Voltage Limits and Currents on Power Systems Essay example

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.

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.

Abstract— this paper presents a brief overview of standards for power electronics. All the standards presented in this paper are currently active and are approved by the Institute of Electrical and Electronics Engineer Standards Association (IEEE-SA) and American National Standards Institute (ANSI).

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.

Power electronics circuits convert electric power from one form to other using electronic devices. By using semiconductor devices as switches power electronics circuits function, thereby controlling or modifying a voltage or current.Power electronics application range from high-power conversion equipment such as dc power transmission to everyday appliances, such as cell phone chargers, cordless screwdrivers, power supplies for computers, and hybrid automobiles. Power electronics includes applications in which circuits process miliwatts or megawatts.Power electronics include conversion of an unregulated dc voltage to a regulated dc voltage conversion of ac to dc, conversion of dc to ac, and conversion of an ac power source from one amplitude and frequency to another amplitude and frequency. These power converters are classified as rectifiers, AC voltage controllers, DC choppers and inverters, which covers wide area of residential, commercial and industrial applications, including computers, transportation and power utilizes [1].

As industries expand, utilities become more interconnected and the use of electricity rises, power quality becomes essential to insure a smooth industrial process. The main problem that severely affects the power’s quality is the presence of the harmonics, which affects the performance of the system. Some of the problem caused by the harmonics are metal parts’ overheating, increasing noises in motors, decreasing the efficiency of the motors, etc. some corrective methods can be used to reduce its effect.

Abstract-the transmission lines are complex systems and the power generation sources are generally far away from the distributing center. The transmission lines congesting or overloading are always a challenge for utilities protection engineers. As a result, a series compensating capacitors are being used to alleviate the transmission lines, and increased the loads capability. However, adding series compensating capacitors (SCC) to the transmission lines will increase the potential risk of subsynchronous resonance (SSR). In fact, SSR leads to a possible torsional interaction and damage the turbine generator shaft when the mechanical frequency falls below the electrical frequency. In this paper, a brief analysis of SSR phenomenon will be addressed by computing the eigenvalues, eigenvectors, and MATLAB/Simulink for simulation incorporated with the IEEE first and second benchmark Model # 1 system.

Abstract—This assignment is based on the CIGRE HVDC benchmark system and deals with understanding and simulating this system in PSCAD/EMTDC. The focus is on the rectifier station of the CIGRE system which has been idealized and simulated in PSCAD. The AC-side real and reactive power and DC-side power corresponding to the firing angle from 0 to 180 degrees has been calculated and plotted. Furthermore, the power balance between the AC and DC-side of the converter has been explained. Index Terms— Converter, EMTDC, HVDC, PSCAD, Real power,

Reactive power compensation can be in a form of series type. In a power line at rated frequency, series compensation technique uses capacitors to decrease the equivalent reactance. The series capacitor generates reactive power to balance a fraction of line’s transfer reactance and this type of capacitor arrangement results improvement in the power transmission network. It increases the angular stability of the power system, improves the voltage stability of the corridor and also optimizes power sharing between parallel circuits [5]. Series compensation can be also implemented by using voltage or current source devices as shown in Figure A:

　　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.

A fundamental advantage of ECS adjustment for effective dynamic thermal storage is that it is relatively easy to implement. Conventional air conditioning and thermostats are designed to perform in slow control loops, on time scales of minutes. ECS adjustment can use time-scale separation and stay away from this “effective dc” loop action. In this sense, an ac feed-forward signal is injected into a drive to adjust power flow on fast time scales, while avoiding interference on slow time scales. The average performance of the ECS system remains intact, and the fast adjustment is transparent to users. Fig. 2 displays this implementation control. Bandpass filtered varying power must be applied with band and amplitude limitations before getting

There are numerous methods which are as follows like (SPWM) First Sinusoidal Pulse Width Modulation, (MCPWM)Second, Multi-Carrier Pulse Width Modulation and (SHE-PWM) and Selective Harmonic Elimination Pulse Width Modulation which are implemented for harmonic elimination specially in multilevel inverter. (MCPWM)Multi-Carrier Pulse Width Modulation strategies are widely used, because they can be easily implemented to low voltage modules. Normally MCPWM can be classified and categorized as Level Shifted PWM (LS-PWM) and Phase Shifted PWM (PS-PWM) methods. (LS-PWM) Level Shifted PWM are characterized into three which are Firstly ,Phase Disposition Technique (PD), secondly ,Phase Opposition Disposition Technique (POD) thirdly Alternative Phase Opposition Disposition Technique (APOD) [45] [46] [47].

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].

As per references [2], [6], [7], [9] any device with nonlinear characteristics which derive their input power from a sinusoidal electrical system may be responsible for injecting harmonic currents & voltages into the electrical system [2, 6, 7, 9 ]. Francisco C. De la rossa [2] have described ,all possible nonlinear loads . Among them few are Power converters such as Variable frequency drives, DC motor controllers, Cycloconverter, Cranes, Elevators ,Steel mills, Power supplies, UPS,Battery chargers, Inverters & ARC devices such as Fluorescent lighting, ARC furnaces, Welding machines. According to authors [2] ,[7] Even linear loads like power transformers can act nonlinear under saturation conditions. This occurs beyond the so-called saturation knee of the magnetizing curve of the transformer. [2],[7].

Keywords: CUK Bridgeless Topology, Fuzzy Logic Controller (FLC), Power Factor Correction (PFC), Proportional- Integral (PI) Controller.