Application, design, and specification of harmonic filters for variable frequency drives

The proliferation of variable frequency drives in industry has led to serious concerns about power quality in electrical distribution systems. This paper presents tables and charts to help the system design engineers address some basic concerns such as the need for harmonic filters, their effect on displacement power factor, etc., without going into a full-scale harmonic analysis of the distribution system. Relative harmonic performance of the different types of drives such as the load commutated inverter (LCI), the current source inverter (CSI), and PWM drives is discussed. A factor called the harmonic factor is defined which can characterize the performance of a drive by a single number. The relation between harmonic factor and the total harmonic voltage distortion is derived. Attenuation of the harmonic voltages by the filters is calculated and presented in the form of generalized curves