Fundamental Frequency Voltage Research Articles

An Equivalent Voltage Index to Quantify the Impact of Harmonics on Shunt Capacitors

Harmonic distortions are known to affect the normal operation and life of power equipment. Shunt capacitor is one piece of equipment that is very sensitive to harmonics. Although limits have been established to limit the harmonic distortions experienced by a capacitor, methods to quantify the harmonic impact with easy-to-understand indices are still at large. This paper aims to address the above gap by proposing an equivalent voltage index. This index is to represent the impact of harmonic voltages and their features (such as peak value) into an equivalent increase in the fundamental frequency voltage otherwise experienced by the capacitor. The main advantage of such an equivalence is that PQ and non-PQ engineers can easily relate the impact to the general capacitor loading concept. The index is especially helpful to understand the impact of harmonics on capacitor and thus to justify harmonic mitigation projects.

Multiple Fault Tolerant Control Strategy for Rotor Field Oriented Induction Motor Drive Fed From CHB Converter With Redundant Cells

The article proposes a postfault control strategy for a rotor field oriented induction motor (RFO-IM) drive fed by a cascaded H-bridge multilevel converter (CHB-MLC) with redundant cells in each phase. The objective of the control strategy is to maintain the torque and speed of the RFO-IM in postfault operation and to maximize the converter's power capability by adding a maximum number of power cells during postfault operation. Furthermore, maximum line voltage is utilized from the redundant cells without increasing the dc-link voltage of power cells, and the motor's operating point in the voltage plane is analyzed and determined for various loading conditions during prefault and postfault operation. In the postfault operation, a common mode voltage of fundamental frequency is also added depending on the motor's loading condition and postfault configuration to distribute power evenly among the remaining healthy cells. Theoretical and graphical analyses include the equation of the operating point in the voltage plane, traversal of the operating point from prefault to postfault operation, and selection of common mode voltage of fundamental frequency based on the fault configuration and the motor's loading. The simulation and experimental data are used to validate the proposed fault-tolerant control approach.

A 510-to-545 GHz Radiating Source With an SIW-Based Harmonic Power Extractor in 40-nm CMOS

This article analyzes the required fundamental-frequency load impedance for third harmonic enhancement in a common-source transistor through investigating the relationship between the third harmonic current, the fundamental-frequency voltage, and the real and imaginary parts of the fundamental-frequency load impedance in the common-source transistor. Then, a harmonic power extractor (HPE) based on a differential substrate-integrated waveguide (SIW) is proposed to provide the required load impedance of the tripler at both the output and fundamental frequencies, thus enhancing the third harmonic power generation of the tripler. The HPE also provides the suppression of unwanted lower order harmonic leakage of the radiating source. In this article, the operation principle of the SIW-based HPE is explained, and the design of a 0.52-THz CMOS radiating source with the SIW-based HPE is detailed. After that, the mechanism of the bulk-bias-control-based frequency tuning technique used in the radiating source is analyzed, and the method of avoiding the parasitic radiation from the oscillator tank of the radiating source is introduced. In measurement, the radiating source achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 1-dBm equivalent isotropically radiated power, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 21.8-dBm radiated power, and 0.32% dc-to-THz efficiency at 524 GHz with a dc power consumption of 20.7 mW under a 0.9-V supply voltage. By using both power supply tuning and bulk bias tuning, the radiating source achieves 6.6% frequency tuning range.

An Improved Droop Control Strategy for Grid-Connected Inverter Applied in Grid Voltage Inter-Harmonics and Fundamental Frequency Fluctuation

This paper presents a current suppression method based on a droop control strategy under distorted grid voltage with inter-harmonics and fundamental frequency fluctuation. In this proposed strategy, the current incomplete derivation controller is employed to decrease the negative impact caused by harmonic and inter-harmonic grid voltage. This method provides a good dynamic response and has low complexity against the inter-harmonics with unfixed fundamental frequency. Based on a mathematical model of the grid-connected inverter, we designed novel instantaneous frequency detection and feed-forward methods to suppress the grid fundamental frequency fluctuation impacts. Then the main parameters were analyzed. The simulation and experimental results verified the feasibility and effectiveness of the proposed method.

An Improved Algorithm for a High Speed Distance Relay Using Walsh Functions.(Dept.E)

An algorithm for calculating the apparent transmission line impedance to the point of fault is presented. This algorithm is based on a half-cycle Window using walsh function technique. The real and the imaginary components of the fundamental frequency voltage and current of the faulty phases are evaluated and used to calculate the impedance, as seen from the relay location. The sampling rate used to test this algorithm is 16 samples/cycle. The algorithm has been tested using digital computer simulation of the sample model. A comparison between this algorithm and four other algorithms, suitable for fault impedance measurement was carried on here with particular reference to their accuracy and speed of calculations.

