Showing papers on "Small-signal model published in 2012"

Modelling and control of photovoltaic panels utilising the incremental conductance method for maximum power point tracking

Abstract: For photovoltaic panels, maximum power point tracking (MPPT) is a crucial process to ensure energy capture is maximised. Various tracking algorithms are available for this purpose. Of these, one of the more common presently implemented is the incremental conductance method. However, no linearised small signal model incorporating an incremental conductance-based MPPT process exists. As will be demonstrated, this is attributed to the formation of a degenerate model when conventional linearisation techniques are applied. In this study, a modelling approach is developed that overcomes this deficiency and permits linearisation of the incremental conductance MPPT algorithm. As a case study adopting this developed approach, a complete small signal dynamic model of the incremental conductance method utilising a boost converter is derived. The model is validated against simulations in PSCAD/EMTDC. This study also presents some applications of the model, such as controller design and stability testing. The results demonstrate that the system is highly robust to variations in the lighting condition.

Unified Three-Terminal Switch Model for Current Mode Controls

Abstract: Current mode controls have been widely used in many power converters with various topologies. Small signal equivalent circuit model is an effective tool for controller design. However, no unified equivalent circuit model applicable to various converters is available. This paper proposes a unified three-terminal switch model for current mode controls with constant frequency and variable frequency modulations operating in continuous conduction mode, providing an accurate and simple equivalent circuit for various converters using current mode control schemes. By identifying the invariant three-terminal structure in current mode control pulsewidth modulation (PWM) converters, which consists of active switch, passive switch, inductor, and closed current loop, the terminal current and voltage relationships are studied and represented by a small signal equivalent circuit. A small signal model for a current mode control PWM converter can be obtained by point-by-point substitution of the PWM switch with its equivalent circuit. The proposed model is verified by simulation and experimental results of various converters, and compared with other models to demonstrate its accuracy. The proposed model is accurate up to half of switching frequency.

Small Signal Modeling of LLC Resonant Converters Based on Extended Describing Function

Abstract: Due to the advantages of low switching loss and high efficiency, LLC resonant converters have been widely used. Based on the extended describing function concept, the small-signal model of an LLC resonant converter is derived in this paper. The equivalent circuit of small-signal model is illustrated so that the corresponding frequency response can be easily obtained by using Is Spice simulation. The well agreement with experimental measurements has verified the accuracy of the derived small-signal model.

Time-Multiplexing Current Balance Interleaved Current-Mode Boost DC-DC Converter for Alleviating the Effects of Right-half-plane Zero

Abstract: In the present study, a time-multiplexing current balance (TMCB) current-mode boost converter is proposed to improve the transient performance. Generally, the crossover frequency of a conventional boost converter is limited to half or less than the right-half-plane (RHP) zero to ensure the system stability. The transient performance of a conventional boost converter is degraded due to its limited bandwidth. The proposed TMCB boost converter extends its bandwidth and moves the RHP zero to a higher frequency to improve the transient performance using two inductors in one channel. Besides, the small signal model of dual phase system which considers cross-couple effect and offset correction is presented. The proposed converter requires an extra inductor and a slight increase in the size of the printed circuit board layout and die size. Using time multiplexing, two inductors were operated in an interleaved phase at a switching frequency of 5 MHz rather than a single inductor system operated at a switching of 10 MHz for the same ripple required. Experimental results show that the TMCB technique is effective in correcting the mismatch in the current of the inductors even if the difference between the inductors is large. Furthermore, the proposed converter can improve the settling time from 52 to 22 μs due to an extended bandwidth.

Modeling Inductive Behavior of MOSFET Scattering Parameter $S _{22}$ in the Breakdown Regime

Abstract: A novel physical small-signal equivalent circuit for accurately modeling an unusual phenomenon of inductive in the breakdown regime of RF metal-oxide semiconductor field-effect transistors is presented for the first time. To remove the low-frequency dispersion of the drain-to-source resistance extracted by a conventional approach, a new extraction method of equivalent circuit element values with the introduction of an inductive network is demonstrated in this paper. Excellent agreement between simulated and experimental data is obtained up to 26.5 GHz in the breakdown region. Therefore, this proposed physical model based on the avalanche breakdown mechanism can accurately be used to predict the RF circuit performance when impact ionization occurs.

