Isolated and soft-switched power converter

• US 6,370,050 B1
• Filed: 09/20/1999
• Issued: 04/09/2002
• Est. Priority Date: 09/20/1999
• Status: Expired due to Fees

• Current Assignee: UT-Battelle LLC
• Original Assignee: UT-Battelle LLC
• Inventors: Peng, Fang Zheng, Adams, Donald Joe
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US09/399,397
• Time in Patent Office: 932 Days
• Field of Search: 363/98, 363/132, 363/127, 363/41, 363/58, 363/37, 363/16, 363/17
• US Class Current: 363/98
• CPC Class Codes: H02M 3/33576 having at least one active switching element at the secondary side of an isolation transformer
• CPC Class Codes: H02M 7/4807 having a high frequency intermediate AC stage
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

An isolated and soft-switched power converter is used for DC/DC and DC/DC/AC power conversion. The power converter includes two resonant tank circuits coupled back-to-back through an isolation transformer. Each resonant tank circuit includes a pair of resonant capacitors connected in series as a resonant leg, a pair of tank capacitors connected in series as a tank leg, and a pair of switching devices with anti-parallel clamping diodes coupled in series as resonant switches and clamping devices for the resonant leg. The power converter is well suited for DC/DC and DC/DC/AC power conversion applications in which high-voltage isolation, DC to DC voltage boost, bidirectional power flow, and a minimal number of conventional switching components are important design objectives. For example, the power converter is especially well suited to electric vehicle applications and load-side electric generation and storage systems, and other applications in which these objectives are important. The power converter may be used for many different applications, including electric vehicles, hybrid combustion/electric vehicles, fuel-cell powered vehicles with low-voltage starting, remote power sources utilizing low-voltage DC power sources, such as photovoltaics and others, electric power backup systems, and load-side electric storage and generation systems.

Claims

1. An isolated and soft-switched power converter comprising:

an isolation transformer;

primary and secondary resonant tank circuits coupled back-to-back through the isolation transformer;

each resonant tank circuit comprising a pair of resonant capacitances present in series as a resonant leg, a pair of voltage sources connected in series as a tank leg, and a pair of switching devices coupled in series as resonant switches and voltage clamping devices for the resonant leg wherein each of the resonant leg, tank leg, and pair of switching devices and voltage clamping devices are connected in parallel to each other; and

a switching controller operable for,

gating off the switching devices to cause a resonant voltage to resonant in each resonant leg, the resonant voltage repeatedly obtaining zero-voltage periods for soft-switching a device powered by the converter, and

gating on the switching devices during zero-current, zero-voltage conditions for soft-switching the switching devices of each resonant tank circuit.

2. The power converter of claim 1, wherein the switching controller is further operable for controlling a flow of electric power between the primary resonant tank circuit and the secondary resonant tank circuit by altering a resonant frequency for gating the switching devices.

3. The power converter of claim 1, wherein the switching controller is further operable for controlling a flow of electric power from the primary resonant tank circuit to the secondary resonant tank circuit by altering a duty cycle defined by a gating sequence for the switching devices of the primary resonant tank circuit, while holding the open the switching devices of the secondary resonant tank circuit.

4. The power converter of claim 3, wherein the switching controller is further operable for controlling a flow of electric power from the secondary resonant tank circuit to the primary resonant tank circuit by altering a duty cycle defined by a gating sequence for the switching devices of the secondary resonant tank circuit, while holding the open the switching devices of the primary resonant tank circuit.

5. The power converter of claim 2, wherein the switching controller is further operable for timing the gating switching devices for the primary and secondary resonant tank circuits to control a flow of electric power between the primary and secondary resonant tank circuits by controlling a phase shift between voltage waveforms generated by the primary and secondary resonant tank circuits.

6. The power converter of claim 1, wherein the switching controller is further operable for controlling a flow of electric power between the primary and secondary resonant tank circuits by altering one or more of the following:

a phase shift between voltage waveforms generated by the primary and secondary resonant tank circuits;

a resonant frequency for gating the switching devices;

a duty cycle defined by a gating sequence for the switching devices of the secondary resonant tank circuit; and

a duty cycle defined by a gating sequence for the switching devices of the primary resonant tank circuit.

7. An electric generation system comprising the power converter of claim 1, further comprising:

a DC electric power generator connected to the primary tank circuit of the power converter; and

an inverter connected to the secondary side of the power converter, the inverter for connecting the system to an electric power grid.

8. The electric generation system of claim 7, wherein the DC electric power generator comprises a battery, further comprising a rectifier connecting the electric power grid to the secondary side of the power converter for recharging the battery.

