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In this paper, a three-port converter with three active full bridges, two series-resonant tanks, and a three-winding transformer is proposed. It uses a single power conversion stage with high-frequency link to control power flow between batteries, load, and a renewable source such as fuel cell. The converter has capabilities of bidirectional power flow in the battery and the load port. Use of series-resonance aids in high switching frequency operation with realizable component values when compared to existing three-port converter with only inductors. The converter has high efficiency due to soft-switching operation in all three bridges. Steady-state analysis of the converter is presented to determine the power flow equations, tank currents, and soft-switching region. Dynamic analysis is performed to design a closed-loop controller that will regulate the load-side port voltage and source-side port current. Design procedure for the three-port converter is explained and experimental results of a laboratory ,prototype are presented. [ABSTRACT FROM AUTHOR]

This paper proposes a simple control method to achieve active sharing of input voltage and load current among modular converters that are connected in series at the input and in parallel at the output. The input-series connection enables a fully modular power-system architecture, where low voltage and low power modules can be connected in any combination at the input and/or at the output, to realize any given specifications. Further, the input-series connection enables the use of low-voltage MOSFETs that are optimized for very low RDSON, thus, resulting in lower conduction losses. In the proposed scheme, the duty ratio to all the converter modules connected in input-series and output-parallel (ISOP) configuration is made common. This scheme does not require a dedicated input-voltage or load-current-share controller. It relies on the inherent self-correcting characteristic of the ISOP connection when the duty ratio of all the converters is the same. The proposed scheme is analyzed using the average model of a forward converter. The stability and performance of the scheme are verified through numerical simulation, both in frequency domain and in time domain. The proposed control method is also validated on an experimental prototype ISOP system comprising of two forward converters. [ABSTRACT FROM AUTHOR]

This paper presents system modeling and nonlinear control design of static compensators (STATCOMs) for fast voltage regulation in the presence of load uncertainty and voltage flicker. A simplified power distribution system is modeled using ideas similar to field oriented control of three phase ac machines. Zero dynamics of the system show that the system is nonminimum phase for certain operating conditions, thus, imposing restrictions on the achievable dynamic response. The control design involves estimation of the load conductance via a gradient-based estimator, and state feedback control to reach an equilibrium point established by the estimated load conductance and knowledge of system parameters. A Lyapunov function is used to establish asymptotic stability in the large for the closed-loop system. To account for practical implementation issues, a new controller relying on feedback of a readily measurable state is also proposed. Simulations results are presented to show efficacy of both controllers with regard to bus voltage regulation and suppression of voltage flicker. [ABSTRACT FROM AUTHOR]

This paper targets the reduction of common-mode voltage in an indirect matrix converter (IMC) through an intelligent space-vector-based modulation technique. This mode of control results in lower dV/dt at the motor terminals, thereby, reducing voltage stress to windings; and reduced output voltage distortion resulting in lower machine losses. The conventional indirect space vector pulse-width modulation method of controlling matrix converters involves independent control of either the rectifying stage or the inverting stage of the converter. However, in this paper, by suitable selection of space vectors, the rectifying stage of the matrix converter generates different levels of virtual dc-link voltage. Therefore, the responsibility of formulating output voltages with a particular magnitude and frequency, which can be translated to different machine speeds, has been transferred solely to the rectifying stage of the IMC. Estimation of the degree of distortion in the three-phase output voltage is another facet discussed in this paper, which aids the sizing and designing of output passive filters. The analysis of output voltage distortion and the proposed modulation strategies have been substantiated by simulations in MATLAB/Simulink and experimentally verified on a scaled down laboratory prototype. [ABSTRACT FROM AUTHOR]

Different power electronic converter topologies have been investigated to integrate renewable energy systems to the grid. Cascaded multilevel converters with a high-frequency link have emerged as a viable candidate for such applications. Electrical isolation can be provided using a compact high-frequency transformer connected in the link thus avoiding a bulky line frequency transformer. The use of cascaded modules allows the generation of a multilevel voltage having low total harmonic distortion but increases the overall system size. In this paper, a 15-level high-frequency ac-link single-stage asymmetrical multilevel converter for grid integration is proposed. The single-stage conversion approach eliminates the dc-link capacitors, resulting in a reduced footprint. The asymmetrical module voltages are generated by the multiwinding transformer having unequal turns on each of the secondaries. This allows the generation of 15 output voltage levels, using only three modules in each phase. A modulation strategy is proposed to generate multilevel output voltage. The effect of switch nonidealities on the output voltage is analyzed and two compensation techniques are developed to improve the voltage profile. A multiwinding high-frequency transformer is designed and characterized for the proposed converter. The presented concepts are verified by simulation and further validated experimentally on a three-phase 15-level converter prototype. [ABSTRACT FROM AUTHOR]

