Voltage Limits and Currents on Power Systems Essay example

Modelling of the series transformer, VSC and LC filter is presented in this section. A time-varying threephase

Fig. 5.10. Control of the dc–dc converter to produce less power under voltage sag: (a) grid voltages, grid currents, actual duty cycle, input voltage of the dc–dc converter, estimated duty cycle; and (b) dc-link voltage.

There are two primary synchronous machines, the synchronous generator and the synchronous motor. Both machines are very useful depending on the application necessary for their use. Depending on the external conditions, it is required to have an understanding of how the synchronous machine should be modeled for each use. The synchronous machine is commonly found in industrial settings, clocks, and power plants. The common factor between these fields is the requirement of running at a constant speed. The synchronous generators used in power plants are common because it is economically efficient to keep the generator running at a constant frequency. Depending on the application, the synchronous machines can be modeled proportionally between the mechanical frequency based on the number of poles and the frequency of current (see theory). Consequentially, the electrical radian frequency is determined be the electrical frequency. Modeling a synchronous machine is a simple task, provided the necessary parameters are known.

Abstract— Voltage sag is the power quality event that occurs due to different kind of short circuit fault and the switching of heavy load. Dynamic Voltage Restorer (DVR) is one of the most common custom power device to compensate the voltage sags Usually DVR is installed between load feeder and source in the distribution system. In this paper approach to compensate voltage sag by using dynamic voltage restorer base on the d-q-0 algorithm is discussed. Simulation is done in MATLAB software and results are obtained.

This paper deals with a Cuk Topology for Power Factor Correction (PFC). Most of the front-end PFC converters are designed using diode bridge and has lower efficiency due to losses with reduced power factor.The current flow, during each intervals of the switching cycle reduces the conduction losses compared to the conventional Cuk PFC Rectifier. The converter also provides protection against inrush current occurring at start-up, decreases input current ripple and reduces Electromagnetic Interference (EMI).It works in the Discontinuous Conduction Mode (DCM) to provide almost unity power factor and low distortions in the input current. To analyse the performance of this converter, a model based on the CUK topology has been designed by using MATLAB/ SIMULINK software and implemented with Proportional-Integral (PI) and Fuzzy logic controller.

In this paper, IEEE 1547.4 standard (2011) is selected to propose microgrid standards for ECRA especially standard of stability of microgrids in different modes.

For the systems where high switching efficiency is needed, it is required and desirable to keep switching frequency much lower. In this state,

Alexander B. Nassif and Jing Yong [7] have proposed a method to identify the consumers generating inter harmonic frequencies. The inter-harmonics can be measured by means of Impedance based approach applied at the metering point. The main idea is that, the inter-harmonic impedance of the system is much smaller than that of an inter-harmonic generating load. This method can identify the source of each inter-harmonic component without having to rely solely on the active power measurement and requires only an approximate value for the inter-harmonic impedance measured at the metering point.

At present there are several reduction or mitigation methods in use to reduce the distortion of the voltage and current from non-linear distribution loads such as variable frequency drives (VFDs). Description of each method with relative advantages and disadvantages are as follows.

A few recent papers [53]-[56] have demonstrated a virtual synchronous machine (VSM) concept, particularly for microgrid applications and usually for distributed generators utilizing the same ac-dc-ac conversion stages. The same concept applied on flywheel based energy storage is discussed in [57]. Given the similarities existed in the MEA power grid and motor controlled thermal storage, it is deemed feasible to implement the VSM concept in this research. A high-level description is shown in Fig. 3. For a synchronous machine in the rotating reference frame, the d-q voltage and current relationship is shown in (1a-b), where vg is the grid voltage, R is the stator resistance, M is the magnetizing, and Ld = Lq = L is assumed. On the other hand, the active front end (i.e., the hex-bridge converter connected to the gird) follows (2a-b) in d-q reference frame at ωc rotating speed, where Rg and Lg are grid tied resistance and inductance, and vc is the output voltage at the converter controlled by modulation index from the dc voltage bus []. The analogy between (1a-b) and (2a-b) is straightforward. By equating the first three terms and varying the modulation indices, md and mq, the active front end mimics the VSM proposed in [ZhongQC]. The purpose of the ac motor-tied inverter (i.e., the left hex-bridge converter in Fig. 3) is to main a constant 270 V dc bus by adjusting the motor speed and torque using conventional vector controls. Given the limited

The growing demand of electricity in a large cities increase the need of high power transmission from remote generating stations. Therefore, for reducing the cost-effective in power transmission, series compensating capacitor (SSC) is used to

protection are designed to achieve required discrimination by sensing that large second harmonic content [1]. The level of second harmonic component of the inrush current has been reduced due to improving in transformer core material and occur power system changes. Additionally, a large second harmonic can also be found in transformer internal fault currents if a shunt capacitor is connected to a transformer in a long extra high voltage transmission line. Therefore, the methods based on the measurement of the second harmonic are not sufficiently effective for differential protective relays [2].

For the last 25 years there has been a great increase in the usage of the solid state electronics technology. This new technology has provided us with the opportunity to have a product with a high quality with an increased productivity due to its high efficiency. Today, we can produce products with high quality at less cost than in the last years, but this new technology has given rise to a new problem, which is the need for a clear electric power.

Power electronic converters, especially DC/AC inverters have been extending their range of use in industrial application because they provide better system efficiency, reduced energy consumption and improved quality of power. The output voltage of inverter could be fixed or variable at a fixed or variable frequency and output waveforms are therefore made up of discrete values, producing fast transition rather than smooth ones [2]. The ability to

　　Since the industrial revolution started, the acceleration of technology development never stopped. However, with the development of new technologies, environment is suffering the consequences. The rate of Carbon dioxide is increasing rapidly. To mitigate this pollution, the concept of electric vehicle arose. The electric vehicles contribute in reducing the carbon dioxide emissions[1]. Thus, the use of electric vehicles is getting more popular as time goes by. As a result of that, electric vehicles must be integrated to the electric grid. They will be treated as electric loads, which means that all concepts of power system will be applied on them. Therefore, when electric vehicles are charged, they will cause voltage drop on the distribution feeders. Hence, the presence of voltage regulators might change the voltage response of the system.