Showing papers on "Output impedance published in 2021"
TL;DR: In this article, the opposite chargeenhancement effect and transistor-like device design were used to achieve a high power of 10 MW/m2 at a low frequency of 1 Hz.
Abstract: Converting various types of ambient mechanical energy into electricity, triboelectric nanogenerator (TENG) has attracted worldwide attention. Despite its ability to reach high open-circuit voltage up to thousands of volts, the power output of TENG is usually meager due to the high output impedance and low charge transfer. Here, leveraging the opposite-charge-enhancement effect and the transistor-like device design, we circumvent these limitations and develop a TENG that is capable of delivering instantaneous power density over 10 MW/m2 at a low frequency of ~ 1 Hz, far beyond that of the previous reports. With such high-power output, 180 W commercial lamps can be lighted by a TENG device. A vehicle bulb containing LEDs rated 30 W is also wirelessly powered and able to illuminate objects further than 0.9 meters away. Our results not only set a record of the high-power output of TENG but also pave the avenues for using TENG to power the broad practical electrical appliances. TENG suffers from two fundamental limitations: high output impedance and low charge transfer. Herein, these limitations are circumvented by leveraging the opposite-charge-enhancement effect and transistor-like device design, thereby achieving the instantaneous power density over 10 MW/m2 at the low frequency of ~ 1 Hz.
83 citations
TL;DR: In this paper, a permittivity-tunable electret composite film, i.e., a thermoplastic polyurethane (TPU) matrix with polyethylene glycol (PEG) additives and polytetrafluoroethylene (PTFE) nanoparticle inclusions, is employed as the triboelectric layer.
Abstract: Triboelectric nanogenerators (TENGs), which hold great promise for sustainably powering wearable electronics by harvesting distributed mechanical energy, are still severely limited by their unsatisfactory power density, small capacitance, and high internal impedance. Herein, a materials optimization strategy is proposed to achieve a high performance of TENGs and to lower the matching impedance simultaneously. A permittivity-tunable electret composite film, i.e., a thermoplastic polyurethane (TPU) matrix with polyethylene glycol (PEG) additives and polytetrafluoroethylene (PTFE) nanoparticle inclusions, is employed as the triboelectric layer. Through optimizing the dielectric constant of the composite, the injected charge density and internal capacitance of the TENG are significantly enhanced, thus synergistically boosting the output power and reducing the impedance of the TENG. The optimal output power reaches 16.8 mW at an external resistance of 200 kΩ, showing a 17.3 times enhancement in output power and a 90% decline in matching impedance. This work demonstrates a significant progress toward the materials optimization of a triboelectric generator for its practical commercialization.
60 citations
TL;DR: A new modeling tool is proposed named as impedance circuit model, visualizing the closed-loop power converter as an impedance circuit with discrete circuit elements rather than an all-in-one impedance transfer function, which can reveal the virtual impedance essence of all control parameters at different impedance locations and/or within different frequency bandwidths.
Abstract: The impedance model is widely used for analyzing power converters. However, the output impedance is an external representation of a converter system, i.e., it compresses the entire dynamics into a single transfer function with internal details of the interaction between states hidden. As a result, there are no programmatic routines to link each control parameter to the system dynamic modes and to show the interactions among them, which makes the designers rely on their experience and heuristic to interpret the impedance model and its implications. To overcome these obstacles, this article proposes a new modeling tool named as impedance circuit model , visualizing the closed-loop power converter as an impedance circuit with discrete circuit elements rather than an all-in-one impedance transfer function. It can reveal the virtual impedance essence of all control parameters at different impedance locations and/or within different frequency bandwidths, and show their interactions and coupling effects. A grid-forming voltage source inverter is investigated as an example, with considering its voltage controller, current controller, control delay, voltage/current $dq$ -frame cross-decoupling terms, output-voltage/current feedforward control, droop controllers, and three typical virtual impedances. The proposed modeling tool is validated by frequency-domain spectrum measurement and time-domain step response in simulations and experiments.
58 citations
TL;DR: In this paper, the authors theoretically proposed a switching device that operates at room temperature, which is an in-plane heterostructure based on a periodically boron-doped (nitrogen-decomposed) armchair graphene nanoribbon, which has been experimentally fabricated recently.
