Showing papers in "Iet Power Electronics in 2008"
TL;DR: In this paper, the operation, design and control of an isolated bidirectional DC-DC converter for hybrid electric vehicle energy management applications are discussed, and different operation modes and boundary conditions are distinguished by phase shift angle and load conditions.
Abstract: The operation, design and control of an isolated bidirectional DC - DC converter for hybrid electric vehicle energy management applications are discussed. Different operation modes and boundary conditions are distinguished by phase-shift angle and load conditions. The absolute and relative output voltage ripple was derived. The dead-band effect and safe operational area are further investigated. The relations between output power and leakage inductance and switching frequency are also presented. The proposed converter was simulated and a prototype was built and tested. Experiments on the converter's steady state and transient operations validated the design and simulation.
349 citations
TL;DR: In this article, a controller design for three-phase voltage-source converters, by which a passive input admittance is ideally obtained, is considered, and two design alternatives, with and without voltage feedforward, respectively, are shown to give similar performance.
Abstract: Current controller design for three-phase voltage-source converters, by which a passive input admittance is ideally obtained, is considered. Two design alternatives, with and without voltage feedforward, respectively, are shown to give similar performance. It is demonstrated how additional parts can be added to the controller while preserving the passivity property. This is applied particularly to resonant parts. The design method is finally applied to converters with an LCL input filter, where it is shown in many cases to compare favourably with a scheme where an inner loop is added for improved damping of the LCL resonance.
191 citations
TL;DR: In this paper, a set of positive output DC-DC converters applying series SEPIC implementing voltage-lift techniques is introduced, and a detailed theoretical analysis for continuous and discontinuous conduction modes is given.
Abstract: The voltage-lift technique is an effective method that could be applied in electronic circuit design. A set of positive output DC-DC converters applying series SEPIC implementing voltage-lift techniques is introduced. Compared with the prototype of the SEPIC converter, these converters can perform positive to positive DC-DC voltage increasing conversion with higher voltage transfer gains. They are different from other existing DC-DC step-up converters and possess obvious advantages, mainly including fewer switches, clear conversion processes and a high output voltage with small ripples. Since the proposed converters avoid using transformers and cascade connection, relative simple structures are beneficial to potential practical applications in future. A detailed theoretical analysis for continuous and discontinuous conduction modes is given. Both simulation and experimental results are provided to verify the main characteristics.
124 citations
TL;DR: In this article, a new approach of direct power control (DPC) of a voltage source inverter for achieving symmetrical grid currents under unbalanced grid voltage conditions is presented, where a phase locked loop is necessary to obtain positive sequence voltage angle.
Abstract: A new approach of direct power control (DPC) of a voltage source inverter for achieving symmetrical grid currents under unbalanced grid voltage conditions is presented. In these situations, negative sequence components appear on the grid voltage vector, leading to distorted currents if the power is maintained constant. Nevertheless, sinusoidal balanced grid currents can be achieved through control. Several current controllers have already been modified to overcome voltage imbalance with good results. Here, sinusoidal grid currents are obtained by directly controlling power, which becomes a novel approach and keeps DPC philosophy. A phase locked loop is necessary to obtain positive sequence voltage angle. A very simple positive and negative sequence calculator is also used so that power references can be modified in order to obtain balanced grid currents. Simulated and experimental results are presented to confirm the validity of the method.
121 citations
TL;DR: Nonlinear and linear models, using averaged model techniques, are given for a class of positive output cascade buck and boost converters and are shown that the proposed linear models are globally asymptotically stable for any number of stages.
Abstract: In recent years, the development of new technologies is requiring wider conversion ratios. A possible solution to this problem is to use n -conventional converters connected in cascade; however, a complex control circuitry is required. An alternative solution is to use an n -stage cascade converter with a single active switch. Nonlinear and linear models, using averaged model techniques, are given for a class of positive output cascade buck and boost converters. These converters use a single active switch. It is shown that the proposed linear models are globally asymptotically stable for any number of stages. The continuous-mode conditions are given with the corresponding design values for the voltage ripples of the capacitors and current ripples of the inductors. Therefore the need of having models for a class of DC-DC cascade converters is satisfied.
98 citations
TL;DR: In this paper, a theoretical study of the analysis and design of the repetitive controller for eliminating harmonics in pulse-width modulation voltage-source inverter systems is presented, where a method of analysing the repetitive control (RC) system from the frequency-response viewpoint is introduced.
