem that it would be expensive.
[0008]
An object of the present invention is to provide a DC leakage detection device for a grid-connected inverter that has a simple structure and requires a small number of electronic circuits.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, there is provided a DC leakage detection device for a grid-connected inverter that includes a plurality of switching elements and is connected to an AC power supply via an inverter that converts DC power of the DC power supply into AC power. Provided.
[0010]
The DC leakage detection device for the grid-connected inverter is magnetized according to the difference between the DC current flowing in the first detected conductor and the second detected conductor of the DC circuit connecting the DC power source and the inverter. A core, a detection coil for detecting DC leakage wound around the core, a first voltage detection circuit for detecting a voltage induced in the detection coil, and a third detected conductor penetrating inside the core An AC current load circuit for supplying an AC current from the AC power supply to the AC power supply, and a second voltage detection for detecting an AC voltage connected to the AC power supply by converting it to an effective value or a rectified average value A circuit, a divider for calculating a value obtained by dividing the detection signal B of the second voltage detection circuit by the detection signal A of the first voltage detection circuit, and an output signal of the divider before connection Sample hole memorized as reference level A circuit composed of a comparator circuit output signal of the divider (B / A) is for outputting the electric leakage determination signal when it becomes less than the stored reference level in said sample and hold circuit.
[0011]
According to the DC leakage detection device for the grid-connected inverter, when an unbalanced DC current (operating current) flows through the first detected conductor and the second detected conductor, the magnetic flux change in the core shifts to a saturated state . Therefore, the output signal (B / A) of the divider and the reference level stored in the sample and hold circuit are compared by the comparison circuit, and a leakage signal for detecting leakage can be output.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is a block diagram showing a configuration of a DC leakage detection apparatus according to the present invention.
[0013]
In the figure, reference numeral 10 denotes an annular core made of a magnetic material such as a cobalt-based amorphous alloy having excellent square characteristics. A coil 11 for detecting DC leakage is wound around the core 10, and the core 10 and the coil 11 constitute a detection unit.
[0014]
A detected conductor (first detected conductor) 13 and a detected conductor (second detected conductor) 14 of the DC circuit are passed through the hole 12 of the core 10. Among these, the anode of the DC power source E is connected to the detected conductor 13 to be a plus power line of the DC circuit, and the cathode of the DC power source E is connected to the detected conductor 14 to be a minus power line. . Reference numeral 15 denotes a load of the DC power supply E, and DC currents I1 and I2 in opposite directions flow through the detected conductors 13 and 14, respectively.
[0015]
20 is an AC output circuit that outputs an AC current, and 21 is a load of the AC output circuit 20. The AC current of the AC output circuit 20 flows through the detected conductor (third detected conductor) 22 that penetrates the hole 12 via the load 21.
[0016]
A voltage detection circuit 30 detects the voltage level induced in the coil 11 and has a function of converting the voltage level input thereto into an effective value or a rectified average value. A comparison circuit 31 compares the voltage detection level 32 output from the voltage detection circuit 30 with a preset reference voltage level 33, and when the voltage detection level 32 falls below the reference voltage level 33. The leakage signal 34 for detecting the leakage of the DC circuit is output.
[0017]
Next, the operation of the DC leakage detection device will be described.
FIG. 2 is a graph showing changes in magnetic flux in the core, and FIG. 3 is a diagram showing a relationship between an alternating current and a coil voltage.
[0018]
First, the alternating current shown in FIG. 3A is caused to flow through the detected conductor 22 by the alternating current output circuit 20 and its load 21. When the magnetic flux in the core 10 changes in the vicinity of the coordinate origin in FIG. 2, if no direct current (zero-phase current) flows through the detected conductor 13 and the detected conductor 14, the change in the magnetic flux in the core 10 is φ1. Not saturated in state. For this reason, the voltage induced in the core 10 by the magnetic flux change φ1 has a voltage waveform substantially similar to the alternating current waveform flowing through the detected conductor 22 as shown in FIG.
[0019]
FIG. 4 is a diagram illustrating a relationship between an AC current waveform and a voltage induced in the core when DC leakage is detected.
When an unbalanced DC current (operating current) is passed through the detected conducting wire 13 and the detected conducting wire 14, the magnetic flux change in the core 10 shifts to the state of φ2, which is a saturated state. When the core 10 is saturated, the voltage induced in the coil 11 by the magnetic flux change φ2 has a smaller amplitude and a distorted voltage with respect to the voltage waveform of FIG. 3B as shown in FIG. It becomes a waveform.
[0020]
As shown in FIG. 2, assuming that the voltages obtained from the coil 11 when the magnetic flux change is φ1 and φ2 are V1 and V2, respectively, if it is known that the applied voltage of the coil 11 has decreased from V1 to V2, DC leakage is detected. be able to. In this embodiment, as shown in FIGS. 3 and 4, the voltage waveform changes from V1 to V2 due to DC leakage, and the waveform is distorted. Therefore, the effective value or the rectified average value of the applied voltage of the coil 11 is used as the voltage detection circuit. The DC leakage is detected by determining at 30 and determining in the comparison circuit 31 that the voltage applied to the coil 11 has decreased from V1 to V2.
[0021]
That is, when a leakage occurs, an imbalance (I1 ≠ I2) occurs in the direct currents I1 and I2 flowing in the opposite directions of the detected conductors 13 and 14, and the difference (| I1-I2 |) is the leakage current. Therefore, in this embodiment, DC leakage can be detected using this difference as an operating current. Further, when no leakage occurs, I1 = I2 and the directions of the currents I1 and I2 flowing through the detected conductors 13 and 14 are opposite, so that the generated magnetic field cancels each other, thereby changing the magnetic flux. Remains φ1 and no DC leakage is detected.
