JP2001298954A - Power supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the distortion factor of output waveform at no load. SOLUTION: A current transformer 28 is installed in an output path, and it is detected whether it is under loaded conditions. Under no-load conditions, a sine waveform table 21 is read out, and the conduction angle of a positive rectifier circuit 14 is controlled on half waves on one side and the conduction angle of a negative rectifier circuit 15 is controlled on half waves on the other side. In predetermined sections of the latter part of both the half waves, an antiphase waveform table 31 is read out, and the value read out is used to control the conduction angle of the rectifier circuit that have not been controlled to gradually discharge electric charges that have been stored in smoothing capacitors 16 and 17 until then.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device which alternately operates a positive rectifier circuit and a negative rectifier circuit of a cycloconverter by input AC power and outputs AC power having a frequency different from that of the input AC power to a load.

[0002]

2. Description of the Related Art As an example of this type of power supply, a power supply using a three-phase generator and a cycloconverter is disclosed, for example, in Japanese Patent Application Laid-Open No. H10-52044. This power supply will be briefly described with reference to FIG. Three-phase generator 11
R-phase terminal 12R and S-phase terminal 12 on the output side of the three-phase winding
The S and T phase terminals 12T are connected to the cycloconverter 13. The cycloconverter 13 includes a positive rectifier circuit 14 and a negative rectifier circuit 15, and the conduction angles of the rectifier circuits 14 and 15 can be variably controlled. In the positive rectifier circuit 14, six thyristors 14Ra, 14Rb, 14Sa,
Two pairs of 14Sb, 14Ta, and 14Tb are connected in series in the forward direction, respectively. These three series connections are connected in parallel with the same polarity. And 14Tb
Are connected to the output terminals 12R, 12S, and 12T, respectively. In the negative rectifier circuit 15, six thyristors 15
Ra, 15Rb, 15Sa, 15Sb, 15Ta,
15Tb are connected in series in the forward direction, respectively, and these three series connections are connected in parallel with the same polarity, and the connection points of 15Ra and 15Rb, 15Sa and 15Sb
The output terminals 12R, 12S, and 12T are connected to the connection points 15Ta and 15Tb, respectively. The positive rectifier circuit 14 and the negative rectifier circuit 15 are connected in parallel with opposite polarities.

A series circuit of smoothing capacitors 16 and 17 is connected in parallel with the positive rectifier circuit 14 and the negative rectifier circuit 15. The connection point between the capacitors 16 and 17 is connected to the neutral point 12N of the generator 11. A load 18 is connected between both ends of the series circuit of the capacitors 16 and 17. The sine waveform table 21 stores instantaneous values at respective points obtained by dividing one cycle of the sine waveform into, for example, 100 equal parts as shown in FIG. When the CPU 22 reads and decodes the program in the program memory 23, the count value of the counter 25 in the RAM 24 is initialized to 0, and the count value of the counter 25 becomes 0 at the cycle (frequency) set by the input means 26. From the maximum address value of the sine waveform table 21 (1
00), the counter 25 is reset and incremented when the maximum address value is reached. The sine waveform table 21 is read using the count value of the counter 25 as an address, and the read value is read. Is input to the conduction angle control unit 27. If the input value is positive, the conduction angle control unit 27 provides two thyristors of the positive rectifier circuit 14 at a timing corresponding to the input value, the three-phase generator 1.
1 and variably controls the magnitude of the conduction angle. This control is such that the larger the value, the larger the conduction angle.
If the input value is negative, the thyristors of the negative rectifier circuit 15 are synchronized with the output of the three-phase generator 11 by two at a timing corresponding to the absolute value of the input value, and the conduction angle is controlled by shifting the phase. I do.

Therefore, when the sine waveform table 21 is read from the address 0, the thyristor of the positive rectifier circuit 14 is turned on, but the conduction angle changes from 0 to a sine wave.
The smoothing capacitors 16 and 17 are charged so that the connection point (output terminal) 28 between the capacitor 16 and the load 18 becomes positive, and power is supplied to the load 18. When the count value of the counter 25 advances and exceeds 50, the value read from the sine waveform table 21 becomes negative, the thyristor of the negative rectifier circuit 15 is turned on, the conduction angle changes in a sine wave shape, and the capacitors 16 and 17 The connection point (output terminal) 29 between the capacitor 17 and the load 18 is charged so as to be positive, and power is supplied to the load 18. Therefore, a single-phase alternating current is supplied to the load 18.

