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Modular multilevel converter (MMC) is a new potential power converter architecture for applications that require high voltage or high power. In investigating the subsynchronous resonance (SSR) characteristics of MMC, detailed small-signal modeling and control design is essential. This paper presents the detailed modeling of MMC in D-Q reference frame and analysis of SSR with MMC connected to a turbine-generator supplying a series compensated long AC transmission line. This paper proposes a novel subsynchronous damping controller (SSDC) that uses a band pass filter (BPF) to extract the subsynchronous frequency components of line current. These subsynchronous frequency components are then injected into the transmission line by an MMC controller, which suppresses them through the generator. Using D-Q model of the study system with a rating of 892.4 MVA at 60 Hz, eigenvalue analysis and transient simulation are used to perform SSR analysis for various series compensation levels from 0.20 p.u to 0.60 p.u in MATLAB-Simulink. The results of eigenvalue analysis are validated with transient simulation for a step disruption of 10% decrement in mechanical input of turbine-generator, which is employed at 0.50 sec and restored at 1.0 sec. Simulation results with MMC show that damping of torsional modes (TMs) improves in high-frequency range of subsynchronous network mode (NMsub), on the other hand, the damping of low-frequency TMs reduces. Therefore, it is clear that the damping of torsional interactions increases with MMC. Finally, SSR characteristics are investigated with a novel SSDC connected to MMC that is activated at 1.50 sec. The results clearly demonstrate the improvement of critical TMs in the system. Thereby reducing the potential risk of SSR at all operating conditions. [ABSTRACT FROM AUTHOR]

The effects of the parasitic gate capacitance and gate resistance (Rg) on the radiofrequency (RF) performance are investigated in LG = 0.15 μm GaN high‐electron‐mobility transistors with T‐gate head size ranging from 0.83 to 1.08 μm. When the device characteristics are compared, the difference in DC characteristics is negligible. The RF performance in terms of the current‐gain cut‐off frequency (fT) and maximum oscillation frequency (fmax) substantially depend on the T‐gate head size. For clarifying the T‐gate head size dependence, small‐signal modeling is conducted to extract the parasitic gate capacitance and Rg. When the T‐gate head size is reduced from 1.08 to 0.83 μm, Rg increases by 82%, while fT and fmax improve by 27% and 26%, respectively, because the parasitic gate–source and gate–drain capacitances reduce by 19% and 43%, respectively. Therefore, minimizing the parasitic gate capacitance is more effective that reducing Rg in our transistor design and fabrication, leading to improved RF performance when reducing the T‐gate head size. [ABSTRACT FROM AUTHOR]

The effects of the parasitic gate capacitance and gate resistance (Rg) on the radiofrequency (RF) performance are investigated in LG = 0.15 μm GaN high-electron-mobility transistors with T-gate head size ranging from 0.83 to 1.08 μm. When the device characteristics are compared, the difference in DC characteristics is negligible. The RF performance in terms of the current-gain cut-off frequency (fT) and maximum oscillation frequency (fmax) sub-stantially depend on the T-gate head size. For clarifying the T-gate head size dependence, small-signal modeling is conducted to extract the parasitic gate capacitance and Rg. When the T-gate head size is reduced from 1.08 to 0.83 μm, Rg increases by 82%, while fT and fmax improve by 27% and 26%, respectively, because the parasitic gate–source and gate–drain capacitances reduce by 19% and 43%, respectively. Therefore, minimizing the parasitic gate capacitance is more effective that reducing Rg in our transistor design and fabrication, leading to improved RF performance when reducing the T-gate head size.

To address the challenges in establishing the state transfer matrix and the complexity of eigenvalue calculation in determining the multi-parameter stability boundaries of high-order nonlinear Vienna rectifiers, a novel numerical computation method is proposed in this paper. This method leverages a numerical stability criterion and a grid variable step search to efficiently calculate these stability boundaries. The small-signal model of the Vienna rectifier is derived by constructing the time-varying state transfer matrix using the periodic solution of the harmonic balance method. Eigenvalues are rapidly calculated via the periodic numerical solution of the state transfer matrix. The proposed parameter sensitivity-based grid variable step search method ensures a fast and accurate determination of stability boundaries. A hardware experimental setup is established to validate the stability boundaries of the Vienna rectifier under various parameter variations, including load, component, and control changes. The experimental results closely match the simulations, confirming the correctness and superiority of the proposed method. [ABSTRACT FROM AUTHOR]

A grid-forming voltage source converter with an integrated step-down transformer could be a promising solution for supplying low-voltage alternating current loads from a medium-voltage direct current supply. However, it may require a control system that gathers feedback signals from both the primary and secondary sides of the transformer, which in turn complicates the derivation of a standard form linear model. The absence of such a model complicates control tuning, as well as the assessment of dynamics and stability of the converter system. The objective of this paper is to address this gap in knowledge. For the case study, a conventional H-bridge converter with a step-down transformer and an α β -frame dual-loop grid-forming controller is considered. Initially, comprehensive guidelines on deriving a standard form linear model for this converter system are presented. Then, the impact of controlling the VSC in a d q frame and the changes in the transformer vector group on the small-signal model of the VSC are analyzed. The aspects of control tuning are also discussed in detail, and the model's accuracy and efficacy are validated both theoretically and through control hardware-in-the-loop (C-HIL) tests using a Typhoon HIL setup. [ABSTRACT FROM AUTHOR]

