AC Part Research Articles

Analysis of Rail Potential and Stray Current with an Unified Chain Model of Dual Traction Power Supply System

In dual traction power supply systems, the overhead catenary system operates in different power supply modes. It passes across the AC section, DC section, and a neutral part, which influences the features and properties of the feedback current and aggregates its effects on stray current and rail potential. This research paper presents an integrated model of an AC and DC traction power system (TPS), along with a unified chain equivalent circuit model, the ground wire through the AC section, and the insulation joints fixed in the AC–DC neutral section under different operating positions. To make a unified impedance and admittance matrix for traction network, a virtual conductor wire has been added in the DC section to make the balance order of the TPS. The influence of reflex system configuration on rail potential, stray current, and distribution of rail potential at AC and DC stations has also been calculated. The simulation results demonstrate that establishing the insulation joints in the AC–DC section and using ground wires in the AC part can significantly decrease the stray current and rail potential.

Bidirectional PWM Converter to Interface AC Part to DC Microgrid with Neutral Potential Balancing

This research presents a description of a bidirectional pulse width modulated converter that functions as a rectifier by using the direct power control strategy and space vector modulation technology. In contrast to the voltage-oriented control strategy, this method minimises the number of internal current loops and requires more tuning. While functioning as an inverter, it applies the space vector modulation technique as well. The approach, on the other hand, is not the same as rectifiers since it calculates the duty ratio of the neighbouring voltage vectors in each small triangle that is generated in each sector that has a period of 60 degrees. In both situations, the neutral point potential has been brought back into equilibrium.

Variasi Frekuensi pada Electric Rotary Table Berbasis Inverter Guna Menurunkan Cycle Time dan Cacat Produk pada Pengelasan Pipa Kapiler

<p><strong><em>Abstract</em></strong><strong></strong></p><p> </p><em>Cycle Time is a matter that must be considered in production time, a good Cycle Time will</em> <em>support the targets that must be met, even if Cycle Time decreases, production will also increase and company turnover will also Increase. In the case study of PT Arisamandiri Pratama, one of its productions is in the form of AC parts, namely capillary pipes which still use a manual rotating table to rotate the pipe to be welded so that it is unable to reach the target of 800 parts / hour with an average Not Good product of 93 parts / day. The design of an inverter-based electric rotary table can reduce cycle time, but how much frequency will affect the results of a welding, not that the faster the welding process the better, the faster the welding will affect the vibration of the table machine which will have an impact on the welding results. By experiment the inverter frequency setting is expected to get a frequency value with maximum speed but no vibration on the rotation table, the frequency used is between 700 Hz to 1500 Hz with an interval of 100 Hz. The experimental results show that the best frequency is 1000 Hz, with a rotation speed of 16 rpm with a production capacity of 935 parts / hour with Not Good products of 59 parts / day or a decrease in Not Good products by 42.1% per day</em>

Design of fuzzy sliding mode controller for islanded AC/DC hybrid microgrid with cyber‐attacks

AbstractThis paper presents a fuzzy sliding mode control method for voltage control of islanded AC/DC hybrid microgrid. The T‐S fuzzy model is utilized to approximate initial non‐linear dynamic model of the microgrid. The fuzzy rules and membership functions are designed according to the coupling relationship between AC part and DC part. To reduce the influence of external disturbance and cyber‐attacks, an integral sliding mode controller is considered. Furthermore, a sufficient condition is proposed with attenuation performance to ensure the asymptotic stability of sliding motion. The set of gain matrices can be acquired via solving the linear matrix inequalities deduced from the Lyapunov stability analysis. The reachability to the proposed sliding mode surface can be guaranteed via switching control law based on a Lyapunov function. In addition, to eliminate chattering performance of the sliding mode control theory, the fuzzy logic controller is designed to optimize the switching region in boundary layers of saturation functions. Finally, the simulation results for the islanded AC/DC hybrid microgrid are implemented to verify the robustness and effectiveness of the designed fuzzy sliding mode control method.