Theoretical Harmonic Spectra of PWM Waveforms Including DC Bus Voltage Ripple—Application to a Low-Capacitance Modular Multilevel Converter

This article develops a new closed-form analytical solution to the harmonic spectrum of the pulsewidth modulated (PWM) output voltage of the single-phase inverter connected to the dc bus with considerable voltage ripple. The solution is based on a double Fourier series expansion in two variables. As the single-phase inverter forms the basic building block of most converters, the developed expressions can be applied to various topologies. This article first identifies the interactions of a single-frequency sinusoidal modulation signal and the carrier signal with the dc bus voltage harmonics. The dc bus voltage harmonics are constrained in this article to multiples of the inverter output voltage fundamental frequency. The analysis is then extended to include a multifrequency modulation signal. Starting from the general solution, new expressions for the output voltage harmonics of the modular multilevel converter (MMC) are developed. The low-capacitance MMC is chosen in this analysis due to inherent low-frequency voltage oscillations in the converter internal capacitors. The MMC analytical harmonic spectrum can incorporate the effects of the circulating current control and third harmonic injection PWM, by including the second- and third-order harmonic components in the modulation signal, respectively. The MMC analytical harmonic spectrum is benchmarked against the experimental results.

An Impedance Model-Based Multiparameter Identification Method of PMSM for Both Offline and Online Conditions

Existing online motor parameter identification methods mostly depend on the fundamental frequency voltage equations, which lead to the unsatisfactory identification effect at low current and low speed operation. This article proposes a parameter identification method based on the high frequency (HF) equivalent impedance model of permanent magnet synchronous motor with HF signal injection at both the dq -axes. This method identifies the resistance and the dq -axis inductances offline and online, along with the flux linkage online. In order to improve the identification accuracy, the parameter sensitivity analysis-based algorithm is proposed to detect the resistance and the flux linkage. Meanwhile, the inverter nonlinearities and the HF influence on parameter identification are compensated effectively. In order not to affect the normal operation of the motor drive, the selection of the amplitude, and the frequency of the injected signal is investigated. The proposed method is validated on a 2.2-kW motor and confirmed by finite element analysis. The experimental results show the good identification effect in different operation conditions.

Energy Storage Requirements Optimization of Full-Bridge MMC With Third-Order Harmonic Voltage Injection

Full-bridge submodule (FBSM) capacitance of an FBSM-based modular multilevel converter (FB-MMC) can achieve a significant reduction with boosted ac voltages, which makes it a promising candidate in voltage-source-converter-based high-voltage-direct-current scenarios in terms of cost reduction and dc short-circuit fault tolerance. With consideration of third-order harmonic voltage injection (THVI), the characteristics of the FBSM voltage fundamental frequency and second-order harmonic fluctuations are analyzed in detail under steady-state and single-line-to-ground fault conditions. Both the optimal phase and amplitude of the injected third-order harmonic voltage are derived constrained by the same modulation margin, based on which the optimized THVI method is proposed. Under the same fluctuation conditions, the comparison of energy storage requirements between the FB-MMC with and without the THVI method is also carried out. The feasibility and validity of the proposed THVI method are verified by simulations on a ±200-kV FB-MMC system and experiments on a laboratory-scale platform. With the same fluctuations as the FB-MMC without THVI, both the simulation results and the experimental results indicate that the FBSM capacitance of the one applying the proposed THVI method can be reduced by about 16%.

