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Research and Design of Microgrid Simulation System Based on Single Chip Microcomputer

With the continuous development of modern power electronics and chip technology, numerical control inverter power supply is more and more widely used in industrial control and civil fields. High performance numerical control inverter has become one of the research focuses in the power supply field. In this paper, a micro grid simulation system based on single-chip microcomputer is designed. The effective value of the load line current of the inverter part is within 2A, the effective value of the line voltage changes within 24V ± 0.07V, the frequency fluctuation is 50Hz ± 0.2Hz, the total harmonic distortion (THD) of the AC bus voltage is not more than 1.6%, and the power output efficiency reaches 91.6%, achieving good performance. In addition, the system can manually set the power supply output voltage frequency by pressing the key, and display the output voltage and current in real time. At the same time, the system has over-current protection function, which greatly improves the safety and stability when the current is too large.

Review of Discrete Fourier Transform During Dynamic Phasor Estimation and the Design of Synchrophasor Units

In a large and complex interconnected power system, the measurement of synchronized bus voltage and line current plays a vital role in the monitoring and precise control of various sophisticated electrical equipment for secure and reliable operation. Phasor measurement units (PMUs) are incorporated into a wide area of the power system to extract the different signals of synchronized phasors. In this paper, the capacity of the PMU phasor estimation algorithm is explored based on discrete Fourier transform (DFT) under different sampling frequency rates during various dynamic scenarios in accordance with the IEEE C37.118.1a-2014 standard. Furthermore, the performance of the DFT algorithm varies according to the phase angle and dynamic parameters such as frequency, frequency ramp rates, modulation frequency, harmonic levels, step change, decaying dc, and noise levels. The simulation results reveal that accuracy of the phasor estimation algorithm based on DFT can be achieved at high sampling frequency rates. Furthermore, the results of DFT-based phasor estimation are compared with Shank’s estimation method (SEM) and the least-squares estimation method (LEM). The presented method is best suited to PMU algorithms development based on DFT for better visualization of the smart electric grid.

Optimized planning of chargers for electric vehicles in distribution grids including PV self‐consumption and cooperative vehicle owners

AbstractThis paper presents a mathematical model to site and size the charging infrastructure for electric vehicles (EVs) in a distribution grid to minimize the required capital investments and maximize self‐consumption of local PV generation jointly. The formulation accounts for the operational constraints of the distribution grid (nodal voltages, line currents, and transformers' ratings) and the recharging times of the EVs. It explicitly models the EV owners' flexibility in plugging and unplugging their vehicles to and from a charger to enable optimal utilization of the charging infrastructure and improve self‐consumption (cooperative EV owners). The problem is formulated as a mixed‐integer linear program (MILP), where nonlinear grid constraints are approximated with linearized grid models.

Development of a Comprehensive Analytical Model of Induction Motor Under Stator Interturn Faults Incorporating Rotor Slot Harmonics

The objective of this article isto developa comprehensive mathematical model of a three-phase induction motor to facilitate stator interturn (SIT) fault related study. A detailed analytical model that includes accurate inductance modeling considering rotor slot harmonics (RSH) under healthy as well as SIT faults is described. The proposed model is developed analytically in a step-by-step manner incorporating the features of RSH. A detailed but simplified analysis considering both magnetomotive force harmonics and air-gap flux harmonics has been presented. An asymmetric model is proposed, including SIT faults, in a single phase of the induction motor in the next stage of the modeling. The effect of saturation has also been considered in the model. The proposed model is validated by comparing the simulation results in transient, steady state, and frequency domain with the experimental results. Comparison shows a high degree of correlation with the results of the actual motor. The contributions of this work are justified by comparing the proposed model with the existing models. This article also shows that a frequency signature related to RSH present in the line current is capable of characterizing the SIT faults.