Static state estimation of islanded AC/DC Hybrid microgrids

In this work, a static state estimation (SSE) approach for the hybrid AC/DC microgrid (MG)s operating in islanded mode is studied. In the islanded mode, the Interlinking Converter (IC) is critical for maintaining equal or normalized power between the AC and DC parts of the Microgrid (MG). Since the power exchange between AC and DC parts of the MG is determined from AC MG frequency and DC bus voltage, these also need to be considered as system variables along with bus voltages. Hence, in the proposed approach, the Weighted Least Squares (WLS) method is used to estimate the steady-state frequency (ω), along with AC bus voltages (magnitude and phase) of AC MG and DC bus voltages of DC MG simultaneously. Further, to incorporate frequency and droop equation of IC measurement, the Jacobian matrix of WLS is revised. The developed WLS-based Static SE is tested on two test systems: i) 12 bus system (6 bus AC and 6 bus DC) and ii) 71 bus system (38 bus AC and 33 bus DC). Moreover, the impact of accuracy classes of measurements is studied on a large Hybrid AC/DC MG (906 nodes AC MG and 118 node DC MG). All the SE results have been validated by comparing the obtained results with the corresponding true values (calculated from load ow analysis).

Improve power quality of charging station unit using African vulture optimization algorithm

In recent years, there is growth in acceptance to consume fewer fossil fuels globally and the manufacturing of electric vehicles (EVs) has become more popular. However, the increase in the number of systems connected to the grid that contain EVs with a huge power capacity leads to unstable working in the power system. To assess the stability of the electric charging station several control approaches in AC part and DC parts during charging mode and discharging modes are tested. African vulture optimization algorithm (AVOA) has been utilized to tune the system controllers (proportional integral derivative (PID)/tilt integral derivative (TID) controllers). The superiority of AVOA is confirmed by comparing the performance with the genetic algorithm (GA). Two objective functions have been used i.e. integral time absolute error (ITAE) and integral square time error (ISTE). AVOA-tuned TID controllers using ISTE were found to be the best to contain the frequency deviations. The results have shown of the AC part and DC part is within an acceptable limit recommended by IEEE standard. Further, maximum peak overshoot, undershoot, and settle time obtained by AVOA-tuned PID and TID controllers are found the best. Finally, the improvement of the performance index obtained by AVOA over its counterpart GA is confirmed.

Hybrid AC-DC distribution system for building integrated photovoltaics and energy storage solutions for heating-cooling purposes. A case study of a historic building in Cyprus

One of the main concerns globally is the phenomenon of climate change thus we have to move to a cleaner and sustainable development in different energy sectors. An important step in this direction is the penetration of more renewables in the electricity grid. Therefore, with the increasing penetration of DC devices, the concept of hybrid AC-DC systems attract more and more attention. This study proposes an innovative hybrid storage system for buildings, in combination with a DC heat-pump to maintain thermal comfort, and a hybrid AC-DC distribution system for the interconnection of the photovoltaic system, battery and electrical loads of the building. Photovoltaics, battery and DC devices are connected to the DC part, avoiding losses from unnecessary conversions, while AC loads are connected to the AC part. This solution has been tested in a historical building in Cyprus and the results indicated significant benefits. For the case of the proposed system the imported energy (<5,4 kWh/day) is limited to the 1/3 compared to the case of typical prosumer. Finally, the overall share of renewables reaches values > 85%. This article describes the innovative system and assess its performance in real conditions regarding the energy consumption/production, indoor comfort conditions, and battery behavior.

Spin Accumulation in Acoustically Excited Ni/GaAs/Ni Trilayers

In this paper, we report the first theoretical results on the acoustic generation of spin accumulation in ferromagnet-semiconductor-ferromagnet trilayers. As a representative material system, we consider a Ni/GaAs/Ni trilayer coupled to a piezoelectric transducer, which injects a planar acoustic wave into the adjoining Ni film. By combining an analytical solution of the spin diffusion equation in the GaAs spacer with results of numerical simulations of the coupled elastic and magnetic dynamics in the Ni films, we quantify an oscillating inhomogeneous spin accumulation in GaAs. It is found that both dc and ac parts of the mean spin accumulation vary nonmonotonically with the spacer thickness [Formula: see text], reaching maximal values at [Formula: see text] mostly close to 0.25 or 0.75 of the wavelength of the injected monochromatic acoustic wave. Remarkably, the transverse wave generates the spin accumulation much more efficiently than the longitudinal one. Our theoretical predictions provide guidelines for the development and optimization of energy-efficient acoustic spin injectors into semiconductors, which should have much lower power consumption than injectors driven by the microwave magnetic field.

