JPS61161970A - Inverter control power source - Google Patents

Abstract

PURPOSE:To eliminate a special overcurrent protecting circuit and an irregular magnetization preventing circuit by selecting the capacity of a coupling capacitor to limit the primary current of an output transformer to the degree not exceeding the current capacity of a switch element at load shortcircuiting time. CONSTITUTION:An inverter 19 is connected with an input side rectifier 2. The inverter 19 has a pair of switch elements 15, 16 provided between the rectifier 2 and an output transformer 20, and coupling capacitors 17, 18. A smoothing condenser 3 is provided between the inverter 19 and the rectifier 2. The capacities of the capacitors 17, 18 are selected to limit the primary current of an output transformer in the degree of sufficiently outputting to a rated load but not exceeding the current capacity of the elements 15, 16, at load shortcircuiting time.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is applicable to a wire feeding motor of an arc welding machine, which starts and stops frequently, and which has a high frequency of short-term load short circuits (motor lock). The present invention relates to an inverter control power supply suitable for variable speed drive of a high speed DC motor.

- [Background of the Invention] In recent years, with the adoption of inverter control for arc # ground power supplies, welding transformers have become smaller and lighter, with a rated capacity of about 20 mm and about 7 to 9 pounds, but the accompanying wire feeding Conventional thyristor control is used in the motor drive circuit, and even with a rated capacity of about 5.150VA, the weight of the step-down transformer is about 4KF. For this reason,
Inverter control is also being considered to reduce the weight of the wire feed motor drive circuit. However, wire feed motors frequently start and stop, and short-term load short circuits (motor locks) occur frequently. Various protection circuits are required to protect the inverter's switching elements from overcurrent and to prevent polarized magnetization of the output transformer due to unbalanced on-time of the switching elements. The significant cost increase compared to systems using transformers and thyristor control was an obstacle to practical application.

[Object of the Invention] An object of the present invention is to provide an inverter-controlled power supply that can operate stably with a simple configuration that does not require a special overcurrent protection circuit or biased magnetization prevention circuit.

[Summary of the Invention] As shown in FIGS. 1 and 2 corresponding to embodiments, the present invention provides a pair of transformers that are alternately turned on and off between the input side rectifier circuit 2 and the output transformer 20. In an inverter-controlled power supply having an inverter circuit 19t constituted by a switching element 15.16 and at least one coupling capacitor 17, 18.29, a smoothing circuit is provided between the inverter circuit 19 and the input rectifier circuit 2. A capacitor 3t is provided separately to generate sufficient output for the rated load, and when the load is short-circuited, the switching element 15.
The coupling capacitor 17.
It is characterized by having a capacity of 18.29 mm.

[Embodiment of the Invention] FIG. 1 shows an embodiment of the present invention used as a power source for driving a wire feeding motor of an arc welding machine.

In FIG. 1, 1 is a three-phase AC power supply, 2 is a rectifier circuit that converts AC input into DC, 3 is a smoothing capacitor, 4 is an inverter circuit for a welding power source that converts the DC output of the rectifier circuit 2 into high-frequency AC, 5 is a welding transformer, 6 is a rectifier on the output side of the welding power source, 7 is a DC reactor, 8 is a current supply chip,
9 is a welding wire, 10 is a wire feed roller, 11 is a wire feed motor, 12 is a base metal, and an arc 13t is formed between the welding wire 9 and the base metal 12.

14 is an inverter-controlled power source for driving the wire feed motor, and a half-bridge type is formed by switching elements (transistors) 15, 16 and coupling capacitors 17, 18 connected between the input side rectifier circuit 2 and the output transformer 20. An inverter circuit 19 is configured. 21 is a short circuit protection fuse for the inverter circuit, 22 is an output side rectifier of the inverter control power source, and 24 is a current limiting resistor for the motor circuit. The wire feeding speed setting signal from the wire feeding speed setting device 25 and the rotational speed signal from the tacho generator 26 are compared in an error amplifier 27, and a control signal is generated from the pulse width controller 28 in response to the amplified signal. switch elements 15 and 16 so that the rotation speed corresponds to the setting signal.
t - Alternately turns on and off to control pulse width.

In this example, the rectifier circuit 2 is smoothed by the capacitor 3.
The capacitors 17 and 18 are charged by the DC output voltage, and when the switch element 15 is turned on, a current flows from the upper side to the lower side in the primary side of the output transformer 20 due to the voltage of the capacitor 17, and then the switch element 15 is turned off. Switch element 1
When 6 is turned on, current flows towards the voltage of capacitor 18.

