IC697MDL750 has the characteristics of low application cost, high operational reliability but difficult programme design, and its internal successful embedded generator fault recording of important operational parameters has a greater practical value, especially for the current development of a large number of small and medium-sized hydroelectric power plant hydroelectric generator sets, which is of great significance to ensure the safe, stable and reliable operation of generator sets.

The system frequency conversion speed control is completed by PLC and frequency converter together, and its principle is shown in Figure 2. Place a pressure sensor in the water station at the water pipe, the transmitter is responsible for the sensor pressure signal is converted to 1 yao 5 V DC voltage signal sent to the PLC closed-loop control module, the signal and the pressure of the given value compared to the PID algorithm, the output from the module of a 4 yao 20 mA (can also be 0 yao 10 V) of the control signal sent to the frequency converter to control the frequency converter output frequency, to achieve the motor stepless speed regulation, to output water supply pipe water to the generator set. The output frequency of the frequency converter is controlled to achieve stepless speed regulation of the motor to stabilise the water pressure of the output water supply pipe at the set pressure.

Is the valve completely open when the water supply system resistance characteristic curve, curve 2 is the rated speed when the pump head characteristic curve, water supply system working point for A, flow rate of qa, head for ha, motor shaft power and the area of O-qa-A-ha-O is proportional. To reduce the flow rate to qb of the main adjustment method has two kinds: the traditional method is to keep the motor (pump) speed is unchanged, the valve will be closed small, resistance characteristics as shown in curve 3, the working point moved to point B flow rate of qb, head for hb, the motor’s shaft power is proportional to the area Oqb-B-hb-O. The use of frequency conversion speed control is to keep the valve opening unchanged, reduce the speed of the motor (water pump)