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SMFCB Digital controller of thyristor exciter for synchronous electromotor

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мбв006 225х107.jpgSMFCB.xxx is a microprocessor control module for thyristor excitation device; it is used as the basic control system for series production of synchronous motors’ thyristor exciters, also for renovation of exciters by changing analog control system to digital.

SMFCB is suitable for amendment of all types of thyristor exciters ever produced in the world.

SMFCB considerably extends functional capabilities of the exciter. Programmable base makes it possible to improve functionality of the device when new software is available, it's makes changes rapidly if needed for Your production. SMFCB prolong life time and uninterruptedness of operation of the electric drive, also reduces operating costs.

SMFCB has open structure. Functionality increases by means of the expansion cards, set in special slots. Some functions are implemented by specially developed external devices. So, you can select the network interface card with the interface and the protocol for integration in the field bus, or organize the coordinated work of the exciter with different systems of the soft start.  

In case of unplanned engine shutdown you may determine the cause from the event log, which saves (in nonvolatile memory) not only  information about time and cause of the event, but also oscillograms of all parameters before and after the event. Also in event log is stored a statistical information.


SMFCB is designed for control of the thyristor exciters of the synchronous electromotor and provides a power of energizing coil by the automatically regulated current, in direct or reactor start of electromotor, synchronous operation, and other operating modes.

The SMFCB makes it possible to drive bridge and zero circuit thyristor rectifiers, including parallel connected thyristors (1, 2, or 4 thyristor for each phase). SMFCB construction structure is on picture 1.

For upgrade of old thyristor systems of excitation of any type, SMFCB it is set in an existing cabinet in changeovers of analog system. When upgrading, save the following parts: the rectifier, panel meters, external terminal blocks, but if necessary they can be replaced with new components


  1. Automatic excitation supply in the function of frequency and phase EMF of slip taking into load of the engine, in conditions of direct or reactor start or start by soft-starter system;

  2. Power saving function (by cos φ );

  3. The possibility of noncontact identification of engine start/stop;

  4. PI-regulator for stabilization of the chosen parameter (excitation current, cosφ)

  5. Engine fail-safety in conditions of short-term power outage to an electromotor or thyristor exciter (for example, action of automatic standby activation)

  6. Continuous automatic control of rotor insulation;

  7. Excitation forcing for engine retraction into synchronism when starting up;

  8. Excitation forcing up for keeping the engine in synchronism in case of stator voltage decrease. If stator voltage is abnormal low or absent, the forcing up does not occur;

  9. Excitation current automatically decreases to the setpoint if rotor is overloaded (e.g. long excitation forcing because of low stator voltage). Moment of overload protect action is defined an rotor  thermal model according to i²t;

  10. Restriction of maximum and minimum excitation current;

  11. Fast field killing rotor by inverting in case of electromotor switch-off;

  12. Blocking of pulses of control by thyristors in alert conditions, thus, for engine switch-off, joins the relay of the alarm signaling;

  13. Logger of events and collection of statistic information:

    1. Recording of the oscillograms of events in a non-volatile memory with reference to real time. You always know the  time and reason of switch-off;

    2. Collection and saving in a non-volatile memory of statistical information on

      • number of switching on and engine switch-offs

      • quantity of emergency shutdowns with distribution on each type of accident

      • the accounting of an operating time of the engine and the controller

  14. Testing mode: is checked the slip sensor and a setting of a working current;

  15. Adjustment mode. It's usually used for commissioning. In this mode, by means of buttons of regulation of current, it is possible to change an angle of control of thyristor rectifier,  the overcurrent protection is operating;

  16. Connection to the circuit of electromotor switch control via status relay:

  17. The module indication displays operation modes, the detailed reasons of accidents/warnings and a relay status. As an option: touch screen color TFT display or the monochrome OLED display with the film keypad;

    Operator panels option
    Color TFT-displayMonochrome OLED-display

    Resolution: 800x400@64K
    Interface: Touch Screen
    Network: RS485 Modbus RTU
    Power supply: 24VDC 0,3A
    Temp. range: 0..+55O

