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Under severe fault conditions in the distribution system, not only input voltages but also input impedances must be considered as unbalanced. This paper presents a new control method for input-output harmonic elimination of the pulsewidth-modulation (PWM) boost-type rectifier under conditions of both unbalanced input voltages and unbalanced input impedances. The range of imbalance in both input voltages and input impedances, for which the proposed method is valid, is analyzed in detail. An analytical approach for complete harmonic elimination shows that PWM boost-type rectifier can operate at unity power factor under extremely unbalanced operating conditions resulting in a smooth (constant) power flow from ac to dc side. Based on the analyses in open-loop configuration, a feedforward control method is proposed. Elimination of harmonics at ac and dc side of the converter affects the cost of dc link capacitor and ac side filter. The proposed method is very useful when the PWM boost-type rectifier is subject to extreme imbalance due to severe fault conditions in the power system. In addition, by using the proposed method, the PWM boost-type rectifier can be operated from the single-phase supply in cases where three-phase source is not available. Simulation results show excellent response and stable operation of the PWM boost-type rectifier under the proposed control algorithm. Experimental and simulation results are in excellent agreement. Index Terms--Harmonic elimination, pulsewidth-modulation (PWM) boost-type rectifier, unbalanced input voltages and impedances, unity power factor.

This paper presents a fully integrated CMOS analog front end for a passive 900-MHz radio-frequency identification (RFID) transponder. The power supply in this front end is generated from the received RF electromagnetic energy by using an RF-dc voltage rectifier. In order to improve the compatibility with standard CMOS technology, Schottky diodes in conventional RF-dc rectifiers are replaced by diode-connected MOS transistors with zero threshold. Meanwhile, theoretical analyses for the proposed rectifier are provided and verified by both simulation and measurement results. The design considerations of the pulsewidth-modulation (PWM) demodulator and the backscatter modulator in the front end are also discussed for low-power applications. The proposed front end is implemented in a 0.35-[micro]m 2P4M CMOS technology. The whole chip occupies a die area of 490 x 780/[micro][m.sup.2] and consumes only 2.1 [micro]W in reading mode under a self-generated 1.5-V supply voltage. The measurement results show that the proposed rectifier can properly operate with a -14.7-dBm input RF power at a power conversion efficiency of 13.0%. In the proposed RFID applications, this sensitivity corresponds to 10.88-m communication distance at 4-W equivalent isotropically radiated power from a reader base station. Index Terms--Backscatter modulation, charge pump, low power, low voltage, pulsewidth modulation (PWM), radio-frequency identification (RFID), rectifier, RF--dc, zero-threshold.

This paper presents a new CMOS integrated analog front-end circuit for 13.56-MHz radio-frequency identification tags. The proposed analog front end consists of a novel CMOS rectified voltage multiplier, a voltage regulator, and a new frequency-shift keying (FSK) demodulator. The proposed single-stage rectifier employing only a PMOS/NMOS pass transistor, an inverter, and one capacitor gets minimal active area and enhances the power conversion efficiency. Moreover, a new technique is used in the proposed FSK demodulator, which includes the data recovery circuit, the multiplexer, the shift register, the phase frequency detector, and the charge-pump circuit. The analog front end has been fabricated in a CMOS 0.35-[micro]m 2P4M technology. The demodulator circuit supports a data rate of 10 kb/s to 1 Mb/s. The power consumption is as low as 0.96 mW, and the chip area without pads is only 0.74 mm x 0.43 mm. Experimental results show that the proposed analog front end works well and confirms the theoretical analysis. Index Terms--Frequency-shift keying (FSK) demodulator, radio-frequency identification (RFID), rectifier, regulator, voltage multiplier.

