JPH08289587A - Parallel operation device for voltage type inverter - Google Patents

Abstract

PURPOSE: To suppress an unbalanced current by connecting each winding of a three-phase induction motor being installed, corresponding to each of the three-phase outputs of voltage type inverter circuits connected in parallel, with the outputs of the the voltage type inverter circuits, and detecting the currents applied to each winding, and balancing the currents of the same-phase windings. CONSTITUTION: A motor 42 is installed, being split with the combination of the windings 421u, 421v, and 421w of three phases of u, v, and w, and the neutral points of several windings are connected with one another. Voltage type inverter circuits (V1) 23 and 24 connected in parallel and the motor 42 are connected directly, and current detectors 61u, 61v, and 61w and current detectors 62u, 62v, and 62w are inserted between both. The output of the current detector is given to a current balancing circuit 7, and the correction signal 701 generated from the deviation detecting circuits 7u, 7v, and 7w of the current balancing circuit 7 is inputted into the drive circuits 232 and 242 of the inverter circuits 23 and 24. The switching element is driven so that the current of each phase of the inverter circuits 231 and 241 may be balanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a parallel operating device of voltage type inverters for driving an electric motor by a plurality of voltage type inverter circuits whose inverter output capacity is expanded.

[0002]

2. Description of the Related Art An example of parallel connection of two voltage source inverter circuits will be described with reference to FIG. FIG. 2 shows a configuration of a main part of a conventional example. 1 is a three-phase power supply, 21 and 22 are voltage type inverter circuits, 31 and 32 are parallel coupling reactors, 41 is a three-phase induction motor (hereinafter simply referred to as an electric motor), Reference numeral 5 is a control circuit. Here, in the electric motor 41, 41u, 41v, 41
w is a U-, V-, and W-phase winding.

That is, the voltage source inverter circuits 21 and 22 connected in parallel with the three-phase power source 1 as an input drive the electric motor 41 through the parallel coupling reactors 31, 32 and 33. Here, the parallel coupling reactors 31, 32, 33 are connected to the output side 311, 3
Voltage source inverter circuit 2 corresponding to windings 41u, 41v, 41w of 12 and output side 321, 322 and output side 331, 332, respectively
It is connected to the output phases of 1 and 22, and combines the outputs of two voltage source inverter circuits to balance them. The voltage source inverter circuits 21 and 22 include drive circuits 212 and 222 that obtain an output of the control circuit 5 that supplies a control signal, and the drive circuit 21 and 22.
It consists of inverter circuits 211 and 221 that form a three-phase bridge with switching elements that operate by 2 and 222.

As shown in the figure, the parallel-coupled reactor 3 connected in parallel is connected to the outputs of the voltage source inverter circuits 21 and 22.
1, 32 and 33 act as an inductance when the output currents are unbalanced, and suppress the current flowing between the inverter circuits 211 and 221. Due to the action of this parallel coupling reactor, the imbalance between the inverter circuits was automatically suppressed to about several percent. In this type of conventional technology, as a cause of the unbalanced current, there are variations in the internal impedance of each inverter circuit and variations in the switching characteristics of the switching elements, so that the unbalance due to the variations is canceled and the load current is balanced. Therefore, the parallel coupling reactor is inserted.

[0005]

However, although the method using the parallel coupling reactor has the effect of suppressing the transient current imbalance due to the variation of the switching characteristics, the steady state due to the variation of the on-voltage of the switching element itself is present. Unbalanced current that is generated as a result, or when the inverter circuit is operated at a low frequency and the output current is close to DC current, the parallel-coupled reactor is demagnetized, and magnetic saturation is caused by the voltage-time product at that time. As a result, the effect of suppressing the unbalanced current is lost. Further, in order to prevent such magnetic saturation, the amount of iron core of the reactor must be increased, and therefore, the parallel coupling reactor becomes large in size, heavy in weight, and there is a problem in terms of operability and economy. there were. Furthermore, when the above-mentioned magnetic saturation occurs, the output current balance between the inverter circuits is easily broken, and the current concentrates on a specific inverter circuit, causing circuit damage. The present invention has been made to solve the above problems,
It is an object of the present invention to eliminate a parallel coupling reactor for suppressing an unbalanced current between inverter circuits connected in parallel, and to provide a device having a small size, improved operability, and a simple structure.

