Single-phase three-level space vector pulse width modulation algorithm for grid-side railway traction converter and its relationship of carrier-based pulse width modulation

A significant problem of three-level neutral point clamped converters is the fluctuation of the neutral point voltage. A space vector pulse width modulation (SVPWM) strategy with neutral point voltage balancing for single-phase three-level converters adopted widely in railway traction drive system is proposed in this study. The relationship between the adopted SVPWM and carrier-based pulse width modulation (CBPWM) with an offset voltage injection (OVI) is analysed in details. Theoretical analysis shows that the adopted SVPWM is a special type of CBPWM-OVI methods, and can balance the neutral point voltage effectively. The high-order harmonics of the line current distribute around twice switching frequencies while the SVPWM algorithm is adopted. These performances of the proposed SVPWM are verified by simulation and experimental tests.