Showing papers on "Harmonics published in 2012"
TL;DR: Of special interest is the development of a higher harmonic rejection system that improves the spectral purity of the x-ray beam.
Abstract: We present the development and characterization of a dedicated resonant soft x-ray scattering facility. Capable of operation over a wide energy range, the beamline and endstation are primarily used for scattering from soft matter systems around the carbon K-edge (∼285 eV). We describe the specialized design of the instrument and characteristics of the beamline. Operational characteristics of immediate interest to users such as polarization control, degree of higher harmonic spectral contamination, and detector noise are delineated. Of special interest is the development of a higher harmonic rejection system that improves the spectral purity of the x-ray beam. Special software and a user-friendly interface have been implemented to allow real-time data processing and preliminary data analysis simultaneous with data acquisition.
419 citations
TL;DR: In this paper, the authors present tools allowing large signal stability analysis of a dc power system, which allows estimation of the domain of attraction of the system operating point, and the impact of the load dynamics on stability is also studied.
Abstract: Electric motor drives and power electronic converters have become increasingly common in advanced power systems. Passive LC filters are used in these systems to reduce the power ripples. These filters are usually poorly damped for reducing the losses as well as the size/weight and the cost of the system. This leads to instability phenomena if the load power exceeds a power limit depending on the filter parameters. The purpose of this paper is to present tools allowing large signal stability analysis of a dc power system. These tools allow estimation of the domain of attraction of the system operating point. It will be shown that this large signal stability analysis gives useful hints on the design of the system to optimize the stability criteria for constant and variable power loads. The impact of the load dynamics on stability is also studied. An electric drive connected to a dc power supply through a poorly damped LC filter is used as a case study. The simulations and the experimentations confirm the analytical results.
283 citations
TL;DR: The obtained experimental results show that the proposed adaptive SRF-PLL highly rejects the undesired harmonics even if the fundamental harmonic frequency of a highly polluted grid voltage abruptly varies.
Abstract: The proper operation of grid-connected power electronics converters needs using a synchronization technique to estimate the phase of the grid voltage. The performance of this synchronization technique is related to the quality of the consumed or delivered electric power. The synchronous-reference-frame phase-locked loop (SRF-PLL) has been widely used due to its ease of operation and robust behavior. However, the estimated phase can have a considerable amount of unwanted ripple if the grid voltage disturbances are not properly rejected. The aim of this paper is to propose an adaptive SRF-PLL which strongly rejects these disturbances even if the fundamental frequency of the grid voltage varies. This is accomplished by using several adaptive infinite-impulse-response notch filters, implemented by means of an inherently stable Schur-lattice structure. This structure is perfectly suited to be programmed in fixed-point DSPs (i.e., it has high mapping precision, low roundoff accumulation, and suppression of quantization limit cycle oscillations). The proposed adaptive SRF-PLL has been tested by means of the TI TMS320F2812 DSP. The obtained experimental results show that the proposed synchronization method highly rejects the undesired harmonics even if the fundamental harmonic frequency of a highly polluted grid voltage abruptly varies.
268 citations
12 Nov 2012
TL;DR: In this article, the authors proposed a close-loop method for suppression of the inner current in MMC, which can be applied to single-phase or three-phase MMCs.
Abstract: Ideally, the inner (the upper or lower arm) current of a modular multilevel converter (MMC) is assumed to be the sum of a dc component and an ac component of the fundamental frequency. However, this current is usually distorted and the peak/RMS value of it is increased compared with the theoretical result. This is because ac current flows through the submodule (SM) capacitors and the capacitor voltages fluctuate with time. The increased currents will increase power losses and may threaten the safe operation of the power devices and capacitors. This paper proposes a novel close-loop method for suppression of the inner current in MMC. This method is very simple and is implemented in stationary frame, and no harmonic extraction algorithm is needed. Hence, it can be applied to single-phase or three-phase MMC. What is more important, this method does not influence the balancing of the SM capacitor voltages. Simulation and experimental results show that the proposed method can suppress the peak and RMS values of the inner currents dramatically. Meanwhile, the harmonic contents in the output current can also be suppressed satisfactorily even when the SM capacitor voltage ripple factor is as large as about ±19%. Therefore, the proposed method can also be adopted to reduce the SM capacitance requirement.
