Department of Power (1999 - Present)
Electrical Engineering
Electrical Engineering, University of Wollongong, Wollongong, Australia
Electrical Engineering
Electrical Engineering, University of Wollongong, Wollongong, Australia
Electrical Power Engineering
Electrical Engineering, Sharif University of Technology, Tehran, Iran
Ali Yazdian Varjani received his BSc. from the Sharif University of Technology in 1989 and his M.Eng. and PhD. in Electrical Engineering from the University of Wollongong, Australia, in 1995 and 1999 respectively. Since 1999 he has been with Tarbiat Modares University, Tehran, Iran, He is currently an associate professor in the Power Electronics department and he is the director of Industrial Electronics lab, Electrical Machines and Drives Lab and Cyber Physical Energy Systems Lab. His current academic interests include a variety of research issues associated with Information and Communication Technology and Industrial Electronics related topics.
Nowadays, an Energy Management System (EMS) located at power grid control centers plays a critical role in ensuring the reliable operation of a grid. The State Estimator (SE) serves as the main interface of EMS with the power grid and because of that, other EMS functionalities rely on its provided data. Recent studies show that the state estimator is vulnerable to various types of cyber-attacks. Among different types of such attacks, the False Data Injection Attacks (FDIAs) are proven to be one of the most stealth ones and attracted much attention. Various countermeasures have been proposed to detect such kind of attacks. However, these approaches are generally based on some assumptions, such as being limited to detecting a specific type of
Utilization of small-scale wind energy conversion systems (WECS) has been grown in recent years. Permanent magnet synchronous generator due to lack of slip rings is a suitable alternative for induction generators to be used in these systems. However, these generators use full power converters which means higher power losses. In this paper, an ultra-efficient three-level converter, called T-type converter, is used in a back-to-back configuration as power electronic interface for PMSG-based small-scale WECS. Then, simulations are carried out to evaluate the efficiency of the system and compare it to conventional two- and three-level back-to-back configurations. Meanwhile, thermal analysis is carried out to investigate the thermal
This study shows a new high step up converter based on the three-winding coupled-inductor. The introduced power converter switches turn on at zero voltage switching (ZVS) condition, and all the diodes turn off at zero current switching (ZCS) condition over the entire operating scope. Therefore, the switching losses diminish, and higher switching frequency is achievable. Furthermore, it has lower EMI noises and higher efficiency due to using the soft-switching technique. The introduced power converter operates at (40 V - 80 V) at the input side. Furthermore, the output power variation is in the range of (50 W-250 W). This converter is therefore ideal for low power photovoltaic (PV) applications.
The single phase shift (SPS) method is the conventional switching strategy for the dual active bridge (DAB) structure. Another switching method is the extended phase shift (EPS) method. In this modulation, the zero voltage switching (ZVS) range increases. In this paper, the effect of the magnetizing inductance of the transformer on the output power value and ZVS range with the EPS control method is studied. Simulation results show correctness of the theoretical analysis.
In this article, a new high step-up transformerless dc?dc converter based on a voltage multiplier and a coupled inductor topology is presented. The proposed converter has two stages. In the first stage, a modified boost converter is designed by the coupled inductor, and in the second stage, a new voltage multiplier by using a coupled inductor is illustrated. In this converter, high voltage gain can be achieved by adjusting the turn ratio of two coupled inductors and the duty cycle, which result in three degrees of design freedom. Using a single power switch with low on -resistance in the converter structure leads to simple control and low conduction loss. In addition, total voltage stresses of active elements are decreased, which increases efficiency. Steady-state performance and theoretical achievements are confirmed by experimental test results on a test setup with one 200-W dc?dc prototype.
