Henan mine crane co., LTD. Product introduction:
For three-phase asynchronous motor speed formula: n = 60 f) (1 - s/p from visible on type, change the power supply frequency f, slip ratio of the motor very logarithmic p and s can achieve the goal of changing speed.From the perspective of the nature of speed regulation, different ways of governing is nothing but change the synchronous speed of ac motor or not to change two synchronous speed.Widely used in the production of machinery is not the change in speed control method of synchronous speed of wound rotor motor rotor series resistance speed governing, chopping speed regulation, cascade speed regulation and application of the electromagnetic slip clutch, hydraulic coupling, such as oil film clutch speed regulation.Change of the synchronous speed changing stator polar logarithmic multi-speed motor, change the frequency control of motor speed
Frequency control of motor speed
The voltage and frequency of variable frequency speed regulation is can not the reversing motor drive, etc.From energy point of view, when there is high speed control method and low speed control method of two kinds: an induction refers to the effective speed control is constant, so there is no slip loss, such as multi-speed motor, frequency control of motor speed and slip loss can be recovered speed control methods (such as cascade speed regulation, etc.).Have slip loss speed regulation method belongs to the low speed, such as rotor series resistance speed control method, the energy loss in the rotor circuit;Electromagnetic clutch speed regulation method of energy loss in the clutch coil;Hydraulic coupler speed regulation and energy loss in the oil of hydraulic coupling.In general slip loss increases with expanding range of speed regulation, if the speed range is not big, energy loss is small.
Frequency measuring instrument and application (5) of base wave frequency inverter output the PWM wave of change, its measurement method with the traditional power frequency sine wave measurement have bigger difference.
1, we usually say the inverter output 380 v, 50 hz, refers to the fundamental wave (sine wave) is 380 v, 50 hz.Inverter output waveform of PWM wave, in addition to the fundamental wave, but the carrier signal.Carrier signal is much higher than the fundamental frequency, and is a square wave signal, contains a large amount of high order harmonic.
2, the common multimeter normally only measure of 45 ~ 66 hz or 45 ~ 66 hz ac sine wave.Part of the true RMS multimeter measurement has a much wider frequency range, many people believe that can be used for frequency measuring, testing.Actually otherwise, because of this the fundamental wave measurement results table and carrier is contained in.The frequency converter, for example, 380 v, the output of the measurement results in more than 400 v.
3, used in inverter testing instrument should have in a variety of PWM waveform in its fundamental ability, strict measure should adopt the way of digital signal processing, which is high speed sampling sample series, discrete Fourier transform with sample series, the fundamental wave amplitude, phase and every harmonic amplitude and phase.
4, there is also a thinking that calibration average (MEAN) can replace the effective value of fundamental component of inverter output PWM signals.Average calibration is equal to the true RMS of sine wave in theory, is equal to the fundamental RMS sine modulation PWM waveform, and easy to implement;Therefore, in many of the instruments used to replace MEAN value is the effective value of harmonic (RMS) or PWM fundamental RMS (h01-2) measurement.But, frequency control of motor speed technology, more and more application of non sinusoidal modulation PWM and general inverter users usually do not know your inverter adopts what kind of modulation mode, MEAN value in PWM measurement limitations is more and more big.
Therefore, variable frequency speed regulation system of electrical parameter test should be used with appropriate bandwidth of frequency conversion power transmitter (including frequency voltage sensor, variable frequency electric current sensor and voltage current modular inverter power sensor) and broadband rf power analyzer (also called a variable frequency power analyzer), broadband rf power analyzer to high-speed communication signal after sampling frequency spectrum analysis, can real time operation the fundamental wave effective value of voltage, current and wave power, also can calculate the true RMS of voltage, current, active power and harmonic parameters.
