Single-phase Currents Research Articles

Analysis of Harmonic Compensation for Grid-side Current of Series Sixfold-circuit “Phase-hopping” AC-AC Frequency Converter

Background: A series sixfold-circuit “phase-hopping” AC-AC frequency converter (SSCPH-AAFC) is an extension of traditional AC-AC frequency converters. Compared to traditional frequency converters, it has the advantages of energy-saving, low cost, and simple control. Additionally, it can increase the upper limit of the frequency conversion to the power frequency. Through multiplexing processing, it reduces the harmonic content of the output waveform, making it suitable for applications, such as large-capacity fan or pump speed control. Objective: Although SSCPH-AAFC reduces harmonic content, the harmonic content of the single- phase and three-phase grid-side currents still reach 14.65% and 10.20%, respectively. To meet national standards for practical application, a compensation circuit needs to be designed to further reduce grid-side current harmonics. Methods: To address harmonic problems, a targeted single-phase current open-loop compensation method was designed based on the analysis of the current waveform defect. The method compensated for harmonics by selecting appropriate trigger angles and reducing the harmonic distortion rate of the power grid to meet the necessary application standards. Results: The method was simulated and analyzed using MATLAB, and the results showed that after single-phase open-loop compensation, the total harmonic distortion (THD) of the grid-side current for a single-phase SSCPH-AAFC was 2.64%, and for a three-phase SSCPH-AAFC, it was 1.80%. Conclusion: This method has a good effect and can meet the standard requirements.

Observer Based Single-Phase Active Current Harmonic Filter for Distributed Industrial Loads

Harmonic currents are introduced into power system as use of nonlinear electrical loads increases. Extra losses are caused by harmonic current stream into effective supply lines. A dynamic power filter engenders harmonic compensating current using a switching inverter. Single-phase current into the harmonic filter connects in parallel to load end and inject current harmonic required by the load feeder to avoid harmonic current in the direction of power system. This report discusses harmonic problem, available harmonic mitigation techniques, basic design of filter, control strategy, design steps of major hardware blocks, modelling and simulation of current harmonic filter in MATLAB SIMULINK setting, component selection, hardware implementation and final results. This filter will eliminate harmonic up to 45th order. The control circuit consists of a peak filter, all-pass filter, low pass filter and adders which are used to produce error signal by comparing harmonic current demand of load and injected harmonic current through switching inductor.

Three-Phase Unbalance Improvement for Distribution Systems Based on the Particle Swarm Current Injection Algorithm

The aim of this study is to improve the three-phase unbalanced voltage at the secondary side of a distribution transformer. The proposed method involves compensation sources injecting three different single-phase currents into the connected point of a grid. The computations of optimal single-phase currents are performed using the circuit analysis method and particle swarm optimization algorithm. An unbalanced three-phase power distribution system model is constructed, including a transformer Δ–Δ connection, V–V connection, load balance, load unbalance combination, and three single-phase compensation current sources. The results show that the voltage unbalance rate of the electricity user side is improved to less than 1%, and the three-phase total compensation apparent power is approximately 0 VA. In the future, the application of the model as an auxiliary service could be achieved by adding an energy storage system.

스코트 변압기 적용 3상 계통의 불평형 전류보상 기법 연구

This paper presents a control algorithm using a Scott transformer to solve the imbalance problem in the three-phase system. Due to the imbalance of the three-phase system, the power system has a deterioration in quality. Here, a power compensation system is designed according to the actual driving environment of railway vehicles. The received three-phase AC power is converted into two single-phase power with a phase difference of 90 degrees through the Scott transformer, and the two loads are connected through a back-to-back converter. In order to minimize the power loss in the system, the back-to-back converter adopts a single three-level NPC converter. This compensation system uses the single-phase current on the secondary side of the Scott transformer for control. In order to solve the problem of voltage distortion caused by the notch phenomenon and phase tracking caused by the leakage inductance of the transformer when directly measuring the voltage on the single-phase side, an observer is cited. In order to verify the performance of the proposed current compensation system, simulations and experiments are carried out under the conditions of switching frequency of 600Hz, M-phase 5kW and T-phase 1kW imbalanced load. The experimental results show that the three-phase current unbalance rate after the current compensator is running has dropped from 67.99% to 0.58%, which fully verifies the excellent performance of the current compensator proposed in this paper.

