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

Proliferation of variable frequency drives in the industry has lead 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 drive feeds such as the load commutated inverter (LCI), the current source inverter (CSI) and pulse-width modulated (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. The methods presented in this paper have formed the basis of the design guidelines for distribution systems with large variable frequency drives