JPH0970179A - Voltage converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously switch the output voltage of a voltage converter to a required value and, at the same time, to obtain the required output voltage in a state that the voltage has a waveform close to a sine wave. SOLUTION: An AC power source 12 is connected to the primary winding 11a of a main transformer 11 and, at the same time, to an inverter circuit 15 through a transformer. A phase controlling and rectifying circuit 18 constituting a DC power source 15 is constituted by connecting thyristors 18a-18d in a bridge and connected to the primary winding 13a of an auxiliary transformer 13 through an inverter main circuit 16. The secondary windings 11b and 13b of the transformers 11 and 13 are connected in series with the output terminal of a voltage converter. The output voltage Eo and its current of the voltage converter is detected by means of detecting means 20 and 23 and inputted to a control circuit 22. Since the circuit 22 adjusts the output voltage Eo by controlling the inverter circuit 14 corresponding to the fluctuation of the AC power source 12, an output voltage Eo having a waveform close to a sine wave can be always obtained continuously from the voltage converter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage converter having a structure capable of adjusting the AC output on the secondary side of a transformer.

[0002]

For example, when an output of a desired voltage is supplied from an AC power supply to a load, a transformer having a winding ratio according to the ratio of the AC power supply to the desired voltage is interposed. Is commonly done. However, while it is necessary to supply a constant voltage on the load side, the voltage of the AC power supply may fluctuate due to various causes. In response to such fluctuations in the power supply voltage, conventionally, for example, a transformer is provided with a plurality of taps and these taps are switched so that an appropriate voltage can always be supplied to the load.

FIG. 5 shows a load tap changer constructed by using a thyristor element so as to electrically perform such tap change. That is, in this one, the primary winding 1a of the transformer 1 is connected to the AC power supply 2, the secondary winding 1b is provided with a plurality of taps 3a to 3f, and the common terminal is connected to the output terminal A. The taps 3a to 3f are connected to the switches 4a to 4f. Thyristor pair 5a and 5b connected in parallel and reverse as control elements
Is for adjusting the on-timing by phase control, and the switches 4a, 4c, 4e are thyristor pairs 5a.
Connected to the output terminal B via the switches 4b, 4d,
4f is connected to the output terminal B via the thyristor pair 5b.

In the above structure, the tap 3a of the transformer 1
From the state where the output voltage e1 is obtained by using the tap 3b
The operation of switching to a state where the output voltage e2 is obtained by using is described. First, in the state before the switching, the switch 4a is turned on, and the drive control is performed so that the thyristor pair 5a is in the completely conductive state. As a result, the output voltage e1 corresponding to the tap 3a is obtained between the output terminals A and B.

In the above-mentioned state, in order to connect the tap 3b from which the output voltage e2 is obtained to the output terminal B, the switch 4b is turned on, and then the thyristor pair 5b is driven and controlled. In this case, in the conduction control for the thyristor pair 5b, as shown in FIG. 6, the conduction angle is initially set large to shorten the conduction time in the cycle, and thereafter, the conduction angle is gradually increased. To control. As a result, the output voltage e1 from the tap 3a and the output voltage e2 from the tap 3b are gradually mixed in a mixed state.
Then, it becomes possible to switch steplessly.

In a small-scale system, FIG.
As shown in FIG. 3, there is a configuration in which the primary winding 6a side of the transformer 6 is connected in series with the thyristor pair 7 as a control element and the coil 8 to be connected to the AC power supply 2. It is intended to control the output voltage of the secondary winding 6b of the transformer 6 by controlling the conduction angle of the thyristor pair 7.

However, any of the conventional structures as described above has the following problems. That is, in the mechanical transformer, there is a problem in that the value of the voltage that can be set cannot be made stepless, and the switching speed is slow, so that it is not possible to quickly cope with voltage fluctuations. Further, since it has a contact mechanism that accompanies an arc, there is a problem that the maintenance cycle is shortened. In the thyristor load tap switching transformer, the switching operation can be performed steplessly, but there is a problem that the voltage waveform greatly changes from a sine wave when switching the voltage between the taps. is there.

