Publication

Abstract : This paper presents a diagnostic study on the regular sampled Space Vector PWM (SVPWM) for sub-harmonics, when operated with fractional carrier ratios in variable frequency applications. Also a modified approach is proposed for refinement of the harmonic profile of SVPWM with a low computational dynamic sampling and carrier generation. When inverters are operated at fractional fundamental frequencies with its carrier frequencies kept constant, the PWM is made to operate with non-integer frequency modulation ratios. The experimental studies carried out under such conditions unveiled the presence of sub and inter harmonics in the inverter outputs. A 1.1 kW induction motor drive has been formulated and developed with the capability to vary the time relationship between different control signals of SVPWM, so as to reason out this uncharacteristic harmonics in the inverter. From the test results it is identified that, a certain relationship has to be maintained between the fundamental, sampling and carrier frequencies in SVPWM, failing which results loss of synchronization amongst the control signals giving rise to uncharacteristic harmonics. A mitigation technique is proposed to maintain a dynamic synchronization by generation of varying frequency carrier signal along with dynamic sampling. Experimental confirmations are presented through harmonic profiles from the proposed dynamic sampled SVPWM and compared with the regular sampled SVPWM. A substantial reduction in the magnitudes of sub harmonics has been observed with the proposed SVPWM compared with the conventional regular sampled SVPWM.