High Frequency Voltage Research Articles

23-level Single DC Source Hybrid PUC (H-PUC) Converter Topology With Reduced Number of Components: Real-Time Implementation With Model Predictive Control

In this paper, a new configuration of single DC source hybrid packed U-cell (H-PUC) converter with reduced number of components is proposed. The proposed H-PUC only requires one dc source, twelve power switches, and three capacitors to provide 23-level output voltage. It is comprised of two high voltage low frequency (LF) and low voltage high frequency (HF) sub-modules which leads to less power losses and higher efficiency of the proposed H-PUC converter. Moreover, a finite control set model predictive control (FCS-MPC) method is proposed to generate 23-level staircase output voltage with low THD and to regulate voltages of three capacitors to their desired values simultaneously. A real-time model of the proposed 23-level H-PUC converter and its suggested FCS-MPC are developed and implemented in OPAL-RT OP4510 platform to evaluate and validate the feasibility of the proposed H-PUC in grid-connected operation mode. The provided real-time implementation results verify and demonstrate the performance and viability of the proposed 23-level H-PUC and its associated FCS-MPC to provide low THD 23-level output voltage and all three capacitors voltages balancing.

Dual-Stage Control Structure for Multilevel Voltage Source Inverters

This work proposes an alternative for total harmonic distortion (THD) attenuation in power inverters by combining two different circuit stages. The Macro stage comprises of a Neutral-Point-Clamped (NPC) multilevel inverter operating in high voltage and low switching frequency. The Micro stage is a two-level three-phase inverter, which is faster and more accurate due to its higher frequency and limited voltage. In this dual-stage approach, the opposite characteristics of the converters lead the Micro stage to correct the distortions of the Macro. It is possible to work with small values of filtering components, lower than the ones needed in a one-stage approach. This way, the presented proposal aims to reduce the physical size of the converter and its costs. The NPC inverter works in open loop with its switching signals generated by optimized pulse patterns (OPP). For correct THD filtering, a resonant control strategy with a Notch filter is designed in the frequency domain, as well as a feedforward structure designed in time domain. Simulation results show that the proposed system keeps voltage THD in acceptable levels for IEEE Standards.

Biofield Frequency Bands-Definitions and Group Differences.

BackgroundIn the biofield literature, it is suggested that electromagnetic energy is part of the biofield. However, little is known about the exact definition of potential electromagnetic biofield frequency bands (FBs).Primary Study Objective: The current study sought to identify biofield FBs and test potential group differences.Methods/Design: High-frequency (i.e. >200 Hertz) voltage was measured at body parts along the spine and the brain.SettingMeasurements were conducted in an electrically shielded laboratory.ParticipantsTwenty experienced biofield practitioners (BPs, sample 1) and twenty-four students (STs, sample 2) participated in the study.InterventionsThe BPs performed a wide set of biofield exercises, while the STs participated in an assessment centre (with exercises such as role play). A total of N = 342 exercises were performed.Primary Outcome Measures: Based on surface electromyography, high-frequency (i.e., >200 Hertz) voltage was utilized as outcome measure.Results10 FBs were identified across all the data sets. The BPs had higher spectral power across these bands compared to the STs.ConclusionThe present paper presents a replicable method for the assessment of electromagnetic FBs which are potentially useful for future biofield research.

On the Rotor Position Self-sensing Capability of Reluctance and IPM Synchronous Motors

Iron saturation affects the low-speed and standstill rotor position estimation of synchronous motors based on high frequency voltage injection, leading to an estimation error. In the case of a heavily saturated machine, the estimation algorithm could even fail, due to the absence of convergence points, making the sensorless drive impractical. This article examines in depth the mentioned problem of convergence in salient rotor machines; a synchronous reluctance motor is assumed as case study since this kind of machine is considerably affected by iron saturation. At first, the article models and describes in detail the high frequency voltage injection estimation mechanism. Then it analyzes the convergence conditions and investigates the dependence of the estimation convergence range on the amplitude and phase of the reference current vector of the drive. Moreover, it proposes different methods to enhance the estimation convergence range, improving the accuracy as well. A comparison between the different approaches is given as well as hints for their design. At last, the impact of airgap space harmonics is pointed out. The results are validated by simulations and experimental tests.