Abstract: A theoretical study of the analysis and design of the repetitive controller for eliminating harmonics in pulse-width modulation voltage-source inverter systems is presented. A method of analysing the repetitive control (RC) system from the frequency-response viewpoint is introduced. Based on this method, a systematic way of optimising the design of the system is proposed. Specifically, the closed-loop repetitive controller is modified by incorporating with a zero-magnitude-and-phase compensator and a lead-lag compensator, to improve the stability and tracking accuracy of the inverter system. It is shown both theoretically and through experiments that the harmonics in the inverter's output voltage at different load conditions can be effectively eliminated with the inclusion of the repetitive controller. The advantage and validity of applying the RC in inverters are therefore demonstrated.
85 citations
TL;DR: In this article, a bridgeless dual-boost rectifier with reduced diode reverse-recovery problems is proposed for power-factor correction (PFC), where the body diodes of the power switches are utilised as output diiodes.
Abstract: A bridgeless dual-boost rectifier with reduced diode reverse-recovery problems is proposed for power-factor correction (PFC). In the proposed rectifier, conduction losses are lowered by essentially eliminating the full-bridge diode rectifier. The body diodes of the power switches are utilised as output diodes. A coupled inductor is designed to reduce the reverse-recovery problems of the body diodes. Zero-current switching is realised when the body diodes are turned off. In addition, for the use of this topology in a practical design, a control strategy is suggested by employing the linear peak current mode (LPCM) control. The LPCM control is implemented on leading-edge modulation, providing an efficient control scheme to obtain a high power-factor. The proposed rectifier is investigated theoretically and its design considerations are provided in detail. Finally, the experimental results based on a 500 W prototype are discussed to evaluate the performance of the proposed rectifier for a PFC circuit.
77 citations
TL;DR: The zero voltage switching (ZVS) boost converter with high-voltage gain is presented to overcome the limit of conventionalboost converter with narrow turn-off period and experiments conducted are presented to verify the effectiveness of the adopted converter.
Abstract: The zero voltage switching (ZVS) boost converter with high-voltage gain is presented to overcome the limit of conventional boost converter with narrow turn-off period. Compared with the conventional boost converter, the adopted converter has wide turn-off period so that the higher output voltage can be achieved. The boost type of active clamp is used to limit the voltage stress of power switch. The resonance based on the output capacitance of power switch and resonant inductance will make the power switches to turn on at ZVS. The circuit configuration, principle operation, system analysis and design consideration of the adopted converter are presented. Finally, experiments conducted on a laboratory prototype rated at 240 W are presented to verify the effectiveness of the adopted converter.
72 citations
TL;DR: In this paper, a three-phase four-wire hybrid power filter using a bridge structure without split capacitors has been proposed, which allows the neutral line of the utility directly connecting to the negative or positive terminal of the DC capacitor located in the DC side of the power converter.
Abstract: A novel power converter topology for three-phase four-wire hybrid power filter is proposed. It is configured by a three-arm bridge structure without split capacitors. The salient feature of the three-phase four-wire hybrid power filter using the proposed power converter is that it permits the neutral line of the utility directly connecting to the negative or positive terminal of the DC capacitor located in the DC side of the power converter. Consequently, the power converter uses less number of power electronic switches to reduce the manufacturing cost. A three-phase four-wire hybrid power filter prototype is developed and tested to demonstrate the performance of the three-phase four-wire hybrid power filter using the proposed power converter. Experimental results show that the proposed three-phase four-wire hybrid power filter using the proposed power converter has the expected performance.
70 citations
TL;DR: A new auxiliary circuit is introduced for buck, buck-boost, forward and flyback converters that provides zero current, zero voltage switching condition for the main switch while providing zero current switching conditions for the auxiliary switch and diodes.
Abstract: A new auxiliary circuit is introduced for buck, buck-boost, forward and flyback converters. This auxiliary circuit provides zero current, zero voltage switching condition for the main switch while providing zero current switching condition for the auxiliary switch and diodes. In this converter family, there is no additional voltage and current stress on the main switch. The proposed auxiliary circuit is applied to a buck converter and the resulting ZCZVT PWM buck converter is analysed and its operating modes are presented. A simple design method for auxiliary circuit is discussed. The experimental results of a 175 W ZCZVT buck converter operating at 100 KHz are presented. Other converter topologies with the proposed auxiliary circuit are also introduced.
