Control of Integrated Three-level and Multi level Converter Topologies with Driving and Charging Capabilities for Switched Reluctance Motor Drive-Train Based EV Application

Abstract

The application of switched reluctance motors (SRMs) for industrial electrical drives is slow despite its simple construction, ruggedness, and extensive research in the past decade. The higher ripples in the torque profile and acoustic noise are the primary disadvantages of SRM. For continuous torque production in SRM, active torque producing phases ideally need to be serially excited via a rectangular current waveform. However, with limited phase voltage applied, this cannot be achieved, resulting in sharing of total torque among the incoming and outgoing phases during the commutation region. The sharing of the total torque among commutating phases majorly accounts for ripples in the torque profile for SRM. Thus, during commutation, the contribution of the incoming and outgoing phase torque towards the total torque needs to be controlled judicially via the employed control algorithm for targeting torque ripple minimization in SRM. In the existing literature, the control techniques developed/proposed for SRM achieve torque ripple minimization for a limited operating region in the torque-speed curve. In order to simultaneously enhance/improve the smooth torque operating region and the torque/ampere ratio, the thesis investigates a new direct torque control (DTC) for a 4-phase SRM. With the investigated DTC scheme, the contribution of the incoming and outgoing phases toward the total torque is monitored as per the respective phases' real-time inductance profile. However, with the limited phase voltage applied via the conventional converter for SRM, the ripple in the torque profile via the proposed DTC scheme can only be minimized to a certain extent. For further enhancing the operating region in the torque-speed curve, the thesis investigates a multi-level converter topology (MLCT) which aids in improving the energization and de-energization of the phase current. The commutation region width is reduced with improved energization and de-energization, resulting in a smooth torque profile for higher operating speeds. With the advancement in control techniques and extensive research towards different MLCTs, SRM-based drive-trains are extensively developed for electric vehicle (EV) applications. Since EVs are powered via a battery storage system, charging them is another area of research concerning SRM-based drive-train. Conventional EV drive-train employing SRM as traction motors have separate on-board charging module/s for charging the battery via AC and/or DC sources. However, on-board charging modules incur an additional cost and are limited in their charging power output due to size and cost constraints associated with the EV drive-train. However, for SRM, its isolated phase winding configuration allows easy integration of driving and charging modes, and such drive trains are termed integrated drive trains. With integrated drive-trains, the requirement of separate on-board charging modules and associated passive element/s is/are eliminated as the traction converter power electronic/s component/s, and the phase winding/s are reconfigured/reutilized to realize the battery charger functionality. In the existing literature, the SRM-based integrated drive-trains neglect their performance validation during the driving mode of operation, which results in higher ripples in torque profiles. Moreover, most proposed ICs do not achieve net zero charging torque production via the charging current within the reconfigured phase winding/s. Thus, a mechanical fixture is used for validating the efficacy of the integrated drive-trains during charging mode, which has practical limitations. The thesis identifies this as an active research area and proposes three-level and multi-level integrated drive trains for SRM with zero charging torque production. In addition, with the implementation of the investigated DTC technique, the performance of the proposed integrated drive-trains is improved for the drive mode of operation.