Capacitance t-C(:F) of capacitor 17.18, input voltage t-EC'l, switching frequency t-f CH@)
Then, the maximum output of this inverter circuit and the transformer
The maximum current on the next side is given by Maximum output = CEf (W) (1) Maximum current - CEf (A) (2), both of which are given by the capacity of the capacitor 17*18 Determined by

In the conventional general half-bridge inverter circuit,
Since the capacitors 17 and 18 are large-capacity electrolytic capacitors that also serve as DC input smoothing, if an overcurrent protection circuit is not installed to detect and cut off overcurrent in the inverter circuit, it may cause problems when starting the motor or when the load is short-circuited. However, in this embodiment, a smoothing capacitor 3 is separately provided between the inverter circuit 19 and the input rectifier circuit 2, and the coupling capacitors 17, 18 are The capacity is such that the maximum output shown by equation (1) is sufficiently large compared to the rated capacity of the wire feeder 11, and even if the maximum current shown by equation (2) flows, the switching elements 15 and 16 are The value was set so that it would not be destroyed. Specifically, when driving a motor with a rated capacity of about 150 W, for example, in a conventional half-bridge inverter circuit, when the DC input voltage is 270 V and the switching frequency is #i, the capacitance of capacitors 17 and 18 is 1. 2.27J
In this embodiment, the gold capacitor, which used to be about F, is replaced with a film capacitor having a small capacity of about 0.022 μF, which can sufficiently withstand charging and discharging at the switching frequency.

With this configuration, the necessary power can be supplied to the wire feeder 11 during normal operation, and the capacitor 17 can be supplied when the motor is started or when the load is shorted due to motor lock.
．． 18 acts as an impedance to limit the transformer-order current, and can prevent destruction of the switching elements 15 and 16 without providing a special overcurrent protection circuit. Furthermore, even if the ratio of the on-time of the switch elements 15 and 16 changes due to pulse width control, for example, if the on-time of the switch element 160 becomes longer, the charging voltage of the capacitor 18 will decrease.
If the on time of the switch element 16 becomes shorter, the capacitor 1
Since biasing of the output transformer 20 can be prevented by increasing the charging voltage of the output transformer 8, a special biasing prevention circuit is not required.

In addition, when used as a power source for driving a wire feed motor attached to an inverter-controlled welding power source as in this embodiment, the input side rectifier circuit 2 and smoothing capacitor 3 can be shared with the welding power source, so the circuit Gold can be further simplified.

Next, another embodiment of the present invention shown in FIG. 2 will be described. This embodiment includes a pair of switching elements 15 and 16 that are turned on and off alternately, and these switching elements and an output transformer 2.
In this case, as well, as in the embodiment shown in FIG. , reduce the capacitance of capacitor 29, ! By separately providing a large-capacity smoothing capacitor 3t on the current input side, a special overcurrent protection circuit or bias prevention circuit can be omitted. However, in this case, the capacitance of capacitor 29 must be twice that of capacitors 17 and 18 in FIG. 1 for the same output.

[Effects of the Invention] According to the present invention, it is possible to drive a welding wire feed motor, etc. with a high MU, which frequently starts and stops and causes load short circuits, without the need to provide a special overcurrent protection circuit or unbalanced magnetism prevention circuit. An inverter-controlled power source with a simple and inexpensive configuration that operates stably even when used is obtained.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of one embodiment of the present invention used as a power source for driving a wire feeding motor of an arc welding machine, - Fig. 2 is a circuit diagram showing only an inverter control power supply of another embodiment of the present invention. be. 2... Input side rectifier circuit, 3... Smoothing capacitor, 15.16... Switch element, 17.18, 29
...Coupling capacitor, 20...Output transformer. $l th

Claims (1)

[Claims] In an inverter-controlled power supply having an inverter circuit comprising a pair of switch elements that are alternately turned on and off and at least one coupling capacitor between an input side rectifier circuit and an output transformer, the inverter circuit and the input A smoothing capacitor is installed separately between the side rectifier circuit,
The capacitance of the coupling capacitor is selected so as to generate sufficient output for the rated load, and to limit the primary current of the output transformer to an extent that does not exceed the current capacity of the switching element when the load is short-circuited. Inverter controlled power supply.