DE2348157A1 - Frequency converter for three phase machines - gives twelve pulse output by use of two inverter stages - Google Patents

Abstract

Undesirable losses and torque modulations can be minimised by using a twelve pulse output. In a frequency converter with an intermediate d.c. stage this is achieved by adding a second output inverter connected via its own smoothing inductor to the output of the supply commutated converter. The inverter sections are arranged to have 30 deg. displacement between output voltages. The output is typically commoned by a choke coil in each phase with a centre tap from each coil feeding the load machine. The system is applicable to any sort of rotating field load.

Description

The invention relates to a converter circuit in the induction machine via a six-pulse self-guided Converter, via a direct current intermediate circuit with smoothing choke and via a line-commutated converter an AC voltage network is connected.

So-called intermediate circuit converter with impressed current in the direct current intermediate circuit and connected three-phase machine are known, e.g. B. from the German Offenlegungsschrift 1 513 518. They are used to drive the induction machine with variable speed, in particular as a single-motor drive. Both a synchronous machine and an asynchronous machine can be used as the induction machine. Of the DC link converter consists of a line-commutated converter that is connected to the AC voltage network, a downstream DC link with the smoothing reactor and. a self-commutated converter. The self-guided The converter contains a quenching or commutation device that only supplies a synchronous machine is to be designed for the start-up of this synchronous machine.

In motor operation, the line-commutated converter, which works as a rectifier, supplies the direct current intermediate circuit with energy from the AC voltage network. The rectifier equipped with controllable valves receives its control pulses from a tax rate that is synchronized with the mains voltage. This tax rate of the line-commutated converter is

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the level of the current in the DC link and thus the level of the output current of the converter are set. Leveling choke arranged in the direct current intermediate circuit
serves for decoupling and smoothing.

The self-commutated power converter, which works as an inverter and is also equipped with controllable valves, feeds the connected three-phase machine with an alternating or three-phase voltage of adjustable frequency. Br converts the direct current of the direct current intermediate circuit into an alternating current. The frequency is usually set by a frequency control signal which is sent to a voltage-frequency converter
is specified, the output pulses via a tax rate that z. B. contains a ring counter, the controllable valves, in particular thyristors, of the self-commutated converter are fed. The self-commutated converter can be operated independently or externally via its tax rate
will.

The self-commutated converter, which is generally six-pulse in a three-phase machine, uses its main valves to switch the direct current of the direct current intermediate circuit cyclically at the specified frequency to the winding phases of the three-phase machine. This requires the already mentioned quenching or commutation device, which is generally implemented with the aid of capacitors and so-called quenching valves. The alternating or three-phase voltage of the induction machine can vary with -cyclic
Switching on the direct current freely through the decoupling effect of the smoothing choke, ie almost independently of the
Form the voltage form in the direct current intermediate circuit. Of the
The current in the DC link remains practically constant during the commutation from one main valve to the other. For the reversal of the energy flow, i.e. for generator operation, the intermediate circuit voltage is at
constant current direction in the direct current intermediate circuit reversed. This is because of the lack of return valves

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by changing the control angle of the machine-side converter possible.

To equip such a DC link converter with a control circuit that is used to keep the current in the DC intermediate circuit provides is also known, e.g. B. from German Offenlegungsschrift 1 814 400 or from the "Siemens-Zeitschrift", 45th year, April 1971, issue 4, pages 195 to 197. From this publication 1 814 400 it is also known to equip the intermediate circuit converter with a speed control circuit that is superordinate to the current control circuit to train.

It is also from the "Siemens magazine", 45th year, April 1971, issue 4, pages 177 to 182 known that the middle Torque of a synchronous machine, which consists of a DC link converter with converters in a three-phase bridge circuit is fed, higher order harmonic moments are superimposed. The order of these harmonic moments is given by an integer multiple of the pulse number of the machine-side converter. For example, join a six-pulse DC link converter, due to the rectangular, non-sinusoidal currents, harmonics in torque with six, twelve, eighteen ... -fold basic frequency. This torque ripple makes itself felt Particularly at very low basic frequencies, this is unpleasantly noticeable due to irregular running and rattling.

