Abstract: This paper presents a novel adaptive dc-link voltage-controlled LC coupling hybrid active power filter (LC-HAPF) for reducing switching loss and switching noise under reactive power compensation. First, the mathematical relationship between LC-HAPF dc-link voltage and reactive power compensation range is deduced and presented. Based on the compensation range analysis, the required minimum dc-link voltage with respect to different loading reactive power is deduced. Then, an adaptive dc-link voltage controller for the three-phase four-wire LC-HAPF is proposed, in which the dc-link voltage as well as the reactive power compensation range can be adaptively changed according to different inductive loading situations. Therefore, the compensation range, switching loss, and switching noise of the LC-HAPF can be determined and reduced correspondingly. In this paper, the reference dc-link voltage is classified into certain levels for selection in order to alleviate the problem of dc voltage fluctuation caused by its reference frequent variation, and hence reducing the fluctuation impact on the compensation performances. Finally, representative simulation and experimental results of a three-phase four-wire center-split LC -HAPF are presented to verify the validity and effectiveness of the proposed adaptive dc-link voltage-controlled LC-HAPF in dynamic reactive power compensation.

Abstract: This paper proposes a hierarchical active power management strategy for a medium voltage (MV) islanded microgrid including a multihybrid power conversion system (MHPCS). To guarantee excellent power management, a modular power conversion system is realized by parallel connection of small MHPCS units. The hybrid system includes fuel cells (FC) as main and supercapacitors (SC) as complementary power sources. The SC energy storage compensates the slow transient response of the FC stack and supports the FC to meet the grid power demand. The proposed control strategy of the MHPCS comprises three control loops; dc-link voltage controller, power management controller, and load current sharing controller. Each distributed generation (DG) unit uses an adaptive proportional resonance (PR) controller for regulating the load voltage, and a droop control strategy for average power sharing among the DG units. The performance of the proposed control strategy is verified by using digital time-domain simulation studies in the PSCAD/EMTDC software environment.

Abstract: Multilevel inverters have an important portion in power processing in power systems. These inverters have some inherent advantages such as ability to operate with high power and voltage, improved output waveform quality and flexibility which make them attractive and more popular. This study proposes a new topology based on the non-insulated dc voltage sources for multilevel inverter with reduced number of switching devices. As a result, it reduces control complexity and gate driver circuits. The proposed topology is a general topology which can be easily extended to a desired number of voltage levels. All of the desired output voltage levels (both odd and even) can be achieved using the proposed topology. The validity of the proposed multilevel inverter is verified with both computer simulation and experimental results from a 15-level laboratory prototype.

Abstract: Voltage sag is a common and undesirable power quality phenomenon in the distribution systems which puts sensitive loads under the risk. An effective solution to mitigate this phenomenon is to use dynamic voltage restorers and consequently, protect sensitive loads. Four basics compensation methods were proposed in the research community to eliminate the voltage sags and minimize the voltage disturbances at load side. This paper provides a review of those voltage compensation strategies with detailed discussions and comparisons to highlight their advantages and disadvantages.

Abstract: This paper presents a methodology for integrated power flow modeling of the impact of geomagnetic disturbances (GMDs) on power system voltage stability. GMDs cause quasi-dc, geomagnetically induced currents (GICs) in the transformers and transmission lines, which in turn cause saturation of the high voltage transformers, greatly increasing their reactive power consumption. GICs can be calculated using standard power flow modeling parameters such as line resistance, augmented with several GIC specific fields including substation geographic coordinates and grounding resistance, transformer configuration, and transformer coil winding resistances. When exact values are not available, estimated quantities can be used. By then integrating GIC into power flow analysis, the changes in reactive power losses and bus voltages can be quantified to assess the risk of voltage instability and large-scale voltage collapse. An example calculation is provided for a North American Eastern Interconnect model.

