Two-port Network Model Research Articles

Three-phase power flow using binary tree search algorithm for unbalanced distribution networks

The main objective of this study is to examine a binary tree (BT) three-phase (3Φ) power flow analysis method for unbalanced distribution networks. A simple and efficient 3Φ power flow solution method for unbalanced radial distribution networks was proposed. This method is based on the BT search structure. Large-scale distribution network problems can be evaluated using current-injection techniques and two-port network models. The power flow solution process was simplified into a set of 3 × 3 matrix operations using the BT-based method. The solution complexity remained unchanged, regardless of the size of the power system. In other words, the performance and robustness of the proposed algorithm were maintained at relatively high values with increasing system size. Furthermore, programming complexity was reduced by standardising the solution process. The effectiveness and accuracy of the proposed model and algorithm were validated using four IEEE standard benchmark feeders and a series of random cases.

Modeling of direct AC/AC hybrid distribution transformer based on relaxed two port network theory

Traditional distribution transformers have shortcomings such as poor dynamic characteristics and unreasonable voltage compensation. It is difficult for them to meet the demand for power quality with the large-scale integration of new energy into the grid. Hybrid distribution transformers (HDTs) are an important means of addressing these issues. They have good flexibility in voltage regulation and huge development potential. To analyze the operating status and losses of an HDT, this study constructs a simplified equivalent impedance model for an HDT. First, the operating principle, characteristics, and voltage regulation range of a direct AC/AC HDT were analyzed. Second, based on the state–space averaging method, we obtain the HDT single-phase average circuit topology and construct an HDT relaxed two-port network model. Third, considering the operating losses of the transformer, Thevenin equivalent parameters of an HDT were derived. Then, a simplified equivalent impedance model for an HDT and the corresponding control strategies are presented. Finally, we verify the correctness and rationality of the proposed theory by constructing an HDT simulation model.

Design of filtering cable with defected conductor layer

Electrical cables, often referred to as ‘blood vessels’ and ‘nerves’ of the industry, play a vital role in the connection of electrical devices. However, traditional cables that lack distributed filtering functions are usually the primary coupling path for electromagnetic compatibility (EMC) problems. An innovative design for a filtering cable, which incorporates insulated electrical wires coated with a specific defected conductor layer (DCL), enables it to achieve distributed filtering advantages along its axis. Microwave network analysis is employed to build the two-port network model of filtering cable, which efficiently analyzes the cascading characteristics of periodic or aperiodic filtering cables. To validate, the flexible printed circuit board (FPCB) with sawtooth dumbbell-shaped DCL and mounted by capacitors is wrapped around the stripped section of the coaxial cable to manufacture a multi-stopband filtering cable. Simulated and measured results demonstrate that the proposed filtering cable can be effectively suppressed in the stopband, which can be adjusted by changing the values of capacitors.

Two-port network model of wind turbine generator for three-phase unbalanced distribution system load flow analysis

An unbalanced electric power system can occur due to unequal lines and/or loads in each phase of the system. For a system with a high level of unbalance, the assumption that the system is balanced becomes incorrect. For a case like this, the system must be analyzed using three-phase approaches because single-phase analysis techniques can no longer be used to obtain accurate results. Therefore, the development of three-phase models of all components of the electric power system, including the wind turbine generating system (WTGS), is very important so that the system can properly be analyzed and its performance can correctly be evaluated. This paper proposes a method to incorporate WTGS in a three-phase load flow analysis of an unbalanced distribution system. The proposed method is based on the previously published single-phase two-port network model. In this paper, the single-phase two-port network model is modified and extended so that it can be applied to unbalanced systems. The model is then included in the three-phase distribution system load flow (DSLF) analysis. The proposed method is validated using 12-node and 19-node distribution systems.

Modelling on Novel Cable Traction Power Supply System and Power Distribution Analysis

Novel cable traction power supply system (NCTPSS) is a kind of long distance co-phase traction power supply system (TPSS), it can effectively solve problems caused by train's passing through electrical phase separation and improve utilization rate of regenerative energy in system, which is an ideal traction power supply mode. However, its structure is relatively complex due to cable power supply pattern, and internal power flow distribution mechanism still needs further study. In order to establish train-network coupling power flow calculation model, in this paper, two-port network model of each system component is established at first, then equivalent solid circuit model of the system is built by external cascade strategy and tearing nodal method. Then, power flow, the change of traction transformer power output and network voltage are analyzed under the condition that trains work in traction and regenerative braking condition, based on actual train operation schedule. The research shows that the proposed model can accurately calculate and detailed reflect electrical characteristics of NCTPSS, traction transformer capacity is effectively decreased compared with that needed in existing TPSS; Regenerative power can feed back to entire cable traction network and be reused by traction trains with high utilization rate inside NCTPSS.

