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A novel center-tapped rectifier with current-balancing and voltage-clamped (CBVC) capability for the LLC resonant converter is proposed. A secondary capacitor is inserted between the contact points of the rectifier diode and the secondary winding of the transformer. The amount of the current flowing through each primary switches and rectifier diodes become almost the same by adopting the CBVC center-tapped rectifier. Equal distribution of the current improves the reliability and lifetime of the primary switches and rectifier diodes. In addition, the voltage across the rectifier diodes in the CBVC center-tapped rectifier is clamped by two times the output voltage. The conduction loss of the rectifier diodes is decreased since the diodes with low forward voltage drop can be used. Moreover, half of the output capacitor is utilized as a secondary side capacitor, which means no additional components. The validity of the proposed converter is verified through experiments on a prototype for 400 VDC input to 45–70 V/4 A output application.

Induction motor current imbalance increases losses, torque ripple and vibrations. Current imbalance is known to appear in artificial lift systems, where motors are driven over long imbalanced cables. Power hardware modifications, namely transposition of cable phases in the wellbore, adjustment of the step-up transformer taps, and addition of balancing inductors have so far been proposed to suppress the imbalance. However, these solutions compromise the system's reliability or involve costly additional equipment, which must be customized according to the cable characteristics. This paper proposes a control method for current balancing of induction motors driven by scalar-controlled variable speed drives. In the proposed method, Second-Order Generalized Integrators (SOGIs) are used to extract the negative-sequence component of the motor currents, which is then suppressed by a Synchronous Reference Frame (SRF) current controller. The frequency and angle information required by the SOGIs and the SRF controller are obtained directly from the scalar algorithm, without needing a position sensor or observer, thus offering a novel, simple, robust and computationally effective implementation, which is also independent of the cable characteristics. The paper presents MATLAB/Simulink simulation results to illustrate the method's operating principles and performance in a variety of transient conditions. Experimental results obtained using full-scale equipment are also provided to demonstrate its effectiveness.

This paper proposes an analytical framework describing how initial capacity and resistance variability in parallel-connected battery cells may inflict additional variability or reduce variability while the cells age. We derive closed-form equations for current and SOC imbalance dynamics within a charge or discharge cycle. These dynamics are represented by a first-order equivalent circuit model and validated against experimental data. To demonstrate how current and state of charge (SOC) imbalance leads to cell degradation, we developed a successive update scheme in which the intercycle imbalance dynamics update the intracycle degradation dynamics, and vice versa. Using this framework, we demonstrate that current imbalance can cause convergent degradation trajectories, consistent with previous reports. However, we also demonstrate that different degradation assumptions, such as those associated with SOC imbalance, may cause divergent degradation. We finally highlight the role of different cell chemistries, including different OCV function nonlinearities, on system behavior, and derive analytical bounds on the SOC imbalance using Lyapunov analysis. [ABSTRACT FROM AUTHOR]

This paper proposes methodology and gate drive circuit that can immediately detect short‐circuit (SC) of multiparalleled SiC‐MOSFETs even under current imbalance condition. Proposed method detects SC current using an integration circuit that can sense di/dt. The detection level of SC current can be adjusted to a desired value regardless of the number of SiC‐MOSFETs connected in parallel. The effectiveness of the proposed approach was experimentally validated for four‐paralleled SiC‐MOSFETs under extreme current imbalance in SC condition. SC was detected within 0.5 μs and all SiC‐MOSFETs were protected without destruction at most 2.2 μs after the onset of SC, for all types of SC 1, 2, and 3. [ABSTRACT FROM AUTHOR]

In this article, a synchronverter-based D-STATCOM with self-synchronization and voltage imbalance compensation capability with independent operation from the power operating modes is proposed. The S-STATCOM's synchronverter base model is first presented in space-vector representation together with its control strategy with standard D-STATCOM control structure. Then, the voltage imbalance compensation loop is proposed, which uses two well-known resonant control structures, the double second-order generalized integrator and a proportional plus resonant controller, in an innovative way to effectively turn the S-STATCOM into a specialized active filter for negative sequence voltage, compensating the voltage imbalance at the point of common coupling by supplying the corresponding oscillating power locally. Simulation and experimental results on a small scale prototype are presented to validate the control strategy, which successfully reduced voltage imbalances from up to 10% to bellow the 2% acceptable levels. [ABSTRACT FROM AUTHOR]

