Variable Voltage Source Research Articles

Adaptive tuned piezoelectric MEMS vibration energy harvester using an electrostatic device

In this paper an adaptive tuned piezoelectric vibration based energy harvesting system based on the use of electrostatic device is proposed. The main motivation is to control the resonance frequency of the piezoelectric harvester with the DC voltage applied to the electrostatic system in order to maximize the harvested power. The idea is demonstrated in a hybrid system consisting of a cantilevered piezoelectric harvester combined with an electrostatic harvester which is connected to a variable voltage source. The nonlinear governing differential equation of motion is derived based on Euler Bernoulli theory, and solved to obtain the static and dynamic solutions. The results show that the harvester can be tuned to give a resonant response over a wide range of frequencies, and shows the great potential of this hybrid system.

Efficient model for modular multi-level converter simulation

Detailed models of modular multi-level converters (MMCs) are cumbersome for electromagnetic transient simulation programs because of their high number of components which involve large simulation times. In this work, the modeling of an MMC is addressed with the objective of reducing the simulation time. First, the MMC structure is presented, including the modulation technique, the voltage balancing algorithm and the circulating current control used to validate the model. Next, an efficient simplified model is proposed. This is formed by just one variable voltage source, one variable capacitor and one variable resistor per arm, regardless of the number of submodules. This simplified model allows the simulation time to be reduced while keeping the dynamics of the MMC. The comparison through several PSCAD simulations with a detailed 5-level MMC model proves its validity during both steady-state and transient conditions (ac and dc short-circuits).

Permanent Magnet Synchronous Machine Parameters Identification for Load Characteristics Calculation

Self reactance Xd in direct axis'd’ and self reactance Xq in quadrature axis ‘q’ influence the load characteristics of the permanent magnet machine. Their calculation methods are known. All calculations should be verified by measurements. Measurement with AC variable voltage and frequency source applied on stator winding is correct when eddy currents do not exist. Other methods evaluate the DC current decay after initial direct current was applied on the stator winding. Accuracy of these methods is lowered because of the numerical evaluation of current decay curve. Another method performs the measurement on the machine loaded as a motor. The load angle ßis measured by a machine set of four machines. The accuracy is lowered by higher harmonics induced in no load in the helping synchronous machine. The load angle can be also obtained by geometrical construction of the vector diagram. In this paper the evaluation of the generator steady state regime of the machine is used. The generator works with different loads consisting of capacitance, inductance or arbitrary impedance or resistance. When the generator transfers from no load to load regime the rotor is shifting and the load angle changes. This angle is measured. The newly proposed measurement methods are simple in special cases of loads. Results of measurements and their experimental verification are published in the paper.

Precision high-value resistance scaling with a two-terminal cryogenic current comparator.

We describe a cryogenic two-terminal high-resistance bridge and its application in precision resistance scaling from the quantized Hall resistance (QHR) at RH = RK/2 = 12 906.4035 Ω to decade resistance standards with values between 1 MΩ and 1 GΩ. The design minimizes lead resistance errors with multiterminal connections to the QHR device. A single variable voltage source and resistive ratio windings are utilized to achieve excellent dynamic stability, which is not readily obtained in low-current measurements with conventional cryogenic current comparators (CCCs). Prototypes of this bridge have been verified by a successful international comparison of high-resistance scaling using two-terminal CCCs in the national metrology institutes of Argentina, Mexico, and the United States.

A real-time and closed-loop control algorithm for cascaded multilevel inverter based on artificial neural network.

