Student Projects

LukaK · ‎05-16-2013

Contact Information

University: University of Ljubljana, Faculty of Electical Engineering

Team Members (with year of graduation): Luka Kosir (2013)

Faculty Advisers: Rasto Fiser

Email Address:log.luka@gmail.com

Submission Language: English

Project Information

Computer guided test bench for frequency converter driven electromotors

Description:

The main goal of the project is to establish a test bench for different types of electromotors (inducton, synchronous). Power range of the application is limited with available eqiupment and space. The solution is power efficient due to DC link used to establish power balance between two frequency converters. Data is acquired with power analyzer and torque transducer.

Products

LabView 2012,
two Danfoss FC302 frequency converter,
LEM NORMA 6000 power analyzer,
LEM NORMA 5255 power analyzer,
LEM NORMA 5235 power analyzer,
ETH DRBK 50 torque transducer,
two Bosch Rexroth MAD100B-0150 asynchronous servo motors,
NI GPIB USB HS Controller,
ADAM 4561 USB to RS 485 converter,

The Challenege

A few challenges motivated me to establish an energy efficient or active test bench for electrical motors:

At the end of the production, it is appropriate to test performance of electromotor, specially if the product is made for exact purpose in low series. It is necessary to obtain multiple charachteristics of the motor with different loads on the shaft, even with the active load. Quality of the product can be evaluated through the heat of the case, torque, vibrations, noise, dynamical performance and so on.
If we have the motor already, and its behavior is unknown to us, due to the lack of the avaliable data, is the most appropriate way to get its performance under the load with this test bench. Our job is to couple shafts, insert basic parameters and run the test.
It is quite possible that we need heat charachteristic of drive under nominal load during long period of time, but we are aware that time and load menas energy and money. Energy is expensive and appreciated good, so passive load like brake is not an effective solution in these days. We need solve this problem too.
Even more, if we have a load charachteristic given like a functon of time, we must be able to import this function in simple .txt file and execute the test.
For educational purposes it would be convenient to demonstrate the energy flow between power grid and motor (converter), energy balance in the DC link, influence of the active load (generator) to the grid, and of course the intensity of the mechanical quantites on the shaft (torque, speed and power).
Malfunctions of the rotor squirell cage are quite often phenomenon. The idea is to change the rotors, run and load the motor and then acqire quantites related to the prediction of malfunctions.

All demands listed above are practically based on acquiring data, so software must be designed in way that different measurement equipment like power analyzers and acquisition modules can be added to application. We must be able to analyze and demonstrate all acquired results of the test in the same LabView program and export them to .txt file.

The Solution

The applicaton is based on LabView 2012 software which coordiantes acquisition, demonstration and logging of relevant quatities. Software dictates speed or torque references to frequency converters. References are sent in FC Danfoss protocol via RS485 serial port. Because port is not integrated in computer, we used USB to serial port converter. User can set all serial communication properties, addresses of the converters and measurement equipment in first tab of the programm.

Next step is to insert motor parameters like rated power, current, frequency and so on to the converter. All relevant motor properties are send to the converter with a custom made user interface.

When we insert all parameters we have to choose between multiple confugiration modes of brake converter. It is possible to choose between speed open/closed loop configuration or torque confuguration. The choice of user is the base for all other settings in software, for example, if user chooses closed speed configuration, it is necessary to insert properties of an incremental encoder. Although all references are consequently based on speed (rpm). If user chooses torque configuration, then the torque transducer is used like feedback and then we operate with references in Nm. So the basic configuration of our software depends on settings of the frequency converter, all software enviroment is adapted automatically.

We can dictate load manually wiht a knob or just set minimum and maximum load and number of measurement points. Programm will generate references in hexadecimal value. When we hit "Run", the test bench must be synchronized first. The procedure is first to run the motor, wait until the reference is reached (status word of the frequency converter) and then run the active brake with the function "flying start" in converter enabled. At every point, all data is acquired with the USB to GPIB converter with GPIB VISA SubVI. User has a chance to manually log the current valuse with special button.

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