Basler Electric DECS-400 - Manual (Page 68)

56 9369700990 Rev R
Torsional filters 1 and 2 are controlled by a zeta numerator (Zeta Num), zeta denominator (Zeta Den), and
a frequency response parameter (Wn). The zeta numerator and zeta denominator settings, Zeta Num 1,
Zeta Num 2, Zeta Den 1, and Zeta Den 2, have a setting range of 0 to 1 with 0.01 increments. The
frequency response settings, Wn 1 and Wn 2, have a setting range of 10 to 150 rad/s with 0.05 rad/s
increments. All torsional filter parameters are accessed on the Parameters tab of the BESTCOMS PSS
screen.
Phase Compensation
The derived speed signal is modified before it is applied to the voltage regulator input. Filtering of the
signal provides phase lead at the electromechanical frequencies of interest (0.1 to 5 Hz). The phase lead
requirement is site-specific and is required to compensate for phase lag introduced by the closed-loop
voltage regulator.
Four phase compensation stages are available. Each phase compensation stage has a phase lead time
constant and a phase lag time constant. Each time constant has a setting range of 0.001 to 6 seconds
with 0.001 second increments. The time constant settings are accessed on the Parameters tab of the
BESTCOMS PSS screen.
Normally, the first two lead-lag stages are adequate to match the phase compensation requirements of a
unit. If needed, the third and fourth stages may be added through the settings of software switches
SSW 6 and SSW 7. SSW 6 and SSW 7 are accessed on the Control tab of the BESTCOMS PSS screen.
Figure 24 illustrates the phase compensation stages and associated software switches.
Figure 24. Phase Compensation Stages
Washout Filter and Logic Limiter
The output of the phase compensation stages is connected, through a stabilizer gain stage, to the
washout filter and logic limiter.
Software switch SSW 9 enables and bypasses the washout filter and logic limiter. SSW 9 is accessed on
the Control tab of the BESTCOMS PSS screen.
The washout filter has two time constants: normal and limit (less than normal). The normal time constant
has a setting range of 5 to 30 seconds with 0.1 second increments. The limit time constant has a setting
range of 0 to 1 second with 0.01 second increments. Washout filter time constants are accessed on the
Output Limiter tab of the BESTCOMS PSS screen.
The logic limiter compares the signal from the washout filter with the logic limiter upper and lower limit
settings. If the counter reaches the set delay time, the time constant for the washout filter changes from
the normal time constant to the limit time constant. When the signal returns to within the specified limits,
the counter resets and the washout filter time constant changes back to the normal time constant. The
logic limiter upper limit has a per-unit setting range of 0.01 to 0.04 with 0.001 increments. The logic limiter
lower limit has a per-unit setting range of –0.04 to –0.01 with 0.001 increments. The logic limiter time
delay has a setting range of 0 to 2 seconds with 0.01 second increments. Logic limiter settings are
accessed on the Output Limiter tab of the BESTCOMS PSS screen.
Figure 25 illustrates the washout filter and logic limiter.
1 + s T
1
1 + s T
2
1 + s T
3
1 + s T
4
PSS Output Before
Gain and Limits Stabilizing
Signal
Include
Exclude
SSW 6
1 + s T
5
1 + s T
6
SSW 7
1 + s T
7
1 + s T
8
P0026-21
12-09-04
Include
Exclude
Functional Description DECS-400