A frequency converter is a device that converts mains frequency power to variable frequency power, acting as an intermediary between the mains frequency power supply and the electrical equipment. A frequency converter is a typical power electronic device, its core hardware consisting of power electronic components and a microprocessor chip. The power electronic components, input/output busbars, and front-end control components constitute the power unit, belonging to the high-voltage or power module category; the main control board with the microprocessor chip at its core, input/output modules, and display and control components constitute the control unit, belonging to the low-voltage or control module category; functional expansion connectors and external components constitute the expansion unit, adapting to various operating characteristics.
When connecting a frequency converter directly to the power grid, the grid capacity, voltage level, and voltage deviation should be fully evaluated. When connecting indirectly through a transformer, the transformer capacity, output voltage, and their deviation should also be considered. Frequency converter outputs contain significant harmonic content. These harmonics not only affect motors to varying degrees but can also conversely pollute the power supply and interfere with other electrical equipment on the grid.
When a power compensation device is connected in the distribution transformer, the waveform of the inverter input current will be distorted, which will degrade the inverter performance and increase the heat generation factor during inverter operation, causing the inverter power output to fall below the normal level.
To achieve optimal electromagnetic compatibility, the inverter's protective casing should ideally be made of iron, the output cables should be shielded using steel conduits, and shielding and isolation measures should be implemented between the power unit and the control unit. If necessary, an input filter or zero-sequence inductor can be installed to minimize the reverse transmission path of inverter noise components.
In practical applications, it has been found that the quality of frequency converters used with motors varies greatly, resulting in poor compatibility between the frequency converter and the motor. This leads to two adverse effects: First, the motor performance is poor during operation, and may even cause serious quality accidents such as deterioration of motor performance and shortened lifespan. Second, the measured parameters during the performance test of the frequency converter motor are unstable, and it seriously interferes with the testing of adjacent motors on the same test platform.
