JPH11285259A - Control method for parallel operation of inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the precision of current balance compensation operation by making a minimum current value calculated from the current values of individual inverters connected in parallel a reference value, comparing this with the current value of each inverter, and shortening the width of a firing pulse for an inverter having a larger current value. SOLUTION: A DC power source 1 is converted into an AC power source by inverters 10, 20 connected in parallel, and the power converting switching elements of each inverters 10, 20 operate simultaneously by firing pulses outputted by a common drive apparatus 3, when an induction motor 2 is driven. Here, current detectors 11, 21 monitor the output currents of individual inverters 10, 20, and a minimum value calculator 5 calculates the minimum value of individual output currents. Then each drive signal controlling quantity computing apparatuses 12, 22 computes a control quantity of a firing pulse width for shortening the firing pulse width of an inverter 10 (or 20) whose output current value current value is larger than this minimum value, and each firing pulse controllers 13, 23 arbitrarily controls the pulse width of a common firing pulse and makes each output current balanced by this firing pulse width controlling quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to one or more induction motors (hereinafter simply referred to as "motors") which are connected in parallel with a plurality of inverters which are constituted by power conversion switching elements and convert DC power into AC power. The present invention relates to a parallel operation control method of inverters that controls an inverter output current to be balanced in an operating device.

[0002]

2. Description of the Related Art When a large-capacity electric motor is operated by an inverter, a plurality of inverters are connected in parallel to realize a large capacity. In this case, the power conversion switching elements forming the inverter are generally driven by simultaneously supplying a plurality of ignition pulses (hereinafter simply referred to as ignition pulses) of a drive signal provided in common. However, in such a case, if the output current of each inverter is not balanced due to variations in wiring and components of the inverter, etc., and current concentrates on a specific inverter, damage may occur. Each inverter monitors the current and arbitrarily shortens the common pulse width of the incoming arc to achieve current balance.

FIG. 2 is an example of a configuration diagram in the case where two inverters are connected in parallel, and the prior art will be described in detail with reference to FIG. The DC power supply 1 is converted into an AC power supply by two inverters 10 and 20 connected in parallel. Motor 2
Are driven by AC power converted by inverters 10 and 20 connected in parallel. Inverters 10, 20
Are driven simultaneously by the ignition pulse output from the common driving device 3, but as described above, the inverters 10 and
The output currents do not become the same value and become unbalanced due to the dispersion of the 20 constituent elements and the like. For example, the current unbalance due to the time until the power conversion switching element becomes conductive / non-conductive or a variation in voltage drop when a current flows. For this reason, the inverters 10, 2
By monitoring the output current of 0 and inputting the output of the average value calculator 4 and the outputs of the current detectors 11 and 21 to drive signal control amount calculation devices (hereinafter simply referred to as control calculation devices) 12 and 22, drive is performed. When the inverter current is larger than the average value of all inverter currents, the pulse width of the ignition pulse of the power conversion switching element is shortened arbitrarily so that the pulse width is shortened and the current is suppressed. By calculating the control amount and arbitrarily controlling the pulse width of the drive signal by the ignition pulse width control devices 13 and 23, the inverters 10 and 20 are controlled.
Current is balanced.

[0004]

SUMMARY OF THE INVENTION
In steps 2 and 22, the pulse width control amount from each inverter current is determined by comparing the output of the average value calculator 4 with the value of the current of each inverter, and calculating and determining it. The inverter having the larger current is controlled so as to reduce the ignition pulse width and reduce the current. However, at this time, no control is performed on the inverter having the smaller current, and only the normal operation is continued. In other words, the control method is to reduce the output current of the inverter with the larger output current of the two inverters, approach the average value of the currents of the inverters, and balance the currents of the inverters. Since the control does not work for the inverter, there is a problem that an error corresponding to the difference between the average value of the current of each inverter and the current value of the inverter having the smaller current always occurs. SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and aims to solve these disadvantages and to provide a more accurate current balance compensation operation in parallel operation of two or more inverters. An object of the present invention is to provide a parallel operation control method of inverters capable of obtaining a compensation operation.

[0005]

Means for achieving the object are as follows: 1) In claim 1, a DC power supply is constituted by a power conversion switching element driven by a firing pulse of a common drive signal. When connecting multiple inverters that convert to AC power in parallel and operating one or more induction motors,
An arithmetic unit that receives the respective inverter current values and outputs a control amount that arbitrarily shortens the ignition pulse width applied to the power conversion switching element so that the inverter currents are balanced; Accordingly, the present invention relates to a parallel operation method of inverters in which the inverters are driven by controlling the ignition pulses so that the inverter currents are balanced, and the arithmetic method of the arithmetic device is controlled by a current detector. Based on the minimum value calculated from the detected current values of the inverters, and comparing the calculated minimum value with the inverter current values, when the inverter current value is large, the ignition pulse width is shortened. This is a method for controlling the parallel operation of the inverters.

