Method and apparatus for bypassing cascaded H-bridge (CHB) power cells and power sub cell for multilevel inverter
Multilevel power converters, power cells and methods are presented for selectively bypassing a power stage of a multilevel inverter circuit, in which a single relay or contactor includes one or more normally closed output control contacts coupled between a given power cell switching circuit and the given power cell output, along with a normally open bypass contact coupled across the power stage output, with a local or central controller energizing the coil of the relay or contactor of a given cell to bypass that cell.
1. A power conversion system, comprising:
a plurality of power stages connected in series to form a multilevel inverter circuit for connection to a load, the power stages individually comprising:
a DC link circuit including at least one capacitance coupled between first and second DC link nodes,
an output coupled with at least one other power stage in the multilevel inverter circuit,
a switching circuit including a plurality of switching devices coupled between the DC link circuit and the output, the switching circuit operative according to a plurality of switching control signals to provide an output voltage having an amplitude of one of at least two discrete levels at the output,
a single relay or contactor, comprising:
a coil,
at least one normally closed output control contact coupled between the switching circuit and the output, the at least one output control contact operative in a first state to allow current to flow between the switching circuit and the output when the coil is deenergized, and operative in a second state to prevent current from flowing between the switching circuit and the output when the coil is energized, and
a normally open bypass contact coupled across the output, the bypass contact operative to allow normal operation of the output in a first state when the coil is deenergized, and to bypass the output of the switching circuit in a second state when the coil is energized, and
at least one DC link control switch coupled between the first DC link node and a rectifier, the at least one DC link control switch operative in a first state to allow current to flow between the first DC link node and a first DC node of the rectifier and in a second state to prevent current from flowing between the first DC link node and the first DC node of the rectifier; and
a controller operative to selectively place the at least one DC link control switch in the second state and energize the coil of at least one of the plurality of power stages to bypass the at least one power stage.
2. The power conversion system of claim 1 , wherein the single relay or contactor comprises:
a first normally closed output control contact coupled between a first internal node of the switching circuit and a first output terminal of the output, the first output control contact operative in a first state to allow current to flow between the first internal node and the first output terminal when the coil is deenergized, and operative in a second state to prevent current from flowing between the first internal node and the first output terminal when the coil is energized; and
a second normally closed output control contact coupled between a second internal node of the switching circuit and a second output terminal of the output, the second output control contact operative in a first state to allow current to flow between the second internal node and the second output terminal when the coil is deenergized, and operative in a second state to prevent current from flowing between the second internal node and the second output terminal when the coil is energized.
3. The power conversion system of claim 2 , wherein the controller is a local controller providing switching control signals to operate the plurality of switching devices of the switching circuit of the at least one power stage.
4. The power conversion system of claim 3 , wherein the at least one power stage comprises:
a first DC link control switch coupled between the first DC link node and a first DC node of a rectifier, the first DC link control switch operative in a first state to allow current to flow between the first DC link node and the first DC node and in a second state to prevent current from flowing between the first DC link node and the first DC node; and
a second DC link control switch coupled between a second DC node of the rectifier and the second DC link node, the second DC link control switch operative in a first state to allow current to flow between the second DC node and the second DC link node and in a second state to prevent current from flowing between the second DC node and the second DC link node; and
wherein the controller is operative to selectively bypass the at least one power stage by placing first and second DC link control switches in their respective second states and selectively energizing the coil of the at least one power stage.
5. The power conversion system of claim 2 , comprising:
at least one local controller providing the switching control signals to operate the plurality of switching devices of the switching circuit of the at least one power stage; and
a second controller operative to selectively energize the coil of the at least one power stage to bypass the at least one power stage.
6. The power conversion system of claim 5 , wherein the single relay or contactor comprises a third normally closed contact coupled between the first DC link node and a first DC node of a rectifier, the third contact operative in a first state to allow current to flow between the first DC link node and the first DC node when the coil is deenergized, and operative in a second state to prevent current from flowing between the first DC link node and the first DC node.
7. The power conversion system of claim 5 , wherein the single relay or contactor comprises:
a third normally closed contact coupled between the first DC link node and a first DC node of a rectifier, the third contact operative in a first state to allow current to flow between the first DC link node and the first DC node when the coil is deenergized, and operative in a second state to prevent current from flowing between the first DC link node and the first DC node when the coil is energized; and
a fourth normally closed contact coupled between a second DC node of the rectifier and the second DC link node, the fourth contact operative in a first state to allow current to flow between the second DC node and the second DC link node when the coil is deenergized, and operative in a second state to prevent current from flowing between the second DC node and the second DC link node when the coil is energized.
8. The power conversion system of claim 1 , wherein the controller is a local controller providing switching control signals to operate the plurality of switching devices of the switching circuit of the at least one power stage.
