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The flying capacitor multilevel inverter (FCMLI) is one of the well-known structures of multilevel inverters having attracted considerable attention because of its merits. In spite of its many advantages, it has some limitations such as high volume and complicated control method because of its bulky capacitors and their voltage balancing requirement. Moreover, the high number of power semiconductors required makes this structure susceptible to failure. To increase the ratio of the number of levels to the number of components, an uneven distribution of capacitor voltages has been suggested in previous reports; however, this approach complicates the control method. Up to now, almost all presented methods suffer from high computational load and/or structure-dependent algorithm. In this paper, a simple state-based and structure-independent method is proposed for capacitor voltage regulation. The proposed method is straightforward and can perform online computation of switching sequences in a computationally efficient manner without any need for stored information or look-up tables. The method is conveniently extendible to any number of cells and levels in an FCMLI structure with arbitrary dc link voltage distribution schemes. Simulation and experimental results show the effectiveness and simplicity of this method. [ABSTRACT FROM PUBLISHER]

This paper presents a direct torque control (DTC) switching scheme based on the direct matrix converter (DMC) using a 12-side polygonal space vector for variable speed control of an induction motor (IM). The conventional DTC scheme-based matrix converter (MC) is limited by 60° sectors of both flux and voltage vectors, which introduce a high torque ripple. The proposed method utilizes twelve 30° sectors of both flux and voltage vectors to increase the degrees of freedom for selection of proper vectors and reduce the torque ripple. The proposed switching scheme for the MC-based DTC of an IM drive select the appropriate switching vectors for control of torque with small variations of the stator flux within the hysteresis band. This improves the degrees of freedom in selecting the vector algorithm and the torque ripple as well. Furthermore, during the large torque demand, the probabilities of transgressing reference vector limits, which are enclosed by 12-side polygonal space vector, are reduced. Extensive simulation and experimental results are presented to verify the effectiveness of the 12-sector space vector switching scheme for the DTC of an IM fed by the DMC. [ABSTRACT FROM AUTHOR]

Efficiency and dynamics of DC-DC converters play a major role in proficiency of renewable energy exploitation. This paper presents a novel DC-DC interleaved buck-boost converter for fuel-cell applications. While keeping the same step-up/step-down voltage transfer ratio, the proposed converter exhibits non-pulsating I/O currents using interleave technique. A damping network is also added to improve the inner dynamics of converter. Besides the steady state operation based on state space averaging (SSA) method, design considerations of converter are thoroughly elaborated. MATLAB/SIMULINK environment is used for simulating the steady state operation of proposed converter, and the experimental results are presented, to verify the theoretical expected merits of the converter including high efficiency, non-pulsating I/O currents and low voltage oscillation. Prototype setup of 360 W and 36 V output voltage for a fuel cell with a brand of "FCgen 1020ACS" Ballard Power Systems, Inc was implemented. Experimental results including efficiency and time domain responses in the steady state show impressive benefits of the proposed converter. [ABSTRACT FROM AUTHOR]

Abstract: Having a voltage transfer ratio lower than unity with a 0.866 upper limit, even lower than 0.866 in the course of experiments because of parasitic components of real power circuits, is one of the shortcomings of matrix converters. This deficiency is one of the greatest impediments to industry adaptation of matrix converters. To surmount this barrier this paper proposes a novel modification in circuit topology of indirect matrix converters (IMC) achieving voltage boosting and unity voltage transfer ratio. Besides preserving the inherent advantages of the conventional matrix converters, such as controllability of input power factor, sinusoidal input/output currents and the ability of bidirectional power flow, the remarkable feature of this solution is that, unlike the other research in this field no special control strategy or additional reactive elements at the DC-link is used and the integrity of the converter has been kept as much as possible. Furthermore a new efficient switching strategy is proposed for the new converter. Simulation results are shown to support the given theoretical analyses and experimental results obtained from a 5kW converter verify the full functionality of the proposed topology. [Copyright &y& Elsevier]