Abstract: We theoretically propose a switching device that operates at room temperature. The device is an in-plane heterostructure based on a periodically boron-doped (nitrogen-doped) armchair graphene nanoribbon, which has been experimentally fabricated recently. The calculated $I$-$V$ curve shows that for a realistic device with interface width longer than $20$ nm, nonzero electric current occurs only in the region of bias voltage between $\ensuremath{-}0.22$ and $0.28$ V, which is beneficial to low-voltage operation. Furthermore, in this case, the electric current is robust against the change of the potential profile in the interface since the metallic impurity-induced sub-bands with delocalized wave functions contribute to the transmission exclusively. This also suggests the high response speed of the proposed device. We also discuss the temperature dependence, the output impedance, the effect of phonons, and the possible regimes to extend our work, which suggest that our model may have potential room-temperature nanoelectronics applications.
49 citations
TL;DR: According to the results here presented, the proposed method is sufficiently accurate and is a promising solution for real-time diagnostic of battery SOH.
Abstract: The capability to assess and monitor the state of health (SOH) of lithium-based cells is a highly demanded feature for advanced battery management systems. Due to the existing relation between SOH and internal impedance, electrochemical impedance spectroscopy (EIS) methods are adopted for SOH diagnosis. Nevertheless, accurate EIS tests demand expensive facilities, long time test procedures, and algorithms with high-computational efforts, which makes them almost unsuitable for on-board systems. This paper presents a new diagnostic method aimed at detecting battery SOH using fast impedance measurements. Key factor is the application of a broadband current signal excitation on the battery; for the application here presented, a pseudo-random binary sequence (PRBS) excitation is adopted. To demonstrate the functionalities of a prototype testbed, several cells of the same manufacturer but presenting different SOHs, due to their past load history, have been subjected to the EIS test, acquiring voltage response under imposed excitation. Finally, test results have been processed: the key step being the clustering of impedance measurements (represented in Nyquist diagram) in different rectangular areas, which are related to actual SOH. The performed experimental test results showed the possibility to determine frequency points in which the impedance measurements dramatically change due to different cell SOH; as a consequence, these peculiar frequencies can be adopted as reference for cluster separation. According to the results here presented, the proposed method is sufficiently accurate and is a promising solution for real-time diagnostic of battery SOH.
47 citations
TL;DR: The results show that the PReSCE circuit eliminates the inrush current and increases the balance speed three times than the parallel pure switched-capacitor equalizer.
Abstract: The traditional pure switched-capacitor equalizer suffers from a large inrush current and low balance speed. An automatic parallel resonant switched-capacitor equalizer (PReSCE) for series-connected battery strings is proposed, which utilizes resonant switched-capacitor to eliminate the inrush current. The parallel ReSC converters not only minimizes output impedance at the low switching frequency, but delivers the excess energy to the low-voltage battery directly from the high-voltage battery in one cycle. Both of the two functions increase the balance speed. All of the switches are controlled by a pair of complementary pulsewidth modulation signals at a fixed operational frequency. Both simulation and experiment are used to verify the theoretical analysis and system feasibility of the proposed circuit. The results show that the PReSCE circuit eliminates the inrush current and increases the balance speed three times than the parallel pure switched-capacitor equalizer.
39 citations
TL;DR: The proposed method can achieve the full-frequency passive of the output impedance of GCI even if the PLL has high bandwidth and the impedance measurement error is up to 60%, which means the adverse stability effect of PLL on the system is eliminated.
Abstract: The wide bandwidth of Phase-Locked Loop (PLL) will increase the negative real part of the output impedance of the grid-connected inverter (GCI), thus destroying the stability of the weak grids. This paper proposes a novel method to improve the system stability through decoupling the PLL and grid impedance. Initially, the coupling relationship between PLL and grid impedance is revealed. It can explain why the choice of PLL bandwidth and the grid impedance magnitude is limited. Then, the decoupling method is proposed where the primary control structure of GCI does not need to change and uses the structured voltage, the product of PCC voltage and grid admittance, as the improved input of PLL. The proposed method can achieve the full-frequency passive of the output impedance of GCI even if the PLL has high bandwidth and the impedance measurement error is up to 60%, which means the adverse stability effect of PLL on the system is eliminated. The theoretical analysis is verified by simulations and experiments.
36 citations
TL;DR: An impedance controller for reshaping the quadrature-axis impedance into a positive resistance in the low-frequency band, which eliminates the negative effect introduced by the PLL and the GVF; therefore, the inverter will operate under very weak grids.
