Working principle of frequency converter
Inverters can be divided into voltage type and current type inverters.
Voltage type is an inverter that converts the DC of a voltage source to AC. The filtering of the DC loop is a current type that converts the DC of the current source to AC. The DC loop filter is an inductor. It is rectifier, rectifier, inverter.
The main circuit of the frequency converter is composed of three parts: a rectifier, a smoothing circuit and an inverter. The "rectifier" converts the industrial frequency power supply into DC power, and absorbs the "flat wave" of the voltage ripple generated by the converter and inverter. Loop.
The figure above is a wiring diagram of the inverter. In the installation of the inverter, there are some problems that need attention. For example, the inverter itself has strong electromagnetic interference, which will interfere with the operation of some equipment, so we can add a cable sleeve to the output cable of the inverter. Or the distance between the control line in the inverter or the control cabinet is at least 100mm from the power cable, etc.
Inverter wiring method
1. Wiring of the main circuit
1. The power supply should be connected to the input terminals R, S, T of the inverter, and must not be connected to the output terminals (U, V, W) of the inverter, otherwise the inverter will be damaged. After wiring, the odd thread ends must be cleaned up. The odd thread ends may cause abnormalities, malfunctions and malfunctions. The inverter must be kept clean at all times. When punching holes in the console, be careful not to let fragments and powder enter the inverter.
2. Between terminals + and PR, do not connect anything other than the recommended brake resistor option, or never short-circuit.
3.Electromagnetic wave interference, the input/output (main circuit) of the inverter contains harmonic components, which may interfere with the communication equipment near the inverter. Therefore, install the optional radio noise filter FR-BIF or FRBSF01 or FR-BLF line noise filter to minimize interference
4. In long-distance wiring, due to the influence of the parasitic capacitance charging current of the wiring, the fast response current limit function will be reduced, and the instrument connected to the secondary side will malfunction and cause malfunction. Therefore, the z* maximum wiring length should be less than the specified value. When the length of the wiring must be exceeded, the Pr. 156 is set to 1.
5. Do not install power capacitors, surge suppressors and radio noise filters on the output side of the inverter. Otherwise, it will cause inverter failure or damage to capacitors and surge suppressors.
6. In order to make the voltage drop within 2%, the appropriate type of wire should be used for wiring. When the wiring distance between the inverter and the motor is long, especially in the case of low frequency output, the torque of the motor will decrease due to the voltage drop of the main circuit cable.
7. After running, the operation of changing the wiring must be performed after the power is cut off for more than 10 minutes and the voltage is checked with a multimeter. For a period of time after the power failure, there is still dangerous high voltage on the capacitor.
2. Wiring of control circuit
The control circuit of the frequency converter can be roughly divided into two kinds of analog and digital.
1.The wiring of the control circuit terminal should use shielded wire or twisted pair, and it must be wired separately from the main circuit and strong current circuit (including the 200V relay program circuit).
2. Since the frequency input signal of the control circuit is a small current, in the case of contact input, in order to prevent poor contact, the small signal contact should use two parallel nodes or use twin contacts.
4.The wiring of the control loop generally selects a cable of 0.3 to 0.75 square meters.
Three, the wiring of the ground wire
1. Due to the leakage current in the inverter, in order to prevent electric shock, the inverter and the motor must be grounded.
2. Dedicated grounding terminal for inverter grounding. To connect the ground wire, use tin-plated crimp terminals. When tightening the screws, be careful not to damage the turnbuckles.
3. There is no lead in tin plating.
4.The grounding cable should be as thick as possible, and it must be equal to or greater than the specified standard. The grounding point should be as close to the inverter as possible. The shorter the grounding wire, the better.
Inverter wiring attention
1. The inverter itself has strong electromagnetic interference, which will interfere with the operation of some equipment, so we can add a cable sleeve to the output cable of the inverter.
2. The distance between the control line in the inverter or the control cabinet is at least 100mm from the power cable, etc.
3. When purchasing the inverter, there will always be the inverter manual. If not, you can download it from the website of the brand you purchased. The contents of the inverter manual are quite detailed, including product introduction, working principle, installation and debugging, etc.
The role of frequency converter:
1. The inverter can adjust the power of the motor to realize the variable speed operation of the motor, so as to achieve the purpose of saving electricity. Examples are embodied in the centrifugal fan and water pump. When the centrifugal fan and water pump use the frequency converter, the operator can adjust the speed according to the frequency conversion, and can easily control the flow according to the needs, thereby saving energy.
2.The frequency converter can reduce the voltage fluctuation in the power line, and avoid the phenomenon of equipment tripping or abnormal operation once the voltage is abnormal.
3. The frequency converter can reduce the impact on the power grid, thereby effectively reducing reactive power loss and increasing the effective power of the power grid.
4. The frequency converter can also reduce the wear between the transmission parts in the machine, therefore, to a certain extent, it also reduces the cost and improves the stability of the system.
5. In addition, the transformer's control functions are very complete, which can be well coordinated with other control equipment or together, so as to achieve centralized monitoring and real-time control, and solve a lot of system compatibility problems for users.
