Design and Stability Analysis of Single-Loop Voltage Control of Voltage Source Inverter

Abstract

A Voltage Source Inverter (VSI) is the important component of an Uninterruptible Power Supplies (UPS), distribution generation systems, power amplifiers, grid emulators etc. A stable and a good quality AC voltage waveform is very much essential for these applications. The classical way of controlling the AC output voltage in a VSI is the double loop voltage control. This requires an inner current loop and an outer voltage loop. Two sensors are required for the operation. For low pulse ratios i.e. for 50 Hz outputs, the double loop voltage control provides only limited voltage regulation. To obtain a pure sinusoidal waveform and to exhibit a good dynamic response compared to double loop voltage control, a single loop Proportional (P) controller is presented for a single phase VSI circuit feeding resistive, inductive and non-linear types of load. This is derived from the PR controller. A single loop P regulator is presented for a single phase VSI circuit with an LC filter feeding a resistive, inductive and a Non-linear load. The desired output voltage is 230 V (rms), 50 Hz. The input DC voltage is taken as 400 V. The voltage THD is 0.039 % and steady state error is found to be 1.067%. For a switching frequency of 5 kHz and resonance frequency of 1.1 kHz, Transfer functions have been derived and bode plots have been obtained. The dynamic control aspect is studied with a sudden change in the load within 0.2 s duration. A comparison is made with SMC for understanding the effectiveness of the single loop voltage controller.