JP2000004587A - Rectifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a power factor reduction which occurs, when a low DC voltage output is obtained from a high AC voltage input without employing a phase advancing capacitor or an active filter. SOLUTION: The secondary side windings of a transformer TR have intermediate taps. Rectifying devices S1-S12 of a rectifier circuit are respectively connected to the taps of the transformer. In order to increase the rectifying output, the ignition phases of the rectifying devices S1-S6 on the full-tap side are controlled. In order to reduce the rectifying output, the ignition phases of the rectifying devices S7-S12 on the intermediate tap side are controlled so as to reduce power factor decline. Circuit configurations, consisting of the rectifying devices which are connected in series to each other in order to obtain high voltages, include a configuration such that the common rectifying devices of the respective rectifying devices classified in terms of taps are connected in series to each other, to reduce the number of necessary devices.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifier for converting AC power into DC power at a variable voltage, and more particularly to a rectifier with improved power factor.

[0002]

2. Description of the Related Art A rectifier of this type is employed, for example, in a thyristor leonard device and controls the speed of a DC motor by controlling a DC output with a variable voltage. Also,
By using the DC output as a forward converter of an inverter or a chopper or a DC power supply, it is configured as a power converter for an AC motor or an electric railway.

In order to obtain a DC output having an arbitrary voltage or a controlled voltage by this type of rectifier, a thyristor having a control electrode, a GTO, and various transistors are used as rectifiers of the device. The ignition phase of the rectifier is controlled according to the output voltage.

FIG. 3 exemplifies a main circuit configuration of a rectifier using a thyristor as a rectifier element. AC power taken in through a delta-star-connected transformer TR is input to three-phase bridge-connected thyristors S1 to S6. And a DC output voltage-controlled by the firing phase control of the thyristors S1 to S6 is obtained. DM is a DC motor indicated as a load.

The rectifier has a mixed bridge configuration in which one of the high-voltage side and the low-voltage side of the rectifier is a diode, a configuration in which rectifiers are connected in series to obtain high-voltage rectification, and a large current. For this purpose, there are various modifications such as a configuration in which rectifying elements are connected in parallel.

[0006]

In the rectifier shown in FIG. 3, the relational expression between the AC input voltage Va and the DC output voltage Vd depends on the load condition. Become.

[0007]

Vd = 1.35 · Va · cosα (1) α: Firing phase angle of the rectifying element The power factor Pf on the AC side is expressed by the following equation (2).

[0008]

Pf = 0.955 · cos α (2) It can be said from these two equations that when an arbitrary DC voltage Vd is obtained from a constant AC voltage Va, the smaller the DC voltage Vd, the larger the ignition phase angle α. Accordingly, the power factor Pf decreases and the power factor deteriorates. That is, the lower the DC voltage is obtained from the higher AC power supply, the worse the power factor is.

In order to solve this inconvenience, the conventional rectifier has a phase-advancing capacitor provided on the AC power supply side to improve the power factor or an active filter provided on the power supply line has improved the power factor. In order to obtain a rectified output in a wide voltage range from a low voltage to a low voltage, a large and expensive power factor correction device is required.

It is an object of the present invention to provide a rectifier capable of reducing a decrease in power factor when obtaining a low DC voltage output with respect to a high AC voltage input without using a phase advance capacitor or an active filter.

[0011]

According to the present invention, in order to solve the above-mentioned problems, a transformer on the AC input side of a rectifier circuit is provided with an intermediate tap, and an intermediate tap is provided in parallel with an element for rectifying the output of a full tap. Provide an element to rectify the output of
When the rectified output is increased, the rectification is performed by the rectifying element on the full tap side, and when the rectified output is reduced, the rectification is performed by the rectifying element on the intermediate tap side.

In a rectifier for obtaining a rectified output of a variable voltage by controlling a firing phase of a rectifier from an AC voltage input to a rectifier circuit via a transformer from an AC power supply, the transformer has a secondary winding with an intermediate tap. The rectifying circuit has a main circuit configuration in which rectifying elements are connected to taps of the transformer and rectifying outputs of the rectifying elements are common, and when the rectifying output is high, the rectifying element on the tap side having a high output voltage is used. When the rectified output is lowered by controlling the firing phase of the rectifier, the rectifying element on the tap side having a low output voltage is controlled by the firing phase.

[0013] In the rectifier circuit, the rectifier may be connected in series to obtain a high voltage, and the rectifier connected in series may be a main circuit configured as a common rectifier for each rectifier for each of the taps. Features.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows a main circuit configuration of a rectifier according to an embodiment of the present invention. The star connection serving as the secondary winding of the transformer TR of the delta star connection has a structure having an intermediate tap.

The rectifier circuit includes thyristors S1 to S6 each having a three-phase bridge configuration which receives an output from a star connection full tap of the transformer TR as an input, and a thyristor having a three-phase bridge configuration which receives an output from an intermediate tap having a star connection. S7
To S12. The thyristors S1 to S6 and the thyristors S7 to S12 are connected in parallel.

In this configuration, in order to obtain a high DC voltage close to the rating in the rectifier circuit, the firing phases of the thyristors S1 to S6 on the full tap side are controlled. When a low DC voltage is obtained, the thyristors S7 to S7 on the intermediate tap side are used.
12 is controlled by the ignition phase.