A grid-side multi-modal adaptive damping control of super-/sub-synchronous oscillations in type-4 wind farms connected to weak AC grid

• A multi-modal damping control (MADC) is proposed to damp multiple oscillation modes independently. • A general design framework for damping multiple oscillation modes is given. • MADC is validated to damp sub-synchronous and super-synchronous oscillations in Type-4 wind farms. Type-4 wind farms connected to weak AC grids have the risk of sub-synchronous oscillation/interaction (SSO/SSI) with multiple oscillation modes, which can lead to unplanned outages and system destabilization. This paper first presents the magnitude and frequency characteristics of the oscillations followed by the control design requirements. Then, it gives a general design of grid-side multi-modal adaptive damping control (MADC) to stabilize multiple oscillation modes. The MADC utilizes an FFT-based inter-harmonic phasor measurement algorithm, which can detect and track multiple oscillation modes simultaneously. The MADC uses bus voltages and line currents as inputs to extract and control each oscillation mode without considering the coupling of the modes due to the frequency coupling effect. The unstable modes are stabilized by injecting phase-shifted currents with multiple frequencies such that the impedance response of the whole system around the concerned frequencies is reshaped. Notable features of the proposed damping control include automatic and independent detection, tracking and suppression of multiple oscillation modes. The proposed MADC's damping performance is validated through extensive electromagnetic transient (EMT) simulations of type-4 wind farms connected to a weak ac grid causing super-/sub-synchronous oscillations. The system model and the proposed damping control are designed and tested in commercial EMT software.

Power Disequilibrium Suppression in Bipolar DC Distribution Grids by Using a Series-Parallel Power Flow Controller

The unbalanced power between positive and negative poles in a bipolar DC distribution network (DC-DN) generates an unbalanced current at the neutral line, which enlarges the power losses of the system and the voltage deviation of DC loads. An unbalanced power suppression strategy based on a series-parallel power flow controller (SP-PFC) is proposed in this paper. The SP-PFC is adopted as the interconnection between two different DC-DNs. The topology and operating modes of SP-PFC are analyzed. Subsequently, SP-PFC output voltage and line current expressions under constant power control are derived. The nonlinear relationship between the output voltage and line current is linearized at the operating point. On this basis, the influences of unbalanced load and receiving-end voltage on the SP-PFC are investigated. A small-signal model of bipolar DC-DN containing an SP-PFC is established, and the system stability is analyzed. A simulation model of the bipolar DC distribution network containing an SP-PFC is built up in MATLAB/Simulink, and the effectiveness of the SP-PFC in the suppression of unbalanced power is verified.

A Fast Actuation Mechanism and Energy-Effective Driving Method for Pulse-Closers

When a recloser detects fault currents in electric power distribution lines, it breaks the line and then restores the line after several fault tests. To check whether fault remains, the recloser performs CO operations (opening the contacts after reclosing them for a while). In this operation, the fault currents flow into the line, potentially causing damage to equipment connected to the line. Therefore, reducing the current-carrying time during the fault test is desirable, but this reduction is difficult because of the slow actuation mechanism of reclosers. In this article, a novel actuation mechanism combining a permanent magnetic actuator (PMA) and a solenoid actuator (SA) is proposed. During the CO operations for the fault tests, the proposed mechanism can rapidly break the closed contacts by hitting the moving contact with the SA. To increase the energy efficiency of the actuation mechanism, a distinctive PMA driving method is also proposed; it weakens the strong holding force of the PMA using assistive magneto-motive force (MMF). The structure and configuration of the proposed mechanism are explained. The performance of the mechanism and the effectiveness of the driving method are studied through cosimulations. Finally, a prototype is developed, and its practicality is verified through experiments.

