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Fan and pump application
Load characteristics of fan and pump is square torque feature, this load is stable, EM9 series inverter is popular in this application because of its economy, reliability and abundant control model.
Fan feature curve 
Fan exhaust volume curve as diagram; when the fan run at rated speed, the exhaust volume and air pressure is same as curve 1; The resistance curve is 2 when input air and air valve is full open, the curve 1 intersect curve 2 at rated working point N.  Mostly the exhaust volume is Qn, the air pressure is Hn, the air valve will block part air pipe to let fan working status move to point E, and then air volume of heating boiler is Qe,the pressure head will be He. If we adopt to reduce the fan speed to adjust the air flow, fan will run as fan feature curve 4 and it intersects with pipe network curve 2 at working point C. It supplys neccessary air flow Qe with fully open pipe network.
According to the similarity law of fan with pump, the air volume, speed and power of fan established the following formula:
 as :
     Q1  The exhaust air before fan   adjustment,m3/h;      
     Q2  The exhaust air after fan adjustment, m3/h;      
     H1  The pressure head before fan  adjustment,Pa;      
     H2  The pressure head after fan  adjustment,Pa;    
     n1  The RPM before fan adjustment,r/min;      
     n2  The RPM after fan adjustment,r/min;      
     N1  The shaft power before fan adjustment,KW;      
     N2  The shaft power after fan  adjustment,KW.
According to the above law, when fan RPM reduce from n1 to n2, the shaft power N2 reduce to N1 *(n1/n2)³; The shaded JECF covering area illustrate the saving energy of comparing inverter adjusting speed to using valve. It will waste energy by using valve to block air for theory and test. Using frequency inverter to adjust fan speed not only can save energy, but also reduce mechanical wear and prolong the equipment lifespan.
System advantages
1)  Stable starting, suitable for large inertia load  control;
2)  Energy saving rate to 20%-60%;
3)  Effectively prevent mechanical wear and prolong the life of the motor, instant tense torque reflect;
4)  Improve power factor, reduce the motor running noise and operation temperature;
5)  Double keyboard interactive switch control, the machine, free choice of choosing machine control or remote control.
6)  Built-in PID regulator, simple system structure of closed-loop control ;
7)  Automatic adjustment of instantaneous output voltage , the output voltage remains stable even if the input power grid is unstable


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