Showing papers on "Output impedance published in 2018"
TL;DR: It can be demonstrated that the proposed method can enhance the stability of grid-connected inverters under weak grid conditions and reduce the impact of PLL perturbations on grid-connecting current and low-order harmonics of the network current can be suppressed effectively.
Abstract: Phase-locked loop (PLL) is commonly used for three-phase grid-connected inverters to obtain the information of grid synchronization, and PLL dynamics are the key factors for stable operation of the inverters. Under weak grid conditions, the coupling between PLL and grid impedance can result in harmonic resonance, or even instability in the system. In this paper, the effect of PLL dynamics and grid impedance on the stability of three-phase grid-connected inverters is studied with the d – q impedance model. Besides, the variable transfer relationship is used to analyze the influence of PLL perturbations on output current under weak grid conditions. To suppress low-order harmonics of the network current caused by PLL perturbations under weak grid conditions, a novel feedforward control method is proposed to compensate PLL perturbations and revise the output impedance, where the operation of the inverter and PLL dynamics have been taken into account in the design process. By analyzing the impedance characteristic of the system, it can be demonstrated that the proposed method can enhance the stability of grid-connected inverters under weak grid conditions and reduce the impact of PLL perturbations on grid-connecting current. The experimental results indicate that the low-order harmonics of the network current can be suppressed effectively, which verifies the analysis.
170 citations
TL;DR: An improved design of current controller, i.e., proportional–integral controller and capacitor-current-feedback active damping, is proposed to reduce the negative effect of PLL on current control and has a strong robustness against wide-range variation of grid impedance.
Abstract: For three-phase LCL -type grid-connected converter, when it is attached to weak grid, current control interacts with phase-locked loop (PLL) via point of common coupling voltage. Consequently, PLL dynamic might deteriorate grid current control and even result in system instability. However, the conventional design method of current controller neglects the impact of PLL, and therefore, it is hard for the current controller to mitigate the negative effect of PLL. In this paper, an improved design of current controller, i.e., proportional–integral controller and capacitor-current-feedback active damping, is proposed to reduce the negative effect of PLL on current control. First, a small-signal impedance model is developed to analyze the impact of PLL on current control. Then, the effect of current controller parameters on the converter output impedance is analyzed, and a design guideline to improve the current controller parameters is presented. With the improved parameters, in precondition of satisfying system stability margin under both stiff and weak grid, the negative effect of PLL on current control can be effectively mitigated without employing additional control strategies. Furthermore, the current control has a strong robustness against wide-range variation of grid impedance. Finally, the experiment demonstrates the effectiveness of the proposed design method.
114 citations
TL;DR: In this paper, a self-powered and highly durable TENG pressure sensor for large-scale pressure detection based on double-side tribological layers of micro-patterned polydimethylsiloxane (PDMS) and PDMS-multi-wall carbon nanotube (CNT) nanocomposites is presented.
112 citations
TL;DR: In this paper, the use of orthogonal binary sequences (OBS) was used to simultaneously measure the output impedance and the grid impedance of a three-phase grid-connected inverter.
Abstract: Grid impedance and the output impedance of grid-connected inverter are important parameters for the operation of grid-connected systems, such as solar, wind, and other distributed-generation resource systems. The impedance mismatch between the grid and the interfacing circuit often generates harmonic resonances that lead to reduced power quality and even instability. Since the impedances usually vary over time as a function of many parameters, online measurements are required for stability assessment and adaptive control of the inverters. Several methods have been proposed for quick, accurate measurements of impedances, but the use of multiple-input multiple-output (MIMO) identification techniques have not been considered. Applying the MIMO techniques, different components of the inverter output impedance or grid impedance can be simultaneously measured during a single measurement cycle. Therefore, the operating conditions of the system can be kept constant during the measurements, and the overall measurement time is significantly reduced. This paper shows the use of orthogonal binary sequences to simultaneously measure the “d” and “q” components of grid-connected inverter output impedance and/or grid impedance. Experimental results based on a three-phase grid-connected inverter are presented and used to demonstrate the effectiveness of the proposed methods.
96 citations
TL;DR: In this paper, a two-stage single-phase inverter with a boost-derived front-end converter was designed to reduce the second-harmonic current (SHC) by using virtual series impedance.
