Impedance Variation Research Articles

Voltage Detection-Based Selective Harmonic Current Compensation Strategies for Photovoltaic Inverters

Voltage and current detection-based harmonic current compensation (VDB-HCC and CDB-HCC, respectively) strategies allow the use of photovoltaic (PV) inverters to enhance the grid power quality. CDB-HCC strategies require converter hardware retrofit by inserting an extra current sensor to measure load or downstream grid currents. On the other hand, VDB-HCC strategies are straightforward solutions employing only embedded measurements used for protection, control, and synchronization purposes. This paper provides a comprehensive comparison of three VDB-HCC strategies: VDB-HCC based on a single current loop (SCL); VDB-HCC based on dual parallel current control loops (DCL); and VDB-HCC based on parallel voltage and current control loops (VCL). The comparison includes the requirement of harmonic detection algorithms, PV array maximum power point tracking (MPPT) performance, stability over grid impedance variations and inverter power rating, steady-state harmonic compensation, enabling transient response, and computational burden. Experimental results using a 1.5-kW commercial PV inverter are conducted. Based on distributed HCC applications by PV systems, VCL has shown the best performance in terms of voltage distortion reduction under weak grids.

Passivity-Oriented Impedance Shaping for LCL-Filtered Grid-Connected Inverters

The passivity theory provides an effective way to tackle the instability due to the inverter-grid interaction, which tells that the system stability can be guaranteed if the grid impedance and the inverter output impedance are both passive. Since the grid impedance is generally passive, the system stability can be immune to the grid impedance variation if the inverter output impedance is also passive. This paper develops a series and parallel impedance shaping method to ensure that the output impedance of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -filtered grid-connected inverter is dissipative up to the Nyquist frequency. Since the inverter output impedance can be decomposed into two passive elements and one active element, its non-dissipative property results from the latter, and thus the virtual series impedance shaping is introduced to cancel out the active element. Unfortunately, it poses impact on the low-frequency loop gain and system phase margin in the meantime. To alleviate this impact, a high-pass filter is inserted in the series impedance shaping function. Subsequently, a virtual parallel impedance is introduced to enhance the passivity robustness, such as against filter parameter variations. Moreover, the proposed method does not require any additional sensors. Experiments from a 6-kW prototype confirm the effectiveness of the proposed method.

Compact high-efficiency energy harvesting positive and negative DC supplies voltage for battery-less CMOS receiver

In this paper, novel compact high-efficiency multi-band rectifiers that supply positive and negative output voltages are demonstrated for energy harvesting applications. The proposed voltage doubler circuits are used as real DC voltage supplies of radio frequency mm-wave CMOS receivers. Operating multi-band rectifiers have a complicated structure that required more resonance networks to force the rectifier to work in multi-band. Novel series and parallel resonance networks are implemented to force the rectifier to operate in dual-band at frequencies of 850 and 1400 MHz. The proposed resonance network eliminates the Schottky diode impedance variation as the input power or frequency changes and supports the impedance matching and minimizes the insertion loss. A novel high-quality sine-shape micro-strip inductor that obtains a quality factor above 65 over the frequency band from 200 to 1400 MHz and inductance equal to 14 ± 2 nH is designed to improve efficiency and enhance performance at low power levels. The first suggested RF voltage doubler rectifier with series resonance feedback between the input and cathode of the diode and parallel resonance operates at two frequency bands of 850 and 1400 MHz and obtains a peak conversion efficiency of 59%, a saturated output DC voltage is 2.5 V, and the conversion efficiency is 40% at RF-input-power of − 10 dBm. This voltage doubler achieves the required DC supply parameter (1.1 V and 450 uA) for biasing the mm-wave receiver at an RF input power of 0 dBm. Otherwise, the second suggested negative voltage rectifier has a maximum simulated conversion efficiency of 65%, saturated negative DC-voltage is − 3.5 V, and the conversion efficiency is 45% at an RF input power of − 10 dBm. The negative voltage rectifier obtains DC supply parameters (− 0.5 V and no current condition used for a gate bias) at − 10 dBm input power.