Modular Multilevel Converter Switching Frequency Harmonics Analysis and Suppression Through Cell Voltage Control

This paper investigates the impact of reference's bias on the high frequency voltage spectrum for the modular multilevel converters (MMC). Analytical solution of the voltage spectrum under carrier Phase Shifted Pulse Width Modulation (PSPWM) is derived using double Fourier integral analysis. The distribution of the switching frequency voltage harmonics is found to be directly related to the ratio between the dc-link voltage and the cell voltage. A control method utilizing this phenomenon is thereby proposed to suppress switching frequency harmonics in the Differential Mode Voltage (DMV) and Common Mode Voltage (CMV). Cell voltage control trade-offs considering different cell numbers, different ac voltages, 3rd harmonics injection, and cell voltage stress are also investigated. The analysis and control method are validated through experiments on a 1.25 megawatt MMC testbed.

MTPA Control Strategy Based on Signal Injection for V/f Scalar-Controlled Surface Permanent Magnet Synchronous Machine Drives

In this paper, a new maximum torque per ampere (MTPA) control method for surface permanent magnet synchronous motors (SPMSMs) controlled by the scalar control (v/f) method is proposed. The scalar control is a sensorless method that controls only the magnitude and the frequency of the stator voltage vector without the information of the rotor position. This method suggests the injection of the high frequency voltage signal in the stator current vector reference frame, which can be calculated from the measured phase currents, to avoid the use of rotor position information. In addition, this method adjusts only the magnitude of the stator voltage to minimize the stator current based on the calculated input power. Another merit of this method is the robustness of the MTPA control to machine parameter errors or variations. With this proposed method, the stator current can be minimized in the whole speed-torque range and the drive efficiency can be improved. Simulation and experimental results are provided to verify the performance of this control strategy.

Total Harmonic Distortion and Output Current Optimization Method of Inductive Power Transfer System for Power Loss Reduction

Inductive power transfer (IPT) system is widely used in material handling. A typical structure of the system takes an H-bridge inverter with an inductor-capacitor-inductor (LCL) resonant filter to realize a constant track current supplying changeless energy to the second side. However, the output voltage total harmonic distortion (THD) of the inverter increases, which causes the increase of output current circulation, when using voltage width control method to eliminate source voltage fluctuating. Therefore, a two-stage converter is proposed to optimize the output current circulation. The two-stage IPT system is composed of a boost converter cascaded with an H-bridge resonant inverter. The boost converter is employed to provide a higher and stable DC bus voltage. The H-bridge resonant inverter operates in a fixed width with a constant switching frequency. With the proposed topology, the THD of the high frequency voltage maintains the minimum value to realize minimum output current circulation in the LCL filter. The soft switching is realized to reduce the losses. Furthermore, expressions of coil and track model are presented by combining the theoretical analysis and finite element analysis (FEA). The experimental results show that over 76.6% efficiency is demonstrated in conditions of an 800 W load at the 14% source voltage fluctuation and the maximum efficiency was 78.6 %. The range of efficiency variation was 2% compared to a full-bridge system with voltage pluse-width control of which was 4.6%.

Dual Quasi-Resonant Controller Position Observer Based on High Frequency Pulse Voltage Injection Method

This paper proposed a dual quasi-resonant controller position observer for conventional pulsating high frequency voltage injection method. The proposed position observer can not only improve the dynamic performance of the sensorless control, but can also compensate the position error fluctuation caused by the dead-time effect. To improve the dynamic performance, the digital bandpass filter in the traditional position observer used to extract high frequency current response is replaced by a quasi-resonant controller firstly. Moreover, an improved Luenberger observer without lowpass filter, which is usually used in traditional position observer to filter the noise in speed information, is adopted in the new position observer. Therefore, dynamic performances can be improved. Then, to reduce the sixth harmonic in the magnitude of position error and speed error caused by the dead-time effect, a frequency adaptive quasi-resonant controller is connected in parallel with the proportional-integral controller in the Luenberger observer. The experiment results verify that the proposed observer can reduce the position estimation error not only in steady state operation conditions, but in variable speed and variable load conditions, and the speed variation range can be widened as well.

