Sampling Rate and Performance of DC/AC Inverters with Digital PID Control—A Case Study

Abstract

The huge influence of the sampling rate on the performance of the digital PID control of a voltage source inverter (VSI) is revealed. It is shown that an appropriately chosen continuous-time model of a digital controller with the PWM power converter behaves like the actual discrete-time system, which allows for a simple controller analysis and design. The variable structure nature of the inverter with both the RC rectifier and an abruptly changing resistive load with two modes of operation within the sampling period is directly taken into account. Two simulation models, a discrete-time PWM and a continuous-time, of an inverter are presented, which are used to tune the PID controller and to evaluate the control performance. The behavior of the system in both modes is explained on the basis of the root loci and frequency characteristics. The results obtained for three sampling rates: 12.8, 25.6, and 51.2 kHz, are presented and compared with an actual VSI experiment. A comparison with other results obtained for this VSI shows that properly tuned PID control outperforms the more sophisticated solutions based on the coefficient diagram method (CDM) and the passivity based control (PBC).

Keywords

• VSI
• PID control
• PWM
• carrier frequency
• variable structure
• THD