Safe stopping of electric motors

April 3, 2023
Products Images Contacts
Safe stopping of electric motors-0

Every day, millions of electric motors carry out production processes in the world. They are widely used in product manufacturing and automation of various industrial processes. Under speed control conditions, it is often necessary to stop the electric motors.

During deceleration of the motor, the energy flow can be reversed, i.e. from the electric motor back to the frequency converter. Whenever the motor rotates faster than the winding is energized, the motor becomes a generator. This happens, for example, when a crane or hoist lowers a load, or when a conveyor conveys material down a slope, or when a fan stops quickly or a high-inertia motor on a shaft slows down.

The stopping of electric motors can be divided into three methods of braking: regenerative, dynamic and mechanical. Dynamic and mechanical braking provide the fastest stopping of the engine, but are very harsh methods. They can seriously damage the operation of both the equipment and its equipment. It is important for us that our customers' equipment works for a long time and is energy efficient. Therefore, in this article we decided to talk about the soft and safe braking and stopping of electric motors. This is regenerative braking.

How is regenerative stopping performed?

If the system has significant friction or other braking factors (such as airflow through a fan), then the energy recovered can be significantly reduced. However, if the regeneration is much higher, the power flow will return to the frequency converter.

Invertek Drive block any flow of current that may flow from the motor (during regeneration) to the mains, so the current flows into the DC link capacitors. When this happens, the voltage across the capacitor rises and can exceed the capacitor's voltage rating if not controlled. If the regeneration continues, the voltage across the capacitors will continue to rise, causing the frequency converter to fail. To prevent this from happening, Invertek's inverters have a DC bus voltage sensing circuit that turns off the IGBT output switches, cutting off current from the motor, and the motor essentially coasts to a stop. The frequency converter will display a "0-volt" overvoltage error.

Three solutions for safe stopping of electric motors

  1. The first solution is to reduce regeneration. When the system regenerates during deceleration, the simplest solution is to reduce the regen, i.e. increase the deceleration time. This can be done by changing the stop time mode parameter P-04 from 0 to 600 s. This method reduces the flow of regenerated energy and it can be absorbed by losses in the system itself or the drive. However, the higher the inertial load, the longer the deceleration time.
  2. The second solution is to turn off the frequency converter. The approach is to simply turn off the output of the frequency converter and let the motor and load coast to a stop. This can be done by changing the mode parameter P-05 (P1-05 to P2 and Eco) from 0 to 1. Deceleration is now disabled and the motor coasts to a stop. The disadvantage of this solution is the lack of control of the engine during a stop. This is inconvenient in the manufacturing industry, but may be suitable for a cooling fan.
  3. The third solution is to connect a braking resistor. But if you need constant acceleration and deceleration, you need a controlled solution. The solution is to connect a resistor to DC to burn the energy. The resistor is turned on and off by an IGBT built into most industrial drives, which is controlled by drive software that monitors the DC voltage and trips as needed. The resistor is usually not included with the frequency converter. It must be selected and purchased separately.

Invertek Drives with IGBT brake switches

Invertek Drives frequency converters are used to control and protect motor drives. They provide a high level of energy efficiency and a wide range of functionalities. Invertek Drives Optidrive E3 and Optidrive P2 have built-in IGBT brake switches. This braking resistor solution is ideal for low to medium power applications. How to correctly choose required value of the brake resistor for the Optidrive? can be found in our previous article.

If you need Invertek Drives frequency converters or accessories, contact the specialists of ZTF Lāsma, who will help you find the most suitable and economically advantageous solution. We are here to support!


Other articles and videos about frequency converters:

Code: OPTBR050INI55
In stock: 4 pcs
Code: ODBR100IN
In stock: 4 pcs
SOLD OUT. Ask for availability
Aleksandrs Čuslins
Aleksandrs Čuslins
Drive control
+371 2933 4363
SICK logo
TORK logo
EMAS logo