Research On The Digital Control Technique Of Single-Phase UPS

This dissertation is focused on the research of the digital control technologies for uninterruptible power supply (UPS). With the popularity of micro-processor, digital controller are widely used in uninterruptible power supply (UPS).The digital control technologies to the output voltage waveform of UPS inverters and the problems caused by the time-delay in digital control are discussed.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.Two different kinds of deadbeat control methods for waveform control technique of single phase uninterruptible power supply (UPS) inverters with only feedback of output voltage are analysed based on pole-placement. The drawbacks of the method which makes only one state-variable (output voltage) achieve a deadbeat dynamic response are pointed out. In addition, the design of a novel deadbeat controller for single phase UPS inverters based on pole-placement method is presented. With this method, all close-loop poles of system are placed at origin with output voltage feedback for achieving fast dynamic response. Furthermore, the feedforward of load current is designed so as to reduce the voltage distortion introduced by load current. The method of design and the results of experiments are given by examples.The reason of the problems caused by the time-delay in digital control is analysed. There are three methods concerning are discussed, which are state observer, modified pulsewidth modulation (PWM) and discrete state-space model of inverter with time-delay.