Unfolder-based single-stage AC-AC conversion system
An power converter includes an unfolder connected to a three-phase source and has an output connection with a positive terminal, a negative terminal and a neutral terminal. The unfolder creates two unipolar piece-wise sinusoidal DC voltage waveforms offset by a half of a period. A three-input converter connected to the unfolder produces a quasi-sinusoidal output voltage across output terminals. Switches of the converter selectively connect the positive, negative and neutral inputs across the output terminals. A PWM controller controls a first duty ratio and a second duty ratio for the converter based on a phase angle of the source and a modulation index generated from an error signal related to a control variable. The duty ratios are time varying with a fundamental frequency of the source. The modulation index relates to output voltage of the converter, peak voltage or current of the source and/or peak current at the output terminals.
1. A power converter comprising:
an unfolder comprising an input connection comprising three input terminals that connect to a three-phase alternating current (“AC”) power source and comprising an output connection with a positive terminal, a negative terminal and a neutral terminal, wherein the unfolder unfolds bipolar AC voltages into two unipolar piece-wise sinusoidal direct current (“DC”) voltage waveforms offset from each other by a half of a period;
a three-input converter that produces a quasi-sinusoidal output voltage across output terminals at an output frequency, the three-input converter comprising a positive input connection connected to the positive terminal, a negative input connection connected to the negative terminal and a neutral input connection connected to the neutral terminal, wherein the three-input converter comprises switches that selectively connect the positive, negative and neutral input connections across the output terminals; and
a pulse-width modulation controller configured to control a first duty ratio d po and a second duty ratio d on for the three-input converter as a function of a phase angle of a phase of the three-phase AC power source and a modulation index generated from an error signal related to a control variable compared to a reference,
wherein the first duty ratio d po and the second duty ratio d on are time varying at a rate related to a fundamental frequency of the three-phase AC power source, and
wherein the modulation index relates to output voltage of the three-input converter, a peak voltage of the three-phase AC power source, a peak current of the three-phase AC power source and/or a peak current of output current at the output terminals.
2. The power converter of claim 1 , wherein a modulation scheme for switches of the three-input converter depends on the first duty ratio d po and the second duty ratio d on .
3. The power converter of claim 2 , wherein the modulation scheme comprises a first modulation scheme when d po is greater than d on and a second modulation scheme when d on is greater than d po .
4. The power converter of claim 2 , wherein the modulation scheme comprises switching of the switches of the three-input converter to produce a positive output voltage at the output terminals during a first half of a switching period of the three-input converter and to produce a negative output voltage at the output terminals during a second half of a switching period of the three-input converter.
5. The power converter of claim 1 , wherein equations defining the first duty ratio d po and the second duty ratio d on comprise first sector equations for a first sector and second sector equations for a second sector, wherein the first sector is when voltage from the positive terminal to the neutral terminal v po is decreasing and voltage from the neutral terminal to the negative terminal v on is increasing and the second sector is when v po is increasing and v on is decreasing.
6. The power converter of claim 5 , wherein first and second sector equations for the first duty ratio d po and the second duty ratio d on are defined as:
d
p
o
=
2
π
sin
-
1
(
M
cos
θ
grid
)
for the first sector;
d
p
o
=
2
π
sin
-
1
(
M
cos
(
θ
grid
-
π
6
)
)
for the second sector;
d
o
n
=
2
π
sin
-
1
(
M
sin
(
θ
grid
)
)
for the first sector; and
d
o
n
=
2
π
sin
-
1
(
M
sin
(
θ
grid
-
π
6
)
)
for the second sector,
wherein:
θ grid is the phase angle of the phase of the three-phase AC power source, and
M is the modulation index.
7. The power converter of claim 1 , wherein the modulation index M is:
M
=
V
xy
1
(
rms
)
V
xy
1
(
rms
)
max
=
V
x
y
1
(
r
m
s
)
π
6
V
m
=
I
m
π
2
I
L
s
m
cos
(
ψ
)
wherein:
V xy1(rms) is a root-mean-square (“rms”) voltage and is the output voltage of the three-input converter;
V xy1(rms)max is a maximum rms voltage of the three-input converter;
V m is the peak voltage of the three-phase AC power source;
I m is the peak current of the three-phase AC power source;
I Lsm is the peak current of output current at the output terminals; and
ψ is the phase angle between the fundamental components of v xy and i xy .
8. The power converter of claim 1 , wherein the pulse-width modulation controller controls switching of the three-input converter to maintain unity power factor at the input to the unfolder.
9. The power converter of claim 1 , wherein a switching frequency of the three-input converter is at least two orders of magnitude higher than a fundamental frequency of the three-phase AC power source.
10. The power converter of claim 1 , wherein d po and d on are centered at a phase angle of 90 degrees of a switching period of the three-input converter for a positive output voltage at the output terminals and are centered at a phase angle of 270 degrees of the switching period of the three-input converter for a negative output voltage at the output terminals.
11. The power converter of claim 1 , wherein the output terminals of the three-input converter are connected to a resonant section, which connects to a rectification section and an output of the rectification section is a DC voltage and the control variable is for controlling the output of the rectification section.
12. The power converter of claim 11 , wherein one of:
the resonant section comprises a transmission pad separated from a receiver pad on a mobile device, wherein the transmission pad transfers power over a gap to the receiver pad as part of a wireless power transmission system;
the resonant section comprises a transformer and the power converter is a DC power supply; and
the resonant section comprises output terminals and the power converter is an inverter.
