Research On Output Control And Parallel Operation Of 400Hz Inverter

400Hz inverters are widely used in airports and on ships.It is very meaningful to research the waveform control and parallel technology for 400 Hz inverters.This paper focuses on the two issues through theory analysis,simulation and experiments.The regular dual-loop control with output voltage and inductor current feedback is analyzed firstly in this paper.The results indicate that the cause of starting inrush current of slave inverter is the coupling relationship between the outer loop and inner loop.Then the paper proposes the output voltage feedforward control.A comparative analysis between the feedback control of inductor current and capacitor current is provided on the basis of inverter output impedance.From the analysis,it can be concluded that the output impedance is smaller and can be further reduce by increasing the gain of inner loop or outer loop regulator when capacitor current feedback control is adopted.On this basis,this paper proposes the improved dual-loop control with additional output voltage feedforward and output current feedforward control.The PR regulator,which can effectively improve the external characteristics,is designed in detail in this paper.The simulation is implemented to verify the practicability of the control scheme and correctness of parameters design.Take a single half bridge for example,the paper analyzes all typical operating modal and points out the influence of dead time on output voltage.Moreover,the voltage distortion mechanism of the inverter under rectified load is also analyzed.The analysis shows that the distortion can be inhibited by decreasing the inverter output impedance at low-order harmonic frequency.Finally,the low-order harmonic resonant control is used in current inner loop with output current feedforward to reduce the impact of dead time and rectified current.The paper points out that using higher order harmonic resonant control will result in instability by analyzing the influence of additional harmonic resonant control.Therefore,harmonic resonant controller with phase compensation is proposed to achieve stability.Besides,a comparative analysis between different discretization methods is provided,which shows the resonant frequency and phase of discrete resonant controller.At last,the impulse invariant method is proved to be the most suitable method.After constructing the equivalent model of master-slave parallel inverter,the paper indicates that the parallel system with output current weighted feedforward works like a inverter under proposed control.The proposed democratic master-slave parallel scheme based on RS-485 communication is described in detail.Furthermore,the mechanism of 485 communication delay is analyzed and mathematic expression of related circulating current is derived.Then,a novel master-slave logic with additional delay is proposed,which can eliminate the related high-frequency circulating current.By deducing the mathematic expression of dispersive circulating current,the paper points out that the filter capacitor and sampling coefficient of inductor current are the main parameters leading circulating current.The combined three phase control based on CAN bus is also provided,which can work well under asymmetrical loadsAt last,three single-phase 15 kVA 400Hz inverter modules are developed.The experiment results of single-phase 400 Hz inverter,parallel operation and three-phase operation are shown in this paper,which validated the proposed control method and correlatively analysis.