Title of Invention

DRIVE DEVICE FOR ROLLING STANDS

Abstract

A drive device for rolling stands, having at least one electric motor and at least one converter via which the electric motor is connected to an AC power supply system, the converter controlling the active-power drain for speed and/or torque of the electric motor. The converter is designed to feed an adjustable reactive power into said AC power supply system. The converter is provided with power semiconductors regulated or controlled by means of a controlling system (7). A device (9) is provided for stipulating a desired reactive power value in accordance with the desired reactive power fed into said AC power supply system.

Full Text

-1A-Description Drive device for railing stands The invention relates to a drive device for rolling stands. Industrial systems which supply large-scale driven, for example AC power supply systems for rolling mills, are subjected to strong inductive reactive power- This leads to local voltage depressions and high 1ine losses. Systems which are weak or remote from generator terminals are particularly affected thereby- It is known to solve the problem by expensive power factor correctors which comprise switched capacitor banks and, if appropriate, additional controlled stabilizers (thyristor power controllers and inductors). It is the object of the invention to specify a drive device by means of which it is possible to achieve simple and more cost-effective power factor correction. This object is achieved according to the invention by means of a drive device rolling stands with at least one converter designed to feed an adjustable reactive power into said AC power supply system, said converter having power semiconductors regulated or controlled by means of a controlling system and a device is -1B- provided for stipulating a desired reactive power value in accordance with the desired reactive power fed into said AC power supply system. In this case, the drive device has at least one three phase AC motor and at least one converter via which the three phase AC motor is connected to an AC power supply system, the converter controlling the active-power drain of the three phase AC motor from the AC power supply system, and being designed to feed an adjustable, in particular capacitive reactive power into the AC power supply system- It is possible in this way to eliminate expensive correctors for the drive device - In an advantageous embodiment of the invention, the drive device is designed in such a way that it compensates the inductive and/or capacitive relative power at least of one device which generates reactive power and is connected to the AC power supply system. This is a particularly advantageous embodiment, since it is possible in this way to eliminate expensive power factor compensators for further devices which generate reactive power, in particular drives which are connected to the AC power supply system. It is possible, in this - 2 - way, to design particularly cost effective drive devices for industrial systems, in particular for rolling mill trains. In a further advantageous embodiment of the invention, the drive device is designed in such a way that it compensates the reactive power in accordance with the fundamental of the AC voltage of the AC power supply system. In a further advantageous embodiment of the invention, the drive device is designed in such a way that star reactive power is compensated in accordance with one or more harmonics of the AC voltage of the AC power supply system, with the result that it is also possible to eliminate filter banks for compensating harmonics. In a further advantageous embodiment of the invention, the drive device has a link voltage computing unit which calculates the link voltage as a function of the voltage of the AC power supply system. It is particularly advantageous that the drive device according to the invention is used for drives in a power range from 1 to 20 MW, advantageously from 2 to 10 MW, or, with reference to an impulse load, in a power range from 2 to 30 MW, advantageously from 4 to 20 MW. The drive device according to the invention has further proved to be particularly advantageous in conjunction with three-phase AC motors in tandem connection, that is to say in the case of circuits in which the three-phase AC motor has open windings which are fed on both sides by converters. The drive device according to the invention is applied, furthermore, in a particularly advantageous fashion to drive rolling stands of a rolling mill train. The drive device according to the invention is used with particular advantage for voltage stabilization of the power supply system by feeding reactive power. The converter of the drive device according to the invention can, moreover, be designed as an air-cooled converter. - 3 - Further advantages and inventive details emerge from the following description of exemplary embodiments, with the aid of the accompanying drawings and in conjunction with the subclaims. In detail: Figure 1 shows a drive device according to the invention. Figure 2 shows a controlling system for a drive device according to the invention. Figure 3 shows a converter arrangement for feeding a three-phase AC motor with component inverter in a three-point circuit on the mains side and machine side. Figure 4 shows a converter arrangement for feeding on both sides a three-phase AC motor with an open winding, with component inverter in a three-point circuit, and Figure 5 shows the use of a converter according to the invention in a rolling mill. Figure 1 shows a drive device according to the invention, having a three-phase AC motor 6 which is connected via a converter and via a transformer 2 or an inductor to a power supply system 1. The converter has a self-commutated rectifier 3, a DC link 4 and a self-commutated inverter 5. The power consumption of the three-phase AC motor 6 from the power supply system 1 is controlled by means of a controlling system 7. For this purpose, the controlling system is stipulated a voltage link value U*ZK which the inverter 5 requires in order to