JP2002142463A - System linkage inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system linkage inverter which minimizes the increase of the number of parts, by removing the malfunction of a leakage detector caused by the initial charge current flowing into the floating capacity of a DC power source at start of linked operation with simple constitution. SOLUTION: This inverter device is equipped with load 17b whose one end is connected to the positive electrode of a DC power source 16 and whose other end is connected to an earth, and load 17n whose one end is connected to the negative electrode of the DC power source 16 and whose other end is connected to an earth, and this regulates the potential to ground of the negative electrode of the DC power source 16 so as to be lower than the lowest potential of commercial power systems 8 and 8' before closing relays 5 and 5' by making the value of being obtained by dividing the impedance of the load 17p by the impedance of the load 17n smaller than the value being obtained by dividing the value being obtained by differencing the voltage amplitude value of the commercial power systems 8 and 8' from the release voltage of the DC power source 16 by the voltage amplitude value of those commercial power systems 8 and 8'.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid-connected inverter device that obtains power from a power supply source such as a DC power supply or a generator. In particular, the present invention relates to a technology for preventing erroneous detection of earth leakage in a transformerless system interconnection inverter device connected from a power supply source to a commercial AC power system without passing through a transformer.

[0002]

2. Description of the Related Art A residential power generation system interconnected with a commercial power system converts DC power generated from a DC power source such as a solar cell or a fuel cell into AC power of a commercial frequency by a system interconnection inverter device. This is a power generation system capable of supplying power to a load in a house via a commercial power system and automatically flowing excess power, which cannot be consumed by the load in the house, to the commercial power system in reverse flow. Note that the DC power supply connected to the grid-connected inverter device may be one obtained by converting AC power generated by a generator or the like into DC power by a converter.

A conventional transformerless system interconnection inverter device used in such a residential power generation system has a configuration as shown in FIG. The system interconnection inverter device 100 includes a booster circuit 2, an inverter circuit 3, a filter circuit 4, and interconnection relays 5, 5 ', and converts DC power supplied from the DC power supply 1 to AC power. The output is converted and output to the commercial power system 8, 8 '.

A DC voltage output from a DC power supply 1 is boosted by a booster circuit 2, and the boosted DC voltage is converted into an AC voltage by an inverter circuit 3. The inverter circuit 3 is connected to the commercial power system 8, 8 ′ via a filter circuit 4, interconnection relays 5, 5 ′, earth leakage breakers 6, 6 ′, and an earth leakage detector 7. Commercial power system 8,
The neutral point 9 of 8 'is grounded in a pole transformer (not shown).

Next, a booster circuit 2 connected to a DC power supply 1
Will be described. The anode of the diode D6 and the n-channel type are connected to the positive electrode of the DC power supply 1 via the reactor L1.
The collector of the IGBT (Insulated Gate Bipolar Transistor) T1 is connected. The cathode of the diode D6 is connected to the positive side of the electrolytic capacitor C1. On the other hand, the negative electrode of the DC power supply 1 is connected to the emitter of the IGBTT1 and the negative side of the electrolytic capacitor C1. The collector of the IGBTT1 is connected to the cathode of the diode D1, and the emitter of the IGBTT1 is connected to the anode of the diode D1.

The operation of the booster circuit 2 having such a configuration will be described. Reactor L when IGBT T1 turns on
When the IGBTT1 is turned off, the energy stored in the reactor L1 is released and the electrolytic capacitor C1 is charged. By controlling the ratio between the on-state time and the off-state time of the IGBT T1, the booster circuit 2 can boost the voltage supplied from the DC power supply 1 to a predetermined voltage (about 350 [V]).

[0007] The voltage detection circuit 10 is connected to both ends of the DC power supply 1 and both ends of the electrolytic capacitor C1, and detects the voltage across the DC power supply 1 and the voltage across the electrolytic capacitor C1 to provide a PWM control circuit. 11 is output. P
Based on the voltage signal output from the voltage detection circuit 10, the WM control circuit 11 controls the IGBTT 1 so that the voltage supplied from the DC power supply 1 is boosted to a predetermined voltage (about 350 [V]).
Determine the ratio of the on-state time to the off-state time,
A PWM drive signal is sent to the gate of the IGBT T1 so that the IGBT T1 performs switching at a switching frequency of about 20 [kHz]. The on / off state of the IGBTT1 is switched by the PWM drive signal. The diode D1 is an IGBT
This is a parasitic diode formed in T1.

