Specific Harmonics Research Articles

Design a New DC-DC Converter for a Grid Connected Photovoltaic System

This paper presents a recent technique for photovoltaic grid connected systems based on the use of the (DPC-SVM) to select the optimal switching states to apply to the inverter, where the extended reactive power is used instead of reactive power. This technique allows achieving an optimal control of the inverter which manifests in controlling the converters using an MPPT algorithm instead of controlling each part separately. This yields to a reduced global control system on a large scale. In this context, we suggest a DC-DC boost converter circuit to ensure better behavior of the system. The FMV technique is used to inject specific harmonics in order to eliminate or minimize the undesired harmonics. The SVM model has also been developed for optimal control of the inverter to prove the high performance of the proposed method. All the results are analyzed theoretically. The simulation has shown that this strategy gives satisfactory performances, improvement of the power factor and a reduction of the THD by 37%.

Opposition-Based Quantum Bat Algorithm to Eliminate Lower-Order Harmonics of Multilevel Inverters

Selective harmonic elimination (SHE) technique is used in power inverters to eliminate specific lower-order harmonics by determining optimum switching angles that are used to generate Pulse Width Modulation (PWM) signals for multilevel inverter (MLI) switches. Various optimization algorithms have been developed to determine the optimum switching angles. However, these techniques are still trapped in local optima. This study proposes an opposition-based quantum bat algorithm (OQBA) to determine these optimum switching angles. This algorithm is formulated by utilizing habitual characteristics of bats. It has advanced learning ability that can effectively remove lower-order harmonics from the output voltage of MLI. It can eventually increase the quality of the output voltage along with the efficiency of the MLI. The performance of the algorithm is evaluated with three different case studies involving 7, 11, and 17-level three-phase MLIs. The results are verified using both simulation and experimental studies. The results showed substantial improvement and superiority compared to other available algorithms both in terms of the harmonics reduction of harmonics and finding the correct solutions.

Analysis of Patterns in the Harmonics of a String with Artificially Enforced Nodes

This study examines the higher harmonics in an oscillating string by analyzing the sound produced by a guitar with a spectrum analyzer. Higher harmonics of a string are simultaneously oscillating modes which have frequencies that are integer multiples of the fundamental frequency of the string. These harmonics can be viewed on an audio spectrum analyzer. They are always present in an oscillating string and contribute to its timbre and tonal quality. Specific higher harmonics can be produced directly by placing nodes (points where the string cannot oscillate) at different lengths along a string. The tone thus produced lacks the fundamental frequency but also has a very different harmonic structure. In a guitar string, for example, it is this harmonic structure which gives rise to the very different tonal quality of a plucked harmonic as compared to the directly excited pitch of the same frequency. We mathematically hypothesized that the higher harmonics in the series of the directly excited 2nd harmonic contain the alternate frequencies of the fundamental series, the higher harmonics of the directly excited 3rd harmonic series contain every third frequency of fundamental series, and so on. We also verify a simple mathematical relationship between two different harmonic series arising from two different boundary conditions that feature the same fundamental mode. To test our hypotheses, we enforced artificial nodes to excite the 2nd, 3rd, and 4th harmonics directly, and analyzed the resulting spectrum to verify the mathematical hypothesis. The data analysis corroborates both hypotheses.

Control Strategy of Single-Phase UPQC for Suppressing the Influences of Low-Frequency DC-Link Voltage Ripple

The single-phase unified power quality conditioner (UPQC) is widely used to improve power quality for sensitive end-users. However, the inherent instantaneous power difference between parallel and series converter will generate significant low-frequency dc-link voltage ripple and degrade the compensation performance of UPQC. The mechanism of dc-link voltage ripple generation and its influences on compensation voltage and current are analyzed in this article. To suppress the influence, a control strategy is proposed for the single-phase UPQC. For parallel converter, a notch filter is introduced in the outer voltage loop to prevent the voltage ripple entering the control loop, the specific order harmonics compensation is proposed in the inner-current loop to reduce the grid current harmonics. For the series converter, the dc-link voltage feedback is adopted to suppress the influence of voltage ripple on the compensation performance. Simulation and experimental results show that the grid current total harmonic distortion (THD) can be reduced effectively with the fixed dc-link capacitance compared with the traditional control strategy. More than half of the load voltage THD are also decreased by the dc-link voltage feedback control. Moreover, with the smaller dc-link capacitance, single-phase UPQC can maintain the better performance under the proposed control strategy.