adjust torque, speed and/or power of the three-phase AC motor 6. The controlling system 7 controls the self-commutated rectifier so as to produce at the output thereof a link voltage U*ZK which corresponds to the desired link voltage U*ZK. Furthermore, the controlling system 7 is fed a desired reactive-power value Q*. The controlling system 7, controls the self-commutated rectifier 3 in such a way that it outputs to the power supply system 1 a reactive power which corresponds to the desired reactive power Q*. In the exemplary embodiment in accordance with Figure 1, the drive device according to - 4 - the invention has a device 9 for stipulating the desired reactive-power value Q*. Said device advantageously stipulates a desired reactive-power value Q* which leads to a reactive-power output of the drive device according to the invention which compensates the reactive-power output of devices 8 generating reactive power to the power supply system 1. In this case, the drive device according to the invention can compensate both the reactive power in accordance with the fundamental of the AC voltage of the power supply system 1, and the higher-frequency harmonic components thereof. Figure 2 shows an exemplary detailed embodiment of the controlling system 7 of Figure 1. In the exemplary embodiment, the controlling system 7 has a link voltage regulator 10, an active-current regulator 11, a reactive-current stipulator 12, a reactive-current regulator 13, a control device 14 and a measured-value conditioner 15. The link voltage regulator 10 determines from the desired link voltage U*2F and from the link voltage UZK a desired value I*W for the active current. The reactive-current stipulator 12 determines a desired reactive-current value I*B from the desired reactive-power value Q*. Desired values for the voltage between the transformer 2 and the self-commutated rectifier 3 are generated by the active-current regulator 11 from the desired active-current value l*w and the actual active-current value Iw. Desired values for the voltage between the transformer 2 and the self-commutated rectifier 3 are likewise generated by the reactive-current regulator 13 from the desired reactive-current value I*B and the actual reactive-current value IB. The outputs of the active-current regulator 11 and the reactive-current regulator 13 are fed to a control device 14 which generates control signals for the power semiconductors of the self-commutated rectifier 3 in such a way that the desired voltages are produced on the AC current side of the self-commutated rectifier 3. In an advantageous embodiment, the outputs of the active-current regulator 11 and of the reactive-current regulator 13 are added by the control device 14. The - 5 - actual active-current value Iw, the actual reactive-current value IB and the link voltage U2K are measured or advantageously determined by means of a measured-value conditioner 15. The latter determines the active current Iw and the reactive current IB from measured values of the current between the transformer 2 and the self-commutated rectifier 3 by means of the orientation of the phase angle of current and voltage of the power supply system 1. The device 9 for stipulating the desired reactive-power value Q* determines the latter, for example, by measuring current and voltage of the AC power supply system 1. In an alternative embodiment, the reactive-power requirement or an equivalent variable is determined, from knowledge of the devices connected to the power supply system, in the device 9 for stipulating the desired reactive-power value Q*. In a particularly advantageous embodiment, the device 9 for stipulating the desired reactive-power value Q* is connected to a higher-order control system or part of such a control system, and determines the reactive-power requirement from knowledge of the devices connected to the AC power supply system 1 and of their operational states. Thus, for example, a plurality of drive devices according to the invention can also have a single device 9 for stipulating their desired reactive-power values Q*. Figure 3 shows a converter arrangement for feeding a three-phase machine, the system-side component converter 33 on the mains side and the component converter 34 on the motor side being designed with GTOs in a three-point circuit, in the same way in each case. The main circuit of a phase module with its snubber network 40 and 41, respectively, is represented in each case. The component converters 33 and 34 each have three such phase modules. Together with the N-side link capacitor 39, the P-side link capacitor 37 forms the DC link via which the two component converters are connected. The P-side snubber charge feedback resistor 36 and the N-side snubber charge feedback resistor 38 are - 6 - connected to the respective side of the snubber networks 40 and 41, respectively. The mains-side component converter 33 is connected on the output side to the system 30 via the transformer 31 and the circuit breaker 32. The machine-side component converter 34 is connected on the output side to the three-phase AC motor 35. In the arrangement in Figure 4, a first converter 74 and a second converter 75 are respectively connected on the output side to a side 71 and 72 of the open three-phase winding of the three-phase AC motor 73. In addition to a doubling of the power, this arrangement achieves a particularly advantageous operational performance, since, assuming an appropriately tuned pulse method, a largely sinusoidal current characteristic is achieved in the motor with a low total harmonic distortion, even in the case of a low switching frequency of the GTO thyristors. On the mains side, the first converter 74 is connected to the power supply system 60 via an optional mains-side supplementary inductor 63 and a first transformer 61, for example in a star/delta connection. The second converter 75 is connected to the power supply system 60 via an optional mains-side supplementary inductor 64 and a second transformer 62, advantageously offset by 30° electrical with respect to the first transformer 61 (for example