Heat transfer enhancement of turbulent channel flow using a piezoelectric fan

This study experimentally investigated the flapping dynamics of a piezoelectric (PE) fan in channel flow and the resultant wall heat-removal performance enhancement. The PE fan consisted of a rigid PZT (Lead zirconate titanate) actuator and a flexible PET (Polyethylene terephthalate) blade. The PE fan in absence of electric excitation or air flow was chosen as the baseline data configuration. The mid-span of the PE fan was illuminated by a laser sheet, and the instantaneous profiles of the PE fan were captured by a high-speed camera system; the structure boundary detection algorithm and fast Fourier transform algorithm were used to identify the flapping amplitude and frequency. The time-averaged heat transfer performance across the channel wall with constant heat flux boundary condition was spatially resolved by the temperature sensitive paint measurement. The piezoelectric fan displayed the largest flapping amplitude at the fundamental resonant frequency of 43 Hz. The amplified flapping amplitude and the increased frequency were achieved with the elevation of the Reynolds number, and correspondingly the resultant heat transfer performances were improved. At a low Reynolds number of 1.37×104, the piezoelectric fan blade flapped synchronously with the PZT actuator, while the flapping amplitude was considerably intensified to 0.72 times the blade length under excitation voltage of fundamental resonant frequency, resulting in a 30% augmentation in the local Nusselt number. At a high Reynolds number of 1.91×104, the flapping frequency was locked to its flutter frequency 64.5 Hz, regardless of the excitation voltage frequency. The flapping amplitude and the resultant heat transfer performance were found to be insensitive to the excitation voltage frequency at a Reynolds number of 1.91×104, although the maximum local heat transfer was enhanced by 46% at an excitation voltage frequency 43 Hz.

Single-Phase Enhanced Phase-Locked Loops Based on Multiple Delayed Signal Cancellation Filters for Micro-Grid Applications

The grid voltage information such as the phase-angle, the frequency, and the amplitude is crucial for the design of synchronization and control of power converters in the micro-grid. The conventional approach to estimate the grid voltage information is accomplished by phase-locked loop (PLL) techniques. Among various existing PLL techniques, filter-based PLLs can provide more accurate estimations even under adverse grid conditions. In this paper, a new single-phase filtering technique based on multiple delayed signal cancellation (MDSC) is proposed for extracting both in-phase and quadrature components of the selected harmonic order of the single-phase grid voltage signal. This MDSC technique can be realized in both the direct-form and the recursive-form. In comparison with existing single-phase cascaded delayed signal cancellation (CDSC) techniques, this MDSC technique utilizes less memory for the extraction of grid voltage fundamental frequency component. The proposed MDSC filter can be applied as a pre-filter to the enhanced PLL (EPLL) for the prompt and accurate estimations of the grid voltage information under adverse grid conditions. Both frequency adaptive and non-adaptive MDSC-based EPLL schemes are proposed in this paper. To validate the effectiveness of the proposed methods, experiments are conducted on the MDSC-based EPLLs and compared with the CDSC-EPLL under various grid voltage disturbances.

Optimal Sizing and Sitting of Distributed Generation for Power Quality Improvement of Distribution Network

The Point of Common Coupling (PCC) where suppliers’ responsibility and customers demand meet is of great concern due to increase degree of voltage variation assessment; valuable indicator of system conditions (voltage profile). Unstable condition of the power system outside operational or statutory limit, an adverse effect of nonlinear loads usually generate harmonics as well as fundamental frequency voltage variations and increase rate of power losses. These loads need to be compensated for. The major concerns of utility operations is to mitigate adverse effect of this system conditions. This research work focuses on optimal siting and sizing of Distributed Generation (DG) in a 43 bus distribution system. Power losses coupled with voltage deviation, considering objective function that compute present percentage losses in 11kV Dikko feeder, Abuja Electricity Distribution Company (AEDC), Suleja Distribution Network, Nigeria. We identified buses with poor voltage profile without DG installation and determined optimal sizing and siting of DGs where losses can be mitigated and power quality improved. ETAP version 12.6 2014 was used for load flow analysis to establish a decisive based case. The total load of the system considered was (3490 + j2700) kVA. Active and Reactive power losses in the system before DG installation were 246.300 kW and 289.903 kVAR respectively. DGs installation in the case study, has a considerable effects on loss reduction in the network. It is observed that 8.10% and 7.20% active and reactive power loss reduction was achieved while bus voltage improved by 0.4%. Genetic Algorithm Optimization techniques programmed in MATLAB 2015 software was used for optimal placement and sizing of the DG in the system.

Optimal Sizing and Sitting of Distributed Generation for Power Quality Improvement of Distribution Network

