JPH03250512A - Electric power conversion system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention is directed to a power conversion system in which a transformer is provided for voltage matching between a power conversion device and an AC power source, and the The present invention relates to a power conversion system that can suppress inrush current flowing through a transformer during recovery from a momentary power outage.

(Prior Art) There are various known power conversion systems related to the present invention, but the conventional technology will be explained here by referring to an uninterruptible power supply that can supply stable constant voltage and constant frequency AC power. .

The uninterruptible power supply device is known, for example, from "Power Electronics, written by Koji Imai, published by Denki Shoin, page 211, Chapter 7.7, Constant Voltage Constant Frequency Power Supply," and a detailed explanation will be omitted.

Figure 4 shows the basic configuration of the uninterruptible power supply, 1]
12 is a transformer, 13 is a rectifier, 14 is an inverter, 15 is a load, 16 is a DC filter capacitor, and 17 is a battery. In this figure, when the normal input AC power supply 11 is normal, DC power is supplied via the transformer 12 and rectifier 13, this is smoothed by the DC filter capacitor 16, and the smoothed DC power is stabilized by the inverter 14. The AC power is inversely converted into AC power, and the AC power of constant voltage and constant frequency is supplied to the load 15.

In addition, when the input AC power supply 11 is abnormal (instantaneous voltage drop or power outage), the power of the battery 17 is discharged, and the inverter 14 converts it back into stable AC power, and the load 15
It has the feature of being able to continue supplying stable AC power without interruption.

In the prior art configuration shown in FIG. 4, there is a problem in that when the input AC power source 11 is turned on again or when a momentary power failure is restored, the inrush power of the transformer 12 becomes extremely large. The B-H curve of the iron core of the transformer 12 is shown in Figure 5, but the B-H curve of the second B-H
In the curve, 51 is the residual magnetic flux density, and B2 is the maximum magnetic flux density during normal use. Generally, the maximum magnetic flux density B2 of the transformer 12 is designed to be close to the saturation magnetic flux density of the iron core, and the transformer 12 is used. .

Therefore, if the phase of the voltage applied to the transformer 12 when the input AC power supply 11 is turned on again or when a momentary power outage is restored is a phase polarity that causes a magnetic flux in the opposite direction to the residual magnetic flux B1,
Although the re-rush current of transformer 12 does not become so large,
If the phase polarity produces a magnetic flux in the same direction as the residual magnetic flux B1, then
The magnetic flux density of the transformer 12 instantaneously exceeds the saturation magnetic flux density, causing a problem that a very large inrush current flows.

Such inrush current is generally 1 of the rated current of the transformer 12.
This is about 5 to 20 times higher, and when such a large current flows, problems occur in the system in terms of coordination with the input AC power supply 11 itself, input-side circuit breakers, other loads, and the like.

For this reason, it is necessary to suppress the inrush current flowing into the transformer 12 when the input AC power supply 11 is turned on again or when the power is restored after a momentary power outage.
In order to double the magnetic flux density B of the iron core of the transformer 12,
A method of reducing the size of the transformer 12 is generally adopted, and as a result, the core size of the transformer 12 increases, and the outer shape of the transformer itself increases.
There was also the problem that the weight was very large.

(Problems to be Solved by the Invention) As described in the prior art with reference to FIGS. 4 and 5, when the input AC power supply 11 is turned on again or when a momentary power outage is restored,
There is a problem in that the rush current of the transformer 12 is generally 15 to 20 times the rated current of the transformer 12, which affects the input AC power supply 11 itself and other loads.

On the other hand, when trying to suppress the inrush current of the transformer 12, which is generally allowed in terms of the system, to about 5 to 10 times the rated current,
It is necessary to lower the core magnetic flux density of the transformer 12, which causes problems such as an increase in polymorphic dimensions of the transformer 12, a significant increase in weight, and a significant increase in price.

That is, the conventional power conversion system has the following problems.

(1) In consideration of instantaneous power outages of the input AC power supply, it is necessary to suppress inrush current in the transformer installed between the AC power supply and the power converter. Also, there was a problem that the weight increased significantly.

(2) Due to the above-mentioned problems, the problem of an increase in the number of locations for installing transformers and an increase in prices occurred, which was extremely uneconomical.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and provides an economical power conversion system that can suppress the inrush current flowing through the transformer when turning on AC power or restoring a momentary power outage. It is intended to.

[Configuration of the Invention (Means for Solving the Problems)] In order to achieve the above object, the present invention provides a power conversion system in which a transformer is provided between an AC power source and a power conversion device. As means for suppressing inrush current flowing through the transformer when voltage is applied to the transformer,
The present invention is characterized by comprising means for exciting the transformer from the power conversion device side for a predetermined time during a period in which the voltage of the AC power source is not applied to the transformer to reduce residual magnetic flux. .

(Function) If the residual magnetic flux of the transformer is reduced, the transformer core will naturally become less saturated, so it is possible to suppress the inrush current that flows into the transformer when turning on the AC power again or when recovering from a momentary power outage. I can do it.

(Example) An example of the present invention is shown in FIG. This figure shows an embodiment in which the present invention is implemented in an uninterruptible power supply as in FIG. 4, and circuit elements with the same numbers as in FIG. 4 have the same functions.