Data-driven fault detection and isolation in DC microgrids without prior fault data: A transfer learning approach

The lack of fault data is the major constraint on data-driven fault detection and isolation schemes for DC microgrids. To solve this problem, this paper develops an adversarial-based deep transfer learning model that can detect and classify short-circuit faults in DC microgrids without using historical fault data. In this transfer learning framework, the knowledge of faults is extracted from the transient features of line currents during normal operating disturbances, which is adversarially augmented and then transferred to a target domain as the labels of faults. With the transferred knowledge, a deep learning model combining convolutional neural network and attention-based bidirectional long short-term memory is trained, which is strengthened by attention and soft-voting ensemble mechanisms. In verification tests, this model reaches a high accuracy of over 90% in classifying various short-circuit faults in a multi-terminal DC microgrid model within a short response time of less than 1 ms. Moreover, it is robust against measurement noises and adaptive to system configuration changes. The test results prove the effectiveness of the proposed method in the protection of DC microgrids without prior knowledge of faults.

ЕЛЕКТРОФІЗИЧНІ ПРОЦЕСИ ДЕГРАДАЦІЇ ЗШИТОЇ ПОЛІЕТИЛЕНОВОЇ ІЗОЛЯЦІЇ СИЛОВИХ КАБЕЛІВ І САМОУТРИМНИХ ІЗОЛЬОВАНИХ ПРОВОДІВ ЗА НЕСИНУСОЇДНИХ НАПРУГАХ І СТРУМАХ

The features of electro-physical processes of degradation of cross-linked polyethylene (XLPE) insulation of power cables and self-carrying insulated wires (SIW) are studied, taking into account water microinclusions and dendrite branches that appear in such insulation during manufacture and operation. It is substantiated that the appearance of non-sinusoidal voltages and cur-rents in power transmission lines (TL) using modern power cables and SIW with solid XLPE insulation causes an increase in electro-physical factors aimed at increasing the pulsating electromechanical pressure on the surface of solid XLPE insulation by liquid conductive microinclusions and dendrite branches and an increase in over time, their sizes along the strength of the exist-ing electric field (EF). The paper defines the patterns of change over time in the magnitude of the stressed volume and the maxi-mum pressure in the XLPE insulation and the additional impact on such patterns of higher harmonic components of electrical voltages and currents during non-sinusoidal processes in such insulation. It is indicated that such electro-physical effects on solid polymer insulation lead to an increase in the intensity of both threshold mechanisms and stochastic ones of destruction of the microstructure of the solid XLPE insulation of power cables and self-carrying insulated wires and require the development of additional regulations for standard conditions for their manufacture and operation. References 10, figures 3.

Robust fuzzy stabilization control for the traction converters in high-speed train

High-speed railways have quickly gained popularity as an environmentally beneficial mode of transportation. In addition, converters and electric motors are becoming more widely used. However, power converters and motors can act as constant power loads when tightly controlled, making the source converters unstable. In this article, robust fuzzy control is proposed for stabilizing power electronic converters feeding a constant power load in a high-speed train. The negative incremental resistance characteristics of the trains are first investigated. Then, utilizing the Takagi–Sugeno fuzzy model and the parallel distributed compensation approach, a robust stabilizing controller is constructed to ensure asymptotic descent of the dynamic system state trajectories toward the equilibrium position. Moreover, using linear matrix inequalities, the intended control gain can be automatically computed. The critical adjustment time of the controller and total harmonic distortions of the line currents are selected to measure and compare the dynamic stability of the designed controller. The suggested technique not only maintains global stability in the face of considerable changes in the constant power loads, but it also offers a fast dynamic reaction time and precise tracking over a wide operating range. Finally, simulations and experiments are performed to validate the proposed approach.