MATLAB SIMULATION RESEARCH ON PERMANENT MAGNET SYNCHRONOUS MOTOR VECTOR CONTROL

According to the mathematical model of PMSM (permanent magnet synchronous motor) and vector control method, PMSM FOC (vector control) simulation model is built on the basis of MATLAB/Simulink environment. The system adopts the rotor field oriented vector control method of id 0 to realize PMSM decoupling control. The speed regulator and current regulator uses the conventional PI control algorithm, and the inverter adopts SVPWM modulation strategies. The simulation results proved the feasibility of the control method, which provides a good theoretical basis for the parameters of PMSM control system hardware settings. At the same time, building simulation model PMSM FOC SPWM modulation strategy on the basis of FOC SPVWM simulation, making FFT (spectrum analysis) comparison between which and the SVPWM modulation's single phase current. The result that the output harmonic of SVPWM modulation is far less than SPWM modulation proves the advantages of SVPWM modulation strategies. 

Method for extracting motor impedance characteristics online

Due to increases in switching frequency, the electromagnetic interference of motor drive systems has been receiving more attention. In a motor drive system, the devices in the inverter produce serious electromagnetic interference during high-frequency switching. It is necessary to model the motor drive system to predict the electromagnetic interference level. Extraction of the motor impedance characteristic is necessary for the modeling of a motor drive system. At present, most research only studies the measurement method of a motor in the static state. However, motor impedance characteristics in the static state cannot represent motor impedance characteristics in operation. In this paper, an online measurement method of motor impedance characteristics is proposed. For the three-phase asymmetric circuit caused by modulation, the motor impedance characteristics in operation are calculated by establishing Kirchhoff voltage equations. A precision power scope PX8000 is used to measure the harmonic components of single-phase voltage, single-phase current, and common-mode current. The time-delay difference of the precision power scope PX8000 between different probes is also considered. Experiments prove that the time-delay difference does not affect the measurement results. Through comparing the motor impedance characteristics measured by different filters, the method of extracting the motor impedance characteristics online is validated. Finally, the motor impedance characteristics in the static state and the motor impedance characteristics of online extraction are experimentally compared. The motor impedance characteristics of the online extraction method proposed in this paper have more advantages than traditional methods.

A Hybrid-Slot Radial-Flux Dual-Stator Permanent-Magnet Machine With Fault-Tolerant Consideration

In this article, a hybrid-slot radial-flux dual-stator permanent-magnet machine (HS-RDPM) with fault-tolerant consideration is presented. On the one hand, the torque density of this structure is improved compared with conventional fault-tolerant permanent-magnet machines (FTPMs). On the other hand, both large torque ripple and weak phase isolation coming from dual stators are optimized. First, radial-flux dual stators with higher torque density are extended to FTPMs innovatively. Second, to decrease torque ripple, dual-layer fractional-slot concentrated winding (DFCW) is used, while optimized rotor and staggered stators are proposed. Finally, the hybrid slots that are composed of deep and narrow notches (DNNs) and large-opening slots are raised to enhance phase isolation; meanwhile, the deflection teeth are proposed to increase slots’ utilization. The comparisons between HS-RDPM with conventional and intermediate structures are made. The higher torque density and smaller torque ripple are testified by back-EMFs and torques. The greater phase isolation is proven jointly by flux just with single-phase current, inductance performances, and back-EMFs varieties after a short circuit. In addition, the loss distributions are studied, while the winding temperatures indicate that the security of the machine under a short circuit can be guaranteed if the current is limited. A prototype is manufactured, and the experimental results verify the correctness of simulations.

