AC mains synchronization loop for precalculated-based PFC converters using the output voltage measure

Common implementations of power factor correction include sensors for the input and output voltages and the input current. Many alternatives have been considered to reduce the number of sensors, especially the current sensor. One strategy is to precalculate the duty cycles that must be applied to every ac main, so the system only needs to synchronize them with the input voltage, and include a simple output voltage loop. The main problem with this approach is the sensibility to any synchronization error, because the input current is not measured, so its evolution is not continuously corrected. This paper shows how the synchronization error alters the current and the power factor, and it proposes several methods to detect and correct this error. All methods use the output voltage ADC, which is already used to control the output voltage, so the cost of the system is not increased. This technique can also be applied to any current sensorless PFC converter, because they are usually affected by leading or lagging currents, so the synchronization can be modified to reduce these effects. Results show that the implementation of this synchronization loop keeps a high-power factor under a wide synchronization error range, while the added logic is not significant.This research was funded by Spanish Ministerio de Economía y Competitividad grant number TEC2013-43017-R

Real-time system for monitoring the electro-thermal behaviour of power electronic devices used in boost converters

© 2016 Elsevier Ltd.Reliability of power electronic devices (PEDs) is a key issue to secure power supplies in modern word, especially, those generated from renewable energy sources. Thermal stress due to switching frequency and environmental conditions are commonest cause of currently unsatisfactory PEDs reliability scores. In this paper, the electro thermal performance of PEDs and related parameters are critically investigated using three types of differently manufactured insulated gate bipolar transistors (IGBTs). Namely, punch through (PT), non-punch through (NPT) and field stop (FS) silicon trench gate technologies. First, currents and voltages of the examined IGBTs were measured under different operating temperatures, switching frequencies and electrical loading conditions. Second, power losses of the examined devices were calculated, in real time, based on their measured currents and voltages using realistic mathematical model embedded in a dSPACE system. Subsequently, the power losses for each device were used as an input to a finite element model to graphically predict heat distributions for each of the monitored devices. Compared to expensive measurements taken by high-resolution thermal imaging cameras, the accuracy of the developed system achieved 97%. The obtained results demonstrate the developed model would serve as an inexpensive and powerful tool for monitoring PEDs thermal conditions

REGULATED TRANSFORMER RECTIFIER UNIT FOR MORE ELECTRIC AIRCRAFTS

The impending trends in the global demand of more-electric-aircrafts with higher efficiency, high power density, and high degree of compactness has opened up numerous opportunities in front of avionic industries to develop innovative power electronic interfaces. Traditionally, passive diode-bridge based transformer rectifier units (TRU) have been used to generate a DC voltage supply from variable frequency and variable voltage AC power out of the turbo generators. These topologies suffer from bulky and heavy low-frequency transformer size, lack of DC-link voltage regulation flexibility, high degree of harmonic contents in the input currents, and additional cooling arrangement requirements. This PhD research proposes an alternative approach to replace TRUs by actively controlled Regulated Transformer Rectifier Units (RTRUs) employing the advantages of emerging wide band gap (WBG) semiconductor technology. The proposed RTRU utilizing Silicon Carbide (SiC) power devices is composed of a three-phase active boost power factor correction (PFC) rectifier followed by an isolated phase-shifted full bridge (PSFB) DC-DC converter. Various innovative control algorithms for wide-range input frequency operation, ultra-compact EMI filter design methodology, DC link capacitor reduction approach and novel start-up schemes are proposed in order to improve power quality and transient dynamics and to enhance power density of the integrated converter system. Furthermore, a variable switching frequency control algorithm of PSFB DC-DC converter has been proposed for tracking maximum conversion efficiency at all feasible operating conditions. In addition, an innovative methodology engaging multi-objective optimization for designing electromagnetic interference (EMI) filter stage with minimized volume subjected to the reactive power constraints is analyzed and validated experimentally. For proof-of-concept verifications, three different conversion stages i.e. EMI filter, three-phase boost PFC and PSFB converter are individually developed and tested with upto 6kW (continuous) / 10kW (peak) power rating, which can interface a variable input voltage (190V-240V AC RMS) variable frequency (360Hz – 800Hz) three-phase AC excitation source, emulating the airplane turbo generator and provide an AC RMS voltage of 190V to 260V. According to the experimental measurements, total harmonic distortion (THD) as low as 4.3% and an output voltage ripple of ±1% are achieved at rated output power. The proposed SiC based RTRU prototype is ~8% more efficient and ~50% lighter than state-of-the art TRU technologies

Thermal characterisation and reliability analysis of power electronic devices in wind and solar energy systems

