Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
1999-11-24
2001-02-20
Wong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C363S021030, C363S126000
Reexamination Certificate
active
06191564
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to power factor correcting electrical converter apparatuses. Power factor correcting electrical converter apparatuses are known, as discussed in U.S. Pat. No. 5,777,866 to Jacobs, et al, for “Power Factor Control for Switched Mode Rectifiers with Improved Representing of Currents in EMI Capacitive Elements”; which is assigned to the assignee of the present application (hereinafter referred to as “the '866 Patent”).
A power factor correcting electrical converter apparatus receives an alternating electrical input from a power source. The apparatus includes an input electromagnetic interference (EMI) filter connected with the power source. A rectifying circuit is connected with the EMI filter for receiving the input and generating a rectified voltage. To reduce the cost of the EMI filter, a capacitor is usually placed across the rectified voltage at the rectifying circuit. However, such a capacitor introduces more input current distortion because it prevents current flowing into the rectifier circuit (usually implemented as a diode bridge) whenever the voltage across the capacitor is greater than the value of the input voltage. A switching mode converter, usually a boost type, is connected between the rectifying circuit and an output to provide a regulated power to the output.
In order to draw a low-distortion input current, the '866 Patent teaches constructing such a power factor control converter using a capacitor sense arrangement to provide a feed-forward signal to a control loop. In particular, the '866 Patent teaches using a sense capacitor to provide a current to a current amplifier driving a pulse width modulator to control a power switch connecting a load to the converter apparatus.
The feed-forward arrangement taught by the '866 Patent is intended to reduce current distortion around zero-crossing of the input current signal. Current distortion is reduced by the enhanced converter of the '866 Patent. However, in that prior art converter apparatus extra protection circuitry is required because the apparatus is not controllable at very light loads. Further improvement of the apparatus' performance is desirable.
SUMMARY OF THE INVENTION
A power factor correcting electrical converter apparatus receives an alternating electrical input from a power source. The apparatus preferably includes an input tracking circuit connected with the power source for tracking the input and providing an input signal at an input tracking node. The converter apparatus includes a rectifying circuit connected with the power source for receiving the input and generating a rectified input, and a filtering circuit connected with the rectifying circuit to filter and smooth the rectified input voltage. This filtering circuit is usually a filtering capacitor connected across the output of the rectifying circuit. An input sensing circuit is connected with the input tracking circuit for receiving the input signal and generating an input-indicating signal at an input-sensing node. An output circuit is connected with the filtering circuit for delivering a regulated power to a load. The output circuit senses an electrical parameter associated with the load to produce an output-indicating signal at an output-sensing node. A feedback circuit is connected with the input-sensing node and with the output-sensing node for receiving the input-indicating signal and the output-indicating signal and generating a gating signal. The output circuit responds to the gating signal to switchingly control connection with the load. The input sensing circuit is configured to impose a delay which causes the input-indicating signal to be out of phase with the input signal. The delay may be introduced in the feedback circuit, in whole or in part, if desired. The phase shift reduces input current distortion and increases input power factor.
For high-performance applications, measures must be taken to reduce the input current distortion around the zero-crossing of the alternating input voltage caused by the filtering capacitor. In previous, prior art converters of the type of the present invention, the feed-forward circuitry pushed more power than was needed or desired at or near zero-crossing points of the input voltage.
By phase shifting, or delaying, the reference current employed to determine gating signals to the output circuit of the converter, the discharging current across the filtering capacitor is increased in the vicinity of the zero-crossing point of the input voltage. The result is a lower residual voltage across the filtering capacitor, which in turn reduces the diode-bridge blocking time caused by the rectifying circuit when the input voltage is less than the residual voltage across the filtering capacitor. A significant consequence of such reduced diode-bridge blocking time is a much-reduced distortion of input current in the vicinity of the zero-crossing point of the input signal.
The apparatus of the present invention may be advantageously employed with any type of converter device in a power factor correcting application, including, but not limited to boost, buck, flyback, forward, SEPIC (Single-Ended Primary Inductor Converter) and Cuk converters.
It is therefore, an object of the present invention to provide a power factor correcting electrical converter apparatus which reduces distortion of input current in the vicinity of the zero-crossing point of the input signal.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.
REFERENCES:
patent: 5777866 (1998-07-01), Jacobs et al.
Lucent Technologies - Inc.
Mondul Donald D.
Patel Rajnikant B.
Wong Peter S.
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