Abstract: The grid-connected inverter is the vital energy conversion device in renewable energy power generation. With the increasing installed capacity of renewable energy, the grid presents characteristics of weak grids with large grid impedance. In general, the inverter often obtains grid synchronization information by the phase-locked loop (PLL) and to suppress the background harmonic and amplitude disturbance of grid voltage, the grid voltage feedforward (GVF) control is also needed. However, previous researches revealed that the PLL and the GVF would shape the quadrature-axis ( $\boldsymbol {q}$ -axis) output impedance of the inverter into a negative resistance in the low-frequency band, and this would be responsible for the instability of the inverter under a weak grid. To resolve this instability issue, this article proposes an impedance controller for reshaping the $\boldsymbol {q}$ -axis impedance into a positive resistance in the low-frequency band, which eliminates the negative effect introduced by the PLL and the GVF; therefore, the inverter will operate under very weak grids. Moreover, the proposed control strategy is only for $\boldsymbol {q}$ -axis impedance reshaping, and it does not affect the output characteristics of $\boldsymbol {d}$ -axis, thus ensuring the ability of the inverter to suppress background harmonics and amplitude disturbance of the grid voltage. The conclusions are verified by experimental results.
36 citations
TL;DR: In this paper, a front-end dc-dc converter with dc transformer (DCX)- LLC resonant converter is proposed to suppress the second harmonic current (SHC) in the front end.
Abstract: In a two-stage inverter, the instantaneous output power pulsates at twice the output frequency (2 f o), generating the second harmonic current (SHC), which will propagate into the front-end dc–dc converter. This article aims for suppressing the SHC in the front-end dc–dc converter with dc transformer (DCX)- LLC resonant converter. The small-signal model of the DCX- LLC resonant converter is proposed, and based on which, the unified small-signal model of the preregulator+ LLC converter is built. Then, the basic ideas for reducing the SHC are proposed, including the determination of the filter capacitors in the preregulator+ LLC converter and the control approach. After that, from a perspective of output impedance, the control schemes for reducing the SHC in the front-end preregulator+ LLC converter are proposed. By inserting a notch filter in the voltage loop and/or introducing a virtual impedance in series with the output rectifier of the LLC resonant converter, the output impedance of the preregulator+ LLC converter at 2 f o is increased and, thus, the SHC can be reduced. Finally, a 6-kVA two-stage three-phase inverter with boost+ LLC converter as the front-end dc–dc converter was fabricated and tested. The experimental results are provided to verify the proposed control schemes.
32 citations
TL;DR: In this article, the authors proposed a mathematical framework for droop-based paralleled dc-dc systems with LLC resonant converters to study the output-port I-V characteristics and small-signal output impedance.
Abstract: The LLC resonant converter is a popular, variable switching frequency dc--dc converter that may be controlled using two methods: charge and frequency control. In this article, the application of LLC resonant converters to input-parallel, output-parallel system is studied. In this respect, the models of output-port I-V characteristics and small-signal output impedance of the charge controlled LLC converter are proposed. In addition, a mathematical framework is developed for droop-based paralleled dc--dc systems. It distinctly identifies the output dc voltage and circulating current modes of stability, even in systems comprising of nonidentical converters. The developed model and the analytical framework are utilized to study the two modes of stability in droop-based parallel-connected LLC converters. It finds the circulating current mode instability for both the charge and frequency control methods, despite a stable output dc bus voltage. The instability inhibits fast response and high closed-loop bandwidth, eroding the reported advantages of the charge control method over frequency control. Further investigation into the output port I-V characteristics reveals the superiority of charge-controlled LLC converters in paralleled systems than the conventional frequency-controlled converters. A novel application of “common inner reference” based “automatic load sharing” strategy is developed and uniquely applied to the charge controlled system. In addition, the effects of component tolerance and communication delay on this strategy are also briefly explored. The theoretical output-port models and the stability analyses of parallel-connected LLC resonant converters are validated through experiments on a hardware prototype. Further, the supplementary video files illustrate the advantage of the charge control method over frequency control in such system. Finally, the proposed automatic load sharing strategy is validated in steady-state and through a step-change in load.
31 citations
TL;DR: A grey-box approach to small-signal stability analysis of complex power systems that facilitates root-cause tracing without requiring disclosure of the full details of the internal control structure of apparatus connected to the system is developed.
