Sevcon Gen4, Applications Reference Manual, Page: 89 / 123

Configuration
Doc. # 177/52701
Rev. 3.3
6-19
Torque mode/speed mode
WARNING: Speed mode (or speed control) is not recommended for on-highway vehicles
as it can cause the traction motor/wheel to remain locked or brake severely if the wheel is
momentarily locked due to loss of traction on a slippery surface and/or mechanical
braking.
The Gen4 controller provides both torque and speed control modes. Objects 2900
h
and 6060
h
are used to set which mode to use. The default setting is torque mode.
WARNING: Always ensure 2900
h
on the master node and 6060
h
on all the traction nodes
(master and slaves) match otherwise motor signals between the master and slaves may
be misinterpreted.
The speed control (speed mode) or speed limit (torque mode) is controlled using PI loops. These
loops are configured at 4651
h
. The following parameters can be configured:

Standard proportional and integral gains (4651
h
, 1+2). Used to configure the loops during
normal operation.

Low speed proportional and integral gains (4651
h
, 3+5). Used to configure the loops at low
speeds (<50 RPM) and during hill hold. These are normally set lower than the standard
gains to dampen oscillation as the vehicle comes to a stop.

Roll back integral gain (4651
h
, 4). Used to boost the integral term to prevent vehicle roll-off
down inclines, particularly when Hill Hold is enabled. Normally, this gain is higher than the
standard integral gain.

dw/dt gain (4651
h
, 6). For speed mode this is used to boost the torque output when a large
increase in speed demand occurs. For torque mode this is used to apply compensatory
torque to damped oscillations induced from the vehicle drive train.

Integral initialization factor (4651
h
, 7). Used to initialize the integral term on entry to speed
limit in torque mode. This factor is multiplied by the actual torque to set the integral term.
Not used in speed mode.

Speed filter pole (4651
h
, 8). Used to filter speed used by speed limit loop.

Speed pre-limit threshold (4651
h
, 9). Speed limit algorithm will start cutting back torque
when speed is within this threshold of the maximum.

Opposing maximum speed limit ramp rate (4651
h
, 10). Rate at which opposing speed limit
ramps back to 0 RPM.
These settings affect how driver demands are interpreted by the controller. In torque mode, the
throttle push translates into a torque demand, which is applied to the traction motor. In speed
mode, the throttle push translates to a speed demand. The controller then calculates the torque
required to maintain this speed.
The difference between these control methods is most apparent when driving on an incline. In
torque mode, when the vehicle is driven uphill, the vehicle speed will decrease due to the
increased load. The operator must apply more throttle demand in order to maintain speed. In
speed mode, the controller will apply additional torque in order to maintain the operator’s speed
demand, without the operator having to increase throttle demand.