Maximum Power Transfer Capability Research Articles

Analysis and Design of Independent DC Bus Structure Multiport Power Electronic Transformer Based on Maximum Power Transmission Capability of Low-Voltage DC Ports

Owing to the diverse connection configurations of dual active bridge converters, a multiplicity of low-voltage DC port structures are anticipated to emerge in the independent DC bus structure multiport power electronic transformer (IDBS-MPET). An inadequate low-voltage DC port structure exacerbates the power imbalance in IDBS-MPET, presenting a risk of overmodulation even when transmitting relatively low levels of power. To overcome this limitation, a design scheme of IDBS-MPET topology based on the maximum power transmission capability of the low-voltage DC ports is proposed in this paper. Three topology design rules are derived from the maximum power transmission capability results of more than 80 typical IDBS-MPET topologies. The symmetrical triple cross-phase connection structure, the symmetrical double cross-phase connection structure and the single-phase connection structure are sequentially identified as the three most optimal structures of low-voltage DC ports. By employing the proposed design methodology, each low-voltage DC port achieves its maximum power transfer capability relative to other configurations. The effectiveness of the proposed design scheme is validated by an optimal designed IDBS-MPET topology with six low-voltage DC ports.

Power system static and dynamic security studies for the 1st phase of Crete Island Interconnection

The island of Crete is currently served by an autonomous electrical system being fed by oil-fired (Heavy fuel or light Diesel oil) thermal power plants and renewables (wind and PVs). The peak load and annual electric energy consumption are approximately 600 MW and 3 TWh respectively; wind and photovoltaic parks contribute approximately 20% of the electricity needs of the island. Due to the expensive fuel used, the Cretan power system has very high electric energy generation cost compared to the Greek mainland. On the other side the limited size of the system poses severe limitations to the penetration of renewable energy sources, not allowing to further exploit the high wind and solar potential of the island. According to the Ten Year Network Development Plan (TYNDP) of the Greek TSO (Independent Power Transmission Operator S.A. IPTO S.A.), the interconnection of Crete to the mainland Transmission System of Greece will be realized through two links: A 150 kV HVAC link between the Peloponnese and the Crete (Phase I) and a HVDC link connecting the metropolitan area of Athens with Crete (Phase II). The total length of submarine and underground cable of the HVAC link will be approximately 174km; it is at the limits of the AC technology and the longest and deepest worldwide at 150 kV level. A number of studies have been conducted by a joint group of IPTO and Hellenic Electricity Distribution Network Operator (HEDNO) for the design of this interconnection. This paper presents briefly the power system static and dynamic studies conducted for the design of the AC link and its operation. Firstly, the paper presents the main results of the static security study regarding the calculation of the maximum power transfer capability of the link and the selection of the reactive power compensation scheme of the cable. Results from dynamic security analysis studies are also presented. The small-signal stability analysis concludes that a new (intra-area) electromechanical oscillation is introduced to the National System after the interconnection. The damping of the electromechanical oscillations is sufficient; however the operation of power system stabilizers at power plants located both at the mainland and at Crete power system can increase significantly the damping of important oscillation modes. Finally with respect to the risk of loss of synchronism after a significant disturbance in the system of Crete, such as a three-phase fault (“transient stability”)- enough safety margin is estimated by means of Critical Clearing Time calculations.

Quasi-oppositional turbulent water flow-based optimization for cascaded short term hydrothermal scheduling with valve-point effects and multiple fuels

