High-precision AC power supplies have important applications in the fields of precision manufacturing, precision measurement and medical care. However,traditional linear power amplifiers are difficult to achieve high power and small size due to low efficiency. Switching power supplies can solve this problem, but are difficult to achieve high precision for errors such as dead zone etc. The audio delta-sigma modulation can suppress error effectively but are not widely used in inverter for its engineering debugging complexity, poor accuracy in higher power and difficulties during digitalization. The article analyzes its error suppression performance in analog and digital model to help engineering debug. It gives a math analysis of the accuracy potential and improvements with PID control taken in outer loop control, which helps improve accuracy in higher power. Difficult problems of digital delta-sigma are analyzed in detail and an integration solution is given in simulation and experiment, which helps understand where is the problem in digitalization. A platform is built with analog delta-sigma inner loop + digital PID outer loop. Experiments show that the voltage THD within 0.1% can be achieved under no-load and light-load conditions (<300W), which has initially reached the application index of the relay protection tester, which proves advantages and feasibility that the analog delta-sigma core + digital PID is used in the high-precision field. The experiment provides an application basis for introducing more digital control, such as digital dual-loop PI, PR and other controls to achieve ultra-high precision, high transient performance, and low debugging difficulty for current sources or voltage sources.
 

High-precision AC power supply,Analog delta-sigma feedback,Digital PID,0.1% voltage THD