Research On The Digital Control Technique Of Output Waveform For Single-Phase UPS

This dissertation is focused on the research of the digital control technologies to the output voltage waveform for UPS. With more and more applications of UPS, the requirements for power supply get improved, so the waveform control technologies, especially the digital control technologies, become the hotspot on the research of UPS technologies. High quality waveform has two characteristics. It has not only nice static characteristic but also well dynamic response. Aiming at these characteristics, repetitive control technology and composite control technology based on repetitive control are analyzed and verified by simulations and experiments. The correlative avoiding bias technologies, which is associated with output voltage waveform control technologies for UPS inverter, is studied.Assuming the current of load as disturbance input, continuous state-space model and discrete state-space model of inverter are established. A precise simulation model taking into account dead-time effect is also established with MATLAB software. These models are the bases of farther analysis. The harmonic component of output voltage is studied. It is analyzed that causing the waveform distortion including dead-time effect and nonlinear load disturbing. Essentiality of the waveform correction technology is pointed out.Repetitive control technology is arising from the internal model principle. It's a compensate control technology which base on period. It can entirety eliminate the distortion of waveform. For the limitation of itself, repetitive control cannot get well dynamic response. The ways of design are given by examples. Stability analyze is carried out on repetitive control system. On the base of analyzing the improved odd-harmonic internal model, an odd-harmonic repetitive control technology is introduced. The method of design and the results of experiments are given by examples.Instantaneous feedback control can improve dynamic response of inverter. While, repetitive control can improve static characteristic of inverter. It can get better waveform, incorporating instantaneous feedback control with repetitive control. Three structures are studied, including state feedback pole assignment control plus repetitive control, voltage differential feedback control plus repetitive control and voltage differential feedback with integral control plus repetitive control. Simulations and experiments prove that it can get very nice static characteristic and well dynamic response.Avoiding bias is an important problem for UPS. It is clear that the small direct voltage included in the output voltage if the inverter bridge can be magnified and converted to very big direct current staying in the primary side of the transformer. Using primary side current feedback as a control element, the bias may be avoided. Two concepts are introduced including soft-ware compensation for bias and hard-ware compensation for bias. A feasible method, which can increase the digital control precision, is put forward. The method of design and the results of experiments are given by examples.