Herein, individual cell currents in parallel connected battery strings are measured using micro‐Hall‐effect sensors. Cells are routinely connected in electrical series and parallel to meet the power and energy requirements of automotive and consumer electronics applications. Cells connected in series have been extensively studied; however, cells in parallel are often assumed to be a "black box" in battery management systems. Poor pack design can result in positive feedback between current and temperature differentials along the parallel string, driving greater levels of heterogeneous behavior and uneven degradation. Herein, a noninvasive multisensor array board using Hall‐effect sensors is used to individually record the current passing through eight parallel connected cells in two different electrical configurations, showing highly heterogeneous current distribution. Characteristic "waves" of current and temperature are found to propagate along the parallel battery string and cell rebalancing is found to occur over hundreds of seconds with individual cell currents of up to 1 C rate. [ABSTRACT FROM AUTHOR]

This article addresses the influence of parameters spread on transient current distribution among parallel-connected silicon carbide (SiC) mosfets and proposes a chips classification method to suppress current imbalance. A comprehensive comparison of parameter spread between silicon (Si) and SiC mosfets is first presented. Then, a new classification criterion, referred to in this article as a distance coefficient of transfer curves (DCTC), is proposed to characterize device spread. In addition, the sensitivity analysis of transient current imbalance (TCI) to device spread is carried out. It is found that TCI increases almost linearly with increasing DCTC. Furthermore, a hierarchical cluster algorithm is developed to achieve an automated chips classification for multiple devices intended for paralleled application. This algorithm may as well facilitate the chip selection process for multiple-chip power module packaging. Moreover, the influence of operating temperature on classification is also discussed. It should be noted that chips classification needs to consider real application conditions and package parasitic. Finally, a test bench with a round layout is designed, to keep circuit layout asymmetry to a minimum, and used to experimentally verify the performance of the classification method. The experimental results validate the effectiveness of the proposed classification method for suppressing TCI. [ABSTRACT FROM AUTHOR]

In an electric vehicle, a large number of lithium-ion cells are connected in parallel. While cells in parallel increase the reliability of the battery pack, it increases the probability of current imbalance between the parallel branches, thus ageing gradient. The current peak in a cell also can exceed the maximum charge current capability of the cell; leading to lithium plating, therefore a safety issue. The temperature gradient within a battery pack amplifies this issue. This work reports the impact of such temperature gradient on current imbalance within parallel connected cells, their long-term impact on degradation and evaluation of current distribution with degradation. Employing a real-world relevant experimental setup, a total of 1400 cycles were performed on a module with four cells in parallel. A temperature gradient of 10 °C was introduced among the cells, and current in individual parallel branches was measured employing Hall-effect sensors. Over the course of the experiment, module capacity decreased by 23.6%. Cells at higher temperature/lower exposure to active cooling experienced higher degradation. However, the cell with the lowest starting capacity, although exposed to nominal module temperature and cooling experienced the highest current amplitude towards the end of discharge/charge and thus the highest resistance degradation. It was found that current in an individual parallel branch was exceeding the maximum rated charge/discharge current by 53%.

