The share of combined cycle power plants (CCPPs) increases every year in Russia and in other countries due their high maneuverability and economical efficiency. Specific characteristics impose some constraints on output power under low frequency conditions. Especially it is important under islanding conditions, because in this situation frequency can significantly deviate from nominal value. Therefore it is necessary to give attention the control system characteristics learning and the development of measures to improve they. It helps to decrease the load disconnection value in the case of emergency situation. At present a lot of works were published, which are devoted to CCPP operation under large frequency deviation from nominal value. The works show that CCPP islanding with active power deficiency is the most dangerous, because there is probability of frequency collapse. The main proposed measures are load restriction. The current research is aimed at the new CCPP frequency control algorithm development, which will help to prevent frequency collapse without load disconnection.