13. A system comprising:
an unfolder comprising an input connection comprising three input terminals that connect to a three-phase alternating current (“AC”) power source and comprising an output connection with a positive terminal, a negative terminal and a neutral terminal, wherein the unfolder unfolds bipolar AC voltages into two unipolar piece-wise sinusoidal direct current (“DC”) voltage waveforms offset from each other by a half of a period;
a three-input converter that produces a quasi-sinusoidal output voltage across output terminals at an output frequency, the three-input converter comprising a positive input connection connected to the positive terminal, a negative input connection connected to the negative terminal and a neutral input connection connected to the neutral terminal, wherein the three-input converter comprises switches that selectively connect the positive, negative and neutral input connections across the output terminals;
a wireless power transfer (“WPT”) primary pad coupled to output terminals of the three-input converter;
a WPT secondary pad electromagnetically coupled to the WPT primary pad over a gap;
a rectifier section coupled to an output of the WPT secondary pad, the rectifier section comprising an output; and
a pulse-width modulation controller configured to control a first duty ratio d po and a second duty ratio d on for the three-input converter as a function of a phase angle of a phase of the three-phase AC power source and a modulation index generated from an error signal related to a converter output variable compared to a reference, the converter output variable from the output of the rectifier section,
wherein the first duty ratio d po and the second duty ratio d on are time varying at a rate related to a fundamental frequency of the three-phase AC power source, and
wherein the modulation index relates to output voltage of the three-input converter, a peak voltage of the three-phase AC power source, a peak current of the three-phase AC power source and/or a peak current of output current at the output terminals.
14. The system of claim 13 , wherein a modulation scheme for switches of the three-input converter depends on the first duty ratio d po and the second duty ratio d on , the modulation scheme comprises a first modulation scheme when d po is greater than d on and a second modulation scheme when d on is greater than d po , and the modulation scheme comprises switching of the switches of the three-input converter to produce a positive output voltage at the output terminals during a first half of a switching period of the three-input converter and to produce a negative output voltage at the output terminals during a second half of a switching period of the three-input converter.
15. The system of claim 13 , wherein equations defining the first duty ratio d po and the second duty ratio d on comprise first sector equations for a first sector and second sector equations for a second sector, wherein the first sector is when voltage from the positive terminal to the neutral terminal v po is decreasing and voltage from the neutral terminal to the negative terminal v on is increasing and the second sector is when v po is increasing and v on is decreasing.
16. The system of claim 15 , wherein first and second sector equations for the first duty ratio d po and the second duty ratio d on are defined as:
d
p
o
=
2
π
sin
-
1
(
M
cos
θ
grid
)
for the first sector;
d
p
o
=
2
π
sin
-
1
(
M
cos
(
θ
grid
-
π
6
)
)
for the second sector;
d
o
n
=
2
π
sin
-
1
(
M
sin
(
θ
grid
)
)
tor the first sector; and
d
o
n
=
2
π
sin
-
1
(
M
sin
(
θ
grid
-
π
6
)
)
for the second sector,
wherein:
θ grid is the phase angle of the phase of the three-phase AC power source, and
M is the modulation index, and
wherein the modulation index M is:
M
=
V
xy
1
(
rms
)
V
xy
1
(
rms
)
max
=
V
x
y
1
(
r
m
s
)
π
6
V
m
=
I
m
π
2
I
L
s
m
cos
(
ψ
)
wherein:
V xy1(rms) is a root-mean-square (“rms”) voltage and is the output voltage of the three-input converter;
V xy1(rms)max is a maximum rms voltage of the three-input converter;
V m is the peak voltage of the three-phase AC power source;
I m is the peak current of the three-phase AC power source;
I Lsm is the peak current of output current at the output terminals; and
ψ is the phase angle between the fundamental components of v xy and i xy .
17. The system of claim 13 , wherein the output variable comprises one of output power, output voltage and output current of the rectification section.
18. A method comprising:
receiving input power at three input terminals of an unfolder, the three input terminals receive the power from a three-phase alternating current (“AC”) power source and, the unfolder comprises an output connection with a positive terminal, a negative terminal and a neutral terminal, wherein the unfolder unfolds bipolar AC voltages into two unipolar piece-wise sinusoidal direct current (“DC”) voltage waveforms offset from each other by a half of a period;
receiving output power from the unfolder at a three-input converter that produces a quasi-sinusoidal output voltage across output terminals at an output frequency, the three-input converter receives the output power at a positive input connection connected to the positive terminal, a negative input connection connected to the negative terminal and a neutral input connection connected to the neutral terminal, wherein the three-input converter comprises switches that selectively connect the positive, negative and neutral input connections across the output terminals; and
controlling, with a pulse-width modulation controller, a first duty ratio d po and a second duty ratio d on for the three-input converter as a function of a phase angle of a phase of the three-phase AC power source and a modulation index generated from an error signal related to a control variable compared to a reference,
wherein the first duty ratio d po and the second duty ratio d on are time varying at a rate related to a fundamental frequency of the three-phase AC power source, and
wherein the modulation index relates to output voltage of the three-input converter, a peak voltage of the three-phase AC power source, a peak current of the three-phase AC power source and/or a peak current of output current at the output terminals.
19. The method of claim 18 , further comprising modulating switches of the three-input converter according to a modulation scheme that depends on the first duty ratio d po and the second duty ratio d on , wherein the method selects a first part of the modulation scheme when d po is greater than d on and a second part of the modulation scheme when d on is greater than d po , and wherein the modulation scheme comprises switching of the switches of the three-input converter to produce a positive output voltage at the output terminals during a first half of a switching period of the three-input converter and to produce a negative output voltage at the output terminals during a second half of a switching period of the three-input converter.
20. The method of claim 18 , wherein equations defining the first duty ratio d po and the second duty ratio d on comprise first sector equations for a first sector and second sector equations for a second sector, wherein the first sector is when voltage from the positive terminal to the neutral terminal v po is decreasing and voltage from the neutral terminal to the negative terminal v on is increasing and the second sector is when v po is increasing and v on is decreasing.