Abstract: Three leg inverters for photovoltaic systems have a lot of disadvantages, especially when the load is unbalanced. These disadvantages are for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the four-leg inverter. Consequently, generation of balanced voltage with sinusoidal waveform is necessary for these inverters. The power stage model of the 4-leg inverter in rotating coordinates dqo is highly coupled. Consequently, controller design procedure is very difficult and complex. On the other hand, adaptive control for 4-leg inverters has not yet been discussed in the literature. This paper proposes the state feedback approach to decouple the system and convert it to a second-order system which has two poles equal to zero. Then, it suggests a compensator to cancel poles of the closed-loop system and to convert the final system to a desired second-order system. Thanks to use of this strategy the transient performance of the system, such as overshoot and speed of response, becomes greatly adjustable. In addition, an STR (Self-Tuner Regulator) is introduced to tune the state feedback matrix and to guarantee the adaptive performance of the system. Simulation results validate that, by using proposed control strategy, the 4-leg inverter generates balanced voltage, with perfect sinusoidal waveform, in spite of the presence RL time-variant loads. [Copyright &y& Elsevier]

Abstract: Three-leg inverters for photovoltaic systems have many disadvantages, especially when the load is unbalanced. These disadvantages are, for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the 4-leg inverter. Most papers dealing with 4-leg inverters suggest classic controllers, such as PI controller, for the system. However, the transient performance of the closed-loop system does not become acceptable. On the other hand, adaptive control of 4-leg inverters has not yet been discussed in the literature. This paper proposes pole-placement control strategy, via state feedback, for 4-leg voltage-source inverters to adjust the transient performance of the closed-loop system. In addition, a STR (self-tuner regulator) is introduced to guarantee the adaptive performance of the controller in the presence of time-variant RL loads. Simulation results validate the theoretical results and proposed control strategy. [Copyright &y& Elsevier]

Abstract: Three leg inverters for photovoltaic systems have a lot of disadvantages, especially when the load is unbalanced. These disadvantages are for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the 4-leg inverter. Most papers dealing with 4-leg inverters ignore the effect of digital delays in control loop and suggest classic controllers, such as PI controller. However, the transient performance of the system does not become adjustable by applying classic control techniques. Additionally, adaptive control techniques have not yet been discussed for 4-leg inverters. This paper proposes the pole-placement control strategy via state feedback with integral state, which is a modern control technique, to control the system. Consequently, resulted system becomes highly robust. In addition, it suggests a Self-Tuner Regulator to guarantee the adaptive performance of the final system. Moreover, it proposes a novel model, considering digital delays, for 4-leg inverters. Simulation results show that transient performance of the system becomes accurately adjustable and the 4-leg inverter generates balanced voltage, with sinusoidal waveform, in spite of the presence of RL time variant loads. [ABSTRACT FROM AUTHOR]

Abstract: Three leg inverters for photovoltaic systems have a lot of disadvantages, especially when the load is unbalanced. These disadvantages are for example, small utilization of the DC link voltage, the dependency of the modulation factor of the load current and the superposition of a DC component with the output AC voltage. A solution for these problems is the four-leg inverter. Most papers dealing with 4-leg inverters ignore the effect of digital delays in control loop and suggest classic controllers, such as PI controller. However, the transient performance of the closed-loop system does not become, accurately, adjustable and acceptable, in most cases. This paper proposes a novel model, considering digital delays, for 4-leg inverters. Then, it applies pole-placement control strategy, via state feedback, to adjust the transient performance of the closed-loop system to a desired second-order system. Simulation results validate theoretical results and proposed control strategy. [ABSTRACT FROM AUTHOR]

In this paper the role of the voltage vectors of a two-level converter on variations of active and reactive power of a Doubly Fed Induction Generator (DFIG) is studied more deeply. Previous approaches only have a qualitative look toward this issue that consequently, leads to extraction of an optimal switching table. With expanding accurate equations describing the variation of active and reactive power, this paper is going to inspect the role of the voltage vectors in active and reactive power control of a DFIG exactly, and to illuminate thoroughly the impression of terms like rotor velocity and load angle variation, neglected in the previous works. Expanding these equations provides the ability of scrutinizing the effect of the converter voltage vectors on active and reactive power of the machine at any operating point. This leads to achievement of a more accurate and optimal switching table. The distinction of this method accounts it as a good candidate for online methods to predict the effect of each voltage vector on active and reactive power variation. [ABSTRACT FROM AUTHOR]