The present invention has been made in view of the above circumstances, and an object thereof is to be able to switch the required output voltage steplessly using an AC power supply as a reference, and to obtain it in a state close to a sine wave. An object is to provide a voltage conversion device capable of doing so.

[0009]

SUMMARY OF THE INVENTION The voltage converter of the present invention adjusts an AC output obtained in a main transformer whose primary winding is connected to an AC power source and a secondary winding of this main transformer. Of the DC power supply, an inverter circuit for converting the DC power supply into an AC output for adjustment and adding the AC output obtained in the secondary winding of the main transformer to the load, and an AC output for the load. A voltage detection unit that detects a voltage, a current detection unit that detects a current of an AC output to the load, and an AC output that should be supplied to the load based on detection outputs of the voltage detection unit and the current detection unit. It is characterized in that it is provided with control means for driving and controlling the inverter circuit so as to compensate for the value of the difference from the actual AC output.

According to the above construction, even if the output voltage obtained by converting the AC power supply by the main transformer fluctuates due to the voltage fluctuation of the AC power supply, the output voltage is detected by the voltage detecting means and the current detecting means. Based on this, the inverter circuit is drive-controlled so as to obtain a desired output voltage, so that the output voltage required for the load can always be stably obtained.

Further, the voltage converter of the present invention is provided with an auxiliary transformer for adding the adjusting AC output by the inverter circuit to the AC output obtained in the secondary winding of the main transformer, It is also possible to connect the primary winding of the transformer to the adjusting AC output side of the inverter circuit and to connect the secondary winding in series with the secondary winding of the main transformer. The adjustment range of can be widened.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIGS. In FIG. 1 showing an electrical configuration, an AC power source 12 is connected to a primary winding 11a of a main transformer 11, and an AC output Et is output between output terminals of a secondary winding 11b. The auxiliary transformer 13 has an inverter circuit 14 connected to the primary winding 13a side and outputs an inverter output Ei to the secondary winding 13b. Each of the secondary windings 11b and 13b of the main transformer 11 and the auxiliary transformer 13 is connected in series, and both terminals thereof are output terminals A and B, so that a combined AC output Eo is obtained. There is.

The inverter circuit 14 includes a DC power supply circuit 15
The DC power supply circuit 15 includes a capacitor 17, a phase control rectifier circuit 18, and a DC power supply transformer 19. The phase control rectifier circuit 18 is formed by connecting, for example, thyristors 18a to 18d as a switching element in a bridge, and each thyristor 18a to 18d is provided with a trigger signal at a predetermined timing as described later. The phase control rectifier circuit 18 is connected to the AC power supply 12 via the DC power supply transformer 19, and controls the AC output of the AC power supply 12 to a desired voltage by controlling the conduction angles of the thyristors 18a to 18d. It is adapted to be converted and given to the capacitor 17.

The inverter main circuit 16 is a general one in which, for example, thyristors 16a to 16d are connected as bridges as switching elements, and each of the thyristors 16a to 16d.
The trigger signal to d is given as described later. Then, the inverter main circuit 16 outputs the DC voltage given from the side of the capacitor 17 as the DC power source to the auxiliary transformer 13 as the AC output set by the trigger signal.

A voltage detecting transformer 20 is connected between the output terminals A and B, and a voltmeter 21 is connected to the output terminal side thereof to form a voltage detecting means. The detection output of the output voltage Eo by the voltmeter 21 is input to the control circuit 22 as a control means. A current transformer 23 is provided in the output line connected to the output terminal A, and the output current is detected by the ammeter 24. The detected current output is input to the control circuit 22. It has become so.

