Optimal trajectory control for LLC resonant converter for LED PWM dimming

• US 9,276,480 B2
• Filed: 12/24/2013
• Issued: 03/01/2016
• Est. Priority Date: 04/23/2013
• Status: Active Grant

• Current Assignee: Virginia Tech Intellectual Properties, Inc.
• Original Assignee: Virginia Polytechnic Institute and State University
• Inventors: Feng, Weiyi, Lee, Fred C., Ji, Shu
• Primary Examiner(s): Houston, Adam
• Application Number:
  US14/140,008
• Publication Number:
  US 20140312789A1
• Time in Patent Office: 798 Days
• Field of Search: 315/186
• US Class Current: 1/1
• CPC Class Codes: H02M 1/0058 by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826
• CPC Class Codes: H02M 3/01 Resonant DC/DC converters
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 3/33561 having more than one ouput with independent control
• CPC Class Codes: H02M 3/33571 Half-bridge at primary side of an isolation transformer
• CPC Class Codes: H05B 45/327 Burst dimming
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/39 Circuits containing inverter bridges
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

Pulse width modulation is provided for controlling a resonant power converter, particularly for dimming of light emitting diode arrays without loss of efficiency. Dynamic oscillation due to the beginning of a pulse width modulated pulse burst is limited by shortening of the first and/or last pulse of a pulse bust such that the first pulse of a subsequent pulse burst close to or to connect with a full load steady-state voltage/current trajectory of the power converter. Pulse shortening made be made substantially exact to virtually eliminate dynamic oscillation but substantial reduction in dynamic oscillation is provided if inexact or even performed randomly.

Claims

1. A method of operating a resonant power converter, said method comprising steps of

generating a pulse waveform comprising pulses at a first frequency for controlling generation of switching signals to control application of input power to said power converter,

generating a pulse width modulated signal comprising pulses of controllable duty cycle at a second frequency, and

periodically interrupting said pulse waveform in accordance with said pulse width modulated signal

wherein said first frequency is sufficiently greater than said second frequency to form pulse bursts from said pulse waveform, each said pulse burst comprising at least three of said pulses.

2. The method as recited in claim 1, wherein said resonant power converter is a LLC resonant power converter.

3. The method as recited in claim 2 wherein said power converter is a multi-channel, constant current power converter.

4. The method as recited in claim 1, comprising a further step of

shortening at least one of a first pulse and a last pulse of a pulse burst.

5. The method as recited in claim 4 wherein a first pulse is shortened such that the voltage on a resonant capacitor due to said first pulse of a subsequent pulse burst increases to correspond to a full load, constant current voltage on said resonant capacitor.

6. The method as recited in claim 4. wherein a last pulse is shortened such that the voltage on a resonant capacitor is brought to a voltage such that a first pulse of a subsequent pulse burst increases voltage on said resonant capacitor to correspond to a full load, constant current voltage on said resonant capacitor.

7. The method as recited in claim 1, wherein said step of generating a pulse waveform is synchronized with said step of generating a pulse width modulated signal such that bursts of pulses having an integral number of pulses of equal pulse width are produced.

8. The method as recited in claim 7, comprising a further step of

shortening at least one of a first pulse and a last pulse of a pulse burst.

9. The method as recited in claim 8, wherein a first pulse is shortened such that the voltage on a resonant capacitor due to said first pulse of a subsequent pulse burst increases to correspond to a full load, constant current voltage on said resonant capacitor.

10. The method as recited in claim 8, wherein a last pulse is shortened such that the voltage on a resonant capacitor is brought to a voltage such that a first pulse of a subsequent pulse burst increases voltage on said resonant capacitor to correspond to a full load, constant current voltage on said resonant capacitor.

11. The method as recited in claim 1, wherein said step of periodically interruption said pulse waveform with said pulse width modulated signal shortens at least one of a first pulse and a last pulse of a pulse burst.

12. The method as recited in claim 11, wherein said step of generating a pulse waveform is synchronized with said step of generating a pulse width modulated signal such that bursts of pulses having an integral number of pulses with at least one of a first pulse and a last pulse of a pulse burst is shortened such that a first pulse of a subsequent pulse burst causes a voltage/current state of the resonant power converter to coincide with a full load steady-state voltage/current trajectory.

13. The method as recited in claim 11, wherein a first pulse is shortened such that the voltage on a resonant capacitor due to said first pulse of a subsequent pulse burst increases to correspond to a full load, constant current voltage on said resonant capacitor.

14. The method as recited in claim 11, wherein a last pulse is shortened such that the voltage on a resonant capacitor is brought to a voltage such that a first pulse of a subsequent pulse burst increases voltage on said resonant capacitor to correspond to a full load, constant current voltage on said resonant capacitor.

15. A resonant power converter comprising

a switching circuit for connecting and disconnecting a resonant circuit and a source of power,

a waveform generator for generating a pulse waveform to control said switching circuit, and

a pulse width modulator for interrupting said pulse waveform to generate pulse bursts having at least three pulses in each pulse burst.

16. A resonant power converter circuit as recited in claim 15, further including

means for shortening at least one of a first pulse and a last pulse of a pulse burst.

17. A resonant power converter circuit as recited in claim 16, wherein said means for shortening at least one of a first pulse and a last pulse includes said pulse width modulator.

18. A resonant power converter circuit as recited in claim 15, wherein said at least one of said first pulse and said last pulse is shortened such that a first pulse of a subsequent pulse burst charges a resonant capacitor to a voltage/current state that coincides with a full load steady-state voltage/current trajectory of said resonant power converter.

19. A light emitting diode array including a resonant power converter wherein said resonant power converter comprises

a switching circuit for connecting and disconnecting a resonant circuit and a source of power,

a waveform generator for generating a pulse waveform to control said switching circuit, and

a pulse width modulator for interrupting said pulse waveform to generate pulse bursts having at least three pulses in each pulse burst.

20. A light emitting diode array as recited in claim 19, wherein said resonant power converter is a LLC resonant power converter.