66 citations
TL;DR: In this article, an advanced position controller design for an interior permanent magnet synchronous motor control system is proposed, based on the linearised system model, an H infin controller is designed to achieve robust performance of the position control system.
Abstract: A novel, advanced position controller design for an interior permanent magnet synchronous motor control system is proposed. The input-output linearisation technique is used to transfer the system model into a linearised system model. Then, based on the linearised system model, an H infin controller is designed to achieve robust performance of the position control system. To improve the system performance, a load estimator is used to compensate the external load and the influence of the parameter variations as well. In addition, a maximum torque/ampere control is applied to increase the output torque of the motor. A digital signal processor, TMS 320LF2407, is used to execute the speed-loop and position-loop control algorithms. As a result, the hardware circuit is quite simple. Several experimental results show that the proposed system has fast transient responses, good load disturbance rejection responses and good tracking responses.
TL;DR: In this article, a constant-frequency reduced-state sliding mode current controller for Cuk converters requiring a fast dynamical response over a wide range of operating conditions is proposed.
Abstract: A constant-frequency reduced-state sliding mode current controller for Cuk converters requiring a fast dynamical response over a wide range of operating conditions is proposed. The various issues concerning the theoretical derivation and implementation of the proposed controller are discussed. Preliminary verification and evaluation of these controllers are performed through simulation and experiment. It is illustrated that commendable control performances can be achieved with the proposed controller.
TL;DR: In this paper, a comparison of two pulsewidth-modulation (PWM) control techniques applied to a single-phase shunt active power filter (SPSAPF) using theoretical and experimental validation methods is presented.
Abstract: This paper presents a comparison of two pulse-width-modulation (PWM) control techniques applied to a single-phase shunt active power filter (SPSAPF) using theoretical and experimental validation methods. A direct current control strategy is implemented using a standard PWM (S-PWM) and a modified PWM (M-PWM) in order to compensate the current harmonics and the reactive power generated by a nonlinear load. The M-PWM technique is based on two comparisons of a triangular high-frequency carrier signal with a low-frequency modulating signal (which represents the load current harmonics) and its opposite. The M-PWM shifts the first significant harmonic rays towards twice the switching frequency and eliminates the spectral rays that are centred around the odd multiples of the switching frequency. The simulation and experimental results are presented with a view to determine which of the M-PWM or the S-PWM performs better in terms of source current total harmonic distortion and reactive power compensation.
TL;DR: In this article, the authors proposed a bidirectional DC-DC converter for a fuel cell electric vehicle driving system based on a zero voltage switching (ZVS) half-bridge converter with center-tapped rectifier at the secondary side of the transformer.
Abstract: System analysis of a bidirectional DC-DC converter for a fuel cell electric vehicle driving system is presented. The proposed converter is based on a zero voltage switching (ZVS) half-bridge converter with centre-tapped rectifier at the secondary side of the transformer. The asymmetrical pulse-width modulation is used in the converter to achieve ZVS feature of power switches and to regulate the output voltage at the desired value. The proposed converter has the advantages of high efficiency, low circuit components and simple circuit configuration. The operating principle and the system analysis are described and discussed in detail. Finally, the experimental results for the proposed converter are provided to verify the theoretical analysis.
TL;DR: In this article, a new family of zero-voltage transition (ZVT) PWM converters is introduced, and a new flyback converter is proposed to achieve zero voltage switching conditions for main switch and zero current switching condition for auxiliary switch.
Abstract: A new family of zero-voltage transition (ZVT) PWM converters is introduced. In this family of converters, zero-voltage switching condition is achieved for main switch and zero-current switching condition is attained for auxiliary switch. A ZVT flyback converter from the proposed family of converters is analysed and various operating intervals are presented. The introduced ZVT flyback converter characteristics are compared with other ZVT converters. A laboratory prototype of this converter is realised and experimental results are shown.
TL;DR: Different switching state sequences of a three-phase three-switch buck-type unity power factor PWM rectifier with integrated DC/DC boost output stage with pulse frequencies of different modulation methods are presented to achieve the same switching losses.
Abstract: Different switching state sequences of a three-phase three-switch buck-type unity power factor PWM rectifier with integrated DC/DC boost output stage are presented. They are analysed concerning switching losses and ripple components at the input (filter capacitor voltage ripple) and at the output (DC link current inductor ripple). For a fair comparison, pulse frequencies of different modulation methods are adopted in order to achieve the same switching losses. The rms value and envelopes and time behaviour of the ripple components are analysed analytically and by simulation, and one advantageous modulation method is determined. The paper provides the basis for a subsequent experimental verification, which is performed in part II.
