Recent Advances in Electrical & Electronic Engineering - Volume 12, Issue 1, 2019

Background: In recent years, demand for electricity has increased considerably, while the expansion of generation and transmission has been very slow due to limited investment in resources and environmental restrictions. Methods: As a result, the power system becomes vulnerable to disturbances and instability. FACTS (Flexible AC Transmission Systems) technology has now been accepted as a potential solution to this problem. This paper deals with the modelling, simulation and fuzzy self-tuning control of a DSTATCOM to enhance the stability and improve the critical fault clearing time (CCT) in a single machine infinite bus (SMIB). A detailed modelling of the D-STATCOM and comprehensive derivation of the fuzzy logic self-tuning control is presented. Results: The dynamic performance of the power system with the proposed control scheme is validated through in a simulation study carried out under Matlab/Simulink and SimPowerSystems toolbox. Conclusion: The results demonstrate a significant enhancement of the power system stability under the simulated fault conditions considered.

As being restricted by factors such as cost, efficiency and size, the development of high-power solar LED street light controller is faced with plenty of difficulties. In case that a structure of two independent DC/DC is applied as the main circuit, it has to face problems such as large size and high cost; in case of applying the bidirectional BUCK/BOOST circuit, it requires change-over switches to control the solar panel and LED light. As being restricted by withstanding voltage, on-resistance and cost, a PMOS device cannot be used as the change-over switch of solar panel and LED light. However, when being used as a change-over switch, an NMOS device must apply the low-side mode under which the negative ends of the mentioned three parts are cut off. In the condition of applying the low-side mode, a differential circuit must be used to detect the voltage of the solar panel. Furthermore, in order to make sure batteries can still be regularly charged after wearing out in daylight, the controller must be supplied with power through a dual power supply circuit that can obtain power from both the solar panel and the battery. The demander has a requirement on extremely low standby power consumption of the product, and thus it is necessary to minimize the circuit that is live while working in standby mode. Methods: The bidirectional BUCK/BOOST circuit structure is applied to the main circuit to realize a higher change-over efficiency while giving considerations to both cost and size. The NMOS device, model IRFB4410ZPBF, with a price of about three yuan, is used as the switching device, and the low-side mode is applied, that is the switches inserted in between negative end of the solar panel or LED light and that of the DC/DC circuit. The low-cost rail-to-rail operational amplifier LM358 is used to form a differential amplification circuit for detecting the voltage of the solar panel. A XL1509-12E1 chip that only costs 0.88 yuan/pc is selected as the main change-over chip for the power supply, which has realized the highly-efficient and low-cost change-over of the power supply. A dual power supply circuit and a step-down protective circuit are designed for the XL1509-12E1 change-over chip. By comparing solar panel voltage with battery voltage, the solar panel booting circuit is realized. Only when solar panel voltage is higher than battery voltage, does the system program start to power it up for running, so that the outage of most of the circuits of the system under standby mode does not consume energy. Furthermore, the solar panel voltage detecting circuit, the solar panel booting circuit and several return difference functions are corrected during system debugging. Results: The circuit board of the entire controller features small size, low cost and high efficiency. It measures about 100*62*18mm in size, costs about 60 yuan, and the charge/discharge change-over efficiency reaches up to over 95%. The controller has many functions: it is capable of operating within a large scope, in which, solar panel voltage is subject to 15~50V, LED light voltage is subject to 15~60V, battery voltage is subject to 10~35V and battery-end charge/discharge current is 10A; it is capable of adapting to monocrystalline silicon/multicrystalline silicon/thin-film and many other kinds of solar panels, as well as lithium/lead-acid and many other kinds of batteries; it is capable of detecting the conversion of day and night, automatically controlling charging and discharging and automatically making adaptive adjustment according to seasonal variations; the current to be consumed during standby will be maintained below 3mA, and thus the power consumption is extremely low. Conclusion: By selecting the bidirectional BUCK/BOOST circuit structure, applying low-side mode for switching of solar panel and LED light, using a differential circuit to detect solar panel voltage, using a low-cost DC/DC chip to realize power supply change-over, designing a dual power supply circuit, introducing solar panel booting circuit and other hardware design, as well as MPPT algorithm, state recognition and control, return difference control and other software design, a solar LED street light control product featuring small size, low cost, high efficiency and multiple functions is successfully developed.