Abstract: The instantaneous output power of the two-stage single-phase inverter pulsates at twice the output frequency $(2f_{{\rm{o}}})$ , generating notorious second-harmonic current (SHC) in the front-end dc–dc converter and the input dc voltage source. This paper focuses on the SHC reduction for a two-stage single-phase inverter with boost-derived front-end converter. To reduce the SHC, a virtual series impedance, which has high impedance at $2f_{{\rm{o}}}$ while low impedance at other frequencies, is introduced in series with the boost diode or the boost inductor to increase the impedance of the boost-diode branch or boost-inductor branch at $2f_{{\rm{o}}}$ . Meanwhile, for achieving good dynamic performance, a virtual parallel impedance, which exhibits infinite impedance at $2f_{{\rm{o}}}$ while low impedance at other frequencies, is introduced in parallel with the dc-bus capacitor to reduce the output impedance of the boost-derived converter at the frequencies except for $2f_{{\rm{o}}}$ . The virtual series impedance is realized by the feedback of the boost-diode current or the boost-inductor current, while the virtual parallel impedance is implemented by the feedback of the dc-bus voltage. Based on the virtual-impedance approach, a variety of SHC reduction control schemes are derived. A step-by-step closed-loop parameters design approach with considerations of reducing the SHC and improving the dynamic performance is also proposed for the derived SHC reduction control schemes. Finally, a 1-kW prototype is built and tested, and experimental results are presented to verify the effectiveness of the proposed SHC reduction control schemes.
91 citations
TL;DR: In this article, an integral droop (ID), inspired by the electrical characteristics of capacitor charging/discharging process, is proposed and applied to a cluster of energy storages (ESs) with high ramp rates.
Abstract: Power allocation in hybrid energy storage systems (HESSs) is an important issue for dc microgrids. In this paper, an integral droop (ID), inspired by the electrical characteristics of capacitor charging/discharging process, is proposed and applied to a cluster of energy storages (ESs) with high ramp rates. Through the coordination of the ID and conventional V-P droop, the transient power allocation in HESSs can be intrinsically realized in a decentralized manner. The high-frequency components of power demand can be compensated by the ESs with ID, whereas the ESs with V-P droop respond to the smooth change of load power. Additionally, the ID coefficient can be designed according to the nominal ramp rate of the ESs with slow response, which helps to extend the lifespan of the HESS. On the other hand, to easily assess the stability of the system feeding constant power loads, a minimum relative impedance criterion (MRIC) is developed. Based on MRIC, it is revealed that the proposed ID can shape the output impedance of the HESS and stabilize the entire system. The feasibility and effectiveness of ID are verified by both simulations and experimental results.
88 citations
TL;DR: A modified modulation technique based on an alternative phase opposition disposition scheme is suggested to effectively control the shoot-through state for boosting the dc-link voltage and balancing the two series capacitor voltages of the MqZS.
Abstract: This paper proposes the combination of a novel modified quasi-Z-source (MqZS) inverter with a single-phase symmetrical hybrid three-level inverter in order to boost the inverter three-level output voltage. The proposed single-phase MqZS hybrid three-level inverter provides a higher boost ability and reduces the number of inductors in the source impedance, compared with both the single-phase three-level neural-point clamped quasi-Z-source inverter and the single-phase quasi-Z-source cascaded multilevel inverter. Additionally, it can be extended to obtain the nine-level output voltage by cascading two three-level pulse width modulation switching cells with a separate MqZS and a dc source, which herein is called a single-phase MqZS cascaded hybrid five-level inverter (MqZS-CHI). A modified modulation technique based on an alternative phase opposition disposition scheme is suggested to effectively control the shoot-through state for boosting the dc-link voltage and balancing the two series capacitor voltages of the MqZS. The performances of both the proposed MqZS-CHI and the modulation techniques are verified through simulation and experimental results.
78 citations
TL;DR: In this article, a broadband continuous-mode Doherty power amplifier (CM-DPA) is realized taking advantage of the non-infinity output impedances of the peaking stage.
