Sundstrand Corporation

Pierre S Thollot

P John Dhyanchand

Vietson M Nguyen

Sampat S Shekhawat

P R Chetty

Gregory I Rozman

Timothy F Glennon

John J Dhyanchand

Alexander Krinickas, Jr

Madan L Bansal

Byron R Mehl

Gary L Galloway

Anand K Upadhyay

W William Wold

The invention is an induction electrical power generation system for generating alternating current varying within a frequency range; the system includes an induction electrical generator (52) for generating the alternating current having a rotor and a stator, the stator having at least one phase winding for outputting the generated alternating current and a plurality of poles with at least two different numbers of poles within the plurality of poles being selected to generate the alternating current, an exciter winding wound on the stator which is driven by AC excitation which varies in frequency during generation of the alternating current and the rotor operating with slip during the generation of the alternating current; a variable speed drive coupled to the rotor for driving the rotor in a speed range during generation of the alternating current; an exciter generator (54) coupled to the exciter winding for generating the variable frequency AC excitation; a speed sensor (56) for producing a signal which is a function of the speed of rotation of the rotor; and a controller (58), coupled to the inverter and responsive to the rotor speed signal, for commanding variation of the excitation frequency as a function of the rotor speed signal, a selection of the at least two different numbers of poles within the plurality of poles as a function of the rotor speed signal to control generation of the alternating current within the frequency range and a magnitude of excitation current produced by the exciter generator.

Induction electrical power generating system with variable numbers of

An excitation system for a brushless generator having a main generator portion including a field winding disposed on a rotor and an armature winding disposed in a stator includes an exciter portion having a set of polyphase exciter field windings disposed in the stator and an armature winding disposed on the rotor and coupled to the main generator portion field winding. A first power converter is coupled to the main generator armature winding and a second power converter is coupled to the set of polyphase exciter field windings. Contactors are operable in a starting mode of operation to couple a source of electrical power to the first and second power converters and are operable in a generating mode to disconnect the source of electrical power from the first and second power converters. A control unit controls the power converters such that the power converters provide AC power to the main generator armature winding and to the set of polyphase exciter field windings during operation of the starting mode so that the rotor is accelerated. The control unit operates the power converters in the generating mode such that the second power converter provides AC power to the set of polyphase exciter field windings and the first power converter develops constant-frequency AC power.

Brushless generator having AC excitation in generating and starting modes

Prior DC-DC converters of the resonant type often require the use of parallel-connected power switches to provide adequate current levels and further require large input and output filters. However, parallel operation of switching devices encounters the problem of current sharing and large filters are disadvantageous from a size and weight standpoint. Such problems are overcome by the DC-DC converter of the present invention which includes a plurality of subconverters having outputs which are combined to produce the output power. Each subconverter includes an inverter and a rectifier for developing a full wave rectified output having a ripple component therein. The subconverters are operated so that a phase displacement of 2.pi./N electrical degrees exists in the output current from one subconverter relative to the output current from other subconverters. The combined output therefore comprises a ripple component superimposed on a DC level, with the ripple component having a smaller amplitude and a greater frequency than the ripple component supplied by prior converters providing the same DC output level. The reduced ripple amplitude and increased frequency result in a reduction in size of the input and output filters. Further, since each subconverter handles only a portion of the total output power, parallel-connected switching devices need not be used.

Multiphase DC-DC series-resonant converter

Bi-directional switches for use with neutral point clamped PWM inverters have utilized clamping switches which are operated alternately with main power switches in the inverter to periodically connect an output terminal of the inverter to a neutral voltage. However, a delay period is typically interposed between turn-off of a main power switch and turn-on of the clamping switch to minimize the possibility of a potentially destructive shoot-through condition. This delay adversely affects the quality of the power developed by the inverter and leads to an undesired increase in the size of snubber circuits coupled across the power switches. In order to overcome these problems, a bi-directional switch according to the present invention includes circuitry for providing a high impedance path in series circuits including the main power switches and the clamping switch so that shoot-through currents are blocked even when one of the main power switches and the clamping switch are simultaneously on. The delays between turn-off of a main power switch and turn-on of the clamping switch can thereby be reduced or eliminated, thereby resulting in improved quality of the output power of the inverter and a reduction in the size of snubber circuits used therein.

