Active power management of islanded interconnected distributed generation

Abstract: The present paper proposes a management of active power in distributed generation considering an islanded mode. Power system is a complex system from the point of view of its constitution, operation and management. Because of energy sources scarcity and energy increasing demand in most of the electrical power systems worldwide, renewable energy exploitation continue to attract researches and exploitation of this weather depending resources. When considering the island mode or without connection to the main grid, of the distributed generation its operation and control became more difficult or uncertain based their dependencies on the weather. Using optimal theory, this paper solve the management of interconnected microgrids operating in islanded mode. Matlab software is used to solve all optimisation problems

Advanced control methods on three-phase inverters in distributed energy resources

“This research is an endeavor to apply new and well-established control methodologies to improve transient response, stability and reliability of three-phase inverters in grid-connected and isolated mode of operation. In the course of studying the effect of these methodologies, model-based control is introduced and is extensively applied which is relatively a new approach. In addition, the application of this concept has been studied on developing “grid-forming” controls to allow wind and solar inverters to support voltage and frequency levels like traditional generators. This research encloses the details of three major works of this research and their possible contributions on improving the performance of three-phase inverters in gridconnected and isolated mode of operation. The first one employs the concept of adaptive control using multiple models and a hierarchical control approach to smoothly switch between isolated and grid-connected modes of operation. In the second work, the features of the first research work have been applied and more nourished to control a grid-forming unit. The interactions of this grid-supporting converter with a grid- forming unit is the main subject of discussion in this work. The last work applies the concept of internal-model control to introduce a new control methodology in power-synchronization method. This approach has tackled the non-minimum phase issue attributed to power-synchronization methodology and offers a robust solution. Furthermore, in this research, detailed stability analysis of all the proposed control structures have been presented. Along with all simulation verification, FPGA-Based Hardware-in-the-Loop (HIL) has been utilized to verify the performance of the discrete control structure. The details of plant modeling, controller design, HIL and experimental results are presented for all of the proposed schemes in each section”--Abstract, page iv

Interligação de microrredes híbridas com um conversor multinível

Nos tempos atuais a eficiência energética e a coordenação inteligente dos recursos da rede são tópicos de maior importância. As microrredes híbridas apresentam-se como uma solução interessante para a integração coordenada de fontes de geração e cargas DC ou AC nos barramentos DC ou AC respetivamente. Isto permite eliminar algumas etapas de conversão que tradicionalmente existem nas redes AC, aumentando assim a eficiência energética. Neste trabalho utilizou-se um conversor multinível para interligar uma microrrede AC a uma microrrede DC. O conversor de interligação é capaz de realizar o controlo das correntes AC, da tensão DC ou da tensão AC, dependendo dos cenários de funcionamento da microrrede híbrida. As correntes AC do conversor foram controladas através das técnicas de controlo por modo de deslizamento (MD) e modulação por largura de impulsos (PWM), partindo dos modelos das variáveis de estado do conversor. As tensões das microrredes AC e DC foram controladas utilizando malhas externas com controladores PI (Proporcional-Integral). O conversor de interligação foi simulado na plataforma MATLAB/Simulink nos três cenários de funcionamento. Os resultados de simulação foram posteriormente confirmados em laboratório através de um protótipo de baixa potência. Os resultados obtidos demonstraram uma resposta dinâmica rápida das correntes AC em ambos os métodos de controlo, com a técnica PWM a apresentar harmónicas mais reduzidas. O controlo de tensão da microrrede DC foi bem efetuado e permitiu reagir adequadamente a mudanças de referência e ao aumento do consumo da microrrede DC. No caso em que existe geração local o conversor foi capaz de realizar o equilíbrio entre a potência produzida e a potência consumida, transferindo o excesso de potência para a microrrede AC. O controlo de tensão da microrrede AC, permitiu regular de forma adequada as tensões trifásicas e reagir a mudanças de referência e variações do consumo.Energy efficiency and smart coordination of grid resources are issues of utmost importance nowadays. Hybrid microgrids are an interesting solution for the integration of AC and DC loads and generation sources in their respective AC or DC buses. This allows for a reduction of voltage conversion stages that are prevalent in the more traditional AC grid, leading to a higher efficiency. In the scope of this work a multilevel converter was used to interconnect an AC microgrid to a DC microgrid. The interlinking converter can control either the AC currents, the DC bus voltage, or the AC bus voltage, depending on the hybrid microgrid operation mode. The converter AC currents were controlled using sliding mode and pulse width modulation (PWM) techniques starting from the converter state variable representation. The AC and DC microgrid voltages were controlled by outer loop PI (Proportional Integral) controllers. The three operation modes of the interlinking converter were simulated using MATLAB/Simulink. A low power laboratory prototype was later used to further confirm the simulations results. The results showed a fast dynamic response of the AC currents, using both control techniques. PWM however resulted in reduced harmonics. The DC microgrid voltage control was successfully implemented and resulted in a good response following changes in voltage reference and DC microgrid consumption. When local power production was available, the converter was able to transfer the excess power to the AC microgrid, thus balancing the produced and consumed local power. The AC microgrid voltage control was capable of adequately regulate the three phase AC voltages and react to changes in voltage reference and local power consumption