Capacitor Voltage Round-Robin Transmission Modes for MMC Distributed Control Systems

Most MMC distributed control systems require the central controller to collect capacitor voltages measured by local controllers to perform the phase average capacitor voltage control. Transmitting considerable capacitor voltages can greatly increase the communication burden in an MMC with numerous submodules. In this letter, we aim to significantly reduce the communication burden with adequate data exchange to maintain the control performance by proposing two round-robin transmission modes with voltage-ripple-filtering capability. The two transmission modes are elaborately designed to filter out specific harmonics for the removal of the low-pass filter in the voltage control loop. The feasibility of the capacitor voltage transmission modes is confirmed by the simulation and experimental results.

Intercomparison of Three Open-Source Numerical Flumes for the Surface Dynamics of Steep Focused Wave Groups

NewWave-type focused wave groups are commonly used to simulate the design wave for a given sea state. These extreme wave events are challenging to reproduce numerically by the various Numerical Wave Tanks (NWTs), due to the high steepness of the wave group and the occurring wave-wave interactions. For such complex problems, the validation of NWTs against experimental results is vital for confirming the applicability of the models. Intercomparisons among different solvers are also important for selecting the most appropriate model in terms of balancing between accuracy and computational cost. The present study compares three open-source NWTs in OpenFOAM, SWASH and HOS-NWT, with experimental results for limiting breaking focused wave groups. The comparison is performed by analysing the propagation of steep wave groups and their extracted harmonics after employing an accurate focusing methodology. The scope is to investigate the capabilities of the solvers for simulating extreme NewWave-type groups, which can be used as the “design wave” for ocean and coastal engineering applications. The results demonstrate the very good performance of the numerical models and provide valuable insights to the design of the NWTs, while highlighting potential limitations in the reproduction of specific harmonics of the wave group.

Application of a Non-carrier-Based Modulation for Current Harmonics Spectrum Control during Regenerative Braking of the Electric Vehicle

The regenerative braking of railway vehicles is widely used in DC railway systems all over the world. This mode of operation provides an opportunity to reuse part of the energy consumed by vehicles, and makes the railway system more energy efficient. During regenerative braking, not only energy management is an issue, but also Electromagnetic Compatibility EMC issues, such as interference of generated current harmonics with a railway signaling system. In this paper, the selective harmonic elimination modulation technique (SHE-PWM) was introduced to the traction drive with a three-level inverter to reduce specific catenary current harmonics generated during regenerative braking. The simulation model of a traction drive appropriate for harmonics analysis was proposed and verified by the measurements in the low-power laboratory drive system. The model was re-scaled to the 3 kV DC system for further study. The model of an induction motor with electromotive force and the method of its calculation was proposed. Furthermore, an analysis of the braking chopper operation was carried out. The asymmetric control of braking chopper was proposed to reduce the current harmonics below limits during chopper operation.

