Frequency converter is a device that converts power supply into frequency conversion power supply, which is between power supply and electrical equipment. Frequency converter is a typical power electronic device whose hardware core is power electronic components and microprocessor chip. Power electronic components, input and output copper bars and front end control components constitute a power unit, which is a strong electricity or power module; Microprocessor chip as the core of the main control board, input and output modules and display control components constitute a control unit, belonging to the weak current or control module; Function extension connectors and external components constitute extension units, suitable for various working characteristics. 

When the inverter is directly connected to the power grid, the power grid capacity, power grid voltage level and voltage value deviation should be fully evaluated;  The transformer capacity, output voltage value and its deviation when connected to the power grid indirectly through the transformer. Inverter output contains rich harmonic content, these harmonics not only have varying degrees of influence on the motor, but also in turn will pollute the power supply and interfere with other electrical equipment on the grid. 

When the distribution transformer is connected with a power compensation device, the waveform of the input current of the frequency converter will be distorted, which degrades the performance of the frequency converter. When the frequency converter runs, additional heating factors will be added, resulting in the power output of the frequency converter can not reach the normal level.

In order to obtain a more ideal electromagnetic compatibility effect, the protective body of the frequency converter had better use iron shell, the output cable is shielded by steel pipe, shielding isolation measures are also implemented between the power unit and the control unit. If necessary, input filter or zero-sequence inductor can be equipped to cut off the reverse transmission channel of inverter clutter components as far as possible. 

In the practical application process, it can be found that the quality of the inverter of the current supporting motor is uneven, resulting in poor fit between the inverter and the motor, causing two adverse effects: the motor performance is poor in the operation process, and even the motor performance deteriorates, the life of the motor is shortened and other malignant quality accidents; In the performance test of variable frequency motor, the measured parameters are unstable and seriously interfere with the test of adjacent motor.