Filter 18.432M

Q: How do I select the inverter capacity when one inverter has multiple motors?

A: When a single inverter is used to drive multiple motors in parallel, it's essential to ensure that the total rated current of all the motors does not exceed the inverter’s rated output current. A 10% safety margin should be maintained. All motors should start and stop simultaneously during operation, rather than being turned on or off individually. In applications like lifting systems, where high starting torque is required, the total motor current should be multiplied by 2 (as motor starting current is typically twice the rated current), and this value must be less than the inverter’s rated current plus its overload capacity. For example, if two motors have a rating of 7.5 kW each with a rated current of 16 A, the combined current would be (16 + 16) × 2 = 64 A. In this case, an 18.5 kW inverter may not be sufficient; a 22 kW unit would be more appropriate. A typical vector control inverter with a rated output current of 48 A and a 150% overload margin can handle up to 72 A, which meets the requirement. It’s important to consider not just current but also torque and overall system safety.

Q: What is the best way to set acceleration/deceleration time and torque boost?

A: The settings for acceleration/deceleration time and torque boost depend on the load characteristics. If the load has high inertia but low starting torque, you should increase the acceleration/deceleration time and reduce the torque boost. Conversely, if the load has high starting torque but low inertia, you can decrease the acceleration time and increase the torque boost. However, longer acceleration times may lead to higher currents over time. Gradually increasing the torque boost can help reduce current until it stabilizes. Starting frequency is often set between 5–10 Hz for smoother operation. Using vector control mode can automatically adjust torque compensation, making the process more efficient and reliable.

Q: How can I minimize interference from the inverter?

A: To reduce interference, several measures can be taken. On the inverter side, use input filters, zero-phase reactors, grounding capacitors, and isolation transformers to suppress conducted interference. Keep input and output lines separate from signal lines, and use shielded cables. For inductive interference, avoid running power and signal lines together, and use magnetic rings or line filters. For radiation interference, pay attention to metal piping and power lines inside the control cabinet. Lowering the carrier frequency can also help reduce noise. On the receiving end, keep sensitive equipment away from the inverter, use shielded cables with single-ended grounding, and add magnetic rings or filter capacitors. Separating ground wires is also recommended to prevent noise coupling.

Q: Can I control the inverter using an electromagnetic contactor on the input side?

A: No, it is not advisable. Frequent switching can damage the charging resistor. Also, if the motor is allowed to free-wheel, it can cause overcurrent, potentially damaging the inverter module.

Q: What should I do if the rectifier bridge is damaged?

A: Damage to the rectifier bridge can occur due to mismatch between the power grid and the inverter. Installing an input AC reactor can help prevent this. Consider installing an AC reactor if any of the following conditions apply: (1) The transformer capacity is over 500 KVA, and the ratio of transformer capacity to inverter capacity exceeds 10. (2) The same transformer supplies thyristor loads or power factor correction capacitors. (3) The three-phase voltage imbalance exceeds 3%. (4) You need to improve the input power factor. These steps can enhance system stability and protect the inverter from damage.