Today, grid-connected photovoltaic systems have gained widespread penetration among renewable energy systems. For low power applications, a single-phase inverter with less power converter is a good compromise for high efficiency. The control must make it possible to extract the maximum power from the photovoltaic modules, ensure good dynamic performance for active and reactive power injection, ensure power quality, and reject disturbances and parameter mismatch. Besides, the controllers of the grid and PV sides should be coordinated. In this study, a fast terminal sliding mode control combined with Direct Power Control is proposed. Thanks to the two-cascaded control loops, simulations and experimental results with a 1?kW test bench have pro
Nowadays, an Energy Management System (EMS) located at power grid control centers plays a critical role in ensuring the reliable operation of a grid. The State Estimator (SE) serves as the main interface of EMS with the power grid and because of that, other EMS functionalities rely on its provided data. Recent studies show that the state estimator is vulnerable to various types of cyber-attacks. Among different types of such attacks, the False Data Injection Attacks (FDIAs) are proven to be one of the most stealth ones and attracted much attention. Various countermeasures have been proposed to detect such kind of attacks. However, these approaches are generally based on some assumptions, such as being limited to detecting a specific type of
This paper presents an extended coupled inductor quasi-Z-source inverter (ECL-QZSI), which has advantages like input current ripple suppression and high gain ability. Adding third coupled winding series with the input inductor causes to reduce high-frequency input current ripple. Among the impedance source converters in the same condition to have equal current ripple, the amount of inductor will be decreased significantly compared to the absence of third series winding. Unlike trans-Z-source inverter, in proposed topology input current is continuous which eliminates protector energy source filter and voltage gain is boosted by reducing turns number of primary winding transformer which decreased costs and volume of the transformer. In compar
Among different micro inverter topologies, single stage micro inverters duo to their lower component, low cost and simple control structure are paid more attentions. One of the biggest problem in single phase micro inverter is power ripple in twice frequency of line. This phenomena causes voltage and current ripple in the side of PV so that designing MPPT controller becomes very hard. To eliminate power ripple (power decoupling) in conventional micro inverters, large electrolytic capacitors are used in parallel of PVs. Drawbacks of electrolytic capacitors are large ESR and lower life cycle in comparison of other type of capacitors. In this paper, a power decoupling method for Single stage flyback based current fed micro inverter is presente
In this paper, a novel soft-switching bidirectional DC-DC converter based on coupled inductors is suggested. This converter includes four switches and a pair of coupled inductors and can achieve high voltage conversion ratio in step-up/step-down modes. Employing the interleaved technique reduces input current ripple and thereby increases the efficiency of the converter. The ZVS turn-on characteristic is obtained in both boost and buck directions for all converter switches. The uncomplicated and efficient control, as well as operation under proper duty cycle, are the other advantages of the suggested converter. A 500W prototype 36V/400V is simulated to validate theoretical conclusions.
The Internet of Things (IoT) refers not only to the connectivity of systems and devices but to the related applications and services that provide monitoring and control of complex systems and services. Micro inverters due to their advantages to central inverters, get more attentions. Conventional micro inverters in solar applications only transfer energy from solar cells to grid or loads. Solar smart inverters in addition to transferring energy, can monitor condition to detect faults and also operate as multi agent systems. IOT interconnection can bring lots of new characteristics to micro inverters. This kind of IoT solar energy system can collect and analyze inverter data, control solar farms, monitor the condition, detect faults and opti
Extension of zero voltage switching (ZVS) range of a Dual active bridge (DAB) converter is important especially at light loads. In this paper, the ZVS range of a DAB converter is increased by cascading a bidirectional buck-boost converter with a DAB converter. This proposed structure increases the maximum input and output currents, so output power can be controlled in a wider range. Simulation results confirm the performance of the proposed configuration.
This paper presents a Flying-Capacitor converter above its resonant frequency considering zero-voltage switching (ZVS) realization and voltage regulation issue due to wide input voltage and output power variations. A new multi-level Flying-Capacitor (FC) dc/dc converter is candidate among the other proposed topologies with lower power device count and soft switching characteristics that results in lower electromagnetic interference and switching losses. ZVS operation under the continuous conduction mode (CCM) operation has achieved undeniable benefits in switching losses and therefore a higher efficiency. In the MOSFET-based converters, the ZVS operation causes lower switching losses in contrary to the wide used zero current switching (ZCS)
This paper presents a resonant switched capacitor converter (SSC) above its resonant frequency to achieve zero voltage switching (ZVS) operation and overcome its voltage regulation issue. The ZVS operation under the CCM operation mode reduces switching losses and improves the converter efficiency more than zero current switching (ZCS) operation below the resonant frequency in MOSFET based converters. In addition, under the CCM operation mode the output voltage can be regulated as the input voltage or load current varies in a wide range. The symmetrical dual structure proposed converter causes the input current ripple and output voltage ripple to be reduced more in contrary to previous researches. Therefore, the input filter and output capac
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