TL;DR: An improved terminal sliding mode control (TSMC) is proposed by the use of a mathematically simple and computationally fast grey prediction (GP) methodology, which is then fine-tuned by using fuzzy control methodology for PWM DC-AC converters as mentioned in this paper.
Abstract: Classical terminal sliding mode control (TSMC) has finite system state convergence time and is insensitive to disturbances and uncertainties within expected limits. However, TSMC may chatter when uncertainty values are overestimated or may exhibit a steady-state error when uncertainty values are underestimated. An improved TSMC is proposed by the use of a mathematically simple and computationally fast grey prediction (GP) methodology, which is then fine-tuned by the use of fuzzy control methodology for PWM DC–AC converters. First, GP methodology is employed to deal with classical TSMC chattering and steady-state error problems. Fuzzy control is then used to tune the GP forecasting value for improved rise time and overshoot characteristics. The system is evaluated by simulation and also by real experiment. Both evaluation methods confirm that the proposed controller achieves low total harmonic distortion under non-linear loading conditions and fast dynamic response under transient loading conditions. Because the proposed grey-fuzzy TSMC methodology is simpler to implement than prior methods and offers more efficient computation, it will be of interest to designers of related control systems.
TL;DR: In this article, a three-level inverter scheme with common-mode voltage elimination and reduced power device count for dual inverter-fed open-end winding induction motor is proposed, which is fed by two threelevel inverters, formed by cascading two two level inverters from both sides.
Abstract: A three-level inverter scheme with common-mode voltage elimination and reduced power device count for dual inverter-fed open-end winding induction motor is proposed. The open-end winding induction motor is fed by two three-level inverters, formed by cascading two two-level inverters, from both sides. These two three-level inverters share the top inverter, thereby reducing the power device count. The switching states with zero common-mode voltage variation are selected for pulse-width modulated switching so that there is no alternating common- mode voltage in the pole voltages and phase voltages. Only two DC links, with half the ratings of a conventional three-level neutral point clamped inverter, are used for the proposed scheme.
TL;DR: In this article, a low-cost and robust active unit for replacing the passive balancing resistors is introduced, and the operating principle of the circuit, analysis the fundamental relationships relevant for the balancing characteristic and gives guidelines concerning component selection.
Abstract: DC voltage links of three-phase power converters are frequently equipped with a series connection of two electrolytic capacitors because of high voltage level. For such a configuration, usually resistors have to be arranged in parallel to each capacitor in order to balance the partial voltages. These balancing resistors, however, have to be dimensioned regarding the worst-case scenario of capacitor's leakage currents; such leakage can lead to high permanent dissipative losses that also appear in case of low actual leakage currents. To avoid these losses to a very large extent, a novel low-cost and robust active unit for replacing the passive balancing resistors is introduced. The paper describes the operating principle of the circuit, analyses the fundamental relationships relevant for the balancing characteristic and gives guidelines concerning component selection. Furthermore, simulation results as well as measurements taken from a laboratory prototype are presented.
TL;DR: In this paper, a novel high efficiency asymmetrical half-bridge converter using a self-driven synchronous rectifier is presented, which improves the system efficiency using the characteristics of the asymmetric half-branch converter and the self-drive rectifier.
Abstract: A novel high efficiency asymmetrical half-bridge converter using a self-driven synchronous rectifier is presented. The proposed converter improves the system efficiency using the characteristics of the asymmetrical half-bridge converter and the self-driven synchronous rectifier. The synchronous rectifier applied to the proposed converter is the new topological synchronous rectifier, which is a slightly modified type of the conventional synchronous rectifier used in the conventional asymmetrical half-bridge converter. The type of the new topological synchronous rectifier slightly changes the transformer structure and the synchronous switch connection in the asymmetrical half-bridge converter with a conventional self-driven synchronous rectifier. The operational principle of the proposed converter is explained in detail. Since the proposed converter utilises the transformer leakage inductor as its resonant inductor, its structure is simplified. A design example for a 90 W (12 V/7.5 A) prototype is discussed in detail. Experimental results are shown for the designed prototype converter under universal AC input voltage (180-265 V). It is shown that the efficiency of the proposed converter can be significantly improved.
