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Abstract
In modern aircraft designs, following the More Electrical Aircraft (MEA) philosophy, there is a growing need for new high-power converters. In this context, innovative solutions to provide high efficiency and power density are required. This paper proposes an unregulated LLC full-bridge operating at resonant frequency to obtain a constant gain at all loads. The first harmonic approximation (FHA) model is not accurate enough to estimate the voltage gain in converters with high parasitic resistance. A modified FHA model is proposed for voltage gain analysis, and time-based models are used to calculate the instantaneous current required for the ZVS transition analysis. A method using charge instead of current is proposed and used for this ZVS analysis. Using this method, an auxiliary circuit is proposed to achieve complete ZVS within the whole load range, avoiding a gapped transformer design and increasing the efficiency and power density. A 28 Vdc output voltage prototype, with 10 kW peak output power, has been developed to validate the theoretical analysis and the proposed auxiliary circuit. The maximum efficiency (96.3%) is achieved at the nominal power of 5 kW.
Highlights
In the field of the More Electrical Aircraft (MEA) philosophy, there is a tendency to substitute mechanical, hydraulic and pneumatic systems with their electrical equivalents in order to increase efficiency and reduce cost and fuel consumption [1,2,3]
It can be concluded that the proposed auxiliary circuit is an overall improvement to the power density of the converter and does not add any significant complexity to the control scheme, as it is a passive solution
It can polarity be seen that themeasurement current sharing fully overlap not of otherwise distinguishable
Summary
In the field of the More Electrical Aircraft (MEA) philosophy, there is a tendency to substitute mechanical, hydraulic and pneumatic systems with their electrical equivalents in order to increase efficiency and reduce cost and fuel consumption [1,2,3]. Aircraft generators typically supply electrical power in AC at variable frequency (360 Hz/800 Hz; see Figure 1); aircraft loads require 28 Vdc [4]. Traditional aircraft rectifiers are based on passive solutions, with low-frequency transformers and diode rectifications. This approach is very robust, but the power density is low and offers limited regulation capabilities. Following the MEA philosophy, active rectifier solutions are being developed These active solutions can be more efficient, with an optimized volume and weight, and can reduce the harmonic content in the AC grid, which increases the lifecycle of the generators. Active aircraft rectifier systems are typically composed of three stages, as shown in Figure 1: an EMI filter, AC/DC rectifier and isolated DC/DC converter
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