Harmonic Extraction Research Articles

A harmonics detection method based on improved comb filter of sliding discrete Fourier for grid-tied inverter

Harmonic detection plays an important role in power quality for grid-tied inverters. Among the various methods, sliding discrete Fourier transform (SDFT) based algorithms have found wide and popular applications due to advantages like simplicity and excellent selectively filtering properties. However, SDFT suffers from disadvantages like slow dynamics and large memory occupation. In this paper, the discrete transfer function of SDFT harmonic extraction method is analyzed, and the SDFT transfer function is divided into three parts: comb filter, resonance controller, and adjustment factor. It is found that the comb filter determines the harmonic component that SDFT needs to detect and the dynamic performance of SDFT. Thus, the comb filter can be improved according to the characteristics of the load current, thereby achieving faster dynamic performance while reducing the digital storage space required for the implementation of the SDFT algorithm. Therefore, a general harmonics detection is proposed, which could detect harmonics by adjusting the comb filter of SDFT according to the characteristics of the load current. Finally, the correctness and effectiveness of the proposed general harmonics detection method are verified by relevant experiments.

Low-power integrated transmitter design using frequency multiplication techniques

This paper proposes an approach to employ frequency multiplication techniques like edge-combining and third harmonic extraction in ultra-low-power integrated transmitter design. The overall power demand of the transmitter is reduced by keeping operating frequency of its components low. For that reason, edge-combining and third harmonic extraction are integrated directly into a switched mode power amplifier. Hence, the radio frequency signal is generated just before it is fed to the antenna. This leads to a reduced power demand of the overall transmitter in comparison to conventional designs where the oscillator and other components are operated directly at the radio frequency.Within this paper we propose an amplifier that generates a 2.4 GHz carrier frequency from a ring oscillator running at a low 200 MHz resulting in a frequency multiplication factor of twelve. The exemplary design is targeted to be used in ultra-low-power short range applications. Hence, our simulations using extracted layout models show that the amplifier provides an output power of approximately -12 dBm at a supply voltage of 0.6 V while consuming 2.4 mW of power fully integrated in a 180 nm 1P6M CMOS process.This demonstrates that the proposed techniques are especially suitable for ultra-low-power transmitter in short range applications. That includes medical and body area network applications.

Nonlinear filtering effects of intrawell matched stochastic resonance with barrier constrainted duffing system for ship radiated line signature extraction

Abstract Harmonic signatures extraction is of key interests in remote passive sonar detection and classification for its relevant to the inherent characteristics of engine and shaft/propeller rotations, of which the long-term challenging problem is to address the weak signatures from heavy noise background in the far field scenario. Signal filtering is often utilized as an essential preprocessing tool to purify the acquired noisy signals for applications, whereas stochastic resonance (SR) based nonlinear filter, has been proven effective for weak signature extraction especially under low signal-to-noise ratio (SNR) conditions. In this paper, a novel intrawell matched stochastic resonance (IMSR) is parameterized and implemented to further improve the output signal-to-noise ratio (SNR) with a barrier constrained quartic double-well potential. It can release the limitation on nonlinear system response, and ease the insufficient time-scale matching constraint and the inaccurate noise intensity estimation on potential parameters tuning. The nonlinear filtering effects are comparatively analyzed, which reflect superior performance and can break through the large sampling rate limitation as well. The distinct merits of IMSR are summarized as follows: 1) a superior low-noise output performance to the interwell response in the sense of nonlinear filtering effect; 2) a wider range of frequency response so that can ease the large sampling frequency limitation; 3) better anti-noise capability that expected to perform well in extracting weak line signatures from heavy background noise. Numerical analysis and application verification are performed to confirm the effectiveness and efficiency of the proposed method in comparison with a state-of-the-art second order matched stochastic resonance (SMSR) method, which reflect superior in different contexts.

Harmonic current suppression method with adaptive filter for permanent magnet synchronous motor

ABSTRACT Due to the distortion of air gap magnetic field and the inherent non-linear characteristics of the inverter, the stator current of permanent magnet synchronous motor (PMSM) contains a large number of high order harmonic components, which distorts the current waveform and generates torque ripple, limiting the application of the PMSM in high speed and precision situations. To solve this problem, a harmonic current suppression method is proposed based on synchronous rotating coordinate transformation theory and adaptive filtering algorithm. The PMSM harmonic mathematical model is established and the coordinate transformation method is used to extract the 5th and 7th harmonic currents. On the basis of the original double closed-loop control system, the harmonic current loop is added, and the harmonic components are suppressed by injecting harmonic voltages. In order to improve the filtering effect and reduce the harmonic content, an adaptive filter is designed to replace the conventional low pass filter in the process of harmonic current extraction. According to the results of coordinate transformation, the adaptive filter continuously adjusts the parameters online through the least mean square (LMS) algorithm to extract the harmonic current. The simulation and experimental results proved the correctness and effectiveness of the proposed method.