Two-port network modeling for bio-heat transfers in lungs

Abstract In open-heart surgery, temperature changes may severely damage organ tissues, therefore a better knowledge of thermal transient effects is required to improve temperature control. Heat transfer in a biological context is usually treated by means of empirical relationships or simple resistance models. In some cases, fairly simplified models only involving thermal resistance R and a heat capacity C are used. More advanced models which may be accurate enough tend to rely on heavy finite element computations. An intermediate model is sought to more accurately describe transient effects. By combining the well-known Pennes’ bio-heat equation combined to a thermal two-port network, a circuit model is proposed to take into account thermal transients in a perfused tissue. A larger frequency band can be taken into account for such an approach. The proposed models may also consider the effect of blood perfusion on the temperature transients, as well as blood temperature fluctuations (as in extracorporeal circulation, for example) and metabolic heat generation. For a simple 1D scenario, sensitivities to different heat or temperature inputs are compared. The obtained impedance expressions are also analyzed for different branch levels of the lung.

Two-Port Characterization and Transfer Immittances of AC-DC Converters–Part II: Applications

This two-part paper presents a general method to model three-phase ac-dc converters as two-port networks for power system stability studies. Part I of the work has developed the two-port network models and identified two types of transfer characteristics that are unique to ac-dc converters and important for system stability. Part II presents the applications of the developed models in stability analysis of different power systems that use ac-dc converters, including grid integration of converter-based generation from wind, PV and other renewable sources, grid-connected dc microgrids and dc distributed power systems, high-voltage dc transmission, as well as hybrid ac-dc power systems. While impedance-based stability analysis has been studied for each of these systems, the new two-port models, especially the transfer immittance models, make it possible and easy to formulate more complete system models to include dynamics and coupling effects that have been ignored or impossible to consider in the past. The methods to study the stability of each type of systems are explained and illustrated by case studies that also highlight the effects of coupling modeled by the transfer immittances on system stability. Each case study also exemplifies a practical stability concern in converter-based power systems.

Synthesis of Wideband High-Quality Factor Delay- Tunable Fully Differential All-Pass Filters

In this article, all possible wideband fully differential second-order voltage-mode active all-pass filters (APFs) based on a common-source differential amplifier are systematically derived using two-port network modeling techniques and symbolic math CAD tools. The proposed APF structure is based on the generic two-transistor differential-pair and all possible combinations of the surrounding impedances. In particular, 26 transfer functions and a total of 180 APF circuits, all of which can have a pole quality factor ( $Q$ ) value greater than unity, are found to be possible. Hence, the proposed topology can be used to produce APFs with dispersive delay as well as flat delay for true time delay elements. The operation of some APFs is verified with simulations and a selected circuit with tunable peak delay is designed and fabricated in a 65-nm CMOS process. The implemented filter achieved a maximum peak delay of 88.4 ps at 31 GHz, a constant delay of 11.5 ps over the frequency band 5–20 GHz, and a delay $Q$ -factor ( $Q_{D}$ ) value of 3.74, while consuming 1.74 mW from a 1-V supply voltage. The fabricated circuit occupies an area of $0.11\times 0.348$ mm2 and experimentally demonstrates an APF with the highest $Q$ value of any published second-order APF known to the authors.

Reconfigurable Transmitarray With Near-Field Coupling to Gap Waveguide Array Antenna for Efficient 2-D Beam Steering

A novel array antenna architecture is proposed that can enable 2-D (full-space) radiation pattern control and efficient beam steering. This solution is based on a gap waveguide array antenna and a reconfigurable transmitarray (TA) that are coupled in the radiative near field. An equivalent two-port network model of the coupling mechanism is presented and validated numerically. The desired TA reconfiguration capability is realized by an $8 \times 8$ array of cavity-backed patch resonator elements, where two AlGaAs p-i-n diodes are integrated inside each element providing a 1-bit phase shift. The TA is implemented in an eight-layer printed circuit board (PCB), which includes radiating elements, fixed phase-shifting inner-stripline sections, impedance matching, and biasing circuitry. The combined antenna design is low profile (~1.7 wavelength) owing to the small separation between two arrays (~0.5 wavelength), as opposed to conventional TAs illuminated by a focal source. The design procedure of the proposed architecture is outlined, and the measured and simulated results are shown to be in good agreement. These results demonstrate 23.5–25.2 GHz −10-dB impedance bandwidth and 23.3–25.3 GHz 3-dB gain bandwidth, a beam-steering range of ±30° and ± 40° in the E- and the H-planes with the gain peak of 17.5 dBi, scan loss $\le3.5$ dB, and TA unit cell insertion loss $\le1.8$ dB, respectively.

