Voltage Oscillations Research Articles

Auxiliary capacitor to enhance oscillation in circuit and reduce current onset delay in HiPIMS discharge: Theory, experiment and simulation

In high power impulse magnetron sputtering (HiPIMS) discharge, generally, the current onset lags the applied pulse voltage by a significant time which can reach to several tens of microseconds, especially at a low gas pressure. The existence of this delay will affect the instantaneous and average power, and in turn, it determines the plasma dynamics and the thin film properties. The origin of current onset delay can be traced back to gas breakdown in E × B fields. This work firstly focuses on the theory and model of gas breakdown in the HiPIMS discharge with parallel electrodes. Theoretically, the breakdown voltage of argon in HiPIMS is about −700 V at gas pressure of 0.45 Pa, while it can exceed −1100 V at pressure of 0.4 Pa. To operate the HiPIMS at a low pressure with a short delay time of current onset, the means using an auxiliary capacitor C connected in parallel with plasma between electrodes to enhance oscillation in circuit (named ECO-HiPIMS) is employed, which can generate a high oscillation voltage during the gas breakdown phase. Choosing a suitable capacitor, this oscillation voltage reaches up to −1322 V at applied pulse voltage of −700 V, and in turn, the delay time can be shortened from around 50 μs (in standard HiPIMS) to less than 5 μs. Finally, the plasma dynamics during gas breakdown phase in HiPIMS and ECO-HiPIMS has been investigated by a two-dimension particle in cell/Monte Carlo (2D PIC-MCC) simulation.

OCNOP Control of Grid-Connected Converters for Single-Phase Open Circuit Fault

An open circuit fault-tolerant operation of a grid-connected inverter requires switching reconfigurations or redundant inverter leg to bypass the faulty device. Such measures led to increased cost and design complexities. In the absence of such reconfiguration mechanisms, a grid-connected inverter with an open circuit fault in one of the inverter legs injects negative sequence current into the grid. The negative sequence current causes oscillation in dc-link voltage and thereby injects lower order harmonic into the grid. The present work proposes a novel control strategy (open circuit nonoscillatory power) to deliver a steady power into a balanced three-phase grid with only two active legs of the grid-connected inverter. The current of these two active phases are controlled to be equal in magnitude and 60° phase apart. This inhibits the flow of negative sequence current and in turn limits the lower order harmonic injection within the permissible limit. A control strategy is also proposed to modify the power references during postfault operation so that the postfault current in two active phases are limited within the converter current rating. The performance of the proposed scheme is compared with the conventional vector control scheme through a simulation study. The simulation results for the proposed control scheme are verified through experimental study in a laboratory prototype.

Energy Storage System Control Strategy for Restraining Overvoltage Caused by Switching Non-Load Power Transmission Lines

During the switching operation of the non-load power transmission lines, the undisired switching overvoltage issue is inevitable, causing grid voltage oscillations, waveform distortion and other phenomena at the end of the non-load power transmission lines, and even lead to the insulation breakdown, all above phenomena probably make the power transmission failure. To avoid the above harmful cases, the formation mechanism of the undisired switching overvoltage issue caused by switching non-load power transmission lines is first analyzed in detail. Based on this mechanism analysis, the energy storage system (ESS) based overvoltage suppression method and corresponding ESS voltage command synthesis algorithm are developed. The method can quickly and effectively restrain the voltage change rate and reduce the voltage difference between the initial value and the steady state value of the power transmission lines, so that the line voltage during the switching operation can be kept within the safety limit range. Finally, a simulation model was built by using MATLAB/Simulink software, and the simulation results verified the effectiveness of the proposed overvoltage suppression strategy.

Robust MMSOGI‐FLL control algorithm for power quality improvement of solar PV‐SyRG pico hydro‐BES based islanded microgrid with dynamic load

The islanded microgrids are vulnerable to stability problems during high penetration of dynamic loads like induction motors (IMs), which results in continuous oscillations in voltage and frequency, resulting in disturbances in the islanded microgrid. In this work, a modified multi-second-order generalised frequency locked loop (MMSOGI-FLL) control algorithm is implemented. This control provides a fast response of the power converter; thereby the microgrid voltage/frequency are stabilised rapidly. Besides, the control also provides the dynamic reactive power for the sudden start of an IM load and regulates the common coupling point voltage in the islanded system. The MMSOGI-FLL control also provides harmonics elimination, fast convergence, DC offset removal and reactive power compensation in the islanded system. The implemented islanded system is a combination of a pico-hydro-based synchronous reluctance generator (SyRG), solar photovoltaic (PV) array and a battery energy storage (BES). The BES is connected at DC link to maintain the power equilibrium under a change in the load and power generation. Moreover, the system used in this work is proficient in feeding the non-linear load and dynamic load of an IM. The performance of this standalone microgrid is validated with extensive tests on the developed prototype, which meets the power quality requirement of the 1547.4 standards.