Next, the inverter circuit 3 connected to the booster circuit 2 will be described. The inverter circuit 3 has four n-channel IGBTs T2 to T5 in a single-phase full bridge configuration as switching means. IGBTT2 and IGBTT
4 is connected to the positive side of the electrolytic capacitor C1 provided in the booster circuit 2 described above.
3 and the emitter of the IGBT T5 are connected to the negative polarity side of the electrolytic capacitor C1 provided in the booster circuit 2 described above. The emitter of IGBTT2 is connected to the collector of IGBTT3, and the emitter of IGBTT4 is connected to the collector of IGBTT5. The cathodes of the diodes D2 to D5 are connected to the collectors of the IGBTs T2 to T5, respectively.
The anodes of the diodes D2 to D5 are connected to the emitters of T2 to T5, respectively. Diodes D2 to D
Reference numeral 5 denotes a parasitic diode formed in the IGBTT2 to the IGBTT5, like the IGBTTT1. Also, IGBT T2 and IGBT
Connection point u between T3 and connection point v between IGBTT4 and IGBTT5
Are connected to the filter circuit 4 at the next stage.

The operation of the inverter circuit 3 having such a configuration will be described. The PWM control circuit 12 has a frequency of 20 [kHz]
Is supplied to the gates of the IGBTs T2 to T5. As a result, the on / off states of the IGBTs T2 to T5 are controlled, and the DC voltage supplied from the booster circuit 2 is converted into a 20 [kHz] pulse voltage substantially equivalent to an AC voltage having a predetermined frequency, and the filter circuit is switched. 4 is supplied.

Next, the filter circuit 4 connected to the inverter circuit 3 will be described. The filter circuit 4 includes reactors L2 and L3 and a capacitor C2.
The connection point u in the inverter circuit 3 is the reactor L
2, and the connection point v in the inverter circuit 3 described above is connected to one end of the reactor L3. A capacitor C is connected between the other end of the reactor L2 and the other end of the reactor L3.
2 are connected. The connection point between the reactor L2 and the capacitor C2 is connected to the next-stage relay 5, and the connection point between the reactor L3 and the capacitor C2 is connected to the next-stage relay 5 '.

The operation of the filter circuit 4 having such a configuration will be described. The filter circuit 4 smoothes the pulse voltage output from the inverter circuit 3, makes the voltage waveform sinusoidal, and outputs it to the commercial power system 8, 8 'connected via the interconnection relays 5, 5'. The voltage output from the filter circuit 4 has a sinusoidal waveform, but contains a high frequency component of 20 [kHz], which is the PWM frequency.

Next, the commercial power system 8, 8 'will be described. AC 100 [V] commercial power systems 8 and 8 ′ are connected in series, and AC 200 [V] is output to the system interconnection inverter device 100 side. The above-mentioned interconnection relay 5 is connected to the commercial power system 8 via an AC line 13U, and the above-mentioned interconnection relay 5 'is connected to the commercial power system 8' via an AC line 13V. The connection point 9 between the commercial power system 8 and the commercial power system 8 'is grounded. The earth leakage breaker 6 is connected to the AC line 13U and the AC line 13V.
Are each provided with an earth leakage breaker 6 '. Further, a leakage detector 7 for measuring a current flowing through the two AC lines 13U and 13V is provided.

The leakage detector 7 has two AC lines 13U, 1
By measuring the current flowing through 3 V, the total current output from the grid-connected inverter device 100 (hereinafter, referred to as the total current) is measured.
In the normal state, the U-phase AC line 13U and the V-phase AC line 13V of the commercial power system 6 are detected.
Therefore, the zero-phase current detected by the leakage detector 7 is zero because the currents of the same amount of positive and negative are flowing.

