PWM capacitor control

Patent metadata

Field	Value
Publication number	US-11807115-B2
Application number	US-202117150437-A
Country	US
Kind code	B2
Filing date	Jan 15, 2021
Priority date	Feb 8, 2016
Publication date	Nov 7, 2023
Grant date	Nov 7, 2023

Abstract

Methods, systems, and devices for controlling a variable capacitor. One aspect features a variable capacitance device that includes a capacitor, a first transistor, a second transistor, and control circuitry. The control circuitry is configured to adjust an effective capacitance of the capacitor by performing operations including detecting a zero-crossing of an input current at a first time. Switching off the first transistor. Estimating a first delay period for switching the first transistor on when a voltage across the capacitor is zero. Switching on the first transistor after the first delay period from the first time. Detecting a zero-crossing of the input current at a second time. Switching off the second transistor. Estimating a second delay period for switching the second transistor on when a voltage across the capacitor is zero. Switching on the second transistor after the second delay period from the second time.

First claim

What is claimed is:

1. An impedance matching network of a wireless power transmission system, comprising:
first and second transistor switching elements having internal body diodes or external antiparallel diodes associated therewith;
a pulse width modulation (PWM)-switched capacitor coupled across the first and second switching elements; and
a controller coupled to the first and second transistor switching elements and configured to control the first and second switching elements by steering current flow away from body diodes into the channels of the first and second transistor switching elements,
wherein the controller comprises zero voltage switching (ZVS) circuitry to control switching to occur when a voltage across the PWM-switched capacitor and the first and second switching elements is near or at zero
wherein the controller includes:
a microcontroller; and
a zero-crossing detection stage having an output sent to the microcontroller, wherein the zero-crossing detection stage includes:
a comparator, and
a current sensor that produces a voltage signal for the comparator; and

a power stage to which the zero-crossing detection stage is coupled, wherein the power stage includes:
gate drivers for driving the first and second transistor switching elements, and
signal isolation for input signals to the gate drivers generated by the microcontroller.

2. The impedance matching network of claim 1 , wherein the controller is a mixed signal implementation.

3. The impedance matching network of claim 1 , wherein the controller is a digital signal implementation that is configured to perform operations comprising:
starting a cycle of a switching period;
detecting a zero-crossing of an input current by a zero-crossing detector when the input current is rising;
scheduling the first transistor switching element to turn off at time t 2 , wherein
t 2 =φ/360°·T, and
T is a period of the input current and phase φ sets an equivalent capacitance of the PWM-switched capacitor to approximately:

C

e
⁢
q

=

C
⁢

1
·

1

2
-

(

2
⁢
φ

-

sin
⁢
2φ

)

/


′

;

scheduling the second transistor switching element to turn on at a time t 5 , wherein

t
5

=

360
⁢
°

-
φ

360
⁢
°

·
T

+

T
delay

and delay T delay is adjusted so zero-voltage switching is ensured for all operating conditions;
finishing the cycle by turning on the second transistor switching element;
turning off the first transistor switching element;
detecting zero-crossing of the input current when the input current is falling;
scheduling the second transistor switching element to turn off at time to, wherein
t 6 =T/ 2+φ/360°· T;

scheduling the second transistor switching element to turn on at time t 9 , wherein

t
9

=

4
⁢
8
⁢

0
∘

-
φ

360
⁢
°

·
T

+

T

d
⁢
e
⁢
l

;

zero voltage switching first transistor switching element;
turning on the first transistor switching element;
turning off the second transistor switching element;
detecting zero-crossing of the input current to start a next cycle when the input current is rising;
scheduling switching element to turn off after
t=φ/ 360· T;

zero voltage switching the second transistor switching element;
turning on the second transistor switching element; and
transitioning to a start of a next cycle.

4. The impedance matching network claim 1 , wherein the first and second transistor switching elements are MOSFET devices.

5. The impedance matching network of claim 1 , wherein the first and second transistor switching elements are gallium nitride (GaN) or silicon carbide (Sid) transistor switching elements.

6. The impedance matching network of claim 1 , wherein the controller is a gate control module for providing a first gate control signal for the first switching element and a second gate control signal for the second switching element, as well as a reference potential for a node between the gates of the first and second switching elements.

7. The impedance matching network of claim 2 , wherein the PWM-switched capacitor provides an equivalent capacitance of

C
⁢
e
⁢
q

=

C
⁢
1
⁢

1

2
-

(

Assignees

• Witricity Corp

Inventors

• Kurs Andre B
• Danilovic Milisav

Classifications

• B60L53/12 Primary

  Inductive energy transfer · CPC title

• H02J50/12 Primary

  of the resonant type · CPC title

• H03H7/40

  Automatic matching of load impedance to source impedance · CPC title

• H03H11/28

  Impedance matching networks · CPC title

• H03K5/1536

  Zero-crossing detectors (in measuring circuits G01R19/175) · CPC title