Knowledge, principle and operation method of frequency converter.
Basic classification of the working principle of frequency converter:Frequency converter working principle has been, so there are so many converters in the world for Mao is not the same? If you cry in this case, I can only say sorry, yes, but they can also do the classification (please open up the brain to process OCD pattern): classification according to the working mode of the main circuit, can be divided into voltage type inverter and current source inverter; switching mode in accordance with the classification, can be divided into PAM control inverter PWM control frequency converter and high frequency PWM inverter control; in accordance with the principle of classification, can be divided into V/f control inverter, slip frequency control inverter and vector control inverter; according to use classification, can be divided into general high performance frequency converter, inverter, high frequency inverter, single-phase inverter and three-phase inverter.
The three major parts of the working principle of frequency converter:This is how the inverter works, but how does it work? Mainly composed of three components. (1) convert the power frequency power to the rectifier of the DC power: it transforms the power frequency power into the DC power supply. A reversible converter can also be constructed using two sets of transistor converters, which can be regenerated for their reversible power direction. (2) absorption in the converter and inverter voltage generated by the pulsating "flat wave circuit" in the rectifier DC voltage is rectified, ripple voltage with power frequency 6 times, in addition the pulsating current generated by the inverter to the DC voltage fluctuation. (3) the DC power conversion for AC power rectifier with "inverter": instead, the inverter is DC power converter for AC power required frequency, to the time the 6 switch off, you can get 3 phase AC output.
Summary of the working principle of frequency converter:Before the work principle of frequency converter is understood, it may be possible to see why the inverter is sacred first Inverter is the frequency power supply (50Hz or 60Hz) converted to various frequency AC power supply, in order to realize the motor speed change operation of equipment. The control circuit controls the main circuit of the rectifier circuit will be converted into AC DC, DC intermediate circuit of the rectifier output smoothing filter, inverter circuit to DC and then reverse into alternating current (and core control circuit: AC - DC - AC the process). And the frequency conversion technology should be born with the need of AC motor stepless speed regulation. The working principle of formula to express the words is: n = 60 f (1 s) /p (1) - N - speed asynchronous motor; F -- asynchronous motor frequency; s - motor slip; P - pole motor. By formula (1), the speed n is proportional to the frequency f. As long as the frequency of F can be changed, the speed of the motor can be changed. When the frequency f changes within the range of 0 to 50Hz, the speed range of the motor is very wide. Frequency converter is to change the frequency of motor power to achieve speed regulation, is an ideal high efficiency, high performance speed control means.
Sinusoidal pulse width modulation (SPWM) of U/f=C with frequency converter control mode:The characteristics of SPWM inverter control way is to control the circuit has simple structure and low cost, the mechanical properties of hardness is also good, can meet the general requirements of smooth speed transmission, has been widely used in various fields of industry. However, when the output voltage is low, the torque is significantly affected by the stator resistance pressure drop, so that the maximum output torque is reduced. In addition, the mechanical characteristics of DC motor can not hard, dynamic torque capacity and static performance is not satisfactory, and the system performance is not high, the control curve will change with the change of the load torque and motor torque, slow response, low utilization rate is not high, due to the stator resistance and the existence of dead time effect of the inverter performance the poor stability, etc.. Therefore, people have studied vector control frequency conversion speed regulation.
The history of the principle of frequency converter:Frequency conversion technology is born with the need of AC motor stepless speed regulation. After 1960s, the power electronic devices through SCR (SCR), GTO (gate turn off thyristor (BJT), bipolar power transistor), MOSFET (metal oxide semiconductor field effect transistor), SIT (static induction transistor), SITH (static induction thyristor (MGT), MOS control MCT (MOS) transistor, thyristor controlled), IGBT (insulated gate bipolar transistor), HVIGBT (high voltage insulated gate bipolar transistor) device to update the development process, to promote the continuous development of power electronics technology (note that because of this, so the inverter is in this background). The beginning of 1970s, PWM VVVF (PWMVVVF) control has aroused great attention. In 1980s, PWM mode optimization, as the core of frequency conversion technology, attracted people's interest and obtained many optimization models, among which the saddle wave PWM model was the best. Since the latter half of the 1980s, the VVVF inverters in developed countries such as the United States, Japan, Germany, Britain and other developed countries have already been put into the market and have been widely used. As to understand the principles of various types of frequency converter, you might as well look at the four changes in the frequency control mode from the simple to the complex.
