Search

The usage of multilevel voltage source converters (VSCs) for high-power applications is becoming more common as the field of power electronic converters continues to expand and progress. In the first generation, cycloconverters were employed for ac excitation in rotor circuits with high rating doubly fed induction machine (DFIM). Two-level and, more recently, three-level VSCs are utilized for ac excitation of DFIM since the introduction of VSCs. There are many decisive factors such as cost, reliability, device count, and power level for choosing converter configuration. This article presents a new factor (electromagnetic vibration (EMV) in stator) to be considered while choosing a converter configuration for DFIM rotor circuit. The impact of rotor side converter architecture on DFIM stator EMV is investigated in this article. In the rotor excitation circuit, two-level VSC and three-level converter are employed with a carrier frequency of 1 kHz. In both situations, the air-gap flux density is studied using a finite element analysis. The Maxwell stress tensor is used to investigate the radial force density distribution in air gap. Since the EMV causes stability issues and disrupts the system performance, structural and EMV analyses were performed to investigate the influence of converter topology on stator vibrations.

The inverter-current proportional feedback (ICPF) active damping (AD) for an LCL grid-connected inverter (LCL-GCI) suffers from adverse gain reduction and loss of inductive ability in the low-frequency zone, making it unsuitable for active damping. To overcome the limitations of ICPF-AD, inverter-current bandpass filter feedback (ICBFF) AD is more conducive to suppressing the resonance of LCL-GCI. However, it is found that the system time delay constrains the damping capability of ICBFF-AD to resonance frequencies lower than those achievable with ICPF-AD. Therefore, this article proposes a second-order lead filter (SOLF) in cascade with the bandpass filter (BF) as an AD controller for inverter-current feedback AD. The analysis illustrates that cascading a SOLF with BF in the AD loop preserves the LCL filter's low-frequency gain and inductive nature resulting in improved dynamic response as compared to the ICPF-AD. Additionally, the cascaded filter AD allows the damping of higher resonance frequency with better noise immunity. The design approach for BF and SOLF is proposed and the effectiveness of the cascaded AD controller in the presence of different grid impedance is presented. The experimental results from a 10 kW laboratory setup corroborate the theoretical analysis.