In an interconnected power system, short-term hydrothermal scheduling (SHTS) portrays a paramount important task in the economic operation of electric power system. SHTS is discerned as a formidable non-convex constrained optimization problem considering the cascade nature of hydro plants, and valve-point loading (VPL) and multi-fuel sources of thermal plants. In the present study, a novel metaheuristic approach, a quasi-oppositional turbulent water flow-based optimization (QOTWFO) is proposed to solve the SHTS problem. Turbulent water flow-based optimization (TWFO) is evolved by the whirlpool prodigy formed in a turbulent flow of water. QOTWFO is an amended version of TWFO, where the quasi-opposition-based learning is pioneered for population initialization and iteration vaulting. It generates a quasi-oppositional solution which has the highest probability to elicit the global optimum solution than a randomly generated solution. Thus, the global searching ability and computational efficiency of the algorithm is enhanced. A new heuristic constraints handling mechanism is proposed to fulfil the equality constraints notably active power balance and dynamic water flow balance. The cogency of proposed QOTWFO is examined on standard benchmark functions, and multi-reservoir cascaded hydrothermal test systems with the cogitation of VPL effects and multi-fuel sources of thermal plants. Besides, Newton Raphson load flow approach is employed to determine power losses and line flows in a 16-bus, and 35 transmission lines hydrothermal power system. To model a realistic power system model, the maximum power transfer capability of each transmission line is taken into account. Simulation outcomes substantiate that, compared with state-of-the-art heuristic techniques, QOTWFO offers better feasible solutions as well as guarantees the robustness of the algorithm.

High-Efficiency Module Design of Solid-State Transformers for Railway Vehicles

The solid-state transformer (SST) can be a promising solution to replace the conventional 50- or 60-Hz main transformer (MTr) for railway vehicles. Unlike the existing SST technologies for stationary power applications, the SST applied to railway vehicles requires severe constraint of installation space and intensive management of heat dissipation. To optimally design the SST module applied to the railway vehicles, which is one of the major components in the whole SST system, the optimal magnetic component designs for high-efficiency and thermal stable operations in the confined installation space are proposed in this article. In order to meet the SST system requirements for ac 25-kV-to-dc 1.5-kV power conversion, an overall SST topology and its control schemes are established. Based on the proposed SST topology, considering the operating drive profile of the urban railway vehicles, the operating sequence of the proposed SST is introduced and verified by simulation. By virtue of the proposed magnetic component design, the optimal number of turns for the inductor and transformer in dual-active-bridge converters can be appropriately determined for 50-kV high-voltage insulation and high-efficiency operation when the installation space for the magnetic components is given. For targeting the 3.0-MW maximum power transfer capability of the proposed SST system, the 300-kW SST modules, operating at 500 Hz and 10 kHz for ac/dc converters and dc/dc converters, respectively, were fabricated and verified by experiment. By two experimental SST module sets, the static performance of the power converters in the SST module and the dynamic operating sequence has been successfully implemented. For the 300-kW full-load operation, 99.7% of power transfer efficiency for the proposed magnetic components and 97.2% of total power efficiency were obtained. As a result, the measured temperature characteristics for the proposed SST module, including the magnetic components, were managed below 125 °C under a severe experimental environment.

The High Frequency Magnetic-Link With Distributed HTS YBCO Windings for Power Converter Applications

High frequency magnetic-link (HFML) is widely used in medium/high voltage power electronic converters for various applications. In this paper, a 440 V, 100 kHz compact HFML is designed with ANSYS/Maxwell software environment where the amorphous material is used as the magnetic core. The HFML is analyzed with solid toroidal cores with various winding configurations. A comparison of the HFML is performed for both the conventional copper winding and superconducting winding. Yttrium barium copper oxide material-based superconductor tape is applied to obtain the maximum power of the HFML. In addition, suitable winding configuration is selected to ensure possible maximum electrical power transfer while minimizing the magnetic saturation in the core. Simulation results show the electrical parameters of the HFML along with its magnetic flux density and power. The proposed HFML design with distributed winding is validated experimentally with a small-scale prototype where it is found that the maximum power transfer capability is increased more than 48% than that of the conventional one.