In order to control the cascaded H-bridges (CHB) converter with staircase modulation strategy in a real-time manner, a real-time and closed-loop control algorithm based on artificial neural network (ANN) for three-phase CHB converter is proposed in this paper. It costs little computation time and memory. It has two steps. In the first step, hierarchical particle swarm optimizer with time-varying acceleration coefficient (HPSO-TVAC) algorithm is employed to minimize the total harmonic distortion (THD) and generate the optimal switching angles offline. In the second step, part of optimal switching angles are used to train an ANN and the well-designed ANN can generate optimal switching angles in a real-time manner. Compared with previous real-time algorithm, the proposed algorithm is suitable for a wider range of modulation index and results in a smaller THD and a lower calculation time. Furthermore, the well-designed ANN is embedded into a closed-loop control algorithm for CHB converter with variable direct voltage (DC) sources. Simulation results demonstrate that the proposed closed-loop control algorithm is able to quickly stabilize load voltage and minimize the line current's THD (<5%) when subjecting the DC sources disturbance or load disturbance. In real design stage, a switching angle pulse generation scheme is proposed and experiment results verify its correctness.

Power Factor Correction Rectifier with a Variable Frequency Voltage Source in Vehicular Application

This paper presents a PFCVF (Power Factor Correction) rectifier that uses a variable frequency source for alternators for electric and hybrid vehicles application. In such application, the frequency of the signal in the alternator changes according to the vehicle speed, more over the loading effect on the alternator introduces harmonic currents and increases the alternator apparent power requirements. To overcome these problems and aiming more stability and better design of the alternator, a new third harmonic injection technique is proposed. This technique allows to preserve a good THD (Total Harmonic Distortion) of the input source at any frequency and to decrease losses in semiconductors switches, thereby allowing more stability and reducing the apparent power requirements. A comparative study between the standard and the new technique is made and highlights the effectiveness of the new design. A detailed analysis of the proposed topology is presented and simulations as well as experimental results are shown.

Design and Investigative Aspects of RF-Low Power 0.18-µm based CMOS Differential Ring Oscillator

This manuscript presents the designing and investigative aspects of a low power, wide frequency range, and delay cell based 3 and 5-stage ring oscillator for RF-Ultra-WideBand application. The wide range of frequency is achieved by using two variable voltage sources i.e. control voltage source (Vcntrl) and tail current source (Vtail). A tail current improvement is responsible to control the charging and discharging time of oscillator. Moreover, the push-pull configuration is also used to attain high frequency. In addition, the proposed work presents the effect of control voltage and tail current source on the oscillator frequency. This work establishes a relation between oscillator frequency and its power consumption. This work also gives a comparison between 3stage and 5-stage ring oscillator. The circuit is implemented in 180 nm CMOS process provided by TSMC. The designed oscillator is measured to cover a frequency range of 1.3 – 5.7 GHz for 3-stage and 1.99 – 3.12 GHz for 5-stage ring oscillator. The simulated circuit draws 0.510 mW of average power for 3-stage ring oscillator and 0.719 mW average power for 5-stage ring oscillator.

A New STATCOM Model for Power Flows Using the Newton–Raphson Method

The paper presents a new model of the STATCOM aimed at power flow solutions using the Newton-Raphson method. The STATCOM is made up of the series connection of a voltage-source converter (VSC) and its connecting transformer. The VSC is represented in this paper by a complex tap-changing transformer whose primary and secondary windings correspond, notionally speaking, to the VSC's ac and dc buses, respectively. The magnitude and phase angle of the complex tap changer are said to be the amplitude modulation index and the phase shift that would exist in a PWM inverter to enable either reactive power generation or absorption purely by electronic processing of the voltage and current waveforms within the VSC. The new STATCOM model allows for a comprehensive representation of its ac and dc circuits-this is in contrast to current practice where the STATCOM is represented by an equivalent variable voltage source, which is not amenable to a proper representation of the STATCOM's dc circuit. One key characteristic of the new VSC model is that no special provisions within a conventional ac power flow solution algorithm is required to represent the dc circuit, since the complex tap-changing transformer of the VSC gives rise to the customary ac circuit and a notional dc circuit. The latter includes the dc capacitor, which in steady-state draws no current, and a current-dependent conductance to represent switching losses. The ensuing STATCOM model possesses unparalleled control capabilities in the operational parameters of both the ac and dc sides of the converter. The prowess of the new STATCOM power flow model is demonstrated by numerical examples where the quadratic convergence characteristics of the Newton-Raphson method are preserved.