254 citations
TL;DR: A scalable transmitter architecture for power generation and beam-steering at THz frequencies using a centralized frequency reference, sub-harmonic signal distribution, and local phase control is presented using a novel method called distributed active radiation.
Abstract: In this paper, we present a scalable transmitter architecture for power generation and beam-steering at THz frequencies using a centralized frequency reference, sub-harmonic signal distribution, and local phase control. The power generation and radiator core is based on a novel method called distributed active radiation, which enables high conversion efficiency from DC to radiated terahertz power above fmax of a technology. The design evolution of the distributed active radiator (DAR) follows from an inverse design approach, where metal surface currents at different harmonics are formulated in the silicon chip for the desired electromagnetic field profiles. Circuits and passives are then designed conjointly to synthesize and control the surface currents. The DAR consists of a self-oscillating active electromagnetic structure, comprising of two loops which sustain out-of-phase currents at the fundamental frequency and in-phase currents at the second harmonic. The fundamental signal, thus gets, spatially filtered, while the second harmonic is radiated selectively, thereby consolidating signal generation, frequency multiplication, radiation of desired harmonic and filtration of undesired harmonics simultaneously in a small silicon footprint. A two-dimensional 4×4 radiating array implemented in 45 nm SOI CMOS (without high-resistivity substrate) radiates with an EIRP of +9.4 dBm at 0.28 THz and beam-steers in 2D over 80° in both azimuth and elevation. The chip occupies 2.7 mm × 2.7 mm and dissipates 820 mW of DC power. To the best of the authors' knowledge, this is the first reported integrated beam-scanning array at THz frequencies in silicon.
243 citations
TL;DR: The main contribution of this paper is the proposal of new modulation techniques for three-phase transformerless neutral point clamped inverters to eliminate leakage currents in photovoltaic systems without requiring any modification on the multilevel inverter or any additional hardware.
Abstract: The main contribution of this paper is the proposal of new modulation techniques for three-phase transformerless neutral point clamped inverters to eliminate leakage currents in photovoltaic systems without requiring any modification on the multilevel inverter or any additional hardware. The modulation techniques are capable of reducing the leakage currents in photovoltaic systems by applying three medium vectors or using only two medium vectors and one specific zero vector to compose the reference vector. In addition, to increase the system utilization, the three-phase neutral point clamped inverter can be designed to also provide functions of active filter using the p-q theory. The proposed system provides maximum power point tracking and compensation of current harmonics and reactive power. To validate the simulation models, an experimental three-phase inverter is used to evaluate leakage currents and the dc link voltage control.
231 citations
TL;DR: In this paper, a supplementary dc voltage ripple suppressing controller (DCVRSC) is proposed to eliminate the second-order harmonic in the dc voltage of the MMC-HVDC system.
Abstract: There are second-order harmonics in the dc voltage and current when the MMC-HVDC system is under unbalanced grid conditions, even if the negative-sequence current controller is employed. This paper presents a supplementary dc voltage ripple suppressing controller (DCVRSC) to eliminate the second-order harmonic in the dc voltage of the MMC-HVDC system. The instantaneous power of the converter arm and phase unit indicates that there are zero-sequence double-line frequency components in the three-phase unit voltages when the ac system is under an unbalanced fault. Since the zero-sequence components cannot be offset by each other, they lead to the second-order harmonic in the dc voltage and dc current. The DCVRSC is developed to compensate the zero-sequence components in three-phase unit voltages. Simulation results based on a detailed PSCAD/EMTDC model prove that the DCVRSC can eliminate the second-order harmonic in the dc voltage. Meanwhile, the ac currents are kept balanced under the unbalanced fault conditions.
228 citations
TL;DR: An energy-based Lyapunov function control technique is developed for a three-phase shunt hybrid active filter (SH-AF) to compensate harmonics generated by nonlinear loads and is applied for balanced operation.