This paper focuses on the analysis and control strategy of a four-switch boost-buck AC/DC converter utilized in power factor correction applications with a wide output voltage range. Given the increasing importance of electric vehicles and the need for high reliability, this study addresses the internal dynamic stability problem that can arise in the converter system. The analysis begins with a thorough examination of the system's min-phase characteristic. Despite this, internal dynamic stability issues persist, requiring a solution to ensure a higher power factor and reliability. To address this challenge, this paper proposes the utilization of a damping RC circuit instead of reducing the loop gain bandwidth. To demonstrate the internal dynamic behavior of the converter, small-signal modeling is employed. This modeling highlights the importance of mitigating internal dynamic instability to achieve the desired power factor and reliability. This study emphasizes the significance of proper analysis and control strategies for boost-buck AC/DC converters in power factor correction applications. By addressing internal dynamic stability using a damping RC circuit, the converter can achieve a higher power factor and enhanced reliability, ultimately contributing to the development of more efficient and dependable EV systems. Finally, the feasibility of the proposed analysis and control strategy is confirmed through comprehensive simulations. The simulation results validate the effectiveness of using a damping RC circuit to address the internal dynamic stability problem, leading to an improved power factor and enhanced reliability. [ABSTRACT FROM AUTHOR]

Summary: In this work, the control of a Single‐Ended Primary‐Inductor Converter (SEPIC) supplied from a photovoltaic energy source and linked at its output to a DC current sink is addressed. The system is used for maximum power point tracking under varying environmental conditions. A strategy based on two loops of control is considered. A peak current mode controller is used for the inner loop, and a Proportional‐Integral (PI) controller is used for the outer voltage loop. Then, a comprehensive time‐domain and frequency‐domain modeling of the inner loop is theoretically addressed and then verified by the switched model of the system implemented in PSIM© software. The obtained results show that the system exhibits accurate tracking of the desired PV voltage while guaranteeing a fast maximum power point tracking under sudden changes in the environmental conditions. The mathematical modeling, design procedures, and the numerical simulations are validated using experimental results obtained from a laboratory prototype. [ABSTRACT FROM AUTHOR]

The grid interconnections for direct-drive wind farms have triggered multiple new sub-synchronous oscillation events, which can prevent the power system from operating safely and stably. However, the excessively high order of the detailed model for large-scale wind farms with multiple direct-drive permanent magnet synchronous generators (PMSGs) connected to power systems poses a challenge when investigating small disturbance stability and instability mechanisms. This study establishes a model of the grid-connected PMSG system based on the voltage/power excitation–response relationship to describe the dynamic characteristics of the port of the PMSG, and the analysis of active and reactive response characteristics of PMSG lays the foundation for model simplification. Based on the unit model, a direct-drive wind farm aggregation equivalence method based on the excitation–response relationship is proposed. The equivalent model obtained by this method is suitable for the small disturbance stability analysis of direct-drive wind farms grid connected system, with good accuracy. The simulation verified the effectiveness of the aggregation model. [ABSTRACT FROM AUTHOR]

This work introduces a generalized version of the pulse width modulation (PWM) switch model applied in the small-signal modeling of converters based on the multistate switching cell (MSSC) operating in discontinuous conduction mode (DCM). It consists of extending the concept formerly introduced by Vorperian for the representation of multiphase converters in DCM, yielding a circuit-based approach that does not rely on matrix manipulations unlike state-space averaging (SSA). The derived dc and ac models are valid for any number of switching states and any operating region defined in terms of the duty cycle, thus allowing for determining the voltage gain and distinct transfer functions. A thorough discussion of results is presented to demonstrate the applicability of the derived models to represent distinct configurations of the MSSC. [ABSTRACT FROM AUTHOR]

The structure of a DC–DC converter connected in series with a 400 Hz inverter is widely used in aviation airborne and ground power systems to provide a medium-frequency AC power supply within a wide input voltage range. To guarantee the dynamic and steady-state performance of a multi-module series converter, it is necessary to individually optimize the control loop and the parameters of each series-connected module. In addition, it is also necessary to consider the input–output impedance matching issues of each converter. In this study, a phase-shifted full-bridge converter employing an average current control strategy is used as the input-side DC–DC converter, and a medium-frequency three-phase four-leg inverter is used as the output-side inverter. The study also conducts a small-signal modeling analysis to reveal the intrinsic relationship between the closed-loop output impedance of the input-side converter and the circuit parameters. It summarizes the optimization criteria for controlling the parameters of the voltage and current loops. By suppressing the peaks of the output impedance of the input-side converter, the impedance matching between the input- and output-side converters is ensured over the entire frequency range, ensuring the stable operation of the overall system. Finally, the correctness of the theoretical analysis is verified through simulation and experimentation. [ABSTRACT FROM AUTHOR]

The virtual synchronous machine (VSM) concept is emerging as a flexible approach for controlling power electronic converters in grid-connected and standalone applications. In this study, we have used the mathematical model of a Virtual machine with a virtual exciter and governor for the standalone inverter to optimize the parameter for small-signal stability. Firstly, the small-signal models of virtual synchronous generator with load have developed, and subsequently, the system eigenvalues were obtained by solving the state Jacobian matrix. Next, the sensitivity of the eigenvalue location on controller parameters has been studied. The parameters are optimized on the basis of the location of dominant eigenvalues using a genetic algorithm. Finally, the optimal controller parameters are used to test the system's dynamics by solving the model equations with Ordinary Differential Equation (ODE) solver. Moreover, our conclusions were also tested using the actual switching devices on Matlab/Simulink. The results indicate that the frequency stability can be enhanced drastically by optimizing a wide range of VSM parameters. The frequency stability sensitivity with respect to load variation has been improved. The transient settling time of system response for optimized values is 0.25 sec which is only 5% of that for general values. The results of this work are relevant for the VSM-based microgrid small-signal stability analysis. [ABSTRACT FROM AUTHOR]

