JPH10271688A - Inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the erroneous detection of leakage so as to improve the reliability by charging a floating capacitor as a measure against counter- grounding existing in a DC power source to a potential at system linkage in advance, when linking an inverter to the system. SOLUTION: Resistors 30 and 31 are provided at both ends of a capacitor 7, and the middle point is connected to the neutral point of an AC power source 15 through a breaker 14, and a voltage detector 21 detects the voltage of the capacitor 7, and a level detector 28 detects the voltage of the capacitor 7 having reached the set level. Then, after floating capacitor 18 and 19 set by an on delay 32 have completed initial charge, a contactor 13 is tuned on, and its auxiliary contact 29 is closed, and stable time is secured with an on delay 33, and the drive of an inverter bridge 8 is started. Hereby, the erroneous detection of a leakage detection circuit can be prevented by lessening the zero-phase current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device which is connected to an AC power supply having a grounding system without a connection transformer from a solar cell, a fuel cell, or the like.

[0002]

2. Description of the Related Art The structure and operation of a conventional transformerless solar cell inverter will be described with reference to FIG. A capacitor 2 is connected to both ends of the solar cell 1 to form a first DC power supply. The first DC power supply includes a boost chopper including a reactor 3, a diode 4, a switching element 5, and a capacitor 7. The circuits are connected to form a second DC power supply.

A switching element 8 is connected to a second DC power supply.
An inverter bridge 8 including diodes 1a to 84 and diodes 8a to 8d connected in parallel to the switching elements 81 to 84 is connected to convert DC to AC. The inverter bridge 8 has a reactor 9 and a reactor 10
A filter composed of a capacitor 11 and a capacitor 11 is connected, and its output is connected to an AC power supply 15 via a contactor 13 and a breaker 14. Floating capacitors 18, 19
Is the stray capacitance of the solar cell 1 with respect to the ground, and its magnitude may be about several μF.

Next, the control will be described. For the boost chopper circuit, a voltage reference 20 and a voltage detector 21
Is compared with the voltage of the capacitor 7 detected at step (a), and the value is amplified by the amplifier 22 and used as a current reference. This current reference is compared with the input current detected by the current detector 6, the value of which is amplified by the amplifier 23 is input as a command value to the PWM circuit 24, and the switching element 5 is subjected to PWM control, thereby controlling the capacitor 7. Is controlled to be constant.

The inverter bridge 8 compares the voltage reference 25 with the inverter output current detected by the current detector 11, and inputs a value obtained by amplifying the value by an amplifier 26 to a PWM circuit 27 as a command value to perform switching. Element 8
It is controlled by PWM control of 1 to 84.

The activation of the inverter bridge 8 is performed when the voltage of the capacitor 7 reaches a set level. When the level detector 28 detects that the capacitor voltage detected by the voltage detector 21 has reached the set level, the contactor 13 is turned on and the auxiliary contact 2 of the contactor 13 is turned on.
A permission signal is output to the PWM circuit 27 through the switch 9 and the circuit is started.

Further, the AC power supply 15 is a single-phase three-wire system, like a general household, and the neutral point is connected to the ground at the pole transformer side. The zero-phase current transformer 16 and the leakage detector 17 are used for leakage detection. Is provided, and when a leakage is detected, the leakage breaker is usually tripped.

[0008]

SUMMARY OF THE INVENTION In a conventional circuit,
When the contactor 13 is off, the floating capacitor 18,
Reference numeral 19 is charged to almost half the voltage of the capacitor 2. When the contactor 13 is turned on in this state,
A zero-phase current for charging the floating capacitors 18 and 19 flows through the diode portion of the inverter bridge 8, and the leakage detection circuit 17 may malfunction.

This will be described with reference to FIG. Assuming that the voltage E1 of the capacitor 2 is 200V, the floating capacitor 19 is charged to 100V with a positive polarity. In this state, the contactor 13 is turned on and the AC power supply 1
When the voltage E3 (100V) of 5 becomes positive polarity, the floating capacitor 19 is charged to about 140V, so that a zero-phase current flows through the route of i1, and the leakage detector 17 malfunctions. On the other hand, the current flowing through the route of i2 charges the floating capacitor 18. When E1 and E2 are equal, i1 and i2 are equal and no zero-phase current flows, but otherwise, a zero-phase current flows.

As described above, in the first stage of the interconnection, a zero-phase current for charging the stray capacitance flows, and a leakage may be erroneously detected. Therefore, an object of the present invention is to solve the above problem and provide a highly reliable inverter device.