Ultrasound generated by alternating current dielectric barrier discharge plasma in quiescent air

Dielectric barrier discharge (DBD) driven by an alternating current (AC) high-voltage power supply, also called silent discharge, has been known for more than a century since Siemens first proposed the term DBD in 1857, and penetrates into our daily lives. In our traditional view, AC-DBD is considered as an ozone generator for disinfection, an electronic emitter for depollution of gas streams, a jet actuator for flow control, and so on. However, the acoustic effect of AC-DBD is always neglected. Here, we demonstrate that an asymmetrical DBD plasma actuator which was powered by sinusoidal AC waveforms with an AC voltage of 16 kVp–p at a high voltage frequency of a few kHz can generate ultrasound in quiescent air by using a pressure-field microphone and a high accuracy phase-lock image Schlieren technique. The frequency of this induced ultrasound is approximately 100 kHz which is much higher than the sin high voltage frequency of a few kHz. It is the first time that ultrasound created by the AC-DBD is observed. This finding provides a comprehensive understanding of AC-DBD and might open up possibilities for novel industrial applications of AC-DBD by using the induced ultrasonic energy. In addition, according to the experimental results, a hypothesis is proposed on the formation mechanism of ultrasound generated by the AC-DBD plasma actuator.

Fault Detection for Covered Conductors With High-Frequency Voltage Signals: From Local Patterns to Global Features

The detection and characterization of partial discharge (PD) are crucial for the insulation diagnosis of overhead lines with covered conductors. With the release of a large dataset containing thousands of naturally obtained high-frequency voltage signals, data-driven analysis of fault-related PD patterns on an unprecedented scale becomes viable. The high diversity of PD patterns and background noise interferences motivates us to design an innovative pulse shape characterization method based on clustering techniques, which can dynamically identify a set of representative PD-related pulses. Capitalizing on those pulses as referential patterns, we construct insightful features and develop a novel machine learning model with a superior detection performance for early-stage covered conductor faults. The presented model outperforms the winning model in a Kaggle competition and provides the state-of-the-art solution to detect real-time disturbances in the field.

Torsional Vibration Analysis of Shaft in an Induced Draft Fan Due to Variable Frequency Drive

The torsional vibration problem of shaft in an induced draft fan (IDF) caused by frequency conversion driving technology is a result of dynamic electro-mechanical coupling behavior during the energy conversion. Therefore, it is difficult to understand the mechanism of torsional vibration by only analyzing the mechanical structure or the electrical structure. In this paper, eigenvalue structural analysis (ESA) and time-domain transient analysis, which are typically used to examine sub-synchronous resonance (SSR), are employed to resolve this issue. It is difficult to develop a linear model for complex controllers with ESA as ESA can cause certain errors during the linearization and estimation of initial values of equilibrium points. On the contrary, time-domain analysis not only offers a small-step integration technique to simulate a realistic condition but also facilitates transient analysis of complex controllers. Transient analysis has been used to study the influence of elastic parameters of shaft, self-damping coefficients, resistance of the stator side, smooth reactance of the stator side, and voltage-frequency ratio on the control of target frequency converters and cascade multilevel high-voltage frequency converters. In this paper,It is also advised to avoid torsional resonance region with torsional-vibration monitoring during the operation of the system, and stator resistance can be added and the voltage-frequency rate can be adjusted to obtain an integrated control of an active torsional-vibration system.

Efficient QR Updating Factorization for Sensorless Synchronous Motor Drive Based on High Frequency Voltage Injection

The conventional methods for estimating the rotor position of permanent magnet synchronous machines, at low speed range and characterized by rotor saliency, rely on high frequency voltage injection in the stator windings. Ordinarily, the rotor position estimation is achieved through the demodulation of the high frequency current response. In this article, an alternative method is presented for detecting rotor position from the rotating high frequency injection current response. The proposed ellipse fitting technique is not affected by signal processing delay effects and it requires the tuning of only one parameter, called forgetting factor, making the studied method suitable for industrial application thanks to its minimal setup effort. The inverse problem related to the ellipse fitting is solved implementing a QR recursive least squares algorithm. Efficient updating QR factorization has been adopted because of its features in terms of numerical stability and required limited computational effort. The proposed sensorless control scheme is validated by means of many experiments.