Scaling Factor Design Based Variable Step Size Incremental Resistance Maximum Power Point Tracking for PV Systems

Abstract: Variable step size maximum power point trackers (MPPTs) are widely used in photovoltaic (PV) systems to extract the peak array power which depends on solar irradiation and array temperature One essential factor which judges system dynamics and steady state performances is the scaling factor (N), which is used to update the controlling equation in the tracking algorithm to determine a new duty cycle This paper proposes a novel stability study of variable step size incremental resistance maximum power point tracking (INR MPPT) The main contribution of this analysis appears when developing the overall small signal model of the PV system Therefore, by using linear control theory, the boundary value of the scaling factor can be determined The theoretical analysis and the design principle of the proposed stability analysis have been validated using MATLAB simulations, and experimentally using a fixed point digital signal processor (TMS320F2808)

AC small signal modeling, analysis and control of quasi-Z-Source Converter

Abstract: This paper addresses the ac small signal modeling of the quasi-Z-Source Converter (qZSC). The linearized control/disturbance-to-system-variable transfer functions of the voltage-fed type quasi-Z-source network are derived, indicating the existence of right half plane (RHP) zero, which could impose limitation on controller design. Analysis on the dynamics introduced by the shoot-through state of the quasi-Z-source network is presented based on the ac small signal model, which is compared with the detailed circuit model for validation. Considering system dynamic characteristics, the qZSC design guidelines for passive component sizing is investigated by parameter sweeping of the small signal model based transfer functions. As another application of the ac small signal modeling, a PI compensator with feed forward control loop is developed for the qZSC in stand-alone operation. Experimental result is provided to validate the effectiveness of the closed-loop control.

A physics-based, small-signal model for graphene field effect transistors

Abstract: In this letter, a small-signal model for the graphene-based field effect transistor based on a physical description of the device’s operation is presented. The small-signal model contains circuit elements similar to classical small-signal models for field effect transistors but these elements differ vastly in their behavior with bias, owing to the different physical behavior of these devices. Intrinsic and extrinsic small-signal models are presented. The high-frequency performance of the models in terms of short-circuit current gain and Mason’s unilateral gain, and associated frequency figures-of-merit, are examined.

Dynamic modeling of DC–DC converters with peak current control in double-stage photovoltaic grid-connected inverters

Abstract: In photovoltaic (PV) double-stage grid-connected inverters a high-frequency DC–DC isolation and voltage step-up stage is commonly used between the panel and the grid-connected inverter. This paper is focused on the modeling and control design of DC–DC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. In the proposed overall control structure the output voltage of the DC–DC converter is regulated by the grid-connected inverter. Therefore, the inverter may be considered as a constant voltage load for the development of the small-signal model of the DC–DC converter, whereas the PV panel is considered as a negative resistance. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied. The theoretical analysis is corroborated by frequency response measurements on a 230 W experimental inverter working from a single PV panel. The inverter is based on a Flyback DC–DC converter operating in discontinuous conduction mode (DCM) followed by a PWM full-bridge single-phase inverter. The time response of the whole system (DC–DC + inverter) is also shown to validate the concept. Copyright © 2011 John Wiley & Sons, Ltd.

Precise modeling based on dynamic phasors for droop-controlled parallel-connected inverters

Abstract: This paper deals with the precise modeling of droop controlled parallel inverters. This is very attractive since that is a common structure that can be found in a stand-alone droop-controlled MicroGrid. The conventional small-signal dynamic is not able to predict instabilities of the system, so that in this paper, the combination of both small signal model and dynamic phasor model (DPM) of parallel-connected inverters is presented. Simulation results show that the dynamic phasor model is able to predict accurately the stability margins of the system when the droop control gains exceed certain values. In addition, the virtual ω-E frame power control method, which deals with the power coupling caused by the line impedance X/R characteristic, has been chosen as an application example of this modeling technique.