Modeling and Analysis of Bridge-Leg Crosstalk of GaN HEMT Considering Nonlinear Junction Capacitances

Gallium nitride high electron mobility transistor (GaN HEMT) has fast switching speed and low threshold voltage, which could result in a severe false triggering voltage pulse at the synchronous freewheeling transistor in bridge-leg circuit when the control transistor turns on. To suppress the crosstalk phenomenon, this article proposes an analytical model about the crosstalk voltage, with consideration of nonlinearities in capacitance-voltage (C-V) of GaN HEMT. By utilizing the equivalent circuit of control transistor and synchronous freewheeling transistor, the number of analytical model parameters to be extracted can be reduced significantly. Besides, the nonlinear characteristic of junction capacitances is taken into account in the model, and the accuracy is verified by the current-voltage (I-V) curve of capacitances. Based on the model, an exhaustive investigation into the impact of device and circuit parameters on the crosstalk phenomenon is conducted. Further, for the purpose of evaluating the oscillation of crosstalk voltage, the damping ratio and oscillation frequency are acquired. The proposed model can be applied to guiding GaN device selection and printed circuit board (PCB) circuit design. The effectiveness and superiority of the proposed model are verified with simulations and experiments on a double pulse test platform.

Neutral-Point Voltage Oscillation Mitigation Scheme for Transformerless Three-Level PV Inverter in LVRT Operation With Selective Space Vector Modulation

In transformerless photovoltaic (PV) generation system, the neutral-point (NP) voltage balancing and the ground current reduction of three-level inverter are carefully regulated using a space vector modulation (SVM) scheme. Nevertheless, in low-voltage ride-through (LVRT) operation, the simultaneous reduction of NP voltage oscillation and common-mode voltage (CMV) has not been researched yet. To overcome these issues, a selective SVM (SSVM) strategy is proposed in this article. First, the NP voltage oscillation of three-level inverter in LVRT operation is analyzed in detail, which reveals that the NP voltage is affected by phase currents and duty cycles. Based on the location of output voltage and the direction of grid currents, the correct small vectors are selected under different power factor angles. Then, the small vector force (SVF) including the grid currents and duty cycle on NP voltage is proposed for the first time. According to the value of SVF, the optimal small vector having the most effective impact on NP voltage among the correct vectors and switching sequence is determined. With the proposed method, the NP voltage oscillation and CMV are reduced simultaneously in LVRT operation. Finally, the effectiveness of the proposed method is verified with experimental results.

Coordinated Power Management and Control of Standalone PV-Hybrid System With Modified IWO-Based MPPT

To augment the photovoltaic (PV) power generation conversion, a maximum power point tracking (MPPT) technique plays a very significant role. This article introduces a hybrid MPPT algorithm integrating modified invasive weed optimization (MIWO) and perturb and observe (P&O) technique under the rapid weather change and partial shading scenarios for the efficient extraction of the maximum power from the standalone PV-based hybrid system. MIWO handles the initial stages of MPPT followed by the application of the P&O algorithm at the final stages in view of acquiring the rapid global peak and maximal PV power. The studied microgrid comprises of the PV system, battery, electrolyzer, fuel cell, and load. A coordinated dc-voltage regulation and power management strategy between each subsystem of the hybrid microgrid is implemented to save the battery from the undesirable charging/discharging operation. Additionally, with the monitoring of dc voltage, the dc/dc converter associated with the battery and dc link plays as an MPPT circuit of the PV without the requirement of an extra dedicated circuit. Takagi-Sugeno (TS) fuzzy controller is adopted for suppressing/mitigating the voltage oscillations of the microgrid during the variations in the solar irradiance/temperature and power demand. The results clearly exhibit the superior performance of the proposed methodology compared with some of the existing techniques.