9. The power conversion system of claim 1 , wherein the at least one power stage comprises:
a first DC link control switch coupled between the first DC link node and a first DC node of a rectifier, the first DC link control switch operative in a first state to allow current to flow between the first DC link node and the first DC node and in a second state to prevent current from flowing between the first DC link node and the first DC node; and
a second DC link control switch coupled between a second DC node of the rectifier and the second DC link node, the second DC link control switch operative in a first state to allow current to flow between the second DC node and the second DC link node and in a second state to prevent current from flowing between the second DC node and the second DC link node; and
wherein the controller is operative to selectively bypass the at least one power stage by placing first and second DC link control switches in their respective second states and selectively energizing the coil of the at least one power stage.
10. The power conversion system of claim 1 , comprising:
at least one local controller providing the switching control signals to operate the plurality of switching devices of the switching circuit of the at least one power stage; and
a second controller operative to selectively energize the coil of the at least one power stage to bypass the at least one power stage.
11. The power conversion system of claim 10 , wherein the single relay or contactor comprises a third normally closed contact coupled between the first DC link node and a first DC node of a rectifier, the third contact operative in a first state to allow current to flow between the first DC link node and the first DC node when the coil is deenergized, and operative in a second state to prevent current from flowing between the first DC link node and the first DC node.
12. The power conversion system of claim 10 , wherein the single relay or contactor comprises:
a third normally closed contact coupled between the first DC link node and a first DC node of a rectifier, the third contact operative in a first state to allow current to flow between the first DC link node and the first DC node when the coil is deenergized, and operative in a second state to prevent current from flowing between the first DC link node and the first DC node when the coil is energized; and
a fourth normally closed contact coupled between a second DC node of the rectifier and the second DC link node, the fourth contact operative in a first state to allow current to flow between the second DC node and the second DC link node when the coil is deenergized, and operative in a second state to prevent current from flowing between the second DC node and the second DC link node when the coil is energized.
13. The power conversion system of claim 1 , wherein the single relay or contactor comprises a third normally closed contact coupled between the first DC link node and a first DC node of a rectifier, the third contact operative in a first state to allow current to flow between the first DC link node and the first DC node when the coil is deenergized, and operative in a second state to prevent current from flowing between the first DC link node and the first DC node.
14. The power conversion system of claim 1 , wherein the single relay or contactor comprises:
a third normally closed contact coupled between the first DC link node and a first DC node of a rectifier, the third contact operative in a first state to allow current to flow between the first DC link node and the first DC node when the coil is deenergized, and operative in a second state to prevent current from flowing between the first DC link node and the first DC node when the coil is energized; and
a fourth normally closed contact coupled between a second DC node of the rectifier and the second DC link node, the fourth contact operative in a first state to allow current to flow between the second DC node and the second DC link node when the coil is deenergized, and operative in a second state to prevent current from flowing between the second DC node and the second DC link node when the coil is energized.
15. The power conversion system of claim 1 , wherein the single relay or contactor is an N-pole, single-throw device, where N is an integer having a value of 3 or more.
16. A power cell for use as a power stage in a multilevel inverter circuit, the power cell comprising:
a DC link circuit including at least one capacitance coupled between first and second DC link nodes;
an output;
a switching circuit including a plurality of switching devices coupled between the DC link circuit and the output, the switching circuit operative according to a plurality of switching control signals to provide an output voltage having an amplitude of one of at least two discrete levels at the output;
a single relay or contactor, comprising:
a coil,
at least one normally closed output control contact coupled between the switching circuit and the output, the at least one output control contact operative in a first state to allow current to flow between the switching circuit and the output when the coil is deenergized, and operative in a second state to prevent current from flowing between the switching circuit and the output when the coil is energized, and
a normally open bypass contact coupled across the output, the bypass contact operative to allow normal operation of the output in a first state when the coil is deenergized, and to bypass the output of the switching circuit in a second state when the coil is energized; and
at least one DC link control switch coupled between the first DC link node and a rectifier, the at least one DC link control switch operative in a first state to allow current to flow between the first DC link node and a first DC node of the rectifier and in a second state to prevent current from flowing between the first DC link node and the first DC node of the rectifier.
17. The power cell of claim 16 , wherein the single relay or contactor comprises:
a first normally closed output control contact coupled between a first internal node of the switching circuit and a first output terminal of the output, the first output control contact operative in a first state to allow current to flow between the first internal node and the first output terminal when the coil is deenergized, and operative in a second state to prevent current from flowing between the first internal node and the first output terminal when the coil is energized; and
a second normally closed output control contact coupled between a second internal node of the switching circuit and a second output terminal of the output, the second output control contact operative in a first state to allow current to flow between the second internal node and the second output terminal when the coil is deenergized, and operative in a second state to prevent current from flowing between the second internal node and the second output terminal when the coil is energized.
18. A method for bypassing a power stage of a multilevel inverter circuit, the method comprising:
using a controller, energizing a coil of a single relay or contactor to open one or more normally closed output control contacts and to close a normally open bypass control contact to bypass an output of the power stage; and
using the controller, opening at least one DC link control switch coupled between the power stage and a rectifier during the bypass of the power stage, the at least one DC link control switch operative in a first state to allow current to flow between a DC link node and a DC node of the rectifier and in a second state to prevent current from flowing between the DC link node and the DC node of the rectifier to prevent current from flowing between the power stage and the rectifier.