Performance improvement in a sensorless surface-mounted PMSM drive based on rotor flux observer

Permanent magnet synchronous motor sensorless algorithms for low speed region are usually based on rotor anisotropy. Although many studies showed a good behavior of this type of control, high frequency voltage injection is required, which causes loud acoustic noise in addition to electrical losses. On the other hand, methods based on back electromotive force or rotor flux observer, which guarantee high performance in the medium–high speed region, do not required voltage injection. In this paper, a rotor flux observer based algorithm performance is analyzed, in order to extend its use also in the low speed region. Behavior both with no-load, linear torque, quadratic torque, constant torque and compressor-load torque is tested, especially focusing on motor starting. Improvements to rotor flux observer algorithms available in the scientific literature are discussed and their effectiveness is verified by experimental results.

Design of an Isolated DC/DC Topology With High Efficiency of Over 97% for EV Fast Chargers

This paper presents an DC/DC topology achieving high efficiency of over 97-% for electric vehicle (EV) fast chargers requiring a very wide output voltage range. The proposed topology consists of an unregulated resonant converter and a non-isolated buck converter. The unregulated resonant converter is responsible for the galvanic isolation for overall system, and the buck converter carries out the charging of the battery inside EV by constant-current or constant-voltage mode control. This structure provides a number of advantages such as easy realization of a very wide voltage range, no circulating-current, zero-voltage-switching operation on all the switches of the unregulated resonant converter running at high frequency and high voltage, and the achievement of high efficiency at every time over the entire battery charging profile. The availability of small passive components is a benefit because it enables the design of high power-density. In this paper, the feasibility of the proposed topology in EV fast charger applications has been verified by a prototype converter developed with the specification of 120-kHz or 50-kHz switching frequencies, maximum power rating of 20-kW, maximum charging current of 30-A, and battery voltage range of 50-650-Vdc.

Dual-Machine Injection Method-Based Sensorless Starting Strategy for Wound-Rotor Synchronous Starter/Generator

Wound-rotor synchronous starter/generator (WRSSG) has been widely adopted in the modern aircraft. The uncertainty of the inductive saliency in WRSSG (the saliency may change, disappear, or reverse during starting process) makes it difficult to implement the sensorless starting in the low speed region. This paper proposes a dual-machine injection method for the sensorless control of WRSSG, which is able to eliminate the dependency on the machine saliency in rotor position estimation. Using the multi-stage structure of WRSSG, in the proposed method, a high frequency (HF) voltage is injected in the main machine (MM) of WRSSG, and HF current response in the main exciter (ME) side of WRSSG is detected and used to estimate the rotor position since the ME is connected with the MM through a rotating rectifier. Experiments about the proposed dual-machine injection method on a WRSSG prototype in low speed region are carried out, and the experimental results verify the effectiveness and advantages of the proposed method.

Electrical treeing in silicone gel under repetitive voltage impulses

Silicone gel is widely used to encapsulate power electronic modules. The weakness of the electrical insulation is surface discharges initiated at the gel-substrate-electrode triple junction and the subsequent formation of cavities; so called electrical trees. The propagation characteristics of cavities under high frequency and fast rise time voltages, which are typical waveforms formed in power electronic modules, have not been fully understood. Thus, in this research, the influence of frequency, rise time, and polarity on electrical treeing under repetitive voltage impulses are investigated. The results show that discharge tracks under positive impulses have filamentary shapes, and discharge tracks under negative impulses have spindle-shapes. The cavity length increases with the frequency and is especially long when the rise time is short under high frequency. This indicates the importance of understanding the cavity propagation characteristics under actual voltage waveforms in power electronics modules.

