Sevcon Limited

Nada Electronics Limited

Chloride Group Limited

Caterpillar Tractor Co.

Aktiebolaget Electrolux

Lumonics Inc.

Sevcon Engineering Limited

David Gurwicz

Albert E Sloan

Grant C Melocik

Graham Burrows

Arthur Wild

William R Ord

Paul Morris

Keith Pacey

Kevin Thompson

Barry Moss

An arrangement for converting an AC supply to a DC supply comprising an inverter circuit and a boost power factor correction stage. The inverter circuit comprises switchable components and utilizes a pulsed waveform indicative of power factor correction for causing some at least of the components repeatedly to adopt a condition permitting the boost power factor correction stage to draw current from the AC supply.

AC to DC conversion arrangement

A laser system comprises an optical head, a power supply and a computer for controlling the power supply. The optical head comprises a pair of mirrors and four pumping sections. Each pumping section comprises a pair of gas discharge lamps pumping an Nd:YAG laser element. The power supply provides the lamps with alternating current at 25 kHz so that the laser system produces a continuous, modulated or pulsed output light beam. The power supply comprises three boost converters connected in parallel for converting three phase mains supply to direct current and four DC-AC converters. Each DC-AC converter converts the DC output from the boost converters to an AC supply for the lamps of a respective one of the pumping sections. Each DC-AC converter comprises a resonant circuit having an inductor and capacitor connected in series, the lamps being connected across the capacitor, a pair of transistors for conducting current through the resonant circuit in alternating directions, and a control circuit for the transistors. The power supply is also arranged to supply alternating current at a relatively high voltage to the lamps for triggering a discharge. In a modification, the output of the power supply is rectified before it is supplied to the lamps.

Laser system

Resonant inverter

A magnetron is powered via an output transformer TR whose primary winding (a) is connected in series with a resonant converter oscillator circuit comprising an inductor (L) and a capacitor (C3) and switching transistors (T.sub.1, T.sub.2) which are connected to positive and negative power supply terminals and are switched by respective current transformers (CT1, CT2). The switching points of the switching transistors are varied so as to vary the output of the circuit by varying the positive and negative flux excursions in the cores of the transformers (CT1, CT2) such that the net flux excursions are sufficient to saturate the transformers and switch off the switching transistors at a predetermined point in each half cycle. The relative positive and negative flux excursions in the transformer cores are controlled by providing additional windings (g) which are connected to a control circuit whcih rectifies the output of these windings and controls the rectified DC voltage appearing across them.

Resonant converter oscillator usable for powering a magnetron

The power supply circuit has an inductor connected to a DC source through a regulating circuit arranged to maintain a constant current in the inductor. A MOSFET is connected to the inductor and to the spark gap so that when the MOSFET is conducting, current is diverted from the inductor to the spark gap. The frequency and mark-space ratio of switching of the switching device is controlled to control the machining process. A second switching device (40) is arranged to conduct when the voltage across a capacitor (34) exceeds a reference voltage. A diode (46) is used to return excess energy to the DC source.

Electric discharge machining power supply circuit

A high frequency converter of push-pull form comprises a center tapped D.C. input supply 16, 17, 18, two solid state switching devices (20, 21) connected in series across the D.C. input terminals, a load circuit including a supersonic frequency transformer 30 and an output rectifier 35, and an oscillatory circuit including at least one capacitor 40 and a parallel inductor 34 connected in parallel with the primary winding 37 of the transformer between the center tapping 19 of the supply and the junction 25 of the switching devices. The switching devices are synchronized to the oscillation of the oscillatory circuit to allow the circuit to oscillate freely for part of a cycle to transfer energy from the inductor 34 to the capacitor 40 to charge the latter to a certain condition in which the voltage across the parallel inductor is substantial and that across the switching device is negligible and only then connect the parallel inductor across the D.C. input terminals whereupon the parallel inductor receives and stores energy from the said supply. Means such as a saturable reactor 33 are connected in series in the load circuit to restrict load current to a low value during a part of the cycle in which the capacitor receives energy from the parallel inductor and until the capacitor is charged to the said condition and the switching means has connected the load circuit across the supply.

