JPH07135777A - Detecting circuit of cross-current of ac output power converter - Google Patents

Abstract

PURPOSE:To increase or decrease the number of AC power converters which are connected in parallel while the operation of the group of the AC power converters is not interrupted by a method wherein the respective cross-current detecting circuit units of the AC power converters are connected in parallel. CONSTITUTION:As resistors R11, R21 and R31 which have same resistance values are connected to current transformers 11, 21 and 31, voltages which are proportional to the output currents of respective power converters 1, 2 and 3 are obtained between both the terminals of the respective resistors. Further, voltages corresponding to the average values of the voltages obtained between both the terminals of the respective resistors R11, R21 and R31 are obtained at the connection points X11, X21 and X31 of resistors R12, R22 and R32. Further, voltages corresponding to cross-currents are obtained between both the terminals of the resistors R12, R22 and R32 respectively. The voltages corresponding to the currents and the cross-currents which are to be alloted to the respective AC power converters are supplied to the control circuits of the respective AC power converters as control signals to control a load so as to be allotted to the respective AC power converters unifirmly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for detecting a cross current between converters in a power supply system in which a plurality of AC output converters such as inverters are connected in parallel and operated in parallel with a common load. is there.

[0002]

2. Description of the Related Art FIG. 7 shows, for example, Japanese Patent Laid-Open No. 4-217822.
It is a cross current detection circuit in the parallel operation system of the conventional converter shown by the publication. In the figure, reference numerals 1, 2, and 3 are AC output converters having the same configuration, for example, inverter devices, and the AC output converters are operated in parallel to supply power to the load 5. 11, 21, 31 are current transformers for detecting the output current of each AC output converter, 12, 22, 32 are cross current detection circuit units of each AC output converter, R11, R
21 and R31 are current transformers 11 and 2 having the same resistance value.
Resistances R12 and R2, which are the first and second burdens of 1, 31
2, R32 is a second secondary load of the current transformers 11, 21, 31 having sufficiently large and the same resistance value as R11, R21, R31, and S11, S21, S31 are
Switches that open during parallel operation, S12, S22, S3
Reference numeral 2 is a switch that opens when the load is shared.

Next, the operation will be described. Load current IL
The three AC output converters 1, 2 and 3 are I1 and I, respectively.
Consider a case where 2 and I3 are output. The output current of each AC output converter is detected by the current transformers 11, 21, 31. Resistors R11 and R2 having the same resistance value in each current transformer
Since R1 and R31 are connected, a voltage proportional to the output current of each AC output converter 1, 2, and 3 is obtained across each resistor. Resistors R12, R2 that are sufficiently large and have the same resistance value as the resistors R11, R21, R31.
2. Since R32 and R32 are connected as shown, the resistance R1
Two resistors R11, R are provided for 2, R22, R32, respectively.
A voltage corresponding to the average value of the voltages generated at both ends of 21, R31 is obtained. This voltage is 1/3 of the load current IL, that is, a voltage corresponding to a current value to be equally shared by the AC output converters 1, 2, and 3. Therefore, X1 point and X2
Between the points, the current to be shared by the AC output converter 1 is X1.
A voltage proportional to the cross current is obtained between the point and the point X3. The load sharing of each AC output converter can be controlled evenly by incorporating the currents to be shared by each AC output converter and the voltage corresponding to the cross current into the control circuit of each AC output converter as a control signal. When the AC output converter 1 is to be stopped, first, the switch S12 is closed, and the voltage generated across the resistors R22 and R32 should be equally shared by the remaining two AC output converters 2 and 3. It is sufficient to load the AC output converters 2 and 3 with a load in proportion to, and then to close the switch S11 and stop the AC output converter 1 at the same time.

[0004]

Since the conventional cross current detection circuit is constructed as described above, when a new AC output converter is added to the AC output converter group operating in parallel, or in parallel operation. When removing some AC output converters from the group of AC output converters that are operating, add or remove the cross current detection circuit unit of the AC output converter to be added to or remove the cross current detection circuit in the loop configuration. Since it is necessary to disconnect the cross current detection circuit unit of the output converter from the cross current detection circuit, it is necessary to stop the entire AC output converter during parallel operation. Therefore, in the case of a continuous operation system that cannot be stopped easily, it is necessary to install a special switching circuit to add a new AC output converter or remove the AC output converter during parallel operation. There was a problem such as Further, since the cross current detection circuit needs to connect the cross current detection circuit units of all the AC output converters that are operated in parallel to one loop, disconnection or disconnection may occur at one place among the wirings between the AC output converters. If there is poor contact, all the cross current detection circuits will not function. Therefore, it is necessary to take measures such as duplicating the wiring between the cross current detection circuit units of each AC output converter. The present invention has been made to solve such a problem, and it is easy to increase or decrease the number of AC output converters in parallel without stopping the AC output converter group in parallel operation. The purpose of the present invention is to obtain a cross current detection circuit that can perform

