Beijing Leader & Harvest Electric Technologies Co., Ltd.
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1. Variable frequency operation of brushless synchronous motor
Abstract: because brushless synchronous motor does not part which may create spark, such as slip ring and carbon brush, it is used widely in site of explosive environment, such as chemical industry and coal mine. With idea of energy saving promoting, brushless synchronous motors need to reconstruct with variable frequency technology. This article states principle, structure and operation mode of brushless synchronous motor, analyzes problems during synchronizing, adjusting and excitation input, puts forward variable frequency operation of brushless synchronous motor.
Key words: brushless synchronous motor, variable frequency, speed adjustment, operation mode ...

2. Medium voltage VFD application on synchronous motor
Medium voltage synchronous motor is widely used as its characters of high power factor, stable speed and low speed simple design, such as fan, water pump, oil pump and so on. For big power low speed load, such as mill and compressor, using synchronous motor not only heightens power factor, but also leaves out variable-speed gear. It lowers system fault rate and simples maintenance.
Because of complicated physical course and difficult controllability of synchronous motor, original speed adjustment system used to install speed/position sensor, which increases fault rate and lowers system reliability.

3. Leader,Harvest VFD application on synchronous motor
According to characters of synchronous motor, we decide to adopt start mode of zero speed variable frequency with exciting current. During starting, exciting current selection is very important.
During operation of piston compressor, its torque pulsation is big and design speed is low. The less speed is, the more pole number of motor is. So electrical angle which is equavalent to space angle of stator and rotor is more. Take an example of motor of 48 pole, a circle of stator and rotor is 24×360=8640º electrical angle. That is, 1 degree of circle is equivalent to 24º electrical angle. Thus, same torque pulsation causes bigger swing of electrical angle, thereby leading to bigger vibration of output current and output power.

Variable Frequency Drive
  • A VFD HARSVERT-A series VFD is a masterpiece of outstanding performance and high reliability, which is widely used for the energy-saving application of the normal motors of fans, pumps ...
  • VA VFD Input current harmonic: <3% (comply with standard IEEE519);
    Input power factor: >0.95(>20% load);
    Output current harmonic: <2.5%; output DC ...
  • VS VFD Vector control for the speed-adjustment of synchronous motor;
    Start ability for starting the synchronous motor with load;
    The response time of dynamic torque: less ...
  • FVS VFD PWM rectifier technology. Energy can flow bi-directionally between power grid and the motor;
    Vector control for synchronous motor;
    Strong start up with load in ...