What is the working principle of a three phase AC asynchronous motor inverter?
The frequency converter is the electric energy control device that transforms the power frequency power to another frequency by the on-off function of the power semiconductor device. We now use the converter mainly adopts the AC-DC-AC mode (VVVF inverter or variable frequency vector control), the first AC power into DC power supply through the rectifier, then the AC power into DC power supply frequency and voltage can be controlled by the supply of electric motive. The frequency converter circuit is usually composed of rectifier, intermediate DC link, inverter and control of 4 parts. The rectifier is a three-phase bridge controlled rectifier, and the inverter is IGBT three-phase bridge inverter, and the output is PWM waveform. The intermediate DC link is filter, DC energy storage and buffer reactive power.
I. operating temperature. The internal electronic components of high power, extremely easy to be influenced by the working temperature of the product, the general requirements for 0 ~ 55 degrees, but in order to ensure the safe and reliable work, use should be considered under the best control in 40 DEG C. In the control box, the inverter shall be installed on the upper part of the box, and strictly comply with the installation requirements in the product specification. Absolutely no heating element or easy heating element shall be installed on the bottom of the converter.
Distance determination of frequency converter and motor, cable and wiring method;The distance between the I. converter and the motor should be as short as possible. This reduces the capacitance of the cable to the ground and reduces the interference of the transmitter.II. control cables use shielded cables, power cables use shielded cables, or from frequency converters to motors, all shielded by threading tubes.The III. motor cable shall be independent of other cables, with a minimum distance of 500mm. At the same time, it is necessary to avoid the long distance parallel wire between the motor cable and other cables, so as to reduce the electromagnetic interference caused by the rapid change of the output voltage of the inverter. If the control cable and the power cable cross, as far as possible so that they cross at 90 degrees angle. The analog signal line associated with the inverter is separated from the main return line, even in the control cabinet.IV. and inverter related analog signal line is best to use shielded twisted pair, power cable shielded shielded three core cable (its specifications than ordinary motor cable large files) or comply with the frequency converter user manual.
The correct grounding of converter is an important means to improve system stability and restrain noise. The smaller the grounding resistance of the grounding terminal of the converter is, the better the cross section of the grounding conductor is not less than 4mm, and the length shall not exceed 5m. The grounding of frequency converter should be separated from the grounding point of power equipment. The signal line shield end to the inverter grounding terminal, the other end of the floating. The frequency converter communicates with the control cabinet electrically.
Heat dissipation: the heating of the inverter is caused by internal losses. In the frequency converter, the main part of the loss is mainly the main circuit, accounting for about 98%, and the control circuit accounts for 2%. In order to ensure the normal operation of the inverter must be reliable, we usually adopt inverter heat dissipation cooling fan; inverter fan installed inside the box body can be internal heat converter away, if the fan is not working properly, should immediately stop running the inverter; inverter power also need to fan in the control cabinet, control cabinet design to air duct reasonable, all air inlet to set dustproof net, exhaust unobstructed, avoid the formation of vortex in the cabinet, the formation of dust accumulation in a fixed position; to select the matching according to the amount of ventilation fan inverter manual, fan installation should pay attention to the problem of earthquake.
