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6.1 Concluding remarks
enables EVs of different ratings to charge and discharge. The individual charging system has grid connected three-phase ac-dc converter and a series connected dc-dc converter with suitable controllers to exchange active and reactive power between the distribution node and the CS. Electric circuit based battery models have been used to represent the aggregated EV battery model. The constraints of EVs are considered by taking into account of vehicles battery characteristics such as state-of-charge (SOC), charge/discharge rate limits and charging/discharging requirements. In addition, to control and coordinate the sudden arrival and departure of EVs and to regulate the specified voltage limit (1±0.13), the CS is externally controlled using a FLC and an aggregator. Here, FLC has been used in place of other traditional control methods; which often results in computational burden due to large number of trigonometric operations. However, the use of FLC does not require neither detailed knowledge of the system under control nor its precise descriptions in terms of mathematical model.
Voltage profile evaluations have been done with different power exchange approaches such as active power, reactive power and combined active and reactive power to forsee the CS behavior. Simulation results shows consistent and accurate results with significant voltage improvement due to real time use of EVs through charging systems. The results show that the charging system and its controllers are found to be efficient in performance; since it provides better voltage control while managing the EVs batteries in the CS.
6.1.3 Theoretical Modeling of Contactless Charging Station
In Chapter III, the theoretical modeling of multiple parallel connected contactless charging system model is described. The developed model has multiple charging panel arrangement connected with an ac bus. The model proposed in this chapter details the basics of contactless system design, converters and controllers required for charging and discharging of EVs. Battery modules are connected to their respective charging points through high frequency coreless coils are described. In addition, the chapter has also investigated the bidirectional operation to facilitate forward and the reverse power flow. All the results obtained in Chapter III are very promising and such a method could be successfully applied for the future implementation of EV charging systems.
6.1.4 Computation of Mutual Inductance for Contactless System
In Chapter IV, an analytical approach for computing the mutual inductance for contactless system is proposed. Unlike transformer coils, the contactless coils are loosely coupled and the secondary of
6.1 Concluding remarks
the coil is connected with the load. The design of contactless system is very complex as the coils are usually misaligned due to variations in the system and worsen the coupling between the coils. The magnetic coupling between the primary and the secondary side depends on mutual inductance between the coils. Hence, mutual inductance is one of the crucial factors in the design of CPT system and will play a key role in determination of efficiency, power transfer, compensation capacitor etc. In order to compute mutual inductance between two coils including all lateral and angular misalignments, an analytical approach is proposed in this chapter. The method proposed is a straight forward approach based on Biot-Savart principle and their integral are computed numerically. The method works by approximating the area of secondary coil with small regions, encompassing the entire square and thereby considering the complete spiral square coils. To carry out this process, a sequence of program routine have been used. In addition, the prosed method is validated using Finite Element Analysis (FEA) and an experimental set-up is built in the laboratory. The commercial 3-D finite element tool ANSYS Maxwell 14.0.0 has been used for validating the analytical model. Finally, the analysis in this chapter compares the results of three mutual inductance calculations. The comparison of numerical values and graphical plots are shown to show the variations of mutual inductance values obtained from the three analysis. It has been observed from the results, larger the distance lowers the coupling between the coils and mutual inductance value has decreased. It has been concluded the analytical and FEA results show a very good agreement and experimental result has an error less than 10%.
6.1.5 Compensation Topologies for Contactless System
It has previously been observed from the literature, only theoretical and simulation studies have been conducted to analyze the suitable compensation topologies in CPT systems. However, the main characteristics of CPT system is the physical isolation between the source and the load as the secondary winding of the coil is movable and connected to the load. For such a loosely coupled system, a systematic analysis can cause significant errors. Overcoming this drawbacks, chapter V has presented an experimental prototype to analyze the four compensation topologies using a practical CPT system.
The study has reported the behavior of CPT system under three different cases and its characteristics plots are generated for wide range of frequency, load and distance such that the real time situations of CPT system can be analyzed. Electric equivalent circuit models of different compensation topologies are developed to explain the mechanism of power transfer in the CPT system. A comparative analysis has been done to compare the efficiency of four compensation topologies with variations in frequency, TH-1345_TPERJOY
load and distance. Thus, the theory of CPT system using compensation topology is verified using an experimental set-up connected to a rectangular primary coil and secondary coil. With these results obtained from the experiments, the theory of CPT system can be well understood and it provides a foundation for future implementation of CPT system.