The method of the invention in one aspect involves electronic power control by varying the amplitude of an electrical power supply voltage, independent of frequency, whereby the output frequency will always be the same as the input frequency. An electrical circuit apparatus for accomplishing this function in a preferred embodiment is also disclosed herein. The preferred circuitry of this aspect of the invention uses four solid state switches, such as IGBT's, four diodes, an inductor, input and output filters and novel controlling circuitry. The controller apparatus and methods of the invention may be used to implement all otherwise conventional converter types, buck, boost, and inverting (and duals of these) versions to obtain different regulating characteristics, including galvanic isolation of the output from the input. The inventive methods and devices may be used in power factor correction, voltage and/or current harmonic filtering and neutralization, line and load conditioning, control of power transfer between two power grids, and programmable control of surges, sags, dropouts and most other voltage regulation problems.

Method and apparatus for electronic power control

A cycloconverter is a power electronic device used to convert constant voltage constant frequency AC power to adjustable voltage adjustable frequency AC power without a DC link. Cycloconverters inject significant harmonics and nonstandard frequency components (i.e., noninteger multiples of the power frequency) into power systems. The impact of cycloconverters on power quality is studied, and the relationships between power quality indices and cycloconverter control strategies are developed. Control strategies are proposed to minimize the power quality impact of the cycloconverters. An innovative group frequency concept is introduced. This is a technique whereby many frequency components in the cycloconverter voltage and current spectra are collapsed into several group frequencies, and the power quality impact of the group frequencies is the same as that of the full spectrum of the cycloconverter signals. Some concepts are illustrated by simulation, and some by measurement at a twelve pulse cycloconverter load.

The power quality impact of cycloconverter control strategies

A modular transformer arrangement providing power to a multi-level power converter includes a plurality of three phase transformers having delta or extended delta connected primary windings and delta or extended delta or wye or zig zag wye connected secondary windings and the multi-level power converter has full bridge power modules inputs connected to isolated secondaries of the transformer modules and outputs connected in series and/or in parallel to provide increased voltage and/or current or multiple phases which can be phase shifted with respect to the input to the transformer.

Modular transformer arrangement for use with multi-level power converter

A method and apparatus for improving the performance of polyphase AC machines. The polyphase AC machines are excited both with a fundamental frequency and with an odd harmonic of the fundamental frequency. The fundamental flux wave and the harmonic flux wave will travel at synchronous speed in the air gap. This facilitates redistributing the flux densities in the machine and thereby increasing the total flux per pole in the machine.

Method and apparatus for improving performance of AC machines

In an AC current control system for controlling multi-phase AC currents supplied from a power converter to a load, the currents are detected and coordinate-transformed into orthogonal two-axis current values i d , i q in a rotating coordinate rotating at an angular frequency ω, and then compared with the references. The deviations are used to determine two-axis voltage values e d *, e q *, which are coordinate-transformed into multi-phase voltage values determining the output voltages of the power converter. The system is characterized in that the voltage value e d * is determined not only from Δi d but also from the product of ω and Δi q , while the voltage value e q * is determined not only from Δi q but also from the product of ω and Δi d . This arrangement makes it possible to provide a voltage component corresponding to the voltage drop across the inductive component of the load which is 90° in advance of the current.

Ac current control system

Following a brief review of the problems arising in the design of dc machines for maximum ratings, the cycloconverter-fed synchronous and asynchronous rotating-field machines with field-oriented control as interesting alternatives to the dc drives will be described. The mode of operation of the cycloconverter is discussed in brief, followed by a description of the principle of field orientation by way of example of the synchronous machine. Oscilloscope records are presented to prove that the dynamic properties of a 1.2 MW drive using this control principle are fully equivalent to those of a dc drive. The drive variant described does not require special motors or motors fitted with internal flux sensing devices. It was originally developed for rolling mill applications but can also be used advantageously in hoists and comparable high-capacity drives running at slow speed.

Cycloconverter Drives for Rolling Mills

A circuit arrangement is disclosed comprising three direct converters which are fed from an a.c. voltage network. The converters are arranged in a Y configuration and are connected to a three-phase load. To increase the transmitted power and to vary the reactive power requirement, the circuit arrangement is provided with means for generating a control voltage for the control unit of at least one of the three converters such that the output voltage of this converter has a periodic waveform which includes essentially no fifth and seventh order harmonics. Additionally, the load-side conductor currents of the three converters are controlled with control signals having sinusoidal waveforms. A particular form used for the control voltage is a trapezoidal waveform.

Circuit arrangement including a number of converters, in particular direct converters, in y connection

A circuit arrangement is disclosed comprising a converter for converting a three-phase system of sinusoidal voltages into three trapezoidal control voltages for controlling control units serving three direct cycloconverters. More particularly, in accord with the invention, the converter acts on the sinusoidal control voltages such that during each region from π/3 to 2π/3 of a half-wave of each particular voltage that voltage is reduced to √3/2 times its peak value, while the other two voltages are amplified or increased by an amount equal to the difference between the aforesaid peak value and √3/2 times such peak value.

Circuit arrangement with a number of cycloconverters, particularly direct cycloconverters in y-connection

The invention concerns a converter arrangement for electrode melting furnaces, particularly for electric slag remelting of metals. A current regulator in the form of a PI controller is associated with the converter arrangement. The former is influenced by an actual current value, a reference current value, and additionally, by a control quantity. The control quantity replaces the current regulation of the regulator by a voltage control in dependence on periodic or aperiodic conditions which may be due to operational causes or to trouble and interfere with the melting process in the furnace. More particularly, for the duration of such conditions, the control quantity causes the output voltage of the regulator, which voltage acts on the control unit feeding the converter, to be limited upward to an adjustable value.

Wolfgang Timpe

Papers

Cycloconverter Drives for Rolling Mills

Circuit arrangement including a number of converters, in particular direct converters, in y connection

Circuit arrangement with a number of cycloconverters, particularly direct cycloconverters in y-connection

Circuit arrangement for supplying electrode melting furnaces