[0011]

In order to achieve the above object, in the inverter device according to the first aspect of the present invention, when the inverter is connected to the system, the floating capacitor for the earth with respect to the DC power supply is connected to the ground. By charging in advance to the potential at the time of system interconnection, it is possible to prevent a zero-phase current from flowing at the time of system interconnection.

In the inverter device according to a second aspect of the present invention, the midpoint potential of the second DC power supply is connected to the ground point of the AC power supply, and the floating capacitor with respect to the earth present in the DC power supply is connected to the second DC voltage. By connecting the inverter to the system after charging to 1/2 of the above, it is possible to prevent a zero-phase current from flowing at the time of system interconnection.

In the inverter device according to a third aspect of the present invention, the midpoint obtained by dividing the second DC power supply by a resistor is connected directly or via a resistor to the ground point of the AC power supply, and the pair of the DC power supply is connected to the ground. By connecting the inverter to the system after charging the floating capacitor with respect to the ground to half of the second DC voltage, it is possible to prevent a zero-phase current from flowing during system connection.

In the inverter device according to a fourth aspect of the present invention, when the inverter is stopped, the connection between the midpoint of the second DC power supply and the AC power supply is turned off. AC power can be disconnected.

In the inverter device according to the fifth aspect of the present invention, the loss of the voltage dividing circuit during the inverter operation can be eliminated by opening the voltage dividing circuit of the second DC power supply during the inverter operation.

In the inverter device according to a sixth aspect of the present invention, the inverter and the AC power supply are connected via the impedance to reduce the level of the current for charging the floating capacitor with respect to the earth present in the DC power supply, thereby reducing the floating capacitor. After charging the inverter, the inverter is connected to the system to prevent a zero-phase current from flowing during system connection.

In the inverter device according to the present invention, the DC power supply and the inverter are connected via the impedance to reduce the level of the current for charging the floating capacitor with respect to the earth present in the DC power supply, thereby reducing the floating capacitor. After charging the inverter, the inverter is connected to the system to prevent a zero-phase current from flowing during system connection.

In the inverter device according to claim 8 of the present invention, in the inverter device according to claim 6 or 7, the impedance is a resistance. In the inverter device according to claim 9 of the present invention, in the inverter device according to claim 6 or 7, by providing a chopper circuit on the DC side of the inverter, the fluctuation range of the DC voltage can be expanded.

In the inverter device according to a tenth aspect of the present invention, in the inverter device according to any one of the second to ninth aspects, the inverter has a half-bridge configuration.

According to an eleventh aspect of the present invention, in the inverter device according to any one of the second to ninth aspects, when the inverter is connected to an AC power supply, the interconnection switch is turned on to turn on the inverter. After an AC power supply is connected, the inverter is driven after a predetermined period has elapsed.

According to a twelfth aspect of the present invention, in the inverter device according to any one of the second to ninth aspects, when the inverter is connected to an AC power supply, the inverter is operated with a low current; After charging the floating capacitor with respect to the earth present in the DC power supply in the inverter operating state, the interconnection switch is turned on, and then the current reference is returned to the normal value.

According to a thirteenth aspect of the present invention, in the inverter device according to any one of the second to ninth aspects, the inverter is not operated in a free wheeling mode, thereby charging the floating capacitor. There is no discharge and operation can be performed without changing the voltage of the floating capacitor.

According to a fourteenth aspect of the present invention, in the inverter device according to any one of the second to ninth aspects, the DC input voltage of the inverter is at least twice the peak value of the AC power supply voltage. As a result, no charging current flows from the AC power supply to the floating capacitor during interconnection.

[0024]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a first embodiment of the present invention. The same elements as those in FIG.

The difference from the prior art is that resistors 30 and 31 are provided at both ends of the capacitor 7, the midpoint of which is connected to the neutral point (earth) of the AC power supply 15 via the breaker 14, and the voltage of the capacitor 7 is Level detector 2 detected by detector 21
After detecting that the voltage of the capacitor 7 has reached the set level at 8, the contactor 13 is turned on after a lapse of time that the floating capacitors 18 and 19 set by the on-delay 32 assume that the initial charging has been completed. The auxiliary contact 29 of the contactor 13 is closed and a stable time is secured by the on-delay 33 so that the inverter bridge 8
Is started.