In the already mentioned "Siemens-Zeitschrift", 45th year, April 1971, issue 4, pages 195 to 197, it is further stated that - due to the current flow in a six-pulse DC link converter - the stator flux a connected asynchronous machine during the commutation of the current from one strand to the next by the angle 60 el. Jumps on.

It can be stated that the harmonics mentioned additional losses and thus undesirable heating

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the induction machine. The abrupt flow changes also mentioned lead to torque pulsations in the connected induction machine, the bearings are stressed, result in an out-of-round run and are out of this Reason also undesirable.

In the already mentioned "Siemens-Zeitschrift", 45th year, April -1971, No. 4, pages 177 to 182, it is stated that the torque ripple when there are special conditions can be reduced considerably by switching from six to twelve-pulse circuits. In this case it has lowest harmonic moment the 12th order. Because of its high atomic number, it is hardly perceived as annoying. Embodiments for such twelve-pulse circuits however, not stated in the cited literature reference.

The object of the present invention is to specify a converter circuit starting from the known intermediate circuit converter which either has a twelve-pulse output current or which has a twelve-pulse reaction on the connected induction machine. This is to ensure that the undesired additional losses and the troublesome torque fluctuations are substantially reduced. The converter circuit should not be limited to the connection of a three-phase synchronous machine, but should be used in all types of induction machines, so z. B. can also be used in a three-phase asynchronous machine.

Based on a converter circuit of the type mentioned at the outset, this object is achieved according to a first embodiment according to the invention solved in that a further six-pulse self-commutated converter via a further direct current intermediate circuit, which contains another smoothing choke, is connected to the line-commutated converter that the two self-commutated converters are controlled offset from one another by 30 ° el, that corresponding AC voltage side Output terminals of the two self-commutated converters each with one another via a center-tapped choke coil

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are connected, and that the induction machine is connected to the center taps the choke coils is connected.

On the basis of the converter circuit mentioned at the beginning, the stated object is achieved according to a second embodiment according to the invention solved in that a further six-pulse self-commutated converter via a further direct current intermediate circuit, which contains a further smoothing choke, connected to another line-commutated converter is, which is connected to the AC voltage network, that the two self-commutated converters on the AC voltage side are connected in parallel on the induction machine and controlled offset by 30 ° el.

These two converter circuits have the property that they generate a twelve-pulse output alternating voltage.

Furthermore, the stated task is based on a converter circuit The type mentioned at the outset according to a third embodiment according to the invention in that a Another six-pulse self-commutated converter via another direct current intermediate circuit, which is another smoothing choke contains, is connected to the line-commutated converter that the two self-commutated converters are controlled with the same control angle, and that the outputs of the two self-commutated converters with two separate winding systems are connected, which are spatially offset from one another by 30 ° in the induction machine are.

Finally, starting from a converter circuit of the type mentioned at the beginning, the specified task is carried out according to a ' fourth embodiment according to the invention achieved in that the six-pulse self-commutated converter is another six-pulse self-commutated converter is connected in series to the line-commutated converter that both self-commutated converter with the same control angle

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controls are, and that the outputs of the two self-commutated converters are connected to two separate winding systems which are arranged spatially offset from one another by 30 ° in the induction machine.

The third and fourth embodiments of the invention have Property, a twelve-pulse reaction in the induction machine to create.

Embodiments of the invention are explained in more detail below with reference to four figures. Show it:

Figure 1 shows a converter circuit with two self-commutated converters, which are connected to one another on the machine side via center-tapped choke coils,

FIG. 2 shows a converter circuit with two DC link converters connected in parallel on the machine side,

Figure 3 shows a converter circuit with two self-commutated. Converters, which are connected to separate winding systems in the induction machine, and

FIG. 4 shows a converter circuit with two series-connected self-commutated converters which are connected to separate winding systems are connected in the induction machine.

The same reference symbols are used in FIGS. 1 to 4 for the same components. Is a corresponding one in a figure There are two components, so it is provided with the addition "a".

