Investigations On Power Distubance Classcification And Power Quality Conditioner In Distribution System

Electric energy is a kind of basic power in the world. Power quality problems are widely attentive by customs. Based on Wavelet theory, adaptive deadbeat vector control theory and digital signal processing technique, and above-studied on the property of power quality issues, power disturbance classification and power quality conditioner are studied. Some experiments and simulations support the researches. All the works contribute to realize the unified power quality conditioning in lOkV distribution systems.The supreme obstacle of traditional power quality conditioners is the cost of power electronic devices in the system. In this paper, a hybrid unified power quality conditioner (HUPQC), the power electronic conditioner is combined with a group of passive power compensation, is presented to solve the problem. The structure of HUPQC consists of a power disturbance monitoring and analyzing subsystem, a power quality conditioner and their control system, etc. All of parts of HUPQC are designed under a unified plan. The double DSP devices are used to sample data and process the signals in the power disturbance monitoring and analyzing part. The power quality conditioner integrates active power compensation with passive power compensation, and improving power quality with improving power factor. The conditioner circuit consists of tri-level PWM converters, in which there are two active power filters (APF) that is a shunt APF and a series APF. They have a unique DC unit. The overall cost of the conditioner system will drop since the passive power compensation device cooperates with the active power compensation device. That will be helpful to apply the power quality conditioner technology in lOkV distribution system.In order to describe the HUPQC system theoretically, the mathematical model of HUPQC is derived by the concepts of space coordinate transform and the switch function. Since PWM converters are the key part of HUPQC, according to the application of this paper, the mathematical model about the series and shunt parts of tri-level PWM converters is presented in ABC coordinate system. Furthermore, the mathematical model of tri-level PWM converter, in dq coordinate system, is derived for the uncoupling control in tri-phase power system. Above this, two-phase linear model is obtained. As a result, the model can be used as a foundation of the theoretic analysis and simulation to the HUPQC.It is one of the important parts for the control of HUPQC to detect the reference compensation signal. The predictive strategy is presented based on Wavelet theory, that means tracing the fundamental signal and replacing with sampling data every half cycle. The fundamental signal is forecasted step-by-step in a half cycle earlier. And the difference between the predicted fundamental and the real time signal is the reference compensation signal. The hardware consists of DSP devices. The software is realized by Mallat algorithm of Wavelet transform. As a result, the time delay is reduced by the predictive detection scheme for sample, coordinate transform, or calculation process effectively. And the compensation effect of HUPQC is improved. It is a better detection scheme for power pollution to be checked in distribution system.The compensation result of HUPQC is effect by the control technology of PWM converters that is used to trace reference compensation signal. In this paper, a new control strategy based on the adaptive deadbeat voltage space vector is presented. This control scheme has a lower sample frequency and a smaller difference between switch frequency and sample frequency. It has many advantages, such as producing zero vectors organically, tracing exactly, non-shaking, etc. And its dynamic response is better. Since the deadbeat control property is effect by the operating system parameters, the deadbeat control parameters are corrected using the scheme, called "on line least mean square method with moving range", in real time by stages. So thecontroller is adaptable to the change of operating s...