Six-Step Mode Control of IPMSM for Railway Vehicle Traction Eliminating the DC Offset in Input Current

In the six-step mode control of the interior permanent-magnet machine (IPMSM), inequality of the positive half-cycle length and the negative half-cycle length will bring about dc offset in the three-phase input current. This paper proposes a six-step mode control scheme of IPMSM for railway vehicle traction to eliminate the dc offset in input current. An approximately continuous rotor position signal is reconstructed in the field-programmable gate array chip. This position signal is used to generate the square drive signal for IPMSM in the flux-weaken region. Rotor position signal error of the resolver will also cause dc offset in the three-phase input current. A novel scheme using phase-locked loop to decrease the rotor position signal error is proposed. And using this scheme, the dc offset is eliminated from the three-phase input current. A seamless transition scheme from six-step mode control to space vector pulse width modulation (SVPWM) mode is proposed. The effectiveness of this six-step mode control scheme is proved by the experimental results.