JPS63194871A - Engine driving type plasma power unit - Google Patents

Abstract

PURPOSE:To stabilize an arc with an AC loaded current quickly responding to the variation in loads by providing the current transformer with the C loaded current of an engine driving type generator as a primary current, rectifying a secondary current of the current transformer and adding it in parallel to the field winding of the generator. CONSTITUTION:At the time of the abrupt increase in a load, the voltage and current characteristic curves of a plasma arc are abruptly changed and a load 5 requests a constant current device 4 for the rapid lift to a load voltage. At this time the current with a set current transformation ratio is induced on the secondary coil by the three-phase current transformer 1a arranged between the armature winding Ar of a generator 2 and a main rectifier 3 and rectified by the auxiliary rectifier 1b of a compensation means. The current rectified by the auxiliary rectifier 1b is fed to a field winding Fg. The majority of the compensation current flowing into a DC power source 6 from a compensation part 1 becomes the field current If to excite the field to magnetize rapidly the field of the generater 2 directly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plasma power supply device used for plasma arc processing, and particularly to a plasma power supply device using the output of an engine-driven generator.

[Conventional technology]

Gas cutting, plasma cutting, etc. are conventionally used as methods for cutting metal.

Recently, plasma cutting using air has been developed and widely used as an alternative to conventional plasma cutting using inert gas as a working gas.

However, the power supplies currently in use for plasma cutting are static types that use commercial power, and are mostly used in factories. In recent years, in order to improve work efficiency, there has been a demand for the development of a plasma power supply device that can be used even at outdoor sites where commercial power sources are not available. In order to supply a stable plasma current as a plasma power supply device for outdoor use, it is necessary to increase the no-load voltage of the conventionally widely used welding generator to satisfy the plasma power supply characteristics and convert it into a plasma cutting generator. It was therefore necessary to make it into a rotary machine driven by an engine.

FIG. 3 shows a circuit of an engine-driven plasma power supply device which is used as a plasma cutting generator by increasing the no-load voltage of a conventional engine-driven welding generator. Reference numeral 2 shown in the figure is an engine-driven generator (hereinafter referred to as a generator), which is composed of a three-phase armature winding Ar and a separately excited field winding Fg. A main rectifier 3 performs full-wave rectification of the output of the power generation a2, and its output is supplied to a chopper type constant current device 4. That is, a chopper type constant current device is connected to the output of the generator 2 to obtain the characteristics necessary for plasma cutting.
This is an engine-driven plasma power supply device that connects the metal to be cut as a load 5 and performs plasma cutting work outdoors. As a general circuit of the chopper type constant current device 4, the one shown in FIG. 4 is used. The chopper type constant current device 4 of this plasma power supply device includes a capacitor C charged by a DC charging current supplied by full-wave rectification of the AC output of an engine-driven generator, and a transistor Tr for switching the charging current of the capacitor C. The current chopped by this transistor Tr is smoothed by a flywheel diode D and a reactor forming a smoothing circuit and is supplied to a load. transistor T
The operation of r is controlled by a control circuit 4b that compares the feedbank signal of the plasma arc current with the reference signal of the output setting device 4a, and performs constant current control so that the average value of the plasma arc current always becomes the set value. .

[Problem that the invention seeks to solve]

However, as mentioned above, if a conventionally known generator is simply engine-driven to create an engine-driven plasma power supply, unlike generators for lighting, power tools, and welding work, the plasma power supply However, it was found that satisfactory characteristics could not be obtained as an engine-driven plasma power supply device unless the problems that arose regarding the transient characteristics with respect to fluctuations in the plasma arc, which is the load, were improved.

That is, when the distance between the plasma arc electrodes, which is the load, suddenly increases, a transient state frequently occurs in which the constant current device of the plasma power supply device is required to rapidly increase the load voltage in order to maintain the plasma arc. At this time, if the engine-driven plasma power supply device was unable to respond smoothly, the stability of the plasma arc would be lost, significantly impeding work efficiency. The reason for this is that in such a transient state, the corresponding operation of the control circuit in the engine-driven plasma power supply device causes the transistor's 4 duty ratio (TON
/ TON + Tovv ) increases rapidly, so the amount of discharge from the capacitor increases rapidly. As a result, the terminal voltage of the capacitor drops, and in order to replenish this drop, the charging power supply section consisting of the generator and the main rectifier attempts to rapidly increase the amount of charge. However, since the charging power supply section consisting of a generator contains a large inductive internal impedance, there is a delay in the start-up, and the terminal voltage of the capacitor drops below a certain limit, causing instability in the chopper section and the load. This makes it impossible to supply stable output to the

The present invention was created to solve the above problems, and aims to provide an engine-driven plasma power supply device that enables a generator to supply a stable plasma arc current in response to a sudden increase in load. shall be.

