108 Chapter 9 Depending on the size of the pack, there may be a need to include other fuses into the overall design along with the MSD. In low-voltage packs, it is generally not necessary to include an MSD, but instead there may be a need to include one or more fuse depending on the system design. Additionally, when it comes to fusing, some OEMs have integrated small fuses directly into the control boards that interconnect the cells. This provides the benefit of additional safety in the event that any single cell, or set of parallel cells, experiences a failure and voltage spike.
Large energy storage systems may not include an MSD-type fuse, but will generally include a fuse of some sort into the pack design as a safety feature. For the larger systems, the fuse may actually be integrated into a battery disconnect unit (BDU). Battery Disconnect Unit Most of these HV electronics components and subsystems are often packaged together into one location in the battery pack. In fact, some component suppliers and OEMs package them into a single physical unit that may be referred to as the BDU. While the BMS is typically mounted separately from the BDU, the BDU serves as the interface to the electric motor, vehicle control- lers, and any communications outside of the vehicle.
Some component suppliers have designed these into “standard” off-the-shelf type units that can be purchased as a single unit and installed in your energy storage system. In these off-the-shelf units, the main contactors, precharge contac- tors, fuses, HVIL circuitry, and other electronics hardware are all integrated into a single unit. Several other companies such as Delphi and Tyco Electronics provide “off-the-shelf” HV units. Depending on your team’s HV electrical experience and the requirements of the application, this could be a good fit and could save your team’s significant engineering time and effort ( Figure 7 ).
Figure 7 Off-the-shelf high voltage (HV) electronics by Delphi Electronics.