SU762109A1 - Single-phase to three-phase voltage converter - Google Patents

Description

The invention relates to a converter technique and can be used to build secondary three-phase power sources designed for frequency starting and controlling the AC drive in cases where a reduction in mass and size is required, with a rather simple structure of the converter device.

Known converters single-phase voltage, allowing to obtain a three-phase voltage without intermediate DC link.

Known transducer contains three pairs of series-connected keys with two-way conductivity. Each key is made in the form of two parallel-parallel thyristors connected at one end to the common power output, and the other ends of each pair of keys are interconnected through the filter throttle winding, the midpoint of which forms the output output of the converter. Single-phase voltage is applied to the input pins of the converter. The corresponding key control algorithm2

This allows us to form a three-phase voltage at the output of the converter [1).

The disadvantages of the converter are the impossibility of matching the supply voltage of the Output voltage, and also not ₅ which is the complexity of the entire device, consisting in the presence of six keys with two-sided conductivity.

A converter is known that contains a single-phase transformer, the secondary winding of which is connected to a sequentially connected rectifier and filter. The filter output is connected to an inverter cell, one output terminal of which forms one of the output terminals of the converter, and the second is connected to the midpoint of the primary winding of the transformer ¹⁵ torus [2].

The disadvantages of the transducer are the impossibility of controlling the frequency as well as the magnitude of the output voltage, which makes it impossible to use it in an hour20 Goat-controlled electric drive.

Also known converter, which allows to convert a single-phase voltage in the three-phase. This converter contains a single-phase transfer762109

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Matrix operating at the same frequency, the ends of the secondary winding of which are interconnected through three pairs of series-connected, fully controlled clips with two-way conductivity. The points of connection of the keys of each of the three pairs form! output pins convert * la | 3}.

The presence of three pairs (or racks) of fully controlled keys with double-sided conductivity complicates the converter, reduces its reliability, which is a shortage of the above-described device.

The purpose of the invention is to simplify the converter and increase due to this its reliability.

This goal is achieved by the fact that ¹³ in a known converter that contains an input single-phase transformer, the ends of the secondary winding of which are interconnected through pairs of serially connected fully controlled keys with two-sided conductivity and a control unit of these keys, two output converter output, the third output output of converter ^{1 is} formed by the midpoint of the secondary>

'windings of a single-phase transformer, and a sequence of control pulses of pairs of serially connected keys follow from the control unit with a shift of π / 3.

The control unit may include a master oscillator, a pulse distributor in the form of a three-phase counting ring, an output voltage control unit, a logic node, and an amplifier-decoupling node. ,

A logical node can be made containing 3-K trigger, its outputs associated with the corresponding inputs of the 2I-2ILI-NE logic element, to the two other inputs of which the corresponding outputs of the pulse distributor are connected, and its output is connected to the logical element NOT; the input and output of which forms the output pins of the logical node, with 3 — K trigger inputs being the control inputs of the logical node. This embodiment of the logical node allows the reordering of the phase sequence of the converter.

Fully controlled switches with two-way conductivity can be made in the form of valve bridges, to the output DC outputs of each of which are connected a switching capacitor and a chain of series-connected windings of inductance and thyristor. The windings of inductance belonging to the keys of the pairs mentioned are magnetically connected with each other.

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FIG. 1 is a schematic diagram of the power section of a single-phase to three-phase converter (a) and a possible embodiment of the converter using an autotransformer (b) £ in FIG. 2 - schematic diagram of the control unit; in fig. 3 - embodiments of the keys of the converter; in fig. 4 is a circuit diagram of a converter, in which a single-phase supply voltage transformer is formed using

g autonomous voltage inverter (AIN); in fig. 5 - timing diagrams explaining the principle of operation of the converter; in fig. 6 - timing diagrams explaining possible algorithms for controlling the converter keys during regulation

"Output voltage; in fig. 7 - timing diagrams explaining the principle of operation of the converter when adjusting the output voltage; in fig. 8 is a timing diagram explaining the principle of operation of the transducer of FIG. 4. with the regulation of the output voltage in the AIN for the case of a change in the order of the alternation of phases.