This paper proposes a novel and simple direct power control (DPC) scheme of a three-phase pulsewidth-modulated rectifier without the use of a predefined switching table. The converter switching state selection is based on fuzzy logic rules, using the instantaneous active and reactive power tracking errors as fuzzy logic variables. The basic idea of fuzzy rules synthesis is based on the knowledge of the instantaneous variation of active and reactive power. According to the input fuzzy variables and in a specific moment, the best switching state of the converter is chosen to restrict the instantaneous active and reactive power tracking errors simultaneously, for maintaining the dc-bus voltage close to the reference value and guarantying the unity-power-factor operation. The main advantages of the proposed DPC scheme, compared to the classical one, are that it is not necessary to use hysteresis comparators, and smooth control of active and reactive power is obtained during all sectors. Finally, the developed DPC was tested both in simulations and experimentally, and illustrative results are presented here. Results have proven excellent performance, and verify the validity of the proposed DPC scheme which is much better than the classical DPC. Index Terms--Direct power control (DPC), fuzzy logic control, instantaneous active and reactive power, pulsewidth-modulated (PWM) rectifier, switching table, unity power factor (UPF).

In this letter, a phase feedforward control (PFFC) for a single-phase boost-type switching-mode rectifier is addressed. In the conventional input voltage feedforward loop, the feedforward signal is fixed regardless of the load level. The proposed phase feedforward signal adjusts according to the load level without sensing the load current. The simulated and experimental results also demonstrate the effectiveness of proposed PFFC. Compared to a conventional feedforward signal, relatively small proportional gain can be used in the proposed PFFC without loss of current tracking performance, which would also increase the overall system immunity against noise. Index Terms--AC-DC power conversion.

This paper proposes a novel synchronous rectifier (SR) driving scheme for resonant converters. It is very suitable for high-frequency, high-efficiency, and high-power-density dc--dc resonant converters with SRs. In this paper, an LLC resonant converter with the proposed synchronous rectification is designed and analyzed. With the proposed driving scheme, the SR body diode conduction is reduced to almost zero. The driving scheme eliminates the reverse-recovery problem of SRs. Both current and voltage stresses are greatly decreased, and the conduction loss and switching loss of SRs are also reduced considerably. The experimental results show that the proposed LLC resonant converter with SRs can achieve low stress, high efficiency, and high power density. Index Terms--High frequency, resonant converter, synchronous rectification.

This paper presents a three-phase voltage-source 36-pulse converter that draws almost sinusoidal currents. The converter results from the combination of a series-connected 12-pulse voltage-source rectifier with a passive voltage-injection circuit and a bidirectional switch, referred to as hybrid injection. The voltage-injection circuit uses a single-phase rectifier bridge and a single-phase transformer. Both the voltage-injection circuit and the bidirectional switch operate at six times the supply frequency and have a low rating. In this paper, the converter operation is explained and analyzed. Subsequently, the converter is evaluated experimentally using a 4-kW 400-Hz prototype, where the [THD.sub.I] of the line currents was measured to be below 1.2%. Index Terms--AC-DC power conversion, aircraft power systems, power quality, rectifiers.

Grid-connected unity-power-factor converters based on one-cycle control (OCC) do not require the service of phase-locked loop or any other synchronization circuits for interfacing with the utility. As a result, these schemes are becoming increasingly popular. However, as the power handled by the converter increases, the power factor deteriorates. To understand quantitatively the cause of poor power factor while negotiating high power loads, large signal models for these schemes are developed. Having understood the cause for poor power factor operation, a modified-OCC-based converter is proposed. This scheme has high power factor while supplying high power loads. Detailed simulation studies are carried out to verify the efficacy of the scheme. In order to confirm the viability of the scheme, detailed experimental studies are carried out on a 3-kW laboratory prototype. Index Terms--AC-DC power conversion, one-cycle controller, power-factor correction, single- and three-phase rectifier.

Synchronous rectification (SR) is mandatory to achieve good efficiencies with low output voltages. If a transformer is driven asymmetrically without dead times, the self-driven SR (SDSR) is a very interesting solution. However, if the transformer is driven symmetrically, the synchronous rectifiers are off during the dead times, and as a consequence, the efficiency is lowered. This paper deals with the optimization of an SDSR system that keeps the rectifiers on even during the dead times. The input voltage is tracked, and the information is used to adapt the gate to the source voltage of the synchronous rectifiers and improve the efficiency. The system has been implemented in a prototype, and the results have been compared with the ones obtained in the same prototype without SDSR. Index Terms--Self-driven, synchronous rectification (SR).