According to FIG. 1, there is a rotary field machine 2, in the present case a three-phase asynchron machine, the rotor shaft 3 for determination the speed η is provided with a tachometer machine 4, via a converter circuit 5 to a three-phase network 6 ait the phase conductors R, S, T connected. The three-phase asynchronous machine 2 is, for example, for operation a rail vehicle provided. The converter circuit consists of a first six-pulse machine clocked

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Converter 7, a second six-pulse machine clocked Converter 7a, a line-commutated converter 8, a first direct current intermediate circuit 9 with a first Smoothing choke 10, which the line-commutated converter 8 with the first machine-side converter 7 connects, and a second DC intermediate circuit 9a with a second Smoothing choke 10a, which connects the line-commutated converter 8 with the machine-side converter 7a. the controllable main valves of the converters 7, 7a and 8 are z. B. arranged in three-phase bridge circuit. You can especially thyristors. The two converters 7, 7a each contain a quenching or commutation arrangement, which is essentially made up of controllable valves and capacitors.

Through the line-commutated converter 8, the first direct current intermediate circuit 9 and the first machine-side converter 7 is a first converter with impressed current in the direct current intermediate circuit 9 formed. Correspondingly, the line-commutated converter 8, the second direct current intermediate circuit 9a and the second machine-side converter 7a, a second converter with impressed current is formed in the direct current intermediate circuit 9a. Such converters are everyone for known per se, z. B. from the "Siemens-Zeitschrift" already cited at the beginning, 45th year, April 1971, issue 4, pages 177 to 182, Fig. 6, and pages 195 to 197, Fig. 1.

The outputs of the power converters 7, 7a, which are not designated in more detail, are each connected via a center-tapped choke coil 11, 13 and 15 connected to each other. The center taps are provided with the reference numerals 12, 14 and 16, respectively. The induction machine 2 is connected to these three center taps 12, 14, 16. Di.e choke coils 11, 13, 15 have the task of different Record instantaneous values in the output voltage.

A tax rate 17, 17a and 18 is assigned to each of the converters 7, 7a and 8. These tax rates 17, 17a and 18 supply

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the controllable valves via the control lines shown with control pulses. The tax rates '17, 17a tax the converters 7, 7a offset from one another by 30 °.

The tax rate 18, which is via a line 19 with a voltage converter 20 is connected to the input of the converter 8 and is thus synchronized with the network frequency, its input signals can in a known manner from an upstream current regulator 21 received. A comparator 22 connected upstream of the current regulator 21 receives a from a current transformer 23 Current actual value I. In the present case, the current converter 23 is arranged in an AC voltage feed line of the converter 8. In principle, it could also be arranged in one of the two direct current output lines of the line-commutated converter 8 because the actual current value I determined is a measure of the sum of the currents in the two DC intermediate circuits 9 and 9a is. In addition to the actual current value I, a current setpoint value I * is also fed to the comparator 22. The one from the comparator The deviation ΔΙ determined between the current actual value I and the current setpoint value I * is applied to the current regulator 21.

The current setpoint I * is taken from a function generator 24 which is connected to a higher-level speed controller 25 is. Its output signal, a torque setpoint D *, is effective also on the tax rates 17, 17a of the two power converters 7 and 7a on the machine. The upstream comparator 26 of the speed controller 25 receives a speed setpoint n * from a setpoint generator 27, which is indicated as a potentiometer as well as the actual speed value η from the tachometer machine

From the current regulator 21, the comparator 22, the function generator 24 and the current transformer 23 existing control circuit for

en

the current I in the direct current intermediate circuit / 9, 9a ensures that the current I is held at a value predetermined by the setpoint generator 27 and the speed η. This Current I is alternately and temporally offset from the converters 7, 7a to the individual phase lines of the induction machine imprinted. The torque of the induction machine 2 receives as a result

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which does not contain a uniform temporal course, but rather contains Harmonics. Since the two converters 7, 7a

but work offset by 30 ° from one another, results in the output side Superimposition by means of the choke coils 11, 13, 15 a twelve-pulse current curve.

