Active Compensation Method Research Articles

Design of a novel 3D tip-based nanofabrication system with high precision depth control capability

The design, analysis, and experimental investigation of a novel 3D tip-based nanofabrication system with high precision depth control capability is presented in this paper. Based on this system, a new depth control method, namely tip displacement-based closed-loop (DC) depth control methodology is proposed to improve the depth control capability. As the force-depth prediction with the commonly-used depth control method, i.e. the normal force-based closed-loop (FC) method, may depend on the machining speed, the machining direction, and the material properties, etc. Compared with the FC method, the DC method decreases the complexity and the high uncertainty. The tip feed system utilizes a non-contact force, i.e. the electromagnetic force, to adjust the tip displacement. Therefore, the tip support mechanism can be used to accomplish the tip-sample contact detection. Additionally, an active compensation method is proposed to eliminate the tilt angle between the sample surface and the horizontal plane. Otherwise the machining depth will change gradually, i.e. getting deeper or lower. Furthermore, a series of patterns have been fabricated on silicon sample surface with the proposed system and method. The maximum machining depth of a single scan reaches 300 nm, which is much larger than that of an atomic force microscope (AFM)-based nanofabrication system. The experimental results demonstrate that the system has advantages of distinguished depth control capability, high machining accuracy, and excellent repeatability, which diminishes the influence of above-mentioned factors on the machining depth. Also, the method has the potential of machining arbitrary 2D/3D patterns with well-controlled depth and high accuracy.

Semiconductor-Based Galvanic Isolation: Touch Current Suppression

This paper presents a comprehensive analysis of the generation mechanism and suppression methods of common-mode (CM) touch current when employing semiconductor-based galvanic isolation (SGI). SGI achieves galvanic isolation by utilizing semiconductor switches to deliver differential-mode (DM) power during their on states while sustaining CM isolation voltage during their off states. In SGI converters, the touch current (TC) is generated as the switch output capacitance is charged by the CM voltage during each turn- on transient. The TC rises as the switching frequency increases, which limits the system power density. This process is modeled by the proposed high-frequency pulse current model and the low-frequency equivalent resistance-based average model. Passive TC suppression approaches are reviewed, and an active TC compensation method has been proposed. A 2-kW EV battery charger with a GaN-based Totem-pole power factor correction stage and an SGI-based dc/dc stage has been built and tested. The touch current has been effectively reduced by 27 dB. It allows the converter to operate at a higher switching frequency to achieve higher power density while meeting the safety standards’ touch current requirement.

Ground-to-satellite time and frequency synchronization link with active carrier phase compensation.

In this paper, a synchronization link between one ground station and one geostationary satellite is established. The ground station receives retransmitted signals from the satellite, measures phase delay along the propagation route, and actively compensates back to its sending signals, realizing real-time phase fluctuation compensation. The transmitted signal contains two frequencies to eliminate common-mode phase noise. The difference between their carrier phase delays is measured. Different modes of carrier phase variation are separated and compensated, achieving a remaining time jitter of ±200 ps. Major sources of error are analyzed, and potential methods for improvement are discussed. The proposed ground-to-satellite link and active compensation method has potential applications in frequency standard dissemination to remote receivers (including ground stations or satellites). These potential applications justify further study of this system.

Modeling Stabilization of Crane-Induced Ship Motion With Gyroscopic Control Using the Moving Frame Method

This paper presents a new method in multibody dynamics and applies it to the challenge of stabilizing ship motion induced by onboard crane operations. Norwegian industries are constantly assessing new technologies for more efficient and safer production in the aquacultural, renewable energy, and oil and gas industries. They share a common challenge to install new equipment and transfer personnel in a safe and controllable way between ships, fish farms, and oil platforms. This paper deploys the moving frame method (MFM) to analyze the motion induced by a crane, yet controlled by a gyroscopic inertial device. We represent the crane as a simple two-link system that transfers produce and equipment to and from barges. We analyze how an inertial flywheel can stabilize the ship during the transfer. Lie group theory and the work of Elie Cartan are the foundations of the MFM. This, together with a restriction on the variation of the angular velocity used in Hamilton's principle, enables an effective way of extracting the equations of motion for an open-loop system. Furthermore, this work displays the results in three-dimensional (3D) on cell phones. The long-term results of this work lead to a robust 3D active compensation method for loading/unloading operations offshore. Finally, the simplicity of the analysis anticipates the impending time of artificial intelligence when machines, equipped with onboard central processing units and internet protocol addresses, are empowered with learning modules to conduct their operations.