Abstract: In this paper, an energy-based Lyapunov function control technique is developed for a three-phase shunt hybrid active filter (SH-AF) to compensate harmonics generated by nonlinear loads and is applied for balanced operation. The method provides compensation for harmonic load current components. The strategy determines the control law that makes the derivative of the Lyapunov function always negative for all values of the states. The dc bus voltage of the SH-AF is maintained to 50 V, which is significantly lower than that of the conventional hybrid active filter. The rating of the active filter in the SH-AF system is much smaller than the one used in the conventional shunt active power filter because the passive filter takes care of the major burden of compensation. The SH-AF performances, during both nominal and severe operating conditions, are then evaluated using a dSPACE DS1104 controller board, supported by a Matlab/Simulink Real-Time Workshop environment. A significantly high correlation between the experimental results and the theoretical model, implemented with Simulink/Matlab, is obtained.
223 citations
TL;DR: In this article, a stator current harmonic suppression method using a sixth-order resonant controller was proposed to eliminate negative sequence fifth-and positive sequence seventh-order current harmonics in a doubly fed induction generator (DFIG) wind turbine system.
Abstract: Voltage harmonics in the grid can introduce stator current harmonics in a doubly fed induction generator (DFIG) wind turbine system, which may potentially impact the generated power quality. Therefore, wind turbine current controllers need to be designed to eliminate the impact of grid voltage harmonics, especially low-order harmonics. This paper proposes a stator current harmonic suppression method using a sixth-order resonant controller to eliminate negative sequence fifth- and positive sequence seventh-order current harmonics. A stator current harmonic control loop is added to the conventional rotor current control loop for harmonic suppression. The overall control scheme is implemented in dq frame. Based on a mathematical model of the DFIG control system, the effects on system stability using the resonant controller, an analysis of the steady-state error, and the dynamic performance, are discussed in this paper. Taking these effects into account, the parameters of the resonant controller can be designed and effectively damp the influence from the grid voltage harmonics. As a result, the impacts of the negative sequence fifth- and positive sequence seventh-order voltage harmonics on the stator current as well as the electromagnetic torque are effectively removed. Simulations and experiments are presented to validate the theoretical analysis.
205 citations
TL;DR: Both simulation and experimental results have shown that low torque ripple and reduced stator current harmonics are achieved by using the proposed PMSM torque predictive control scheme.
Abstract: The direct torque control (DTC) technique of permanent-magnet synchronous motors (PMSMs) receives increasing attention due to its advantages in eliminating the current controllers and quicker dynamic response, compared with other motor control algorithms. However, high torque and stator flux ripples remain in the system when using DTC technologies. This means large stator voltage and current harmonic contents exist in the PM motors. Since the variation of motor electromagnetic torque is related to the voltages that are applied to the motor, by analyzing the relationships between stator flux, torque, and voltages, a PMSM torque predictive control scheme is proposed in this paper. In each digital signal processor cycle, the optimized voltage is utilized to reduce torque ripple, and the voltage vector angle is determined by the output of torque and flux hysteresis controllers. The proposed scheme is simulated and experimentally verified. Both simulation and experimental results have shown that low torque ripple and reduced stator current harmonics are achieved by using the proposed scheme.
201 citations
TL;DR: In this paper, a synchronous-frame repetitive controller for three-phase UPS inverters is presented, which minimizes the repetitive control time delay to one-sixth of the fundamental period such that the dynamic response is significantly improved.
Abstract: This paper presents a novel synchronous-frame repetitive controller for three-phase UPS inverters. Distinguished from conventional repetitive control techniques, the proposed synchronous-frame approach minimizes the repetitive control time delay to one-sixth of the fundamental period such that the dynamic response is significantly improved. In order to overcome the harmonic distortions under severe load conditions (e.g., unbalanced and nonlinear), in this paper, three synchronous rotating frames are deliberately selected, in each of which the repetitive controller is incorporated. Resultantly, the (6n ±1)th harmonics as well as the triplen harmonics are compensated. Moreover, a high-performance fourth-order linear phase infinite-impulse-response filter is applied to further enhance the accuracy of steady-state tracking. The proposed controller is programmed on the 16-bit fixed-point digital signal processor (TI TMS320LF2407) and eliminates high-resolution current sensors for cost effectiveness. Simulations and experimental tests have been carried out based on an 18-kW three-phase UPS system. Low total harmonic distortion (<;0025;) has been achieved under heavily distorted nonlinear load and unbalanced load. Fast dynamic response has been demonstrated during step load transients.
