Analysis of relaxation of varistor-posistor voltage limiting device in photovoltaic modules during renewal of lighting
The features of the operation of the circuit method based on a structure of a varistor-PPTC fuse type being in thermal contact to protect the photovoltaic cells from overvoltages arising from the partial shading of the photovoltaic modules of solar arrays are considered. The conditions for the relaxation of the functional characteristics of such voltage limiting devices to the initial state which does not affect the operation of the photovoltaic module during renewal of lighting of the photovoltaic cells are analyzed. It is established that the temperature and resistance dependences of the PPTC element, which determine its state, have a relaxation character at small values of such parameters of the voltage limiting device as the passport values of the resistance of the PPTC element in the conducting (“cold”) state and thermal resistance of the voltage limiting device. The relaxation time is of the order of a few seconds. For large values of the indicated parameters, a situation may occur when such relaxation is absent and the voltage limiting device maintains an active low-conductive (“hot”) state.