Abstract: This paper develops a grey-box approach to small-signal stability analysis of complex power systems that facilitates root-cause tracing without requiring disclosure of the full details of the internal control structure of apparatus connected to the system. The grey-box enables participation analysis in impedance models, which is popular in power electronics and increasingly accepted in power systems for stability analysis. The Impedance participation factor is proposed and defined in terms of the residue of the whole-system admittance matrix. It is proved that, the so defined impedance participation factor equals the sensitivity of the whole-system eigenvalue with respect to apparatus impedance. The classic state participation factor is related to the impedance participation factor via a chain-rule. Based on the chain-rule, a three-layer grey-box approach, with three degrees of transparency, is proposed for root-cause tracing to different depths, i.e. apparatus, states, and parameters, according to the available information. The association of impedance participation factor with eigenvalue sensitivity points to the re-tuning that would stabilize the system. The impedance participation factor can be measured in the field or calculated from the black-box impedance spectra with little prior knowledge required.
TL;DR: In this paper, a coordinated adaptive moment of inertia and virtual impedance control strategy is proposed to accelerate the active power adjustment process of the virtual synchronous generator system, which helps to complete the first frequency modulation and improve the inertia adjustment ability.
Abstract: The application of virtual synchronous generators in the power system eases the pressure on the grid caused by penetration of lots of power electronic devices, but worsens the dynamic frequency stability of the grid Meanwhile, in order to solve the problem of power coupling in low-voltage micro-grid systems, most measures introduced virtual impedance technology to adjust the equivalent output impedance of the system Therefore, most studies have adopted the adaptive control strategy of the moment of inertia, to improve the dynamic frequency adjustment of the grid However, it will cause the frequency response speed reduction problem In order to deal with the contradiction between the moment of inertia and frequency response speed, the voltage phasor relationship of the micro-source - grid system under signal disturbance in the introduction of virtual impedance is analyzed Then an adaptive virtual impedance control strategy is proposed to accelerate the active power adjustment process of the virtual synchronous generator system, which helps to complete the first frequency modulation and improve the inertia adjustment ability Finally, combining these two control strategies, a coordinated adaptive moment of inertia and virtual impedance control strategy is proposed From the perspective of the moment of inertia and virtual impedance, the proposed method fully exploits the control advantages of the virtual synchronous generator system and achieves the purpose of adjusting the inertia of the virtual synchronous generator system while considering the acceleration of the frequency response speed The comprehensive simulation results verify the feasibility and effectiveness of the proposed method
TL;DR: A hybrid harmonic suppression scheme is proposed to enable the further improvement of the adaptability of VSG, which mainly consists of a local voltage harmonic control loop and an adaptive grid current-controlled loop.
Abstract: The power quality of virtual synchronous generator (VSG) inevitably deteriorates in the presence of local nonlinear loads and distorted grid. In this paper, the conflict involved in the simultaneous elimination of distortion for both the inverter local load voltage and the grid exchanged current is first described. A unified control structure is presented that enables a tunable tradeoff between the two constrained harmonic sources. Then, a hybrid harmonic suppression scheme is proposed to enable the further improvement of the adaptability of VSG, which mainly consists of a local voltage harmonic control loop and an adaptive grid current-controlled loop. The local voltage harmonic control loop aims to scale down the inverter output impedance via a negative feedback loop, while the grid current-controlled compensator is intended to counteract the adverse effects from a weak grid via an additional voltage, which leads to substantially lower total harmonic distortion for both the local load voltage and the grid current at the same time. Small-signal modelling is performed to investigate the system stability and its robustness to parameter perturbations. The effectiveness of the proposed methodology is verified using hardware-in-the-loop simulations.
TL;DR: The inductor current feedforward control and the additional voltage feedback control are proposed for the VSG to reshape its impedance and it is revealed that the low-frequency interaction between the VSGs and the LVSM can be mitigated.
Abstract: Source-side virtual synchronous machines (VSG) and load-side virtual synchronous machines (LVSM) are gradually utilized together in the microgrid to provide virtual inertia and damping. However, instability occurs in the islanded microgrid system due to the interaction dynamics between the VSG and the LVSM, which has been investigated in this paper. At first, the dq-frame impedance models of the VSG and the LVSM are established and compared. It is revealed that the d-d channel impedance of LVSM behaves the negative resistor with a V-type magnitude in the low-frequency range, which easily interacts with the d-d channel impedance of the VSG and leads to instability of the system. Thus, the inductor current feedforward control and the additional voltage feedback control are proposed for the VSG to reshape its impedance. It diminishes the impedance magnitude and generates the active impedance of the VSG. In this way, the low-frequency interaction between the VSG and the LVSM can be mitigated. Besides, the proposed control preserves the dynamic performance of the system. Finally, simulations and experiments verify the effectiveness of stability analyses and the proposed suppression method.