Correlation between OCVD carrier lifetime vs temperature measurements and reverse recovery behavior of the body diode of SiC power MOSFETs

The reverse recovery (RR) behavior of SiC MOSFET body diode is of great importance in power application, where these devices are used in a wide range of operating temperatures. The carrier lifetime in the drift region varies with temperature, and it heavily affects the tailoring of the RR current, opening reliability issues related to the RR voltage amplitude and to possible anomalous voltage oscillations during the recovery. From the users' point of view, it would be useful to have a simple technique able to give predictive information about the body diode RR behavior of commercial devices over the whole range of working temperatures. An experimental-simulation approach is presented in this paper to correlate the carrier lifetime measured by simple OCVD measurements versus temperature with the RR behavior of the body diode, that can be useful at the design stage of power converters. Simulations of the body diode reverse-recovery are performed for a wide range of carrier lifetimes. This allows to estimate the effect of changes of carrier lifetime with temperature on the body diode switching transients. Preliminary results obtained with a 1700 V/5A commercial MOSFET are shown.

Simultaneous Tuning of AVR and PSS Using Particle Swarm Optimization with Two Stages

This work presents a new method for simultaneous adjustment of automatic voltage regulator (AVR) and power system stabilizer (PSS) parameters to control voltage oscillations and damping in a synchronous generator using the particle swarm optimization algorithm (PSO) with two stages. The increment of a new stage aims to improve the efficiency of the PSO method, providing a better performance of the system. The algorithm was developed in Matlab software and used for the linearized 3-order model of a synchronous generator connected to an infinite bus. To analyze the performance of the controllers an objective function was used based on the system time response to a change in the reference voltage. The results were compared with the values found by the classical design method of the conventional tuning technique.

Theoretical Harmonic Spectra of PWM Waveforms Including DC Bus Voltage Ripple—Application to a Low-Capacitance Modular Multilevel Converter

This article develops a new closed-form analytical solution to the harmonic spectrum of the pulsewidth modulated (PWM) output voltage of the single-phase inverter connected to the dc bus with considerable voltage ripple. The solution is based on a double Fourier series expansion in two variables. As the single-phase inverter forms the basic building block of most converters, the developed expressions can be applied to various topologies. This article first identifies the interactions of a single-frequency sinusoidal modulation signal and the carrier signal with the dc bus voltage harmonics. The dc bus voltage harmonics are constrained in this article to multiples of the inverter output voltage fundamental frequency. The analysis is then extended to include a multifrequency modulation signal. Starting from the general solution, new expressions for the output voltage harmonics of the modular multilevel converter (MMC) are developed. The low-capacitance MMC is chosen in this analysis due to inherent low-frequency voltage oscillations in the converter internal capacitors. The MMC analytical harmonic spectrum can incorporate the effects of the circulating current control and third harmonic injection PWM, by including the second- and third-order harmonic components in the modulation signal, respectively. The MMC analytical harmonic spectrum is benchmarked against the experimental results.

Novel driver circuit for switching performance improvements in SiC MOSFETs

Silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors (MOSFETs) are expected to be an attractive replacement for Si MOSFETs in high power applications due to their high blocking voltage, high switching speed, and low switching losses. However, a high switching speed can lead to voltage and current overshoot as well as oscillation during the switching process, which results in additional losses and severe electromagnetic interference. It can also exceed the limit of the SiC MOSFET and cause irreversible damage to the device. Based on an analysis of the SiC MOSFET switching process voltage and current overshoot and oscillation generation mechanism, a voltage-injected active gate driver (AGD) was proposed. The proposed AGD can suppress the voltage and current overshoot and oscillation by injecting voltage into the gate of the SiC MOSFET during specific switching stages. Experimental results show that when compared with the conventional gate driver (CGD), the proposed AGD can suppress the voltage and current overshoot peaks by 16% and 12%, while reducing voltage and current oscillation times by 58% and 31%, respectively.

Simulation and visualization of the interference phenomena inside DC SQUID with interferometric circuit model

Flux modulated static current-voltage characteristics are the basis of DC SQUID being the flux-to-voltage convertor utilized in high-performance magnetic field measurement systems. Those static behaviors are the results of the internal quantum interference between two Josephson junctions. However, the interferometric working principle and the interference phenomena are difficult to be intuitively visualized, either through simulation with conventional models, or through the in-situ measurement inside DC SQUID. Therefore, we redraw the equivalent circuit of DC SQUID in form of the microwave interferometer, and transform it into a concise dynamic system model to study the interferometric mechanism. The double-slit like interference phenomena inside the DC SQUID are visualized through simulations of the AC oscillation current and voltage along the SQUID washer. The concept that DC SQUID is a microwave integrated circuit working as the microwave interferometer rather than a static nonlinear transducer is demonstrated and emphasized. Those concepts help users and designers improve their understandings of quantum interference mechanism of DC SQUID for both circuit design and the practical application system development.

