Research On The Power Theory And Its Application In AC Electrical Power System

Traditional power theory, is assumed that the electrical system is single-phase sinusoidal system or three phase sinusoidal symmetrical system. Thus the active power, reactive power, apparent power and power factor of the concept is very clear. But in recent decades, due to the rapid development of power electronics, the problem with non-linear loads associated with the proliferation of power electronic devices has greatly increased. When the voltage or current is distorted or unbalanced, the power phenomenon of system can't be completely correctly interpreted and described by the traditional concept. Thus, the establishment of power theory including waveform distortion and system unbalance become an important topic of power system analysis.In this paper, the research work of modern power theory is carried out both by frequency domain analysis method and time domain analysis method. The frequency domain analysis method is used to interpret physical meaning of the power phenomenon in electrical system, and solve the problem of power measurement. The time-domain analysis method is used to solve problem of real-time compensation and harmonic detection of electrical system.The frequency domain analysis method is suitable to explain the physical meaning and essence of the phenomenon of power of the electrical. Accordingly this, this paper points out the inadequacies of Budeanu definition, and analyses the power phenomena of sinusoidal system, sinusoidal unbalance system and non-sinusoidal unbalance system, and provide a practical guidance for the measurement of the electrical system. This paper adopts the definition of effective apparent power, and proves its scientific from the relation between the line losses and the apparent power squared. It points out that the most commonly used quantities, vector apparent power and arithmetic apparent power, do not accurately reflect the actual loss and cause large errors when used to calculate the power factor. The effective apparent power and the corresponding power factor power definition is suggested to measure the power quantity in non-sinusoidal unbalanced system.Time domain analysis method is real-time and suitable to work as the guidance for real-time compensation of power electronic devices. This paper analyzes basic concepts of FBD theory, Instantaneous Power Theory and GNP theory and compares their scope of application. Then the compensation effect of real-time simulation is compared, and different methods for different compensation target is analyzed. There are three compensation strategies, constant instantaneous power, sinusoidal current waveform, generalized Fryze, in non-sinusoidal unbalanced three-phase system.The Instantaneous Power Theory is simple and practical, and can be used to calculate the reactive power instantaneously, so it is widely used in practical engineering. Based on the instantaneous power theory, this paper analyses two basic methods of real-time detection of harmonics, p-q arithmetic operation and ip-iq arithmetic operation, compares their pros and cons, and scope of application. Then this paper analyses a detection method for random harmonic, and proves it is fast and accurate by simulation result.