The Point of Common Coupling (PCC) where suppliers’ responsibility and customers demand meet is of great concern due to increase degree of voltage variation assessment; valuable indicator of system conditions (voltage profile). Unstable condition of the power system outside operational or statutory limit, an adverse effect of nonlinear loads usually generate harmonics as well as fundamental frequency voltage variations and increase rate of power losses. These loads need to be compensated for. The major concerns of utility operations is to mitigate adverse effect of this system conditions. This research work focuses on optimal siting and sizing of Distributed Generation (DG) in a 43 bus distribution system. Power losses coupled with voltage deviation, considering objective function that compute present percentage losses in 11kV Dikko feeder, Abuja Electricity Distribution Company (AEDC), Suleja Distribution Network, Nigeria. We identified buses with poor voltage profile without DG installation and determined optimal sizing and siting of DGs where losses can be mitigated and power quality improved. ETAP version 12.6 2014 was used for load flow analysis to establish a decisive based case. The total load of the system considered was (3490 + j2700) kVA. Active and Reactive power losses in the system before DG installation were 246.300 kW and 289.903 kVAR respectively. DGs installation in the case study, has a considerable effects on loss reduction in the network. It is observed that 8.10% and 7.20% active and reactive power loss reduction was achieved while bus voltage improved by 0.4%. Genetic Algorithm Optimization techniques programmed in MATLAB 2015 software was used for optimal placement and sizing of the DG in the system.

Energy Storage Requirement Optimization of Hybrid Modular Multilevel Converter With Circulating Current Injection

This paper analyzes the characteristics of the submodule (SM) voltage fundamental frequency and second-order harmonic ripples with the consideration of negative voltage state of the full-bridge SM. The optimal operation point, which minimizes the fundamental frequency ripples, is derived. Both the design principle and analytical expressions for SM capacitance dimensioning are presented, and the comparison between energy storage requirements with and without negative voltage states in the arm reference voltages are also carried out under the same constraints on the transmission power, modulation index, and SM voltage fluctuations. However, the SM voltage fundamental frequency ripples increase significantly with reactive power increasing. Therefore, a circulating current injection (CCI) method is proposed in order to suppress the ripples caused by reactive power. Comparative simulations on a ±200 kV hybrid modular multilevel converter (MMC) and experimental results on a laboratory prototype verified the correctness of the presented design principle and the effectiveness of the proposed CCI method. It is shown that the energy storage requirements of the hybrid MMC with negative voltage in arm reference voltages can be reduced about 15%, and it achieves a significant reduction about 45% with the proposed CCI method.

Characteristics Analysis of Capacitor Voltage Ripples and Dimensioning of Full-Bridge MMC With Zero Sequence Voltage Injection

Compared to the conventional half-bridge submodule-based modular multilevel converter (MMC), the full-bridge submodule (FBSM) capacitance of FB-MMC can be reduced significantly with consideration of negative voltage state of the FBSM, which has benefits to cost and size reduction. This paper analyzes the characteristics of the FBSM voltage fundamental frequency and second-order harmonic fluctuations of the FB-MMC without and with zero sequence voltage injection (ZSVI) comparatively. The analyses show that ZSVI has almost no impacts on the FBSM voltage fundamental frequency fluctuations, while the second-order harmonic components become 5/6 times of the one without. Based on these analyses, with the same fluctuation constraint as the case without ZSVI, the FBSM capacitance dimensioning method is also presented. The correctness of the presented analyses is verified by comparative simulation results on a ±200 kV FB-MMC system and experimental results on a laboratory platform. The simulation and experimental results indicate that the FBSM capacitance of the FB-MMC can achieve a reduction about 10% with ZSVI.

Harmonic Virtual Impedance Design for Parallel-Connected Grid-Tied Synchronverters

In recent years, synchronverters have become a preferred control solution for the integration of renewable energy sources and battery systems to power networks. In this control strategy, the converter acts as a fundamental frequency voltage source and, as such, is unable to deal with harmonic power quality issues. In this paper, the harmonic control is frequently addressed using virtual impedances; however, they have been seldom studied for synchronverters. This paper presents a detailed design procedure for harmonic virtual impedances applied to parallel-connected synchronverters. The proposed method offers a tailor-made design of the converter output impedance and large stability margins. The method is used to decouple the dynamics of the synchronverter control, and the proposed virtual-impedance is explained in detail. The obtained results showed the output impedance of each synchronverter can be designed to achieve a tradeoff in power quality between current and voltage. In addition, the effect of frequency variations was explored and two solutions were provided and compared. All the control system improvements were experimentally validated using two 15-kVA battery-supported synchronverters connected to a distorted weak grid.