[0005]

A cross current detection circuit according to the present invention includes a current transformer for detecting an output current of each converter, a first secondary load connected to each current transformer, and a first secondary load. A second secondary load having a sufficiently larger impedance than the first secondary load in which one terminal is connected to one output terminal of the current transformer, and all the other terminals of each current transformer are commonly used. The other terminals of the second secondary load are connected in common via a switch, and the cross current control signal of each AC output converter operated in parallel by each of the first and second secondary loads is connected. To get it. Further, the current transformers that detect the output currents of the respective converters, the first and second secondary loads having equivalent impedances connected in series to the respective current transformers, and the first and second respective loads. All of the secondary load connecting parts are connected in common via a switch, and one output terminal of each current transformer is connected in common, and they are operated in parallel by each of the first and second secondary loads. The cross current control signal of each AC output converter is obtained.

[0006]

Since the cross current detection circuit units of the AC output converters that are operated in parallel are connected in parallel,
The procedure of increasing or decreasing the number of parallel AC output converters can be easily performed without stopping the AC output converter group in operation.

[0007]

【Example】

Example 1. FIG. 1 shows a first embodiment of the present invention. In the figure, 1, 2, and 3 are three AC output converters operating in parallel,
Reference numeral 4 is an AC output converter that is to be newly operated in parallel with the AC output converters 1, 2, and 3. 11, 21, 3
1, 41 are current transformers that detect the output current of each AC output converter, and R11, R21, R31, R41 are the first two of the current transformers 11, 21, 31, 41 having the same resistance value. Next load is resistance, R12, R22, R32, R42 is R1
The resistances S13, S23, S33, S, which are the second secondary loads of the current transformers 11, 21, 31, 41, which are sufficiently larger than 1, R21, R31, R41 and have the same resistance value.
Reference numeral 43 is a switch that is closed when the load is shared.

Next, the operation will be described. Now, load current IL is I in each of three AC output converters 1, 2 and 3.
Consider the case of sharing 1, I2, and I3. The output current of each AC output converter is detected by the current transformers 11, 21, 31. A resistor R1 having the same resistance value for each current transformer
Since R1, R21, and R31 are connected, a voltage proportional to the output current of each AC output converter 1, 2, and 3 is obtained across each resistor. Resistors R11, R21, R3
Resistor R1 that is sufficiently larger than 1 and has the same resistance value
2, R22, R32 are connected as shown,
Connection points X11, X21 of the resistors R12, R22, R32,
X31 has three resistors R11, R21, and R31, respectively.
A voltage corresponding to the average value of the voltages generated at both ends is obtained. This voltage is 1/3 of the load current IL, that is, a voltage corresponding to a current value to be equally shared by the AC output converters 1, 2, and 3. Also, the resistors R12, R22, R32
A voltage proportional to the cross current is obtained at both ends. The load sharing of each AC output converter can be controlled evenly by incorporating the currents to be shared by each AC output converter and the voltage corresponding to the cross current into the control circuit of each AC output converter as a control signal.

When the AC output converter 1 is to be stopped, first, the switch S13 is opened, and at the same time, the load sharing of the AC output converter 1 is reduced to reduce the voltage across the resistor R11 to zero.
As the load on the AC output converters 2 and 3,
The AC output converter 1 may be stopped. Next, a case will be described in which the AC output converter 4 is newly operated in parallel with respect to the AC output converters 1, 2, and 3 which are in parallel operation. The cross current detection circuit units 12, 22, 32 of the AC output converters 1, 2, 3 already in parallel operation are connected in parallel, respectively. Therefore, the cross current detection circuit unit 42 of the AC output converter 4 has the AC output converter 1 at the connection points Y1 and Y2.
It may be connected in parallel with a few cross current detection circuit units,
It is not necessary to stop the AC output converters 1, 2, 3. In this way, one of the AC output converters operating in parallel is stopped, or a new AC output converter is added to the AC output converters operating in parallel. Even when operating in parallel, the operating state can be changed promptly without requiring a special switching circuit.

FIG. 2 shows a modification of the first embodiment. Portions corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. The difference from the first embodiment is that the switches S16, S17, S26, S27, S36, S3.
7 is added, and other points are the same as in the first embodiment.

