Selection 1) the purpose of using frequency; constant voltage control or constant current control. 2) The load type of the inverter; such as vane pump or positive displacement pump, pay special attention to the performance curve of the load, the performance curve determines the way of application method. 3) Matching of the inverter with the load; I. Voltage matching; The rated voltage of the inverter is in accordance with the rated voltage of the load. II. Current Matching; Ordinary centrifugal pump, the rated current of the inverter is in accordance with the rated current of the motor. For special loads such as deep water pumps, etc., refer to the motor performance parameters to determine the inverter current and overload capacity with the maximum current. III. Torque Matches; This may occur when a constant torque load or a deceleration device is present. 4) When using the inverter to drive the high-speed motor, the output current value increases due to the small reactance of the high-speed motor and the increase of the harmonic. So for high-speed motor inverter selection, its capacity to slightly larger than the selection of ordinary motor. 5) If the inverter to run long cable, this time to take measures to suppress the long cable to the ground coupling capacitor, to avoid the inverter output is insufficient, so in this case, the inverter capacity to enlarge a file or in the inverter Outputs the output reactor. 6) for some special applications, such as high temperature, high altitude, this time will cause the inverter derating, the inverter capacity to enlarge a block. Control schematic design 1) first confirm the inverter installation environment; I. working temperature. Inverter is a high-power electronic components inside, very vulnerable to the impact of the working temperature, the product generally requires 0 ~ 55 ℃, but in order to ensure safe and reliable work, use should be considered leave room, the best control below 40 ℃ The In the control box, the inverter should be installed in the upper part of the box, and strictly abide by the installation instructions in the product manual, absolutely not allowed to heat the element or easy to heat the components close to the bottom of the inverter installation. II. Ambient temperature. When the temperature is too high and the temperature changes greatly, the condensation inside of the inverter is prone to occur, and its insulation performance will be greatly reduced, and may even lead to short circuit accidents. If necessary, the desiccant and the heater must be added to the tank. In the water treatment, the general water vapor are relatively heavy, if the temperature changes, then the problem will be more prominent. III. Corrosive gases. Use of the environment If the corrosive gas concentration, not only will corrode the components of the lead, printed circuit boards, but also to accelerate the aging of plastic devices, reducing insulation performance. IV. Vibration and Shock. The control cabinet with the inverter is subject to mechanical vibration and shock, which can cause poor electrical contact. Huai'an thermal power on the emergence of such a problem. At this time in addition to improve the mechanical strength of the control cabinet, away from the vibration source and the impact of the source, but also the use of anti-seismic rubber pad fixed control cabinet and internal electromagnetic switch and other components of vibration. After the equipment has been in operation for a period of time, it should be inspected and maintained. V. Electromagnetic interference. Inverter in the work due to rectification and frequency conversion, the surrounding produce a lot of interference with electromagnetic waves, these high-frequency electromagnetic waves on the nearby instruments, instruments have some interference. Therefore, the cabinet instrumentation and electronic systems, should use the metal shell, shielding the inverter interference on the instrument. All the components should be reliable grounding, in addition, the electrical components, equipment and instrumentation between the connection should be shielded control cable, and the shield should be grounded. If the processing is not good electromagnetic interference, often make the whole system can not work, resulting in control unit failure or damage. 2) the distance between the inverter and the motor to determine the cable and wiring methods; I. inverter and motor distance should be as short as possible. This reduces the ground capacitance of the cable and reduces the source of the interference. II. Control cable Use shielded cable, power cable use shielded cable or from the inverter to the motor all with a threading machine shield. III. The motor cable shall be independent of the other cable traces with a minimum distance of 500 mm. At the same time should avoid the motor cable and other cables long distance parallel alignment, so as to reduce the inverter output voltage caused by rapid changes in electromagnetic interference. If the control cable and the power cable cross, as far as possible so that they cross the 90 degree angle. The analog signal lines associated with the frequency converter are routed separately from the main circuit, even in the control cabinet. IV. The analog signal cable related to the inverter is preferably shielded twisted pair cable, the power cable selection shielded three-core cable (its specifications than ordinary motor cable large file) or follow the inverter user manual.