TL;DR: In this paper, Ghimire et al. extended the model to include propagation effects and showed that the predicted efficiency is limited by phase velocity mismatch for emission below the band gap and by absorption above the gap.
Abstract: The observation of nonperturbative high-order-harmonic generation in periodic solids has been interpreted in terms of a two step process comprising tunnel ionization and radiation from electrons undergoing frequency modulated Bloch oscillations in a strong laser field [Ghimire et al., Nat. Phys. 7, 138 (2011)]. Here we extend the model to include propagation effects. We show that the predicted efficiency is limited by phase velocity mismatch for emission below the band gap and by absorption above the band gap. The efficiency of harmonics scales with the square of the carrier density, suggesting that direct seeding could lead to higher yield. The emitted harmonics should have a temporal profile consisting of a train of subcycle pulses with duration on the order of 650 as depending on the crystal thickness.
TL;DR: The experimental observation of 1D and 2D self-accelerating nonlinear beams in quadratic media shows that the intensity peaks of the first and second harmonics are asynchronous with respect to one another, but the coupled harmonics exhibit joint acceleration within the nonlinear medium.
Abstract: We present the experimental observation of 1D and 2D self-accelerating nonlinear beams in quadratic media, which are also the first nonlinear self-accelerating beams in any symmetric nonlinearity. Notably, we show that the intensity peaks of the first and second harmonics are asynchronous with respect to one another, but the coupled harmonics exhibit joint acceleration within the nonlinear medium. Finally, we demonstrate the impact of self-healing effects on the jointly accelerating first and second harmonics.
TL;DR: A method to monitor solder fatigue in a voltage source inverter insulated gate bipolar transistor power module by detecting the change of an inverter output harmonic is presented.
Abstract: Condition monitoring power semiconductor devices can inform converter maintenance and reduce damage. This paper presents a method to monitor solder fatigue in a voltage source inverter insulated gate bipolar transistor power module by detecting the change of an inverter output harmonic. It is shown that low-order harmonics, caused by nonideal switching, are affected by the device junction temperature, which in turn depends upon module solder condition. To improve the detection accuracy of the phenomenon, the inverter controller is set to cause harmonic resonance at the target harmonic frequency. The would-be resonance is suppressed by an outer control loop where the control action can be used as the condition monitoring signal. Simulation and experiment are presented to validate the method and evaluate its performance in operation.
TL;DR: A combination of low- and high-frequency hybrid active power filter to operate in parallel for better performance and a combination of feedforward and feedback controller is designed for the proposed conditioner.
Abstract: This paper proposes a combination of low- and high-frequency hybrid active power filter (APF) to operate in parallel for better performance. The individual hybrid APF is a series combination of L-C filter with the corresponding voltage source inverter. The dc links of both the inverters are connected in parallel, and the voltage of the dc link is maintained by the low-frequency inverter (LFI). The low- and high-frequency inverters eliminate lower order and higher order harmonics, respectively. In addition, it is possible to design the LFI such that it can also compensate the reactive power of the load. The individual L-C filter of the hybrid topology is designed to take care of specific order of harmonics that are predominant in the load. A combination of feedforward and feedback controller is designed for the proposed conditioner. The performances of the proposed topology and the controller are first examined by MATLAB/SIMULINK-based simulation. An experimental prototype is also designed to confirm the usefulness of the proposed system.
TL;DR: A novel six-band hysteresis technique to efficiently control the seven-level packed U cells (PUC) converter using the advantages of the flying capacitor and the cascaded H-bridge topologies is proposed.
