Research On Waveform Control Technique For Inverters Based On Internal Model Theory

The output waveform correction technology of PWM inverter is studied in this dissertation. An effective feedback control scheme for PWM inverters should have the ability to track sinusoidal instructions precisely and to suppress load current disturbance effectively, and with a fast error dynamic performance.Taking the load current as disturbance input, state variable equations for both single-phase and three-phase PWM inverters are firstly derived. It is analyzed that causing the waveform distortion including dead-time effect and load disturbing. Essentiality of the waveform correction technology is addressed. As for three-phase PWM inverters, both models in the stationary frame and rotating frame are derived and compared.In order to achieve high-precision steady-state waveform and fast dynamic performance, repetitive control combined with instantaneous feedback control is addressed. Basing on the research of repetitive control, an improved dual-loop controller, which is simple in structure and easy to apply, is proposed to improve dynamic performance. With the cooperation of both controllers, the error converges faster and a high accurate sinusoidal output waveform is attained.Waveform compensation for three-phase inverters is discussed. Both control strategy in stationary frame and rotating frame is analyzed. And the multiple control law for single-phase inverter is extended to three-phase system with simulation result and experiment result.In rotating frame, a PI controller can force the output waveform to track a sinusoidal instruction. The equivalent form for the PI regulator in stationary form is deduced and a resonant link is proposed. The implementation of delta transform in digital filter design is analyzed and carried out on fixed-point DSP. Based on dual-loop control, two novel dual-loop plus resonant control is proposed and studied.