DE3626812C2 - Arrangement for speed adjustment of a single or multi-phase induction machine - Google Patents

Description

The invention relates to an arrangement according to the preamble of claim 1.

Arrangements of this type are from DE-OS 28 56 574 known.

The low-frequency generated by the known arrangement Voltages and currents, their first harmonic or fundamental frequency one lower than the mains frequency Frequency, have a high harmonic content, in particular the harmonic corresponding to the mains frequency is particularly pronounced. This is disadvantageous in that than it is with induction machines, which are optionally with mains frequency or using the generic arrangement with the other operated at lower frequency when switching can occur in particular under certain load conditions, that the induction machine does not rely on that of the arrangement delivered basic vibration frequency, but with the pronounced harmonic corresponding to the network frequency continues without changing the speed and the basic frequency only noticeable as vibration on the machine. But also in cases in which the induction machine with its Setting the speed to the basic frequency is the strong harmonic content that supplied by the known arrangement Voltages and currents disadvantageous because of the harmonics lead to additional moments that the desired moment from the Counteract the fundamental vibration, i.e. reduce it.

Accordingly, there is the problem underlying the invention in improving the generic arrangements so that that the currents and voltages they deliver a lower harmonic content, especially one more favorable ratio of the fundamental vibration amplitude to Amplitude of the harmonics corresponding to the mains frequency, exhibit.

The above task is accomplished by the in the labeling section of claim 1 resolved features.

The measure according to the invention has the effect that the the arrangement delivered current forms compared to the at known arrangement occurring are significantly smoothed and the current between the individual network half-waves that are used for Creation of the fundamental oscillation against the mains frequency lower frequency in the individual half-waves of the load voltage or the load current are strung together, not more gaps. The amplitude spectrum of that of the invention The delivered voltages and currents is through arrangement a much more favorable ratio of the fundamental vibration amplitude on the amplitudes of the harmonics, in particular the one that corresponds to the network frequency, and accordingly it also exists under critical load conditions no longer the risk of an induction machine after switching from the mains voltage to the voltage supplied by the arrangement not on its fundamental frequency sets, but while maintaining their speed continues with the harmonic whose frequency is the mains frequency corresponds. The lower harmonic content and in particular which are essential compared to the amplitude of the fundamental reduced amplitude corresponding to the network frequency Harmonics are also much less, the moment  additional moments counteracting from the fundamental vibration, so that the moment from the fundamental vibration through the Harmonics are no longer weakened in an impermissible manner becomes.

From the literature references Keuter, Tscharn: "Schaltungen von Sets. . . "in ETZ 1986, H. 5, pp. 200-207 and Sauer, Körting: "AC power controller with forced extinction" in industrie-elektrik + elektronik, 1975, No. 3, pp. 25-28 switched freewheeling circuits for AC and three-phase controllers known, where the freewheel is indispensable, because the actuator is forcibly deleted.

The subclaims relate to preferred configurations of the Subject of the main claim.

Compared to the known arrangement, which is primarily for the Use when driving induction machines with mains frequency and another solid, still relatively tall, smaller one Frequency was suitable, as was the case with induction machines, for example is the case for driving centrifuges the arrangement according to the invention in particular if it is used according to claims 7 to 9, now also for use with induction machines for positioning of working machines, where from the mains frequency to feed frequencies must be switched, which is only a very small fraction of the network frequency.

The invention is illustrated below using exemplary embodiments explained in more detail.

The drawing shows:

Figure 1 an inventive triple-stranded assembly with freewheel thyristors without the ignition of the individual thyristors causing circuit part;

Figure 2 shows the equivalent circuit diagram for a strand of the arrangement according to Figure 1 and the associated course of the voltages and currents in the course of the series of four here, namely positive grid half-cycles to create a positive load half-cycle of a frequency reduced compared to the grid frequency;

Figure 3 shows the current profile in the arrangement according to Figure 2 for lead angle α = zero assuming U _i = 0;

Fig. 4a and Fig. 4b the current curve with the current fundamental and the harmonic spectrum obtained by FOURIER analysis;

Figure 5a to Figure 5c the load currents in the arrangement according to the invention with free-wheeling semiconductors compared to the load currents in an arrangement without free-wheeling semiconductors according to the prior art, in each case with fundamental oscillation and associated harmonic spectrum on the basis of different gate angles (counter voltage = 0); and

Figure 6a to Figure 6c the influence of different gate angles α₁ and α₂ for the main and freewheeling thyristors on the load current shape in the arrangement according to the invention.

In Figure 1 of the drawing, an arrangement according to the invention is shown schematically, the illustration of the freewheeling semiconductors and semiconductors of the three-phase current regulator designed to ignite the individual thyristors being omitted because these circuit parts are familiar to the person skilled in the art and their control of the Arrangement necessary operation according to the invention results from the current and voltage profiles shown in the drawing and described below.

The arrangement shown in Figure 1 has three strings connected in a star, whereby, as is also the case with the known arrangement discussed at the outset, the same parts of the three-phase controller are inserted into each strand, each consisting of two main thyristors T1 _p and T1 _n exist, which are in series with the respective machine winding W with inductance L and ohmic resistance R, in which a counter voltage u _i is usually also generated in operation. Free-wheel thyristors connected antiparallel to each other are connected in parallel to the individual machine windings W.

