Zero Sequence Current Components Research Articles

Single-Phase Charging of Six-Phase Integrated On-Board Battery Charger Using Predictive Current Control

Integrated On-Board Battery Chargers (IOBCs) have shown promise as an elegant charging solution for electric vehicles in recent literature. Although the three-phase charging technique of IOBCs has extensively been discussed in the literature, single-phase charging is still a challenging research topic. The Predictive Current Control (PCC) approach has shown many benefits, including a straightforward algorithm, simple implementation, comparatively quick response, and appropriate performance, when compared to conventional control techniques. This paper investigates the impact of single-phase charging of a six-phase-based IOBC system with different winding configurations using PCC, which, up to the best authors’ knowledge, has not been conceived thus far. Under single-phase charging, the zero-sequence current component is utilized to ensure zero torque production during charging mode. Since the impedance of the zero subspace is highly affected by the employed winding design, the performance of PCC with different winding layouts of either induction machine (IM) or permanent magnet synchronous machine (PMSM) is investigated and compared. The proposed method is experimentally validated using a 1.1kW six-phase IM and a 2 kW 12-slot/10-pole PMSM. Finite Element analysis is also carried out to investigate the effect of single-phase charging mode on the induced radial forces and vibration level when PM machine is employed.

Theory and simulation analysis of parallel operation after main transformer replacement

As one of the most important main equipment in the power system, the safe and stable operation of transformer plays a vital role in ensuring the reliability of power supply. Because the three-phase parameters of the main transformer are not the same, the parameters of each phase and the three-phase load of the power grid are also different, resulting in a certain degree of asymmetry between the three-phase current and voltage of the transformer during normal operation. There will be negative sequence and zero sequence current components. The degree of asymmetry is generally small for the high-voltage power grid, but it has a large impact on the low-voltage side of the main transformer. In this paper, the parameters of two main transformers in a substation are quite different, but when they need to run in parallel, whether they can run in parallel, what are the conditions of parallel operation, these problems have been studied in theory and simulation. The results show that the two main transformers can be operated in parallel under suitable conditions. The actual operation result of a substation’s main transformer is normal, which further verifies the correctness of theoretical calculation and simulation.

Zero-sequence current suppression control for fault current damper based on model predictive control

In a multi-terminal direct current (MTdc) system based on a modular multilevel converter (MMC), high-speed and large interruption capability direct current circuit breakers (dc CBs) are required for dc fault interruption. However, commercializing these breakers is challenging, especially offshore, due to the large footprint of the surge arrester. Hence, a supplementary control is required to limit the rate of current rise along with the fault current limiter. Furthermore, the operation of the dc CB is not frequent. Thus, it can lead to delays in fault interruption. This study proposes the indirect model predictive control (MPC)-based zero-sequence current control. This control provides dc fault current suppression by continuously controlling the zero-sequence current component using circulating current suppression control (CCSC) and by providing feedback to the outer voltage loop and inner current loop of MMCs. The proposed control is simulated for pole-to-pole and pole-to-ground faults at the critical fault location of an MTdc system. The simulation is performed in Real Time Digital Simulator (RTDS) environment, which shows that the predictive control reduces the rate of rise of the fault current, providing an additional 3 ms after the dc fault occurrence to the dc CB to clear the fault. Besides, the energy absorbed by the dc CB’s surge arrester during the pole-to-pole and pole-to-ground fault remains the same with the proposed control.

Testing Ground Fault Protection of Generating Units With Frequency-Selective Grounding

This paper experimentally evaluates responses of ground fault protection for synchronous generators, which are grounded using frequency-selective grounding. Frequency-selective grounding is designed to provide a low ground impedance path (similar to solid grounding) for high frequency zero-sequence current components. This grounding system also provides an impedance similar to a low-resistance grounding for low frequency zero-sequence current components. The frequency-dependent equivalent impedance of frequency-selective grounding can affect ground potential and current, which are typically used as inputs for ground fault protective relays. Effects of frequency-selective grounding on ground fault protection are experimentally evaluated using a 7.5 kVA synchronous generator. Experimental tests are conducted for different implementations of ground fault protection, when responding to fault and non-fault events. Evaluation results detailed in this paper demonstrate the negligible effects of frequency-selective grounding on responses of different ground fault protective relays.

