JPH07106066B2 - Parallel connection circuit of single-phase inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is designed to operate a plurality of single-phase inverters that output alternating current with the same operation signal in parallel without causing current imbalance. A parallel connection circuit of single-phase inverters that can perform

[Conventional technology]

FIG. 6 is a main circuit connection diagram showing a conventional example in which output current unbalance does not occur in a plurality of single-phase inverters that operate in parallel by receiving the same operation signal. Represents a connection circuit.

In FIG. 6, the direct current side of the first inverter 3 constituted by a single-phase bridge connection of four metal oxide semiconductor field effect transistors (hereinafter abbreviated as MOS FETs) 31 to 34, and the same four MOSs. The common DC power supply 2 is connected to the DC side of the second inverter 4 configured by the single-phase bridge connection of the FETs 41 to 44, but these inverters 3 and 4 are connected from a control circuit (not shown). Since the same operation signal is given, AC power can be supplied to the common load 5 by connecting the AC output sides of both inverters 3 and 4 in parallel with each other.

By connecting a plurality of inverters in parallel in this way, it is possible to cope with an increase in the capacity of the load 5. However, when the load 5 is directly connected to the inverters, generally, the output impedance of the first inverter 3 and the second inverter 4 are connected. However, even if both inverters 3 and 4 are operating with the same operation signal, there is a disadvantage that the respective output currents become unbalanced.

Therefore, the reactor 11 is connected to the output side of the first phase U1 of the first inverter 3 and the reactor 13 is connected to the output side of the first phase U2 of the second inverter 4, respectively.
Both are connected in parallel via 13 and then connected to one end of the load 5. Similarly, the reactor 12 is connected to the output side of the second phase V1 of the first inverter 3, and the reactor 14 is connected to the output side of the second phase V2 of the second inverter 4, and these reactors 12 and 14 are connected. After connecting the both in parallel via this, this is connected to the other end of the load 5. The impedance values of the four reactors 11 to 14 are used as the first inverter 3
And the output impedance value of the second inverter 4 is made sufficiently large, and if these four reactors 11 to 14 are manufactured so as to have impedances of equal value, the DC power source 2 and the first inverter 3 are passed through. Since the ratio of the difference between the impedance value of the path to the load 5 and the impedance value of the path from the DC power supply 2 to the load 5 via the second inverter 4 can be made small, the output currents of the inverters 3 and 4 can be reduced. Such parallel connection circuits are often used because the imbalance can be eliminated.

[Problems to be solved by the invention]

However, the reactors 11 to 14 used in the conventional circuit shown in FIG.
Since it must be configured to a value that is sufficiently large compared to the output impedance of 3 and 4, the reactors 11 to 14
Has a large size, increases weight, and increases costs. Further, since the reactors 11 to 14 are inserted into the AC output circuit of the inverter, the capacity of the inverter must be increased by that amount, and therefore the size of the entire apparatus is increased and the cost is increased. Further, if the inductors 11 to 14 are not manufactured to have the same inductance value, the current imbalance cannot be suppressed, which causes various inconveniences such as an increase in the price of the reactors 11 to 14.

Therefore, it is an object of the present invention to balance the output currents of the inverters operating in parallel without increasing the inverter capacity and reducing the output impedance of the inverters.

[Means for solving problems]

In order to achieve the above purpose, multiple unit inverters that output single-phase alternating current are connected in parallel, and the same operation signal is given to each unit inverter for synchronous operation and power is supplied to a common load. In the parallel connection circuit of the inverters, a first conductor of each of the unit inverters through which the first phase AC output current of its own flows, and a second conductor of at least one of the remaining unit inverters through which the second phase AC output current flows And are wired in close proximity to each other, and the second conductor through which the second-phase AC output current of its own flows, and the first conductor of at least one of the remaining unit inverters through which the first-phase AC output current flows are wired in close proximity to each other. In addition, the first conductor of the at least one unit inverter, in which the first-phase AC output current flows, and the second conductor, in which the second-phase AC output current flows, are arranged close to each other.

