Basler DECS-250 Digital Excitation Control System

Core hardware architecture and power supply of the whole machine

1. Two types of independent power sources

Control power supply: Provides power to the motherboard, logic, communication, and human-machine systems, with dual redundant specifications of 24/48VDC, 120Vac/125V AC/DC, and isolation design;

Working power supply: excitation power level power supply, compatible with three-phase/single-phase AC/DC, with three excitation output levels of 32/63/125V, and a wide frequency range of 50~500Hz suitable for PMG permanent magnet machine excitation power supply;

Tip: It is recommended to install ICRM surge suppression module for low impedance mains power supply to prevent damage to the power board caused by power on impact.

2. Excitation power unit

Adopting PWM switching power circuit, standard output 15ADC (55 ℃), short-term 10 second forced excitation 30Adc; Output terminals F+/F - are connected to the magnetic field of the brushless excitation machine, without electrical isolation, and the casing is reliably grounded.

3. Signal acquisition system

Generator three-phase voltage E1/E2/E3: compatible with PT secondary up to 600Vac, single-phase can be short circuited to E2;

Generator three-phase CT (CTA/CTB/CTC): supports 1A/5A transformers, and three-phase current is a necessary condition for PSS and reactive power calculation;

Bus voltage B1/B2/B3: synchronization, voltage matching, grid monitoring;

Cross current CT terminal CCCT: used for parallel current sharing of multiple machines;

The excitation acquisition is built-in and can detect excitation voltage, current, and rectifier diode ripple (EDM diode fault monitoring).

4. Front panel of human-machine interface

128 × 64 backlit LCD, four-way navigation key, Edit key, Reset key; Front Type-B USB local debugging port; Multiple status LEDs: pre positioning, restricted action, PSS activation, mode tracking, zero balance indication;

Menu layering: metering, setting, protection, restriction, synchronization, logic, communication, system parameters, supports contrast, automatic scrolling, sleep backlight, multilingual switching, graded password permission control parameter modification.

Five major excitation regulation operation modes (core control functions)

Supports 5 independent adjustments, disturbance free internal tracking between modes, dual PID gain groups can automatically switch, and each mode is configured with 3 sets of pre positioning fast setting values.

AVR automatic voltage regulation (main mode)

Closed loop stabilization of terminal voltage, supporting adjustable soft start boost slope; External adjustable contacts, 4-20mA/-10~10V analog, Modbus remote fine-tuning; Suitable for both islanding and grid connected applications.

FCR excitation current constant current mode

Manual standby, PT disconnection, maintenance conditions, constant excitation current output.

FVR excitation voltage constant voltage mode

Commonly used for unit simulation, system model testing, and fixed excitation output voltage.

VAR reactive constant mode

Lock in reactive power output for grid connection and suppress reactive power fluctuations.

PF power factor constant mode

Standard control for power plant grid connection, fixed power factor, automatic droop mode for active power below the set value.

Supporting adjustment function

Pre Location: 3 sets of preset excitation values, one click switching of external contacts, supporting both instantaneous and gradual switching rates;

Internal and external tracking: Internal tracking (local modes follow each other, switching without impact); External tracking (dual DECS redundancy with one primary and one backup linkage);

Transient excitation enhancement: When the short-circuit voltage drops sharply in the power grid, the excitation is automatically raised to enhance the transient support of the fault;

Two options for parallel current sharing scheme: reactive power droop compensation, cross differential CT current sharing, and Ethernet network reactive power sharing;

Line voltage drop compensation: remote load point constant voltage control.

Synchronizer and voltage matching optional module

Built in automatic synchronizer (optional model with xXXXA logo), used for generator grid connection and closing control, with complete synchronization logic:

Synchronization criteria: triple locking of sliding frequency, sliding angle, and pressure difference, supporting two synchronization algorithms: PLL phase-locked/predictive;

Transformer phase compensation, ratio matching coefficient, eliminate PT ratio/phase shift errors;

Bus/generator voltage loss and fault determination logic can be set to allow for dead bus closure;

Output speed regulation pulses to adjust the frequency of the prime mover, supporting both continuous and pulse speed regulation outputs;

Independent voltage matching function: automatically tracks the difference in bus voltage before closing, reducing the synchronous voltage difference.

