DC Current and Torque Ripple Mitigation in Modular PMSG Drives for Multi-MW WECSs with Linear PWM Inverter Modulation

Abstract

The paper analyzes a torque and DC-current ripple mitigation strategy in a modular axial-flux permanent magnet synchronous generator for multi-MW Wind Energy Conversion Systems (WECSs). The machine modules are aligned with one another and driven by the same shaft. Each module is connected to its own two-level converter and the converters are paralleled at the DC side. In order to reduce the DC-side current harmonics and the ripple in the resultant torque, a phase shift between the converters' PWM carrier signals is implemented. The converters are operated within the linear PWM modulation range. A mathematical analysis is carried out. A criterion for the best choice of the phase shift in two-and three-module configurations is developed. Theoretical results are compared with those from simulations in Matlab/Simulink, verifying the soundness of the method.

Electric Stress in Power Electronics Applications

“…In [7] the approach of sequential command applied to SPWM modulation was proposed. The expression for the DC side current was developed.…”

“…Substituting the expression of the approximated DC side current, developed in [7], in (5), an approximate expression of…”

“…• comparing the effect on capacitor dielectric ageing of a well-established modulation technique, i.e., Sinusoidal Pulse Width Modulation (SPWM), versus sequential command SPWM [7]. Classical control strategies, in fact, may prove sub-optimal when using the electric stress as a benchmark.…”

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

“…An approximated analytical expression for the electromagnetic torque and the dc bus voltage was developed in [3,9], which shows the main harmonics in the torque and the dc voltage along with the dependencies of each harmonic on the shift angle of the carrier signal ψ c µ where µ is the module number (here, µ = 1, 2, 3, 4). Such analytical approximated expression proved to be accurate for estimating both harmonic order and amplitudes for both the torque and dc voltage when compared with results of a Simulink model [3]. The choice ψ c µ = {0 0 , 90 0 , 180 0 , and 270 0 } cancels the harmonics of the order (h = m f ± 3, 2m f , 3m f ± 3 where m f is the frequency modulation ratio) and the least order harmonics left in the torque and voltage expressions is 4m f .…”

“…The WECSs with Sequential Command was proposed in [3]. The conversion system involves the connection of a two-level IGBT converter with each module of the machine.…”