Sharif Digital Repository

This paper introduces a high efficiency AC voltage regulator based on an AC/AC buck converter cascaded by a transformer in series with the input voltage. The AC/AC converter uses an overlap time in the gate signals to solve the commutation problem. Non-use of any snubber circuits and current sensors leads to lower cost, smaller size and simpler hardware. The converter generates only the compensation term which results in smaller switches and, thus, lower cost. Simulation and experimental results verify the performance of the proposed topology  

Small Permanent Magnet Synchronous Generators (PMSG's) are widely used in low power wind turbines. In order to inject the electrical power, generated by PMSG, to the grid, a back-To-back AC/AC power electronic converter is required. In this paper, a novel low cost efficient AC/DC converter is proposed for rectifier stage to obtain the maximum power per ampere of PMSG by using Power Factor Correction method. The new structure is based on DCM SEPIC converter. Reducing the number of semi-conductor switches has decreased converter cost. Additionally, other advantages of this Converter are employing easy control method to obtain the maximum power per ampere and using Synchronous inductance of... 

Power electronics is becoming an underpinning technology for modern power systems. Power converters are increasingly used in various applications implying different levels of importance in power systems. Hence, optimal decision-making for manufacturing, control, operation and maintenance of them requires understanding of their importance in the power systems. Furthermore, identifying the converters importance may be beneficial for simplifying the system-level reliability modeling in a large Power Electronic based Power Systems (PEPSs). Thereby, a Failure Mode, Effects and Criticality Analysis (FMECA) approach is proposed in this paper in order to figure out the importance of converters in... 

This paper proposes a model-based design approach for microgrids considering the aging of power electronic devices under different operating conditions. The proposed approach takes into account the physics of failure mechanisms in converter components as the failure prone devices in power systems. Furthermore, it considers the impacts of load profile on the aging of converter components and system performance. This approach facilitates accurate and optimized design of power electronic-based microgrids. According to this approach fragile links of power converters for a specified application can be identified. Moreover, the weakest converters based on their function in the microgrid can be... 

Brushless Doubly-Fed Induction Generator has attractive features to be the first choice in next generation of wind generators. However, its efficiency and power-to-weight ratio are slightly lower in comparison to induction machine with the same rating. Considerable part of these imperfections arises from the rotor design, which produces magnetic field with considerable undesirable spatial harmonics. This paper proposes a novel rotor configuration to reduce spatial harmonic distortion of air-gap magnetic field as well as improving some drawbacks of the conventional structure, including unequal magnitudes of rotor bar currents, teeth saturation at low average air gap magnetic fields, high core... 

One of the most significant parameters that the electronic designers are trying to increase, is the reliability or the effective lifetime of the circuit. For example the designers are always trying to achieve higher efficiency. One of the most important influence of the greater efficiency is the reduction of the thermal stress on the components, that leads to increase of the reliability. In this paper the reliability of two different industry-based structures as an AC/DC converter, have been compared. These circuits are from two different generations of power supplies in a particular industry, which the first introduced structure has greater efficiency due to soft switching. FIDES method has... 

This paper proposes to use a back-to-back converter as the interlink between a utility grid and a microgrid. To justify this proposal, two modes of operation are explained and the benefits of the back-to-back converter over conventional static switches are shown. In mode-1, the inter-link converter injects prespecified amounts of active and reactive power to the microgrid. This mode is identified as PQ control mode. Mode-2 is the voltage control mode in which, the back to back converter controls the voltage of the microgrid and maintains the power quality of the current drawn from the utility grid in spite of nonlinear and unbalanced loads in the microgrid  

In this paper, a distributed secondary power sharing approach with low bandwidth communication network is proposed for low voltage direct current (LVDC) microgrids. Conventional droop control causes voltage drop in the grid and also a mismatch on the current of converters in the case of consideration of the line resistances. Proposed control system carry out the current value of the other converters to reach the accurate current sharing and suitable voltage regulation as well. Voltage and current controllers locally regulate the voltage and current of converters as a secondary controller. Secondary controller is realized locally and the communication network is only used to transfer the data... 

Stray capacitance of transformer winding is an important parasitic element influencing the behavior of the switching power converters, especially for high-voltage transformers. There are various methods for calculating the stray capacitance in transformers and inductors with ordered windings. However, an ordered winding is less likely with an increased number of turns and layers. In this paper, it is shown that a slight disorderliness in winding leads to a considerable difference between the value of winding stray capacitance of the former ordered winding and its slightly disordered scheme. Therefore, regular methods for calculating the stray capacitance have significant errors in a... 

