Application of ABB frequency converter
What are the differences between PWM and PAM?PWM is English Pulse Width Modulation (pulse width modulation), according to the law must change the pulse of the pulse width in a tone adjustment output and waveform.PAM is the abbreviation of Pulse Amplitude Modulation (pulse amplitude modulation) in English. It is a modulation way to change the pulse amplitude of pulse column according to a certain rule to regulate the output value and waveform.
What is the difference between a voltage type and an electric current type?The main circuit of the inverter can be divided into two categories: voltage is DC voltage source converter for AC inverter, the DC circuit is the filter capacitor current is DC converter; current source for AC inverter, the DC circuit filter inductance stone.
Why is the voltage of the inverter proportional to the current?Asynchronous motor is the torque between the current flowing through the motor flux and rotor as a result of the interaction, at rated frequency, but only if the voltage will reduce the frequency, then the magnetic flux on a large magnetic circuit saturation, the motor will be seriously burned. Therefore, the frequency and voltage should be changed proportionally, that is to say, to change the frequency, to control the output voltage of the converter at the same time, to keep the flux of the motor to be certain, and to avoid the occurrence of the weakening of the magnetic flux and the saturation of the magnetic flux. This control mode is mostly used in fans, pumps and energy saving inverters.
When the motor is powered by an industrial frequency power supply, the current increases when the voltage drops; for the inverter, if the voltage drops when the frequency drops, then does the current increase?When the frequency drops (low speed), if the output is the same power, the current increases, but the current remains almost constant under a certain torque.
What is the starting current and starting torque of the motor when the inverter is in operation?Using frequency converter operation, with the acceleration of the motor, accordingly improve the frequency and voltage, the starting current is limited to 150% rated current (according to the type of machine is 125%~200%). The starting current is 6~7 times of direct starting with the mains frequency power supply, so the mechanical and electrical impact will be produced. It can start smoothly with frequency converter (longer starting time). The starting current is 1.2~1.5 times the rated current, the starting torque is 70%~120%, the rated torque; for the inverter with automatic torque enhancement, the starting torque is above 100%, and the full load can start.