TL;DR: Experimental results of a comparative evaluation of two different modulation methods for a three-phase buck+boost PWM rectifier identify one modulation method to be clearly superior regarding the input filter capacitor voltage ripple and the DC link inductor ripple values.
Abstract: This paper presents experimental results of a comparative evaluation of two different modulation methods for a three-phase buck+boost PWM rectifier. The measurements, which are performed on a 5 kW digital signal processor controlled prototype, verify the analytical calculations and simulations in part I and identify one modulation method to be clearly superior regarding the input filter capacitor voltage ripple and the DC link inductor ripple values. Finally, also the EMC noise emission levels are comparatively analysed for the modulation methods.
TL;DR: In this paper, a comparative study of hysteretic controllers for single-phase voltage regulators used in low-voltage applications is presented, which demonstrates that the operation of the current-mode controller is extremely robust with respect to power-component tolerance and the VM controller is a simple, low-cost control solution.
Abstract: A comparative study of hysteretic controllers for single-phase voltage regulators used in low-voltage applications is presented. The voltage-mode (VM) and current-mode (CM) control schemes considered here are designed with identical specifications. The regulator performance is evaluated in aspects such as load transient response, switching frequency design and component tolerance effects. Other aspects such as complexity and cost are also considered. Experimental results are reported in order to validate the theoretical predictions. Essentially the study demonstrates that: (1) both VM and CM controllers exhibit high performance for nominal power components, (2) the operation of the CM controller is extremely robust with respect to power-component tolerance and (3) the VM controller is a simple, low-cost control solution.
TL;DR: In this paper, a two-quadrant converter for adjustable speed drive with regenerative braking, wind energy conversion systems and small hydro interconnections with induction generators is presented. But the converter is characterised by smaller power losses and reduced electromagnetic interference problems.
Abstract: A new topology for a two-quadrant converter is presented. In the AC/DC transfer mode, the converter works as a rectifier with near sinusoidal input currents, whereas in the DC/AC transfer mode, it works as a square-wave pulse switching inverter. The converter is characterised by smaller power losses and reduced electromagnetic interference problems. Possible applications in adjustable speed drive with regenerative braking, wind energy conversion systems and small hydro interconnections with induction generators are also discussed.
TL;DR: A novel voltage source full-bridge DC-DC converter with phase shift modulation using a high-frequency cycloconverter with zero-voltage and zero-current switching operations and the steady-state operation principles of the converter are analysed and discussed.
Abstract: A novel voltage source full-bridge DC-DC converter with phase shift modulation using a high-frequency cycloconverter is proposed. Both zero-voltage and zero-current switching (ZVZCS) commutation for full-bridge active power switches and zero-voltage switching operation for cycloconverter bi-directional switches are obtained. Soft switching operation is provided in a wide range of voltage regulation without utilising an auxiliary inductor in the primary side of an isolating transformer. To implement this DC-DC converter as a multi-function DC–AC inverter, a reference signal is traced by the control system to adjust the output voltage according to the variations of the reference signal. Therefore desired output waveforms are provided by selected reference signals. Hence the proposed circuit operates as a multi-function converter. Based on the simulation and experimental results, the steady-state operation principles of the converter are analysed and discussed. Experimental results from a 24 V-DC input and 20 kHz fixed switching frequency laboratory prototype is presented to introduce both the switching operation and the multi-function performance of the converter.
TL;DR: In this article, a buck zero-current-switching (ZCS) pulsewidth-modulated converter was used for battery chargers to manage resonant converters flexibly.
Abstract: A resonant converter has low switching losses, a small circuit volume and high power density and is also light. High-frequency switching converters have replaced conventional hard-switching converters. This study utilises a buck zero-current-switching (ZCS) pulse-width-modulated converter for battery chargers to manage resonant converters flexibly. An auxiliary switch is inserted into the resonant loop to control the resonant time. The operating modes of the circuit and the equivalent circuits are identified by analysing the operating principles of the charger circuit, based on the turn-on conditions of the active switches. The equations that are used to determine the circuit parameters are obtained from the equivalent circuits. The developed charger provides the advantages of hard-switching and resonant converters with constant-frequency control, reduced resonant time and the operability of all switching components in the charger under a ZCS condition, markedly reducing switching losses. Experimental results reveal the theoretical effectiveness of the developed novel battery charger circuit. The developed battery charger has a practical mean charging efficiency of over 90% and is highly suited to high-frequency operations with high charging efficiency.
