JPH09149661A - Parallel inverter system and current balancer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the construction of equipment by a method wherein a signal expressing the unbalance between output currents between a plurality of inverters in accordance with the fluxes of current balancers. SOLUTION: The output feeders Wi and Wj of the inverters in two systems are let through the annular magnetic cores CR of current balancers BX12-BX23 so as to have the respective current directions opposite to each other. Therefore, if both the currents are balanced, the fluxes are also balanced and the difference between the two currents is zero. If both the currents are not balanced, a flux proportional to the difference between the currents is generated. A voltage (e) proportional to the unbalance flux is induced in a coil CL and outputted as a flux detection signal. As the flux detection signal is proportional to the unbalance value between the currents of the feeder Wi and the feeder Wj , the unbalance between the output currents of the two system inverters is indicated. For instance, the detection signal of a flux detector MX12 shows the current unbalance between feeders W1X and W2X.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a parallel inverter system in which a plurality of inverters are connected in parallel and a current balancer used therein. For more information,
1 is a parallel inverter system configured to detect an unbalance of output currents of a parallel inverter by using a current balancer, and a current balancer used for the parallel inverter system.

[0002]

BACKGROUND OF THE INVENTION Parallel inverter systems are used to supply a large alternating current of a predetermined frequency to a load. This parallel inverter system uses multiple inverters
The current of the common DC power supply is converted into an AC current of a predetermined frequency to supply the common load.

A plurality of inverters operate in synchronization and output alternating currents of the same frequency, the same phase, and the same rating. The output current of each inverter is supplied to the load through the power supply line. The lengths of the power supply lines are set to be the same as much as possible, and the imbalance of the output currents of the plurality of inverters due to the difference in impedance of the power supply lines is reduced.

Further, a current balancer is provided on the power supply line for the output current to balance the output current among the plurality of inverters. The current balancer has a configuration in which the feed lines for the output currents of the different inverters are passed through the annular magnetic core in opposite directions, which causes the imbalance of the currents flowing through the feed lines due to mutual induction via magnetic flux. Is suppressed.

[0005]

Even if a current balancer is provided on the feeder line for the output current, the output currents of the plurality of inverters cannot be perfectly balanced, and some imbalance remains. In that case, if an imbalance increases due to some abnormality, it is necessary to detect it and perform appropriate protection coordination, but such a measure cannot be taken because there is no simple imbalance detection method in the past.

In order to detect an imbalance by force, it is necessary to measure the output currents of a plurality of inverters and calculate the difference between them, but providing such means complicates the configuration of the device. Is not preferred.

The present invention has been made to solve the above problems, and an object thereof is to realize a parallel inverter system and a current balancer that obtain an unbalanced display signal with a simple configuration.

[0008]

According to a first aspect of the present invention, a mutual induction of opposite polarity via magnetic flux is applied between a plurality of inverters connected in parallel and the outputs of the plurality of inverters. A parallel inverter system having a current balancer, wherein a signal representing an unbalance of output currents of the plurality of inverters is obtained based on a magnetic flux in the current balancer.

In the first invention for solving the problems, the plurality of inverters are IGBTs (insulated gates).
It is preferable to use a bipolar transistor) as a switching element in order to achieve both a high switching frequency and a large output current.

Further, in the first invention for solving the problem, it is preferable that the plurality of inverters are full-bridge type inverters in terms of high efficiency. Further, in the first invention for solving the problem, the current balancer is configured such that the output power supply lines of the inverters of the two systems are penetrated through the annular magnetic core so that the current directions are opposite to each other. It is preferable in terms of simplification.

Further, in the first invention for solving the problem, it is possible to obtain a signal indicating the imbalance of the output current based on the induced voltage of the coil wound around the annular magnetic core, which simplifies the configuration. In terms of

According to the first invention for solving the problem, since the signals representing the unbalance of the output currents of the plurality of inverters are obtained based on the magnetic flux in the current balancer, the unbalanced display is achieved by the simple structure. A parallel inverter system that obtains signals can be realized.

A second invention for solving the problem is a current balancer in which output supply lines of two inverters are passed through an annular magnetic core so that current directions are opposite to each other. The current balancer is characterized in that a magnetic flux detecting means for detecting the magnetic flux therein is provided.

