A Control Method in Systems with Periodic Signals for Suppressing Higher Harmonic Components in the Subway Car Traction Current

The Moscow Metro has internal signaling systems that ensure safety and optimal speed of trains. The train's traction electric drive shall not interfere with the operation of these systems during stops or movement. The traction current main harmonic components have frequencies of 300 Hz and its multiples, which are produced by rectification of the 50 Hz three-phase AC power supply voltage. In addition, the traction current harmonic composition includes components with frequencies that are multiples of the 50 Hz power supply frequency: 100, 150, 200 Hz, etc., which are caused by malfunctions of the rectifier at a combined traction and step-down substation, such as loss of voltage in one of the rectified phases or a the three-phase voltage unbalance. Therefore, to reduce the influence of the traction electric drive current harmonic composition, the information signal encoding frequencies are selected in intermediate bands. However, while the train is moving, the frequency of the motor and, accordingly, of the currents varies. When these frequencies are superimposed on the 300 Hz fundamental harmonic component, subharmonics with a large amplitude can occur, which produce interference in the signals used in the collision prevention and cruise control systems. Given that the traction current is a periodic signal, an algorithmic method for adjusting the traction current harmonic composition is proposed, which is based on the control method in repeating systems. By using this algorithm, the voltage converter module, which is part of the transmission electric drive, can be used as an active filter. The algorithm has been tested on the traction electric drive of a subway train car and has shown a tenfold reduction in the 300 Hz harmonic component amplitude.