DC microgrids encounter the challenges of constant power loads (CPLs) and pulsed power loads (PPLs), which impose the requirements of fast dynamics, large stability margin, high robustness that cannot be easily addressed by conventional linear control methods. This necessitates the implementation of advanced control technologies in order to significantly improve the robustness, dynamic performance, stability and flexibility of the system. This article presents an overview of advanced control technologies for bidirectional dc/dc converters in dc microgrids. First, the stability issue caused by CPLs and the power balance issue caused by PPLs are discussed, which motivate the utilization of advanced control technologies for addressing these issues. Next, typical advanced control technologies including model predictive control, backstepping control, sliding-mode control, passivity-based control, disturbance estimation techniques, intelligent control, and nonlinear modeling approaches are reviewed. Then the applications of advanced control technologies in bidirectional dc/dc converters are presented for the stabilization of CPLs and accommodation of PPLs. Finally, advanced control techniques are explored in other high-gain nonisolated (e.g., interleaved, multilevel, cascaded) and isolated converters (e.g., dual active bridge) for high-power applications.

Review on Advanced Control Technologies for Bidirectional DC/DC Converters in DC Microgrids

Many commercial controller implementations for dc-dc converters are based on pulse-width modulation (PWM) and small-signal analysis. Increasing switching frequencies, linked in part to wide bandgap devices, provide the opportunity to increase operating bandwidth and enhance performance. Fast processors and digital signal processing offer new computational techniques for power converter control. Conventional control techniques rarely make full use of operating capability. The objectives of this paper are to present an overview and link to literature on conventional modulation and control techniques for hard-switched dc-dc converters, identify performance limits associated with conventional small-signal-based design, discuss geometric control approaches, and compare strategies for control tuning. The discussion shows how current mode controls have alternative state feedback implementations, and describes unusual opportunities for large-signal control tuning. Considerations for minimum response time are described. Comparisons among tuning methods illustrate how geometric controls can achieve order of magnitude dynamic performance increases. The paper is intended as a baseline tutorial reference for future work on power converter control.

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A Tutorial and Review Discussion of Modulation, Control and Tuning of High-Performance DC-DC Converters Based on Small-Signal and Large-Signal Approaches

Nowadays, sea traveling is increasing due to its practicality and low-cost. Ferry boats play a significant role in the marine tourism industry to transfer passengers and tourists. Nevertheless, traditional ferry ships consume massive amounts of fossil fuels to generate the required energy for their motors and demanded loads. Also, by consuming fossil fuels, ferries spatter the atmosphere with CO2 emissions and detrimental particles. In order to address these issues, ferry-building industries try to utilize renewable energy sources (RESs) and energy storage systems (ESSs), instead of fossil fuels, to provide the required power in the ferry boats. In general, full-electric ferry (FEF) boats are a new concept to reduce the cost of fossil fuels and air emissions. Hence, FEF can be regarded as a kind of dc stand-alone microgrid with constant power loads (CPLs). This article proposes a new structure of a FEF ship based on RESs and ESSs. In order to solve the negative impedance induced instabilities in dc power electronic based RESs, a new intelligent single input interval type-2 fuzzy logic controller based on sliding mode control is proposed for the dc–dc converters feeding CLPs. The main feature of the suggested technique is that it is mode-free and regulates the plant without requiring the knowledge of converter dynamics. Finally, we conduct a dSPACE-based real-time experiment to examine the effectiveness of the proposed energy management system for FEF vessels.

A New Intelligent Hybrid Control Approach for DC–DC Converters in Zero-Emission Ferry Ships

With the penetration of renewable generation and tightly regulated power electronic loads, the power quality and stability of modern dc microgrids are greatly challenged. To solve this problem, energy storage systems (ESSs) are widely proposed. Unfortunately, most of the existing control methods for ESSs can only ensure the stability of dc microgrids with small signal disturbances, which may not be satisfying for real-time applications where large signal disturbances exist. Moreover, they are usually designed for low boost ratio and low power converters, negating their suitability for grid-scale applications. To ensure the large signal stability of dc microgrids using high boost ratio interleaved converter interfaced ESSs, this article proposes a new backstepping control strategy with finite-time disturbance observers. Its effectiveness is verified by simulation and experiments carried out on an interleaved double dual boost converter.