Dead-Zone Free Control Scheme for H-Bridge Buck–Boost Converter

The H-bridge buck-boost converter shows better efficiency compared to all other buck-boost converter variants due to the ability to work in buck and boost modes. The existence of dead-zone in voltage gain during mode transition due to the maximum and minimum duty limitations results in instability and oscillations in output voltage. This dead-zone is eliminated by overlapping the buck and boost gate signals, which results in efficiency decrement due to high switching loss. Using a common compensator in all the modes in the H-bridge buck-boost converter results in poor dynamic performance. In this article, dead-zone free control (DZFC) scheme with increased efficiency and improved dynamic performance is proposed to mitigate the dead-zone during mode transition. In the proposed DZFC scheme, dead-zone elimination is independent of the values of mode boundaries, which reduce the transition mode duration. The proposed DZFC scheme improves the efficiency during transition modes by reducing the switching loss, a generalized small-signal model valid for the buck, boost, and transition modes and a control design is proposed for improved dynamic performance. The proposed DZFC scheme is verified experimentally on a hardware H-bridge buck-boost converter prototype.

Voltage Coupling Enhancement for Transient Gate Overvoltage Suppression of Insulated Gate Trigger Thyristor in Ultrahigh di/dt Pulse Applications

In this article, a voltage coupling enhancement (VCE) technique is developed to suppress the transient gate overvoltage of an insulated gate trigger thyristor (IGTT) in ultrahigh di/dt pulse applications. It is found that, due to the gate–cathode voltage ( VG – VC ) coupling associated with the intrinsic gate–cathode capacitor ( Cgc ) and inevitable common source inductance ( LC ) of IGTT, the gate voltage ( VG ) would oscillate with the cathode voltage VC (= LC × di/dt ), which produces high gate–cathode voltage ( VGC ) oscillation. This easily leads to device failure especially at high di/dt pulse condition. Enhanced VG − VC coupling by increasing intrinsic Cgc can contribute to the close following of VG against VC , suppressing the transient gate overvoltage. Thus, a modified dummy gate IGTT (DG-IGTT) structure with increased Cgc is specially designed as a practical implementation of the VCE technique. Experimental results show that the DG-IGTT has a low gate overvoltage ( VGC- max) of 31.2 V, whereas the VGC- max of conventional IGTT is over 136.7 V. In addition, the DG-IGTT in Kelvin source package can further achieve a much lower VGC- max of 18.5 V at ultrahigh di/dt of 32.4 kA/ μ s. The DG-IGTT successfully works at the repetition rate of 200 Hz, indicating the proposed VCE technique is promising for improving device robustness in ultrahigh di/dt and repetitive pulse applications.

Cellular Pathophysiology of Mutant Voltage-Dependent Ca2+ Channel CACNA1H in Primary Aldosteronism

The physiological stimulation of aldosterone production in adrenocortical glomerulosa cells by angiotensin II and high plasma K+ depends on the depolarization of the cell membrane potential and the subsequent Ca2+ influx via voltage-activated Ca2+ channels. Germline mutations of the low-voltage activated T-type Ca2+ channel CACNA1H (Cav3.2) have been found in patients with primary aldosteronism. Here, we investigated the electrophysiology and Ca2+ signaling of adrenal NCI-H295R cells overexpressing CACNA1H wildtype and mutant M1549V in order to understand how mutant CACNA1H alters adrenal cell function. Whole-cell patch-clamp measurements revealed a strong activation of mutant CACNA1H at the resting membrane potential of adrenal cells. Both the expression of wildtype and mutant CACNA1H led to a depolarized membrane potential. In addition, cells expressing mutant CACNA1H developed pronounced action potential-like membrane voltage oscillations. Ca2+ measurements showed an increased basal Ca2+ activity, an altered K+ sensitivity, and abnormal oscillating Ca2+ changes in cells with mutant CACNA1H. In addition, removal of extracellular Na+ reduced CACNA1H current, voltage oscillations, and Ca2+ levels in mutant cells, suggesting a role of the partial Na+ conductance of CACNA1H in cellular pathology. In conclusion, the pathogenesis of stimulus-independent aldosterone production in patients with CACNA1H mutations involves several factors: i) a loss of normal control of the membrane potential, ii) an increased Ca2+ influx at basal conditions, and iii) alterations in sensitivity to extracellular K+ and Na+. Finally, our findings underline the importance of CACNA1H in the control of aldosterone production and support the concept of the glomerulosa cell as an electrical oscillator.