An Active Power Ripple Mitigation Strategy for Three-Phase Grid-Tied Inverters Under Unbalanced Grid Voltages

This letter proposes an active power ripple mitigation strategy for the three-phase three-wire grid-tied inverter. Under the unbalanced grid voltage scenarios, the double-line frequency oscillation will have occurred on the inverter output power and the dc-link voltage. Traditionally, the three-phase four-wire or the three-phase four-leg topology could be adopted to deal with this issue. Besides, the negative and the zero-sequence current component can be controlled to cancel out the power ripple. However, the circuit cost and control complexity might be increased. Therefore, a virtual phase-current regulation (VPCR) method is developed by adding compensation to the current feedback of the fault voltage. The compensation value is consistent with the voltage drop ratio, which can effectively offset the actual power ripple. The main feature of the VPCR is its simplicity, whereas it can be realized via the digital signal processor without adding extra circuit components. Theoretical analysis and mathematical derivations of the VPCR will also be revealed. Finally, a 3 kW prototype circuit with both simulation and experimental results verify the performance and feasibility of the proposed strategy. The experimental results show that the output power ripple can be eliminated with 64.3% via the proposed VPCR.

Ground Fault Protection in Frequency-Selective Grounded Systems Fed by a Single Transformer

This paper presents experimental results for performance tests of ground fault protection schemes applied to a frequency-selective grounded system supplied by a single transformer. Frequency selective grounding systems are designed to present low ground impedance (similar to solid grounding) to high frequency zero-sequence current components and impedance like that of a low-impedance grounded system to fundamental zero-sequence components. The variable impedance of the grounding scheme can impact the response of ground fault protection in terms of accuracy and timing. The laboratory setup includes a single 35kVa 3-phase source transformer with a 340/208-volt secondary voltage. Experimental results detailed in this paper demonstrate the response that may be expected of various types of GFP schemes under fault and non-fault events and conditions.

Ground Fault Protection of Synchronous Generators with Frequency-Selective Grounding

This paper experimentally evaluates responses of ground fault protection for synchronous generators, which are grounded using frequency-selective grounding. Frequency-selective grounding is designed to provide a low ground impedance path (similar to solid grounding) for high frequency zero-sequence current components. This grounding system also provides an impedance similar to a low-resistance grounding for low frequency zero-sequence current components. The frequency-dependent equivalent impedance of frequency-selective grounding can affect ground potential and current, which are typically used as inputs for ground fault protective relays. Effects of frequency-selective grounding on ground fault protection are experimentally evaluated using a 7.5 kVA synchronous generator. Experimental tests are conducted for different implementations of ground fault protection, when responding to fault and non-fault events. Evaluation results detailed in this paper demonstrate the negligible effects of frequency-selective grounding on responses of different ground fault protection relays.

Location of double-circuit grounded cross-country faults in GUPFC-compensated transmission lines based on current and voltage phasors analysis

This paper presents an accurate fault location algorithm for double-circuit grounded cross-country (DCGCC) faults in double-circuit transmission lines (DCTLs) compensated by a generalized unified power flow controller (GUPFC). The algorithm incorporates synchronous current and voltage phasors at both end buses of the line. The proposed algorithm determines the accurate location of simultaneous faults occurring in both line circuits in three basic steps. In the first step, the faulty sections are identified using a zero-sequence current analysis. In the second step, the accurate location of a fault in the circuit on which only a series converter is installed is calculated. Next, by employing the calculated zero-sequence current of this fault point, the zero-sequence current component of the other line circuit, which is equipped with series and shunt converters, is obtained. Finally, the accurate fault location in this circuit is calculated. The calculation process and the derived equations for all DCGCC fault types are described in detail. The GUPFC considered in this study along with the test network is modeled in MATLAB/Simulink environment. The simulation results confirm the accurate performance of the proposed algorithm for various fault types occurring in different operating conditions.

MODWT-XGBoost based smart energy solution for fault detection and classification in a smart microgrid

Electrical power being the key driver for any technology driven development, an intelligent technology enabled smart grid which ensures reliable, environment-friendly and power quality certainly provides the necessary fillip to the urban intelligence. This study introduces a novel differential approach of microgrid fault detection and classification as a smart grid enabler. The proposed microgrid protection scheme (MPS) involves an initial phase of pre-processing through anti-aliasing and filtering out of noise of the retrieved system parameters. This is followed by feature extraction process using Maximal Overlap Discrete Wavelet Transform (MODWT) with an abstract wavelet family of mother wavelet ‘FejerKorovkin’ and three level of decomposition. The differential energy calculated for both three-phase current and its zero-sequence current component at each of the decomposition level of MODWT finally serves as input to an Extreme Gradient Boost (XGBoost) based machine learning model to achieve incipient fault detection and classification. The combination of MODWT and XGBoost as an intelligent MPS working upon a pre-processed de-noised system signals, hitherto untried as per the knowledge of the authors, is tested using standard IEC microgrid test model under varied topological configurations, operational modes, fault conditions, etc. The simulation results, so extensively obtained, prove the effectiveness and robustness of the proposed approach of MPS. The MPS is additionally verified on an IEEE 13 bus microgrid model to reinforce the clam of efficiency.