Analysis and design of average current mode control using describing function-based equivalent circuit model

Abstract: A small signal model for average current mode control based on equivalent circuit is proposed. The model uses the three-terminal equivalent circuit model based on linearized describing function method to include the feedback effect of the side-band frequency components of inductor current. It extends the results obtained in peak-current model control to average current mode control. The proposed small signal model is accurate up to half switching frequency, predicting the sub-harmonic instability. The proposed model is verified using SIMPLIS simulation and hardware experiments, showing good agreement with the measurement results. Based on the proposed model, a new feedback design guideline is presented. The proposed design guideline is compared with several conventional, widely used design criteria to highlight its virtue. By designing the external ramp following the proposed design guideline, quality factor of the double poles at half of switching frequency in control-to-output transfer function can be precisely controlled. This helps the feedback design to achieve widest control bandwidth and proper damping.

Method for establishing high-voltage direct-current small signal model

Abstract: The invention discloses a method for establishing a high-voltage direct-current small signal model. The method includes that (1), models are established in software SSAP (source service access point) which is object-oriented and modular, each direct-current power transmission project is independently packaged into a module, and each module and a corresponding synchronous generator model are equally connected into a total augmentation state equation of a system; (2), a direct-current power transmission system increases electric quantities of stable-state running balancing points on the basis of description of a quasi-stable-state equation of a convertor station including a rectifying station and a inversion station and a direct-current power transmission circuit differential equation, and a small signal linearization model is established; and (3) a main control system of the direct-current power transmission system includes fixed current control or fixed power control of the rectifying station and fixed arc quenching angle gamma control or fixed voltage control of the inversion station, and controllers are described by transfer functions. The scale of the system is not limited, and the method is suitable for analyzing electric system low-frequency oscillation also called small interference stability, and is applicable to searching measures for suppressing low-frequency oscillation.

Multibias neural modeling of fin field‐effect transistor admittance parameters

Abstract: The goal of this study is to develop an artificial neural network (ANN) approach to model the fin field-effect transistor (FinFET) small-signal admittance parameters. The model is determined for the whole device as well as for the actual transistor, which is obtained after de-embedding the effects of the probe pads, transmission lines, and substrate. The extracted model is validated in a wide range of operating bias conditions up to 50 GHz. In comparison to the earlier developed ANN-based model of the FinFET scattering parameters, although the same accuracy is achieved, the proposed technique exhibits the main advantage of a reduced model complexity. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2082–2088, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27020

Modeling and design of the LLC resonant converter used in solar array simulator

Abstract: An LLC resonant converter has been used to provide the electrical characteristics of solar arrays. In this paper, its small signal model is derived based on the extended describing function concept. The corresponding frequency response can be easily obtained from IsSpice simulation of the equivalent circuit model. Furthermore, a closed-loop compensation controller is designed according to the derived small-signal model. The experimental measurements have really proved that the stable and fast transient response can be achieved in the system. The system output voltage and current can be adjusted simultaneously to match the electrical characteristics of photovoltaic output.

Small signal analysis and control design of current-fed full-bridge isolated dc/dc converter with active-clamp

Abstract: This paper presents a systematic derivation of small signal model of current-fed isolated full-bridge dc/dc converter with an active clamp. Active-clamp is an active snubber helps to absorb turn off voltage spike across the power semiconductor devices, thus limiting or clamping the voltage across the devices. Inherently, it results in zero-voltage-switching (ZVS) of all devices (main and auxiliary) resulting in low switching losses and higher efficiency. State space averaging technique is used to derive the small signal model. A fixed frequency two-loop average current control with fixed frequency duty cycle modulation is designed to operate the converter for wide variation of load (1∶10) and input voltage (1∶2). A design procedure is illustrated. Frequency response curves using MATLAB and simulation results using PSIM 9.0 are presented to verify the stability of the control system as well as to observe the transient response with step-change in load and input voltage.