Abstract: Traditional LED drivers with multiple converters for powering up multiple strings in parallel suffer from high system volume and cost. The reported literature with single converter and dynamic bus voltage offers compact designs. However, the performance on power consumption is degraded. Meanwhile, all the aforementioned approaches require multiple current regulation elements, which inflict current balance errors due to mismatches. A compact single-inductor multiple-output parallel-string LED driver with time-multiplexing control is, thus, proposed. It can independently optimize local bus voltages for power loss reduction. In addition, a single time-shared control loop is proposed for current regulation in multiple parallel strings, resulting in a dramatic reduction of current balance errors. A 0.35 μm CMOS prototype achieves 2.8 times loss reduction over the reported literature, with a current balance error well controlled below 1.7%. The control scheme also offers flexible dimming for advanced backlighting operations.

Abstract: In this study, a simple digital power control technique for single-phase grid-tie converters is proposed. The suggested technique is based on the application of dead-beat control theory to the instantaneous powers in the virtual two-axis reference frame. A voltage estimation scheme is added to the proposed direct power control algorithm that allows grid voltage sensorless operation. The simulation and experimental results confirm that the proposed control strategy provides fast, accurate and decoupled power control with a lower alternating current distortion.

Abstract: In this brief, a new low-power level shifter (LS) is presented for robust logic voltage shifting from near/sub-threshold to above-threshold domain. The new circuit combines the multi-threshold CMOS technique along with novel topological modifications to guarantee a wide voltage conversion range with limited static power and total energy consumption. When implemented in a 90-nm technology process, the proposed design reliably converts 180-mV input signals into 1-V output signals, while maintaining operational frequencies above 1-MHz, also taking into account process-voltage-temperature variations.Post-layout simulation results demonstrate that the new LS reaches a propagation delay less than 22 ns, a static power dissipation of only 6.4 nW, and a total energy per transition of only 74 fJ for a 0.2-V 1-MHz input pulse.

Abstract: The increase in the power levels of photovoltaic (PV) energy conversion systems has resulted in new large-scale grid connected configurations that have reached the megawatt level. This substantial increment in the power levels imposes new challenges to the grid interfacing converter, and therefore results in new opportunities to be explored. This work introduces a new medium voltage multilevel scheme based on a three-phase cascaded H-bridge (CHB) converter and multiple PV strings. The proposed configuration enables a large increase of the total power capacity of the PV system, while the introduction of a multilevel converter helps to improve both power quality and efficiency and medium voltage operation at the grid side. The main challenge of the proposed configuration is to handle the inherent power imbalances that occur not only between the different cells of one phase of the converter but also between the three phases. Simulation results of a 7-level CHB PV system are presented to validate the proposed topology and control method.

Abstract: Conventional dynamic voltage restorers (DVRs) are connected to the power grid through power-frequency transformers. These bulky and costly transformers cause voltage drop and power losses. In this paper, a high-frequency-link dynamic voltage restorer (HFL-DVR) is proposed based on transformer-isolated topologies. This topology facilitates independent operation conditions for each phase in a three-phase system. It enjoys relatively low cost, low losses, and small size. Also, it is free from transformer inrush currents. Small-signal ac equivalent circuit for the power stage including HFL-DVR is derived based on an averaged modeling approach. Transfer functions are obtained to study the effect of inputs such as dc-link voltage, grid voltage, and the load current on the output of HFL-DVR. In order to obtain acceptable properties such as transient overshoot, setting time, and steady-state error, a PID controller is added to the system. This shows that the effect of disturbances on the output of HFL-DVR can be reduced. The experimental results are obtained from a 220V/50Hz HFL-DVR setup. The simulation and experimental results have been compared to verify theoretical aspect of the proposed DVR for both symmetrical and asymmetrical voltage sag conditions.