The converter of single-phase voltage to three-phase (Fig. 1a) contains an input single-phase transformer 1, the ends 2 and 3 of the secondary winding 4 of which are interconnected through pairs of serially connected, fully controlled switches with two-sided conduction 5,

⁰ 6 and 7, 8, as well as the control unit of these keys (5-8), shown in FIG. 2. Output pins 9, 10 and 11 of the transducer are formed by the connection points of the key pairs 5, 6 and 7, 8, as well as the midpoint

, the secondary winding 4 of the transformer I. The control unit contains a master oscillator 12, a pulse distributor 13,> made on three triggers 14–16 ZK type, on a recalculating three-phase circuit, voltage control unit 17, logic node 18 and amplifying node 19, output pins 20-23 of which are the outputs of the control unit and are connected to the control inputs of the corresponding keys 5-8. Logical

_5, node 18 includes a trigger 24, as well as logic elements 2I-2ILI-NOT 25 and NOT 26. The corresponding inputs of node 17 of voltage regulation are connected to one input of logic element 2I-2ILI-NE 25, and the other inputs are connected to direct and in> These are the output pins of the trigger 24. The output of the logic element 2I-2IL-NE 25 is connected to the input of the logic element NO 26. The outputs of the logic elements 26 and 25 form the outputs of the logic node 18 and are connected to the input terminals of the reinforcing ⁵ decoupling node 19.

FIG. 1 shows an embodiment of the converter when in quality

single phase transformer 1 using5

There is an autotransformer. In this case, the ends 2 and 3 and the output terminal I of the converter are formed by tapping the winding of the autotransformer. The transformer can either lower the supply voltage (see Fig. 1 b) or increase it.

As keys' 5-8 with two-sided conductance, for example, one- or two-operation thyristors, connected in parallel, can be used in parallel, as in FIG. 1 b (switching unit is not _10- cauldron), or keys in the form of diode rectifier bridges with key elements in the DC diagonals. FIG. 3 shows some possible embodiments of such keys. Each key contains a rectifier bridge 27 and 28 and a key element, in this case, the thyristor 29 and 30 in the diagonal DC. To switch thyristors 29 and 30, choke 31 is used (see Fig. 3a), the windings of which are connected in series with thyristors 29 and 30 and capacitors 32 and 33. To improve the mass-dimensional parameters of the switching node and reduce the overvoltages on the converter elements can The switching node scheme shown in FIG. 3 b. and

At small values of the output power of the converter, the primary single-phase voltage can be formed using an autonomous inverter 34 of the voltage AIN (see Fig. 4). Key element cops converter ¹⁰ may be formed in the diode-transistor embodiment (see. Fig. 7).

The principle of operation of the converter is explained by time diagrams (see Fig. 5) _βί where and ι is the primary network voltage supplied to the winding of the transformer 1; ύ «- and ϋ - control signals from the outputs 20-23 of the amplifying and developing unit 19 supplied to the inputs of the switches 5-8 of the converter; (3–— output phase voltage of the converter.

The Converter operates as follows.

The timing generator 12 determines chas- _A g Toth modulation (and therefore the inverter output frequency) and synchronizes the operation of all components of the control unit. The pulse distributor 13 provides counter-switching switching of successively connected keys 5, 6 and 7, 8 of racks ^{50 of the} converter, as well as a 60-degree shift of the control pulses with the keys of the racks relative to each other (see, VI th + and »Fig. 5). Logic node 18 sets either the advance by 60 degrees, or the same lag of the control pulses Pg ”, and in relation to the control pulses and th, and ,,. Amplification and decoupling node 19 provides the necessary galv6

Nitski isolation and amplification of control signals. Output pins 5-8 of the converter, which, in accordance with a given agglomerate, provide modulation of the output voltage. At the output pins 9-11 of the converter, three-phase voltage curves are formed (see Fig. 5).