Current imbalance in multistring light-emitting diodes (LEDs) is a critical issue. It may cause overcurrent in one or more LED strings, leading to rapid degradation. In this paper, a mixed high-order compensation networks-based wireless power transfer system is proposed to generate multiple constant current outputs. It is composed of an LCC resonant network in the transmitting side, a series resonant network, and multiple CLC resonant rectifiers in the receiving side. The CLC resonant rectifiers are connected in parallel to form multiple independent output channels, and each channel is then connected to an LED string. Based on the analysis of the T resonant circuit and the modeling of coupling coils, multiple constant output currents can be derived. As a result, current balance can be achieved, which is very suitable for driving multistring LEDs. The proposed system also offers a modular, scalable, and maintenance-free design, which can significantly reduce the construction cost and the control complexity. In addition, the inverter in the transmitting side can achieve zero phase angle. A laboratory prototype with dual independent output currents is built to verify the proposed method. The experimental results agree well with the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents the development of a machine learning model for sorting SiC MOSFET devices for paralleling. A multivariate linear regression model is developed and trained with device parameter data (as input) and current imbalance data (as label). Each of the training devices is successively paralleled with one reference device to generate the current imbalance (label) data. Devices with close values of current imbalance when individually paralleled with the reference device are expected to have relatively balanced current sharing when paralleled among themselves. This model is trained with 40 devices and tested with 20 devices. The model shows accuracies of 87.93% and 97.48% in predicting transient and steady state current imbalances, respectively. These accuracy values are obtained by comparing the model's prediction for the 20 testing devices with the actual current imbalance values when these devices are paralleled with a reference device. Based on current imbalance predictions made by these models, the devices are grouped into classes for paralleling applications. The selection of devices for paralleling based on predictions from these models result in a satisfactorily balanced current distribution. The model's performance at higher temperatures is also satisfactory. [ABSTRACT FROM AUTHOR]

The massive installation and deployment of electric vehicle (EV) charging infrastructures requires designing efficient and convenient testing tools for the field testing. This paper presents a novel testing system for the EV off‐board charger, in an application such as field testing and maintenance. The authors discuss the design theory and hardware implementation of the system in first. Two typical charger testing scenarios using the proposed tester are discussed. In addition, the modular structure of the system provides the user with a high degree of flexibility, which allows them to configure their own testing systems according to their applications. Three digital processing approaches for constraining high‐frequency components and harmonics are introduced. The authors demonstrate that the digitalised traditional filter has an overwhelming advantage than the statistical filters in the experimental results. They also validate the function of the proposed testing system with a DC 60 kW charger, by finishing testing items such as the regulation accuracy, current imbalance and extreme temperature testing. Finally, they present a comparative study of recent EV charger testing systems. [ABSTRACT FROM AUTHOR]

This paper proposes a method to suppress the capacitor current imbalance between the phase legs of a three‐phase inverter circuit. This circuit consists of half‐bridge modules and DC‐link capacitors closely connected to each module. It can be designed for low stray inductance between power semiconductor devices and DC‐link capacitors in each module. However, in the conventional structure, the stray inductance between the phase legs may lead to an imbalance in the capacitor current due to the DC‐side resonance phenomenon under a higher switching frequency condition by using a SiC MOSFET. This paper presents the analyses of the equivalent circuit considering the circuit configuration, which suggests that capacitor current imbalance occurs depending on the stray inductance between phase legs. To suppress the capacitor current imbalance, a delta‐type bus bar connecting phase legs is proposed. The experiment results at 300 V and 4.6 A demonstrate the suppression effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A hybrid Linear Quadratic Regulator (LQR) and Proportional-Integral (PI) control for a MicroGrid (MG) under unbalanced linear and nonlinear loads was presented and evaluated in this paper. The designed control strategy incorporates the microgrid behavior, low-cost LQR, and error reduction in the stationary state by the PI control, to reduce the overall energetic cost of the classical PI control applied to MGs. A Genetic Algorithm (GA) calculates the parameters of LQR with high-accuracy fitness function to obtain the optimal controller parameters as settling time and overshoot. The gain values of the classical PI controller were determined through the improved LQR values and geometrical root locus. When MG operates in the grid-tied mode under unbalanced conditions, the controller performance of the Current Source Inverter (CSI) of the MG is considerably affected. Consequently, the CSI operates in a negative-sequence mode to compensate for unbalanced current at the Point of Common Coupling (PCC) between the MG and the utility grid. The study cases involved the reduction of the negative-sequence percentage in the current at the PCC, mitigation of harmonics in the current signal injected by the MG, and close related power quality issues. All these cases have been analyzed by implementing an MG connected at the PCC of a low-voltage distribution network. A numerical model of the MG in Matlab/Simulink was implemented to verify the performance of the designed LQR-PI control to mitigate or overcome the power quality concerns. The extensive simulations have permitted verifying the robustness and effectiveness of the proposed strategy.

