Test Stand Automation and Control
plan • visualize • automatize
plan • visualize • automatize
The imc OMEGA software platform is the integration software for all imc test stands. It was developed in-house by imc and is being continuously developed further.
imc OMEGA consists of two part:
1. Basic software
2. Modular test types
As a result of basic, standardized software with a fixed range of functions, the user interface of all imc test stands is the same. This minimizes the training required and allows all customers to benefit from the further development of our basic software.
The basic software provides general functions for test administration and test parameters. It monitors the critical threshold values to protect test objects and controls the data storage for recorded measurements and calculated test results. It also contains password controlled user administration, which controls user access to the various fields and manages user rights.
The test stand allows for monitored manual control. Via input instruments on the user interface, the operator can adjust test stand process quantities and perform manual testing such as, for example, switching on supply voltage individually, release of the test object or load machine, and specifying RPM or maximum torque. According to input, measurement data acquisition and communication with the test stand, the periphery test object or controller of the test object continue to run in the background. The threshold values of the test stand are monitored and, if exceeded, an error message is issued, testing is discontinued and the test stand placed in a safe state.
Test plans allow cyclical test repetition and cascading of predefined tests. This allows the test object to be subjected to a whole series of tests that do not need to be explicitly started one after another by an operator. Such sequences can therefore run, for instance, overnight, over the weekend or over a longer period of time (endurance tests).
The imc OMEGA test software offers a variety of modular test types. These can be selected modularly depending on the test tasks and motor types. The following descriptions are therefore abstractly independent of the motor types.
For a better overview, the test types can be divided into the following categories:
Test types that can be conducted without a load unit, operating the DUT in idle mode without external load beyond its own inherent inertia, are termed load-free test types. These include:
The Parameter-Identification method is a turnkey, model-based procedure for determining the characteristic parameters of an electronically commutated permanent electromotor.
The DUT is placed in its mounting in accommodation to the physical test mechanism and electrically connected. Once the safety mechanisms have been locked, the motor is energized or braked, in order to produce a dynamic change of rotation speed. During the process of energizing, the DUT’s value limits are monitored in order to prevent it from becoming overloaded. After conclusion of the test, the DUT’s primary descriptive parameters, as well as derivative parameters, are calculated. Subsequently, the DUT is released so that it can be removed or discharged from the mounting.
The dynamic flux table measurement determines the magnetic flux in the d and q direction as a function of the impressed total current. For this purpose, the test specimen is dynamically loaded and measured the resulting load points. In addition, the ohmic losses as well as the friction and iron losses of the test object are recorded..
For dynamic flux table measurement, the DUT is connected to the inverter. At the beginning of the test, the winding resistances of the test object are determined in a DC current supply. The test specimen is then accelerated to the test speed and then dynamically accelerated and decelerated by various current presets in the d and q directions. For each individual current step, the current angle is also varied step by step.
At the end of the test, the friction torque is measured again in a downward ramp and the winding resistance is determined in a DC current supply. With the aid of these measured data, the influence of the moment of inertia in the speed ramps is compensated, as well as the heating of the windings during the test
The Parameter-Identification method is a turnkey, model-based procedure for determining the characteristic parameters of a brush-commutated permanent DC motor.
The DUT is placed in its mounting in accommodation to the physical test mechanism and electrically connected. Once the safety mechanisms have been locked, the motor is energized or braked, in order to produce a dynamic change of rotation speed. During the process of energizing, the DUT’s value limits are monitored in order to prevent it from becoming overloaded. After conclusion of the test, the DUT’s primary descriptive parameters, as well as derivative parameters, are calculated. Subsequently, the DUT is released so that it can be removed or discharged from the mounting.
Passive test types is a term used for those types in which the test object is mechanically connected to a driving machine and is not energized itself.
When permanent magnet motors are actuated externally, they induce a voltage which can be measured at the machine’s connection terminals. The induced voltage is proportional to the rotation speed and the excitation. During this test, the DUT is not powered.