Coordinated control of distributed renewable energy in bipolar DC microgrid based on modulus transformation

The coupling between the positive and negative poles of the bipolar DC microgrid will influence the voltage control which makes it difficult to compute the parameters of the control loop independently. The unbalanced voltage in the bipolar DC microgrid is a special power quality problem. The suppression of unbalanced voltage is a significant work in operation planning. In this paper, the expressions of voltage unbalance coefficient and distribution line current is deduced to investigate the influence of unbalanced loads on voltage deviation, voltage unbalance coefficient, and current distribution accuracy. On this basis, the common-mode and differential-mode consensus control of the bipolar DC microgrid is proposed to improve the dynamic performance of the control system and reduce the voltage deviation and voltage unbalance coefficient. In addition, the small-signal stability is analyzed in this paper. To verify the effectiveness of the proposed modulus control method in the bipolar DC microgrid, a MATLAB/Simulink simulation platform, and a low-voltage experimental platform are established. The proposed modulus control is better than the droop control in regulating unbalanced voltage. In addition, it is still effective under the influence of load change. Moreover, the unbalanced voltage can be controlled when addition PV and BEMS are added in the bipolar DC microgrid.

Short-Circuit Fault Diagnosis on Induction Motors through Electric Current Phasor Analysis and Fuzzy Logic

Online monitoring of induction motors has increased significantly in recent years because these devices are essential components of any industrial process. Incipient fault detection in induction motors avoids interruptions in manufacturing processes and facilitates maintenance tasks to reduce induction motor timeout. Therefore, the proposal of novel approaches to assist in the detection and classification of induction motor faults is in order. In this work, a reliable and noninvasive novel technique that does not require computational demanding operations, since it just performs arithmetic calculations, is introduced for detecting and locating short-circuit faults in the stator windings of an induction motor. This method relies on phasor analysis and the RMS values of line currents, followed by a small set of simple if-then rules to perform the diagnosis and identification of stator winding faults. Obtained results from different experimental tests on a rewound induction motor stator to induce short-circuit faults demonstrate that the proposed approach is capable of identifying and locating incipient and advanced deficiencies in the windings’ insulation with high effectiveness.

Disturbance Observer Based on Fixed Time Sliding Mode Control and Optimal State Observer for Three-Phase Three-Level T-Type Inverters

This paper presents the advanced control method together with the disturbance rejection method with the aims to obtain the low of total harmonic distortion (THD). The expectation of the paper is that the output voltage is satisfied the requirements of the EN 62040 with the THD is less than 5%. Therefore, this paper proposes a new disturbance observer (DOB) without the requirement of the information of the first derivative disturbance for the three phase three level (TPTL) T-type inverter system. The proposed DOB is based on the information of the measurable states, which are used such an inversed model of T-type inverter to find the information of real disturbance. First, the DOB was designed based on the given measured and estimated states. However, to design the DOB, the state observer is required. Therefore, second, the state observer (SOB) was designed based on linear matrix inequality (LMI) to identify the optimal poles of the state-tracking error function. Third, the estimated states were used to construct the fixed time (FT) sliding mode control (SMC) to control the T-type inverter system. Fourth, the Lyapunov condition was used to verify the correction of the proposed method. The performance of the proposed control strategy is validated by simulations and experiments during steady-state, transients caused by load change, and unbalanced grid conditions. The estimated states precisely tracked the measured states. The output signals precisely converged to the predefined trajectories in a predefined time and the tracking errors are small. The obtained results showed that the proposed control method provided excellent steady-state and good performances with low THD in the line currents, zero steady-state error in the output voltage, and a very fast dynamic response.

Protection of DC Microgrids Based on Complex Power During Faults in On/Off-Grid Scenarios