Figure 2 shows the equivalent circuit diagram for one of the three strands of the arrangement according to Figure 1 and, in addition, the basic voltage and current curve when stringing together several, here four positive voltage half-waves of the mains voltage to achieve a load half-cycle of lower frequency, each time only the lined up positive network half-waves and the associated positive load half-period are shown. It is sufficient to consider the single-phase circuit according to Figure 2 for the current and voltage curve, since the individual strands are symmetrical to each other and interact in the usual way in three-phase systems.

The positive or negative half-wave of the voltage at the load is formed by stringing together n - optionally cut - half-waves of the mains voltage. The current is then set in accordance with the ohmic resistance R and the inductance L of the machine winding, the counter voltage U _i induced in this and the firing angle α with which the individual thyristors are ignited. The electricity must be reduced towards the end of the half period. For this purpose, the freewheeling thyristor T2 is no longer triggered. The mains voltage remains until the current (and thus the main thyristor T1) is extinguished.

The reproduced in Figures 3 and 4a form of the machine current was calculated based on the parameters noted there and determines therefrom by means of Fourier analysis of the harmonic spectrum shown in Figure 4b, by means of a computer program. For the calculation, a counter-voltage U _i which was constant over the half-period was assumed.

Figure 3 shows the current profile for α = 0, U _i = 0. After 9 grid half-periods, T2 is no longer ignited. Electricity reduction takes place in the 10th half of the grid. After a pause until the end of the grid half-cycle, the negative half-cycle of the load follows. The fundamental frequency is

At larger values of ωT, the current may go out only in the 2n + 2g-th half-period (g = 0, 1, 2,...) negative mains voltage. The next half period of the load can only after the following positive grid half-period connect. The frequency ratio results in

After the switchover point, the current within the "Quenching angle" ωt₂ = β.

According to Figure 3, β for ωT = 5 and α = 0 results, for example, at 125 °, so that the current is extinguished in the 2nth half of the network.

FOURIER analysis

The voltage and current forms can be analyzed according to FOURIER. In the images 4a and 4b, the current waveform is shown again, together with the respective current fundamental and the harmonic spectrum.

For a single-phase circuit according to an equivalent circuit similar to that in Figure 2, but without free-wheeling semiconductor arrangements, the current forms were also calculated. The result is shown in the pictures 5a to 5c in comparison with the results according to Figures 4a and 4b. This comparative representation shows particularly clearly the advantages achieved with the invention over the prior art.

It can be seen that the harmonic content is due to use a freewheeling thyristor is significantly reduced. In addition, the fundamental vibration amplitude is increased. Essential here is the 11th harmonic, which is the current harmonic the network frequency. Table 1 shows the amplitude of the 11th harmonic in comparison to the fundamental oscillation amplitude.  

Table 1

Ratio of line frequency amplitude to fundamental vibration amplitude

At large control angles, the amplitude of the harmonic larger than that of the fundamental vibration without a freewheel.

By using different control angles for the main thyristor and the freewheeling thyristor, the harmonic spectrum of the freewheeling circuit can be further positively influenced. In Figures 1 and 2, which relate to arrangements with freewheeling thyristors, the control angle for the freewheeling thyristor α _{n, 2} = 0 ° was selected.

Table 2 shows the influence on the ratio of the 11th harmonic to the fundamental vibration.

Table 2

Ratio of the network frequency amplitude to the fundamental vibration amplitude at the control angle α₂ = α₁ and α₂ = 0

Claims (7)

1. Arrangement for adjusting the speed of a single-phase or multi-phase induction machine with a multi-phase semiconductor three-phase controller, in particular thyristor three-phase controller, the switching pulses of the semiconductors of the three-phase controller being generated in such a way that a selectable number of successive positive voltage half-waves and successive negative voltage half-waves in each phase, the output voltages of the three-phase controller form a multi-phase three-phase voltage system, the first harmonic of which has a frequency corresponding to the selected number of successive voltage half-waves of one or the other polarity lower than the frequency of the supply network, characterized in that the windings of the induction machine with free-wheeling semiconductor - Arrangements are connected, which alternate with the switching of the individual half-waves by an associated semiconductor of the three-phase controller be aged. 2. Arrangement according to claim 1, characterized in that the Free-wheeling semiconductors are free-wheeling thyristors. 3. Arrangement according to claim 1 or 2 for three-phase induction machines in star connection, characterized in that the free-wheeling semiconductor pairs between a phase connection and the star point are switched.   4. Arrangement according to claim 1 or 2 three-phase induction machines in a delta connection, characterized in that the free-wheeling semiconductor pairs between two phase connections are switched. 5. Application of the arrangement according to one of the preceding Claims for positioning an induction motor driven work machines, characterized, that the induction motor first started up at the mains frequency the load by measuring the current or cos ϕ Nominal speed is determined and then for the intake of the Work machine in the desired position by alternating Switching through several successive ones positive half waves and several consecutive negative half waves of the mains voltage with free running between the individual half waves a supply voltage with a first harmonics of lower than the network frequency if necessary variable frequency and on the determined Load coordinated, possibly variable amplitude generated becomes. 6. Application according to claim 5, characterized in that the Induction motor with variable cutting angle of the Three-phase controller with gradually increasing supply voltage is ramped up from the mains frequency. 7. Application according to claim 5 or 6, characterized in that at the supply voltage, which is the first harmonic of has a lower frequency than the mains frequency, the frequency and the amplitude are controlled so that the Brake acceleration remains constant regardless of load.