In the second invention for solving the problem, it is preferable that the magnetic flux detecting means is a coil wound around the annular magnetic core in terms of simplification of the configuration. According to the second invention for solving the problem, since the magnetic flux detecting means for detecting the magnetic flux in the annular magnetic core is provided, it is possible to realize a current balancer for obtaining an unbalanced display signal with a simple configuration. it can.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a block diagram of the parallel inverter system. This device is an example of an embodiment of the present invention.

In FIG. 1, three inverters 1, 2,
3 is connected to the DC power source E in parallel. The inverters 1, 2 and 3 are all full-bridge type inverters. In the inverter 1, 1A, 1B, 1C and 1D are switching elements. Switching elements 1A-1D
For example, a bipolar transistor, an IGBT, a MOS FET or the like is used.

The bipolar transistor is preferable in that the output current is increased. The IGBT is preferable in that the switching frequency is increased and the output current is increased.
The MOS FET is preferable in that the switching frequency is further increased.

These switching elements 1A to 1D are driven by a driving device (not shown) to be turned on and off at a predetermined frequency. At that time, the pair of switching elements 1A and 1D and the pair of 1B and 1C are turned on and off in mutually opposite phases to convert the current of the DC power source E into an AC current and output it from the output terminals 1X and 1Y.

The inverters 2 and 3 have the same structure. These three inverters 1 to 3 operate in synchronization with each other to generate output currents of the same frequency, the same phase and the same rating.

One output terminal 1 of the inverters 1, 2 and 3
X, 2X, and 3X are feeder lines W1X, W2X, and W3, respectively.
It is commonly connected to one end X of the load B via X. The other output terminals 1Y, 2Y, 3Y of the inverters 1, 2, 3 are commonly connected to the other end Y of the load B via the power supply lines W1Y, W2Y, W3Y, respectively.

The equivalent circuit of the load B is represented by a series circuit of an inductance L, a resistance R and a capacitance C. An alternating current having a frequency corresponding to, for example, a series resonance frequency is supplied to the load B from the inverters 1, 2, and 3.

Of the power supply lines W1X, W2X, W3X, W
Current balancer BX for combination of 1X and W2X
12 is provided, a current balancer BX13 is provided for the combination of W1X and W3X, and a current balancer BX23 is provided for the combination of W2X and W3X.

Further, of the power supply lines W1Y, W2Y, W3Y, a current balancer BY12 is provided for a combination of W1Y and W2Y, a current balancer BY13 is provided for a combination of W1Y and W3Y, and W2Y and W2Y.
A current balancer BY23 is provided for the 3Y combination.

As shown in FIG. 2, each of the current balancers BX12 to BY23 has a ring-shaped magnetic core CR through which the output power supply lines Wi and Wj of the two systems of inverters are penetrated so that their current directions are opposite to each other. There is. For example, a ferrite core is used as the magnetic core CR. The ferrite core is preferable because it has excellent high frequency characteristics.

In the magnetic core CR, magnetic fluxes due to currents flowing through the power supply lines Wi and Wj are generated in opposite directions. The currents induced in the power supply lines of the other party by these magnetic fluxes are in the opposite directions to the output currents, and the mutual balance action of the output currents is performed.

That is, the current balancers BX12 and BY
The output currents of the inverters 1 and 2 are balanced by 12, the output currents of the inverters 1 and 3 are balanced by the current balancers BX13 and BY13, and the output currents of the inverters 2 and 3 are balanced by the current balancers BX23 and BY23. A balancing action is performed. In this way, the output currents are balanced among the three inverters 1, 2, 3.

Each current balancer is provided with a magnetic flux detector, which is a feature of this device. That is, the current balancer BX12 is provided with the magnetic flux detector MX12, the current balancer BX13 is provided with the magnetic flux detector MX13, and the current balancer BX23 is provided with the magnetic flux detector MX23.
23 are provided. Further, the current balancer BY12 is provided with a magnetic flux detector MY12, and the current balancer BY1 is provided.
3, a magnetic flux detector MY13 is provided, and the current balancer BY23 is provided with a magnetic flux detector MY23.

FIG. 3 shows a detailed configuration of the current balancers BX12 to BY23 equipped with magnetic flux detectors. FIG. 3 shows an example of an embodiment of the current balancer of the present invention. The coil CL wound around the magnetic core CR is an example of an embodiment of the magnetic flux detectors MX12 to MX23. A resistor r is connected between the terminals of the coil CL, and a voltage e generated across the resistor r serves as a magnetic flux detection signal.