in a star/delta connection). This arrangement leads to particularly favourable perturbations on the system, in particular when, as in the present example, the converters comprise component converters in a three-point circuit. Even given synchronization of fundamentals of the self-commutated mains power converters, the result in this case is a sinusoidal current characteristic with a very low total harmonic distortion. The two converters 74 and 75 each have mains-side component converters 66 and 65, respectively, and machine-side component converters 69 and 70, respectively, which are connected in each case via a DC link 67 and 68, respectively. The two DC links 67 and 68 are - 7 - electrically separated from one another. All the component converters 66, 65, 69, 70 are designed using a three-point circuit, preferably with RC-GTOs. Figure 5 shows the use of an operating device according to the invention in a rolling mill. The material to be rolled 103 is rolled in the rolling stands 104, 105, 106, 107, which are driven by electric motors 99, 100, 101, 102. The motors 99, 100, 101, 102 are fed by a power supply system 90 via one transformer 91, 92, 93, 94 each and one converter 95, 96, 97, 98 each. In a possible exemplary embodiment, the transformer 91, the converter 95 and the three-phase AC motor 99 are part of a drive device according to the invention, which compensates the reactive power generated by the drive devices of the other rolling stands 105, 106, 107. The proportion of drive devices according to the invention for reactive-compensation power factor connection and known drive devices is essentially governed by the requirement for capacitive reactive power in order to compensate the inductive reactive power of conventional drive devices. However, it is more important in practice to have a design in which all the drives of a rolling mill train are designed according to the invention and compensate the reactive power of the drives of other rolling mill trains. -8- WE CLAIM: 1. A drive device for rolling stands, having at least one electric motor and at least one converter via which the electric motor is connected to an AC power supply system, the converter controlling the active-power drain for speed and/or torque of the electric motor; characterized in that , said converter is designed to feed an adjustable reactive power into said AC power supply system; said converter having power semiconductors regulated or controlled by means of a controlling system (7); and a device (9) is provided for stipulating a desired reactive power value in accordance with the desired reactive power fed into said AC power supply system. 2. A drive device as claimed in claim I, wherein t is designed to compensate the reactive power at least of a device (8) which generates reactive power and is connected to the AC power supply system. 3. A drive device as claimed in claim 2, wherein it is designed to compensate the reactive power in accordance with the fundamental of the AC voltage of the AC power supply system. -9- 4. A drive device as claimed in claim 2 or 3, wherein it is designed to compensate reactive power in accordance with one or more harmonics of the AC voltage of the AC power supply system. 5. A drive device as claimed in any one of the preceding claims, wherein the converter is designed as a converter with a DC link in a three-point circuit. 6. A drive device as claimed in any one of claims I to 4, wherein the converter is designed as a converter with a DC link in an n-point circuit, n being greater than or equal to 2. 7. A drive device as claimed in any one of claims 1 to 6, wherein the disconnectable power semiconductors are designed as GTGs, that is to say as Gat(c) Turn Off Thyristors. 8. A drive device as claimed in any one of claims 1 to 7, wherein the converter has disconnectable power semiconductors which are designed as MCTs, that is to say as MOS Controlled Thyristors. 9. A drive device as claimed in any one of claims 1 to 8, wherein the converter has disconnectable power semiconductors which are designed as power transistors, in particular as ISBTs, that is to say Insulated Gate Bipolar Transistors. - 10 - 10- A drive device as claimed in any one of claims 1 to 9, wherein the disconnectable power semiconductors are designed to be reverse conducting. 11- A rolling mill train with one or more rolling stands (104, 105, 106, 107) for rolling material to be rolled CI03), in particular a rolling strip, wherein at least one rolling stand is driven by a drive device as claimed in any one of the preceding claims. 12. A rolling mill train as claimed in claim 11, wherein the majority of the rolling stands, in particular all the rolling stands (104, 105, 106, 107) are driven by a drive device as claimed in one of claims 1 to 10- 13. Method for rolling steel by means of a rolling mill train as claimed in claim 11 or 12, wherein the drive devices for the rolling stands are designed to compensate the reactive power generated by other rolling mill trains. A drive device for rolling stands, having at least one electric motor and at least one converter via which the electric motor is connected to an AC power supply system, the converter controlling the active-power drain for speed and/or torque of the electric motor. The converter is designed to feed an adjustable reactive power into said AC power supply system. The converter is provided with power semiconductors regulated or controlled by means of a controlling system (7). A device (9) is provided for stipulating a desired reactive power value in accordance with the desired reactive power fed into said AC power supply system.

Documents:

02104-cal-1997-abstract.pdf

02104-cal-1997-claims.pdf

02104-cal-1997-correspondence.pdf

02104-cal-1997-description(complete).pdf

02104-cal-1997-drawings.pdf

02104-cal-1997-form-1.pdf

02104-cal-1997-form-2.pdf

02104-cal-1997-form-3.pdf

02104-cal-1997-form-5.pdf

02104-cal-1997-gpa.pdf

02104-cal-1997-priority document.pdf

2104-CAL-1997-(04-10-2012)-FORM-27.pdf

2104-CAL-1997-CORRESPONDENCE 1.1.pdf

2104-CAL-1997-FORM-27.pdf

2104-CAL-1997-PA.pdf