In this paper, we propose a new time-frequency based analysis method that monitors the state of the high temperature superconducting (HTS) cable system in a real-time manner and detects the current imbalance of HTS cable system. The new time frequency-based method utilizes the cross Wigner-Ville distribution to analyze the time-frequency localized phase difference of the reflected signal, which varies depending on the insulation characteristics of the HTS cable system. Also, a real-world AC 22.9 kV 50 MVA HTS cable system and a current source are used to validate the performance of the new monitoring method in order to detect current imbalance phenomenon. [ABSTRACT FROM AUTHOR]

The constructive asymmetry of the untransposed overhead lines of a high voltage alternating current is the cause of a great number of difficulties in their operation and modeling. In order to model the operating regimes of such lines, the symmetrical component method, based on constructive symmetry and thus the symmetry of the equivalent phase parameters, is inappropriate, which is why many research papers have been dedicated to either setting up improved modeling methods or to returning to phase coordinate modeling. This paper intends to justify a paradox found on some untransposed overhead lines of a high voltage alternating current during the no-load operating conditions by performing phase coordinate modeling. In such a situation, the transmission or distribution operators measured significant negative values for the active powers on one or two phases at the beginning of the lines. Considering the case of a real untransposed overhead line operating under no-load conditions, the paper starts from presenting the recorded electrical values. Then, the paper moves on to outlining the Carson’s simplified computing relations for calculating the series and shunt primitive equivalent parameters and Kron’s transformation relationships for calculating the phase equivalent parameters. After applying them to the real line, the calculation of the power flow for the no-load operating conditions, which is applied to an equivalent scheme of the line consisting of nine identical octopoles, is performed. Both the untransposed line and its transposed variant are studied here. The values of the electrical amounts obtained by the calculation for the untransposed line are basically similar to those obtained by measuring on the real line, which gives a mathematical confirmation of the so-called paradox. Its occurrence represents the effect of the asymmetry of the equivalent phase capacities, which causes a redistribution of the active powers between the phases of the network to which the overhead line operating in no-load conditions is connected.

In order to study the influence of traction transformers with different connection modes on the negative sequence current of traction power supply system, the current imbalance degree theory of traction transformers with different connection modes is analyzed, and the mathematical models of current imbalance are obtained respectively. Based on MATLAB simulation software and with impedance angle difference and the current ratio as the variables, the mathematical model is simulated numerically, and the current imbalance three-dimensional surface graphs of every traction transformers are obtained. The simulation results show that the impacts of the negative sequence vary with factors such as traction load size, phase difference and traction transformer connection model. [ABSTRACT FROM AUTHOR]

The current imbalance between stator phase windings could shorten the motor life and affect the drive performance, whereas in case of multiphase drive applications, there is not a general current balance control strategy that can apply to symmetrical inverters with any phase number m. Based on the generalized symmetrical component theory, this letter analyzed the values of relative symmetrical components of the multiphase systems in balanced and unbalanced cases. Then, developed from the conventional rotor-flux oriented control (RFOC), the current-balance RFOC is proposed to compensate the current imbalance for symmetrical m-phase inverters. Finally, the experimental results from the five-phase and nine-phase drive systems confirm the validity of the control strategy in eliminating current imbalance. [ABSTRACT FROM AUTHOR]

This work focuses on current sharing between punch-through insulated gate bipolar transistors (IGBTs) connected in parallel and evaluates the mechanisms that allow overall current balancing. Two different control strategies are presented. These strategies are based on the modification of transistor gate-emitter control voltage VGE by using an active gate driver circuit. The first strategy relies on the calculation of the average value of the current flowing through all parallel-connected IGBTs. The second strategy is proposed by the authors on the basis of a current cross reference control scheme. Finally, the simulation and experimental results of the application of the two current sharing control algorithms are presented. [ABSTRACT FROM AUTHOR]

