Toma-Leonida Dragomir

This paper describes the implementation of a parameter observer (PO) intended to estimate the capacitance and equivalent serial resistance of a capacitor (ESR). The implemented observer consists of a dynamic second-order discrete-time system. The input signal of the observer is the voltage at the terminals of the capacitor measured during its discharge across a variable resistance in two steps. The implemented observer can be used in quasi-online or offline mode. The theoretical and experimental supporting materials provide a comprehensive picture of the implementation and conditions of use of the PO. The experimental verification was carried out with a microcontroller with Cortex^®-M7 core architecture. The sampling time of the PO was 20 μs, and the estimation of the parameters was obtained before the end of the discharge of the capacitor. In the cases described in the paper, this means approximately 25 ms. Due to the PO’s capabilities (estimation speed, reduced computational complexity and precision)—proved by the experiments carried out on three electrolytic capacitors of 100 μF, 220 μF and 440 μF—the implementation is of interest for several applications, primarily in the field of power electronic applications.

Monitoring the condition of electrolytic capacitors in practical applications is a topic that has been and remains the subject of much research. This article is part of research in this area. It develops a parameter observer (PO) and proposes its use for the determination of the equivalent capacity and equivalent serial resistance of electrolytic capacitors. The observer is an integral-open-loop type second-order system, the input of which is the voltage at the capacitor terminals measured during a two-stage capacitor’s discharging process through a variable resistor. The PO estimates the so-called time constant of the discharging circuit for each of the two stages from which values the capacitor’s parameters are calculated. The use of PO is illustrated for determining the output capacitor parameters of a buck DC–DC converter. The experiments were performed with two electrolytic capacitors with the nominal values 100 μF and 470 μF. Compared with other monitoring methods that use observers, the proposed observer is faster in tracking error mitigation, e.g., 10⁻³ s in comparison with 5·10⁻³ s or more. The low computational volume of the discrete-time PO allows the prospect of implementation in real time.

Pollution caused by plastic materials has a great impact on the environment. The biodegradation process is a good treatment solution for common polymers and biodegradation susceptible ones. The present work introduces new insight into the biodegradation process from a mathematical point of view, as it envisions a new empirical model for this complex process. The model is an exponential function with two different time constants and a time delay, which follows the weight loss profile of the polymer during the biodegradation process. Moreover, this function can be generated as the output variable of a dynamic exogenous system described through state equations. The newly developed models displayed a good fit against the experimental data, as shown by statistical indicators. In addition, the new empirical model was compared to kinetics models available in the literature and the correlation coefficients were closest to 1 for the new empirical model in all discussed cases. The mathematical operations were performed in the MATLAB Simulink environment.

The management of electricity consumption by household consumers requires multiple ways of consumer monitoring. One of these is the signature i(v) determined by monitoring the consumer voltage-current trajectory. The paper proposes a novel method for obtaining signatures of 2-multiple consumers, i.e., a pair of consumers connected in parallel. Signatures are obtained from samples of the voltage at the consumers’ terminals and of the total current absorbed by the consumers, measured at a frequency of only 20 Hz. Within the method, signatures are calculated using genetic algorithms (GA) and nonlinear regression, according to a procedure developed by the authors in a previous paper. The management of the data selected for the signature assignment represents the novelty. The method proposed in this paper is applied in two case studies, one concerning household consumers within the same power level, the other for household consumers of different power levels. The results confirm the possibility of obtaining signatures of i(v) type.

The discrete-time optimal control law denoted fhan is often used in practical implementations as well as in the research field of control systems. The present paper shows that by reevaluating the design conditions, the control loop driven by fhan achieves a permanent oscillating regime instead of a stable state. Under these circumstances, the fhan control law becomes a suboptimal solution. To further improve the behaviour, a complementary control action is proposed based on the proper discrete-time model of the double-integrator plant in order to eliminate the oscillating regime and stabilize the control loop. The effects of the proposed solution are illustrated through examples. From the practical point of view, implementing the solution is immediate because only the resources needed for the implementation of fhan control law are used.