Stability and Multiconstraint Operating Region of Grid-Connected Modular Multilevel Converter Under Grid Phase Disturbance

Grid-connected converters may operate under grid fault conditions, such as the short-/open-circuit and the transmission line switching, which may be accompanied by a phase angle difference between the grid and converter. This variation will affect the normal operation of the converter since its phase-locked loop is not able to track the grid voltage phase angle immediately. In this article, an instability phenomenon with unregulated ac line current is identified in a modular multilevel converter (MMC) based high-voltage direct-current transmission system when there is a sudden phase angle change on the grid side. A set of analytical constraints is developed for the MMC in terms of the Lyapunov stability, the modulation index, and the maximum power transfer capability. Then, a multiconstraint operating region of the MMC under various phase disturbances is derived. Moreover, the parameter influence on the operating region is analyzed and two stability-enhancing methods for the MMC system are proposed. Finally, the boundaries of the operating region and the stability-enhancing methods are verified by simulations and laboratory measurements of three-phase grid-connected MMCs.

Impact of Grid Strength and Impedance Characteristics on the Maximum Power Transfer Capability of Grid-Connected Inverters

Continuously expanding deployments of distributed power generation systems are transforming conventional centralized power grids into mixed distributed electrical networks. The higher penetration and longer distance from the renewable energy source to the main power grid result in lower grid strength, which stimulates the power limitation problem. Aimed at this problem, case studies of inductive and resistive grid impedance with different grid strengths have been carried out to evaluate the maximum power transfer capability of grid-connected inverters. It is revealed that power grids with a higher short circuit ratio (SCR) or lower resistance-inductance ratio (R/X) provide higher power transfer capability. Moreover, under the resistive grid conditions, a higher voltage at the point of common coupling (PCC) is beneficial to increase the power transfer capability. Based on mathematical analysis, the maximum power curves in the inductive and resistive grids can be found. Moreover, a performance index is proposed in this paper to quantify the performance of the system with different parameter values. Finally, the effectiveness of the analysis is verified by simulation.

Smart Grid Planning Analysis Considering Multiple Renewable Energy Resources and Energy Storage Systems of User Side

The integration of renewable energy resources and storage systems makes power delivery route reconstruction after the N-1 fault taking place more complicated. To solve the calculation problem of smart grid power transfer capability, the time-varying characteristics of renewable energy resources and storage systems were analyzed. Based on this, an N-1 recovery model was proposed on the base of the transfer capability index. Through making the calculation formula of the transfer capability index linear and adopting the artificial intelligence (AI) optimal algorithm based on topology simplification, the operation modes of the power grid, new energy generations and new energy storage systems can be optimized and the maximum power transfer capability of the grid can be achieved.

Gallium Nitride Inverter Design with Compatible Snubber Circuits for Implementing Wireless Charging of Electric Vehicle Batteries

High-frequency wireless power transfer (WPT) technology provides superior compatibility in the alignment with various WPT standards. However, high-efficiency and compact single-phase power switching systems with ideal snubber circuits are required for maximum power transfer capability. This research aims to develop an inverter using Gallium Nitride (GaN) power transistors, optimized RCD (resistor/capacitor/diode) snubber circuits, and gate drivers, each benefitting WPT technology by reducing the switching and conduction loss in charging electric vehicle batteries. A full-bridge GaN inverter was simulated and instituted as part of the wireless charging circuit design. The RCD circuits were adjusted by transferring maximum power from the power supply to the transmitter inductor. For verification of the simulated output, lab-scale experiments were implemented for two half-bridges controlled by gate drivers with corresponding snubber circuits. After authenticating the output results, the GaN inverter was tested with an input range of 30 V to deduce the success of charging electric vehicle batteries within an efficient time frame. The developed inverter, at 80 kHz frequency, was applied in place of a ready-to-use evaluation board, fully reducing less harmonic distortion and greatly increasing WPT system efficiency (~93%). In turn, the designed GaN inverter boasts considerable energy savings, resulting in a more cost-effective solution for manufacturers.