Abstract: The critical currents of the Japanese ITER TF conductors made through an internal-tin and bronze process were preliminarily estimated to be about 5.7K, which approximates the design value of 5.7K, and about 6.1K, respectively, at 68kA and 11.8T using a short conductor sample. To investigate the influence of the current distribution in the sample conductor, a simulation was performed using a lumped circuit model of a cable and static electrical field model for jackets. The simulation results show that a large, non-uniform current distribution is established due to magneto-resistance of the copper in the joint and an imbalance of contact resistance of the strands to the copper and by poor soldering between the copper shoes, results which make a precise evaluation of the critical current performance difficult. The analytical results indicate that the current sharing temperature of the internal-tin and bronze process conductors is expected to be 6.0K and 6.7K, respectively, when the current distribution is uniform. In addition, solder filling of the joints makes the current distribution uniform due to the normal resistance in the high field zone, and the current sharing temperature can be estimated as almost the same as when the current distribution is uniform. The other possible solution is to use a thin copper plate with a low RRR to reduce the influence of magneto-resistance and any non-uniformity in contact resistance. Conductor performance is under-estimated in this case because the non-uniform current distribution still remains. However, the reduction in the estimated current sharing temperature is expected to be a few hundred milli-Kelvins, which seems acceptable as a margin in a qualification trial. [Copyright &y& Elsevier]

Abstract: This paper presents a 2D finite-element analysis of the induced eddy currents on motor and oil well casings of an electrical submersible pump (ESP) oil lifting system. Simulation results revealed that the increase in motor-casing conductivity and/or permeability decreases the eddy-current density on the well casing, contrary to that on the motor casing. Further increase in one or both of these parameters leads to a decrease in both current densities as a result of the skin effect phenomenon. However, the increase of well casing conductivity and/or permeability increases the eddy-current density on the well casing, while that on the motor casing remains unchanged. Increasing the fluid-mixture conductivity does not have any effect on the eddy-current density on the well casing, and for further increase in the fluid conductivity it decreases drastically, contrary to that on the motor casing which remains constant. The higher the current imbalance (including single phasing) and/or motor eccentricity, the higher is the maximum eddy-current density. Consequently, the increase of eddy-current density leads to an increase of the motor and well casings’ temperature, where the latter is known to accelerate the corrosion rate. It can be concluded that the design parameters and the construction of the motor and well casings play an important role in their corrosion. [Copyright &y& Elsevier]

Abstract: This paper presents non-uniformity or imbalance in the transport current of the superconducting toroidal-field coil (TFC) made of multistage cable-in-conductor (CICC) due to inductive current in a strand-to-strand (STS) soldered joint of cylindrical shape and also the relaxation of the inductive current in the conductor. Using an NbTi CICC consisting of 486 strands, a joint sample is fabricated and experimented. An external magnetic field of symmetric trapezoidal waveform is vertically applied to the sample joint. The field maximum and the ramp rate (dB/dt) maximum are 1T and 0.25T/s, respectively. Voltage taps and Hall probes are utilized to measure the inductive voltage and current. Experimental results are analyzed numerically using an infinite electrical transmission line model, which is found to explain our sample system well. The flattop induced current is proportional to the dB/dt. Being different from our expectation that the inductive current will distribute widely over the cross-sectional surface of the joint, it localizes to a narrow region; a triplet located in the outer-most side of the joint, for instance. The relaxation phenomenon in the induced current is observed experimentally. From numerical analysis, the relaxation length is found to increase logarithmically with decreasing dB/dt and saturate at a certain value of dB/dt. [Copyright &y& Elsevier]

