Large-signal Model Research Articles

Active Damping Control of Cascaded DC Converter in DC Microgrids Based on Optimized Parallel Virtual Resistance

In dc microgrid, the cascaded dc system has been extensively employed. However, the negative impedance characteristics of the converter may induce system instability. This article proposes an optimized parallel virtual resistance (PVR) based active damping control to improve the stability of the cascade dc system in the dc microgrid. The advantage of this method is that it not only meets the closed-loop dynamic performance of the source converter (SC), but also meets the stability requirements of matching the input impedance of the load converter. The stability range of PVR under full load and its influence on the output impedance of SC in cascade system are determined. Additionally, a large-signal model is constructed by using state-space averaging method to investigate the open-loop stability in the cascaded dc system. The suggested control stability requirements are investigated by using the Lyapunov indirect approach, and a matching PVR is then adopted to ensure system stability. Finally, the performance of the control strategy is verified by establishing a MATLAB simulation and experiment platform.

Impact of Reactive Current and Phase-Locked Loop on Converters in Grid Faults

The precise control of output power by grid-connected converters relies on the correct identification and tracking of a grid voltage’s phase at the converter terminal. During severe grid faults, large disturbances cause the converter’s operating point to move away from the stable equilibrium point during normal operation. This leads to oscillations of both the active and reactive power fed into the grid. Using large-signal modelling, this study investigated the converter’s dynamic processes during and after such fault situations. The investigation considered the influence of the converter’s phase-locked loop (PLL), responsible for phase tracking, as well as that of the DC link on the converter-grid system, which has a major influence on the active power exchange with the grid. On this basis, this study also focused on the reactive current reference’s influence during and after fault clearing. Furthermore, an easily implementable strategy for reactive current injection, leading to minimum power oscillations, was presented. The results and the optimized strategies were validated via controller hardware-in-the-loop tests.

Stability Control Strategies for Bidirectional Energy Storage Converters Considering AC Constant Power Loads

In islanded AC microgrids, negative impedance characteristics of AC constant power loads (AC CPLs) easily introduce large signal instability to the system, while energy storage systems sometimes compensate for the dynamic characteristics of AC CPLs, and increase the system stability. Although energy storage control techniques and characteristics have gained a lot of attention, few studies have derived quantitative design guidelines for energy storage systems from the aspect of stability improvement. In order to fill this gap, this paper proposes stability control strategies for bidirectional energy storage converters considering the characteristics of AC CPLs to guarantee large signal stability of islanded AC microgrids. The presented control techniques create quantitative limits for the DC bus voltage loop control parameters of the energy storage DC/DC converter and the integral control loop control parameter of the energy storage DC/AC converter, and also interpret the positive stability influence of energy storage systems and the negative stability influence of AC CPLs. The structure of the paper is as follows. Firstly, DQ coordinate transformation is adopted, and AC microgrid nonlinear models with the energy storage system in charging and discharging states are constructed. Then, large signal models are constructed depending on mixed potential theory. Stability control strategies for bidirectional energy storage converters are obtained, and AC CPLs power, storage system equivalent resistor, and micro power source power are all taken into account. Finally, based on simulation and experimental results, it is obvious that regulating the control parameters of the energy storage converter significantly increases the large signal stability of islanded AC microgrids without extra equipment. The method is very simple and easy to implement.

A large-signal scaling model of high-power GaN microwave device

With the rapid development of wireless communications, GaN HEMT, which has various advantages of high power density, high electron mobility, and high breakdown threshold, receiving increasing attention. Microwave power amplifiers based on GaN HEMTs are widely used in many fields, such as communication, medical, and detection instruments. In the accurate design of GaN microwave power amplifiers, reliable RF large signal model is vitally important. In this paper, a scalable large-signal model based on EEHEMT model is proposed to describe the properties of multifinger AlGaN/GaN high electron mobility transistor (HEMT) accurately. A series of scaling rules is established for the intrinsic parameters of the device, including drain-source current <i>I</i><sub>ds</sub>, input capacitance <i>C</i><sub>gs</sub> and <i>C</i><sub>gd</sub>, which take into account both the gate width of a single finger and the number of gate fingers. With the proposed scalable large-signal model, the performance of the L-band GaN high-efficiency power amplifier with a gate length of 14.4 mm is analyzed. This amplifier demonstrates outstanding performance, with the output power reaching to 46.5 dBm and the drain efficiency arriving at over 70% of the frequency range from 1120 MHz to 1340 MHz. Good agreement between the simulations and experiments is achieved, demonstrating the excellent accuracy of the proposed model. Moreover, the proposed model can further predict the performance of high-order harmonics, providing an effective tool for designing advanced high-power and high-efficiency microwave power amplifiers. Certainly, the EEHEMT model fails to characterize the dynamical behavior induced by trapping and self-heating effects. Thus, for further consideration, scaling models for the thermal resistance and heat capacity need further investigating to broaden the application scope of the proposed model in the case of continuous waves.