Background: The integration of distributed renewable energy sources into the conventional power system network has created opportunities for electricity customers to reduce their electricity cost. This paper investigates the optimal power scheduling of a hybrid energy system connected to the grid in the presence of demand response strategy and inconvenience cost. Methods: A new proposed method of calculating the inconvenience cost which is dependent on total home appliance load, Customer Interruption Cost (CIC) and delay time operation of home appliances is proposed. The hybrid energy system consists of solar photovoltaic (PV) module and battery bank storage system. The home appliance scheduling is formulated as a non-convex mixed integer programming with a binary decision variable to switch ON/OFF the home appliances. The optimization objective is to minimize both the total daily electricity cost and inconvenience cost of a residential customer with different time-shiftable, power shiftable home appliances and customer time preference constraints. Results: The results show that it is important to schedule home appliances and include their inconvenience cost so that home appliances are not only shifted to the lower electricity tariff periods but can also start at their customer preferred operation times. Conclusion: The results also show that the hybrid energy system is able to cater for all the energy requirements of home appliances during the day, reducing power demand from the grid by a significant percentage and thus, relieve the power system network and afford electricity consumers significant monetary savings.

Background: Output polarity of the sub-function is generally considered to reduce the area and power of a circuit at the two-level realization. Along with area and power, the power-density is also one of the significant parameter which needs to be consider, because power-density directly converges to circuit temperature. More than 50% of the modern day integrated circuits are damaged due to excessive overheating. Methods: This work demonstrates the impact of efficient power density based logic synthesis (in the form of suitable polarity selection of sub-function of Programmable Logic Arrays (PLAs) for its multilevel realization) for the reduction of temperature. Two-level PLA optimization using output polarity selection is considered first and compared with other existing techniques and then And-Invert Graphs (AIG) based multi-level realization has been considered to overcome the redundant solution generated in two-level synthesis. AIG nodes and associated power dissipation can be reduced by rewriting, refactoring and balancing technique. Reduction of nodes leads to the reduction of the area but on the contrary increases power and power density of the circuit. A meta-heuristic search approach i.e., Nondominated Sorting Genetic Algorithm-II (NSGA-II) is proposed to select the suitable output polarity of PLA sub-functions for its optimal realization. Results: Best power density based solution saves up to 8.29% power density compared to ‘espresso – dopo’ based solutions. Around 9.57% saving in area and 9.67% saving in power (switching activity) are obtained with respect to ‘espresso’ based solution using NSGA-II. Conclusion: Suitable output polarity realized circuit is converted into multi-level AIG structure and synthesized to overcome the redundant solution at the two-level circuit. It is observed that with the increase in power density, the temperature of a particular circuit is also increases.

Background: All existing time delay estimation methods, i.e. correlation and covariance, depend on second or higher-order statistics which are inapplicable for the correlation of alpha-stable noise signals. Therefore, fractional lower order covariance is the most appropriate method to measure the similarity between the alpha-stable noise signals. Methods: In this paper, the effects of skewness and impulsiveness parameters of alpha-stable distributed noise on fractional lower order covariance method have been analyzed. Results: It has been found that auto-correlation, i.e. auto fractional lower order covariance,\ of non delayed alpha-stable noise signals follows a specific trend for specific ranges of impulsiveness and skewness parameters of alpha-stable distributed noise. The results also depict that, by maintaining the skewness and impulsiveness parameters of α-stable noise signals in a certain suggested range, better auto-correlation can be obtained between the transmitted and the received alpha-stable noise signals in the absence and presence of additive white Gaussian noise. Conclusion: The obtained results would improve signal processing in alpha-stable noise environment which is used extensively to model impulsive noise in many noise-based systems. Mainly, it would optimize the performance of random noise-based covert communication, i.e. random communication.

