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Efficient transistor modeling is an essential step toward improved fabrication processes and reliable circuit design. This places more pressure on the model developer to consider the physical relevance, accuracy, and simulation convergence rate. This paper proposes an improved gray-box modeling technique that combines the accuracy of the neural network (NN) technique with the physical insight of the equivalent circuit (EC) approach. The extrinsic part of the device was characterized by an extended electrical EC to accurately characterize distributed parasitic effects, especially in the mm-wave frequency range. A hybrid technique of EC and NN is used to simulate the intrinsic transistor. Instead of employing a black box, a gray box of interconnected NN models of the intrinsic branches’ admittances was utilized. This approach addresses the challenges of extracting reliable values for the intrinsic capacitances, conductances, and resistances, particularly in the presence of higher measurement uncertainty. Additionally, the NN model provides accurate simulations of the bias and frequency dependence in the active region of the device. The proposed approach was applied to GaN High Electron Mobility Transistors (HEMTs) of various sizes on SiC and Diamond substrates under different bias conditions and across a wide range of frequencies. The simulation results exhibited an excellent agreement with the measurements and verified the validity of the proposed approach for small-signal modeling and linear circuit design. This work could also be extended to develop large-signal models for nonlinear circuit design applications.

Traditionally, to characterize the response of droop-controlled systems RMS models have been used. However, as it is demonstrated in this work, when droop control is applied to doubly-fed induction generators, RMS models do not allow to predict the system stability and dynamic response. Thus, in this article, a linearized small-signal model that overcomes the limitations of RMS models is presented. The proposed model is validated by simulation in MATLAB/Simulink demonstrating that it allows to accurately analyze the stability and dynamic response of the system under study. This model is an interesting tool that can be used in future works to design and adjust grid-forming controllers for doubly-fed induction generators.

This paper explains the implementation of a small-signal model for a new five-level series resonant inverter structure. The proposed circuit combines the advantages of multilevel inverters and the characteristics of the physical phenomena, resonance. The small-signal model offers the possibility to design a linearized linear time-invariant (LTI) model around an equilibrium point based on the first-order Taylor series. After that, the performance of the proposed five-level series resonant inverter and its small-signal model are evaluated in MATLAB/Simulink environment. Compared with a MATLAB model generated using the system identification toolbox, the developed small-signal model exhibited a good accuracy in frequency and time domains. In addition, a hardware test bench is developed to validate the proposed model. Both simulation and experimental results show that the proposed multilevel resonant inverter is very interesting for high-voltage high-frequency applications. As a perspective, from the results obtained, we suggest the use of small-signal AC analysis for multilevel series resonant inverter modeling. The paper contains rich information on the recently used tools for dynamic systems modeling and analysis of nonlinear processes that can be applied to modeling and analyzing other power electronics inverters.

In high-reliability applications, DC/DC converters should realize high-efficiency and fast-transient in harsh environments. Thus, the circuit parameter design and the reliability design are both critical. The secondary-side control circuit has a faster transient and a simpler gate-drive than the primary-side control circuit, which has been used for over twenty years. However, the detailed design procedure and analysis of the high-reliability secondary-side control circuit have not been presented in the literature. This article introduces a secondary-side control circuit design and its small-signal modeling procedure with a peak-current-mode-control (PCMC) forward converter. The reliability design and evaluation for thick-film converter are demonstrated. A 100-watt prototype is manufactured, and its steady-state waveforms and transient waveforms are tested and then compared with other high-reliability products. The experimental results show that the peak efficiency reaches 90.6%; the load transient response is 330mV/ $560~\mu \text{s}$ ; and the mean-time-between-failure (MTBF) value is 481 kilo-hours, proving the fast-transient and high-reliability features of the secondary-side control circuit.

The concept of virtual synchronous machine (VSM) was proposed to deal with the shortcomings of low inertia and damping of traditional control strategies for power electronic converters. But what if all distributed energy resources and controllable loads in a microgrid adopt the VSM control strategy, and will it present better performance than conventional droop control-based microgrid (DMG)? In this paper, the VSM-based microgrid (VSMG) is analyzed. The small-signal modeling of the VSMG is studied at first. Then static stability and dynamic characteristics of the VSMG are analyzed and compared with the DMG in both frequency-domain and time-domain. With the growing scale of microgrids, their modeling and simulation are becoming significant computational burdens. Inspired by the participation factor analysis of the VSMG and the concept of coherency in power systems, the VSMG small-signal model is equivalent to a modified third-order synchronous generator (SG) model in this paper. The equivalencing involves gray-box system identification and is realized by estimating equivalent electrical parameters alternately and iteratively. The equivalent SG (EqSG) model is compared with three representative model order reduction methods to verify its effectiveness. Simulation results confirm the accuracy of the EqSG model substituting detailed VSMG model in time-domain simulations.

It's very important to maintain the inverter zero-voltage-switching(ZVS) for inductive power transfer (IPT) system, especially for those high power applications. The ZVS condition can be obtained via regulating the inverter operating frequency of the IPT system. A modeling method based on the energy-amplitude and phase is proposed and corresponding controller is designed to maintain the inverter ZVS condition for IPT. The dynamic model of the ZVS for the half-bridge inverter is developed firstly. To facilitate the dynamic performance analysis and controller design, the original time-variant model is linearized with small-signal method at its operating point, which yields to a 4 order transfer function model. A PI controller which maintains ZVS condition via regulating the inverter operating frequency is designed based on the transfer function. An IPT prototype is built to verify the proposed theory. Experiments show that the controller traces the reference of the ZVS angle within 20 ms under various perturbation, which verifies the correction and effectiveness of the model and controller.

Research advances on renewable energy systems have increased the interest in the use of isolated power supplies composed of power converters based on high-frequency transformers. Such power equipment generally presents high internal impedance, which amplifies the effects of harmonic voltages produced by nonlinear loads that draw currents with high harmonic content. Some sensitive loads, e.g., electric motors and distribution transformers, may not properly operate when supplied by extremely distorted voltages. Series active power filters (SAPFs) are suitable to mitigate this inconvenient, being capable of providing harmonic voltage compensation and minimizing the distortion of supply voltages. In this context, this work addresses the small-signal modeling, control system implementation, and experimental validation of a single-phase SAPF. The proposed approach is solely employed for harmonic voltage compensation purposes, thus allowing loads to be supplied by a nearly sinusoidal voltage. During the modeling process, the operating steps are analyzed in detail, while the presence of parasitic elements is taken into account. An equivalent circuit is also derived, which is used to provide an easy understanding of the interactions among the SAPF, load, and power supply. From this model, transfer functions can be obtained so that it is possible to design the control loops used by the SAPF. Experimental results with distinct types of loads are presented to evaluate the SAPF performance in both steady-state and transient conditions.