Power electronic converters (PECs) are used for conditioning the flow of energy between renewable energy applications and grid or stand-alone connected loads. Insulated gate bipolar transistors (IGBTs) are critical components used as switching devices in PECs. IGBTs are multi-layered devices made of different coefficient of thermal expansion (CTE) based materials. In wind and solar energy applications, IGBT’s reliability is highly influenced by the operating conditions such as variable wind speed and solar irradiance. Power losses occur in switching transient of high current/voltage which causes temperature fluctuations among the layers of the IGBTs. This is the main stress mechanism which accelerates deterioration and eventual failures among IGBT layers due to the dissimilar CTEs. Therefore, proper thermal monitoring is essential for accurate estimation of PECs reliability and end lifetime. Several thermal models have been proposed in literature, which are not capable of representing accurate temperature profiles among multichip IGBTs. These models are mostly derived from offline modelling approaches which cannot take operating conditions and control mechanisms of PECs into account and unable to represent actual heat path among each chip. This research offers an accurate and powerful electro thermal and reliability monitoring tool for such devices. Three-dimensional finite element (FE) IGBT models are implemented using COMSOL, by considering complex heat interactions among each layer. Based on the obtained thermal characteristics, electro thermal and thermo mechanical models were developed in SIMULINK to determine the thermal behaviour of each layer and provide total lifetime consumption analysis. The developed models were verified by real-time (RT) experiments using dSPACE environment. New materials, such as silicon carbide (SiC) devices, were found to exhibit approximately 20°C less thermal profile compared to conventional silicon IGBTs. For PECs used within wind energy systems, PECs driving algorithms were derived within the proposed models and by adjusting switching frequency PECs cycling temperatures were reduced by 12°C which led to a significant reduction in thermal stress; approximately 27 MPa. Total life consumption for the proposed method was calculated as 3.26x10-5 which is approximately 1x10-5 less compared to the other both methods. Effects of maximum power tracking algorithms, used in photovoltaic solar systems, on thermal stress were also explored. The converter’s thermal cycling was found approximately 3 °C higher with the IC algorithm. The steady state temperature was 52.7°C for the IC while it was 42.6 °C for P&O. In conclusion, IC algorithm offers more accurate tracking accuracy; however, this is on the expense of harsher thermal stress which has led to approximately 1.4 times of life consumption compared to P&O under specific operating conditions

Proposal for Preprogrammed Control applied to a Current-Sensorless PFC Boost Converter

The development of front-end converters for power factor correction and DC link voltage control of electronics converters such as, UPS, Inverters, and Switched Power Supplies, has been attracting great interest from the scientific community that works toward the achievements of cost reduction, high efficiency, and reliability. In this context, this paper proposes an innovative micro processed control technique for sinusoidal input line current imposition of front-end sensorless Boost converters, named in this work as BOOST-PFC-SSC. The proposed method is based on experimental acquisition of sequences of gate-to-source signals for different load conditions. These signals correspond to a complete cycle of the AC input voltage and are recorded in the microcontroller memory in order to be reproduced when used in a Boost converter, eliminating thus the use of a current sensor and predictive operations each switching interval, simplifying the control module executor. Aiming to prove the proposed digital concept, a 600W Boost-PFC-CSL was built and analyzed in laboratory and the main experimental results are presented herein.Conselho Nacional de Desenvolvimento Científico e TecnológicoDoutor em CiênciasO desenvolvimento de conversores pré-reguladores para realização da correção do fator de potência de entrada e controle da tensão no barramento DC dos mais diversos tipos de equipamentos eletrônicos, como por exemplo, UPS, Inversores de Tensão e Fontes Chaveadas, tem atraído grande interesse por parte da comunidade científica que busca redução de custos, alto rendimento e confiabilidade operacional. Dentro deste contexto, esta tese de doutorado apresenta como principal contribuição uma nova concepção de controle pré-programado para imposição de corrente senoidal na rede CA de alimentação de um conversor Boost, atuando como pré-regulador sem a utilização de sensor de corrente, denominado neste trabalho de conversor BOOST-PFC-SSC. O método proposto consiste na obtenção experimental de uma tabela de seqüências de pulsos de gatilho correspondentes a um ciclo da tensão CA de entrada, para cada condição de carga ensaiada. Esta tabela de seqüências de pulsos é gravada em um microprocessador que reproduz os sinais de gatilho e assume o acionamento do conversor Boost, dispensando, portanto, o uso de um sensor de corrente e operações preditivas a cada intervalo de chaveamento, simplificando o controle do módulo executor. No sentido de comprovar e validar a proposta, um protótipo de 600W foi submetido à técnica de controle desenvolvida e os resultados experimentais são apresentados