Locomotive traction motor usually adopt inverter power supply. To test the function of the test equipment and performance indicators put forward higher requirements:
1
、the test equipment has a wide bandwidth, and in a wider frequency range can obtain higher measurement accuracy;
2
、test base wave frequency could be less than 5 hz, conventional measuring instrument can stable readings;
3
、inverter switching frequency is low, harmonic content is rich, and the signal is not strict periodic signal, the Fourier transform, need longer time window.
To correctly measure the traction inverter output wave voltage RMS, must pay attention to:
1
、the right frequency conversion power measuring device. Voltage, current sensor and the bandwidth of the instrument should be reasonable and correct measurement mode (fundamental RMS mode), the output frequency satisfies the requirement of accurate level and so on.
2
、traction converter according to the fundamental RMS (close to the theoretical value) is consistent with the actual measurement result is the premise of switching frequency, carrier frequency is high enough (at least 20 times greater than the fundamental frequency). Indeed, the traction inverter switching frequency tend to be low, generally less than 1 KHZ, and the fundamental frequency is higher, so does not meet the conditions.
3
、to the fundamental RMS accurate and stable measurement, the premise is the inverter output for periodic signal (Fourier transform) for periodic signal. In fact because of the traction inverter switching frequency is low, when the switch frequency is not the fundamental wave frequency integer times, the output signal is not periodic signal. For example: switching frequency is 500 hz, the wave frequency is 60 hz, if the base of the current cycle time since the beginning of the zeroth pulse wave, will be at the end of the ninth 1/3 of the pulse time, and the next fundamental wave cycle, will begin from ninth 1/3 of the pulse time, obviously, the two fundamental wave cycle is not the same signal, that is to say, the inverter output is not periodic signal (when switching frequency is higher, the relatively weak aperiodic performance)