The use of power electronic circuits in a wide range of applications has resulted in distorted current waveforms in the power system. This results in nonsinusoidal voltage drops across the transformers and transmission line impedances, resulting in a nonsinusoidal voltage supply at the point of common coupling. Asymmetrical distribution of large, 1-ϕ loads further complicates the issue by causing imbalance in the line currents of the 3-ϕ system. Not only should this imbalance be compensated, other parameters, such as the current total harmonic distortion and the power factor should also be maintained as per the norms. However, the requirements of harmonic free current waveforms and good power factor, under nonsinusoidal voltage conditions, are contradictory to each other. Under these conditions, an optimum performance is the best one can achieve. This paper proposes a new scheme for balancing the currents and obtaining the best compromise between the power factor and current distortion under nonsinusoidal voltage conditions. The technique does not use p-q theory and does not require sequence transformation for power calculations, even though the current is unbalanced. All the details of this work are presented. [ABSTRACT FROM AUTHOR]

In an electric vehicle, a large number of lithium-ion cells are connected in parallel. While cells in parallel increase the reliability of the battery pack, it increases the probability of current imbalance between the parallel branches, thus ageing gradient. The current peak in a cell also can exceed the maximum charge current capability of the cell; leading to lithium plating, therefore a safety issue. The temperature gradient within a battery pack amplifies this issue. This work reports the impact of such temperature gradient on current imbalance within parallel connected cells, their long-term impact on degradation and evaluation of current distribution with degradation. Employing a real-world relevant experimental setup, a total of 1400 cycles were performed on a module with four cells in parallel. A temperature gradient of 10 °C was introduced among the cells, and current in individual parallel branches was measured employing Hall-effect sensors. Over the course of the experiment, module capacity decreased by 23.6%. Cells at higher temperature/lower exposure to active cooling experienced higher degradation. However, the cell with the lowest starting capacity, although exposed to nominal module temperature and cooling experienced the highest current amplitude towards the end of discharge/charge and thus the highest resistance degradation. It was found that current in an individual parallel branch was exceeding the maximum rated charge/discharge current by 53%. [ABSTRACT FROM AUTHOR]

In this letter, a current-sharing method is studied for eliminating current imbalance problem among three single-phase modules in a three-phase three-switch power factor correction converter. The operating principles and design considerations are analyzed and discussed. A 750 W laboratory prototype is implemented and tested to verify the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

• A pack comprising the electro-thermal coupling of individual cells was developed. • Z shape module shows a significant advantage over a ladder configuration. • The correlation between system inhomogeneity and design parameters was quantified. • Contact resistance has the highest impact on the inhomogeneity of a system. • There is not a strong correlation between system inhomogeneity and C-rate. Cell-to-cell variations can originate from manufacturing inconsistency or poor design of the battery pack/thermal management system. The potential impact of such variations may limit the energy capacity of the pack, which for electric vehicle applications leads to reduced range, increased degradation along with state of health dispersion within a pack. The latter is known to reduce the accessible energy and the overcharging/discharging of some of the cells within a system, which may cause safety concerns. This study investigates the short-term impact of such effects, which is highly important for designing of an energy storage system. A generic pack model comprising individual cell models is developed in Simscape and validated for a 1s-15p module architecture. The results highlight that a number of cells and interconnection resistance values between the cells are the dominant factors for cell-to-cell variation. A Z shape module architecture show a significant advantage over a ladder configuration due to the reduced impact of interconnection resistance on differential current flow within the module. Current imbalance is significantly higher for a ladder system and its magnitude is not dependent on the module current. Capacity variation does not have a significant impact on the system. By increasing the capacity variation from 9% to 40% the current inhomogeneity increases from 4% to 13%, whilst 25% resistance variation leads to 22% current dispersion. Further, a linear relationship is observed between the current inhomogeneity and thermal gradient (Δ T). A 30 °C Δ T leads to 24% current variation within the module. [ABSTRACT FROM AUTHOR]

