JPH0787793A - Current balancing device of d/a converter parallel-connect type inverter - Google Patents

Abstract

PURPOSE:To use up to the rated limit of an inverter capacitor by changing output voltage of either of D/A conversion parts according to the amount of unbalance and then adjusting the output voltage on the output side of either of the D/A conversion perts so that two sets of output current are equal. CONSTITUTION:D/A conversion parts 1 and 2 are connected in parallel via a rectifier 6 from an AC power supply and at the same time current detectors 4 and 5 are connected to the output side of each D/A conversion part and then a voltage regulator 7 is connected between the current detector 4 and the D/A conversion part 1. Then, the primary coil winding of each electric motor is connected to the current detectors 4 and 5. Also, a same current comparator 8 is connected to the current detectors 4 and 5 so that current I1 and I2 from the current detectors 4 and 5 can be compared and at the same time a controller 9 for the voltage regulator is connected between a current comparator and the voltage regulator, thus eliminating the problem of unbalance of two sets of current values of the electric motor and using an inverter capacitor up to a rated limit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention independently connects two sets of inverse conversion units for inversely converting DC to AC, and drives one AC electric motor with output currents from the two sets of inverse conversion units. In this case, when imbalance occurs in the output current values of the two sets of inverse conversion units, the imbalance is detected and the two sets of output current values are made to coincide with each other, so that any inverse conversion unit is overloaded. The present invention relates to a current balance device for a reverse inverter parallel type inverter which is prevented.

[0002]

2. Description of the Related Art A general electric motor drive inverter sets a V / F pattern as shown in FIG. 2, inputs this set value into the inverter in advance, and outputs the inverter according to this pattern. There is. For example, F = 50
At Hz, V = 400V, F = 10Hz, V = 8
For example, V = 50V at 0V and F = 5Hz. The inverter of this type has a simple structure and is inexpensive, and is often used as a standard type general-purpose inverter.

[0003]

However, in such an inverter, when the V / F pattern is once set and input, when the inverter is operating at a certain V / F, for example,
For example, when F = 25 Hz and V = 200 V, it is not possible to change even if only the voltage needs to be changed. In other words, with F = 25Hz, V is 180V or 220
It cannot be changed to V. Further, in the conventional drive system in which the output sides of the two sets of inverse conversion units are directly connected to the two temporary windings of one electric motor, respectively, the outputs of the two sets of inverse conversion units are driven by the same control command. The currents do not match and become unbalanced by several percent or more, and the output of the inverter decreases accordingly. Moreover, this imbalance occurs due to an error in manufacturing the primary winding, which causes different load sharing rates.

According to the present invention, when an imbalance occurs in the output side currents of two sets of inverse conversion units, the imbalance is eliminated, the current values of the inverse conversion units are made uniform, and the load currents are evenly shared. The purpose is to enable use up to the rated limit of the inverter capacity.

[0005]

The present invention has been made to achieve the above object, and two sets of inverse conversion units for inversely converting DC to AC are connected in parallel, and outputs from the two sets of inverse conversion units. A single AC motor is driven by an electric current, and two independent sets of parallel windings are formed so that the primary winding of this motor is connected as a load to each of the inverse converters. In the inverse converter parallel inverter, the output voltage of either one of the inverse converters is output according to the current comparator that compares the output currents of the two sets of inverse converters to detect the amount of unbalance. The gist is that a voltage regulator for adjusting the output voltage is provided on the output side of either one of the inverters so that the two sets of output currents have the same amount.

[0006]