Abstract: In this paper, a broadband continuous-mode Doherty power amplifier (CM-DPA) is realized taking advantage of the noninfinity output impedances of peaking stage Specifically, the carrier PA of the designed DPA operates in a continuous class-J mode when the peaking PA is in the OFF-state, where the output impedance of the peaking PA has some influences on the carrier PA When the peaking transistor is in the OFF-state, the load impedance variation of the carrier transistor versus noninfinity peaking impedance is presented in this contribution The proposed method surmounts the back-off drain efficiency deterioration of DPAs at two side working bands through elaborately processing the noninfinity peaking impedance This paper also presents a method to derive the required OFF-state output impedance of the peaking stage by the carrier PA in a symmetrical broadband DPA A broadband CM-DPA working over 16–27 GHz (bandwidth of 51%) is designed and fabricated for interpreting our theories The simulated load trajectory of the carrier transistor is in line with the design space of continuous class-J mode Under continuous wave excitation, experimental results show the drain efficiencies of 465%–635% at 6-dB output back-off power levels and 56%–753% at peaking power levels The maximum output power of this DPA is 438–452 dBm with a gain of 94–115 dB across the whole working band Furthermore, a 20-MHz LTE modulated signal with a peak-to-average power ratio of 74 dB is also applied to the fabricated CM-DPA at 22 GHz At an average output power of 375 dBm, measurement results show the adjacent channel power ratios of −302 and −501 dBc before and after digital predistortion, respectively
78 citations
TL;DR: In this paper, a real-time and nondestructive method is developed to identify dynamic impedance parameter for SOH diagnosis ECM (SDEM) of lithium ion battery (LIB) in an equivalent circuit model.
68 citations
TL;DR: This paper presents a noninvasive online parametric identification of three-phase ac power impedances to assess small-signal stability of grid-tied inverter systems by using well-known impedance-ratio-based stability criteria.
Abstract: This paper presents a noninvasive online parametric identification of three-phase ac power impedances to assess small-signal stability of grid-tied inverter systems by using well-known impedance-ratio-based stability criteria. The identification technique is integrated into the control of an existing grid-tied inverter for the estimation of wide bandwidth ac grid impedances, on top of its original power conversion function. This is accomplished in practice by injecting a short-time small-signal pseudorandom binary sequence (PRBS), a digital approximation of white noise which is wide bandwidth in nature, on the inverter control loop so that all frequencies of interest at the impedance measurement point can be excited at once. Then, digital processing is performed in the integrated control platform where the parametric ac grid impedance is extracted from the measurement of voltage and current over the length of PRBS injection. Moreover, a procedure on how to identify the output impedance of the inverter is deployed so that the parametric source and load impedances can be used to verify the system stability by means of the generalized Nyquist stability criterion. The technique is validated via hardware-in-the-loop real-time simulation. This paper focuses on the identification of balanced three-phase ac impedances in dq reference frame and a dq diagonal-dominant stability analysis which is typical of low-voltage distribution grids.
54 citations
TL;DR: A simplified equivalent model is proposed to investigate low-frequency (LF) stability of dc microgrids by using an impedance-based approach considering exact models of microgrid components and shows that the LF stability of a dc microgrid is approximately independent of droop types.
Abstract: In this paper, a simplified equivalent model is proposed to investigate low-frequency (LF) stability of dc microgrids This is done by using an impedance-based approach considering exact models of microgrid components In order to apply the impedance-based stability criterion, a multi-bus dc microgrid is first categorized as multiple interconnected single-bus dc microgrids Then, each single-bus system is classified into two subsystems: subsystem#1 which only includes voltage-controlled (VC) DGs and subsystem#2 which includes the rest of the dc microgrid components It is shown that due to the absence of LF interaction between subsystems, the dominant LF modes of a single-bus dc microgrid are mainly determined by the droop controllers of VC-DGs The studies also show that the droop controller of each VC-DG accounts for the LF complex conjugate zeros at the output impedance of each VC-DG; and the internal interaction among these zeros can result in LF poles, which are the origin of LF current/power oscillations in dc microgrids Through further analyses, it is shown that our findings for single-bus dc microgrids can be extended to any multi-bus dc microgrid as well Owing to this fact, a simplified equivalent model, which can lead to the order reduction of the overall system, is proposed for the analysis of LF stability of dc microgrids Thanks to the simplicity and generality of the proposed equivalent model, the effect of different parameters, such as number of VC-DGs, internal voltage controller of VC-DGs, and the microgrid line impedances on the LF stability of dc microgrids is comprehensively investigated The studies also show that the LF stability of a dc microgrid is approximately independent of droop types (current or power) A complete set of simulation studies are provided which further supports the effectiveness of the proposed model
TL;DR: A real-time implementation for the online stability analysis using MIMO-identification methods, where the stability of grid-connected system is rapidly assessed in the dq domain using orthogonal injections and Fourier techniques.
