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The focus of this paper is the study of direct alternating-current (ac)–ac converters, beginning by buck, half-bridge, full-bridge, and push–pull converters. From the basic converters, we apply a simple methodology to make the use of switches in commercial configurations possible. Following that, eight voltage restorers supplied either on the line side or on the load side are proposed. A comparative evaluation of these topologies concerning implementation, complexity, and component effort is presented. It is notable that some of the studied topologies are known in the literature and others are new. For one of the presented topologies, the design of a 3-kVA voltage restorer is developed, and experimental results are shown, certifying the correct operation of the drive strategy used. [ABSTRACT FROM AUTHOR]

This paper presents a field-programmable gate array (FPGA)-based real-time digital simulator for power electronic apparatus based on a realistic device-level behavioral model. A three-level 12-pulse voltage source converter (VSC)-fed induction machine drive is implemented on the FPGA. The VSC model is computed at a fixed time step of 12.5 ns, allowing a realistic representation of insulated-gate bipolar transistor (IGBT) nonlinear switching characteristics and power losses. The simulator also models a squirrel-cage induction machine, a direct field-oriented control system, and a pulsewidth modulator to achieve the real-time simulation of the complete drive system. All the models have been implemented using very high speed integrated circuit hardware description language (VHDL). Real-time simulation results have been validated using the measured device-level IGBT characteristics. [ABSTRACT FROM AUTHOR]

An input filter is necessary for a matrix converter (MC) system to improve the input current quality with low harmonic components, as well as to reduce the input voltage distortion supplied to the MC. However, the input filter's characteristics make the input power factor (IPF) obtained at unity only in the presence of high output loads, and the IPF degrades significantly under light-load conditions. In this paper, we propose a new direct space vector modulation (DSVM) method to achieve the required displacement angle between the input voltage and input current of the MC. A new switching strategy is introduced based on the maximum compensated angle. Then, power factor compensation algorithms using the new DSVM method to achieve the maximum IPF are presented, in which compensation algorithm I is based on using the input filter and power supply parameters to estimate the optimal compensated angle. Compensation algorithm II is subsequently proposed using a proportional–integral controller to overcome drawbacks presented in compensation algorithm I. Simulation and experimental results are shown to validate the effectiveness of the proposed compensation algorithms. [ABSTRACT FROM AUTHOR]

In this paper, a robust digital voltage-mode controller (DVMC) is proposed for a fifth-order boost point-of-load converter. Salient features of the proposed topology are compared with a conventional boost converter. Mathematical models are formulated using a discrete-time modeling technique and then employed in the compensator design, which uses the digital direct design approach. The DVMC is designed to ensure load voltage regulation. Robustness theory is applied directly in the digital domain, and then, various robust stability criteria describing sensitivity functions are formulated. The controller is designed to satisfy robustness criteria and then evaluated over a range of disturbances in spite of the fact that it maintains regulation. To confirm this, design simulations have been carried out on a 25-W 12–36-V converter system. Experimental results are provided to validate the concept and also to verify the range over which the designed controller is robust. [ABSTRACT FROM AUTHOR]

There is a strong trend in the photovoltaic inverter technology to use transformerless topologies in order to acquire higher efficiencies combining with very low ground leakage current. In this paper, a new topology, based on the H-bridge with a new ac bypass circuit consisting of a diode rectifier and a switch with clamping to the dc midpoint, is proposed. The topology is simulated and experimentally validated, and a comparison with other existing topologies is performed. High conversion efficiency and low leakage current are demonstrated. [ABSTRACT FROM AUTHOR]

This paper proposes a method to obtain the rotor position of switched reluctance motors (SRMs) by means of voltage measurements. It is shown that the combination of a motor and a power-electronic converter defines a resonant circuit, comprising the motor phase inductances and the parasitic capacitance of converter switches, power cables, and motor phase windings. For salient machines, in general, the associated resonance frequency of the circuit depends on the rotor position. In the position-estimation method, an initial voltage distribution is imposed over the impedances of the resonant circuit after which the circuit is let to oscillate freely. During this phase of free oscillation, the induced voltage over a phase winding exhibits a damped oscillatory behavior, from which position information can be retrieved. An overview is given of the different possibilities to trigger the voltage resonance. It is shown that the proposed position-estimation method has favorable characteristics such as measurement of large-amplitude voltages, robustness against temperature deviations of motor and power semiconductors, very high update rates for the estimated position, and absence of sound and disturbance torque. Experimental results are given for a sensorless commutation scheme of an SRM under small load. [ABSTRACT FROM AUTHOR]

In this paper, the optimum turns ratio of an interphase reactor (IPR) with a double-tap changer is presented with mathematical analysis. The relation between the total harmonic distortion (THD) of the input current and the turns ratio is introduced, and based on the relation, the optimum turns ratio when the THD is minimal is obtained. Via another relation between the ripple coefficients of the output voltage and the turns ratio, the optimum turns ratio is derived when the ripple coefficient is minimal. Meanwhile, using the optimum turns ratio, a new formula to calculate the critical value of IPR is written. Some computer simulation results and experiments are included to support the theoretical analysis of optimum design. [ABSTRACT FROM AUTHOR]

AC voltage and phase regulators based on tap changers implemented with silicon-controlled rectifiers and triacs are widely used due to their robustness. Tap changing is achieved under natural commutation of semiconductors during the zero crossing of current, so that the response time exceeds the half cycle of the mains. High-power transistors and gate turn-off thyristor switches make new and faster tap commutation techniques possible to achieve several tap changes in one half cycle. This paper analyzes and synthesizes a dual-tap chopping stabilizer with a compensating transformer, with a pulsewidth-modulation frequency of about 5 kHz and a new soft-switching technique achieved by two auxiliary small-power branches. Unlike other supercyclic ac soft-switching solutions, the new commutating method allows zero current turn-off, several times in a half cycle, for any sign combination of voltage and current, thus reducing the electrical stress in the switches and the electromagnetic emission. Zero-crossing current detection is not needed. A technical study and an evaluation of the power of the required components are done on the commutation techniques that extend the application field of tap changers to the reduction of the fast perturbations of the mains as flicker, voltage harmonics, voltage oscillations, etc. Experimental results with insulated-gate bipolar transistor switches are obtained in a 1 kVA prototype. [ABSTRACT FROM AUTHOR]

Half-cycle symmetry selective-harmonic-elimination pulsewidth-modulation (SHE-PWM) problems may have a large number of valid solutions, which are beneficial to the optimization design. This paper proposes a novel generalized formulation of half-cycle symmetry SHE-PWM problems for multilevel inverters. The advantages of the proposed formulation include simplicity in format, flexibility in PWMwaveforms, and a broad solution space. A method to obtain initial values for the SHE-PWM equations according to the reference modulation index M and the initial phase angle of output fundamental voltage is proposed and investigated thoroughly. Take a five-level inverter with M = 0.75 as an example; six sets of solutions for two typical initial phase angles of 0°? and 90°? are presented. Simulations and experiments are carried out. It is demonstrated that the experimental results agree well with simulated ones, which proves the validity and practicability of the new method proposed. [ABSTRACT FROM AUTHOR]