Model Predictive Control With Reduced Common-Mode Current for Transformerless Current-Source PMSM Drives

The integrated dc-link choke can replace the bulky transformer in current-source converter (CSC)-fed motor drive systems to bear the common-mode voltage (CMV). However, the common-mode (CM) resonance will be excited by the specific harmonics in the CMV, which causes excessive CM current in the loop. Moreover, due to the high-order filter, the $LC$ / $CL$ resonance is prone to be induced at the rectifier and inverter sides, respectively. In this article, the model predictive control (MPC) scheme is proposed to tackle the CM resonance and filter resonance simultaneously. In the low-speed region, besides restraining the peak-to-peak (PTP) magnitude of the CMV at the rectifier side, the third-order harmonic of the CMV generated by the inverter is extracted and then penalized in the cost function to further suppress the CM current. With the increase of the motor speed, the control objective of the inverter side controller switches to the PTP magnitude of CMV suppression because of the alleviation of the CM resonance. The capacitor voltage of both rectifier and inverter sides are regulated via the cost function as well, which can mitigate the current harmonic distortion and improve system stability. The simulation with 1MVA rated power and the scaled-down experiment shows that the proposed scheme can suppress both the CM resonance and the $LC$ / $CL$ resonance effectively with a low switching frequency.

Accurate Harmonic Calculation for Digital SPWM of VSI With Dead-Time Effect

This article presents an accurate model of a digitally controlled voltage-source inverter with the dead-time effect. The impact of two nonlinear behaviors of digital sinusoidal pulsewidth modulation and dead time on the output waveform is analyzed in the time domain. The problematic waveform with sinusoidal pulsewidth modulation is displayed, which highlights the necessity of establishing a new model. In the frequency domain, considering the dead-time effect on the current double Fourier transform is used to give a harmonic expression without a current sign function. Furthermore, this avoids the error caused by the measurement of the current polarity, so the exact amplitude of each harmonic of the output voltage can be accurately calculated, which is important for eliminating specific harmonics and improving power quality. Moreover, the problem caused by the current zero crossing is solved. The result of the analysis is verified by simulation and experiment on DSP and SIC platform. And the result shows that the harmonics and their amplitudes are in good agreement with our formula.

Theoretical and Simulation Investigations on Flow Ripple Reduction of Axial Piston Pumps Using Nonuniform Distribution of Pistons

Abstract The output flow ripple of the axial piston pump is one of the excitation sources for the hydraulic system vibration. The amplitudes of its specific harmonics must be reduced to avoid the resonance with the hydraulic pipeline. In this paper, a method on the nonuniform distribution of the pistons is put forward to adjust the flow ripple. The deflection angles of the pistons are used to describe the distribution rule. The distribution rule is imported to the Fourier expansion of the flow rate of each single-piston chamber, and then every single flow rate is superposed to obtain the Fourier coefficient of total flow rate that becomes the function of deflection angles. After this, objective optimization design is carried out to reduce the amplitudes of specific harmonics. Finally, the dynamic simulation model of the nonuniformly distributed axial piston pump is established to verify the effects of objective optimization. The results show that the amplitude of the ninth harmonic of the flow ripple can be reduced by about 40%, and the reductions are about 99% for the 18th and 27th harmonic.

General Principle of Symmetrical Flux Linkages in Stator-Permanent Magnet Machines

The even order harmonics of the flux linkage naturally exist in every armature coil of stator-permanent magnet (PM) machines, while it is usually a basic requirement to have the symmetrical phase flux linkage free from even order harmonics. Thus, the specific harmonics must be eliminated after the coil connection. In this article, the general mechanism of the even order harmonics elimination in various stator-PM machines is investigated, and it is found that either the opposite PM polarities or the opposite coil polarities of the two adjacent phase coils can guarantee the elimination effect, and hence, the symmetrical phase flux linkages. This principle can be applied to both bipolar flux and unipolar flux machines. The analysis is validated by finite-element method and the test results of the prototype machine.

