Total Harmonic Distortion Improvement Research Articles

THD improvement of piezoelectric MEMS speakers by dual cantilever units with well-designed resonant frequencies

In this study, a piezoelectric MEMS (Micro-Electro-Mechanical-System) speaker with thoughtfully selected resonant frequencies of dual cantilever units is designed and implemented. Based on the lead zirconium titanate (PZT) thin film with superior piezoelectric coefficient, the cantilever diaphragm is designed through the modal analysis. In the 1.5mm by 1.5mm cantilever array, a high-frequency actuation unit with resonance of 13.1kHz and a low-frequency actuation unit with resonance of 6.35kHz constitute the proposed piezoelectric MEMS speaker. The boost of sound pressure level (SPL) due to the resonant mode of low-frequency actuation unit reduces the total harmonic distortion (THD) around the subharmonic frequency of high-frequency actuation unit. Meanwhile, the asymmetric triangle diaphragm reduces the maximum stress in the structure when operating at the resonant frequency, thereby mitigating the THD spikes resulting from the nonlinear structural behavior. In pressure-field measurements, the proposed design can reach SPL ≥ 70.0dB from 2.7kHz to 15.0kHz with only 0.179 Vrms input. At the same time, THD remains below 3.0% from 3.2kHz to 20kHz. The outstanding performance under larger input signal and bias voltage is also verified. Actuated by 0.354 Vrms and 2 VDC bias, the maximum SPL achieves 111.9dB and the SPL is higher than 80.0dB from 3.3kHz to 14.1kHz. Furthermore, THD is lower than 3.0% from 1.0kHz to 8.9kHz. A promising solution of piezoelectric MEMS speaker for in-ear applications is demonstrated in this study.

Efficiency and PF Improving Techniques with a Digital Control for Totem-Pole Bridgeless CRM Boost PFC Converters

A totem-pole bridgeless boost converter is one of the most promising topologies for the power factor correction (PFC) stage in high-power applications due to its high efficiency and small number of components. However, due to the totem-pole structure of the field-effect transistor (FET), very high switching loss occurs via the reverse recovery current of the body diode. To solve these problems, critical mode (CRM) control is a good solution to achieve the valley switching technique. With valley switching of CRM control, the switching loss decreases drastically with decreasing turn-on voltage. But, although the CRM control enables valley switching, it is hard to make an exact valley switching control with general zero-voltage detection circuits. In addition, when a frequency limitation scheme is applied to prevent a very high frequency, the switch can operate with hard switching at the boundary of the frequency limitation. Furthermore, the CRM boost PFC has a low PF and high total harmonic distortion (THD) under light-load conditions due to the large negative current resulting from resonance between the inductor and parasitic capacitance. It becomes worse at near-zero input voltage since the resonance current becomes larger near zero-input voltage. Therefore, in this paper, a totem-pole bridgeless boost PFC converter with high efficiency, high PF, and low THD is developed using TMS320F28377 by Texas Instruments. Based on the basic digital structure of the totem-pole bridgeless converter, the proposed controls help with exact valley switching, PF and THD improvement, and frequency limitation. The prototype converter is verified using 90–264 VAC input voltages and 450 V/3.3 kW output specifications.

Integrated Damper Cage for THD Improvements of Variable Speed Salient-Pole Synchronous Generators for the More Electric Aircraft

Wound field synchronous generators (WFSGs) have been implemented as aircraft main ac power generation for decades. The trend of moving toward more electric aircraft (MEA) made dc and variable-frequency ac buses favorable for the next-generation power systems in aircraft, as opposed to constant frequency ac grid systems. The minimization of the generators’ output voltage total harmonic distortion (THD) is an ever-more critical objective, especially for variable-frequency power systems where this target has to be met within the whole range of operating speeds. In conventional, constant speed, and WFSGs, a number of consolidated techniques are implemented to meet this requirement. In variable-speed SGs intended for the MEA, these techniques are no longer fully effective and new methodologies are thus necessary. This article replaces the conventional squirrel-type damper cage with a new integrated damper cage (IDC) located at the interpole regions. The proposed IDC, while acting as a mechanical structure to retain the field windings at high operating speeds, also achieves very low-voltage THD values at different speeds, thus complying with the power quality requirement. A 250-kVA prototype is designed, analyzed, built, and tested to prove the proposed concepts and methodologies.