Modeling and analysis of N-port DC-DC converters

Abstract: Multi-port DC-DC converters are very attractive because they have the potential to combine different energy sources and management strategies. Their utilization is not only facilitating the entrance of the alternative energy sources into the market but is also reducing the cost and size of conventional energy sources. In this paper, the modeling and analysis of such power electronic devices with N ports are discussed. The derivation procedures of the power flow equations, the large signal model (LSM) and small signal model (state space model) (SSM) are presented. A transformation method to convert the N-windings transformer of the converter from a Star topology to a more suitable modeling topology is also presented. The modeling procedure is demonstrated for a 5-port DC-DC converter. Simulation is then used to compare the LSM and SSM models and observe their performance with respect to a detailed model (DM).

Small signal modeling and networked control of a PHEV charging facility

Abstract: The introduction of communication systems to power system controllers have brought in another layer of complexity in their design and operation. In this paper a Plug-in Hybrid Electric Vehicle (PHEV) charging facility is studied. A linearized model of the facility is built including both the dc/dc and dc/ac converters of the Distributed Energy Resources (DER). In addition, a control strategy that includes both local and networked loops is proposed to monitor and control the dc bus voltage of a Local Energy Storage (LES) unit. This dc bus voltage is crucial to the self-sustaining capabilities of the system. Impacts of different communication factors to the system stability are analyzed. Lastly, the small signal model, control strategy, and stability analysis are verified with real time simulations.

A proposed control strategy of PMSM for deep field-weakening and square-wave mode

Abstract: In order to achieve higher speed range over base speed, a proposed field-weakening control method of PMSMs is introduced in this paper. Only one current regulator based on controlling the amplitude of current vector is used for deep flux-weakening control. At the same time, the proposed control can be applied in square-wave mode where output voltage of inverter is constant. Its stability analysis is presented by small signal model. The proposed control method is verified by simulations and experiments.

Modeling, Control and Implementation of a Lithium-ion Battery Charger in Electric Vehicle Application

Abstract: The rapid development of Electric Vehicle powered by lithium-ion battery has resulted in significant interesting to charging device. However, the nonlinear characteristics of lithium-ion battery increase the complexity of charger designing. In this paper, to overcome the disadvantages, battery model is established and its parameters are evaluated adopted an exponential fitting method. Then an appropriate control strategy is proposed based on small signal model to realize the proposed charging strategy. Finally, experimental results from a laboratory prototype are shown to verify the feasibility of the proposed strategies.

Compact small-signal model for RF FinFETs

Abstract: Modeling of the small-signal equivalent circuit of SOI FinFETs through SPICE simulations is presented. A compact model implemented in Verilog-A predicts well the DC characteristics of RF SOI FinFETs and allows the extraction of the intrinsic conductance, transconductance and capacitances at any selected operating point. The intrinsic small-signal equivalent circuit composed of those extracted lumped elements is used in SPICE simulator. This paper compares the parameters extracted from both DC and wideband S-parameter methods.

Comparison of latch-based and switch-based, sampled-data, three-phase, PWM, voltage-source inverter models for dynamic analysis

Abstract: A switch-based, sampled-data, three-phase, pulse width modulated (PWM), voltage-source inverter (VSI) model for dynamic analysis has been derived and compared with the existing latch-based model. Comparisons were made for both time-domain, large-signal and z-domain, small-signal analyses. The switch-based model has the advantage of including inverter switching ripple current in the time-domain, large signal analysis, with minimal computational effort. The z-domain, small-signal model is made time-invariant using an approximation, with the limitations of using this approximation discussed. The switch-based z-domain model shows no significant difference from the latch-based model. This result confirms the validity of the latch-based analysis for z-domain for controller tuning, as long as the approximation needed for time-invariance is valid.

Dynamic modeling and analysis of T-source electronic inverter using state space technique

Abstract: T-Source inverter is a single stage power converter which can be used as a cost effective alternative for Z-source inverter. Dynamic modeling and analysis of T-source inverter (TSI) is vital for the determination of system limits, components selection for T-shape impedance network and controller design. A novel dynamic model of TSI in continuous conduction mode using the state space approach has been derived here. The derived model has been analyzed by introducing a disturbance in both the load and source side of the TSI. The stability, limitations and component selection of TSI have been done using pole-zero map and frequency response plots. The mathematical models are verified by Matlab / Simulink and experimental results. Key words: T-Source Inverter, dynamic model, small signal model, state space model, continuous conduction mode.

