Research And Design Of Voltage Tracking Retainer Based On The Single Phase Coordinate Transformation

With the development of information science and technology, people pay more attention to the level of power quality. Due to the extensive use of non-linear devices, a large number of harmonic pollution exists in power grid, causing voltage fluctuation and frequency variation. In many companies, the interruption of equipment operation which is caused by AC contactor tripping due to power quality will bring huge economic losses and even casualties. Although this problem can be solved by using uninterruptible power supply (UPS), on account of the huge volume of UPS as well as cost, their applications in industrial enterprises are not convenient. Many domestic industrial enterprises are troubled by poor power quality, and there are scare reliable products on the market designed to solve the above problem, now it is an urgent need to strengthen innovation and transformation of scientific and technological achievements, and to develop a product in response to the above situation with independent intellectual property rights.Aiming at the problem of AC contactor tripping causing by voltage fluctuation, under-voltage and voltage interruption, the research is done as follow:(1) Functional and technical requirements of grid voltage tracking retainer applied in industrial enterprises are analysed, and the overall system structure diagram and control strategies are determined.(2) A continuous state model and a discrete digital model to the main inverter circuit of the voltage tracking retainer are established, the equivalence principle of full-bridge PWM inverter is derived, and it is proved that the full-bridge PWM inverter can produce equivalent sine wave.(3) The single-loop and double-loop control strategies to single-phase PWM inverter are analysed. In view of the traditional double closed-loop control in the AC system can’t fully play the fast tracking ability of PID, the method of d-q coordinate transform on single-phase is mainly researched, and the method is used in double-loop control to get an improved with DC tracking characteristic dual-loop control strategy. The improved control strategy is studied by building Matlab experimental simulation model.(4) Based on the overall system architecture, the hardware circuits of each part are designed in detail, in order to ensure reliable, a variety of anti-interference design methods are used in the system, and the designed hardware circuits are debugged carefully.(5) According to the functional requirements, each part of the software programs are written, including voltage state judgment, A/D sampling and phase tracking, protection and so on. These software programs are debugged combined with hardware circuits and the feasibility of control and the reliability of hardware are verified.In this thesis, the improved double-closed loop control algorithm can solve the above problem perfectly. The power grid voltage tracking retainer is trigged to output sinusoidal voltage by analyzing the state of voltage fluctuation, the output voltage will keep the AC contactor working to overcome short-term problem of poor power quality, and to guarantee continuous and stable operation of the industrial equipment.