Active compensation filter

#The present invention claims priority from DE 10 2007 021 978.6, filed May 10, 2008.

#In the following, an active compensation filter will be described which, for example, lends itself for the application in the electric power supply of a land vehicle. This may involve a power supply (accumulator in a vehicle electric system) for vehicles, which is connected in series with one or several central or distributed d.c. voltage/d.c. voltage converters (DC/DC converters) as a voltage stabiliser.

#Due to the ever increasing electrification of motor vehicles, the demand for electric energy in motor vehicles is increasing considerably. In addition, the power consumers in motor vehicles impose increasing requirements to the quality of the power supply (voltage stability and low interference signal susceptibility). This does not only apply to “comfort consumers” (audio system, navigation system, air conditioning system, etc.), but in particular to function or safety relevant consumers (onboard computer, brake control system, fuel injection control system, etc.) of the motor vehicle. In the case of occurring load peaks, for example, in particular during the starting operation of the motor vehicle, this may have the effect that consumers which have already been activated do no longer function properly or are subjected to interference signals via the power supply because of the load applied by the starter. While, in the case of the audio system, this may be experienced as “merely” annoying, critical functional abnormalities may occur in other function or safety relevant consumers (onboard computer or the like). Such interference effects are particularly noticeable in the start/stop mode of motor vehicles, which for fuel economy reasons is increasingly favoured.

#FIG. 1 schematically shows an overall circuit diagram of a power supply of a motor vehicle with several consumers, into which an active compensation filter is integrated.

#FIG. 2 schematically shows a DC/DC converter which is connected in series with an active compensation filter illustrated in the form of a block diagram.

#FIG. 3 schematically shows a circuit diagram of an active compensation filter from FIG. 1 or 2, respectively.

#Identical or similar components or assemblies with identical or similar functions are identified with the same reference numerals in the figures.

#FIG. 1 shows a portion of the electric system of a motor vehicle. A battery B, more precisely an accumulator, may put a combustion engine (not shown) into operation upon the actuation of a key switch S, the ignition key, via a starter A. The battery B also feeds a DC/DC converter W which provides stabilised 12 V from the uncontrolled voltage of the battery B from 8 V to 14 V for a plurality of electric consumers V1 . . . Vn (audio system, navigation system, air conditioning system, etc., or onboard computer, brake control system, fuel injection control system, etc.). In place of a single central DC/DC converter W for several electric consumers of the motor vehicle it is also possible to provide a plurality of decentralised DC/DC converters W for each or some of the plurality of the consumers V1 . . . Vn. An active compensation filter 10 is connected between the/each DC/DC converter(s) W and the consumers V1 . . . Vn. The active compensation filter 10 may additionally also be connected in the supply line between the battery B and the/each DC/DC converter(s) W.

#In FIG. 2, the active compensation filter 10 is shown as a detailed block diagram compared to FIG. 1, with the filter 10 being connected in series with the DC/DC converter W from FIG. 1. The active compensation filter 10 has a high-pass filter HP which is to be coupled with a supply voltage line from the DC/DC converter W. This supply voltage line carries/supplies an essentially constant supply voltage is, however, superposed by interference voltage components. The high-pass filter HP serves to detect frequency and amplitude of interference voltage components of the supply voltage—DC voltage-free. The high-pass filter HP may also be part of a bandpass filter, provided the frequency components of the interference voltage components are merely situated within a determinably frequency band. The active compensation filter 10 has a signal amplifier SV which is connected in series with the high-pass filter, which amplifies detected interference voltage components and feeds them as output signals to a coupling transformer L1/L2. The coupling transformer L1/L2 is connected in series with the signal amplifier SV. A primary side L1 is fed by an output of the signal amplifier SV. A secondary side L2 of the coupling transformer is looped into the supply voltage line from the DC/DC converter W.