Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-07-18
2004-06-22
Sherry, Michael (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S133000, C363S097000, C363S056060
Reexamination Certificate
active
06754091
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an apparatus and method of power conversion to efficiently convert a DC voltage to a high frequency and high voltage AC waveform with high power capability for a variety of applications, including pollution control, environmental remediation equipment, and medical apparatus. Specifically, the present invention relates to an optically controlled power converter which incorporates push-pull technology and an efficient transformer (with a 0.999% coupling) to produce a high voltage and high frequency waveform for a load (such as, for example, a dielectric barrier plasma discharge) by conditioning the input power supplied to the load while also recovering and storing unused converted energy, for subsequent use by the load.
BACKGROUND OF THE INVENTION
High frequency and high voltage waveforms with high power capability are used in various industrial, commercial and military applications, such as in environmental remediation equipment and processes.
In the past, equipment for the creation of such waveforms required the use of series resonant converters, which are electrically inefficient because of the circuit topology employed. A series resonant converter uses a step-up transformer with a high leakage inductance to resonate with the load capacitance. Additional resonant capacitors are located on the transformer primary. The transformer conducts electricity for the full 360 degree cycle. In such systems, the winding resistance of the primary and secondary transformer windings, along with the losses of the oscillating circuitry, contribute to an inordinately high total energy loss. Thus, for example, a typical prior art system designed to deliver 15 kilowatts (kW) is likely only to deliver 3 kW of power to the load. Another disadvantage of series resonant converters is that they must employ switching transistors to switch for a full 180 degree conduction angle and operate almost exactly at the resonate frequency to avoid large destructive transient voltages. Finally, these types of systems are bulky, heavy, require large amplifiers to drive loads through variable frequencies, are limited in output power, and are quite expensive to operate. Thus, a highly efficient, high frequency power converter is needed for applications which require a large amount of power.
Accordingly, it is an object of the present invention to provide high frequency, high voltage AC power that includes operation at up to 25 kHz, 25 kW with high efficiencies.
It is another object of the present invention to provide for efficiencies up to 85%.
It is another object of the present invention to provide variable power (to 25 kW) by changing the pulse duration of pulse-pairs, by regulating the applied voltage.
It is still another object of the present invention to match the timing of the switching transistors to the timing of the load, to optimize power transfer.
It is still another object of the invention to vary the voltage by changing the individual pulse width of the power switching transistors.
It is yet another object of the present invention to control power switching with the use of insulated gate bipolar transistors (IGBTs).
It is yet still another object of the present invention to provide a pulse width modulated, push-pull driven parallel resonant converter which has an energy recovery system.
It is yet still another object of the present invention to provide a pulse width modulated, push-pull driven parallel resonant converter with an active free-wheel.
It is an additional object to provide a transformer: (1) which is highly efficient; (2) has a better than 0.999 coupling coefficient; (3) in which both sides of the transformer receive power and transmit power on both sides of the positive and negative sine wave; and (4) which has multiple windings arranged such that the high voltage output is shielded by components near ground potential which, in turn, permits higher voltage with improved efficiency.
It is an additional object of the present invention to provide a step up power converter using transistors configured in a push-pull circuit with a multiple winding transformer to couple power efficiently to a resonant load.
It is a further object of the present invention to provide a step up power converter which drives any load by conditioning the input power supplied to the load while also recovering and storing unused energy for subsequent use by the load.
Additional design advantages and novel features of the invention will be evident from the drawings and the description set forth herein.
SUMMARY OF THE INVENTION
The present invention is a highly efficient, high frequency power generator for applications which require a large amount of power (over 5 kW) in either a pulse or continuous mode. The present invention utilizes an optically controlled power converter to control kilowatts (or more) of supplied power in microseconds by employing an input rectifier, an energy storage network, a resonant power switching mechanism, control electronics optically coupled to the resonant power switching mechanism, a coupling transformer, a secondary oscillating circuit having the load, and electronics for energy recovery. The power converter of the present invention employs pulse width modulation techniques to deliver short pulses of energy to a secondary oscillating circuit (which is coupled to the load to be driven) to provide regulation and control. The electrically controllable conduction angle of the secondary oscillating circuit determines the amount of energy delivered to the load and, thus, can be used to regulate the output voltage. The resonant power switching mechanism employs a free-wheel transistor which allows the remaining energy in the current limiting inductor included in the transformer primary circuit to be returned to an energy storage capacitor via the energy recovery network, maintaining a high system efficiency in addition to avoiding the large transients from off-frequency operation.
The transformer of the present invention has a better than 0.999 coupling coefficient. It has multiple windings arranged such that the high voltage output is shielded by components near ground potential which, in turn, permits higher voltage with improved efficiency. Further, both sides of the transformer receive power and transmit power on both sides of the positive and negative sine wave.
The novel features of the present invention will become apparent to those of skill in the art upon examination of the detailed description or can be learned by practice of the invention. It should be understood, however, that the detailed description is provided for illustration purposes only. Various changes and modifications within the scope of the invention will become apparent to those of skill in the art from the detailed description of the invention and claims that follow.
REFERENCES:
patent: 5293308 (1994-03-01), Boys et al.
patent: 5381327 (1995-01-01), Yan
patent: 6018467 (2000-01-01), Majid et al.
Reass William A.
Schrank Louis
Laxton Gary L.
Morgan DeWitt M.
Sherry Michael
The Regents of the University of California
Wilson Ray G.
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