Next, the operation of the first embodiment of the present invention will be described with reference to FIG. The initial voltage of the floating capacitor 18 is VC18, and the initial voltage of the floating capacitor 19 is V
19. Assuming that the voltage of the capacitor 2 is E1, the voltage of the capacitor 7 is E2, and the voltage of the AC power supply 15 is E3, the currents i1 and i2 when the contactor 13 is turned on have the following relationship.
The impedance of the circuit through which i1 and i2 flow is Z.

[0027]

I1 = (1 / Z) × (E3-E2 + E1-VC18) (1) i2 = (1 / Z) × (E3-VC19) (2) The following equation is established from the relationship with the capacitor 2.

[0028]

Equation 18 VC18 + VC19 = E1 Equation 3 When Equation 3 is substituted into Equation 1, the following equation can be obtained.

[0029]

I1 = (1 / Z) × (E3-E2 + VC19) Expression 4 Further, resistors 30 and 31 are provided at both ends of the capacitor 7, and the midpoint of the resistors 30 and 31 is set in the AC power supply 15 through the breaker 14. Since it is connected to the neutral point (earth), the voltage of the capacitor 7 is charged to the set value and then the voltage of the floating capacitor 19 is charged to the value represented by the following equation for the time set by the on-delay 32. You.

[0030]

VC19 = (1/2) × E2 Equation 5 When this Equation 5 is substituted into Equations 4 and 2,

[0031]

I1 = (1 / Z) × (E3-E2 / 2) (6) i2 = (1 / Z) × (E3-E2 / 2) (7) = I2.

That is, the contactor 13 can be turned on without passing the zero-phase current. In this way, by initially charging one of the floating capacitors to 1/2 of the DC side voltage of the inverter bridge 8, no zero-phase current flows during interconnection, so that the leakage detector does not malfunction. Thus, a highly reliable inverter device can be configured.

Next, a second embodiment of the present invention will be described. FIG. 3 is a configuration diagram of the second embodiment. Here, only points different from the first embodiment are described.

First, the first different point is that the capacitor 7
Is divided into two, a capacitor 7a and a capacitor 7b. In such a configuration, the resistor 30,
31 is connected to each of the capacitors 7a and 7b, and a resistor 34 is connected between the connection point of the capacitors 7a and 7b and the neutral point (earth) of the AC power supply 15.

In the case where the capacitor 7 is divided into two, even if a resistor is connected to each capacitor, the voltage dividing impedance is low.
It is connected between the connection point 7b and the neutral point (earth) of the AC power supply 15 so as to limit the current for initially charging the floating capacitors 18 and 19.

The second difference is that the capacitors 7a and 7
The point that a relay 35 is provided between the connection point b and the neutral point (earth) of the AC power supply 15. The operation of the relay 35 will be described with reference to the timing chart of FIG.

The relay 35 is turned off while the inverter bridge 8 is stopped, and turned on before the operation of the inverter bridge 8 starts. When the relay 35 is turned on, the floating capacitors 18 and 19 start to be charged, and the floating capacitors 1 and 19 are charged.
The contactor 13 is turned on after a lapse of the time when it is considered that the charging has been completed by the contacts 8 and 19.

In this manner, the inverter bridge including the ground point can be disconnected from the AC power supply while the inverter bridge is stopped. Next, a third embodiment of the present invention will be described.

FIG. 5 is a block diagram of the third embodiment.
Here, only points different from the first embodiment are described. The difference from the first embodiment is that a relay 35 is provided in series with the resistors 30 and 31.

The operation of the relay 35 will be described with reference to the timing chart of FIG. The relay 35 is turned off while the inverter bridge 8 is stopped, and turned on before the operation of the inverter bridge 8 starts. When the relay 35 is turned on, the floating capacitors 18 and 19 begin to be charged, and the contactor 13 is turned on after a lapse of time that the floating capacitors 18 and 19 are considered to have completed charging. And
When the contactor 13 is turned on, the relay 35 is turned off,
The resistors 30 and 31 are disconnected.

In this manner, the resistors 30 and 31 are disconnected during the operation of the inverter bridge, and the power consumption of the resistors 30 and 31 during the operation of the inverter bridge can be prevented.

As shown in FIG. 7, even when the inverter bridge is a half bridge, after the floating capacitors 18 and 19 are initially charged via the relay 35 and the resistor 34, the resistor 34 is short-circuited by the contactor 13 to start the inverter. The same effect can be obtained by starting.

Next, a fourth embodiment of the present invention will be described. FIG. 8 is a configuration diagram of the fourth embodiment, and the same elements as those in the related art are denoted by the same reference numerals and description thereof will be omitted.