A single-stage soft-switching converter is proposed for universal fine voltage applications. A boost type of active-clamp circuit is used to achieve zero-voltage switching operation of the power switches. A simple dc-link voltage feedback scheme is applied to the proposed converter. A resonant voltage-doubler rectifier helps the output diodes to achieve zero-current switching operation. The reverse-recovery losses of the output diodes can be eliminated without any additional components. The dc-link capacitor voltage can be reduced, providing reduced voltage stresses of switching devices. Furthermore, power conversion efficiency can be improved by the soft-switching operation of switching devices. The performance of the proposed converter is evaluated on a 160-W (50 V/3.2 A) experimental prototype. The proposed converter complies with International Electrotechnical Commission (IEC) 1000-3-2 Class-D requirements for the light-emitting diode power supply of large-sized liquid crystal displays, maintaining the dc-link capacitor voltage within 400 V under the universal line voltage (90-265 [V.sub.rms]). Index Terms--Active clamp, single stage, voltage-doubler rectifier, zero-current switching (ZCS), zero-voltage switching (ZVS).

This paper describes the conception and analysis of a unidirectional hybrid three-phase rectifier suitable for medium-and high-power applications. The rectifier is composed of a single-switch diode bridge boost-type rectifier in parallel with a pulsewidth modulation (PWM) three-phase unidirectional boost rectifier. The objective is to obtain a structure capable of providing sinusoidal input currents with low harmonic distortion and dc output voltage regulation. The diode rectifier operates at low frequency and has a higher output power rating. Therefore, the PWM unidirectional rectifier is designed to operate with a small power rating and at a high switching frequency. The total harmonic distortion of the proposed structure varies between 0% and 32%, depending only on the amount of power processed by the PWM three-phase unidirectional rectifier. The rectifier topology conception, principle of operation, control scheme, and simulation and experimental results of a 20-kW laboratory prototype are also presented in this paper. Index Terms--High-power application, hybrid rectifier, power factor improvement, pulsewidth modulation (PWM) unidirectional rectifier.

The challenge in controlling a three-phase pulsewidth modulation (PWM) rectifier under balanced conditions arises from the fact that the state-space averaged model reported in literature has a multi-input--multi-output nonlinear structure and furthermore exhibits a nonminimum phase feature. In this paper, a simple single-input-single-output model is constructed by separating the d-axis and the q-axis dynamics through appropriate nonlinear feedforward decoupling while maintaining nearly unity power factor operation. With the proposed model, the nonminimum phase feature inherent in an ac-to-dc rectifier becomes a simple right-half-plane zero appearing in the small-signal control-to-output transfer function. In addition, the model exhibits a close similarity to a dc-dc boost converter under both large-signal and small-signal operating conditions. This makes it possible to extend the system analysis and control design techniques of dc-dc converters to the three-phase PWM rectifier also. The validity of the proposed model has been verified experimentally in the frequency domain under open-loop operation of the PWM rectifier. The usefulness of the model is further demonstrated through closed-loop operation of the rectifier with both voltage mode and inner-current-loop-based schemes. Index Terms--Pulsewidth modulation (PWM) power converters, voltage mode control.

This paper discusses a transformerless hybrid active filter integrated into the 6.6-kV, 1-MW adjustable-speed motor drive having a three-phase diode rectifier at the front end. The hybrid filter consists of an active filter using a three-level diode-clamped pulsewidth modulator converter rated at 60 kVA, and a 250-kVA passive filter tuned to the seventh harmonic frequency. They are directly connected in series without a transformer. This circuit configuration enables one to use 1.2-kV insulated gate bipolar transistors because the dc voltage of the three-level converter is 1.32 kV (20 % of 6.6 kV). Voltage balancing control characterized by superimposing a sixth harmonic zero-sequence voltage on the active filter voltage reference in each phase is introduced to the three-level converter with triangle carrier modulation. Experimental waveforms obtained from a 400-V, 15-kW downscaled system verify the viability and effectiveness of the proposed hybrid filter, keeping the two dc capacitor voltages well-balanced. Index Terms--Active filters, diode rectifiers, harmonics, hybrid filters, passive filters, three-level converters.

