SYNTHESIS METHODOLOGY FOR SIMPLIFIED ZVT TOPOLOGIES APPLIED TO BIDIRECTIONAL PWM POLES / METODOLOGIA DE SÍNTESE DE TOPOLOGIAS ZVT SIMPLIFICADAS APLICADAS A PÓLOS PWM BIDIRECIONAIS
Rafael Concatto Beltrame
DATA DE PUBLICAÇÃO
Among the soft-switching techniques, the zero-voltage-transition (ZVT) technique has been accepted well by the industry due its attractive characteristics, such as simplicity, low losses in the auxiliary commutation circuit (ACC), operation with soft-switching for a wide load range, and closest operation to the PWM converter counterpart. In three-phase voltage-source inverters (multipole converters), a substantial diversity of ZVT topologies has been proposed to improve the performance of the converters, such as the ZVT circuits with six auxiliary switches, which meet the demand for high efficiency, low current and voltage stresses in semiconductor devices, and operation in high switching frequency. Aiming to make the ZVT multipole converter even more attractive to the industry, many topologies have been proposed to reduce the number of auxiliary switches and, consequently, the cost related to the ACC, by means of an integrated auxiliary circuit that provides conditions to commutate every semiconductor device of the multipole converter under zero-voltage condition. Regrettably, these structures introduce some restrictions on converter operation, such as the requirement for synchronized switching events in the PWM poles, resulting in more complex modulation techniques, with poorer power quality than the six auxiliary switch ZVT. To avoid these restrictions, simplified ACCs have been proposed, where the ACC is simplified individually per PWM pole. An important consequence of this approach is that the PWM poles can be modulated independently in multipole applications, allowing the application of any modulation strategy. However, the known simplified ZVT topologies were derived by multiple attempts due to the lack of a synthesis methodology, as had been proposed to integrated topologies. Thus, this work proposes a novel concept to generate simplified ZVT topologies to each bidirectional PWM pole. With the proposed methodology, the already known simplified ZVT topologies are systematized, as well as new topologies can be derived. Additionally, in order to address the benefits and constraints of integrated and simplified ZVT topologies, in this work a comparison is made between the concepts of integration and simplification of ZVT auxiliary circuits applied to bidirectional PWM poles, where the concepts of each approach are defined, recognizing their main advantages and limitations. So, the modulation strategies, the resulting losses in the main and auxiliary circuits and the harmonic content of the voltage synthesized by two selected topologies are theoretically and experimentally analyzed. Therefore, it is demonstrated that when the load demands a voltage with low harmonic content, the simplified ZVT topologies are indicated. However, when the number of components in the auxiliary circuit is the main concern, the integrated ZVT topologies can be employed.
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