DE3725923A1 - Converter system having an intermediate-circuit DC voltage which is obtained by means of a rectifier - Google Patents

Abstract

The invention relates to a converter system, especially for controlling long-stator, three-phase linear motors of electric railways, having an intermediate-circuit DC voltage which is obtained by means of a rectifier, from which invertors are supplied which produce a variable-voltage and variable-frequency multi-phase supply, voltage control being carried out by pulsed operation of the invertor at low motor frequencies, and by summation of individual voltage elements at relatively high motor frequencies. In order to avoid the previously normal gaps in the propulsion force and braking force without using output transformers, making available an output voltage which is low in harmonics and ensuring an adequate motor voltage during starting by increasing the substation output voltage, it is proposed that operation without any transformers be carried out at all frequencies via a multi-point invertor having high-power semiconductors (16) which can be cut off, during which operation a plurality of DC voltage elements (+/M; M/-) can be connected in series on the input side and during which a voltage adjustment, especially in the range of high motor frequencies, can be achieved by variation of the individual intermediate-circuit voltages via the rectifiers (14, 14'), the invertor (16) being operated predominantly at full load, with the same wave form of the output voltage. <IMAGE>

Description

The invention relates to a converter system, in particular for Control of long-stator three-phase linear motors of electrical trains, such as it is further defined in the preamble of claim 1.

Through the publication of the Transrapid Magnetic Railway Consortium for the drive equipment of the Transrapid test facility in Emsland (TVE) "Power supply / Line Switchgear / Control and Regulation" AEG-TELEFUNKEN-BBC-Siemens, an arrangement comparable to FIG. 1 is known in which the drive is supplied with energy the power supplied by the state network 1 (110 kV) is transformed down in a converter system. For example, see the contribution by Parsch and Cießow "The drive equipment of the Transrapid 06 with iron-based synchronous long stator motor" on p. 5, Figure 4. The converter system also consists of high-voltage transformer 2 (110/20 kV) and converter transformer 3 located in the substation , A three-phase rectifier 4 , a DC intermediate circuit 5 constant voltage, alternating converters 6 and output transformers 7 . The rectifiers 4 serve to ensure a constant DC link voltage and the inverter 6 to provide a frequency and voltage variable three-phase system.

The inverters 6 are divided in pairs into two groups I and II and are used alternately to feed the motor winding 8 in the sections. The motor section corresponding to the respective location of the vehicle is connected to the respective section cable 10 or 11 via three-phase high-voltage vacuum contactors 9 . The circuitry used here to feed the motor sections alternately from two section cables (trestle procedure) makes it possible to maintain the thrust when driving over a section change and at the same time to switch the vacuum contactors without power.

By regulating the drive, the tensile force and speed of the vehicle are influenced: the current in the stator winding is set so that the correct amplitude and phase position is available for the desired drive or braking force. In order to regulate the synchronous long stator motor, information about the pole position of the motor, ie precise information about the vehicle location, is required. This is done with the help of an inductive poll position measurement. It consists of a medium frequency transmitter on the vehicle and a crossed measuring winding 12 on the track. Brake actuators and braking resistors (not shown) are also provided to dissipate the braking energy fed back into the substation by the vehicle during braking operation.

During operation of the vehicle there are - depending on the traveling speed or motor frequency - two regions of operation: direct feed: Here, the inverters feed directly in line and motor (cf. Fig. 2a.). Transformer feed: Here, transformers 7 are switched on between the inverter and the line to increase the voltage (see FIG. 2b).

The direct mode serves the approach ( f = 0 to 60 Hz). Here, four three-phase transformers with primary-side center tapping are provided, each of which are powered by two parallel-connected, pair-forming three-phase alternators 6 . At higher driving speeds ( f = 60 to 250 Hz), the system switches to transformer operation.

