DE19941170A1 - Self-symmetrising supply system has semiconducting switches in sub-converters that are loaded voltage symmetrically without active regulation or additional circuitry - Google Patents

Abstract

The supply system has a frequency converter and a transformer with several similar converter modules, each with two sub-converters (F11,F12,..) in the form of 4-Q circuits and at least one transformer each, whereby the number of primary windings corresp. to the number of sub-converters and the primary windings are inductively coupled together and have good coupling to the single secondary per transformer. Semiconducting switches in the sub-converters are loaded voltage symmetrically without active regulation or additional circuitry.

Description

The results of the development of new fast switching semiconductor switching elements with reverse voltages of more than 2 kV leads to the execution of low-loss Power electronics circuits in the MW range and thus also on low-mass Configurations of power converters. With increasing reverse voltage, the number of necessary elements and thus the complexity and probability of failure Systems with high voltage; circuits can therefore be used for forming tasks also specify for new objectives. One in the field of rail and vehicle technology Known problem is the low-mass version of the high-voltage feed Frequencies that are lower than 50 Hz. So far, the feed has been particularly dimensioned but weighty transformers. Their job is to get the high Reduce input voltage to such an extent that drive motors have a view of their mass and losses can be optimally interpreted. In addition to this main function of It also fulfills the important additional condition of a transformer Safety consideration of the desired galvanic isolation from the supply network. The low-weight design of the electric drive machines depends closely on the thermal Resilience of the windings and thus with their cooling ability and isolation issues. Also an inexpensive design of the engine feeding frequency converter speaks for a greatly reduced voltage. The principle advantageous use of a transformer is likely to continue in the medium term, whereby the safety aspect of galvanic isolation is of particular importance. He closes the direct use of an exclusively power electronic feed system for drive units approximately according to DE 196 14 627 A1. After this registration As in DE 196 15 855 A1, a cascaded converter circuit is operated in such a way that that the windings of three-strand electrical machines lying at their output can be supplied with a frequency variable voltage. Because the inductive coupling the (three-strand) machine windings are weak and dependent on the operating state, there is no possibility of self-symmetrizing the voltage. The presupposed direct Connection of the drive machines does not allow an even distribution between the feeding ones Partial inverter and therefore requires a very high isolation effort with all Consequences for the design of electrical machines. Are elsewhere Proposals for complex circuit additions are described, such as B. an additional Voltage divider in front of the converter, with the help of which an even voltage distribution  to be enforced. These and other suggestions are great with the basic idea Reliability through high simplicity, not compatible.

The following main features therefore exist for the task set according to the invention:

• - Circuit consisting of frequency converter and transformer with the increased Frequency is operated.
• - Circuit consisting of a limited number of sub-circles with as much as possible the same structure and identical switching elements and one if possible same load according to current and voltage.
• - Avoiding circuits that, for example, in the event of a fault. B. in the event of control failure or Control loops lead to instability and uneven voltage distribution. Out of this derived is the goal of specifying a self-balancing circuit.
• - Avoidance of difficult arrangements in terms of insulation or design by moving functions from the primary to the secondary side.
• - Accident control by disconnecting faulty circuit parts and Circuit redundancy.
• - Function of minimum smoothing of the current input and influencing reactive current through the converter.
• - Low-loss design through the selection of limited switching and operating frequencies Power electronics and transformer.
• - Transformer with high quality magnetic circuit for fundamental vibrations up to the range of 1 kHz and design with well coupled windings of the primary side and the Primary windings with the secondary winding.
• - Regenerative and multi-system capability of the circuit (reversal of the energy flow).
• - Highly reliable execution of the driver circuit and control.

The representation of the invention is described in a detailed description and Presentation of the circuit by 12 figures and their explanations made.

FIG. 1a shows the consisting of smoothing reactor, Umrichterschaltkreisen and transformer circuitry of the transducer assembly.