The control and regulating circuit described so far is supplemented by a torque regulator 28 with an upstream comparator 29, to which both the speed-dependent nominal torque value D * formed by the speed regulator 25 and an actual torque value D are fed. In the present case, the actual torque value D is determined by a torque computer 30 to which the actual value of the motor voltage Ujj is fed _{from a voltage converter 31 and the actual value of the motor current I M from a current converter 32.} In principle, the actual torque value D of the induction machine 2 can also be determined in any other way.

The output signal of the torque controller 28 is denoted by n ″. It takes into account the slip of the three-phase asynchronous machine and is added to the signal for the actual speed value η in an adder 33 as a correction variable. The corrected output signal η 'of this adder 33 is fed into a voltage-frequency converter 34 which is connected to the control inputs of the two control sets 17, 17a. The output signal η ^{1 of} the adder 33 thus serves as a control voltage for the two control sets 17, 17a. The two converters 7, 7a are thus controlled with the same control angle but offset from one another by 30 °. The rotary machine 2 is thus fed with a twelve-pulse alternating current.

In the converter circuit according to FIG. 2 there are two separate ones Converters available, each of which has a self-commutated converter 7 or 7a and a line-commutated converter 8 or 8a, which are connected to one another via a direct current intermediate circuit 9 or 9a with smoothing choke 10 or 10a. the

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Line-commutated converters 8, 8a are separated from secondary windings a power converter transformer 35 is fed from the AC voltage network 6. The two self-guided Converters 7, 7a are direct on the AC voltage side connected in parallel with their outputs. The induction machine 2 is connected to the connection lines.

The control and regulating circuit with which the converter circuit according to FIG. 2 is operated essentially corresponds to that of Figure 1. However, it should be noted that two current control loops are present, for which the current setpoint I *, which is formed by the function generator 24, is jointly specified will. Each line-commutated converter 8, 8a has its own tax rate 18 ors. 18a assigned. These tax rates 18, 18a are each synchronized with the AC input voltage of the converters 8, 8a. That's through the lines 19, 19a indicated. A separate current regulator 21 or 21a with comparator 22 or 22a is connected upstream of each control set 18, 18a. The comparators 22, 22a receive, on the one hand, the common current setpoint value I * and, on the other hand, the actual current value separately I and I supplied. These current actual values I, I are supplied by current transformers 23 and 23a, each in a Conducting the separated secondary windings of the Stromriohter transformer 35 lying.

The other components of the control and regulation circuit and their ^ functional structure correspond to that of FIG. 1 and therefore do not need to be explained again.

The two power converters 7, 7a on the machine side are in turn operated six-pulse. As a result of the control of the converters 7, 7a offset from one another by 30 ° el, that of the rotary field machine 2 supplied output current of the converter circuit in turn twelve-pulse.

In Figure 3, a converter circuit is shown that largely corresponds to that of FIG. Again, a self-commutated six-pulse converter 7 is via a rectifier

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current intermediate circuit 9 with smoothing choke 10 to a line-commutated Converter 8 connected. Furthermore, a second self-commutated six-pulse converter 7a is via a second direct current intermediate circuit 9a with second smoothing choke 10 also connected to line-commutated converter 8. This line-commutated converter 8 is on the AC voltage side directly or via a converter transformer 36 connected to an alternating voltage network 6.

In contrast to the converter circuit according to FIG Outputs of the two self-commutated converters 7, 7a with two separate winding systems 37, 38 in the induction machine 2 connected. These two winding systems 37, 38 are which is not immediately apparent from FIG. 3, arranged offset from one another by 30 ° in the induction machine 2.

The control and regulating circuit which is assigned to the converter circuit in FIG. 3 shows the same structure as that in FIG. 1 and therefore does not need to be explained again. In the present case, a torque computer 30 is also provided. It is sufficient if the torque computer 30 is _{supplied with the motor current I M} and the motor voltage Uj, only one of the two winding systems 37, 38. In the case shown, the voltage converter 31 and the current converter 32 are arranged in the supply lines to the winding system 37. The voltage-frequency converter 34 feeds the two control sets 17, 17a with the same input signal. As a result, the two converters 7, 7a are controlled with the same control angle.

