This paper presents the description of the current distortion produced to the grid by voltage-source active rectifiers switched by PWM. In recent years, high demands are placed on the development of the power electronics such as high performances, high switching frequencies, high efficiency, etc. Therefore the aim of the paper is the cognition of the influence combination of switching frequencies and dead time durations on harmonics orders and values in an input current spectrum. The paper summarizes the parameters influences on the calculations of current total harmonic distortion (THDI) and presents interesting results of two THDI definitions. If the THDI is calculated up to the frequency which is higher than the switching frequency, the result will be different from the result which is obtained according to IEC standard. Therefore, this paper proves that total harmonic distortion has to be calculated up to the harmonics orders that are higher than the switching frequency of the converter.

Keywords: Harmonic analysis, Power quality, Pulse width modulation (PWM), Total harmonic distortion, Voltage-source active rectifier