Solar Photovoltaic (PV) energy conversion has gained much attention nowadays. The output power of PV panel depends on the condition under which the panel is working, such as solar radiation, ambient temperature, dust, wind speed and humidity. The amount of falling sunlight on the panel surface (i.e., solar radiation) directly affects its output power. In order to maximize the amount of falling sunlight on the panel surface, a solar tracking PV panel system is introduced. This paper describes the design, development and fabrication of the solar PV panel tracking system. The designed solar tracking system is able to track the position of the sun throughout the day, which allows more sunlight falling on the panel surface. The experimental results show that there was an enhancement of up to a 64.72% in the output power of the PV panel with reference to the fixed orientation PV panel. Further, this study also demonstrates that the full load torque of the tracking system would be much higher than the obtained torque, which is required to track the position of the sun. This propounds, that the proposed tracking system can also be used for a higher capacity PV power generation system.

Background: This paper presents dynamic performance analysis of isolated wind-diesel power system. A dual mode controller is proposed for pitch control of wind turbine generator. Methods: The parameters of the controller are optimized by Differential Evolution (DE) algorithm. The hybrid model was simulated with the proposed load frequency controller (LFC) by considering step load perturbation. The minimization of time multiplied integral of absolute error is considered as the objective function. The performance of the proposed controller is compared with the published result of the optimal controller. Further, the performance of the system is investigated by incorporating Super Conducting Magnetic Energy Storage (SMES) and Fuel Cell (FC). Also, the dynamic performance is investigated for changing step load perturbations. Furthermore, the response of the system is analyzed towards random loading. Results: Finally, sensitivity analysis is done by varying the system parameters and operating conditions from their nominal values. Conclusion: The simulation results show that the proposed dual mode DE optimized controller gives better transient and steady state response.

Background: In this paper, experimentation fault-tolerant control for permanent magnet synchronous motor drive system using the direct torque control technique is presented. Methods: Synchronous machine drive system requires uninterrupted and more secure conditions during operations. Results: Therefore the diagnostic of voltage source inverter and synchronous motor faults are needed for improving system availability. Conclusion: This article aims to propose an accurate open-phase fault detection and fault-tolerant inverter of a permanent magnet synchronous motor using direct torque control technique. Experimental implementation is carried out on powerful dSpace DS1104. The validity of the proposed method has been experimentally verified.

Background: Meter placement, which can determine sufficient measurements for the successful estimate implementation, plays a crucial role for state estimation of the power system. For ensuring the robustness of state estimation against bad data in measurements, fail data from attackers and loss of measures; the measurement redundancies are necessary. Methods: This paper proposes a new method based on the observation reliability criteria of the bus to solve the optimal meter placement problem in the power network. The goal of this work is to enhance the effect of measurement redundancies and achieve any desired rates of robustness for state estimation. Regarding the practicability of the method, some practical aspects, such as zero injection bus, the presence of conventional measurements, the change of network's topology, or computational time, were also considered. Result: The simulations on IEEE RTS 96, 14-bus, 30-bus, 57-bus and 2383-bus test systems were tested for evaluating the effect of the proposed approach. The simulated results showed that the proposed method is flexible, practical and feasible in solving the meter placement problem for real power networks. Conclusion: Based on the observation reliability of buses we can enhance the effect of redundancy significantly and achieve any desired robust rates of state estimation.

Backgrounds: In order to guarantee safe and efficient operation interaction in open network environment, a new dynamic trust monitoring and updating model based on behavior context is proposed in this paper. Methods: Setting four behavior attributes such as security, availability, reliability and performance. Then utilizing the fuzzy clustering and information entropy mathematical methods to carry out the effective synthesis on such attributes. Conclusion: The effectiveness and efficiency of the schema are verified by simulation.

Background: With the large-scale Doubly Fed Induction Generator (DFIG) wind turbine integrated into the power system, the DFIG inertia response of the wind turbine should be provided. Also, the frequency response should be similar to the conventional generation technologies. This paper investigated the influence of frequency response term and wind speed conditions on system frequency control. Methods: The specific operating conditions of four control strategies, including inertia control, droop control, over speed control and pitch angle control were researched in this paper. Multi-factor coordinated frequency control strategy of DFIG wind turbine was established based on the above researches. The strategy was composed of wind speed ranging from low to high. Results: According to the simulation results, the DFIG wind turbine, which was based on multifactor coordinated frequency control strategy, could respond to the system's frequency change of power grid, effectively. Conclusion: It helps system frequency return to stable states better and faster than DFIG wind turbine and also could reduce the fluctuation of system frequency.