In this study, the degradation characteristics of radio frequency (RF)-low-noise amplifiers (LNA) due to a total ionizing dose (TID) is investigated. As a device-under-test (DUT), sample LNAs were prepared using silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs) as core elements. The LNA was based on a cascode stage with emitter degeneration for narrowband applications. By using a simplified small-signal model of a SiGe HBT, design equations such as gain, impedance matching, and noise figure (NF) were derived for analyzing TID-induced degradations in the circuit-level performance. To study radiation effects in circuits, the SiGe-RF-LNAs fabricated in a commercial 350 nm SiGe technology were exposed to 10-keV X-rays to a total ionizing dose of up to 3 Mrad(SiO2). The TID-induced performance changes of the LNA were modeled by applying degradation to device parameters. In the modeling process, new parameter values after irradiation were estimated based on information in the literature, without direct measurements of SiGe HBTs used in the LNA chip. As a result, the relative contributions of parameters on the circuit metrics were compared, identifying dominant parameters for degradation modeling. For the TID effects on input matching (S11) and NF, the base resistance (RB) and the base-to-emitter capacitance (Cπ) of the input transistor were mostly responsible, whereas the transconductances (gm) played a key role in the output matching (S22) and gain (S21). To validate the proposed approach, it has been applied to a different LNA in the literature and the modeling results predicted the TID-induced degradations within reasonable ranges. [ABSTRACT FROM AUTHOR]

Disturbances to the power system may lead to relative swing between synchronous generator rotors, causing low-frequency oscillation problems in the absence of damping. In this article, based on the single-machine infinity system containing flexible distribution transformer and synchronous generator, the linearized state equations of the system is deduced by the small-signal modeling. The mechanism of flexible distribution transformer on the rotor speed of synchronous generator is analyzed. The influence factors of flexible distribution transformer on the rotor speed of synchronous generator are analyzed. The equation of the additional damping provided by the flexible distribution transformer to this system is constructed. It was concluded that by controlling the output voltage of the regulating converter in the flexible distribution transformer, the rotor speed of the synchronous generator can be varied to increase the system damping. An additional damping control strategy for flexible distribution transformer is proposed. The simulation verifies that the proposed control strategy can effectively suppress the oscillation amplitude of each electrical quantity and shorten the oscillation duration when the system is subjected to large and small perturbations. The proposed additional damping control strategy of flexible distribution transformer can effectively improve the damping of the system and alleviate the problem of low frequency oscillation. [ABSTRACT FROM AUTHOR]

A high-step-up DC–DC converter (DDC) is commonly used in micro-grids, renewable energy source (RES) integration, uninterruptible power supplies, hybrid vehicles, and other applications to deal with intermittency in power sources. Solar photovoltaic (SPV) is a prominent RES due to its many benefits, but its output voltage must be enhanced for high-voltage (HV) applications; hence, various topologies are suggested for desirable gain in the literature. Nevertheless, contemporary topologies exhibit restricted gain, higher device stress, analysis on restricted performance metrics, constrained handling capacity for input variations, relatively lower reliability, and suboptimal device utilization. This work investigates a new Z-source with switched-capacitor (HZSSC)-based hybrid step-up converter to solve the aforementioned restrictions and adapt PV voltage dynamics. Additionally, this paper presents MIL-HDBK-217F-based methodology for evaluating converter-level reliability, assessing the implications of device parametric variation on overall reliability, conducting a detailed analysis of figure of merits, performing thermal modeling, and executing small-signal-modeling to demonstrate operational efficacy. In-depth mathematical analysis of both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are conducted. The detailed comparison analysis shows that the suggested converter outperforms traditional converters in voltage-gain, voltage-stress, device-utilization, and reliability. Additionally, a 400 W, 220 V laboratory-scaled prototype shows 68 % reliability after 20 years. The hardware test outcomes validate the accuracy of both the mathematical investigation and simulation findings. [ABSTRACT FROM AUTHOR]

Summary: Unified small‐signal modeling approaches are of paramount importance for the design of controllers and closed‐loop control systems in power electronic converters. In this sense, this work proposes the small‐signal analysis of non‐isolated dc‐dc converters employing the three‐state switching cell (3SSC) in discontinuous conduction mode (DCM). The modeling technique relies on the very same principles of the pulse width modulation (PWM) switch while not involving matrix operations, but only basic concepts related to electric circuits. Considering that the waveforms associated with the terminals of the 3SSC in DCM have a common behavior in all basic dc‐dc converters, it is possible to derive the small‐signal models for both operating regions of the 3SSC, that is, non‐overlapping mode (NOM) and overlapping mode (OM). Thus, one can effectively demonstrate that the same circuit can represent both modes, even though the coefficients that describe the models are calculated from distinct equations. The theoretical claims are validated in the frequency and time domains while comparing the model with the converter. The obtained results evidence that the unified model can accurately represent converters based on the 3SSC in DCM. [ABSTRACT FROM AUTHOR]