Design and analysis of ultrahigh-frequency (UHF) micropower rectifiers based on a diode-connected dynamic threshold MOSFET (DTMOST) is discussed. An analytical design model for DTMOST rectifiers is derived based on curve-fitted diode equation parameters. Several DTMOST six-stage charge-pump rectifiers were designed and fabricated using a CMOS 0.18-[micro]m process with deep n-well isolation. Measured results verified the design model with average accuracy of 10.85% for an input power level between -4 and 0 dBm. At the same time, three other rectifiers based on various types of transistors were fabricated on the same chip. The measured results are compared with a Schottky diode solution. Index Terms--CMOS analog circuits, integrated circuit modeling, rectifiers, ultrahigh-frequency (UHF) integrated circuits.

Optimum design consideration and implementation of a novel synchronous rectified soft-switched phase-shift full-bridge dc/dc converter with a primary-side energy storage inductor for server adapter application is presented in this paper. By employing a primary-side energy storage inductor, the main switches can achieve a soft-switching condition, and there is little reverse recovery loss in the body diodes of a secondary-side rectifier due to relatively slow downslope of the triangular current. Since the output capacitive filter reduces the voltage stress across the rectifiers, the synchronous rectifier with a lower breakdown voltage rate can be utilized to improve the conversion efficiency dramatically. Thus, this converter can obtain relatively high conversion efficiency for some medium-power applications with low output voltage and high output current, such as the server adapter. Several key optimum design considerations of this converter are also presented in detail in this paper. Finally, a 100-kHz, 300-W (12 V/25 A) laboratory-made prototype for a given server adapter application is built up based on the proposed optimum design procedure of this converter to verify all the theoretical analysis and evaluations. Index Terms--Inductor, phase-shift full bridge (PSFB), soft switched, synchronous rectifier (SR).

A systematic analysis of line-current distortions of the discontinuous-conduction-mode and the continuous-conduction-mode boundary boost power factor correction converter due to valley switching (VS) and switching-frequency limitation, where VS is either maintained or lost after the onset of switching-frequency limitation, is provided. Closed-form expressions for the line current are derived. It is shown that if the switching frequency is limited and VS is not maintained, the line current is more distorted with voltage-mode control than with current-mode control. The effects of line-current distortions are demonstrated with both simulation and experimental results. Index Terms--Boost converter, discontinuous conduction mode (DCM)/continuous conduction mode (CCM) boundary, line-current distortion, power factor correction (PFC), single-phase rectifier, switching-frequency limitation, valley switching (VS).

The implementation of a bridgeless power factor correction (PFC) boost rectifier with low common-mode noise is presented in this paper. The proposed implementation employs a unique multiple-winding, multicore inductor to increase the utilization of the magnetic material. The operation and performance of the circuit were verified on a 750-W, universal-line experimental prototype operating at 110 kHz. Index Terms--Boost converter, bridgeless, magnetic integration, power factor correction (PFC).

In this paper, the first single-loop current sensorless control (SLCSC) in continuous current mode (CCM) for single-phase boost-type switching-mode rectifiers (SMRs) is developed and digitally implemented in a DSP-based system. Compared to the conventional multiloop control with one inner current loop and one outer voltage loop, there is only one voltage loop in the proposed SLCSC, where the voltage loop's output is used to shift the nominal duty ratio pattern generated from the sensed input and output voltages. Because of no current loop, the efforts of sampling and tracking inductor current can be saved. It implies that the proposed SLCSC is simple and very adaptable to the implementation with mixed-signal ICs. First, the effects of shifting nominal duty ratio pattern on the input current waveform are analyzed and modeled by considering the inductor resistance and conduction voltages. The result of analysis shows that the pure sinusoidal current can be inherently generated by the nominal duty ratio pattern where the current amplitude is roughly proportional to the controllable phase of nominal duty ratio pattern. Then, a voltage controller is included to regulate the dc output voltage by tuning this controllable phase. Finally, some simulated and experimental results have been given to demonstrate the performance of the proposed SLCSC. Index Terms--Power factor correction, sensorless control, switching-mode rectifier (SMR).