High-Precision Sensorless Drive for High-Speed BLDC Motors Based on the Virtual Third Harmonic Back-EMF

In order to improve the performance of the high-speed brushless direct current motor drives, a novel high-precision sensorless drive has been developed. It is well known that the inevitable voltage pulses, which are generated during the commutation periods, will impact the rotor position detecting accuracy, and further impact the performance of the overall sensorless drive, especially in the higher speed range or under the heavier load conditions. For this reason, the active compensation method based on the virtual third harmonic back electromotive force incorporating the SFF-SOGI-PLL (synchronic-frequency filter incorporating the second-order generalized integrator based phase-locked loop) is proposed to precise detect the commutation points for sensorless drive. An experimental driveline system used for testing the electrical performance of the developed magnetically suspended motor is built. The mathematical analysis and the comparable experimental results have been shown to validate the effectiveness of the proposed sensorless drive algorithm.

An Active Oscillation Compensation Method to Mitigate High-Frequency Harmonic Instability and Low-Frequency Oscillation in Railway Traction Power Supply System

This paper investigates the high-frequency harmonic instability (HHI) and low-frequency oscillation (LFO) phenomena in high-speed railways, and proposes an active oscillation compensation method to mitigate these HHI and LFO. Such mitigation method introduces the input voltage oscillating components of grid side to the control loop of the grid-side converter, which helps to mitigate the voltage oscillation variables and restore the steady state of the train and traction network (simplified as “train-network”) system. From the perspective of train-network impedance, this paper proposes the train impedance models with and without the mitigation process. The generalized Nyquist analysis method is used to analyze the stability of the system with and without the mitigation. Finally, the mitigation method is verified by simulated and experimental data, to be capable of suppressing both HHI and LFO effectively.

Observer-based Fault-Tolerant Control of DC-AC Converters in Wind Turbines for Ancillary Service

In this paper, a generic model of DC-AC converters is introduced and an active fault compensation method for the realization of fault tolerant ancillary services of wind power plants is proposed. Ancillary services include the ability to support the grid with reliable and stable power supply which is an increasingly important requirement of single wind turbines and wind farms. The reduced model presents the positive, negative and zero sequence of the three phase system and can therefore take asymmetrical faults of the electrical power system in a wind power plant into account. It is shown that the model-based scheme is able to reconstruct actuator faults and to operate the wind turbine fault tolerant against typical faults in the three-phase power system.

Active Damping Stabilization for High-Speed BLDCM Drive System Based on Band-Pass Filter

The tight-speed regulation of the motor drive system can yield constant power load characteristics, which may lead to a negative admittance effect and destabilize the power supply. In order to overcome this problem, active damping compensation techniques have been widely used. However, the conventional active stabilization based on the low-pass filter combined with current reference injecting need a strong tradeoff between achieving effective active compensation and reducing the dynamic coupling. For this reason, a novel active damping compensation method based on the band-pass filter is proposed in this paper. The method is to feedback a portion of the dc-link voltage changes into the injecting nodes. Both the strategies of the current reference stage injecting and the voltage reference stage injecting have been analyzed. Simulation results show that the strategy of voltage reference injecting can avoid the coupling among system dynamics and the compensator. Finally, an experimental driveline platform based on the two identical high-speed magnetically suspended brushless DC motors coupling system is established. Experiential results verify the effectiveness of the proposed active stabilization method.

Improved Neutral Current Compensation With a Four-Leg PV Smart VSI in a LV Residential Network

Loads in low voltage (LV) residential areas are mainly single-phase types which are supplied from a delta/wye connected distribution transformer with a grounded neutral conductor creating a three-phase (3P) four-wire (4W) distribution system. The unbalanced single-phase load distributions in traditional 3P-4W LV networks cause significant neutral currents which can result in the overloading of the neutral conductor and electrical safety concerns for customers. In this paper, the dependency of the load generated neutral current on the distribution line variable zero sequence R/X ratios is developed, and a new decentralized robust active neutral compensation method is proposed using a multifunctional transformerless 3P four-leg (4L) photovoltaic (PV) smart voltage source inverter (SVSI). System stability is verified from the bode analysis and the improved neutral compensation is evaluated from the circuitry model analysis. Actual single-phase customer loads with real sun irradiance and temperature profiles are used with an urban 3P-4W LV network model from Australia and implemented in simulation using the PSCAD/EMTDC software to verify the efficacy of the proposed controller in real world distribution networks. Different transient faults analyses and point of common coupling dynamic voltage regulation are also performed and faster fault recovery, better neutral compensation, and optimized voltage profile are achieved from the designed PV-SVSI.

Active power compensation method for single‐phase current source rectifier without extra active switches

The existing active power decoupling methods for single-phase current source rectifiers (SCSRs) usually involve a lot of additional semiconductor devices or energy storage units, which is adverse to cost and efficiency. This study proposes an active power decoupling method to buffer the double-frequency ripple power. The main circuit is configured by adding only a decoupling capacitor and a diode to the traditional SCSR. Compared with the existing ones, the added components are minimised. The operating principle and modulation scheme are described. A closed-loop control method is developed to enhance twice the line frequency ripple power compensation performance. The guide for the selection of the decoupling capacitance is also discussed. Simulations and experimental results are presented to show the effectiveness of the method.