A Time-Delayed Filter Based Suppression Method of Circulating Current in Modular Multilevel Converters

In modular multilevel converter (MMC), the existence of second- and other even-order harmonics in the circulating currents can have a negative impact on the operation of the converter. To mitigate the dominant second-order harmonic circulating current, the harmonic extraction method plays an important role in steady-state accuracy and dynamic performance of circulating current suppression. This article proposes a time-delayed filter-based approach to suppress the circulating current. Operating principles and filtering characteristics of the time-delayed filter are investigated. The proposed solution achieves accurate suppressing and frequency-deviation adaptation with simple implementation. Experiments from a single-phase grid-connected MMC have been conducted to validate the correctness of the proposed solution.

Wideband Harmonic Voltage Feedforward Control Strategy of STATCOM for Mitigating Subsynchronous Resonance in Wind Farm Connected to Weak Grid and LCC HVDC

For the wind farm connected to line-commutated converter-based high-voltage direct-current (LCC HVDC) and weak grid at sending end, subsynchronous resonance (SSR) is prone to occur due to the impedance interactions among wind farm, weak grid, and LCC HVDC. First, the mechanism and characteristics of this SSR are analyzed based on the impedance method. With the increase of the output power for wind farm or the decrease of the transmission power for LCC HVDC, the wind farm tends to cause SSR. Moreover, with the decline of the grid stiffness at sending end, the studied system easily causes SSR. Then, a wideband harmonic voltage feedforward control strategy of static synchronous compensator (STATCOM) is proposed to suppress this SSR. For the proposed damping controller of SSR, a constant voltage amplitude-based harmonic extraction method is designed without using filter. The harmonic extraction error of the proposed strategy is a constant |V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> |, which is induced by the difference between the constant voltage amplitude V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> and actual voltage amplitude V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> . By the theoretical analysis and simulation, this constant error |V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> - V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> | can be automatically counteracted by the PI controller of STATCOM. Finally, experimental results verify the validity of the proposed strategy.

Comparison of digital lock-in amplifier and fast fourier transform algorithms for quartz-tuning-fork enhanced spectroscopy

A near-infrared methane (CH4) gas sensor system was implemented using a quartz crystal tuning fork (QCTF) based photoelectric detector and a fiber-coupled distributed feedback diode laser emitting at 1.653 μm. Wavelength-modulation with second-harmonic (2f) detection method was investigated. For signal processing, two different demodulation algorithms, i.e. Fast Fourier Transformation (FFT) and digital lock-in amplifier (DLIA), were developed and completely compared for harmonic signal extraction. Experimental results show that the SNR of WMS-2f signals using the proposed FFT algorithm can be improved by 2.5 times on average than the common DLIA method, which agrees well with the theoretical value of 2.7 times achieved with the simulated spectra data. In comparison, the proposed FFT algorithm shows better performance on signal processing efficiency and simplification, when a QCTF was used as a photoelectric detector or an acoustic transducer.

Single Phase Power Factor Improvement Based Instantaneous Power P Q Theorm

This paper presents how to harmonic disturbance reduce on single phase power system. One of the most popular method is harmonic signal extraction with instantaneous power p q theorm. This algorithm implemented to harmonic cencellation by active power filter circuit be paralled with the non linier load. This filter generates of current compensation that are injected into the grid to improve power quality. This Filter is built by an inverter circuit that consists of a mosfet switch array and capasitor mounted on DC link side. Two types of loads are resitive inductive and resistive capasitive produce of current source wave form that close pure sinusoid. Simulation results show the THD index fell to the level of 2.7% in accordance with IEEE 519 standard rules which states that the harmonics content of the power system may occur below 4%, indicating that the power system can be categorized as having good quality.

