An improved active front end non-regenerative rectifier system employing a five-limb inductor

Variable frequency drives (VFDs) draw discontinuous current from the power system resulting in current distortion and consequently voltage distortion. Limiting current distortion to levels recommended in IEEE 519-1992 improves system efficiency, increases reliability, and limits voltage distortion that can adversely influence sensitive loads. This paper revisits a non regenerative active front end system that has been studied in the past but offers significant improvements to make it acceptable to the drives industry. A three-phase current injecting inductor, required in the topology, is constructed in a five limb fashion and is shown to be helpful in limiting non characteristic harmonics. Since the current injected into the split dc bus capacitor is a 360Hz ripple, it is proposed that the main dc bus capacitor be split into film capacitor for ripple current and optimally reduced electrolytic capacitor for the main energy storage requirements. Experimental results are given based on the suggested improvement and low distortion levels that were not achieved in the past have been shown to be attainable. Comparison between a standard three-limb inductor and a five-limb inductor is made to highlight the performance improvements achievable. Adoption of the topology for common dc bus applications is also proposed.