Small-signal Model Research Articles

InP DHBT Analytical Modeling: Toward THz Transistors

InP double heterojunction bipolar transistors (InP DHBT) are one of the key technologies considered for terahertz applications. Improvement of their frequency performance is challenging and strongly dependent on various parameters (manufacturing process, geometry, epitaxial structure). In this article, a novel method is developed to take into account these parameters and predict the frequency performance of the technology. This approach consists of rebuilding the S-parameter matrix of the small-signal model. Elements of the small signal model are identified, and their assessment is described in detail. Once calibrated with the present state-of-the-art device features, the model shows a good agreement with the measurements. Based on this result, analysis of the emitter and base technological features are performed along with optimizations of the vertical structure. Finally, the necessary optimizations for developing a terahertz transistor are detailed. This works provides guidelines for technological improvement and opens the way for designing transistors operating at frequencies above a terahertz.

Combined Control Strategy for Proportional Current Sharing in DC Microgrid Clusters

The integration of adjacent DC microgrids (MGs) results in the formation of a DC MG cluster which can increase the system power supply capacity. This study proposes a control strategy for DC MG clusters which combines communication-free control and distributed fixed-time control to simultaneously achieve current sharing and voltage regulation with excellent transient characteristics. Firstly, a communication-free control, which presents greater flexibility than the distributed control, is used in the DC MG layer. Subsequently, the distributed fixed-time control is used in the DC MG cluster layer to balance the output current of each MG. The optimal control parameters are obtained by using the zero-pole distribution diagram and establishing a small-signal model of the DC MGs; the stability of the proposed control strategy is also verified. Different scenarios are considered to validate the plug-and-play capability and controller performance by using a DC MG experimental prototype. Real-time hardware-in-the-loop (HIL) verification containing three MGs is conducted using two RT-boxes to prove the scalability of the proposed cluster control.

A Novel Digital OTA Topology With 66-dB DC Gain and 12.3-kHz Bandwidth

The paper introduces an enhanced digital OTA topology which allows increasing the DC gain thanks to the adoption of an inverter-based output stage. Moreover, a new equivalent small-signal model is proposed which allows to simplify the circuit analysis and paves the way to new frequency compensation strategies. Designed using a 28-nm standard CMOS technology and working at 0.3-V power supply, post-layout simulations show a 66-dB gain and a 12.3-kHz gain bandwidth product while driving a 250-pF capacitive load. As compared to other ultra-low-voltage OTAs in literature, an increase of small and large signal performance, respect to area occupation, equal to 4.6X and 1.5X, respectively, is obtained.

Destabilizing Attack and Robust Defense for Inverter-Based Microgrids by Adversarial Deep Reinforcement Learning

The droop controllers of inverter-based resources (IBRs) can be adjustable by grid operators to facilitate regulation services. Considering the increasing integration of IBRs at power distribution level systems like microgrids, cyber security is becoming a major concern. This paper investigates the data-driven destabilizing attack and robust defense strategy based on adversarial deep reinforcement learning for inverter-based microgrids. Firstly, the full-order high-fidelity model and reduced-order small-signal model of typical inverter-based microgrids are recapitulated. Then the destabilizing attack on the droop control gains is analyzed, which reveals its impact on system small-signal stability. Finally, the attack and defense problems are formulated as Markov decision process (MDP) and adversarial MDP (AMDP). The problems are solved by twin delayed deep deterministic policy gradient (TD3) algorithm to find the least effort attack path of the system and obtain the corresponding robust defense strategy. The simulation studies are conducted in an inverter-based microgrid system with 4 IBRs and IEEE 123-bus system with 10 IBRs to evaluate the proposed method.

An Aging Small-Signal Model for Degradation Prediction of Microwave Heterojunction Bipolar Transistor S-Parameters Based on Prior Knowledge Neural Network.

In this paper, an aging small-signal model for degradation prediction of microwave heterojunction bipolar transistor (HBT) S-parameters based on prior knowledge neural networks (PKNNs) is explored. A dual-extreme learning machine (D-ELM) structure with an adaptive genetic algorithm (AGA) optimization process is used to simulate the fresh S-parameters of InP HBT devices and the degradation of S-parameters after accelerated aging, respectively. In addition to the reliability parametric inputs of the original aging problem, the S-parameter degradation trend obtained from the aging small-signal equivalent circuit is used as additional information to inject into the D-ELM structure. Good agreement was achieved between measured and predicted results of the degradation of S-parameters within a frequency range of 0.1 to 40 GHz.