[0005]

In the conventional power supply device of this type, when the load 18 is connected, the electric charges charged in the capacitors 16 and 17 are consumed by the load 18, so that the distortion factors are not compared. A stable and stable voltage waveform is output. However, under no load condition, the capacitors 16, 1
7 is not discharged to the load, for example, when the positive rectifier circuit 14 is in the operating state, the capacitors 16 and
When the operation is switched to the negative rectification circuit 15 in a state where the positive charge is charged in the positive charge 17, that is, the connection point (output terminal) 28 side of the capacitor 16 is charged, the capacitors 16,
The electric charge charged at 17 is consumed only by the negative rectifier circuit 15, and the voltage of the output terminal does not drop from the peak value until then. Further, as shown by the solid line in FIG.
At the moment when the operation is switched to 5, the potential of the output terminal 28 suddenly changes from a positive peak value to 0, and an inflection point occurs in the voltage waveform, resulting in a large distortion waveform. Such a problem is described in the above 3
This is not limited to a power supply device that converts phase AC power into single-phase AC power using a cycloconverter, but also occurs in a power supply device that converts the frequency of AC power using a cycloconverter.

[0006]

According to the first aspect of the present invention,
An anti-phase waveform table is provided in which the anti-phase waveform of the second half of the half-wave of the sine waveform is stored, and when the load is determined by the determination means, the sine waveform table is repeatedly read, and according to the read value, Then, the conduction angle of the positive rectifier circuit and the negative rectifier circuit is alternately controlled for each half-wave, and when it is determined that there is no load, an anti-phase waveform is obtained in each predetermined second half section in reading the sine waveform table. The table is read, and the conduction angle of the rectifier circuit that is not the rectifier circuit that has been controlled so far is controlled in accordance with the read value.

According to the second invention, a load table in which a sine waveform is stored, a substantially first half of a half wave of the sine waveform,
There is provided a no-load table in which the antiphase waveform of the weak part in the latter half is stored. When a load is applied, the conduction angle of the positive and negative rectifier circuits is alternately controlled by the value read from the load table. The conduction angle of the positive / negative rectifier circuit is alternately controlled by the value read from the load table.

[0008]

FIG. 1 shows an embodiment of the first invention, in which parts corresponding to those in FIG. 4 are denoted by the same reference numerals. In the present invention, an anti-phase waveform table 31 is provided in addition to the sine waveform table 21. When the sine waveform table 21 shown in FIG. 3A stores, for example, an instantaneous value (sampling value) of one cycle of a sine waveform at addresses 0 to 100, the second half of the positive half wave and the second half of the negative half wave As shown in FIG. 3B, the phases of the sine waveforms in the sections of the sections, for example, addresses 30 to 50 and 80 to 100 are inverted, and the instantaneous values of the waveform that rises or falls from zero are addresses 30 to 50 and 80 to 100, respectively. Are the anti-phase waveform tables 31 respectively. That is, the values obtained by moving each value of the addresses 80 to 100 of the sine waveform table 21 to the positive side so that the value of the address 80 becomes 0 are the values of the addresses 30 to 50 of the reverse phase waveform table 31. 21 are shifted to the negative side so that the value of the address 30 becomes 0, and the values of the addresses 80 to 100 of the antiphase waveform table 31 are shifted to the negative side.
Is the value of In addition, 0 to 3 of the antiphase waveform table 31
Each value of 0, 50 to 80 is zero. In other words, the anti-phase waveform table 31 has addresses 30 to 50 and 80 to 1 as addresses.
Only 00 may be provided.

