Pulse Energy Modulation Research Articles

Single-Phase Buck–Boost Inverter With Pulse Energy Modulation

As a popular low-cost solution for achieving both buck–boost and dc–ac conversions in distributed generation systems, the flyback-type buck–boost inverters operating under discontinuous conduction mode (DCM) have linear modulation under low power but bad dc voltage utilization under high power, whereas the buck–boost inverters under continuous conduction mode (CCM) have better dc voltage utilization under high power but more low-order harmonics under low power. In order to combine the advantages of DCM and CCM, a pulse energy modulation (PEM) technique is proposed and studied in this article, enabling the single-phase buck–boost inverter to operate under both DCM and CCM and switch between them seamlessly. The operation principle of the single-phase buck–boost inverter is introduced, and the PEM technique is specifically analyzed and modeled. The small-signal modeling analyses and results of PEM on the buck–boost inverter are compared with the commonly used sinusoidal pulsewidth modulation (SPWM), showing that PEM provides better performance and stability to the investigated single-phase buck–boost inverter.

Hybrid Modulation and Power Decoupling Control on Single-Phase Bridge Inverter With Buck-Boost Converter

Single-phase H-bridge inverters provide a convenient and flexibly modulated solution to the dc–ac power conversion at once undergoing an inherent power mismatch between dc and ac sides. This article introduces a novel hybrid modulation technique that combines conventional sinusoidal pulsewidth modulation (SPWM) with pulse energy modulation (PEM) for a new single-phase bridge inverter with active power decoupling based on the front-end buck-boost converter. The proposed single-phase bridge inverter diverts the second-order ripple power into a small film capacitor at the buck-boost converter. The proposed hybrid modulation technique modulates the bridge inverter with PEM under discontinuous conduction mode (DCM) and with SPWM under continuous conduction mode (CCM), thus achieving zero-current turn-on compared with SPWM under DCM and removes a sampling circuit as compared with PEM under CCM. A 400-W single-phase inverter system has been built in Power Simulation (PSIM 11.0) to validate the theoretical analysis. Both hybrid modulation and active power decoupling control have been implemented in the experimental prototype using DSP TMS320F28335. The simulation and experimental results show that the second-order ripple power has been successfully mitigated with active power decoupling control, and the bridge inverter is able to work under both DCM and CCM with hybrid modulation.

Pulse Energy Modulation for a Single-Phase Bridge Inverter With Active Power Decoupling Capability

Single-phase voltage-source bridge inverters are widely used in energy storage systems (ESS) and distributed energy resources to transfer dc power to grid-side ac power. The most popular modulation strategy for controlling the ac output of bridge inverters is known as carrier-based pulsewidth modulation (PWM), which varies the duty cycle of the inverter switches at a high switching frequency to achieve a target average line-frequency output voltage or current. Regarding most carrier-based PWM techniques only enable the bridge inverters to operate under continuous conduction mode (CCM) due to the nonlinearity of discontinuous conduction mode (DCM), a pulse energy modulation (PEM) technique is proposed in this article to control single-phase bridge inverters based on energy packets, enabling the inverter to operate under both DCM and CCM and switch between them seamlessly. A single-phase bridge inverter with voltage boosting and power decoupling capabilities is examined as a case study. Small-signal analyses have been conducted for the inverter system with both L-filter and LCL-filter, and the resonant spike of LCL-filter is attenuated in PEM. Simulation and experimental results verify the feasibility of PEM on the investigated single-phase bridge inverter under both DCM and CCM.

A Users Guide to Holmium Laser Lithotripsy Settings in the Modern Era

Endoscopic stone surgery has gone through rapid technological advances in the last decade with the development of next-generation holmium lasers. These systems allow the user to adjust multiple parameters that can optimize fragmentation efficiency during ureteroscopy (URS). Parameters include an increased range in pulse energy (PE), frequency (Fr), and manipulation of the pulse duration (PD). More recently, introduction of pulse modulation with the Moses TechnologyTM provides pulse modulation with energy delivered over two pulses. In light of these developments, it may be difficult for the urologist to understand how to best utilize laser settings in the modern era. We provide an overview of how PE, Fr, and PD affect three different aspects of laser lithotripsy performance: (A) Fragmentation, (B) Stone retropulsion, and (C) Laser fiber-tip degradation (Table 1). Table 1 Relationship between pulse energy, frequency, pulse duration, and pulse modulation on laser lithotripsy performance parameters.