The DC microgrid is an effective platform for integration of renewable energy sources, energy storage systems, and smart electronic loads. However, the integration of distributed generators can result weak fault currents with change in its direction during fault conditions, which lead to failure of conventional over-current relays with poor coordination. The above scenario may exhibits relay mal-operation and force the DC microgrid into blackout mode which is extremely undesirable. Thus, this paper proposes an complex power concept (real and imaginary), which can be extracted using Fast Fourier Transform (FFT) to construct the effective protection schemes for rapid short-circuit fault detection and fault isolation in a DC microgrid. To achieve fault isolation, solid-state DC circuit breakers are used in conjunction with proposed real and imaginary power, which is extracted from the total FFT power signal (i.e. by using bus voltage and line current). Further, the relay trip threshold value for real and imaginary power is also determined under various pole-pole (P-P) and pole-ground (P-G) fault scenarios in the DC microgrid. The proposed protection scheme is validated on simple and modified IEEE 9-bus DC microgrids under various P-P and P-G fault scenarios during On/Off-Grid modes through MATLAB/Simulink software. The simulation results reveal that the proposed protection scheme based on real and imaginary power has accurately identified the fault in the simulated DC microgrids. Thus, the proposed complex power based fault identification approach can be quite effective for protection of DC microgrids during On/Off-Grid scenarios.

Prediction interval estimation of dynamic thermal rating considering weather uncertainty

Uncertainty and randomness of weather bring challenges to the accurate estimation of dynamic thermal rating (DTR). To reduce the impact of weather factors on the DTR predictions and to further enhance transmission line ampacity. An ensemble empirical mode decomposition quantile regression temporal convolutional network (EQRTCN)-based interval prediction model is proposed for DTR. Different from the existing DTR techniques, the model overcomes the effects of weather non-smoothness and uncertainty on prediction intervals with low quality by ensemble empirical mode decomposition (EEMD) and quantile regression theory. In this work, a k-means clustering algorithm is first used for the time boundary condition division by considering the coupling between line currents and weather parameters. Then, based on different time boundary conditions, the DTR interval prediction model is proposed by using EEMD, quantile regression theory and temporal convolutional networks. Finally, the proposed improved method for ampacity calculation is incorporated in the EQRTCN to calculate the prediction interval of DTR. The model simulation results demonstrated that the proposed DTR prediction framework effectively reduced the uncertainty introduced by meteorological parameters in interval predictions and provided safe guidance for power dispatch. • Propose a novel EEMD-guided TCN model based on the QR method. • Design a novel time boundary condition division method. • Propose an improved method for line ampacity calculation.

Input Current Step-Tripling for 12-Pulse Rectifier Using a Passive Four-Tap Changer

To effectively suppress the input line current harmonics of a 12-pulse rectifier under slightly complex hardware, this article proposed an input line current step-tripling scheme for a 12-pulse rectifier using a novel passive four-tap changer (FTC). The proposed FTC consists of a retrofitted four-tap interphase reactor (RFT-IPR) and four auxiliary diodes. Two auxiliary diodes are connected to the inner taps of the RFT-IPR, but the other two auxiliary diodes are connected to the outer taps of the RFT-IPR. The inner and outer auxiliary diodes modulate and increase the output current states of the rectifier bridges together first; then, the FTC extends the 12-step to 36-step input line current, and the near sinusoidal input current with 3% THD is obtained. The proposed FTC not only has a very low capacity (2.6% of the output power) but also does not require any active switching device aside from four auxiliary diodes; thus, the proposed scheme is a cost-effective, reliable, and efficient solution to harmonics pollution. An experimental prototype with an output power of 2.4 kW is built, and the correctness of the theoretical analysis is verified by the experimental results.

АЛГОРИТМ ВЫЧИСЛЕНИЯ ЕМКОСТНЫХ ТОКОВ ПРИ ОДНОФАЗНОМ ЗАМЫКАНИИ НА ЗЕМЛЮ, ИСПОЛЬЗУЮЩИЙ ПАРАМЕТРЫ АВАРИЙНОГО И ДОАВАРИЙНОГО РЕЖИМОВ