An Iterative Hybrid Harmonics Detection Method Based on Discrete Wavelet Transform and Bartlett–Hann Window

The current signal harmonic detection method(s) cannot reduce the errors in the analysis and extraction of mixed harmonics in the power grid. This paper designs a harmonic detection method based on discrete Fourier transform (DFT) and discrete wavelet transform (DWT) using Bartlett–Hann window function. It improves the detection accuracy of the existing methods in the low frequency steady-state part. In addition, it also separates the steady harmonics from the attenuation harmonics of the high frequency part. Simulation results show that the proposed harmonic detection method improves the detection accuracy of the steady-state part by 1.5175% compared to the existing method. The average value of low frequency steady-state amplitude detection of the proposed method is about 95.3375%. At the same time, the individual harmonic components of the signal are accurately detected and recovered in the high frequency part, and separation of the steady-state harmonics and the attenuated harmonics is achieved. This method is beneficial to improve the ability of harmonic analysis in the power grid.

Spectral Narrowing Accompanies Enhanced Spatial Resolution in Saturated Coherent Anti-Stokes Raman Scattering (CARS): Comparisons of Experiment and Theory.

We demonstrate theoretically and confirm experimentally the mechanism by which spectral narrowing accompanies enhanced spatial resolution in a saturated coherent anti-Stokes Raman scattering (CARS) signal that is demodulated at the third harmonic (3f) of the pump modulation frequency (f). Under these modulation conditions, theory predicts a narrowing of the full width at half-maximum (FWHM) of the CARS spectrum by a factor of 2.0 with respect to that of the spectrum obtained by demodulation at the fundamental frequency. Theory also predicts an improvement of spatial resolution by a factor of 1.7. Experimentally, narrowing of the FWHM of the CARS spectrum of 1,4-bis((E)-2-methylstyryl) benzene (MSB) crystals by a factor of 2.5 is observed upon saturation. Further experimental confirmation is provided from investigating diamond particles, for which spectral narrowing was enhanced by a factor of 2.8 and spatial resolution was enhanced by a factor of 2. Details of the mechanism and execution of the saturated CARS experiment are elucidated and limits to its applicability are suggested, one of which is the conclusion that the saturation approach is not suitable for extraction of harmonics beyond 3f. In this work, we have developed a more comprehensive understanding of the correlation between the observed experimental results and experimental factors than has been previously reported.

An Improved Control Method Based on Source Current Sampled for Shunt Active Power Filters

Active power filters (APFs) are dynamic power electronic devices that suppress harmonics and reactive power. To simplify the detection and extraction of traditional APF harmonics and reactive current, this paper proposes a direct source current control based on a three-phase three-wire shunt APF. The compensation principle and control method of the source current are analyzed systematically. The currents can be controlled without static errors by a proportional-integral (PI) controller in d-q rotating coordinates. Therefore, the compensation accuracy and dynamic performance of the system can be improved by the control strategy. Moreover, considering the grid voltage fluctuations, a droop regulator is proposed to address the impact of DC-link voltages on APF power losses and compensation performance. The regulator is combined with a traditional voltage outer loop PI control to achieve a comprehensive optimization between the power loss and compensation performance of the APF system. Finally, the inner current loop and the outer voltage loop form a double closed-loop cascade PI control structure to achieve the control effect of the APF. Simulation and experimental results verified the validity and feasibility of the APF control approach.

Extraction of Several Harmonics from Trigonometric Polynomials. Fejer-Type Inequalities

Given a trigonometric polynomial $${T_n}(t) = \sum\nolimits_{k = 1}^n {{\tau _k}\left( t \right),{\tau _k}\left( t \right): = {a_k}\cos kt + {b_k}\sin kt}$$ we consider the problem of extracting the sum of harmonics $$\sum \tau_{\mu_s}(t)$$ prescribed orders µs by the method of amplitude and phase transformations. Such transformations map the polynomials Tn(t) into similar ones using two simple operations: the multiplication by a real constant X and the shift by a real phase λ, i.e., Tn(t) → XTn(t — λ). We represent the sum of harmonics as a sum of such polynomials and then use this representation to obtain sharp Fejer-type estimates.

