In the development of the inverter test system according to the design scheme, some technical problems were encountered. After hard work, these problems were solved one by one.
The main technical difficulties and solutions are introduced as follows. (1)
Rated loading in the test process, it is necessary to detect the working characteristics of the inverter under the rated load. The so-called rated loading requires the output current of the inverter to be stable at the rated current, with an error of ± 5, if the rated current of the 3-phase 15kW/400V Inverter is 33A, how can such a large and stable load be simulated?
The commonly used loading method is magnetic particle brake loading. Its main disadvantage is that the loading needs to have a heat dissipation device, and the magnetic particle should be replaced frequently, which is costly.
The method adopted after exploration is 'double Motor loading '.
The details are as follows: the two motor shafts are mechanically connected. When testing a frequency converter with an output voltage of 400 V, the 400V motor is connected to the output of the frequency converter, and the frequency converter is controlled to run first, with an output frequency of 50Hz, turn on the 200V motor again--
50kW transformer output, since the power frequency of 200V motor is 50Hz, which is equal to the frequency of 400V motor, the rotating speed of the two motors is the same, and the output current of frequency converter is small at this time.
After that, the output frequency of the frequency converter was gradually increased, the speed of the 400V motor was accelerated, the rotation speed of the two motors varied, and the torque increased. The 200V motor became the load of the 400V motor.
As the output frequency of the inverter gradually increases, its output current increases continuously, when the output current reaches the rated current (Error less than 5)
When, stop increasing the output frequency of the inverter and realize the rated loading.
On the contrary, when detecting a 200V inverter, the 200V motor is connected to the inverter output and the 400V motor is connected to the power supply, thus meeting the loading requirements of the 200V and 400V inverters.
This loading method works very well, making full use of 10 pairs of motors, one of which must be the main motor and the other is the load motor.
When the test inverter is 15kW, the main motor consumes 15kW and the load motor consumes 15kW, so the maximum power consumption of the whole system is 30kW.