Abstract: In this paper, the authors propose a novel six-band hysteresis technique to efficiently control the seven-level packed U cells (PUC) converter. The proposed PUC combines advantages of the flying capacitor and the cascaded H-bridge topologies. The novel control strategy is proposed in order to insure a good operation of the PUC converter in both inverter and rectifier modes. In case of rectifier operation, the proposed six-band controller is designed to draw a sinusoidal line current (load current in case of inverter operation) with a unity power factor. Harmonics contents of line current (or load current) and rectifier input voltage (or inverter output voltage) are very low which permits the reduction of the active and passive filters ratings resulting on a very high energetic efficiency and a reduced installation cost. The proposed concept was validated through experimental implementation using real-time controller, the DS1103 of dSpace.
TL;DR: In this paper, a variable sampling period filter phase-locked loop (VSPF-PLL) was proposed for three-phase systems, which is based on a sliding-Goertzel-transform-based filter.
Abstract: This paper proposes a novel variable sampling period filter phase-locked loop (VSPF-PLL) for use in the general area of three-phase systems. It is based on the concept of variable sampling period, which allows to automatically adjust the sampling frequency to be NPLL times the line frequency. Conventional three-phase PLL are based on synchronous reference frames (SRFs) to estimate the phase error between the PLL and the input signals. However, SRF transform fail when the voltage waveforms are distorted. In this paper, a sliding-Goertzel-transform- based filter is used in the loop to reject disturbances, such as unbalanced voltage and harmonics. It allows to detect the positive sequence present in the systems without errors. Characteristics of VSPF-PLL, including its mathematical model as well as steady state and dynamic responses, are discussed in this paper. The method is implemented in a DSP and tested using typical disturbances, such as frequency steps, unbalances, harmonics, saturation, and line-to-ground fault. Comparative simulations are performed between the proposed VSPF-PLL and some of the most common three-phase PLL described in the literature. Advantages of the proposed system over the methods analyzed are also discussed. Structural simplicity, robustness, and harmonics rejection are other attractive features offered by the proposed system.
TL;DR: In this paper, an improved software PLL is designed, which is capable of accurately and rapidly tracking the frequency and phase angle of the fundamental grid voltage under distorted grid conditions, and a proportional integral plus resonant (PI-R) current controller in the synchronously rotating reference frame is employed to simultaneously regulate the fundamental and harmonic components of rotor currents without any sequential component decomposition.
Abstract: This paper presents enhanced control strategies for doubly fed induction generator (DFIG)-based wind power generation systems under distorted grid voltage conditions. The mathematical model of DFIG, in view of the fifth- and seventh-order components of grid voltage harmonics, is proposed and analyzed in detail. Based on the analytical model, further studies are conducted on the distortions of stator/rotor currents and the oscillations in the stator active/reactive powers as well as the electromagnetic torque, where the impact of DFIG's load conditions is considered. Meanwhile, alternative rotor current references are calculated to enhance the uninterruptable operation capability of the wind-turbine-driven DFIG systems under distorted grid conditions. An improved software PLL is designed, which is capable of accurately and rapidly tracking the frequency and phase angle of the fundamental grid voltage under distorted grid conditions. A proportional integral plus resonant (PI-R) current controller in the synchronously rotating (dq) reference frame is employed to simultaneously regulate the fundamental and harmonic components of rotor currents without any sequential component decomposition. Experiment results on a 3-kW DFIG prototype demonstrate the correctness of the analytical results and the effectiveness of the software PLL and PI-R current controller when the grid voltage is distorted.
TL;DR: It is shown that rotor loss reduction is lower than expected in the MMF space harmonic amplitude and frequency distribution, and some considerations about the harmonic impact are given.
Abstract: Fractional-slot permanent-magnet (PM) machines have several advantages, but they suffer from the high content of space harmonics in the air-gap magnetomotive force (MMF) distribution. The MMF space harmonic amplitude and frequency depend on the particular combination of numbers of slots and poles. Such harmonics induce losses in the rotor since they are not synchronous with the rotor speed. This paper compares several kinds of machines with the same stator lamination but with different numbers of phases; three-, five-, and seven-phase PM machines are considered. Several winding configurations are compared, changing the number of poles but maintaining the same number of slots. Although in each case there is a reduction in terms of harmonic content, it is shown that rotor loss reduction is lower than expected. Some considerations about the harmonic impact are given. Although no experimental results are given, this paper refers to previous works in which rotor losses have been investigated and measured experimentally.