Impacts of MT-HVDC Systems on Enhancing the Power Transmission Capability

In this paper, improvement in the power transfer capacity of transmission lines (TLs) by utilizing a multi-terminal high voltage direct current (MT-HVDC) grid is discussed. A multi-terminal HVDC grid designed for wind power can be used as an extra transmission path in interconnected systems during low wind conditions, and provides extra dynamic stability and security. This paper deals with the power transfer capacity as well as the small signal (SS) stability assessments in less damped oscillations accompanying inter area modes. Computation of the maximum allowable power transfer capability is assessed via DC optimal power flow-based control architecture, permitting more power transfer with a definite security margin. The test system is assessed with and without the exploitation of MT-HVDC grid. Simulation work is done using a generic computational framework i.e., international council on large electric systems (CIGRE) B4 test bench with a Kundur’s two area system, shows that voltage source converters (VSCs) provide excellent control and flexibility, improving the power transfer capability keeping the system stable.

A Dynamic WPT System With High Efficiency and High Power Factor for Electric Vehicles

Dynamic wireless power transfer (WPT) for charging electric vehicles (EVs) overcomes some of the problems associated with EVs battery size and weight as well as distance range limitation and long charging duration. High efficiency and fixed output voltage of WPT systems are of great importance for reducing operating cost and facilitating battery charging, respectively. On the other hand, utilizing the maximum power transfer capability of a WPT system leads to a capital cost saving of the system. In this article, the product of transferred power efficiency and input power factor (η·PF) is regarded as a criterion to make near full usage of the system power transfer capacity as well as reduce the capital and operating cost of the system. An optimal frequency-tracking method is proposed to maximize η·PF of the system taking into account possible abrupt changes in the coupling coefficient of the WPT system due to deviations of EV from alignment with the track along the road. In addition, the output voltage of the system is regulated simultaneously by an on-line adjustment of the primary inverter duty ratio. The optimal frequency-tracking method and voltage regulation are validated by extensive simulation and experimental results.

Phase-Shift Modulation for a Current-Fed Isolated DC–DC Converter in More Electric Aircrafts

This paper discussed an active-bridge-active-clamp (ABAC) topology that is suitable for highpower more-electric-aircraft applications. Though conventional modulation techniques can be applied to ABAC converters, they present drawbacks, such as increased low-voltage (LV) current ripple and limited power transfer capability. To address these problems, a phase-shift-modulation (PSM) scheme is proposed to provide clean dc terminal current at the LV side while maintaining high power transfer capability and efficiency in a wide operating range. The proposed PSM has a complete switching harmonics cancellation on the LV terminals independent of the operating conditions. This results in high quality power without any ac components, thus minimizing passive filtering. In addition, when terminal voltages vary from their nominal values, the proposed PSM can improve the maximum power transfer capability of the ABAC converter compared to the conventional approach. The theoretical claims are validated by both simulation and experimental results on a 10-kW 270-V/28-V ABAC converter.

ANALISIS TRANSFER DAYA PADA SALURAN TRANSMISI 150 KV DARI GARDU INDUK AIR ANYIR KE GARDU INDUK SUNGAILIAT PLN AREA BANGKA

Ketersediaan energi listrik yang cukup dan berkualitas merupakan tuntutan yang harus dipenuhi oleh PT. PLN (Persero). Penyaluran tenaga listrik melalui saluran transmisi 150 kV dengan jarak yang relatif panjang dan menggunakan kawat penghantar jenis aluminium selalu mengalami perubahan arus dan tegangan sehingga menimbulkan kemampuan pengiriman daya listrik menjadi tidak setabil. Pengaruh lainnya juga dapat diperoleh dari perubahan faktor daya dan sudut fasanya. Metode yang digunakan adalah metode analisis persamaan dalam bentuk hiperbolis. Pada penelitian ini menunjukkan bahwa kemampuan transfer daya dipengaruhi oleh sudut fasa. Kemampuan transfer daya aktif maksimum adalah sebesar 1962,71 kW pada VS yaitu 150∠75⁰ dan VR yaitu 150∠0⁰ dengan selisih sudut fasa adalah 75⁰. Sedangkan pada VS = 150∠75⁰ dan VR = 145∠0⁰ kemampuan transfer daya aktif adalah sebesar 1911,97 kW dengan selisih sudut fasa yang sama yaitu 75⁰. Penelitian ini memperlihatkan bahwa kemampuan transfer daya aktif dipengaruhi oleh tegangan. Kemampuan transfer daya aktif maksimum untuk nilai VR = 150∠0⁰ pada VS yang konstan yakni 150∠90⁰ adalah sebesar 2134,49 kW. Sedangkan Untuk nilai VR = 145∠0⁰ pada VS yang konstan yakni 150∠90⁰ adalah sebesar 2078,03 kW.