9. The electric generation system of claim 7, wherein the power converter operates to unidirectionally to deliver power from the DC electric power generator to the electric grid.

10. The electric generation system of claim 7, wherein:

the DC electric power generator comprises a battery and a second DC electric power generator configured to recharge the battery; and

the power converter operates to unidirectionally to deliver power from the DC electric power generator to the electric grid.

11. The power converter of claim 1, wherein the primary resonant tank circuit boosts an input voltage to a higher voltage and the higher voltage is applied to the isolation transformer.

12. The power converter of claim 1, further comprising an inductor coupling an input voltage source to the primary center rail.

13. An isolated and soft-switched power converter, comprising:

an isolation transformer including a primary input node, a primary output node, a secondary input node, and a secondary output node;

a primary resonant tank circuit comprising,

a primary top rail,

a primary center rail,

a primary bottom rail,

a first primary resonant capacitance present between the primary top rail and the primary center rail,

a second primary resonant capacitance present between the primary center rail and the primary bottom rail,

a first primary resonant switch connected between the primary top rail and the primary center rail,

a second primary resonant switch connected between the primary center rail and the primary bottom rail,

a first primary clamping diode connected between the primary high-voltage rail and the primary center rail,

a second primary clamping diode connected between the primary center rail and the primary bottom rail,

a first primary tank capacitor connected between the primary top rail and a primary tap node,

a second primary tank capacitor connected between the primary tap node and the primary bottom rail,

the primary center rail being connected to the primary input node of the isolation transformer, and

the primary tap node being connected to the primary output node of the isolation transformer; and

a secondary resonant tank circuit comprising,

a secondary top rail,

a secondary center rail,

a secondary bottom rail,

a first secondary resonant capacitance present between the secondary top rail and the secondary center rail,

a second secondary resonant capacitance present between the secondary center rail and the secondary bottom rail,

a first secondary clamping diode connected between the secondary top rail and the secondary center rail,

a first secondary tank capacitor connected between the secondary top rail and a secondary tap node,

a second secondary tank capacitor connected between the secondary tap node and the secondary bottom rail,

the secondary center rail being connected to the secondary input node of the isolation transformer, and

the secondary tap node being connected to the secondary output node of the isolation transformer.

14. The power converter of claim 13, wherein the secondary resonant tank circuit further comprises a second secondary clamping diode connected between the secondary center rail and the secondary bottom rail.

15. The power converter of claim 14, wherein the secondary resonant tank circuit further comprises:

a first secondary resonant switch connected between the secondary top rail and the secondary center rail; and

a second secondary resonant switch connected between the secondary center rail and the secondary bottom rail.

16. The power converter of claim 13, further comprising:

a primary bottom-rail terminal connected to the primary bottom rail for connection to a low-potential terminal of a DC voltage source;

a primary center-rail terminal for connection to a high-potential terminal of the DC voltage source; and

an inductor connected in series between the primary center-rail terminal and the primary center rail.

17. The power converter of claim 13, further comprising:

a resonant inductor connected between the primary input node of the isolation transformer and the primary output node of the isolation transformer.

18. The power converter of claim 13, wherein:

the first primary resonant capacitance comprises a discrete electrical capacitor connected between the primary top rail and the primary center rail; and

the second primary resonant capacitance comprises a discrete electrical capacitor connected between the primary center rail and the primary bottom rail.

19. The power converter of claim 13, wherein:

the first primary resonant capacitance consists essentially of stray capacitance inherently present in the first primary resonant switch and the first primary clamping diode; and

the second primary resonant capacitance consists essentially of stray capacitance inherently present in the second primary resonant switch and the second primary clamping diode.

20. The power converter of claim 13, further comprising a switching controller operable for gating the first and second primary switches to cause:

a primary resonant voltage to resonate between the first primary resonant capacitance and the second primary resonant capacitance;

a secondary resonant voltage to resonate between the first secondary resonant capacitance and the second secondary resonant capacitance; and

the secondary resonant voltage repeatedly obtaining zero-voltage periods for soft-switching a device connected between the secondary center rail and the secondary bottom rail.

21. The power converter of claim 13, further comprising a switching controller operable for soft switching of the first and second primary resonant switches by:

gating on the first primary resonant switch during current conduction by the first primary clamping diode; and

gating on the second resonant switch during current conduction by the second primary clamping diode.

22. The power converter of claim 21, wherein the switching controller is further operable for controlling a flow of electric power between the primary resonant tank circuit and the secondary resonant tank circuit by altering a resonant frequency for gating the first and second primary resonant switches.

23. The power converter of claim 21, wherein the switching controller is further operable for controlling a flow of electric power between the primary resonant tank circuit and the secondary resonant tank circuit by altering a duty cycle defined by a gating sequence for the first and second primary resonant switches.

