Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Reexamination Certificate
2000-04-06
2001-09-25
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
C307S105000
Reexamination Certificate
active
06295216
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to power supply apparatus and methods of operation thereof, and more particular, to rectifier circuits and methods.
Rectifier circuits are commonly used in power supply apparatus, such as uninterrupted (or “uninterruptible”) power supplies (UPSs), motor drives, and the like, to produce a DC voltage from an AC input voltage provided from an AC power source, such as a utility line. For example, in online UPS applications, a passive rectifier may be used to generate a DC voltage from a utility AC voltage, with the DC voltage being regulated and transformed back into an AC output voltage to provide a clean, regulated source of AC power for devices such as computers or telecommunications equipment.
One problem often associated with the use of passive rectifier circuits is the generation of undesirable levels of current harmonics at the AC input of the rectifier, i.e., currents having frequencies that are multiples of the fundamental frequency of the AC input voltage. For example, a typical passive three-phase rectifier circuit may generate high levels of fifth, seventh and higher order odd harmonics. The generation of such harmonics has become the subject of increasing concern, as these harmonic currents can result in the need for increased current carrying capability in the AC system.
Techniques have been proposed for reducing the magnitude of such harmonic currents. These techniques include the use of passive or active filters that are coupled to the input of the rectifier and which suppress the harmonic currents generated at the rectifier input. The generation of harmonics may also be reduced by using active rectification circuits, for example, switched rectifier circuits that can be controlled to reduce the magnitude of harmonic currents at the rectifier input.
Although these techniques can be successful in reducing harmonics, they can have various disadvantages. Passive filters typically are frequency selective, i.e., only suppress a selected harmonic. Consequently, multiple passive filter circuit may be needed to suppress multiple harmonics. Active filtering and rectification schemes may require complex switching networks and associated control electronics.
SUMMARY OF THE INVENTION
According to embodiments of the invention, improved control of harmonic input currents generated at the input of a rectifier circuit may be achieved by using a selective harmonic current inducing circuit that induces a harmonic component in current delivered to a load coupled to the rectifier circuit output. Preferably, the phase and magnitude of the induced harmonic current is controlled to suppress a selected harmonic current at the rectifier input. For example, a sixth harmonic current may be injected into a DC current flowing between a passive three-phase rectifier circuit and a load, Such as an inverter or battery charger. The magnitude and phase of the sixth harmonic current may be controlled such that seventh and higher order odd harmonics at the rectifier circuit input are significantly reduced. The injected sixth harmonic current preferably is generated responsive to the AC voltage at the rectifier input. As this technique may increase the magnitude of a fifth harmonic at the rectifier circuit input, a fifth harmonic filter may be coupled to the rectifier input to reduce total harmonic distortion. The harmonic current control capability can be integrated into current or voltage regulation circuits that serve other function in the apparatus. In this manner, a relatively simple and cost effective technique for reducing overall input harmonics may be provided.
In particular, in embodiments of the invention, a power supply apparatus includes an AC input port and a rectifier circuit, coupled to the AC input port, that produces a DC voltage at a rectifier circuit output from an AC input voltage at the AC input port. The apparatus further includes a selective harmonic current inducing circuit, coupled to the rectifier circuit output, that induces a harmonic component in a current delivered to a load from the rectifier circuit output. The selective harmonic current inducing circuit may control a phase and a magnitude of the induced harmonic current component in order to achieve selective suppression of a harmonic input current at the AC input port.
According to other embodiments of the invention, the power supply apparatus further includes a filter circuit, coupled to the AC input port, that selectively suppresses a first harmonic current at the AC input port. The selective harmonic current inducing circuit controls the phase and magnitude of the induced harmonic current component such that a second harmonic current at the AC input port is suppressed. For example, for a three-phase passive rectifier circuit, the filter circuit may suppress a fifth harmonic input current, and the selective harmonic current inducing circuit may control the phase and magnitude of an induced sixth harmonic current component such that a seventh harmonic input current at the AC input port is suppressed.
According to other embodiments of the invention, a power supply apparatus includes an AC input port and a rectifier circuit, coupled to the AC input port, that produces a DC voltage at a rectifier circuit output from an AC input voltage at the AC input port. A selective harmonic inducing current regulator circuit, coupled to the rectifier output, regulates a DC component of a current delivered to a load coupled to the rectifier circuit output and selectively induces a harmonic component in the current delivered to the load. The selective harmonic inducing current regulator circuit may control a phase and a magnitude of the induced harmonic current component such that selective suppression of a harmonic input current at the AC input port is achieved.
In embodiments of the invention, the selective harmonic inducing current regulator circuit may comprise a current control circuit that controls the current delivered to the load responsive to a current reference signal. The selective harmonic inducing current regulator circuit may further include a first current reference signal generating circuit that generates a first current reference signal that commands a DC current component for the current delivered to the load. A second current reference signal generating circuit may generate a second current reference signal that commands a harmonic current component for the current delivered to the load. A combining circuit may combine the first and second reference current signals to generate a third current reference signal, which is applied to the current control circuit. The second current reference signal generating circuit may include a reference signal generating circuit, coupled to the AC input port, that generates a reference signal that is synchronized to the AC input voltage, and a phase and magnitude control circuit that generates the second current reference signal from the reference signal.
According to still other embodiments of the invention, a power supply apparatus includes an AC input port and a rectifier circuit, coupled to the AC input port, that produces a DC voltage at a rectifier circuit output from an AC input voltage at the AC input port. A filter circuit is coupled to the AC input port and suppresses a first harmonic current at the AC input port. A selective harmonic inducing current regulator circuit is coupled to the rectifier, regulates a DC component of a current delivered to a load coupled to the rectifier circuit output and selectively induces a harmonic component in the current delivered to the load to thereby suppress a second harmonic current at the AC input port.
According to other embodiments of the invention, an uninterruptible power supply (UPS) apparatus includes an AC input port and a rectifier circuit, coupled to the AC input port, that produces a rectified DC voltage at rectifier circuit output from an AC input voltage at the AC input port. A selective harmonic current inducing voltage regulator circuit, coupled to the rectifier ou
Akbari Edward
Faria Des
Grudzinski Piotr
Zhang Hong
Laxton Gary L.
Myers Bigel & Sibley & Sajovec
Powerware Corporation
Wong Peter S.
LandOfFree
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