Dual active bridge isolated bidirectional DC converter (DAB-IBDC) has a poor efficiency at light loads and non-unity voltage conversion ratio. In this paper the current stress of the converter is analyzed and the effect of maximum phase shift ratio and leakage inductance on the current stress of the converter is investigated. In order to increase the efficiency of the converter and reduce the current stress, the current stress optimization has been done and the design procedure is presented. Simulation results are used to validate the results of the theoretical analysis. © 2017 IEEE  

This paper presents a new nonlinear current control strategy based on backstepping control and high-order sliding mode differentiator in order to employ distributed generation (DG) unit interfacing converters to actively compensate harmonics/interharmonics of local loads. The converter-based DG unit is connected to a weak grid (with uncertain impedance) and local load (that can be parametrically uncertain and topologically unknown) through an LCL filter. The proposed strategy robustly regulates the inverter output currents and delivers pure sinusoidal, three-phase balanced currents to the grid. The new controller demonstrates the robust performance and robust stability of the DG unit system... 

Vulnerability of power electronic converters in DC microgrids in case of fault occurrence in DC cables necessitates using a fast fault detection and isolation scheme. In this paper, a modified, fast and selective protection scheme has been presented, which provides the required tripping of low voltage DC (LVDC) microgrids. This protection scheme has been developed based on the natural characteristics of the fault current, in which the first and second derivatives of the fault current have been employed to define thresholds for discriminating between faulted and non-faulted situations. To enhance fault detection capability of the protection scheme, definition of thresholds have been improved... 

This article describes the development of an 18 kV, 30 kW power supply for a pulsed current load with the maximum current of 20 A and a di/dt equal to 100 A/μs. The achieved output ripple is less than 0.01%. In such a high level of precision, the most important issues are considerable difference between the instantaneous and average output powers, as well as insufficient reaction speed of the converter to the fast load change. Very low level of the voltage feedback and its sensitivity to the noise. The first issue necessitates a notable overdesign of the converter switches if the output voltage precision is dedicated to the converter. The second issue raises the problems relevant to... 

The reliability of power electronic based converters has become increasingly important due to their wide-spread use in industry. An effective method to increase the availability of converters is to use condition monitoring systems for planning scheduled maintenances. This paper provides a method to monitor the condition of IGBTs in a back-to-back converter based on their on-state voltage measurement. Using the proposed system adds limited number of elements to the circuit but can be implemented independent from the converter. Considering the converter topology has made the proposed method applicable for condition monitoring of switches in different back-to-back converters. This advantage... 

In this study, a new LLC resonant converter for high-voltage high-power applications is introduced. The introduced power converter is a two-phase interleaved full-bridge based that uses a transformer with secondary and tertiary windings to obtain higher output voltage. Zero voltage switching (ZVS) at MOSFETs turn on and zero current switching (ZCS) for all the output diodes at turn off are achieved for a wide range of input voltage (100 V-200 V) and output power (200 W-1500 W) variations. Simulation results show a 95% peak efficiency. © 2021 IEEE  

This paper investigates several current control methods for load balancing and power factor correction based on distribution Static Compensator (STATCOM). Two different configurations are considered for STATCOM; a three leg inverter, and three single phase inverters. It is assumed that the STATCOM is associated with a load that is remote from the supply. After a brief introduction, control structure based on PWM method and simulation results using PSCAD are presented. Next, the same system is simulated using hystersis control method. Both methods employ the instantaneous symmetrical components theory for load balancing and power factor correction. At the end, a comparison between two methods... 

A matrix converter is a voltage/current source AC/AC frequency converter. In grid-connected operation of a variable-speed permanent magnet synchronous wind power generator, the matrix converter is normally controlled as a voltage source converter. In this control method, the generator-side voltage is synthesized from the grid-side voltage source. However, in the stand-alone mode of operation, the grid-side stiff voltage source is not available, and the input filter of the matrix converter is unstable. In this article, a new control method is presented that controls a permanent magnet synchronous wind generator in a stand-alone mode with a matrix converter as a current source converter. The... 

This paper presents an effective current injection method for a single phase grid-connected PV inverter with LCL filter. The main objective of the proposed control strategy is to compensate the resonance effect of the LCL filter. In the proposed control strategy, a resonance compensator is augmented to the conventional proportional resonance (PR) controller to attenuate current oscillations in resonance frequency of LCL filter. The proposed strategy robustly regulates the output current of grid connected inverter in various grid impedances and provides a high quality current injection capability for the PV inverter in harmonic polluted condition of the grid voltage. The performance of the... 

A dc-dc resonant converter has the advantage of overcoming switching losses and electromagnetic interference which are the main limitations of high frequency power converters. Nevertheless, the modeling and stability analysis of dc-dc resonant converters are considerably more complex than pulsewidth modulation counterparts. The conventional averaged linearized model of the resonant converter has limitations due to averaging and linearization. First of all, the linearized model has large modeling error in presence of large variations of reference voltage and input voltage. Furthermore, Converging area for stabilizing controllers is smaller in the averaged model. In order to overcome these...