CuK DC-to-DC switching converter with input current shaping for unity power factor operation

• US 5,442,539 A
• Filed: 10/02/1992
• Issued: 08/15/1995
• Est. Priority Date: 10/02/1992
• Status: Expired due to Term

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Brkovic, Milivoje, Cuk, Slobodan
• Primary Examiner(s): STEPHAN, STEVEN L
• Application Number:
  US07/956,669
• Time in Patent Office: 1,047 Days
• Field of Search: 363/16, 363/37, 363/89
• US Class Current: 363/89
• CPC Class Codes: H02M 3/005 using Cuk converters

Abstract

A DC voltage to a load is provided from a rectified AC power line source with unity power factor using Cuk dc-to-dc switching converter, either unisolated or isolated extensions, operated as an automatic current shaper with unity power factor performance. This is obtained by operating the Cuk converter in a discontinuous inductor current mode (DICM) at a constant switching frequency and constant duty ratio without input current feedback control customarily used, but operating in an open-loop fashion. Even though the Cuk converter is operated in DICM, its input current is nonpulsating and flowing throughout the switching cycle, unlike other converters having pulsating input current in DICM, thus reducing input harmonic currents due to switching frequency and its harmonics. Further improvement is obtained and even the remaining ripple in the input current is entirely eliminated to result in ideal, clean, harmonic-free input current waveform with unity power factor performance, when the coupled-inductor and/or integrated magnetics extensions of the Cuk converter conditions are implemented. They could be operated at low to moderate switching frequency, thus providing high efficiency and without the need for additional input filtering customarily used in other converters.

Claims

1. A process for ideally providing a DC voltage to a load from a rectified AC power line source with unity power factor using a Cuk dc-to-dc converter which comprises

an input inductance, an energy transfer capacitance, an output inductance, and an energy storage capacitance in parallel with a load,

means for connecting said input inductance, said energy transfer capacitance, said output inductance and said load in series to form a series circuit,

said series circuit having a junction between said input inductance and said energy transfer capacitance, and a junction between said energy transfer capacitance and said output inductance,

and switching means for alternately connecting said junction between said input inductance and said energy transfer capacitance, and said junction between said energy transfer capacitance and said output inductance, to return current paths for said rectified AC power line source and load,

said process comprising operation of said switching means in a discontinuous inductor current mode at a constant switching frequency with a controlled duty ratio which remains constant for a given condition of AC power line voltage and load current, thereby providing ac-to-dc conversion with unity power factor, and making the average input current to the Cuk converter directly proportional to rectified AC power line voltage without any need for input current feedback control,

said Cuk converter having nonpulsating input current even in discontinuous inductor current mode unlike all other switching converters having pulsating input current in discontinuous inductor current mode, thereby minimizing high frequency harmonic currents fed back to the AC line.

2. A process as defined in claim 1 wherein said Cuk converter is provided with an energy transferring capacitance that is smaller by two orders of magnitude than said energy storage capacitor, whereby the need for special circuitry to limit the high input in-rush current during start-up or shorted load conditions is obviated.

3. A process as defined in claim 1 wherein said input and output inductances of said Cuk dc-to-dc converter are coupled on a common core designed to provide zero-ripple current through said input inductor, thereby eliminating the high frequency harmonic ripple currents through said input inductance entirely without the need for additional input current filtering and with input inductance a few orders of magnitude smaller than required for the same zero ripple condition without coupling, thereby minimizing current distortion occurring at cusps of AC line voltage without the need to increase switching frequency.

4. A process as defined in claim 3 wherein said energy transfer capacitance is divided into two capacitances, and further comprises an isolation transformer having a primary winding connecting first of said two capacitances to said return current path for said source and having a secondary winding connecting a second of said two capacitances to said return current path for said load.

5. A process as defined in claim 4 wherein said input and output inductances of said Cuk converter are coupled on a single magnetic core together with said isolation transformer and designed to meet zero-ripple conditions simultaneously on input and output inductances, thereby eliminating high frequency harmonic currents from both input and output without the need for additional filtering.

6. A process as defined in claim 1 further comprising operation of said Cuk dc-to-dc converter with feedback voltage control of said duty ratio to regulate said DC voltage against AC line voltage and load current changes.