Harmonic

About: Harmonic is a research topic. Over the lifetime, 44833 publications have been published within this topic receiving 495922 citations. The topic is also known as: overtone & partial.

Piezoelectric energy harvesting from concurrent vortex-induced vibrations and base excitations

Abstract: We investigate the potential of using a piezoelectric energy harvester to concurrently harness energy from base excitations and vortex-induced vibrations. The harvester consists of a multilayered piezoelectric cantilever beam with a circular cylinder tip mass attached to its free end which is placed in a uniform air flow and subjected to direct harmonic excitations. We model the fluctuating lift coefficient by a van der Pol wake oscillator. The Euler–Lagrange principle and the Galerkin procedure are used to derive a nonlinear distributed-parameter model for a harvester under a combination of vibratory base excitations and vortex-induced vibrations. Linear and nonlinear analyses are performed to investigate the effects of the electrical load resistance, wind speed, and base acceleration on the coupled frequency, electromechanical damping, and performance of the harvester. It is demonstrated that, when the wind speed is in the pre- or post-synchronization regions, its associated electromechanical damping is increased and hence a reduction in the harvested power is obtained. When the wind speed is in the lock-in or synchronization region, the results show that there is a significant improvement in the level of the harvested power which can attain 150 % compared to using two separate harvesters. The results also show that an increase of the base acceleration results in a reduction in the vortex-induced vibrations effects, an increase of the difference between the resonant excitation frequency and the pull-out frequency, and a significant effects associated with the quenching phenomenon.

A Decentralized Power Management and Sliding Mode Control Strategy for Hybrid AC/DC Microgrids including Renewable Energy Resources

Abstract: This paper presents a new decentralized robust strategy to improve small and large-signal stability and power-sharing of hybrid AC/DC microgrids and improve its performance for nonlinear and unbalanced loads. In addition to the sliding mode controller for DC/DC converters, for the sake of improving power sharing and regulating active and reactive powers injected by distributed energy resources, and moreover, controlling harmonic and negative-sequence current in the presence of nonlinear and unbalanced loads, two separate controllers for positive sequence power control and negative sequence current control are designed based on the sliding mode control and Lyapunov function theory, respectively. The theoretical concept of the proposed robust control strategy, including mathematical modeling of microgrid components, basic theorems, controller design procedure, and robustness and closed loop stability analysis are outlined. Also, this direct power/current/voltage control scheme is governed by a new hybrid AC/DC hierarchical control scheme that exploits a harmonic virtual impedance loop and voltage compensation scheme. To show the effectiveness of the proposed robust control scheme, offline time-domain simulations are done on a hybrid AC/DC wind/photovoltaic/fuel-cell microgrid with nonlinear and unbalanced loads in MATLAB/Simulink environment, and the results are experimentally verified by OPAL-RT real-time digital simulator.

Apparatus and method for matching harmonics

Abstract: An apparatus of a power amplifier is provided. The apparatus includes an input boosting circuit configured to match a second harmonic input signal using a harmonic control circuit of an input stage to maximize an efficiency and an output power, a die cell configured to receive and amplify an output signal of the input boosting circuit, and an output boosting circuit configured to receive an output signal of the die cell and to match a second harmonic output signal of the output signal of the die cell using a harmonic control circuit of an output stage to maximize the efficiency and the output power.

Computation of the periodic steady state in systems with nonlinear components using a hybrid time and frequency domain methodology

Abstract: The basic principles of an efficient new methodology for the calculation of the nonsinusoidal periodic steady state in power systems with nonlinear and time-varying components are described. All linear parts, including the network and part of the loads, are represented in the frequency domain, while nonlinear and time-varying components, mainly loads, are represented in the time domain. This hybrid process is iterative, with periodic, nonsinusoidal, bus voltages as inputs for both frequency domain solutions and time domain simulations: a current mismatch is calculated at each bus and used to update the voltages until convergence is reached. Thus the process, but not the solution, is decoupled for the individual harmonics. Its efficiency is enhanced by the use of Newton type algorithms for fast convergence to the periodic steady state in the time domain simulations. Potential applications of this methodology are in the computation of harmonic power flow and in the steady state initialization needed in the calculation of electromagnetic transients. >

A Comparison of Control and Modulation Schemes for Medium-Voltage Drives: Emerging Predictive Control Concepts Versus PWM-Based Schemes

Abstract: Control and modulation schemes for ac electrical drives synthesize switched three-phase voltage waveforms that control the electrical machine. Particularly in medium-voltage applications, the aim is to minimize both the switching losses in the inverter and the harmonic distortions of the stator currents and the torque. For a given modulation scheme, lower switching losses usually imply higher distortion factors and vice versa. This tradeoff can be described by a hyperbolic function, as shown in this paper for pulsewidth modulation (PWM). A number of predictive control concepts are rapidly emerging. Their characteristic hyperbolic tradeoff functions are derived, compared with each other, and benchmarked with respect to PWM and offline optimized pulse patterns (OPPs). It is shown that predictive schemes with long prediction horizons shift the performance tradeoff curve toward the origin, thus lowering both the switching losses and the harmonic distortions. As a result, at steady-state operating conditions, these predictive schemes achieve a performance similar to OPPs, while providing a superior dynamic performance during transients.