A flexible control strategy with overcurrent limitation in distributed generation systems

Distributed Generation (DG) systems are typically interfaced with distribution lines by modern power converter devices, which their controllers and dynamic behaviours are significantly influenced by unbalanced grid faults. The active and reactive power control with positive-negative sequences (PNS) is one of fundamental of power converter control under grid fault conditions. This paper proposes a reference current generator (RCG) based flexible power control strategy to enable regulation of active and reactive power with minimizing active and reactive power oscillations. Current limitation control is embedded into the RCG in order to keep maximum current injection in safety limitation for overcurrent protection under grid faults and harmonic distortions. The proposed control strategy has been also accomplished maximum active power and minimum reactive power transfer capability to electric grid. The analytical expression of active and reactive power oscillations depending on flexible control parameters are comprehensively investigated as theoretically and examined with simulations. Fractional order proportional integral (FOPI) controller is preferred to minimise steady state error of AC current regulation and provide faster processing time instead of conventional PI and proportional resonant (PR) controllers. An important contribution for similar previous studies is that PNS voltage and current components are separated by dual average filter based phase locked loop (DAPLL) which is firstly proposed in this paper. The performance of proposed controller is compared with multiple complex-coefficients filter (MCCF-PLL) based controller. Theoretical analysis and simulation results verify the correctness and effectiveness of the proposed solution.

An Optimal Thévenin Equivalent Estimation Method and its Application to the Voltage Stability Analysis of a Wind Hub

A simplified voltage stability analysis method is to use a static Thevenin equivalent to represent the electrical connection to a load center. Assuming fixed values of the Thevenin voltage and reactance, a power-voltage ( $PV$ ) curve analysis can be performed to find the voltage collapse point and stability margin. This paper proposes a method to compute the static Thevenin equivalent voltage and reactance of a power system using measured data. The method is validated with simulated PMU data and with 24-hour SCADA data at a wind hub on a medium voltage transmission system in the US western system. For the wind hub, the Thevenin equivalent parameters are used to compute the maximum power transfer capability of the wind hub as constrained by voltage stability. Then the method is extended to online application by using short data windows and forgetting factors.

A novel supplementary frequency-based dual damping control for VSC-HVDC system under weak AC grid

The Voltage-Source-Converter based High Voltage Direct Current (VSC-HVDC) system which is connected to weak AC grid, under the widely used Vector Current Control (VCC), may experience oscillations and even dynamic instability due to the Phase-Locked-Loop (PLL) dynamics. This paper proposes a novel supplementary control, i.e., supplementary frequency-based dual damping control (SFDDC), to enhance the stability margin for VSC-HVDC system under weak AC grid conditions. Based on the tracked frequency from PLL, the SFDDC approach introduces the power-based and AC voltage-based damping components to mitigate the instability induced by the larger PLL gains. A small-signal model of VSC-HVDC system is developed, and validated by the detailed electromagnetic transient (EMT) simulation. Then, the SFDDC dynamics are evaluated and the feasible region of the introduced damping coefficients are calculated. Finally, this paper investigates the maximum available power (MAP) and evaluates the critical short-circuit ratio (CSCR) for VSC-HVDC station, under the proposed control approach. The results show that, by proper selection of the dual damping coefficients within recommended range, the proposed SFDDC approach can effectively mitigate the instability issue induced by PLL, improve the maximum power transfer capability and enable the VSC-HVDC station operate in extremely weak AC grid conditions, even at SCR = 1.0. In addition, without control strategy switching, the over-current can be limited to an acceptable value by the proposed controller during the solid three-phase to ground fault scenario.