In the magnetic core CR, a magnetic flux due to a current flowing through the power supply line Wi and a magnetic flux due to a current flowing through the power supply line Wj are generated in opposite directions. Therefore, when the two currents are balanced, the magnetic flux is also balanced and the difference therebetween becomes zero, but when the two currents are unbalanced, a magnetic flux proportional to the current difference is generated. An induced voltage e is generated in the coil CL in proportion to this unbalanced magnetic flux, and becomes a magnetic flux detection signal. The magnetic flux detection signal is the power supply line W
Since it is proportional to the amount of imbalance between the current of i and the current of the feed line Wj, this indicates the imbalance of the output currents of the two-system inverters.

That is, the detection signal of the magnetic flux detector MX12 indicates the current imbalance of the power supply lines W1X and W2X, and the detection signal of the magnetic flux detector MX13 indicates the current imbalance of the power supply lines W1X and W3X. The detection signal of MX23 shows the imbalance of the currents of the power supply lines W2X and W3X. The detection signal of the magnetic flux detector MY12 indicates the current imbalance of the power supply lines W1Y and W2Y, and the detection signal of the magnetic flux detector MY13 indicates the current imbalance of the power supply lines W1Y and W3Y.
The detection signal of Y23 indicates the imbalance of the currents of the power supply lines W2Y and W3Y.

In this way, the imbalance of the output currents in the power supply lines is detected for all combinations of the two inverters out of the three inverters. Such imbalance detection can be realized by a simple configuration in which a magnetic flux detector is attached to an existing current balancer provided on the power feed line.

As the magnetic flux detector, it is preferable to use a coil wound around a magnetic core because the structure is extremely simple. The magnetic flux detector is not limited to this, and various types such as a semiconductor magnetic flux detecting element may be used.

The current imbalance detection signal of each power supply line is full-wave rectified by a rectifier circuit REC and compared with a predetermined reference value TH by a comparator CMP as shown in FIG. To do. The judgment signal of the comparator CMP is given as an input signal to an appropriate protection coordinator (not shown), and when the imbalance exceeds the allowable limit, the protection coordinator cuts off the switching elements of the inverters 1 to 3 or the DC power source E. It shuts off the SCR that is a regulator.

[0034]

As described in detail above, according to the first invention for solving the problem, it is possible to obtain a signal indicating the imbalance of the output currents of a plurality of inverters based on the magnetic flux in the current balancer. Therefore, it is possible to realize a parallel inverter system that obtains an unbalanced display signal with a simple configuration.

Further, according to the second invention for solving the problem, since the magnetic flux detecting means for detecting the magnetic flux in the annular magnetic core is provided, the current for obtaining the unbalanced display signal can be obtained with a simple structure. A balancer can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an example of an embodiment of a parallel inverter system of the present invention.

FIG. 2 is a conceptual diagram of a current balancer.

FIG. 3 is a diagram showing an example of an embodiment of a current balancer of the present invention.

FIG. 4 is a block diagram of an example of an unbalanced detection signal processing device.

[Explanation of symbols]

 1-3 Inverter 1A-3D Switching element W1X-W3Y Feeding wire BX12-BY23 Current balancer MX12-MY23 Magnetic flux detector B Load CR Magnetic core CL Coil REC Rectifier CMP Comparator

Claims (7)

[Claims] 1. A parallel inverter system having a plurality of inverters connected in parallel, and a current balancer that causes mutual induction of opposite polarities via magnetic flux between the outputs of the plurality of inverters. A parallel inverter system, characterized in that a signal representing an unbalance of output currents of the plurality of inverters is obtained based on the parallel inverter system. 2. The parallel inverter system according to claim 1, wherein the plurality of inverters use IGBTs as switching elements. 3. The parallel inverter system according to claim 1, wherein the plurality of inverters are full-bridge inverters. 4. The current balancer according to claim 1, wherein an output magnetic feed line of an inverter of two systems is passed through an annular magnetic core so that the current directions thereof are opposite to each other. The parallel inverter system according to one. 5. The parallel inverter system according to claim 4, wherein a signal representing an imbalance of the output current is obtained based on an induced voltage of a coil wound around the annular magnetic core. 6. A current balancer having an annular magnetic core through which output feed lines of two systems of inverters are passed such that their current directions are opposite to each other, and a magnetic flux detecting means for detecting magnetic flux in the annular magnetic core. A current balancer characterized by being provided. 7. The current balancer according to claim 6, wherein the magnetic flux detecting means is a coil wound around the annular magnetic core.