Multi-harmonic Control Research Articles

CSNS-II multi-harmonic LLRF upgrade and commissioning

The second phase of the China Spallation Neutron Source (CSNS-II) will employ a dual-harmonic RF system to mitigate the significant space charge effects associated with 500 kW beam power. To address this, three magnetic alloy loaded cavities, characterized by their wideband and high-gradient properties, will be integrated as multi-harmonic cavities in the upgrade project. Additionally, the current LLRF control system hardware, based on the CPCI platform, is encountering issues related to discontinuation and performance limitations. This paper presents the testing and verification of hardware upgrades and multi-harmonic control system algorithms for the magnetic alloy loaded cavity LLRF control system, ensuring the effective implementation of the multi-harmonic control algorithm within the new hardware framework.

Complementary split ring resonator-inspired multi-HCN for implementation of an efficiency-enhanced inverse class-F2,3 PA

This article introduces a conceptual framework for enhancing the efficiency of an inverse class-F2,3 (F2,3−1) power amplifier (PA) through the incorporation of an innovative metamaterial-based multi-harmonic control network (multi-HCN). In the recommended approach, the multi-HCN comprises two resonant cells inspired by square-shaped complementary split ring resonator (CSRR), which are configured to suppress unwanted harmonics and to obtain the desired waveforms. The primary focus is to showcase how CSRRs can be effectively employed to form a shunt resonator through the etching of the conductive pattern of the proposed multi-HCN. Apart their harmonic tunability, CSRRs offer various noteworthy attributes such as impressive wave restoration capabilities and the capacity to address spatial limitations. To assess the efficacy of the proposed methodology, a class-F2,3−1 PA is devised and constructed utilizing a commercially available 10 W GaN HEMT device. The presented class F2,3−1 PA yields a commendable drain efficiency (DE) ranging from 50.3 % to 84 % and achieves an output power within the range of 38 dBm to 41.2 dBm across the bandwidth of 3.3 GHz to 3.7 GHz. These significant performance metrics serve as compelling evidence, validating the effectiveness of the proposed approach. Furthermore, this achievement establishes the design as a promising path for creating high-performance, affordable PA suitable for emerging communication systems.

A feasibility study of a post-buckled beam for actuating helicopter trailing edge flap

Active trailing edge flaps (TEFs) are one of the most promising devices for helicopter vibration reduction. Smart actuators such as the piezoelectric stack actuators (PEAs) are used for TEF actuation. PEAs possess high energy density and have large force in dynamic condition but are limited to small displacements. In this investigation, we study a linear to rotary motion amplification mechanism (AM-2) based on a pinned-pinned post-buckled beam to actuate trailing edge flaps. A linear motion amplification mechanism is developed and coupled with AM-2 to amplify angular flap deflections. Experiments are conducted on bench top-test setup, and maximum flap angle deflections of the order of 12A degrees are achieved in the static case. An aeroelastic analysis is performed and 91 % reduction in helicopter vibration is obtained with multiharmonic control inputs.

Experimental active vibration control of gear mesh harmonics in a power recirculationgearbox system using a piezoelectric stack actuator

An experimental study of an active shaft transverse vibration control system forsuppressing gear mesh vibratory response due to transmission error excitation in a highpower density gearbox is presented. The proposed active control concept employsa piezoelectric stack actuator to deliver the control force through a secondarybearing. A versatile test stand that includes a closed-loop, power recirculating,dual-gearbox set-up capable of high load transfer is specially designed for this work. Theunderlying controller for computing the actuation signal is based on a modifiedfiltered-x LMS algorithm with a robust frequency estimation technique. In order to avoid thecommon out-of-band overshoot problem, an integrated adaptive linear enhancer is alsoapplied. Both single mesh frequency and multi-harmonic control cases are examined toevaluate the performance of the active control system. Additionally, the impact of theadaptive linear enhancer order as well as the controller adaptation step size on activecontrol performance is evaluated. The experiments performed show more than 10 dBreduction in housing vibrations at certain targeted mesh harmonics over a range ofoperating speeds.