A Hybrid Quasi-Single-Stage AC-DC Converter with Low Twice-Line-Frequency Output Voltage Ripple

Power factor correction (PFC) converters have been frequently employed in various switching power supply devices to reduce input current harmonics. However, the PFC converter suffers from an obvious twice-line-frequency output voltage ripple due to the instantaneous power imbalance between constant output power and variable input power. Suppression of twice-line-frequency ripple usually can be realized by the post-stage DC-DC converter of the two-stage cascade PFC converter; however, the two-stage cascade PFC structure is challenging to realize high efficiency since the energy is transferred twice. To achieve high power factor, high efficiency, and low twice-line-frequency ripple, a hybrid quasi-single-stage (QSS) AC-DC converter is presented in this paper, which consists of a dual output hybrid Boost/Flyback PFC converter and a Buck ripple compensation circuit (RCC). The fundamental principles of the proposed converter and the critical conditions of operation mode transition are discussed in the paper. To confirm that the twice-line-frequency ripple is effectively suppressed, the small signal model of Buck RCC is built and analyzed. Moreover, the main characteristics, including operation mode transition angle, input current, power factor, and switching frequency of the proposed hybrid QSS AC-DC converter, are analyzed. By building a 120 W experimental prototype to validate the feasibility of the proposed hybrid QSS AC-DC converter, the experimental results show that the proposed converter can realize PFC function with high efficiency and extremely low twice-line-frequency output voltage ripple.

Power distribution technique and small-signal modeling of grid-integrated solar PV system with hybrid energy storage systems

A model of a grid-integrated AC/DC microgrid with the assimilation of renewable energy resources and supercapacitors with battery storage-based hybrid energy storage is considered in this paper. The insertion of renewable resources and energy storage devices in the existing power grid requires rigorous analysis of the power balance and system stability. The microgrid is designed to absorb/deliver the defined power from/to the utility grid in a bidirectional manner. To simplify the power control strategy, the total power requirement in the system is divided into slow and fast varying components. So, the grid and battery will share the slowly varying components and the supercapacitor will suppress the fast varying components. This control strategy ensures improved performance by retaining the unity power factor operation of the grid, faster DC link voltage recovery, and harmonic mitigation. Again, a double-loop control structure based on small-signal modeling of the system is presented for stability analysis of the proposed system. MATLAB/Simulink results along with real-time simulation results are provided in this paper for verification of the proposed control technique.

Investigation on grid-following and grid-forming control schemes of cascaded hybrid converter for wind power integrated with weak grids

The conventional line commutated converter based high voltage direct current (LCC-HVDC) system is no longer suitable for transmitting wind power integrated with weak grids. Therefore, a cascaded hybrid converter consisting of LCC and modular multilevel converter (MMC) connected in series is considered as a promising solution in this paper. And a grid-following (GFL) control scheme and a grid-forming (GFM) control scheme are designed for the cascaded hybrid converter. To investigate the stability performances of the proposed two control schemes, this paper develops a small-signal model of the cascaded hybrid HVDC system for wind power integrated with weak grids. Then, based on the eigenvalue analysis method, several issues of concern are investigated for the proposed GFL and GFM control schemes, including their tolerance to a weak grid and a low wind power output, significant participants and sensitivity to parameter detuning. Based on the analysis results, one of the two that is more suitable for weak grids is recommended. The time-domain simulations implemented in PSCAD/EMTDC confirm the validity of the model and analysis results.Index Terms—Cascaded hybrid converter, grid-following, grid-forming, wind power, weak grids.

Detailed analysis and modeling of improved cascade buck converter

ABSTRACT – This paper presents ready-to-use nonlinear and linear averaged models of an improved cascade buck converter (ICBC) for the first time. A detailed steady-state analysis is also given, providing its operating modes, equilibrium values, and design guidelines. The modelling process consists of two stages. First, the nonlinear model is obtained using the state-space averaging technique. Subsequently, the averaged model is linearised by applying the small-ripple approximation and the small-signal model is achieved. Furthermore, the developed small-signal model is employed to derive three significant transfer functions of the converter. The proposed converter model is valid for the continuous conduction mode (CCM) when the duty cycle is lower than . To be used in validation studies, an exemplary converter with rated power that steps down input voltage to is designed. The accuracy of theoretical analyses is confirmed by the simulation results of the designed converter. Similarly, all proposed models are validated with the simulations done in both frequency-domain and time-domain. The results show that the proposed parametric model response closely matches that of the switching (non-parametric) model and hence it can be safely used for controller design in feedback systems.