However, for example, if a ground fault occurs on the grid-connected inverter device 100 side with respect to the earth leakage detector 7, the currents flowing through the U-phase AC line 13U and the V-phase AC line 13V become unbalanced, and the earth leakage detector The zero-phase current detected at 7 has a positive or negative value. Earth leakage detector 7
Outputs an electric leakage detection signal to electric leakage breakers 6, 6 'when the absolute value of the zero-phase current becomes equal to or greater than a predetermined value. The earth leakage breakers 6, 6 'trip according to the earth leakage detection signal output from the earth leakage detector 7. As a result, when an electric leakage occurs, the electric circuit is immediately cut off, electric shock and fire can be prevented, and the electrical equipment of the system interconnection inverter device 100 and the commercial power system 8, 8 'can be protected.

However, the system interconnection inverter device 1
The DC power supply 1 connected to 00 forms parasitic stray capacitances 14 and 14 ′ with the ground. Therefore, when the interconnection relays 5, 5 'are switched from the open state to the closed state to start the interconnection operation, the commercial power system 8, 8'
Flow of the zero-phase current for charging the stray capacitances 14 and 14 ′ may cause a malfunction of the leakage detector 7.

A solution for preventing such a malfunction is disclosed in Japanese Patent Application Laid-Open No. 10-271688. FIG. 6 shows this system interconnection inverter device. Note that the same parts as those of the conventional system interconnection inverter device of FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted. The difference between the conventional grid-connected inverter apparatus 200 having the function of preventing a leakage fault detection from the conventional grid-connected inverter apparatus 100 shown in FIG. 5 is that an electrolytic capacitor C3, resistors 15p and 15n, and a breaker 6 '' are provided. It is a point. The positive side of the electrolytic capacitor C3 is connected to the positive electrode of the DC power supply 1,
Is connected to the negative electrode of the DC power supply 1. One end of the resistor 15p is connected to the positive side of the electrolytic capacitor C1, and one end of the resistor 15n is connected to the negative side of the electrolytic capacitor C1. Further, a connection point between the resistors 15p and 15n is connected to a neutral point 9 of the commercial power system 6 via a breaker 6 ''.

The operation of the grid-connected inverter device 200 having such a configuration will be described. When starting the interconnection operation, first, the breaker 6 ″ is turned on. afterwards,
After the voltage detection circuit 10 detects that the voltage of the electrolytic capacitor C1 has reached a predetermined value (350 [V]), it is determined that the stray capacitors 14 and 14 'have completed the initial charging. The system relays 5, 5 'are turned on.

Thus, the stray capacitance 14 of the DC power supply 1
Since the reference numeral 14 'is initially charged to the potential at the time of interconnection before starting the interconnection operation, the leakage detector 7 malfunctions due to the leakage current of the zero-phase current flowing when the interconnection relays 5, 5' are turned on. Can be prevented.

[0019]

However, in the method for preventing leakage error detection by the circuit configuration of the grid-connected inverter device 200 shown in FIG. 6, the number of components is greatly increased. More specifically, as shown in FIG. 7, such a method for preventing the detection of an erroneous earth leakage is performed by equalizing the stray capacitance charging currents I1 and I2 of the two paths flowing when the interconnection relays 5 and 5 'are turned on. This is a method of reducing the current to zero.

That is, in order to make the current values of the stray capacitance charging currents I1 and I2 flowing through the paths in the drawing equal,
The midpoint potential of the electrolytic capacitor C1, that is, the resistors 15p, 1
The charge state of the floating capacitors 14 and 14 'is adjusted by matching the 5n connection point potential with the midpoint potential of the DC power supply 1, that is, the connection potential of the floating capacitors 14 and 14'.

Therefore, as compared with the conventional grid-connected inverter device 100 shown in FIG. 5, in addition to the addition of the resistors 15p and 15n for generating the midpoint potential of the electrolytic capacitor C1, a path through which the stray capacitance charging current I1 flows. Therefore, it is necessary to add the electrolytic capacitor C3, which greatly increases the number of parts.

FIG. 7 shows that the stray capacitance 1 of the DC power supply 1 during the period when the output voltage of the commercial power system 8, 8 'is a positive half cycle.
4 and 14 ′, connection states between the grid-connected inverter device 200 and the commercial power systems 8 and 8 ′.

