ABSTRACT
This paper proposes a cascaded half-bridge multilevel converter (MLC) topology for stationary battery energy storage systems (BESSs). Commonly, many lowvoltage battery modules are connected in series to create the DC-link of the inverter. Due to difference in electrochemical characteristics, voltage imbalance happens among different modules during the charge-discharge operation, which negatively affects the lifetime of the battery pack. The proposed cascaded topology allows achieving fast balancing among individual modules. The switching-in and out of each module is done by a half-bridge converter whose output is cascaded with other half bridge converters to form a staircase DC-link voltage. A four-switch H-bridge converter finally alternates this AC bus into multilevel DC voltage. The topology features less harmonics, lower voltage variations, filter-less off grid operation and a reduced size for the interfacing filter inductor with the grid. A three phase inverter is connected with DC bus which is used to drive the PMSM which in turn runs the vehicle. The pulses generated using HALL sensor readings is combined with speed controller gate signals and thereby operating the motor at required speed. A vehicle model is coupled with the motor and the speed of the vehicle with various constraints is noted.
INTRODUCTION
To reduce the carbon footprint of power systems, the energy sector has undergone a rapid transformation in the last few years, with renewable energy sources (RESs) steadily replacing the conventional power generators. Among the RESs, wind and solar photovoltaic (PV) are widely spread and have the highest penetration on the grid due to their considerable potential. However, these RESs exhibit an intermittent power output unlike the conventional power generators. Battery energy storage systems (BESSs) provide a suitable solution to reduce this power fluctuation and improve the reliability while reducing the total cost of energy for consumers. The stationary BESS is traditionally based on a standard two-level voltage source inverter (VSI) fed by a battery pack. A battery pack typically consists of multiple cells connected in series to achieve the high DC-link voltage of 350-400V. The series connection allows charging and discharging at the same current but the terminal voltage and state of charge (SoC) of each cell remain different due to electrochemical differences among the cells. When one cell exceeds the cut-off voltage during the operation, it can lead to an uncontrollable state that can cause permanent damage to the battery pack. Therefore, it is essential to integrate a battery management system (BMS) along with the battery pack. The BMS safeguards the safety limits and prevents overcharging and discharging by disconnecting the whole battery pack if necessary. A BMS is generally classified into passive and active balancing circuit. The passive BMS performs balancing by dissipating the excess energy of the cells with higher terminal voltage on shunt resistors. The active BMS performs balancing by redirecting the energy from the most charged cells to the least charged cells using semiconductor switches along with intermediate energy buffers (capacitors/inductors). The active BMS entails high cost and complexity compared to the passive one but features higher efficiency and faster balancing. Multilevel converters (MLCs) are widely used in BESSs for off-grid and on-grid applications. In a typical MLC configuration, individual battery modules are cascaded in series through the converter switches instead of being directly connected, which results in a staircase DC link voltage. The number of voltage levels in the staircase waveform is proportional to the number of cascaded modules. Besides the cascaded configuration, different MLC topologies are reported in the literature. These include neutral-point-clamped converter, flying capacitor configuration, magnetically coupled and capacitor clamped structure. To increase the power density, MLC topologies comprising a combination of battery modules and ultra-capacitors are also reported.

Block Diagram