JP2552001B2 - Frequency converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention includes a large-capacity capacitor connected in parallel to a DC circuit formed by a converter section and an inverter section, and performs pulse width modulation control in the inverter section. The present invention relates to a frequency conversion device for obtaining an AC power supply having an arbitrary voltage and frequency.

[Prior Art] Conventionally, a frequency conversion device capable of controlling an AC power supply to an arbitrary voltage and frequency has been used as a means for supplying an AC power supply to a television, a radio broadcasting device, an information processing device, or an AC motor. in use.

For example, Figure 2 shows "Electronic Components and Applications (ELECTRONIC COMP
ONENTS AND APPLICATIONS), VOL.3, NO.1, 1980 11
Monthly issue, pages 6-16, "Analog control system for AC motors with WP M variable speed drive" by W Bee Lothink ("Analogue control syste"
m for a, c, motor with PWM variable speed dri
FIG. 10 is a circuit diagram of a frequency conversion device of a conventional example that embodies the circuit diagram indicated by fig4 in “ve“ WBROSINK) ”.

In FIG. 2, (1) is a contact that is an electrical contact, (2) is an input transformer that transforms an AC voltage from an AC power source into a predetermined voltage, and (3) is a diode (31) that converts the AC voltage into a DC voltage. ) To (36), a converter (4) is a large-capacity capacitor (here, a large-capacity) connected in parallel to a DC circuit formed by the converter (3) and an inverter (5) described later. A filter capacitor is used), and (5) is an inverter unit. The inverter section (5) uses a transistor inverter including transistors (51) to (56) and flywheeling diodes (61) to (66). And (10
1) is a current limiting resistance that prevents inrush current, and (102) is a current limiting resistance short-circuit switch.

Further, R, S, T at the left end of FIG. 2 show each phase of the three-phase AC power supply, and the AC power supply is supplied from here.
Further, U, V, W at the right end of the figure indicate each phase of the three-phase AC motor drive-controlled by the inverter.

 Next, the operation will be described.

First, before starting the inverter section (5) which is the main circuit, the contact (1) is turned on with the current limiting resistance short-circuit switch (102) being opened. The AC voltage of each phase (R phase, S phase, T phase) input from the AC power supply is transformed into a predetermined voltage by the input transformer (2), and the diodes (31) to (31).
It is rectified into a direct current by the converter section (3) composed of (36).

Here, in order to prevent the inrush current from entering the inverter unit (5), the large capacity capacitor (4) is charged to the rated value via the current limiting resistor (101). This is called initial charging, and the large-capacity capacitor (4) has a function of smoothing the rectified DC voltage waveform.

Next, after confirming that the large-capacity capacitor (4) has been charged to the rated value with, for example, a connected voltmeter, the current limiting resistance short-circuit switch (102) is turned on. This allows
A base signal is given to the transistors (51) to (56), and the inverter section (5) starts operation.

In the inverter unit (5), pulse width modulation (hereinafter,
(Referred to as PWM) means is employed to generate several pulses during a half cycle of the AC voltage, and to make the width of each pulse different, thereby bringing the AC output closer to a sine wave. When the voltage is adjusted by this means, the width of each pulse is changed.

The load current during operation of the inverter unit (5) as described above flows through the current limiting resistance short circuit switch (102).

[Problems to be Solved by the Invention] As described above, in the conventional frequency conversion device, the large-capacity capacitor (4) is initially charged through the current limiting resistor (101), and after charging, is fed to the inverter unit (5). A current limiting resistance short circuit switch (102) is used to input a smoothed DC voltage.

However, when the current limiting resistance short circuit switch (102) is used, there is a problem that the device itself becomes large and expensive.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a frequency converter including a small-sized and inexpensive initial charging circuit.

[Means for Solving the Problem] A frequency conversion device according to the present invention is a switching unit that causes a control power supply to connect and disconnect an arbitrary one phase of an input terminal of a converter unit and an arbitrary one phase of an output terminal of an inverter unit. When,
An initial charging circuit including a current limiting unit for limiting a current flowing from the control power source to the large capacity capacitor is provided to perform the initial charging of the large capacity capacitor.

[Operation] In the frequency conversion device according to the present invention, the initial charging circuit of the present invention including the switching unit and the current limiting unit is used to switch the initial charging of the large-capacity capacitor before starting the inverter unit. By doing so, it is possible to effectively prevent inrush current by supplying current from the control power supply, and the large and expensive current limiting resistance short-circuit switch used for conventional initial charging is no longer required, making it compact and inexpensive. It became possible to make it a new device.