TL;DR: The proposed algorithm can restore the dispersing spectral leakage energy caused by the DFT and regain its harmonic/interharmonic magnitude and respective frequency and not only high precision in integer harmonic measurement can be retained but also the interharmonics can be accurately identified, particularly under system frequency drift.
Abstract: The discrete Fourier transform (DFT) is still a widely used tool for analyzing and measuring both stationary and transient signals in power system harmonics. However, the misapplications of the DFT can lead to incorrect results caused by some problems such as an aliasing effect, spectral leakage, and picket-fence effect. A strategy of recursive group-harmonic power minimizing algorithm is developed for systemwide harmonic/interharmonic evaluation in power systems. The proposed algorithm can restore the dispersing spectral leakage energy caused by the DFT and regain its harmonic/interharmonic magnitude and respective frequency. Every iteration loop for harmonic/interharmonic evaluation can guarantee to be convergent using the proposed group-harmonic bin power algorithm. Consequently, not only high precision in integer harmonic measurement can be retained but also the interharmonics can be accurately identified, particularly under system frequency drift. The numerical example is presented to verify the proposed algorithm in terms of robust, fast, and precise performance.
TL;DR: In this article, a generalized phase-matching model is proposed for the generation of high-order harmonics using laser pulse energies in the few-μJ range at high repetition rates.
Abstract: We investigate the generation of high-order harmonics using laser pulse energies in the few-μJ range at high repetition rates. We analyse how the conversion efficiency is influenced by the tight focusing geometry required for the generation of high-order harmonics under these conditions. A generalized phase-matching model allows us to discuss macroscopic phase effects independent of focal length. We present experimental results using the example of a 100 kHz laser system to generate harmonics up to the 27th order in Ar with a photon flux up to 3 × 109 photons s−1 into one harmonic order. High-repetition-rate femtosecond or even attosecond light sources open new possibilities for a broad range of applications such as time-resolved photoelectron spectroscopy and microscopy in the extreme ultraviolet regime.
TL;DR: An application of FORTRAN feasible sequential quadratic programming is presented to find the optimal sizing of parameters of C-type passive filters for minimizing the total voltage harmonic distortion of nonlinear loads, where maintaining a given power factor at a specified range is desired.
Abstract: In its broadest sense, passive filters have been a very potent technique for power system harmonic suppression because of their possible different frequency response characteristics that can achieve a certain required harmonic filtering target, also due to their simplicity and economical cost. This paper presents an application of FORTRAN feasible sequential quadratic programming to find the optimal sizing of parameters of C-type passive filters for minimizing the total voltage harmonic distortion of nonlinear loads, where maintaining a given power factor at a specified range is desired. The optimal design of the C-type passive filter as an alternative to the conventional passive filtering techniques is introduced, and a detailed comparison of the results between an uncompensated system and a C-type filter are discussed by means of different numerical examples, considering source and load nonlinearities, while taking into account compliance with the IEEE standards 519-1992 and 18-2002.
TL;DR: The proposed method is capable of estimating the accurate values of frequency, amplitude, and phase angle of the distorted current or voltage signals for a wide range of sampling frequency and measurement noise.
Abstract: Harmonic, which is becoming more and more important day by day in the emerging power system, is one of the most critical power quality parameters. In this paper, the estimation of signal parameters via rotational invariance technique (ESPRIT)-based method is proposed with an accurate model order (the number of frequency components) estimate for power system harmonic and interharmonics detection. It is demonstrated that, even for high noise signal, the proposed algorithm is able to accurately estimate the number of frequency components present in the signal. The proposed method is capable of estimating the accurate values of frequency, amplitude, and phase angle of the distorted current or voltage signals for a wide range of sampling frequency and measurement noise. The robustness of the proposed method has been tested on several simulated synthetic signals and measured experimental signals for different nonlinear loads.
TL;DR: The structure and the mathematical model of a two-stage saturable MCR (TSMCR) are proposed and it is shown that the maximum current harmonics of the novel MCR can be limited to 3.61% of the rated output current.