TL;DR: Theoretical analysis of the output matching network is presented, focusing on the impact of the non-ideally infinite output impedance of the auxiliary amplifier in back off, due to the device’s parasitic elements, to follow the desired impedance trajectories across the 2.8 GHz to 3.6 GHz range.
Abstract: This paper discusses the design of a wideband class AB-C Doherty power amplifier suitable for 5G applications. Theoretical analysis of the output matching network is presented, focusing on the impact of the non-ideally infinite output impedance of the auxiliary amplifier in back off, due to the device’s parasitic elements. By properly accounting for this effect, the designed output matching network was able to follow the desired impedance trajectories across the 2.8 GHz to 3.6 GHz range (fractional bandwidth = 25%), with a good trade-off between efficiency and bandwidth. The Doherty power amplifier was designed with two 10 W packaged GaN HEMTs. The measurement results showed that it provided 43 dBm to 44.2 dBm saturated output power and 8 dB to 13.5 dB linear power gain over the entire band. The achieved drain efficiency was between 62% and 76.5% at saturation and between 44% and 56% at 6 dB of output power back-off.
TL;DR: A novel virtual capacitance control strategy that directly controls the input voltage of the PLL and does not need to change the internal controller parameters and structure is proposed, which can reduce the effect of the high line impedance by compensating for the P LL output angle deviation.
Abstract: As the share of wind power in the power system increases, the power grid exhibits the characteristics of a weak grid. The dynamic stability issues of the grid-connected doubly fed induction generator (DFIG)-based wind turbines caused by the interaction between the phase-looked loop (PLL) and rotor current controller (RCC) by high grid impedance have become acute, especially during low-voltage ride-through. In this article, the output impedance model of the DFIG is derived, where the dynamics of the PLL have been first taken into account. In addition, the interaction between the PLL and RCC is analyzed. Furthermore, a novel virtual capacitance control strategy that directly controls the input voltage of the PLL and does not need to change the internal controller parameters and structure is proposed. The proposed control strategy can reduce the effect of the high line impedance by compensating for the PLL output angle deviation. Subsequently, the interaction between the PLL and RCC becomes weaker, and the phase margin of the DFIG system during the severe grid fault increases. Meanwhile, the applicability of the proposed control strategy is presented. Finally, the effectiveness of simulation and experimental results is presented.
TL;DR: The contradictory between harmonic current and inrush fault current suppression for VSG is well solved and the experiment results validate the proposed control method.
Abstract: For the virtual synchronous generator, the voltage-controlled harmonic suppression method will seriously deteriorate the magnitude of inrush fault current in the moment of grid symmetrical fault, because the suppression effects of harmonic current and inrush fault current are mutually constrained from the perspective of its output impedance. For this issue, a harmonic current and inrush fault current coordinated suppression method is proposed to achieve both good results of harmonic current suppression in normal grid and inrush fault current limitation in fault grid, which mainly includes a passive branch, an active branch and an improved virtual synchronous generator (VSG) control. The passive branch is installed between the PCC and grid to introduce an additional voltage variable. Meanwhile, with the proper feed-forward of the PCC voltage and additional voltage, the active branch is used to increase the mid/high frequency impedance viewed from the grid fault point to VSG, and also decrease the harmonic impedance viewed from the PCC to VSG. Then, not only the transient inrush fault current is limited, but also the harmonic current introduced from the nonlinear load is mostly absorbed. Moreover, the improved VSG control is used to limit the steady-state fundamental frequency fault current. Therefore, the contradictory between harmonic current and inrush fault current suppression for VSG is well solved. Finally, the experiment results validate the proposed control method.
TL;DR: In this paper, a two-stage GaN Doherty power amplifier with a small auxiliary transistor was designed and characterized at millimeter-wave (mm-wave) frequencies, where the low output impedance of the auxiliary transistor loads the Doherty combining network, which lowers the power added efficiency.
Abstract: A 24–28-GHz two-stage GaN Doherty power amplifier (PA) is designed and characterized. At millimeter-wave (mm-wave) frequencies, the low output impedance of the auxiliary transistor loads the Doherty combining network, which lowers the power added efficiency (PAE) in back-off. In this design, a small periphery auxiliary transistor is used to increase the output impedance of the auxiliary transistor. The periphery ratio of the auxiliary and the main transistors is 77%. Even though, compared to symmetric Doherty PAs, the load modulation of the main transistor is reduced, this amplifier still achieves 32% and 23% PAE at 6 and 9-dB output power back-off, respectively. Attributing to the small auxiliary transistor, the amplifier obtains a small signal gain of 19 dB. The maximum output power of the amplifier is 4 W with a peak PAE of 42%.