Active Compensation Method for Light Source Frequency Drifting in <inline-formula> <tex-math notation="LaTeX">$\Phi $ </tex-math></inline-formula>-OTDR Sensing System

Phase-sensitive optical time-domain reflectometry ( $\Phi $ -OTDR) has the ability to make a measurement on external disturbance dynamically along the sensing fiber by monitoring the interference fading pattern variance of the Rayleigh backscattering waveform through continuous probe pulse injection. However, even if there is no disturbance, the received $\Phi $ -OTDR trace will still show slow but noteworthy distortion due to light source frequency drifting (LSFD). This trace-to-trace slow distortion makes it challenging to capture low-frequency event. In this letter, an active compensation method based on laser frequency sweep and cross-correlation calculation has been proposed to suppress the influence of LSFD. With the proposed active compensation method, the tracking of LSFD can be realized, and the trace-to-trace distortion can be greatly suppressed. The experimental result has shown that a vibration event of 0.5 Hz has been identified successfully under mean frequency drifting speed of 1.68 MHz/s, which extends the application realm of the $\Phi $ -OTDR sensing system to quasi-static measurement.

Investigation of Series-Connected IGBTs in Fast High-Voltage Circuit Breaker

The ECRH system on J-TEXT tokamak requires fast circuit breakers as switches to cut off the 80 kV power supply within 20 μs when failure occurs. Series connected IGBTs is a better choice for the breaker than mechanical switch and thyristor in this case. The voltage balance among IGBTs is the main issue that needs investigation. This paper presents a two-stage active gate trigger time compensation method to ensure the voltage balance among IGBTs. The test environment consists of a 1500 V/10 A circuit with 3 IGBTs which are connected in series. The experimental result shows that the method can effectively improve the dynamic-voltage balance and has a certain extent meaning for the solution of voltage balance of series connected IGBTs .

Improved Selective Harmonics Elimination Scheme With Online Harmonic Compensation for High-Power PWM Converters

To reduce the low-order harmonics produced by the high-power pulsewidth-modulated (PWM) converters, selective harmonic elimination (SHE) scheme is commonly used due to its superior harmonic performance at low switching frequency. However, as an off-line modulation technique, the SHE scheme itself lacks the capability to realize the active compensation of the grid background harmonics. To enable the active compensation ability of the SHE-modulated PWM converters, this paper proposes an active compensation method through the jittering of SHE phase angle. The proposed method can realize the real-time compensation of the preexisting system background harmonics in high-power PWM converters' system. An application example on a high-power PWM current-source rectifier (CSR) system is provided in this paper. Experimental results show that the proposed method can effectively attenuate the line current harmonics caused by the grid background harmonics in the high-power PWM CSR systems.

Compensating for Tissue Changes in an Ultrasonic Power Link for Implanted Medical Devices.

Ultrasonic power transfer using piezoelectric devices is a promising wireless power transfer technology for biomedical implants. However, for sub-dermal implants where the separation between the transmitter and receiver is on the order of several acoustic wavelengths, the ultrasonic power transfer efficiency (PTE) is highly sensitive to the distance between the transmitter and receiver. This sensitivity can cause large swings in efficiency and presents a serious limitation on battery life and overall performance. A practical ultrasonic transcutaneous energy transfer (UTET) system design must accommodate different implant depths and unpredictable acoustic changes caused by tissue growth, hydration, ambient temperature, and movement. This paper describes a method used to compensate for acoustic separation distance by varying the transmit (Tx) frequency in a UTET system. In a benchtop UTET system we experimentally show that without compensation, power transfer efficiency can range from 9% to 25% as a 5 mm porcine tissue sample is manipulated to simulate in situ implant conditions. Using an active frequency compensation method, we show that the power transfer efficiency can be kept uniformly high, ranging from 20% to 27%. The frequency compensation strategy we propose is low-power, non-invasive, and uses only transmit-side measurements, making it suitable for active implanted medical device applications.

Comparative study on passive and active projector nonlinear gamma calibration

This paper compares the active and passive projector nonlinear gamma compensation methods for phase error reduction. The active method modifies fringe patterns before their projection to ensure sinusoidality; the passive method, in contrast, compensates for the phase error after capturing those distorted sinusoidal fringe patterns. Our study finds that the active method tends to provide more consistent high-quality fringe patterns regardless of the amount of projectors defocusing; yet the effectiveness of the passive method is diminished if the measurement condition deviates from the calibration condition. Experimental results will be presented to demonstrate the differences between these two nonlinear gamma compensation methods.

