SU650185A1 - Ac power-to-dc power converter - Google Patents

Description

one

This invention relates to electrical engineering for the conversion of electrical energy.

Converters of alternating current energy to direct current energy 12 are known.

The first ones do not provide output voltage regulation. The latter have a wide range of regulation, but with deep regulation they have low energy-economic indicators.

Also known asymmetrical controlled six-pulse bridge units 3.

The known unit contains a three-phase transformer, the secondary windings of which are connected to incompletely controlled rectifying bridges, which are connected in parallel through equalizing reactors.

A disadvantage of the known converter is that regardless of the required control range for it, it is necessary to include in each bridge at least three thyristors.

This leads to high costs and large conversion losses.

The aim of the invention is to improve the energy-economic indicators with partial regulation.

To do this, the bridges are combined into two parallel groups of three bridges each, with the thyristors in the first group one in order of phase alternation in the anode arms, and the other in cathode arms, in order of alternation of phases in each group two thyristors in the anode and cathode shoulders.

FIG. 1, 2 shows circuits of thyristor semi-phase control units, differing in their range of adjustment. The circuit of FIG. 1 allows for an adjustment range of 17% Ed (20 - 25% Ud), the circuit of FIG. 2 - 33% Ed (40% Ud). FIG. Figure 3 presents the most important oscillograms of currents and voltages of aggregates with a semi-phase control.

Conversion units (Fig. 1 and 2) contain the transformer 1, in which the number of secondary windings can be varied so that it is a multiple of two or six; three-phase bridges 2-7, connected in parallel in two groups of three bridges, and in the diagram of FIG. 1 in the upper group in the bridges the thyristors are arranged one by one in the order of phase alternation in the anode arms, and in the lower group - in the cathode arms; in the scheme of FIG. 2 in the bridges of each group in the order of phase alternation, two thyristors are included in the anode and cathode arms; equalization reactors 8 and 9, which, respectively, unite the anode and cathode arms of the upper and lower groups of bridges; In addition, the circuit (Fig. 2) contains reactors 10 and 11, which, respectively, combine the cathode & 1e and the anode arms of the upper and lower groups of bridges; reactors 12 and 13 are needed to equalize the instantaneous voltage of parallel operating groups when transformer 1 has two secondary windings.

Each bridge of the unit contains a gap of valves 14-19, the numbering of which corresponds to the following alternation of semi-phases 14-a; 15-b; 16 s; 17 - / - / a; 18- / - / b; 1944 p.

The rectifier assembly (according to the scheme of FIG. 1) operates as follows.

The unit thyristors, evenly distributed between all the half-phases of the three-phase system, are pulsed with an angle delay, a, varying from 0 ° to 120 °.

When the unit operates as uncontrolled, the unit voltage is greatest and equal to:

Ua, l, l7 (J, (l + osi),

where t / do is the voltage of the aggregate during a half-half course; f / 2 - phase secondary voltage

transformer; 7 - angle switching valves. When thyristor ignition is delayed in the voltage curve of each bridge, characteristic dips arise at the site corresponding to the operation of each thyristor. FIG. Fig. 3a shows the oscillogram of the voltage of bridge 2. It shows that the cathode group of diodes works almost in the usual key of the non-controlling bridge, the angle of the valves (120 ° -1-7). The work of the anode group, containing the thyristor, is subject to a different law, in accordance with the peculiarities of semi-phase control. In the anode group, instead of the delayed thyristor, at the beginning, diode 16 works, delaying its burning by 60 °, then diode 15 lights up with 60 ° ahead. If the angle ai; 120 °, valve 15 interrupts its operation during the burning time of the thyristor proportional to the angle (120 ° -KI).

Reactors 8 and 9 equalize the voltages of their groups in such a way that two constant voltages arise, shown in FIG. 36, the envelopes of which pulsate in different phases. Applying the voltage of the groups to the common tires, we obtain the voltage of the aggregate shown in FIG. 36 in bold line.

The equalizing current in this case is limited in the unit (Fig. 1) by the inductive resistance of the windings of the transformer 1, in the unit (Fig. 2) by the inductive resistance of the transformer and reactors 12 and 13.

It can be seen in FIG. 36 that the diaphragm control Af / i in the process of semi-phase control is not equal to the difference t / d, and f / ds is the voltage of the unit with n type-phase course (). It is equal to:

L „. ±, 00, (, 7-25).,

101-0,577 /

where is the relative magnitude of the load current.