In view of the above problems, the present invention eliminates the malfunction of the leakage detector due to the initial charging current flowing into the floating capacity of the DC power supply at the start of interconnection operation with a simple configuration, and minimizes the number of parts. It is an object of the present invention to provide a grid-connected inverter device which is limited to a minimum.

[0024]

Means for Solving the Problems To achieve the above object, in a grid-connected inverter device according to the present invention,
A booster circuit for boosting a DC voltage output from a DC power supply having a capacitance component with respect to ground; and an inverter for converting a DC output from the booster circuit into an AC having a plurality of switching means having rectifiers connected in anti-parallel. A circuit, switching means for opening and closing the connection between the inverter circuit and the commercial power system, and a ground potential adjusting means connected to at least one of a positive electrode and a negative electrode of the DC power supply, and the ground potential adjusting means comprises: By the time the switching means is closed, the ground potential of the negative electrode of the DC power supply is adjusted to be lower than the minimum potential of the commercial power system.

The ground potential adjusting means may include a first load having one end connected to the positive electrode of the DC power supply and the other end grounded, and one end connected to the negative electrode of the DC power supply and the other end grounded. A second load, in which case the open voltage of the DC power supply is greater than the voltage amplitude value of the commercial power system and the impedance of the first load is The value obtained by dividing the value obtained by dividing the impedance by the impedance of the commercial power system from the open voltage of the DC power supply may be made smaller than the value obtained by dividing the value obtained by dividing the voltage amplitude value of the commercial power system. Further, from the viewpoint of cost reduction, the first and second loads may be resistances.

Further, from the viewpoint of more reliably preventing the malfunction of the leakage detector, the output voltage of the booster circuit is determined by the difference between the voltage amplitude value of the commercial power system and the ground potential of the negative electrode of the DC power supply. After the size is increased, the opening / closing means may be closed.

Further, from the viewpoint of more reliably preventing malfunction of the earth leakage detector, it is preferable that the inverter circuit starts driving after a lapse of a predetermined period since the opening / closing means is closed. From the viewpoint of power consumption reduction,
Preferably, the ground potential adjusting means includes a switch means, and the switch means can open and close the connection between the electrode of the DC power supply and the ground. In the case where the above two means are performed together, it is preferable that the switch means be opened during a period from when the opening / closing means is closed to when the inverter circuit starts driving. .

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a system interconnection inverter device of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of the system interconnection inverter device of the first embodiment. In FIG. 1, the same components as those of the conventional system interconnection inverter device of FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, a solar cell is used as a DC power supply. Since the solar cell 16 has a parasitic stray capacitance component between the positive electrode and the housing and between the negative electrode and the housing, the positive and negative electrodes of the solar cell 16 are usually grounded via the floating capacitances 14 and 14 ′, respectively. Become.

There are various types of solar cell modules such as a roof-mounted type and a building material integrated type.
The value of 14 'differs depending on the type of module. In a module in which a reinforcing metal plate connected to the ground, such as a building material integrated type, is disposed on the back side of the solar cell 16, the reinforcing metal plate and the electrode of the solar cell 16 face each other to form a parallel flat plate. In some cases, the stray capacitance increases and reaches several μF.

In this embodiment, the zero-phase current is 3
When the current exceeds 0 [mA], the leakage detector 7 that trips the leakage breakers 6, 6 'is used. Also,
A diode D7 is provided between the solar cell 16 and the booster circuit 2 to prevent a current from flowing backward.

One end of a load 17p is connected to the positive electrode of the solar cell 16, and one end of a load 17n is connected to the negative electrode of the solar cell 16. Further, the other end of the load 17p and the load 17n
, And the connection point is grounded.

The setting of the impedance of the loads 17p and 17n will be described below. The impedance of the load 17p is Zp, the impedance of the load 17n is Zn, the open voltage of the solar cell 16 is Voc, the voltage amplitude value of each of the commercial power systems 8, 8 'is Vac, the positive electrode potential of the solar cell 16 is Vp, The negative electrode potential is set to Vn.

