JPS61150672A - Control circuit of inverter - Google Patents

Abstract

PURPOSE:To prevent a charging resistor from burning out by shortcircuiting a resistor for limiting a charging current by the current of a switching element energized after a smoothing condenser of an inverter arrives at the prescribed voltage, and releasing the inhibit of an operation command. CONSTITUTION:The normal-open contact 88Pa of a relay 88P is connected with both ends of a charging current limiting resistor 11. When a power reactor 1 is started, a capacitor 2 is charged through the resistor 11. The voltage (v) divided from the charging voltage by resistors 3, 4 is input to a comparator 7. A reference voltage divided by resistors 5, 6 is input through a voltage stabilizer 15 from a rectifier 14 to the comparator 7. When the voltage (v) exceeds a reference voltage, the comparator 7 outputs to turn ON a TR18, a relay RY is operated to close a contact RYa. Then, the relay 88P is operated, the contact 88Pa is closed to shortcircuit the resistor 11. A normal-closed contact RYb, not shown, is opened to release the inhibit of the operation command. Thus, even if the operation command switch remains ON and it is started, it can prevent the resistor 11 from burning out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control circuit for an inverter that converts DC power into AC power.

[Conventional technology]

Conventionally, in this type of inverter, when the power supply side switch is closed while the smoothing capacitor in the DC intermediate circuit is not charging, a very large rush current flows into the smoothing capacitor via the rectifier, and this rush current This leads to a serious accident in which the elements of the rectifier are permanently destroyed.

Therefore, as shown in Fig. 2, the output voltage (DC voltage) of the DC voltage smoothing capacitor 2 provided on the output side of the forward converter l is divided by a resistor 3.4, and this divided voltage and The comparator 7 compares the reference voltage VB produced by the resistor 5.6, and if the divided voltage becomes larger than the reference voltage VR, the transistor 9 is driven via the amplifier 8, and the SCR ignition circuit is activated. 10 is activated, and the charging resistor 11 of the capacitor 2 is activated.
5CR12 and short-circuit it so that the output voltage of the forward converter 1 is supplied to the inverter 13 without power loss. In this state, the operation command switch (not shown) is turned on, and the capacitor 2 is connected to the inverter 13. Apply the output voltage,
There is one in which an inverter 13 is used to convert the power into alternating current power at a predetermined frequency.

Note that the rectifier 14 is for generating a low voltage power supply for operating the control circuit parts such as the comparator 7, and the DC voltage converted here is stabilized by the voltage regulator 15 and used for the comparator 7 etc. Supplied to the circuit section.

[Problem that the invention seeks to solve]

However, in the configuration shown in FIG. 2, the ON conditions for the operation command switch are not regulated in any way by the circuit, so if the power switch 16 is turned on while the operation command switch is in the ON state, the inverter 13 is turned on at the same time. state, and the capacitor 2 is no longer charged to the predetermined voltage.

For this reason, the charging voltage of capacitor 2 is not established either, so 5
CR12 is also not turned on, and DC power is continuously supplied to inverter 13 via charging resistor 11. As a result, a problem occurred in that the short-time rated charging resistor 11 was burned out.

[Means for solving problems]

The present invention solves the above-mentioned problems.In order to prevent the charging resistor from burning out, the present invention provides a switching element that is activated when the charging voltage of the smoothing capacitor reaches a predetermined value. Conduction of element ζ: Therefore, the charging resistor is short-circuited, and an interlock is provided to establish the high voltage of the smoothing capacitor within the operating conditions given to the inverter.

[Effect]

The operation command is interlocked until the charging voltage of the smoothing capacitor reaches a predetermined value, so even if the operation command switch is left on, the inverter will not immediately go into operation when the power is turned on. It's gone,
Burnout of the charging resistor is prevented.

〔Example〕

Hereinafter, the present invention will be described in detail based on illustrated embodiments. ” Figure 1 is a circuit diagram showing one embodiment of the present invention, and the same parts as in Figure 2 are represented by the same symbols.Although Figure I!1 describes the case where a relay is used, relay contacts are used. It may be replaced with a switching element.In the lEi diagram, the normally open contacts 88P& of the relay 88F are connected to both ends of the charging resistor 11.Using the input side voltage of the relay 88Ptf forward converter 5, the relay RY is connected to both ends of the charging resistor 11. When the normally open contact RYa is closed, the normally open contact 88Pa is connected to both ends of the charging resistor 11, and the normally closed contact 88Pb is connected in parallel to the smoothing capacitor 2. It is connected to open the connected discharging resistor 17.The relay RY that operates this relay 88P is connected so that the charging voltage of the smoothing capacitor 2 is connected to the resistor 5.
When the voltage exceeds the reference voltage vR determined by 6, the output signal of the comparator 7 is manipulated so that the transistor 18 is turned on. The operation sequence circuit 19 serves as an operating condition for the normally open contact RYaH17 relay 88P, and also as an interlock condition for the operation command signal together with the normally closed contact RYbH abnormality detection signal ALM.
(Anto-game) 20.

Here, as operation commands, since the induction motor 21 is connected to the inverter 13, a forward rotation command, a reverse rotation command, and a zero run command are input to the operation sequence circuit 19, and the logical sum signal of these is input to the AND gate 20. It is configured such that it is input as an operation command signal for the inverter 13 only when the interlock is released by the abnormality detection signal ALM or the relay RY.

Therefore, in this unconventional configuration, the smoothing capacitor 2
Until the charging voltage reaches a predetermined voltage, the relay RY does not operate, the input signal of the controller 20 becomes "L" level, and no operation command is output.

However, when the predetermined voltage is reached, the input signal of the AND gate 20 becomes "H" level, passes through the AND gate 20 as an operation command signal, and is applied to the inverter 13.

At this time, the relay 88P also operates, and both ends of the charging resistor 11 are short-circuited by the contact 88Pb, and the resistor 17 connected to both ends of the capacitor 2 is opened by the contact 88Pb. .

This causes the inverter 13 to start a reverse conversion operation. At this time, both ends of the resistor 11 are short-circuited to the contact point 39Pa, so that power loss is suppressed and the charging time is shortened.

In this way, in this embodiment, the operation command signal is interlocked until the charging voltage of the smoothing capacitor 2 reaches a predetermined value, so even if the operation command switch remains on, the power can be turned on. As a result, the inverter 13 does not immediately enter the operating state, and the charging resistor 1
1 burnout is prevented. In addition, a semiconductor switching element such as an SCR may be used as the relay contact in the above embodiment in order to achieve a non-contact state.

〔Effect of the invention〕

As explained above, according to the present invention, the operation command signal is interlocked until the charging voltage of the smoothing capacitor reaches a predetermined value. Therefore, even if the operation command switch is turned on until t, the inverter does not immediately go into operation, the charging resistor is prevented from burning out, and maintainability and safety are improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing a conventional circuit. ■... Forward converter, 2... Smoothing capacitor, 7...
- Comparator, 11... Charging resistor, 13... Inverter, 19... Operation sequence circuit, 20... AND gate, RY. 88P...Re-shi-.

Claims (1)

[Claims] The DC output voltage of the forward converter is charged to a smoothing capacitor via a charging resistor, and when the charging voltage reaches a predetermined value, the charging resistor is short-circuited and reverse conversion is performed based on the operation command. A switching element that operates when the charging voltage of the smoothing capacitor reaches a predetermined value in an inverter control circuit that applies the charging voltage of the smoothing capacitor to the inverter that starts operation and converts it into AC power of a predetermined frequency. An inverter control circuit configured to short-circuit the charging resistor and release an interlock of an operation command given to the inverter by conduction of the switching element.