Voltage Oscillations Research Articles

A novel intelligent-based method to control the output voltage of Proton Exchange Membrane Fuel Cell

The Proton Exchange Membrane Fuel Cell is a low-temperature electrochemical device that offers promising advantages such as higher efficiency compared to conventional power sources, possibly a green choice with avoiding air polluting problems. The mentioned advantages will be obtained once the Fuel Cell is accurately and efficiently controlled. Experimentally, there are two significant problems in efficiently controlling of the Fuel Cell voltage including high-speed voltage oscillations and low-speed dynamic response. As well, the co-evolution ribonucleic acid genetic algorithm is presented as a novel algorithm to obtain the optimal control parameters. This algorithm is motivated from the biological Ribonucleic Acid and encodes the chromosomes by Ribonucleic Acid nucleotide basics and accepts some Ribonucleic Acid operations. Present work adopted some genetic operators to preserve the diversity of individuals, and individuals are separated into two sets. Different evolutionary methods are considered for these two sub-populations for compromising between exploration and explanation. Primarily, a comprehensive model of Proton Exchange Membrane Fuel Cell is presented. For presenting a simple application and reliable industrial control system, this paper showed a lead-lag controller. Firstly, this control system is adjusted to a certain operational point. Despite to reveal appropriate information considering the present condition of the plant, its efficiency will be decreased by varying the situations. So, the next step is employing the proposed co-evolutionary ribonucleic acid genetic algorithm for obtaining optimum values for controller parameters versus the varying conditions as well as fault occurrences. Finally, the obtained results are presented for efficiency validation of suggested control system, and these obtained results are analyzed.

On-Line Detection of Voltage Transformer Insulation Defects Using the Low-Frequency Oscillation Amplitude and Duration of a Zero Sequence Voltage

The insulation degradation of a voltage transformer winding is not easy to find, but it may ultimately cause the transformer to explode, leading to accidents such as phase-to-phase short circuits. At present, power transformers, lightning arresters, and other equipment have on-line methods to detect the insulation state. However, there is no mature method for the on-line monitoring of voltage transformer winding insulation. In this study, a small current disturbance method based on a zero-sequence loop is proposed. The characteristic parameters of the low-frequency oscillation of zero-sequence voltage after a disturbance are used to evaluate the insulation state of the winding and detect faults. Theoretical modeling, simulation tests, and field tests show that when the insulation resistance of the voltage transformer winding is in the range 0–40 kΩ, a low frequency oscillation of about 10 Hz can be detected on the zero-sequence voltage, and its amplitude and duration are proportional to the degree of damage to the insulation. This can hence be used as a criterion for the on-line detection of voltage transformer winding insulation defects.

Analysis and design of a sustainable microgrid primarily powered by renewable energy sources with dynamic performance improvement

Sustainable microgrid primarily powered by renewable energy sources is a recent concept to fulfill the pledge of delivering reliable power supply for upcoming power systems. This study presents a microgrid system primarily powered by wind and solar energy sources and identifies the issues related to the design, operation, and control of the system. The system is designed and simulated to detect the practical issues involved in the control and operation of the sustainable microgrid system based on wind and solar sources. The technical challenges and a brief plan of conceptual methods to detect some of the technical issues are presented for further analysis. To achieve power quality improvement, effective control architecture is described here. Furthermore, an advanced random pulse position modulation technique for the voltage source inverter is proposed to influence the DC-link inductor which further reduces the harmonic distortion. A current injected control loop (CICL) is also proposed to improve the dynamic behavior of microgrid, due to change in solar radiation and wind speed, which causes DC bus voltage oscillation and, hence, affects in proper system operation. The simulation results report that the microgrid system powered by renewable energy sources have a good performance.