Abstract: Magnetically controlled reactors (MCRs) are usually used as three-phase shunt reactors. They have low harmonic distortion independent of the third harmonic current because most three-phase MCRs are delta connected. However, as arc suppression coils, MCRs are operated in the single-phase mode, and the harmonics can be much higher than those of three-phase MCRs. In this paper, the structure and the mathematical model of a two-stage saturable MCR (TSMCR) are proposed. There are two stages with different lengths and areas in the iron cores. The stages saturate at different times when the TSMCR outputs reactive current. The current harmonics of the first saturated stage can be compensated for when the second stage begins to saturate, to reduce the total harmonics of the output current. The mathematical model that reveals the distribution characteristics of the current harmonics for the TSMCR is also presented. A study of the mathematical model indicates that there are two key factors that affect the total current harmonics of the TSMCR. One is the parameter k, which represents the area ratio of the second stage to the first stage. The other one is the parameter m, which represents the ratio of the length of the first stage to the total length of the magnetic valve in the iron core. The simulations and experiments show that the maximum current harmonics of the novel MCR can be limited to 3.61% of the rated output current when k and m are chosen according to the theoretical mathematical model.
TL;DR: In this paper, a variable on-time controller for a critical conduction mode (CRM) buck PFC front-end converter for isolated high-brightness LED applications is proposed.
Abstract: For high input voltage (>;264 Vac) ac/dc applications, a buck power factor correction (PFC) converter is a good choice because of its low output voltage, high efficiency, lifetime improvement, and cost reduction by using a low voltage rating (<;200 V) electrolytic capacitor. However, due to the inherent dead angle of the input current, the harmonics of the buck PFC converter are high, which limits its application in lighting systems. In order to make the buck PFC converter meet the harmonics requirements (IEC61000-3-2, Class C) in lighting applications, this paper proposes a variable on-time controller for a critical conduction mode (CRM) buck PFC front-end converter for isolated high-brightness LED applications. By feedforwarding the input voltage and regulating the on-time of the switch, the high-order harmonics can be reduced to meet the lighting system limitations. Experimental results obtained on a 150-W CRM buck front-end PFC prototype show that the efficiency of buck PFC exceeds 96% during the entire line input range (250-530 Vac) at full load, and the current harmonics content can meet the harmonic requirements.
TL;DR: In this article, a frequency adaptive phase-locked loop (PLL) is proposed for single-phase systems, which is based on the concept of variable sampling period technique, already implemented in a three-phase digital synchronization method proposed by the authors.
Abstract: This paper proposes a frequency adaptive phase-locked loop (PLL) for use in single-phase systems. The main objective is to obtain a reliable synchronization signal even in polluted grids, where the fundamental frequency is contaminated with harmonics, or present variations in phase, amplitude, and/or frequency. The proposed PLL is based on the concept of a variable sampling period technique, already implemented in a three-phase digital synchronization method proposed by the authors. This single-phase method allows us to automatically adjust the sampling frequency to be an integer multiple of the line frequency. In this case, the phase error is calculated just by one multiplication, thereby reducing implementation. A sliding Goertzel transform-based filter is also used in the loop to reject the undesired effects of this phase error detector and line disturbances, such as harmonics. To stabilize the loop, a controller that maximizes the bandwidth with an acceptable transient is introduced. The characteristics of the proposed single-phase PLL are described and the experimental results obtained from a DSP implementation are presented. A set of comparative simulations between the proposed PLL and some single-phase PLL described in the literature are conducted to validate the method. The advantages of the proposed system over other methods analyzed are also dealt with. The robustness of the system is verified by the experimental tests conducted as well as by the harmonic filtering properties. The system is also characterized by its simple architecture, which allows us to provide a high dynamic response with a very much reduced number of calculations.
TL;DR: A rigorous method to introduce the concept of in-loop filters and window functions into PLL systems is presented and enables smoother estimation of the signal parameters such as phase angle, frequency, and amplitude in the presence of noise and harmonics.
