Search

This paper deals with the capability of pulse width modulation (PWM) dimming operation added to the high-power factor-integrated buck-flyback converter (IBFC), which was developed in previous works for LED lighting applications. First, the two main dimming techniques will be introduced, namely, analog dimming and PWM dimming. Then, the three main PWM dimming schemes found in the literature, that is, enable dimming, series dimming, and parallel dimming, will be briefly discussed. Afterwards, the IBFC topology will be tested performing both analog and enable dimming. In addition, a new proposal is introduced: the high-frequency series PWM dimming technique, which overcomes all the challenges faced when developing PWM dimming capabilities in low slew-rate constant-current fixed-frequency-controlled converters and offers all the advantages of PWM dimming over analog dimming while maintaining good efficiency. The proposed dimming-technique control loop, as well as the laboratory tests, will be presented, discussed, and compared to analog dimming and PWM dimming, showing satisfactory results in terms of dimming ratio, input current total harmonic distortion (\THDI), and power factor. [ABSTRACT FROM AUTHOR]

This paper presents a single-stage converter to drive high-intensity discharge metal halide lamps. The integration of two discontinuous conduction mode boost converters, in an interleaved way, with a half-bridge voltage inverter and the use of a square-current waveform applied to the lamp, results in an electronic ballast with high power factor and reduced power spectrum spread, avoiding fluctuations inside the discharge tube. To stabilize the lamp current and power, a feedback control loop was designed and implemented. The overall result was a ballast with an efficiency of 90% and a power factor above 0.98. [ABSTRACT FROM AUTHOR]

This paper presents the analysis, design, and experimental performance verification of a serial type line conditioner. Since it processes only a fraction of the load power, the overall converter losses tend to be lower and the efficiency of the conditioner higher. Regarding the dynamic performance, the line inductance, which results in a positive zero in the transfer function of the plant, is taken into consideration when designing a voltage controller with higher bandwidth for faster response. In addition, a virtual resistance is included in the control of the system to damp oscillations often seen for operations at light load and with nonlinear load conditions. Experimental results obtained with a 10 kVA prototype of a serial line conditioner fed from the load side and the proposed feedback control scheme are presented to demonstrate the superior performance of the line conditioner. [ABSTRACT FROM AUTHOR]

In this paper, a modified Z-source inverter (ZSI) with specific modulation techniques is proposed to reduce leakage currents in three-phase transformerless photovoltaic (PV) systems. The new topology only requires an additional fast-recovery diode when compared with the original structure. On the other hand, the pulsewidth modulation technique is entirely modified in order to reduce the leakage currents through the conduction path. Simulation results for the three-phase transformerless PV system operating in two cases, i.e., connected to a grid and connected to a grounded RL load, are presented. Experimental results of leakage currents in three-phase ZSIs connected to a RL load are obtained to validate the theoretical and simulation models. [ABSTRACT FROM AUTHOR]

In the paper, a new five-level (5L) converter is presented. It is called 5L-active-neutral-point-clamped with coupled-inductor (5L-ANPC-CI) and consists of a three-level bidirectional (3L-B) commutation cell connected to two parallel basic commutation cells. The proposed topology can be seen as two cascaded current stages controlled at different frequencies. The high-current stage is specific to the 3L-B cell controlled at low-frequency, while the low-current stage corresponds to the parallel cells with coupled-inductor controlled at high-frequency (HF). Due to this advantage, the new converter appears as a useful solution to increase the output current, while the switched current through the HF power devices is reduced. The operation principle of the new structure is verified by simulations both for single- and for three-phase topologies. Experimental results for single-phase 5L-ANPC-CI converter on a low-voltage test bench are also provided to validate the proper operation of this concept. [ABSTRACT FROM AUTHOR]

This paper presents first an overview of the well-known voltage and current dc-link converter topologies used to implement a three-phase PWM ac–ac converter system. Starting from the voltage source inverter and the current source rectifier, the basics of space vector modulation are summarized. Based on that, the topology of the indirect matrix converter (IMC) and its modulation are gradually developed from a voltage dc-link back-to-back converter by omitting the dc-link capacitor. In the next step, the topology of the conventional (direct) matrix converter (CMC) is introduced, and the relationship between the IMC and the CMCs is discussed in a figurative manner by investigating the switching states. Subsequently, three-phase ac–ac buck-type chopper circuits are considered as a special case of matrix converters (MCs), and a summary of extended MC topologies is provided, including three-level and hybrid MCs. Therewith, a common knowledge basis of the individual converter topologies is established. [ABSTRACT FROM PUBLISHER]

