Capacitor ESR and C Monitoring in Modular Multilevel Converters

Abstract

The capacitor is one of the weakest components in the module multilevel converter (MMC). The rise of equivalent series resistance (ESR) is a prominent character to monitor the lapsed capacitor, but current researches only focus on capacitance and neglect ESR of capacitors in the MMC. This paper proposed a sorting-based monitoring strategy for capacitors in the MMC, which monitors not only the capacitance but also the ESR of capacitor. This paper reveals the relationship among the capacitor's ESR, capacitance, current and energy. Based on the relationship, the ESRs and capacitances of submodule (SM) capacitors in the arm are indirectly sorted, respectively, and only the capacitor with biggest ESR and the capacitor with smallest capacitance in the arm are monitored. The proposed strategy not only realizes both ESR and capacitance monitoring in the MMC, but also proposes a simplified monitoring algorithm for MMCs with large number of capacitors. The simulation and experimental results confirm the effectiveness of the proposed monitoring strategy for MMCs. 1

Review of Health Monitoring Techniques for Capacitors Used in Power Electronics Converters

“…However, the measurements and calibrations of individual capacitors in the first stage could be challenging due to the large number of capacitors [69]. The sorting technique is also applied in [74] to sort the SM, which features the highest ESR or the lowest capacitance in each arm of the MMC. The sorting process is based on the relationship between the energy and ESR and the current and capacitance of each SM; it is expressed as [74]: The sorting technique is also applied in [74] to sort the SM, which features the highest ESR or the lowest capacitance in each arm of the MMC.…”

“…The sorting technique is also applied in [74] to sort the SM, which features the highest ESR or the lowest capacitance in each arm of the MMC. The sorting process is based on the relationship between the energy and ESR and the current and capacitance of each SM; it is expressed as [74]: The sorting technique is also applied in [74] to sort the SM, which features the highest ESR or the lowest capacitance in each arm of the MMC. The sorting process is based on the relationship between the energy and ESR and the current and capacitance of each SM; it is expressed as [74]:…”

“…The sorting technique is also applied in [ 74 ] to sort the SM, which features the highest ESR or the lowest capacitance in each arm of the MMC. The sorting process is based on the relationship between the energy and ESR and the current and capacitance of each SM; it is expressed as [ 74 ]: where , , , are the fundamental angular frequency, amplitude of the fundamental capacitor current component, and amplitudes of the fundamental and second-order capacitor voltage components, respectively. and are proportional to the ESR and capacitance.…”

“…These errors could lead to incorrect decisions regarding maintenance, thereby increasing expenditure. Various studies [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 ], which are discussed herein, have reported on the health monitoring of capacitors. Capacitance monitoring methods are capable of estimating the capacitance of both Al-Caps and MPPF-Caps; therefore, they would be more beneficial and suitable for different applications.…”

Submodule power balancing control of modular multilevel converters under capacitor degradation

“…This method is further extended to estimate C and ESR using a sorting‐based capacitance monitoring. In this method, capacitance of only one SM capacitor having the biggest ESR and smallest capacitance of SM capacitor in the arm is estimated [29]. An improved RSM‐based capacitance estimation method is presented to enhance the SM capacitor monitoring accuracy by utilising the voltage sensor measurement range [30].…”