Dual-buck arbitrary voltage divider with one output having reduced ripples

In this paper, a dual-buck voltage divider is further studied to provide two arbitrary, instead of balanced, voltage outputs. The two voltage outputs can be the same or different and are robust against parameter drift. The low-frequency ripples in one output are significantly reduced by actively diverting low-frequency ripple currents away from the corresponding output. Note that these are achieved by designing an advanced controller, without changing the topology. The controller consists of a PI controller to split the voltage, a repetitive controller and a resonant controller to deal with the low-frequency ripples at different frequencies. Experimental results are presented to validate the effectiveness of the proposed strategy

Efficiency comparison between the LLCL and LCL-filters based single-phase grid-tied inverters

An LLCL-filter is becoming more attractive than an LCL-filter as the interface between the grid-tied inverter and the grid due to possibility of reducing the copper and the magnetic materials. The efficiency of the LLCL-filter based single-phase grid-tied inverter also excites interests for many applications. The operation of the switches of the VSI is various with different modulation methods, which lead to different efficiencies for such a single-phase grid-tied inverter system, and therefore important research has been carried out on the effect of the choice of PWM schemes. Then power losses and efficiencies of the LLCL-filter and the LCL-filter based single-phase grid-tied inverters are analyzed and compared under the discontinuous unipolar, the dual-buck and the bipolar modulations. Results show that the efficiency of LLCL-filter based inverter system is higher than the LCL- filter based independent on the modulation method adopted. Experiments on a 2 kW prototype are in good agreement with results of the theoretical analysis

Reducción del desequilibrio de voltaje mediante el uso del interruptor de transferencia estática, en una micro-red

En el presente artículo se plantea el modelo de una micro-red bipolar desequilibrada en corriente continua. Se presentan los resultados de un conjunto de maniobras la cual tiene como objetivo reducir el desbalance de voltaje y por ende minimizar las pérdidas de potencia usando los interruptores de transferencia estática STS. Para el desarrollo de este artículo se tomó en cuenta la simulación de la micro-red original sin generación distribuida GD y la micro-red con GD. Todos los casos de estudio fueron simulados en el software ATP Draw. En ambos casos se analiza el desbalance de voltaje con y sin el uso de los interruptores, en el nodo más alejado de la micro-red para observar la diferencia de voltajes entre ellos. Los resultados obtenidos en el presente artículo se lograron con la correcta ubicación de los interruptores STS la reducción de pérdidas de potencia, desbalance de voltaje cumpliendo con el rango límite del porcentaje de desbalance %VU entre líneas y por ende reduciendo la caída de voltaje en cada una de las líneas.In this article, the model of an unbalanced bipolar micro-network in direct current is proposed. The results of a set of maneuvers are presented which aims to reduce voltage unbalance and therefore minimize power losses using static transfer switches STS. For the development of this article, the simulation of the original micro-grid without distributed generation DG and the micro-grid with DG was taken into account. All study cases were simulated in the ATP Draw software. In both cases, the voltage unbalance is analyzed with and without the use of the switches, in the furthest node of the micro-network to observe the voltage difference between them. The results obtained in this article were achieved with the correct location of the switches STS, the reduction of power losses, voltage imbalance, complying with the limit range of the percentage of imbalance %VU between lines and therefore reducing the drop. voltage on each line

Convertidores balanceadores de voltaje: Estado del arte

Las microredes han sido propuestas como una alternativa para la integración de módulos de energía distribuida, los cuales tienen un menor impacto ambiental, además se han presentado estudios comparativos entre sistemas de distribución de energía en CD y el convencional en CA, resultando favorable trabajar en CD. Es por ello que actualmente se están desarrollando microredes con sistemas de distribución en corriente directa. Tradicionalmente un bus de CD está compuesto por dos hilos (positivo y negativo), sin embargo un bus de dos hilos no es suficiente para cubrir las necesidades de todos los tipos de cargas y es por ello que se opta por un sistema de distribución de 3 hilos (positivo, negativo y neutro). Estos últimos tienen un problema de desbalance de voltaje al conectar cargas entre uno de los rieles y el neutro, siendo necesario un convertidor que regule dichos desbalances en el bus. En este artículo se presenta una revisión de los convertidores balanceadores de voltaje reportados en laliteratura.Palabra(s) Clave(s): balanceador de voltajes, micro-redes, sistema de distribución en CD