In this paper, a new three-level (3L) converter is presented. It is called 3L Vienna neutral-point-clamped (3L-VNPC) converter and consists of two stacked high-frequency (HF) commutation cells working with a shared power device. The HF cells are connected to a single-phase switched bridge controlled at low frequency. The 3L-VNPC topology is extended to 3L active VNPC (3L-AVNPC) concept, which is generalized for five levels (5L) and N odd voltage levels (N \L). The proposed multilevel converters can be seen as two cascaded voltage stages. The high-voltage stage is specific to the single-phase switched bridge, while the low-voltage (LV) stage corresponds to the stacked HF cells with shared power devices. The new concept AVNPC is a useful and suitable solution for medium-voltage applications, where small modulation index (M) is as crucial as large M. The analyses of the new converters are verified by simulations both for 3L and for 5L topologies, and their features are generalized for N\L. Experimental results for single-phase 3L-AVNPC converter on an LV test bench are also provided to validate the proper operation of the new concept. [ABSTRACT FROM AUTHOR]

This paper proposes a multimode digitally controlled boost converter with PID autotuning and constant frequency/constant off-time hybrid pulsewidth modulation (PWM) control. Constant off-time PWM control is introduced in this converter for avoiding the limit cycle oscillation and maintaining a constant dc gain of the control-output transfer function for a high conversion ratio. Discrete-time modeling of constant off-time PWM is given and verified. An autotuning PID compensator based on frequency-response measurement is adopted to compensate the output stage with variable gain and variable corner frequency. PFM is also included in this controller to improve light load efficiency. A new method of automatic PWM/PFM mode switching without current sensing is proposed. Sufficient loop stability margin and optimal efficiency are obtained by using these techniques for a boost converter operating over wide ranges of output voltages, load currents, and external components. Experimental results are shown for an asynchronous boost converter with 2.5-V input voltage, 3–12 V, and 1–400 mA output. [ABSTRACT FROM AUTHOR]

This paper proposes an isolated three-phase rectifier power-factor correction using two single-phase buck preregulators in continuous conduction mode. The use of the Scott transformer renders a simple and robust rectifier to operate with unity power factor. With only two active switches, the rectifier is able to generate symmetrical currents in the line and a regulated voltage output without any necessary synchronous switches. The proposed control technique with sinusoidal pulse width modulation uses a feedforward of the output inductor current and only one voltage control regulates the output. Complete simulation results under closed-loop operation are given and a 12-kW prototype has been implemented in the laboratory, which demonstrated to operate successfully with excellent performance, and thus can feasibly be implemented in higher power applications. [ABSTRACT FROM AUTHOR]

The novel multilevel circuit topologies are proposed in this paper. They are called multilevel circuit topologies based on switched-capacitor and diode-clamped converters (MCT-BSD). The topology structure and the operation principle, including the working states’ transitions of the diode-clamped part, the voltages balancing mechanism of the dc link capacitors, and the pulse width modulated carrier control strategy are given. The switched-capacitor circuits contribute not only to balancing the voltages of capacitors but also to boosting the output voltage with a certain input dc voltage. The validity of the MCT-BSD is verified by simulations and experiments. The results show that balancing the voltages of capacitors, boosting the output voltages, and operating under the three-phase condition are all realized effectively in the MCT-BSD. The simulations also show the generalization of the MCT-BSD for n-level topologies. [ABSTRACT FROM AUTHOR]

Despite the rapid growth of self-commutated inverter technology, the well-known current source inverter (CSI) has not achieved significant practical application so far. This raised the question regarding the fundamental criteria that could either prevent or promote the use of such inverters, especially considering emerging fields of application such as grid integration of renewable sources. This paper will, thus, focus on a systematic comparison between circuits based on the CSI and voltage source inverter (VSI). For such purpose, dimensionless benchmark factors were derived. The pulse width-modulated CSI with its inherent step-up capability alongside the indirect CSI (ICSI) with only two high-frequency switches features very interesting characteristics in terms of low switching losses and high inductor power density. However, both topologies show constraints with respect to the provision of reactive power. Two experimental setups have been implemented demonstrating the technical feasibility of different CSI solutions as a grid interface. [ABSTRACT FROM AUTHOR]

