Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2000-09-29
2002-05-07
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06385056
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to unidirectional AC/AC and DC/AC converters and a 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 in which energy is delivered from a rechargeable battery to an output, and vice versa. The UPS charges the battery when line is present and simulates line voltage when line fails. However, a low-cost UPS usually produces a square wave voltage that has adequate RMS level. In-the following disclosure, the term converter refers to a block performing an essential function 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, rate at which the current is regulated is very limited in order to maintain a 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 a battery charging, the UPS acts like an SPS. Conventional SPSs commonly use power factor correction to produce a sinusoidal input current. By contrast, a sinusoidal current for charging the battery is very rare in UPSs.
SUMMARY OF THE INVENTION
The present invention is intended to provide SFA and UPS producing highly accurate AC output voltage. The SPA and UPS offer an increased efficiency where the accuracy is nonessential. The SPA or UPS can be built using only two switches. A sinusoidal current charging a battery is often inherent as no additional power components are required.
An instantaneously interruptible power source (I
2
PS) is introduced in this disclosure and the disclosure of the co-pending application titled “Low-Cost Switching Power Amplifier and Uninterruptible Power System with Sinusoidal Output,” filed on even date herewith. 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. Usually, accuracy of the output voltage produced by the UPS is nonessential. However, the employment of the bi-directional I
2
PS, in place of a traditional UPS, results in reduced power dissipation. A less frequent correction of the output voltage is necessary. The I
2
PS is unidirectional, unless otherwise noted.
The unidirectional or bi-directional I
2
PS according to the present invention converts a supply voltage or voltages into an AC output voltage. In one embodiment, a converter means converts the supply voltage or voltages into a primary current. A transformer means has a primary winding with the primary current applied thereto and a secondary winding for providing a secondary current in response to the primary current. A capacitive means provides the AC output voltage. A switching means selectively applies the secondary current to the capacitive means. In another embodiment, an inductive means provides a return voltage or voltages. A first switching means selectively applies the supply voltage or voltages to the inductive means. A rectifying means limits the return voltage or voltages. A capacitive means provides the AC output voltage. A second switching means selectively applies the AC output voltage to the inductive means. In yet another embodiment, a converter means converts the supply voltage or voltages into a primary voltage. A transformer means has a primary winding with the primary voltage applied thereto, and a secondary winding with a tap for providing a secondary voltage in response to the primary voltage. An inductive means is coupled to the tap for attaining a current and providing a return voltage or voltages. A rectifying means limits the return voltage or voltages. A capacitive means provides the AC output voltage. A switching means is coupled to the secondary winding for selectively applying the current to the capacitive means. In still another embodiment, a voltage source provides the supply voltage or voltages. An inductive means attains a current and provides a return voltage or voltages. A switching means selectively applies the current to the voltage source. A rectifying means limits the return voltage or voltages when the current is substantially equal to zero. A capacitive means provides the AC output voltage in response to the current.
A corrective current is equal to at least a portion of an inductive means current attained by the inductive means. The corrective current is inherently interrupted. Specifically, the respective switching means selectively applies the inductive means current to the output capacitor. When the switching means is conductive, the corrective current is equal to the inductive means current. Otherwise, the corrective current is zero. The inductive means comprises at least one inductor and/or transformer. The inductive means current is continuous if an inductor is used. Conversely, a primary current of a transformer can be interrupted. In particular, a flyback transformer provides a secondary current when the primary current is interrupted, and vice versa. Therefore, one current continues to flow in the form of the other current.
The corrective current recharges the output capacitor. Specifically, a current flowing through the output capacitor is equal to a difference between the corrective current and the output current of the I
2
PS. The latter current may be zero since no minimum load is required. Any bi-directional I
2
PS is capable of charging the battery when a low frequency voltage, in particular line voltage, is applied across the output capacitor. Preferably, the charging is carried out at both halves of the AC voltage so that an average value of the charging current drawn from the AC source is zero. Moreover, the bi-directional I
2
PS can produce quasi- or pure-sinusoidal charging current. Obviously, any bi-directional I
2
PS can operate as a unidirectional I
2
PS. A conventional power supply can be then substituted for the battery.
Two types of the I
2
PSs can be distinguished according to presence of the switching means between the inductive means and the output capacitor. In one type, the switching means effectively separates both parts. Therefore, the inductive means may consist of a flyback transformer to attain the corrective current and to provide for line isolatio
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