As an important component of a photovoltaic power generation system, an MPPT converter is responsible for the maximum power point tracking control of photovoltaic cells. However, the converter is prone to overheating and shutdown when there are sudden heat dissipation faults, such as poor environmental ventilation and cooling device failure. The shutdown of the converter causes the output of the photovoltaic cell to be cut off, which seriously affects the reliability and economy of photovoltaic power generation. To address this, the temperature rise characteristics of power devices are analyzed in this paper by taking a 300 W MPPT converter as the object. Then, a control method for a photovoltaic MPPT converter when there is a sudden heat dissipation fault is proposed by combining the traditional MPPT algorithm with an active thermal management strategy. Through the dynamic limitation of the device duty cycle and the hierarchical adjustment of the device switching frequency, the proposed method is able to actively adjust the device loss, so as to fully exploit the output power of the converter. Related experiments show that the proposed method can retain the photovoltaic output of the converter during the heat dissipation fault to the greatest extent and reduce the economic loss of photovoltaic power generation before the repair of the heat dissipation fault. From the experimental results, this paper constructs a performance evaluation index of the proposed method and analyzes the influencing factors on the performance of the method.