SU1046050A1 - Three-phase rectifier for resistance welding machines - Google Patents

Description

The invention relates to welding. And can be used in contact dc welding machines used in work technicians. A three-phase rectifier for resistance welding machines C 1 is known. The disadvantages of the known three-phase rectifier are the large masses and dimensions of the transformer due to the low switching frequency of the controlled valves, significant ripple of the output voltage, causing uneven current distribution over two simultaneously operating phases and instability of the device, which degrades the quality of welding and increases power consumption. The closest to the invention. is a three-phase rectifier for resistance welding machines, containing an input rectifier connected to an AC mains supply, the output of which is connected to the primary windings of single-phase transformers through serially connected controllable and unmanaged valves, each of which includes a demagnetizing winding and a secondary A winding connected through uncontrolled valves to the three-phase output rectifies. 2, The disadvantage of the known rectifier is the complex structure of the transformer magnetic circuit, which is necessary for the mutual demagnetization of the active rods. This leads to an increase in the size and weight of the device and limits its scope. The aim of the invention is to expand the scope, reduce the weight and size of the rectifier by reducing the time of demagnetization of the magnet tubes of single-phase transformers. This goal is achieved by the fact that in a three-phase rectifier for resistance welding machines, containing an input rectifier connected to an AC power supply network, the output of which is connected through serially connected controlled and non-controlled valves to the primary windings of single-phase transformers, each of which includes a demagnetizing winding and so r a secondary winding connected through uncontrolled gates to the output of a three-phase rectifier, each of the single-phase transformers is supplied with additional and the first and second uncontrolled valves, and each of the demagnetizing windings of the transformer is provided with an additional output, while the cathode of the first of the additional valves is connected to the end of the corresponding demagnetizing winding, the additional cathode of the second additional valve is connected, the windings are connected in series and according to through additional valves, the anodes of which are combined, FIG. Figure 1 shows the principle electrical circuit of the rectifier, Fig. 2 shows the instantaneous values of currents and voltages for the rectifier. The device contains an input relay 1, which is connected to the AC mains, three single-phase transformers 2 each containing one primary 3. one demagnetizing winding and one secondary winding 5. The positive output of the input rectifier 1 is connected to the combined anodes completely controlled valves 6 (for example controlled valves with circuits, artificial switching, the cathode of each of which is connected to the anode of one of the uncontrolled fans 7. Start each of the primary windings 3 but to the cathode of one of the uncontrolled valves 7, and the ends of the primary windings 3 are combined together and connected to the negative output of the input rectifier 1. The ends of the secondary windings 5 of the transformers 2 are combined together, form a common potential point and connected to the first output 8 of the device, and the beginning secondary windings 5 of transformers 2 are connected to each other through uncontrolled gates 9 and connected to the BTOpbiM output of the device 10. Demagnetizing windings k of three ranformators 2 are connected in series and according to gates 11 from each pair of further uncontrolled eveennyh proxy valves. the anodes of which are combined, and the cathode of the valve 11 from each pair of non-controlled valves is connected to the end of one of the demagnetizing windings k, to the additional output of which is connected the cathode of the valve 12 from this pair of uncontrolled valves. FIG. Figure 2 shows diagrams of instantaneous values of currents and voltages on elements. A mitele, the transformer cores of which are made of anisotropic steels with a hysteresis loop rectangularity factor close to 1, FIG. 2 The following symbols are accepted: and - instantaneous voltage value on rectifier 1 (diagram 13), B instantaneous value of flux induction in transformer 2 magnetic circuit (dia1 frame 1 t) in the case of a rectangular hysteresis loop (diagram 15) - branch current transformer 2, reduced to primary windings (diagram 16J, .2jJv, spun on uncontrolled valves 11 and 12 (diagrams 17-20). The device works as follows. The input rectifier 1, when connected to a three-phase mains supply, ensures constant a positive The voltage on the controlled valves 6 and the uncontrolled valves 7 connected to them. Control pulses for opening and closing the previously activated control valves 6 are supplied from the control system alternately through 1/3 of the period corresponding to the selected frequency, and the pulses The locking of the previously turned on valves 6 is applied simultaneously with the supply of the next pulse to the opening of the controlled valve 6 that was not operating in the previous interval of 1/3 of the period. In the steady state, the current from the input rectifier 1 flows in a closed circuit through the controlled valve 6, the uncontrolled valve 7 and the primary winding 3 of each transformer during 2/3 perybda. . The voltage from the input rectifier 1, applied to the primary winding 3 of each transformer 2, provides a continuous unidirectional change in the magnetic flux in its magnetic core during 2/3 of the period (Fig. 2, diagrams 13, 1). h. Continuous unidirectional iz; The flow in the magnetic cores creates a positive voltage on the terminals of the secondary windings 5 connected to the anodes of the uncontrolled gates 9. and a positive voltage on the terminals of the demagnetizing windings connected to the uncontrollable valves 11 (Fig. 2, diagram 19). In the welding circuit connected to the output terminals 8 and 10, the current generated every 1/3 period by two simultaneously working secondary windings 5 of two transformers 2 flows, each 1/3 of the period two demagnetizing windings k with uncontrolled valves 11 two simultaneously operating transformers 2 provide the flow of demagnetization current with the help of valves 12 through part of the turns between the beginning and the additional output of the demagnetizing winding k of the third transformer 2 (Fig. 2, diagrams 16-18). Since demagnetizing windings k are connected in series and according to uncontrolled valves 11, a voltage equal to the sum of the voltages of the two other demagnetizing windings k is applied to the part of the third transformer 2 (Fig. 2, diagrams 13, 19, 20) . The applied voltage causes a continuous unidirectional change in the flux in the magnetic core of the third transformer and ensures the restoration of the magnitude of the induction to its initial state during the period (Fig. 2, diagram 1).

