Harmonic Mitigation in Traction Drives

In railway traffic the low friction between wheel and rail causes long braking distances, normally much longer than the sight distance of the driver, i.e. if the driver starts the braking when a problem on the track is discovered, it might be too late to brake the train. Therefore, safe railway traffic can not only rely on the driver. It is necessary to have a signalling or even an automatic surveyor system, especially in densely populated areas, which supervises the positions of different trains along the track and organises the traffic. Such a system uses train detection systems to control whether a certain section of the track is occupied or not. Train detection systems can unfortunately be disturbed by harmonics, generated by the drive system of a rail vehicle. To reduce the risk of disturbance, the choice of modulation strategy and the use of line filters are critical tasks. In the design stage of the filter, it is necessary to be able to predict the generation of harmonics. This work presents fast algorithms for calculation of harmonics, generated by a traction drive system. The traction drive system, here described, is based on three phase induction motors, fed from voltage source machine and line converters. Non-ideal commutations are taken into account, which is urgent as these will generate undesirable low frequency harmonics. It is possible to compensate the effects of the non-ideal commutations, and in this work following compensation methods are investigated: - Dead time compensation, where the differential between the integral of the inverter output voltage, or rather the output flux, and the voltage time area reference, is fed back to the control system. - Position asymmetry compensation, in which the DC-component in the machine converter phase currents is fed back to the control system. - Compensation of a remaining DC-bias in Hall-effect current transducers. In the method, the fundamental component in the DC-link current is fed back to the control system. The compensation methods are found to effectively reduce the low frequencies. Thus the weight of the filters onboard the trains can be minimised, which considerably saves energy and costs of components

How to control SiC BJT with high efficiency?

SiC Bipolar Junction Transistor has many benefits such as low on-state voltage drop, high switching speed and high maximum operating temperature. However it has one major disadvantage that it needs current to be turned on. This causes an increased power requirement of the driver circuit compared to voltage controlled devices like MOSFETs and IGBTs. The proposed driving concept is based on a verified Darlington typology together with a voltage compensation component which gives a solution to this problem. The proposed driving concept is evaluated by both simulation and experimental results. The investigation of parallel connection of SiC BJT transistors that use the proposed drive concept is also included in this paper

Analytic prediction of electromagnetic behaviour

The amount of electrical loads and the complexity of the electric system in a vehicle is increasing at the same time as the allowed development time is getting shorter. Possibilities to predict the electromagnetic behaviour is therefore of great importance. In this paper, a method for determining the parasitic components affecting crosstalk in a cable harness is proposed. The method suggests that a more complex ground structure should for calculation purposes be replaced by equivalent ground planes. Calculated parameter values are compared to values gained from simulation in a circuit model for investigation of crosstalk. It is shown that also an approximation of the parasitic components will give a good comprehension of the crosstalk effects in the cable harness

Prediction of Parasitic Components in an Automotive Environment

The amount of electrical loads and the complexity of the electric system in a vehicle is increasing at the same time as the allowed development time is decreasing. Possibilities to predict the electromagnetic behaviour is therefore of great importance. This paper addresses the problems of low frequency electromagnetic crosstalk between cables in a harness. Analytical expressions for estimation of the parasitic inductances and capacitances are employed and compared to measured as well as simulated results. The results show that an analytical calculation of the parameters is a good way to start to analyse the crosstalk since the parameter values agree well with both the simulated and measured values. When the values for the parasitic components are estimated, they can be employed in circuit simulations in order to investigate the sensitivity to crosstalk for different conductor layouts

Star-C - A novel converter topology

The Star-C is a new multilevel converter topology that is characterized by presenting a close to perfect sinusoidal output voltage. Its main purpose is to reduce the electromagnetic emissions that can interfere with other equipment placed nearby and to provide a high output power quality without the need of external filters. At the same time, the Star-C requires a significantly lower amount of components than multilevel converters able to reach similar performance. This work introduces the novel converter topology, explains its control and modulation and compares it with conventional two- and three-level converters in terms of THD, efficiency, current ripple and cost. The results show that the Star-C offers a THD that is up to ten times lower than its closer contester. Additionally, its efficiency is slightly higher due to the fact that zero current switching is used. On the other hand, the cost and size of the Star-C is significantly higher than the other converters under comparison. However, this work does not include the cost of the external filters that each converter might require, which is expected to reduce the cost gap between the Star-C and conventional converters. Note that this paper is based on the findings in "Star-C - A new converter topology" by Alexander Holmström

Electric roads : Reducing the societal cost of automotive electrification

In this article five scenarios for fully electric road transport in Sweden are compared, looking at the total system cost for different combinations of battery systems, vehicle equipment and charging solutions, including the use of Electric Road Systems (ERS). The main objective of this work is not to provide accurate price estimations, but to help understanding the main cost drivers of transport electrification and to illustrate how the final system cost is influenced by the different parameters considered. The main conclusion obtained is that, despite the substantial initial investments required for the deployment of electric roads, a system featuring only static charging and vehicles with large size batteries results in a higher total system cost. Moreover, due to the much larger number of light duty vehicles in the fleet, the deployment of an ERS system that can be used by both long-haul and light duty vehicles is substantially more advantageous than a solution restricted only to long-haul vehicles