Fully digital hysteresis modulation with switching-time prediction

Abstract

This paper proposes a digital hysteresis-modulation technique based on switching-time prediction. Sampling controlled variables several times within a switching period, it ensures a dynamic performance comparable to that obtainable with analog hysteresis modulation. Compared to conventional digital hysteresis modulation, it avoids frequency jitter since it predicts switching transitions. Compared to hysteresis modulation based on the detection of the zero crossing of current errors, it avoids external analog circuits. Compared to pulsewidth-modulation (PWM) techniques, it ensures faster dynamic response. These advantages are obtained at the expense of increased signal-processing requirements and of control complexity. Switching-frequency stabilization and synchronization with an external clock can be obtained extending the techniques proposed for analog hysteresis modulations. The proposed predictive algorithm does not require knowledge of load parameters and only a rough estimation of the inductor value, which can be easily self-adjusted. The proposed solution is suited for high-performance current (or sliding-mode) control where the digital hardware has enough computational power to allow multiple samples within a switching period. The proposed modulation technique has been applied to a sliding-mode control of a single-phase uninterruptible power supply (UPS). Experimental results confirm the effectiveness of the proposed approach

Sliding-Mode Control for a Three-Phase Unity Power Factor Rectifier Operating at Fixed Switching Frequency

“…This problem can be solved if analog hysteretic comparators are used but at expenses of additional hardware [16]. Other solutions can be adopted by using predictive control and the DSP timers to decide the switching time [17].…”

A First Order Sliding Mode Controller for Grid Connected Shunt Active Filter with a LCL Filter

“…A filter is required between a VSI and the grid, reducing harmonics of the output current and imposing a current-like performance for feedback control. A simple series inductor (first order output filter) can be used [Stefanutti (2006)], but the attenuation of high frequency components, due to switching frequency, is not very pronounced. In addition, a high voltage drop is produced and the inductor, required in the design, is very bulky [Bouchafaa (2010)].…”

Model-Based Control for a Three-Phase Shunt Active Power Filter

“…Despite this, and with the aim of increasing robustness with a fast dynamic response, sliding mode control (SMC) is the best alternative to be used [20]. Here there is a lack of research using this technique due to the following drawbacks: a) the cross-coupling between controllers through the neutral point voltage which causes severe interferences between controllers [21] and b) the variable switching frequency of the SMC which is unwanted in most industrial applications [22]. Some authors have reported several alternatives to fix the switching frequency, being the digital hysteretic modulators the most common solution [23], [24].…”

“…This problem can be solved by using analog hysteretic comparators but at the expense of increasing the hardware [25]. Other solutions are adopted by using predictive control and DSP timers in order to decide the switching time [22]. It is worth to mention that the fixed switching frequency algorithms generally assume a decoupling between controllers, which is usually obtained by removing the neutral point voltage influence from the dynamics of the controllers.…”