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Ahmadreza Amirahmadi

Bio: Ahmadreza Amirahmadi is an academic researcher from University of Central Florida. The author has contributed to research in topics: Solar micro-inverter & Three-phase. The author has an hindex of 12, co-authored 34 publications receiving 521 citations. Previous affiliations of Ahmadreza Amirahmadi include University of Shahrood & Infineon Technologies.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a three-phase dc-ac converter with two-stage zero voltage switching (ZVS) operation for grid-tied PV system is proposed which will reduce cost per watt, improve reliability, and increase scalability of MW-class solar farms through the development of new solar farm system architectures.
Abstract: Module integrated converters (MICs) in single phase have witnessed recent market success due to unique features such as improved energy harvest, improved system efficiency, lower installation costs, plug-and-play operation, and enhanced flexibility and modularity. The MIC sector has grown from a niche market to mainstream, especially in the United States. Assuming further expansion of the MIC market, this paper presents the microinverter concept incorporated in large size photovoltaic (PV) installations such as megawatts (MW)-class solar farms where a three-phase ac connection is employed. A high-efficiency three-phase MIC with two-stage zero voltage switching (ZVS) operation for the grid-tied PV system is proposed which will reduce cost per watt, improve reliability, and increase scalability of MW-class solar farms through the development of new solar farm system architectures. The first stage consists of a high-efficiency full-bridge LLC resonant dc-dc converter which interfaces to the PV panel and produces a dc-link voltage. A center points iteration algorithm developed specifically for LLC resonant topologies is used to track the maximum power point of the PV panel. The second stage is comprised of a three-phase dc-ac inverter circuit which employs a simple soft-switching scheme without adding auxiliary components. The modeling and control strategy of this three-phase dc-ac inverter is described. Because the dc-link capacitor plays such an important role for dual-stage MIC, the capacitance calculation is given under type D voltage dip conditions. A 400-W prototype was built and tested. The overall peak efficiency of the prototype was measured and found to be 96% with 98.2% in the first stage and 98.3% in the second stage.

141 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a new zero-voltage switching (ZVS) control method that is suitable for low-power applications such as three-phase microinverters.
Abstract: This paper presents a new zero-voltage switching (ZVS) control method that is suitable for low-power applications such as three-phase microinverters. The proposed hybrid control method increases the efficiency and power density of the microinverters and features both reduced number of components and easy digital implementation. ZVS is achieved by controlling the inductor current bidirectional in every switching cycle and results in lower switching losses, higher operating frequency, and reduced size and cost of passive components, especially magnetic cores. A 400 W prototype of a three-phase inverter and its hybrid control system have been designed and tested under different conditions to verify the effectiveness of the controller. Efficiency measurement and comparison of the three different current modulation schemes have been conducted, and the inverter exhibits peak efficiency of 98.4% with fixed reverse current boundary conduction mode modulation.

79 citations

Journal ArticleDOI
TL;DR: In this article, a center point iteration P&O with variable perturb in frequency was proposed, which is suitable for various power curves, especially the LLC microinverter power curves.
Abstract: Maximum power point tracking (MPPT) is an essential technique to harvest PV power under varying environments. Perturb and observe (P& O) algorithms are the most broadly used MPPT due to their effectiveness and simplicity. However, it is difficult to balance the tracking speed and oscillation requirements in the conventional P& O with fixed perturb. Adaptive P& O techniques have been proposed as a solution to these problems. However, they are based on duty cycle modulation for conventional pulse width modulation converters. None of them deal with the variable frequency modulation for resonant converters. In this paper, a center point iteration MPPT is proposed, with its variable perturb in frequency. The proposed scheme overcomes the drawbacks of conventional P& O with a simple calculation. Moreover, it is suitable for various power curves, especially the LLC microinverter power curves, which may confuse conventional MPPT algorithms. The effectiveness of the proposed MPPT method was verified in theory. A 300 W prototype was constructed, and the experimental results verified the effectiveness of the proposed center point iteration MPPT. An advanced version was also introduced in order to accelerate the tracking speed.

