High Power Factor Hybrid Rectifier

This paper presents the analysis of a new single-phase hybrid rectifier with high power factor (PF) and low harmonic distortion current. The proposed rectifier structure is composed of an ordinary single-phase diode rectifier with parallel connection of a switched converter. It is outlined that the switched converter is capable of shaping the input line current waveform, assuring high PF and low total harmonic distortion (THD). The power rating of the switched converter is less than 50% of the total output power; assuring reliability in the proposed hybrid rectifier. A pulse width modulation (PWM) control strategy was developed, imposing quasi-sinusoidal line input current waveform and limiting the switched converter power contribution. It was found that the line input current harmonic spectrum is in accordance with the harmonic limits imposed by IEC61000-3-4. The principle of operation, the mathematical analysis, and simulated results are also presented in the paper.http://dx.doi.org/10.4314/njt.v33i4.

Fundamentals of a Multi-Phase, Neutral-Point Clamped Multilevel Inverter

The conventional five-level diode-clamped inverter suffers from the problem of many active power switches when extended to multiphase system. As a consequence, increasing number of gate drive circuits are required; resulting in complex system circuitry. This paper presents the fundamentals of a multiphase, neutral point clamped multilevel inverter configuration capable of reducing the number of active power switches in the conventional topology for multiphase system. The proposed multilevel inverter configuration generates five line-to-line voltage levels for multiphase systems. From the generalized model, an exemplary 5-phase, 5-level line-line NPC inverter supplying an RL load is considered. The operational and modulation principles and the switching patterns are outlined. The THD, as a performance index, of the line voltage output waveform of the proposed 5-phase, 5-level line-line NPC inverter is similar to that of the corresponding well-known conventional 5-phase, NPC diode-clamped inverter. The proposed inverter achieves this with fewer power circuit components and simplicity. The validity of the proposed multilevel inverter is verified through simulations and experimental results

Single-Phase DC-AC Boost Converter

This paper describes a new power conversion circuit topology for single-phase DC-AC boost converter, based on the dc-dc boost converter. It comprises an H-bridge, fed from a single input dc source through a boosting inductor. Change of load current flow is achieved with four current-steering diodes. The proposed boost inverter configuration performs single stage power conversion, which minimizes switching losses and attains higher efficiency as compared to the conventional boost inverter. The steady-state operating principle of the power circuit configuration and control strategy are described. A multi-loop structure controller is used to ensure a high dynamic performance. Computer simulations demonstrate the feasibility of the proposed boost inverter.http://dx.doi.org/10.4314/njt.v33i2.1

Hybrid Modulation Scheme for Cascaded H-Bridge Inverter Cells

This work proposes a switching technique for cascaded H-Bridge (CHB) cells. Single carrier Sinusoidal PWM (SCSPWM) scheme is employed in the generation of the gating signals. A sequential switching and base PWM circulation schemes are presented for this fundamental cascaded multilevel inverter topology. With these proposed concepts, it is now possible to generate equal average switching signal patterns in all the constituting power semiconductor switches. This results in equal switching loss dissipation and equal power sharing in CHB multilevel inverter modules; and therefore technically modularizes the cascaded system. A 4-cell cascaded structure has been used to exemplify the proposed switching technique. Outlines with switching functions are given for the proposed modulation strategy. For a modulation index of 0.9, a THD value of 14.62% has been achieved in the output voltage waveform of the exemplanary 4-cell cascaded configuration. Verification of the performance of the proposed control technique is done through simulations and experiments.http://dx.doi.org/10.4314/njt.v34i1.2

A Three-Phase Boost DC-AC Converter

This paper describes a power conversion circuit conguration for three-phase boost dc-ac converter (inverter) based on the dc-dc boost converters. It naturally generates in a single stage three-phase ac voltages whose peak values are greater than the dc input voltage. This property is absent in the conventional three-phase inverter, as it inherently bucks. The proposed three-phase inverter comprises three dc-dc boost converters whose individual output voltages are modulated sinusoidally. Sliding mode controllers are designed to perform a robust control for the three boost dc-dc converters. Computer simulations and spectral analysis demonstrate the feasibility of the proposed three-phase inverter. The inverter is intended to be used in three-phase electric drives and uninterruptible power supply (UPS) systems

