Showing papers by "Johann W. Kolar published in 1997"

A novel three-phase utility interface minimizing line current harmonics of high-power telecommunications rectifier modules

Abstract: Based on the combination of a three-phase diode bridge and a DC/DC boost converter, a new three-phase three-switch three-level pulsewidth modulated (PWM) rectifier system is developed. It can be characterized by sinusoidal mains current consumption, controlled output voltage, and low-blocking voltage stress on the power transistors. The application could be, e.g., for feeding the DC link of a telecommunications power supply module. The stationary operational behavior, the control of the mains currents, and the control of the output voltage are analyzed. Finally, the stresses on the system components are determined by digital simulation and compared to the stresses in a conventional six-switch two-level PWM rectifier system.

Basic considerations and topologies of switched-mode assisted linear power amplifiers

Abstract: This paper presents a combined power amplifier system consisting of a linear amplifier unit with a switched-mode (class D) current dumping stage arranged in parallel. With this topology, the fundamental drawback of conventional linear power amplifiers-the high loss-is avoided. Compared to a pure class D (switching) amplifier, the presented system needs no output filter to reduce the switching frequency harmonics. This filter (usually of multistage type) generally deteriorates the transient response of the system and impairs the feedback loop design. Furthermore, the low-frequency distortions of switching amplifiers caused by the interlock delay of their power transistors are avoided with the presented switched-mode assisted linear amplifier system. This can be considered as a master-slave system with a guiding linear amplifier and a supporting class D slave unit. The paper describes the operating principle of the system, analyzes the fundamental relationships for the circuit design, and presents simulation results. Finally, various further topologies of switched-mode assisted linear amplifiers are given.

Novel aspects of an application of 'zero'-ripple techniques to basic converter topologies

Abstract: Based on a short summary of the theoretical basics of the zero-ripple current phenomenon a special zero input current ripple boost converter topology as presented in the literature is investigated. It is shown that the complete suppression of the input current ripple of the system is only given in a theoretical extreme case. For a practical realization only such a ripple reduction of the input current of the basic converter structure is obtained as corresponds to a simple low-pass input filter. This is proven by a detailed analysis also for a zero-ripple Cuk and for a zero-ripple SEPIC converter structure. Furthermore, it is shown that the realization of a zero-ripple Cuk or zero-ripple SEPIC converter is not linked to a magnetic coupling of the input and output inductors, but can also be achieved by a simple rearrangement of the elements of the basic converter structures. There one can see that the operating behavior of a zero input current ripple SEPIC converter is equivalent to the operating behavior of a buck-boost converter stage with LC input filter. Finally, the advantages and disadvantages of the different realization approaches of zero-ripple topologies are compared. Also, an outlook towards the planned further treatment of the topic is given.

A novel three-phase three-switch three-level high power factor SEPIC-type AC-to-DC converter

Abstract: In this paper, the topology of a new three-phase three-switch three-level PWM rectifier system is derived based on the basic structure of a DC-to-DC SEPIC power converter. The system is characterized by full controllability of the power flow (independent of the level of the output voltage) and by a sinusoidal mains current shape in phase with the mains voltage. The operating principle of the power converter is explained based on the conduction states of a bridge leg within a pulse period. The stationary operating behavior is analyzed by digital simulation based on the control of the mains phase currents by independent ramp-comparison controllers. Furthermore, a mathematical description of the operating behavior of the three-phase system including the coupling of the phase current controllers (given due to the floating mains star point) is discussed. Finally, results of an experimental investigation of a laboratory model of the power converter are presented.

A novel concept for regenerative braking of PWM-VSI drives employing a loss-free braking resistor

Abstract: In this paper a simple circuit for feeding back the braking energy from the DC voltage link of a three-phase PWM AC drive system into the mains is proposed. The operating behavior of the system which consists of a series connection of a line-commutated three-phase bridge and a turn-off power semiconductor device and in principle does not require passive components is discussed. The stationary operating behavior is analyzed by analytical calculations and by digital simulation and represented in graphical form. Furthermore, the effects on the mains caused by the system for braking operation are analyzed and compared to the conditions for motoring operation and/or to the conditions for feeding of the DC link by an uncontrolled rectifier bridge. Finally, measures for guaranteeing high system operational safety are discussed and the advantages and disadvantages of the circuit are compiled in the form of an overview.

Synchronization of the switching action of hysteresis current controlled parallel connected power electronics systems

Abstract: A method and apparatus for operation of an electrical power conversion system having first and second partial systems connected in parallel. Each partial system includes an inductor and an electronic switch for controlling electrical power transferred through the partial systems. A control circuit controls operation of the electronic switches. The control circuit includes devices for generating a first control signal error and a second control signal error as a function of a reference and current flowing in the inductors. Hysteresis devices receive the first and second control signal errors and provide first and second outputs, respectively, upon intersection of the first and second control signal errors with selected threshold values. Delay devices coupled to the electronic switches receive and delay transmission of the first and second outputs to the electronic switches.