Method for Determining Battery Pack Isolation Resistance Via Dual Bus Monitoring
A method for measuring and calculating the isolation resistance of a battery pack is provided, the method being invulnerable to changes in the bus voltage that may take place between measurements.
1 . A method of calculating an isolation resistance R ISO for a battery pack, the method comprising the steps of:
(a) measuring a first voltage VP 0 between a positive bus of said battery pack and ground;
(b) measuring a second voltage VN 0 between a negative bus of said battery pack and ground;
(c) determining whether said VP 0 is less than, or greater than, said VN 0 , wherein if said VP 0 is less than said VN 0 , the method further comprises the steps of:
(d) inserting a known resistance R STN between said negative bus of said battery pack and ground;
(e) measuring a third voltage VP 1 between said positive bus of said battery pack and ground;
(f) measuring a fourth voltage VN 1 between said negative bus of said battery pack and ground; and
(g) calculating said R ISO from the equation R ISO =[R STN *(VP 1 /VN 1 −VP 0 /VN 0 )]; and wherein if said VP 0 is greater than said VN 0 , the method further comprises the steps of:
(h) inserting a known resistance R STP between said positive bus of said battery pack and ground;
(i) measuring a fifth voltage VP 2 between said positive bus of said battery pack and ground;
(j) measuring a sixth voltage VN 2 between said negative bus of said battery pack and ground; and
(k) calculating said R ISO , from the equation R ISO =[R STP *(VN 2 /VP 2 −VN 0 /VP 0 )].
2 . The method of claim 1 , wherein steps (a) through (k) are performed repeatedly.
3 . The method of claim 1 , wherein if said VP 0 is equal to said VN 0 in step (c), then steps (d) through (g) are performed.
4 . The method of claim 1 , wherein if said VP 0 is equal to said VN 0 in step (c), then steps (h) through (k) are performed.
5 . The method of claim 1 , wherein step (d) further comprises the step of closing a switch SN, wherein closing said switch SN inserts R STN between said negative bus of said battery pack and ground.
6 . The method of claim 1 , wherein step (h) further comprises the step of closing a switch SP, wherein closing said switch SP inserts R STP between said positive bus of said battery pack and ground.
7 . The method of claim 1 , wherein steps (a) and (b) are performed simultaneously.
8 . The method of claim 1 , wherein steps (e) and (f) are performed simultaneously.
9 . The method of claim 1 , wherein steps (i) and (j) are performed simultaneously.
10 . The method of claim 1 , further comprising the step of coupling said battery pack to a drive train of an electric vehicle, wherein said battery pack provides power for said drive train.