Визначення оптимального значення опору резистора заземлення нейтралі в мережах 20 кВ

At present, there is an objective need for a solution in the power system of Ukraine problems of improving the principles of construction of network topology by voltage classes and types of performance on based on scientifically sound technical solutions using modern methods and technologies. The article is devoted to the study of the optimal value of the resistance of the neutral grounding resistor in 20 kV networks. Distribution electric networks of Ukraine with a voltage of 6 (10) kV are included in the final link systems of providing consumers with electric energy. They are in direct interaction both with the consumer, and regional and main electric networks. Therefore, the state and the operation of 6 (10) kV electrical distribution networks has a significant impact on performance reliability, quality and efficiency of the integrated power system of Ukraine. Transition from voltage level 6 (10) kV on 20 kV is an actual and priority step to increase the efficiency of operation distribution network and a significant reduction in electricity losses. The paper presents the types of resistors and options for their installation in the neutral voltage network 20 kV. The relationship between the resistance of the neutral grounding resistor and the single-phase current is established short circuit, which directly affects the types of relay protections, as well as their number. Simulation of the 20 kV network operation mode was performed, based on the results of which the optimal one was chosen the value of the resistance of the neutral grounding resistor in the presented network, which is achieved sufficient sensitivity of relay protection devices at the lowest short-circuit current. This one was chosen for the study neutral grounding method, because resistive grounding has the following advantages: no arcs high-frequency overvoltages and multiple damages in the network; no need to disconnect the first single-phase earth fault; reducing the likelihood of impressions of staff and outsiders at single-phase short circuit; almost complete exclusion of the possibility of transition of single-phase circuit to ground in multiphase; simple implementation of sensitive and selective relay protection single-phase ground fault.

Research on Series Arc Fault Detection and Phase Selection Feature Extraction Method

Series arc fault is one of the important causes of electrical fire in industrial and mining enterprises. It is of great significance to study the series arc fault detection and phase selection feature extraction method to ensure safe and stable operation of electrical equipment and to guide line maintenance. Arc fault experiments under different current and circuit conditions with a three-phase motor and inverter load were carried out. A new arc fault detection and phase selection method based on single-phase current was proposed. First, wavelet threshold noise reduction, piecewise linear fitting, and first-order difference processing were performed on single-phase current signals to filter out noise interference and highlight fault features. Second, fractional Fourier transform (FRFT) was applied to the first-order differential signal to construct the amplitude matrix of the signal from the time domain to the frequency domain. The local features of the amplitude matrix were effectively extracted, and the feature vector of arc fault with lower dimension was established by combining the two-level block singular value decomposition (SVD) method. Finally, an arc fault detection and phase selection model was established using a support vector machine (SVM) optimized by grid search (GS) and particle swarm optimization (PSO) algorithm. The applicability of the model in single-phase multiload was analyzed. The results showed that the proposed method could realize series arc fault detection and phase selection in three-phase motor and inverter circuits, and it can also be used to single-phase multiload circuits.

Using the new configuration of the current transformer as a safe current meter

The normal functioning of energy systems cannot be achieved without solving the most important issue, which can be formulated as a reliable and safe measurement of electric current. For this purpose, an industrial current transformer is most often used, which has a number of significant disadvantages during operation. These deficiencies can be corrected using an improvement in the design of the current transformer. The device of a similar current transformer, the results of studies of the electromagnetic field of an industrial current transformer and a current transformer with an improved configuration are presented in this article. In addition, the results of the experiments of the samples under study are set out, suggesting the possibility and preference of using a similar design of current transformers for measuring single-phase current of industrial frequency.

Summation of Supraharmonics in Neutral for Three-Phase Four-Wire System

Due to the increase in electronic loads such as LED lamps, power supply units for computing loads, voltage frequency drives in industries; high-frequency distortion is introduced into the power system. These high-frequency components appear due to the switching components of different power electronic converters present in the mentioned loads. The switching frequency components are most often in the range of 2 kHz to 150 kHz referred to as supraharmonics. The paper aims to show, with simulations and measurements, how supraharmonics sum in neutral and to quantify the neutral supraharmonic current as a ratio of single-phase current. This paper defines characteristics of supraharmonic emission that influence their summation in the neutral conductor through studies of devices connected in a balanced three-phase four-wire system. The paper further defines the relation of the supraharmonics emission with the number of devices connected at each phase. A mathematical model to predict the supraharmonics in a neutral conductor based on single-phase current and the number of devices is further proposed.

