Temperature of a link capacitor

Abstract

To determine the temperature of a link capacitor (C) of a link converter () more accurately with less expenditure, a device and a method are described, in which the link capacitor (C) is modeled as a series interconnection of an equivalent capacitance (CS) and an equivalent series resistance (ESR), wherein a modeled capacitor current (i) flows across the equivalent series resistance (ESR). A modeled capacitor power loss (P), from which the capacitor temperature (T) is determined by means of a specified temperature model, is calculated from the modeled capacitor current (i) and the value of the equivalent series resistance (ESR) by means of a first relationship of the form P=f(i, ESR). Direct measurement of the capacitor temperature (T), of the capacitor current (i), or of the capacitor power loss (P) is not required. For example, a measurement of the capacitor voltage (u) and a further calculation of the modeled capacitor current iand finally of the capacitor power loss (P) are sufficient. The method can be used for the monitoring and processing of the capacitor temperature (T), particularly the switching-off of an element, preferably at least part of the link converter (), when a maximum temperature, such as a preset maximum temperature, is exceeded. The method can also be used to determine the temporal progression of the capacitor temperature (T(t)) and also to determine the remaining service life (RL) of the link capacitor (C) of a specified relationship, preferably by means of the Arrhenius formula.