Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
1999-12-30
2001-07-03
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C363S037000
Reexamination Certificate
active
06256211
ABSTRACT:
TECHNICAL FIELD
This invention relates to a circuit device for driving an a.c. electric load, and more particularly, to a device of a type incorporating a rectifying bridge which has a first input connected to one terminal of the electric load and a second input connected to an outlet of an a.c. main supply.
BACKGROUND OF THE INVENTION
The simplest way of varying the supply voltage to an electric motor, or resistive/inductive load, is that of using a Triac device effective to partialize the main voltage being applied to the motor. This technique is cost-efficient, but has a problem in that it introduces harmonics in the current waveform of the main supply.
Stringent European standards have set restrictions on the harmonic contents of main current, and today's trend favors the use of circuit devices based on bridge structures which produce PWM (Pulse Width Modulation) signals and are less prone to introduce harmonics.
Several types of drive circuits for a.c. motors are known from the literature. These circuit types use basically d.c./a.c. switches with inverters, whereby a sinusoidal voltage is output which can be varied in amplitude and frequency in quite an independent manner. All these conventional type circuits are based on bridge circuits producing PWM signals.
The d.c. voltage is obtained by rectifying and filtering the main supply voltage according to a scheme which is known per se and essentially as shown in
FIG. 1
of the accompanying drawings.
A rectifier diode is connected in parallel to a filter capacitor, and to a switch having the electric motor, or another electric load such as a lamp or an electric oven, connected across it. These drive circuits have a drawback in that, additionally to introducing harmonics in the waveform of the main current, they incorporate fairly expensive components.
On the other hand, approaches based on the use of Triac devices lead to acoustic noise being generated by d.c. motors, when such motors are regulated by phase partializing. Such is the case with kitchen hoods, for example, where this technique is often used for supplying and driving the suction fans for cost reasons.
The higher order harmonics thus produced cause metal parts and the magnetic circuits associated with the motor to vibrate, thereby producing a rattling noise which is objectionable by the house occupants.
For varying the voltage applied to an a.c. load, it has been proposed to drive electric motors by a partialized main voltage sinusoid, as achieved by controlling the conduction angle of a thyristor. In this way, the voltage at the load is made to depend on the turn-on angle alpha of the thyristor. However, not even this method can solve the problem of harmonics appearing on the main current.
SUMMARY OF THE INVENTION
Embodiments of the invention provide a circuit device for driving a.c. loads, which have constructional and functional features such that the load can be connected directly to the a.c. supply line, thus drastically reducing the probability of current harmonics being introduced on the supply line, and overcoming the limitations and drawbacks of available prior art solutions.
The embodiments of the invention provide a double bi-directional loop-back link connected in parallel to the electric load. Advantageously, the first and second links are activated alternately by the positive and negative half-waves of the main supply when the switch is in the “off” state.
Presented is a circuit device for driving an a.c. electric load, incorporating a rectifying bridge that has a first input connected to one terminal of the electric load and a second input connected to an outlet of an a.c. main supply. The rectifying bridge has output terminals connected to a power switch which is controlled by an electric signal. The circuit device has a circuit loop-back link connected in parallel to the electric load, and a second circuit loop-back link connected in parallel to the electric load. The first and second links are alternately activated by the positive and negative half-waves of the main supply when the switch is in its “off” state.
The features and advantages of a device according to the invention will be apparent from the following description of an embodiment thereof, given by way of non-limitative example with reference to the accompanying drawings.
REFERENCES:
patent: 5563487 (1996-10-01), Davis
patent: 6069810 (2000-05-01), Wissmach et al.
patent: 0 221 574 A2 (1987-05-01), None
patent: 0 573 197 A1 (1993-12-01), None
Cucuccio Antonino
Di Guardo Mario
Milazzotto Antonino
Nicosia Nicola
Galanthay Theodore E.
Han Jessica
Iannucci Robert
Seed IP Law Group PLLC
STMicroelectronics S.r.l.
LandOfFree
Circuit device for driving an a.c. electric load does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Circuit device for driving an a.c. electric load, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Circuit device for driving an a.c. electric load will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467446