When performing a functional test or the like on only a predetermined device of the device group during parallel operation, it may be necessary to disconnect the cross current detection circuit unit of the device. For example, a pressure resistance test is an example. So switch S1
Among S6, S17, S26, S27, S36, and S37, a predetermined cross current detection circuit unit can be disconnected by opening a switch of the device to be tested, and the device can be in an independent operation state. There is an effect that a functional test or the like can be performed for the device of (3) regardless of other devices in parallel operation.

Example 2. FIG. 3 shows a second embodiment of the present invention. In the figure, 1, 2 and 3 are three AC output converters that are in parallel operation, and 4 is an AC output converter that is to be newly operated in parallel with the AC output converters 1, 2 and 3. 1
1, 21, 31, 41 are current transformers for detecting the output current of each AC output converter, R13, R23, R33, R43.
Are current transformers 11, 21, 31, 41 having the same resistance value.
The first secondary burden of the resistors, R14, R24, R3
4 and R44 have the same resistance value and the resistance R1
The resistors S14, S24, S34, and S44, which are the second secondary loads of the current transformers 11, 21, 31, and 41 having the same or equivalent resistance values as 3, R23, R33, and R43, share the load. It is a switch that sometimes closes.

Next, the operation will be described. Load current IL
The three AC output converters 1, 2 and 3 are I1 and I, respectively.
Consider a case where 2 and I3 are output. The output current of each AC output converter is detected by the current transformers 11, 21, 31. Resistors R13 and R2 having the same resistance value in each current transformer
3 and R33 are connected, the output currents I1 and I of the AC output converters 1, 2 and 3 are connected across the resistors.
2, a voltage proportional to I3 is obtained. Also, the resistor R1
A current corresponding to the average value (I1, I2, I3) / 3 of the currents flowing through the resistors R11, R21, and R31 flows through the resistors R14, R24, and R34, so that three resistors are provided at both ends of the resistors R14, R24, and R34. A voltage corresponding to the average value of the voltages generated across R13, R23, and R33 is obtained.
This voltage is 1/3 of the load current IL, that is, a voltage corresponding to a current value to be equally shared by the AC output converters 1, 2, and 3. For example, for the AC output converter 1,
The voltage corresponding to the current to be shared across the resistor R14 is
Since a voltage corresponding to the output current is obtained at both ends of the resistor R13, the load sharing of each AC output converter can be uniformly controlled by incorporating these voltages as control signals into the control circuit of each AC output converter. The difference between the voltage across the resistor R13 and the voltage across the resistor R14 is the voltage corresponding to the cross current.

In this embodiment, the current transformers 11, 2 are
The output currents of 1 and 31 are three resistors R14 and R2.
4, split into R34 evenly. Therefore, the resistance R
The voltages across 14, R24, R34 are always the same regardless of the load sharing of the AC output converters 1, 2, 3. Therefore, if the impedances of the resistors R14, R24, R34 are set small and the output currents of the current transformers 11, 21, 31 are increased, even if external inductive noise enters the wiring between the AC output converters. Resistors R14, R24, R34
Since the noise voltage at the point becomes small, it is less likely to be affected by external noise. Next, a procedure for stopping the AC output converter 1 will be described. In this case, the load sharing of the AC output converter 1 is reduced at the same time when the switch S14 is opened, the voltage across the resistor R13 is set to 0, and the load is loaded on the AC output converters 2 and 3, and then the AC output converter 1 is switched on. It suffices to stop, and it is extremely easy to stop a specific device in parallel operation.

A case will be described in which the AC output converter 4 is newly operated in parallel with respect to the AC output converters 1, 2 and 3 which are in parallel operation. The cross current detection circuit units of the AC output converters 1, 2, 3 which are already in parallel operation are connected in parallel. Therefore, the cross current detection circuit unit of the AC output converter 4 may be connected in parallel with the cross current detection circuit unit of the AC output converters 1, 2, and 3 at the connection points Y1 and Y2. There is no need to stop 3.

FIG. 4 shows a first modification of the second embodiment. Parts corresponding to those in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted. The difference from the second embodiment is that
This is the addition of switches S15, S25 and S35,
Others are the same as in FIG.

In the figure, when it is desired to stop the AC output converter 1, first the switch S15 is opened and the resistor R
24, R34 with a current equivalent to 1/2 of the load,
All the loads are transferred to the other two AC output converters 2 and 3. Next, switch S14 is opened and at the same time S15 is closed,
The AC output converter 1 may be stopped. Thus, there is an effect that the load can be shared more quickly.