Single-Phase Differential Buck–Boost Inverter With Pulse Energy Modulation and Power Decoupling Control

This paper presents a single-phase differential buck–boost inverter that possesses both buck–boost and active power decoupling functions without adding any power electronics or increasing the complexity of driver circuits, as compared with the previous differential inverters. Two types of operating principles are introduced: the unipolar operation with new pulse energy modulation technique enabling the inverter to operate under both discontinuous conduction mode and continuous conduction mode, and the bipolar operation with energy-based active power decoupling delivering the second-order ripple power into the output film capacitors, thus eliminating the large electrolytic capacitor at the dc side. Small-signal modeling analysis is conducted to show the characteristics of the proposed system and control. Simulation and experimental results verified the feasibility of operating principles for the differential buck–boost inverter and successful power decoupling with substantial reduction of second-order component in the dc current.

Tungsten disulfide - graphene oxide as saturable absorber for passively Q-switched mode-locked Nd: GdTaO4 laser at 1066 nm

Tungsten disulfide (WS2) & Graphene oxide (GO) based saturable absorber (SA) was demonstrated and studies for passively Q-switched mode-locked Nd:GdTaO4 laser. The fabrication process of mixed SA was described. Passively Q-switched mode-locked operation with sub-600ps pulses was obtained by using this SA. Taking into account the simpler manufacturing progress, larger single pulse energy and better modulation depth, the mixed WS2-GO saturable absorber seems to be good way as suitable saturable absorber for solid state lasers.

Pulse shortening mode-locked fiber laser by thickness and concentration product of carbon nanotube based saturable absorber

The dependence of thickness and concentration product (TCP) of single-wall carbon nanotubes saturable absorber (SWCNTs SA) on stabilizing and shortening pulsewidth in mode-locked fiber lasers (MLFLs) was investigated. We found that an optimized TCP for pulse energy and nonlinear self-phase modulation (SPM) enabled to determine the shorter pulsewidth and broader 3-dB spectral linewidth of the MLFLs. The shortest MLFL pulsewidth of 418 fs and broad spectral linewidth of 6 nm were obtained as the optimized TCP was 70.93 (μm•wt%), which was in good agreement with the area theorem prediction. This significant effect of TCP on pulse energy, SPM, pulsewidth, and spectral linewidth of MLFLs suggests that the TCP represents the total amount of SWCNTs in SA, which can be used as one of important and key parameters for characterizing the passive MLFL pulsewidth.

Slow amplitude modulation in the pulse train of a self-mode-locked Ti:sapphire laser

Periodic pulse-train amplitude modulations have been observed in a Kerr-lens self-mode-locked Ti:sapphire laser when the size of an intracavity slit is reduced below its optimal value for stable mode locking. These transient processes are dominated by 100-500 kHz periodic pulse-energy modulations and are inherent to the Kerr-lens mode-locking mechanism based on the intensity dependent transverse-beam profile of the laser and the long gain relaxation lifetime (3.2 ps) of the Ti:sapphire rod. We observe that when the slit width is decreased from 2 mm to 1.4 mm the modulation period increases from 2 ps to 10 mu s and amplitude modulation deepens to almost 100%. An explanation similar to repetitive self-Q-switching and undamped relaxation oscillation is presented, which is consistent with the experimental results. A large low-frequency timing jitter on the order of submicroseconds, associated with the periodic pulse-train modulations, is also observed. The timing jitter is analyzed by incorporating the pulse energy modulation into the phase variation through the Kerr effect and consistent results are obtained. We have determined the cavity parameters to control these detrimental processes for stable mode-locked output. The observation of the amplitude modulation further confirms the Kerr-lens self-focusing model of self-mode locking in Ti:sapphire lasers. >

Pulse energy modulation of the cw-mode-locked 1.32 μm Nd-YAG-laser by drive frequency detuning

The frequency of an acousto-optic mode-locker is detuned from the fundamental resonance frequency of the cavity resulting in undamped oscillations of the laser pulse energy. The envelope of the mode-locked pulse train consists of spikes 10 μs wide with a repetition time of 46 μs. The energy of the mode-locked pulses in a spike is increased by up to a factor of 50 compared to a cw-mode-locked pulse. The pulse width can be as short as 700 ps.