DC Voltage and Torque Ripple Mitigation in Modular PMSG Drives for Off-Shore Multi-MW WECSs with Linear SPWM modulation

Abstract

A multi-modular axial flux machine is used for wind energy conversion systems (WECSs) where each module is connected to its own two-level converter. All converters are connected in series at the DC side to allow HVDC transmission. In the paper, an in-depth reasoning for the control of each individual voltage. A phase shift between PWM carrier signals of the neighbouring converters is implemented. A mathematical analysis is carried out. A criterion for the best choice of the phase shift to minimize dc voltage and torque harmonics is proposed.

Performance Comparison between Sequential Command SPWM and MLI-NPC in Multi-MW drives for WECSs

“…The modulation is SPWM with sequential command in which the carrier signals of the converters are shifted among them such that each carrier phase angle is ψ c 1 = 0 o , ψ c 2 = 90 o , ψ c 3 = 180 o and ψ c 4 = 270 o as shown in Figure 1b. The control of individual dc bus voltage for series connected converters was discussed in deep in [8]. The SPWM with sequential command conversion system is compared with a 5L NPC where the PD PWM modulation is used as depicted in Figure 2 with the AFPMSG module windings connected in series in order to elevate the line to neutral EMF to four times that of each module.…”