Sliding-Mode Control of Four-Leg Inverter With Fixed Switching Frequency for Uninterruptible Power Supply Applications

In three-phase transformerless uninterruptible power supply applications, a four-leg inverter is an excellent solution to handle the full unbalanced loading condition. A sliding-mode control (SMC) system is well known for robustness, simple implementation, high stability, and suitable solution for variable structure systems like power converters. However, it suffers from the chattering problem, variable switching frequency, and high electromagnetic compatibility noises. In this paper, a high performance SMC system is proposed to control the output voltage of the four-leg inverter with fixed switching frequency. In the proposed SMC system, as a considerable achievement, not only chattering problem is reduced significantly, but also the robustness, regulation, and dynamic response of the SMC system are not affected. Also, the derivation and implementation of the proposed SMC is so simple with less current sensors and without high computational burden. Furthermore, fixed switching frequency offers remarkable simplicity of the converter and filter design. Several experimental results on a 3-kW test bench verify the superior performance of the proposed SMC system according to the IEC62040-3 standard.