[0006]

The present invention is configured as follows. That is, (a) a plurality of voltage source inverter circuits connected in parallel, and (b) each of the neutral point common connection windings provided corresponding to the three-phase output of the plurality of voltage source inverter circuits. Type inverter circuit, a motor connected to the power side, (c) a current detector for detecting the current of the output of the voltage type inverter circuit, and (d)
It comprises at least a current balancing circuit for inputting this current detector output and generating a signal for balancing the currents of the same phase windings, and (e) a drive circuit for obtaining this current balancing circuit output.

[0007]

With this solution, the windings of the motor are connected in parallel by connecting each phase output of each inverter circuit corresponding to each of the plurality of three-phase windings to which the neutral point of the motor is connected. The same effect as that of the coupling reactor can be obtained. That is, the inductance component of the motor winding is sufficiently larger than the inductance component of the parallel coupled reactor,
Further, the iron core of the electric motor itself hardly causes magnetic saturation, and has an effect of balancing the output currents of the respective inverter circuits. Furthermore, it is possible to detect current deviations of the same phase and obtain a correction signal that makes them zero, thereby balancing the output currents of the inverter circuit.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the essential structure of an embodiment of the present invention represented in a manner similar to FIG. 2, in which 23 and 24 are voltage type inverter circuits, 42 is an electric motor, and 61u, 61v, 61w and 62u. , 62v, 62w
Is a current detector, and 7 is a current balancing circuit. Here, in the voltage source inverter circuits 23 and 24,
Reference numerals 231 and 241 have the same functions as the inverter circuits 211 and 221 shown in FIG. 2, and the drive circuits 232 and 242 receive the control circuit 5 output as well as the current balance circuit 7 output correction signal.
To get the 701. In the electric motor 42, u, v,
Three-phase w windings 421u, 421v, and 421w are divided and provided separately, and the neutral points of the respective windings are connected.

The voltage source inverter circuits 23, 24 connected in parallel and the electric motor 42 are directly connected as shown in the drawing, and current detectors 61u, 61v, 61w and current detectors 62u, 62v, 62w, 62v, 62w is inserted. The output of this current detector is given to the current balancing circuit 7,
The correction signal 701 generated from the deviation detection circuits 7u, 7v, 7w of the driving circuit 2 for the voltage source inverter circuits 23, 24
The configuration is input to 32, 242.

In such a system, the current balancing circuit 7 detects the deviations of currents of the same phase by the deviation detection circuits 7u, 7v,
A 7w output correction signal is given, and each drive circuit 232, 242
The output of the control circuit 5 is corrected according to the output of the current balancing circuit 7, and the switching element is driven so that the currents of the respective phases of the inverter circuits 231 and 241 are balanced.

[0011]

As described above, according to the present invention, the parallel coupling reactor is removed, the electric motor is skillfully utilized, and the phase current balance control is introduced to reduce the imbalance of each inverter circuit output. It is possible to provide a device having a simple structure in which the capacity can be made equivalent to the number of units connected in parallel and the size and cost are reduced.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a system diagram showing a conventional example.

[Explanation of symbols]

 1 Three-phase power supply 21 Voltage source inverter 22 Voltage source inverter 23 Voltage source inverter 24 Voltage source inverter 31 Parallel coupling reactor 32 Parallel coupling reactor 33 Parallel coupling reactor 41 Three phase induction motor (motor) 42 Three phase induction motor (motor) 5 Control Circuit 61 Current detector 62 Current detector 7 Current balancing circuit 701 Correction signal

Claims (1)

[Claims] 1. A parallel operating device for a voltage source inverter, which drives a three-phase induction motor by connecting a plurality of voltage source inverter circuits in parallel, corresponding to each of the three-phase outputs of the voltage source inverter circuits connected in parallel. And a parallel operation current balancing means for connecting each winding of the three-phase induction motor and the output of the voltage source inverter circuit, detecting the current flowing through each winding, and balancing the winding currents of the same phase. A parallel operation device for a voltage source inverter, which is characterized in that