Patent Application
20140049880
The use of power electronic devices such as a set of inverters to control a motor drive or other electrically powered device is well known. Components of one prior art motor control system are shown in
The transformer 110 includes primary windings 112 that excite a number of secondary windings 114-122. Although primary windings 112 are illustrated as having a star configuration, a mesh configuration is also possible. Further, although secondary windings 114-122 are illustrated as having a delta or an extended-delta configuration, other configurations of windings may be used as described in U.S. Pat. No. 5,625,545 to Hammond, the disclosure of which is incorporated herein by reference in its entirety. In the example of
Several functional components of inverters can be subject to high thermal stress during operation. When high temperatures occur, such as a result of temporary overload operation or other operation outside of base ratings, inner temperatures of the components can reach or exceed critical temperatures. Such systems may be cooled by circulating cool water and/or air through the components in order to absorb heat and reduce the component temperature. Nonetheless, it is desirable to sense the temperature of the component to identify when the component approaches a critical temperature.
The large number of temperature measuring locations in a power electronic circuit, and the high thermal stress conditions of operation, make it difficult to adequately sense the temperature of a power electronic device.
This document describes methods and systems that attempt to solve at least some of the problems described above, and/or other problems.
In an embodiment, a power electronic device may include a housing, a conductive element positioned within the housing and rated for at least a medium voltage, a cooling system in fluid communication with the conductive element, a plurality of temperature sensing tags and a data collection unit having a receiver that is configured to receive signals from the antennae of the temperature sensing tags. The cooling system may have a plurality of outlet conduit elements that are positioned within the housing. Each of the tags may be attached to one of the outlet conduits and may include a power supply, a temperature sensor, and an antenna.
As used in this document and in the appended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used in this document have the same meanings as commonly understood by one of ordinary skill in the art. As used in this document, the term “comprising” means “including, but not limited to.”
Electronic drive systems such as those illustrated in
For long-term reliable operation, it is desirable to monitor the temperature of power electronic devices. Components that may be monitored include, but are not limited to, inductors, transformers and semiconductor devices (IGBT, MOSFET, thyristors, etc.). However, the large number of temperature measuring locations in a power electronic device creates a challenge because the locations are often at a high voltage potential with respect to ground and to each other. Therefore it is a problem to have power supply and data wires to communicate with the sensors which are in contact with high voltage. In addition, these locations are in a powerful electromagnetic environment, caused by large currents containing high harmonics, as well as high alternating voltages. The sensors generate very small electrical signals which could easily be disturbed by the strong electromagnetic fields, which poses yet another challenge.
A cooling system is in fluid communication with the conductive element. The cooling system may one or more conduits that circulate air, water, or other gas or liquid through the area of the conductive elements. As shown in
A temperature sensing tag 311a is positioned to contact the outlet conduit 213 and detect the temperature of the outlet conduit. Optionally, any number of temperature sensing tags 311a . . . 311n may be used, such as one tag for each conduit. The temperature sensing tags may be positioned within the transformer housing, optionally at or very near to the point where the conduit interfaces with the component. The tags may be oriented so that each tags are each positioned along an axis that is substantially perpendicular with that of its neighboring tags, to reduce the risk of arcing. The temperature sensing tags may each include a power supply, a temperature sensor, and an antenna so that they can wirelessly send signals corresponding to the sensed temperature to a remote data collection unit.
Optionally, the tags may be of the type known as radio frequency identification (RFID) tags, which serve as passive temperature sensors. In some embodiments, the tags may harvest energy from ultra high frequency (UHF) fields, capture the energy and store it in an energy storage device (such as an internal capacitor) for use as a power source. The tag may sense the temperature when the storage device's charge reaches a threshold (such as substantially or fully loaded), and then transmit a signal with the sensed temperature along with an identification code for the tag. For example, the power supply for a tag may include an induction coil positioned to harvest magnetic energy from a field near the windings (or other components) when the windings are operational and convert the magnetic energy to a voltage. Other configurations are possible. In some embodiments, the power supply may include a battery. In other embodiments, the power supply may be a thermoelectric device that can generate a voltage due to the temperature differential between a hot outlet tube and air inside an enclosure.
The signals from the tags are received by one or more data collection units 350 that are configured to receive signals from the antennae of the temperature sensing tags. Each data collection unit may include a transmitter, a processor, and a memory. The memory may contain programming instructions that, when executed, the processor to send, via the transmitter, a polling signal to one or more of the temperature sensing tags. The polling signal may actuate a response that the data collection unit 350 will receive and use to determine the temperature sensed by the tag.
Data communication between the tags and data collection unit may occur by any suitable means. For example, the communication may use radio waves at VHF or UHF frequencies. If so, sensing data and sensor identification data for a tag may be stacked together in a short telegram and sent via the tag's antenna to the transmitter station. All the involved tags/sensors may operate in the same manner and send a data telegram in the data collection unit at periodic intervals, such as every 30 seconds. This may be accomplished by “blind” transmissions, where each tag emits its signal in an uncoordinated manner on a carrier frequency, common for all sensor elements. The repetition rate is may be preset to any suitable time, such as about 30 seconds. If the telegrams of two or more sensors collide, the probability for interference between the telegrams could be reduced by arbitrarily choosing small repetition time offsets (added to the basic period while sensor presetting, for instance at assembly time) and another additional small variation per sensor on a cycle by cycle base. The data collection unit may continuously listen for telegrams, identifies the sender of each telegram, and assembles the data in a bundle to be transferred it to an automation/monitoring unit. Alternative, all the sensor elements may be controlled by the transmission unit. If so, the sensors may not emit any signal until they are interrogated by a message from the data collection unit. The triggers may be coordinated to give enough idle time to every sensor to gather and store enough energy to be able to answer on the next request.
In various embodiments, it may sufficient to gather sensed temperature values within time periods of about 30 seconds. This may be sufficient for most cases of power electronic circuits, where the size of the involved components is so large as to limit the maximum slope of temperature change over time. Other configurations may require shorter or longer cycles. Taking 30 seconds as an example, then a reasonable time division is 1 second for data transfer (proposing an upper limit) and 29 seconds for energy harvesting. If the sensor element handles both the harvesting and communication in parallel, then uninterrupted harvesting would be possible.
While several embodiments of the invention have been described in this document by way of example, those skilled in the art will appreciate that various modifications, alterations, and adaptations to the described embodiments may be realized without departing from the spirit and scope of the invention defined by the appended claims.