74 citations

Proceedings ArticleDOI
21 Oct 2010
TL;DR: In this article, the authors proposed the theory and application of a new designing method of the Fractional Order PID (FOPID) controller for boost converters, where the derivation and integration orders are of fractional order rather than integer.
Abstract: This paper proposes the theory and application of a new designing method of the Fractional Order PID (FOPID) controller for boost converters. FOPID is a PID where the derivation and integration orders are of fractional order rather than integer. A FOPID is an extension to classic integer order PID controllers, that potentially promises better results. The method is based on the use of a Multi-Objective optimization evolutionary algorithm called Strength Pareto Evolutionary Algorithm (SPEA). Other controller methods cannot guarantee a good start-up response but the proposed method can provide an excellent start-up response besides desired dynamic response. The optimum fractional order PID coefficients for the desired control objectives are included and designers can implement each of them based on objective functions priority. A comparison between the optimum integer order PID controller and optimum fractional order PID controller is presented in the paper. The simulation and some experimental results prove the superiority of the fractional controllers over the integer controllers.

45 citations

Journal ArticleDOI
TL;DR: In this article, a dual-mode current modulation method combining boundary conduction mode (BCM) and zero voltage switching (ZVS) was proposed to improve the efficiency of the microinverter.
Abstract: Boundary conduction mode (BCM) zero voltage switching (ZVS) current control is a promising soft switching method for microinverter applications. In this letter, different BCM ZVS current control modulation schemes are compared based on power losses breakdown, switching frequency range, and current quality. Compared to continuous conduction mode current control, BCM ZVS control decreases MOSFET switching losses and filter inductor conduction losses but increases MOSFET conduction losses and inductor core losses. Based on the loss analysis, a dual-mode current modulation method combining ZVS and zero current switching schemes is proposed to improve the efficiency of the microinverter. The experimental results show that by using this proposed current modulation scheme, higher efficiency of 0.5% can be achieved with no additional cost for a 400-W three-phase microinverter.

42 citations


Cited by
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Journal ArticleDOI
TL;DR: This collection of GaN technology developments is not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve.
Abstract: Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

788 citations

Journal ArticleDOI
TL;DR: In this article, the authors provide an introduction, review, and framework for the category of high-step-up coupled-inductor boost converters, which are categorized into five groups according to the major topological features.
Abstract: High-step-up, high-efficiency, and cost-effective dc–dc converters, serving as an interfacing cell to boost the low-voltage output of renewable sources to the utility voltage level, are an important part in renewable energy systems. Over the past few years, there has been a substantial amount of studies devoted to high-step-up dc–dc converters. Among them, the category of coupled-inductor boost converters is widely researched and considered to be a promising solution for high-step-up applications. In this paper, these converters are categorized into five groups according to the major topological features. The derivation process, advantages, and disadvantages of these converters are systematically discussed, compared, and scrutinized. This paper aims to provide an introduction, review, and framework for the category of high-step-up coupled-inductor boost converters. General structures for the topologies are proposed to clarify the topological derivation process and to show potential gaps. Furthermore, challenges or directions are presented in this paper for deriving new topologies in this field.

325 citations

Journal ArticleDOI
TL;DR: A novel FOPID controller design method based on an improved multi-objective extremal optimization (MOEO) algorithm for an automatic regulator voltage (AVR) system and the proposed MOEO algorithm is relatively simpler than NSGA-II and single-objectives evolutionary algorithms, such as genetic algorithm, particle swarm optimization (PSO), chaotic anti swarm (CAS) due to its fewer adjustable parameters.

246 citations

Journal ArticleDOI
TL;DR: The chaotic NSGAII algorithm is used as the optimizer to search true Pareto-front of the FOPID controller and designers can implement each of them based on objective functions priority, validate the superiority of the fractional order controllers over the integer controllers.

194 citations

Journal ArticleDOI
TL;DR: In this paper, a chaotic ant swarm (CAS) optimization method was used to optimize the tuning of FOPID controller, in which the objective function is composed of overshoot, steady-state error, raising time and settling time.
Abstract: Fractional-order PID (FOPID) controller is a generalization of standard PID controller using fractional calculus. Compared to PID controller, the tuning of FOPID is more complex and remains a challenge problem. This paper focuses on the design of FOPID controller using chaotic ant swarm (CAS) optimization method. The tuning of FOPID controller is formulated as a nonlinear optimization problem, in which the objective function is composed of overshoot, steady-state error, raising time and settling time. CAS algorithm, a newly developed evolutionary algorithm inspired by the chaotic behavior of individual ant and the self-organization of ant swarm, is used as the optimizer to search the best parameters of FOPID controller. The designed CAS-FOPID controller is applied to an automatic regulator voltage (AVR) system. Numerous numerical simulations and comparisons with other FOPID/PID controllers show that the CAS-FOPID controller can not only ensure good control performance with respect to reference input but also improve the system robustness with respect to model uncertainties.

165 citations