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Inverter Braking by De-Saturating Power Transistors

IP.com Disclosure Number: IPCOM000209588D
Original Publication Date: 2011-Aug-10
Included in the Prior Art Database: 2011-Aug-10
Document File: 3 page(s) / 268K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

In the field of inverter brakes, used e.g. in motor controls, there is often a requirement to brake the load. In order to do that, energy is removed from the appliance. Traditionally there are a number of methods to achieve this. Regenerative braking and external resistor braking allow for a high performance, but add significant costs to the production of the system. Internally fitted resistor brakes provide an intermediate level of functionality and add reasonable costs to the system. Therefore they are fitted as standard for some markets.

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Inverter Braking by De-Saturating Power Transistors

Idea: Peter Lonsdale, GB-Congleton

In the field of inverter brakes, used e.g. in motor controls, there is often a requirement to brake the load. In order to do that, energy is removed from the appliance.

Traditionally there are a number of methods to achieve this. Regenerative braking and external resistor braking allow for a high performance, but add significant costs to the production of the system. Internally fitted resistor brakes provide an intermediate level of functionality and add reasonable costs to the system. Therefore they are fitted as standard for some markets.

On the other hand, DC (Direct Current) braking and compound braking provide a low level of performance, but do not add significant costs to the system. Thus, they can be found in products for markets, in which the customers do not want to spend money on more advanced braking systems. These drives have no means to absorb excess energy in the system. This can lead to problems in certain situations, such as light load operation, when the drive is subject to repeated mains bursts and surges. The excess energy gradually increases the DC link voltage until the drive trips, meaning it shuts down to protect itself. Step changes in the mechanical load can also cause momentary instability, which causes an excess of regenerated energy that can not be dissipated. This, again, will provoke the drive to trip. If users experience these problems, they are forced to upgrade their system to higher performance braking systems, which may be overrated for their application. Then, there are also customers that can use the less advanced braking systems, but their application performs worse than they would desire. Therefore, an intermediate solution with low additional costs would be advantageous, that aims at the field between low cost DC or compound braking systems and the high cost resistor or regenerative braking systems.

In the following a solution is proposed, which allows to absorb energy in an inverter drive system using the already existing main power components of the system mentioned above. Usually the power switching transistors are operated by switching between fully on, which means they are saturated, and fully off, as this gives the highest efficiency. In their regular use, the switching device is intended to convert the power with as little absorption as possible. In this solution, however, the switching device
is deliberately de-saturated into a state between "on" and "off", in order to dissipate energy. A device in this state behaves like a resistor absorbing energy from the drive.

In conclusion, in regular drive operation the switching device operates on its regular terms, switching between fully on, which means they are saturated, and fully off. Yet, when braking the motor the switching devices are de-saturated in order to absorb energy from the motor.

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