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.

Phase‐matched second‐harmonic generation in a polymer waveguide

Abstract: Quasi‐phase‐matched second‐harmonic generation has been observed in a periodically poled nonlinear optical polymer waveguide. Key elements in this demonstration include novel nonlinear optical polymers that can be spin coated, the design and fabrication of periodic electrodes for periodic poling and the optimization of waveguide parameters to obtain single‐mode waveguides with a large overlap between fundamental and harmonic modes. Phase matching of the d33 nonlinear optical coefficient occurs over a distance L=230 μm.

A Space Vector PWM Scheme for Multifrequency Output Voltage Generation With Multiphase Voltage-Source Inverters

Abstract: Multiphase variable-speed drives, supplied from two-level voltage-source inverters (VSIs), are nowadays considered for various industrial applications. Depending on the drive structure and/or the motor design, the VSI is required to generate either sinusoidal voltages or voltages that contain a certain number of sinusoidal components (ldquomultifrequency output voltagesrdquo). The existing space vector pulsewidth-modulation (SVPWM) schemes are based on selection of (n-1) active space vectors (for odd phase numbers) within a switching period and they yield either sinusoidal voltage or sinusoidal fundamental voltage in combination with a limited amount of other harmonic terms. This paper develops a SVPWM scheme, which enables multifrequency output voltage generation with arbitrary values of various sinusoidal components in the output voltage. The method is based on initial selection of (n-1)2/2 active space vectors within a switching period, instead of the common (n-1) active vectors. By properly arranging the sequence of the vector application, it is possible to provide an automatic postreduction of the number of applied active vectors to (n-1), thus maintaining the same switching frequency as with the existing schemes while simultaneously avoiding the limiting on the generated sinusoidal output voltage components. Theoretical considerations are detailed using a five-phase VSI. The experimental verification is provided using a five-phase two-motor series-connected induction motor drive, supplied from a custom-designed five-phase DSP-controlled VSI.

Analytical analysis of the harmonic effects of a PWM AC drive

Abstract: A novel analysis is presented of the harmonic content of current, torque pulsations, and harmonic copper losses of a three-phase induction machine fed by a two-phase pulsewidth modulation (PWM) inverter. The purely analytical results are based on the assumption that the switching frequency is high compared with the fundamental frequency. It is shown that the results hold accurately for frequency ratios f/sub s//f/sub 1/>9. >

Predictive sorting algorithm for modular multilevel converters minimizing the spread in the submodule capacitor voltages

Abstract: The modular multilevel converter is a suitable topology for bidirectional ac-dc conversion in high-voltage high-power applications. By connecting submodule circuits in series, a high-voltage waveform with excellent harmonic performance can be achieved with a very high efficiency and low switching frequency. The balancing of the capacitor voltages will, however, become increasingly difficult as the switching frequency is reduced. Although the capacitor voltages can be kept balanced over time even at the fundamental switching frequency, the spread and thus also the peak variation in the capacitor voltages will typically increase at lower switching frequencies. This paper presents a capacitor voltage balancing strategy which aims to combine a low switching frequency with a low capacitor voltage ripple. This is done by a predictive algorithm that calculates the amount of charge that must be stored in the submodule capacitors during the following fundamental frequency period. The converter is then controlled in such a way that the stored charge in the submodule capacitors is evenly distributed among all the submodules when the capacitor voltages reach their maximum values. In this way, it is possible to limit the peak voltage in the capacitor at switching frequencies as low as 2-3 times the fundamental frequency. The capacitor voltage balancing strategy is first validated by simulation results at 110 Hz switching frequency. It is observed that when the proposed method is used, the capacitor voltage ripple is 35% lower compared to the case when a conventional sorting algorithm is used. The capacitor voltage balancing strategy is also validated experimentally at 130 Hz switching frequency. The experimental results show that it is possible to combine the proposed method with previously presented circulating-current control methods.