# US 2018/0323654 A1 · PWM Capacitor Control

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- Number: US 2018/0323654 A1
- Document ID: US20180323654A1
- Status: Published application
- Kind: A1
- Application number: 16/038,569
- Filed: 2018-07-18
- Published: 2018-11-08
- Earliest claimed: 2016-02-08
- Assignees: WiTricity Corporation
- Applicants: WiTricity Corporation
- Inventors: Andre B. Kurs; Milisav Danilovic
- Web page: https://patentgrep.com/patent/US20180323654A1

## CPC

- B60L 53/12: Inductive energy transfer
- H02J 50/12: of the resonant type
- H03H 7/40: Automatic matching of load impedance to source impedance
- H03H 11/28: Impedance matching networks
- H03K 5/1536: Zero-crossing detectors (in measuring circuits G01R19/175)
- H03K 7/08: Duration or width modulation {; Duty cycle modulation}
- H03K 17/133: {in field-effect transistor switches}
- H03K 17/284: in field effect transistor switches
- H03K 2217/0009: AC switches, i.e. delivering AC power to a load
- Y02T 10/70: Energy storage systems for electromobility, e.g. batteries
- Y02T 10/7072: Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
- Y02T 90/14: Plug-in electric vehicles
- B60L: PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES (arrangements or mounting of electrical propulsion units or of plural diverse prime-movers for mutual or common propulsion in vehicles B60K1/00, B60K6/20; arrangements or mounting of electrical gearing in vehicles B60K17/12, B60K17/14; preventing wheel slip by reducing power in rail vehicles B61C15/08; dynamo-electric machines H02K; control or regulation of electric motors H02P); SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES (electric coupling devices combined with mechanical couplings of vehicles B60D1/64; electric heating for vehicles B60H1/00); ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL (control or regulation of electric motors H02P); MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION

## 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.

## Claims

### Claim 1

(canceled)

### Claim 2

A variable capacitance device comprising:
a capacitor;
a first transistor comprising a first-transistor first terminal, a first-transistor second terminal, and a first-transistor gate terminal, the first-transistor first terminal electrically connected to a first terminal of the capacitor;
a second transistor comprising a second-transistor first terminal, a second-transistor second terminal, and a second-transistor a gate terminal, the second-transistor first terminal electrically connected to a second terminal of the capacitor, and the second-transistor second terminal electrically connected to the first-transistor second terminal; and
control circuitry coupled to the first-transistor gate terminal and the second-transistor gate terminal, wherein the control circuitry is configured to adjust an effective capacitance of the capacitor by performing operations comprising:
generating an alternating ramp signal having peaks and troughs that are timed to correspond with zero-crossings of an input current, and
switching off the first transistor in response to the ramp signal crossing a first reference value.

### Claim 3 (depends on 2)

The device of claim 2, wherein switching off the first transistor in response to the ramp signal crossing the first reference value comprises switching off the first transistor in response to the ramp signal crossing when the ramp signal has a first slope, and
wherein the operations comprise switching on the first transistor in response to the ramp signal crossing the first reference value when the ramp signal has a second slope.

### Claim 4 (depends on 3)

The device of claim 3, wherein the operations comprise:
switching off the second transistor in response to the ramp signal crossing a second reference value when the ramp signal has the second slope; and
switching on the second transistor in response to the ramp signal crossing the second reference value when the ramp signal has the first slope.

### Claim 5 (depends on 3)

The device of claim 3, wherein the effective capacitance of the capacitor is controlled by the first and second reference values.

### Claim 6 (depends on 3)

The device of claim 3, wherein the second reference value has a value that is the negative of the first reference value.

### Claim 7 (depends on 2)

The device of claim 2, wherein the operations comprise switching on the first transistor following a fixed time delay after the ramp signal crosses the first reference value following a peak or trough in the ramp signal.

### Claim 8 (depends on 2)

The device of claim 2, wherein the operations comprise switching on the first transistor after the ramp signal crosses the first reference value following a peak or trough in the ramp signal.

### Claim 9 (depends on 2)

The device of claim 2, wherein operations comprise switching on the first transistor after the ramp signal crosses the first reference value and in response to a zero-voltage condition across the capacitor.

### Claim 10 (depends on 2)

The device of claim 2, wherein the first and second transistors are selected from the group consisting of: silicon MOSFET transistors, silicon carbide MOSFET transistors, or gallium nitride MOSFET transistors.

### Claim 11 (depends on 2)

The device of claim 2, wherein the capacitor is electrically connected to a high-voltage impedance matching system.

### Claim 12

A high-power wireless energy transfer system comprising:
a variable capacitance device comprising:
a capacitor;
a first transistor comprising a first-transistor first terminal, a first-transistor second terminal, and a first-transistor gate terminal, the first-transistor first terminal electrically connected to a first terminal of the capacitor;
a second transistor comprising a second-transistor first terminal, a second-transistor second terminal, and a second-transistor a gate terminal, the second-transistor first terminal electrically connected to a second terminal of the capacitor, and the second-transistor second terminal electrically connected to the first-transistor second terminal; and
control circuitry coupled to the first-transistor gate terminal and the second-transistor gate terminal, wherein the control circuitry is configured to adjust an effective capacitance of the capacitor by performing operations comprising:
generating an alternating ramp signal having peaks and troughs that are timed to correspond with zero-crossings of an input current, and
switching off the first transistor in response to the ramp signal crossing a first reference value; and
an inductive coil electrically coupled to the variable capacitance.

### Claim 13

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 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.

### Claim 14 (depends on 13)

The impedance matching network of claim 13, 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.

### Claim 15 (depends on 13)

The impedance matching network of claim 13, wherein the controller is a mixed signal implementation.

### Claim 16 (depends on 13)

The impedance matching network of claim 13, wherein the controller is a digital signal implementation and includes:
a microcontroller;
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.

### Claim 17 (depends on 13)

The impedance matching network of claim 13, 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 t2, wherein
t2=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
eq
=
C


1
·
1
2
-
(
2

ϕ
-
sin


2

ϕ
)

/

π
′
;
scheduling the second transistor switching element to turn on at a time t5, wherein
t
s
=
360

°
-
ϕ
360

°
·
T
+
T
delay
and delay Tdelay 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 t6, wherein
t6=T/2+φ/360°·T;
scheduling the second transistor switching element to turn on at time t9, wherein
t
9
=
480

°
-
ϕ
360

°
·
T
+
T
del
;
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.

### Claim 18 (depends on 13)

The impedance matching network claim 13, wherein the first and second transistor switching elements are MOSFET devices.

### Claim 19 (depends on 13)

The impedance matching network of claim 13, wherein the first and second transistor switching elements are galium nitride (GaN) or silicon carbide (SiC) transistor switching elements.

### Claim 20 (depends on 13)

The impedance matching network of claim 13, 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.

### Claim 21 (depends on 13)

The impedance matching network of claim 13, wherein the PWM-switched capacitor provides an equivalent capacitance of
Ceq
=
C


1

1
2
-
(
2


ϕ
-
sin


2


ϕ
)
/
π
where C1 is an impedance value of the capacitor and φ is a phase delay.