Current Harmonic Characteristics Research Articles

Harmonic Resonance Analysis and Impedance Remodeling Method of Multi-Inverter Grid-Connected System

The harmonic and resonant characteristics of a multi-inverter grid-connected system can negatively affect power quality when weak grid conditions are present. In this paper, firstly, harmonic currents are modeled for the inverter, the correctness of low-frequency harmonics and high-frequency harmonics are verified in closed loop, and the characteristics of harmonic currents are analyzed when the parameters are varied. Secondly, the resonant characteristics of the inverter with feed-forward link are analyzed, and a multi-inverter grid-connected equivalent model based on the triple-decomposition conductance is developed and analyzed in conjunction with the resonant modal analysis method. Then, a harmonic resonance impedance reshaping method is proposed to suppress the background harmonics using improved weighted average current control (WACC), suppress the system resonance based on the point of common coupling (PCC) paralleling virtual conductance method, and improve the stability margin of the system combined with impedance reshaping resonance suppression method. Finally, simulations and comparison of results with different suppression methods verify the superiority and effectiveness of the proposed method.

A new symmetric modular eleven‐level inverter using single and double source unit for low voltage applications with reduced number of switches

AbstractThis study proposes a modular multilevel inverter for low‐voltage applications, including ac‐coupled renewables and energy storage systems. These inverters require many switches and gate drivers in their structures, which complicates the control system, reduces efficiency, and increases costs. This study introduces a new modular multilevel inverter that can produce five levels of positive voltage using only six power switches and five DC voltage sources. The basic unit is composed of a single‐ and double‐source (SDS) unit. SDS reduces the number of power electronic components, such as the insulated gate bipolar transistors, freewheeling diodes, gate driver circuits, dc voltage sources, and blocking voltage by switches. The proposed topology can boost the number of output voltage levels and decrease the number of switching devices and voltage stress using some combinations of basic submodules. The performance of the proposed 11‐level single‐phase inverter is compared with that of the conventional structures and recent symmetric topologies considering the number of switches, cost, and efficiency. The waveform quality and both the voltage and current harmonic characteristics were determined in accordance with IEEE 519–2014. Finally, an 11‐level prototype was constructed to validate the theoretical analysis, feasibility, and effectiveness of the proposed inverter.

Widespread compact fluorescent lamp evaluations in 50 Hz electrical network

Rapid development in electrical technology has imposed strong challenges to modern power system. Power quality has become a great concern due to proliferation of power electronic technology in modern electrical loads. Specifically for lighting load such as compact fluorescent lamps (CFLs), one of the concerning issues is harmonics. CFL is a cost-competitive and energy efficient compared to incandescent lamp. Inevitably, CFL produces harmonics current due to nonlinearity behaviour of the electronic ballast circuit. This paper presents a study on the widespread installation of CFL lamps in electrical power network. Initially, the harmonic current characteristics of local-branded CFL was identified from laboratory measurement. Then, a simulated CFL model was developed in MATLAB/Simulink to replicate the identified characteristics. The same step was repeated for other two different brands where eventually all models were embedded into a distribution network. The results show that at low voltage level, with installation more than 50 units for each type of CFL, the harmonic voltage distortion exceeded the 8% total harmonic distortion (THD) limit as stipulated in EN50160 standard. However, at higher voltage, the amount of THD decreased to average 0.94% and further down to average 0.28% at small transmission voltage level.

High-Performance Control Simulation of PFC Converter for Electric Vehicle Charger

In order to solve the problems of low power factor and large harmonic pollution of some electrical equipment connected to the power grid, such as electric vehicle charger system, the author proposes a high-performance control simulation study of a PFC converter for electric vehicle charger. Using the staggered parallel boost power factor correction circuit topology of electric vehicle chargers as the front stage, its high power factor and low harmonic current characteristics can reduce the pollution to the power grid, and the detailed design process and loss analysis of the circuit are given. Through the digital control method and hardware optimization design, the loss is reduced, and the conversion efficiency of the power factor correction converter in the full power range is high, which meets the efficiency requirements of the platinum version and achieves the goal of energy saving and environmental protection. The test results show that the actual efficiency of the experimental prototype is 97.43%, 97.55%, and 97.36%, which are far higher than the efficiency requirements of the platinum version. Conclusion. The high-performance control of the PFC converter of the electric vehicle charger has certain guiding significance for the application in the electric vehicle.