The difference from the conventional one is as follows. A resistor 30 and a relay 37 are connected to both ends of the contact of the contactor 13,
The resistor 31 and the relay 37 are connected to both ends of the other contact of the contactor 13, and when the voltage of the capacitor 7 reaches a predetermined value by the level detector 28, the coil 37C of the relay 37 is driven to turn on the relay 37. Let it. Thereafter, when the time for completing the initial charging of the floating capacitors 18 and 19 elapses and the on-delay 38 is turned on, the PWM circuit 27 operates and the inverter bridge 8 is driven. Thereafter, when the time to complete the charging of the floating capacitors 18 and 19 elapses with the inverter bridge 8 being driven and the on-delay 39 is turned on, the coil 13C of the contactor 13 is driven to turn on the relay 13 and turn on the system. At this time, the contactor auxiliary contact 29 is also turned on, and the output of the current reference circuit 25 is gradually increased by the setting device 33.

Next, the operation of the fourth embodiment will be described with reference to FIG.
This will be described with reference to the time chart of FIG. Level detector 2
When the voltage of the capacitor 7 reaches a predetermined value (inverter start condition) by 8, the relay 37 is turned on at time t 1, and a current for charging the floating capacitors 18 and 19 flows from the AC power supply 15 via the resistors 30 and 31. This current is limited to a low level at which the leakage detection circuit 17 does not operate.

The on-delay 38 is connected to the floating capacitor 18,
19 is set to the time estimated to be initially charged, and at time t2, the inverter bridge 8 is set to the operating state. At this time, since the current reference V25 is at zero or a low level close to zero, almost no current flows through the resistors 30 and 31, so that the floating capacitors 18 and 19 are charged to the operating state of the inverter bridge 8.

The on-delay 39 is connected to the floating capacitor 18,
19 is set to the time estimated to be charged in the operation state of the inverter bridge 8, and at time t3, the contactor 1 is turned on, the resistors 30 and 31 are short-circuited, and the inverter bridge 8 is connected to the system.

At this time, the contactor auxiliary contact 29 is also turned on, and from the time t4, the setter 33 gradually returns the current reference V25 to a normal value for interconnection. In this way, the floating capacitor on the DC power supply side is initially charged with the current limiting resistor to start the inverter, and even in the inverter operating state, the current limiting resistor is short-circuited after current limiting charging of the floating capacitor. The value can be limited to a low value, and a highly reliable inverter device in which the leakage detector does not malfunction can be configured.

In the fourth embodiment, if there is no variation in the switching elements, the charging voltage of the floating capacitors 18 and 19 does not change before and after the operation of the inverter. 1
The inverter operation may be started when 3 is turned on.

In the fourth embodiment, the resistance 3
0 and 31 may be replaced with reactors. Also,
In the fourth embodiment, instead of providing the resistors 30 and 31 on the AC power supply 15 side, the resistors 30 and 31 may be mounted on the DC power supply side as shown in FIG. The effect is the same. However, in this case, since a DC contactor is used, the size of the device is increased.

The step-up chopper circuit as the second DC power supply may be a step-down chopper circuit. FIG.
In such a half-bridge inverter circuit, the same operation and effect can be obtained by attaching the resistors 30 and 31 to the two wires of the AC power supply 15. In the case of a single-phase three-wire system, it can be handled by inserting a resistor into three wires.

In the full-bridge inverter bridge as described above, the switching elements 81 and 84,
Switching elements 82 and 83 are turned on and off simultaneously,
By operating in a method without the free wheeling mode, the operation can be performed without changing the voltages of the floating capacitors 18 and 19.

Even when there is no step-up chopper circuit serving as the second DC power supply and the inverter bridge is directly connected to the first DC power supply, the floating capacitor is initially charged to the value at the time of operation, so that it can be started at the time of startup. The zero-phase current can be prevented from flowing.

Before the contactor 13 is turned on, the voltage of the capacitor 7 is controlled so as to be charged to the peak value of the AC power supply voltage or more. Actually, the voltage is controlled to about 1.2 × 2√2 × E3 including the control margin and the voltage fluctuation, so that no current flows from the AC power supply during interconnection.

[0055]

As described above, according to the present invention, after the stray capacitance of the DC side power supply is initially charged to the state during the interconnection operation of the inverter via the current limiting impedance, the inverter is put into the interconnection. Thus, the zero-phase current can be reduced to prevent erroneous detection of the leakage detection circuit, and a highly reliable inverter device can be configured.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is an operation explanatory view of the first embodiment of the present invention.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a timing chart according to the second embodiment of the present invention.

