Multi-level rectifiers
Multi-level rectifiers are provided. A multi-level rectifier may convert a medium AC voltage to a medium DC voltage. A multi-level rectifier may comprise an input inductor, a set of diodes, a set of switches, and a DC link comprising a set of capacitors. One end of the input inductor is coupled to the input AC voltage and the other end of the input inductor is coupled to a pair of diodes that are series connected. The set of switches may be regulated such that the inductor may be coupled to a DC voltage point of the DC link. A multi-level rectifier may operate under a set of operation modes. Each operation mode may be determined from the input voltage and the inductor current. Accordingly, a sinusoidal voltage at the fundamental frequency of the input voltage may be synthesized by selectively switching between adjacent operation modes of the set of operation modes. A multi-level rectifier may be used in connection with a medium voltage to low voltage DC/DC converter to form a power conversion system that converts a medium AC voltage to a low DC voltage.
1. A system of converting voltages, comprising:
an inductor coupled to an AC voltage source, a first diode, and a second diode;
a set of switches;
a set of diodes comprising the first diode and the second diode, the first diode and the second diode coupled in series;
a DC link comprising a set of capacitors and having three or more DC voltage points; and
a control module configured to generate a set of switching signals to regulate the set of switches, the control module further configured to:
determine a voltage difference between a reference output voltage and a measured output voltage;
determine a reference current signal based on the voltage difference, the reference current signal having the same frequency as the input voltage; and
select a first DC voltage point and a second DC voltage point of the three or more DC voltage points based on the reference current signal;
wherein the set of switches and the set of diodes are configured to couple the inductor to a DC voltage point of the three or more DC voltage points.
2. The system of claim 1 , wherein the set of switching signals are generated based on the AC voltage of the AC voltage source.
3. The system of claim 1 , wherein the control module is further configured to determine a first time duration and a second time duration, the inductor coupled the first DC voltage point in the first time duration and the inductor coupled to the second DC voltage point in the second time duration.
4. The system of claim 1 , wherein the first DC voltage point and the second DC voltage point are adjacent.
5. The system of claim 1 , wherein each switch of the set of switches is a semiconductor switch with an anti-parallel diode.
6. The system of claim 1 , wherein each switch of the set of switches is a semiconductor switch with an anti-parallel diode.
7. The system of claim 1 , further comprising:
a second inductor coupled to a second AC voltage source, a third diode, and a fourth diode;
a second set of switches; and
a second set of diodes comprising the third diode and the fourth diode, the third diode and the fourth diode coupled in series;
wherein the second set of switches and the second set of diodes are configured to couple the second inductor to the DC voltage point, and the first AC voltage sources and the second AC voltage sources correspond to a first phase and a second phase of a three-phase power system.
8. The system of claim 1 , further comprising a DC/DC converter comprising a set of DC/DC converter cells, the set of DC/DC converter cells being series stacked, each of the set of DC/DC converter cells is coupled to a capacitor of the set of capacitors.
9. A method of converting voltages, comprising:
coupling a system to an AC voltage source, wherein the system comprises:
an inductor coupled to the AC voltage source, a first diode, and a second diode;
a set of switches,
a set of diodes comprising the first diode and the second diode, the first diode and the second diode coupled in series,
a DC link comprising a set of capacitors and having three or more DC voltage points, and
a control module configured to generate a set of switching signals to regulate the set of switches, the control module further configured to:
determine a voltage difference between a reference output voltage and a measured output voltage;
determine a reference current signal based on the voltage difference, the reference current signal having the same frequency as the input voltage; and
select a first DC voltage point and a second DC voltage point of the three or more DC voltage points based on the reference current signal;
wherein the set of switches and the set of diodes are configured to couple the inductor to a DC voltage point of the three or more DC voltage points.
10. The method of claim 9 , wherein the set of switching signals are generated based on the AC voltage of the AC voltage source.
11. The method of claim 9 , wherein the control module is further configured to determine a first time duration and a second time duration, the inductor coupled the first DC voltage point in the first time duration and the inductor coupled to the second DC voltage point in the second time duration.
12. The method of claim 9 , wherein the first DC voltage point and the second DC voltage point are adjacent.
13. The method of claim 9 , wherein each switch of the set of switches is a semiconductor switch with an anti-parallel diode.
14. The method of claim 9 , wherein each switch of the set of switches is a semiconductor switch with an anti-parallel diode.
15. The method of claim 9 , wherein the system further comprises:
a second inductor coupled to a second AC voltage source, a third diode, and a fourth diode;
a second set of switches; and
a second set of diodes comprising the third diode and the fourth diode, the third diode and the fourth diode coupled in series;
wherein the second set of switches and the second set of diodes are configured to couple the second inductor to the DC voltage point, and the first AC voltage sources and the second AC voltage sources correspond to a first phase and a second phase of a three-phase power system.
16. The method of claim 9 , further comprising coupling a DC/DC converter to the system; wherein the DC/DC converter comprises a set of DC/DC converter cells, the set of DC/DC converter cells is series stacked, and each of the set of DC/DC converter cells is coupled to a capacitor of the set of capacitors.