TL;DR: In this article, a new multilevel space vector modulation (SVM) technique, termed mapped hybrid SVM, is presented, which enables the use of three-level SVM with multi-level inverters without introducing any carrier level modulation or phase shifts.
Abstract: A new multilevel space vector modulation (SVM) technique, termed mapped hybrid SVM, is presented. The SVM technique enables the use of three-level SVM with multilevel inverters without introducing any carrier level modulation or phase shifts. The proposed technique is theoretically analysed for five-, seven- and nine-level inverters and then generalised for the m-level inverter, validated by simulation using Matlab/Simulink and confirmed practically for a five-level, shunt, active power filter.
TL;DR: In this article, a small-signal model of the superboost converter is presented, where peak-current-mode control is applied to reduce its resonant nature as well as to facilitate the overall system design.
Abstract: The fourth-order converter known as superboost converter is used in the space power systems because of the continuous input and output currents it provides. Peak-current-mode control is applied to reduce its resonant nature as well as to facilitate the overall system design. The small-signal models of such a converter do not exist in the public domain literature and its dynamical features are not known. The modelling based on consistent and easily applicable technique is introduced. The dynamic characterisation shows that the converter may incorporate both resonant right-half-plane zeros and poles, which effectively limits its usage in terms of usable duty ratio and also makes the control design challenging. The theoretical analysis indicates that the usable duty-ratio range can be extended by selecting the values of the inductors properly. Because of the nature of the inductor-current feedback, the open-loop converter has resonant output features but the input is resonant free. The application of the output-voltage feedback recovers, however, the resonant nature at the input boosting the converter sensitivity to input-filter instability. Experimental evidence is provided to validate the theoretical predictions.
TL;DR: In this paper, the buck, boost, buck-boost, and Cuk power converter is presented for fuel cell applications, where all the switching devices are under zero-current switching during turn-on and zero-voltage switching during turning off.
Abstract: A family of soft-switching power converter is presented for fuel cell applications. The salient points are that all the switching devices are under zero-current switching during turn-on and zero-voltage switching during turn-off. The family of the circuit presented includes the buck, boost, buck-boost and Cuk converter. The active switches in the converter undergo zero-capacitive turn-on losses unlike switches in other soft-switched topologies discussed in the literature. The switches do not experience any over voltage/over current stress proportional to load as in resonant converters. This soft-switching technique can also be applied to other classical switched mode power converters. A detailed mathematical analysis of the converter under steady state is carried out, and experimental results obtained from a prototype are presented. The converter was also connected to a model toy car driven by fuel cells for the demonstration of the application.
TL;DR: In this article, a technique to calculate the current waveform for both close-up and remote short-circuit faults on DC supplied railways and subways is presented, which can be easily executed with the help of a calculator or a spreadsheet program.
Abstract: A technique to calculate the current waveform for both close-up and remote short-circuit faults on DC supplied railways and subways is presented. Exact DC short-circuit current calculation is best performed by sophisticated computer transient simulations. However, an accurate simplified calculation method based on second-order approximation which can be easily executed with the help of a calculator or a spreadsheet program is proposed.
TL;DR: In this paper, a single-switch structure of single-and three-phase transformerless controlled rectifiers is proposed and analyzed, which consists of a common rectifier, an input inductor filter, a high-frequency operated switch and a diode-capacitor ladder network.
Abstract: New single-switch structures of single- and three-phase transformerless controlled rectifiers are proposed and analysed. These structures consist of a common rectifier, an input inductor filter, a high-frequency operated switch and a diode-capacitor ladder network. The latter, in its known application as a multiplier, is used for increasing the input voltage. A new scheme of a diode-capacitor network, which can be used as a divider to reduce the input voltage, is also proposed. The detailed analysis of the steady-state mode is performed and simple formulas for the calculation of step-up and step-down rates of the voltage are derived. Transient analysis of the proposed circuits, by solving the recurrent equations and by using the z-transform, is also performed. Since the proposed schemes do not consist of any transformers and/or any inverters, their operation is very efficient; no high harmonics and/or a DC component are produced, and so the input current and voltage waveform are close to the sinusoid. The power factor of such structures reaches unity and their weight is low, compared with those having a transformer. A laboratory model of one of the proposed structures has been built and tested. The experimental results confirm the convertergraves efficiency and the correctness of the theoretical analysis.