Abstract: This paper reports on efficient interfacing of typical vibration-driven electromagnetic transducers for micro energy harvesting For this reason, an adaptive charge pump for dynamic maximum power point tracking is compared with a novel active full-wave rectifier design For efficient ultra-low voltage rectification, the introduced active diode design uses a common-gate stage in conjunction with supply-independent biasing While this active rectifier offers low voltage drops, low complexity and ultra-low power consumption, the adaptive charge pump allows dynamic maximum power point tracking with implicit voltage up-conversion Hence, efficient energy harvesting with high-resistive transducers, eg, electromagnetic generators, becomes possible even at buffer voltage levels far above actual transducer output voltages Both interfaces are fully-integrated in a standard 035 μm twin-well CMOS process The designs are optimized for sub-mW transducer power levels and wide supply voltage ranges Thus, these presented transducer interfaces are particularly suitable for compact micro energy harvesting systems, such as wireless sensor nodes or medical implants The active diode rectifier achieves efficiencies over 90% at a wide range of input voltage amplitudes of 048 V up to 33 V The adaptive charge pump can harvest with a total efficiency of close to 50%, but very independent of the actual buffer voltage This charge pump starts operating at a supply voltage of 08 V, and has an input voltage range of 05 V-25 V Finally, results of harvesting from an actual electromagnetic generator prototype are presented

Abstract: This paper presents an optimization of the voltage doubler stages in an energy conversion module for Radio Frequency (RF) energy harvesting system at 900 MHz band The function of the energy conversion module is to convert the (RF) signals into direct-current (DC) voltage at the given frequency band to power the low power devices/circuits The design is based on the Villard voltage doubler circuit A 7 stage Schottky diode voltage doubler circuit is designed, modeled, simulated, fabricated and tested in this work Multisim was used for the modeling and simulation work Simulation and measurement were carried out for various input power levels at the specified frequency band For an equivalent incident signal of –40 dBm, the circuit can produce 3mV across a 100 k? load The results also show that there is a multiplication factor of 22 at 0 dBm and produces DC output voltage of 50 V in measurement This voltage can be used to power low power sensors in sensor networks ultimately in place of batteries

Abstract: A new approach to improve the power quality of high-power medium voltage multilevel drives is presented. A modular transformers strategy in conjunction with modular power electronics cubes is developed. By applying this technology, the input current harmonics decreases to well below the requirement of IEEE 519-1992 while the amount of capacitance installed in the drive is significantly reduced. In addition, by employing modular transformers technology and efficient cooling, power density of the drive is increased by 15%. The input power factor of drive is also improved. This paper details the new approach, analyses, and test results.

Abstract: DC line voltage drops as well as converter power losses have significant impacts on precise control of power flow in multiterminal VSC-HVDCs using DC voltage droop. When DC voltage droop controls are used in multiterminal VSC-HVDC, due to unequal DC bus voltages the DC line voltage drops causes large amount of power flow deviations in the DC network. DC line power losses and converter power losses also cause DC grid power flow deviations. To achieve precise control of power flow in the DC network, it is necessary that the power deviations occurring due to each of these factors be eliminated. With simulation of a five terminal VSC-HVDC system in PSCAD/EMTDC it is demonstrated how to achieve precise control of power flow in multiterminal VSC-HVDC by accounting for each of these three factors.

Abstract: In this paper, a new cascade active-front-end converter based on dual-boost/buck converters is proposed for an intelligent universal transformer (IUT), which allows adjusting the power factor to control both the active and reactive powers between medium and low voltage levels. Compared to the traditional cascade H-bridge converter, it has much enhanced system reliability owing to no shoot-through problems and lower switching loss with the help of using power MOSFETs. In addition, a unified control scheme is proposed for active-reactive power control and individual voltage balancing control, which is modular and easy to implement. In the end, a laboratory three-unit cascade active-front-end converter based on the half-bridge dual-boost/buck converter is constructed and tested. The experimental results verified the feasibility and effectiveness of the proposed active-front-end converter and the unified control scheme for IUT.