With the continuous improvement in battery life requirements, the modeling, analysis and management of battery pack life become an important topic in the design of electric vehicles. A more realistic and generic modeling method coupling the electrochemical, thermal, SEI formation model of cells, fluid dynamics and the series-parallel circuit model is proposed to accurately describe the coupling relationships and quantify the inconsistencies, including temperature and current. A life model including capacity fade and reliability is established to evaluate the life of lithium-ion battery pack system (LIBPs). And a model implementation method is established to raise the computational accuracy and efficiency, then, it is validated from the perspective of electrochemical, degradation, thermal performance and coupling effect using experiments. Moreover, the multiphysical behavior and life of LIBPs in different situations are analyzed and predicted, followed by the analysis of coupling effect, inconsistency, reliability and economy. The results show the degradation rate of LIBPs first decreases and then accelerates in the whole life. Furthermore, adding series cells is uneconomical to extend the life of LIBPs. Finally, a SoH balanced management method of changing the airflow direction is proposed to extend the life of LIBPs, and the optimal strategy for different SoH inconsistency are obtained. • A more realistic and generic model of battery pack is developed. • More comprehensive physical models are coupled for more accurate analysis and design. • Stochastic uncertainty and reliability are described by the percentile life model. • Quantitative analyses of coupling effects and inconsistencies have been carried out. • A SoH balanced management method and optimal strategy for battery pack is studied. [ABSTRACT FROM AUTHOR]

A hybrid Linear Quadratic Regulator (LQR) and Proportional-Integral (PI) control for a MicroGrid (MG) under unbalanced linear and nonlinear loads was presented and evaluated in this paper. The designed control strategy incorporates the microgrid behavior, low-cost LQR, and error reduction in the stationary state by the PI control, to reduce the overall energetic cost of the classical PI control applied to MGs. A Genetic Algorithm (GA) calculates the parameters of LQR with high-accuracy fitness function to obtain the optimal controller parameters as settling time and overshoot. The gain values of the classical PI controller were determined through the improved LQR values and geometrical root locus. When MG operates in the grid-tied mode under unbalanced conditions, the controller performance of the Current Source Inverter (CSI) of the MG is considerably affected. Consequently, the CSI operates in a negative-sequence mode to compensate for unbalanced current at the Point of Common Coupling (PCC) between the MG and the utility grid. The study cases involved the reduction of the negative-sequence percentage in the current at the PCC, mitigation of harmonics in the current signal injected by the MG, and close related power quality issues. All these cases have been analyzed by implementing an MG connected at the PCC of a low-voltage distribution network. A numerical model of the MG in Matlab/Simulink was implemented to verify the performance of the designed LQR-PI control to mitigate or overcome the power quality concerns. The extensive simulations have permitted verifying the robustness and effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

The constructive asymmetry of the untransposed overhead lines of a high voltage alternating current is the cause of a great number of difficulties in their operation and modeling. In order to model the operating regimes of such lines, the symmetrical component method, based on constructive symmetry and thus the symmetry of the equivalent phase parameters, is inappropriate, which is why many research papers have been dedicated to either setting up improved modeling methods or to returning to phase coordinate modeling. This paper intends to justify a paradox found on some untransposed overhead lines of a high voltage alternating current during the no-load operating conditions by performing phase coordinate modeling. In such a situation, the transmission or distribution operators measured significant negative values for the active powers on one or two phases at the beginning of the lines. Considering the case of a real untransposed overhead line operating under no-load conditions, the paper starts from presenting the recorded electrical values. Then, the paper moves on to outlining the Carson's simplified computing relations for calculating the series and shunt primitive equivalent parameters and Kron's transformation relationships for calculating the phase equivalent parameters. After applying them to the real line, the calculation of the power flow for the no-load operating conditions, which is applied to an equivalent scheme of the line consisting of nine identical octopoles, is performed. Both the untransposed line and its transposed variant are studied here. The values of the electrical amounts obtained by the calculation for the untransposed line are basically similar to those obtained by measuring on the real line, which gives a mathematical confirmation of the so-called paradox. Its occurrence represents the effect of the asymmetry of the equivalent phase capacities, which causes a redistribution of the active powers between the phases of the network to which the overhead line operating in no-load conditions is connected. [ABSTRACT FROM AUTHOR]