[Embodiment] A preferred embodiment of a frequency conversion device according to the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the frequency conversion device according to the present invention. Here, the same members as those of the conventional example shown in FIG. 2 are designated by the same reference numerals, and the duplicated description will be omitted.

The characteristic feature of this embodiment is that, as shown in FIG.
The point is that an initial charging circuit (7) using the control power source (8) as a power source is provided. In this embodiment, the switch (71)
An initial charging circuit is constituted by the current limiting resistance means (which uses the winding resistance of the insulating transformer) (72) for limiting the flow of electricity. And the switch (71)
Has one end connected to the R phase of the converter section (3) and the other end connected to the U phase of the inverter section (5) to form a single-phase rectifier. Here, the R-phase and the U-phase are used to connect to the control power supply (8), but the invention is not limited to this, and any one phase of the converter section (3) and any one of the inverter sections (5) may be connected. It suffices if the phases are connected.

Next, the operation of this embodiment will be described. Prior to starting the inverter section (5), which is the main circuit of this frequency conversion device, the insulating power transformer (7) is connected to the control power supply (8).
The switch (71) is turned on via 2) to perform the initial charging of the large capacity filter capacitor (4). In FIG. 1, a single-phase rectifier is composed of two diodes (31) and (34) in the converter section (3) and two flywheeling diodes (61) and (64) in the inverter section (5). Is configured, and the large-capacity filter capacitor (4) can be initially charged.

Most of the winding impedance of the insulation transformer (72) used in this initial charging circuit is a resistance component and its resistance value is also large, so a small size is sufficient and it has a sufficient current limiting effect. .

The switch (71) may be any switch that connects and disconnects the main circuit and the control power supply (8), and may be a mechanical switch by contact or a switch using a semiconductor.
For this reason, it is not necessary to use a large-sized and expensive current limiting resistance short-circuit switch as in the prior art, so that the frequency conversion device can be downsized and the cost can be reduced.

Next, after confirming the completion of charging of the large-capacity filter capacitor (4) to the rated value by measuring with a voltmeter, the switch (71) is opened. Thus, when the initial charging of the large-capacity capacitor (4) is completed, the initial charging circuit (7) is disconnected from the main circuit. Then, when the contact (1) is turned on, each phase (R phase, S
Phase, T phase) input AC voltage, input transformer (2)
Is transformed into a predetermined voltage via. Then, the transformed AC voltage is rectified into a DC voltage by the converter unit (3), and further, the DC voltage is smoothed by the charged large-capacity capacitor (4). This smooth DC voltage is input to the inverter unit (5), the inverter unit (5) is started according to the same operation as in the conventional example, and the U of the controlled AC power supply is controlled.
Phase, V phase, W phase are output.

In the above embodiment, confirmation of completion of charging of the large-capacity filter capacitor (4), opening of the switch (71) and closing of the contact (1) can be performed manually as described above. It is also possible to automatically perform a series of operations of the switch (71) and the contact (1) by using a control means.

Further, in the initial charging circuit (7) of the large-capacity filter capacitor (4), the protective fuse is omitted and the winding resistance of the insulating transformer is used as the current limiting resistance means (72). It is also possible to provide a resistor. Also in this case, the same preferable effects as described above can be obtained.

Furthermore, in this embodiment, a transistor inverter is used for description, but a semiconductor other than this may be used.

[Advantages of the Invention] As described above, in the frequency conversion device according to the present invention, the large-capacity capacitor is initially charged using the initial charging circuit that uses the control power supply as a power source. Initial charging can be performed by the initial charging circuit using the flow means, and the device can be downsized and inexpensively configured.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a frequency conversion device according to the present invention, and FIG. 2 is a circuit diagram of a conventional device. In FIG. 1, (1) is a contact, (2) is an input transformer, (3) is a converter section, (4) is a large-capacity capacitor, (5) is an inverter section, (7) is an initial charging circuit,
(71) is a switch, (72) is a current limiting resistance means, and (8) is a control power supply. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A converter section, in which a rectifying element is connected in a bridge type, converts an AC voltage input to an input terminal into a DC voltage, and a large-capacity capacitor that smoothes the DC voltage converted by the converter section. The switching element and a rectifying element that flows current in the opposite direction are connected in parallel, and the building blocks are connected in a bridge type.The DC voltage smoothed by a large-capacity capacitor is converted to an AC variable voltage from the output terminal. In a frequency conversion device having an inverter section for outputting, a switching means for connecting and disconnecting an arbitrary one phase of the input terminal of the converter section and an arbitrary one phase of the output terminal of the inverter section to a control power supply, An initial charging circuit including a current limiting means for limiting a current flowing from the control power source to the large capacity capacitor, Frequency conversion device and performs electric.