    Resolution: 128x64@1b
    Interface: 3x3 film-buttons
    Network: RS485 Modbus RTU
    Power supply: 24VDC 0,1A
    Temp. range: -40OC..+75OC

  18. Additional =24V inputs may be programmed for Customer needs; there are 2 free inputs available;

  19. For upgrade of exciting devices with two groups of thyristors (one for excitation, another for dynamic braking) in the SMFCB controler is implemented function separate control of groups of thyristors. Two boards of pulse amplifiers of  are for this purpose applied.  For VTE-11DE exciting devices, this function is used for switching of basic and forcing groups of thyristors for power saving support, and reservation of thyristor rectifiers. Built-in USB-B interface for setting-up using Ajuster;

  20. The built-in USB interface for regulation by means of the Ajuster software;

  21. Integration into automatic process control system: telemetry and remote control over an RS485 serial network or Internet using MODBUS/RTU ASCII or MODBUS TCP/IP; all the parameters are available. Available network cards:

  • Network cards


    of installation



    Modbus RTU, RS232 1200...115200 BPS, insulation 3kV         

    inside SMFCB



    Modbus RTU, RS232 1200...115200 BPS, insulation 3kV     

    inside SMFCB



    Modbus RTU
    1cn. RS232 1200...115200 BPS, insulation 3kV
    1cn. RS485 1200...115200 BPS, insulation 3kV
    1cn. RS485 115200 BPS, insulation 3kV 

    inside SMFCB



    Modbus RTU:
    1cn. RS485 1200...115200 BPS, insulation 3kV
    1cn. RS485 115200 BPS, insulation 3kV     
    Modbus TCP/IP:
    1cn. Ethernet 10/100 MBPS, insulation 1.5kV 

    inside SMFCB



    Modbus RTU:
    1cn. RS485 1200...115200 BPS, insulation 3kV
    Profibus DP:
    1cn. RS485 0,5...12 MBPS, insulation 3kV 

    inside SMFCB



    Modbus RTU
    4cn. RS485 1200...115200 BPS, insulation 3kV
    6 DO  =24V 100mA  6 DI  =24V    

    outside SMFCB

Protective features

  1. Short circuit in load and in the thyristors rectifier
  2. Long operation in an asynchronous mode;
  3. Field loss / low field current protection;
  4. Rotor insulation breakdown on the ground;
  5. Excitation overloading (rotor thermal model I²t).;
  6. Erroneous switching on the energizing current, on the switched-off electromotor, in case of  the faulty position of signal contacts of AC switchgear electrical trip circuit
  7. Faulty position of signal contacts of AC switchgear electrical trip circuit;
  8. Frequent electromotor start-ups;
  9. Stator low voltage;
  10. Change of power direction;
  11. Signaling of the need of preventative engine maintenance
  12. Proof of field discharge resistor current
  13. Failure of control circuit of the thyristor

Структура контроллера МБВ

Fig1. SMFCB structure chart  

Synchronous motors s tart-up

Exciters with digital control system (SMFCB), allow to realize direct and reactor start-up of synchronous motors in function of sliding frequency and stator current.

They are ready to cooperation with high-voltage soft starters and frequency converters, using the interface boards which are mounted in SMFCB.

reactor start of synchronous motor.jpg

Fig. 2a. Starting a 10MW synchronous motor through a current limiting reactor

Пуск двигателя от ПЧВС

Fig. 2b. Soft starting a 4MW synchronous motor through a frequency converter

For interplay of Exciters with soft-starters and frequency converters, are using the next interface boards:


Interface board


Type of soft-starter



1 pc. discret input =24V



1 pc. digital input =5-24V, 0-600kHz (active signal is frequency)



2 pcs. current input 4-20mA
2 pcs. current output 4-20mA
6 pcs. discret input =24V
2 pcs. discret output =24V, 100mA
3 pcs. RS485 Modbus RTU up to 115200 BPS



2 pcs. discret input =24V
1 pc. digital input =5-24V, 0-1500Hz (active signal is duty cycle)
1 pc. analog input 0-100mV (shunt)



