DSP Based Realization of Pre-Processed Discontinuous PWM Schemes for 3-Limb Core Coupled Inductor Inverters

Abstract

The design of most power electronic systems is ultimately linked to the devices being used, the system efficiency and the system cost. A Digital Signal Processor (DSP) based 3-phase Pulse Width Modulation (PWM) switching scheme for a 3-Limb Core Coupled Inductor Inverter (CII) is presented as a low cost controller solution to provide better excitation for the magnetic core. This is consistent with lowering the cost of the power converter system with the use of a 3-limb core, as opposed to three separate inductors, and reduced switch count for the inverter. A modified interleaved discontinuous PWM scheme is examined that restrains the main inductor magnetic flux to lie within the magnetic core. This basic guideline for a suitable PWM scheme is to guarantee that all the inverter switching states maintain a zero inductor net winding voltage for the three phases. The scheme also smoothens the high frequency winding current ripple. In a practical sense, such a scheme normally requires extensive control and PWM tasks which calls for a high-end processor with parallel and post-processing capacities, hence increasing system costs. A low cost solution, by manipulating the original conceptual scheme, is introduced as an alternative Pre-Processed PWM scheme for a DSP environment, using only one carrier signal. Experimental results verify that the DSP PWM module can successfully implement the target scheme in a less complex manner. The DSP realization of the PWM scheme not only provides cost effectiveness by eliminating the need for a high-end processor, but also minimizes the size of the control circuitry. Experimental results confirm that the DSP based scheme offers the same system high power conversion efficiency as the original conceptual PWM scheme, due to benefits related to the reduction of the high frequency winding current ripple