Research On Digital High-precision Inverter Based On Delta-sigma And PID Double-loop Control

High-precision AC power supplies have extremely important applications in precision manufacturing,precision measurement and other fields.Traditional linear power amplifiers have high accuracy,but low efficiency,low power,and difficulty in increasing power density;switching power supplies have high efficiency and high power,but dead zone and other factors make it difficult to achieve high accuracy.Based on the Delta-Sigma modulation method and PID control,this paper studies the realization method of power-level high-precision AC power supply.This article first studies the time-domain modeling method of the Delta-Sigma modulation method,and analyzes its control characteristics.Considering time delay and other factors,establish the time-domain mathematical models of analog Delta-Sigma control and DeltaSigma+ PID voltage double-loop control in the inverter,and derive the noise shaping of the first,second and third-order systems and the impact of characteristics and delays.The advantages of the dual-loop control based on Delta-Sigma+ PID voltage in error suppression and anti-load interference are proved,and the stability criterion of the dual-loop system is given.By building an analog Delta-Sigma inner loop digital PID outer loop bench,a total harmonic distortion(THD)of 0.1% voltage was achieved,which proved the ability of this control method to improve accuracy.Second,in view of the problem of poor anti-interference and poor scalability of analog Delta-Sigma,this article further studies the high-speed sampling problem for digital DeltaSigma control.In this paper,an isolated Delta-Sigma analog-to-digital converter(Analog to Digital Converter,ADC)is used to achieve high-speed serial sampling;the simplified decoding filter and parallel computing capabilities of FPGA solve the problem of low digital sampling speed,large delay,and low accuracy.On this basis,using dual-loop control,a 500 W highprecision AC voltage source with a THD of 0.091% was realized under the Si C MOSFET halfbridge test bench,and high steady-state control accuracy and transient response speed were obtained.Third,this article further researches the all-digital high-precision AC current source of Delta-Sigma voltage inner loop + PID current outer loop.A time-domain model of Delta-Sigma voltage + inner loop PID current outer loop is established,and the derivation proves its highprecision potential compared with conventional PWM control.The stability criterion of the dual-loop design is obtained by analysis,which is based on Si C MOSFET.The experimental platform has been implemented to achieve a high-precision AC current source with a THD of0.077%,and has excellent transient characteristics under load switching.This paper systematically solves the modeling and design problems of Delta-Sigma control and the double-loop control system in the time domain after the PID outer loop is added,and proposes the corresponding stability criterion.Both theory and experiment prove the doubleloop system possess good control accuracy and transient response speed.In this paper,a very low THD high-precision voltage source and current source are realized based on the Si C MOSFET inverter topology.The high-precision AC power supply based on dual-loop control proposed in this paper has a wide range of application prospects.