Integrated control strategy for smooth switching of the PV and battery‐storage micro‐grid based on operation state tracking

Micro-grid which connects with the main grid can operate under the grid-connected mode or the islands mode. During the switching process between the two operation modes, if the control strategy is not complete, there will be problems such as the AC bus voltage oscillation and current surge, which will result in the switchover failure. An improved energy storage inverter control method based on operation states tracking is adopted for the optical storage micro-grid using master–slave control, which solves the problem of control variables mutation. Secondly, an improved software phase-locked method based on grid phase state tracking is proposed in an energy storage inverter. The problem of instantaneous mutation of the phase angle is solved by cooperating with the micro-grid operation state control signal during operation mode changes. Through the improvement of the two control strategies above, the transient shock phenomena of the micro-grid voltage and current during the switching process is obviously improved, and the harmonic content of the AC voltage and current is obviously reduced. Finally, a detailed model of optical storage micro-grid is established in MATLAB/Simulink, and the correctness and practicability of the improved control strategy are verified by simulation.

Contribution to the analysis of PWM inverter parameters influence on the partial discharge inception voltage

The work presented in this paper deals with the influence of pulse width modulation (PWM) power supply parameters on the partial discharge inception voltage (PDIV). For a given system supplied using PWM, the behavior of partial discharges may be different from a classical AC or DC power supply configuration. An experimental study was conducted in order to observe changes in PDIV levels with respect to PWM parameters such as duty cycle, switching frequency and voltage rise time. Measurements were done on a simple twisted pair of enameled wires, placed inside a climatic chamber for control of the environmental conditions. The experimental results show that the PDIV depends mainly on the waveform of the voltage oscillations; a voltage oscillation with a low frequency would favor the appearance of partial discharges (PD) because the probability of the presence of an initiatory electron to initiate the discharge is higher. Moreover, the waveform shape depends mainly on the rise time of the voltage and the length of the power cable. A parameter that also has a significant effect is the duty cycle; a low duty cycle in unipolar power is favorable for the appearance of PD.

Neutral-Point Voltage Analysis and Suppression for NPC Three-Level Photovoltaic Converter in LVRT Operation Under Imbalanced Grid Faults With Selective Hybrid SVPWM Strategy

Balanced issues of neutral-point (NP) voltage in the neutral-point-clamped (NPC) three-level photovoltaic converter have been studied in depth. Numerous algorithms for NP voltage control have been proposed and proven to be effective in normal operations. However, most of the previous studies fail to consider the effect of imbalanced loads on NP voltage, especially under low-voltage-ride-through (LVRT) condition, which faces problems of imbalanced grid voltages and low power factor. In this paper, through derivation of NP current model for different loading conditions, the behavior of NP voltage under LVRT condition is comprehensively analyzed for the first time. Then, theoretical limitations of NP voltage control based on two common space-vector-pulsewidth modulations (SVPWMs) that three-nearest-vectors and symmetric SVPWM are investigated, and additional low-frequency oscillation in NP voltage is analyzed. This oscillation is dominated by fundamental frequency and has different generation mechanisms under different imbalanced grid faults. Then, a novel method of selective hybrid SVPWM, as selective combinations of SVPWM and virtual SVPWM according to different imbalanced grid faults, is proposed to effectively suppress NP voltage oscillations in LVRT operation without any complex improvements and increase of dc-link capacitor values. Finally, the analytical result and performance of the proposed method are confirmed in an existing 300 kW NPC converter.

Influence of a power supply model on simulated Hall thruster discharge voltage oscillations

Hall thrusters are spacecraft propulsion devices that generate and accelerate plasma to provide thrust. Despite the use of constant voltage supplies to power these devices, complex finite-rate and convective effects lead to significant discharge current oscillations in most operating modes. In this paper, we demonstrate the interaction of finite impedance in the electrical harness with fundamental oscillatory behavior of the thruster by implementing a self-consistent harness model in a physics-based Hall thruster code. Results confirm previous work that voltage ripple is directly proportional to the total impedance for the majority of reasonable harnesses lengths. However, for extremely long harness lengths, results indicate that nonlinear coupling eventually dominates to reduce the voltage ripple with increased impedance.

