Pulse width modulation control for a multilevel converter
A method for controlling multiple switching devices ( 15 a - d, 75 a - b ) of a multilevel converter ( 1, 70 ) includes providing a plurality of carrier signals (C 1 -C 6 ) and a reference signal ( 34, 80 ), the reference signal ( 34, 80 ) having a waveform range divided in a plurality of contiguous bands (B 1 -B 6 ), dynamically allocating the plurality of carrier signals (C 1 -C 6 ) to the multiple switching devices ( 15 a - d, 75 a - b ), and generating pulse width modulation signals ( 18, 77 ) to generate switching events of the multiple switching devices ( 15 a - d, 75 a - b ) based on a comparison of dynamically allocated carrier signals (C 1 -C 6 ) with the reference signal ( 34, 80 ), wherein the plurality of carrier signals (C 1 -C 6 ) have a phase shift between the carrier signals (C 1 -C 6 ), and wherein the plurality of carrier signals (C 1 -C 6 ) are dynamically allocated to the multiple switching devices ( 15 a - d, 75 a - b ) such that for each switching device ( 15 a - d, 75 a - b ) the plurality of carrier signals (C 1 -C 6 ) are rotated and selected based on a position of the reference signal ( 34, 80 ) with respect to the plurality of bands (B 1 -B 6 ).
1. A method for controlling multiple switching devices of a multilevel converter, comprising:
providing a plurality of carrier signals and a reference signal, the reference signal comprising a waveform range divided in a plurality of contiguous bands,
dynamically allocating the plurality of carrier signals to the multiple switching devices, and
generating pulse width modulation signals to generate switching events of the multiple switching devices based on a comparison of dynamically allocated carrier signals with the reference signal,
wherein the plurality of carrier signals comprises a phase shift between the carrier signals, and
wherein the plurality of carrier signals are dynamically allocated to the multiple switching devices such that for each switching device the plurality of carrier signals are rotated and selected based on a position of the reference signal with respect to the plurality of bands.
2. The method of claim 1 , wherein the phase shift (T shift_phase_new ) between the carrier signals is
T
shift
_
phase
_
new
=
π
N
levels
-
1
=
π
2
·
N
,
wherein N is the number of cells of one phase, and N levels is the number of line-neutral voltage states of the multilevel converter.
3. The method of claim 1 , wherein each switching device comprises a rotating carrier signal that is a function of the plurality of carrier signals, and wherein a selected carrier signal corresponds to a band that is instantaneously occupied by the reference signal.
4. The method of claim 3 , wherein the rotating carrier signal (CR n ) of each switching device is
CR
n
=
∑
i
,
j
,
m
B
i
·
K
j
·
C
m
,
n
=
1
…
6
,
wherein B i is a binary signal that is equal to 1 (one) or 0 (zero), K j is a coefficient having the value of −1 or 1, and C m corresponds to the carrier signals.
5. The method of claim 4 , wherein B i is equal to 1 (one) when the reference signal is within band i, and is equal to 0 (zero) when the reference signals is outside band i, where i corresponds to the number of the plurality of contiguous bands.
6. The method of claim 1 , wherein switching from a first carrier signal to a second carrier signal takes place at a crossing from a first band to a second band.
7. The method of claim 1 , wherein the dynamically allocating of the plurality of carrier signals is performed by a finite state machine.
8. The method of claim 1 , wherein the multilevel converter is configured as a cascaded H-bridge multilevel converter or a modular multilevel converter.
9. The method of claim 1 , wherein the reference signal comprises a waveform that has a substantially sinusoidal shape.
10. The method of claim 1 , wherein the plurality of carrier signals comprise a waveform having a substantially triangular shape.
11. A multilevel converter for producing a multiphase AC power supply, comprising:
a plurality of power cells for supplying power to one or more phases, each power cell comprising multiple switching devices incorporating semiconductor switches, and
a pulse width modulation controller connected to each of the power cells for controlling a voltage output of the plurality of power cells by controlling a switching event of each of the switching devices by pulse width modulation,
wherein the pulse width modulation controller is configured to
dynamically allocate a plurality of carrier signals to the multiple switching devices, and
generate pulse width modulation signals to generate switching events of the multiple switching devices based on a comparison of dynamically allocated carrier signals with a reference signal,
wherein the plurality of carrier signals comprises a phase shift between the carrier signals, and
wherein the plurality of carrier signals are dynamically allocated to the multiple switching devices such that for each switching device the plurality of carrier signals are rotated and selected based on a position of the reference signal with respect to the plurality of bands.
12. The multilevel converter of claim 11 , wherein the multilevel converter is configured as cascaded H-bridge multilevel converter or modular multilevel converter.
13. The multilevel converter of claim 11 , wherein the phase shift (T shift_phase_new ) between the carrier signals is
T
shift
_
phase
_
new
=
π
N
levels
-
1
=
π
2
·
N
,
wherein N is the number of cells of one phase, and N levels is the number of line-neutral voltage states of the multilevel converter.
14. The multilevel converter of claim 11 , wherein the plurality of carrier signals are dynamically allocated utilizing a finite state machine in communication with the pulse width modulation controller.
15. The multilevel converter of claim 11 , wherein an output of the multiphase AC power supply is connected to a load comprising an electric machine.