Abstract
The rapid decrease in conventional energy resources and their harmful impact on the environment has brought the attention of the researchers towards the use of renewable energy technologies. The renewable energy systems are connected to Direct Current (DC) micro-grids via power electronic converters where the load conditions are unknown and network parameters are uncertain. These conditions call for the use of robust control techniques such as Sliding Mode Control (SMC) in order to regulate the grid voltage. However, SMC has a drawback of operating the power converter at variable switching frequency which results in degrading the power quality. This paper introduces a fixed frequency sliding mode controller that does not suffer from this predicament. A novel double integral type switching manifold is proposed to achieve voltage regulation of a DC micro-grid, in the presence of unknown load demands and un-modeled dynamics of the network. Rigorous mathematical analysis is carried out for the stability of the closed loop system and the technique is experimentally validated on position of a DC micro-grid using a specially designed test rig. For benchmarking purposes, a conventional Proportional Integral (PI) controller is also implemented. An improvement of 2.5% in rise time, 6.7% in settling time and reduction of voltage dip by 31.7% during load transaction is achieved as compared to the PI controller. The experiment confirms the hypothesis that fixed frequency SMC shows better performance than its counterpart in the phase of introduced disturbances.
Highlights
Exponential increase in the energy demand due to massive industrial growth and urbanization has called for the installation of new generation units
To fill the above-mentioned research gap, this paper presents a fixed frequency Sliding Mode Control (SMC) based approach to track the reference voltage of each source connected to the micro-grid
Each source in the Direct Current (DC) micro grid comprises of a DC–DC converter as shown in Figure 2, where input voltage from the renewable energy source is denoted by Vin, IL is the instantaneous inductor current, Vout is the output voltage of the converter, Rload is the load resistance, C is the capacitance of the output filter capacitor while L is the inductance of the coil
Summary
Exponential increase in the energy demand due to massive industrial growth and urbanization has called for the installation of new generation units. Connecting RERs and energy storage banks to Alternating Current (AC) micro-grids requires multiple conversions (DC–AC and AC–DC) that result in unwanted power loss and reduced efficiency [7,8]. These techniques are not completely parameter independent and require some knowledge of the system specifications like inductance of the coil and capacitance of the filter stage This calls for the need of a robust controller that can control the nonlinear dynamics of the power converter in order to tightly regulate the voltage in the presence of unknown load demands and uncertain grid parameters. The proposed technique achieves the desired performance by controlling a boost converter that regulates the grid voltage and ensures proper current sharing in the presence of un-modeled dynamics caused by uncertain load and line variations without using observers, which add cost and complexity to the design.
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