A Novel STATCOM Model for Dynamic Power System Simulations

This paper introduces an advanced model of the STATCOM suitable for steady-state and dynamic simulations of large-scale power systems. It allows for a comprehensive representation of the STATCOM's AC and DC circuits-this is in contrast to current practice where the STATCOM is represented using an equivalent variable voltage source which is not amenable to a proper representation of its DC circuit. The new STATCOM model comprises a voltage source converter (VSC) in series with an LTC transformer. The former is represented by a complex tap-changing transformer whose primary and secondary windings would correspond, in a notional sense, to the VSC's AC and DC buses, respectively. The magnitude and phase angle of the complex tap changer correspond to the amplitude modulation index and the phase shift that would exist in a PWM inverter to enable either reactive power generation or absorption purely by electronic processing of the voltage and current waveforms within the VSC. The numerical technique employed to solve the STATCOM model is the Newton-Raphson method for both operating regimes, the steady-state and the dynamic-state. The latter involves discretization of the STATCOMs and synchronous generators differential equations so that the nonlinear algebraic equations and the discretized differential equations are linearized around a base operating point and assembled together in a unified frame-of-reference for robust iterative solutions.

Variable Voltage Source Inverter with controlled frequency spectrum based on Random Pulse Width Modulation

This paper presents a new method for single phase variable voltage inverter based on Random Pulse Width Modulation. In Random Pulse Width Modulation based inverter, the frequency spectrum of the output current and voltage waveforms becomes continuous because of the randomization of the switching function of the devices controlling the output voltages. This paper establishes a theory that if the distributions of the random numbers generated by the random source are kept within certain limit with respect to the peak value of reference sinusoidal waveform, the frequency spectrum can be controlled. On the basis of the results, a novel drive using variable tap changing transformer (optional) and adaptive random number generator, to control the ratio between the numbers generated by the random source and the reference waveform has been suggested that will guarantee a better power quality profile for a broad range of output voltages . DOI: http://dx.doi.org/10.11591/ijpeds.v2i1.150

STATCOM Stabilizer based on Fuzzy Logic Control for Damping Power Oscillation

Problem statement: In power systems, there exists a continuous challenge to improve dynamic performance of power system. Approach: Static Synchronous Compensator (STATCOM) is a power electronic based device that has the capability of controlling the power flow through a line. This study applies the Static Synchronous Compensator (STATCOM) to control the power flow during dynamic period. To verify the effect of the STATCOM on dynamic performance, the mathematical model and control strategy of a STATCOM was needed to be presented. The converters of STATCOM were represented by variable voltage source with associate transformer leakage reactance and the voltage source and the reactance were transformed into current injection. The current injection model of STATCOM was modeled into power flow equation and thus it was used to determine control strategy. This study applies the fuzzy logic control to determine the control strategy of STATCOM. The swing curves of the three phase faulted power system without and with a STATCOM was tested and compared in various cases. Results: The swing curve of the system with STATCOM based fuzzy logic control had the less amplitude during the dynamic period. Conclusion: STATCOM can improve the dynamic performance of the system after disturbance.

A Megawatt-Scale Power Hardware-in-the-Loop Simulation Setup for Motor Drives

We report on the application of a 5-MW variable voltage source (VVS) amplifier converter for utilization in power hardware-in-the-loop (PHIL) experiments with megawatt-scale motor drives. In particular, a commercial 2.5-MW variable speed motor drive (VSD) with active front end was connected to a virtual power system using the VVS for integrating the drive with a simulated power system. An illustrative example is given, whereby a 4-MW gas turbine generator system, including various loads, is simulated and interfaced with the VSD hardware in the lab through the VVS using current feedback to the simulation. Mechanical loading is applied to the motor via an identical 2.5-MW dynamometer connected to the same shaft. This paper first describes the PHIL facility, illustrates the challenges of powering a motor drive from a controlled voltage source converter at the multimegawatt scale, and provides experimental results from dynamic simulations. While certain challenges remain with the accuracy of the interface, it is concluded that PHIL simulations at the megawatt power level are possible and may prove useful for validating models of drive systems in the future.