Abstract: This paper addresses the concept of in-loop filters in phase-locked loop (PLL) systems. The in-loop filters are derived from an optimization perspective, and an analytical method to design the controlling parameters of a PLL with in-loop filters is also presented. Such filters can also be selected as conventional window functions in which case they can be tuned to reject certain frequency components similar to the discrete Fourier transform. In this paper, a rigorous method to introduce the concept of in-loop filters and window functions into PLL systems is presented. This method enables smoother estimation of the signal parameters such as phase angle, frequency, and amplitude in the presence of noise and harmonics. The in-loop filters can be adjusted to completely remove specific harmonics. The method is first developed for a single-phase enhanced PLL system and is then extended to three-phase PLLs including the well-known synchronous-reference-frame PLL. Simulation and experimental results are also included.
TL;DR: Measurements reveal that, for the conditions optimum for harmonic generation, the orientation is produced by preferential ionization which depletes the sample of molecules of one orientation.
Abstract: We produce oriented rotational wave packets in CO and measure their characteristics via high harmonic generation. The wave packet is created using an intense, femtosecond laser pulse and its second harmonic. A delayed 800 nm pulse probes the wave packet, generating even-order high harmonics that arise from the broken symmetry induced by the orientation dynamics. The even-order harmonic radiation that we measure appears on a zero background, enabling us to accurately follow the temporal evolution of the wave packet. Our measurements reveal that, for the conditions optimum for harmonic generation, the orientation is produced by preferential ionization which depletes the sample of molecules of one orientation.
TL;DR: In this paper, the frequency response of the zeroth- and second-order filters is established and illustrated and it is demonstrated that, for orders greater than or equal to two, the filters are able to form zero flat phase response about the operation frequency and then able to provide instantaneous estimates.
Abstract: Recently, the TaylorK Kalman filter was proposed for estimating instantaneous oscillating phasors. Its performance was examined through time-domain simulations using the benchmark test signals specified in the IEEE Standard for Synchrophasors for Power Systems. It was discovered that the estimation error level was abruptly reduced by a factor of ten from the second order, mainly because those filters were able to provide instantaneous phasor estimates. In this paper, the frequency response of the zeroth- and second-order filters is established and illustrated. They demonstrate that, for orders greater than or equal to two, the filters are able to form zero flat phase response about the operation frequency and then able to provide instantaneous estimates. By assessing the behavior of the estimates before signals with harmonics, or noise, not contemplated in the signal model, the frequency response method leads us to design more robust filters, referred to as TaylorK Kalman-Fourier, because they incorporate the whole set of harmonics in their multiharmonic signal model. It turns out that the bank of comb filters achieved with K = 0 is equivalent to that of the discrete Fourier transform, with a computational cost of one and a half products per harmonic estimate, which is lower than the FFT cost for more than eight components, and the bank of fence filters obtained with K = 2 is similar to that of the Taylor2 Fourier transform but with the advantage of providing estimates devoid of delay and needing only four products per harmonic set of estimates. Due to their instantaneous character, and computational simplicity, those estimates are certainly very useful for real-time harmonic analysis and power system control applications.
TL;DR: The proposed dc link APF, which is composed of two series-connected bidirectional boost converters, intends to eliminate the input current harmonics and exhibits better total harmonic distortion of the ac line current when compared with the traditional ac side shunt APF.
Abstract: In this paper, a dc link active power filter (APF) for three-phase diode rectifier is proposed. The proposed dc link APF, which is composed of two series-connected bidirectional boost converters, intends to eliminate the input current harmonics. It is paralleled at the dc link of the diode rectifier and is coupled to the ac input with three line-frequency switches. Compared with the full power processed power factor correction (PFC) solution, the dc link APF is partially power processed in that it only compensates for the harmonic current component at the dc link. Thus, it features with lower power processing. Moreover, it exhibits better total harmonic distortion of the ac line current when compared with the traditional ac side shunt APF. Voltage and current loop models are developed for average current control, and the selection of the current loop bandwidth is presented. Switching stresses of the ac APF, the dc link APF, and the six-switch PFC are also calculated and analyzed. Experimental and simulation results demonstrate the effectiveness of this dc link APF.