JPH01234062A - Controlling method for ac power supply - Google Patents

Abstract

PURPOSE:To miniaturize and lighten a transformer, by converting DC into a high-frequency AC through a first conversion means and by rectifying said high-frequency AC into a reference-frequency AC through a third conversion means after rectifying said high-frequency AC through an insulating transformer and a second conversion means. CONSTITUTION:A DC power supply 1 is composed of a thyristor rectifier and a smoothing circuit, and said DC is inputted to a first conversion means of a first inverter 10. Said first inverter 10 is formed by the single-phase bridge rectifier connection of an arm composed of transistors 10U-10Y and an inverse- parallel diode to subject said DC to a high-frequency pulse width modulation to convert said DC into AC and to output said AC. Then, said output is caused to perform ON-OFF action by a signal of the maximum value of conducting width of a primary side firing signal via an insulating transformer 3 and a second conversion means of a second inverter 20 to rectify alternately positive and negative high-frequency pulses. Then, said DC output is inputted to a third conversion means of a third inverter 30 to convert said output into a pulse-width modulated reference frequency AC power and to give said AC power to a load 8 via a sine wave filter 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling an AC power supply that is insulated from a power supply and outputs an AC with little waveform distortion.

(Prior Art) FIG. 4 is a main circuit connection diagram showing a conventional example of an AC power supply device that is insulated from a power source and outputs alternating current with little waveform distortion.

Electronic devices such as computers often require an AC power source that not only has almost no voltage fluctuation or frequency fluctuation, but also has slight waveform distortion and is isolated from the power supply. , the conventional circuit shown in FIG. 4 is used for such applications.

In Fig. 4, a DC power supply 1 that outputs smooth DC power with no voltage fluctuations (such DC power is connected to a thyristor rectifier that converts commercial power to DC, for example, and a thyristor rectifier connected to the next stage of this or an accelerator) ), the power supply side inverter 2
The AC output from the inverter 2 on the trA side is insulated by the isolation transformer 3, and then converted back to DC by the rectifier 4, but the AC output from the inverter 2 on the power supply side is If the frequency of is made as high as possible, the insulation transformer H3 can be made smaller and lighter, which is economical.

The rumble component included in the DC output from the diode rectifier 4 is absorbed and removed by the DC filter circuit 5, which is composed of a reactor and a capacitor, so the smooth DC thus obtained is transferred to the load side. The inverter 6 converts the output into alternating current again, but in order to reduce the harmonic components contained in the output alternating current, the load-side inverter 6 performs pulse width modulation control, for example, to obtain the desired voltage and frequency. Exchanges will be held. This alternating current is waveform-shaped by a sine filter and is applied to the load 8 as an alternating current with a sinusoidal waveform without distortion.

[Problem to be solved by the invention]

By the way, an AC power supply device configured with the conventional circuit shown in FIG. 4 and designed to insulate the AC supplied to the load from the DC power supply side is configured to convert the DC power to AC power as described above. Since the desired alternating current is output from the load side inverter 6 after being insulated and converted to direct current again, it is necessary to smooth the output direct current of the diode rectifier 5 after insulation. Since it is necessary to install a DC filter circuit 5 consisting of a capacitor and a capacitor, there is a disadvantage that the device becomes large.

Therefore, the purpose of this invention is to eliminate the need for a circuit that smoothes the output of a rectifier that converts alternating current to direct current, which is insulated from a direct current power source, and to generate alternating current with a desired voltage and frequency with less waveform distortion from an inverter installed at the next stage. The purpose is to make it possible to extract the

[Means for Solving the Problems] In order to achieve the above object, the control method of the present invention includes the following:
The first converting means, the second converting means, and the third converting means are configured separately by connecting arms formed by a semiconductor switching element and a diode connected in antiparallel to the semiconductor switching element, and the first converting means converts the input direct current into high-frequency alternating current by pulse width modulation control, supplies this alternating current to the second converting means via the isolation transformer, and converts the second converting means into a high-frequency alternating current of the isolation transformer primary drive signal. By operating with a signal having the maximum conduction width, the input AC of the second conversion means is converted to DC and applied to the third conversion means,
By operating the converting means at a period corresponding to the reference frequency, the third converting means outputs pulse width modulated alternating current.