The impedance Zp of the load 17p and the load 1
Since the midpoint obtained by dividing the open circuit voltage Voc of the solar cell 16 by the impedance Zn of 7n becomes the ground potential, Zp / Zn = │Vp│ / │Vn│ is established. Here, the expression (1) is satisfied from Vp> 0 and Vn <0. Zp / Zn = −Vp / Vn (1) Further, since Voc = Vp−Vn, equation (1) can be expressed as equation (2). Zp / Zn = (Voc + Vn) / (− Vn) (2) Here, assuming that the following equation (3) holds.
From the expressions (2) and (3), the relationship of the expression (4) is established. Zp / Zn <(Voc−Vac) / Vac (3) (Voc + Vn) / (− Vn) <(Voc−Vac) / Vac (4) Further, the expression (4) can be rearranged into the expression (5). Can be expressed as −Voc / Vn <Voc / Vac (5) Here, since Voc> 0, Equation (5) becomes Equation (6). Vn <−Vac (6) From the expression (6), the negative electrode potential Vn of the solar cell 16 is lower than the lowest potential −Vac of the commercial power system 8 ′. That is,
By setting the impedance of the loads 17p and 17n so as to satisfy the above equation (3), the loads 17p and 17n are adjusted such that the ground potential of the negative electrode of the solar cell 16 is lower than the lowest potential of the commercial power system 8 '. It will operate as a ground potential adjusting means.

Before starting the interconnection operation with the interconnection relays 5 and 5 'closed, the IGBTT1 in the booster circuit 2 is switched to output the output voltage of the booster circuit 2, that is, the output voltage of the electrolytic capacitor C1. It is assumed that the terminal voltage Vch is set so as to satisfy the relationship of the expression (7). Vch> Vac−Vn (7) Here, the potential on the positive side of the electrolytic capacitor C1 is represented by Vp2
Then, Vp2 = Vn + Vch (8) Therefore, from the expressions (7) and (8), the relationship of the expression (9) is established. Vp2−Vac> (Vn + Vch) − (Vch−Vn) = 0 (9) Here, equation (9) can be expressed as equation (10). Vp2> Vac (10) That is, by setting the expression (7), the potential on the positive side of the electrolytic capacitor C1 of the booster circuit 2 can be adjusted to be higher than the maximum potential of the commercial power system.

The voltage Vuo across the commercial power system 8 and the voltage Vvo across the commercial power system 8 'are Vuo = Vvo = Vac
× sin (2π × f × t). However,
f is the commercial frequency, and t is the time. In the present embodiment, the voltage Vuo across the commercial power system 8 and the commercial power system 8 ′
Is set to 100 [V] and the commercial frequency is set to 60 [Hz], the voltage amplitude value Vac of the commercial power system 8, 8 'is 141 [V]. In addition, the solar cell 16
Is 250 [V]. Load 17p, 1
A resistor is used for 7n, and the resistance of the load 17p is set to 200 [kΩ] and the resistance of the load 17n is set to 800 [kΩ] so as to satisfy the above equation (3). With this setting, the positive electrode potential Vp of the solar cell 16 becomes 50 before the interconnection operation starts.
[V], the negative electrode potential Vn of the solar cell 16 is fixed at -200 [V]. As in the present embodiment, the loads 17p and 17n are changed to high impedance loads so that the loads 17p and 17n are changed.
Current flowing through the load 17p, 1
7n can reduce power consumption. Further, by using resistors for the loads 17p and 17n, the cost of the ground potential adjusting means can be reduced.

Further, the system interconnection inverter device 300 includes a control circuit 18 for controlling on / off of the booster circuit 2, the inverter circuit 3, and the interconnection relays 5, 5 'based on an output signal from the voltage detection circuit 10. Is provided.

The operation of the system interconnection inverter device 300 having such a configuration will be described. First, interconnection relay 5,
Reference numeral 5 'denotes an open state, in which the booster circuit 2 and the inverter circuit 3 are not driven and the interconnection operation is not performed. In this case, since the solar cell 16 is in the same state as open, the output voltage of the solar cell 16 matches the open voltage Voc.

