Overview
Technosoft motion control drives are used in a plethora of industries and depending on the application type and characteristics, their power ranges from just a few watts to High Powered (8KW) applications, such as the AGV industry.
Here the phenomenon of regenerative braking, although not limited only to the cases of high power applications, is certainly more important and has clear and visible effects. This is the process in which the mechanic energy (usually present in the load in the forms of kinetic or potential energy) is converted to electric energy in the motor and is flowing back toward the power supply due to the presence of our drive which allows 4 quadrant operation. Most power supplies cannot accept this energy. Even for battery powered applications, while the batteries can recharge, their management systems usually don’t permit the high transfer rate (power). The only elements that will be able to store some of that energy are the capacitors present on the motor supply bus.
To alleviate this effect, one can add external capacitors (thus increasing the energy storage capacity, but also increasing the in-rush current at power-on) or installing chopping resistors with the help of a brake chopper. For the second option, the value of the resistors must be calculated based on the load and braking duty cycle and they have to be connected to the power source lines only when a certain voltage threshold (set by the user) is reached, to effectively dissipate the excess energy as heat.
To make use of the chopping resistor, most of our drives use their 4th inverter phase that will be commanded based on the DC bus voltage, thus connecting the resistor to the supply lines and dissipating the excess energy. In some cases however, when such a configuration is not possible, Technosoft provides the BC90100 BX brake chopper module as a solution. This module can work with the Technosoft drives and doesn’t require any programming at all – the configuration is done only at the drive level.
What are the reasons for the regenerative energy
The regenerative energy is generated during rapid deceleration of the motor or in applications with vertical loads where the normal power losses present in the system are not enough to cover for the needed braking force and will flow back to the power supply of the drive. As explained above, this can lead in certain cases to an increase in the DC bus voltage.
This creates a potentially dangerous situation because the voltage can rise to a level where the over-voltage protection of the drive will be triggered, resulting in the deactivation of the control loops and of the PWM outputs of the drive. In turn, this will eliminate the braking force, the load will stop freely but in an uncontrolled manner (depending on the remaining energy and the friction forces of the system).
Features and usage of the BC90100 BX module
The BC90100 BX module is an effective and easy way of dealing with the regenerative energy. This is due to its universal applicability to Technosoft drives.
The module works by being connected to the power supply lines, having a range of voltage from 12V to 80V and maximum current of 160A. The chopping resistor will be connected directly on the BC90100 BX module, which will be commanded via a digital output from the drive in use, both PNP or NPN type of outputs are supported.
Using the EasyMotion Studio II software, the presence of the BC90100 BX module can be indicated in the “Setup | Protections and limits” section, this will enable the user to set the voltage threshold at which the BC90100 BX module becomes active (i.e. when the chopping resistor will be connected to the circuit), as well as which of the drive outputs will be used to generate the said command.
Remark: The value of the voltage threshold must be set lower than the over-voltage protection of the drive, since the purpose of the chopping resistor is to avoid the situation where the over-voltage protection is triggered, but slightly higher than the one of the power supply to prevent accidental activation of the BC90100 BX. The over-voltage value can be found in the “Drive Data” section of the Protections and limits page:
Once the above mentioned settings are done, the drive will monitor the supply voltage and will command the BC90100 BX module via the selected output, thus effectively limiting the voltage level of the DC bus.
Connectivity of the BC90100 BX brake chopper module with Technosoft drives
The following diagram is an example of how to connect the BC90100 BX module to an iPOS4850 BX-CAT-STO:
The BC90100 BX module must be connected together with the drive(s) on the “+” and “–“ of the power supply.
The chopping resistor will be connected between the RES+ and RES- pins of the BC90100 BX module.
The selected digital output pin of the drive will be connected to the J2 connector of the module:
– if the drive output is “PNP” type: CMD+ will be connected to the output and CMD- to drive “GND”
– if the drive output is “NPN” type: CMD+ will be connected to “+Vlog” and CMD- to the output.
Conclusions
The BC90100 BC brake chopper module is a device specifically designed for applications in which regenerative energy can be significant while the drive either can’t control the brake itself (as it can happen with any drive controlling a stepper motor) or the integrated brake chopper functionality of the drive is not enough.
It is also important to note, that in a machine where there are more drives/motors on the same bus it is enough to have only one BC90100 BX module to limit the overall DC bus voltage.
Want to learn more about how the Micro 4804 can transform your application? Contact our team today!