Adaptive Droop Control Strategy for Load Sharing in Hybrid Micro Grids

Energy management becomes essential when distributed energy sources such as solar, wind, and fuel cell are connected in a micro-grid. In this paper, using a combination of two powerful neural network tools and fuzzy logic, intelligentization, and adaptation of droop control along with voltage and current control as one of the most common methods of decentralized control is done. One of the essential features of this method is its fast performance and the need for telecommunication infrastructure. In this paper, we provide a comprehensive control system that enables proper operation in both upstream and island network modes for both AC and DC microgrids. The proposed method is simulated to evaluate its effectiveness. The proposed structure, by adapting the control system by ANFIS structure, can properly distribute power between distributed products in a brilliant way and without the need for operators and costly telecommunications infrastructure in the face of severe disturbances such as change. The state between the connection and the island or fault occurrence ensures the stability of both the AC and DC parts of the microgrid. The results show the effectiveness of the proposed method.

Operator splitting based structure-preserving numerical schemes for the mass-conserving convective Allen-Cahn equation

The mass-conserving convective Allen-Cahn (MCAC) equation is an important component of phase field modeling for the multiphase fluid coupled with a flow field. It inherits the maximum bound principle (MBP) from the classic Allen-Cahn equation, in the sense that the time-dependent solution under appropriate initial and boundary conditions preserves a uniform point-wise bound in the absolute value for all time. In this paper, we develop two structure-preserving numerical schemes for the MCAC equation based on the operator splitting approach. In particular, the advancing of the MCAC equation at each time step is split into two (first-order splitting in time) or three (second-order splitting in time) stages, and each of the stages consists of either a mass-conserving AC equation or a transport equation. The mass-conserving AC part is then discretized by using the classic finite volume approximation in space and the stabilized exponential time differencings in time and the resulting system can be efficiently solved via fast Fourier transform based algorithms. The transport part is solved by explicit strong stability preserving Runge-Kutta substeppings combined with a maximum-principle-satisfying finite volume method. Optimal error estimates are derived for the proposed fully-discrete schemes, as well as preservation of the discrete MBP and conservation of the mass. Various numerical examples are also presented to verify the theoretical results and demonstrate the performance of the proposed schemes.

Holomorphic embedding power flow modeling of autonomous AC/DC hybrid microgrids

Developing an effective and reliable power flow (PF) tool is of great significance for the steady-state analysis of autonomous AC/DC hybrid microgrids (MGs). In this paper, a generalized PF model is constructed based on holomorphic embedding (HE). With a well-designed embedding technique, the nonlinear PF problem is modeled into an embedded system, which comprehensively accounts for the distinct features of islanded hybrid MGs (such as droop-regulated distributed generations (DGs) and AC/DC interlinking converters (ICs), the variation of system frequency and its effect on admittance matrix and loads in AC part). The embedded system has a generalized structure with a constant sparse matrix, which not only enables it to be solved recursively and efficiently, but also facilitates wide applicability and convenient operation. Moreover, the proposed HE-based model features a deterministic germ that relates to a physical state, which allows it to inherit the merit of the canonical embedding in converging to upper-branch solution reliably and unambiguously, without dependency on initial estimates of state variables. The feasibility and applicability of the proposed model are validated on 3 test systems of different sizes. Furthermore, the computational efficiency and convergence performance are also evaluated.

AC compensation of 3D magnetic diagnostic signals in DIII-D and National Spherical Torus Experiment-Upgrade (NSTX-U) for real-time application.

A time domain algorithm has been developed to remove the vacuum pickup generated by both coil current (DC) and induced vessel current (AC) in real time from three dimensional (3D) magnetic diagnostic signals in the National Spherical Torus Experiment-Upgrade (NSTX-U) and DIII-D tokamaks. The possibility of detecting 3D plasma perturbations in real time is essential in modern and future tokamaks to avoid and control MHD instabilities. The presence of vacuum field pickup, due to toroidally asymmetric (3D) coils or to misalignment between sensors and axisymmetric (2D) coils, pollutes the measured plasma 3D field, making the detection of the magnetic field produced by the plasma challenging. Although the DC coupling between coils and sensors can be easily calculated and removed, the AC part is more difficult. An algorithm based on a layered low-pass filter approach for the AC compensation and its application for DIII-D and NSTX-U data is presented, showing that this method reduces the vacuum pickup to the noise level. Comparison of plasma response measurements with and without vacuum compensation shows that accurate mode locking detection and plasma response identification require precise AC and DC compensations.