Abstract: Grid impedance has a major effect on the operation of inverter-connected systems, such as renewable energy sources. Stability of such system depends on the ratio of the inverter output impedance and the grid impedance at the point of common coupling. Because the grid impedance varies over time with many parameters, online grid-impedance measurement acquired in real time is most preferred method for observing the stability. Recent studies have presented methods based on multiple-input-multiple-output (MIMO) identification techniques, where the stability of grid-connected system is rapidly assessed in the dq domain. In the methods, orthogonal injections are used with Fourier techniques, and the grid impedance d and q components are measured. The Nyquist stability criterion is then applied to assess the stability. This paper extends previous studies, and presents a real-time implementation for the online stability analysis using MIMO-identification methods. The practical implementation is discussed in detail and experimental results based on a grid-connected three-phase inverter are provided to demonstrate the effectiveness of the methods.
TL;DR: In this paper, an impedance-based method is presented to systematically investigate the interaction between multiple trains and a traction network, focusing on evaluating the harmonic instability problem. And the theoretical results are further validated by the simulations and experiments.
Abstract: This paper presents an impedance-based method to systematically investigate the interaction between multiple trains and a traction network, focusing on evaluating the harmonic instability problem. First, the interaction mechanism of the multitrain and the traction network is represented as a feedback interconnection of the two subsystems, i.e., an equivalent output impedance of the traction network and an equivalent input admittance of the multitrain. Then, the harmonic instability is evaluated through a series of pole-zero diagrams drawn from the closed-loop transfer matrix of the multitrain and network system. The interaction system is unstable, and the harmonic instability will happen if there are some high-frequency poles of the closed-loop system locating in the right-half plane. This method is used for analyzing the harmonic instability phenomena, the characteristics, influential factors, and potential mitigation schemes. The theoretical results are further validated by the simulations and experiments.
TL;DR: In this article, a power-voltage control strategy based on voltage feedback control of the inverter LCL filter capacitor is proposed to overcome the interactive stability issues, including harmonic oscillations when connected to a weak ac grid, which limits the integrated power rating of distributed generators.
Abstract: The conventional power-current controlled grid-tied inverter suffers from interactive stability issues, including harmonic oscillations when connected to a weak ac grid, which limits the integrated power rating of distributed generators. To overcome preceding drawbacks, a novel power-voltage control strategy, based on the voltage feedback control of the inverter LCL filter capacitor, is proposed in this paper. A dynamic model of the inverter output impedance is developed in the rotating d–q frame. This model includes main circuit parameters, phase-locked loop (PLL) dynamics, and regulator parameters. Frequency characteristics of the output impedance, contrastive analysis between the conventional power-current strategy and proposed power-voltage strategy based on generalized Nyquist criterion are presented to show superiority of the latter in a weak grid. The impedance analysis proves the power-voltage controlled inverter can stably operate in a weak grid. The stability of the grid-tied inverter system remains unchanged with increasing PLL bandwidth and delivered power, thereby effectively raising the rated power injection level of the inverter in a weak grid. A low-power inverter prototype is built and tested in the laboratory. The simulation and experimental results verify the effectiveness of the proposed control strategy.
TL;DR: In this article, a novel impedance matching method based on combined CCM and discontinuous conduction mode (DCM) operation of an impedance matching converter was proposed to extend the impedance-matching range.
Abstract: Maximum power transfer is an important index for an inductive power transfer (IPT) system to make full use of its power transfer capability, and such a capability is usually realized by impedance matching. Traditionally, impedance matching is implemented by placing a power electronics converter such as a dc–dc converter at the secondary side of an IPT system. However, the power electronics converter and its operation mode directly affect its impedance-matching range, which is very limited if a traditional power converter only operates at continuous conduction mode (CCM). To extend the impedance-matching range, this paper proposes a novel impedance matching method based on combined CCM and discontinuous conduction mode (DCM) operation of an impedance matching converter. The impedance-matching range is fully analyzed for CCM and DCM operation, respectively, by taking variation of coupling coefficient into consideration. The analysis results show that the impedance-matching range can be extended by more than double that of the traditional impedance matching method. In addition, a maximum power transfer tracking method is developed using the proposed impedance-matching range extension method, and the experimental results have verified the feasibility of the tracking method.
