Comparison of Three-Phase Active Rectifiers For Aircraft Application

In aircraft applications, there has been an increasing trend related with the More Electric Aircraft (MEA), which results in rapid rise in the electrical power demand on-board. One of its goals lies in minimizing weight and volume of the electrical subsystem while maintaining good power quality and efficiency. The main purpose of this paper is to present and analyze an electrical design of three-phase Boost rectifier, three-phase Buck rectifier and three-phase Vienna rectifier for 10 kW active rectifiers and compare them in terms of weight, volume, efficiency etc. Moreover, the design is obliged to comply with DO-160 standard for avionic equipment with 230 V AC, 360-800 Hz grid conditions. Even though all proposed solutions satisfy the standard requirements, it will be shown that the Vienna rectifier has the lowest volume and therefore, the better solution overall. However, due to increased number of semiconductors and additional circuitry required for soft start-up, the Buck rectifier would prove to be the safest solution failure-wise

Comparison of Three-phase Active Rectifier Solutions for Avionic Applications: Impact of the Avionic Standard DO-160 F and Failure Modes

In aircraft applications, there has been an increasing trend related with the More Electric Aircraft (MEA), which results in rapid rise in the electrical power demand on-board. One of its goals lies in minimizing weight and volume of the electrical subsystem while maintaining good power quality and efficiency. The main purpose of this paper is to present and analyze an electrical design of a three-phase Boost rectifier, a three-phase Buck rectifier and a three-phase Vienna rectifier for output power level of 10 kW and compare them in terms of weight, volume, efficiency etc. Moreover, the design is obliged to comply with specific sections of DO-160 standard for avionic equipment with 230 VAC, 360-800 Hz grid conditions. Even though all proposed solutions satisfy the standard requirements, it will be shown that the Vienna rectifier has the lowest volume and not considering failure modes, the better solution overall. However, due to increased number of semiconductors and additional circuitry required for soft start-up, the Buck rectifier would prove to be the more robust solution failure-wise

Contributions to The Design Methodology of Three-phase Active Rectifiers to Comply with Avionic Standards: Input Voltage Distortion and Phase Loss

