The scarcity of fossil fuel and the increased pollution leads the use of Electric Vehicles (EV) and Hybrid Electric Vehicles (HEV) instead of conventional Internal Combustion (IC) engine vehicles. An Electric Vehicle requires an on-board charger (OBC) to charge the propulsion battery. The objective of the project work is to design a multifunctional on-board charger that can charge the propulsion battery when the Electric Vehicle (EV) connected to the grid. In this case, the OBC plays an AC-DC converter. The surplus energy of the propulsion battery can be supplied to the grid, in this case, the OBC plays as an inverter. The auxiliary battery can be charged via the propulsion battery when PEV is in driving stage. In this case, the OBC plays like a low voltage DC-DC converter (LDC). An OBC is designed with Boost PFC converter at the first stage to obtain unity power factor with low Total Harmonic Distortion (THD) and a Bi-directional DC-DC converter to regulate the charging voltage and current of the propulsion battery. The battery is a Li-Ion battery with a nominal voltage of 360 V and can be charged from depleted voltage of 320 V to a fully charged condition of 420 V. The function of the second stage DC-DC converter is to charge the battery in a Constant Current and Constant Voltage manner. While in driving condition of the battery the OBC operates as an LDC to charge the Auxiliary battery of the vehicle whose voltage is around 12 V. In LDC operation the Bi-Directional DC-DC converter works in Vehicle to Grid (V2G) mode. A 1KW prototype of multifunctional OBC is designed and simulated in MATLAB/Simulink. The power factor obtained at full load is 0.999 with a THD of 3.65 %. The Battery is charged in A CC mode from 320 V to 420 V with a constant battery current of 2.38 A and the charging is switched into CV mode until the battery current falls below 0.24 A. An LDC is designed to charge a 12 V auxiliary battery with CV mode from the high voltage propulsion battery.
- Bi-directional DC-DC converter
- Boost PFC converter
- Electric vehicle
- Low voltage DC-DC converter
Fig 1. Block Diagram of Power distribution in EV
EXPECTED SIMULATION RESULTS:
Fig 2.Simulated Results of Charging operation of the propulsion battery (a)Voltage and (b)Current in Beginning Point(c)voltage and (d)current in Nominal Point (e)voltage and (f)current in Turning Point(g)voltage and (h)current in End Point
Fig 3. DC link voltage and current during G2V operation (The current is multiplied by 100 for batter visibility)
Fig 4.Voltage and Current of Auxiliary battery during charging
(Current is multiplied by 10 for better visibility)
The second stage of OBC i.e. DC-DC converter is essential as it regulates the battery voltage and current. The most common method of charging Li-Ion batteries i.e. CC/CV mode charging is obtained by using a DC-DC converter in this chapter. The Battery is charged from 320 V to 420 V in a CC manner with a constant current of 2.38 A and further in a CV manner by keeping the battery voltage fixed at 420 V. The designed DC-DC converter supports Bi-directional power flow and the V2G mode of operation is simulated with the V2G controller, a new concept of LDC is designed here by utilizing the OBC to charge in Auxiliary battery from the propulsion battery. A single stage controller is developed in order to maintain a desired voltage across the Auxiliary battery.
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