Control of Grid-Tied Multiple Distributed Generation Systems With Cooperative Compensation Capabilities

This article deals with a cooperative controlof multiple distributed generation (DG) systems with power quality (PQ)-enhancing capabilities. This control algorithm is realized using an adaptive harmonic signals extraction method based on variable weight mixed norm least mean fourth–least mean square adaptive detection. This adaptive technique extracts all the necessary information required for the development of the proposed cooperative control algorithm. With this control algorithm, the voltage source inverters (VSIs) of the DG systems contribute to PQ improvement by mitigating harmonics and reactive currents in the distribution system. This algorithm operates the VSIs in maximum power generation and total harmonic distortion (THD) improvement modes. In maximum power generation mode, the algorithm utilizes the remaining capacity of the VSIs for compensation of nonactive currents drawn by the dedicated loads. Upon finishing the dedicated loads’ compensation, the remaining capacity is spent for compensation of the loads dedicated to other DG systems that are not in the position to render full compensation services. In THD improvement mode, the algorithm prioritizes compensation of harmonic currents generated by the loads. The efficacy of the proposed cooperative control algorithm for multiple DG systems is demonstrated via simulation and hardware-in-the-loop-based experimental results.

SOA-MZI photonic sampler with a post-distortion linearization technique.

We present a post-distortion linearization technique for a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) photonic sampler. The sampling source is an active mode-locked laser producing 12.6 ps-width pulses with a repetition frequency of 10 GHz. The mathematical model for the linearization technique is presented and then evaluated for the quasi-static regime, i.e. sampling continuous-wave signals, and for the dynamic regime, i.e. sampling sinusoidal signals. A significant improvement in terms of total harmonic distortion (THD) equal to 23.4 dB is observed for a modulation index equal to 80% in the quasi-static regime, matching the highest observed THD improvement in the dynamic regime.

Design, characterisation, and digital linearisation of an ADC analogue front-end for gamma spectroscopy measurements

<p class="Abstract">This work presents the design, experimental characterisation, and digital post-distortion (i.e., digital linearisation) of a MHz-range ADC analogue front-end prototype for a gamma radiation spectrometry system under development at the National Center for Nuclear Research (NCBJ) in Poland. The design accounts for the electrical response of the gamma particle detector in providing signal conditioning and ADC protection against high-voltage spikes due to occasional high-energy cosmic radiation, as well as proper ADC clocking. As the front-end inevitably introduces nonlinear distortion and dynamic effects, a characterisation is performed to quantify the actual performance in terms of Total Harmonic Distortion (THD) and Effective Number of Bits (ENOB). Thus, a digital linearisation based on both static and memory polynomial models is successfully applied by means of post-distortion processing, guaranteeing a substantial improvement in THD and ENOB, and demonstrating the effectiveness of the hardware/software method for gamma radiation spectrometers. </p>

Adaptive Predictive Control with Neuro-Fuzzy Parameter Estimation for Microgrid Grid-Forming Converters

Model predictive control (MPC) is a flexible and multivariable control technique with better dynamic performance than linear control. However, MPC is sensitive to parametric mismatches that reduce its control capabilities. In this paper, we present a new method of improving the robustness of MPC to filter parameter variations/mismatches by easily implementable parameter estimation. Furthermore, we extend the proposed technique for wider operating conditions by novel neuro-fuzzy estimation. The results, which are demonstrated by both simulations and real-time hardware-in-the-loop tests, show a steady-state parameter estimation accuracy of 95%, and at least 20% improvement in total harmonic distortion (THD) than conventional non-adaptive MPC under parameter mismatches up to 50% of the nominal values.