Alternatively, the first conductor and the second conductor are twisted with each other via an insulator and wired.

[Action]

According to the present invention, when AC output sides of a plurality of single-phase inverters are connected in parallel, a first-phase AC output current of a certain inverter and a second-phase AC output current of another inverter are balanced by magnetic coupling. Further, the second-phase AC output current of a certain inverter and the first-phase AC output current of another inverter are balanced by magnetic coupling, and the first-phase AC output current and the second-layer AC output current of the same inverter are further balanced. The AC output currents of all the inverters are balanced by magnetic coupling so that both the first and second phases are balanced. This magnetic coupling is the current obtained by applying two sets of windings to the iron core. A balancer, or conductors with the same amount of current but opposite directions are made as close as possible or twisted through an insulator, so current of the same value flows in this magnetic coupling. Come, only the mutual inductance of the two conductors can reduce wiring inductance, also if current is unbalanced, by the difference current and the mutual inductance,
The induced voltage is generated so that the currents are balanced, and the current imbalance between the inverters is eliminated.

〔Example〕

FIG. 1 is a main circuit connection diagram showing the principle of the present invention.
The figure shows the case of connecting single-phase inverters in parallel.

In FIG. 1, by connecting the four MOS FETs 31 to 34 to the direct current side of the first inverter 3 which is configured by connecting the single phase bridges, and also the four MOS FETs 41 to 44 are connected to the single phase bridges. A common DC power supply 2 is connected to the DC side of the configured second inverter 4, and the AC side of these two inverters 3 and 4 is connected to the first current balancer 17 and the second current balancer as magnetic coupling. By connecting a common load 5 to both of the first inverter 3 and the second inverter 18 via
It can be operated in parallel with the inverter 4. The two inverters 3 and 4 operate with the same operation signal, but the illustration of those parts is omitted because it is not directly related to the present invention.

The connection of the above current balancers 17 and 18 is as follows.
That is, the first phase U1 of the AC output of the first inverter 3 is applied to the load 5 via the first current balancer 17, and the second phase V1 of the AC output of the first inverter 3 is connected to the first current balancer 17 and the second current V1. To the load 5 via the current balancer 18, the first phase U2 of the AC output of the second inverter 4 to the load 5 via the second current balancer 18, and the second phase of the AC output of the second inverter 4. Since V2 is directly connected to the load 5, the AC outputs of both inverters 3 and 4 are eventually the first phase U1 and U2, and the second phase.
V1 and V2 are connected in parallel at the input terminal portion of the load 5 after passing through both current balancers 17 and 18, respectively.

Here, the first current balancer 17 and the second current balancer 18 are both configured so that two windings are magnetically coupled, and when the currents flowing through these windings are equal, the respective windings are The induced voltage of becomes almost zero, but if the current of one winding tries to increase more than the current of the other winding,
A voltage in the direction of decreasing the current is induced in the winding, and a voltage in the direction of increasing the current is induced in the other winding.

FIG. 2 is an explanatory circuit diagram for explaining the principle of the present invention shown in FIG. 1 in more detail. In FIG. 2,
Each of the switches 21 and 22 is a switch that represents the switching operation of the inverter, and the inverter output resistance 24
And 28 respectively represent the output impedance of the inverter by the resistance component, and a first loop circuit in which a switch 21, a DC power supply 22, a load 23 and an inverter output resistance 24 are connected in series, and a switch 25. The current source 26, the load 27, and the second loop circuit in which the inverter output resistance 28 is connected in series are magnetically coupled by the current balancer 20.

FIG. 3 is an equivalent circuit diagram equivalently representing the explanatory circuit shown in FIG. 2, in which the switches 21 and 25 shown in FIG.
DC power supplies 22 and 26, loads 23 and 27, and inverter output resistors 24 and 28 are the same as those shown in FIG. The second
The current balancer 20 shown in the figure is represented by the balancer leakage inductances 20A and 20B and the balancer mutual inductance 20M in the equivalent circuit shown in FIG.

