Passive Cell Balancing - Nuvation Energy NUV300-BC-12 Product Manual

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The current limit given above is magnitude only—i.e. charge current limit is positive.
7.6.2.3. Current Limiting Response Times
The current limiting control loop can be tuned for stable and responsive behavior in a variety of
systems. Two independent settling times are provided to allow independent adjustment of the
response to decreases in current limits (attack time) and increases in current limits (decay time).
stack_current_limit.attack_settling_time
▪
Settling time for decreases in current limits
▪
Typically this is between 1 and 5 seconds
stack_current_limit.decay_settling_time
▪
Settling time for increases in current limits
▪
Typically this is on the order of 10x larger than stack_current_limit.attack_settling_time
stack_current_limit.nonlinear_rolloff
▪
Enables a non-liner roll-off of the current limits when set to True (i.e. a value of one)
▪
Current limits will follow a linear response when set to False (i.e. a value of zero)
Since the attack time determines how quickly the current limits can respond before a potential fault
conditions opens a switch, it is critical to have sufficient control bandwidth here to avoid tripping
faults.
A non-zero settling time is critical in most applications to avoid oscillations in the presence of noise
and other imperfections in high-power control of the DC current in the charger and/or inverter.
When the nonlinear roll-off is enabled, the slope of the current limits at the end of the
charge/discharge regions will be smaller (closer to zero) than the linear response. A nonlinear roll-off
will reduce large changes in variables (such as the cell voltage) on the current limit output.

7.6.3. Passive Cell Balancing

When multiple cells are connected in series to form a larger battery stack, it is important to ensure
each cell is giving equal contributions to the system. The effects of a single low State-of-Charge or a
single high State-of-Charge cell will dominate the performance of the large battery stack. The act of
equalizing State-of-Charge of multiple series-connected cells is called balancing and there are many
types of balancing.
Nuvation Energy BMS implements a passive balancing solution. Cells with high State-of-Charge are
discharged via internal bleed resistors which are enabled on a per-cell basis. Properly adjusting the
algorithm settings for your cells is necessary to achieve a well-performing system.
A number of configurable settings are used to fine-tune the passive balancing algorithm for voltage,
temperature, current, and duty cycle.
The balancer must be enabled for balancing to take place.
Document ID: NE-PM-002
Nuvation Energy Low-Voltage BMS - Product Manual
109 Rev 1.2, 2021-03-03
Curie Update 1