This paper presents the design and control of a single-stage charge-regulated varying-frequency flyback switch-mode rectifier (SMR). First, the ratings of key constituted circuit components are derived, and accordingly, the power circuit is designed and implemented. Then, a novel charge-regulated, varying-frequency, current-controlled pulsewidth modulation (CCPWM) switching scheme is developed. In the proposed control scheme, the switch turn-on time is fixed, and the turn-off time interval is determined by the comparison result between the low-pass filtered switch current and its current command. The proposed switching scheme possesses the features of without slope compensation, having more dispersedly distributed harmonic spectrum, robust current tracking control, and ease of implementation using off-the-shelf integrated circuits. Finally, the quantitative and robust voltage regulation controls considering nonlinear behavior are made. Good dc output voltage regulation and ac input power quality control performances under wide load range are obtained. Some simulated and measured results are provided to demonstrate the performance of the developed SMR. Index Terms--Charge-regulated, current-controlled pulsewidth modulation (CCPWM), flyback converter, nonlinear behavior, power factor correction (PFC), robust control, switch-mode rectifier (SMR), varying switching frequency.

A high-efficiency high step-up dc-dc converter is proposed for fuel cell power systems. The proposed system consists of an input-current doubler, an output-voltage doubler, and an active-clamp circuit. The input-current doubler and the output-voltage doubler provide a much higher voltage conversion ratio without using a high turns ratio in the transformer and increase the overall efficiency. A series-resonant circuit of the output-voltage doubler removes the reverse-recovery problem of the rectifying diodes. The active-clamp circuit clamps the surge voltage of switches and recycles the energy stored in the leakage inductance of the transformer. The operation principle of the converter is analyzed and verified. A 1 kW prototype is implemented to show the performance of the proposed converter. The prototype achieved a European efficiency of 96% at an input voltage of 30 V. Index Terms--Active-clamp circuit, input-current doubler, voltage-doubler rectifier.

Hybrid activepower filter with injection circuit (IHAPF) shows great promise in reducing harmonics and improving power factor with a relatively low capacity active power filter, but suffers from dc-side voltage instability that inadvertently impacts the compensation performance and safety of the IHAPF. In this paper, two new methods are proposed to overcome this major technical challenge with a hysteretic control and energy release circuit, and a controllable pulsewidth modulation (PWM) rectifier. Modeling, theoretical analysis, and experimental results have verified that both methods can stabilize dc-side voltage within a certain range. A prototype IHAPF system was built incorporating the PWM rectifier dc voltage control scheme, and installed in a 220 kV substation in Southern China. It demonstrated significant improvement in harmonics reduction and power factor. The dc voltage stability issue was also resolved with the new design. Index Terms--Active power filter, dc-side voltage, energy release circuit, harmonic voltage, pulsewidth modulation (PWM) rectifier.

A three-phase Y-rectifier is formed by the star connection of single-phase unity-power-factor rectifier systems and represents a highly interesting concept for the realization of the input stage of high-power telecommunications power supply modules using established single-phase technology. However, for stable operation, control and balancing of the independent dc output voltages of the phase rectifier systems is required. A novel, easy-to-implement dc output voltage control concept is proposed in this paper. Here, the mean value of all three dc output voltages is controlled, and, in addition, always two out of the three dc voltages are compared and balanced. The basic operating principle of the control is described, the theoretical limit for the admissible asymmetric loading of the dc voltages is calculated, and numeric results for a 10-kW system are given. Finally, the theoretical considerations are verified by measurements on a 3 x 1 kW Y-rectifier prototype. Index Terms--AC-DC power conversion, asymmetrical load, output voltage balancing.

An active current injection network for a three-phase rectifier is proposed. The proposed circuit uses three bidirectional switches operating at low frequency and a half-bridge inverter operating at high frequency. It also uses an inductor in order to make the Current modulation. Because only 3.7% of the total power delivered to the load is processed by the injection network, the proposed converter offers high efficiency, and not only a high power factor is obtained but also the total harmonic distortion is reduced. Operation, analysis, simulation, and experimental results are shown in this paper. Index Terms--Current injection, high power factor, rectifiers, three-phase.