Detection of Ferroresonance Oscillations in Medium Voltage Networks

This paper presents a new algorithm for the detection of ferroresonance oscillations in medium voltage (MV) power systems. The proposed method is based on an analysis of estimated flux resulting from the voltage in open delta voltage transformer (VT) connection. The testing results proved that the new solution is capable of identifying quickly and reliably ferroresonance oscillations and it does not maloperate during faults. In addition, this method is simple for hardware implementation. The developed solution has been thoroughly tested on simulation runs (from the MATLAB2019b/Simulink program), as well as recorded signals.

Enhanced Control Scheme for a Three-Phase Grid-Connected PV Inverter under Unbalanced Fault Conditions

This paper presents an improved control strategy to cancel the double grid frequency oscillations in the active power, reactive power, and DC-link voltage of a three-phase grid-connected photovoltaic (PV) system under unbalanced grid condition. To achieve these goals, an enhanced positive–negative-sequence control (PNSC) to remove oscillations of active power and an instantaneous active–reactive control (IARC) to mitigate the fluctuations of active and reactive power, simultaneously, are suggested. These methods are also effective to reduce the oscillations of the DC-link voltage. To track the desired unbalanced or harmonic reference currents, improved proportional resonant (PR) current controllers have been designed using the Bode frequency analysis. Simulation studies are carried out via Matlab/Simulink® software to verify the effectiveness of the suggested control strategies.

Proportional complex integral based control of distributed energy converters connected to unbalanced grid system

The high penetration of distributed energy resources (DERs) consisting of photovoltaic and fuel cell and wind power plants into the modern power grid results in several challenges such as stability and reliability. In this regard, this paper proposes proportional complex integral (PCI)-based control scheme of distributed energy inverter (DEI) connected to the utility grid to overcome limitations of synchronous rotating coordinate systems based control schemes. The dynamic performance, power quality and stability of the grid connected DEI are enhanced in contrast to proportional integral (PI)-based control scheme during unbalanced and distorted grid voltages. A noteworthy contribution of this paper is that the third-order (3rd) current harmonic stemmed from the DC-link voltage (DC-LV) oscillations is eliminated at the grid side. Elimination of the DC-LV oscillations contributes to reducing the size of the DC capacitance and increasing the lifetime of the power conversion system. Active power reference is calculated in a closed-loop control system based on the DC-LV controller or based on maximum allowable active power injection according to the control objectives. Another contribution to previous studies is to eliminate the need for a phase locked loop (PLL). The complexities and additional hardware requirement for phase estimation are reduced. The performance comparison for two control schemes has been evaluated in terms of dynamic response, removing active power oscillations (APOs) for the DC-side voltage stability, removing reactive power oscillations (RPOs) for the AC side voltage stability, reducing the DC-LV oscillations for the elimination of third-order current harmonic and protection of the inverter from overcurrent. The effectiveness and availability of the proposed control scheme are confirmed through a set of case studies.

Electronically Tunable Mixed Mode Quadrature Oscillator Using DX-MOCCII

A new electronically tunable quadrature oscillator is presented using a biquad band pass filter. The new band pass filter is designed using two dual X second-generation multi-output current conveyors (DX-MOCCIIs), two grounded capacitors, two grounded resistors and one NMOS transistor working in the triode region. It is used to design a four-phase voltage and three-phase current output quadrature oscillator simultaneously. The frequency of the oscillator can be tuned externally through the MOS gate voltage without affecting the condition of oscillation. The phase noise, frequency stability and nonideality analysis are given. The functionality of the oscillator circuit has been confirmed by SPICE simulation and also hardware realization using commercially available IC AD844.

Design and Implementation of a Dual-Input Single-Output Photovoltaic Converter

In many solar inverters, a dc/dc converter is mainly located between the solar arrays and the inverter. This study presents an enhanced maximum power point tracking (MPPT) algorithm for photovoltaic (PV) systems that drives solar array voltages to track a reference value and decreases fluctuations and oscillations in PV voltage. Different from the previously presented methods, a novel MPPT method is proposed that ensures tracking accuracy by considering output voltage in addition to input voltage and currents. The proposed method detects d I / d V variations, compares the output voltage with the desired reference to shift operation mode and refreshes step size. The digital filtering, enhanced PI, and perturb-and-observe (P&O) tracking features of the proposed MPPT method make it robust to mitigate source fluctuations and sensitivity to partial shading based oscillations. In order to validate the success of the proposed method, a test rig has been installed with dual boost converters. The performance improvements have been verified by both simulation and experimental results that are compared to InCon and P&O MPPT methods. It is also confirmed by experimental results that the proposed MPPT method provides robust control capability in terms of tracking the reference voltage and rejecting the effects of various shading situations on solar arrays.