Environmental Engineering Reference
In-Depth Information
the voltage swing range shown in Figure 2.12 is bounded on the lower end at 30 V
and on the upper end at 50 V. These voltage bounds include dc average plus ac
ripple content on the system voltage bus.
42 V system voltage
Proposed standard
'Class A'
Addition to standard
'Class B'
58 V
58 V
55 V
Overvoltage
Overvoltage
Peak charging
50 V
48 V
Normal
operation
Normal
operation
Proposed
voltage swing
Proposed
voltage swing
Peak discharging
30 V
30 V
Start swing
Start swing
21 V
21 V
Undervoltage
No operation
Undervoltage
No operation
Figure 2.12 Voltage definition of 42 V PowerNet standard (ISO draft is Class A
and industry proposal is Class B)
Some clarification is necessary to explain why two different proposals for the
upper voltage bound are exhibited here. The ISO draft, based on industry and
consortia input through FAKRA in Germany, is that vehicle alternator clamping
voltage level at 50 V is feasible with production tolerance components. This caveat
was accepted during the draft stage of the 42 V PowerNet specification as it was not
intended for ISA/ISG applications. When ISA arrived on the scene in the form of
mild hybrids, it was quickly learned that the upper bound of 50 V was inadequate to
allow for 36-cell NiMH packs necessary in order to meet cold engine cranking
torque levels. With 36 cells the upper voltage bound had to be increased by 5 V in
order to have some margin for regeneration mode voltage swing. The industry
proposal for a 55 V upper bound was found to leave insufficient margin for alter-
nator load dump clamping using available components (avalanche diodes or active
clamping transistors) and never exceed the industry limit of 60 V as the upper
bound to maintain non-hazardous voltage level status.
The debate raised by mild hybrid actions on 42 V PowerNet vehicles continues
with no resolution in sight. The point to be made here is that the Class A standard as
originally developed is the draft de facto standard. The Class B proposal is a de jure
standard with an uncertain future.
A focused study was performed by Leonardi and Degner to compare the per-
formance of a 42 V PowerNet ISG with that of a 300 V ISG, both rated for mild