Disturbances to the power system may lead to relative swing between synchronous generator rotors, causing low-frequency oscillation problems in the absence of damping. In this article, based on the single-machine infinity system containing flexible distribution transformer and synchronous generator, the linearized state equations of the system is deduced by the small-signal modeling. The mechanism of flexible distribution transformer on the rotor speed of synchronous generator is analyzed. The influence factors of flexible distribution transformer on the rotor speed of synchronous generator are analyzed. The equation of the additional damping provided by the flexible distribution transformer to this system is constructed. It was concluded that by controlling the output voltage of the regulating converter in the flexible distribution transformer, the rotor speed of the synchronous generator can be varied to increase the system damping. An additional damping control strategy for flexible distribution transformer is proposed. The simulation verifies that the proposed control strategy can effectively suppress the oscillation amplitude of each electrical quantity and shorten the oscillation duration when the system is subjected to large and small perturbations. The proposed additional damping control strategy of flexible distribution transformer can effectively improve the damping of the system and alleviate the problem of low frequency oscillation.

This paper focuses on the analysis and control strategy of a four-switch boost-buck AC/DC converter utilized in power factor correction applications with a wide output voltage range. Given the increasing importance of electric vehicles and the need for high reliability, this study addresses the internal dynamic stability problem that can arise in the converter system. The analysis begins with a thorough examination of the system’s min-phase characteristic. Despite this, internal dynamic stability issues persist, requiring a solution to ensure a higher power factor and reliability. To address this challenge, this paper proposes the utilization of a damping RC circuit instead of reducing the loop gain bandwidth. To demonstrate the internal dynamic behavior of the converter, small-signal modeling is employed. This modeling highlights the importance of mitigating internal dynamic instability to achieve the desired power factor and reliability. This study emphasizes the significance of proper analysis and control strategies for boost-buck AC/DC converters in power factor correction applications. By addressing internal dynamic stability using a damping RC circuit, the converter can achieve a higher power factor and enhanced reliability, ultimately contributing to the development of more efficient and dependable EV systems. Finally, the feasibility of the proposed analysis and control strategy is confirmed through comprehensive simulations. The simulation results validate the effectiveness of using a damping RC circuit to address the internal dynamic stability problem, leading to an improved power factor and enhanced reliability.

There are some significant nonlinearity and delay issues in photovoltaic (PV) system circuits. Therefore, it is very difficult for the existing classic linear control theories to be used in PV systems; this hinders the design of the optimal energy dispatch by considering real-time generation power forecasting methods. To solve this problem, an overall linearized model with variable weather parameters (OLM-VWP) of the PV system is proposed on the basis of small-signal modeling. Meanwhile, a corresponding simplified overall linearized model with variable weather parameters (SOLM-VWP) is presented. The SOLM-VWP avoids analyzing delay characteristics of the complex high-order PV system. Moreover, it can reduce hardware cost and computation time, which makes analysis of the transient performance index of the PV system more convenient. In addition, on the basis of the OLM-VWP and SOLM-VWP, a delay-time model with variable weather parameters (DTM-VWP) of the PV system is also proposed. The delay time of the system can be accurately calculated using the DTM-VWP, and it provides a preliminary theoretical basis for carrying out real-time energy scheduling of the PV system. Finally, simulations are implemented using the MATLAB tool, and experiments are conducted. The results verify that the proposed linearization model of the PV system is accurate and reasonable under varying irradiance and temperature conditions. Meanwhile, the results also verify that the proposed SOLM-VWP and DTM-VWP of the PV system are feasible. Additionally, the results show that some transient performance indexes (delay time, rise time, settling time, and peak time) can be solved by means of equations when the circuit parameters and real-time weather parameters are given. [ABSTRACT FROM AUTHOR]

The impact of subsynchronous oscillation (SSO) on grid security is becoming increasingly prominent with the rapid development of a large new energy base. However, the SSO modes and characteristics in complex power systems where series-complementary AC systems, DC systems, wind farms, and thermal power plants co-exist simultaneously are still not well understood, and relevant research has yet to be conducted. To address these issues, this study aims to investigate the SSO oscillation modes and the participation of specific influencing factors using eigenvalue and participation factor analysis. Additionally, the influence of system operation mode and control parameters on the SSO characteristics is studied through eigenvalue analysis. The findings of this study suggest that multiple oscillation sources and the co-existence of various oscillation patterns in hybrid AC–DC transmission systems cause SSO problems. The SSOs arise due to inappropriate system operation or parameter selection. As the series compensation increases, the system tends to become unstable. The system stability improves when the wind power output increases or the thermal power output decreases while keeping the output power of other sources constant. On the other hand, the system stability decreases as the DC transmission power gradually decreases. In terms of the control parameters, a higher value of the inner-loop proportionality coefficient of the converter current on the rotor side of the wind turbine results in a more unstable system. However, the rotor-side converter outer loop parameters and the stator-side control loop PI parameters have a negligible effect on the oscillation frequency and damping of the system. Matlab time domain simulations are conducted to verify the accuracy of the theoretical analysis. [ABSTRACT FROM AUTHOR]

