WO2008005999A1

WO2008005999A1 - Push-push inverter

Info

Publication number: WO2008005999A1
Application number: PCT/US2007/072783
Authority: WO
Inventors: Tranh Nguyen
Original assignee: Tranh Nguyen
Priority date: 2006-07-03
Filing date: 2007-07-03
Publication date: 2008-01-10

Abstract

A line-isolated inverter comprising two line-isolated SMPSs (SMPS1, SMPS2) and two added switches (Q1, Q2). Each SMPS (SMPS1, SMPS2) pushes a current into the load (R1) while the other SMPS's added switch provides return path for the load current, during the half-period it is active. The SMPSs (SMPS1, SMPS2) operate in turn to provide AC output voltage.

Description

APPLICATION FOR INTERNATIONAL PATENT

Push-Push Inverter

Inventor:

Tranh T. Nguyen

1552 Magnolia Avenue

Rohnert Park, CA 94928

A Citizen of United States of America

Push-Push Inverter

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of U.S. Provisional Application No. 60/818,473 filed on JuI. 03, 2006, entitled "Push-Push Inverter", specification of which is herein incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to the technical field of power conversion, and more particularly, to a DC-AC inverter..

BACKGROUND

[0003] Typically, a line-isolated inverter has an isolated DC-DC switch-mode converter to transform an available DC power source voltage into appropriate DC voltage such as 160V, followed by a H-bridge inverter, Figure 1. Such a conventional inverter is rather inefficient and large due to double conversion, the first one being a DC-DC conversion needed for voltage level adaptation and isolation, and the other DC-AC conversion. There is an intermediary DC bus due to the need for storing intermediary energy, necessarily DC form. Need for energy storage increases with power level of such conventional inverters, hence more weight, size and cost. [0004] Thus there is a need for simpler and more efficient line-isolated inverters.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide a switch-mode inverter capable of generating sine wave output at high efficiency.

[0006] To achieve the object, the DC input voltage is modulated according to a full- wave rectified reference sine wave at high switching frequency and propagated through two high-frequency power transformers but only one at a time, each one for each half sine portion of the sine wave. Output rectifiers and high-frequency reconstruction filters rectify and reconstruct each half sine one at a time. Two switches each controlled to turn on and off at line frequency to provide return paths for the half sine voltages as appropriate. The inverter thus can be considered as two modulated-reference off-line switched-mode power supplies (SMPS) working in push-push configuration to convert a DC voltage into isolated AC sine wave at the output, something that an SMPS cannot do, as they are suitable for providing only DC output voltages.

[0007] Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention, as defined in the claims, can be better understood with reference to the following drawings. The drawings are not necessarily to scale, emphasis instead being placed on clearly illustrating the principles of the present invention.

[0009] FIG. 1 is a block diagram of prior art line-isolated inverter.

[0010] FIG. 2 is a diagram illustrating the invented line-isolated inverter of the invention.

[001 1] FIG. 3 is a schematic illustrating an alternate embodiment of the invention.

[0012] FIG. 4 is a schematic illustrating an alternate embodiment of the invention.

[0013] FIG. 5 is a schematic illustrating an alternate embodiment of the invention.

[0014] FIGS. 6A-6C illustrate waveforms at the outputs of the inverter of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] With reference to FlG. 2, the invented push-push inverter comprises two identical line-isolated power converters also called switch-mode power supplies (SMPS) SMPSl and SMPS2 working in tandem to provide a sine wave AC voltage to a load Rl . The power converters SMPS1-SPMS2 are conventional SMPS modified with a switch Ql located at or near its output terminals 10 to act as a short-circuit to ground reference when needed, which is during one of the two half-sines of an ideally sinusoidal reference voltage Vl, Figure 6A, while the added switch Q2 of SMPS2 acts as a short-circuit to ground reference during the other half sine. SMPSl is only active during the positive half-sine of the reference voltage Vl during which interval switch Q2 is closed so that a half-sine current flow from left to right in the load Rl and returns via inductor L2 and switch Q2. Vice-versa, SMPS2 is active during the negative portion of the reference voltage Vl during which interval switch Ql is closed so that a half-sine current flows from right to left in the load Rl, Figure 6B, and returns via inductor Ll and switch Ql . Thus the load Rl see an alternative current, Figure 6C.

[0016] The power modulators 12 and 12' of SMPS1-SMPS2 are conventional power modulators of conventional SMPSs. Thus depending on the specifics of the applications, SMPSl and SMPS2 can be a conventional fly-back converter, forward converter, half- bridge converter, push-pull converter, or full-bridge converter, etc... controlled with pulse-width modulation, pulse frequency modulation, phase shift modulation etc... Indeed there is no inherent limitation as to modulation scheme or circuit topology of SMPS that can be used in the invented push-push inverter. Figure 2 shows dual rectifiers Dl, D3 and D2, D4 usually found in push-pull, half-bridge or full bridge SMPSs. Similarly, two resonant or quasi-resonant SMPSs modified with the shorting switches Q1 -Q2 can be used in the invented push-push inverter. SMPSs designed with zero-voltage switching ZVS or zero-current switching ZCS can also be advantageously used. Typically silicon- carbide rectifiers are used in the inverter for their virtually zero reverse recovery time, but other rectifiers with appropriate snubbers may be suitable, depending on the application. [0017] Block 300 is a opto-coupler isolated synchronizer which detects the zero- crossing instances of the reference sine wave Vl to provide appropriately timed drive signals to complementary switches Q1-Q2.