2) The parallel operation of the inverter according to claim 1, wherein the arithmetic method of the arithmetic unit is based on a value set in advance to the minimum value of each of the inverter current values. It is a control method. That is,
In the conventional method, the pulse width control amount from each inverter current is determined by comparing, calculating and determining the average value of the current value of each inverter and the average value of the current value of each inverter. The current value of the inverter and the minimum value of the current value of each inverter are compared and calculated, and the inverter with the larger current has a control to shorten the ignition pulse width and reduce the current. Make it work.

[0007] By taking such means, the problem can be solved by the following operation. Compare the current value of each inverter with the average value of the current value of each inverter, which is the conventional method,
In the method of calculating and determining, for the reasons described above,
There was a problem that an error was always generated by the difference between the average value of the current of each inverter and the current value of the inverter with the smaller current. By comparing the minimum values of the currents, the current value of the inverter having the larger current is controlled to be closer to the current value of the inverter having the smaller current, thereby stabilizing the control and realizing the current balance. It becomes possible. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0008]

FIG. 1 is a block diagram showing an embodiment to which the present invention is applied, which will be described in detail. In this description, the parallel operation of two inverters will be described as an example. However, since the principle is the same even when the number of inverters operating in parallel is plural, the explanation is omitted. In FIG.
The DC power supply 1 includes two inverters 10 connected in parallel,
20 converts it into an AC power supply. Further, the electric motor 2 is driven by an AC power source converted by the inverters 10 and 20 connected in parallel. The power conversion switching elements (not shown) constituting the inverters 10 and 20 are simultaneously driven by the ignition pulse output from the common driving device 3, but as described above, the inverters 10 and 20
The output currents do not become the same value and become unbalanced due to the variation of the constituent elements.

[0009] For example, current imbalance is caused by variations in voltage drop when a current flows when a power conversion switching element is turned on / off or when a current flows. Therefore, the current detector 1
The output currents of the inverters 10 and 20 are monitored by the inverters 1 and 21, and the minimum value of the current of each inverter output by the minimum value calculator 5 and the output of the current detectors 11 and 21 are used as a drive signal control amount calculation device (hereinafter, referred to as a control signal arithmetic unit) Simply referred to as a control arithmetic unit) 12,
By inputting the signal to the inverter 22, the width of the ignition pulse of the power conversion switching element of the drive signal can be arbitrarily set, for example, when the inverter current is larger than the other inverter currents, the ignition pulse width is shortened and the current is suppressed. The ignition pulse width control amount to be shortened is calculated, and the ignition pulse width control devices 13 and 23 are calculated.
By controlling the pulse width of the drive signal arbitrarily, it becomes possible to balance the currents of the inverters 10 and 20 more accurately than before.

[0010]

As described above, according to the present invention, 2
When one or more induction motors are operated by operating more than one inverter in parallel, a more stable current balance compensation operation can be provided, which is extremely useful in practice.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing an example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Induction motor 3 Driving device which generates an ignition pulse 4 Average value calculator 5 Minimum value calculator 10, 20 Inverter 21 Current detector 22 Drive signal control amount calculation device 13, 23 Arc pulse width control device

Claims (2)

[Claims] An inverter for converting a DC power supply to an AC power supply, which is constituted by a power conversion switching element driven by an ignition pulse of a common drive signal, is connected in parallel, and one or more induction motors are connected. When operating, an arithmetic device is provided which receives the respective inverter current values and outputs a control amount for arbitrarily shortening the ignition pulse width given to the power conversion switching element so that the inverter currents are balanced. In the parallel operation method of the inverters, each of which is driven so that the respective inverter currents are balanced by driving the respective inverters with the controlled ignition pulses according to the calculation result of the calculation device, Is calculated based on the minimum value calculated from the current value of each of the inverters detected by the current detector, and is compared with the current value of each of the inverters. A parallel operation control method for an inverter, wherein the ignition pulse width is shortened when the current value is large. 2. The parallel operation control method for an inverter according to claim 1, wherein the arithmetic method of the arithmetic device is based on a value set in advance to the minimum value of each inverter current value.