Filter 18.432M

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

A: When an 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 switched on or off individually. In certain applications like lifting systems, the calculation differs. Instead of just summing the motor ratings, you need to multiply the total rated current by 2 (as the motor’s starting current can be twice the normal). This value must then be less than the inverter's rated current plus a 150% overload margin. For example, if two motors each have a rated current of 16A, the total would be (16 + 16) × 2 = 64A. In this case, an 18.5KW inverter might not be sufficient; instead, a 22KW model is more appropriate. An inverter with a rated output current of 48A and a 150% overload margin (72A) would be suitable for this load.

It’s important to note that real-world applications require considering not only current but also torque and safety factors. Experience shows that simply matching current values isn’t always enough—torque and system stability are equally critical.

Q: How do I set acceleration and deceleration time and torque boost?

A: The settings for acceleration/deceleration time and torque boost depend on the load characteristics:

1. If the load has high inertia and low starting torque, set a longer acceleration/deceleration time and a lower torque boost.

2. If the load requires high starting torque and has low inertia, use a shorter acceleration/deceleration time and a higher torque boost. However, longer acceleration times can cause prolonged high current flow.

3. Gradually increase the torque boost until the current stabilizes. If the current starts to rise again, stop the torque compensation.

4. Set the starting frequency higher, around 5–10Hz.

5. Use vector control mode for automatic torque compensation.

Q: How can I minimize interference from the inverter?

A: To reduce interference, consider the following measures:

1. On the input side: Install an input filter, a zero-phase reactor, a grounding capacitor, or an isolation transformer to suppress conducted interference.

2. For inductive interference: Separate power lines from signal lines, use shielded cables, and install power line filters or magnetic rings to ground properly.

3. For radiation interference: Ensure proper shielding of metal piping and power lines inside the control cabinet. Reducing the carrier frequency can also help.

For the affected devices:

1. Keep them away from the inverter as much as possible.

2. Use shielded signal cables and connect the shield at only one end.

3. Use magnetic rings and filter capacitors for additional protection.

4. Insert a power line filter into the power supply line.

5. Separate the ground wires to prevent noise coupling.

Q: Can I use an electromagnetic contactor on the input side to start or stop the inverter?

A: No, it is not recommended. Frequent switching may damage the charging resistor. Also, if the motor is running freely during shutdown, it could cause overcurrent and potentially damage the inverter module.

Q: How can I solve rectifier bridge damage?

A: Rectifier bridge damage can occur due to mismatch between the power grid and the inverter. To prevent this, consider installing an input AC reactor. You should install an AC reactor if any of the following conditions apply:

1. The transformer capacity exceeds 500KVA, and the ratio of the transformer capacity to the inverter capacity is greater than 10.

2. The same power transformer is used with thyristor loads or power factor correction capacitors.

3. The three-phase voltage imbalance of the power supply exceeds 3%.

4. Improving the input power factor is necessary.