[0018] Not shown for clarity in the description of the invented inverter are the respective feedback circuits of SMPSl -SMPS2. Such conventional feedback circuits are familiar to the skilled in the art, therefore need no further description here. [0019] One limitation of the inverter described above is its inability to properly drive a complex load. However that limitation is irrelevant in the case of grid-tied inverter which is the primary application of the invented inverter. In exchange for the complexity of driving MOSFET-based synchronous rectifiers inside SMPS1-SMPS2, complex load can be driven. Figure 3 illustrates such an inverter for complex load. [0020] While previous embodiments have their reference voltage Vl located on the primary side, i.e. on the same side as the power modulator 12, the designer can also choose to locate the control circuit on the secondary side, Figure 4. Similarly, the added switches Q1-Q2 may be located before or after the current smoothing inductors L1-L2, if they are present on the output side of the SMPSs, see Figure 5. The skilled artisan knows that inductors must be present in switch-mode power converters to either store some energy or to smooth a current. They can be located on the primary side or on the secondary side of the isolation transformers Tl , T2, or in the case of flyback converters, integrated into the isolation transformers T1-T2.

[0021] From the description above, a number of advantages of the invented inverter become evident:

[0022] (a) Only an added switch and its simple control is necessary to use conventional SMPSs to implement the invented inverter. Thus any SMPS manufacturer can easily make this new type of inverter.

[0023] (b) The modulation of SMPS at the primary side results in lower switching and copper losses for the high frequency transformers used in the invented inverter, therefore they can be smaller and even more efficient.

[0024] (c) The opto-coupler isolated synchronizer switches at line frequency therefore it is very inexpensive. Likewise the added switches operate at line frequency therefore their switching losses are extremely low.

[0025] (d) All topologies of SMPS are equally usable in the invented inverter.

[0026] (e) The basic control scheme of the invented inverter is that of conventional

SMPS, with a minor addition of a full-wave rectification circuit and a synchronization circuit well known to the skilled artisan.

SUMMARY, RAMIFICATION AND SCOPE

[0027] Accordingly the reader can see that the invented switch-mode inverter embodies only two additional switches and a synchronization circuit compared to conventional SMPSs, yet it is capable supplying high power AC voltage from an isolated DC power source, which can simply be rectified AC from mains. [0028] Although the figures illustrate only generation of single phase AC, multiple switch-added SMPSs can form a polyphase isolated inverter. Inverters are rather generic in terms of electronic circuit. They can be considered also as audio amplifiers which are fundamental building blocks of most analog electronic systems including servo control, motor drive, etc...

[0029] While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will occur to those of skill in the art without departing from the spirit and scope of the invention herein. Therefore it must be understood that the illustrated embodiments have been set forth for the purposes of examples and it should not be taken as limiting the invention as defined by the following claims.

[0030] The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself.

[0031] In addition to the equivalents of the claimed elements, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements. [0032] Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.

Claims

CLAIMSWhat is claimed is

1. A line-isolated switch-mode inverter converting a DC voltage into AC voltage comprising a first and a second SMPSs, each with an added switch at or near its output, the first SMPS for providing a half sine voltage to push a current in a first direction into a load while the added switch of the second SMPS provides return path to the load current back to the first SMPS, and vice versa, the second SMPS for providing a half sine voltage to push a current in a second direction into a load while the added switch of the first SMPS provides return path to the load current back to the second SMPS, each SMPS having at least one rectifier in its output section, which has two output terminals, a synchronization circuit for turning on the first and second added switches during predetermined intervals, wherein the alternating operation of the first and second SMPSs provide AC voltage at the load.

2. The inverter of claim 1 wherein its SMPSs are line-isolated SMPS such as flyback, forward, half-bridge, push-pull, full bridge.

3. The inverter of claim 1 wherein its SMPSs operate in at least one of the following modes: hard switching, zero-voltage-switching, zero-current-switching, zero- transition-switching, resonant switching, quasi-resonant switching.

4. The inverter of claim 1 wherein its SMPSs operate in at least one of the following modulation methods: pulse width modulation, pulse frequency modulation, phase- shifted modulation, hysteretic modulation, self-oscillating modulation.

5. The inverter of claim 1 wherein its SMPSs operate in pulse frequency modulation during predetermined intervals and in pulse width modulation in other predetermined intervals.

6. The inverter of claim 1 wherein its SMPSs have synchronous rectifiers in their output section.

7. The inverter of claim 1 wherein the added switch to each SMPS is located near its rectifiers.

8. The inverter of claim 1 wherein the added switch to each SMPS is located at its output terminals.

9. The inverter of claim 1 wherein each SMPS comprises at least one high frequency isolation transformer.

10. The inverter of claim 1 wherein the added switches are of one of the following types: MOSFET, IGBT, thyristor, controlled silicon rectifier, bipolar transistor, modulated conductivity transistor, solid-state switch.