Load Voltage Variations Research Articles

Multiple Control Strategies for Distributed Battery Energy Storages in Microgrid DC Fast Charging Stations to Improve Load Voltage Variations, Mutual Power Exchange with the Grid and Islanded Mode Operation

Multiple Control Strategies for Distributed Battery Energy Storages in Microgrid DC Fast Charging Stations to Improve Load Voltage Variations, Mutual Power Exchange with the Grid and Islanded Mode Operation

Design and Robustness Analysis of Multiple Extended State Observer Based Controller (MESOBC) for AVR of the Power System

Automatic voltage regulator (AVR) is installed on the synchronous generators in the power system and plays a very important role in maintaining the generator output voltage besides changes in load demand, parametric uncertainties, and operating temperature. As the load is continuously varying in the system, the AVR needs controllers to track and regulate the voltage of the synchronous generator much faster. This paper shows an initial attempt to design a robust multiple extended state observer (MESO) to estimate the variation in lump disturbances (i.e., load demand and parametric uncertainties) from all the components of the AVR. MESO-based controller (MESOBC) can track such matching and mismatching of both types of irregularities and regulate the terminal voltage of the generator accordingly. MESOBC performance is matched with strong published AVR designs for a standard condition, ±30% load voltage variation and for simultaneous changes in AVR parameters with ±30% load voltage variations. Integrated square error (ISE) is chosen as an objective function to compare the output of MESOBC with other published AVR designs in view of graphical AVR responses and by calculating various numerical values for AVR responses. At last, the robustness of MESOBC is also checked through sensitivity analysis, and it is seen that MESOBC guaranteed robust performance for the AVR of the power system under diverse operating conditions.

Small Scale Stability of Isolated Rural Microgrid Based on Load Characteristics

Rural areas are either weakly connected to grid or have no grid access. Therefore, hybrid system is only solution for continuous undisrupted power supply. Also these rural microgrids have specific types of load. Small systems are more vulnerable to load disturbances and therefore, frequency and voltage variation have post disturbance effect on the system stability. Four different types of loads having exponential voltage and frequency characteristics are considered for the study. EPRI Load modeling has been considered based on aggregate index calculation. The system is studied for step increase/decrease in load as well as input power to the wind energy system and also the post effect of voltage & frequency change on the load with its influence on the system is considered for study purpose. The isolated microgrid proposed has wind energy system with PMSG and biogas genset (BG) with synchronous generator (SG). The system is designed in such a way that any increase/decrease in load and input power to wind is taken up by the biogas system. No additional reactive power compensator is envisaged. Accordingly, the controllers are tuned using Integral Square Error criterion for mitigate variation in load voltage & frequency.

Study of Dual Active Bridge With Modified Modulation Techniques for Reduced Link Current Peak Stress and Harmonics Losses in Magnetics

High-frequency-link power-conversion is gaining popularity in recent days due to reduction of the size and weight of the converters for various applications. The performance of the dual active bridge heavily depends on the nature of modulation strategy used and on the loading conditions. Look-up table (LUT) based output power and output voltage dependent modulation strategies to investigate the peak current stress and harmonics in high-frequency link current is proposed in this article. The modulator is, thus, simple to implement. The peak stress, the harmonics (total demand distortion) in link current, and associated losses due to the proposed techniques are compared in four main cases, namely, first, single-phase shift, second, dual-phase shift, third, triple phase shift, and, fourth, modified phase shift (MPS)-I, -II, and -III. In MPS-I, weighted aggregate of harmonic currents minimization including fundamental component is carried out to achieve the minimum conduction losses in the magnetic elements. The same method is extended for minimizing the peak-to-peak ripple in the link current as MPS-II. In MPS-III, the desired total demand distortion in the ac-link current is enforced. The variation of voltage transfer ratio between input and output is taken into consideration using two-dimensional (2-D) LUT. Moreover, the requirement of 2-D LUTs are eliminated by using suitable curve-fitting exercise for the output load voltage variation and 1-D LUTs of coefficients. A detailed simulation study, associated mathematical analysis of the methods adopted and experimental verification are presented from 1 kW prototype.