[Means for solving problems]

A concrete means for achieving the above purpose is to rectify the output of the generator and use it as input to a chopper type constant current device, and use the output of the constant current device to generate an engine-driven type plasma power device for plasma cutting. An engine characterized in that a current transformer is provided that uses the alternating current load current of the generator as a primary current, and the secondary current of the current transformer is rectified and applied in parallel to the field winding of the generator. The method is to use a drive type plasma power supply device.

[Effect]

By using the above means, changes in the AC load current output from the generator are detected as changes in the detected amount of secondary current of the current transformer, and the field winding of the generator is detected as a change in the detected amount of secondary current. The AC load current quickly responds to changes in the load and maintains the stability of the plasma arc.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing connections of main parts of an embodiment of the present invention,
FIG. 2 shows a static external characteristic curve of the engine-driven plasma power supply device in the example. First, the configuration of an embodiment of the present invention will be explained.

In FIG. 1, 1 is a compensator according to the present invention, and 1a
is a three-phase current transformer which is a current detection means, and lb is an auxiliary rectifier which is a compensation means. 2 is the generator, which is composed of a three-phase armature winding Ar and a field winding Fg. A main rectifier 3 performs full-wave rectification of the output of the generator 2, and its DC output is supplied to a chopper type constant current device 4. 5 is a load device such as a cutting torch. The constant current device 4 includes a capacitor C, a transistor Tr, a shunt H, a reactor, an output setting device 4a, a control circuit 4b, and the like. 6
is a DC power supply for supplying exciting current to the field winding Fg of the generator 2. The three-phase current transformer 1a is arranged between the armature winding Ar of the generator 2 and the main rectifier 3, and its secondary winding is connected to the auxiliary rectifier ib. The DC output full-wave rectified by this auxiliary rectifier 1b is connected in parallel to the field winding Fg with the same polarity as the output of the DC power supply 6.

Now, when the engine is started and the power generator A2 is activated and excited, the generator 2 and the main rectifier 3 supply DC power to the constant current device 4, and the capacitor C in the constant current device 4 is charged. When the operator turns on the switch S, the transistor Tr starts switching and supplies the plasma arc current smoothed by the reactor L and flywheel diode D to the load 5 via the output terminals 4d and 4c. . During operation, the generator 2 and the main rectifier 3 continue to charge the capacitor C to constantly replenish its discharge. When the switch S is set to "F", the switching of the transistor Tr is stopped and the supply of plasma arc current is stopped.

The control wholesale circuit 4b compares the feed puncture signal of the plasma arc current from the shunt I with the reference signal from the output setting device 4a to control the transistor Tr so that the average value of the plasma arc current always becomes the set value. constant current control.

The static external characteristics of the engine-driven plasma power supply device as described above are shown in FIG. Curve a in FIG. 2 is an external characteristic that droops moderately due to the inherent internal impedance of the generator 2, and curve a is a constant current characteristic curve obtained by the constant current device 4 described above. Further, curve C is a voltage-current characteristic curve of a plasma arc. By adjusting the output setting device 4a, a constant current characteristic curve is established, b2. b8. ..., for example, the intersection point P l, P with the curve C2
2. P3. ..., the operating point moves and the plasma arc current increases to 1. , I2°Il, etc.

During the switching stop period of the transistor Tr, that is, in a no-load state, the capacitor C is charged to a no-load voltage corresponding to 10 points. Also, the output setting is 1. ．． 12,1
3. Under steady load conditions such as..., condenser C
are p , 7 , p 2rr , p , respectively
It is balanced at a charging voltage corresponding to s..., etc., and the surplus voltage with respect to the average load voltage is
It is substantially absorbed by the F'' period (Toff).

The operation of the embodiment of the present invention configured as described above will be explained.

As an example of the operation of the engine-driven plasma power supply device, the operation on the constant current characteristic curve b2 when the set value current of the output setter is 12 in FIG. 2 will be described. In the case of a steady load condition, the voltage-current characteristic curve of the plasma arc shows C2 and operates at the intersection point P2 when the output set value current is 12. In this way, when the plasma arc is being used under a steady load condition, that is, under stable conditions, the conditions under which the plasma arc is used may suddenly change for some reason. For example, in a transient state when the distance between the electrodes is suddenly shortened, the fluctuation of the plasma arc current I is
This can be handled by discharging the chopper circuit of the capacitor C and the transistor Tr, and the power generation a2 and main rectifier 3 are in a rest state and do not contribute to the transient characteristics.