TL;DR: A DFIG wind farm impedance model considering different rotor speeds is developed to indicate that the proposed model can provide more accurate modeling and stability analysis results.
Abstract: The oscillation phenomenon frequently occurs in large-scale grid-connected doubly-fed induction generators (DFIG) wind farms and the impedance-based analysis has gradually become a widely used method to analyze the wind power oscillation issues. The rotor speed of each wind turbine (WT) is usually different as an important factor to determine the operating point and affect the output impedance. This brief develops a DFIG wind farm impedance model considering different rotor speeds. The impedance of each WT is firstly obtained according to various rotor speeds and all the WTs are aggregated considering the complex frequency coupling effects to describe the overall wind farm impedance. The comparison between the simplified aggregation method of wind farms and the proposed model is given to indicate that the proposed model can provide more accurate modeling and stability analysis results.
TL;DR: An output impedance model for a VSynC-based DFIG is proposed to analyze the grid-connected stability in weak grids and is validated by direct current disturbing theory, frequency scanning method, generalized Nyquist criterion, and time-domain simulation.
TL;DR: A new faulty section identification and fault distance estimation technique for three-terminal transmission line (TTL) based on the derivation of three indices by solving non-linear equations with iterative method utilizing synchronized measurements from three ends of the line is proposed.
Abstract: A new faulty section identification and fault distance estimation technique for three-terminal transmission line (TTL) is proposed in this paper. It is based on the derivation of three indices by solving non-linear equations with iterative method utilizing synchronized measurements from three ends of the line. In the absence of synchronization, an angle synchronization operator is derived for building a common reference among the three terminals. The efficacy of the technique is verified by generating several fault cases on an existing Indian 400 kV TTL using PSCAD/EMTDC software. Reported results demonstrate the capability of the presented technique for all types of fault on three-terminal transposed/untransposed as well as the non-homogeneous transmission line. It also provides accurate fault location under comprehensive variation in type of fault, line length, fault inception angle, complex fault impedance, source impedance, and current transformer (CT) saturation condition. Its accuracy remains almost constant despite errors in line parameters, as well as synchronization and noise in the measured signals. The initial guess has a minimal impact on the accuracy and convergence of the presented technique. The attained results reveal higher accuracy and better robustness of the proposed technique in comparison with those of several existing techniques.
TL;DR: In this paper, a voltage-mode three-input single-output multifunction first-order filter employing commercially available LT1228 IC for easy verification of the proposed circuit by laboratory measurements is presented.
Abstract: This paper presents the design of a voltage-mode three-input single-output multifunction first-order filter employing commercially available LT1228 IC for easy verification of the proposed circuit by laboratory measurements. The proposed filter is very simple, consisting of a single LT1228 as an active device with two resistors and one capacitor. The output voltage node is low impedance, resulting in an easy cascade-ability with other voltage-mode configurations. The proposed filter provides four filter responses: low-pass filter (LP), high-pass filter (HP), inverting all-pass filter (AP-), and non-inverting all-pass filter (AP+) in the same circuit configuration. The selection of output filter responses can be conducted without additional inverting or double gains, which is easy to be controlled by the digital method. The control of pole frequency and phase response can be conducted electronically through the bias current (IB). The matching condition during tuning the phase response with constant voltage gain is not required. Moreover, the pass-band voltage gain of the LP and HP functions can be controlled by adjusting the value of resistors without affecting the pole frequency and phase response. Additionally, the phase responses of the AP filters can be selected as both lagging or leading phase responses. The parasitic effects on the filtering performances were also analyzed and studied. The performances of the proposed filter were simulated and experimented with a ±5 V voltage supply. For the AP+ experimental result, the leading phase response for 1 kHz to 1 MHz frequency changed from 180 to 0 degrees. For the AP- experimental result, the lagging phase response for 1 kHz to 1 MHz frequency changed from 0 to -180 degrees. The design of the quadrature oscillator based on the proposed first-order filter is also included as an application example.
TL;DR: In this article, a power-electronics-based photovoltaic emulator (PVE) is proposed to achieve fast-dynamic response, as well as, to emulate accurately in all regions of the current-voltage ( I-V ) characteristic curve.