Induction Motor Fault Diagnosis Based on Zero-Sequence Current Analysis

This paper presents some considerations regarding the application of the stator zero-sequence current component (ZSC) in the fault detection of cage induction machines, including the effects of magnetic core saturation. Faults such as rotor cage asymmetry and static, dynamic, and mixed eccentricity were considered. The research started by developing a harmonic motor model, which allowed us to obtain a voltage equation for the zero-sequence current component. The equation allowed us to extract formulas of typical frequencies for particular fault types. Next, in order to verify the effectiveness of ZSC in induction motor fault diagnosis, finite element calculations and laboratory tests were carried out for the previously mentioned faults for delta and wye connections with neutral wire stator winding configurations.

Improved Comprehensive Control of Modular Multilevel Converter under AC/DC Grid Faults and Harmonic Operation Conditions

Recent applications of modular multilevel converter (MMC) have posed various problems such as ac/dc grid faults, asymmetric operation conditions, ac grid voltage excessive harmonics, and ac circulating currents, which deteriorate the system's performance and also threaten the safe operation. In this article, an improved comprehensive control architecture of MMC is proposed to maintain a stable voltage control, eliminate harmonics in ac-side and circulating currents, and dc-bus voltage ripple under ac/dc grid faults and harmonic operation conditions. The proposed comprehensive control consists of improved hierarchical voltage control and repetitive controller-based arm current control. The improved hierarchical voltage control, including a novel negative-sequence current injection and dc-circulating current injection-based leg-averaging control and their seamlessly switching handling, enables the MMC to operate under various operating conditions, thereby producing the arm current reference for inner-loop control. The proposed repetitive controller-based arm current control can recognize the control of multifrequency components of arm current without separating positive-, negative- and zero-sequence current components of ac-side currents and circulating currents. Finally, the simulation and experimental studies of the three-phase MMC were carried out in detail, and the findings demonstrate the efficiency and merits of the proposed control method.

A Current Reallocation Strategy to Attenuate the Peak Arm Current of the Modular Multilevel Matrix Converter

The modular multilevel matrix converter (M3C) is a promising candidate for direct ac-to-ac conversion systems. This paper proposes a novel arm current reallocation strategy for the M3C to attenuate the peak arm current. The principle of the proposed strategy is to dynamically adjust the distribution of the positive-sequence current components among the three star-figure subconverters according to their respective instantaneous zero-sequence current components. First, a square-value-based strategy is proposed and its performance in attenuating the peak arm current at different current conversion ratios is evaluated. Then, the impacts of the proposed strategy on the root-mean-square value of the arm current and submodule capacitor voltages ripple are analyzed. Based on the analysis, an algorithm for determination of the reallocation coefficient, and embedment of the proposed strategy in the existing control methods is developed. Based on the proposed strategy and depending on the current conversion ratio of the M3C, up to 14.6%–21.6% of the peak arm current can be attenuated. Performance and effectiveness of the proposed current reallocation strategy are verified by simulation studies conducted in the MATLAB/Simulink software environment.

An Improved Torque Density Pseudo Six-Phase Induction Machine Using a Quadruple Three-Phase Stator Winding

The nine-phase six-terminal induction machine has recently been proposed as a promising contender to the conventional six-phase asymmetrical winding machine in terms of torque density, phase current quality, stator winding simplicity, and fault-tolerant capability. However, the relatively lower dc-link voltage utilization of a single neutral arrangement in multiphase machines with multiple three-phase windings represents, in general, a technical challenge when compared to windings with isolated star points. Therefore, this paper proposes a new pseudo six-phase winding layout suitable for medium-voltage high-power induction machines, which employs quadruple three-phase stator winding sets, while providing the same terminal behavior of a nine-phase six-terminal winding. Additionally, like the traditional six-phase winding, two possible neutral arrangements can be configured. The proposed winding configuration provides the same dc-link voltage utilization as in conventional dual three-phase winding machines with isolated neutrals. The effect of the circulating zero-sequence current component experienced with a single neutral arrangement can also be avoided. A 1.5 Hp prototype induction machine is used to experimentally validate the proposed six-phase winding layout under both healthy and fault conditions.

Decoupled Vector Space Decomposition Based Space Vector Modulation for Dual Three-Phase Three-Level Motor Drives

In this paper, a novel space vector modulation (SVM) strategy is proposed and designed for dual three-phase three-level motor drives based on vector space decomposition (VSD), which could be applied for high-power and high-reliability applications. The key of the proposed method is to design two decoupled groups of voltage vector candidates for synthesis on α − β subspace and x − y subspace, respectively. The two decoupled groups of voltage vectors will synthesize respective voltage references on α − β subspace and x − y subspace, while having no impact on each other. The redundant small voltage vectors and zero-sequence voltage vectors are utilized to mitigate voltage oscillation in midpoint of dc link and suppress zero-sequence current component for dual three-phase windings with a common neutral. For comparison, another VSD-SVM strategy is designed based on traditional solution, which cannot offer closed-loop control on x − y subspace. Both simulation and experiments have been given to verify that the proposed decoupled VSD-SVM can suppress harmonic components on x − y subspace besides tracking torque components on α − β subspace. Furthermore, the harmonic performance of the proposed decoupled VSD-SVM has been compared with the traditional VSD-SVM strategy and the carrier disposition based pulsewidth modulation.

