**ABSTRACT**

Enhancing power cycling capability of power semiconductor devices is highly demanded in order to increase the long term reliability of multilevel inverters. Ageing of power switches and their cooling systems leads to their accelerated damage due to excess power losses and junction temperatures. Therefore, thermal stresses relief (TSR) is the most effective solution for lifetime extension of power semiconductor devices. This paper presents a new thermal stresses relief carrier-based pulse width modulation (TSRPWM) strategy for extending the lifetime of semiconductor switches in single-phase multilevel inverters. The proposed strategy benefits the inherent redundancy among switching states in multilevel inverters to optimally relieve the thermally stressed device. The proposed algorithm maintains the inverter operation without increased stresses on healthy switches and without reduction of the output power ratings. In addition, the proposed algorithm preserves voltage balance of the DC-link capacitors. The proposed strategy is validated on single phase five level T-type inverter system with considering different locations of thermal stresses detection. Experimental prototype of the selected case study is built to verify the results. Moreover, comparisons with the most featured strategies in literature are given in detail.

**KEYWORDS**

- Lifetime extension
- long term reliability
- multilevel inverter
- pulse width modulation (PWM)
- thermal stresses relief

**SOFTWARE: **MATLAB/SIMULINK

**BLOCK DIAGRAM**

** **Fig. 1. A schematic diagram of PWM controlled full bridge *n*-level T-type inverter

**EXPECTED SIMULATION RESULTS**

** **Fig. 2. Simulation results of the proposed strategy at TSD in *SA*11 at *mi*=0.85.

** **

** **Fig. 3. Simulation results of the proposed strategy at TSD in *SA*11 at *mi*=0.45.

Fig. 4. Simulation results of the proposed TSRPWM strategy at TSD in *SA*12 and *mi*=0.85.

**CONCLUSION**

This paper has proposed a new carrier-based modulation strategy, called TSRPWM, for single phase multilevel inverters. It retains the same benefits as the conventional carrier PWM methods, i.e., a simple and easy implementation, but presents a significantly reduced power losses and thermal stresses of the stressed semiconductor devices. The main idea of the new proposed strategy is adaptively selecting the redundant switching states in each switching cycle, in order to optimize power losses through the thermally-stressed device. Therefore, both of the junction temperature and temperature cycling of the stressed device are reduced by the proposed strategy compared with normal mode operation of the device. The results of simulation and experimental prototypes are conformed and verified the new proposed concept. A generalized implementation of the proposed TSRPWM, to provide thermal stresses relief for any of the components and for any n-level inverters, is also presented. Moreover, the proposed strategy maintains the inverter operation with the same output ratings, and voltage balance over DC-link capacitors. Finally, the performance of the proposed strategy is compared with the prominent strategies in literature, and the distinction of the proposed strategy has become clear.

**REFERENCES**

[1] Shaoyong Yang, A. Bryant, P. Mawby, Dawei Xiang, Li Ran, and P. Tavner, “An industry-based survey of reliability in power electronic converters,” *IEEE Trans. Ind. Appl.*, vol. 47, no. 3, pp. 1441–1451, May 2011.

[2] S. E. De Leon-Aldaco, H. Calleja, and J. Aguayo Alquicira, “Reliability and mission profiles of photovoltaic systems: a FIDES approach,” *IEEE Trans. Power Electron.*, vol. 30, no. 5, pp. 2578–2586, May 2015.

[3] B. Ji, X. Song, E. Sciberras, W. Cao, Y. Hu,0 and V. Pickert, “Multiobjective design optimization of IGBT power modules considering power cycling and thermal cycling,” *IEEE Trans. Power Electron.*, vol. 30, no. 5, pp. 2493–2504, May 2015.

[4] U.-M. Choi, F. Blaabjerg, and K.-B. Lee, “Study and handling methods of power IGBT module failures in power electronic converter systems,” *IEEE Trans. Power Electron.*, vol. 30, no. 5, pp. 2517–2533, May 2015.

[5] P. A. Mawby, W. Lai, H. Qin, O. Alatise, S. Xu, M. Chen, and L. Ran, “Study on the lifetime characteristics of power modules under power cycling conditions,” *IET Power Electron.*, vol. 9, no. 5, pp. 1045–1052, Apr. 2016.