A Fast Time-Domain Current Harmonic Extraction Algorithm for Power Quality Improvement Using Three-Phase Active Power Filter

Harmonic current estimation is the key aspect of Active Power Filter (APF) control algorithms to generate a reference current for harmonic compensation. This paper proposes a novel structure for harmonic current estimation scheme based on Trigonometric Orthogonal Principle (TOP) and Self Tuning Filter (STF). The key advantages of the proposed method are its simplicity, low computational burden and faster execution time in comparison to the conventional harmonic current estimation approaches. The TOP method provides a simple and fast approach to extract the reference current, while STF provides a simplified structure to generate the required synchronization signal that eliminates the need of a Phase Locked Loop (PLL) algorithm for synchronization. As a result, it exhibits less complexity in implementation and less consumption of microcontroller`s resources; thus, the proposed method can be implemented using a low-cost microcontroller. It is shown in the paper that the proposed method provides 10 times gain in processing speed as compared to the conventional DQ method. The proposed approach is analyzed in detail, and its effectiveness and superior performance are verified using simulation and experimental results.

Order-domain-based Harmonic Injection Method for Multiple Speed Harmonics Suppression of PMSM

Torque ripple degrades the performance of a permanent magnet synchronous motor (PMSM). Harmonic injection method can minimize torque ripple well by suppressing the speed harmonic. But its performance under transient conditions is not satisfactory. Moreover, too much computation and complex parameter adjustment limit its application in multiharmonic suppression of speed. Therefore, this article proposes an order-domain-based harmonic injection (OHI) method for multiple speed harmonics suppression under both steady-state and transient conditions. In the OHI method, speed harmonics are extracted as feedback signals and suppressed by a speed harmonic controller. The speed harmonic controller is designed based on real and imaginary parts. The relations among the voltage, current, and speed harmonics are derived. According to these relations, speed harmonics are adjusted directly by voltage harmonics. For faster harmonic extraction, the real-time angular-domain Fourier transform (AFT) is proposed by improving an AFT algorithm. The OHI method has less calculation and simpler parameter adjustment compared with existing methods. So, it is more suitable for multiharmonic suppression of speed. Due to the extremely fast respond of speed harmonic control loop, the OHI method is effective even under transient conditions. The OHI method is simulated and experimentally evaluated in PMSM servosystem.

Extraction of the instantaneous speed fluctuation based on normal time–frequency transform for hydraulic system

The instantaneous speed fluctuation is the most direct manifestation of system dynamics behavior, which reflects the running status of the hydraulic system. It is crucial to mine the information contained in instantaneous speed fluctuation and extract them accurately. This paper first introduces the instantaneous speed measurement of the hydraulic system, and it is found that the instantaneous speed signal with an equal angle sampling is a harmonic signal. Next, causes of instantaneous speed fluctuation for hydraulic system are derived by kinetics analysis, where the working mechanism of the axial piston motor and the inevitable misalignment of the shafts are concerned. Then the normal time–frequency transform and the inaction method are introduced, and its high accuracy for harmonic signal extraction in additive noise is verified by comparing with the wavelet packet method with simulation analysis. Finally, the validity of the cause analysis and the extraction method are verified by experiments under different working conditions. The experimental results show that the frequencies of the instantaneous speed fluctuation components can be displayed automatically by normal time–frequency transform spectrum and their waveforms can be extracted accurately by the inaction method. It is also found that the change of the rotating speed and torque can be presented by the variety of the magnitude of the instantaneous speed fluctuation components at the 7th order and the 14th order, respectively. Cause analysis and accurate extraction of the instantaneous speed fluctuation will provide theoretical support and data support for the performance evaluation, state monitoring, and fault diagnosis of the hydraulic system.

Power Quality Improvement with Mitigation of Harmonic Distortion in Three-phase System Based on Shunt Active Power Filter Mechanism

In response to rising business cost and global environmental concerns, this research proposes a mechanism to improve power quality by reducing total harmonic distortion (THD) in three-phase three-wire system using shunt active power filter (SAPF). Three control algorithms are utilized to achieve a reduction in THD: DC-link capacitor voltage, hysteresis current, and harmonic extraction algorithms. The proposed SAPF mechanism is ideal for small-scale businesses and residential projects keen on energy conservation and natural resources preservation. In the study, simulations were carried out using MATLAB/Simulink. To verify, a prototype was fabricated and experiments were undertaken. The simulation and experimental results are in good agreement. The proposed SAPF mechanism could reduce THD of the system from 41.47% to 15.07%.