Complete set of limiters (protecting excitation/generator boundaries)

All restricted instruments are equipped with two sets of parameters for primary and secondary devices, with automatic offline/grid connection switching and support for external scaling adjustment of analog signals

OEL overexcitation limit

Two algorithms: summation type (smooth adjustment) and takeover type (direct forced clamping); Offline two-level current limiting, grid connected three-level stepped current limiting, with inverse time heating curve, distinguishing between instantaneous high margin and long-term low excitation limits, with dV/dt voltage drop temporary excitation function.

UEL under excitation limit

To prevent phase instability, it has a built-in standard PQ curve and up to 5 custom PQ boundary curves, adapted to the requirements of the unit's phase test.

SCL stator current limit

Divide the stator current threshold into high and low levels, and gradually lower the excitation after exceeding the time limit to avoid stator overheating.

VAR reactive power limit: fixed upper and lower boundaries of reactive power.

V/Hz low-frequency magnetic flux limitation

Low frequency automatic voltage reduction to prevent iron core saturation, with adjustable segmented slope.

More than 20 built-in protection functions of the whole machine

Divided into six categories: voltage, frequency, active and reactive power, excitation, synchronization, and custom protection, all of which can be set with two action logics of alarm/trip. There are two sets of fixed value groups for the main and auxiliary:

Voltage category: 27 under voltage, 59 over voltage, loss of voltage acquisition LOS;

Frequency category: 81O overclocking, 81U low-frequency, low-speed alarm below 10Hz;

Power category: 32R reverse power (to prevent motor condition from dragging backwards), 40Q demagnetization protection (based on PQ leading phase curve to determine demagnetization);

Excitation body: excitation overvoltage, excitation overcurrent, ED excitation diode short circuit/open circuit monitoring, PMG power loss, excitation circuit short circuit;

Synchronous protection: 25 synchronous checks (non synchronous locking);

8-channel custom programmable protection: can monitor any analog quantity (RTD, temperature, expansion module signal), four channel threshold segmented alarm delay.

Grid Code Grid Compliance Control (High and Low Voltage Traverse LVRT Core)

Meet the high and low frequency, high and low voltage ride through standards of domestic and foreign power grid guidelines, divided into three major control modules:

APC active power control

Normal constant active power; Frequency offset enters LFSM frequency limiting mode, and the active power is increased or decreased according to the droop curve; Set power up/down rate, high/low power limit, and stable cooling time for fault recovery.

LVRT reactive power control (5 standard modes)

Q (U) voltage related reactive power, Q (P) active related reactive power, constant reactive power, constant power factor, third-party external settings; Each control curve can be customized with inflection points and PT1 response time constants, and remote communication faults can lock the current PF/Q.

Power grid fault diagnosis: continuous operation zone for high and low voltage, high and low frequency, delayed tripping zone, and immediate tripping zone. Fault recovery requires voltage and frequency stabilization timing to be completed before grid connection; Provide testing function to artificially offset voltage frequency to simulate power grid disturbances.

PSS power system stabilizer (optional, IEEE PSS2A/2B/2C standard)

To suppress low-frequency oscillations in the power grid, three-phase CT current collection is required before activation

Dual input structure: speed deviation+active integral signal, filtering out shaft torsional vibration interference;

Multi stage high pass washout filtering, second-order torsional vibration filtering, and four stage phase advance compensation components;

Two independent parameters (light and heavy load automatic switching), power switching threshold;

Output limiting and terminal voltage suppression protection to prevent overvoltage caused by excessive voltage regulation of PSS;

BESTCOMS has a built-in parameter calculation tool that automatically matches the inertia and excitation time constants of the unit.

Stability PID tuning system

AVR/FCR/FVR/VAR/PF/OEL/UEL/SCL all circuits have independent PID, providing three tuning modes:

20 sets of industry standard prefabricated PID parameters;

Manually input the generator T'do and excitation Te to automatically calculate the gain;

The whole machine is automatically auto tuned, and the dynamic characteristics of the excitation system are automatically identified under no-load conditions, generating the optimal Kp/Ki/Kd with one click;

Distinguish between normal operating conditions and PSS switching of two sets of gains to suppress overshoot and oscillation.

