PRIMARY UNIT CONTROL OF RESONANT INDUCTIVE POWER TRANSFER SYSTEM FOR OPTIMUM EFFICIENCY

• US 20130154373A1
• Filed: 12/14/2011
• Published: 06/20/2013
• Est. Priority Date: 12/14/2011
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: LISUWANDI, Eko Tan, Dissanayake Bogoda, Thilani Imanthika
• Granted Patent: US 9,041,254 B2
• Time in Patent Office: Days
• US Class Current: 307/34
• CPC Class Codes: H02J 5/005 with inductive power transfer for charging H02J7/025
• CPC Class Codes: H02J 50/12 of the resonant type

Abstract

A circuit and method for wirelessly coupling an electrical energy between an electrical energy source and at least one load is provided. The circuit comprises a primary unit and at least one secondary unit. The primary unit includes an input node for receiving an input voltage produced by the energy source; a transmitter circuit including a transmitter coil configured to generate an electromagnetic field; and a regulator. The regulator is configured to sense a current consumption of the primary unit, determine a gradient of the current consumption with respect to different input voltages, and determine an optimal input voltage based on the gradient. The at least one secondary unit comprises a receiver circuit and a load. The receiver unit includes a coil that wirelessly and inductively couples with the electromagnetic field of the primary unit to receive power therefrom. The receiver unit further includes a regulator circuit configured to provide a constant power to an output node.

Claims

1. A circuit for wirelessly coupling electrical energy between an electrical energy source and at least one load, comprising:

a primary unit comprising;

an input node for receiving an input voltage produced by the energy source;

a transmitter circuit including a transmitter coil configured to generate an electromagnetic field; and

a regulator configured to;

sense a current consumption of the primary unit,

determine a gradient of the current consumption with respect to different input voltages, and

determine an optimal input voltage based on the gradient of the current consumption of the primary unit with respect to different input voltages; and

at least one secondary unit, each secondary unit comprising;

a receiver circuit including;

a receiver coil to wirelessly and inductively couple with the electromagnetic field of the primary unit to receive power therefrom;

a regulator circuit configured to provide a constant power to an output node; and

a load coupled to the output node.

2. The circuit of claim 1, wherein:

the transmitter circuit further includes a DC to AC converter; and

the electrical energy source is DC.

3. The circuit of claim 1, further comprising a DC/DC converter for producing a DC output in response to an input DC voltage and to a feedback signal.

4. The circuit of claim 1, wherein the optimal point for the input voltage is based on an indirect determination of the power requirement of the at least one secondary unit by the primary unit.

5. The circuit of claim 1, wherein the optimal point of the input voltage is based on the gradient of the current consumption with respect to the input voltage, being equal to or below a predetermined threshold.

6. The circuit of claim 2, wherein:

the primary unit further comprises a DC/DC converter coupled to the input node, operative to produce a DC signal and accept a feedback signal; and

the regulator comprises;

a sense resistor coupled to the output of the DC/DC converter;

a current sensor configured to sense the current through the sense resistor and to produce an output signal proportional to the current through the sense resistor; and

a digital logic and memory circuit coupled to the output of the current sensor, configured to provide a feedback signal to the DC/DC converter and to store a current value at every voltage step, respectively.

7. The circuit of claim 2, wherein:

the primary unit further comprises a DC/DC converter coupled to the input node, configured to produce a DC signal and accept a feedback signal; and

the regulator comprises;

a sense resistor coupled to the output of the DC/DC converter;

a transconductance amplifier to sense the current through the sense resistor and to produce an output signal proportional to the current through the sense resistor across an output resistor;

an A/D converter coupled to the output of the transconductance amplifier, configured to sense a voltage across the output resistor of the transconductance amplifier;

a digital logic and memory circuit coupled to the output of the A/D converter, wherein the memory is configured to store a current value at every voltage step; and

a D/A converter coupled to the output of the digital logic and memory circuit, configured to provide a feedback signal to the DC/DC converter.

8. The circuit of claim 1, wherein the at least one secondary unit is configured to obtain power wirelessly from the primary unit through inductive coupling.

9. A method for controlling electrical wireless power transfer in an electrical power transfer system comprising a primary unit configured to generate an electromagnetic field and at least one secondary unit configured to couple with the electromagnetic field and provide a regulated output voltage to its respective load, the method comprising:

ramping an input voltage in the primary unit in a first direction;

sensing a current consumption in the primary unit at predetermined input voltage steps;

storing a current consumption for each input voltage in a memory;

calculating a gradient of the current consumption with respect to input voltage for each voltage step;

recording the gradient of the current consumption for each voltage step in the memory;

comparing the gradient between each voltage step to a predetermined first threshold;

determining an optimal input voltage in the primary unit, wherein an optimal input voltage is at an input voltage where the gradient is equal to or less than the predetermined first threshold.

10. The method of claim 9 further comprising:

setting the input voltage at one voltage step further in the first direction of the determined optimal input voltage; and

keeping the input voltage fixed at one voltage step further in the first direction of the determined optimal input voltage for a predetermined delay period.

11. The method of claim 10 wherein the predetermined delay period is based on at least one of (i) how fast the load of the at least one secondary unit changes and (ii) a minimum speed at which the primary unit can react to the change in its supply voltage.