Recently, a new multilevel inverter--Hexagram inverter has been reported for medium-voltage (MV) variable-speed drives (VSDs). This paper will propose a Hexagram rectifier as the active front end for the Hexagram-based MV VSD systems. The control of the Hexagram rectifier is based on one-cycle control--an excellent control scheme for switching power converters. With the proposed control scheme, unity power factor at the source side can be achieved, the six modules will equally share the output power, and the voltage stress of the converter will be reduced six times. A 1-MW simulation model and a 1.2-kW experimental prototype have been built to demonstrate the proposed Hexagram rectifier and its control scheme. Index Terms--Multilevel systems, pulsewidth-modulated (PWM) power converters, rectifiers, variable-speed drives (VSDs).

A new double-ended type zero-voltage switching (ZVS) half-bridge zeta (HBZ) converter employing a double-ended rectifier (DER) is proposed. The proposed DER for the HBZ converter provides a bidirectional powering path in the rectifier. As a result, the improved voltage waveform of the rectifier reduces the output filter size and voltage stresses on rectifier components. Moreover, it offers a wide ZVS range. In addition, to minimize the secondary snubber loss, a simple lossless snubber is adopted. The operational principles and characteristics of the proposed converter are to be analyzed and verified experimentally. Index Terms--Double ended rectifier (DER), half-bridge zeta (HBZ) converter, single-ended rectifier (SER), zero-voltage switching (ZVS).

In this paper, an improved current-doubler rectifier with coupled inductors is proposed. The proposed rectifier can extend duty ratio to reduce the peak current through the isolation transformer winding and lower output current ripple as well as voltage stress of the rectifier diodes. In this study, a 500-W prototype with a full-bridge phase-shift converter, the proposed rectifier, with input voltage of 400 V and output voltage of 12 V was built. Theoretical analysis and experimental results have verified that the proposed rectifier is attractive for high step-down voltage and high-power applications. Index Terms--Coupled inductors, current-doubler rectifier, full-bridge phase-shift converter, isolation transformer, tapped inductor.

A single-phase boost rectifier system with conventional low-bandwidth voltage loop exhibits poor dynamic response. A simple method is presented to improve the dynamic response of the rectifier without affecting its steady-state performance. A fast voltage controller is used to improve the dynamic response of the rectifier. The increased low-frequency ripple at the output of the voltage controller is filtered out using a new filter. Design methodology for the voltage loop is presented. The filter is simple enough for analog and digital implementations. Low input current distortion, fast voltage-loop response, and improved dynamic response against line and load disturbances are demonstrated experimentally on a 300-W digitally controlled boost rectifier operating at a switching frequency of 100 kHz. Index Terms--AC-DC power conversion, boost rectifier, current control, digital control, dynamic response.

The necessity of the compactness of the converters in many applications imposes the reduction of the size of their different components when it is possible. In this paper, a control method allowing the use of a small size dc-link capacitor ([C.sub.o]) for the cascade of voltage controlled-rectifier/inverter-motor drive system is proposed. This is achieved by adding the power balance equation in the system's model and the application of an exact I/O feedback linearization technique in a way that the rectifier controller compensates any sudden change in the inverter load, which is here an induction motor. Since the exact I/O feedback linearization technique is sensitive to the uncertainties over system parameters, a robust control strategy based on sliding mode controller (SMC) is proposed. By this approach, the dc-link voltage ([v.sub.dc]) becomes almost insensitive to the load variations. As a result, the level of [v.sub.dc] could be stabilized with a small [C.sub.o]. Without any considerations of the RMS current stress on the [C.sub.o], a calculation method of a minimum dc-link capacitor [C.sub.o](min) based on its storage energy is proposed. All the investigations are shown by computer simulations and the performance of controlled system is verified by experimentation results. Index Terms--Controlled rectifier, induction motor, I/O linearization technique, sliding mode control, small dc-Link capacitor.

The output center-point voltage of a hysteresis current-controlled three-level, unidirectional PWM rectifier is not naturally stable. This paper shows that the balancing of the center-point voltage can be realized by adding an offset to the input current-reference and that this offset results in a change of the relative on-times of the redundant switching states. The space-vector representation of the input rectifier voltage and current is used to help explain the effect of the current-offset injection on the output center-point voltage. The influence of the offset-current injection on the mains currents as well as the control and center-point characteristics are analyzed and verified by measurements. Finally, the design of the center-point controller is presented and its dynamic performance experimentally demonstrated. Index Terms--Center point voltage control, hysteresis current control, three-phase three-level rectifiers.