Reducing the inductors of rectifiers having two outputs to improve power density

In this paper, a recently reported single-phase rectifier with two outputs (RECTO) is improved to reduce the neutral inductor and the grid inductor, by moving the neutral inductor away from the path of the grid current. The neutral inductor does not carry the grid current any more so the current stress of the neutral inductor can be significantly reduced, and the size of the inductor becomes much smaller. In theory, the current stress can be reduced by at least three times and the size of the inductor can be reduced by nine times. At the same time, the grid inductor can be reduced to achieve the same level of grid-current switching ripples because of the changed operation modes and modulation strategy. Together, the reduced neutral and grid inductors help improve the system power density. It is worth noting that the voltage and current stresses of the switches and the other features of the RECTO, e.g., two dc outputs and unity power factor, are not affected. Comparative experimental results are presented to demonstrate the reduction. If the two load currents are the same then the neutral inductor is only required to handle the switching ripples. This improved RECTO is particularly suitable for applications with two balanced loads without increasing the cost much

Isolated Three-port DC-DC Converter Employing ESS to Obtain Voltage Balancing Capability for Bipolar LVDC Distribution System

A bipolar low-voltage DC (LVDC) distribution system used in residential and building applications requires AC-DC converters and voltage balancers that balance the two DC bus polarities. The bipolar DC bus voltage level only relies on the voltage balancer tied with the AC grid. An isolated DC-DC converter for an energy storage system (ESS) with the voltage balancing capability is proposed to prevent the bipolar voltage level collapse caused by the failure of the grid-tied voltage balancer. The proposed converter topology is an enhanced three-port dual-active-bridge (DAB) converter which can balance the bipolar DC voltage level without complex control. Furthermore, it has less current stress in power switches than that of the conventional three-port DAB converter. The effectiveness of the proposed converter is verified with a 3-kW prototype converter

Research on Advanced Three-port Dual-Active-Bridge (DAB) Converters for DC Microgrid

Department of Electrical EngineeringThree-port dual-active-bridge converter (DAB) has been studied to integrate three DC units into one converter. it can increase power density as well as cost-effectiveness with small number of components. However, it has power correlation among the three ports, which brings complexity to control. This thesis investigates advanced thee-port DAB converters to overcome the power correlation issue the conventional converter suffers from and even achieve higher power density and higher efficiency. Two-inductor three-port DAB converter is proposed to eliminate the power correlation issue without additional control. It uses only two series power inductors, whereas the conventional has three of them. The proposed converter is theoretically analyzed and compared with the conventional converter. The effectiveness of the proposed converter is verified by a simulation software, PSIM and a 5-kW prototype converter. Dual-transformer three-port DAB converter using two transformers is also introduced. It removes the above-mentioned problem that the conventional converter has. It can fully use its transformer magnetizing inductances to extend the zero voltage switching (ZVS) capability at low power. The magnetizing design methodology is proposed to effectively extend the ZVS capability. The validity of the proposed magnetizing design method is verified by PSIM and a 3-kW prototype converter. A voltage balancer for bipolar low-voltage DC (LVDC) distribution is proposed using Two-inductor three-port DAB converter. A bipolar LVDC distribution system used in residential and building applications requires AC-DC converters and voltage balancers that balance the two DC pole polarities. The proposed balancer can balance the bipolar voltage levels in case of grid-tied voltage balancer failures. It can balance the bipolar DC voltage level without complex control. Furthermore, it has less current stress in power switches than that of the conventional three-port DAB converter. The effectiveness of the proposed converter is verified with a 3-kW prototype converter.clos

Active Control of Voltage Ripples in Power Electronic Converters

Two major challenges, i.e., bulky electrolytic capacitors and isolation transformers, remain as critical obstacles for further improvement on reliability, power density and efficiency of power electronic converters, which are mainly used to reduce low-frequency voltage ripples and high-frequency common-mode voltage ripples, respectively. In order to overcome the two challenges, the most straightforward way is to simply combine existing solutions developed for each of them. However, this would considerably increase system complexity and cost, which should be avoided if possible. In this thesis, these two challenges are innovatively addressed in a holistic way by using active control techniques. This thesis first focuses on the reduction of low-frequency voltage ripples in conventional half-bridge converters, after adding an actively-controlled neutral leg. As a direct application of this strategy, a single-phase to three-phase conversion is then proposed. After that, a ρ-converter with only four switches is proposed to significantly reduce both low-frequency ripples and high-frequency common-mode ripples in a holistic way. It is found that the total capacitance can be reduced by more than 70 times compared to that in conventional full-bridge converters. As a result, there is no longer a need to use bulky electrolytic capacitors and isolation transformers. Then, the ρ-converter equipped with the synchronverter technology is operated as an inverter for PV applications. Another converter is also proposed for the same purpose but with reduced voltage stress. In order to further reduce the total capacitance and to reduce the neutral inductor in the ρ-converter, a new type of converter, called the θ-converter, is proposed. Finally, two actively-controlled ripple eliminators are proposed to reduce low-frequency ripples in general DC systems while the aforementioned research is focused on some specific topologies. Extensive experimental results are presented to validate most of the developed systems while the rest are validated with simulation results