# DC-DC Buck Converters with Quasi-Online Estimation of Filter Capacitor Equivalent Parameters
## 5 Conclusions  
The article proposes two novel DC-DC buck converter schemes designed to monitor the ESR and equivalent capacitance of filter capacitors. For this purpose, parameter observers are used to calculate the equivalent parameter values of the capacitors quasi-online.  
In the first scheme, the capacitor parameters are calculated by real-time processing of the voltage at the capacitor terminals during a discharge/charge process. By using the charging sequence, the duration of the estimation operation is reduced.  
Figure 15: Integrated circuit diagram associated with the DC-DC buck converter in Figure 12. The integrated chip includes 6 switches (T-sw\({}_{\text{g}}\), i,j= {[1,2]}\); T-sw\({}_{\text{L}}\) i = {[3,4]}), the LM2596 circuit, the LDO circuit, and the microcontroller. The unembedded components are the filtering capacitors \(C21\), \(C22\), the VEN resistors \(R_{ext1}\), \(R_{ext2}\), the temperature sensors, the inductance L\({}_{1}\), and the input capacitors \(C1\), \(C2\).  
The second scheme achieves the output filtering by using two or more capacitors connected in parallel. In this way, the monitoring of the filter capacitors receives the advantage of the continuous supply of the load from the converter. The advantage of this connection type is that at least one filter capacitor remains connected and assures a non-interrupted supply of energy to the load. The equivalent parameters of each component capacitor are estimated in real time using two monitored discharges.  
The experiments performed with both schemes, using electrolytic filter capacitors, shows that: (i) the estimation processes take approx. 40 ms; (ii) the equivalent capacity value is estimated with a precision of less than 0.25%; (iii) the estimation of the ESR value is performed with a precision dependent on both ESR and VEN resistor values.  
The implementation of both schemes is associated with the acceptance of some compromises, such as limitations in the design of VENs imposed by the correlated values of the load resistance, as well as transient regimes of small amplitude occurring during the monitoring of the filter capacitor.  
The estimation principles used in the two schemes are not limited to the proposed DC-DC buck converters. They are applicable in similar situations that need capacitor monitoring. Several future research opportunities open in this context, primarily by the application of the principles described in the proposed schemes for power converters and by the implementation of one of the two monitoring principles.  
Conceptualization, D.-V.C., C.B., S.N. and T.-L.D.; methodology, T.-L.D.; software, D.-V.C. and C.B.; validation, D.-V.C., C.B., S.N. and T.-L.D.; formal analysis, D.-V.C. and S.N.; investigation, C.B. and T.-L.D.; resources, C.B.; data curation, D.-V.C. and C.B.; writing--original draft preparation, T.-L.D.; writing--review and editing, D.-V.C., C.B. and S.N.; visualization, D.-V.C. and S.N.; supervision, T.-L.D. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.