Control of a Resonant Converter

• US 20080266908A1
• Filed: 03/24/2006
• Published: 10/30/2008
• Est. Priority Date: 04/01/2005
• Status: Active Grant

• Current Assignee: NXP B.V. (NXP Semiconductors NV)
• Original Assignee: NXP B.V. (NXP Semiconductors NV)
• Inventors: Halberstadt, Hans
• Granted Patent: US 7,944,716 B2
• Time in Patent Office: Days
• US Class Current: 363/21.02
• 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 3/3376 with automatic control of output voltage or current
• 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

The invention deals with the control of a resonant LLC converter by use of control parameters. The primary current flowing in the resonant tank and a voltage at a predetermined point in the resonant tank are monitored and control parameters are set for a high side conduction interval and control parameters are set for a low side conduction interval, the control parameters for the two conduction intervals being: a peak current of the interval and a predetermined voltage of the interval. The resonant converter comprises series-arranged controllable switches to be connected to the supply source. The resonant converter is operated by setting up criteria for turning off a switch in accordance with criteria including the four control parameters.

Claims

1. A resonant converter for supplying electrical energy from a supply source (Vs) to a load, the resonant converter comprising first and second series-arranged controllable switches to be connected between supply source terminals, a control device (CL) for generating control signals for opening and closing the first and second switches, a resonant tank in electrical connection with the first and second switches, the resonant tank comprising a resonant capacitor (Cr), wherein one of the first and second switches is turned on and a current flowing in the resonant tank is monitored and a voltage at a predetermined point in the resonant tank is monitored, a first conduction interval occurs while the first switch is turned on and a second conduction interval occurs while the second switch is turned on, and wherein two control parameters are set for the first conduction interval and two are set for the second conduction interval, the control parameters for the two conduction intervals being:

a peak current of the interval and a predetermined voltage of the interval, and wherein the first and second switches are turned off in accordance with criteria including the four control parameters.

2. A resonant converter according to claim 1, wherein the first switch is turned off when a first criterion or a second criterion is fulfilled, the first criterion being that the current is larger than the peak current, the second criterion being that a minimum time has lapsed after the switch is turned on and that the voltage is below a level set by the predetermined voltage of the interval, and wherein the second switch is turned off when a first criterion or a second criterion are fulfilled, the first criterion being that the current is smaller than the peak current, the second criterion being that a minimum time has lapsed after the switch is turned on and that the voltage is above a level set by the predetermined voltage of the interval.

3. A resonant converter according to claim 1, wherein the four control parameters are set in order operate the resonant converter in accordance with a desired operation mode.

4. A resonant converter according to claim 1, wherein the four control parameters are set in order to stabilize a desired operation mode of the resonant converter, and wherein a stabilization loop incorporates the four control parameters in the stabilization procedure.

5. A resonant converter according to claim 3, wherein the desired operation mode is a mode where the output power is controlled.

6. A resonant converter according to claim 5, wherein the output power is controlled by setting the control parameters according to a value of a single operation parameter.

7. A resonant converter according to claim 6, wherein regions of the single operation parameter is defined and wherein the output power is controlled by setting the control parameters according to a value of a single operation parameter in the region.

8. A resonant converter according to claim 6, wherein the single operation parameter is adjusted in accordance with the supply voltage and the operation frequency of the converter.

9. A control logic (CL) for controlling a resonant converter, the control logic comprising output logic (OL) for controlling first and second series-arranged switches to be connected between supply source terminals, at least one comparator where a current in a resonant tank of the resonant converter and a voltage at the a predetermined point in the resonant tank is inputted, and where the current and the voltage is compared to control parameters, two control parameters are set for the first conduction interval occurring while the first switch is turned on, and two are set for the second conduction interval occurring while the second switch is turned on, the control parameters for the two conduction intervals being:

the peak current of the interval and a predetermined voltage of the interval, and wherein the at least first and second switches are turned off in accordance with criteria including the four control parameters.

10. A method of controlling a resonant converter for supplying electrical energy from a supply source (Vs) to a load, the resonant converter comprising first and second series-arranged switches to be connected between supply source terminals, a control device (CL) for generating control signals for opening and closing the first and second switches, a resonant tank in electrical connection with the first and second switches, the resonant tank comprising a resonant capacitor, the method comprising the steps of:

monitoring the current flowing in the resonant tank and a voltage at a predetermined point in the resonant tank, comparing the current in a resonant tank of the resonant converter and a voltage at the a predetermined point in the resonant tank to control parameters, two control parameters are set for the first conduction interval occurring while the first switch is turned on, and two are set for the second conduction interval occurring while the second switch is turned on, the control parameters for the two conduction intervals being;

the peak current of the interval and a predetermined voltage of the interval, turning the first and second switches off in accordance with criteria including the four control parameters.

11. Computer readable code for enabling a programmable device to perform the method of claim 10.