Converters

An alternator for an internal combustion engine driven vehicle comprises a permanent magnet rotor mounted in operation for rotation with the engine crankshaft, a wound stator within which the rotor extends, rectifying means connected to the output of the stator, and a pulse controlled DC chopper regulator supplied from the output of the rectifier means and adapted to control the output from the rectifier and to supply the so controlled output to the vehicle battery for charging thereof.

Chopper-controlled alternator for battery charging

A converter includes a resonant oscillatory tank circuit comprising a capacitor and an inductor, at least one switching circuit including a solid state switching device in parallel with a diode connected to apply a predetermined potential difference from a DV supply to the inductor, and synchronizing means responsive to the oscillation of the oscillatory circuit for switching on the switching means for a fraction of a cycle when the instantaneous value of the oscillatory potential difference across the inductor is already not less than a predetermined value, to delay the fall of the said oscillating potential difference and inject energy from the supply into the oscillatory circuit, and a load circuit coupled or connected to the tank circuit in series with the inductor.

A converter includes a resonant oscillatory tank circuit comprising a capacitor and an inductor, at least one switching circuit including a solid state switching device in series with a diode connected to apply a predetermined potential difference from a DV supply to the inductor, and synchronizing means responsive to the oscillation of the oscillatory circuit for switching on the switching means for a fraction of a cycle only when the instantaneous value of the oscillatory potential difference across the inductor is already not less than a predetermined value, to delay the fall of the said oscillating potential difference and inject energy from the supply into the oscillatory circuit, and a load circuit coupled or connected to the tank circuit.

DC-AC Converter including synchronized switching

A control circuit is provided for a d.c. motor for sensing the temperature of the field winding and automatically reducing the temperature of the field winding when the temperature exceeds a preselected value.

Control circuit for a D.C. motor

A pulse controller for controlling the current supply to a plurality of d.c. loads through a respective main thyristor for each load is provided with digital circuitry operable to maintain the mark-space ratios of voltage applied to the loads in a relationship to one another which is set by a differential control circuit while the mark-space ratios are simultaneously varied in response to a drive control circuit. The controller may be used to control two d.c. motors respectively driving right-hand and left-hand traction wheels of a battery-electric vehicle, to provide differential drive when the vehicle negotiates a curve.

Thyristor pulse controller for plural loads

A pulse controller for a reversible d.c. series motor is provided, in place of the conventional freewheel diode across the armature and field and plugging diode across the armature, with a unidirectional current path connected across the armature and field and containing sufficient impedance to prevent build-up of motor current in interpulse periods when the motor is in a plugging mode, and switch means for shorting out the impedance during normal motoring.

Pulse controllers

In electrical circuit means having a load, an SCR pulse controller in series with the load and including a commutation capacitor, a transmission line connected to the load and pulse controller to supply the load from a D.C. source, and, a reservoir capacitor shunting the transmission line, the provision of control means which during interpulse periods of the controller by repeatedly discharging the reservoir capacitor limit the voltage to which the reservoir capacitor charges above the voltage of the source.

D.C. Electrical circuit means

A thyristor pulse controller in which current supply to each of a plurality of d.c. loads is controlled by respective main thyristors and a single commutating capacitor common to all the main thyristors is provided, the capacitor being connected across the main thyristors to commutate them one at a time at intervals not less than the time required to forward charge the commutating capacitor from the d.c. source and to reverse the charge on the capacitor.

A separately excited speed-controlled D.C. motor which has constant armature current and pulse-controlled field current has its armature connected by way of a bridge rectifier and an inductor to an A.C. source of substantially greater r.m.s. voltage than the rated supply voltage of the armature, the inductor serving to regulate the armature current. The field winding is connected to a field excitation supply and to a thyristor chopper and the mean current through the field winding controlled by the thyristor chopper thereby to control the armature torque and therefore the speed. The field winding may comprise two field coils arranged to produce opposing magnetic fields, the thyristor chopper serving to control the net magnitude and direction of the motor field. A thyristor chopper may be provided in the armature circuit to maintain a constant armature current during plugging of the motor.

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Gateshead, United Kingdom

David Gurwicz