Measurement, event and fault recording

1. Full dimensional real-time measurement

Generator three-phase voltage/current, positive and negative sequence components, active/reactive/power factor, accumulated electrical energy, bus electrical quantity, excitation parameters, PSS output, synchronous slip, external analog input; Automatic reversal of reactive power and power factor symbols in motor mode; Support front-end panel and software multi window floating monitoring.

2. Three major functions of event recorder

SOE event sequence: 4ms high-precision time scale, storing 1023 displacement records, covering input/output, protection, and mode switching; Support IRIG-B/NTP network timing;

COMTRADE standard fault recording: up to 6 sets of waveforms, pre triggered+fault segment sampling, can be exported to PC for analysis;

Long term trend recording: up to 720 hours of continuous storage of 6 key variables for long-term condition analysis;

All alarms are classified as self-locking/non self-locking, and power failure can save the latch fault.

Extended hardware module (CAN bus communication)

AEM-2020 Simulation Expansion Module

8 analog inputs, 8 RTD temperature sensors, 2 thermocouples, 4 analog outputs; Used for collecting and outputting unit temperature and external control signals.

CEM-125/CEM-2020/CEM-202 Contact Expansion

Expand multi-channel switch input/relay output, remote logic control, all called by BEST logic programmable logic.

Input/output resources

Main switch quantity: 16 isolated inputs (fixed start stop+14 programmable); 11 programmable relay outputs+1 hardware watchdog normally closed alarm;

Analog auxiliary channels: V ± (-10~10V), I ± (4~20mA), used for remote reactive power/voltage bias, PSS testing, and limiting scaling;

The expansion module extends IO, temperature measurement, and analog signals through the CAN bus.

Communication system (compatible with multiple buses)

Front panel USB: local BESTCOMSPlus debugging, firmware upgrade;

Backplane DB9 serial port: dual machine DECS primary and backup tracking;

RS485 Modbus RTU: remote monitoring and adjustment of upper PLC, complete reading and writing of fixed values, alarms, and metering;

Ethernet (copper/fiber optic optional): Modbus TCP, network reactive power sharing;

CAN bus: connect AEM/CEM expansion module;

Optional Profibus DP industrial bus;

All communications have communication fault locking logic, and communication interruptions can maintain the current excitation setting.

BEST logicPlus programmable logic (whole machine flexible control core)

No need to modify hardware, software Boolean logic can be freely configured:

Logic components: switch input/output, protection status, limit action, timing, comparator, mode switching, pre positioning, communication failure;

Support self-locking, interlocking, delay window, threshold comparison;

Prefabricated standard logic: circuit breaker failure, synchronous locking, parallel current sharing, protection tripping logic; Users can customize and store multiple sets of logic schemes to adapt to different secondary circuits of power plants.

Supporting upper software BESTCOMSPlus

Windows specific configuration monitoring tool, core functions:

Read and write machine parameters, interface configuration adjustment, PID automatic tuning;

Real time curve step response analysis and waveform recording analysis;

Import and export of parameter files, batch copying for multiple units;

4 firmware online upgrade;

5 logic offline simulation, no need to power on to debug logic;

6. Automatic export of measurement data at regular intervals and storage of reports.

Installation, wiring, and maintenance

Installation: Standard 3U 19 inch rack, embedded panel with optional cover plate; It must be installed vertically to ensure heat dissipation, with an ambient temperature of -40~+70 ℃;

Terminal partitioning: power supply, excitation output, CT/PT acquisition, control input, relay output, various communication, expansion interfaces; Pull out bracket, pull out automatic short-circuit CT to prevent open circuit high voltage;

3 Wiring requirements: Separation of strong and weak electricity, single end grounding of shielded wire, and keeping high-power power cables away from the acquisition signal line;

4. Maintenance: No regular disassembly and maintenance; Idle spare parts are powered on for 30 minutes every year to activate electrolytic capacitors; The faulty machine should be returned to the factory, and self disassembly and repair are prohibited; Disconnect all communication and acquisition terminals during the withstand voltage test.