Abstract: The dynamic performance of a photovoltaic (PV) emulator is critical for testing applications with fast maximum power point tracking (MPPT) algorithms. In this article, a power-electronics-based PV emulator (PVE) is proposed to achieve fast-dynamic response, as well as, to emulate accurately in all regions of the current–voltage ( I–V ) characteristic curve. The control scheme of the proposed PVE consists of an instantaneous output impedance matching (IOIM) controller based on load resistance feedback to generate the voltage reference signal and an inner boundary control (BC) scheme to regulate the converter at a given reference within a short period of time. The IOIM controller overcomes the drawback of conventional PVEs that suffer from oscillating reference signal in a certain region of the I–V characteristic curve. Moreover, use of load resistance feedback in the reference generation algorithm allows the decoupling of the reference signal generator from the inner control loop. The BC scheme adapts a corrected second-order switching surface to achieve a faster response time and robust operation with switching converter loads. Detailed small signal model of the PVE is derived to design the IOIM control loop and to ensure a stable and fast convergent emulation in the entire I–V characteristic curve. Experimental results of a 130 W ( V MPP = 35.2 V, I MPP = 3.69 A) prototype are presented with both resistive loads and an MPPT converter to verify its performance under fast varying irradiance and load conditions.
TL;DR: It is proved that, through a canonic approach, sinusoidal oscillators based on second-generation voltage conveyor (VCII) can be implemented, removing the need for additional voltage buffer for practical use, which is one of the main limitations of the current mode (CM) approach.
Abstract: The aim of this paper is to prove that, through a canonic approach, sinusoidal oscillators based on second-generation voltage conveyor (VCII) can be implemented. The investigation demonstrates the feasibility of the design results in a pair of new canonic oscillators based on negative type VCII (VCII−). Interestingly, the same analysis shows that no canonic oscillator configuration can be achieved using positive type VCII (VCII+), since a single VCII+ does not present the correct port conditions to implement such a device. From this analysis, it comes about that, for 5-node networks, the two presented oscillator configurations are the only possible ones and make use of two resistors, two capacitors and a single VCII−. Notably, the produced sinusoidal output signal is easily available through the low output impedance Z port of VCII, removing the need for additional voltage buffer for practical use, which is one of the main limitations of the current mode (CM) approach. The presented theory is substantiated by both LTSpice simulations and measurement results using the commercially available AD844 from Analog Devices, the latter being in a close agreement with the theory. Moreover, low values of THD are given for a wide frequency range.
TL;DR: It is presented that the power sharing performance of a general microgrid synchronized by Global Positioning System is essentially determined by equivalent output impedance, and a novel adaptive virtual impedance control approach, which implements different values of virtual resistance for d and q-axis is proposed accordingly.
Abstract: Global Positioning System (GPS) based control has recently been reported as a replacement of droop control to achieve fixed frequency operation in islanded microgrids. This article presents the perspective that the power sharing performance of a general microgrid synchronized by GPS is essentially determined by equivalent output impedance. A novel adaptive virtual impedance control approach, which implements different values of virtual resistance for d- and q -axis, is proposed accordingly. The virtual resistance concept is implemented comprising a basic local implementation for output impedance shaping, and a sparse resistance tuning network for the compensation of mismatched feeder impedance, which demands no knowledge of actual output impedance. The resistance tuning network utilizes the consensus protocol and only requires neighboring interactions among DG units. A complete tuning of output resistance for a given load condition results in accurate active and reactive power sharing even after communication is interrupted and will still outperform conventional droop control methods if load changes during the interruption. Small-signal analysis based on delay differential equations model of the overall microgrid is performed to investigate the adverse impact of communication delays on system stability. The efficacy of the proposed approach is validated by both simulation and experimentation.
TL;DR: This letter proposes a passivity-based dual-loop vector voltage and current control method for grid-forming voltage-source converters (GFM-VSCs) that is guaranteed in both the voltage control mode and the current-limiting mode with a wide range of time delay.
Abstract: This letter proposes a passivity-based dual-loop vector voltage and current control method for grid-forming voltage-source converters (GFM-VSCs). A passive output impedance of GFM-VSC is guaranteed in both the voltage control mode and the current-limiting mode with a wide range of time delay. The frequency-domain analysis, simulation and experimental tests validate the effectiveness of the approach.
