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Direct current (DC) microgrid consists of many parallel power converters that share load currents through the inductance of DC/DC converters. Usually, the inductance parameters are dependent on the physical implementation of the system, and their values may not match their nameplates. Such disparities could lead to unequal response characteristics of the system, which can potentially reduce the performances of the DC microgrid operation. This paper proposes a robust control strategy for inductive parametric uncertainties of DC/DC converters using an optimal control method with integral action. To achieve such a goal, the system model parameters with nominal values are transformed into parametric unmatched uncertainties to form a robust control problem, which is then transformed into a linear quadratic regulator problem. The inductance uncertainties are stabilized with the uncertainty dynamic algebraic Riccati equation (UDARE) using state feedback gain under linear quadratic regulator. The closed-loop control with integral action is adopted to achieve a steady-state error of zero on the DC-link voltage at any uncertainty of the inductive parameter, which subsequently ensures the equal load current sharing. Off-line simulations and real-time validations based on OpalRT have been conducted to demonstrate the effectiveness and robustness of the proposed robust control strategy.

Abstract:Based on an analysis of original social network data collected from 407 households in an urban community in Northern Nigeria, this article evaluates whether patronage relationships between households have consequences for children's educational attainment. A “social resources” perspective suggests that patronage ties may serve as a form of social capital that activates upward social mobility for entire families, thereby yielding more than simple transitory returns on social connections. An alternative “social constraints” perspective suggests that patronage ties may have no effects (or negative effects) on the schooling of clients' children, since patron-clientage reflects prevailing social inequalities and exists for reasons other than the promotion of dynastic mobility among clients and their families. In the case study reported in this article, the latter pattern holds, and the results are interpreted with reference to the historical record, which shows that a latent function of patron-clientage is the preservation of intergenerational status immobility.

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