If the transformer cores are made of anisotropic steels, for which the hysteresis loop rectangularity coefficients are close to 1 (Fig. 2, diagram 15), then for increments of inductions in the magnetic circuit for 2/3 of the period, when controlled valves 6 and for 1/3 of the period when the induction returns to its initial state (Fig. 2, diagram H, the equations I (u-Au,) ai I & - - I iuu-.u, -u OiVA where B is the instantaneous value of induction in magnetic conductor, the area of the magnetic conductor cross section; the total number of turns of the delimiting winding, t the enformer j is the number of turns of the demagnetizing winding between the beginning and the additional output; the instantaneous value of the voltage on the rectifier 1, reduced to the full turn of the demagnetizing about, the coils TO is the voltage drop, caused by the loss of copper in the primary resistance of the primary winding f the active resistance of the valves 6 and 7 and the loss in inductance of the scattering of the primary winding, reduced to the turns of the demagnetizing winding, the voltage drop caused by the losses in the active resistance of N turns of the copper, demagnetizes k winding it, in the active gate resistance 11 .i lossy inductor in scattering demagnetizing coil, the voltage drop due to lossy asset prefecture resistance of copper windings N demagnetizing

windings 4, in the active resistance of the valve 12 and losses in the inductance dissipate a part of the demagnetizing winding.

The reduction of losses in the magnetic conductor is achieved by the equality of the increments of the magnetic induction, determined by

equations (1) and (2,

8o

eight.

those. "| V (/ BO /,

from where

4Ku u.u,) dt- | 5iI

11.1 l (U-AU, -A.Ua) (3) of equation (3) determines the ratio of the total number of turns of the demagnetizing winding + to a part of its turns N. Due to the use of single-phase transformers with magnetic cores made of thin-sheet steels with small specific losses at higher frequencies, it becomes possible to increase the operating frequency to values close to 1000 Hz. This rectifier with additional leads connected in series and in accordance with uncontrolled gates ensures the device to operate on private hysteresis reversal cycles of near symmetric ones, which allows working with large induction increments. By increasing the operating frequency from 300 to 900-1200 Hz, the total mass and dimensions of the transformers of the device proposed are reduced in comparison with the transformer of the known device and reach 36-37 kg. The losses in rectifier transformers are 1.7 times less than in TVT-7.16 transformer used in the MTPV-1207 machine (the basic object The manufacturability of the designs of single-phase transformer magnetic cores saves working time in the manufacture of the device; besides, the transformers can be mechanized The simple design of transformers allows the manufacture of three, four, and more phase rectifiers, distinguished by the best use of 7 rectifier valves and active materials. About transformers The listed advantages allow to expand the field of application of the proposed device, since O iSOSO becomes possible to use it in DC welding machines used in work technicians, where the known devices could not be effectively used.

Claims (1)

(57? THREE-PHASE RECTIFIER FOR CONTROL WELDING MACHINES, comprising an input rectifier connected to an AC mains supply, the output of which is connected through series-connected controlled and uncontrolled valves to the primary windings of single-phase transformers, each of which includes a demagnetizing winding and a secondary; connected through uncontrolled valves to the output of a three-phase rectifier, characterized in that, in order to expand the scope, reduce the mass and dimensions of the rectifier by reducing the time of demagnetization of the magnetic cores of single-phase transformers, each of the single-phase transformers is equipped with additional first and second uncontrollable valves, and each of the demagnetizing windings of the transformers is equipped with an additional output, while the cathode of the first of the additional valves is connected to the end of the corresponding demagnetizing winding, to the additional the output of which is connected to the cathode of the second additional valve, and the demagnetizing windings are connected in series and according to clear through additional valves, which combine anodes.