First, before the interconnection relays 5 and 5 'are closed, the control circuit 18 sends a command signal to the PWM control circuit 11 to output the booster circuit 2, that is, the voltage Vch across the electrolytic capacitor C1. Is the voltage (350
[V]), the booster circuit 2 is driven. afterwards,
After the voltage Vch across the electrolytic capacitor C1 reaches the voltage (350 [V]) during the interconnection operation, the driving of the booster circuit 2 is stopped.

In this state, when the control circuit 18 closes the interconnection relays 5 and 5 'during a period in which the output voltages of the commercial power systems 8 and 8' are in a positive half cycle, the stray capacitance 14 of the solar cell 16 is reduced. , 14 ′, the grid-connected inverter 300 and the commercial power system 8, 8 ′ are as shown in FIG. 2A, the negative electrode potential Vn of the solar cell 16 and the potential of the anode of the diode D5 are equal to each other and are -200 [V]. When the output voltage of the commercial power system 8, 8 'has a positive peak value, the AC line 13V of the commercial power system 8'
Side potential becomes the minimum (-141 [V]), and the diode D
The potential of the cathode of No. 5 is -141 [V]. As described above, the diode D5 does not conduct because the cathode has a higher potential than the anode. Therefore, interconnection relays 5, 5 '
When the switch is closed, the leakage current flowing through the floating capacitors 14 and 14 'is eliminated by the path I shown in FIG. 2A, so that the leakage current flowing through the floating capacitors 14 and 14' can be greatly reduced. . Thereby, the earth leakage breaker 6,
The leakage current of the trip reference value 30 [mA] or more of 6 'does not flow, and the malfunction of the leakage detector 7 can be prevented.

FIG. 2A shows that the electrolytic capacitor C
The potential Vp2 on the positive polarity side of 1 is equal to the potential of the cathode of the diode D2, and Vp2 = Vch + Vn = 150 [V]. When the output voltages of the commercial power systems 8 and 8 'have positive peak values, the potential of the anode of the diode D2 is the highest on the AC line 13U side of the commercial power system 8 (14).
1 [V]), so that the cathode of the diode D2 has a higher potential than the anode, and the diode D2 does not conduct. That is, if the positive polarity potential of the electrolytic capacitor C1 in the booster circuit 2 is higher than the highest potential of the commercial power system 8, the floating by the route II shown in FIG. There is no leakage current flowing through the capacitors 14, 14 '.

As described above, since the leakage current flowing through the floating capacitors 14 and 14 'can be eliminated by the paths I and II, the zero-phase current can be reduced to zero and the malfunction of the leakage detector 7 can be reliably prevented. Can be.

When the interconnection relays 5, 5 'are closed during a period in which the output voltage of the commercial power system 8, 8' is negative half cycle, the stray capacitances 14, 14 'of the solar cell 16 and the system interconnection inverter FIG. 2B shows a connection state between the power supply system 300 and the commercial power system 8, 8 '. Also in this case, similarly to the case of FIG.
Since the leakage current flowing through 4 'can be eliminated, the zero-phase current can be reduced to zero and the malfunction of the leakage detector 7 can be reliably prevented.

The control circuit 18 controls the interconnection relay 5,
After elapse of a predetermined period from the closing of 5 ', the booster circuit 2 and the inverter circuit 3 are driven. As the predetermined period, the delay time may be ensured so that the time when the interconnection relays 5 and 5 ′ are closed and the time when the booster circuit 2 and the inverter circuit 3 start driving do not coincide with each other. One cycle of the output voltage cycle of system 8, 8 '(60 [H
In the case of z], 16.6 [ms]) is sufficient. After the interconnection relays 5, 5 'are closed, the control circuit 18 starts driving the booster circuit 2 and the inverter circuit 3, so that the inverters are not activated before the interconnection relays 5, 5' are closed. The IGBTs T2 to T5 provided in the circuit 3 are not turned on. Therefore, when the interconnecting relays 5, 5 'are closed, the stray capacitance 14, via the IGBTs T2 to T5,
The current for charging 14 'does not flow, and the malfunction of the leakage detector 7 does not occur.

Next, a system interconnection inverter device according to a second embodiment will be described with reference to a circuit diagram shown in FIG. The difference from the system interconnection inverter device of the first embodiment is that switch means 19 and 19 'are provided between the loads 17p and 17n and the ground, respectively. Note that, for example, a relay or the like may be used as the switch means 19, 19 '.