Two-Port Network Modeling and Stability Analysis of Grid-Connected Current-Controlled VSCs

Converter–grid interactions tend to bring in frequency-coupled oscillations that deteriorate the grid stability and power quality. The frequency-coupled oscillations are generally characterized by means of multiple-input multiple-output (MIMO) impedance models, which requires using the multivariable control theory to analyze resonances. In this article, instead of the MIMO modeling and analysis, the two-port network theory is employed to integrate the MIMO impedance models into a single-input single-output (SISO) open-loop gain, which is composed by a ratio of two SISO impedances. Thus, the system resonance frequency can be readily identified with Bode plots and the classical Nyquist stability criterion. Case studies in both simulations and experimental tests corroborate the theoretical stability analysis.

Miniaturized array antenna with reduced beam squinting

In this paper, we propose a novel multi-band series-fed array of patch antennas, a three-element linear resonant array operating at five distinct frequencies. A wide-band phase-shifting network compensates for the inter-element phase differences of radiating elements, which results in the reduction of beam squinting over the operating frequency range. Compared to a resonant series-fed array with conventional phase-shifters, beam squinting is reduced by 70%. Also, the length of the suggested phase shifters is less than quarter wave-length (at f = 6.78 GHz). Size reduction of the radiating elements also contributes to the miniaturization, and compared to a conventional array of printed dipoles, directive radiation is obtainable with fewer radiating elements. Based on the two-port network model for radiating patches, a practical computational method—which results in the usage reduction of computational resources—is presented to calculate the final realized gain of the series-fed arrays. The proposed array operates within 5.4–7.45 GHz frequency range, which makes it suitable for current and future Wi-Fi, or mobile network applications. Besides, the design principles apply to any series-fed array antenna operating at dominant (TM010) resonant mode. The performance of the proposed array is validated via experimental measurements, and the results indicate a good agreement with the simulations.

Study on load adaptation of capacitive power transfer system with a four-plate compact capacitive coupler

This paper proposes an LCL-L compensated capacitive power transfer (CPT) system with a four-plate compact capacitive coupler to achieve load adaptation. The coupling principle of four plates is explained, and the formulas between the cross-coupling capacitances and port capacitances are deduced by establishing a two-port capacitive network model of the coupler. The resonant frequency is designed to be unchanged whether the pick-up is removed or moved back to simplify system control. The model of the coupler and AC impedance model of CPT system are established, and the parameter design method is given. Finally, the feasibility and effectiveness of the proposed topology and its parameter design method are verified by simulation and experimental results.

Two-port network model of fixed-speed wind turbine generator for distribution system load flow analysis

Load flow analysis has always been used in determining the steady-state operation of an electric power or distribution system. For conventional power system without wind turbine generator, the method for load flow analysis has been well established. However, for modern system embedded with wind turbine generator, the investigation of analysis method is still an active research area. This paper proposed a new method to integrate fixed-speed wind turbine generator into distribution system load flow analysis. The proposed method is derived based on two-port network theory where the parameters of induction generator of the wind turbine generator are embedded in general constants of the two-port network. The proposed method has been tested and verified using a representative electric distribution system.

Automatic Generation of Differential-Input Differential-Output Second-Order Filters Based on a Differential Pair

In this paper, the generation of differential-input differential-output second-order active filters based on a common-source differential amplifier is systematically conducted using two-port network modeling techniques which enable exploiting the power of symbolic math CAD tools. Starting from a generic two-transistor differential-pair structure, and the maximum possible number of surrounding impedances, all possible filters are derived and classified. In particular, 35 transfer functions and a total of 876 filters are found to be possible. Due to employing a $2\times 2$ transmission matrix representation of each transistor, flexibility in examining parasitic effects on the derived transfer functions is achieved and can be easily automated within the design framework. Selected filters are constructed and experimentally verified using discrete transistors. The operation of some filters is also verified with simulations using a 65-nm CMOS process.

A New Two-Port Network Model-Based Pilot Protection for AC Transmission Lines

Conventional pilot protections used for EHV/UHV ac transmission lines require data synchronization between the two terminals of transmission line, and their performances are affected by the line capacitive charging current and load conditions. To tackle these problems, this paper proposes a new pilot protection scheme based on two-port network model of ac transmission lines. The new protection scheme calculates the two-port network parameters from the online measurements via the sequence components method, and then compares the solved parameters with their setting values to distinguish the internal and external faults. It does not require the data synchronization between two terminals of the transmission line. Moreover, its performance is not affected by the line capacitive charging current and load conditions. The applicability of the proposed scheme for series compensated lines is also analyzed. Effectiveness and accuracy of the proposed protection scheme have been verified by simulation tests.

