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Karimi-Ghartemani M.,Mississippi State University | Khajehoddin S.A.,Sparq Systems | Jain P.,Queens University | Bakhshai A.,Queens University
IEEE Transactions on Power Electronics | Year: 2013

This paper presents a method for design and control of dc-bus capacitance and transients in a renewable single-phase grid-connected converter. Conventionally, a proportional (P) or proportional-integrating (PI) controller is commonly used and the design stage is performed using trial-error or using a simplified analysis that does not take the dynamics of the current control loop into consideration. This paper proposes 1) a systematic and efficient method for design of dc-bus PI controller gains; and 2) an accurate method for the design of the dc-bus controller gains without neglecting the dynamics of the current control loop. Two main objectives are to have control over the amount of output current harmonics and over the level of bus fluctuations caused by random input power swings. The proposed method is transparent and it provides a convenient and rigorous insight for the designer to properly select the size of dc-bus component and to determine the controller gains. © 2012 IEEE. Source


Khajehoddin S.A.,Sparq Systems | Karimi-Ghartemani M.,Mississippi State University | Jain P.K.,Queens University | Bakhshai A.,Queens University
IEEE Transactions on Power Electronics | Year: 2013

This paper presents a control design approach for optimum dynamic response in single-phase grid-connected renewable converters with minimum energy storage components. This is a crucial matter in realizing compact and robust converters without use of bulky and sensitive electrolytic capacitors. Nonoptimum dynamic response results in undesired interruptions of the maximum power point tracking and reduction of the overall efficiency of the system. Common practice is to select a large dc-bus size in order to reduce the double-frequency ripples that cause harmonics and to slow down the dynamic response to avoid large fluctuations on the bus caused by random input power jumps. This paper shows that both problems can be addressed to a great extent by improving the control system and without need to excessively increase the size of the bus component. This paper proposes a control system to achieve these goals and provides an analytical design method to optimize both dynamic response and output current harmonics. The proposed method succeeds to reduce the size of bus component several times without compromising the system performance. Details of the proposed method, mathematical modeling of the bus control and current control systems, simulations, and experimental results are presented and discussed. © 2012 IEEE. Source


Khajehoddin S.A.,Sparq Systems | Karimi-Ghartemani M.,Mississippi State University | Bakhshai A.,Queens University | Jain P.,Queens University
IEEE Transactions on Power Electronics | Year: 2013

This paper presents a new method for controlling the exchange of power between a single-phase distributed generation system and the grid. Rather than controlling the active and reactive powers separately and through the media of current signal as is done by the conventional techniques, the proposed controller acts directly on the instantaneous power. This eliminates the conventional need for calculating the active and reactive powers; a calculation that involves filtering/phase-shifting and slows down the system responses and adds to computational complexity. This paper first formulates a nonlinear structure from a purely mathematical approach based on minimizing a cost function. The minimization procedure generates a reference for the current signal which is subsequently used in the current control loop. This paper then derives an equivalent linear counterpart for the nonlinear structure. Moreover, it is also shown that the idea of controlling the instantaneous power does not require a separate loop for the current. Having replaced the nonlinear part with its linear equivalent, a control loop that comprises linear time-varying elements is obtained. This paper further develops a linear time-invariant model of the loop for stability and design purposes. The proposed control system is successfully applied to a photovoltaic system and performance evaluation results (using computer simulations and a laboratory experimental setup) are presented. Desired performance and robustness of the proposed method is verified by testing it within different operating conditions. © 1986-2012 IEEE. Source


Karimi-Ghartemani M.,Queens University | Khajehoddin S.A.,Sparq Systems | Jain P.K.,Queens University | Bakhshai A.,Queens University | Mojiri M.,Isfahan University of Technology
IEEE Transactions on Power Electronics | Year: 2012

This paper presents a method for addressing the dc component in the input signal of the phase-locked loop (PLL) and notch filter algorithms applied to filtering and synchronization applications. The dc component may be intrinsically present in the input signal or may be generated due to temporary system faults or due to the structure and limitations of the measurement/conversion processes. Such a component creates low-frequency oscillations in the loop that cannot be removed using filters because such filters will significantly degrade the dynamic response of the system. The proposed method is based on adding a new loop inside the PLL structure. It is structurally simple and, unlike an existing method discussed in this paper, does not compromise the high-frequency filtering level of the concerned algorithm. The method is formulated for three-phase and single-phase systems, its design aspects are discussed, and simulations/experimental results are presented. © 2011 IEEE. Source


Patent
Sparq Systems | Date: 2014-03-12

Provided are single phase and multiple phase DC-AC inverters with soft switching, and related methods and uses. The DC-AC inverters comprise at least one voltage source inverter circuit or at least one current source inverter circuit having a DC input and an AC output including a first component at a fundamental frequency and a ripple component at a frequency higher than the fundamental frequency; wherein the ripple component is of a sufficient magnitude that the voltage source inverter circuit output current reverses polarity and allows the at least one inverter circuit to operate with zero voltage switching; or wherein the ripple component is of a sufficient magnitude that the current source inverter circuit output voltage reverses polarity and allows the at least one inverter circuit to operate with zero current switching. The circuits and methods may be used with grid-connected renewable energy sources.

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