1 pc. discret input =24V
1 pc. digital input =15-24V, 0-75Hz (active signal is duty cycle)
1 pc. analog input 0-100mV (shunt)



4pcs. programmable analog inputs up-to 24V(by requirements specification)   

According to the specification, we will develop any module for SMFCB


The exciter life time is more than 20 years, therefore special attention we pay to energy efficiency.
SMFSB saves energy consumed by stator and rotor of electromotor.
In stator saving is reached by operation in a automatic mode by cosφ
In rotor saving is reached by construction of insulating transformer (UNICORE technology) and thyristors rectifier structure (presence of primary and accelerate group of rectifiers)  

режим работы стд

The main mode is cos φ = 1 (power factor stabilization). The regulator automatically (depending on loading) sets an energizing current in which the synchronous motor consumes the minimum active capacity (P=min) and reactive power is equal to zero (Q=0). It match to movement of a B-point along the cos φ = 1  line on the V-curve pattern.

SMFCB allows to organize group system of a reactive power compensation of loading. In this mode, the synchronous motors, entering into group, compensates the reactive power node load according to the abilities.

SMFCB guarantee functioning of engines in a safe zone which is limited: boundary of stability of cos φ = 1 and nominal values of current of a rotor and stator. 


Connection of exciters in system of a group compensation of reactive power of a node of loading.

The range of operation of the automatic regulator of excitation in group system of a reactive power compensation of a node of loading

Events logging and statistics gathering  

The process start/stop of engine, switch on/off of control system , statistical information are recorded in nonvolatile memory.

Each event stored as the 16-seconds oscillogram, included data 8 second before and 8 second after the event, with real time reference. The buffer capacity is 31 oscillograms.

Information available:
  • Reason and time of motor stop (oscillogram contains information about the event 8 seconds before and 8 seconds after)

  • Time and parameters of motor start-up (the oscillogram of start-up is recorded

  • Time of switching off of control system. The event is accompanied 16-sec by the oscillogram (it simplifies the analysis of unauthorized supply switching off)

  • Time of switching on of control system. The event is accompanied 16-sec by the oscillogram after power-up

Statistics data
Segmet of Statistical information is stored separately. The “Statistics” contains the following information:
  • Total operating time of the engine in hours (this counter can be zeroed)

  • Time remained before preventative engine maintenance  (when time will expire, the warning signaling will be turned on)

  • Total operating time of control system (without a reset counter to zero)

  • Quantity of switching on of the engine

  • Quantity of emergency shutdowns of the engine,  with distribution on each type of accident
  • In the service program "Ajuster", all quantity of emergency shutdowns is accepted to 100%, the line charts, allow to appreciate frequent causes of shutdowns and to take measures selectively

The event log and statistical information, it is possible to load on the PC by means of the Ajuster service application, and to save as report in the Excel format. Reports forms are stored as Excel-templates. You can change the report template by the form used in your firm.

журнал событийотчёт по статистике

Window of event log and statistical information in Ajuster.

Report of statistical information in Excel window

Additional service functions

Mode of drying of windings: on a rotor of the idle engine small current flow.
The Key of Parameters (KP) - a microboard of a non-volatile memory, is used for storage of the copy of set-points of parameters.
For fast changeover of the faulty controler on reserve, KP (from a faulty controller) is put to reserve.
When the power is turn on, parameters from KP are copied in the reserve controler therefore setup is disappears.
KP can be stored separately from SMFCB, connecting them only for a starting-up or service (for synchronization of data in KP and the SMFCB controler).

Adjustment mode (it is generally used for determination of the correct alternation of phases in case of exciter input in maintenance, in this mode, by means of buttons of regulation of current, it is possible to change an angle of control of the thyristor rectifier, as much as possible the current protection thus functions;.

Technical features

Size: 234x174x141 millimeters (width x height x depth)
Weight: 2.9 kg
Supply voltage:
-AC voltage: 100-380 V
-DC voltage: 140-250 V
Power consumption: 15 watt
Operating temperature range: -40…+85 ºС