Basler DECS-100 Digital Excitation System Debugging Guide

2.5 Soft start and voltage matching

Soft start time: adjustable from 1 to 7200s (1 second step), controls the generator voltage to climb from residual voltage to the set value, effectively suppressing voltage building overshoot

Voltage matching (optional): Match the output voltage of the generator with the bus voltage, with an accuracy of ± 0.5% and an adjustable speed of 1-300s (0.01s step), supporting both "hold" and "restore" modes

Front panel indication and operation

The DECS-100 front panel provides 8 red LED indicator lights (see Figure 2-1) for quick diagnosis:

Meaning of LED indicator light

Overexcitation Shutdown: The magnetic field overvoltage exceeds the set value for 10 seconds, and the device has been turned off (flashing for 5 seconds after power on)

Generator Overvoltage: The generator voltage exceeds the set value for 0.75 seconds, and the device has been turned off (flashing for 5 seconds after power on)

Loss of Generator Sensing detects a loss of sensation and outputs an alarm to close the contact (flashing for 5 seconds after power on)

Overexcitation Limiting: The excitation current exceeds the OEL set value (if it does not recover after the delay, it will be turned off and flash for 5 seconds after power on)

Underexcitation Limiting: Reactive power below UEL curve (if not restored after delay, turn off and flash for 5 seconds after power on)

Var/P.F. Mode Active VAR or PF control mode activation (requires 52J/K open contacts and software enabled)

Manual Mode Active FCR Manual Mode Activation

Underfrequency Active: The generator frequency is below the V/Hz inflection point setting and underfrequency adjustment is being performed

The flashing indicator function of all LEDs when powered on again after the fault is turned off provides a convenient means for on-site engineers to trace the fault history.

Function description and working principle

4.1 Hardware Architecture (Figure 3-1)

The signal flow of DECS-100 can be divided into the following paths:

Voltage induction path: The three-phase voltage connected to the E1/E2/E3 terminals is divided and anti aliasing filtered before being sent to the ADC for 96 samples per cycle. The VC-A signal is simultaneously sent to the zero crossing detection circuit for frequency measurement.

Current sensing path: The B-phase current at CT1/CT2 terminals is sent to the ADC through internal CT and conditioning circuits for calculating the effective current value and power/power factor.

Excitation power path: The AC power input from terminals 3/4/5 is rectified and filtered before being supplied to the power amplification stage. The microprocessor generates a PWM drive signal based on the PID calculation result to control the power switch and outputs it to the F+/F - terminals.

Auxiliary input path: The -3~+3Vdc signal from terminals A/B is sent to the ADC through a 1k Ω input impedance for remote setting value adjustment.

Contact input path: The 13Vdc internal power supply provides status signals through 5 dry contact inputs (6U/6D/52J/52K/52L/52M/VM), which are isolated by optocouplers and sent to the microprocessor.

4.2 PID Control Algorithm and Stable Parameters

The AVR/FCR loop of DECS-100 adopts PID (Proportional Integral Derivative) control algorithm:

Proportional gain Kp: The output is proportional to the error. If Kp is too small, the response will be slow, and if it is too large, overshoot will increase. Typical values range from 1 to 1000.

Integral gain Ki: eliminates steady-state errors. Increasing Ki can accelerate steady-state convergence, but excessive Ki may lead to oscillation.

Differential gain Kd: Provides lead correction, suppresses overshoot and oscillation. Typical values range from 1 to 10 (0.01 steps).

Differential time constant Td: Filter out noise introduced by numerical differentiation, with a typical value of 0.01~0.03 (adjustable from 0~1).

Loop gain Kg: Roughly adjust the overall gain level of the PID algorithm to speed up or slow down the response speed.

The PID window of BESTCOMS provides the function of automatically calculating recommended PID parameters based on the generator time constant T'd0 and the excitation machine time constant Texc. Table 5-1 provides 20 sets of preset stable parameters - corresponding to T'd0 ranging from 1.00s to 10.5s (with a step of 0.5s), Texc is approximately T'd0/6.

4.3 52L/M and 52J/K contact logic

DECS-100 switches operating modes through two sets of external dry contacts:

52L/M status, 52J/K status, DECS-100 operating mode

Closed AVR mode activated, no droop, VAR/PF disabled (standalone/independent operation)

Open close droop mode activated, VAR/PF disabled (parallel to grid or islanded multi machine droop)

Disconnect VAR/PF mode activation (parallel to the grid, reactive power/power factor regulation)

The 52L/M terminal is usually connected to the auxiliary contact of the generator circuit breaker, which opens when the circuit breaker is closed, causing the DECS-100 to enter parallel operation mode. The 52J/K terminal is usually connected to the auxiliary contacts of the grid side circuit breaker - the contacts are disconnected during parallel operation, making the VAR/PF function available.