The converter circuit shown in Figure 3 has because of the rotationally offset Arrangement of the winding systems 37, 38 result in that a twelve-pulse reaction occurs in the induction machine 2.

In the converter circuit in FIG. 4, a rotary field machine 2 is again used, which has two separate winding systems

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37, 38, which also spatially by 30 ° against each other are arranged rotationally offset. Here, too, each winding system 37, 38 has its own self-commutated converter

7 or 7a fed. However, the two self-commutated converters 7, 7a - differ from the converter circuit according to Figure 3 - here connected in series on the DC side and via a common smoothing choke, which is provided with the reference numeral 10 ', to a line-commutated converter

8 connected. The smoothing choke 10 'is for double The value of the current that each of the smoothing reactors 10, 10a carries in the converter circuit according to FIG. 3. Of the Line-commutated converter 8. is preferably via a converter-transformer 36 connected to the AC voltage network 5. The control and regulation circuit corresponds to that of Figure 1 and therefore does not need to be explained again in detail. However, the two tax rates will apply 17, 17a the same input signal that is supplied by the voltage-frequency converter 34 is supplied. The steering angle for both converters 7, 7a are thus the same size. Here, too, there is a twelve-pulse effect on the induction machine 2.

4 claims
4 figures

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Claims (4)

- 13 - VPA 73/3267 patent claims 1.J converter circuit in which an induction machine is connected to a six-pulse self-commutated power converter, via a direct current intermediate circuit with a smoothing choke and connected to an AC voltage network via a line-commutated converter is, characterized in that a further six-pulse self-commutated converter (7a) via a further DC intermediate circuit (9a), which contains a further smoothing choke (10a), to the line-commutated converter (8) is connected so that the two self-commutated converters (7, 7a) are controlled offset from one another by 30 ° el, that corresponding output terminals on the AC voltage side of the two self-commutated converters (7, 7a) each have a center-tapped choke coil (11, 13, 15) are connected to one another, and that the induction machine (2) is connected to the Center taps (12, H, 16) of the choke coils (11, 13, 15) is connected (Figure 1). 2. Timing converter circuit in which a three-phase machine is connected to an eech-pulse self-commutated converter via a direct current intermediate circuit with smoothing choke and connected to an alternating voltage network via a line-commutated converter is, characterized in that a further six-pulse self-commutated converter (7a) via a further direct current intermediate circuit (9a), which contains a further smoothing choke (10a), to a further line-commutated converter (8a) is connected, which is connected to the AC voltage network (6) that the two self-commutated converters (7, 7a) on the AC voltage side of the induction machine (2) connected in parallel and controlled offset from one another by 30 ° el (Figure 2). 3. Converter circuit in which a three-phase machine is operated via a six-pulse self-commutated converter, via a direct current intermediate circuit with smoothing choke and via a line 509816/0431 -H- - 14 - VPA 73/3267 guided converter is connected to an AC voltage network, characterized in that a further six-pulse self-commutated converter (7a) via a further direct current intermediate circuit (9a), which is a further Smoothing choke (10a) is connected to the line-commutated converter (8) that the two self-commutated Converters (7, 7a) are controlled with the same control angle, and that the outputs "of the two self-commutated Converters (7, 7a) are connected to two separate winding systems (37, 38) in the induction machine (2) are arranged spatially offset from one another by 30 ° (Figure 3). 4. Converter circuit in which an induction machine has a six-pulse self-commutated converter, via a direct current intermediate circuit with smoothing choke and via a line-commutated converter is connected to an AC voltage network, characterized in that with the six-pulse self-commutated converter (7) a further six-pulse self-commutated converter (7a) in series the line-commutated converter (8) is connected, that both self-commutated converters (7, 7a) with the same Control angles are controlled, and that the outputs of the two self-commutated converters (7, 7a) with two separate Winding systems (37, 38) are connected in the induction machine (2) spatially offset from one another by 30 ° are arranged (Figure 4). 509816/0431 / IS Blank page