The control circuit 22 includes the thyristors 16a to 16d of the inverter circuit 16 and the phase shift control rectifier circuit 18.
The trigger signals of the thyristors 18a to 18d are generated and given, and the trigger signals are generated based on the detection signals from the voltmeter 21 and the ammeter 24 as described later.

Next, the operation of this embodiment will be described with reference to FIG. The main transformer 11 outputs the AC voltage supplied to the primary winding 11a by the AC power supply 12 to the secondary winding 11b side as an AC output Et. In the inverter circuit 14, the control rectification circuit 18 is connected via the transformer 19.
The control circuit 22 applies a trigger signal to each of the thyristors 18a to 18d at a predetermined timing with respect to the AC input given to the control circuit so that a predetermined DC power supply voltage is obtained. As a result, the capacitor 17 is set to a predetermined DC power supply voltage Ed.

Then, the control circuit 22 applies a trigger signal to each of the thyristors 16a to 16d of the inverter main circuit 16 to generate a predetermined AC output and output the AC output Ei via the auxiliary transformer 13. Become.

As a result, between the output terminals A and B, an output obtained by adding the AC output Et of the main transformer 11 and the AC output Ei of the auxiliary transformer 13 can be obtained as the output voltage Eo. In this case, two AC outputs Et and Ei
In consideration of the voltage value and the phase, as shown in FIG. 2, a combined vector when the AC outputs Et and Ei are treated as vectors is obtained as the output voltage Eo.

On the other hand, the output voltage Eo output from between the output terminals A and B is detected by the voltmeter 21 via the transformer 20, and a load is connected between the output terminals A and B. Then, the value of the current supplied to the load is detected by the ammeter 24 via the current transformer 23. The voltmeter 21 and the ammeter 24 can detect the actual voltage value and phase of the output voltage Eo, and the control circuit 22 can detect the voltage value and the phase based on the detection result.
Each thyristor 16a to 16a of the inverter main circuit 16 is calculated so as to obtain the difference from the preset standard output voltage and match the actual output voltage Eo with the standard output voltage.
A trigger signal is applied to d.

Therefore, for example, even when the voltage of the AC power source 12 fluctuates, the inverter circuit 14 is controlled by the control circuit 22 so that the output voltage Eo generated between the output terminals A and B at this time is detected and becomes the standard output voltage. It is possible to always obtain an output voltage corresponding to the standard output voltage by controlling the drive of. In this case, the voltage fluctuation of the AC power supply 12 may occur for a long time or may occur instantaneously.
Any of these can be controlled correspondingly within the response time.

Further, as the adjustable range of the output voltage Eo, as shown by the hatched area in FIG. 2, the AC output Et obtained from the AC power source 12 to the secondary winding 11b by the main transformer 11 is set. On the other hand, the voltage value and the phase value can be adjusted within the range of the maximum voltage obtained by the inverter circuit 14. Therefore, it is possible to obtain an output voltage having a sine wave or a waveform close to it by adjusting the AC output Ei that adds the phase distortion.

When the output voltage Eo is to be obtained without using the inverter circuit 14, the primary winding 13a of the auxiliary transformer 13 is short-circuited so that the current flowing through the secondary winding 13b. Thus, the voltage generated in the primary winding 13a is canceled. Therefore, for example, by implementing a configuration in which a switching element or a relay switch for short-circuit operation is connected, this can be implemented.

According to the present embodiment as described above, the output voltage having a waveform close to a sine wave is continuously corresponded to the standard output voltage without performing the switching operation such as the tap switching in response to the fluctuation of the AC power supply. Moreover, since the mechanical switch is not used, the maintenance interval can be lengthened.
Then, according to the present embodiment, the capacity of the inverter circuit 14 can be reduced to about Ei / Eo of the load capacity,
The overall size can be made smaller than that of the configuration using the inverter circuit corresponding to the load capacitance.

