Load Current Variation Research Articles

EMBEDDED CONTROLLED ZVS DC-DC CONVERTER FOR ELECTROLYZER APPLICATION

An Electrolyser is part of a renewable energy system (RES) and generates hydrogen from water electrolysis that is used in fuel cells. A static DC-DC converter is required to couple the Electrolyser to the system DC bus. This paper presents the design of three soft-switched high-frequency transformer isolated DC-DC converters for this application based on the given specifications. It is shown that LCL- type series resonant converter with capacitive output filter is suitable for this application. Detailed theoretical and simulation results are presented. Due to the wide variation in input voltage and load current, no converter can maintain zero-voltage switching for the complete operating range. The experimental results are compared with the simulation results and they are almost similar.

Particle swarm optimisation-based neuro-controller design for DC/DC buck converter

This paper presents voltage mode control of buck converter by a simple neuro-controller (NC) which is trained by the particle swarm optimisation (PSO) algorithm. Structure of controller, PSO algorithm and training of neural networks (NN) is discussed in details. The dynamic performance of the controller under input voltage change and load current variations are presented and discussed in the simulation environment.

A 2D transient numerical model combining heat/mass transport effects in a tubular solid oxide fuel cell

The purpose of this study is to present a 2D transient numerical model to predict the dynamic behavior of a tubular SOFC. In this model, the transient conservation equations (momentum, species and energy equations) are solved numerically and electrical and electrochemical outputs are calculated with an equivalent electrical circuit for the cell. The developed model determines the cell electrical and thermal responses to the variation of load current. Also it predicts the local EMF, state variables (pressure, temperature and species concentration) and cell performance for different cell load currents. Using this comprehensive model the dynamic behavior of Tubular SOFC is studied. First an initial steady state operating condition is set for the SOFC model and then the time response of the fuel cell to changes of some interested input parameters (like electrical load) is analyzed. The simulation starts when the cell is at the steady state in a specific output load. When the load step change takes place, the solution continues to reach to the new steady state condition. Then the cell transient behavior is analyzed. The results show that when the load current is stepped up, the output voltage decreases to a new steady state voltage in about 67 min.

DC–DC Converter-Aware Power Management for Low-Power Embedded Systems

Most digital systems are equipped with dc-dc converters to supply various levels of voltages from batteries to logic devices. DC-DC converters maintain legal voltage ranges regardless of the load current variation as well as battery voltage drop. Although the efficiency of dc-dc converters is changed by the output voltage level and the load current, most existing power management techniques simply ignore the efficiency variation of dc-dc converters. However, without a careful consideration of the efficiency variation of dc-dc converters, finding a true optimal power management will be impossible. In this paper, we solve the problem of energy minimization with the consideration of the characteristics of power consumption of dc-dc converters. Specifically, the contributions of our work are as follows: 1) We analyze the effects of the efficiency variation of dc-dc converters on a single-task execution in dynamic voltage scaling (DVS) scheme and propose the technique for dc-dc converter-aware energy-minimal DVS. 2) is then extended to embed an awareness of the characteristics of dc-dc converters in general DVS techniques for multiple tasks. 3) We go on to propose a technique called for generating a dc-dc converter that is most energy efficient for a particular application. 4) We also present an integrated framework, i.e., , based on and , which addresses dc-dc converter configuration and DVS simultaneously. Experimental results show that is able to save up to 24.8% of energy compared with previous power management schemes, which do not consider the efficiency variation of dc-dc converters.

Load Current Model of Electric Apparatus Based on Load Voltage Characteristics during Voltage Sag

This paper describes the measurement-based load current model of electric apparatus after a voltage sag occurrence. The terminal voltage and load current of a personal computer (PC), an inverter fluorescent light and an incandescent light were measured to find out the dependences of load characteristics on the voltage sag. The magnitude of the load current after voltage sag depends on both the magnitude of residual voltage and the time period of voltage sag. In order to make it possible to take account of these transient load characteristics in the power quality estimation, a load current model is proposed. The load current waveform is obtained using the database of harmonic component of load current and time variation in the parameters of load voltage characteristic. The proposed model enables us to estimate the load current within an error of about 5% when the voltage sag occur.

