Grid-connected plug-in electric vehicles (PEVs) are considered as one of the most sustainable solutions to substantially reduce both the oil consumption and greenhouse gas emissions. Electric vehicles (EVs) are broadly categorized into low power EVs (48/72 V battery) and high power EVs (450/650 V battery). Low power EVs comprise two-wheelers, three-wheelers (rickshaws), golf carts, intra-logistics equipment and short-range EVs whereas high power EVs consist of passenger cars, trucks and electric buses. Charger, which is a power electronic converter, is an important component of EV infrastructures. These chargers consist of power converters to convert AC voltage (grid) to constant DC voltage (battery). The existing chargers are bulky, have high componentsβ count, complex control system and poor input power quality. Henceforth, to overcome these drawbacks, this thesis focuses on the onboard charging solutions (two-stage isolated and single-stage non-isolated) for the low voltage battery EVs. Power factor correction (PFC) is the fundamental component in the EV charger. Considering the specific boundaries of the continuous conduction mode (CCM) operation for AC-DC power conversion and their complexity, the proposed chargers are designed to operate in discontinuous conduction mode (DCM) and benefiting from the characteristics like built-in PFC, single sensor, simple control, easy implementation, inherent zero-current turn-on of the switches, and inherent zero diode reverse recovery losses. Proposed converters can operate for the wide input voltage range and the output voltage is controlled by a single sensor-based single voltage control loop making the control simple and easy to implement, and improves the system reliability and robustness.
This thesis studies and designs both single-stage non-isolated and two-stage isolated onboard battery chargers to charge a 48 V lead-acid battery pack. At first, a non-isolated single-stage single-cell buck-boost PFC AC-DC converter is studied and analyzed that offers reduced componentsβ count and is cost-effective, compact in size and illustrates high efficiency. While the DCM operation ensures unity power factor (UPF) operation at AC mains without the use of input voltage and current sensors. However, they employ high current rated semiconductor devices and the use of diode bridge rectifier suffers from higher conduction losses. To overcome these issues, a new front-end bridgeless AC-DC PFC topology is proposed and analyzed. With this new bridgeless front-end topology, the conduction losses are significantly reduced resulting in improved efficiency. The low voltage stress on the semiconductor devices are observed because of the voltage doubler configuration. Later, an isolated two-stage topology is proposed. The previously proposed bridgeless buck-boost derived PFC converter is employed followed by an isolated half-bridge LLC resonant converter. Loss analysis is done to determine optimal DC-link voltage for the efficient operation of the proposed conversion. The converters' steady-state operation, DCM condition, and design equations are reported in detail. The small-signal models for all the proposed topologies using the average current injected equivalent circuit approach are developed, and detailed closed-loop controller design is illustrated. The simulation results from PSIM 11.1 software and the experimental results from proof-of-concept laboratory hardware prototypes are provided in order to validate the reported analysis, design, and performance