A filter is required to eliminate the high-frequency switching ripple present in the input current of a matrix converter (MC). Design of such a filter requires an estimation of the higher harmonic components present in the input current. This paper presents a simple closed-form analytical expression for the RMS input current ripple injected by the MC. The expression shows the variation with load power factor and is independent of the output frequency. This is used in a step-by-step procedure to design various input filter components from the specifications of allowable total harmonic distortion in the grid current and distortion in the input voltage. The MC is modeled for the grid frequency component in order to evaluate the design for input power factor and voltage drop across the filter. A damping resistance has been designed ensuring minimum ohmic loss. The analytical estimation of the ripple current and the proposed design procedure have been validated by simulations in MATLAB/Simulink and experiments on a laboratory prototype. [ABSTRACT FROM PUBLISHER]

Power supply voltages in digital systems have reduced considerably in recent years, and often digital components requiring different voltages are present on the same board. This has increased the demand for multiple output power distribution systems with tight individual load voltage regulation. This paper presents a power distribution system having a central power supply that acts as a controlled current source whose output is connected to individual loads on a time shared basis. All the magnetics are concentrated in the converter acting as the current source. The current source can be realized by a current controlled buck, buck-boost, or single-ended primary inductance converter (SEPIC). First, a comparative analysis of buck, buck-boost, and SEPIC based implementation of the current source is carried out. Next, a buck-based current source implementation with constant frequency pulse-width modulation control for the output voltages is described. Detailed component and control design, simulations, and experimental results for a 100-W prototype are presented. [ABSTRACT FROM AUTHOR]

Dual active bridge (DAB) based converters offer the benefit of smaller volume due to high-frequency isolation and controllability of active power flow, making them attractive for various applications, such as renewable energy generation, plug-in hybrid vehicles, and distribution systems. This paper presents a novel converter topology along with a modulation strategy for a DAB-based three-phase ac to dc converter. The major benefits are single-stage conversion, no unreliable intermediate dc-link capacitor, reduced number of switches, i.e., only two active switches on the ac side, simple control scheme, open-loop unity power factor operation, bidirectional power flow, and partial soft-switching. This paper presents the analysis of all the operating modes of the converter, resulting in the analytical estimation of power transfer and rms winding current and investigation of soft-switching conditions for the power devices. Simulation and experimental results have been presented to demonstrate the advantages of the proposed technique and accuracy of the analysis.1 [ABSTRACT FROM AUTHOR]

Power electronic transformers (PETs) offer the advantage of size and weight reduction compared to line-frequency transformers by operating at much higher frequencies than line frequency. In this paper, a push–pull-based ac/dc PET has been proposed and analyzed. The PET offers bidirectional power flow between single-phase ac and dc, using the dual-active bridge principle. Such a system may find applications in interfacing plug-in hybrid and electric vehicles to the grid. The proposed PET offers advantages of open-loop unity power factor operation, soft switching of secondary-side converter power switches for all operating points, high power density owing to use of a high-frequency transformer, and high utilization factor (UF), compared to previous work. Analysis has been done for power transfer, UF, and soft switching. Simulation and experimental results have been provided to demonstrate the operation of the PET. [ABSTRACT FROM PUBLISHER]

A winding design approach is proposed to create a single motor winding, which is able to produce both radial force and torque. This approach can be used to design new bearingless motors, as well as to transform conventional motor designs into bearingless motors by simply modifying the winding end connections. The resulting winding has two sets of terminal connections, one for torque and one for suspension. The suspension terminals experience no motional-electromotive force when the rotor is centered, which means that the suspension drive can have a low voltage rating and that rotor vibrations can be passively dampened by simply short-circuiting the suspension terminals. Bearingless motors that use these so-called dual purpose no voltage windings can be designed to have higher torque density and lower losses associated with the magnetic suspension operation than traditional bearingless motors, which utilize separate torque and suspension windings. It will be shown that many popular winding designs, including fractional-slot and concentrated windings, can be realized as dual purpose no-voltage windings. The proposed approach applies to traditional $p\pm 1$ pole-pair bearingless motors, as well as the bearingless consequent-pole and ac homopolar motors. Fractional-slot motor winding theory is used to derive the new winding requirements and a generalized design procedure; example designs are explored through finite element analysis and experimental results from a hardware prototype of a bearingless ac homopolar motor. [ABSTRACT FROM AUTHOR]