(Operation) The present invention alternately outputs positive and negative high frequency pulses obtained by pulse width modulation in the first conversion means that inputs DC, and supplies them to the second conversion means via the isolation transformer. At this time, the second conversion means is operated with the signal with the maximum conduction width of the isolation transformer primary side drive signal, so the bright frequency that was output alternately between positive and negative current is eliminated. The pulse is rectified and becomes a pulse with a high frequency on the positive side only.Therefore, by switching the third conversion means at the frequency of the output AC, distortion can be reduced without providing a smoothing circuit on the output side of the second conversion means. There is little interaction.

〔Example〕

FIG. 1 is a main circuit connection diagram showing an embodiment of the present invention,
FIG. 2 is a time chart showing an example of the operation of each conversion means in the embodiment circuit shown in FIG. 1, and the content of the present invention will be described below using FIG. 1 and FIG. .

In FIG. 1, the DC power supply designated by reference numeral 1 is a power supply that outputs smooth, constant voltage DC, and includes, for example, a SIRISK rectifier that converts AC from a commercial power supply into constant voltage DC, and a DC output of this SIRISK rectifier. It consists of a smoothing circuit that absorbs and removes the pulsation contained in the

The DC from this DC power supply 1 is input to a first inverter 10 as a first conversion means.
The inverter 1o is a semiconductor switching element, and is formed by connecting an arm consisting of tenotransistors IOU, IOV, IOX, 'IOY and a diode connected in antiparallel to these in a single-phase bridge. Since the first inverter 10 modulates the high frequency pulse width and sequentially turns on and off so that the output voltage is alternately positive and negative as much as possible, the first inverter 10 converts the input DC into extremely high frequency AC and outputs it. It turns out.

By applying this high-frequency AC power to the primary side of the isolation transformer 3, isolated AC power can be extracted from the secondary side of the isolation transformer 3, but the frequency of this AC power is higher than that of the commercial power supply. Since the value is much higher than the frequency, the isolation transformer 3 can be made small and lightweight.

A second inverter 20 as a second conversion means is connected to the secondary side of this isolation transformer 3, and this second inverter 20 also has transistors 20 U, 20 V, 20 X, as semiconductor switching devices. 20Y
The second
By turning each transistor of the inverter 20 on and off in response to the maximum value of the conduction width of the primary firing signal of the isolation transformer 3, the alternating positive and negative high-frequency pulses output by the first inverter 10 are rectified. . Through such an operation, the second inverter 20 can receive and receive reactive power from the load 8.

The DC output from the second inverter 20 is transferred to a transistor 30 U as a semiconductor switching element.

It consists of a single-phase bridge connection of arms consisting of anti-parallel connections of 30V, 30X, 30Y and diodes.
The third inverter 30 as the third conversion means is manually powered,
By switching the third inverter 3o at a cycle corresponding to the reference frequency of the output AC, the third inverter 3o can extract AC power at the pulse width modulated reference frequency. The waveform-shaped alternating current can be applied to the load 8 by the sine filter made up of the following.

The first inverter described above 10. The operations of the second inverter 2° and the third inverter 30 are shown in the time chart of FIG. That is, Fig. 2 (a) shows the state of the intersection between the sine wave and the triangular wave, Fig. 2 (b) shows the firing signal of the first phase transistor 10U of the first inverter 10 and IOX, and Fig. 2 (h) ) is the firing signal of the second phase transistors IOV and IOY of the first inverter 10, FIG. 2(d) is the output voltage of the first inverter 10, and FIG. 2(e) is the first phase transistor of the second inverter 20. The ignition signals of 20U and 20X, Fig. 2 (f) are the ignition signals of the second phase transistors 20V and 20Y of the second inverter 20, Fig. 2 (g) is the output voltage of the second inverter 20, Fig. 2 (h) is the firing signal of the first phase transistors 30U and 30X of the third inverter 30, FIG. ) respectively represent the output voltage of the third inverter 30.