In order to be able to control the main harmonic of the output voltage of the converter, various algorithms for controlling the 5–8 keys of the inverter can be applied by introducing a controlled adjustment pause </. FIG. 6 presents three possible control algorithms, and the first algorithm (A) provides linearity of the adjustment characteristic, the second (B) forms the output voltage curve with less linear distortions, and the third (B) provides the best quality of the output current of the converter. Algorithm (B) requires an increased number of switchings of keys 5–8 and, therefore, is characterized by somewhat worse energy indicators. FIG. 7 shows timing diagrams explaining the principle of operation of the converter in regulating the output voltage according to algorithm B (see Fig. 6). The digital indications in FIG. 7 indicate to which blocks in FIG. 3 includes processes, and correspond to the notation adopted in FIG. five.

Node 17 regulation of the output voltage that implements each of the above algorithms can be performed in different ways and has its own structure.

In the case when the primary single-phase voltage is formed using an autonomous voltage inverter 34 (see Fig. 7) _? regulation of the output voltage is more rational to provide directly to the AIN through the use of appropriate algorithms for switching its keys. In this case, the voltage on the windings of the transformer 1 has the form shown in FIG. eight.

A frequency-controlled electric drive often requires a change in the direction of rotation (reverse) of the electric motor. The proposed solution allows you to perform this operation in various ways. The output frequency of the transducer (in terms of the fundamental harmonic) is ί ^ = ίι - (q, where G is the primary voltage frequency, and 1 _M is the modulation frequency or the switching frequency of the keys 5-8. From the above Equation it can be seen that with 1 _m frequency changes , the frequency 1 ₂ also changes, in this case, if the frequency of 1 _m moves from the Tdc <| area to the ί _Μ > ί area ₍ , the phase sequence of the converter changes. You can also reverse the rotation of the electric motor in a different way. Input 35 of the trigger 24 signal "+ 1"

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K — input 36 of the signal “O” (see ϋ k and ϋ "" in Fig. 8), and the inputs of the logic element 2I-2IL1I-NOT 25 'signals from the corresponding outputs of the voltage control unit 17 at the output of the converter 9 —1 | there is a direct order of alternation of phases A, B, C. At time 1 _and when the input signal 35 of the flip-flop 24 receives a logical signal "0", and at input 36 the signal "+1", the order of the phase alternation changes and becomes A, C, In (see Fig. 8), the reverse is carried out.

Appropriate scope of the first method of reversing is a synchronous drive, and the second - an asynchronous drive.

Thus, the proposed device is simpler known, which characterizes it as more reliable, and for some applications even cheaper. This is determined by the fact that the number of semiconductor elements of the power part of the converter, as well as the switching units in the thyristor version, is reduced by a third. By eliminating one of the control channels, the amplifying and decoupling, logical nodes, as well as the voltage control unit of the control unit, are simplified.

One of the possible areas of application of the device is its use on an electromotive transport to power three-phase traction motors (prc single-phase mains).

Claims (4)

Claim 1. Single-phase voltage to three-phase converter, mainly for a frequency-controlled electric drive, containing an input single-phase transformer, the ends of the secondary winding of which are interconnected via pairs of connected fully controlled keys with two conduction connected in series and the control unit of these keys two output pins of the converter, characterized in that that, in order to simplify and increase reliability, the third output terminal of the converter is formed by the middle point of the phase phase transformer secondary winding, and the sequence of control pulses of pairs of serially connected keys follow from the control unit with a shift by лЗ. 2. Converter π. 1, characterized in that said control unit includes sequentially connected master oscillator, pulse distributor in the form of a three-phase scaling ring, an output voltage control unit, a logic node and an amplifier knitting unit whose outputs are outputs of the control unit. ¹⁵ 3. Converter on PP. I and 2, characterized in that in order to change the phase sequence, the logical node includes an LK trigger, its outputs connected to the corresponding inputs of the 2I2IL-NOT logic element, to the two other inputs of which the corresponding outputs of the pulse distributor are connected, the output is connected to the logical element NOT, the input and output of which form the output outputs of the logical node, and L — K the trigger inputs are the control inputs of the logical node. 4. Converter for PP. I and 2, characterized in that fully controlled _{} 0 the} keys are made in the form of valve bridges, to the output DC outputs of each of which are connected a switching capacitor and a chain of series-connected windings of inductance and a thyristor, and the windings of inductance, And belonging to the mentioned key pairs, they are magnetically connected with each other.