Tightly regulated power electronic converters show negative impedance characteristics and behave as a constant power load (CPL) which sink constant power from their input bus. This incremental negative impedance characteristics of tightly regulated point-of-load converters in multi-converter power systems have a destabilising effect on source converters and may destabilise the whole system. Similar phenomena also occur in many situations like dc microgrid, vehicular power system. Here, the authors present a robust pulse-width modulation-based sliding-mode controller for a dc/dc boost converter feeding the CPL in a typical dc microgrid scenario. A non-linear surface is proposed which ensures constant power to be delivered to the load. The existence of sliding mode and stability of the sliding surface are proved. The proposed controller is implemented using OPAL-RT real-time digital simulator on a laboratory prototype of dc/dc boost converter system. The effectiveness of the proposed sliding-mode controller is validated through simulation and experimental results under different operating conditions.

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In recent years DC micro-grid has been widely accepted as one of the promising solutions to integrate renewable energy sources and to supply power to critical loads such as data centres, remote villages and communication stations. However, DC micro-grid has a fundamental stability challenge due to constant power load (CPL) characteristics of point-ofload converters, which introduce destabilising effect in the system. This study presents a sliding mode control based nonlinear control scheme for a solar photo-voltaic based DC micro-grid in the presence of CPLs. The objective of the proposed control scheme is to tightly regulate the DC bus voltage and mitigate the destabilising effects of CPLs. The stability of the system is analytically established and a limit of CPL is obtained. Furthermore, a charging/discharging algorithm is implemented for battery bank interfacing bidirectional converter which facilitates three modes charging namely constant current, constant voltage, and float mode, to enhance the battery life. The validation of the effectiveness of the proposed scheme is done through simulation and experimental results. It is found that the proposed control scheme ensures desired operation of the DC micro-grid under various operating modes and maintains system stability with CPL under variations in the primary resource and load demand.

Envelope tracking (ET) applications demand high tracking bandwidth and high efficiency using a DC-DC converter. Design based on small-signal models using fixed frequency digital pulse width modulator (DPWM) often results in limited closed-loop bandwidth. This paper proposes a mixed-signal hysteresis current control (MSHCC) in a DC-DC buck converter with an analog current-loop and a digital voltage controller c( ). This achieves robust stability and parameter insensitive current ripple by sampling the output voltage at the rising edge of high side gate signal. A fixed-gain power amplifier driven by a buck converter can be assumed to be a constant resistive load. Thus the load current information is directly obtained from the reference command, which further improves the tracking performance. The real-time tuning of c( ) using the proposed MSHCC achieves fast recovery with an inherent current limiting, and the use of the internal model control (IMC) further minimizes the tracking error. A fixed frequency operation can be achieved through a real-time band adaptation. The proposed controller is implemented using an FPGA device.978-1-4673-9550-2/16/$31.00 ©2016 IEEE