Research On The Unified Power Quality Conditioner (UPQC) And It's Control Strategies

As the most important energy in contemporary society, electric power is widely used in our daily life as well as industry and agriculture. Additionally, the sustainable development of power has a vital effect on the sustainable development of economic and society, especially for China, its national economy is developing rapidly. So the stability and security of power grid and the power quality directly affect the development of national economy. Meanwhile, although the rate of productivity is improved dramatically with the increasingly application of novel power electronic equipments, the power quality problems arise at the same time. Those problems of power quality result in not only ruined electrical facilities, but also a serious threat to the security and stability of power system. Therefore, this research focused on improving power quality is of great significance.As novel power electronic equipment improving power quality, the unified power quality conditioner (UPQC) integrated with power electronics technology, power system technology, computer control technology, and control theory. UPQC can ensure the power quality for both the power customer and the electricity supplier and have great performance in various applications, such as metallurgical industry, chemical industry, mining, hospitals, electrified railway, as well as HVDC. In conclusion, UPQC, with enormous potential in application, is an important development trend of power electronic technology in power system.The shunt active power filter (APF) can reduce harmonic current injecting into power system by compensating the current from nonlinear load. Meanwhile, the series active power filter can protect a specific load by eliminating the harmonic voltage from power system, but it cannot reduce the harmonic current from load. Therefore, UPQC is constituted by integrating with the above active power filters, due to their complementary compensation performance.The structure of UPQC, the detecting method of power quality, and the compensation strategy are analyzed in detail in this paper. A main circuit topology suitable for UPQC is proposed considering its functional optimization and the technology promotion. An improving detection technology for UPQC is also proposed according to the research of the existed voltage and current detection technology and algorithms. A modified compensation and control strategy for UPQC is proposed on the basis of the research of the voltage and current compensation methods.The main content of this paper are as follows:1. A topology of UPQC integrated with the series and shunt parts are proposed, based on the research of the structure, function and mathematical model of the series and shunt compensation part. Besides that, the selecting principle of power circuit component such as IGBT, transformer, the DC capacitors and the inductor is demonstrated.2. An advanced dq0 algorithm is proposed according to the analysis of the existed current and voltage detection techniques of UPQC. The appropriated simulation in the three-phase voltage detection of UPQC has been done to verify the algorithm.3. An practical method of advanced dq0 algorithm in three-phase current detection is proposed. And the appropriated simulation has been done.4. A novel detection algorithm in single-phase series voltage compensation is proposed based on an improved PLL techniques verified by theory and experiment.5. The control algorithm and the theoretical basis of voltage and current compensation in series and parallel compensation parts of UPQC are presented. Based on the research of various compensation methods, a new compensation and control strategy for UPQC is proposed.6. A mini-compensated energy with best-compensated voltage for series voltage compensation strategy is proposed.7. The simulation focused on deadbeat control algorithm of series voltage compensation has been done to verify the algorithm.8. A novel current compensation and control strategy is proposed by combining the negative load current with the active current absorbed from grid by the DC capacitor. And the simulation has been done to verify the algorithm.9. The design of detection and control circuit, the principle of software design and the structure of main soft module in the UPQC prototype are presented. And the hardware design, the software design of communication module, display module and keyboard module for monitoring control system of UPQC are shown as well.10. An UPQC topology integrated with PV grid-connected converter is proposed. The simulation study and topology design is done to verify the strategy.