On the other hand, in a transient state when the distance between the electrodes suddenly changes and becomes longer, that is, when the load suddenly increases, the voltage-current characteristic curve of the plasma arc suddenly changes from C2 to C7, and the load 5 is connected to a constant current device. 4, change the operating point from P2 to p 21
requires a sudden jump to the load voltage corresponding to . At this time, the three-phase current transformer 1a, which is a current detecting means disposed between the armature winding Ar of the generator 2 and the main rectifier 3, has a current of the set current transformation ratio flowing through the secondary winding. It is induced in the line and rectified by the auxiliary rectifier 1b, which is a compensation means. The auxiliary rectifier 1
The current CT rectified by b is supplied to the field winding Fg.

The compensation current ICT obtained by the compensation section 1 consisting of the three-phase current transformer 1a and the auxiliary rectifier 1b has a waveform completely similar to the charging current tg that charges the capacitor C from the main rectifier 3, and has a magnitude similar to that of the three-phase transformer 1b. A direct current having a magnitude proportional to the current transformation ratio of the transformer 1a can be obtained. When this compensator l is viewed from the field winding Fg of the generator 2, which is a load, the DC power supply 6 is a voltage source, whereas the compensator 1 shows a current waveform similar to the charging current Ig. It is a current source. Most of the compensation current rct flowing from the compensator 1 into the DC power supply 6 becomes a field current If that excites the field, and directly increases the magnetization of the field of the generator 2 rapidly. In other words, in a transient state when the distance between the electrodes suddenly changes and becomes long, the charging current Ig rapidly increases due to the increase in the load current, but on the other hand, the terminal voltage of the capacitor C suddenly drops.This phenomenon can be explained as the change in the charging current [g This makes it possible to quickly detect and increase the field magnetization by increasing the excitation current If.

Due to the above action, the charging current rg which is the output of the generator 2
It is possible to accelerate the rise of the

On the other hand, since the outputs of the auxiliary rectifier 1b of the compensation section 1, which is a current source, and the output of the DC power supply 6, which is a voltage source, are connected in parallel with the same polarity, the compensation section output voltage corresponding to the compensation current ICa is
DC type′j! In some cases, the output current exceeds the output current of X6. At this time, by configuring the DC power source 6 with a reversible DC power source such as a battery or a DC generator, a compensation current of 1. A part of A flows in, the current IB from the DC power supply 6 decreases by that amount, and the field current If becomes the compensation current 1
It does not increase as all of the cT adds up. Therefore, in a steady state, the external characteristic surface vAa of the generator 2 shown in FIG. It becomes possible to obtain.

The present invention is not limited to the embodiments described above; for example, the engine-driven plasma cutting apparatus may be of a multi-phase type other than three-phase type. Multi-phase current transformers are not necessary just because the current transformer is multi-phase; it is sufficient to have a current transformer that can sufficiently respond to transient conditions such as rapid changes in load, and there is no need to insert it in every phase.

〔Effect of the invention〕

As described above, by using the present invention, it is possible to improve the transient characteristics of a sudden increase in output caused by load fluctuations in a plasma power supply device that uses a plasma arc as a load. That is, by detecting fluctuations in the alternating current (AC) load current output of the generator using a current transformer and creating a current source that rectifies the secondary current of the current transformer and supplies it to the field winding, transient conditions can be detected. This improves the time delay in the charging current supplied to the constant current device and maintains the stability of the plasma arc. The present invention, which produces the above-mentioned effects, provides an engine-driven plasma power supply device that allows efficient cutting work at outdoor work sites. Furthermore, the means created by the present invention has a simple configuration and can achieve greater effects than ever before.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the main parts of an embodiment of the present invention, and FIG.
The figure shows a static external characteristic curve of a plasma power supply device in an example. FIG. 3 shows an engine-driven plasma power supply device that is an improved version of a conventional welding generator, and FIG. 4 is a detailed diagram of a chopper type constant current device. Symbols in the figure indicate the following. 1... Compensation section 1a... Three-phase current transformer (current detection means) 1b... Auxiliary rectifier (compensation means) 2... Engine-driven generator Ar... Armature winding Fg...・Kai hn winding 4・
... Constant current device 5 ... Load (plasma arc generating part) 6 ... DC power supply ICT ... Compensation current Ig ... Charging current Fig. 1 Fig. 2 □ connected Fig. 3

Claims (1)

[Scope of Claims] A plasma power supply device for rectifying the output of an engine-driven generator to input it to a chopper type constant current device, and performing plasma cutting with the output of the constant current device, comprising: the engine-driven generator; A current transformer whose primary current is an alternating current load current is provided, and the secondary current of the current transformer is rectified and applied in parallel to the field winding of the engine-driven generator. Engine-driven plasma power supply.