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This paper proposes a new type of voltage swell/sag compensator based on single-phase Z-source AC/AC converter. The proposed topology employs a pulse width modulation (PWM) Z-source AC/AC converter along with a transformer. A commutation strategy to drive the AC/AC converter is employed to realize snubberless operation. Circuit analysis is provided. Simulation and experimental results at 20% voltage...
An alternative method is presented in this paper to identify the harmonic components of non-linear loads in single phase power systems based on artificial neural networks. The components are identified by analyzing the single phase current waveform in time domain in half-cycle of the ac voltage source. The proposed method is compared to the fast Fourier transform. Simulation and experimental results...
Distribution grids are increasingly populated by a variety of renewable energy sources, which create new opportunities in terms of efficient use of energy and can also help to improve power quality. In fact, they are connected to the grid by means of power switching interfaces (PSI) which are capable to control power flow and waveform of absorbed currents as well. They can therefore contribute to...
This paper is focused on active and reactive power consumption and power losses in the consumer power system depending upon supply voltage quality. Supply voltage level deviations from rated voltage affect directly power consumption and power losses in the consumer power system. Active and reactive power relation to supply voltage is characterized by load factors. In the paper a practical method for...
This paper presents a control system based on a repetitive controller to compensate key power-quality disturbances, namely voltage sags, harmonic voltages and voltage imbalances, using a dynamic voltage restorer (DVR). The control scheme deals with all three disturbances simultaneously within a specified bandwidth. The control structure contains a feed-forward term to improve the transient response...
This paper presents a comparison study between the operation of a back-to-back and a matrix converter induction motor drive under the presence of faults in the power switches of these converters. These two topologies are functionally equivalent in terms of input power quality and energy regeneration capabilities but need to be compared in terms of performance under faulty conditions as well due to...
In future grid codes wind farms will have to fulfill demanding fault ride through requirements. Among several grid faults the voltage swell is a critical event. Wind farms with doubly-fed induction generators will not be able to fulfill the new grid code requirements without additional fault mitigation equipment. In this publication the applicability of the dynamic voltage restorer and the static...
Power converters operated in unsymmetrical three-phase electrical systems will generally work asymmetrically. This introduces disadvantages for the operation of the electrical power system, such as non-characteristic harmonics in voltage and current. In this paper, a method is presented to control the behavior of electrical equipment based on line-commutated current converters using unsymmetrical...
The present paper addresses the control of doubly fed induction generators under unbalanced voltage sags considering the converter limits. A control strategy is proposed by choosing certain current reference values in the positive and negative sequences so that the torque and the DC voltage are kept stable during such unbalanced sags considering the converter limits.
This paper investigates the interactions which arise between grid connected photovoltaic inverter systems and the electrical grid. In particular, it considers the effect of grid voltage harmonics and grid impedance on the current control performance of grid connected inverter systems. In these photovoltaic inverter systems it is usual to control unity power factor, sinusoidal, current into the grid...
This paper deals with shunt active power filtering for power quality improvement under unfavourable non-linear load and source conditions. A simple hybrid control strategy is used, based on a numerical integrator proportional (IP) DC bus controller combined with a phase-locked loop (P.L.L.) output to generate reference currents. A second analogue current controller is developed to insure- three phase...
The aim of this paper is to propose an over current limitation and voltage control strategy for a grid connected inverter with a LC output filter used in distributed generation and in case of voltage sag. This strategy relies on the control of LC output filter voltage with a resonant controller. This controller has to control current and load voltage throughout voltage sag. Generally, resonant controller...
This paper focuses on the effects of voltage sags, both symmetrical and unsymmetrical, on the three-phase synchronous machine (SM). Voltage sags on SM cause speed variations, current and torque peaks and hence may cause tripping and equipment damage. The consequences of voltage sags on the machine behaviour depend on different factors such as sag's magnitude (or depth), duration, initial point-on-wave...
Grid codes are being revised to include additional requirements for renewable energy, as the installed power increases. Therefore it is needed to develop control systems that are able to fulfil those new requirements, which usually include the ability to operate under unbalanced grid voltages without polluting the grid, among others. This paper presents a three-phase inverter for connection of photovoltaic...
This paper presents a fast on-load tap changing regulator used to correct unbalanced voltages. This regulator uses the semi natural commutation in order to improve the response. The proposed topology injects the voltage in only phase in order to balance the three phase system.
Over the past decade, power quality (PQ) issues became increasingly important. The most cited PQ problems are voltage dips, harmonic distortion and transient phenomena. The tarification method which is mostly used, tarifies the instantaneous active power. When absorbing harmonic power, e.g. when using an active filter, the customer has to pay for this. To overcome this, a tarification method is proposed...
Application of high efficiency energy storage techniques may stimulate in a near future a larger exploitation of renewable energy sources. Energy storage, in fact, not only can improve the quality of produced power, but also make possible the implementation of sophisticated energy management strategies, fully decoupling the power delivery from power generation. In such a scenario, Vanadium Redox Batteries...
The systematic use of Active Power Filters, APFs, to compensate nonlinear loads, has extended the use of the instantaneous reactive power theory. Originally, the p-q theory appeared; it obtained constant instantaneous power in the source side after compensation. Later, other formulations have been developed. They have allowed different compensation objectives to be obtained. Nevertheless, all of them...
This contribution deals with a shunt-type active power filter designed mainly for railway applications (50-Hz and 16.7-Hz electrification systems) which is able to compensate undesired harmonic currents as well as reactive power. Its control algorithm employs an optimized DFT-based fundamental current and voltage estimator generating an accurate control reference signal. The APF configuration, the...
Reliability and power quality are two aspects of motor drives which have been gaining the attention of the industry. In fact, as the processes increased in number and complexity, the criticality of each component also increased. This paper proposes the usage of a PWM rectifier to accomplish a fault-tolerant motor drive with optimal performance and power quality. The system uses a hardware reconfiguration,...
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