Quasi three-level power converter
The present disclosure provides a power converter, comprising: a positive terminal, a neutral terminal, a negative terminal, a first intermediate node, a second intermediate node, and an AC terminal. Vertical and horizontal switches are configured to switch a DC voltage between the positive and negative terminal to an AC voltage at the AC terminal. The AC voltage comprises three main voltage levels. A transition between any two of the main voltage levels follow a trapezoidal shape with at least one voltage sub-level.
1 . A power converter, comprising:
a positive terminal;
a neutral terminal;
a negative terminal, wherein a first DC link capacitor connects the positive terminal with the neutral terminal and a second DC link capacitor connects the neutral terminal with the negative terminal;
a first intermediate node, wherein a first vertical switch connects the positive terminal with the first intermediate node and a second vertical switch connects the first intermediate node with the neutral terminal;
a second intermediate node, wherein a third vertical switch connects the neutral terminal with the second intermediate node and a fourth vertical switch connects the second intermediate node with the negative terminal; and
an AC terminal, wherein a first horizontal switch connects the first intermediate node with the AC terminal and a second horizontal switch connects the second intermediate node with the AC terminal,
wherein the vertical and horizontal switches are configured to switch a DC voltage between the positive and negative terminal to an AC voltage at the AC terminal, the AC voltage comprising three main voltage levels, a transition between any two of the main voltage levels following a trapezoidal shape with at least one voltage sub-level, wherein each of the vertical switches are made of directly series-connected power semiconductor devices.
2 . The power converter of claim 1 ,
wherein the vertical switches are configured to switch based on a modulation waveform at a fundamental frequency, wherein the fundamental frequency is 50/3 Hz, 50 Hz or 60 Hz; and
wherein the horizontal switches are configured to switch based on a carrier waveform at a carrier frequency, wherein the carrier waveform is a triangular carrier waveform.
3 . The power converter of claim 2 ,
wherein a switching signal for the horizontal switches is based on a comparison between the carrier waveform and the modulation waveform.
4 . The power converter of claim 2 ,
wherein the vertical and horizontal switches are configured to switch based on a space vector modulation, and wherein one phase leg comprises:
a first switching state (P) in which the AC voltage at the AC terminal equals to a positive voltage at the positive terminal;
a second switching state (N) in which the AC voltage at the AC terminal equals to a negative voltage at the negative terminal;
a third switching state (L) in which the AC voltage at the AC terminal equals to a zero voltage switched from the neutral terminal via the second horizontal switch to the AC terminal; and
a fourth switching state (U) in which the AC voltage at the AC terminal equals to a zero voltage switched from the neutral terminal via the first horizontal switch to the AC terminal.
5 . The power converter of claim 4 , wherein the horizontal switches are configured to enable:
during a positive cycle of the modulation waveform, only a transition between the first switching state (P) and the third switching state (L);
during a zero crossing point of the modulation waveform, only a transition between the third switching state (L) and the fourth switching state (U); and
during a negative cycle of the modulation waveform, only a transition between the second switching state (N) and the fourth switching state (U).
6 . The power converter of claim 2 ,
wherein each of the horizontal switches comprises at least two switching cells, each of the at least two switching cells of the respective horizontal switch being configured to output a zero and at least a positive voltage.
7 . The power converter of claim 3 ,
wherein each of the horizontal switches comprises at least two switching cells, each of the at least two switching cells of the respective horizontal switch being configured to output a zero and at least a positive voltage.
8 . The power converter of claim 4 ,
wherein each of the horizontal switches comprises at least two switching cells, each of the at least two switching cells of the respective horizontal switch being configured to output a zero and at least a positive voltage.
9 . The power converter of claim 5 ,
wherein each of the horizontal switches comprises at least two switching cells, each of the at least two switching cells of the respective horizontal switch being configured to output a zero and at least a positive voltage.
10 . The power converter of claim 6 ,
wherein the at least two switching cells of the first horizontal switch are arranged in series between the first intermediate node and the AC terminal; and
wherein the at least two switching cells of the second horizontal switch are arranged in series between the second intermediate node and the AC terminal.
11 . The power converter of claim 10 ,
wherein two successive switching cells of the series of the at least two switching cells are configured to switch with a mutual time delay corresponding to a dwell time.
12 . The power converter of claim 11 ,
wherein the switching cells are configured to shape the transition between any two of the main voltage levels of the power converter based on the dwell time.
13 . The power converter of claim 11 ,
wherein the dwell time is the same or is different for two switching cells of the series of the at least two switching cells.
14 . The power converter of claim 12 ,
wherein a branch controller is configured to adjust the dwell time for each switching cell based on a balance of voltages among capacitors in the respective switching cell.
15 . The power converter of claim 11 , further comprising:
a branch controller configured to provide the switching signal and adjust the dwell time for each switching cell.
16 . The power converter of claim 15 ,
wherein the branch controller is configured to adjust the dwell time for each switching cell based on a balance of voltages among capacitors in the switching cell.
17 . The power converter of claim 6 ,
wherein each of the at least two switching cells comprises at least one main switch, at least one auxiliary switch, and a switching cell capacitor.
18 . The power converter of claim 17 ,
wherein each of the at least two switching cells further comprises a resistor arranged in series with the switching cell capacitor.
19 . The power converter of claim 17 ,
wherein each of the at least two switching cells further comprises a resistor arranged in parallel with the switching cell capacitor.
20 . The power converter of claim 1 , further comprising:
a central controller configured to provide switching signals, wherein the switching signals comprise pulse width modulation, for switching the vertical switches and the horizontal switches.