Multi-Stage-Structure-Based Rotor Position Estimation for a Wound-Field Synchronous Starter/Generator in the Low-Speed Region

This paper proposes a novel on-line rotor position estimation method for an aircraft wound-field synchronous starter/generator (WFSSG) in the low-speed region. The method is based on the fact that mutual inductance between stator and rotor windings of the main machine (MM) varies with the rotor position, so it is independent of magnetic saliency. High-frequency (HF) rotating voltage is imposed in the stator windings of the MM, and the rotor position information is extracted from the HF response current signals in the stator windings of the main exciter (ME) in WFSSG. Theoretical expressions of the HF response current signals containing rotor position information in the rotor and stator windings of the ME are derived. Then, harmonics in the ME stator windings are analyzed, and optimum frequencies of the injected HF voltage for MM and excited voltage for the ME are obtained. Also, a novel signal processing method without time delay is adopted to improve the signal-to-noise ratio of the extracted rotor position information. The performance of the proposed method is verified by the experimental results, and accurate rotor position can be estimated even if the magnetic saliency of the MM changes greatly during the start-up process.

RESEARCH OF INFLUENCE OF HIGH-FREQUENCY ELECTRICAL FIELD ON SOWING QUALITY OF CEREAL SEEDS

A study on the effect of high-frequency electric field on cereal seeds to increase seed germination and plant growth is presented. The study was conducted in the treatment of winter wheat seeds. High-voltage electric fields are one of the promising means of influencing crop seeds. One of the areas of use of high frequency high voltage electric fields is pre-sowing seed treatment, storage and processing. Experimental studies were conducted in the laboratory on a specially designed installation using a high-frequency high-voltage source. Processing doses have been established which make it practical to use a high-frequency, high-voltage electric field in electrotechnical winter wheat seed systems. Positive influence of high-frequency electric field on increase of sowing qualities and yielding properties of seeds is established. The optimal mode for determining the winter wheat field is the micro field, the mode is 16.8 kJ per 1 kg energy, the hour is 4 seconds, and the laboratory laboratory is 20% similar.

Noise Spectrum Shaping of Random High-Frequency-Voltage Injection Based on Markov Chain for IPMSM Sensorless Control

The high-frequency (HF) voltage injection method can accurately estimate the rotor position of an interior permanent magnet synchronous motor (IPMSM) at low speed and zero speed. However, the fixed injection frequency for the traditional HF-voltage injection method will produce loud audible noise. The random HF-voltage injection method has a spread spectrum, which can reduce the audible noise. However, random HF voltages are controlled by constant probability rules, and it is inevitable that continuous multiple random numbers are larger or smaller than the mathematical expectation in the digital implementation, which will lead to spectrum concentration of the HF current. Thus, the random HF-voltage injection method cannot reduce the audible noise effectively. A novel random HF square-wave voltage injection method for an IPMSM based on the Markov chain (MC) is proposed to reduce the audible noise. The transition of the injected HF square-wave voltages obeys the MC instead of constant probability rules, which not only can shape the power spectrum of the HF current but also enable the explicit control of the HF current time-domain performance to reduce the audible noise. In order to reduce the position error caused by the phase mismatch between the HF current and the demodulation signal, an enhanced signal processing method is presented. Then, the power spectra density of the proposed method is analyzed to verify the effectiveness. Finally, the correctness and the effectiveness of the proposed method are verified by experiment on a 2.0-kW IPMSM drive platform.

A High-Frequency High Voltage Gain Modified SEPIC With Integrated Inductors

With the rapid development of photovoltaic and fuel cell stacks, high voltage gain converters are urgently demanded. Conventional boost is limited by the exaggerated duty cycle, it is impossible to obtain a high voltage gain while ensuring efficiency. Therefore, a zero-voltage switching (ZVS)-modified SEPIC converter that combines a voltage multiplier cell with traditional SEPIC is proposed in this paper. With detailed parameters design process, this presented converter works at zero voltage switching (ZVS), while obtaining high voltage gain without extremely high duty cycle. Besides, voltage stress is also reduced and low-voltage component with lower parasitic parameters can be used, thus efficiency is maintained. In order to further improve the power density, an integrated inductor scheme is adopted in this paper without changing intrinsic working states of the two inductors. A 36-W prototype is built, and experiments are conducted to verify the advantages of the proposed converter. The efficiency is up to 91.5% at full load.