A Process to Reduce the Electromagnetic Vibration by Reducing the Spatial Harmonics of Air Gap Magnetic Flux Density

In this article, a process for reducing the electromagnetic vibration and noise by changing the shape of the stator is presented. Although the fundamental wave of the air gap magnetic flux density contributes to the average torque of the motor, other spatial harmonics which were except the fundamental wave of that cause vibration and enfeeble the output of the motor. Therefore, it is important to reduce the spatial harmonics for performance of the motor. Through the proposed process, it is possible to obtain an objective function to reduce the specific harmonics by assigning weights to each spatial harmonic. The reduction in the fundamental wave is minimized and it is possible to reduce the spatial harmonics that have an adverse impact on vibration. After the process, a model can be found that maintains the electromagnetic performance as much as possible while optimally reducing the vibration. To verify the process, the electromagnetic vibrations by a radial force of the proposed and conventional models were compared, and it was confirmed that the electromagnetic vibration of the proposed model was reduced. The validity of the analysis was proved through finite-element analysis.

Acoustic localization and tracking of a multi-rotor unmanned aerial vehicle using an array with few microphones.

In recent years, the current technological improvements of unmanned aerial vehicles (UAV) have made drones more difficult to locate using optical or radio-based systems. However, the sound emitted by UAV motorization and the aerodynamic whistling of the UAVs can be exploited using a microphone array and an adequate real time signal processing algorithm. The proposed method takes advantage of the characteristics of the sound emitted by the UAV. The intrinsic harmonic structure of the emitted sound is exploited by a pitch detection algorithm coupled with zero-phase selective bandpass filtering to detect the fundamental of the signal and to extract its specific harmonics. Although three-dimensional position errors are less when signals are filtered within the antenna bandwidth, experimental measurements show that accurate estimates with only a few selected harmonics in the signal can be obtained with the localization process. Kalman filtering is used to smooth the estimates.

25.M. Workshop: Improving migration health information systems: Task-Force for facilitating action

Abstract Health information systems have not kept up with the demands and needs created by the sharp rise in human mobility over the past three decades. Most health information systems operate in national silos, and fail to provide a fully accurate, reliable and timely picture of the health and health care situation of a world on the move. As such, health needs of a large number of international migrants go unrecognized, and health systems fail to produce the evidence required for migrant-sensitive service planning, monitoring and public health action. The generation of such essential evidence relies on the inclusion of migrant health in health information systems in a consistent, comparable and ethically acceptable manner. A high-level consensus conference in Pecs (October 2019) noted the need for greater harmonisation and international cooperation on migrant health information systems, including data collection, analysis and dissemination. Taking the status quo of health information systems as a starting point, the workshop aims to present steps towards health system reforms which make information systems more sensitive and responsive to the health needs of increasingly mobile human populations. To this end, the workshop brings together researchers, policy makers and health professionals from different fields and institutions, to share existing knowledge, and by jointly exploring the following questions: What measures can we take to facilitate the harmonisation of migrant health indicators and data collection methods to ensure cross-border comparability, compatibility and completeness of data?How can we effectively improve international cooperation and governance of data management in order to share and transfer data for reasonable analysis, advocacy, and action?How can we initiate health systems reforms towards the above aims, considering that health systems are complex adaptive social constructs which are often resistant to change and not linear?What ethical and data protection considerations must be made when collecting, analysing and sharing migrant health data?How can build the required human resource capacities? Key messages Evidence based development of ‘migrant sensitive health care system’ requires specific, consistent and comparable health data Health systems harmonization on the field of migration requires supportive policy, guidance, infrastructure and trained human resources

Controlling airgap magnetic flux density harmonics in synchronous machines using field current injection

In this paper, a method to control the harmonic content of the magnetic flux density in the airgap of a synchronous machine is presented. Voltage harmonics in one phase as well as the exciting magnetic forces can be affected. Switched power electronics were used to provide the field current to a synchronous machine, the control added specific current harmonics to the DC field current in order to minimize either voltage harmonics or magnetic forces. The method is verified and compared with simulations and experiments on an existing electrical machine.