Synthesis, structural, impedance, optical, Mössbauer characterizations and magnetic studies of Pb-containing germanate compounds

The orthorhombic antiferromagnetic germanate minerals Pb2Fe2Ge2O9 and Pb2Mn2Ge2O9 have been prepared via solid state reaction procedure. An extensive study of structural, dielectric, optical and magnetic properties of both the germanates have been investigated by employing different measurements such as X-ray diffraction, FTIR, SEM, impedance, UV–Vis–NIR & Mössbauer spectroscopic and magnetometary. Rietveld refinement of room temperature XRD patterns revealed that both the compounds crystallize in the orthorhombic space group Pbcn. FTIR spectrum exhibits the presence of M−O & Ge–O bonds which confirms strong chemical bonding. Morphological analysis through SEM showed good crystallinity of both the samples. The variation of dielectric constant, loss tangent and impedance with frequency have been studied and it has been established that both the germanates are semiconducting at 300K (RT) which may be attributed to the stacking of ions at grain boundaries. The optical band gaps estimated by UV–Vis–NIR spectroscopic measurements further confirms the semiconducting nature of the prepared germanates. 57Fe Mössbauer spectroscopic measurement on synthesized Pb2Fe2Ge2O9 sample was carried out at RT. The obtained values of IS and QS showed that iron is in Fe3+ high spin state (t2g3eg2,s=5/2) and occupy two different sites, Fe1 and Fe2. The field dependent magnetization measurements show that both the compounds display dominant paramagnetic nature at 300K. The temperature dependent magnetization data reveal very sharp first order type AFM to PM transition at TN ∼50K and TN ∼8K for Pb2Fe2Ge2O9 and Pb2Mn2Ge2O9, respectively, and weak FM nature below Neel temperature. The field dependent properties of both the compounds have been analyzed by drawing the M versus H plots at low and room temperatures. The values of calculated effective magnetic moment 6.07μB and 3.95μB for Fe3+ and Mn3+ ions are in the high spin states (t2g3eg2,s=5/2 and )t2g3eg1,s=2.

Identification of hydration stages: An innovative study of ultrasonic coda waves using integrated sensing element (ISE)

In this study, a piezoelectric-based integrated sensing element (ISE) is prepared and preliminary employed for monitoring the hydration process based on the dominant mechanism of acoustic impedance variation of cement and coda wave idea. The results of the signal for a period of 24 h show that three different stages (0–2 h/2–12 h/12–24 h) of the cement during hydration can be distinguished by the reflected coda wave combined with its frequency-domain component, while the first arrival waveform shows almost the same pattern due to the wave trajectory only in packing material. Moreover, the wavelet analysis of the coda wave can distinguish these three stages, in line with the results from the time-domain waveform, energy, and frequency-domain spectrum.

The influence of external operating conditions on membrane drying faults of proton-exchange membrane fuel cells

A study of the influence of water management failure can help improve water management strategies, relieve flooding or drying faults. To explore the influence of drying faults on proton-exchange membrane fuel cells (PEMFCs) under different operating conditions, this study adopted an experimental measurement method combining a cathode voltage drop, voltage signal and electrochemical impedance spectroscopy (EIS). First, multiple sets of drying experiments were performed under different operating conditions, cathodic pressure drop and voltage data were collected during the experiments, and dynamic EIS measurements were performed. Then, by analyzing the pressure drop and voltage trends, the influence of different operating conditions on drying faults was obtained. In addition, the EIS results were parametrically identified using an RL(RQ-RC) equivalent circuit model to obtain ohmic, charge transfer, and mass transfer impedance values. Finally, the evolution and influence of drying faults were verified by impedance variations. The experimental results showed that the ohmic and charge transfer impedance increased significantly with the degree of drying fault, while the mass transfer impedance showed only a small fluctuation or slight increase. Increasing the cathodic back-pressure relieved drying; a larger cathodic stoichiometric ratio increased the drying rate, and a higher cell temperature was more likely to cause severe drying.

Variación de la impedancia eléctrica a lo largo de cinco años postimplantación y relación con el umbral de confort máximo (MCL) en adultos portadores de implante coclear

IntroductionThe maximum comfort level (MCL), threshold level (THR) and electrical impedance change in the postoperative period of the cochlear implant for months until they stabilize. The objective of this article is to establish the variation during 5 post-surgical years of impedance, and its relationship with MCL in unilaterally implanted adults. MethodsRetrospective study over 5 years, with 78 adult patients implanted with MED-EL in a tertiary hospital from the year 2000 to 2015. The variation in impedance, MCL and the relationship between them were analyzed in basal (9-12), medial (5-8) and apical electrodes (1-4), performing an inferential ANOVA analysis of repeated measures with comparisons between consecutive times, corrected with Bonferroni criteria. Results33 men (42.3%) and 45 women (57.7%), with a mean age of 52.7 ± 14.6 years. “Stability” was considered the time of follow-up without statistically significant differences between one visit and the next. Changes in impedance in medial electrodes ceased to be statistically significant at 3 months, and in apicals at 6 months, with mean values of 5.84 and 6.43 kohms. MCL stabilized at 2 years in basal and apical electrodes, and at 3 years in medial, with mean values of 24.9, 22.7, and 25.6 qu. There was a correlation between MCL and impedance in medium electrodes up to 3 months and in apical ones up to one year. ConclusionsElectrical impedance drops significantly in medial and apical electrodes up to 3 and 6 months. MCL increases significantly up to two years. Impedance is related to MCL up to 6 months.

Grid Harmonics Suppression for Three Phase Dual-Frequency Grid-Connected Inverter Based on Feedforward Compensation

Using a low pulse ratio, the electromagnetic interference and switching loss of an inverter can be effectively reduced, particularly in high-power applications. However, due to variations in grid impedance, it is a challenging task to achieve stable operation of an LCL-type grid-connected inverter (GCI) using the active damping method with low pulse ratio. Thus, a novel three-phase dual-frequency GCI is presented to ensure the symmetry of the output power and the stable operation of the system address stability issues. The proposed inverter topology in this article is composed of two inverters in parallel, which are, respectively, a power inverter unit (PIU) and an auxiliary harmonic elimination unit (AHEU). To reduce the switching loss and improve the inverter efficiency, the switching frequency of the PIU is relatively low, injecting current into the grid. Moreover, the feedforward compensation method is used in AHEU. AHEU operates at high switching frequency to generate a current component that is symmetrical with the ripple com-ponent, improving the power quality, without extracting the current harmonic as the current reference. The operating principle of feedforward compensation is explained, and a proper parameter design procedure is presented in this paper. Since L filters are used for the proposed inverter, the system can operate stably where the ratio of switching frequency to fundamental frequency is low. A 10 kW laboratory prototype was built. The experimental results showed that the grid current ripple could be effectively eliminated and the THD of the grid current was 3.01%. The proposed inverter has good stability in a weak grid, and the efficiency of the proposed inverter is 95.98% at rated current, which is 0.81% higher than the traditional GCI, effectively increasing the efficiency of the system.

Factors influencing the induced primary emission and induced secondary emission in the frequency range of 2 to 150 kHz

The induced primary emission leads to changes in the primary emission of a device and the induced secondary emission leads to changes in the propagation of supraharmonics in the adjacent phase due to the connection of single-phase loads spread over three phases in an installation. The induced primary emission and induced secondary emission are shown to give a significant contribution to the total emission measured at a given point in an installation. The induction of the emission is caused by the inductive and capacitive coupling among the conductors within the cables. This paper presents an analysis of four parameters that impact the magnitude of the induced emissions. Simulations carried out in COMSOL, show that the type of cable used impacts the induced emission and studies show that shielded cable with a stranded conductor with the shield grounded will lead to a reduction in the induced emissions. Among the other parameters, i.e., the load and transformer impedance and the length of the cable, the length of the cable is dominating in deciding the magnitude of the induced emissions. Analysis is carried out using Monte Carlo simulation and varying parameters stochastically. For all investigated parameters there is a strong frequency dependency. The stochastic variation of the load impedance in one phase causes a variation of 5% whereas the change in length of the cable leads to a maximum 40% variation in the considered frequency range for induced primary emission. Measurement results are presented to validate the results.

Lever-inspired triboelectric respiration sensor for respiratory behavioral assessment and exhaled hydrogen sulfide detection

Enhancing the flow sensitivity of the triboelectric respiration sensors (TRSs) is crucial in detecting shallow oral/nasal breath signal. The modulation of contact-separate distances between dielectrics is a simple and convenient tactic to enhance the output sensitivity of TRSs compared with the complex composite materials and microstructure design of the triboelectric dielectrics. Herein, a lever-inspired TRS with adjustable contact-separate distances between arms was designed for simultaneous respiratory behavioral assessment and exhaled hydrogen sulfide (H2S) detection. Results show that the TRS with the optimal length ratio of power arm to resistance arm (1:2) possesses excellent respiration sensing behaviors in measuring flow rate (0.5–8 L/min) and frequency (0.25–1 Hz), enabling the flow sensitivity under oral/nasal respiration. Meanwhile, an in-situ self-assembled Fe2+ doped polypyrrole (FPPy) sensing film was rationally selected as one of the back electrodes of triboelectric layers owing to the selective reaction between ferrous ions (Fe2+) and H2S. Under the optimal synthesis condition of FPPy film, the prepared TRS exhibits good H2S sensing performances, including a high response of 25.21% (10 ppm), good sensing repeatability (±0.46%), and low detection limit (1 ppm). Finally, a sensing mechanism on account of the impedance variations is proposed and verified based on the composition changes of the sensing materials unveiled by multiple analytical methods. This work proposes an effective way for building a flow-sensitive respiration monitoring device, and provides new insights into the impedance-induced sensing mechanism via establishing a linkage between interfacial gas chemisorption and output signals.

Multimodal CMOS Biosensor for Microbial Growth Monitoring

This paper describes a new biosensor prototype that uses microscale electrodes to measure impedance, pH, and temperature changes caused by bacterial growth <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-vitro</i> . The prototype uses multiple sensor geometries to optimize sensitivity, and employs custom circuits including an integrated CMOS lock-in amplifier (LIA) for multi-frequency impedance measurement. The gold-plated interdigitated electrodes (AuIDEs), iridium oxide (IrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )-based pH electrodes, and snake-shaped gold resistance-temperature detectors (RTDs) electrodes are implemented on a flexible PCB. The custom integrated LIA is designed and fabricated in a 0.18-μm CMOS technology with 1.8 V supply voltage. The overall sensitivity of the LIA is 240 mV/nA with a current detection sensitivity down to 1 pA. A pH measuring circuit is designed using an operational amplifier with a very low input-bias-current. A Wheatstone bridge circuit with a network of resistors and RTD electrode is used to measure RTD resistance changes caused by temperature fluctuations. The whole system is enclosed into a self-contained platform developed to monitor bacterial growth by measuring the impedance as well as the environmental growth parameters such as pH and temperature. The fabricated multi-frequency LIA was employed to test the impedance of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E. coli</i> cells with different concentrations at multiple frequencies. The results showed that the IDE can measure the impedance variation caused by the bacterial activity with sensitivities of 36.62%, 34.37%, 33.29% and 20.23% at 1, 2, 4, and 10 kHz frequency, respectively. The fabricated pH electrodes showed linearity with a linear regression (R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) value of 0.99 and can measure pH changes ranging from 4 to 10, with a sensitivity of 36, 52, and 68 mV/pH for sensing areas of 4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 9 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and 16 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The temperature sensor measurements showed that the 4 mm × 4 mm RTD gold-printed temperature electrodes had a linear relationship between resistance and temperature with a R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> value of 0.996, and the higher sensitivity of 36 (Ω/°C) compared to other tested RTD geometries. The prototype was successfully used to perform bacterial growth measurements <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-vitro</i> .

Passivity-Based Partial Sequential Model Predictive Control of T-Type Grid-Connected Converters With Dynamic Damping Injection

LCL-filter interfaced three-level T-type converters (LCL-3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C) have been widely used in low-voltage applications due to their elevated power quality. However, there exist several problems. To begin with, the performance of the finite-control-set model predictive control (FCS-MPC) controlled 3LT2C relies on an accurate system model and measurement. Consequently, output performances will be influenced when model parameter mismatches, grid impedance variation, and the dead-time of power devices occur. In addition, the robustness of the FCS-MPC controller may also encounter challenges under disturbances and noise. Further, LCL-filter has the resonance problems in the grid currents, which may endanger the system stability. To solve these problems, a passivity-based (PB) partial sequential MPC (PSMPC) with dynamic-damping (DD) injection (DDPB-PSMPC method), which outperforms FCS-MPC and ensures the asymptotic stability, is proposed. First, the passive output voltage based on the Euler-Lagrange (EL) model is obtained using dynamic damping injection. Second, by embedding passive output voltage into MPC, a passivity-based PSMPC robust controller is designed to enhance its anti-disturbance abilities and achieve resonance suppression. Finally, to avoid the time-consuming of weighting factor selection, a PSMPC that allocates non-conflicting objectives in the same layer is introduced. Experimental results on 10-kW prototype demonstrates its excellent performance over existing techniques.

Adaptive triple-fed antenna and thinned RF-chip integration into ultra thin flexible polymer foil

AbstractAttaching a wireless transmission system comprising a radio frequency (RF)-chip and a dipole antenna to dielectric material of largely different permittivity leads to strong variation of the antenna feed impedance. Due to the severe impedance mismatch between the RF-chip and the antenna, the performance of the system may deteriorate drastically. The proposed antenna provides three feed points, which show respective feed-point match to 100 Ohm balanced feeds for three different dielectric environments (free-space and half-spaces of permittivity 4 and 42, respectively). Thereby, the RF-chip incorporates three 100 Ohm balanced output ports that are connected to the antenna from whom only one can be selected to provide the output signal. The respective other two output ports are shorted by an internal switching circuit that is controlled by external DC voltages. The measurement of the reflection coefficient of the stand-alone antenna and the chip agree well with the simulations, allowing to interconnect these two components. Further, the radiation pattern of the whole system is measured for two different scenarios showing good functionalities.

Controlled release of adeno-associated virus from alginate hydrogel microbeads with enhanced sensitivity to ultrasound.

Adeno-associated virus (AAV)-based gene therapy holds promise as a fundamental treatment for genetic disorders. For clinical applications, it is necessary to control AAV release timing to avoid an immune response to AAV. Here we propose an ultrasound (US)-triggered on-demand AAV release system using alginate hydrogel microbeads (AHMs) with a release enhancer. By using a centrifuge-based microdroplet shooting device, the AHMs encapsulating AAV with tungsten microparticles (W-MPs) are fabricated. Since W-MPs work as release enhancers, the AHMs have high sensitivity to the US with localized variation in acoustic impedance for improving the release of AAV. Furthermore, AHMs were coated with poly-l-lysine (PLL) to adjust the release of AAV. By applying US to the AAV encapsulating AHMs with W-MPs, the AAV was released on demand, and gene transfection to cells by AAV was confirmed without loss of AAV activity. This proposed US-triggered AAV release system expands methodological possibilities in gene therapy.

Wideband RF rectifier circuit for low-powered IoT wireless sensor nodes

This paper proposed a broadband RF-rectifier circuit. The design is matched through a combination of a wideband resistance compression network (RCN) with a modified short-stub matching network (MN) for Terminal-1 (T1) and a Π-MN for Terminal-2 (T2). The RCN incorporates the two terminals using a transmission line (TL) of 50 Ω. The TL-MN parameters are analyzed and evaluated in the design using closed-form equations. The HSMS2850-based prototype model demonstrates that the peak RF-to-DC power conversion efficiencies (PCE) realized at 3 dBm input power (Pin) are (76.92%, 70.53%, 69.75%, 67.54%) for (1.82, 2.13, 2.45, and 2.67 GHz), respectively. The prototype is terminated with a 1 kΩ load terminal (RL) and attained a maximum average output DC voltage VDC of 2.52 V. The model is tested in the ambient environment and achieved a T1(T2) VDC of 0.350(0.230) V. This approach also mitigated the impact of impedance variations imposed by diode non-linearity. The RF harvester drive a low-power evaluation module (EVM) for T1(T2) at 0.600(0.470) V.

Model reference adaptive controllers with improved performance for applications in LCL-filtered grid-connected converters

This work presents a control strategy combining a direct Model Reference Adaptive Control (MRAC) with a robust state feedback for current control of grid-connected converters with LCL filters operating under grid impedance variations. The MRAC is based on a gradient law, providing properly current reference tracking and voltage disturbance rejection. The inclusion of a state feedback inner loop provides robust active damping of the filter resonance for an entire range of grid impedances. A systematic control design procedure is proposed, and the combination of both control actions in a multi-loop approach does not add significant computational complexity. The proposal allows to increase the MRAC gains adaptation dynamics, providing suitable responses under grid current reference variations and under typical grid voltage disturbances, including grid faults. Performance indexes as the grid-currents total harmonic distortion and the mean squared error are also improved. In addition, robust stability analysis based on Lyapunov functions are carried out for the inner control loop and for the outer control loop, considering the grid impedance uncertain and with unmodeled dynamics. The strategy is implemented in a commercial digital signal processor, and the compliance of the grid currents with the IEEE 1547 Std. is verified with controller hardware-in-the-loop and experimental results in a 5.4 kW prototype.

Complex impedance analysis of soft chemical synthesized NZCF systems

&#x0D; &#x0D; &#x0D; &#x0D; The soft chemical method was adopted to prepare of cobalt-substituted nickel-zinc ferrites (Ni0.95-x Zn0.05COx Fe2O4 for x = 0.01, 0.02 and 0.03). We have recently studied their structural, morphological, and magnetic properties, initial permeability, and dielectric constant. They were found to be with cubic ferromagnetic spinel structure, the morphology of which is suitable for high-density recording media. The impedance has a major role in characterizing the electrical and magnetic properties of the sample, which are dependent on their permeability and dielectric constant. So, this study will verify the values obtained before. Next, the energy stored in a capacitor is directly proportional, and its size is inversely proportional to the dielectric constant. Similarly, the resistance offered by a material to the magnetic field to pass through it is related to permeability. This study will focus on the variation of impedance with Co2+ concentration. The results were derived with the equivalent circuit model. The impedance analysis is also important in the biological field having a name of Bio-Impedance Analysis (BIA), for determining nutritional status, and many more.&#x0D; &#x0D; &#x0D; &#x0D;

Measurement System of the Mean and Sub-Cycle LV Grid Access Impedance From 20 kHz To 10 MHz

This work presents a novel measurement method to characterize long-term and short-term variations of the LV grid impedance from 20 kHz to 10 MHz with configurable time, frequency and amplitude resolutions. The characterization of the grid access impedance in this frequency range is vital for the design and development of NB-PLC and BB-PLC technologies. The measurement system is valid for in-home, indoor cable networks and for the harsh conditions of the LV distribution grid, where a large input dynamic range and strong protection mechanisms against high-amplitude impulsive noises are required. Its accuracy is evaluated by comparison to a precision impedance meter for a wide set of impedance values, obtaining a maximum deviation within ± 8%. First trials of the grid impedance sub-cycle variations caused by commercial appliances and for frequencies assigned to BB-PLC are also presented in this paper. The results demonstrate that the grid impedance is highly time-varying within the mains cycle, both in amplitude and phase. These first outcomes point at the need to evaluate the accumulative effects of sub-cycle variations in the LV distribution grid, so that equalization algorithms in the next BB-PLC technologies could be developed to overcome the impact of these fast variations.

A comprehensive study of grid impedance and its reliability effects on variable frequency drive

&lt;p class="Text"&gt;Grid impedance is one of the most important parameters for the satisfactory operation of variable frequency drive (VFD) and their interaction with other utilities connected to the same grid. In this research investigation a new approach to analytical evaluation and verification of grid impedance, and short circuit current is discussed. VFD under identical operating and loading conditions is connected to different grid capacities and configurations, being considered in this investigation. Grid impedance variation in terms of measured or estimated values, due to different grid connectivity affects the commutation of uncontrolled front-end rectifiers. This impacts the nonlinearity of input current wave shape, causing a significant change in current harmonics (THDi) and ripple current of DC link. This paper comprehensively investigates the reduction of DC capacitor lifetime and losses of DC inductor, and diode with various grid capacity and configurations under standard load conditions. High-frequency harmonics impact (2-9 kHz) on DC inductor losses is also analyzed. A VFD of 250 kW is considered for entire practical measurement including distortion effects and MATLAB simulation. This research may give a good insight into the sizing of VFD front-end devices. The reliability impact of VFD is also one of the important outcomes of this research.&lt;/p&gt;

A Ka-Band CMOS Power Amplifier With OP1dB Improvement Employing a Diode-Connected Analog Linearizer

This paper presents a 30-36 GHz CMOS power amplifier (PA) with a diode-connected analog linearizer dedicated to improving the output power and power-added efficiency (PAE) at 1-dB output compression point (OP1dB). The proposed analog linearizer performs a gain expansion, simultaneously introducing little phase distortion. In addition, a design procedure of the matching network between the analog linearizer and PA is analyzed to mitigate the impact of impedance variation caused by the control voltage and input power. As a proof of concept, the circuit is fabricated in a 65-nm CMOS process with a 0.31 mm2 total area. Measured output power and PAE at OP1dB are > 13.4 dBm and > 12.4%, where maximum improvement of 2.2 dB and 5.9% is achieved at 31 GHz when the analog linearizer is active. The saturated output power of > 16.2 dBm is obtained with the saturated PAE of > 21%. Applying a single carrier 256-QAM signal with a bandwidth of 400 MHz and a peak-to-average power ratio (PAPR) of 10.4 dB, the PA with the proposed analog linearizer can achieve the adjacent channel power ratio (ACPR) of -34 dBc at the output power of 6 dBm.