The radio frequency spectrum is currently congested due to the advancement in wireless communication systems. For these system, low noise-figure linear amplifier is crucially needed to design the front-end receiver and amplify very low-power received signals without significantly degrading their qualities. Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) has wider linear dynamic range and thus represents an excellent alternative for designing highly linear Low Noise Power Amplifier (LNA). Also, GaN as a wide bandgap material could be very optimistic to work in harsh and noisy environment such as earth space for satellite communications. In this work, global optimization technique-based noise-models are presented and then used to design LNAs. An extensive review of state-of-the-art GaN HEMT based low noise amplifier is given in this paper. Then different topologies of the low noise amplifier are explored. The techniques of bandwidth enhancement are also reviewed. The design of low noise amplifiers using the developed GaN HEMT model is done at X and K bands of frequencies. The performances of the designed LNAs are compared with state-of-the-art reported LNAs in terms of the Noise Figure (NF), gain and bandwidth. The paper presented very interesting results for the cascade, which exhibited the best NF of 1.6-2 dB and a gain of 14.5-16.4 dB within a bandwidth of 9 to 11 GHz. The highest gain of 25-27 dB was achieved by the quadrature cascode LNA with slightly higher NF of 2.1-2.5 at an operating frequency of 8-12 GHz. [ABSTRACT FROM AUTHOR]

A new small-signal modeling of a three-level boost (TLB) converter, as well as the design methodology for a double-loop controller, are presented in this paper. Unlike the conventional modeling of the TLB converter, which involves three state variables, the suggested modeling is based on two state variables; hence, simple transfer functions can be obtained. The proposed method is operable at a full duty ratio using unified modeling approaches, regardless of the mode changes. The analysis shows that the transfer functions of the two operation modes are identical. This suggests that the small-signal modeling of the TLB converter is identical to that of a conventional single-level boost converter. Hence, this implies that a linear feedback controller is applicable for all operational ranges. The method to design a double-loop controller using a proportional-integral controller is shown in a stepwise sequence. In addition, a capacitor voltage unbalancing controller is described. Simulations and experimental verifications are conducted to verify the effectiveness of the small-signal analysis and control system design. [ABSTRACT FROM AUTHOR]

V $^{2}$ control architecture is popular due to its simple compensation and fast load transient response. The stability margin of an analog V $^{2}$ controlled buck converter improves as the input voltage or capacitor effective-series resistance (ESR) increases. However, due to voltage-loop sampling, stability margin of a digital V $^{2}$ controlled buck converter degrades as the input voltage or capacitor ESR increases. Intuitively, it can be said that this happens due to sampling as sampling eliminates the ESR ripple from the output voltage. However, to get more clear insight and to propose a stabilizing solution, this article proposes an approximate discrete-time model-based framework. Analysis shows that the stability boundary of the controller's gain depends on the input and output voltages, and ESR. The stability boundary of the controller's gain is enhanced using an additional ramp compensation. Furthermore, a discrete-time small-signal model is developed to assess the slow-scale behavior of the buck converter. The model demonstrates an existence of complex conjugate poles with a low value of ESR. An analytical expression of critical value of ESR to keep the poles on the real axis is presented. To improve the load transient performance with a low ESR, a lag-lead compensator design technique is proposed. The proposed controller is realized in an FPGA device. Effectiveness of the proposed controller and accuracy of the analysis are validated experimentally. [ABSTRACT FROM AUTHOR]

This article suggests a unified modeling approach to the analysis of tapped-inductor converters. The leakage inductance, inherent to coupled magnetic structures, and the associated snubber circuit effects were considered and incorporated into the suggested model. The proposed nonideal tapped inductor switcher model is formulated as an equivalent subgraph that can help to model most, if not all, converter topologies that comprise a two-winding tapped inductor. Both the continuous current mode and the discontinuous current mode were modeled. To validate the proposed approach, analysis of a Flyback converter with an RC snubber is presented. Theoretical prediction of the steady-state and small-signal behavior of the converters were confirmed by simulation and experimental results. [ABSTRACT FROM AUTHOR]

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.

Grid-connected inverter-based photovoltaic (PV) systems play an important role in Distributed Power Generation (DPG). For this application, quasi impedance source inverter is very suitable due to its ability to increase or decrease the output voltage of the inverter in a single-stage and high reliable condition. Conventionally, to remove the harmonics, which are yielded by switching the grid-connected inverter, LCL filters are utilized at the inverter output. These filters can cause some problems at the Point of Common Coupling (PCC). The aim of this paper is to improve the quality of the injected power of the photovoltaic array, which is connected to the low voltage grid by quasi-Z-source inverter (QZSI). For this purpose, a two-stage control procedure containing DC and AC stages is performed. In the DC stage, the dynamic characteristics of the quasi-Z-source network are investigated by small-signal analysis. Using the transfer functions obtained from the dynamic model, the capacitor voltage of the quasi-Z-source network is suitably controlled to generate the appropriate voltage to the grid interface inverter. In the AC stage, in order to inject high-quality current into the grid as well as eliminating the resonance peak caused by the LCL filter, a systematic procedure is used to design the PR controller parameters and active damping coefficient. Simulation of the overall system includes solar panels, maximum power point tracking algorithm, quasi-Z-source inverter, and LCL filter to model the grid-tied PV system with the possible details. Simulations are carried out in MATLAB/Simulink environment, and results depict suitable performance of the studied power conditioning system with designed parameters.

The small-signal stability of large-scale interconnected microgrids needs to be analyzed to find the most dominant dynamic behaviors. In this paper, a comprehensive and easy-expandable module-based modeling method is proposed, which is expandable to many interconnected AC microgrids through circuit breakers, i.e. synchronous microgrids. Another certain requirement is validating such a large model, which is satisfied using a well-known Prony analysis method. The large-scale interconnected AC microgrids are implemented in a real-time digital simulator to provide input waveforms for the Prony analysis. On the other hand, the dynamic modes of the proposed model are calculated by eigenvalue analysis, and their contributions in each state variable are identified using the participation matrix. In the proposed validation method, the participating modes in each state variable are compared with the natural frequencies of its estimated waveform by Prony analysis. It is concluded that there is a good matching between the participating modes in the state variables and the contributing frequencies in their waveforms that verifies the proposed modeling method.

