Simulating the Traction Electric Drive Operation of a Trolleybus Equipped With Mixed Excitation Motors and a DC-DC Converter

Switching to the new type of a traction drive, from direct to alternating current, cannot be performed instantly in public transportation. The reason is the large fleet of vehicles and associated costs. In most countries in Europe and Asia, this process takes years. Therefore, the fleet of trolleybuses develops in two directions simultaneously. The first is the purchase of new trolleybuses, that is, the renewal of fleet with modern machines with an alternating current traction motor. The second is the overhaul and modernization of "outdated" machines, in order to improve their performance. Most "obsolete" trolleybuses are equipped with direct current traction motors of serial or mixed excitation. It is possible to achieve substantial energy savings and to improve the characteristics of the traction electric drive with such engines by using a pulse control system and by optimizing control algorithms. The goal of this study is to increase energy efficiency and to improve the characteristics of the trolleybus traction electric drive, equipped with a direct current motor of mixed excitation. This is accomplished by improving this drive's control system based on the pulse control system via DC-DC. The feasibility of the tractive electric drive has been tested through imitation and physical modeling. A mathematical model of the DC motor with mixed excitation has also been improved. A special feature of this model is taking into consideration the saturation of the elements of a magnetic wire of the traction motor based on the preliminary performed calculations of a magnetic field using a finite element method. By combining these components, the improved mathematical model of the entire trolleybus electric drive has been built. The operation of the trolleybus electric drive under a start mode has been simulated. The results have confirmed the increase in the energy efficiency of the traction electric drive by reducing the loss for excitation. The comparison has proven that the losses of energy decreased from 0.587 MJ (0.163 kWh) to 0.531 (0.1475 kWh) MJ, by 9.54 %.