This paper proposed a control method for output and circulating currents of modular multilevel converter (MMC). The output and circulating current are controlled with the help of arm currents, which ...contain DC, fundamental frequency, and double frequency components. The arm current is transformed into a stationary reference frame (SRF) to isolate the DC and AC components. The AC component is controlled with a conventional proportional resonant (PR) controller, while the DC component is controlled by a proportional controller. The effective control of the upper arm and lower arm ultimately controls the output current so that it delivers the required power to the grid and circulating current in such a way that the second harmonic component is completely vanished leaving behind only the DC component. Comparative results of leg-level control based on PR controller are included in the paper to show the effectiveness of the proposed control scheme. A three-phase, five-level MMC is developed in MATLAB/Simulink to verify the effectiveness of the proposed control method.
Renewable energy sources are growing in importance and reshaping power systems through microgrid (MG) networks. Some relevant issues in the management of an MG need to be addressed, such as voltage ...and frequency control, power balance between sources (sharing) and distributed loads, stability, security, power quality, etc. As a contribution, this manuscript presents a power management of AC MGs based on concepts of microeconomics theory for market equilibrium. The prices of active and reactive energy are informed through the AC voltage parameters such as magnitude, frequency and angle. This approach allows several sources and loads to operate with no extra communication interface. Experiments are provided to validate operation in many different operational scenarios using a hardware-in-the-loop environment.
In many electrical and electronic applications there is the need to have an efficient measurement over the State-of-Health (SoH) and the State-of-Charge (SoC). The SoH is an indirect measurement ...about the age of the battery while the SoC indicates the energy stored in the battery. The SoC and SoH are commonly referred in papers and scientific reports. However, their design and implementation procedure is very often left behind. Moreover, the implementation is not trivial. This paper presents the design and implementation of lead-acid battery SoH and SoC. The purpose is to present carefully the procedure showing how to design and implement the SoH and SoC estimators. The SoH estimation is based on obtaining the battery internal resistance. The SoC is based on the Coulomb Counting method, valid for charging and discharging processes. Experimental results using a 12V/2.3Ah battery show the efficacy of the proposed design and implementation method.
Passive filters are widely used in electrical system for power quality improvements. Their first installations date from 1940s and their advantages make them an attractive and standard solution. ...However, passive filters have their filtering characteristics deteriorated due to parameter variation, caused by aging and temperature. Additionally, a capacitor bank for power factor correction is designed for specific loads and may not supply the right amount of reactive power when loads keep being added or changed. A solution to overcome such undesired effects is presented in this paper. There are two shunt compensators, with design and control based on the Conservative Power Theory. They are employed as supporting a tuned passive filter plus a capacitor bank. They contribute towards a better passive filter performance with reduced processed power. The addition of those shunt compensators would be cost-effective for weak grid conditions and smart grid advanced energy management control. A case study is presented in order to prove the compensators efficacy and the power quality improvement.
This paper investigates connecting renewable energy sources such as solar, wind and the others to the microgrids through power electronic interfaces for active power provision and also harmonic, ...unbalance, and reactive power compensation under both symmetrical and asymmetrical voltage sources. The four-leg converter topology is applied because of its better controllability in four-wire systems applications. Two instantaneous current decomposition techniques, namely conservative power theory and instantaneous power theory are studied to show the similarities and differences between these techniques from performance perspective in active power filter. The studied system is a three-phase four-wire grid which includes unbalanced and non-linear loads, and has negligible line impedances. The control strategy is implemented in abc-frame which allows for selective load current provision by distributed generators interface converters. The principles supporting the developed control strategy are discussed and the results are demonstrated through digital simulations conducted by means of PSIM.
This paper discusses the use of a Cascaded H-bridge Multilevel Inverter (CHMI) as shunt active power filter (SAPF) for selective disturbing currents compensation. The main feature of the proposed ...approach is the use of independent DC sources, with reduced DC-link voltages, which makes such a topology an ideal candidate for medium and high power applications with increased reliability. The developed control strategy regulates independent DC-link voltages in each H-bridge cell and allows selective compensation under a variety of voltage conditions without requiring any kind of reference-frame transformation. The selective compensation strategies are based on the decompositions proposed in the Conservative Power Theory (CPT), which result in several current-related terms associated with specific load characteristics. These current components are independent from each other and are used to define different compensation strategies, which can be selective in minimizing particular effects of disturbing loads. In order to validate the possibilities and performance of the proposed control strategies, a three-phase grid with unbalanced nonlinear loading and negligible line impedance was simulated in PSIM considering ideal and deteriorated voltage conditions.
This paper presents a control approach based on frequency response for a hybrid active power filter. A hybrid active filter is a combination of an active power filter and a tuned passive filter. The ...active power filter is connected in parallel with a Tuned Passive Filter inductor. The control principle is based on eliminating line current harmonic by PI controller acting into a voltage-sourced converter. The proposal control diagram is described carefully. Numerical results are presented in order to show the efficiency of the control proposal.
Este artigo propõe um sistema de controle digital simplificado para um condicionador unificado de qualidade de energia (UPQC). O UPQC é composto por um filtro ativo paralelo (FAP), empregado para o ...condicionamento da corrente drenada da rede, e por um filtro ativo série (FAS), utilizado para o condicionamento da tensão entregue à carga. O FAP e o FAS são controlados a partir da medição da corrente na rede e da tensão na carga, respectivamente, ao invés da medição da corrente do conversor paralelo e da tensão de saída do conversor série. Dessa forma, eliminam-se algoritmos complexos para geração dos sinais de referência dos conversores, uma vez que os sinais de referência das malhas de controle são senoidais e podem ser gerados internamente em um processador. A modelagem dos filtros ativos, a estratégia de controle proposta e o projeto dos controladores são apresentados em detalhes. Resultados experimentais obtidos em um protótipo de 2,5kW são apresentados para validar o sistema proposto.
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