Abstract: Dominion Virginia Power's Conservation Voltage Reduction program has demonstrated energy savings of up to 4% by optimizing off-peak voltage. The key innovation is incorporating end-of-line voltage data from every customer meter, which eliminates the need to maintain an electrical model of the feeder. CVR is accomplished via DMS control of the load tap changer based on voltage feedback from AMI meter data. Analysis of AMI voltage data determines a subset of meters representing the lowest customer voltages; these meters are read every 15 minutes and used to determine the optimal feeder voltage. A statistical evaluation of pilot feeders shows a CVR factor of 0.92% reduction in energy for each 1% reduction in voltage. In addition, customer voltage monitoring identifies operational issues prior to customer calls. The program is projected to save an average of 2.8% of annual energy when applied system-wide, and may be expanded to accomplish on-peak demand reduction.

Abstract: The growth of world energy demand and the environmental concerns lead to an increase of renewable energy production over the last decade. The increased number of grid-connected photovoltaic (PV) systems gave rise to problems concerning the stability and safety of the utility grid, as well as power quality issues. Lately, PV generators are required, according to the new German Grid Code (GC), to contribute to the grid stability and to provide grid classical functions during normal and abnormal operation. The purpose of this article is to investigate and optimize the standard voltage regulation methods for low voltage (LV) grid-connected PV systems. Reactive power supply strategy proposed by the German GC Q(U) is investigated and simulated performing load flow analysis on a European residential network benchmark. In order to improve the reactive power transfer in the system, an optimized algorithm of voltage regulation is designed with the aim of minimizing the losses in the system for a better integration of PV power generation into the grid.

Abstract: The generation of power by photovoltaic (PV) systems is constantly increasing in low-voltage (LV) distribution grids, in line with the European environmental targets To cope with the effects on grid voltage profiles during high generation and low demand periods, new solutions need to be established In the long term, these solutions should also aim to allow further more PV installed capacity, while meeting the power quality requirements In this paper, different concepts of energy storage are proposed to ensure the voltage quality requirements in a LV grid with high PV penetration The proposed storage concepts can cooperate with reactive power methods and can be used to avoid grid reinforcement and active power curtailment For the study, a residential LV grid with high share of PV generation is used Simulation results show substantial benefits for the LV feeders operation, as well as an increased potential for local consumption

Abstract: A charge pumping apparatus includes a voltage pumping unit for pumping an input voltage, a voltage pumping control unit for controlling the voltage pumping unit according to a comparison result between the input voltage and an input criterion voltage and a comparison result between an output voltage output from the voltage pumping unit and an output criterion voltage, and an optimum power point tracking unit for tracking an optimum power point in the case of detecting that the output voltage decreases lower than the output criterion voltage, and adjusting an input impedance to change the input criterion voltage to a voltage corresponding to the optimum power point, wherein the optimum power point is a power point where an input power according to the input voltage becomes a maximum. Since the optimum power point is tracked by measuring only a voltage without a current sensor, a power loss is small.

Abstract: This paper addresses the voltage fluctuations caused by the output variability of photovoltaic (PV) systems. Due to the significant line resistances inside a distribution network, variations in the active power produced by a PV system can lead to fluctuations in bus voltages and result in the excessive tap-change operations of voltage regulation devices. Based on the voltage sensitivity analysis, the paper presents a reactive power control method for PV systems to mitigate the voltage fluctuations. The method is local and obviates the need for remote measurements. Also, the method considers the loss associated with the reactive power production. The performance of the method is illustrated on the IEEE-123 bus distribution network. Measurements from two actual PV systems are taken into account and the wavelet based fluctuation power index is used to evaluate the method performance. Simulations (in OpenDSS) are presented to assess the voltage regulation characteristics under different load conditions.

Abstract: We define the voltage across an area of a resistive network by suitably combining voltages at buses (nodes) on the border of the area. The new voltage across the area satisfies circuit laws. The same concept works to define the voltage angle difference across an area of a DC load flow network and the complex voltage difference across an area of an AC load flow network. We first define the voltage across a cutset of lines, and then derive and explain the voltages across areas, including generalizations to several voltages across an area and multiple areas. The new voltages across areas seem promising for both power system monitoring and network reduction, and we describe their application to monitoring area stress.