Measurement and automatic monitoring insulation resistance of AC/DC mixed unearthed networks

Where the danger of electric shock is high, for example underground mines or medical equipment directly connected to a patient, special ungrounded power systems (unearthed networks) may be used to minimize possible leakage current to the ground. In mixed unearthed networks (AC/DC-IT) comprising alternating and direct current circuits, AC part of system is connected with DC part through rectifyer valves. Commutation of the valves causes cyclic variation of configuration of the entire galvanically connected network. A distinct feature of AC/DC-IT systems is that voltages between all points of AC side and ground may have mean value different from zero. This characteristic parameter can be used as a signal to determine fault and position to ground or decrease in insulation resistance. However, it also affects the results of the network equivalent insulation resistance measurements when a DC source is used to check insulation. The paper presents a solution to eliminate this effect and proposes a device model to measure and monitor insulation resistance. The results of this study can be applied in the design and manufacture of automatic resistance measuring and monitoring devices for AC/DC mixed unearthed networks.

Islanded AC/DC microgrids supervisory control: A novel stochastic optimization approach

Load demand has locally met the distributed energy resources (DERs) under an infrastructure that is called microgrid. In this paper, a new supervisory control approach is presented based on MPC method, using a stochastic optimization model. The objective function (OF) of the proposed central controller consists of the combined cost-based and system-based parts. Indeed, the setpoints of DERs are updated by the supervisory control method to regulate voltage and frequency to their nominal values as well as to decrease the generation costs. The stochastic optimization formulation is conducted based on MPC structure. Moreover, the uncertain nature of DERs is considered in the optimization formulation and MPC framework using several scenarios. In addition, the effect of reactive power on frequency is considered in this paper and the results show better voltage and frequency regulations. The algorithm is implemented on a modified IEEE 33-bus test system with AC and DC parts. Furthermore, several cases and the sensitivity analysis are accomplished to show the efficiency of the proposed model.

Enhancement of power quality issues for a hybrid AC/DC microgrid based on optimization methods

The purpose of this paper is to study the harmonic behavior of hybrid microgrids (MGs). To achieve the desired goal, a modified active power filter (MAPF) and a power filter compensator kit (PFCK) modules have been used to improve the harmonics of the AC part of the system. The main challenge and feature of this research is the optimization of MAPF and PFCK controller gain coefficients hierarchical, using Harris hawk optimization (HHO), grasshopper optimization algorithm (GOA), artificial bee colony (ABC), and differential evolution (DE), respectively. Following, this technique was applied in the three control loops including, voltage and current harmonics, and system controller error to reduce the range of the mentioned harmonics to the permissible range. The method will be interesting considering that the PI and PID tuning is based on parallel feed-forward. The programmed objective functions include the three components current THD, voltage THD and controller error hierarchically. From the point of view of the MGs hierarchical control, the method presented in this study will be implemented in the second level of hierarchical control. In order to improve the operation of the DC part of the grid, a boost converter module (BCM) has been introduced in the form of a new synchronization scheme. The output of the simulation shows the reduction of the harmonic amplitude of the system by the mentioned modules.

The Possibility of Enhanced Power Transfer in a Multi-Terminal Power System through Simultaneous AC–DC Power Transmission

The feasibility of power transfer enhancement, through simultaneous AC–DC power transmission in a two-terminal transmission network, has been proposed earlier by the authors, and the concept is well established. To meet the increase in demand for electricity, a new technique is proposed in this article to increase the use of existing transmission lines in addition to independent control of AC and DC power flow. This paper extends the concept to a three-terminal transmission network by considering a power tapping from the middle of the line. DC is also superimposed in the already existing three-terminal AC transmission system. In the proposed topology, a multi-terminal simultaneous AC–DC system is used, which is integrated with a zig-zag transformer and more than two voltage source converter (VSC) stations. Each terminal may represent an area of the power system. Anyone/two-terminal(s) may act as sending end, whereas the remaining two/one terminal(s) may act as receiving end. Power can flow in either direction through each segment of the transmission system. At sending end, VSC converts a part of AC to DC and injects it into the neutral of the zig-zag transformer. On receiving terminal, DC power is tapped from neutral of zig-zag transformer and fed to VSC for conversion back to AC. The concept is verified in the digital simulation software PSCAD/EMTDC.