Bi-directional switch for neutral point clamped PWM inverter

A proportional base drive circuit which overcomes the problems of the prior art relative to relatively long turn-off time of power switches in an inverter and the absence of protection circuitry therefor includes a current transformer having a primary winding coupled to a main current electrode of a pair of power switches and first and second secondary windings each of which develops regenerative currents proportional to load current. First and second auxiliary switches are coupled between the secondary windings and the control electrodes of the power switches. Means are included for operating the auxiliary switches in synchronism with the power switches so that the power switches operate in rapid fashion. Means are also included for disabling the power switches when an overcurrent condition is sensed.

Proportional base drive circuit for transistorized bridge inverter

Prior types of neutral point clamped PWM inverters have included memories for storing a plurality of PWM waveforms, one of which is utilized to control switches in the inverter to maintain an output parameter within prescribed limits. Such types of inverter controls, however, cannot provide the necessary degree of regulation in some applications. To overcome this problem, an inverter control according to the present invention permits on-line generation of PWM patterns for a neutral point clamped PWM inverter. The control includes circuitry for generating a depth of modulation signal representing the deviation of the output of the inverter from a desired level. A microprocessor and memory are coupled to the generating circuitry for calculating switching points for the inverter switches during operation of the inverter based upon the depth of modulation signal for a given number of pulses to be produced during each half cycle of the output. Timer modules are coupled to the microprocessor for developing switch control signals for each switch from the switching points so that the switches are operated to reduce the deviation of the output from the desired level.

Control for a neutral point clamped PWM inverter

A soft-start circuit for an inverter having a switch which is operated in accordance with the output of an oscillator includes a ramp generator coupled to the oscillator for generating a cycle ramp signal synchronized to and having the same period as the oscillator output, the cycle ramp signal also having an amplitude which periodically increases between first and second levels. Means are included for generating a soft-start signal having an amplitude which increases between the first and second levels, the length of time required for the amplitude of the soft-start signal to increase from the first level to the second level being substantially longer than the period of the cycle ramp signal. Means are coupled to the ramp generator and to the soft-start signal generating means for comparing the two signals to develop a pulse width modulated enable signal having a series of pulses of gradually increasing pulse width. Means are coupled to the comparing means and to the oscillator for gating the oscillator output with the pulse width modulated enable signal to derive switch control signals for the switch in the inverter. The switch is thereby operated at gradually increasing duty cycles immediately following turn on of the inverter.

Soft-start circuit for a power converter

In power circuit designs, it is sometimes necessary to connect two or more semiconductor power switches in parallel and to simultaneously operate both so that current levels in excess of the rated current handling capability of one of the devices can be conducted. Such operation, however, encounters the problem of current sharing which results from variations in the characteristics of the parallel-connected devices. The method of the present invention obviates the difficulties encountered with current sharing by operating N parallel-connected semiconductor devices one at a time in sequential fashion so that each device conducts an average current equal to the desired average output current divided by N.

Method of operating parallel-connected semiconductor switch elements

A push-pull converter has transistor power switches which conduct alternately to connect a DC source with the primary windings of an output transformer. A turn-off snubber circuit is connected with each power switch. When a power switch is turned on, snubber current pulses flow in the circuits connected with both switches. A switch current sensor circuit has a current transformer with an output winding inductively coupled with each of the conductors connected between the power switches and the primary windings of the output transformer. The snubber current pulses through the conductors are 180.degree. out of phase and are suppressed in the current transformer output. The switch current signal from the secondary of the current transformer is free of snubber current pulses and is used in a flux balance circuit and in a pulse-by-pulse current limiter.

Growing community of inventors

Rockford, IL, United States of America

Pierre S Thollot