Detection and suppression of parasitic DC voltages in 400V AC grids

Grid connected static power converters inject parasitic DC currents due to the offset in current sensing, control imperfections, assymetries in power switches and other secondary effects. Ever growing number of grid connected converters contributes to an increase of DC bias in AC grids, and this brings the cores of distribution transformers closer to saturation and increases their power losses. This paper provides sensitivity analysis of distribution transformers to the DC bias, and considers solutions for detecting and compensating the parasitic DC components in AC grids. Active compensation methods can be advantageously used in suppressing the DC bias at grid connection point of the power converter. The sensing approach proposed in this paper makes use of saturable ferromagnetic cores and a low cost DSP for signal analysis and processing. Proposed algorithm uses distortion of the magnetizing current of a parallel connected saturable core due to the bias. Experimental results demonstrate the capability for detecting and compensating the bias voltages far below 1 mV in 0.4 kV grids. The paper describes the principles of DC bias detection and it provides the guidelines for the proper design of magnetic components. High precision of the proposed DC bias sensing is thoroughly verified on the experimental setup connected to a 0.4 kV grid.

Active Speed Compensation Method of Direct Torque Control System and Stability Analysis

By analyzing characteristics of the DTC (direct torque control) system in electrical driving system, a shortcoming of the classical DTC method is to point out that it is unable to decouple the mutual interference between torque and speed, so that when a running asynchronous motor subjected to an instantaneous impact load, rotor speed and its deviation appears excessive fluctuations that can not be quickly restored to the initial set value. In this research, under conditions that without sensors for measuring load torque and rotor speed, to an electrical drive systems contains DTC devices, a novel ASCC (active speed compensation control) method is proposed based on ADRC (active disturbance rejection control) theory, on account of DTC model of asynchronous motor, a multiobjective observer is designed to regulate both the speed and the torque, and a proof of asymptotic stability that related this new control systems with the observer is made by theoretical deduction. Finally stimulating results show that this method can overcome the shortcomings of classical DTC system and greatly enhance the ability of the high-speed driving system to deal with unexpected impact loads.

Study of optical design of Blu-ray pickup head system with a liquid crystal element.

This paper proposes a newly developed optical design and an active compensation method for a Blu-ray pickup head system with a liquid crystal (LC) element. Different from traditional pickup lens design, this new optical design delivers performance as good as the conventional one but has more room for tolerance control, which plays a role in antishaking devices, such as portable Blu-ray players. A hole-pattern electrode and LC optics with external voltage input were employed to generate a symmetric nonuniform electrical field in the LC layer that directs LC molecules into the appropriate gradient refractive index distribution, resulting in the convergence or divergence of specific light beams. LC optics deliver fast and, most importantly, active compensation through optical design when errors occur. Simulations and tolerance analysis were conducted using Code V software, including various tolerance analyses, such as defocus, tilt, and decenter, and their related compensations. Two distinct Blu-ray pickup head system designs were examined in this study. In traditional Blu-ray pickup head system designs, the aperture stop is always set on objective lenses. In the study, the aperture stop is on the LC lens as a newly developed lens. The results revealed that an optical design with aperture stop set on the LC lens as an active compensation device successfully eliminated up to 57% of coma aberration compared with traditional optical designs so that this pickup head lens design will have more space for tolerance control.

Performance comparison of input current ripple reduction methods in UPS applications with hybrid PEM fuel cell/supercapacitor power sources

An uninterruptible power supply (UPS) system with different input current ripple reduction methods is proposed, and a comparison research has been conducted about these methods. The proposed UPS system consists of a 63-cell 300W proton exchange membrane (PEM) fuel cell stack, two 16-cell supercapacitors (SCs) in series, a high-efficiency push–pull DC/DC converter and a half-bridge DC/AC inverter. Besides that the traditional push–pull DC/DC converter has inherent advantages of low input-current stress and high voltage conversion ratio, the SCs, LC filter, and an active clamp circuit are employed to reduce the input current ripples in the UPS system. First, the input current ripple generation and performance without an external component are analyzed and modeled in the PEM fuel cell. Then the input current ripple reduction methods mentioned above are proposed and operated in the designed UPS system. Finally, the experimental results show that the input current ripple can be further reduced by using different current ripple reduction approaches, and the active compensation method has better performance than the passive compensation method. The input current ripple is less than 5% of the rated input current.

3상 계통 연계형 인버터에서의 전류 고조파 감쇄를 위한 능동형 피드포워드 보상 기법

This paper proposes a current harmonic compensation method for the grid-connected inverter, especially caused by the grid impedance. Grid impedance causes low order harmonics in the grid current and deteriorates power quality. This paper analyzes the negative impact of the grid impedance, and proposes an active feedforward compensation method. Proposing method verified through simulation and experiment with 3-phase 1.5kW voltage source inverter prototype.