Relevance Single-phase earth faults are the most common type of damage in networks with an isolated neutral. At the same time, there are no universal solutions for localization and search of single-phase circuits. The availability of information on the capacitive currents of a damaged line can become the basis for the development of new relay protection and automation algorithms for the localization and elimination of single-phase short circuits in networks with an isolated neutral. The current trend in 6–35 kV distribution networks is the development and implementation of intelligent power grid technologies that allow for high-precision measurements and data transmission. The article presents, developed by the authors, an algorithm for calculating capacitive currents in single-phase earth faults using technologies of intelligent electrical networks. Aim of research Development of an algorithm for calculating capacitive line currents in single-phase earth fault using the parameters of emergency and preemergency modes. Creation of a simulation model of a device implementing the developed algorithm, and subsequent evaluation of the algorithm based on the results of simulation modeling. Research methods The study of the developed method was performed in the Matlab Simulink software package. Results An algorithm for calculating capacitive currents in a single-phase earth fault using the parameters of emergency and pre-emergency modes is presented and described in detail. The conducted studies of the developed algorithm using simulation modeling have shown high accuracy in calculating capacitive currents in the single-phase earth fault mode.

Low Frequency Ripple Reduction in Input DC Current and AC Line Currents With 240$^{\circ }$ Clamped Space Vector PWM in Grid-Connected Photovoltaic Converters

Low Frequency Ripple Reduction in Input DC Current and AC Line Currents With 240$^{\circ }$ Clamped Space Vector PWM in Grid-Connected Photovoltaic Converters

Reducing Low-Frequency Ripple Using Alternative Output Capacitor Connection on Integrated Converters for LED Drivers

Although advantageous in several aspects, the integration of converters leads to a loss of independence between the converter's stages, since both stages are controlled by the same active switch. This condition makes it impractical to adopt control techniques that act on the duty-cycle to mitigate the low-frequency ripple at the output current without distorting the line current. The low-frequency ripple transferred from the bus voltage to the LED current has been studied for integrated converters operated at constant duty-cycle. To comply with IEEE 1789-2015 recommendation, the integrated converters use large capacitors to mitigate the low-frequency ripple. Converters operating in discontinuous conduction mode (DCM) have been widely adopted because they transfer less ripple to the output than converters operating in continuous conduction mode (CCM). A novel circuit arrangement for the buck-boost power control (PC) stage integrated with a buck-boost power factor correction (PFC) stage is explored in this paper as a technique to minimize the low-frequency output ripple for converters operating at constant duty-cycle and CCM. The proposed circuit provides current feedback to the bus capacitor, acting to reduce the output current and bus voltage low-frequency ripple. A dynamic model for the proposed converter in CCM is obtained and used to determine the output current modulation as a function of converter parameters. It is shown that the proposed topology leads to a smaller low-frequency ripple than a conventional counterpart at the same operating point. A 95 W design example and a prototype supplying an LED load of 98.8 V / 960 mA for the proposed circuit and the conventional counterpart are presented. The experimental results show that the proposed arrangement can achieve similar results to the conventional circuit in efficiency, THD, or semiconductor stress, while the obtained output current modulation equals to 8.66 % is 3.5 times lower than that in the conventional circuit at same operating point and component values.

Adaptive Fuzzy Supplementary Controller for SSR Damping in a Series-Compensated DFIG-Based Wind Farm

Although using a series compensation technique in a long transmission line effectively increases the transmittable power; it may cause a sub-synchronous resonance (SSR) phenomenon. Gate-controlled series capacitor (GCSC) is an effective method for SSR damping by controlling the turn-off angle. In the previous studies, a constant supplementary damping controller (SDC) was used for controlling the turn-off angle, which can mitigate the SSR phenomenon. However, these methods can not capture the maximum transmittable power at different operating points. In this paper, a fuzzy logic controller (FLC) is proposed to compute the gain of SDC based on the wind speed and the error between the measured and reference line currents for transferring as much power as possible and damping the SSR phenomenon simultaneously. Using the MATLAB/SIMULINK program, the proposed method is tested at different operating points to validate its effectiveness and robustness. Compared to the traditional method (constant SDC), the maximum transmittable power, as well as SSR damping, is achieved in all studied cases by the proposed method (variable SDC).