COMPENSATION OF INPUT CURRENT HARMONICS IN PARALLEL MULTIPLE VOLTAGE SOURSE INVERTERS
An increasing proportion of the rolling stock of railways and subways passes from collector
motors with rheostat-contactor control systems to asynchronous electric drive, which is controled by autonomous voltage inverters. This leads to a significant improvement in the energy efficiency of the electric rolling stock, namely, to an increase in the efficiency of the electric rolling stock and a reduction in operating
costs. However, the asynchronous electric drive also has its drawbacks, namely, it causes a significant emission of higher harmonics of traction currents in the contact network (catenary) and electrical rail circuits of
railway automation, exacerbates the issue of the quality of electrical energy in the contact network and electromagnetic compatibility of traction currents and rail automation.
The classical method of combating higher harmonics of traction currents on an electric rolling stock is
the use of passive low-pass filters of various configurations. However, this method has significant drawbacks, namely, it causes significant mass dimensions, has a significant cost, and also has a sufficiently low
efficiency of suppressing low-frequency harmonics of traction currents. This calls for a further search for
ways to reduce the emission of higher harmonics from traction inverters by concentrating not additional filter devices, but the introduction of more efficient control algorithms for traction inverters that lead to improved electromagnetic compatibility.
Proposed the synchronization of the control systems of several parallel connected independent voltage
inverters powered from the same network and realization of the mutual shift of the key control signals for the
compensation time makes it possible to realize the compensation effect of the higher harmonics of the input
currents, thus achieving a significant improvement in the ripple ratio of the input current and the DC harmonic distortion factor. The simulations carried out have confirmed that the proposed algorithm for compensation of higher harmonics in the multi-invertor system allows to significantly reduce the emission of
higher harmonics into the power supply network when realizing single-pulse and pulse-width modulation
modes. The proposed compensation method is applicable not only for the electric rolling stock, but also for
any multi-invertor system powered from the common electrical network