Control Design, Stability Analysis and Experimental Validation of New Application of an Interleaved Converter Operating as a Power Interface in Hybrid Microgrids

This paper presents a new and specific use of a bidirectional interleaved converter to perform a power interface in hybrid microgrids. The converter is responsible for regulating the power flow between the direct-current (DC) microgrid and the rest of the hybrid microgrid by controlling the DC microgrid voltage. The authors present a detailed modeling of the mentioned system in order to develop the system control design and a stability analysis. In addition, the authors propose a new control design strategy aiming at improving the voltage control disturbance rejection characteristic, while maintaining a good dynamic behavior regarding the reference tracking functionality. In this hybrid microgrid topology, a back-to-back converter connects the main grid to the AC microgrid. The main objective of this converter is to provide a high-power-quality voltage to critical and sensitive loads connected to the microgrid. The interleaved converter adjusts the DC microgrid voltage according to the operational voltage of the back-to-back converter DC link. In the DC microgrid case, the variation of load and generation connection could lead to serious voltage sag and oscillations that could be harmful to the sensitive loads. The voltage controller must be capable of rejecting these disturbances in order to maintain a high-power-quality voltage. Furthermore, experimental results are provided in order to validate this specific application of the interleaved converter and the presented control design strategy.

Investigation of chaos and memory effects in the Bonhoeffer-van der Pol oscillator with a non-ideal capacitor

In this paper, the voltage fluctuations of the Bonhoeffer van der Pol oscillator system with a non-ideal capacitor were investigated. Here, the capacitor was modeled, using a fractional differential equation in which the order of the fractional derivative, α, is also a measure of the memory in the dielectric. The governing fractional differential equation was derived using two methods, namely a differential and integral approach. The former method utilized a hierarchical resistor-capacitor (RC) ladder model while the latter utilized the theory of the universal dielectric-response. It was found that the dynamical behavior of the potential across the capacitor was affected by the parameter α and, therefore, the memory of the system. Additionally, findings indicate that an increase in the memory parameter was associated with an increase in the energy stored in the dielectric. Furthermore, the effects of the dynamical behavior of the voltage on the capacity of the dielectric to store energy was examined. It was found that oscillation death resulted in a higher amount of stored energy in the dielectric over time, as compared to behavior, which displayed relaxation oscillations or chaotic fluctuations. The relatively-lower stored energy resulting from the latter types of dynamical behavior appeared to be a consequence of the memory effect, where the present accumulation of energy in the capacitor is reduced by previous decreases in the potential. Hence, in this type of scenario, the dielectric material can be thought of as “remembering” the past behavior of the voltage, which leads to either a decrease, or an enhancement in the stored energy. Moreover, an increase in the fractional parameter α, under certain conditions, led to the earlier onset of the chaotic voltage oscillations across the capacitor. On the other hand, the corresponding phase portraits showed that the chaotic behavior was heightened, in general, with a decrease in α. The non-ideal capacitor was also found to have a transitory nature, where it behaves more like a resistor as α → 0, and conversely, more like a capacitor as α → 1. Here, a decrease in α was linked to an enhanced metallic character of the dielectric. Finally, a possible link between the complexity of the voltage noise fluctuations and the metallic character of the non-ideal capacitor will be discussed.