Here, the individual transformers 7 serve in the conventional sense of a step-down transformation, which, however, can be raised by secondary-side series connection for the line feed beyond the primary voltage. For this purpose, vergleichlich Fig. 2b, the secondary windings 7b of, for example four output transformer 7 connected in series. The transformers serve, on the one hand, in conjunction with the series connection of the four secondary windings to increase the inverter output voltage, to enable voltage control in the upper frequency range and, on the other hand, due to the phase offset of a step-shaped - upper vibration-reduced - output voltage. The inverters are operated at full level, ie without pulses; the voltage control takes place by so-called phase swiveling.

In direct operation, only one pair of inverters is switched on, the others are not controlled. The primary winding 7 a of the active transformer only acts as a current divider choke, feeding into the line via the center tap. The secondary windings are switched off. The active pair of inverters works for voltage control in pulse mode (cf. FIG. 2a).

The two food states are switched after the Inverter pairs without power via contactors. The thrust or Braking force of the vehicle interrupted for approx. 1 second.

It is not only the interruption in thrust that is undesirable. Especially at Direct operation only has a maximum motor voltage of approx.1.1 kV per phase achieved, which means that only low acceleration at substations far switching sections is reached.

Here, the invention sets in with the task without using output transformers to avoid the thrust and braking force gaps, an upper to provide low-vibration output voltage and by increasing the substation output voltage one ensure sufficient motor voltage when starting. Here is from cheaper inverter circuits with high performance half that can be switched off headed out.

The object is achieved according to the invention according to the characterizing Features of claim 1 solved. Further advantageous configurations can be found in the subclaims.

Show it

Fig. 1, 2a and 2b known Umrichtereinrichtungen described

Fig. 3 shows the principle of the new converter system using a three-point inverter

Fig. 4 shows the circuit of a three-point inverter

Fig. 5 curve of the output voltage of a three-point inverter

Fig. 6 Scheme of a five-point inverter

Fig. 7 curve of the output voltage of a five-point inverter

Fig. 8 basic thrust and speed curves in comparison.

To FIGS. 1, 2a and 2b position has been taken already.

In Fig. 3, 16 is a three-point inverter, which is fed by two rectifiers 14 , 14 ', which in turn are supplied by a rectifier transformer according to reference numeral 3 in Fig. 1 . The two rectifiers 14 and 14 'are switched in series on the output side. In addition to a + and a - output, a medium or partial voltage tap M that can be loaded with active power in each direction is provided. There are two direct voltage networks or partial voltages that can be connected in series. Voltage adjustment is achieved especially in the area of high motor frequencies by varying the individual partial voltages. The inverter works in full control. The three taps are led to the inputs of the inverter 16 . The outputs of the inverter are labeled RST . With 17 and 17 'two smoothing capacitors are shown. Each intermediate circuit is a brake actuator 18 or 18 'switchable, which switches the braking energy to brake resistors 19 , 19 ' during braking operation (generator operation).

Fig. 4 is the internal circuit of a three-point inverter removed bar. The main thyristors 20 , 21 , 23 , 24 and the coupling and free-wheeling diodes 22 , 25 , 26 , 27 can be seen (per phase). With +, -, M again the three feed points and with 17, 17 ' the two - here only present - smoothing capacitors. Such three-point inverter ter are known per se. What is new is the type of application for the present purpose. Due to a special sequence in the control of the GTO-Thyri, it is possible that the valves are only acted upon with the voltage of one of the smoothing capacitors 17 or 17 'connected in series or with double the voltage.

If, for example, for a phase R and a positive half-wave, for example, only valve 20 is actuated and 21 is not yet activated, then (see FIG. 4), assuming phase S , the following current profile is switched to "-": M , 22 , 20 , R , load L 1 , S. Ie half of the voltage is due to L. If valve 21 is also activated, the current flow starts from + and the full voltage (step change) is present. In the same way, the backward direction is then correctly deleted and the process is repeated for the negative half-wave. Via the rectifier 14 , 14 ', the partial voltages can be varied and thus any intermediate voltage value can be set at the load L.

Fig. 5 shows the achievable voltage waveform at full load of a three-level inverter. With a subdivision of the DC voltage supply - as described on two series-connected supply systems (three-point inverters) - the harmonic content of the output voltage can be reduced compared to a "normal" inverter. By further subdividing the feed (five-point inverter) according to FIG. 6, the output voltage can be achieved with four stages cf. Fig. 7. With this curve shape, the harmonic currents caused by the capacitance of the line connection can be kept within limits. Circuits with even higher quality multi-point inverters are also conceivable.