12. The method of claim 9 wherein, after the predetermined delay period expires, the method further comprising:

ramping the input voltage in the primary unit in a second direction, wherein the second direction is opposite to the first direction;

sensing the current consumption in the primary unit at predetermined input voltage steps;

storing a current consumption for each input voltage in a memory;

calculating a gradient of the current consumption with respect to input voltage for each voltage step;

recording the gradient of the current consumption for each voltage step in the memory;

comparing the gradient between each voltage step to a predetermined second threshold value; and

if the gradient at a voltage step is greater than the predetermined second threshold value, then returning to the step of ramping the input voltage in the primary unit in the first direction.

13. The method of claim 12 wherein the predetermined second threshold value is the same as the predetermined first threshold value.

14. The method of claim 9 wherein ramping the input voltage in the first direction comprises increasing the input voltage at predetermined voltage steps and at predetermined time intervals.

15. The method of claim 14 wherein:

the voltage steps are uniform; and

the time intervals of each sample are uniform.

16. The method of claim 9 wherein a gradient in the first direction that is greater than a predetermined first threshold value but less than gradient in the previous voltage step, indicates that at least one secondary unit achieved regulation of its respective load.

17. The method of claim 12 wherein a gradient in the second direction that is greater than a predetermined first threshold value, indicates that at least one secondary unit lost regulation of its respective load.

18. The method of claim 9 wherein the first predetermined threshold is set to be larger than the inherent random offsets, repetitive dynamic variations and systematic inaccuracies in the primary unit and the at least one secondary unit.

19. The method of claim 9 wherein:

there are a plurality of secondary units; and

the optimal input voltage in the primary unit is at a last change in gradient.

20. The method of claim 12, wherein each voltage step in a first direction is larger than each voltage step in a second direction.

21. The method of claim 12, wherein a voltage step size is reduced every time the direction of the ramp changes, until a predetermined minimum voltage step size is reached.

22. A method for controlling electrical wireless power transfer in an electrical power transfer system comprising a primary unit configured to generate an electromagnetic field and at least one secondary unit configured to couple with the electromagnetic field and provide a regulated output voltage to its respective load, the method comprising:

varying an input current of the primary unit as a function of input voltage;

incrementally measuring a current gradient of the primary unit as a function of input voltage;

comparing the current gradient to a predetermined threshold; and

determining an optimal input voltage in the primary unit, wherein an optimal input voltage is at an input voltage where the current gradient is equal to or less than the predetermined first threshold.

23. A method for controlling electrical wireless power transfer in an electrical power transfer system comprising a primary unit configured to generate an electromagnetic field and at least one secondary unit configured to couple with the electromagnetic field and provide a regulated output voltage to its respective load, the method comprising:

in step 1;

setting an input voltage in the primary unit to a predetermined V_min value;

increasing the input voltage by a predetermined voltage step;

sensing a current consumption in the primary unit at each input voltage value; and

storing the current consumption at each input voltage value in a memory;

in step 2;

calculating a gradient of the current consumption with respect to input voltage for the voltage step; and

storing the gradient as a present-gradient in a memory;

in step 3;

comparing the present-gradient to a first reference gradient;

if the present-gradient is less than or equal to the first reference gradient, then keeping the input voltage fixed for a predetermined delay period; and

going back to step 1 after an expiration of the predetermined delay period;

if the present-gradient is greater than the first reference gradient, then going to step 4;

in step 4;

changing the input voltage in the primary unit to a predetermined V_max value minus the predetermined voltage step, wherein the predetermined V_max value is higher than the predetermined V_min value;

increasing the input voltage by the predetermined voltage step;

sensing a current consumption in the primary unit at each input voltage value;

storing the current consumption for each input voltage value in a memory;

calculating a gradient of the current consumption with respect to input voltage for the voltage step; and

storing the gradient of the current consumption as the present-gradient in a memory;

in step 5;

comparing the present-gradient to the first reference gradient;

if the present-gradient is greater than the first reference gradient, then;

setting the input voltage to V_max;

keeping the input voltage fixed at V_max for the predetermined delay period; and

upon expiration of the delay period, going back to step 1;

if the present-gradient is less than or equal to the first reference gradient, then;

storing the present gradient as the minimum reference gradient setting a V_low to V_min and V_high to V_max; and

continuing with step 6;

in step 6;

changing the input voltage in the primary unit to (V_low+V_high)/2,

increasing the input voltage by the predetermined voltage step;

sensing a current consumption in the primary unit at each input voltage value;

storing the current consumption at each input voltage value in a memory;

calculating a gradient of the current consumption with respect to input voltage for the voltage step; and

storing the gradient as a present-gradient in a memory;

in step 7;

calculating a gradient of the current consumption with respect to input voltage for the voltage step; and

storing the gradient as a present-gradient in a memory;

in step 8;

comparing the present-gradient to the first reference gradient and a minimum reference gradient;

if the present-gradient is greater than the minimum reference gradient, and less than or equal to the first reference gradient, then going to step 10;

otherwise, going to step 9;

in step 9;

if the present-gradient is greater than the first reference gradient, then setting the V_low to the present input voltage of the primary unit;

if the present-gradient is less than or equal to the minimum reference gradient, then setting V_high to the present input voltage of the primary unit; and

repeating steps 6 to 8;

in step 10;

keeping the input voltage fixed for the predetermined delay period; and

after an expiration of the predetermined delay period, repeating the method by going back to step 1.