In the equivalent circuit shown in FIG. 3, when the switches 21 and 25 are turned on at the same time, the voltage equation of the first loop circuit is the following equation (1), and the voltage equation of the second loop circuit is the equation (2). It is represented by. However, this equation (1) and (2)
In the equation, I ₅ is the current of the first loop circuit, I ₆ is the current of the second loop circuit, E is the voltage of the DC power supplies 22 and 26, R ₁ is the resistance value of the inverter output resistance 24, and R ₂ is the inverter output resistance 28. And resistance value, L ₁ is the inductance value of balancer leakage inductance 20A, L ₂ is the inductance value of balancer leakage inductance 20B, M is the inductance value of balancer mutual inductance 20M, and R is the resistance value of loads 23 and 27. .

As is clear from the expressions (1) and (2), when the current I ₅ of the first loop circuit is about to become larger than the second loop circuit current I ₆ , the second side of the left side of the expression (1) is The voltage indicated by the term is induced to operate so as to reduce the first loop circuit current I _5, and the voltage indicated by the second term on the left side of the equation (2) is induced to change the second loop circuit current I ₆ to Since an attempt is made to increase it, the first loop circuit current I ₅ and the second loop circuit current I ₆ will eventually settle to equal values.

In the circuit of the embodiment of the present invention shown in the above item 1,
The output current of the first phase U1 of the inverter 3 is I ₁ , the output current of the second phase V1 is I ₂ , the output current of the first phase U2 of the second inverter 4 is I ₃ , and the output current of the second phase V2 is When I ₄ is set, the condition where these respective currents are balanced is given by the following equation (3).

I ₁ = I ₃ = −I ₂ = −I ₄ (3) Here, the condition of I ₁ = −I ₂ can be established by the first current balancer 17, and the condition of −I ₂ = I ₃ is the first. Since it can be established by the two-current balancer 18, the following equation (4) is obtained by the first current balancer 17 and the second current balancer 18.

I ₁ = -I ₂ = I ₃ (4) On the other hand, the following equation (5) is established by Kirchhoff's law.

I ₁ + I ₂ + I ₃ + I ₄ = 0 (5) After all, the above equations (4) and (5) satisfy the current balance condition shown in equation (3). That is, by installing two sets of current balancers 17 and 18 at the positions shown in FIG. 1, there is no risk of the output AC current becoming unbalanced when both inverters 3 and 4 are operated in parallel. I understand.

In the circuit shown in FIG. 1, when the magnetic coupling as described above is used to balance the AC output currents when a plurality of single-phase inverters are connected in parallel and operated,
Various combinations other than those shown in FIG. 1 may exist at the insertion position of the current balancer using the magnetic coupling, and the number of combinations jumps as the number of parallel-operated single-phase inverters increases. However, in any case, the first phase current and the second phase current of the AC output of all the single phase inverters may be magnetically coupled in some combination. .

FIG. 4 is a main circuit connection diagram showing the first embodiment of the present invention. When two single-phase inverters are connected in parallel, the conductor of the first phase AC output current and the second phase are connected. The magnetic coupling is obtained by arranging the conductor through which the AC output current flows through the conductor as long as possible and as close as possible.

In FIG. 4, the first inverter composed of a single-phase bridge connection of four MOS FETs 31 to 34 and the same four inverters
The second inverter composed of the single-phase bridge connection of the MOS FETs 41 to 44 is connected in parallel to each other, and the DC power supplied from the DC power supply 2 common to both is converted into the single-phase AC power, and the Power is supplied to the load 5, but the conductor 51 in which the first phase current I ₁ of the first inverter flows and the conductor 52 in which the second phase current I _{2 of} the first inverter also flows are made as close as possible over a long distance. By arranging them, magnetic coupling occurs when the currents I ₁ and I ₂ flow, and this magnetic coupling serves as a current balancer, so that the current balance condition shown in the following equation (6) is obtained.