Analysis and Design of Ideal Transformer-Like Magnetic Coupling Wireless Power Transfer Systems

An ideal transformer-like (IT-like) magnetic coupling wireless power transfer system is proposed in this article, which can achieve a large constant power and efficiency output over a wide transfer range. First, the general circuit model is presented along with the analysis of fundamental and harmonic current characteristics. Then, the IT-like operation mechanism with a fixed desired secondary-primary current amplitude ratio independent of mutual inductance is proposed, based on which the transfer range capable of both power and efficiency is greatly improved. The corresponding parameter criteria and implementation methods, including the zero-phase-angle mode and the zero-voltage-switching mode are derived and verified in a practical prototype. The experimental results show that the proposed system can take the output power, transfer efficiency, transfer range, and current characteristic into account at the same time, with strong position robustness and high tolerance to variable couplings.

Research on Elevator Operation Harmonic Current Characteristics Analysis and Electrical Fire Detection Technology

The elevator will generate high-frequency harmonic current during operation, and the leakage current generated by the high-frequency harmonic current to ground will cause interference to the residual current type electrical fire monitoring detector due to the existence of parasitic capacitance in the distribution line. This paper analyzes the high-frequency interference signals generated during the operation of elevators and studies the residual current analysis method based on digital filtering technology. Firstly, the causes of false alarms generated by residual current type electrical fire monitoring detectors are analyzed according to the residual current interference signals generated during elevator start-up. Then, the frequency characteristics of the disturbance signal of the elevator in different operating states are proposed by analyzing the spectrum of the disturbance signal during the stationary, ascending, and descending processes of the elevator. Finally, the method of using a fast Fourier transform to analyze the residual current in elevator distribution lines is presented. The experimental results show that the frequency of the residual current interference signal generated when the elevator is running is mainly distributed above 3000 Hz, the energy of the interference signal at 3700 Hz is the largest when the elevator is stationary, and the energy of the interference signal at 4500 Hz is the largest when the elevator is ascending or descending. The amplitude of the signal can be used as a criterion for whether the distribution line generates leakage.

Analysis and Control of Current Harmonic in IPMSM Field-Oriented Control System

There is a certain amount of current harmonics in interior permanent magnet synchronous motor. In order to accurately control the current harmonic, this article focuses on three aspects: establishing current harmonic calculation model, extracting current harmonic, and designing current harmonic regulator. A current harmonic calculation model, which considers the effect of voltage harmonics induced by current controllers and digital control delay on the initial phase angle of voltage harmonics, is established for the first time. With the help of multiple synchronous rotating frame transformation, a current harmonic extraction method more suitable for motor drive field, which aims to extract the current harmonic characteristics of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis currents, is proposed. On this basis, the controlled quantity and control quantity are unified in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> coordinate frame for analyzing the coupling relationship of current harmonic characteristics. And then a PI current harmonic regulator, including current harmonic decoupling and voltage harmonic initial phase angle compensation, is constructed, so as to realize the effective control of current harmonics. Finally, the effectiveness and superiority of the proposed method are verified by simulation and experiments.

Analysis of harmonic current characteristics injected into unility grid by urean rail transit

Non-liner electrical devices are heavily used in urban rail transportation, which is a typical case of the trend of power-electronics on the power demand side of new energy-dominant power system. Analysis of harmonic current injection caused by urban rail transportation is of great significance to the safety and stability of the power grid as well as power quality. Based on actual test data of a certain urban rail transportation, the electric power consumption throughout a whole day is analysed; harmonic current content as well as 95% probability of the 2nd to 25th harmonic currents is calculated; assessment with reference to the national standard limits is carried out; the correlation between dominant harmonic current and fundamental apparent power through curve fitting is revealed. Then, harmonic current content and potential risk caused by the no-load closing magnetizing inrush current are investigated. Finally, the key research issues on technology supervision and management of urban rail transportation harmonic current injection are discussed. The work of this paper may be a technical reference for the planning, operation, and harmonic current prevention of the increasing rail transportation in the new energy-dominant power system.

