Inverter can achieve one or two or even more, but need to follow some principles - Database & Sql Blog Articles

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A frequency converter can control one or more motors, but it must follow specific guidelines to ensure safe and efficient operation. This article provides a detailed explanation of key considerations when using a single inverter to drive multiple motors. First, equipment selection is crucial. When choosing an inverter, the operating conditions must be carefully evaluated. If the motors do not need to be started or stopped during the inverter’s operation, the inverter’s capacity should only be slightly higher than the total power of all connected motors. In such cases, it's essential to ensure that the inverter is completely stopped before switching any contactors or changing the motor’s operating state. During active operation, direct start/stop of individual devices must be avoided. However, if motors need to be started or stopped at any time, the inverter’s capacity must be significantly increased. The starting current of a motor can be up to 5–7 times its rated current, so the inverter must handle this surge. The required inverter power is calculated by adding the peak starting power (multiplied by 5–7) to the total running power of other motors. If many motors are frequently switched, the inverter can be sized based on this value without additional amplification. But if only a few motors are controlled, it's safer to increase the inverter rating by one level. For AC contactors used with motors that require frequent start/stop, their rated current should be one level higher than the motor’s. Thermal relays or motor protectors are also necessary to prevent overloads and protect both the motor and inverter. These devices should be selected based on the motor’s rated current. Other important factors include cable length. Long wiring between the inverter and motors can cause issues like high-frequency currents, leakage, and inaccurate readings. For example, Fuji inverters recommend that motor cables under 3.7kW should not exceed 50 meters, while those above 3.7kW should be under 100 meters. If the line is too long, an output filter may be needed. In some cases, thermal relays might not function properly even with short cables, especially in 400V systems. To resolve this, you can use an output filter or lower the inverter’s carrier frequency. When using filters, the total motor connection length should not exceed 400 meters. Practical applications often involve using a single inverter for multiple small motors, such as in production lines or roller kilns. This setup reduces costs, minimizes failure rates, and simplifies maintenance. For instance, in 1996, a factory used one 11kW Fuji inverter to control 15 0.55kW cycloidal gear motors. These motors could be started or stopped individually, and the system operated smoothly for years without issues. Imagine how many inverters would be needed if each motor had its own unit. The cost, space, noise, and heat generation would be much higher. Using a single inverter makes the system more efficient and manageable. Finally, electrical schematics vary depending on the application. While this article provides general guidance, the actual design must match the specific control requirements. It’s always best to consult with an experienced engineer for accurate implementation.