I ₁ = −I ₂ (6) The first phase current I ₁ of this first inverter is passed to the load 5 via the conductor 53 in series with the above-mentioned conductor 51, and the second
When the second phase current I ₄ of the inverter is supplied to the load 5 via the conductor 54, if magnetic coupling is generated by bringing these conductors 53 and 54 close to each other as much as possible, the current balance shown in equation (7) is used. The condition is obtained.

I ₁ = −I ₄ (7) Further, the second phase current I ₂ of the first inverter is caused to flow through the conductor 55 in series with the conductor 52, and the first phase current I ₃ of the second inverter is changed. If magnetic coupling is generated by flowing it to the conductor 56 and bringing both conductors 55 and 56 as close as possible,
The current equilibrium condition shown in equation (8) is obtained.

-I ₂ = I ₃ (8) Since the current balance condition shown in the above equation (3) can be obtained from these equations (6), (7) and (8), the conductor through which the AC output current flows is If arranged as shown in the figure, the AC output currents of the two single-phase inverters operating in parallel can be balanced.

FIG. 5 is a main circuit connection diagram showing a second embodiment of the present invention and shows a case where two single-phase inverters are connected in parallel. That is, the first inverter composed of four single-phase bridge connections of four MOS FETs 31 to 34 and the first inverter similarly composed of four single-phase bridge connections of four MOS FETs 41 to 44 are connected in parallel with each other. As in the first embodiment circuit shown in FIG. 4, the DC power from the DC power supply 2 common to both is converted into single-phase AC power and is supplied to the common load 5.

In the second embodiment circuit shown in FIG. 5, the first-phase current I ₁ of the first inverter is passed through the electric wire 61, and the second-phase current I ₂ is passed through the electric wire 62. The magnetic coupling is generated by twisting and 62. Wire as well
The first phase current of the first inverter on the electric wire 63 that is connected in series with 61
I _{1 is made} to flow, and the second phase current I ₄ of the second inverter is made to flow in the electric wire 64 twisted with this electric wire 63. In addition, the second-phase current I ₂ of the first inverter is applied to the electric wire 65 that is in series with the electric wire 62, and the first-phase current I ₃ of the second inverter is applied to the electric wire 66 twisted with the electric wire 65. As a result, magnetic coupling is generated between the twisted wires, and the current balance condition shown in the equation (3) is finally satisfied as in the case of the first embodiment shown in FIG.

The current balancer used in the principle circuit shown in FIG. 1 has a structure in which two windings are provided in the iron core, and the leakage inductance values L ₁ and L ₂ shown in the equations (1) and (2) are used. However, since it is extremely large compared to the wiring inductance, the output impedance of the inverter is increased. However, in the embodiment circuits shown in FIGS. 4 and 5, the wiring itself is used for magnetic coupling. , And the wiring inductance values are L _A and L _B , respectively, the magnetic coupling leakage inductance values L ₁ and L ₂ obtained in this way are the following (9) when the mutual inductance value is M. ) And (10).

The magnetic coupling shown in _{L 1 = L A -M ...... (} 9) L 2 = L B -M ...... (10) i.e. Figure 4 or Figure 5,
The output impedance of the inverters connected in parallel is smaller than the output impedance in the case of independent operation of the inverters.

As apparent from a comparison between the principle circuit of FIG. 1 and the embodiment circuit of FIG. 4 or FIG. 5, it is clear that the magnetic coupling composed of the conductor 53 and the conductor 54 in the embodiment circuit of FIG. ,
Alternatively, even if there is no magnetic coupling formed by the electric wire 63 and the electric wire 64 in the embodiment circuit of FIG. 5, there is no problem in balancing the current, but as described above, these magnetic couplings cause The output impedance of the inverter can be reduced and the other magnetic coupling (with the conductor 55 in FIG. 4).
56, or the magnetic coupling formed by the electric wires 65 and 66 in FIG. 5).