07 Jun 2021
TL;DR: In this article, a mm-wave low-noise-amplifier (LNA) architecture capable of achieving simultaneous power and noise matching over a large bandwidth is proposed.
Abstract: A novel mm-wave low-noise-amplifier (LNA) architecture capable of achieving simultaneous power and noise matching over a large bandwidth is proposed. It is shown that by magnetically coupling a pair of inductors connected at the gate and drain of a transistor, a loss-less (series-series) feedback path from the drain-current to the gate is generated which: 1) Increases the transistor input impedance magnitude, 2) generates a real-impedance part which can be controlled for power-matching, and 3) brings the optimum noise source impedance close to the optimum power matching impedance. The prototype is fabricated in TSMC 28-nm bulk CMOS process. The measured chip is functional from 22.2 to 43 GHz, while providing 21 dB of peak gain, minimum NF of 3.5 dB, and an average IIP3 of −3 dBm.
TL;DR: It is verified that using the fast dynamics GESO with the low-stiffness actuator can achieve low output impedance and stable interaction under the reachable frequency of a human and the present closed-loop linear parameter varying system can be verified to be quadratically stable.
Abstract: This article investigates a closed-loop torque-controlled variable stiffness actuator (VSA) combined with a disturbance observer for enhancing low output impedance. We implement the generalized extended state observer (GESO) for conveniently testing the stability of the time-varying VSA system. In our application, the GESO is also required to serve the operation of the low- and high-impedance task. Here, the most important aspect is to consider the influence of the physical stiffness on the output impedance, because the VSA has been regulated with the closed-loop torque control. Through the interaction-torque experiments, we verify that using the fast dynamics GESO with the low-stiffness actuator can achieve low output impedance and stable interaction under the reachable frequency of a human. These properties contribute to perform the low-impedance task. When performing the high-impedance task, where a large torque command is needed, the high-stiffness actuator and the slow dynamics GESO are implemented to achieve high bandwidth and proper tracking performance. The continuously variable observer responses in accordance with the stiffness values are achieved via the gain-scheduling control. Moreover, the present closed-loop linear parameter varying system can be verified to be quadratically stable. The VSA system is then implemented on a knee exoskeleton for a sit-to-stand application. The reference command of the exoskeleton is a joint torque, calculated from the inverse dynamics. This torque signal is also used as the reference command of the stiffness motor of the VSA. The effectiveness of the exoskeleton system is experimentally verified with one healthy volunteer. Subsequently, another two healthy volunteers also successfully experienced the system.
TL;DR: A new voltage-mode (VM) analog filter is proposed that is composed of three plus-type single output DDCCs and only grounded passive elements that are important when the integrated circuit fabrication is involved and has the feature of easy cascadability with other VM structures.
Abstract: A new voltage-mode (VM) analog filter is proposed in this paper The proposed circuit is composed of three plus-type single output DDCCs and only grounded passive elements that are important when the integrated circuit fabrication is involved It has three high input impedances and one low output impedance As a result, it has the feature of easy cascadability with other VM structures Passive element matching constraints and extra additional active devices are not needed for it Non-ideality analyses such as non-ideal gain and parasitic impedance effects are also given Many simulations through SPICE program and several experimental studies are included
TL;DR: In this paper, the authors proposed a stability-oriented line inductance stability domain assessment approach for weak grids with CPLs, which has less conservatism and high efficiency than two previous improved stability criteria.
Abstract: Weak grids are gaining considerable attention since power generation resources are remote from constant power loads (CPLs), which results in low-frequency/harmonic oscillation. Meanwhile, due to the play, and plug demand of modern power system, the line inductance of weak grids often changes, which is also regarded as the variation regarding short circuit ratio (SCR). Based on this, the conventional impedance-based stability operation point assessment approaches should be expanded into stability domain assessment approach considering the line inductance variation. Therefore, the stability-oriented line inductance stability domain assessment approach for weak grids with CPLs is proposed in this paper. Firstly, the source impedance matrix of weak grid, and load admittance matrix of CPLs are separately built. Secondly, an improved stability forbidden domain criterion is proposed through related mapping transformation process, which has lower conservatism than two previous improved stability criteria. Thirdly, the improved stability forbidden domain criterion is switched into the condition that the intermediate matrices are Hurwitz. Meanwhile, the line inductance stability domain is directly obtained through these intermediate matrices, and guardian map theory. Finally, the simulation, and experiment results illustrate that the proposed approach has less conservatism, and high efficiency.