Efficient field-circuit co-simulation method for GaN-based high power microwave devices

Due to the development of the third-generation semiconductors representative of gallium nitride (GaN), the microwave power devices are developing towards higher power, higher efficiency and high integration. However, the electromagnetic field effects are more significant inside the device. As a result, circuit-level based simulation techniques can no longer satisfy the accuracy requirements of device design. Therefore it is necessary to urgently establish the field-circuit co-simulation techniques to couple the active GaN devices with passive electromagnetic structures. In this work, we propose a high-precision discontinuous Galerkin time-domain method to analyze the performances of GAN-based high-power microwave devices. The extracted large-signal compact model of the GaN HEMT is incorporated into the electromagnetic field equations. A local time-stepping technique is adopted to remove the constraints of nonlinear compact models and multiscale elements on the stability conditions of the global algorithm. The comparisons among numerical simulations, experimental results, and software calculations demonstrate the excellent accuracy and efficiency of the proposed method, which can provide a theoretical analysis and design tool for the high reliability design of advanced high-power microwave devices.

C-Band 30 W High PAE Power Amplifier MMIC with Second Harmonic Suppression for Radar Network Application.

In order to meet the application requirements of radar networks for high efficiency and high second harmonic suppression (SHS) of power amplifiers, this paper proposes a C-band 30 W power amplifier (PA) microwave monolithic integrated circuit (MMIC) based on 0.25 μm gallium nitride (GaN) high electron mobility transistor (HEMT) process. The proposed PA uses a two-stage amplifier structure to achieve high power gain. A topology with SHS is designed in the output-matching network. Besides, the large signal model load pull simulation and the harmonic control technology in the output stage are used to improve efficiency. The high-power additional efficiency (PAE) and high SHS of the PA MMIC are achieved simultaneously. In the 5-6 GHz frequency range, multiple indicator measurements of the proposed PA show that output power is over 45 dBm, the PAE is more than 57%, the SHS exceeds 45 dBc, the power gain is greater than 24 dB, which are conducted under the condition of 100 μs pulse width and 10% duty cycle. In addition, the size of the PA MMIC, including bonding pads, is 3.3 × 3.1 mm2.

Large-Signal Equivalent Circuit for Datacom VCSELs – Including Intensity Noise

Optical interconnects (OIs) continue to require more and more sophisticated driver and receiver electronics as higher baud rates are pushed in datacom, mainly due to the bandwidth stagnation of the optoelectronic components such as the vertical-cavity surface-emitting laser (VCSEL) in the transmitter as well as the photodetector (PD) in the receiver. Another important focus is maintaining high energy efficiency for the OIs. For both cases, a reliable equivalent circuit model for high-speed VCSELs is required for link optimization. This work is an extension of our previously presented large-signal VCSEL equivalent circuit model, where noise is added to the physical processes that the VCSEL model is based on. Thus, a new step is taken in the strive of developing an even more accurate physics-based large-signal VCSEL equivalent circuit model for datacom applications. Following a detailed description of the VCSEL noise modelling, a presentation is given on simulated results of VCSEL relative intensity noise (RIN) spectrum and eye diagrams under 28 Gbaud on-off keying (OOK) and pulse-amplitude 4 (PAM4) modulation, and that are compared with corresponding measurement results. Good agreement is found over a wide range of VCSEL driving conditions and temperatures. A 28-GHz-bandwidth VCSEL is applied for the demonstration, and the presented noise extended VCSEL equivalent circuit model was implemented in Verilog-A, and the simulations were performed using Cadence Spectre.