As is clear from FIG. 2, by comparing the magnitude relationship between the sine wave and the triangular wave, the first inverter 10 outputs a high frequency voltage alternately between positive and negative through pulse width modulation control. After insulating this voltage, it is rectified by the second inverter 20 to obtain a pulsed DC voltage (see FIG. 2 (g)). This second inverter 2
The third inverter 30 to which the output voltage of 0 is input performs a switching operation at the cycle of the reference frequency, thereby obtaining a pulse width modulated AC voltage of the reference frequency (see FIG. 2 (N)).

In this case, the DC voltage output by the second inverter 20 is given to the third inverter 30 without being converted into smooth DC power using a DC filter circuit, and is isolated from the power supply and is an AC voltage with few harmonic components. Power can be extracted from this third inverter 30.

First phase transistors 20U and 20 of second inverter 20
X is operated so that both are in the on state for a very short time in order to maintain the load current, but the second
The phase transistors 20V and 20Y also operate in such a way that they are simultaneously turned on for a short period of time.

FIG. 3 is a time chart showing the details of the firing signal of the second inverter 20, in which FIG. 3(a) shows the output voltage of the first inverter 10, and FIG. The firing signals of the first phase transistors 20U and 20X, and FIG. 3(C), the firing signals of the second phase transistors 20V and 20Y of the second inverter 20 are respectively generated.

In FIG. 3, T1 is the period in which the conduction width of the first inverter 10 is at its maximum as described above, T2 is the period in which the first inverter 10 does not generate an output voltage, and T is the period in which the upper side of the second inverter 20 This is the period in which the arm and the lower arm are turned on. In the actual circuit,
A limit is set for the output voltage of the first inverter IO, and during the period when the first inverter 10 is not outputting the output voltage (
At Tt in FIG. 3), the upper and lower arms of the second inverter 20 are ramped (Tz in FIG. 3) to perform switching.

〔Effect of the invention〕

According to this invention, the first conversion means converts the direct current from the power source into high frequency alternating current that is pulse width modulated, and after insulating this high frequency alternating current from the power source side via the isolation transformer, the inverter After being rectified by the second converting means, the third converting means converts the AC power to the reference frequency, and supplies the AC power to the load via a sine filter for waveform shaping. With such a circuit configuration, the output alternating current is insulated from the power supply side, and alternating current with less waveform distortion can be obtained. Also the first
Since the alternating current outputted by the converting means has a high frequency, the insulating transformer can be made smaller and lighter.

Furthermore, by rectifying the high frequency alternating current obtained from the secondary side of the isolation transformer with an inverter, which is the second conversion means,
Since it is controlled so that the reactive power of the load can be sent and received,
In order to smooth the DC output from this second conversion means,
This eliminates the need for a DC filter circuit consisting of a large-capacity glue and a capacitor, which has the great effect of making this AC power supply smaller and lighter.

[Brief explanation of the drawing]

Fig. 1 is a main circuit connection diagram showing an embodiment of the present invention, Fig. 2 is a time chart showing an example of the operation of each conversion means in the embodiment circuit shown in Fig. 1, and Fig. 3 is a main circuit connection diagram showing an embodiment of the present invention. FIG. 4 is a time chart showing the details of the firing signal of the second inverter in the embodiment shown in the figure, and FIG. This is a main circuit connection diagram. ■・・・DC power supply, 2...Power supply side inverter, 3...
- Isolation transformer, 4... Diode rectifier, 5... DC filter circuit, 6... Load side impark, 7...
sine filter, 8... load, 10... first inverter as first conversion means, 20... second inverter as second conversion means, 30... third as third conversion means Invanniya-

Claims (1)

[Claims] 1) The first conversion means, the second conversion means, and the third conversion means are configured separately by bridge-connecting an arm formed by a semiconductor switch element and a diode connected in antiparallel to the semiconductor switch element, and the first conversion means is configured separately. The converting means converts the input direct current into high-frequency alternating current by pulse width modulation control, supplies this alternating current to the second converting means via the isolation transformer, and drives the second converting means on the primary side of the isolation transformer. By operating with a signal having the maximum conduction width of the signal, the input AC of the second conversion means is converted into DC and applied to the third conversion means, and the third conversion means is operated at a cycle corresponding to the reference frequency. A method for controlling an AC power supply device, comprising: causing the third conversion means to output pulse width modulated AC.