Continuous power source with bi-directional converter

• US 4,277,692 A
• Filed: 06/04/1979
• Issued: 07/07/1981
• Est. Priority Date: 06/04/1979
• Status: Expired due to Term

• Current Assignee: TAB Products Company LLC (H S Morgan Limited Partnership)
• Original Assignee: TAB Products Company LLC (H S Morgan Limited Partnership)
• Inventors: Small, Kenneth T.
• Primary Examiner(s): SHOOP JR, WILLIAM M
• Application Number:
  US06/045,573
• Time in Patent Office: 764 Days
• Field of Search: 307/64, 307/66, 363/96, 363/97, 363/131, 363/133, 363/134, 363/135, 363/139
• US Class Current: 307/66
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02M 7/797 using semiconductor devices only
• CPC Class Codes: Y02B 70/30 Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
• CPC Class Codes: Y04S 20/20 End-user application control systems

Abstract

A power source provides continuous AC power by employing a bi-directional converter which interfaces a rechargable DC power storage device with AC mains power and AC loads. The bi-directional converter includes a transformer having first and second windings coupled in reverse polarity through dual switching means in parallel with one another. The switching means are coupled to a state controller responsive to conditions at the AC mains terminal, the AC load terminal and the DC power terminal. There are two general operating conditions, an active condition wherein DC power is provided to the AC load, and a standby condition wherein power is recovered by the DC storage device. In the standby condition, the converter operates in a so-called "flyback" mode to recover power and to direct it to the DC storage device. In the active condition, the converter is pulse-width modulated according to a predetermined duty cycle to produce an AC sine wave output at the AC load terminals. Where the AC load includes reactive components, the converter operates to recover unused power from the load and to transfer power back to the DC power source whenever the polarity of the output voltage differs from the polarity of the output current.

Claims

1. An apparatus having first and second DC power terminals for use in transferring electric power between an AC power system and a DC power storage device, such as a battery, said apparatus comprising:

a push-pull transformer having a first winding for interfacing with said AC power system, and a second winding, said second winding having a first end tap, a second end tap and a center tap, said center tap being coupled to said first DC power terminal;

a flux storage transformer capable of storing flux for a period which is large compared to a switching frequency of current through said flux storage transformer comprising a third winding and a fourth winding, said third winding being in a first current path with third and fourth end taps and said fourth winding being in a second current path with fifth and sixth end taps, said third and fifth end taps having the same polarity, said third end tap being coupled in said first current path to said first end tap of said push-pull transformer and said sixth end tap being coupled in said second current path to said second end tap of said push-pull transformer, said fourth end tap being coupled in said first current path to said second DC power terminal and said fifth end tap being coupled in said second current path to said second DC power terminal;

first bi-directional switching means in said first current path;

second bi-directional switching means in said second current path;

means for pulse width modulating said first switching means and said second switching means on and off to direct current flow in said first and second current paths in a first direction to said first and second DC power terminals;

said first and second switching means each including a diode which is responsive to a forward bias in said first and second current paths, respectively, to permit current flow only in a second direction in said first and second current paths, respectively, through said first and second DC power terminals, said second direction being the reverse of said first direction;

said modulating means being constrained to modulate only said first switching means or only said second switching means so as to define a permissable current path alternately

(a) from said second DC power terminal in said first direction through said first current path into said third winding of said flux storage transformer in order to generate a flux, which, upon opening of said first switching means, induces a current in said fourth winding in said second direction through said second current path back to said second DC power terminal without reversing current flow polarity in said first winding of said push-pull transformer, or

(b) from said second DC power terminal in said first direction through said second current path to said fourth winding of said flux storage transformer in order to generate a flux, which, upon opening of said second switching means, induces a current in said third winding in said second direction through said first current path back to said second DC power terminal without reversing current flow polarity in said first winding of said push-pull transformer,

such that the duty cycles of said switching means determine whether net DC power flow is from or to said DC power terminals.

2. A continuous AC power source for use with a DC power storage device, such as a battery, said power source comprising:

a bi-directional converter coupled between said power storage device and AC input/output terminals, said bi-directional converter including a first transformer means for coupling to said AC input/output terminals, second transformer means coupling said first transformer means to said power storage device and operative to store flux, and bi-directional switching means;

a switch coupled between an AC mains source and said AC input/output terminals; and

a controller coupled to sense the input AC power, the output AC power and battery current and further coupled to control said switch and said converter, said converter being operative to modulate said bi-directional switching means at a rate substantially higher than the operating frequency of said AC power source to transfer power from said battery to said AC input/output terminals only when said switch is open and the polarity of the sensed load voltage is the same as the polarity of sensed load current.

3. A continuous power source according to claim 2 wherein said bi-directional switching means of said bi-directional converter further comprises a first externally controlled switch, a second externally controlled switch, a first diode coupled across said first switch, a second diode coupled across said second switch, and wherein said first transformer means comprises a first input/output transformer having push-pull primaries and a center tap, and wherein said second transformer means has a first winding coupled in a first current loop through said first switch and one primary of said first transformer, said second transformer further having a second winding coupled in a second current loop through said second switch and a second primary of said first transformer, and wherein the polarity of coupling between said first winding and said second winding is reversed, said first and second switches being coupled to a first terminal of a DC power source and said center tap of said first transformer being coupled to the other terminal of said DC power source.

4. In a power source having a bi-directional converter, a controller coupled to said bi-directional converter, a battery coupled to said converter, and AC input/output terminals coupled to said converter, a method for converting DC power to AC power and AC power to DC power, said method comprising the steps of:

monitoring the voltage phase and level of an AC source across said input/output terminals;

monitoring the voltage phase of an AC load, across said input/output terminals;

establishing a current through push-pull windings on the battery side of an input/output transformer which is coupled to said input/output terminals, said current being established by a second transformer which is capable of storing flux sufficient to sustain continuous current flow at an intended AC operating frequency, said second transformer having a first winding and a second winding, said first and second windings being interactive and in reverse polarity to one another relative to said push-pull windings;

monitoring the current established through said input/output transformer as a consequence of said flux; and

in response to monitored current and voltage, causing a first current through said first winding of said second transformer to switch on and off according to a preselected duty cycle and at a rate substantially higher than said intended AC operating frequency to induce a second current in said second winding to flow in a reverse sense relative to a source of current through said second transformer, said duty cycle being selected to supply either net power to said AC load or recover net power for charging said battery.

5. In a circuit for transferring power bi-directionally between an AC source or load and a DC storage device such as a battery, a method for transferring electrical power therebetween comprising:

pulse width modulating current into a flux storage device at a switching frequency substantially higher than a desired AC operating frequency and controlling said pulse width modulating to establish said AC operating frequency; and

suppressing with flux storage substantially all transient power components at frequencies substantially greater than said operating frequency such that power is generated substantially only at said operating frequency and with a desired waveform.