Optimization-based open-loop selective harmonic elimination pulse width modulation for multilevel inverter flying capacitor voltage balance considering load power factor variation

In this article, Newton–Raphson optimization-based selective harmonic elimination pulse width modulation is investigated for open-loop control of flying capacitor multilevel inverter. Proposed control strategy has allowed giving up current and voltage measurement instrumentations and sensors used in case of closed loop–based control. Proposed control strategy generates accurate switching angles, capable to balance flying capacitor voltage and eliminate lower order harmonics considering load power factor variation. Algorithm performances are verified by simulation and experiments, and obtained results prove that proposed technique does effectively eliminate specific harmonics and balance capacitor voltages while getting inverter output voltage with desired number of levels.

Optimization-based selective harmonic elimination for capacitor voltages balancing in multilevel inverters considering load power factor

In this paper, SHE based on Newton–Raphson algorithm is used for open-loop control of flying capacitor multilevel inverter. Without measuring current and capacitor voltages, as well as not using any controller and voltage feedback, proposed control strategy generates accurate switching angles, capable of balancing flying capacitor voltage and eliminates lower order harmonics while considering load power factor variation. Efficiency and robustness of proposed algorithm are verified by simulation and experiments. Results show that proposed method does effectively eliminate specific low-order harmonics, and inverter output voltage is resulted in low total harmonic distortion with desired number of levels and balanced capacitor voltages.

Fast calculation method of optimal flux‐barrier‐end position for torque ripple minimisation in SynRMs with and without PMs

This study presents a simplified analytical model for synchronous reluctance machines (SynRMs) with and without permanent magnets (PMs) to rapidly investigate the influences of flux-barrier-end angles or salient poles angles on the torque ripple. With the proposed method, the optimal flux-barrier-end angles or salient poles angles can be computed directly to eliminate a specific torque harmonic. To further minimise two main low-order torque harmonics, a compensation strategy is adopted by choosing different optimised flux-barrier-end angles or salient poles angles in rotor adjacent poles. Moreover, two types of optimal combinations are evaluated and compared with transient finite element analysis. The results show the torque ripple can be significantly reduced in the optimised SynRMs with and without PMs and the average torque loss is acceptable. Finally, the prototype motor of five-phase SynRMs without PM is built and tested to validate the analyses.

Research on hybrid SHEPWM based on different switching patterns

<span>This paper presents a hybrid pulse width modulation (HPWM) strategy based on different switching patterns of selective harmonic elimination pulse width modulation (SHEPWM) for the three-level neutral point clamped (3L-NPC) converter. Specific low-order harmonics can be eliminated by SHEPWM at low switching frequency, while the remaining high-order harmonics can be selected to be simply filtered by additional hardware. Large oscillation waveform usually occurs in the transition instant between two diverse modulation situations, therefore switching between distinct switching patterns can be problematic if no effective means is taken, especially when the effect of smooth and fast transition at any time is considerable. A universal and valid control strategy, which maintains the high-quality output voltage and current, is proposed and implemented in this paper to address this issue. Simulation results obtained from MATLAB/SIMULINK are presented to analyze the performance and validate the feasibility and effectiveness of this control scheme.</span>

Phase-Shifting Transformer Combined with the Novel SHEPWM for Harmonics Reduction in Medium-Voltage Inductive Loads

In this paper, a novel approach is proposed to reduce the impact of harmonics in the high-power medium-voltage squirrel-cage induction motor. An inverter with a minimum switching frequency is required for this load type to reduce the snubber and switching losses. Phase-shifting transformer is selected as an interface between the three-phase supply and the inverter. This is to reduce the impact of low order harmonics and consequently reducing total harmonic distortion (THD). Selective harmonic-elimination pulse width modulation (SHEPWM) is employed as a control technique in the inverter to eliminate specific low-order harmonics. Thereby, many low order harmonics are reduced further. By this way the THD of the system is reduced significantly and consequently the better and cleaner energy is obtained. In this research, PSpice simulation verified by MATLAB is used to estimate the harmonics content of the currents in high-power medium voltage induction motor.