FIG. 5 is a configuration diagram of a third embodiment of the present invention.

FIG. 6 is a timing chart according to the third embodiment of the present invention.

FIG. 7 is a configuration diagram using a half-bridge inverter.

FIG. 8 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 9 is a timing chart according to the fourth embodiment of the present invention.

FIG. 10 is a configuration diagram of a modified example of the fourth embodiment of the present invention.

FIG. 11 is a configuration diagram using a half-bridge inverter.

FIG. 12 is a configuration diagram of a conventional inverter device.

FIG. 13 is a diagram illustrating the operation of a conventional inverter device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Solar cell 2 ... Capacitor 3 ... Reactor 4 ... Diode 5 ... Switching element 6 ... Current detector 7 ... Capacitor 8 ... Inverter bridge 8a, 8b, 8c 8d Switching element 9, 10 Reactor 11 Current detector 12 Capacitor 13 Contactor 14 Breaker 15 AC power supply 16 Zero-phase current transformer Device 17: Leakage detector 18, 19: Floating capacitor 20: Voltage reference 21: Voltage detector 22, 23, 26 ... Amplifier 24, 27 ... PWM circuit 25 ... Current reference 28 ... Level detector 29 ... Auxiliary contact 30,31,34 ... Resistance 32,33,38,39 ... On delay 35,37 ... Relay

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takuo Itami 1 Toshiba-cho, Fuchu-shi, Tokyo Inside the Toshiba Fuchu Plant (72) Inventor Kenichi Kimoto 1-Toshiba-cho, Fuchu-shi, Tokyo Toshiba Fuchu Plant (72) Inventor Noriyuki Onishi 1 Toshiba-cho, Fuchu-shi, Tokyo Inside the Fuchu Plant, Toshiba Corporation

Claims (14)

[Claims] In an inverter apparatus, a DC power supply having a capacity to ground is connected to an AC power supply having a ground by an inverter, and the inverter is connected after charging the capacity to a potential at the time of system connection. An inverter device characterized in that: 2. An inverter device linked from a second DC power supply comprising a chopper circuit connected to a first DC power supply having a capacity to the earth to an AC power supply having a ground by an inverter, wherein An inverter for connecting the inverter to the AC power supply by connecting a midpoint potential of the DC power supply to a ground point of the AC power supply and then turning on a connection switch for connecting the inverter and the AC power supply. apparatus. 3. An inverter device linked from a second DC power supply comprising a chopper circuit connected to a first DC power supply having a capacity to the earth to an AC power supply having a ground by an inverter. After connecting the midpoint obtained by dividing the DC power supply with a resistor directly or via a resistor to the ground point of the AC power supply, a connection switch for connecting the inverter and the AC power supply is turned on to connect the inverter to the AC power supply. An inverter device characterized by being interconnected to the inverter. 4. The inverter device according to claim 2, wherein when the inverter is stopped, the connection switch is turned off and the connection between the midpoint of the second DC power supply and the AC power supply is also turned off. Features inverter device. 5. The inverter device according to claim 3, wherein the voltage dividing circuit of the second DC power supply is opened during the operation of the inverter. 6. An inverter device for connecting a DC power supply having a capacity to ground to an AC power supply having a ground by an inverter, wherein the inverter and the AC power supply are connected via an impedance, and then the impedance is changed to the impedance. Turn on the interconnection switches connected in parallel,
An inverter device, wherein the inverter is connected to the AC power supply. 7. An inverter device which is connected from a DC power supply having a capacity to ground to an AC power supply having a ground by an inverter, wherein the DC power supply and the inverter are connected via an impedance, and then connected to the impedance. An inverter device, wherein a connection switch connected in parallel is turned on to connect the inverter to the AC power supply. 8. The inverter device according to claim 6, wherein said impedance is a resistance. 9. The inverter device according to claim 6, wherein said inverter has a chopper circuit. 10. The inverter device according to claim 2, wherein said inverter has a half-bridge configuration. 11. The inverter device according to claim 2, wherein the timing of connecting the inverter to the AC power supply is such that the inverter is driven after a lapse of a predetermined period since a connection switch is turned on. An inverter device characterized in that: 12. The inverter device according to claim 2, wherein when the inverter is connected to the AC power supply, a current reference of the inverter is increased from a value lower than a set value. An inverter device characterized by the above-mentioned. 13. The inverter device according to claim 2, wherein the inverter does not operate in a free wheeling mode. 14. The inverter device according to claim 2, wherein a DC input voltage of said inverter is at least twice a peak value of an AC power supply voltage.