Power difference between the DC side and the AC side of an inverter caused Low-frequency ripple current in the DC side. To reduce this current ripple, a traditional method is to use a large electrolytic capacitor to compensate this power difference. This reduces the reliability of the converter as the electrolytic capacitor is of low lifetime. Recently, power decoupling module is recommended to replace the large electrolytic capacitor. In this paper, a control method for boost type power decoupling module is proposed to reduce the current ripple of the DC side to zero. Hence, the DC voltage ripple also reduced to zero. The proposed control method only requires the ripple voltage of the DC side. Therefore, the cost of the power module is small and the module is plug-and-play. A prototype of boost-type power decoupling module with the proposed control implemented in 1 kW and 2 kW single-phase inverter with 380 V DC-link voltage is constructed. The results show that the proposed control method can fully compensate the second-order harmonic voltage of the DC side, and the input current ripple reduces to less than 8%.

Recently, in grid-connected Photovoltaic (PV) systems, the modular cascaded H-bridge Multilevel PV Inverters (MLPVIs) has attracted many researchers because of high-quality output waveform with each semiconductor device operating at the lower switching frequency and a possibility to reach high-voltage without using the step-up transformer in high-voltage grid-connected PV systems, which reduce the system cost. The inverter is one of the most unreliable parts of the PV system operating in different environmental conditions, and the MLPVI requires more number of power semiconductor switches, which increases the probability of failure. In order to provide reliable operation, it is important to predict the lifetime of an inverter by considering the mission profile. This paper mainly concentrates on the lifetime estimation of the modular cascaded H-bridge MLPVI by considering the mission profile. The power loss calculation and electro-thermal analysis have been conducted to unveil the thermal loading of MLPVI. A cycle counting algorithm has been applied to recognize the mean junction temperature and amplitude of the temperature swings of each thermal cycle. A Monte Carlo analysis is used to obtain the lifetime distribution of the power devices by considering the parameter variation. At last, the lifetime of a 5-kW grid-connected 1-phase, 5-level modular cascaded H-bridge MLPVI is studied based on the lifetime models of power devices.

Aluminum electrolytic capacitors (Al-Cap) are widely used in the DC-links of many power converters. Al-Cap is of low lifetime, which limits the reliability of the power converter. Therefore, it is important to predict the accurate lifetime of the Al-Cap to assist to design a high reliability power converter. At present, the lifetime prediction model of the Al-Cap is of low precision due to the ignorance of the influence of the AL-Cap's equivalent series resistance (ESR) variation caused by the temperature. The varied ESR increases the energy loss of the Al-Cap, which leads to extra temperature risen. Therefore, this paper investigates the lifetime predication influenced by the ESR variations in an Al-Cap by using Simplorer and Icepak co-simulation. The temperature variation of the Al-Cap is obtained by the Simplorer and Icepak co-simulation. An accurate Al-Cap lifetime predication in a 1kW single-phase inverter is simulated. Simulation result shows that the accuracy of the Al-Cap's lifetime with considering the ESR loss improved over 21% compared that without considering the ESR loss.

Electrolytic Capacitor (E-cap) is one of the lifetime bottlenecks in power electronic converters. In the last two decades, various active power decoupling circuits have been proposed to improve the reliability of the DC link by eliminating the DC-link E-caps. However, additional active devices could change the stresses of the existing converters, whether the system reliability is improving or not is still an open question. This paper investigates the reliability of the single-phase H-bridge inverter with active power decoupling circuit. The parameter variations in IGBT lifetime model are considered. The Weibull distribution of the key components is obtained from Monte Carlo analysis, and the reliability of the whole system is estimated by the system Reliability Block Diagram (RBD) method. As a case study, 2 kW single-phase H-bridge inverter with passive E-caps and active power decoupling circuits are presented. It is shown that the active power decoupling method is applied to H bridge inverter, and the lifetime of decoupling capacitor can be improved significantly, but it has different effects on system reliability in different applications. In addition, the difference on system reliability of fixed parameter and parameter variations is shown in conclusions.

LLC resonant converter is most frequently effective DC/DC converter to improve the power density and efficiency of DC charging module in electric vehicle power supply. Soft-switching technique can be applied in the topology to reduce the switch losses. However, DC charging module brings about 27% of failures in Electric vehicles (EV) charge device. The aim of this paper is to evaluate the reliability of a 3.8 kW LLC resonant converter as DC charging module in both component level and system level. The power losses of mainly power components are deduced and the thermal model together with the lifetime model are built to evaluate the reliability of the LLC resonant converter in component level. The converter level reliability is obtained by the component level reliability, Weibull distribution and Reliability Block Diagram (RBD).

In single-phase power inverter systems, when the load is nonlinear, output current will contain various harmonic currents. DC-side current will be disturbed by various harmonic currents at the AC-side. It is very harmful for the security, stability and reliability of the system. Power decoupling module compensating for the pulsation power has only been discussed in some papers in theory. However, these methods are difficult to be used in the actual circuits. In this paper, a novel power decoupling method of power-decoupling by applying Discrete Fourier Transform (DFT) is proposed to analyze the DC-side current real-timely. Various harmonic currents can be mitigated respectively with the appropriate control of capacitor voltage. To prove the correctness and feasibility, a simulation model of the H-bridge inverter based on the power-decoupling module has been established.