Three-Phase Three-Level Flying Capacitor PV Generation System with an Embedded Ripple Correlation Control MPPT Algorithm

This paper presents the implementation of a maximum power point tracking (MPPT) algorithm in a multilevel three-phase photovoltaic (PV) system using the ripple correlation control (RCC) method. Basically, RCC adopts the inherent oscillations of PV current and voltage as perturbation, and it has been predominantly used for single-phase configurations, where the oscillations correspond to the 2nd order harmonics. The implementation of an RCC-MPPT algorithm in a three-phase system has not been presented yet in the literature. In this paper, the considered three-phase three-level converter is a three-level flying capacitor (FC) inverter. The proffered RCC method uses the 3rd harmonic components of PV current and voltage for the estimation of the voltage derivative of the power dPpv/dVpv (or current, dIpv/dVpv), compelling the PV array to operate at or very close to the maximum power point. The analysis and calculation of the low-frequency PV current and voltage ripple harmonic components in the three-phase flying capacitor inverter is presented first, with reference to centered carrier-based three-level PWM. The whole grid-connected PV generation scheme has been implemented by MATLAB/Simulink, and detailed numerical simulations verified the effectiveness of the control method in both steady-state and dynamic conditions, emulating different sun irradiance transients.

A simple electronic device to experiment with the Hopf bifurcation

We present a simple low-cost electronic circuit that is able to show two different dynamical regimens with oscillations of voltages and with constant values of them. This device is designed as a negative feedback three-node network inspired in the genetic repressilator. The circuit's behavior is modeled by a system of differential equations which is studied in several different ways by applying the dynamical system formalism, making numerical simulations and constructing and measuring it experimentally. We find that the most important characteristics of the Hopf bifurcation can be found and controlled. Particularly, a resistor value plays the role of the bifurcation parameter, which can be easily varied experimentally. As a result, this system can be employed to introduce many aspects of a research in a real physical system and it enables us to study one of the most important kinds of bifurcation.

Understanding the characteristics of nano mineral oil under nonstandard oscillatory impulse voltage

This paper illustrates the breakdown strength of oscillatory impulse voltage for different barrier electrode gap with the dispersed titania (Tio2) nanoparticles in the mineral oil. The breakdown strength varies with addition of surfactant added in the nanoparticles and with different frequencies. Comparison is done by undergoing breakdown tests using alternating current (AC), direct current (DC), and lightning impulse voltages. Tests are to be done to prove that sin bidirectional oscillatory impulse voltage (SBOIV) provides higher breakdown strength when titania is dispersed in mineral oil and higher than other standard voltages.

A 600V PiN diode with partial recessed anode and double-side Schottky engineering for fast reverse recovery

In this paper, a novel 600 V PiN diode for fast recovery is proposed and the operation mechanism as well as the high dynamic ruggedness of the device are analyzed in detail. The proposed structure features the alternating P/N region with partial recessed P region at anode side and the P Schottky as well as the N Schottky contacts at both sides. In on-state, the carrier injection efficiency can be modulated by adjusting the work function of the anode P Schottky contact (WSA), which is based on MSC (Metal-Semiconductor-Contacts) concept. As a result, the fast recovery is realized due to the reduced amount of the stored carriers and the shortened carrier extraction path. In off-state, the leakage current can be effectively suppressed attributed to the rapid pinch-off of the depletion layer. The forward voltage drop (VF) and the reverse recovery time (trr) of the proposed structure can be adjusted by changing the depth of the P Schottky contact (tra) on the sidewall, without sacrificing the breakdown voltage (BV). The proposed structure achieves a trr of 75ns which is 45.7% and 33% lower than that of the conventional PiN and the MPS structure at the same VF of 0.965 V, respectively. Moreover, the total amount of holes in the N buffer layer can be supplemented by adjusting the work function of the cathode N Schottky contact (WSC) during reverse recovery, resulting in a high-dynamic ruggedness with suppressed voltage oscillation and voltage overshoot.

