Research On Single-phase Z-Source Inverter Based On Digital Control Technology

Inverters are widely applied to photovoltaic power generation systems and power transmission systems and other fields.Compared with traditional inverters,Z-source inverters have more advantages in the fields of topology and performance.In order to ensure the quality of the output waveform,this paper combines the Z-source inverter with digital control technology to realize the dual-loop feedback control of the single-phase voltage type Z-source inverter system.This paper focuses on the study of the key technology of the system hardware circuit and the voltage-current double-loop feedback control strategy,combining the software with hardware.The main work contents of this paper are as follows: Design of the overall research scheme.Starting from the topology of single-phase Z-source inverter circuit,studying the key technologies involved in the hardware through quantitative analysis of the working principle of pass-through state and non-pass-through state,mainly including SPWM modulation technology,drive technology and current-voltage sampling technology.Through the comparative study of three kinds of SPWM modulation technologies based on the shoot-through vector,the constant switching frequency of the shoot-through vector modulation method is finally determined.1.Design of the overall research scheme.Starting from the topology of single-phase Z-source inverter circuit,studying the key technologies involved in the hardware through quantitative analysis of the working principle of pass-through state and non-pass-through state,mainly including SPWM modulation technology,drive technology and current-voltage sampling technology.Through the comparative study of three kinds of SPWM modulation technologies based on the shoot-through vector,the constant switching frequency of the shoot-through vector modulation method is finally determined.2.Completion of the calculation and selection of circuit hardware parameters of single-phase Z-source inverter system,mainly including the selection and loss analysis of inverter bridge switch tube,design of Z-source network capacitance and inductance,selection of input diode,analysis and design of filter circuit and the like.3.Based on the working principle of the system,the mathematical model is established and the transfer function is obtained.Combined with the PID control theory,the feedback control mode of the outer voltage loop and inner current loop is constructed and the rationality of a control algorithm is verified through utilizing system Bode diagram,root locus diagram and response curve drawn by MATLAB.After sampling the capacitance and the output inductance current of the Z-source network,the control algorithm is implemented on the DSP controller to generate four independent SPWM signals.After driving amplification,the bridge MOSFET is switched on and off.4.Simulation and experimental testing.Firstly,Simulink platform is used to simulate a grid-connected system,analyze the current frequency and phase of the grid-connected system,calculate the harmonic distortion rate and power factor of the grid-connected system,and verify the theoretical effect.After that,the open-loop system and the closed-loop system under off-grid condition are simulated and tested,and the results are compared and analyzed to verify the advantages of the closed-loop system in terms of waveform quality and system stability.Finally,the actual circuit is built and tested in the laboratory,and the experimental output waveform is analyzed to verify that the system meets the design requirements.