In the case of the invention, therefore, the required procedure is different from that previously Voltage setting largely according to the motor requirements the feeding rectifiers. The inverters mainly work in Full control with the same curve shape of the output voltage. Only in the lower frequency or voltage range (<10 Hz) there is still a pulse Operation of the inverter may be necessary to avoid disturbing current to avoid vibrations. The number of in series in the inverter GTO thyristors to be switched depend on the choice of the number of stages. The The converter system according to the invention is fully compatible with the conventional ones Electricity feed-in processes, such as leapfrog or alternating step processes.  

In addition to saving the output transformers of considerable weight (together e.g. around 80 t) and the not inconsiderable costs, the will Creation in the substations simplified. Especially in the foreground However, there is the avoidance of thrust and braking force gaps as they do were previously unavoidable.

Fig. 8 shows a comparison of the basic shear force and speed developments. The two upper curves relate to the speed, the lower to the thrust, with the system according to the invention being shown in full lines and the old one in dashed lines. The thrust force gap in the known converter system due to the switchover from direct supply to transformer operation is clearly recognizable (approx. 1 second). A similar interruption also occurs when braking. The speed V associated therewith in FIG. 8 remains in the known converter system for this time (acceleration zero) and only increases further after the thrust force F is reinstated. In contrast, the thrust force F remains constant in the converter system according to the invention and the speed can increase continuously with uniform acceleration.

Because the GTO inverters generate significantly lower overvoltages than conventional thyristor inverters at the moment of commutation and the reactive voltage drop of upstream transformers no longer needs to be taken into account, the substation voltage can be increased considerably (e.g. by 20%) for the same limit stress on the cables. . As a result, the switching section lengths can be increased by about 50%, ie the route lengths can be more than doubled. This brings decisive economic advantages either in a smaller number of substations to be installed or in fewer switching points along the route. Another advantage of the converter system according to the invention is the possibility of being able to provide the full output voltage U even at speeds below 100 km / h (approx. 50 Hz). This was previously not the case with output transformers and led to a dangerously reduced motor current when approaching the substation. These advantages more than outweigh the certain additional effort for rectifier feed.

Claims (6)

1. converter system, in particular for controlling long-stator three-phase linear motors of electrical railways, are fed with a DC link voltage obtained by rectifier from the inverter, which provide a voltage and frequency-variable multiphase supply, the voltage control by pulse operation of the inverter and at low motor frequencies at higher motor frequencies by summation of individual partial voltages, characterized in that a transformerless operation at all frequencies via a multi-point inverter with switchable high-power semiconductors ( 16 ) takes place, in which several partial direct voltages (+ / M; M / -) in on the input side Series are switchable and in which a voltage adjustment, especially in the area of high motor frequencies by varying the individual intermediate circuit voltages via the rectifier ( 14 , 14 ') can be achieved, the inverter ( 16 ) predominantly in full control at g easier curve shape of the output voltage is operated. 2. Converter system according to claim 1, characterized in that the different partial DC voltages are formed from separate rectifier stages, which are brought out on the output side to form at least one common voltage divider tap on the multi-point inverter ( 16 ). 3. Converter system according to claim 1 or 2, characterized in that two rectifier stages ( 14 , 14 ') with a medium, in each direction loadable with active power medium voltage divider handle ( M ) are provided, which feed to a three-point inverter ( 16 ) ( Fig . 3). 4. Converter system according to claim 3, characterized in that between each one output of the rectifier stages (+ or -) and the associated common voltage divider tap ( M ) each have a smoothing capacitor ( 17 , 17 ') is connected in parallel. 5. Converter system according to one of the preceding claims, characterized in that four rectifier stages with assigned voltage divider taps feed on a five-point inverter ( Fig. 6). 6. Converter system according to one of the preceding claims, characterized characterized that about the type of control of the change richters, a stepped output voltage waveform can be achieved.