A Hybrid Interleaved DC-DC Converter Based on Buck-Boost topologies for Medium Voltage Applications

DC-DC power converters with high voltage gain are primary components for renewable energy generation such as offshore wind farms. As the DC-DC converters installed in these farms should have limited size and weight, the non-isolated DC-DC converters are the most suitable choose for the offshore wind farms. Although, several DC-DC converters with high voltage gain have been developed for offshore wind farms. Most of them includes large count of semiconductors or experiences high voltage stresses. In this paper, a reduced components count converter is proposed for the collector system of offshore wind farms. The proposed topology is a modular input parallel output series non-isolated DC-DC converter. It is a hybrid interleaved structure which combines two buck-boost topologies into a single converter. The proposed converter aims to offer high voltage gain with reduced voltage and current stress on the converter's components. Moreover, the interleaved PWM offers limited output voltage ripple and supply current ripple. The operation modes and the steady-state performance of the proposed converter are analysed. In addition, a small signal model based on the state space averaged method is developed for the proposed converter. The accuracy of the developed model is verified using the converter's switching model. Furthermore, the output voltage control scheme utilizing a simple PI controller for the proposed converter is presented.

Small Signal Modeling and Transient Cross-Regulation Analysis of Peak-Current-Mode-Controlled SIDO Buck LED Driver

Small Signal Modeling and Transient Cross-Regulation Analysis of Peak-Current-Mode-Controlled SIDO Buck LED Driver

Assessment of Linear Quadratic Regulator Based Optimal Stabilization of Weak-Grid-Following Inverter Interface

An optimal state- feedback based decentralized stabilizing control scheme for weak-grid connected inverter interfaces is proposed here. Linear Quadratic Regulator (LQR) based feedback control options viz. small-signal perturbations in the reference signals, and in the control gains are explored for the same. It is shown that, with full-state feedback of local control variables, the stability enhancement is not much effective with gain perturbations. Rather, the reference set-point change is shown to stabilize the inverter to weak-grid interconnection. Eliminating the need of communication assisted auxiliary inputs or the need for their estimation, the proposed approach is effective in achieving stability margin enhancement for wider range of X/R ratios and grid impedances. The cost of achieving stabilization using totally device-level information is the compromise made in set-point adjustment. However, this can be adopted for emergency weak-grid scenarios in a generic power system. The proposed control augmentation is analysed for different operating scenarios in which one or the other control loops are enabled, and corresponding modifications in the controller are discussed. The proposed claims are validated using small-signal models, simulation studies in MATLAB/Simulink as well as with a power-hardware-in-the-loop (PHIL) experimental setup.

Admittance-Based Stability Analysis of Resistance-Emulating Controlled Grid-Connected Voltage Source Rectifiers

Due to low cost and high reliability, resistance-emulating control (REC) is an emerging approach for grid-connected voltage source rectifiers (VSRs). However, small-signal stability issues of the grid-connected VSR with REC are currently rarely studied. In this paper, the small-signal dq-admittance model of the grid-connected VSR with REC is first built and the small-signal stability superiority of the VSR with REC in weak-grid connection is revealed. First, a dq-admittance model of the grid-connected VSR with REC is established. The admittance characteristics of the grid-connected VSR with REC and the grid-connected VSR with traditional dual closed-loop control (DCC) are analyzed and compared. Then, the influence of short circuit ratio (SCR), voltage-loop bandwidth and the output power on the stability of the VSR with REC and DCC is analyzed based on the generalized Nyquist criterion. The stability comparison results indicate that the VSR with REC has better adaptability to the weak grid and can achieve a higher bandwidth at the voltage loop. Besides, it is found that the DCC controlled VSR is more suitable for light-load operation than the REC controlled VSR. Finally, the correctness of the analysis is verified by experiments.

Impact of Time Delay on the Control Link in Small Signal Dynamics of LCC-HVDC System

The time delay in the control link will affect the small signal stability of the line commutated converter based high voltage direct current (LCC-HVDC) system. This paper establishes the small signal model for the LCC-HVDC system considering the time delay in the control link. Then, based on the developed models, the movement feature of the eigenvalue loci with varying time delay under different AC system strength is investigated, the impact of the time delay on the system stability margin is quantitatively evaluated, and the frequency band affected by the time delay is identified. Subsequently, influence mechanisms of time delay on system stability are revealed from the perspective of the system damping characteristic by decomposing different damping paths. Moreover, impacts of time delay on DC current/voltage controller's stability margin are investigated. Theoretical analysis and simulation results indicate that, the increase of time delay at the rectifier-side will continuously deteriorate the system stability, as well as the system dynamic performances, while in most cases the increase of the time delay at the inverter-side imposes a non-monotonic effect on the system stability, which is weakened first and then slightly strengthened. Therefore, in certain scenarios, the larger time delay at the inverter-side may play a positive role in the system stability to some extent. The results can provide certain technical reference for the identification of key influencing factors causing the system oscillation and reasonable selection of control parameters in practical LCC-HVDC projects.