Adverse Impact of STATCOM on the Performance of Distance Relay

FACTS devices like the Static synchronous Compensator (STATCOM), are mostly used to enhance the maximum power transfer capability of the transmission Line (TL) system. A Matlab simulation model of Distance Relay protection of TL, with connected STATCOM at the mid-point for optimum power transfer is presented. The STATCOM’s impact on the operation of the relay is assessed with the effects on the relay misoperation in the third zone of protection coverage, during fault conditions, in four different locations.The wrong measured fault impedance by relay resulted to misoperation in zone 3 (under reach phenomena). The simulation result indicates a slight increase in the measured impedance of 1.33 Ω over the actually expected impedance setting (72.02 Ω) of the relay at 220 km protection coverage of zone 3 along the TL. This variation is about 4 km distance outside the expected distance protection coverage for fault in zone 3 as proven.

Resonant inductive power transfer for an E-bike charging station

This paper presents the design and the experimental tests of an E-bike 300-W battery charger for a cyclo-station based on wireless power technology. In particular, a series resonant inductive power converter with an E-geometry magnetic core topology is proposed. A mathematical model is developed and a performance analysis is conducted to determine the voltage transfer function, maximum power transfer capability, efficiency for different air-gaps (1–3cm), and misalignments (0.5–1.5cm). Also, it is performed analytical and experimental investigations of the minimum and maximum relative frequency points of active input power and efficiency in order to determine how these points changed as the resistance load varied. The results of the analyses indicated that the maximum frequency points of active input power are different from the maximum frequency points of efficiency and the zero-frequency points of reactive input power. This means that maximum power transfer and efficiency conversion are not obtained in correspondence with the resonant frequency. For this purpose, it is conducted a wide frequency characterization of 30–50kHz around the designed resonant frequency of 40kHz. An iterative electrical and magnetic design procedure is proposed based on 3D finite element analysis. Simulation and experimental results are presented for a full-sized prototype. The design of the E-bike battery charger is validated in terms of rated input voltage and output power for different air-gap configurations.

Optimising power transmission options for marine energy converter farms

This paper introduces a techno-economic analysis framework to assess different transmission options for marine energy converter (MEC) farms. On the technical front, the feasibility of the transmission options considering supply quality constraints and the optimal sizing of reactive power compensation to allow maximum real power transfer capability in the subsea transmission cable have been considered. The economic viability of different transmission options are measured based on component costs and the costs associated with the transmission losses. A case study has been presented in the paper, which demonstrates the application of this techno-economic analysis framework on a range of MEC farm sizes and distances from the shore. The results characterise the performance of different transmission system options with respect to three key design parameters – distance to shore, array power and transmission voltage – and provide guidance for system design.

Impedance‐compensated grid synchronisation for extending the stability range of weak grids with voltage source converters

This paper demonstrates how the range of stable power transfer in weak grids with voltage source converters (VSCs) can be extended by modifying the grid synchronisation mechanism of a conventional synchronous reference frame phase locked loop (PLL). By introducing an impedance-conditioning term in the PLL, the VSC control system can be virtually synchronised to a stronger point in the grid to counteract the instability effects caused by high grid impedance. To verify the effectiveness of the proposed approach, the maximum static power transfer capability and the small-signal stability range of a system with a VSC HVDC terminal connected to a weak grid are calculated from an analytical model with different levels of impedance-conditioning in the PLL. Such calculations are presented for two different configurations of the VSC control system, showing how both the static power transfer capability and the small-signal stability range can be significantly improved. The validity of the stability assessment is verified by time-domain simulations in the Matlab/Simulink environment.