Current Stress Reduction and Voltage Total Harmonic Distortion Improvement of Flying-Capacitor Modular Multilevel Converters for AC Machine Drive Applications

This article proposes a method to determine the average submodule (SM) capacitor voltage for reduced current stresses and better total harmonic distortion (THD) of the phase voltages in a flying-capacitor modular multilevel converter (FC-MMC) for medium-voltage ac machine drive systems. Higher ripple is induced in the low-frequency voltage of the SM capacitors by partially alleviating the low-frequency power fluctuation in one half-arm. With this ripple value, the average SM capacitor voltage is determined so that its fluctuations are kept within the limit of the SM capacitor voltage. Consequently, the ac-circulating current amplitude can be decreased with partial alleviation of the low-frequency power fluctuation. Thus, current stresses in switching devices, inductors, and flying capacitors are reduced. In addition, the THD of the phase voltage is improved in low-speed operation. The feasibility of the proposed control strategy has been confirmed through a simulation and experiment.

Optimum operation of low voltage variable‐frequency drives to improve the performance of heating, ventilation, and air conditioning chiller system

A tremendous increase in the industrial and commercial applications of low voltage variable frequency drives (VFD) has been observed in the last decade. VFD are mainly used for energy saving and reliable speed control of industrial motors in an electrical system. However, power quality issues are becoming more apparent due to the installation of VFD. In this paper, a nonintrusive technique has been employed to determine the optimum operation of VFD system for improving the performance of heating, ventilation, and air conditioning centrifugal chiller system. The effect of load and speed ratios of VFD systems on total harmonic distortion (THD), power factor, distortion loss ratio, temperature, and efficiency has been investigated. The measurement of these parameters has been carried out by performing a series of experiments under variable operating conditions. The binomial relations have been developed between the various performance parameters and the operating conditions. Based on experimental results, optimum operating conditions have been proposed and implemented for the VFD system. Moreover, the results have been compared with the existing operating conditions and indicate a considerable improvement in THD, power factor, distortion loss ratio, efficiency, and the annual cost of energy consumed.

High dynamic performance power quality conditioner for AC microgrids

This paper deals with power quality problems encountered in weak AC microgrids and solutions for mitigation. A power electronic converter can be used as an effective power quality conditioner to compensate non-idealities in currents drawn from the grid. A power quality conditioner consisting of three power converters connected to a common DC link is analysed. One of these converters acts as an active power filter for removing unwanted harmonics in grid currents feeding a non-linear load. The other two converters instead remove the harmonics from the voltage at the terminals of a sensitive load. The control of the shunt converter is designed to be fast enough for power quality servicing but also has a fast disturbance rejection capability. Simulation and experimental results validating the concept are provided along with obtained total harmonic distortion improvements.

An Advanced Two-Stage Grid Connected PV System: A Fractional-Order Controller

A fractional-order (FO) based controller for a grid-connected PV system is presented in this paper. A single phase two-stage grid-connected photovoltaic generator (PVG) is used to test the performance of the FO controller. The main objectives of the proposed controller are: (1) To regulate the output voltage of PVG at a point where the maximum power is drawn. (2) Constant DC-link voltage control. (3) Power factor control (PFC) at the inverter output with low total harmonic distortion (THD). To solve the first problem, a non-linear control method known as fractional-order back-stepping control (FOBSC) is used to regulate the output voltage of PVG. A maximum power point tracking (MPPT) technique known as perturb and observe (P&O) is used to generate a reference voltage which is suitable for tracking the maximum power generation of PVG. The generated reference is used to regulate the output voltage of PVG using FOBSC. The DC-link voltage fluctuation problem is tackled using FO based PI controller. The last objective is achieved through utilizing FOBSC to obtain maximum power factor of the grid. Lyapunov candidate function is used to verify the stability of the system. To test the performance of the proposed controller, it is compared to conventionally known Integer-order (IO) controller, where the results have shown a significant improvement in THD and efficiency of the system. The proposed controller offers 0.94%, 1.43% and 1.86% lower THD in comparison with IO controller at 100%, 80% and 70% of the power generation capacity of PVG, respectively . The overall efficiency of the system for 100%, 80%, and 70% of the dynamic powers of the system is noticed to be better in case of FO controller.

