Safe battery energy management systems, battery management system nodes, and methods
A system and method for hierarchical arc fault monitoring in an energy storage system, where the energy storage system includes a plurality of stacks that are electrically coupled together. Each stack includes a plurality of battery management system nodes that are electrically coupled together. The method includes (1) obtaining respective electrical measurement values for each stack; (2) determining, for each stack, that the stack is free of arc faults, using the respective electrical measurement values for the stack; (3) obtaining electrical measurement values for the energy storage system; and (4) determining that the energy storage system is free of arc faults outside of the plurality of stacks, using (a) the electrical measurement values for the energy storage system and (b) a subset of the respective electrical measurement values for each stack.
1. A method for safe operation of an energy storage system including at least a first stack of a plurality of battery management system nodes, the method comprising:
causing each battery management system node to operate in a respective operational mode where an isolation switch of the battery management system node is closed, such that each battery management system node is capable of providing electric power to a load electrically coupled to the energy storage system; and
in response to a signal for the first stack to operate in a safe mode, causing a first subset of the battery management system nodes to operate in respective bypass modes, while causing a second subset of the battery management system nodes to continue to operate in respective operational modes, to reduce at least one of a voltage and a current of the first stack.
2. The method of claim 1 , wherein causing the first subset of the battery management system nodes to operate in respective bypass modes comprises, for each battery management system node of the first subset:
isolating a battery of the battery management system node from a direct-current to direct-current (DC-DC) converter of the battery management system node; and
electrically short circuiting an output port of the battery management system node.
3. The method of claim 1 , wherein causing the second subset of the battery management system nodes to continue to operate in respective operational modes comprises, for each battery management system node of the second subset, causing a DC-DC converter of the battery management system node to transform a battery voltage to a voltage across an output port of the battery management system node.
4. The method of claim 1 , wherein each battery management system node of the first stack is a member of either the first subset of the battery management system nodes or the second subset of the battery management system nodes, in the safe mode.
5. The method of claim 1 , further comprising changing a division of battery management system nodes of the first stack between the first and second subsets of battery management system nodes.
6. The method of claim 5 , further comprising periodically changing the division of battery management system nodes of the first stack between the first and second subsets of battery management system nodes.
7. The method of claim 5 , further comprising changing the division of battery management system nodes of the first stack between the first and second subsets in response to a signal to change one or more of a voltage and a current of the first stack.
8. The method of claim 1 , further comprising generating the signal for the first stack to operate in the safe mode in response to detection of a fault in the energy storage system outside of the first stack.
9. The method of claim 8 , wherein the fault in the energy storage system is an arc fault in the energy storage system outside of the first stack.
10. The method of claim 8 , wherein the fault in the energy storage system is failure of a communication subsystem outside of the first stack.
11. The method of claim 1 , further comprising generating the signal for the first stack to operate in the safe mode in response to a user command.
12. A method for safe operation of an energy storage system including at least a first stack of N battery management system nodes, N being an integer greater than one, the method comprising:
operating the first stack in a normal mode; and
in response to occurrence of an event, changing an operating mode of the first stack from the normal mode to a safe mode, the safe mode being at least partially characterized by each of M battery management system nodes of the N battery management system nodes operating in a respective bypass mode, M being an integer less than N, the respective bypass mode of each of the M battery management system nodes being characterized at least partially by (a) a respective isolation switch of the battery management system node being open and (b) a respective shorting switch of the battery management system node being closed.
13. The method of claim 12 , the safe mode being further characterized by N minus M of the battery management system nodes operating in respective operational modes.
14. The method of claim 12 , wherein:
a voltage across the first stack in the normal mode is equal to V 1 ;
a voltage across the first stack in the safe mode is V 2 ; and
V 2 is less than V 1 .
15. The method of claim 12 , wherein the event comprises a fault outside of the first stack.
16. The method of claim 12 , wherein the event comprises a user command to enter the safe mode.