CS223433B1 - Connection of the transformer mainly for capacitous semiconductor converters - Google Patents

Abstract

The object of the invention is to connect a transformer for power semiconductor converters which uses the attenuation properties of the transformer for frequencies higher than working. It is an object of the present invention to provide at least one of the following side of the transformer is immediately on start of phase coil winding connected a capacitor interference suppressor, connected to, for example, a star or triangle, or is in common a star conductor and another ground capacitor are connected.

Description

(54) Transformer start-up, especially for power semiconductor converters

It is an object of the invention to provide a transformer for power semiconductor converters that utilizes the attenuation properties of the transformer for frequencies higher than the operating frequencies. It is an object of the invention that at least one side of the transformer is connected directly to the start of the winding of the phase coils by a transistor suppression element formed by capacitors connected for example in a star or delta, or another capacitor is connected between the star.

The invention relates to a transformer circuit, in particular for power semiconductor converters.

The operation of power semiconductor devices generates interfering voltages whose magnitude greatly exceeds the permissible interference limits.

For the suppression of semiconductor devices, an LC filter in L, T or A cell design, usually connected to mains leads, is usually used. The chokes, which are the necessary and most expensive part of the filter, are comparable in size and weight to the size and weight of the interference suppression device itself.

If current-compensated chokes are used, the size and weight of the filter is greatly reduced, but its cost increases. In addition, due to the high attenuation requirements, a filter with only one filter can be sufficient in some cases.

Some power converters include a power transformer that is either located in the same cabinet, switchboard, or spatially separated from it. In these cases, the interference suppression is done so that the filter is connected upstream or downstream of the transformer. This method of suppressing the transducer has the advantage over the above-described ones that the presence of a transformer increases the suppression of interference voltages in the 0.15 to 30 MHz band by about 10 dB, but the suppression device remains as bulky. Another disadvantage is that there is a loss of energy on the chokes. The attenuation of the power supply transformer for frequencies higher than the working ones results from its physical properties and from the fact that the parasitic inductances and capacities of the transformer start to affect the signal transmission at higher frequencies.

These drawbacks are largely eliminated by the connection of the transformer, in particular for the power semiconductor converters according to the invention, characterized in that at least on one side thereof a transverse interference suppression element formed by capacitors is connected immediately to the start of the coil windings.

Alternatively, the capacitors of the suppressor element are connected in a star such that each of the capacitors is always connected between the start of the phase coil winding and the input / output terminal of the transformer and the neutral. An additional capacitor is connected between the common point of the star-connected capacitors and the ground terminal.

In a further alternative, the capacitors of the suppressor element are connected in a triangle so that each one is connected between the start of two adjacent phase coils and the input and output coils respectively. transformer output terminals. In another possible connection of the transformer according to the invention, the capacitors of the suppressor element are connected both in the star and in the delta.

The main advantage of the transformer connection, especially for the power semiconductor converters according to the invention, lies in the simplification of the whole interference suppression regulation of the converter, because by using the attenuation properties of the transformer the interference filter becomes a part of it. At the same time, the entire device is less bulky and lighter in weight compared to the device hitherto used.

Furthermore, it is advantageous that the capacitors form a cell with a substantially higher resonant frequency than with the independently connected filters, with the leakage inductance of the transformer L or λ.

Fig. 1 is a schematic diagram of a transformer for explaining its attenuation function for frequencies higher than working, and Fig. 2 is a schematic diagram of a transformer according to the invention.

FIG. 1a shows, for comparison, a known transformer circuit diagram whose individual elements are applied at lower (operating) frequencies. The diagram consists of a voltage source with an internal resistance Ri and a series connected resistor and an inductance of the primary winding R _l1 and L _b with a magnetic resistor R _m connected in parallel to the inductance of the primary winding. Similarly, the resistance and inductance of the secondary winding p ² Rv2 (where p is the transformer ratio) and L ^{2 are} connected in series on the secondary side. A load resistor R2 is connected in parallel. Mutual inductance M is considered between the primary and secondary windings.

Fig. 1b shows a replacement scheme of a higher frequency transformer consisting of a parallel combination of an internal resistor R1 and a spare capacitor Ci with a primary winding capacity of a ground and a parallel combination of a load resistor R ₂ and a spare capacitor C ₂ with a secondary winding capacity of a ground , wherein the two parallel combinations are connected via a further series-parallel combination formed by the series connection of resistance and leakage inductance of the primary winding R _L and L _s i, resistance and leakage inductance L ² RV2 and IS2 / P ² to which is connected in parallel spare capacitor C12 with a capacity between the primary and secondary windings.