Measurement-Based Nonlinear SPICE-Compatible Photovoltaic Models for Simulating the Effects of Surges and Electromagnetic Interference within Installations

An emerging area of interest within photovoltaic (PV) centred research is the simulation of the propagation of electromagnetic interference (EMI) and surges within PV installations. An overarching constraint in all simulation-based research is the accuracy of the models employed. In general, for PV-focussed simulations, nonlinear models are utilised for direct current (DC) analyses, whilst linearised models are employed for analyses involving surges or conducted electromagnetic interference. For large-signal electromagnetic interference and surges, the following two problems arise: (1) the aforementioned linearisation is only valid for the small-signal case, and (2) as they are constructed using only DC measurements, traditional large-signal PV models are generally only valid for DC conditions. Therefore, neither of these approaches can properly represent real-world PV behaviour under dynamic conditions. To overcome this limitation, this article proposes a more suitable model, compatible with Simulation Program with Integrated Circuit Emphasis (SPICE), and which results from the combination of two sub-models: one for large-signal DC cases, and one for small-signal alternating current (AC) cases. Consequently, the combined model enables improved modelling of the effects of large-signal transient perturbations to be performed, as well as cases involving small-signal AC and large-signal DC perturbations. The model parameters are extracted using data from two different classes of measurement setups: the first utilised a vector network analyser (VNA) to produce small-signal AC impedance results (covering a frequency range between 1 Hz and 50 MHz), and the second produces DC current-voltage curves. Both classes of measurement setup consider the device under test at multiple operating points. Key results include: (1) an improved SPICE-compatible PV model which caters for large-signal transient simulations, as well as for small-signal AC and large-signal DC cases, (2) improvements in the modelling of reverse bias behaviour when compared to the standard SPICE diode implementation, (3) the correct implementation of a voltage-dependent total capacitance (suitable for large-signal simulations), (4) modelling parameters for both a small (10 W) and a large (310 W) PV module, (5) measurement results which de-embedded the parasitic effects of the test setups employed, and (6) above 1 MHz, the physical layouts of the cells within the PV modules begin to influence the observed impedances.

Advanced Theoretical Models for Broadband Klystron Development

Broadband klystrons (BBKs) offer the potential of both high power and broad-bandwidth performance as microwave amplifiers. Staggered tuned bunching circuit and filter-loaded output cavity are the mainstream techniques adopted for developing such devices. However, in the design and optimization stage, the accurate and fast theoretical models are still missing before final particle-in-cell (PIC) simulations are conducted. In this article, the small-signal theory of klystron has been derived from accurate large-signal models used in KlyC, where complex mode field distribution, relativistic effects, mode coupling, and precise space charge model are fully considered in the final analytic formulas compared with existing simplified models. Furthermore, mode coupling theory with partially beam-loading conditions has been developed in KlyC to analyze the filter-loaded output cavity and overall klystron performance in the large-signal domain. An example of the retrofit design of 100-kW five-cavity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band klystron is then presented to demonstrate the advanced design methodology based on the above fast theoretical models. The 3-D PIC simulation finally verifies this BBK design, showing −1-dB bandwidth of 200 MHz is attainable with output power over 100 kW, where the maximum discrepancy between theoretical models and PIC is within 2% in the whole bandwidth.

Real‐time resilient microgrid power management based on multi‐agent systems with price forecast

AbstractMicrogrids have emerged to diversify conventional electric generation using small‐scale distributed generation. Large efforts have been put into designing control strategies to optimise the power schedules of microgrids, however, verification that such control systems also are reliable in terms of stability during normal operation and fault conditions is needed. This study presents a hierarchical distributed control system that fulfils these conditions for an AC microgrid. The stability maintained by proposed controller, considering the large signal model, is analysed with the use of Lyapunov's direct method. Resilient control distribution is achieved by the implementation of suitable forecast models and fault‐tolerance mechanisms to avoid single points of failure. The resilience of the control system is verified with the use of graph theory. The stable and resilient operation of the proposed control system is tested by a real‐time microgrid model implemented with an OPAL‐RT real‐time simulator, combined with a communication network built with Raspberry Pis, testing the control system presented under normal and faulty conditions. Simulation results show a stable operation in terms of voltage and frequency in both conditions, resilient operation is shown for the faulty condition case. Additionally, cost minimisation performance is included to validate optimal power management capabilities.