Coherent emission from the stack of Josephson junctions with the non-uniform inductive interaction

During last decade, considerable efforts were made to achieve coherent emission from stacks of many Josephson junctions. It is known that strong emission from a junction in the presence of external magnetic field appears at the so-called Fiske steps in the IV-characteristic at voltages which correspond to frequencies of geometrical resonances. However, it is possible to obtain resonant steps in long junctions without external magnetic field. The periodical movement of fluxons is excited due to some disorder in the distribution of critical currents along junctions. The so-called zero-field steps are formed in the IV-curve due to the interaction of fluxons with oscillations of voltage at Josephson frequencies. We investigated numerically IV-characteristics and the dependence of the average square of ac voltage at the end of the stack of two long Josephson junctions on the average voltage. Junctions interacted inductively with each other. We introduced not only the Gaussian distribution of critical currents along junctions but also the Gaussian distribution of coefficients of the interaction between junctions (mutual inductances). Zero-field steps in the IV-characteristic were found at voltages which corresponded to frequencies of in-phase collective modes in the stack as well as to frequencies of uncoupled junctions. Zero-field steps appeared in the hysteretic region of the IV-curve. There appeared also jumps of voltage from the resistive branch to the zero-field step. We showed that there existed distributions of mutual inductances along junctions which provided jumps to voltages at which the average square of ac voltage at the end of the stack (which is proportional to power of emission) was larger than that for the stack with the uniform distribution of mutual inductances.

Comparing Anodic Bubble Behavior of Anodes from Anisotropic and Isotropic Cokes in Laboratory Scale Aluminum Electrolysis Cells

During production of aluminum in Hall-Héroult cells, carbon anodes electrochemically oxidize to form mainly CO2. The CO2 bubbles block the anode working surface during growth and coalescence, leading to cell voltage loss and voltage oscillations. Lower grade isotropic petroleum cokes are currently being introduced to anodes worldwide, but little is known about effects of coke quality on the unavoidable voltage losses linked to bubble formation. To investigate this, a pilot carbon anode series was made with various blended ratios of isotropic to anisotropic coke. The anodes were characterized with respect to voltage oscillations related to bubble formation and release, wettability toward electrolyte and surface roughness before and after electrolysis. Results showed that voltage noise caused by gas bubbles was reduced for anodes containing isotropic coke. For blended anodes of isotropic and anisotropic coke, the potential oscillation amplitude was reduced by ∼0.19 V compared to a 100% anisotropic coke anode. The percentage of the anode surface screened by gas bubbles was also reduced as isotropic coke was introduced. Increased wettability between electrolyte and two anodes containing isotropic coke was observed after anode polarization. The reduced bubble screening on the anode surface was attributed to better wetting between anode and electrolyte.

Morphology Evolution during Delithiation of Li-Pb Alloys: Oscillatory Electrochemical Behavior

We report on a study of morphology evolution following de-lithiation of Li-Pb alloys, produced by the electrochemical lithiation of Pb particulate and sheet electrodes. Electrochemical titration and time of flight measurements were performed in order to determine the intrinsic diffusivity of Li, , as a function of alloy composition, which ranged from 10−12–10−10 cm2s−1. Morphology evolution was studied under conditions of galvanostatic and potentiostatic dealloying. For the particulate electrodes, we observed dealloyed morphologies corresponding to Kirkendall voids, negative dendrites, void nodules and conventional bicontinuous nanoporous structures. In the case of Pb sheets, similar dealloyed morphologies were obtained under galvanostatic dealloying conditions, however, in the case of potentiostatic dealloying, we did not observe the formation of large volume bicontinuous nanoporous structures. For Pb sheets lithiated to a composition corresponding to the Li8Pb3 phase and galvanostatically dealloyed at current densities ∼1 mAcm−2, voltage oscillations were observed with periods of 70–90 s and amplitudes ranging from 20–130 mV. Current oscillations were also observed for potentiostatic dealloying at 1 V vs Li+/Li. The possible mechanism of these oscillations is discussed and attributed to a salt film precipitation and lift-off process.

