# DC-DC Buck Converters with Quasi-Online Estimation of Filter Capacitor Equivalent Parameters
## 4 Discussion  
1. The paper proposes two new DC-DC buck converter schemes shown in Figures 9 and 12. They are intended for real-time simultaneous estimation of the equivalent capacitance and the ESR of the converter filter capacitor. In both schemes, a PO coded on a microcontroller is used for estimation purposes. The schemes differ from the original converter scheme [29] by adding a microcontroller, some VENs composed of discharge or charge resistors with the related switches and temperature sensors, and in the first case also a stabilized voltage source. The VEN resistances are adopted taking into account the recommendations in Appendix A. Failure to comply with these recommendations results in high values of the dispersion of \(R_{se}\), therefore, ESR calculation. Both schemes work in a quasi-online mode. This means that while estimating, the connection between the monitored capacitor and the converter load is interrupted for a few milliseconds. From the point of view of the continuity of the connection between the load and the converter during estimation, the first scheme operates in a quasi-online mode, while the second operates in an online mode. 2. The first scheme (Section 3.2) provides the equivalent parameters of the capacitor based on the estimation with a PO2 of the values of the equivalent time constants related to the discharge/charge process of the capacitor. The VEN only serves to charge the capacitor. Its discharge is carried out through the load resistance of the converter. Estimating the time constant of the charging process with a PO2 (Section 2.1) is a novel approach that requires prior experimental calibration of the \(K\) parameter, according to the capacitor charging conditions (Section 2.2). During parameter estimation, the scheme is in quasi-online mode of operation, characterized by the short-term disconnection (approx. 0.040 s) of the capacitor and the load from the converter. This means that the proposed scheme can trigger the estimation of the capacitor parameters only when the load is disconnected from the converter. Depending on the power load tolerance, this can be performed intermittently, more or less often, or when the converter is off. Compared to the conditions in Appendix A, in the experiments presented in the paper, we worked with \(\rho_{R}=27.54\) and \(\rho_{2}=0.06358\). As such, the condition \(\rho_{R}\gg 1\) was met, while the condition for \(\rho_{2}\) to be as close as possible to 1 could not be met for reasons of limiting the current through the circuit. This fact influenced the dispersion of the calculated \(\hat{R}_{se}\) values, the average value being \(6.58677\%\). Consequently, the experiments with the scheme in Figure 9 show that PO2 can determine with a very good approximation the value of the equivalent capacity through a single discharge/charge process. Since the value of \(\rho_{2}\) is small, the determination of the ESR value, however, requires performing a series of successive experiments and averaging the obtained values. 3. The second DC-DC buck converter configuration (Section 3.3) uses a pair of capacitors for filtering, connected in parallel, and a VEN consisting of two resistors. The estimation of the parameters of each capacitor is completed alternatively by processing the discharge voltage of each capacitor across each of the resistances of the VEN. The novelty of the proposed scheme lies in the sequential investigation of the two capacitors. The estimation of the equivalent parameters is completed for one capacitor at a time, while the load, together with the second capacitor, remains connected to the converter output. As a result, the scheme operates in a quasi-online measurement regime during which neither the filtering operation nor the load supply from the converter is interrupted. In this process, the filtering capacity changes in steps.