Further, according to the present embodiment, since the adjusting AC output obtained by the inverter circuit 14 is output by using the auxiliary transformer 13, the inverter circuit 14 is isolated from the main system. Since it is possible to reduce the ground insulation, it is possible to protect the inverter circuit 14 from various surge voltages generated in the system, and to flexibly cope with the case where the high-voltage AC power supply 12 is used. In addition to being able to do so, it is also possible to change the adjustable area, which increases versatility and expands the range of application.

FIG. 3 shows a second embodiment of the present invention. The difference from the first embodiment is that the auxiliary transformer 13 is not provided. That is, the inverter circuit 25 is configured such that the AC output terminal of the inverter main circuit 16 is directly connected to the secondary winding 11b of the main transformer 11 in series.

In the case of this configuration, the inverter circuit 25
Since the output terminal of the inverter is directly connected to the output terminals A and B, the thyristor 16a of the inverter main circuit 16 is connected.
It is necessary to always drive 16d to 16d, but in the state where they are driven by giving an appropriate trigger signal, by controlling the phase and voltage value of the output of the DC power supply 15, the adjustment AC output Ei is obtained. You will be able to output.

Therefore, similar to the first embodiment,
It becomes possible to continuously obtain an output voltage with a waveform close to a sine wave corresponding to the standard output voltage without performing a switching operation such as tap switching in response to the fluctuation of the AC power supply. By adopting a configuration that does not use an auxiliary transformer, a simple and inexpensive configuration can be obtained, which is suitable when the power source voltage of the AC power source 12 is low.

FIG. 4 shows a third embodiment of the present invention. The difference from the first embodiment is that it is applied to a three-phase system. That is, the main circuit 27 connected to the three-phase AC power supply 26 is the primary winding 2 of the three-phase main transformer 28.
It is connected to 8a, 28b, 28c. An inverter circuit 30 is connected to the three-phase AC power supply 26 via a transformer 29 for a regulated power supply. The inverter circuit 30 includes a phase control rectifier circuit 31 as a DC power supply circuit, a capacitor 32, and an inverter main circuit 33. The output terminal of each arm of the inverter main circuit 33 is connected to the primary windings 34a, 34b, 34c of the auxiliary transformer 34. Secondary windings 28d, 28e, 2 of the main transformer 28
8f are the secondary windings 34d, 3 of the auxiliary transformer 34, respectively.
4e and 34f are connected in series and output terminals A, B,
It is connected to C.

Although not shown in the figure, in this configuration also, voltage detecting means,
A structure corresponding to each of the current detecting means is provided, and the phase control rectifier circuit 3 is based on the detected outputs.
1 and a control circuit as control means for driving and controlling each thyristor of the inverter main circuit 33. Also, according to the third embodiment as described above, it is possible to obtain substantially the same effect as that of the first embodiment.

The present invention is not limited to the above embodiment, but can be modified or expanded as follows. The inverter circuit is a P that uses GTO, in addition to the thyristor.
WM inverter or transistor inverter,
Further, an inverter circuit using FET, IGBT or the like can be used. The phase control rectifier circuit may be provided as necessary. As the voltage detecting means and the current detecting means, other commonly used ones may be used as long as the voltage and the current of the AC output can be detected. The voltage detection by the voltage detection means is performed by the main transformer 11
The output may be detected so that the output is detected.

[0032]

As described above, according to the voltage converter of the present invention, the following effects can be obtained. That is, according to the voltage conversion device of claim 1, when the AC output obtained from the AC power source through the main transformer is deviated from the desired output voltage, the AC output by the inverter circuit is added. It becomes possible to obtain a desired output voltage. Therefore, it is possible to deal with the voltage fluctuations steplessly without performing tap switching, and it is possible to always obtain the waveform of the output voltage as a sine wave. Also, the capacity of the inverter can be made smaller than the load capacity, and the overall size can be reduced.

According to the voltage converter of the second aspect, even when there is a phase shift between the output voltage and the AC power source,
By correspondingly controlling the drive of the inverter circuit, it is possible to obtain the output voltage in which the phase shift is corrected.