This paper develops a magnetic equivalent circuit model suitable to the design and optimization of the synchronous ac homopolar machine. The ac homopolar machine is of particular interest in the application of grid-based flywheel energy storage, where it has the potential to significantly reduce self-discharge associated with magnetic losses. The ac homopolar machine features both axial and radial magnetizing flux paths, which requires finite element analysis to be conducted in 3-D. The computation time associated with 3-D finite element modeling is highly prohibitive in the design process. The magnetic equivalent circuit model developed in this paper is shown to be a viable alternative for calculating several design performance parameters and has a computation time which is orders of magnitude less than that of 3-D finite element analysis. Results obtained from the developed model are shown to be in good agreement with finite element and experimental results for varying levels of saturation. [ABSTRACT FROM AUTHOR]

A winding design approach is proposed for the bearingless ac homopolar and consequent pole motors that utilizes the same coils for both suspension force and torque production. This enables a “pure” bearingless motor design, where the same iron and copper are used for both magnetic bearing operation and torque production, and can result in more optimal machine performance. Separate terminal connections are provided for suspension and torque operation; the suspension terminals experience no motional-emf when the rotor is centered, thereby reducing the required voltage rating of the bearingless drive compared to other “dual purpose” winding designs. It is shown that only certain combinations of stator slots, phases, and poles yield suitable winding designs; most notably, the number of motor pole-pairs must be co-prime with the number of phases. A design procedure is proposed which allows the designer to simply modify end-connections of many conventional armature windings, including both integral- and fractional-slot windings; an example winding design is presented and analyzed using 3-D finite element analysis (FEA); and a hardware prototype has been constructed with experimental results included to validate the proposed design approach. [ABSTRACT FROM PUBLISHER]

A solid-state transformer is a three-phase ac/ac converter with a high-frequency transformer. Due to advanced features like high power density, on demand var support and frequency regulation, solid-state transformer is an enabling technology for the modern power distribution system. It can also find application in high-power-density motor drives. The single-stage solid-state transformer considered in this paper is capable of bidirectional power flow and open loop power factor correction. This topology uses a minimum amount of copper and has relatively few semiconductor switches. One major problem in this converter is the commutation of leakage energy which results in power loss, reduction in switching frequency, loss of output voltage, and additional common-mode voltage switching. This paper presents a source-based commutation strategy along with a novel modulation technique resulting in elimination of additional snubber circuits, minimization of the frequency of leakage inductance commutation, recovery of the leakage energy, and soft switching of the output converter. The topology and its proposed control have been analyzed. Simulation and experimental results confirm the operation. [ABSTRACT FROM AUTHOR]

This paper presents a systematic step-by-step design procedure for the input filter of a current source rectifier (CSR). The design is based on the specifications of allowable ripple in the input voltage of the CSR and high-frequency harmonic components in the grid current. Analytical techniques have been developed to estimate the ripple present in the input current and to model the converter for fundamental or grid frequency. The analysis is done for carrier-based and space-vector modulation of the current source rectifier and the model at grid frequency is used to evaluate the design of the filter for grid power factor, voltage drop across filter, etc. A damping resistance is designed ensuring a minimum power loss. The analysis and design of the input filter have been verified by simulations in MATLAB/Simulink and experimental tests on a laboratory prototype. [ABSTRACT FROM AUTHOR]

A dual-active-bridge-based single-stage ac/dc converter may find a wide range of emerging applications such as interfacing plug-in hybrid vehicles with the ac grid, interconnection of dc grid, etc. This type of converter can be used due to unique features such as 1) high-frequency isolation resulting in a) high power density and b) safety and voltage matching; 2) bidirectional power flow; 3) soft switching leading to higher efficiency. In this paper, a modulation strategy has been proposed that results in 1) open-loop power factor correction; 2) zero current switching in the ac-side converter for all load conditions; 3) linear power relationship for easy control implementation; and 4) Zero voltage switching in the load side converter. The converter with the proposed control has been analyzed. Simulation and experimental results on a 1-KW prototype confirm the advantages. [ABSTRACT FROM AUTHOR]

This paper presents system modeling and control design for fast load voltage regulation using static compensators (STATCOMs). The modeling strategy gives a clear representation of load voltage magnitude and STATCOM reactive current on an instantaneous basis. The particular coordinate transformation employed here also facilitates extraction of linearized system dynamics in conjunction with circuit simulators. It is rigorously shown that the control problem of load voltage regulation using reactive current is nonminimum phase. Linear and nonlinear controllers for the regulation problem are designed and compared via simulation results. Internal dynamics of the STATCOM are modeled using the same strategy. Lyapunov based adaptive controllers are designed for controlling the STATCOM reactive current while maintaining its dc bus voltage. Simulation results of the controlled STATCOM integrated with the load bus voltage controller are presented to show efficacy of the modeling and control design. [ABSTRACT FROM AUTHOR]