Measuring average of phase voltage of a frequency converter based on an idealized waveform

摘要

A method and arrangement for determining the effective time of a voltage pulse of phase voltage generated by a frequency converter provided with an intermediate voltage circuit, the voltage pulses of the phase voltage being generated from the upper and lower voltage levels (U_DC, 0) of the intermediate voltage circuit, the voltage levels showing a difference in potential (U_DC). The method includes generating a first reference voltage (U_ref1) and a second reference voltage (U_ref2); scaling the phase output voltage by the scaling coefficient (k); comparing the low-pass filtered phase output voltage with the first reference voltage (_Uref1); detecting a time instant (t₁) when the low-pass filtered phase output voltage exceeds the first reference voltage (U_ref1); comparing the low-pass filtered phase output voltage with the second reference voltage (U_ref2); detecting a time instant (t₂) when the low-pass filtered phase output voltage is lower than the second reference voltage (U_ref2); and calculating the effective time of the voltage pulse on the basis of the time between the first and the second time instants and a constant term.