The electrical model and harmonic characteristics of ZnO varistor considering unipoilar impulse aging polarity effect

The frequent and high amplitude unipolar impulse currents during the process of switching-on AC filter banks can accelerate the aging of arresters in some ultrahigh-voltage direct-current (UHVDC) and HVDC transmission systems, and result in polarity effect of zinc-oxide (ZnO) varistors. Hence, an improved ZnO varistor electrical model considering the polarity effect caused by unipolar impulse aging was proposed under power frequency voltage. Accelerated aging test under a negative polarity 15/35 µs impulse current was conducted on ZnO varistor samples to validate the proposed model. Furthermore, the current waveform and harmonic characteristics of the leakage current and its resistive component were simulated. Comparative analysis revealed that the simulation results were generally consistent with the test results. Based on the results, it's inferred that the variation of even-order harmonics are attributed to the polarity effect, and can be considered as one of the aging criterion of arresters.

Low Switching Frequency SPWM Strategies for Open-Winding Machine With Low Current Harmonics

In this article, two novel sinusoidal pulsewidth modulation (SPWM) strategies with simple implementation are proposed for an open-winding machine fed by isolated dc-bus dual two-level three-phase inverters to reduce switching frequency and current harmonics. The proposed strategies utilize zero sequence voltage injection and unbalanced reference voltage distribution to generate discontinuous PWM with low current harmonics and less switching action. Two different zero sequence voltages are introduced in this article corresponding to two proposed PWM strategies with different switching actions in a PWM cycle. The novelty of this article is low current harmonics and less switching actions in a PWM cycle compared with the conventional SPWM strategy. Moreover, compared with the subhexagonal center PWM strategy, the proposed SPWM strategies have advantages of easy implementation and half switching commutations with the same current harmonic characteristics. The superiority of the proposed SPWM strategies is validated by simulation and experiment results.

Suppression of Beat Phenomenon for Electrolytic Capacitorless Motor Drives Accounting for Sampling Delay of DC-Link Voltage

Beat phenomenon is an important issue for the practical application of electrolytic capacitorless motor drives. In this study, the characteristics of stator current harmonics caused by the voltage sampling delay are analyzed. Further, the beat phenomenon generated from the interaction between the harmonics and the fundamental currents is investigated, and the envelope feature of the stator current is derived mathematically. For the purpose of suppressing the beat phenomenon, a voltage reconstruction strategy is proposed to reduce the influence of dc-link voltage sampling delay at the six times of grid frequency. By utilizing the reconstructed dc-link voltage for calculation of PWM duty ratio, the beat phenomenon can be attenuated significantly. The proposed method can be integrated into motor control system easily. Experimental results show the effectiveness of the proposed strategy in a prototype of electrolytic capacitorless permanent magnet synchronous motor drive.

A non-intrusive load identification algorithm based on deep learning and a compound feature

Aiming at the limitations of using a single feature for load identification, a non-intrusive load identification algorithm based on deep learning and compound features is proposed. The pixelated V-I trajectory characteristics and current harmonic characteristics are extracted by analyzing the load data under high-frequency sampling. Using the feature extraction capabilities of neural networks, the combination of pixelated V-I trajectory features and current harmonic features is realized. Finally, the composite feature is used as the new load feature to train the neural network for non-invasive load identification. The experimental results show that the two-layer neural network constructed by the algorithm can take advantage of the complementarity between the two features, thereby improving the load identification ability.