Method of programming a hearing aid by a programming device

A battery-powered hearing aid (1) is programmed via a programming device (2), the hearing aid (1) having a battery (11) and a line connection (3, 4) for connecting the battery (11) to the programming device (2). The programming device (2) uses a variable voltage source (5) and an input comparator (6) with a first and a second input terminal and an output terminal to output a variable voltage to one input of the input comparator (6) and determining the voltage of the hearing aid battery (11) by using the second input of the input comparator (6) of the programming device (2). By ramping the output of the variable voltage source (5) used as a reference, the voltage of the battery (11) can be determined with great accuracy using existing hearing aid programming circuitry.

Fully Digital Control of Multilevel Cascade Inverter with Variable DC Voltage Sources

Cascaded multilevel inverters have been widely applied for the applications of high voltage and high power systems. The input power sources for a cascaded multilevel inverter requires separate dc voltage sources, and available dc sources include batteries, photovoltaic arrays and fuel cells...etc. If variations or fluctuations occur at the input voltage, the harmonic distortion of the inverter output voltage will increase. The conducting angles of switches in the conventional cascaded multilevel inverters are obtained by the use of Fourier series to minimize the harmonic distortion of output voltage. The traditional method is complex and difficult to implement on a single chip, especially when the input voltage sources can not remain constant and stable. A switching control algorithm is proposed for cascaded multilevel inverter with variable dc voltage sources. The proposed control combines the output voltage feedback and the input voltage feed-forward method to achieve dynamic control and low distortion of the inverter output voltage. Analysis, simulations and experimental results are presented to demonstrate the superiority of the proposed system.

Harmonic Mitigation and Power Factor Improvement using Fuzzy Logic and Neural Network Controlled Active Power Filter

This work focuses on the evaluation of active power filter which is controlled by fuzzy logic and neural network based controller for harmonic mitigation and power factor enhancement. The APF consists of a variable DC voltage source and a DC/AC inverter. The task of an APF is to make the line current waveform as close as possible to a sinusoid in phase with the line voltage by injecting the compensation current. The compensation current is estimated using adaptive neural network. Using the estimated current, the proposed APF is controlled using neural network and fuzzy logic. Computer simulations of the proposed APF are performed using MATLAB. The results show that the proposed techniques for the evaluation of APF can reduce the total harmonic distortion less than 3% and improve the power factor of the system to almost unity.

High Aspect Ratio Microcolumns to Manipulate Single Electrons on a Liquid Helium Surface for Quantum Logic Bits

Electrons are bound to the surface of liquid helium by the image potential due to the induced polarization of the helium. The potential varies as the reciprocal of the distance of the electron from the surface so that the energy levels for the electron motion perpendicular to the surface are those of a one-dimensional hydrogen atom with very small charge. In order to make quantum logic elements (qubits) using the ground state and first excited state in this potential, individual electrons must be confined over microelectrodes which are individually connected to variable voltage sources so that the electron energy levels can be shifted in and out of resonance with applied microwave radiation. The electrodes consist of an array of gold columns, about 1.2 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$muhbox m$</tex> tall and 200 nm in diameter, separated by 500 nm. These are grown by electroplating on the ends of leads deposited on a silicon substrate by e-beam lithography. The leads are covered by a dielectric layer and then a metal ground plane, so that the electric field from the leads is screened. We describe, here, our technique for fabricating this system and present the numerical computations of the electric fields from the electrodes.