The operation of the switch means 19, 19 'will be described. Since the switch means 19 and 19 'are in the closed state until the interconnection relays 5 and 5' are closed, the system interconnection inverter device of the present embodiment until the interconnection relays 5 and 5 'are closed. The circuit state of 400 is the same as that of the system interconnection inverter device 300 of the first embodiment. After the interconnecting relays 5 and 5 'are closed, the control circuit 1 is turned on within a period until the booster circuit 4 and the inverter circuit 5 are driven.
8 sets the switch means 19, 19 'to the open state. As a result, the loads 17p and 17n are electrically disconnected from the ground. Therefore, when the inverter circuit 3 is driven, useless power consumption does not occur in the loads 17p and 17n. Further, as in the system interconnection inverter device 500 shown in FIG. 4, the switch means 19 '' may be provided between the connection point between the load 17p and the load 17n and the ground. Thus, the number of switch means can be reduced as compared with the system interconnection inverter device 400 shown in FIG. 3, and cost reduction can be achieved. The operation of the switch means is the same as that of the system interconnection inverter 400 shown in FIG.
Is the same as

In the grid-connected inverter devices of the first and second embodiments, resistors are used for the loads 17p and 17n. However, the present invention is not limited to this.
The loads 17p and 17n only need to have impedance, and therefore, for example, a reactance or a combination of reactance and resistance may be used.

[0048]

According to the present invention, the ground potential adjusting means adjusts the ground potential of the negative electrode of the DC power source to be lower than the minimum potential of the commercial power system before the switching means is closed. The current flowing through the stray capacitance parasitic on the power supply can be reduced. Also, there is no need to add a capacitor unlike the related art. This can minimize an increase in the number of parts and prevent malfunction of the leakage detector provided between the grid-connected inverter device and the commercial power system.

According to the present invention, the ground potential adjusting means includes a first load having one end connected to the positive electrode of the DC power supply and the other end grounded, and a first load connected to the negative electrode of the DC power supply and the other end grounded. And the impedance ratio between the first load and the second load is equal to the ratio between the absolute value of the positive potential and the absolute value of the negative potential of the DC power supply. This makes it possible to keep the negative electrode potential of the DC power supply constant irrespective of the magnitude of the current flowing to the ground potential adjusting means or the impedance of the ground potential adjusting means. This facilitates adjustment of the negative electrode potential of the DC power supply. Further, by increasing the impedance of the first load and the impedance of the second load, it is possible to reduce the power loss in the ground potential adjusting means.

According to the present invention, the value obtained by dividing the impedance of the first load by the impedance of the second load is a value obtained by subtracting the voltage amplitude value of the commercial power system from the open voltage of the DC power supply. Since it is smaller than the value obtained by dividing by the voltage amplitude value of the system, the ground potential of the negative electrode of the DC power supply can be made lower than the lowest potential of the commercial power system. As a result, the current flowing through the stray capacitance parasitic on the DC power supply can be reduced, and malfunction of the leakage detector provided in the power system can be prevented.

Further, according to the present invention, since the first and second loads are resistors, an inexpensive ground potential adjusting means can be realized.

Further, according to the present invention, after the output voltage of the booster circuit becomes larger than the difference between the voltage amplitude value of the commercial power system and the ground potential of the negative electrode of the DC power supply, the switching means is closed. Therefore, it is possible to eliminate the current flowing through the stray capacitance parasitic on the DC power supply. Thereby, it is possible to more reliably prevent the malfunction of the leakage detector provided in the power system.

Further, according to the present invention, the inverter circuit starts driving after a lapse of a predetermined period from when the opening / closing means is closed, so that the switching means of the inverter circuit is used when the opening / closing means is closed. No current flows. Thereby, it is possible to more reliably prevent the malfunction of the leakage detector provided in the power system.

Further, according to the present invention, the ground potential adjusting means includes the switch means, and the connection between the electrode of the DC power supply and the ground can be opened and closed by the switch means, so that the ground potential adjusting means operates. When not necessary, the ground potential adjusting means can be electrically disconnected from the electrode of the DC power supply or the ground. As a result, useless power consumption does not occur in the ground potential adjusting means, and energy saving can be achieved.