Power Quality Improvement of Distribution System using D-STATCOM

This paper focuses on the improvement of the power quality that is being distraught by same elements that defines a power system namely reactive power need of load time to time and harmonic distortion due to some switching of power electronic devises as well, which are couple of many. MATLAB Simulink model is used to show the performance of D-STATCOM (Distribution Static Synchronous Compensator), which is dealing with a balanced reactive load which will introduce deficit in the reactive power of the system and a resistive inverter load which will introduce harmonics in the system. The effects of these loading condition before the D-STATCOM is connected and after it is connected are compared chronically, and the effects on Total Harmonic Distortion (THD) and on power factor as well. Altered form of Synchronous Reference Frame (SRF) theory is used in the controller of D-STATCOM which controls the compensating current at PCC. Simulation results shows the effectiveness of D-STATCOM in compensating reactive power following the improvement of THD as well as the sending end power factor.

Notice of Removal: A Comparative Study Between PI and Type-II Compensators for H-Bridge PFC Converter

Removed.

A Low-Phase Noise ADPLL Based on a PRBS-Dithered DDS Enhancement Circuit

This paper aims to design an all-digital phase-locked loop (ADPLL) intended for professional digital audio data conversion applications. The method used for designing is based on an analogy between analog PLL and ADPLL. Managing a low-jitter effect, a comparative study between discrete voltage-controlled oscillator (DVCO) and direct digital synthesis (DDS) based on a pseudorandom binary sequence (PRBS) generator is performed. The features of the design in this work are high-precision and low harmonic distortion DDS which is combined with ADPLL. For model-based design validation, a rapid register transfer level (RTL) with VHSIC hardware description language (VHDL) is practiced and the dynamic performance result indicates a significant improvement in total harmonic distortion (THD) ([Formula: see text][Formula: see text]dB) and a better resolution of 18.97[Formula: see text]bits for audio applications based on the aid of phase dithering DDS enhancement circuit.

Harmonics Mitigation in a Steel Industry Using 11-Level Cascaded Multilevel Inverter-Based DSTATCOM

Use of nonlinear loads in power distribution networks is expanding day by day, which results in the deterioration of the power quality of the system. An induction furnace (IF), which is an indispensable component of the steel industry, is one such typical example of a nonlinear load. It injects a considerable amount of harmonics into the supply network and consequently the performance of other loads in its vicinity gets affected. An 11-level cascaded multilevel inverter (CMLI)-based distribution static compensator (DSTATCOM) is implemented to mitigate the harmonic content of an IF in a steel plant. A Simulink model of an IF has been developed using experimental data obtained on-line from an industrial IF using a power quality analyzer. The solution methodology proposed using CMLI-based DSTATCOM reveals the effectiveness of the proposed control strategy for voltage sag mitigation and total harmonic distortion improvement of both load current and voltage as per the IEEE standards. The results obtained are also compared with that reported in the literature recently.

Optical Parametric Multicasting Linearization Based on Distortion Correcting Tables

Distortion correcting tables generated by a calibrating sequence are effectively used as a postprocessing method to equalize the nonlinear response of a parametric multicaster. The proposed linearization method is implemented in a broadband parametric multicaster and a 25 dB improvement in total harmonic distortion of 55 signal copies is demonstrated experimentally.