Unipolar sinusoidal pulsewidth modulation (SPWM) full-bridge inverter brings high-frequency common-mode voltage, which restricts its application in transformerless photovoltaic grid-connected inverters. In order to solve this problem, an optimized full-bridge structure with two additional switches and a capacitor divider is proposed in this paper, which guarantees that a freewheeling path is clamped to half input voltage in the freewheeling period. Sequentially, the high-frequency common-mode voltage has been avoided in the unipolar SPWM full-bridge inverter, and the output current flows through only three switches in the power processing period. In addition, a clamping branch makes the voltage stress of the added switches be equal to half input voltage. The operation and clamping modes are analyzed, and the total losses of power device of several existing topologies and proposed topology are fairly calculated. Finally, the common-mode performance of these topologies is compared by a universal prototype inverter rated at 1 kW. [ABSTRACT FROM AUTHOR]

Multilevel cascaded H-bridge converters have found industrial application in the medium-voltage high-power range. In this paper, a generalized modulation technique for this type of converter based on a multidimensional control region is presented. Using the multidimensional control region, it is shown that all previous modulation techniques are particularized versions of the proposed method. Several possible solutions to develop a specific implementation of the modulation method are addressed in order to show the potential possibilities and the flexibility of the proposed technique. In addition, a feedforward version of this technique is also introduced to determine the switching sequence and the switching times, avoiding low harmonic distortion with unbalanced dc voltages. Experimental results are shown in order to validate the proposed concepts. [ABSTRACT FROM AUTHOR]

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]

In this paper, a three-level three-leg ac–dc–ac converter for single-phase applications is investigated. The operating principles and control strategies for the topology are presented. It is shown that dc-link voltage balancing and its reduction are important objectives in the system design. The proposed pulsewidth modulation (PWM) strategy permits the dc-link capacitor voltage balance and also its reduction. The three-level converter is compared to the two-level converter in terms of rms switch currents, harmonic distortion, losses, and costs. Experimental and simulation results are presented to validate the theoretical studies. [ABSTRACT FROM PUBLISHER]

This paper presents a three-stage 18-level inverter design with a novel control method. The inverter consists of a series-connected main high-voltage, medium-voltage, and low-voltage stages. The high-voltage stage is made of a three-phase, six-switch conventional inverter. The medium- and low-voltage stages are made of three-level inverters constructed by H-bridge units. The proposed control strategy assumes a reference-input voltage vector and aims to operate the inverter in one state per sampling time to produce the nearest vector to that reference. The control concept is based on representing the reference voltage in 60^\circ-spaced two-axis coordinate system. In this system, the inverter vectors’ dimensions are integer multiples of the inverter's dc voltage, and the expression of the inverter's vectors in terms of its switching variables is straightforward. Consequently, the switching signals can be obtained by simple fixed-point calculations. The approach of the proposed control strategy has been presented, the transformed inverter vectors and their relation to the switching variables have been defined, and the implementation process has been described. The test results verify the effectiveness of the proposed strategy in terms of computational efficiency as well as the capability of the inverter to produce very low distorted voltage with low-switching losses. [ABSTRACT FROM PUBLISHER]

The zero-voltage transition (ZVT) pulsewidth- modulation (PWM) converters with resonant auxiliary circuit (RAC) are gathered and analyzed by means of a common topology derived in this paper. Its operation modes are identified and analyzed. Moreover, a similarity transformation is applied to the three-state-variable system in such a way that the whole system dynamics can be represented in a two-dimensional state space. With this representation, the soft-switching conditions are easily defined. In addition to the unified analysis of the ZVT PWM converters with RAC, a theoretical comparative analysis addresses the converter current and voltage stresses, as well as the time-delay intervals taken during the main-switch turn-on process. By means of this analysis, the main characteristics and constraints of the converters are identified. Moreover, a novel design methodology is presented. It is based on the soft-switching-condition abacus obtained from the analytical description of the common ZVT-RAC topology. Besides the soft-switching conditions, a set of performance parameters is also plotted into the soft-switching-condition abacus, making it a simple and useful tool for the proper design of a ZVT-RAC converter. An experimental efficiency comparison is also carried out among three ZVT-RAC boost converters. The experimental results have been obtained from ZVT PWM boost prototypes operating at 1 kW and 100 kHz. [ABSTRACT FROM AUTHOR]