TL;DR: In this article, a virtual series impedance was introduced to increase the output impedance of the grid-connected inverter only at the dominated lower harmonic frequencies to improve the injected grid current quality.
Abstract: The injected grid current of the voltage-controlled grid-connected inverter has serious distortion due to the low frequency harmonic components in the output voltage, which is resulted by the dead time of the drive signals of the power switches, and the distortion cannot be eliminated even when an output voltage closed loop is incorporated. This paper introduces a virtual series impedance to increase the output impedance of the grid-connected inverter only at the dominated lower harmonic frequencies; thus, the injected grid current quality can be improved and the dynamic performance of the grid-connected inverter is not deteriorated. Experimental results from a 6-kW single-phase grid-connected inverter confirm the effectiveness of the proposed method.
TL;DR: In this paper, a hierarchical control for flexible operation of a microgrid is proposed, which consists of inner, primary and secondary levels, and the results demonstrate the disturbance rejection performance and the flexibility of the proposed control scheme.
TL;DR: In this article, a crossed frequency output impedance matrix model is proposed to describe the terminal characteristics of a dc-dc converter around its switching frequency range, and a high-frequency equivalent circuit model for the converter is then developed to predict the beat frequency oscillation in parallel and cascaded systems, which results from the interaction of power converters with different switching frequencies.
Abstract: The interaction of power electronic converters in a microgrid can introduce system instability and power quality issues Existing investigations focus on interactions either in low-frequency regions, such as the constant power load, or in very high-frequency regions like electromagnetic interference However, interactions of power converters around their switching frequency range are not included In fact, the interaction of dc–dc converters with different switching frequencies can introduce beat frequency oscillation in certain cases Since additional frequency component (beat frequency) is generated, traditional impedance concept is no longer the tool for beat frequency oscillation analysis and new models need to be developed In this paper, a crossed frequency output impedance matrix model is proposed to describe the terminal characteristics of a dc–dc converter around its switching frequency range A high-frequency equivalent circuit model for the converter is then developed to predict the beat frequency oscillation in parallel and cascaded systems, which results from the interaction of power converters with different switching frequencies Finally, design guidelines are proposed to avoid potential beat frequency oscillation in a dc nanogrid Experimental results for both parallel and cascaded systems validate the accuracy and effectiveness of the proposed prediction method and design guidelines
TL;DR: A virtual phase-lead impedance stability control strategy aiming at rectifier station can effectively mitigate the dc-side oscillation of the VSC–HVDC system without affecting the load performance of the inverter station.
Abstract: In the maritime VSC-HVDC system supplying power to passive network on the island, the dc side of the system is prone to oscillation and even instability, which is resulted from the negative incremental input resistance characteristic of the inverter station First, a virtual phase-lead impedance stability control strategy aiming at rectifier station is proposed This control strategy can effectively mitigate the dc-side oscillation of the VSC–HVDC system without affecting the load performance of the inverter station Then, the dc impedance model of the VSC–HVDC system is built, including the output impedance of the rectifier station, dc cable impedance, and the input impedance of the inverter station In addition, the oscillation mechanism of the VSC–HVDC system is analyzed by impedance-based Nyquist stability criterion The reason why rectifier station fails to mitigate the dc-side oscillation using traditional virtual resistance stability control is that the output impedance of the rectifier station exhibits negative damping characteristic outside the control bandwidth of voltage outer loop For this issue, the proposed control strategy can correct the output impedance of the rectifier station to exhibit positive damping characteristic outside the control bandwidth of voltage outer loop, thus mitigating the dc-side oscillation of the VSC–HVDC system Finally, simulation and experiment results validate the proposed control strategy and analysis
TL;DR: An integrated energy harvester system targeting Internet of Things sensor applications such as a wireless temperature sensor capable of 3-D maximum power point tracking and able to extract power from a small form factor TEG, having low source impedance.