Boundary Conduction Mode Controlled Power Factor Corrector With Line Voltage Recovery and Total Harmonic Distortion Improvement Techniques

The proposed line voltage recovery (LVR) and the total harmonic distortion improvement (THDI) technique improve power factor (PF) and total harmonic distortion (THD) over a wide line voltage range in boundary conduction mode controlled power factor corrector (PFC). The LVR detects the input line root-mean-square voltage to generate the digital equivalent code to the THDI for optimizing the THD by tuning the on-time value at different line voltages. In addition, the LVR and the THDI provide a feedforward path to reduce the ripple of the feedback voltage for further improving the THD. Therefore, the PFC controller can keep high PF and low THD over a wide line voltage. Experimental results demonstrate that the peak PF value is 0.998 and the minimum THD is 1.7% by the test circuit fabricated in a TSMC 800-V ultrahigh-voltage process with the universal line voltage range of 90-264 V.

Nonlinear cross-talk mitigation in polychromatic parametric sampling gate

New technique for cancellation of nonlinear cross-talk in polychromatic parametric sampling gate is described and quantified. The method relies on a newly derived look-up table method that achieves equalization and suppresses nonlinear response associated with parametric sampling operation. The new cancellation scheme is implemented in a framework of a specific parametric photonics assisted analog-to-digital conversion (ADC) copy-and-sample-all (CaSA) architecture. A 20 dB improvement in total harmonic distortion is demonstrated experimentally.

Magnetic Motor Nonlinearity Modifications for Total Harmonic Distortion Improvement of an Elliptical Miniature Loudspeaker

This study reports an effort to reduce total harmonic distortion (THD) for a miniature loudspeaker by magnetic motor modifications including under yoke, polar piece, and magnet. It leads to the variation in force factor Bl(x). The micro-tensile test and finite element method is employed to get Bl(x) vs voice-coil displacement x curves. Finite element simulation is further utilized to modify motor thence force factor curves. The manufactured prototypes of the miniature loudspeaker based on finite element simulation are further analyzed for sound pressure level (SPL) and THD. Additionally, an analytical model is also developed for getting THD. It is concluded that motor modification is a promising alternative for THD reduction.

새로운 정류방식을 이용한 전기추진선박의 고조파 저감

현재 대형선박에서 다이오드 정류기를 이용한 AC-DC 전력변환장치를 주로 사용하고 있으며 이는 총고조파왜형율을 줄이기 위하여 다중펄스를 출력할 수 있는 상치환변압기가 추가적으로 설치되어야 한다. 이 경우 상치환변압기의 설치로 인해 공간적, 경제적 손실이 발생한다. 본 논문에서는 LNG 운반선 등과 같은 대형선박에서 현재 운용중인 다이오드 정류기를 대신하여 SCR, IGBT등의 소자를 이용하는 새로운 능동형 정류방식을 제안하여 저전압 전원의 이용이 가능하고 전력선 부하에 의해 발생하는 고조파 발생을 줄이며 또한, 기존의 방식에서 사용하는 상치환변압기를 제거하여 경제적인 이점도 얻고자 하였다. 현재 대형선박에서 운용중인 전기추진시스템에 제안한 시스템을 시뮬레이션 한 결과, 추진전동기 입력 전류 및 전압 파형에 포함된 총고조파왜형율이 개선됨을 나타내었다. Currently, the AC-to-DC power conversion system using diode rectifiers is mainly used in large vessels. Also, to reduce the total harmonic distortion(THD) of current and voltage, this system requires an additional phase-shifting transformer which can be powered multi-pulses. In this case, due to the installation of the transformer, the spatial or economic loss occurs. This paper presents a novel active rectification scheme using silicon controlled rectifier(SCR) or insulated gate bipolar transistor(IGBT) devices on behalf of the diode rectifiers which are currently operating in large vessels such as LNG Carrier(LNGC). The proposed system can use the low voltage source and reduce current and voltage harmonics generated by nonlinear loads connected to the power distribution bus and save economic costs by removing the phase-shifting transformers which are used in conventional system. Computer simulations are performed under the electric propulsion system which is operating in current large vessel. The results are shown in support of the improvement of THD included in the current and voltage wave forms of propulsion motor.