[0022]
According to such a DC leakage detection device, since the simplest configuration in which the coil 11 is wound in a toroidal shape is employed on the annular core 10, the structure is very simple. For this reason, the DC leakage detection device according to the purpose can be easily and freely manufactured. In other words, measurement sensitivity, measurement accuracy, etc. can be freely controlled by combining the type and size of the core 10 and the number of penetrations of the conductors 13 and 14 to be detected. Is obtained.
[0023]
In addition, the electronic circuit necessary for detecting the leakage is very simple and requires a small number of parts, so that an inexpensive DC leakage detection device can be provided.
(Second embodiment)
Next, a DC leakage detection device in which the DC leakage detection device is applied to a grid interconnection inverter will be described.
[0024]
FIG. 5 is a block diagram showing the configuration of the DC leakage detection apparatus according to the second embodiment. The DC leakage detection device includes a plurality of switching elements 40a, 40b, 40c, and 40d, and an inverter 42 that converts DC power of the DC power supplies 41a and 41b into AC power, and AC power supplies 43a and 43b are connected relays 44a. , 44b, the DC power supplies 41a, 41b, the detected conductor (first detected conductor) 13, the detected conductor (second detected conductor) 14, and the inverter 42 This corresponds to the DC circuit described in one embodiment. As in FIG. 1, the core 10 and the coil 11 constitute a detection unit, and the detected conductors 13 and 14 of the DC circuit are passed through the hole 12 of the core 10.
[0025]
Here, the AC output circuit of the DC leakage detection device uses an AC power supply 43a or 43b to which the inverter 42 is connected in an interconnected manner. Thereby, the configuration of the AC output circuit can be simplified, and the DC leakage detection device can be provided at low cost. However, when the AC power supply 43a (or 43b) in which the inverter 42 is connected to the AC output circuit is used, the AC current 45 flowing through the load 21 of the AC output circuit also changes when the voltage changes. A voltage detection circuit (first voltage detection circuit) 46 detects a voltage level induced in the coil 11, and has a function of converting the voltage level input thereto into an effective value or a rectified average value. Yes. For this reason, the DC currents I1 and I2 of the detected conductors 13 and 14 are equal to each other (I1 = I2), and the output of the voltage detection circuit 46 changes even if no leakage occurs. There was a risk of becoming.
[0026]
In order to avoid such erroneous detection, the output signal A of the voltage detection circuit 46 and the voltage of the AC power supply 43a are converted into their effective values or rectified average values by the voltage detection circuit 47 (second voltage detection circuit). The signal B is input to the divider 48, and the output signal (B / A) of the divider 48 is set as a determination target (voltage detection level) for DC leakage detection. Before the inverter 42 is connected to the AC power sources 43a and 43b, there is no difference between the positive DC current I1 and the negative DC current I2 flowing through the detected conductor 13 of the DC circuit. Therefore, the output signal (B / A) of the divider 48 before the interconnection is stored in the sample / hold circuit 49, and this output signal is used as a reference level 50 for the output signal (B / A) after the interconnection. As a result, it is possible to accurately detect only the DC leakage component.
[0027]
【The invention's effect】
As described above, according to the DC leakage detection device of the present invention, it is possible to freely operate the measurement sensitivity, the measurement accuracy, etc. only by configuring a detection unit with a simple structure, and the required number of electronic circuits is small. It is possible to provide a low-cost grid-connected inverter DC leakage detector.
In addition, it is possible to simplify the configuration of the AC output circuit by using an AC power source connected to the inverter, and to accurately detect only the DC leakage component.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a DC leakage detection apparatus according to the present invention.
FIG. 2 is a graph showing changes in magnetic flux in the core.
FIG. 3 is a diagram illustrating a relationship between an alternating current and a voltage of a coil.
FIG. 4 is a diagram showing a relationship between an AC current waveform and a voltage induced in a core when DC leakage is detected.
FIG. 5 is a block diagram showing a configuration of a DC leakage detection apparatus according to a second embodiment.
[Explanation of symbols]
10 Core 11 Coil 12 Hole 13 Detected conductor 14 Detected conductor 20 AC output circuit 21 Load of AC output circuit 22 Detected conductor 30 Voltage detection circuit 31 Comparison circuit 40a, 40b, 40c, 40d Switching element 41a, 41b DC power supply 42 Inverters 43a, 43b AC power supplies 44a, 44b Interconnection relay 45 AC current 46 Voltage detection circuit 47 Voltage detection circuit 48 Divider 49 Sample / hold circuit 50 Reference level 51 Comparison circuit

Claims (1)

In the DC leakage detection device for a grid-connected inverter that is composed of a plurality of switching elements and is connected to the AC power supply via an inverter that converts the DC power of the DC power supply into AC power.
  A core that is magnetized in accordance with a difference between a direct current flowing in a first detected conductor and a second detected conductor of a DC circuit connecting the DC power source and the inverter;
  A detection coil for detecting DC leakage wound around the core;
  A first voltage detection circuit for detecting a voltage induced in the detection coil;
  An alternating current load circuit for supplying an alternating current from the alternating current power source to a third detected lead wire penetrating inside the core;
  A second voltage detection circuit for detecting an AC voltage connected in an interconnected manner by converting the effective value of the voltage of the AC power supply to a rectified average value;
  A divider for calculating a value obtained by dividing the detection signal B of the second voltage detection circuit by the detection signal A of the first voltage detection circuit;
  A sample and hold circuit for storing the output signal of the divider before connection as a reference level;
  A comparator circuit that outputs a leakage determination signal when the output signal (B / A) of the divider is below a reference level stored in the sample and hold circuit;
  A DC leakage detection device for a grid-connected inverter, comprising:

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