SU680121A1 - Direct frequency converter - Google Patents

Description

one

The invention relates to a converter technique, namely to direct thyristor frequency converters.

Direct frequency converters with current-limiting chokes are known.

at the input or at the output of the converter 1.2,

A disadvantage of the known converters is that in order to limit the starting and emergency currents during the operation of the converter on the motor, the inductance of the input chokes must be calculated from the conditional allowable rate of increase of the emergency load currents. On the other hand, the inductance value in the input circuits of the converter cannot be chosen sufficiently large, since it is limited by the admissible angle of overlap of the converter valves and the switching losses in them. In addition, at high power of the converter, the input voltage losses begin to play a significant role, and during the operation of the converter with forced switching, the phenomenon of so-called pumping

voltage on the switching capacitors of the forced switching devices.

Therefore, when a sufficiently large inductance is included in the input circuits of the converter, it always tends to exclude adverse side effects. For example, in the three-phase inverter circuit shown in 2, the input chokes are connected in series with each of the six thyristors, and the chokes included in the reciprocating valves are magnetically coupled. In this case, part of the magnetic energy accumulated in one of the chokes prior to switching enters the other choke at the time of switching and after it.

Claims (1)

Such an input choke switching circuit makes it possible to slightly increase the inductance of the input chokes. Odaako it would be most expedient to use inductors of the converter such chokes, the value of inductance of which in emergency and start-up modes of operation could increase sharply nci compared to inductance in normal mode of operation. The closest in technical essence and the achieved result is a converter, which consists of connected to the input terminals through the main windings of three-phase current limiting throttle valve bridges magnetically interconnected, forming the output terminals of the converter 3 with their inputs. However, the known converter has the same disadvantages listed above. the invention is the improvement of the technical and energy performance of the converter. For this, the current-limiting sleep choke is an additional winding that is connected to the additional input DC source and its magnetizing force is directed oppositely to the magnetizing force of the main windings of the Drossels. FIG. 1 - presents the proposed generator; Fig. 2 shows the curve of a namapichi lcd ferromagnetic core of a drossel. The converter consists of a thyristor switch 1 in the form of three valve bridges consisting of thyristors 2-7 of one bridge, and a current-limiting drossel 8, the choke 8 consists of the main windings 9-11 and an additional demagnetizing windings 12 placed on one ferromagnetic core, windings 9, 10, and 11 are connected to the corresponding anodic and cathodic groups of gates, bridges, and the leads from their midpoints are connected to the input pins of the converter. The demagnetizing winding 12 is connected to the source of a constant current 13, the principle of the device is that when direct current flows through the ra magnetizing winding 12 in the ferromagnetic core, the demagnetizing force (N razm) directed towards the magnetizing current of the load (N, is applied, and we will have a drop (≤ razm) opposite to the magnetizing load current (N). expanding it by the magnitude of the magnitude of the nascene force (Nnas) - In this case, the heart of the throttle will be saturated in the opposite direction in the entire range of variation of the load current of the converter. However, as soon as the load current (Ngr) exceeds a certain maximal value and the resulting magnetizing force (Nrez) turns out to be less than the magnetizing saturation force (), the core will become dissatisfied. At the same time, the dynamic magnetic permeability will increase tenfold (the operating point will move to the straight line section of the magnetization curve), which will sharply reduce the rate of current increase in the windings 9-11, For example, for electrical steel E-330 with a change from H 5000 a / m to H 1000 a / m dynamic magnetic permeability increases 85 times and the inductance of throttle accordingly increases. Thus, it can be seen from the above that the current-limiting choke, having a demagnetizing winding and operating in the saturation mode, i.e. having a relatively small inductance value in the operating mode, makes it possible to significantly limit the current increase rate in the emergency and start-up modes of converter operation. the limited amount of commutative energy loss and the allowable magnitude of the voltage on the windings, which leads to an improvement in the energy performance of the converters. Claims of the invention A direct frequency converter consisting of main gate windings of three-phase current limiting throttle valve bridges connected to the input terminals through the main windings of the three-phase current limiting throttle, which form their input stresses of the converter, characterized in that, in order to improve the technical and energy indicators, the current limiting choke provided with an additional winding which is connected to an additionally introduced direct current source, the magnetizing power of this winding being magnetized and directed against the magnetizing force of the main windings of the throttles, Sources of information taken into account in the examination of h Proceedings of the meeting on the automated AC electric drive (25-28 May 1955), M, Publisher of the Academy of Sciences of the USSR, 1958, p. 135-136 . 2, For vka Franshsh No. 2239800, H 02 M 7/04, 01.08.73, 3, USSR Author's Certificate No. 450293, cl, H 02 M 5/27, 01 L 1.72. n size L foot j H f1 nose (Rig.2