Future photovoltaic (PV) inverters are expected to comply with more stringent grid codes and reliability requirements, especially when a high penetration degree is reached, and also to lower the cost of energy. A junction temperature control concept is proposed in this study for the switching devices in a single-phase PV inverter in order to reduce the junction temperature stress, and thus to achieve improved reliability of a PV inverter. The thermal stresses of the switching devices are analysed during low voltage ride-through operation with different levels of reactive power injection, allowing an optimal design of the proposed control scheme with controlled mean junction temperature and reduced junction temperature swings. The effectiveness of the control method in terms of both thermal performance and electrical performance is validated by the simulations and experiments, respectively. Both test results show that single-phase PV inverters with the proposed control approach not only can support the grid voltage recovery in low-voltage ride-through operation but also can improve the overall reliability with a reduced junction temperature.
Iet Power Electronics, 2014, Vol 7, Issue 8, p. 2050-2059