Fig. 1c is a simplified replacement diagram of the transformer for determining its attenuation, which consists of an internal resistance R _{b of the} total resistance R, a total dissipation inductance L _s and the resulting replacement capacitor C with a total capacity.

Fig. 2 shows a circuit diagram of a three-phase transformer according to the invention.

The transformer T input terminals are labeled 1, 2, 3, and the output terminals connected to the drive input N are Γ, 2 ', 3'. Immediately at the start of the phase winding coils Ii _{f of the} primary winding, a transverse suppression element is formed, in this case consisting of a star-connected suppression capacitors C _u and a _delta- connected suppression capacitors Ci _d . Similarly, immediately at the beginning of the phase coils L _{£ 2} of the secondary winding is connected in a cross interference suppressor member comprising a back suppressors and capacitors _C2 connected in star and the interference-suppression capacitors C _2d connected in delta. An additional interference suppression capacitor C _pl is connected between the common point of the interference suppression capacitors C _1f on the primary side of the transformer T and the ground terminal, and similarly on the secondary side the interference suppression capacitor C _p2 is connected. To explain the function of the transformer in the higher frequency range, we start from the substitution scheme shown in Fig. 1. In the higher frequency band, the magnetic flux of the transformer decreases to such an extent that the magnetization inductance is negligibly small compared to the scattering inductance L _s . Due to the decrease of the inductive coupling, the basic relationship determining the transformer ratio is no longer valid

where

Ul is the primary stress,

U2 is the secondary voltage, and starts to apply _by _ ^υ Ί _ _ 5 «2 _

The insertion loss b _h in this band consists of the attenuation b ^ _L caused by the scattering inductors L _s and the attenuation bh _C caused by the winding capacities, i.

h = bt ^{b b} hhL hc log

Rf R uC

R _t ^R r ~ 7r

2+ 2

This implies that the attenuation of the transformer for the higher frequency range can be increased by increasing its dissipation inductances and parasitic capacitances to ground. An increase in stray inductance is generally not desirable to increase losses in the normal operating mode, while increasing the parasitic capacitances to ground will not affect the normal operating mode, but can greatly increase transformer attenuation.

Said transformer attenuation properties can be utilized to reduce the interference generated by the semiconductor converters by the arrangement of the invention. This circuit is characterized in that the suppression capacitors L _1f , respectively.

l _2f , eventually L _id , resp. _12d are located directly on the winding terminals of the transformer, being an integral part thereof, and located inside the vessel. At the same time, the connection points of the capacitors need not only be at the end points of the winding, but also with respect to the availability of capacitors with a corresponding breakdown voltage, these connection points can also be at the tap winding of the transformer. The capacitance value of the suppression capacitors is determined from the transformer stray inductors that replace the filter inductance and the desired attenuation.

Claims (5)

SUBJECT Transformer connection, in particular for power semiconductor converters, characterized in that transistors (C _1f , C _2f or Cw, respectively Cw) are connected immediately to the start of the winding of the phase coils (Lif or L _2f ) at least on one side thereof. and C _2d , respectively). Transformer connection according to claim 1, characterized in that each of the suppression capacitors (Ci _f and C ₂ fj, respectively, is connected between the start of the winding of the phase coils (L _1f and L _2f and the input (1, 2, 3j, respectively the transformer output terminal (Γ, 2 ', 3') and the neutral. 3. Connection of the transformer according to claim 1 or 2, characterized in that between the common point odVYNÁLEZU rušovacích capacitors (C _lf, resp. C _2f) connected in star and the ground terminal is connected further suppression capacitor (C _L, respectively. C _p2 j. Transformer circuit according to claim 1, characterized in that each of the suppression capacitors (Ci _d and C _2d j, respectively) is connected between the winding starts of two adjacent phase coils (Lu and L _2f , respectively) and the input (1, 2, 3), respectively the output (Γ, 2 ', 3'j of the transformer terminals). Transformer connection according to claim 1, characterized in that the suppression capacitors (Cif and C ₂ f, respectively) are connected in a star and the suppression capacitors (C _1d and C _{2d respectively} ) in a delta.