As described above, by switching the control of the thyristor according to the level of the rectified output, the AC voltage Va is changed.
And the DC voltage Vd, the power factor Pf (cos α) can always be kept at a large value close to 1.

[0018] Now, the case of obtaining a low DC voltage Vd ₁ to the rectifier output, full tap side and the intermediate tap side of the respective ignition phase of the thyristor alpha _f, alpha _t, the voltage Va _f, when the Va _t, the following equation Become.

[0019]

[Equation 3] Full tap side: Vd₁= 1.35 · Va_f・ Cosα_f ... (3) Middle tap side: Vd₁= 1.35 · Va_t・ Cosα_t ... (4) In these equations, Va_f> Va_tTherefore, cos α
_f<Cosα_tTo obtain the same rectified voltage.
The thyristors S7 to S12 on the side of the _tThe small
And a power factor Pf close to 1 can be obtained.

Conversely, when a high DC voltage is obtained for the rectified output, the thyristors S1 to S6 on the full tap side are controlled because the voltage on the intermediate tap side is insufficient. At this time, the AC voltage Va and the DC output voltage Vd become close to each other, and the power factor Pf does not decrease.

[0021] Here, the voltage of the intermediate tap with respect to the voltage of the full tap of the transformer TR is decided cos [alpha] _f the allowable power factor range (e.g., up to 0.7), thereby to determine an intermediate tap voltage Va _t .

Further, when the control of the thyristors S1 to S6 and the control of the thyristors S7 to S12 are switched according to the level of the rectified output, the control of both thyristors is provided with a range in which the thyristors overlap each other, so that the continuous rectified output voltage change is achieved. Can be switched.

In this embodiment, a case is shown in which a two-stage rectified output is switched using a transformer having one intermediate tap. However, when the variable range of the DC voltage is wide or the allowable power factor range is narrow, By increasing the number of taps of the transformer and the number of parallel elements of the rectifier circuit, it is possible to switch to three-stage rectified output.

(Second Embodiment) FIG. 2 shows an embodiment of the present invention, in which thyristors of a rectifier circuit are connected in series to obtain a high-voltage rectified output.

In order to obtain a high-voltage rectified output for a high-voltage motor, generally, a plurality of rectifiers are connected in series in view of their breakdown voltage, and they are controlled at the same phase and firing phase angle.

When this method is applied to the case of FIG. 1, each of the thyristors S1 to S6 and S7 to S12 is a series connection circuit of a plurality of thyristors.

In the present embodiment, as shown in FIG. 2, instead of connecting all of a plurality of thyristors constituting a rectifier circuit for each tap in series, some thyristors are used for a full tap and for an intermediate tap. Use.

FIG. 2 shows a case in which two rectifiers are connected in series to obtain a high voltage output. The thyristors S1 to S6 and S7 to S12 which are the same as those in FIG. S13 to S18 are provided.

In this configuration, thyristors S1 to S6
The withstand voltage in S7 to S12 is larger than the voltage difference between the full tap and the intermediate tap of the transformer. Further, the thyristors S13 to S18 perform the firing control in accordance with the switching to any of the firing control of the thyristors S1 to S6 and the firing control of the thyristors S7 to S12.

As a result, the rectified output can be increased by the withstand voltage of the thyristors S13 to S18, and the required number of rectifying elements can be reduced.

In the above embodiments, the case where a thyristor is used as the rectifying element is shown. However, the same operation and effect can be obtained by using a configuration using another element. Further, a mixed bridge configuration in which one of the high voltage side and the low voltage side of the rectifying element is a diode may be employed. Further, a configuration in which the transformer connection method is changed can be adopted. Furthermore, the present invention can be applied to a device using a rectified output as a DC power source such as an inverter.

[0032]

As described above, according to the present invention, the transformer on the AC input side of the rectifier circuit is provided with an intermediate tap, and the element for rectifying the output of the intermediate tap is provided in parallel with the element for rectifying the output of the full tap. In order to increase the rectified output, the rectifier is rectified by the rectifying element on the full tap side, and when the rectified output is reduced, the rectifying element is rectified by the rectifying element on the intermediate tap side. The present invention can be applied to a rectifier that reduces the power factor when a low DC voltage output is obtained for a high AC voltage input without using a conventional phase-advancing capacitor or active filter.

[Brief description of the drawings]

FIG. 1 is a main circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a main circuit configuration diagram showing another embodiment of the present invention.

FIG. 3 is an example of a main circuit of a conventional rectifier.

[Description of Signs] TR: Transformers S1 to S18: Thyristor

Claims (2)

[Claims] 1. A rectifier for obtaining a rectified output of a variable voltage by controlling a firing phase of a rectifying element from an AC voltage input from an AC power supply to a rectifier circuit via a transformer, wherein the transformer has a secondary winding in the middle. With a tap, the rectifier circuit has a main circuit configuration in which a rectifier element is connected to each of the transformer taps and a rectifier output of each rectifier element is shared. A rectifier, wherein the rectifier controls the firing phase of the rectifier element and, when lowering the rectified output, controls the firing phase of the rectifier on the tap side having a lower output voltage. 2. The rectifier circuit according to claim 1, wherein the rectifier is connected in series to obtain a high voltage, and the rectifier connected in series has a main circuit configuration in which the rectifier is a common rectifier for each of the taps. The rectifier according to claim 1, wherein: