System Impedance Research Articles

Transformer-Coupled TES Frequency Domain Readout Prototype

Frequency-domain multiplexing (fMUX) is a mature readout scheme for transition edge sensor (TES) detectors in the millimetre and sub-millimetre bands. It is implemented at MHz carrier frequencies for the South Pole Telescope, POLARBEAR, and Simons Array and is planned for deployment on the LiteBIRD space polarimeter. The existing implementations couple to the detectors with low-noise, low-input-impedance superconducting quantum interference device (SQUID) transimpedance amplifiers and rely on complex arrangements to achieve sufficient linearity and dynamic range. We introduce a new cryogenic amplification scheme that couples the multiplexed TES devices to a traditional, high-linearity, high-dynamic-range, field-effect transistor amplifier using a novel high-turns-ratio, wide-band cryogenic transformer. We characterize the bandwidth, transimpedance, input impedance, and system noise of the transformer-coupled fMUX system to demonstrate that it is a promising candidate for MHz frequency-domain multiplexing without the use of SQUIDs. For the initial prototype, we demonstrate a bandwidth of 1.5–6 MHz, transimpedance of $$267 \pm 2 \,{\Omega}$$, input impedance of $$0.2\,{\Omega}$$, and system noise $$16 \pm 3\,{\mathrm {pA}}/\sqrt{{\mathrm {Hz}}}$$. We also present an optimized design which will have amplifier noise contributions of approximately $$5 \,{\mathrm {pA}}/\sqrt{{\mathrm {Hz}}}$$, comparable to the SQUID contribution in the existing systems.

An Improved Controlled-Frequency-Band Impedance Measurement Scheme for Railway Traction Power System

Railway traction power system (TPS) impedance affects the stability and operation performance of connected power electronics devices (i.e., electric trains) with the closed-loop control system. In order to identify the detailed TPS impedance, the wideband-response-based impedance measurement technique has become attractive for its fast execution time and accuracy, especially the chirp-based technique for its bilateral controllability of injected wideband disturbance. However, for the reason that the disturbance device is directly powered by the measured system, the fundamental component separates some harmonic clusters in the frequency domain and leads to unsatisfactory uniformity of the injected wideband disturbance. In this article, a segmented-chirp-based technique is proposed to eliminate this phenomenon caused by the fundamental component, where the chirp signal is segmented and carried on the fundamental only when the amplitude is relatively smooth on top (or bottom), which facilitates a uniform wideband distribution to keep a good measurement accuracy. Meanwhile, the presented modular disturbance circuit with a flexible topology can better adapt to the various industrial engineering conditions. Finally, the detailed measurement results based on the simulation and downscaled experimental system validate the effectiveness of the proposed measurement scheme.

A Novel Passive Method for the Assessment of Skin-Electrode Contact Impedance in Intraoperative Neurophysiological Monitoring Systems

Intraoperative Neurophysiological Monitoring is a set of monitoring techniques consisting of reading electrical activity generated by the nervous system structures during surgeries. In order to guarantee signal quality, contact impedance between the sensing electrodes and the patient’s skin needs to be as low as possible. Hence, monitoring this impedance while signals are measured is an important feature of current medical devices. The most commonly used technique involves injection of a known current and measurement of the voltage drop in the contact interface. This method poses several problems, such as power consumption (critical in battery-powered systems), frequency dependency and regulation issues, which are overcome by using a passive method. The fundamentals of the method proposed in this paper are based on the utilization of the variation suffered by the input random signal when a known resistance is connected in parallel to the input terminals of the low-noise amplifier (LNA) of the analog front-end of the acquisition system. Controlling the connection of the resistors and computing the root mean square of the LNA output voltage has been proved to be a useful tool to assess that the contact impedance is suitably low, allowing the user to know if the neural measurements obtained are valid.

Efficient computation of optimal open-loop controls for stochastic systems

Optimal control is a prominent approach in robotics and movement neuroscience, among other fields of science. Methods for deriving optimal choices of action have been classically devised either in deterministic or stochastic settings. Here, we consider a setting in-between that retains the stochastic aspect of the controlled system but assumes deterministic open-loop control actions. The rationale stems from observations about the neural control of movement which highlighted that relatively stable behaviors can be achieved without feedback circuitry, via open-loop motor commands adequately tuning the mechanical impedance of the neuromusculoskeletal system. Yet, effective methods for deriving optimal open-loop controls for stochastic systems are lacking overall. This work presents a continuous-time approach based on statistical linearization techniques for the efficient computation of optimal open-loop controls for a broad class of stochastic optimal control problems. We first show that non-trivial departure from the optimal solutions of classical deterministic and stochastic approaches may arise for simple synthetic examples, thereby stressing the originality of the framework. We then exemplify its potential relevance to the planning of biological movement by showing that a well-known phenomenon in motor control, referred to as muscle co-contraction, occurs naturally. More generally, this stochastic optimal control framework may be suited to other fields where the design of optimal open-loop actions is relevant.

A Novel Microstrip Line Balun With Transparent Port Impedance and Flexible Open Arm Structure

In this letter, a novel microstrip line balun with transparent port impedance and unconnected flexible output arms is presented. The proposed balun is designed from a symmetric four-port device with an open end at its isolation port. To achieve balun function, a shunt stub is attached between the unbalanced port and the virtual open-ended port to generate a transmission zero under the even-mode circuit. Its odd-mode circuit is treated as an impedance transformer, where the transformer is independent of the terminal impedance. In addition, the proposed balun has flexible open arm branches and does not require a closed loop structure, which provides design flexibility to integrate with other devices compared to conventional closed-loop branch line baluns. The theoretical design equations are derived first to prove the design concept. Then, two prototypes are designed with 35 $\Omega $ system impedance and loaded with 50 and 75 $\Omega $ port impedance, and the measured results match well with the simulation, which further validates the proposed design theory.

Output Impedance Modeling and High-Frequency Impedance Shaping Method for Distributed Bidirectional DC–DC Converters in DC Microgrids

Output impedance characteristics of interfaced converters of energy sources are the important indicators to assess the anti-interference ability of the dc microgrids. However, the output impedance is often approximately modeled by neglecting the impacts of delay units. In order to accurately study the anti-interference ability, the output impedance of an energy storage system is modeled with the consideration of the coupling characteristics of the current control gains and the delays caused by digital control and switching. The constraint mechanism of the coupling factors to impact the effective bandwidth of current loop in a load current feedforward system is also revealed. Then, an impedance shaping method is proposed to improve the anti-interference ability by optimally shaping the high-frequency output impedance, and also to improve system performances in terms of increasing the bandwidth of inner loop and the stable margin of outer loop. The simulation and experimental results both clearly validate the correctness and feasibility of the proposed impedance shaping method.

Bronchodilator Response Assessed by the Forced Oscillation Technique Identifies Poor Asthma Control With Greater Sensitivity Than Spirometry

Persistent bronchodilator response (BDR) following diagnosis of asthma is an underrecognized treatable trait, associated with worse lung function and asthma control. The forced oscillation technique (FOT) measures respiratory system impedance, and BDR cutoffs have been proposed for healthy adults; however, the relevance in asthma is unknown. We compared BDR cutoffs, using FOT and spirometry, in asthma and the relationship with asthma control. Data from patients with asthma who withheld bronchodilator medication for at least 8h before a tertiary airway clinic visit were reviewed. All subjects performed FOT and spirometry before and after salbutamol administration, and completed the Asthma Control Test. FOT parameters examined included respiratory system resistance (R5) and reactance (X5) at 5Hz, and area under the reactance curve (AX). BDR was defined by standard recommendations for spirometry and based on the 95th percentile of BDR in healthy adults for FOT. Fifty-two subjects (18 men; mean age, 53 ± 18 years) were included. BDR was identified more frequently by FOT than spirometry (54%vs27%of subjects). BDR assessed by X5 and AX, but not R5, was associated with spirometric BDR (χ2, P< .01) and correlated with asthma control (X5: rs= -0.36, P< .01; AX: rs= 0.34, P= .01). BDR measured by reactance parameters identified more subjects with poor asthma control than did spirometry (AX, 69%vsspirometry, 41%). BDR assessed by FOT can identify poor asthma control. Reactance parameters were more sensitive in identifying poor asthma control than spirometry, supporting the use of FOT to complement spirometry in the clinical management of asthma.

Adaptive impedance‐based out‐of‐step detection of synchronous generator without any network reduction

An adaptive technique for out-of-step (OOS) protection by modifying the impedance-based method is proposed in this study. Impedance-based methods are powerful and are operational in the power system as the main protection of OOS conditions. The setting of these relays depends on some parameters of the generator and power system that should be updated for the setting. The presence or absence of generator units in a power plant and transient conditions directly affects the machine dynamic parameters. Service or not in service of power lines and power system configurations can change the impedance of the power system at the generator terminals. Furthermore, to use the methods in a multi-machine power system, an equivalent two-area system is needed that is a complicated and time-consuming procedure. It should be made clear that these complexities limit the application of the impedance-based methods. Therefore, to remove these complexities, all factors that influence the relay setting are considered together in this research. The simulation results show that the proposed adaptive technique overcomes some of the problems and difficulties associated with impedance-based methods as well.

Substation Grounding Grid Diagnosis Applying Optimization Techniques Based on Measurements and Field Tests

Considering urban substations ground grid diagnosis, some real-physical constraints result in measurement process challenges: 1) limited length between electrodes used to measure the equivalent impedance of the grounding system; 2) to determine the current that flows from ground grid conductors to the earth; and 3) to determine the grid resistance. In this scenario, an adequate diagnosis of the safety offered by the ground grid under test when a ground fault occurs is not a trivial task. This article describes a methodology that allows a reliable diagnosis regarding the safety provided by a substation ground grid. The methodology is applied to the parameters obtained in performed field tests. The method has two steps. First, the fall-of-potential method with reduced distances between electrodes is used to determine the equivalent impedance of the grounding system. Then, the ground current is obtained. In both stages, optimization techniques are applied to the specific equations that govern the phenomenon under investigation. Comparative case studies considering real-life data illustrate the effectiveness of the method.

Impedance Modeling and Stability Analysis in Vehicle-Grid System with CHB-STATCOM

Recently, the low-frequency oscillation (LFO) frequently happens in the vehicle-grid system of high-speed railways when electric multiple units (EMUs) are put into operation. As a possible solution, a single-phase cascaded H-bridge static synchronous compensator (CHB-STATCOM) directly connected to the traction network is applied to dynamically compensate the reactive power of vehicle-grid system. This paper focuses on the impedance modeling and stability analysis in the vehicle-grid system with CHB-STATCOM. Firstly, the vehicle-grid system is simplified to a single-phase rectifier with large grid inductance. The accurate dq -frame impedance of the rectifier system with CHB-STATCOM is derived in detail. Secondly, through the generalized Nyquist stability criterion (GNSC), the influence of CHB-STATCOM and its different control parameters on the stability of rectifier system is revealed. Thirdly, the excellent performance of CHB-STATCOM in suppressing the LFO and the accuracy of theoretical analysis are verified via time-domain simulations. Finally, to further verify the effectiveness of CHB-STATCOM in real applications, a dSPACE based controller hardware-in-the-loop (HIL) simulation platform is established, which includes the physical control circuits of eight EMUs. The experimental results show that the CHB-STATCOM has a good dynamic compensation effect and can efficiently suppress the LFO.

Combination of Orthogonal Injections in Impedance Measurements of Grid-Connected Systems

Impedance-based stability criterion has become a popular method in determining the stability of grid-connected systems. Recent studies have presented the utilization of various pseudo-random-sequence (PRS) perturbations for rapidly and accurately obtaining the impedances required for the stability analysis. A major drawback of the PRS is, however, that the signal power is linearly distributed over many harmonic frequencies. As the injection amplitude must be kept small to avoid too strong nonlinear distortions, it becomes challenging to provide enough power to the whole frequency band of interest.This work proposes a novel perturbation that is synthesized by summing up several independently designed orthogonal PRS injections. As the orthogonal sequences do not have power at common frequencies, the resulting combined signal can be tailored to have a specific spectral-power distribution at each frequency band of interest. As a consequence, the system impedances can be accurately measured over a wide frequency band. The performance of the method is verified through experimental measurements of a 2.7 kW grid-connected system, where grid impedance measurements and terminal inverter output admittance measurements are performed.

13.8 kV Operation of a Peak-Shaving Energy Storage Equipment With Voltage Harmonics Compensation Feature

This paper presents the development and operation on 13.8kV distribution systems of a peak-shaving equipment with battery energy storage. This equipment injects active power to grid during peak times (when the cost of energy is higher) and charges its battery banks from the grid at the off-peak times (when the energy has a low producing cost). The equipment is based on a multilevel converter coupled to the grid through a 2.4kV:13.8kV transformer. In addition to the peak-shaving functionality, a feature of compensation of harmonics on the distribution voltage is included, without the need for any extra sensor nor hardware (apart from the ones already in use for the peak-shaving). The compensation of voltage harmonics is performed through the emulation of a harmonic resistance in order to damp resonances between system impedances that are excited by non-linear loads. This approach is very appealing to distribution systems, where the non-linear loads are not accessible and are scattered. Experimental results obtained on a 13.8kV test substation are presented.

Исследование влияния подстилающих сред на импеданс системы из двух произвольно расположенных параллельных линейных антенн

Исследование влияния подстилающих сред на импеданс системы из двух произвольно расположенных параллельных линейных антенн

Study on the Quantitative Relationship Between Harmonic Amplification and Cable Length

With the large increase of the wide-frequency and high-order harmonic in power electronic based systems as well as the wide use of cables with large distributed capacitance in modern power grids especially renewable energy generations, the harmonic amplification in cables becomes a serious problem. Some researchers have paid attention to this problem, but the quantitative relationship between harmonic amplification and cable length has not been determined, which is studied in this paper to cover the shortage. First, the influence factors of harmonic amplification are converted into two rotation phasors. These factors, including cable parameters, harmonic frequency and equivalent harmonic impedance of power system, are converted into the initial amplitude, phase and angular frequency of the rotation phasors. Then, the solution of harmonic amplification factor (HAF) is converted to solve the reciprocal of the amplitude of the sum of the two rotation phasors. With the cosines law, HAF and the cable length segments where harmonic exceeds the limit can be figured out quantitatively. The analysis method and conclusions proposed can help to guide cable length planning for avoiding harmonic exceeding the limit or to analyze the cause of harmonic exceeding the limit. Correctness and effectiveness are verified by the simulation and field cases.

Generalized MIMO Sequence Impedance Modeling and Stability Analysis of MMC-HVDC With Wind Farm Considering Frequency Couplings

Recently, small-signal stability of the modular multilevel converter (MMC) based high-voltage direct current (HVDC) transmission for wind farm integration has attracted great attentions. The impedance-based frequency-domain method is an effective tool for such studies, in which the accuracy of the impedance model is of significant importance. Currently, the decoupled single-input single-output (SISO) sequence impedance of the MMC-HVDC system with wind farm is commonly used due to the simplicity in stability analysis. However, since both the MMC and wind farm exhibit frequency coupling behaviors, the decoupled SISO sequence impedance model may lead to inaccurate stability conclusion under certain conditions. In order to improve the model accuracy, based on the harmonic state-space (HSS) modeling approach, this paper proposes a generalized multi-input multi-output (MIMO) sequence impedance model of the MMC-wind farm system. The proposed MIMO impedance model can effectively capture the frequency couplings in the interconnected system, based on which the coupling mechanism of multi-frequency components within the MMC is then revealed. To facilitate the interconnection analysis, the model truncation criteria is proposed and validated by comparing the accuracy of the MIMO model with different truncated dimensions. In addition, this paper considers the internal impedance network of the wind farm when developing the aggregated wind farm impedance model for interaction stability analysis. Finally, the proposed MIMO sequence impedance model is applied to accurately predict the instability of the MMC-HVDC connected wind farm system.

Amplitude comparison based pilot protection for renewable power teed line

Fault behaviors of inverter-interfaced renewable energy generators (IIREGs) are quite diverse from those of synchronous generators (SGs). They show the variable system impedance, the limited current and low inertia, so the proportional brake differential protection installed on the transmission line has a high risk of failure for phase-phase failures. To cope with this adaptive problem, a new pilot protection was proposed considering huge difference in both current amplitudes. Also, an improved criterion is given for the scenario with a teed line. The existing protection principles focus on the fault current characteristics of IIREGs excessively, so they cannot operate correctly once IIREGs do not output the fault current. This happened when IIREGs produce no power or the circuit breaker exactly reclose on permanent failure. However, the proposed method has good performance for the above cases. The proposed method only requires current amplitude information, and in this case the strict synchronizing measurement is not necessary. Case studies are performed under different fault conditions, and they confirm the proposed method has good performance under different fault conditions. Furthermore, it is also verified using field-testing data.

Principal Component Regression and Its Application in Power Harmonic Emission Level Evaluation

Accurate harmonic emission level evaluation is the basis of distinguishing the responsibility of harmonic pollution between power supply system and consumer. A new harmonic emission level evaluation method via principal component regression (PCR) is proposed in this paper. Firstly, the principle of PCR is analyzed. Then, harmonic impedance of supply system is evaluated by PCR-based method. Subsequently, harmonic emission level of supply system and consumer is evaluated according to the harmonic impedance of supply system. This technique has the advantage of high accuracy in estimating harmonic emission level. The effectiveness of the proposed method was verified by computer simulations and field test.