Dual second-order generalized integrator phase-locked loop (DSOGI-PLL) is widely used in grid-connected system for grid synchronization because of its simple implementation and good filtering capability. However, the frequency characteristics of DSOGI-PLL affect the impedance modeling of the system, which in turn affect the impedance-based stability analysis. In order to improve the accuracy of system modeling, in this paper, the equivalent transfer function of positive-sequence calculator (PSC) block constructed in αβreference frame in DSOGI-PLL is presented in dq reference frame, where the relationship between DSOGI-PLL and traditional synchronous reference frame PLL (SRF-PLL) small-signal model is investigated. Then, based on the established model, DSOGI-PLL and SRF-PLL are compared from the tracking characteristics and robustness characteristics. It is further demonstrated that DSOGI-PLL is able to improve the robustness performance of PLL while maintaining the same tracking performance as SRF-PLL. Finally, simulation results are presented to validate the established model and frequency characteristic analysis.

Grid-forming (GFM) inverters are dc–ac converters that regulate their ac terminal voltage and frequency in response to real-time measurements. Recent developments on GFM controls have focused on a particular dispatchable virtual oscillator control whose implementation features a nonlinear Andronov–Hopf oscillator at its core. In this article, we systematically model and study this controller, its synchronization dynamics, as well as its stability. We show that system voltages and frequency are regulated in a decentralized and autonomous manner while exhibiting nonlinear droop-like behavior. Small-signal models are formulated for an individual inverter connected to an infinite voltage bus in addition to systems of interconnected GFM inverters. These models allow us to characterize dynamical stability and synchronization. Robustness is shown after sweeping key system parameters under the aforementioned models that capture system performance. Numerical simulations and experimental results validate the analytical developments. [ABSTRACT FROM AUTHOR]

High-power bidirectional dc–dc converters are being widely employed in renewable energy interfacing, energy storage, electric vehicle charging, military, aerospace, and marine applications. Among various bidirectional topologies documented in the literature for dc–dc power conversion, the split-pi converter invites special attention with regard to applications involving multi-phase systems requiring high-power density. This paper endeavors to present the small-signal modeling of the split-pi converter in its various operating modes. Subsequently, the dynamic characteristics of the converter are studied, and appropriate control design is presented for stable operation of the converter. Frequency response plots are illustrated, and a hardware prototype model of the converter is designed and implemented. [ABSTRACT FROM AUTHOR]

This work studies the small-signal direct and cross-coupling audio-susceptibilities of the independent-input series-output boost converter with peak current-mode control. The converter functions in the continuous-conduction mode and comprises n-connected identical boost modules whose inputs are fed from separate voltage sources and outputs connected in series. Expressions for the module direct (self) and cross-coupling audiosusceptibilities are derived in symbolic form. The expressions explicitly show (n) as a variable and take into account the sampling action of the current loops. In addition, audiosusceptibilty frequency responses following the closure of the voltage feedback loops are generated and the influence of increasing n is discussed. Detailed simulations using PSIM are performed to support the analysis. [ABSTRACT FROM AUTHOR]

In this paper, a reduced‐component switched‐capacitor boost multilevel inverter (SC‐BMLI) topology is proposed for off‐grid and on‐grid applications. Recently, switched‐capacitor‐based multilevel inverter (MLI) topologies have been employed to avoid the need for multiple isolated direct current (DC) sources when compared with traditional cascaded MLIs. To generate a nine‐level stepped‐up voltage across the load, the SC‐BMLI needs only eight power switches and two capacitors. To get the appropriate nine‐level switching pattern, phase disposition pulse width modulation (PD‐PWM) has been used. An extended 13‐level boost multilevel inverter (BMLI) is also discussed in this paper. The proposed topology is connected to the grid to control the grid current using synchronous reference frame‐based proportional–integral controller. A small‐signal modeling and analysis has been discussed in detail for the phase‐locked‐loop (PLL). Moreover, to prove the superior performance of the SC‐BMLI, comparative analysis with an existing single DC source MLI has also been performed. The feasibility of the 9‐level and 13‐level proposed topologies, with and without the grid‐connection, is evaluated by Matlab/Simulink simulation and verified by an experimental study using the OPAL‐RT 4510 real‐time platform. Further, prototype model of nine‐level BMLI has been developed in the laboratory using DSpace 1103 controller and results are compared with simulation. [ABSTRACT FROM AUTHOR]

In this research, four different equivalent circuit models that characterize the substrate/buffer loading effect for GaN high electron mobility transistor (HEMT) on Si substrate have been investigated. Y‐parameter measurements of an open de‐embedded structure have been used to characterize this effect in GaN HEMT on Si. An optimization technique based on hybridization between two meta‐heuristic techniques, which are particle swarm optimization (PSO) and grey wolf optimization (GWO) has been developed to extract physical relevant model elements. The proposed optimization technique is applied on GaN HEMTs of different sizes and validated by means of S‐parameters fitting. In addition, the extracted elements are evaluated in terms of their reliability and scalability. The proposed PSO‐GWO technique shows a very good agreement with previous research results. It has been found that the circuit topology of both resistive and capacitive shunt branches is more accurate in characterizing conductive and displacement substrate/buffer leakage current, respectively. The results of this research validate the applicability of the proposed technique and the model topology for small and large‐signal modeling of GaN transistors on Silicon substrate. [ABSTRACT FROM AUTHOR]

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.