Recital analysis of multilevel cascade H-bridge based active power filter under load variation

This paper investigates a 13-level cascaded H-bridge (CHB) converter for shunt active power filter (SAPF) application to minimize the total harmonic distortion (THD) of source current under load variation. The converter configuration comprises of six H-Bridge cells per leg. Carrier-based phase disposition PWM is used as a modulation strategy to control the switches of 13-level CHB topology. An instantaneous real and reactive power technique based harmonic current extraction method is implemented to extract the reference currents. The proportional-integral controller is implemented to control the DC voltage of the SAPF. The proposed 13-level CHB SAPF performance is compared with two-level voltage source SAPF, three-level CHB SAPF, five-level CHB SAPF and nine-level CHB SAPF. The proposed work is implemented using Matlab/Simulink. The comparative performance analysis of THD, harmonics, active power, reactive power and power factor are presented.

Integration of Solar PV With Low-Voltage Weak Grid System: Using Maximize-M Kalman Filter and Self-Tuned P&amp;O Algorithm

This paper introduces a novel self-tuned perturb and observe (SPO) algorithm for quick maximum power point tracking (MPPT) and a novel maximize-M Kalman filter (MMKF)-based control technique for optimal operation of grid-integrated solar photovoltaic (PV) energy conversion system, where linear/nonlinear loads are attached at point of common coupling (PCC). The proposed SPO is the improved form of perturb and observe (P&O) algorithm, where inherent problems of traditional P&O such as steady-state oscillation, slow dynamic responses, and fixed step size issues, are successfully mitigated. Therefore, SPO tracks maximum power peak (MPP) very rapidly, and it very accurately extracts maximum power from the PV array. The extracted power is used to meet the active power requirement of loads, and after meeting the load demand, the excess power is supplied to the grid. During power feeding, the power quality and power management are maintained by the MMKF-based control technique. In control strategy, the MMKF is used for fundamental harmonic component extraction from the grid voltage and load current, even when the grid voltage is characterized by adverse situations, such as sag, swell, harmonic distortion, dc offset, etc. Here, the SPO MPPT algorithm and MMKF-based control techniques are tested on a developed prototype. The efficient and reliable performances of SPO MPPT algorithm and MMKF-based control algorithm, in dynamic as well as in steady-state condition, are demonstrated under insolation variation conditions, nonlinear loading, as well as in different grid disturbances such as overvoltage, undervoltage, phase imbalance, harmonics distortion in the grid voltage, etc.

Optimal Dynamic Harmonic Extraction and Suppression in Power Conditioning Applications

Power quality in electrical systems is a basic requirement that should be guaranteed. Nonetheless, the increase of power-electronics-based applications and other nonlinear loads have induced harmonic distortion degrading the power quality; therefore, effective methods to measure and suppress such distortion need to be developed. The main contributions of this article are the following: the development of a novel fast-converging optimal estimator to determine online the harmonic components of a time-varying signal, which can be used for analysis and control purposes; the usage of the estimator to generate reference signals for an optimal control system in order to suppress the harmonics components; and the experimental validation of the proposed methodology as a feasible solution for industrial applications. The proposal considers practical assumptions such as the signal to be analyzed is corrupted with noise and contains time-varying harmonics (i.e., no steady-state condition is assumed). As an application of the harmonic estimator, the following two experimental tests are carried out: first, the optimal determination of the harmonic components of the current waveform in a nonlinear load, and second, the usage of harmonics information to mitigate them through of an active power filter, which is controlled by using an optimal trajectory tracking control scheme.

Improved instantaneous power theory based current harmonic extraction for unbalanced electrical grid conditions

This paper presents a novel harmonic extraction method named as “virtual input signal based instantaneous power theory (VIS-IPT)”. In this study, VIS-IPT is tested in a shunt active power filter (SAPF) for improving the performance under unbalanced electrical energy quality issues. In the operational process, VIS-IPT is used to generate the compensation signals consisting of harmonic/reactive currents. In the proposed method, reference signal generation is extracted for each phase, separately. In VIS-IPT, the compensation signals are obtained from the calculated powers through multiple-phase inverse Clark transformation. In this way, it eliminates the drawback of conventional IPT which calculates the undesired average reference under unbalanced situations. Moreover, the additional use of PLL for synchronization is eliminated in the proposed method. In this context, a three-phase SAPF system with nonlinear load groups is constructed and analysed in Matlab/Simulink environment in order to prove the efficacy of the proposed method. In addition, the proposed VIS-IPT method is compared with the conventional IPT method through a variety of case studies. The proposed method is examined under different case studies including balanced/unbalanced/distorted voltage and balanced/unbalanced load conditions. The case studies show that the proposed method has excellent compensation capability performance in comparison with the conventional method.