According to the voltage converter of the third aspect, since the AC output of the inverter circuit is output via the auxiliary transformer, the auxiliary transformer is provided even if there is a difference between the capacity of the inverter circuit and the scale of the AC power supply. This makes it possible to compensate for this, and a configuration in which the AC output has a width can be provided.

According to the voltage converter of the fourth aspect, since the power is supplied from the AC power source as the DC power source through the rectifier circuit with a small capacity within the range of the adjusting voltage, the configuration is simple and compact, and the cost is low. Can be done.

According to the voltage converter of the fifth aspect, the voltage of the DC power supply can be controlled and added by the phase control rectifier circuit, and the voltage adjustment by the inverter circuit can be easily performed.

[Brief description of drawings]

FIG. 1 is an electrical configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an operation explanatory view showing an adjustable range of the output voltage.

FIG. 3 is a view corresponding to FIG. 1, showing a second embodiment of the present invention;

FIG. 4 is a view corresponding to FIG. 1, showing a third embodiment of the present invention;

FIG. 5 is a view corresponding to FIG. 1 showing a conventional example.

FIG. 6 is a waveform diagram of output voltage when taps are switched.

FIG. 7 is a view corresponding to FIG. 1 showing a different conventional example.

[Explanation of symbols]

11 is a main transformer, 12 is an AC power supply, 13 is an auxiliary transformer,
Reference numeral 14 is an inverter circuit, 15 is a DC power supply circuit, 16 is an inverter main circuit, 17 is a capacitor, 18 is a phase control rectification circuit, 19 is a DC power supply transformer, 20 is a transformer (voltage detection means), and 21 is a voltmeter. , 22 is a control circuit (control means), 23 is a current transformer (current detection means), 24 is an ammeter,
25 is an inverter circuit, 26 is a three-phase AC power supply, 28 is a main transformer, 30 is an inverter circuit, 31 is a phase control rectifier circuit, 32 is a capacitor, 33 is an inverter main circuit, 34
Is an auxiliary transformer.

Claims (5)

[Claims] 1. A main transformer having a primary winding connected to an AC power supply, a DC power supply for adjusting an AC output obtained in a secondary winding of the main transformer, and an AC power for adjusting the DC power supply. An inverter circuit that converts the output to an AC output obtained in the secondary winding of the main transformer and supplies the load to a load; a voltage detection unit that detects the voltage of the AC output to the load; Current detection means for detecting the current of the AC output, and to compensate for the value of the difference between the AC output to be supplied to the load and the actual AC output based on the detection outputs of the voltage detection means and the current detection means. And a control means for driving and controlling the inverter circuit. 2. The control means determines the voltage difference and the phase difference of the actual AC output obtained from the voltage detection means and the current detection means with respect to the set AC output, and corrects the values of these differences. The voltage conversion device according to claim 1, wherein the voltage conversion device is configured to drive and control the inverter circuit. 3. An auxiliary transformer for adding an AC output for adjustment by the inverter circuit to an AC output obtained in a secondary winding of the main transformer, wherein the primary winding of the auxiliary transformer is the inverter. The voltage conversion device according to claim 1 or 2, wherein the voltage converter is connected to the adjusting AC output side of the circuit and the secondary winding is connected in series to the secondary winding of the main transformer. 4. The DC power supply is configured to include a DC power supply transformer, a rectifier circuit, and a capacitor, and an AC output obtained from the AC power supply through the DC power supply transformer is rectified by the rectifier circuit. 2. The capacitor is configured to be obtained between terminals of the capacitor.
4. The voltage conversion device according to any one of 3 to 3. 5. The voltage control circuit according to claim 4, wherein the rectification circuit is a phase control rectification circuit configured to include a switching unit capable of controlling a rectification operation and configured to adjust a voltage value of the DC power supply. Converter.