The invention provides a method and an apparatus for estimating an RMS current (Ic,rms) of an intermediate circuit capacitor (CZWK) for a complete system of a battery (1), an inverter (9) and an N-phase electrical machine (6), wherein, in the complete system, the inverter (9) converts a DC power received from the battery (1) for the purpose of energizing the electrical machine with N phase currents, and wherein the RMS current (Ic,rms) of the intermediate circuit capacitor to be estimated is calculated according to a calculation rule which is supplied with predefined switching times (tLow,off, tHigh,off) of the N phases of the electrical machine, measured phase currents (ISu, ISv, ISw) of N-1 phases or N phases of the electrical machine and a predefined battery direct current (IBatt) as input variables. This makes it possible to exactly estimate the RMS current (Ic,rms) of an intermediate circuit capacitor for any desired pulse patterns for controlling the inverter.
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