Medha Transportation LLC
Medha supplies IGBT based traction (propulsion) converters ranging from 1.1 MW upto 4.5 MW and higher power ratings for installation on ac-ac traction vehicles including Locomotives, Diesel Multiple Units, DEMUs, EMUs and Metros.
Medha's traction converters are designed to suit project requirement including building of new traction vehicles and retrofit or modernization or replacement of old (GTO or Thyristor) converters with IGBT traction converters.
Newer generation Diesel / Electric locomotives, EMUs, DMUs and Metro cars equipped with AC Traction Motors require sophisticated Traction Converters to control these motors as part of propulsion system.
Diesel locomotive and DMU propulsion system architectures provide rectified alternator output as stable DC link bus voltage input to the Traction Converter. Traction Converter could be a combination of one or more inverters each controlling one or more traction motors.
EMU and Electric locomotive propulsion system architectures typically provide secondary winding of traction transformer as input feed to the Traction Converter. Traction Converter would have multiple line converters which convert single phase AC input to a stable DC link bus voltage. A combination of one or more inverters converts this DC bus voltage to 3-phase power controlling one or more traction motors each. For Metro cars, depending on OHE voltage or third rail DC voltage, traction converter may include line converters and inverters or only inverters. .
Traction Inverter drives/ brakes one (independent motor control) or multiple (bogie control) Traction Motors. DSP is used for implementing Vector motor control using Space Vector PWM for complete VVVF control of traction motor in both motoring and dynamic/ regenerative braking operation. Input power is typically taken from stable DC Link voltage (from diode rectifier or line converter) and torque command is received from locomotive control system.
Independent motor control typically used in locomotives has the advantage of better wheel slip control (better adhesion), better Tractive effort independent of wheel diameter variations and also better availability of locomotive power in cases of inverter or motor failures.
Medha uses IGBT devices in all Traction Inverters for better efficiency and reliability. Gate drive cards control IGBTs and protect them against various short circuit conditions. Optic fiber communication is used between Traction Computers (DSPs) and Gate drive cards for noise immunity. Various current, voltage and temperature sensors are used for monitoring and protection of both inverter and motor.