This paper presents a new control scheme for an active front-end rectifier using model-based predictive control. The control strategy minimizes a cost function, which represents the desired behavior of the converter. Future values of currents and power are predicted using a discrete-time model. The active and reactive powers are directly controlled by selecting the optimal switching state. The main advantages of this method are that there is no need of linear current controllers, coordinates transformations or modulators. The rectifier operates with sinusoidal input currents and unity power factor. Simulation and experimental results are presented to verify the performance of the proposed power control scheme. Index Terms--AC-DC power conversion, power control, predictive control.

In this paper, a new strategy for voltage balancing of distinct dc buses in cascaded H-bridge rectifiers is presented. This method ensures that the dc bus capacitor voltages converge to the reference value, even when the loads attached to them are extracting different amounts of power. The proposed method can be used for an arbitrary number of series H-bridges, different voltage levels, and different power levels in unidirectional or bidirectional rectifiers. To reduce the current harmonics and distortion, the input current is programmed to be sinusoidal and in phase with the input voltage; however, it is possible to adjust the input power factor to control both the active and reactive powers. In the proposed approach, both the low frequency (stepped modulation) and high frequency [pulse-width modulation (PWM)] switching methods are utilized to improve the performance of the rectifier. Using theoretical analysis, the acceptable load power limits for a rectifier with N-H-bridge cells are derived. The validity of the proposed method is verified by simulation and experimental results. Index Terms--Active rectifier, cascaded H-bridge, multilevel converter, power-factor correction, voltage balancing.

This paper presents a systematic design optimization approach for inductors and capacitors in diode front-end rectifiers for voltage source inverters. Analytical relationships between various design variables, operating conditions, and performance and physical constraints are established under nominal, overload, and inrush conditions. A new method to analytically calculate the inrush current is developed considering the nonlinear characteristics of the inductor core materials. A design optimization program based on the established analytical relationships and a genetic algorithm is developed. Examples show that the optimization process can lead to a smaller/lower cost inductor and capacitor design. Experiments are conducted to verify key analytical relationships and the optimized design. Index Terms--Design optimization, genetic algorithm, three-phase rectifier.

This paper deals with the power quality improvement in a conventional electronic load controller (ELC) used for isolated pico-hydropower generation based on an asynchronous generator (AG). The conventional ELC is based on a six-pulse uncontrolled diode bridge rectifier with a chopper and an auxiliary load. It causes harmonic currents injection resulting distortion in the current and terminal voltage of the generator. The proposed ELC employs a 24-pulse rectifier with 14 diodes and a chopper. A polygon wound autotransformer with reduced kilovolts ampere rating for 24-pulse ac-dc converter is designed and developed for harmonic current reduction to meet the power quality requirements as prescribed by IEEE standard-519. The comparative study of two topologies, conventional ELC (six-pulse bridge-rectifier-based ELC) and proposed ELC (24-pulse bridge-rectifier-based ELC) is carried out in MATLAB using SIMULINK and Power System Blockset toolboxes. Experimental validation is carried out for both ELCs for regulating the voltage and frequency of an isolated AG driven by uncontrolled pico-hydroturbine. Index Terms--Electronic load controller (ELC), isolated asynchronous generator (IAG), pico-hydroturbine, 24-pulse bridge rectifier.

In this paper, an exact solution of a circuit model for a three-phase rectifier with constant-voltage load and ac-side reactance that operates in the continuous conduction mode is presented. Obtained results are compared to the results provided applying sinusoidal approximation, published previously. It is shown that the sinnsoidal approximation provides acceptable re. suits at low output voltages, with the accuracy being decreased for the output voltages approaching to the discontinuous conduction mode boundary. Computational complexity of the exact solution is about the same as for the solution obtained applying sinusoidal approximation. Index Terms--Alternator, commutation, converter, generator, load matching, load regulation.