Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2002-05-04
2003-10-28
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
Reexamination Certificate
active
06639815
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to unidirectional or bi-directional DC/AC converter. This includes switching power amplifier, AC power source, frequency converter, line conditioner and uninterruptible power source.
BACKGROUND OF THE INVENTION
Many terms exist to describe various types of devices used for power conversion. The following definitions are provided in order to avoid any conflict of terms. A switching power supply (SPS) is an AC/DC or DC/DC converter. A switching power amplifier (SPA) is an AC/AC or DC/AC converter. An SPA that produces a fixed frequency is commonly referred to as inverter, AC voltage regulator, AC power source, line conditioner, frequency converter, etc. An SPA that amplifies a variable frequency is often narrowed to class-D amplifier, whereas other techniques exist. An uninterruptible power source/supply/system (UPS) is a bi-directional DC/AC converter. The UPS charges a battery when line is present and simulates line voltage when line fails. In the following disclosure, the term converter refers to a block performing power conversion within a parent apparatus.
Conventional SPA and UPS each comprise an output inductor that continuously delivers a current to an output capacitor. Moreover, a feedback signal introducing delay and phase shift is used to determine that current. Only an optimal level of the current is established. In particular, a rate at which the current is regulated is very limited in order to maintain high stability. However, variations of load impedance over amplitude and frequency are often rapid and unpredictable. A precise correction is simply impossible since, at the end of every switching cycle, the correction is either insufficient or continues while no longer required. In order to minimize an output voltage ripple, a powerful output filter is used. However, this further contributes to unpredictability of load impedance. Unless a well-behaved load is used, the high accuracy is unattainable with traditional techniques. This includes most sophisticated class-D amplifiers. Usually, the accuracy of the output voltage produced by the UPS is nonessential. However, an excessive switching results in reduced efficiency. During the battery charging, the UPS acts like an SPS.
Class-D amplifiers are plagued by numerous inherent flaws. Pulse width modulation (PWM) and other modulation schemes are used to average the input and feedback signals. Moreover, the output voltage is obtained by averaging the pulse train in the output filter. The result is slow response time and sluggish performance. The output voltage is never on target as the output inductor “drags” it around. Even if the output voltage is precisely equal to the input voltage, multiplied by gain, class-D amplifier will overshoot or undershoot. The output voltage is thus corrected and/or falsified in every switching cycle. Moreover, increased cost and reduced efficiency of class-D amplifiers are unacceptable. No-load operation can produce large resonant currents in the output filter. Minimum load matching the main load is often required. Problems associated with power devices offer many other examples. In order to correct even a tiny overshoot at peak current, the output inductor has to be fully discharged and fully recharged. The result is increased response time and overblown current ratings. But even the switching itself is troublesome. Dead time is excessive in order to take into account temperature dependence and device differences. Output capacitance of the complementary switch and intra-winding capacitance of the inductor add up causing enlarged supply voltage spikes and ringing. Parasitic power supply capacitance coupled to the floating driver is also added. To make it worse, the switches are paralleled by clamping diodes due to poor quality of intrinsic body diodes. Schottky diodes, usually recommended, have particularly large junction capacitance. Yet another example is reverse energy flow, also known as power supply pumping. Power supply capacitors have to be severely oversized as to store energy returned at low frequencies. Pushing energy back and forth dramatically worsens EMI/RFI.
An instantaneously interruptible power source (I
2
PS) is introduced in the abovementioned “Precision Switching Power Amplifier and Uninterruptible Power System,” U.S. Pat. No. 6,385,056, dated May 7, 2002, and “Switching Power Amplifier and Uninterruptible Power System Comprising DC/DC Converter for Sinusoidal Output,” U.S. Pat. No. 6,362,979, dated Mar. 26, 2002. A unidirectional or bi-directional I
2
PS is equivalent to a conventional SPA or UPS respectively. However, some intrinsic features of the I
2
PS are in sharp contrast to common flaws of the conventional devices. The I
2
PS can instantaneously interrupt the correction, wherein a precise correction can be accomplished in every switching cycle. Moreover, the I
2
PS can become idle by the end of every switching cycle or remain idle over a period of many cycles. The I
2
PS is thus idle when no correction is necessary. If accuracy of the output voltage is nonessential, as in case of the UPS, a less frequent correction of the output voltage results in reduced power dissipation. The I
2
PS is unidirectional, unless otherwise noted.
SUMMARY OF THE INVENTION
The present invention is intended to provide an SPA comprising an I
2
PS for producing a precise AC output voltage. A converter provides an internal supply current. A fine amplifier rapidly delivers a fine current to the output capacitor. The converter and the fine amplifier can be.combined or used separately.
The switching power apparatus according to the present invention provides an AC output voltage in response to an AC input signal. A power supply means provides at least one supply voltage. A first and second inductive means attain a first and second corrective currents, and provide a first and second return voltages respectively. A first and second rectifying means limit the first and second return voltages respectively. A capacitive means provides the AC output voltage. A first switching means has a first reference terminal and a first supply terminal, and is coupled in series with the first inductive means for selectively applying the first corrective current between the power supply means and the capacitive means. A second switching means has a second reference terminal and a second supply terminal, and is coupled in series with the second inductive means for selectively applying the second corrective current between the power supply means and the capacitive means. A converter means has a first and second input terminals for converting a voltage appearing therebetween and providing a supply current to at least one supply terminal. The first input terminal is coupled to one of the terminals of the first switching means and the second input terminal is coupled to one of the terminals of the second switching means.
In another embodiment, a power supply means provides at least one supply voltage. A pair of inductive means each attain a corrective current and provide a return voltage. A pair of rectifying means is separately coupled to the inductive means for limiting the respective return voltages. A capacitive means provides the AC output voltage. A pair of switching means is separately coupled in series with the inductive means for selectively applying the respective corrective currents between the power supply means and the capacitive means. An amplifier means provides a fine current to the capacitive means in response to the AC input signal and the AC output voltage.
A voltage shifter according to the present invention provides a first binary output signal referenced to a first output potential in response to a first binary input signal referenced to an input potential and provides a second binary output signal referenced to a second output potential in response to a second binary input signal referenced to the input potential. A first current source means provides a first current in response to the first and second binary input signals. A resistive means provi
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