Proportional-Resonant and Slide Mode Control for Single-Phase UPS Inverter

Slide mode control (SMC) is recognized as the most robust control with high stability, while the proportional-resonant (PR) control shapes the output waveform closely according to the reference sinusoidal signal. Keeping in view the characteristics of slide mode and PR control, a cascaded controller is proposed for bipolar single-phase uninterruptible power supply (UPS) inverter. The outer voltage loop uses the PR control while the inner loop uses the SMC. Chattering in the SMC has been removed using smoothed control law in narrow boundary layer condition. The stability of the controller has been analyzed using Lypunov stability criteria. The smoothed control law applied to the pulse width modulator results in fixed switching frequency of the inverter. The performance of the controller has been analyzed for single-phase inverter through simulations and experiments for both the linear and non-linear loads. The performance of controller has been compared with the other techniques of SMC and standard controllers. The proposed controller shows significant improvement in terms of reducing the total harmonics distortion to 0.5% for linear load and 1.25% for non-linear load, strong robustness, and fast response time of only 0.3 ms.