En el mercado de la aviación civil, en constante crecimiento, siempre ha habido una continua necesidad de mejora en muchos campos. Como respuesta a los rápidos avances en la ingeniería eléctrica, ha emergido la tendencia llamada “avión más eléctrico” (“More Electric Aircraft” o MEA). El objetivo es reducir las emisiones de C02, implementando nuevas tecnologías en el avión. El modo natural de hacer más pequeñas las emisiones es reducir el peso total del avión, que a fin de cuentas reducirá los costes operativos y el consumo total de combustible. La tendencia MEA se refleja principalmente en sustituir piezas mecánicas, neumáticas e hidráulicas, pesadas y de alto coste de mantenimiento, por equivalentes eléctricos. Este trabajo se centra en proporcionar contribuciones en el campo de los rectificadores trifásicos activos que podrían ser empleadas en el avión del futuro, cumpliendo a la vez con los requisitos de las normas de aviónica, como por ejemplo la DO-160G. la conversión CA/CC se realiza normalmente rectificadores multipulso pasivos que, aunque son tremendamente fiables, presentan inconvenientes, tales como el peso, el volumen, el rendimiento y la falta de controlabilidad. Los rectificadores activos pueden superar todos estos retos, teniendo en cuenta que la fiabilidad no debe verse afectada significativamente. En esta tesis se proporciona en el capítulo 2 un resumen del estado del arte de los convertidores CA/CC trifásicos, seguido de mi primera contribución en el capítulo 3, en relación con las emisiones de corriente por debajo del 10 % de distorsión armónica total trifásica (THD) según la norma DO-160G. Se ha propuesto una metodología de diseño que traduce los requisitos individuales de armónicos a un perfil de admitancia que debe considerar la carga trifásica conectada para cumplir totalmente con este requisito. La metodología de diseño se ha implementado en el sistema de referencia síncrono dq. Los límites de admitancia propuestos se aplican al rectificador trifásico de topología “buck” (reductora). En este caso se muestra que el ancho de banda del controlador de corriente usado en el modelado de la admitancia no es un parámetro muy exigente. Por otro lado, se demuestra que el filtro diferencial para la Interferencia electromagnética (EMI) es crítico, debido a su bastante baja impedancia característica. Con posterioridad el diseño se analiza exhaustivamente y se verifican los resultados de simulación. La misma metodología se ha aplicado al rectificador trifásico de topología “boost” o elevadora, específicamente el rectificador VIENNA. Se muestra que en este caso existe un compromiso entre el tamaño de la bobina y el ancho de banda del controlador de corriente y que, para el mismo tamaño de componentes magnéticos, el rectificador de tipo “boost” requiere un ancho de banda del controlador de corriente mayor que su equivalente de tipo “buck”. Asimismo, se demuestra que las topologías de tipo “boost” son más insensibles al diseño del filtro EMI, debido sus sensiblemente más pequeños condensadores de entrada, en relación con los de tipo “buck”. Finalmente, los resultados se verifican por medio de simulación y de un prototipo de 10 kW basado en tecnología SiC. En el capítulo 4 se muestra la segunda contribución principal de este trabajo y se pretende proporcionar una estrategia de control robusta para un rectificador trifásico de tres hilos, basado en topología “boost” con seis interruptores, que soporte un caso de fallo de fase, con el fin de cumplir el requerimiento de fallo de fase de la norma DO-160G. La idea fundamental reside en el control de las componentes de secuencia positiva y negativa del sistema trifásico tras producirse el fallo. Por tanto, el control de corriente en lazo cerrado implementado en el rectificador consiste en cuatro controladores PI idénticos, dos para las componentes d y q de cada secuencia. Debido a que cada caso de fallo de la red genera valores únicos de los vectores de tensión de secuencia positiva y negativa, se presenta una derivación matemática de las componentes d y q de cada secuencia rotativa. La extracción matemática precisa de las componentes de tensión y corriente de secuencia positiva y negativa, tienen que soportar cualquier escenario de fallo de red. El número total de casos analizados es nueve, de los cuales tres están relacionados con cortocircuitos fase-fase, tres con fases abiertas y tres con fallos fase-neutro. Adicionalmente se proporciona una relación matemática entre las amplitudes instantáneas de casa fase y las componentes de secuencia positiva y negativa. Esta relación aplicada en las corrientes y tensiones trifásicas de entrada proporciona una manera simple de detectar los nueve casos de red, de forma que se pueden suministrar las adecuadas referencias del controlador de corriente que garantizan el flujo óptimo de potencia. Finalmente, el análisis propuesto está respaldado por resultados de simulación y experimentales, estos últimos obtenidos de un prototipo de 3.45 kW basado en semiconductores “full-SiC”. En el último capítulo, se presenta un resumen de las contribuciones y conclusiones principales de este trabajo y una visión de posibles trabajos futuros. ----------ABSTRACT---------- In the ever-growing market of the civil aerospace industry, there has been a constant need for improvement in many fields. Due to rapid advancements in the field of electrical engineering the trend called More Electric Aircraft (MEA) has emerged as a response. Its goal is to reduce CO2 emissions by implementing new technologies in the aircraft. The natural way of minimizing the emissions is by decrementing the total weight of the airplane which will in turn reduce operating costs and total fuel consumption. The MEA trend is predominantly reflected in replacing heavy and maintenance costly hydraulic, pneumatic and mechanical parts of the aircraft system with electrical equivalents. This work is focused on providing contributions in the field of three-phase active rectifiers that could be employed in the future airliners, while complying with requirements from avionic standards such as DO-160G. The AC/DC conversion is mainly done by passive three-phase multi-pulse rectifiers that are extremely reliable, but present significant drawbacks in the weight, volume, efficiency and lack of controllability. The active rectifiers can overcome all these challenges, keeping in mind that reliability must not be significantly impaired. In this thesis a review of the state-of-the-art three-phase AC/DC converters is done in Chapter 2, followed by first main contribution regarding low-frequency current emissions under 10 % three-phase voltage Total Harmonic Distortion (THD) from DO-160G in Chapter 3. The design methodology is proposed that translates the individual harmonic requirements to an admittance profile that the connected three-phase load must consider in order to be fully compliant with this requirement. The design methodology is chosen to be carried out in synchronous reference frame or dq frame. The proposed admittance limits are then applied to the three-phase buck-type rectifier. It is shown that in this case, the bandwidth of the current controller used for input admittance shaping is not a very demanding parameter. On the other hand, design of input Electromagnetic Interference (EMI) differential filter is demonstrated to be critical due to its rather low characteristic impedance. The design is afterwards extensively analyzed and verified by simulation results. The same design methodology is then applied on the three-phase boost-type rectifier, namely the VIENNA rectifier. It is shown that in this case there exists a trade-off between input inductor size and current controller bandwidth, and that, for the approximately same size of magnetic components, the boost-type rectifier requires higher current controller bandwidth than its buck-type counterpart. It is also demonstrated that boost-type topologies are rather insensitive to the EMI filter design due to rather small values of the input capacitors compared to the buck-type case. Finally, the results are verified by simulation and conducted on a 10 kW SiC prototype. In Chapter 4, the second main contribution of this work is reflected and it aims to provide a robust control strategy for a three-phase three-wire six-switch boost-type rectifier against arbitrary input phase failure scenario, in order to cope with the single-phase loss requirement of DO-160G. The fundamental idea lies in control of positive and negative sequence components of the three-phase system after the failure occurrence. Therefore, the applied rectifier closed-loop current control consists of four identical PI controllers, two for each sequence d and q components. Since each grid fault case generates unique values of positive and negative sequence voltage vectors, a mathematical derivation of d and q components of each rotating sequence is presented. The precise mathematical extraction of necessary positive and negative sequence voltage and current components needed to cope with any grid fault scenario is proposed. The total number of analyzed failure cases is nine, where three are related to phase-to-phase short-circuit, three to open-phase case, and three to phase-to-neutral fault. Moreover, a mathematical link between instantaneous amplitudes of each individual phase and positive and negative sequence component values is also provided. The derived link utilized on input three-phase voltages and currents provides a simple way of detecting the nine grid failure cases so that adequate current controller references can be provided which guarantee optimal power flow. Finally, the proposed analysis is backed up by simulation and experimental results, conducted on a full SiC 3.45 kW prototype. In the last Chapter, a summary with highlighted contributions and conclusions from this work is addressed and a vision of possible future work is provided

DC/DC Fixed Frequency Resonant LLC Full-Bridge Converter with Series-Parallel Transformers for 10kW High Efficiency Aircraft Application

In modern aircraft designs, there is a need for new high power isolated DC/DC converters. Full bridge derived topologies are appropriate for these specifications. Aircraft specifications are demanding and a high power density is needed. In order to decrease volume, reactive component, such as the transformer have to be optimized in volume, weight and loses. High frequency is needed to decrease inductive component core size and magnetic integration is a key factor. With the use of high frequency, topologies that take advantage of both ZVS and q-ZCS can offer the best results. Resonant topologies have a lot of benefits for this kind of requirement in this application. In this paper, a comparison of different state of the art full-bridge based topologies is made. A detailed explanation of the benefits of the Series-Parallel solution is provided. Experimental result of the prototype are also shown to prove the concept