FIG. 1b represents a Teilumrichteranordnung primary winding with which the installation can be completed by two switches, in order to make partially in case of failure a disconnection.

Fig. 2 shows the feed circuit together with a drive system for a traction motor. It is referred to the time profile of the voltages at various points.

Fig. 2.0 shows the sinusoidal mains voltage of low frequency.

Fig. 2'.1 shows the pulsed, low harmonic voltage of the input converter.

Fig. 2'.2 shows the pulsed voltage of a converter.

Fig. 2'.3 shows the voltage curve in the intermediate circuit.

Fig. 2'.4 shows the pulsed voltage curve on the transformer primary winding.

Fig. 2'.5 shows the smoothed voltage curve in the intermediate circuit of the drive converter.

Fig. 3 shows the modulated with the input frequency output current of the transformer.

Fig. 4a shows a converter circuit, which are used from two converter groups and two similar transformers for the direct supply of two windings of a drive motor. The output voltages are variable in frequency and out of phase.

Fig. 4b shows the largely sinusoidal output voltages at the two windings of the motor.

A prerequisite for a low-mass version of the frequency converter is a defined load according to current and voltage, a limited overload in the event of a fault, in which partial converters can be switched off, as well as a relatively high output frequency, which can be used to reduce the mass of the transformer. In order to simultaneously meet the existing requirement for low harmonic network load, the way is taken to operate the input converter with a largely sinusoidal voltage. This objective can best be met by pulsed operation with voltage blocks at a frequency that is a high multiple of the mains frequency, approximately in the range of 1 kHz, if a mains frequency of 16 2/3 Hz is assumed. With pulses of the same voltage level and identical pulse patterns of the partial converters and a temporally sinusoidally broadened pulse duration and a time offset of T _p / 2n (T _p period), the pulse pattern of individual partial converters can be used with a limited number of z. B. 3 converters can already achieve a favorable value for harmonic reduction. The additionally required inductance, which may be necessary for further current smoothing, is used exclusively to reduce harmonics with a high atomic number and can be designed with a small mass. With a minimum number of three partial converters, an effective reduction in the system mass can already be achieved.

For line voltages with z. B. 15 kV and the currently available IGBT modules with 3.3 kV Reverse voltage results in a total of 16 partial converters, if the requirement corresponds to the fact that two units should be able to be switched off in the event of an error. Which In the medium term, the provision of modules with 6.5 kV reverse voltage will be released later a reduction in the number of partial converters to 8. With voltage reserve according to today's  Stand-sized partial inverters with an intermediate circuit voltage of 1.5 kV can be operated with a specific mass of about 50 g / kW (or less) produce. Here is a low-loss operation with a pulse frequency of about 1 kHz and indirect cooling of the semiconductor components is provided via the base plate. The cascaded converter for 15 kV is thus z. B. by a performance-related mass of about To characterize 0.8 kg / kW.

By operating the transformer at a frequency of 400 to 500 Hz, the the required specific mass can be reduced to less than 0.2 kg / kW. This is from 2 to Comparing 2.5 kg / kW with the conventional transformer means a reduction by more than a factor of 10.

This is for services from z. B. 2 MW the system mass of the system to about 1 kg / kW or less to estimate. In addition to the obvious weight saving, the special incentive to significantly reduce losses compared to a conventional transformer solution. Regardless of the multi-stage application of Converter circuit can halve the losses compared to the web design of the Achieve transformers without much difficulty. Another positive point is the possible design of the system according to the invention with a low overall height.

In Fig. 1a, the circuit of the converter arrangement W consisting of converter F and transformer T is shown together with the smoothing inductance L _g . According to the invention, the cascaded partial converters F ₁₁ to F _n1 with their corresponding partial voltages U _F1 to U _Fn in the sum U _{Fe are achieved} largely sinusoidally by the offset pulse operation. By choosing certain pulse widths in the sequence of a half period, a certain pulse frequency and a suitable pulse offset of the partial voltages, specific harmonics in the voltage addition U _Fe and thus in the mains current can be suppressed. A certain minimum number of partial converters n and a certain pulse frequency f _{T are} necessary to achieve defined results.

