Research On Digital Control Technique For Inverters With Instantaneous Capacitor-current Feedback

Good sinusoidal output waveform, fast dynamic response, excellent load characteristic and high precision of output voltage are known as the advantages of dual-loop instantaneous control with capacitor feedback. But it is hard to realize the dual-loop instantaneous control with digital scheme, because there is delay time of sampling and computing and lack of real-time regulation for digital control. Based on the state-observer, a novel digital control scheme for dual loop instantaneous feedback inverter is present in this thesis. A decoupling control strategy is proposed under the feedback of capacitor current. To fix the gain of inverter, DC decoupling is employed. A digital controller with inner current loop is designed using a new sampling sequence of capacitor current, and the average capacitor current in a switching period is reflected in real-time. A measuring method of current based on a discrete model of the full-bridge PWM inverter is proposed to compensate the delay time of sampling and computing. To increase the precision of output voltage, a filtering method for controlling the outer instantaneous voltage loop is adopted. The inverter is modeled in MATLAB. The output characteristics and the factors which affect the output characteristics are analyzed. A 1kVA prototype is developed. The simulation and experiment results show that the performance of inverter with this novel digital control strategy is the same as the performance of the inverter with analogy control strategy.