Device for detection of the phase current asymmetry in the three-phase lines of non-traction consumers

electrified railway transport receives power from the power system and operates on a single-phase current, which leads to uneven loading of networks of the traction power supply system. There is a danger of overload and additional losses of active power and electrical energy of three-phase electric motors by reverse sequence currents, therefore, any information obtained about the values (phase currents and voltages) allows carrying out corrective actions for the level of asymmetry. In this paper, discuss the design of the device for detecting the asymmetry of phase currents in three-phase lines is proposed. It is shown that the device can convert the DC current difference and measure three linear currents in a three-wire three-phase circuit.

A knowledge-based diagnosis algorithm for broken rotor bar fault classification using FFT, principal component analysis and support vector machines

Despite their ruggedness and reliability, induction motors experience faults due to stresses and manufacturing errors. Early detection of these faults is important in preventing further damages and minimising down-time. In this study, a machine learning algorithm is proposed for detection and classification of broken rotor bar (BRB) faults according to their severity. Removal of high frequency components then amplification was performed on the measured single-phase current. Features were then extracted using FFT and principal component analysis (PCA). Support vector machines (SVM) was used for classification. Two classification schemes were analysed; one classifying in one step and another in two steps. Experiments were performed to evaluate the algorithms by analysing their recognition rates. Six different SVM kernels were studied. Recognition rates as high as 97.9% were achieved. False negative rate as low as 0% was also realised. Furthermore, it was found out that using more principle components does not yield significant improvements.

A Simplified Indirect Technique for the Measurement of Mechanical Power in Three-Phase Asynchronous Motors

Abstract This paper presents an indirect method for measuring the mechanical power produced by three-phase induction motors. The proposed technique is based on the hypothesis that three-phase induction motors are balanced systems that transform electrical power into mechanical one. The measurement of a single phase current is used to estimate the mechanical power generated at the axis. The relationship between electric current and mechanical power is generally non-linear. By expressing the quantities in p.u., this trend is approximated with a second order polynomial. From the analysis of the mechanical power characteristics related to 13 motors we obtained the parameters of the interpolating parabolic curves of motors from 1.1 kW to 75 kW rated power. The proposed technique can be easily adopted in order to monitor the mechanical power of three phase induction motors using only one phase current transducer. Starting from the motor nameplate no experimental measurement or other data are necessary to estimate the mechanical power. This technique can be widely used in low cost multipoint measurement system able to monitor the mechanical power where no other transducer or voltage divider are necessary.

Design of a 5.4 kJ/s three-phase resonant converter based on a lithium polymer battery

This paper describes the design and manufacture of a 5.4 kJ/s three-phase resonant converter based on a 22 and 44 V lithium polymer (LiPo) battery as a high density power supply. Using the low LiPo battery input voltage generates a relatively high current that causes problems such as a large current burden on the used components and high peak-to-peak noise when the switch is turned off. To resolve such problems, the three-phase resonant converter in this work is used to handle the high input current. In the three-phase inverter structure, the amount of current flowing in a single switch is smaller than that of a single-phase current. In addition, the delta-star structure is intentionally introduced to reduce the turns ratio which helps to decrease the current on the transformer's primary side when the same output power is required. Furthermore, components such as series and parallel resonant capacitors are placed on the secondary side of the transformer, which have a high voltage and low current. These voltage and current conditions of the secondary side are more appropriate for commercialized film capacitors, which normally use series and parallel resonant capacitors because the film capacitors have been manufactured with high voltage and low current rated capacity. In terms of the design procedure, the used delta-star three-phase resonant circuit is redrawn on the secondary side of the transformer as a single-phase resonant equivalent circuit for the three-phase resonant converter design. Based on the simplified design, the operating mode and simulation of the 22 and 44 V LiPo battery-based chargers were analyzed, and the comparison of the resistor and capacitor load test results for the two chargers verifies both the aforementioned features and the performance of the proposed chargers using 300 and 150 A of the LiPo battery. The advantages are confirmed, and the capacitor bank is charged to 600 V for 80 ms, achieving power efficiencies of 82 and 92.5% for the 22 and 44 V based capacitor chargers, respectively.