Further, according to the present invention, there is provided means for determining whether a load is present or not. In this example, a current transformer 32 is provided as a current detector on an output path of the cycloconverter 13 to the load 18, and the output of the current transformer 32 is input to the state determination unit 33, and the load 18 is changed according to the detected current value. It is determined whether the power is supplied to the load 18 or the load is not supplied to the load 18. The control for the cycloconverter 13 is changed as follows depending on whether the load state or the no-load state. That is, as shown in FIG. 2, the CPU 22 periodically checks the judgment state of the state judgment unit 33 (S1), and controls the cycloconverter 13 only by the sine waveform table 21 if no load is applied (S2). The control of the cycloconverter 13 by the waveform table 21 is performed by a method similar to the above-described conventional method. Therefore, load 1
8 is supplied with single-phase AC power of the frequency set by the input means 26. During the control using the sine waveform table, the process periodically returns to step S1 to check whether or not there is no load.

The state determination unit 33 determines that there is no load, and when this state is detected by the CPU 22, the current counter 25
Is the discharge region, that is, whether or not the count value is in the range of 30 to 50 or 80 to 100 in the example shown in FIG. It is checked (S3), and if it is not in the discharge region, the control of the cycloconverter 13 by the sine waveform table 21 is connected (S4). During the control by the sine waveform table, the process returns to step S3 every time the counter 25 is advanced by one, and it is checked whether the count value is in the discharge region.

If it is determined in step S1 that there is no load, and the count value of the counter 25 at that time is in the discharge region,
Alternatively, when the count value of the counter 25 is in the discharge region by the control using the sine waveform table in the no-load state in step S4, the control is shifted to the control using the antiphase waveform table 31 (S5). That is, the anti-phase waveform table 31 is read using the count value of the counter 25 at that time as an address, and the conduction angle of the rectifier circuit which is not the rectifier circuit which has been controlled so far is controlled at a timing corresponding to the read value. .

For example, address 0 of the sine waveform table 21
From the state where the positive rectifier circuit 14 is controlled, the count value of the counter 25 becomes 30. That is, when the counter enters the discharge area, the counter phase waveform table 31 is read with the count value of the counter 25, and Negative rectification circuit 15 according to
Control. Therefore, the connection point 28 between the capacitors 16 and 17 is controlled based on the control by the positive rectifier circuit 14 in the no-load state.
The negative rectifier circuit 15 is controlled by the value read from the reverse phase waveform table 31 in a state where the positive charge is charged to the vicinity of the positive maximum voltage of the sine waveform on the side, so that the output terminals 28 of the capacitors 16 and 17 are controlled. The positive charge on the side gradually discharges.

When the count value of the counter 25 enters the discharge region 80 to 99 from the section of 50 to 79, similarly, the section 50 to 7
9, the negative charge is charged to the output terminals 28 of the capacitors 16 and 17 near the negative maximum voltage of the sine wave by the negative rectifier circuit 15. Is controlled, and the capacitors 16,
It gradually discharges to 17 negative charges. Even during the control by the anti-phase waveform table 31 in step S5, the process returns to step S3 every time the count value of the counter 25 is incremented by one, and it is checked whether the count value has changed from the discharge area to the control area by the sine waveform table. Will be

In order to operate in this manner, the output terminals 28,
The voltage between 29 changes, for example, into a sine wave shape with considerably small distortion as shown in FIG. 3C. As the discharge area, 90 ° to 1 in one cycle of the sine wave (0 ° to 360 °)
In the range of 80 ° and 270 ° to 360 °, the distortion between the sine waveform of the voltage between the output terminals 28 and 29 in the no-load state is selected to be as small as possible. When it is determined whether to control the positive rectifier circuit 14 or the negative rectifier circuit 15 according to the polarity read from the waveform table, the polarity is determined as the reverse phase waveform table 31 as shown by the broken line in FIG. May be stored. Further, the sine waveform memory 21 stores only a half-wave of the sine waveform, and switches the rectifier circuits 14 and 15 which are controlled each time the reading at the last address of the sine waveform memory 21 is completed, thereby reading the sine waveform memory 21 at the first address. And the opposite phase waveform table 31 also corresponds to a half-wave of a sine waveform, for example, as shown in FIG.
A memory storing only the values of 30 to 50 in B may be used.