Unified large signal modeling method for DC-DC converters in DCM

Abstract: A simple and general large signal model for DC-DC converters in discontinuous conduction mode (DCM) is proposed in this paper. The proposed large signal model has the following advantages: 1) unified and general, 2) simple and convenient to be derived, 3) both the steady-state model and small signal model can be obtained easily. Large signal averaged circuit model is built, and small signal model can be derived from it. In this model, the active switch is modeled by a current source, the diode is modeled by a voltage source and the inductor is modeled by a current source. The proposed modeling method is also convenient to be applied to various DC-DC topologies. The Pspice simulation was used to verify the proposed model. A 12 V input and 1.5 V output buck converter was built to verify the analytical analysis.

Small signal modeling and analysis of interleaved active-clamp forward converter with parallel input and series-parallel output

Abstract: The small signal model of an interleaved active clamp forward converter with parallel input and series-parallel output is presented in this paper. With interleaved control schemes for two phases in the proposed combined converter, the second side windings of the transformers can work in series when the input voltage is low while in parallel when input voltage is high. In order to predict the system dynamic behavior and optimize the loop control, the small signal model is derived in this paper. Based on this model the closed loop compensation is designed and the theoretical dynamic behavior is obtained. Finally, the prototype circuit is built. Both the simulation and experiment results are presented to validate the small signal model.

Modeling and Control Design of Flyback Power Supply System Based on Topswitch

Abstract: In this paper, the AC small signal model of single-ended flyback power supply in CCM mode using average switching elements model approach is introduced. Analysis and establish power supply model based on TOPSwitch chip, and design controller with frequency domain method. The results of MATLAB simulation certify that compensation network is reasonable. 32W prototype is developed, output ripple is less than 5% and voltage regulation rate is about 2%.

Direct extraction technique of π‐topology small‐signal equivalent circuit model for Si/SiGe heterojunction bipolar transistor

Abstract: A developed direct extraction technique of small-signal π-topology Small signal equivalent circuit model for Si/SiGe heterojunction bipolar transistor is presented.The intrinsic model parameters are analytically extracted. The extraction procedure is performed using new set of exact equations that do not need numerical fitting, special polarization of the device or any kind of post processing. Flat frequency response of the extracted parameters is obtained. Excellent agreement is noticed between S-parameters measurements and its simulated counterpart using the extracted model in the frequency range from 40 MHz to 20 GHz at different bias conditions. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:584–589, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26635

Stability analysis of the quasi-Z-Source DC/DC converter based on small signal model

Abstract: Focus is on the stability analysis of the quasi-Z-Source (qZS) DC/DC converter based on a small signal model. Control system of the converter is described and its transfer function for the small signal model is presented. The stability estimation was carried out. The results of the analytical analysis, simulation and experimental investigation showed that a DC/DC converter based on the qZS-network has limited but predictable stability margin.

H-bridge Hybrid Converter Modeling and Synthesize with Power Sharing Analysis

Abstract: In this paper hybrid converters with double inputs are investigated. Mainly any possible topologies are constructed and only one of them is chosen and modeled in none ideal format, by state space averaging method. After that small signal model and equilibrium point of that model is calculated. Finally with power sharing analysis the best point in efficiency was calculated.

Graphical small-signal modeling based on the inductor waveform

Abstract: A graphical small-signal modeling based on the inductor waveform is presented in this paper. Small-signal perturbation is superimposed on the large-signal inductor waveform under steady-state condition and then the output voltage variation from small-signal perturbation is calculated by equivalent circuit. As a result, the small-signal transfer function (control-to-output transfer) is derived This approach to model switching DC-DC converter power stages has the merits: 1) the modeling is very clear and is simple whether the converter operates in the continuous conduction mode (CCM) or the discontinuous conduction mode (DCM) and 2) the modeling is simple and easy to understand and derive. With a boost converter operating in CCM and DCM as an example, the proposed small-signal modeling is shown to be easier