FIG. 5 shows a second modification of the second embodiment. Parts corresponding to those in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted. The difference from the first modification of the second embodiment is that the zener diodes ZD11 and ZD1.
2, ZD21, ZD22, ZD31, and ZD32 are added, and the other points are the same as in FIG.

In the figure, when it is desired to stop the AC output converter 1, first the switch S15 is opened and the resistance R
24, R34 with a current equivalent to 1/2 of the load,
All the loads are transferred to the other two AC output converters 2 and 3. Next, switch S14 is opened and at the same time S15 is closed,
The AC output converter 1 may be stopped. At this time, if the switch S15 fails and is not closed, the current transformer 11 is in an open state and thus generates an overvoltage, but the Zener diodes ZD11 and ZD12 are connected in parallel to the current transformer 11 and the overvoltage is generated. Can be prevented. Thus, the Zener diodes ZD11, ZD12, ZD2
1, ZD22, ZD31, ZD32 are current transformers 11, 1
The effect of protecting 2 and 13 from overvoltage occurs.

FIG. 6 shows a third modification of the second embodiment. Parts corresponding to those in FIG. 5 are designated by the same reference numerals, and detailed description thereof will be omitted. The difference from the fifth embodiment is that the switches S16, S17, S26, S27, S36 and S37.
Is added, and the other points are the same as in FIG.

When performing a functional test or the like on only a predetermined device in the device group during parallel operation, it may be necessary to disconnect the cross current detection circuit unit of the device. For example, a pressure resistance test is an example. So switch S1
Among S6, S17, S26, S27, S36, and S37, a predetermined cross current detection circuit unit can be disconnected by opening a switch of the device to be tested, and the device can be in an independent operation state. There is an effect that a functional test or the like can be performed on the above device regardless of other devices in parallel operation.

[0022]

As described above, according to the present invention, the effect of increasing or decreasing the number of AC output converters in parallel can be easily performed without stopping the AC output converter group in operation. There is.

Further, in particular, according to the second aspect of the present invention, there is an effect that it is difficult to be influenced by induction noise.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing a modified example of the first embodiment of the present invention.

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

FIG. 4 is a circuit diagram showing a first modification of the second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a second modification of the second embodiment of the present invention.

FIG. 6 is a circuit diagram showing a third modification of the second embodiment of the present invention.

FIG. 7 is a circuit diagram showing a conventional cross current detection circuit.

[Explanation of symbols]

 1, 2, 3, 4 AC output converter 5 Load 11, 21, 31, 41 Current transformer Snn (where nn is a number) Switch Rnn (where nn is a number) Secondary load ZDnn (where nn is a number) ) Zener diode

Claims (5)

[Claims] 1. A current transformer that detects the output current of each converter in a cross current detection circuit of a power supply system in which a plurality of AC output converters are connected in parallel and operate in parallel with a common load. A first secondary load connected to each of the current transformers and a second secondary load having a sufficiently larger impedance than the first secondary load of which one terminal is connected to one output terminal of each current transformer. Secondary load of each of the current transformers, all the other terminals of the current transformers are commonly connected, and the other terminals of the second secondary load are all commonly connected via a switch, A cross current detection circuit for an AC output converter, which is configured to obtain a cross current control signal of each AC output converter that is operated in parallel by the first and second secondary loads. 2. The other terminal of each of the current transformers is connected to a second terminal.
2. The cross current detection circuit for an AC output converter according to claim 1, wherein all of them are commonly connected through the switch. 3. A current transformer that detects the output current of each converter in a cross current detection circuit of a power supply system in which a plurality of AC output converters are connected in parallel and operate in parallel with a common load. A first secondary load having one terminal connected to one terminal of each of the current transformers, and
Each of the first secondary loads having an impedance equivalent to that of the second secondary load and having one terminal connected to the other terminal of the first secondary load and the other terminal connected to the other terminal of each of the converters. 2 secondary loads, all of the first and second secondary load connections are connected in common through a switch, and all the other output terminals of each current transformer are connected in common. A cross-current detection circuit for an AC output converter, which is configured to obtain a cross-flow control signal of each AC output converter that is operated in parallel by the first and second secondary loads. 4. The AC output converter according to claim 3, wherein a second switch is provided between each of the first and second secondary load connecting portions and the second secondary load. Cross current detection circuit. 5. The cross current detection circuit for an AC output converter according to claim 4, wherein a Zener diode is connected between the output terminals of each of the current transformers.