Optimal control topology-based efficiency improvement of single-stage three level resonant AC/DC converters

In this paper, an optimal control topology for improving the efficiency of AC-DC three level single stage power factor correction (SSPFC) converter using artificial bee colony (ABC) algorithm is proposed. ABC algorithm is one among the renowned algorithms that utilises the cleverness of swarm bees and it imitates the food searching nature as well as the dancing activities of actual bee colonies. The ABC algorithm optimises the gain parameters based on the converter's output load voltage variations. From the attained gain parameters, the minimum load voltage variation has been achieved. By using the proposed method, the converter's switching component stresses, high circulating current, total harmonic distortion (THD) and low efficiency has been reduced. In addition, the proposed optimal control topology is dependent on the converter's input value as well as the load value changes and it maintains constant conversion efficiency with improved power factor. The proposed circuit is implemented in the MATLAB/Simulink platform and the effectiveness is analysed by comparing it with the conventional techniques. The comparison results demonstrate the superiority of the proposed approach and confirm its potential to solve the problem.

중요부하를 갖는 계통연계형 인버터의 고조파주입에 의한 단독운전방지 기법

The utility-interactive inverter with critical loads should supply continuous and stable voltage to critical loads even during the grid fault. The conventional control method which performs current control for grid-connected mode and voltage control for stand-alone mode undergoes the critical load voltage variation during grid fault. The critical load voltage may have large transient when the inverter performs mode transfer after the islanding detection. Recently, the indirect current control method which does not have the transient state during not only islanding detection but also the mode transfer has been proposed. However, since the voltage control is maintained even during the grid-connected mode it is difficult to detect the islanding. This paper proposes an active anti-islanding method suitable for the indirect current control method which does not have NDZ(Non-Detection Zone).

Effects of long-shunt and short-shunt connections on voltage variations of a self-excited induction generator

This paper presents a comparative study of steady-state performances of both long-shunt and short-shunt configurations of an isolated self-excited induction generator under various loading conditions. Both simulated and experimental results are clearly compared to examine the effects of both connections on load voltage variation of the studied induction generator. The analyzed results show that the long-shunt configuration can maintain lower load voltages while the short-shunt connection has better voltage variation under higher load voltages.

Performance investigation of a current-controlled voltage-regulated PWM rectifier in rotating and stationary frames

Active front-end rectifiers with reduced input current harmonics and high input power factor will be required in the near future for utility interfaced applications. In order to meet the new and more stringent regulations with force-commutated switches, the voltage source inverter approach is superior to the conventional current source approach, in terms of number of components and control options. However, the straightforward power angle control of the rectifier is characterized by a slow response and potential stability problems. This paper proposes a current-controlled PWM rectifier as an alternative. It provides near sinusoidal input currents with unity power factor and a low output voltage ripple. Moreover, it produces a well-defined input current harmonic spectrum, exhibits fast transient response to load voltage variations, and is capable of regenerative operation. PWM pattern generation is based on a carrier technique and the current controller is implemented in the: (a) stationary (abc) frame; and (b) rotating (dqo) frame. The design and the performance of the two controller options are investigated and compared. >

A force commutated solid state synchronous tap-changer for R-L loads

Abstract Whenever the required load voltage variation is over a limited range, it is preferable to use tap-changers to supply power to inductive loads. This improves the line power factor over the conventional phase control scheme. This paper shows that further improvement in the power factor is possible when force-commutation is used for such a purpose. This paper also suggests a suitable force commutated, trouble-free power circuit for the implementation of the suggested method.

Improvements in a Thyristor Controlled Static on-Load Tap-Changer for Transformers

A new type of static on-load tap-changer based on forced commutation is suggested in this paper as a better alternative to the conventional type of tap-changers. The response of the proposed tap-changer is very fast. Any required amount of load voltage variation can be obtained without introducing any phase shift in the output voltage. Experimental verification of the basic principles have been carried out which establish the feasibility of the proposed scheme. A number of theoretical and experimental results are presented.

A solid-state synchronous tap-changer permitting a selective reduction of line harmonics

Whenever the required load voltage variation is over a limited range, it is preferable to use tap-changers to supply power to the resistive loads. This improves the power factor over the conventional phase-control method. However, when phase control is used in conjunction with a tap-changer, the resulting voltage waveform will have a sufficient amount of harmonies. Thus, a method of reducing any one unwanted line harmonic to a low value is proposed in this investigation. A power circuit to implement the proposed scheme is also suggested.