Influence of force load on the stability of ultrasonic longitudinal–torsional composite drilling system

This study aimed to investigate the problems of system detuning, amplitude attenuation, and even vibration stop after the load was applied to the acoustic system during ultrasonic-assisted vibration processing. In the theoretical part, the overall theoretical model of the ultrasonic longitudinal–torsional composite drilling system (ULTCDS), including the longitudinal–torsional composite horn, transducer, and load was established based on the four-terminal network, combined with the longitudinal and torsional vibration equations of the variable cross-section rod. Also, the influence of the load on the input impedance and output amplitude of the acoustic system was preliminarily analyzed. In the simulation part, the static and dynamic drilling force was simulated by the pre-stressed modal and transient dynamic analyses, and the influence of the force load on the resonant frequency and output amplitude of the system was further explored. In the experiment part, the static force loading test and the ultrasonic drilling test of titanium alloy were designed. The micro-morphology of drilling holes under different processing parameters was observed, and the influence of force load on the system characteristics and stability was explored. The results showed that when the system was subjected to a force load greater than 400 N, the system current and frequency were greatly offset, the electromechanical conversion efficiency reduced, and the amplitude was attenuated to below the amplitude at empty load. In the ultrasonic-assisted drilling of titanium alloy processing, the acoustic system undergoes an obvious detuning phenomenon and the drilling quality is attenuated when the current increased by more than 60% and the frequency changed by more than 350 Hz, affecting the stability of the system and the ultrasonic-assisted processing effect.

EXTH-19. IBRUTINIB MODULATES BLOOD-BRAIN BARRIER INTEGRITY TO ENHANCE CHEMOTHERAPY PERMEABILITY

Abstract BACKGROUND The blood-brain barrier (BBB) poses a major treatment challenge for malignant brain tumors. Ibrutinib is an FDA approved Bruton’s tyrosine kinase (BTK) and bone marrow x-linked tyrosine kinase (BMX) inhibitor indicated for the treatment of B-cell lymphomas. BMX is highly expressed in endothelial cells and is suggested to regulate cytoskeletal organization and barrier function in epithelial cells. We hypothesize that inhibition of BMX by ibrutinib in brain endothelial cells will disrupt the integrity of the BBB to increase drug permeability. METHODS Protein expression and phosphorylation of BMX was confirmed in immortalized mouse brain endothelial cells (bEnd.3). Endothelial barrier integrity was evaluated with increasing doses of ibrutinib (1–30μM) for 24hrs via the ACEA xCELLigence system (impedance) and the ECIS TEER24 system (resistance). Paracellular permeability of doxorubicin was measured by fluorescent spectrophotometry. Junctional protein expression of VE-Cadherin and F-actin cytoskeletal organization were detected by fluorescent staining. Ibrutinib’s effect on efflux pumps, ABCB1 and ABCG2, was performed by flow cytometry using specific substrates, valspodar and FTC, respectively. RESULTS Ibrutinib decreased endothelial cell impedance in a dose-dependent manner over 24hrs, with transient decrease by 46% at 30min with an optimal dose of 1μM, and partial recovery by 4hrs. TEER was decreased by 60% at 3hrs. Ibrutinib enhanced doxorubicin permeability by 30%; attributed to the transient disorganized nature of actin cytoskeletal filaments 2hrs post treatment. No effects on VE-cadherin expression or localization were observed. Ibrutinib successfully inhibited activity of ABCB1 and ABCG2 in a dose-dependent manner. CONCLUSION Our results suggest ibrutinib causes transient disruption of the brain endothelial monolayer due to cytoskeletal disorganization and ABC transporter inhibition to enhance permeability of doxorubicin. Further studies using ibrutinib and cytotoxic agents are warranted in glioma bearing animals. We propose that using ibrutinib as an adjunctive therapy may enhance drug delivery to patients with malignant brain tumors.

Systematic Common-Mode Filter Design for Inverter-Driven Motor System Based on In-Circuit Impedance Extraction

Inverter-driven induction machines often suffer from premature bearing failure due to high-frequency common-mode (CM) voltage and induced CM current. One effective remedy is adding a CM filter to suppress the CM current. Optimal CM filter design requires prior knowledge of both noise source and termination impedances. With an improved in-circuit impedance measurement setup, the CM noise source impedance of a high-power inverter-driven motor system with strong background noise can be extracted. The setup also protects the measurement instruments from surges and transients from the harsh operating environment. The extracted noise source impedance allows a CM filter to be designed systematically without overdesigning. In the evaluation of the first-order single-inductor and second-order LC filters, it is found that the second-order CM filter is prone to differential-mode to common-mode (DM-to-CM) conversion, especially at the resonant frequency caused by the leakage inductance of the CM choke and the equivalent DM capacitance of the line-to-ground capacitors. Therefore, an additional DM inductor is necessary to curb the mode conversion, which may not necessarily result in final size reduction as compared to that of first-order single-inductor filter.