Research On Control Strategies For Single Phase Inverter Source Based On Composite Observers

Single phase inverter source is mainly used for uninterruptible power supply, airborne power, locomotive auxiliary power supply, new energy power generation and other applications. Many factors affect the performance of single-phase inverter output voltage, while non-linear load is the main reason causing the increase of output voltage harmonic components. The paper focuses on single phase inverter power supply problems with nonlinear loads, making a detailed study of control strategy for single-phase inverter power.Firstly, this paper analyzes the flaws of the single closed-loop PI control strategy:PI controller can not perfectly track the sine wave-the given signal; the steady-state error of the amplitude and the phase angle can not be eliminated. Aiming at these problems, this paper puts forward a control strategy of the single-phase inverter based on the parallel observer.Secondly, from the perspective of non-sinusoidal periodic of the Fourier decomposition, the paper establishes continuous and discrete state space mathematical model of non-sinusoidal periodic signal. On this basis, instantaneous harmonic estimation that takes advantage of parallel observer estimating online each harmonic from non-sinusoidal periodic signals is proposed. And the closed-loop frequency response of algorithm is analyzed.Thirdly, this paper puts forward using instantaneous harmonic estimation extract fundamental wave from output voltage enriched with harmonics. And fundamental AC components are transformed to DC components by Park transformation. Then the PI control can eliminate the amplitude and phase error between reference fundamental wave and output fundamental wave. Finally, amplitude and phase control quantity is transformed to fundamental component by reverse Park transform. Thus, the fundamental voltage closed-loop tracking control of zero steady state error is realized by Park transform. For the distortion in the output voltage caused by the harmonics in the filter inductor, this paper proposes using current observation to obtain voltage drop in the filter inductor and tracking to the fundamental control component as feed forward to eliminate harmonic voltage drop in filtering inductance. All the harmonics can be assumed to be equivalent to external noise signal. If a control loop could be built around the noise signal, with a high feed back gain for the noise alone, the closed loop gain for the noise becomes smaller to realize the harmonic suppression. The simulation model of control strategy in Matlab/Simulink can verify the validity of algorithm.Finally, improvement on single-phase inverter power circuit by adding frequency dividing circuit doubles the switching frequency of system. And the control board circuit and monitoring unit circuit based on TMS320F2808are designed. The experiment proves the validity of single-phase inverter control strategy based on parallel observer proposed in this paper.