In this figure, a rectifier 13 is constructed of a rectifier capable of bidirectional power conversion of AC power to DC power or DC power to AC power. A rectifier capable of bidirectional power conversion is
For example, Toshiba Review Vol. 44, No. 9 (1,989) No. 737
A system such as that illustrated in FIG. 2 on page 1 is well known, and detailed description thereof will be omitted.

When the input AC power source 11 is momentarily interrupted or power out, and the voltage of the input AC power source 11 is no longer applied to the transformer 12, this is detected and the rectifier 13 uses the DC power of the battery 17 to generate AC power. , energizes the transformer 12. At this time, if the AC voltage generated by the rectifier 13 is gradually reduced,
The magnetic flux of the transformer 12 also decreases in response to the applied voltage,
The residual magnetic flux also decreases.

FIG. 2 shows a B-H curve of the transformer 12 to explain the reduction in residual magnetic flux according to the present invention. Before applying AC voltage to the transformer 12 from the rectifier 13, the residual magnetic flux is 81, but when it is gradually reduced, the area of the hysteresis curve on the B-H curve in FIG. When the voltage approaches zero, the residual magnetic flux of the transformer 12 can also be reduced to approximately zero.

Therefore, by gradually reducing the voltage applied to the transformer 12 by the rectifier 13, the residual magnetic flux of the transformer 12 is also significantly reduced, and the transformer 12 is re-energized by turning on the AC power supply 11 again or recovering from a momentary power outage. However, the difference between the residual magnetic flux of the iron core of the transformer 12 and the saturation magnetic flux is large, and the inrush current of the transformer 12 is reduced.

Therefore, the inrush current of the transformer 12 is reduced by the embodiment of the present invention compared to the conventional one, and when the inrush current of the transformer 12 is suppressed to the same level, the transformer 12 can be made smaller and lighter than the conventional one.

In the above description, the voltage is gradually reduced when the transformer 12 is excited by the rectifier 13, but the exciting voltage may be a predetermined voltage below the rated voltage.

A voltage is applied to the transformer 12 by the rectifier 13 to create a transformer]
The time to excite the input AC power supply 11 is not particularly limited, but may be a general momentary power outage period (for example, about several hundred milliseconds), taking into account the DC power loss of the battery 17. A switch is provided between the switch and the transformer 12, a current limiting element is connected in parallel to the switch, the switch is once opened, and the switch is turned on again after the input AC power supply 11 is restored. You can. In this case, since the transformer 12 is pre-excited via the current limiting element until the switch is turned on again, the inrush current is similarly suppressed.

FIG. 3 is a diagram showing another embodiment of the present invention, in which 19
is a current limiting element, and 18 is a switch. It is detected that the voltage applied to the input AC power supply 11 is no longer applied, and the output voltage of the inverter 14 is transferred to the transformer 1 via the switch 18 and the current limiting element 19.
2 for a predetermined period of time. It is clear that if the voltage applied to the transformer 12 at this time is smaller than the rated voltage of the transformer 12, the residual voltage of the transformer 12 will also decrease, and the rush current of the transformer 12 can be suppressed.

In the embodiment shown in FIG. 3 as well, a switch may be provided between the transformer 12 and the input AC power supply 11, and the switch may be temporarily opened in the event of a long power outage.

In the above description, the energy for reducing the residual magnetic flux of the transformer 12 uses the DC power of the battery 17, but if the load 15 is a rotating body such as an AC motor, this rotational energy can be used. However, the present invention does not particularly limit the source of energy that excites the transformer 12.

Further, the system of the power conversion device to which the present invention is applied is not particularly limited, and various design changes can be made without changing the gist of the present invention.

[Effects of the Invention] According to the present invention, the transformer provided between the AC power source and the power converter has an inrush current because the residual magnetic flux of the transformer is reduced when the AC power source voltage is reapplied. can also be reduced. As a result, the following effects can be obtained.

(1) Since the inrush current of the transformer is reduced, the transformer can be made smaller and lighter than before in order to suppress the inrush current to a predetermined value.

(2) By making the transformer smaller and lighter, the installation space can be reduced and the cost can be reduced.

[Brief explanation of drawings]

Fig. 1 is a main circuit configuration diagram showing one embodiment of the present invention, Fig. 2 is a B-H curve diagram for explaining the present invention in detail, and Fig. 3 is a main circuit diagram showing another embodiment of the present invention. FIG. 4 is a main circuit diagram of the conventional device, and FIG. 15 is a B-H curve diagram for explaining the operation of the conventional device. 11... Input AC power supply, 12... Transformer, 13...
- Rectifier, 14... Inverter, 15... Load, 1
6... DC filter capacitor, 17... Rose y
IJ18... Switch, 19... Current limiting element.

Claims (1)

[Claims] In a power conversion system in which a transformer is provided between an AC power supply and a power conversion device, when the voltage of the AC power supply is applied to the transformer, the AC A power conversion system characterized by comprising means for reducing residual magnetic flux by exciting the transformer from the power conversion device side for a predetermined time during a period in which power supply voltage is not applied to the transformer.