Temperature Equalization of a Multilevel Converter’s Low-Voltage Cell Power Modules

Abstract

The reactive power compensator based on a multilevel converter contains series-connected low-voltage power cells. Each low-voltage cell is a full bridge consisting of two power modules. The air flow from the cooling system is heated under the first power module, and the second module following the first one is cooled less efficiently. The temperature difference under the modules of one cell reaches 10 °C. The article proposes a control algorithm with which the switching losses are redistributed between the modules so that to reduce the temperature difference. By changing the matching of the pulse-width modulation of the switches to the positive and negative bus of the cell DC link, the required ratio of switching losses between the two power modules is achieved, which makes it possible to reduce the temperature of the hottest one of them. A low-voltage power cell thermal model developed in the PSIM environment and a radiator model calculated using the finite element method are considered. The parameters of the simplified thermal model are estimated; the losses in power cells at zero output voltage are determined, and the ratio of their operation at zero output voltage is changed. The study results have shown that the proposed algorithm equalizes the temperatures and reduces the temperature under the module by 10 °C during operation at rated load.