24. The power converter of claim 15, further comprising a switching controller operable for:

soft switching of the first and second primary resonant switches by gating on the first primary resonant switch during current conduction by the first primary clamping diode, and gating on the second primary resonant switch during current conduction by the second primary clamping diode;

soft switching of the first and second secondary resonant switches by gating on the first secondary resonant switch during current conduction by the first secondary clamping diode, and gating on the second secondary resonant switch during current conduction by the second secondary clamping diode; and

timing the gating of the first and second primary resonant switches, and the first and second secondary resonant switches, to control a flow of electric power between the primary resonant tank circuit and the secondary resonant tank circuit by controlling a phase shift between voltage waveforms generated by the primary and secondary resonant tank circuits.

25. The power converter of claim 24, wherein the switching controller is further operable for controlling a flow of electric power between the primary resonant tank circuit and the secondary resonant tank circuit by altering a resonant frequency for gating the first and second primary resonant switches.

26. The power converter of claim 25, wherein the switching controller is further operable for controlling a flow of electric power between the primary resonant tank circuit and the secondary resonant tank circuit by altering a duty cycle defined by a gating sequence for the first and second primary resonant switches.

27. The power converter of claim 14, wherein:

the first secondary resonant capacitance comprises a discrete electrical capacitor connected between the secondary top rail and the secondary center rail; and

the second secondary resonant capacitance comprises a discrete electrical capacitor connected between the secondary center rail and the secondary bottom rail.

28. The power converter of claim 14, wherein:

the first secondary resonant capacitance consists essentially of stray capacitance inherently present in the first secondary clamping diode; and

the second secondary resonant capacitance consists essentially of stray capacitance inherently present in the second secondary clamping diode.

29. The power converter of claim 13, wherein the primary resonant tank circuit boosts an input voltage to a higher voltage and the higher voltage is applied to the isolation transformer.

30. An isolated and soft-switched power converter, comprising:

an isolation transformer including a primary input node, a primary output node, a secondary input node, and a secondary output node;

a primary resonant tank circuit comprising,

a primary top rail,

a primary center rail,

a primary bottom rail,

a first primary resonant capacitance present between the primary top rail and the primary center rail,

a second primary resonant capacitance present between the primary center rail and the primary bottom rail,

a first primary resonant switch connected between the primary top rail and the primary center rail,

a second primary resonant switch connected between the primary center rail and the primary bottom rail,

a first primary clamping diode connected between the primary top rail and the primary center rail,

a second primary clamping diode connected between the primary center rail and the primary top rail,

a first primary tank capacitor connected between the primary top rail and a primary bottom node,

a second primary tank capacitor connected between the primary tap node and the primary bottom rail,

the primary center rail being connected to the primary input node of the isolation transformer,

the primary tap node being connected to the primary output node of the isolation transformer,

a primary bottom-rail terminal connected to the primary bottom rail for connection to a low-potential terminal of a DC voltage source;

a primary center-rail terminal for connection to a high-potential terminal of the DC voltage source, and

an inductor connected in series between the primary center-rail terminal and the primary center rail;

a secondary resonant tank circuit comprising,

a secondary top rail,

a secondary center rail,

a secondary bottom rail,

a first secondary resonant capacitance present between the secondary top rail and the secondary center rail,

a second secondary resonant capacitance present between the secondary center rail and the secondary bottom rail,

a first secondary clamping diode connected between the secondary top rail and the secondary center rail,

a second secondary clamping diode connected between the secondary center rail and the secondary bottom rail,

a first secondary resonant switch connected between the secondary top rail and the secondary center rail,

a second secondary resonant switch connected between the secondary center rail and the secondary bottom rail,

a first secondary tank capacitor connected between the secondary top rail and a secondary tap node,

a second secondary tank capacitor connected between the secondary tap node and the secondary bottom rail,

the secondary center rail being connected to the secondary input node of the isolation transformer, and

the secondary tap node being connected to the secondary output node of the isolation transformer; and

a switching controller operable for gating the first and second primary switches to cause

a primary resonant voltage to resonate between the first primary resonant capacitance and the second primary resonant capacitance,

a secondary resonant voltage to resonate between the first secondary resonant capacitance and the second secondary resonant capacitance, and

the secondary resonant voltage repeatedly obtaining zero-voltage intervals for soft-switching a device connected between the secondary center rail and the secondary bottom rail.

31. The power converter of claim 30, wherein the switching controller is further operable for soft switching of the first and second primary resonant switches by:

gating on the first resonant switch during current conduction by the first primary clamping diode; and

gating on the second resonant switch during current conduction by the second primary clamping diode.