Electric vehicles (EV) are gaining popularity due to current environmental concerns. The electric drive, which is constituted by a power converter and an electric machine, is one of the main elements of the EV. Such machines suffer from common mode voltage (CMV) effects. The CMV introduces leakage currents through the bearings, leading to premature failures and reducing the propulsion system life cycles. As future EV power converters will rely on wide bandgap semiconductors with high switching frequency operation, CMV problems will become more prevalent, making the research on CMV mitigation strategies more relevant. A variety of CMV reduction methods can be found in the scientific literature, such as the inclusion of dedicated filters and the implementation of specific modulation techniques. However, alternative power converter topologies can also be introduced for CMV mitigation. The majority of such power converters for CMV mitigation are single-phase topologies intended for photovoltaic applications; thus, solutions in the form of three-phase topologies that could be applied to EVs are very limited. Considering all these, this paper proposes alternative three-phase topologies that could be exploited in EV applications. Their performance is compared with other existing proposals, providing a clear picture of the available alternatives, emphasizing their merits and drawbacks. From this comprehensive study, the benefits of a novel AC-decoupling topology is demonstrated. Moreover, an adequate modulation technique is also investigated in order to exploit the benefits of this topology while considering a trade-off between CMV mitigation, efficiency, and total harmonic distortion (THD). In order to extend the results of the study close to the real application, the performance of the proposed AC-decoupling topology is simulated using a complete and accurate EV model (including vehicle dynamics and a detailed propulsion system model) by means of state-of-the-art digital real-time simulation.

Star-connected multiphase AC drives are being considered for electromovility applications such as electromechanical actuators (EMA), where high power density and fault tolerance is demanded. As for three-phase systems, common-mode voltage (CMV) is an issue for multiphase drives. CMV leads to shaft voltages between rotor and stator windings, generating bearing currents which accelerate bearing degradation and produce high electromagnetic interferences (EMI). CMV effects can be mitigated by using appropriate modulation techniques. Thus, this work proposes a new Hybrid PWM algorithm that effectively reduces CMV in five-phase AC electric drives, improving their reliability. All the mathematical background required to understand the proposal, i.e., vector transformations, vector sequences and calculation of analytical expressions for duty cycle determination are detailed. Additionally, practical details that simplify the implementation of the proposal in an FPGA are also included. This technique, HAZSL5M5-PWM, extends the linear range of the AZSL5M5-PWM modulation, providing a full linear range. Simulation results obtained in an accurate multiphase EMA model are provided, showing the validity of the proposed modulation approach.

Neutral point voltage control converters (NPVCC) are being considered for AC drive applications, where their additional degree of freedom can be used for different purposes, such as fault tolerance or common mode voltage (CMV) reduction. For every PWM-driven converter, the CMV is an issue that must be considered since it can lead to shaft voltages between rotor and stator windings, generating bearing currents that accelerate bearing degradation, and can also produce a high level of electromagnetic interference (EMI). In light of these considerations, in this paper a three-dimensional reduced common mode voltage PWM (3D RCMV-PWM) technique is proposed which effectively reduces CMV in five-phase six-leg NPVCCs. The mathematical description of both the converter and the modulation technique, in space-vector and carrier-based approaches, is included. Furthermore, the simulation and experimental analysis validate the CMV reduction capability in addition to the good behaviour in terms of the efficiency and harmonic distortion of the proposed RCMV-PWM algorithm.