Active and reactive power regulation, unbalanced current compensation, and harmonic current mitigation are the most significant functionalities typically embedded to a three-phase multifunctional gridconnected inverter. However, a vital control feature minimally addressed in the literature is the capability to adjust the grid power factor to the minimum value required by standards or grid codes. Hence, this paper presents an adaptive compensation approach to perform dynamic power factor regulation under varying power demand and unpredictable energy generation, also withstanding non-ideal voltage conditions. To demonstrate such an approach, a global power factor definition is first introduced, being validated upon bidirectional power flow conditions and under unbalanced and distorted voltages. Secondly, a simple algorithm is devised to attain scaling coefficients used on compensation purposes, allowing to instantaneously weigh up reference control signals to track a desired grid-side power factor value. As a result, the strategy can be used to retrofit the controllers of grid-connected inverters with little effort, limiting distribution losses and improving power quality. Simulations and analyses of a representative real study case are conducted to illustrate how the proposed approach copes with unpredictable distributed energy resources and variable load demands. Moreover, experimental results considering a grid-connected inverter prototype are shown to validate the feasibility of the control approach to real-life implementations.
A detailed analysis and validation of the DC-DC boost converter based on the three-state switching cell (3SSC) type-A are presented in this paper. The study of this topology is justified by the small amount of research that employs 3SSC-A and the advantages inherent to 3SSC-based converters, such as the division of current stresses between the semiconductors, the distribution of thermal losses, and the high-density power. Therefore, a complete static analysis of the converter is described, as well as the study of all voltage and current stresses in the semiconductors, the development of a loss model in all components, and a comparison with other step-up structures. Additionally, the small-signal model validation is accomplished by comparing the theoretical frequency response and the simulated AC sweep analysis. Finally, implementing a simple controller structure, the converter is experimentally validated through a 600 W prototype, where its overall efficiency is examined for various load conditions, reaching 96.8% at nominal load.
Large amounts of active power injection by inverter-interfaced distributed energy resources (DER) is a common cause of overvoltage in low-voltage networks. Hence, local active and reactive power control (i.e., Volt/Watt and Volt/VAR, respectively) are adopted to limit voltage rise, leading to active power curtailment. This paper proposes an automatic control strategy to steer non-dispatchable (nd-DER) and dispatchable (d-DER) inverters in low-voltage networks, mitigating overvoltage through local and coordinated Volt/Watt and Volt/VAR functionalities. Active power curtailment is avoided whenever possible. The method does not require i) the implementation of optimization algorithms or ii) knowledge about line impedance parameters or the location of DERs. The control approach exploits the power flow dispatchability of lowvoltage networks comprising one point-of-common coupling with the distribution grid, allowing DERs close to the distribution transformer to also contribute to voltage regulation by only using a low-bandwidth communication link. Simulation results show the flexibilities of the proposed approach and demonstrate that energy exploitation can be increased by up to 25% for the considered scenario in comparison to conventional local Volt/Watt or Volt/VAR schemes. Experimental results based on a laboratory prototype with three inverter-interfaced DERs certify the applicability of the approach to real-life implementations.
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