Fixed frequency AC current controller for a three phases voltage source inverter

Abstract

The performance of AC current supplies depends on the characteristic of the current control technique. Constant switching frequency, high dynamics and robustness are the main criteria for selecting current regulators. A linear controller allows obtaining constant switching frequency, which generates a well-defined harmonics spectrum. Nonlinear controllers are more robust and enable to obtain higher current dynamics, but are characterized by widely varying switching frequency. Used for a long time for current control of DC-DC converters, peak current controllers also allow imposing a constant switching frequency with fast dynamics of the current loop. However, they generate a static error. In this paper, we propose an adaptation of an AC current control method with constant switching frequency firstly developed for one phase AC current controller and applied for an AC three phases current controller. This controller is a hybrid controller using both sliding mode control and peak current control. The sliding mode controller generates robustness properties according to load parameter variations. The peak controller method ensures rapid dynamic response and a fixed switching frequency and is well adapted to the current tracking issues like harmonic filtering. In addition, its implementation is relatively simple. The principle of the AC current controller for a three-phase system is detailed. An average model of this controller is proposed, which takes into account fast reference variations. This model enables to determine the time response and the current overflow for given controller parameters. To explain the irregular current behavior, not foreseen by the average model, a mathematical analysis adapted from the chaos theory is done. Both simulations and experimental results are given to validate theoretical modeling.