ANN Based Current Controller for Hybrid Electric Vehicles

The use of Hybrid Electric Vehicles (HEVs) across the world is growing enormously every day. The single-phase bi-directional convertors are presented in this study for HEVs on-board charging(OBC). In HEVs, we use power electronics converters for the converting and inverting operations. Artificial Neural Network(ANN) is presented in this study for simple operation and high optimization approaches. ANN control technique regulates the system's THD and enhances charging system optimization, enables two-way power delivery that is from the grid to vehicle and the vehicle to grid. An ANN based current controller model that achieves fast-dynamic reaction and that improves grid current harmonic characteristics is proposed in this study. The system's THD is reduced by the ANN controller being suggested. The results prove the validity and feasibility of design and control technique of the proposed integrated charging system.

Current harmonic suppression for permanent magnet synchronous motor based on phase compensation resonant controller

Permanent magnet synchronous motor always suffers from air gap field distortion and inverter nonlinearity, which lead to the harmonic components in motor currents. A resonant controller is a remarkable control method to eliminate periodic disturbance, whereas the conventional resonant controller is limited by narrow bandwidth and phase lag. This article presents a novel resonant controller with a precise phase compensation method for a permanent magnet synchronous motor to suppress the current harmonics. Based on the analysis of the current harmonic characteristics, the proposed resonant controller for rejecting a set of selected current harmonic components is plugged in the current loop, and it is parallel to the traditional proportional–integral controller. Furthermore, the stability analysis of the proposed resonant controller is investigated, and the parameters are tuned to get a satisfactory performance. Compared with the conventional resonant controller, the proposed resonant controller can achieve good steady-state performance, dynamic performance, and frequency adaptivity performance, simultaneously. Finally, the experimental results demonstrate the effectiveness of the proposed suppression scheme.

Analysis on Displacement Angle of Phase-Shifted Carrier PWM for Modular Multilevel Converter

This paper provides theoretical and experimental discussions on the characteristics of the modular multilevel converter (MMC) when phase-shifted carrier sinusoidal pulse-width modulation (PSC-SPWM) is applied. Harmonic-cancellation characteristics of output voltage and circulating current are analyzed on the basis of a general implementation of PSC-SPWM with two freedom displacement angles. Five available PSC-SPWM schemes with different carrier displacement angles were obtained, and a detailed performance comparison about output voltage and circulating current harmonic characteristics is presented. On the basis of the equivalent circuit with ideal transformer representation of the SMs, capacitor voltages affected by PSC-SPWM schemes are also briefly analyzed. The proposed PSC-SPWM schemes can unify two different cases of odd and even SM situations for output voltage and circulating current harmonic minimization, respectively. Lastly, the optimal schemes for practical MMC application were verified by simulation and experiments on an MMC prototype.

Comparative analysis of super high-speed permanent magnet generator electromagnetic and temperature fields with the PWM and uncontrolled rectifiers

ABSTRACT This paper presents a study on the influence of different rectifiers on a super-high-speed permanent magnet generator (SHSPMG), which is used in a micro-gas turbine distributed generation system. Taking a 117 kW, 60,000 r/min SHSPMG as an example, the influence of PWM and uncontrolled rectifiers on the generator performances were studied comparatively. The current harmonics and its total harmonic distortion were analysed firstly, and the variation characteristics of voltage and current harmonics were obtained. Based on the 2-D electromagnetic analysis model, the losses of the generator with different rectifier load were studied, especially for the rotor losses, and the mechanisms of the losses variation were determined. By using the method of the 3-D coupling field between fluid and temperature, the temperature distributions of the SHSPMG connected with the PWM and uncontrolled rectifiers were calculated, respectively, and the influences of the different rectifiers on the generator temperature field were studied. It could be found that the PWM rectifier has the advantages of reducing generator losses and optimizing temperature distribution.