Further, according to the present invention, the ground potential adjusting means has a switch means, which can open and close the connection between the electrode of the DC power supply and the ground, and closes the open / close means. Since the switch means is closed during the period from when the inverter circuit starts to be driven, when the ground potential adjusting means does not need to operate, that is, when the inverter circuit is driven, the ground potential adjusting means is connected to the DC power supply. It can be electrically disconnected from the electrode or ground. As a result, useless power consumption does not occur in the ground potential adjusting means, and energy saving can be achieved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a system interconnection inverter device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a connection state between a stray capacity of a solar cell connected to the grid-connected inverter device of FIG. 1 and a commercial power system.

FIG. 3 is a configuration diagram of a system interconnection inverter device according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating another configuration of the system interconnection inverter device according to the second embodiment of the present invention.

FIG. 5 is a configuration diagram of a conventional system interconnection inverter device.

FIG. 6 is a configuration diagram of a conventional grid-connected inverter device with a function to prevent erroneous earth leakage detection.

7 is a diagram showing a connection state between a stray capacitance of a DC power supply connected to the grid interconnection inverter device of FIG. 6 and a commercial power system.

[Explanation of symbols]

Reference Signs List 1 DC power supply 2 Booster circuit 3 Inverter circuit 5, 5 'relay 6, 6' Leakage breaker 7 Leakage detector 8, 8 'Commercial power system 14, 14' Floating capacity 16 Solar cell 17p, 17n Load 19, 19 ', 19 '' Switch means 300 Grid-connected inverter device of first embodiment of the present invention 400 Grid-connected inverter device of second embodiment of the present invention 500 Grid-connected inverter device of another configuration of second embodiment of the present invention 500

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5G066 HA01 HA30 HB05 LA04 5H007 AA05 AA06 BB07 CA01 CB05 CC03 CC12 CC14 DA05 DA06 DC02 DC05 EA02 GA03 GA06

Claims (8)

[Claims] 1. A booster circuit for boosting a DC voltage output from a DC power supply having a capacitance component with respect to ground, and a plurality of switching means having rectifiers connected in anti-parallel. In a system interconnection inverter device comprising: an inverter circuit for converting into an alternating current; and switching means for opening and closing the connection between the inverter circuit and a commercial power system, a ground connected to at least one of a positive electrode and a negative electrode of the DC power supply. A potential adjusting means is provided, and the earth potential adjusting means adjusts the earth potential of the negative electrode of the DC power supply to be lower than the lowest potential of the commercial power system before the switching means is closed. System interconnection inverter device. 2. A first load, one end of which is connected to a positive electrode of the DC power supply and the other end of which is grounded;
The system interconnection inverter device according to claim 1, further comprising: a second load having one end connected to a negative electrode of the DC power supply and the other end grounded. 3. An open voltage of the DC power supply is greater than a voltage amplitude value of the commercial power system, and a value obtained by dividing an impedance of the first load by an impedance of the second load is an open voltage of the DC power supply. The system interconnection inverter device according to claim 2, wherein a value obtained by dividing a voltage amplitude value of the commercial power system from a voltage is divided by a voltage amplitude value of the commercial power system. 4. The system interconnection inverter device according to claim 2, wherein said first and second loads are resistors. 5. The switching means is closed after an output voltage of the booster circuit becomes larger than a difference between a voltage amplitude value of the commercial power system and a ground potential of a negative electrode of the DC power supply. Item 5. The system interconnection inverter device according to any one of Items 1 to 4. 6. The system interconnection inverter device according to claim 1, wherein the inverter circuit starts driving after a lapse of a predetermined period from when the opening / closing means is closed. 7. The system according to claim 1, wherein said ground potential adjusting means comprises a switch means, and said switch means can open and close a connection between an electrode of said DC power supply and a ground. Interconnected inverter device. 8. The ground potential adjusting means includes a switch means for opening and closing the connection between the electrode of the DC power supply and the ground, and the switch means is in a closed state. 7. The system interconnection inverter device according to claim 6, wherein the switch means is in an open state during a period from when the inverter circuit starts driving.