Abstract: This brief introduces an integrated energy harvester system targeting Internet of Things sensor applications such as a wireless temperature sensor. The proposed design provides 1-V regulated voltage boosting the input voltage (0.27–1 V) from a thermoelectric generator (TEG). To ensure the maximum power extraction, the proposed energy harvester includes multiple circuit level techniques. First, the reconfigurable capacitor charge pump distributes on-chip capacitors to required step-up stages. This approach optimizes the silicon area by utilizing 100% of on-chip capacitors regardless of charge pump conversion gain. Second, the design is capable of 3-D maximum power point tracking, matching a source impedance to input impedance of the energy harvester. Thus, the proposed design is able to extract power from a small form factor TEG, having low source impedance. The reconfigurable capacitor charge pump has the highest power density while delivering power up to $500~{\mu W}$ . Experimental results show end-to-end power efficiency of 64% @ 1–V output voltage, and an input impedance matching range of $1 {\Omega } - 5~{\mathbf{k}}{\Omega }$ . The energy harvester was fabricated in 130-nm CMOS standard technology with an active area of 0.835 mm2.
TL;DR: A method to measure the equivalent impedances of the traction network and the 4QC of the electric train in the stationary frame for stability analysis and the stability and oscillation issues of the train–network system can be identified using measured impedances.
Abstract: Instability and oscillation issues have frequently occurred in high-speed railways due to the impedance mismatch versus frequency between the four-quadrant converter (4QC)-based high-speed train and the traction network (hereinafter train–network). However, solely utilizing the mathematical deduction to quantify the impedances seems to be difficult owing to unknown detailed parameters of both traction network and electric train. This paper proposes a method to measure the equivalent impedances of the traction network and the 4QC of the electric train in the stationary frame for stability analysis. A disturbance circuit consisting of antiparallel insulated gate bipolar transistor (IGBT) modules and an excitation load is adopted by means of the pulsewidth modulation (PWM) signal to drive the IGBTs. Consequently, a desired broad spectral excitation is then generated to measure the output impedance of the traction network. When injecting the harmonics twice, which are linearly independent at the same frequency, the input impedance of the 4QC can be calculated at the corresponding frequency considering the frequency-coupled effect. The proposed method shows a good measurement accuracy. Additionally, the stability and oscillation issues of the train–network system can be then identified using measured impedances. Both simulation and experimental results validate the effectiveness of the proposed measurement method.
01 Sep 2018
TL;DR: This dual inductor hybrid converter (DIHC) features fewer number of switches and more effective switch utilization than a recently reported hybrid Dickson converter, leading to substantially less conduction losses presented by a smaller equivalent output impedance.
Abstract: This paper presents a new 48 V-to-1 V hybrid converter. The converter utilizes two interleaved inductors to achieve complete soft-charging of flying capacitors to efficiently support high output currents. This dual inductor hybrid converter (DIHC) features fewer number of switches and more effective switch utilization than a recently reported hybrid Dickson converter, leading to substantially less conduction losses presented by a smaller equivalent output impedance. Experimental results verify the converter's operation principles and advantages in a 300-kHz 20-W prototype achieving 95.02% peak efficiency and 225 W/in3 power density. Its advantages and performance promise a good candidate converter architecture for applications that require large conversion ratios and high output currents, such as data centers and high-performance digital systems.
TL;DR: A grid-voltage-sensorless control strategy is proposed for the R-APF with series LC-filter and shows good accuracy of the emulated resistance and functionality of the DC-link voltage control.
Abstract: Voltage-sensorless control has been investigated for voltage source inverters (VSIs) for many years due to the reduced system cost and potentially improved system reliability. The VSI-based resistive-active power filters (R-APFs) are now widely used to prevent the harmonic resonance in power distribution network, for which the voltage sensors are needed in order to obtain the current reference. In this paper, a grid-voltage-sensorless control strategy is proposed for the R-APF with series LC -filter. Unlike the traditional resistance emulation method, this proposed control method reshapes the output impedance of the R-APF at the harmonic frequencies, which is independent of the current reference. A fundamental grid-voltage estimation method is also proposed to control the dc-link voltage. The performance of the proposed control method is verified in both simulations and experiments. The results show good accuracy of the emulated resistance and functionality of the dc-link voltage control. With the proposed method, the cost of the R-APF can also be reduced with potentially improved system reliability.