Backstepping Control for Large Signal Stability of High Boost Ratio Interleaved Converter Interfaced DC Microgrids With Constant Power Loads

The cascade connection of two dc-dc switching converters for constant power supply is studied. The source converter is of boost type while the load converter is of buck type. The natural unstable behaviour of the cascade connection for both on and off states of the boost converter is counteracted by a sliding-mode control strategy that combines unstable trajectories to generate a stable one for the regulated boost converter dynamics. Experimental results using an electronic load to emulate a buck converter-based constant power load are in good agreement with the theoretical predictions. A similar agreement is later obtained when a buck converter with a dynamic behaviour close to an instantaneous constant power load is employed instead of the electronic load.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2018.5098

Sliding-mode control of a boost converter under constant power loading conditions

This paper proposes a digital sliding-mode controller for a DC-DC boost converter under constant power-loading conditions. The controller has been designed in two steps: the first step is to reach the sliding-mode regime while ensuring inrush current limiting; and the second one is to move the system to the desired operating point. By imposing sliding-mode regime, the equivalent control and the discrete-time large-signal dynamic model of this system are derived. The analysis shows that unlike with a resistive load, the boost converter under a fixed-frequency digital sliding-mode current control with external voltage loop open and loaded by a constant power load, is unstable. Furthermore, as with a resistive load, the system presents a right-half plane zero in the control-to-output transfer function. After that, an outer controller is designed in the z-domain for system stabilization and output voltage regulation. The results show that the system exhibits good performance in startup in terms of inrush current limiting and in transient response due to load and input voltage disturbances. Numerical simulations from a detailed switched model are in good agreement with the theoretical predictions. An experimental prototype is implemented to verify the mathematical analysis and the numerical simulation, which results in a perfect agreement in small-signal and steady-state behavior but also in a small discrepancy in the current limitation due a small propagation delay. Some efficient solutions have been proposed to mitigate the inrush current in the experimental results.

Fixed Switching Frequency Digital Sliding-Mode Control of DC-DC Power Supplies Loaded by Constant Power Loads with Inrush Current Limitation Capability

A nonlinear control strategy is proposed for the output voltage regulation in a boost converter that supplies a constant power load. State-feedback linearization is used to transform the nonlinear average dynamics of the inductor current in the converter into a linear average dynamics of the inductor current in a virtual mesh, which consists in the series connection of a voltage source, a resistor, and the converter inductor. In the virtual mesh, the resistor introduces damping to contribute to the system stability, while the voltage source indirectly regulates the output voltage. Conditions for the control parameters to ensure the system stability are given. The control can be implemented analogically, this requiring some linear circuits based on operational amplifiers, an analogue divider, and a pulsewidth modulator. Experimental results show a fast recovery and zero steady-state output voltage error in the response to large-signal disturbances in both input voltage and output power.

Nonlinear Control for Output Voltage Regulation of a Boost Converter With a Constant Power Load

This article presents a nonlinear control based on pulsewidth modulation (PWM) and an estimation mechanism of the output power to regulate the output voltage of a boost converter supplying a constant power load (CPL). The controller uses three parameters $K_{p}$ , $K_{E}$ , and $K_{A}$ lending the regulator an adaptive nature. The behavior of the latter can be expressed in terms of the dynamic description of three errors. Namely, first, current error, i.e. , difference between the average value of the inductor current and its equilibrium value, second, output voltage error, i.e. , deviation between the output voltage and its desired equilibrium value, and, second, power error, i.e. , difference between the output power estimated value and its actual value. The analysis of the dynamic behavior of the three errors results in a parametric region in the plane $K_{p}$ – $K_{E}$ in which the system stability is guaranteed. The regulator exhibits fast and precise responses in the presence of disturbances in the input voltage and the load power. Conduction losses provoke steady-state errors in both current and power estimation but do not affect the output voltage tracking.

http://nportal0.urv.cat:18080/fourrepo/rest/audit/digitalobjects/DS?objectId=imarina%3A8996448&datastreamId=DocumentPrincipal&label=imarina%3A8996448&mime=application/pdf&lang=en

Blanca Areli Martinez-Trevino

Papers

Sliding-mode control of a boost converter under constant power loading conditions

Fixed Switching Frequency Digital Sliding-Mode Control of DC-DC Power Supplies Loaded by Constant Power Loads with Inrush Current Limitation Capability

Nonlinear Control for Output Voltage Regulation of a Boost Converter With a Constant Power Load

PWM Nonlinear Control With Load Power Estimation for Output Voltage Regulation of a Boost Converter With Constant Power Load

Sliding-mode control of a boost converter supplying a constant power load