Auxiliary quasi-resonant dc tank electrical power converter

• US 20060109694A1
• Filed: 07/01/2005
• Published: 05/25/2006
• Est. Priority Date: 11/24/2004
• Status: Active Grant

• Current Assignee: Fang Z. Peng
• Original Assignee: Fang Z. Peng
• Inventors: Peng, Fang Z.
• Granted Patent: US 7,126,833 B2
• Time in Patent Office: Days
• US Class Current: 363/37
• CPC Class Codes: H02M 7/4826 operating from a resonant DC source, i.e. the DC input voltage varies periodically, e.g. resonant DC-link inverters

Abstract

An auxiliary quasi-resonant DC tank (AQRDCT) power converter with fast current charging, voltage balancing (or charging), and voltage clamping circuits is provided for achieving soft-switched power conversion. The present invention is an improvement of the invention taught in U.S. Pat. No. 6,111,770, herein incorporated by reference. The present invention provides faster current charging to the resonant inductor, thus minimizing delay time of the pulse width modulation (PWM) due to the soft-switching process. The new AQRDCT converter includes three tank capacitors or power supplies to achieve the faster current charging and minimize the soft-switching time delay. The new AQRDCT converter further includes a voltage balancing circuit to charge and discharge the three tank capacitors so that additional isolated power supplies from the utility line are not needed. A voltage clamping circuit is also included for clamping voltage surge due to the reverse recovery of diodes.

Claims

1. An auxiliary quasi-resonant dc tank converter, comprising:

an ac power supply and an ac bus;

a dc power supply for providing dc current to a dc bus;

an inverter having at least one phase leg connected to said ac bus and connected across said dc bus, said inverter having at least one main switching device per phase leg;

a quasi-resonant dc tank circuit coupled in parallel with said dc power supply for generating a quasi-resonant voltage across said dc bus, said quasi-resonant dc tank circuit including,

an upper resonant capacitor and a lower resonant capacitor connected in series as a resonant leg,

a first dc tank capacitor, a second dc tank capacitor, and a third dc tank capacitor connected in series as a tank leg,

an auxiliary quasi-resonant circuit coupled across the junction of said upper and lower resonant capacitors, the junction of said first and second dc tank capacitors and the junction of said second and third dc tank capacitors, said lower resonant capacitor being coupled across said dc bus, said resonant leg being coupled across said tank leg, and

a first clamping means coupled across said upper resonant capacitor.

2. The auxiliary quasi-resonant dc tank converter of claim 1 wherein said auxiliary quasi-resonant circuit further comprises a resonant inductor.

3. The auxiliary quasi-resonant dc tank converter of claim 2 wherein said auxiliary quasi-resonant circuit further comprises a series combination of said resonant inductor and auxiliary switching means.

4. The auxiliary quasi-resonant dc tank converter of claim 3 wherein said auxiliary switching means further comprises a first auxiliary resonant switch and diode to provide positive resonant current through said resonant inductor and a second auxiliary resonant switch and diode to provide negative resonant current through said resonant inductor.

5. The auxiliary quasi-resonant dc tank converter of claim 4 wherein said auxiliary quasi-resonant circuit further comprises a second clamping means comprising a series combination of diodes coupled across said tank leg to clamp the voltage on said first and second auxiliary switches.

6. The auxiliary quasi-resonant dc tank converter of claim 1 wherein said first clamping means further comprises a clamping switch and clamping diode.

7. The auxiliary quasi-resonant dc tank converter of claim 1 further comprising a charge circuit coupled across the junction of said first and second dc tank capacitors and the junction of said second and third dc tank capacitors

8. The auxiliary quasi-resonant dc tank converter of claim 7 wherein said charge circuit further comprises a transformer coupled across said resonant inductor feeding a diode bridge to charge said second tank capacitor.

9. The auxiliary quasi-resonant dc tank converter of claim 8 wherein the primary of said transformer provides resonant inductance to the circuit.

10. The auxiliary quasi-resonant dc tank converter of claim 7 wherein said charge circuit further comprises an outside dc power supply to maintain voltage in said second tank capacitor.

11. The auxiliary quasi-resonant dc tank converter of claim 1 wherein each phase leg of said inverter includes two series-connected main switching devices each coupled with an anti-parallel diode.

12. The auxiliary quasi-resonant dc tank converter of claim 1 wherein a dc power supply is connected across said dc bus, said dc power supply comprises a diode rectifier bridge for receiving the input power from a power system and for providing dc voltage.

13. The auxiliary quasi-resonant dc tank converter of claim 1 wherein a dc power supply is connected across said dc bus, said dc power supply comprises a thyristor rectifier bridge for receiving the input power from a power system and for providing dc voltage.

14. The auxiliary quasi-resonant dc tank converter of claim 1 wherein a dc power supply is connected across said dc bus, said dc power supply comprises a converter for receiving the input power from a power system and for providing dc voltage, said converter having at least one main switching device per phase leg.

15. The auxiliary quasi-resonant dc tank converter of claim 1 wherein each phase leg of said inverter has its own resonant dc tank circuit and is connected to each other through magnetic coupling, and further the tank leg of the quasi-resonant dc tank circuit of each phase leg is coupled to each other.

16. A method for controlling an auxiliary quasi-resonant dc tank converter for generating a quasi-resonant dc bus across an inverter without transmitting real power and carrying dc current, said converter comprising an ac power supply and an ac bus, a dc power supply for providing dc current to a dc bus, an inverter having at least one phase leg connected to said ac bus and connected across said dc bus, said inverter having at least one main switching device per phase leg;

a quasi-resonant dc tank circuit coupled in parallel with said dc power supply for generating a quasi-resonant voltage across said dc bus, said quasi-resonant dc tank circuit including an upper resonant capacitor and a lower resonant capacitor connected in series as a resonant leg, a first dc tank capacitor, a second dc tank capacitor, and a third dc tank capacitor connected in series as a tank leg, an auxiliary quasi-resonant circuit coupled across the junction of said upper and lower resonant capacitors, the junction of said first and second dc tank capacitors and the junction of said second and third dc tank capacitors, said lower resonant capacitor being coupled across said dc bus, said resonant leg being coupled across said tank leg, and a first clamping means coupled across said upper resonant capacitor, a second clamping means to clamp the voltage on said first and second auxiliary switches at tank voltage, comprising the steps of;

turning on said auxiliary quasi-resonant circuit to establish a quasi-resonant current to a specific level for assisting resonance of said dc bus from the dc tank voltage of said dc tank leg to zero when said clamping diode conducts or when a relatively low current flows through said clamp switching device;

gating off said clamp switching device when said quasi-resonant current reaches a specific level or when a high current flows through said clamp switching device to start a resonance on said dc bus;

clamping said dc bus to zero voltage using said second clamping means;

turning on main switching devices of said inverter when a reverse resonant current is needed to boost the resonant dc bus voltage back to the dc tank voltage;

maintaining said auxiliary quasi-resonant circuit on until said reverse resonant current reaches a specific level;

changing state of said inverter to a predetermined setting;

allowing said dc bus to resonate back to the tank voltage of said dc tank leg;

turning on said clamp switching device after the voltage of said dc bus reaches the tank voltage of said dc tank leg; and

turning off said auxiliary quasi-resonant circuit when the resonant current through said resonant inductor is substantially zero.