A large percentage of the adjustment range corresponds to large load currents. 15 In FIG. Zv shows the oscillograms of currents in gates 14-19 of bridge 2. It is seen from the oscillograms that, ahead of its natural ignition time, diode 15 lights up. This leads to a reduction of the reactive current and to a forced decrease in the effective value of the current consumed from the network when constant load current of the unit. FIG. 3G shows the waveform of this current at, ai-

5; 120 °. It indicates that in the process of semi-phase control, the amplitude of the primary step to the step decreases by 6 parts so that when the pulse shape becomes canonical and the amplitude is Ve the load current, the value of which is unchanged by reducing the load. This current evolution with decreasing voltage guarantees high power factor values.

5 and the efficiency of the aggregates according to the scheme of FIG. 1 and FIG. 2. At the same time, the shift coefficient at the end of the adjustment range is equal to the initial one and, consequently, 4-5% higher than that of the prototype, and the ripple of the rectified voltage of the unit according to the scheme of FIG. 1 at the end of the adjustment range is 4-5 times lower than that of the prototype with an equal voltage.

The unit according to the scheme of FIG. 2 has two stages of adjustment. First floor completely

5 coincides with the operation of the unit according to the scheme of FIG. 1. The second stage begins when the first group of thyristors (black) is locked, the voltage of the unit is lowered. With the subsequent gradual locking of the second group of thyristors in the voltage curve of the bridges, along with the existing positive half-phase, the second characteristic symmetric dip will grow negative half-phase.

5 In FIG. The rear shows an oscillogram of the voltage of bridge 2, fig. 2 at the second stage of adjustment, ai 120 °; 60 ° a2 120 °. Since the instantaneous voltage of the cathode arms of the upper group and the anode arms

0 the lower group of bridges became different, these shoulders are united through equalizing reactors 10 and I.

The voltages of the groups fed through equalizing reactors 12 and 13 of the aggregate, adding up according to the law of the average, form the voltage of the aggregate. The envelope of this voltage will correspond to the "bold curve in fig. 36, and the average value is less than the voltage of the uncontrolled bridge by Af / 2

A. - ° ;, 100 (33 - 40)%.

1 - (}, 01 / i

As can be seen from the waveform of FIG. The second stage of adjustment, the diodes adjacent to the second group of thyristors (whites), will start burning alone, but not more than 60 °, others will tan 60 ° ahead, i.e. they will behave the same way as considered groups of diodes adjacent to black thyristors when changing “1. Therefore, the primary current of the transformer 1 of the unit of FIG. One more step will be reduced by a step by 1/6 of the load current so that at 2 120 ° the pulse shape will become canonical and the amplitude will be 4/6 of the load current, the magnitude of which due to the change in load resistance is unchanged.

Such an evolution of the current with decreasing voltage in the first and second stages of regulation ensures high values of the power factor and efficiency of the unit according to the scheme of FIG. 2 over the entire adjustment range.

The pulsation of the rectified voltage of the aggregate (Fig. 2) at the end of the adjustment range remains many times lower.

Work units (Fig. 1, 2) is impossible without leveling reactors. The power of each reactor, equivalent to a double-winding transformer, must be greater than or equal to 0.04 to 5t, where Sn is the rated power of the transformer.

In the aggregates of FIG. 1, 2 thyristors work under light conditions both in terms of acting reverse voltage and

current, as they reduce the duration of their burning from nominal to zero. Diodes, in contrast, are additionally loaded. In the diagram of FIG. 1 by 1/6, and in the diagram of FIG. 2 - on / s part of the load current. Taking into account the higher reliability and lower cost of diodes, it should be recognized that the redistribution of the load is beneficial.

Claims (3)

1. An AC-to-DC energy converter containing a three-phase transformer, the secondary windings of which are connected to incompletely controlled rectifying bridges, which are connected in parallel through equalizing reactors, in order to improve the energy-efficiency indicators with partial regulation, the bridges are combined into two groups of three bridges each, and in the first group of bridges the thyristors are located along one in the order of phase alternation in the anode arms, and the second in the cathode arms. 2. A converter as claimed in Claim 1, characterized in that in the bridge of each group, in order of phase rotation, two thyristors are included in the anode and cathode arms. Sources of information taken into account in the examination 1.F. I. Kovaleva et al., Semiconductor rectifiers of the semiconductor, M., Energie, 1967, with. 104-105. 2.Sh. M. Razmadze, Conversion Schemes and Systems, M., Higher School, 1967, p. 173. 3. I. M. Chizhenko et al. Fundamentals of transformative technology, M., Higher School, 1974, p. 159. A li l /// l Current nepStmou 1 aase, a