In FIG. 2, if it is not the discharge region in step S3, the process may proceed to step S2 to perform control using a sine waveform table. In this case, every time the counter 25 is incremented by one in step S2, step S1 is executed.
Return to. In the above description, the rectifier circuits 14 and 15 are controlled using the sine waveform table 21 and the antiphase waveform table 31 in the no-load state. However, in the no-load state, a dedicated no-load table is provided. The conduction angles of the rectifier circuits 14 and 15 may be selectively controlled only by the values read from the table. In this case, as the no-load table, for example, as shown by a solid line in FIG. 7, addresses 0 to 30 are the first half of the positive half-wave sine wave, and addresses 30 to 50 are addresses 30 in FIG. 3B.
Similarly to the solid line of ~ 50, the lower half of the half-wave of the opposite phase waveform rising from zero, addresses 50-80 are the first half of the negative half-sine wave, and addresses 80-100 are the lower half of the sine wave. A waveform whose portion falls from zero is stored. In the control, the conduction angle of the positive rectifier circuit 14 is controlled by the read values in the sections of addresses 0 to 30 and 80 to 100, and the conduction angle of the negative rectifier circuit 15 is controlled by the read values in the sections of addresses 30 to 80. In this case, the control of the positive rectifier circuit 14 and the control of the negative rectifier circuit 15 may be selectively performed by using only the stored waveforms of the addresses 0 to 50 and distinguishing the first half wave and the second half wave of the sine wave. As shown by the dashed lines in FIG.
A value obtained by making the waveforms of the 80 to 100 portions in opposite phases may be stored, and the positive rectifier circuit 14 and the negative rectifier circuit 15 may be controlled according to the sign of the read value.

In the above description, the present invention is applied to the case where three-phase AC power is converted into single-phase AC by a cycloconverter. In general, input AC power is converted by a cycloconverter into AC power different from the frequency of the input AC power. It can also be applied to power supply devices.

[0017]

As described above, according to the present invention, the no-load state is detected, and in that case, the smoothing capacitor has been charged up to the latter half of each half-wave of the generated single-phase sinusoidal current. Since the charges are gradually discharged, a stable waveform having a small distortion rate of the generated single-phase AC voltage can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing an example of a processing procedure according to the embodiment of the present invention.

3A and 3B are diagrams for explaining the relationship between a sine waveform table 21 and an antiphase waveform table 31, and FIG. 3C is a diagram illustrating an example of an output voltage waveform at the time of no load according to the present invention.

FIG. 4 is a block diagram showing a conventional power supply device.

FIG. 5 is a diagram for explaining a sine waveform table 21;

FIG. 6 is a diagram showing an example of an output power waveform of the conventional device at no load.

FIG. 7 is a diagram showing a storage example of a no-load table.

Claims (2)

[Claims] 1. A power supply device that alternately operates a positive rectifier circuit and a negative rectifier circuit of a cycloconverter by input AC power and outputs AC power having a frequency different from that of the input AC power to a load, wherein a sine waveform is stored. A sine waveform table, an anti-phase waveform table in which the anti-phase waveform of the latter half of the half-wave of the sine waveform is stored, means for determining whether the load is in a load state or no load state, and the sine waveform in a load state Means for repeatedly reading the table and alternately controlling the conduction angle of the positive rectifier circuit and the negative rectifier circuit for each half cycle of the sine wave at a timing corresponding to the read value; The above-mentioned inverted phase waveform table is read in a predetermined latter half section in the reading of the waveform table, and a time corresponding to the read value is read. Grayed power supply apparatus characterized by comprising means for controlling the conduction angle of the rectifier circuit towards non-rectifying circuit which controls until then, the. 2. A power supply device that alternately operates a positive rectifier circuit and a negative rectifier circuit of a cycloconverter by input AC power and outputs AC power having a frequency different from that of the input AC power to a load, wherein a sine waveform is stored. A load table, a no-load table in which the first half of the sine waveform half-wave strong half part and an anti-phase waveform of the second half weak part are stored, a means for determining whether the load state or no load state, A means for repeatedly reading the load table in a state, and alternately controlling the conduction angles of the positive rectifier circuit and the negative rectifier circuit for each half cycle of the sine wave at a timing according to the read value; In the state, the no-load table is repeatedly read, and the positive rectifier circuit and Means for alternately controlling the conduction angle of the negative rectification circuit, and controlling the conduction angle of the positive rectification circuit or the conduction angle of the negative rectification circuit that is not controlled in the first half strong part in each second half weak part. A power supply device, characterized in that: