P.D. Ziogas

Programmed PWM techniques to eliminate harmonics - A critical evaluation

The authors establish the superiority of programmed PWM (pulsewidth modulation) techniques over the conventional carrier-modulated PWMs and provide a critical evaluation of the programmed PWM schemes applied to single and three-phase inverters, thereby providing the framework and guidelines for the selection of the appropriate technique for each application area. Evaluation criteria include harmonic loss factor and total harmonic distortion factors defined at the input and output of the inverter terminals. A simple low-cost solution for obtaining the required PWM switching points is proposed. Selected results are verified experimentally.<<ETX>>

An active power factor correction technique for three-phase diode rectifiers

A novel active power factor correction method for power supplies with three-phase front-end diode rectifiers is proposed and analyzed. The implementation of this method requires the use of an additional single switch boost chopper. The combined front-end converter draws sinusoidal AC currents from the AC source with nearly unity input power factor while operating at a fixed switching frequency. It is shown that when the active input power factor correction stage is also used to regulate the converter DC bus voltage, the converter performance can improve substantially in comparison with the conventional three-phase AC-to-DC converters. These improvements include component count reduction, simplified input synchronization logic requirements, and smaller filter refractive components. Theoretical results are verified experimentally. The proposed method has the disadvantage of substantially increasing the current stresses of the switching devices and the high-frequency ripple content of the prefiltered AC input currents. >

State-of-the-art carrier PWM techniques: a critical evaluation

With the introduction and wide acceptance of gate-turnoff power drives, e.g., bipolars, power FETs, GTOs, the switching behaviour of converters has reached the point where further improvements in firing and switching networks bring out only marginal benefits. Consequently, the research interests in the area of static converters have been shifting toward improving the process of power conversion through a combination of novel circuit topologies and improved voltage and harmonic control PWM (pulsewidth modulation) techniques. As a result, several such techniques have been proposed lately. Although these techniques are clearly superior to the original sine PWM technique, little or conflicting data is available about their merits relative to each other. A critical evaluation of the aforementioned PWM techniques on the basis of application is provided, thereby giving the framework and guidelines for the selection of the best technique for each area of application. >

A novel approach for minimizing high-frequency transformer copper losses

A graphical and numerical method of calculating and minimizing losses in windings, that generalizes previous findings, has been introduced. Using electromagnetic theory and MMF diagrams in both space and time a method is proposed that provides insight into the mechanism of skin and proximity effect losses and that also yields quantitative results. Using this method, several winding geometries for various topologies are covered. The analysis and optimization process is experimentally verified using an interleaved flyback transformer. The mathematical treatment justifying the use of the field method and which is essential in arriving at any numerical result is presented are more general equations for the calculation of copper losses are derived. The relation between the fields in the transformer and copper losses is emphasized. Also, the tools necessary to derive optimization diagrams are provided. >

A novel active current waveshaping technique for solid-state input power factor conditioners

A novel input power factor correction method that uses a closed-loop active current waveshaping technique is presented. The novel feature of the method is that nearly sinusoidal input currents are obtained at constant switching frequencies. Moreover, the method exhibits instantaneous current control, which results in very fast response and increased switch reliability. Selected predicted system performance and design methods were verified experimentally on a 1 kVA laboratory prototype. >

The Delta Modulation Technique in Static PWM Inverters

Pulsewidth modulation (PWM) techniques are employed in voltage-source inverters to produce a variable output voltage containing the least possible harmonic distortion over a wide frequency range. To achieve these objectives, compromises are made in terms of control circuit complexity, smoothness of inverter operation, and overall system reliability. The delta modulation (DM) technique fulfills the aforementioned performance requirements with a minimum of circuit complexity, smooth inverter operation and with improved system reliability.

Design aspects of synchronous PWM rectifier-inverter systems under unbalanced input voltage conditions

The effects of input line voltage unbalance are analyzed, starting with the distortion in the input line currents and extending to the DC bus components and inverter output line voltages and currents. Analytical results are used to obtain system design curves as a function of the input voltage unbalance for all major system components. Key predicted results were verified on a 2 kVA prototype unit.<<ETX>>

Analysis and Design of Forced Commutated Cycloconverter Structures with Improved Transfer Characteristics

Forced Clommutated Cycloconverters (FCCs) are converter structures capable of providing simultaneous voltage and frequency transformation without the need of intermediate stage reactive components. Consequently, they are well suited for high power density variable frequency applications. This paper focuses on the analysis, design and performance characteristics of some novel FCC structures, which require less control complexity and yield better voltage utilization than presently known structures.

Analysis and design of a three-phase synchronous solid-state VAr compensator

A three-phase synchronous solid-state VAr compensator (SSVC) system that uses a three-phase pulsewidth-modulated (PWM) voltage-source inverter is presented and analyzed. The proposed SSVC system can compensate for leading and lagging displacement power factor. Pulsewidth modulation is used as a means of reducing the size of reactive components. The SSVC system is analyzed under self- and independently-controlled DC bus voltage operating conditions. Other areas of investigation include the design of SSVC filter components for both approaches and the closing of the loop around the reactive power command signal. Predicted results are verified experimentally for the case of the SSVC working with a self-controlled DC bus. >

Performance analysis of a PWM inverter VAr compensator

The performance of a three-phase solid-state reactive power compensator with fast dynamic response is analyzed. The compensator consists of a three-phase pulse-width modulated voltage-source inverter connected to a self-controlled DC bus. The principal advantage of this scheme is that it can maintain a near-unity source power factor without sensing and computation of the associated reactive power component. A mathematical model for the compensator connected across a variable power factor load is derived. The frequency response is obtained for open-loop operation. This allows the design of the controller. Predicted results are verified experimentally for both open and closed-loop responses. >