The harmonic state-space (HSS), the dynamic phasor (DP), and the generalized dq (GDQ) modeling are three widely used methods for small-signal analysis of ac power electronic systems. By reviewing their principles and deriving their mathematical relationships, this paper proposes a unified framework for all the three approaches. The unified modeling reveals that the linearization and transformation can be exchanged flexibly in the modeling process, and the initial phase takes a role in transforming the GDQ model into the HSS or DP model. Case studies on a three-phase voltage-source converter in unbalanced power grids are provided for validation. The relationships of three modeling methods are verified by mathematical proofs and time-domain simulations. The unified frequency-domain model is further validated through the frequency scan in experiments. Insights of the unified modeling framework and recommendations from engineering perspectives are finally discussed.

This paper presents theoretical and experimental analysis of up-converted coherent population oscillations (Up-CPO) in semiconductor optical amplifiers (SOAs) for tunable optical phase shift applications at high frequencies. The study of Up-CPO frequency response is carried out by a small-signal analysis of a SOA modeled by two calculation sections in order to better take into account the nonlinear effects such as the SOA gain saturation. We demonstrate that we can fully determine the dynamic parameters of Up-CPO from the experimental frequency response of an optical probe signal obtained by cross-gain modulation mechanism. The Up-CPO frequency responses are measured for three SOAs with different cut-off frequencies up to 18.45 GHz. We finally validate experimentally the obtained analytical frequency responses for the three SOAs over different operating points, each characterized by the corresponding optical gain.

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.

A type of peak-value dc voltage control (denoted as PK control) was proposed in the literature for supporting the use of a smaller dc-side capacitance when the single-phase voltage source converter is operated as a static synchronous compensator. Although it was demonstrated to operate stably under several conditions, it will be revealed in this article how the PK control will suffer from a more severe small-signal stability issue under nonideal grid conditions than the conventional method of controlling the average value of the dc voltage (denoted as Avr control). Especially, it will be shown how the PK control is sensitive to some of the control parameters. To obtain these results, a parameter-oriented stability analysis method is developed in the linear time-periodic framework. Then, it is utilized for parametric stability assessments of the Avr and PK control. Finally, both frequency- and time-domain experimental results verified the effectiveness and accuracy of the applied method in the presented analysis. [ABSTRACT FROM AUTHOR]

This article reports on a scalable, temperature-dependent small-signal and noise model of a 50-nm metamorphic high-electron-mobility transistor (HEMT) technology. The model is valid for temperatures ranging from 5 to 297 K. The highest scalability is achieved by using a distributed model topology. The model is able to predict the small-signal and noise performance of 2–8 finger transistors with absolute gate widths ranging from 10 to 480 $\mu \text{m}$. Short gate width transistor fingers (5 $\mu \text{m}$) and wide transistor fingers (100 $\mu \text{m}$) are covered by the model. The model is valid over a very broad bandwidth from 0.1 to at least 150 GHz. Furthermore, the model covers all reasonable bias points of the given transistor technology. To the best of the authors’ knowledge, this is the first scalable HEMT model that is able to predict the small-signal and noise performance at arbitrary cryogenic temperatures. The scaling ratio related to the absolute gate width of the model is the highest among small-signal models reported in the literature. [ABSTRACT FROM AUTHOR]

This article presents a small-signal model for power-electronics converters that use a typical control structure in wind energy applications: the double synchronous reference frame current control. The article considers the presence of unbalanced currents and voltages, and analyzes their impact on the frequency couplings of the converter. In addition, it is revealed that, in the presence of negative-sequence voltage synchronization, the converter presents an additional coupling at $-2f_1-f_{\text{p}}$. [ABSTRACT FROM AUTHOR]

Charge control for resonant converters introduces an inner feedback loop that improves the system dynamic characteristics. However, small-signal modeling is not as straightforward with charge-controlled resonant converters as it is with current mode hard-switching topologies, due to the nature of resonant behavior. Conventional small-signal models for charge-controlled resonant converters are developed based on the converter input and output energy balance. This simplified approach overlooks the dynamics of the magnetizing inductor current and generates errors in small-signal frequency response. To improve the analytical model and enable high-bandwidth design, this article proposes a new methodology for modeling charge-controlled resonant converters. The energy stored in the resonant tank is analyzed using the theory of extended describing function, which accounts for the effect of the magnetizing current. This methodology applies to a wide range of charge control variants, such as bang-bang charge control and hybrid-hysteretic control. To demonstrate the modeling procedure, this article considers a high-order, five resonant-component half-bridge CLLC resonant converter as a case study. The proposed analytical model is applied to a 1 kW, 400-V/3.3-A power supply prototype for simulation and experimental validation. The proposed model successfully predicts the frequency response of the resonant converter across frequency and load conditions, providing rapid frequency-domain evaluation in the design process. [ABSTRACT FROM AUTHOR]

