The power saving principle of the inverter!

I’ve often heard people say that inverters can save energy, and those who make this claim usually accept it without fully understanding why. The question is, does an inverter really save power? And if so, how much? Is it more effective at high frequencies or low frequencies?

Here are some key questions:

1. If two identical motors are running at 50Hz, one with an inverter and one without, both operating at their rated speed and torque, will the inverter save power? And by how much?

2. What if the motor’s torque isn’t at its rated level, but the speed and frequency remain the same (still 50Hz)? How much power can the inverter save in this case?

3. Under no-load conditions, how much can be saved? Which of these scenarios offers the greatest energy savings?

Answer: Inverters can indeed save energy, and in certain applications, they can reduce electricity consumption by over 40%. However, in other cases, using an inverter may actually consume more power than not using one.

Inverters save energy by reducing voltage under light loads. For constant-torque loads, such as pumps or compressors, the energy savings are minimal because the torque doesn’t change much with speed. However, for variable-torque loads like fans, where power consumption is proportional to the 1.7th power of speed, energy savings become significant when the motor runs slower. On the other hand, using inverters on oil well pumps may lead to higher losses due to braking resistors during deceleration.

Of course, if the application requires speed control, the energy-saving benefits of an inverter are still clear. But in cases where speed control is unnecessary, the inverter won’t save power—it only improves the power factor.

1. When two identical motors run at 50Hz, one with an inverter and one without, and both operate at rated speed and torque, will the inverter save power?
A: In this scenario, the inverter only improves the power factor and doesn’t save energy.

2. If the motor’s torque is below its rated value, but the speed and frequency remain at 50Hz, how much energy can the inverter save?
A: With automatic energy-saving mode enabled, the inverter can reduce voltage slightly, saving some power—but the savings are not very significant.

3. What about under no-load conditions? Which of the three scenarios saves the most power?
A: Under no-load conditions, drag-type loads don’t save much power.

For example, the concept of “closed-loop control” is sometimes misunderstood. Closed-loop doesn’t just mean a speed sensor feedback. Vector control with frequency regulation is also closed-loop. V/F control, on the other hand, is open-loop. PID control of temperature, pressure, or flow is also considered closed-loop. These can all be controlled via an inverter. So the definition of closed-loop should be broadened.

Another point to consider: the idea of “braking” is sometimes misinterpreted. It's not just about stopping—there are different types of braking, and some are more efficient than others.

1. Inverters do not always save power. There are many situations where they may not offer any real energy savings.

2. As an electronic device, inverters themselves consume power—about 3% to 5% of the rated power.

3. It is true that inverters can save power when used properly, but there are specific conditions required:

- High-power motors with fan or pump-type loads;

- The inverter must have built-in energy-saving features;

- Long-term continuous operation.

Without meeting these conditions, the inverter may not save power. Saying that inverters always save energy without considering these factors is misleading or even commercial hype. Understanding the original function helps you use it more effectively. Always pay attention to the application context and usage conditions to ensure proper and safe operation, otherwise you risk being misled.