Abstract : Several relatively new inverter detection and protection circuits are presented, including detection circuits for current, voltage, overheating, power phase loss, and grounding faults. Among them, the detection circuit based on linear optocouplers is noteworthy due to its good linearity, ease of isolation, and high sensitivity, and has broad application prospects. These detection and protection circuits can be directly used in the design and implementation of inverters, with good results. Keywords : Inverter, Detection and Protection, Optocoupler, Sensor 1 Introduction In general-purpose inverters, the main function of the detection circuit is to feed back the operating status of the inverter and motor to the microprocessor. The microprocessor then processes the data according to a prescribed algorithm and provides control or protection signals to various circuits to achieve the purpose of controlling the inverter output and protecting the inverter and motor. The detection circuit mainly includes DC voltage detection circuits, current detection circuits, output voltage detection circuits, and temperature detection circuits required for electronic thermal protection of the inverter and motor. In vector control inverters, speed detection circuits and magnetic flux detection circuits are also included. The accuracy of the feedback detection of the control system largely determines the quality of the control system. Improving the measurement accuracy will improve the control performance of the entire system. Therefore, the detection circuit is an important component of the variable frequency speed control system, equivalent to the system's "eyes and touch." The rationality of the detection and protection circuit design directly affects the reliability and control accuracy of the system. [b]2 Commonly Used Detection Methods and Devices for Variable Frequency Drives 2.1 Current Detection Methods[/b] The current detection signal of the variable frequency drive can be used for motor torque and current control, as well as overcurrent protection. The main detection methods include the direct series sampling resistor method, the current transformer method, and the Hall sensor method. [b][align=center]For more details, please click: Design of General Variable Frequency Drive Detection and Protection Circuits[/align][/b]