Converter with active damping of the intermediate circuit voltage

Abstract

In a method for operating a controllable converter with an intermediate circuit capacitor, the control behavior can be improved by transmitting, depending on an intermediate circuit voltage applied to the intermediate circuit capacitor, an additional power component via the controllable converter such that the electric current that is generated by the controllable converter for the additional power component counteracts an oscillation of the intermediate circuit voltage. The additional power component is transmitted by the controllable converter to a connected motor as a pulsating additional torque. Also described is a controllable converter with a control unit for carrying out a method, wherein the controllable converter has semiconductors that can be switched off, and an intermediate circuit capacitor designed as a film-type capacitor.

Claims

1. A method for operating a controllable converter connected to a motor and having an intermediate circuit capacitor embodied as a film capacitor, the method comprising: transmitting via the controllable converter an additional power component in dependence on an intermediate circuit voltage of the intermediate circuit capacitor such that an electric current generated for the additional power component counteracts an oscillation of the intermediate circuit voltage only when a periodic oscillation of the intermediate circuit voltage is detected and when this periodic oscillation lies in a predetermined frequency range that includes a resonant frequency composed of the intermediate circuit capacitor and a motor inductance of the motor; and transmitting the additional power component to the motor as a pulsating additional torque.

2. The method of claim 1, wherein a nominal voltage of the controllable converter is less than or equal to 1000 V.

3. The method of claim 1, wherein a nominal voltage of the controllable converter is equal to 400 V.

4. The method of claim 1, further comprising measuring the intermediate circuit voltage at the intermediate circuit capacitor or the current through the intermediate circuit capacitor to detect the periodic oscillation of the intermediate circuit voltage.

5. The method of claim 4, further comprising filtering the measured intermediate circuit voltage or the measured current.

6. A controllable converter comprising semiconductors that can be switched off, an intermediate circuit capacitor embodied as a film capacitor, and a converter regulator controlling the semiconductors and configured to transmit via the controllable converter an additional power component in dependence on an intermediate circuit voltage of the intermediate circuit capacitor such that an electric current generated for the additional power component counteracts an oscillation of the intermediate circuit voltage only when a periodic oscillation of the intermediate circuit voltage is detected and when this periodic oscillation lies in a predetermined frequency range that includes a resonant frequency composed of the intermediate circuit capacitor and a motor inductance of the motor, and transmit the additional power component to the motor as a pulsating additional torque.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The following describes and explains the invention in more detail with reference to the exemplary embodiments depicted in the figures, in which:

(2) FIG. 1 shows a converter with a voltage intermediate circuit,

(3) FIGS. 2 and 3 show an electric drive system in each case,

(4) FIG. 4 shows a regulation diagram, and

(5) FIG. 5 shows a section of an active current regulator.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(6) FIG. 1 shows a controllable converter 1 with an intermediate circuit capacitor 2. In this case, the controllable converter 1 converts a voltage U.sub.ZK, which is applied to the intermediate circuit capacitor 2, into an AC voltage, which is applied to the three outputs of the controllable converter 1. For this purpose, the controllable converter 1 uses semiconductors 7, which are switched accordingly, The capacitor current i.sub.C flows through the intermediate circuit capacitor 2.

(7) Depending upon the set voltages, power is transmitted via the converter 1. In this case, in addition to the power desired for operation, which, for example, causes a torque on a motor not shown here, an additional power component can be transmitted, which causes a current i.sub.C through the intermediate circuit capacitor 2 and counteracts a fluctuation present in the intermediate circuit voltage U.sub.ZK.

(8) FIG. 2 shows a drive system 5 as a typical application for a controllable converter 1. In this case, the intermediate circuit with its intermediate circuit capacitor 2 is supplied with energy via a diode rectifier 11, also referred to as a diode bridge, from a power supply network 4. This energy is further transmitted via the controllable converter 1 to a motor 3 connected there. The controllable converter 1 can be used to control or regulate the behavior of the motor 3, in particular with respect to its torque or speed. The controllable converter 1 can be used to eliminate fluctuations in the intermediate circuit voltage U.sub.ZK by transmitting an additional power component P.sub.add to the motor 3. This additional power component P.sub.add then causes an additional torque in the motor 3. For a more precise description of the controllable converter, reference is made to the description for FIG. 1 and the reference symbols used there.

(9) FIG. 3 shows a further exemplary embodiment of a drive system 5. To avoid repetition, reference is made to the description for FIG. 2 and the reference symbols used there. In contrast to the previous exemplary embodiment, a further controllable converter 1 is arranged here instead of the diode rectifier 11. The two controllable converters 1 that are now present now enable damping of the intermediate circuit voltage U.sub.ZK to be performed by both converters 1. Depending upon the distribution between the two converters 1, this then causes currents in the power supply network and an additional torque in the motor.

(10) FIG. 4 shows a simplified regulation diagram for performing the method. Based on a voltage detection 8, the value of the intermediate circuit voltage U.sub.ZK is transmitted to a filter 6. In this case, the filter 6 can only transmit the intermediate circuit voltage U.sub.ZK in specific frequency ranges or filter out specific frequencies in order to improve the behavior of the method for eliminating voltage fluctuations. In this case, the frequencies can be fixed or obtained in dependence on the motor frequency.

(11) This filter 6 is an optional component of the regulator which can quite easily be dispensed with if the damping of the intermediate circuit voltage U.sub.ZK is to be damped over a wide band. Dispensing with the filter 6 enables the motor frequency f.sub.Mot and the intermediate circuit voltage U.sub.ZK to be fed directly to the regulator 9. The regulator 9 determines from the value of the intermediate circuit voltage U.sub.ZK, directly or from the filtered signal, the additional power component P.sub.add to be transmitted by the controllable converter 1 to reduce or eliminate the voltage fluctuation at the intermediate circuit capacitor 2. The converter regulator 10 converts this information back into switching pulses for the semiconductors 7. In this case, the tasks of the regulator 9 and the converter regulator 10 can be combined in one hardware assembly for regulating the converter 1. Parts of the converter regulator 10 for controlling the active components of the current by the controllable converter 1 are shown in FIG. 5. Both the setpoint torque M.sub.soll for the motor 3 of the drive system 5 and the additional power component P.sub.add are converted into respective current components i.sub.add, .sub.iSR,soll. These current components are added together and produce the setpoint for the active current .sub.iq,soll within the converter regulator 10. The active current regulator is then converted in a known manner into control pulses for the semiconductors 7 of the controllable converter 1.

(12) In summary, the invention relates to a method for operating a controllable converter with an intermediate circuit capacitor. To improve the controllable converter, in particular in respect of its regulation behavior, it is suggested that, in dependence on an intermediate circuit voltage applied to the intermediate circuit capacitor, an additional power component is transmitted via the controllable converter in such a way that the electric current produced for the additional power component counteracts oscillation of the intermediate circuit voltage by means of the controllable converter. The invention further relates to a controllable converter with a regulating unit for carrying out a method of this kind, wherein the controllable converter has semiconductors that can be switched off and an intermediate circuit capacitor, wherein the intermediate circuit capacitor is embodied as a film capacitor.

(13) In other words, the invention relates to a method for operating a controllable converter with an intermediate circuit capacitor. To improve the controllable converter, in particular in respect of its regulation behavior, it is suggested that, in dependence on an intermediate circuit voltage applied to the intermediate circuit capacitor, an additional power component is transmitted via the controllable converter in such a way that the electric current produced for the additional power component counteracts oscillation of the intermediate circuit voltage by means of the controllable converter, wherein the additional power component is transmitted to the motor in the form of a pulsating additional torque by means of the controllable converter.