A simple fuzzy logic based robust active power filter for harmonics minimization under random load variation

Widespread applications of power electronic-based loads continue to increase concerns over harmonic distortion. However, it is desired to draw purely sinusoidal current from the distribution network, but this is no longer the case with new generation loads, consisting of power electronic converters. The current harmonics produced by these non-linear loads further result in voltage distortion and leads to various power quality problems. This paper, therefore, deals with a simple fuzzy logic based robust active power filter to minimize the harmonics for wide range of variations of load current under stochastic conditions. The proposed control scheme is very simple and it is also capable of maintaining the compensated line currents balanced, irrespective of the unbalance in the load currents. The proposed methodology is extensively tested for wide range of variable load current under stochastic conditions and results are found to be quite satisfactory to mitigate harmonics and reactive power components from the utility current. The results presented in this paper clearly reflect the effectiveness of the proposed APF to meet the IEEE-519 standard recommendations on harmonic levels.

Low-Harmonic, Three-Phase Rectifier That Applies Current Injection and a Passive Resistance Emulator

A new three-phase diode bridge rectifier that provides low harmonic distortion of the input currents applying current injection technique is proposed in this paper. The rectifier applies a novel passive resistance emulator consisting of four diodes and a transformer with the volt-ampere rating of 3.57% of the rectifier-rated power. Optimization of the transformer turns ratio is performed in order to minimize the input current total harmonic distortion (THD). It is shown that with the optimal turns ratio the input current THD equals 3.72%. Dependence of the input current THD on the load current is analyzed, and it is shown that at low load currents the rectifier operates in the discontinuous conduction mode with the THD of 7.79%. The analytical results are experimentally verified on a 2 kW rectifier, indicating that the input current THD lower than 8% is provided within a wide range of the load current variations applying simple circuitry.

Improvements in Biasing and Compensation of CMOS Opamps

In this paper, we present modifications to the constant-g m bias circuit and Miller-lead compensation of operational amplifiers which eliminate or minimize some of their shortcomings. First, we demonstrate how parasitic pad capacitance can cause instability in the constant-g m bias circuit, and show that the transconductance is constant only for specific bias conditions. Next, we suggest a new circuit topology that requires 75% less compensation capacitance to achieve stability. We also discuss problems with Miller-lead compensation that arise from temperature, process, and load variations. Finally, we present a new biasing technique to correct these problems, and, through simulation, demonstrate a 40∘ improvement in phase margin over load current variations.

A novel method of output voltage stabilization with respect to load current variation in noncontact energy transfer

This paper examines a noncontact energy transfer system which can stabilize the load voltage with no-feedback control. A detachable transformer used in the system has a leakage inductance. Therefore, load voltage decreases greatly in proportion to load current. A feedback control circuit of the noncontact energy transfer system is more complicated than that of the contact energy transfer system. Consequently, even if without feedback control, a noncontact energy transfer system which can maintain the approximate fixed load voltage is required. The authors have analyzed the load voltage characteristic in detail and researched the mechanism, and found a novel method which minimizes the load voltage drop rate by using optimized capacitance value of two resonant circuits. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(2): 63–74, 2005; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20032

Aircraft starter/generator control unit design

This research aims to develop a controller for aircraft starter/generators using a digital signal processor (DSP) TMS320C25. A starter/generator is a DC machine carrying on two reverse operations - motor and generator. The whole control activity includes current control for motor operation, voltage control for generator operation, and electronics actions in the transitions for mode changes. Field control is the key issue of this research. A PWM DC chopper is employed for the field drive. A switching type of shunt field resistances is proposed to armature current control so that the motor operation can maintain sufficient output torque for engine starting. A DSP voltage regulator is prototyped and verified. The switching nature of the PWM drive makes variable structure control (VSC) a reasonable choice for control design. The experimental results demonstrate that VSC has much better performance than a continuous PI controller. Robustness tests against rotating speed and load current variations also give supporting results

