New advanced power conversion systems play an essential role in the extension of range and life of batteries. This paper proposes a new modular multilevel converter with embedded electrochemical cells that achieves very low cell unbalancing without traditional balancing circuits and a negligible harmonic content of the output currents. In this new topology, the cells are connected in series by means of half-bridge converters, allowing high flexibility for the discharge and recharge of the battery. The converter features a cell balancing control that operates on each individual arm of the converter to equalize the state of charge of the cells. The paper shows that the proposed control does not affect the symmetry of the three-phase voltage output, even for significantly unbalanced cells. The viability of the proposed converter for battery electric vehicles and the effectiveness of the cell balancing control are confirmed by numerical simulations and experiments on a kilowatt-size prototype.

This paper evaluates the performance of modular multilevel converters with integrated battery cells when used as traction drives for battery electric vehicles. In this topology, individual battery cells are connected to the dc link of the converter submodules, allowing the highest flexibility for the discharge and recharge. The traditional battery management system of battery electric vehicles is replaced by the control of the converter, which individually balances all the cells. The performance of the converter as a traction drive is assessed in terms of torque-speed characteristic and power loss for the full frequency range, including field weakening. Conduction and switching losses for the modular multilevel converter are calculated using a simplified model, based on the datasheet of power devices. The performance of the modular multilevel converter is then compared with a traditional two-level converter. The loss model of the modular multilevel converter is finally validated by experimental tests on a small-scale prototype of traction drive.

Traditional Modular Multilevel Converters (MMCs) need a special care to be taken for starting and for operation at low motor speeds in traction drives. Indeed, the low-frequency current may cause a significant unbalance between the converter sub-module capacitor voltages and then disturb the output waveforms. MMCs with the battery cells integrated inside the sub-modules are an alternative configuration where the traditional battery management system of battery electric vehicles is replaced by the control of the converter, which individually balances all the cells. The paper evaluates the low frequency operation of the MMCs with embedded battery cells when used as traction drives for battery electric vehicles by means of numerical simulations obtained from Matlab/ Simulink and eexperimental results from a down-scaled prototype. Results confirm that MMCs with embedded battery cells do not present any operational issue in traction drives even at low speed.

Double‐star modular multilevel converters with embedded battery cells are a ground breaking technology for the power converter of electric vehicles. In this topology, the battery cells are connected in series via half bridge DC–DC buck converter and can be independently discharged and recharged. This paper proposes a novel control system for this converter topology that can charge the battery cells from the grid at unity power factor and instantaneously balance them in terms of their state of charges without affecting the grid voltages and currents. The grid current controller is designed and implemented in the stationary reference frame using a proportional‐resonant controller, while the state of charge balancing algorithm is designed using sorting algorithm and circulating current control. The simulation and experimental results have demonstrated that the proposed control strategy can effectively charge the battery cells with a negligible distortion of the grid current and can ensure the balance of cells during the recharge without affecting the grid current.

This paper proposes an error compensation algorithm based on synchronous reference frame phase-locked loop for accurate phase estimation of the distorted three-phase voltages including asymmetrical phase voltages, harmonics, and dc offset. These errors cause undesirable periodic ripples with grid frequency in the traditional PLL and significantly degrade the overall performance of the grid-connected converters. In this paper, the effects of the errors are comprehensively analyzed in the stationary and synchronous reference frames. In particular, the errors are estimated and compensated by controlling the α-axis and β-axis components in a PLL to be balanced. The proposed compensation algorithm can be implemented by some integral operations followed by simple Integral-controllers. The performance and robustness of proposed compensation technique are investigated under distorted grid conditions. The proposed technique is numerically and experimentally verified using Matlab/Simulink and Dspace1202 control board platform.