New Topology For Single-Phase, Three-Level, SPWM VSI with LC Filter

Multilevel inverters that provide more than two levels of voltage to achieve less distorted dc-ac conversion have attracted many contributors. This paper presents a new simplied topology for single-phase, sinusoidal pulse width modulated (SPWM) three-level SPWM voltage source inverter (VSI) with LC filter. To keep the power circuit component count to a minimum, the proposed three-level topology simplies the conventional three-level inverter conguration to that of a full-bridge, two-level inverter, with only one added auxiliary power switch. Operational principles, with switching functions are analyzed. The performance characteristics of the proposed inverter are predicted using simulation process in simplorer schematic environment. Assessment of the proposed inverter is done by comparing it with the conventional single-phase, two and three level SPWM inverter under the conditions of identical supply dc voltage, switching frequencyand loading

Experimental Implementation of Single-Phase, Three-Level, Sinusoidal Pulsewidth Modulation (SPWM) Voltage Source Inverter (VSI) with R-L Load

The quest to achieve less-distorted dc-ac power conversion has resulted in the proliferation of many multilevel inverter configurations. This paper presents an experimental report of a simplified topology for single-phase, SPWM, three-level voltage source inverter wit R-L load. To keep the power circuit component count to a minimum, the three-level topology simplifies the conventional three-level inverter configuration to that of a full-bridge, two-level inverter, with only one added clamping power switch. Operational principles, with experimental switching functions are given. Laboratory prototypes of the simplified three-level inverter and the conventional full-bridge, two-level inverter were built. Assessment of the 3-level inverter is done by comparing its experimental voltage waveforms and the corresponding FFT analyses with those of the conventional full-bridge, 2-level inverter under the conditions of identical supply dc voltage, switching frequency and loading

Analysis of Harmonic Injection to the Modulation of Multi-Level Diode Clamped Converter in a Normal and Over Modulation Mode

This paper explores the analysis of third and ninth harmonic injection to the modulation of a multilevel diode clamped converter (DCC) at a varying modulation index. The spectral distributions of the various multi-level waveforms obtained under normal modulation index of 0.8 and over modulation index of 1.15 were presented in this work. The contribution of this paper is rooted in the introduction of ninth harmonic component to higher-levels of diode clamped converters with reference to the existing third order harmonic injected modulation with detailed Simulink models of 3rd, 5th and 9th voltage levels. The analysis and results obtained from this work shows appreciable reduction in the magnitudes of harmonic distortion values thus ensuring optimum and efficient devices performance.Keywords: harmonic injected modulation, spectral analysis, pulse width modulation, diode clamped converter, modulatio

Utility Interfaced Pulse-Width Modulation of Solar Fed Voltage Source Inverter Using Fixed-Band Hysteresis Current Controller Method

This paper describes a utility interfaced pulse-width modulation of solar-fed voltage source single phase full bridge inverter. The proposed system has to do with the conversion of solar energy into electrical energy; boosting the dc power; inversion of the dc to ac and then synchronization of the inverter output with the utility, and consequently, reduction of the total harmonics distortions in the supply. The proposed system will ensure steady state availability and suffciency of power supply to its areas of applications. To achieve this, current sensor, xed-band hysteresis current controller and lter were employed to ensure proper injection of power to utility side and vice versa. The computer simulations and spectral analysis of the system obtained from Simplorer Software were presented. This proposed system is designed for use in residential houses and industries

Space Vector Pulse Width Modulation of a Multi-Level Diode Clamped Converter with Experimental Verification

This paper presents the analysis of a multi-level diode clamped converter (DCC) which is implemented using space-vector pulse width modulation (SVPWM) technique, widely considered as the most efficient and easily applied modulation technique in most industrial drives and control applications. It also focuses on the step by step development of MATLAB /SIMULINK modeling of the space vector pulse-width modulation and the spectral analysis of the resultant waveforms obtained from the modulation results were carried out.  Results of the simulations obtained from DCC using SVPWM were equally presented and analyzed. This paper used generic on-time application method to realize the application time for the zero vector and two adjacent active vectors in determining the switching process of the multilevel DCC, quite unlike the look-up table which is common in this area. To verify the analysis, a small scale experimental work, was carried out. All experimental works were done in the laboratory and the results confirm the simulation results obtained from the SIMPLORER Student version 6 Software used in simulating the un-modulated three-level diode clamped converter