Spin–glass behavior in Shastry–Sutherland lattice of Tm[formula omitted]Cu[formula omitted]In

The spin–glass behavior in the ferromagnetic phase of Tm2Cu2In was investigated by dc–, ac–magnetization, and non-equilibrium dynamics characterizations. An argon arc–melted polycrystalline sample of the compound of Tm2Cu2In was found to adopt the Mo2FeB2–type tetragonal structure (space group P4/mbm). The temperature variation of dc–magnetization exhibits a ferromagnetic behavior with Curie temperature TC = 32.5 K. The zero field cooled (ZFC) and field cooled (FC) magnetic curves show the thermomagnetic irreversible behavior below TC. The field dependence of irreversible temperature follows the Almeida–Thouless line. The frequency and ac–driven field dependent anomalies in ac–susceptibility results indicate the existence of a spin–glass state in Tm2Cu2In. The time dependence of magnetization further supports the spin–glass behavior observed in Tm2Cu2In. The frequency dependence of the freezing temperature in the real part of ac–susceptibility has been analyzed on the basis of a power–law divergence and Vogel–Fulcher law. The obtained results reveal that Tm2Cu2In belongs to the ferromagnetic canonical spin–glass class of compounds.

Interconnected hybrid AC-DC microgrids security enhancement using blockchain technology considering uncertainty

Recently, interconnected (networked) hybrid AC-DC microgrids have been attracted lots of attentions due to both technical and economic advantages, compared to the conventional interconnected microgrids. In such a system, the DC sources, e.g., solar energies, are connected to the DC busses, while the AC sources, e.g., wind turbines, are connected to the AC busses. Hence, the entire efficiency of the system can be increased significantly. Also, it is more economical than the conventional grids due to removing power electronics interfaces that convert DC to AC power. Although there exist many advantages associated with such a system, there exist many challenges as well. For instance, the energy management of the system, from the system level perspective is more challenging since any changes in any subsystem (AC or DC parts) can potentially affect the energy management of the entire system. To this end, in this paper, a new modified sine cosine algorithm (SCA) is developed to find the optimal solution. Moreover, to increase the security of the power trading within the hybrid AC-DC networked microgrids, the blockchain technology is used and adopted. To make a realistic model, a stochastic load flow, based on copula mode has also been employed. Results demonstrate the effectiveness of the proposed blockchain-based hybrid networked AC-DC microgrid energy management framework.

Backstepping Predictive Control of Hybrid Microgrids Interconnected by Neutral Point Clamped Converters

In this work, DC and AC parts of hybrid microgrids are interconnected by a neutral point clamped—NPC converter controlled using a new backstepping predictive (BP) method. The NPC converter is controlled to operate in the DC microgrid voltage control mode or in the AC microgrid power control mode. The novel backstepping predictive controller is designed using the dq state space dynamic model of the NPC converter connected to the hybrid microgrid. The designed BP controller regulates the DC voltage or AC injected power, balances the capacitor voltages, controls the AC currents, and enforces the near unity power factor. Simulation (MATLAB/Simulink) and experimental (laboratory prototype) results show that the converter can regulate the DC voltage in the DC microgrid interconnection point, by adjusting the AC power conversion to compensate variations on the loads or on the distributed renewable energy sources in the DC microgrid. AC currents are sinusoidal with low harmonic distortion. The obtained BP controller is faster at balancing capacitor voltages than PWM (pulse width modulation) control with carrier offset. The fast AC power response allows the converter to be used as a primary frequency regulator of the AC microgrid. This research is appropriate for power and voltage control in hybrid microgrids with renewable energy.

Sequential network‐flow based power‐flow method for hybrid power systems

This paper presents a sequential network-flow graph-based method for a steady-state power flow solution in hybrid multi-terminal power systems. The proposed method is a unique and novel one, which differs from other established methods that involve the use of modified versions of classical power flow methods. The proposed method formulates a power flow problem as a maximum network-flow problem and solves it using a push-relabel max-flow algorithm. The solution procedure solves AC and DC parts sequentially, while accounting for voltage source converter losses using a generalised converter model. The proposed flow-Augmenting method solves the power flow problem using matrix vector multiplication in its most abstract form, and it is independent of system parameters and network configuration. The proposed formulation is computationally efficient, as it is based on matrix vector multiplication, and is scalable, because the formulation works as a graph-based method, which, inherently, allows for parallel computation for added computational speed. Further, unlike previously reported methods, the proposed method does not rely on Jacobian matrix formulation or any matrix inversion. This proves to be a strong advantage for the proposed method, as a significant reduction in computational time is observed, as a result. The proposed method is validated on 5-bus hybrid system and CIGRE B4 DC system.