Abstract : A primary-standby circulating water pump control system based on a frequency converter, soft starter, and LOGO! controller offers advantages such as excellent control performance, simple software design, easy-to-use hardware interface, high reliability, and high cost-effectiveness. Keywords : Frequency converter; Soft starter; LOGO!; Control system 1 Introduction In previous circulating water pump control systems, a large portion of the motors were constant-speed driven systems. Much of their electrical energy was consumed by the frequent starting and stopping of the pumps to adapt to changes in water supply. Furthermore, accurate monitoring of the water level at all times was impossible, making accurate pump start-up and shutdown difficult. This not only caused the motors to operate in an inefficient range, shortening their lifespan, but also resulted in a high equipment failure rate due to frequent starting and stopping, leading to serious water waste and a large workload for system maintenance and repair. Variable frequency speed control, with its superior performance in energy saving and constant pressure, can solve the above problems in circulating water pump control systems. A primary-standby circulating water pump control system based on LOGO! (Programmable Logic Controller) in conjunction with a frequency converter and soft starter can achieve excellent control performance. 2. Control System Design The variable frequency circulating water pump control system mainly consists of LOGO!, frequency converters, soft starters, pressure sensors, level sensors, power distribution devices, and water pumps. The 230RC series LOGO! and ACS frequency converters and PSS series soft starters are selected as the control core. The frequency converter uses the ACS series water pump-specific frequency converter, which has functions such as vector control, overcurrent, overvoltage, undervoltage, frequency converter overheat protection, frequency converter thermal protection, motor thermal protection, motor overheat protection, stall protection, instantaneous IGBT shutdown (BX) protection, fuse blown protection, external fault protection, motor overload (V/F) L 3j, and frequency converter overload protection. Combined with the PSS series soft starter and WSP300 pressure transmitter, the control effect is excellent, the software design is simple, the hardware interface is easy to implement, and the reliability is high. The overall system has a very high cost-performance ratio. [b][align=center]For details, please click: Design of a Main and Backup Circulating Water Pump Control System Based on LOGO[/align][/b]