Investigation on the Selection and Design of Step-Up/Down 18-Pulse ATRUs for More Electric Aircrafts

Multi-pulse autotransformer rectifier units (ATRUs) have been widely used in aviation applications due to their rugged structure, cost-effectiveness, and high-reliability features. In this paper, up to six types of autotransformers for an 18-pulse ATRU are investigated, aiming to provide an optimal selection guideline for a proper structure. By conducting a thorough comparative study on the kilovoltampere (kVA) rating of the autotransformers and the current harmonic characteristics over a wide voltage step-up or step-down range, the asymmetric delta–polygon (DP) structure is considered as the most promising choice. Subsequently, an example 18-pulse ATRU with such structure is adopted as the front end of an alternative current (ac)/ac converter powering an onboard hydraulic pump. After analyzing the operational principle, accurate mathematical expressions among the overall voltage gain $K$ , the total harmonic distortion (THD) of the line current, and the kVA rating of the autotransformer were carefully deduced. Before conclusions, the theoretical analyses were verified by simulations and experiments. It is shown that the THD of the input line current of the designed 10-kW ATRU is 6.74%, the rated efficiency reaches 98.5%, and the autotransformer’s weight is merely 3.3 kg.

Reduction of Rotor Harmonic Eddy-Current Loss of High-Speed PM BLDC Motors by Using a Split-Phase Winding Method

Low-order harmonic currents in high-speed permanent magnet brushless dc (PM BLDC) motors cause large rotor eddy-current loss, resulting in high temperature rise and even overheating in the rotors, thus their application in the field of high-speed drive is limited. The rotor eddy-current loss can be reduced by using a split-phase winding method. In this paper, various time–space orders of harmonic eddy-current losses in the rotors of the PM motors with and without split-phase winding are quantified. The calculated results indicate that the rotor harmonic eddy-current losses generated by the low-order harmonic currents, which inherently exist in PM BLDC motors, are greatly reduced. Furthermore, associated with the characteristics of harmonic currents of PM BLDC motors, the mechanism of drastically reducing the rotor harmonic eddy-current loss of high-speed PM motors by using the split-phase winding method is revealed and experimentally validated.

A Nearest Level PWM Method for the MMC in DC Distribution Grids

For modular multilevel converters (MMCs) applied to medium-voltage dc distribution grids, using the traditional nearest level modulation (NLM) as in HVdc systems can lead to severe current distortion due to significantly reduced module numbers. This paper proposes a hybrid modulation method combining NLM and pulse width modulation (PWM) where only one module per arm operates under PWM mode. The proposed nearest level PWM (NL-PWM) method not only significantly reduces the current distortion, but also avoids the complicated voltage balancing control in each module. The harmonic characteristics of NL-PWM are derived using double Fourier transform, which provides a theoretical basis for selecting the module number and switching frequency for medium-voltage applications in accordance with grid harmonic requirements. Finally, the harmonic characteristics and feasibility of the proposed modulation method are validated by simulation and experimental studies on an MMC with six modules per arm. The simulated and experimental results reveal that NL-PWM has better voltage and current harmonic characteristics over NLM and CPS-PWM, thereby suiting the application of MMC with few models.

Two harmonic analysis of short circuit current in wind farm

With the increase of capacity and the improvement of economy, doubly-fed induction generator (DFIG) is gradually becoming the most widely used wind power generator in the world. DFIG has different characteristics of transient operation from the synchronous generator and its short-circuit current is affected by the converter control mode, thus when there is a voltage sags occurs, the short-circuit current of the wind farm may contain a certain amount of two harmonic. Power transformer is one of the most important power equipment in power system and the normal or not of transformer protection determines the safe and stable operation of power system. At present, the main protection of transformer is longitudinal differential protection. In order to correctly identify the inrush current, it is usually equipped with two harmonic braking measures to ensure the reliable operation of differential protection. Therefore, when the transformer failure occurs in wind farm, the protection may refuse to operate due to the reason that the short-circuit current contains a certain amount of two harmonic. Focused on the large-scale application of DFIG and the lack of the short-circuit current harmonic characteristics analysis, this work is devoted to the study of two harmonic characteristics and their influence on transformer protection when the grid voltage occurs in a non-depth drop. Through the analysis of the short-circuit current, harmonic components under different control modes of converter research the characteristics and production mechanism of the two harmonic currents of the doubly-fed wind power generator. This also lays a solid foundation for the improvement of transformer protection. Finally, the correctness of the analysis is verified by the experiments of short-circuit and time-domain simulation.