Experimental observation of synchronised oscillating edges in electrical lattice with series‐connected tunnel diodes

Herein, the authors experimentally characterise the dynamics of voltage edges oscillating in a transmission line with regularly spaced two series-connected tunnel diodes (TDs). They clearly observe the mutually synchronised behaviour of the edges supported by each TD, which can be utilised to generate large-amplitude and low-phase-noise oscillatory voltages. They establish the fact that the response time of the device for state-transition is the key to qualitatively determine the edge oscillation, i.e. a single large-amplitude edge develops for sufficiently a large response time, whereas two larger and smaller edges coexist and are synchronised for short response time.

Monolithic GaN Half-Bridge Stages With Integrated Gate Drivers for High Temperature DC-DC Buck Converters

This paper presents a GaN based synchronous buck DC-DC converter, which monolithically integrates gate drivers and a half-bridge power stage in a 3-μm enhancement-mode (E-mode) GaN-on-Si process. The fabricated synchronous converter with integrated gate drivers is based on E-mode GaN MIS-HFETs (metal-insulator-semiconductor heterojunction-field-effect-transistors), which have a large gate swing of 10 V due to the insertion of 20 nm high-k gate insulator Al 2 O 3 . At 100 kHz, the proposed DC-DC integrated circuits (ICs) exhibit good thermal stability at high temperatures up to 250 °C for 25 V down conversion. Furthermore, four different designs (asynchronous and synchronous) including converters with external drivers were systematically evaluated at different input voltages and duty cycles, the GaN-based DC-DC converters with integrated gate drivers exhibit small voltage overshoots and oscillations due to reduced parasitic inductance and chip size. These results validate the advantages of monolithic, lateral integration of half-bridge GaN ICs with gate drivers for high temperature power converters.

A Reconfigurable Low-Voltage and Low-Power Millimeter-Wave Dual-Band Mixer in 65-nm CMOS

In this paper, we propose, investigate, and demonstrate a reconfigurable low-voltage and low-power millimeter-wave mixer in a 65-nm CMOS, which can be switched as either a subharmonic mixer (SHM) or a fundamental mixer (FM) for the dual-band applications. Based on a modified Gilbert mixer topology, the proposed CMOS mixer can operate at a low supply voltage and low local oscillator (LO) pumping power while providing good performance in both SHM and FM modes. To the best of our knowledge, this is the first reported Gilbert SHM based on the stacked switching quads in a low-voltage CMOS technology. Under 1-V supply voltage and −3-dBm LO pumping power, the measured conversion gain (CG) of the proposed CMOS mixer is −4.8 ± 1.5 dB from 34 to 56 GHz and −0.1 ± 1.5 dB from 17 to 43 GHz in the SHM and FM modes, respectively. The measured double-sideband (DSB) noise figure (NF) is 18.5–20 dB from 37 to 49 GHz and 12.4–14 dB from 17 to 35 GHz in the SHM and FM modes, respectively. The measured input third-order intercept point (IIP3) is 2.9 and 3.4 dBm, respectively, for the SHM and FM modes at the LO frequency of 22 GHz. In addition, the total dc power consumption of the proposed mixer including output buffers is 7 mW in both the operation modes.

Solid-State Single-Port Series Damping Device for Power Converters in DC Microgrid Systems

In dc microgrid systems, power converters with input filters sometimes encounter unwanted input voltage and current oscillations, due to interactions among the bus impedance, filters, and converters. This paper presents a solid-state single-port series damper (“ S 3 damper”) that can deal with such oscillations. The damper, which is connected in series between the input filter and the converter, is realized by operating a transistor as an ac resistor. It lowers the quality factor of the filter and thus increases the damping effect on the interaction between the filter and the converter. It also increases the input impedance of the filter to avoid voltage and current oscillation between the filter and the bus. In addition, the transistor is regulated at a low dropout voltage to reduce power dissipation. The control mechanism is autonomous. Furthermore, the proposed damper does not require any power capacitor or inductor, favoring high compactness and reliability. Modeling, design, and comprehensive analysis of the S3 damper will be provided. A prototype damper for a commercially available 100 W dc–dc converter operated on a 48 V bus has been built and evaluated.