The extended describing function (EDF) method is widely used in modeling the resonant converters. This article finds that the model of the phase-shift controlled resonant converter deduced by this method might be inaccurate especially when the duty-cycle is close to 1. The reason behind it is investigated, showing that derivation of the inverter bridge model based on its fundamental harmonic will cause error. A novel model of the inverter bridge by Fourier analysis is proposed. Incorporating the novel model into the EDF-based resonant model, the accuracy of the phase-shift controlled resonant converter is greatly improved. A series–series compensated inductive power transfer system is fabricated in the lab to verify the validity of the proposed model. [ABSTRACT FROM AUTHOR]

Duty-cycle control is a widely used control method of resonant converters. In this article, the existing model of duty-cycle controlled resonant converters is found to have discrepancy compared with the simulation and experimental results. The reason behind is investigated, showing the phase change in the output voltage of the inverter bridge caused by the duty-cycle perturbation was ignored in the existing model. The phase change law is highly dependent on the duty-cycle scheme used, which is further determined by the forms of the carriers and the switching sequences of the resonant converters. With this consideration, improved models of both full-bridge and half-bridge resonant converters with different duty-cycle control schemes are rederived. It is revealed that different duty-cycle control schemes lead to different phase curves of the duty-cycle-to-output-voltage transfer functions, therefore care should be taken when selecting the appropriate duty-cycle control scheme. In the end, a series-series compensated wireless power transfer system is built to verify the validity of the proposed models. [ABSTRACT FROM AUTHOR]

Constant on-time control (COT) has been widely adopted in buck converters because of its simplicity, fast transient response, and high light-load efficiency. However, the increasing power demands of CPUs and AI/ML engines is pushing voltage regulators to support higher output currents, which typically requires the use of multiphase operation. However, since most high-performance COT schemes utilize ripple as a control variable, the ripple cancellation point in multiphase designs imposes difficult stability concerns, limiting performance, and robustness. In this article, a novel ultrafast transient COT (UFTCOT) control scheme is proposed to enable fast and robust operation even in multiphase converters. The small-signal models of the proposed control scheme are derived based on a describing function technique, whose theoretical results are compared, along with simulation and measurement results, to contrast the proposed UFTCOT technique to exiting approaches. [ABSTRACT FROM AUTHOR]

For a photovoltaic (PV)/battery power system consisting of PV module, energy storage system, and local load, using a three‐port converter (TPC) instead of several single‐input converters is more desirable, such as simpler circuit, higher efficiency, lower cost, and centralized control without communication circuit. In this paper, a TPC is proposed and analyzed, which includes operating modes, steady‐state performance, and parameter design. Compared with other converters, the proposed TPC has a low cost, compact structure, and a more flexible voltage relationship among all ports. Moreover, energy management and control methods are further proposed for PV/battery systems based on the proposed converter, which can achieve maximum power point tracking (MPPT) of PV module and constant output voltage. In order to design the control loop and realize multivariable optimal control, a small‐signal model of the converter is obtained in each operation mode. Then a detailed decoupling design approach based on a small‐signal model is provided to allow a separate controller design for the proposed converter. Finally, the validity of the proposed converter and its energy management and control method are verified by experimental results. [ABSTRACT FROM AUTHOR]

This work presents a detailed RF characterization of 28-nm FD-SOI nMOSFETs at cryogenic temperatures down to 4.2 K. Two main RF Figures of Merit (FoMs), i.e., current-gain cutoff frequency (ft) and maximum oscillation frequency (fmax), as well as parasitic elements of the small-signal equivalent circuit, are extracted from the measured S-parameters. An improvement of up to ~130 GHz in ft and ~75 GHz in fmax is observed for the shortest device (25 nm) at low temperature. The behavior of RF FoMs versus temperature is discussed in terms of small-signal equivalent circuit elements, both intrinsic and extrinsic (parasitics). This study suggests 28-nm FD-SOI nMOSFETs as a good candidate for future cryogenic applications down to 4.2 K and clarifies the origin and limitations of the performance.

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.

Several small-signal impedance models have been reported for type-III wind turbines for use in impedance-based system stability studies. Common to these models is the assumption that the dc bus between the rotor- and stator-side converters is an ideal voltage source. Under this assumption, there is no dynamic coupling between the two converters and the turbine can be represented by the impedance of the stator-side converter in parallel with the impedance of the induction generator with the rotor-side converter behind it. The assumption is well justified above the second harmonic frequency but introduces considerable error at lower frequencies, especially within 20-30 Hz of the fundamental frequency in which dc bus voltage control is active and dc bus capacitor impedance is high. This paper presents the development and application of full-order sequence impedance models for type-III turbines that include dc bus dynamics. The new models also consider the coupled current responses created by each of the converters as well as their coupling across the dc bus. Inclusion of these additional dynamics leads to more accurate prediction of turbine impedance responses and turbine-grid system stability. A comparison with existing models is presented to show the utility and limitation of each model. A practical resonance problem is also presented to demonstrate the application.

The paper presents a two-phase interleaved boost converter (IBC) providing higher step-up conversion ratio compared to the conventional IBC. The circuit consists of a crossly connected diode-capacitor cell which provides the extra boost up. The two identical capacitors of the cell are charged in parallel and discharged in series providing high voltage gain at considerably low duty ratio. Switching operations, ripple and average currents through inductors are analyzed in continuous conduction mode (CCM). Ripple in input current is also improved. The voltage stress across the semiconductor devices is less in the proposed converter. Also, boundary load condition is derived. Small-signal modeling is carried out and a control circuit is enabled in the voltage mode control framework. Power losses are analyzed and 96.53 % efficiency is achieved. Finally, the proposed converter is designed and implemented, and experimental results are provided. [ABSTRACT FROM AUTHOR]