Compact small‐signal equivalent circuit statistical analysis model of microwave wide bandgap gallium nitride high electron mobility transistors

In the fabrication process of wide bandgap gallium nitride high electron mobility transistors (GaN HEMT), due to the process error, process fluctuation, material defects, and other factors, wide bandgap semiconductor transistors produced in different batches will also have dispersed fluctuation of electrical characteristics under these special working conditions, which results in deviations between ideal software simulation parameters based on device model and the actual measurement parameters. Some statistical analysis methods like principal component analysis, factor analysis, and multivariate statistical regression in this article are introduced to process S-parameter which can be measured from different batches of CGH40010 GaN HEMT and statistical model parameters can be got from them. Error of S-parameter comparison are less than 10% between calculation results of established small-signal statistical equivalent circuit model (ECM) and S-parameter sample measurement results. Monte Carlo simulation based on statistical model can be well adopted to predict dispersed fluctuation of electrical characteristics for different samples and which can be used as the basis of large-signal ECM statistical model.

Large-Signal Equivalent-Circuit Model of Asymmetric Electrostatic Transducers

This article presents a circuit model that is able to capture the full nonlinear behavior of an asymmetric electrostatic transducer whose dynamics are governed by a single degree of freedom. Effects such as stress-stiffening and pull-in are accounted for. The simulation of a displacement-dependent capacitor and a nonlinear spring is accomplished with arbitrary behavioral sources, which are a standard component of circuit simulators. As an application example, the parameters of the model were fitted to emulate the behavior of an electrostatic MEMS loudspeaker whose finite-element (FEM) simulations and acoustic characterisation where already reported in the literature. The obtained waveforms show good agreement with the amplitude and distortion that was reported both in the transient FEM simulations and in the experimental measurements. This model is also used to predict the performance of this device as a microphone, coupling it to a two-stage charge amplifier. Additional complex behaviors can be introduced to this network model if it is required.

Global Stability Analysis for Synchronous Reference Frame Phase-Locked Loops

This article analyzes the global stability of synchronous reference frame phase-locked loops (SRF-PLLs) from a large signal viewpoint. First, a large-signal model of SRF-PLL is accurately established, without applying any linearization method. Then, according to the phase portrait and Lyapunov argument, the global performance of SRF-PLL is discussed in the nonlinear frame. Compared with the small-signal analysis methods, the proposed analysis, not relying on the small-signal model and linearization method, provides a global discussion of the SRF-PLL performance. The contributions of this article are as follows. First, it is found that SRF-PLL has infinite equilibrium points, including stable points and saddle points. Second, it provides a way to divide the global region of SRF-PLL into many small regions. In each small region, the SRF-PLL only has one stable equilibrium point. And for any initial states <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$(\tilde{\theta }(t_0),\tilde{\omega }(t_0))$</tex-math></inline-formula> in a small region, all states <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$(\tilde{\theta }(t),\tilde{\omega }(t)),t&gt;t_0$</tex-math></inline-formula> will remain in this small region, and SRF-PLL will converge to the unique stable equilibrium point of this small region. Third, by dividing the global region of SRF-PLL into many small regions, it is found that when the frequency of grids varies largely, the SRF-PLL will converge to a new equilibrium point that is far away from the original equilibrium point. It is the reason why the frequency convergence of SRF-PLL has many oscillations and SRF-PLL has a rather slow dynamic, when the frequency changes largely. The experimental results are provided to verify the proposed global stability analysis of SRF-PLL.

Physical Insight Into Hybrid-Synchronization-Controlled Grid-Forming Inverters Under Large Disturbances

This letter analyzes the impact of hybrid voltage- and power-based synchronization control on the transient stability of grid-forming (GFM) inverters. It is found that the added voltage-based synchronization loop exploits the phase angle difference to resist frequency deviation, whose function is similar to the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">damper winding</i> of synchronous generators. By resembling the large-signal model of such hybrid synchronization control (HSC) to the power-angle swing equation, it is proved that the HSC brings higher damping to the system and thus, enhances the transient stability of GFM inverters. Further, a comparative study of two active power controllers, i.e., the droop controller with a low-pass filter and the proportional-integral (PI) controller, is given. It is revealed that the HSC with the droop controller equivalently decreases the active power reference, which leads to better transient stability behavior than that of using the PI controller. The theoretical findings are corroborated by experimental tests.