Control of AC/DC Modular Multilevel Converter

In recent years, a special attention is paid to grid connected multilevel converters. These converters have specific use in industry in a high power, medium-voltage and high-voltage applications. This paper presents new control algorithm for single-phase AC/DC modular multilevel converter with target application as a traction converter connected directly to trolley wire. The proposed control strategy presents resonant controllers for converter current control with fundamental frequency adaptation. The fundamental frequency estimation and voltage synchronization is based on Second Order General Integrator Phase Locked Loop (SOGI-PLL). Furthermore, this paper presents robust voltage balancing technique for multilevel converter based on energy calculation of DC-link capacitances. It provides voltage balancing of multilevel converter cells with unbalanced load. The resulting control algorithm has low total harmonic distortion of converter trolley current even under unbalanced load condition. The algorithm was experimentally verified on the low voltage laboratory prototype with 3 H-bridge cells.DOI: http://dx.doi.org/10.5755/j01.eie.24.6.22282

Unbalanced synchronous reference frame control of singe-phase stand-alone inverter

This paper presents harmonic damping schemes of the single-phase stand-alone inverter. The unbalanced synchronous reference frame technique is selected to control fundamental frequency voltage at the point of common coupling. The output voltage and the inductor current of the inverter are transformed to the unbalanced synchronous reference frame in which the proportional-integral regulators are used to force the error signals in the dq axes to zero. This control scheme does not require an orthogonal signal generator, and it is equivalent to the ideal proportional-resonant regulator. Harmonic regulators, orders 3rd, 5th, 7th, and 9th are added to minimize the voltage harmonics caused by the connected nonlinear load. The proposed controller is compared with the commonly-used multi-resonant controller. Simulation and experimental results of a 1.5-kVA inverter with the proposed control scheme exhibited excellent harmonic damping of the output voltage, caused by a highly nonlinear load and fast transient performance, which were better than the conventional resonant controller.

Qualitative Identification of the Static Pull-In and Fundamental Frequency of One-Electrode MEMS Resonators.

This paper attempts to qualitatively identify the static pull-in position, pull-in voltage, and fundamental frequency of one-electrode microresonators from a physical perspective. During theoretical derivation, a generalized one-degree-of-freedom (1-DOF) model in nondimensional form derived using the differential quadrature method (DQM) is first introduced and then transformed for frequency normalization. Based on the deduced formulas, the upper and lower bounds of the static pull-in position and pull-in voltage are both deduced through mathematical proof. To distinguish the monotonic and nonmonotonic behavior of the fundamental frequency versus direct current (DC) voltage, a critical condition decided only by cubic stiffness is then determined. For the first time, two extreme static positions, as well as the corresponding fundamental frequencies and DC voltages to identify different frequency behaviors are derived, and their variations versus cubic stiffness are then discussed and verified. During the simulation process, a high-order DQM and COMSOL 2D model are both applied for numerical analyses. Guided by nondimensional results, typical behaviors with specific physical parameters are examined in detail. Results demonstrate that the curve tendencies between all the qualitative results and quantitative numerical simulations in dimensional form agree well with each other, implying the possibility of using 1-DOF model to qualitatively discuss physical parameters effects on the system statics and dynamics.

Integrated Power-Quality Monitoring Mechanism for Microgrid

With the penetration of renewable energy, the power quality (PQ) becomes the important issue for operation stability of power system. The efficient monitoring mechanism for different multiple PQ disturbances is the fundamental infrastructure for modernization of power system. However, the diverse PQ signals result in numerous analysis techniques and make the integration of PQ monitoring difficult. To resolve the above-mentioned problem, the Prony-based PQ analysis mechanism is proposed in this paper. The commonly seen PQ disturbances, such as the fundamental frequency deviation, harmonics, interharmonics, voltage fluctuations (flickers), and PQ events, can be easily analyzed and detected with Prony-based technique and integrated for the design of monitoring system. The performance of proposed analysis mechanism can be verified by the implementation in the Pingtung ac microgrid of Taiwan.

Six‐phase SVPWM with common‐mode voltage suppression

There are two common-mode voltages (CMVs) in a six-phase machine with two Y-connected windings shifted by 30°, which bring adverse effects on the six-phase system. In this study, a method of six-phase space vector pulse width modulation (SVPWM) is proposed, which can suppress the magnitude and frequency of the two CMVs. First, all basic vectors are divided into 16 classes, from which two classes of basic vectors are selected. With these two classes of basic vectors, some auxiliary vectors are constructed according to an optimisation model. Then a reference vector is synthesised by using these auxiliary vectors. There are two kinds of synthesis schemes, single-class synthesis and two-class synthesis. Finally, optimal sequences of the basic vectors that play a role in each switching period are obtained. The experimental results show that the peak-to-valley value of CMV is only one-third of the DC-bus voltage of the converter in the two-class synthesis, and the frequency of CMV is only three times of the line voltage fundamental frequency, which is far below the switching frequency of the converter.