Common-Mode Response Overlapping vs. Shaping in Rail-to-Rail Op-Amp Input Stages

In this paper, a circuit technique—common-mode (CM) response overlapping—for maintaining the small-signal behavior of rail-to-rail amplifiers nearly constant over the whole input CM range, is introduced. This technique modifies the CM response of the rail-to-rail input stage adequately by means of two constant input floating voltage sources, which are adjusted by using a static tuning section. Its performance is compared with a second technique—CM response shaping—, which is also based on two variable input floating voltage sources, but relies on a dynamic feedback tuning loop. Experimental results obtained from two 3-V 0.8-μm CMOS single-stage rail-to-rail amplifiers, which operate with CM response overlapping and shaping, respectively, are provided.

Automatic Coupling Control of a Loop–Gap Resonator by a Variable Capacitor Attached Coupling Coil for EPR Measurements at 650 MHz

A coupling coil was fabricated that can electrically change the magnetic coupling with a loop–gap resonator (LGR) for EPR studies at 650 MHz. It is composed of a single-turn coil and a coupling control circuit that includes a varactor diode. The coarse control of the magnetic coupling is made by mechanically changing the distance between the LGR and single-turn coil. The fine control is obtained by changing the capacitance of the varactor diode that is connected in parallel with the single-turn coil. This capacitance is controlled by changing reverse voltage from a variable bias voltage source. Because this can be located far from the resonator, remote control of coupling of the LGR is possible. Automatic coupling control (ACC) was accomplished by negative feedback of the DC component in the radiowaves reflected from the LGR to the coupling control circuit when the LGR was irradiated precisely at its resonant frequency. To accomplish this, automatic frequency control (AFC) is used. In EPR measurements of a phantom that included a physiological saline solution containing a nitroxide radical, it was confirmed that the drifts in the coupling and resonant frequency caused by the perturbation of the resonant nature could be sufficiently compensated by the ACC and AFC systems. In the in vivo EPR studies, it was found that the deviation of coupling at the chest of a mouse is greater than that at the head of a rat, but the ACC system could compensate for the respiratory motions of a living animal.

A new configuration of single-phase symmetrical PWM AC chopper voltage controller

With the increased availability of power MOSFETs and insulated gate bipolar transistors, a new generation of simple choppers for AC inductive loads is foreseen. These new power semiconductors ease the use of forced commutations of thyristor switches to improve the supply power factor, even with highly inductive loads. The AC controllers with thyristor technology can be replaced by pulsewidth modulation (PWM) AC chopper controllers which have important advantages. In this paper, a symmetrical PWM AC chopper designed to operate with single-phase inductive loads with a reduced number of controlled switches is described. The operation as a variable voltage source of this converter is evaluated. This includes the conversion characteristics, harmonic generation, harmonic distortion factor, and input power factor. By digital simulation, these characteristics are investigated theoretically, and to correlate the measurements with theory, an experimental setup is presented to confirm the analytical analysis.

Impedance frequency characteristics of MAGLEV power feed circuits

AbstractIn Japan, the MAGLEV (magnetically levitated train) is now well along in development testing. The MAGLEV power source must supply a variable voltage and variable frequency source, and contains many higher harmonics which cause many problems such as inductive interference. Thus it is necessary to clarify the impedance frequency characteristics of the MAGLEV power feed circuit.In view of this situation, experiments and investigations concerning the impedance frequency characteristics of the coils for propulsion and the power feeding circuit at the Miyazaki Test Track have been performed but no theoretical analysis has been done.Thus a theoretical analysis was performed in this paper by applying the inverted L equivalent circuit to the coil for propulsion, from which the characteristics of the coils for propulsion were analyzed.In addition, the characteristics of the power feeding circuit could be clarified by assuming the equivalent circuit of the power feeder line.As a result, the measured values and calculated values were almost equal in both the characteristics of the coils for propulsion and those of the power feeding circuit.