In Fig. 2 the diagram with the most important parts of grid feed-N, converter F, transformer T as well as drive A and the motor M is shown.

Fig. 2'.1 shows a corresponding pulse pattern of the sum voltage U _Fe for the case of three partial converters, while the input voltage of a partial converter U _{Fn is} shown in Fig. 2'.2. The height of the voltage pulses is of the same type, their width is changed sinusoidally. U _F1 and other partial voltages differ from U _Fn only in the temporal offset of the pulse pattern. The degree of smoothing that can be achieved increases with the number of partial converters and the pulse frequency. It is thus achieved that primarily the high interference frequency of 2n caused by the pulse operation. f _T (with f _T the pulse frequency) is to be suppressed by the smoothing inductance L _g . With the system voltage thus achieved, there are only minimal differences compared to the sinusoidal mains voltage U _N according to FIG. 2.0. The very low harmonic operation is possible with a minimized smoothing device and small losses.

As shown in Fig. 2'.3, in which U _{dn shows} the voltage curve in the intermediate circuit of the partial converter n, the fluctuation .DELTA.U with twice the supply frequency of U _N in the size of 10 ÷ 15% of the mean value is permitted by the capacitor C. . A suction throttle circuit on the primary side of the transformer would be complex for insulation reasons and is not implemented here. Possibly. necessary smoothing measures are expediently carried out on the secondary side with little effort. In the intermediate circuit of converter A, which consists of a rectifier and an inverter, a suction throttle arrangement is provided according to FIG . So that z. B. the voltage U _dM according to Fig. 2'.5 in the intermediate _circuit with little fluctuation.

As indicated in Fig. 2'.4, these are. Inverters F ₁₂ to F _n2 all with identical and simultaneous pulse patterns, that is, pulsed synchronously. The voltages U _Tn as the input voltage of the primary windings of the same type with the number of turns w _p result in magnetic fluxes which are superimposed identically in the transformer magnetic circuit E and induce the common secondary winding with the number of turns w _s . The voltage U _T a generated there has the same fundamental frequency as U _T , but is reduced in relation to the input voltage U _N in the ratio of the number of turns w _s / nw _p .

As shown in FIG. 3, the pulsating power corresponds to the transformer current in such a way that its share of the fundamental frequency is modulated with the input frequency. The design of the transformer and the partial inverters feeding it must take into account the larger maximum current value.

A supplement to the converter circuit of F by the switches S1 and S2 is indicated in FIG. 1b. In the closed switch position of S1 and S2, the converter F is in a functional state and supplies the voltages just described to the primary windings w _{p of} the transformer in a pulsed form. If the monitoring circuit detects a malfunction in the rectifier GR or in the inverter WR, the winding w _p can be switched off by opening the two switches S1 and S2. This is followed by a resymmetry of the voltages with higher voltage pulses in the ratio n / n - 1 in the operationally remaining circuit. If a fault in the existing symmetrical voltage distribution is excited by faulty control or generally by switching processes, the proposed switching of the converter F, its 4-Q configuration ( FIG. 1b) with IGBT modules and their antiparallel diodes, and the aforementioned high-quality inductive coupling of the transformer T does not cause unstable behavior, even when control is not provided. It is assumed that in the case of a frame-shaped magnetic circuit on at least one half of the primary windings are positioned axially in close proximity and with little magnetic scatter. This ensures that the winding quickly communicates its change in voltage to a larger group of primary windings in a compensatory sense. This balancing effect is reinforced by the fact that the directional current flow of the diodes accelerates the compensation process even further.

System applications in which drive motors are fed directly and to a limited extent with a variable frequency compared to the mains voltage U _N and transmitted by the transformer are also possible and can also be carried out in a suitable form.