Open-Phase Fault Detection in Delta-Connected PMSM Drive Systems

This letter presents an open-phase fault detection method for delta-connected permanent magnet synchronous machine (PMSM) drive systems. This method is based on zero sequence current component (ZSCC) and stator currents. First, the model of the delta-connected PMSM is established under healthy and fault conditions. Then, the expression of the ZSCC is presented, and fault indicators are defined based on the ZSCC and stator currents, which are used for the open-phase fault detection and location. Finally, both the simulation and experimental results validate the effectiveness of the proposed method.

Demagnetisation fault detection in PMSM using zero sequence current components

A demagnetisation fault detection method for a delta-connected permanent magnet synchronous machine (PMSM) based on zero sequence current components (ZSCC) is proposed. The model of the delta-connected PMSM with the demagnetisation fault is first established. Then the expression of the ZSCC is presented for the delta-connected PMSM, and an equivalent fault severity index which can quantify the demagnetisation degree is obtained, being not limited by the partial or uniform demagnetisation. Finally, the simulation results show that the potential of the proposed fault severity index for the demagnetisation fault detection.

Wavelet Based Induction Motor Fault Diagnosis Using Zero Sequence Current

Induction motor stator fault is diagnosed by applying Discrete Wavelet transform on zero sequence components. The single phasing stator fault is created and diagnosed in the induction motor model developed in stationary reference frame, under varying load conditions. The stator inter-turn incipient fault is created and diagnosed in the induction motor experimental setup as well under no load condition. The qdo components are calculated from Park’s equations. The faults can be diagnosed from wavelet transform of the zero sequence current components. PSD is used for diagnosing the fault and the statistical value is used for verifying the result. The energy is calculated using Parseval’s theorem. The energy and the statistical data calculated from the wavelet coefficients of zero sequence current components are used as fault indicators. The energy value is able to reveal the fault severity in the induction motor stator winding. Power spectral Density along with Discrete Wavelet Transform plays very important role in diagnosing the fault.

Online Interturn Fault Diagnosis of Permanent Magnet Synchronous Machine Using Zero-Sequence Components

This paper develops an online interturn fault diagnosis method for permanent magnet synchronous machine (PMSM). The mathematical model of the PMSM with interturn fault is established. The zero-sequence voltage component and zero-sequence current component are analyzed in the PMSM, respectively. Then, the new fault indicators are defined to remove the influence of the variation of the rotor speed and an effective frequency tracking algorithm is presented to extract fault indicators. In this proposed method, not only the interturn fault can be effectively detected, but also the phase in which this fault occurs can be accurately identified. The experiments are carried out and the experiment results verify the effectiveness of the proposed method.

Independent Control of Input Current, Output Voltage, and Capacitor Voltage Balancing for a Modular Matrix Converter

This paper presents a novel control scheme for the modular matrix converter (MMxC), in terms of balancing capacitor voltages in addition to controlling output voltage and input current along with a comprehensive mathematical model. The proposed technique has been designed based on a fully decoupled current control of the positive-, negative-, and zero-sequence components of each MMxC subconverter in addition to the feedforward instantaneous power control to suppress the capacitor voltages fluctuation. The frequency of the zero-sequence is the output frequency for the load. Therefore, the positive-sequence current component is used to control the input current to achieve unity input power factor, the negative-sequence current component is used to balance the capacitor voltages among all MMxC arms, and the zero-sequence current component is used to control the output voltage. The effectiveness of the proposed control scheme for controlling the MMxC has been verified theoretically, using simulation software, and experimentally, using a laboratory prototype based 3 kVA, 200 V.

Comparative study of reference currents and DC bus voltage control for Three-Phase Four-Wire Four-Leg SAPF to compensate harmonics and reactive power with 3D SVM

In this paper the performances of three reference currents and DC bus voltage control techniques for Three-Phase Four-Wire Four-Leg SAPF are compared for balanced and unbalanced load conditions. The main goals are to minimize the harmonics, reduce the magnitude of neutral current, eliminate the zero-sequence current components caused by single-phase nonlinear loads and compensate the reactive power, and on the other hand improve performances such as robustness, stabilization, trajectory pursuit, and reduce time response. The three techniques are analyzed mathematically and simulation results are compared. The techniques considered for comparative study are the PI Control, Sliding Mode Control and the Backstepping Control. Synchronous reference frame theory (SRF) in the dqo-axes is used to generate the reference currents, of the inverter.