A new diagnostic method for winding short-circuit fault for srm based on symmetrical component analysis

Winding short-circuit is one of the more common faults in switched reluctance motors (SRM). This paper takes an in-depth look at winding short-circuit. The characteristic of non-sinusoidal intermittent single phase current, fundamental components are extracted to reconstruct four phase symmetrical currents based on spectrum analysis of phase currents. The method of symmetrical component is used to calculate positive and negative sequence components of reconstructed currents, where then the ratio between positive and negative sequence component is seen as a fault feature and the diagnostic criterion is proposed. The simulation and experimental results are presented to confirm the implementation of the proposed method.

Двухпроводная система электропередачи трёхфазного тока

The considered two-wire three-phase current power transmission system contains two phase number transformer converters (PNTC). The first converter (PNTC-1) converts the symmetrical system of three-phase currents of the power supply source into a single-phase current with concurrently increasing the voltage of the two-wire line via which the electric power is transmitted over a significant distance to the second converter (PNTC-2). The second converter reduces the voltage and converts the single-phase current into a symmetrical system of three-phase currents. Currents are converted in each transformer converter by means of a three-phase transformer having a special winding connection diagram and two capacitor banks (phase converting elements). The article presents the PNTC-1 analysis results based on which mathematical expressions have been obtained for the impedances of the phase converting elements and for the voltage, current and power capacity of these elements, transformer, and load. The phasor diagram for the PNTC-1 has been drawn along with graphic dependences of the converter currents and reactive power values of the phase converting elements as a function of load cosjL,and the dependences of capacitor bank capacitances on the load current. Mathematical expressions for all parameters of the PNTC-2 are given.

Three‐Phase Current Control by Dynamic Reconstruction of Undetected Currents for AC Motor Drives

SUMMARYThis paper proposes new three‐phase current control methods for AC motor drives, which detects only a phase current from among three‐phase currents. The first proposed method first detects a phase current, and then estimates the two‐phase current in the stationary reference frame using the detected single phase current. The second proposed method first detects a phase current, then synthesizes the two‐phase quasi‐current in the dq rotating reference frame, and finally produces two‐phase current estimates by extracting the positive‐phase component from the quasi‐current. The third proposed method produces two‐phase current estimates by filtering out the negative‐phase component from the quasi‐current. This paper presents the principles and detailed characteristic analyses of the proposed methods and validates them on the basis of extensive experiments.

交流モータのための未検出電流の動的復元による三相交流電流制御法

SUMMARY This paper proposes new three-phase current control methods for AC motor drives, which detects only a phase current from among three-phase currents. The first proposed method first detects a phase current, and then estimates the two-phase current in the stationary reference frame using the detected single phase current. The second proposed method first detects a phase current, then synthesizes the two-phase quasi-current in the dq rotating reference frame, and finally produces two-phase current estimates by extracting the positive-phase component from the quasi-current. The third proposed method produces two-phase current estimates by filtering out the negative-phase component from the quasi-current. This paper presents the principles and detailed characteristic analyses of the proposed methods and validates them on the basis of extensive experiments.

Brushless DC Motor Electromagnetic Torque Estimation with Single-Phase Current Sensing

The purpose of this paper was to find an effective method for measuring electromagnetic torque produced by a brushless DC motor with single-phase current sensing in real-time. A torque equation is derived from the theory of brushless DC motor. This equation is then validated experimentally with a motor dynamometer. A computer algorithm is also proposed to implement the electromagnetic torque estimation equation in real-time. Electromagnetic torque is a linear function of phase current. Estimating the electromagnetic torque in real-time using single-phase current is not appropriate with existing equations, however, because of the rectangular alternating-pulse nature of the excitation current. With some mathematical manipulation to the existing equations, the equation derived in this paper overcame this limitation. The equation developed is simple and so it is computationally efficient, and it takes only motor torque constant and single-phase current to evaluate the electromagnetic torque; no other parameters such as winding resistances, inductances are needed. The equation derived is limited to the three-phase brushless DC motor. It can, however, easily be extended to the multiphase brushless DC motor with the technique described in this paper.