106 Chapter 9 DĂŝŶŽŶƚĂĐƚŽƌKƉĞŶ ͬWƌĞͲŚĂƌŐĞ ŽŶƚĂĐƚŽƌKƉĞŶ ;EŽƵƌƌĞŶƚ&ůŽǁŝŶŐͿ DĂŝŶŽŶƚĂĐƚŽƌKƉĞŶ ͬWƌĞͲŚĂƌŐĞ ŽŶƚĂĐƚŽƌůŽƐĞĚ ;ƵƌƌĞŶƚ&ůŽǁŝŶŐͿ DĂŝŶŽŶƚĂĐƚŽƌ ůŽƐĞĚͬWƌĞͲŚĂƌŐĞ ŽŶƚĂĐƚŽƌKƉĞŶ ;ƵƌƌĞŶƚ&ůŽǁŝŶŐͿ Figure 4 Main and precharge contactor positions. High-Voltage Interlock Loop Many high-voltage energy storage systems also include a safety feature that is called the HVIL. The HVIL essentially creates a closed circuit when the battery pack is sealed; if one part of the pack is “opened,” the circuit is broken and the contactors are opened in order to prevent current from flowing.
But it is important to note that the HVIL is not a single compo- nent that can be installed in the battery system, but rather a series of components, software, and controls along with an integrated pack design that will not allow for the pack to be opened until the HVIL is disengaged. The purpose of this is to ensure that the energy storage system is safe to work on when it is opened up for service or maintenance. One method of accomplishing this is through connecting the HV cables to an interlock circuit that reports the status to the battery pack controller.
With this type of system, when the BMS controller recognizes when one of the interlock circuits is opened, the battery pack controller will send a message to the contractors to force them to open therefore the high-voltage bus can be discharged and the pack opened safely. The other method of doing this is to connect the HV power through an MSD device that has a fuse integrated into it. In this case, once the MSD is removed the circuit is opened and voltage will cease to flow. Fuses Most automotive high-voltage energy storage systems are also designed with an MSD as an integral part of the HVIL circuit (as mentioned above). The MSD, also called a mid-pack