In a general-purpose inverter, as shown in FIG. 3, when a reverse inverter parallel inverter is used to drive an electric motor having two independent parallel stator windings, the current I1 is originally I2 has the same value. However, due to the difference in performance of the inverse converter, the stator winding, and the iron core, the difference in wiring length between the inverter and the motor, the current I1 of the two parallel windings is increased.
And I2 are different. That is, one becomes large and the other becomes small. At this time, if the larger current exceeds the rated current of the inverse conversion unit 1 or 2, the inverse conversion unit becomes overloaded, so that it becomes necessary to reduce the inverter output and use it. This means that the inverter needs to be used below the rated capacity, and in order to solve this lack of capacity, it is sufficient to reduce the larger current or increase the smaller current. Since the electric current of the motor changes depending on the magnitude of the applied voltage, a voltage regulator is provided on one of the output sides of the inverse conversion units as shown in FIG. A current detector is provided for each of the detectors, and a current comparator for comparing the detection current of each detector is provided. When the currents I1 and I2 of the two sets of parallel windings do not match, the voltage regulator automatically adjusts the voltage until the currents I1 and I2 of the two sets of parallel windings match or become equal. Therefore, as the voltage regulator, the voltage can be changed automatically, and the voltage adjustment range is small enough to correct the difference between the currents I1 and I2. An electric autotransformer, a thyristor voltage regulator, etc. are suitable. ing.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A current balance device for an inverse converter parallel type inverter of the present invention will be described below with reference to the illustrated embodiment. In the figure, reference numerals 1 and 2 denote primary windings M of AC motor M in parallel.
1 and M2 are inverse conversion units independently connected to each other. The inverse conversion units 1 and 2 are connected in parallel from an AC power source via a forward converter 6 and are connected to the output side of each inverse conversion unit. The current detectors 4 and 5 are connected, and the voltage regulator 7 is connected between the one current detector 4 and the inverse conversion unit 1. The primary windings of the electric motor are connected to the current detectors 4 and 5, respectively.

The same current comparator 8 is connected to each of the current detectors 4 and 5. The current comparators are connected so that the currents I1 and I2 from the current detectors 4 and 5 are compared with each other, and a voltage regulator controller is provided between the current comparator and the voltage regulator. 9 is connected.

Therefore, as described above, a voltage regulator is provided on one of the output sides of the inverse conversion section, a current detector is provided on the output side of each of the two sets of inverse conversion sections, and the detected currents of the detectors are compared. Since the respective current comparators are provided, when the currents I1 and I2 of the two sets of parallel windings do not match, the voltage regulator automatically adjusts the voltage until the currents I1 and I2 become equal. Since the voltage adjustment range at this time is only the correction of both currents, a small capacity such as an electric autotransformer or a thyristor voltage adjuster may be used.

[0010]

EFFECT OF THE INVENTION The current balance device of the reverse converter parallel type inverter of the present invention has two reverse conversion units for reverse conversion from DC to AC.
In parallel with each other, output currents from the two inverse converters drive one AC motor, and the primary windings of the motors are connected to each other one of the inverse converters as a load. In a reverse converter parallel inverter having two independent parallel windings, a current comparator that detects the unbalance amount by comparing the output currents of the two inverse conversion units, and the unbalance amount. According to the above, since the output voltage of one of the inverters is changed so that the output voltage of one of the inverters is changed so that the output current of the two sets becomes equal, Even if you use a commercially available general-purpose inverter, you can eliminate the imbalance of the current values of the two sets of electric motors by adding one simple and small voltage regulator, and do not increase the inverter capacity more than necessary. Moreover, the inverter output There is an advantage, such as can be used in the rating without having to please.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a current balance device for a reverse converter parallel type inverter of the present invention.

FIG. 2 is a comparison diagram of frequency and output voltage.

FIG. 3 is a circuit diagram of a conventional inverse converter parallel inverter.

[Explanation of symbols]

 1, 2 Inverse conversion unit 4, 5 Current detector 6 Forward converter 7 Voltage regulator 8 Current comparator 9 Voltage regulator controller M AC motor M1, M2 Primary winding

Claims (1)

[Claims] 1. An inverse conversion unit for inversely converting DC to AC.
In parallel with each other, output currents from the two inverse converters drive one AC motor, and the primary windings of the motors are connected to each other one of the inverse converters as a load. In a reverse converter parallel inverter having two independent parallel windings, a current comparator that detects the unbalance amount by comparing the output currents of the two inverse conversion units, and the unbalance amount. A voltage regulator for adjusting the output voltage is provided on the output side of either one of the inverters so that the output voltage of one of the inverters is changed so that the two sets of output currents have the same amount. Inverter parallel type inverter current balance device characterized by.