Averaged large-signal model of a DC-DC isolated forward resonant reset converter for a solar cell battery charger using internet of things: implementation

Averaged large-signal model of a DC-DC isolated forward resonant reset converter for a solar cell battery charger using internet of things: implementation

Averaged large-signal model of a DC-DC isolated forward resonant reset converter for a solar cell battery charger using internet of things: implementation

In this study, an analysis and modeling circuit for controlling battery charge solar cells based on data management through internet of things (IoT) is presented. For this proposed, a DC-DC forward resonant reset converter is employed and can be charged at a constant current and constant voltage. Data management of various parameters using IoT technology is provided, via which notifications can be sent to an external application. The proposed converter can give an output voltage of 14.4 VDC for a voltage range including between 9 and 18 VDC, using an isolated transformer and a halfwave rectifier circuit. The main switch of the forward resonant reset converter can operate under a zero-turn-on condition. This approach has the benefit of utilizing a leaking inductance. Llkp and resonant capacitor Cr to reset the remaining flux saturation on the high-frequency transformer. A simulation model prototype was created and tested at a set switching frequency of 50 kHz, 14.4 VDC constant output voltage, and output power of approximately 29 W. An efficiency of 96% at maximum full load can be reached. The proposed analysis techniques and mathematical model were verified via simulation and experimental results, and the obtained results are in agreement with the theoretical analysis.

Towards generation of indistinguishable coherent states

We have addressed the characteristic distinguishability of coherent states in the temporal domain from a directly modulated quantum well-based gain-switched laser diode. We identify adjustable parameters to generate indistinguishable coherent states from an electrically pumped semiconductor laser using small-signal and large-signal models. The experiment confirms the generation of indistinguishable signal and decoy coherent states as predicted by the numerical simulation. In addition, the potential for indistinguishability has been explored in different types of coherent states.

Improved active power control of virtual synchronous generator for enhancing transient stability

Virtual synchronous generators (VSGs) are widely used as grid-forming control converters in the inverter-dominated power system. Similar to synchronous generators (SGs), there would also be transient instability of VSGs under certain conditions. In this paper, the transient dynamics of VSGs during gird faults are fully investigated based on the large-signal model. It is revealed that the significant deteriorative of active power control loop (APCL) is the main factor on the transient stability of VSGs. Thus, for enhancing transient stability during grid faults, an integrator-based feedback loop is introduced for APCL. Then, an enhanced active power control of VSGs is presented with transient stability enhancement during grid faults. Moreover, the impacts of different integral parameters on the transient stability of VSGs are studied. Finally, the validity of the transient stability enhancement of VSGs is demonstrated by the hardware-in-loop (HIL) results.

Modeling and Compound Closed-Loop Control of Single-Phase Quasi-Single-Stage Isolated AC-DC Converter

The single-phase isolated quasi-single-stage AC-DC converter has many virtues, such as high power density and efficiency; however, its grid current closed-loop control has not been solved. This paper aims to solve the remaining gap based on a large-signal model. In this paper, the large-signal model of this converter under triple-phase-shift modulation is built for the first time. It is verified that the built model is a zero-order linear system. Based on this built model, the effect of grid harmonics on this converter grid current is analyzed. The theoretical analysis reveals that the grid voltage low-order harmonics will cause the same order grid current harmonics and only varying the parameters of the filter is not an effective method to solve this problem. For the purpose of eliminating the effect of grid voltage harmonics on the grid current and realizing the zero-error control of the fundamental component of the grid current, a grid current closed-loop control strategy based on the proportional-resonant compound odd-mode repetitive controller is proposed. The operation principle, parameter constraint, and design rule of the proposed compound control strategy are analyzed comprehensively. The theoretical analysis and the compound control strategy put forward in this paper are tested, with detailed experimental results.

An Extensive Large Signal Equivalent Circuit Model of GaAs-PIN Photodiode

Based on the variation trend of the depletion layer of GaAs-PIN photodiode (PD) under different optical power and reverse bias voltages, an extensive large-signal equivalent circuit model that characterizes PD in non-punch-through and punch-through states is proposed in this article. According to the analysis of the PD’s depletion layer variation, the nonlinear parameters of the model are described by exponential function and Gaussian function. To verify the reliability of equivalent circuit model, on-chip measurements were performed on PIN-PD fabricated by commercial GaAs process, and the measured <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> and reflection coefficient agree with the proposed model simulation results well. Furthermore, using the proposed model for simulation with CAD tools shows that reducing junction capacitance has potential in improving PD output power and gain flatness. At the same time, the model provides a certain reference for selecting bias condition in the design of the PD matching network and fabricating PD with high power output.