The plot of the induced voltage provides information on the windings and on the extent of the excitation over the circumference. Measurement of the induced voltage represents a simple method to diagnose the DUT’s electromagnetic characteristics.
With this type of test, the relevant measured variables of the induced motor voltages and the angle of rotation of the motor axis are recorded. After evaluating the test, the motor voltages can be displayed over the angle of rotation and the order spectrum of the motor voltages. In addition, the harmonic distortion is calculated for all motor voltages.
With the help of this information, the deviation of the motor voltage from the desired curve can be assessed.
In electrical motors, the motor’s internal structure causes cogging torques. These occur when the motor rotates and can be measured at a slow rotation speed. During this test, the DUT not powered. The measured plot of the torque provides information on the DUT’s internal structure. Measurement of the torque represents a simple method to diagnose the DUT’s electromagnetic characteristics.
The DUT is connected with the test stand’s load machine via a coupling. Once the test starts, the load machine drags the DUT for a specified time towards a target speed. The load machine holds this target rotation speed constant for the duration of the data acquisition. After conclusion of data acquisition, the load machine brakes the DUT’s motion down to a standstill.
The drag torque test determines the loss torque of a passively towed DUT as a function of the speed. Here, the average moment over a mechanical revolution is always considered. The torque fluctuation within one revolution can be determined by a cogging torque test.
The drag torque is usually determined mainly by the bearing friction. But also other loss moments, such as Eddy current torques in a permanently excited motor or the air friction of a firmly connected fan wheel are included in the measurement result. In addition, the mass moment of inertia of the test object (plus coupling and measurement side of the measuring shaft) can be determined with the drag torque test.
To measure the drag torque, the electrically non-contacted test object is dragged by the load machine with the specified gradient to a defined speed (nprüf) and then brought to a standstill again with the same gradient. The test is carried out one after the other in both the positive and negative direction of rotation.
The encoder test serves to assess the quality of the device encoder. For this purpose, the angle signal output by the device under test is compared with that of a reference encoder. In addition, the angle signal of the DUT encoder is displayed in relation to the generator voltage of the motor.
The contacted test object is towed by the load machine to a constant speed, see figure. When the setpoint speed is reached, both the terminal voltages of the DUT and the angle signal of the encoder and the reference encoder signal are recorded during the test time.
Active test types is a term used for test types in which the test object is mechanically connected to a load machine and energized.
The characteristic curve test is used to determine the average behavior of the powered motor over one revolution as a function of the speed. This means that the motor can be characterized in its capacity as a converter from electrical to mechanical energy. For this purpose, currents, voltages and torque are recorded as a function of the speed and from this the electrically consumed power, the mechanically output power and the efficiency are determined. The determined characteristic curves depend on the control of the motor, in particular on the specification of the d and q currents over the speed. The characteristic curve test can be used to determine the performance that can be achieved with a specific control strategy in order to provide a starting point for further optimization.
The dynamic characteristic curve test measures the entire speed range of a test object in a short time. This minimizes the heating of the motor. If measurements are to be made in the thermally steady state or if the control speed of the test object current controller is insufficient, a static characteristic curve test is the better choice.
The test can only be used for current-controlled test objects. If the device under test cannot be operated in this mode, the torque-controlled characteristic test must be used.
At the beginning of the test, the test item is dragged by the load machine with the gradient to the starting speed and then the current is switched on. During a parameterizable waiting time, the test item swings in so that a stationary torque is set on the shaft. After this waiting time, the speed of the load machine is increased linearly from the steady start speed to the stop speed. After the stop speed has been reached, the device under test first waits for it to settle. The load machine then drives the test item to the starting speed again while it is switched on. This double ramp approach allows the torque characteristic to be corrected by the proportion of the moment of inertia. If the starting speed is reached again, the test object current is switched off. After a further settling time, the load machine brings the test object to a standstill by following a linear ramp with the gradient. After the end of the test, the load machine drags the passive test object over an upward and downward ramp. This is used to determine the commutation angle for the evaluation of the characteristic travel.