An on-chip 96.5% current efficiency CMOS linear regulator using a flexible control technique of output current

This paper proposes an on-chip 96.5% current efficiency CMOS linear regulator using a flexible control technique of output current (FCOC). By the use of the FCOC technique, the proposed circuit realizes flexible output current drive according to the load current variation. Therefore, the proposed linear regulator ran supply stable output voltage using the FCOC technique. The linear regulator is fabricated by double-metal 1.2-/spl mu/m CMOS technology. The number of transistors is 46 and the die size is 0.423 mm/sup 2/. The fabricated linear regulator achieves a fluctuation of output voltage less than 6.81 mV/sub p-p/ at a frequency of output current f(I/sub out/) ranging from 1.8 Hz to 100 MHz. Moreover, the fabricated on-chip CMOS linear regulator can achieve 96.5% current efficiency.

Modeling of cross-regulation in converters containing coupled inductors

A general model of the multiple-winding coupled inductor is described, in which all parameters can be directly measured. The magnetics and the resulting cross-regulation models are employed in a tutorial explanation of the mechanisms by which leakage inductances and effective turns ratios affect cross regulation and discontinuous conduction mode boundaries in a multiple-output converter with arbitrary number of outputs. Analytical results are found for the discontinuous mode boundaries and for the steady-state characteristics when one of the outputs operates in discontinuous conduction mode. Three basic approaches to coupled-inductor design are compared: near-ideal coupling, practical moderate coupling, and the zero-ripple approach. It is shown that the best cross regulation can be obtained via the zero-ripple approach with relatively loose coupling in applications where there is at least one output whose load current variations are relatively small so that all windings can always operate in continuous conduction mode. The conclusions are supported by experimental results.

Dynamic Measurements of the Main Electrical Parameters of a Dc Machine

Since in many applications of dc machines an accurate knowledge of the dynamic mathematical model is necessary, it is desirable to have simple measurement methods to obtain the different parameters required. A new approach of defining the electrical parameters of a dc machine is shown. The measurement techniques provide dynamic resistance and inductance characteristics which are shown to be very much off the usual values taken from a linear approximation. Resistance values are measured by modified voltage drop methods, and inductance values are measured by load current variations. In case of transient behavior, like sudden short circuits or sudden load variations, the linear model cannot be applied, and the dynamic resistance and characteristics used in the nonlinear differential equations describing the system provide a good model within experimental error. The results show in particular how the armature inductance is dependent on the load as well as on the speed of rotation.

A 28 Volt, 0 to 150 AMP Power Supply Incorporating a Multi-Section Morgan Chopper

A novel technique has been developed which enables a Morgan Chopper to be used in a system having wide input voltage and load current variations. A multi-section Morgan Chopper is programmed as a function of these variables to maintain a more constant chopping frequency. This and other special circuit techniques have been incorporated in a production 28 volt power supply which regulates better than ± 1% over wide input voltage and load current variations. One version of this supply having output capability of 4200 watts is packaged in a full ATR case and weight 75 pounds (figure 1).

A Transistor Pulse Generator for Digital Systems

A design procedure is developed for a new transistor pulse generator circuit suitable for use as a building block in a digital system. The circuit produces a pulse whose shape is relatively independent of variations in transistor parameters and load current. Pulse durations in the range 0.5 microsecond to 20 microseconds and load currents of several hundred milliamperes may be obtained.

A stable source of high voltage

A stabilized high-voltage low-current supply suitable for use as a voltage reference in the 1000 V region is described. With elementary temperature control a stability of ±1 part in 10 000 over a day is obtained. Effects due to stray varying magnetic fields of 15 gauss are less than 1 part in 30 000. A load current variation of 400 μA will alter the output by 1 part in 10 000. A load of several milliamps can be obtained.