A NOVEL HIGH-GAIN DC-DC CONVERTER APPLIED IN FUEL CELL VEHICLES

Fuel cell cars should have DC-DC converters with high efficiency, low voltage stress, small size, and high gain. Nevertheless, the requirements are not met by traditional two-level, three-level, or cascaded boost converters. In this work, a novel non-isolated DC-DC converter with switched capacitor and switched inducer is proposed. The proposed non-isolated DC-DC converter exhibits a common ground structure, ensuring high gain, a broad input voltage range, and minimal voltage stresses across components. The comprehensive study includes an analysis of component parameters, the elucidation of the working principle, and thorough comparisons with other high-gain converters. To establish a dynamic model, the small-signal modeling approach and state-space averaging method are employed. Experimental and simulation data affirm that the suggested structure performs as intended. The experimental prototype operates within an input voltage range of 25V to 80V, featuring a rated output voltage of 200V and a rated power of 100W. The converter achieves its most efficient state at 93.1%, an aspect that may be underappreciated. Importantly, the recommended converter is deemed suitable for fuel cell vehicles, offering a promising solution to address their unique requirements.

Blackbox Small-Signal Modeling of Grid-Connected Inverters in Asymmetrical Power Grids

Blackbox Small-Signal Modeling of Grid-Connected Inverters in Asymmetrical Power Grids

A Proposed Simulation Approach for Teaching the Design of a DC Motor using MATLAB

This paper deals with the design of speed and torque control of DC motor drive. The PI control scheme is proposed for the system, and it is usually used in DC motor drives. The proposed control schemes guarantee the asymptotic stability of the closed-loop system. The converter that is used in the system is a 4-quadratic switch-mode DC-DC converter. The design is based on a small signal model and verified using a large signal model. To illustrate the developed control schemes, the performance of the closed loop system is simulated using MATLAB. The simulation, analysis, and discussion are introduced to present the efficiency of the scheme.

Small-signal behavioral-level modeling of InP HBT based on SO-BP neural network

In this paper, Snake Optimizer-Back Propagation (SO-BP) neural network algorithm has been proposed to model the small-signal characteristic of InP heterojunction bipolar transistors (HBTs). The SO algorithm can effectively improve the problem of local optima encountered by the BP neural network algorithm. The InP HBT small-signal models have been constructed by using Back Propagation (BP) algorithm, the Genetic Algorithm-Back Propagation (GA-BP) algorithm and the Snake Optimizer-Back Propagation (SO-BP) algorithm. The experimental results verify that the proposed SO-BP neural network algorithm model has the lowest error rate between simulated and measured data. Hence, the SO-BP algorithm is a more effective approach for modeling the small-signal characteristic of InP HBT. The accurate small-signal behavioral-level model of HBT has significant reference value for the application of microwave and millimeter-wave integrated circuits (MMICs).

An improved VSG control strategy based on transient electromagnetic power compensation

Virtual synchronous generator (VSG) not only increases the inertia of grid-connected system, but also brings the problem of active power oscillation under grid disturbance. Therefore, VSG control strategy and system model order reduction method with transient electromagnetic power compensation are proposed. The closed-loop active power small signal model of the system is established, and the influence of transient electromagnetic power compensation on the power stability of VSG is analyzed based on root locus method. By removing the items which have little influence on the stability of the system in the small signal model, the order is reduced to obtain the equivalent second-order model of the system. According to the second-order model, the quantitative design criteria of the system parameters are given. The proposed transient electromagnetic power compensation strategy not only increases the transient equivalent damping of the system, but also does not affect the primary frequency modulation characteristics and will not cause large overshoot of the output active power. The experimental results are consistent with the theoretical analysis, which testify the effectiveness and correctness of the system control strategy and the model reduction method.

Research on Low-Frequency Oscillation Damping Control of Wind Storage System Based on Pareto and Improved Particle Swarm Algorithm

Aiming at the low-frequency oscillation problem of high-proportion wind power and energy storage connected to the power system, this paper establishes a system small signal model according to the matrix similarity theory, which lays a foundation for the research on oscillation characteristics, mechanism analysis, and suppression measures. Combined with the different installation positions of the inverter-side converter and the inverter-side POD (Power Oscillation Damper) controller of the energy storage device, the suppression mechanism and damping oscillation ability of the two on low-frequency oscillation were analyzed. Under multiple optimization objectives, the parameters of the damping controller are optimized by Pareto and improved particle swarm algorithms. Finally, through Matlab/Simulink simulation, the effectiveness of the Pareto and improved particle swarm algorithm in suppressing low-frequency oscillation of the system is verified.