The characteristic curve test determines the average behavior of the motor over one revolution as a function of the speed. The focus is on characterizing the properties of the motor as a converter from electrical to mechanical energy. For this purpose, currents, voltages and torque are measured as a function of the speed and thus the electrical power consumed, the mechanical power output and the efficiency are determined. The determined characteristic curves are always dependent on the control of the motor, in particular on the specification of d and q current versus speed. The characteristic check determines the performance of the control strategy and is the starting point for further optimization in the control algorithm.
The static characteristic test measures the behavior of the motor at various specified constant speeds. Measurements are made over a time interval that starts when the desired speed is reached and the motor current has stabilized. Compared to the dynamic characteristic curve test, in which the entire speed range is measured, the static method can only make statements about the measured speeds, but these are usually more precise. Above all, the dynamics of the test object current regulator have a significantly lower influence here.
The load machine drags the active test item to the first speed n1. After a settling process, there is a stationary moment on the measuring shaft and the measuring time is started. This process is repeated for the other speeds n2 to n8 after the measuring time has elapsed. The test current and current angle for the individual speeds, which lead to a maximum torque, can be taken from the measurement data of the flow table measurement for the individual speeds.
Due to their electromagnetically asymmetrical structure, the torque on electro motors fluctuates over a single revolution. This torque ripple amounts to a problem in various applications, for instance in electrically assisted steering in the automotive industry.
By measuring the torque ripple at a fixed rotation speed and a specified torque value, it is possible to obtain information on a motor’s behavior in the target application. In this test, the DUT is actively powered and the test procedure can be parameterized individually.
The DUT is connected with the test stand’s load machine via a coupling. Once the test starts, the load machine drags the DUT for a specified time towards a target speed value. Once the system’s transient states have subsided, the DUT is powered up and a steady-state torque on the shaft emerges. The DUT’s controller then regulates the shaft torque to the specified value. The rotation angle and shaft torque are recorded over a specified time duration. Once this time elapses, the shaft torque is regulated down to zero and the load machine runs the DUT down to a standstill.
The resistance measurement determines resistances of the 3 windings of a three-phase motor. By comparing the measured resistances can be seen on the one hand how evenly the windings are performed. On the other hand, deviations from the expected resistance may indicate winding errors, e.g. a wrong winding number or insulation fault. Finally, the winding resistance can also be deduced from the winding temperature.
In the resistance measurement, a constant measuring current is impressed into the test object in three different configurations in order to determine the three string resistances independently of one another. The following procedure has proven useful:
The inductance measurement is used to measure the winding inductance of a motor. In this case, the change in inductance over a mechanical revolution and thus the dependence on the rotor position is detected.
First, a DC current is impressed through two terminals of the DUT to measure the terminal resistance of the motor. Subsequently, a sinusoidal alternating current is impressed on the same two terminals and the test specimen is slowly rotated by the load machine, so that the terminal inductance can be absorbed above the angle of rotation. At the end of the test, the terminal resistance is measured again.
The flux table measurement serves to determine the magnetic flux in d- and q-direction as a function of the impressed total current. For this purpose, the test specimen is measured in static load points. In addition, the ohmic losses, as well as the friction and iron losses of the test specimen are recorded.
With the help of the obtained information, an optimal control of the motor can be calculated as a function of the speed. That is, it can be calculated for each predetermined speed, and current and voltage limit of the total current and current angle that meet a certain torque request with minimal current effective value. This automatically minimizes ohmic losses and maximizes the efficiency of the entire drive system.
For static flow table measurement, the DUT is connected to the inverter. At the beginning of the test, the winding resistances of the test object are determined in a DC current supply. The test specimen is then towed by the load machine to the test speed. Here, the friction torque of the test specimen is measured as a function of the speed. Now the DUT is energized in several operating points. The amount of (total) current is gradually increased. In addition, the current angle is varied step by step for each individual current step. There are adjustable cooling pauses between the individual energisations.
At the end of the test, the friction torque is measured again in a downward ramp and the winding resistance determined in a DC current supply. With the aid of these measurement data, the influence of the moment of inertia in the speed ramps is compensated, as well as the heating of the windings during the test.