TL;DR: A novel active control method is proposed for mitigating the input current ripple, which adopts double-channel current feedbacks including an additional ripple current feedback channel and the normal one, and is validated by the experimental results on a 5 kW prototype.
Abstract: When an existing photovoltaic (PV) system is upgraded to a residential PV/battery system, the single-phase PV inverter under both input conditions of battery and PV should be properly controlled to restrain the input current ripple and grid-current harmonics. To do this, equivalent circuits of PV array and Li-ion battery pack are first constructed and respectively analyzed. The analysis results show that the input current under the battery pack may contain serious ripple component due to the low internal impedance of the battery pack, which cannot suppress the ripple current caused by the inherent power coupling problem of the grid-connected single-phase inverter. Then, based on the small signal model of the boost dc–dc convertor, a novel active control method is proposed for mitigating the input current ripple, which adopts double-channel current feedbacks including an additional ripple current feedback channel and the normal one. To provide the feedback signal, a third-order general integrator is introduced to extract the current ripple. Besides, a proportional-resonant controller is used to restrain the grid-current harmonics. Finally, the control parameters are obtained using MATLAB toolbox, and the proposed control strategies are validated by the experimental results on a 5 kW prototype.
TL;DR: In this paper, a fixed-valued capacitor (C_{r}$ ) at the common-base node is designed to introduce a common-mode parallel resonance at the desired second harmonic, boosting the commonmode voltage swing and subsequently its output power.
Abstract: We present a novel method of maximizing the output power and efficiency of millimeter-wave and terahertz signal sources, which are based on the push-push topology. In this method, the common-mode impedance of a differential Colpitts oscillator operating in the odd mode is maximized by introducing a fixed-valued capacitor ( $C_{r}$ ) at the common-base node. This capacitor is designed to introduce a common-mode parallel resonance at the desired second harmonic, boosting the common-mode voltage swing and subsequently its output power. The proposed method is analyzed using a high-frequency even-mode $\pi $ -model. Analytical expressions of input impedance are derived and are used for calculating the common-mode resonance frequency and the required value of $C_{r}$ . Two 0.3-THz voltage-controlled oscillators (VCOs) are implemented in a 130-nm SiGe BiCMOS process. It is shown that by using the proposed technique, the output power is improved by more than 6 dB, as compared with the conventional approaches. The implemented VCOs work from 292 to 318 GHz and 305 to 327 GHz, delivering a peak output power of 0.6 and 0.2 dBm, with a dc-to-RF efficiency of 0.8% and 0.9%, and can achieve a phase noise of −108 and −105 dBc/Hz at 10-MHz offset, respectively. As compared with the prior state-of-the-art Si-based tunable signal sources and arrays working above 270 GHz, this paper shows the lowest phase noise and the best figure-of-merit, while having an excellent output power, a tuning range, and a dc-to-RF efficiency.
TL;DR: A hybrid virtual impedance method is proposed, which uses both the feedforward of the PCC voltage and the feedback of the output current to develop the harmonic output impedance of the VSC in a wider range, without the potential overmodulation or instability problems caused by the conventional methods when the desired virtual impedance varies in a wide range.
Abstract: This paper presents a flexible compensation strategy for voltage source converter (VSC) connected to an unbalanced and harmonic distorted grid, which can achieve flexible tradeoff between the two common control targets, i.e., compensating the voltage at the point of common coupling (PCC), and compensating the output current of the VSC. To achieve the control target, a hybrid virtual impedance method is proposed, which uses both the feedforward of the PCC voltage and the feedback of the output current to develop the harmonic (including the negative sequence) voltage references. Compared with the conventional virtual impedance methods using only feedforward or only feedback, the proposed hybrid method can control the harmonic output impedance of the VSC in a wider range, without the potential overmodulation or instability problems caused by the conventional methods when the desired virtual impedance varies in a wide range. The effectiveness and superiority of the proposed strategy is theoretically analyzed and experimentally verified.
TL;DR: This paper analyzes the interaction between capacitive or inductive LTI prefiltering and an -path mixer or filter, leveraging an analysis technique based on the impulse response of the adjoint network.