A Radio Propagation Model for Dense Wireless Networks

This paper proposes a model of radio frequency signal propagation in the free space that can be used not only in the far field region of the transmitting antenna like the Friis propagation model for large scale fading, but it can also be employed when the antennas are very close to each other. The modeling starts from a transfer function of the exact two-port network model used to represent the coupling between two antennas in free space. The Z parameter network of the system is used to model the power attenuation as function of the distance between the antennas. Subsequently, a new mathematical model is proposed and compared with the Z parameter network model and shown to have small mean squared error. Such model has the advantage of replacing the Friis formula without the restriction to avoid measuring signals in the near field of the antenna. Furthermore, some practical experiments are carried out in an open field environment and the results are compared. The validity of the new model is demonstrated which can be used for any distance between the antennas and, therefore, it can also be employed to model dense wireless networks.

Low-Cost Series-Fed Microstrip Antenna Arrays With Extremely Low Sidelobe Levels

This paper presents a new method of designing and implementing low-cost series-fed microstrip antenna arrays with low sidelobe levels by applying standard single-layer PCB technology. The method is based on the Z-parameter characteristics obtained from the electromagnetic full-wave simulation of the array elements by using a two-port network model. Two types of antenna arrays are designed and presented with the use of the proposed method. The first type is a uniform linear array with sidelobe level of 24.2 dB at the 24.125 GHz frequency band. The second type is a nonuniform linear array that provides at least 50% more physical space between the central patches to be used in 2-D arrays; this antenna has sidelobe level of 25 dB at 24.125 GHz. Both antennas achieve an excellent performance in the entire bandwidth of 250 MHz.

Measurement of diesel exhaust fluid concentration in urea-SCR after-treatment system

In an effort to meet the established emission standards Selective Catalytic Reduction (SCR) is used to reduce NOx emissions with diesel exhaust fluid (DEF) as additive in the exhaust of diesel engines. ISO 22241-1:2006 specifies the quality characteristics of DEF in order to maintain efficiency and hence, it is essential that the concentration of urea in DEF is accurately monitored. In this paper, a measurement system is designed, developed and tested for measuring the concentration of urea in DEF. The design involves piezoelectric ultrasound transmitter and receiver with associated electronics operating at a frequency of 4 MHz. The concentration of urea in DEF is measured (i) by measuring the time of flight of ultrasound waves between transmitter and receiver (ii) by measuring the amplitude of received signal in terms of frequency using voltage-to-frequency converter. The measurement system is modeled using two-port network model for piezoelectric transmitter/receiver and transmission line model for DEF medium. The prototype of measurement system is fabricated with all associated electronics and tested for variation in concentration of urea in DEF. The results from prototype are in close agreement with the results obtained from analytical model. The measurement system is tested for repeatability and sensitivity to temperature.

Modeling and Optimization of Multiground TSVs for Signals Shield in 3-D ICs

This paper presents an effective loop impedance extraction method and a model of a signal through-silicon via (TSV) surrounded by multiground TSVs. According to this method, the effective coupling substrate capacitances of multiground TSVs with different numbers and placements are calculated. Based on the calculated values of the resistance-inductance-capacitance-conductance (RLCG) parameters, the equivalent circuit and a two-port network model are established. The S -parameters of the model are validated by the simulated and measured results. Then, the effect of different patterns of ground TSVs on the central signal and coupling capacitance are discussed. Note that the hexagon pattern proposed in this paper can save the occupied area prominently without damaging the signal integrity.

A Frequency-Tracking and Impedance-Matching Combined System for Robust Wireless Power Transfer

One of the greatest challenges to power embedded devices using magnetically coupled resonant wireless power transfer (WPT) system is that the amount of power delivered to the load is very sensitive to load impedance variations. Previous adaptive impedance-matching (IM) technologies have drawbacks because adding IM networks, relay coils, or other compensating components in the receiver-side will significantly increase the receiver size. In this paper, a novel frequency-tracking and impedance-matching combined system is proposed to improve the robustness of wireless power transfer for embedded devices. The characteristics of the improved WPT system are investigated theoretically based on the two-port network model. Simulation and experimental studies are carried out to validate the proposed system. The results suggest that the frequency-tracking and impedance-matching combined WPT system can quickly find the best matching points and maintain high power transmission efficiency and output power when the load impedance changes.