Transistor Frequency Converters for Induction Heating Output Frequency 6 - 50 kHz

Transistor Frequency Converters for Induction Heating Output Frequency 6 - 50 kHz

Our TRMK-series frequency converters are designed to supply power to equipment that incorporates technology such as that used in induction heating, hardening, smelting and/or other applications where a parallel resonant circuit is required.


TRMK Converters consist of an input power supply switch (QS), a controlled rectifier (1), suppressor (2), current converter (3), and starting circuit (4), and spike/surge protection (5). Supply power is provided by LV or HV mains (50 Hz) through a matching transformer (sold separately).

All regulating, monitoring and control functions are handled by a PLC-based system. A closed-loop water cooling system is used to control the temperatures of the various electrical/electronic components of the system.

TRMK Design

Frequency converter is built into two connected heavy-duty steel cabinets with an IP-43 protection rating. The left cabinet contains the rectifier, converter, suppressor, input/output terminal boards, voltage sensors and over-voltage protection components, water temperature and flow sensors and a cool-water distributor with its own pressure and temperature sensors. The lower-half of the right cabinet contains the pump and a water-to-water heat exchanger. Control circuits including the controller rack and PLC are mounted in the upper half. Forced air circulation is provided for both partitions. Air cooling is assisted by a water-to-air heat exchanger located mid-cabinet.

Water cooling is accomplished through a two-circuit system. The closed inner-loop provides cooling of thyristors, transistors, and the suppressor. The circuit is designed with non-ferrous (non-conductive) materials and filled with a low-conductive liquid. The power circuits contains disc-shaped thyristors(dual-cooled) and IGBT transistors (also water-cooled).

System temperatures are constantly monitored and regulated by the central controller. The open outer-loop system is fed by the customers external water supply. In addition to its enhanced overall design and construction, the new control circuit system helps the TMK-series frequency converters achieve outstanding performace in the field of current converters.

Advantages of TRMK

  • high efficiency throughout the entire output range, over 90%
  • modifiable range of output power from 10% to 100% of the nominal value
  • modifiable range of output frequency (fmin – fmax) 40% - 100% of the nominal value
  • a closed-loop cooling circuit with a low-conductive water helps reduce the negative electrochemical effects to the cooling components and provides improved insulation for the power circuits
  • start and run reliability within a wide range of load impedance
  • converter design also facilitates installation in a dusty environment
  • perfect galvanic separation of control and power circuits
  • clear and simply-interfaced controls provide quick system fault location in order to decrease down-time
  • high-interference immunity for control circuits

TRMK Specifications

Frequency converters for induction heating, hardening and melting furnances requiring a parallel resonant circuit:

Type U2
fmin - fmax
TRMK - 1 600 15 6 - 15 100 120 160
25 10 - 25 100 120  
50 20 - 50 60    
500 15 6 - 15 80 100 120
25 10 - 25 80 100  
50 20 - 50 50    
400 15 6 - 15 60 80 100
25 10 - 25 60 80  
50 20 - 50 40    
TRMK - 2 600 15 6 - 15 200 250  
25 10 - 25 160 200  
50 20 - 50 100    
500 15 6 - 15 160 200  
25 10 - 25 120 160  
50 20 - 50 80    
400 15 6 - 15 120 160  
25 10 - 25 100 120  
50 20 - 50 60    

Type marking

Model Number legend for frequency converters:

Dimensional sketch

This project was endowed and implemented by financial support through state funds from the Ministry of Industry and Commerce.

The composition of our TRMK frequency converter allows for the design of other variations of this technology. Please don't hesitate to contact us. Our engineering team welcomes the opportunity to discuss any technical implementation scenarios with you. 



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