Further, since the magnetic coupling used in the embodiment circuits shown in FIGS. 4 and 5 does not use the iron core, the value M of mutual inductance is smaller than that of the wire balancer using the iron core. Therefore, the change of the difference current, that is, d (I ₅ −I ₆ ).
It is suitable for high frequency inverters and large capacity inverters with large / dt or d (I ₆ −I ₅ ) / dt.

〔The invention's effect〕

According to the present invention, when a plurality of single-phase inverters are operated in parallel while operating with the same operation signal, the first-phase AC output current of one inverter is balanced with the second-phase AC output current of another inverter. Magnetic coupling, or magnetic coupling that balances the second-phase AC output current of one inverter with the first-phase AC output current of another inverter, and further balances the first-phase and second-phase AC output current of a specific inverter. By providing the magnetic coupling, the current imbalance of each inverter during parallel operation can be suppressed without relying on the conventional reactor insertion having a large impedance, so that the output impedance of the inverter is not increased, and therefore the inverter The capacity does not have to be large. Further, since the reactor is not used, there is an advantage that the size of the device is suppressed and the cost is not increased. Furthermore, when the above magnetic coupling is achieved by a conductor that carries an inverter AC output current or a close arrangement or twisting of the currents, it is possible not only to realize a smaller size and lower cost than a current balancer using an iron core. In addition, since mutual inductance can be reduced, it is particularly suitable for inverters that perform switching operation at high frequencies and large capacity inverters, and because an iron core is not used, it is possible to contribute to downsizing and weight reduction of equipment and cost reduction. Also have.

[Brief description of drawings]

FIG. 1 is a main circuit connection diagram showing the principle of the present invention.
FIG. 1 is an explanatory circuit diagram for explaining the principle of the present invention shown in FIG. 1, FIG. 3 is an equivalent circuit diagram equivalently showing the explanatory circuit shown in FIG. 2, and FIG. FIG. 5 is a main circuit connection diagram showing the first embodiment, and FIG. 5 is a main circuit connection diagram showing the second embodiment of the present invention. FIG. 6 is a main circuit connection diagram showing a conventional example in which output current unbalance does not occur in a plurality of single-phase inverters that receive the same operation signal and operate in parallel. 2,22,26 …… DC power supply, 3 …… First inverter, 4 ……
2nd inverter, 5,23,27 …… load, 11,12,13,14 …… reactor, 17 …… first current balancer as magnetic coupling,
18 …… Second current balancer as magnetic coupling, 20 …… Current balancer, 20A, 20B …… Balancer leakage inductance, 2
0M …… balancer mutual inductance, 21,25 …… switch, 24,28 …… inverter output resistance, 31 to 34,41 to 44 ……
MOS FET, 51-56 …… conductor, 61 …… 66 …… electric wire.

Claims (2)

[Claims] 1. A plurality of unit inverters that output a single-phase alternating current are connected in parallel, and the same operation signal is given to each unit inverter for synchronous operation to supply electric power to a common load. In the connection circuit, the first conductor of each of the unit inverters, through which the first phase AC output current of its own flows, and the second conductor of at least one of the remaining unit inverters, through which the second phase AC output current flows, are arranged close to each other. The second conductor through which the second-phase AC output current of its own flows, and the first conductor of at least one of the remaining unit inverters through which the first-phase AC output current flows, in close proximity to each other, and A parallel connection circuit for inverters, characterized in that a first conductor through which a first-phase AC output current of at least one unit inverter flows and a second conductor through which a second-phase AC output current flows are arranged close to each other. . 2. The inverter parallel connection circuit according to claim 1, wherein the first conductor and the second conductor are twisted with each other through an insulator and wired. Parallel connection circuit.