Abstract: Switch $R-C$ passive $N$ -path mixers and filters enable interference-robust radio receivers with a flexibly programmable center frequency defined by a digital multi-phase clock. The radio frequency (RF) range of these circuits is limited by parasitic shunt capacitances, which introduce signal loss and degrade noise figure. Moreover, the linear periodically time varying nature of switch $R-C$ circuits results in unwanted signal folding which needs to be suppressed by linear time- invariant (LTI) prefiltering by passive LC filters. This paper analyzes the interaction between capacitive or inductive LTI prefiltering and an $N$ -path mixer or filter, leveraging an analysis technique based on the impulse response of the adjoint network. Previously reported results for an inductive source impedance are derived in a simpler fashion, while providing circuit intuition. Moreover, new results for $N$ -path receivers with a shunt capacitor, and a combination of a series inductor and shunt capacitor are derived, as well as design criteria to minimize loss and frequency shifting in the peak response of these circuits.
TL;DR: This paper presents an impedance-based analysis of a grid-connected dc active distribution system, where DGs equipped with active positive feedback islanding detection schemes and a high penetration level of constant power loads (CPLs) are considered.
Abstract: Active dc distribution systems are gaining widespread acceptance in modern power distribution grids. Islanding detection is very crucial for safety and protection purposes in active distribution systems; therefore, distributed generators (DGs) are usually equipped with active islanding detection methods to detect grid disconnection conditions. The high penetration level of tightly regulated converters to interface both DGs and loads and the poorly damped LC networks structured by the filtering inductors, feeder impedances, and bus capacitors can cause severe stability problems. This paper presents an impedance-based analysis of a grid-connected dc active distribution system, where DGs equipped with active positive feedback islanding detection schemes and a high penetration level of constant power loads (CPLs) are considered. The output impedance of a DG equipped with active islanding detection schemes is derived, and the interactions of the system impedances are discussed to characterize the dynamics of the dc distribution system. Moreover, the performance of multiple DG systems with the islanding detection schemes is investigated and thoroughly addressed. A simple, yet effective, stabilization method is also developed. Detailed time-domain nonlinear simulations and experimental results validate the analytical results.
TL;DR: In this article, a general and systematic approach to programmable and reconfigurable emulation of power impedances is proposed, which not only enables the impedance value to be programed, but also allows the characteristics of the impedance to be reconfigured instantly during the operation.
Abstract: Starting with a brief review on the existing methods of impedance emulation, this paper addresses a general and systematic approach to programmable and reconfigurable emulation of power impedances. The proposed approach not only enables the impedance value to be programed, but also allows the characteristics (i.e., type) of the impedance to be reconfigured instantly during the operation. Based on the proposed control method, emulation of at least six types of emulated power impedances (EPI) can be easily attained. In particular, it is theoretically and practically demonstrated that the impedance characteristic can be emulated through a combination of different functions. The systematic derivation of these functions is explained. New techniques that compensate the circuit power losses are introduced. This general approach has been practically verified in several EPI. Both steady-state and dynamic performance of these EPI confirm the programmability and reconfigurability. It is envisaged that the proposed method can be applied to a range of functions, such as power filtering, energy storage, and even power conversion based on direct impedance control.
TL;DR: The voltage-mode universal filter employing the active building block, called voltage differencing differential difference amplifier (VDDDA) is introduced and the results agree well with theoretical anticipations.
Abstract: In this paper, the voltage-mode universal filter employing the active building block, called voltage differencing differential difference amplifier (VDDDA) is introduced. The proposed circuit configuration has single output voltage node and five input voltage nodes. All input voltage nodes exhibit high impedance with low output impedance of the output voltage node, which is completely cascaded without the use of any external voltage buffer. The proposed filter realizes bandpass (BP), lowpass (LP), highpass (HP), allpass (AP) and bandstop (BS) filtering functions with using the same circuit topology. The output filtering response function can be obtained by appropriately applying input voltage without any matching condition. The control of the natural frequency and the quality factor can be done electronically and independently. The proposed circuit comprises three VDDDAs, two grounded capacitors and single grounded resistor. The workability of the proposed filter is investigated via PSpice simulation program and experimental results. The results agree well with theoretical anticipations.