FIG. 4a illustrates an example in which the transformers T1 and T2 w of the same design with the secondary windings _S1 and w _s2 mlt iron cores E1 and E2, and with two groups of primary windings w _p1 to w _p3 and w _p4 to w _p6 divided are . The frequency converters F are also divided into the two groups F _G1 and F _G2 ; the input voltages are U _Fe 1 and U _Fe 2, which add up to the total voltage U _Fe , FIG. 4b.

It is further assumed in FIG. 4a that the drive motor M is equipped, for example, with two windings which are operated offset by 90 °, the windings wma and wmb of which are to be fed with correspondingly phase-shifted voltages U _T1a and U _T2a FIG. 4c. It should also be taken into account that the motor does not have to be operated at frequency 0, but that sufficient power for operating the drive is only available from the transformer above a certain minimum frequency f ₀ . The voltage at the transformer U _T rises with increasing frequency, so that the drive can be supplied with increasing power. The maximum value of the power is reached at a frequency f ₁ , which is already several times higher than the input frequency or the feed frequency of the network. This means that a weight advantage similar to that of a transformer with only one unit can be achieved even when using several transformer units and the converter circuit cascaded on the network side. The effects of a power restriction at low frequencies are e.g. B. easily tolerable with asynchronous motors and can be minimized under certain conditions even with synchronous motors.

Claims (7)

1.Infeed system consisting of frequency converter and transformer for low-mass conversion of a high alternating voltage of low frequency into one or more lower voltages of higher frequency by using several similar converter modules, each consisting of two partial converters, which in turn are connected via a DC link and cascaded on the input side and the output of which carries a voltage which is a fraction of the input voltage and whose frequency at full power is a multiple of the input frequency, characterized in that the similar partial converters are designed in a 4-Q circuit and are connected to at least one transformer, where the number of primary windings corresponds to the number of partial converters, the primary windings per transformer are inductively coupled with high quality and in turn have good coupling with one common secondary winding per transformer, d The voltage of the primary windings is selected so that high-blocking semiconductor switches can be used in one stage in the partial inverters, which are stress-balanced without active regulation with regard to voltage distribution or an additional circuit, but the number of partial inverters per transformer is at least 3. 2. Feed system according to A1, characterized in that the voltage of the input converter consists of a sequence of similar pulse patterns which are offset from each other and the pulse frequency is about 1 kHz, while the Output converter with synchronized pulse trains and approximately twice the pulse frequency are operated, the fundamental frequency of the secondary voltage being the frequency of the Input voltage is superimposed. 3. feed system according to the above claims, characterized in that the DC intermediate circuits of the frequency inverters with the same size intermediate circuit capacitors C are equipped, the limited voltage fluctuations of  Allow 10 to 15% of the mean with double the feed frequency and one Transformer design is selected which is the current modulated with this frequency and thus a correspondingly increased effective value electromagnetic and thermal taken into account, the voltage fluctuations in downstream filter elements be included on the low voltage side. 4. feed system according to the above claims, characterized in that in the event of faults in partial inverters, these are deactivated by additional switches be taken, and the remaining inverters take over the operation, whereby the design of the switching elements for the maximum value of those occurring in the event of a fault Tension occurs. 5. feed system according to the above claims, characterized in that the secondary voltage is chosen so that the converter of the prime mover (or machines) with single-level semiconductor switching elements (without Series connection) are equipped and from an insulation and thermal point of view for an appropriate machine design with low mass and high Torque leads. 6. feed system according to the above claims, characterized in that the driver circuits for the IGBT modules via optical fibers and thus with galvanic isolation can be controlled, their power supply also galvanic separated by transformer, and that additional functions such as short circuit circuit and the delivery of monitoring signals with the help of optical fibers are integrated. 7. feed system according to the above claims, characterized in that The converter and transformer with separate cooling circuits are designed in this way Inverter is structured by modular series arrangement so that assembly and Replacement of partial circles of the converter can be easily made.